2 10 74 https://digitalcollections.lakeheadu.ca/files/original/37cabe0e7ea7bfdd9ba9dcbc494adb36.pdf cd719f14ad23652fa7736dc1061d666b PDF Text Text Eleventh Annual Institute on Lake Superior Geology May 6-8, 1965 University of Minnesota St. Paul Minnesota �11thAnnual AnnualInstitute Institute on lith Superior Geology Geology Lake Superior Sponsored by: 3ponsored Minnesota Minnesota Geological Survey of Minnesota Minnesota University of and The Twin The Twin City Geologists Wicons,i GIoccaj ad Na1ur Hiry 9igj 3811 M;rior pci,,t flc. Madj5Qfl, WI 63; i �r7j ch§Technical Technical tlJI Sessions n I I I., > (TZR .----- a '-- ST PAUL CAMPUS CAMPUS 1 J �COMMITTEES Local Committee Local Hogberg General Chairmen - P. K. K. Sims and R. R. K. Hogberg Program Program Arrangements Social P. P. K. K. Sims Sims Judy Holmes Keith Knobloch I(nobloch CnarLes Matsch Cnarles Jane Titcomb Jane Titcomb Sarah Tufford Sarah D. y.;. Lindgren Lindgren D. W. George Austin George R. R. K. K. Hogberg Hogberg Field Field Trip t. K. R. K. Hogberg Hogberg D. D. H. H. Yardley Yardley Institute Secretary Secretary Institute D. H. Hase, D. Hase, State State University Universityof of Iowa Iowa Institute Eoard Board of Directors Institute M. M. W. W. Bartley, M. M. W. W. J3artley Bartley & & Associates, Associates, Port Port Arthur, Ontario A. A. T. T. Broderick, Broderick,Inland InlandSteel SteelCompany, Company, Istipeming, Ishpeming, Michigan Michigan D. H. Hase, State University of Iowa, Iowa City, Iowa D. H. Hase, State University of Iowa, Iowa Iowa H. Lepp, Lepp, Macalester MacaLester College, College, St. Paul, Paul, Minnesota Minnesota H. A. A. K. K. Sneigrove, Snelgrove, Michigan Michigan Technological Technological University, University, Houghton, Houghton, Michigan �11th Annual Institute on 11th Annual Institute on Lake SuperiorGeo1o~ Geolo_ Lake Superior May May 66 -- 8, 8~ 1965 PRO GRAM PROGRAM Thursd, Thursday?May May 66 8:00 - 9:20 a.m. a.m, Registration and coffee coffee hour9 hour 9 2nd floor floor of of Student Student Center, center, St. Paul Paul Campus st. Campus Technical sessions,9 2nd Technical sessions 2nd floor, f1oor~ Green Hall 8:45 -- 9:00 9:00 Business Meeting...........D. Hase, Secretary, Meeting ••••••••••• D. H. H. Hase~ Secretary, conducting Session II Co-chairmen: and Ralph John W. W. Gruner and Marsden 9:00 Progressive contact metamorphism of the Biwabik Iron-formation on on the 9:20 9:40 10:00 10:45 11:05 11:25 12:15 Nesabi ,........Bevan M. French Mesabi range, range, Minnesota....................... Minnesota •••••••••••••••••••••••••••••••• Bevan M. The distribution of manganese in the Biwabik Iron-formation, Minnesota.••••••••••• Minnesota Henry Lepp . . . . . . . . . • ~ ••••••••• ..•...... .. .e ••.• •.•.• •.•.• •. c •. •• •.•.•.•.•.•.•.• .• •. .~ .••• •• ••.• •.Henry Some aspects of of iron-formations in Australia and South Africa.. . . . •. . . . . ........ . . , . . , . . . . . . . . •. . . . . . . . . . . . . .Gene Africa •••••••••••••••••••••••••••••••••••••••••••••••• • Gene L. L. LaBerge Coffee break Structure and and lithology of of the metamorphosed Biwabik Biwabik Iron-formation, Iron-formation, Dunka River area, area, Eastern Mesabi district, district, Minnesota••• Minnesota. . Bil1 Bonnichsen Structural control control of of the Mount Mount Wright-Mount Wright-Mount Reed Reed iron iron deposits, Structural .Bill J. Clarke Quebec •••••••.••••••.••••••••••••••••••••••• • • • • • •.•. •• Peter J. Quebec...... . ........ .... . . . . . . . . . . . . . . . . . .o ........ . •.Peter Petrology of the silicate iron-formation in the Republic mine area, area, Marquette County, County, Michigan............Tsu—Ming Michigan•••••••••••• Tsu-Ming Ban Han and and James James W. W. Villar Villar Luncheon, Student Center, Luncheon, Center~ 2nd floor, floor, North Star star Ballroom Ballroom Session II II Co—chairmen: Co-chairmen: 1:30 1:55 2:15 2:35 2:35 2:50 3:35 3:35 3:55 3:55 4:15 4:15 George M. M. Schwartz and James Neilson Tectonics of the Keweenawan basin, basin~ western Lake Superior Superior S. White region. . . . . . . . . . . . . . . . . . . .. .o .• ,• • region ••••••••••••••••••••• • Walter S. . •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. •. .WaJ.ter of western western Lake Lake Superior...........Richard Superior•••••••••• Richard J. J. Wold An aeromagnetic survey of The Sauble geophysical geophysical anomaly, anomaly, Lake Lake County, County, Michigan.....................G..HowardJ. Michigan••••••• o • • • • • • • • • • • • • • • ~ • • Howard J. Meyer Meyer and and WilliamJ. William J. Hinze Hinze Contributions of rock rock physics physics to to geology•••••••••••••••Robert geology..,...........Robert J. J. Willard Coffee break Geological analysis and remedial action action in in an open pit rock slide. slide ••••••••••••••••••••••••••••••••••••••••••••••• D. H. H. Yardley rock . . .. . . . . . . . . . . . . . . . . . . . ,. . . . . . . . . . . . . . . . . . . . . .D. Measurement of in-situ stresses in in aa St. st. Cloud quarry-quarry--aa Measurement progress progress report. report •••••••••••••••••••••••••••••••••••••• . ......... .... •. .... .. . . ..... ..... .. . Charles Char1es Fairhurst Fairhurst An example of statistical analysis and possible interpretation and interpretation of of Hill, Skanee quadrangle, quadrangle, Upper structural data from Arvon Hill, Peninsula, Michigan ••••••••••••••••••••••••••••••••••••• J. D. Juilland Peninsula, Michigan. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . J • 1 �Thursday9 May Thursday, May 66 (continued) ~continued) Annual Annual Banquet Twins Motor Motor Motel Motel 1975 University Avenue (University at at Prior) Prior) 6:00 6:00 p.m. p.m. 7:00 Social Hour Social Dinner Address: Professor Campbell Campbell Craddock Craddock will will speak speak on on 'Geologic QfGeologic Professor structure of West West Antarctica,' Antarctica, 'I a summation summation of six six structure austral austral seasons seasons of field work work illustrated illustratedwith withmany many of field colored pictures. pictures. fine colored Friday, May May 77 Friday, Co—chairmen: Co-chairmen: 9:00 9:00 9:20 9:40 Session III III Carl E. E. Dutton Dutton and and H. H. L. L. James Stratigraphy, structure, structure~ and and granitic granitic rocks rocks in in the the Marenisco—Watersmeet Marenisco-Watersmeet, Stratigraphy, E0 Fritts'~ Fritts area, area, Michigan. Michigan•••••••••••••••••••••••••••••••••••••• .. .. .. .. ... .. .. ... .., .. .. .. .. . . •.. . Crawford E. Ages of mafic dikes near Granite Falls, near Granite Gilbert N. N. Hanson Minnesota •••••••••••••••••••••••• Glen R. Hixmnelberg, Himmelberg~ Gilbert structure and stratigraphy stratigraphy of of the the Knife Knife Lake Group Group east east of of Ely, Ely, Structure and a •a•a•a. Minnesota...... Minne sota •••••••••• ••••• ••• • •,John John C. C. Green . . . ~. •••••••••••••••.•••• . . . . . .. . . . .... .. . . . . e ••e a. ••a.•. a•a. Coffee break Spiroff,. Keweenaw fault, Houghtori Houghton County, Michigan •••••••••••••••••• Kiril Spiroff~ Keweenaw fault, County, Michigan.... ... .. s... •• .lCii'il The sedimentology sedimentology of the the Precambrian Precambrian Rove Rove Formation Formation in in , B. Morey Morey --northeastern northeastern Minnesota.., Minnesota••••••••••••••••••••••••••••••••••••• G. B. ~ .. . . . .. . .. . .. .. .. ... .. ... . ... . .G. Petrology Petrology of the the Amberg Precambrian Precambrian crystalline crystalline complex, complex, .Dennis northeastern northeastern Wisconsin...,.... Wisconsin••••••••••••••••••••••••••••••• Dennis p. P. Rebello ....... Sedimentation of Middle Precambrian quartzites quartzites in in Sedimentation of R;chard W. OJ'akangas~ W. Ojakangas Finland. F;nland ..•,•.•.•.•.•.•.•.•.•$• •. ., •. •. •. •. •. •.•..• •. •. .0 .• •. •. ••,• •• •, •. •, •..• •. •. •. ." ..Richard • •. •• 1'\ Luncheon, Center, 2nd floor, Luncheon, Student Center, floor, North Star Ballroom Minnesota........,.,........,..GlenR. . 10:00 10:40 11:00 11:00 11:20 11:40 •.•,.,...• .... ..I. 12:15 Co-chairmen: 1:30 1:50 Session IV G. A. A. Thiel Thiel and and Don Don Lindgren Lindgren G. A study on the the hydrology hydrology of of potholes potholesin inMinnesota••••• Minnesota.....George Schwartz A study on George M.M.Schwartz -~' Geology of the the Fillmore County district iron ores, L. Bleifuss southeastern southeastern Minnesota..,. Minnesota•••••••••••••••••••••••••••••••••• R, L. ...... ... . .... .......... . ,. ,R, Organic geochemistry geochemistry of of Rossburg Rossburg peat peat bog, bog, Aitkin Aitkin County, County, F. M. M. Swain, Swain, Mykola Mykola Nalinowsky, Malinowsky, and and David David Nelson Minnesota•••••••••••••• Minnesota.............F. Preliminary Prelimina:ry results results of of geochemicaT geochemical prospecting prospecting north north of of the the Marqu~tte ••••••••••••••••••••••• Kenneth Segerstrom Marquette iron iron range, range, Michigan Michigan......................Kenneth Coffee Coffee break break Protoclastic borders borders of of the the felsite felsite near near Bergland, Bergland, Protoc1as;ic Michigan..........0.........Joseph Michizan •••••••••••••••••••••• Joseph P. P. Dobell Dobell and and Robert W. W. Leonardson Some aspects aspects of of the the pegmatites pegmatites in in the the Feich Felch district, district, Dickinson Dickinson Some •••••••••••••••••••••••••••••••••••• Geoffrey W. W. Mathews Mathews County, Michigan County, Miehigan...................................Geoffrey . 2:10 2:10 2:30 2::30 2:50 3: 20 3: 3:40 3:40 2 2 �Friday9 May Friday? May 77 (continued) (continued) 7:30 —- 9:Lk5 9:45 p.m. U. S. S. Bureau of Mines, Mines, Research Research Center, Center, Fort Tour of U. Bus will leave at 7:30 Snelling. 7:30 p.m. p.m. from Student Student Snelling. Center, st. St. Paul Campus with an intermediate stop center, at Twins Motor Motel and and will will return return to to the the same same at locations. Saturday, May 8 Saturday? 8:00 a.rn. to 8:00 a.m. to 6:00 6:00 p.m. p.m. Field trip trip to to St. st. Cloud Cloud district. district. Buses will depart Field from and and return return to to the the Student Student Center, Center, St. St. Paul Paul campus. campus. from Field trip willinclude include tour tourofofthe theCold ColdSpring Spring Granite Granite Field trip will CompanyO s finishing visits Companys finishingplant plantandand visitstotothree three"granite: 'granite' quarries. Participants will will be be provided provided with with aa guideguidehats are hard book and. and lunch. clothes and and are advised. advised. lunch. Field clothes Authors and and Technical Technical Session Session Chairmen Chairmen BLEIFUSS, R. L...........Mines BLEIFUSS, R. L••••••••••• Mines Experiment Experiment Station, Station, University University of of Minnesota, Minnesota, Minneapolis Minneapolis BONNICHSEN, BILL....0...Department BONNICHSEN, BILL ••••• o • • • Department of of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minne sota, Minneapolis Minneapolis ~X ,. CLARKE, PETER PETER JJ.........Department CLARKE, •••••••••• Department of of Natural Natural Resources, Resources, Province Province of of Quebec, Quebec, Quebec, Canada Quebec, Geophysics, University CRADDOCK, CAMPBELL •••••••.Department Department of Geology and and Geophysics, University of of CAMPBELL..... Minnesota, Minneapolis Minneapolis DOBELL, JOSEPH DOBELL, JOSEPH P....... P•••••••••.Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan Michigan " DUTTON,CARL CARLE...........U. E••••••••••• U. S. S. Geological Geological Survey, Survey, Madison, Madison, Wisconsin Wisconsin ADUTTON, FAIRHURST, CHARLES•••••••.School School of of Mineral Mineral and and Metallurgical Engineering, FAIRHURST, CHARLES..... University of Minnesota, Minnesota, Minneapolis Minneapolis FRENCH, BEVAN M •••••••••• Theoretical Division, Goddard Space Space Flight Flight Center, Center, M..........Theoretical Greenbelt, Maryland Greenbelt, Maryland )(FRITTS, CRAWFORD E••.•••• E......U. XFRITTS, CRAWFORD U. S. S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado GREEN, GREEN, JOHN C............Department C•••••••• o • • • Department of of Geology, Geology, University University of of Minnesota, Minnesota, Duluth Duluth GRUNER, JOHN JOHN W.o W..........Professor and GRUNER, ••••••••• Professor Emeritus, Emeritus, Department Department of Geology and University of of Minnesota, Minnesota, Minneapolis Minneapolis Geophysics, Geophysics, University Company, Ishpeming, HAN, TSU-MING Cleveland-Cliffs Iron Comp2ny, Ishpeming, Michigan TSU-MING,•••••••••••• . . . . .,. . . Cleveland—Cliffs HAN, .. Institut HANSON, GILBERT GILBERTN.l'l •••••••• Institut fur Kristallographie und Petrographie, Petrographie, HANSON, ... Sonneggstrasse, Zurich, Switzerland Sonneggstrasse, Zurich, S\\I:Ltzerland / Geology, University University of j('HASE, D. H••••• , •••• o • • • • Department of Geology, of Iowa, Iowa, Iowa Iowa City, City, XHASE, D. k~ Iowa HIMMELBERG, HThIMELBERG, ..Departm.nt GLE:J R.. R••••••• Departm,mt of of Gtology Gt~ology and and Geophysics, Geophysics, University of GIE Mirmesota, Minneapolis Minl!~apol:'Ls Minnesota, HINZE, XNZE, ~ 'V': , (, '. ,;lJ \ !~'~i\.. Geology, Michigan University, 7J '" WILLIAM ~f.[LLI.AM J.........Department J ••••••••• Department of of Geology, Michigan StateState University, ~t ~i~\ j/l>';'>:: East Lansing, Michigan J3 ,f �P .,~N·".I' ,'vV' () AHOGBERG, .J( HOGBERG~ R.R.K............Minnesota K••••••••••••Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, JAMES, JAMES~ Minneapolis H. L•••••••••••••• G0010gical Survey, Survey, Minneipolis MiQDo~polis L............U.D.S.S.Goological JUflL.A1D, J. JUILLAND, J. D..........Michigan D••••••••.•• Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan ,.;zLaBERGE, LaBERGE, GENE L•••••••••• National Research Council Council of of Canada, Canada, Geological Geological L.........NationaJ. Survey of Canada, Canada, ottawa, Ottawa, Ontario LEDNP1RDSON, ROBERT W.. LEONARDSON, ROBERT W••••• Department of of Geology Geology and and Geological Geological Engineering, Engineering, . .Department Michigan Technological Technological University9 University, Houghton, Houghton, Michigan Michigan Michigan LEPP, HENRy•••••••••••••• HENRY.............Department Paul LEPP, Department of of Geology, Geology, Macalester College, College, St. st. Paul LINIJGREN, DONALD DONPLD W W.......Lindgren & Lehmann, Lehmann, Inc., Inc., Wayzata, Wayzata, Minnesota LINDGREN, ••••••• Lindgren & MALINOWSKY, MYKOLA••••••• Department of of Geology Geology and and Geophysics, University University of of MALINOWSKY, MYKOLA.......Department Minnesota, Minnesota, Minneapolis MARSDEN, RALPH W ••••••••• U.S.S.Steel Steel Corporation, iJuluth Duluth W...,....U. Corporation, MATHEWS, GEOFFREY W Reserve University, University, •••••• Department of Geology, Western Reserve W......Department Geology, Western Cleveland, Ohio Ohio of Geology, Geology, Michigan Michigan State University, MEYER, HOWARD HOWARD J...........Department J •••••••••• Department of University, East Lansing, Lansing, Michigan MOREY, G. DepartmentofofGeology Geologyand and Geophysics, Geophysics, University University of of MOREY, G. B•••••••••••••• B............Department Minnesota, Minneapolis Minnesota, NEILSON, JAMES. JAMES•••••••••••Michigan Technological University, University, Houghton, Houghton, Michigan Michigan ... ... . . . .Michigan Technological NELSON, DAVID •••••••••••• Department of of Geology Geology and and Geophysics, Geophysics, University University of NELSON, DAVID...........Department Minnesota, Minneapolis OJAKANGAS, OJAKANGAS, RICHARD RICHARD W.....Department W••••• Department of of Geology, Geology, University University of of Minnesota, Minnesota, Duluth REBELLO, DENNIS REBELLO, DENNIS P.......Department P•••••••• Department of of Geology, Geology, Western Western Reserve Reserve University, University, Cleveland, Ohio Cleveland, SCHWARTZ, GEORGE M M......Professor and SCHWARTZ, GEORGE ••••••• Professor Emeritus, Emeritus, Department Department of Geology and Geophysics, University of of Minnesota, Minnesota, Minneapolis Minneapolis Geophysics, University SEGERSTROM, KENNETH......U. SEGERSTROM, KENNETH •••••• U. S. S. Geological Survey, Survey, Denver, Colorado Colorado P. K•••••••••••••••Minnesota K..,..0.......Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, J i~ SIMS, P. / Minneapolis SPIROFF, KfltIL...........Department KIRIL ••••••••••• Department of Geology and and Geological Geological Engineering, Engineering, SPIROFF, Michigan University, Houghton, Houghton, Michigan Michigan Michigan Technological Technological University, SWAIN, SWAIN, F. F. M•••••••••••••• Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis Minneapolis THIEL, G. A•••••••••••••• A.............Professor THIEL, G. Professor Emeritus, Emeritus, Department Department of of Geology and Geophysics, University of of Minnesota, rfLnnesota, Minneapolis Minneapolis Geophysics, University VILLAR, JAMES W W.........Cleveland—Cliffs VILLAR, Jfu~ES •••••••••• Cleveland-Cliffs Iron Iron Company, Company, Ishpeming, Ishpeming, Michigan Michigan WHITE, WALTER WALTER S.........U. S•••••••••• U. S. S. Geological Geological Survey, Survey, Beltaville, Beltsville, Maryland WHITE, WILLARD, ... .U. S. Bureau Bureau of Mines, Mines, Minneapolis Minneapolis 'WILLARD, ROBERT ROBERT J.... J •••••••• U. S. 4 L. �'/WOLD, RICHARD J J........,.Department WOLDt RICHARD •••••••••• Department of of Geology, Geology, The The University University of of Wisconsin, Wisconsin, Madison, Wisconsin Madison, YARDLEY, D, H.....,......School YARDLEY, D. H•••••••••••• School of Mineral and and Metallurgical Engineering, Engineering 9 University of University of Minnesota, Minnesota, Minneapolis 55 �GEOLOGYOF OF THE THE FILLMORE DISTRICT GEOLOGY FILLMORE COUNTY COUNTY DISTRICT IRON ORES,SOUTHEASTERN SOUTHEASTERN MINNESOTA MINNESOTA IRON ORES, R. L. L. Bleifuss Bleifuss R. Station Mines Experiment Station */ University of Minnesota, Minnesota, Minneapolis— MinneapolisIron ores have been known to exist in southeastern southeastern Minnesota Minnesota since the the earliest earliest geological reconnaissance of the area by the since 9 Owen's Owen s survey survey in in 1852. The development of the the Fillmore County district was stimulated stimulated by by the the demands demands for for iron iron ores ores during during World World War II, II, and initial ore shipments shipments were made in in 1943. 1943. Cumulative tons, iron-ore million tons, iron—ore production production through through 1964 1964 has has been been about about 6t 6 million Reserves and current current production production is is about about -t million tons per per year. year. Reserves and carried on on the the tax tax rolls rolls in in 1964 1964 are are in in excess excess of of 2* million million tons. tons. 2t The iron ores lie on Paleozoic limestones ranging ranging in in age age from from the Middle Ordovician to to Middle Devonian. Devonian. The commercial ore bodies are restricted restricted to to two two dolomitic limestone limestone units: units: the the Middle Middle Ordovician Ordovician The Galena Formation, Formation, and and the Middle Devonian Devonian Cedar Cedar Valley Valley Formation. Formation. The iron ores, ores, and the widespread iron-rich weathering residuum residuum which which is is developed on nearly all of the formations formations in the the area, area, has has been been Member, of the Cretaceous Windrow ~Tlndrow assigned to the lower, lower, Iron Hill Member, Formation. Formation. The clays, sands, sands, and gravels gravels overlying overlying The unconsolidated unconsolidated clays, the the ores are assigned to the upper, upper, or or 0Ostrander same strander Member Member of of the the same formation. Previous investigators have postulated that the the ores ores in in the the district originated by intensive chemical chemical weathering, which which resulted resulted in the widespread replacement of certain certain favorable favorable dolomitic dolomitic limelimepaper on the stone by iron. iron. In the most recent paper on the area, area, stone bedrock units by In the postulated Sloan (1964) (1964) agrees agrees with the the Cretaceous Cretaceous age of the iron ores postulated by previous workers, workers, and further emphasizes the the importance importance of of humid, humid, temperate, to to sub..tropical sub-tropical climatic that prevailed prevailed in in the the temperate, climatic conditions that area during the time of the transgression of the Cretaceous seas seas over Minnesota. The present study has produced evidence that the the ores ores are are siderite-rich beds that originated originated during during the the related to primary siderjte-rjch transgression of of the the Devonian Devonian seas. seas. The uniform thickness, thickness, chemical chemical transgression composition, and physical characteristics of of the the ore are preclude preclude their their composition, formation by by the the surficial surficial weathering of of aa normal normal dolomitic dolomitic limestone limestone formation without an an intermediate intermediate concentration concentration step. step. The author believes that the the physical-chemical phy"sical-chemical conditions required required to precipitate precipitate relatively pure pure siderite siderite in in an an otherwise otherwise normal normal carbonate carbonate environment environment relatively during the the Devonian. Devonian. This would require a euxinic were present during environment in an estuary or bay with limited mixing of of normal normal marine marine waters. The by streams streams draining draining a The iron iron was wastrffilsported transported in in solution by low-lying coastal plain under arid arid or or semi-arid semi-arid climatic climatic conditions. conditions. ~/Work done on of the theMinnesota Minnesota Geological Geological Survey Survey on behalf of — Work done 66 �The ultimate ultimate source of the drainage The source of iron iron was was the the normal normal sediments sediments of drainage basin; no basin; no specific iron-rich iron-rich source source beds beds are are required. required. The ores are not necessarily dependent upon unique Cretaceous climatic conditions, conditions 9 and the advisability of placing them within the Formation is is dubious. dubious. the Windrow Formation 77 �*/ STRUCTURE AND AND LITHOLOGY LITHOLOGI OF STRUCTURE OFTHE THEMETJ\MORPHOSED METAMORPHOSED BIWABIK BIWABIK IRON— IRONFORMATION, FORMATION, DUNKA DUNKA RIVER AREA, AREA, EASTERN MESABI MESABI DISTRICT, DISTRICT,MINNESOTA MINNESOTA- Bill Bonnichsen Bill Bonnichsen Department of Geology Geology and and Geophysics Department University of of Minnesota, Minnesota, Minneapolis Minneapolis A three-mile—long three-mile-long belt of of metamorphosed metamorphosed Biwabik Biwabik Iron-formation Iron-formationA in the Dunka River area, Babbitt, Minnesota, Minnesota, at area, near Babbitt, at the eastern eastern end of the Mesabi Range, is being developed developed by Erie Erie Mining Company Company as as aa Range, is taconite property. property. age, rests with profound The The Biwabik Biwabik Iron-formation, Iron-formation, Animikian Animikian in age, profound on granitic granitic rocks rocks of of the the Giants Giants Range Range batholith batholith and and is unconformity on unconformity overlain Formation. The Pokegama Pokegama Quartzite, Quartzite, overlairi conformably conformably by by the the Virginia Virginia Formation. which lies immediately immediately below the the Biwabik Biwabik Iron-formation Iron-formation in in other other parts parts these of the Mesabi range, virtually absent absent at at Dunka Dunka River. River. All of these range, is virtually older rocks have been intruded and thermally metamorphosed by the Keweenawan Duluth Duluth Gabbro Gabbro Complex. Complex. The iron—formation iron-formation and other other PreKeweenawan cambrian rocks are covered locally by as much as 100 feet of as much as 100 feet of glacial is drift. iron—formation ranges in thickness from At Dunka Dunka River, River, the iron-formation from 175 to 300 feet, to feet, and varies as as much as 100 feet in in aa short short distance distance much as 100 feet horizontally horizontally as aa result resultofofboth bothdepositionaJ. depositionaland and structurally— structurallyinduced thinning and induced and thickening. The Lower Lower Slaty, thickening. The LowerCherty, Cherty, Lower Slaty, Upper Cherty, and Upper Cherty, and Upper Upper Slaty Slaty Members Members of of the the Biwabik Biwabik Iron-formation Iron-formation are recognizable recognizable at at Dunka and, except except for for aa markedly markedly thinned thinned are Dunka River River and, Lower Lower Cherty Cherty Member, Member, the the formation formation is is similar similar in in thickness thickness and and stra— stratigraphy to to other other localities in in the the Eastern Eastern Mesabi district. district. AA persistent persistent 55- to 15-foot diabase sill, sill, believed to to be be part part of of the the Duluth Gabbro Complex, Complex, occurs occurs throughout throughout the the property property at at the the same same stratigraphic position stratigraphic position in in the the Upper Upper Slaty Slaty Member. Member. The minerals minerals of of the the Biwabik Biwabik Iron-formation—-quartz, Iron-formation--quartz,magfletite, magnetite, The fayalite, ferrohypersthene, ferrohypersthene,hedenbergite, hedenbergite,hornblende, hornblende, cummingtonite, fayalite, curniiiingtonite, and lesser amounts of diopside, diopside, actinolite, actinolite, andradite, andradite, calcite, calcite, and and pyrrhotite--are characteristic of of a high temperature metamrophic metamrophic environment. The mineralogy and paragenesis are similar similar to to that that at at environment. the the Reserve Reserve Mining Company Company (Gundersen (Gundersen and and the Peter Mitchell mine of the 1962). Quartz is the most abundant mineral in in the the iron— ironSchwartz, 1962). Quartz is formation, formation, and grains grains developed in relatively pure layers are are as as much as as 55 to 10 mm. in diameter. diameter. Magnetite, Magnetite, the the second second most most abundant abundant mm. in mineral, mineral, has haR been coarsened by the the metamorphism; its its grain-size grain-size varies varies considerably from from layer to in general, general, increases increases northward northward considerably to layer but, but, in through the property. property. The taconite shows shows reI.iograde reh'ograde metamorphism metamorphism with hydrous iron—silioat,e forn-thg at the expense iron-si1icateLr1itxer] miner-a] ~s fOl"lJli ng at expense of ofanhydrous anhydrous varieties. *1 ~/Work — Work done partly on on behalf of of the the Minnesota Geological Geological Survey Survey done 8 �The Biwabik Biwabik Iron-formation Iron—formationand andoverlying overlying Virginia Virginia Formation The Formation 0 SE. strike N. 25—35°E. and dip 15-35° The outcrop belt strike N. 25-35°E. and 15-35 SE. The outcrop belt of these these rocks is truncated at angle by the at a slight angle the intrusive intrusive Duluth Gabbro Gabbro Complex9 and in the northern part of the area both formations are Complex, Southward9 the iron-formation extends cut out completely. completely. Southward, extends uninteruninterruptedly down-dip beneath the overriding gabbro and Virginia FormaFormation and can can be be mined mined for for some some distance below the the outcrop by open-pit methods. the structure is superficially Although the superficially simple, simple, the the iron-formairon-formalocally faulted and and folded folded and and is is pervasively pervasively jointed. jointed. A few tion is locally steeplydipping steeply-dipping faults that strike northward and northwestward cut and displace the formation; do not exceed a few formation; maximum displacements do ofwhich whichare arerelated related to to the tens of feet. Small-scale folds, folds, some some of the northward-trending faults, faults, produce local flattening of the the beds and and belt. Two of systematic joints, subwidening of the outcrop outcrop belt. Two sets sets of systematic joints, subparallel to parallel to the major fault sets, sets, and many other joints joints occur throughthroughout the rocks at at Dunka Dunka River, River. The north— north- and northwest-trending faults and appear to regional and systematic systematicjoint joint sets sets appear to be be related related to regional stress patterns; stress patterns; most most of the other other structures stnlctures are are probably probably related to to emplacementofof the the gabbro. emplacement gabbro. 99 �STRUCTURAL CONTROLOF OFTHE TI MOUNT STRUCTURAL CONTROL MOUNT WRIGHT lrJRIGHT -MOUNT REED REED IRON IRON DEPOSITS, DEPOSITS,QUEBEC QUEBEC Peter J. Clarke J. Clarke Department of of Natural Natural Resources, Province Province of of Quebec, Quebec, Quebec, Quebec, Canada The Mount Wright Wright -- Mount Reed district, district, located located about about midway midwaySchefferville in northern Quebec, Quebec, has between Seven Islands and Scheffervifle proven to iron ore. ore. to be be an important source of concentrating grade iron The district contains the southern extension of of the the Labrador Labrador Trough, Trough, which has been deformed and and metamorphosed by the Grenville Grenville Orogeny. Orogeny. by the it is underlain by Proterozoic Proterozoje metasediments, metasediments, including gneisses, It gneisses, marble, quartzite, quartzite, iron-formation iron-formation and and aluminous aluminous schists, which rest rest marble, on a basement of remetamorphosed remetamorphosed granulite granulite and and gneiss. gneiss. Acidic and and basic intrusions are common common in in the the gneisses gneisses below below and and above above the the iron-formation respectively. The Proterozoic Proterozoic metasediments change change in in sedimentary sedimentary facies facies from near-shore deposits in the the northwest northwest to to deeper deeper water water deposits in in the the southeast. southeast. Their structural structural style style varies varies in in different different parts parts of absence of of folds folds of of the the district, district, depending on the presence or or absence depending on the presence two structural trends (northeast two (northeast to to east east and and northwest northwest to to north). north). In a part of the district relative simple simple folds of only one one trend trend dominate; in another part cross dominate; cross folds folds are are developed, and and folds folds of of both trends are are about equally equally abundant. abundant. Much of of the the valuable valuable oxideoxidefades facies iron—formation iron-formation occurs in in the the cross-.folded cross-folded zone, zone, and and the the important iron deposits lie in structural basins separated by domes of older iroD deposits lie in structural basins gneiss. \~ere Wherethe thecross-folds cross—foldsare arespaced spacedrelatively relatively uniformly, uniformly, iron gneiss. are repeated repeated at atabout aboutfour—mile four-mile intervals on a rough rough grid deposits are intervals on with axes with axes trending northeast northeast to east east and and northwest to north. north. 10 �PROTOCLASTIC BORDERSOF OFTHE THE FELSITE PROTOCLASTIC BORDERS NEAR BERGLAND, NEAR BERGLAND, MICHIGAN MICHIG.Ai~ Joseph P. Dobell and Robert W. Joseph W. Leonardson of Geology Geology arid and Geological Michigan Geological Engineering, Michigan Technological University, Houghton, Houghton, Michigan Michigan Technological University, Department rock located located along the north side An intrusive side An intrusive mass massofoffelsitic felsitic rock of Gogebic Lake near Bergland, Michigan, shows Bergland, Upper Michigan, showsdistinctly distinctly protoclastic borders at protoclastic at contacts contacts with basalt and and sandstone which indicates that the rock was at least partially solidified at at the time of emplacement. Zones showing protoclastic structure vary in width from from one to four four feet, feet, and grade away from contacts to a directionless fine fine grained felsite. felsite. The The most conspicuous features of these border zones are are aa distinct distinct banding banding resembling resembling flow flow (fluxion) (fluxion) structure or zones structure or banding, and and aa granular texture texture which which gives the the weathered sedimentary banding, sandstone or a granule conglomrock the appearance of a very coarse sandstone erate. erate. 11 �MEASUREMENT IN-SITU STRESSES SAINT MEASUREMENT OFOFIN-SITU STRESSES IN INAA SAINTCLOUD CLOUDQUARRY QUARRY A PROGRESS A PROGRESS REPORT REPORT Charles Fairhurst Charles School of Mineral School of Mineral and and Metallurgical Metallurgical Engineering Engineering University of Minnesota Minneapolis Minnesota99 Minneapolis The phenomenon is well well known known to to quarry quarry workers The phenomenon of of rock rock Iipressure;Q 'pressure is workers and often results in effects such such as undesired fracturing of blocks during quarrying. Modification Modification of of quarrying quarrying procedures procedures appears appears to to affect affect the the incidence incidence of of pressure pressure effects. effects. The paper paper describes describes surface surface strain strain gauge gauge and and borehole borehole deformation deformation measurements now now in in progress progress in in aa Saint Saint Cloud Cloud quarry quarry to to determine determine the the measurements magnitude and and orientation orientation of of the the stresses stresses considered considered to to be be responsible responsible magnitude for the pressure pressure effects. effects. The The geology geology of of the the area area is is briefly briefly described. Preliminary results results from from one one quarry quarry suggest suggest that that subsubstantial (4000 lb. (lateral) stresses stresses exist stantial (4000 lb. per sq. sq. in.) in.) horizontal horizontal (lateral) in the the directions directions suspected suspected by by the the workmen. workmen. Further Further tests, tests, which will be be discussed, discussed 9 are are planned planned to to determine determine whether the the stresses stresses are are regional regional (i.e. (i.e. externally externally developed) developed) or or residual (i.e. (i.e. internally internally developed, developed 9 for for example example during during cooling). cooling). residual Hast Hast (1958) (1958) has measured measured high high horizontal horizontal stresses stresses in in underground underground mines in in Scandinavia. Scandinavia. The major major axes axes of of the the stress stress ellipsoids ellipsoids at at various points points appear appear to to be directed directed towards towards the the center center of of earthearthquake activity in Scandinavia. Scandinavia. He He suggests regional suggeststhat that similar regional stresses may stresses may be expected expected in the the Great GreatLakes Lakes region region of ofNorth NorthAmerica. America. The possibility that the Ule stresses stressesmay may be be residual residual isissuggested suggested by by The possibility that the fact fact that thatpressure pressure effects effectsare aremost most serious serious in in the the finer-grained finer-grained the rocks. 12 �PROGRESSIVE CONTACT OF THE THE BIWABIK CONTACT METAMORPHISM METAMORPHISM OF BH1ABIK IRON-FORMATION ON ON THE THE MESABI IRON-FORMATION HESABI RANGE, RANGE, MINNESOTA MINNESOTA Bevan Bevan M. M. French Theoretical Division, Division, NASA, NASA, Goddard Space Flight Center, Center, Greenbelt, Greenbelt, Maryland Flight The Biwabik Iron-formation, on on the the Mesabi range range in in northern northern Biwabjk Iron—formation, Minnesota, is is the the middle middle unit unit of of the the three-fold three-fold Animikie Animikie Group Group of of Minnesota, Middle Precambrian Precambrian age. age. On the the eastern eastern end end of of the the range, range, the the Middle Animikian rocks have been intrusive Duluth Duluth Animikian been metamorphosed metamorphosed by the intrusive Complex; mineralogical changes changes in in the the sediments, sediments, particularly particularly Gabbro Complex; in the iron-formation, appear appear related related to to the the gabbro. gabbro. From From the the data of of the present present study, study, four four metamorphic zones zones may may be distinguished within the Biwabik Iron-formation by changes changes in in mineralogy along along the the strike strike of of the the formation formation toward toward the the gabbro gabbro contact: contact: (1) unaltered taconite taconite extends from the the western limit of (1) unaltered of the the Mesabi range range approximately approximately to to the the town town of of Aurora. Aurora. It It is is composed composed of of Mesabi quartz, magnetite, magnetite, hematite, hematite, siderite, quartz, siderite, ankerite, ankerite, talc, and and the the iron iron Of silicates chamosite, chamosite, greerialite, greenalite, minnesotaite, stilpnomelane. Of minnesotaite, and stilpnomelane. these, only quartz, quartz, hematite, hematite, chamosite, chamosite, greenalite, greenalite, siderite, siderte, and and these, some are considered considered primary. primary. The textures of of the the other other some magnetite are minerals indicate indicate aa secondary secondary origin, origin, possibly possibly through through diagenesis diagenesis or low-grade metamorphism prior to intrusion intrusion of the Duluth Gabbro Gabbro Complex. Complex. (2) (2) transitional taconite contains the same mineralogy but exhibits extensive extensive replacement replacement by by quartz quartz and and ankerite. ankerite. Incipient exhibits metamorphic changes changes in in this this zone zone are are the the partial partial reduction reduction of of hematite hematite metamorphic to magnetite and the appearance of clinozoisite clinozoisite in in the underlying underlying Pokegama Pokegama Formation. Formation. (3) (3) moderately metamorphosed taconite taconite is is characterized by development of the iron-rich amphibole amphibole grunerite grunerite and and by by the the disappearance disappearance Calcite appears from of original original iron iron carbonates carbonates and and silicates. silicates. of reaction of of ankerite ankerite and and quartz quartz to to form form grunerite. grunerite. (4) taconite, within two miles of the Duluth (4) highly metamorphosed taconite, Gabbro contact, Gabbro contact, is is completely completely recrystallized recrystallized to to aa metamorphic metamorphic fabric fabric and is composed chiefly of quartz, quartz, iron amphiboles, amphiboles, iron and iron pyroxenes, pyroxenes, magnetite, and rare and calcite. calcite. Small veins and and pegmatites pegmatites magnetite, arid rare fayalite fayalite and this zone zone may represent introduction of reported from from this represent. minor intl"odnction of material from the gabbro. gabbro. The following mineralogical mineralogical changes changesoccur occuralong alongthe the strike strike of The following of the iron-formation iron-formation toward toward the gabbro gabbro contact: contact: (a) (a) partial partialreduction reductionof ofhematite hematite to tomagnetite magnetite (in the Pokegama Pokegama Formation) Formation) (b) development of clinozoisite (in (c) formation formation of grunerite (c) 13 13 �(d) (d) (e) (e) (f) (f) (g) (g) appearance of iron-rich clinopyroxene appearance clinopyroxene (hedenbergite) (hedenbergite) disappearance of hematite appearance of ferrohypersthene appearance of graphite (from organic matter). All the changes, changes, which represent the complete complete transition from from unmetamorphosed to highly metamorphosed taconite, taconite~ occur within a a horizontal distance of of about about two two miles miles near near Mesaba. Mesaba. iron-formation Compositions of the carbonate minerals in the iron—formation by combining combining refractive refractive index index measurements measurements with with X-ray X-ray were determined by diffraction data to obtain values for for the Ca, Ca~ Fe, Fe~ and Mg components. components. In unaltered taconite, taconite~ siderite siderite compositions compositions approximate approximateCa5F'e75Mg20; Ca5Fe7y~gzo; at ankerite compositions same material compositions from from the the same material are are quite uniform at calcites that approximately Ca53Fe24Mg2j. Ca53FeZ4MgZ3. The The calcites that appear appear in in the themetameta- morphosed taconite are andand Mg—poor, morphosed taconite areFe-rich Fe-rich Mg-poor~ approximating approximatingCa9Fe10Mg1. CaB9Feld1g1. No definite change in siderite siderite or No definite change in or ankerite ankerite compositions compositions is noted along the the strike of BiwabikFormation; Formation;there there is is no indicanoted along of the the Biwabik tion of progressive progressive removal removal of of iron from from the the carbonate carbonate with increasing increasing metamorphism. By contrast, contrast~ calcites from the metamorphosed taconite increase in Ca, Ca, becoming becoming virtually virtually pure pure CaCO3 CaCO) near near the the gabbro. gabbro. The present study indicates that metamorphism of the Biwabik Iron-formation by the the Duluth Gabbro Complex was largely Isochemical i"'o~hemical and was was characterized by progressive progressive loss loss of 0fH20 H20 ;:r1d COZ. characterized chiefly by CO2. There is no indication that the original mineralogy consisted cons~sted only magnetite, or that large quantities of other components of quartz and aDd magnetite, components were introduced introduced into into the the sediments sediments from fro!ll the the gabbro, gabbro, as as has has been been proposed (Gundersen (Gundersen and and Schwartz, Schwartz, 1962). 196Z). 14 l4 �STRATIGRAPHY,STRUCTURE, STRUCTURE,fu~D ANDGRANITIC GRANITICROCK~/IN R0CK1IN THE STRATIGRAPHY, THE MARENISC0-WATERSMEE AREA, }\1ARENISCO-WATERSMEET AREA, MICHIGAN—' MICHIGAN- Crawford CrawfordE.E.Fritts Fritts Survey, Denver, S. Geological Survey, Denver, Colorado U. S. detailed mapping mapping near near Lake Lake Gogebic, Gogebic, Michigan, Michigan, reconnaissance, reconnaissance, Recent detailed Recent the Marenisco-Watersmeet area recorded by the and review of data from the Michigan Michigan Geological Geological Survey Survey since since 1900 have have led led to to reinterpretation reinterpretation of of regional stratigraphy stratigraphy and and structure. structure. The Tyler Slate of the the Gogebic regional an east—plunging east-plunging anticline anticline west west of of the the Range wraps around the nose of an lake and conformably conformably underlies aa thick thick sequence sequence of of south-dipping south-dipping metametalake and volcanic and metasedimentary rocks, rocks, which apparently underlies the the Michigamme Slate Slate (fig. (fig. 1, 1, on page). North North of Cup Cup Lake, Lake, graded graded Michigamme on next page). bedding in in quartzite formerly fornlerly interpreted interpreted as as folded folded and and overturned overturned of the the Marenisco Marenisco Range Range indicates that rocks there actually strata of are are right right side side up. up. Similarly, Similarly, near near Kakabika Kakabika Falls, Falls? pillow pillow structures structures metavolcanjc rocks indicate that strata in metavolcanic strata of the Turtle Range also also are right side up. up. The The principal structurebetween betweenMarenisco Marenisco and and principal structure Water&neet, therefore, is is aa south-dipping south-dipping monocline. monocline. Although Although Watersmeet, therefore, diamond-drill data indicate indicate aasynclinal synclinalflexure flexurenear nearBanner BannerLake, Lake, field evidence at present present does does not not require require tight tight folding field evidence at folding or largefor scale there. However, large throw throw accounts accounts for scale faulting there. However,a afault fault of large MarenisCo, and it westward disappearance the westward disappearance of of the Tyler Slate near Marenisco, is possible that that other other faults faults will will be be found found farther farther east east as as mapping mapping is continues. Rocks formerly formerly mapped mapped as as Presque Presque Isle Isle Granite Granite include include at at least least Banded gneiss three of different ages. ages. Banded gneiss three distinctive distinctive lithologic units of and a younger younger equigranular equigranular granite granite unconforinably unconformably overlain overlain by by the the Tyler Slate Slate west west of of Lake Lake Gogebic Gogebic probably probably are are pre-Animikie pre-Animikie in in age. age. Tyler Well granitic to to quartz foliated, well well lineated, lineated, biotite.-rich, biotite-rich, granitic Well foliated, monzonitic gneiss gneiss intrudes rocks rocks stratigraphically stratigraphically above above the the Tyler Tyler south and east of and probably probably is is post-Aniinikie post-Animikie in in age. age. of Marenisco Marenisco and In the Marenisco-Watersmeet area, the metamorphic grade of Animikie area, Animikie strata, in in general, general, increases southeastward toward the center of a strata, in part, part, by by the the post—Animikie post-Animikie gneiss. gneiss. It It is is broad zone zone underlain, underlain, in likely, therefore, that the the metamorphism metamorphism accompanied accompanied and and perhaps perhaps likely, therefore, of this this gneiss. gneiss. followed emplacement emplacement of ~/Work done in cooperation — Work done in cooperation with the Geological Survey Division with of the Conservation the Hichigan Michigan Department of Conservation 15 �Yondoto Falls 1]] ----~ 1]] I o 0 I I I I 2 3 4 5MILES 5 MILES I I I I I EXPLANAT I EXPLANAT zz zz «« i~ ~ Jacobsville Sandstone Jacobsville Sandstone UNCONFORMI TV UNCONFORMITY cr cr 0l0l } ::;:::;: «« 00 uu w crcr o0 0..0 ON a N zz nI Rocks Rocks near Cup Cup Lake Lake Interlayered amphibolite, Interloyered amphibolite, metogroywacke metagraywacke, phyllitic phyllilic schist, and and porphyritic schisl, parphyrilic metotuff metatuff; minor minor conglameralic quarlzite parI conglomerotic quortzite in lower part ~ cr Ol ::; « 0 u uJ w cr aa.. Keweenawan Series Keweenawan Un/CONFORM/TV UNCONFORMITY Tyler Slate Siale Graywacke.slote overlying thin Graywacke-slale thin basal basal conglomerate conglomerate £INCONFORM/ TV UNCONFORMITY Gronitic to Quartz quartz monzonitic nonzonitic gneiss Granitic to gneiss u-,,:;.~ ~, Granite Michigarnme Michigamme Slate Slate FT-T'T'll U:i±.IJ Metamorphosed pillow lavas lovos and and luffs tufts Metamorphosed pillow ~ Metatuffs Metatuffs and and metasedimentary metasedimentary rocks racks Stratigraphic Straligraphic position position uncertain; uncerlain; possibly possibly younger lhan thon pre—Animikie younger pre-Animikle granite rzJI!llJ Banded gneiss gneiss Rocks Rocks near Bonner Banner Lake Lake -1".&, phyilitic schist and and other athermetasedimentory metasedimentary phyllitiC schist rocks, undivided; undivided, may racks, may also also include include metatuff metatuff lean iron -- fa formation ~, lean r ";',0 ti an" carbonaceous slate slale • , carbonaceous Figure II. Preliminary geologicmap mapofofthe the Marenisco Marenisco —Wotersmeet area,Mlchillan, Michigan,showinll showingtentative tentative interpretation interpretation -Watersmeet area, Preliminary geologic of strotigraphy andstructure structurebybyC.C.E.E.Fritts, Frifts, 1965, of stratigraphy and 1965. �STRUCTUREAND ANDSTRATIGRAPHY STRATIGRAPHYOF OFTHE ThE KNIFE LAKE STRUCTURE LAKE GROUP GROUP EAST OF ~ HINNESOTJl:/ EAST OF ELY ELY9 MflESOTA/ John C. Green Green John C. Department of of Geology Geo1or Minnesota, Duluth University of Minnesota~ In the Gabbro Lake quadrangle just east of Ely, Lake 1.5-minute 15-minute quadrangle Ely~ Minnesota~ Precambrian Precambrian Knife Knife Lake Lake rocks rocks occur occur in in two two belts. belts. The The Minnesota, southern belt~ composed of of schist, schist, gneiss, gneiss 9 and and migmatite, is derived belt, composed from graywacke, graywacke 9 conglomerate, conglomerate 9 and and arkose, arkose~ and and is is intruded intruded and and metametathe Giants Giants Range Range batholith batholith of of .Algoman Algoman age. age. It is faulted morphosed by by the against the the basal basal part part of of the the older but but lower-grade lower-grade Ely Greenstone Greenstone against on the north north side side of of the the belt, belt, along along the the major major North North Kawishiwi Kawishiwi fault. fault. on The northern and and wider belt has been metamorphosed only to the the chlorite zone, zone. its Its contact contact with the the underlying Ely Ely Greenstone Greenstone is is with a basal conglomerate. mostly faulted, faulted, but locally conformable ~nth conglomerate. Above this this are, are, successivelY9 successively, 0-2,500 0—2,500 feet feet of of mixed mixed felsic felsic tuff and and Above elastic sediments, feetofofchloritic chloritic clastic elastic sediments, clastic sediments, 1,500_LI.,.5OO 1,500-4~500 feet sediments, mafic volcanic volcanic unit unit 0-2,250 0-2,250 feet feet thick, thick, and a thick thick a predominantly mafic sequence felsic volcanic volcanic rocks, rocks, mainly pyroclastic, pyroclastic, as as much as sequence of felsic 8,000 feet feet thick. thick. Within Within this this unit unit near near Fall Fall Lake Lake is is aa.500-foot 500-foot bed of of siliceous siliceous limestone limestone and and chert chert conglomerate. conglomerate. The felsic felsic bed volcanic rocks interfinger with mafic volcanics similar to Ely volcanic rocks with mafic volcanics to Greenstone northwest of Fall Lake, Lake, and are faulted against mafic Greenstone volcanics and sediments of unknown correlation in the northwest and north-central north—central borders borders of of the the area. area. Knife Lake time in in this this area area evidently evidently was one one of of great great crustal crustal disturbance, disturbance, with rapid erosion of the older greenstones and the rocks rocks that intrude intrude them~ them, and and extensive extensive volc&~ic volcanic activity, activity, probably mostly underwater. An active, active, island arc type of environment is envisioned. This This activity activity culminated culminated in in the batholithic intrusions intrusions and extensive faulting of the Algoman and Algoman orogeny. orogeny. *1 ~/work — Work done done ononbehalf behalf of theof Minnesota the Hinnesota GeologicalGeological Survey 16 16 Survey �PETROLOGY OF IRON-FORMATION IN THE THE REPUBLIC IlEPUBLIC PETROLOGY OFTHE THE SILICATE IRON-FORMATION MINE AREA, AREA,IVL4RQUETTE M.ARQUETTE COUNTY, COUNTY, MICHIGAN MICHIGAN Tsu-Ming Hanand and James JamesW. W.Villar Villar Tsu-Hing Han Cleveland-Cliffs Iron Iron Company, Company, Ishpeming, Michigan Michigan Cleveland—Cliffs The iron-rich metasediments at at the the Republic mine mine can can be be subsub- divided into four four lithologic lithologic types types according according to to major major mineraJ. mineral constituents. stituents. These include aa quartz-specular hematite-muscovite conglomeratic the Goodrich FOTI~ation Formation and and three conglomeratic member at the base of the lithologic types within the Negaunee Iron-formation, Iron-formation, which normally and major major reflect a close close relationship between stratigraphic stratigraphic position and mineral assemblage. assemblage. In In descending descending stratigraphic stratigraphic order order the the mineral mineral assemblages generally are: are: quartz-specular quartz-specular hematite, hematite, quartz-magnetite, quartz-magnetite, and quartz-grunerite-magnetite. The type type characterized by the and latter assemblage, assemblage, the subject subject of this study, study, is as much as 500 SOO feet thick and commonly contains a series of sill-like amphibolites. and commonly contains a series of sill-like amphibolites. The rock is typically banded as a result of compositional variations in in the the ratios ratios of of quartz, quartz, magnetite, magnetite, and and grunerite. grunerite. variations Bands Bands with with oolites oolites of of quartz-magnetite, quartz-magnetite, quartz-grunerite-magnetite, quartz-grunerite-magnetite, Locally, carbonate occurs as a and grunerite-magnetite are are common. common. Locally, major constituent of of some some bands. bands. Five generations generations of minerals are are recognized: recognized: (1) (1) scattered scattered Five grains of original elastic clastic quartz and and fine-grained fine-grained magnetite, magnetite, (2) (2) quartz, magnetite, grunerite, garnet, calcite, hornblende, and quartz, magnetite, grunerite, garnet, calcite, hornblende, pyroxene, during regional regional metamorphism, metamorphism, (3) stilpnomelane, pyroxene, formed formed during minnesotaite, hornblende, hornblende, and calcite, minnesotaite, calcite, formed during retrograde metamorphism, (4) (4) quartz-calcite, quartz-hematite, quartZ-hematite, and and an an unidentified unidentified brownish green silicate, silicate, formed as fracture fracture fillings subsequent subsequent to metamorphism, and and (5) (S) martite and hematite, hematite, formed formed from from magnetite magnetite and grunerite during supergene supergene oxidation. oxidation. Paragenetic studies studies indicate indicate that that grunerite grunerite formed, formed, at least least in part, at the expense of magnetite and quartz during metamorphism part, in the Republic mine mine area. area. This is indicated by the following observations: observations: (1) growth of gTIlnerite porphyroblasts in in nearly nearly pure pure magnetite magnetite (1) grunerite porphyroblasts bands, bands, (2) presence presence of magnetite-quartz remnants (2) remnants within within grunerite grunerite bands, bands, (3) (3) magnetite grains within grunerite bands exhibit irregular or subrounded crystal outlines in contrast to subhedral and euhedral ruagnetite in in assemblages assemblages lacking lacking grunerite, magnetite grunerite, (4) common common development development of thin grunerite grunerite layers between (4) magnetite and and quartz bands, bands, and and (S) (5) growth of grunerite along the borders of magnetite-rich veinlets that that cut cut quartz quartz bands. bands. This reaction is further substantiated substantiated by determinations of ferric ferric and ferrous ferrous iron contents of the iron—formation, iron-formation, which reveal 17 17 �the quantities of magnetite and an inverse relationship between the grunerite. This does does not not preclude preclude the the participation participation of of other other reactants reactants This such iron silicates silicates in in the the development development of of such as as carbonates and layered iron grunerite. grunerite. 18 18 �AGES MAFIC DIKES NEAR NEAR GRANITE GRANITE FALLS9 FAIJLS, MINNESOTkMINNESOTk~/ AGES OF OF MAFIC Glen and Gilbert Gilbert N. Glen R. R. Himnielberg Himmelberg and N. Hanson Hanson Department of Geology and and Geophysics University of Minnesota, Minnesota9 Minneapolis, Minneapolis9 Minnesota Precambrian rocks exposed in the Minnesota River valley near Granite Falls9 Falls, Minnesota consist of interlayered metamorphic rocks iiitruded by numerous numerous mafic dikes. intruded by dikes. Existing structures structures in in the the metametamorphic rocks rocks resulted resulted from from dynamothern-ial dynamothermal metamorphism metamorphism about 2.6 billion years years ago. ago. AA later 1.8 b.y. b.y. thermal event is reflected in potassi~~-argon potassium-argon and rubidium-strontium ages of biotite from the metamorphic rocks. rocks. The dikes can be divided petrographically into into tholeiitic diabase, hornblende hornblende andesit.e, andesite, and olivine olivine diabase. diabase. Older tholeiitic several varieties of hornblende diabase dikes are cross-cut by several andesite dikes. dikes. In addition, addition, shear shear zones, zones, which by field evidence could have formed during the late stages stages of of the the 2.6 2.6 b.y. b.y. event, event, cross-cut cross-cut the the tholeiitic tholeiitic diabase diabase but but are are cut cut by by hornblende hornblende andesite andesite dikes, dikes. One of the hornblende andesite dikes is intruded by a 1.8 b.y. granitic b.y. granitic body. body. The relative age of the olivine diabase with respect to the other dikes was not not determined determined in in the the field. field. In In this this study, study, a potassium-argon potassium-argon determination on on hornblende hornblende from from the the metamorphosed metamorphosed country rock rock gives an an age age of of 2.8 b.y., b.y., which which indicates that the hornblende was not not affected affected by by the the 1.8 1.8 b.y. b.y. thermal event. Hornblende from a tholeiitic diabase dike gives an age of 2.0 2.0 b.y.; b.y.; four four of of the the varieties varieties of of hornblende hornblende andesite andesite dikes dikes age gave concordant biotite and and hornblende potassium—argon potassium-argon ages ages of of 1.7 1.7 —1.8 b.y. b.y. the 2.0 2.0 b.y. b.y. age age is is real, real, the the shearing occurred between between 2.0 2.0 If the If, however, however, this 2.0 b.y. and 1.8 boY, ago. If, b.y. value reflects reflects the the ago. loss of argon at 1.8 b.y., b.y., the intrusion of the tholeiitic diabase and the the shearing could have taken and taken place place at at the the close close of of the the 2.6 2.6 b.y. b.y. metamorphic metamorphic event. event. ~/Work done done on on behalf of the the Minnesota Geological Geological Survey -'Work 19 19 �AI EXAMPLE OF STATISTICAL AN EXAJ.\I!.J'LE OF STATISTICAL A1\ALYSIS ANALYSIS AND AND POSSIBLE POSSIBLE INTERPRETATION INTERPRETATION OF STRUCTURAL HILL, SKANEE STRUCTURAL DATA DATA FROM FROM ARVON ARVON HILL, SKMJEEQUADRANGLE, QUADRANGLE, UPPER UPPER PENINSULA, PENINSULA, MICHIGAN MICHIGAN J. D. D. Juilland 1912-B Woodman Drive Drive Houghton, Michigan Skanee quadrangle, quadrangle, Upper Peninsula of Arvon Hill is located in Skanee Michigan, about about 13 l miles northeast Michigan, northeast of of L'anse. L 9 anse. Regionally, the area is underlain by Lower Precambrian metamorphic rocks, rocks, which which are are overlain overlain unconformably unconformably by by .Animikian Animikian metasediments. Younger glacial deposits are virtually absent except along the the flanks flanks of the the hill. hill. Five major types of rocks have been recognized in the Argon Hill area, namely, quartzite (Ajibik), gneiss, migmatite, migmatite, area, (Ajibik), aniphibolite amphibolite gneiss, granitic rock, rock, and and dioritic dioritic rock. rock. The last four rock rock types types form form the the Lower Precambrian or Archean basement; the quartzite occurs on the the basement; the flanks of of the the hill. hill. An An anticlinal structure structure is is inferred inferred from from the the distribution of the rock rock units. units. Foliations, joints were Foliations, lineations, lineations, and and joints were recorded recorded and and plotted plotted on on Schmidt nets nets for statistical analysis. analysis. Structural data data from from the the for statistical Lower Precambrian Precambrian rocks rocks were Lower were separated from those of the theAnimikian Animikian rocks. The The present-day present-day structure observed observed in the rocks was analyzed analyzed first. The Thelimbs limbsofofthe the quartzite quartzite were then rotated rotated back to horizontal. first. were then back to for the The The same same amount amount of rotation for the underlying underlying rocks rocks was used, used, thus position before rotating all structures to their theirassumed assumed position before folding folding of all structures the quartzite. These new sets sets of of readings readings were were plotted, plotted, contoured, contoured, and interpreted as as the the pre—quartzite pre-quartzite structure. structure. As indicated indicated by by BadgleyQs Badgleys Joints were were analyzed analyzed separately. separately. As Joints 'triangle of of intersection, intersection,Ii the \'triangle the joint joint system system in in the the Lower Lower Precambrian Precambrian rocks resulted two periods of stress, rocks resulted from two stress, whereas the joint joint system in the quartzite is the result result of of only only one one period, period, the the second. second. It is concluded that at least two two periods of folding affected affected the the area as a result of forces forces from from approximately approximately the the same same direction. direction. 20 �SOME IRON-FORMATIONS IN AUSTRALIA AUSTRALIA AND AND SOUTH SOUTH AFRICA AFRICA SOME ASPECTS ASPECTS OF OF IRON-FORMATIONS Gene L. L. LaBerge Gene LaBerge Postdoctoral Fellow Fellow National Research Research Council Council of of Canada Canada Canada, Ottawa Geological Survey of Canada~ The extent of Proterozoic iron-formations in the the Hamersley only recently. The Range of Western Australia has has been been recognized recognized only Range, which covers about 40,000 square miles miles,1 probably Hamersley Range~ contains more exposed exposed iron-formation iron-formation than than any any equivalent area in the the world. Three banded iron-formations having an aggregate thickness of more more than than 31500 ,5OO feet feet and, and, probably, probably~ aa total total of of more more than than 80,000 80 1000 feet sediments occur occur in in the the area. area. feet of Proterozoic sediments In South Africa, Africa, aa more more or less continuous belt of Proterozoic iron-formation that is part of the Transvaal System extends for for more than 800 miles. miles. The iron—formation iron-formation is locally more than 5,000 feet thick, thick, but is generally 800—2,000 feet 800-2 1 000 feet feet thick. thick. A A brief account account of of the the general general Proterozoic Proterozoic stratigraphy and and the stratigraphy of the iron-formations from from each each area area will will be be presented presented to to show how they differ from the stratigraphy stratigraphy of the Lake Superior iron—formations region. Layers of altered pyroclastic rocks rocks in the the iron-formations indicate indicate that that there there was was volcanic volcanic activity activity during during much much of of the the time time the iron—formations iron-formations in in each each area area were were being being deposited. deposited. the Certain features iron—formations in Western Australia features of the iron-formations and and South Africa Africa are are very very similar to to those those in in iron-formations iron-formations in in the Lake Superior region, others—-notably the occurrence of region, but others--notably crocidolite crocidoflte asbestos asbestos and and the the virtual virtual absence absence of of granules--are granules——are distinctly distinctly different. There is more similarity between Australian and South African iron-formations than there is between iron-formation of either with the Lake Superior area ~nth Superior region. region. 21 �THE IN THE THE DISTRIBUTION DISTRIBUTION OF OFMANGANESE MANGANESE IN THE BIWABIK IRON-FORMATION, BIWABIK IRON- FORt\1ATION, MINNESOTA MINNESOTA Lepp Henry Lepp Department of Geology, st. Paul Geology, Macalester College, St. The weighted mean mean Mn Mn content content of of the the Biwabik Biwabik Iron.-formation Iron-formation based on 948 individual samples samples is is 0.48 0.48 per per cent. cent. This represents represents an enrichment of about about 4.8 4.8 times times the the mean mean crustal crustal abundance abundance (Clarke) (Clarke) of this this element. element. The Biwabik shows a mean Mn/Fe ratio of 0.016 as compared to a crustal average of 0.022 for this ratio, ratio, thus indicating a slight geochemical separation separation of of Mn Mn and and Fe. Fe. Samples of iron-formation that have been oxidized without appreciable leaching or iron enrichment have considerably lower Mn/Fe ratios ratios than than do unoxidized taconites. taconites. Core samples of ores (enriched oxidized taconites containing containing more more than than 40 40 per per cent cent Fe) Fe) show only a slightly slightly lower lower mean mean Mn/Fe Mn/Fe ratio ratio than than unaltered unaltered taconite, taconite, but their mode and median for this ratio The ratio are much lower. lower. The sideritic iron—formation contain the most manganese sideritic sections of the iron-formation and the goethite-rich oxidized sections sections contain contain the the least. least. There appears appears to to be be no no significant significant variation variation in in the the Mn content content There of the Biwabik laterally if only only unoxidized samples samples are are considered. considered. There is, is, however, however, a significant significant difference between the the four four members; members; the means in in per per cent cent Mn Mn are are as as follows: follows: Lower Cherty Cherty -- 0.67, Lower Lower Slaty -. Slaty - 0.44, Upper Cherty Cherty -- 0.34, Upper Slaty Slaty - 0.29. In an attempt variations in in the the Mn content content aa attempt to to show the local variations trend surface surface was computed for an an area area with closely closely spaced spaced holes. holes. The trend surface f(TJ,V,W) ) accounts for 52 per cent surface (%Mn (%Mn == Xn = f(U,V,W) of the sum sum of of squares. squares. Deviations from from the trend surface surface cut cut across across thus suggesting of the variability the formation formation thus suggesting that some some of variabilitymay may be be the secondary oxidation planes. due to due to secondary oxidation and and leaching leaching along along joint joint planes. ) 22 �SOME ASPECTS SOME ASPECTSOF OFTHE THEPEGMATITES PEGNATITESIN IN THE THE FELCH FELCH DISTRICT DISTRICT,9 DICKINSON DICKINSON COUNTY, COUNTY, MICHIGAN HICHIGAN Geoffrey W. Geoffrey W. Mathews Mathews Department of Geology Department Geology University, Cleveland, Cleveland, Ohio Western Reserve University, cut the the pre-Animikian Numerous simple, simple, unzoned un zoned pegTnatites pegmatites cut units in in the the Feich Felch district. district. Size and shape shape of of the the metamorphic units pegmatites vary from small small sinuous sinuous bodies in the the Mill Pond Granite Gneiss to to large large irregular irregular masses masses in in the the Solbert Solbert Schist. Schist. to subdivide the the pegmatites into meaningful In an attempt attempt to groups, pegmatites groups, the Be, Be, Mo, Mo, and and Ti contents of twenty unclustered pegmatites were determined determined spectrographically. spectrographically. Ratios of the concentrations of of these these elements elements provide provide aa basis basis for for separating separating the the pegmatites pegmatites into into two two distinct distinct groups. groups. AA similar similar analysis analysis was run on the granite granite dikes and samples of of the the granite granite gneiss gneiss in in the the Feich Felch district. district. Seven of and samples the pegmatites (Group II pegmatites), pegmatites), characterized by a relatively relatively high Ti:Be+Mo ratio, ratio, plot in in the the same same area area of of aa relative-percent relative-percent triangle diagram as the Group the granite granite dikes dikes and and the the granite granite gneiss. gneiss. Group comprisingthe the remaining remainingthirteen thirteen of the II pegmatites, comprising the pegmatites pegmatites and characterized by by a relatively relatively low low Ti:Be+Mo ratio, ratio, plot plot in in aa distinctly different different region region on on the the diagram. diagram. Correlation coefficients coefficients Be—Mo, Be-Ti, Be-Ti9 and Mo-Ti Mo—Ti also emphasize the difference between between Be-Mo, the two groups. groups. Group II pegmatites and the the granite dikes and gneiss show small small positive positive correlations between Be Be and Mo Mo and relatively show large negative correlations between Be-Ti and and Mo-Ti. Ho-Ti. Group II II pegpegmatites have a large positive correlation between Be-Mo and small small correlations between Be-Ti and Mo-Ti, positive and and negative negative respectively. respectively. Mo-Ti, positive There appears to to be be no simple simple relation relation between geographical geographical loca.tion, size, size, shape, shape, or or host host rock rock unit unit and and the the two two groups groups of of location, pegmatites. The strikes strikes of of bodies bodies within within the the different different groups, groups, however, are divergent. divergent. Strikes of Grou.p Group II pegmatites are are confined confined however, are 0 E., to the range N. 80° E., whereas the the strikes of Group II to N. 300 30 0 E. E. -- N. 80 peginatites are seemingly haphazard. pegmatites are haphazard. It is suggested suggested that the in the the Felch the two two groups groups of pegmatites in district district represent represent either either (1) (1) different different parental parental sources, sources, or or (2) (2) intrusion at at different stages stages of of the the progressive progressive differentiation differentiation of of intrusion a single parent magma under different different tectonic tectonic controls. controls. 23 23 �LAKE COUNTY, THE SAUBLE SAUBLE GEOPHYSICAL GEOPHYSICAL ANOMALY, ANOMALY, LAKE COUNTY, MICHIGAN MICHIGAN THE Howard J. J. Meyer and Howard and William J. J. Hinze of Geology, State University, Geology, Michigan Michigan State University, Lansing, Michigan Michigan East Lansing, Department Department A detailed gravity and magnetic survey was conducted of the A Sauble anomaly of Lake County, County, Michigan. This outstanding outstanding anomaly anomaly is a circular magnetic and gravity high having residual maximum and 22 22 milligals milligals respectively. respectively. The The comcomamplitudes of 1,130 gammas and bined gravity gravity and and magnetic lnagnetic analysis analysis method method utilizing utilizing Poisson's equation was applied applied to to the the residual residual anomalies, anomalies. An idealized idealized case case was employed employed to to check check the accuracy accuracy of of the the combined combined analysis analysis method. method. form, size, The composition, composition, form, size, and depth of the anomalous body were studied further by depth determinations and by fitting idealized cases to the observed anomaly anomaly profiles. profiles. It was concluded that that the the anolnalous body body is is a very basic Precambrian intrusive stock. The anomalous The the body and the the Precambrian surface in this elevation of the top of the area is about 8,000 to 99000 feet below 9,000 feet below sea sea level. level. 24 �THE THE SEDINENTOLOGY SEDIMENTOLOGY OF THE THEPRECAMBRIAN PRECAMBRIAN ROVE ROVE FOPUATION FORMATION NORTHEASTERN MINNESOTA-! MINNESOTA~/ IN NORTHEASTERN G. B. Moray Morey G. B. Department of Geology Geology and and Geophysics9 Geophysics, University of Minnesota9 Minnesota, Minneapolis The Middle Middle Precambrian Rove Formation, the upper part of the the The Formation, the Aninikie Group, Group, is estimated to to be at least 3,200 feet thick, Animikie thick, and is and the is exposed between northwestern Cook County, County, Minnesota Minnesota and Thunder Bay is aa sequence sequence of of gra~~acke, grayacke, Bay district, district, Ontario. Ontario. It is argillite, locally abundant argillite, abundant intraformational intraformational conglomerate, conglomerate, quartzite, quartzite, and carbonate carbonate rocks. rocks. This sequence was deposited some some time between 2.0 b.y. b.y. ago in a northeast-trending basin, b.y. and 1.7 b.y. basin, the the conconfiguration of which which was was probably controlled by a pre-existing pre—existing figuration structural structural grain. grain. Detailed mapping in the South Lake 7*-minute 7i-minute quadrangle, quadrangle, combined with a field and laboratory study study of approximately 150 other scattered stratigraphic stratigraphic sections provide provide aa basis basis for for the the recognition of four informal lithologic units. units. From oldest to to youngest these these are: are: (1) lower argillite, (1) argillite, 400 feet thick; (2) (2) transition transition beds beds of of inter— interbedded argillite and graywacke, grayacke, 70 argillite and 70 -- 100 feet feet thick; thick:; (3) (3) thin-bedded graywacke, gra~Nacke, as much as as 2,000 feet thick; thick; and (4) (4) upper graywacke— gra~Nacke­ quartzite, at least 700 feet quartzite, feet thick. thick. It is concluded that the argillite argillite and and associated associated graywackegraywackesandstone and and graywacke-siltstone graywacke-siltstone units units were were deposited deposited in in moderately sandstone deep, quiet quiet water water which which was was probably probably marine. marine. Repeated sedimentation sedimentation deep, units one to three feet thick indicate indicate sediment sediment transport and and deposition A sedimentation unit reconstructed deposition by by turbidity turbidity currents. currents. A from composite sections sections consists of (1) (1) a basal conglomeratic gray— graywacke, (2) wacke, (2) aa structureless structure1ess unit unit that that grades grades indistinctly indistinctly into into (3) (3) a graywacke that that is is overlain overlain by by (4) (4) aa laminated laminated graywacke, graywacke, graded grayvJacke by (5) (5) small-scale cross-bedding, or or (6) (6) conwhich may be modified by torted one or several torted bedding. bedding. Any Anyone several of these may be absent, absent, but the argillite. unit unit is is always always overlain overlain by by (7) (7) an argillite. Post-depositional Post-deposition31 soft-sediment soft-sediment structures structures such such as as load load casts, casts, flame structures, clastic dikes, dikes, bed pull-aparts, pull-aparts, overfolds, overfolds, and flame structures, clastic micro-faults micro—faults indicate indicate rapid rapid deposition of of Rove sediments, sediments, active active bottom currents, and post-depositional post-depositional deformation. deformation. A A detailed analysis analysis of of paleocurrent directional indicators indicators such such as groove casts, casts, flute flute casts9 casts, dendritic dendritic ridges, ridges, as grain lineations, lineations, groove and and cross-bedding show that the turbidity currents had a southerly southerly trend perpendicular perpendicular to to the the axis ~xis of of the the Rove Rove basin. basin. However, ripple ripple marks, winnowed lag deposits at at the the tops tops of many graywacke graywacke beds9 beds, and festoon-type festoon-type cross-bedding show that the the turbidities were later modified by by bottom currents currents that that trended trended southwesterly southwesterly parallel parallel to to the axis of the the basin. basin. —'Work ~/Work *1 done the Minnesota Geological Survey Survey done on behalf of the 25 �The heavy minerals of of the the Rove Rove are are characterized characterized by by epidote— epidotegroup minerals, sphene, and tourmaline~ minerals, apatite, apatite, sphene, tourmaline, and are typical of pre-Middle Precambrian igneous rocks now exposed north of the present outcrop area of the Rove Formation. Formation. Thin section and and X-ray analyses of 200 200 samples show that the the angular, poorly sorted grains of elastic graywackes consist of angular, clastic quartz and plagioclase (niü_An25) embedded plagioclase (AnlO-An25) embedded in in an an argillaceous argillaceous matrix matrix that now consists of quartz, chlorite, chlorite, and and muscovite. muscovite. The finefinegrained, fissile fissile argillite argillite and mudstone have have the the same grained, srone mineralogy and micro-textures micro-textures as as the the graywacke. graywacke. to pre-Keweenawan tilting removed an unknown Erosion subsequent subsequent to the formation formation prior to the the deposition of Lower Keweenawan amount of the sedimentary rocks. rocks. The intrusion of Middle Keweenawan igneous rocks sedimentary Rove Formation to to a variety of caused local metamorphism of the Rove mineral, assemblages now now assigned assigned to to the pyroxene- and mineral assemblages and hornblende— hornblendehornfels facies, hornfels facies, but but the the remainder remainderisisessentially essentiallyunnieta.morphosed. unmetamorphosed. 26 26 �SEDIMENTATION OFOFMIDDLE FINLAND SEDflVIENTATION MIDDLEPRECAMBRIAN PRECJMBRIANQUARTZITES QUJRTZITES IN IN FINLAND Richard W. W. Ojakangas Department Departmentof of Geology, Geology,University University of Minnesota, Minnesota, Duluth quartzites, metamorphosed 1,800 m.y. m.y. ago, The Jatulian quartzites, ago, were studied in in eastern, eastern, central, central, and and northern northern Finland Finland to to decipher decipher the the studied sedimentary history of the the original original sandstones. sandstones. Erosional remnants remnants thick, indicate an initial of the formation, formation, several hundred meters thick, distribution over over an an area area of of about about 400,000 400,000 km2. km2. The quartzites at at some localities localities are are completely completely recrystallized~ recrystallized; at at other other localities localities some they are are sheared sheared but but retain retain sedimentary sedimentary characteristics. characteristics. Most Most of of the quartzites were formed under the under conditions conditions of of the the amphibolite amphibolite facies, facies, with the degree of metamorphism increasing from east to west. west. The sandstones sandstones were mainly clayey orthoquartzites, orthoquartzites, clayey subsubarkoses, arkoses, and and clayey clayey arkoses. arkoses. The clayey matrix has been recrystallized into Zircon is is the the only abundant nonopaque nonopaque detrital heavy into mica. mica. Zircon mineral; mineral~ most other heavy minerals were formed formed during during metamorphism. metamorphism. The source rocks were mainly granitic with indeterminate proporproportions of granites and and gneisses. gneisses. Zircon varieties indicate derivation from both para- and ortho-gneisses. Large parts of the formation are mineralogically and tex~urally evidently detritus on on the the are texturally mature; mature; evidently weathered, vegetation-free vegetation-free landmass, as well as as similar similar sediment sediment landmass, as supplied by by streams streams from from the the east, east, was was reworked reworked by by wind wind and and then then by by supplied the shallow shallow sea. sea. Clay was probably carried carried into the sea sea vuth with quartz sand, sand, separated separated there there by by wave wave and and current current action, action, and and then again again mixed mixed with with sand sand prior prior to to burial. burial. Carbonates and shales shales were deposited deposited upon the sandstones. upon the sandstones. Analysis of of cross-bedding indicates that the the major paleocurrent Analysis movement in the Jatulian Sea was toward the west-northwest, with a prominent current current movement movement toward toward the the south-southwest. south-southwest. secondary but prominent secondary One of these currents probably moved parallel to the shoreline shoreline and the other other normal normal to to it. it. The The sea sea probably probably transgressed transgressed eastward eastward upon upon the a stable, stable, low-lying low-lying landmass. landmass. 27 �PETROLOGYOF OFTHE THE AMBERG M'ERG PRECPJYRIAN PETROLOGY PRECAMBRIAN CRYSTALLINE CRYSTALLINE COMPLEX, NORThEASTERN NORTHEASTERN WISCONSIN WISCONSIN COMPLEX, Dennis P. Rebello P. Rebello Department of Geology Western Reserve University, University, Cleveland, Cleveland, Ohio Reconnaissance study study of of parts of of northeastern Wisconsin by J. A. A. Cain and Quinnesec J. and others has resulted resulted in in recognition recognition of the Quinnesec Formation, pink mberg AmbergGranite, Granite,and andgray grayAniberg Amberg Granite. Granite. Detailed Formation, mapping of approximately approximately 100 square square miles during the summer summer of 1964 has has resulted resulted in in the the identification identification of of an an additional additionalunit, unit, the the.Amberg Amberg addition, diabase and basalt dikes were found found Granodiorite. In addition, cutting the the granitic granitic units. units. The Quinnesec Formation Formation include include greenstones greenstones and and meta-basalts, meta-basalts, which contain contain plagioclase plagioclase and and hornblende hornblende and and minor minor amounts amounts of of chlorite, chlorite, epidote, epidote, and and quartz. quartz. The unit is is exposed exposed along along the the north north and and northnortheastern boundaries of this area area and and in in aa small small triangular patch patch south south of of Amberg. Amberg. The major part part of of the the area is underlain by the the pink Amberg niberg The Granite, which is Granite, is circular circular in in outline. outline. The rocks rocks are are fresh, fresh, massive, massive, coarse-grained coarse-grained pink pink granites. granites. Locally they they have aa rapakivi rapakivi tex±ure. texture. Xenoliths of Quinnesec Formation and gray Amberg _~berg Granite are are not microcline-perthite, sodic uncommon. The rocks are are composed of microcline-perthite, sodic oligoclase, quartz, biotite, and and hornblende. hornblende. Minor Minor shear shear zones zones are are present. Lineation and foliation are are poorly poorly developed. developed. The The unit unit intrudes the the gray gray J3mberg Amberg Granite, and the the Granite, Amberg Amberg Granodiorite, and Quinne sec Formation. Formation. Quinnesec The gray gray Amberg is exposed exposed in the center center of of the the area area Pmberg Granite is and is almost surrounded surrounded by by the the pink pink unit. unit. It consists consists of of fresh, fresh, massive, massive, medium- to fine-grained gray gray granites granites composed composed of of orthoclaseorthoclaseperthite, oligoclase—sodic oligoclase-sodic andesine, andesine, quartz, quartz, biotite, biotite, and and hornblende. hornblende. The rnberg Amberg Granodiorite Granodiorite covers covers most most of of the the southeastern southeastern part part of of The the area. area. It is is coarse-grained, coarse-grained, altered, altered, and and has abundant abundant xenoliths xenoliths of the Quinnesec Formation. Formation. Shear zones and mafic schlieren schlieren are are common throughout the unit. The rocks consist of orthoclase—perthite, orthoclase-perthite, oligoclase—andesine, quartz, biotite, oligoclase-andesine, biotite, and ffild hornblende. hornblende. Modal analyses analyses and and chemical chemical analyses analyses for for alkalies alkalies suggest suggest that that the the granitic units units represent represent independent independent intrusions. intrusions. Field Field and and petrographic petrographic data data point point to to aa m.agmatic magmatic origin for for the the granites. granites. 28 �A STUDY ON ON THE THE HYDROLOGY MINNESOTA~I A STUDY HYDROLOGYOF OFPOTHOLES POTHOLES IN IN MINNESOTA- M. Schwartz Schwartz George M. Professor Emeritus, Department of Geology Professor Emeritus, Department University of of Minnesota, Minnesota, Minneapolis study of of the hydrology of potholes (ponds) (ponds) in Minnesota by A A study the writer and and associates associates has has been been carried carried out out since since 1962. 1962. Potholes and adjacent adjacent lakes were selected selected in in various parts of the state state to and to represent as as many different topographic and geologic situations situations as as represent practical. Detailed Detailed observations observations were were made made on on 39 39 potholes and and lakes lakes and limited observations on about about 60 60 others. others. The field field work included sinking sinking test holes adjacent to shore shore to determine the the character character of of the the soil soil and and the the depth depth of of the the water water table, table, observing the the water (and (and ice) ice) levels levels in in the the ponds, ponds 9 collecting collecting bottom bottom observing sediments, the bottom sediments according sediments, and classifying samples of the to soil soil type. type. Limited X-ray X-ray and and pollen pollen studies studies of of selected selected samples samples also made. made. Cross-sections Cross-sections and and graphs graphs were prepared prepared of of all all were also pertinent pertinent data. data. Tentative results results and and conclusions conclusions include include the the following: following: 1. The glacial deposits adjacent to the water are extremely 1. are reasonably permeable as variable lithologically, but but most. most are as shown shown by movement of water out of of test test holes. holes. 2. No consistent consistent relation relation exists exists between the open open water surface surface 2. No and the the groundwater surface surface except except in in the the Anoka Anoka Sand Sand Plain. Plain. 3. Most of the the ponds and and lakes show show a similar similar pattern pattern of of 3. fluctuation of of the the water water levels levels throughout throughout the the year. year. Li. 4. With few exceptions, al'e exceptions, the water levels in the ponds are determined mainly mainly by by the the relation relation of of precipitation precipitation to to evapotranspiration. evapotranspiration. 5. In highly permeable soil, soil, such such as as in in the the Anoka Anoka Sand Sand Plain, Plain, 5. the surfaces coincide and fluctuate the open water and groundwater surfaces fluctuate together by movement of water water from one one to to the the other as required by Li, 4, above. 6. 6. Most lakes and potholes do not contribute significant significant quantities of water water to to underground underground storage. storage. The bottoms of potholes normally consist of silt, 7. silt, clay, clay, and 7. organic matter. 8. S. In ponds ponds that that lose lose water water by by seepage, seepage, the the water water level level rises rises during the the spring spring break-up and periods periods of heavy rains, rains, then then declines declines far beyond possible possible loss loss by by evapotranspiration evapotranspiration and and continues continues to to far freeze—up; collapse of the ice occurs in severe decline after the freeze-up; cases of loss loss of of water. water. In contrast, remain relatively relatively contrast, most ponds remain stable while covered covered by by ice. ice. — Funds to :/Funds to start start the program were made available in 1962 by the the Minnesota State State Soil Soil Conservation. Conservation. Supervision of the project project and and funds were were provided by the Department of Agricultural additional funds Engineering. 29 �PRELIMINARY RESULTS OF GEOCHEMICAL GEOCHEMICAL PROSPECTING PROSPECTING PRFJJIMINARY RESULTS OF NORTH NORTH OF OF THE THE MARQUETTE MARQUETTE IRON IRON RANGE9 RANGE? MICHIGAN MICHIGAN Kenneth Segerstroni Kenneth Segerstrom Survey, Denver? Denver, Colorado U. S. Geological U. Geological Survey? Colorado material Geochemical prospecting by means of sampling of surficial material has been conducted in Marquette County during the past two field field seasons. More than 600 samples samples have been collected and and chemically chemically analyzed for for their their total total heavy-metals heavy-met~_s content. content. Many of the samples samples were also analyzed analyzed for copper, copper? lead, lead? zinc, zinc, and manganese, manganese? and and some some samples were examined examined spectrographically for for cobalt? cobalt, nickel, nickel, and other other elements. elements. AA few few were assayed assayed for for gold gold and and silver. silver. Preliminary results resultshave have encouraged encouraged the the continuance continuance of ofsampling sampling Preliminary in so-called Northern 11Northern Range, Range?:1 just justnorth northofofthe theDead Dead River River in the so-called discouragedits its continuance in the the Southern storage and have continuance in 11Southern storage basin, and have discouraged Range," between between the the Dead Range," Dead River and and the the Marquette Iron Range. Range. In the the Northern Range Range good good results have been been obtained obtained on on the the lee lee side, side, Northern glacially speaking, of ridges ridgesofof resistant pre-Animikiegraywacke graywacke speaking, of resistant pre—.Animikie and volcanic volcanic rocks rocks which whichlie lie on on the the limbs limbs and and crest crest of an an anticlinoriuni. anticlinorium. and The ridges ridges are are bordered to the north and and south south by synclinal synclinal valleys underlain by by poorly ridges tend tend poorlyresistant resistant slate. The The stoss stoss side side of ridges to have have a thick till cover and the valleys are deeply filled ~nth with to glaciofluvial sand. glaciofluvial sand. Soils underlain by the sand do the till and the sand not not show show concentrations concentrations of of heavy heavy metals. metals. The best results are are obtained where the cover of of surficial surficial materials materials (chiefly (chiefly glacial) glacial) colluviun derived is thin, thin, and and where where there there are are abundant abundant adrnixtures admixtures of of colluviu..m is from from the the bedrock bedrock ridges. ridges. Anomalous copper and and lead or zinc, Anomalous concentrations concentrations ol' of copper zinc, of of the the order of hundreds of parts per million, million, have shown up in samples samples taken in Nt N sec. sec. 30, 30, T. T. 49 49 N., N., R. R. 27 27 W. W. In that area area of of no no mines mines or or prospects, the exposed bedrock locally contains fine—grained prospects, fine-grained disseminated pyrite and galena. galena. In In the same same township, township, lesser anomalies anomalies that that are are likewise likewise apparently unrelated unrelated to to known known sulfide sulfide SE- sec. deposits have shown up in SEt sec. 21, 21, NW sec. sec. 27, 27, &3- sec. 26, 26, and N'vJt NT4 sec. sec. 36. 36. NWt 30 st �KEWEENAWFAULT, FAULT, HOUGHTON COUNTY, MICHIGAN KE"WEENAW HOUGHTON COUNTY, MICHIGAN Kiril Kiril Spiroff Michigan Michigan Technological Technological University, Universitys Houghton, Michigan wifl describe a few of the geologically The talk will geologically interesting interesting features found found associated with the features the Keweenaw Fault in Houghton County, Michigan. 31 31 �__________ _______ ORGANIC GEOCHEMISTRYOF OF ROSSBURG,llEAT ROSSBURGPEAT BOG, ORGA1'HC GEOCHEMISTRY BOG 9 AITKIN COUNTY, COUNTY 9MINNESOTA—' MINNESOTA- F. M. M. Swain 9 Mykola Swain, Mykola MalinowskY9 Malinowsky, and and David Nelson of Geology Geology and and Geophysics, Geophysics, Department of of Minnesota Minneapolis University of Minnesota,9 Minneapolis sees. 18 and and 19, 19~ Rossburg peat bog occupies about 600 acres in secs. T. 47 N., R. R. 25 W. W. and sec. T. sec. 24, T. 47 47 N., N. 9 R. R. 26 26 W., W., Aitkin Aitkin County, County, Minnesota. Minnesota. Coarse-detritus, Coarse-detritus 9 reddish brown Sphagnum moss peat exbends extends to depths of of from from 12 12 to to 19 19 feet feet and and is is underlain underlain by by fine-detritus, fine-detritus 9 to dark brown to black copropel, coprope1 9 and and sapropel-peat sapropel-peat to to depths of of 22 22 feet feet or more. more. Below the peat lies slightly slightly calcareous calcareous and and organic organic clay clay to depths of 27 feet to feet or or more, beneath beneath which which lies lies sand. sand. Moisture content content of the peat peat is is 85-90%; 85-90%; that of of the the underlying clay 50-68%, 50-68%9 and and of of the the sand sand 34%. 34%. Ignition loss ranges from 67.6% clay to 96.5% in the the peat and from 11.0% 11.0% to to 15.5% 15.5% in in the the clay clay and and sand. sand. pH values increase increase gradually from from 4.0 at at the surface surface of of the the peat peat to to the peat and are about 6.8—7.0 7.2 at the base of the 6.8-7.0 in the clay and sand. Eh values gradually decrease from from +420 mv at the the surface surface of of sand. Eh my at my at 28 feet the peat to -20 mv feet in in the sand; sand; in in general, general 9 Eh values values are are negative below below 16 16 feet feet in in the the peat. peat. negative Kjeldahl nitrogen K.jeldahl nitrogen averages averages about about 1% i% in the upper 33 feet of the peat, 2.8%; it decreases peat 9 below which it increases to between 1.8% and 2.8%; abruptly to 0.5% or less in in the the underlying underlying clay. clay. Protein amino amino acids show distribution consistent with with variations in type of peat and nitrogen nitrogen content. content. Basic Basic amino amino acids occur throughout the the peat peat and and indicate prevailingly prevailingly acid acid conditions conditions in in the the history history of of the the bog. bog. Total carbohydrates average about about 100 mg/gm expressed as as glucose glucose equivalent in Sphagnum peat, peat, but decrease to 50-70 mg/gm mg/gm in in copropelic coprope1ic peat. peat. Glucose Glucose and and arabinose arabinose are are the the predominant predominant mononaccharides. mononaccharides. aromatic hydrocarbons and hydrated phenols increase Saturated and aromatic in total amount from 2x10—4 mnount from 2xlO- 4 g/g gig at at the the surface surface of of the the moss moss peat peat to to 4 4x104 gig ',4x10g/g at 44 feet, feet, below below which which a decrease decrease occurs to base of moss peat. Absorption Absorption spectra spectra of chromatographic chromatographic fractions fractions show show that that 2-naphthol 2-naphthol is is an an important important hydrocarbon hydrocarbon constituent constituent of of the the moss moss peat. peat. It It is 4_s suggested suggested totohave haveformed formed either either froma protein—naphthylamine a protein-naphthylamine from by by Bucherer Bucherer reaction: reaction: NH3 (NH4)2 4 ,OH ;' .: "',-" :.:-, NH 22 i: ~ .' ~, ;:;..-~ +H 0 2 or from from aa plant-growth plant—growth accelerator (auxin) (auxin) such as naphthyiacetic naphthylacetic acid: acid: CH2 COOH CH 2 CO OH ~:; .......... ~/Work Work i ...-., :1 "1 :1 b~~aif~of 1 done partly partly on behalf of the the Minnesota Geological Geological Survey Survey done 32 32 �Beta-carotene Beta-caroteneasas observed observedininUV-visible UV-visiblespectra spectraisis aa significant componentofofthe thecopropelic copropelicpeat peatbut but is is nearly absent component absent from from the overoverlying moss It isisinterpreted originating from moss peat. It interpretedasas originating fromphytoplankton phytoplankton whenthere therewas wasa alake lakein in the the area. Pheophytini!:a from when area. Pheophytin from chlorophyll relationship to to facies fades of of the the peat. peat. shows a similar relationship Carbonyl-group compounds observed in IR spectra are are quantitatively more important in the moss peat than in in the underlying lake peat. peat. The organic analyses aid aid in in understanding the developmental the deposits deposits and in evaluation of them history of the them as as commercial commercial of plant nutrients sources of nutrientsand and peat peatchemicals. chemicals. sources 33 �TECTONICS OF THE THEKEWEENAWAN KEWEENAWAN BAS~N, TECTONICS OF BASN, WESTERN LAKE SUPERIOR REGION-SI REGION~/ WESTERN LAKE SUPERIOR ~valter S. S. White ~Jhite Walter U. S. Geological Geological Survey, Survey, Beltsville, Maryland U. S. Beltaville, Maryland The subsurface of the thewestern western Lake Lake Superior Superior region region The subsurface structure structure of has been analyzed by combining surface surface geologic, geologic, aeromagnetic, gravity, and paleomagnetic paleomagnetic data. data. Surface attitudes and and map map patterns patterns gravity, and suggest that the Keweenawan sedimentary rocks have the general the upper Keweenawan form of a lens thickening to southeast, away from aa featheredge featheredge to the the southeast, along the shore of of Lake Lake Superior. Superior. Graphic subtraction subtraction of the Minnesota shore the assumed gravitational effect of this sedimentary lens from the Bouguer anomalies anomalies of of the the region region leaves leaves aa residual residual anomaly anomaly due due primarily to to the the mafic mafic lavas lavas and and intrusives. intrusives. When residual maps for various assumed thicknesses of the sedimentary sedimentary rocks are compared with the the aeromagnetic aeromagnetic maps, maps, the the patterns patterns more more or or less less coincide coincide when when with the thickness thickness of sedimentary sedimentary rocks rocks under the the Bayfield Peninsula Peninsula is is the The analysis leads to recognition assumed assumed to to be be at at least least 25,000 25,000 feet. feet. of the following stages stages in in the the tectonic tectonic history history of of the the region: region: (1) Accumulation, Accumulation, during during middle middle Keweenawan Keweenawan time, time, of a thick thick (1) series of lava flows and and mafic intrusives intrusives in in two two basins basins or or troughs, troughs, separated separated by a positive positive area area that that trends trends more more or or less less north-south north-south across the Bayfield. Peninsula, Wisconsin, Wisconsin, in which which the lavas Bayfield Peninsula, lavas are are thin or or absent. absent. (2) Evolution Evolution of of the the present present Lake Lake Superior basin, basin, with with axis axis (2) trending northeast, late Keweenawan Keweenawan time. time. northeast, during late the Ashland syndilne (J) syncline and the major faults (3) Development of the Keweenaw, Lake Owen) Owen) still later in of the region (Douglass, (Douglass, Keweenaw, Keweenawan time. time. the Duluth Gabbro Complex is a sheet of fairly uniform If the Duluth Gabbro thickness dipping to to the the southeast under Lake Superior, Superior, the the combined combined thickness of gabbro should attain a maximum somewhere somewhere gabbro plus lavas should under under the the lake. lake. The gravity maximum is actually about 10 miles northwest of the Minnesota shore shore of the lake, lake, suggesting that that the gabbro pinches out out beneath beneath the the lavas lavas somewhere somewhere near near the the shore. shore. ~/Published with the permission of of the Director, U. S. S. Geological Geological — Published with Director, U. Survey Survey 34 34 �CONTRIBUTIONS CONTRIBUTIONS OF ROCK ROCK PHYSICS PHYSICS TO TOGEOLOGY GEOLOGY Robert J. J. Willard Robert Willard u. S. S. Bureau of Mines, Mines, Minneapolis Minneapolis U. Laboratory Laborato~ study study of rock rock behavior behavior can be a useful guide to to understanding understanding of of rock rock behavior behavior in in the the field. field. A goal of of rock rock physics physics A goal research at the the Bureau of Mines Mines Minneapolis Center is the identificaidentification, tion, classification, classification, and definition of rock and mineral properties that influence behavior behavior under under laboratory-imposed laboratory-imposed stresses. stresses. AA signifisignifithe current research effort involves petrographic petrographic analysis analysis cant part of the of rock fabric fabric in in core core samples. samples. material can can be be regarded regarded as as having having some some degree degree of of Most rock rock material Most fabric anisotropy, anisotropy, as expressed by population parameters of mineral species, species, aa tangible end-product end-product of of geologic geologic history. history. Such parameters of compositional anisotropy may at times be reflected in the mechanical response stresses. response of laboratory specimens to artifically-created stresses. example, tensile failure For example, failure studies in such rocks as granite and gneiss show show definite of fracture fracture path characteristics characteristics definite correlation of with fabric anisotropism, as expressed in in feldspar, feldspar, amphibole, amphibole, mica, and quartz. quartz. Similarly, Similarly, field correlation exists for for rocks having rift, grain, grain, bedding, bedding, or other planar features, features, resulting in fracture rift, fracture patterns patterns which which are are used used to to advantage advantagebybyquarr3nnen. quarrymen. Shear failure, failure, on the other hand, hand, is not necessarily related related to fabric anisotropy. anisotropy. Inclusion of fabric study can supplement supplement fabric anisotropism in field field study correlation of of deformed deformed and/or and/or fractured fractured rock rock material material with stresses correlation to which it has been subjected during its geologic history. history. Such Such fabric study study can can be facilitated facilitated by by petrographic petrographic work without without use use of of fabric Thus, by making thin sections normal to to core axes a U—stage. U-stage. Thus, a drilled from field-oriented rock in in three, three, mutually-perpendicular directions, a three-dimensional three-dimensional picture picture is is obtained obtained of of fabric fabric directions, a anisotropy such such as, as, e.g., e.g., foliation. foliation. Rock physics is using this anisotropy approach in the the testing testing of an oriented block from the the St. approach st. Cloud area to correlate fabric fabric anisotropy anisotropy with with field field anisotropy. anisotropy. 35 35 �AN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY OF WESTERN \,oJESTERN LJ\KE LAKE SUPERIOR J\N Richard J.J. Wold Wold Department of of Geology, Geology, The University of Wisconsin, Wisconsin, Madison, Madison, Wisconsin In March 1964, over the the l96'4, an an aeromagnetic aeromagnetic survey survey was was conducted over western half half of of Lake Lake Superior, SUperior, covering covering the the area area westward westward from from the the tip tip of of the the Keweenaw Keweenaw peninsula peninsula to to Duluth, Duluth, Minnesota. Minnesota. The survey survey concon7,500 miles miles of north-south flight flight lines spaced at six-mile sisted of 7,500 intervals. A intervalS. A digital recording proton precession magnetometer system system installed in in aa Navy Navy P2V-5 (Neptune) (Neptune) aircraft, aircraft, flown flown 3,000 feet feet above above sea level, in the survey. survey. level, was used in The results results of the survey survey indicate indicate aa very very flat flat magnetic magnetic character character over the the major major portion portion of of Lake Lake Superior. Superior. Several known geologic features are are traced traced by the anomalies: the the Keweenaw, Keweenaw, Douglas, Douglas, the magnetic anomalies: and Lake Owen faults, faults, and and the the Gogebic Gogebic and and Marquette Marquette iron iron ranges. ranges. The existence of the the Isle Royal fault appears to be confirmed, confirmed, and possibly it it extends extends as as far far east east as as Superior Superior Shoals. Shoals. The The existence existence possibly questionable;9 however, however, a fault may be of a North Shore fault is questionable present south south of of Isle Isle St. st. Ignace. Ignace. present Western Lake Superior appears to be underlain by by aa syncline, syncline, bounded on the north and south south by major fault systems, systems, which continues continues southeasterly into into the the eastern eastern half half of of Lake Lake Superior. Superior. southeasterly 36 36 �GEOLOGICAL GEOLOGICAL ANALYSIS AND AND REMEDIAL REMEDIAL ACTION ACTION IN AN AN OPEN OPEN PIT PITROCK ROCK SLIDE SLIDE D. H. H. Yard.ley Yardley D. School of of Mineral Mineral and and Metallurgical Metallurgical Engineering9 Engineering, School University of ofMinnesota, Minnesota, Minneapolis Minneapolis Tworock rockslides slides in the wall of an Two thesame same 't<Tall an open open pit pitininiron—formation iron-formation were studied to to determine determinethe thecause causeofofthe the slope slope failures, failures, and were studied and to propose remedialmeasures measurestotoprevent preventfurther further failures. failures. propose remedial The upperslide slide zone zone is is about The upper about 200 200 feet higher higher in in elevation elevationarid and LOO feet feet west of the lower one. one. 400 Although the the immediate immediate cause cause of of Although the the rock rock failures failures was was mining mining activity, activity, the the real real cause cause of of the the instabilinstability is the the presence of geologic structural structural defects. defects. is o SE. A iron—formationstrikes strikes N.35°E. The iron-formation N.J5°E. and and dips l2 system of of 12°SE. A system near—vertical joints near-vertical joints cuts the strata; strata; the most prominent set set strikes strikes A 50- to N.145°W,, N.45°W., parallel to the pit wall and and to to the the ore-trough. ore-trough. A o 100-foot thick fault zone that strikes N.5O°E. and dips 25—3O°SE lOO-foot strikes N.50 E. 25-JO oSE crosses the upper slide slide area area and and the the top top of of the the lower lower one. one. the upper upper slide slide is is aa J-foot 3—foot chloritic chioritic "green 'green shale shale The base of the layer. and permeable permeable to to water, the material material is is layer. iNhere Where it is fraculred fractured and water, the physically weak weak and and tends tends to to ttsqueeze "squeeze out.,J is stratistratiphysically out. This layer is graphically above above the the lower lower slide slide area. area. The chronology chronology of of the the slope slope failures and check check surveys surveys also also support support the the conclusion conclusion that that the the two two failures and slides are are not not expressions expressions of a single deep-seated cause cause and and thus thus slides single deep-seated could be treated treated independently. independently. j Remedial action action for for the the lower lower unstable unstable zone zone consisted consisted of of changing changing Remedial the sequence so so as to to decrease the the ratio ratio of of weight to to potential the mining sequence failure failure plane plane area. area. The upper slide slide area constituted an an unusual problem problem because economic considerations required haulage over rock-fill and over the economic unstable zone zone where all the elements creating instability instability still still The remedial the slide rock and exLsted. existed. The remedial design involved removal removal of the installation of post-tensioned post-tensioned cables cables in in rock rock back—fill. back-fill. The system system il is designed designed to to provide provide lateral lateral restraint restraint to to the the 'squeezing' 'I squeezing layer, layer, is increased frictional frictional resistance resistance at at the the back-fill back-fill bench bench interface, interface, and increased shear shear resistance within the back-fill by placing it in compression. This is believed to be the first designed use of postcompression. tensioned rock—fill rock-fill for for control control of of aa potential potential slide slide zone. zone. 37 37 � https://digitalcollections.lakeheadu.ca/files/original/5c09d2e9390894b4e68e13c6d3cb7f62.pdf 0bdef7544f3da876e9226dffa2551051 PDF Text Text FID TRIP GUIDE ST. CLOUD GRANITE DISTRICT CENTRAL MINNESOTA by R. K. Hogberg Minnesota Geological Survey University of Minnesota prepared for 11th ANNIJIiL INSTITUTE ON LANE SUPPRIOR GEOLOGY St. Paul, Minnesota, May 8, 1965 conducted by The Twin City Geologists �CONTENTS Page Introduction. . . Production ...... •••••••• •••a•••S5 2 ,.................. .•... •.•.....a• 2 •••••• •• a history. • . . , • , • • a Research by the General 3 a..••aa•aea•a 3 a•aaaaaaa•a•aaa•aaaaaaaaa a•aaaa•aaaaaaaaa••a 6 aaaaa 7 . . a i . a a •i• a a a a a a a a a a a a a •. a . a a 8 .....,.... 8 St. Cloud Gray Granodiorite. . a • a a a a • a as a. a a a a $ • • a. a a.. e.• a a as.. a 9 St. 9 geology. . . a a a • . a a • a . a a a • a • a • Rocklle C rysta].. quarry. . .. . a • a gray quarry. a a a a a a a a a a a a aaoaaa••aaaaaaa•aa •aaaaaa Shiely—Petters aggregate quarry. . • . • . •aaa•a.aaaaa aaaaaaaa• Introduction. • a • a a • a • a a • a a a a a . • a a a a a a a a a a • a a a • • • • • • • Cloud Red Granite. • • • • • as a a • a a a a a a a a a a • a aa • • a Quartz latite porphyry. •. . . . a • • ..•aa a . .aaaaaaaa•a a .' a a a a a a a a . • . a a a a • • a a . . a • a 10 Basalt and granite References cited. . .. a 10 a a a • a a •a a •a•. 12 aaaaaaaaaaaaaaaaaaaaaa 1 aa•aaaaaa•.aaaaa..••aaaaa• •a$• ILLUSTRATIONS Route of field trip, a • a. a a a a a a a a a a a a a a a a • a . a a a • Figure 1—-Generalized geologic section St. Cloud district.55555..... ii �ROCKVILLE ROUTE OF FIELD TRIP (Modified from Minnesota Highway Dept. Map) Scale ]:lLlóO �INTRODUCTION The purpose of this field trip is primarily to see the quarrying and processing operations of granite dimension stone in the St. Cloud district of central Minnesota. The Cold Spring Company will host the tour of their plant at Cold Spring. Leaders for the field trip will be I H. Yardley and R. K. Hogberg. Production History Quarrying began in the St. Cloud district in 1868, near the site of the present town of Sauk Rapids. The first salable products were rough From the late l880s until the late dimension stones and paving blocks. l92Os the sale of dimension stone rose steadily and reached a peak of $4,281,700 annually in 192:3. The major demand was for dimension stones obtained from St. Cloud Red, St. Cloud Gray, and Rockville granites.' From 1929 until the end of World War II sales were depressed and reached a low of $396,800 in 1943. The processing plants for dimension stone have decreased in number and increased in size since the early 190QU5 At present (1965) there are about 20 small granite processing plants, whereas in 1915 a record of 89 finishing plants were operated in Minnesota. However, due to consolidations and increased automation three of the plants-—two of which are located in the St. Cloud district——account for nearly all of the sales. One of the largest such plants in the world——that of the Cold Spring Granite Company—is our first stop. The 'hard' dimension stone industry of Minnesota has centered in the St. Cloud district. Those commercial quarries outside of the district—— in the Minnesota River valley and near Lake MUle Lacs—-are operated by St. Cloud—] ased firms. 2 �Sales of granite in the State in the decade 1952-1962 averaged The Rockville and the St. Cloud Gray "granites" about $3,327,000 annually. constitute most of the present sales from the St. Cloud district. Research by the Industry In recent years research by the industry has been largely confined The results have been quite success- to the field of product development. ful, have and resulted in the development of many new uses of dimension "granites in building construction. Among the new uses are: (1) precast monolithic wall units composed of a regular mosaic of 'granite blocks or, 'granit&' chips, in random arrangement, both set in a cement base; (2) floor tiles or patio-type pavements composed of granitic slabs with split or broken joints; "tumble stone," and built-up veneer (3) walls of split face ashlar or (4) various types of window unit facings composed veneer. granite Granite facings, the bread and butter of the industry, are specified in larger and thinner units than previously; as quarry of now result, the a blocks must be extremely large and free of fractures. GENERAL GEOLOGY The available geologic data on the St. Cloud district obtained by Margaret Skillman Woyski in 1945 and 1946. in a Ph.D. dissertation in 1946 and the largely Her work resulted a published paper in the Bulletin of the Geological Society of America in 1949. (Minn. was In 1961, Goldich and others Geol. Survey Bull. 41) published K/Ar and Rb/Sr ages on rocks of district and reviewed the current state of knowledge of the geology of the region. As a result of expansion of old quarries and opening of new quarries—- especially the Shiely—Petters "aggregate" quarry——excellent exposures are now available to observe the geologic relationships of the district. 3 �The commercial rock t,pes of the district have been given informal names such as St. Cloud Red, St. Cloud Gray9 Rockville, etc. These names have been used in the published literature (Woyski, l9149; Goldich and In addition, each of the others, 1961) and are now well established. companies has assigned many trade names to the dimension stones they sell. Figure 1 Generalized Geologic Section - (millions of years) 0.01 to 0.035 Quaternary Cenozoic Character and Distribution Age System and Period Era St. Cloud District Stratified drift; sandy and clayey till ——unconforrnity— 90 Upper Mesozoic Cretaceous Small vpockets of sandy, clayey, shaly and less commonly lignitic sedi— ments I i—unconformity— (basalt and granite porphyry dikes) Penokean Middle I Intrusive Rocks Precambrian l,62l'0 Younger granites (St. Cloud Red, Rockville, Crystal Gray, and quartz latite dikes) I 1,780 Older granodiorite and related rocks (St. Cloud Gray Granodio rite) —-unconformity— Thomson Formation (slate, graywacke and schist) Inim±kie Group The rocks that have been quarried for dimension stone in the St. Cloud district are igneous rocks of intermediate and felsic composition that are Penokean (post—Animikian' in age (Goldich and others, 1961, p. 101—122). They intrude pelitic sedimentary rocks, now metamorphosed to medium—grade schists, and apparently were emplaced subsequent to the peak of deformation in the Penokean orogeny. The intrusive rocks distinguished by Woyski (19249) 4 �can be grouped according to age relations observed in the field into three classes: and (3) (1) basalt older granodiorite and related rocks, (2) younger granites, and granite porphyry dikes. Within the district, the older intrusive rocks are represented by the St. Cloud Gray Granodiorite. This rock underlies a roughly circular area at least three miles in diameter that lies south of St. Cloud. The rock has been dated by the K/Ar method at 1.78 b.y. (Goldich and others, 1961, p. 104). The younger granites comprise several types of intrusive rocks of intermediate to felsic composition. The major facies that were distinguished by Woyski (1949) are the St. Cloud Red Granite, Rockville Porphyritic Granite, and quartz latite porphyry. The St. Cloud Red Granite is a coarse-grained augite—hornblende granite. The Rockville Porphyritic Granite is a fine— to medium—grained microcline-quartz monzonite. The quartz latite porphyry has phenocrysts of hornblende and plagioclase in a felsitic groundmassQ All the rocks of this group are altered to some degree by late-stage deuteric and hydrothermal solutions. The sequence of alteration as recognized by Skillman (1946) was albitization, formation of chlorite—epidote—calcite, arid silicification. The late intrusive rocks include basaltic dikes and granite porphyry dikes that dominantly occupy N. 50° E.-trending fractures in the older rocks. Preliminary results on K/Ar dating of hornblende (G. N. Hanson, oral communication, 1965) from a basaltic dike from the Diamond Pink quarry, three and one—half miles southeast of St. Cloud, indicate that the dikes are somewhat younger than the Penokean rocks dated by Goldich and others (1961) but older than Keweenawan. The St. Cloud district was a positive area from late Middle Precambrian to late Cretaceous time. In the early Cretaceous(?) 5 (Sloan, 1964) a thick �kaolinitic regolith was developed on the bedrock surface. Reworking of the regolith by the late Cretaceous sea resulted in the relatively thin succession of sandy, clayey and shaly sediments found in isolated pockets throughout the district. Pleistocene drift consisting of sandy and clayey till and stratified silts, sands, and gravels mantles the irregular Precanthrian rock surface. The greatest thickness of drift known in the district is a north-trending sandy moraine that crosses highway 213 between Rockville and Cold Spring. Quarries in the older granodiorite and younger granites are located in a swampy area within and south of St. Cloud, where highs'' on the undulating Middle Precambrian bedrock surface form low knobby outcrops and lows are filled by a thin mantle of glacial outwash materials. of younger granites that protrude from the glacial outwash sands Outcrops and gravels in the valley of the Sauk River and its tributaries are the sites of several other quarries. ROCKVILLE QIL4RRY Cold Spring Granite Company The Rockville quarry, within the Rockvifle Porphyritic Granite, has been the largest producer of dimension stone in Minnesota for many years. The relatively wide spacings of the joints and the general consistency of color, grain-size, and texture enable the operators to meet the demand for quarry blocks of consistent quality. The shape and limits of the quarry are governed by two steeply-dipping intersecting N. 550 across spacing 350/4,50 W. and The spacing between fractures ranges from 25 to 55 feet. E. N. 50_100 fracture sets, which strike respectively N. E.-trending fracture that dips the quarry. A 600_700 A NW cuts diagonally sheeting that dips gently to the southwest has a that ranges from 5 feet near the top to 30 feet near the bottom of the quarry. 6 �The quarry is located within a belt of outcrops of the Rockville that extends from St. Cloud southwestward to Richmond. The Rockville crosscuts the St. Cloud Gray Granodiorite and has irregular contact with the St. Cloud Red Granite to the north and east of the quarry. Inclusions of schistose material are quite abundant in the Rockville within the upper part of the quarry. The Rockville is a pink to reddish—gray porphyritic microcline quartz The potassic feldspar is pert.hitic and forms large crystals monzonite. The groundmass is fine— to medium-grained and is 1-6 cm. in length. composed of about equal quantities of gray quartz and white plagioclase (andesine-oligoclase) and contains about 10 percent biotite. Easily recognized accessory minerals are hornblende, plagioclase and magnetite. Myrmekitic quartz, replacement rims of early plagioclase, and some pyrite- bearing epidote veinlets are thought to represent late stage deuteric and hydrothermal late— stage activity. Aplite dikelets commonly less than 5 cm. wide fill fractures. CRYSTAL GRAY GRANITE QUARRY Cold Spring Granite Company The Crystal Gray quarry, which is 100-150 feet east of the Sauk River, was opened about 25 years ago by the Pyramid Quarry Company. It was purchased about 10 years ago by the Cold Spring Company who has operated it since that time. The quarry was completely flooded by overflow of the Sauk River in early April, 1965. The quarry is bounded on the north and south by vertical fractures that strike N. )45 ). and on the east and west by vertical fractures that strike N. 45° . A fracture set that strikes N. NE., and a five-foot basalt dike that strikes N. cross the quarry diagonally. 80° W. and and dips 80° 60° E. and dips 80° NW., The fractures have a 5- 7 to 30—foot separation. �The sheeting fractures have approximately a 5-foot separation in the upper part and a greater separation in the lower part of the quarry. A prominent sheeting fracture which is 20-35 feet below the quarry rim strikes N. W. 40 and dips 100_iSo SW. towards the Sauk River. The Crystal Gray is a porphyritic quartz monzonite that has somewhat smaller phenocrysts than the Rockville. It is a distinctively purplish to greenish-gray facies of the younger granites and quarry. average is known only at this The pinkish-gray potassic feldspar phenocrysts are perthitic and 10 mm. in length. The medium—grained groundmass consists of approximately 30 percent opalescent quartz, 30 percent greenish-gray plagioclase (andesine to oligoclase), and 10 percent biotite. accessory minerals are magnetite, plagioclase, and The hornblende. Crystal Gray appears to have had a crystallization history similar to the Rockville. to Observable Skiliman (1946) suggests that the gray coloring is due the almost complete assimulation of xenoliths of St. Cloud Gray Granodiorite. Alteration is strong along fractures in the rock, and is indicated by the presence of pyrite, chlorite, and reddish feldspars. On the west side of the quarry, bedrock is overlain by 5—10 feet of stratified glacial drift. On the east side the bedrock capping consists of about J feet of kaolinite-rich regolith, about 10 feet of Cretaceous sandy shale and clay, and a 3— 5-foot layer of sand and gravel. SHIY-PETTERS AGGREGATE QUARRY Introduction The Shiely—Petters quarry was opened in 19499 after the operating company abandoned an attempt to use nearby waste rock, from former quarry operations, for production of aggregate. from Approximately half the production the plant is sold for railroad ballast; the remainder is shipped to markets that require high—grade aggregate. 8 The quarry is approximately 850 �9 50 about of consists and granite, augite—hornblende red to pink grained coarse— a is It quarry. the of wall west the in Gray Cloud St. the in and wall north the along monzonite quartz microcline with associated stringers dike-like and masses irregular small as seen be can Red Cloud St. The Granite Red Cloud St. Gray. Cloud St. the in veinlets surround that halos alteration greenish-black mottled to red to pink in resulted granites, younger the from emanated which alteration, hydrothermal stage late A 1946). (Skiliman, granites younger the by metasomation of degree the reflect to thought is rock the in feldspar potassic and quartz of quantity chalcopyrite. and pyrite, magnetite—illmenite, are minerals accessory The identifiable Easily feldspar. potassic pink percent 10 arid quartz, gray or blue percent 15 augite, and hornblende percent 15 oligoclase), (andesine- plagioclase bluish-gray percent 50 granodiorite, hornblende augite fine—grained to The inclusions. biotite-rich approdmately of consisting medium- a is rock unaltered and hornblende black to gray dark abundant quarry. contains and altered, somewhat pinkish-gray, is it Commonly the of ends west and east the in exposed is Gray Cloud St. The Granodiorite Gray Cloud St. quarry. the of part lower the in feet 25 about to increases spacing the surface; the near feet five about of intervals at spaced is sheeting The NE. 70° dips and W. 800 N. strike fractures sheeting respectively, east and north, northwest9 trend that sets fracture steeply-dipping three stops. previous the at examined quarries the in those to addition In to contrast in fractured, intensely are quarry the within rocks The deep. feet 140—60 is it direction; north-south a in wide feet 300—450 and direction east—west an in long feet �percent perthitic potassic feldspar9 30 percent quartz9 10 percent white plagioclase (andesine—oligoclase), and 10 percent biotite. Easily identifiable accessory minerals are hornblende, magnetite, and hematite. The crystallization history probably was similar to that of other fades of the younger granites. Skiliman (1946) suggests that the St. Cloud Red differs from the other younger granites mainly in having incorporated substantial quantities of the earlier-crystallized St. Cloud Gray Granodiorite. She attributes the pronouncedly red color to intense alteration by late-stage hydrothermal solutions. The sequence of hydrothermal alteration as recognized by Skillman (1946) was albitization, formation of chlorite-epidote—calcite, and silicification. The intense albitization of potassic feldspars released iron as hematite. A less intense alteration marked by chlorite-epidote-calcite is shown by irregularly colored green rocks that are adjacent to closely spaced fractures. Quartz Latite Porphyry Quartz latite porphyry is exposed as massive rock units in the north wall of the quarry. is Skiliman (1946, p. 81) says the quartz latite porphyry later than the St. Cloud Gray and St. Cloud Red. Phenocrysts of hornblende and bluish—gray plagioclase occur in a dark pink felsitic groundmass. Potassic feldspar and quartz in the rocks are thought to have been introduced by late—stage deuteric solutions. Basalt and Granite Porphyry Dikes The late intrusive rocks exposed in the quarry consist of basaltic dikes and granite porphyry; minor pegmatite, quartz veins, and chloriteepidote—calcite veinlets cut the rocks. The basaltic dikes range in width from 1 to 50 feet and average about 5 feet. They occupy three joint sets: 10 (1) N. 35°—50° W., 70°—80° NE., �a in set are 11 s. groundmas granulitic and these, of some of aggregates and hornblende, biotite, oligoclase, quartz, feldspar, potassic perthitic of consist phenocrysts The fractures. post-basalt the fill dikelets porphyry granite narrow Very andesine). (zoned plagioclase and olivine, and uralite augite, of mixtures various of consist cores the plagioclase; and magnetite, glass, basaltic of proportions equal approximately of composed margins chilled have They amphiboles. bluish-green and plagioclase sodic of amounts anomalous containing rock acidic more to basalt normal a from composition NE. trend and gypsum some contacts. 75o_900 E.9 50°—70° N. (3) W. The 35°_L()° N. hematite-stained are dikes massive; conjugate wall the to 600 joints jointing columnar horizontal rudimentary have NW. in vary dikes 70°_80° dip and contain that zones mylonitized are fractures Post-basalt and Most some and NW., 70°—90° E., loO_200 N. (2) �REFERENCES CITED Goldich, S. S., Nier, A. 0., Baadsgaard, H., Hoffman, J. H, and Krueger, H. W., 1961, The Precambrian geology and geochronology of Minnesota: Minn. Geol. Survey Bull. 41, l93 p. Skiliman, Margaret W., 1946, Intrusives of central Minnesota: Unpublished Ph.D. Thesis, Univ. of Minnesota, 211 p. Sloan, R. E., 1964, The Cretaceous System in Minnesota: Minn Geol. Survey Rept. mv. 5, 64 p. Woyski, Margaret S., 1949, Intrusives of central Minnesota: America Bull., v. 60, no. 6, p. 12 999—1016. Geol. Soc. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1965 Description An account of the resource Institute on Lake Superior Geology. University of Minnesota, St. Paul, Minnesota. May 6-8, 1965. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1965 Contributor An entity responsible for making contributions to the resource R.L. Bleifuss Bill Bonnichsen Peter J. Clarke Joseph P. Dobell Robert W. Leonardson Charles Fairhurst Bevan M. French Crawford E. Fritts John C. Green Tsu-Ming Han James W. Villar Glen R. Himmelberg Gilbert N. Hanson J.D. Juilland Gene L. LaBerge Henry Lepp Geoffrey W. Mathews Howard J. Meyer William J. Hinze G.B. Morey Richard W. Ojakangas Dennis P. Rebello George M. Schwartz Kenneth Segerstrom Kiril Spiroff F.M. Swain Mykola Malinowsky David Nelson Walter S. White Robert J. Willard Richard J. Wold D.H. Yardley Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/a15a5e130c20b64c45aa696010cca14f.pdf b21924937cbd5a866330efbd12a51453 PDF Text Text /SrT, %_ —W•#' .1W Twelfth Annual Institute on Lake Superior Geology May 6-7,1966 In Conjunction with the Mineralogical Society of America and the Society of Economic Geologists Host: Michigan Technological University Sault Ste. Marie, Michigan �U INSTITUTE BOARD OF DIRECTORS M0 A. D. H. A. W. Bartley, M. W. Bartley & Associates, Port Arthur, Ontario T. Broderick, Inland Steel Company, Ishpeming, Michigan H. Hase, State University of Iowa, Iowa City, Iowa Lepp, Macalester College, St. Paul, Minnesota K. Sneigrove, Michigan Technological University, Houghton, Mich, INSTITUTE SECRETARY- TREASURER D. H. Hase, Dept. of Geology, The State University of Iowa, Iowa City, Iowa 52240 LOCAL COMMITTEE General Co—chairmen: A. K. Snelgrove and C. E. Kemp Social Hour Arrangements R, D, Burns K. D. Card P. E, Giblin Mrs. Jean R. Moran R. R, Ranson J. D. T. V. C. R. A. Robertson E. Smith J. Smith Venn Walker W. White (Chairman) R. R. Ranson D. E. Smith V. Venn Ladies Mrs. D. Howe, Mrs. C. E. Kemp, Mrs. R. R, Ranson, and Mrs. A. K. Sneigrove MINERALOGICAL SOCIETY OF AMERICA C 0mm it tee L, G, Berry Queen's University Kingston, Ontario J, A. Mandarino Royal Ontario Museum Toronto, Ontario G. R. Switzer U.S. National Museum Washington, D.C. SOCIETY OF ECONOMIC GEOLOGISTS Committee E. N. Cameron University of Wisconsin Madison, Wisconsin J. S. Stevenson McGill University Montreal, Quebec R. J. Weege Calumet & Hecla, Inc. Calumet, Mich. —1— �I FIELD TRIP LEADERS Institute on Lake Superior Geology - M. P. 5, J. J. E. M, A. Elliot Lake: Frarey, Geological Survey of Canada Giblin, Ontario Department of Mines Roscoe, Geological Survey of Canada Robertson, Ontario Department of Mines (Leader) Mineralogical I Society of America — Manitouwadge: J. A, Mandarino, Royal Ontario Museum E, G, Pye, Ontario Department of Mines (Leader) Society of Economic Geologists K. D,. Card Ontario Department of Mines D, Rousell Laurentian Univ. I Sudbury: J, M. Holloway International Nickel Co. of Canada, Ltd. P. Potapoff Falconbridge Nickel Mines, Ltd. B. E. Souch International Nickel Co. of Canada, Ltd. G. Thrall International Nickel Co. of Canada, Ltd. J, S. Stevenson McGill University (Leader) I 1 I I I I I I I —ii— I �PROGRAM 12th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY in conjunction with MINERALOGICAL SOCIETY OF AMERICA and SOCIETY OF ECONOMIC GEOLOGISTS Michigan Technological University Sault Ste. Marie Branch Sault Ste. Marie, Michigan Wednesday. May 4, 1966 Eastern Daylight Saving Time* :OO a.m. Pre—session Field Trip, Mineralogical Society of America. Meet at Manitouwadge Hotel, Manitouwadge, Ontario, for tour of zinccopper mines. (See Guidebook) Thursday, May 5 :OO a.m. Pre—session Field Trip, Mineralogical Society of America (continued). Assemble at Marathon, Ontario, and examine road cuts en route to Sault Ste. Marie, arriving early evening. Thursday, May 5 Eastern Standard Time 7:00 p.m.—9:OO p.m. Registration, Science Building, Michigan Tech. University, Sault Ste. Marie Campus. Friday. May 6 :Oo * — 9:00 a.m. Ontario Registration (continued). is on Eastern Daylight Saving Time. �1 —2— Friday, May 6 (continued) PLENARY SESSION I Science Building Co—chairman: E,3.T. 9:00 I A0 K. Sneigrove and C. Ernest Kemp I Vice President Kenneth J. Shouldice, Director of Sault Ste. Marie Branch, Michigan Technological University Regional Geology of the Sault Ste. Marie Area.....,...C. Ernest Kemp Metallogenic Study, Lake Superior— ChibougamauRegion.......,............S.M. Roscoe Recent Investigations of Raised Shorelines, East Shore of Lake Superior and the Sault Ste. Marie Area. . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. Tovell, C. F. M. Lewis, and R. E. Deane Aeromagnetic Studies of Eastern Lake Superior.William and James W. Trow J. Hinze, Norbert W. OTHara, for Relaxation Aeromagnetic, Gravity, and Sub-Bottom Profiling Studies inWestern Lake Superior.........0......... .................Richard J. Wold and Ned A. Ostenso New Bathymetric Map of Lake Superior and Some Geological Implications............... .......W. R. Farrand, J. H. Zumberge, and J. Parker Copper Deposits of the Batchawana Area, p.m. Ontario. . . . • . . . . . . . . . . . . . . . . . . . . . . . . . .P. E. Giblin Interval a0m. 9:05 9:25 9:50 Welcome: .....W 10:15 Pause 11:15 11:40 12:05 Lunch SESSION IIA INSTITUTE ON LAKE SUPERIOR GEOLOGY Science Building Co—chairmen: F. S. Turneaure (University of Michigan) and P. E. Giblin (Ontario Department of Mines) I I I E.S.TO 2:00 2:30 3:00 Some Aspects of Huronian Paleogeography and Sedimentation in the Canadian Shield.Grant M. Young The Geology and Geophysics of the Moose River Belt, Northern Ontario.........A. S. MacLaren New Field Studies of the Keweenawan I LavasofMinnesota.........,..........JohnC. Green Pause for Relaxation I I �—3— Fridays May 6 (Continued) 4:00 p.m. 4:25 4:45 Precambrian Stratigraphy and Structure of the Tower, Minnesota Quadranglee...Richard W. Ojakangas Cutting Oriented Samples,......,....John Q. St. Clair Sugar Loaf Conglomerate, Marquette County, Michigan. Spiroff .... , ,......•a.....,. . .Kiril Annual Banquet Windsor Hotel, Sault Ste. Marie, Ontario Eastern Daylight Saving Time 6:45 p.m. 7:30 Social Hour Dinner Address: "Modern Trends in Precambrian Exploration" Dre Duncan R. Derry SESSION IIB INSTITUTE ON LAKE SUPERIOR GEOLOGY Brady Hall Co—chairmen: D. H. Hase (State University of Iowa) and J. S. Stevenson (McGill University) E.S.T. Michigan's Building Stone Resources..Joseph P. Dobell Occurrence of Base Metals South of Dead River, Negaunee Quadrangle, Marquette County, Michigan,...,,,00.0.....,.......Wil1ard P. Puffett Geologic Structure East and South of the 3:00 Keweenaw Fault Based on Geophysical Evidence. . • • • .. .,. . , . . . •. . ._.. .L. 0. Bacon Pause for Relaxation A Structural Analysis of the Michigamme 4:00 Slates,..,..,.....,W. 0. Mackasey and A. M. Johnson Zoning of the White Pine Copper Deposit, 4:25 Ontonagon County, Michigan, . a a a .e a a .e. a. . a o.. . a. ...,,.,.,..,Alexander C. Brown and John W. Trammell 2:00 2:30 . Annual Banquet Windsor Hotel, Sault Ste. Marie, Ontario �1 -4Friday, May 6 (Continued) Eastern Daylight Saving Time 6:45 7:30 p.m. Social Hour Dinner Address: "Modern Trends in Precambrian Exploration" Dr. Duncan R. Derry I Saturday, May 7, 1966 I SESSION lilA INSTITUTE ON LAKE SUPERIOR GEOLOGY and SOCIETY OF ECONOMIC GEOLOGISTS Science Building Co—chairmen: I I E. N. Cameron (University of Wisconsin) and R. J. Weege (Calumet and Hecla, Inc.) I E.S.T. New Zealand Ilmenite Sands................M. E, Volin Irish Strata—bound Base Metal Deposits............... K. Sneigrove • • • • • • • •.• • • . . • . • . .A. Notes on Lake Superior Type Iron Ores at 9:45 Barsua, Orissa, India..................G. G. Suffel The "Rock Cut", Lower St. Marys River, 10:05 ,Harold J. Lawson Michigan..,......, ee Engineering Geology on New Second Lock, St. 10:25 Marys Falls Canal....,..,...,.....Terrence J. Smith Pause for Relaxation The Probability of a Single Station Being a 11:10 Representative Sample in a Magnetic Survey..L. 0. Bacon, W. A. Longacre, and A. Stevens Results of Detailed Geochemical Prospecting in 11:30 the West—Central Part of the Negaunee Quadrangle, Michigan... ........ . .Kenneth Segerstrom 9:00 9:25 I . ....... ,.. .. PLENARY SESSION II Science Building 12 noon 1:30 INSTITUTE ON LAKE SUPERIOR GEOLOGY: Business Meeting. Briefing on Field Trips. Post—session Field Trips start. Institute: Algoma Steel Plant Elliot Lake, Ontario, Uranium.(See Guide- Society book) * of Economic Geologists: Nickel—copper.(See Guidebook); Sudbury, Ontario, I �—5— Saturday. May 7,(continued) SESSION IIIB MINERALOGICAL SOCIETY OF AMERICA Brady Hall Co—chairmen: L. G. Berry (Queen's University) and J. A. Mandarino (Royal Ontario Museum) ESOT 9:00 p.m. 9:25 Michipicoten Scheelite Deposit near Michipicoten Harbour, Ontario...... .......... , . .. .. . . .Louis Moyd A Barite-Quartz Phase in the Firesand River Carbonatite, Wawa, Ontario......... ... .. . . . ...,,.....,.e.,.E. Wm. Heinrich and Richard W. Vian Clay Minerals in Glacial Deposits, Houghton, 9:4.5 ...... Baraga, and Ontonagon Counties, .....A. P. Ruotsala, G. J. Koons, and S. C. Nordeng The Mn—Bearing Minerals of Champion Mine, 10:05 Champion, Michigan.................Larry L. Babcock Unique Intergrowth of Calcite and Pyrite............. 10:25 • . . . • • • . . • . . . • . . • . . • • . . . . . . • . • . • • . • . .Paul W. Zimmer Pause for Relaxation Short—Range Chamical Variations in a Managanoan 11:10 Axinite from the Mesabi Range, Minnesota........... ....................................Bevan M. French Textural Relations of Hematite and Magnetite 11:30 in Some Precambrian Metamorphosed Oxide Iron Formations......... . • • • ........ . . . .Tsu—Ming Han PLENARY SESSION II Science Bui1ding 12 noon 1:30 INSTITUTE ON LAKE SUPERIOR GEOLOGY: Business Meeting. Briefing on Field Trips. Post—session Field Trips start. Institute: Algoma Steel Plant Elliot Lake, Ontario, Uranium. (See Guidebook) Society of Economic Geologists: Sudbury, Ontario, Nickel—copper. (See Guidebook) �1 THE MANGANESE-BEARING MINERALS OF CHAMPION MINE, CHAMPION, MICHIGAN Larry L. Babcock Michigan Technological University Hought on Champion Mine is a tthard iron ore producer on the southern limb of the Marquette synclinorium, The mine vicinity underwent staurolite-grade regional metamorphism during the post—Animikie, pre-Keweenawan interval. Manganese-bearing quartz shear veins, generally conformable with the schistosity of the host Negaunee iron formation, are found at depths greater than 2,000 feet below the No. 7 shaft collar. These veins cut non—schistose host rock containing major percentages of spessartine and spessartine—andradite, with the former garnet zoned on the latter. Associated minerals include tabular hematite, magnetite, anhydrite, talc, manganese carbonates, diopside, actinolite, and manganoan cummingtonite — Tourmaline, molybdenite, pyrite, and chlorite are associated with some manganese carbonates. Randomly oriented actinolite, hematite, and talc folia, and other criteria indicate that the manganese minerals are late—stage metamorphic. The presence of zoned garnets suggests that the processes of contact metasomatism acted to remobilize primary manganese in an iron—rich environment. Spessartine—andradite (spandite) has been reported from the contact metasomatic manganese ores of India, i.e., "kodurites". tirodite. Other manganese minerals under study include jacobsite, rhodonite, rhodochrosite, manganosiderite, manganankerite, kutnahorite, and several associated unknowns. Jacobsite, MnFe2O4, has 'previously been unreported from the Western hemisphere. Champion represents the first known occurrence of an amphibolitegrade manganese—bearing iron formation in the Western hemisphere, with mineralogical similarities to deposits in Norway, Some of the above minerals have been Sweden, India, and Japan. reported from Franklin, New Jersey. �I GEOLOGICAL STRUCTURE EAST AND SOUTH OF THE KEWEENAW FAULT BASED ON GEOPHYSICAL EVIDENCE L. 0. Bacon Michigan Technological University Houghton Gravity and magnetic data indicate that a Middle Range of basalt lavas lies beneath the Jacobsville sandstone and that this is the north limb of a shallow syncline, plunging to the west at a low angle. The South Range of basalt lava is the southern limb of this syncline. The north side of the Middle Range lavas is interpreted as a fault contact downthrown to the north. Within the graben structure between the Keweenaw fault and the Middle Range fault there appears to be a third fault. These faults appear to be cut by three to four cross faults to account for local anomalies. Maximum thick- ness of the Jacobsville sandstone is of the order of 10,000 feet. �3 THE PROBABILITY OF A SINGLE STATION BEING A REPRESENTATIVE SAMPLE IN A MAGNETIC SURVEY L. 0. Bacon, W. A. Longacre, and A. Stevens Michigan Technological University Hought on In a magnetic survey one presumes that each station reading is a representative sample of the magnetic field of the immediate area. A study of this assumption in a glaciated region indicates that, for the areas studied, variations in magnetic field around the point are randomly distributed and that the probability of a value deviating from the mean of the field in the area is essentially that to be expected from a single valued field where variations follow the Gaussian error curve. Magnitude of the anomalies varies as a function of the type of overburden, underlying rock type, and thickness of cover over the magnetic source. �4 ZONING OF THE WHITE PINE COPPER DEPOSIT, ONTONAGON CO., MICHIGAN Alexander C, Brown University of Michigan Ann Arbor John W. Trammell Copper Range Company — As described by White (l96O) the top of the cupriferous zone at the White Pine copper deposit is characterized by an abrupt Present studies indicate that 'this zonation of Cu—Fe sulfides. narrow fringe occurs at only one position in any vertical section and forms a blanket—like surface between the cupriferous zone and Although ore horizons at the overlying barren pyritic shales, White Pine show strict stratigraphic control, the sulfide fringe, marking the uppermost limit of chalcocite mineralization, occurs at various stratigraphic levels near and above the ore horizons0 In general this surface cross—cuts bedding at gentle angles, but locally it appears to be more irregular. Disseminated chalcocite, native copper, and native silver are the dominant ore minerals of the cupriferous zone; pyrite and minor amounts of chalcopyrite occur in the shales above. The transition between these zones (normally measured in inches) consists of digenite, bornite, and. chalcopyrite in ascending order. Textures indicate replacement of iron—rich sulfides by copper-rich minerals. Abnormal concentrations of disseminated Cd, Zn, and Pb sulfides occurs immediately above the curiferous zone and in the marker bed; they have not been observed within the cupriferous zone proper. ?t3tripey*t It is suggested that the Cu—Fe transition represents the farthest advance of a copper "front't, behind which syngenetic or diagenetic pyrite was replaced by chalcocite and native copper. Silver in the Nonesuch was probably associated with the copper front0 Cd, Zn, and Pb were swept ahead of the front and formed anomalous concentrations immediately above the cupriferous zone. Sulfur may have been partially removed from the present cupriferous zone during copper mineralization. I I I * White, W0 S., "The White Pine Copper Deposit:" Econ0 Geol, V0 55, pp. 402—414 1 �U 5 MICHIGAN'S BUILDING STONE RESOURCES Joseph P. Dobell Michigan Technological University H ought on An investigation of the building stone resources of the State of Michigan was undertaken in the summer of 1965. Emphasis was on undeveloped materials in the Upper Peninsula of Michigan but a number of areas in the southern part of the state were also studied. Geologic investigation consisted of selecting and visiting the potential building stone deposits, determining the geology of the local site, sampling the deposits, and evaluating factors such as proximity of the material to transportation facilities, location of the potential quarry, and possible water and overburden problems. In the course of the field work the most common building stone collected was of the type used as decorative aggregate surfacing for pre—cast concrete slabs. Colorful and durable materials of this category were obtained from thirty-four localities in the Precambrian terrain of Michigan's Upper Sandstone, limestone and dolomite suitable for Peninsula. dimension stone were obtained from fourteen different sites. Eight localities yielded decorative stone which could be cut Terrazzo stone into polished slabs up to four feet square. could be quarried from seven locations and five rock types are suitable for use in the lapidary arts. The mineralogy of all specimens was determined by microscopic study of thin-sections. Standard chemical analyses were provided by the Institute of Mineral Research at Michigan Tech. The same agency also has conducted abrasion, hardness, absorption, specific gravity, compressive strength, modulus of rupture,and freeze—thaw tests on all specimens. Funds for this investigation of the building stone resources of Michigan were provided by the Michigan Department of Economic Expansion. The project was proposed and administered by the Institute of Mineral Research at Michigan Technological University. �ij 6 NEW BAThIMETRIC MAP OF LAKE SUPERIOR AND SOME GEOLOGICAL IMPLICATIONS * J. H.Zumberge Grand Valley State College V. R. Farrand University of Michigan J. Parker White Pine, Michigan Parker has compiled a new bathymetric map with a 100-foot contour interval for the eastern half of Lake Superior on the basis, of recent U.S. Lake Survey souddings. This map has"been completed, in connection with the University of Miàhigan Lake Project, by the addition of the best depth data The strong 'valleyavailable for the western half of the basin. and-ridge topography of the eastern part of the basin contrasts Superior strongly with the rest of the lake where broad, emooth—floored basins are the. characteristic form. However, Sbbottom depth recorder (Sparker) surveys show that bedrock valleys similar in size to those of the eastern basin exist also in the west, where they have been áompletely filled with glacial and postglacial sedimints so that they no longer find expressIon in the topography of the lake bottom. In one of these buried valleys near the Minnegota coast late Pleistocene sediments are more than 700 feet thick. In the eastern.: basin, on the other hand, Pleistocene sediments form, in general, only a thin veneer over a rugged bedrock topography which resembles that of. the Finger Lakes area of New fork. * See map, back cover �7 SHORT-RANGE CHEMICAL VARIATIONS IN A MANGANOAN AXINITE FROM THE MESABI RANGE, MINNESOTA Bevan M. French Laboratory for Theoretical Studies National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, Maryland A new occurrence of the calcium borosilicate axinite has been identified in a pegmatitic vein cutting metamorphosed Biwabik iron formation on the eastern Mesabi ange, Minnesota. The mineral occurs as yellow—brown, poorly—crystalline patches associated with Two different large crystals of quartz and potassium feldspar. size fractions of the crushed axinite, separated by identical heavy—liquid and magnetic methods, give different chemical — 100 + 150 mesh) gives: SiO2 41,66, compositions. Fraction 1 18.00, Fe2O3 0.10, FeO 3,27, MnO 11.66, A1203 Ti02 0.01, B2O 5.96, +1100) 1.26, Na20 _llOo) O.01j, H20 MgO 0.25, CaO 18.00, H20 mesh) gives, by contrast: + 200 0.15, K20 0.02. Fraction 3 ( — 150 Similar significant A1203 14.23, Fe203 1.95, FeO 5.25, MnO 10.60. differences exist in unit—cell parameters of the two fractions obtained by computer treatment of X—ray powder diffraction data. An unexpected discrepancy in the calculated unit—cell contents of the Fraction+ can be removed by substituting about 25 percent and aluminum, although the existence of both Mn Mn as Mn ) with Refractive same silicate has yet to be demonstrated. Mn+3 in the indices of the two fractions appear identical within the 1.678, = 1.678, determinative uncertainty (+0.003): = 1.692 (Fraction 1). ( ( ( Petrographic and electron microprobe studies suggest that the more iron—rich axinite (Fraction 3) has originated by fracture— controlled alteration of the original axinite during a period of more ''*idespread secondary alteration indicated by (1) idespread sericitization of feldspar, and (2) almost complete chioritization of garnet. Relative higher Po2 values during this latter stage are indicated by the increased Fe+3/Fe2 in Fraction 3 and are consistent with the suggested partial conversion of Mn'2 to �COPPER DEPOSITS OF THE BATCHAWANA AREA, ONTARIO P. E, Giblin Resident Geologist Ontario Department of Mines Sault Ste0 Marie Recent exploration in the Batchawana area, Ontario, located 40 miles north of Sault Ste. Marie, has led to new and significant discoveries of copper; underground development at one property; and production of copper from another. Copper deposits are of three types: Fissurefilling calcite—quartz veins, carrying 1. chalcocite, bornite, chalcopyrite, and native copper. Breccia pipe depo sits, in which the mineralization 2. consists of chalcopyrite, pyrite, molybdenite, galena, and sphalerite. Disseminated chalcopyrite, pyrite, and molybdenite in 3, altered quartzfeldspar porphyry, possibly representing a porphyry copper type of deposit. Deposits of the first Breccia pipe deposits are suggests mineralization is the third type may also be type occur in Keweenawan strata, found in Archean rocks: K— dating The deposit of Keweenawan in age. of Keweenawan age. Copper deposits of the area are probably associated with magmatic activity of middle to late Keweenawan time, which in the eastern Lake Superior region appears to have been restricted to the immediate vicinity of the present lake basin. It is suggested that the Archean terrain near the east shore of Lake Superior might warrant prospecting for breccia pipe and disseminated deposits of copper and molybdenum. I I I I I I �.9. NEW FIELD STVDIE3 OF ThE KEWEENAWAN LAVAS OF MINNESOTA John C. Green University of Minnesota Duluth, and Minnesota Geological Survey Field work was begun in the suier of 1965. on the Keweenawan lavas and related intrusive rocks of northeastern Minnesota, with •the support of the National Science Foundation and the Minnesota Geological Survey. Detailed mapping along the shore of Lake Superior in Lake and Cook counties has been concentrated on a restudy of the stratigraphic sequence, estimates of thickness, and direction of flow of the lavas. Measurements of 118 ropy structures at the tops of flows and of 38 bent pipe amygdules at the bases of flows show no clear preferred erientation and thus no uniform direction of flow or of regional slope in the area studied. Petrographic and preliminary x-ray studies show that lavas of intermediate composition are more abundant than heretofore recognized. An extensive area of flows, of both felsic and mafic composition, has been found well within the area previously mapped as Duluth Gabbro Complex northeast of Isabella. Minor intrusions, possibly oonnected with the Duluth Gabbro Complex at depth, show compositions that range continuously from troctolite, much .of which is banded, to highly leucocratic granophyric granite. All intrusive phases contain xenoliths of anorthosite. �I 10 TEXTURAL RELATIONS OF HEMATITE AND MAGNETITE IN SOME PRECAMBRIAN METAMORPHOSED OXIDE IRON—FORMATIONS TsuMing Han Cleveland—Cliffs Iron Co0, Ishpeming, Mich. Hematite—magnetite is a common ore mineral assemblage in the Precambrian oxide ironformations. The textural relationship of the two minerals changes with the grade of metamorphism. in the low-grade metamorphosed iron formations (ore minerals co—existing with fine—grained dusty quartz and/or sheet iron silicates), one may find hematite with magnetite rims; hematite crystal outlines reappearing in partially oxidized magnetite; magnetite veinlets in fine—grained hematite; fractures in hematite bands cross—cut by magnetite; and magnetite crystals embedded in jaspilites. These textural relations suggest that magnetite is stable whereas hematite tends to be reduced to magnetite during the metamorphism. In iron formations of medium—grade metamorphism (ore minerals co-existing with medium-grained fairly clean quartz and/or double— chain iron silicates), specularite embedded in fine—grained magnetite; specularite containing magnetite remnants; magnetite cross—cut by specularite; and specularite bands with relicts of magnetite clusters are commonly observeth Such features suggest that during the metamorphism speculariteia stable phase whereas magnetite tends to be oxidized to specularite. Hematite and magnetite in iron formations of high—metamorphic order are more or less simultaneously developed, and commonly associated with coarse—grained clear quartz and/or double— and single—chain iron—rich silicates However, the cross—cutting of specularite by magnetite in some ores may suggest the earlier development of specularite0 In conclusion, reduction and oxidation do occur in iron formations during metamorphism although in general ore mineral assemblages are governed by those of the ppe-metamorphic Such processes are believed to be repponsible for the sediments0 development, at least in part, of the magnetite—bearing jaspilite, oölitic magnetite and specu1aritemagnetite ore types. The degree of such types of metamorphism tends to improve the concentrating characteristics of ores and has a direct effect on the process chosen for iron ore beneficiation. I I �11 A BARITE—QUARTZ PHASE IN THE FIRESAND RIVER CARBONATITE, WAWA, ONTARIO E. Wm. Heinrich and Richard W. Vian The University of Michigan Ann Arbor The Firesand River alkalic complex, 4.5 miles east of Wawa, Ontario, is unusual in that it consists predominantly of carbonatite with a highly subordfriate outer ring of rnafic to ultramafic alkalic silicate rock. The carbonatite core is composite, with an inner core of rauhaugite encircled by sovite The ferruginous rauhaugite body, which and silicate sóvite. appears to be pipe—like and vertical (in contrast to the sovite ring, which represents the accretion of a series of inward— dipping cone—sheet slices), is itself a composite of several texturally and mineralogically distinctive rocks. Among these are 1) a porphyritic phase in which calcite phenocrysts are set in a finer-grained matrix of iron—bearing carbonate; and 2) a This rock contains barite barite—quartz-carbonate rock. euhedra, quartz grain fragments deeply corroded by carbonate, and euhedral smoky quartz crystals, some as long as three inches. Most of the quartz grains appear to have been metamorphosed, showing undulatory extinction, mosaic structure, and a strong parallel alignment of "bubble train" inclusions. Against the carbonate they are locally armored by "reaction rims" of very fine-grained ferruginous feldspar. It is concluded that this unusual rock was formed by the carbonatization of a quartzite cut by small quartz veins into which were introduced (in order): 1) barite, 2) alkali feldspar, and 3) carbonate. �U 12 AEROMAGNETIC STUDIES OF EASTERN LAKE SUPERIOR William J. Hinze, Norbert W. O'Hara and James W. Trow Michigan State University East Lansing A regional aeromagnetic survey was conducted to determine the relatively unknown basement geology and tectonics of eastern Lake Superior and the eastern half of the Northern Peninsula of Michigan. During this survey approximately 6,500 miles of flight lines spaced at six—mile intervals were recorded with a digital recording proton precession magnetometer system. The results of the survey generally supported the geological interpretation that the Lake Superior structural basin consists of thick basic volcanies overlain by clastic sediments. This basin extends southward into the Northern Peninsula of Michigan with the basic volcanics of the Keweenaw Peninsula curving southward through Stannard Rock and Grand Island. The Isle Royale fault parallels the general curvature of the Keweenaw Peninsula to the vicinity of Superior Shoal where it là terminated by a cross fault striking from Ashburton Bay to the Keweenaw Peninsula, A fault on the north side of Michipicoten Island continues to the southeast toward Gargantua Point and northward, paralleling the shoreline at a distance of 10 to 15 miles. Midway between Michipicoten Island and Pie Bay, this fault turns northwest and continues south of the Slate Islands to the volcanics outcropping on the islands of Nipigon Bay. South of Michipicoten Island the basic volcanics have been uplifted by an east—west striking fault which may be a continuation or a branch of the Keweenaw fault. On the east side of the basin, south of these basic volcanics, the volcanics appear to be discontinuous with major volcanic rock areas extending southwest from Mamainse Point and the eastern margin of the Northern Peninsula of Michigan. I I I I I �13 THE "ROCK CUT", LOWER ST. MARYS RIVER, MICHIGAN Harold J. Lawson Project Engineer U. S. Army Corps of Engineers Sault Ste. Marie, Michigan The "Rock Cut" is a channel nearly two miles long and 300 feet wide cut through Trenton limestone that was initially excavated in 1904. It is between Neebish Island in the St. Marys River and the mainland of the Eastern Upper Peninsula. Completion of the project permitted large navigation ships to take a more direct route downbound to Detour Passage at the northern tip of Lake Huron. The work consisted of constructing cofferdams upstream and downstream of the cut, 9,000 feet apart; dewatering the area; channeling and line drilling the ledge rock on the east and west channel limits; blasting and removing the rock to adjacent disposal areas; constructing an ashlar masonry guide wall at the channel limits on the ledge rock; flooding the area; and removing the cofferdams within the channel. blasting was done without blasting mats. The blasts were all monitored with a seismograph to maintain an Energy Ratio of 1.0 or less and to prevent excessive concussion. The largest blast was l,00 lbs. of 60% hi—velocity gelatin. Usually the The blasts were less than half this amount. The work started in late summer 1960 and was completed in January, 1961. �1 14 A STRUCTIJ RAL ANALYSIS OF THE MICHIGAIvllE SLATES W, 0. Mackasey and A, M. Johnson Michigan Technological University Hought on The Animikie Michigamme slates of Michigan's Upper Peninsula represent a thick monotonous assemblage of fine—grained elastic rocks which apparently lack marker horizons suitable for interpretation by conventional field methods, For this reason, a statistical structural analysis utilizing small—scale features should be considered. A preliminary investigation during the fall of 1965 was started in the Covington area to test the applicability of this Outcrops along a ten—mile stretch of highways M-2 and method. U.S. 141 north of the BaragaIron County line were examined. Features measured within the slates included bedding, rock cleavage, axes of minor folds, and lineations produced by inter section of bedding and cleavage, etc. These data were plotted by means of an equal-area stereonet. periods of deformation have been recognized and some information on the style of folding has been obtained. Two Such studies may provide useful clues in determining the complex history of deformation of the Anirnikie rocks of the Upper Peninsula. Further work, on a continuing basis, is planned. I U I I I I I �15 THE GEOLOGY AND GEOPHYSICS OF THE MOOSE RIVER BELT, NORTHERN ONTARIO A. S. MacLaren Geological Survey of Canada Since 1959 the Geological Survey of Canada and the Ontario Department of Mines have cooperated in systematic aeromagnetic surveys of the Precambrian Shield of Northern Ontario. In 1965 a major anomalous magnetic zone named the Moose River magnetic belt was recognized in these surveys. This feature extends for a distance of 160 miles south of James Bay and transects the Superior Province trends at a large angle. It coincides with granulites, gabbro, and basic dykes and is cut by a major fault along which ultramafics occur0 Detailed gravity and magnetic work indicate that the granulite and gabbro occurring explained magnetic belt can be by local magnetic and gravity measurements over surface material. major in this This magnetic belt lies on the east flank of a gravity feature, the Kapuskasing gravity anomaly. �16 1 MICHIPICOTEN SCHEELITE DEPOSIT NEAR MICHIPICOTEN HARBOUR, ONTARIO I Louis Moyd Curator of Minerals National Museum of Canada A scheelite deposit on the shore of Lake Superior about 12 miles west of Michipicoten Harbour was explored. The host rock is a nearly vertical northwest—trending septum of biotite and hornblende schist about 200 feet thick enclosed in a large body of granodiorite. Scheelite is irregularly distributed through quartz pods which form vein—like elongate swarms along the central portion of the tabular mass of schist, The mineralized zone can be seen under the lake and has been traced inland for about a mile. The quartz pods are lenticular and vary greatly In size. Each swarm consists of pods, side by side or en echelon in both horizontal and vertical aspects, with long axes paralleling the foliation of the enclosing schist, Individual swarms may reach 30 feet in width, but are irregular and patchy, with some portions along the strike of the zone nearly free of the pods. Individual pods are separated by septa of contorted schist from a fraction to several inches in width, Locally, adjoining portions of two or more pods have coalesced, with the intervening schist completely replaced or now represented only by strings and patches of coarsly crystallized mica and feldspar. The scheelite is in the form of cream to buff anhedral grains and clusters from i/ inch to about 12 inches in diameter, Most of the scheelite occurs near the margins of the pod, or if well within them, along the zones of coarsely crystallized mica and feldspar which represent earlier schist septa. I I I �17 PRECAMBRIAN STRATIGRAPHY AND STRUCTURE OF THE TOWER, MINNESOTA QUADRANGLE. Richard V. Ojakangas University of Minnesota Duluth The Tower 74 minute quadrangle is a strategically located area in the older Precambrian rocks of northeastern Minnesota. Rocks representing the Ely Greenstone, the Soudan Iron Formation, the Knife Lake Groups, and the Algoman granitic complex are present. Mon of the area is underlain by Knife Lake rocks, but a large nose of Ely Greenstone is present in the eastern portion of the area, entering from the adjacent Soudan quadrangle. The minor lower portion of• the Knife Lake unit is comprised of conglomerates, impure quartzites, and tuffaceous rocks. These an overlain by a great thickness of alternating graywackes and •slates' (formerly mudstones). Most of the rocks have been only slightly metamorphosed, but metamorphic grade increases to the south. Pillows in the Ely Greenstone and graded graywacke beds in the Knife Lake permit top, determinations and structural interpretations. A series of tight, generally eastward—plunging folds cross the quadrangle. Overturned greenstones and graywackeslate beds are conaon. Aerial photo analysis revealed abundant lineaments in the area, generally trending about N. 35 E; one can be traced into a fault with about 1,000 feet of horizontal displacement. this area under auspices of the Minnesota Geological Survey. Major objectives are the solution of the regional structure (several workers are involved) and the sedimentary history of the Knife Lake rocks. Work is continuing in �l OCCURRENCES OF BASE METALS SOUTH OF DEAD RIVER, NEGAUNEE QUADRANGLE, MARQUETTE COUNTY, MICHIGAN* Willard P. Puffett U. S. Geological Survey Marquette, Michigan In the south half of the Negaunee quadrangle, Marquette County, Michigan, rocks of early Precambrian age are bounded on the northwest and on the south by metasedimentary rocks of the Animikie Series of middle Precambrian age. The lower Precambrian rocks include massive and layered greenstones of the Mona Schist, pyroclastic rocks of the Kitchi Schist, and a syenite—diorite—granodiorite pluton that intrudes the Mona The metasedimentary rocks to the northwest, in the Schist. Dead River Basin, rest on an erosional surface cut on the pluton. The metasedirnentary rocks in the southern part of the area are on the north limb of the Marquette syncline and are separated from the lower Precambrian rocks by a profound unconformity. Small and widely separated deposits of base—metal sulfides have been found in the lower Precambrian rocks, The most common type is chalcopyrite with sparse pyrite in steeply—dipping These veins have been found in both quartz-carbonate veins. massive greenstone and coarsely crystalline granodiorite. They range in thickness from a few inches to more than 5 feet, and some can be traced along strike for several hundred feet. The sulfides make up only a small part of the veins and commonly are most concentrated near the footwall. Assays of selected specimens of vein material indicate that gold and silver are not present in measurable quantities. Small amounts of chalcopyrite and copper carbonates occur in a shear zone in greenstone that has been carbonatized and Tests for heavy metals in this shear zone indicate sericitized. a rather broad mineralized area in which both copper and zinc occur in anomalous amounts. No zinc minerals have been identified. In one locality, galena has been found with chalcopyrite in a quartz vein in granodiorite near its contact with greenstone. Elsewhere chalcopyrite has been found in joints in the granodiorite; no other vein material is exposed. Some of the veins occur in topographic lineaments that are conspicuous on aerial photographs. Areas containing sulfide—bearing veins also coincide with magnetic lows shown on aeromagnetic maps of the region. Commonly the aeromagnetic lows occur above diabasic intrusions, suggesting a possible genetic relationship between the sulfide-bearing veins and diabase * Publication authorized by the Director, U. S. Geological Survey. Work done in cooperation with the Geological Survey Division of the Michigan Department of Conservation0 �19 METALLOGENIC STUDY, LAKE SUPERIOR-CHIBOUGAMAU REGION* S. M. Roscoe Geological Survey of Canada Mineral deposits in the region are assOciated with rocks are te'ctonic activities of five different ages: Early Archaean (—3.1 to 2.7 x109 yrs.) iron formations, Zn and Cu — bearing iron suiphide deposits, Ni, Cr, asbestos, Cu—Ni, Cu, and Au deposits in volcanic, sedimentary, and associated ultrabasic, basi; and acidic intrusive rocks. Late Archaean (—2.7 to 2,4 x 109 yrs.) Mo, Li, and Be in Kenoran pegmatites; minor Pb—Zn veins; Au and Cu—Mo deposits associated with late Archaean alkalic volcanic and intrusive rocks; remobilized early Archaean deposits. Early Aphebian (—2.4 to 2,0 x i09 yrs.) conglomeratic U-Th deposits in Huronian rocks; veins containing native silver, Cu, Pb—Zn, Au, or U associated with Nipissing diabase and correlative intrusives0 Late Aphebian (—2,0 to 1.6 x l0 yrs.) iron formations in Animikean strata; Zn—Pb—Cu — bearing pyritic deposits in White— water strata in the Sudbury basin; Ni—Cu deposits associated with the Sudbury irruptive0 Neoheikian (—1.3 to 0.9 x 109 yrs.) native copper and other Cu deposits in Keweenawan strata; Ag deposits associated with basic intrusives; Pb—Zn and pitchblende veins; disseminated Cu deposits in breccia and in acidic intrusives; Nb and Cu deposits in alkalic syenite complexes. Analyses of minor element contents of suiphide minerals and lead isotope analyses aid in classification of deposits and interpretation of their histories with respect to associated rocks dated by K—Ar and Rb—Sr methods. Many deposits contain radiogenic lead presumably generated during inter—orogenic It is not clear in every case whether this was added periods0 at the time of formation or at a time of metamorphism of the deposit. * See map, inside back cover �20 CLAY MINERALS IN GLACIAL DEPOSITS, HOUGHTON, BARAGA, AND ONTONOGAN COUNTIES, MICHIGAN A. P. Ruotsala, G. J. Koons, and S. C. Nordeng Michigan Technological University Hought on The clay—sized fractions from surficial glacial tills, outwash, and lacustrine deposits from 13 Baraga, Houghton, and Ontonogan County localities have been examined by x—ray diffraction. Results show that the clay fraction of most recent deposits consist of lute (clay—mica) and chlorite approximately in equal amounts. Clay fractions from older glacial deposits contain substantial amounts of expandable mixed—layer clay minerals in addition to illite—chiorite. Basal reflections of expandable clays typically consist of single broad 12.6 peaks or double 11.2 - 12.6 peaks which expand to 17 upon treatment with ethylene glycol. The difference in clay mineralogy with depth may represent a weathering sequence in the local area and suggests the possibility of. correlation of glacial deposits on the basis of clay mineralogy. �21 ORIENflD CHANNEL SAMPLES John Q. St. Clair Mining Geologist, Duluth, Minnesota Chqnnel samples of rock outcrops may be easily taken and oriented in the field by using a specially—equipped, lightweight Romelite gasoline motor unit operating two parallel, diamonds impregnated sawing blades spaced about one inch apart on the high—speed drive spindle. The same unit may be used to trim the specimens to• required dimensions, a convenient size being 1" by 1" in cross— section and 6" in length. Water collant may be supplied by a standard portable pressure tank. Orientation of the channel samples is accomplished by using a simple goniometer device in conjunction with an ordinary Brunton compass. �______ 22 RESULTS OF DETAILED GEOCHEMICAL PROSPECTING IN THE WEST—CENTRAL PART OF THE NEGAUNEE QUADRANGLE, MICHIGAN* Kenneth Segerstrom U. S Geological Survey Denver, Colorado Surficial materials in Marquette County were sampled and analyzed for lead, copper, and zinc during 1963-64 (Segerstrom, 1965).** Five areas where anomalously high concentrations of base metals were found in the soil were sampled in greater The 1965 localities and their microtopographic detail in 1965. 200 feet. Where setting were mapped at a scale of 1 inch anomalies were especially high, small portions of the larger mapped area were resampled and remapped at 1 inch = 50 feet. Four of the five major areas are in T. 49 N., R. 27 W., as sec. 36, and vicinity sec. 35, N follows: NE I sec0 30, NW sec. 7, of corner secs. , 9, 16, 17. The fifth area is in W sec0 12, T. 49 N., R. 2 W. T. 49 N., R. 27 W., and adjacent NE Analytical results from the entire 1963—65 mapping program indicate that anomalous concentrations of lead, copper, and zinc in soils of the region are in large part post—glacial and reflect a local source. Results from the 1965 work have made it possible to delineate within each of the five areas relatively small targets for further exploration. Their geologic setting indicates that most of the targets in the first, fourth, and fifth areas may reflect sulfide mineralization along crosscutting (north— striking) faults or shears, The mineralization indicated by targets in the second and third areas appears to be largely related to bedding-plane (east—striking) shears. I I I •1 * Work done in cooperation with the Geological Survey Division of the Michigan Department of Conservation. ** Segerstrom, Kenneth, 1965, "Preliminary Results of Geochemical Prospecting North of the Marquette Iron Range, Michigan (abs.): in 11th Ann. Inst. on Lake Superior Geology, St. Paul, Minn., p. 30. I �23 ENGINEERING GEOLOGY ON NEW SECOND LOCK, ST. MARYS FALLS CANAL SAULT STE. MARIE, MICHIGAN Terrence J. Smith U. S, Army Corps of Engineers Sault Ste, Marie, Michigan As part of navigation improvement between Lake Huron and Lake Superior, the U. S. Army Corps of Engineers is replacing an obsolete lock with a new lock 1,200 feet long, 110 feet wide and 32 feet deep, Construction is on Cambrian sandstone and shaly sandstone which dips three degrees west. The sandstone is massive, and hard The shaly sandstone to very hard, with soft shaly seams. is hard with soft seams, slakes readily, and deforms and rebounds when unloaded. Good-quality rock was required for maximum stability. Consequently, more than 7,000 linear feet of 6—inch diameter core were drilled and examined. Construction requirements are unique because the lock is in a trench excavated O feet below river level on an island of Adjacent structures rock separated from land by adjacent locks. and rock are protected against blast damage by pre—splitting or close—line drilling and broaching, and blasts are monitored with a seismograph. Dangerous hydrostatic forces are controlled during construction with cofferdams and by dewatering adjacent locks. A foundation grout curtain, drain and weep holes, and lateral drains in the lock floor, metal waterstops between lock wall monoliths, and a strutted lock floor will protect the structure against hydrostatic forces after construction Approximately 950,000 cubic yards of rock, old lock masonry and overburden,will be removed, and 350,000 cubic yards of concrete will be placed during excavation and construction, The lock will be completed in August 1967 at a cost of O million. �24 IRISH STRATA-BOUND BASE METAL DEPOSITS A, K. Sneigrove Michigan Technological University Hought on In the Central Plain of Eire two important stratiform zinc— lead deposits, Nenagh and Tynagh, are about to come into production. A disseminated zinc—lead deposit, Riofinex, and a disseminated copper deposit, Gortdrum, are being explored. These deposits occur in Lower Carboniferous limostones, some as massive suiphides, other as disseminations; some conformable with limestone bedding, others evidently remobilized andforming replacements and veinlets. Association with or near Waulsortian The Reef Limestone muds is common but not necessarily genetic. paleophysiography is fairly well established, and provides a broad guide in ore search. Tuffs may indicate volcanic exhalative contribution of metals, including relatively high silver values, thus differentiating these deposits from the Mississippi Valley type. The deposits occur near normally faulted inliers, and Armorican (late Carboniferous) movements may account for their diplogenetic character as well preservation of gossans. Mantle fissures have been invoked as regional controls of mineralization. Geochemical dispersion as determined at Tynagh was predomin— ately mechanical and syngenetic with till. Cu, Zn, Pb, and Hg dispersion trains are detectable in stream sediments and are related to soil/till anomalies rather than bedrock source in Peat is a largely undetermined areas of glacial overburden. factor as a metal collector. Conditions favorable for the occurrence of strata—bound Isotope and other geochemical deposits appear to be widespread. studies are needed for a better understanding of genesis and improved exploration techniques in this renascent mineral industry. I I I I �25 SUGAR LOAF CONGLCNERA'?E, MARQUETTE COUNTY1 MICHIGAN Kiril Spiroff Michigan Technological University Houghton A few miles to the north of. Sugar Loaf. Peak on the shores of Lake Superior is a conglomeratic outcrop which is of particular interest. It is located in Section 20, T. 49 N., R. 25 1., being.6 miles north of Marquette, Michigan. The boulders making up the conglomerate are up to a foot• diameter and are of weathered granite and red shaly sandstone. They overlie a gray granite and grade into a red, horizontal bedded sandstone believed to be of Cambrian age. This outcrop, having shaly sandstone boulders along with in granite boulders, corroborates the belief as expressed in an article1'by the writer that the Cambrian. sandstone is substantially a product of an older sandstone, probably Sibley. 1. Spiroff, Kiril, 1952 "Sandstones near L'Anse, Michigan". Rocks cM Minerals, 1.1. 27, No. 3-4, p. 149. �26 NOTES ON LAKE SUPERIOR TYPE IRON ORES AT BARSUA, ORISSA, INDIA G0 G. Suffel University of Western Ontario London, Ontario, Canada The Barsua mine, 250 miles 1961 to supply the new Rourkela Reserves were 117 million tons, than half sinter ore. Expected west of Calcutta, was opened in steel plant, 42 miles north. between 5.2 and 64.5% iron, more output was 3.0 million tons yearly. Barsua is on the Precambrian Bonai iron range, which extends f or 75 miles as a ridge of peaks and saddles from 2,600 to 3,000 feet in elevation, with ore confined to the top. Relief is 1,300 feet. Dips are steep and structures are complex. "Banded hematite—quartzite" about 900 feet thick, is part of the Iron—ore Series, largely shale with local limestone, unconformable on Archaean—type metamorphic rocks. The Series was folded, and intruded by the Singhbhum granite about 203 m.y. ago. Six varieties of hematite ore are found. Massive hard cap— ore comprises only 3.7%. Most production comes from porous laminated ore, over 59% iron, comprising about 49% of reserves. Unfortunately at least 34% of total reserves is "Blue Dust", nearly 60% iron but difficult to handle and requiring sintering. Complex structures seen in the pit have three causes: original soft—rock deformation, seen locally in hematite—jasper; tectonism; slumping due to leaching and oxidation. Similarities to ores and iron formations of the Animikie are numerous and counterparts of almost all types can be found in Michigan or Minnesota. According to recent work, even the age of the sediments is comparable. In contrast, geothite, magnetite, The ores specularite, and iron silicates seem virtually absent. fade out downward, usually at less than 200 feet. Laterite caps the ferruginous shales and there are over 4 million tons of lateritic ore, $ I I I I �27 RECENT INVESTIGATION OF RAISED SHORELINES, EAST SHORE OF LAKE SUPERIOR AND THE SAULT STE. MARIE AREA Walter M. Tovell Curator of Geology Royal Ontario Museum Toronto C. F. M. Lewis Geological Survey of Canada R, E. Deane* The eastern shoreline of Lake Superior and the Sault Ste. Marie area have yielded some good evidence for the former levels of Lake Superior. The investigations of Stanley (1932) and Farrand (1960) have been added to by surveys of raised or perched beaches at Montreal River Harbour, Batchawana and Sault Ste. Marie. These studies strongly suggest that water planes were present up to nearly the 1,100 ft. contour both in the Batchawana Bay area and at Sault Ste. Marie. These data suggest that Lake Algonquin penetrated into the Superior Basin, All profiles presented have been surveyed by transit. The report is the preliminary stage of a general program for a more precise correlation of water planes between the Sault Ste. Marie area and the Southern part of Georgian Bay, by the Royal Ontario Museum, and a general investigation of the history of the Lake Huron Basin by the Geological Survey of Canada. * Deceased. �1 28 NEW ZEALAND IIIVIENITh SANDS M. E. Volin* Director, Institute of Mineral Research Michigan Technological University Houghton Ilmenite and lesser amounts of zircon, rnagnetite, rutile, monazite, and gold occur in beach sands distributed along the .1 West Coast of the South Island for a distance of over 200 miles. Extensive accumulations form raised beaches, associated dunes, and filled lagoons around the outlets of the larger rivers. Detritus deposited off—shore was sorted and transported along the coasts by northward—trending littoral currents, and resorted by wave and eventually wind action. The sands have a uniform grain—size distribution with the various mineral reporting into size classes according to their hydraulic equivalences. Ubiquitous quartz is accompanied by heavy silicates, mica, and The ilmenite is found in discontinuous lenses in some spinels. the beaches and in lesser amounts distributed throughout the dunes. Clean ilmenite grains from the active beaches have nearly a stoichiometric ratio of iron to titanium, but microscopic study shows minor rutile intergrowths occurring along the basal planes, minor hematite composites containing ilmenite ex—solution bodies, and clouds of silicate inclusions less than 10 microns in size. Leucoxenization is not notable; apparently the New Zealand climate has not been favorable for this process0 A consolidated "iron pan", conforming with the ground surface, a feature of the old beaches, and the sands in both the old beaches and dunes are coated with yellow iron oxide and contain concretions up to several inches in diameter. These features, along with the presence of heavy silicates, complicate mineral separations by conventional methods, and the fine inclusions in the ilmenite are a problem in maldng a commercial product. is I I I I * Fulbright-Hayes New Zealand0 Grantee (1965), University of Otago, Dunedin, �29 AEROMAGNETIC, GRAVITY, AND SUB—BOTTOM PROFILING STUDIES IN WESTERN LAKE SUPERIOR Richard J. Wold and Ned A. Ostenso Department of Geology, The University of Wisconsin Madison, Wisconsin The structure of western Lake Superior is studied by magnetic, gravity, and sub—bottom profiling surveys. About 7,500 miles of north—south aeromagnetic tracks were flown, 275 bottom gravity stations occupied, and 900 miles of sub—bottom profiles obtained. The magnetic and gravity surveys support the structural interpretation of White (1966)* for the far western part of the area and indicate a medial ridge, extending southwestward from the western end of Isle Royale that, divides the area east of the Bayfield Peninsula into north and south basins or synclines. The north syncline is cut by a fault that extends westward from Isle Royale, runs north of Isle Royale, and continues eastward to the edge of the survey area. Another fault extends from Isle St. Ignace to the eastern end of Isle Royale and may continue southwestward along the medial ridge. The sub—bottom reflection profiles show many interesting details, such as sediment—filled troughs and old stream channels. The penetration of the reflected wave was 0,25 sec., distinct horizons deeper than 0.1 sec. being commonly observed. * White, W. S., "The Tectonics of the Keweenaw Basin, Western Lake Surv Prof. aDer 524 E 23p. 1966. Superior Region:" U..e �U p .30 SCRE ASPECTS OF HURONIAN PALEOGEOGRAPHY AND SEDIMENTATION IN THE CANADIAN SHIELD Grant Pt. Young University of Western Ontario London, Ontario) Canada A sequence of formations almost identical to those of the of Manitoulin Island in Lake Huron. The pr.-Oowganda Proterozoic rocks of the north shore of Lake Huron appear to be a unique occurrence in Canada. In the north shore region the unconformity beneath the Oowganda Formation is local and an unbroken succession of Proterozoic rocks occurs at McGregor Bay. However, rocks thought to be correlatives of the Gowganda Formation and younger Aphebian sedimentary rocks are widespread throughout the Churchill Province and may be recognized in parts of the Superior and Slave original" Huronian occurs in the McGregor Bay area, north—east Provinces, so that 2. the unconformity beneath the Oowganda Formation i. of regional significance. • I I In the McGregor Bay area the Gowganda Formation conformably succession by the Lorrain Formation, a banded "cherty" quartzite, overlies the Serpent Formation and is followed in upward - I a white vitreous quartzite, and ferruginous slates, siltstone* and quartzite. The iron—bearing beds are thought to be approximate equivalents of the Animikie iron formations of Port Arthur and the south shore of Lake Superior. The oldest Proterozoic rocks of Michigan and adjoining areas are thought to be correlatives of the Cobalt Group of Ontario. The absence of the older Huronian rocks in the north-central United States may be attributed to the presence of a positive area there in pre— Cobalt times. Paleocurrent analysis and dimensional fabric analysis indicate an essentially southerly direction of transport of the Hurorian sediments of the McGregor Bay area. Abundant sedimentary structures indicate that all the Huronian sediments of the McGregor shallow—water conditions. A comparison of the Lower Proterozoic sediments of Canada with - Bay area were deposited in those of south-west Greenland, Scandinavia, India, and Australia suggests the existence of frigid conditions over a large part of the earth's surface at that time. I .1 I �31 UNIQUE INTERGR(MTH OF CALCITE AND PYRITE Paul W. Zimmer The Hanna Mining Company Iron River, Michigan A rather unique intergrowth of calcite and pyrite is here described. These crystals were found in the (Iroveland Iron Mine of the Ranna Mining Company near Iron Mountain, Michigan. The pyrite and calcite show evidence of simultaneous crystallization. The pyrite grew on the vertical symmetry planes of the calcite with the triad symmetry axis of the pyrite parallel to the triad inversion axis of the calcite. This intergrowth gives the geometric symmetry of the Ditrigonal hemimorphic class to the combination. It is felt that because the intergrowth does not satisfy the symmetry of the calcite in its entirety, the pyrite was the "seed' crystal to the intergrowth. The interspacings of the planes in the calcite in the direct ion of the triad axis is very close to the spacings of the planes in the pyrite in the direct ion of the tritd axis and it is felt that this similarity in spacings was the controlling factor to this unique intergrowth. More work is needed in the field of crystallogeny. Evidence of partial parallel orientation of crystals may be characteristic of simultaneous crystallization that can be used in the interpretation of age relations in mineral deposition. ��REGIONAL GEOLOGY OF THE SAULT STE. MARIE AREA C. Ernest Kemp Michigan Technological University Sault Ste. Marie, Michigan p INTRODUCTION The contact between the Precambrian Canadian Shield and the main body of Paleozoic rocks to the south is nowhere more obvious than in the Sault Ste. Marie 'area. Here a marked unconformity is reflected in changes in the vegetation and topography. The• that the visitor going from one area to the next is immediately aware of the 'marked difference between the two regions. result is This paper will be confined to the areas near or adjacent the twin cities of Sault Ste. Marie in Michigan and Ontario, although better known areas of geological interest can be found beyond the limits of this discussion, at Blind River to the east and Wawa to the north. For the student of' geology the area is rich in diversity of lithology, structures, topography, and mineralogy. Being' close to Lakes 'Superior and Huron, and to the St. Mary's 'River, it is an area of considerable natural beauty which has become a popular tourist center for visitors from both Canada and the United States. to Although regional geological studies of this region have been made since early in the nineteenth century, only a few have dealt specifically with areas involved in this paper, and some of these are noted in the references.*' Since the discovery of uranium at Theano Point, copper in commercial quantities near Mamainse, Ontatio,, and dolomite in Chippewa and Mackinac Co!lntiós in Michigan, more detailed work has been carried on. However, there • are many interesting,' unsolved geological problems throughout the district, to of the fact that there is still a consider- say nothing able potential for the discovery of new, economically valuable, deposits. Sault Ste. Marie, Ontario and Sault Ste. Marie, Michigan are situated north and south, respectively, of the rapids in the St. Marys River. These rapids are fifteen miles downriver from the outlet of Whitefish Bay, Lake Superior, and forty-seven miles upriver from Lake Huron. The general direction of the river is slightly north of east from Whitefish Bay to St. Mary's Rapids. At the rapids which are also the location of the famous locks and over the head of which passes the International Bridge lintcing * Numbers refer to references listed at the end of this paper. �U p 2 t the two cities the river drops about twenty feet southward and }lows into Lake Huron at Detour. and then turns Climate and Ventation The area immediately surrounding the two Saults has a typical northern continental climate modified by the proximity of Lake Superior. The latter his in the path of the prevailing windp, and most of the major air masses in migrating eastward have to pass over the lake before reaching the Saults. It is fl interesting to note that this area lies only a relatively short distance south of a tongue of sub—ArctThc climate which encompasses the southern tip of James Bay. The severity of the winters increases rapidly landward from the shores of the lake, part ice ularly in the Ontario section of the area. Total precipitation approaches 30 inches annually, and average mean temperatures range from 64.6°F in July to l5.S°F in January.l7 Inland from the lake it is not uncommon to find temperatures of ..400F, and unofficial records are far below that. A noticeable difference in vegetation separates the areas underlain by Precambrian rock from those underlain by Paleozoic, even though a veneer ef Pleistocene deposits partially covers them all. Originally there was probably a greater similarity of vegetation between the two areas, but cultivation and more intensive logging of the flat lands characteristic of the Paleozoic areas have radically changed the flora. The vegetation on the Precambrian areas consists mostly of maple, birch, and aspen, and extensive areas of coniferous growth. Such farm land as exists is generally confined te small glacial drift—filled valleys between rocky hills with little soil cover. The Paleozoic areas, on the other hand, comprise broad areas of farm 'forested areas of hardwood, including beech, and extensive sand plains and swamps on which conifers dominate. Dense dedar growth characterizes the southern Paleozoic area. land, part of the 1 paper deals with five distinguishable subsections of the geology of the Sault Ste. Marie area and its environs, viz. This Granite Complex 2. Metamorphic Complex 1. 3• 4. 5. 1 Keweenawan Paleozoics Glaciation g I 1 L. �3 Granite Comlex From Sault Ste. Marie, Ontario northward to the Montreal River and westward to Lake Superior lies an area which, with . the exception of the Keweeawan, to Le describeQ later consists almost entirely of granite and granite gneiEs.°,l2 fn this area there are a few extensions of the metasediments and meta- volcanics to be found farther east, but anyone travelling through this country is bound to be impressed by the overwhelming amount of granite and granite—like rocks. The granites are mostly pink and quite uniform in the southern end of the area. Both gray and reddish varieties, sometimes porphyritic and often with pegmatitic phases, occur in the northern end. Granodiorite monsonite, and related phanerites are also present in smaller amounts. The gneisses are well banded and are very likely metasediments; they contain large masses ef amphibolite and biotite schists, which may be xenoliths of partially granitized basic volcanics or intrusives. The granites are mapped as Algoman but more intensive study of the batholiths is likely to Show several different ages of granite activity. Some younger granitesl° have been recognized but a complete description of the age relationships is beyond the scope of this paper. The entire granite area is cut by basic dikes)4 The dikes are often sheared to some degree and have been altered to chloritic and serititic equivalents. Some fresh diabase dikes are obviously of i younger age, and ire presuMed to bs Keweeawan. Characteristically the granite areas are rugged, with relief as much as 800 feet.. The drainage is youthful with several lakes and many swift-running streams. The soil is generally thin except in the valleys, End in many places thegranites form rugged rock bluffs. Where the basic dikes cut the granite masses, differential erosion of the dikes has resulted in deep chasms, the most obvious erample of which is at the mouth of the Montreal River. Here the walls of the ccnyon are practically the contact surfaces of the dike which is now visible only during stages of low water. The area here called the Granite Complex has not produced any commercially valuable deposits, although some near misses have occurred and there Is a possibility that a copper porphyry type of deposit will be developed near the edge of the Keweenawan.' The original discovery of uranium in 194.8 by Robert Campbell, which set off one of the greatest staking rushes in hi4pry, occurred in the northern end of this area at Theano Point.'4 Here mineral- ization is found along the contacts of one Of the dikes cutting a pegmatitic phase of the granite. Pitchblende and related minerals are sufficiently concentrated in hydrothermal veins to have warranted some serious development lork. Several other similar occurrences of pitchblende were found, the most noteworthy of which was in a similar geological environment north of the Montreal River on the property which has become the Ranwick mine. Here specimens �4 of massive pitchblende are found along with some selenides such as clausthalite, PbSe, and a mineral close to Klockmannite, CuSe. Native selenium has also been reported. Although an adit was driven into the potential ore zone, bulk sampling yielded results The mine has since too low to continue further development. become a tourist attraction and the property continues to yield excellent samples of pitchblende for the mineral collector. Several pits and adits scattered throughout the area are testimony to earlier hopes of developing some of the mineralized veins which contain chalcopyrite, galena, and spalerite, but none of them has proved of sufficient size or grade to be minable. Metamorphic Complex Extending eastward from the Granite Complex to the area north of and including Bruce Mines, the geology is radically The dominant rock types of this extensive area are different. metasediments and metavolcanics with some large basic igneous intrusire, This area includes part of the type section of the Huronian.' This area is dominated by prominent hills of quartzite, metaconglomerate, and diabase. The topography in many parts is In some of the valleys quite rough, with relief about 600 feet. between the ridges north of the town of Bruce Mines enough glacial debris has accumulated to provide soil for farming, and although the flat areas are not very extensive, they seem to be relatively fertile. The area also contains many lakes; drainage is in the youthful stage. The general strike is northwesterly, and in the abundant outcrops north of Bruce Mines the ridges and valleys tend to The Murray fault has been traced follow the regional strike. through the middle of the area and strikes northwesterly as well,' Secondary faults probably associated with the Murray fault system occur throughout the area. With the Murray fault almost along its axis, the main structure is a syncline, boldly outlined by resistant quartzite ridges. To the south a paralleling anticline can be traced, with the south limb exposed along Highway 17 near Desbarats where some conspicuous ripple marks are preserved in the quartzites outcropping in road cuts along the highway. (See Elliot Lake guidebook in this program.) Most of the rocks in this area are considered Lower and Middle Huronian, though some of the greenstones, which have been called the "Basement Series", are possibly Archean.2,1° The age relationship of the diabasos and metadiabases is not completely clear; some of them have been considered Keweenawan, and others probably much older. The Huronian rocks are mostly quartzites, metaconglomerates, and metagraywacke. Minor outcrops of Lower Huronian limestone occur; and some slates and a metamorphosed chert—like siltstone are associated with the more prominent One formation in particular deserves special mention quartzites. I I �U r 5 that is the very colorful Lorraizie metaconglomerate which contains jasper and white quartz pebbles in a white matrix and and forms a conspicuous horizon. Economically the area has yielded a few minable deposits most noteworthy being the copper deposits of Bruce Mines. Here, veins ef quartz, siderite, ankerite and chalcopyrite cut the diabase and were rich enough to sustain an intermittent operation in the past with a total production of between 300,000 and 400,000 tons of ore since discovery in 1646. many similar occurrences of chalcopyrite are known throughout the area. Galena and sphalerite in veins cutting metamorphic rocks completely surrounded by granite yielded a small production at Jardun Mines north of Garden River. Other lead-zinc occurrences are also known. Iron formation inter— bedded with metavolcanics or quartzite, magnetite concentrations as magnatic segregations in some of the larger basic igneous the masses, and some vein deposits of specularite in the quartzites have led to prospecting for iron. The last type yielded a small tonnage of high grade ore from the old Stobie mine near Gordon Lake. No. substantial quantities of iron ore are known. Gold has been mined from quartz veins near Ophir, north of Bruce Mines, but results were disappointing. The diabase has been quarried for road ballast and a rather extensive processing plant was erected eastof the Bruce Mines and operated for a few years during World War I. More recently the quartzite of the Bellevue ridge has been quarried for use by the Algoma Steel Company in Sault Ste. Marie, Ontario. Altheugh results of mining attempts have been generally disappointing there is still reason to believe that, with modern techniques, deposits of economic value may yet be found. Prom Harmony Bay north of Sault Ste. Marie, Ontario, and extending north to Mica Bay, the granites and metavolcanics are overlain by basic lavas and clastic sediments of Keweenawan age.1 As these rocks are similar in all respects to the Keweenawan of Michigan it is reasonable to assume that they represent an extension of the lavas found in Upper Michigan and Michipicoten Island. In this area rocks of Keweeawan age are never more than five miles from the shore. They lie comformably on the erosion surface of the older granites or on the Mamainse diakast, an older and more altered basic rock mass, mapped by Moore' asà:single lithologic unit but actually containing a variety of metavolcanics. The exact correlation ef the Mamainse diabase is not clear and in places it is difficult in the field to distinguish between this rock and the overlying Keweewanan. The topography of the area underlain by Keweenawan rocks is generally less rugged than the adjacent granite areas, but the total relief is about as great • The area is one .of ridges formed by the upturned edges of the flows and the conglomerates, so that the ridges trend in the same direction as the strike of the beds. t �________ 6 Along the shore of Lake Superior these ridges form long peninsulas The extending into the lake or islands paralleling the shore. topographic similarity between this shoreline and that of the northeastern part of the Keweenaw Peninsula of Michigan is striking. Cutting the Keweenawan are intrusives of felsite and felsite porphyry, which, curiously enough, appear to be more metamorphosed than the enclosing basic lavas, Thse acidic rocks constitute a very minor part of the Keweenawan,1 The rocks of the area mapped as Keweenan are amygdaloidal basalts and basalt porphyries and in the thicker flows the rocks grade into dolerites and gabbro. These flow units are interbedded The dip of the entire with conglomerates and sandstones. Keweenawan is generally westward toward the Lake Superior basin and dips average around 300. All of the formations have been affected by faulting but no large—scale displacement has been The general direction of the faulting is either parallel noted. to the strike and dipping normal to the beds, or at right angles to these and dipping vertically, Mineralization along the fault I I zones, some of which are brecciated, i inthé'foi ofcopper minerals, including minor amounts of native copper. This led to an early interest in the area in hopes of finding dépôits similar to those mined in Michigan. Recent interest in the area has resulted in the development of one producing mine and two promising prospects. The mineralization appears to be of three different types as described by Giblin.3 These are fissure—filled vein deposits, breccia pipe deposits, and disseminated deposits in what appears to be a copper porphyry type of occurrence. The latter two contain molybdenum as well as copper and occur outside the Keweenawan area but all seem to be associated with a post—lava flow period of mineralization, and therefore may be late Keweenawan in age. Some of the felsites have been explored for hydro-thermal clay deposits. Paleozoics South and west of St. Mary's River lies the area described as Paleozoic. Actually areas of Paleozoic rocks can be found in the previously described subdivisions, but these are minor and in themselves would not contribute much to the geological history This area represents the northern rim of the of the region. Michigan Basin, and therefore includes the oldest of the Paleozoic sediments found in the State.1 The rocks are quite unaltered and nowhere is there any evidence of igneous activity; therefore this subdivision provides a completely different topography as well as lithology from the Dips are very gentle, mostly to the south preceding subdivisions. and occasionally flat. Some local northerly dips are encountered. I I I I �7 The lowest formation in the series is a sandstone which has been correlated with a massive sandStone farther we4 and is considered therefore to be Middle or Lower Cambrian,' although ne direct evidence of this can be found in this area. This sandstone, known as Jacobsville crops out in numerous places and is especially well defined in die area of the locks. A well drilled to a depth of 1,500 feet south of Sault Ste. Marie, Michigan, failed to penetrate the bottom of this formation, but three miles north of the St. Mary's River along Highway 17, conglomerates in the Root River appears to be the basal conglomer- ate of the series. If this is the Jacobsfllle, and the origin of the latter is as postulated by Hamblin,4 it really as part of the Michigan Basin. Overlying Munising formation which can be seen outcropping along the shores of Whitefish Bay and in the Tahquamenon Falls. This latter sandstone is agreed to be the oldest formation of the Basin and is Upper Cambrian in age. does not fit this sandstene is the It is quite different in character from the red Jacobsvillo, being more thoroughly sorted, in some places a very pure quartz sand, and more uniform in thickness. It represents the farthest known advance of the Late Cambrian seas. Some gray sandstone and Shales found along the shores of Lake Superior near Mica Bay and Alona Bay are very likely of this age. Above the Cambrian, the Ordovician is represented by shales and limestones which crop out only sparingly. On St. Joseph's Island the limestone is highly fossiliferous, and crops out only a short distance from the Precambrian basement. The islands from St. Joseph south to the north tip of Druimnond in Lake Huron and west to the mainland contain many areas of Ordovician outcrops and in the Neebish cut there are excellent exposures.7 The material thro*n Onto 'the .:bank5 during the excavation yields good Ordovician samples. The most prominent of the Paleozoic formations are those of Silurian age. They crop out along an east-west, north—facing cuesta and all along the shores of Lake Huron at the south end of this area. These rocks are chiefly dolomite and the cuesta is an extension of the Niagara cuesta of New York and Ontario. In many places the dolomite is elposed or covered by only a very thin overburden. Where Lake Huron and the former glacial Lake Nipissing6 have eroded the dolomites, cliffs and other shore line features . have been developed. The Devoniant is present in only very minor amounts, outcropping near St. Ignace, particularly along the shores of Lakes Huron and Michigan, and in the c'its along the approaches to the Mackinac Lridgôa, The Devonian..eflthe Upper Peninsula consists of the Mackinac Breccia, a formation well described by Landes Ehlers, the and Stanley.t Several prominent sea stacks, now stranded retreat of the Lake since the Nipissing stage of the glacial development of the Great Lakes, occur along the shore in and near St. Ignace. Economically the Paleozoic has yielded metallurgical—grade �a dolomite as well as dolomite for construction purpose.5 Two prominent quarries are operating today, one at Cedarville and the other on Drummond Island. Sandstone of Cambrian age has been used for building stone, but none is quarried today. Pure quartz sandstone of Upper Cambrian age crops out along the shore of Whitefish Bay, particularly at Naomikong Point. Here the sandstone is almost of glass—sand quality without any b'eneficiation, but development of the deposit is interdicted by the Federal Forest Service, as the area is one being developed for tourists and the two operations are not considered compatible. Several attempts to find oil in the Paleozoics have failed. No systematic geopiysical work for the purpose of locating possible petroleum—bearing structures appears to have been done. Some bituminous shales and shaly limestone have been encountered, and reports of oil in some of the wells dug in the district have led to sporadic interest..ia As this area represents the margin of the Michigan Basin, and as the sediments are known to become thicker toward the center of the Basin, the possibility of oil and gas traps along pinch—outs or shoe—string deposits cannot be ruled out, although evidence is very meagre. Glaciat ion The entire area has been deeply affected by the Pleistocene glaciation, and all of it was covered during the Mankatoan substage of the Wisconsin.13 The evidences of recent glaciation are everywhere present, and it is not improper, in studying an area such as this, to discard the term flRecenttt and to include present time in the Pleistocene. During the time of maximum glaciation all of the area being discussed was under the áe, and not even nunataks could have occurred. All of the features which the glaciers left were formed at the bottom of the tremendous ice sheets, or represent features developed during the last stages of the retreat of the ice. In the resistant rocks of the Precambrian are found large These glacial valleys, reminiscent of mountain glaciation. valleys have a modified U-shaped cross section, and are therefore bounded on both sides by steep rocky walls and have a characterThese valleys appear to radiate away from istically flat floor. the highland areas, and were thereftre possibly carved out by tongues of ice descending from the ice caps which probably dominated the highlands during the last stages of the glaciation, while the main mass of the ice retreated to the north. This accounts for the east—west direction of the valley of the Goulais, That and the north-south direction of the valley of the Root. these valleys should also tend to follow zones of rock weakness, such as shear zones, columnar jointed dikes, and similar linear features is self—evident. Glacial grooving and striations are pronounced throughout the outcrop area, and are particualrly noticeable in the quartzites I �9 of the Precambrian and some of the dolomite ridges of the Paleozoic. Glacial polish occurs on some of the exposed quartzites and, due to only minor weathering, some exfoliation can been seen. In places where the Precambrian rocks crop out through the glacial drift, typical roches moutonnees are common. Whereas the area underlain by the Precambrian is characterized by the erosional features of glaciation, the area underlain by the Paleozoics contains mostly constructional features.* Here the topography is dominated by the flat plains which formed the floor of former glacial lakes.9 These plains are formed by varved clays and sand, and their featureless surface is broken only by some deeply eroded river valleys, morainal ridges and hills, the prominent dolomite cuesta previously mentioned, and a second, less prominent Cambrian cuesta, over which the Tahquamenon River flows to form the Tahquamenon Falls. Outwash plains, some with prominent gravel areas, occur south of the edge of the Precambrian, and are common in other parts of the area. Post—glacial uplift of the entire eastern end of Lake Superior accounts for many of the topographic features in the area.** Raised beaches are common in the area north of Sault Ste. Marie, To the south, and are responsible for some thick gravel deposits. the drowned lower reaches of the rivers0flowing into Lake Superior, such as the Waiska and the Tahquamenon,' are evidence of gradual tilting of the Lake basin. Economically, the glaciation of the area has resulted in valuable deposits of gravel, many of which have been used for road building and concrete aggregate. The varved clays have provided reasonably fertile farm land, and the sands are being used as fill. The glacial gravels are alo a source of excellent ground water, much of which is artesian. j. abstract in this program. * See, however, Farrand ** See Tovell et al. abstract. Ref erences 1. Cohee, George V. (1945) Stratigy of Lower Ordovician and Cambrian Rocks in the Michigan Basin. U.S. Geol. Surv. Oil and Gas Investigations, Prel. Chrtg. 2. Canada Collins, W. H. (1925) North Shore of Lake Huron. Geological Survey, Memoir 143, No. 124, Geological Series. Written at Methodist Hospital, Rochester, Minnesota. �______________ 1 10 3. Giblin, 4, Hamblin, William K. (1958) The CambraSandstones of Northern Michigan, Michigan Geological Survey, Pub, 51. 5. Hogberg, Carl G. (1960) Some Aspects of the Limestone Industry P. E. (1966) Recent Exploration and Mining Developments Paper presented at Convention in the Batchawana Area. Ont. of Prospectors and Developers Association, March, 1966. (see also abstract in the present program). in Michigan. Paper presented atA,LM,E, Meeting, Houghton. 6. Hough, Jack L. (1958) Geology of the Great Lakes. of Illinois Press. University I 7. Kowaiski, John Jt1 (1961) Silurian Lithology and Correlations. I 8. Unpublished. G.M., Landes, K. K.,Ehlers, G. M.,Stanley/(1943) Geology of the Mackinac Straits Region. Michigan Geological Survey, Publication 44, Geological Series 37. 9. Leverett, Michigan State University. I Frank (1929) Moraines and Shorelines of the Lake Superior Region. U.S. Geol. Surv. Prof. Paper 154—A. 10. McConnell, R. G. (1927) Sault Ste0 Marie Area, District of Algoma, Ontario Dept. of Mines, 35th Annual Rpt., Vol. 35, 1953, pp. 1—52. I PartI, 11. Moore, E. 5, (1926) Mississagi Reserve and Goulais River Iron Ranges. District of Algoma. Ontario Dept. of Mines, Vol. 34, Part 4, 1925, pp. 1—33. 12. (1927) Batchawana Area. District of Algoma. 1 Ontario Dept. of Mines, 35th Annual apt. Vol. 35, Part II, 1926, pp. 53—85. 13. Moore, IL C, (1958) Introduction to Historical Geology, 2nd Ed. McGraw—Hill Book Co. I 14. Nuffield, E, W. (1956) Geology of the Montreal River Area, Ont. Dept. of Mines, 64th Annual apt. Vol. 64, Part 3, 1955. 15. Ontario Dept. of Mines, Ontario Minerals in Your World, 1 1965 Review. 16. Thomson, Jas. E. (1954) Geology of the Mamainse Point Copper Ont. Dept. of Mines, 62nd Ann. Rpt., Vol. 62, Part 4, Area, 1953. 17. U.S. Weather Bureau, Sault Ste. Marie, Mich. 1 Personal communi- cation. 18. Van Lier, K. E. and Deutsch, Morris (1958) Reconnaissance of the Ground—Water Resources of Chippewa County. Michigan, Michigan Geological Survey, Progress Report No. 17. 1 I �Figure I. Geology of the SouR Ste. Marie Area �GEOLOGY AND MINERAL DEPOSITS OF THE MANITOUWADGE LAKE AREA* by E. G. Pye Resident Geologist Ontario Department of Mines Port Arthur, Ontario Introduction In 1931, the Manitouwadge Lake area was surveyed for the Ontario Department of Mines by Dr. J. E. Thomson, now Chief Geologist; and on his geological map, published in 1932, he noted an occurrence of gossan and sulphIde mineralization at the site of the now famous Geco mine]-, But despite this it was only many years later that any interest was paid to the discovery. This may be owing to the commonly held opinion that "greenstone" belts of small area do not lead themselves to the occurrence of large mineral deposits — the favourable prospecting area at Manitouwadge Lake is only about 35 miles square. It may also be because of the many prospectors highly metamorphosed condition of the rocks consider that schists and gneisses are unfavourable to ore depoIn any event, the area was avoided until as late as 194.7, sition. when the suiphide deposit at Manitouwadge Lake was first staked. But even at that time, it was difficult to arouse interest in the discovery; and after two years, the prospector, Moses Fisher, was compelled to let his claims lapse because of failure to attract a mining company to undertake development. In 1953, two prospectors, Roy Barker and William Dawidowich of Geraldton, Ontario, decided to visit the area. Upon relocating the ulphide deposit, with which they were much impressed, they decided to stake. The sulphide deposit was examined by W. S. Hargraft, consulting mining engineer, and upon his recommendation, the property was quickly taken up by General Engineering Company, Limited; Consolidated Howey Gold Mines, Limited; and H. W. Knight and associates on a partnership basis, Diamond drilling in August and September indicated the possibility of a copper—zinc— silver ore body0 Geco Mines, Limited, was incorporated in October, and it was not long before the results of further drilling * Published by permission of the Provincial Geologist, Ontario Department of Mines0 Reprinted from the Second Institute on A. K. Lake Superior Geology, "Geological Explorationtt. Sneigrove ed,9 Michigan Tech Press, 1957. Subsequent developments will be discussed at the mine by the author. 1. Thomson9 Jas, E,, "Geology of the Heron Bay — White Lake Area," Ont, Dept. Mines, Vol. XLI9 Pt0 6, pp. 34—47 (with map No. 4i), 1932. �___ I N 2 a deposit of such importance that the biggest staking rush in the history of Ontario, and one of the biggest in the history of Canada, was precipitated. indicated Location of Area Means of Access I. Manitouwadge Lake area forms a small but very important part of the Heron Bay - White , 1 The Lake region along the north shore of Lake Superior. As shown in Fig. lt it lies about midway between two transcontinental railways, the Canadian National Railways line on the north and the Canadian Pacific line on the south; it is 170 miles east—northeast of the Canadian Lakehead, and 200 miles northeast of Houghton, Michigan. The area i. accessible by an Ontario Department of Mines access road connecting Manitouwadge Lake with the Trans-Canadahighway along the north shore of Lake Superior; by a spur railway line built, south from Hillsport by the Canadian National 'Railways; and by a second railway line,, built north from Hemlo by the Canadian !acific Railway. General Geolozv. All the'consolidated rocks exposed in the Manitouwadge Lake area' are of Precambrian age. They have been divided into three main groups: (1) A system of closely folded and intensely. metamorphosed, volcanics. and sediments, which, together with horizons of amphibole — biotite gneiss and banded iron formation, are believed to be of Early Archaean age; (2)' An assemblage of igneous rocks, of post—Early Archaean and possibly of Algoman age; and (3) .Diabase dikes, which have been correlated tentatively with basic intrusives of teweenawan.age exposed' around Lake Nipigon and along the 'northwest shore of Lake Superior. . I ''.1i V c c : A prominent series' made up largely of horn— blende sc st is exposed south and west of .Wowun Lake. It forms *' See instead map on inside back cover for location. . I i 1 �3 a well—defined belt, width, which extends Lake, and up to and possibly, exceeding two miles in from this locality southwest to Manitouwadge thence westward across the southwest corner of the map area. Two varieties of hornblende schist are present. One shows little evidence of banding; the other is characteristically finely laminated and resembles a thin bedded sediment in structure. Excillent exposures of the non—laminated hornblende schist are found in the west part of the belt. In places where shearing has not been too intense, vestiges of original pillow structures can bstseen. The pillows are somewhat irregular in shape and do not permit satisfactory top determinations. But their presence is significant, for they indicate that the hornb].ende schist is of volcanic origin. In consideration of the mineralogical composition — the typical shhist consists of about 50 percent hornblende with lesser amounts of andeline and a little quarts, sphene, and magnetite — it is probable that the rock is the metamorphosed equivalent of original basic lava. Thin horizons of laminated hornblende schist separate the lava flows. They are particularly well—developed in the vicflifl The rock itself is similar mineralogically to the variety Just described except that, at the expense of plagioclase, quarts is an essential rather than an accessory constituent. A further and more striking difference, of course, is the thfcn bedded structure — black layers of material rich in hornblende alternate with grey layers rich in plagioclase and quarts. These layers range from a small fraction of an inch to several inches in thickness. The laminated hornblende schist is found in places to contain lenticular fraptents of greenstone, from less than an inch to six inches and up to about three inches in thickness. The two characteristics — stratification and fragmental structure — indicate that the original rock was a of Manitouwadge and Rose lakes. tuffaceous sediment deposited subaqueously during the period of volcanism. e : As the north margin of the volcanic series s approac , we —developed horizons of sedimentary gneisseseare found to alternate with bands of hornblende schist. These increase in both number and thickness to the north so that, within a short distance,the series gives way to one in which the principal ferrcmagnesian mineral is biotite. Four principal varieties of sedimentary gneisses have been recognised. They are biotite gmeiss, quartz—oligoelase4iotite gneiss, quartzite, and quarts—microcline gneiss. In view of the evidence presented by petrologists to the effect that clay minerals combine to form chlorite and sericite, and that theie in turn combine to form biotite during metamorphism', it is thought that the biotite gneiss, the quarts— 2. Barker Alfred, "Metamorphism, A Study of the Transformations of Rock Masses," Methuen & Co., Ltd., London, 11, 45—61, 1950. �I p 4 oligoclase—biotite gneiss, the quartzite, and the quartz—micro— dine gneiss are the altered equivalents of shale, argillaceous sandstone, quartz sandstone, and arkose, respectively. Amphibole—Biotite Gneiss: In many places throughout the series the sedimentary gneisses are found to be interrupted by lenticular masses of amphibole—biotite gneiss of dark colour, This coarse to very coarse granularity; and striking appearance. rock is made up largely of anthophyllite, hornblende, and biotite, with small amounts of quartz, oligoclase, and magnetite. Red garnets are also commonly present0 They occur as large porphyro— blasts, ranging from about one—half inch to two inches or more in diameter, and in places make up 25 percent of the rock mass. The amphibole-biotite gneiss is frequently found to grade, by disappearance of amphibole and, when present, also of garnet, Because of this it is considered to into typical biotite gneiss. may represent the highly metamorphosed be sedimentary origin — equivalent of a calcareous, chloritic grit or basic tuffaceous sediment that was developed at the same time as the enclosing It is included with the sedimentary gneiss on the generalrocks. ized geological map. it Iron Formation: Commonly intimately associated with the amphilbole—biotite gneiss is a peculiar banded rock. This banded rock consists of layers of coarse-grained quartz, from a fraction of an inch to a foot or more in thickness, alternating with equally thin or thinner layers of one or more of amphibole schist, garnetiferous amphibole—biotite schist, and a very coarse amphibolite, In the field it has been variously termed quartz— chlorite rock, quartz—amphibole rock, quartz-amphibole-pyroxene rock, and iron formation. Since the rock is distinctly banded, since the schist or amphibolite layers contain disseminated crystals and thin seams of fine granular magnetite, since individual horizons can be traced by dip needle and magnetometer, and since these horizons are very persistent and follow the folded pattern of the sedimentary gneisses, it is thought that "iron formation" is the most appropriate term. I Post-Early Archaean (Algoman?) I Basic Metaintrusives: Small lenticular bodies of metagabbro are found in a number of places within or close to the belt of volcanic rocks These bodies have intrusive relations with the Early Archaean formations, but are themselves cut by granite and pegmatite0 For the most part they consist of a medium— to coarse— grained rock made up of about equal amounts of dark-green horn— I I �5 blende and plagioclase, with small amounts of biotite, quartz, and magnetite. outcrop. This rock is generally quite massive in the Granitic Rocks: The most abundant igneous rock found in the Manitouwadge Lake area is biotite granite gneiss. Together with massive granite, migmatite, and pegmatite, it occurs in three (1) the extreme southeast corner of the principal localities: area; (2) the extreme northwest corner; and (3) the whole of the The granitic rocks to the northwest and south— northeast quarter. ea8t are believed to represent a single large mass, in which .the Ear1yrchaean rocks form a deeply infolded inclusion; those in the northeast quarter of the area are believed to represent a satellite of the main mass, which has been localized along the major synclinal axis (see Structural Geology). Associated with the granite gneiss, migmatite, and the rnedium—grained, massive, intrusive biotite granite, and cutting the Early-Archaean formations, are dikes and sills of pegmatite It occurs as: and aplite0 The pegmatite is of three ages. (1) dikes which cut metagabbro inclusions in, and which are themselves truncated by, the massive biotite granite; (2) irregular bodies which grade into, and hence represent a phase of, the massive biotite granite; and (3) dikes, which cut the massive biotite granite. Some of the pegmatites are preore in age, and onthe properties of Geco Mines, Limited, and Willroy Mines, Limited, they were instrumental in the local— ization of the ore deposits Algonkian The diabase forms The youngest rock exposed is diabase, a number of narrow, but fairly persistent north—south dikes, some of which are localized along transverse faults (see Fig, 2). In that these dikes cut sharply across all the other consolidated rocks, including the various granitic rocks, it is thought that they are of Algonkain or Late Precambrian age. It is possible that they could be correlated with similar rocks of Keweenawan age, that crop out to the west of the area in the vicinity of Lake Nipigon. �6 Structural Geology Folding: The rock type described as iron formation is the only one that occurs in sufficiently distinct and peràistent horizons to be useful in outlining the structural geology. Examination of the generalized geological map of the area shows that, in the vicinity of Wowun Lake on the east, the iron formation and the gneisses strike southwest and dip vertically to steeply north. Proceeding westward to Fox Creek and the Geco mine, however, the formations assume an east-west strike; and still farther west, midway between Fox and Nama Creeks, they strike northwest and dip 50°N. Finally, at the west side of the map area, the formations assume first a northerly strike and then double back on themselves to strike northeast again. They delineate a large trough or synclinal fold, which dip measurements indicate to be asymmetrical and overturned to the north. Other dip measurements, at the nose of the fold, indicate a plunge to the northeast of from 15 to 25 degrees. In the eastern part of the area, lineation and drag folds indicate a steeper plunge of about 40 degrees. 1 Faulting: After the major folding, the Manitouwadge Lake area suffered a series of disturbances that resulted in the development of a large number of faults. These faults are of (1) Longitudinal or strike faults, which more or three types: less parallel the formations along the south limb of the syncline; (2) transverse faults, which strike in a general north-south direction; and (3) diagonal faults, which strike northwest, obliquely to the other faults. All are represented in the field by deep linear depressions in the topography. An example of a major strike fault is the Agam Lake fault, which strikes due west, from north of Manitouwadge to almost the west boundary of the map area, just north of and roughly parallel to the belt of volcanic rocks. This fault is pre—ore in age, and is represented by a wide zone of graphitic schist, in places mineralized with pyrite and pyrrhotite. The magnitude and direction of movement along this break have not been determined. However, the fault appears to truncate a number of pre-ore, right—hand transverse faults, and at the same time, appears to be terminated by the north—south, post—ore, left—hand Fox Creek fault, I At least three periods of movement are thus indicated. A possible fourth period of disturbance may be responsible for the fault that extends diagonally across the area from northwest to southeast0 In regard to this fault, the offsets shown by the In the northwest section of the rock formations are of interest. area, the formations dip rather flatly to the southeast. Here the displacement was lefthand, or east side to the north. In the I I �7 southeast section of the area, the formations dip about 650 to the Here the displacement was right—hand, or east side to northwest. the south, To the east of the Geco mine, the formations dip Here the formations have been traced across the fault vertically. Such anomalous to Wowun Lake without any apparent offset. conditions can be explained satisfactorily by assuming that the displacement along the fault was mainly vertical, and that the South of Mose Lake, relative movement was up on the west side. a diabase dike was localized along this diagonal fault. But the diabase has been brecciated, Further, north of the Geco mine, the fault cuts and offsets two diabase dikes. In view of these facts and the simple vertical displacement indicated, it is thought that the two or more movements represented occurred in Lake Precambrian time. Mineral Deposits All the important mineral deposits discovered to date are Their locations are shown in Fig. 2:. suiphide replacement bodies. They strike and dip parallel to the formations that contain them, and have been found in or closely associated with either iron formation or a variety of sedimentary rocks. A determination of the lead isotope ratios of a sample of galena, from one of the occurrences, by mass spectrometer is reported by J. T. Wilson of the University of Toronto to indicate an age of 2,60O 120 million years.3 According to Wilson, the indicated age is close to that of leads found in the Golden Manitou and Barvue deposits in Quebec and the gold ores of Timmins in Ontario0 The lead from Manitouwadge Lake, and those from the other deposits, are all much older than the Sudbury nickel-copper ores, which are believed to have been formed in Late Precambrian time. In view of this, it is reasonable to assume that the ore minerals were deposited during the period of granitic intrusion, and that they are of Late Archaean or Algoman age0 Sulphide replacement deposits Deposits in Iron Formation: in iron formation have been found on the properties of Lun—Echo Gold Mines, Limited about the nose of the Manitouwadge syncline, and Wiliroy Mines, Limited, on the south limb of the syncline. As mentioned previously, the iron formation is a banded rock, in which layers of quartz alternate with layers of amphibole schist, garnetiferous amphibole schist, or coarsegrained amphibolite. In 3 Wilson * J0 T0, personal correspondence. Two miles northwest of Nama Creek, �A the replacement deposits found in this rock, the metallic sulphides heal fractures in the quartz and occur aseeither masses or disseminated crystals and grains replacing the minerals of the schist or amphibolite layers. Where massive replacement has occurred, the deposit is a strikingly banded one, in which layers of sulphides alternate with layers of mineralized quartz. On the other hand, where disseminated replacement has occurred, the sulphides appear to be localized along planes of foliation, which they accentuate. The principal sulphide present is pyrrhotite. It is invariably accompanied by considerable pyrite, subordinate amounts of sphalerite and chalcopyrite, and in some case also by I galena. The replacement deposits in iron formation may thus contain values in copper, lead, and zinc. Silver is also Some of the usually. present, and adds to the over—all value. deposits tend to be lenticular and of small extent. On the ban—Echo property, for example,. three of them have been thoroughly tested by diamon4 drilling. In each, commercial grade material, across widths up to and exceeding 25 feet, was indicated. But none of the deposits was found to have a length greater than 500 feet, and each of the three was found to decrease in width and grade two deposits, with depth. In contrast to the Lun—Echo occurrences sufficiently rich located on the Willroy property, appear to be These are-known as the No. 2 and No. 3 ore and large to make ore. shaft zones. At the present time (19561 a vertical 4—compartment is being sunk as a prelude to their underground development. QecgpOr Body . south and 1800 here extends easteast of the Willroy No. 1 zone, and from the Wiliroy for a horizontal length of 2,650 feet • Like I 1 The Geco ore body is exposed about 600 feet feet ward No. 1 zene, it lies within the horizon of highly sericitized quartz—feldspar—biotite gneiss, which is bordered on the north by garnetiferous amphibole—biotite gneiss and biotite granite, and on the south by quartzite. It is a lode fissure rather than in Pig. 3, a simple disseminated replacement deposit. As shownthe West, can be divided conveniently into three sections: it Central, and East. The West section of the ere body lies west of Pox Creek. It has a length of 1,200 feet at the surface, ranges up to 220 feet in thickness, and rakes to the east at about 40 degrees. is in every respect similar te the Willroy No. 1 zone, In part and consists ef highly sericitized gneiss mineralized with it metallic suiphides, chiefly pyrite and chalcopyrite, and cut by occasional quartz stringers. But here the sulphides replace the I I �9 host rock outward from a narrow, tabular core of massive ore made up of pyrite and sphalerite, with considerable pyrrhotite but relatively small amounts of chalcopyrite This core occurs near the south wall of the ore body, within a few feet of the sericitized gneiss—quartzite contact0 It decreases in width and tends to pinch out both to the west and with depth. To the east, the West section is cut off sharply by the Fox Creek fault, so that 're east of the creek, the extension of the ore body lies approximately 250 feet to the north. This extension, or Central section, extends eastward from the fault for a distance of 50 feet, to a point where it is truncated sharply by a zone of north—south diabase dikes, Near the surface th idd.le section has an average width of 5 feet. Like the West section, it consists of a core of massive suiphides, chiefly pyrite and sphalerite. This is enclosed by an envelope of iron, copper, and subordinate zinc sulphides disseminated throughout sericitized gneiss, But here the core is much wider than in the West section, and the envelope of disseminated material is narrower and, in places, below ore standards0 Near the surface, the ore of the Central section is thus rich in zinc but poor in copper0 With depth the core of the ore body decreases in width and tends to tongue out, whereas the bordering disseminated ore increases in width and grade. The net result of this is a gradual transition from a high—grade zinc and low-grade copper ore near the surface, to a high-grade copper and low-grade zinc ore at This deep ore, rich in copper but containing low values depth0 in zinc, is identical in character to that found in the West section of the ore body, and there is little doubt that it represents the eastward extension of the West section down the general rake of the ore body. As mentioned above, the Middle section of the ore body is truncated by a zone of north—south diabase dikes, The East section of the ore body lies east of these dikes and extends for a horizontal length of about 600 feet near the surface, It is identical to the central section in character, except for three features: Cl) both the core of massive sulphides and the envelope of disseminated ore are narrower and tongue out eastward; (2) the core of massive suiphides attains its maximum thickness of about 50 feet at a depth below the surface of 700 feet, and pinches out upwards; and (3) at the east margin of the zone of diabase dikes, the core is represented by massive pyrrhotite and pyrite, and phalerite does not become an important constituent until a depth of about 500 feet is reached, The East section, at or close to the present erosion surface, thus represents the upper limit of the east—raking ore body0 The Geco ore body has been tested by diamond drilling to a To this depth, the three sections vertical depth of 1,300 feet0 are estimated to contain 15,227,251 tons of ore having an average �10 grade of 1.76 percent copper, 3.4 percent zinc, and 1.77 ounces of silver per ton,6 Mineralization I and Paragenesis I The principal ore minerals in all the known deposits are Galena is often also present, and chalcopyrite and sphalerite. is particularly prominent in the Wiliroy No. 2 ore zone, but nowhere does it occur in sufficient quantity to be of economic importance, Silver is present in every deposit. It has not been recognized as such, Assaying of samples from the Geco ore body indicates that high values in copper are usually accompanied by high values in silver, and the thought has been expressed than the silver is present in solid solution in the chalcopyrite.1 A qualitative spectrographic analysis of chalcopyrite from the Geco ore body indicated the presence of tin, which may also prove to be of economic importance.° Associated with ore minerals in all the deposits are Small amounts quartz, in small veinlets, pyrite, and pyrrhotite. The paragenesis, as of cubanite and mgrcasite have been found. given by Langford for the Geco occurrence, is as follows: (1) (2) (3) (4) (5) (6) formation of pyrite; fracturing and introduction of quartz; formation of pyrrhotite; formation of chalcopyrite, overlapped in part and followed by; formation of sphalerite; and formation of galena. The presence of exsolution textures of sphalerite in chalco pyrite and of chalcopyrite in sphalerite indicates that the Geco ore minerals were formed at high temperatures, and that the deposit, according to Lindgren's1° classification, is of 6. 7. The Northern Miner, April 5, 1965, p. 41. Langford, F. F0, "Geology of the Geco Mine in the Manitouwadge Area, District of Thunder Bay,tt: Unpubl. M.A. thesis, Queen's University, Kingston, Ontario, 1955. , Oo 9, Cit0 Qp, 10. Lindgren, W0, "Mineral Deposits," McGrawHill Book Co., Inc., New York, 1933 I �11 hypother1 type.]-]- This conclusion follows from the work of Buerger,-'- who points out that chalcopyrite unmixes from sphalerite at temperatures of 350 to 400°C, and from the work of Edwards,13 who states that sphalerite unmixes from chalco— pyrite at temperatures of 500 to 600 C. Structural Controls of Ore Deposition One of the most interesting aspects of geological survey work is speculation as to the reasons why ore deposits are where they are after the ore deposits have been discovered and partly Such speculation, in the hope that it may prove developed0 useful to further exploration, will constitute the balance of The structural controls of ore deposition in the this paper. Manitouwadge Lake area may be considered under two headings: Major controls, and minor controls. Major Controls The major controls over the deposition of the ores were the folded structures and certain pre—ore faults. Folded Structures: In regard to the folded structures, dip determinations, and measurements of lineation made apparent by the parallel alignment of elongate biotite flakes and prismatic crystals of amphibole, indicate a regional plunge of the This plunge ranges from l5_250 in formations to the northeast. the west section of the area to about 400 in the east section. Of interest is the fact that the rake of all the known ore bodies or mineralized zones, and in the case of the Geco ore body, also of the zonal arrangement of suiphides, is in the same direction and at the same angle as the plunge of the formations. Pre—Ore Faults: One of the most interesting features of the area is the localization of the Geco and Willroy No. 1 ore bodies along a very persistent horizon of sericitized quartz— feldspar—biotite gneiss. At the Geco mine, this horizon is cut by north—south dikes of pegmatite, which are terminated abruptly 11. Langford, F. F., op cit. l2 Buerger, M. W., "IJnmixing of Chalcopyrite from Sphalerite," Am,jrra1., Vol. 25, pp. 534—53, 1934. 13. Edwards, A. B., "Textures of the Ore Minerals," Aust. Inst0 of Mm. and Met., Melbourne, Austra1ia 1947. �12 by the massive suiphide core of the ore body and do not appear in This indicates expected positions on the other side of the core. that the massive suiphides were localized in a fault zone, and that this zone served as a channelway, along which the hydrothermal solutions, that effected the sericitization of the gneiss and the deposition of the ore minerals, actually migrated. At first consideration, it would appear that this fault zone, which is post—pegmatite in age, was developed after the formation of the major syncline, But the horizon of sericitized gneiss has been traced continuously across the area for a distance of 4 miles, throughout this length it is everywhere conformable to the folded unaltered sediments enclosing it. Because of this, and because the alteration indicates the presence of a continuous channeiway during the epoch of mineralization, it i concluded that the sericitized gneiss represents a bedding fault that was deformed with the other rock formations during the regional folding. The other ore bodies or mineralized zones in the area do not occur along persistent horizons of altered rock. Nevertheless, it is thought that they also may have been localized along folded bedding faults — faults that were of limited lateral extent and and were formed as parallel structures merely subsidiary to the In this regard, it "break" represented by the sericitized gneiss. is to be noted that mineralized zones containing pyrite and pyrrhotite have been found in numerous localities throughout the area, but that it is only close to the horizon of sericitized gneiss that such zones contain any significant amounts of copper, zinc, or silver0 Minor Controls The minor features which are known to have exerted some influence in the localization of the ore bodies are: (1) intrusive—sediments contacts; (2) local curves or bends in the formations; and (3) the presence of flat—lying bodies of granite pegmatite. I 1 Intrusive—Sediments Contacts: Examination of Fig. 3 shows that the Geco ore body lies within sericitized gneiss, which is bordered to the north by biotite granite and by garnetiferous amphibole—biotite gneiss. Where the sericitized gneiss is bordered by the granite, the best widths and values in copper have been found, On the other hand, where it is bordered by the garnetiferous amphibole-biotite gneiss, both to the west and to the east, the widths and metallic content decrease, and even It would thus appear that the sericitic alteration becomes weak. the contact, between the granite and the sericitized gneiss, localized the structural adjustments that provided the open spaces necessary for the migration of the ore—forming fluids and the deposition of the metallic suiphides. I �13 A second examp1e illustrating the effect of intrusive— sediments contacts on the localization of ore, is found in the Wiliroy No, 3 zone. Here the mineralization lies in a band of This iron formation, and the suiphide iron formation. mineralization within it, have been traced for 2,300 feet. But the zone only attains ore grade where, over a length of 1,200 feet, the iron formation is bordered along its footwall side by a narrow, sill like body of pegmatite. Local Curves or Bends in the Formations: A second minor but nevertheless important control over the localization of the ore bodies was the presence of local curves or bends in the formations. As shown in Fig, 3, the formations in the vicinity of the Geco ore body strike roughly east—west for a considerable distance, and dip vertically to steeply south. Near the west boundary of the area represented however, the horizon of sericitized gneiss assumes a The ore body strike of N. 550 W. and a dip of 65° to 750 N.E. occurs where the sericitized gneiss strikes east—west and has a vertical or near—vertical dip. Similar conditions are found on the Wiliroy property. Here there are three ore bodies, all of which trend roughly east—west, and all of which terminate westward at points where their respective host rocks curve sharply to assume northwest strikes and flatter dips0 The reason for the localization of the four ore bodies, along the east—west portions of their favourable host rocks, close to points of deflection in attitude, is found at the Geco mine. It was mentioned previously that the massive sulphide core of the ore body is localized along a fault zone which truncates bodies In the sericitized gneiss adjacent to the massive of pegmatite. suiphides numerous drag folds have been mapped. These drag folds are of two types: one type is "Z" — shaped in plan and is compatible with the major Manitouwadge syncline; the other type is "5" — shaped in plan and hence is a "reverse" structure incompatible with the major field. Such "reverse" drag folds have been found only in the horizon of sericitized gneiss, and it is logical to assume that they are expressions of the movement which culminated in the post—pegmatite faulting. They plunge at about 40° E., and indicate that the block of ground north of the fault moved down and to the west. A relative displacement of this type would result in the development of favourable open spaces along Thus, as pointed the steep—dipping portions of the fault zone. out by Newhouse,4 if one portion of a fracture surface dips steeply, and the other portion has a lower angle of dip, and if the hanging wall moves relatively down, the hanging wall will ride on the flat—dipping portion as a supporting surface, This will separate the hanging wall from a footwall along the steeply— dipping portion of the fracture surface to form an opening. 14. Newhouse, W. H., "Structural Feature Associated with Ore Deposits," in Ore Deposits as Related to Structural Features, Princeton University Princeton, N. J0, p. 17, 1942. �14 Presence of Flat-LviAr: Bodies of Peatite: The third minor contrel ever the localization of the ore bodies in the area was the presence of small, flat—lying bodies of pegmatite extending acress horizons of' favourable host-rocks. At the Geco mine the north—south pegmatites that. are truncated by the massive suiphide core dip at flat angles, in places eastward, in other places westward. These pegmatites are typically massive, pink, unaltered varieties. But, within a foot or two of their contacts, they are somewhat sericitized, and display fractures healed by metallic sulphides. According to Walter Claz'ks, chief geologist at Geco Mine, Limited, the disseminated ore in the sericit'ized gneiss toads to improve in' grade as the contacts of these flat—lying. bodies are approached. Similar re—ore pegwatites cut across the ore zone at the Willroy No.: 1 ore bedy. As each of the two pegiqatites are approached from below, an increase in the width and/or grade of the ore body ±1 apparent. Because, of this it is thought that the flat—lying pegmatites served as relatively impermeable barriers, which inhibited the migration' of the oreforming fluids and thus effected sulphide deposition in the seri— citized gneiss at or close to their contacts. Conclusions S . fl — ''I Exploration and developient work at the various properties permits tentative' acceptance of certain valuable conclusions about the mineralization in the area. These facts are as follows: "(1) The mineral deposits are of Archaean age and may' be realted genetically to the granitic rocks. All the knot' mineral deposits ,are replacement deposits, '(2) either disseminated or lode fissure in character, and occur in either iron formation or sedimentary gneiss. '(3) ,The mineral deposits were formed at high temperatures, and may be considered as representative of Lindgren' s hypothermal class. (4) 'The' deposits are controlled in their attitudes by the major folded structures, and rake flatly eastward paraflel to lineations. I ' lie within a preore folded fault zone that is' represented in the field by a persistent horizon of sericitized quartz—oligoClase—biotite gneies, or they lie within small, parallel structures 'close to the horizon of sericitized gneiss. '(5) They (6) All 'the important ore bodies are found where the formations' strike roughly east—west, and adjacent to the east of places 'where those formations curveS sharply to assume a northwest strike and relatively flat dips to the north. (7) Two ore bedies, the Geco and the Willroy No. 3, ,are localized along the contacts between granite or pegmatite and their respectitefavourable host rocks. (6) tn'two cases, at the Geco mine and in the Willroy No. 1 ore body, flat bodies of pegitatite served as relatively impermeable barriers, which inhibited the migration of the ore—forming fluids ?1 �U 15 effected a;eulphide deposition in the host rock at or close to note that in several loóalities and to their contacts. It is of interest in the area, the horizon of sericitized gneiss has. boen found to disappear beneath outcrops of• flat-lying pegmatiteso Such occur at west end of the Gecô ore body, in the extreme north— wist corner of the Willroy property, and again between the llama Creek and kin—Echo properties. In each of these places favourable ore structures may exist. But it seems unlikely that sulphide bodies can be located beneath the peuatites by geophysical methods. Rather, it is concluded that successful exploration will necessitate detailed geological mapping, to determine the approximate location and trend of the sericitized gneiss beneath the pegaatites, followed by expensive diamond drilling. �Fig. 2. Generalized geological map of the Manitouwadge Lake area. Fig. 3. Surface plan showing generalized geology in the vicinity of the Geco ore body (modified after company plans). �16 TOUR LOG* MANITOUWADGE TO SAULT STE. MARIE The rocks of the region are all Precambrian, ranging in age from Keewatin to Keweenawan. Mileage 0.0 35. Manitouwadge. Route 614. 5 Hemlo. 37.1 STOP 1 Junction Trans-Canada Highway 17, turn east. Rock cut bnN side of road in a gray quartz monzonite gneiss aundant undigested amphibolitic inclusions. Strong jointing. Glacial grooves and polish. with The dominant rock type at this stop has the composition of a quartz monzonite. Quartz, orthoclase and microcline, sodic andesine, hornblende and biotite are the major minerals. The plagioclase occurs as prophyroblasts with crenulated margins. Orthoclase is found as anhedral grains often intergrown with microcline, Quartz forms in elongated pods or is interstitial and intergrown with feldspars. Myrmekitie intergrowths are common along plagioclase boundaries. Accessory minerals are large euhedral and anhedral grains of dark brown sphene, apatite, zircon and magnetite. Alteration products are pennine, epidote, and sericite. The dark inclusions in the quartz monzonite are distinctly schistose in thin-section. Dark minerals are hornblende and chloritized biotite. A mosaic of sericitized, untwinned sodic andesine forms the groundmass of the subalighned mafics. Rounded grains of quartz are evenly distributed throughout the section. Unaltered poikilitic microcline porphyroblasts are quite common. Epidote, allanite, sphene, apatite, and magnetite are the minor constituents. 67. 7 105. 7 White River. Canadian Pacific Railways divisional point. Scattered outcrops of metasedimentary rocks enroute. Good exposures of massive quartz diorite in contact with Granite pegmatite and diabase dikes. The route now crosses several infolded belts of Keewatin and Temiskaming metasedimentary and metavolcanic rocks. STOP 2 iic schist and gneiss. *From "Geology of the Lake Superior Region", National Science Foundation, Fourth Summer Conference for Geology Teachers, Michigan Technological University, June, James M. Neilson, Conference Director; Joseph P. Dobell, Associate Director (who is also responsible for petrographic descriptions). Reproduced by 1965. permis sion, �17 Mileage — 2, cont'd, Meta-rhyolite. In a thin section of the distinctly schistose tmetarhyoliteTM the major minerals, in order of abundance, are quartz, orthoclase, muscovite, biotite, and epidote. Orthoclase occurs as scattered large subhedral crystals and in intergranular positions throughout the rock, It also occurs with quartz in the pink lenses so prominent in hand specimens. The single thin section examined provided no convincing evidence that the rock is a metavolcanic. STOP 118,3 Rock cuts in phyllitic sericite schist south of Catfish Lake. 119. 3 STOP 3 123. 5 Magpie River, incised in glacial sandplain. 124. 5 Wawa intersection. Continue on 128. 0 Road intersection. Road to right leads ot Michipicoten Harbour; continue on Highway 17, to left... 128, 8 Michipicoten River. 140. 3 Old Woman River and Lake Superior to the west. 146, 7 Rock cut at Red Rocks Lake. 157. 5 STOP 4 Outcrops of amphibolite, biotite-chiorite schist, pillow lavas (?) etc. Outcrops of Dore Conglomerate and lineated rhyolite breccia. Dore Conglomerate. The matrix of the Dore conglomerate in this area is a quartz mica schist, Biotite is more abundant than muscovite. Numerous oligoclase crystals look like original clastic fragments. An altered pebble of granite is elongated parallel to the schistosity and sheathed with biotite. Feldspars in the pebble have been fractured and are separated by fine grained feldspar or bands of quartz. Highway 17. A thin section of the amphibolite prominent at this stop was examined. About 65% of the rock consists of pale green hornblende, 25% is andesine and 5 to 7% is biotite. Minor constituents are quartz, pyrrhotite, pyrite, spheno, hematite and chlorite. The chlorite is restricted to fracture zones. 166 2 Coidwater River, 1703 Sand River. 177. 3 STOP 5 Agawa Bay scenic lookout. A series of large rock cuts with posures will be seen for the next seven miles. Quartz monzonite and other rock types. I �18 Mileage this stop a distinctly sheeted white rock of quartz monzonitic composition predominates, A point-count modal analysis indicates that microcline comprises 35% of the rock, oligoclase 34%, quartz 29% At and micas less than 1%. The texture is granular and senate, Rounded grains of quartz occur as inclusions in turbid oligoclse and a second of quartz partially replaces the oligoclase. Biotite, now much altered to chlorite, was probably contemporaneous with the oligoclase. The clear rims of al.bite which occur on most of the oligoclase grains appears to be earlier than the second generation of quartz. Microcline and muscovite, in this order, are the last minerals to form. A few grains of garnet, partially altered to chlorite, and zircon are present. generation Gradational with the quartz monzoite is a coarser grained light pink granite phase. In this rock quartz and microcline are the major minerals. Oligoclase grains have been partially altered to sericite and frequently have clear albite are present. rims, Chloritized biotite and a few flakes of muscovite A third rock type noted at this stop occurs as inclusions of tightly folded micaschist. The chevron folding is marked in hand specimen by thin quartz bands and in thin section by biotite which forms good polygonal arcs. About 20% of the rock is biotite, 45% quartz and 30% orthoclase, Zircon, magnetite and apatite are minor accessories. 178, 2 Agawa River, 180.4 Agawa Bay campground in Lake Superior Provinical Park. 189. 1 Ranwick Uranium tctouristtt mine. 190. 7 Note stratification in glacial gravels on left, 191.7 STOP 6 Montreal River. Gorge was created by erosion of columnar3itflDasalt dikes intruding granite gneiss. This very fine-grained rock shows no alteration except the chlorite on slickensided joint surfaces. Fresh laths of labradorite surround rounded Magnetite and grains of augite and pigeonite in a typical diabasic fabric. apatite 193. 9 are the minor accessories. Elevated Glacial Lake Algonquin cobblestone beach about 200 present lake levels, Granite gneiss exposed in cut. 198.4 Alona Bay Lookout. 203. 4 Extensive road cuts in Archean rocks. 207, 4 feet above Contact of Keweenawan gZloidal basalts and granite boulder conglomerate. The flows and STOP 7 Mamainse Bay on Lake Superior. beds parallel the shore and dip to the west under Lake Superior. �19 Mileage Amygdaloidal basalt, Laths of partially albitized calcic plagioclase indicate an original diabasic texture. Pyroxenes have altered to chlorite and 'limonitet1, Magnetite is abundant. Two types of amygdules are present. In one type the wall of the cavity is lined with a thin band of carbonate which is followed by wider bands of a chlorite and a center filling of carbonate. In the second type there may be several concentric bands of carbonate separated by chlorite or by chalcedony zones and the center filling is chalcedony. In hand specimen, the is 214. 4 chalcedony is a pinkish white color and calcite pink to light red to faintly greenish in color. Keweenawan basaltic flows are much in this evidence along the highway in area. 226,3 Batchawana River. 232, 3 STOP 8 iss Chippewa River. Xenolithic inclusion of diabase in granitic at falls. 1 The gneiss is the major rock type at this stop. Dark bands in Gneiss. this rock consist dominantly of actinolite, chlorite, epidote and albite to- gether with small amounts of quartz, carbonate, sphene and apatite. Light colored bands are quartz and orthoclase together with small amounts of oligoclase. The feldspars are turbid with alteration products. Acicular clusters of actinolite and rounded grains of epidote and sphene are present and some chlorite was noted. The opaque minerals are limonite-stained pyrite and magnetite. 242, 5 Batchawana Bay. 254, 9 Goulais River. 262, 0 STOP 9 Rock cut, Rough road for 5 miles. I Rock cut, Altered diabase dike cutting granitic gneiss; note in contact zones. Lamprophyre near south contact, this dike the diabasic texture is fairly well preserved. The pyroxene (augite) is altered to amphibole along the margins of crystals and the plagioclase (An65) is partially or completely altered to an aggregate of sericite, epidote group minerals, and carbonate. Minor constituents are In magnetite, biotite, chlorite and sphene. 272.4 Sault Ste0 Marie, Ontario P1 �U THE RELATIONSHIP OF MINERALIZATION TO THE PRECAJIBRIAN STRATIGRAPHT, BLIND RIVER AREA, ONTARIO* • • * James A. Robert son Geologist Ontario Department of Mines Toronto, Ontario paper preSented at the 17th Annual Meeting of the Geological Association of Canada, Toronto, May 29, 1965, and reproduced by permission of the Director of the Geological Branch, Ontario Dept. of Mines, for a Field Trip t! Elliot Lake, May 7—8, 1966, sponsored by Institute on Lake Superior Geology. £ �U 2 TABLE OF CONTENTS Page Abstract . . . a . • Introduction * . • . Acknowledgments . . . . General Geology . . . . Economic Geology . . . Conclusion . . a . . Selected Bibliography a Description of Stops . 2 3 • . . • . a . . a . . . • a 9 a . 10 3 . . 4 12 SKETCH MAPS AND FIGURES Figures 1. 2. 3. 4a 5. 6. Location of Blind River area. Blind River area, general geology. Table of Formations Lateral variation in Bruce Group. Uranium deposits in Quirke syncline. Distribution of copper deposits relative to Nipissing diabase. I ABSTRACT This paper is a result of a continuing investigation, begun in 1953, by government geologists and mining companies. The Archean rocks are Keewatin greenstones intruded by Algoman granites for which the geological age has been determined as about 2,500 million years. These granitic rocks consist of gneissic granodiorites and massive, slightly radioactive quartz The Archean complex was eroded to a peneplain with monzonite. valleys in the less resistant rock types. The Lower Huronian consists of the Lower Mississagi Formation, the Middle Mississagi Formation, the Upper Mississagi Formation, the Bruce Conglomerate, the Espanola Formation, and the Serpent Formation. These formations contain a great variety of sedimentary rocks such as conglomerate, argillite, siltstone, greywacke, limestone, and Thickness and facies changes indicate a northwesterly quartzite. source, northerly overlap, and deposition in shallow water controlled by basement topography. The Lower Huronian formations unconformably overlie the Archean rocks and in turn are Unconformably overlain by the Middle Huronian formations. The Middle Huronian rocks consist of the Gowganda and Lorrain formations of conglomerate, greywacke, quartzite, and arkose. There are three phases of post—Huronian igneous activity: (1) dikes and sills of Nipissing diabaso; (2) the Cutler granite; and (3) dikes of olivine diabase. I I I I I I I �3 Age dating methods give the age of the Nipissing diabase as million years, and the granite at Cutler as 1,750 million A few dikes of Keweenawan olivine years (Penokean orogeny). diabase are tentatively dated at 1,100 million years. 2,130 Copper mineralization is associated with the Nipissing diabase. Uranium ores in quartz—pebble conglomerates, near the base of the Lower Mississagi Formation, are generally considered Uranium to be placer deposits modified by later events production from the Blind River mining camp to the end of 1962 was valued at 944,373,25O. This was derived from 44,937,7l tons of ore grading approximately 0.1 percent U308. INTRODUCTION This paper is a discussion of the Precambrian rocks and Lake area of Ontario mineralization in the Blind River — (Fig. 1).* Blind River is located on the north shore of Lake The town Huron half way between Sudbury and Sault Ste. Marie. of Elliot Lake (Fig. 2) lies 20 miles northeast of Blind River. The area is served by the Canadian Pacific railway, the ThansCanada highway and by other roads. Elliot Early geological mapping was carried out by Logan. and Murray following the discovery of cper at Bruce Mines in i46 (Logan Later mapping was carried out by W. H. Collins 163, Chap. 4). in 1915 (Collins 1925). In 1953 uranium was discovered in the district which subsequently became Canada's chief source of uranium. Since 1953 extensive geological worL has been carried out by the Ontario Department of Mines, the Geological Survey of The Canada, mining companies, and interested individuals. Ontario Department of Mines has been responsible for regional mapping; this was carried out by E. M. Abraham in 1953—1956 (Abraham 1953, 1957) and has been continued by the writer since J. P. McDowell (1957, 1963) 1957 (Robertson, J. A. 1960 et investigated the sedimentary features of the host rocks of the uranium mineralization. ACKNOWLEDGMENTS The co—operation and interest of members of the Ontario Department of Mines, the Geological Survey of Canada, of many employees of mining companies, and of students and professors in both Canadian and American Universities, is gratefully The writer is indebted to R. Balgalvis of the acknowledged. Ontario Department of Mines for preparation of the figures. * See instead map on inside back cover for location. �4 GENERAL GEOLOGY The bedrock of the area falls into three broad units the (l the These are: distribution of which is shown on Fig. 2. Archean basement consisting of Algoman granite and Keewatin—type greenstone; (2) the Huronian edimentary rocks made up of the Bruce Group and the Cobalt Group and (3) the Post—Huronian intrusive rocks comprising the Nipissing diabase, the Cutler granite, and olivine diabase believed to be Keweenawan in age (only the Cutler granite is shown in Fig. 2), The structure is also illustrated on Fig. 2. In the north is the Quirke syncline and in the south the Chiblow anticline, the south limb of which is repeated by a major east—striking the Murray Fault. The fold axes strike slightly north fault of west and plunge gently west giving the sedimentary units a Bedding—plane slips, thrust faults, reverse—S shaped outcrop. and near—vertical faults which strike either northwest or parallel to the axial planes of the folds are common, The fault pattern, jointing, dragfolds, and other structural features suggest a north—south compression formed the folds, Figure 3 is a Table of Formations giving more detail than it is possible to show on Fig, 2. It has been Department policy to retain Collins' nomenclature making modifications only where S, M, Roscoe (1957) and P. J, Pienaar (1963) of the necessary. Geological Survey of' Canada have introduced a nomenclature using The differences are in names rather than in ideas, local names, The Keewatin-type rocks underlie the eastern portion of the Quirke syncline and are exposed to the southeast of the syncline, The rock—types found include massive and pillow lavas, pyroclastic rocks, and sedimentary rocks including lean iron formation. Strike is northwest and dips generally steep northeast. Metamorphism is of chlorite facies rising to amphibolite in hybrid zones close to contacts with the Algoman granite. Granitic rocks of Algoman age (2,500 million years; Fairbairn, Lowdon, Van Schmus et al 1963) from approximately half the area These granitic rocks may be divided into two shown on Fig. 2, (1) medium— to coarse—grained, gneissic to massive broad groups: granodiorite, generally grey to pink in colour with abundant inclusions derived from the Keewatin and 2) massive red quartz monzonite generally without inclusions and slightly radioactive. A body of the second typo is found in the Quirke Lake area. I The Huronian sedimentary rocks lie unconformably on the Algoman-Keewatin complex. A topographic low was developed over the greens4one belt, with local ridges controlled by the harder members (Fig0 5). Remnants of pre—Huronian soils are preserved particularly over the granitic rocks, The present chemical constitution of these soils suggests that they were formed under reducing conditions0 I I �5 The Lower Mississagi Formation contains the known uranium deposits and has ben studied in dótail. The general sequence consists of greenish rkose with or without uraniferous quartz-' pebble conglomerate bands and beds followed by grey quartzite, followed near Elliot Lake by argillite and impure quart zite. Cross—bedding and pebble orientation studies by McDowell (1957, 3. 1963) and Pienaar (1963) indicate the currents flowed from the northwest but were markedly. influenced by basement topography. Ore—conglomerates occur largely it valleys in the basement óurface (Fig. 5). Thickness of the Lower Mississagi Formation increases from 0 at the north shore of Quirke Lake through 600 feet near Elliot Lake to more than 1,000 feet south of the Murray Fault. As northward overlap is pronounced (Fit. 4) ore—beds at'n Pronto, Nordic, and Quirke are progressively younger. The Middle Mississagi ormation normally consists of a basal polymictic conglomerate followed by argillite. The conglomerate was used aS a marker horizon during exploration drilling. The upper part of the argillite sequence is characterized by ripple marks. The argillite thickens from less that 100 feet at the north shore of Quirke Lake to over. 750 feet near Elliot Lake (Fig 4).. Near the crest of the Chiblow anticline the conglomerate is about 5 feet thick and the argillite only 40 feet but on the south limb of the Chiblow anticline, both north and soith of the Murray Fault, the Middle Mississagi is represented by 000 feet of This indicates deeper water to the south quartzite and ef the area mapped, siltstone. The Upper Mississagi Formation Consists of greinish arkose on the north limb of the Qüirke syncline but elsewhere of well— Thickness ranges from 600 feet at Quirke bedded grey Lake to 1 500 feet near Elliot Lake and to a maximum of 2,700 quartzite. feet on tAe south limb of the Chiblow anticline, repeated south of the Murray Fault at Blind River. Current direction is from the northwest but the influence of basement topography is much diminishe4. Facies and thickening relationships again indicate deeper water to the south and southeast. The Upper Mississagi Formation is followed disconforinably by the Bruce Conglomerate — which consists of boulders of white granite and greenstone in a partially sorted1 slightly pyritic, siliceous greywacke matrix. The conglomerate can be traced There are marked local variathroughout than 200 feet tions in thickness but the unit thick. the entire district • isgenerallyless . three units, all of are mappable within the Elliot Lake district; a lower unit, The Espanola Formation consists pf which characterized by limestone — the Brñce Limestone; a middle unit, characterized by mudstone and greywacke — the Espanola Greywacke; and an upper ónit having a mirked development of ferruginous dolomite — the Espanola Limestone. Throughout much of the area mapped the Cobalt Grouperests unconformably on the Bruce Limestone. �1 6 The Bruce Limestone consists of thinly interbedded cream— coloured limestone and siltstone. Differential weathering and drag—folding give the rock a spectacular appearance. Where the unit is complete, the thickness is generally 100 feet. The Espanola Greywacke and Espanola Limestone members can be only distinguished by the brown—weathering dolomite bands. Both members are characterized by iñtraformational breccias, siltstone and conglomerate dikes, mud cracks, and ripple marks. These indicate shallow water deposition and tectonic disturbance. Occasional quartzite beds show crossbedding from the northwest and become more common to the northwest. Where complete the thickness of the Espanola Greywacke is 300—400 feet and that of the Espanola Limestone 150 feet. The Espanola Formation is overlain by the Serpent Formation — a white feldspathic quartzite only exposed in the northern and eastern sections of the Quirke syncline. The maximum known thickCrossbedding, and ness of the 3erpent Formation is 1,100 feet. lithology and thickness changes in individual members again show derivation from the northwest. Ripple marks and mud cracks indicate shallow water conditions. The lateral variation in thickness of the formations of the Bruce Group is illustrated in Fig. 4. The Bruce Group is followed unconformably by the Cobalt Lake area consists of Group which in the Blind River the Gowganda Formation and the Lorrain Formation. Within the map—area the Gowganda Formation rests on all formations between the Upper Mississagi and the Serpent Formation. Locally the contact can be seen truncating the bedding of the underlying formation and consolidated fragments of the underlying rocks are found in the lowermost beds of the Gowganda Formation. Elliot The Gowganda Formation is a heterogeneous assemblage of conglomerate, greywacke, quartzite, and aril1ite. These rock types are found throughout the sequence though the lower part is characterized by boulder conglomerate and the upper by quartzite and argillite. Within the area mapped the Gowganda Formation is about 2,000 feet thick. Dense The origin of the Gowganda Formation is in doubt. boulder conglomerates, quartzites, and argillites are definitely water laid; varved conglomerates and greywackes probably formed under conditions characterized by alternate freezing and thawing although some authorities would ascribe these rocks to turbidity currents; and sparse boulder conglomerates with disrupted grey— wacke matrix may be either tillites or mudf low deposits. Locally in the Quirke syncline the Gowganda Formation is overlain by a few hundred feet of well—stratified, crossbedded, arkosic quartzite tentatively correlated with the basal Lorrain0 The wellknown white quartzite with jasper conglomerate has not been found in the area. I �7 Following Huronian times the region. was subjected to tectonic The folding and faulting (briefly s"arised earlier) and the intrusion of the Nipissing diabase took place. The Nipissing diabase 'is divided into two phases: the earlier comprises large stress. irregular sifl-like gabipro bodies and the' later numerous vertilal dikes striking either northwest 'or west • The gabbroic 'bodies, the distribution of which shows marked structural control (Fig. 6), are differentiated frem gabbre to diorite. and, in some, cases, to granophyre. The copper deposits of the district are relAted spatially and genetically to these gabbroic bodies. Alteration (albitization, chioritization, and Carbonatization) associated with either dikes Or sills is.on a small scale but has locafly effected the uranium deposits. 'According to Tan ,Schmus (lan 1963) the gabroic bodies have a probable age of Schmus fl 2,170± 200 million years,' 'and a minimum age of 1,950 million years. . -. ' . . The only granite. of probably post-Huronian age is the Cutler Batholith to the south of Spragge. Age determinations, obtained by Fairbairn (1960) Wetherill (1960), and the Geological Survey of Canada (Lowdon 1461 fl flq.) whilst obscure in interpretation, range between 1,750 and 1,3W million' years and determinations on metamorphic mica in adjacent rocks give 1,400.million years. Sedimentary rocks of probable Ruronian age on 'the islands south of the Cutler batholith shoi an increase in metamorphism towards the Cutler bathelith. Staurolite schists and meta— quartzite are found between the batholith and the Murray Fault and as inclusions in 'the batholith. These rocks, long thought to be Archean in. age1 may be the metamorphosed' equivalent of the southern' facies of the Middle Missiesagi Formation and therefore of Huronian' age. Volcanic rocks at Spragge may. be the equivalent, of Hurronian volcanic' rocks described by .Frarey '(1961, 1962) at Thessalon. However, .,no valcanic .rocks have, been identified in the undoubted Huronian rockS of the Blind. River area 'as found north of the Murray Fault. The relationships of, the Cutler batholith will be further studied in the 'coming' field season. ..A few olivine diabase dikes Strike northwest throughout the district. Tan Schmus (personal communication) has recently established an age of. 1,190± 50 million years for olivine diabase which cuts the Cutler granite. Similar olivine diabase dikes are found throughout the 'north' shore tof Lake Huron and elsewhere give 1963). a date of 1,000 a 11100 million years (Lowdon fl The' olivine diabase dikes are displaced by the Murray' Fault' indicating late tectonic disturbance. At surface the fault has a vertical to steep southerly dip. .The vertical displacement of the fault is:6,000 stratigraphic feet,. south side up and the horizontal displacement measured on magnetic anomalies associated - with olivine diabase' dikes is 5,000 feet north•stde east. 1. Subsequently modified to 2,130± 80 million years; Tan Schmus, personal communication. �B ECONOMIC GEOLOOT Two types of ore deposit have aroused interest - the uranium— sulphide veins. Investigations into the. possible use of Bruce Limestone as a neutralizing agent in the Uranium mills and the use of Nipissing gabbro as road material were beth dropped at an early stage. The uranium deposits are found (Fig. 5) as quartz—pebble pyritic conglomerate beds in zones controlled by basement topography. In the Quirke syncline the relationship of the uraniferous conglomerates to granite—greenstone contact areas and valleyS over softer zones in the greenstone belt is clearly demonstrated by surface drilling and mining operations. At Pronto, bearing conglomerates and post-Huronian copper—bearing quartz- . . . . however, there is no clear relationship to basement geology which raises the possibility that there may be other economic uranium deposits underlain by granite. The ore—zones strike northwest—southeast and are controlled by basement structures. Original sedimentary structures preserved in the rocks indicate the zones are parallel to the depositional The Quirke zone (the largest in the area) is 32,000 feet long and•from 6000 to9 000 feet wide. The Nordic zone is 19,000 toot long and from 4,460 to 6,000 feet wide. The Pronto deposit and the unworked zones are of smaller dimensions. currents. The uraniferous quartz-pebble conglomerate and green arkose is characteristic of the Lower Mississagi Formation and has been used by Thomson (1962) as a marker horizon in tracing the Archean-Huroniafl boundary between Lake Timagami and Blind River. Locally where overlap brings Upper Mississagi into close proximity with the basement, arkose with thin, slightly radioactive pebble bands is found. The uranium—mineralization is thus associated with the basal beds of the Huronian and the distribution over a wide area suggests a syngenetic origin. The conglomerates consist of well-rounded, well sorted, quartz pebbles in a matrix of quartz, feldspar and sericito and have an I sequence I average pyrite content of 15 percent. Monazite and zircon are characteristic heavy minerals. Brannerito and uraninite are found in the matrix. Thucholite is found locally and may line fissures in the ore beds1 Th. ore—minerals are brannerite, uraninite and monazite. Roscoe has shown the uranium—thorium ratio (1:3) is comparable to that.of the basement. The lateral variation in the ore-mineral and uranium-thorium ratios as studies by Roscoe (1959) and D. Robertson (1962) are best explained by the relative stability of monazito during transportation. Locally, individual . conglomerate bands may assay as . . high as 20 lbs. or more U3O per ton, but over mining widths of the order of 9—30 feet average grade is 2-3 lbs. U30g per ton. _ I I �____ 9 with the ore conglomerate is generally greenish in colour and is crossbedded. It is probable that the conglomerate accumulated as placer deposits derived from weathered red-phase Algoman granite and that the uranium—bearing minerals were altered and redistributed during diagenesis, during the different periods of tectonic• stress, and definitely during the introduction of diabase. There is no evidence in the area mapped by the writer, of crosscutting uranium mineralization. Alternative theories include deposition from hydrothermal fluids derived from post—Huronian granite as suggested by Davidson (1957) and biogenic precipitation of uranium derived from weathered basement but transported in solution as proposed by Derry (1960). Although almost one billion dollars worth of uranium oxide have been extracted there are large drill—indicated reserves left. When marketing conditions for uranium improve, the Elliot Lake area should again be a major producer. By—products include small The arkose interbedded amounts of thorium and rare earths. The copper deposits of the north shore of Lake Huron have been known since the 1840's. These are normally veins of quartz, chalcopyrite, with or without pyrite, specularite, and carbonate. Favourable structural conditions occur near or in large differ— entiatéd Nipissing gabbro bodies (see Fig. 6). In the area under discussion the veins trend parallel to the major fold axes and to the Murray Fault. Contact metasomatic deposits are also found associated with the upper contacts of sill—like gabbro—bodies. Prospecting has been carried out and a few properties have shipped small tonnages of ore. The main producer in the area is the Pater mine at Spragge where 700 tons of 2.0 percent copper are hoisted a day and treated at the Pronto concentrator. At Pater, quartz, pyrrhotite, and chalcopyrite, are found in a shear zone slightly oblique to the Murray Fault and located in the metamorphic rocks of possible Huronian age. Epidiorite is thought to represent metamorphosed Nipissing gabbro. CONCLUSION The area is one of extreme importance in the long-range economy of the country in this nuclear age. The deposits of uranium and copper should continue to interest the prospector, mine; and the public. Elliot Lake area contains excellent The Blind River exposures of extremely interesting Precambrian rocks of diverse type. The area is readily accessible and is ideal for research prograames. r �I 10 SELECTED BIBLIOGRAPHY Abraham E.M. 19k3: Geology of Long and Spragge townships, Blind River uranium area, District of Algoma (prelim. map 1957: The north shore of Lake Huron from &ladstone to and report); Ontario Dept. Mines townships; j Spragge Royal Society P.R. 1953—2. The Proterozoic in Canada; of.Canada, Special Publications S No. 2,pp. 59—62. C.I.M.M. 1957: Mining, metallurgy and geology in the Algoma uranium area; (published for the Sixth Commonwealth Mining and Metallurgical Congress, 1957); Canadian Inst.. Mm. Met. W. H. The north shore of Lake Huron; Geol. Surv. Canada, 1925: Mem. 143. Collins,. Davidson C.F. 195G: 1958: . On the occurrence of uranium in ancient conglomerates; Economic Geol., Vol. 52, pp. 668 — 693. (Discussion in subsequent issues). Uranium in ancient conglomerates — a reply; Economic Geol.,.. Vol. 53, pp. 687 — Derry, D.R. 1960: I 889. Evidence on the origin of the Blind River uranium deposits; Economic Geol., Vol. 55, pp. 906 — 27. Fairbairn, F.W., Pinson W.H., and Hurley, P.M. Minezal awl rock ages at Sudbury - Blind River, 1960: Ontario; Geol. Assoc. Canada Proc., Vol. 12, pp. 41 — 6., Frarey M.J. l61a: 196lb: 1962: Dean Lake, District of Algoma; Geol. Surv. Canada, map No. 5—1961. Wakwekobi Lake, District of Algoma; Geol. Surv. Canada, map No. 6—1961. Bruce Mines, Ontario; Geol. Surv. Canada; map No, 32—1962. Logan, W.E. 1863:. Lowdon J. A. ]460: 1961: The Geology of Canada (with accdmpanying atlas). Age—determinationfl Geol. Surv. Canada, Rept. No. 1, Isotopic ages, Paper 60—17. Age—determinations; Geol. Sun. Canada, Rept. No. 2, Isotopic ages, Paper 61—17. I. I �U 11 Lowdon J.A. fl a]. 1*62: Ijedeterminations and geological 1963: Age—determinations and geological studies, Geol. Sun. Canada, Paper 62.17. studies; Geol. Surv. Canada, Paper 63—17. McDowell1 J.P. 1951: 1963: • sedimentary petrology of the Mississagi quartzite in the Blind River area; Ontario Dept. Mines, Geol. Circ., No. 6. A paleocurrent study of the Mississagi quartzite (Ph.D. Thesis, along the north shore of Lake Huron. John Hopkins University). The Pienaar Pd. l9&3: • Stratigraphy, petrology, and genesis of the Elliot Group, Blind River, Ontario; including the uraniferous conglomerate; Geo].. Surv. Canada,. Bull. 83. Robertson, D.S., and Steenland, W.C. The Blind River uranium ores and their origin; 1960: Economic Geol.,.Vol.. 55, pp. 659.— 694. Robertson, D.S. Thorium and uranium variations in the Blind River 1962: ores; Economic Geol., Vol. 57, pp. 1175 — 1184. Robertson, J.A. Geology of part of the Blind River area, Ontario; 1960: (M. 1961: Sc. Thesis Queen's.University, Kingston). Geology of Townships 143 and 144.; Ontario Dept. Mines, G.R.No.4. Geology of Townships 137. and 138; Ontario Dept. Mines, . 1962: l963a: l963b: l963c: 1963d: 1964: Roscoe S.M. 1*57: 1959: 0. R. No. 10. Geology of Townships 155, 156, 161, and 162; Ontario Dept. Mines, G. R. No. 13. Geology of the Iron Bridge area, Ontario; Ontario Dept. Mines, G.R. No. 17. Preliminary map of Township 149; Ontario Dept. Mines, P. 193. •• Preliminary map of Township 150; Ontario Dept. Mines, P. 192. Geology of Scarf e, Mack, Cobden, and Striker TownshJps; Ontario Dept. Mines, G.R. No. 20. Geology and uranium dipositsQuirke Lake — Elliot Lake, Blind River area, Ontario; Geol. Surv. . Canada, Paper 56—7. ratios in conglomerate and On thorium - uranium asseciated rocks near Blind River, Ontario; Economic Geol., Vol. 54, pp. 511 — 512. �1 12 Roscoe, S.M., and Steacy, H.R. 1958: On the geology and radioactive deposits of Blind River region; Atomic Energy of Canada Ltd., A. Conf0, l5/P/222. Schmus, W.R. Geochronology of the Blind River — Bruce Mines area, 1965: Ontario, Canada; Journ. Geol., Vol. 73, No. , pp. 755—780. Thomson, Jas. E. Extent of the Huronian system between Lake Timagami 1962: and Blind River, Ontario; j the Tectonics of the Canadian Shield; Royal Soc. Canada, Special Publications No. 4, pp. 76 — 89. Van Schmus,W.R0 Rb—Sr age determinations of the Nipissing diabase, 1963: north shore of Lake Huron, Ontario, Canada; Journ. of Geophysical Research, Vol. 68, No. 19, pp. 5589 — 5593. Wetherill, G.W., Davis, G.L., and Tilton, G.R. Age measurements on minerals from the Cutler 1960: batholith, Cutler, Ontario; Journ. of Geophysical Research, Vol. 65, No. 8, pp. 2461 — 2466. MAPS AND AtDENDA Geol Surv. Canada Ontario Dept. Mines Map Map Map Map Map ll8lA, Iron Bridge Area 5-1961, Dean Lake 6-1961, Wakwekobi Lake 32—1962, Lake George 3 2—1962, Bruce Mines I Geol. Report 17, Iron Bridge Area Map P303, Sault Ste. Marie Sheet Lake Sheet Map P304, Blind River — Vol. XLVIII, Part XI, 1939, Geology of the Flack Lake Area Elliot Beger, R. M. 1963: Geology of the Pater Mine, Blind River Area; (M.S. Thesis, Michigan College of Mining and Technology, Houghton). I I I I �13 DESCRIFflON OF STOPS Between Highway 17 a Highway 548 junction and Desbarats East of Saült Ste. Marie,Ontario Stop 1 Lorrain Formation. In this area Lorrain Formation are exposed as Li three members follows: of the 1/2 mile east of junction (22 miles east Of Sault Ste, Roadside outcrops of pink to buff—coloured, medium to coarse-grained quartzite of. the Lorrain Formation, member #3. In this vicinity, the member attains a thick- Marie) • ness of 2,000 feet. It is commonly feldspathic or pebbly (quartz and jasper) and characterized by large cross—beds. About 1/2 mill east i:s a series of outcrops, mostly of pinkish quartzose siltstone or fine—grained quartzite, in • • part spotted with hematite clots, of Lornin member f2. Some purplish layers nearby. The ouartzite is somewhat similar to host rock at• disseminated copper showings about 1.5 miles north of this locality. Large roadcut 1 mile to the east. Prominent display ef ripple marks in greyish si].tstone—quartzite, just above base of Lorraiü member #1. Successive bedding planes exhibit widely divergent ripple mark orientation. Shear the zone on south aide of road. Stops la and b are rigarded as optionil; stop Ic will be sufficiently long to permit taking of photographs. STOP 2 Proceed 7 miles east to second roadcut past Portlock side— road. The cut is in Oowganda Fonation, about 1,300 feet below the top of this unit which here i8 striking about N6OE and dipping 20 NW. Greywacke-argillité, making up the bulk of the rock, carries disoriented frapients of pink— grey silt none and sparser granitoid blasts. The oedimentary pieces are thought to represent an interbed disrupted by penecontemporaneous slide or slump. east to junction of Highway 17 and 112L1 Continue 3 miles Oranophyric Nipissing diabase is on Line sideread. side, and on the sideroad just north of the outcrops of Sparse conglomerate of the Bruce highway Centre south are Conglomerate Fermation and grey laminated limestone of the B"uce Limestone member of the .Espanola Formation. These sedimentary units are thin here, probably not exceeding 100 feet. The diabase is part ofa large sill which follows around the Bruce Mines anticline. Bruce Proceád one mile into Bruce Mines. This village is of flgj historical interest. It was the first settlement on the north share of Lake Huron1 established at the site of the earliest copper mining operation by the white man in mainland Canada. Mining was done sporadically for about 75 years, up to 1921. The depoSits consisted of quartz— �1 14 carbonate veins mineralized ih chalcopyrite, pyrite, specularite and bornite. Similar veins are widespread in the district, and will be seen at Stop 5. The classical work of Logan and Murray followed the discovery of Bruce Mines. Stop 4 From Bruce Mines continue east for about 15 miles to outcrops at the east end of the Thessalon by—pass. This is at the western margin of the Thessalon Formation, a volcanic assemblage previously classed as (a) Keewatin (Archean) or (b) Keweenawan, but now included in the Huronian. The formation consists mainly of uniform-looking, fine—grained metabasalt, commonly amygdaloidal, but generally lacking other volcanic features. As well as here at Thessalon, such volcanic rocks, correlated with the Thessalon Formation,occur in the Huronian sequence about 14 miles north of Bruce Mines and also about 9 miles northeast of Sault Ste. Marie; at this last area they have been named the Duncan Formation. In all three areas, thin sedimentary intercalations are found, including quartz— pebble conglomerate beds generally similar to the Elliot Lake uranium ore. At this stop, the metabasalt is exposed, and a few hundred feet to the north along Highway 129 are a few beds of feldspathic quartzite, probably iñterbeds. Hiy Three miles east on Highway 17, just east of Livingstone Creek0 Low roadcuts here of Archean gneiss, pre-Huronian basement. This basement rise extends southeastward for about 20 miles almost to Blind River. It is bounded on the north by the Murray Fault and passes under Lake Huron on the south. The basal Huronian contact is visible only at a few places, notably on small islands in Lake Huron south The regolith frequently mentioned in of this stop. descriptions of Elliot Lake district has not been recognized in this vicinity. An age determination using hornblende obtained at this stop, done in the G.S.C. laboratory, gave a figure of 2620 m.y., indicating the maximum age of the Huronian. Its minimum age, as determined by dating whole rock and mineral samples from the intrusive Nipissing diabase, is approximately 2150 m.y. STOP 5 Continuing terrane at eastward, Highway 17 soon leaves the basement Sowerby, where it crosses the concealed Murray Fault and traverses the Gowganda Formation for about 4 miles to this stop. At this stratigraphic level the formation is characterized by conglomeratic greywacke— argillite ("tillite") and a few low outcroos are visable along the road in this interval. At this stop a roadcut exposes a quartz stockwork in sparse greywacke conglomerate and feldspathic quartzite; chalcopyrite, specularite, siderite and calcite occur in the veins, which are quite typical of the numerous vein copper occurrences in this district. I Hiy Eastward, the highway continues to follow the Gowganda I I �15 Formation from about 20 miles, keeping close to the northeast side of the Mississagi River from the town of Iron Bridge on. At the large, right-angle bend in the river not far above its mouth, the highway recrosses the Murray Fault, crosses the narrow eastern extremity of the basement rocks seen at Stop 7, and follows feldspathic quartz— ite of the Lower Mississagi (Matinenda) Formation to the town of Blind River. From Blind River eastwards for 6 miles, the road follows ouartzites and argillites of the Middle Mississagi Formation to Algoma Mills. At Algoma Mills (Lake Lauzon) the Murray Fault crosses the road. From Lake Lauzon to Pronto subdivision (4 miles) the road lies in sparse i11ite ?) corglomerates, greywackes, etc. of the Gowganda Formation. The discovery locality for the Blind River uranium deposits is at Pronto Mine. From Pronto eastwards through Spragge to the junction of Highways 10 and 17 the road follows the Murray Fault. Undoubted Lower Huronian rocks lie north of the road for distances of 1/4 to 1 mile and to the south lie metamorphic rocks (mafic meta— volcanics, schists, and epidiorites) and the Cutler Batholith (probable age 1750 m.y.). At Spragge is the Pater Mine — the only producing copper mine on the north shore, From the junction of 10 and 17, follow l0 to Elliot Lake (l miles)0 The Murray Fault is crossed immediately north of Highway 17 and to the east of the road greenish arkoses of the Upper Mississagi can be seen resting on a local high in he granitic basement. Granitic rocks and gneisses cut by numerous diabase dikes are exposed in road cuts to Depot Lake, From Depot Lake to Buckles Mine the road follows the strike of Keewatin sediments, These are greywackes and lean iron formation. At Buckles the scarp Northwest of of the Lower Mississagi is clearly visible. Buckles the road follows a fault which displaces the Lower Mississagi. Elliot Lake Programme Sunday Stops for a.m. Transportation will leave the hotel at Stops the Elliot Lake trip will be marked on map 2032. 12, 13, 14 are on the road from Quirke Mine to Flack Lake They lie in the uppermost and the White River Road0 formations of the Cobalt Group — not exposed elsewhere in These stops will only be made if the Blind River area. time permits. Stop 6 Upper Mississagi Formation: well—bedded feldspathic Note cross—bedding, also bedding—plane quartzites. lineat ions0 �1 16 Stop 7 Stop S Uppermost beds of Upper Mississagi Formation, contact with Bruce Conglomerate. Bruce Conglomerate (characteristic composition, texture, weathering) reworked tillite? Nipissing diabase transgressive sill; texture, banding, alteration and metamorphism of country rock. Contact Bruce Conglomerate — Bruce Limestone. Bruce Limestone, bedding, composition, drag—folds, metamorphic minerals — idocrase, grossularite, wollastonite; thin sill of diabase west side of road. Gowganda Formation Tillite type sparse boulder greywacke conglomerate. composition, texture, striated boulders. Sb Stop9 Note Well bedded dense conglomerate + quartzite beds and lenses. Note composition, texture, boulder shapes, packing, graded bedding. Unconformity between Gowganda and Serpent formations (Denison Side Road). Stop 10 Panel side road to Serpent River and Quirke Lake. Location Outcrop of mines - Influence of Geology on Topography. Note delicate banding of Middle Mississagi conglomerate. (varying?) and rafted pebbles in more argillaceous Intersection of cleavage and bedding. sections. Stop 11 Return to Highway 105. Road largely over Espanola FormOutcrop at junction of Panel Road and road to ation. Quirke No. 2 shaft. Espanola, dolomitic mudstones, note siltstone dikes, intraformational breccia, bedding, weathering, other outcrop on road show mudcracks, ripple marks, ball structUres, etc. Stop 12 West of Quirke Mine road climbs up onto Archean basement After about three miles granite gives way to (granite). Keewatin massive and pillowed mafic Keewatin lavas. These become strongly shattered and a prominent valley North of represents the outcrop of the Flack Lake Fault. this fault is the Rawhide syncline of which only the north The upper units of the Cobalt Group limb is preserved. are well exposed along the highway which runs through some of the finest scenery in the district. Return to Elliot Lake for lunch which will be at 1 p.m. At lunch representatives of the mining companies will join the group and they will give brief descriptions of the geology and other features of interest at their operations. Following lunch the group will leave the hotel (2:30 p.m.) and proceed south on Highway 105. I I I �17 Stop 15 If time permits a brief stop will be made at Buckles Mine to discuss the influence of geology on scenery. Stop l Texaco gas station, junction of Highways 1O and 17. Staurolite-mica schists of the Spragge Group (believed meta—Ruronian); note twinning on some crystals, alteration to pinnite, and crude grading. Stop 17 3 1/2 miles west. Brief stop at Murray Fault. few localities where this fault is exposed. Stop l Pronto Mine. One of the This is the discovery area. Points of Interest 1. Albitization of feldspathic quartzites at junction of mine road and access trail. 2. Bedding, composition, colour, and texture of Lower Mississagi Formation and changes as ore—zone is approached. 3, Discovery 4. Pre-Huronian regolith and Archean - Huronian contact 5. Surface workings — the only excellent exposures of typical locality ore—conglomerates. 6. Note also hanging wall quartzites. Pronto Thrust Fault Formal termination of field trip. �• • • • •BRIDGE IRON :.::::::: 0 • • p's •• • :• ••• •. • • : • : • : ———————— : • • ••:•: x Cutler granite 0 ' 2 4 6 8 Scale of Miles I0 HI I + I Algoman granite ( )(I Keewatin greenstone Bruce group J.1 Cobalt group x LEGEND GENERAL GEOLOGY BLIND RIVER AREA FIG. 2 I �UNIT LITHOLOGY AGE MILLION YEARS CENOZOIC RECENT 8 Sand, gravel PLEISTOCENE GREAT UNCONFORMITY PRECAMBRIAN PROTEROZOIC KEWEENAWAN INTRUSIVE PENOKEAN INTRUSIVE NIPISSING INTRUSIVE Olivine diabase 1,190 Granite I,750 Quartz diabase 2,130 HURON IAN COBALT GROUP LORRAIN Quartzite Conglomerate, grey wacke G OWGAN DA UNCONFORMITY BRUCE GROUP SERPENT ESPANOLA BRUCE CONGLOMERATE UPPER MISSISSAGI MIDDLE MISSISSAGI -- Quartzite Limestone, greywacke Conglomerate Quartzite Argillite Conglomerate LOWER MISSISSAGI Argillife Quartzite, U—congIomerate Conglomerate Arkose + U—conglomerate UNCONFORMITY ARCHEAN ALGOMAN INTRUSIVE Granite K E E WAT I N Volcanic and sedimentary rocks FIG.3 TABLE OF FORMATIONS 2,500 �CM4 FIG. 4 ElO I 1000 Vertical Scale NI Limestone & Quartzite U—conglomerate A rgilIi te Conglomerate MIDDLE MJSSISSAGI Qu or tz I te NJ 13 PA -24 Z-5 - I UPPER MISSISSAGI Greywacke Bruce Limestone BRUCE CONGLOMERATE ESPANOLA SERPENT 2000 FEET Z-5-2 ———— —- LATERAL VARIATION IN BRUCE GROUP oI ———— MISSISSAGI LOWER �TWP. 143 .3 TWP. 144 SCHEMATIC NOR DIC CROSS—SECTION PAR DEE PECORS B — A-B-C ,-. 1—Base of Middle Mississogi Conglomerate TWP. 150 r$y FIG.5 HISKEY 0 LI] 6 Format! - Lower Miss, /ron Form a outcrop; magnetic ai Greei Gr H Cong/or 4 —1000 FEET —800 i—200 [—400 [—600 —0 2 Scale of Miles URANIUM DEPOSITS IN QUIRKE SYNCLINE ————————————— II I �FIG.6 — I, DISTRIBUTION OF COPPER DEPOSITS RELATIVE TO NIPISSING DIABASE ———————————— �U I SUDBURT NICKEL IRRUPTIVE TOUR Organized at the request of the Society of Economic Geologists and the Institute en Lake Superior Geology Prepared by Sudbury Field Trip Coittee: K. D. Card Ontario Department of Mines J. N. Holliway, International Nickel Co. of Canada, Ltd. P. Potapoff, Falconbridge Nickel Mines, Ltd. D. Rousell Laurentian University B. E. soucE International Nickel Co. of Canada Ltd. G. Thrail, international Nickel Co. of Canada, Ltd. J. S. Stevenson, McGill University (Leader) �1 2 TABLE OF CONTENTS Page Introduction Geology. • . Bibliography Tourlog. Geological . • , . . , . . . . . . • . . . . . 2 3 ,.,..... 9 , . 4 map, Sudbury Basin SUDBURY NICKEL IRRUPTIVE TOUR n I INTRODUCTION I Sudbury has been going f or a long time. To quote from Hewitt — "The first mine that was located in the Sudbury (1964) p. area was the Murray mine; it was discovered in l3 along the right of way during construction of the Canadian Pacific Railway. A gossan zone was observed in a rockcut (1) and copper mineralization was identified, The mine was opened in l9, and the ore From l4 to l9O was smelted and refined at Swansea in Wales, prospecting continued in the Sudbury area and during those first few years many of the major deposits of nickel—copper ore, including the Frood, Creighton, Stobie, and Copper Cliff mines, were discovered." Since that early period, many important discoveries have been made, and today we have l producing mines. These include in the South Range, from (see accompanying map for location): the west to the east; the Totten, Crean Hill, Ellen Pit, Creighton, Clarabelle, Murray, Frood—Stobie, Garson, Falconbridge, East, and Maclellan mines; and in the North Range, from west to east: Hardy, Boundary, Onaping, Levack, Fecunis and North mines. As active mines, but not producing at the moment, we have, in the South Range, the Copper Cliff North, Little Stobie, and Kirkwood mines, and in the North Range, the Coleman and Strathcona mines. As indicating the continued growth of mining in the Sudbury Basin area, it may be of interest to note that this past summer (1965) International Nickel opened No. 9 shaft at its Creighton mine. This shaft will go down to 7,150 feet, making it the deepest continuous mine shaft from surface in the Western Hemisphere, I (1) Although not marked as a stop on the accompanying sketch map, we will try to stop en route briefly at the Discovery cut and see ore in placeG I �3 GEOLOGY The nickel irruptive, because it contains the world's largest concentration of nickel sulfide ores, is for that very reason, unique in its geology, and all geological studies of The irruptive is a late it should be made with that in mind, Precambrian layered complex whose dominantly inward dipping members form a north—easterly trending ellipse 37 miles long by 17 miles wide. The rocks southeasterly outside the basin consist of a conformable series of steeply dipping, southward facing, volcanics and sediments intruded by Murray and Creighton granites and by the Sudbury gabbro. Elsewhere around the basin, the rocks consist of a complex of granites, gneisses and included basic rocks, The rocks outside the basin are cut by breccia zones, a fraction of an inch to a mile in width; this breccia is known as the Sudbury breccia, or more locally, the Frood breccia. The rocks inside the basin comprise the Whitewater series of gently dipping volcanic breccia and tuff, slate and groywacke (sandstone), The irruptive consists principally of micropegmatite These rocks are layered, (granophyre) and, below this, norite, but the layering is quite gross and requires detailed mapping with careful attention to the petrography to bring out the layering. The uppermost phase of the micropegmatite and therefore of the irruptive, is a quartzite breccia that is matrixed by irruptive derived igneous material, referred to by Stevenson (1963, p. 415) as pepper—and—salt micropegmatite. This breccia forms a layer between the more normal micropegmatite and the The border rock at the base of the overlying volcanic breccia, norite is the well—known quartz—diorite, the principal occur rences of whici are the tongues or dikes commonly known as the offsets, that extend outward from the norite, Primary features, structural and petrographic, of the irruptive are best studied in the North Range rocks. This is because the South Range rocks, in contrast to those of th North Range, have been subjected to extensive overthrusting and consequently, the primary layering and petrographic features have been considerably modified by dynamic metamorphism and recrystallization. With respect to the orebodies themselves, their occurrence has been very succinctly described by Hewitt (1964, p. 91) "The nickelcopper suiphide orebodies are found as follows: along the footwall contact of the norite in mineralized shear zones or in mineralized embayments of quartz diorite. These are called 0contact" or "marginal" deposits; Creighton, Falconbridge, Levack, Murray and Garson are of this type. Orebodies also are found in the quartz diorite offsets. The FroodStobie, Worthing ton, Victoria Nickel Offset, and Copper Cliff orebodies are of �I offset type. Three main types of ore are recognized: disseminated .sulphides largely in quartz diorite; massive sulphides along zones of shearing and brecciation; sulphide veins, and stringers in sheared and brecciated quartz diorite and country rock. The ore may lie in either the quartz diorite or the adjacent footwall country rocks. Both the Creighton and Falconbridge mines have been developed to depths greater than 6,500 feet. the • 'The principal pyrrhotite, ore minerals are pentlandite, nickeliferous chalcopyrite, cubanite, niccolite, gersdorffite, maucherite, and sperrylite. The average grade. of ore is about 2 percent nickel and 2 percent copper, but it varies from ore, body to orebody.' The principal ore—minerals are indeed those mentioned by Hewitt but it is interesting to note that Hawley (1962, p. 41) states that some 4.0 metallic minerals occur. • BIBLIOGRAPHY - SUDBURY BASIN GEOLOGY This rather comprehemsive post-1955 bibliography will show temporary studies of Basin geology. Pre-1955 referencea, including those to the important 'standard works' on Sudbury, may be found in the reference lists of several of the authors listed here. For easier reference, the material, in this bibli.— graphy has been arranged into several groups, and .within each group a chronological sequence has been followed. the great variety of disciplines that are being used in con- 1 •ICAL SURVEY OF CANADA Geological Survey of Canada (1958). Map 1063*, Sheet 41 N.E. Geological compilation, coloured, from near Sault Ste. Marie to near Cobalt Scale 1 in. to 8 miles. Siidbury, , Geological Survey of Canada, 11965) Sudbury, Ontario, aeromagnetic .:. sqr1e's, Mip 7067G. 2. I ONTARIO DEPAMWENT OF MINES . 2a. Thomson Vol. Annual Reuorts (1957) Geology of Sudbury LIV 11*56), 146. Jas. K. Basin: Pt. III, I . Howelt (19.57), Glowing avalanche deposits of the Sudury'Ba8In: Vol. LIV, Pt. III, (1956), 57—89. Williams Phemister, 'Vol. T. C., (1957) The Copper Cliff Rhyolit. LIT, Pt. III (1956), 91—116. Thomson, J. Pt. VI, (1958), Geology K. (1957,, 1—36. in Maim Np.: of .Falconbridge twp.: Vol. LIVI, 1 I .1 �______________, _____________ 5 2b. Geological Reports (1960), Uranium and thorium deposits at the base of the Huronian System in the district of Sudbury: No. 1, pp. 1—40. (1961), Maclellan and Scadding twps., district of Sudbury: No. 2, pp. 1—34. Card, K. D., (1965), Hyman and Drury townships: 2c, No. 34. Preliminary Reports Langford, F. F,, (1960), Geology of Levack twp. and the northern part of Dowling twp., District of Sudbury: 1960—5. Card, K. B., (1962), Geology of the Sudbury sewage tunnel: 2d. Preliminary Maps (Scale 1 in. 1/4 mile) Geology and compilation Jas. E. Thomson, (1953) p. 41 Lumsden twp. p. 42 Hanmer twp, p. p. p. p. 1962—63. issued 1960. 43 Dowling twp. 44 Balfour twp. 45 Rayside twp. 46 Fairbank twp. p. 52 Maclellan twp. Geology and compilation Jas, E. Thomson 1957—59 (issued 1960). p. 105 Espanola sheet, 1 in. = 2 mi. geological compilation by Jas. E. Thomson, (1961), (issued 1961). 1/4 mi., geology by K. B. Drury twp., scale 1 in, Card, et al, 1960, (1961), (issued 1962). p 134 1/4 mi., geology by p. 202 Denison twp., scale 1 in. K. D. Card et al. (issued 1962). p, 203 Graham twp., scale 1 in, — Card et al, (issued 1963). 1/4 ml., geology by K. D. p0 247 Waters twp., scale 1 in, Card et al, (issued 1964). 1/4 ml., geology by K. D. 1/4 ml,, geology by K. D. Foy twp., scale 1 in. Card etal, (issued 1965). p. 315 1/4 mi., geology by p. 316 Bowell twp., scale 1 in, K, D, Card et al, (issued 1965). �______________, ______________ __________ 1 6 2e. Miscellaneous Hewett, D. F., (1964), Rocks and minerals of Ontario: Circular No. 13. 3. Geol. SCIENTIFIC JOURNAL PUBLICATIONS Zietz, I. and Henderson, R. G. (1955), The Sudbury aeromagnetic Geophysics, Vol. XX, map as a test of interpretation methods: No. 2, pp. 307—317. Mamen, C. (1955) Nickel Rim Mines Ltd.: I Can. Mm. Journ., June. Lockhead, D. R. (1955), Falconbridge Ore Deposit, Canada: Geol., Vol. L, No. 1, 42—50. Econ. Mitchell, C. P. and Mutch, A. D. (1956), Geology of the Hardy District, Ont. Can. Inst. Mm. Met., Mine, Sudbury Vol. 49, February. Wilson, H.D.B., (1956), Structure of lopoliths: Bull. Geol. Soc. Am,, 67, 29—3OO, I Speers, E. C. (1957), Age relations of the common Sudbury breccia: Journ. Geol., vol. 65, 497—514. Thomson, J. E, (1957), Questionable Proterozoic rocks in the Sudbury— Espanola area: Roy. Soc. C. Special Pub. No. 2, Proterozoic in Canada. (1957), Recent geological studies in the Sudbury camp: Can. Mm. Journ. 7, 4, 109—12. Zurbrigg, H. F. et al. (1957), The Frood—Stobie mine in Structural geology of Canadian ore deposits: Can. Inst. Mm. Met., 343. Can. Mm. Journ. (1959) The Falconbridge Story — Geology: 116—127. Clarke, A. M. and Potapoff, P. (1959) Geology of McKim mine: Assoc. Can. Proc. 67—SO. Hamilton, W. (1960) Silicic differentiation of lopoliths: Geol. Congress, XXI Session, Part XIII, 59—67. Vol. (1960) Form of the Sudbury lopolith: 6, pt. 4, 427—447. Geol. Intern. Can. Mm., Stevenson, J. 5. (1961) Origin of quartzite at the base of the Whitewater series, Sudbury basin, Ont.: Intern. Geol. Congress, XXI Session, Part XXVI Supp. Vol. Sect. 1-21, 32—41. (1961) Recognition of the quartzite breccia in the Whitewater series, Sudbury basin, Ont.: I I I I Trans. Roy. Soc. Canada, Vol. LV, p. 57—66. I �7 Hood, P. J, (1961), Paleomagnetic study of the Sudbury basin: Jourri. Geoph. Res., Vol. 66, 1235—1241. Strangway, D, W. (1961), Magnetic properties of diabase dikes: Journ. Geoph. Res., Vol. 66, 3021—32. Hawley, J. E,, et al. (1961), Pseudo-eutectic intergrowths in arsenical ores from Sudbury: Can. Mm. 6, 555—575. Hawley, J. E. (1962), The Sudburyores: origin: their mineralogy and Can. Mm., Vol. 7, Pt. 1—207. Stevenson, J. S., (1963), The upper contact phase of the Sudbury micropegmatite: Can. Mm., Vol. 7, Ft. 3, 413—419. Thode, H. G. (1962), Sulfur isotope abundances in rocks of the Sudbury district and their geological significance: Geol., 57, 565—57g. Econ. Davis, T. E. and Slemmons, D. B. (1962), Observations on order— disorder relations on natural plagioclases, III Highly ordered plagioclases from the Sudbury intrusive: Norsk. Geol. Tidss., Vol. 42, Pt. 2, 561—577. Thomson, J, E. (1962), Extent of the Huronian system between Lake Timagami and Blind River, Ontario: Roy Soc. Canada, Special Pub. No. 4 Tectonics of the Canadian Shield, 76—9. Bucher (1963), Cryptoexplosion structures caused from without or within?, (astroblemes or geoblemes?); Am. Journ. Sc., Vol. 261, 597—649. Dietz, R. 5. (1963), Cryptoexplosion structures: Am. Journ. Sc., Vol. 261, discussion: Sopher, S. R. (1963), Paleomagnetic study of the Sudbury irruptive: Geol. Surv, Canada Bull. 4, 90. Kullerud, G. (1963), Thermal stability of pentlandite: Mm, 1, 353—366. Card, K. D. (1964), Metamorphism in the Agnew Lake area, Sudbury district, Ontario: 1011—1030, Geol, Soc. America, Bull., Vol. 7.5, Dietz, R. 5, (1964), Sudbury structure as an astrobleme: Geol,, Vol. 72, 412—434. Journ. Strangway, D, we (1964), Rock magnetism and dike classification: Journ. Geol. V. 72, 64—663. Kullerud, G, and Yoder, H. S., Jr. (1964), Sulfide—silicate reactions, Ann, Rept., Geophys. Lab. Yr. Bk. 62, 218—222. �1 8 Borchert, H. and Lamby, B. (1964), Mikroskopische untersuchungen an erzproben aus der Falconbridge-grube (Sudbury) und daraus resultierende genetische folgerungen: Zeits.fUr Erzbergbau u. Metall,, XVII, 645—653. Stevenson, J. S. (1964), Sudbury in Terms of Upper—Mantle Petrology: Geol. Soc. Am. Abstract in Sec. E., A.A.A.S., Montreal meeting 1964, p. 18. Hawley, J. E. (1965), Upside—down zoning at Frood, Sudbury: 1 Econ, Geol, 60, 529—575. A. J. and Kullerud, G. (1965), Sulfurization in nature: two examples: Geol, Soc. Am., Abst. p. 113. Naldrett, Simons, P. Y. and Dachille, F, (1965), Shock damage of minerals in shattercones: Geol. Soc. Am. Abst. p. 153. Vos, M. A. and Moorhouse, W, We (1965), Quartz diorites from the North Range, Sudbury: Can. Mm., Abst. in v. 8, pt. 3, Naldrett, A. J. and Kullerud, G. (1965), Investigations of the nickel—copper ores and adjacent rocks of the Sudbury district, Ontario: Geoph. Lab.. Wash. D. C., Year Book 64, pp. l77—188. Deals largely with Strahcona orebody. 4. I Pe 402. I I RADIOGENIC AGE DETERMINATIONS (Radiornetric dating) I Geological Survey of Canada, Age determinations (J. A. Lowdon et al.) and Geological studies, structural provinces etc. (C. H. Stockwell et al.) Paper 60—17 (1960) " " " " 61—17 (1961) 62—17 (1963) 63—17 (1963) 6—17 (1964). Massachusetts Inst. of Technology, Annual Progress Reports to U.S. Atomic Energy Commission 1958 to present, on variations in isotopic abundances of strontium, calcium and argon and related topics (variously refer to work on Sudbury specimens) particularly, "Re—examination of Rb—Sr whole — rock ages at Sudbury; Dec. 1964, 225-228. Davis, T. L. et al. (1957), The ages of rocks and minerals: 1 Carnegie Inst. Wash, Yr. Bk, Vol. 56, pp. 164—171. Wetherill, G. W. et al, (1957), Age measurements on rocks north of Lake Huron: Trans. Am. Geoph. Union, 38, 412. Fairbairn, H. W. et al. (1960), Mineral and rock ages at Sudbury— Blind River, Ont.: Geol0 Assoc. Can, Proc. Vol. 12, p. 41—66. I I �______________ 9. (1961), The relation of discordant Rb—Sr mineral and whole rock ages in an igneous rock to its ti of crystallization and to the time of subsequent Srö(/Sr metamorphism: Geochim, et Cosmochim. Acta, vol. 23, p. 135— 144. Faure, G, et al, (1964), Whole rock Rb—Sr age of norite and micro— pegmatite at Sudbury: Journ. Geol., 72, 4—54. Fairbairn, H. W., et al. (1965), Re—examination of Rb—Sr whole—rock Geol. Assoc, Canada Proc. 16, 45—101. ages at Sudbury: Slawson, W. F. and Russell, R. D. (1965), Age of major minera1 izations in Ontario: Geol, Soc. Am, Abst. p. 156. 5. GUIDE BOOKS Guide Book for Field Trip No. 7 (1953), Sudbury area, in conjunction with joint annual meeting in Toronto, one of Geol, Soc. Am. and Geol, Assoc. Canada (by Sudbury geologists). Geological Field Trip. Guide Book Sudbury area (1957): Sixth Commonwealth Mm. and Met, Congress, Sudbury, Ontario, (by congress committee at Sudbury.) TOUR LOG With respect to this particular tour, we thought that, because of the very close relation between the ore-bodiesiand the irruptive and therefore because of the fundamental importance of the irruptive, we might take advantage of the detailed studies that are currently being made of the irruptive and would restrict our tour, in the time that is available, to the irruptive itself, The briefing and discussion on Saturday evening at Laurentian University and the stops on Sunday, have therefore been arranged with this specific objective in mind. We will Copper Cliff and en route Copper Cliff reach our first stop by driving from Sudbury through to near the Copper Cliff North and Clarabelle mines, we will have several views, no stops, of Inco's Smelter. Copper Cliff offset, Clarabelle Road, STOP 1 This is a type locaflty for the quartz—diorite phase of the norite, Ore specimens from nearby mines will be provided here, �I 10 We will drive from Stop 1 east to the Levack highway, thence north 1—1/2 miles to the Discovery Cut at the Murray Mine, stop here briefly and return south along the highway to Regent St0 in Sudbury and then along Frood Road, driving by the Frood and Stobie Mines, joining Highway 69 and thence to Stop 2. I STOP 2 South Range norite, both the fresh ?tbrowh_blacktt norite 1e widespread, altered "green norite", From here we will continue northward along Highway 69, across the norite and into the micropegmatite, Stop 3. STOP 3 Typical South Range, foliated micropegmatite0 1 1 From Stop 3 we will drive north along 69 over a hill of black Onaping tuff into the farmlands of the Chelmsford valley underlain by Onwatin slate and the Chelmsford sandstone0 We will continue through Val Caron and Hanmer to the turn-off, to the right of the Ella (Capreol LakeWest Bay road, one mile south of Capreol. We will drive along this road for about 3 miles to Stop 4, 1/2 north of the Ella Lake campground. Stops 4 and 5 will be concerned with the North Range phase of the irrupt ive. STOP 4 North Range Norite, I This is on the township line between Norman and Capreol townships. We will wallcwestward along this line and in doing so will cross several members of the irruptive, which here trends north0 Stop 4a: Stop outcrops along the road are of lower gray norite0 I westward across the slough, a fine—grained, sharp textured norite, overlying the medium-grained gray norite, outcrops on the hillside0 4b: Stop 4c: outcrops of fine-grained mafic phase of the last, on the same hillside0 Stop 4d: farther west up the hillside, outcrops of pink norite. the last of the outcrops on this line are of the lowermost member of the micropegmatite, a coarse—grained, salmon— coloured member0 Stop I I 4e: Return to buses for trail lunch in Ella Lake campgrounds, and drive back along Ella Lake road to C. N, Railway crossing; this is Stop 5. I I �STOP 5 North Range Micropegmatite. Walk westward along the railway. Stop 5a: outcrop along railway of upper micropegmatite, a fine to medium gray member. Stop 5b: farther west on railway, outcrop of breccia at top of micropegmatite. From here we will walk along the railway a short distance, to a tote—road of the new hydro line (incidentally, one of the new E.H,V. lines of the Ontario Hydro), then northwards to Stop 5c. En route, most of the outcrops on left (west) side of the road are of Onaping volcanic breccia. Stop 5c: about l000'north along tote—road on the south side to study outcrops of breccia and the uppermost phases of the irrupt lye. Stop 5d: continue along tote—road for a short distance to look at other outcrops of the irruptive and the breccia. Return via tote-road and railway to bus, drive back along Ella Lake road to Highway 69, turn south on 69 then left on the GarsonFalconbridge road, route 545 to Stop 6 which is l/2mile south of the junction of 545 with 541. STOP 6 Typical South Range, foliated micropegmatite. From this stop we will drive south over South Range norite, turn left, geologically at the footwall, and continue in footwall greenstone, to Falconbridge townsite, where we will have a chance to drive by the Falconbridge Smelter and be able to see in the distance towards the east, the headframes of the Falconbridge and the East mines. Ore specimens from nearby mines will be provided From Falconbridge we will return and drive southwesterly here. past the Garson mine and back to Sudbury. �LEGEND SOUTH MANNE BOOTS 54542 ACTIVE MINE M)NE PR000CINO FAA LT S FOOTWAIS ROCKS TOTTEN OOARTZITE BRECCIA IWSERE MAPPED TO DATE) ONOPING TOFF LNICKEL J SANDSTONE ONWATIN OLATE CSELMSPOKO MORITE MICROPEOMOTITE ± o • iJIllhlIll _______ O DI 2 S KILOMETERS 4 NIL ES S 2 540 IS aaaaaaaaaaa )ALWNBRIDGE cv • MACLENNAN SUDBURY BASIN GEOLOGICAL MAP I — — �PREVIOUS ANNUAL MEETINGS of INSTITUTE ON LAKE SUPERIOR GEOLOGY First 1955 Minneapolis, Minnesota University of Minnesota Second 1956 Houghton, Michigan Michigan College of Mining and Technology Third 1957 East Lansing, Michigan Michigan State University Fourth l95 Duluth, Minnesota University of Minnesota, Duluth Fifth 1959 Minneapolis, Minnesota University of Minnesota Sixth 1960 Madison, Wisconsin Geology Department, University of Wisconsin and Wisconsin Geological and Natural History Survey Seventh 1961 Port Arthur, Ontario Canadian Institute of Mining and Metallurgy, Lakehead Branch, and Ontario Department of Mines. Eighth 1962 Houghton, Michigan Michigan College of Mining and Technology Ninth 1963 Duluth, Minnesota University of Minnesota, Duluth Tenth 1964 Ishpeming, Michigan Mining Companies: Inland Steel, Cleveland—Cliffs Iron, Jones and Laughlin, North Range Eleventh 1965 St. Paul, Minnesota Minnesota Geological Survey and University of Minnesota �Zn, Cu, Ag, Pb, Au in massive iron sulphide deposits in Archaean volcanic rocks Al Fe deposits in Archaean iron formation A2 0 Cu, Pb, Zn, Au quartz veins associated with Proterozoic gabbro Cl areas of abundant Au deposits (see abstract) Geological Survey of Canada By S. M. Roscoe, reproduced by permission of C2 Cu disseminated in sodic porphyry C3 Mo, Li, Be in Kenoran pegmatites C4 Cu-Mo, Pb-Zn veins Dl uraninite in pyritic Huronian quartz pebble conglomerate -F D2 Ag-Co-As bearing calcite veins associated with Nipissing diabase D3 Bi Cu, Cu-Au 'veins' with gabbro-anorthosite Ni, Cu-Nj with ultrabasic rocks and gabbro sedimentary rocks Keweenawan volcanic and B2 Cu veins assocjated with gabbro—peridotite B3 F2 El Zn-Pb-Cu-Ag-pyrite deposits in Animikean volcanic rocks ZOO miles B4 asbestos in Archaean ultrabasic rocks 100 chalcopyrite in breccia zones F3 Fl chalcocite, native copper in pitchblende veins associated with Keweenawan diabase dykes F4 U, Fe, apatite Zn-Pb, Pb-Ag veins Nb, alkalic syenite F5 E2 Ni-Cu-Pt associated with Hudsonian gabbro METALLOGENIC STUDY, SAULT STEMARIE TO CHIBOUGAMAU PRINCIPAL TYPES OF MINERAL DEPOSITS, THEIR GEOLOGICAL ASSOCIATIONS AND AGES II — ——————————————————r �(see abstract) By W. R. Farrand, J. H. Zumberge, and J. Parker — — — — — — — — — — — — — — — — I_I DnNIvMEmlC CHART ir rI -II — — � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1966 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Sault Ste. Marie, Michigan. May 6-7, 1966. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1966 Contributor An entity responsible for making contributions to the resource Larry L. Babcock L.O. Bacon W.A. Longacre A. Stevens Alexander C. Brown John W. Trammell Joseph P. Dobell W.R. Farrand J.H. Zumberge J. Parker Bevan M. French P.E. Giblin John C. Green Tsu-Ming Han E. Wm. Heinrich Richard W. Vian William J. Hinze Norbert W. O'Hara James W. Trow Harold J. Lawson W.O. Mackasey A.M. Johnson A.S. MacLaren Louis Moyd Richard W. Ojakangas Willard P. Puffett S.M. Roscoe A.P. Ruotsala G.J. Koons S.C. Nordeng John Q. St. Clair Kenneth Segerstrom Terrence J. Smith A.K. Snelgrove Kiril Spiroff G.G. Suffel Walter M. Tovell C.F.M Lewis R.E. Deane M.E. Volin Richard J. Wold Ned A. Ostenso Grant M. Young Paul W. Zimmer Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/914bfd47574dffafd8ce8132d6703a58.pdf 20e580fa2bfddbbe3ce84367c828bbc5 PDF Text Text 7i -(2 S -1ETh* 'TH 13 ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY Department of Geology Michigan State University and Geological Survey Division Michigan Department of Conservation East Lansing, May Michigan 1-2, 1967 �13th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY Kellogg Center Michigan State University East Lansing, Michigan May 1—2, 1967 BOARD OF DIRECTORS - INSTITUTE ON LAKE SUPERIOR GEOLOGY A. T. Broderick, Inland Steel Company, Ishpeming, Michigan D. H. Hase, University of Iowa, Iowa City, Iowa W. J. Hinze, Michigan State University, East Lansing, Michigan P. K. Sims, Minnesota Geological Survey, Minneapolis, Minnesota A. K. Sneigrove, Michigan Technological University, Houghton, Michigan SECRETARY-TREASURER - INSTITUTE ON LAKE SUPERIOR GEOLOGY D. H. Hase, Department of Geology The State University of Iowa, Iowa City, Iowa 52240 LOCAL COMMITTEE W. J. Hinze H. B. Stonehouse (Technical Session Chairman) H. F. Bennett J. A. CoIwell G. E. Eddy (Field Trip Chairman) H. J. Hardenberg C. E. Prouty R. C. Reed S. B. Romberger R. Ehrlich J. H. Fisher B. T. Sandefur J. W. Trow The Field Trip conducted in connection with the Institute was held in the Grenville Province of Southeastern Ontario, in the BancroftMadoc Area, on April 29-30. It was led by Dr. H. B. Stonehouse, Department of Geology, Michigan State University. A Field Trip Guide is available. �PROGRAM 13th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY Kellogg Center Michigan State University East Lansing, Michigan Sunday, April 30, 1967 8:00 10:30 p.m. Smoker - Centennial Room, Kellogg Center Monday, May 1, 1967 7:45 a.m. Registration - Lobby, Kellogg Center 8:40 TECHNICAL SESSION I - AUDITORIUM Co-chairmen: J. W. Avery and C. E. Dutton Welcome C. E. Prouty The Structural History of the 'Archean" Rocks of UpperMichigan W. E. C. Taylor Geology of Part of the East Gogebic Range, Michigan William C. Prinz Stratiçjraphy, Structure and Metamorphism of Upper Animikie Rocks in the Marenisco-Watersmeet Area Crawford E. Fritts Keweenawan Volcanic Rocks Near Ironwood, Michigan Harold A. Hubbard Mineralogy and Petrology of the Mineral Lake Intrusion, Northwestern Wisconsin James F. Olmsted Structure and Stratigraphy Including Precambrian Tillite in Eastern Dead River Basin, Marquette County, Michigan . .Willard P. Puffett A Study of Clastics in the Negaunee Iron Formation of Michigan Robert W. Henny Influence of Faulting on Deposition of Clastic Interbeds in Negaunee Iron Formation Near Palmer, Michigan. . .Jacob E. Gair �3 Monday, May 1, (continued) 12:30 p.m. Luncheon 1:30 TECHNICAL SESSION II - AUDITORIUM .Big Ten Room Co-Chairmen: R. K. Hogberg and H. B. Stonehouse Geochronology in the Lake Superior Region K-Ar Hornblende Ages for Granites and Gneisses and K-Ar Ages for Dikes in Minnesota The Geochronology of the Keweenawan Rocks at White Pine, Michigan S. S. Goldich Gilbert N. Hanson Sambhudas Chaudhuri and Gunter Faure John A. Colwell Geochemistry of the Nipissing Diabase. Oxygen Isotopic Evidence of Metamorphism in the Biwabik Iron Formation, E. C. Perry, Jr. and Minnesota J. W. Morse A Spectrochemical Method for Differentiating Between Carbonate and Silicate Fades An Aeromagnetic Survey of Lake Huron A Regional Geophysical Study of the Por.t Coldwe.U Complex, Ontario Thomas Waggoner G. B. Secor, W. J. Hinze, N. W. O'Hara, and J. W. Trow J. D. W. J. Characteristics of Magnetic Data over Major Subdivisions of the Precambrian Shield ANNUAL BANQUET 6:30 p.m. Big Ten Room, Kellogg Center Address: Search for Precambrian Life" Professor Elsa S. Barghoorn Harvard University G. Corbett, Hinze, and B. Secor A. S. MacLaren and B. Charbonneau �4 Tuesday, May 2, 1967 8:40 a.m. TECHNICAL SESSION III - AUDITORIUM Co-Chairmen: L. 0. Bacon and A. S. MacLaren Gravity Anomalies Over Lake Superior and Surrounding Area and Their Structural M. J. S. Innes and A. K. Goodacre Implications J. S. Steinhart, S.R. Heat Flow in Lake Superior Hart, and T. J. Smith Progress of Geophysical Studies in Richard J. Wold Lake Superior Relationship Between Seismic and R. P. Meyer and Aeromagnetic Surveys in Eastern L. Ocola Lake Superior Identification of Seismic Refractors in Henry Halls and the Lake Superior Syncline G. F. West Refraction Seismic Surveys on the MidContinent Gravity Anaomaly in Minnesota and Wisconsin Preliminary Magnetotelluric Resistivity Results Across the Wisconsin Arch. 12:10 p.m. Luncheon 1:20 Business Meeting - Auditorium 1:30 TECHNICAL SESSION IV - AUDITORIUM S. H. Tohnson and P.R. Farnham . Forrest L. Dowling Centennial Room Co-Chairmen: R. A. Hoppin and W. T. Swenson Hydrocarbon Compounds in Igneous Rocks. E. Win. Heinrich Copper Mineralization in Animikie Sedi— ments of the Eastern Marquette Range, Robert C. Reed Michigan Textures and Compositions of Silicate and Sulfide Ore Minerals from Mineralized P. W. Weiblen enry Hall Zone, Duluth Gabbro Complex Subdivisions of the Negaunee Iron ForJoseph J Mancuso and mation, Sections 7, 8, T 47 N, Jack W. Avery R 26 W, Michigan Evidence on the Physical Environment of Gene L. LaBerge Iron Formation Deposition Paleobiology of a Precambrian Shale. . . Elso S. Barghoorn Some Properties of Michigan Cherts. . . Allan M. Johnson and Albert P. Ruotsala . �PALEOBIOLOGY OF A PRECAMBRIAN SHALE Elso S. BarghoornW The existence of both coal and petroleum in shale sequences of Precambrian age in the Lake Superior region has been demonstrated in recent years. Although these 'fossil fuels" occur in miniscule amounts in terms of post-Precambrian sediments, they are of great theoretical interest in problems of the antiquity of Precambrian life and the organic geochemical indicators of biological processes in ancient terrestrial environments. Attention is centered here o the paleobiological aspects of the Nonesuch Shale of Northern Michigan, but reference is made also to the much older "Michigamme" coal and associated shale. Concerning the latter, chemical analyses, X-ray diffraction studies, petrographic examination and paleontological study indicates that the coal is a true coal, partially metamorphosed and of biological origin, probably derived from blue—green algae. The Nonesuch Shale, a 1000 million year old economically important cupriferous sedimentary ore shows remnants of organic preservation interpreted as algal residues and quite remarkably, the presence of small amounts of a syngenetic paraffiriic crude oil. Analysis of the oil reveals the presence of a wide range of aliphatic and aromatic hydrocarbons. Gas liquid chromatographic analysis of organic extractives of the shale reveal the presence of the isoprenoid hydrocarbons phytane and pristane, presumably derivatives of chlorophyll breakdown. Another presumed chlorophyll derivative a vanadyl porphyrian complex has been identified. A general discussion is presented concerning the presumed paleoenvironment of the Nonesuch Shale deposition. (1) Department of Biology, Harvard University; Cambridge, Massachusetts. �THE GEOCHRONQLOGy OF THE KEWEENAWAN ROCKS AT WHITE PINE, MICHIGAN Sambhudas Chaudhuri(1) and Gunter Faure(2) Age determinations by the total-rock Rb-Sr method of several suites of felsite from the White Pine area of Michigan indicate dates ranging from 978+40 m.y. to 1100+25 m.y. A specimen of felsite from Government Peak of the Porcupine Mountains was dated at 1042+6 m.y. Assuming that the Porcupine Mountains are an anticline, this date sets an upper limit to the time of deposition of the overlying Nonesuch Shale. Another upper limit is provided by dates of 1107 m.y. and 1180 m.y. for two pebbles from the lower sandstone unit in the White Pine Mine. Nine samples of mineralized and unmineralized rock from the basal section of the Nonesuch Shale exposed in the mine workings of the White Pine Mine were analyzed. These samples form a good co-linear array in coordinates of Rb87 / Sr86 and Sr87 / Sr86. The apparent age, calculated from the slope of the isochron, is 1075± 50 m.y. The initial Sr87 / Srd6 ratio is 0.7080+0.001. The apparent age for the Nonesuch Shale is interpreted to be slightly greater than the time of deposition because of the probable incorporation of inherited radiogenic Sr8' into the sediment at the time of deposition. The isotope composition of strontium of a thin bed of limestone in the basal portion of the Nonesuch Shale was measured. The Sr07 / Sr86 ratio was found to be 0.7058. Using the data of Hurley, Fairbairn and Pinson on the isotope composition of carbonate rocks, a time of deposition of about 1000 m.y. is indicated for this limestone. This appears to be the first age determination of a carbonate rock by the isotope composition of its strontium. The isotope composition of lead extracted from chalcocite in the ore at the White Pine Mine was found to be anomalous. This suggests that the lead in the ore was mixed with radiogenic lead and favors an epigenetic rather than a syngenetic origin for the copper sulfide in the basal portion of the Nonesuch Shale. (1) (2) Department of Geology, Kansas State University; Manhattan, Kansas. Department of Geology, The Ohio State University; Columbus, Ohio. 6 �7 GEOCHEMISTRY OF THE NIPISSING DIABASE John A. Coiweii(l) The Nipissing quartz diabase intrusives occur as sheets and dykes intruding the Huronian rocks in the area between the eastern end of Lake Superior and Lake Temiskaming. An acceptable age for the Nipissing is about 2.1 billion years * , and is significant in placing a lower limit on the age of the Huronian in Ontario. Pe trographic, chemical, and spectrographic studies indicate that the various phases of the diabase, which range from olivine norites to granophyres and aplites can be explained as due to gravitational differentiation of the diabase magma. Lateral as well as vertical differentiation has occurred in the sheet intrusions due to their undulating character. * References: Lowdon, J. A., et al. 1963. Age determinations and geologic studies. Geological Survey of Canada Paper 62-17, p. 92. Van5chumus, R. 1965. The geochronology of the Blind River-Bruce Mines Area, Ontario, Canada. Jour. Geol., v. 73, p. 755—780. Department East of Natural Science, Michigan State University; Lansing, Michigan. �8 A REGIONAL GEOPHYSICAL STUDY OF THE PORT COLDWELL COMPLEX, ONTARIO John D. Corbett(1), William 5. Hinze(2), and George B. ecor(2) Regional geophysical studies were conducted on the north shore of Lake Superior in the vicinity of Marathon, Ontario, to study the structure of the Port Coidwell Complex, a sub-circular intrusive approximately 16 miles in diameter. Surface geological mapping indicates that the complex is composed predominately of syenitic rocks with a discontinuous peripheral band of gabbro. A positive magnetic anomaly is associated with the intrusive, but strong negative anomalies correlate with the gabbro on the east and northeast margins. Analysis of a suite of oriented samples shows that the gabbroic rocks have a strong, variable remanent magnetic polarization. The results of two and three dimensional magnetic model analysis, using both induced and remanent magnetic polarizations, proved to be only partially successful in matching the observed anomaly. A highway gravity profile from White River to Schreiber, Ontario, a distance of 110 miles, shows a positive 65 milligal gravity anomaly over the Port Coidwell Complex. Comparison of this anomaly with the theoretical gravity effect of two and three dimensional models based upon available geological information indicates that the Complex consists primarily of gabbroic rocks extending to a depth of 8 miles. The intrusive is an asymmetric truncated funnel structure having a near vertical contact on the east and an approximate 450 contact on the west. Combined gravity and magnetic analysis utilizing Poisson's relation was employed as an alternate method of investigating the physical properties of the intrusive. The results of this study verify the presence of a strong remanent magnetic polarization associated with the gabbro along the eastern margin and also indicate a strong, positive remanent magnetic field over the central portion of the complex. This evidence suggests an explanation for the difficulty in matching the observed magnetic anomaly with the magnetic model study. (1) Geophysical Division, The Anaconda Company; (2) Department of Geology, Michigan State University; East Lansing, Michigan. . , Utah. �PRELIMINARY MAC NETOTELLURIC RESISTIVITY RESULTS ACROSS THE WISCONSIN ARCH Forrest L. Dowling(l) Magnetotelluric resistivity measurements have been made at five of a projected fourteen sites across the Wisconsin Arch. Surface electric impedances are being computed from the measurements to yield apparent resistivity and phase information as a function of frequency. Resistivity models of the crust and upper mantle are fitted to the measured curves. Tentative results are to be presented. w Geophysical and Polar Research Center, University of Wisconsin; Madison, Wisconsin. �10 STRATIGRAPHY, STRUCTURE, AND METAMORPHISM OF ROCKS IN THE UPPER PART OF THE ANIMIKIE SERIES IN THE MARENISCO-WATERSMEET AREA, MICHIGAN * Crawford E. Fritts (I) Recently completed mapping has shown that a monoclinal sequence including the Copps Formation of Allen and Barrett (1915) and four con- formably overlying stratigraphic units is at least 40,000 feet thick. This sequence is placed above the Menominee Group within the Animikie Series of James (1958) and is interpreted as one of the least deformed parts of what Allen and Barrett (1915, p. 131) referred to as the "Michigamme slate series' of late Huronian age. A thin conglomeratic quartzite at the base of their Copps Formation is correlated with Goodrich Quartzite of the Marquette district. At least 10,000 feet of graywacke—slate of the Copps Formation and many thousands of feet of east-trending, graywacke-slate in the upper part of the monocline near Paulding are lithologically similar to rocks in the Marquette and Iron River -Crystal Falls districts mapped as Michigamme Slate, which previously was thought to be about 5, 000 feet thick. It would appear that east—trending rocks formerly interpreted as isoclinally folded Michigamme Slate in a broad region east of the map area may actually be part of the monoclinal sequence. An east-trending fault accounts for a 5-mile apparent right lateral offset of Ariimikie rocks near Barb Lake and for the abrupt termination of iron—formation at the Banner exploration. The fault also forms the north boundary of a dome-like stock of the Wolf Lake Granite of Allen and Barrett (1915). Emplacement of this granite, metamorphism of the Animikie Series, and displacement along the fault most likely occurred during the Penokean orogeny in post-Animikie, pre-Keweenawan time. References: Allen, R. C., and Barrett, L. P., 1915, Contributions to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geol. and Biol. Survey, Pub. 18, geol. ser. 15, p. 13—164. Hamblin, W. K., 1958, The Cambrian sandstones of northern Michigan: Michigan Geol. Survey Pub. 51, 146 p. James, H. L., 1958, Stratigraphy of pre-Keweenawan rocks in parts of northern Michigan: U.S. Geol. Survey Prof. Paper 314-C, p. 27—44. * Work done in cooperation with the Geological Survey Division of the Michigan Department of Conservation U. S. Geological Survey; Denver, Colorado. (1) �rr mafic lava flows Keweenawan Series UNCONFORMITY Graywacke—slute near Paulding of Allen and Barrett 11915) Wolf Lake Granite wg UNCONFORMITY ks, quartzific sandstone k, Cj Jacobsville Sandstone of Hamblin 1958) L) Hcc -.iz 2 e bu EXPLANATION 4 B 0 MILES 1 Cup Lake z Figure I--Generalized geologic nap of the Morenisco—Watersmeet area, Metatut f and tuffaceus metagraywacke; mb'rar quartzite, conglomerate, and magnetic iran-formation i/n lower part, includes possible pillow /ava(y) east of Cup Lake Rocks near ci Graywacke near Banner Lake Upper part includes magnetic iron-formation, especially south of Barb Lake fault bt, metatuff and magnetic iron -formation bf, p//low lava and fragmental va/conic racks Rocks near Blair Lake bu, mefavo/canic and mefasedimentary racks undivided 0 Mich. Gneiss gn near Mount Kimberly r Grnnite near Nelson Creek UNCONFORM/TYf?) part of Ankn/kie Series, possibly older than granite near Ne/son Creek Magnetic sfrata of Marenisco Range Strotigraphib position uncerfai/n possibly ml UNCONFORMITY Copps Formation of Allen and Barrett/IBIS) Groywacke-slafe overlying thin basal conglomerate �INFLUENCE OF FAULTING ON DEPOSITION OF CLASTIC INTERBEDS IN NEGAUNEE IRON-FORMATION NEAR PALMER, MICHIGAN * Jacob E. GairW Interbeds and lenses of ciastic sedimentary rocks-—graywacke and impure quartzile—•-rre conspicuous in the chemically deposited hematitic, meg netitic, and sideritic Neaunee Iron-Formation near Palmer, Michigan (S. A. Tyler and V;. H. Twenhofel, 1952; J. T. Mengel, 1956; J. F. Davis, 1965.) The ciastic interbeds range in thickness from about 1/30 inch to S9 feet, Detrital quartz occurs not only in discrete layers hut also a- scattered grains in many ferruginous leminee of iron-formation. Clastic sediment in the south—central part of the Palmer hasin makes up 3 to 9 percent of the Negaunee: 3 to 6 psrcent measured in discrete layers and an estimated 2 to 3 percent as scoterec1 querta jreins. In any one drilled section, there are h'mdred3 of rather evenly spaced clastic lenses less than 1/2 inch thick and relatively fcw irregularly spaced layers more than 1. foot thick. In several drill cores of 300 to 700 feet of iron-formation, oniy a few intervals of more than 10 feet do not contain some clostic sedimentary beds. In contrast to the iron-'fcnnatioj-A near Palmer, the Negaunee of neighboring areas end :recamb:ian iron-fcrmation generally are virtually devoid of clastio debris. The depositional environment near Palmer during Negaunee tiate, therefore, must have differed in some respect from that of ncighrorin areas and from that of most other Precambrian iron•iormstions. South of the areas c.i ciasti—bearing iron-formation——along the south ec'ge of Lhe Palmer basin and to tIi west far about 2 miles al.ong the flank of the lvIarquctto rynclincrilmm-—cra;:itjc gneiss older than the Negaunee has beer. piLfted to die south along conspicuous zones of shearino and fauting. dthouqh ost of d e movement in the fault zones occurred ter c.epcsition of the Negaunee Iron—Formation, it is inferred from the oresanci e cl' obe:::jyn iron—formation adjacent to the faults that diploceme befl, 'a at 1mst as early as Negaunee time, and that the c1atic mF riel c !nsn-formatjon was eroded : (Continued next page) * Publication wthorized h the Director, U. S. Geological Survey. Work done in cooperation with the Geological Survey Division of the Michigan Department of Conservation. U. S. Geological Surrey; 1i �12 from the up-faulted areas of gneiss. The numerous small lenses of clastic sediment isolated in the iron-formation suggest that unconsolidated detritus collecting at the edge of upfaulted areas was repeatedly dislodged in small portions by minor crustal movement in the fault zones and dumped into iron-silica muds accumulating to the north. References: Davis, J. F., 1965a (1) A petrologic examination of iron-formation associated graywackes and pyroclastic breccias within the Negaunee formation of the Palmer area, Marquette district, Michigan: Unpub. Ph.D. thesis, University of Wisconsin, 179 p. (2) Petrology of Precambrian iron-formation and associated rocks, Palmer area, Marquette district, Michigan: Geol. Soc. Am., Program, 1965 Annual Meeting, p. 42. Mengel, J. T. , Jr., 1965, The relationship of clastic sediments to iron-formation in the vicinity of Palmer, Michigan: Unpub. M. S. thesis, University of Wisconsin. Tyler, S. A. and Twenhofel, W. H., 1952, Sedimentation and stratigraphy of the Huronian of upper Michigan: Am. Jour. Sd., V. 250, p. 1—27; 118—151. �GEOCHRONOLOGY IN THE LAKE SUPERIOR REGION S. S. Goldich1 During the past 10 years advances in the analytical techniques and a growing appreciation of the geologic factors have broadened the scope and usefulness of radiometric dating. Specific advances include improvement in the lead-alpha method, application of K-Ar to amphiboles, developm ent of Rb-Sr through the whole-rock and mineral-component technique, and the wider application of U, Th-Pb isotopic analyses. Early lead—alpha age determinations on Lake Superior rocks are not reliable. The large number of K—Ar and Rb-Sr determinations made in a number of laboratories, largely on micas, are analytically reliable within the limits of error assigned. The micas, however, are highly susceptible to metamorphism, and mica ages, as a result, cannot be assumed to give the time of initial crystallization or formation. In some cases K-Ar ages on hornblende have given some assistance, but the greatest progress in penetrating the metamorphic barriers has come through the use of Rb—Sr and U-Pb analytical procedures. K-Ar and Rb-Sr age determinations on micas from the Morton Gneiss of southwestern Minnesota, for example, indicate an age of 2.5-2.6 b.y. The improved lead-alpha method, however, gave an age of 3.0 b.y. for zircon, and isotopic U-Pb determinations on zircon from the Morton Gneiss gave Pb207/Pb206 ages of 3.2 b.y. and a conchordia age of 3.5 b.y. Isotopic U-Pb age determinations on zircon concentrates and Rb-Sr data for whole-rock and mineral component samples from the Lake Superior region show some of the geologic complexities that are now becoming apparent. One of the geologic factors that complicates the interpretation of radiometric ages is the effect of weathering on the K-Ar, Rb-Sr, and U-Pb decay systems. Department of Earth and Space Sciences, State University of New York; Stony Brook, New York. �IDENTIFICATION OF SEISMIC REFRACTORS IN THE LAKE SUPERIOR SYNCLINE H. C. Halls(1) and G. F. west(l) P-wave velocities at hydrostatic pressures of up to 2 kilobars have been measured in Keweenawan volcanic and sandstone cores collected from numerous localities around Lake Superior. Seismic refraction surveys seem to indicate as many as four refractors within the upper 15 Km. of the crust beneath the lake. An attempt here is made to identify the refractors in terms of Keweenawan geology by comparing the velocities obtained in the laboratory and the field. Some implications of these results on the regional structural picture will be presented. Geophysics Laboratory, Department of Physics; University of Toronto; Toronto, Ontario. �K-Ar HORNBLENDE AGES FOR GRANITES AND GNEISSES AND K-Ar AGES FOR DIKES IN MINNESOTA Gilbert N. HanSon(l) A number of investigators have shown that hornblerides retain radiogenic argon during metamorphism to a greater extent than do the micas. As a comparison with K-Ar and Rb-Sr ages for biotite and other ages, such as zircon U-Pb, K-Ar ages have been determined on hornblende concentrates from six igneous and metamorphic rocks in Minnesota. Hornblende from the Giants Range Granite near Ely gives an average K-Ar age of 2.6 by, from the Saganaga Granite an average age of 2.65 by, from the Knife Lake schist near Birch Lake an age of 2.65 by, from the Rockville Porphyritic Granite at Rockville an age of 1.80 by, from the Morton Quartz Monzonite Gneiss at Morton an average age of 2.6 by, and from the hornblende-pyroxene gneiss at Granite Falls an age of 2. 75 by. In each case the hornblende age is essentially the same or older than the biotite ages and essentially the same or younger than the zircon U-Pb ages. Mineral and whole-rock K-Ar ages indicate that besides the late Keweenawan mafic intrusions at about 1.1 by there are two more periods of mafic intrusion in Minnesota at 1.6-1.8 by and at about 2.1 by. (1) Department of Earth and Space Sciences, State University of New York; Stony Brook, New York. 15 �HYDROCARBON COMPOUNDS IN IGNEOUS ROCKS E. Wm. Heinrich(1) Solid uraniferous hydrocarbon compounds in igneous and hydrothermal rocks have long been known (1868) from Swedish (granite—gneiss, iron-ore skarns, pegmatites, veins), Canadian (pegmatites), and Australian occurrences (Cu lodes). In 1928 Ellsworth applied 'thucholite' (Th, U, C, H, 0-lite) to radioactive hydrocarbon in pegmatites in Ontario and Quebec. Since then other occurrences of thucholite have been noted in veins and lodes, including Boliden, Sweden; Goldfields, Saskatchewan; Port Arthur and Blind River, Ontario; Laxey, Isle of Man; Witwatersrand, South Africa; and Front Range, Colorado. Non-radioactive hydrocarbons in such deposits, being less conspicuous, have not been recorded as frequently. Among these are solid bitumen and methane in the Keweenawan Cubearing basalts of northern Michigan. Until recently all such material was reported only from calc-alkalic igneous rocks (granite to basalt) and their derivative dikes, veins and lodes. In the late 1950's organic compounds (solid and gaseous) were discovered in alkalic rocks of the Kola Peninsula, U.S.S.R. In the Khibina and Lovozero massifs large quantities of hydrocarbon gases occur in intergranuler pores, microfractures and vacuoles in minerals. They are composed of 70-90% hydrocarbons and 3-10% hydrogen with some CO2 and CO. Among the hydrocarbons methane predominates; also present are ethane, propane, commonly isobutane, rarely pentane. Volumes up to 243 cm3/kg have been obtained. In Colorado carbonatites and related thorium veins in the Wet Mountain district (Fremont and Custer Counties) and in the Iron Hill district (Gunnison County) have long been known to emit fetid gas when broken. Our studies on the Goldie carbonatite show this gas is a mixture of C5 and C6 hydrocarbons along with F2, HF and F20. The fluorine has been derived from the radioactive structural degradation of fluorite, and the noisome odor comes from the fluorinated hydrocarbons. Several genetic theories have been applied to the origin of thucholites: 1) radioactive polymerization of natural gas or petroleum; 2) interaction of uraninite and aqueous solutions containing organic materials (oil—water emulsion); 3) derivation from humic coal constituents. Whatever the process, there is evidence that this carbon at one time was biogenic-sedimentary. For gaseous (Continued next page) (l) Department of Geology and Mineralogy, The University of Michigan; Ann Arbor, Michigan. �and solid hydrocarbons of alkalic rocks and carbonatites the evidence is strong that these compounds are primary and rnagmatlc or hydrothermal and that the carbon is juvenile: 1. They occur in primary vacuoles formed and filled at the time of crystallization of such host rock-forming species as nepheline. 2. The ratios of individual hydrocarbon compounds are specific for a particular mineral. 3. Wall rocks of the complexes contain anomalously high amounts of methane for about 100 meters from the contact. 4. No geologically realistic models can be constructed that show that sedimentary natural gas or petroleum could have reached the alkalic rocks. 5. The 12C /13C ratio of gases and bitumens from alkalic rocks differs markedly from those of sedimentary gases and petroleum. �A STUDY OF CLASTICS IN THE NEGATJNEE IRON FORMATION OF MICHIGAN RobertW. Henny(l) An investigation was conducted on the relationships between a number of clastic lens-shaped bodies and a portion of the Negaunee Iron Formation. The principal study area was located at the abandoned Moore Mine in the Cascade Range, a downfaulted block on the southern flank of the Marquette Synclinorium, approximately 12 miles south of Negaunee, Michigan. Here the iron formation is continuously exposed in cross—sectional profile along its strike for a distance of 0.3 mile (360 feet wide.) More than forty clastic lenses ranging from a foot to over a hundred feet in length and up to fifty feet in width were mapped in detail. The depositional relationships between the lenses and the iron formation are varied; the majority of lenses are essentially conformable with the iron formation. Some of the conformable lenses are gradational at their lateral boundaries, some exhibit miniaturized on-lap off-lap features, while others have merely warped the underlying layers of iron formation. The unconformable lenses are of two types, channel fills and isolated blocks. The iron formation contains a two percent background of rounded sand grains which are equally dispersed among the chert and hematite layers. This percentage of sand grains is observed to increase noticeably when a clastic lens is approached from beneath. The clastics consist of metamorphized mixtures of rounded and angular fragments of chert, hematite, quartz, quartzite and granite, together with varying quantities of sand all in a matrix consisting of varying proportions of , chert and hematite. Petrographic and binocular analyses were used to divide the clastics into five lithological groups and a number of sub-groups on the basis of their mineralogical and textural characteristics. It is deemed significant that only one lithology is found in a given lens and that a particular lithology always maintains the same depositional relationship with the iron formation. A method for chemically disaggregating some of the clastics was developed enabling roundness, sphericity, and size distribution analyses to be made. Results showed the sand grains to be similar to those found in typical beach washed sands. Using the above relationships, mechanisms of deposition are postulated for each lens type. The analysis is then extended to several other clastic zones in the immediate vicinity with areal correlations made. (Continued next page) Department of Geology, Michigan State University; East Lansing, Michigan. �9 Conclusions would support a shallow water environment of deposition where chert and hematite were deposited in alternating layers under proper environmental conditions. The major source of clastics was derived from a low lying land mass to the south. Except for one occurrence all the clastics observed appeared to have been well worked sediments prior to their transportation into the basin. Re-worked beach sands were regularly supplied to the basin while occasionally off—shore currents created lenses and beds of sands out into the basin. The dispersion of these sands appears to have been a normal condition in the area since they are observed throughout the area. During intervals when portions of the basin were above wave base or even above water level, clastics were introduced to the basin by stream transport. Finally at a few localized areas large masses of clastics were rapidly deposited via slides and/or turbidity currents. �20 KEWEENAWAN VOLCANIC ROCKS NEAR IRONWOOD, MICHIGAN * harold A. HubbardW Two sequences of Keweenawan volcanic rocks are present in the Ironwood area, Michigan, west of the 90th meridian. A younger sequence, about 15,000 feet thick, is equivalent to the Portage Lake Lava Series of Keweenaw Point. An older sequence of traps of the South Range, about 8,000 feet thick, is separated stratigraphically from the younger rocks by more than 7,000 feet of sedimentary rocks. These volcanic rocks have previously been described as one continuous sequence. The equivalents of the Portage Lake may be traced to outcrops of the Portage Lake Lava Series on Keweenaw Point by a continuous broad band of large linear magnetic anomalies. Their lithologic continuity is also confirmed by the presence of many ophitic basalts and volcanic conglomerates in both areas. The upper flows of the South Range contain groundmass feldspars that are uniformly more sodic, and generally finer grained, than the Portage Lake flows. A few of the upper South Range flows are porphyritic, having feldspar phenocrysts as much as 1-1/2 inches across. The lowermost South Range flows are interbedded with a few well-sorted lower Keweenawan-type sandstones. West of Bessemer, the lowest flow is a 'pillow" lava whose emplacement locally contorted the upper few inches of the underlying even-bedded sandstone layer. These features indicate that the lower Keweenawan sandstones in the South Range traps probably are an uninterrupted sequence. Re-examination of regional relationships may show that the oldest volcanic rocks in some localities should be assigned to the lower Keweenawan or that the middle Keweenawan should be sub-divided. Although no consolidated rocks are exposed in the 2-mile-wide belt between the uppermost South Range extrusive rock and the lowermost Portage Lake flow, the belt is characterized by uniformly small magnetic anomalies that differ in character from those of the South Range and Portage Lake volcanic sequences. These unexposed units (Continued next page) * Publication authorized by the Director, U. S. Geological Survey. Work done in cooperation with the Geological Survey Division of the Michigan Department of Conservation. 1 U. S. Geological Survey; Washington, D. C. �21 are probably sedimentary rocks or acid volcanic rocks. East of the Ironwood area, the band of linear magnetic anomalies associated with the South Range traps diverges from that of the Portage Lake. Kenneth Books of the U. S. Geological Survey has found that the paleomagnetic field directions of the Portage Lake Lava Series near Ironwood are similar to those of the lavas of Keweenaw Point, and that the paleomagnetic field directions of the South Range traps are distinctly different. The paleomagnetic properties of the rocks within each sequence are internally consistent. For these reasons a significant age difference between the sequences Is indicated. �22 GRAVITY ANOMALIES OVER LAKE SUPERIOR AND SURROUNDING AREA AND THEIR STRUCTURAL IMPLICATIONS M. j. s. inries(1) and A. K. Goodacre(l) During 1963 and 1964 the Dominion Observatory carried out reconnaissance underwater gravity measurements in Lake Superior, and regional gravity surveys over the adjacent Canadian Shield in Ontario. These surveys outlined large areas of relatively positive Bouguer anomalies in Lake Superior and in a zone extending 600 km north from Chapleau through Kapuskasing to Moosonee on James Bay. The anomalous areas reflect large quantities of basic material that have been emplaced high within the crustal column, perhaps through process of crustal rifting. Geological and geophysical mapping by provincial and federal government departments has defined a north to north-east. trending zone of shearing and faulting with associated linear magnetic anomalies. This fault zone, and the gravity and magnetic anomaly belts cut directly across regional trends of early Precambrian rocks. Uplifted blocks of high-grade metamorphic rocks, minor basic and ultrabasic intrusions, and the presence of alkaline intrusive complexes together with the disappearance of the Archaean volcanic-sedimentary rocks along the axis of the gravity high suggest that the Kapuskasing fault zone may be a deeplyeroded counterpart of an East African rift valley. Gravity and magnetic anomaly patterns over the Michigan Basin suggest a possible extension of this structure to the south. Dominion Observatory, Department of Energy, Mines, and Resources; Ottawa, Ontario. �23 SOME PROPERTIES OF MICHIGAN CHERTS Allan M. Johnson(l) and Albert P. Ruotsala(1) Michigan Pleistocene gravel deposits contain some aggregate types that fail under freeze-thaw and other severe conditions. Cherts, of the variety associated with carbonate rocks, comprise a large percentage of the non—durable aggregate. The major minerals comprising cherts, in highly variable proportions, are quartz, calcite, and dolomite. X-ray diffraction patterns exhibited peaks attributable to clay minerals and possibly some unstable hydrated calcium silicates. Textures of the minerals comprising cherts also vary considerably. Petrographic studies of quartz showed that sizes varied from coarse sand to cryptocrystalline varieties. An X-ray line broadening technique indicated an average grain size of 700 angstroms for cryptocrystalline quartz. Water vapor adsorption values were variable and apparently reflected the available surface area. Cation-exchange capacities of Michigan cherts were found to be low and on the order of those exhibited by kaolinite (3 to 15 meq/100 gm). Evidently these two phenomena are related. Dissolution rates of calcium and magnesium from cherts were also variable and may be useful in predicting the durability of chert under freeze-thaw conditions. Department of Geology and Geological Engineering, Michigan Technological University; Houghton, Michigan. �24 REFRACTION SEISIvIIC SURVEYS ON ThE MID-CONTINENT GRAVITY ANOMALY IN MINNESOTA AND WISCONSIN S. h. JohnsonO) and P. R. Farnham0Steep gravity and magnetic gradients over the prominent Midcontinent gravity anomaly suggest major fauling of Middle Keweenawan basic igneous rocks which are thought to underlie Upper Keweenawan red clastics into southeastern Minnesota. Seventy short (4-8 miles) refraction profiles were taken at regular intervals perpendicular to the anomaly trend. Results indicate a vertical displacement of at least 7000 feet along the southward projection of the Douglas fault into eastern Minnesota and a similar vertical displacement along the projection of the Lake Owen fault in western Wisconsin. The resulting horst structure is bounded on both sides by thick wedges of presumably Upper Keweeriawan red clastics. No clastics appear to overlie the horst except in possible graben structures within the western part of the horst itself. The presence of thick wedges of sedimentary material on both sides of the horst as suggested by gravity data is confirmed. Underlying the red clastics in the flanking sedimentary troughs appear to be Keweenawan basic extrusive igneous rocks close to the fault and older Precambrian crystalline basement at a greater distance from it. In southeastern Minnesota, the basement is overlairi by up to 4000 feet or more of Keweenawan red clastic sandstones and Paleozoic sediments. Department of Geology and Geophysics, University of Minnesota; Minneapolis, Minnesota. �EVIDENCi ON THE PHYSICAL ENVIRONMENT OF IRON-FORMATION DEPOSITION Gene L. LaBerge(1) Physical features, such as size, shape, and character of the grains, bedding characteristics, and sedimentary textures and structures indicate that iron-formations may have behaved essentially as particulate sediments at the time of deposition. Granule—bearing iron—formations have a grain size and a variety of sedimentary features remarkably similar to those of sandstones. Non-granular (even-bedded or "banded") iron-formations have a grain size and bedding characteristics similar in many respects to siltstones or argillites. There are, in fact, a number of important similarities between iron-formations and clastic limestones which will be pointed out. Microscopic features in granule bearing iron-formations suggest that many granules have been formed by reworking of earlier formed silt size particles--perhaps from a non-granualr iron deposit. In other words, it appears that most iron-formations, particularly the chert in them, may have been initially deposited as silt size particles. The factors controlling the size of these "original(?)" silt size particles is problematical; however, it is possible that their size may have been organically controlled. Physical conditions, such as depth of water, current action, and wave action would have been paramount in determining whether the resulting deposit was thinly laminated silt size particles or more massively bedded and of sand size grains. If this hypothesis is correct, the nature of observable physical features should provide impoartant clues regarding the depositional environment--both physical and chemical--in which iron-formations formed. Department of Geology, Wisconsin State University; Oshkosh, Wisconsin. �26 CHARACTERISTICS OF MAGNETIC DATA OVER MAJOR SUBDIVISIONS OF THE PRECAMBRIAN SHIELD A. S. MacLaren(l) and Brian CharbonneauU) Airborne magnetic data when correlated with regional geology indicate major dislocations at contacts of subdivisions of the Canadian Precambrian Shield. These are described between the Superior and Churchill provinces in Manitoba, between the Grenyule and Superior provinces south of Sudbury and east of Chibougamau in Quebec. An internal disruption of the crust in the Superior province is described and contrasted with the 'fronts between the Churchill and Superior provinces and between the Grenville and Superior provinces. It is concluded that airborne magnetic data is useful in the delineation of major rift zones and sub-provinces in Precambrian Shield areas. Geological Survey of Canada; Ottawa, Ontario. �SUBDIVISIONS OF THE NEGAUNEE IRON FORMATION SECTIONS 7, 8, T47N, R26W, 1v1ICHIGAN Joseph j. wiancusoU) and Jack W. Avery(2) Accurate stratigraphic correlations within the Negaunee Iron Formation have been difficult previously because of the apparent mineralogical and textural uniformity present coupled with the lack of persistant marker horizons. However, recent work on the unoxidized and related oxidized iron formation of sections 7 & 8 T47N, R26W has made it possible to subdivide the Negaunee Iron Formation into 8 members based on mineralogy, texture, and metallurgical analyses. The subdivisions, which vary in thickness from less than 50' to over 300', were originally distinguished for economic reasons, but have been clarified, refined and extended to include several marker horizons which can be traced laterally for more than a mile. Members were picked to include layers which could be recognized and traced through the unoxidized iron formation and its oxidized equivalents. (All of the hematite and goothite that has been noted is secondary after magnetite, siderite, or iron silicate.) Because of stratigraphic work the structure of the northeastern portion of the Marquette Range has been greatly clarified. The extreme apparent thickening of the iron formation and the apparent complex system of diabase sills can be successfully explained by repetition due to a series of east-west and north-west trending fault systems. The correlations can be traced very generally south through the Bellevue and Empire sections of Cleveland Cliffs but more detailed work must be done in order to delineate fades changes and thickness changes in the individual members. (1) Department of Geology, Bowling Green University; Bowling Green, Ohio. Jones & Laughlin Steel Corporation; Negaunee, Michigan. �RELATIONShIP BETWEEN SEISMIC AND AEROMAG NETIC SURVEYS, EASTERN LAKE SUPERIOR R. p• ivleyerW and L. Ocoia(1) In the course of seismic work along the 1963 east-west Main Line a fault has been found in about the position predicted from Seismic evidence rests princiaeromagnetic data (Hinze, et al) pally on the redundancy of data provided by three remote-controlled tape recording buoys moored northeast of Keweenaw Point combined with data taken by the University of Toronto at Otter Cove, Ontario, . in 1963 (Steinhart) References: Hinze, W. J., N. W. O'l-Iara, J. W. Trow, and G. B. Secor, "Aeromagnetic Studies of Eastern Lake Superior," Geophysical Monograph No. 10, 1966. Steinhart, John S., "Lake Superior Seismic Experiment: Shots and Travel Times, J. Geophys. Res., Vol 69, No. 24, 1964. (I) Department of Geology and Geophysics, The University of Wisconsin; Madison, Wisconsin. 2B �MINERALOGY AND PETROLOGY OF THE MINERAL LAKE INTRUSION, NORTHWESTERN WISCONSIN James F. Olmsted(l) The Mineral Lake Intrusion is a 4500 meter thick tabular body which has been emplaced near the base of the Middle Keweenawan volcanic series of northwestern Wisconsin. It is a moderately well differentiated strataform intrusive consisting of: ultrabasics 1%, anorthosltic olivine gabbro 11%, cjabbroic anorthosite and anorthosite 73%, ferrodiorite 8% and granitic rocks 7%. A basal chill zone has been located and its iron rich composition indicates that it is not representative of the whole intrusive but is the product of the differentiation. A pronounced primary laminar arrangement of piagioclase laths is developed parallel to the base of the intrusion, suggesting the direction of flow during emplacement, but with rare exception, compositional layering is absent. Cryptic zoning of the mineral constituants has been determined with compositions varying from the base upward as follows: Clinopyroxene (Wo39, En42, Fs19) to (Wa36, En28, Fs36), Orthopyroxene (En70, Fs30) ton42, Fs58), Olivine (Fo65, Fa35) to (Fo22, Fa78) and Plagioclase (An60) to (An20). Plagioclase composition is constant from just above the basal chill zone nearly to the base of the ferrodiorite, suggesting the plagioclase was in contact with a large volume of liquid. Olivine is confined to the lower anorthositic olivine gabbro and the ferrodiorite. that during crystallization The trend of fractionation toward enrichment in iron and decrease in silica is similar to that of most large basic intrusions in which crystallization took place under low P0 conditions. This is confirmed by the strongly reduced state o2f iron throughout much of the intrusion. The highly anorthositic composition is explained by early crystallization of large amounts of mafic minerals which tended to settle in the magma body during its upward transport, while the lower density, more tabular plagioclase crystals were carried upward and concentrated at higher levels. The iron rich chill zone further indicates that considerable amounts of magnesian mafic minerals were removed from the magma before it reached the present level of exposure. (Continued next page) (1) College of Arts and Sciences, State University of New York; Plattsburgh, New York. �30 The strong orientation of the plagioclase laths and lack of compositional banding supports the view that any movement of the magma was in one direction (parallel to the base and upward along its tilted surface) rather than in the form of convection currents. This hypothesis is further supported by the presence of small volumes of ultrabasic rocks near the base and gradual upward decrease in mafic content until the anorthositic composition is obtained. �31 OXYGEN ISOTOPIC EVIDENCE OF METAMORPHISM IN TEE BIWABIC IRON-FORMATION, MINNESOTA E. C. Perry, Jr.0) and J. W. Morse(1) Oxygen isotope fractionation between coexisting quartz and magnetite (expressed as 1000 1nM) has been measured in samples collected along the easternmost 60 miles of the Biwabic Iron-formation outcrop belt. Fractionation varies from about 7 .5 (corresponding to about 7000 C) at the Duluth Gabbro Complex contact to a maximum value of 24. 3 (which probably corresponds to a temperature of (ioo° C). The metamorphic aureole produced by the Duluth Gabbro Complex is narrow and isotope fractionation measured between Auroa and Keewatin is constant within 1.5 units. Minnesota Geological Survey, The University of Minnesota; Minneapolis, Minnesota. �3 GEOLOGY OF PART OF ThE EAST GOGEBIC IRON RANGE, MICHIGAN * William C. prinz(1) Recent work in and near T. 47 N., R 44W. in the East Gogebic iron range essentially substantiates the mapping reported by R. C. Allen and L. P. Barrett in 1915, with a few noteworthy exceptions. Apparent thickening of the Ironwood Iron—Formation is now attributed to repetition of beds by strike faults; and the so-called "great graywacke-slate member" of the Ironwood is probably the Palms Quartzite brought up along these faults. Mafic volcanic breccia or agglomerate, tuff, and greenstone in the eastern part of the township are interbedded with rocks equivalent to either the upper part of the Ironwood IronFormation or the Tyler Slate. These strata are overlain unconformably by the Copps Formation of Allen and Barrett (1915). Large sills of mafic igneous rock that cut the Ironwood Iron-Formation have been metamorphosed, and one of them is truncated by Keweenawan basalt flows; they are therefore older than the Keweenawan. The unconformity at the base of the Copps still is recognized as one of great magnitude, but no evidence has been found to indicate that granite was emplaced during the post—Ironwood, pre-Copps interval. In this area, t.h Pr.que Isle Granite is a mixture of granite gneiss, and schist of early rather than middle Precambrian age. Rocks formerly described as "metamorphic phases" of the Palms Quartzite adjacent to the granite are mainly lower Precambrian gneiss. The close proximity of iron-formation and gneiss in the southeastern part of the township and the local absence of the Palms Quartzite are explained by faulting. The geologic structure of the Animikie Series is complex in the eastern part of T. 47 N., R. 44W. and the western part of T. 47 N., R. 43 W. To the west the period of major deformation of these rocks postdated the Keweenawan basalt flows, whereas to the east it was pre-Keweenawan. * Work done in cooperation with the Geological Survey Division, Michigan Department of Conservation. (1) U. S. Geological Survey; Beltsville, Maryland. �33 STRUCTURE AND STRATIGRAPhY, INCLUDING PRECAMBRIAN TILLITE, IN EASTERN DEAD RIVER BASIN, MARQUETTE COUNTY, MICHIGAN * Willard P. PuffettW The Dead River Basin in Marquette County, Michigan is a northwest-trending lowland floored by metasedimentary rocks of middle Precambrian age. Lower Precambrian rocks bound this basin in the Negaunee 7 1/2' quadrangle; they include layered amphibolite and massive greenstone of the Mona Schist on the north border and granodiorite and syenite on the east and south. Sheared metavolcanic rocks, mainly rhyolitic tuff, extend into the central part of the basin from the east, separating rnetasedimentary rocks on the south from those on the north. The metasedimentary rocks in the southern part of the basin include thin ferruginous graywacke, a thin iron-formation, and a thick sequence of slate, in part pyritic and carbonaceous. These strata are correlated with the Michigamme Slate. , The metasedimentary rocks underlying the north flank of the basin are markedly different from those on the south, and include coarse conglomerate as much as several hundred feet thick, conglomeratic graywacke, and chioritic graywacke and slate. A few contorted thin beds of pinkish-gray arkose are interbedded in the slates. These north-flanking rocks are probably in the basal part of the Arilmikie Series and are much older than the metasedimentary rocks underlying the southern part of the basin, which have been downfaulted for hundreds to thousands of feet along a zone of shearing now occupied by the metavolcanic rocks. Of particular interest in the northern group of strata are widely scattered rounded to subangular boulders of granitic rocks in the slates and graywackes. These boulders range in size from a few inches to nearly two feet in diameter. In some areas only one or two boulders are present in exposures of several hundred square feet of slates and graywackes; in other areas the boulders form lenses or beds that can be traced for several tens of feet. The anomalous occurrence of the very coarse material in the slates and graywackes is a significant and identifying feature of rocks that are considered tiflites in other Precambrian terranes, and a glacial origin is suggested for the metasedimentary rocks north of Dead River in the Negaunee 7 1/2' quadrangle. * Publication authorized by the Director, U. S. Geological Survey. Work done in cooperation with the Geological Survey Division of the Michigan Conservation Department. (1) U. S. Geological Survey; Marquette, Michigan. �34 COPPER MINERALIZATION IN ANIMIKIE SEDIMENTS OF THE EASTERN MARQUETTE RANGE, MICHIGAN R. C. Reed Early exploration in Kona dolomite of Middle Precambrian age copper mineralization at three locations in the eastern Marquette iron range. Veins of copper minerals were also encountered in iron formation in a mine at Ishpeming, Michigan. This is one of two areas of significant copper in Animikie sediments known to the writer. exposed The eastern-most mineralization is located in the NE 1/4 NW 1/4 section 1, T. 47 N., R. 25W. Chalcocite occurs in a tan, highlysheared siliceous slate, in veins and irregular masses, occasionally replacing pyrite. It is closely associated with quartz, chlorite, sericite and minor dolomite. At depth, some native copper is also found in red quartzite, occupying fractures and interstitially replacing quartz boundaries. Chalcopyrite replaced by ixior bornite is found approximately 4500 feet to the west in the NW 1/4 SE 1/4 section 2 of the same township. It occurs in veins, pods and coarse clastic bands in gray and tan slate. This mineralization, also, is associated with quartz, dolomite, chlorite and sericite. On the north limb of the syncline, near Enchantment Lake, copper was exposed by a test pit in the SW 1/4 NE 1/4 section 32, T. 48 N., R 25 W. Chalcopyrite, bornite, chalcocite are present in siliceous dolomite and vein quartz. Specular hematite and pyrite also occur. Veins of copper mineralization were exposed by development in the Cliffs Shaft iron mine in section 13, T. 47 N. , R 27 W. The veins cut the upper part of the Negaunee iron formation approximately 725 feet below the surface. The dominant mineral is bornite followed by chalcopyrite, pyrite and hematite. Bornite replaces chalcopyrite and is in turn penetrated by specular hematite. Most of the pyrite occurs as somewhat spherical masses of crystals enclosed in quartz. Spectographic analysis of ore samples from the Kona formation show the mineralized rock to be practically devoid of trace elements. Some titanium and manganese exist and barium and strontium were found in the eastern-most mineralized area. (Continued next page) (1) Geological Survey Division, Michigan Department of Conservation; Lansing, Michigan. �35 It is concluded that this mineralization most nearly approximates copper sulphides with some native metal found within and surrounding intrusives in the Keweenawan of Michigan. Similar mineralization has been reported within and adjacent to Keweenawan diabase intruding Animikie sediments in Minnesota. �3: AN AEROMAGNETIC SURVEY OF LAKE HURON G. B. ecor(1), w. j. HinzeW, N. W. OIHaraU) arid J. W. TrowW A regional aeromagnetic survey was conducted to determine the basement geology and tectonics of Lake Huron. During this survey approximately 6100 miles of flight lines spaced at six mile intervals were recorded with a digital recording proton precession magnetometer. The analysis of the aeromagnetic data combined with known geology suggests the following interpretation. The gneiss-amphibolite assemblage of Grenville age found in the northwestern portion of the Parry Sound District extends under Georgian Bay to the eastern shore of the Bruce Peninsula. A granite gneiss province underlies the Bruce Peninsula and continues southward toward Lake St. Clair. A discontinuous belt of positive magnetic anomalies extends from the Thumb of Michigan northeasterly to Killarney, Ontario. These anomalies originate from basic rocks, perhaps amphibolite such as are encountered elsewhere in the Grenville Province. The western portion of Lake Huron is divided into four major magnetic provinces with approximately east-west boundaries. The northern province coincides with the Penokean Fold Belt. The province immediately to the south in the vicinity of the North Channel is predominately granitic. This province lies adjacent to a basic igneous complex which extends south to Rogers City, Michigan. The province south of Rogers City and north of Alpena, Michigan has tentatively been correlated with an extension of the Animikie lithologies from the Northern Peninsula of Michigan. The Grenville Front trends southwesterly from the vicinity of Killarney, Ontario, through the eastern end of Manitoulin Island and continues southward to the northern tip of the Thumb of Michigan. (U Department of Geology, Michigan State University; East Lansing, Michigan. �37 HEAT FLOW IN LAKE SUPERIOR JohnS. SteinhartW, s. R. Hart(l), and T. J. Smith(1) The Lake Superior region is of particular interest to heat flow studies because of its location on-trend with the mid-continent gravity high and its situation on a crust which reaches anomalous thickness (>55 km). During summer 1966, 92 heat flow stations were occupied from the U. S. Coast Guard cutter Woodrush, concentrated chiefly in the central and western areas of the lake. Using oceanic sediment probe techniques, 75 of these stations achieved sediment penetrations (5-7 meters) such that corrections for the annual temperature cycle of the bottom water are rather small (0%). Uncorrectec heat flow values for these stations range from 0.43 — l.24J cal/cm —sec, and delineate two distinct regions: a belt along the western shore characterized by low values (0 . 4 0 and a central region of higher but very uniform values (1 .0 - 1. 2). The twenty measurements in this central region, covering an area of 5000 km2, show a mean deviation of less than 5%, and the average value for the region agrees within 10% with adjacent land borehole measurements reported by Roy and Birch. Values in the eastern lake are too scattered to establish a pattern but suggest at least a small region of lower values (0.7 — 0.8), with variations of up to 0.4 occurring in lateral distances of 15 km. A general correlation seems to exist between crustal structure and heat flow in the Lake Superior region. — The new data on the mean annual bottom water temperature of Lake Superior, considered with the data already in hand, supports the hypothesis that mean annual bottom temperature of temperate lakes is independent of climatic differences. This means that the heat flow measured in such lakes is not affected by small long term temperature fluctuations, provided the lake stays in the temperate class. U) Department of Terrestrial Magnetism, Carnegie Institution of Washington; Washington, D. C. . 9) �39 A SPECTROCHEMICAL METHOD FOR DIFFERENTIATING BETWEEN CARBONATE AND SILICATE FACIES Thomas waggoner(1) A spectrochemical method of differentiating a predominantly magnetite-chert-carbonate fades from a magnetite-chert-silicate facies has been developed and successfully applied to the primary magnetite—chert deposits of the Negaunee Iron Formation. Interpretation of the spectrochemical data depends on the distribution of the elements: magnesium, manganese, aluminum and iron. Manganese ions substitute readily for cations in the iron carbonates and only to a very minor extent in the iron silicates; the amount of manganese present can be used to approximate the quantity of carbonate present. A plot of manganese values versus magnesium values shows a trend of both elements which indicate higher concentrations of carbonate and possibly silicate. The Mn substitution is controlled by ion availability. To evaluate the amount of silicate present when both Mg and Mn values are high, a plot of magnesium values versus aluminum is considered. Aluminum occurs exclusively in the iron silicates which are products of a similar chemical environment to those of carbonates and magnetite. The comparative analysis becomes vague when detrital feldspar contributes to the aluminum values. High iron values in conjunction with low Mn and Mg values may show the presence of iron oxides, but caution must be exercised in accepting the apparent analysis due to the variable iron substitution of both the carbonate and silicates. Similarly, low Mg and Mn values with lower Fe show a predominence of chert. Indications are that the actual silica and phosphorous values do not help evaluate the fades types. Silica cannot be used to correlate facies types due to its erratic occurrence which is governed by stability fields not sufficiently clear at the time of the present study. Phosphorous has little value in making an accurate correlation due to its dependence on a pH condition and not on the other elements or their stability fields. (Continued next page) The Cleveland-Cliffs Iron Company; Ishpeming, Michigan. �:3 A practical use for determining a carbonate facies from a silicate facies is in ore separation and blending. Silicate ore is twice as hard as carbonate ore so that metallurgical difficulties are apparent. To predetermine the type fades, the spectrochemical method could be utilized, when standardized, for given types of carbonate—silicate ore. �41 TEXTURES AND COMPOSITIONS OF SILICATE AND SULFIDE ORE MINERALS FROM MINERALIZED ZONE, DULUTH GABBRO COMPLEX P. W. Weiblen(1) and Henry HaIIU) Mineralized gabbro samples from International Nickel Company's test pit on Spruce Road, near the South Kawishiwi River, Lake County, Minnesota, have been studied by microscopic and electron microprobe methods, as a first step in an investigation of the textures and compoitions of the mineralized rocks of the Duluth Gabbro Complex. The predominant rock type is a troctolite containing 10-20 percent olivine (Fa50), 50—70 percent plagioclase (zoned An50_65), 15—30 percent pyroxene (En35Fs20Wo45 and En61Fs36Wo3), 5—10 percent sulfide, 5-10 percent iron oxides, and minor biotite. Plagioclase and olivine occur as cumulate minerals; other phases are interstitial. Grab samples range in modal composition from anorthosite to troctolite having as much as 50 percent olivine. Silicate grains range in size from a few millimeters to several centimeters. The sulfide minerals have three textural modes of occurrence: 1) Interstitial, associated with or enclosed in interstitial pyroxene. Myrmekitic intergrowth with late stage interstitial pyroxene and plagioclase. 3) Fine—grained inclusions in silicates. The textures suggest that the sulfide minerals formed from an immiscible sulfide melt in a silicate melt in which gravity settling was the dominant rock-forming process. 2) Chalcopyrite, cubanite, pentlandite, hexaçonal and monoclinic pyrrhotite, and sparse sphalerite are the sulfide phases. Chalcopyrite and cubanite are intergrown; pentiandite forms separate grains, commonly euhedral, fractured, and enclosed in chalcopyrite or pyrrhotite. Sphalerite occurs as inclusions. Compositions of chalcopyrite, cubanite, pentlandite, and pyrrhotite are approximately stoichiometric within the error of electron microprobe analyses (1-5 percent). Department of Geology and Geophysics, University of Minnesota; Minneapolis, Minnesota �12 PROGRESS OF GEOPHYSICAL STUDIES IN LAKE SUPERIOR Richard J. Vold(1) Since 1964 the University of Wisconsin has been conducting an underwater gravity survey of Lake Superior and has occupied a total of 759 gravity stations. Since 1965 it has also been conducting a sub—bottom profiling survey, obtaining over 2300 miles of profiles. The results of the studies through 1965 were reported at the 1966 meeting of the Institute on Lake Superior Geology. Last seasons gravity efforts were concentrated east of 860 / longitude and west of 88° W longitude. The Isle Royale fault can be traced eastward to at least 88° W longitude. Between Isle Royale and the Keweenaw Peninsula a gravity low seems to reflect the synclinal structure. East of 86° V'J longitude a rel.ative gravity high indicates that the Keweenawan basic volcanics pass eastward through Michipicoten Island and turns south off Cape Gargantua. The gravity high continues its trend south just touching Mamainse Pt. where the gravity expression of the volcanic s disappears. The sub-bottom profiling appears to have penetrated to bedrock (upper Keweenawan or Lower Cambrian sandstone) in most areas. A few sub-bottom valleys were found, notably the deep trough just south of Beaver Bay, Minnesota which contains over 1000 feet of sediments. In the area between Isle Royale and the north shore up to 750 feet of sedimenLs were penetrated. Most of the deep north-south topographic features in eastern Lake Superior are filled with about 400 feet of sediments. A north-south profile in the center of a valley at 85°l6'VV longitude showed several deep gouges or eastwest sub—bottom valleys, with the largest being over 10 miles wide with over 600 feet of sediments. Department of Geology and Geophysics, University of Vvisconsin; Madison, Wisconsin. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1967 Description An account of the resource Institute on Lake Superior Geology. Michigan State University, East Lansing, Michigan. May 1-2, 1967. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1967 Contributor An entity responsible for making contributions to the resource Elso S. Barghoorn Sambhudas Chaudhury Gunter Faure John A. Colwell John D. Corbett William J. Hinze George B. Secor Forrest L. Dowling Crawford E. Fritts Jacob E. Gair S.S. Goldich H.C. Halls G.F. West Gilbert N. Hanson E. Wm. Heinrich Robert W. Henny Harold A. Hubbard M.J.S. Innes A.K. Goodacre Allan M. Johnson Albert P. Ruotsala S.H. Johnson P.R. Farnham Gene L. LaBerge A.S. MacLaren Brian Charbonneau Joseph J. Mancuso Jack W. Avery R.P. Meyer L. Ocola James F. Olmsted E.C. Perry Jr. J.W. Morse William C. Prinz Willard P. Puffett R.C. Reed N.W. O'Hara J.W. Trow John S. Steinhart S.R. Hart T.J. Smith Thomas Waggoner P.W. Weiblen Henry Hall Richard J. Wold Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/294356dd6f6accae5a2df2b677204335.pdf e09761aa4bca8a891f0732d5bf36e316 PDF Text Text SPONSORED BY DEPARTMENT OF GEOLOGY, WISCONSIN STATE UNIVERSITY, SUPERIOR AND MINNESOTA GEOLOGICAL SURVEY MAY 5.6.7, 968 0 R �VCHNICAL SFSSIONS 43STRACPS For 14TH ANNUAL INSTITUTE ON IAK]F SUPERIOR GDDLOGY Held On Campus Of UISCOUSIN &TATE UNIVERSITY, SiJp4COi, VJLiCONSIN HcCASKILL HALL May 6—7, 1968 PECRNIC;'.L S3SION CHAIRMAN A. B. DICKAS �14th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY McCASKILL HALL WISCONSIN STATE UNIVERSITY SUPERIOR, WISCONSIN May 6-7, 1968 BOARD OF DIRECTORS - INSTITUTE ON LAKE SUPERIOR GEOLOGY P. K. Sims, Minnesota Geological Survey, Minneapolis, Minnesota A. K. Sneigrove, Michigan Technological University, Houghton, Michigan VI. J. Hinze, Michigan State University, East Lansing, Michigan D. H. Hase, University of Iowa, Iowa City, Iowa A. B. Dickas, Wisconsin State University, Superior, Wisconsin SECRARY-TREASURER1 INSTITUTE ON LAKE SUPERIOR GEOLOGY D. H. Hase, Department of Geology The University of Iowa, Iowa City, 52240 LOCAL CO4ITTJii1 TECHNICAL SESSIONS CO)41T1'EE A. B. Dickas (Chairman) P. C. Tychsen J. P. Mengel VI. LUnking R. Johnson FIELD TRIP COMMITTEE B. Bonnicheen and W. C. Phinney (Co—Leaders) The field trip conducted in connection with the Institute was held in the Duluth Complex area of Ely, Minnesota on Sunday, May 5th, 1968. This Minnesota Geological. Survey, trip was hosted by the P. K. Sims, Director. Extra field trip guides are available. 2 �fr—' PROGRAM Ito 14th Annual 2!I11SUPERIOR GEOLOGY :: c.c.i: ait:. E?iIIc; •ç•j ON k.KE INSTITUTE MoCaskill . C EIJI0IJ .;L Auditorium •%c3j.rct IJ State 2L*5( CToi. 2JH6 Wisconsin University Superior, Wisconsin HC:t* May 5, 1968 Sunday1 :yç p.m. 8:00 — 10:30 = &1L2 .I1i'Y.:U1 2oCco Smoker 2JJ0 and Advanced Registration b6._1k0L1&rJ. E00. ILTY). Union Hiawatha Room, Student Monday, May 6, 1968 (t) cL: 7:45 a.m. rcCLI ]t)T21 = :2t-kt19 Hall Registration — Lobby, ?McCaskill 8:30 a.m. EL1I?JPJ.: SESSION I TECHNICAL C:AwC, 1. 1., / -t1/ 0i4iT11 Auditorium 3, 2::R. . 1:0L4*1):;mM C. Iverson and L. Bleifuss Co—chairmen: .1elcome McCaskill1. • . . r: t&I70 Meyer, President c&t00t0 coo- o1:: c't.1cVlisconsin State University, Superior Karl tJ. I'::i :2a :t: oo&:ofc*Iron hCv Formations .1L50Minnesota rI Trace Elements in Henry Lepp 1 t)- t'-:.: t\,1 " 2A --th Eemnts in the Duluth Gabbro \7 1/ :—' '(—' Larry A. Haskin and Barton Denechaud Geophysical Study of ):iS-Vi Lake 3j::r:2L.C3: Superior 7:&i4:32I CJH 3. I 00: :4 Richard J. VJold ->3CC 2 L-L. [c* Mo V. .o Keweenawan 3fl&k:3t :t The Paleomagnetism of Middle 4. . 5, 2 iç3J.yiA Units Volcanic H. C. Palmer ¼-e ;>fr;ec51 Rb—Sr Ages of Intrusions Along the c230fQ(cJ) .0o& I 00:1 Keweenawan Fault in Northern Michigan Sambhudas Chaudhuri, •I•.. G. Faure and Douglas G. Brookins ?I An Investigation -.0:0 Velocity, 0: '1 of — the Vertical 3 -2 Density and Porosity Distribution in the I&0:1120ThJ>l. Sandstone, I :.62{3C?),Houghton I Thoil County, 1110:11:9 Jacobsville Michigan Lloyal 11: 0. Bacon, R. W. Ingalls 010> 0:Q :3 >9-2:3 0310 and J. F. Stafford .3: A — Gravity . -1ILI1i &3g>:o: Survey0:2. of a cIIHoo:o Portion of the 701010t03I If-I 0 1c.Greenstone .c ;o8\o--co3Belt 9J. inC Northeastern FUn flon 10000: Saskatchewan YC0c!0:Sfli ( 0LI Cc)Th;20 6. 7. .-, LfzccTo:1 1Gendwi11 Donald 8. ¶29 — 12:30 C- C,X> p.m. L—-: .. IL 211 The Penokean the -90> and 0: Hudsonian Orogeriies in if 3: .o>f the flco t:r:) Io.oo241 Great Lakes Region, 1001I))102and coolthe 02 Age of ')'0-sSi>s.:0:t: Front .6:3993 Grenville 9. Church c1 William R. 1- Luncheon jOn Hiawatha >j,6'- 32 Room, Student Union 1 2 1 I 3 �1:30 :'. : T•p.m. McCaskill TECHNICAL SESSION II - t,1A1gi Co—chairmen: ILO 1. A 2. LfrII1t23!2A1iiA21f Auditorium R. W. 014 Marsden 4AA_21and OAA$G. <C L. LaBerge I1 $t fAiA0C 51A 1L3hr UAOKYAI Framework Stratigraphic and Structural of the L Vermilion District and Adjacent Areas, NorthtLl_ 41L !l4113flA eastern Minnesota Ufll lk1 Paul K. Sims, G. B. Morey, A P. W, Ojakangas and W. L. Griffin of Volcanism, Sedimentation, and Stratigraphy S< I j41 the Western Vermilion District, Northeastern Minnesota 1 Richard W. Ojakangas and G. B, Morey Geology of the Duluth( Complex in the Perent Lake and Kawishiwi Lake Quadrangles, Lake and Cook County, Minnesota .CIV2Th Jr. rk:.1C Donald iI M. Davidson, ofr Rocks of ) Possible Coutchiching ILC An Investigation C Age, Walberg Creek Area, St. Louis County, Minnesota ] A, I S. Viswanathan and Paul K. Sims h 11 1 > Iron i < of the Biwabik A Formation, Metamorphism Dunka River Area, Minnesota t LL< Bill Bonnichsen Differentiation Sequence of the Great Lakes Ijlj < I' Nickel Intrusion C'; t3-<-,-AIT '.,Ai<<CX- -and '7 Reeve N. D ( MacRae I 5, - J. j< 1 Lakes Nickel b?rL_' Assemblages of the Great Sulfide Intrusion R Mainwaring Paul B, A LL1 1 of a Selected A At Lake Superior: Area of Study Progress Report 1) P. C. Brown, oseph W. Horton, C I Davidson, A. B. Dickas, D. W. 4Lt'70 Afl4and dt1< W, Lunking P. ¶4 K. JAfl21)eiJ Roubal C ci -H :1At -ts {AL1J IjI 2 '< 1-. 3. 2 I — 1 k. 5. 6. l C c I <l-t 11 I 11 JL< r - . 5c 2 1_ 7. 14 8. ¼ — 111 r< L ANNUAL BANQUET 6:30 p.m. 13ij'7< 771 II C427Ic Sky Lounge, Student Center Address: S1CS44CLU1 1<17. t(ACA32iA.t LjJ;2 F0JLA2tiA/C2"Recent Lunar Exploration Results" McCauley Dr. John F. USGS Branch of Astrogeology J 2< C54'71171 4 , Itrizona �Tuesday, Nay 7, 1968 — I 8:+O (jI3I a.m. 73 7 TECHNICAL 117ELJ7: SESSION III — 37CC The Federal—Provincial -1i7*Z :7fl 41 i7 7I3 Committee on Huronian Stratigraphy LbL1 —— Progress Report James A. Robertson, K. D. Card and M. J. Frarey 1, 71: 1 — 2. j ik; Stratigraphic Relationships of Some Keweenawan 3 43 111itC Wisconsin and Rocks of Michigan L3L LI — — A. Hubbard Distribution Patterns of 3" Harold 7 3. +. Auditorium I3kii4t115i371 J. W. 1&! and P.c E. Giblin C[ Trow Co-chairmen: 1. McCaskill LtJ C- EI Post-glacial Sediments in Lake Superior William R. Farrarid Bottom Palynological Study :0CiLL: of Post—glacial :.cT.7i3jj La35J Sediments from Deep-Water Localities viT 43:(y;,!i73 ;tc13;CC2> in tx: Lake Superior William S. Benninghoff and Ij' L(I Judith M. Franklin I 1i" _ Through New Light on ci ThC Animikie Algal LC4L Structures C; t Darkfield Illumination W. W. Moorhouse Origin for Three Precambrian Possible Glacial r 4icr o3 (Huronian) Conglomerates, North 1h Shore of Lake Huron 'X J y;c . k 5. I cr flL- 3I R jlfl\ I CC 6. L 1) G. Features of the Bloomer Moraine, Ice—stagnation 3 8. Northwest 13; Wisconsin Robert F. cLt€3HCCJC C! Black Y(T!; The (i Seaman Method of Mineral Identification as Used at i; Lake ?P7 Superior State College 1 - C C. 12:20 p.m. 0 C M. Young and F. W. Chandler 7. Ernest 34xa Kemp T:?:ciiç Luncheon Hiawatha Room, Student Union b 1-' �1:15 p.m. Business Meeting — McCaekill Chairman: Paul K. Sims 1:30 p.m. T:cHtiTc.L SESSION IV — McCaskifl Auditorium Co-chairmen: 1. 2. Auditorium 0. Durfee and H. H. Vloodard Current Investigations of Meteorite Impact Structures in the Canadian Shield Michael IL Deuce and Nicholas N. Short Petrographic Evidence for a Meteorite Impact Origin of the Sudbury Structure, Ontario 3. Bevan 74. French Progress of Geologic Investigation of the }4ellen Granite, Ashland County, Ylisconsin Michael 4. 5. M. Katzman Varieties of flows tu the North Shore Volcanic Gr'oup, Minnesota John C. Green Structure and Significance of Intrusive Sandstone I)fles of the Siamo Slate of the Marquette trough, Upper Peninsula, Michigan 6. 7. 8. C. McA. Powell the Sedimentology of the Middle Precambrian Thomson Formation 0. B. t4orey and P.W. Ojakangaa The Sequence of Geological Events in the Marquette Iron Range During the Penokean Orogenic/Metamorphic Cycle Larry L. Babcock Cbert Bed Characteristics in the Lake Superior It-on Formations Joseph T. Mengel 6 �r AUTHORS BLACK, R. :a F. Technological University CC2C3lJWv Michigan Technological University LT&FH1 TT<TflfC 1*LTSTTlTT University of Michigan University 7-7fflT-rJcj LY12;Y-; ofL)Wisconsin, Madison BONNICHSEN, B. Minnesota BROOKINS, C:"•[ G. 3VTifl,L D. Vc Kansas Michigan BABCOCK, L. L. CCCI BACON, L. OI' 0. C: BENNINGHOFF, L:;$TlIJ:,:S-&T W. C S. C BROWN, (: kl Geological Survey State IT University LU:I.k:LCCl1ç Wisconsin State C'ILT R. C. 3 jTrTr:T University, T1LII t.CC CL4 Superior K. CARD, CI: D. :II-rtCCC> Ontario Department of Mines 1C © CHANDLER, F. Cj W. C, University of Western Ontario CHAUDHUPI, S. Kansas State ::T University L3ITTT CHURCH, W. R. University of TI Western Ontario (IT.ITir- dcCJ DAVIDSON, D. M. 1JT'I CC(Cj[ JR. C 1 DAVIDSON, D. W. DENCE, Cc;J,:.zIc[ N. CIC,[ R. C DENECHAUD, B. C rt1:tiç University of Minnesota, Duluth q(rcp' lIT: Tt Wisconsin State University, ick&inTLiJt Superior 15!j[tflrf Ijt7 s: : Dominion -II(:II 1V1% Observatory 1tUJcLici (Ontario) University of Wisconsin, Madison C DICKAS, A. B. FARPAND, C R. II1C :,:mCrCcI W. Wisconsin T1LR5OCC State University, Superior University of Michigan i :IT FAURE, G. Ohio State .JL—I University JL FRANKLIN, J. N. Oakland (Michigan) Community College C - N. C J. Geological Survey of Canada FRENCH, B. N. C Goddard riçIirsC:C-i Space Flight Center GENDZWILL, D. Saskatchewan Research Council YtVJ FRAPEY, C cInt :rtc43c iIIi tE©) GREEN,II J. C. University of Minnesota, Duluth X?H [;!•• GRIFFIN, W. L. Minnesota Geological Survey HASKIN, L. il.:l'TI, CU7 A. University of C!E Wisconsin, Madison HORTON, J. V W. Wisconsin State 4i4j University, Superior HUBBARD, ,TVaVfV H. 'V Cpr A. U. cc S. Geological Survey INGALLS, r I:TA[ liT R. W. Michiganir Technological University }C4L2J; KATZMAN, N. CIJt M. Michigan State University KEMP, C. B. Lake LEPP, H. CI Macalester College C±T1rJiCd LUNKING, W. Wisconsin State University, Superior — I: I C MACRAE, 'C fl72 14t1 J:iJ1t©J 9LZ *ii Superior 4fl% 2•CL CY9 N. D. C' NAINWARING, P. R. --[in State College 4i:T-.rt. University of Western Ontario -rCn:; L2tI :rc University of ';c Western Ontario C: (continued on next page) 5C r'CJCCj 7 �:ircftC c1fi AUTHORS (continued) MENGEL, J. T. Ii"3 Wisconsin State University, Superior cccrciik cck:tc? MCORHOTJSE, 'J (H •Vi. University of Toronto MOREY, G. B. Minnesota V!. OJAKANGAS, R • vi,. H. C. PALMER, PO!ELL, C. McA. REEVE, E. J. i. 4-r cf i-c Geological Survey Minnesota, cc ccUcDuluth i:inic Lyrniz; ctofMJ University 19'yI Ontario ç Western University of fckh1icctc University •ccc Northwestern University of Wisconsin, Wkecc•ccccfcc? Milwaukee I7cc'&Lt7f c•L •cicyic. iccp cct, ci ROBERTSON, J. A. Ontario Departlilent of Mines ROUBAL, jc.) R. Wisconsin State University, Superior SHORT, N. M. Goddard Space Flight Center 3IL, p, Pr Minnesota !c. cc-ca Geological iccc ct ci•. Survey SIMS, ::. H.. STAFFORD, J. F. icc: 1icc'c L : !fci: •ccit3 cic-.ai University Michigan flkc. Technological VISVJANATHAN, S. 2_ccccpc &c 7cL:;Nf of •- Minnesota, University .L Minneapolis ILi IiR. J. hOLD, University rci&c of ct Wisconsin, i cc.cLc: Milwaukee Uc. YOUNG, G. M, ci c:&-:cT! University of Western•:.ci.ccc.c Ontario ci . 8 I �4UJ :'''rC-mr FORMATIONS TRACE 0*01hiflI1 ELEMENTS 4710137100 IN rIl MINNESOTA IRON :0171 1' 0011 1.0011 Chairman Henry Lepp, 7jj rjc:c .14Lr: Department of Geology J.E-1437 'oc4;r': 12 Macalester College 0101 St. Paul, rJ-. Minn. C p -;, investigation of minor This is a progress report on a continuing 101171 oo0110o0.crO10o -cccooo. 00c4t1IK7ii-JiLr' oI.OLo'o1J•O=rOoii01 PA' 30 The elements cobalt, nickel, elements in Minnesota 011Cr Ci iron 1oca formations. r:4r'-I:?CIcCJLl)1i 047 00'AcCii'O'SIY. •-l03ci rOOT GSC_r171i71i1c in composite samples of the C and gallium were determined CC ci A1 7iwabik iron 00 11C jl 3_ 01 3 7c-r material from the formation, the Tromxnald formation, and of oxidized A COOL K00110V Ic 1rl01Ci©7 APT 01I001 :r01J magnetite, iron Biwabik formation. LCJ.!,. flIC-0' 'CS! Samples 1vi.:CH'C of CE© <701 silicate (grunerite), ICI5fOACAO formation also were chert, and dolomite separated from the Biwabik Cc 11:1=101 71O0r ICc ::.iOJCflO rC4J 000101101001017 011IC- 414 14 çCiC% analyzed. of the Cobalt and gallium 0110000 0111140 were determined at IC- the 010 fl'fl laboratories 0j00-J:c1;0A'r21I'o, t0 A composite analysis. II General Atomic Corporation by neutron activation IC 010 01 C- 11 ; cobalt and i6 sample of the — CI Biwabik iron formation showed7 9.51 p.p.m. 101 Composites of Oxidized Biwabik formation gave gallium. p.p.m. I3 L thesimilar 0 0 )r North A composite sample of the Trommald formation from results. IfIAo1 The cobalt and 27 p.p.m. gallium. Cuyuna district C_ showed 36 p.p.m. CV S p.p.m. South Cuyuna district 5_L composite showed 25 p.p.m. cobalt and 01P 57 1L00 the Biwabik Analyses of minerals separated from specimens of gallium. 00 P[} TP344. AvIlTPc; 04 c'p''o'fc1Iy CCJ.ICi240.j014' formation show cobalt to range from 1.7 p.p.m. in chert to 10.1 p.p.fli. 00 'c_I oIl cL17'C7 000 :H'vLso 14 zo1 and for Gallium values for chert are 1.8 p.p.m. in iron silicates. ii010 A&oic00C 7'[i7-7 GOCV 01A 4771 c,-C7'ir iron silicate, 1C51Ji 3: 18 OP p.p.m. CV)L3[ Icr time of Nickel is colorimatrically at the 010 being ciCV IthJ determined 00P101 000. ciCLo7. OLA OIXPA01017C7 070101 A ;01A010074 7C1 and Preliminary results this writing replicate analyses are being run. :1001 •ycA. pcr.o acoI 40010 oi, ;P19 0000010 op 5coTt XCC PcICP;c highest indicate that A "C1correlate :2,:r cobalt. The CVCJJ. VIp. nickel :1çJ:.s to eO7 ci&r2 with j1i( .$'c0.2 000.0, seems nickel values were found in samples of the Trommald formation. 11 Very little is available in the published literature on trace -c CCI Moreover, as pointed out elements Cr iron 501 in '(07 formations r.•cCVY5: COA 70:CV<7:A LTL:A c0-2\tc?uyA0/ or 200 ironstones. viewed with caution bi by James (1966) the available analyses must be 5 L4 II 0 7 samples by because OA00Vt0 marked differences have been reported • for JdJ the 3j1 samepublished CcT7 Oi .:1'AJ 10,J001 11AOTJ; :1CV_ comparison with the few different hYCA9SJ laboratories. The k0 even O1LC 'JOCV t00AA A.yi; :c001 the realiza— values that are available, therefore, must be viewed t7C.Th 1) 'CA7i2.! CAACC7 L0 r%i;Ts with and the - analytical tion çF' that '7'3 the variation in values due to the analyst variation. p? method may be as great greater thanthat between sample &C& or 9J00 .1OJ 7Y13J2. 7WA i±Ii1 corroborate the The results of this investigation to date seem to JO Ic; 1J 0. AcOJ0 AY0IA OJC ¶3 rocks in that A work of Landergren (1948) on trace elements s5_A1r in iron richformations are the abundances in these AZii trace :AA element €'yyl7f:"4..V5E14/L: C.i77ij 0j", iron V:t,:710. Precambrian There low eJ'77 .0i[ when compared 1fi;3CVC tot similar CCCAAi values in younger A1yAC. ironstones. 7acciC0A0.0Af in the Cuyuna appears toA; be a general increase in trace elements CVAV 1 5:AAiC c4yt. basin. district which AJt represents the deeper A*WA part ofA the depositions.]L 11.4 001=1 c c:4oo :0,31 0 01' ]t : - S L — . 01.'I't4 L — L — L J4 11 e17' C4J C I 17 C VOOR CO ic _v 01 7.01 'I r0: r :;ri r r7 1 I l L C 1 — — iiiN jCj Ak 7ij C 1 0J2,0 cffiCI c'j-acc iJiAA i.3c ri:i0Ct; 0 I c . — [Ii 3 0 1, 01 I :T C3 'L23A ti : jc.ijYjo e3:J 5CJ sedimentary rocks: James, H. 1966, Chemistry of 73: the iron—rich f:CT :k•2A IEi L., CVI: 7iiq 1 U. S. Geol. Surv., Prof. paper 440..-w, 60 mi p. Swedish iron ores Landergren, Sture, 'Pc:1. 1948, On the geochemistry of and associated C.)tL4fli17 rocks: Sueriges A&IA&J)Lt Geol. u][3f Under., Arsbok 42, No. 5, Ser. C, JN. 496, 3TL p. 9lT 182 ocic- 9 �II JICC1 f1iil./j GABBRO :!TJ;1 THE DULUTH RARE-EARTH ElEMENTS IN Wis., Madison jpCZP:tIiO of •i:1 CCIlI5Pk !5!i of :sssL:s1cS Chemistry, University Larry Haskin, Department Ci' CU j_ University of us., Madison CI ±L' Department of Chemistry, jBarton Denechaud, -I_ ç — I, I 1 Rock samples been analyzed for (C U __ from the Duluth complex have S 'UI 1t the gabbros Like most of — [1 I rare earths by a neutron activation method. —S and diabases investigated from other locations, the DuluthI gabbros C' p I and lower ratios IC_CC rIE haveS significantly lower total rare—earth contents CI _51C Variations in rare— 5_C C of light heavy rare earths than basalts. C SiC_I to C for Duluth samples CC I _ I s will earth abundances with rock typeC and location 'C Thsi be discussed. C — C U — ij 1 — I C : I C CE — C I L E 1 — C — — — I ' 1 1 I 10 to C U —— J �01 COP}tk8 J. STUDY S' 'ilfl Of GEOPUYSICL Richard J. SP •3tP12r:F L:Jc SUPL'11110P Jld, .ssistant Professor ;.nran! ??75s30r v;c cZS-iof r.Geology 'fl?t' Derartr.ient tept of'4'l Jisconsin c:.:ir4n ttnnz'&Lty of University Milwaukee II 'sa,kee 1964 tic theDtn'.truitj University isconsin has been;omLL:.xqc conducting tf of bIroawi.z !uu bee-i Since U54 32t".Upof yr Lake Iak Superior and has occupied an underwater gravity survey SC '*wista'tW' gçVjt1;j7 The 'uL,otity majority La3:o and bays. test, lake ntztz.o'u sfl over 1600 gravity in the ga'c.t 'w stations nn .iâCiO grid with closer ??:'•; a1Zc of tiu' the vtcttcc€ stations an are located .cc.ccd on w a.a five mile çnA of & FH The survey with L & tiXVit7was as conducted &Wu.ota vatS spacing V. in t.Di) some T*8V. areas. 'The £S.CJS provided by pXCV.dt1 underwater ra%isatecE gravimeters saO and the positioning was L0PC Service Corporation. Sct.s:'iot *r' a; octr;ie't .crt tVSd te :.ôtt' fO'G 3: .i is tc . rat 9et tiL sPJ! ?' aeromagnetic vaflcy 4ata ;h aazamag!t;aX The gravity dataart1rttssn analyzed .n in c's¼rbSutt conjunctionii with Tba. western .z. the kb cce.;e'iI part data f%Q13G5 suggest two major5tXCCflt?'Ui structural features t3 flOS' 3.ar'a:*J in ru..Grc t north—south One of taati.zee;is1.ca aridge rI 1 running of the lake. Cnr tV the features :ie .4C'..s. The second major feature is a ridge xajvz' Xsahzn in the i2ta vicinity of 91 0O'. extending southwestward from Isle iloyale. r;ut! f 33 j)'LI. 2ne ni.c•. exii"c sstv'ec:i*'itü "r C.e Roa&.e. s a rt:g* tt 9ot n' 4:y north 1'st rcct.S Both gravity and magnetics indicate a ffalor major?&V...t fault just 1v4 aM n&gieti (!.'%tC: Superior Shoal. sat c? of Isle :r,'... Hoyalee trending to Ta'i the area of tkvsriot en'tw.erd ¾o trst5'ns eastward 3 PrefltIjtc from frcb Isle St. ..nother fault noted a' in rhe the r*urntscss magnetics trending ;...t .otec There Th.ozt gravity. Ignace tc. to Isle Royale :.e is .J.sc also confirmed by the eonfi wod b:' tt.. Rr.c.c..e fault extending is no ot4r.c*evidence in the gravity for the postulated Pc_tze'da from Superior Shoal to the Keweenaw Peninsula. t:oa r! Itile ,.isctne tt v. tbe rs, ;it ftc the poatu is ,ttpnthr ihos.t 4.t tn hti'j-..4 ,h. nk'rtt ibl.l: C at *cute p'.tl.L$t.A o'kthe ths basis btiai of an Most of postulatedb7 by EiVLs Hinze on MN.L ci the Itte faults supported by the 'e Ztut:tEC by tas aeromagnetic survey in Lake Superior are Li'.eastern crtcnt tat 3vp:w.t..r the The two rae strongest positive anomalies in gravity Et2Vi-5 'ttc CI5C4t7 survey. Ft.&y wLt.''.magnetic €L?4 r. highs. They eastern..&t part the Lake correspond with Ot9ttfl: GZofV4,c ap-uoa\ tc&cid Michipicoten Island. fltk ss occur around Stitc&Ar" Standard Rock and tpo;thq:tt northwest of 141 *30W orovr auce ctrr',sb ;n&ti'r Cnrd!$t fl ttt j,.i1e anaec' .jM'n r nØ Een rafl flr tn lot r.4taiLe. cc4 Ic eet. 1vs Bt:p.x!.oi ecnt s'igpcrt tie 4.;t'iLTh 2 th3t t! itLc £VL,'Ct ty!fleflne cs.; *rctt:t tAa E'.nrst. ecLty field ix. etstn ta The gravity field in eastern Lake Superior does not show the :he strong anomalies seen in western Lake Superior except for the low i seems 9:.a'â to support the suggestion 'tG field $ttht,, The north Superior Shoal. ett :.t CofS%thcfltZ r.rts.Cs that the Lake Superior syncline curves around the Keweenaw Peninsula to the southeast. te tt U 11 �?±7LPALEOMAGNETISM Li±7JjII±i4±7I1±7±7V 4:jCj± KELENAWAN VOLCANIC UNITS OF V MIDDLE THE H. C. Palmer, Assistant Professor F4±7±7±7c 1±7±7hI&Ji of Geophysics 7±7±t±71777±7 Department .i22)±7c :LJj9±7:r:! I51111 'L Jty)I ±71 London, of Western Ontario, Ontario 7) The University J/ T1 i:\- l !C.± Middle Paleomagnetic results1±7ri from over 300 samples of ±7 7L1.±7 - ± Keweenawan volcanics and sills from the Lake Superior region ±7 ±7±7 ±71 The logan sills, the sections of volcanics —1 have been obtained. 9IW!±7J ±7x-J 4±71L!7! polarity. :1CJTC±±79±7C±7 L have reversed ';I.±7 volcanics at Alona Bay and -±7itt the Osler all positive CI Island 1I1J'7is1: of ± ±7i±t ![1±7 of 7!JIvolcanics t! The 1)±77 section on i.±7±7;. ±- Michipicoten I The North of Minnesota, the lavas at ;,( ±7Shore C _i±±_ volcanics polarity. :'— I±7T!C. both ±7.i±ic±7:L±7jL±7&rPoint 1776±7±7 have ±7±71±7 ±7 ±7±7 at Mamianse JJ±.±7(31 Gargantua Point and the section ;J.,±7±71 o reversed All ±711 sections ±7±7±7±7±71?:. p76L±±±±7.itp sequences. normal and reversed •C±Ve±e±7 polarity ±77. 77Vi, 500 N) 77±7±71±7±7±7 (mean 148 ±7: polarity ±1±7±71±7grouped J±77CC2 ±7:1±7 pole positions III C 77 yield±7 closely •7?±7JCI±7±7I7;±7C 77±7 .Lti !717±7 which are different from the pole positions calculated from sections of positive- ppolarity which are also closely grouped about a mean 340 The assymetry of normal and reversed r N N. position of 1770 VJ, ThI 1 but small 5_ directions of magnetization may be attributed to a very hard I t±7177 to all secondary component 77 ±7-7L ±7of magnetization which has been added 7V±71 I76pI ±77:597C.±!it :±7R±7.t eruption. these 7±7I7.LKe±7 Keweenawan rocks subsequent to 7± their 777:775±7 r' 1 ±!.\_ i: .77! — — ±7 L iC)±/! ±7±77 ±7±7 ±7±7±7±7 1 ±7 1 ±7 ±7 — 1 r ±7 — I I I I 12 I —II I ±7 — �4:1zINTRUSIONS .fJ2T1LLN4, JaL1V1 AGES ij4215 OF RB-SR 1115j0; THE 1UEENAVJAN . L. t4: NORTHERN t292fo1 MICHIGAN ALONG FAULT IN 'j :: S. 1; StCl115Univ., o'sLs. Manhattan Chaudhuri, Department Geology, Kansas State '>sjssLoosoiS of st Cso iL2gy ±E5S5c1T 4Jo2QcL tt5]f51551e 15']! o;'. 1150; r1 15J sssj; 1j15y55, IL' Geology, Ohio State University, Columbus G. Faure, :0;5istIS0;22t Department of L3!Jstl 0; I,50L577ci of Geology, Ott15r'S'EL D. G. :ESDOLI,o)bm Brookins, Department Kansas State Univ., Manhattan . n15'' .,i'i'I5 552151 50; 555Cr 4 In northern Michigan several bodies occur at' 1515 different 0515012: intrusive '124 21111572 the T0]5115 ?socL-:s &50;0;51 0.0ce.4'*2] 1152015 2 :1r:'ts15551 near y55 the Keweenawan locations fault. These bodies occur near 14 ioi;:15 11r2c51 Series', 5115,05.1 but their base &772''t!421 of the0;t25&12 Middle 1stoo;s..oss Keweenawan .15.011.51%. Portage Lake :155 Lava 1411:22(15 572'. not ls,7 clear. exact geologic age 575: and T05. mode of origin are ,-:-15107t, 51515 I 4555755 from 1515] tk.'s ¶515 felsite '5(1.' sS7&s 515, & 5-4 samples Rb—Sr •1•11)flI1 whole rock study of four the IS-tos' Bare £ initial I 0 Hills yields a least—sciuares isochron age of 934 ÷ 6 m.y. with 415 14 Sr (87/86) = 0.7166 + 0.0003. A similar study of the syenodiorite 5T 44:15 "1l.'Y'T41' 11455 Bohemiaarea 4. 25 4.5? m.y. with initial 6711. c15of :0 1130 JLi-.7' + of Shs' st' the Mount .41124714. yields age 6L5 an 5,7/42.1. •f1'j; Sr (87/86) Cst,;. 0.7045 ÷0; 0.001. — 11 2 415 4 705(4:3,470;' SICk?. of 7516 These 777517 suggest 444], .SCIat1/OSIs least 5547 two"i51ciLL17'7 distinct 7;14.j periods igneous 717047 data 55 53 4J 44.late J5 Precambrian I activity in Michigan during Sc time, an early syenodioritic 1 u.'h "S— S -0 5j and later felsitic These two intrusions also intrusion intrusion. c — 4 47. 1 PP 4 <Ott 51734121025 12(1< large 25 -•74) difference 551564.2515 641567]544.'0;:45 ]15tt:15.± 15 resulted from different 152-6<1145:41 magma sources as .indicated by the /3; 14 Sr (87/86) ratio. .J,1.117 :2, 151 in AS initial 1515is 15xss rs:',st soS •527,l:,-651250;LS SC 15 SC of 77<74 lsSICTS 71550;571454 Since both2osso.J1.oss: contemporaneity and consanguinity the Mount Bohemia 1' are 5511 the Middle Keweenawan syenodiorite and Portage Lake Lave Series 6 IF '1' /111462S7;< -' 7I-7fi7515172712 possible 5154'CL and J2.k71I117'S-1-09 plausible, the period of intrusion of'2 tOss the syenodiorite 7.14544. 71,71.54 57146 Bare cOllist '07 Later 45471447515 emplacement of the 5-'7475771570'7-jIj.' L57754 71155 4]s0;s the 27 1511705156754, 70 may date culuminatjon of1 extrusion. 7515 775115:7 '?-1T15(55.170 SIs 15 Hills felsite may have occurred at when the Keweenawan 272277' 7575< tss -550;:s'50;51] cl a10 time sedimentation was already o.lrs:e.J.;' s.in '57 progress. •C.152-Sis,< (F 13 — �'s7!•&:r ::r THE ¶11tT VERTICAL fIi AN INVESTIGATION OF fTI VELOCITY, DENSITY AND Tt ;_r rii ., Cr POROSITY DISTRIBUTION IN THE JACOBSVILLE SANDSTONE, HOUGHTON COUNTY, MICHIGAN Ifr4J)t! EI;j ti jkcIt JtII S iit 1ItlAtI University iL:c Professor Geophysics, Michigan Technological ©C of Y jI Michigan Tech. University u Applied Geophysics, P. W. Ingalls, Senior in WTILIttIt71 J. F. Stafford, Senior in Applied Geophysics, Michigan Tech. University &TIIt. L. 0. Bacon, :T t It ..jLI)IL c:cIn:aa M L)I:Ci t]'0 dttt laboratory ILCC1;It? study was made of the pulse velocity, density - and porosity on core samples taken at ten foot intervals from a 3628 foot -L diamond drillii hole in the Jacobaville sandstone near Rice Lake, Houghton I4izLCTh •LYFiLLY kt.i±tr County, Michigan. A A 9 1 — - jI"1 Calculations based on the data provides a vertical velocity func3 Z of 1200 feet and a velocity tion, V = 10,200 - 2.1+2 z to a depth, z, III z. The large velocity gradifunction to 3600 feet of V = 8100 + 1.90 IL these functions were extrapolated I_3 ent might cause considerable error if Cm to depths below 1200 feet and 3600 feet respectively; therefore use of r disconCl _( ç11 to the )_L-L first major velocity a constant velocity of 9000 ft/sec LIt I3jL3k.33c1 3bCLL3t I'Ck tI is recommended Ii 313 discontinuity C1:; bL! that b-C Cft/sec beyond tinuity of It:L 13000 C:: and CL iIt,7LCtL&ILCi l'Itt±ILHL -StibiL. It 3I/ULCftJ:ItL for IL)t useti LUL on all reflection seismic calculations. L ft 'I f- 'L i1 Ij U I iC L0 19 U j 3Ittt 5 area—2 -b3 reBacon's Li-b Application of the constant value functions to C of Rice Lake C C_ miles I flection data (1964) from a location 10 southwest CY feetCaand the C gives a thickness of formation of 10,000 3_the I Jacobsville IL discontinuity of approximately 2000 — major velocity depth first it to the U .3141 Cr3 feetCIt:IPiz.i in that area. & tt-ttIfl ItLIC CCII LCILCL L 11) CI1 Itl CbL;lLL[. .ciC;-' II.tolItthe uLcC CIt-A 111t1i-L H3 L3LP The average value of zi porosity 1200 foot depth is 14.2 per—_ 1200 feet the porosity Below -_ cent with aCItJT range of 10C to 17 percent. _C decreases to 3.5 percent at 3600 feet. The density of the Jacobsville L-II - cubic centimeter to the 1200 had an average L_ value of 2.25 grams per t A b C;C.lItC LLAt IC-411 bi-Ui- PIt foot depth and .i-3b/hC33313CLi a constant 2.55 grams per ftLL.C cubic centimeter below 1800 ' I3 fta ir.lli &jIts C: U It t- It feet. 11+ I It �;Hc(LJH: I5T GRESTONE A GRAVITY OF SASU'SCS PORTION5OF THY THE'1iJit FLIN FLON Z5J7HY :f £. 5: Lg:cSrS SURVEY ST. L IN *TLSLT BELT •HJNORTHEASTERN SASKATCHEWAN tT'iiLJ5i '.r•(i! r' iI D. Gendzwill, Assistant Research Officer t' , C-S Saskatchewan Research )C Council 2(c:1;Rm:. Saskatchewan Saskatoon, F itSc'.FC2. I iFiCX, A C'C5JLc) .Cf;.t' C1CC5t7 :LCj 5SPrecambrian C'ftS CC Amisk An 5HS interpretation of thetC2tCH B.ouguer gravity in the Lake—FUn Flon Area of northern Saskatchewan shows that the outcropping Sk Group of basic to acidic volcanics and clastic — Amiak sediments is limited with more or CC rocks (C in depth to a maximum of about 55 kilometers. Lighter !tL4ThJ(] JTCCC1TCflt less uniform CJi CC-CUCit5 density underlie (nCi.C:; tthe C ::tH Amisk 1 CCC.C Group. Granite and granodiorite r but are also Most - limited '5 E_,L 9_ic sequence rocks intrude the in depth. C volcanic TCC,Jr C)i1 t'C of density variations not5CTbCT persist to depths of more than 3 to 5 5 :ii S do 1ciCJ 5 the t• 5C t5 CtccL kilometers. h:cnw CCL .'t.S •.H_ Sj: 5ç j? — L 1 jiS 1Tht 5.&&tçCo J(flz:Fa çS C:C Densities;5C of 1585 rocki?.&1Ci samples were determined in thet5laboratory. -E ci-*CL-C 1TCCH1 Irii shows Analysis of the 4V1 ddensities ittS;'Yc that some basic volcanic rock units :i75Li(have 57 mean densities . C1LCi itC-;as. 2.66, IC have mean densities as low other C5H51C units as C F volcanic rocks due to variationsI high as 3.03. Gradations in density of 1.)( anomalies. u::CCc5. 111Cc (:sI. gravity H. metamorphic in JJH'LT grade or composition cause broad y ç 5 1C11C*- 11y1H•1C i:J1 the C:54 area iC Ct11CC1C S-Mt S Crustal seismic work in shows that P wave velocities of H Sj). .5 Ctct?;C, ç', with J152Hi exist to Sc depths 55c11( cS JC515SC? 6.0 to 6.15 km/sec ofJQ 10SJkmSt to km... Material t.:vzcF<such &C11SCrflt±mt5this:SC5?Sy i,55 velocity 11CC at -T1CtJL such depth C11Cc can tCcL€!LT/ only be 5si low density rock as grano— supports 11 diorite. This conclusion 2; i the gravity interpretation since St SC This low density both methods 5 indicate lighter material at depth. tTC@Amisk Sw&S tfr-t*hC rock might)e2;cc111ccL represent. older 1rocks on tC.:ctS which the Group 111111 was deposited 5 s'ScSSC CCfS.t5tmaterial 1LC ?iL& 1155 emplaced cc€C CCtMCLLICCtC5 or it could indicate an t.L,tLLI/ increased quantity of granitic 55 5t 1C1C ]ISLbf HiLl 5iv( at St depth. in the ccci. SC rocks 5511 Amisk 1 5 i'1 :c I 1 ' . -If; 15 -- L �I 'p 1lL THE PENOKEAN [JTV AND HUDSONIAN OROGENIES IN THE GREAT LAKES REX3ION, .jV1L HFLIL.1,_cFI._JI -:y' :THE GRENVILLE FRONT AND THE AGE OF 51 a 1- 1 i — - i Williai:i R. Church 11] Assistant£_Professor II. L Department of Geology-jUniversity of 1estern Ontario, I.1F?y/London -' i —-r----. ]k -— SI I p 1 1-. L I the Penokean orogeny define an [ --.--.;---- .-. during Huronian rocks deformed 1I —--..--- —--•-.---L--approximately east-west trending fold belt modified in the form ofI a fS 17 II as far large Z—shaped orocline, which extends from Minnesota to. Ontario _c nJ1 eastZ as the Grenville Front. The long held view that the folds in the Huronian of Ontario are coeval with r— those of the Penokean fold belt of — Lake Superior region is supported the by the correlation made by Young r the "Ani— (1966) of the Cobalt Group of Ontario with the — lower part of :L -T'4 This correlation is based on mikie Series" of Michigan. II ItTH iD the occurrence 2F1thI _ tillite, aluminosilicate— including exotic rock types of in both units H J1IIJ LI —Fl _-I 1 -H. bearing orthoquartzite, and banded ferruginous quartzite. _c- . i_1 — — I — I — — I L I S 1 1 1 I I I — — — 11 I I, F I F I I m I -if' , Nipissing diabase of- Ontario, which has a Rb—Sr age ofI -' isochron IE4-_ 2100 m.y. (Van Scbmus, 1965), was intruded after initiation __I — l(I - of Penokean the latter deformation (Church, 1965), andL it is therefore certain, if 4 1— of the Huronian and the major age is valid, that both the deposition Fj H - H L 7 - The Huronphase of£ Penokean deformation are older than Ca. 2100 m.y. I1 1I=, of the order of ian of Ontario is everywhere metamorphosed, and ages 2000 m.y. cited by Fairbairn, Pinson, andr Hurley (1966), and also I flLF and volcanics, Knight (1966), to represent the age of Huronian sediments ¶ I metamorphism. more probably minimum ages of the Penokean are — ? LIr I 1 ) — 11) F t; ji II F I — — F 1 a — L — a — -, — F a III rII- 1 — — I I I F F r I — I c:i:L of the Huronian of Ontario :c:. is irregularly developed Metamorphism Hg;. :%!L•f!(•1!2 sequence. both geographically and with reference to the Penokean fold I,margin of the southern H is most strongly It along the northern I z cLi developed c:t_ r1 LIt: from lower greenschist _ - _ -Th_ belt of folded Huronian, where it varies in grade _I L (Card, ) (chlorite) to lower almandine—amphibolite (staurolite) facies 1 ½k rLr J strongly Secondary diabase deformation is also 196Lf). :1!!\Z1: post—Nipissing 7Xr (: . r t:lnTTc ©cA-•? pre—dating the developed in this region, andV early Penokean structures 1 '_l : deformation. diabase are usually completely transposed by the later ii ;ft V-i -, weakly developed Towards the south the secondary deformation is more 7L — 1_'i, With respect to the second 'and large -, scale primary folds are prominent. L' -L pre—kineniatiC, phase of deformation, metamorphism in the north —1 was syn—kinematic whereas to metamorphism was both pre- or : the south the Y!L ]k::I! •I? :Ip.1cnL:i*xMT The relationship of the earlier metamorphism, and post—kinematic. 5_ 1_1(9 _ to the secondary during kyanite <-' j '17 which I \_,J was ,—- formed in orthoquartzites, I 1) 4_ Andalusite in quartzites, deformation is C not at present entirely L I clear. I_ the post-1dne— —— and biotite and garnet in pelites, were produced during r eT In Michigan, granites and associated pegmatic phase of metamorphism. iv be post—deformation and post—metamatites considered by James I T- R (1955) -:7 rr.: to and James, 1965). morphic have ages of ca. m.y. (Aldrich, Davis, r 1900 r the isotopic data of These ages being minimum ages they corroborate n r r - - I[ I1- & =I ' : I I I T i I j I I: a ) i cr -: I I J r i - I ii1J[ . — i EF L I ;' 11 — ia II I I I a LL/ I N j; r — 1 ::ii1( L j I I 1 I LLI I a 1 1 I a Il[. I ' TL' t E I a a &i- (continued on next page) ' I -r ] rS-13 — �I l that Fairbairn, ?L ThI Pinson andI Hurley (1966) and Knight (1966) in suggesting 1__ I the regional metamorphism of the is' related to fl Huronian 1C - the Penokean I1Th_[I) given an orogeny, rather than to the Hudsonian orogeny which is commonly -C T1 intrusive into age of Ca. 1750 m.y. _— However, granitee and the penatites the Huronian have both Rb-Sr T— of Ca. -j- ages 1D of Ontario j1 I '1—1 isochron I lj and Rb-Sr 1E 1967), 1750 m.y. (Wetherill, Davis and Tilton, 1960; Davis and others C — ICTI _9C The granites '—I described as Hudsonian. and- may therefore correctly be —L—I -C' post—date t1/fT; the jIiji second I7IF*c31 phase I3IjIj metaCIIIIV' of Penokean deformation and regional L Brooks morphism, but pre—date a late phase of brittle deformation. -j j IL Jk 1'—TJ[ p (1967), considers the pre—granite deformation and regional metamorphism I—IIT1,1 Iof the Huronian in the vicinity of the Front to coincide with — ILLI — -.1 Grenville the formation of the Front, from which it therefore follows that the I Grenville Front mustI be a Penokean feature. It is not jconceivable that it was also feature at the time of Huronian sedimentaL1 L 1 C_L a 1 significant 7 __ -positive T tion, the area east of the Front possibly being a region of Ifl 1 FDC—__ttThe late relief during early Huronian time T1_ (Young, 1968). I phase of post-granite brittle deformation, which is quite strongly developed I 1L) 1 along the northern margin of the southern belt of Huronian, may be L1J 9E' related to the post—granite cataclastic deformation commonly observed The cataclastic deformation, according to Brooks along the Front. T 7 \FI : (1967) deforms Keweenawan olivine—diabase dykes, and is therefore 2c&JIL7 probably Grenville in age. — — — 1 I 1 1 ( _- — 1 — — I — 1 L — 1111 1 1 1 _ I [ — I 1 — It I I I 1II(2'' — 1L 1j -S-I, r- 1 'rm I' I — I L _ L — I L — tt — r — T1 i L i 3 — — 1 I !MY — I i: i — 1 The length of time during which Phanerozoic orogenic eventsc takes i I C less. place is in general of the order of tens of millions of years or r -Gc -' 7 The age of the t)flI difference in OH[ CC7. éfL Penokean and ç.':r Hudsonian ;!7J. orogenies is of j:( the . L=' In terms of Phanerozoic geology therefore, the Peno— L— m.y. order of 350 L 1 during kean orogeny represents no more than a relatively minor episode f 3 2400 n.y. to 1700 m.y. a period of' crustal from 1T-' stability r extending L 7 I of Alternatively, the Penokean orogeny may represent the initial phase CF 2 — -r LTh Th Hudsonian the break down in crustal stability leading ILJ C 1,__t i—i— to the extensive _ of sediments in the _j cycle of &maatic activity. The general L -' _1% e I- absence age range 2100 would tend to Lb. support the latter possibility. .t. to c: 1700 m.y. ±: — L F i — ) I I —\ '' ç — Y — — 1 I : I ——- I ( — 4 (— i j r t1t; kY (continued on next page) 17 :":Pi! 1 r �REFERENCES i-r ct r -1i: 0 Ages of minerals Aldrich, L. T., Davis, G. L. and Jaries, H. L. 1965. from metamorphic and igneous rocks near Iron Mountain, Michigan. - oUr Jour. Petr. 6, 41+5_LF72. 7.0 7A. - c) _c) c . - % U L2b 1.ti:tL ç.-3-: L.tt oo]3o J-o; 3Ptthe 3c)p: 1--IJ3 J]01tIL.;. metamorphism along Grenville Front, Brooks, E. R. 1967. Multiple America., Bull. 78, =3== North of Georgian Bay, Ontario. Geol. Soc. LtP33PI, 1267—1280. L I : 3€ tioiffDistrict, gn:.-3.-t area, Sudbury -tJo- OA-.-t-.)t, Card, K. D. 196k. Metamorphism in the Agnew Lake 3;pj;, ?U,LrU1AUYUc)o 1011—1030. tUo-,2JL ?'PJ Geol. Soc. -'oUL. Am., Bull. 75, OU7J-TJO..T Ontario, 3iYtUtt.c)c) Canada. 23-3--t- -•4.tn UUc . 3ti0 Penokean .iorogeny in I)y:,j:Lp I0of the Ontario --4-Ninth 3t* c)iAiiiF, 3k,.R.3.°E1. status ç.)0 Church, W. 1966. The cç YU0td1?JUS 7i737Lakes $J 1P: --.itrpU Chicago, :.-34\,; p. 25. Conference onJO) Great Research 71cc z.o. -0 -.0---0-...'- S. P., rI31c-.7,,, Geochronology %ct.J_71)7L0Lc)' of 03001 Aldrich, .'._ 1967. .o—t.-v.0-.-, and L. T. Davis, G. L., Hart, 0 H. Abeli50*,0 I in P. the Grenvjlle .-. 379—386 d Province in Ontario, Canada., 71. .c) = .7. ). —.5 c. ,1._u. 10. .7!03r .:70J27. son, Ann. .oo-.cU. Pept. of the Geophysical Lab., Carnegie Inst 00 Y' of S0401t30'L4010' OTto Director 00 ..--çP ]1.o0O. Year Book 65, 'OO)-. 10. . - , - H. H., and Hurley, ::Uto,, 1U P.Y& M. 1966. Preliminary ?1 W., Pinson, W. L U° I M.I.T.—1381-lk. 3 whole—rock age of Huronian sediments, Ontario. V 0 :c7-U: 3.o, g--po-om,Ui.- Ann. Aiit0 Prog. Fourteenth Rept., =c00:.1sAU.S. U.c3-. Atom. Energ. Comm., 127-128. .o--Tt.0 Fairbairn, 3. U- c A I ' I 1= oc7 ?U.c'oUUookt 37; 1955. Upi the a7oUol '7 cc.. L. James, H. 31/5 ,_,i:03. Zones of regional metamorphism in Precambrian cU U of Northern Michigan. Geol. 3 L Soc. — America, Bull. 66, lk55—l'+88. -.- 7c S i0 oppc:,aA,tstudy '50'; of Knight, C. J. U 1966. n-;-: whole cUdo Tt-ccoU. Rb—Sr rock L30-A ages of "'.Cf0.'o-r. volcanics -iTton tY3 33 ,k..c1 M,I.T.-1381—11+. 137o-tk-, cPo-co the North Shore of ot' Lake .:3o £tpc';r Huron, Ontario, Canada. 30U32025 ir.022 IToP, 129—139. Fourteenth Ann. Prog, Lc)7-D' Atom. Tt.0.i'. Comm.,, o-ocA- Energ. dg71 Rept., U.S. Mines t[t3 'h2-Tt *20 70t0c0 Van Schmus, P. 1965. The geochronology of the Blind River --, Bruce 03:2 3:"o2Ttt' -d5H-oU'tt0t. .7• 00t:—:Lo.. Canada. area, Ontario, LLACO Geol. 73, 755—780. ..ou:t Jour. '100 &oio 030032=uct,OV.-c)measurements 3t .1. Wetherill, G. :U5AAJTtTt.cG. = L., .-., and Tilton, G. R. 3'3/1, 1960. Age 0; ii., Davis, i::=--5 Jour. I3& Ontario. Pc)C-.tioTLo,,7 dtTt 0233I2, 7.ooso on minerals from the Batholith, Ut.s Cutler -0'/ 5B20.:c3.,t t3571 Cutler, - Geoph. Pea. 6, 2k6l—2+66. )? ''10) Young, the McGregor Bay area, cOt0cc.*37'004.41-7of t 5c±cTt 0._c cG.37M. 1966. 'A2:.c Huronian stratigraphy Ontario:c:. relevance It c7-,0,,_. to -o4!the tr: LakeOTtTttAc..d0t the paleogeography Superior to 'o.L.o UooTh'.o:ococ7tOTU4O4t/ of region. I.TtJc: Canadian Jour. 203—210. Uor0 JTtjt,3' Earth Sci. 3, 0;A0Tt 3 J0C--0L0tc of ,oO Ontario. structures700c in Huronian 3d02-Tttttoioi rocks 0337220 Uo,r- oOoo'.-ottocAo —.- 1968. 3-:3e3 Sedimentary 0r.,';3&73c)7-)2)7) 10. Palaeogeog. PalaeocLjm, Palaeoec. k, 103 0- 125—153. tc=C-. 0t7)c 18 �5727,']P '.7 t.77S ATD 31111z1571 <2317. F'531-SiJllS[ 31i31 : STRUCTURAL 921 VEIILION '52525j7 5:; STRATIGRAPHIC FPANE!OPK :'71ja' CF THE !-,[7155721-<<'s A31[152.. 111 [±12112 :<15l7 It 3121 DISTRICT MD ADJACT ARFS, NORTHEASTEPJ MINNESOTA <1i['72I"3131s1,i21 3131701. Director, SJL,'31 c31-c-c P. K. Sims, 77 15217317:;1€, S'255'7:i52 55&51 Survey, Minnesota Geological Minneapolis, 31555"31 27- 1*ht 3131:317175531, Minn. 55<75<, 0,013 Minnesota 55n"Hçr - Survey -B. Morey, Geologist, Geological 552,''555j33131,, Department 72 21o5514515255551' of :31Geology, 431,o:525o University R. W. 575-&3152. Ojakangas,513.313553155555"; Assistant Professor, i]IiH"31:'<5<1t;' fJ ''- arid Minnesota of Minnesota, Duluth, Geological Survey J G. 7 5- W. 5. <Sc-? :1152, 1}s31<J5.5.31r<.'ss.. L. Griffin, Geologist, Minnesota 112311553152Geological 312'5'111721S1, Survey 1 ,31 311 1' 7< 1 551 ,< S,c.0'571?15517,. 11152 31 :5531-5-':, district, 155555131.5117 in '111' northern J'C3[31 311531:t7 The Vermilion St. Louis County, lies ,<.01055 between <311171313131 1155 7255*j 3155.315 H tgo. 731 Vermilion batholith the 315711 the ':721' 55553<21 on the north and Giants Range521215211 batholith 7:2-'. 'S4sr 52 5135255 21 on (1 /c I_ rocks "Ha It contains the dominantly l31[ mafic0 volcanic that '131k comprise 3<,, '7u55 Ely 1 - 571g'-Th55 I 3131;L55 rocks the Greenstone and- younger clastic have- been called the <11 that 5 <1 550 i31Ic - Lake 1< Knife Group. — I 255 <<a'.' Iron—formations of Keewatin0 'type, which include the 3113131 at 5251 several @31 )44f.1[ 7231c-t1 I3,.c.5557.55;!.:. positions Soudan, occur stratigraphic i'57131.'1F,15ç1331 5±131 Greenstone Ely in the ".1555 2135511 311H.:i,-sL\1 157 171r3 and in the overlying volcani—clastjc .5' '311"1L72155572 13.5531313<;. • 3131'ci 31 rocks. 31311s31 A "1031105555 variety 1555' of 5<71 porphyries 3*331111121 101 the I <- bedded rocks and "1 intruded in part 3131o are contemporaneous with them. 2 <55 1 <571 13 07LI1'017 131 .II55 All the bedded rocks are_57151 older than the intrusive rocks of the 7Vermilion jr_3'f.,.lo, Giants 311' -i4<< and Range batholiths, which have been dated as Algoman <.55550 (2,+OO— 1 1,55011' 31155,,311 2,750 rn.y.) in age 0by S. S. Goldich I __ I< and others. The Algoman intrusive 5. 55-1 2 31 r-refl<'--r" with 557<1 rocks in 255553117 2< the area aI'31syntectonic are to the±152metamorphism H'1' respect '3 5555315551. <113131 311 55717311331531.73131 and deformation of '.31 the ±3113 older 'oL',';' rocks. 1.5513.52 '<15131 10 the south, 31355 5231 'a — 5 < I-; 5 1 ' J '' 31 ' ) 55 31. 55 — I < <1531 The 5152 ;'i.: 31:.'s355'55''55'bt.7,5271 1115231. described 51133 district sequence of bedded 73155±152 rocks in 1:., the 55312111-5,55'.35531153173555 resembles ¶31'3111315535?31 that <55greenstone •" i 2 belts 1 from the 3131' of Canada by A. M. Goodwin _ < <31 and others. In gene7,1t3131'52[, volcanic 51572, initial ral, "11.L72c713131 flows, 5555'11'<1s I' [1131529 dominantly 1131125' basaltic composition, "131"a in 55115331,4551.7J5-'511< pass 13335 1<1'<' upward into volcaniclastic rocks of intermediate and, locally, felsic com55 5512 ,, 517,31155 3.3151< 4,57.31 these position, and 313315555- in 3157 turn 7'55,5a'n. upward '5<37<555557';, into 3,351531 clastic 7'41311.333'317i5551557 rocks, .3'I.15'017113L33 sedimentary pass 211555'.,, o 1r31 L55 mainly originally 2'l graywacke g' 03 composition. 1.- 311473< '7 mudstones <'531 311<1 and 5_513157 of similar Depo3, sition of iron—rich sediments <2 ?.mt=:1152 311-31553, ;7<5131 735255' 7<4315<17 numerous ,'< 3101]yi<< times, particularly was 15513 repeated 1"H t-52'3t 7L<710 51 5t.314'31'55.7235 parts 52< in 231 the lower 3155355, and intermediate 722121 of 3131the 5is 31:7.331552155. 171315113155-52 •n7:t'ai-5'555, sequence. volcanic 3155:511 and clastic 2< Jt21 152553131155,.' 31313131were 555f, extruded Pillowed basaltic flows 7'35':j'1j55355.311' 13131311-,-during 5i::55'52 y3 155131152.I57 31(1, of locally the deposition 'o5531 '313<3.33 :31755,71317:' and 31,531573170' rocks. the volcaniclastic 3135555. clastic 10<523,, '3131: '5ss'1" 31I 3< <1313±1377 511;'3131' from To judge .7: :52: their distribution 3157 H-c- 31 and thickness, the flows and associated 3152 1 volcaniclastic rocks accumulated 5371 ss'3 '.'s,'52 ±52 Ct'23151, in local 5<553<314,3155,15 '52'3131" to great thicknesses fl3<', volcanic 7231,<:5 :51,512155'L discontinuous centers<1s21c and formed .11111571131 C55 '3155' 72" 1' contrast, 531 :35 '305755) the deposits. In 1531. 5311331105553.75 31'3157'P 5531313131? 1152. 315111s, 55'31.75 younger rocks probably were deposited 7 '313112:1 clastic .3<1<31.1' 14.i1,.n'31315:. over .31 a 31155331 much wider area. <1 57 11 a ,., _ 1_41' C - a 11H _ 55 55 35 il- 1 55< 31'S 2".31 rocks .:15<5.,- of 1<.31',31( The the 72331' Vermilion 5'22553±755L5531< district ?±-<721::' .55! are 151[3c'31'2<31 9553 Vermilion 5'<;.cJO 357 separated from the 3155 high-angle fault, 52 571 3131 batholith by a major t-55_,i1øl,_ 5 Ho Vermilion fault, 3152 the and lesser —57 31155555,-15731375 ,'33553,531, 3331's 53131331 faults. 315355". sub—parallel and branching 315375555573-31 1731'-,,.abrupt 3"51a5531'.:transition 311552.55<1 SIts from The 121131' granite "HIlL and4,3313117<31<3.4,1 associated high—grade 3171313-731<535531 metamorphic 31.2'11&sT:531 1<5555 ,"C-'c13155 335552 rocks on .31 *'ta31i:55'tt the north 155711131± side of the 0 5- 5, 0 55'31 fault 5 5755 1 to greenachist—facies rocks in the r 55° 311<31 that district proper suggests ]031 <.31 Vermilion the 131531 -' 5131_ _.t fault 553 had a dominantly '31 0 II' ci The 11153< vertical component of movement. 55 Jt':31131531•:'s. '5"< v:52i '55133112331 Precambrian I1135<,55'3155'3571. displacement of steeply—dipping 131<37531 3555,35:31 a 55 rocks along metamorphic L.'57<311'1123555531:'t;'1:31'f branching fault 511,3 is 5251<1 left lateral—-a 5531,555545-31 horizontal .5235552 s'331'-<7,'31:.-'7553L '?'3:;'31ss. C'7< one distance of mile——sug317531' 111153159155511.315131 31552there 555'-n' 131313 gesting that also "311 was a 131<53<:n315.3131"i7.4, substantial horizontal 155'."31I"5311'H<3. .331111331<.5557513'3155"H"5'-' component of move3557-1531. 55531-00-11'! initially prior 55131 ment. --'' formed ±i15saLl,3 1155 s"31';53<7to '1 have 7,5515739 The fault is thought 172 [5113111 "•<l Lsss. to or 3155' during 071<131', 51<12553<73131<0, Sul 5155. 57;31'< 35512-.5 4,55-31 3113<117553155311.1555 13n, '5 igneous intrusion but to have moved also subsequent to emplacement. 311152L..-2c't'513115531 II 55 1 1 I — <55 — '1 5 31 5555 31: 7171 3115512 135? the :131- district, 55.1ss'52, 355< the On '51.7the south side of '35: the ":531 granitic 31'5-51.31 ['3531 rocks 5031:5731 of "331 ±ai;.. 1_ 1J5231 ,57'Giants Range batholith have intrusive relations to the17 older 5—" volcanic — S , — — '- - l< 31<311, on (continued 5531 next <12.553 page) 571031<3, is 19 �t d&i-r iL: 2i.iicr rocks. Adjacent to the batholith, the older and sedimentary bedded rocks are regionally metamorphosed to the aiuiphibolite 2' t-cLlocally 1cLJ jt 2TC--E facies 12 both along and across strike. Staurolite and almandine are i2&J developed in pelitic rocks having appropriate composition, the mafic rocks are rnetariiorphosed to amphibolites. h (81LL c±itiz :1tJ% La:TAg i•cj:rii -çy,2;Iv)t$;: --- h-Th -t-5 YL •L t-,&: 1•- -•: are Internally, the rocks comprising the Vermilion district i±c::L locally, Tt:s12L;;the 1t strata deformed by both folding and faulting. xcept 5:ax- .i It dip steeply and generally plunge steeply, thus, the present earths ft2the t2- 7:-r2v: 2T.L24 to surface is essentially a section perpendicular plunge. 1E4J Faults of variable trend cut the rock sequence and break it into 2 t is -H &l Correlation from block to block a number of separate blocks. LJI 22c,difficult, and complicated distinguishing 1-e by the difficulty of 1Lt TTh2o minor and intermediate-scale folds from lithologic lenses. -ii&z- -!2& I S :.H1t; i•i 2't:i-.'2J2 2 i;iY2 o2c t J --L 1 I 2 l 1i 11 I :1t--c .itI22t. xi l- sulfides, c•2f-ç-22 2tt:!Y 1JC72 2'-.2J The and copper :_-i_-r widespread showings of disseminated iron 43221 the 7-223'ç and 2:2-243and uri quartz along fault zones, the occurrence of iron sulfides 22L3#1-23 -243r22 t2 resemblance 22 of the rock to t243,-2 that --In in areas known 22 to contain 43 sequence :I2-2c3M2.-2'2 43 4343 a 23172443137 34321©% 2f 143 r J1232. as 4L2II3232 2fl13iY warrant investigation of the region base metal sulfide deposits Formerly the district potential source of base metal sulfide ores. more 42S323L yielded j 212143i 2433223Rki&74312 hematite, Ji332C. 17ç having 17i 22 2-f was a significant of R'2 high—grade 21 17L13 -743222 source 77317fj17-27 cf :Lt23., than t?123: 2. $100 million worth of iron ores. .'i& tt1t22C 2 -- 2 hi:22t2-. 12 '' C l,I 2 , :i f2:. ç I 20 �I L.'_ i-LH VOLCANISM, SEDIMENTATION, OF THE i'i 1716-i _ICC /AND STRTIGPAPHY i•iINNESOTA. 21.UICcCc.12U.i..1 WESTERN VEPiJILION DISTRICT, NC'RTHEASTi Ci'LCL-13-: j1Q5162r}C; CI.,-,:CC1 .iIf,5ir. I -. R. J. Ojakangas, 521 11616225 Professor 5242tIjl;C2 Assistant of Geology Department 1-54of ili.nnesdta, Univcroity £2.2SU2C2fl -2 iU,F71,711i.L16fr Duluth. and -.717_C Minneso.ta Geological Survey I,1c..CiC 1.7:;r.IiCiC 7-#.,4..CICIC -1 and G. B. iIoi'cy, Geologist Lc.xC- ic-1L_;.-.9r..C.\ Minnesota Survey, Minneapolis .ic1LC1 LI flc{.14 Geological y :i- - ) - - c' a . a wide 1- in .L Louis 3U-.i1j[ 2.22 ic;. The Vermilion district County 1.:L. k2L 116 northern U'C162141C16 St. C42E2C2 --7 -------C.-C--—--------... 17- contains either one of two of 1) assigned to 'C rocks that in the past have been domigroups are the Ely Greenstone, composed 161 —1L —)2 (1) —c C large groups. These sediments, T nantly of pillowed mafic flows with minor diabase, tuffaceous 'CT .Jt Lake C Group, 1—_ T and lenses ofT iron—formation, and (2) the overlying Knife I composed of a heterogeneous mixture of clastic volcaniclastic sediU r 1C[I —— and the Saganaga Granite intrudes the Ely at the 'T Greenstone JI;_L ments. Because 2 '-— eastI end of the district, arid because the r Knife Lake Group contains peb-i these two groups bles derived from the granite, it has been assumed - that U:i were formed in separate Ltti22L1i ZL and j;2; distinct -22Li$2 geologic environments 2L2;iC;LLtL:22 separated '22Li:6iL22i2 in Li2LUfThisC- stratigraphic time by a- period of igneous intrusion and 2 L" erosion. ii2 concept led most early workers — to assign almost all occurrences of pu— lowed mafic flows to the Ely Greenstone without regard to their detailed L.2 — The areal distribution of these rocks was stratigraphic relationships. 1LrUpTr©,; then iC;i\C explained qby structural P ;rL1tL:2C isoclinal folding. 22;&C t%iiTh complexities L?222I2tLr1c2LL such as tight - -variety I 2 l :c— I LC — C I C L I — e C C 1 -li 1 71 11 i1 I h — r — j 1 6 I U C F -1 — I — I 1 1 .i Detailed end of in the '1L western CF1i LT 21; Ct7f12i field studies ;27ti2ii at the ;2 the district, vicinity of Tower .311 arid Soudan, indicates that IIno major unconformity exists 11 between the rocks previously assigned to and the Knife ; Ely Greenstone 1LL 2 the Rather, the lithologic associations and tectonic history in Lake Group. , _ _ i r rc this part of the Vermilion district appears to "volcanic : to- be analogous 1_ pile accumulations1t in Archean basins Goodwin '— I' cr of Canada as described by Ld (1967), in which thick sequences of mafic flows grade through increasing _1c (; T ) proportions of volcanic fragmental rocks to thick piles of felsic pyro— Jc) —cT r clastics intercalated with and overlain by clastic ::,i ir::c:!:c sediments. I L a i £ L Li — I L[ i; ;;: t: 1 1 I L i1 a )I JL ;r' ' "* ' J ' -:tc f j — — c- — I — tJ' Three principle r(•:1 t:IE:.L. lithologic ::2 assemblages are Tt: tentatively recognized in the Tower—Soudan area, but their age relationships to one- another are 'obscured by stratigraphic complexities, faulting and folding. ' — L FrT b_I i ; t:IIL ' \::' 1b I , 31r fLT :c The oldest rocks, composed primarily of pillowed mafic flows with 1: minor amounts of intrusive diabases and' diorite, tuffaceous sediments, D1 III _ L —1 ' of iron-formation that extend _tr ,* and lenses from Tower eastward through 3 TVflL1 •4J-J The second assemblage t $ Ely, are still assigned to the Ely Greenstone. t1/, —-"-nc ic consists jpredominantly ofi "typical" gray to black graywacke andL inter— The remaining 1 bedded slate with rare tuffaceous beds and mafic- flows. 2 -/ It is composed of t 2 assemblage is.. characterized by its- heterogeneity. L CJ',t ' r' i ' L _' _ I (5 I I - J I I 21 a (continued on t;(';Lc:: :o next page) 21 '\;r I �II .1 I I' several lensoid and gradational rock units including iCc C I lLl tuffaceous= (greenish gray) graywacke and greenish-gray interbedded slate, feldapathic quart= -C-I - lmIW IC zites, conglomerates, quartz-rich tuffs, quartz porphyries, pillowed LIL Hfl1 'C1111 H1 sericite schists, volcanic agglomerates flows, minor ilL Jr mafic to intermediate CCL75 2 black slates, and iron-formations and breccias, _ greenstones, 6iS diabasic -: — (including the Soudan Iron Formation which has traditionally been UL =\ -4H CTI3i c3 assigned LI Thus it contains rock to the Greenstone). U11 ?l upper part of the L IC U C3 Ely jr51 = - Y types that are both typical of and intermediate between the other two assem1Ll 1L711 %ç L1a23 1L H1= =1 Pjllowed mafic flows are not necessarily indicative of the early blages. 5flTh(! ¶LfL cH stages of this volcanic accumulation and, therefore, cannot be assigned jç: z;ci'. ¶©± 1' 74©! HCliTL> IIICTI rfl[ ILH! apriori to the Greenstone.! This stratigraphic i)L Ely 3 succession presents J!333L in establishing many as yet unresolved problems, especially iLl _ stratigraphic CI 1L_ formal stratigraphic names for rocks in the two younger lithologic h assemblages, and in redefining between the Ely L TC\II a regionally 1pAIr useful —C 1fl contact J Greenstone and the Knife Lake Group. C 5J CC I I C-j _c -l r1 J L S t"L'j L clcFlH — L tLHtL a I a S c 1c,' 3? _ L I ?' Ij I rr, ]St L 3)-Hii, ¶ I J I C 3i43 Ht 1Th C- S — ; 1 Lll:llTI j 3 CC!L5? y I1 'k- in lL II this area of low— Original sedimentary features are abundant LF rocks have all grade metamorphism. The sedimentary 'V1i the- essential characteristics of true volcaniclastic sediments in that =— L3 Lr?1 L the clastic constituents have their counterparts in associated volcanic rocks and LI r tYHt Lt5 1JQ appear to gray-= have- been derived from them iT cz by rapid, contemporaneous erosion. The wacke beds of the intermediate and upper litholo.c assemblages C' H c—Tht commonly display excellent graded bedding, some- have loadedt soles, and some show -c c,Ic,C D7C33 porphyry scour features. The conglomerates, generally composed of quartz LH clasts minor iron—formation clasts, commonly have "disrupted framei ç—& and L C :3_!TJ r?:j1 They are works" with the pebbles not being in contact with each other. 2T3!!, t 7;r[.••;4 k t-x interbedded )' I1__ with and commonly grade into gritty and sandy quartz-rich Th__ t tuffs which are difficult to distinguish from quartz that ,,4J porphyries ' [ ki were çL q The gradpenecontemporaneously extruded or emplaced at shallow depths. j rkJ?k E ing and the gradients JLt fl r' "disrupted frameworks" indicate that basin 'ic— were sufThe ficient for turbidity currents and submarine slumping to be active. L' _( .c1 _1' I:,Th IJrc2 --ç '' lack of large—scale cross-bedding and features, and C related 1cr- the preservadeep tion of fine laminations suggests deposition in at least moderately ff I - rc' c/!: :k )) 1% D' ji C ! — C I I H C / — C C s 5 U 0 3CI) ) - iJt I S L ' SI 3çfl L c 1 ' "çi1 ' J- i cTi1 -Tj -: ! Ei: ; rL 1 —rS (_I I r i The thickness of the pile is difficult of complex !!" Ti4c2;c!!:!;i to estimate because rji!c3L•tS! tt!134I, +0,OOO feet structure, but probably totals somewhere between 10,000 y' Tcc1c and -q:-ff and hence is probably of geosyncinal !!c!•Tdimensions. tiTt Pt:e 5! S S a S 'S I '!1 ' water. a : 1t i — j ii C 22 ?:, !C �(2Ifl2t ,7J.J44::4-2.Jri2Ics-. L/tKE r)%.I$i LAKE QUADRANGLES, KAWISHIWI AND tIflIct J7 4171 1-747411-11 tk5II /L 11F COMPLEX IN THE PERET LAKE GEOLOGY OF THE IL1C DULUTH J17.21 747iitE274J:A 127; COOK 5-'211%COUNTY, C4 1174', MINNESOTA AND 217 1:442-1.2.1 74 2.12ac/.2..::rH Davidson, Jr. Donald M. Li74'cwai Assistant Professor Department -?42.2t9.R41of IL Geology Univ3r3ity .11of'1L:nrJedY[ Iiaesot - Duluth, iinnnesota "da quadrangles c1t'dltS 1712 : ;$a4L•P.are 1/2 - minute "474 Perent JY2- 4412 Lake 4274 and144c:h441 Kawishiwi ±12120 Lake ? 7 7174 The '7412 4J"" 2. - 17' thirty miles north "'1112 located in Lake and Cook about 4 1 .a counties, Minnesota, r 2. a a i74t..7171 Field mapping and research was done during 1966 and -. ,. 441 of Little Marais. IC2.. i:a4aaa:- 1-2 Geological 74±: -41720412 41"a? 1967 and was "2.1 by the Minnesota Survey. 2-2- supported a'.': 74 — I 1 —, — 71,12271/'Complex '.41.2.1-2.4 1241 c,l the '17c± Duluth The .4111041 area isliIcc'-1222.4. situated 2/1 in the part of and 174- upper '<aT.i;"' 74/2.1 4I4fc.714 12cti .41441;4V74 mainly The bedrock 1122.1- 1 consists -2211102. of gabbroic and associated granophyre. 1122-7471411211 74"12;.:171i2— 2 and 4 troctolitic anorthosite, although troctolite, gabbro, anorthosite I 1I4-od/a-112-t4; 11±1412: Leucocratic rocks, in -7474-74 1/41174types 47/9-41have 172-0 also 74i:j '1:1-121 intermediate rock been noted. I,2':71c11742'i is ¶41 Also of -74 interest d2.2L12—the 1711.complex. L74J.d11 17412/ 41.41ca741127:2 addition to the granophyre, intrude .c 1774 c4I.4/1.i1.-/,'l medium—grained 74 IM I1I JI I the presence of a weakly mineralized (Cu—Ni), fine— to a 74± the r-f'olo'-o41274 11122.-I gabbroic anorthosite, 112a.-1711±±-' similar 1±a, to a , part of the mineralized rock in 274 41171:2 a,1.1.2.-U1Ii,71±±1212dc Gabbro- Lake quadrangle, South Kawishiwi River area. Structural analysis 1 a "Jil i'7441112—2-22'-C:t 171.741217740177. 2'2j4i'4hIis t 741:c 4414-2.1112 1-i74 with ''S'- recent and interpretation being coordinated geophysical investi14.11-9.1:2-0 ,4)1 I a a" Preliminary71—'L analysis of the fracture pattern 17'lPPlIal 2-a gations, as yet unfinished. suggests distinct trends, 11114112 which 0±171. may 412-4 have 727442-1241.212implications 42. on the tectonics 2.1 /-74'J'2-1 two 4 -7441471-4741 0:12-11-27 al '::7.-.i of the 74174 Lake .l4v-12:l Superior /2' Basin. If — i" "a 1 1 I a_ j 714 7 '''' — 2" 23 I — I �I OF ROCKS 1jICiiC:!rJCOTJTCHICHING A1 :777777 OF POSSIBLE 777:7 77-7 INVESTIGATION 77777777777(7707: AGE, AREA, ST. LOUIS COUNTY, iiINNESOTA CREEK WAIBERG IL{t7L5 7Ij S. Vi ino.than, )Cufl,t622t1 T:cIijn u7iJ:771CO ssocite arid Research ct212J i7or'2[ Assistant ICflIL'LtV Dopart.ert i9 of L) Goloy Minnesota, Minneapolis University of I I 2T — C — —% and Sims, Director ii -Li Is I; 2t7y Minnesota Geological Survey, Minneapolis 77 UI!I :1-1271; Paul K. 7; —. r (Ely) pillowed The discovery of a cataclastic gneiss -1-:L;2i 1yl1fK. below Keewatin metasedimenta during reconbasalts, amphibolites, and minor intercalated r [7 — -; -2 of 1967 led to L 1naissance mapping in the Walberg Creek area in the summer The area a detailed field investigation r followed by laboratory studies. 1along its conis on the northern fringe of the "1 Giants Range batholith, LIIL east of Idington. tact with the Ely—Knife Lake sequence of rocks, just 1 I —2 complex anti— The cataclastic gneiss occurs on the northwest limb t -I of a dine, three miles Th '- wide, that Lr trends east_northeasterly and plunging The core of the foldr is occupied by a foliated horn—= steeply eastward. ç 1 blende granodiorite of Algoman age, cut by an apliticC- leucogranodiorite. Inclusions of Both of these intrusive rocks are mylonitized at places. —) of the fold. amphibolite occur rarely in the granodiorite Ui ,l within the _r core 27:7i7T1 I I U CL — 1 — C II I I ' — j - LI 1 L rU1Cr j ¶51 fl C I: — 2 i7s1 I ]F 1 C- — I ft U I\iJr -y I — 3 I [ I HI Three possible explanations gneiss L I _UI were con— 1ii for the cataclastic sidered during the mapping: — f U S It1 22t12L21t represents 1J21, part of a succession that is older than the green— 2 stone, and thus is equivalent to the Coutchiching of A.C. Lawson. r5° It represents a sheared facies of the foliated I 1 I'JL hornblende grano— diorite that characterizes the core of the anticline, and modified in represents a segment of the Keewatin 1L volcanics, texture and composition by shearing with synchronous introduction of granitic ]1_'material. 1. 2. t — It — 3. Th r 1 L determination Results of © petrographic studies, modal D:T L1V.7:1. analyses, ' and _ — - E•. critical )_ of the jcompositions of plaoclases and;' hornblendes from the : 1 1 below. lithologic units, using the electron ••cL1}*; microprobe,: are summarized tL1. ' k a ri Lri' The cataclastic gneiss is !IP 'L i"I; composed of 52cT percent hornblende, LUi',. -? 12—26 calcic oligoclase, 3—12 percent K—feldspar, 1—5 percent percent 67—73 L z and - r a ) a' c& apatite, pyrite quartz, of epidote, .; . _ and &—-- total •' 1-5 percent k± -.1Ot-•Y.i sphene, .:; : ,.--;-;..J7 -'c-:? The The plagioclase ranges rJin composition from i8 — 27d opaques. L-1 hornblende contains 11.6—12.9 percent MgO, l5.i-—l7.1+ Spercent Fe-oxides, 1flrIF phenocrysts L The gneiss contains plagioclase and 11.7—12.2 CaO. - percent L ) r J L Most of the plagioclases are 'interpreted as a relict volcanic texture. t R 1 ' h n 5L and saussuritized; microscopic evidence indicates that the K—feldspars -— . J ---. '' I ' - - rj• — ' j' -- ' — 1[ L — - y — n ;; 3 - -c ' ) : S ' — quartz were •>JP introduced into 51!.?; the rock. :;Tr/, .; L I r( 4 t!LICi J L L :1 L hornblend-e, 53 percent andesine, 1—2 The '.7 amphibolite has S%1 39 tc percent ' percent sphene, percent K—feldspar, 1 percent quartz, and a tot1 of 6 r! :. 3JL- p - •: (continued on next page) 24 :'a �The plagioclaSe is unzoned and has a chlorite, apatite, and opaques. NJ (;FLiui 4'3F1F-F45IF i-&?:& 17.1f The hornblende contains 11 percent MgO, composition of An_Ank. hI The presence of euhedral zoned percent CaO. percent iiFe-oxides'and t2.1 — ¶&5— —— indicative of a volcanic parentage. relict plagioclase phenocrysts is & tVI < tI -- N---Li -FLi — i — — I — I c-_ F discontinuous layers geneThe jnterlayered ::F;I4 metased3inents 4z4N2iI i. ±LiLiC occur as FIYIiLiLi; by biotiteand are represented -rally three inches to one foot thick, — schist with minor amounts of horn— -F plagioclase (An2)_quartz—microclifle ILL — s—7 0b1ende_plagioClase.4fliCrOc11fle_qu'tz schist with subordinate itHi i*2I --'-.--- - ( - I —— — -<: I blende, — i2_ — 1 (An31)_epidotemicroClifl biotite, and striped hornblende_plagiOClase I— quartz rock. ::;.:cFy F L F - — percent Li The foliated hornblende granodiorite is composed of 15—18 F1 lr __— calcic albite, 8-12 perquartz, itii6 percent K-feldspar, 5k-59 percent sphene cent hornblende, and a total of about 1 percent biotite, chlorite, --1 has sodic oligoclase and apatite. The plagioclase is distinctly zoned, percent cores, and ranges from An to An1 • The hornblende contains io.8 I_i CaO. The rock is MgO, 17.9 percent Fe-odds, and +1.3 percent _iF L lE L allotrioand hornblendes with has myrmekitic intergrowths morphic-granular, and -1 Ni poikilitic quartz. 4[F-%i/N — L — F I — I L L — — I — — — II F — — I — — L — Ir l__ F — __C— L _4 — 1tt7t1i2 L Graphical analyses of these data lead to the following conclusions: LL I the amphibolite in closely resembles The cataclastic gneiss Ci) 2 _iI_and hence are textures Both rocks have composit.ofl. )!_ relict .4JL HAflf volcanic represent the Coutchiching therefore, does not meta—igneous. The gneiss, —t formation. of A.C. Lawson, which is a metasedimentary 7 foliated hornbleflde granodiorite The cataclastic gneiss and the(2) — -1 gneiss The plagioclase in the are two distinctly different rock types. ' C, I granodiorite, shearing of the -— by Qi1 (÷ L -iJ An2,,) is too calcic to be produced the composition An10; shearing of has plagioclase granodiorite for tile 1 _' :— zç D 'i:i c';F4- rr f) - I I N ç1:w L i — F — F ) Ii I lL)I ) ' t plagioclase. a more calcic L _ r- I I ' L i [ this rock would produce (JL L a more sodic and ' — not W amphibolite which has: a (3) On the other hand, shearingI of- the produce the more sodic plagio— calcic plagioclase (+ An1,6) could indeed : -'--lic < I-%_c clase observed T, in the cataclastic gneiss. O;ç7c.i4f: we conclude that From and laboratory evidence, *!<:. the tc• available field ] ?--._c >•rT !?• modified the Keewatin volcanics, -#- is the cataclastic gneiss of Lk' -- c_ C]•!! •:- ay segment Ir cy7kTC synchronous introduction _ bc 'in texture- andr composition shearing with ni ri Algoman pluton. This conclusion of granitic material by the invading 1R1 IL[ that the L U 1967) is tonsistent with observations elsewhere (Griffin, L1 jJ -modified various country rocks by metasoniatiC of 11 -r rL i1YC cr Giants Range ' I r - — 1 Uj — — — ( 1 r :i _I -<•:-!-• ",-., -c-: I ç ¼ I & (_ i-I IThi I4! rf batholith has c arnphibolite. processes, including the development of granodiorite from 25 �•44• 1-'i/A :E[/L:LY. :L7i 1CC .L*C/jt7Ri iCLACc!ALLr.3. THE BIWABIK IRON FORMATION, META}4OPPHISM OF AREA, MINNESOTA 71LES7 PJL4, DTThKA RIVER - .k1C1.; )LYC&1:L AAiiBill Bonriichen. iI-3Cf7 Cj1tC/ASurvey AC ;C.Zt14/ACCA Geological Geologist, CYC:CCL- -v. Minnesota , YCi: Mesabi /AA1JCLrange CZ'CA .t I&5l eastern 14/AC.ii\/ end of ;7 the RiverFCCS area is Altat the LtC Dunka iCAIC L'A2 The /A7 J..\44s-C /A-AAC:i. CC. -AC/ACICAC :C: :LC A71 where the Biwabik Iron Formation lies unconformably on older granitic CCItL: flC-C-A = The iron rocks and is IL-C overlain conformably by the Virginia Formation. tL.CC7AL 5cC,C?:C?.:/A facies formation was intruded and metamorphosed to the pyroxene hornfels CCILC C*/ACThtlcfl CLC1 &.C;CLCL rCtCC: C/A CC—C CC/A CC. The iron formation is tC C'C/AC-. C:--CCtiC by mafic rocks i1.C-CLCC of the overlying Duluth Complex. L7 /AAJ•f — 350 CirAC. --C—-CJ/A/AcCC il; beneath the Duluth C-i/AC Complex. •tk:ti SE., iCC-c/-ICC ai CCCI1JC and CC/AC dips 15 IC C/AC- thick 175—300 feet Ill —, members are JLV/-/( mined for ICtheir The Upper Cherty and portions of adjacent CrLrSCCCC :C3/Afl&?. Company. :C L/-.1ft1&1 tICC L-:7 =t1ti miles along C7:C CCCC/A,*-C± for content strike by Erie Mining /ACIti ftC three magnetite C.. j= &?T cC rJ ,b/A tt'iY — Sc /A11 C -CCL.CCCA- IC, '' CC,A4LtiA, C Ccomposed -1,/Ci -tC/ACC:i6.CffJLi7 C.,quartz, 7CC-C magnetite, dominantly of .;.iCIC&.fliACC is Ci cC-:C-C formation The iron :1.C:/-- ,C /A:- CC :ftLC ;7Le2 •tiCi-41 i- Ly local CC 1C/A-J by pyroxenes, fayalite, and amphiboles; these are accompanied = r II4l i quantities - ii: pyrrhotite, apatite, /A of garnets, plagioclase, biotite, = 4I1i'/A CCft: ic. :i.CCc C-&Ff; C.A • wollastonite, talc, ite, calcite, serpentine and1JCCW/ other minerals. ttCi I[ graph- L C LCCL CjC!:Cl ,- -LIft. L.A/A CCftACC and IC54 'C/CC during CLL: PC/A IC/AIC content C/A/A I did not The the Cmetamorphism J:-t change L.Vl magnetite where C much original grain size, especially CC c of - the magnetite retains its ta/Aeft C-liti most Quartz CC the C/C,C2;/A is 1C I-1CL4ti. by CCI'ferrohypersthene. Z/AC1CThKtiPCCCLC J/A,/ CC IjL I 17.LC enclosed it is poikilitically /A1/ACCC 82jC/A7 CCIACCS IF-i 5CC -c..ci.C size is -e,CC AlCC'IC abundant L.CCLC mineral and was /-t'-.cCI. entirely CCC'CC:J recrystallized; its grain ALftflC./A/AC. -c/Ati/A .CCc. log (average amer) = A (perCiLft u-Ct/AC-/A4: 7i.?by: 'C related to C:CCtACti'd ta abundance approximately C -' ratios of 1(11 /0 The LC 0 C IC - A and B are constants. cent quartz) + B, where ' C/A 11j1 111 /A1r =,C coeisting quartz and niagnetite from the iron formationL imply that 700 -= /A 1/A/A/A C - SL the C. Cwas the maximum metamorphic temperature Aattained beneath — 750 = C= iIrj1 Complex. C—4'iC Duluth =r-,-=4--. llL = st n ti=ft r - - 1 1 4- crL'/A I I — — A :7 — CI I CC-C'. ''I ft/PCCc4/A rr j1 r _ _=&-r -fta- CC1ft Orthopyroxene most abundant ferromagnesian silicate; ISmost H. the tftj/A,:.:c7 Ci i/ASCii. s is AC I —= Fe/(Mg + Fe) ratio of greater than t==cCr CL with an atomic 1/A ferrohypersthene is II 1+ Fe) ratio of orthopyroxene, occurring LI The maximum Fe/(Mg 50 percent. /percent. == r = ft 76.7 7 in rocks ¶1 that contain quartz- and fayalite, is approximately I/A/ftC-Cl, iLincftrocks CACSC, A j/ALd portion the CC-tiC ferrohypersthene, occurring that tiCijCCCS-C,A'. contain suffiCC:of C C-/A :14Cc-Cl cC - CCCC L/C/ACCCCCCCC) LC.CL/A-CC/C CC/A. cient C//ACt. iron, crystallized as pi pigeonite and inverted to ortho— CC/A.CCSLI? Alt-/A CCItt-CA/i initially C-CCt1/Aic-iCcg .C[rc., pyroxene cooling. IC/AC/cl/A during - 1 — C 4 ti I I -.- I I & .-;C .1-I-C :ç/A('.c cCCI':'t/L.Al.::.. geneIt--& iron A/A/C/c formation, Calcium pyroxene is abundant in parts /11k-A of the -1/At-C1•?Li :C'-t;-:/A ICC CAiC/AT.jA4CI1C ICI Fe/(Mg + c/A C ti-Ct., is hedenbergite Most with a rally where quartz predominates. CIA/AC C/dC/ALL//A :-/Ait/ACr'/AC: /AbtLCs/AICl/A 7/Ac/tAil//AC/AI-i/C/ALL] 'i abundant, isCt locally CC/a/A/CC50 7C and 70 C --: CCC Fayalite ratio between percent. IA.) CC/tIc/A Fe) c,'11ct-/A'///C. //A- CIL/!/-c,C It occurs with quartz f/A commonly Cp3sparse. C/CACti: generally where CC Ca pyroxene :Cft c/iCC/ill/C is fl ÷ Fe) ratio be-; /A or and has an average Fe/(Mg ofCftCrlC/'/A approximately 90.7 percent; ratio. /11/cU-C /Ac .:.k-C/A :, :ftcjjjTh/A CCC. locally, where quartz 1/cC is absent, fayalite has Al a Alt/C/A lowerJC/A"'71/AFe/(Mg + Fe) -t. /A5CCCt/ 1Ci-ca&Li-.; - CII .t 7Cft /A C — •/Ci'I/t -C/Al li/c/Act C/AC/AC formation; Cummingtonite is common throughout most %i1/ has Ca C/I//c iron CtCcC the C/CC 1.-CC) i-/A. CCC oCca !/cti/Al/Ai.iCt I/i C texturally is C/AL j:7 C to 80 - percent. Most cummingtonite 1 Fe) ratio of 50 Fe/(Mg + 14 /P fayalite. The Fe/(Mg + Fe) & late; it replaces ferrohpersthene mainly, t and cccti./— rind less. S- percent li-cl/A:- c/Cc//CC/A/c ratio of the /2/C tAlc/Ac/C minor /-CC/ACCCC; amount C-A' of -C/AC/I/AC early cummingtorite is ftGO Cc-/LA/CC t &/- ft CA — 1 tiCL'ti /Lc -C A/A/C/C page) (continued 41L/AitcjCcCA1-iI on -C-S iaext 26 4 srI. Ittic �3fl-:l .rtiH Small amounts :[1I tt p-t,t ttyt- 1-Ttttt.formation; fcii-ILLct' of hornblende are present throughout the iron cThtIL Lt 7t 7Ct £ILiv1 HIL ?IL tI-L.JJI2L metamorphism but most replaces hedenbergite. ILt-d .y- rt' H.1;-IL.'• some formed LhIL during prograde I 25 to 75 L + 7Fe) ratios The Fe/(Mg encountered in hornblende range from ILLL ti. A1203 c11l1 weight Jli}'± percent t '33t- of -Yll Mg. ç.. The Fe generally 1 -.:p1IL predominates kits III IL over c percent; 71 Cfl11. in hornblende ranges from 2.+ to 10.2 percent. H.j '-- — :• - ILILILI (ILi.abundant ILtUILttt iron carbonates tIL-Fr contained The It-IL iron formation cILt-ILIt originally ILYf Htlii and 1itL°H, to pyroxenes '1J 1;11 Jt,11ñ2 these lVtIIH IQ11H and hydrous iron phyllosilicates; were converted IL metamorphism was isochemifayalite during prograde metamorphism. The r _1_Cl Locally, fayalite t cal, except for loss of the original H20 and CO2. 1 IL and pyroxenes- constitute quartz—free layers; these imply that the origi_ '1 to = CI =çl_t directly nal siderite-rich and ankerite—rich layers were converted ]1 IL1 Thu I fayalite rather than progressing through an intermediate IL and pyroxenes amphibole step. H 1 r l1tt_flIL r Lt I1 IL —1IL: I — H. LtLIL[ I R -- — — 1\ — 1 — -tt ILt-tIL .rt c-.t-•tILzILlif tt. ta ;fLt.:i t1LLtLt t.ILcT Prior to metamorphism the iron formation contained several percent Most of this was expelled during of 1120 and C02, with CO2 predominating. l.tILthbyIL1120) 7iV-1'LLIL :IILChS metamorphism; however, (probably dominated IL-Vt IL. a small proportion 1ll IL 1 IL HO combined ThIL residual lILiftlIL L-.C PILLItIL remained along grain boundaries and fractures. This IL tYILt \LJtIL mineL11 other ta6? Ihyrous ILIL, with :the pyroxenes and fayalite to form amphiboles and ti-l1L, iTS filled ILH. ILLIL Numerous JIL1ILLIL hairline fractures, with tILL— CUlT'— Th•StH tL&IL Jp:-trttt rals as the rocks cooled. gj 14 mingtonite and oriented perpendicular to the layering, are the probable t'ltTfltiL%71.it&IL Similar :tt cummingtonite— escape route for a portion of the volatiles. ILtnt dH.J54tI in the overlying Virginia Formafilled veins are conspicuously developed lZ,l©lt iq-i1 -ILyi1 .-tLLIL 1;1TS1 -c thin veins, along with JIIIILL±1 locally abundant ILtIl. biotite-t 1.1. in TLIL the LI tt These tion. ILL-.ttt. It7H:I-VtCtIHx portion 1)7tILt that Itlttc ata substantial basal part of the m-:ILIL Duluth Complex, .c-sm r H- suggest r escaped from the iron formation sz1ot wiTS ILt Virginia of the volatiles which and the PIta overlying Duluth Cominto the LILT-IL TL(111n Formation during metamorphism migrated y fr IL ±.:HlL X 1 l-=l •t- .4 L ifILIL.rttt- :ti T-tc LcDIL faHi 5i L tf tL-JL- iy L IL Jtii I1IL — st IL c .r-ct 7tIçIL* t::')' lt: Ij4?L P14 Hnt IL . .-:1r:IL -H-L i4 L1 I plex. 27 — tVIL*ILd ILuL �IFI, I(3 THE JJ1.1I-71 NICKEL 1i1JIrLT1IIF111IF1PI73.NSE 8822u12C.i2 GREAT LAKES CF:F12 DI'ERENTIJkTION UEIICE OF INT2USION :7712 1iF77227731, IJIFiL F University of Jestern Ontario 1Ft1121'I IL FF7 119112 2117 N.I D. MacRae, Department of Geology, 'y7..5rLT 1 1111 I Geology, University of 'us., 1IL of E. J. Reeve, Department I I MilwaukeeI 212 cross—cutting 7177.7771772:7 77iIjriL jL 17-7171F#Th7177 body of Great LF1JF#F Lakes Nickel intrusion is. a 771 The ¶±2};' 1712*Ft Thi1 ILH-- Ft. 7 1•. William area, gabbro in the Keweeriawan Rove shale of the u) Ontario. The intrusion is at least 1 1/2 miles in length, 1500 177 east. 721 20 degrees toward the 71fl 221 plunges 71(77 feet in width and approximately 7:f72477171ri II direct evidence )7777' F 71 In north—south section it is funnel—shaped, but no fF12-IF j1g 7177rI mainly 911I Rock types consist of olivine LF F been found. of a feeder has 1112 il gabbro, troctolite and anorthositic gabbro. Within the lower olivine [3 has become 711 I —enrichment _I71I which gabbro is a broad horizon of Ni-Cu sulfide 177_ companies 77F1J with property in 21_77 711 the772 focus of attention for several mining -' % 7377- horizon sulfide I Chromian spinel is scattered throughout the 71 the U area. _'L_ F— 71 1U7 extensive and conformand particularly concentrated in a remarkably 1-112iC:I7fl 177 3©7ç71, (:y[71 .211777121[fI(12 .21177 7777 sulfide horizon. .77771 7127L77 177 layer of chromitite above the able thin II7 77. —2 41 I ) \7 . rF L J — 'i _77 1 'l, L-I RI £( I 1 77 I I — — C — - )ILI ,JI( _ 1 77 i:.c..::. traced 72714777121 by .7121 7771147177±2 means 2HL1 217117777771 Compositions major 111221717771-1 mineral 7177171177471 phases were 7777: the 7FF©7$77 27712777121 of 171 T localities, 77 _3 from various but I 71 of the electron microprobe for samples An average 77I77 1171 _71ts— intersection. 3c1; particularly core 2-c from one complete drill —t 1; distance upward I 211 toward less mafic composition L11 with increasing trend 77177 _(I 177 short section the _ from the base 77 I_f 71 is apparent, but within any one 777111 1717711111:731 mixed. 7171171172777711 is pattern 7775 considerably III 77 Cl 71 1 1 1 I 77 FF 1 f 1 I 12.713i717131411177.±L:.IfS textural 1. 77Ft7177FFl. relationships 1771177725,#71©717711 117171713172177 variations, 171±77L71 of 177371 basis .7772 chemical On the _ 1_.1I lLIj of 1 that at the time I 1 and mineral associations- it is concluded :c7'171111.c:1177: crystalline component. .77111511777,.±.l71,1L171 711.1, 71777777515 371, SIIFIIII-2151117L7. 711,177: injection magma 771177-71 had an unusually large 717171,7777 the 7777711 IL 71 28 �SULFIDE ASSEMBLAGES I.4LLHJ1ito S3±2MJXtS± OF t)FTHE '±±. GREAT J ±C11 LAKES NICKEL 110.111 JitP IL i u10; INTRUSION :1 SI'Ifl pri'I :±'Itpto1 Student, 'IJa1ibiJ'I'I±, H. Department of Geology, University ILt Mainwaring, ±±Zirtto'I Senior LHC311toLi. 1 Ontario pCi3estern t Ctoto• .•t.."P.1Ci1=1 of Ontario,3 London, P. '° PP II ppi.i intrusion it , The Great Lakes Nickel is located in the south— {P01 of district, Ontario. itP" toito7 CI,P ]iJflVC,1I IFQi' Lp0110t1CLto1, Thunder central part Pardee township, Bay ,V$ — 1 I HP ...oa I I 1.LI'I and toI'±1 I'IiI±toQIto of mafic sills The tot one 'I'I'IP of a great number iT±.ttoto,lc:ttotto is ±ILto intrusion '1 a Hto to This particular intrusion is interesting dikes in the area. iIL21ato horizon because of its differentiated nature and the sulfide III it. 11Pl:tito:IIpi,. iCflh-.Jfij located within 11 °i4 I C I Cto13I'I1P to ±ct 31T,1p'IC. ®Iti=3 T,i1P1HlL,3 oit in order Sulfidet4H.H,HiIQ'IIH1p1.3HH11 assemblages wereIPIP® examined optically iP. sulfides and r 'I CIil [I determine the nature and mutual relations of the H1'I then U.'I•to1studied ttii±&p7 with .:i.P3):.J3HPC were Certain of .toP these assemblages silicates. I:H'I,±t iTIppt±'I i)L the electron microprobe. the CC'IP. aid of IH ±1P i j -- 7i totoitttoI primary tipd and H1.01. found 'Ip ILt to ±FP: 'I)ttoPji. to ttto be St of The sulfides were two kinds: p of high The primary magmatic assemblage consists secondary. _1 system. — 1- ± a temperature sulfide phases belonging to the Cu—Ni—Fe—S I C ili a C 111 chalcopyrite, These include two toll-° phases of pyrrhotite, pentlandite, 11P IN lIla a11 assemblage consists of rnackinawite, toi and'IL cubanite. The secondary °flLJto marcasite, and nickeloan toIL torto'I±I.,toA5 pyrite. p 11P[,. ,1 — 1i1t ' 1' I — It I ±I. H r — C, 3[ _ appears to Mackinawite have exsolved from chalcopyrite and I r1'I AtT and Delabio, pentlandite at a- very low temperature (Chamberlain 1I Clark, !l ± 'I'I P9P'Ito.t 1965; .., ( P i 1 1966). Gt'IpI(PtolI'It1, it Itt .lI.a'Hp:io.Ci iiy$S:;1C of On ib1ti Ct the basis textural and mineralogical evidence, immiscible j1t ata appears the sulfides crystallized from an 'Ii çJc that rims are L Sulfide droplets surrounded by oxide sulfide liquid. HP I in miniature common. These may represent closed sulfide systems (Chamberlain, 1966). r1 I'IIlI-' toL' °'°' Cam to I al ± l C and PigLAi tPLL,HI I101ttt, to ± origin to,'I,tit to to explain Several ideas attempting tttoP3r±LiIto the tot lItopilot oooHt.fr, H:iiHIaH,. Hi JIIC.l.a Pr ment of sulfide Coa minerals area considered. a_ 1s the HI IC 29 develop- �LAI INTERDISCIPLINARYC±1tJC STUDYCl OFJ\A SECTED AREA OF 1.2--; PROGRESS REPORT SUPERIOR: f ]i4±flii10t of 4;1:Chemistry i11:04 J. W., Associate Professor, Department Brown, P. C., Professor, Department of Geography I D. W,, Associate Davidson, Professor, Department of Biology V , P. Associate I Dickas, A. B., Professor, Department of Geology C Lunking, W., Faculty Assistant, Department of Geology 1.) K., Associate Professor, Department of Chemistry Roubal, 5.21. 2. Horton, r - U — I -. 11 I .: 21 s-. she University, :5; :1 authors i::121 above 172; are )-: 2.on00-2 ±2 .1-17 All the the fs;'o faculty of Wisconsin State fso11i;:; -1515j 5. Superior, Wisconsin. : J1I 'N __ State University, An interdisciplinary group Superior, 5 from Wisconsin - ± 2 comprised of members from the departments of biology, chemistry, geo—s graphy and geology have completed a pilot baseline study of a selected C fe" f5. sooth --y. -2 Cl a-area of study is hhl±4% 7 03 hI IlL --oo1 The area the south shore of Lake Superior. 2:401 2along •rm two—mile stretchb of 16shoreline from the base of Wisconsin Point to a 1 Sections 35 andI 36 of — _i of '1 point east of the mouth Morrison Creek, in 0 (;: — L iJi L 1 - 1 — I , 1 9N and P13W, Ca — i 5I1 ILls — -; ±272022±2201 o- tur14 sediment sieving analysis, 405-4:, 1 -0 ;-H for study were: .or 'Looi;C: ±2 11': j:.o-l Parameters selected 6;_, I 1_ — II bidity, ;— pH, electrical conductivity, dissolved oxygen, total dissolved .7' -L46 -'-4;33 .10-22 cioe dis'-'-;*N''I' ets±2oC solids as well .44, as qualitative analyses for certain selected ions S *4 were obtained along a set of five solved in the lake water, Data traverses spaced one—half mile apart along and at right angles to the I_ were taken 2L 4 -.at water depth inil L shoreline. Samples along these traverses :.opIoi. ±2 15' 10±lr.5 tervals of ten (10) feet, from surface to bottom, to '2 a 222112222 maximum depth of .I5 21:322±24.01.i 41112 2 thirty (30) feet, resulting in .# a 22±2 set of ten samples of of water and four YLC-ooC:LL ijLo& per traverse. O'Lt'142' sediment samples : 1 11 ,-l 1 ., — o5s±,1osoto;:Leo;sC±L:.±5dfto.oc sJo-. 'H- 52 ;-;.1:4,55 1! *se±2 - 1±3 ..;t 1 r 1 1 1. '.-41'CL. '5i .5 ±15 .4 traverse At each station, lake bottom samples with a- Peterson 5-1211: 111711.. -f were caught 57'f (-:41-.,,,' ± ,..1-OOcl dredge. 4 One hundred (lao) grains were oven-dried and size :1 '2 of each II sample , .6 '. or _o 15 employing I 3:21 I I sorted aa 10—unit sieve nest.fl rI 1 The 1 median size ranged from a .16 Il -, , 4 r negative 2.70 0 (small pebbles) to a positive 3.05 0 (very fine sand) -;H I.:rJ15:4 1241 ; 213513 :2s.-NL:L,'o value. j22111C1 high Along L027,the f35typical 'Cf±1 traverse, medium 1-1-1.2. sand 0541 was found on the beach and in the littoral zone. Fine ,s52. II—' sand was recorded at the ten (10) #14 r;::-1J'7. foot and the twenty (20) fr-I. foot depths and very 'ine sand was dredged at :L21 ±2': 11 2 '' depth. r _, the2quarthe thirty I (30) foot Using Trask (1932 . ±2 deviation (coefficient of L4'I tile sorting) varied from 1.51 to 0.69 --.I'-' -C ' -I — I These results indicate well sorted clastics, he skewness (symmetry) I 2I 41a negative 2.21 to a positive I urtosis ranged from 1.09 while the fTYi2ItA 2101135.1 ranged from a negative (peakedness) O.+2 to ria negative 0.21 '±2-'' 0:51 CO •.. II' II1 1< . [ -. .. — r-:s: — :5',I4, 1 1 ) 1 I - - — Ic .•.f-','1'41I; I U — -. — I L, 'r22'vtf statistics, 1 1lj4 — [ ._ 41 .,, — - - - - , — -- " 6'" '- ..41.4 4t00Cld3.tIfH,,C .0:N.1±a standard ,.±r.:L.202 distribution 11 These statistics indicate of the Lake Superior 26'01i.kS',r0[C' 14 the I:141,. considering I: '3 clastics within the area studied, This ía not unusual 4 I lI lake within the The few S high energy conditions ofi the six-fathom mark. 007211 1,112 zones or:2-or -±2:1-LU a-:--: floor 235-IC' to anomolous which are recorded -.5-341.1113 1541 are attributed 1L4i1S lake 2-11 :' ±2 small s--:;.1s1-:: 0;__' 312:2111141pockets TL2'52 11 of clay 02222 which :70-02410 into surface are slowly being 404110'' -lb. transported f7ri 9.1 Sjf;: slumping ;I from 1-214 ±2Irao I; 2Jo[-41 deeper water. 423211-3'. ±2±-s 2±2032f: These clays, C1Y1122 derived gravity along the -. - . — LU 2 2, 41 13 f, &7I21 — — . - 13 . l 1 16 1.1:. :--±2241502; in ±2:-1,3'a •; P. D., Origin and Environment I of Sediments Petroleum, s-h LL7-:'--sjcoo of Source pp. 71-72, Gulf Publishing Company, 1932, o.:r±2o: (-log2) 1511 on All calculations 1223 phi a-fl aL1L2 22241 based ±211 scale Trask, 0041222 l - 2 (continued '16.on 5 next page) -L 30 �Cl 'ice as the region elecethe in t. the ?..It.were iec Ce.iilSor11 south shoreI.line, initially deposited iirctN thece Lake the in s:b.ejc ck the:ing the WleecThSo c eroeprih lacustrine sediments during the Wisconsin Superior. Lake of al bigr. etee :t:t et lake ICe 'i%I the ancestral glacial high water ma:k Duluth, .e , e' e±Tha :ethclece. Secchi 0Ap 4C Ilie a?tee? &e cet;eeee.n,ed ,ee of turbidity water was determined byCt; means )jrC0l eofI the The 'c a depth of 55 6 (1.67 Sightings on the disk cC ranged from Ii.;,., average eecen? cNrc valueeeoc was 1h&, ec;?QL'c,O okir1 of el NI cx? a depth meters) to 12 (3.66 meters). The intensity iT;rect• 2.95 meters. Sunlight was approximately of the same 2,95 ?Cth Lyre depths I. U'& the OJIICAICdata thJC?indicate U ri0!). ULAthat T,le I at liA?Ci1L all CJL ?Nt,tI?OL re CloltIi, These during determinations. e)c I:.IcCJC eyr,).i?C±'LCl action and shoreline L;;.:.c.?eco;x1. Creth wave where water transparency wasCete; determined, Ur '?yrfieC the suspension to increase d,° yyr ,tinrey eyre; cit tO; . C sediment currents an amount eeer•e: of ceei eee held xiyr : ;ymid-lake. eI& t;J :eeIe ci cc1 in turbidity ill above ;Iy; I otC as determined U'/C. that disk. t.t1lCithl ee e.thcd.:?cl:?L thIth &Cioi li oCIf ct Beckman IC? means cc ei,C of a tcurtce by tI eN rite water 4.ç, ycotnc; Thee pH of the samples ee. was obtained .CtOithl ?j .t.frryyr ;ftyrp cc Oft. S R-' Sargent Noc No pH meter with f'e Ox) 0 Model No. S—30072-15 combination electrode. The average 8.02. pH ranged from a low value of 7.84 to a high of ecril those thee taken rest as lie compared ectIftt with highr values, Lie e.optie" CT?.LL'e $?'t7.90. cNU. The value was C1h1 Cf of I increased leaching LcttoiOiC0io,' ?IctO at n:,JUoSilver Lte.. Bay, Minnesota,may be the due IC tocctCLtyTr•. et; shore of Lake e11te alkaline certhe earthsIcece from INc the eel redthee clays alongIce the south thkiteti,e ejettoc t CLatC Superior. ro: 0: it left approximately CL!i efrJc ,1. ctiir:thee. Freas type cells withcccell constantsccofct?eceLt0oi T;Ntie conductivity IceriC r OxCO r Model RC cont 0.3 reciprocal ohm were used in conjunction with a 17: ft operating at .cxi.'C. 1. cL-it'. LC,L JLc1ttrcmcettc jç -. lee. ductivity bridge from Industrial InstrumentsJIInc. Ic I: eft 'cc LI Specific conductivity". C17 s 1000 Hz, to determine the electrical 1711717 104.5, thIN with a oiL C of of :°:N'H5 OIl250 2± 15 i eoct:cftyrc conductance C) had an average value :e,ecct 1e:: (k ftc x10l0 at Homogeneity was within C" reasonable limits, S c,; CC + 1.2. standard deviation 17 thirty samples down to Cr2r1712.'CL-l? eeoC tiNiest ft that thel cc17ei cc dtcrn according to conductivity and indicated 01 oIL-LIft IC lecte-Lo': iS (30) feet depths were still within the active mixing zone. ccL A e: 1 — C C _ 1r C ;f.ftth IctI Ne aste stIll it Ce 'I xr Ieee cee an ee,rcyt from tee W;Ltthcct *.e. t. ranged cc cmeasured Dissolved oxygen, as teeth by the Jinkler method, Cc 171,''17T surface ft 'he Hoerlayer titci to 10.5 parts avarage of 10.8 JJILL'lC-e parts per fi'C million i eecc. at theceec [I 17 per million at the ten (10) and twenty (20) foot levels, and to io.6 .17115Cc 0117 CeLl Thus there was no J.ecel. Ieee level. tIe'.1 (30) the thirty .211 foot 17-million tilLilee at ft lee parts JtectHc per .eelLetNe,e. :17tiIL7 et ceeLu trotfrom tIc-ceo i' Cdepth to significant iniCe theticparts per million one tee variation eftel 1t0. from the mixing zone. 3ftir'1t'LJ-t the tIe tte:eee 17 octoHi another, 211 and apparently sampleseec-s were all taken triLl ç jt ec°c el :sl ç - xrC i •' 11te 100°C, e';tetoel cthfjer ceeCecioeec,o, 'Hot s..rzeectt17C. Nftt . averaged Total solids, determined by evaporation atcc parts per million. :2110cc0 71.5 71 .5 eN or a yrce1c-tCthe I.e use of fx'ec-o. involved Qualitative dissolved rN dticccJ.e ft ions -r oue,rtrer of cc determination Reading YeVreeland Iloretter.. Icc-se'S Fisher C1.; Duo—Spectranal Model 80 DirectS.ceeLeYf:tHixn.caJc NcC.eL ct and cc-2 a e17:17e jIlt so 17 ions 171 1 I 17 C I a detailed analysis was not performed, Spectroscope. While and iron. •treeNee e.eleoere'0 far 1cc-ct found etc are cc; sodium, calcium, 17$7:e000-a magnesium Sc-I tic: .Lcc potassium, 3. 5: Upper Part II Crcc-ec:irtI:JofcC iJrcecJtt'. 11. ci N., M., tel andftftcccncl Prokopovich, Stratigrajthy Cede. Swain, IF. h,COSt? :',' Soc. 0217 Bull. Geol. i1J17,.. Superior, eoJott SXttCc-: erce;'cceo cc' cicose Coo .rct'ce CI. Sediments of Silver Bay Area, Lake of 527 ('Tori/Co Amer., 68, (1957). 502 52.7 1. 4. :t Let; the the .5cereNe*i tc1 Hoicleed Public rOStLeCI Health Association, Standard:/uctl,eC's Methods for 'IyoI,;:l?trs c-rH..re American 1td' 4, American 1 Examination of Water and iaste Water, twelfth- edition, I: 1J! New 17cYork, N.Y. 10089, ft , i e Public Health Assoc., Inc., 1790 Broadway, F (1965) A (continued teece eN on cx; next reef page) 31 1 �is• samples showed only small L.' variations '? the water The quality of' sampled, it is from site to site, and thus, within the CSL area •i'Dr1 and 1ong—she cn.rrerts have produced concluded that wave action a fairly homogeneous region vithin the study area. I&LJ 's{, v; iA J:':ui L::LiL qp- These data, assumed to be normal considering the near pristine condition of the lake, could be employed on a quantitative evaluation of possible future pollution of western Lake Superior. ;- %:t 32 �J rrJY rrL iJ:cJ.n: J rJ-IIR; •J Jt4Jli-J HiJEONIAN STRATIGRAPHY -:.t --. THE FEDERAL - PROVINCIAL COMMITTEE ON ?R-CL'TJ,Y PIPJPCIL PRCGRSS ROIT crli-3rteXIU Mic hines, 2ccLccttl; -Ontario -r A. t. Robertson, Geologist, of cf Jc.t ncDeparb:;cat J. Toronto, Ontario prrtcict of limes, Jr-Jt-i Department Geologist, Ontario J-. Card, -J- JliCiEc-l-; K. D. -, Sudbury, Ontario (cL •Jtt. Jcc:;Lci Geological Survey of Canada, Ottawa, N. J. Jrc:c-e4 Frry, Geologist, Ontario S -- I-o1js icti --s ----o--'--=/d L ) This paper (a) reviews the history of geological work in the Ji ttLi. i(b) summarizes the A Lake — Sudbury area, c0 Marie — SaultCSte. cliJcl Huronian --ce c,t i:ic3J P-Jc;rtH —Pi--itctJ Jo terms of reference of iJ the Federal-Provincial Committee on -c.: ccJtt-trcc .di4$lirLJi?tcJLliJiliEi ci cJ• Stratigraphy, (c) summarizes the recommendations of the committee, lid coIjrr the anticipated I further work of the committee "_I to date, and (d) outlines ----O !:ooccH:ccc r-tLt1cT.cJ-o-c.±li°r :•;L specific problems requiring and further research. S. Elliot J — r -c — C - S.CL - Joo 1. IIiCI :iI:-2ttC The Huronian te : a cfl be J t.orclili.as: rcrt 'U-Es defined to 1I cli ji cT'tJLc.; nc-LcccliiC? i-t occurring Jcl.tcrJ.t "The assemblage of sedimentary and volcanic rocks in the vicinity of the North Shore of Lake Huron, Cobalt, Ittlilictoli on the 2cl*J-unconformity Ifli tcctlicli and cliii lying with li-ili1li marked cci clt.li-ct areas and ccl adjacent Llic CIfltli °r• lit*li diabase A-i tlrA-I by U f d1J li-ciA Archean and intruded the Nipissing ". — I - L T - 2. -. ccciolio-t c-liciclc Recommended ct Huronian IAIIclIliLli[tt Stratigraphic Nomenclature: Jic-cli-'rc: Nipissing i*tcicclic Diabase S5 - Intrusive Contact_ -- EILL15JItcLSuper ccttiir Ck:ctc Huronian Group :cc c/°li (Top not seen) 's-ç1- J1N-cl Cobalt Group tc U:River ocr :dli-Atcn Bar Formation -fl:c-t -ci seen) ccU' (Top not Ii; a5oi:i c c:Acc5 GordonI4AliIli Lake Formation tliCili.ctcilit tti>icL°! Formation Lorrain (Local Members) Gowganda Formation cccocc (Local Members) Unconformable to disconformable contact Jc'ccç-;tic o!CiJtli Quirke Lake Group lr-t-çcct&c-it Serpent Formation fi Ct 1OCiI Espanola Formation :g)Ili5. UrtLc$ Bruce Formation Local tiscontormable Contact cr- next t-eiA-page) tccc. (continued on 33 t)9-of -Jcc:oA (Local Members) �Rough Lake Group Miesissagi Formation Pecors Formation Ranisay Lake Formation Local Disconformable Contact Elliot Lake Group HcKiin Formation (Local. volcanic assemblages Matinenda Formation (Uranium deposits lie at base of Hatinenda to be individually named) Formation) Unconformity — Archean The Principal Reference S Groups and Formations listed I Reference Sections for the to define the Ruronjan in each (a) The "Original Huronian" (b) The Blind River - Elliot (c) The "Southern Huronian' e Mines area. 3. Of three areas: urn Mining area. anola — Sudbury belt. A composite section in the Elliot Lake area will contain reference sections for the individual foxeations and principle reference sections for the groups. It is recommended that this composite section becomes the principal reference section for the Ruronian Supergroup. These principal, reference sections and reference sections to be measured, described1 and marked daring the next two years. 4. 3k �S?tSICiE?4NiWAN flBskWdi ROCKS STRATIGRAPHIC R2LATIONS3HIPS OF SOK3 S'1tLTW2A2fl EXtOtBiPE OW MIcHIGAN AN]) !ISCQNSIN tOF !CttCGPN MW 7TSCONSZN Geologist Harold A. Hubbard., Gn.ufle* ttSsgtTs,D.t C. W U. S. Geological Survey, 7ashington, tLte34 A. t!t&fl. t 81 Gc1E14aL 5wva n- ?:ct'.jc 1ac v.can5t Zvnettat •nnren re-4fl1tatt*b. ,t Ls strtttgttp2 ant. ntw:trfl j.g pt's1c ovr ywkere bawi ssaijç'td .j. ; t.'b Ceeet*zt b't ittrti ': tatter sf Identification of an extensive pre—Portage Lake volcanic formaat extersivo eS tion requires re—evaluation of the stratigraphy and structure of larger area. ext tttA LKvça 3t3&3 northern Michigan 4I% and 7isconsin, and perhaps over an even acn'ezt M.oKi.tct Neweenawan volcanic rocks to C :-.C.3 Ca voi.s,asi.1 Previous workers have assigned all of the 1.ffsrSouth Range differ the traps trq€ a2 the lava sequence, of the the 8cttb foz.cc atwe a9v& tsepanc e but the the same distribution ôiisttibtttifl2 from the Portage lithologically, magnetically, and in areal aM Sn s.-cal 1Ltho1og±caty tr4pe of the tbzt traps separate the Lake Lava Series. TJnconformities appear to Eepcat4 Laze ryiatSne0 South Range South RaLt from fto& overlying ovei'.yin formations. wotvrM and pinches out east r Ser± ;ban' westward Thee Portage Lce Lava Series thins itt P rts.e. ias9 higher flows .'J.ozt Magnetic anomalies suggest that the bigtsr tTi nusfl1 Mellen, Yisconsin. of Hells: c1i; t,ha Jest of the pinchout, on the Wert t the W .cht't.. LjuyIthe ttwlower icw,rflows. tin;. extend Xc4he? fartherWesst west than tX'âfl6 undisturbed conglomeratic Lsturbc coitgto"in'atiO Bad River, steeply eeplT dipping but otherwise sandstone ¾LeCopper 0c5pr Harbor Conglomerate is disconforiable on partly of the e1DtD1t of eroded felsite of ths the tre traps of the orc-c.g ie1t.:' z,f -, oX ns* South 3;ntIt Range. RA.t. The Portage Lake Lava eM Black and Series thins by wcrs more than thsr. a third between the mouths of the B2s"k vaic by and the Bad River thrust Montreal Rivers, a distance of about 15 miles, is not now needed to explain the absence of the Portage Lake Lave Series :r tha! -ht mguer.nLir Lase& 1cs Ju;oc±biai spear t a4 sir.ab.et' tnt nt 4t.tflc ar.on...ise wgg; }eat te t.d SJrsr ;jt Lt&i ct rtarei o 'u Ssrbov ur4etr&Lt' ts dSatoThfl'bt :' 9n P*ratt )4iks a;t thtr tctie.' Urn snCw of *" ?srte 'tsI te 'at tbciist $,ttrat Mvcrs; t óJ.&nn : 't r gt! to ZL t.S tr4ed ,5att tht abcsi:e nf the Pc?tcLgt take ia'e Sefls on ': the Bad1t-fs? River. r. B.i o r Co., wJsconls)4 Misconsin), bae'- EX Ctc4Bayfield Sjsti t" SoiVs traps of the South Viest Watztof? Mellen, flellcnbnear 'at Davis Hill (T44fl, :ap Z •'t Bufl 'tintj iz;. .. sn ±e Xatftea. Y'nw a5Tisa ? ki)G the eesra toseparate ;c;r*L tie appears to f an angular unconformity 563) of uncertain Range and the Northern Flow Series of Aldrich (1923, p. 563) JWac Davis Hill with the thea,e.c%txar;a conglomerate at ILÜrteAcorrelated c o.zesi the at relative age. &ge.. Aldrich correlation c4d this thU casrci&i .n as Ccntome?ete tas*axaw Pstand itt ht "Great "of"ciKeweenaw Point he used "Groat Conglomerate The conglomerate Tr..t :wsfløu4r&t.O faulting. tza to thrust proof of ?e;etC-ttcc) repetition ofcfstrata etntt due ptooi Risga(Aldrich, tAl4xia. of IrA the E,cttb South Range ?apt' of at Davis Hill Iis conformable with ';1r5 the traps Lsttr tLt2 k3 the traps of the ¼be irsp cf the s'ibe ss31'e.t:atti3 of 1929, 125—126), resembles rsststaiee some conglomerates of 929 p. :fl...t2bt fragmental andesites, and fl,mSGt&. atthsts*, South.t Range, similar interbedded ft Bt,z 3az4c,contains c, )cba..n. szt)r tt,erbecds:e Aldrich ".10: (1923) (1523 Zc'ttFesrFlow TttsSeries Satt3soff La The Southern contains bST.SX' similar felsite. •wxLat.a :o1g.,n0 "The 334t4*t bate Davis Hill together have ray,.a B Lii and the conformable t,teCyt1t overlying conglomerate at ant tk et,iz*zsYji.* Range in Tn3(* IS of the traps :repa aX of Lba the South 5,ttth a magnetic :3tt'fl pattern similar tc to Uax that c the ztht:aar The conglomerate has little matrix material Z%SicMretb at et Davis Hill trsi Michigan. ma fragments .tn in the Copper tc f?v.t7cv.ve atai whereas pebbles are set in a matrix of smaller tO Hill appears Lww.?ate *v £zwta }ifl aAC6 to Thus, the conglomerate at Davis co t2a.ltt vS C'azig atre.e Harbor Conglomerate. Lake be part of the traps of the South Range. Poace3 The existence of the ah'a correlation, should be considered Owens fault, requiredt4' byA24rf Aldrich's Ovona fisu.i nvixed as not yet demonstrated. of cn the lower member of is untu 0rbe tfc. on The Jacobsville Sandstone is unconformable and at Sturgeon Falls, ogsbic c2 Lake Gogebic the South Range traps east of This unconformity has been used by by ae.r1 nearly' all writers to ssnxitcviLty 'ut5 tna tssct Thi Michigan. Nfu)iiz.c'Ze Portage Pctsg* the Isc'abe 4 cJ.cSandstone Zcsdor.neis %cyounger ycrnga'than can the demonstrate that the Jacobsville Lake tst'tc Lava Series. eriesD Mke ter.a WI: pitt the r"tsatin xhCfltafls pjt .: tryst t4Iir4.. t:ingn&tfltt at tea ntt.ec re set tt a ic'tt'iz pert ,f te r4 at ke 'a h is J:otc LLe Serdav3e !C2 li tci" tt* cer:&t the rTtde fltc r.'Set'fltt f t)t Lnte ..;)7:Lfltt'ti, swtS itt th se: :iabt' aia at Etrgrm fl.Us f.J ttit31' k' tS 3ot t Bangs raj,e aet tt39tflgtt tfliLt (continued on next page) if, *Jork done .Zr' the Geological Cc'1'gaa1 S'.zx ;ey' D.' tieitr4 in cooperation Survey Division cur*per's cieg with the PubUcation mthorized by by Coantios. ?ubtioati,n authartred of;k.: the!iJo}ssgaL Michigan Dtpt,. Dept. off Conservation. at the Director, U.'I. S.LGeological SurceyJZrccto:.. Ceo1ors Survey. ;ti 35 �_______ t b r't [I ':* 'c ): tti iJ .t .1j-:.1t rnJt: 1'2 5fl'c The unconformity at the top of the traps of the South Range •c-:i.Pc: On the northern Minnesota shore, may be regional in extent. tTc same ¶•iL? paleorna;netic pa..CL2.fle:7. y field1 direction South Range type rocks have the r L.. L rocks as the traps of the South Range, whereas the higher volcanic An unpaJ differ in lithology and paleoniagnetic field direction. C,:.:L River '7.sy near Pine City, conformity can (-j) be inferred along the St. Croix 1ct 4i:e - (1967), and Minnesota from the aeromagnetic maps of Si:ns and Ziietz some of the volcanic rocks at nearby Taylors Falls appear to be •:Ythe b- South Range (Hall, 1901). similar to the Ha traps of -ruc iti4 c: tC2 c f&d 3.]it; )-1± C-t L ¶-1: F'z1•TJ •gyt D ;k; 72-er;. ;-r s:-' C References: r -k VAiC:[ Aldrich, H.R., 1923, Magnetic Surveying on the Copper Bearing Rocks of 'wisconsin, Econ. Geol., v. 18, p. 562—574. CC.-LCtC &e -c .L?2( Iron Range of lisconsin, 1929,j The Geology of the Gogebic ç;? Yc 1isc. t-2Ji7 History Surv., Bull. 71. —c--Geol. 51C and Natural U*y $r-) 1f Butler, The CrV:: Copper Deposits Th:;: ? BS., Burbank, V.1.3., and others, 1929, JIL . 37-*7 i:-A of Michigan, U. Lr S. Geol. Survey Prof. Paper 144. :?J ic-. -a-ccfi; of Y Keweenawan &-!r;L DuBois, P.M., 1962, Paleomagnetism and Correlation 1L iocks, Geol. Survey of Canada, Bull. 71. L -rj s:i . j tc-' i dci5'z:L Soc. Hall, C. W., 1901, Keweenawan area of eastern Minnesota, Geol. ---I --.. ., Bull., v. 12, p. 313-342. Am., )._.,, - JLr.:---21 pre-Cainbrian .r9G Aeromagnetic and Inferred Sims, P. K. and Zietz, --,- xI., 1967, Paleogeologic Map of East Central Minnesota and part of IJisconsin, 4--. UcCI Y .is-ti ., e 13 JS. Geol. Survey, a GP—563. U. 53. (continued on next page) 36 :zt- �______ ___________ TABLE OJ' NOLNCLATU1 I oisr Nonsuch and younger formations C7t - CtCCConglomerate IC,4iji-C (including Great Copper Harbor Ei C Cong].oerate as used by Butler and Burbank) Sediments include abundant pebbles of C of the iC-J CL:flTCC volcanic rocks derived from traps South Range I vL(ttM ! $itk Portage Lake Lava Series CLicC 2LCC!Ccinclude ijL!CZ abundant Interbedcled h! II.sediments II pebbles 4II-= of C volcanic rocks derived from traps of the South Range z unconformity — ___ -- ——- fljiy kiiCt Y&L! Traps of the South flange It.&;tJ1iC -cis1 2 flows, basaltic andesite 1rC fragmental rock; felsites conglomerate 1Etat Davis including the conglomerate Hill Andesitic basalt flows :cwcY liember: !W?1I1, LCJtCC Lower &r- ICC Upper lIember: 1 1 1Zi I -C Quartz sandstone NOTE: Sc • Ct :CI çi C:c c7f Cc CLt*li\ Aldrichs Southern Flow Series is equivalent h 32 kL& ;FLn (1923) CaC CC in Michigan. to part of the traps of the South Range I equivalent to C the His Northern Flow Series may be I Portage Lake Lava Series. — 37 �Lfl Ct1CC16II l7Li[JPCC1CYI PLI-631I*J-C CFPOSTGLACIAL 1 CL &LLLCHE:iSEDIMENTS DISTRIBUTION PATTERNS OF IN 11P1C.L Li1t6jiLiHIL LAKE SUPERIOR C, tH:cicCiL i;LLC -, jcLLi:1rl)1; Frd, Assoc.iat, Professor William R. IC ;rc 1 I\ri R Department of D Geology and Mineralogy —F I1 University of Michigan Ann Arbor,-i Michigan — — C! C on some 100 cores LCEl L for study, a distinct Based now available I (c rL of the lake tC— deeper —C?- parts ltIi F1CJ pattern of sediment distribution in the from U I?. - no cores in shallow water, that is, have is C emerging. We )16 16 which to about 800 feet brown mud, O to 400—foot depths. From 400 C iLIiIHLdi W2 This brown 1eILl dIll -:± i;ilC4!ifrtLlLiIItittiJ 11.1. i-L& 1 is is gritty the uppermost sediment. g1HLi hy in some places, l,iL CC1 cent smaller CL than 1 mud averages 82 c-Cs cm. H in thickness and 44 per stratified and J not C weakly III it appears to be massive or micron; ClltlILi1Hj2Q JLlt 11cLCV 11ileILCI11I JgI11tI of hydrotroilite. contains moderate amounts C — 6 1L I& r' I I-— I ! C I CJC I ? clay tu a1lLJCI I:ICIL,Y 1L7H, brown 11•tL ILL.ltltIIIac 11H1 Underlying the mud is a very fine-grained gray -:Cy 1 r4l brown mud which, in water depths greater than 800 feet where the — __This gray clay is r-1-massive FC tC the topmost &CC!C4I C1413 sediment. is lacking, LC11 I(i becomes LLlJC4LL4 i-tLL13IHHFH thickness H 1HILI i/ CCF. CL; it LFi?.LiYLLICI1 averages 98 cm. in thickness and IiI!IHiLLI attainsI 11CCLFHJL a maximum known 111 C and 85 per cent of this clay is finer than 1 micron. cm; of 445 C 1 1 JI C11_ gray The the massive clay is marked by the abrupt C — lower — contact of 1 The varved clay appears to be -C1 laminations. iL_IYl I —1L 4nC of varve appearance I C 1C gray clay except for the presence of the identical to the overlying L.LLOCL L*HC-iuiaFL©1140 distinct laminations. I 4 jr 1 lI_LILL fl R I6 IT — [ C CL III L — stratigraphy C. CC-I CLHbLCY of Pollen and geochemical studies,I as well as theCCLtCI I4 I is —I no sedimentation CIt_! these sediments, suggest that very little or LII — nL uI the central 01)6 occurring at present in parts of Lake Superior deeper 1C 0 The massive gray clay is apparently a late—glacial LC L1 800 feet. than ;14lt6the CC OTI1O© deposit which lake bottom. OTt exposed •H0I;C01C on ;C;Co;:0iiiLlli 'WLiILCik is Co still I cL! 4 6 4 1 3ff 1 �icfftToMSEDIMENTS I ILIMSUcCIcFROM ItIS-& PALYNOLCGICALSIllS' STUDY kim OF 7;:S.lI*STLlAciTcAl,-1 POSTGLACIAL BOTTCII .ll.lI:ir,LdiIfj.l ?cIti Iln1ncimiLOCALITIES 'f-5jfTCYif Iji-li IcC IJfThRI&f: DEEP-WATER IN LAKE SuPERIOR 1:51 W. L"?' University Botany, The u-1H:cact ifof:3Ci71d1c Jri-Ilc-cc?I.. Department lcmc;cctjngrcc:c, Professor, S. c Benninghoff, Michigan, if !ScL-Cccda.c of .Acur Arbor Ar:::c-Ann and c-giuIttrt I:cc.ic.ca.c.Judith N. Franklin, Sa.c1:ciru Assistant Professor 5'ac'di: .i-L 17i Orchard Ridge Campus of Oakland Community College i'ji Farmington, -nfl .1, --- Michigan ' I'd\ LI_F --k---- I 1 Ucicca:-f cfl1deep—water flIt- V-iTh-i•i Ia-cf ..:cca Ii taken Palynological investigations cores from fuy11:a:±naLc:I Itacicu ScLcc;tcrc-r.L:c of ?J long Farrand revealed IS' CJc::flfi ict1c I;lIlI3cilmbt :CriIcifIl5 ca-cl 1962 aIl1:- by Zumberge and areas 1961 and cip ailci in Jr .f51:1: ar:-icc-ofiS Lake Lift: Superior 5ilI1ILLIct ca1:Jilt;_:iL cicc,au.f.cacavc, ii&1i iLl youngest sediment ac'ca-S 1::-' of microfossils, even in the a itiilYiLiIL'i surprising paucity n_ -C 1* rca -I '[ layers, and steep gradients in distributional anomalies (Benninghoff, for further c]7tillr inquiry Icati-ic ccii was ccvi suggested calif by: i;cftid/1 Need c'd IclI Taylor, and ficIll'd till ticDole, St 1968). Ic, the III fcct;fli;t a. —fica (b) (a) -c--ca the cc.is:nscjccj general itm'caca'-cccc absence idof — plankton general ttctiti.7scarcity Lutciricic remains, ci-Churin n Ucci aid pollen and spores, (c) the variation but local abundance of fossil ar-i ha uaccrS.ac:c-i i- cIl,u in Cc cores atciliL I ci non-arboreal arboreal to equivalent levels c?lc--ciim-cr: ccci pollen pcc.fltc ratios i-utaru Itatcircd.ca-rtc: ItcLIt= Itt widecccat Cd) the UncUt,different ;i,.ffSc:cau, c-ca, tn-S different .cS1Ia-.cct nUn fLcscmi.-icifrom locations water depths, and Scccc-ccc and ctcc-ag:cfHcof cc?degraded d'c'ccccIt—c1d:iccc1c_i 5cIlLnllli spread occurrence and fcc-:.u,S. local scarcity fossil bi-saccate r-r--ch ct-c crtrcarcu .1-ic;: :.i;;c.it. rather i-utica cic-c'tfimr fhcc-imJurllll ct ,c'- JISa:-?resemble rccct-rctu :;ca—Jclr dccc; that .:itc ctlii conifer jc-c1: pollen grains certain early Tertiary forms -: Itt-; rccuiiihiclL1 II means Opportunity -1:: explore problems by UTI;: iictUc cirtic forms. f.:cactu cac;iaccc. these cJep;::c*i; cUll to than Quaternary Y Umct imTh of greater sampling flexibility came in 1967 when the University of Michigan Glacial Geology and Polar Research Laboratory was given 92 _It nc —- 3 to 5 meters long, flbJt1i? I ru by the geothermal bottom sedimentr cores, each imi Terrestrial urn t &' the Carnegie — ci Washington research team of Institution of I_ chic MagnetismI Laboratory. The photographed, and logged r cores were split, Xi Cores were then c1t selected according toI their location, stratigraphically. C_ Utt-t ftc-it their cii analyzed c:ici:cati. for u-crII'civc to tic be water-depth, bottom physiographic vctcr-li-ic fLc or icc:57- Cci cac :;c'ca'- setting ac-c-LcirThe study was ca supported Ilklarge ItiiJi Ia.I part Sic' by .dacL.rca National Science microfossils. Uchi uSic-:' ucci c. r-tctdin c-iccNSF Sc-CSummer Ida in 51:c.unccr-d-j Shithtmcl-5-fl Foundation -c-icc Grant I-nIt Itt-Jill GA-l122 c-crc7 and aided by an Research Participact-c bitt 'cc tion Ucliuc Grant. ISc--crf;c- i1 1LcaII Il _li_ fcci.-.fl hI i1fluiq •I-:c'.i if 1T Cci rtimlLt ¶ — 1 n? Ii :' I'-I-ic 5 t6ii — — 1 — k-J=fl.kLI cc,ti I [ - Lt-' 5iXparti11;: tic-i waters Itidi itiC Microscopic —c-jc'tci planktonic and airborne -D cic-IttUict -rorganisms crcauccra. in the cles cat such as pollen and spores falling onto the lake surface would be c-fCc-ct cc-c2-t'Sc icacacciccit: c-tic bottom flhtfici-tI€I ca :iftnrt expected icc to ;ccIcctciccai contribute 1.niicP more or less ct-ca.itc-c evenly to accumulating sedii-ed ic-ic- I. spores tail hat and urrcc-tIc:f ic-f -i Near 54 -ca It-cacacci absence of and scarcity of pollen ments. cf-uplankton urIc lcc- forms fcc-cc:tt uctcc: Sr ICc aIim cci lc'5's alci Ic-icc-a ca-icc--ccSti at uc: in theue:u-me±asediments frIrIcluf implied redistribution before deposition on -1:5-n the bottom. L'c ccitt-cc ctc-itTh:tcct'cctccI To test 'Sc Cut fIrthe i.ed'ct.titt assumption C 11 of LIt-cc-cc'S lateral transport and gcc greater sedimentation cccc-arfccrcc ct-iI —-along JCf2 lines norrEIc nearer the shore, analyses cores lI 1 -- were made of selected J1ii-fltYnitic-c-r cca—the concentration graccfr:cJ:ca, cores 15cc cccl. to U: adjacent shores. mal For in tifr a cmctuc-nctcl series of c-it 8 cia--ui 1:ptSccJt-iw ac-cc dients and tac-tittill spores c's at 0.05 core depth show an Lcnct*iicfft( increase from cUcitci of It pollen 'cc-I 'Lii cab 5- IcESma i-c--ti-i nearshore areas (1,000 to 3,000 m from shore) to offshore (25,000 m) T5_I — — cincac-clhtciis hi cc-it c-IIcutc-.c5:fl 4' ffg 5 this -I'cLci relation locations. There are indications, however, -- '-i- that not Even where pollen cc-tI and cc-pcnnued spores c-cc-crc were J-:c.'d-relacccl cn:t©cS 'dc-c oriented the same areas. inc-ic in Fin Cuz-s cc--clJ..c-rcc tic;all cii cc-tScc, clcc:i,ca -hlcnh'a; ci.-ci-cim;ch "ccSic-tic-' •c:accscc1c. tively abundant, t1:cc the only plankton microfossils cl;nc: -itt 57? found were diatom fruscrckI-ccc -bc-c-Il-- I: cu-I cicic-f-- and c-?:fccccll:cI€lt5 iLl-it' '-ttaiict sponges, tules cccii CL-crc-c and simple rsictc1t iccludnlcr spicules (megascieres) ofcfresh—water cc--u'-Lc-cu lILt icc-bc-tact •YcICit StiLt Cc-c-c-cc ic ilIc-cdeur these Sicicuc: in concentrations twoi-ac:, to three orders c-c'it of magnitude less iSacc than tc;k1 the Itcuccuct thin pollen 'jc:crrc-cc those for 'c-cl ian. c-rccf and spores, -cjlIlk-Lt? 1_u-rm - -c — It_ caid— 1 I — - -?'Pt7L mc?, next 'c--im'd (continued page) — ..on - 3k'5 - -" - ,cim— -—- 39 — �jc 553 C? -3 !rfl(fll1 ! •3 3•d, 5 CL:L.0Iand 335), l1oç14:int;, given .55333.stratigraphic 3 577. tI; C;]bA The j1Th52 relative abundance of pollen spores ;114e taken within 3 C c j groups tIld be correlated levels could even within of cores ac 'c not 1a) could the abundance be correlated with a 13 3 a few miles of each other, nor C Some promise is indicated 4c -CC'— small d1dI)3 135 given matrix lithology or size grade. S C1d for correlation of pollen and spore abundance with bottom topography, i'_J C j 3 for CIv 4h needed adequate however, but considerably more sampling will be 3n_ a _ (I CtC l3 —13 1 — I II IN - o l1Ia3 jl 5)1JJ. t --3c1 % I l II L c — lCI V — I 1 L testing. ACC333l7 groups 5113 of 5I 3C3iC.;ii. •; •)j343IL to SC 3e5;c;crsL5 Shift in3 the non-arboreal arboreal m;f)!i pollen within ;L;• ratio 115) .: CLL:I5 —c11 i_L between nearby d l33 a1 — ]L of cores may have significance for differentiating çT 5 35 present) and distant sources (only long3 INs sources of pollen (more NAP 3 a a and oak), although differential 31 LCJsc a0 range AP present, such as pine, spruce, a 5ttoç3; cci;t:C3i311 placering 35 ofFC3I1L33C pollen and 3CL spores tby bottom currents remains a possible 131I i3 L li iI d13 cause. I III 33 conifer ) 33i1451SCfossil 5c3C:c bi-saccate All the flSL 'Js cores examined have degraded Il - been exhumed These must have -a pollen resembling early : Tertiary forms. Li 0 There are 3 —C 3 from geologically older deposits and then re-deposited. conifer pollen small variations in the absolute densities of the ancient Ca ancient conifer 3 populations, but much greater variation in the ratio of c _I referable to Quaternary age. SIt is possipollen to pollen definitely — N ;3 - of transport and sedimentation —3 3 ble are indications S C that these variations ii —topographic depressions. 11 C along 53 depositional in certain bottom 3a#L3 51 gradients L ancient grains But the greatest Jmystery is the source or sources of the 1361glacial LtI4 3333 311133-IC 33113175613111 by 43 Ctt:1 613 3753 reworked that were evidently action. C3N:' (3 l 1 13I 3 I Ll — l J I I I I ç1I 31_C1 Ic I I1 1 33 -t cr773-Is to contributed little 75s .73133313 133333-3 sediments 3 Microfossil has 333373173361 of bottom 3c*CL61cCa IL analysis Superior and Ca CN. its biotic 1301 LL in Lake 35 organisms the3 post-glacial history of C 513 Suspended the lake. 113 i5 province, but more to knowledge of sedimentation in 131 3 75 ]j1 levels4 of the water 3533 in offshore areas 5are evidently particles in dli the upper 3— 33135 flh;,a.c:n 53353.3:31 Pollen and ,53355-35c3 1337533 dIv)3S1i.7) 3-n inshore areas 3111±51 transported laterally with shallow water. CRC552Ct33 133 133537)37 to 1333±437 flocculant £IL:s,3353:33tJ. material 17 :I3335n.3JL 13o3t byINbottom .13 1133 spores are probably moved also in bottom I3&1333 ClOt 3;137-1333 153 33Cc(I4C1 LII_C The wide variation from place 11 currents and gravity flows of sediments. 131 in proportions 375 1I2LI13C3to place in pollen and spore accumulation densities and 33uL)so1cd3s)I.tctEv 345543330) particulates indicates 3t35c17 5e37 355353753; tIN;t .31L3333) of -51.751-3533377 different categories within that class of 73333111 3 of the nature of j75ti strongly process for particles 1 that the- sedimentation E_t descent to the bottom. 30313333 533 71313one CCCof IN 35375L27 3-333130175 3..C6113- 33 7333 these5 13) microfossils is not simple vertical R — 1 J 11 I — — — I 1 T . ic c flt 3- sC I-1_ - • 3-d-_c Il .73137 +0• Ca_ I33 ç5c v — �Th - NEW LIGHT ON THROUGH :':: ANfl'IIKIE AI.WL TyLr-STRUCTURES rCtC;'?j1¼ LS5rI[iCjt. DAR1'IELD ILLUN INATION W, 1 , S9!t5 W. Moorhouse, Professor Department CC 7Cfl; of Geology University of Toronto Ontario, rSC111C Canada 1 1 ¼ci:n Algal filaments and rnYt;; 1'71z other 'j5E5 Animikie :..7rsc structures are preserved in some cherts as lines of inclusions of minerals such as hematite, of organic U\1 ! r Such inclusions may be quite unimpressive matter II 5 ra-1 r- in ordi— ;L, _— or of fluids. 5 3 JL character, and nary illumination, and yet acquire a three-dimensional _11, <rv — '[i irt; darkfield illumination. greater continuity, in -even an appearance of ¼ 'HL :'-c Grain boundaries and which ¼ n" cracks, C ?LL(i in darkfield may simulate filaments, reveal their true nature in phase-contrast, available with the same gr1 equipment as ¼ darkfield. l &- ' L ¼JCu ' -cr , 4 LL -C,', — ryr '¼ — - It is possible i) that 55[1 replacement :ryyrci©y: (diagenetic) cherts can be distinguished from cherts deposited in cavities by the character of their — 'r darkfield nor phase contrast appears to be of much inclusions. Neither yr,1 value in interpreting microetructures in carbonate or silicate rocks, 1 because the strong contrasts in index of refraction emphasize the exist¼ ing grain boundaries and texture, at the subtle —, expense of the more F traces of organic remains. _ç mr U ir ) — LfJJ j �73 POSSIBLE GL'LCIAL 277133731 .3'Ji< ?7:3 ORIGIN ±727. FOR ThREE PRECrJ1BRLN L. •: ' -Ill: OF NORTH ..I4.J_ SHORE I ,i i_1)t3T L J<.. 313 CONGI (HtJRONIAN) <rrp-<7<<clr <f. m)77:iP.c — .wIf LUcE M .rt:n.anaip- Ct?L P Assistant The G. N. 37 Western <fl Young, <cai<*& Professor, )t2Qr:3(1-13 IT? University :i31237$3 of 13113.31:73 Ontario, P.l1C<<). T311311< r113 if'c Departhent of 317 Geology, London, Ontario The F. !, 13 Chandler, 11133. It Graduate :1:1 _Cfi Student, )5C)3$Thi1Ir 3t3 University 3t[ f]i33f :-;' of ) II Western <3J32I3) Ontario, C75I7f73 ' Lc<r Department of 31 Geology, 31 )n1V .11731:, London, Ontario f Cli For origin has 3TT7Z more 2:-ty3 than 1 3<3): been suggested 31qjC. fifty years 3131321 a glacial 1C333C 71 Recent work for the Gowganda Formation of Ontario. 77) III confirmed <333w <3L' has 3<v<'H 1431i )1313<313f31: <P7 the of early workers. The Gowganda Formation includes a wide r-=_ 3<3 opinion -_ ,. p I variety of rock types including polymictic paraconglomerates, ortho— 11 conglomerates, sandstones, siltstones and massive and laminated C-1,, The laninated argillites commonly contain large dropped argillites. 1L of about thickness Gowganda Formation clasts. The f3Yt;r3 143pL3t has a3232 a '3 maximum .rs3 12333 :r7©i. i1/333[' ;4t?3H1% 3,000 ft. (in the southern part of the outcrop belt) and the present C areal extent is of the order of 8,000 square miles, 731 31.7t3t J4<3 <3t ;173fl1)3 32. P,l f ry3 I 1P — ' r - 7 CL , -J -. fl : - C - L Regional paleocurrent (Lindsey, 'C <Ju <P!L)Pu}Q 1967, Young, PJ(Tf IfILI investigations Rfr3. •rc3f: -cTI3LP 1968) indicate Formation was N fri TC 3 that P14i the Gowganda f__I -cI_p derived from a northerly of 30 new chemical analyses of argillites and matrix source. Results 1? materials 3711 from Inc-1LT the Gowganda conglomerates <i13: 1331C7 indicate 1313 :3a3 differences 3&c3I.cIP3-qc 3ct3T3ic3 chemical hf-jJ between the western parts of the Gowganda outcrop cr;-t eastern and Li: Jfr 31ta C-i13.II3. c: i33-Jjf> belt. These differences are consistent with differences in the hinterland çt I33 32L33 ;clct as )-P-:r33)TT37V P7 :Y 'ct C-Pj[)--f<fE C of indicated P3 similar P. i2'k373t3 by YI3T ;3J3<t studies. C31';f131< Glacial 13L3f3 deposits ucPr. aa3-;ct age <h; paleocurrent p: described by Pettijohn (1943) were and Puffett (1967) from areas in r 3 —CT Michigan, 1 - r-' C'3i3 :;,&c i -- ii .)1•- c — — Polymictic conglomerates also occur lower <Ir) çt E).L333f331t1 •31s33_ in '<1< the 3) Huronian 313 succession ThtI'31-s T.C_.: The most extensive of of Z?: Ontario. tçP333; )fCCa.1*.!H .c'i&f<4.c of these form1 part 32. )I3 :- the Bruce ptp.I3 and The conglomerates of the BruceP and Vfhiskey Formations (Roscoe, 1957). 1 33< Whiskey Formations contain successively larger amounts of sand—sizep3 material. The Bruce conglomerate has a present minimum extent of about 1,700 sq. miles and F3 a maximum thickness of the order of 600 ft. The Whiskey area of the 1,000 a.331 conglomerate a ;:.<c ic: .33:2 of t: 1IIcPT3fP is known .3ftlIrY to cover an 3 6tc order 133) sq. miles and has a maximum ICtt tIT thickness Ct-3ttT3.CT?Tt. of :1 about 600 ) c — < I, : '$ 2 H J I iç3r 3if i:Thft ft. Although many geologists the of glacial ;;cCi:3P5 mentioned ct'I9'.? ii<. possibility .t,.l . these L — origin for conglomerates they were formerly: interpreted as mudflows 1L lpC — Dropped clasts have been found in bedded related to tectonic uplift. • 3 6;.? If; <2??'' t13, 7j;3 tIl. j)<!:rf(<:iC sediments above both conglomerates. Together with this new evidence the following support :cr <i')iIS<: points 4©?3a a glacial origin for these conglomerates: j'I ttX ' ?- — ;3a :1 rr':it 1' II 1. The widespread occurrence nature X32t'13 and homogeneous PC' %33:)t33 of the conglomerates. -'c33)L31t© 2. C?. The polymictic nature of the conglomerates, <13! çCfp:P.. I with (*s'P,7;C?i3 many plutonic rock fragments. 3. 7314 (t: ç Ii Chemical immaturity of the conglomerate matrix materials. (continued on 0c next page) )*i?:. �S r4ttencse f isig,ifloit The &:alCi' 'ib.absence of zt evidence of significant topographic relief tectonicsuM activity V t4jor5fl9 n.kcf øt' or teft.or,.Q in the source area. J?i 4. Lt the sot'.c orq , The ?vuii conglomerates ia.c vary S. in tbt:nvsee thickness from Cbz c,cg)oaomttcse place to place, but •j4.*tQ i) ')j4Cd. bt there is au gradual thickening from source. td3ktsirg LWaway i?,Tá) DDIL?Stc 5. ...., opt:no ' ti.. Urn oacjt4tec t pK.i*r stcAtttaL orierba' 6. Kcçtr4,c Elongate & megaclasts of all three conglomerates exhibit a r.ti%.rai regional preferred azimuthal orienta- tion. I st z ttttos wcter Most of ttth the etw,asei associatedsedtaeat. sediments*&n wereae,oafts3 deposited i4cut 7. in shallow water. tJst 'c Glacial interpretation *5' of these conglomerates Thc.itl icflrpcta±iw. tcwltYa..3pisLainit.keeping ?cseptizwith dtk .ee!?tt *ib5titvtiC investigations, wattt,.3rs. both recent paleomagnetic Animikie Lake ;S ?1is bc. ciin 4,.the he 2h?gi7 iktsoff the Superior region ou c@(Symons, Thspecis 1966)a1and GowgandaYoncuton Formation or of Ontario u.ire .tç'&i '.viinlisttheecwe$ie Sto:t £97j (Symons, 1967) wEt which indicate ba€: high iatat,.ito latitudes tinthese these !'9stC13 regions 1J in Early c' a.r4Lttc Proterozoic fltS?CViO times, t4s.'i References: tn.rçrt t s Presssbsz La 'iL 11. Lindsey, D.A., Za5.flCaP7 DA', ., 1966. Sediment transport in a Precambrian ice age: i96G Seni#tt .. 154, t4i24. The Huroniari Gowganda Fcthati*c0 Formation. £QiSZY3Cc titi Science, v. p. 1442—3. LSL. p. 2. 2. Pettijohn, I'ou, F.J., Petttü.-, çsi* .., Puffett, 3, Patfl' 3. ., Gout- " Iç In.tct"rt em tty s/ta; {g earari tsst !cSnr nirt, ?azvt14 At.si Xr.tt W.P., 1967. .z.9& Structure and stratigraphy,s including Precambrian tillite in eastern Dead River Basin, i'Iarquette County, Mt'cUsan Michigan '4.$.ct..' (abst.) 13th Annual Inst. on Lake Superior C:n.t;9 It!at i4apaior Geology, p. 33. tsoit pa % 4. , 1943. Basal HuronianC*bgJ.?7tflt+U conglomerates 3! of %crn'nzte, Menominee £)vrzDt?t 190.. Ec4 and districts, CC! Calumet QtAt&t1t JStfl.OlflqMichigan. Kttjpzt1. J. Geol. v. 51, p. 387. 3fl., Roscoe, itcw** BY...? S.M., 15'.T. 1957. Geology uranium deposits,QCQu.c Quirke i,tk.t Lake w = acal©y ziand ..2-3.nLs topAcLt';,. , Elliot rss0 Paper 56-7. Tiflvt !.stku 6.. Lake, Blind River, 3s..wi.o.. Ontario. Geol. Ce*i- Surv. Can. With i2v&Symons, D.T.A., 1966. A paleomagnetic study z' onth5 theGtLfU.rtc5 Gunflint, 5. ;tuinijrnatA'i flidr 5. Spas 196C0 A i@bj1and satCuyuna tiir iron ranges Mesabi, S.,certur region. etns*i in .:t the :us Lake t'&s Superior flc.11. Econ. ttbta Geol. v. t,ra 61, p.a 1336—1361. j6 t, nt c.., a of . 1967. Paleomagnetism rocks nokL near t"tv Yn 'cY oc1a3t '5 of Precambrian Ontario. Can. Journ, Xenkt n&.—n69. Earth Sciences, v. 4, SS.DOb3 'Va ., p. 1161-1169. 6. tt. Symons, D.T.A., E;.ttua9 Di'. 7. Young, ioz, 3CM.,. G.M., L$S 1968. Btditer:r-r Sedimentary ct structures in Huronian of it, En: r&.ea rocks : :sts *1 r'.';t Ontario. Palaeogeography, Palaeoecology, Cai 7siaeat;ç ttp? Y: Palaeoclimatology, Pc:i aec iinflJny, 2h'ir. 3t Cobalt, Ctt*ltç .'. 4, J., v. a tr p. ],2:3 125—153. �'ft itti jftifp/'f .f'/tIL NORTHWEST Lcit. if i-f/P• CL//I FEATURES 12-f 1f-1f.f' Tfi'fiLf'ii WISCONSIN* tic-fitti OF THE BLOOMER MORAINE ICE—STAGNATION - IIo.::-i2'f..Li: Robert F. J.it-Y'$icCEi.Black, :it1a-k.., Professor ft-c-cct.C,Ic-cciof ii Geology Department University of Wisconsin Madison, Wis. -Yc1cccccc t-/c; S I _II i/Vt /i2,c ic--c -/ of ./-///V? part J-C/t The outer -li/c/-CC/IC Lobe c/I' Late—Woodfordian (Cary) -i-i the i-f/I Chippewa ---' / of IIIL characteristic a striking and age stagnated in situ, leaving behind a i_ s—a a'-' c- ice—stagnation c H glacial or dead—ice features assemblage of forms. The -If/I -I-i buried The /.//ii '-ci, ice c-/cc-li/il-a It//tic. of melting i/i/c- of partly are the t..Ii1 result Icc-i- blocks. C/.ICL:/,1 out lilt northeast l_./-'c-l/" is characterized Iric.Jl-tfc/-Cc 1/ of Bloomer J/Ici-Ia/' ic/tI-fl-i lakes moraine ic/i /. kettle 'IJcIJC'c.iC/I' c-cnc-'ci by b-I: small I(commonly ccltcc2C-l/iHIt.r4 iiL..IlessJI'//i-c-/ than 1/4 mile C.across, although a f/Ia few Thixc-Jr larger /'tiC ones are i'c'/C 5LtIL/I121/. 21 i--J1 j< ¶/I I - -ici i '/' cc- -t:c i-it-hf. i-f"i-' kettles, present),i- of kettle swamps, of /iic-ii of ci intervening 'Ic- :;I-rc,cc- and c/I dry /Vic CT till and -irregular 21,1 c CC1 small knobs of red, sandy, stony C' 'I kame deposits. 21 dark / i--ScIlarge mounds c-Il p j /ci-C ii jc-=c —iiS grew \i-cNumerous genetically-related, Ti-,, during deglaciation c f/I I Csurface These mounds / c-ti debris plunged through as water and the& ice. & I— Lrii.cfc i/ic-i -C/IL Cr C El/it include l//.'I/cL.cCIL conical /lcC-\-Iiic/i'. moulin )cc:ici--c kames, straight sinuous eskers and icticI/Icilicicrevasse iiruuit-c'li.'/ to cci I &ri' large C sizes, and like deposits from fills of different "butte ' — 1_K— i//c feet f-ic/-i 2/cc to ;c'fst-iI;r -iiL-c-L lakes.. 12//a Generally, cc-c-Hi 20 'It- 60 formerly f/cice—walled relief if is only Licicc-i-c-fJi-ti ii-'C'iI C/i-— C a_ in the knob Cc and c-in swale topography, but some of the kanes and ice— /i&/_ C 1//cI I -u/I Iclargest mounds Cc are one walled lake deposits exceed 200 feet. The c-1-a —_ _ mileLi in diameter. Several &-I/V( P ¶3/' are aligned ic--i- c- northeasterly and northwesterly, ic-cc movement. /ciç'-///I//c/V c-%lLI.c--:-c-r1t 3/C.-i/'-/ACi/i-Cc-/i to ti/i-' former Ic-i-C/iCc' ice parallel and perpendicular /1/c the c-c c - — c c /' ic , 1. — & -i 1 V y/ L U t- — 1_i- c 1 — 'i-:: present fc-t-C/9/c'I geometry cc--tIii'-D-; of i -I/C-/Icc-. -./tlake ll/tlti/I/)/IL/i/ cci-L -// c-i--C-ill-/ic The -ii c/ti the ice—walled deposits and exposures -. i-a -r c-1L show them to have been the material large openings with ponded r tic-h /_ water iCti '/i/l/ .Ccc/clIiIc, /2 f-iccDebris was supplied c-tic/ic-"I-IiCtitcil/C f-chic/ic much of the time the deposits were being licci i//c' laid /V/c,i. down. it-/Ifli Ci_'I/c.,Il C -, at various places around the periphery of the openings, building 1,C i/-C '— C deltas and slump a/i1 '. ._Lj_ ridges. Much ofic/I-' the material is bedded; most is /t-ti.l: ,a_-rCciL_c/I1_ i,Y/cIl-r///f./'/I'/l -C-ft//ic--' '-Vi-] .iC/3cIcfc.'LI/1c.t't-cc --/;LcI/fI-/cii t/c/cCiiI/ poorly—sorted, fine—grained clastics unsuited for f/IC construction aggrej i0& -icC ¶//—1 i-c-ic-i-c gates. Locally, poorly—sorted, clastics are inter— Y2=c i-/I coarse—textured c- i-- / 11c- sediment. Small stratified with till and other —cl/i C/cu' kettles dot the tops 'c-.i-cC—ct--i-/I-/a c/I/Ill C ti/IcC ic-i/cci:/c-ccaIi of c-c-i-.some -cJ'1 of the Lii /Lt/IC large ice—walled lake deposits, and I/CciIi-C large lii'kettle lakes adjoin them. cat /icViews from the top of mounds are excellent. - several C r'-L)c-I/ c/i/te i/I- /2-i/11- C/cl" Some k//iC are I/-i. now in Chippewa Park, the 1Ccci--it best 4/Ic) are outside it. C-- but ic/it.- i/ti-c, fill.c-IC. County :/i///tfll' it/Ic c/l I —c/ c-c- should i-i A larger area the better -aic be set c- aside to preserve some of ic/I-l/cI-C/-i-1,l//cc-cc5/'-i-c//i-c IC,.cCL now [c/CCprotected. yL/-/}t'c-/c///I. representative features not ci of , 'c-i- I ¶3 1 cc—, - ici — j 3 ri ' & 'ii- 1 ' ccl ti — C/I c-ri/c C J /'c-Ci. it-i- lit--il ic-- the r-iI.t'cc;tC- by *Field '1CC-C work leading 11/c. 'tcI'c-ciabstract this C//CC//C: c-Ic-i was supported National IicditI/t to .f-iccic-f/cPark :Y.rck Service. 4k �tw oi nv rjr:ptkLZQ is ts, THE SEAMAN METHOD OF iINERAL IDENTIFICATION AS USED AT LAKE STATE COLLEGE tME SUPERIOR Si"fl2 AZ 4.(STh>. C. Ernest Kemp WnssL Yei' of c:aszt.sc tt v:wnt e! Chairman, Department i: st . Geology and Geography .'xf 04cawt$7 Lake Superior State College Sault Ste. Mat.e Marie,Ucbi1rar Michigan £a;..t )*ao rct) t ffihipst t# srfrtta::cu lAit t!cr, tc4't 7'r *ws' f;ttj 7o.' 1s sp;caSt tc m."zncc'p a, n&cctrtztin r..tsr' ati*it t.t 1.s tsst tL., LtcS4flrzLCi .:t1'ai IJye':.: t'7..aeau.ut At Michigan Technological University unique method of mineral identification has been taught for over forty years. useful '&c a This tCJLZO., method, the method, many a1"c:.ttszn advantages as a ti'!C:'. "%tMMt S.'Ac has !'3y Z& Seaman ii.to i iteci :tt Oat&*'h approach to macroscopic, nondestructive mineral identification, and besides be,nç ca useful tool for teaching the fundamentals of,Y. a;sd t•caL3ee being 3Ctb At Lake Superior State College, .'t tc. Ft4%SttCC an appreciation for, mineralogy. SC: r.iA4 has 3A b.ar'r.. kth,iedbut tccwith eitt' MTU, the theez.r sameate method been adopted Sa branch of ts'U .?c primary ptia-n' is based on cleavage as the e1;.?a1: P5 modifications. The system 3g property. Because cleavage is directly related to crystal btC&.re1 structure rdr_tI and has not been intensively studied, it is believed 'I.lSD-r this method can be developed further ttC, and should be more widely t?Lc t•; th.t bow gc3 LtLCc &q The paper will attempt to show how the method has been .ttsu'3çb adopted. tAt. ps.-t' and how it could be improved. tL:r; !tC4 &.i.d ban LY weaknesses applied, its advantages and its fk.'5tst'j;V tfl'gt gilbez%.. to y 3atsc: itt cs!.V flntisn u.iiiCfl It f.ft f :fl5 .j1tS2ICiV#i' stiLtt1'• .tt f! rviW aji4 si'! a3r si' ttd ,fl:cr.2r,s aLtEl? 1+5 �flACT STRUCTURES 7:'C74I3J 54 545454554 7 541154HJ'54IN 13 THE CURRENT IN-esIcLsP,515543 INVESTIGATIONS 54OFIi'MEORITE CANADIAN 1541 SHIELD 554L3C&tL1 Ont. '14,54":tLt9(5 (5bs,;y55,ci1'1:, •'(5SX5 54445., L(5Ltssc, Research (5fy .4555 ?:t54t4CS(5C1 R. Dence, Scientist, Dominion Observatory, Ottawa, 71, Md. . 54 (5:i'-t 411(541,5 c;:'54,,:: 1.5(5. Space Flight Center, Greenbelt, 4(5(54:44,54 j(5c#55 NASA, Goddard Nicholas C's 547 1(5,5: H. Short, Michael 1 (54455-4(5.7 11 large ancient 6I' (5555L yiIlll meteorite (5':H545 54(5. 5(5(5 of '(5 possible Scientific (5:54 4471771 14; investigations I) I' 1 7 (4 in 1950 with the study of the craters in the Canadian Shield began 5lss41;s'8:Icw of .54 the V. B. Meen and SIts the discovery 5, 4:553Y, '1C1'sCrater 5kI 51 Pleistocene New Quebec by'V Ps54(5.54SMS' 55444 of c (5s By 1955 a systematic search (51S' in 1951. Ordovician Brent Crater (5:55-5554 Several '454'IL(5 44754(5 5445443 underway. craters was :i'j7,'(45(5 (55(5(54(47(5 q541 (5452(5. for aerial m3.C44,5444's35 photographs 54(5 and maps other 55574(54, 15(5 '54157(5 of which 5(55(5 C:.1*54Yi. have been studied, .554154557' :)744454'SJ' t,ts"541.si' 'Hc"J dozen circular structures ''?- approximately 's.5,t';s '.7154":W 5.;7:2fl4-21i'(5'n.:e .1:.(55( of meteorite impact. (541515 kr;.I-i', 'Es show (57 are 16 known to positive evidence 2k 4 4 I S . 54(55575,' C's' based on tk,t' the541541545515 analysis 's'? of topography C47;'5d54 (5541 s-s' 1s'st;sC Early 11 investigations were ''II41's and .5514(5 lunar ,?t?I:444741W. "(4;,"; Barringer crater, Arizona 5454ti" ' 5454;t:Lrsts41 4444t15; 54,,(5L11(5hi'iii5I data taking 5551 44(5,k$5(5 and surface structural and seismic methods (55'. (555(5 (55(51 .54441111.::'.,. '4754411551'(5 154(5 The use of ItS gravity, magnetic (55(5454 55 craters as :5(5 models. -(5(4W J111 and at depth was begun at Brent in 1953, 155 Ci' I to (5 probe promising structures These crater. 5 11 drillingY'(5 at the same 1 5 was followed in 1955 by diamond 4' (5 55' in use, so that geophysical data are available methods have '(55 continued (5455 11(5 24 5(5 (5"1J*(5 sites for ¶5:55' (544:51, carried (5547515-4 out at seven -(545. been 15:1- .s'74: has (51(41 drilling for 17554(5 most (5(55:7754(5(5 craters and :5(55 (5545,. of rock core. 54':1k'(5 feet f.ss'. (5(57(55, of 7ts:: IJCI holes and '.s(411(5 over 35,000 1(5 (541(5'. S.(5sI-S't(5 two a total CII thirty I 44 75 I ' 4 (5'1 C (5 ç C' L s 44- ."i' IS'S cIC'L1'1 core and of drill 5577 mineralogic 's54s5C'54-1V- study 1(47 Detailed petrographic and (515 5515(5 57,i,155.5(5I concentrated on .1.' At first .54sslt efforts ,;154r54 were 111s'?. 11i'11 71(5 surface 4437155.1441 samples began in 1961. (535::54's(5 41,4-4,') high pressure (517 c';44;'2" 141ryr'19.lc(5.,:"54;4.: 44)4 fragments 4444(5 and (54154 the shockproduced, ;: for (5':'5:SyC"55 i41'44j's"7yTh' .54': a(54455Jc' search meteorite 1st 4 1' (5 stishovite, as recorded atr Barringer (5 polymorphs of quartz, coesite and 7' to 55 (5 C44 1_Q WI elusive, largely due This(5 search continues but has proved 47 Crater. 5L.)T51-5 54sss'54&, recrystallization 1,5 in these old, deeply C,41,E5i"silt7';11 and 551L(5'55415'5't'51the i54tasl54 alteration '54's abundant 5155' C other 5l4 criteria of shock Thus attention has turned to 4 eroded craters. 44 744 1554'75 5(5554444.7: meteorite craters, (5(5554.5 underI1'&L'55 ;3'c"(y ':isC(5osC7'44(515 metamorphism known from meteorites, recent (5575541(57775 i'(4 1(5544:1 "I 54 These include H4 1'1 experiments. ground nuclear and laboratory shock 51, [S's tests planar (57 and other mafic(51447444445415, minerals, of 's1 5' (5(51*71 %1S7J-© : 44 *51'I ',547"41;f)MSIQLS- 4(5 the development of ,.k5'17i(4754 kinking SIlL in :5:yt' mica 317 :47 (54'f:5 (5(5151 feldspars5' orientations and 'ii'sL,'41.:71545 441: 5i''lQH1 in quartz .t.5ji'44t(5.1 .7(5' s,s i'5'; '54.7-1*ctc'1e features with distinctive crystal '7'k5 '(5:5'1'41i 'Ic t154 in the (5544554;S'H',tji"CAphases, 545'S:' particularly .1154 (thetomorphic) JS1417'54(5 i"t 'ss*s5,I547i7 flIt: of and peculiar isotropic 544444;,,y', at the i6 (47,54744(51 4(51.are 55: found 44741 54 12 Well—preserved 215 :49y51754'.(57[S54 examples 1fl;"sC111(5'(471 framework silicates. .-,.,j,,,,.55,,,,k' I(5 C I 14 i) 15 I C (5 1 1 I :5i554'(55455 Canadian '54-44514'.y5,(5 craters. (5555, (55554T7, ;'.,:"1,I1",fl,7'55 particular (.11'74.:45454L(5L attention has been :'5't's5412544' craters i'1: Canadian In the analysis of 754 1.154.74(554 541 701,554(5 scsSlSIS(5:'ji.1s514"(5 41'41,15, arid grades of shock metamorphism 1(4,i(5L54.5.542 54"'71sL54h':154 given relationships between It's 44441(5 c the 1-1551 to "44(5457(55(57 54(5 diameter) Vl;(5 .4 ¶7jIH1s'Brent 7i''": (3.7 :- km The extensively drilled ,151J5 1 541".; .s7i(55c5, (54(55y(5k' crater structure. 1-15151(5(5 747.747(55' craters '7') "(5 of simple 5'(54:;55'!75' (5' .4 74.47515(5(5757(5:4. 545 craters and 54 West 174;1'"4 Hawk 441(5744(54' Lake (2.7' km) are representative 557 rocks 'i'i'55 72.5(5(5 s* :4,4 altered fragments of glass and 54! 15s'57s1; 44145454 511154(5 (5",i5144i5't'5t. with a lens of breccia containing .5-17 741; ft,ï-i' 1*5. underlain by fractured auto'j',,7s255.s44(-;. 554'1'47-(4 :':.5444ssss54CS55l: 771", (5744 at various grades (555,574(5 of (55 shock metamorphism, (57 (5s:3744,kSS&:71 454 7,5( .s't's*stLarger craters, w'nken downwards. 5(54(54147 i'544 74c;,11(55','3l chitonous 75'447,41'(55, rocks, in L's which '4i'i'5 shock zones ",:4',4;L'(5:5(Ht "C / and [ 55 S2 441J such as at IClearwater Lake (14 and 32 km), at La Malbaie (35 km) 55(554.544 whichh55,s shock zoning similar uslcsssl (55151777 5,s'stss-s77,t'tc Manicouagan (60 km), have central' s5455 peaks 7,in 554*, ,sss,. 121 13144'441 I 5i' — 4115555 :t.' 1' :'.'7 next (continued page) ,,';5.5i'57 on J �T eigJ trji The central :.L* developed. to that in the autochthone at Brent is region is surrounded by an annulus of breccia, and 1LCC1: massive, probably -cidLd. 1'y have a peripheral depression ft½T 1-1? shock melted igneous rocks. They Lc>:tt, hasaC>7 been produced at1 1iki crater form instead of an elevated rim. This C the Suffield Research Station, Alberta in alluvial TE materials by a 11LL1LGlat ;c surface explosion of 500 tons of çj TNT, and has been recognized L1 suggest a mechanical many cryptoexplosion structures. These studies rather than volcanic origin for central peaks in Lunar craters. :it-f wk :a:LC jUj,- tLct•i-i! :;.*ç rtL21;) ;ct \C?. Lf7 icW2 •?0 �O-ibb A 1'iTORITTIYPACT II IPACT OiIGIN :n0.-(1D07:71jlbCd ft 2:ToI P MtthiaC?flF PETROGAPHIC VIDNC tay t.cr:m2-r! sTh2C1'.RE, d±!:&r::c; OF THLL SUDEIJRY STAUCTUR, ONTARIO -tw and coc: c-ca!: .bcorcL cc and M Planetology Eranch, National Aeronautics :nc:: 1hao:cto] tat d-aco1aFrench, Bevan ?-an-a: M. tpc:-a Flight CLLgI.:Center, :atec: Administration, Goddard Space 20:01- Idnal :1:2::! O-c:. tUdicoc Space '2-cot land Greenbelt, :sc-!L-cIc Maryland - cpe:b-::: :ib::t&.L to byanr:oicaty o: rock :c-b: specimens subjected to hypervelocity Recently, studies of Pc:cnlf. ctl?ct:a: nate-oral:? impacts and by by meteorite ty c-at:n coal expinancua '5R1£c:Hrb shock elosions ant lb-3a waves generated by artificial sO: araL o4o:J ccI cab.: which U oh and mineralogical criteria a:: abo.basd s-as: have some petrecaan-bn: petrographic nor bcot: established 1965; i0l-5O of such processes (El Goresy, of ouch p-coos:: ta jH. c-lyon: -U or-b talc::: appear to Ia be cocoqon unique indicators These effects, which appear a, 1967b). 1-: I 1' Chao, 1967a, Short, 1966; --c-.t-c-:tao. normal geological c-rg.-coa-. deformat-cat ttncs pntr--ic ch.stnct1y different by nos:.:. CaO0.rJatlb ::tc::oacr: from those produced by such as cc ytocoLt: ocof 0.5 fc—psaa C tcaaal.I a-riof ci fthigh—pressure polymorphs (1) nIt:: .: tion, include: ) formation ra:c:J on decomposition reactions 011 :d bc-an!-si 22cc fual i,cirsics.1 coesite and stishovite', (2-) (2) unusual fusion and s_a developwidespread indicating temperatures Cl in excess of 1500 C; (3) 2 L in a asets of pplanar lamellae a a 0 quartz; (4) multiple ment of cleavage in (notably octO - -OOOland lOl3, I p V quartz, oriented pallel1 toc specific planes, features in associated ma:::cras -Ui together a: with 2: faa-Ac development p-act:: of of analogous a:-C.cigcc: planar tcl -tb disordering of single crystals of quartz and Ilaccanoug b :1 oslo oryo.C: of cactrica intense 5cp:09 (5) feldspar; I 5) inc-rose original g-incb lbphases ybas-awhich whachpreserve 2rc:-rra feldspar, ott-an often pa-odocc:cng producing glasslike folanyar-. cccl structures. oct-at-br-as. qgrain asia boundaries h-anal:.:::: and coca some e-,lo-.: lal. explained :oata:± -H: I aacc—t:nc:ts :o.-:.:o-t Dietz (1964) argued that meteorite impact corigin L:lSHt (195-4) Sudhury basin, the #1 with H e° associated of structural peculiarities ± the I South 2-c-c-b Range 2.:. tgoo:oL and the cbs 21:: cJt cc.::.carcrc chiefly the overturning ta;-h.:.tc of .5! rnetasediments ala-: on the the a-: U an Dietz yiewed :2 ecc: the Nickel La- JJtecawidespread of 2:d.hanySudbury bc:::4: breccia. w*f.aap:cac—.ddevelopment fe l.c:'-cc-n:of the Sulbob Sudhury IncUs basin as 4: he a1e!Th0a0rct_f andand :.ac1J cc.-?: in Irruptive an as derived internally emplaced Formation the overlying Onaping F:::a.t1on c- 0: .0an!. Oca-cp1iag lIe to±t 22cc.; ohs le. cccl: :1: '. He an "extrusive a 000U-i± vs lopolith a: _of 0 represented a "chill- zone of ash—flow tuffs, in which evidence0 0 view was tie: This c'tew 1mpact—produced shock metamorphism might be found. dnha t:acb--p: c-th:-:o-i nho-:ft rca iaiccrthoE.cac:; ba development ''Ian 1 supported by OX andI discovery of the widespread b-, his prediction an :.: wan basin, and it was coca the hofanal cc c-?oa-: ac--b: :.rCcOi of cones in older rocks around the Sudbury hasI. 5:2:10cc- -coos:: cc-: shatter basement rocks in the I;-XoobIdesirable deal:-cbl: i-n '-i Ican-can cii thought to c-anal:.:: examine inclusions of older cX:o:J-I? 5—u-nbc' i:-:: Onaping Formation. 2: a-tie thick, is the The approximately :2-u-! 4000 feet dr.:;o.ngFormation, ?ctanttc:- alnran.rnOtb Us: --:hfosc LII Onaping U occupies the center of the ct-c :— na of the lowest member of !hitewater series which (micropegmatite) :1-a cocoa: '--fl--i-n: basin. :-:n-liee the upper The Tb: 2:formation :-ajccb on overlies lato Sudbury of —a -——a' from it by a— alp unitI of Sudbury Nickel1 Irruptive, and is separated at the ln KU quartzite and 2: and "quartzite .:unoc: a-fof of tengs largeHIcob-: blocks -:2 ofç4oani-o: 2: breccia' composed the r:-ecUou: v4c.rhe:-s hoot aocSoaoaf r:nto.z-:cb Previous workers have considered tOO interstitial melt ±ntereth tb: a-a] -c material. extrusive fragmental ab-onifli f0:.gcL?.T:OU corn: ioc:ecl sea-ic-s U Onaping formation be oa complicated series of caciattc:i to in ha lae--1n -Ia: relation oc to the ga:: cot ocI at-a volcanic arocks and its ,r-ac-: exact an: origin and c-alan.tur cola can 171flows, c-an, hut —-cc:lrsn:a o-i-pt-i-c: have ha-a not no: been Leer:definitely ueVisoia- established. oUch Nickel Irruptive NIcciasi. Jcso- Pil 1tI rC5 A:: — : Is e:d aciahobte 0 5t :L 1:: : - c--.gio. o1 -Lo :r:.t.4: felt that f rnd. il — J 1 I c1-r basso:':: oca5 in t cc.:i l_ H - - ( t) a--na: the -cbs U-na-' c-n- formation: foot ac:t:-n: (1) pre:'-:accU- :.:c-c-p-nail It has been previously accepted that Onaping material; (2) also aevitro. -I devitrified numerous glassy -canfragments fc-ay:a:ta of o-,,-u.nana-,:c contains :.p to 2: Lana. of tens of .-arck:aoc - rocks cc--abe up contains numerous :colu:i inclusions various "basement" o-:r-tb an: ;cccacc-:e c-n: e-°ofo-020c-oC ha-ge size, from ba-:1 large el gradation Ic in ±::fc:an: fragment lb add olco : agaei-fatcc': exhibits 5-1 an (3) :1: size; feet in contact : (4) --i: abase c-sactoto fine La: OS cabal- :0at tic:the opp1an c:cc:o-oot blocks a: at the material upper respect to the coning it: i-cob t;;:-:: ':h c-as-sot U concentricc: zoning in rock types with tao: aac-taos-it exhibits correlated with 2oire&:,J-a: formations U- definitely ctetinl-aTy -:: :aniarad wiLl': -c-&c-in: be 51 cannot 5-nato roars-i a (5) basin margin sOnyts arc a single apparently deposited as clot-na--I-el (6) H?was we onne:cecU -? outside Sudbury basin;; :1 ccci a: do the :2: Sultn:oca- U an: saa :2 g°: catecLol: :2' also - 1ççi co-:±inua-t cc (continued on nc-at nextco-og: page) a 8 �*fl 0 'Ct' unit during czrp Su aa brief period of time. Preliminary petrographic investigations (French, 1967a, 'za tT0 '91.9E1of 'ycis'S,c;nS &JD?TCV2'L4tf4M33 f.13) inclusions l967b) provide evidence that quartzofeidspathic a IC 3tr9t?J ot4ap&pojonaaD Fcrinatiori bow microscopic textures basement rocks in the Onaping 4UiW, su; zr' ACTa generated bys.3r3zG$ L&SZVUV4 Sc-cCmo meteorite typical of rocks subjected to sh'c: jresruu'es yncqi ,vu.jlZ!93.A! ZJ0Vtt tO by artificial explosiond. paanimS Ci) planar These include: impact or t'. ee;q .pntOWc $4 -cJ'r.QOibcd ,.wtstJ lOi3 features in quartz, concentrated at or near the OOOl and I" %% 4tJOUIW* '1t50U t213 planar features (2) intense deformation and development of planes; s-nc1tn tw'r.'wvJa. :aIav ;o .1xL4s\ç tvsgc1 in 'oa;fl2'Cfl associated feldspar; (3) unusual deformatioflal flow textures 'Cc ':') These "melting" by shock. that may 'S be the result¶ of JD selectiveint..smaller C.. /q fragments that constitute features are also observed ci' *flV rarely ..-sx 1tQ13 4'C" 4;tflqcvu the matrix of the inclusions. ats zç4ws 'aLo'y;('vn Subsequent studies of additional inclusions have allowed the jo tt3tat.a7i pflsflV uaibacu-j tentative recognition of five types or grades of deformation which ', -o ;': n::L' e.peS 40 "i' pccoa Q$J The petrographic original shock intensities. may reflect increasing .I0O3 \L affic 99fl%P.t'! compared with material from textures observed pa.tawç can taa be tn qualitatively padw 7n* Kessel, Germany, and the Brent ieteor Arizona, the Pies J101')11 Crater, r..fl 4: 'n"i%t3 'flO'2hiatV between the groups are gradational and Crater, Ontario. Boundaries ce;:Wc!ttT ueu4eq 6Ji%4' adtoa thina.re section. The observed in a single several ' grades "may be eq - development Ca 190t4': Lw atiX":s (i) of multiple are characterized by: different 'grades d IUD1ttP $.aetb'Wfltttt and feldspar; f s.POtJSt (2) preferential sets of planar features in quartz 'qvaj 'in, €ztur6 sçaw2' of feldspar; 7W5MAfl (3) strong deformation destruction and recrystallization p.1w 7")r"J$'*P !.rwwpy.; recrystallization of associated quartz; of feldspar and complete ;c p*te"i&QVC t:fPrRtit .iiCw.zfl €'te-'¼s 1flrLC4..! eutectic . melting in strongly deformed development of local e;e.G$&O1. (4) LGFSP :n&d:' incipient melting of2r,ç"in to an the whole £tA.ene inclusionfl'&ZOtfl (5) inclusions ;c tfl VN £:I wfl 6•Jqs Sit' showing incipient flow texture; aggregate of heterogeneous glasses at; IcTaccs of :otnflow d eua' .o.iz3oa;o; '-n3development structure, with sw2saIfrP and strong complete fusion (6) ,;:;V'at* ra mineral t'- fragments 'tc-rLr-an; wai&?3c into rock and admixtures of o'..'27 s:.a14Xj4.P' zO shocked and unshocked Q7fttIPUtL 1cG.tL pU! 'V fllS•f the molten material. etwwele the Reent collateral evidence for meteorite impact, predicted by •qt itt-kin taze;rrCC .03 pe:"-% f.q (1) the recognition'-sovdw of high_temperature impact theory, includes: flfl peJer inclusion, and (2) the discovery cc4t20DL eJtfl.PSIa-CR;4 fusion (melting of sphene) in one t,V3 (planar features in quartz) in %tSIb.T45 criteria of shock wç 4i3 weakly_developed eatkcva; wy and related pa3; 2qarL nnnrt'L) Levack breccia inclusions and walirock in the footwall c• tr ',qc. tiVSiQ3 vo}9cttCts breccias along the North Range of the Sudbury basin. tn. q'42 'riatc Suora ds¾21I £znurE lihese observations establish a strong similarity between Sudbury iSP'iw C'46b!QdQC St.C qwrqnue V gQfls iceegm;eq Lr4ptl3 which a meteorite impact origin is either and other structures for Fe .70j s Bfr for the ptJwc ITV7JO Acceptance of an impact origin indicated. proven strongly UG'$- or Jt aC'M 4C te Lit) a03 fl's petrographic it! L 'pG3%c4pt4 imply: ;axdaq tii2 (1) that shock_induced Gudbury structure would pttcn also periods in excess inc ono..,flZ ;ecr_—?to04 years; Lcrqçtq of 1.5 billion featuresz can I 1s33 ser. be preserved for ..%$ spc,.ed 7 at 950CL3 :o t may c' :rq C flVha udhury, constitute (2) that shatteranea' cones, which ie uomrnon OTW T V eç'. air4r4o ig3qO t(c;OY DU'fa.L lcnfl-'svtt otooritc impacts £ccr definite criterion for meteorite impact', and (3) that Z0,, atracn.In (C large voluniesir,,vdir of processes involving may produce CA T1#tW ;': SCfl*fl or£ trigger igneous Gw9Qt-' 1.ZC Cfl itoSUS magma and economic ore o•wuu; a.t deposits. iew3v,. tscdsj impact origin helps to explain the The theory of' mofoorite It)the Sudbiiry tinetore eq c; of the Onaping jcç'& r-1Ipo thetitt nature and peculiaritleS of ;e aç ttcv.xç. s prs 70NickelBuithfla There is, however, no unit analogous to the Formation. ca flWZP structures, ')$4! atJOTj - Sfrtc) 3flC,$ '1fl impact and the impact of the larger known Irruptive ! qv any A'W JO artlittle to1Z*3\L-j tvJitrç cJTS%T'I the long—standing problempte of the theory can contribute o; S)0etT$ LIV'- 0(4TatfltU G4 710t0.ArS and its associated ore Jo deposits. origin and emplacement of this body ,n,grz—9c%Jt :a43 'psut!co 4u3A0W1dW9 ;c woj; £pac ?''1 ?t?6: t Ltflfl:.7 accc 'c n:o- fl;osttv pr'r;lUV i14t atnatCa ctcU'P1 fl fl N a ti n- 'rtT '-oaP ., e'et flC ',nt.LG 4 t St crec c v" e; ) an t'4 'itj n. pa pr' -;tCtt(V%t1Aa tXD!'.'I t' o ;: zat ' tartn gp:flq n n ) fl j •A' t0 'fl cflJ 2'tr4 ;: s.;—cijn'. ' TBt0t1t w-' 9t.t'-s0 t\r art sac3 :q roc:,'t' ( nc cn LSv eq flfl,, t42O v - jifl?c fl nmt aai ent..:e aa!rrr.S i41U2t, wt a o;udtad j-.t&r t-r-q'r;t, o;.wo;n ai '- tD'fl 2W:'Ott (It at;tOfln *nLfl Lxia fl P :ec.o6P9rqs 4 n. Q'Jlfl) sts s- 'ntqattr o qvc j2t (continued on next page) pnnnt'rcg s; :°w -e2,c' u çs'ntosB Lf 9 r..y fl'4 Cfl'j v:,.s ;; : ea8 ' '&i;a.t , 4 ;---';t' 3&'fl lwiOtflfl . a tOO ncnft M 2ir! -,.,a' esv &-zadtt'.;' ;nLtw,. vntqnj its t) fl f tn .v. �.i.r the :i hit-tel Nickel orreOt on.] unlikely 1-h. that lot hi :100? it seems ott: ofcFknow1ede, At present state Air the ::roseat c:C rico si So: cod Ste of the iupact vthich formed the holop oh be the direct re.3ult top Si c oo.r the tIre d iroco roorho could Irruptive hart c::r:or:i sod ot :ratl no.] tool li could have exercised structural control OCJLJ arorrci impact an boo but otr-:-h. such to nar.ln basin, 7-70 view 0± of the hi SO iteW iotion. his road-1 In inricrtion... processes tialready in directing igneous ?roo! 0 p:::000000 - -: It 1:r-rT 000 ILdicr.ro structure hie hi; iii rroo:y ol .tr0 importance or meteorite tory of the Sudbury l- iror I So imuact i:pcc S inSrthe ro-roroanie of flcx hi]-.e thocofec pc:oo:d co atootro: lit too does not contradict any of the theories nroposed to account for the acts 7tL icotret et trot:: riot ant on.: aOco-7-er tflio Resolution of the terrestrial and extraterrestrial Pr cc_or tote. of or ic-ti .i--nopti i-i Nickel Irruptive. 7 .r L. components Sudbury 0history will depend on future detailed studies zOThI. .t ofI o._ of the hi:- structure hir;otoroof ofcts theti-ott basin cod and tiethe -it-tractor character no.1 andschotihiase subsurface orhizr: extent of of the Nickel Irruptive itself. 1. ' -_ of hit hi*z-r I:olriiro itor References Pc for lb.] oo5oc:.rChao, Impact metamorphisr, in P.H. Abelson, oiL edo, 1015r:ir !oot00000.or1:ilnn.H,.iO Chao E.C.T. Y.OJh (l967a)•, hou Researches in Rercr,inciic.o 4oGeochemistry, flonclicc.o.r:o v0 2, New York, John Jiley and Sons, 6:0.0 pp. 204—233. 2 ' [tr cihi r Chao, E.C.T. (l967b), Shock effects of certain rock—formingy, minerals, Science, 156, 192—202. - Dietz, R.S. .OCSh (1964), Sudhury structure as an astrobleme, J. Geol., toot 72, 412—434, srO- PT :965 tattoo icr-ac S aid ito iS.Scoc Sr El and its-sootY si5nificance in impact ILr±to P0 Goresy, A. (1965), Baddeleyite 456 glasses, 2. J. 2:o:ro-e, Geophys. too.-. 2es., 52. 70, 5455 3453_3456 0io -i:ctcrl rr bitt r c-bcircHo'no structure, Ontario: boo-rio B.M. P1t; ii(1967a), 967-o Sudhury French, evidence for an 1094—1098. i:;:Oh.:i!:t: .!24CO fl origin(LIt by meteorite impact, ci !rT!i T7r' or some petrographic .— Science, 156, -2 Stit .:rc:.cp±o &]t my no: oicrro btteol: French, B.N. (1967b), structure, Ontario: Some petrographic h.fO ;r2 Sudhury evidence for aan origin by L meteorite impact, NASA Document 56 p. x—64l—67—67, 56 0! -r- tr-r5rc 0 0Oi Ij 0hroa: Short, N.N. (1966), Shock pressures in geology, J! Geol. hih- Education, 14, 149—166. a a 50 �ill 11±1±7 71-N 111 1±I71-.-172 ±7(2±7211 MIIT11Fit PROGRESS OF GEOLOGIC INVESTIGATION OFThE THE HILET 611sLI(:LTci GRANITE, - :ISOOi... -11. UT11CcLiIN ASHL.ND ±51± COUNTY, XatlsIc Michael M-, ii. Iatunan Graduate Student State 5:2±6.11 2122.2.1: Michigan II2 t2252i. 2—S 22 University, East Lansing -; 11 121 1-c 1 tllcl; City ±-±11 215 Ii of The72=11 Mellen Granite is 2-1212-4. ±1.212 west and north the 412 located 1 granite body, 1Lj County, _ The main II Mellen, Ashland _-i. of Jisconsin. 1-, in the southern half i 5-4 12 encompassing some 13 square miles, lies W. 2221t-4L1I17I N, )k11c.115t2:3IL211-L1L12.H2k.plll VJ 1;. P 3 N, and the northern portion of T 44 of 124-.± T 45 P 3 — L I — IL I I1 14j4.; c;141F' unconformably 1L::-c-1--;x.sL:-7 2overlay (2±-±.:. and .21. basalts Keweenawan gabbros Middle .CiI '1 .1 the Animikian Tyler = formation 54 and are unconforrnably overlain by -755554 .11; 15-27; 15.2 t6..4nr The granite is intrusive sIc :-511t1; 15-22,fl Oronto the Upper I1-k122 Kevreenawan :122; Group. L1I421 It SIlL 2-Ic Mj.:U-1175T4sis55.Is;c24 gabbros and basalts into the Middle Keweenawan and1511-21.1522 intrudes --and Li— 4 22 abuts against the Animikian P Tyler formation; the granite is older 2411 42ç4±5 12: 2151717I1212-2S.. Controls 21121 for emplacement appear to be 517221Oronto 5$C21.t. U5..2.1217-.= than 214-21 the Group. -1-15L12-sL1; ft=.15: :55sjT2 slip 55 the 5215area. 22555 sIft. northwest ic:4114f451-1 trending .22.2±12 in l::s-zc±.-L-7, strike the 111512 'cross faults' v 1 ii] I 4iI2 — — — — I I iLiI 21 al-n s-::11 :4: 1.21117-.2.4L15. -P.rcc 1151I4112c15:1I2.IlSIT The :2IJ:SI Mellen S Granite is composed of -three mineralogically4-517 and :22l±212142.57..s;122Y.—.1, 5i--ir1522 5-512I17; distinctive texturally phases; (1) a 2121-52-2 coarse t121222-.grained porphyritic LI. a (rl,-25.s 15 —:±i.r--12, 1.2 27411 fl.t221 t,11225 granite, 7kSl3Li'15-4-, equigranular to porphyritic (2) medium grained, quartz 115 557115524In monzonite, and (3) a2 725.9 ©rpt.y-;..s: to 5--1..;;2-NJ porphyritic fine to medium grained, 4-Q 1212±2521 tcis:---t-li-J5granodiorite. 1IJ5.1514 The fL.4H72 monzonite 4.,; SIS-SItI: 15/I P114 quartz and granodiorite equigranula± -5=5- -1-25k/I 12-1/IS- -4277's '1214 body, I[7;2-J2;t7 of the 1511±111-7 -- boundary phases, which 7'24-2: 1-./I-J7 occur only 45, at the are It-n southern -.;r;c-; 1- and 5-15:-4 the 54 ns:nstc transitional. The 5544-555 contact between quartz monzonite ,-I-55-;- SLL 5—s±. porphyritic) 5-55/I55 granite, on hand, --1-5-714 varies considerably; in 2172the 1±2other -2 712 222 -23SI 42.15 22-455-452 pISnct 222. c-2:j -2places this 222'2,211t contact is sharp /Istswith no apparent gradation, while It contact I 42 JJ elsewhere the The coarse grained porphyritic 5 is transitional. aSS 11 granite 74 is the predominant phase. -=4 - = The intrusive apparently occupies xti.2::'TI..751215. rocks. 5'-1S-12 12 a sill-like position generally concordant 2±-5.=111±-2 52c1.t2 1-c 211112-2±154: 2222-212-111:2:; to -1124 surrounding 1-72 the -17 I) - —2-21 1 21 I 11 4!J L t't 17 — -5c. surrounding 55-:5I-21212-SSL/ It-I;--15.-:Stll is -11Lr 1172112111524 Is :; the The granite not 2± an2211112-2-51.5*7 immediate differentiate of ±12 2:521 2212-2--;. but -±s± 21.4 2± 125it may -55: have gabbros L71ft5 developed -1 of -4255-74:by ±77anatexsis -54-154221or 24 granitization 1554s'.2 LJ71LI2 = 1272 from :1:2-211 a 4 deep— Animikian sediments, with 5 subsequent !±:2.-:r 551272 :4:15 --Ls11L I:n-Lt(;:±-:-:. mobilization, 1';I.2It22I1I22 . or 121 seated parent magma. 51 h -— �a rYrLC NORTH SHORE VARIETIES OF sLThtti;CC IN THE ssi FLOWS JSSS 5f5:(J3Lt VOLCANIC GROUP, MINNESOTA John C. Green Associate Professor University of i1innesota Duluth IC; Survey iinnesota Geological and ;-c 51sttrc -r rn7c47 ,571L4 474-:fl7 CflirL - a to North Shore Volcanic Group o Keweenawan U,•.t14t,' age, once trconsidered sstt, of •54 'beThe exclusively basalt and rhyolite, ['Y Ci has been found during 1'-ici7. the C:IC course 4tV47 of lakeshore, wide sampling, and miles recent detailed mapping of 58 r'4 TC1-j 'L51 - Vi'L7 — 41-[i1L1 4SJik at a i V it7f 1- 7LdV -'7çi 7 — •L9 of tholeiite. - t ti t Ti 2i — a fl9-I5' 5rI4LLt of 5 Ct chemical analysis of 22 specimens, to include representatives of a nearly LE1C 1-1 complete series ranging from both olivine tholeiite and alkali-olivine 5f•.5 Ci[Ic[ 4ttt:517 1rcA52 4477Th basalt through trachybasalt and mafic quartz JC: :44 CCLs7s latite or I7 dellenite to fel— -IL So far the alkali basalts are not known to be widesic quartz latite. '-1-s rI51-— information, spread, preliminary 1c 51-ct but the other compositionalI types, 1 _1- from stratigraphic and geographic appear to be well intermixed throughout the 1The only clear exception is that at least the extent of the sequence. 71-f'11n entirely uppermost 1500 feet that are exposed in Minnesota are composed Ct 4 4 C I a C ;r 1L7: An cJ outline of the characteristics of c the different compositional classes of flows is given in the accompanying C5VL 2tr PTicU table. flt7Lkt}, i&1TL ?S ii57 C:ñI!f ;Jn:: rvc's Older 7cir5 terminology in this district can be roughly equated compo:f71-' sitionally as follows: "ophites" are tholeiites; "melaphyres" are -— "porphyrites" siliceous tholelites, andesitic to 77L .LO!JL7 basalts FIL7H! 72f trachybasalts quartz—latites; and both C are trachybasalts, alkali—basalts, and mafic jCi "rhyolites" are quartz latites. and 57T r77 J5c5 L 1- , -h' fl1_ •7s5-r L 51- (continued on rn ncxt page) a' 52 �'f Quartz latite 7271+ T . oa1L;!i7 3.5-5.5 'Ut' LJ:cQ Ij19 .*:t tp?:2?c, up to 1000 100-600 viscous ;:iL))' fl1ZTf€ kf:crTt highly vesicular, breccia 1'4 ttt lflçI cl/l2;:::yo platy, subhorizontal columns in thick flows stretched, irregular, round pyroclastic evidence rare; top zones poorly ex- i7c Ti t'fi"f'fi - :" .flifft2i4 &:itFqI: VC)L Zfl C' itFrj ;o 'fUtiIIt2 :crC.x7 flif-Thflt4' t?fff,I.t[ =:2r& ( . III ( Cth f'Jf: ff ,rC.L I I iz?C.Yii I Tii?7if4t'f:ie-J4 — L'I.f- It'7 — ,,m _ L_____i_±1%l .i_ —— 62-65 Mafic quartz latite 51—56 2.5-5 Trachybasalt 1—2 viscous mostly porphyritic (plagioclase, quartz, rarer orthoclase, augite); flow— banding common — — I — I a iii if-" :.nr,riii <.. ,v t:J!I' I "LF1 I fTfl'iiflj F'i, ,_ _1IC I: ;v5TrT 1 Yc)L :2 :. :1 HS EflS:.-C F,. :'CiVft: := I Generalized Characteristics of Lavas of the North Shore Volcanic Group Tholeiite '+6-51 <1 porphyritic (plagioclase, augite, rare olivine, K—feldspar) up to 200 highly vesicular, some breccia sub-horizontal, platy round or stretched top zones poorly exposed posed. i TABLE 1. Alkali basalt '+7 1—2.5 up to 250 20-100 2Lji: C2 columns ::ktY l'e.: IV:td T- one 1 1 aphanitic clase, augite) K—feldspar; (1 to rather viscous I I I :':i,.jri &t I ic.'klTfl I 1l o/:.L C sheeted top zones; big columns in medium thick flows round or irregular stretched at base and top quartz, agate common in amyg— dules; 1 Sj02 wt.% K2Owt.% Textures porphyritic (plaglo— some Interstitial generally porphyritic only chilled margins are porphyri— (plagioclase) tic (plag.) Ophitic interstitial K— feldspar fine banding in some Plag. —augite micrographic intergrowths in mediumgrained thick flows 15—100 very fluid Thickness Range, feet common more viscous than tholeiites ropy or smooth 100 Relative viscosity roughly corrugated 10-50 Structures flow tops I I trtkUl 4 ;,- least well known stretched scoriaceous rubble lower massive part small jointing vesicles Other olivine common; mostly crystallized after flow; Calcic zeolites common miles thick flow traceable over 5 �STRUCTURE AND 2c:13Im CkPP :CJJV( INTRUSIVE SIGNIFICANCE OF m SANDSTONE DYKES IN THE 1(Z .Ci [-rXL _l OF THE MARQUETTE TROUGH, SIAMO SLATE CUPPER PENINSULA, MICHIGAN LtCfLLOL 11. trc:tkI Research Fellow C. McA. '•iCf-Cf; Postdoctoral J3'[1Cf13 C.7i Powell, NASA T3313CfSJCf 31 Tt7Cf©iX? c. 1 Department of Cf Geology Northwestern I I University Evanston, Illinois nicTm a a J meters long Sandstone dykes up to than 3C 15 cms CmLCN 3IrLC wide C5(1Cr and :iCce more 3cJLC:Q; IICfLIC three CrThM[L 33I33i7, X13L cleavage in transect the bedding, and are essentially parallel toI the ml Cf These clastic dykes are the CfJI com;çy Siamo CfrE=r Slate 3ThCf[I of 5• the Marquette ©:4' Cf 3IijO7I tCCf( . trough. :2CfC:9Negauriee, and are composed of mon in the zeolite—facies slates east of CfCi CIb to 6O% fine— to very fine—grained sandstones commonly containing up EfC1 L 1(3 Detailed study of large thin-sections (up to 7 dolomitic I1_ Cf carbonate. ribbons lie along the x 16 cms) has Cf I shown that pelitic L3J I 1f cleavage inI both i the 1iC slates and the interbedded psammites. Individual cleavage ribbons y band which are refracted in the psammite can be traced from one pelitic L1 —, IP: 3 Microstructures through a psammitic layer into- the next pelitic 3 C: T band. indicate that in the disrupted sandy laminations within the slate 3 iC— r the IJ and were dykes were formed penecontemporaneously with the cleavage, :Cfl emplaced by forceful C1flCJ,© intrusion upwards. Both the cleavage and the dykes of the Siamo Slate during L may have been produced by tectonic dewatering L b_C either late diagenesis of very low-grade metamorphism. tw 3•'•! L iL a r3': irytI 1' f ' - jil t V1 I 32e1 r ti 51C JCCrb. L _ ttr i3: — C 5k I !I' �,j' ' j. 41 MIDDLE 771 j PRICA1iBRIAN '7 r 57>rri THE SEDIMENTOLOGY OF THE sC7ZV174M THOI'ISON FOR1vLTION* > G. B.c Morey, Geologist 1k >7-5 $ 5t IS'I5.CS Minnesota Geological survey, Minneapolis and 51Is'rf 71717775.1 Professor R. W. Ojakangas, Assistant 7775tçç77f>'7 77 L5!>L) lL-'c"ss'-'[ 'I \I> Department of Geology University of 77'>7i'71('7>'3'7 Minnesota, Duluth L 7r$ ! •t: :: 7 5.7 of Canton, gs I and The i77'U77SU5.5.'7.77777. Thomson Formation 77ii is LI'7777777(7'77 exposed T7'I7 in 77755 parts Pine, >C77-ms• i>L -5. counties 5.-i of 77' Louis 5. (7 Ii >7 southern St. northeastern Minnesota. The formation -'C 5'>L5 77 1— 5" 9 1, TLI was folded and metamorphosed during the Penokean orogeny (1,700 million 7 -ygI 7'> >'LT,A1 textures >_r' 77jI structures years old), but primary sedimentary and are well 555, 777 the 'L tc an 5575 excellent 5117s1k7'r&1(ltik, area r57i77ts to i5sL_I15i775555' !it';L7 making it preserved in Cloquet-Cariton area, 7TI15.111C7 study sedimentologic features. I77.s5i5r';CiL5ciF>tJijtiiIi5i 777797i. S I ir-' I 5r' 7'j 'SL1 stratigraphy ii7Iiç7 structure 7L7c'7L7Lc15.7'i7 of 777 the Thomson '217777n7i Formation in the The £'I777'c77w77i77 and k I ir7 5' area 17 '7r has >[LJ' Cloquet-Cariton been described by L. A. Mattson (1958). 'L 77 , i> approximately 7' I 7>_I '7 5'5''1C 77 >i'77 Mattson estimated that 3,000 feet of the formation is s77 exposed along a north—south section, three miles long, that is composed 711111 rl-1 77 &7 with many minor folds "5' — on of three major synclines and two anticlines — 'I folds are open and symmetrical, strike 15 5V nearly east— their limbs. Most j 7'77I I -° iJ'7 '7 i I 2 5'L I west. ):ss7r I, I C. i; r47 5 7I777 77 is 771 characterized in this area PT K' slate, 5Tçj The7 formation 7®ic by intercalated IL two t? siltstone, and graywacke. Detailed Fg analyses of 5. ThIL sections, measured I77 —in thickness at the type 1I IP1 Canton aggregating 565 feet locality near 1 -1 about [ -I 7 indicate that graywacke comprises 34 per cent, siltstone 34—42 IL' per cent, and slate 23—31 per cent of the formation. Although¶ individual iinter— r. graywacke or siltstone beds (defined as the 7interval between slate F) be more than 10 feet Th2 beds) may thick, most are thin. Seventy—two per cent of the graywacke beds and 83 per cent of the siltstone beds are less thaxi l5! 80 per cent of J — less one foot thick and more Ithan the slate interbeds are . I j ii' pronounced '" than half a foot thick. Because — such c of features as Ci) 2 jV individual beds, :(2) lateral continuity of sharp bottom contacts and - '-' c' gradational ? —' r 7—tc tops, (3) r-1,4'-well—defined internal structures common to other e Ii 4 frç turbidite—d.eposited sequences, and (4) sedimentary features that exhibit 7r J r consistent directional properties, the graywacke and siltstone beds are \j r@ by CL L interpreted as individual sedimentation units, apparently deposited ()? - A_CT -.---e waning sediment laden turbidity currents. I Irs a I 1 C5" 57>55.515 east or west, and h7j plunge >s>t777t77l0°—20 a 'O I j iT t _I — i L 5 e 2 a l11 L: çir II 1L\t1 5' gIL L [')t ir I i ( 1 ,r ;e; ); L - 1 ç; I r I_ _ - —, _'_-, L r1agc 2 L"; 7t: L A detailed analysis T!) of crossbedding and of slump structures ILl cT?, indicate that much of the sedimentary material was deposited by currents ? OO4 t1 presence of strucflowing southward down a regional slope. However, the zeYR p'c groove casts, which trend tures cf&.flfl tentatively interpreted E}5;44Q1 as flute and ) Lt to :; y:Ci- some currents probably flowed. east—west, implies that perperidicm1r .:3a 1 - flILtTT rc 1 . J4 *\iork done Yj( on z?ct. behalf of •rT. the Minnesota Geological Survey. cr ( 2t next page) (continued on . 55 I -: �paleoslope. fIS LISV'l±d the of ISV' dip of the inferred IPV'II-'.©5S f-SI direction SIPIl Cl LC $I.L'l,71LLV LIlt I comIV—the graywackes are I SLIVII:reveal I-It IV that f-Il tIllL'cCV TIC X—ray and thin section studies ICC SITILtL. tCIIcl 2-28 percent feldspar, 1-10 percent rock -SI VIl CCl SIS.I5VVN OL1Cquartz, ciLIlSI II L,_55 posed of 1-f35 percent consisting It'VS: etSI it. Lmaterial 11115 C'ICLILTII ;i1LIofII quartz, 5 LT'LCZ muscofragments, S.9.-"Sf l9—8 percent matrix Mineralogically, the V V vite, and calcite. & I chlorite, and 1—17 percent graywackes. 1,!:LL I-I' the :ICLlVL.LPLCl E:7:Cl SI of siltstones ILCLI are fine—grained equivalents LI C C1 ' jIL,'L 1-1111 similar rocks :11 Cl tIu:tL.I&'T ILl other 'L: correlation LII *t,CIt5CILSLL SlITI:nIFl with The of the Thomson Formation :LlLi :r:.xSIlg L: IC CC since Irving first suggested Ttlr cC tIVt 7V.p. dS'CC•,IS-ft CIt region in TISI the Lake has been debated 1C7IlSIck Superior '1 T:57I.CCCtS. tTIcl11SlCL physical isolation Ij1t,l, C MJSs IV ILl a MiddlekZ'LLC,t<T'If.IXL Precambrian age in 1883, but the formationts r c The marked similarity of the mine— has left all correlation in doubt. I'lLtIlIlLI-l IS VT 'FILl-Il Thomson Formation with those 'Cl VT TI-Y ralogic and Itdc sedimentologic aspects of the TI-S OfLC V11 !tL&LLsIIILCSI-I .CIt.ILL'i L3 151 implies that both -. I. 1IlS1 Cl tLVTS;LlinFCl fltLIf LI :SIlIItP, CCL CLII' observed the Viiddle Precambrian Rove Cl'':LLIl Formation 1111 i:_.,:C. CXLS SLLCIcI4 I-LLI"l and were deposited IILVV terrain formations were 'IV? derived a IiI'iu.LCl similar source :VI:Lt I. 'lLI from V IV:, SC LV C-CL' processes. by similar I T - 'F , I :- 56 �Pt:? 9J3 •.::;AJi I:! t:RiLtC :::i;i. EVENTS IN THE TiLE SEQUENCE OF MARQUETTE I::;r IRON RANGE THE GEOLCGICAL ; •:;fl 1j!L!c THE PENOKEAN OPCGENIC,4ET[MORPHIC CYCLE DURING P :54 h!L? Cl tit? ::i :IJL Research ( ;:I.'CJ19 J:; &;Ct*L Engineer, ;i"L. Babcock, Research Institute ofPT:LI Mineral :L:. \t,t;çy,i: . . Michigan Technological University, Houghton, Michigan i2C i 1\.:L.1:±. r1Qb.11L. Larry Li f : rISL 1Ct I 4L Four Penokean (post-Animikian, pre-Keweenawan) deformational phases j field stuare discernable on the basis of photo—lineament and regLonal _c4 ]?[4 (_ I The—chronological sequence of deformational events, respective dies. 1V) _ M J major compressional axis intensity of each .J.t trend,, and C apparent regional .H.LH54 1.511 syl phase are listed below: 1 4 j jjtd L ' L-5 L I I t' -; -1 ' I S (N82—8+°W) — Moderate to strong £ 4 - . . . . D2 : (NL3_k5°E) - Very weak D3 iii - WeakC (N6-8°E) Dk (N12—l4°W) .:1. .5. ...5: Very strong - Sr rotation I S _t 900 counterclockwise This sequence indicates that an approximate I C - to late Penokean of the major compressional- stress occurred )L from early 15 555. 45.55SY. by James. 1..4:.I..:.s t(S IL!<y. has been described time. Post_Dk regional thermal metamorphism i Sf :'L45 t.:,.fl!: 5555::ô,S,5j515 :415 granites, r5511 45'..' 45 and migmatites 5ST Pre-Animikian 4541j:C,Z..5.r banded granitic gneiss, L.a porphyritic granite "core" in the complex south of the Marquette r 'I_4 Included within the core region are roof pendants, migma— synclinorium. Porphyritic 41 assimilated 5? L5L/ L5 sediments. 5 tite belts, and partially Animikian 1 granite is synkinematic with D • Intense D2 folding of the Republic 14 rj had negliwhich Trough appears to have been a focalized basement event, .ç r I — The Republic Trough acted tee— 7L effect on adjacent structures. gible 4-4 :s45.Js 5S:511.I:i, complex during later deformational tonically as a portion of the southern JL I5 - 1 flank !s't- — 1 — £ 1 — — 1 phases. 1; ©44i1rTh14, Events .kJ4 which occurred between and 1i• Dk include district— :;cs51411c7, phases D2 5II. wide mafic dike intrusion, minor D folding end stress—releasing fracturing, and increased regional uplift. 14. rj L1 15 5t — J çl1I — 4 — I -- ç and WNW, NNW and and EW and NS :5,i:J NNE -14. 55 141ç ENE, Conjugate sets which sIi•i.cr trend Ste_C of re-— during the early C were developed —s-ti Pre-Cambrian and acted as sites çs[L -' foci of nine- regional J H newed fracturing until late Keweenawan time. The 4 _— a line which 4 and 4j N60_7Lf°W, define lineament fans, trending N16—30°E 4 rdimensional axes of the southern complex congruent to the present major Us. _s axes trend N82—8k°W and sugand porphyritic granite core. These three ,-ssr ::4s-sss.gest 4 a zone of major regional 5:Li4 uplift. k 1- — 1 Ii - I £ - £ - s— — — — 1 — ii — s--sa4 s :ss.t 4 e_. (continued on next page) 57; l is _r- �may The fliL1Tfl Animikian sediments present in the Marquette ?i synclinoriufli 7.i!:..U7U17': 31L 3i;I% c€31k:,J 3Uan 1:3[U4Jiti,t,73 1U: elongated basin on te ci be of ancient have been in an : fllfluC;1 tL3&[ 33t.Lc CT 3 deposited aTt and southern complexes. wrench—fault system which di1aced the northo:n 1mr1tPm.1 ,3j..t71PI ticmt. ,U:PtiPU basin and present major axis of The postulated wrench_fau1t/StllCtUral 7 — N32—8k°W. the Marquette synclinorium trend 4 U1U3571Th l7fl Pfl -flc— — 1:1 fl flic 3;1 east—west folding of the Marquette Province was subjected to a of The southernI portion Ui!'U.cUU*7kC3 CJflUIUL1U flt: 3: ff•: the Superior Induring late Penokean time. major north—south compressional stress J1t1331 cflTcr7P 23Ti II' synclinorium is attributaUP tense 1 ] — I ——- U I — ble to oth increased uplift in the southern complex and major northsouth compression. 'c 2 PJJ immediately adjacent to the The JJ[t2HJ7 PTtV L33 cP11 portion of the northern complex 3 P'3. T;yxc 3)737.© block during the Penokean oroMarquette synclinorium acted as a stable —[ genic cycle. :3fl333 3Tcti fl metamorphism, dynamic arid Prior to late Penokean 37 z:::32Jc7 regional thermal U!pF-.•. m7rLc=rfl 7p ipIXi Superposiiofl insignificant. dynamo—thermal effects were relatively LJ deformational phases is manifested by N52 W fault L5 of the major -: D1 and 7L fold structures, and NLF5_i+8°W macrolineaments. zones, northwest-plunging 11rj Portions of the biotite, garnet, and staurolite isograds shown by James are congruent to northwest trending macrolinearnents. r 3 — P — Pc 2' — — U rI I U Reference — r Precambrian James, H.o L., cr 1955, Zones of Regional Metamorphism in the 66, 1, pp. 1455—1488. pt. of Northern Michigan, Bull. 'mr1G. S. A., v. 3 — 58 ii �ETI'Ufl'KE IRON ]j'OPMATIONS Li\.KL SUPERIOR :..:cK IUKIIUSIN IlKTHE TI lAKE SKUEUIUR CTERISTICS •UZ.t KilT :KEr:i CHERT BE]) CHA Ke7aJt4.,; P;cc.re; Joseph T. Mengci., ProfessOr KoaooKco:it Department of ofG.2IOK ceoiey Wisconsin State University Superior iTLUoUL ITo Six thousand bed thickness measurements establish the KE r throughout the Lake similarity of the non-granular cherts -f metamorphic rank or Ob_ t the age, Superior region regardless of about associatedU iron mineralogy. The typical chert bed is lo rco tUtU in 00 common with ooooUL Bed thicknesses to are log lLt -.©K normal, bl•t 1 cm. ©Oi thick. those of younger detrital sediments. -I lUlL ot& — or I — ftOft o IfI) 'c)fI structures composed of II c0 composite Thicker chert beds are ft0ILl0L0c bedding; f,:wt SOO tT0itf 00©0O lToiiog oscillaSome lenses exhibit cross tTUL0rO fCy0.0: smaller lenses. tion ripple marks are present locally. No lense or bed coalesces lLf0[tIiOc li01, with V7 vertically adjacent layers. I 0'Ji — L j ;j-L tU0 the too TIM ofl0M%ft$f ?0-ic 0 s00LLU:Lt0H..; ©TIP for The evidence argues against a secondary origin I0 beds comparability to detrital typical OL chert bed and indicates 0©L0;OL IL f Enigmatic amoeboid ç> found in and adjacent 0! to lio the fr.:n iron formation. Icoot oftAotheoomo same origin. layers suggest that is 0! to otooM. IS!. not all chert 0! Ic 1 ]!; TI! 59 �ANNUAL MEETINGS of liC;.±.S.t11/JtF INSTITUTE ON LAKE 51JD} SUPERIOR GEOLCOY Sponsor Number Year First yITc,L)A Minnesota Minneapolis, t.J4c St5.Pr1 Michigan Houghton, University of Minnesota Second 1955 1cI9 1956 Third 1957 East 1tL..•. Michigan ccx Lansing, Michigan State University Fourth 1958 Duluth, Minnesota University of Minnesota )J iSt Duluth Fifth 1959 r..1;i3teL Minneapolis, Minnesota rftr<:I:;: University of .:: Minnesota £LL Sixth 1960 cct:Lcc Madison, Wisconsin 35cc Geology i'ct2 tLrI Department, University of Wisconsin and Wisconsin Se:c cty;tc Geological LI J.j,Lit .. History and Natural Survey Seventh 1961 5 I'J• Arthur, 5tL Port Ontario Canadian Institute of $lL1j)II 2'; Mining and Metallurgy, i,Iv: Lakehead Branch, and 1 Ontario of Y.i iCI1 Department Mines Eighth 1962 Houghton, Michigan .-,I:C'X. tIc:cI Michigan College of 5 Mining and Technology rI Place (L: Michigan College of Mining and Technology .;i2'ItL1t j[ Y2t &I/Icti. ti14 LI CILL* tc . &5 Ninth 191S: 1963 IK,1cLh.. Duluth, Minnesota University of Minnesota Duluth Tenth 1964 ItI Ishpeming, tc1SL Michigan Mining Companies: Inland Steel, Cleveland-Cliffs Iron, S.ticItR Jones and Laughlin, North Range itt4* Li 111cc ctcct Eleventh 1965 tcE %t1L Minnesota c,Lccct4 St. St. Paul, Tie1fth 1966 Sault Ste. Marie, Michigan ThirteenthI 1967 East Lansing, . Michigan Fourteenth 1968 Superior, Wisconsin rt Etc.. 'tctc !.tcc.ght) ltc ,IIt. L. Minnesota Geological cQH' University of Survey c'Lccclr and ;.1 Minnesota II'• Michigan Y1 cc5Stcc Technological University r rj Z-I University Michigan State C-.J EIL;- LL .tLI,2j Geological and Michigan Survey I 2fl.JJL 4I. Department of Geology trcc tLUL L35 L-., University ISic' c-4c I Wisconsin State t (o11'ril. ctc SSaa:i3oFa and Minneo1 I,'cLo.iL Survey 60 �9 R{[gratitude 1 -J:dny+2is! given to A special note o± 1? Kruk Dr. Arthur F. ©± Art Chairman of the Department of Wisconsin State University, Superior iTh f L or (?&57 design consideration cover 61 � https://digitalcollections.lakeheadu.ca/files/original/d83788cb2209624be318b39a90663b46.pdf 52c7589a0f2307bb12f416c07519b817 PDF Text Text Guide 1o, Field Trip 'n Th'" Dllluth Complex near Ely, Minne.ota In.titute Oil Lake Sllperior Geology May 5 and 8, /968 by Wm. C. Phinney Univer.ity of Minne"ota �I ELY ~\. •• . ' ....••• ...' ,<F • EXPLANATION Granitic rocks ? Gran.tic int, usian 01 Arrow lake Bald Eaqle Intrusion (gabbro troctolite) a DULUTH COMPLEX IN ~ ~ A"ow Lake IntruSion (OOObro 8 troctolite) LAKE COUNTY Ko_ishi"", Intrusion (troctolite) ..... .... [;'··1 ~ • o Stops 5 ~OMILES �field Trlp in Dll1tlth co-plu f.ut of Ely, HUlll..ot. In.rittlt. On Lcke Stlperior Glolol1 Hay S .nd 8, 1968 IntrodtltUon On th.. ,ccOIIPIIllYinl up th.n .ra aisht .top••bOWEl. How....r. lt 1. unl1kaly th.t .11 .top' w111 b. vilit.d .nd they w111 not D.ca••arily b. viait..d in the n.... ri~.l ord.r liven. a.c.uee of the larl' numb.r of r.gl.tr.nta for the li.ld trlp (ov.r 200) it iI nec••••ry tblt ••verll group. "i.it tb. outcrop•• i-u1t.naouely .nd ••cb Iroup will b••tlrting .t diff.r.nt outcropl. Hop.fully ••ch group will ~ka I .ini.~ of .ix atop" Gen.tll GeolOlic R.1atlona Gener.l ..ppiDI of the Seology in north,.at.rn Hinn••ota ov.r the p•• t fev ye.r. has .bOWEl th. Ilbbroic. ~luth coapl•• to b••••rlas o( lnortho.ltic, tro~tolitic, granodiorlti~••nd Iranltic intrual"... Th.a. intruai"... outcrop in an .rcuat. p.tt'rn .xt.nding .bout ISO ml1•• north....tw.rd (roil Duluth tow. rd. tb.. IUIrth.uurn tip of l'UnJluot.. Old.r granit•• , .ehi.t., gr••n.too.....nd .lat•• occur .long the bl.al ~ontact on th.. northweat; Ind n.t. ~~.nlw.n flowa for- th.. upp.r cont.et to the .outh- Rldio""'tric dlting of lircon. froll rhyolitic flove .nd sranitic fraction. of the munic.tion) ~luth ~OIIpl.x indi~lt. (5ilv'r .nd Gr.en, 1963 Ind p.r'onll COlI- thlt the lntru-iv•• end th.. flov. ar••Iaenti.lly eontamporan.ou. to within experill8ntal error. at 1120 + IS million y..ara. Stop. 1. 2. 3, and 4 ara loeltaG in the Gabbro Lak. 15 IliDtlte quadranll. for which a d.teilad leologi~ ..p i. aVliI.ble through the Hinn.lot. �Sto~ GoIo1ollical Sur"e,. 15 II1tlu~ ,- 5, 6, 7 aIl4 8 .... locate<! ill the FoUIt Co:nter quadratl.Ie vlulttl aOIM p .... Uodul")' . .ppiog h •• bea.. tlcc.olDplhh.d but no ._ologic ..p 18 availabla. A ubulation of _-re fo'r the ... ariollll lIDitil of thl! Cabbro LalLa Quad- About 400 thiR •• ctlOfla han huon atud1ed and CQuota raDsl.. 18 incl...aed. of lSOO or _de. paiatll in .ach chi" ."cHoq b. . . the lllDdaJ. .. cs.-c... h. ~t a.- ...d u .. bui_ for of the 'l'oeIL ....ltl1 thera 18 ...1Ib.tantial ".dactoa of the IIOde about an .... '1'• • • but ill S....r.l ••ch type can be di.tllll~.h.d fro. another 00 textural differallc••• The old.at btruah. . . .d " I t ."t.... 1'" unit of tlla Duluth cO"'l'bx in tha two 'luAdranal•• t& ••bbroie anorthoaita (80 to 901 p1as1oel...). . . .n A _ppable lillie of anorthodt1c: .&bbro (70 co 80:: plagioc1&..) Dccun 18 tha ~w>ro J...oJl.- quadt-ale AI' .. "Ilit "!thin the gabbroi" &l\orthodte. In d l of th... pla.locl... -ric:h uDiu the only cu",uhte-type ll1",ral ia plaslocLa.. of about An 6S -.1....:ala ara int.ntitial. to An 7S co-poiition. Tha re..iodar of tha Tha abundanca ...01 ta.["ra1 rahtiOns of the .ario... iDtanUUal ion_S.....ian phaau of tan ..y be ....01 aa • buia for diatinsuiahing .maller Croaa-cuttinS ~nita within tha gabbrolc anorthoatce. at~t"ral r.1.tio... baa.d on detai1&d obearvationa of a..l1er unita within the gabbrolc anorthoait. aod planar plagioclaa. orientation ln a..ll .reaa, indi.,.te that the gabbroic anortho.lte conatata of a number of lntrusloD8. Intr...iYa into the gabbroic anorthoaita ara at leut threa _jar troetol1tie to sabbroic iotrueiol\8 and othar .....l1er intnMiYea. Gabbro £,d" intr~alva 10 the q...,jrallg1&'. fr08 S..ld E..gla Lake to tha .outh ia • lI&jor which 1& diff.rantiat"d fro", • troctolit" II&rgin to • g.bbro eore. Layering and plauar phaiocla•• ori.ot.tion indieate thi. intrusion to be �til m'" ~n~~o O~ ~oa op .uw•• ol '11.1 o~qCflI .(n.nlll ....q 1111 11 lOV qf!nOqlTI eu02 TI~Td.(l ~IIU 'T .~;oq llqlo 0' l'l'" "'11.1 UAD~ ".ydooo~ 'uO~T '~lddo~ T''PTV pn "'11 lO 'lnOl~o~l UftO~q lATqllA~ 'Ilnrno 'ql ]0 ,,~vIl~n~~o TI~IUr- ~JmOVO~' ~lqlO 11. lATq'lIdll a'll JO l.uqlno. 1I0TerInaT ~I'U ln~:IO '~nyn' '~aAfB AlJ • T'TTI~d '002 P'2lPTXO '~'J~n"41 P..... ~.lP ''1. 01 .vo .{Tao 'ql lnq 01 p.~panq yl"q 111.1 01 ~o ·v•••ol aOT'''~dx. lael m~l l~lllJ<Y.) 111.1 jO ~n~~o I al 111.1 'T •• ~va~~n~~o "'ql lO '11.1 ~lld ~1.alT ATq'n~ 'l~'lVO~'ql '~IAT1 TI,I'I. "11 1~1l1lO~ JO ..I.T"". . . . .noplA 'l~allJ"~~O T'~"'llol 1J1ll0"0~1 'I~aq P"'In~'TP ~ ~n~~o "Ill 110 UADq. lOU Il. l"q I~" Ol'l.q.~ I~ Ul "lPOO ••• ~1'~' IVTAV.dmO~~1 loa TTlA pv. d.. o'TI II'l[TP Ilnol~~l 100T'''11a, q~' ITlv.~p.nb pn ~eyT~' TllIAIS 'oolln~lllT 011.1... 10 ll~ lIO~j 'l~1d aJ Alq"""ld 'llJwoq PIOlill ll"n JO 'PI~OJ ~lOlq'l.I' P"P"I'I.-Tl"A Iq] 'J uOJ~lvl 'lql 10 UlIl.. 01'1'" 11Ilpuno.un. "'11 JO uonll""l'" 'p"uJI~'-l,ulJ V 1.....11.(11 IOJddJP Aldill' .111. 'T'Il 0' PUg Olqqll JO ITlvup1nb ~'lUe:> 11l~Od "lUllT ''I. 01 ln~~o I ~llddl ~Oj UDT'"~lUl ~1'oToll"d ""VIol: ·••o~~. ~or.... '111 "l 'O'TV - ( - .al'~" pul 'P'qllTdmO~~1 P"Tll'l"ll a..q ·r.lnOl~O~l I JO 'ln~~o Ulq10 1"'1. 'TIIl JO •• ~. I'll 1noql"01q1 "TP 9 lftoq. 'TIll JD llid lOr. . I'll ·.yIUf~pI"b I~" o~q~ ~"1l111 'lUol",y~ul Iq " . . 'VOl~lV' • IllTA UO''''llO' IllT0110n llTl .(tyl~"l~n~lS 11'lU"i! "'11.1 JO amos "]J,oql~oal 1<[1 II~JqA UOl'~lol ~or.. Pll~ al 'l'l"'Ol I'll a, 1'" Mqou,., Illl0'lllOU, ~n-lJ'IlP _qlnol l~.d qHA "HVlll lOATI"ll"l 'r.l11TPVJ IlJh... 'IUOll~od T'~lV'~ 1". ]011 IAIII vOllnnvJ 'Jql JO IIJpn]. l~ld "'''IIl\T~vT Il(l ]0 'l,,]:;m~ll 11fll-u,nq ·] ••• ~~oo 1111 01 .1'Pu.ddl 'l nATI l"ltlll_" lllll JO 1'" ·VOll1•• I'O~~ 0l pldlll'_IUD~ �• • 4 • til' allClrthoaitlf;: rock. but rather iD the troctoUte in<;ludi". the dike-like .Ppl"o.ll of troctolite ....cloned ••r11Ir. Th. troctolite 11> the vlciPity of thl .dUd.. u..... Uy cOlltalu -.ny uu:.lu.lllllni 10"'" of which .ppear to b' fin, Itliud t.bbro. otheu are boratet. which fo~tloD, ~,. ha¥e b.... part of th_ Vlrlln1& fD~tlon and Itl11 othera Ite labbroic lDOtthoalt... or lroo Vithin th_ .lbbr01e .n<l troctollt1c r~k. th_ av1Ud.. occur with vlriO\>8 cOllbiDIUona of ty,'. ,ud .1~. of liliclte m1~r.l.. tn ea.a cal•• the hOlt il vary pl.,loci... rich and ill other. quite olh'1rle rich. lD._ c.... the hoer 11 .... ry cOltae-lrained and 1n other_ quit. f101-lrI1,,14. howevlr, chi .ulfl~••pp•• r end aUrlnl 1-r.1.... til n••rly all c••••• to fill thl ioelrarlc•• b'~'D th, p11.10c1,•• �• • i~ •••• 1~ •• •• •i •• • ••0 •i• I •~ •• • • •• i • ••" •i • • •= • ... • -• -" -• -• • - • - • ... • • • • • • . ... • • -• ,.• .,'" • • • • • • -• -•• • -• -- -• • -, •- I- -- • • .' - -• • "' • - - " -- - - " - -• •• ..,.• Q, i. •• • •,~ • • •• •• Ii•• •• •• •• •• •-' • ~. • w w •• • • •• •w •• w • •• •• ~• •• •• • •i• i • w • • w w ••• ••• •• !• ••J i ~ • • •• •l •• ~ ••• •~ ;~ • • •• ~ • •• •• •• •• I ~ • • I • ••• w • •• •w •w w • •• • •• •• • w •• • ! • • w • ~ • •• w •w •• ! • ~ •• • • • •w • •• w •w • " • " • w • •• •w • •• ! w •• •g ••• •• •w • w w • • • • •• • "• •w •w • w w • ••w • •• •• Z • •" "• • •• •w• • • ! • • w •• " •w I • " " w • • ••w • • • • • • w • •• " •w• " •w •• • • " " ADorthc.ittt Gabbro ( "') • •• ~ I Jl'orlUc ADorthc.lte (37) I• • •• Cabbroic Anorth...lu (l76) '1- -• • ~ ....1 Contact loo.... of c.bbrolt ADorth...lta (11) ADorth...lu Troctolite (l~ lIorito! South • • of c..bbrolc Coatact •• -• '1- F , (6) ~~t.hlvl lroc:toUte f •• AUlic. • eU) ~ 50\1tb l.h'1ab1vi PolUUt!t Troctolite (27) •• I1ar.ln of hld Eall. Illcr...1.... (12) c.ntul Zone of Bald !alh Intrua:i<>n (7) '1 ,r Q \)iu of So ..th ll:..,hbbrl 1D t 'CO.a1on (68) ADorthoal~ 10 South ':_hhtvl 10c.....100. (6) ••• l• • •w• • �Individull1 Stopa Stop 11 thh gOlla. Stop 12 ae"oll&bly fneh ,urfac.. of • ..lUcIa C&ll bl! found 111 thl. teat pit from whlch urea took. b..lk u..pl... Agaio • ".-ril!ty of taxt...,.,a and IIlnara1.a c.n b. ael!n. Stop '3 Stop h Stop '5 Stop 16 '1 Stop '8 Stop nea-r b 1I>t-r... 1o" .how. 1I:I,;:1...io ~ of So..th l:_hhiV1 t-r~tolite a"d a vad..ty of t ••t"N•• Cootact batva..o gabb-roic .oo-rthosit.. &lid dike-llke app.ndag.. of troctolite. aalld10g .nd 10clu.iOO8 ~y ba .....n in the troctolit.. which i. lacad with pag~titic 'lei..... Th.. cORpleX ....tur. of the COlltact .lao ... y ba .aao. Gravity influenca4 tha 8.ttling of oliviAI! to produca gr.datiooal byuing. Thta outcrop in tha II1ddh. of the troctoUn ba.1I:I .how&" aeVlil-r.l l:udJ cycl_ of sudation.-l J'-yl:u. o-r th-r"" typ,,* of ,abbroic .no-rtho.ire occu-r h .. r... 111 f:act, .n inclusion nf one typ" io anoth"r .ay ba s....o. Simil.r o..tcrop. form a monotono... p.tt.. rn of g.bb-roit ano-rtho.ite over tens of squa-r.. IIlile. io thi••1'.... 1'\00 Th.. fine_g-r.ined ~-r,io of thi. intrusioo .how. aff..ct. of ••aimilatioo of tha ...-rroundiog g.bbroic &Oo-rrho.ire. w"ll banded zona of thi. intz... ion indicat... the comple. lI.r..rs of th. iotru.ioo and '''I,a.ra the dynamica lnvol~d. The gr.oitic e.. tern ...-r'io of thi. intrusion haa some incl~ions at the .o..th and of the o..tcrop. The granite exteod. nearly 8 Ddla to the north but eod. abo..t One to two huod-red yards "outh of the ro.d. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1968 Description An account of the resource Institute on Lake Superior Geology. Wisconsin State University, Superior, Wisonsin. May 6-7, 1968. Date A point or period of time associated with an event in the lifecycle of the resource 1968 Contributor An entity responsible for making contributions to the resource Henry Lepp Larry Haskin Barton Denechaud Richard J. Wold H.C. Palmer S. Chaudhuri G. Faure D.G. Brookins L.O. Bacon R.W. Ingalls J.F. Stafford D. Gendzwill William R. Church Paul K. Sims G.B. Morey R.W. Ojakangas W.L. Griffin Donald M. Davidson Jr. S. Viswanathan Bill Bonnichsen N.D. MacRae E.J. Reeve P.R. Mainwaring J.W. Horton R.C. Brown D.W. Davidson A.B. Dickas W. Lunking R.K. Roubal J.A. Robertson K.D. Card M.J. Frarey Harold A. Hubbard William R. Farrand W.S. Benninghoff Judith M. Franklin W.W. Moorhouse G.M. Young F.W. Chandler Robert F. Black C. Ernest Kemp Michael R. Dence Nicholas M. Short Bevan M. French Michael M. Katzman John C. Green C. McA. Powell Larry L. Babcock Joseph T. Mengel Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology https://digitalcollections.lakeheadu.ca/files/original/03cef75d9ec3cc907fdd12d97a288082.pdf 3915f7abb5aab6dff27864b48fd34248 PDF Text Text TECHNICAL SESSIONS SESSIONS ABSTRACTS For 15TH ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY Sponsored by DEPARTMENT OF GEOLOGY WISCONSIN STATE UNIVERSITY, UNIVERSITY, OSHKOSH, OSHKOSH, WISCONSIN May 8—9, 8-9, 1969 Wisconsj, Geo!ogsa1 VliscOnsi:l Geo'ogjr-a ~r.'" . to '" •l ,.ard ,U Naturat Hbto B:m'c,',' ,.,N <l!ural History Sr'cy 381/Minoral M;nr Po:nt RO.d uS11 RocI Madison, Wi VII 531"05 ---------------------------------~~---- ---- �15th Annual Institute Institute on Lake Superior Superior Geology Wisconsin State University Oshkosh, Oshkosh, ¶'Jisconsin Wisconsin May 8—9, 8-9, 1969 1969 Institute Institute Board of Directors J. W. Avery (Treasurer), *J. (Treasurer), Jones F& Laughlin Laughlin Steel Steel Corp., Corp., Negaunee, Michigan Michigan *R. *R. C. C. Reed (Secretary), (Secretary), Michigan Geological Survey, Survey, Lansing. Lansing, Michigan. A. A. K. K. Sneigrove, Snelgrove, Michigan Michigan Technological Technological University, University, Roughton, Houghton, Michigan. W. J. Hinze, Hinze, Michigan State W. J. State University, University, East Lansing, Lansing, Michigan A. A. B. B. Dickas. Dickas, Wisconsin vlisconsin State University, University, Superior, Superior, Wisconsin G. G. L. L. LaBerge, LaBerge, Wisconsin State University, University, Qshkosh, Oshkosh, Wisconsin Permanerit *Permanent members. members. Local Committee Committee G. L. G. L. LaBerge (General (General Chairman) Chairman) B. B. E. E. Karges B. B. K. K. McKnight HcKnight N. W. Jones N. W. R. G. G. Hennings Hennings R. Sally LaBerge Field !,rip Trip Committee Committee L. hleis L. 'ft.]. W. Weis ..-......) C. E. E. Dutton >-Co-leaders Co-leaders C. G. L. LaBerg~ LaBergJ G. L. �'0' ~ ~ ~ ~ '06,y LM· //// //;~ .,.....,.,.,.~,..., w. ) ELMWOOD AVE. ~ .-. #. ~1 r-' jJ)'''R"§P D'0 ~~.~ (J •. t.:l~ Li w > e::t r tA•••~.8 ~_~0 - W;;'0 z~ z I B 0 t(Z9i! Lj /'>~ ~a2C:~ ~ W TECHNICAL SESSIONS ALGOMA BLVD. D 0 [1 ........ TITUTE iJ'OLOGY r-::t. 35 34 33 ~lJ' f\-2?rV ~) r:~-=-..::J ...ARK1NG ~ I F KEY TO CAMPUS CAMPUS BUILDINGS BUILDINGS KEY TO Aibee Hall I. Albee Hall BungRlow 2. Bungalow 3. Music Mu.lc Annex Annex 4. 4. Dempsey Dempsey Hail Hall 5. Guidance Psychology Center & Psychology Guidance Center Reeve Memorial Union 6. Reeve 7. Campus School 7. Swart Carepus 8. Science Center 8. Ha\sey Halsey Science 9. 9. Planeta;lu!n Plnetarlun 10. l-larrlngton Harrington Flail Hall 111. L Donner Donner 1-fall Hall 12. Pollock Poilock House 12. Hou.e 13. Radford Radiord Hall Hall 13. Hall 14. Webster Web.ter Hall 15. Taylor Taylor Hail 15. Hall 16. Breeze 16. Bree.e Hall Hall 17. C leman. Hail Hall Clemans 17. 18. Fletcher F letcher Hail Hall 18. 19. Forrest Forre.t R. R. Polk Polk Library Library 19. 20. Heating Heating Plant Plant 20. Woodland House Hou.e 21. Woodland Nel.on Hall Hall 22. NelsOn 23. Swewart 23. Swewart Flail Hall Hall 24. Evan. Hall 24. Evans 25. 25. Ciow Clow Social Soclal Science Science Centet Centet Elmwood Commons Common. 26. Etmwood 27. House Hou.e of of Education Eclucatlon 28. 28. Gruenhogen Gruenhagen Hail Hall Commons River Commons 29. River 30. 30. East Ea.t Hall Hall 31. 31. Scott ScottF-fall Hall 32. 32. Site Site of of Fine Fine Arts Art. Building Bulldlng 33. 33. Extended Extended Services Service!!. 34. Speech 34. Speech Clinic Clinic 35. Center 35. Te.tlng Testing Center 36. 36. Comrnurrlty Community House House �1. PROGRAM PRO G RAM Wednesday., Nay 7, Wednesday, May 7, 1969 1969 7:30 a.m. a.m. to 5:30 p.m. of volcanic, volcanic, Field trip to exposures of a variety of sedimentary, and and intrusive sedimentarYi intrusive rocks in in a volcanic belt belt in L. W. W. Weis, in central Wisconsin. Co-leaders: Co—leaders: L. C. C. E. E. Dutton, and and G. G. L. L. LaBerge. LaBerge. Thursday, May 8, Thursday, 8, 1969 1969 7:30 a.m. a.m. to 9:00 a.m. am. 9:00 85 a.rn. 8'45 a.m. hour, gymnasium (basement), (basement), Registration and coffee hour, Swart School. Swart Campus School. Technical Sessions, Little Theater (second (second floor), floor), Swart Swart Technical Sessions, Campus School. School. Welcome, Welcome, Roger E. E. Guiles, Guiles, President, President, Wisconsin State University, Oshkosh. Oshkosh. Session II Co-chairmen: 9:00 9: 00 9:20 9: 20 930 9:L0 9:40 10:00 10:30 10:50 11:10 11:30 Gregory Gregory Mursky Mursky and and M. N. E. E. Ostrom Rubidium-Strontium ages of Keewanawan Keewanawan intrusives Range, intrusives near near Mellen and South Range, Wisconsin S. Chaudhuri Chaudhuri,J D. Hisconsin S. D. G. G. Brookins, Brookins) and and G. G. Faure Faure from the K-Ar dating dating of of two twodyke.-.swarrns dyke-swarms from D. Lake Superior Superior D. York and H. H. C. C. Halls Halls north shore of Lake Isotopic Baraboo and Isotopic dating dating of the the Barahoo R. Waterloo Quartzites R. H. H. Dott, Dott, Jr. Jr. Geology of the Saganaga-Northern Light Light Lakes Lakes area, Minnesota-Ontario Minnesota-Ontario .... .... S. S. S. Goldich and C. G. N. N. Hanson Hanson area, Coffee break (in (in gymnasium downstairs) downstairs) and pre-Keewatin(?) pre-Keewatin(?) Precambrian granitic rocks and para-gneiss of the the Nashwauk-Buhl Nashwauk-Buhl sector, sector, para—gneiss Northern Minnesota--metamorphic or igneous complex? S. S. Viswanathan and W. W. C. C. Phinney Phinney of the the Duluth Duluth Rare Earths in rocks and minerals of E. B. B. Denechaud, Denechaud, and and L. L. A. A. Haskin Complex ... T. P. P. Pas-ter, Paster, E. Solution iron in in Solution and and deposition of iron sediments George H. H. Spencer, Spencer, Jr. Jr. Lunch Break (Student Lunch (Student Union) Union) Session II II Co-chairmen: 1:00 1:00 1:20 Wm. ~m. J. Hinze and I. I. Edgar Odom The Geology of the Sbuth South Range Range Quadrangle, Quadrangle, Douglas Douglas County, Wisconsin ..... R. County, R. W. W. Johnson and and J. J. T. T. Mengel, Mengel, Jr. Jr. to the the Relationships of regional magnetics to bedrock geology of the the South South Range Range Quadrangle, Quadrangle, Douglas Douglas County, County, '•isconsin Wisconsin ... A. B. B. Dickas, Dickas, E. E. U. H. Frodeson, Frodeson. B. A. Kososki, B. A. Kososki, and C. C. A. A. Wolosin �2, 2. Thursday, May 8,1969 8,1969 (continued) Thursday, (continued) Session II (continued) (continued) 1:40 Shallow in western Shallow seismic seismic refraction profiles in Lake Superior and their relation to Superior their relation to geologic geologic structures Rodolfo structures. Rodolfo Anzoleaga, L. C. C. Ocola and and R. R. P. P. Meyer Anzoleaga, L. 2QO 2:00 Shallow Shallow seismic seismic studies studies in western Lake Superior Richard J. J. Wold lfilold 2:20 2: 20 seismic profiling profiling in in Green Green High resolution seismic Bay Bay P. Meyer Robert P. 240 2:40 Coffee break break 3:10 studies of of Michigan Michigan Electrical anisotropy studies Precambrian rocks Donald G. G. Hill Hill 3:30 A A regional gravity survey survey of southwestern Minnesota J. Ikola Rodney J. 3:50 A reconnaissance paleomagnetic study of A the Series in in the the the South Range Lava Series Peninsula of western Upper Peninsula Michigan R. Middleton, J. Murray and and G. G. Aho Aho R. Middleton, J. 14:10 4:10 Seismic Seismic refraction studies of the the Ames Anticline, Am~s, Ames, Iowa .. L. V. Anticline, Iowa .. Wm. P. P. Staub Staub V. A. A. Sendlein and Wm. 4:30 A magneto-telluric study of the northeastern Lake Superior area Lake Hans Hans Tammemogi 5:20-6:30 Pioneer Inn Inn Cocktail Hour, Pioneer 6:30-7:30 Banquet, Pioneer Inn Inn Banquet, 7:45 Address: by Professor Paul Paul M. M. Clifford, Clifford, of of McMaster McMaster speaking on on "Structural IlStructural evolution evolution University speaking in aa Keewatin Keewatin belt and the nature of in Archaean orogenesis". . Friday, Friday, May 9, 9, 1969 1969 Session III Co-chairmen: Co—chairmen: 9O0 9:00 9:20 9: 20 A. E. A. E. Boerner and Robert C. C. Reed Geology of the the southern southern part part of of the the Bill Bonnichsen Duluth Comp1ex, Complex; Minnesota ...•............. Bill Felsic rock associations of the the Duluth Complex Donald M. M. Davidson, Davidson" Jr. Jr. Petrology of the Rearing Pond Pond Intrusion, Mellen, Wisconsin James F. Olmsted Intrusion, Mellen, James F. Coffee break break Hydrothermal alteration of a a breccia pipe George A. A. Armbrust deposit, Batchawana Bay, deposit} Bay, Ontario Ontario George The Rainy Lake "greenstone" Ojakangas "greenstone" belt belt ..•.... Richard W. W. Ojakangas Exploration of the the Round Round Lake Lake Anomaly, Anomaly, Wayne R. Sawyer County, County, Wisconsin R. Zwickey Zwickey Lunch Break (Student (Student Union) Union) (Little Theater, Theater, Swart Swart Campus Campus School) School) Business Meeting (Little . 9'40 10:00 10:30 10:50 11:10 11:30 1:00 �3. Friday, 9, 1969 1969 (continued) (continued) Friday, May 9, Session IV IV Co—chairmen: Co-chairmen: 1:30 1:50 2:10 2:30 2: 30 2:50 3:20 3: 20 3:40 3:0 L.:l0 4:10 A. Poppin Foppin and John John S. S. Owens Owens Richard A. Ma.fic Mafic dikes dikes in in the the Precambrian Precambrian rocks rocks of Gogehic Gogebic County, Michigan .... Robert G. County, G. Schmidt and and Virgil Virgil A. A. Trent Trent Geologic examination of pipeline trench through Geologic Range, Michigan Hichigan Virgil A. A. Trent the East Gogebic Range, Rejuvenated faults as a Rejuvenated Precambrian faults cause of Paleozoic structures in cause in G. B. southeastern Minnesota G. B. Morey and D. D. C. G. Rensink Rensink Statistical the Portage Lake Lake Statistical study of the Lava Series Stephen C. C. Nordeng Coffee break Organic structures from from the the Negaunee Negaunee (iron) Marquette Range, Range) (iron) Formation) Formation) Marauette Michigan thomas G. G. Wygant and Joseph J. J. Mancuso Thomas Bars and and Troughs, Troughs, Formation of Longshore Bars Lake Superior, Ontario John S. S. Mothersill Stratigraphical Stratigraphical and and sedimentological comparison of early Proterozoic rocks of S.E. S.E. Wyoming and the Great Lakes region Lakes Grant M. M. Young Saturday, May 10, 1969 1969 Saturday. 7:30 a.m. a.m. to 5:30 p.m. p.m. Field trip trip to to exposures of aa variety of Field of volcanic, volcanic, sedimentary) and intrusive rocks in a volcanic belt sedimentary) and intrusive rocks a volcanic in central Uisconsin. Co—leaders: L. Wisconsin. Co-leaders: L. W. Weis, Weis, C. G. L. L. LaBerge. LaBerge. C. E. E. Dutton, Dutton, and G. �4. L. AUTHORS AND TECHNICAL SESSION CHAIRMEN AHO G AHO, G , • ANZOLEAGA, RODOLFO ANZOLEAGA, RODOLFO University, Michigan Technological University, Houghton, Houghton, Michigan University of Wisconsin, Madison, Madison, Wiscons vJiscons in ARMBRUST GEORGE A. A. ARMBRUST, GEORGE i Iowa University, University,Cedar CedaiFAlls, F1s, Northern Iowa Iowa BOERNER~ A. A. EE. BOERNER, Anaconda-American Brass Ltd., Port Port Arthur, Ontario BONNICHSEN, BILL BONNICHSEN, BILL .........• Cornell University, Ithaca, New New York York University, Ithaca, BROOKINS, BROOKINS, D. D. GG Kansas State Kansas State University, University, Manhattan, Kansas CHAUDHURI, SAMBUNDAS CHAUDHURI, SAMBUNDAS Kansas State University, Manhattan., Manhattan~ Kansas CLIFFORD, PAUL M CLIFFORD, PAlTL M HacMaster University, Hamilton, Hamilton, Ontario MacMaster University, DAVIDSON, DONALD M., M., JR. JR. DAVIDSON, DONALD University of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, I"linnesota Minnesota DENECHAUD, E. E. BB. University of Wisconsin, Madison, Madison, Wisconsin DICKAS, A. A. BB DICKAS, Wisconsin State State University, University, Superior, Superior, WI s cons in vJisconsin ROBERT H., H., JR. JR. DOTT, ROBERT of Wisconsin, Wisconsin, Madison, Madison, University of Wisconsin lr.!isconsin DUTTON, CARL CARL EE. DUTTON, U.S. U.S. Geological Survey, Survey, Madison, Madison, Wisconsin FAURE, FAURE, GUNTER Ohio State University, Columbus, Columbus, Ohio Ohio FRODESON, E. E. W~7. FRODESON, Wisconsin State University, University, Superior, Superior, Wisconsin v.Jisconsin GOLDICH, S. S. S S Northern Illinois University, DeKaib, DeKalb, Illinois HALLS) H. H. CC HALLS, Toronto, Toronto, Toronto, Ontario University of Toronto, HANSON, HANSON, GILBERT NN. State University of New York, State York, Stoney Stoney Brook, New York Brook, HASKIN, LARRY A HASKIN, A University of Wisconsin, Madison, Madison, ~~7isconsin Wisconsin HILL, HILL, DONALD GG. Michigan State University, University, East East Lansing, Lansing, Michigan �5. 5• HINZE, HINZE? WILLIAM WILLIAM JJ Michigan State State University., University, East Lansing, Lansing, Michigan Michigan HOPPIM, RICHARD A HOPPIN? A Iowa, Iowa City, City, Iowa University of Iowa, IKOLA,RODNEyJ IKOLA, RODNEY J Minnesota Geological Survey, Survey? Minneapolis, Minneapolis, Minnesota JOHNSON, JOHNSON, R. R. W W State University, University, Superior, Superior, Wisconsin State Wisconsin KOSOSKI, B. KOSOSKI, B. AA ~isconsin State State University, University, Superior, Superior, Wisconsin Wiscons in Wisconsin LaBERGE, GENE L LaBERGE, L Wisconsin State University, Oshkosh, Oshkosh, Wiscons in Wisconsin MANCUSO, JOSEPH J MANCUSO, J Bowling Bowling Green State University, Bowling Green, Ohio Ohio MENGEL. JOSEPH T., MENGEL T., JR . . . . . tATisconsin Wisconsin State StateUniversity, University, Superior, Wisconsin MEYER, MEYER~ ROBERT ROBERT PP University of Wisconsin, Madison, Madison, W is cons in Wisconsin MIDDLETON, R R Michigan Technological University, University, Houghton, Houghton, Michigan MOREY, MOREY, G. G. BB Minnesota Geological Survey, Survey? Minneapolis, Minneapolis, Minnesota MOTHERSILL, MOTHERSILL, JOHN SS . . . . , ... Lakehead Arthur, Ontario Lakehead University, University, Port Arthur, MURRAY, J MURRAY, J Technological University, University, Michigan Technological Houghton, Michigan Houghton) MURSKY, GREGORY MURSKY, GREGORy of Wisconsin, Madison, Madison, University of WI scans in Wisconsin NORDENG, STEPHEN C NORDENG, C University, Michigan Technological University, Houghton, Michigan 000LA, LEONIDAS CC OCOLA, Madison, University of Wisconsin, Madison, Wisconsin ODOM, I. ODOM, I. EDGAR Northern Illinois Illinois University, University, DeKaib, DeKalb, Illinois OJAKANGAS, RICHARD RICHARD W. W University of Minnesota-Duluth, Duluth, Minnesota OLMSTED, JAMES JAMES F. F State University of New York, York, College at Plattsburg, Plattsburg, Plattsburg, New New York York �66,. OSTROM, M. OSTROM, M. EE Wisconsin Geological Geological Survey, Survey, Madison, Madison, Wisconsin Wiscons in Wisconsin OWENS, JOHN OWENS, JOHN SS....•........ The Hibbing, The Hanna Mining Co., Agents, Hibbing, Minnesota FASTER, PASTER, T. T. PP University of Wisconsin, Madison, Madison, Wisconsin PHINNEY, PHINNEY, WILLIAM CC University of Minnesota, Minneapolis, Minneapolis, Minnesota REED, REED, ROBERT ROBERT CC Michigan Geological Survey, Survey, Lansing, Lansing, Michigan RENSINK, D. RENSINK, D. G. G .... of Minnesota, Minneapolis, Minneapolis, University of Minnesota . U.S. Geological Survey, Washington, D.C. D.C. SCHMIDT, ROGERT GG. SENDLEIN, L. L. V. V. AA. SENDLEIN, . . Iowa State University, Ames, Ames, Iowa Iowa Iowa SPENCER, GEORGE H., SPENCER, H., JR. JR Duluth, Duluth, Minnesota STAUB, WILLIAM P STAUB, College of St. St. Thomas, Thomas, St. St. Paul, Paul, Minnesota TAMMEMOGI, HANS HANS Toronto, Toronto, Toronto, Ontario University of Toronto, TRENT, VIRGIL A TRENT, A U.S. Geological U.S. Geological Survey, Survey, Washington, Washington, D.C.. D.C. VISWANATHAN, SS of Minnesota, Minnesota, Minneapolis, Minneapolis, University of Minnesota WEIS, LEONARD W WEIS, W Bay, Fox Fox University of Wisconsin-Green Bay, Campus, Menasha, Menasha, Wisconsin Valley Campus, WOLD, WOLD, RICHARD JJ University of Wisconsin-Milwaukee, Wisconsin-Milwaukee, Milwaukee, Wisconsin Milwaukee, WOLOSIN, C. A A WOLOSIN, C. Wisconsin State State University, Superior, Superior, Wiscons in Wisconsin WYGANT, THOMAS WYGANT, . Bowling Green State State University, Bowling Bowling Green, Ohio Green, D YORK, D University of of Toronto, Toronto, Toronto, Toronto, Ontario Ontario YOUNG, YOUNG) GRANT NM University of Western Ontario, Ontario, London, London, Ontario ZWICKEY. ZWICKEY~ WAYNE Zinc Corp., Platteville, Platteville, New Jersey Zinc Wisconsin �7. PROFILES IN IN WESTERN WESTERN LAKE LAKE SHALLOW SEISMIC REFRACTION PROFILES TO GEOLOGIC GEOLOGIC STRUCTURES STRUCTURES SUPERIOR AND THEIR RELATION TO Rodolfo Anzoleaga, Leonidas C. C. Ocola and and Robert Robert P. P. Meyer Rodolfo Anzoleaga, Leonidas Department of Geology and and Geophysics Geophysics Geophysical Geophysical and and Polar Research Center University of Wisconsin, Madison, Madison~ Wisconsin, Wisconsin, 53706 53706 The shallow structure structure of of the The the western half of Lake Superior is is interpreted on the the basis basis of four four seismic refraction profiles interpreted on profiles along aa line line between Knife River River (Minnesota) (Minnesota) and and Otter-Cove Otter-Cove (Canada). (Canada). Five refractors are are observed. observed. The first (3.3-3.5 (3.3-3.5 km/see) km/sec) is is at a a The first depth except depth of of 0.3-0.5 0.3-0.5 km km and and aa thickness thickness of of 1.2 1.2 km km on on the the average, average except for aa 50 wide T7depression at about about 150 km east of for 50 km wide Y;depression 1i centered at Knife River. where this refractor reaches reaches aa thickness thickness of of 3.5 3.5 km. km. Knife River. (4.5-4.7 km/see) km/sec) is 1.4 km thick east of the the depression The second (4.5-4.7 and 2.5 and 2.5 km under and and west west of of it. it. This refractor pinches pinches out out at at about 30 km east of about of Knife Knife River. River. The third (5.4-5.6 (5.4-5.6 km/see) km/sec) is is about 6 km km thick thick east east and and under under the the depression wedging out towards about towards The fourth Knife River where its its thickness is is less less than than one one km. km. The Knife (6.5 km/sec) for about 120 km from from Knife Knife River River to to the the east east (6.5 km/see) is is found found for fifth (6.9 with with aa dip dip of of about aboutLt°. 4°. The fifth (6.9 km/see) km/sec) is is at at aa depth depth of of 8-10 depression. This refractor is is not not 8-10 km km under under and and east east of the depression. observed as as first arrivals on on the the profiles profiles between Knife River and observed first arrivals the depression. the The satisfies the requires the The model model which which satisfies the observed observed gravity requires 6.9 6.9 km/sec km/sec material material to to continue continue under under the the 6.5 6.5 km/sec km/sec refractor refractor towards Knife Knife River. River. The topography of the 6.9 6.9 km/sec upper interface--as interface--as required required by by the the gravity--is gravity--is probably probably related related to to the the northward continuation of the Mid-Continent Gravity High in the part of of Lake Lake Superior. Superior. westernmost part �88.. HYDROTHERMAL ALTERATION OF OF A A BRECCIA BRECCIA PIPE PIPE DEPOSIT, DEPOSIT, EATCHAWANA BAY, BATCHA~vANA BAY, ONTARIO ONTARIO George A. A. Armbrust Department of Physics and Earth Science Department Science University of Northern Iowa, Iowa, Cedar Cedar Falls, Falls, Iowa, Iowa, 50613 50613 The Tribag mine is situated approximately 45 45 miles northnorthwest of Sault Ste. northwest Ste. Marie, Ontario. Ontario. Precambrian rocks exposed in the area consist consist of: of: acid basic metavolcanics, metavolcanics) rnetasediments metasediments acid to basic and iron formations; formations; granite; granite; diabase diabase dikes dikes and and sills; sills; and a series and a of olivine basalts interlayered with conglomerate and sandstone. sandstone. The metavolcanics, metasedjmen-ts metasediments and formations represent and iron formations an accumulation of 30,000 30,000 feet feet of material was later intruded material which was by granitic batholiths. batholiths. All are faulted faulted and and intruded intruded All of these rocks are by diabase dikes and and sills. sills. Overlying this older rock complex complex is is aa thick series series of into the the Lake Lake of olivine olivine basalts basalts which were were extruded extruded into Superior basin. basin. Conglomerate and sandstone sandstone are are interlayered interlayered with with the basalts, basalts, which dip southwest the southwest at at 20 20 to to 40 40 degrees. degrees. Felsite bodies bodies intrude the volcanic and and sedimentary sedimentary layers. layers. The Tribag mine is is in in the the Breton Breton breccia, breccia, one of five five breccia the eastern eastern margin margin of of Township Township 28, 28, Range Range 13. 13. The pipe pipes near the has surface dimensions of 1,400 by 350 350 feet, feet, and the size increases has slightly with depth. depth. The sub-rounded The breccia contains contains angular to to sub-rounded fragments sodic granite, granite, basic basic volcanics, volcanics, fragments of of trondhjemite or sodic felsite, and. diabase. These are felsite) and diabase. are set set in in a. a matrix of of quartz, quartz) calcite., calcite, pyrite pyrrhotite, pyrite., pyrrho-tite,chalcopyrite, chalcopyrite, sphalerite, sphalerite, marcasite marcasite and galena. Minor amounts molybdenite, scheelite, amounts of molybdenite, scheelite, fluorite, fluorite) laumontite and also occur occur in in the the matrix. matrix. barite also j Secondary effects on the rock fragments fragments include include hematization, hematization, sericitization, kaolinitization, chioritization, chloritization, sericitization, silicification, kaoljnjtjzatjon, and minor carbonatjzatjon. carbonatization. A small amount of pyrite and and leucoxene leucoxene are associated with sericitized sericitized biotite. biotite. Hematization of the the feldspars preceded brecciation. feldspars brecciation. Quartz, Quartz, sericite, and kaolinite kaolinite mineralized areas. areas. Hydrothermal chlorite chlorite are abundant near highly mineralized bears no special special relationship to to the the mineralized mineralized areas. areas. the extrusion of basaltic magma Hydrothermal alteration and the have both been dated at near 1,050 million years years by the the K-Ar nearby have method. An amygdaloidal dike having a a similar similar mineralogic composition to the basaltic lava cuts the the breccia at the Tribag mine. This indicates a mlne. a possible genetic relation between the Middle Keweenawan extrusives and and the the Tribag Tribag copper copper deposit. deposit. The presence of abundant sericite sericite and and quartz quartz in in and and near near the the The mineralized at Tribag, Tribag along mineralized zone zone at along with with the the mineralogy mineralogy and and general general geologic setting, setting, suggests depositions depositions in a a moderate moderate to to high The large amount of open intensity environment. The open space space between between breccia fragments pressure fragments suggests suggests deposition in a a relatively relatively low pressure environment. �9. GEOLOGY OF THE SOUTHERN PART PART OF OF THE DULUTH COMPLEX, COMPLEX, MINNESOTA:! MINNESOTA' DULUTH Bill Bill Bonnjchsen Bonnichsen Sciences Department of Geological Sciences Cornell University, Ithaca, Ithaca, New New York, York, 14850 l85O Two Two groups groups of of intrusive intrusive igneous igneous rocks are abundant abundant in in the the southern part of of the the Duluth Complex. Complex. The earliest group is the The is the Anorthositic Series; it Series; it consists anorthosite consists primarily of gabbroic anorthosile and troctolitic anor-thosjte. and.t~octolitic anorthosite. In In general, general, the mafic minerals (olivine, pyroxenes7 (ollvlne, pyroxenes, oxides) oxides) in these rocks rocks are paragenetically later later than than the the plagioclase. plagioclase. The is the the Troctolitic Troctolitic The latest group is Series in which troctolite Series in which troctolite and and augite augite troctolite are the most common rock types. rock types. Plagioclase Plagioclase and generally are are contemporaneous contemporaneous and olivine divine generally in these rocks in these rocks and are paragenetically earlier earlier than than the the accompanying pyroxenes and and oxides. oxides. The Troctolitjc Troctolitic Series Series is is present along the western margin of the the southern part of the the Duluth Duluth Complex and intrudes rocks of the the Anorthosjtjc Series that Anorthositic that lie lie to the east. east. The Anorthositic Series Series is hypothesized hypothesized to to be be genetically related to is some of the Keweenawan to some flows; flows; it is is suggested that some flows represent differentiated some flows liQuids liquids that were expelled from from magma chambers chambers in in which rocks of the Anorthosj-tjc Anorthositic Series were accumulating accumUlating by by crystal crystal settling. settling. the Anorthosj-tjc Anorthositic Series After the Series had had been been emplaced, emplaced, troctolitic magma evidently intruded along a a widening fracture fracture zone zone to to form form the the Troctolitic Series between the Anorthositic Series to the east and Troctolj-tjc Series between the Anorthositic Series to the the Early and Middle Precambrian Precambrian basement basement complex complex to to the the west. west. The sulfide deposits in the the southern part the Duluth Complex The sulfide deposits in part of of the Complex that that currently are of economic interest interest for for their their Cu-Ni Cu-Ni potential potential are are believed believed to to be be syngenetic syngenetic segregations segregations within within the the lower lower part part of of the Troctoljtic the Troctolitic Series. Series. "Work done :!Work done on behalf of the Minnesota Geological Geological Survey. Survey. �10. RUBIDIUM-STRONTIUM AGES OF KEWEENAWAN INTRUSIONS NEAR MELLEN AND SOUTH SOUTH RANGE RANGE IN IN WISCONSIN WISCONSIN S. Chaudhuri Chaudhuri and and D. G. Brookins S. D. G. Department of Geology Kansas University, Manhatton, Manhatton Kansas Kansas State State University, Kansas 5665014 66504 and G. G. Faure Faure Department of Geology Ohio State University, Columbus Ohio Columbus, Ohio, Ohio,143210 43210 Rubidium—strontium Rubidium-strontium ages ages were measured on whole rocks rocks and mineral separates separates from the Mellen Granite and and the the Mellen Mellen Gabbro Gabbro in in Wisconsin. Wisconsin. A suite of porphyritic granite chosen for isotopic isotopic study of the Granite was was collected collected from from sections sections3232and and33, 33,T'45N, T45N, R3W. Mellen Granite Samples in the Samples of of the the Mellen Mellen Gabbro Gabbro were were obtained obtained from from outcrops outcrops in the In addition, a whole-rock rubidiumvicinity of Mineral Lake. of Mineral Lake. In addition, a strontium age was determined determined on on monzonite monzonite which which cuts cuts the the iKeweenawan Keweenawan basalts near South South Range Range in in Douglas Douglas County, County, Wisconsin. Wisconsin. The ages wer1calulated bybyusing werelcal~Iulated usingthe thedecay decay constant constant for for Rb87 Rb 87 = 1.39 xx 10-~ 10- y- . The calculated age of whole rocks and biotites from the The Sr87/Sr86 porphyritic granite granite is is 9140 940 + Sr 87 /Sr 86 ratio ratio of of primary primary + 12 m.y. porphyritic strontium is is found to be 0.7137 0.7137 ++ 0.0005. Samples of the Mellen Gabbro range in values of Sr87/Sr86 Sr 87 /Sr86 ratio ratio from from 0.7057 0.7057 to to 0.7161. 0.7161. The isotopic composition of samples do not the The isotopic of these these samples not agree agree with with the isochron the porphyritic granite. granite. The Mellen Gabbro isochron defined defined by the appears assuming it to to be be related to appears to to be be about about 1100 1100 m.y. m.y. old old by assuming related to the the intrusion of the the Duluth Duluth Gabbro. Gabbro. The whole-rock whole—rock rubidium-strontium isotopic The isotonic analyses analyses of the the 87 The initial Sr87/Sr86 monzonite yield an age age of of 935 935 ++ 15 15 rn.y. m.y. The-initial Sr /Sr 86 ratio is is 0.7100 ++ 0.0008. (1) the porphyritic granite west of Our data indicate that (1) Gabbro, and the cognate Mellen is much younger than the Mellen Gabbro, unlikely, (2) (2) the emplacement of relationship of these two rocks is unlikely, the the porphyritic granite granite near Mellen Nellen was was contemporaneous contemporaneous with with that that of of The data also demonstrate that the monzonite near South Range. Range. The that the the 87 /Sr 86 Sr87/Sr86 ha~e significantly significantly high high initial initial Sr granite and the monzonite have ratios, which point a rubidium-rich environment ratios, point to their origin in a indicate aa previous previous crustal crustal history history for for these these rocks. rocks. and may indicate �11. II. THE FELSIC ROCK ASSOCIATIONS OF THE DULUTH COMPLEX Donald N. Davidson; Davidson Jr. Donald M. Jr. Department of Geology Department University of Minnesota~ Minnesota Duluth, University of Duluth, Minnesota, Minnesota~ 55812 55812 supported by by the the Minnesota Minnesota Geological Geological Field research has been supported Survey in Kawishiwi Lake, Lake, Lake Lake Polly Polly and and Kelso Kelso Mountain Mountain quadrangles, quadrangles; Lake and and Cook Cook Counties; Countjes Minnesota. Lake Minnesota. This subsequent This research and subsecuent revealed the the presence of several several laboratory investigation have revealed felsic felsic rock rock types types spatially spatially associated associated with with anorthositic anorthositic and and gabbroic Complex. gabbroic rocks rocks of the Duluth Complex. Rock types types thus Rock thus far delineated are: granite) granodiorite, granite, granodiorite, grano-gabbro) dioriteC?). These rocks are are grano-gabbro7 granophyre, granophyre, and diorite(?). rocks of the the gabbro complex with at least least genetically younger than rocks two separate intrusive intrusive periods. periods. indicates Petrographic evidence indicates the dioriteC?) diorite(?) may be the be aa hybrid from intrusive intrusive hybrid rock type derived from of gabbroic gabbroic rocks. rocks. contamination of �12. RELATIONSHIPS TO THE RELATIONSHIPS OF REGIONAL MAGNETICS TO OF THE THE SOUTH SOUTH RANGE RANGE QUADRANGLE, QUADRANGLE, BEDROCK GEOLOGY OF DOUGLAS COUNTY, COUNTY, WISCONSIN A. B. B. Dickas A. and E. W. W. Frodesen~ Frodesen B. E. B. A. A. Kososkj Kososki and C. C. A. A. Wolosin (Students) (Students) Department of Geology Geology Wisconsin State University3 University, Superior, Superior, Wisconsin, 54880 54880 Bounded by latitudes latitudes 46° 46° 33' 33' to 46° 37.5' 37.5' and longitudes longitudes 910 91° to 46° 52.5' to 92°~ 92° the 52.5' to the South South Range in central central Douglas Douglas Range quadrangle lies in County) approximately five County) five miles southeast southeast of of Superior, Superior, Wisconsin. Wisconsin. During the Fall and Winter of 1968-69. one one hundred hundred and forty forty station readings employing aa Schmidt readings Schmidt type type vertical magnetometer were recorded along all primary and secondary secondary roads within the northern northern recorded thirty-six square mile sector of this t~irty-six this quadrangle. quadrangle. This spacing spacing yields ylelds a a density of four four stations stations per square square mile. mile. A A centrally located station was located base and and drift drift analysis. analysis. As the the was used for base magnetometer was initially initially zeroed zeroed at all other other at this this position, all station data, data, after proper corrections, are relative to station to the the base point. The The purpose of this study study was to determine the degree to which surface rriagnetics magnetics would wouldreveal reveal the the structure structure and and trend trend of the northern Wisconsin bedrock when buried under several several tens tens to to hundreds of feet of Pleistocene hundreds Pleistocene till. till. Outcrops common Outcrops are not at all common in this this region. As and Mengel (these (these proceedings), proceedings), As outlined by Johnson and this quadrangle is subdivided by the Douglas Douglas Fault Fault into into two two this petrologic provinces. provinces. North of the fault the Pleistocene till and Recent lake sediments sediments overlie sandstones interbedded interbedded with shale, shale, the the Recent lake latter all of Keweenawan (Cambrian?) (Cambrian?) age. The thickness of of these these clastics is estimated by the Wisconsin Geological Geological Survey Survey to to be be in in elastics excess of twenty twenty thousand thousand feet. feet. In the magnetic trend trend In this this province the is non-uniform. Regionally, is Regionally, a a northeast-southwest strike strike is is observed at a a rate of 400 400 to to 600 600 increasing in magnitude to the northwest at gammas per gammas per mile. Scattered and apparently non—related non-related magnetic noses and interrupt this this weak regional trend as and closures closures interrupt as they range in from north-south north-south to to east-west. east-west. These orientation from These anomalies, anomalies, which have a a residual magnitude of 100 to to 200 200 gammas) gammas) might be attributed in the the subclastic subclastic basement basement to mineralogic irregularities either in complex or within the the surficial surficial till. till. The latter is is the more more probable probable cause Keweenawan (Cambrian?) (Cambrian?) cause due due to to the very great thickness of the Keweenawan the basement basement complex. complex. sandstones overlying the South a strong strong and uniform South of of the the Douglas Douglas Fault is found a regional magnetic fabric fabric striking striking NN 75° 75° E. E. As many as as seven seven separate trends, trends, marked marked by related related closures, separate closures, are present forming a a "wash-board" effect. effect. Each trend averages one—half one-half mile mile in in width, width" has 800 to 1600 gammas and can can be traced has aa residual residual amplitude of 800 across across the entirety of of the the study study area. area. Station control suggests suggests these trends possess possess on their northwest these trends nor~hwest flank a a magnetic gradient �13. that is that is two to three times as found on on the the opposing opposing as steep as that found flank. flank. These are in agreement with the the known These differing differing gradients gradients are southerly dip dip of the basaltic flows flows erratically erratically exposed exposed in in the the region. region. Assuming aa 30 30 to to L0 40 degree dip flows (various (various dip within the flows sources) sources) and and magnetic magnetic trends trends averaging averaging one-half mile, mile, basaltic basaltic flows flows up to three three thousand thousand feet feet in thickness thickness associated with each trend up would be be expected. expected. In the North Shore Shore Volcanic Volcanic group, group, In stUdies studies on the J. C. C. Green (1968) (1968) lists the "common" "common" thickness thickness for for flows flows similar similar in in J. composition to the South South Range Range quadrangle quadrangle group to be ten ten to to fifty fifty feet. feet. From the view~ it it would thus thus seem logical the g~ophysical geophysical point of views the effects of multiple mUltiple rather that each magnetic trend is recording the than single layer conditions. than conditions. Considering the pe-trogrephy petrography of this Considering the quadrangle as outlined by by Johnson Johnson and Mengel (these (these proceedings), proceedings), the magne-tics are recording recording either basalt—basalt magnetics are basalt-basalt or or intrusiveintrusiveextrusive sequences, sequences. The N) RR 13 13 WW is is marked marked by a a The trend trend centered centered In in section section 15, 15, TT 47 7 N, gabbroic gabbroic outcroD) outcroD, while while that that trend trend centered centered in in section section 11, 11, TT 477 N W is In the latter 13 W is closely associated with with basaltic basaltic exposures. In the R 13 area aa magnetic is located located on the the axis axis of a a positive magnetic reversal reversal is closure, supportin b evidence for arenaceous units lying lying closure, suggesting suggesting supporting evidence for between flows flows as found found northeast along along strike strike by by Johnson Johnson and and Mengel. Mengel. It thus pattern is is related related to a a more It thus seems seems that that this this \!vJash-board uwashboardf11 pattern complex situation than a a simple layered basalt basalt sequence. sequence. hi1e While magnetic magnetic trends trends can be be traced traced throughout this this area, area~ their continuity is is interrupted. interrupted. In South Range Range In the the center of the South left-lateral off-setting off-setting is is noted. noted. This quadrangle an apparent left-lateral is remarkedly coincident with the western border of the large large trace is mass seen seen in in sections sections31, 31,3232and and3333ofof T 48 N, R 12 N. W. The gabbro mass T Ll.8 gabbro mass appears to to be true offset rather than than gabbro mass appears be associated with aa true a a cancellation of the the magnetic trends. trends. It would seem logical logical It would thus seem that this off-setting off-setting is is a a result of left—lateral left-lateral transform transform faulting. faulting. Possibly at a later date the the gahbro gabbro was was activated and conceivably partially used the fault plane plane as an avenue avenue of of intrusion. intrusion. Final this faulting--intrusion faUlting-intrusion relationship analysis of this relationship will will have to await the local local basement basement rocks. rocks. eventual age dating of the This transform fault, This fault. with a a strike of NN 30 30 to to 40° 40° N~ is is parallel parallel to known in in the the Lake Lake Superior Superior area. area. to other similar fault patterns known Each of these faults faults strike strike at at right to the the regional regional right an~les an1es to structural grain. grain. Nhile While the apparent amount of off—setting off-setting in in the South Range area measures approximately approximately one mile) is postulated mile, it is this fault this fault is is part of the very fault system very extensive extensive transform fault by Thiel Thiel (1956) (1956) and and-Coons, Woollard and and Hershey Hershey (1967). (1967). portrayed by Coons, Woollard References Coons, R L. Coons, R. L., Woollard, P .. and Hershey, Hershey, C., G., Woollard, G. C. P.. Significance Significance and and Analysis of Hid-Continent Amer. Assoc. Amer. Assoc. Pet. Pet. Geol., 51, 51, December, December, pp. pp. (1967), Structural (1967), Gravity High, High, Bull. Bull. Gravity 2381-2399. 2381-2399. �iLl.. 14. Green. J. Green, (1968); Varieties of Flows in the North Shore Volcanic J. C., C.. (1968), Group, Minnesota ~1innesota (abstract), (abstract)? Proc. Froc. Institute Institute on Lake Superior SuperlOr--Group, Geology, pp. pp. 52~S3. 52--53. Johnson R. R. W. W. and and Menge1~ Mengel, J. J. T. T.,~ (1969), Johnson, (1969), Economic Implications Implications of of the the South South Range Range Quadrangle, Quadrangle, Douglas Douglas County, Countv, the Geology of (abstract)~ Proc. Proc. Institute Institute on on Lake Lake Superior Superior Geology. Geology. Wisconsin (abstract), Thiel) Thiel, E.; E., (1956), (1956), Correlation Correlationof ofGravity GravityAnomalies Anomalieswith withthet Keweenawan Geology Geology of of Wisconsin Wisconsin and and Minnesota~ Minnesota, Bull. ul1. Geol. Keweenawan Geol. Soc. Soc. Amer., 67~ 67, p. p.TO79. Amer., 1079. �15. BARABOO AND WATERLOO WATERLOO QUARTZITES QUARTZITES ISOTOPIC DATING OF THE BARABOO Dott, Jr. R. H• B. Dott, and Geophysics Geophysics Department of Geology and University University of of Wisconsin, Wisconsin, !4adison, ~adison, Wisconsin, 53706 53706 The long has be correlative The Baraboo Quartzite Quartzite long has been assumed to be (i.e. between between about 2.5 2.5 and and with Huronian and/or Animikean rocks (i.e. 1.6 b. 1.6 b. y. y. old). old). This was based only upon This correlation, correlation, however, however, was similarities of lithology and seauence similarities sequence of quartzite, iron iron formation, formation~ beTween the the Baraboo Baraboo region and northeastern dolomite and slates between Wisconsin and and adjacent adjacent Michigan. Michigan. Isotopic Baraboo and its inferred Isotopic dating dating suggests suggests that that both both the the Baraboo and its equivalent near (25 miles miles east east of of Madison) Madison) are are equivalent near Waterloo, Waterloo, \Jisconsin Wisconin (25 younger than Animikean. Animikean. Rb8?Sr07 Rb 87 _Sr 87 dating of five five samples samples of of dark dark rhyolite that underlies rhyolite that underlies the the Baraboo Quartzite yields an isochron of l.51+ .7Rb87 1'~11~ 0.0 0.04l xx 10 10 9years years(assung (assuw~ng ~ Rb 87decay decayconstant constant of of 1.47 1.47 x 10 yr. 10 yr.and initial Sr°°/Sr Sr /Sr 7 ratio of 0.705 0.705 ++ 0.005). and an initial 0.005). AA K-Ar date date was was attempted for a K-Ar a phyllite zone zone near near the the-top of the the top of quartzite the formation, formation, but quartzite in in the the hope hope of of dating dating metamorphism of the the potassium content was too low the low to provide aa meaningful result result 6 (760 +50 x 106 yrs.). (760 ~ 50 x 10 yrs.). The younger age limit of red) red) Baraboo-type Baraboo-type quartzite seems seems to to be be provided provided near Waterloo, ~aterloo, however. however. Bass (in Bass (in Tuve, Tuve, 1959) reported a'Rb·-Sr for muscovite muscovite from from aa a Rb-Sr date date of of 1.44 1.44 b. b. y. y for that cuts cuts the the "Waterloo IlWaterloo Quartzite", Quartzite") and and Goldich, Goldich, coarse pegmatite that et ~t al ~l (1966) (1966) reported reported aa K-Ar date of of l.'41 1.41 b. b. y. y. from from muscovite muscovite in a schistose zone within that that quartzite. quartzite. It Baraboo-Waterloo type It appears appears that the Baraboo-.Waterloo type quartzites quartzites of of southern Wisconsin originally were as sands in a a subsiding subsiding mobile were deposited as belt between about about 1.4 1.4 and and 1.5 1.5 billion years ago, thus the quartzite belt quartzite probably is probably is both both post-Anirnikean post-Animikean and and post-Penokeari. post-Penokean. This This strengthens the the possibility that the the Baraboo Baraboo is is a a southern, thicker thicker equivalent equivalent of of the Sioux Quartzite, the Quartzite, which is is known known only to be from 1.2 1.2 to to 1.7 1.7 billion years old old (Goldich, (Goldich, et al, aI, 1966). 1966). Rb-Sr dating of three three samples of the Baxter Hollow~ranite (on the south side of. the samples of the Baxter Hollow Grite (on the south side of,the Baraboo Syncline) allow Syncline) a total range of 1.36 1.36 -- 1.67 b. b. y., y" so so does does a not indicate not indicate if the granite is is older older or younger than the the quartzite, quartzite. �16, 16. GEOLOGY OF LIGHT LAKES LAKES AREA AREA OF THE THE SAGANAGA-NORTHERN LIGHT MINNESOTA-ONTARIO S. Goldich S. S. Division of Geology Geology Northern Illinois University, DeKaib, DeKalb, Illinois, Illinois, 60115 60115 and C, N. G. N. Hanson Department of Earth and and Space Space Sciences Sciences State State University of New Ne~7 York York at at Stony Stony Brook, Brook, New New York, York, 11790 11790 The Early Precambrian rocks The rocks along the Minnesota-Ontario boundary are are of special special interest because they were were involved involved in two orogenies giving rise to granites of two ages. giving of two ages. The older granite, granite) defined and pre-Knife Lake, Lake, is is typified typified by the the geologically as post-Keewatin and Saganaga Granite (tonalite) which was folded Keewatin Granite (tonalite) was emplaced in folded rocks and and was was eroded rocks eroded to to supply cobbles and and boulders boulders to the the Knife Knife Lake sediments, sediments. The younger Algoman granite was defined geologically as post-Knife Lake and pre-Animikie. as pre-Animikie. Examples Range Examples are the Giants Range Granite Granite. Granite and the Snowbank Granite. The in the the Saganaga-Northern Light Lakes Lakes area The Keewatin Keewatin rocks rocks in are some intermediate intermediate to to silicic pyroclastic are basaltic basaltic volcanics volcanics with with some rocks and graywacke. rocks graywacke. The Northern Light Light Gneiss Gneiss is is aa fine-grained fine-grained leucocratic rock of of trondhjemitic trondhjemitic composition that leucocratic rock that represents represents a a in the the Keewatin Keewatin volcanic volcanic pile. pile. The NW-SE synkinematic intrusive in is well well exposed structure developed during during the the Laurentian Laurentian orogerly orogeny is By contrast the Algoman along Trafalgar Bay along Bay of Northern Northern Light Light Lake. Lake. By orogeny the folding folding of the the Knife Knife Lake Group Group orogeny which which resulted resulted in the developed NE-SW structures mapped by J. W. Gruner west west and developed structures mapped J. W. and southwest of Saganaga Saganaga Lake. Lake. The Saganaga Granite was was emplaced in the metavolcanics The Saganaga Granite the Keewatin metavolcanics and Northern Northern Light Gneiss in aa late kinematic and Light Gneiss kinematic stage of the the Laurentian orogeny. It was followed followed by by the the intrusion intrusion of of quartz quartz dioritic dioriticplutoris plutons It in the the vicinity of Icarus Icarus Lake Lake east e~st of of Northern Northern Light Light Lake, Lake. The in F. Grout, latter latter vJere were referred referred to to as as l'younger younger syenites" syenites n by by F. F. F. Grout. In In our interpretation of the the structural structural development development of of the the region, the Northern Light Gneiss and the Saganaga Saganaga Granite formed formed a region, F. R. R Harris massif that rose rose diapirically diapirically along along faults. faults. F. Harris has has recently mapped the granite-greenstone contact contact along the north shore On the of Saganaga Saganaga Lake Lake as as aa fault. fault. the west side the the displacement was was accomplished by by downfoldirig downfolding of faults. of the the Knife Knife Lake Lake beds beds and and along along faults. Thus the Laurentian massif was rising throughout the time of deposition Lake, and and the the conglomerate conglomerate which deposition of the the Knife Knife Lake, which rests rests on on the is the the basal Knife Lake Lake unit in the the Saganaga Saganaga Granite Granite and and which which is basal Knife unit in the vicinity of Cache Bay occupies a a higher position in in the Knife Lake succession as as a a whole, whole, as earlier earlier determined determined by by J. J. W. W. Gruner. Gruner. The present interpretation does not require the large large amount of F. Grout's Grouts erosion and avoids the structural structural problems problems inherent inherent in in F. F. F. earlier interpretation interpretation in in which the the Saganaga batholith batholith was was emplaced emplaced later tilted tilted to to the the west west during during the the in aa vertical position and was later Algornan orogeny. orogeny. Algoman �17. ELECTRICAL ANISOTROPY STUDIES OF MICHIGAN PRECAMBRIAN ROCKS ROCKS Donald G. G. Hill Department Department of Geology Michigan Michigan State State University, University, East East Lansing, Lansing, Michigan, Michigan, 48823 8823 Alternating Alternating current current dielectric dielectric constant constant and electrical conductivity conductivity measurements selected rock samples samples collected collected measurements were made on selected from from the the Precambrian Precambrian of Michigants Michigan's Northern Northern Peninsula. Peninsula. The The directional variation d~rectional variation (anisotropy) studie? (anisotropy) of these properties was studied with wlth variations variations in in rock fabric, fabric, lithology, lithology, and signal signal frequency, freque~cy, in In the range the range from from 20 20 to 300,000 cps. cps. Measurements were ~vere made using uSlng both to 300,000 two and and four electrode methods. two methods. Theoretical methods of interpreting geoelectrical data data generally assume that assume that earth earth materials materials do not exhibit significant tri-axial do significant tri-axiai aniso-tropy. anisotropy. The this study to date indicate indicate that that some The results results of this rocks, rocks, particularly particularly those with pronounced lineation or banding are those with lineation or banding are characterized by characterized by strongly anisotropic electrical properties. This strongly electrical properties. aniso-tropy is increasingly increasingly evident at lower anisotropy is lower frequencies, frequencies, in in the the range of those used in E. range used in E. M. M. and I. I. p. P. prospecting. prospecting. This study has confirmed the confirmed the theoretical theoretical prediction that the electrical anisotropy symmetry is symmetry is related related to to rock fabric symmetry. symmetry. Thus laboratory laboratory and/or field electrical field electrical anisotropy measurements may be be used to predict rock fabric symmetry. symmetry. �18. A A REGIONAL REGIONAL GRAVITY GRAVITY SURVEY SURVEY OF OF SOUTHWESTERN SOUTHWESTERNMINNESOTA:/ MINNSOTA' Rodney J. J. Ikola Ikola Minnesota Geological Survey Survey University of University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota, Minnesota, 55455 5555 Approximately 2500 2500 gravity stations stations have been established by by the the Minnesota Geological Survey Survey in in southwestern southwestern Minnesota. Minnesota. The majority of the stations stations are are located located on a a two mile grid with wider spacing control is is limited. limited. The presented as as aa where vertical control The results are presented Bouguer gravity map contoured at at 22 and and 10 10 milligals. milligals. The area underlain by the Morton Gneiss, Gneiss, which is is exposed at Morton in the the Minnesota River valley, valley, is is represented on the gravity map as as a a generally smooth smooth featureless featureless area. area. The contact between between the the gneisses represented by exposures at Morton Gneiss Gneiss and more more mafic mafic gneisses Granite Falls is is marked by by a a sharp sharp gravity gravity gradient. gradient. Within ~lithin the the area of the mafic gneisses gneisses there there are are two two positive positive gravity gravity anomalies, anomalies, one the other north of Granite Falls, Falls, which are one south of of Dawson and the thought to represent mafic intrusive intrusive rocks. rocks. Granitic intrusive bodies are Granitic lows on on the the are indicated by gravity lows A gravity low at New Ulm corresponds to to known outcrops of A granite in the the Minnesota River valley. granite valley. A much larger gravity low low extends to the the extends from from south south of of Granite Granite Falls Falls in in the the valley valley westward westward to South Dakota border. border. Outcrops Granite and the Outcrops of the the Sacred Heart Granite granite at the Larsen Larsen quarry are present within this this low. low. map. map. Areas rocks with associated sediments Areas of possible mafic mafic volcanic rocks are are delineated by the gravity gravity survey. survey. One One example is is an elongate elongate in the the extreme extreme western part of the the positive anomaly at Hendricks, in state. state. A series series of anomalies anomalies extending extending from from Lake Lake Beriton Benton southeastward A also are are thought thought to to be be caused caused by by niafic mafic volcanics and to Worthington also associated sediments. sediments. A positive gravity feature extending westward from from Hutchinson Hutchinson to A to Lake Lillian may represent the Lake the southern a sedimentary southern edge edge of a sequence lies unconformably unconformably on the sequence of of Middle Middle Precambrian Precambrian age, age, which which lies older Precambrian. Precambrian. The areal extent of the Sioux Formation is is not readily delineated by by the the gravity gravity method. method. appears to to be be little little or or In many areas there appears difference between the the Sioux Formation and the older rocks rocks no density difference on which it it was deposited. deposited. ~I ~1Work Work done done on behalf of the Minnesota Geological Geological Survey. Survey. �~--------"---------I--------r--------;------, r r-- --- ----- ~ , ~ i ~ I .. __ ... ... - .. -._-_ .. _ . .-;I I / I , "0QUARRY QUARRY I f. i.-.-. I I 1+/ I :/J?4>~ MORTON ~O ~ ....J I Ii, ! , i EN D R IC KS HENDRICKS --J .-- ..,I ' " LARSEN 10 L L., 1-' !I , HEART I' , ._.~ HUTC~INSON C f----------.------.-.---, 0 0 r----....J----.-.!:.~KE. L1L~~~i.. i DAWSON DAWSON ! )_ I o i ~ I 'L , I __ ._.-i I , \, .__L . ~./'t>­ i <[I ~~ f-, F- 0 1 ~ ~ LAKE LAKE BENTON BENTON _j 0 <l. J I I' , I I .r-.---........ I I 1 r.--------,----.-.-----l.--T------.-.j o -I ~ J: i fH- i• I :::l I ! 0 °1~ C/) (J) :.-__ . I I i I I I, ! I ,I l-·-------·t·-·---·-------·-l·-----·----I,' , I I I i I i WORTHINGTON WORTHINGTON0 O i SCALE seA LE 5 0 W miles I !, IOWA o WA TI.iP MAP -PAVI TY GRAVITY SHOWING SHOW'ING i SuV. Y SURVEY LOC.A LI TI T'wNTiONE LOCALITIES 1\IlENT!ONED IN II' ST1CT OF ABSTRACT OP' OF OF SO UT -1w STIN 1yUNNESOT.A. SOUTH"WESTERN IyINI'.7 S OT..A.. _ �20, 20. THE GEOLOGY OF THE SOUTH SOUTH RANGE RANGE QUADRANGLE, DOUGLAS COUNTY, COUNTY~ WISCONSIN WISCONSIN Rudolf W. W. Johnson (student) (student) and Joseph T. T. Nengel, Mengel, Jr. Jr. Department of Geology Wscons1 WisconsinState StateUniversity, University, Superior, 54880 Superior, Wisconsin, Wisconsin, 54880 Copper Copper shows shows are found wherever Keweenawan lavas lavas outcrop in are found Douglas County contains a substantial substantial percentage of of the the known known outcrop a majority of the Pleistocene outcrop and a subcrop of subcrop of the the lava lava sequence, sequence, all of which must must be be looked looked on on as as prospective for prosp~ctive for copper. copper. No detailed mapping of the the bed bed rock rock geology geology of this of thlS county county has has been published since the turn of the present century. century. The Wisconsin State University (Superior) (Superior) Geology The Department, in cooperation with the State Geological Survey Department, Survey has recently begun mapping along the the Douglas Douglas Copper range near the City of Superior of Superior to to provide provide basic information on on bed bed rock rock geology. geology. The purpose of this this mapping is purpose is to determine the nature and geometry of of the geometry the bedrock units the bed rock units present and to establish the the character character of of their their geophysical responses to serve serve as as a a guide guide to systematic copper prospecting in the drift-covered areas. The South Range, Range, Wisconsin Wisconsin 7-1/2 minute quadrangle is 7-1/2 is the first area to to be be mapped. mapped. the first northwestern Wjcsj. northwestern Wisconsin. The South Range quadrangle is The is located about 5 5 miles southeast southeast of Superior) of Superior) Wisconsin, Wisconsin, on flank of the Lake Superior on the the south flank basin. basin. It and It lies lies near near the the middle middle of the the Douglas Douglas Copper Range and exhibits exhibits geology representative of that of the entire entire Range. Range. The quadrangle the steeply south-dipping Douglas Douglas fault which quadrangle straddles the brings the Keweenawan lava brings lava flow sequence in contact with younger flow sequence sandstones to the the north. north. The flows are typically tholeiitic tholeiitic basalts The flows with medium grained ophitic interiors interiors and amygdoloidal margins. margins. Individual flows flows are less than 100 feet thick t~ick and dip SSE SSE are typically less at 35--40°. 3540°. A at A horizon marked by by basaltic basaltic cinders cinders and and fine-grained fine-grained quartz sandstone occurs near the the middle of the exposed sequence in in southwest corner corner of of T147N_R12W. T47N-R12W. the southwest Medium South Range percentages percentages of ilmenite is widely distributed distributed in in the the to coarse grained gabbro is quadrangle. The typical rock consists of of equal equal plagioclase and pyroxene, pyroxene) together with a a few few per cent cent of plagiociase or titanjferous titaniferous magnetite. magnetite. A gabbro gabbro body, body, centering centering in in 32-48N--12W 32-48N-12W underlies about four four A part of of the the quadrangle. quadrangle. square miles of the northeastern part body are exposed in in the NW 1/4 of Anorthositic portions of this body 32-48N-12W; 32-48N-12W; reddish portions crop crop out out along along the the Amnicon River south of Bardon State Park and finer grained portions occur within the the Park. Park. The gabbro body body is is not not noticeably noticeably layered layered in in character. character. The Douglas fault fault cuts cuts off the the gabbro to the the north in in the SE SE 1/4 of Douglas 29-48N-12W, 29-48N-12W, but but elsewhere elsewhere it it is is bounded bounded by by the the lava lava sequence. No lava-gahbro lava-gabbro contact exposures exposures are are known, known, but the suspected position is is marked by magnetic anomalies. anomalies. l/ �21. Outcrops S70W from the the main body across across the the Outcrops of gabbro gabbro extend S7OW S 1/2 1/2 of 1-7N-13W S 1-47N-13W in in aa zone zone about about 500 500 feet feet wide. wide. These outcrops lavas both both to to the the north north and and south. south. A A body of reddish are bounded by lavas granodiorite outcrops in in l5-47N-13W. 15-47N-13W. Its Its boundaries are covered, covered~ but the the high mafic mineral content of the border portions, but portions, and and the of lavas lavas immediately immediately to to the the west west suggest suggest that thatthe thecoufltiy co un ll'Y occurrence of rock is is basaltic basaltic lava. lava. A basaltic dike with excellent columnar joint development has intruded intruded the the granodiorite granodiorite body. body. Magnetic joint relations suggest that other intrusives intrusives are present present in in the the southern southern relations half of the the quadrangle, quadrangle, but a a thick cover of Quaternary sands sands and clays cover the the entire entire area. area. Minor native copper and and copper copper sulfide sulfide mineralization mineralization is is found found The best of in fractures in in amygdaloidal amygdaloidal lavas. lavas. in amygdules amygdules and along fractures the observed mineralization mineralization occurs occurs at at about about the the horizon horizon of of the th the observed fragmental materials boundary of the fragmental materials and close to the western boundary Exposures of the gabbro are too limited to principal gabbro mass. mass. Exposures the possibility possibility of of sulfide sulfide segregations segregations within permit evaluation of the it, it. sulfides into into the the lava lava sequence sequence can can be Local introduction of sulfides noted to the southeast southeast of of the the gabbro gabbro in in the the Poplar Poplar quadrangle. quadrangle. �22, 22. HIGH RESOLUTION SEISMIC PROFILING IN GREEN BAY P. Meyer Meyer Robert P. Department of Geology and Geophysics Geophysics Center Geophysical and Polar Research Center University Madison, Wisconsin, 53706 University of of Wisconsin., Wisconsin) Madison~ 53706 Several thousand thousand miles miles of high resolution--high frequency Several frequency seismic seismic reflection in Green Bay, Lake Lake Michigan) reflection profiling in Green Bay, Michigan, have have provided provided both test for for this this technique technique and and aa surprising amount aa test amount of data on the the sediments structural history history of of the the Bay. Bay. Eutrophic sediments under and structural sediments, characterized low reflectivity, sediments, characterized by by low reflectivity, have have been consistently found when predicted from from the acoustic acoustic data. data. The converse is is not not found true,1 for for sediments sediments of this this type type have have been found found where where the the true and, in this this case, case, entrapped gas gas bubbles are reflectivity is high and, thought responsible. Underlying the the eutrophic muds, muds) are seen, seen, yet unsampled, finely finely layered sediments, sediments) themselves greatly contorted contorted unsampled, dimly appears appears as as aa reflective reflective conformable conformable layer. layer. and resting on what dimly foot. Resolution kc, pulse pulse used used is is about about one one Resolution of the single cycle, 77 kc, Maximum penetration achieved was was about about 150 150 feet. feet. The method appears appears to have have great promise in in combined and detailed geological-geophysical geOlogical-geophysical studies of the immediate immediate sub-bottom including programs in eutrophication and and mineral mineral search. search. �23. A A RECONNAISSANCE PALAEOMAGNETIC STUDY STUDY OF OF THE THE SOUTH SOUTH RANGE RANGE LAVA SERIES IN THE WESTERN UPPER PENINSULA OF MICHIGAN LAVA SERIES J. Murray, G. G. Aho Aho (Graduate (Graduate Students) Students) R. R. Middleton, Middleton, J. Department of Geology and Geological Engineering Michigan Technological Technological University, University, Houghton, Houghton, Michigan, Michigan, 49931 993l Michigan A total of eleven block samples samples of of the the South South Range Range Lava Lava Series Sel'ies were collected at at Silver Silver Mountain,, Mountain, Bond in the the Bond Falls, Falls, and Wakefield in the Upper Upper Peninsula Peninsula of of Michigan. Michigan. Forty core western part of the specimens inch diameter diameter were were obtained obtained from from the the samples. samples. specimens of one inch Remanent a Permalli spinner Remanent Magnetism was was measured using a magnetometer. A-C demagnetization studies studies were were carried carried out to to test test stability. The The results of the the survey survey were were compared compared the remanence stability. with previously published published palaeomagnetic studies studies of the Lake Superior region. �2'4. 24. FAULTS AS AS AA CAUSE CAUSE REJUVENATED PRECAMBRIAN FAULTS OF PALEOZOIC STRUCTURES IN IN SOUTHEASTERN MINNESOTA C. G. B. B. Morey and D. D. G. G. Rensink Rensink Minnesota Geological Survey Survey and and and Geophysics Geophysics Department of Geology and University of of Minnesota, Minnesota, Minneapolis, Minneapolis Minnesota, Minnesota, 551455 55455 j The upper midwest is is part part of of a a tectonically stable stable province province large sedimentary basins and arches in Paleozoic characterized by large rocks. It is is known large basins and arches It known that that the the large basins and arches overlie equivalent features on the the Precambrian surface3 surface, and that a a close equivalent features correlation commonly exists between small-scale structures in commonly exists Paleozoic Paleozoic rocks rocks and and inferred older structures structures in the the basement rocks. features and The detailed relationships between basement features Paleozoic structures structures seldom have established, however, however, because Paleozoic have been been established, the basement basement is covered and and integrated data on on subsurface geology geology the is covered and and geophysics rarely rarely are are available. available. Such Such an integrated study study has been been completed completed of of aa recently recently recognized Paleozoic Paleozoic structure--called the anticline--in Dakota Dakota County, County, Minnesota. Minnesota. the Vermillion anticljne--jn The \Jermjlljon Vermillion anticline anticline is is aa northeast-trending northeast-trending structure about wide. It It is is doubly doubly plunging about six miles miles long and two miles wide. and asymmetrical asymmetrical in in cross-section; cross-section; the the northwest northwest limb dips about about and limb dips 20 feet/mile, limb dips dips about about 40 40 feet/mile. feet/mile. 20 feet/mile, whereas the southeast limb The anticline is modified by at least two northwest-trending crossfaults and and one northeast-trending fault faults fault that that parallels parallels and and is is slightly southeast of the anticlinal axis. axis. The faults faults are are interpreted interpreted as as having having steep steep dips dips and and reverse reverse movements; movements; the the apparent apparent vertical displacement displacement does does not exceed 100 feet feet on any of the faults. Concurrent Paleozoic Paleozoic deposition deposition and and vertical vertical movements movements in Concurrent in the the (1) vicinity the anticline are indicated indicated by: by: (1) displacement on on vicinity of the the cross-faults apparently apparently decreases decreases upward upward in in the the section, section) (2) (2) thinning thinning of of several several stratigraphic intervals intervals in in Cambrian Cambrian strata strata occurs over the the fold fold crest, crest, and (3) (3) an erosional unconformity separates rocks at at the the fold fold crest. crest. separates Cambrian and Ordovician rocks An analysis analysis of structural and isopach contour maps maps for various intervals within the Paleozojc section indicates that warping in intervals within the Paleozoic section indicates that warping in aa northwesterly direction took place prior to movement along the crossfaults) and and ~Jas was sufficient sufficient to to modify modify the the depositional depositional pattern pattern during during faults, late Cambrian Cambrian time. time. That movement along along the the the middle part of late northeast-trending fault fault took place during the the last phase of Cambrian deposition or before the first first phase of Ordovician deposition is is before the indicated by by the the Cambrian-Ordovician Cambrian-Ordovician unconformity, unconformity, where where approximately approximately indicated 30 feet feet of Cambrian strata 30 strata are are missing. missing. Combined drilling and geophysical geophysical data data in in this this area area indicates indicates Ve~million an-ticline anticline in that the Vermillion in part part overlies overlies an an uplifted block of Middle Keweenawan basalt called called the the Hudson-Afton Hudson-Afton horst. horst. The basalt basalt �25, 25. is is in fault fault contact with Upper Upper Keweenawan Keweenawan sedimentary sedimentary rocks rocks on on three three sides; apparent apparent vertical vertical displacement displacement on on these these faults faults is is on on the the order order sides; of 8,000 of 8,000 to 12,000 feet. feet. Two of the three Paleozoic faults faults coincide with with the the Precambrian faults, that geographically coincide faults, suggesting suggesting that they have resulted from minor isostatic they isostatic readjustments readjustments in in the the Other nearby nearby Paleozoic Paleozoic structures~ structures such basement. Other such as as the the HudsonHudsonanticline, also are geographically coincident with the Afton anticline, Hudson—Afton Hudson-Afton horst, suggesting suggesting aa similar similar origin origin for for them. them. �26. 26 FORMATION OF LONGSHORE-BARS AND TROUGHS, TROUGHS, LAKE SUPERIOR, ONTARIO ONTARIO S. Mothersill John S. Department of Geology Lakehead Lakehead University, University, Port Port Arthur, Arthur, Ontario Grain size analyses of of 186 186 samples samples from from the the axes axes of of longshuic-longshul'Cbars and troughs troughs along the lake shelf shelf at Batchawana Batchawana Bay Bay and and Pancake Pancake bars Bay, Lake Lake Superior, Superior, Ontario, Ontario, show the the longshore-bar sands Bay~ sands to to be be and finer finer grained than the adjacent shoreward shoreward longshoielongshol'ebetter sorted and trough sands. sands. In addition the the longshore-bar sands are unimodal and tend to to be be positively positively "skewed" whereas the tend "skewed" whereas the longshore-trough sands sands iTIay either unjinodal unimodal or may be either or biwodal bimodal and and show show aa tendency towards negative skewness. skewness. This This would would suggest suggest that that the the longshore-troughs longshore_rOUghS were formed by the were formed the action of breaking waves that preferentially set the finer grained particles into into motion. motion. These finer grained the finer particles were were then then moved moved lakeward lakeward by the undertow to form the the particles by the to form longshore-bar areas. areas. �27. STATISTICAL STUDY OF THE PORTAGE PORTAGE LAKE LAKE LAVA LAVA SERIES Stephen C. C. Nordeng Nordeng . - Department of Geology Geology and and Geological Geological Engineering Department of Engineering Michigan Technological University, University) Houghton, Houghton, Michigan, Michigan) 49931 993l The frequency frequency of occurrence of conglomerates in the Portage Lake Lava Series fits fits aa Poisson distribution, distribution, implying that such events intervals. events occur at random intervals. The frequency distribution for for thickness thickness of of the the different types types of lava flows flows and for the conglomerates fall impossible fall in the impossible region for the Pearson Pearson Type Type Curves. Curves. The single exception exception was was ophitic ophitic (coarse-grained) (coarse-grained) flows flows with a a cellular amygdaloidal top top which have aa Type Type II (Beta (Beta "J" IlJ" shaped) shaped) distribution. distribution. This type of distribution can result from aa random variable operating over an an upper and and lower lower limits, limits. The failure of other interval with definite upper The failure types, the overall thickness distribution, distribution, to to fall in in aa types, including the class is is reflected in their standard deviations being similar class commonly equal to to the the mean. mean. This This shows an overabundance of thin flows degree of of fluidity fluidity for for the the lavas. lavas. flows suggesting a high degree transitions as as aa Narkov Harkov process process gives gives Treating the flow type transitions an expected sequence sequence of of textural textural and and flow flow top top combinations combinations as as follows: follows: 1) cellular top; top; 2) 2) melaphyre melaphyre with with fragmental fragmental tops; tops; 1) me1aphyre melaphyre with cellular 3) ophites ophites with with fragmental fragmental tops; tops; 3) ophites with with cellular cellular top; top; 1+) ) ophites glomerophorphyri-tes with cellular tops; 5) glomerophorphyrites tops; 6) 6) glomerophorphyrites glornerophorphyrites This is with fragmental tops; tops; and and 7) 7) conglomerate. conglomerate. This is accompanied by aa tendency toward greater flow flow thickness. thickness. Plotting the the flow flow types types as Plotting as a a time time series and smoothing shows shows four incomplete cycles of this four this type type in in the the Portage Portage Lake Lake Lava Lava Series, Series. �28. l ; THE RAINY LAKE BELT::/ LAKE "GREENSTONE "GREENSTONE" BELT' Richard W. W. Ojakangas Ojakangas Department of Geology University of Minnesota, Minnesota, Duluth, Duluth Minnesota, Minnesota, 55812 55812 j The 'iKeewatin Greenstone Greenstone Belt" Belt" of of A. A. C. C. Lawson Lawson (1887, (1887, The Rainy Lake 'Keewatin 1913) has been restudied in 1913) in detail detail on the United States States side side of of the the International Boundary. Boundary. The wide in in this this area, area, The belt, belt, 22 to 33 miles wide trends is bounded sides by Lawson's Lawson's "pre-Keewatin trends ENE ENE and and is bounded on both sides ll Series of biotite schists. schists. The dominant rocks within Coutchiching Series" the belt are schists, massive "tuffaceous" the are chlorj-tjc chloritic schists, "tuffaceous" greens-tones, greenstones, minor rock rock types types include include pillowed pillowed greenstones, greenstones, and meta-arkoses; minor conglomerates, and conglomerates, and "felsic Hfelsic tuffs". tuffs". These rocks rocks are generally interbedded and gradational. gradational. Most of the metasedimentary rocks rocks in the area are vertical or lineations generally plunge to the ENE at angles nearly vertical and lineations of of 3Q0 30° to to 500. 50°. Lawson interpreted the structure here as a a Lawson interpreted the regional regional structure here as synCline composed of Coutchiching biotite biotite schists schists on on the the outside, outside, syncline composed greenschists and Keewatin greenschis-ts and greenstones greens-tonesnearer nearerthe thecenter) center and Huronian (Seine) the center. center. of In light of (Seine) meta-arkoses meta-arkoses and and conglomerates at the this study, study, a a different structural structural interpretation interpretation seems seems more more probable. probable. in the the bioti-te biotite schists the meta-arkoses Graded beds in schists and and cross-beds cross-beds in in the stratigraphic tops. tops. provide information on stratigraphic Tops in the meta-arkoses towards -the the south} are consistently towards south, rUling ruling out out any any syncline within the unit. unit. The belt appears to be in fault fault contact with the biotite schists to to the the North North and and South: South: shear shear is is evident evident and and the the structure structure schists directions within'the Ilgreenstone belt" and the adjacent based on top top directions within the "greenstone bioti-te schists schists is is difficult difficult to to resolve resolve without without the the presence of these biotite these faults. biotitic and and chloritic chioritic A unit composed of of intimately intimately interbedded. interbedded biotitic schists to form aa gradational unit i!greenstone schists appears appears to unit between the "greenstone belt" and the biotite belt" biotite schists. schists. Apparently the assemblage of the "greenstone is gradational with and and overlain overlain by by the the biotite biotite "greenstone belt" belt" is The entire entire sequence of the the region thus represents a schists. The sequence of thus represents a thick accumulation which resulted from from relatively relatively continuous continuous deposition; deposition; volcaniclastic volcaniclastic sediment, sediment, clastic clastic sediment, sediment, and and minor volcanics grade upward into dominantly clastic (terrigenous?) upward (terrigenous?) sediment. sediment. Sulfides Sulfides are are quite quite commonly commonly disseminated in these these rocks rocks and small gossans several localities. localities. from the the small gossans were noted at several Rocks from Little some gold the Little America America Mine Mine which which produced produced some gold in the the 1890's 1890's from the the south south edge edge of of the the "greens-tone "greenstone belt" shear zone at the belt" contain gold and contain anomolous and silver, silver, and and rocks rocks from from aa few few other other localities localities contain anomolous values of gold, values gold, silver, silver, and and copper. copper. 'Work done :/Work done on behalf of the the Minnesota Minnesota Geological Geological Survey. Survey. �29. PETROLOGY OF THE REARING POND INTRUSION, INTRUSION, MELLEN9 WISCONSIN MELLEN, J. F. J. F. Olmsted Department of Physics Physics and and Earth Earth Sciences Sciences State Science State University College of Arts and Science Plattsburgh, Plattsburgh, New York, 12901 Intrusion is is part of the Keweenawan igneous The Rearing Pond Intrusion complex limb of the Lake Lake Superior syncline syncline complex which which lies lies along along the the south limb of the in Wisconsin. The intrusion is is roughly elliptical in plan and displays graded banding which dips toward the center from all displays directions, suggesting suggesting that that it it has has aa funnel-like funnel-like shape. shape. The directions, intrusion in contact the Mineral intrusion lies lies directly directly north north of, of, and and in contact with~ with9 the Mineral Lake anorthositic unit unit of of the the complex. complex. These two units are mineralogically and texturally in strong contrast with one another and the field field as as well as under the and are are readily recognizable recognizable in the microscope. The Intrusion is is emplaced emplaced into into what what appears appears The Rearing Pond Intrusion to to be be South Range Range type Middle Keweenawan volcanics, volcanics, but probably Lake Intrusion. Intrusion. earlier than the Mineral Lake The Rearing Pond Intrusion contains three major rock units that The The three types are best are in the the field. field. are readily distinguishable in described by listing the the cumulus cumulus minerals minerals in in order order of of abundance, abundance, according to the practice of of L. L. R. R. Wager Wager and and co-workers. co-workers. The earliest unit unit is earliest is an olivine cumulate (peridotite) (peridotite) which forms forms an outer shell, shell, followed followed by aa plagioclase-olivine cumulate (picritic (picritic gabbro), the latest part of the intrusion gives way to a a gabbro), which in the plagioclase-pyroxene-olivine cumulate cumulate (gabbro). (gabbro). The latter two two units The second combined form the core core or or inner inner zone zone of of the the intrusion. intrusion. The gabbro) also also contains contains fairly fairly large large amounts amounts of what unit (picri-tic (picritic gabbro) appears to be intercumulus appears to be intercumulus pyroxene which actually may also be cumulus. This thesis is is developed on the the basis of the fact fact that the This thesis banding noted above is banding noted above is largely due to the the variation of the content The fact of these poikilitic pyroxene pyroxene crystals. crystals. The fact that these crystals a pile of plagioclase and olivine could not have have developed in a crystals lying on the the bottom of the magma chamber can be reasonably crystals well shown shown on on textural textural grounds. grounds. Mineral compositions compositions in each of the Mineral the three units units show small changes but fractionation is changes is not not strong. strong. Plagioclase varies from from about An. An . ..80 80 (cores) the picritic gabbro gabbro to to about about An. An . ..60 60 (cores) (cores) (cores) in in the in the the latest gabbro. in gabbro. Normal zoning is is very common common and and in in any any crystal crystal the the change from core to rim is from 10 to 15 percent, percent, in either rock -type. type. Olivine and orthopyroxene both both have have compositions compositions either rock in the the range range of 80 percent Mg end-member in the peridotites to about 80 Mg the about LIttle difference is 65 in the the gabbros. gabbros. Little is seen seen 65 percent Mg end-member in in. the mineral mineral compositions compositions between between the the peridotite and in. the and the the picritic Intercumulus gabbro. Intercumulus myrmekite is is common common in in the the latest latest gabbros gabbros indicating fractionation has has proceeded. proceeded. indicating the the extent to which fractionation picritic �30. 30. RARE EARTHS IN IN ROCKS AND MINERALS MINERALS OF OF THE THE DULUTH COMPLEX T. T. P. P. Faster, Paster~ E. E. B. B. Denechaud, Denechaud, and L. L. A. A. Haskin Department Department of Chemistry University of Wisconsin, Madison, Madison, Wisconsin, Wisconsin, 53706 53706 Rock Rock samples samples of of all all principal principal types types from from the the Duluth Duluth Gabbro Gabbro complex in in Gabbro Gabbro Lake Lake quadrangle, quadrangle, Lake Lake County~ County, Minnesota, Minnesota, have have been complex analyzed for for rare rare earths. earths. As a first first approximation, the the relative relative As a abundances of the the whole rocks appear to reflect only the rare-earth abundances whole rocks Separated minerals from mineralogical compositions compositions of of the the rocks. rocks. from aa troctolite, a gabbro, and and aa pegmatite pegmatite are are now now being being analyzed. analyzed. troctolite, �31. MAFIC DIKES IN THE PRECAMBRIAN,ROCKS PRECAMBRIAN ROCKS OF OF GOGEBIC GOGEBIC COUNTY, COUNTY, MICHIGAN~/ MICHIGAN' Robert G. G. Schmidt and Virgil Virgil A. A. Trent Trent Robert U. U. S. S. Geological Geological Survey, Survey, 11ashington, Washington, 0. D. C., C., 20242 20242 Dark, sulfide-bearing, maf ic dikes dikes of of two two ages ages are are common common in Dark, mafic the of the the Gogebic Gogebic area. area. Although there is is the older Precambrian rocks of a a considerable range range in in the the dimensions, dimensions, composition, composition, age, age, texture, texture, and metamorphism, the most abundant dikes are hornblendeand degree degree of metamorphism, rich.:, containdisseminated disseminatedpyrite~ pyrite, and and are are moderately moderately metamorphosed. rich, contain The The youngest youngest dikes dikes are are mostly unmetamorphosed and at least some are younger than the oldest "South "South Range Range Traps". Traps". Detailed study study of the the dikes provides provides information useful in solving the geology of the dikes information useful the geology the enclosing rocks. rocks. The same general field field relations have been found found in in the Marenisco area and and in in the the area area south south of of Ironwood and Ramsay, Ramsay, 10 10 to to 20 miles to to area Ironwood and 20 miles the west. west. Most older dikes trend trend northeast, northeast, but but some some trend trend eastward; eastward~ younger dikes dikes trend trend northeast and and northwest; northwest; and both types appear to be joint well—defined younger dikes were found joint controlled. controlled. Many well-defined found within the the older dikes dikes in both areas, areas, and in exposures near McDonald Lake young young dikes dikes seem seem more more abundant abundant in in the the old old dikes dikes than than in the Lake in the adjacent granitic rocks. rocYs. Old dikes dikes are are particularly abundant Old abundant and thicker in a a northeast3-mile-wide belt Ironwood and and Ramsay. Ramsay. trending 3—mile--wide belt 22 miles miles south of Ironwood Some Some are are at at least least 600 600 feet feet wide, wide, and and others others can can be be traced traced several miles; drift on the south intermittently for for several miles; thick glacial drift us from from determining determining the the full full width width of of this this dike dike swarm. swarm. prevents us Furthermore, no hornblendic hornblendjc dikes dikes were were identified in the Furthermore, no the IronwoodIronwoodRamsay area age, and these older dikes dikes are Ramsay area within within rocks rocks of Animikie Animikie age, and these rare or perhaps perhaps absent absent in in the the northernmost northernmost 2-mile--wide 2-mile-wide band of prepreAnimikie granitic granitic rocks. rocks. dikes cropping out in the the central part of the Marenisco Most dikes quadrangle which intrude intrude metasedimentary rocks and derived gneiss quadrangle and schist are young, Both older and young, diabasic types. types. Both and younger dikes are common in the Presque Isle Granite to the south. are in Presque Isle Granite to the south. Although the old dikes near Ironwood old dikes Ironwood and Ramsay are undeformed, many are essentially undeformed, the Marenisco area are strongly strongly sheared. sheared. in the All dike contacts contacts we we have have seen are chilled. chilled. Even though a a particular contact is not exposed, we interpret partiCUlar interpret the abrupt diminution of grain size size to to represent represent aa chilled margin. margin. Most dikes have relatively uniform uniform compositions compositions and several large large and grain sizes, but sever.l ones are notably on~s.are notably inhomogeneous. inhomogeneous. Rhythmic color banding of of unknown unknown origin and local local segregations segregations of of llgabbroic gabbroic pegmatite" o~lgln.and pegmatite" were found. found. Diabasie textures Dlabasl: textures predominate predominate but but eQuigranular equigranular gabbroic textures are ar2 common in ln the coarse—grained coarse-grained bodies. bodies. */ done in cooperation with the , -"Work - W?rk.done the Geological Geological Survey Division of the of tne Michigan Mlchlgan Department Department of Conservation, Conservation. - �32, 32. The older The older dikes dikes owe owe their present mineralogical assemblage to metamorphism under conditions of the greenschist facies (Turner the upper greenschis-t facies (Turner and Verhoogen, and Verhoogen, 1960), 1960)j followed a very unevenly unevenly distributed distributed followed by a retrograde metamorphism. retrograde metamorphism. The fresher rocks contain mainly hornblende and plagioclase, plagioclase, but and but chlorite, epidote, clinozoisite, clinozoisite, and calcite chlorite, epidote, are also present in most places, places, depending upon the extent extent of of metamorphic effects. effects. retrograde metamorphic The younger dikes The dikes are are augitic, augitic, with strongly zoned plagioclase laths; locally these dikes are considerably altered, laths;.locally altered, perhaps perhaps deuterically. deuterlcally. The possibility that a a late late period of metamorphism has affected has affected some area must must still still be be some of of the the young young dikes dikes in this area tested. tested. In both the retrograde or deuteric In both types types of of dikes dikes either the effects, effects, or both, both, principally principally affected the the mafic mineral, mineral, but locally the plagioclase is is preferentially preferentially altered. Our work to date does not not permit to say anything regarding direction of metamorphic permit us us to gradients. The old hornblendjc hornblendic intrusives intrusives may be be contemporaneous contemporaneous with sills that that cut cut the the Ironwood Ironwood Iron-Formation east of sills of Wakefield. Wakefield and are truncated by lower Keweena.wan Keweenewan strata as truncated W. C. C. Prinz Prinz (1967). (1967). as mapped by W. The younger augitic dikes intrude lower Keweeriawan Keweenawan quartzite and quartzite and some of the the ttSouth "South Range to Range Traps" Traps?? both both at at Bessemer Bessemer and, and, according to C. E. E. Fritts Fritts (written (written communication, communication, 1966), just just west of of the the Cisco Cisco C. Branch of the Ontonogon River. River. Appreciable magnetic variations are are rarely found associated with the old old mafic mafic rocks rocks observed, observed, but a the a very notable exception exception is is the the magnetite-rich sill magneti-te-rich rock rock in in the the northern northern part part of of the the metamorphosed sill described by W. W. C. C. Prjnz Prinz (1967). (1967). The The augitic augitic dikes dikes contain enough magnetite to magnetite to be detected with aa small small hand hand magnet magnet and generally have strong with them. them. Near Ironwood and strong magnetic magnetic anomalies anomalies associated with Ramsay the anomalies anomalies are sign, in contrast are probably probably all all of of positive positive sign, to to the the consistently negative negative anomalies anomalies associated with dikes of Keweenawan by Keweenawan age age farther farther east east in northern Michigan as described by J. R. Balsley, H. L. James, and K. L. Wier, (1949). Near Marenisco J. R. Baisley, H. L. James, and K. L. Wier, (1949). diabase dike dike anomaly was determined to be be of negative negative sign. sign. one diabase A special interest in the dikes developed when it it was noted noted that that many of the the large large mafic mafic masses masses contain contain sulfides. sulfides. The largest are at at least 600 600 feet wide and and perhaps perhaps 3000 3000 feet feet long. long. Disseminated sulfide least generally ranges 0.20.l4 0.2-0.4 per per cent. cent. Semi-quantitative Semi-quantitative spectrographic analyses analyses and atomic absorption spectrometry determinations determinations indicate indicate low low copper, copper nickel, spectrometry nickel, cobalt, cobalt, and and silver contents in in all all these these rocks. rocks. An attempt was made made to to relate relate age and and minor element composition of the mafic rocks, rocks, but no age differences were noted although there is is a suggestion suggestion significant differences of somewhat amounts of titanium, of somewhat higher amounts titanium, beryllium, beryllium, copper, copper, and augitic dikes. dikes. we strontium in the younger, augitic For the present we conclude that that although although sulfide—bearing, conclude sulfide-bearing, neither type type of dike is is of economic interest for its its metal content. content. �33, 33. References Baisley, J. J. R.; R., James; James H. Balsley, H. L., L., and and Wier, Wier, K. L., L., 1949, Aeromagnetic 199, Aeromagnetic survey of of parts parts of Baraga, survey Baraga, Iron, Iron, and and Houghton Houghton Counties, Counties, Michigan, with preliminary S. Geol. Geo1 preliminary geologic geologic interpretation: interpretation: U. U. S. Survey) Geophys., Prelim. Rept. Rept. Survey., Geophys., Inv. mv. Prelim. Prinz, w. W. C., C., 1967, 1967, Pre-Quater'nary Pre-Quaternary geologic geologic and and magnetic magnetic map map and and Prinz, sections of of part of the eastern Gogebic sections Gogebic iron iron range, range, Michigan: Michigan: U. U. S. S. Geol. Geol. Survey Survey Misc. Misc. Geol. Geol. mv. Inv. Map MapI_1497, 1-497. Turner, F. J., and and Verhoogen, Turner, F. J., Verhoogen~ John, John, 1960, 1960, Igneous Igneous and and metamorphic petrology: 2nd ed., N. Y., Y., McGraw—Hill McGraw-Hill Book Book Company, Company, 2nd ed., New York, York, N. 69L p. 694 p. �3L4 34. SEISMIC REFRACTION REFRACTION SURVEY OF THE AMES ANTICLINE, AMES, AMES, TOt'A IOWA L. V. A. Sendlein L. V. A. Sendlein Department of Earth Science Science University, Ames, Iowa State University, Ames, Iowa, Iowa, 50010 50010 and W. W. P. P. Staub Staub Department of Geology College of of St. St. Thomas, Thomas, St. St. Paul, Paul, Minnesota, Minnesota, 55101 College 55101 If Ames, Ames, Iowa Iowa lies lies astride astride the the mid-continent mid-continent gravity gravity high. high. this geologic this important important anomaly anomaly is is to to be be properly properly understood, understood, geologic information is is essential. essential. The method was was The seismic refraction method selected selected to to investigate investigate the the geology geology of of the the drift drift covered Ames Ames region because of its its economy economy and and reliability. reliability. There There is is a a remarkable remarkable correlation between seismic selsmlC and gravity data from the the Ames Ames region. region. This suggests that the This correlation suggests field is is influenced by the thickness of residual gravitational field glacial structure. Seismic data were used used glacial drift drift as as well as geologic structure. produce a a structure contour map of a a high speed Mississippian to produce marker horizon. horizon. The map illustrates an arched horst (Kinderhook) marker is consistent with the the residual residual gravity gravity map. map. Evidently the that is horst is associated with the the mid-continent mid-continent gravity gravity high. high. �35. SOLUTION AND DEPOSITION OF IRON IRON IN IN SEDIMENTS SEDIMENTS G. H. G. H. Spencer, Spencer, Jr. Jr. 619 619 First American Bank Building Building Duluth, Minnesota, 55802 55802 iron minerals minerals are are found found in in many many geologic geologic Sedimentary layers of iron areas associated associated with with volcanic volcanic materials materials sandstone, areas sandstone, clays, clays, limestones and even even coal coal beds. beds. The theories of of origin of of these these iron bearing conflicting because an inability inability to iron bearing beds beds are are often often conflicting because of an to discover the the chemical chemical and and sedimentary processes processes involved in the discover the different environments. j Dissolution of of iron acid waters waters may may be be due Dissolution iron in ln acid due to to either dissolved volcanic gases or to organic acids produced by by bacterial In acid acid volcanic waters, action on plant material. In waters 5 northern lakes, lakes, and possibly in Pre-Cambrian seas iron has and seas , iron has been leached from from bottom sediments either as chlorides or sulfates or as organic complexes. Organic complexes or chelates chelates of of iron iron are are soluble soluble to to several thousand parts per million and and are are as as effective effective solvents solvents several for for iron as volcanic waters. waters. , as aa carbonate, Deposition of iron as carbonate, silicate, silicate, sulfide sulfide or even as an an oxide oxide is due to to aa gradual or sudden relative relative increase as is due increase of This may may be be due due to to loss of gases gases from from alkalies in in solution. solution. This loss of solution by a a pressure or temperature temperature change change or or to to actual actual increase increase of alkalies ions ions in in solution. solution. A few examples of the the various various types types are discussed. �36. A MAGNETO-TELLURIC STUDY STUDY OF OF THE THE NORTHEASTERN LAKE LAKE SUPERIOR AREA Hans Tammemogi Hans Department of Physics University of of Toronto, Toronto, Toronto~ Toronto, Ontario University from stations stations at at Port Port Arthur, Arthur,1'iarathon, r1arathon, Chapleau Results from Chapleau and Michipicoten Island Island will be be presented. presented. These include include polarization polarization and anisotropy studies, as as well as geomagnetic depth sounding and and anisotropy studies, well as magneto-telluric resistivity profiles. Preliminary results indicate indicate magneto--telluric resistivity Drofiles. anisotropy and and unusually unusually high high apparent apparent resi.stivities. resistivities. �37. GEOLOGIC EXAMINATION OF PIPELINE TRENCH EAST GOGEBIC GOGEBIC RANGE, RANGE, NICHIGAN!/ MICHIGAN:'!/ THROUGH THE EAST Virgil Trent U. S. Geological Survey, U. S. Geological Survey, Washington, Washington, D. D. C., C., 20242 20242 surficial deposits deposits exposed exposed along along 16 16 miles miles of of a. a Bedrock and surficial natural gas pipeline trench through the Wakefield-Marenisco area natural area prior to to backfilling. backfilling. Thirty-five samples samples were were collected collected were mapped prior for hand hand specimen and laboratory The location of the pipeline for laboratory study. study. The on standard topographic base maps was was facilitated on standard topographic base maps facilitated by pipeline survey maps supplied through the courtesy of Williams Bros. Bros. Co. Co. of Tulsa, Okla. Geologic data obtained from the trench across the southern southern half of the Marenisco 7-1/2 minute quadrangle were compared with data from previous geologic mapping. mapping. The 88- to to 10-foot--deep IO-foot-deep trench trench exposed shallow shallow ledges ledges in many places, places, and and numerous cuts were were made made exposed in many numerous cuts into bedrock. Near the center of the Wakefield NE quadrangle in in the SW SW 1/4 of sec. 28, W.,1 1toto2 2feet feetof of white white Quartzite quartzite was sec. 28, T. T. 47 44 W., 347 N., N., R. 3434 exposed for for 20 20 feet feet along the the trench and numerous scattered scattered boulders of thinly laminated siliceous dolomite were found 200 200 feet to the east. Sunday Quartzite and/or Bad Bad These rocks probably represent Sunday This trench trench exposure River Dolomite. Dolomite. This exposure extends extends the the known area underlain by these these units southward one mile from exposures mapped by W. C. Prinz (U.S.G.S.). (U.S.G.S.). It is the of these these W. C. It is the southernmost occurrence of middle Precambrian Precambrian rocks. rocks. W., the the South T. 47 47 N., N., R. R. 3434 44 W., South of of Wolf Wolf Mountain Mountain in in sec. sec. 35, 35 T. trench exposed a a wide belt of gneissic rock striking northeast appears to which appears to be quite similar to rocks rocks which crop out near the Recent center of the Marenisco quadrangle. quadrangle. Recent mapping in in sections sections 28, 28, 21, and and 22, 22, T. T. 47 47 N., N., R. R. 43 43 W., W., support support the the thesis thesis of of R. R. C. C. Allen Allen 21, and L. and L. P. P. Barrett Barrett that that these rocks rocks were derived from metasedimentarv metasedimen-tarv rock of their Palms Formation. Formation. Paragneiss and paraschist which crops out in the crops the center of sec. sec. 28, 28, T. T. 47 47 N., N., R. R. 43 43 W., W., can be traced outcrops to the where, over a traced in aa series series of outcrops the northeast, northeast, where, a distance of of 1/2 1/2 mile, mile, their transition distance ~ransition to metasedimentary rock of the the Palms Formation Formation is is evident. evident. Numerous blasted exposures of the Presque Presque Isle Isle Granite along along the that many of the the the trench trench in the the Marenisco Marenisco quadrangle quadrangle suggest that transitional lithologic changes in in this unit are a result of stress mineral formation formation and and mineral mineral alteration. alteration. Rather Rather abrupt transitions from granite granite porphyry, porphyry, pegmatitic pegmatitic granite, granite, or equigranular granite granite from ll a mottled, Tl con taminated-appearing to a mottled, "contaminated—appearing" rock containing wisps or lameliae micaceous minerals minerals and which grade from incipient lamellae of dark micaceous Work ~/Workdone doneinincooperation cooperation with with the the Geological Geological Survey Division the Michigan Department of of the of Conservation. Conservation. �38. to good foliation foliation are are common. common. No evidence was found along the trench for granite of more age, and geologic field field mapping to date for more than one age, indicates indicates this this granite granite intrudes intrudes the the Animikie Animikie strata strata with with considerabl.e considerable previously reported reported by by R. R. C. C. Allen Allen and and L. L. P. P. contact effects as previously Barrett. Barrett. Two wide wide fracture were exposed in cuts in granite along Two fracture zones zones were the trench east of the Marenisco mine the mine road. road. Previous mapping gave gave Fault traces are little extent of of fracturing. fracturing. are little indication of the extent zones from 66 to 24 24 inches inches wide within marked by mylonitized shear zones the shattered rock. the rock. The radioactivity was continuously monitored along the the pipeline model T-l T-l scintillator. scintillator. Higher than ordinary trench using a McPhar model readings readings were noted in sections of sheared granite, granite, and mass effect effect was along the the bottom bottom of of the the trench. trench. Thin sections of was quite apparent along pegmatitic granite contain sphene, sphene, zircon, zircon, allanite, allanite, and probable monazite as as common common accessory accessory minerals; biotite biotite enclosing enclosing many many of of shows radiation halos. halos. A chemical analysis of these minerals shows megascopic sphene sphene crystals from from pegmatitic pegmatitic granite granite in in the the Presque Presque Isle Granite gives gives 1500 1500 parts parts per million (ppm) (ppm) yttrium, yttrium, 1000 ppm Isle lanthanum, niobium, suggesting that the Presque Isle lanthanum, and and 300 300 ppm niobium, pegmatitic pegmatitic granite granite has has aa higher background radioactivity than other intrusive intrusive rocks in in the the area. area. Radioactive thorium oxide is commonly associated with the rare earth earth elements elements and and sphene. sphene. Glacial deposits deposits were were very well exposed along the 16 miles of Glacial pipeline trench. trench. Boulder till till made made up up the the bulk of of the material material but swamp accumulations and and stratified sand and gravel deposits swamp or bog accumulations were exposed exposed locally. locally. Clearly, profile section section such such as as Clearly, an extended profile that a that provided provided by aa pipeline pipeline trench would be be of great value in a study of the surficial surficial deposits. deposits. Because pipeline excavations are are temporary temporary and and progressive, progressive, Because geologists concerned with areas through which they pass pass should should be be forewarned construction. The forewarned about the planned construction. The State Geological Surveys are are probably probably in the best best position to to provide provide this Surveys in the this important information to interested interested workers. workers. �39. PRECAMBRIAN PRECAMBRIAN GRANITIC GRANITIC ROCKS ROCKS AND AND PRE.-KEEWATIN PRE-KEEWATIN (7) (?) PARA-GNEISSES OF THE NASHWAUK-BUHL SECTOR, SECTOR, NORTHERN MINNESOTA _METAMORPHIC OR IGNEOUS COMPLEX? COMPLEX? S. Viswanathan Viswanathan and and William C. S. C. Phinney Minnesota Geological Survey Survey Department of Geology and Geophysics Geophysics University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota, Minnesota, 55455 55455 Previous and petrology petrology of of the the granitic granitic Previous knowledge of the geology and complex north of the Nashwauk-Buhl sector of the Mesabi iron range, in limited to to the the work work of of I. I. S. S. Allison in Northern Northern Minnesota, Minnesota, has been limited (1925). Allison regarded this area as being part of an elongate (1925). Giants Giants Range Range batholith (Algoman) (Algoman) extending for for some some 100 miles from the vicinity of Grand Grand Rapids Rapids to a point 15 15 miles and the to a miles east of Ely and having an average width of of 88 miles. miles. He believed that that the the batholith batholith attained its maximum width, a north-south attained its width, about about 18 18 miles, miles, in a direction in the area of our our present present study. study. Detailed some 500 500 square square Detailed reconnaissance reconnaissance geological geological mapping mapping of of some miles north of the Nashwauk-Buhl sector of the range during the summer of 1968 has shown shown that the the width width of of the the batholith batholith in in this this is substantially SUbstantially less than previously believed, believed, and that it area is seldom exceeds 88 to to 10 10 miles. miles. Further, our work has revealed that that Further, the the granitic granitic rocks rocks exposed exposed in in this this area area are are mappable mappable as as four four major major zones; from south to north northeast-southwest trending conformable zones; these are: are: Zone (1) (1) a a medium-grained, massive biotite biotite granite granite (8 (8 Zone miles long and 44 miles wide), (2) a coarse-grained, coarse-grained, foliated, foliated, wide), Zone (2) granite (12 (12 miles miles long long and and 55 miles miles wide), wide), Zone Zone (3) (3) porphyritic biotite granite a medium-grained, a medium—grained, muscovite- and biotite-bearing gneissic granite which is is garnetiferous garnetiferous in places (15 (15 miles long and 4 miles wide) and and miles wide) is associated with several types of of inclusions inclusions of of Knife Knife Lake Lake is (Timjskamjarj) affinities, affinities, and and Zone Zone ('4) fine-grained, compactly compactly (Timiskamian) (4) a a fine-grained, foliated (15 miles miles long long and and 44 miles miles wide). wide), foliated biotite-muscovite granite (15 (4) and (3) (3) could be ascribed to processes of The evolution of zones (4) partial melting and replacement of pre-existing sedimentary country (Knife Lake Group) Group) during during metamorphism. metamorphism. rocks (Knife '4 the area is is characterized by thick sequences The western half of the (Ely) pillowed pillowed basalts basalts (massive (massive as as well well as as of presumed Keewatin (Ely) schistose)) ortho-amphibolites, striped schistose), striped (para) (para) epidote-amphibolites, epidote-amphibolites, minor intercalated meta—sediments, meta-sediments, gabbro dikes dikes and a a suite of granitic rocks rocks altogether altogether different different from from those those in the eastern eastern half half granitic in the of the area in that they contain hornblende and are granodioritic in composition. Within this complex) complex) it it is is possible possible to to map map aa meta— metasedimentary--migmatitic rock rock unit, unit, measuring measuring at least sedimentary--migmatitic least 10 10 square square miles, miles, is petrographically petrographically diverse. diverse. The unit is is composed composed of of quartzquartzthat is plagioclase-biotite--epidote-gneisses, plagioclase-biotite-epidote-gneisses,quartz-plagioclase--b±otite--quartz-plagioclase-biotitemuscovite-gneisses, quartz—plagioclase--hornblende-biotite-epidotequartz-plagioclase-hornblende-biotite-epidotegneisses, gneisses, quartz-plagioclase-biotite-staurolite (7) (?) rock, rock, quartzplagioclasebiotite-epidote--sillimanite (?) •-gneisses, plagioclasebiotite-epidote-sillimanite (?) -gneisses, layered hornblende—quartz-plagioclase hornblende-quarTz-plagioclase rocks, rocks, hornblendites, hornblendites, and granitic This unit unit is be of of pre-Keewatin is tentatively considered to to be mylonites. This (1) it is is stratigraphically stratigrahica1iy below age following reasons: reasons: (1) it below age for the following �40. the presumed Keewatjn volcanic and meta—volcanic sequence, Keewatin (Ely) (Ely) volcanic and meta-volcanic sequence, and (2) it it is is wholly wholly unlike unlike any any known component of the Knife (2) Knife Lake Lake Group. Group. The implications implications of this find could could provide a fresh fresh impetus to the the this find provide a Coutchiching controversy. controversy. In addition addition to to conventional conventional petrographic petrographic work, work, the the techniques techniques of of In oxygen isotope isotope geochemistry and and trace element analysis and major and trace element analysis by x-ray fluorescence and electron microprobe microprobe methods methods are fluorescence and are being used in the study of the rocks discussed herein. the herein. �410 SHALLOW SEISMIC STUDIES IN IN WESTERN LAKE LAKE SUPERIOR SUPERIOR Richard J. J. Wold v.70ld Department of of Geology Geology University of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin9 53201 University of 53201 A continuous seismic seismic reflection profiling profiling program program was was begun begun in in A Lake Superior in in 1965 1965 with with an an EG&G EGG Boomer, Lake Superior Boomer 9 continued continued in in 1966 with an an EGG Sparker. The regional regional study ended in 1967 with a EG&G Sparker. The a Bolt air—gun air-gun used as as the seismic energy used energy source. source. Altogether some 6000 6000 miles of profiles were obtained in in Lake Lake Superior. Superior. This paper will report report on on the of the the tip tip of of the the Keweenaw Keweenaw Peninsula. Peninsula. the profiles obtained west of Sufficient detail detail was was obtained in most areas Sufficient areas to correlate from one one profile profile to to the the next next so so that that an isochron map was was constructed of -the material above above "bedrock". the material "bedrock!!. The isochron map shows shows lines lines of of equal equal difference; large numbers indicate indicate thick accumulations reflection time difference; above ?bedrock? Iibedrock" and thin accumulations are indicated indicated by small isochron isochron numbers. Several buried valleys are outlined on Several on the the isochron isochron map. map. Two impressive valleys valleys parallel parallel the the north-shore north—shore from to Isle impressive from Duluth to Isle It is is quite quite likely likely that that the the valley valley closest closest to to shore shore is is due due Royale. It to differential erosion between between volcanics volcanics and and sediments. sediments. Other to valleys are observed near the center of the Lake Superior Syncline valleys to outline outline it. it. The data also indicate indicate the the apparent apparent and seem to the underlying underlying bedrock bedrock in in many many areas. areas. direction of dip of the �42. p42. ORGANIC STRUCTURES (IRON) FORMATION, FORMATION, STRUCTURES FROM THE NEGAUNEE (IRON) MARQUETTE RANGE, RANGE, MICHIGAN G. Wygant and Joseph J. J. Mancuso Thomas C. Department of Geology Bowling Green State State University, University, Bowling Bowling Green, Green, Ohio, Ohio, '43'O2 43402 In the the course of aa continuing In the mineralogy and continuing study of the stratigraphy of the the Negaunee (Iron) (Iron) Formation, Formation, curious curious structures structures were found which in in form form and and occurrence appear to be organic in origin. origin. These structures are present in in specimens specimens taken taken from from the the magnetite-chert-silicate unit of the Negaunee Formation Formation which which is is exposed in the Empire Pit, exposed Pit) Palmer, Palmer, Michigan. Michigan. The iron formation formation at at this this locality has has suffered suffered the the least least amount amount of metamorphism, structural is known in the the Marquette structural deformation, deformation, and and oxidation that that is Iron Range. Range. the structures are If the In origin, origin, it would add are indeed organlc organic in credibility to to the theories which postulate postulate an organic or biochemical biochemical control on on the control the deposition of iron iron formation. formation. �""': :,";{/ '':'-',,--:',' . -' "',~' ': ... " , ' . . " ç .3 1 ' . ' I .:! ii- ":' - I i. : " ...., 2mm 2 mm , — 2 •r ::: .:. :.. ' \ '& L 2 mm - ....... '. ~ it '" 2 - - - — I .1 , ,,' .. . ,', . ... ... I I ;'" '-' .. ~,,:,,: .":~: " ' ' �L4.LL 44. K-Ar K-Ar DATING DATING OF TWO DYKE-SWARMS FROM THE NORTH SHORE OF LAKE SUPERIOR D. H. C. C. Halls Halls D. York and H. Physics Geophysics Division3 Division) Department of Physics Toronto, Toronto, Toronto, Ontario Ontario University of Toronto, geographic'.ly . .Whole been carried carried out out on on two two geographi0~J Jy Whole rock K-Ar dating has been Four Superior. dlst1nct sets sets of of dyke.s dykes from distinct from the the north north shore shore of Lake Superior. Four MjChiP±C0t1 dykes from north of of MichipicoteJl dykes from aa swarm swarm in in the the Pukaskwa Pukaskwa region) region north The among Island, 1020 and and 1070 1070 m.y. m.y. The scattel' scatter among Island, give K-Ar ages between 1020 and it seems the results results lies lies within the range of experimental experimental error error anJ it seems the 1050 JT1.V. ago. that all the the dykes dykes in this this group were emplaced emplaced about about 1050 m.~'· ago. each gwarrn were Two dykes dykes from the Sibley Peninsula-Grande Portage Portage swarm were each and analysed in duplicate and give mean ages of approximately approximately. 1150 lISa and analysed of dvkes m.y. It therefore) that that this this set set of dvkes Is 1S It appears, appears, therefore, 1210 m.y. Whether more region. measurably measurably older older than those from the Pukaskwa region. Whether more Sibley_Grande than than one one age age of emplacement is represented in the Sibley-Grande general The results Portage dykes remains to to be be determined. determined. The results in in general Portage dykes their radiogenic radi0g'-° argon indicate that that the the diabase diabase dykes dykes have have retained retained their argon indicate material for K-Ar extremely extremely well well and and are are evidently evidently satisfactory material for K-Ar dating in this age range. dating range. �L5 450 STRATICRAPHICAL, AND SEDIMENTOLOGICAL STRATIGRAPHICAL SEDIMENTOLOGICAL COMPARISON OF EARLY PROTEROZOIC ROCKS ROCKS OF S.E. S.E. WYOMING AND THE GREAT LAKES LAKES REGION Grant N. t1. Young Department of Geology University of Western Ontario, Ontario, London, London~ Ontario The The Huronian Huronjan rocks rooks of the the north shore of Lake Huron were 2.5 and and 2.1 2.1 b.y. b.y. ago ago (van (van Schmus, Schmus, deposited between approximately 2.5 1965) and and were were folded 1965) folded in an orogeny (Penokean?) (Penokean?) which was was initiated more than 2.1 2.1 b.y. b.y. ago ago (Church, (Church, 1966). 1966). The Animikie "Series" "Series!! of of the the Lake laid down between 2.0 2.0 and 2.5 2.5 b.y. b.y. ago Lake Superior region was was laid (Aldrich et et al. al.) 1965). A recently suggested stratigraphic correlation of the Huronian succession with the of the the upper part part of the lower part part of of the the Animikie Animikie (Young, lower (Young~ 1966) 1966) results results in a a combined sequence of of sedimentary formations which closely resembles resembles that sequence sedimentary formations that of Early Proterozoic rocks of the the Medicine Medicine Bow Bow Mountains Mountains of of S.E. S.E. Wyoming. Wyoming. Early Proterozoje The Wyoming rocks were deposited between 1.65 and 2'41 2.41 b.y. b.y. ago (Allan Hills et al., The stratigraphic succession (Allan al., 1967). 1967). The succession in in the the Medicine (1926) and Medicine Eow Bow ~10untains Mountains area area was was described described by Blackwelder (1926) been divided divided into into two two parts parts by by Houston Houston (1967). (1967). The has recently been lower is aa highly varied succession lower part, part, the the Deep Deep Lake Lake Formation) Formation, is highly varied chloritic schists, schists, metaconglomerates, metaconglomerates, quartzite and siliceous of chioritic marble. Quartz in the the basal basal part part of of the the Quartz pebble pebble conglomerates in succession are are strongly reminiscent of of the the basal basal uraniferous uraniferous conglomerates Formation is is conglomerates of the Ontario Huronian. The The Deep Lake Formation succeeded succeeded by by the the more more extensive extensive Libby Libby Group Group which which oversteps oversteps the the commonly lies lies directly directly on on basement basement rocks. rocks. older units and commonly The oldest unit of the Libby Group contains polymictic interpreted by by Blackwelder Blackwelder as as tillites. tillites. conglomerates which were interpreted Associated finely finely laminated argillites contain scattered scattered (ice (ice rafted?) rafted?) clasts. The overlying Heart Formation is a a highly varied succession succession The mudstones and and sandstones sandstones with with ball and pillow of meta—siltstones., meta-siltstones) mudstones pillOW structures, cross beds. beds. These two formations formations structures, ripple marks and cross Formation of Ontario (a (a correspond very closely with the Gowganda Formation twofold division of the the Gowganda Gowganda is is possible possible in in many many areas). areas). Above the Heart Formation of of Wyoming Wyoming occurs occurs the the Medicine Medicine Peak Peak Quartzite, Quartzite. This unit This unit closely resembles resembles the Lorrain Formation of Ontario in that upwards, both contain jasper jasper both become progressively mature upwards, pebbles, kyanite (probably a metamorphic derivative from kaolin) pebbles, (probably a kaolin) and the chrome mica fuchsite. the fuchsite. The overlying overlying Lookout Lookout Schist Schist and. and Sugarloaf Quartzite of the the Wyoming area show show close similarity similarity to the Gordon Lake respectively of of Ontario. Ontario. Thicknesses Lake and and Bar River Formations respectively of the corresponding units units are are closely closely comparable comparable in in the the two two areas. areas. The regions occur in similar The Early Proterozoic rocks of both regions tectonic settings settings (southern edge of of the the Superior craton) craton) and and display display tectonic (southern edge remarkably similar similar sedimentary sedimentary structures structures in in corresponding corresponding formations. formations. The in such such widely separated areas The presence presence of of tillites tillites in widely separated areas as as Wyoming Wyoming and (Chibougamau) indicates indicates an and N. N. Quebec Quebec (Chibougamau) an extensive extensive North North American American glaciation in in Early Early Proterozoic Proterozoic times times and and lends lends support to the the idea idea glaciation support to that contemporaneous. that these deposits are approximately contemporaneous. �46. References Aldrich., L.L. T. T., Davis, Davjs G. Aldrich) G. L. and H. L., L., 1965. 1965. Ages of minerals and James, James, H. from igneous rocks near Iron Mountain, Michigan. Michigan. from metamorphic and igneous J. J. Petrol.5 Petrol., V. v. 6, p. 445. p. j I... 5. Hills)F., F. Gast, Gast)P.P.W., W.,Houston, Houston R. R.S.S.and and Swainbank J J.J. G.., G., Allan Hi11s Swainbank., 9 1968. 1968. Precambrian Precambrian geochronology geochronology of of the the Medicine Medicine Bow Bow Mountains, Mountains Bull. Bull. Geol. Geo1. Soc. Soc. Amer., Amer., v. p. 1757. 1757. V. 79, p. j Blackwelder, E., Blackwelder, E. 1926. 1926. Precambrian Precambrian geology of the the Medicine Medicine Bow Mountains. Bull. Geol. Geol. Soc. Soc. Amer., v. v. 37, 37, p. p. 615. 615. Bull. j Church W. Church, W. R. R.~ 1966. The Penokean orogeny orogeny in in Ontario. Ontario. The status of the Penokean Prog. Ninth Conf. Conf. on Great Great Lakes Lakes Research, Research, Chicago, Chicago p. p. 25. 25. Prog. j Houston, R. R. S., S., 1967. 1967. Geologic map of the the Medicine Bow Bow Mountains, Mountains~ Albany and and Carbon Carbon countjes counties,Jyorning. Wyoming. Plate 1, 1, Mem. Mem. 1 1 (in (in press), Geo1. Surv., Surv., Wyoming. Wyominp. press), Geol. van Schmus, Schmus, R., R., 1965. 1965. The geochronology of the the Blind Blind River-Bruce River-Bruce Mines area., Ontario, Canada. area, Ontario, Canada. Jour. Ge01., v. v. 73, 73 p. p. 755. 755. Jour. Geol. j Young) G. Young, G. M., M., 1966. 1966. Huronian stratigraphy of of the the McGregor McGregor Bay Bay area, area) Ontario; the Lake Lake Superior Ontario; relevance relevance to to the the paleogeography of the region. Can. p. 203. 203. Can. J. J. Earth Earth Sci., Sd., v. v. 3, 3 p. �L7 47, EXPLORATION OF THE ROUND LAKE LAKE ANOMALY, ANOMALY, COUNTY, WISCONSIN SAWYER COUNTY, Wayne R. R. Zwickey The The New Jersey Zinc Company Plattevj11e Wisconsin, Platteville~ Wisconsin~ 53818 53818 The Round Lake magnetic anomaly, located located on on the the east east side side of The Round Round Lake Lake in in T41N) T'JN R7W, Round R7W, Sawyer Sawyer County, County, Wisconsin, Wisconsin, was was discovered by In 1960 a Wisconsin Geological Geological Survey Survey dip dip needle needle survey survey in in 1914. 1914. In a and The New New Jersey Jersey Zinc Zinc Company Company investigated investigated this this intense intense and 1961; l961 The magnetic anomaly anomaly by by detailed detailed magnetic magnetic and and gravity gravity methods, methods, negative magnetic as well well as diamond drilling. as drilling. The this investigation investigation will will The results of this be discussed. -= � https://digitalcollections.lakeheadu.ca/files/original/614a122132f4385220a1c4d955129e39.pdf 06be3b139084257ee0756ebd1180b55a PDF Text Text �U h I CENTRAL WISCONSIN VOLCANIC BELT Leonard W. Weis University of Wisconsin-Green Bay Fox Valley Campus By: Gene L. LaBerge Wisconsin State University-Oshkosh With The Collaboration Of: Carl E. Dutton U. S. Geological Survey Madison, Wisconsin Guidebook for Fifteenth Annual Institute on Lake Superior Geology, May, 1969 �U I TO: Dr. Carl E. Dutton, who pointed out the significant exposures from his first hand knowledge of the area. He gave freely of his time and knowledge--both of particular areas and from his 40 years experience in the Precambrian of the Laira Superior region. His generous help, encourage- ment, and thought-provoking approach made preparation of this Guidebook a stimulating learning experience. L.W,W. G.L.L. �I ACKNOWLEDGMENTS The success of any field trip depends in large part upon the cooperation and We wish to express our thanks to all assistance of many individuals and organizations. those who have played a part in this trip. Mr. George Hanson, Director of the Wisconsin Geological and Natural History Survey furnished the Geologic Map of Wisconsin. Financial support for publishing the guidebook was furnished by the Geology Departments of WSU-Oshkosh, UW-Center System, and UW-Green Bay. given both in drafting and handling of the trip. drafting maps are due Man Student help has been generously Special thanks for her work in Poythress, of WSU-Oshkosh. The manuscript was typed by Mrs. Pamela Spaulding. In addition, we wish to thank the following property owners for permission to visit their properties or use their facilities: Employers Insurance of Wausau Mr. & Mrs. Robert Zielsdorf, Wausau Mr. Ray Slocum, Wausau Mr. Alfred Reimes, Town of Easton Mr. Herman Marquardt, Town of Easton �I U GEOLOGIC MAP OF WISCONSIN I AFTER BEAN, 1949 I SCALE OF MILES Milwaukee Formation (cbofly doiomt,c shIe( Niagara Formation (dolomde) Maquoketa Formation (dokomti shale) Platteville-Galena Group (doiomite odh some f,mestoee) St. Peter Formation (soodst000) Prairie du Chien Group ;LI (dniomte) Upper Cambrian Group (chefiy sandstones) Lake Superior Group (sandst0005) Quartzite, Slate and Iron Formation Gabbro and Basalt Granite and Undifferentiated Igneous and Metamorphic Rocks Border of Wisconsin (Cary) Drift Border of Older Drift Umv*ity of Wisconsin Wisconsin Geological and Natural History Survey George F. Hanson, Director and State Geologist ELEVATION ABOVE SEA LEVEL IN FEET 0 10 20 30 40 HORIZONTAL SCALE IN MILES �U SHORT GEOLOGIC HISTORY OF WISCONSIN ii The bedrock of Wisconsin is separated into two major divisions: (1) older, predominantly crystalline rocks of the Precambrian Era, which were extensively deformed after their deposition by movements of the Earth's crust; and (2) younger flat-lying sedimentary rocks of the Paleozoic. The Precambrian Era lasted from the time the earth cooled, over 4,000 million years ago, until the Paleozoic Era which began about 500 million years ago. During this vast period of 3,500 million years sediments, some of which were rich in iron and which now form our iron ores, were deposited in ancient oceans, volcanoes spewed forth ash and lava, mountains were built and destroyed, and the rocks of the upper crust were invaded by molten rocks of deep-seated origin. Only a fragmentary record of these events remains but, as tree stumps attest the former presence of forests, the rocky roots tell the geologist of the former presence of mountains. At the close of the Precambrian Era most of Wisconsin had been eroded to a rather flat plain upon which stood hills of more resistant rocks as those now exposed in the Bamboo bluffs. There were still outpourings of basaltic lava in the north and a trough formed in the vicinity of Lake Superior in which great thicknesses of sandstone were deposited. The Paleozoic Era began with the Cambrian Period, the rocks of which indicate that Wisconsin was twice submerged beneath the sea. Rivers draining the land carried sediments which were deposited in the sea to form sandstones and shales. Animals and plants living in the sea deposited calcium carbonate and built reefs to form rocks which are now dolomite—a magnesiumrich limestone. These same processes continued into the Ordovician Period during which, as indicated by the rocks, Wisconsin was submerged three more times. Deposits built up in the sea when the land was submerged were partially or completely eroded at times when they were subsequently elevated above sea level. During the close of the Ordoician Period, and in the succeeding Silurian and Devonian periods, Wisconsin is believed to have remained submerged. There are no rocks outcropping in Wisconsin that are younger than Devonian. Absence of this part of the rock record makes interpretation of post-Devonian geologic history in Wisconsin a matter of conjecture. Available evidence from neighboring areas, where younger rocks are present, indicates that towards the close of the Paleozoic Era, perhaps some 250 million years ago, a period of gentle uplift began which has continued to the present. During this time the land surface was carved by rain, wind and running water. The final scene took place during the last million years when glaciers invaded Wisconsin from the north and sculptured the land surface. They smoothed the hill tops, filled the valleys and left a deposit of glacial debris over all except the southwest quarter of the State where we may now still see the land as it might have looked a million years ago. Prepared by U. of W. Geological and Natural History Survey, 1963. ..-.1 �2. CENTRAL WISCONSIN VOLCANIC BELT I This field trip represents a progress report in the early stages of the investigation of the Precambrian geology in central Wisconsin. Although we cannot provide many of the answers, we have identified a number of problems in the area. Some of these problems are presented in the following Guidebook with the hope that at least a few answers will be forthcoming. Introduction Precambrian volcanic and sedimentary rocks cut by intrusions of a wider range in composition and separated by broad expanses of gneisses and granites were mapped at the beginning of this century in central Wisconsin. Recent inves- tigation suggests that these volcanic and sedimentary rocks are similar in type, arrangement and separation to the greenstone belts which make up a substantial part of the Early Precambrian portions of the Precambrian Shield in many continents. They are lithologically similar, and may be roughly comparable to the Uobile Beltstt of most post-Precambrian geosynclines. Both appear to have formed in areas of prolonged tectonic activity. The rocks which will be visited are presumably considerably younger than the greenstone belts of Canada, yet their similarity to these belts cause us to believe that central Wisconsin may be part of a heretofore unrecognized greenstone belt. �3. Lithology Within a greenstone belt, the volcanic rocks range in composition from basalt to rhyolite, and typically form sequences with pillowed basalts at the bottom and grade uqward through andesites to rhyolites at the top. This general sequence may be incomplete, repeated, or reversed in a particular area. Some greenstone belts are composed predominantly of mafic volcanics; some have greater amounts of felsic rocks. The central Wisconsin area appears to have a greater than normal anount of rhyolitic volcanics, but their relationship to the basalts is not clear. The sediments of a greenstone belt consist largely of graywacke and slates with lesser amounts of chemical sediments (mainly cherty iron—formations). These sedimentary sequences may overlie, underlie, be sandwiched between the volcanic sequences, and some sediments (particularly iron—formations) occur within the volcanic sequences. Intrusions into the volcanic—sedimentary rocks range in composition from peridotite to granite, and in some areas (as at Wausau) alkaline complexes, including nepheline syenites, are present. Intrusive igneous activity appears to have occurred over a very long period; some intrusions may represent the "feederstt and dikes associated with the volcanism which characterizes the belts. Later batholithic intrusions of more granitic rocks seem to bring the tectonic cycle to a close. Relative Determining the relative age of rocks within a greenstone belt requires unravelling the complex structure so characteristic of these regions. Because there are no fossils available to determine the relative age, it is necessary to resort to various "sequential" features (such as pillow structures and graded bedding) and structural techniques to determine stratigraphic tops (since many beds dip nearly �4. vertically, the, erosion surface is essentially a cross section), The relationship of structure (tectonic activity) and igneous and metamorphic activity which have affected certain parts of the sequence may be interpreted differently by different workers due to shortage 3f outcrops at critical locations. of stratigraphic sequence often cannot be found. Thus, a unique solution to the problem As new evidence is found and as new concepts and tools are available, the relative age of certain units may be changed—— hopefully toward a more accurate sequence. On a broader scale, the relative age of one greenstone belt as compared to others in a given area is even more difficult to ascertain because the belts are almost invariably separated from one another by batholithic expanses of gneisses and granitic rocks, Individual bodies of granite are not of sufficiently large size to show age relationships between adjacent belts. Furthermore, radiometric age dating on the granites yields the date of intrusion (or later metamorphism) and gives only a minimum age for the intruded rocks, As a result, the ages of greenstone belts in a particular shield area can be established in only a very general way. Absolute Absolute (radiometric) age determinations show that almost all the recognized greenstone belts in the Canadian Shield are more than about 2,500 million years old. In fact, they are generally referred to as Archeangreenstcne belts because of their age. The absolute age determinations available for a few rhyolite and granite localities in Marathon County indicate that rocks were formed about 1,500 million years ago. Therefore, this greenstone belt may be nearly 1,000 million years vounaer than most other greenstone belts, If this proves to be true, then an understanding of the rocks in central Wisconsin would contribute significantly to our knowledge of middle �I 5, and late Precambrian history of the Canadian Shield, Although we do not yet have anything like a clear—cut picture of the geological history of the central Wisconsin area, we are proposing the "greenstone belt" concept as a working hypothesis for your evaluation. Thus, central Wisconsin may be an important area which will add to the overall story of the development of the North American continent, particularly during middle Precambriir tine. Economic Significance 'n the past five to ten years, there has been developing an increasing awareness of the imprtance of greenstone belts as targets for prospecting activities. outgrowth of 'the tormulation of a new concept of ore genesis. This i an The concept of strata— bccnd sulfide and volcanic exhalative deposits has given great impetus to prospecting in volcanic—sdiiientary sequences which are represented by greenstone belts. In sirplest terms, this concept relates the formation of many disseminated and massive sulfide ores to ocanic activity rather than to later hydrothermal activity. Many of the large suIfide deposits (both massive and disseminated) in the Canadian Shield (for exmp1e, Manito.wadge, Timmins, Noranda, Mattagami, Timagami, and others) as well as many pos -Precambrian sulfide deposits have recently been interpreted as volcanic exhaative in 'rigin. In fact, there are relatively few greenstone belts in the Canadian Shield that do not contain important sulfide ore deposits. Therefore, the importance of recogaizlt.g central Wisconsin as possibly a greenstone belt seems self evident, Rot general features and economic importanc' of greenstone belts, the intere;ted rder is referred to: "Symposium on Strata—bound Sulfides and their Formative Enironment", Canadian Mining and Metallurgical Bulletin, Sept., 1965, and otl;er articles listed in the references. �6. Previous Work A comprehensive account of the regional geology in the area, "Geology of North Central Wisconsin", by Samuel Weidman was published in 1907 as Bulletin XVI of the Wisconsin Geological and Natural History Survey. Considering that the field work was done about the turn of the century, it is remarkably thorough in its areal coverage. The publication is very good insofar as outcrop location and description is concerned, but Weidman does not attempt to interpret the geologic setting for the area as a whole. While certain revisions may be possible in the map and stratigraphic sequence presented by Weidman, the chances would presumably be relatively minor and involve both additional data and use of geologic concepts not developed at the time the Bulletin was published. The geology of the Wisconsin Rapids—Wausau area was examined in 1917 to 1921 as part of a land classification survey by the Wisconsin Geological Survey. Township maps showing location and classification of outcrops and a series of related geologic reports are in files in Madison. Selected aspects of the geology in the central Wisconsin area were discussed by Emmons (l953b), who was leader of the 17th Annual Tn—State Geological Field Conference in 1953. However, the theme for his work is very different from ours, and we will not be stopping at any of the exposures visited on the 1953 trip. Particular aspects of the geology in the Wausau area have also been covered in a number of theses prepared at the University of Wisconsin. Recent work by the U. S. Geological Survey and the Wisconsin Geological Survey has resulted in a series of four open file sheets on the Precambrian geology of northern Wisconsin compiled by Carl E. Dutton and Reta E. Bradley. The interesting variety of formations seen during field checking have led to the present field trip. The purposes of this field trip are to examine the different rock types in the area and attempt to determine how well they fit a concept which may tie together �7. all of the rocks into a logical relationship. So far as we know, this is the first attempt to interpret the tectonic setting for the central Wisconsin area. Keep in mind, 1 I however, that this is a progress report in the early stages of an investigation, and the greenstone belt concept should be considered as a working hypothesis. Therefore, we will examine some of the rock types in an attempt to determine the tectonic setting of the area. Because we are trying to show features which suggest that central Wisconsin is part (or all) of a greenstone belt, a brief statement pointing out the relevance of each stop will be given. Stop 1 illustrates features of felsic intrusions into greenstone belts. Both syenite and granite are intrusive into the greenstane; however, we do not know the relative age of these intrusions to one another �STOP 1. Assembly Point at Employers Insurance. This exposure Is fairly represertative of the syenite in :he Wausau area. Most of the syenite at this stop is acLually a quartz syenite A few miles northwest are exposures of nepheline syenite and çuarries in gray and in red syenite. Mineralogically, the syenite contains potassium feldspar, plagioclase, sodic hornblende, biotite, sodic pyroxene, minor apatIte, zircon, magnetite, carbonate, with or without quartz. In some samples, the feldspar is highly perthitic, consisting of almost any mixture of sodic plagioclase and potassium feldspar. boundaries between feldspars are common in some samples. appreciable percentage of samples from certain localities. Highly sutured Quartz makes up an The mafic minerals, especially the hornblende, are typically very poikilitic (i.e., include numerous other minerals——especially apatite). Some of the hornblende has been altered to fine—grained biotite, magnetite, and carbonate At a number of places immediately west of Wausau, the syenite contains masses of quartzite. In most cases, there appears to have been a reaction between the syenite and quartzite to produce a halo of magnetite—bearing "granite" around the inclusions or pendants of quartzite. The typical syenite Is weakly to non—magnetic, and is composed mainly of highly perthitic alkali feldspar and probably sodic hornblende. or may not be present. Quartz may As one approaches a quartzite body within the syenite, the quartz content increases; the hornblende is replaced by biotite, accompanied by a notable increase in the magnetite content. A small scale example (not containing all the features described above) may be seen in the roadcut on U.S. 51 about 500'(?) east of the parking lot behind Employers Insurance. �9. Crochiere farm, Sec. 29 T 29N R 6 E Artus Creek Greenstone. (Pillow Lavas) (1968 Tn—State Stop 3..) One of the most abundant rocks in many greenstone belts is pillowed basaltic and andesitic lavas. In fact, as it is used in the Lake Superior region, the term denotes a somewhat metamorphosed intermediate to basic volcanic rock. The greenstone color derives from the abundance of chlorite, epidote, and actinolite in most examples. greenish You will notice on the colored geologic map that the major area of mafic in this region lies west of Wausau. Although there are exposures of volcanics basic volcanics east of the Wisconsin River (northeast of Wausau), they are preI sumably of more limited extent. At this stop, there are numerous exposures of pillowed greenstone with pillows U exposed in the outcrops farther south from the road. better of the pillows at this stop. Figure 2 shows an example Due to the irregular fracture pattern on the surface of the outcrops, the pillows are best seen on the southwest-facing ledges formed by joint surfaces. The pillows range in size from less than one foot to at least three diameter. feet in Pillow shape indicates top to the southeast, and in some places, it appears that the dip may also be to the southeast. not pillowed. Note that all exposures (all flows?) are Pillowed greenstones are typically interlayered with non-pillowed greenstone, and at least some of the non-pillowed material is a basaltic tuff as illustrated at the next stop (Figure 3). The rock consists of sodic plagioclase, amphibole (actinolite?), chlorite, and minor quartz; a typical greenstone mineralogy. epidote, Epidote and amphibole are the major minerals in some samples, and carbonate is common in some. At the time of formation, the selvages around the pillows were probably a hydrous basaltic glass (palagonite); however, the selvages are now dominantly quartz and epidote. The rock probably owes its present mineralogy to the metamorphism it has undergone. Greenstone belts are commonly intruded and separated by granitic rocks. greenstone is intruded by granite at Hwy. 29 and Co. Rd. 0. This �10. Figure 2. Pillow structures in greenstone at Artus Creek. Top of flow is toward the upper right hand side of the photo. Figure 3. Tuffaceous phase of Artus Creek greenstone. is approximately lOOx. Magnification �ii STOP . Artus Creek Greenstone. (Massive Phase) THIS IS AN EXTREMELY DANGEROUS PLACE BECAUSE OF POOR FOOTING KEEP OFF THE OTJTCROP! AND IS HAZARDOUS FOR THE PEOPLE BELOW YOU. A relatively new roadcut has exposed massive greenstone in which it is nearly impossible to determine the attitude. Several parallel slabby zones on the north side of the road strike N6O°E and dip 3O°SE and may represent original layering of the unit. Inasmuch as definite shear zones are present, the slabby zones may also be formed by shearing. Poorly formed, and poorly preserved, pillow structures may be seen at several places on the exposure. Some flows——or parts of flows——do not develop pillow structures; they simply crystallize as massive greenstone. cut on the north side of the road are the "best pillows. At the western end of the Other pillows elongated N6O°E can be seen on the top of the eastern end of the cut on the north side of the road, but they are not well enough preserved to determine stratigraphic tops. In the central, massive, part of the exposure is a tuffaceous phase of the greenstone. A number of thin sections of this material reveal relatively well preserved shard structures (Figure i). To see the shards, break the rock to get a fresh surface, wet the surface, and examine it with your hand lens (your TONGUE is an indispensable geologic field tool). Massive greenstone may also be flow material which does not contain shards. Petrographically, the rock consists of chlorite, carbonate, relict plagioclase laths (near albite in composition), amphibole (actinolite?) and extremely fine grained Some sections show extensively epidote and zoisite. Quartz is not especially uncommon. uralitized pyroxene. (Pyroxene altered to fine grained amphiboles.) More or less circular patches of chlorite or carbonate may represent vesicle filling. Some fractures are filled almost entirely with epidote—zoisite. In most slides, the intergranular texture is well preserved, even though the mineralogy has been. �12. modified considerably. In general, this seems to have been a rather coarse grained basalt alternating with tuUaceous material. The occurrence of fragmental material interbedded with pillowed greenstone is not uncommon, but it poses problems as to the environment of eruption and deposition. Some of the fragmental layers have a texture similar to graywacke and a composition nearly the same as the pillowed layers; other layers contain sharply angular fragments which may represent basaltic tuff. Eecause pillow lavas are generally taken to indicate subaqueous eruptions, or at least flQwing of lava into a body of water, the following questions may now be raised: 1) Do the fragmental layers represent material from subaerial eruptions ("lava fountains") which was carried by wind and/or water to the site of deposition? 2) To what extent are the fragmental layers derived from the erosion of adjacent volcanic islands? 3) May the fragmental material (and the pillow lavas) be formed during subaqueous eruptions? �l3 STOP 3. Marshall Hill Conglomerate. This exposure is an example of what seems to be the youngest Precambrian rock in the Wausau area, and although it illustrates no principle of greenstone belts, it is important in interpreting the geologic history of the area. At different places where it crops out, the formation is variously a conglomerate and/or a "quartzite". The conglomerate at this locality contains pebbles and boulders up to eight inches in diameter of rhyolite, greenstone (basalt), trachyte, chert (or jasper), and quartite. It is of interest that granite pebbles are conspicuously absent, even though there are abundant glacial boulders less than half a mile to the north, and outcrops of granite within a mile. Until recently, the only readily accessible exposures of Marshall Hill conglomerate occurred two miles east northeast of here. The roadcuts here expose a much fresher part of the Marshall Hill conglomerate. In thin sections, the rock shows abundant sericite, both within the pebbles and in the matrix. Fine hematite is abundant and disseminated. In the samples examined, most of the fragments are rounded and range in size up to about one-half an inch in diameter. Angular to rounded quartz grains occur in the matrix, and occasional pebbles of "dirty quartzite" were found. Both texture and composition suggest that a vast majority of the fragments are altered volcanics (probably rhyolite) . material are decidedly subordinate. Fragments of definitely non-volcanic The abundance of sericite in the matrix suggests that it too may be derived from volcanic material. A large volcanic component in the conglomerate is not surprising considering the close spatial relationship of the conglomerate to rhyolite. Because the contacts are not exposed, the relationship of the conglomerate to the underlying rocks is uncertain at this stop. However, on the west side of the Wisconsin River at the Brokaw Dam (Figure 4), a similar conglomerate and "quartzite" �Partly Looking Figure 4. G.L.L. the west Sketch of the on Rhyolife side of the relationship ONSIN Banded covered Partly non-banded west I River rhyolite Wisconsin between RI S. II at and Brokaw. conglomerate 'I Approximately 50' Scale I — N. — r —I I— �— 1 S. — Figure 5. G.L.L. 2 l'Approximately Scale • 2 I mile 2 —I Lookrng west — 2 Stop8 U — typse en the east side of the I Stop 7 I River. relationships of Wisconsin DiagrammatiC sketch showing the structurol rhyolite Mainly tuffaceous and conglomeratic Stop 9 I the rock Silt stone Tuffaceous N. — —.—.— ..I — I I — �16. unconformably banding. overlie fresh, unmetamorphosed, rhyolite with The elastic rocks are vei- 1 flow(?) therefore, younger than the rhyolite at that locality. On the east side of the Wiscoasin River (Figure. 5), the 'tructtral relationships indicate that the conglomerate Is not only youT7,er than the rholite, but a siltstone—tuff sequence (Stop .) ocur between them. This sequence is further confirmed by exposures alcrg the railroad track between Wausau and Brokaw (on the west side of the hill at Stop this trip. ; however, time wiLi, not permit visit'ng these exposures on Thus, the conglomerate may be the youngest Precambiari rok in this area. �I STOP 4, Tuffite. Tnis exposure Lilustrates ore cf the features assoc4ated with acid volcanisi; tIat is, the Irixing of vo1canc and fine dental me-.terial in water laid d€posits. The rock is primarily a tuffite (tuffaceous s.ltstone) or a bedded tuff. We will see at least one lapilli tuff layer as we proce-d down che hill. Along the railroad track at the west side of the hill are ood expures of tuff and agglomerate stratigraphically underlying, and trachyte and conglonerate ovenlyirp the tuffite. Lapilli tuff layers are interbedded with the fine grained material, much of which is also tuffaceous. In thin section, these rocks consist of virious size fragments of quartz and feldspar (plagioclase is the dominant recognizable variety) in a f1n. grained matrix of quartz, altered feldspar(?), sericite, chlorite, and carbonate. Many fragments consist of a fine mosaic of minerals which are virtudily indistinguishable from the matrix material. Most or all of the fragments are ery angular and at least some are almost certainly of volcanic origin. The rock, therefore, is herein classified as a tuffite. Others may classify it as a volcanic—rich graywacke, or argillite, or a bedded tuff with appreciable detrital material. The beds generally strke nearly N—S and dip from 30—40°W, although t'iere are local variations in the attitud,. Therefore, the roadcut is almost parallel to the strike so that we are seeing a rather restricted stratigraphic suence. Slump structures (folds) ranging in sie from a fraction of at, incFi t' nearly a foot high are at several horizons (Figure 6. t least one of the massive unts appears to be a slumped bed, with randomly oriei ed blocKs within a massive layer. It is possible that these slump structures were caused by earthquakes accompanying e volcanic activity during the deposition of the layers. �I 18. I I Figure 6. structures in the tuffite at Stop . relatively straight and evenly bedded; Slump are Most layers however, slumped layers are not uncommon. Figure T. "Conglomeratic rhyolite" representative of much of the rhyolite at Highland Grove (Stop 8) and in the Wausau area in general. �I I 19 Near the north end of the exposure (at ti top of the hill) is a quartz feldspar porphyry dike with an exposure width of about 40 feet. not well exposed, so we do not know the true width of the dike. 1h ontacts are �I I PRELIMINARY GEOLOGIC MAP OF THE AREA EAST OF WAUSAU, WISCONSiN Adapted from Thomas I I I2 I HYBRID I GRANITE A. Henricksen & Robert METAGABBRO I4I METADIABASE [51 GREENSTONE 161 FELSIC METAVOLCANICLASTIC 1969 Stevenson GRANITE 131 L.W.W. U. 0 I I I Miles 2 —I 1 �I Dells of the Eau Claire River. Stop 5, At the Dells of the Eau Claire River we have our felsic volcaniclastic rocks. trs ex:ensL:e exposure of The abundant vertical and horizontal surfaces show the principal joint systems, which are approximately normal to each other. joints is generally parallel to the banding. of N35-40E, One set of The banding is vertical with a strike A few mafic bands are present. Several textures are seen in the volcaniclastic rocks. Some bands are Others have granulare with grains mostly in the coarse silt to very fine sand range. large grains set in a fine grained groundmass and, according to Weidman, are all por— phyries. In some bands schistosity occurs with the long dimensions of the micas and amphiboles aligned. Minor con- The abundant minerals are quartz, feldspar, mica and amphibole. stituents include carbonates and opaque minerals. covite. Biotite is more abundant than mus- On stained slabs potassium feldspar is far more abundant than plagioclase. From preliminary study, we think it possible that the banding is parallel to original layering and that some of these layers are sedimentary in origin. gestive for a sedimentary origin is the granular texture of some bands. amphiboles are aligned only in some of the bands. Most sug- The micas and Volcanic origin for many bands, especially those in which the large grains are clearly phenocrysts, is recognized. However, comparison of the texture of granular bands here with some bands at other locations, particularly Stop 6, cause us to continue the search for conclusive evidence of sedimentary origin. Orientations at Stops 5, 6 and 7 show a slight curving for this volcaniclastic belt, with the trend more northerly to the east. The possibility that Stops 5 and 6 are at similar stratigraphic positions can be seen on Figure 8, p. 23. �U 21. STOP 6 Felsic volcaniclastic rocks and greenstones along the Eau Claire River in section 27, T 29 N, R 9 E The rocks e. include both felsic volcaniclastic rocks and greenstones. In the vicinity of the bridge the rocks exposed along the banks are generally volcaniclastic; a quarter of 1 mile to the southwest the rocks exposed along the river are greenstones, with a I patches of felsic volcaniclastic rocks occurring beside greenstones and on the side from away in I the river. On the west of the river felsic volcaniclastic rocks occur a belt roughly a half mile wide. The relationship to the granitic rocks to the northwest is described following the description of this stop. The felsic volcaniclastic rocks vary in banding from very thin bands about ½ mm, thick to bands about 2 cm. thick, Th greenstones They are usually very fine to fine grained. do not show clear banding or layering. The strike of the volcanic- -i,tic units varies from N35E to N5OE, while dip is vertical to very steep towards iie west. 1 I bu South of the stop a few partial pillows were seen in the greenstones, they are not well enough developed for determining orientation. Shearing with an orientation parallel to the layering of the volcaniclastic units occurs many places. It shows best where there are micaceous minerals. The felsic volcaniclastic rocks consist primarily of fine silt size grains of feldspar, quartz, biotite, hornblende, carbonates and opaques. feldspar and plagioclase occur. Both potassium They are usually clear and frequently untwinned, re- quiring staining to tell them apart and from quartz. the samples and do not have relative percentages yet. We have just started staining In the sheared bands biotite and hornblende are more common than in the unsheared ones, The greenstones have a varied mineralogy. Preliminary study shows that amphibole and plagioclase are the most abundant minerals, with grain sizes up to I I I .3mm., although usually not over 1 mm. as do epidote and chlorite. Opaque minerals, including pyrite, occur, �22. To the west and north of Stop 6, along Pleasant View Road, felsic volcaniclastic rocks and granitic rocks occur, with the latter north of the former. volcaniclastic rocks are similar to those of Stop 6. rocks and the volcaniclastics is buried. The The contact between the granitic The granitic rocks are exposed in a ditch- crop at the junction with East Tower Road, and here they look like "granite". On the crest of the hill the material was exposed by the telephone company when it buried its cables. The samples were collected this April. The granitic rock shows great variability in hand specimen, particularly in color, but prior experience in the area shows that a noticeable color variation may be independent of similarity of major mineralogic content. Although age relation of the units is unknown, yet we suggest the following possibilities as the most likely. The variability of the "granite" (i.e., rocks) and its close relation to the volcaniclastics, which contain significant amounts of potassium feldspar, give the following possibilities: the volcaniclastics and "granite" are related in origin, or the granite is younger than the volcaniclastics and we see a border phase which is variable because of the incorporation of older volcaniclastics. The absence of recognizable granitic pebbles in the volcanic- lastics suggests that the granite was not exposed at the time of formation of the volcaniclastics, although we recognize the possibility that pebble-bearing volcaniclastics can occur in the five hundred feet between the northernmost exposure of the felsic volcaniclastics and the southernmost exposure of the "granite." �24. STOP 7. Big Sandy County Park The felsic volcaniclastic sequence here is steeply tilted with an orientaMafic units up to a foot thick occur at various intervals tion of roughly N65E65NW. and have the same orientation as the felsic bands. parallel to the banding. Some units seem to be sheared Feldspar grains are visible in many bands. The groundmass of the felsic volcaniclastic rocks is composed of grains in the very fine silt range while the large grains are in the coarse silt to very fine sand range. In some sections the large grains are phenocryStS, while in some they may be sedimentary particles. The groundmass is composed principally of biotite, feldspar and quartz, with opaque minerals up to 57 (estimate) in some bands. The large grains are predominantly plagioclase. From stained slabs we found that plagioclase is far more abundant than potassium feldspar. The mafic units have a similar mineralogy, with biotite far more abundant and quartz much less abundant. The grain size is more uniformly silt size. Included in the opaque minerals is pyrite, which is easily seen in the hand specimen. Comparison of the felsic volcaniclastic rocks in the belt visited at Stops 5, 6 and 7 shows potassium feldspar more abundant to the southeast and clase more abundant to the northwest, plagio- Despite this mineralogic difference, the grain size and band thickness is generally the same, Some mafic units within the felsic volcaniclastic bands presumably owe their greenish black color to the abundance of biotite plus, perhaps, very fine opaque minerals. As mapping has proceeded, we have enlarged the area of felsic volcaniclastic rocks at the expense of the greenstones shown on Weidmants map. localities we have mapped. However, in his text he describes many of the �j Corrections to Figure 5. The Stop numbers on Figure 5 are for th 32nd Annual Tn-State Geological Confcrence, 1968. The table shows the corresponding stop numbers for this field conference. I. L, S. C. Tn-State Stop 3 Stop 7 Stop 4 Stop 8 Stop 8 Stop 9 The Institute is visiting the Marshall Hill conglomerate on the west side of the Wisconsin River because the exposures are fresher and larger than those on the east side. �I 26. STOP 8. Highland Grove "Conglomeratic Rhyolite" WE WOULD BE SORRY TO LOSE YOU IN THE WOODS!!! PLEASE FOLLOW INSTRUCTIONS CAREFULLY. This exposure illustrates a variety of rocks present in the "rhyolite" area as mapped by Weidman and may be typical of the features associated with rhyolitic volcanic activity in general. They include: massive fine—grained rhyolite, some of which may be flow banded; porphyritic rhyolite, with a variable amount of quartz and feldspar phenocrysts; and conglomeratic rhyolite. At least three types of rhyolite, with the relationships shown in the accompanying sketch (Figure 9 ), are present in exposures in the woods south of the school. A massive, fine grained, generally non—porphyritic rhyolite forms the small cliff and the break in slope of the hill. South of this massive unit are porphyritic rhyolite and "conglomeratic" rhyolite in that order. To the north is In the conglomeratic phases, both more porphyritic and "conglomeratic" rhyolite. pebbles and matrix are rhyolitic, and both angular and rounded fragments occur. The contact between the massive (non—porphyritic) unit and the porphyritic unit is a vertical cliff suggesting that the sequence may be standing nearly vertically. N Scale Po r ph yr it i C I": Approximately 50' and "Conglomera tic Porphyrific R hyo life Rhyolife J I"Conglome rat ic" GLL Rhyolite Figure 9. �I 27. In the farmyard east of the woods, the "conglomcratic' rhyolite contains a Note block of flow(?) banded material about 5' long in a coarsely fragmental matrix. that many fragments have good flow banding, although definite flow banding has not been seen in outcrop. Note that the conglomeratic units so well developed in the woods are not exposed along the road. Fragmental texture is present in nearly all material from this locality. Approximately 757 of the exposure is conglomeratic. The finer grained material is Some samples of porphyritic rhyolite contain deformed shards largely tuffaceous. and other features suggestive of welded tuffs, and non-porphyritic rhyolite contains probable shard structures. Glacial boulders with good flow-banding may be found in the woods and farmyard, but as stated above, we have not observed definitely flow-banded rhyolite in outcrop. Thin sections of the rhyolite reveal a fine quartz-feldspar matrix, more or less sericitized. some samples. Patches of carbonate and quartz veins are relatively common in Although the gragmental nature is evident in most hand specimens, the similarity in composition between fragments and matrix make thin section determination of grain boundaries difficult. generally show shard structures Thin sections of the fine grained rhyolite Similar rhyolite from the outcrop at Ninth St. and Winton Ave in Wausau contain unusually well preserved shard structures (shown in Figures 10 and 11). Spherulitic and axiolitic structures are present in some slides. Asquith (1964) reported shard structures in rhyolite from the Brokaw Quarry on the west side of the Wisconsin River north of Wausau in the NW-l/4 Sec. 11, T.29N, R.7E. (Minnesota Mining & Manufacturing operates the quarry to obtain roofing granules) and in a number of Precambrian rhyolites farther consin. He interprets them as welded tuffs. south in Wis- The shard-bearing phases of the rhyolite in the Wausau area may also be, at least in part, welded tuffs. �28 Figure 10. Shard structures in rhyolite from Ninth Street and Winton Avenue, Wausau. Magnification approximately 140x. Figure 11. Shard structures with phenocrysts in rhyolite from Ninth Street and Winton Avenue. Magnification approximately 140x. �29. Therefore, the rhyolites in the Wausau area seem to have formed in more than one way--some may have been flows, some presumably are welded tuffs (ignimbrites). some may have formed from "mud flows", and some may be intrusions. Bedded (water laid) material such as that at Stop 4 may represent eroded volcanic material or may have resulted from direct volcanic (tuff) contribution to the sedimentary basin If this is a subaerial deposit, how is it related to the bedded tuffs we saw at Stop 4? Both east and west of the Wausau area are large exposures of metamorphosed, sheared rhyolite. Due to the almost complete lack of shearing and metamorphism of the rhyolites in the immediate Wausau area, we feel that these rocks are younger than the altered rhyolites and may represent a renewal of acid volcanism within the greenstone belt �:30. REFERENCES Asquith, G. B., 1964, "Origin of the Precambrian Wisconsin Rhyolites", Journal of Geology, Vol. 72, pp. 835-847. Dutton, C. E. and Bradley, R. E., 1968, "The Precambrian Geology of Northern Wisconsin", U. S. Geol. Survey, open file report, four maps. Emmons, R. C., l953a, Guidebook for 17th Annual Tn-State Geological Field Conference, 11 p. Emmons, R. C., l953b, "The Argument", in Geol. Soc. Amer., Memoir 52, pp. 111-117. Goodwin, A. M. (editor), Precambrian Symposium: The Relationship of Mineralization to Precambrian Stratigraphy in Certain Mining Areas of Ontario and Quebec, The Geol. Assoc. of Canada, Special Paper No. 3, 144 p. Goodwin, A. M. and Gross, W. H. (co-chairmen), 1965, "Symposium on Stratabound Met. Bull., Vol. 68, Sulfides and Their Formative Environment", Can. Mi pp. 253-300. Goodwin, A. M. and Schklanka, R., 1967, Archean Volcano--Tectonic Basins: Pattern, Can. Jour. Earth Sci., Vol. 4, pp. 777-795. Form and LaBerge, G. L., and Weis, L. W., 1968, A Greenstone Belt in Central Wisconsin? Guidebook for 32nd Annual Tn-State Geological Field Conference, 42 p. Weidman, Samuel, 1907, The Geology of North Central Wisconsin, Bull. XVI, Wisconsin Geological and Natural History Survey, 697 p. �ITINERARY FOR 15th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY FIELD TRIP Section 1. Go north on Westwood Dr., turn 1 and Assembly Point are at Employers Insurance. right on Bridge St., cross over U.S. 51, turn north onto U.S. 51. Turn west on Co. A, Stop go 5 miles to Stop 2. Stop 2, go east on Co. A to U.S. 51, turn south to Co. WW, turn east. From to Stop 3 on west side of Wisconsin River. Go 1½ miles From Stop 3 continue east on Co. WW to Co. W., turn south, go 1 mile to Stqp 4. Stop 4 continue south on Co. W to Wis. 52 (Wausau Ave.), turn east. At Co. Y turn south, go 2 miles to Marathon County Park at the Dells of the Eau Claire, Stop 5. From Lunch will be served after visiting the outcrop. From Stop 5, continue south on Co. Y to Co. Z, turn west for 1½ miles to Eau Claire Rd., turn south 1½ miles to Forestville Rd., turn east, cross bridge to Stop 6. NO SMOKING AT STOP 6, From Stop 6, return to Eau Claire Rd., turn south 1/8 mile to Pleasant View Rd., turn west. Notice ditch crops. Turn west on Co. Z, turn south on Co. J and park in Mara7. thon County Park on the Big Sandy, From Stop 7, go north on Co. J, go west on Co. Z. Continue west on Hamilton Rd. mile. Turn north on 25th St., go 3/4 mile to Stop 8. about From Stop 8 continue north to Wis 52, turn west. Turn south at 6th St. (Co. W), west on Bridge St., cross Wisconsin River, U.S. 51, and return to Assembly Point. Section 2. Point are at Employers Insurance. Go north on Westwood Dr., 1 and Turn north, turn east on Bridge St., cross U.S. 51, Wisconsin River, to Wis. 52. Stop then east and northeast on Wis. 52 to 25th St., turn south to St 8. Continue east on Co. From Stop 8, go south on 25th St., turn east on Hamilton Rd. Z, turn south on Co. J and park in Marathon County Park on the Big Sandy, Stop 7. From Stop 7, go north on Co. J, turn east on Co. Z to Pleasant View Rd., turn south. Notice ditch crops. Turn north at Eau Claire Rd., go 1/8 mile, turn east on Forestville Rd., cross bridge to Stop 6. NO SMOKING AT STOP 6. From Stop 6, return to Eau Claire Rd., turn north to Co. Z, turn east to Co. Y, Lunch turn north to Marathon County Park at the Dells of the Eau Claire, Sto2 5. will be served after visiting the outcrop. From Stop 5 go north on Co. Y to Wis. 52, go west. (Sixth St.) and go about 2½ miles to Stop 4. In Wausau turn north on Co. W From Stop 4, go north on Co. W to Co. WW, turn west, cross Wisconsin R. to Stop 3. From Stop 3, go west to U.S. 51, go north to Co. A go west 5 miles to From Stop 2, go east on Co. A to U.S. 51, south on Belt Line, exit to Assembly Point. �t— !i-- - i1,tes — ———— Annual 1. L.S.G. ROUTE MAP 15th ——.——— � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1969 Description An account of the resource Institute on Lake Superior Geology. Wisconsin State University, Oshkosh, Wisconsin. May 8-9, 1969. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1969 Contributor An entity responsible for making contributions to the resource Rodolfo Anzoleaga Leonidas C. Ocola Robert P. Meyer George A. Armbrust Bill Bonnichsen S. Chaudhuri D.G. Brookins G. Faure Donald M. Davidson Jr A.B. Dickas E.W. Frodesen B.A. Kososki C.A. Wolosin R.H. Dott Jr S.S. Goldich G.N. Hanson Donald G. Hill Rodney J. Ikola Rudolf W. Johnson Joseph T. Mengel Jr R. Middleton J. Murray G. Aho G.B. Morey D.G. Rensink John S. Mothersill Stephen C. Nordeng Richard W. Ojakangas J.F. Olmsted T.P. Paster E.B. Denechaud L.A. Haskin Robert G. Schmidt Virgil A. Trent L.V.A Sendlein W.P. Staub G.H. Spencer Jr Hans Tammemogi S. Viswanathan William C. Phinney Richard J. Wold Thomas G. Wygant Joseph J. Mancuso D. York H.C. Halls Grant M. Young Wayne R. Zwickey Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/bd5c5a0c6722f2c323493f2323ab4367.pdf af6474daa8932e237f88edd277e33cc0 PDF Text Text -ç — — I: .t. F Geology Superior Lake On nstitute I S a >f• i\tA I v r �TECHNICAL SESSIONS ABSTRACTS and FIELD GUIDES 16th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGV heLd cit LAKEHEAD UNI VERSITV Thanaeir. Bay, Ont May 6 - 9, 1910 Edited by JL. Talbot J.M. Franklin C. Kuatra �TABLE OF CONTENTS INSTITUTE DIRECTORS AND LOCAL COMMITTEE 1. PROGRAM 2. ABSTRACTS OF TECHNICAL SESSIONS 7. FIELD TRIPS A- Proterozoic formations in the Thunder Bay Area. 49. 8- Sturgeon River Metavolcanic Metasedimentary Formations in the Beardznore-Geraldton area. 69. C- The Port Coldwell alkalic complex 8S. �—1— 16-tk AnvwsZ INSTITUTE ON LAKE SUPERIOR GEOLOGy Lake head UrL.Lvex4Lty Thandv. Bay, OntaLo May 7-8, 1970 INSTITUTE BOARD OF DIRECTORS * 3. * R. A. N. A. G. M. W. Avery (Treasurer), Jones F, Laughlin Steel Corp., Negaunee, Michigan. C. Reed (Secretary), Michigan Geological Survey, Lansing, Michigan. K. Snelgrove, Michigan Techological University, Houghton, Michigan. J. Hinze, Michigan State University, East Lansing, Michigan. B. Dickas, Wisconsin State University, Superior, Wisconsin. L. LaBerge, Wisconsin State University, Oshkosh, Wisconsin. W. Bartley, Thunder Bay, Ontario. * Permanent members. LOCAL COMMITTEE Chairmen: M. N. Bartley E. Mercy Progrcxnne Committee: GeneraF Members: 3. Talbot F. Harris A. Boerner 3. Mothersill V. B. Cook A. Temple FIELD TRIP COMMITTEE C. Kustra 3. Franklin H. Loubat E. Brinley �-2- "P R 0 G R A M" Tate day, Ma9 5th, 1970 6.00 p.m. Field Trip '8' (Ceraldton-Beardjnor) leaves the Prince Arthur Hotel, Thunder Bay, Ontario. Wed4e2day, 7.00 p.m. Field Trip May 6th, 1970 'B' returns to Prince Arthur Hotel 7.00 p.m. to Institute Registration — Prince Arthur Hotel 10.00 p.m. 7.00 p.m. American Institute of Professional Geologists, Dinner3 Prince Arthur Hotel Thwt4ç4y, M04 7th, 197Q 7.30 a.m. to 9.00 a.m. Registration, Main Cafeteria, LAKEHEAD UNIVERSITY �-.3- $ E S SI °.JL Thwchday, May 7th, 1970 Page 8.15 R. Oja Keweenanwan Copper Deposits in the Archean of Northwes tern Ontario 31 8.30 D. C. Mulder Ore Controls and Open Pit Geological Procedures in Steep Rock Iron Mines 30 Limi ted 9.00 W. •F. Read Is the Limestone Mountain Structure an Astrobleme? 36 9.20 S. Viswanathan A classification of granitic rocks with reference to Giants Range Batholith, Northern Minnesota 40 9.35 G. N. Hanson R. Malhotra K-Ar Ages of Mafic Dikes in Northeastern Minnesota 19 9.50 C. W. Keighi.n Age and Petrology of the Fort Ridgely Granite, Southwestern Minnesota 26 10.10 W. Bonnichsen The southern part of the Duluth Complex 10 and associated Keweenawan rocks, Minnesota 10.40 J. D Mancuso Structure of the Duluth Gabbro Complex 27 in the Babbitt area, Minnesota J. D. Dolence 11.10 J. C. Green Ultrainafic bodies in the Vermilion District near Ely, Minnesota 11.40 J. M. Berkson C. S. Clay Side-Scan Sonar Survey of the Lake Superior floor near Freda, Michigan 12.00 NOON - LUNCH - Student Cafeteria 17 9 No. �-4- SESSTOM 2 jNo. 'AjteA.vzoovz' 1.00 Business 1.30 M. Y. Meeting Deformation of the Seine conglomerate I-lsu in 2.00 11. M. Mooney et al Refraction Seismic Investigations of Northern Midcontinent Gravity High 2.30 IL N. Annells Keweenawan Volcanic Geology of Michipicoten Island, Lake Superior 3.00 3. Wood Evidence for a Tropical Climate and Oxygenic Atmosphere in Upper Huronian Rocks of the Rawhide Lake - Flack Lake area, Ontario. 3.30 G. M. Young Widespread occurrence of Minerals 4.00 C. Powell 20 the Rainy River area, Ontario. P. M. Clifford 28 7 45 A luminous in Aphebian Quartzites Structurat and+rnetwnorphic history 35 of the Marquette Sync linoriurn 4.30 W. Jenks Root severance and tectonic transport of orebodies in Metavolcanic Host Rocks 25 'EvekvLvlg' 6.00 p.m. CoaktaLto 7.75 p.m. Baitque.t - CAFETERiA - RESZVENCE Vlt'1ING ROOM AVVRESS: speaking - Lakahac4 WvLv&ui.ig Lcththead th'tkvexaUg J. C. Rudolph, of GENERAL EXPLORATION CO. OF CANADA LTD. on 'A philosophy of exploration'. �-5.- FtLday, MayUh, 1970 SYMPOSIUM ON GREENSTONE BELTS LB. Wilson- General Chairman 'Mokn,üig' 9.00 U. B. Wilson Introduction 9.15 L. D. Ayres Synthesis of early Precambrian Stratigraphy north of Lake Superiqr 9,45 Z. Peterinan Early Precambrian Geology of the Rainy Lake District 34 S. Goldich 10.15 P. Clifford Mt. St. Joseph 14 10.45 W. C. Brisbin The structure of the Northern Lake of the Woods Greens tone Belt, a Deformational Mosaic 12 11.15 R. H. RidIer Archaean Volcanic Stratigraphy of the Kirkland-Larder Lakes area of Northeastern Ontario. 37 11.45 DISCUSSION 12 NOON LUNCH - Student Cafeteria An Archaean Volcano S �-6F'viday, May Slit, 1970 Page No. 1.30 G. N. Hanson S. Goldich Early Precambrian Geology of the Saganaga-Northern Light Lakes area, Minnesota- 18 Ontario. A Model for Tectonic Variation of 'Granitic Terrain' in Southeastern Manitoba 16 Geology of a Greenstone Belt in Minnesota: Rainy Lake to Lake of the Woods 32 D. H. Watkinson Geology of the Alkalic rock - Carbonatite complex at Prairie Lake, Ontario. 44 3.30 P. NI. Clifford Behaviour of an Archaean Granite Diapir 13 4.00 R. W. Hutchinson Mineral Potential in Greenstone Belts of Northwestern Ontario 22 4.30 H. B. Wilson CONCLUDING REMARKS 4.45 End 4.45 DINNER (Field Trip participants are advised to have dinner before leaving Thunder Bay) 6.00 Departure for Field Trip "8". 2.00 1. F. Ermanovics 2.30 R. 3.00 IV. Ojakangas Teahnicc2 Sws.Lon4 Field Trip "C". Field Trip "V". (Geraldton-Beardinore) (Port Coldwell) (Atikokan) Buses will depart from the University but will call at Hotels as necessary. * * * * * * * * * * * * Sa-ttvtday, May 9th, 1970 8.00 a.m. Departure for Field Trip "Y'. (Gunf lint-Sibley) Buses will depart from the Prince Arthur Hotel 7.30 p.m. (approx.) RETURN OF ALL FIELD TRIP BUSES. �-7- KEWEENAWAN VOLCANIC GEOLOGY OF MICIIIPICOTEN ISLAND, LAKE SUPERIOR it. N. ANNELLS Postdoctorate Geological Survey of Fellow Canada, Ottawa ABSTRACT Recent re—mapping and petrographic examination by the author of the Keweenawan lava flows building Michipicoten Island shows that they form a highly differentiated 11,500—foot sequence of types ranging from coarse ophitic olivine—bearing basalts through olivine—free basalts and andesitic types to glassy porphyritic andesites and rhyolites. Some volcaniclastic horizons are intercalated in this south—dipping lava series and a few intercalations of conglomerate and sandstone outcrop at the west end of the island. The different- lava types are well intermixed and there is no obvious vertical gradation or cyclic distribution of lava types in the Michipicoten island succession. The lavas tend to occur in grouj,s of petrographically similar flows which can be traced as distinct strati— graphic units; an andesite group near the top of the succession can be followed across the entire island, a distance of 16 miles along strike. Near the median part of the succession the lavas show some lateral variation which may be the result of simultaneous extrusion of different flow types at the same general level from different vents. An agglomerate bearing large angular and rounded blocks of island lava types outcrops on the northwest shore of the island, and indicates proximity to an eruptive vent. The lower half of the exposed lava sequence is intruded at numerous different horizons by sheet—like or lentJ.cular bodies of pink acid quartz porphyry crowded with large phenocrysts of feldspar and quartz. These bodies are sometimes discordant the lava flows and field evidence suggests that they are intrusions Basic intrusions are extremely rare on Michipicoten Island, only about six very thin basic inclined sheets being found on the entire shoreline. to The varied basalt—andesite—rhycalite sequence and associated volcaniclastic rocks of Michipicoten Island are believed to have been erupted from a central volcano fed by a high level magma source. The presence of large volumes of acid material in the island sequence is a phenomenon' very similar to that seen in the Icelandic central volcanoes, which consist of highly diffentiated lavafvolcaniclastic edifices inter— finggred with widespread flood basalts and often intruded by acid material. �-8- SYNTHESIS OF EARLY PRECAMBRIAN STRATIGRAPHY NORTH OF LAKE SUPERIOR LORNE D. AYRES Ontario Department of Mines Toronto A section from Lake Superior Park to Geraldton, Ontario crosses three major, east-trending, Early Precambrian, lithologic and structural elements of the Superior Province of the Canadian Shield. From south to north these are the northern part of the Abitibi island arc, the Quetico sedimentary basin, and the southern part of the Keewatin island arc. Both the Abitibi and Keewatin arcs are formed from coalescing, subaqueous, basaltic shield volcanoes capped by subaerial to subaqueous, felsic to intermediate pyroclastic cones. Volcaniclastic greywacke sequences derived from felsic volcanism accumulated in intervolcano basins and partly overlap the felsic pyroclastic deposits. Small trondhjemite cratons within the island arcs were a local sOurce of sedimentary detritus. Although the island arcs have easterly trends, individual basins and volcanoes have diverse trends. Along the north edge of the Abitibi arc from Schreiber to Wawa, three isolated sedimentary formations were deposited in intervolcano basins, but they are all tongues of an extremely thick greywacke and siltstone formation deposited in the Quetico basin north of the arc. The formations become progressively younger from west to east. The sedimentary rocks of the Quetico basin, which are equivalent to the Couchiching Formation of western Ontario, overlie and intertongue with. the volcanic formations of the Abitibi arc and the source area was probably within the arc. Along the north edge of the basin, however, the sedimentary rocks underlie and intertongue with the volcanic formations of the Keewatin arc.! In this area, Keewatin volcanism is thus younger than Abitibi volcanism. �-9- SIDE-SCAN SONAR SURVEY OF THE LAKE SUPERIOR FLOOR NEAR FREDA, MICRIGAN J. N. BERKSON & C. S. CLAY University of Wisconsin Geophysical and Polar Research Center ABS TRACT Approximately 300 miles of side-scan sonar profiles were made in Lake Superior near Freda, Michigan. The instrument scans to the side approximately 1/4 mile and gives the location of features on the lake floor which scatter sound. The shape of the scattering features can often be correlated with geological features. The ship's tracks were close enough together so that nearly continuous sonar coverage was obtained. Underwater photographs and divers were used to identify some of the scattering features. Three distinct bottom types were observed in the survey area: rocky, sandy, and bedrock. The bedrock appears to correlate with the Freda sandstone, which outcrops on the land. This study was supported in part by The National Center for Atmospheric Research and The Office of Naval Research. �-10THE SOUTHERN PART OF THE DULUTH COMPLEX AND ASSOCIATED KEWEENAWAN ROCKS, MINNESOTA BILL BONNICHSEN Cornell University, Ithaca, N.Y. 14850 A B ST EtA CT The southern part of the Duluth Complex was reported to consist mainly of troctolitic rocks and older anorthositic rocks at the 15th Annual Institute on Lake Superior Geology and elsewhere (Bonni— chsen, 1969). Geologic mapping in several 7½—minute quadrangles in the Babbitt—Hoyt Lakes area (Bonnichsen, 1970) shows that troctolitic rocks lie north and west of the principal occurrences of anorthositic rocks, thus forming the footwall side of the complex in the same manner as at Duluth (Taylor, 1964). Between Duluth and the Babbitt—Hoyt Lakes area, troctolitic rocks predominate across the width of the complex; exposures of anorthositic rocks are restricted to isolated occurrences and inclusions within the troctolitic rocks, rather than large areas with contiguous outcrops. In 1969, the writer suggested that troctolitic magmas had intruded along a contemporaneously widening fracture zone between the previously—formed anorthositic rocks to the east and the Early and Middle Precambrian basement to the west. Field work during the summer of 1969 and examination of drill core in recent months tends to substantiate this view. Recently obtained knowledge on the variety and diversity of rock types within the southernpart of the complex indicates the development of the troctolitic rocks was a complex event involving multiple injections of magma, the incorporation of a great amount of previously—formed Keweenawan igneous rocks as inclusions and the development of relatively small quantities of Fe— and Ti—rich magma, some of which was ultramafic, from nagmas which initially were troc— tolitic. Much of the 1969 field season was devoted to looking for and examining outcrops along, and east of, the eastern or hanging wall margin of the complex. This margin, for the first 30 miles north of Duluth, is mainly a contact between troctolitic and locally anor— thositic rocks to the west and gabbroic and dioritic intrusives to the east. Exposures of mafic volcanics are uncommon east of the southern part of the complex, except within one or two miles of Lake Superior. �In the Mt. Weber—Greenwood Lake area, about 40 miles N.N.E. of Duluth, a number of granophyre exposures occur but the area underlain by granophyre is much less than shown on the 1932 Minnesota state geologic map. Gabbros, ferrogabbros, and magnetite troctolites are exposed north of the granophyre area; these rocks are responsible for the intense magnetic anomalies in that area. Exposures of rhyolite, other felsites and magnetic basalts occur south of the granophyre area. In the central part of this volcanic area is a one—fourth mile long outcrop area of strongly—laminated, locally cross—beddé4,::weakly meta— morçhosed, feldspathic rock that is interpreted to be equivalent to the Virginip Formation; this occurrence is about 25 miles east of the footwall of the complex where other Virginia Formation is exposed. Bodies of hornfels are common throughout the southern part of the complex; many of these, especially in the Babbitt—Hoyt Lakes area, are inclusions of the Virginia Formation which forms the foot— wall of the complex in that area. The majority of hornfels bodies in the southern part of the complex, however, are considered to be metamorphosed basalt, probably of Keweenawan age. This type of horn— fels occurs throughout the complex, including along the western marIt is suggested that along parts of the western margin of the gin. complex between Duluth and Hoyt Lakes, the footwall consists of vol— canics which overlie the Virginia Formation and the equivalent Thompson Slate, much like the situation af Duluth. A feature of interest in the southern part of the complex are a number of bodies of titaniferous peridotite and similar ultra— These dike— or sill—like bodies are known from drilling inafic rocks. These rocks are to locally have thicknesses of hundreds of feet. characterized by lithologic heterogeneity, medium to coarse grain sizes, local rhythmic layering and abundant titanaugite, olivine, and ilmenite; locally, magnetite, graphite, plagioclase, and pyrrhotite are abundant. These rocks may have crystallized from liquids approximating their present composition because they are the latest intru- sive rocks known inthat area and because fine—grained dikes with identical mineralogical compositions cut adjacent rock bodies in the vicinity of the large peridotite bodies. Re ferenc es: Bonnichsen, Bill, 1969, Geology of the southern part of the Duluth Complex, Minnesota; Proc. of 30th Annual Mining Symposium, Univ. of Minn.; p. 89—93. Bonnichsen, Bill, 1970, Geologic maps of the Duluth Complex in the i3abhitt—Hoyt Lakes area, Minnesota; geologic maps and accompanying explanation for the Allen, Babbitt, Babbitt NE, Babbitt SE and Babbitt SW 7½—minute quadrangles, 1/24,000; on open file with the Minnesota Geological Survey, University of Minn., Minneapolis, Minn. Taylor, R. B., 1964, Geology of the Duluth Gabbro Complex near Duluth, Minnesota; Minn. Geol. Survey Bull. 44, 63 p. �-12THE STRUCTURE OF THE NORTHERN LAKE OF THE WOODS GREENSTONE BELT, A DEFORNATIONAL W)SAIC. W. C. BRISBIN University of Manitoba ABSTRACT The structure of the northern portion of the Lake of the Woods greenstone belt may be described as a complex mosaic, consisting of the effects of several deformation events, each of which has been developed spatially to differing degrees. Individual domains, within the mosaic, may show strain effects of one, or more, of three widespread and dominant tectonic events, the chronology and tectonic styles of which are remarkably persistent. The earliest deformational period is manifest by folds in layering which are seldom unaffected by later events. Where structural overprinting is poorly developed the evidence suggests that these folds were developed by a flexural mechanism, under conditions of low mean ductility, where layer contacts were active. These folds are interpreted as having developed post lithification and prior to any major metamorphic event. Large areas of the greenstone belt show evidence of a second deformational event which has led to the development of a penetrative and tectonically active foliation. Differential movements, either leading to, or on, the foliation have resulted in passive folds which, in many areas, have been superimposed on earlier sets. Evidence on, all scales, from deformed clasts to deformed early plutons, indicates that strain during this event was accomplished by a combination of simple shear and differential pure shear. The directions of extensive strain and simple shear movements during this event had strong vertical components; the strain effects of this event are linked to the reorganization of upper crustal masses which accompanied the emplacement of the numerous granitic diapirs which have intruded the greenstone. The third period of deformation is portrayed best in many of the The earlier areas where the second period penetrative foliation occurs. foliation served as an active surface for the development of flexural folds on all scales; from microscopic crenulations, to mesoscopic kink bands, to major folds with structural relief of several thousand feet. Movement directions during this event were variable within, and between, suggesting a wide variety of late stress conditions both temporally and spatially. domains, �-13- BEHAVIOUR OF AN ARCHAEAN GRANITE DIAFIR PAUL M. LIFF0RD Department of Geology McMaster University A B S T R A C t Much evidence now is available linking part, possibly all, of the deform.ation in Archaean greenstone belts with the emplacement of diapiric granites. This is now well documented for the Keewatin—type belts of the Canadian Shield, and their analogues in Southern Africa, Western Australia and elsewhere. These granites are large ovoid, lobate masses in plareview, commonly heterogeneous internally. Between clusters of such granites lie linear and stellate arrays of volcanic—sedimentary rocks — greenstones. set in a granite seas + The Bainaji Granite about 300 kins. N.N.E. of Thunder Bay is one such granite mass. It and the Carling Granite lie N.W. and N.E. respectively of the Lake St. Joseph volcanic—sedimentary basin. Pillows in the lavas within 500 metres of the Baxnaji Granite margin have suffered considerable flattening in a plareparallel to the margin. The amount of flattening increases towards the granite, reaching values of about 80%, with an average of 60% in this distance. In the same zone, "granitic" dykes which emanate from the granite into the lavas are buckled. The axial surfaces of the buckles are statistically parallel to the granite margin. The shortening implied by the dykes is 40% or less. Both these flattening features suggest that emplacement of the granite led to effective compression of the lower levels of the supracrustal pile on axes everywhere normal to the granite margin, and that there was probably stretching on subvertical axes in order to accommodate the distortion. The discrepancy between compressions in pillows and dykes suggests that the dykes were intruded some time after compression commenced. At certain localities right at the granite margin, tlchocolate• tablet" boundinage occurs in already flattened lavas. This implies late extenson in all directions within the plane parallel to the granite margin. This in turn implies an axially symmetric stress field, whose unique symmetry axis lay normal to the granite margin. The best explanation for this late stage extensional strain is that the granite was then being inflated by the introduction pf low—viscosity granitic material (? magma). �-14- MT. ST. JOSEPH - AN ARC}IAEAN VOLCANO PAUL M. CLIFFORD Department of Geology McMaster University ABSTRACT An Archaean composite strata—volcano is preserved about 300 kms. N.N.E. of Thunder Bay. Despite severe deformation and modest metaorphism, a fairly clear picture af the histary of this volcano, Mt. St. Joseph, can be gained. The lower portion of the valcana pile is now some 2700 metres thick, but allowance for tectonic flattening raises this to 3700 metres at least, and the true thickness was probably much more, if large xeno— liths within flanking granites can be assigned to this sequence. This effusive sequence, dominantly mafic, consists af unstructured flaws intercalated with piflowed lavas, autobreccias and pillow breccias. About two—thirds up the sequence, there is an erosional unconformity developed on a diarite intrusive into the lavas. A conglomerate lies on the unconformity, and this is succeeded by the upper levels of the effusive sequence. Abave the effusive sequence lie about 3250 metres of volcanic fragmental rocks af mainly silicic composition — the çplosive seqnce. The lower units af the sequence consist of large accidental blocks in a finer grained matrix. The higher units are generally finer—grained. The effusive racks are commonly vesiculated. The degree ot vesiculation in pillows generally increases with height in the pile. This implies progressive shallowing af the water into which the lavas were emitted. The upward decrease. in size of adcidental fragments in the explosive sequence suggests an increase in the intensity of explosive force as the volcano matured. Chemically, lavas range from 45% to 75% 5i02. The change from effusive to explasive activity occurred at abaut 58% 5i02. The estimated explosive index af the volcano is less than ten. The silicic materials now preserved form a relatively minor portion of the total volume of volcanic rocks. In an Osborne—type plot, the lavas 'evolve' on a line intermediate between the lines for Skaergaard and the Cascades. The volcanic history, taken in conjunction with the tectonic development of the area, implies very restricted areas of deposition, �—Is— capable of accepting considerable thicknesses of volcanic rock and derived sediments. This, in turn, implies considerable crustal mobility at the time. Note that no deformed belts occur without a volcanic pile. The local mobility and the vulcanicity are inextricably linked for this area, as they seem to be for analgous areas elsewhere. �-16- A MODEL FOR TECTONIC VARIATION OF 'GRM4ITIC TERRAIN' IN SOUTHEASTERN MANITOBA I. F. ERMANOVICS Geological Survey of Canada, Ottawa A B ST RA CT The Precambrian rocks of the Superior (Structural) Province of southeastern Manitoba, between latitudes 51 and 54 degrees fall into three groups: metavolcanic—sedimentary rocks (domain I); an adjacent, hybrid mobile zone (domain II) and a siliceous (sialic) nucleus (domain III). Domain III, situated between 510 15' and 30' N, comprises augen-gneiss and weakly layered to stratiform layered gnefss (SO per cent of the domain) whose compositions range from quartz monzonite to gran— odiorite; mafic hornblende gneiss and amphibolite are abdundant locally. Siliceous mafic—noor quartz monzonite to granodiorite intrude these gneisses and the magnetite content of the massive rocks is correlatable to regional magnetic 'highs'. Metavolcanic—sedimentary rocks (3 per cent of domain III) and mafic granodioritic gneiss occupy relict keels of folds; 'down—plunge' views of such structures show that these remnants are underlain by siliceous gneiss and massive rocks peculiar to rocks of domain III. Rocks of domain II, flanking belts of uietavolcanic—sedimentary rocks, consist of high—grade aluminoüs and inafic gneiss intruded by diapiric mafic granodiorite to quartz gabbro; large bodies of quartz monzonite are absent from this domain. The coarse—grained igneous rocks may be the intrusive equivalents (cogenetic magtnas) of the lavas of domain I and both domains constitute the total volcanic—sedimentary tectogene. A seismic !break!, located along the lithologic boundary between domains II and III, indicates displacement of the Conrad discontinuity downward beneath domains I and II with respect to domain III. Thus if the seismic break is a fault (albeit annealed by later intrusions) and if the volcanic—sedimentary tectogene is underlain by rocks of domain III, then the sialic nucleus (domain iii) is exposed by virtue of erosion. It is concluded that the volcanic—sedimentary rocks were deposited upon a sialic (relatively siliceous) basement which is now represented by !granitic gneiss'. �-17- ULTRA}IAFIC BODIES IN THE VERMILION DISTRICT NEAR ELY, MINNESOTA JOHN C. GREEN University of Mitinesota, Duluth ABSTRACT A few dozen pods of harzburgitic peridotite have been intruded into the greenstones of the belt immediately north of Ely (Nevton Lake Formation). They range up to two miles in length by up to 1,000 feet in width. They have undergone varying degrees of serpentinization, evidently after emplacement; tectonic fractures uniformly crosscut magmatic minerals and textures (olivine and poilcilitic pyroxene) and predate serpentinization. They carry negligible Ni, Cu, Au,, and Pt — group values and about 5,000 ppm Cr. No significant amounts of asbestos have been seen. Art area in the Ely Greenstone east of a1l Lake contains unserpentinized ultramafic rocks, transitional to gabbros, that are characterized by hornblende and biotite instead of olivine. �-18- EARLY PRECAMBRIAN GEOLOGY OF THE SAGkNAGA-NO1HEBN LIGHT LAKES AREA, MINNESOTA-ONTARIO G. N. HANSON State University of New York at Stony Brook Stony Brook, N. Y. 11790 5. 5. GOLDICH Northern Illinois University DeKalb, Illinois 60115 ABSTRACT The principal Early Precambrian rock units in the Saganaga—Northern Light Lakes area of Ontario and Minnesota, from oldest to youngest, include the Keewatin volcanic and related rocks, the Northern Light Gneiss, the Saganaga Tonalite, formerly called the Saganaga Granite, and the Knife Lake Group. These units were intruded by numerous small plutons and dikes. The Northern Light Gneiss, the Saganaga Tonalite, and syenodioritic to granodioritic phases of a small pluton at Icarus Lake, from oldest to youngest on the basis of field relationships, have been dated by the Rb-Sr, whole-rock technique. The isochron ages range from 2700 to 2750 m.y. and are indistinguishable but suggest that these rocks formed within a time span o' less than 100 m.y. and probably less than 50 m.y. all Modal and chemical analyses show that the greater part of the Northern Light Gneiss is trondhjemitic. in composition. As suggested originally by Frank Grout the gneiss nay have resulted from the lit—par—lit injection of the Keewatin greenstones during a period of folding. The gneiss, however, may have been formed by folding and metamorphism of a Keewatin volcanic pile composed of basaltic, trondhjeniitic, and rhyolitic volcanic rocks, and possibly some sediments. The Saganaga Tonalite is a late or postkinematic intrusion emplaced in the greenstones and the Northern Light Gneiss, and inclusions of both rock types are found in the tonalite. The Icarus Lake pluton intrudes both the Northern Light Gneiss and the Saganaga Tonalite. It wnsists of an older western phase of syenodiorite and a younger eastern phase of granodiorite. Both rocks are alkalic, containing aegerine-augite and hastingsite. Rb—Sr and K-Ar mineral ages from the principal rock units range from 2500 to 2700 n.y. and are difficult to interpret. In part these ages may be related to faulting and alteration. Movements on the major fault zones ceased before the deposition of the Anini.ikie sediments. Metamorphism is low-grade, greenschist facies of the Abukuma type. �-19- K—AR AGES OF btkFIC DIKES IN NORTHEASTERN MINNESOTA C. N. HANSON and R. MALMOTRA Department of Earth and Space Sciences State University of New York Stony Brook, New York ABSTRACT Sixteen mafic dikes in the Vermilion District, Minnesota and in the Saganaga—Northern Light Lakes area, Minnesota—Ontario botder, give K—Ar whole—rock and mineral ages of 2600 m.y.., 19002000 m.y., 1500—1600 m.y., 1400 n.y., and 100—1100 n.y. One sample of a Logan Sill near Suomi, Ontario gives a whole—rock K—Ar age of .1380 m.y. The dikes range in composition from hornblende andesite with modal quartz and microcline to tholeiitic basalt. There does not appear to be a clear—cut difference in composition as a function of age nor. a difference in strike. Most dikes have a north—northwest strike in the Vermilion district and a northerly strike in the Saganaga— Nor them Light Lakes area. Dikes with ages greater tjtan 1500 m.y. have a characteristic alteration, possibly due to burial metamorphism, as shown by highly sericitized plagioclase and the development of actinolite, chlorite, The younger dikes do not show epidote, sphene, prehnite, and calcite. this same style of alteration nor are they as highly altered. The dikes which give 1500—1600 m.y. whole rock K—Ar ages are extensively altered, and these ages may indicate the time of recrystallization rather than the time of intrusion. �-20DEFORMATION OF THE SEINE CONGLOMERATE IN THE RAINY RIVER AREA, ONTARIO MAO-YANG HSU and PAUL M. CLIFFORD Department of Geology McMaster University ABSTRACT The Seine conglomerate exposed betweexi t&ine Centre and Flanders, > Ontario, is of Archaean age ( 2500 m.yj. The conglomerate has been subjected to low—grade regional metamorphism, so that pebbles now lie in a fine—grained foliated matrix of mica schist. The foliation is intensely developed over the whole area studied, but mineral lineation is indifferently developed. Pebbles vary in lithology, shape, size and orientation. Most are good approximations to oblate triaxial ellipsoids, with the XY planes parallel to foliations and the )( axis commonly subparallel to mineral lineation or to intersections of bedding with foliation. Elongations of pebbles on a major fold hinge are parallel to the fold axis. We think that buckling preceded passive slip or flow. Principal planes of finite strain cannot be identified with any confidence in the field. A new method has been developed which allows the calculation of finite strain ellipsoids from average axial ratios uieasured in any two rectiplanar surfaces in an outcrop oriented at a fairly large angle one to another. Plots based on these calculations for thirty—four stations show that the average pebble shape is an oblate triaxial ellipsoid, with axial ratios which vary independently of location when followed parallel to the foliation trace. Pebbles of different tithology occurring on fold limbs lie along the same defor— macion path. This means that original pebble orientations were about the same for all lithologies studied, and that ductilities varied from lithology to lithology. Pebbles of the same lithology lying on the same shortening curve, imply that pebbles of roughly identical shape had different original orientations. Mildly deformed granite pebbles seem not to have suffered rotational strain. A few examples of ripple marks and cross—bedding in metarenites intercalated with the conglomerate imply that the palaeo transport direction was generally towards the present day south. A plot of volcanic pebble orientations against axial ratios of individual pebbles, measured �-21-. in the foliation plane (parallel or sub—parallel to bedding) has a skewed unirnodal distribution. A comparable plot for planes normal to foliation has a symmetrical unimodal distribution. These imply that the original volcanic pebbles were deposited with their original iCY planes parallel or sub—parallel to the bedding plane with their longest axes generally easterly. �-22- MINERAL POTENTIAL IN CREENSTONE BELTS OF NORTHWESTERN ONTARIO R. W HUTCHINSON University of Western Ontario ABSTRACT The distribution of producing metal mines has, until recently, suggested that the Archaean greenstone belts of northwestern Ontario were favourable only for gold deposits and iron formations, in con— trast to similar belts of northeastern Ontario — northwestern Quebec that are obviously favourable f or base metal suiphides as well as gold and iron formations. The metal distribution is no longer so distinctive. Important base metal deposits were discovered at Manitouwadge in 1953 and recently near Uchi and Sturgeon Lakes in northwestern Ontario. Important iron production has commenced from Algoman—type iron formations in eastern Ontario. Detailed geologic work in the northwestern Ontario greenstone belts shows extensive development of rhythmically—banded, shelf—fades "Coutchiching—type" rocks, of immature, first—cycle "Tiiniskarning—type" rocks and of thick, well differentiated "Keewatin—type" volcanic sequences1 All these have lithologic counterparts in the Abitibi region, where the latter are long—recognized hosts for base—metal sulphides, and where the stratigraphic succession of the three "types" appears similar. Age dating methods fail to reveal any significant age differences between these rocks in northwestern Ontario and their counterparts in eastern Ontario—Quebec. All these features suggest that the greenstone belts of northwestern Ontario are similar in origin and age to those farther southeast, and therefore that all have more—or—less equivalent mineral potential for base metal sulphide, iron formation, and gold deposits. These three types of deposit appear metallogenically characteristic of Archaean sequences. They may be lithofacies—related equivalents of one another; the base metal sul— phides forming under reducing conditions near exhalative centres, the iron formations forming under oxidizing conditions remote from the centres, and the gold of similar exhalative derivation but perhaps initially "fixed" in other sedimentary lithofacies such as pyritic or carbonate iron formations, or montmorillonitic, volcanic—derived Timiskaming sediments. Locally, as at Manitouwadge, the northwesterly greenstone belts have been more highly metamorphosed than those of Ontario—Quebec, �-23- and this complicates exploration for base metal deposits. It Vs essential to recognize markedly metamorphosed exhalative centres. These centres, originally defined by accumulations of felsic flows, pyroclastics and cherts may be represented by quartz—sericite schists or gneisses, quartzites, quartzitic "conglomerates" or "breccias". Their bulk composition is important, for it survives metamorphisw, but primary textures may be much altered or obliterated. Minor— element geochemical studies of oxide, sulphide and carbonate—facies iron formations may be useful in guiding exploration from remote lateral lithofacies toward exhalatLve centres. �-25-ROOT SEVERANCE AND TECTONIC TRANSPORT OF OREBODIES IN METAVOLCANIC HOST ROCKS WILLIAM F. JENKS University of Cincinnati ABSTRACT Association of lenticular, concordant, semi—concordant, and cross—cutting massive sulfide bodies with mafic and felsic volcanic sequences is well known. Some are clearly of submarine exhalative or replacement origin. Others may well be related to subaerial volcanism, but near sea level in a zone of negative crustal movement, since preservation of near surface phenomena in a eugeosynclinal environment requires relatively rapid covering and burial. Meta— volcanic sequences originating in active and subsiding tectonic belts have been subjected to all postvolcanic events affecting the enclosing metasedimentary rocks; they may have undergone deformation by overthrust faulting, nappe folding, and refolding. Separation of the volcanic pile (and associated ores) from its roots during such deformation would be expected. These structures, in meta— volcanic terranes, can go unrecognized because of originally complex volcanic—stratigraphic relations, transposition by sliding, md deep folding and metamorphism. Tectonic severance appears to be the reason for the absence of obvious plutonic source rocks in many metavolcanic sequences and their ores. Separation of ores from roots may be more than 50 1cm if we take Alpine deformation as a model. Certain types of volcanic masses such as rhyolite domes would yield to tectonic transport in a manner controlled by local contrasts in ductility, shape, and size., The deformational style is quite unlike that produced in regularly layered rocks. Orebodies, with their normal envelopes of hydrothermal alteration, may 'be transported in an environment especially susceptible to structural irregularity because they are in ductile shells adjacent to irregular volcanic masses. Resultant structural details would be expected to be still more complicated by selective flowage of some sulfide minerals and by migration in response to new chemical gradients. �-26- AGE AND PETILOGY OF THE FDffl' RIDGELY GRANITE, SOUTHWESTERN MINNESOTA C. W. KEIGHIN Northern Illinois University, DeKalb, Illinois ABSTRACT A number of small outcrops of granite were mapped by .Lund in 1949 in the Minnesota River Valley west and southwest of Fort Ridgely. Lund (1956) described the Fort Ridgely Granite as a pinkish—gray porphyritic granite with aligned phenocrysts, some of which are two inches or more in length. Lund suggested that the granite may represent a less contaminated and more massive phase of the Morton Gneiss. Preliminary whole-rock Rb-Sr data give an isochron age of 2650 m.y. If this value is accepted, the Fort Ridgely granite is similar in age to granite in the valley south of Sacred Heart and is much younger than the Morton Gneiss, 3300—3550 m.y., as reported by Goldich in 1968. Two rock types are present in outcrops of the Fort Ridgely Granite. A dark—gray rock containing plagioclase, quartz, K—feldspar, hornblende, and biotite appears to be older than a leucocratic phase composed of K-feldspar, quartz, plagioclase, and minor biotite. Textural features suggest granulation and recrystallization with the development of intricately sutured contacts between quartz and feldspar. It appears possible that the Fort Ridgely Granite may be an older rock that was metamorphosed 2650 m.y. ago. Additional isotopic analyses, field, and laboratory studies are being made to eliminate one of the two alternatives. �-27- STRUCTURE OF ThE DULUTH GABBRO COMPLEX IN ThE BABBIfl AREA, MINI'IESOTA J. D. Mancuso and J. D. Dolence Humble Oil & Refining Company ABSTRACT The Babbitt area is located about 60 miles north of the City of Duluth juSt northeast of where the trend of the trace of the lower contact of the Duluth gabbro complex changes from north to northeast. The complex in this area intrudes Archean greenstone, AlgOman granite, and Animikie iron formation and slate-argillite. The basal contact of the complex is irregular; the dip ranges from almost vertical to flat, but generally dips to the southeast. Major influences on the structure of the contact are i) stratiraphic: the gabbro selectively rode on top of the iron formation, 2) pre-gabbro folding: an anticline is reflected at the base of the complex, and 3) faulting: both pre and post-gabbro faulting affect the floor of the complex. Various geologic features at and beneath the complex are indicated by aeromanetics and The termination of the iron formation beneath the complex is gravity. suggested by an inflection in the aeromagnetic data, arid a probable contact between greenstone. and granite is indicated by gravity. We suggest that the complex was intruded as irregular sheets It cut weaker units such as the and caine up from the southeast. Virginia slate, utilized the Virginia slate--Biwabik iron formation contact, a pre-existing zone of weakness, as a platform to ride upon, and stoped, plucked, and assimilated pre-gabbro rock on its way up. The bottQm of the intrusion probably did not influence the structure of the older rocks, but instead its structure was influenced by preexisting conditions. �-28REFRACTION SEISMIC INVESTIGATIONS OF THE NORTHERN MIDCONTINENT GRAVITY HIGH HAROLD M. MOONEY, CAMPBELL CRADDOCKt, PAUL R. FARNHAM2, STEPHEN H. JOHNSON3, AND GARY VOLZ4 Department of Geology and Geophysics University of Minnesota Minneapolis, Minnesota A B S T R A C T Eighty—seven seismic refraction profiles have been obtained to define the geologic structure in the upper crust associated with the Midcontinent Gravity High in Minnesota and Wisconsin. The seismic measurements were taken across a fixed spread of seven geophones from distances up to 13 km. A structural section was prepared for each profile by interpretation of the travel—time graph, and the individual sections were compiled into regional cross sections. Measured seismic velocities in bedrock fall in the 2.5 — Observed velocities can be assigned to seven groups corresponding to Paleozoic, upper, middle, and lower Upper Kewee— nawan strata, Middle Keweenawaivolcanics, pre—Keweenawan felsic intru— sives, and pre-Keweenawan mafic intrusives. These groups display good continuity through the area and allow tentative correlation of rock bodies between geologic provinces. 7.1 km./sec. range. The St. Croix Horst and its flanking basins underlie the Midcontinent Gravity High and its parallel gravity lows north of Minn- Minimum throw along the western and eastern boundary fault zones reaches about 3.0 and 2.0 km. Sedimentary rocks in the Eastern eapolis. Basin reach a thickness of at least 2.6 km. A complex horst—like structure also underlies the Midcontinent Gravity High in southern Minnesota; an uplifted basaltic bady is bordered by sedimentary basins about 3.0 km. thick. Middle Keweenawan basalts are nresent lncilly in the Eastern and Western Basins underlying the Upper Keweenawan strata. Rocks probably equivalent to the Oronto Group are rare in the Western Basin, conmion in small basins on the St. Croix Horst, and abundant in the Eastern Basin. Rocks probably enulvalnt to the Bavfield Group are extensive in the Western and Eastern Basins, but they have not been found on the St. Croix Horst. The Bayfield Group seems to be several km. thick across Douglas County north of the Douglas Fault, and it does not appear to increase in thickness under the Bayfield Peninsula. �-29- 1. Department of Geology and G°oohystcs, University of Wisconsin, Madiqon Wisconsin, 53706. 2. Department of Geology, College of St. Thomas, St. Paul, Minnesota. 3. Department of Oceanography, Oregon State University, Corvallis, Oregon, 97331. 4. Chevron Oil Comnany. Houston. Texas. 77027. �-30ORE CONTROLS AND OPEN PIT GEOLOGICAL PROCEDURES AT STEEP ROCK IRON MINES LIMITED DAVID C. MULDER Steep Rock Iron Mines Limited, Atikokan, Ontario ABSTRACT The ore controls of the Middle Arm orebodies of the Steep Rock Iron Range have been well established as the result of an almost continuous programme of mapping, sampling, and development drilling from 1945 to the present time, during which period Steep Rock Iron Mines Limited has shipped a total of thirty—five million tons of ore. The remarkably uniform stratigraphic sequence of the Steep— rock Group, which lies within a sedimentary—volcanic sequence of Archean age, has proven to be the most useful ore control, particularly with regard to projections on the smaller scale. A major fault system strikes from 020 to 065 with steep dips mainly to the east; a minor fault system strikes a fairly consistent 115 with steep dips to the Both fault systems are of post—orezone age with the north and south. majority of the vertical and horizontal offsets ranging from 15 feet to Cross—cutting and conformable altered basic dykes of post— 60 feet. orezone age often occupy planes of weakness, such as faults and strati— graphic contacts, and are erratically distributed causing considerable dilution of high grade ore to crude ore in the mining process. Sill— fication of the Goethite Member is quite erratic on the larger scale, and produces a type of crude ore which is difficult to beneficiate. planning, The above ore controls play a very important role in pit Due to the complexity of both on the short and long term. the total geological picture, it is continually necessary to gather new data and reinterpret previous vertical projections. A major underground development drilling programme, which commenced in 1967 and is presently nearing completion, is establishing the position of the major geological contacts at the proposed ultimate pit elevation for pit planning purposes. Highly successful new techniques in drilling and identifying rubbly goethitic formations were developed during the early stages of this progranune. The drilling results provide an invaluable control when projecting the geology on the vertical plane below the present pit bottom. Experience has provided invaluable guidelines in the form of approximate limits of projection with relation Besides estimating reserves over the to allowable limits of error. long term, the Geology Department plays a vital role in controlling the recovery of ore during the daily mining operations. �-31-. KEWEENANWAN COPPER DEPOSITS IN TIlE ARCHEAN OF NORTHWESTERN ONTARIO by R. OJA Thunder Bay, Ontario AB ST RA CT A number of copper showings related to breccia zones in highly metamorphosed sedimentary rocks and in granitic gneisses have been discovered north of Lake Superior but south of the volcanic—sedimentary Leitth—Geraldton—Little Long Lac gold belt in Northwestern Ontario. Geological mapping and diamond drilling has been carried out at some of the more promising prospects. The mineralization, which occurs in breccia zones up to 150 feet wide, consists primarily of pyrite and chalcopyrite with small quantities of bornite. The breccia zones are seen to accompany both large and small fault zones. The largest fault zones are thought to cut both the late Keweenawan—Logan diabase sill as well as the Keweenawan sedimentary and volcanic formations of the Sibley and Osler series. �-32OF A GREENSTONE BELT IN MINNESOTA: RAINY LAKE TO LAKE OF T}E WOODS GEOLOGY Richard W. Ojakangas University of Minnesota, Duluth and Minnesota' Geological Survey ABSTRACT A poorly exposed greenstone belt located between Rainy Lake and Lake of the Woods is currently being explored actively by drilling. Outcrops are, in general, found only within fifteen miles of the Rainy River; the clays of Glacial Lake Agassiz cover the rest of the area. A generalized geologic map has been drawn on the bases of the limited .,outcrops, aeromagnetic maps, asd a gravity map furnished by IL Ikola. The structural trends and lithologic assemblages are similar to those in adjacent Canada (Fletcher and Irvine, 1955; Ontario Department of Mines Map 2115, 1967). Pillowed greenstones, felsic to intermediate metavolcarjics, metatuffs, and metasediments are the main rocks of the belt. Most bedding and foliation trends northeastward and dips steeply, and apparently reflects the limbs of major folds. Lineations in the metavolcanics, metatuffs, and metasediments generally plunge steeply to the southwest or northeast. Lineations in gneisses and granites have variable orientations. Outcrops exist on three zones of pillowed greenstone. One zone south of Bircbdale is apparently four miles wide and appears to lie within a northeast—trending syncline. Another zone just east of Clementson is less than a mile wide and appears to be on the southeastern flank of another northeast—trending syncline. The third zone trends east—west in the vicinitg of Indus and Manitou. Several small and large granitic plutons are present in the belt; all except a big body on Lake of the Woods contain abundant K-feldspar. The metamorphic grade of the metatuffs and metasediments is generally high; biotite and blue—green amphibole are common whereas chlorite is relatively scarce. Biotite—quartz—plagioclase schists, hornblende— quartz—plagioclase schists, and biotite-.hornblende—quartz—plagioclase schists are common. Hornblende—quartz—plagioclase gneisses are prevalent in the western and southern parts of the area near the larger plutons. �—33- The youngest rocks in the area are northwesterly trending dioritic dikes up to hoc wide. Some are intermittently exposed over a total distance of 65 miles in Minnesota and Ontario. These contain plagio— clase, bornblende, quartz, and opaques. ft. Minor gossans were observed in the field. Cores from holes drilled in the belt on state—owned land contain pyrite, pyrrhotite and minor chalcopyrite. These minerals are disseminated in the metavolcanics, inetatuffs and metasediments, and are massive in thin zones of black shale. Iron formation is associated with metasediments in the southeastern part of the area. References: Fletcher, 63rd 0 L., & Irvin, T. N., 1955, Geology of the Emo Area: Annual Report, Ontario Department of Mines, Part 5, 36 p. Ontario Department of Mines, 1967', Kenora—Fort Frances Sheet, Geologicaj Compilation Series, Map 2115. �-34EAIUJY PRECAMBRIAN GS)LOGY OF THE RAINY LAKE DISTRICT Z. E. PFTTEBIIAN U. S. Geological, Survey, Denver, Colorado 80225 S. S. GOLDICH Northern Illinois University, DeKalb, Illinois 60115 ABSTRACT Geologic relations of major rock units in the Rainy Lake region have been,.variously interpreted since the classic studies of A. C. Lawson around the turn of the century. Although radiometric dating has not resolved the controversy over the relative ages of the Keewatin and Coutchiching Series, many ages determined by different methods have provided some insight into the complex history of this region. Results of total rock Rb—Sr dating of major units in the area are summarized below: Unit Isochron4ge (ni.y'. I Initial Sr87/Sr86 Algoman Granites: Small stocks, Rainy Lake 2540 ± 90 0.7015 ± 0.0009 Vermilion Granite 2680 ± 95 0.7005 ± 0.0012 Keewatin Series 2595 ± 45 0.7005 ± 0.0009 Coutchiching Series 2625 ± 85 0.7011 ± 0.0023 Uncertainty represents the 95% confidence level Isochron ages for the Coutchiching and Keewatin Series probably register a metamorphic event since zircons from both units as well as from the Laurentian Granite gives ages of about 2750 m.y. as reported by S. H. Hart and G. L. Davis in 1969. The age of 2680 m.y. may represent the time of emplacement of the Vermilion Granite. Mineral ages of small stocks of Algoman Granite show discordances between biotite and muscovite. Three muscovites average 2650 m.y. whereas biotite ages are as low as 2150 xn.y. Loss of radiogenic strontium preferentially from the biotites may have lowered the total rack isochron. Older ages for the muscovites may approach the true time of emplacement for these granites. �-35STRUCTURAL AN!) METAMORPHIC HISTORY OF ThE MARQUETTE SYNCLINORIUM DR. C. McA. POWELL University of Cincinnati ABSTRACT The Menominee Group of the early Proterozoic Marquette Synclinorium is composed of three formattons: the Ajibik Quartzite grades conformably upwards into the Siamo Slate which by stratigraphic transition and inter— digitation passes into the overlying Negaunee Iron Formation. Structural analysis of the Siamo Slate reveals two periods of deformation. The first deformation, was the more intense, and produced the main east— west folds, and was accompanied by development of a quasi—vertical slaty cleavage. Tabular sandstone dykes and thin pelitic foliae intruded parallel to the cleavage during deformation indicate that the cleavage formed when the sediments were only partially lithified. Fb deformation continued after cleavage formation, and rotation of the more competent psainmitic beds accompanied by plastic deformation in the interbedded pelitic layers produced refraction of cleavage. Little or no heat accompanied the F1deformation. Subsequent to Fb the Marquette Synclinorium was affected by thermal metamorphism of regional extent. Isograds centered on a sillimanite— grade node near Republic cut obliquely across the Ft structures. Relict diagenetic textures and structures including overgrowths on rounded quartz grains are preserved in all metamorphic facies as high as the staurolite facies near the western end of the Marquette Synclinorium. In the lower metamorphic grades, the banding produced by intrusive pelitic cleavage foliae is accentuated owing to reconstitution of the intrafolial phyllosilicates and migration of silica into the interfolial At higher grades crystallization of more randomly oriented lenses. phyllosilicates has reduced the microscopic banding, and many of the large, overgrown, detrital quartz grains have polygonized into smaller equidimensional grains. The regional metamorphism involved thermal recrystallization only, and did not produce preferred dimensional orientation of quartz. A weak deformation, I after the climax of the thermal metamorphism produced a steeply plunging, crenulation lineation, La, and a few open angular folds. Pennine chlorite was developed later in many of the rocks during widespread retrogressive metamorphism. �-36IS THE LIMESTONE MOUNTAIN STRUCTURE AN ASTROBLEME? W. F. READ Lawrence University ABSTRACT Limestone Michigan. Mountain is located about 10 miles WNW of Baraga, The term "Limestone Mountain structure" is here used to include, not just the "mountain" itself, but flso Sherman Hill, another Ordovician disturbed outlier about 2 miles to the northeast,:.artd.an:jarea of Jacobsville sandstone a mile and Hill. a half south of Sherman Exposures are limited due to abundance of glacial drift. If the structure has a center, i€s location is not revealed by known exoosures, Ellis Roberts (1940) and Thwaites (1943) attributed the deformation here to a major fault striking NE, Bucner put Limestone Mountain on the TectonicMap of the United Stites (l9e4) a&.a possible 'cryptovolcanic structure!. If the structure is considered as an astrobleme, then the Ordovician outliers presumably belong to an encircling graben or downwarp. Limestone Mountain is, in general, a syncline, but with much cross— faulting and other complexities, In Sherman Hill, the limestone (actually dolomite), though perhaps slightly synclinal, is nearly flatlying. Joints are so numerous in both places as to give the rock a "shattered" appearance. Thin The disturbed Jacobsville exhibits both folding and faulting. sections show grains of quartz and feldspar with microstructures similar to those found in quartz and feldspar from generally accepted astroblemes. However it cannot be said with certainty that the Jacobsville here has been Ishocked. No shatter cones or breccia dikes have yet been found. Available gravity and magnetic readings suggest structural complexity in the area but do not particularly favor either the astrobleme or the NE—trending..fault hypothesis, �-37.ARCHAEAN VOLCANIC STRATIGRAPHY OF THE KIRKLAND-LARDER LAKES AREA OF NORTHEASTERN ONTARIO R. H. RIDLER University of Western Ontario ABSTRACT The Archaean volcano—sedimentary complex of the Kirkland— Larder Lakes area has served as a tectonic—stratigraphic model in the Superior Province for over thirty years. Traditionally, an older, predominantly volcanic sequence, the Keewatin, is separated by a pronounced angular unconformity equivalent to the Laurentian orogenic epoch from a younger predominantly sedimentary sequence, the Timislcaniing. The Timiskaming complex also includes a suite of hyperalkaline igneous rocks unique in the Superior Province (Cooke and Moorhouse, 1969; Roscoe, 1965). The accessibility, mineral wealth and geological complexity have encouraged so much geological study that the area ranks as one of the best mapped in the Superior Province (Thomson, 1948). Recent volcano—stratigraphic studies (Ridler, 1969 — 1970), suggest a revision of the classical stratigraphy into a succession of three maf Ic to salic volcanic cycles (Fig. 1). The Tirniskaming volcanic complex (Fig. 1) represents the salicvolcanic culmination of the second cycle. Thus, the Tirniskaniing complex is not only preceded but also followed by volcanics traditionally classified as "Keewatin". Further, a major volcanic centre co—axial with the Lebel Syenite is recognized and correlated closely with the salic phase of the second cycle. Typical Archaean volcano—genic ,sediments associated with this centre include several fades of exhalative iron formation. The volcanic rocks within a few miles of Kirkland Lake tend to be anomalously alkaline and sub-siliceous compared to Archaean calc— alkaline suites. Older, sub—alkalic tholeiites, andesites and dacites are succeeded gradually by under-saturated hyper-alkaline volcanics. Thus the uniquely alkaline volcanics of Timiskan:ing complex are preceded and presaged by a trend to potash enrichment. This overall increase in potash with time makes relative potash content a useful local index for correlation. In place of the traditional concept of a pre—Timiskamir.g orogeny followed by peneplanation, the author suggests a history of polyphase deformation consistent with the concept of a continuously evolving volcanic mobile belt. "Granjti" cobbles in Timiskazuing conglomerates record erosion of pre—Timiskaming hypabyssal plutons (Hewitt, 1963), during an early, geographically restricted, non-orogenic period of deformatlou. At least two periods of ductile deformation within the mobile belt followed Timiskaming sedimentation. �-38REFERENCES: Cooke, D. L., and Moorhouse, W. W., 1969, Timiskanting Volcanism in the Kirkland Lake Area, Ontario, C&ntada: Can. J. Earth Science, v. 6, no. 1, pp. 117—132. hewitt, I). F., 1963, The flmiskaming Series of the Kirkland Lake Area: Canadian Mineralogist, v. 7, pt. 3, pp. 497—522. Ridler, R. II., 1969, The Relationship of Mineralization to Volcanic Stratigraphy in the Kirkland Lake Area, Northeastern Ontario, Canada; Unpublished Ph.D. Thesis, U. of Wisconsin, Madison, p. 141. Ridler, R. II., 1970, Relationship of Mineralization to Volcanic Stra— tigraphy in the Kirkland—Larder Lakes Area, Ontario: Proc. Geol. Assoc. Can. v. 21, pp. (not known at this time). Roscoe, S. M., 1965, Geochemical and Isotopic Studies, Noranda and Matagaini Areas; Symposium on Strata—Bound Sulphides, Bull. Can. Inst. Mitt. Met. v. 58, no. 641, pp. 965—911. Thomson, J. E., 1948, Geology of Teck Township and Kenogami Lake Area: Ont. Dept. of Mines, Ann. Rept., v. 57, pt. 5, pp. 1—53. LiST OF iLLUSTRATIONS: Fig. 1 — idealized Stratigraphic Synthesis of the Kirkland Lake Area with folding removed. �BASALTS DACITE TUFF MAFIC LAVA COMPOSITIONS 2 I .4 TO RHYODACITE TRACHYT E LAVAS TUFFS ROUND 5,000' TUFFS LAKE BATHOLITH THOLEIITE 1,000'— PACAUD MINOR BASANITE PILLOW LAVAS THOLEIITIC PILLOW 6,900'— 28,000' BASALTS CATHARINE (BOSTON) MINOR TUFFS & BRECCIAS ANDESITE 0' — 23,000' SKEAD (McELROY) PYPOCLASTICSIf ALL BASALTS 0"— 34,000 MCVITTIE TRACHYTE, SYENITE CONGLOMERATE, GREYWACKE I000— II. 000' TIMISICAMING MINOR I PILLOW LAVAS I O'—SOOO' THOLEIITIC ANDESITES HIGHWAY II oa COMPLEX TUFFS -2--a IRON FORMATION GREYWACIC E 7 C C-) IRON F0RMA1ON .,,,— SUL PHIDE (Co) — eoUSoOM"".%,, — SILL C LOCALLY\ ______"" C,., SHEARED CONTACT ( 40) DIFFERENTIATED -J a EsITE01hhhhhhih1IIiIIIIIIIIIIIIIIII'0: •'.'9.y':t :1:;::oo Fe _,,OXIOE 7 AREA WITH FOLDING REMOVED KIRKLAND LAKE _____ OF THE __________ IDEALIZED STRATIGRAPHIC SYNTHESIS ______ — ARCHEAN LOWER 'ST CYCLE ARCHE AN MIODLE 2ND CYCLE RCHEAN UPPER 3RD CYCLE — NJ (S A x2o R.H. RIDLER,; Figure I (5 -- ----' th -O —I C) rn (-3 r r r C) —I —I Ca) r —I Ca, r 0-O 0 z 0 -q 1>± '1 fl �-4O- A ULASSiIUAflCbi 0 GRAiCLI'IU aQUKS iJITh Rthu Pu GIANTS RAP.G JIATHOLITFI, N.iRThiRi L'LIJ'1'A5UTA S. i'iinnsota Goniogical thrvey, University : rliniiu rmth 24inneapolis, Minnesota 55455 A B S T it A U P Figure 1 shows a clnsification or granitic and relate6 roc Vavo'ired by many field geologists. The inadequacy of this scherac and some of its flaws became apparent while investigating granitic rocks from the western part of the Giants -Range tatholith (Algn:nj in Northern iinnesota. For example, rocks which plotted in Uc acianollitc: field were found to lack the characteristics of ar udarncllite: their plagioclases+ were aibite rathor than olioclae, and their muscovite conthnt was as high as 10 percent iiistrd of Lei.nj insignificant. A revised classification proposed in this paper, :il'own in Figaro 2, differs substantiaaly iron the other erie, zln(i. mainly as follows: (1) The edamelllte field is compressed, and the upper limit of its quartz content fixed at 30 percent as against 50 percent. chane is made lecause adamellites that plot below the 10 quartz level (Group 1 adamollites) arid those that plot above the 30 percent quartz level (Group 2 a1ameilites) show the This percent followinj important petrographic differences: 1 adamel.lites but rniy be present in amounts as hih as (a) muscovite is rare in Group 10 percent in Group 2 adamellites, (b) plagioclase in Group 1 gonorally ãdaraellites is more caicic than that in Group 2 adameilites, aid (c) non—opaque dalcic trace minerals (sphene, enidote, apatite) in Group 1 adat;iellites total more than 1 percent, whereas Group 2 generally have a substantially lo'er content of those trace minerals. adarnellitos (2) The granite Itoh is extended not only laterally to incJ1xie the Group 2 ádarnellites, tat also vertically upto the 61) ercent quartz level. �—41- (3) The upper liimit of 30 percent quartz fixed for the adFwellite field is extended towards the Flagioclase-Quartz jnin and the Alkali feldspar—unrtz join; thereby, the granodiorite, tonalito and l'ranite fields of the classification shown in Figure 1 have teen sub—divided into the granodiorite (c30 percent quartz)—quartz granodiorite S>'30 percent quartz), tonalite (<30 percent quartz)—quartz tonalitc (>30 percent quartz) and the syehogranite c30 percent. quartz)—.rarito (>30 percent quartz) fields. Although one cannot assert that feldenar types rt:vc'nl the tectn:ic ,;rouping of c'r&tites, a correlatioji betweezi In the Yeldspar tyne as well as colour, One could thus have niodified root the the noenc1ature of granites, therefore, it ainrals. two scouts to oxist. is desiratl to izLlicvte text,'ire, alteration, a;.d Qccassory ncuavz like calcic oligoclasegranit&', "microcline—albite—granite", "nicroclinc— "orthocla;..e— ic olloc1ase—gran ite", etc. In general terms, these three inodif led root names are correlatable with synkineinatic, late— kineina tic, and pos t-.kiueina tic grani tes, respectively. ml crocline—calc An application of the revised classification combined wit!' 'idd osorvations has enabled no to recognize twelve distinctiv major rock. units in the western part ot' the Giants Rane batholith where only t.wo principal units were distinguished previously. adjacent areas of the lake Superior region, and elsewhere, needs to Le Its applicability to tested. �-42Figure 1 U1ir;siVication of granitic and relatwi rock; favotred by ninny flr!1c1 geoio:ists; it is Lased on the modes of quartz, K—Yeldspar and plagic— c1are rocalcuin ted to 100 percent. Quartz 50 50 Granite iorite Adainelli te 10 ite I $srcniod ion te -feldspar 33 67 90 rlairc �-43- Fjgire 2 The revised classification; it is based on the modes of alkali feldspar, plagioclase and quartz recalculated to 100 percent. Quartz 90 90 Quartz 60 Granite 30 30 Syeriograni te Adarne lute Granodiorite 10 In /sY 10 'eld;par includes dhite — An0..5) 35 65 P1 (An( �—44— GEOLOGY OF TEE ALKALIC ROCK — CARBONATITE COMPLEX AT PRAIRIE LAKE, ONTARIO DAVID H. WATKINSON Department of Geology University of Toronto ABSTRACT The Prairie Lake complex of ijolitic rocks and carbonatite (age: 1112 million years) is intrusive into granitic gneisses 25 miles northwest of Marathon, Ontario. The complex has positive relief, is somewhat circular in plan, and is composed of concentric arrangements — of carbonatites and rocks of the pyroxenite — melteigite — urtite series. The latter series has two culminations: nepheline— rich rocks characterized by melanite, wollastonite and alkali feldspar with interstitial calcite and nepheline —feldspar intergrowths; and Pyroxenitic pyroxene—rich rocks characterized by magnetite and biotite. The rocks are often separated from carbonatite by micaceous zones. carbonatites are strongly banded with near—vertical dips; banding is Most a consequence of biotite and olivine + magnetite concentrations. carbonatites are calcite—rich, but some are dolomitic and breccias Pyrochlore is with groundmass dolomite intrude the calcitic rocks. common in the carbonatites and in calcite—rich interstices and lenses in pyroxenites. In some zones pyrochlore contains as much as 30 weight Z U3O. Some fenitized country—rock occurs at the contact with The complex is interpreted to have formed by intrusions carbonatite. of magmas generated by strong differentiation of a carbonated, neph— elinitic parent. ijolite �—45— EVIDENCE FOR A TROPICAL CLIMATE AND OXYGENIC ATMOSPHERE IN UPPER HURONIAN ROCKS OF THE RAWHIDE LAKE - FLACK LAKE AREA, ONTARIO JOHN WOOD Department of Geology University of Western Ontario ABSTRACT The upper Huronian of the Rawhide Lake-Flack Lake Area Ontario is comprised of four formations - the Gowganda, Lorrain, Cordon Lake and Bar River, in ascending stratigraphic order. The Gowganda Formation consists of orthoconglomerates (with clasts up to 2 metres in diarqeter), paraconglomerates, graded greywackes, finely banded siltstones, finely banded arkoses (with dropped stones), and massive arko ses. The Lorrain Formation can be divided into three parts. Rocks in the lower part, although variable in grain size and colour, are all arkosic. Feldspar (both sodic and potassic) is fresh near the base, but towards the top becomes progressively more weathered until only pseudomorphs are visible. Diaspore, kaolinite,and pyrophyllite are present at the top of the lower unit and at the base of the middle unit. Concentrations of heavy minerals including hematite and U/Th minerals are associated with these aluminous minerals. The middle Lorrain is a sequence of interbedded kaoliniti quartzites and quartz jasper pebble conglomerates, while the upper Lorrain is essentially an orthoquartzite sequence. Feldspar is not present in the middle or upper parts of the Lorrain Formation. In contrast rocks of the Gordon Lake Formation are quite feldspathic and much finer grained. Van-coloured quartzo-feldspathic siltstones and shales with intraformational breccias are the dominant rock types. Chert is present near the bottom and top of the formation while gypsum and anhydrite are concentrated in the lower parts. Authigenic hematite and hematite ooliths occur in the middle and upper parts of the formation. Ripple marks and shrinkage cracks are present throughout. The Bar River Formation consists essentially of cross-bedded orthoquartzites (often cemented by hematite), with some interbedded siltstones. The ltter who contain shrinkage cracks are ripple marked, and include many small scale sedimentary intrusions. Most geologists who have studied sediments of the Cowganda Formation have concludea that these rocks were deposited during a frigid climatic regime. Accepting their conclusions and using feldspars as indicators of climatic conditions, there would appear to have been a rapid aninelioration of climate while sediments of the lower Lorrain Formationwere being deposited. Diaspore and kaolinite are considered to be the products of 'in situ' feldspar alteration under tropical climatic conditions. The presence of kaolinite and pyrophyllite in drill-core samples from -3,500 feet rule out a late surface weathering origin for these minerals. This change from frigid to tropical conditions is represented in a stratigraphic thickness of 160 metres. These tropical conditions persisted while sediments �—46— of the middle and upper Lorrain Fottuation were being laid down. The clatic hematite beds in the Lorrain Formation, the hematite ooliths in the Gordon Lake Formation and the hematite cement in the Bar River orthoquartaites, together with the presence of suiphates in the Gordon Lakc Formation, are indicative of an oxidising atmosphere in upper Ruronian times. This conclusion is important in relation to uranium exploration. The chert, aniaydrite, gypsum, and hematite as well as demonstrating conditions of chemical sedimentation provide nvre evidence for proposed correlations of upper Ruronian rocks with those of the Animikie Series Marquette Range Supergroup of Michigan. Postulation of a tropical climatic regime during deposition of part of the upper Huronian sequence removes one of the previous barriers to this correlation, for previously only frigid climatic regimes have been documented in the Ruronian, while the ferruginous sediments of Michigan were considered to have been deposited pnder tropical or sub-tropical conditions (James et al.). REFERENCES Frarey, M. J. 1966. Discussion: Huronian stratigraphy of the McGregor Bay area, Ontario: Relevance to the paleogeography of the Lake Superior region, by Grant N. Young. Can. J. Earth Sci. 3, 997. James, H. L., Clark, L. D., Lamey, C. A, and Pttijohn, F. J. 1961. Geology of central Dickinson County,+Michigan, U.Sk Geol. Surv. profess. Papers, 310; �—47-- WIDESPREAD OCCURRENCE OF ALUMINOUS MINERALS IN APH.EBIAN QUA.RTZITES GRANT M. YOUNG of Geology University of Western Ontario Department ABSIRACT After the conclusion of the world-wide Kenoran thermo-tectonic events (Ca. 2.5 b.y. ago) there was development of the first extensively preserved stable shelf assemblages of the geological record. Rocks of this type were first studied in Canada in the region north of Lake Huron by Murray. (1849) and Logan and Sterry Hunt (1855). The Huronian succession includes several polyrnictic conglomerates which have been interpreted as glacial deposits. The youngest of these conglomerates (Gowganda Formation) is thick and extensive and has recently been considered correlative with other early Proterozoic (Aphebian) tillites in a large area extending from S.E. Wyoming to the Keewatin District of the N.W.T. (Young, in press). The upper stratitified unit of the Gowganda Formation is overlain by a thick (5-6,000 ft.) quartzite formation (Lorrain) that is also very extensive. Many different subdivisions of this unit have been proposed, but on a regional scale, a threefold subdivision seems most reasonable. The lowest subdivision is a varicoloured (red, white and green) succession of felspathic grits and sandstones. This is followed by a unit charac— tensed by the presence of quartz and jasper pebble conglomerates and the uppermost unit is an extremely pure orthoquartzite. In many areas the middle unit and the lower.part of the upper unit contain aluminous minerals such as kaolinite, diaspore, pyrophyllite, kyanite and andalusite (Church, 1967; Chandler et al., 1969). These minerals are thought to represent an in situ weathering (bauxitization) process which occurred shortly after deposition and gave rise to kaolinite which wa.s later changed by further diagenesis and metamorphism to the other minerals listed above. The reasons for invoking this mode of origin rather than origin by deposition of "primary" kaolinite at the time of sedimentation or by late post depositional weathering are as follows: - 1. Fresh felspars are abundant in other Huronian outcrops. 2. The kaolinite commonly occurs as "clots" of the same order of size as the associated quartz grains, suggesting that each clot represents an altered felspar grain. 3. It is difficult to envisage the conditions under which fine Jcaolinitic crystals could be sedimented together with coarse quartz grains (see Ojakangas, 1965, for discussion of the same problem in Jatulian quartzites of Finland). 4. In some sections metamorphic minerals may be seen developing from kaolinite. �—48— Aluminous minerals similar to those of the Lorrain Formation occpr in quartzites in the lower part of the Animikie "Series" = Marquette Range Supergroup (Church and Young, in press) of the south shore of Lake Superior (Keyes Lake quartzite, Sturgeon quartzite, Ajibik quartzite and Breakwater quartzite). Kaolinite is also present in the Baraboo and Barron quartzites of Wisconsin and pyrophyllite and diaspore were reported from the Sioux quartzite of Minnesota and South Dakota (Berg, 1931). Kyanite is present in the Medicine Peak Quartzite of S.E. Wyoming, the Petaca Schist of New Mexico and kaolinite, andalusite and diaspore have been found in the Hurwitz C quartzites of the Keewatin District of N.W.T. Bimodal size distribution in many of these quartzites may indicate that much of the clastic material was wind transported prior to sedimentation in an aqueous medium (Folk, 1968). Similar aluminous quartzites of similar age from other continents include those of Finland (Jatulian quartzites), Brazil (Jacobina Series), India (Iron Ore Series) and South Africa (Witwatersrand System). Some of these extremely widespread quartzites may be deposits formed as a result of post-glacial transgression. If the formation of kaolinite in the quartzites took place under climatic conditions similar to those unde,r which present day bauxites and laterites are formed, there must have been a significant amelioration of climate following deposition of the Cowganda Formation and its possible correlatives. REF ERENCES Berg, B. L. 1937. An occurrence of diaspore in quartzite. .v. 22, pp. 997—999. Amer. Mineralogists Church, W. R. 1967. The occurrence of kyanite, andalusite and kaolinite in Lower Proterozoic (Ruronian) rocks of Odtario (abst.) Tech. Prog. Geol. Assoc. Can. Meet. Kingston, Ontario, pp. 14-15. ft. and Young, C. M. (in press). Discussion of the Progress report of the Federal-Provincial Committee on Huronian stratigraphy. Church, W. Can. J. Earth Sc. v. 7. Folk, Bimodal süpermature sandstones: product of the desert R. L. 1968. flc,or. XXIII International Geological Congress Section 8; Genesis and Classification of Sedimentary Rocks. pp. 9-32. Logan, W. B. and Sterry Hunt, H. T. 1855. Esquisse geologique du Canada. Bossange et fils, Paris. 100 pp. Murray, Alexander. 1849. On the north coast of Lake Huron. Canada, Rept. Prog. pp. 93-124. Geol. Surv. Ojakangas, R. W. 1965. Petrography arid sedimentation of the Precambrian Jatulian quartzitesof Finland. Bull. Comm. Geol. Finlande. No. 214, 74 pp. Young, G. M. (in press). An extensive Early Proterozoie glaciation in North America? Palaeogeog. Palaeoclimat. Palaeoecol. �—49— PROTEROZOIC ROCKS IN THE THUNDER BAY AREA May 9, 1970 Prepared by. J. M. Franklin, Lakehead University, Thunder Bay CR. Kustra, Ontario Department of Mines, Thunder Bay �— 50A— lOji 1 (a): Microfossils in Gunflint chert from shore of Lake Superior near Schreiber, Ontario; spheroids are Huroniospora, filaments are Gunflintia. 1 (b): Side view of a weathered block of Sibley stromatolites; note polygonal columns of Conopiyton. Plate 1. �—51— Guide to the Proterozoic Rocks of the Northwestern Lake Superior Area, Ontario INTRODUCTtON: The Froterozoic rocks of Northwestern Ontario, which form part of the "Animikie" and Keweenawan unit; represent one of the most complete geological records of middle and late Proterozoic sedimentation and igneous activity in eastern North America. These rocks are virtually uninetamorphosed and only slightly deformed. Mineral deposits in these Proterozoic rocks include silver in Keweenawan dykes and the Rove Formation, iron in the Gunf lint Formation, nickel in mafic intrusive rocks, copper in various volcanic and sedimentary strata, and lead-zinc-barite associated with the Sibley Group. During the last century, the famous Silver Islet mine Currently, a minor produced over three million dollars in silver. amount of silver is recovered from the Creswel mine near Stanley (Fig. 1). GENERAL GEOLOGY The Proterozoic rocks lie unconforinably on the peneplained Archean surface. Archean meta volcanic and meta sedimentary rocks form a "belt" extending from west of Shebandowan to Thunder Bay city. Another similar belt crops out in the Schreiber—Big Duck Lake area To the north, the Geraldton-Beardmore belt may be (Pye, 1964). traced westward by aeromagnetic interpretation under Lake Nipigon, and may possibly join with the Lac Des Mille Lacs—Atikokan belts. The remainder of Archean outcrop is composed of intrusive and metamorphic granitic rocks, and small ultrainafic bodies. The Proterozoic rocks are subdivided as shown - Proterozoic in Table 1. TABLE 1 — Stratigraphy of Northwestern Ontario Neohelikian basalt, minor rhyolite and sedimentary rocks Osler Group: gabbro plugs Intrusive rocks: undersaturated plugs layered bodies northeast trending dykes Logan diabase sills Paleohelikian red beds, stromatolite zone Sibley Group: Apheb ian Animikie Group Rove Formation: shale iron formation Gunf lint FormatioB: �—52— APHEB IAN The Gunflint Formation (Figs. 1*, 3, 4, 5) has been studied in detail by Goodwin (1956) and Moorhouse (1960), the Rove Formation by Morey (1967). Much of the descriptive detail is taken from these authors. Gunf lint Formation (adapted from Goodwin, 1956) Deposition of the Gunflint Formation was in part cyclical. A basal conglomerate member is overlain by two members each composed of chert, tuffaceous shale, and carbonate—taconite submembers. These members are in turn overlain by a discontinuous limestone member, (Fig. 2 and Table 2). The Gunf lint Formation was deposited 1635±24 million years ago (Faure and ICovach, 1969). -TABLE 2Stratigraphy of the Gunf lint Formation (modified from Goodwin 1956) Limestone—dolomite member Upper Member Taconite—chert carbonate submember; taconite (west) fades chert carbonate (east) facies Tuffaceous shale submember Algal chert submember Lower Member Taconite—chert carbonate submember; west taconite facies chert carbonate facies east taconite facies Tuffaceous shale submember Algal chert submember ICakabeka conglomerate member (a) Basal ICakabeka Conglomerate Member This member ranges to five feet in thickness and is composed of polymictic conglomerate. Clasts of Archean volcanic rocks and granite are cemented in a matrix of chlorite and quartz. The unit is discontinuous but persistent. (b) Lower Member The lower algal chert submember (Fig. 2) consists of reef—like mounds of finely banded black, red, and white oolite chert. These mounds are intergrown or cemented in dolomite. This submember forms the western margin of Gunf lint outcrop (Fig. 1), but is continuous only to the west of ICakabeka Falls. It contains abundant microflora remains (Baarghorn and Tyler, 1965) (Plate la). The lower tuffaceous shale submember ranges to 20 feet thick and overlies the lower algal chert in the area west of ICakabeka Falls is composed of fissile black shale containing much volcanic ash. * see back cover �Fig. 2 (4) f WEST STOPS DESCRIBED IN FIELD GUiDE S S s S a • S.... • S S S S S S • • s S S S r.sSsSSSSSSSSSS S S S S S S S S S S S 55*55 SS S S S s—c2j S 5555 SSSS S SS SS S S . .. . S S S s S S S S S s S S S CONGLOMERATE MEMBER S S S S S S S S 10 S .5 A'A/(ABE/(A S S S 0 S * — SCALE — S S • S S S S • • a S • S 0 MILES S S S S . S S S S S S EAST s CHERT S S •S S • S . 5,S THUNDER BAY S S S S .. . . S S 5SS • S... LOWER CHERT 55 SS 55 555 sSS SSS SSS * S 5555 • . Longitudinal section of the Gunflint formation (after Goodwin, 1956). 0 • S , •*,S5S5555çry_)r,.....%4__,__ * • S S • S S S S 5 S S S • S 55 5 S S S • S S S S S 5 S S S 5 S • S • 5 S S S • S 555S S S S S S S VERY. SCALE 0 50 100 150 TACONITE S S CARBONATE'Ø',, S S S EAST S S S S �0 0 Vs $ $1 FIIiIIIIllllh1 I DD o Z:f 0 D 00 ________ ____ _______ ______ 0 GROUP SHALE FAULT 5,_q_ s 0 0 c_;--s $ 0 0 0'• 0 0 0 o 0 0 ".4 0 0 D. $ $ 0 $ 0 S S $ $ o o $ D_.,'0 4 0 2 o 0 0 0 / 0 s 0 $ Q D $ D' o_0:5 $ r' 0 o s a $ 0 $ $ :2 So D" ' .-rb;s --3:q4?$ sç '1:1 $ $ 0 C' :ç -0 S_'o -;'P--_Y\ ' •:c -4-'J---; S_ _)0 SCDP.a.',., .0 0 __oj") ,, :t-' ;c_ o Aa 0 o $ i___D S r S $ 0roc;_2——_1 ts,?— DDt5 Figure 3. ARGIL LUTE — TUFF METAVOLC ANI CS Di,' o'Do:s - $ D;s;% D'D 'o D DJD FORMATION p1 NETASEDIMENTS SIOLEY ROVE GRANITE GUNFLINT E —' D LEG 0 0 0 S $ $ S $ $ S _ S $ $ -I— * —p S - V V V p p p p p p q . p p w ('I p �V V V - ç.V V V V V -% 1 0 E SHALE FORMATION LE METASEGISENTS ROVE GRANITE G UNFLINT BAY THUNDER 1--'-' -# -— +% V V V. — ;—=- — —-- N D — -S — — -r — ________ GROUP FAULT ARGILLITE — lUFF SIBLEY — — —z-—_ . a 84Y -4± -1-4- -47,V - -4-\ 2 V V V V V V VV :_€ - >V V 1 4n, -4- -F' + ±4-tt -4- -fr —4- -i-, r -1--P--f-' —I. * — r — -—_ :—:-=-_-7-+- + —-—'t-4-f--i-f-i± -I- cV j-E rH0t'° _rt V — - —I1— .AxE 55. -f 4 - -t — SCALE — 4 MILES C) a' N �' Figure 5. g0 If ii I' I, 'So ci 1 ;1 1 0 D D D D %D D 0 0 0 D -L ......................+...., .:cc•:c:c>>>C4 D DDDD _____' cFLAKE STEWARD BAY BLACK ;-i, /IY '%....L(...:- 2 a - SCALE — 0 4 MILES s-s— ÷÷+ ++ I DØDD1 D GROUP D —— FAULT ARGILLITE — lUFF SI8LEY GRANITE DIASASE LEGEND o D i of DD) :;D3_.ts �—53— The uppermost submember of the lower member is subdivided into three facies (Fig. 2). The lower west taconite fades, which is 150 feet thick, extends northeastward from Gunf lint Lake to Kakabeka Falls, is composed of wavy—banded granular chert, carbonate, and The lower half contains disseminated greenalite granules oxides. in pale grey chert; siderite forms local beds. The upper half contains increasing amounts of hematite and magnetite. This fades grades upward into jaspilitic upper algal chert and grades laterally into the lower banded chert—carbonate facies. The lower banded chert—carbonate facies extends from Kakabeka Falls to Thunder Bay city, and consists of 4 to 6 inch siderite beds, with interbedded 2 to 6 inch grey cherty beds. Carbonaceous material and pyrite are common in shale interbeds. This facies grades into granular taconite towards the northeast. The lower east granular taconite fades extends from Thunder Bay city to Loon Lake. The basal 2 to 6 feet are formed of inter— The upper 10 to 20 feet consist bedded granular chert and ankerite. of interbedded red to green mottled chert and dolomitic limestone. This facies grades upward into the tuffaceous shale submember of the upper member. (c) Upper Member The upper algal chert submember extends west from Nolalu to Gunf lint Lake and consists of basal granular chert overlain by algal chert and, in the Mink Mountain area, amygdular basalt flows. The flow and algal chert are overlain in turn by granular chert and bedJasper beds grade into tuffaceous shale of the overlying ded jasper. submember. The tipper tuffaceous shale is the only continuous submember in the Gunf lint Formation and forms a key stratigraphic marker (Figs. It ranges to 100 feet thick and thins laterally in either 3, 4). direction from Kakabeka Falls. It consists of black tuffaceous shale and siltstone with interbedded siderite and pyrite and extensive beds The ash contains ellipsoidal structures which of volcanic ash. resemble mudballs and are composed of concentric layers of small angular tuff fragments, arranged about a larger central fragment. The upper tuffaceous shale submember grades into the upper tac— The upper taconite facies onite and banded chert—carbonate submember. extends from Gunf lint Lake to the City of Thunder Bay (Fig. 2), and is composed of wavy bands of granular greenalite—bearing chert. The greenalite—bearing granules are round to oval, evenly distributed throughout a layer, and appear to have formed "in situ". The unit exibits a rusty weathering, contains abundant hematite and magnetite in granules towards the top, and grades laterally (Fig. 2) into the upper banded chert—carbonate facies which extends from west of Thunder Bay city to Loon Lake. The latter facies consists of interbedded The carbonate consists of siderite grey chart and brown carbonate. Brecciation and folding, apparently with lesser dolomite and ankerite. contemporaneous with deposition, are common. �—54— (d) Upper Limestone Member The upper limestone member marks the top of the Gunf lint Formation. Minor chert beds, illite and volcanic shards are present, and tuffaceous shale is most prevalent in the eastern area of Gunf lint outcrop. Stratigraphic Interpretation Goodwin (1956) concluded that Gunf lint deposition occurred in a shallow basin which had limited circulation with an open sea. After initial algal activity in the neritic zone, volcanic activity (tuff— argillite) was accompanied by sinking of the basin. Silicate—bearing material (taconite) was deposited in the deepest portions while in the neritic, or intertidal zone (between Kakabeka Falls and Thunder Bay city) banded chert—carbonate formed. Further to the northeast, the lower east taconite facies formed in agitated, oxygenated, waters. As the basin filled, conditions of algal growth returned, initiating the "Upper Gunf lint?' cycle. Volcanic activity, marked by local basalt flows and crustal unrest, terminated the upper algal chert deposition and resulted in widespread distribution of pyroclastics of the upper tuffaceous shale. Downwarp— ing resulted in.deposition of granular iron silicate rocks in the deeper, southwest portion of the basin, while on the shallow northeast shore, chert carbonate was deposited. As the basin filled, sporadic but violent volcanic activity was accompanied by entry of sea water, resulting in formation of the upper limestone member. Basinal sinking set the stage for deposition of the Rove shale. Goodwin (1956), in drawing an analogy with the Santorin volcano of the Aegean Sea, suggests that volcanism was the chief source of iron and silica. Alternatively, Rough (1958) suggests deposition in a fresh water basin, with material derived through weathering of adjacent landmass, and deposition controlled by limnie cycles. Clearly, re—evaluation of both ideas is necessary in light of recent data on both Santorin (Butozova, 1966) and bottom sedimentation studies in Lake Superior, (Nothersill, 1969). Rove Formation The Rove Formation conformably overlies the Gunf lint Formation and consists of up to 3200 feet of argillite and sandstone (Morey, 1967). Morey subdivides the Rove into three lithologic units, which are, in ascending order: (1) lower argillite, (2) transition sequence, and (3) thin—bedded greywacke. The Lower argillite is the dominantly exposed unit in Ontario and consists of grey to black highly fissile, thin-bedded, pyritic shale, with minor limestone and san4stone beds. Calcite and dolomite concretions are common near the base of this unit. The transition sequence consists of interbedded argillite and The topmost thin—bedded greywacke, consisting of grey to pink greywacke and sandstone, is the thickest unit of the Rove, and is exposed predominantly in northern Minnesota. sandstone. �—55— Morey notes that sediment transport was from the north and that material was derived from Archean granite, gneiss and greenstone. PALEOHELIKIAN Siby Group he Sibley Group is a red bed sequence, deposited 1298±33 million years ago (Rb—Sr whole rock isochron, Franklin, 1970) extending from the Sibley Peninsula north to Armstrong, Ontario, and east to Rossport. The seven units which compose the Sibley Group are (a) basal conglomerate (b) sandstone (c) sandy red muds tone (d) (e) chert—stromatolite limey red mudstone purple mudstone limestone (f) (g) Polymictic basal conglomerate lentils are most common on the Locally derived Gunf lint taconite western margin of Sibley outcrop. boulders are found where the Sibley overlies the Gunf lint, but gran— itic boulders prevail where the Sibley overlies Archean rock. Lentils range to 15 feet in thickness, and occur in pre—Sibley valleys. Cream, green, and pink sandstone forms the lowest semicontinuous unit of the Sibley Group, and attains a thickness in the basin margins of over 200 feet. Beds are poorly graded; ripple marks and cross beds are present throughout, but are common only in the eastern margin of sedimentation near Rossport. Beds are composed of 50 to 70 per cent quartz, up to 8 per cent chert, 5 per cent feldspar, and 5 per cent mica, cemented with calcite and minor barite. Syneresis cracks are common near Edward Island. At the top of the unit, interbedded sandstone and mudstone mark the beginning of the sandy red mudstone unit. The sandy red mudstone unit is composed of less than 50 per cent quartz and feldspar clasts, in a red hematite—carbonate—clay—feldspar Bedding is matrix, and ranges to 300 feet thick near Rossport. moderately well developed. Brecciation and soft—sediment folding are common in this unit; chaotic conglomerate lentils are exposed in the western margin of outcrop near Dorion. In the area south and east of Nipigon, the sandy red mudstone is separated from the limey red mudstone by a thin, but laterally continuous, chert unit. To the north and west of Nipigon a stro— matolite unit may occupy the same position. The stromatolites exposed 1 using l.47x10U yr. Rb87 decay constant; using l.39x1011 yr. constant, age is 1376±33 m.y. The latter may be compared with the date of Faure and Kovach (1969). �a —56— at Disraeli Lake and near Stewart Lake belong to the group Conophyton (Hoffman, 1969), formed of vuggy columnar "cone in cone" structures The chert facies ranges to 10 feet in thickness at Ross— (Plate lb). port, and is composed of finely laminated grey to black chert and brown dolomite. Anthraxolite, accumulations are common along the base of this unit. The overlying limey red mudstone contains less than 20 per cent coarse microcline with less than 2 per cent hematite. The clay expands itt ethylene glycol, and is a mixed layer chlorite—montmor— illonite, similar to corrensite (Peterson, 1961). The feldspar is very fine—grained (less than 10 p diameter) and is probably authigenic. The overlying purple mudstone unit is finely laminated, moderately but irregularly fissile, and is composed of approximately 40 per cent each of corrensite and microcline, with less than 4 per cent hematite, less than 15 per cent quartz, and minor calcite. Less than 10 per cent coarse clastic material is present in most of this unit. The uppermost limestone unit is grey to buff, poorly bedded, and crops out only north and west of Nipigon. The Sibley Group is distributed over both the edge of an older mobile belt (the Penokean orogenic deformation of Aphebian rocks) and the stable Archean craton. Deposition occurred in a basin restricted on the south and west by uplifted Aphebian rocks. A shallow, periodically dry, basin transgressed northward over the craton. Material was derived from both the Aphebian highlands and adjacent Archean granitic rocks in a semi—arid, warm environment, (Franklin, 1970). NEOHELIKIAN Osler Grçp Volcanic and sedimentary rocks of the Osler Group disconformably overlie the Sibley Group and are exposed on an arcuate belt of islands parallel to the shore of Lake Superior, and on Black Bay Peninsula (Ont. Dept. Mines Map 2137). The lavas are similar to those of the Portage Lake Lava Supergroup (DuBois, 1962) and are composed of thin, laterally extensive sheets of vesicular, tholeiitic flood basalt with minor interf low greywacke beds, & rhyolite (quartz porphyry) bodies. Intrusive Rocks The four types of intrusive rocks present in this area are as follows: Logan sills: laterally extensive thin diabase sheets, (a) cutting Archean, Aphebian, and Paleohelikian rocks northeast—trending gabbro dykes, parallel to the (b) shore of Lake Superior, extending from Pigeon Point to Edward Island �—57— layered mafic bodies, as at Great Lakes Nickel Company (c) property in Pardee Township dykes and associated stocks cutting all Helikian and (d) Aphebian rocks. The Coldwell syenite complex near Marathon is an undersaturated laccolith, similar in age to the other Helikian intrusive rocks (Pairbairn et al, 1959). STRUCTURE Structural deformation is limited to block faulting and regional tilting, imposed during and after Keweenawan intrusive and volcanic Two parallel major fracture or fault zones bound the block periods. of Aphebian and Paleohelikian rocks exposed in the northwestern Lake The most northerly of these is a steeply dipping Superior region. fracture zone, five miles in width extending from west of Whitefish Lake to east of Pass Lake. Dragfolding of sediments along faults suggests slight uplift of the southern side. The northern boundary is marked by a fracture zone which is occupied by the northeast— trending dyke set. The block between these faults has been slightly tilted, resulting .in a 3 to 5 degree dip of the sediments to the southeast. ACKNOWLEDGEMENT The authors wish to acknowledge the assistance of S. Spivak, who compiled and drafted the figures. S ELECT ED REFERENCES Baarghorn, D.S. & Tyler, S.A., 1965; Micro—organisms from the Gunf lint chert: Science, v. 147, p.563—577. Butuzova, G.Y., 1966; Iron ore sediments of the fumarole field of Santorin volcano, their composition and origin: (Zhelezorudngye osadki fumarol 'ngo polya vulkana Santorin, ikh sostav i genezis): Doklady Akad. Nauk., S.S.SR., v.168, no.6, p.1400—1402. DuBois, P.M., 1962 Paleomagnetism and correlation of Keweenawan rocks: Geol. Survey, Canada, Bull. 71. Fairbairn, B,W., Bullwinkel, 113., Pinson, W.B., & Burley, P.M., 1959; Age -investigation of syenites from Coldwell, Ontario: Proc. Geol. Assoc. Can., v.11, i'l4ll44. �—58— SELECTED REFERENCES Faure, G. & Kovach J., 1969; The age of the Gunf lint Iron Formation of the Animikie Series in Ontario, Canada. Ohio State University Laboratory for Isotope Geology and Geochemistry Contribution no. 8. Franklin, J. M., 1970; Metallogeny of the Proterozoic rocks of Thunder Bay District, Ontario, Ph.D., thesis, Unpublished., University of Western Ontario, London, Ontario. Goodwin, A.M., 1956; Facies relations in the Gunf lint Iron Formation: Econ. Geol., v.51, no.6, p. 505—595 Roffmaii, H.J.., 1969; Stromatolites from the Proterozoic Animikie, and Sibley Groups, Ontario: Geol. Survey, Canada, paper 68—69, Rough, J.L., 1958; Fresh—water environment of deposition of Precambrian banded iron formations: Jour. Seth Pet., v.28, no. 4, p.414—430. Moorehouse, W. W., 1960; Gunf lint Iron Range in the vicinity of Port Arthur: Ont. Dept. Mines, v.LXIX, pt.7, p.1—leO. Morey, G.B., 1967; Stratigraphy and sedimentology of the Middle Precambrian Rove formation in Jour. Sed. Pet., northeastern Minnesota. v.37, p.llS9—ll62. Mothersill, J. 5., 1969; A grain size analysis of longshore— bars and troughs, Lake Superior, Ont., Jour. Sed. Pet., v.39 no.4, p.l3l7—l324. Peterson, N.M.A., 1961; Expandable chloritic clay minerals from upper Mississippian carbonate rocks of the Cumberland plateau, in Tenn.: Am. Mineralogist, v.46, p.1745—1764. Pye, E. G., 1964; Mineral deposits of the Big Duck Lake area; Ont. Dept. Mines, Geol. Rept. no. 27. �—59— DESCRIPTION OF STOPS Mileage count begins west of Nolalu, a small community on Highway 590, approximately 35 miles southwest of Lakehead University, and may be reached via Highways 17—11, 588 and 590. Mileage 0.0 STOP 1 The exposure is located in the 1.8 miles west of Nolalu. bed of the Whitefish River, on the north side, approximately OO feet downstream from the bridge. LOWER GUNFLINT MEMBER, LOWER ALGAL CHERT UBMEMBER OVERLYING BASAL CONGLOMERATE AND ARCHEAN ASEMENT (FIG. 2) Lower algal chert in the shape of concretionary, cthuli— flower—like growths, forms an irregular, hummocky surface. It is underlain by a thin veneer of basal (Kakabeka) conglom— erate, resting unconformably upon metamorphosed, little weathered Archean granodiorite. The chert forms thiqly banded, white, red and black algal structures resembling piles of inverted thimbles; red, white and brown chert—hetnatite oolitic granules are dispersed within Fossil microflora occur in the darker, almost the structures. black, variety of chert. Note several exposures of -algal chert mounds in the area between the road and the river bank. 1.9 Co—op store, NolaLu. 2.4 Junction, Highways 588 and 590. 17.9 Turn north on Highway 590. Junction, Highways 590 and 17—11. Outcrop is the road cut 300 feet north of junction, west side of Highway 17—11. STOP .2a BASAL KAKABEKA CONGLOMERATE, LOWER ALGAL CHERT SUBMEMBER (FIG. 2). Basal conglomerate, grading-upward into reddish, lower algaL chert and granular chert, consists of pebbles of white quartz, chert and jasper set in a matrix of sandy quartz grains and minor carbonate (calcite). Near the north end oif the outcrop, the Gunf lint Formation is in fault contact with Archean granitic gneiss. �-bU- STOP 2b Road cut, west side of Highway 590, 250 feet south of junction and 500 feet south of stop 2a. UPPER CHERT-CARBONATE EAGlES (FIG. 2). Orange—brown weathered, banded chert—carbonate is inter— bedded with tuffaceous shale. 18.3 STOP .3 Entrance to kakabeka Falls Park. Proceed over old bridge to parking lot by Greenmantle restaurant, thence by foot to falls rim. UPPER TIJFFAGEOUS SHALE SUBHEMER (FIG. 2) Kakabeka Falls drop 128 feet intp a gorge formed in fissile, thinly bedded upper tuffaceous shale subinember (Goodwin, 1956). A more resistant, massive two—foot bed of thinly banded chevt—carbonate caps the escarpment. 18.7 Access road to Ontario Hydro station. Turn right just before Proceed to the parking lot by the the Kakabeka Falls motel. station, thence by foot to the west side of the plant, via a cat—walk over the penstock pipes. Follow the riverbank for approximately 600 feet to the spiliway cut. Beware of poison ivy. Be advised that permission to trespass the Hydro property must be obtained from the plant supervisor. The spiliway serves as a safety valve to bleed-off excess water in the event of generator failure at the power station. STOP 4 UPPER TUFFACEOUS SHALE SUBMENBER (FIG. 2) The best section of upper tuffaceous shale submember is exposed at this locality. Pyrite—bearing chert of the upper algal chert submember occurs at the base of the section; it is overlain by shale containing pyrite nodules and calcareous concretions, interbedded shale and tuff and a tap of thinly bedded upper chert—carbonate. One of the best exposures of "mud ball tuff" in the shale occurs near the bottom ofthe section; the tuff is formed of closely packed ellipsoidal structures, elongated along the Individual ellipsoids contain small, angular fragbedding. ments of uniform size, grouped concentrically around a larger The remainder of the materihl comprising the shard fragment:. beds consists of fragments of lava in a groundmass of a green, clay material. (Goodwin, 1956) �—6 P- Note downwarping of beds on the west side of the exposure and the fault filled with quartz—carbonate and anthraxolite. Return to Highway 17—11 and proceed east. 19.2 Junction Highways 17-11 and 590 north. Proceed on Highway 590 north. 29.0 Thunder Bay city limit, the Nor'westers, 30.1 Junction, Highways 590 and 130. 37.0 Lakehead University. 38.0 Intersection, High St. Good view of the mesa topography of Highway 590 ends. and Oliver Road (Highway 130) Turn left at the traffic lights and proceed up High Street. 38.6 STOP 5 Entrance to Hillcrest Park. UPPER LIMESTONE MEMBER (FIG. 2) Hillcrest Park. The park stands about 160 feet above the level of Lake Superior and offers a panoramic view of Thunder Bay harbour, the Sleeping Giant, the Welcome Islands, Pie Island and the Nor'westers. Dolomitic limestone and chert layers are exposed at the base of the flag pole and bell. Follow stairs to base of hill where the fragmental limestone of Goodwints upper limestone member is exposed. The rock consists of many angular to rounded chert fragments in a matrix of coarsely crystalline, iron—bearing carbonate, and thin chert Interbeds. Traces of volcanic shards and frag— ments occur in the limestone (Goodwin, 1956). Proceed north on High Street. 40.1 Intersection with Balsam St. 40.7 Huron St., 300 feet south of Highway 17—11. Huron St., then immediate left. Turn left on Balsam Street. Turn right on �—62— 42.1 Bridge over Current River, cross bridge, turn right into Boulevard Lake Park and proceed 0.3 miles; park on right side of road. Traverse begins on creek bed. STOP 6 LOWER CäERT-CAR.BONATE FACIES (FIG. 2) The lower chert-carbonate facies is overlain by the upper tuffaceous shale subñiember. An upstream traverse encounters ferrugineous carbonate, interrupted by thin layers and lenses of granular and algal chert, and dark, fissile shale. At the beginning of the traverse, note the rounded chert lenses showing concretionary structures, attributed to action of Please refrain from sampling some of the better prealgae. served structures. Features to observe include stylolite surfaces lined with anthraxolite, pyrite veinlets, imbrication of thin chert layers and the striking, weathered appearance of the rock. Under the bridge, a bed of gray, massive limestone, enclosing pancake—like lenses of serpentine material, and interrupted by a thin band of pyrite—bearing chert, is over— lain by upper tuffaceous shale. Note the humrnocky upper surface of the limestone at the shale-limestone interface. Several hundred feet north of the bridge, at the lookout, East of the bridge, in the a diabase sheet caps the shale. picnic area, several well developed river terraces are preserved. Prom bridge, proceed east along Arundel Street. Turn left on Hodder 43.1 Intersection, Arundel St. and Hodder Ave. Ave. at Hodder Avenue Hotel. 44.1 Highway 17—11, 44.7 Park car and Scenic lookout. View of Thunder Bay harbour. walk 500 feet east to roadcut, on north side of road. Exercise extreme caution. STOP 7 Turn right. UPPER LiMESTONE MEMBER OVEELAIN BY DIABASE Sill of Logan diabase overlies argillite and fragmental The contact is gently limestone of the upper limestone member. undulating and visible effects of contact metamorphism are In thin section, however, a microporphyroblastic little evident. texture is developed in the argillite. Pyrite is altered to pyrrhotite. �—63— Note the lenticular chert patches within the limestone, some veined with pyrrhotite, exhibiting agate textures. Turn right. 46.1 highway BOO. 47.5 highway 17-11 (Nipigon highway). 66.1 Blende Creek. The outcrop is situated 200 feet northwest of the highway and is accessible by a dirt road +located approximately 0.7 miles southwest of the intersection of Highway 17—11 with Highway 587. STOP S Turn left. UPPER CHERT-CARBONATE FACIES (FIG. 2) Regularly bedded upper chert-carbonate is interbedded with thin, fissile tuffaceous shale and underlain by cross— bedded to massive greywacke. The severe drag folding of the chert-carbonate beds on the northwest side of the outcrop is a manifestation of a regional fault system Note that chert layers are brecciated and cemented +by A vertical fracture at the east end of the outcarbonate. crop is filled with fragments of chert carbonate cemented by calcite. 66.8 highway 587. 68.8 First roadcut beyond West Loon road, on northwest side of highway. STOP 9 EAST TACONITE FACIES, LOWER MEMBER (FIG. 2) The exposure shows wavy-banded, hematitic greenalite taconite, locally folded and brecciated. A thin band of algal structures at the top of the section is correlated with the upper algal chert fades southwest of Thunder Bay. 0.0 Intersection of highways 17—11 and 587. on 2.3 Proceed southeast highway 587. Quarry on west side of highway 587. and walk back. Park on top of hill �STOP 10 ROVE FORMATION Rove shale is black, carbonaceous, and forms part of the lower argillite unit (Morey, 1967); it contains several large, irregular "mushroom" shaped concretions. The concre— tions are composed of calcite with pyrite—marcasite bands and anthraxolite, and appear to have formed diagenetically. Remnant shale bedding planes are evident in some concretions. Shale beds are warped around the top and bottom of some concretions. Concretions are found throughout the lower argillite, and more commonly, have a distinct ablate spheroid shape. Proceed southeast on Highway 587. 4.1 A large area of outcrop extends along the north side of the C.N.R. railway tracks and Highway 587 where they parallel Pass Lake. STOP lla SIBLEY GROUP - +ROVE FORMATION At the western end of this outcrop, a sandstone quarry provides an excellent exposure of Sibley sandstone. In the railway cut at the western edge of the quarry, Rove shale is altered to a reddish colour. This alteration affected the Rove for several feet below its contact with the Sibley Group. Basal conglomerate is absent at this point but is exposed to the east behind the small railroad house along the siding opposite the Pass Lake station. Clasts in the basal po1ymictic conglomerate are composed of 93 per cent Gun! lint iron formation, 6 per cent quartz and 1 per cent granite. Boulders are of variable size and angularity, and are cemented in a sandy matrix. The contact with overlying sandstone is sharp; only a few pebbles are found in the base of the overlying unit. The sandstone is moderately to poorly indurated, thick bedded at the bottom of the section, and composed of quartz, with minor chert and feldspar, in a calcite matrix. STOP llb At the west end of Pass Lake, a quarry, which may be reached by a short road leading from Highway 587 just east of the entrance to Sibley Provincial Park, has an excellent exposure of the contact between Rove shale and Sibley sandstone. The contact is occupied by a thin porphyritic dia— base sheet. Sandstone beds have a few poorly developed cross laminations and ripple marks. Very little basal conglomerate is present in this outcrop. Return to Highway 587 and follow it 11—17. back to Highwar �—65— 0.0 From the intersection of Highways 587 and 11—17, proceed east toward Dorion and Nipigon. 3.3 East Loon Road 5.2 Outcrop on southeast of road. STOP 12 SIBLEY GROUP, BRECCIATED RED MUDSTONE This outcrop of highly brecciated conglomeratic red mudstone probably forms either the lower part of the limey red mudstone or upper part of the sandy red mudstone. Balls of red mudstone and fragments of angular chart, sandstone and mudstone are cemented iii red mudstone of similar composition, suggesting an intraclastic conglomerate. Possibly periodic, rapid flooding off adjacent Archean highlands caused chaotic re—distribution of partially consolidated muds. S.ich conglomerates are common along the western margin of, Sibley outcrop and are generally lenticular in shape. On the eastern margin of Sibley outcrop brecciation is less chaotic. Continue east on Highway 17—11. 14.3 Note outcrops of brecciated red mudstone. 38.4 Historical marker, west side of Highway 17—li ilear Beaver Valley tent and trailer park. STOP l3a RED ROCK CUESTA This cUesta. stop provides a panoramic view of the Red Rock Diabase forms a cap on the "red rock" of Sibley mud-- stone. The colour is due to less than 2 per cent hematite which coats clay, feldspar and carbonate grains. Progeed to the next major road—cut. 38.6 Road—cut. STOP 13b DLABASE SILL CUTTING ARCHEAN ROCKS AND SIBLEY GROUP At the north end of the road—cut, a diabase dyke leaves Archean rocks, cuts across the Sibley section and becomes a On the top of the road—cut a small selvage of Logan sill. Sibley mudstone may be seen. The chilled margin at the base of this sill in the road cut gave a K—Ar age of 1000±140 million years (Franklin, 1970). Fractures in this sill are �—66— filled with pectolite and calcite. An almost complete Sibley section is evident along this hill. Above the limey red mudstone, a white weathering unit which forms a steep cliff beneath the diabase,is composed of purple mudstone overlain by limestone Unfortunately, access to these units is difficult, Proceed east along Highway 11—17 to the town of Nipigon. 431 STOP 14 Nipigon lookout and historical marker. CUESTAS This lookout provides a panoramic view of the Nipigon— Red Rock area. Diabase capped cuestas form high flat topped hills in the, area. Islands in the distance are composed of Osler basalt. 0.0 From lookout, continue east on Highway 17—11 to the 17— 11 intersection; continue on Highway 17. 69 Small outcrops of interbedded white sandstone and red sandy mudstone are exposed in road cuts near Fire Hill. 14.0 A thick sheet of columnar—jointed diebase caps the Sibley Group at Kama Bay. 14.5 First lookout, Kama Hill. STOP 15 SANDY RED MUDSTONE, SIBLEY GROUP A broad anticline of sandy red mudstone is exposed in the prominant road cut to the north of this lookout. Sof t— sediment deformation probably produced this structure. Three thin diabase sheets follow bedding planes; the sills pinch out, and locally cut across bedding at a high angle. Proceed southeast along the highway towards the second lookout. Kama Hill may be cut by a northeast—trending fault system. Movement has resulted in uplifting of the west side. Thus the sandy red mudstone north of the first lookout, although low in the stratigraphic section, is slightly higher in elevation than those beds described in the next stop. This fault cuts the hill between the "anticline" and the first lookout. 15.3 Second (southern) lookout. �—67— STOP 16 In the roadcut to the north of the second lookout, the following features may be observed: (1) Two thin Keweenawan diabase sills, partially replaced by carbonate, cut across the poorly developed bedding plane at a low angle. Finely lamiqated chert of the chert—stromatolite unit (2) cuts out below the lower sill. Up to six Inches of anthraxolitic carbonate has accumulated at the base of the chert. An oily smell may be detected when this anthraxolite is freshly broken! Limey red mudstoneabove this unit is marked by many (3) cream—coloured spots, (average diameter ½ inch)! Similar spots are evident throughout this unit, and commonly have a siiall amount of graphite or hydrocarbon at the center. In thiii seçtion, the only apparent.mineralogical change in the spots is the lack of hematite coa4ing on clay and carbonate grains. (4) Irregular, flame—shaped, bleached zones follow fractures and bedding plane cleavage in the red lintey mudstone. Leaching of hematite, and destruction of clay minerals and feldspar has occurred along the fractures! Above the road cut and overlying talus slope, the purple (5) mudstone crops out. It is more highly fissile,a4 cokltains approximately 4 per cent hematite, which coats.vexy fine .grained corrensite and microcline, and forms blades of spec— ularite in tiny vugs. Bleaching along fractures is common in this rock! End of Trip For anyone interested in a more complete view of the Sibley Group, two additional areas should be visited. (1) From Rossport, a boat trip to Quarry Channel and Wilson Islands, which lie one to two miles off shore, will allow the visitor to see an almost complete section of Sibley rocks! Op Quarry Island, Rove shale is overlain by a thick section of Sibley sandstone. Here, crossbeds and ripple marks are abundant. On Channel Island, the upper part of the sandston unit, sandy The latter is disconformably over— red muçistone units are all exposed. lain by Osler volcanic rocks. The stromatolites near Disraeli Lake may be reachdd by follow(2) ing the Armstrong road noflhfrow Hurkett for 21.6 m.iles, to the Disraeli Lake road, which connects the Armstrong road with the Spruce River road �—68— 800). Follow the Disraeli Lake road west for 222 miles past Proceed Shillabeer and Seagull creeks to the Disraeli campground road. for 3 of a mile beyond this, to the first bu8h road leading •north. Blocks of stroniatolite are strewn Follow this road for two miles. Stromatolite blocks are common along side the road for some distance. throughout the Disraeli area, and may be found in outcrop and float along most of the bush roads. (Hwy. �—69— ThE BEARDMORE-GERALDTON BELT May 6 and 9, 1970 Prepared by W. 0. Mackasey, Ontario Department of Nines, Toronto Published by permission of the Chief Geologist, Ontario Department of Mines �—71— Guide to Sturgeon River Metavolcanic—Metasedirnentary Formations in the Beardmore—Geraldton area INTRODUCTION This field trip is a one—day excursion to illustrate •the stratigraphy and structure of an Early Precambrian metavolcanic— metasedimentary sequence in the Beardmore—Geraldton area (Fig. 1), 120 miles northeast of Thunder Bay. Late Precambrian sedimentary rocks and diabase sheets will also be examined. The area is part of an east—trending metavolcanic—metasedimentary belt that is at least 60 miles long and is bounded by younger granitic batholiths except on the west where it is covered by Lake Nipigon and by Late Precambrian diabase sheets. The Mineral potential of the region has been studied since the turn of the century; the first memoir of the Geological Surveyof Canada described the geology and mineral deposits of the t1Nipigon Basin" (Wilson, 1910). iron was the magnet which attracted most of the early prospectors, but the discovery of gold in 1925 near the present town of Eeardmore established the area as a major gold camp. Many gold mines were in operation in the late 1930's, but several of the smaller ones closed down with the entry of the United States into the Second World War. Major producers were the Leitch, Little Long Lac, Hard Rock Consolidated Mosher and MacLeod— Cockshut Mines. Macleod—Mosher Cold Mines Limited is the only mine Interest in iron, pyrite ,and base still operating in the area. metal sulphide deposits is continuing. The' pulp and paper industry has played a m4jor role in the economy ot the area in recent years, while tourism and commercial fishing are also important industries. Many of the Stops for the field trip were suggested by Dr. Discussions with Dr. L. D Ayres, and his review of E. G. Pye. Mr. S. Spivak, Lakehead the paper, are greatly appreciated University, drafted the figures. GENERAL GEQLUGY Regional Setting The metavolcanic—metasedimentary sequence is part of the Early Precambrian Superior Province of the Canadian Shield and occurs along the boundary between two major east—trending, lithologic and structural units of the Superior Province. These are the northern Keewatin belt composed piedominantly of metavolcanic and granitic rocks (Goodwin, 1966)and ametsedimentary—granitic complex, termed �—72— the Quetico belt by Stockwell (1964). The relationship between these two belts has been considered in recent papers by Goodwin (1968), Kalliokoski (1968) and Ayres (1969, 1970). Goodwin and Kalliokoski postulate that the Keewatin belt is older than the Quetico belt while Ayres suggested that Quetico rocks are over— lain by those of the Keewatin belt. Early Precambrian Metavolcanic and Metasedimentar"T Rocks 1. Lithologies: A — Metasediments Metasedimentary rocks form two distinct lithologic groups: a thick sequence of relatively uniform greywacke, siltstone, and argillite that is predominantly within the Quetico belt; and a thinner sequence more variable and coarser—grained of conglomerate, greywacke, argillite and iron formation that isinterlayered with metavolcanic formations of the Keewatin belt. The finer—grained metasediments within the Quetico belt and the southern part of the Keewatin belt have been tentatively correlated with the Couchiching formation by many authors (liorwood and Pye, 1955; Macdonald, 1942; Pye, 1952). The coarser grained metasediments within the Keewatin belt form part of the Windigokan series of Tanton (1921). B — Metavolcanics The metavolcanic rocks in the southern part of the area are predominantly maf Ic to intermediate, massive, pillowed and amygdaloidal flows. In the northwestern part of the belt, however, intermediate to felsic volcanic breccias and flows are abundant. 2. Stratigraphic Relationships: Reconstruction of the stratigraphy is difficult because of paucity of good exposure along contacts, deformation by folding and faulting, and interfingering of the various units. In the southern part of the area the finer—grained relatively un:iform metasediments (Couchiching) are overlain in most cases by the coarser—grained lithologically heterogeneous m?tasediments (Windigokan). Both of these units thin northward and interfinger the metavolcanic sequence. The finer—grained metasedimentary unit contains a thin but laterally extensive mafic metavolcanic unit that defines the boundary between the Quetico and Keewatin belts. Metasediments above and below this metavolcanic unit are lithologically similar (Peach, 1951; Mackasey, 1970). Metasedimepts above the metavolcanic unit are part of PyeTs (1952) group B defined in the eastern part of the �L A 6 -F -p 4 -4- + -,- .++4+t ... - S . c+i\\ ±pf? S'S +1s • ' .. + ..'+\\4tP. • V S D \ D D '. D • - 0 D D iY LI LI • . ÷ __S 5 S 5 . 5 S . S S S S S 4; S . . . . . SIISS . . . + t. 0 -, Ø'5 D — S D/ 6- DC • •• S I - LI 6 Figure 1 - D s . • . 1+ • S 5 0+ -4- 4 ++ . s...-.' sl+r+ (.J-* ..t-.. tt+.S4S1S S .\ 1W-. S - -. yy.•.•.• •.... 4 2 SCALE 0 S . —— • — __D 6MILES S I + 4 i- + -1- + + S . -I— 7—s 4- ÷ -- + ± -s- -r -t ÷ II + -4- -4 + 4 4 -r -+ -t- -f t 1-4 -,- . • . — 5__55S___S - _: - - — fl;—j-——— 6 —- LI LI —4- 0 ..• D —I-i LI PAINT MAFIC FEL SIC DIABASE LAKE FAULT INTRUSIVES NTRUS1VES o s S S S S S I 2 4. 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I . ra74!c . eli.' lb —f4-tp.•.•.•-•-•-•-•-•-•-,.s +—; + r+ •••t +%'•••••••••••••••••'S N +.-f-' 4 ± t_ +.&..................4.!Jr. . - Y'÷# ± *I••••5b•••a VM S a- . 5 S4 t•••••••••••% + o,._ ç.si _____D(T___ olr..j1D I/C 1'°rLDt— BEARDMORE:i n • D,SoDt_ — — LI • . . . . .-.'- ,•• . . . , • a S ttervie . . S ' D12,I!42-Th-i iE1 &1Li-E-T :7 — 5 • • "" • -"'"-'' oNa-... 10 0 D 5 -4- -,- — + +-4- • ÷± •.::rVVs'Y t' . . ' - :*•S.S.S.a.S .t 0 '+ . - D.---O- • —: 2= o o N D D + -I- . S • _ ?;;tttit:*it • 7:,-,,t-f 5,. t:: nr.-.. 6tC. t-JTcT-i :t2Z DDe •:- r rf5 ' '##" ÷ f's.!. r. — --i)D D -' E .+ +t "')+-44+4++#gfr)c tcj+÷÷y . ' + tfk + er + ±F5, 11+.+ . y-t.-. K +÷t+t• N '—% D 0 t' r dcx. ___ I Ri �—72 B— ABITIBI BELT —ø.j- QIJETICO KEEWATIN BELT BELT NORJ/ sourti U lilliHi Iii —— —— LEGEND FINE METAGREYWACKE COARSE 2 AND METAGREY WACKE FELSIC METAVOLCANICS MAFIC METAVOLCANICS METASILT STONE AND METACONGLOMERATE FIELD TRW STOP APPROXIMATE Figure 2. SCALE IN MILES After AYRES I 1969 biagrammatic cross-section showing relationship between Abitibi, Quetico, and Keewatin belts. Section through Abitibi belt approximately corresponds to JackfishMiddleton area (Walker, 1967); section through Keewatin belt approximately corresponds to Little Long Lac area (Pye, 1952). �—73— belt. Near Geraldton the finer—grained metasediments (Pye's group B) are disconformably overlain by conglomerate (Pye, 1952)\which is the lowermost unit of the upper metasedimentary sequenc (Windigokan or group A). The same general lithological changes havd been observed in the Beardmore area (Mackasey, 1969) but disconformble relationships have not been recognized. A mafic to intermediate volcanic unit overlies the upper (Wind— igokan) metagediments in the Beardrnore area. •3,. Origin The metasediments in the Beardmore—Geraldton belt thin and become coarser grained to the north. The metavolcanic rocks on the oiher hand, are thickest in the northern part of the belt and thin southward (Bruce, 1937; Macdonald 1942, 1943). Ayres (L969) suggested that the metavolcanic rocks of the Beard— more—Geraldton area were part of an east—trending metavolcanic arc that is now represented by the Keewatin belt. This arc developed in an older sedimentary basin within which metasediments of the Quetico belt were deposited Volcanism commenced with subaqueous extrusion of mafic to intermediate flows that built up submarine shield volcanoes. The flows interfinger southward with the metasediments of the basin. Later felsic pyroclastic volcanism built subaqueous to subaerial cones on top of the older mafic shield volcanoes, The change in sedimentation from relatively uniform fine— grained sand and silt to more heterogeneous, coarser grained gravel, sand, and silt corresponds to the initiation of major felsic volcanism and the emergence of the volcanoes above sea level. (Ayres, 1969) The coarser—grained metasediments of the upper metasedimentary formations contain abundant clasts of felsic to intermediate volcanic rocks. Figure 2 is a diagrammatic cross—section (after Ayres, 1969), showing the interfingerlng relationships existing between rqcks of the Keewatin and Quetico belts. Igneous Activity and Regional Metamorphism The metavolcanic—metasedimentary sequence has been intrudad by large felsic batholiths ranging in composition from granitic gneiss to quartz diorite. These batholiths form the north and south boundaries of the Beardmore—Geraldton belt. Relatively small lenticular bodies of mafic intrusives occur in the central part of the belt. �—74— Most of the metavolcanic—metasedimentary sequence has been metamorphosed to greenschist facies but metamorphic grade increases southward within the Quetico belt (Macdonald, 1942; Peach, 1951). Structure The early Precambrian metavolcanic—metasedimentary sequence has been isoclinally folded along east—trending axes. Detailed work by Elorwood and Pye (1955) and Pye (1952), based on surface and subsurface mapping and geophysical data, outlined the style bf folding in the Geraldton area. Several prominent east—trending faults have been recognized. The Paint Lake fault is a major structural discontinuity in the Beardmore area and marks a change in both lithology and structural style. South of the fault, interbedded metasediments and mafic metavolcanic flows are folded along east—trending axes, but to the north, intermediate to felsic pyroclastic rocks predominate and fold axes trend north and northwest. Late Precambrian Rocks Relatively flat—lying sedimentary and volcanic rocks uncon— formably overlie Early Precambrian rocks in many places along the north shore of Lake Superior. Rare exposures of conglomerate, sandstone, shale, and dolomite of the Sibley Group are present in the western part of the Beardmore—Geraldton area near Lake Nipigon. Keweenawan diabase forms north—trending dikes throughout the Beardmore—Geraldton area and flat—lying sheets near Lake Nipigon. A diabase sheet, 400 to 650 feet thick forms a cuesta just east of Beardmore. The sheet dips gently westward and at the Leitch Gold Mine, four miles west of Beardmore is 1871 feet below surface (Benedict and Titcomb, 1948; Ferguson, 1967). Porphyritic diabase dikes, locally known as "Greenspar porphyry" are thought to be older than the sheets and equigranular dikes. Late faulting has disrupted the Keweenawan diabase sheets and dikes and probably represents reactivation of older faults. Pleistocene Thick deposits of sand and gravel are present throughout the belt and in some areas outcrop is scarce. Spillway channels, and deltaic sand and valley train deposits have been outlined by Zoltai (1965). Wave—cut terraces and sand dunes are found near Lake Nipigon. ECONOMIC GEOLOGX Concentrations of gold, silver, iron, copper, nickel, molybdenum, �—75— pyrite, zinc, lead, tungsten, sand and gravel are present within the Beardmore—Geraldton belt. Gold and Silver The Northern Empire Nine (near Beardmore), which began operation in March 1934, was the first producer in the region. By 1940, 11 mines were in operation. Today, however, MacLeod—Mosher Mines Limited, near Geraldton, is the sole producer. The gold deposits, which contain minor silver, were classified by Horwood (1948) into four types: 1. Simple fractures filled by quartz veins, 2. Shear or breccia zones containLng both quartz and sulphides, 3. Fracture zones containing quartz stringers, and 4. Fracture zones containing massive pyrite. Most of the gold deposits occur in metasediments of the upper (group A or Windigokan) formation but gold mineralization is also found in the lower metasedimencary formation, in metavolcanic rocks, in early felsic and mafic intrusive rocks, and along the contacts between different lithologic units, Iron. Iron deposits in the belt are interbedded with clastic meta— sedimentary rocks and are composed of interlayered hematite and/ or magnetite with greywacke and argillite and, in places, jasper, chart and iron silicates. Sulphides Chalcopyrite, pyrite, sphalerite, pyrrhotite, and galena occur in fracture—filling quartz veins and in shear zones. Many of the known occurrences are in the metavolcanic rocks north of the Paint Lake Fault. Nolybdenite occurs near the west end of the belt in quartz veins and is also disseminated with chalcopyrité in altered quartz diorite Copper and nickel sulphides are associated wicha gabbroic intrusion in Elmhirst Township. A brecciated pyritic iron formation at least 2½ miles long within metavolcanic rocks in Summers Township has been explored for its sulphur contentS Other Commodities Ninor scheelite was recovered from the gold ores of tUe tittle Long Lac Nine during the Second World War (Pye, 1952). Sand and gravel deposits have been used in highway and railroad construction. �—76— SELECTED REFERENCES Anonymous, 1965; Ayres, L. D. 1969; Longlac, Ontario; Ontario Department Mines, Geol. Survey. Canada. Aeromagnetic series, Map 7102 G. Early Precambrian stratigraphy of part of Lake Superior Provincial Park, Ontario, Canada, and its implications for the origin of the Superior Province; Unpublished Ph.D. thesis, Princeton University, 399 pages. Synthesis of Early Precambrian stratigraphy north of Lake Superior (abstract); see this volume. Benedict, P. C. & Titcombe, J. A. 1948; Bruce, E. L., 1935; 1937; The Northern Empire Mine; in Structural Geology of Canadian Ore Deposits; C.I.M.M., p. 389—399. Little Long Lac gold area; Ontario Depart—j 1935, 6Op. ment Nines, v.44, pt.3, The eastern part of the Sturgeon River area; Ontario Department Mines, v.45, pt.2, 1936, p.l—59. Carlisle, D., 1963; Pillow breccias and their aquagene tuffs, Quadra Island, British Columbia; Jour. Geol., v.71, p.48—71. Ferguson, S. A., 1967; Leitch Gold Nines Limited,. surface plan of eastern part of property, parts of Eva and Summers Townships, District of Thunder Bay; Ontario Department Mines, Geol. Map P.484. Goodwin, A. N., 1966; Archaean protocontinental growth and mineralization; Can. Mm. Jour., v.87, No. 5, p • 57—60. 1968; Henderson, J.F., 1953; Henderson, J.F., & Brown, I.D., 1966; Evolution of the Canadian Shield; Proc. Geol. Assoc. Canada, v.19, p.1—14. On the formation of pillow lavas and breccias; Trans. Roy. Soc. Canada, v.47, ser. III, Sec. 4, p.23—32. Geology and structure of the Yellowknife greenstone belt, District of Mackenzie; Geol. Surv. Canada, Bull. 141, 87 p. �—77-. Horwood, H, C., 1948; General structural relationships of ore deposits in the Little Long Lac—Sturgeon River area; in Structural Geology of Canadian Ore Deposits; C.IM.M. Horwood, H. C., & Pye, E. C., 1955; Geology of Ashmore Township; Ontario Department Mines, Vol. 60, Pt. 5, 1951, lOSp. Kalliokoski, J., 1968; Structural features and some metallogenic patterns in the southern part of the Superior Province, Canada; Can. Jour. Earth Sd., v.5, p.ll99—l208. Laird, H. C., 1937;- The western part of the Sturgeon River area; Ontario Department Mines, v.45, pt. 2, 1936, p.60—117. Langford, C.. B., 1929; Macdonald, R. D., 1942; Geology at the Beardmore—Nezak Gold area; Ontario Department Mines, Vol. 37, pt.4, 1928, p.83—108. Geology of the Kenogamisis River area; Ontario Department Mines, v.49, pt.7, 1940, p. 12—28. 1943; Geology of the Hutchison Lake area; Ontario Department Mines, v. 50, Pt. 3, 1941, 2lp. Mackasey, W. 0., 1968— Preliminary Maps of District of Thunder Bay Ontario Department Mines Dorothea Tp. P479 196S Sandra Tp. P480 1968 Irwin Tp. P481 1968 Walters Tp. 1969 E539 Leduc Tp. P540 1969 Eva Tp. (in press) Summers Tp. (in press) 1970; Peach, P. A., 1951; PrelimInary report on the'geology of the Blaclcwater—Beardmore area; Ontario Department Mines, Prel. Rept. 1951—7, 6p. Petti}ohn, F. J., 1943; Archean sedimentation; Geol. Soc. America Bull., v.54, p.925—972. Pye, E G., 1952; Geology of Errington Township, Little Long Lac area; Ontario Department Mines, v.60, pt. 6, 1951, l4Op. Pye, E. Tashota--Geraldton sheet; Mines, Map 21102. C.. 1952, & Harris, F. R., Fenwick -K. C., & Baillie, J., 1966; Ontario Department �—78— Stockwell, C. II., 1964; Fourth report on structural provinces, orogenies, and time—classification of rocks of the Canadian Precambrian Shield, in Age determinations and geological studies, pt. II, geological studies; Geol. Surv. Canada, Pap. 64—17 (pt.II), p.1—21. Tanton, T. L., 1921; Explored routes in a belt traversed by the Canadian National Railway between Long Lac and Nipigon; Cecil. Survey, Canada, Sum., Rept., 1917, pt. E. p.1—6. Tyson, A. E., 1945; Report on gold belts in the Little Longlac— Sturgeon River District; Can. Mining Jour., Vol. 66, no.12, p.839—850. Walker, J.W.R., 1967; Geology of the Jackfish—Middleton area; Ontario Department Mines, Geol. Rept. 50, 41 p. Wilson, A. C. W., 1910; Geology of the Nipigon Basin; Can., Memoir 1. Zoltai, S.C., 1965; Ceol. Survey Surficial Geology, Thunder Bay District; Ontario Department Lands and Forests, Map 5 265. �—79— FIELD TRIP The starting belt can exposure field trip has been designed as a one—day excursion from Geraldton, where some of the oldest rocks of the be viewed, and finishing south of Beardmore at an of the younger, Sibley Group rocks., A cross—section of the belt, made by traversing north on secondary Highway 801 in Walters Township (near Jellicoe), has been chosen to show the variety of metasedimentary and meta— volcanic rocks types. Although some of the exposures along the highway are relatively small, larger outcrops occur along strike and, in &ome cases, can be reached by means of trails and/or boat The tour continues west to Beardinore, the Leitch Gold Mine area, and Lake Nipigon to examine Keweenawan diabase exposures, folded iron—rich metasediments, and vplcanic structures Emphasis has been placed on the viewing of megascopic features and field relationships. ROUTE The Road Log has been set—up to enable use by others at a later date. I The Location of all Stops are shown on map in Figure 1. relative position of some Stops has also been located on the cross—section in Figure 2. Time limitations may not allow viewing ofall Stops listed. Some stops are intended for viewing frrom the bus only. Conservation of Outcrop Several groups will be making this tour in conjunction with the 1970 Lake Superior Institute, and possibly on an individual basis at a later date. Care should be taken to preserve the more delicate features when collecting specimens, making hardness tests, etc. �—80— DESCRIPTION OF STOPS ae 0.0 Leave junction of Highways 11 and 584 (south of Geraldton). Head west on Highway 11 (Trans Canada Route). 2.5 Turn right and leav.e Ejighway 11. 0.0 Head northeast on gravel road. 0.6 South side of road under power line. STOP 1 This outcrop consists of fine grained clastic sediments with interbedded conglomerate and iron formation. Porphyry similar to that associated with the nearby gold deposits can be found on the north side of the exposure. Drag folds and crenulations reflect the regional, structure. Note stretched pebbles, gentle plunges of crenulations, and quartz veining. Backtrack to Highway 11. 0.0 Junction to Highway 11 and gravel road. Highway 11. 4.0 South side of Highway 11 about 400 feet west of Magnet Walk south on old bush road for about 400 feet then turn west (right) aht old headframe timbers and continue for approximately 300 feet to outcrop area. Head west on Creek. S 27.1 This marks the location of the disconformity separating group A and group B sediments as outlined by Pye (1952). The thin bedded, fine grained clastics of group B (lithologically similai to the Quetico metasediments) are overlain by Timiskaming—type conglomerate. See Pye (1952, P17) for photograph of lichen—free outcrop. General store at Jellicoe (Rock and mineral dealer) 30.8 North side of Highway 11 near bush road. STOP 3 33.0 Road cut of Timiskaming—type greywacke succession sediments with well developed graded bedding. These sediments form part of the "Windigokan series" as mapped by Tanton in 1917. Junction of Highways 11 and 801, �—81— G.0 Head north on Highway 801 (gravel). 1.2 Road cut at crest of ridge. STOP 4 This stop illustrates the thin bedded aspect of the fine— Bedding is grained "black slate" sediments in the area. more easily recognized on the weathered surface along the top of the road •cut. 1.4 Outcrops on the north side of the road, approximately 800 feet northwest, display well bedded argillite, siltstone and greywacke with thin iron—rich layers. The magnetic expression of this horizon can be traced for several miles west along strike, (see O.DM.—G.S.C. Map 7102G, 1965). 2.4 North end of road cut on east side of Highway 801. STOP 5 2.8 Fine grained green lavawith jasper amygdules. Breccia fragments are visible on weathered surface of outcrop. On Highway 801, north and south of the gate to Pasha Lake Lodge. STOP 6 These relatively small exposures serve to illustrate facies changes in the sedimentary rocks. The southern exposure (broken outcrop) displays the blocky, massive nature of the sandstones in the area. The northern exposure is typical "Windigokan" conglomerate. klthough jasper pebbles are readily apparent in the conglomerate, pebble counts indicate that jasper is only a minor constituent. These two rock units can be traced for several miles along strike. 4.3 STOP 7 The road cut at top of ridge. Massive mafic lava typical of the area. Note epidotic alteration and minor copper mineralization. The disrupted banded and massive cherty horizons present in this outcrop area can be found at several locations along stike, and are thought to be the result of fumerolic activity. 5.6 West end of Paint Lake. �—82— STOP 8 6.2 STOP 9 This lineament can be traced for (Paint Lake Fault). several miles along strike and is considered a major Pebbles and boulders in the sedimentary fault zone, rocks on the south side of the fault have undergone marked plastic deformation. Road cut at "5" turn on east side of Highway 801. Stops 9 and 10 serve to illustrate the fragmental character of the voloanic rocks north of the Paint Lake Fault. The weathered surface at the south end of the road cut reveals the agglomeratic nature of these volcanic rocks. The irregular and feathery edges of some fragments suggest that the pyroclastic material was in a plastic condition when deposited, Note: outcrop. 69 STOP 10 Please do not damage the south part of the Outcrop on the east side of Highway 801. Volcanic breccia containing Ttcigar_shaped?t tapered frag— merits up to six inches long. This marks the last stop of the cross—section on Highway 801. Now backtrack to Higway 11. 0.0 Junction of Highways 11 and .801. Head west on Highway 11. 12.0 STOP 11 14.7 Highway 11 passes through a wind gap in a north trending cuesta. The cuesta is formed by a west dipping diabase sheet which intrudes the Archean rocks. Junction of Highways 11 and 580. 0.0 Turn right and coptinue on Highway 580. west to Lake Nipigon). 4.4 Turn right at intersection and head northwest along gravel road entering Leitch Mine area. 4.5 Outcrop ridge approximately 200 feet south of gravel road, Scattered outcrops to north of road. (This road heads �—83-- STOP 12 This stop illustrates tight drag folding in a unit composed of interbedded fine grained clastic sediments, jasper, and hematite—rnagnetite layers. Note If collecting specimens, please do not mar the the crenulated section of the southern exposure. Most of the "mineral showings" near the mine have ben covered with waste rock from underground workings. Keep away from fenced off areas. Continue west on (Highway can be reached by following service Highway 580. road, or by backtracking). 6.4 Lake Nipigon (Poplar Lodge) and end of Highway 580 0.0 Head north (right turn) along gravel road. Peninsula near large red—stained cottage. (Note: road conditions may require leaving vehicle up to 1000 feet south of here). STOP 13 ExcelJent exposures of pillow lava, anygdaloidal lava an4 volcanic breccia can be found along the shore in this vicinity, and on the nearby islands. Pillow breccia may be observed along the waterline of the northern tip of the peninsula. Here well packed pillow lava grades into breccia containing isolatedpillows. This occurrence is similar to pillow breccia described by Henderson (1953), Henderson and Brown (1966) and Carlisle (1963) Now return to Highway 11 0.0 Junction of Highways 11 and 580. 11 (cross Blackwater River). 0.8 Turn east (left) off. Highway 11 and follow gravel road (Empire Mine Road). Cross railway track and continue Head south on Highway east. ii STOP 14 Power line. Examine exposures along power line clearing for approximately 1200 feet south of road. Footpath crosses some of the best exposures. This Stop illustrates age relationships between two of the Proterozoic diabase intrusives, as well as their lithological differences. �-84— Outcrops near the road are of a wide, north striking, porphyritic diabase dike that closely resembles Matachewan diabase. The altered green feldspar phenocrysts in the dike have given rise to the local term "Greenspar porphyry". Faulted offsets of what is believed to be the same dike, can be followed for more than ten miles to the north. A contact between porphyritic diabase and younger massive diabase is exposed on the first main ridge south The younger diabase is believed to be a of the road. part of the same diabase sheet seefl at STOP 11. Inclusions of foliated mafic lava and rounded to angular fragments of granitic material and quartz can be observed further south along the footpath. Return to Highway 11 and enter Beardmore. 0.0 Leave Beardmore and head south on Highway 11. count begin at railway crossing. 8.6 Road cut on east side of Highway 11. STOP 15 Mileage This stop demonstrates the unconformable relationship existing between the Proterozoic strata of the region and the underlying Archean rocks. Pink sandstone of the Sibley Group rests with angular unconformity on an eroded Quetico metasediment surface. Fragments of the underlying rock can be found suspended in what is a possible paleosol or limestone layer along the unconformity. the pink colour of the sandstone is caused by the presence of approximately 0J% hematite. (3. M. Franklin, personal communication). �—85— THE PORT COLOWELL ALKALI COMPLEX May 9, 1970 Prepared by F. PUSKAS* *present address: The International Nickel Company of Canada Ltd., Copper Cliff, Ontario. �—87— Guide to the Port Coldwell alkalic complex INTRODUCTION: The Port Coldwell Alkali Massif (Fig. 1) is located within an Archean volcanic—sedimentary belt extending along the North shore of Lake Superior near Marathon. Previous work on the complex consists of reconnaissence work by Kerr (1910), detailed mapping by Tuominen in 1958—1959 (O.D.M. Prelim. Map P 114) and by Puskas in 1960 (O.D.M. Prelim. Map P 114, revised). The the western contact of the complex wag mapped by Walker (1956); easter-n contact by Thomson (1931) and Milne (1964). The present study was largely carried out by the writer and associates while employed by the Ontario Department of Mines. The author wishes to express his thanks to Professor Henri Loubat of Lakehead University and Clarence Kustra, Ontario Department of Mines, Resident Geologist, for their constant interest and co—operationh S. Spivak drafted the diagrams. FIELD AND GENETIC RELATIONSHIPS The Port Coldwell Alkali Massif (Fig. 1) lies within the eugeosynclinal portion of an Archean volcanosedimentary belt, approximately 18 miles wide and extending westward from White Lake, along the north shore of Lake Superior. The volcanosediments have been tightly folded in a N 70°E less important, more northerly trending, structures direction; may be attributed to cross—folding. The Archean rocks have been successively intruded by sill— like bodies of basic and ultrabasic composition, granitoids, dikes of diabasic composition, and lastly by the Port Coldwell Alkali Massif. The Alkali Massif is a lopolith (Puskas, 1964; Corbett, circular in plan and approximately 580 sq. kilometers in The Massif is considered to typify the so—called (Benson) Laccomorphic class of emplacements. 1968) area. The rocks of the massif can be divided into two groups However, called here the Main Group and the Secondary Group. in common with many intrusions of this type the long crystal— lisation history has resulted in numerous complex and sometimes confusing cross cutting relationships. The Main Group is composed of gabbros, the oldest and more-peripherally located rock—type Map unit 2), and laurvikites Both the gabbros and laurvikites can exhibit (Map unit 3). rhythmic layering which dips inward at moderate angles. The �—88— laurvikites highest in the group are commonly porphyritic. Several zones are recognized within the main group. Upper Lower Inner Inner Outer Zone Zone Border Zone 'B' Border Zone 'A' Border Zone massive layered layered massive chilled laurvikite laurvikite gabbro gabbro gabbro The Secondary Group is composed of an older, saturated series which includes syenodiorites (Map Unit 4) and nordmarkites (Map Unit 5) and a younger, undersaturated, series with several varieties of feldspathoidal syeniie (Map Unit 6). Generally, within this group, rocks comprising the saturated series are peripheral to the felds— pathoidal syenites. Except for the feldspathoidal syenites, which are layered at some localities, the rocks Of the Secondary Group are massive and apparently structureless. The Secondary Group is characteristically associated with xenolithic bodies. Although widespread, these bodies are thought to belong to one large unit, the so—called Coubran Lake meta— volcanic cap. Common variants, generally gradational one to the other, include aphanitic amygdular and diabasic volcanics. The 'cap' rocks and the rocks of the Secondary Group are preferentially concentrated in that portion of the massif which is west of Wolf Camp Lake. (ref to Stop 3, Fig 4). It is noted that the 'cap' appears to be 'free—floating' in the north and 'attached' in the southern part1 These and other relationships suggest a near—roof situation of the present level of exposure. The Port Coldwell magma, which apparently contained solid plagioclase fledspar, was emplaced (1) from a probable source located to the SSW, (2) by a process of doming, stoping, and forceful injection, and (3) at P—T conditions sufficient to gener ate a thermal aureole within the pyroxene—hornfels facies. The rocks of the aureole show rheomorphic veining, and ana— texites which commonly exhibit flow layering or schlieren trending parallel to the immediate gabbro contact. Areas of more intense migma development were probably controlled by the distribution pattern of favourable.lithologies as modified by folding, faulting and emplacement characteristics of the massif. The coincidence of numerous geological contacts with lineaments is compatable with a magma cooling history involving doming and fissuring, with probable block subsidence, and the 'near—roof' level of Massif exposure. �AGE RELATIONSHIPS The volcanosedimentary assemblage was intruded by various bodies which are as follows (oldest first): — sill—like bodies of basics and ultrabasics, granitoids, dikes of diabase, and the Port Coldwell Alkali Massif. The diabase dikes are typical of those reported throughout the Superior Province and which have been dated at approximately 1700 m.y. The author originally thought the Port Coidwell Alkali Massif to have been intruded in the northwest by a younger granitoid, the so—called Little Pic River batholith (Puskas, 1964). But the observed field relations are better explained by assuming the formation of a palingenetic magma from an overlying granite. Minerals front the massif give ages of 1065 m.y. (K—Ar, Rb—Sr ages on biotites from nepheline syenites from Stop 5) and 1225 m.y. (Rb—Sr age on perthite from the laurvikite)(Fairbairn et al, 1959). In view of the widespread contamination of the magma further work is necessary. However, the massif is similar in age to the widespread Keweenawan intrusives of the Superior Basin (1000± myra) and may be from the same parental magma. ECONOMIC GEOLOGY The Port Coldwell Alkali Massif has been prospected for iron, base metals, radioactive minerals, nepheline, perthitic feldspar, and building stone. To date there has been no ore production. Iron The exposed gahbros along the periphery have been investigated for iron and base metals. The iron occurs as ilmenomagmetite—enriched layers or bodies, one inch to 70 feet wide, predominantly conformable to the layering of the adjacent gabbros. The high titanium content, 5 to 8 percent, and sub—marginal tonnages make the deposits uneconomic at this time. Base Metals Base metal investigations by various companies, including Moneta Porcupine; Lakehead,: Denison Mines, Keevil, Anaconda, and Conwest Exploration, have concentrated on the coarser grained, massive, gabbros (Inner Border zone 'A'). Stone Small scale quarrying of both 'red' and 'black', i.e. thirk varieties of laurvikite was begun in 1927 and continued into the l930's on a property located approximately 2 3/4 miles north of �—90-- Marathon and transected by the C.P.R. Although these syenites, particularly the 'dark' varieties, are similar to the famous laurvikites from Norway, no markets could be secured and maintained. Nçpheline Denison Mines Limited in 1960 attempted to determine the nepheline potential of the feldspathoidal syenites from two areas However,. located south of Highway 17 and west of Red Sucker Cove. nepheline separation proved hard to achieve, and iron content of the concentrate was too high, so the project was abandoned. SELECTED REFERENCES The following is a selected list of references pertaining to the geological features discussed in this report: Adams, F. P., 1900; On the Probable Occurrence of a Large Area of Nepheline-Bearing Rocks on the Northeast Coast of Lake Superior, Journal of Geology, Vol. VIII, pp 322—325. Coletnan A. P., 1898; Port Coldwell Region, Ann. Rep. Bur. of Mines, Ont., pp 146—149. Coleman A. P., 1899; Dykè Rocks near Heron Bay, Ann. Rep. Bur. of Mines, Ont., pp 172—174. Coleman A. P., 1899; A new Analcite Rock from Lake Superior, Journal of Geology, Vol. VII, pp 431—436. Coleman A. 7., 1900; Heronite or Analcite Tinguaite, Ann. Rep. Bur. of Mines, Ont., pp 186—191. Coleman A. P., 1902; Syenites near Port Coldwell, Ann. Rep. Bur. of Mines, Ont., pp 208—213. Collins & Camsell, 1913; The Nepheline and Alkali Syenites of the Port Coldwell Area, Transcontinental Excursion Cl, Toronto to Victoria and return via Canadian Pacific and Canadian Northern Railways, Guide Book No. 8, Part 1, pp 16—24. Corbett, J., 1968; Farrand, W. R.-, 1960; Paper presented to I.L.S. meeting at East Lansing. Former Shorelines in Western and Northern Lake Superior Basin, Unpublished Ph.D., dissertation, Dept. of Geology, University of Michigan, Ann Arbor. + �.• ____________________ . — .._...........LLIr,a —91— Fairbairn, H. 1959; et al, Rough, J 1.,, Kerr, H. L., Age investigations of syenites from Port Coldwell, Ontario, Geol. Assoc. Canada, Proc. Vol. 11, pp 141—144. 1958; 1910; Geology of the Great Lakes, University of Illinois Press, Urbana, Illinois, Chapter II. Nepheline Syenites of Port Coldwell, Ann Rep. But. of Mines, Ont., pp 194—232, with map. Logan, Sir Win. E., 1847 Report of Ptogress, G. . C. Logan, Sir. Wm. E. 1863 Geology of Canada, pp 29—30. pp 80—81, 480, 647. Mime, V. G., 1967; Geology of Cirrus Lake—Bamoos Lake area; Ontario Department of Mines, Report 43. Puskas, F. P., 1964; Geology of the Port Coldwell Area, Open File, O.D.M. T.B. Thomson, Jas. E., 1931; Geology of the Heron Bay Area, O.D.M., Vol. XL, pt 2. Thomson, Jas. E., 1934; Unpublished Ph.D. dissertation, Department of Geology, Wisconsin University, Madison, Wise. Walker, T. L., & Parsons A. L., 1927; lJniversity of Toronto Studies, Geol. Ser. No. 24, pp 28—32. Walker, 3. W. R., 1956; Geology of the Jackfish—Middleton Area, District of Thunder Bay, Ont. O.D.M. Geol. Cir. No. 4. �-92— DESCRIPTION OF STOPS The town of Marathon is at one of the few naturally protected harbours along this part of the North shore of Lake Superior. An extensive sand and gravel deposit underlies the townsite and extends eastward to Heron Bay and northward approximately 2½ miles. To the north these sand and gravel deposits are seen to overlay broad terrace of varved clays which trends parallel to the present course of the Big Pie River for more than 50 miles + (Farrand, 1960). There are at least six beach terraces at Marathon (Thomson, Puskas, 1964). The highest beach is 710 feet above Mean Sea Level or 108 feet above the present surface of Lake Superior (Hough, 1958). The vertical interval between these beach terraces is 5 to 45 feet. Walker (1956) states that the vertical interval between terraces occurring 20 or more miles to the west is 5 to 10 feet. These differences may indicate a relative increase in the rate of post glacial isostatic adjustment to the east in dir— ection of the Marathon area. 1934; qae 0.0 Intersection of Highway 17 and turn off to Marathon. Continue south east on Highway 17. 2.4 Eastern contact of Massif with country rock. STOP 1 (Fig. 1 & 2) is a 2 mile traverse across the eastern part of the massif beginning at the contact of gabbro and anatexite. (Fig. 2) Because of the close proximity of, the country rocks to a considerable portion of the traversed gabbros, the gabbros are highly charged with xenoliths, variably assimilated, and variably hybridized. STOP1A EASTERN CONTACT OF MASSIF (Fig. 2). The local contact zone between gabbro, occurring as a topographic 'high', and anatex±tes shows the following features; (1) in plan, the contact appears flexured or arcuate. (2) dip relations of contact indicate 'on— lap' by anatexite. �— -I- + I — 'fr—s .L 0 E-E EL rr-— n: ------2 MILES a LAKE Port Coldwell Igneous Complex SUPER/OR Bay OLDWELL Pen/nsa/c Figure 1. -I;--—-- —, +c -4-\- -n—- r_ -:?—_-= r.r..cjr.. c—_ z-_—= =—_:-= --—- + —4-f1_nnn r+ 4--- ; 2i.: ISLAND --- p/c -4.- -I- -Lti+t 1-4- + GROUP SECONDARY PlC I GRANITE ROCKS SYENITES SYENODIORITE NEPHELINE PRE—COLOWELL COMPLEX LITTLE 1: I' N) (0 �—92 8 — APPROXIMATE Pig. Z Contacts between dountry rock', gabbros and laurvikites. LiMIT OF PYROXENE —HORNFELS ISOGRAD �—93— (3) 'flow—layering' exhi)bited by anatexite are parallel to the contact and contact irregularities. C) presence of areas of breccia development. These field relations, schematically illustrated in Fig. 3, can best be explained by assuming the peripheral development of migma ,in the country rocks surrounding the cupola of gabbro. Breccia development appears to be, in part, the product of an irregular cooling history involving magma pulsatidn followed by fissuring and intrusion of more— peripheral areas. Note the abundant xenoliths in the gabbro (apparently reflecting the 'high' level of cupola exposure); the rheomorphic dikes of granophyre with tourmaline±prehnite in the anatexites; and dikes of laurvikite in the gabbros. The laurvikite dikes commonly show; (1) angular inclusions of gabbro, obviously locally derived; (2) contact relations indicative of emplacement during periods of extension; (3) composite appearance. Thin âections of the anatexites show porphyroblasts of •(in decreasing order of relative abundance); clinopyroxene, IC—spar, quartz, orthopyroxene (Fs 25—35), biotite, oxides, and sulfides. l4ineralogically the anatexites lie within the orthopyroxene clinopyroxene — plagioclase triangular field of an ACF plot for the pyroxene—honfels fades. Physical and/or optical alignment of some of the minerals especially plagioclase (An20 to An40), is not uncommon. The gabbros vary from fine to coarse grained but all varieties are essentially anhydrous two pyroxene gabbros with or without phenocrysts of plagioclase of (An65_70). The medium to coarse gabbros of 'Inner Border Zone A' show. anomalous amounts of quartz and K—spar, probably due to assimilation. Thin sections of the syenite dikes, generally composite, show perthites (generally extensively exsolved, patch perthite) with varying proportions of aegirine—augite, riebeckite, calcite, zircon, fluorite, quartz, and oxide (ilmenite ± magnetite). These dikes are considered to be apophyses from the main body of laurvikite. OO Turn round and proceed north towards Marathon. �—94— STOP lB XENOLITH-HYBRIDIZED GABBRO—BANDED GABBRO (Fig. 2) A large, relatively inhomogeneous, xenolith of anatexite appears to be engulfed within massive, inclusionbearing, hybridized gabbro. Massive gabbro is overlain by gabbro with discontinuous and/or disturbed layering, and moderately well developed foliation of plagioclase. These gabbros are essentially two pyroxene, olivine poor, bictite—oxide (magnetite present up to 15 percent) rich, rocks. STO? 1C GABBROS - LAURVIKITES (Fig. 2) Continuation of traverse northward, along Highway 17, across layered gabbros, with zones of anatexite and intrudand layered laurvikites. ed by dikes of laurvikite; The gabbros show; (1) rhythmic (and cryptic) layering; (2) foliated and possibly lineated fabric as exhibited by plagioclase and clinopyroxene; (3) zones of reaction inclusions; (4) several ring (?) dikes, with associated apophyses, of láurvikite. Greater volume of dikes is indicative of the nearness of contact with overlying laurvikites. Dike emplacement occurred during periods of gabbro extension. The gabbros contain pagioclase, clinopyroxene, olivine (up to Fa75±5) with minor, but significant amounts of ilmenomagnetite, biotite, sodic amphibole, apatite, idding— site, sulf ides, and antigorite. The contact between overlying, layered laurvikites and layered gabbros appears conformable and gradadional over a short distance. The laurvikites show; (1) zones of abundant xenoliths; (2) colour variation from dark green to red corresponding to a transition, apparently gradational and cyclic, from a more melanocratic, anhydrous mineralogy, further characterized by the presence of hematite perthite; - -a �IN I / LI THOLOG Y POSTULATED WITH RELATIONS ROCKS. CUPOLA DEVELOPMENT. Contact relations shown at Stop la / / COMPOSITION TOURMgLINE + PREHNITE. GRANOPHYRIC Fig. 3 (2) GABBROIC CHARACTERIZED 0Y PARALLEL CONTACT ARE COMMON. ANATEXITES ARE FLOW LINES, SCHLIEREN, WHICH WITH GABBRO — DRAG FOLDS le 'BLEACHED APPEARANCE. (3 PRESENCE OF INCLUSIONS OF LOCAL LITHOLOGIES AND RESTITE. (1 PRESENCE OF RHEOMORPHIC VEINS AND DIKES Iii AUREOLE ROCKS OF ON -LAP CONTACT COUNTRY NOTE PRESENCE IN SULPHIDE TYPICAL OF 'BOULDERY' GOSSAN ZONE BEARING Dr GABBRO, XENOLITHS OF GABBRO TRACE OF CUPOLA PORTION (2) 1N GRAINED, OF OF COMPOSITE Stop la ---1 LAURVIKITE. PERIPHERY DIKES OF COARSER — INCLUSIONS PHASES. IN HISTORY. AN OF CRYSTAL — REFLECTING PRESENCE OF NUMEROUS COUNTRY ROCK. PRESENCE OF NUMEROUS OF HYBRIDIZED PRESENCE BY DEGREE SULPHIDES COOLING APPARENTLY VARIATION CHARACTERIZED IRREGULAR LINITY GABBRO (I) MARKED �Fig. 4 Contact relations between xenolith and massif a w (p I �—95— (3) feldspars variably foliated; (4) mafic schlieren, the attitude ot which is conformable with the attitude of layering; (5) 2.4 0.0 gradation into more pegmatitic or porphyritic varieties. The laurvikites are primarily composed of perthitic feldspar, with variable amounts of aegirine—augite, olivine (up to Fa100), barkevikitic amphibole, biotite, iddingsite, quartz, zircon, fluorite and calcite. Variations in mineral compositions, and in the thermal histories of alkali feldspars may be cyclic. Marathon turn—off. Continue west on+Highway 17. 2.3 STOP 2 DARK GREEN LAIJRVIKITE - LAURVIKITE PEGMATITE (Fig. 1) These rocks aresimilar to the laurvikites from The perthites from the pegmatites are extensively exsolved, patch perthites, which are more sodic (Or27) than the less exsolved, braided perthites (Or62) from the less—pegmatitic, laurvikitic host. Oslo. 4.7 STOP 3 CONTACT BETWEEN LAURVIKITE AND BASIC METAVOLCANIC XENOLITH. (Fig. 1 & 4). This section of the highway reveals a broad exposure of the contact phase of syenite which can be seen to grade into more normal laurvikite. The basic metavolcanic is basaltic in composition and comprises a portion of the so—called Coubran Lake metavolcanic cap. Although more commonly amygdular in appearance, fine grained to aphanitic phases are distributed in such a manner as to suggest the contacts are flat lying. The contact between the overlying basaltic cap and the medium to coarse—grained, red coloured, hornblende— rich syenite is generally sharp and fragmented. The syenite, which is a hydrated equivalent of the laurvikite, contains abundant mafic clots, stringers, wisps and veinlets from 2 to 6 inches in size. These 'enclaves', which are amphibolite or syenodioritic in composition, tend to be aligned parallel to the contact. fL.5 STOP 4 TRA}ISITIONAL PHASE OF LAURVIKITE (Fig. 1). To the south similar rocks reportedly (Tuominen) �—96— exhibit both gradational and sharp contact relations to an overlying "syenodiorite" phase of netavolcanic cap rock. Because of the gradational relations the syenites were included with the syenodiorites on the revised map. Thin sections show phenocrysts of alkali feldspar (unexsolved) in a fine—grained groundmass of alkali feldspar (highly exsolved) ophitically enclosed by barkevikite. Relict clinopyroxene (variety augite — sodic augite) has been observed. Hematite staining of feldspars is generally extensive. This mineral assemblage is not much different from the 'darker' varieties of porphyritic laurvikite and likewise this rock type appears to represent a 'high' level variety. 8.6 STOP 5 NEPHELINE SYENITE (Pig. 1, 5 & 6). This outcrop (Fig. 5) is typical of nepheline syenites where in contact with 'diabasic' lava. The gross zonation within the feldspathoidal body is generally parallel to the contact with the 'diabase'. The diabase is variably nephelinized. One can conclude that, (1) there were at least two periods of dilation and emplacement (Fig. 61); (2) emplacement of feldspathoidal magma was controlled by jointing within the 'diabase' (see Figs. 6a, 6b, 6c); (3) emplacements along the more vertical joints preceded those along flats lying joints (Fig. 6c); (4) where present, the later feldspathoidal intrusions show nepheline pseudomorphed by the zeolite natrolite (with associated thomsonite) which is orange in colour. 16.8 STOP 6 LAURVIKITE (Fig. 1) 'Red' contact variety of laurvikite highly charged with inclusions of nearby 'diabase'. 18.4 STOP 7 PEGMATITE (Fig. I & 7). Traverse along a composite, nepheline (zeolitized) pegmatite emplaced into gabbros (Fig. 7). �—97— . ;' TRAIL TO GORDIE a LAKE 0 a S a \ Fig. 6c Fig. 6b .-T-_ IS — a a 0 C 0 - : ' : • 0 o -: . 0 0 0 0 a 0 a o C, 0 ZEOLI TIZE D FELDSPATHOIDAL INCLUDE C 0 LEGEND SYEN1TE S 0 0 FEMAGS. BIOTITE + BARKEVIKITE AVENITE WITH 0 8IOTITE + BARKEVIKITE C TUN NEL BARKEVIKITE — NEPHELINE LII VARIABLY NEPHELINIZED 8 SYENITE DIABASIC SUCKER LAVA (Pp a 0 COVE NONOMARKITE NUMEROUS INCLUSIONS LINE AIdE NTS OF OIABASIC" 1/4 LAVA U) I/B 0 SCALE Fig. 5 Nepheline syenite — "Diabase" contacts. /4 MiLE Stop 5 �LOOKING NORTH LOOKING NORTH — DYKE z—...— FGCN D LAVA ifl BIOTITE + flRKEVIKITE "DIABASIC SYENITE WITA VARIABLY NEPHELINIZED NEPHE LINE 25° NE 15° DIP 50° NE 40° DIP Stop 5 F€LDSPATHOIDAL SYENITE, FEMAGS, INCLUDE BIOTITE + BARKEVIKITE L ZEOLITIZED S Details of nepheline syenite veins. (See Fig. S for location). STRIKE NW 50° DIP 55° NE Rig. 6 OF COMPOSItrE �Pig. 7 West contact of CROSS OF DYICE SECTION Stop 7 �-100- ACKNOWLEVGMENIS Front Cover Photo, Sibley Park, near Thunder Bay, Ontario. Courtesy of Ontario Departn?ent of Travel & Publicity Geological Maps. All maps used in the field guides were modified from. Ontario Department of Mines maps. Maps covering the Field Trips are:Atikokan - Lakehead Nipigon - Tashota - Schreiber Geraldton Port Coldwell 0DM Map 2065 0DM Map 2137 0DM Map 2102 0DM Ptelim Map 114 Mr. Sam Spivak drafted all of the diagrams except those on pages 41 & 42. Many of these diagrams were compiled by Mr. Spivak from several sources, and many of the originals were rough field sketches. His patience and resourcefulness is duly acknowledged by the editors. The Committee would also like to acknowledge the secretarial services of Mrs. Jean Helliwell, for so ably organizing us in assembling the manuscript and pushing us towards the deadlines. �ro - 0 0 SCALE BAY THUNDER 2 MILES ISLANDS c5, WELCOME Am LANE MOTOR HOTEL ® SUPER/Of? LAKE UPTOWN MOTOR HOTEL HOLIDAY INN INTERNATIONAL ROYAL EDWARD HOTEL SLEEPING GIANT MOTOR MOTEL NOR-SHOR MOTOR HOTEL SHOREL INE MOTOR HOTEL 0 ® PRINCE AR THUR HOTEL � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1970 Description An account of the resource Institute on Lake Superior Geology. Lakehead University, Thunder Bay, Ontario. May 6-9, 1970. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1970 Contributor An entity responsible for making contributions to the resource R.N. Annells Lorne D. Ayres J.M. Berkson C.S. Clay Bill Bonnichsen W.C. Brisbin Paul M. Clifford I.F. Ermanovics John C. Green G.N. Hanson S.S. Goldich R. Malhotra Mao-Yang Hsu R.W. Hutchinson William F. Jenks C.W. Keighin J.D. Mancuso J.D. Dolence Harold M. Mooney Campbell Craddock Paul R. Farnham Stephen H. Johnson Gary Volz David C. Mulder R. Oja Richard W. Ojakangas Z.E. Peterman C. McA. Powell W.F. Read R.H. Ridler S. Viswanathan David H. Watkinson John Wood Grant M. Young Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/d56384bb82b7055c0dd8947ef3feb5c3.pdf 6eac8e3073122c599c349c7c53f10d11 PDF Text Text 17TH ANNUAL 17TH A UA INSTITUTE ON LAKE SUPERIOR UPERIOR GEOLOGY MINNESOTA DULUTH, MINNESOTA MAY 5-8,1971 MAY 5-8,1971 1 -4', �TEOINICAL ThGL?J CAL SESSIONS ABSTPACFS ABSTRACfS and FIELD GUIDES GUIDES for the the 17th 17th A\'NU.t\L ANNUAl.. INSTITUTE ON ON L!\.KJ:: LKE SUPERIOR INSTITUTE SUPERIOR GEOLOGY GEOLOGY Sponsored by Sponsored UNIVEPSI1Y ; IIr-,rNESOTA,DULUTI DULUTHI UNIVEPSIfl OF OF IINNESOTA, held at held DULU'fl!, ?IINNESOTA DULUTIl, i'UNNESOTA ..lay 1971 Jay 55 -- 8, 1971 Edited D.ll. Davidson Edited by by D. D.G. Dafoy Darby D.G. J.e. Green J.C. Green J.A. Grant Grant �TABLE OF TABLE OF COYI'EN]7S CONTENTS Page No. Prtge ~~o. INSTITIJTE A!\JDLOCAL IDCAL CCLt1IflEE CCl:IMITTEE INSTI'IlJTE DIRECTORS DIRECRS AND PIJGRAt4 (TflLE of ctpirgwrS pt*R 4S1RfrtCrS) ABSFRACI'S OF OF TECIWICAL TECINICAL SESSIONS ABSTRACTS SESSIONS 11 2 2 77 FIELD FIELD TRIPS Shore Volcanic Group A - North Shore Group (Keweenawan) 73 B - Cross-Section, Precambrian Rocks, Rocks, Minnesota I'brtheastern Northeastern ~tinnesota 97 C - ~Iesabi Mesabi Range Range - Biwabik Taconite US 128 D - Vermilion District 141 �-1-1- 17th 17th Annual INSTITIITE ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE ON Sponsored by University of of Minnesota, Minnesota, [*iluth Duluth at Duluth, Duluth, Minnesota May S5 -- 8, 1971 May INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS INSTITUTE Laughlin Steel Steel Corp., * J. IV. W. Avery Avery (Treasurer), (Treasurer), Jones Jones &Laughlin Corp., Negaunee, Negaunee, Michigan. ilichigan. C. C. Reed Reed (Secretary), (Secretary), Michigan J'Hchigan Geological Geological Survey, Survey, ;"Iichigan. Lansing, Michigan. D. M. M. Davidson, Davidson, University University of D. of Minnesota, Minnesota, [Ailuth IW.uth Duluth, Minnesota Minnesota W. J. Hinze, State University, East W. J. Hinze, Michgian Michgian State East Lansing, Lansing, Michigan. A. B. Dickas, Dickas, Wisconsin State Superior, University, Superior, Wisconsin State University, Wisconsin. Wisconsin. G. LaI3erge, Wisconsin Wisconsin State State University, University, Oshkosh, Oshkosh, G. L. U LaBerge, Wisconsin. Wisconsin. U. W. [;1. ],V. Bartley, Bartley, Thunder Thunder Bay, Bay, Ontario Ontario ** R. * Permanent * members menvers LOCAL C(J.·tUTTEE LOCAL CCt1ITrEE Chairman: Coordinating Oiainiian: D. D. M. M. Davison Davison Arrangements Connittee: Committee: R. W. R. W. Marsden C. L.L. Matsch lttsth C. Program Program Comnittee: Coninittee: D. C. D. G. Darby Darby 3. J. C. Green Green Field Trip Committee: Conrrni ttee: J. J. A. Grant Grant A. R. R. 14. W. Ojakangas Ojakangas �-2-2- PROGRAM ~~y 4, 1971 1971 Tuesday, May 5:00 p.m. p.m. Field (North Shore Shore Volcanics) leaves Field Trip Trip A (North Volcanics) leaves Hotel liadisson Hadisson Duluth. Hotel Duluth. Wednesday, May ~,~y 5, 1971 1971 6:00 p.m. p.m. to 7:00 p.m. p.m. 7:00 p.m. 7:00 p.m. to 9:30 p.m. Field Trip A A returns to to Duluth Duluth Institute Registration Registration - Poolside, Hotel Radisson Duluth Radisson Duluth Tnursday, ~hy 6, 1971 1971 Thursday_, May 7:30 a.m. to 12:00 a.m. a.m. Registration, Superior Superior Street StreetFoyer, Foyer,Hotel IbtelDuluth Duluth �-3- SESSION S E S S ION 11 i,lorning ;lorning Thursday, l11Ursday, i.fay 1971 'ay 6,6, 1971 Symposium on Keweenawan Keweenawan Geology Geology—- Lake Superior Region Region Symposium Co-chairmen: Co-chainnen: Jack and Walter Jack Phillips and 1/alter White Page No. No. 8: 45 8:45 J. C. C. Green Green IntroductoryRemarks Remarks Introductory 9:00 IV. White Iv. & Keweenawan lVesterrunost KeweenawanStratigraphy Stratigraphy ofofTYesternimost Michigan Hichigan 71 9:20 N. K. N. K. Ih.xber Huber The Keweenawan KeweenawanGeology Geology Isle Royale, The ofofIsle ;.1ichigan Michigan 31 9:40 II. A. A. Hubbard Hubbard H. Keweenawan Geology Geology of the the Porcupine Porcupine Keweenawan ;"buntains, tuntains, Western Upper Peninsula 30 20 Others ~·,tichigan Uchigan 10:00 J. C. C. Green Green of the theNorth North Shore Shore Voltanic Vo1tanic Stratigraphy of Group Northeast Bay, 1innesota ;··linnesota Group Northeastof of Silver Bay, 10:20 R. R. N. N. Annells Armells Middle ~·liddle Keweenawan VolcanismofofEastern Eastern Lake Keweenawan Volcanism Lake Superior 7 7 10:40 A. P. Jtotsala A. P. Ruotsala Characteristicsof ofSome Some Alteration Alteration Minerals ~tinerals Characteristics Lake Lava Lava Series, Michigan Portage Lake Series, Michigan 59 11 :00 11:00 IV. T. T. Jolly W. Fades Puinpellyite Facies Zeolite and Prehnite Prehnite -- Pumpellyite Zeolite and theKeweenawan Keweenawan Basalts Northern in the Basalts of of Northern :.tichigan The Role Roleof of Volatiles Volatiles Michigan II: II: The 34 11: 20 11:20 T. A. T. A. Vogel Vogel & R.J. R.J. Chemically Zoned Native Copper Chemically Zoned Native Copper and and from White IVhite Pine Pine Michigan Michigan Rohrbacher Chalcocite from 11 :40 11:40 1!. C. C. halls H. Halls G. G. F. F. West \\Test 12:00 12: 00 DON NOON The Isle Royale Royale Fault Fault & The Mjourn for Adjourn for Lunch Lunch There 'vi1l be a lunch lunch meeting meeting of Board of the There will be of the the Board of Directors Directors in the Hotel Radisson Radisson ililuth fuluth—. - location to be be announced. announced. hotel 70 25 �-4- SESSION S E S S ION 22 Afternoon Thursday, Thursday, May 6, ~my 6, 1971 Symposium on on Keweenawan Keweenawan Geology Geology -- Lake Superior Superior Region Region Co-Chairmen: Co-01ainnen: 1:40 1:40 2:00 2:00 2:20 2:20 J. Leone K. Siiis Raymond J. Leone and and Paul K. Sims J. T. T. Mengel, Mengel, Jr.& Jr. Exploration J. Exploration Geology Geology of of Douglas Douglas County, County, R. R. A. A. Hendrickson Hendrickson Wisconsin Wisconsin D. Davidson ,Jr. D. vI. M. Davidson,Jr. Ne,.. View View of of the the Duluth Duluth Complex, Complex, A New A Minnesota B. Bonnichsen B. Bonnichsen in the the Southern Southern Part Part of of the the Hornfelses in Hornfelses Page Page No. No. 47 13 13 11 Duluth Complex, Il1luth Complex,?•linnesota Minnesota 2:40 2:40 M. M. G. G. i4idrey M.ldrey & P. W. W. Weiblen P. Reinvestigation of of "Red "Red Rocks" Rocks" in Reinvestigation in the the Pigeon Pigeon Point Point Area, Minnesota Minnesota 53 53 The Great Logan Logan Paleomagnetic Paleomagnetic Loop Loop The Great 58 58 3:00 3:00 to Coffee Break to 3:20 3:20 3:20 3:20 W. A. Robertson Ibertson W. A. W. F. F. Fahrig Fahrig W. & 3:40 3:40 A. Me.ttis A. 1'-attis Lower Lower Keweenawan Keweenawan Sediments Sediments of of the the Lake Lake Superior Superior Region Region 45 4:00 4:00 D. Myers D. ;"fyers The and Tectonic Tectonic Significance Significance The Sedimentology Sedimentology and of the Bayfield of the Bayfield Group, Group, Wisconsin Wisconsin 54 4:20 4:20 C. Merey G. B. B. ~brey Revised Keweenawan I{evised Keweenawan Subsurface Subsurface Stratigraphy, Stratigraphy, Southeastern Minnesota 50 50 4:40 H. C. Halls H. C. C. F. F. West West C. and Stratigraphy of the the Shallow Shallow Structure Structure and Lake from Seisnic Seismic Refraction Refraction Lake Superior Superior Basin Basin from Measurements Measurements 23 & ******** * * * * * * **** **** ** Evening 7:30 p.m. p.m. Banquet -- Great Hall Banquet Hall - Hotel Radisson Radisson Duluth Duluth - ADDRESS ADDRESS -- Dr. Carl Carl R. R. i\nnhausser Arrmlausser Economic Economic Geology Geology Research Research Unit Unit University University of of Witwatersrand Witwatersrand Johanneshurg, South South Africa Africa Johannesburg, �-5-5— S E S S ION 33 SESSION !trning ~'brning Friday, May 7, Friday, 7, 1971 1971 General General Session Session Co-Chaitnen: Co-Chairmen: Cedric. Cedric. L. L. Iverson Iverson and and J. J. Ka11iokoski Kalliokoski Page It. No. Page 8:40 8:40 F. C. F. C. Tan Tan 4& E. C. Perry, Perry,Jr. Jr. Implications of Carbon Carbon Isotope Isotope Ratio Ratio Variations in in Carbonates Carbonates from from the the Biwabik Biwabik Variations Iron Iron Formation, Formation, Minnesota Minnesota 64 9:00 9:00 S. Viswanathan, S. Viswanathan, Ii. C. C. Perry, E. Perry, Jr. J r. & P. Sims 4 OxygenIsotopic Isotopic Studies Studies of Oxygen of Early EarlyPrecambrian Precambrian Granitic and and Metamorphic Rocks Rocks from from the the Western Giants Range Range Batholith, WesternPart Part of of the Giants Northeastern Minnesota Northeastern Minnesota 66 9:20 G. 1. LaBerge LaBerge G. L. Some Geology of Harathon County County Volcanic of the ?larathon Some 39 Belt P. O. Banks Banks 4~ P. 0. W. Van Sc!llTlUS W. R. R. Van Schmus Rocksof of Iron Chronology of Precambrian Precambrian Rocks chronology L. L. A. A. Prince Prince 4& Geochronology of the the Giants GiantsRange P~ge Granite Granite Geochrono]ngy 57 10:20 G. Klein G. Precambrian Clastic Paleotidal Sedimentation Sedimentation Precambrian Clastic Paleotidal 36 10:40 Pt. ii!inze, Continental Continental Rifts W. Jinze, H. iiavidson,Jr. D. Daviclson,Jr. I). Iv!, & 4 R. Roy 11:00 1\la1an & It C. R. C. Malan 1]. A. A. Sterling D. 9:40 9:40 10:00 G. C. N. . I·ranson Hanson Fj and Dickinson Dickinson and 99 Counties, Michigan Michigan Thoriumin in PreDistribution of Uranium Uranium and and Thorium cambrian Rocks of of the Western cambrian Rocks Western Great Great Lakes Lakes 29 42 42 Region 11:20 20 11: N. 11[. N. Pt. O'Hara 4& w. J. I:inze Hinze Lake nichigan Michigan Aerornagnetic Aeromagnetic Survey Survey 56 56 /u An Aeromagnetic Survey Survey of Southern of the Southern ofMichigan ~lichigan Peninsula of 35 iv. 11:40 11 :40 . R. 1. L. Kellogg Kellogg 4l]" Pt. J. W. J. I-Jinze Hinze 12:00 NWN 12:00 NOON — - Lunch �-6-6- SESSION S E S S ION 44 Afternoon Afternoon 1971 Friday, Friday, I,1ay lay 7, 1971 General Session Co-Chairmen: Co-Chainnen: C. Tychsen 1'chsen Meredith F. E. Ostrom and and Paul C. Page No. Page No. 1:20 1:20 Business of the the Institute Institute &zsiness Meeting Meeting of 1:40 1:40 M. S. S. M. 2:00 2:00 J. Mancuso t,.1.ancuso J. J. J. F. Dimroth & E E. J. Chauvel .J. 2:20 2:20 W. ]Aihling W. fuhling Precambrian Iron Formation Precambrian Formation at at Copper Copper ~·ibuntain, FremontCounty CountyWyoming 1Vyoming Nbuntain, Fremont 18 2:40 E. Frodeston F. Frodeston Some Sedimentary in the the Lower Lower Sonic Sedimentary Structures in Cherty nember Fonnation: Memberofofthe the Bhvabik Biwabik Iron Formation: Cherty The Virginia Virginia Horn The Horn Area Area 32 32 3:00 G. Spencer Spencer G. Chert in Sediments Sediments Chert in 62 3:20 J. Mathersill ~bthersill Limnogeological ofThunder Thunder Bay, Bay, Limnogeological Studies of Lake Superior, Superior, Ontario Lake Ontario 51 3:40 R. Shegelski R. Shegeiski TI1e ofThunder Thunder Bay, Bay, The General General Stratigraphy Stratigraphy of Lake Lake Superior 61 4:00 4: 00 End of Technical End of TecJmical Sessions Sessions Lougheed & Hematite Pseudomorphic After After Biogenic Biogenic Pyrite in the the Negaunee Negaunee Iron Iron Formation Fonnation Pyrite in Textural Facies Facies Analysis of Precambrian Textural Precambrian Cherty Ironstones Ironstones *** * * * **** **** **** ** ** 5:00 5: 00 (Dinner and lodging are included and lodging included in the field field trip trip fee.) fee.) Departure for for Field Field Trips: Trips: Field Field Field Field Field Trip A Trip Trip BB -Trip CC -Trip UD -- North Shore Volcanic Group Volcanic Group Cross-section, Precambrian Rocks Precambrian Rocks Mesabi j\!esabi Range Taconite Range -- Biwabik Biwahik Taconite Vermilion District District Vemiilion Buses will will depart Buses depart from from Hotel Hotel Radisson Radisson Duluth. Duluth. *********** Saturday, nay May 8th, 1971 Saturday, 6:00 to to 7:00 (approx .) (approx.) REThRNOF OFALL ML FIELD RETIJRN FIELD TRIP TRIP BUSES. BUSES. 41 41 15 15 �-7- -7-- KEWEENAWAN VOLCANISM VOLCANISM OF OF EASTERN EASTERN LAKE LAKE SUPERIOR. SUPERIOR. MIDDLE KEWEENAWAN R. N. N. ANNELLS R. Geological Survey Survey of of Canada, Canada, Ottawa. Ottawa. ABSTRACT Following the study of the Michipicoten Island Island Keweenawan flows flows reported reported elsewhere (Annells, (Annells, 1970), srone type type of detailed stratigraphic/petrographic 1970), the same has been carried out on the Keweenawan volcanic rocks study has rocks of the the Mamainse Point, the east shore shore of Lake Lake Superior. Superior. Point, Alona Bay and Cape Gargantua sections on the three east east shore shore sections sections are are mostly mostly made made up up of of inafic mafic olivine—tholefite olivine-tholeiite These three types of texture, accompanied by by aa smaller smaller number number types of medium-coarse medium—coarse ophitic or diabasic texture, of fine—grained fine-grained olivine—poor olivine-poor tholeiite tholeiite flows. flows. Flows of intermediate composition composition found in these these sections sections and and the the flows flows show show little little variation variation in in mineralogy. mineralogy. were not found Small rocks occur occur interbedded interbedded with with the the Small volumes volumes of both basic and acid pyroclastic rocks flows flo\vs in the the lower part of the 14,300 foot foot Mamainse Point section, section, and and conglomerconglomerates partings showing good cross—bedding cross-bedding outcrop in in the the upper upper half half ates with with sandstone partings of this this section and in that that at at Cape Cape Gargantua. Gargantua. Evidence of the simultaneous availability of basaltic and and rhyolitic rhyolitic material material of the is is seen in the Mamainse Matnainse Point Point section; section; plugs, plugs, dykes dykes and and sheets sheets of of fine-grained, fine—grained, often flow—laminated flow-laminated and and autobrecciated leucorhyolite leucorhyolite occur occur at at all all levels levels of of this this one such intrusive sheet was found to section and one to he be composite, composite, having having aa 2—foot 2-foot basal selvage of fine—grained fine-grained basalt and and aa 50—foot 50-foot acid acid upper upper part. part. Fetrographic Petrographic similarities found found in in flows flows of of the the Mamainse Mamainse Point Point and and Cape Cape good basis basis for for lateral lateral correlation correlation of of these these two two Gargantua sequences provide aa good sequences. Near the basal unconformity of theMamainse therlamainse section section there there occurs occurs aa highhighly olivine-tholeiite flow flow crowded crowded with large large plagioclase plagioclase ly distinctive glomerophyric olivine—tholeiite laths concentrated concentrated in spherulitic clusters up laths up to to two two inches inches in in diameter diameter (Ciblin, (Giblin, 1969); aa flow flow of of exactly similar type 1969); type outcrops 40 40 miles NNW NNW along along strike strike near near the the base of the the Cape Gargantua section section (Ayres, (Ayres, 1969). 1969). Both these occurrences are assoBoth these ciated with with aa group group of olivine-tholeiite olivine—tholeiite flows ciated flows rich rich in in large large pseudomorphs pseudomorphs after after \vhich may make up up to to 35 35 per per cent cent by by volume volume of of the the rock rock in in parts parts olivine phenocrysts which of such flows This striking similarity of the flows at at Mamainse Mamainse Point. Point. This the flows flows in in the the levels of the lower levels the Mamainse Point and Cape Gargantua piles piles suggests suggests simultaneous simultaneous effusion of the the same S~le mafic magma supply supply over over aa wide wide area area to to preduce pr~duce lava lava flows flows of of sii,!lar extent to to that that of of the the Greenstone Greenstone Flow Flow of of the the Michigan Michigan Keweenawan. siIIl~Lar extent Point, Alona Alana Bay Bay and and Cape Cape Gargantua Gargantua flo9s f1o'to.{s are are also also petrographical— petrographicalThe Mamainse Hamainse Point, ly similar to olivine—tholeiite flows ly to the the olivine-tholeiite flows forming the the basal part part of of the the Michipicoten Michipicoten Island section and it is possible that that these these latter latter flows, flows, also also cut cut by by acid acid intruintrusions, sions, may represent the the upper part of of an an extensive extensive and and largely largely uniform uniform flood flood babasalt pile whose earliest members rest rest directly directly on on the the Archaean Archaean on on the the east east shore shore of of Lake Superior. Superior. The more highly differentiated differentiated andesite andesite and and rhyolite rhyolite flows flows of of Hichipicoten Island are thus interpreted Michipicoten Island are thus interpreted as as being being of of much much later later extrusion extrusion than than the the A general increase in the deMamainse Point, Point, Alona Alana Bay Bay and and Cape Cape Gargantua Gargantua flows. flows. A flows is gree of alteration alteration of of lava lava flows is apparent apparent as as the the Keweenawan Keweenawan lava lava pile pile is is followed followed downwards of the the Michipicoten Michipicoten Island Island section section to to the the base base of of the the downwards from from the the top top of Mamainse Point Point section. section. Mamainse �-8—8— Some differences differences in general chemistry exist between flows Some flows newly newly analysed analysed from from Island and and Maniainse Mamainse Point the Island Island flows flows the Michipicoten Island Point sections; sections; 36 36 analyses of the tholeiitic trend trend of moderate iron—enrichment iron-enrichment on on an an Nfl MFA plot; plot; aa similar similar plot plot follow a tholeiltic of 46 analyses of Mamainse Point flows flows gives gives aa tholefitic tholeiitic trend trend of of high high iron—enrichiron-enrichment. References; References: Annells, R. N., N., Annells, It. 1970, geology of of Michipicoten Michipicoten Island, Island, 1970, Keweenawan volcanic geology Lake Superior Lake Superior; Program, Program, 16th 16th Ann. Ann. Inst. Inst. on. on. Lake Geol., Thunder Bay, Bay, Ont., May May 1970, 1970, 7. 7. Ceol., Ayres, L. L. D., D., 1969, 31 and 30, 30, Ranges 20 20 and and 19; 19; 1969, Geology of Townships 31 Ontario Dept. Dept. Mines Ceol. Geol. Rept. Rept. 69,38. 69,38. Giblin, P. E., E., Giblin, P. 1969, Prelim. Geol. Geol. Naps Maps 553 553 and and 555. 555. 1969, Ontario Dept. Dept. Mines, Mines, Prelim. �-9—9— CHRONOLOGY OF PRECAMBRIAN ROCKS ROCKS OF OF IRON IRON AND AND DICKINSON COUNTIES, MICHIGAN P.O. P.O. Banks Department of Geology Geology Case Western Reserve University, University, Cleveland, Ohio, 44lO6 44106 and W.R. Van Schmus W.R. Department of Geology Geology University of Kansas, Kansas, Lawrence, Lawrence, Kansas, Kansas, 6604k 66044 U—Pb analyses of cogenetic zircon suites and Rb-Sr whole rock analyses U-Pb from from selected Precambrian Frecambrian units units in Iron and Dickinson Counties, Michigan, suffice to for this classic suffice to establish an internally consistent chronology for area. Stratigraphic nomenclature used herein is adopted from from James et et al. al. (1961). (1961). Zircons from the Norway Lake Gneiss, which underlies the Dickinson Zircons from the Group, 2375 m.y., but Group, yield aa concordia intercept age of approximately 2375 Rb-Sr from the Norway Lake Gneiss do not define define an an Rb-Sr whole whole rock rock analyses analyses from isochron, and the isotopic isotopic composition composition of of Pb Pb from from separated separated feJ.dspars feldspars is isochron, is abnormal. Thus, from the Thus, we we conclude that that the 2375 m.y. m.y. "age" obtained from zircons zircons is is probably the the result result of complex metamorphism and deformation of the Norway Lake Gneiss and does not indicate indicate its its true true absolute absolute age. age. The 2375 m.y. m.y. event event that that affected the the Norway Lake Gneiss may be pre—Dickinson, pre-Dickinson, 2375 thus establishing a possible older limit for for the the age age of of the the Dickinson Dickinson Group. Group. Earlier published zircon analyses suggesting suggesting aa much greater greater antiquity antiquity for for the Dickinson Group etal., Group (2700 (2700 m.y. or more: Aldrich Aldrich et al., 1965) 1965) are are interpreted interpreted to reflect detrital detrital zircon zircon components components in in the thernetasedimentary metasedimentary gneisses. gneisses. The pre—Animikie pre-Animikie Porphyritic Red Granite, Granite, whose whose field field relation relation to to the the Dickinson Group is is uncertain, gives aa zircon zircon conoordia concordia intercept intercept age age of of approximately rock Rb—Sr approximately 2100 2100 m.y. m.y., and whole rock Rb-Sr analyses are also consistent consistent with this We interpret interpret this this age age to be post-Dickinson, thus bracketing this age. age. We the age of the Dickinson Group between 2100 2100 m.y. and, and, perhaps, perhaps, 2400 2400 m.y. m.y. , A single zircon analysis from from the Hemlock Volcanios Volcanics of of the the Animikie Animikie A but the the zircon zircon is is somewhat somewhat discordant, discordant, Series yields a Pb-Pb age of 1985 m.y., but so that that the concordia intercept intercept age is is expected expected to to be be slightly sligh~ly older older at at approximately 2000 2000 m.y. m.y. Rb-Sr whole rock analyses on the the post-Animikie post-Animikie Feavy Peavy Complex Complex yield yield Rb—Sr an age of approximately 1700 m.y. approximately 1700 m.y. However, However, previously published mineral age age determinations determinations on other post—Animikie post-Animikie units units indicate indicate that that the the Animikie Animikie Series is is definitely al., 1965). 1965). Thus, Series definitely older older than than 1900 1900 m.y. m.y. (Aldrich (Aldrich et etal., deposition of the Animikie Series appears to to be be bracketed bracketed in in the the interval interval between 2100 2100 m.y. m.y. and and 1900 1900 m.y. m.y. A A maximum age of 2100 m.y. m.y. for the Animikie Animikie Series, Series, in in conjunction conjunction with with published Rb-Sr data on on the the post—Huronian post-Huronian Nipissing Nipissing Diabase Diabase (2160 (2160 rn.y.) m.y.) and on Huronian 1-luroniansediments sedimentsthemselves themselves(2285 (2285m.y.) m.y.) (Van (Van Schmus, Schmus, 1965; 1965; Fairbairn Fairbairn et al., 1969), 1969), severely severely restricts restricts possible possible correlations correlations between the Animikie etal., Animikie Series and the Huronian formations of the North Shore of Lake Huron. Series Shore of Lake Huron. �—10— -10- References Aldrich, L.T., Davis, Davis, C.L., G.L., and and James, James, FI.L., H.L., 1965, 1965, Ages Ages of of minerals minerals from from metamorphic and and igneous igneous rocks rocks near near Iron Iron Mountain, Mountain, Michigan: Michigan: Jour. Petrology, v. ~ v. 6, 6, pp. pp. +47-472. 447-472. Fairbairn, H.W., H.W., Hurley, Hurley, P.M., P.M., Card, Card, K.D., K.D., and Knight, Knight, C.J., 1969, Fairbairn, Correlation of radiometric radiometric ages ages of ofNipissing Nipissingdiabase diabaseand and1-luronian Huronian CorrelaL on of metasedimen-ts with with Proterozoic Proterozoic orogenic orogenic events in Ontario: Can. metasediments Jour. Earth Sci., Sd., i. Jour. Earth v. 6, pp. Lt89_497. 489-497. James, ILL., H.L., Clark, Clark, L.D., Lamey, C.L., C.L., and Pettijohn, F.J., F.J., 1961, Geology Geology James, L.D., Lamey, U.S. Ceol. of central Dickinson County, County, Michigan: Michigan: U.S. Geol. Surv. Surv. Prof. Prof. 310, 176 176 p. p. Paper 310, Van Schmus, Schmus, R., R., 1965, The geochronology of the Blind River—Bruce River-Bruce Nines Mines area, area, Ontario, Canada: Canada: Jour. Jour. Ceol., Geol., v. v. 73, 73, pp. pp. 755-780. 755-780. �—11--11- HORELSES IN THE DULUTHCOMPLEX, COMPLEX,MINNESOTA MIIESOTA HORNFELSES THE SOUTHERN SOUTHERN PART PART OF OF THE DULUTH Bormichsen Bill Bonnichsen Cornell University Hornfels of feet feet in in Hornfels bodies ranging from less than an inch to thousands of dimensions are abundant in the southern part of the Duluth Complex. They dimensions are were derived from from a wide wide variety of initial rock types, types, many of which occur in the complex footwall. footwall. The The most most abundant abundant types types were derived from argillaceous ceous sediments of the Virginia Formation, Formation, mafic to intermediate volcanic rocks of Keweenawan age and various intrusive rocks indigenous to the complex. rocks complex. Others include iron iron formation, formation, quartzite quartzite and and d.ioritic dioritic rocks rocks from from the the prepreKeweenawan basement basement and. and clastic Keweenawan age. age. elastic sediments sediments of probable Keweenawan Virginia inclusions are are very very similar similar to to metamorphosed metamorphosed footwall footwall Virginia; Virginia; however, the relative relative mineral mineral proportions are hovrever, the the grain grain size size is is larger larger arid and the are slightly different. The silicate mineralogy of argillaceous inclusions inclusions inincludes coexisting cordierite, orthopyroxene, biotite, cludes cordierite, orthopyroxene, biotite, plagioclase and and potassium potassium feldspar. Minor amounts amounts of of pyrrhotite, pyrrhotite, graphite, ilmenite and and traces of chalchalgraphite, ilmenite copyrite and pentlandite are common, but olivine and and Ca pyroxene invariably but olivine pyroxene are invariably absent. Various types types of of relict relict se.imentary sedimentary structures structures are distinguishable distinguishable in all but the smallest smallest of of hornfelsed hornfelsed Virginia Virginia inclusions. inclusions. all inclusions are are characterized characterized by by their lack of of relict Volcanic hornfels inclusions their lack sedimentary structures, local round round to ellipticalplagioclase plagioclase and and Ca pyroxene structures, local to elliptical segregations that probably were segregations were amygdules amygdules and their mineralogy. They consist largely of niagneof plagioclase plagioclase and and Ca pyroxene, and normally contain abundant magnepyroxene, and tite and tite and orthopyroxene (commonly (commonly inverted invertedpigeonite). pigeonite). Olivine, brown brown hornblende, apatite, ilmenite, and and traces traces of biotite biotiteoccur occurininsome some bodies bodies but but none none apatite, ilmenite, graphite, or or more more than than traces traces of of potassium potassium are known knovm to contain cordierite, cordierite, graphite, feldspar. FeO+MgO of various The proportions of of weight weight percent percent 3102, Si0 , Al20~ and. and FeO+MgO 2 types of hornfelses hornfelses and equivalent equivalent rocks rocks are are plotted ploted in in figure figure 11 (Bonnichsen, (Bonnichsen, in prep.). A, B prep. ). The A, B and CC groups are materials from from the the Virginia Virginia Formation, Formation, vlhereas the the D, EE and and FF groups groups are are volcanic volcanic hornfelses homfelses and. and their equivalents. whereas Note Note that, that, although although both both groups groups show show considerable considerable range range in their proportion A12O3. of Si0 the Virginia materials have higher proportion of Al 0 . , SiOa, the Virginia have a higher proportion 2 2 3 The group A unmetamorphosed Virginia and and equivalent hornhomA samples are unmetamorphosed felses from the felses the footwall footwall of of the the complex. complex. The group BB samples are are from from incluinclusions vlithin within the complex. sions complex. Note their depletion in 8i0 relative to the A 5102 the A 2 group. This This suggests suggests that Si02 8i02 was lost from from the inclusions; inclusions; this this loss loss is is accompanied by a similar depletion of K20 ~O in several several samples samples and and suggests suggests loss loss of aa grantic grantic partial partial melt melt during during the the hornfelsip.g hornfelsipg process. process. The group CC samples samples are are from the margins margins of hornfels bodies and and thus thus were in in direct direct contact with with initial the the intrusive intrusive rocks. rocks. Their Their compositions compositions deviate further from from the initial deviate farther values than do those of group B; B; they are considered to be refractory resiresiduals which which had had become become nearly nearly equilibrated equilibrated with vlith the the adjoining adjoiningmagnias. magmas. Part group BBrocks feldspars and and cordierite of the the group rockscontain containtexturally texturallyinterstitial interstitial feldspars which are interpreted interpreted as as recrystallized recrystallized partial partial melts. melts. During the hornfelsing process aa melt melt with ,nth the the composition composition ofofcordierite cordieritearid, and alkali alkali feldspar evidently developed after a granitic fraction had had been been lost. lost. Hornfelses with the group C where this this later type type of melt melt C compositon are considered to have formed formed where had been lost. The formation of granitic dikes dikes and and the the production production of of abundant abundant C pyroxene are the biotite and orthopyroxene orthopyroxene at at the expense of olivine arid and Ca principal effects on the enclosing intrusive intrusive rocks assimilation rocks \vrought wrought by the the assimilation of such partial melts. �—12— -12- Si02 :7 Figure I. 'F A1203 FeO* A 00 E F. c@ 50 to 41203 AI203 V v vV v V vV to to FeOtMgO FeO+ MgO V v Group E consists of hornfelsed. basalts; they they have have bulk bulk compositions compositions that that hornfelsed basalts; show little deviation from from the the compositions compositions of of ordinary ordinary basalts. basalts. Group Group FFrocks, rocks, however, have and Si02 Si02 and and higher higher Ti0 Tb22 and and FeO have lower lower K20 and FeO contents contents than than ordinary hornfelses may have been inbasalts and and have high high Fe/Mg Fe/Mg ratios. ratios. Two of these hornfelses trusive residual residual liquids liquids which which separated separated from from trocto].ite troctolite but but the the other other one one evidently is aa hornfe].sed hornfelsed volcanic rock that that contains contains probable probable relict relictaxnygdules. amygdules. dently is volcanic rock Sample D D is is an magnetite-richbasaltic basaltic rock from an unmetamorphosed unmetamorphosed magnetite-rich from along along the the eastern margin of the complex; its Fe/Mg ratio is is like that of group F. The margin of complex; its Fe/lf~ ratio volcanic rock in group F may initially have had a composition composition similar to that that of sample D. D. If so , it material during during so, it lost lost aa substantial amount amount of granitic granitic material hornfelsing process. the hornfelsing process. in the The abundance and distribution of hornfelsed volcanic rocks in system of southern part of the complex supports the concept that an extensive system Keweenawan flows was present throughout the region and had been laid down Kew"eenawan flOivS was dOim on an erosion erosion surface surface cut cut in in the the Middle Middle Precambrian Precambrian rocks. rocks. The the Theintrusion intrusion of the an Troctolitic Series Series and accompanying crustal extension evidently broke up the volcanic volcanic rocks. rocks. As distributed throughout As a result result the the hornfelses hornfelses are are widely ddely distributed the southern half of of the the complex. complex. Many l~ of of the the large large bodies occur occur as as septum septum betvreen adjacent intrusive intrusive bodies. bodies. The great number of inclusions of various between adjacent types along the the footwall types footwall of the complex indicated that the intruding troctoconsiderable mechanical mechanical strength. strength. Evidently, litic magmas had considerable Evidently, these thesemagmas magmas were mushes were in the the form form crystal-rich crystal-rich mushesduring duringemplacement. emplacement. Ref: Bonnichsen, the Duluth Duluth Complex, Complex, St. st. Bonnichsen, B. B. (in prep.); prep.); The southern part of the Louis and Lake of Minnesota, Minnesota, Lake Counties, Counties, Minnesota; Minnesota; to to be be publ. publ. in in Geology Geolor of Schwartz commemorative volume;P.K. P.K. Sims, Sims, ed. G.M. Schw"artz connnemorative volume; �-13—13— A NEW VIEW OF THE DULUTH DULUTH CO~PLEX, COMPLEX, MINNESOTA A by Donald H. M. Davidson, Davidson, Jr. Jr. University of Minnesota, Duluth Duluth and Minnesota Geological Survey Hinnesota ABSTRACT A B S T R ACT The late Precambrian (Keweenawan) (Keweenawan) Duluth Complex is is a sequence generally discordant intrusive rocks of generally rocks extending extending northeastward northeastward from from Duluth to to 1-loyland, Hovland, Minnesota Minnesotain in a a roughly roughly crescentic crescentic configuration. The the Complex Complex is is bifurcated bifurcated on on the the east east and and south south The outcrop outcrop pattern of the by rocks rocks of the the North Shore Shore Volcanic Volcanic Group. Group. in Table 1, 1, three three rock rock series series (anorthosite, (anorthosite, As may be noted in troctolite—olivine gabbro gabbro and and felsic) troctolite-olivine felsic) constitute the the major petrologic petrologic units of the Complex. units the Complex. Anorthosite series rocks were apparently emplaced as large, crystal-liquid as crystal—liquid masses massesinin ~.,hich whichcumulus cumulusplagioclase plagioclaseisis the the prepredominant mineral. mineral. The anorthositic rocks, which form the central portion dominant rocks, t.,hich of the of the Complex, Complex, have been subsequently intruded intruded by by the the troctolite troctolite series series along the northern and western footwall footwall and and by by the the olivine olivine gabbro gabbro series series to troctolites and to the southeast. The The troctolites and gabbros gabbros are are aa sequence sequence of of genergenerally containing cumulus plagioclase and and olivine olivine and and poik— poikally layered layered rocks rocks containing ilitic pyroxenes. The The basal basal troctolite series dips gently (15°) towards dips gently (15°) towards Lake Superior, Superior, whereas whereas the Lake the attitudes of the the upper upper olivine olivine gabbro gabbro series series vary (e.g. Sawbill vary from northward dips dips of of 40° 40° (e.g. Sawbill Lake Lake area) area) to to southward southward at low Q5°) cLS°) angles angles (e.g. (e.g. along along the the Brule Brule River Prong). Felsic series at rocks are are predominantly granophyric granite which occur rocks occur as as subhorizontal subhorizontal sheet—like masses sheet-like masses above aboveboth bothmargins marginsofofthe theolivine olivine gabbro gabbro series. series. Separate minor arate minor intrusives as the Endion Sill, Sill, the the Beaver Beaver Bay Bay Complex Complex intrusives such as and to be younger than than the the Duluth Duluth Complex, Complex, and the the Hovland Complex appear to whereas only Lie the Gunflint Gunflint Prong Prong Layered Layered Complex Complex appears appears older. older. Petrologic relationships sources derived derived from from the the mantle, mantle, to to relationships suggest suggest multiple magma sources account for account for the the petrogenetic sequence of the the Duluth Duluth Complex. Complex. The Duluth Complex Complex is is coincident coincident with with the the axis axis of of the the Mid—Continent Mid-Continent Gravity High. High. Footwall shearing and the the asymmetric asymmetric position position of of the the Complex Complex with with respect respect to to the the Lake Lake Superior Superior Syncline Syncline suggest suggest Complex Complex emplacenent consanguinous emplacencnt consanguinous with with rifting. riftine. Gravity studies to to date date suggest suggest the Complex thins thins or is absent beneath Lake Lake Superior. Superior. Dominant Complex Complex the N.20E.—N.SOE.) are common fracture trends trends (N.-. (N.-~.90E. or W. W.,, ~.20E.-~.80E.) common throughout throughout 90E. or the Lake regional post—intrusive post-intrusive extension. extension. the Lake Superior area suggesting regional Significant base-metal base—metal mineralization mineralization occurs occurs within within selected Significant troctolite controls afforded afforded by by host host troctolite series series horizons horizons with local ore controls rock lithology and structural settling settling shelves. shelves. Should the proposed funnel the central complex complex be verified, subsurface subsurface funnel configuration configuration of the exploration of the the Southern Complex Complex appears appears warranted. ~varranted. �Table 1. Table 1. Summary of Principal Petrologic Series and Units, Units, Duluth Complex, Complex, Minnesota Late Minor Hinor Intrusive Complexes Felsic Troctolite— TroctoliteDuluth " G hb Duluth Complex CompleX01i Gahbro Ol l.Vl.ne ,cambrian a ro cambrian (l.ltO.2b.y.) (l.10.2b.y.) Endion Sill Sill Er.nst~ W. W. C., G., 1960, 1960, Jour. Jour. Ernst, Beaver Bay Complex Gehman, H. H. M., M., Jr., Jr., 1957, 1957~ Unpub. Unpub. Ph.D. Ph.D. Thesis, Thesis, Univ. Univ. of of Minn. Minn. Konda, T., 1970, 1970, Contr. Contr. Min. Mm. Pet., Konda, T., Pet., Vol Vol 29, 29, p. p. 338—344 338-344 Hovland Complex Hoviand Complex Jones, N., N., 1963 Unpub. Unpub. M.S. M.S. Thesis, Univ. Univ. of Minnesota Granophyric Granite and and Minor Felsic Hinor Intrusives Davidson, D. D. M., Jr., Jr., 1969, 1969, Minn. ~linn. Geol. Geol. Surv. Surv. Misc. Misc. Map Ser., Ser.~ M—7, M-7, M—8 M-8 Grout, F. F., F., and and others, others~ 1959, 1959, Minn. Minn. Geol. Geol. Surv. Surv. Bull. Bull. 39. 39. Grout, F. Grout, F. F., F., and and others, others, 1959, 1959, Minn. Minn. Geol. Geol. Surv. Surv. Bull. Bull. 39. 39. Grout, F. Basal Troctolite Troctolite ,1969, Minn. Minn. Geol. Geol. Surv. Surv. Rept. Rept. Inv. mv. 99 Phinney, W. C. C.,1969~ Phinney, W. 44 Bull. R. B., B., 1964, 1964~ Minn. Minn. Geol. Geol. Surv. Surv. Bull. 44 Taylor, R. Central Anorthosite Early Minor Ninor Intrusive Complexes North ~orth and Anorthosite Inclusions Bonnichsen, Bill, Bill, 1969,30th 1969,30th Annual Annual Min.Sympos.,Univ.Minn.pp.8993 ~lin.Sympos. ,Univ.Minn.pp.89-93 Bonnichsen, ,Univ.Mlnn.pp.89—93 Bonnichsen, Bill~1969~30th AnnualI'lin.Sympos. Hin.Sympos.,Univ.Minn.pp.B9-93 Bonnichsen, Bill,1969,3Oth Annual Misc. Map Davidson, D. D. }[., Jr.~ 1969, Minn. Minn. Geol. Geol. Survey Survey Misc. Hap M., Jr., Ser. 1—7, Ser. H-7~M—8 M-B Sd. Mem. Phinney, W., W., 1966, N.Y. State, State~ Mus. Mus. Sci. Hem. Vol.18, Vol.18, p.135—147 p.135-l47 1966, N.Y. Phinney, 44 Taylor~ R. R. B., B., 1964, 1964, Minn. Minn. Geol. Geol. Survey Survey Bull. Bull. 44 Taylor, Gunflint Prong Prong Sill Sill Babcock~ R.C., R.C., 1959, 1959, Unpub. Unpub. M.S. M.S. Thesis, Thesis, Univ. Univ. Wisc. Wise. Babcock, Brule Lake Sills Bull. 39. Grout and and others, 1959, 1959 ~ Minn. Hinn. Geol.Survey GeoI. Survey Bull. 39. Granoels Granofels Shore Pet., Pet.~ Vol. Vol. 1, 1, p. p. 286—303 286-303 Upper Olivine Gabbro ,e Anorthosite Anorthosite Principal References Principal Unit Series Map Ser. Ser. M—7, D.H., Jr., Jr., 1969, 1969~ Ninn. lorinn. Geol. Geol. Survey Survey Map M-7, N—8 H-B Davidson, D.M., Volcanic Volcanic Group Group Volcanics— VolcanicsUndifferentiated ;-1iddle 'Ii ddle Lower Duluth Complex Early Hinor Minor Early Intrusive Intrusive Complexes Gunflint Gunf lint Prong Layered Complex Complex Nathan~ H., 1969, 1969, Nathan, H., I I Unpub. Ph.D. Thesis, Univ. Unpub. Ph.D. Univ. Minn. Minn. I HI ~I �-15-15— TEXTURAL FACIES IRONSTONES* FACIES ANALYSIS ANALYSIS OF OF PRECAMBRIAN PRECAJfBRIAN CHEItTY CHERTY IRONSTONES* by by Erich Dimroth, Dimroth, Service de Pl'Exploration Erich Exploration geologique des Richesses Richesses Naturelles, Naturelles, Quebec, Quebec, P.Q. P.Q. Ministere des and Jean-Jacques Jean—Jacques Chauvel, Chauvel, Departement de Geologie, Rennes, France France Universite Rennes, Rennes, ABSTRACT A B S T R ACT cherty ironstones ironstones are are very very similar similar to to those those Textures of Precambrian cherty of limestones limestones (Dimroth (Dimroth 1958). 1958). Accordingly the the methods of limestone limestone petrology petrology can be applied in the the study study of of ironstones. ironstones. Ironstones can be be conceived to Ironstones to be composed of textural textural elements. elements. Textural ironstone types are defined by the the kind kind and and proportion proportion of of textural textural elements present. present. Textural facies facies types types compose compose thin thin (3 (3 feet—lOO feet-lOO feet) feet) units; they they are either texturally texturally homogeneous, homogeneous, or or are are comcomstratigraphic units; textural rock rock types types that that form form beds beds alternating alternating in in aa posed of several textural characteristic sequence. sequence. It It is to determine determine the the paleo— paleois generally possible to environment envi~onment in which the the various textural textural facies facies types types formed, formed, and and by by sections, to gain a view of of the the paleogeography paleogeography correlation of of stratigraphic sections, of the depositional basin. of the following following textural textural elements elements in in the the ironstones: ironstones: We distinguish the I I Orthochems — 1. Femicrite: A A past of fine—grained fine-grained iron iron silicate silicate (minnesotaite, (minnesotaite, Femicrite: 1. sti1pnome1ane) from iron iron silicate silicate and and iron iron carbonate carbonate stilpnomelane) or of siderite derived from muds. 2. 2. ~~trix chert; chert: Matrix 3. Cement chert: Cement chert: 3. deposition. Chert deposited as as aa silicagel silicagel matrix. matrix. after Chert that that formed between allochem allochem grains grains after chert and and cement cement chert chert can can be be distinguished distinguished only only in in some some Matrix chert hematite tones. hematite irons ironstones. II IL — Allochems 1. Pellets: particles 0.2 0.2twa. mm. across unsharply unsharply bounded, bounded, Ellipsoidal particles Pellets: Ellipsoidal 1. Pellets are interpreted as aggregated always embedded in matrix chert. Pellets are interpreted as aggregated always embedded in matrix chert. particles. with the premission of the *Published with the Deputy Minister, Department Department of Natural REsources, REsources, Quebec. Quebec. �-16—16— Entraclasts: Fragments of the unconsolidated sediment that 2. Intraclasts: that have been been redeposited. redeposited. Previously (James, (James, 1954) 1954) described from from intra— intra(large intraclasts) intraclasts) and and as as "granules" "granules" (= (= sandformational conglomerates (large sand— size intraclasts). 3. 3. Oolites and and Pisolites. Pisolites. 4. 4. Shards: Shards textures. Two sub—types sub-types predominate Shards are complex textures. (a) (accommodation (a) welded welded and and extremely extremely deformed deformed oolites oolites and and intraclasts intraclasts (accommodation shards). (b) shards fragments of oolites and and (b) shards composed mainly mainly of peeled off fragments shards). intraclasts (exfoliation (exfoliation shards). shards). types are are defined defined by the the combination combination of of textural textural elements elements Textural rock types present. Main types types are: are: I. I. Femicrites: II. II. Matrix Matrix chert: chert: Laminated or ribboned silicate—carbonate silicate-carbonate ironstones. ironstones. Lamina~ed Laminated or ribboned cherts, cherts, generally generally with pellets. pellets. III. intraclastic or or oolitic oolitic ironstones. ironstones. III. Cemented intraclastjc IV. Intraclastic or oolitic rocks with chert chert matrix. matrix. IV. V. Intrafemicrjtes: Intrafemicrites: Intraclasts embedded embedded in in aa femicrite femicrite matrix. matrix. types, particularly containing containing shard shard textures, textures, are are quantitatively quantitatively Some other types, less important. important. The paleogeographic application of the the method will be be demonstrated demonstrated at at the the example of the lower jaspilite member of the the Sokoman Sokoman Ironstone Ironstone in in the the western half of the the Labrador trough trough between between latitudes latitudes 54°45'N 54°45'N and and 55°15'N. 55°l5'N. Close to Close to the the western margin of the trough trough this this stratigraphic stratigraphic unit unit is is thickly bedded bedded finely finely intraclastic intraclastic locally represented by a massive or thickly and oolitic (facies type type 1). 1). Toward o.olitic chert chert cemented cemented hematite hematite ironstone (facies this type grades into into interbedded interbedded oolitic—intraclastic oolitic-intraclastic hematite hematite the east this ironstone with chert alternating with with laminated matrix chert cement cement or or matrix, matrix, alternating chert containing type 2). 2). This type type is is thin thin to to medium medium chert containing hematite hematite (facies (fades type bedded (2—30 (2-30 cm.) em.) andcharacteristically andcharacteristically shows shows lenticular lenticular bedding. bedding. It It grades into aa type type that that contains contains intercalated intercalated beds, beds, 2—100 2-100 cm. ern. thick, thick, basinwards into east the oolitic intra— femicrite (facies (facies type type 3). 3). Farther east intraof laminated femicrite beds are lacking in type clastic beds type 4 and finally finally type type 55 is is composed composed only only of of laminated femicrite femicrite with interbeds of of laminated laminated femicrite femicrite bearing bearing matrix matrix chert. Facies types 33 and 4 are characterized characterized by by siump slump structures structures and and Pacies types structures indicating strong synsedimentary deformation. structures deformation. Toward the the centre centre of the trough types 4 and 3 reappear, and grade into a facies containing of the types 3 reappear, and grade into a facies containing interbeds (2 cm.) em.) intraclasts intraclasts and and pisolites pisolites embedded embedded in in interbeds with very coarse (2 matrix chert chert (facies (facies type type 6); 6); the intraclasts and pisolites were very soft at time of deposition. soft deposition. Facies is tentatively interpreted interpreted as as Facies type 1 is a sand bar facies that that separates separates aa lagoonal lagoonal environment environment (not (not discussed discussed here) farther west from from the the open open basin. basin. Facies Facies type type 22 has has been been deposited deposited here) in the intratidal. intratidal and in the and shallow shallow sub-tidal sub—tidal zone zone in in the the foreshore foreshore of the sand bars. facies and and bars. Types Types 33 and 4 represent represent a relatively relatively deep deep subtidal subtidal facies �-17—17— facies zone zone 55 was was deposited deposited in in aa relatively relatively deep deep basinal basinal environment environment fades (maybe 50-100 m. water depth). Facies type 6 was likely deposited on Fades type 6 was likely deposited (maybe 50—100 m. depth). shallow sub-tidal the centre centre of the the Labrador Labrador sub—tidal shoals that extended in the trough. The coarse intraclastic and pisolitic beds may represent represent storm layers. layers. References: James, II. James, H. L., 1954: Sedimentary of iron iron formation. formation. Sedimentary facies fades of v. 49, 49, p. p. 235—293. 235-293. v. Econ. Geol., Econ. Ceol., Dirmroth, 13., 1968: Dimroth, E., 1968: Sedimentary textures, textures, diagenesis and sedimentary Ironstones. N. N. Jb. Geol. Geol. environment of certain Precambrian Eronstones. Palaeont., Abh. v. 130, 130, p. p. 247—274. 247-274. �—18— -18- IRON FORMATION At COPPER FORMATION AT COPPER PRECAMBRIAN IRON MOUNTAIN, FREMONT COUNTY, COUNTY, WYOMING MOUNTA IN, PREMONT H. Duhling, Jr. Jr. William H. Natural Resources Research Institute Institute University of Wyoming, Wyoming, Laramie ABSTRACT A B S T R ACT iron formation formation is is exposed exposed along along the the south-facing south-facing Precambrian banded iron flanks Shoshoni, in in flanks of of Copper Copper Mountain, Mountain, approximately 15 miles north of Shoshoni, northeastern Frenont Fremont County, County, Wyoming. Wyoming. The Precambrian metamorphic comcomconsists of interlayered interlayered quartzofeldspathic quartzofeldspathic gneisses, gneisses, amphibolites, amphibolites, plex consists amphibole schists, schists, peliric pelitic rocks, rocks, and iron iron formation formation into into which which granite, granite, complex pegmatite, and mafic dikes and sills have been intruded. The pegmatite, sills been intruded. has been metamorphosed to has to the the kyanite-muscovite kyanite-muscovite subfacies subfacies of of the the almanalmandine-amphibolite facies. facies. Sedimentary rocks rocks of Paleozoic or Cenozoic dine-amphibolite the Precambrian Precambrian complex complex on on all all sides. sides. age abut the The mineralogical composition of of the the iron iron formation formation is is very very simple, simple, quartz, and and any any combination combination of of blue-green blue-green hornhornconsisting of magnetite, magnetite, quartz, blend, Magnetite, in blend, grunerite, and and cummingtonite. curnrningtonite. Magnetite, in all degrees of alteration to hematite, hematite, occurs in in thin thin laminae laminae and and fine fine clusters clusters with with angular, angular, sharply embayed boundaries and as very fine fine inclusions inclusions in in quartz quartz and and amphibole grains. grains. Banding is is developed by apparent increase increase in in grain the expense expense of of quartz quartz and and amphibole amphibole grains. grains. size of the magnetite at the The iron formation, formation, interlayered interlayered with amphibolite amphibolite and and quartz-mica quartz-mica schist, is is exposed for for a distance of of about about 66 miles miles over over an an approximate approximate schist, width of of 1000 1000 feet. feet. The strike of of the the formation formation is is NN 80°E 80 0 E and and the the dip dip is to the the south. south. is 70° 700 to Liberation and concentration tests tests indicate indicate the the presence presence of of roughly roughly million iron and 22% 22% silica. silica. The The million tons tons of concentrates concentrates containing 56% iron fine magnetite in in quartz quartz and and amphibole amphibole grains grains and and the the amount of very fine amount interstitial quartz quartz in in the the magnetite-rich magnetite-rich bands bands account account for for amount of interstitial the high high silica content of the the the concentrates. concentrates. l3~ 13¾ Rail comes within ten ten miles of of the the outcrop outcrop area, area, but but Rail transportation comes the nearest markets for a blast furnace furnace feed feed are are over over 240 240 miles miles away. away. the markets for to market, market, high silica silica content, content, low low tonnage, tonnage, and and steep steep The distance to to indicate indicate that that this this iron iron formation formation has has aa questionable questionable dip combine to economic potential. potential. �-19—19— Selected References References 1. 1. Duh1ing, William William H., H., Jr, 1970, 1970, Oxide Oxide facies facies iron iron formation formation in in the the Duhling, Owl Creek Mountains, Mountains, northeastern Fremont Fremont County, County, Wyoming: unpublished MS thesis, thesis, University University of of Wyoming, Wyoming, 92 92 p. p. 2. 2. G1iozzi, James L., L., 1967, 1967, Petrology and and structure structure of of the the Precambrian Precambrian Gliozzi, James rocks the Copper Mountain district, district, unpublished unpublished PhD PhD dissertation, dissertation, rocks of the University of Wyoming, 141 141 p. p. 3. 3. Kopp, S., 1964, 1964, Reconnaissance geology geology of of metamorphic metamorphic strucstrucKopp, Richard S., tures district, Fremont County, County, Wyoming: tures of of the the Copper Copper Mountain Mining district, Compass, v. 43, p. p. 6-20. 6~20. Compass, v. 4. 4. Millgate, Mi11gate, M. M. L., L., Gliozzi, G1iozzi, James James L., L., 1966, 1966, Reconnaissance Reconnaissance of of iron iron forforin the the Copper Copper Mountain Mountain area, area, Fremont Fremont County, County, Wyoming: Wyoming: unpubmation in lished Survey of of Wyoming Wyoming files. files. lished report Geological Survey �-20- Stratigraphy of the North Shore Volcanic Group Northeast of Silver Bay, Minn. by John C. Green University of Minnesota, Duluth Minnesota Geological Survey A B S T RAe T A sequence of flows and flow vPups, totalling about 21,500 feet, makes up the northeast limb of the North Shore Volcanic Group of Keweenawan (late Precambrian) age between Tofte and Grand Portage. Exposures are generally good to excellent along the Lake Superior shore or abandoned wave-cut cliffs, and although cut by several large intrusive bodies and obscured by glacial cover over wide areas, many of these lithostratigraphic units can be traced inland from Lake Superior for many miles. Table 1 shows the informal volcanic units at the northeast limb (top of section at Tofte,base at Grand Portage); Table 2 gives the sequence (less well established because of faulting and intrusion) of the upper part of the southwest limb from Tofte as far as Palisade Head near Silver Bay. The Schroeder basalts at the top of the southwest limb are at least in part equivalent to the Lutsen basalts of the northeast limb. The basal 5,000 feet, near Grand Portage, Minn., have reversed magnetic polarity (Lower Keweenawan) whereas all the rest have normal polarity (Middle Keweenawan). The lowermost 250 feet of lavas on Lucille Island, directly overlying the basal Upper Precambrian Puckwunge Sandstone, are porphyritic melabasalts with abundant olivine and augite phenocrysts, identical to those in the same stratigraphic position at Nopeming, west of Duluth. �—2]— -2J- Table 11 Stratigraphy of (Tofte to Grand Portage) of of of Northeast Northeast Limb Linb (Tofte North Shore Volcanic Group Group (Exclusive (Exclusive of of Interf Interflow low Sediments) Sediments) Approx. Approx. - Thickness() Thickness.J ft.) Lithostratigraphic unit unit Lithic eharacter Character Lithic Top (near Tofte —- Lu Lutsen) Top (near t sen) 1020 -- Lutsen basalts olivine tholeittes tholeiites olivine basalts, olivine 160 160 Terrace Point basalt flow Thomsonite—bearing ophitic Thomsonite-bearing ophitic basalt basalt 310 310 Good Harbor Harbor Bay Bay andesites andesites brown, porphyritic andesite, brown, andesite, trachyandesite 360 flow Breakwater trachybasalt flow brown, columnar, granular trachybasalt 500 Grand I1arais Marais rhyolite flow pink, pink, red, red, gray porphyritic porphyritic rhyolite rhyolite 600 Croftville basalts various fine—grained fine-grained basalts basalts felsites Devil Track felsites aphyric flows aphyric and and porphyritic rhyolite flows Red Cliff basalts amygdaloidal, amygdaloidal, ophitic olivine basalts 1300 Creek felsite felsite Kimball Creek pink to to tan, tan, porphyritic felsite 1800 Marr Island lavas lavas mixed tholeiitic basalt,intermediate, intermediate) tholeiltic basalt, felsic lavas felsic lavas 1000 Brule River basalts granular—diabasic granular-diabasic amygdaloidal amygdaloidal basalts basalts 3500 3500 Brule River rhyolite flow pink pink to gray porphyritic rhyolite Hoviand Hovland lavas lavas mixed porphyritic basalt, basalt, trachybasalt, trachybasalt, rhyolite 200 Red Rock rhyolite flow red, porphyritic rhyolite red, 260 Deronda Bay andesite flow flow gray-brown, gray—brown, aphyric andesite 4500 Grand Portage basalts basalts nixed tholeiitic mixed tholeiitic to to diabasic diabasic basalts basalts Base (at Grand Portage) (at 1020 — 400-900 400—900 4000 21,430 2l~430 (est. ) (est.) �-22—22— Table 22 Stratigraphy of Upper Upper Part of Southwest Limb (Tofte (Tofte to Palisade Palisade Head) Head) of North Shore Volcanic Group to Approx. Thickness Thickness (ft.) (ft.) Lithostratigraphic unit Lithic character character 4000 Schroeder basalts ophitic olivine olivine amygdaloidal, ophitic tholeiites >300 >300 trachybasalt flow flow Manitou trachybasalt red-brown, red—brown, granular trachybasalt to basalt (at Tofte) Tofte) Top (at (more (more of the Schroeder basalts) basalts) >280 >280 Bell Harbor lavas lavas tholeiites, aphyric aphyric quartz tholeiites, trachybasalts >300 Palisade rhyolite rhyolite flow flow gray to pink, pink, porphyritic rhyolite gray to lavas Baptism River lavas mixed lavas, mostly basalts basalts Few 100's �~23-2 3— SHALLOW THE LAXE LAKE SUPERIOR SHALLOWSTRUCTURE STRUCTUREAND ANDSTRATIGRAPHY STRATIGRAPHYOF OF THE FROM SEISMIC SEISMICREFRACTION REFRACTIONMEASUREMENTS MEASUREMENTS BASIN FROM F1.C. Halls Halls and C.?. H.C. G.F. West Geophysics Laboratory, Dept. Dept. of Physics, University of of Toronto. ABSTRACT Between 1966 and 1969 thirty—three thirty-three seismic seismic refraction refraction profiles profiles were obtained in Lake Superior using aa single ship sonobuoy sonobuoy technique technique (Halls (Halls and and West, 1971). 1971). The seismic data have led led to to aa number of of conclusions conclusions concerning concerning the shallow shallow structure structure and and stratigraphy of the late Precambrian Keweenawn basin the that underlies the the lake: lake: that Faults with their bound the (1) their north north side side downthrown downthrown at at least least 1—2 1-2 1cm krn bound the north (1) Isle Royale Royale and and Michipicoten Michipicoten Island. Island. shores of Isle (2) the Keweenawan basin just just southeast southeast of of Isle Isle Royale Royale The northern limb of the (2) appears appears to to have undergone a deformation that that is is perhaps perhaps related related to to movement movement along the the Isle Isle Royale Royale fault. fault. (3) In to the the main basin between Isle Royale and the the Keweenaw Peninsula, In addition addition to (3) there the Slate Islands Islands in in the the there is is aa suggestion of of a smaller one southwest of the part of of the the lake. lake. northern part (4) (4) Cambrian Bayfield—Jacobsville Bayfield-Jacobsville sandstones sandstones appear appear Late Keweenawan or early Cambrian to underlie most of Lake Superior. Superior. Although the the site of the the lake lake is is governed governed to by the the position of the the underlying basin, the the principal principal factors factors determining determining the the size and shape of the the lake depression depression are are the the distribution distribution of of the the Bayfield— BayfieldJacobsville sandstones and their their susceptibility susceptibility to to erosion erosion compared compared with with older older rocks. rocks. (5) For those seismic profiles that have a certain degree of geological geological For those profiles that (5) control, such such as as those between Isle Royale and the control, the Keweenaw Peninsula, refraction refraction agree well with those those estimated estimated (Halls, (Halls, 1969) 1969) from from sasple sample velocities generally agree in the the laboratory. laboratory. One notable exception occurs in in those those profiles profiles measurements in that that lie just off the the Minnesota Minnesota shore. shore. Here velocities of of 55 km/s km/s are are recorded. recorded. These values are typical typical of of Freda—Copper Freda-Copper Harbor Harbor sandstones, sandstones, but but the the presence presence these rocks rocks adjacent to to the the Minnesota coast coast is is discounted discounted on on magnetic magnetic of these evidence. Instead the velocities of S5 km/s are assigned assigned to to the the North North Shore Shore volcanics that that crop crop out out along along the the mainland. mainland. The apparently low velocities of these these rocks rocks compared compared to to those those for for volcanics volcanics between Isle Isle Royale and the the Keweenaw kmfs) can be explained if Peninsula (5.7—6.2 (5.7-6.2 km/s) if the the North Shore Shore sequence sequence contains contains a greater proportion of interflow interflow sediment sediment and/or and/or amygdaloidal amygda10idal flow flow top top material. material. The seismic penetration of the (6) the refraction refraction profiles profiles was was generally generally insufficient insufficient (6) to to record the the Upper Refractor (Berry (Berry and West, 1966) 1966) with velocity 6.7± 6.7± km/s. km/s. However, one profile profile northeast of of Isle Isle Royale Royale recorded recorded aa velocity velocity of of 6.5 6.5 km/s km/s at a depth of of about about 66 km. km. This observation demonstrates the the existence existence of of Upper Upper Refractor—type Refractor-type velocities in the the marginal parts parts of the the Keweenawan basin. basin. �-24—24— References and G.F. G.F. West. West. 1966. 1966. An interpretation of the first first arrival data Berry, M.J. and of the the Lake Superior experiment experiment by by the the time—term time-term method, method, Bull. Bull. Seismol. Seismol. Soc. Amer., 56, Soc. 56, 141—171. 141-171. Halls, H.C. H.C. 1969. 1969. Compressional wave velocities of of Keweenawan rock rock specimens specimens from the Lake region, Can. Can. Jour. Jour. Earth Earth Sci., Sci., 6, ~, 555—568. 555-568. from the Lake Superior region, Halls, H.C. and and G.E. G.F. West. West. 1971. 1971. AA seismic refraction refraction survey in in Lake Lake Superior, Superior, Halls, H.C. Can. Jour. Jour. Earth Earth Sci.(In Sci. (In press). press). Can. �—25— -25- THE THE ISLE ROYALE FAULT FAULT B.C. H.C. Halls and and G.F. G.F. West West Geophysics Laboratory, Dept. Dept. of Physics, University University of of Toronto. Toronto. ABSTRACT A fault bounding the northwest shore of Isle Royale was originally postupostuA fault lated by by Irving Irving and and Chamberlin (1885) lated grounds. However, with (1885) on physiographic grounds. the exception exception of of recent recent aeromagnetic aeromagnetic studies studies (Wold and Ostenso, 1966; Hinze et the and Ostenso, al., 1966) very little extra evidence has been produced as as to to whether the the faiTt faurt al., 1966) really exists. The aeromagnetic data show a linear linear anomaly that that follows follows the the northwest shore of Isle Royale and extends eastward to to Superior Superior Shoal. Shoal. Although the sediments, it the anomaly anomaly indicates indicates aa contact contact between between Keweenawan volcanics and sediments, does or faulted faulted one one (Halls, (Halls, does not not reveal whether the contact is a stratigraphic or Evidence to 1970). to date for the so—called so-called Isle Isle Royale fault fault has therefore therefore been been 1970). rather inconclusive. This lines of evidence that that support support This paper discusses some lines the existence existence of the the fault, fault, in the the light of new magnetic and and seismic seismic data: data: the (1) (1) Seismic data (Halls (Halls and West, West, 1971) 1971) show that that the the uppermost layer that that underlies the channel north of Isle Royale and also the the region region further further northeast northeast underlies the the Slate Islands Islands has has aa velocity velocity of of about about 3.7 3.7 kin/s km/s and toward the and aa thickness of about 1—2 This seismic layer is all but continuous 1-2 km. km. This continuous with witih a similar similar one one in in eastern Lake Lake Superior can be firmly firmly identified identified as as Eayfield—.Jacobsville Bayfield-Jacobsville Superior that can sandstones. These thought to the Isle IsleRoyale Royale channel channel These rocks rocksare are thus thus thought to underlie the and if so, so, their their existence existence necessitates necessitates the the inclusion inclusion of of the the Isle IsleRoyale Royale fault fault with its downthrown downthrown side with its side to to the the north. 1970) show a remarkably (2) Paleomagnetic Books, 1968; 1968; Palmer, Palmer, 1970) Paleomagneticdata data (e.g. Books, consistent pattern pattern for for Keweenawan extrusive extrusive rocks. rocks. Whereas the the lower parts of the the volcanic sequence (such (such as as the Osler and South Range Range lavas) lavas) tend tend to to be be reversely magnetised, the upper parts such as the the Isle Isle Royale Royale and and Portage Portage Lake Lake reversely magnetised, the lavas are are normal. normal. In the the Isle Royale channel channel a linear linear magnetic anomaly anomaly (C (C in in Fig.l), Fig.l), which which is is attributed to to Keweenawan volcanics, is is strongly strongly positive positive with with an attendant minimum to to the the north, north, signifying that that the the volcanics are are normally normally an attendant magnetised. Anomaly CC continues continues beyond beyond the the channel channel to to both both the the east east and and west west where it broadens considerably considerably to to form form anomalies anomalies AA and and DD (Fig.l). (Fig.l). The sharpness and DD together together with the the seismic seismic data that the thevolcanics volcanics of anomalies A,C and data indicate that are overlain Thus north of the postulated Isle by Keweenawan are Keweenawan sedimentary sedimentary rocks. rocks. Thus the Isle If Royale fault buried, normally magnetised, Keweenawan volcanics. Royale fault there there are are buried, volcanics. the Isle Royale 'fault' 'fault' anomaly were due due to to aa stratigraphic stratigraphic contact contact the magnetic Isle between volcanics and and sediments sediments it it would imply imply that that the the sedimentary sedimentary unit unit was was sandwiched between two two thick thick sequences sequences of of normally normally magnet3sed magne~ised volcanics volcanics (i.e. (i.e. the Isle Isle Royale Royale lavas the lavas and those causing anomalies A,C A,C and and D). D). Such a sequence is of course possible but it is not a known feature feature of of Keweenawan Keweenawan stratigraphy. stratigraphy. is of course The only thick thick sedimentary unit unit that that occurs occurs in in the the Keweenawan Keweenawan volcanic volcanic sequence sequence is that is that in Michigan and Wisconsin but it lies lies between the the normal normal and and the the reversely magnetised sequence (e.g. (e.g. Meshref and and Hinze, Hinze, magnetised parts of the volcanic sequence 1970). Thus in 1970). in northern northern Lake Lake Superior Superior aa duplication duplication of of the the normally normally magnetised magnetised volcanics through movement along along the Isle Royale Royale fault fault is is favoured favoured over over aa through movement the Isle stratigraphic sequence of a sedimentary unit between between two two normal normal volcanic volcanic ones. ones. (3) of Fig.l Fig.l shows shows that that the the Isle Isle Royale Royale 'fault' 'fault' anonaly(E) anomaly (E) The magnetic map of (3) A weakening of the gradually assumes a more southerly trend trend toward toward the the west. A the gradually assumes anomaly in this anomaly this direction is more compatible compatible with the the presence presence of of aa fault fault rather rather than aa stratigraphic volcanic-sediment volcanic—sediment contact than contact (Balls, (Halls, 1970). 1970). �—26— -26- (4) Anomaly.C in Fig.l is essentially continuous continuous with aa belt of of prominent prominent the Minnesota shore before before turning turning positive anomalies that extends along much of the south and the Bayfield-Peninsula and terminating terminating in in aa hook-shaped hook—shaped anomaly over the Eayfield—Peninsula (Wold and and Ostenso, 1966). White (1966) (1966) concludes concludes that that this this anomaly is is due due to to volcanics in the upper .part sequence. The volcanics volcanics part of the Keweenawan extrusive sequence. Isle causing causing anomaly anomaly C C should should thus thus be be equivalent, equivalent, at least in part, part, to the Isle Royale lavas. lavas. Again, aa fault fault would be be necessary necessary to to explain explain the the apparent apparent of the the sequence. sequence. duplication of The foregoing foregoing observations therefore therefore all tend to to suggest suggest that that the the Isle Isle Royale fault fault does does exist. exist. A A two—dimensional two-dimensional magnetic model interpretation of the Isle Isle Royale Royale fault fault anomaly anomaly at at its its eastern end (Balls, 1970) suggests that the the (Halls, 1970) fault dips to the fault the south. south. The fault fault is is thus thus of reversad reversed type type as as its its downthrown do'~thrown side is is to to the the north. north. The displacement along along the the fault fault is is at at least least 1—2 1-2 km. km. The reversed nature the fault fault and and its itsincreasing increasingsoutherly southerlytrend trendtoward toward the the west west nature of of the that support the the idea idea initially initially raised Irving Chamberlin (1885) (1885) that (Fig.l) support raised byby Irving andandChamberlin it it is of the the Douglas Douglas fault fault in in Wisconsin. Wisconsin. is an easterly continuation of References Books, K.G. K.G. 1968. 1968. Magnetisation of the lowermost Keweenawan lava lava flows flows in in the the area, USGS Prof. Prof. Paper Paper 600—0, 600-D, 248—254. 248-254. Lake Superior area, Halls, H.C. B.C. 1970. Halls, 1970. Geological interpretation of geophysical data data from from the the Lake Lake Superior region, region, Ph.D. Ph.D. Thesis, University University of of Toronto, Toronto, 203 203 pp. pp. Halls, H.C. B.C. and G.E. West. 1971. Halls, G.F. West. 1971. A A seismic refraction survey in in Lake Superior, Superior, Can. Sci. (In (In press). press). Can. Jour. Jour. Earth Sci. O'Hara, N.W., N.W., Trow, Trow, J.W. J.W. and and Secor Secor G.B. G.B. 1966. 1966. Hinze, W.J., O'Hara, of eastern Lake Superior, Superior, AGU AGU Mono., Mono., 10, la, 95—110. 95-110. Aeromagnetic studies studies Observations on the junction between Irving, T.C. 1885. 1885. Observations Irving, R.D. R.D. and Chamberlin, T.C. the eastern eastern sandstone sandstone and and the the Keweenaw Series Series on Keweenaw Point, Point, Lake the Superior, Bull.US. Bull.US. Geol. Geol. Surv., Surv., 23, ~, 385—498. 385-498. Meshref, W.M. W.J. 1970. Meshref, W.M. and Hinze, W.J. 1970. Geologic interpretation interpretation of of aeromagnetic aeromagnetic data data in in western western Upper Upper Peninsula of Michigan, Michigan, Mich. Mich. Geol. Geol. Surv., Sun., Kept. Rept. of of lxiv., Inv., 12, 25 25 pp. pp. Palmer, B.C. and correlation correlation of of some some Middle Middle Keweenawan H.C. 1970. 1970. Paleomagnetisni Paleomagnetism and rocks, Lake Lake Superior, Superior, Can. Can. Jour. Jour. Earth Earth Sci., Sd., 7, 1410—1436. rocks, 1410-1436. l? White, W.S. W.S. 1966. 1966. Tectonics of the the Keweenawan basin, western Lake Lake Superior Superior region, region, White, USGS Prof. Prof. Paper Paper 525—E, 525-E, 23 23 pp. pp. Aeromagnetic, gravity and sub—bottom Wold, R.J. R.J. and and Ostenso, Ostenso, N.A. N.A. 1966. 1966. Aeromagnetic, sub-bottom studies in western Lake Superior, AGU Mono., Mono., 10, profiling studies Superior, AGU 10, 66—94. 66-94. �FIGURE FI GURE 89° 40' 89°20' 4a"OO' 48°OO' 88°40' $9°0O' THUNDER ---------- I 88°20 B8°0O' 88°00' BAY — ROVE FORMATION — — NORTH SHORE VOLCANICS 47° 50' a + -60$ 600 c1t:) ct=' — E ._—a.—-—ç D I F') N - V y TI V V '-I -...l SCALE V I 6 ••• i n — —, ISLE ROYALE VOLCANICS TI, 1V/ s COPPERHARBOR HARBOR CLASTICS CLASTICS COPPER 89c2O• $9000' _.- X——'-Y— X-·-··Y- 88° 40 ES MILES CONTOURS (X tOO) 100) CONTOURSIN IN GAMMAS GAMMAS 1* 88 0 20' 20' 88° 88 0 00' NORTHERLY LIMIT OF OFKEWEENAWAN KEWEENAWAN VOLCANICS VOLCANICS NORTHERLY LIMIT Total intensity magnetic magnetic map map of o tnt Total intensjty the Isle Isle Royale Royale channel. channel. Survey H. C. C. ILdIs Halls Survey by by N. F. West West in in 1966, 1966, using using aa shipborne proton precession spacing: and C. G. F. spacing: About About 33 miles. miles. N 300 c1:csjt in extreme Profile orientation: N 30 0 W., W.,except extreme northeast where it it is is more more northerly northerly 87°40' I �-28- RELIABILITY OF U-PB AGES OF SPHENE IN NORTHEASTERN MINNESOTA AND NORTHWESTE~~ ONTARIO G. N. Hanson Department of Earth and Space Sciences State University of New York Stony Brook, New York and E. J. Catanzaro Department of Geology Southampton College Southampton, New York A B S T R ACT U-Pb ages have been determined on sphenes from early Precambrian granitic rocks in relatively undisturbed areas and in a thermal aureole. The granitic bodies investigated are the Icarus pluton and the Saganaga tonalite in Ontario and the Linden Syenite and Giants Range Granite in Minnesota. A total of six sphene concentrates were analyzed. One sphene from the Linden Syenite had an unfavorable U/Pb ratio and no age could be calculated. Three sphenes from the Saganaga tonalite, the Icarus pluton, and the Giants Range Granite gave internally concordant U-Pb ages of 2710 ± 30 m.y. 'T'ivo sphenes from the Giants Range Granite and the Linden Syenite were internally discordant, but gave Pb207/Pb206 ages of 2730 and 2740 m.y., respectively. It is suggested that the discordance may be related to a relatively high uranium content in one sphene and to shearing of the host rock in the other. Sphene from near the contact of the Giants Range Granite with the 1100 m.y. Duluth complex gives internally concordant 2700 m.y. ages at 7.4 kilometers from the contact. As the contact is approached the sphene ages become internally discordant suggesting lead loss at 1100 m.y. At about one-half kilometer from the contact, where biotite and hornblende have lost essentially all of their radiogenic argon, sphene still retains about 60% of its radiogenic lead. �-29- CONTINENTAL RIFTS William J. Hinze Dept. of Geology Michigan State Univ. Donald M. Davidson Dept. of Geology Univ. of Minnesota, Duluth Robert F. Roy Dept. of Geology and Geophysics Univ. of Minnesota A B S T R ACT Comparison of late Precambrian, linear, tectonic features transecting the Mid-Continent region of the United States (e.g., the Mid-Continent and Mid-Michigan Anomalies) with relatively recent continental rift zones, such as the East African Rift System, indicates many similarities suggesting a common mode of origin. Hence, a mechanism is proposed for the development of linear Precambrian rifts and subsequent overlying sedimentary basins based upon observed geological and geophysical characteristics of modern rifts. Dissimilarities in stage of development, depth of erosion and geological age are parameters which limit the extent of comparison. Rift formation is initiated by plate splitting and subsequent upwelling of low velocity layer material into the upper mantle along the base of the crust. Although inherently denser than adj acent mantle rocks, the low velocity layer material becomes lighter and therefore rises upon partial melting and fractionation. Uplift of the earth's surface and igneous activity along pre-existing zones of weakness is associated with the vertical rise of this material, while lateral movement results in thinning and rupture of the crust producing extensional rift grabens. Subsequent magmatic activity in the rift zones results in local structural downwarping. Upon cooling, the low velocity layer residuml becomes dense and ultimately sinks into the mantle causing the uplifted rift zone to deflate. The convergent movement of adjacent mantle material into the void produced by the sinking residuum places the crust under compression, thus accounting for not only compressional features associated with rift systems, but the subsequent development of sedimentary basins over rift zones. �—30— -30- Keweenawan Geology of of the the Porcupine Porcupine Mountains, Mountains, upper Peninsula, Peninsula, Michigan Michigan Western Upper Harold A. Hubbard A. Hubbard u. Geological Survey Survey U. S. S. Geological Washington, 0. C. 20242 D. C. 20242 Washington, ABSTRACT The Porcupine Mountains, Mountains, Michigan, are are underlain by by tue the upper upper northwarLl-dipping limb of of an an overturned overturned asymmetric asymmetric anticline, antiline, not northward-dipping limb not aa dome with quaquaversal ~ua~uaversal dios dips as as usually usually shown. shown. The anticline is is faulted near its its axis1 axis, and at the southern margin the mountains mountains middle middle margin of o the diDpi1i to overturned Keweenawan volcanic rocks are thrust over over steeply steeply dipping Keweenawansedimentary sedimentaryrocks. rocks. The rocks, which upper Keweenawan The middle middle Keweenawan Keweenawan rocks, which are younger than Lava Series, can can be be divided divided into intotwo two are younger than the the Portage Porta3e Lake lake lava sequences. The Theolder older se~uence, sequence,which whichincludes inducesmost nostof of the he volcanic se~uences. volcanic of fine-grained fine-grained northward-dipping rocks the mountains, mountains, co:isists consists of rocks in the mafic to to intermediate intermediate lava lava flows flows and and two two interbedded interbedded felsic felsic lava lava flows. flows. southern felsic flow flow is is nonporphyr nonporphyritic The southern itic and and constitutes about half the outcrrp outcrop area. area. The younger younger sequence, se~uence, which which is is present present only only in in the the easternmost part part of of the the mountains, mountains, consists consists of of gently gentlyeastward eastwardand. and easternmost northeastward-dipping fine-grained and aphanitic flows flows overlain by volcanic conElonerate conglomerate and sandstone. The younger sequence se~uence is either either in fault contact or unconformable on on the the older. older. Both Both sequences se~uences are are repeao1L in part in fault slices repeated in in imbricate imbricate fault slices in inthe the southeasteru southeastern part of of the mountains. mountains. A A tear fault separates separates these rocks from the the upper Keweenawan rocks to to the the east. east. In the the Copper Harbor Conglomerate Con81omerate consists consists of of saidstone sandstone the north, north, the interbedded lavas. It appears to be conformable on middle containing interbedded lavas. It appears to be conformable on middle containing Keweenawan lavas in the lake of the Clouds valley. To the south tle Keweenawan lavas in the Lake of the Clouds valley. To the south ofo the mountains, the theupper upperKeweenawan Keweenawan rocks are folded in in an asymmetrical as~nmetrical syncline with with aa steep steep north limb. structural relIef syncline limb. The The structural reliefbets-een between the the size of and the synciline syncline is is more more than than 8000 8000 feet. feet. The size of the the PorcuPorcumountains iid sug3ests that the Keweenawan rocks of pine Mountain of western Mountain structure suggests icichiganwere were strongly st;unly folded in Michigan in post-Freda time, time, and not just just broadly warped. �—31--31- ThE KEWEENAWAN THE OFOFISLE ROYALE, MICHIGAN MICHIGfu~ KEWEENAWNGEOLOGY GEOLOGY ISLE ROYALE, N. King Huber U.S. U.S. Geological GeologicalSurvey Sury Menlo Park, California California 94025 94025 ABSTRACT A B S T R ACT Isle Royale lies on the north limb limb of the Lake Superior syncline, syncline, Royale lies and the the stratigraphic section exposed on the island is correlative correlative with the the much-studied much—studied middle middle Keweenawan Keweenawan Portage Portage Lake Lake Lava Lava Series Series and upper }ZeHr.awan Copper Harbor Conglomerate Cunglomerate on the Keweenaw Peninsula, on Keweenawan on the the south limb of of the the syncline. syncline. Dips of of the the strata strata range range from from less less than than 5Q0; 100 to over 50°; 10° side of of the the they are generally steeper on the north side the south and and average less than 20°. 20°. island than on the less than Exposures on Isle Royale indicate a minimum thickness thickness of of 10,000 10,000 feet for for the the Portage Lake Lava Series at The base feet at this this locality. locality. The baseofoftiiei the series is not exposed. exposed. As on on the the peninsula, the the series series consists consists largely largely of basaltic and andesitic lava flows, flows, with lesser amounts of of interfiow interflow sadiotaoy and tuffaceous rooks. sedimentary rocks. No felsie felsic flows flows are known from outcrops, although one has about outcrops, has been reported from diamond drilling, about 6,200 feet below the the top top of of the the lava lava series. series. The interflow clastic clastic rocks rocks do not not crop generally do crop out, out, and mast most of the individual units are are known only only from diamond drilling. drilling. Within the the lava lava series, series, which probably probably contains contains over a hundred flows flows in the the exposed section, section, certain stratigraphic units units representing flows or groups of flows flows can can be identified identified representing individual lava flows and traced on the basis and and basis of characteristic textures or structures, and relative stratigraphic stratigraphic position. position. Twelve such units have been distinguished distinguished within the the sequence and and provide stratigraphic stratigraphic and and structural structural control control for for geologic mapping. On both the Keweenaw Peninsula and Isle RoyaTh, Royale, the the Copper Copper Harbor Conglomerate is is largely derived from lowermost Keweenawan volcanic source source terranes, shed debris debris into the subsiding Lake Superior basin from from terra as, which shed opposite sides; sides; for for Isle Royale, this would be from from the the North Shore Royale, this Volcanic Group of of Gehman Gehman (1958) (1958) in in Minnesota. Minnesota. The depositional en'i:onment environment Volcano Group is is interpreted as as being one of a combination of fluvial fluvial and and lacustrine lacustrine conditions resulting in piedmont fanglomerates fanglomerates and and playa lake lake or or flood flood conditions plain deposits. deposits, Royale, various various sedimentary features On Isle Isle Royale, features indicate that that the the general direction of sediment transport was easterly, easterly, with aa range range from from northeast to to southeast. In thio this same direction the the Copper Harbor increases in Conglomerate Jr.i-eases in thickness thickness and and in in textural textural and and compositional maturity--namely conglomerate, through through aa mixture of of cobble cobble maturity——namely from a boulder conglomerate, and pebble conglomerates conglomerates and and sandstone, sandstone, to to sandstone sandstoneand andinudstone. mudstone. In a miles this distance of 20 miles this clastic wedge thickens thickens from from aa minimum minimum of of 1,500 feet feet to over 6,000 feet feet between stratigraphic marker horizons; the the top of of the the formation formation is is nowhere nowhere exposed and and the total thickness must be top appreciably greater. greater. �-3232— SOME PRIMA.RY PRIMARY SEDIMENTARY SEDIMENTARY STRUCTURES STRUCTURES IN IN THE SOME THE LOWER LOWER CHERTY CHERTY MEMBER tJfMBER OF OF THE THE BIWABIK IRON FORMATION BI~/ABIK FORMA.TION : VIRGINIA HORN HORN AREA ERIC FRODESEN Department of Geology and Geophysics Geophysics University Wisconsin, Madison, University of \.Jisconsin, Madison, Wisconsin 53706 53706 BSTRACT A B S T R ACT A The writer wri ter discovered di scoverecl and collected collected some some unusual unusua I sedimentary sedimentary oF the the Biwabik structures in the theLower Lower Cherty Cherty Member t-lember of Biwabik Iron Iron Formation Formation addition of at aa locality localitynea;r near the theMidway Midway addition of Virginia, Virginia,Minnesota. Minnesota. Polished Polished and x—radiographs overturned and and disturbed disturbed bedding bedding reresections and x-radiographs reveal reveal overturned sembling convolute—type convolute-type bedding, bedding, load load casts casts with with flame flame structures, structures, and and other structures structures characteristic characteristic of of soft soft sediment sediment deformation. deformation. SmallSmall— other scale cross-bedding cross—bedding and small small local local thrust thrust faults faults also also are are present. present. Recent experiments experi ments on on the the Formation formati on of of contorted contorted structures(McKee s truc tures (Mcl<ee and and Goldberg, show that that convolute—type convolute-type bedding bedding and and small—scale sm~ll-scale thrust thrust Goldberg, 1969) 1969) show faults, simi lar to to those those found in the Biwabik, Biwabik, can be be formed formed by by loading loading similar found in mud which was was deposited deposited on an existing existing slope slope of of 15—20 a semi—cohesive semi-cohesive mud 15-20 degrees. The The preservation of the the fine fine alternating alternatin~ dark dark and and light light laminae, laminae, small—scale small-scale cross—bedding, cross-bedding, and possible possible graded graded bedding, bedding, suggest suggest that that these wave base with only periodic these rocks rocks were deposited below wave periodic current activity. The alternation of the The the laminae laminae is is generally attributed to to seaseasonal changes{Hough, changes(Hough, 1958), or periodic periodic influxes of iron—rich and ironiron— sonal 1950), or influxes of iron-rich and impoverished impoverished layers layers due to to tectonic tectonic activity activity coupled coupled with with isostatic isostatic semi—rigid crust, crust, or or aa cornbina,tion combination oF adjustment of of a. a semi-rigid of the the two two procecess procecess (Cullen, 1963). 1963). Cullen's Cullen's idea idea that (Cullen, that banded iron iron formations formations can can he be rerell garded as as corresponding corresponding to aa syn-orogenic syn—orogenic "flysch "f1ysch' type of deposition deposition type of applications in explaining explaining some some of the structures found may have applications the structures found in in the the Lower Cherty Member. Similar sedimentary sedimentary structures structures are are found found in in the the Lower Member. Similar laminites of of documented flysch facies. The presence presence of ofallochthonous The allochthonous black chert chert pebbles pebbles within within the the beds beds poses poses aa problem as to to mode of of emplacement. Turbidity Turbidity currents, currents, subaqueous subaqueous sliding or or gliding gliding down down aa slope, slope, or or ice mechanisms have have to be ininsliding ice rafting rafting mechanisms to be voked explain their their presence presenceg voked to to exrlain If represent the the products proc'ucts of of chemical chp.mical weathering If iron iron formations formations represent under warm humid conditions in in semi—restricted semi-restricted basins, basins, then then ice ice rafting rafting under is not not aa very very likely is likely possibility. If, If, however, however, the the iron iron formations formations were were �-33—33— deposited rlepositerl in aa cool cool polar pot~rclimate climateasassuggested suggestedby bypaleonagnetic paleomagnetic data data (Symons, 1966),then thenthese thesepebbles pebblesmay may productofofice ice transport. (Symons, 1966), behe thetheproduct structures are are characteristic characteristic of Iff thesc these sedimentary sedimentary structures of the the entire entirefor— formation, and iron iron Formations general, then detailed regional mation, and formations inin ~eneral, then aa detailed regional study study could produce someenlightening enlighteningresults. results. could pro~uce SOMe refer~nces: 1'efercnces: Cul Ten,D•. U.J., 1963, Tectonic Tectonic implications implications of Cullen, J., 1963, of banded banded iron formations: formations: Jour. p.327—392. Jour. Sed. Sed. ret., Pet.,v.33, v.33, p.387-392. Gruner, J.'., Mineralogy andandgeology thethe Mesabi Gruner, J.l !.,l96, 1946, i~ineralogy geologyofof MesabiRange: Range: Office of Iron Range ofthe theComisioner Commisionerofof Iron RangeResources Resources and and t Rehabilitation, rehabilitation, St. Paul, Paul, tlinn. f1inn& 127 ppe 127 Pp. Gundersen, J.N., end Schwartz, 196Z, The geology geologyof of the metaGundersen, J.N., and G.M. G.M. Schwartz, 1962, The metamorphosedRi\-.abik SiwabikIron IronFormation, Formation,Eastern Eastern~lesabi Mesabidistrict, district, morphosed Minnesota:Minn. Minn.Geol. Geol.Sur. Stir. Bull. Bull. 43, Minnesota: 43, 137pp. l37pp. resh_waterenvironment environmentofofdeposition deposition of of PreHough,J.L., J.L., 1958, Yough, 1958, Fresh-water Precambrian iron formations: p. 41t+_1130. cambrian iron formations: Jour. Jour.Sed. Sed. Pet., Pet.,v.28, v.l8, p. 414-430. James, H.L., 1966, Chemistry of of the J~mes, H.L., 1966, Chemistry the iron—rich iron-rich sedimentary sedimentary rocks: rocks: 'J.S).S. Prof. Paper (-4O41, 6lpp. IJ.S.G.S. Prof. Paper 440-Iy" 61pp. Mcee, ~1c:\ee, E.fl., on formation formation of of conE.0., and and M. M. Goldberg, Goldberg, 1969, 1969, Experiments Experiments on torted Bull., v.80, torterl structures structures ininmud: mud: G.S.A. G.S.A. Bull., v.BO,p.23l—24-+. p.23l-244. Symons, P.T.A., 1966, A peleomagnetic paleomagneticstudy study on on the the Gunflint, Gunflint, Mesabi, Symons, ~.T.A., 1966, A Mesabi, and Cuyuna the Lake Lake Superior Superior Region; Region: and Cuyunairon iron ranges ranges in in the Econ. Econ. Geol., Geol., v.G1, v.61,p.p.1336—1361. 1336-1361. hite, \.'hi te, [l.A., [l.A., 1954, Thestratigraphy stratigraphy and 195 1f, The and structure of ofthe theMesabi ~1esabi Minnesota: ]{angc, ta: Minn. Hinn. Geol. Ceoi. Sur. Sur. Bull. Bull. 38, 38, 92pp. 92pp. Range, fHnneso �-34—34— ZEOLITE AND AND PREHNITE—PUELL?ITE PREHNITE-PUMPELLYITE FAdES FACIES IN INTHE THE KEWF.ENAWAN KEHEENAHAN BASALTS OF NORTHERN HICH:LGAN ROLE OF OF VOLATILES VOLATILES OF NORTHERN MICHIGANII: II: THE THE ROLE Wayne WayneT.T. Jolly Jolly ofSaskatchewan Saskatchewan University of Saskatoon, Canada Saskatoon. Canada ABSTRACT A B S T RAe T Keweenawpeninsula, peninsula, ~lichigan, :Iichigan. The lava flows flows of of the the Ke\\'eena,\v Thetholeiitic tholeiitic lava have undergone underone metamorphism of the the zeolite ite have metamorphism of zeoliteand andprehnite—punpelly prehnite-pumpellyite facies. the latter, fractures and upper flow flO\\1 contacts contacts latter, rocks rocks along along fractures facies. In In the been transformed have been transformed to to monomineralic monomineralic rocks rocks (metadomains) (metadomains) corposed composed of either pumpellyite pumpellyite or or epidote, epidote, depending depending on on stratigranhic stratiranhic position of position metadomains are are enriched enriched in in CaO CaO and and /\1')03 A1,O retitive in the pile. These metadomains relative to their their unaltered unaltered basalts basalts through of pre-existlnG pre—exiting plagio— to through albiti.zation albitization of plagioclase. Bulk compositions of the the altered altered parts parts of of the the flows, flows, deduced deduced re through ,veighted weighted averages averages of of the through the rock compositions, compositions, are sinilar similar to to ti1e parental basaits. parental basalts. Thus, Thus, little or no material was was added added from from extraneous extraneous sources. This metamorphic differentiation occurred occurred as as aa result result of of migration of of both both volatile volatile and non-volatile components over short and non—volatile components over Calcium distances through aa fluid fluid pressure pressure gradient zradient with \vi thr'f< r f<P total t l' Calciumalinninum silicates silicates were were formed formed preferentially preferentially near rupture alwninum rup~S~e zones, zones, at its its lowest lowest levels. levels. Theoretical considerations suggest where PP was at differentiation ofofessentially homogeneous that mdamorphic metamorphic differentiation essentially homogeneous bodies bodie~ of of rock thim P l' During the theKeweenawan Ke\\1eenaHan rock may mayoccur occuronly onlywhen whenPf Pfisisless less tian metamorphic event, dehydration. As As aa metamorphic event,the the rocks rocks underwent underwentext~g~rve etensve dehydration. depth from result, secondary phases phases decreases decreases with uith depth result, water content content of of secondary from water—rich or more) more) to water—acor epidote water-rich chlorites chlorites and and zeolites zeolites (1120=12% (H 0=12% or to '\-later-poor 2 (H about 2%). 2%). At lowest exposed levels levels P02 P0 may have have reached reached levels levels (HO0 about 2 2 sutficient sufficient to to subdue formation of pumpellyite in in favor favor of of pistacitic pistacitic epidote. PCOZ was very low 10\\1 during during the the peak peak of of the the metamorphic metamorphic event. event, Co2 �—35— -35AN AN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY C1" GF THE THE SOUTHKciilJ PENINSULA OF MIOsiIGAN MI~dIGAN PENINSULA OF SOUTHE Richard L. J. Hinze L. Kellogg and William 3. Geology Department of Geology Michigan State University Lansing, Michigan Hichigan East Lansing, ABSTRACT A B S T R ACT Only fragmentary direct information is is available on on the the basement basement complex underlying the Phanerozoic sediments of of the the Michigan Michigan Basin Basin because of the the limi;ed limited and poorly distributed basement basement drill drill tests. tests. To supplement this limited limited information information a a regional regional aeromagnetic survey has has aeromagnetic survey been of of thethe Southern Peninsula. Approximately 17,000 17,000 miles of beenconducted conducted Southern Peninsula. Approximately total magnetic intensity total intensity data data were were recorded recorded along along north—south north-south flight flight lines spaced at lines at three three mile intervals. intervals. A hasement A basement configuration map prepared prepared from from magnetic magnetic depth depth estimates estimates and basement basement drill drill tests and tests confirms that the basement surface surface under under the the Southern Peninsula of Ni Michigan has the the form form of of an an oval oval depression depression reachreachiar has ing aa maximum maximum depth depth of of approximately 15,000 feet ing feet below sea sea level level on on the the western shore shore of of Saginaw Saginaw Bay. Bay. A A basement high underlies the the Howell Howell .Anticilne and Anticline roughly north-south and aa roughly north—southstriking strikingregional regional basement basementtrough trLg plunges into into the boundarypoint poin of of Indiana, Ohio, plunges the basin basinfrom from the thecommon common boundary Ohio, and iIichigan Ilichigan to to the the vicinlty vicinity of 42°30'N. The map map shows a broad basement north\-lest in in the the extreme extreme southwest southwest corner corner of of the the platform striking northwest peninsula. Interpretation of the :esidual =~sidual aeromagnetic aeromagnetic map map in in conjunction conjunction with with geologic and other regional geophysical data seologic and other data from from the the Southern Southern PeiLtsula Peninsula and indicates that that the the basement basement of of the the :1ichigan Hichigan Basin has and adjacent areas indicates geologic history. history. Several Several basement provinces are are defined had a a complex complex geologic basement provinces defined on the basis of magnetic and and isotope isotope of magnetic and gravity gravity anomalies, anomalies, lithologies lithologies and ages of samples obtained from basement drill holes, and extrapolation of samples obtained from basement drill holes, and extrapolation of of known Precambrian geology from the the margin of of the the basin. basin. The Penokean province can be traced from into the can be from northern northern Nichiga Michigan and and Wisconsin Wisconsin into the area the northern the Southern Southern Peninsula. Peninsula. In this area the province province northern portion portion of the is characterized is characterized by east—southeast east-southeast striking striking anomalies. anomalies. Central and southwestern Michigan Michigan isis underlain rocks correlating correlating underlain primarily primarily by by felsic felsic rocks with the the Central Province. Basement rocks in Basement rocks in southeastern southeastern ~lichigan, Michigan, which which strike strike generally generally north—northeast are interpreted as as mafic mafic and and felsic felsic gneisses and north-northeast are interpreted amphibolites. amphiboli tes. They are correlated correlated with the the Grenville Grenville province province which \vhich is bounded on the west is on the west by by aa line line extending extending south-southwest south—southwest from from Saginaw Bay to south to Michigan— to west \vest of the the HowellAnticline HowellAt,ticline and and then then du.e du.e south to the MichiganOhio boundary. A A Keweenawan rift rift zone zone characterized characterized by by mafic mafic intrusives, intrusives~ extrusives and uplifted uplifted gneisses gneisses transects irom the the extrusives transects the the Peninsula from ic.neousactivity activity area to southeastern Traverse Bay Bay area southeasternMichigai Nichigan. Keweenaean Ke\veenmVan igneous mayalso also be be reflected reflected ininthe may thenumerous numerous local local magnetic magnetic anomalies anomalies in -• southwest whichoccur occuralong alongnorthvest norLn'eststriking strikingtrE!lllds treds whith soutlHvest Mi-htgan Nichigan which \vhich the regional pattern. parallel the regional gravity gravity anomaly anomaly pattern. �-36—36— PRECAMBRIAN CLASTIC CLASTIC PALEarIDAL SEDTI1ENTATION PRECAMBRIAN aarna SEDENTATION GEORGE deVRLES KLEIN GEORGE deVRIES Dept. of Geology, Univ.ofofIllinois, Illinois, Urbana, Dept. of Geology, Univ. Urbana, Illinois, Illinois,61801 61801 ABSTRACT ABSTRACT The Lm;er Fine-grained of Scotland Scotland and and The Precanbrian Precrbriari Lower Fine-grained Quartzite Quartzite of both both the Precaubrian Precanbrian Sterling Sterling Quartzite and and Precanbrian Preccmbrian part part of the the Wood Canyon Formation easternCalifornia California and are Wood Canyon Formation of of eastern and Nevada Nevada are characterized by primary primary sedimentazy sedimentary features which are characterized by features which are indicC'ltive indicative of sediment transport and and deposition deposition by bytidal tidal currents. sediment transport currents. Sedimentary structures structureswhich which occur occur in these these formations fonnations are are grouped grouped into sty seven which are produced by seven associ~tions associations which am produced by seven sevenphases phasesofof tidal tidal sediment sediment transport: transport: ASSOCIATION 1: 1: Cross-stratification sets, Cross-stratificationorganized organized into into herringbone herringbone sets, with bipolar-bimodal bipolar—bimodal orientation;parallel parallellaminae; laninae; these these features with orientation; features indicate indicate tidal tidal current current bedload bedload transport transport with with bipolar bipolar reversals reversals of of flow directions directions (Reirieck, flow (Reineck, 1963). 1963). ASSOCIATION 2: Reactivation surfaces:Multimodal Multimodalfrequency frequencydistribdistribASSOCIATION 2: Reactivation surfaces: utions of cross-strata utions cross-strataset setthickness thicknessand andofofdip dipangles; angles;unirnodal unimodal orientation of directional directional current orientation of current structures structures parallel parallel to to basin basin topographic strike; producedbybytime—velocity t:ime-veloci ty assymetry assymetry of of topographic strike; allallproduced tidal tidal current current flow flow (Klein, (Klein, l970a3. 1970a). ASS<X;IATION 3: Interference ripples; superposition ASSOCIATION 3: Interference ripples; superpositionofofcurrent current ripples ripples at 900 crests and at 90 0 and and 1800 180 0 on on crests and slip slipfaces facesofofdunes, dunes,sand sandwaves waves and and internal cross-strata; cross-strata;"B-C" "B-C" sequences sequences ClIf of cross-strata cross-strata overlain overlain by by micro-cross-laninae; highly-variant highly-var! antorientation orientation of of current current ripples; micro-cross-lcminae; all late-stage emergence runoff prior prior to all produced produced by by late-stage emergence runoff to anergence emergence of of an intertidal flat (Klein,1963,1970a,l970b). an intertidal flat ~Klein,1963,1970a,1970b). ASSOCIATION It: 4: Cross-stratification with flasers fla.sers and and clay clay drapes; drapes; Cross—stratification with flaser bedding; flaser bedding; lenticular lenticular bedding; bedding; "tidal "tidalbedding'; bedding"; convolute convolute bedding; all all produced alternation bedding; produced by by al terna.tion of ofbedload bedloadand and suspension suspension sed:imentation associated alternating bedload bedload and and slack-water slack-water sedimentation associated with with alternating tidal current tidal currentflow flow(Reineck (Reineckand andWunderlich,l968a,1965b; Wunderlich,1968a,1968b; Wunderlich, Wunderlich, 1970).• 197Q) ASSOCIATION 5. \lJashout structures, structures,sane sanefilled filled with mUd-chip with mud—chip ASSOCIATION 5. Washout conglanerates; rill casts; all allproduced produced by by tidal tidal scour scour conglctnerates; rill marks; marks;flute flute casts; (Van Straaten,1954; Straaten,l951j; Reineck, (Van Reineck, 1967; Klein,1970a). �—37— -37- ASSOCIATION 6: 6: MUdcracks; Mudc racks; mt intraformational conglanerates; rafo tin ational congicrie rates; birdseye structure; allproduced producedby byexposure exposure and and evaporation (Shinn,1968). stricture; all, Tracks and and trails; trails; burrowing burrowing structures, "escape" ASSOCIATION 7: Tracks structures,"escape burrows; all all produced burrowingorganisns orgaxüausadapted adaptedtotoaa tidal tidal burrows; produced by by burrowing regime (Rhoads,1967; (Rhoads,l967; Remneck 1968). Reineck and others, others, approximatedin in these Precanbrian paleotidal paleotidal ranges can be be approximated ranges can similar to rock units units finn rock from analysis of fining-upward sequences similar date, Late those occurring in in prograding prograding tidal copstlines. COAstlines. To date, Precambrian paleotidal ranges from from 0.3 paleotidal ranges 0.3 to to 13.0 meters meters have been measured. This Late measuitd. This Late Precanbrian Precaubrianpaleotidal paleotidal range rangevariation variation is tidal less than thRn the theknown known variation variation measured measured along along Holocene Holocene tidal ranges fran fran 00 to to 17.5 17.5 meters). meters). Perhaps coasts (variation of tidal ranges Precambri~n range variation is not greatly greatly difforent different is not Precanbripn paleotidal range fran present-day present-day variation. If further work substantiates such Precambrian, it a a limited paleotidal paleotidal range range variation variationfruit fram the Precambrian, poses critical critical problems poses problems for various various geophysical geophysical pxtblms problens that that have have been and age earth-moon systan. systen. beenproposed proposedfor forthe the origin origin and age of of the earth-noon REBERENCES REFERENCES CITED intertidal zone sediments: Jour. Klein, C.deV,1963, G.deV,1963, Bay Bay of of Plindy Fundy intertidal Jour. Sedimentary Sedimenta~ Petrology, Petrology, v. v. 33, 33, p. 844-854 8tb—85t -——,l97Oa, dynanics of intertidal sand ---,1970a, Depositional and dispersal dYnanics sand bars: Jour. Sdimentary S~dimentar,yPetrology, Petrology, v.v.140, 40, p. p. 1095-1127. --—,1970b, Tidal Quartzite -- The Lower ---,1970b, Tidal origin of of aaPrecambrian Precambrian Quartzite Pinc—grairdQuartzite Quartzite (Dalradian) (Dairadian)ofof Isl~; Islay. Scotland: Fine-grained Scotland: Jour. Jour. Sedimentary Sedimentary Petrology, Petrology, v.v.140, 40, p.p.973—985. 973-985. Reineck, H.E., H.E., 1963, un Bereic;h der sudliche Nordsee: Reineck, 1963, Sedimentgefuge Sedimentgefuge im Bereich der Nordsee: Abh. ~enckenbergischen SenckenbergischenNaturfor. Naturfor.Gesells. Gesells. No. 5O5, p. p. 1-138. Abh. No. 505, 1-138. --—,1967,Layered Layeredsediments sediments tidal flats, flats, beaches ---,1967, ofoftidal beaches and and shelf bottoms, p. 191-206: in Lauff, p. 191-206: in Lauff, (hR., G.H., Editor, Editor,1967, 1967,Estuaries: Estuaries:Am. Am. Assoc. Assoc. Adv. Sci. Sci. Pub. Pub. No. No. 83. 83. Reineck, H.E., and WUnderlich, H.E., and Wunderlich,F,F,1968a, 1968a,Classification Classification and and origin origin of flaser 99-1014. fiaserand and lenticular lenticularbedding: bedding:Sedimentology, Sedimentology, v. v. U, ll,p.p. 99-104. ---, &, ---, &, ---, ---,1968b, 1968b, Zeitmessugnen Natur und und ZeitanessugnenananGezeitenschichten: Gezeitenschichten: Natur Musetun, v. Museum, v. 97, 97, p. p. 193—197 193-197 Reineck, H.E., H.E., Dorjes, Dorjes, J, J, Gadow, Garlow, 5, S, and and Hertwick, 0,1968, S3dimentologie, Reineck, 0,1968, Sadiznentologie, Faunenzoniening and Faunenzonierung und Faziesabfolge vor vor der der Ostkuste Ostkuste der der inneren inneren Jeutschen Deutschen Bucht: Bucht: Senck. Senck. Lethaea, Lethaea, v.v.149, 49, p. 261-309 261-309 �-':;8—L8— Rhoads, D.C.,1967, and subtida subtidal D.C.,1967, Biogenic Biogenic reworking reworkingofofintertidal intertidal, and sediments in in Bamstable sediments BarnstableHarbor Harborand and Buzzards Buzzards Bay, Bay, Massachusetts: Massachusetts: Jour. Jour. Geo1or, Geology, 'r. v. 75, p. 461-476. t. b61—L76. E.A.,],968,Practical Practicalsignificance significance of of birdseye birdseye structure structure in in Shinn, E.A.,1968, carbonate rocks: rocks: Jour. Sedimentary Petrology, v. v. 38, carbonate Sedimentar,y Petrology, 38, p. p. 215—223. 215-223. Van Straaten, Van Straaten, L.M.J.U., L.N.J.tJ., 1954, 195h, Sedimentology Sedimento1o'ofof Recent Recenttidal tidal fla.t flat and the thePsamnites Psanmitesdu duC0ndroz Condroz (Devonian): (Devonian): Cleol. Geol. en en deposits and Mijnb., v. i6, Mijnb., v. 16, 25-47. p. 25-217. Wunderlich, F,1970, envirornent ofofthe T1NellenkopfschenWunderlich, F,1970, Genesis and and environment the "Nellenkopfschenschichten Il(Lower sian, EInsian,Rheinian RheinianDevonian) Devonian) at at locus locus typicus typicus in in schichten"(Lower canparison ecinparisonwith withmodern modem coastal environments enviroanents of the Cern GeImclTI n Bay: Bay: Sedimentary Petrology, Petrology, v. 240, Jour. Sedimentar,y 40, p. 102-130. 102-130. �-39—39— GEOLOGYOF OF THE SOME GEOLOGY THE 'ARATHON MARATHON COUNTY COUNTY VOLCANIC VOLCANIC BELT BELT by Gene L. L. LaBerge Wisconsin Geological Survey and and Department of Geology Geology Wisconsin State University Oshkosh, Wisconsin Oshkosh, ABSTRACT ABSTRACT The area east The east of Wausau in Marathon County consists consists largely largely of of rocks which range range in in composition composition from from basaltic basaltic to to rhyolitic. rhyolitic. volcanic rocks The rocks are mainly to the southeast and and the the rhyolitic rhyolitic rocks rocks The basaltic rocks to top of the sequence is northwest: northwest; to the the northwest, northwest, suggesting suggesting that that the the top of the however, however, no no definite definite evidence evidence of of stratigraphic stratigraphic top top \vas was found. fond. Trachytes are a1.. so present edge of of the the napped mapped area. area. Sedimentary are also pr?sent at at the the northwestern northwestrn edge rocks rocks are virtually virtually absent. absent. The volcanic rocks The rocks have been intruded by v;rious various sized masses of of gabbro, and syenite. syenite. There appears appears to to have been been gabbro, diorite, granite, and several ages of granitic intrusion. intrusion. Available radiometric ages ages indicate indicate are late late Middle Niddle Precambrian. Precambrian. that the rocks arc Structurally, the the area is is characterized by at least least two two directions directions Structurally, of large large scale faulting faulting with with niajor major fault faultzones zonestrending trendingapproximately approximately N8O°E to to N60°E. 1180°£ ~~60°E. The \vhich also shows shows up on the aeronagnetic aeromagnetic The faulting, faulting, which up well well on map many of mapcovering coveringthe the area area mainly mainly west west of of Wausau, Wausau,has hasresulted resalted in many of the lithologli units units being in Perhaps the lithologic in fault fault contact. contact. Perhaps the most significant fault zone is is the the N300E N3OF trend fault zone trend whiàh which has has produced produced aa zone zone nearly nearly aa mile mile in the the Eau Eau Claire Claire River River valley in in which mylonite mylonite is is aa major major rock rock wide in This zone truncates type. This truncates the N8O°E—N60°E N800E-N600E trend trend more prevalent prevalent to to the the ,,,,est. west. The current napping project, The current mappins project, funded funded by the the Wisconsin Geological Geological S"rvey, has Survey, revealed significantly significantlymore morevolcanic volcanicrocks rocksthan than shownOLI on has revealed areare shown Weidinan's 1907 map. \veidman's 1907 map. This This has has important importantimplications implicationsfor formineral min al exploration A previously unreported gold prospect, on tion programs. A on which mining attempted about 1920, 1920, is is probably probably the the most most interesting interesting locality locality from from was attempted an economic point point of of view. view. References Dutton, E. (1970) Dutton, C. C. B. E. and and Bradley, Bradley, R. R. E. (1970) "Lithologic, and "Lithologic, Geophysical, and ;·lineral :•lineralCommodity CommodityHaps MapsofofPrecambrian Precambrian Rocks Rocks in in Wisconsin"; Wisconsin"; U.S.G.S. Miscellaneous Geologic InvestigationsMao Map 1-631. Geologic Investigations 1—631. Henderson, J. J. IL, Henderson, R., Tyson, Tyson, ;i). R. (1963) "Aeromagnetic N. S., S., and Page, Page, J. 3. R. (1963) "Aeromagnetic Map of the Wausau Area, Wisconsin"; Map of Wisconsin"; U. U. S. G. G. S. Geophysical Investigations Map Map CP—40l. GP-40l. Laberge, G. U. and l,Jeis, LaBerge, G. 1. L. W. Iv. (1968) Central Weis, L. (1968) "A 'A Greenstone Greenstone Belt Belt if in Central Wisconsin?", Guidebook Guidebook for for 32nd 32nd Annual Annual Tn—State Tri-State Geological Geological Field Field Wisconsin?, Conference. �—40— -40- Weidman, S. S. (1907) (1907) The The Geology Geology of of North North Central Wisconsin; Wisconsin; Wisconsin Geological and Natural History History Survey Survey Bulletin Bulletin 16. 16. Weis, L. W. W. and and LaBerge, LaBerge, C. G. L. 1. (1969) (1969) "Central Wisconsin Volcanic Volcanic Belt," Belt," Weis, L. Guidebook for 15th Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. �—41— -41- HEMATITE PSEUDOMORPI-1IC AFTER BIOGENIC BIOCENIC HE~1ATITE PSEUDOMORPHIC AFTER PYRITE IN INTHE THENEGAUNEE NEGAUNEE IRON IRONFORMATION FORMATION N. M. S. S. Lougheed and J. J. 3. J. Nancuso Mancuso Bowling Green State University, Green, Ohio 43403 43403 University, Bowling Green, ABSTRACT A B S T R ACT Spherules (limonite), ranging in diameter from from Spherules of of hematite (limonite), 5 microns microns to to 20 20 microns microns but generally of similar size in each each as disseminated disseminated octahedral octahedral crystals crystals particular population, as well as of pseudomorphic hematite occur in in many laminations laminations of of the the Negaunee Negaunee iron formation. formation. Mineral associations associations include include chert, chert, magnetite, magnetite, iron iron carbonate, silicates. A A common associate is is fossil fossil fila— filacarbonate, and iron silicates. A tentative conclusion based on two mat algae. algae. A two microprobe mentous mat Thermal experiments carbon in the filaments. filaments. Thermal analyses indicates indicates carbon in the result considerableremoval removal of the filamentous material suggesting suggesting result ininconsiderable the presence presence of both both amorphous amorphous carbon carbon and and graphite. graphite. Framboidal pyrite with diameters ranging from 55 microns to to 20 20 microns sedi— nlicrons and and pyrite octahedra, octahedra, occurring in two two unconsolidated sediinents with contrasting contrasting environments, environments, one one aa Pleistocene fresh ments with fresh water water lake deposit, deposit, the lake the other a Recent marine tidal tidal lagoon, unequivocally unequivocally demonstrate their their biogenic biogenic origin. origin. Paleozoicanalogs analogsofofsomewhat somewhatsimilar similar lithology lithology to to iron iron formation formation P-Jzoic the following associations: carbonate, biogenic biogenic euhedral euhedral the following associations: chert, carbonate, pyrite, biogenic framboidal pyrite, framboidal pyrite pyrite 55 microns microns to 20 microns microns in diameter, diameter, to 20 sparce euhedral magnetite microflora. magnetite and and fossil fossil microfcunz: microfauna and/or microflora. the biogenic biogenic origin origin of of pyrite. pyrite. They further demonstrate the have A finely laminated A finely laminated chert chertcarbonate carbonatespecimen specimen from from the thePennsylvanian Pennsylvanian formation, Texas, Texas, clearly shows the Dimple formation, the transition transition of of biogenic biogenic pyrite to pseudomorphic hematite hematite (limonite) (limonite) by by oxidation. oxidation. features are These various various features are illustrated by photomicrographs phbtomicrographs to to that the support the the hypothesis hypothesis that the spherules spherules of of hematite (limonite) (limonite) possibly other other hematite hematite in in the theNegaunee Negaunee iron formation formation are pseudomorphic after biogenic biogenic pyrite, pyrite, and together pseudomorphic after together with the the presence presence of the bio~enic bio3enic (in part) genesis of probable probable algal algal mat mat strongly strongly support the (in part) of the Negaunee Negaunee iron formation. of iron formation. and and �—42— -42- DISTRIBUTION OF URANIUM URANIUM AND AND THORIUM THOP.IUM IN PRECAMBRIAN PRECAMBRIAN ROCKS RE GION ROCKS OF OF THE THE WESTERN WESTERN GREAT GREAT LAKE: LAKE: RE3ION by Roger C. Roger C. N~alan and and David Sterling Malan David1_A Sterling ommission, Grand Thiorado U.S. Atomic Energy Energy :::ommission, Grand Junction, Junction,:::olorado U.S. Atomic AE<:::;TRACT AECTRACT 1 Prospecting during during the the 1950 1950's resulted in Prospecting s resulted in the the discovery discovery of of several several uranium and thorium prospects in Precambrian rocks in the westuranium and thorium prospects in Precambrian rocks in the westeconomic deposits ern Great Lakes Lakes region region of of the the United United States. States. No No economic deposits ern Great were delHeated the few few small small exploration efforts that were delineated by by the exploration efforts that were were underunderSince then exploration for for radioradiotaken. Since then there there has has been been very very little little exploration active minerals minerals in active in that that region. region. In Wisconsin Wisconsin and and inin upper upper Michigan, Michigan, Lower, Lower, Middle, PreIn Middle, and and Upper Upper Precambrian silicic cambrian silicic and and hyperalkalic hyperalkalic plutonic plutonic rocks rocks contain contain anomalous anomalous In upper amounts of upper Michigan, Michigan, amounts of disseminated disseminated radioactive radioactive minerals. minerals. In the Middle Middle Precambrian Animikie Series contains uranium uranium veins veins in in the Precambrian Animikie Series contains slate, monazite placers placers in in conglomerate, conglomerate, and and irregular concentraslate, monazite irregular concentrations utanium in iron iron formation adjacent to to slate. tions of of Ul anium in formation adjacent slate. These These prosprospects do do not of uranium uranium or or thorium thorium that that pects not contain contain important important reserves reserves of are at present are economically economically mineable mineable at present but but some some may may contain contain large large long-range, low low-grade resources. long-range, - grade re sources. For Forexample, example, limited limited sampling sampling indicates that that masses masses of indicates of silicic silicic igneous igneous rocks rocks in in northeastern northeastern WisWiscousin may contain contain 50 50 to to lOO 100parts parts per per million consin may million uranium. uranium. This This is is greater than than the the uranium uraniumcontent content in inany any of of about about 250 250 bulk samples greater of igneous rocks rocks that analyzed in in aa recent of igneous that have have been been analyzed recent study study of of the the distribution of uranium rocks in in the the distribution of uranium and and thorium thorium in in Precambrian Precambrian rocks western United United States. potentially great great low-grade low-grade resource resource of of western States. AA potentially thorium may thorium may exist exist in in the the monazite monazite placers placers in inAnimikie Animikie conglomconglomerates in erates in the the Marquette Marquette Range, Range, upper upper Michigan. Michigan. In other other areas areas of of the the world, world, stratiform stratiformuranium uraniumdeposits depositsin inMiddle Middle In Precambrian Precambrian coarse coarse clastic clastic sediments sediments are are of of major major importance. importance. The world's world's greatest resource of uranium is is in The greatest known known resource of uranium in basal '::asal conconglomerates of the Middle Middle Precambrian Huronian Series glomerates of Precambrian Huronian Series in the Elliot Lake Blind River Elliot Lake -- Blind River district district in in southern southern Ontario. Ontario. Important stratiform uranium deposits deposits have have not not been been discovered discovered in in the the stratiform uranium Animikie Series which is in Animikie Series which is in part part correlative correlativewith withthe theHuronian; Huronian; �________ -4343— however, however, limited limited sampling sampling ia L.1. the the iviarquette Ivlarquette Range, Range, upper upper Michigan, Michigan, indicates that anomalous anomalous amounts indicates that amountsofofuranium uraniumare are present present in in coarse coarse clastic facies. Also in the the Animikie Animikie in the Also uranium/thorium uranium/thorium ratios in elastic Blind River Marquette Range and in the Huronian in the Elliot Lake River Marquette Range and in the Huronian in the Elliot Lake -- Blind More study area increase increase in in descending descending stratigraphic stratigraphic positions. positions. More study of of area the distribution of uranium the distribution of uranium and and thorium thorium in in the the Animikie Animikieisis warranted. warnnted. CELECTED REFERENCES :ELECTED REFERENCES T.llsley, ':llsley, C. C.T., T., Bills, Bills, C. C. W. W., Some geoand Pollock, Pollock, J.W. J. W.,, 1958, Some chemical methods of uranium exploration, exploration, in inSurvey Survey of of Raw Raw chemical methods Materials Resources: Materials Resources: United United Nations, Nations, New New York, York, Proc. Proc. Second Second lnternat. Conf. Energy, 1958, v. 2, Internat. Con£. Peaceful Peaceful Uses Uses Atomic Atomic Energy, 1958, v. 2, p. p. 126-130. , James, H. James, H. L., L.,1958, 1958,Stratigraphy Stratigraphyofofpre-Keweenawan pre-Keweenawan rocks rocks in in parts parts of Northern Michigan: Michigan: U. U. E E Geol. Geol. Survey Survey Pro£. Paper314-C, 314-C,42 42 p. p. of Northern Prof. Paper King, J. W., W.,1960, 1960,Report Reportofofexamination, examination,Little Little WolfMining Mining&& MinMinKing, Wolf erals, Inc., erals, Inc.,Anklam AnklamProperty PropertyBig BigFalls, Falls,Waupaca WaupacaCounty, County, WisconWisconsin: file rept. sin: U.S. U. S. Atomic Atomic Energy Energy Comm. Comm. open open file rept. Malan, C., and and Sterling, Sterling, D. Do A., A.,1969, 1969,An Anintroduction introduction to to the the disdisMalan, R. R. C., tribution thorium in in Precambrian Precambrian rocks tribution of of uranium uranium and and thorium rocks including including the the results results of of preliminary preliminary studies studiesin inthe thesouthwestern southwesternUnited United States: States: U.S. U.S. Atomic Atomic Energy Energy Comm. Comm. AEC-RD.-9, AEC-RD-9, 54 54 p., p., open open file. file. Roscoe, Roscoe, S. S. M. M., 1969, 1-luronian Huronian rocks conglomerates rocks and anduraniferous uraniferous conglomerates Canadian shield; shield: Geol. Geol. Survey Survey Canada Paper 68-40. 68-40. in the Canadian , Stead, F. F. W., F. J., Stead, W., Davis, Davis, F. J., Nelson, Nelson, R. R. A., A., and and Reinhardt, Reinhardt, P. P. W., W., 1950, Airborne Airborne radioactivity radioactivity survey survey of of parts parts of 1950, of Marquette, Marquette, DickDickinson, and open— inson, and Baraga Baraga Counties, Counties, Michigan: Michigan:U.S. U. S.Geol. Geol.Curvey :urvey openfile map. file map. Vickers, R. of t>-e te Goodrich Vickers, R. C., C.,1956a, 1956a,Geology Geology and and monazite monazite content content of Goodrich Quartzite, Quartzite, Palmer Palmer area areaMarquette Marquette County, County, Michigan: Michigan: U.S. U. S. Geol. Geo!. Survey Bull. Bull. 1030-F. Survey 1030-F. 1956b, Ai Airborne rborne and and ground groundreconnaissance reconnaissanceofofpart partof of the the ----syenite complex near near Wausau, Wausau, Wisconsin: U.S. syenite complex U. S. Geol. Geol. Survey Survey Bull. 1042-B. �Is.. .c g (/) • lii,Oll.tsdiI ~~ - o o a "'" o I :;= g;;'~~ ~~ ~~ O4! 4 l5S 50565' 8 fl. I 4515 il 0 - V t;%,ir III 1545_C1 •'l'' C E] ~i !: .. ~ (~ ?:t,"t.i. ;'''° Ui,iii,soolli,,t. ltl - ~ ~ u~ C C ~ ~ / I / o o Ul '" ~ I 50 146104Sre,,t.4 dtstil. ~ 15 ~ 0 5, SOlO. 444 isosaStis is C.sbi,en yl.'.!.o.; C154401ltUt,11.pi.o I Slot 05 II S •l 545' !!611 11,41. ~~ ~ ., -:0440,' ~ 0 =;;; fl - Jiddn IIfIJqn,e'd D ii ! :.~ ! I i f : c . 'iii 0 c 0 ~ '" ~ .. --., , I 1 I I I '"." c I I I 1 I Lakes fll*!6441r4!llt 4.11 c ~ 0 . '" Greet n n• . < '. • : 0; .! 3<" Sec horn I-I £!,oe.,, #•flsI 44144!, lId Ut SO IMi ~ i~ — ,__— <D~ • :;;. .i E~ .. ~'ii - ;; : ., co Precambrian, s ! 0.- ;. ~ bi 'I,. - i'I": -,..- ~ <; Map - -- ~i: . ~ i u ";; "0 0 0 GaochronoIoic ~ :;. ~ ood . . I:,':?. : ~~ ;:; Geologic . (I,le,n QIfl4. t15 .44 ~ D I ." ~ I G.n,,oIIzeo ! Kt#,.lIk,Ic,t!ee C $!l afl'I,!L. ;; - '" '" I '" 2 ;.: en. —4 ''6 .; 35 i ! 111111_LI . ~:. I ~ t I •.l.ih C—i,. . A ~ ~ = mj, , -44- ~ ~ ~ ~ .;, I a. II: " C 0 ~ ..J ~ C> ~ . q: u e0 " ~ ~ :E Q. 0 '"u0 C> '" " I ~ ~ c 0 <9 0 "" 0 0 <9 ... 00 ~ ~ �-45—45— LOWER KEWEENAWAN KEWEENAWAN SEDIMENTS THELAKE LAKE SUPERIOk SUPERIOR REGION LOWER SEDHlENTS OFOFTHE REGION Allen F. Mattis Mattis Allen F. Department Department of Geology Geology of Minnesota, Hinnesota, Duluth Duluth University of A B S T RAe T ABSTRACT Lower Keweenawan sediments directly directly underlie underlie the the Keweenawan Keweenawan Studies of the quartz— volcanic series in the the Lake Superior Superior region. region. quartzvoi:anic rich Puckwunge Formation (Minnesota) rich (Minnesota) and the Bessemer Formation Formation (Michigan (Michigan and Wisconsin), Wisconsin), which include thin section petrography, heavy mineral and mineral analysis, and measurement of paleocurrent indicators, indicators, provide provide new new data data analysis, and Keweenawan events. events. on Lower Keweenawan The Puckwunge Formation of Cook Cook County, County, northeastern northeastern Minnesota, Minnesota, from is exposed along along aa 25 25 mile mile belt belt extending extending westward westward from is LT.termittently intermittently exposed Pigeon Point on Lake Lake Superior. Superior. Although the lower contact contact of this this formation is is not exposed, exposed, outcrops of of the the formation formation thicken thicken from from 30 formation feet on Grand Portage Island to to over 100 100 feet feet in in the the westernmost \vesternmost feet of basal conglomerate exposures. Fifteen feet feet-of conglomerate exposed exposed on on Grand Grand Portage Portage exposures. Island contains flat flat chips chips and pebbles of of argillite argillite and and slate, slate, probably probably Island derived from the underlying Rove Rove Formation, Formation, and and rounded rounded pebbles pebbles of of feldspar content quartzite. Thin section examinutioi examination indicates indicates total total feldspar content quartzite. ranges from 20 percent percent in the eastern exposures to only a trace in the western outcrops. Unit Unit quartz is the dominant quartz uype, type, with up up to to Zircon, apatite,and apatite, and 20 percent polycrystalline polycrystalline quartz quartz being beingpreseriI. present. Zircon, with tourmatourma— epidote are the the common common nonopaque nonopaque accessory accessory heavy heavy ininerais, minerals, with line also the outcrop belt. also present in the central portion of the to only a trace in the Nopeming, just just west of of Duluth, Duluth, 25 25 feet feet of of quartzite quartzite and and quartzquartz-At Nopeming, conglomerate are •:->.oosed }T the basal (?) quartzite-pebble are exposed bere&: beneath quatnJte—pebble conglomerate (?) Keweenawn Keweenawan flow over a distance distance of of half half aa mile. mile. In the the sand—sized sand-sized fractions, unit quartz quartz is is the LUe dominant dominant quartz quartz type, tye, with polycrystalline fractions, unit polycrystalline also preseit. present. Zircon is the principal nonopaque accessory heavy quartz also is the amounts of of a;atite apatite and and tourmaline tourmaline present. present. Gravity mineral, with minor amounts and magnetic suggest the the presence presence of of aa tabular, tabular, and magnetic profiles profiles across across the the area na suggest dike—like dike-like mafic body beneath the the Puckwunge exposures exposures at at Nopeming; Nopeming; aa greater degree of recrystallization in in the the lowermos: lowermost sediments sediments may may be be related to related to this this probable intrusive. intrusive. and and The Bessemer :-:ohigai-r BessemerFormation Formationof of Hichigan and Wisconsin lHsconsin is intermittently intermittently exposed :nile belt belt extending extending eastward exposed along along aa 40 mile eastward from from >leflen, ~le~len, Wisconsin. formation is is over 150 The fonnation 150 feet thick thickwhere where both both the the upper upper i-td and lower lower contacts are are visible. visible. A contacts A basal conglomerate contains rounded pebbles pebbles of basal conglomerate contains rounded quartz, qu;E2ite, quartzite, flint, flint, and and jasper jasper in in aa qnartzite rruartzite matrix. matrix. In the the sand—si-:d qunrtz is sand-sized fractions, fractions, unit unit quartz is the dominant dominant quartz type, type, with polycrystalline quartz quartz also also present. present. The average total feidsrar feldspar content content is less than than 10 10 percent. percent. Zircon is is the tlte dominant nonopaque nccesscry accessory h!avy withapatite, apatite, rutile. rutile, and heavy hliner&I, ltlineral, \vith and tourmaline tourmaline also also present. presenL �—46— -46- sediments along both limbs the lower lower IKeweenawan Keweenawan sediments Exposures of the the Lake SuperiorSync:ine Synclinesuggest suggestthe thedeposition depositionofof aa thin thin sheet of the Lake Superior sheet of sediment throughout throughout the region. The cross-bedded, rippie—mariced, ripple-marked, of sediment the region. The cross—bedded, of Hell well rounded well sorted sorted quartz—rich quartz-rich sediment sediment composed composed of rounded grains suggests aa shallow shallow water waterenvironment. environment. Cross-bedding, mark, Cross—bedding,ripple ripple mark, in these these sedimentary sedimentary rocks rocks indicate indicate and parting lineation measurements in sediment transport, transport, with the the sediments sediments a general southerly direction of sediment being derived from the the Pre—Keweenawan Pre-Keweenawan rocks rocks to to the the north. north. Thus, Thus, these these Lower Keweenawan sediments were probably deposited deposited during during the the northward transgression of of aa sea into into the transgression the region, region, and were apparently the the final final region prior to to formation formation of of sediment deposited in the Lake Superior region the Lake Superior Syncline. Syncline. �—47— -47- EXPLORATION GEOLOGY GEOLOGY OF OF DOUGLAS DOUGLAS COUNTY, COUNTY, w::scoNSIN WISCONSIN by Joseph T. T. Mengel, Mcnge1, Jr., Jr., Professor and Ronald A. A. Hendrickson Department of Geology Geology Wisconsin State University, University, Superior, Wisconsin 54880 54880 and and and Natural Natural History History Survey, Survey, Madison Madison 53706 53706 Wisconsin Geological and ABSTRACT A B S T R ACT The oldest bed rock units in Douglas County are are the the Keweenawan Keweenawan basaltic fissure flows flows of the St. St. Croix horst south south of the line lin~ Brule, raple, Wentworth, Wentworth, South Range, Brule, Maple, Range, Pattison State Park, Park, Patzau. Patzau. These flows flows have a N6OE3SS N60E35S attitude along tha the north margin margin of of the the horst and N5OE15S N50E15S along along the the south. south. They are intruded by "red "red rock" .95 b.y. b.y. and and by aa gabbro gabbro mass mass in in 32—48N— 32-48Nin 15-47N-13W,K/Ar l5—47N-13W,K/Ar dated at .95 12W. l2W. flows occur again south of the line Totagatic River— Basaltic flows RiverOunce Creek where the attitude is N4SE3ON N45E30N and and there there are are extensive extensive conglomerate lavas. conglomerate and sandstone interbeds with the lavas. Native copper ides are copper and and copper copper suif sulfides are found found in in ainygdaloidal amygdaloidal horizons and along fractures wherever the the Keweenawan Keweenawan lavas lavas outcrop. outcrop. Almost all lava outcrop is within the the following following limits: limits: (1) A a,uth of of the the line Brule—Patzau A 22 mile wide wide band band south Brule-Patzau (2) (2) A nile wide band north of A 22 mile of the the line line Winnebaujou—St. Winnebaujou-St. Croix River in 43N-14w 44N-13W 43N—14W and 44N—13W (3) (3) 43N-15W The NW half of 43N—1SW (4) (4) The south half of 44N-15W 44N—l5W and SW quarter 44N-14W 44N—14W (5) (5) The NE quarter of 45N—l2W 45N-12W (6) The SE haf half of of 43N—1OW, 43N-lOW. especially especially along along the the valley valley of of Dingle Creek in sections 12 and 13 where an an extensive extensive section is exposed the last last century and a half the properties During the half the properties listed below have all all been the have the locus of shafts and/or test test pits and and drilling drilling for for copper in in the the lavas. lavas. �—48— -48- Location Property Nature NE 12—43N—1OW l2-43N-lOW Weyerhauser Amygdaloid Ainygdaloid and and in assoc. sediments SW 28—43N—1OW 28-43N-lOW Williams Ashbed amygdaloid NW 6—43N—13W 6-43N-l3W Superior Copper Mines C.F. C.F. Irving Mon 5, 5, pI. 25 p1. 25 8—43N—13W SW 8-43N-l3W Copper Mine Dam (? ) Ainygdaloid Amygdaloid (?) SE 34—44N—J.4W SE 34-44N-l4W Nowell (Crotty Brook Arnold) ArnoL) Nowell (Crotty Brook (? ) Anygdaioici Amygdaloid (?) SE 14—44N—13W SE l4-44N-l3W Aac ía Arnold Amygdaloid Amygdaloi<l 7N—liJ NE 31-4 3l-47N-l4W Culligan Amygdaloid SE 28—47N—14W 28-47N-l4W Bardon Amygdaloid Amygdaloid('l) () SW l4-47N-l4W 1447N—14W SW Copper Creek Creek Cc1:ier Amygdaloid NE 8—47N—13W 8-47N-l3W Fond Fond du Lac Lac Amygdaloid SE 2—47N—l3W 2-47N-l3W Starkweather Wisconsin Edwards Zdwards NWdip dip 75 NW NE strike 75 Centerll—47N—13W ll-47N-l3W Amnicon Center Fissure vein vein4—6' 4-6' wide wide Narrow steeply dipping Narrow steeply dipping vein Houghton Amygdalcid Amygdaloid NE 8—47N—12W 8-47N-l2W Badger Amygdaloid Nnygdaloid (?) NW NW 1O—47N—12W lO-47N-l2W Chippewa Fractured Fractured Amygdaloids Amygdaloids St 1O—47N—12W SW lO-47N-l2W Copper King King Amygdaloid (?) (?) Amygdaloid 23--48N--lOW NE 23-48N-lOW Cascade Amygdaloid (?) (?) Miygdaloid NE NE Percival, Jr. Jr. Percival, Amygdaloid NE NE 27-48N-lOW 27—48N—1OW Percival Veinlets ininamygdaloid amygdaloid NW NW 28—48N—1OW 28-48N-lOW Astor Amygdaloid SE 29—48N—12W 29-48N-l2W Mrnicon Amnicon Amygdaloid (?) Mtygdaloid SE SE 34-48N-l3W 34—48N—13W Catlin Amygdaloid 4—47N-12W 4-47N-l2\.J 24-48N-lO\.J 24-48N—lOW �—49— -49- The the The U. U. S. S. Bureau of Mines Mines reported on extensive tests of the Property in 1947 and the the Chippewa Chippewa Property Property in in 1955. 1955. Weyerhauser Property The Keweenawan Oronto Group occupies the the Lake Superior Superior syneline syncline of the Croix River. Resouth of the line lineWinneboujou, Hinneboujou, Solon SolonSprings Springs—- St. Croix Shale, and portedly the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, the Nonesuch Nonesuch Shale, and the the Prospecting in Freda Sandstone units are all present in this area. Prospecting Freda Sandstone units are all present in this area. the the syncline syncline has has centered centered on on attempts attempts to tolocate locatea acopper—bearing copper-bearing facies facies of the the Nonesuch Nonesuch Shale, but but has hasbeen beenhampered hampered by by complete complete absence absence of outcrop except the St. St. Croix River Valley. Valley. except along the lower portion of the Conglomerates in: NWNW NWNW 10— 10Conglomerates have have been reported from exploration tests in: half lO—45N—1OW, 44N-llW, SW corner 3l—44N—1OW, 3l-44N-lOW, WW half 10-45N-lOW, SWSW SWSW l6—45N—llW, l6-45N-llW, NE 27—45N-lOW, NENE 34—45N—llW, 10—46N—llW, NESE 25—46N—11W; NE corner corner 27-45N-lOW, NENE 34-45N-llW,SESE 10-46N-llW, NESE 25-46N-llW; Shale rrom from.near center of 34-47N-llW; Sandstone NE 3-45Nnear thethe center of 34—47N—llw; andand Sandstone fromfrom NE 3—45N— NWSWll-46N-lOW, ll—46N—lOW, W Whalf half 15—47N—1OW, lOW, SW SW 8—46N—lOW, 8-46N-lOW, NWSW l5-47N-lOW, SE SE19—47N—1OW. 19-47N-lOW. Waterwells do estimated 200 200 foot foot depth depth of of sandy sandy Waterwells donot not penetrate penetrate the estimated overburden in this area. overburden in this References Grant, Grant, U. U. S., S., 1901, 1901, Preliminary Preliminary Douglas County, Wisconsin: Douglas 6, 55 p. p. 6, 55 report on the the copper—bearing copper-bearing rocks of report Wisc. Wise. Geol. and and Nat. Nat. Hist. Hist. Surv. Surv. Bull. Bull. Holliday, it. W., Holliday, R. W., 1955, Investigation Investigation of of Chippewa Chippewa copper—nickel copper-nickel prospect prospect near Rockmont, Rockmont, Douglas County, County, Wisconsin: Wisconsin: U.S. Bur. Mines Rept. Rept. U.S. Bur. mv. 5114, Inv. 5114, 11 11 p. p. Irving, R. R. Do, D., 1883, 1883, Copper-bearing Copper—bearIng rocks Irving, rocks of Lake Superior: Superior: Mon. 5, 5, 464 464 p. p. Geo1. Survey Mon. Ceol. U. S. S. U. ,p Smith, N. H. C., 1947, 1947, Copper deposits of Douglas County, County, Wisconsin: U.S. Bur. 4088, 7 7 p. p. Bur. Mines MinesRept. Rept. Inv. mv. 4088, Sweet, F. E. T., 1880, Geology Geology of in T., 1880, of the the western western Lake LakeSuperior Superiordistrict district in Geology of Wisconsin 1873—1879: 1873-1879: Wisconsin Wisconsin Geol. Geol. Survey, Survey, v. v. 4, 4, p. 305-362. 305—362. �-50—50-REVISED KEWEENAWAN KEWEENAWAN SUBSURFACE SUBSURFACE STRATIGRAPHY STRATIGRAPHY SOUTHEASTERN MINNESOTA SOUTHEASTERN B. Morey B. Morey Minnesota Geological Survey Minnesota Geological Survey Minneapolis~ Minnesota Minnesota Minneapolis, G. G. ABSTRACT TheMid-continent Mid—continent Gravity High themajor majortectonic tectonicfeature feature of of the The Gravity High is isthe the Detailed geophysical northern mid-continent mid-continent region. region. Detailed geophysical surveys surveys over over the the 600 600 northern mile-long consists mainly mainly of ofa asequence sequence of babamile—longbelt belt show showthat that the the structure consists saltic lava blocks that are saltic lavaflows flowswhich whichform formsteep—sided steep-sided blocks are an an average average of about about 40 miles wide wide and and several several miles miles thick. Clastic rocks 40 miles rocks occur occur in flanking flanking babaBecause much much of of sins and in grabens grabens and the blocks. blocks. Because sins and andaxial axial basins basins on on top top of of the the structure isis covered rocks, little little is is known the covered by by Paleozoic Paleozoic rocks, knownabout about the the rocks rocks However, the the Paleozoic away outcrop area area around around Lake Lake Superior. Superior. However, awayfrom from their their outcrop cover is is relatively southeastern severaldrill drill holes cover relativelythin thinin in southeasternMinnesota, Minnesota, and and several holes Of particular particular have penetrated considerable thicknesses strata. Of have penetrated thicknesses ofofIceweenawan Keweenawan strata. rocks which whichflank flank and andoverlie overlie the interest here here are are the the sedimentary sedimentary rocks the St. Croix Croix an uplifted upliftedbasalt basaltblock blockin in southeasternMinnesota. Minnesota. horst, an southeastern Keweenawan sandstone shalehave havebeen beenknown known fromthe thesubsurface subsurfacefor for aa Keweenawan sandstone andand shale from Because ofoftheir red color, color,they theyhave havebeen been grouped grouped together together ununhundred years. Because hundred their red der the Red Red Clastic Series, Series, aa"temporary" IItemporaryllname name proposed proposed by der the byHall Hall and and others others in 1912. Mooney Mooney and Geophys. Res., Res., v. v. 75, 75,p.p. 5056-5086) have have 1912. andothers others (1970, (1970, J. J. Geophys. 5056—5086) subdivided number of and concluded concluded that sevsevsubdivided these these rocks rocks into aa number of seismic seismic units, and eral of already named of their theirsubdivisions subdivisionscould couldbebecorrelated correlatedwith with already named formations. formations. A detailed detailed petrographic petrographic study study of Ii,000 4,000 feet feet ofofdiamond diamond drill drillcore corefrom froma number a number thepresence presence leastthree threelithologically lithologically of localities localitieshas hasdemonstrated demonstrated the of of atatleast distinctintervals intervals whichmore—or-less more-or~less correspond correspond to seismic units. Therefore, distinct which to seismic it will be be recommended in prep.) it will recommended (Morey, (Morey, in prep.) that thatthe theterm termRed Red Clastic Clastic Series Series be be abandoned andreplaced replacedby by aa more moresuitable suitable nomenclature. nomenclature. Accordingly, Accordingly, three three abandoned and formations be recognized: recognized: (1) Hinckley Sandstone, Sandstone, a abuff tan rock rock conconformations will will be (1) Hinckley buff to to tan taining 95 (2) Fond du Lac Lac Formation, Formation, consisting consisting of 95 percent percent or or more more quartz. quartz. (2) Fond du intercalated intercalated moderate moderate red red shale shale and and sandstone sandstone containing containing 6o 60 percent percent quartz, 30 30 percent orthoclase, orthoclase, microcline microcline and and sodic sodic plagioclase, plagioclase, and 10 percent percent"granitic" "granitic" percent and 10 rock fragments. fragments. (3) (3) An An as as yet yet unnamed unnamed formation, consisting ofofdark darkreddish— reddishformation, consisting brown mudstone containing plagioclase brown mudstoneand andsandstone sandstone containingvariable variable amounts amountsofofquartz, quartz, plagioclase of intermediate intermediate composition, composition, and and aphanitic aphanitic igneous igneous rock rock fragments. fragments. The The first first two formations are known known from two formations are fromsurface surface exposures, exposures,however howeverthethethird third formation formation is confined sub—surface. confined entirely entirelytotothe the sub-surface. A stratigraphic stratigraphic analysis A analysis indicates indicates that that in in the the flanking flanking basins, basins, the the ununnamedformation formationisisoverlain overlain by by the du Lac LacFormation, Formation,which whichininturn turn is gradanamed the Fond Fond du gradationally tionallyoverlain overlainbybythe theHinckley HinckleySandstone. Sandstone. On the horst, horst,the theunnamed unnamed On top top of of the formation overlies formation overl ies basaltic basalticrocks rocksand and is locallyoverlain overlainbybyHinckley HinckleySandstone; Sandstone; is locally at places, places, aa regolith regolithasasmuch much as as 100 100 feet thick thickseparates separates the the two two formations. formations. Either the the Fond Fond du du Lac Lac Formation Formation was was wasnever neverdeposited depositedonontop topofof the the horst, ororwas removed prior to to Hinckley removed prior Hinckley deposition. Any attempttoto explain explain the the geologic geologic evolution evolution of of this structure Any attempt structuremust must take take thesestratigraphic stratigraphic relationships. into account account these relationships. �-51—51— LIMNOGEOLOGICAL STUDIES OF THUNDER THUNDER BAY, BAY, STUDIES OF LAKE LAKE SUPERIOR, ONTARIO ONTARIO J. S. Mothersil1 Mothersill S. LAKEHEAD UNIVERSITY LAICEHEAD ABSTRACT A B S T R ACT studies were carried carried out out in in Thunder Thunder Bay, Bay, Limnogeological studies Lake Superior during the the 1970 1970 field field season. season. Ponar grab samples and Ph1eger taken at one hundred and forty—seven forty-seven and Phleger cores were taken stations stations on a 1.5 mile grid for geochemical and mineralogical In addition three echo sounding traverses analyses. In three echo traverses were carried out using an an MS MS 26F 26F metric metric echo echo sounder. sounder. Thunder Bay which is partly silled to to the the south south by an an east—northeast trending horst from Victoria Island east-northeast Island to to Spar Spar Island basins. Recent sediments sediments which Island contains contains three separate basins. bay—floor grade from a thin cover the bay-floor thin veneer of of sand, sand, less less than than centimeters thick, thick, to clay—silts, up to 14 33 centimeters to aa sequence of clay-silts, meters thick, thick, in in the the central central parts parts of of the the basins. basins. Tight foldfoldclay-silts in in the the deepest deepest part part of of the the central central ing of the Recent clay—silts basin is probably caused caused by by gravity gravity slumping. slumping. Geochemical investigations the bottom-sediments investigations of of the bottom—sediments show that there appears to towards negative Eh and low pH values in the the to be be aa tendency tendency towards deep—water areas. deep-water areas. In the the vicinity of the Kaministikwia Delta anomalous Eh and pH measurements were recorded recorded which were were anomolous probably caused by industrial pollutants entering entering the the bay bay from from the the Kaministikwia River. River. overlie Pleistocene Pleistocene The Recent sediments unconformably overlie varved sediments of undetermined thickness. The Recent clay— thickness. claythe Pleistocene varved sect±on sectton each each form form aa silt section and the typical thin upper typical syndiagenetic sequence with a relatively thin oxidized zone (initial (initial stage) stage) and and aa lower lower reduced reduced zone zone (early (early burial stage). stage). The oxidized zone zone is is caused caused by by the the dissolved dissolved oxygen in the the trapped trapped waters of of the the upper upper layers layers of of sediment sediment and the the action of of aerobic aerobic bacteria. bacteria. The depletion of oxygen results results in the the underlying reducing reducing zone zone with anaerobic anaerobic and aa sharp sharp increase increase in in pH. pH. conditions and �—52— -52- REFERENCES Bissell, H. H. J., 1959, 1959, Silica in sediments of of the the Upper Upper Paleozoic of the the Cordilleran Cordilleran area. area. Spec. Publ. Spec. Pubi. of Soc. Soc. Econ. Econ. Paleontologists and of and Nineralogists, Mineralogists, 7, pp 150—185. 7, 150-185. Dapples, E. E. C., 1962, 1962, Stage of diagenesis in in the the developdevelopment of sandstones. sandstones. Bull, Bull, Ceol. Soc. Geol. Soc. Am., Am., 73, 73, pp 913—934. 913-934. pp Emery, Emery, K. K. 0. O. and and Rittenberg Rittenberg S. S. C., C., 1952, 1952, Early diagenesis of California Basin sediments in in relation to to origin of oil. Bull. Am. Am. Assoc. Assoc. Petrol. oil. Bull. Petrol. Geologists, Geologists, 36, 36, pp 735-806. pp 735—806. Larsen, C. Larsen, G. and and Chilingar Chilingar C. G. V., V., 1967, 1967, Introduction. Introduction. In In Diagenesis in in sediments. sediments. Univ. Univ. of of Southern Southern California, Los Angeles, Angeles, pp pp 1—17. 1-17. W. H., H., 1942, 1942, The rate of deposition of of sediments: sediments: Twenhofel, W. a major factor connected with aiteration alteration of Jour. Sedimentary sediments after deposition. deposition. Jour. 12, pp pp 99—110. 99-110. Petrology, 12, Changes produced by microC. E., E., 1942, 1942, Changes ZoBell, C. organisms in in sediments sediments after after deposition. deposition. Sedimentary Petrology, 12, 12, pp pp 127—136. 127-136. Jour. �—53— -53- REINVESTIGATIONOF OF "RED "RED ROCKS" REINVESTIGATION ROCKS" IN THE THE PIGIY)N POINT AREA, PIGEON AREA, MINNESOTA MINNESOTA C. M::drey, Jr., and and P. P. W. W. Weiblen Weiblen M. G. Mudrey, Jr., Minnesota Geological Survey Survey and University of Minnesota, Minneapolis ABSTRACT ABSTRACT Keweenawan granitic rocks rocks of reddish reddish color color as as exemplified exemplified by the "red rocks" rocks" of the the Pigeon Point, Cook Cook County, County, area area are are divisible into red quartzites, quartzites, porphyritic red red rocks rocks and and granular granular with this this division division reduces the problem red rocks. rocks. Retnapping Remapping with problem of of excess granophyre abundance associated with the the Pigeon Pigeon Point Point sill. sill. Reddish quartzites quartzites contain abundant recrystallized quartz Reddish quartz iicrstitial sericite—biotite feldspar— with minor minor interstitial sericite-biotite and granophyric feldsparquartz intergrowths. A faint foliation A faint foliationdefined defined by by biotite biotitelinea— lineation and tion quartzite inclusions inclusions and relict relict bedding bedding can be discerned in quartzite found in intermediate rock rock of dioritic dioritic composition. composition. Porphyritic red rock displays euhedral feldspar feldspar phenocrysts in a granophyric quartz—feldspar quartz-feldspar groundmass. groundmass. This rock type cuts Miaro— the Pigeon Point gabbro. Miarothe Rove formation and and intrudes the litic cavities are found filled with calcite and zeolite minerals. cavities zeolite Granular and feldspar feldspar Granular red rock contains granoblastic quartz and tic groundmass groundinassof of quartz quartz and and feldspar feldspar with with minor set in a granophy granophyric minor sericite-biotite and epidote. epidote. sericite—biotite and and rounded grains or sphene and Phase relations relations and overgrowths on quartz suggest suggest that that aa sedimentary parentage is is possible, possible, however intrusive intrusive relations relations on on Pigeon Point require that the granular red rocks rocks must must have have been been a crystal mush. Point area area in in excess excess The abundance of red rock in the Pigeon Point of that to be expected by differentiation has been noted since of that since 1893, the eastern eastern exposures exposures of of 1893, and is is part of a reinvestigation of the Keweenawan rocks rocks in in Minnesota. �—54— -54- THE SEDIMENTOLOGY AND TECTONIC SIGNIFICANCE THE SIGNIFICANCE OF OF THE THE BAYFIELD GROUP, GROUP ~ WISCONSIN HISCONSIN AND MINNESOTA MINNESOTA Wallace Darwin Darwin Myers, Myers~ II II University of Wisccnsin Wisconsin ABSTRACT ABSTRACT A study of the mineralogical and A and physical physical characteristics characteristics of of the the Bayfield Group was made to determine 1) 1) depositional depositional environment, environment, paleogeography, and source terrane paleogeography, terrane during during Bayfield Bayfield time, time, 2) 2) the the of the nature of the contact contact of ofthe theBayfield BayfieldGroup Group with with the the older olderOronto Oronto Group, Group, and and 3) 3) the early of the the Douglas Douglas fault. early history of fault. study included included detailed detailedmapping mapping of of Bayfield Bayfieldand andOronto Oronto Field study Group rocks outcrops, the lithology lithology Group rockstotoestablish establishthe thelocation locationofof all all outcrops, and stratigraphy of of all stratigraphic and stratigraphy all formations, formations, the the geographic geographic and and stratigraphic distribution distribution of of sedimentary structures and the the structural relationships relationships between rock rock bodies. bodies. Analyses of rock rock specimens specimens in in the the laboratory laboratory included 1) 1) petrographic study of the the bulk bulk mineralogy mineralogy and and textural textural characteristics of sandstone specimens, 2) 2) x—ray x-ray diffraction diffraction study study of of the the clay mineralogy of shale beds and and chemical chemical analyses analyses of of the the boron boron conconcentration of the clay mineral illite, 3) 3) x—radiography x-radiography study study of of the the sedimentary structures, structures~ and and 4) 4) internal stratification of selected sedimentary statistical study of directional sedimentary structures. structures. Petrographic studies of Bayfield Bayfield Group Group sandstones sandstones indicate indicate that that constitutes approximately approximately 80 80 percent percent of of framework framework grains, grains, that that quartz constitutes the feldspar population is dominated dominated by microcline, microcline, and and that that Bayfield Bayfield the feldspar Group sandstones sand·stones are are better better sorted sorted and and exhibit exhibit aa higher higher degree degree of of rounding than than the the Freda Freda Sandstone of the the Oronto Oronto Group. Group. The high compositional compositional and and textural textural maturity The high maturity of ofthe theBayfield BayfieldGroup Group suggests that that the suggests the source source area area for forthese thesesediments sediments was was not not aa simple simple volcanic terrane. Petrographic Petrographic data that the the Bayfield Bayfield and and volcanic data indicate indicate that Freda possibly recycling of of the the Freda Freda Freda sandstones sandstoneshad hada asimilar similar source; source; possibly Sandstone was an an important important source source of of sediments sediments during during Bayfield Bayfield time. time. The Tl~ sedimentary structures of the the Bayfield Group are those which are typically developed in fluvial are fluvial environments, environments~ including including trough trough cross— crossbedding, current ripple marks, sandstones, mudcracks, bedding, marks, channel sandstones, mudcracks, and associated structures. structures. The stratification and bed forms forms of the the Bayfield Group are Group are characteristic of those those formed formed in in the the upper upper part part of of the the lower— lowerwith modern alluvial (Harms and and Fahnestock, Fahnestock, 1965). 1965). By analogy ,.,ith alluvial flow regime (Harms channels channels the the general geologic setting of of the the Bayfield Bayfield Group Group can can be be inferred to to have been an alluvial plain plain characterized characterized by by loz—gradient, 100.,-gradient, perennial streams. streams. The strong N40°E N400E trend trend of of trough trough cross— crossmeandering, perennial bedding indicates was from the indicates the the direction of sedimentary transport transport was the southwest to the the northeast. This inference is is supported supported by the the orientation tion of parting lineation and and current current ripple ripple marks. marks. �—55— -55- the Bayfield and and Oronto Oronto Groups Groups is is not not exposed; exposed; The contact of the petrographic data provide~he provide the clearest evidence of the petrographic the nature of of this this boundary. On the the basis of the the high compositional compositional and and textural textural maturity maturity boundary. Group sandstones, exhibited by Bayfield Group sandstones, it it is is suggested suggested that that these these elastics represent represent a new cycle of sedimentation in clastics in the the synclinal synclinal Lake Lake This interpretation is supported by the contrasting Superior basin. basin. This supported the contrasting clay mineralogy mineralogy of the two sequences (illite— clay (illite- and and chlorite—rich chlorite-rich Oronto Oronto rocks, but kaolin—rich rocks, kaolin-rich Bayfield Bayfield rocks). rocks). compelling evidence evidence that:the that: the Douglas Douglas fault fault was was active active There is no compelling during Bayfield time. time. Conglomerates are are known known at at only nittytwo two exposures exposures of the Douglas Douglas fault, the fault, and in each case their their distribution distribution is is restricted restricted to to the zone immediately adjacent the adjacent to to the the fault. fault. Furthermore, Furthermore, the conglomconglomerates do do not not resemble true tectonic conglomerates either erates either texturally texturally or or compositionally. Additional evidence is provided by the the orientation orientation of directional sedimentary structures structures at at the the Douglas Douglas fault fault localities. localities. These structures which include include parting parting lineation and and cross-bedding, cross—bedding, show show structures which no apparent relation to the Douglas fault. to the fault. Thus, Thus, there is no geologic evidence of major faulting faulting during during Bayfield, Bayfield, or or at at least least Orienta, Orienta, time. time. �—f LAKE LAKE MICHIGAN MICHIGAN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY by W. O'Hara Norbert W. Great Lakes Research Division University of Michigan Arbor, Mi Michigan Ann Arbor, chigan William J. J. Hinze Hinze Department of Geology Michigan State University East Lansing, Lansing, Michigan Michigan E;t ABSTRACT A B S T R ACT The Precambrian Precambrian basement basement complex complex beneath beneath Lake Lake Michigan, Michigan, which which lies lies on the western western and and northern northern flank flankofofthe thePaleozoic PaleozoicMichig.E.n Michigan Basin, Basin, is is only known from a few widely scattered basement drill holes around the scattered drill holes around the perimeter of of the Lake and and aa single single drill drill hole hole -ithin within the Lake Lake on on 3eaver Beaver Nevertheless, the basement geologyof of Lake LakeMichigan MichiganisissignifisignifiIsland. Nevertheless, basement geology cant frameworkofofthe theMidcontinent Midcontinentandand critical to cant to the the Precambrian Precambrian framework is iscritical to the extrapolation extrapolation of ofbasement basement structural structural trends trendsfrom from Lake Lake Superior, Superior, orth— Northinto the fill this ern Michigan, and Wisconsin into theMichigan Michigan Basin. Basin. To To fill thisgap gap an an em Michigan, and aeromagneticsurvey surveyconsisting consistingof of 7,000 7,000 miles miles of of total aeromagnetic total magnetic magnetic intensity were collected along flight traverses separated data were separated by by six six mile mile intervals. intervals. traverses were were flown flown over over northern northern Lake Lake Michigan in aa general northFlight traverses east direction and over southern Lake Lake Michigan in in aa northwest northwest direction. direction. The residual total magnetic intensity map map prepared from from the the collected To general the magnetic data exhibits three regional regional magnetic magnetic positives. positives. In anomalies are related in in aa direct direct manner manner to to gravity gravity anomalies anomalies on on the the periperimeter of the Lake. Lake. The strikes northwest northwest from from the the The southernmost southernmost positive postive :rikes Michigan shore from from +2° 42 0 to 13° 43 0 30'N. 30'N. This anomaly is associated with aa positive and and local local magnetic magnetic positives positives extend— extendsoutheast striking gravity positive icLg across southwestern southwestern Michigan Michigan and northeastern ing across northeastern Indiana Indiana into into Ohio. Ohio. It It is gravity and and magnetic magnetic anomaly anomaly in in northeastern northeastern is on strike with the positive gravity Indiana which has been found found by basement basement drilling drilling to to be be underlain underlain by by basalts basalts similar to Keweenawan flows flows of of the Lake Lake Superior Superior region. region. The central central regional positive, which is made up of several individual anomalies, roughly easteast— anomalies, strikes strikes roughly 450 0 0 t140 The northern components west across ·the Lake between 44 and 45 15'N. The northern components of the l5'N. this anomaly can be traced into into Wisconsin and and across across the southern southern Peninsula Peninsula this of Lchigan except where they are transected by the Mid—Michigan rift Michigan except where they are transected by the Mid-Michigan rift zone. zone. trends are believed to be assrciated with the the Penokean basement basement provprovThese trends associated with ince. A A marked regional magnetic anomaly minimum striking east-west east—west occurs occurs to the north of the regional regional positive. positive. The anomaly is on on strike strike with the the felsic felsic rocks of the Mountain—Amberg Mountain-Amberg area area of of Wisconsin Wisconsin which which is is also also charcharacterized by magnetic magnetic minimums. minimums. The minimum reappears reappears east east of of the the Mid—Michi— Mid-Michigan rift rift zone anomaly and and strikes strikes east—southeast east-southeast across across to to Lake Lake Huron. Huron. The The northern regional positive magnetic anomaly anomaly strikes strikes north—south north-south from from Traverse Traverse where it it bifurcates bifurcates with with one one limb limb extending extending Bay to north of Beaver Island where north—northwest through Lake north-northwest Lake Superior Superiortotothethe Keweenawanbaa basalts Keweenaw Keweenawan alts ononKeweenaw Point. The other limb the eastern eastern portion of of the the Northern Northern Point. limb continues continues into the Peninsula of Michigan and another another segment segment of of this this branch branch connects connects to to the the Keweenawan flows on Mamainse Point. flows on Mamainse Point. In the the Traverse Bay area the regional connects to the positive becomes becomes strongly negative and connects the south with the the midmid— Michigan gravity and and magnetic magnetic anomaly. anomaly. �-57—57— GEOCHRONOLOGY OF THE GIANTS RANGE GRANITE L. A. PRINCE FRECE AND L. A. AND G. G. N. N. HANSON HANSON State University of New York Stony Brook, N. N. Y. Y. 11790 ABSTRACT A B S T R ACT Seven whole rock samples of two—mica, two-mica, foliated foliated quartz ~uartz monzonites monzonites from the central part of the Giants Range Granite, Granite, north of Hibbing, Hibbing, Minnesota, give aa Rb—Sr Rb-Sr isochron isochron age age of of 2670 2670 1) and a 3r87/Sr86 ± 65 m.y. (Rb (Rb 87 x 10yr _1) Sr 87 /Sr 86 initial initial 87 AS A == 1.39 x i0'11 yr ratio ratio of 0.7002 ± 0.0019 0.0019 at at the 95% confidence level. level. Epidote, plagioclase, potassium feldspar, biotite—chiorite, apatite plagioclase, feldspar, biotite-chlorite, apatite and and muscovite separates from one of these whole rock samples give muscovite separates samples give mineral —whole rock ages ranging from 2350 m.y. for epidote -whole ages ranging from 2350 m.y. for epidotetoto26140 2640 m.y. m.y. for muscovite. mineral—whole rock ages muscovite. The lowered mineral-whole ages suggest suggest that at least least one event event occurred after intrusion of the granite, at granite, but that that the individual mineral phases the phases were not completely homogenized homogenized with Sr 87 /Sr 86 ratios. ratios. The 2350 m.y. epidote-rock respect to their 5r87/5r86 m.y. epidote—rock age age probably is is a maximum for the time of the last last event. event. The mineral data provide no conclusive evidence for for the sequence se~uence of of events after intrus on, but are not inconsistent events intrusion, inconsistent with aa regional regional low-grade low—grade metamorphism at around 1600 m.y. This is in agreement with U—Pb U-Pb data data on on sphene sphene This whole rock age is Giants Range Granite which suggest suggest an an age age of of and zircon from the Giants 2700 for hornblende from from the the Giants Giants 2100 m.y. n.y. and also with K-Ar K—Ar ages for Range Granite which generally generally are are 2600—2100 2600-2700 m.y. m.y. These ages ages however are older than most of the Rb—Sr Rb-Sr and and K—Ar K-Ar ages ages for for biotite biotite however are which range from 2260—2630 2280-2630 m.y. m.y. The age of the post-kinematic post—kinematic Linden Linden Syenite Syenite just just to to the the north north also also limits limits the the age ae of the syn— syn?b207_Pb2u6 data on sphene to late—kinematic late-kinematic Giants Giants Range Range Granite. Granite. Pb207_Pb206 sphene and aa Rb-Sr b—Sr mineral—whole mineral-whole rock rock isochron isochron with with an an initial initial ratio ratio of 0.7009£-0.0004 suggest an age for the Linden Syenite Syenite of of about about 0.1009±O.000b 2700 m.y. 2100 m.y. 87 /Sr 86 initial The low Sr initial ratios from from both the the Linden Linden Syenite Syenite Sr87/5r86 and the the Giants Giants Range Granite suggest suggest aa source source with aa low low Rb/Sr Rb/Sr and ratio, perhaps mantle, and and it is is unlikely that appreciable appreciable ratio, perhaps the mantle, mixing with preexisting continental crust crust took place. place. �—58— -58- THE GREAT GREAT LOGAN PALEOHAGNETIC PALEOMAGNETIC LOOP —- THE POLAR THE WANDERING PATH FROM FRaN CANADIAN SHIELD ROCKS ROCKS DURING DURING THE THE HELIKIAN HELIKIAN ERA ERA by W. A. W. A. Robertson }{obertson Geomagnetic Laboratory Energy,Mines Energy,I'Iines & & Resources Resources Ottawa, Ottawa, Ontario w. F. Fahrig H. Geological Survey of Canada Ottawa, Ontario Ottavla, ABSTRACT ABSTRACT Normally magnetized dykes dykes and reversely reversely magnetized sills sills of of Neohelikian age age near the the north west take Superior Superior form form west shore of Lake two distinct distinct paleomagnetic groups groups with mean pole positions of two 179W, 35N, 179\\1, 35N, and 140W, 47N 47i'J respectively. respectively. Thermal and and alternating alternating field field paleomagnetic studies studies and and the study of magnetic properties and opaque opaque minerals minerals indicate that and that directions directions of magnetization of of these rocks were acquired at at the the time time of of their their intrusion. intrusion. Field these rocks evidence indicates indicates that evidence that the the reversely magnetized sills are older than the normally magnetized magnetized dykes than the normally dykes and radiogenic age determinations indicate intrusion between 1000 1000 and and 1100 1100 m.y. m.y. ago. ago. These pole pole positions, positions, together with those for the These the Franklin Franklin intrusions pole pole at at l67E-08N, 167E—08N, assigned age 675 m.y., the intrusions 675 m.y., the Abitibi dykes, the NacKenzie MacKenzie dykes, at at 134W. 134W, 27N, 27N, assigned aged 1150 m.y. m.y. and the Igneous events, at Igneous at 171W, l71W, 4N, 4N, assigned assigned age age 1200 1200 iu.y. m.y. are are used used to to define Logan's Loop, the pole pole took took in in Neohelikian Neohelikian define Loop, the the path path that. that the time to the Canadian Shield. Shield. Other poles well defined defined time relative to magnetically, but less well dated, magnetically, dated, from from rocks rocks of of this this era era fit fit the curve quite well. the of available that the available data data supports supports the the hypothesis hypothesis that the Analysis of relative polarmovement movement that gave rise Logan's Loop Loop was was prerelative polar that gave rise totoLogan's preceded and followed follmved by vis a vis ceded and by polar stability vis vis North America, quite rapid rapid during during the the forforwhereas polar movement may have been quite The depositional environment of Neohelikian the loop. loop. The Neohelikian mation of the rocks of the Canadian Shield should be tested tested against against their their rocks of the probable paleolatitude as probable as indicated by the the 5 key points on Logan's Logan's Loop. �—59— -59- CHARACTERISTICS CHARACTERISTICS OF SOME SOME ALTERATION MINERALS, MINERALS, PORTAGE FJRTAGE LAKE LAKE LAVA LAVA SERIES, SERIES, MICHIGAN MICHIGAN A. A. P. p.RUOTSALA RUOTSALA Michigan Technological University Michigan Technological ABSTRACT Many silicate, carbonate, Many silicate, carbonate, and and oxide oxide minerals minerals are are associated associatedwith with copper mineralization mineralization in the Portage Series and copper in the Portage Lake Lake Lava Lava Series and associated associated conglomerates. complete listing listing was was published published by Butler and and Burbank'. Burbank l • conglomerates. AA complete Amygdule studied by Amygdulezoning zoningpatterns patterns associated associated with with mineralization mineralization were studied 2 Stoiber and and x-ray x-ray diffraction Stoiber and Davidson Davidson .. Chemical and diffraction studies studies are are being being carried out out at atMichigan Michigan Technological Technological University on on a continuing continuing basis. carried basis. In the the past -'n, In past some some of of these these studies studies were weresupported supportedby bythe theCalurnet Calumet Divisi Divisi:::n, Universal Universal Oil Oil Products Products Company. Company. Epidote isis characterized characterized by Epidote by wide wide ranges ranges in in unit unit cell cell dimensions. dimensions. In general, general, epidotes epidotes from from amygdaloids amygdaloids have have larger larger unit unit cell cellvolumes volumes than than those those from conglomerates. congloITlerates. Calcites wide ranges ranges inin trace trace element composition, especially especiaiy Calcites show show wide eleITlent cOlnposition, in Mg, and and Mn. Mn. There is a a positive positive correlation correlation bebeThere is in concentration3 concentratiois of Fe, Fe, Mg, tween Mncontent contentand andcopper copperITlineralization mineralizationininthe theKearsarge Kearsargeamygdaloid, amygaloid, and tween Mn and therefore is potentially potentially useful useful as as an an exploration exploration tool therefore is tool in in the the district. district. 3 in many ITlany forms and at virtually every every stage sh.ge of of the the Chlorite occurs in forms and sequence in alteration sequence in the the district. district. An An interesting interesting occurrence occurrence is is as an essentially pure essentially pure clay clay mineral ITlineral in inthe the fault faultgouge gouge in in the the Allouez Allouez Gap Gap Fault Fault This is and of the the Kingston Kingston Mine4. Mine~. This is one one of of the the few, few, if if not not and hanging hanging wall wall slip of the the only only occurrence occurrence of of pure pure clay clay chlorite chloriteknown, known. It essentially of of It consists consists essentially In ITluch much of ofthe thehanging hangingwall wallslip, slip, chlorite chlorite is is intimately the type Ub lIb polytype5. polytype 5 . In intiITlately absorption properties (plastic and and liquid liquid mixed with hematite. The The water water absorption properties (plastic liITlits) greaterfor for chlorite-hematite chlorite-heITlatite mixtures mixtures than than for for pure pure chlorites, chlorites, limits) are; are greater suggesting the the pas possibility of SOITle some ITlixed mixed layering layering of of chlorite chlorite and suggesting sibility of and hematite. heITlatite. References Cited Cited 1. Butler, Butler, B. B. S., S.,and andW. W.S.S.Burbank Burbank(1929) (1929) The The copper copper deposits deposits of of U. S. Geol. Geol. Surve., Surve., Prof. Prof. Paper Paper144, 144, 238 238 pp. pp. Michigan. U.S. 2. Stoiber, R. E. E.and andE.E.S.S.Davidson Davidson(1959) (1959)Amygdule AITlygdule mineral mineral zoning zoning in Stoiber, R. the Portage the Port age Lake Lake Lava Lava Series, Series, Michigan. Michigan. Econ. Econ. Geo!. v. 54, Geo. v. 1444-1460, p. 1250-1277 and p. 1444-1460. p. 1250-1277 �-60—60— 3. Ruotsala, P., S. S.C. C.Nordeng, Nordeng,and andR. R. 3.J.Weege Weege(1968) (1968) Trace Ruotsala, A. A. P., Trace elements the elements in in accessory accessory calcite -- aa potential exploration tool in the Michigan Copper District. District. Cob. of Mines MinesQuart., Quart., Jour., Jour., Michigan Copper Colo. School School of (International Geochemical Exploration v. 64, 64, p. p. 451-455. 451-455. (International v. Symposium) 4. Ruotsala, Ruotsala, A. A. P. P. (1968) (1968) Clay Clay alteration alteration associated associated with with mineralization mineralization Clays and and Clay ClayMin., Mm., v. in Michigan Copper v. 16, 16, in the Michigan Copper District. District. Clays p. 400-402. p. 400-402. 5. Brown, B. Brown, B. E.,, E., and and S. S. W. W. Bailey Bailey(1962) (1962) Chlorite Chlorite polytypism. polytypism. Am. ,v. 47, Am. Mineral. Mineral.,v. 47, p. p. 819-850. 819-850. �—61— -61- THE THE GENERAL GENERAL STRATIGRAPHY STRATIGRAPHY OF OF THUNDER THUNDER BAY, BAY, LAKE LAKE SUPERIOR SUPERIOR R. J. J. Shegelski LAKE-lEAD UNIVERSITY LAKEHEAD ABSTRACT A B S T R ACT Petrographic studies of the sediments taken from from Thunder Bay Bay combined with x-ray diffractometer analysis have indicated indicated distinct lithologic types in the the bottom sediments sediments of of Thunder Thunder Bay. Bay. Stratitypes in graphic correlation correlation of of thc the bottom bottom sediments sediments from from Thunder Thunder Bay Bay has has the aid aid of of echo echo sounding sounding traces. traces. These traces been developed with the boundaries, nature and thickness indicate the boundaries, thickness of the various litholithofacies. facies. The sediments in in Thunder Thunder Bay Bay can can be be divided divided into into five five categories; categories; (1) (2) Weathered Weathered Varved Clay, (1) Varved Clay, Clay, (2) Clay, (3) (3) Intermediate Intermediate Clay, Clay, (4) Upper Upper Deltaic Sediment, Sediment, (5) Sediment. The Varved (4) (5) Upper Upper Trough Sediment. Clay is overlain is of Post Post Valders Valders glacial glacial origin origin and and is is disconformably discoi:fom*Lj overlain by the Weathered and Intermediate Intermediate Clays. Clays. The latter are are products products of weathering of of the the older older Varved Varved Clay. Clay. The Intermediate Clay is conformably overlain overlain by by Upper Upper Deltaic Deltaic and and Upper Upper Trough Trough Sediment. Sediment • conformably The .T he latter units are sediments sediments derived derived dominantly dominantly from from the the Kaministikwia Kaministikwia River. River. Thin Thin iron iron and and manganese manganese beds beds are are formed formed through through diagenetic diagenetic solution, upward migration, migration, and precipitation at solution, at a chemical chemical interface interface in the Upper Sediments. Sediments. �—62— -62- CHERT IN SEDIMENTS SEDIMENTS by G. G. Spencer Spencer Duluth, Minnesota A B S T R ACT ABSTRACT silica solution solution becomes becomes supersuperAmorphous silica is produced when aa silica some silicates silicates are are dissolved dissolved saturated and a precipitate forms or when some in acids. In the silica is is in a colloidal form and remains remains In either case case the so for long periods of of time. time. Eventually crystallization begins, begins, and heating the substance can speed up the the process to to aa great great extent. extent. In In natural conditions conditions opal opal is is the the first first step step followed followed by by chalcedony chalcedony and and finally cristobalite. All of these finally these forms forms of silica silica have have been been termed termed chert. Chert has·long has long been regarded as a chemical precipitate. Chert precipitate. This is sufficient to to explain explain hot hot spring spring deposits deposits and and hydrothermally hydrothermally view is deposited chert or opal opal near near the the surface. surface. Cooling volcanic waters become supersaturated with silica silica in in solution solution and and amorphous amorphous is is deposited deposited as as a sinter or in in thin thin layers. layers. There are, are, however, many other other environments environments in in which which chert chert is is found found such as: as: a) a) b) c) c) d) d) e) e) f) f) g) black slate with chert lenses or beds limestones limestones with chert nodules or joint joint fillings fillings bedded cherts containing sponge spicules cherts spicules or Radiolaria Radiolaria chert stringers in oxidized sulphides sulphides chert stringers and crusts in fillings of vesicles in in lava lava flows flows agate fillings oxide granules chert chert as as a a matrix for iron oxide opal or chert chert replacing organic matter The author author ascribes chert to to the the decomposition decomposition of of clays, clays, detrital detrital In acid environsilicates, ash or sand grains in in carbonates. carbonates. In silicates, volcanic ash ments alumina alumina and and alkalies alkalies are are removed removed and and aa silica silica gel gel is is left. left. In alkaline waters waters silica is dissolved and and is deposited deposited in in aa more more neutral neutral zone or will replace a dissolving particle such such as as organic organic matter. matter. The relative solubility solubility of of alumina and alkalies compared to relative and alkalies to silica is is the the determining factor. factor. iturata (1946) investigated investigated many many silicates silicates ,vhich which produced gels when i'lurata (1946) \<Then treated with acid. He alumina ratio ratio of 1:1 or or treated with Hefound foundthat that aa silica silica totoalumina 2:3 was Other silicates silicates prpduced was conmion common toto gel forming silicates. Other produced silica gel forming particles larger than than colloidal size or were not not affected affected by by acids. acids. Any particles silicate structure from from which alumina has has been been removed removed is is halfway halfway along along to chert. to becoming chert. In and silicate iron formations formations mixed with ,.,rith quartz, quartz, minerals In carbonate carbonate and become unstable when when the the temperature temperature is is raised raised and is removed from from the the and CO, CO. is point sediment. The ionization ionization of at whicli ,..d lich Doint of \vater water increases increases up up to to 230° 23°CC at silica both in in quartz and silicates becomes hecomes increasingly incren3in~ly soluble. soluble. Sand grains such as as grains in oolites oolites might might dissolve and secondary silicates such �-63—63— minnesotaite and and stilpnonielone stilpnomelone would appear. appear. Chert in this this case case is is minnesotaite clearly clastics clearly diagenetic diagenetic and and came came from from aa breakdown of original elastics even if the the original texture texture remained remained the the same. same. formations would appear to to be be examples examples of of late late Precambrian iron formations they would also contain contain early early diagenetic diagenetic silica silica diagenetic chert although they as well. as Silica content is these rocks because Silica and and iron iron oxide content is higher in these of the the loss loss of carbon dioxide, dioxide, water, water, and small small amounts amounts of of alkalies alkalies in in solution. �—64— -64- IMPLICATIONS OF CARBON ISOTOPE RATIO VARIATIONS IN IN CARBONATES CARBONATES FROM THE BIWABIK BIWABIK IRON FORMATION, FORMATION, MINNESOTA F. C. C. Tan and E. F. E. C. C. Perry, Jr. Jr. Minnesota Geological Survey Survey University of Minnesota Minneapolis, Minnesota 55455 Minneapolis, 55455 ABSTRACT A B S T R ACT Carbon isotope ratios from carbonates of of the the Biwabik Biwabik Iron—formation Iron-formation obtained from core samples of Mesabi Deep Drilling Drilling Project Project (Pfleider (Pfleider and and others, 1968) 1968) show the following significant features. others, features. 13 (1) SC SC13 values values of of carbonates carbonates associated associated with with magnetite magnetite from holes holes (1) 5 and 7 show a range of from —7 -7 to to —19 -19 per nil mil (relative (relative to to aa Cretaceous Cretaceous belemnite standard standard calcite calcite PDB) PDB) in in comparison comparison with with1he he carbonates carbonates from from is strongly correlated the magnetite-free (0 to SC 13 is the magnetite—free horizons horizons (0 to -7 —7 per per mil). mu). with magnetite magnetite content content in in hole hole 7. 7. 13 (2) The Gc SC13 values values of of carbonates carbonates from magnetite and non—magnetite (2) The non-magnetite horizons of hole 2 with one exception, do not show1ignificant horizons of hole 2 with one exception, do not show1~ignificant difference difference range of from in contrast with holes holes 55 and and 7. 7. They exhibit a SC from —7 -7 to to —19 per -19 per mU.. mil. 13 (3) values do do not not show show any any significant significant stratigraphic stratigraphic (3) The The bC C13 values correlation correlation with with tlia the percent iron. iron. (4) between (4) There There appears appears to to be be a correlation between individual members of of the the Biwabik Biwabik Iron—formation. Iron-formation. 13 C1-3 values and the ~C the 13 In explaining the observed correlation between magnetite and and the the 13 values based on our SC our preliminary preliminary results, results, we we proposed proposed (Perry (Perry and Tan, 1970) that that aa diagenetic diagenetic oxidation—reduction oxidation-reduction reaction reaction producing producing permitted exchange exchange between between organic organic carbon carbon and and magnetite from hematite permitted carbonate carbon reservoirs: reservoirs: r 44FeO bFeO +CO 6 Fe 22033 +C + C(organic)~f----~~Fe 33044 + CO 22 (organic) (1) (1) 12 13 C1202 Fec 0 C 0 + FeC3O3 2 3 (2) (2) < 12 13 cC1-3O 0 + + FeC2O3 Fec 0 2 3 recent detailed detailed studies studies have have strengthenI~ strengthen our Our recent our previous previous observaobservavalues (—18 tion on hole 7 but have found anomalously low SC (-18 per per nil) mil) tion from from the the non-magnetite non—magnetite horizons of hole 22 (Lower (Lower Slaty Slaty Unit). Unit). These anomalous values may be related related to to metamorphic metamorphic reactions reactions accompanying accompanying the intrusion of the the the Duluth Complex because hole 22 is is located located near near metamorphic zone zone (1) (1) of French French (1968). (1968). C13 values Our observation that that there is a correlation between ~el3 and the and the individual members of the Biwabik Iron—formation Iron-formation would suggest suggest l3 variations that SC1-3 variations are are depositional depositional or or early early diagenetic diagenetic features features that the the ee and bear no relationship relationship :o ~o the the genesis genesis of of niagnetite magnetite (model (model above). above). The �-65—65— l3 values may be explained by the differences in IC13 bC the variable variable contributions contributions of organic carbon and oceanic bicarbonate to of to the the depositional depositional or or diagenetic environments. environments. 13 SC13 values of We are currently investigating the theoC of co—existing co-existing graphite-tarbonate pairs and oxygen isotope fractionation graphite-carbonate fractionation between between cocoquartz—magnetfte at various stratigraphic existing quartz-magnetite stratigraphic levels levels of of holes holes 22 and 7 to to see if they have different diagenetic diagenetic or metamorphic metamorphic histories. histories. Co—existing quartz—carbonate oxygen isotope Co-existing quartz-carbonate isotope fractionation fractionation In in samples samples from hole 2 compared to that that in in holes 55 and and 77 suggests suggests that that the the post— postdepositional history of these these two two areas areas is is indeed indeed different. different. References rrench, B. B. French, M. , (1968) Progressive contact metamorphism of the M., the Biwabik Biwabik Iron—formation, Mesabi Mesabi Range, Ninnesc:a, Minn. Minn. Geol. Iron-formation, Range, Minnesota, Geol. Surv. Surv. Bull. Bull. 45, 45, Univ. Univ. of Minn., Minneapolis. Ninneapolis. Tan, F. Perry, E. E. C.C., Jr., and Tan, F. C., C., Significance of carbon carbon isotope isotope Perry, , Jr., variations in carbonates from from the the Biwabik Biwabik Iron—formation, Iron-formation, Minnesota. Minnesota. symposiumononthe thegeology geology and and genesis genesis of International symposium of Precambrian Precambrian iron/manganeseformation formationand andore oredeposits, deposits, Kiev, Kiev, 1970 1970 (In (In Press). iron/manganese Pfleider, E. E. P., P.,Morey, Morey, C. G. B., B., and and Bleifuss, Bleifuss, F. R. L. L. (1968) Mesabi deep deep drilling project, project, progress report repo~t no. no. 1, 1, Minnesota Ninnesota section, section,AIME AIME forty— fortymeeting, Dniv. Univ. of Ninn., Minn., Minneapolis. Minneapolis. first first annual meeting, �—66— -66- Oxygen isotopic studies of Early Early Precambrian Precambrian granitic granitic and and metamorphic rocks from from the the western western part part of of the the Giants Range batholith, Northeastern Northeastern Minnesota Minnesota S. Viswanathan, Viswanathan, E.C. s. E.C. Perry, Jr., Jr., and and P.K. P.K. Sims, Sims, Minnesota Geological Survey, University of Minnesota, Geological Survey, University of Minnesota, Minneapolis, Minnesota 55455 55455 ABSTRACT A B S T R ACT objectives: (1) demonstrate that that oxygen oxygen The paper has two main objectives: (1) to to demonstrate isotope geochemistry is a valuable tool tool in in elucidating elucidating granite granite petrogenesis, petrogenesis, provided it is is integrated integrated with with detailed detailed field field and and laboratory laboratory studies, studies, and and (2) to to give give values values for~(018/016)guartz for f(O18/016)qrtz in (2) in the the Early Early Precambrian Precambrian granitic granitic and metamorphic metamorphic rocks, which are rather scarce and rocks, data for wnich scarce in in the the literature. literature. Geologic mapping of of aa 500—square 500-square mile mile area area in in the the western western part part of of the the 2.1 b.y. b.y. old Early Precambrian Giants Range batholith of 2.7 of northeastern northeastern Minnesota has revealed eleven eleven distinct distinct granitic granitic phases phases (Sims (Sims and and others, others, 1970). 1970). Field observations, petrography, petrochemistry, petrochemistry, and and trace trace element element geochemistry suggest that that five five of of the the phases phases are are magmatic, magmatic, four four are are metasomatic, metasomatic,_ and two are anatectic. anatectic. r 18 16 The ~O 10 ratios of quartz separated from from 28 28 rocks, relative relative to to meIo'8/o'6 Standard Mean Ocean are presented presented in in the the accompanying table. Ocean Water Water (SNOW), (SMOW)Jare table. The values are consistent with the the postulated postulated genetic genetic grouping grouping for for the the Early Precambrian granitic succession. succession. The following following conclusions conclusions can can be be drawn from the the data: data: (1) Values of of 9 to to 10 permil are characteristic of relatively (1) Values relatively uncontaminated, probable mantle—derived uncontaminated, mantle-derived granites granites and and granodiorites. granodic~ites. These tharhave been reported for are consistent with the the S(O18/ol6quartz ~(018/016)quartz values values that-have granites, granodiorites, granodiorites, and and tonalites, tonalites, which which range range from from about about plutonic granites, 9 to to about 11 permil (Taylor, (Taylor, 1968, 1968, p.34). p.34). (2) several special special (2) Values Values greater greater than 10 permil require one of several explanations, such such as: as: 18 (a) syntexis of large amounts amounts of of 0018—rich -rich country rocks rocks (a) into a primitive or first—cycle first-cycle granitic granitic magma magma 18 18 (b) co-mingling co—mingling of an 0 -enriched —enriched magma and a primitive (b) or first first cycle granitic magma 18 (c) of 0018_ sediments (c) anatexis of —rich rich sediments �—67— -67- 18 (d) potash metasomatisin metasomatism of of aO'8—rich -rich sediments sediments (d) potash (e) recrystallization (treptomorphisin) (treptomorphism) of of (e) simple recrystallization relatively 018_ 018—rich clastic sediments such such as r ich elastic arkoses and graywackes, which thereby thereby assume assume aa granitic fabric and composition (f) recrystallization recrystallization of of granites granites under under shearing and (f) aplogranites, accompanied by crushing to produce aplogranites, late—tectonic metasomatism in mobile zones late-tectonic (g) post-consolidation post—consolidation eataclasis, cataclasis, and and other other (g) episodes which which facilitate facilitate exchange exchange metamorphic episodes origin and granitic rocks rocks of of magmatic magmatic origin and between granitic between through a pore—fluid pore-fluid medium medium 018_ O'8—rich r ich country rocks through (h) post-consolidation (h) post—consolidation endoblastesis/autometamorphism endoblastesis/autometatOrphism involving 018018—enriched enr iched fluids (i) processes such as imbibition (i) as petroblastesis and imbibition in which the the participants are are O'8—rich 018_r ich sediments sediments and 018-enriched fluids 018—enriched fluids (j) selective (j) selective exchange between granitic intrusions and 018_ host rocks rocks O'8—rich r ich host (k) tectonic tectonic styles styles of of emplacement, emplacement, whether whether synkineinatic, synkinematic, (k) post-kinematic or late—kinematic, late-kinematic, and and post—kinematic 18 (1) early segregation of aO'8—depleted -depleted minerals which (1) in O'8—enrichment 018- enr ichment in in late late granitic granitic differentiates. differentiates. results in (3) in granitic rocks of anatectic origin origin are nearly nearly (3) The The values values observed in identical to to those those of of their their source source rocks. rocks. They are either low or high such granitic granitic rocks rocks were were formed formed from from O'8—poor 018_poor or or depending on whether such OIS_rich 018_r ich sources, respectively. respectively. The values will be grossly grossly different different only only if: if: (i) the the anatectic anatectic melt melt undergoes undergoes subsequent differentiation, differentiation, and (ii) (i) (ii) the the consolidated anatectic melt is subjected to to later later metasomatism metasomatism (see (see data data under "C" "e" and "0 (2)", of of table). table). "D (2)", (4) The main main intrusive phases of (4) The of granites granites and and granodiorites granodiorites of of maginatic magmatic origin have values nearly identical to those of their satellitic phases identical to those of their satellitic phases (sve (sve data under "A" "A" of of table). table). Interestingly, Interestingly, a value of 9.2 9.2 permil permil was obtained for for a leucogranite (satellitic (satellitic late—magmatic late-magmatic differentiate) differentiate) that that transgresses an 018—rich Ol8_r ich metasedimentary host host rock rock having having aa value value of of 12.4 12.4 transgresses perinil. permi!. This result indicates that there indicates that there was was hardly hardly any any oxygen oxygen communication differentiate and and its its alB-rich o8—rich late-magmatic differentiate between the satellitic late—maginatic metasedimentary metasedimentary host host rock. rock. This is is in in sharp sharp contrast contrast to to the the conclusion conclusion of of Shieh and Taylor (1969, (1969, p.353) p.353) who report report that: that: "Samples "Samples from from tiny tiny intrusive intrusive bodies and dikes and from the marginal portions portions of of most most of of the larger plutons 18 /0 16 ratios igneous rocks have unusually high 0 018/016 ratios relative to "normal" "normal" igneous rocks from from �—68— -68- the central portions of plutons. This is interpreted interpreted to to be the the result result of large-scale large—scale oxygen isotopic essentially molten of isotopic exchange exchange between between essentially molten igneous igneous rock and metasedimentary country country rock, rock, either either through through aa medium medium of of aqueous aqueous 1I fluids or or by by contamination contamination with with xenolithic xenolithic blocks blocks of of country country rock. rock." fluids (5) The The sequence: sedimentary (5) sedimentary parent parent ——)' -~ partially partially granitized sediment --~granitic —>-granitic rock progressive sediment rock of of metasomatic metasomatic origin origin reflects a progressive decrease in the 018/016 0 18 /0 16 ratio, and and encompasses encompasses only only aa narrow narrow range range of of 11 to 2 permil, and (6) Global comparisons of oxygen isotopic isotopic ratios ratios from from granitized granitized 18 /0 16 ratios of the sequences should not not be attempted, attempted, unless: unless: Ci) sequences (i) the 0018/016 parent rocks of two widely separated separated granitized granitized sequences sequences are are comparable, comparable, and (ii) their geological settings are nearly identical. (ii) are nearly identical. 18 16 Problems involving a possible time—dependence time-dependence of of the the 018/0 0 /0 16 ratios in in minerals from from specific specific rock—series, rock-series, representing representing the the entire entire geological geological column, column, are under study by one one of of us us (Per;y). (PerJY). Ref e—ences cited References Shieh, Y.N. Y.N. and H.P. Taylor, Shieh, Taylor, Jr. Jr. (1969): Oxygen and hydrogen isotope isotope studies studies in the the Santa Santa Rosa Rosa Range, Range, Nevada Nevada and and other other areas: areas: of contact metamorphism metamorphism in Contr. Mineral. and Petrol., v.20, p.306—356. Contr. Mineral. p.306-356. Sims, P.R. P.K. and and others others (1970): (1970): Geologic Geologic map map of Minnesota, Ribbing Hibbing Sheet Sheet Sims, (scale 1:250,000): 1:250,000): Minn. Minn. Geol. Geol. Survey, University of of Minnesota, Minneapolis. Minneapolis. Taylor, H.P. Jr. Taylor, H.P. Jr. (1968): (1968): The oxygen oxygen isotope isotope geochemistry geochemistry of of igneous igneous rocks: rocks: Contr. Mineral. p.1-71. Contr. Mineral. and Petrol., v.19, p.'—71. Other useful References Allison, 1.5. I.S. (1925): (1925): The The Giants Giants Range Range batholith batholith of of Minnesota: Minnesota: Jour. Jour. Geology, Geology, v.33, p.488—508. p.488-508. v.33, Goldich, S.S. S.S. and others (1961): (1961): The Precambrian Precambrian geology geology and and geochronology geochronology of Minnesota; Minn.Geol. Minn.Geol. Survey Bull.41, University University of of Minnesota, Minnesota, Minneapolis, p.62—65. p.62-65. �-69—69— Table .{'* b(O 18 /0 16 ratios of of quartz in Early Precambrian granitic )SMOW ratios SNOW and metamorphic metamorphic rocks from the western part of the and the Giants Range batholith batholith of Northeastern Minnesota Range (perlil) (perilil) Average (permil) A. Rocks of magmatic origin: origin: (1) Granodiorites Granodiorites (main (1) (main intrusive intrusive phase, phase t two two samples) samples) 9.4 —- 9.9 (2) Leucogranodiorite Leucogranodiorite (satellitic (2) (satellitic phase of of (1), (1). one one sample) sample) 9.7 9.7 9.8 9.8 (3) Granites Granites (main (main intrusive phase, phase t (3) two two samples) 9.5 9.5 —- 9.6 9.6 (satellitic phase phase (4) Leucogranites (satellitic of (3), (3)t two two samples) samples) 9.2 —- 9.6 9.4 10.7 -— 11.4 10.9 10.9 B. Rocks ~~.Rocks of metasomatic origin: origin: (1) (five samples) samples) (1) Granites (five 10.2 (2) Aplogranite (one (2) (one sample) sample) (3) Partially granitized (3) volcanogenic metasediments (three samples) (three samples) 10.4 — 10.4 - 12.5 11.1 11.1 9.2 9.2 —- 10.1 10.1 9.6 9.6 c. C. Rocks of anatectic anatectic origin: origin: (derivatives of relatively relatively alB_poor source rocks) rocks) 0'8—poor source (1) Quartz tonalites (four (four samples) samples) (1) (2) K-feldspathized K—f eldspathized tonalite tonalite (2) (one sample) 12.1 12.1 D. D. Parent volcanogenic metasediments metasediments of: of: (1) B (four (four samples) samples) (1) Group Group B 11.1 — 1l.1 - 12.9 12.2 �—70--70- ZONED NATIVE NATIVE COPPER CrIEHICALLY COPPER AND A<\lD CHALCOCITE CHALCOCITE FROM FRaN CHEMICALLY ZONED WHITE PINE, NICIIIGAN WHITE PINE, MIChIGAN T. A. A. Vogel Geology Department Michigan ~ichigan State State University University East East Lansing, Lansing, Michigan and T. T. J. J. Rohrbacher Staff Geologist Staff \'~ite White Pine Copper Company Pine, Michigan \.Jhite White Pine, tHchigan ABSTRACT A B S T R ACT A the copper ore are minerals at at White ~.Jhite Pine, A microprobe study of the Hichigan, has shown that that zoned copper—mineral copper-mineral grains occur in in the the Michigan, has This zoning is ore-bearing of the the Nonesuch Nonesuch Shale. Shale. This is developed develofled ore—bearing horizons of in the most type of in both both chalcocite chalcocite and and native native copper, copper, and and the most prominent type zoning is zoning is iron enrichment towards to\vards the the edge edge of of the the grain. grain. Some chalcocite grains grains are are highly highly zoned, chalcocite zoned, containing about about four four times times as as as in much iron (at least the edge of of the the grain grain as in the the core. core. least 10%) 10%) on the iron (at Aluminum, magnesium siliconshaH showthe thesame sametype typeofof zoninf, zoning, hut Aluminum, magnesium andand silicon hut are to a lesser extent. are developed to extent. copper grains are also zoned respect to iron, Many native native copper grains arewith also zoned with respect to iron, with the edge of the iron wi th the edge of the grain grain containing containing about about twice t\<7ice as as much much iron (about 1%)asas the the core. an enrichenrich(about 1%) core. All zoned zoned copper copper minerals show show an ment of iron iron towards of the ment of towards the the edge edge of the grain; grain;however, ho\·7ever, both both within ,·7ithin and and between between samples, samples, the the amount amountofofzonin~ zoningand andthe therelative relative proportion proportion This variation zoned to unzoned grains highly variable. varia1)le. This variation does c:oes of zoned to unzoned grainsisis highly not appear to be be controlled controlled by by the the major majorlitholof,ic lithologic variAtions variations in not appear to in the ore ore zone, zone, but but may be controlled controlled by uy subtle differences in lithology or by environmentrttat the the time variations in by variations chemical environment time of of in the local chemical deposition. Any Any j:lotlel modelofof'1re 're Genesis genesis must must take take into account account the the occurrence, occurrence, minerals. distribution and and type distribution type of of zoning in in these these copper copper minerals. �—71— -71- STRATICRAPHY OF KEWEENAWAN KEI.vEENAWAN STRATIGRAPHY OF WESTERNMOST i-JESTERN}[OST MICHIGAN HICHIGAN W. S. Wtite W. S. i-n1i te U. S. Geological u. Survey Agriculture Research Center Center Beltsville, Naryland Beltsville, Maryland E. R. R. Brooks E. Department of Earth and Physical Science Science California State State College College Hayward, California Hayward, H. 3. A. A. Hubbard U. S. S. Geological Survey Survey U. Washington, D.C. D.C. Robert F. Robert F. Johnson 449 Boynton Avenue Berkeley, Berkeley, California J. T. J. T. Wilband iVilband University of Toledo Toledo Uepartment Department of Geology Geology Toledo, Ohio ABSTRACT A B S T R ACT surveysprovide provideaa skeletal skeletal Recent geologic geologic and and aeromagnetic aeromagnetic surveys fracieworkfor forthroughgoing throi:ghgoing stratigraphiccorrelations correlations of framework stratigraphic of the the Keweenawan rocks rocks of westernmost westernmost Michigan. Michigan. The stratigraphy of the the middle and upper Kel.".eenawan Fceweenawan rocksofof the the Keweenaw Peninsula has rocks Keweenaw Peninsula long been known in in great great detail, detail,thanks thanks to tothe thelarge largeamount amount of of drill—hole and drill-hole and surface geologic information. information. The recent recent work perpermits certainty, mits certain certain key key horizons horizons to to be be traced, traced, with with moderate moderate certainty, westward into Wisconsin. Wisconsin. Stratigrapitic relationships relationships for for the the middle middle and and upper upper Keweenawan Keweenawan Stratigraphic rocks best shown rocks are best shown in a longitudinal stratigraphic section section drawn drawn rocks and having along strike of of the the middle middle Keweenawac Keweenawan rocks along the general strike most striking striking base the Nonesuch Nonesuch Shale rlA.tum plane. The The most base of the Shale as as aa datum (1) The predominantly features of such such aa diagram diagram are the the following: following: (1) TIle predominantly features of basaltic Portage Lake Lake Lava Lava Series Series maintains maintains aathickness thicknessofof10,000— 10,000basaltic Portage 12,000 from 1-loughton Houghton to tothe near 12,000 feet feet from theJHack BlackRiver Riverand andisis thinnest thinnest near the Ontonagon Ontonagon River. IItt is isabout about 8000 8000 feet thick thick atatthe theMontreal Montreal River. (2) (2) An An unnamed lenticular unnamed lenticularunit, unit,10,000 10,000feet feetthick thick at at the Liver on Presque Presque Isle River River and and pinching pinchinp, out out near near the the Ontonagon River on the the and the the Montreal Montreal River River on on the the west, west, lies liesabove above the thePortage PortageLake Lake east and Lava Series Series and and below below the the predominantly sediientary sedimentaty Copper Copper Harbor Harbor Conglomerate. to fine— Conglomerate. The The unit is mainly mainly composed composed of fineunit is of thin thin aphanitic to grained andesitic andesitic flows flm,s and and contains contains minor rhyolite rhyolite and and intermediate intermediate rocks, the top. top. It to represent represent accumulation rocks, particularly near the It seems seems to \Vithin fe\.". miles of aa volcanic center south of of the the Porcupino Porcupine within a few center south Mountains. (3) HarborConglomerate Conglomerate less than than 500 500 feet feet f·jountains. (3) The The Copper Copper Harbor is isless thick over over the thick tile thick part of the theunnamed unnamed unit, unit,and and4000—5000 4000-5000 feet thick near the tIle pinchouts pinchouts of of tile theunnamed unnamed unit. combined thickthickthick near unit. (4) The combined ness of of tue tlle three three units units suggests sugr,ests aa strongly strongly asynnetric asymmetric basin, basin, deepening from aa minimum minimum near more than 25,000 25,000 deepening from nearthe the Ontonagon OntonagonRiver River to to more feet between the the next next feet between the Black Blackand andPresque PresqueIsle IsleRivers, Rivers, and and then, then, in in the 15 than 10,000 10,000 feet the 15 miles miles toto the the \Vest, west, thinning thinning rapidly rapidly toto less less than feet at at the Montreal These findinf's findings reinforce reinforce the hontreal River. These the concept concept that that the themiddle middle rather than Keweenawan Ke\VeenaVlan lavas lavas accumulated in separate tectonic tectonic basins basins rather in aa single single large large one. one. the �-72—72— The Ke,,,eenawan lavas, so-called South South Trap Trap The lower lower Keweenawan lavas, !'"hich which form form the the sc—called Range, lie beneath the the Portage Portage Lake Lake Lava Series, Series, from from lie unconfonnably unconforably beneath &hich they differ in in lithology, lithology, metamorphic grade, ("hich they differ grade, and magnetic properties. The feet consists consists predominantly of very properties. The lowennost lowermost 5000 feet thin basalt the next 4000 feet feet mainly to thin basalt flows, flows, and and the next 4000 mainly of aphanitic to The uppermost fine-grained flows flows of intermediate intermediate composition. composition. The uppermost part fine—grained of this sequence is iseverywhere everywhere concealed concealed by by the the Jacobsville JacobsvilleSandstone Sandstone this sequence or deep deep overburden, overburden, but inferred from from gravity gravity and and magnetic magnetic data data or but is is inferred This lower is lC,000 to to consist consist largely largely of of felsic felsic flows. flows. This lower sequence sequence is 10,000 and uncertainty and perhaps perhaps20,000 20,000feet feetthick, thick, the the difference difference reflecting reflecting uncertainty about the location location of about the of the the top. top. The rocksare are more metamornhosedthan than the middle The lower lm"er Keweenawan Keweenm"an rocks more metamorphosed middle Their metamorphic grade appears metamorphic grade appears to to increase increasewestward westl,vard— Keweenmvan. Keweenawan. actinolite is actinolite found in Hisconsin but is is rare rare near near Ironwood. Ironwood. is found Wisconsin but Kenneth Books Hooks has found that that the the lower and middle Keweenaw€n Keweenawan rocks also also differ differ from rocks from one another in in magnetic magnetic direction. direction. In contrast contrast with with the the belts belts of of middle middle and and upper upper Ke,,,eenal,van Keweenawan rocks, roes, In dips of of bedding bedding generally generally decrease decrease !"'ith with stratirraphic dips stratigraphic depth in in the lower Keweenawan Ke\veenawan belt. belt. If If this this represents represents soutlnvard southward thickening thickening rather rather than Lian folding, folding, it it suggests suggests that that the the axis axis of of the the lower Keweenal,van Keweenawan basin lay lay to to the the south. south. �-73—73— THE NORTH SHORE SHORE VOLCANIC GROUP GROUP May 5 and 8, 1971 by Prepared by C. Green John C. University of Minnesota, Minnesota, Duluth Minnesota Geological Survey �—74--74- Croup The North Shore Volcanic Group John C. C. Green Introduction Previous Work Hork and and Acknowledgments. Acknowledgments. Detailed mapping of the Minnesota A. S. E. Sandberg's Sandberg's study study (1938) (1938) of of the the shore of Lake Superior began with A. Grout and Schwartz (1939) section between Duluth Duluth and and Two Two Harbors. Harbors. Grout (1939) and and (1957) studied the the intrusions intrusions and and flows flows in in eastern eastern Lake Lake County; County; Gehman (1957) the lakeshore Two Harbors Harbors and and Split Split Rock Rock Grogan (1940) (1940) mapped the lakeshore between Two River; Schwartz (1949) River; (1949) studied the Duluth Duluth area; area; and and Grout Grout and and others others (1959) (1959) mapped most of of Cook Cook County. County. Most of of the the data data reported reported in in this this account derive from studies by the account the writer who, starting starting in in 1965, 1965, has has mapped the shoreline between Silver Bay and Grand Grand Portage, Portage, with conconsiderable reconnaissance inland (Green, (Green, 1966; 1966; 1968a; 1968a; 1968b; 1968b; 1970). 1970). The report does, however, however, also also lean lean considerably considerably on on Grout Grout ~ etal. report does, al. (1959) (1959) and, for for the Duluth-Two Duluth—Two Harbors area, on and, on Sandberg Sandberg (1938). (1938). The field field studies have have been supported by the studies the Minnesota Geological Geological Survey, Survey, and and most of the laboratory studies have been supported by the National studies the Science Foundation. Sincere gratitude for for this this support is is extended extended to to both agencies. agencies. The writer's ideas ideas have benefitted benefitted from from discussions discussions with many other geologists rocks, esoecia11y esnecially many other geologists concerned concerned with with Keweenawan Keweenffivan rocks, including Bill Jr., H.H.Hubbard, including BillBonnichsen, Bonnichsen, D. D. M. M. Davidson, Davidson, Jr., Hubbard, C. G. B. B. Morey, Horey, W. W. C. C. Phinney, Phinney, ·P. W. Weiblen, and and W. W. S. White. P. W. S. White. Regional Setting. "North Shore has been ~egional Setting. The name "North Shore Volcanic Volcanic Group" Group" has been used used et al. al. (1961) (1961) for by Goldich et for the the lavas lavas and and interbedded sediments of Late Precambrian. rocks, as well Precambrian age in northeastern Minnesota. These rocks, as and sedimentary sedimentary rocks rocks in in the the as all all other Late Precambrian volcanic and district, have traditionally been called"Keweenawad'by called "Ke~veenffiolan" by Lake Superior district, rocks exposed on the general lithic and structural correlation with rocks and paleomagnetic Keweenaw Peninsula of Michigan, Michigan, but recent radiometric and investigations as \-lell indicate that that aa more more precise precise investigations as well as geologic mapping indicate stratigraphic stratigraphic framework framework is is needed needed to to adequately adequately describe describe the the complex complex events and and deposits deposits in in this this area. area. series of Late Precambrian events In (Grand Portage In the the northeast northeast corner corner of of }linnesota Minnesota (Grand Portage area) area) the the lowest lowest Upper Precambrian flows which in flows overlie a thin quartzite (Puckwunge) (Puckwunge) \.;rhich 1.n turn turn overlies, overlies, apparently disconfornably, disconformably, the the shales shales and and graywackes graywackes Of 6f the Middle Precambrian Rove Formation;here hereboth both sequences sequencesstrike strike nearly the Rove Formation; nearly east—west and dip at approximately 10° east-west 100 to to the the south. south. At the the southwest southwest end of the basin immediately west west of miles away), of Duluth (155 (155 miles away), the lowest lowest Upper Precambrian flows flows also conformably conformably overlie thinquartzite quartzite (Puckoverlie aa thin (Puck— wunge?) which there there overlies the the vertically folded slates and metagray— metagraywackes of the the Middle }tiddle Precambrian Thomson Formation, Formation, which is is correlated with the the Rove. Rove. Here the flows flmols strike north and dip dip at at about about 25° 25 0 to the unconformity here here reflects and subsesubseeast. The angular angular unconformity reflects the the diastrophism and quent the Penokean Penokean orogeny, orogeny, which which evidently evidently did did quent erosion associated with the the northeastern northeastern corner corner of of the the state. state. Across the the axis of the the not affect the flows Lake Superior Syncline in northern Wisconsin and Michigan the lowest flows �MINNESOTA \-n I ONTARIO J) I I \ '—-7 - rHCVL AND EARLY PRECAMBRIAN GRAND M AR A IS LEGEND LUTSEN JOFTE uACONITh INTRUSION S i., '\~r KEWEENAWAN INTRUSIONS Wf0J KEWEENAWAN LAVAS "'to FIELD TRIP STOP I -....J U' \Jl I ITLC MARAIS MARAIS ER BAY JBEAVER BAY BAY LAKE SUPERIOR SCALE ° ! •O HARBORS WISCONSIN MINN. 10 20 Miles MICHIGAN 30 40 �—76— -76- conformably overlie aa similar similar quartzite (Uessemer) that in in turn overlies overlies quartzite (Bessemer) Middle Precambrian shale and and graywacke with only only minor discordance. discordance. These quartzites have always been referred to as as Lower Lower Keweenawan, Keweenawan, but but no no radiometric age determinations are are available available and and they they may may be be much much older older than the volcanic volcanic rocks rocks of of the the iCeweenaw Keweenaw Peninsula. The North Shore Volcanic Group is cut The cut by aa. great great variety variety of of intrusive intrusive rocks rocks that are are also also of of Late Late Precambrian Prec&~brian age. age. These range range from from the the great great Duluth Complex, Complex, dominated by anorthositic and and troctolitic troctolitic rocks, rocks, to to smaller sills, sills, stocks, stocks, dLkes, dikes, and irregular plutons of of diabase, diabase, 'crro— ferroabbro, trachybasalt, granocdorite, an gabbro, troctolite, troctolite,syenogabbro, syenogabbro, trachybasalt, granodiorite, and. Someofofthese thesebodies bodiesalso also cut cut the the older graoQphyric, adamellite. Some older rocks rocks grarophyricadanellite. to the to the north, north,northwest northwestand andwest west of ofthe themain mainLate LatePrecambrian Precambrian outcrop outcrop area of Cook Countyand andthe the Thunder BayDistrict District area (e.g. (~.g. the the Logan intrusives intrusives of Cook County Thunder Bay of Ontario). of Ontario). Paleonagnetism and Age. Recent paleomagnetic studies studies (Dubois, Paleomagnetism Recent paleomagnetic (Dubois, 1962; 1962; Beck Deck that two and Lindsley, Lindsley, 1969; 1969; Books, Books, 1968; 1968; Palmer, 1970) 1970) have have shown shmm that two reversals of magnetic polarity occur within reversals 'loTi thin the Late Late Precambrian Precambrian volcanic volcanic rocks of the Lake Superior The 1m-rest lowest strata stnta show 'nor'ial" rocks Superior district. district. The shoYr "normal" (north—seeking) polarity polarity similar to to orientations orientations in the underlying (north-seeking) underlyinp; Middle Precambrian rocks, rocks, but but this this group group of of rocks rocks has has not not been been recognized reconized in Precambrian Minnesota. Keweenawan Books (1y68) (l9~8) has ha.s proposed that the Lover Lower —- Middle ~eweenawan Books boundary be redefined the second reversal where redefined at at the second macnetic magnetic reversal where rocks rocks of normal polarity. The North reversed polarity aresucceeded succeeded by by rocks of' of normal North po]arity are Volcanic Group Groupcontains containsatatthe the ba.se base of of the Shore Volcanic t~e section section atatGrand Grand Portage Portage about 5000 feet feet of lavas lavas tnat that show reversed polarity, and and are are thus thus Lower Lower Keweenawan magnetically defined. defined. The thick wedge of flows Keweenawan asasmagnetically The thick wedge of flows west west of Duluth that underlie ut overlie the Puckwunge Duluth that underlie the theDuluth Duluth Complex Complex but Pucki-runge (?) (?) quartzite have quartzite but on on have not not been beenadequately adequatelytested testedinin the the laboratory, laboratory. hut regional magnetic magnetic maps maps give aa negative negativemagnetic map;neticanomaly anonaly which which implies implies regional reversed polarization. Furthermore reversed polarization. very similar to Furthermorethey theyare arelithically lithically very reversed-polarity lavas of of Grand Grand Portage. Portage. The the reversed—polarity The remainder remainder of of the ::orth North Shore Volcanic Volcanic Group polarity, Grouphas hasnormal normalmagnetic magnetic polarity,similar similar to to the bulk bulk of of the the associated associated intrusive intrusive rocks rocks and and to to the the rocks rocks of the Keweenaw Peninsula. Only available on on rocks rocks Onlylimited limited radiometric radiometric age age determinations determinations are are yet yet available of al. (1961) of the the North North Shore Shore Volcanic Volcanic Group. Goldich Goldich ~~ (1961) found aa !! ~~. 1.1 ±± 0.1 b.y. 1.1 intrusive rocks rocks of of the the Duluth Duluth Complex Complex b.y. age for associated intrusive and K/Ar K/Ar methods, and and Silver Silver and and Green Green (1963) (1963) found found an an isotopic isotopic by Rb/Sr and age age of 1.125 by U/Pb isotopes in in zircons zircons of of both both lavas lavas and and intrusive intrusive rocks rocks and Mellen, Mellen, Wisconsin Wisconsin areas. areas. Paure Faure et al. al. (1969) (1969) determined determined from the Duluth and the age of the Endion sill, sill, which cuts cuts the flows flows at at Duluth, Duluth, as as 1.092 1.092 b.y., b.y., the age and that that of of the the Duluth Duluth Complex Complex .at at Duluth Duluth as as 1.115 1,115 b.y. b.y. by by the theRb/Srmethod. Rb/Srmethod. However, all of these sampled rocks rocks are in areas of normal magnetic However, rr..agnetic polarity polarity, to the the age so no data are available available as as to a~e of the Lower Keweenawan lavas lavas of, of, for for Grand Portage Portage area. area. Hanson and Malhotry (1970) (1970) have recently instance, the Grand a 1.380 b.y. (K/Ar) of aa "Logan "Logan Intrusive' Intrusive" in in southern southern Ontario, Ontario, found a b.y. age (K/Ar) indicate the the possible possible age age span span of of the the Lower Lower Keweenawan. Ke'lveena"ran. Isotopic which may indicate studies over over the the range range of of Upper Upper Precambrian Precambrian rocks rocks iii in the district district are are U/Pb studies currently in in progress. progress. �—77— -77- Structure Structure The Group is is that that of of aa The general structure of the North Shore Volcanic Group great nest of dishes tilted tilted gently gently to to the the southeast into ofmshes into Lake Lake Superior. Superior. endthe thestrata strata at at the strike slightly At the the northeast northeast end the base base strike slightly north north of of west and dip about about 10—12° 10-12° south, south,whereas whereasatat the the southwest southwest end, end, 155 155 miles miles away, they strike north and and dip about 25° east. east. In between the strikes strikes c-raually converge convergealong alongthe theshore shoreof of Lake LakeSuperior Superiorasashigher higher stratigraphic stratigraphic gradually levels are reached, reached, until flows strike to the the shore shore in in the the levels are until the the flows strike parallel parallel to vicinity southwestern vicini ty of ofSchroeder, Schroeder, Torte, Tofte,and andi,utsen Lutseninin southvresternCook Cook County. County. Herethe the highest highest stratigraphic stratigraphic units are the dip Here are exposed, exposed, and and the dip is approxiapproximately 12° to the southeast. southeast. The lavas lavas are The are intruded by a great variety and bulk of intrusive intrusive rocks, rocks, including several large large diabasic diabasic sills sills at at Duluth, Duluth, the the Beaver Beaver Bay Bay Complex, Complex, includim several the 1-iovland andReservation ReservationRiver River diabase diabase complexes complexes and and the the Logan intrusions. the Hovland and intrusions. Where Hhere these intrusions are are discordsnt discordant and and abundant abundant they they have have deformed deformed the the lavas considerably, lavas considerably, with local strongly divergent strikes and and steep steep to to overturned dius. dips. Along with the thick glacial cover inland, inland, they they have have also made made difficult difficult to to impossible impossible the the long-distance long-distance tracing tracing of of stratigraphic major flows or or groups roups of in the the lava lava series. series. Several Several maj or flows of similar similar flows, flovrs, units in however, can be traced inland from the lakeshore for however, can be for at at least least 15 15 to to 25 25 miles. miles. Faulting is COffi.J;lon in the flows flows near the areas of abundant intrusions intrusions (such (such is common as from Silver ~jilver Bay Day to to Little Little:iarais). :'1arais). These faults appear to to be be of of minor as displacement and are are :r.lostly mostly transverse and steeply dipping with no displacement no strongly strongly preferred strike or displacennnt, displacemnnt, but aa few few longer lon~er strike—faults strike-faults have have been been found, one one of which probably extends for found, for at least five five miles. thickness of the has been measured and and estimated estimated by by The thickness of the lava succession has feet between and Split Split ~)andberi!, and Gror-an Grof.\an (l90) (19)j·0) as as 23,148 behreen Duluth Duluth and Sandberg (19::38) (1938) and 23,lB feet Rock complex) by adding Pock River (the (the beginning beginning of of the the Beaver nay Bay intrusive complex) Whether the lakeshore. ~TIether the individual individual flow thicknesses thicknesses intersected along the lakeshore. j.ile at at Split Split Rock Rock River Biver is this conforms to the is not not this conforms the true true thickness of the pile Northeast of the Beaver Bay Complex about 5000 lmovn. Hortheast 5000 feet feet of of lavas lavas are are known. estimated recent mapping to form the lakeshore section section between between 'ilver Silver estimatcd from recent Rortheast of and Lutsen, where Bay and the uppennost flows at 'T'ofte. IJortheast Tofte uppermost flows at °ofte. Bay the flows are are parallel to the shore, lavas totalling about about 16,500 16,500 feet feet the flows have River diabase diabase near near }iovland. Hovland. Below been measured measureddovn downtotothe the Reservation Reservation River have been (northeast of) this is an older section of about 5,000 feet of (northeast of) this is an older section of about 5,000 feet of lavas, lavas, for for total on on this thislimb limb of ofabout about 21,500 21,500 feet. a total Estimate50f volcanic volcanic thicknesses thicknesses by by constructing constructing cross—section cross-section profiles Estimateof profiles give between between 11,000 Tofte, above above the the Duluth Duluth Complex, give 11,000and and18,000 18,000feet feet at at Tofte, depending 20°. Although Although the the average average on ass~~ed assumed dips dips between 12° and 20°. deDendng on is very little control on dips near dip at Tofte is about 12°, there is very little control on dips near the the at Tofte is about 12°, dip flow contacts. contacts. base section as as the thefew fe,., inland inland outcrops outcrops rarely rarelyexpose expose flow base of of the section northeast at at the theCascade Cascade River, River, about about 15,000 15,000 feet feet of of lavas lavas above above Farther northeast of 12°; another the Duluth Duluth Complex Complex are calculated with an average dip of 12°; another are calculated with an average dip lies beneath thick section, section , possibly possibly as much much as thick, here here lies beneath thick as as 5,000 5,000 feet feet thick, '. the Complex. Complex. ~ �—78--78- GenerallDesptiq Description, The North Shore Volcanic Group bears many resemblances, both physically physically and chemically, to plateau lava sequences of various geologic geolo~ic ages. ages. Similarities to the Tertiary Tertiary plateau plateau lavas lavas of of eastern eastern Iceland Iceland are are to the particularly particularly striking. striking. The lavas lavas are almost entirely subaerial, subaerial, showing showing highly vesicular (now (nmr amygdaloidal) amygdaloidal) upper portions and and massive interiors, interiors, and.various various types types of of jointing, jointing, surface surface features, features, and and textures textures depending depending and on their specific composition. composition. Evidence of submarine extrusion extrusion is is almost almost Portage and entirely limited to the at Grand Portage and at the base of the section both at Nopeming, west west of Duluth, the lowest flow Duluth; at at Nopeming, flow is is piflowed pillowed and and on on Portage Island the lowest flow shows shmrs spheroidal spheroidal forms that could could Grand Portage possibly be pillows, but excellent, excellent, thick—rinded, thick-rinded, vesicular vesicular pillows pillows constitute the lakeward side of the island aa few constitute aa flow flow on the few flows flmrs above above of the the section. section. Unequivocal hut but less well—formed well-formed pillows and and the base of pillow-breccia have been seen seen only only rarely rarely higher higher in in the the section. section. These pillow—breccia could or stream stream beds beds on on the the lava lava surface. surface. The could have have formed in local lakes or flows tabular, and since some individual flows flows are are in general tabular, flows or or flow flow groups groups can can be traced along strike for at least 20 miles, the general general impression is is that that of of aa broad, terrain. In contrast contrast broad, rather flat volcanic terrain. to clear to the the situation situation in in eastern eastern Iceland, Iceland, however however (Walker, (Walker, 1964), l96), no no clear evidence of volcanic centers, representing shield or composite evidence composite volcanoes White contemporaneous with the plateau volcanism, has yet been found. found. \'mite contemporaneous (1960) on to some Keweenm-ran (1960) has has drm-rn drawn attenti attention to the the remarkable remarkable extent extent of some Keweenawan flows (especially in Michigan) Michigan) and with ample justification flows justification calls calls them flood basalts. basalts. Interflow sediments of the the section. section. They Interfiow sediments make make up up aa minor minor part (l—3) of -part (1-3%) are principally red, cross—bedded sandstones, that occur sporadically are red,cross-beddedsandstones, sporadically as as beds aa few few inches inches thick thick between flows, flows, but but aa few fe"T local local accumulations accumulations of of over 100 feet feet are are found. found. Conglomerate is is rare. rare. Some Some sand has has filtered down into down into cavities cavities in the upper unper parts of flows, f10vs, and and also also forms forms aa matrix for flow—top breccia for flow-top breccia in in others. others. These sediments appear a.ppear to have been deposited by occasional temporary streams winding across the volcanic surface. There is is little evidence evidence of of erosion. erosion. Pyroclastic deposits deposits are are but welded tuff and mixed sand and extremely scarce, scarce, but and shards shards have been the Cascade IIiver River in Cook County (Johnson reported from the (,Tohnson and and Foster, 1965) 1965) and basaltic to to andesitic flow top breccia, is is present present andesitic breccia, breccia, other than flow in a few localities. , exception of of aa high high potassium potassium content content in in some some oaf mafic With the exception ic and intermediate abundance of of rhyolite, rhyolite, the the compositions compositions of of the the lavas lavas members and the relative abundance are also also very very similar to those those of plateau lava series in Iceland and are and elsewhere. vhere. characteristics and and abundance abundance of of the the Table 1 shows the general characteristics major types. types. The most abundant general type is is olivine olivine basalt 'basalt of of several several varieties; varieties; important, and distinctive variety is is mottled mottled (ophitic), (ophitic), one widespresd, widespread, important, and is is similar similar to to what what has has been called olivine tholeiites in other areas. and areas. Rough columnar These typically have ropy surfaces and and were very fluid. fluid. col~~nar joints are Other olivine olivine basalts basalts are with diabasic are common. common. Other are coarser, coarser, some i-rith and some ,.ith with other other characteristic characteristic textures. textures. In the Tofte—Lutsen Tofte-Lutsen area, area, high in the section, is a group in of olivine base.1ts th abundant, abundant, small basalts "ri with (1-3 phenocrysts or or crystal crystal clots. clots. At section (1—3 nun) mm) bytownite' bytownit&phenocrysts At the base of the section both t at Duluth Duluth and and on on Lucille Lucille Island Island east east of of Grand Grand Portage Portage are are distinctive distinctive basalts basa.lts that contain abundant phenocrysts, 2—3 2-3 mm across, across, of of augite augite and and �_____ ______ TABLE 1 Generalized Characti±ritics Characteristics of of Major Major Lava Lava Types Types of of North North Shore Shore Volcanic Volcanic Group Group ___ ~ I Wt % % Si02 Si0 2 -_ -_. ' --~ ,. --...--.......... I 2 ·~"-··""'''''''·~''-'''''''''''-''''-'''~~··i''''~· Wt %% MgO -..---~.--'.<.~."'-"'.' .. _ ..•,,_'__ "~_ _~ 46-49 1 0.1-0.5 I ~ ~--~·_""""~:~'.....,-'T-'·_.-.~ ~ · I{ Andesite— t"P. Intermediate Andesit~:i Intermediate Trachyandesite Quartz Tr~rtz Latite L~~ Quartz Quartz Tholelite I ~- " - - - - " , .. , . • .~-w••• _ -" ~".~~~ ••• ~.-+,~. Wt %%1(20 K 0 -, Tholei te I Olivine :ic 1 Olivine Characteristic Tholeilte Characteri~~~i~te 4,,52-57 52-57 50—51 50-51 ! 0.6-0.9 ~'~l.·.~ ~ol.AA' .!::..~< 1-,,•• 1,--.' •• _.,,-, 1 ."~.- ~"'-" ·~·~,.._'S...·_"' 5.9:6.8 5. 9-6 . 8 1 I I __ "',.. ,""~ ••• .,J • • • • ~ ~ I • , 1 Very fine— finet Very fine— finegrainS, inter— l grained, inter~ grained, granular. Some pot— { granular. commonly porphyritic (plag., ~ flow structure, ~ phyritic , ..1 augite) (plag., fine oxidationoxidation— i, fine banding Ophitic Occasionally Occasionally porphyritie porphyritic (plagioclase) --------.--.--------!..-----~---~-~t~:~~~~-.-~--+----~ 72—75 72-75 2.8—5.0 2.8-5.0 3.9—6.2 3,.9-6.2 r '_<'~~', 0.9- 1 • 9 ,.,--,~ <J .. _ _ ;· ·",· P _ > ' _ • - . _• •- ~ ~ , " ' _ ••.•• -:... . < - I aphanitic~ . aphanitic, mostly pot— porphyritic (plag., (plag.,. augite, 01.) augite, oh) . . _ _~--~ .- 0.0—0.4 0.0-0.4 ,,,n"~"·.·~,.,-.•~,,·,,,. ,'-~.~ ..,< , .• ~"'_'_, .I •... , < •• ,, ..•, .•--.- .. --. aphanitic aphanitic to to felsitic;aphyric felsitic; aphyric or porphyritic (plag., orthoclase, (plag., ) quartz, mag., pyrox.) pyrox. occas. spherulitic ~.--_ _,--.;,::::~:lt::l~~~.~ . . - — J 62—65 62-65 ._- ! : Thickness, Thickness, feet feet Range '- --.--.,,' j'" -" I ' l \ Textures t ': - 1.9—2.7 1.9-2.7 .•Y. _ _ w .• .• ~yolite ithyolite ..~~~'-~·~~,.. ..,..-".-·.-'''' --..~•...".-.-...."....-.~...,.--~ -"'. ~~-~"~---'-'-'-~---~ _.V·_·__ 1 I 4. 3-5. 9 1. 9-4 . 5 11:9—4.5 ~ ~;~'-<'~~""_ '"-->-"'"'-'~/"""~-"';""'~1--~-'>""'.w.".>--."'-•.,./A~_~C'~~'_"h,,·_, t-'_.,··",._·.·r;.,,·~ . ,..'.,. ".~., !I' __ . Quartz Quartz Latite Latite I' . 50-1300 50—1300 perhaps 3500 3500 1 2 0 ' " · ·_..5 . 0=500 ..·· 50—500 120 — ···------struc~~:-t:=-:-:py--i~c==~=tc=:=::--i·:::=:- -====:-c'oIiIIDo~ .'.. -- ]- -~ >100 <1 to >100 ~." ·I6~46 10—40 ·"' ' 30—150 30-150 ~ -,·--···l 'so 80 - 1 50—240 50-240 ~ i 1". . var:Gibier' varIable 80—200 80-200 - Structures smooth, ropy flow tops oi;ti';;- jointing j vesicular wrinkled scoriaceous rubble scoriaceous, rubbly vesicular, rolled, flow—banded platy, sub—horizontal big columns in thick irejilai tâ ,'~~~~~:~:h~:i~~~~~l ··t-~~~:i~:}~::T.::-t~~~ii,irreg;;i;r-ts~if;~~~;~g;;iarh~~~~;!!~:~~l - sheeted tops[" small, irregular small, 1rregiIar subhorizontal, flows platy .. round stretched 'o"r" or ···... i . stretched, round vesic1es round or 1rregu1ar stretched ...._,··_- . stretched or round round ~ ~--_ ·-··-~·i ~ ~ -14 ,-- ,-- - - ~ . _·--_····_..·. ~."i'----. __ -- -.~~- - - ~~"Q ~ .,~_.-.. '".~-~--'very_fluid Other ! very fluid 1 more viscous ~ brown—weathering brown-weathering I few flow : pink, pink, red, red, or more_viscous contacts exposedt exposed light Characteristics ;omewhat variable variable contacts Characteristics J, pipe amygdules some contain tomewhat light gray gray at at base ~ ~ more more 1(20, K20, ! segregation veins, l segregation veins, i Kspar; ~ vesicle cylinders quartz, agate agate vesicle cylinders ~: quartz, I common in cavities l common in cavi ties' columnar centers ve·si-~i;;~·_ -·--l--·;(;~d·-~-;· 'i;~~g~i~·~+·;t~et"~h'ed --- ~-. -"'-'--- -----..- 1 I i ~ ~~ ---.. -.-.-.. -.. -".. ! - i l··.-,-.----- .- . -.- ---,.. l Ksr I Ij --+;tretch~d· O~.. t"';~~:iche~f I I I I f. ~~~:~·ched·: - " " - . _.. • -,- - �—80— -80- (serpentinized) olivine: olivine: these these are are particularly unusual unusual in (serpentinized) in having ferromagnesian instead of of plagioclase plagioclase phenocrysts. phenocrysts. Another moderately abundant and distinctive distinctive rock rock ty-pe type is tholeiite" which is is is the the "quartz tholeiite fine grained grained and and slightly slightly more more siliceous siliceous and and viscous viscous aphanitic or very fine The quartz—tholeiites than the olivine olivine basalts. basalts. The quartz-tholeiites characteristically characteristically have a rubbly or brecciated top with the highly vesicular vesicular fragments fra~ments set set in in aa matrix of washed-in washed—in red sand sand or or occasionally occasionally calcite calcite and and zeolites. zeolites. They also ~ thick, along subhorizontal subhorizontal also commonly commonly show narrow oxidation bands, bands, 1-3 mm flowage planes. planes. This quartz—tholeiite quartz-tholeiite grades grades into into more more potassium—rich potassium-rich varieties (trachybasalt, (trachybasalt, trachyandesite) that that can can be be distinguished distin~uished only only by chemical analysis and and microscopic study; study; patches of of interstitial interstitial KK feldspar are are present present in these these rocks feldspar rocks but are invisible in in hand specimen. speci~en. Intermediate varieties are are nearly all all porphyritic with plagioclase, plagioclase, augite, ausite, magnetite, and in some magnetite, SOTIe specimens iron—rich iron-rich olivine olivine phenocrysts; phenocrysts; they they have have the compositions of andesites, trachyandesites, and the and intermediate intermediate quartz quartz Most are aphanitic, but one latites. Most one unusual flow, flow, here here called called the the Manitou Manitou trac~ybasalt, is exceptionally thick (at (at least least 300 300 feet) feet) and and granular, granular, traciybasalt, is for 55 miles although it it originally continued continued for an an and can be traced for These flows in both both directions. directions. 'I'hese flows are commonly cOTlJ1!1only brown or unknown distance in red and irregularly jointed jointed or with platy,subhorizontal joints. joints. The felsic The felsic lavas lavas are anomalously abundant abundant for for aa simple simple differentiation differentiation series from aa basaltic basaltic parent parent magma. mae;m.a. They are red, pink, or or light li~ht gray. gray, These flows composition of of quartz quartz latites. lati tes. 'l'hese flows tend to be much and have the composition thicker than the other other types: types: the thickest is is 1300 feet, feet, aa few few miles ~iles east east of Grand Marais; Marais; the 3500' 3500' Brule Flyer River rhyolite rhyolite west of of Hovland Hovland may may be aa lava dome. dome. Their top surfaces are mostly strongly strongly flow—banded, flow-banded, vesicular, vesicular, and. contorted, b~t but not not brecciated, brecciated, and and their their bases bases are are cornmonly commonly flow-banded flow—banded and contorted, brecciated. Spherulites are are occasionally occasionally present. present. Jointing Jointin~ and locally brecciated. ranges across in the thickest flows flows to sub— subranges from large columns 44 feet across horizontal platy joints; joints; small tectonically—produced tectonically-produced parallel fracture fracture sets a a few mID ccooling joint joint fragments fra~ments into into sets mm apart commonly break up the ccooling felsites are are porphyritic, with ,-rith quartz quartz and and small pieces. Most of the felsites feldspar feldspar phenocrysts (oliogclase—andesine (oliogclase-andesine and/or orthoclase) orthoclase) but but some some are only weakly porphyritic porphyritic or or arhyric. aphyric. Poikilitic quartz surrounding are stout stout alkali—feldspar alkali-feldspar laths ("snowflnke ("snowfla1:e texture:) texture';) is is aa common common microscope texture in the thicker thicker flows. flows. Even these siliceous siliceous lavas lavas have have evidently evidently flowed great distance; distance; one one lava lava or or ffow flowed aa great ..J..mr group group can can be be traced traced for for at B.t least 23 miles miles \-lest west from the Devil Track Fiver, least River, Grand Grand Marais (see (see man, Man, fig. 1). fig. 1). Alteration The lavas lavas have been strongly stronlJ,ly but irregularly irrerularl;v affected affected by b;f secondary secondary solutions that have deposited denosi ted low—temmerature lml-temner?ture minerals in in vesicles, vesicles> solutions fractures, and other some of the minerals of fractures, other cavities, cavities, and and -altered altered sot'!.e of the the no fresh fresh olivine divine has lavas themselves. For instance, instance, no has been been detected detected in in any of of the the lavas, lavas, although although it it is is common the intrusive diabases. any co~mon in the diabases. A zonation of of this alteration alteration is is anparent; anparent; at at Duluth Duluth and and at R.t Grand Granel broad zonation of the the ~round~ass groundmass Portage (in (in the lower lower parts parts of of the the lava lava section) section) r'uch ~uch of has been been converted convertedtoto actinolite actinolite (although many larger pyroxene has (althoup::h nan'.' laT£ser aurites aur.j te:=> are unaffected) unaffected) and has been been saussuritized. saussuritized. [ere Iere also andsome SOIne plagioclase plar:ioclase has also the minerals characteristicallyquartz, quartz, prehnite, prehnite, calcite, calcite, the arnygdule amygdule p.dnerals areare characteristically �-81—81— epidote, and chlorite, epidote, chlorite, the the same basic assemblage as as is is found found in in the the Porta~e Lav~ Series Keweenaw Peninsula (Stoiber (Stoiber and and Davidson, Davidson, Portage Lake Lake hava Series on the Keveenaw 1959). In and northeast of Duluth K—feldspar K-feldspar is is also also occasionally occasionally found, found, In arid laumontite becomes becomes abundant. and laumontite in the section section variouS various zeolites, zeolites, Higher in along with vith calcite, caThite, are are dominant dosnant except along except In in the the quartz quartz tholeiites tholeiites and similar agate, crystalline quartz and and chlorite chlorite are are common. common. similar lavas levas where aaate, The most most abundant abundant zeolites The zeolites are are laumontite, stilbite, heulandite, thorrsonite and scolecite scolecite but but analcite, analcite, natrolite, natrolite, mesolite, mesolite, mordenite, thomsonite and apotbvllite have also and apophyllite ~lso been found. Saponite is is common in olivine basalts. Andradite carnets garnets have been discovered in in several several localities localities amydules and andveins veinsfrom froma awide widerange range lavatypes tres (basalts in ~!'lY8dules of of lava (basalts to rhyclites) and and levels levels in rhyolites) in the the sequence, sequence, and and traces traces of ofnative nativecopper copper have have been found foundininseveral severallocalities. localities. Thus the secondary zonation in in the been Thus the secondary zonation :rorth Shore Grout spans spans both both the deeper—level, iTorth Shore 1oThanic Volcanic Group deeper-level, higher—temperatre higher-temperature tyte of the Keweenaw Peninsula and the higher—level, cooler tyte charactertype of the lCe,.,eenaw Peninsula and the higher-level, cooler type characteristic of istic of the the icuer Imler parts partsof ofthe theTertiary Tertiaryplateau plateau lavas lavas of of eastern eastern Iceland Iceland as described upper, zeolite—free is as described by by Walker 'ilalker (1960). (1960). Walker's Halker' s uDper, zeolite-free zone zone is apparently not represented representedinin Hinnesota. innesota. According Accordingtotohis his estinates, estirsates, the apparently not the presently exposed top of the exposed top the section sectionon onthe theLake Lake Sunerior Superior shore shore could could have have been anrrcxirratel'r 5,000 5,000 feet feet below the surface surface during been approximately belm., the during mineralization. Althoughdetailed (tetal led1-Tork workhas hasnot notyet yet been been done, done, no JUthou~h no clear clear cross—cutting cross-cutting relations of' to stratigraph the relations of zeolite zeolite zones zones to stratirr,raphywithin witp_~~ thelavas lavashave havebeen been recocnized. hut reco~nized, but the theevident evidentUpper Upper Precambrian, Precambrian, nostvolcanic postvolcanicunconformity unconformity ;·rhi-chch;;robe.bly Shore must mineralization, wit' probablyfollm.,s followsthe the~Torth lorth Shore must have havepostdated postdated the the mineralization, since it it does since does crosscut the zeolite ZGolite zones. zones. It should be be stressed, It stressed, however, however, that none of the flows flows has has been been entirely entirely in fact, converted to to secondary secondary minerals. In fact, the the plaioclase plagioclaseand and augite augite are are tynic8,11yunaltered unalteredororonly onlylocally locallyaltered altered mostmafic maficand andintermediate intermediate tvicall'r in in most has typically typically rocks. althour:h no no fresh olivine olivine has has been been discovered, discovered. There There h~s rocks, although been sore oxidation oxidation of of the the opsnue minerals, especially especially of of nagnetite, been sor.e opaque minerals, magnetite, and and interrsediate and ni~eonite is iscoirnonly com~only oxidized borders. In many nany intermediate and pi'eonite oxidizedatat its its borders. felsic lavas, plarioclase pladoclasephenocrysts phenocrysts have have been been albitized and/or zeolitized: zeolitized; felsic lavas. albitized and/or Fresh, undevitrified volcanic some could be be deuteric. deuteric. Fresh, volcanic someofofthis this alteration alteration could glass present in in occasional samples, r,lass is is still still present occasional samples,notably notably inina abasalt basaltfrom fromabout about t"m r'liles r10uth of Brule River. River. two miles ,{est west of of the mouth of the the Prule Etnra•iv The Thias of of the ;orth The lavas !.JorthShore ;3horeVolcanic VolcanicGroup Group can can be be conveniently conveniently divided lithostratipTanhic units unitsof ofcoherent coherent petrographic petrographic divided into into several several lithostratir'ranhic character the basis of character nrimarily nrimarily on on the of exposures exposures at or or near nearthe theLake L~ke Superior Superior shore. Hany of these shore. these units can ca,n he be traced traced for for aDoconsiderable considerable distance distance inland, but interruntions and structural structural corwlicatipns complicatiens by by intrusive intrusive bodies bodies inland, buU nterruntions and as well lacial denosits as \·rell -as as ;o;lacial denosi tsprevent prevent the thereconstruction reconstructionof' of aacomplete, complete, conconp • tinuous sequence. ofJoclear tinuous sequenc cleartrend trendofofconnositional compositionalchange chanF':e is isevident evidentfrom from base to top; at the base to top; in in fact, fact,although althou~hthe themost r'lost ferrora-'nesian ferro~arrnesinn lavas lavas occur occur at the base, flows, in in the Tofte—Lutsen area,are areentirely entirely olivine olivine ~ase, the the unnermost u:!Jnermost flmrs, Tofte-Lutsen area, oasalts. It basa,lts. It should 3hould be be kept kent in in rind r;ind also also that that aamajor ma,jor stratigraphic stratigraphic break break. mayoccur occurbeheween the Grand GrandPortap-e Portagelava lavasection section (sho'ing f:lay t"teen the (shO\.,ing reversed reversed magnetic magnetic polo.ri ty) and and the llig-her strnta. polarity) the lhgher strata. qir Table lists the To.ble 22 lists the informal informal stratigraphic strntif.rcmhic units unitsnroposed proposed for for the the northeast limb liMb (Torte (Tofte to toGrand Gr8.nd Portage) Porta,g;e) forth ~JorthShore ;3horeVolcanic Volcanic Group, Group, with "lith estimated thicknesses thicknesses and and ~eneral characters,and and Table Table 33 their estimated general lithic lithic characters, Ltivessimilar sinlar data p:ives data for forthe thesouthwest southwest limb. limb. 'I'his tabledepends depends largely largely This latter latter table on the work (1038) and and Grogan Grogan(1940), (iqito), penclin.Q; pending restudy. restudy. on the "lork of of Sandberrr Sandberr:: (1°38) �—82— -82- Table 22 Stratigraphy of of Northeast Limb (Tofte-Grand (Tofte-Grand Portage) Portage) North Shore Volcanic Group (Exclusive of interflow sediments) (Exclusive of sediments) Approx. Approx • ..IhiCkness(ft. ThigkneaL&Q) Lithostratigraphic Lithostratigraphic unit unit Lithic character character Lutsen basalts divine basalts, olivine basalts. olivine olivine tholeiites tholeiites 160 Terrace Point basalt flow flow thomsonite—bearing ophitic ophitic basalt thomsonite-bearing 310 Good Harbor Bay andesites brown, porphyritic porphyritic andesite, brown. trachyandesite 360 Breakwater trachybasalt flow flow brown, brown, columnar, columnar,granular granular trachybasalt 500 Narais rhyolite Grand Marais rhyolite flow flow pink, red, gray pink, gray porphyritic porphyritic rhyolite 600 Croftville basalts various fine-grained fine—grained basalts Devil Track felsites aphyric and porphyritic rholite rholite fJows flows Red cliff basalts basalts amygdaloidal, amygdaloidal, ophitic olivine basalts 1300 Kimball Creek felsite pink to to tan, tan, porphyritic porphyritic felsite felsite 1800 Marr Island Island lavas tholeiitic basalt, basalt, intermediate, intermediate, mixed tholeiitlc felsic felsic lavas 1000 Brule River basalts granular-diabasic granular—diabasic basalts 3500 Brule River fhyolite fhyolite flow pink to to gray porphyritic porphyritic rhyolite rhyolite (est.) 4000 (est.) Havland lavas Hovland lavas mixed porphyritic porphyritic basalt, basalt, trachybasalt, trachybasalt, rhyolite 200 Red Red Rock rhyolite flow flow red. red, porphyritic porphyritic rhyolite 260 Deronda Bay andesite andesite flow flow gray-brown, aphyric aphyric andesite andesite gray—brown, Grand Portage basalts basalts mixed tholeiltic tholeiitic to to diabasic diabasic basalts basalts Top 'fop 1020 1020 1020 400—900 400-900 4500 Base �—83— -83- Table 33 Generalized Stratigraphy of Southwest Limb (Tofte—Nopeming) (Tofte-Nopeming) North Shore Volcanic Group Group (exclusive (exclusive of interflow sediments) Approx. TbLekness_'ft) Thickness (it) Lithostratigraphic Unit Lithic character Tp 4000 Schroeder basalts ainygdaloidal ophitic ophitic olivine olivine tholeiltes amygdaloidal tholeiites >300 > 300 Manitou trachybasalt flow flow red—brown granular trachybasalt to red-brown to basalt (more of of the the Schroeder basalts) (more > 280 > 280 > 3CC' > 3CO few 100's few — — mostly quartz tholeiites, other other basalts Palisade rhyolite rhyolite flow flow gray to pink, gray to pink, porphyritic rhyolite Baptism River lavas mixed lavas, mostly basalts basalts — Beaver Beaver Bay intrusive complex — basalts, one felsite mixed basalts, felsite River basalts basalts Gooseberry River 3200 — Bell Harbor lavas lavas -- —. LaFayette Bluff, Bluff, Silver Silver Creek Creek Cliff Cliff intrusions intrusions — — — 1025 fine—grained basalts Two Two Harbors fine-grained "melaphyres", "melaphyres", some quartz tholeiites 1615 Larsmont ophitic ophitic basalts basalts amygdaloidal ophitic basalts. amygdaloidal ophitic olivine divine basalts. — — Knife River River diabase intrusion — Knife — — — — — 4930 Sucker River basalts mixed basalts, basalts, mostly ophitic 4400 Lakewood basalts mixed basalts, mostly non—ophitic non-ophitic — 3600 3600 — mixed basalts, basalts, andesites, andesites, felsites felsites Lakeside lavas lavas — diabase sill sill — Endion diabase — Endion — Leif Erickson Park lavas lavas 2560 — Lester River diabase diabase sill sill — Lester — Duluth Complex — Duluth — 2300 Nope'iuingbasalts basalts Nopeming Base Puckwunge Sandstone Sandstone Puckwunge — — mixed basalts, basalts, andesites andesites — porphyri tic meLbasalts, melc.basal ts, diabasic diabasic porphyritic basalts basalts �_____ —84--84- References Beck, M. M. E., Beck, E., and and Lindsley, N. C., 1969, 1969, Paleomagnetism of the the Beaver Beaver Bay Bay N. C., Complex, Minnesota: Jour. Jour. Geophys. Complex, Minnesota: Geophys. Res.,v.74, Res.,v.74, p. p. 2002—2013. 2002-2013. Books, Books, K. K. G., G., 1968, Magnetization of the the Lowermost Lowermost Keweenawan Keweenawan lava lave flows flows in in the Lake Lake Superior area, area, in Geological Survey Research 1968: the 1968: U. U. S. S. Geol. Geol. Prof. Paper 600—n, p. D248—254. Survey Prof. 600-D:-p. D248-254. Dubois, P. P. M., H., 1962, Paleomagnetism and correlation Dubois, correlation of of Keweenawan Keweenawan rocks: rocks: Geol. Sun. Surv. Canada Canada Bull. Bull. 71, 71, 75p. 75p. Geol. Faure, G., G., Chaudhuri, Faure, Chaudhuri, S., S., and Fenton, M. M. D., D., 1969, Ages of of the the Duluth Duluth Gabbro Gabbro Complex and of the Endion Sill, Duluth, Minnesota: Jour. Jour. Geophys. Geophys. Res., Res., v. 74, p. p. 720—725. v. 74, 720-725. Gehman, H. Gehman, H. M., M., 1957, The Beaver Beaver Bay Bay Complex, Complex, Lake Lake Co., Co., Minn.: Minn.: unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Univ. of of iinnesota. Minnesota. Goldich, Goldich, S. S. S., S., Nier, A. A. 0., Baadsgaard, Baadsgaard, Halfdan, Halfdan, Hoffman, Hoffman, J.H., J.H., and and Krueger, Krueger, 11. 1961, The The Precambrian Precambrian geology geology and and geochronology geochronology of of Minnesota: H. tJ., W., 1961, Minn. Minn. Geol. Geol. Survey Survey Bull. Bull. 41, 41, 193 193 p. p. Green, J. Green, J. C., C., 1966, New field field studies studies of of the the Keweenawan Keweenawan lavas lavas of of Minnesota ~linnesota (abs.): Program, 12th 12th Ann. Ann. lnst. Inst. on on Lake Lake Superior Geology, Sault (absJ: Program, Sault Ste. Ste. Marie, Mich., p. p. 9. 9. physical characteristics of Late Precambrian lavas Ch~ical and and physical lavas Cheaical ---of, 1968a, northeastern Minnesota (abs.): (abs.): Amer. Geophys. Geophys. Union Union Trans., Trans., v. v. 49, 49, p.363. p.363. Types and structures of flows , 1968b, Types flows of of the the North North Shore Shore Volcanic Volcanic Group, Group, ---Minnesota (Summary): Program, (Sununary): Program, 14th 14th Ann. Ann. lnst. Inst. on Lake Superior Geology, p. 52-53. p. 52—53. , 1970, Geology of North Shore Volcanic Group, Group, in in Summary Summary of of Fieldwork Fieldwork ----1970, Ed's., Minn. Minn. Geol. Geol. Survey Survey Inf. lnf. Circular Circular 8, 8, p. p. 19—20. 19-20. 1970, Sims Sims and Westfall, Westfall, Ed's., Grogan, R. R. M., M., 1940, 1940, Geology of a part of the Grogan, the Minnesota Minnesota shore shore of of Lake Lake Superior Superior northeast unpub.Ph.D. Ph.D. thesis, thesis, Univ. Univ. of Minn. northeast of of Two ~yo Harbors, Harbors,1-finn.: Minn.: unpub. GrEiut, F. F., F., Sharp, Sharp, R. R. P., P., and Schwartz, G. G. M., N., 1959, 1959, The The geology geology of of Cook Cook Greut, F. Minn. Geol. Geol. Survey Survey Bull. Bull. 39, 39, 163 163 p. p. County, Minn.: Minn. Hanson, C. G. N., N., and and Maihotra, Malhotra, R., R., 1970, 1970, K—Ar K-Ar ages ages of of mafic mafic dikes dikes in in northeastern northeastern Hanson, (abs.): Program, Program, 16th Ann. lnst. on Lake Minnesota (abs.): Ann. Inst. Lake Superior Geology, Geology, Thunder Thunder Bay, Bay, Ontario, p. p. 19. 19. Johnson, C. C. H., and and Foster, Foster, R. R. L., L., 1964, 1964, Contaminated Contaminated Precambrian Precambrian ash—flow ash-flow cuff, tuff, Johnson, Cascade River, River, Minnesota Minnesota (abs.): (abs.): Geol. Geol. Soc. Soc. Amer. Amer. Special Special Paper Paper 82, 82, p. p. 102. 102. Palmer, Palmer, H. H. C., C., 1970, 1970, Paleomagnetism and and correlation correlation of of some some Middle Middle Keweenawan Keweenawan rocks, Lake Lake Superior: 6, p. rocks, Superior: Can. Can. Jour. Jour. Earth Earth Sci., Sci., v. v. 7, 7, No. No.6, p. 1410—1436. 1410-1436. across Keweenawan lavas at Duluth, Minnesota: Sandberg, A. A. E., E., 1938, Section across Minnesota: Geol. Soc. Geol. Soc. Amer. Amer. Bull., Bull., v. v. 49, 49, p. p. 795—830. 795-830. >i. 1949, The The geology geology of the Schwartz, G. G. 1'1., 1949, the Duluth metropolitan area: area: Mfnn. Hinn. Geol. Survey Survey Bull. Bull. 33, 33, 136 136 p. p. Geol. �—85— -85- page 22 Silver, L. L. T., T., and and Green, Green, J. J. C., C., 1963, Silver, 1963, Zircon ages for for Middle Keweenawan rocks rocks of the Amer. Geophys. of the Lake Superior Region (abs.): (abs.): Amer. Geophys. Union Trans., Trans •• v. v. 44, 44, p. 107. p. 107. Stoiber, R. S., 1959, 1959, Amygdule Amygdule mineral mineral zoning in the Stoiber, R. E., E.• and and Davidson, Davidson, E. E. S., Portage Lake lava series, series, Michigan copper district: district: Econ. Econ. Geol. Geol. v. v. 54, 54, p. 1250-1277. p. 1250—1277. Walker, G. G. P. P. L., 1960, 1960, Zeolite zones and dike distribution in relation to the structure basalts of eastern Iceland: structure of the basalts Iceland: Jour. Jour. Geology, v. 68, 68, p. p. 515—528 515-528 1964, Geological investigations in eastern Iceland: Iceland: Bull. Bull. Voic., Vole., v. 27, 27, — - - , 1964, p. 351-363. p. 351—363. �—86— -86- Field Trip Trip A A Field The North North Shore Shore Volcanic Volcanic Group Group Leader: Leader: John C. C. Green Green University of Minnesota, ~finnesota, Duluth are intended intended to give aa broad broad picture picture of of The stops stops described below are to give the the chemical, chemical, petrographic, and and structural varieties varieties of of lavas lavas of of the the Group, Group, some representative exposures of of the the minor minor intrusions intrusions that that cut cut the the flows, flows~ and the general structural characteristics characteristics of of these these Upper Upper Precambrian Precambrian racks. rocks. The area northeast of of Silver Silver Bay, Bay~ where where Green Green has has done done most most of of his his work, work, is is stressed. The trip excludes the the Duluth Complex, Complex, aspects aspects of of which which have have been been or are covered elsewhere (GSA Guidebook, ILSG 1968 Guidebook, Guidebook, and Field Field (GSA 1956 Guidebook, Trip BB of this program). of this program). Many more stops are listed below than will be possible to examinein but they included for examine in a one—day one-day trip, trip, but they are included for the benefit of those those who can can visit or or revisit revisit the the area area at at aa later later time. time. The U.S.G.S U.S.'G.S 7 1/2 minute quadrangle name nameisis given given for for each The stops stops which 7 1/2 minute quadrangle each stop. The which are planned as as a minimal frameworkfor forField Field Trip Trip A are designated planned minimal framework A are designated with with an an asterisk after are listed listed for asterisk afterthe thenumber. number. Mileages Mileages are fordistances distancesbetween between easily identifiable along USUSHighway for easily identifiablepoints points along Highway 61 61 (not (not cumulative cumulative mileage mileage for wholetrip)~ trip), for thethe U.S.A.fCanada whole for travel traveleither eithersouthwest southwest (starting (startingatat u.S.A./Canada or northeast Midway border—- Pigeon River: left—hand left-hand column) column) or northeast atatthe the ~fidwayRoad, Road, border (St. Louis Louis Co. Co. 13), 13),Nopeming, Nopeming,WESt west of of Duluth: Duluth:right—hand right-hand column). column). Mileages are in for side trips tripsoff offHwy Hwy 61 in parentheses parentheses or or not not given. given. All All stops stops are are for side 61 are shown on 1. Descriptions between stops stops are are written written for for southwestward southwestward shown on Fig. Fig. 1. The total total distance travel. The distancecovered covered isisapproximately approximately160 160 miles mileseach eachway. way. travel. stops volcanic volcanic structures are well well preserved. preserved. Visitors Visitors are are At At several several stops structures are destroying them, urged to refrain refrainfrom from loosening, loosening~removing removing or otherwise otherwise them~ urged since they they constitute irreplaceable evidence for for flow flow direction, direction, etc., etc., constitute irreplaceable since and valuable teaching students and teachingfeatures featuresfor for local local students and future future visitors. visitors. and are are valuable GoingGoing SW SW NE 7.4 -0:0 7.4 0.0 3.7 3.7 3.7 Minnesota—Ontario (Pigeon Start of Trip River, Minnesota-Ontario (Pigeon Point, Point, Trip A A -— Pigeon River, Travel SW along flat post—glacial lake bed, Minn. quad.). SW along flat post-glacial bed, — Mich. quad.). Minn. then rise rise along along shoulder shoulder of ofa alarge large NE-trending dike then NE—trending dike of of the Several road Keweenawan road cuts cuts ininMiddle MiddlePrecambrian Precambrian IceweenawanLogan LoganIntrusions. Intrusions. Several Excellent views Rove Formation shales small branch dikes. Excellent views cut by small branch dikes. Rove Formation shales Pigeon from parking rest rest areas areastotothethe Wauswaugoning Bay, Bay, Pigeon easteast overover Wauswaugoning from parking (Rove Fm. Point (thick (thickcomplex complex Keweenawan Keweenawan sill)~ Susy Islands (Rove Fm. and and sill), Susy flo's), Hat Lower Royale(Keweenawan (Keweenawan flows), Hat Point Point Lower Keweenawan Keweenawanflows), flows), Isle Isle Royale with Mount Mount Josephine (Logan dike). Josephine (Logan At Stop 1. Logan Formation (Grand (Grand Portage Portage quad.) quad.) At Logandik~ dike and and Rove Roc Faauction Stop 1. the top of the the rise riseisisa adeep deepcut cuttrirough through the the thick thickKeweenawan Keweenawan the top Farther oint. diabase dike that forms Mt. Josephine and Hat Point. Farther forms Mt. Josephine and flat diabase dike that the are good cuts in the Rove down the highway the southwest are good cuts in the Rove highway to down the Formation which is here dominated by graywacke. which is here dominr4lc-J by graywacke. Formation �—87— -87- Going SW Going NE (At the the base base of of the the slope slope an an interesting interesting detour detour can can be be (At to Grand Grand Portage Chippewa village and bay and made to to the the SE to SE Grand Portage National National Monument. Monument. The base of the Upper Precambrian sequence forms forms Grand Portage Island. Island. Continue out the west end of the the village to to Highway Highway 61). 61). 7.4 7.4 0.0 0.0 14.8 basalts, Grand Portage (Grand Stop 2.* Basal Lower Keweenawan basalts, (Grand At the top of the next rise (at the Junction Portage quad.). the top the rise (at the Junction Portage quad.). of Cook Co. Co. 17) 17) are are low cuts exposing basalts near or at of at the the These basalts base of the Keweenawan reversed reversed polarity polarity sequence. sequence. have aa somewhat somewhat diabasic texture and have been strongly though have though not not completely retrograded to prehnite—pumpellyite prehnite-pumpe11yite facies facies minerals. Amygdules contain weathered agate, Amygdu1es agate, prehnite, and and epidote. epidote. The basal Upper Uppe~ Precambrian sandstone sandstone (Puckwunge) (Puckwunge) underlies underlies the the gentle slope to the the north but is is not exposed exposed at at the the highway. highway. It It can be seen by bushwhacking about about 1/4 1/4 mile to to the the NNW. NNW. It is is aa clean-looking, somewhat feldspathic feldspathic quartz sandstone, sandstone, in in marked marked conconclean—looking,somewhat trast to low sandstones to the the red, red, immature, immature, volcanic volcanic interf interf10w sandstones above. above. The anC all the is underlain lowland beyond beyond is underlainby bythe theRove RoveFm. Pm.,, and the ridges ridges are are held up held up by by large large Logan Logan dikes. 3.0 11.9 Stop Stop 3. 3. Tholeiitic basalt and and porphyry porphyry dike dike (Grand (Grand Portage Portage quad.). quad.). unmaintained little Walk or drive off off Highway Highway 61 61 on on an an inconspicuous, inconspicuous,unrnaintained branch on the lake side to to an an old cabin cabin site site at at aa small small cove cove (1/8 (1/8 mile). On RR (SW) (SW) is the the basal, massive portion portion of of aa fine—grained fine-grained the Lower Keweenawan Grand Grand Portage Portage lavas. lavas. On tholeiitic basalt of the the the L is a thick, thick, compound dike dike of of porphyritic porphyritic trachybasalt trachybasalt that that trends E A large swarm of similar dikes is E into into lake. lake. A is present present in in this studied. They are are unusually unusually rich rich ji in Fe and K. K. this area and is being studied. 3.7 3.7 11.1 Stop 4. 4. Stop Red Rock rhyolite rhyolite (Mineral Center Center quad.). quad.). At Deronda to the the SE SE to to the the breccia—rubble breccia-rubble base base of of Bay the beach leads out to feet) porphyritic porphyritic rhyolite rhyolite flow flow which which is is the the aa thick (over (over 600 feet) uppermost flow found to to show show magnetic reversal reversal by by Books Books (1968). (196 8 ). More scenic exposure can can be seen seen by climbing climbing up up the the ridge ridge and and walking out to to the the point point on on the the open open lake. lake. Less scenic but more accessible exposure is in in a road road cut cut 1/2 1/2 mile mile beyond. beyond. 4.6 10.2 Stop 5. 5. Reservation River Diabase and and abandoned abandoned beach beach ridges. ridges. (Mineral Center quad.) quad.) At the the top top of the the next rise rise is the the eastern edge of the extensive Reservation River River diabase diabase complex: complex: one characteristic phase phase is is exposed exposed here here that that shows shows faint faint banding banding on on sonic surfaces. Lcrge some Large gravel the lowland lowland to to.the northeast, gravel pits pits in n the the northeast, mined out for the the new highway, highway, were large abandoned beaches of late postglacial Lake Lake Superior. Superior. Excellent Excellent smaller, smaller, later ridges can still still be be seen seen on on aa little little track that that goes goes to to the the lake lake shore shore can the base base of of the from the the slope. slope. �—88— -88- Going Going Going Going SW NE SW 9.0 9.0 5.8 10.0 il.8 14.8 --00 0.0 4.0 ----". 0.0 4.8 0r 0.0 0.0 10.6 10.6 Cross Reservation River and out of Grand Portage Indian Indian Slope is is at at contact contact of of Reservation River diabase Reservation. Slope complex and lavas (a (a rhyolite rhyolite here). here). 6.* Hovland porphyry Stop 6.* porphyry lavas. lavas. (Hoviand (Hovland quad.) Opposite aa on the lake side are exposures of a remarkable house the remarkable porphyritic trachyandesite lava flow with platy plagioclase phenocrysts up to 10 cm em across. across. By following following the the low scarp to to the the NE behind aa house (private (private property) two two flows flows can can be be ueen, ~een, the the top top of of the the one being vesicular and showing a slightly uneven crust. lower one crust. These are near the the base of of the the Middle Keweenawan Keweenawan (normal (normal polarity) polarity) lava sequence, sequence, and and are are assigned assigned to to the the Hovland Hovland lavas. lavas. They are are here cut by a large large dike, dike, at at least 22 miles long, long, of brown elinopyroxenephenocrysts, phenocrysts, that that also trachyandesite with with small. small.elinopyroxene crops out across across the the road. road. Highway descends to to old old lake—bed lake-bed flat; flat; then, then, past past Big Big Bay, Bay, rises onto higher higher ground ground of of Hovland Hovland Diabase Diabase complex. complex. Cross Flute Reed River, River, pass pass through village of Hovland at Chicago Bay, Bay, and and up onto aa large large sill—like sill-like body body of of syenogabbro. syenogabbro. Many road road cuts; cuts; some some show good foliation of of plagioclases, plagioclases, dipping dipping gently gently S. S. Syenogabbro, basalt pillow-breccia, pillow—breccia, and rhyolite at Brule Stop 7. 7. Syenogabbro, Brule River (Marr River (Marr Island quad.). Opposite Naniboujou Lodge, Lodge, park in in lot of Judge Hagney tmgney State State Park. Park. Walk up trail, trail, cross rivet river on footbridge, footbridge, Take care and follow fisherman's W bank. bank. Take care -— and follow fisherman's trail and bushwhack up W steep and unstable slope in in places. places. At footbridge footbridge is is medium—grained, medium-grained, foliated syenogabbro of of "Hovland "Hovland diabase diabase complex." complex." This is cut by basalt dike, dike, then gives way to a rather coarse—grained coarse-grained basalt aa later basalt lava with chlorite chloritescraps scrapsand andamygdules. mnygdules. Soon overlain by by Soonthis this is is overlain basaltic—scoriaceous tuff—breccia. basaltic-scoriaceous tuff-breccia. After a short short gap gap in in exposure, exposure, steep bank resumes resumes which is made of basalt pillow—breccia, steep pillow-breccia, with altered volcaniclastic matrix. This is is one of the the few few places places where evidence for evidence for underwater extrusion can can be seen seen in in the the North Shore Shore Volcanic Group (others (others are are on on Grand Grand Portage Portage Island Island and and WWof of Duluth Duluth in the Lower Lmyer Keweenawan). Keweenawan). Farther upstream this this can can be be seen seen to to overlie the altered, altered,flow—banded flow-banded and rled top top of aa very very large porphyricic porphyritic and styi swirled rhyolite the Bride Brule has has cut cut aa deep deep gorge gorge above. above. rhyolite flow through which the Return by fisherman's trail tr~il at at top top of of bank. bank. After crossing After crossing the the Brule (Arrowhead) (Arrowhead) River, River, the the highway rises rises over and cuts cuts through through three three hasalts basalts of of the the Brule Brule River River group, group, then then crosses a porphyritic trachyandesite trachyandesite or or intermediate intermediate quartz quartz latite latite the }larr Island lavas lavas at at Paradise Paradise Beach. Beach. AA few few more low low cuts cuts of of of the Marr Island this mixed group are this are passed passed in in next next 33 miles. miles. 3.8 3.8 5.8 Stop 3•x Stop 8.~ Porphyritic ~arr Island Islan~ Porphyritic intermediate intermediate quartz cuartz latite latite of p Marr lavas one one mile mile past past Cook Co. lavas Co. 14 (Kadunce (Kadunce Creek quad.) quad.) Two large road cuts cuts on N. thick, intermediate intermediate quartz latite latite road N. side of a thick, K 0) plagioclase, ferroaugite, and rare lava (62% (62% SiO Si0 , 4.1% K 0)with with plagioclase, ferroaugite, and rare 2 2 ex-olivine ana magnetie magnetitephenocrysts. phenocrysts. Contacts not exposed. exposed. ex—olivine an , �-89—89-Going SW Going NE 1 1/2 miles to the the west at Kadunce Creek (Kodonce (Kodonce River) River) miles to State Park a thick porphyritic felsite is exposed, especially especial~y in in a deep dl~ep and narrow canyon that begins about 1/8 mile upstream upstream from highway highway -— this this is part of the from the Kimball Kimball Creek Creek felsite felsite group, group, also exposed in Kimball and Cliff creeks farther also farther west. west. Excellent wave—cut cliffs abandoned wave-cut cliffs of of Nipissing Nipissing stage. stage. 7.3 3.2 3.2 Stop 9. 9. Olivine basalts of of Red Red Cliff Cliff series series (Kadunce (Kadunce Creek Creek quad.). quad.). Just past large gravel pit and and creek creek gully, gully, highway highway rises rises onto onto aa series flows totalling totalling between between series of of 5 or 6 ophitic olivine basalt flows 400 and 900 feet feet in thickness. thickness. Amygdules contain contain saponite,laumontite, saponite,laumontite, calcite, quartz, calcite, quartz, and and agate. agate. Plagioclase phenocrysts have floated floated to to top 0.5% K20. K 0. top in some, some, sunk to to bottom bottom in in others. others. 47% Si02 Si0 , 0.5% 2 2 Past Durfee Creek (near (near top of Red Cliff basalts) highway (and (and cliff) pass onto Devil Devil Track Track felsite felsite group, group, here here composed composed Nipissing cliff) of two thick flows. of flows. 9.6 1.0 Stop 10.* Felsite of Devil Track sEries, series, at promontory of of abandoned abandoned Nipissing wave—cut wave-cut cliff. cliff. N N side of highway, 0.85 0.85 miles west of of Pink, nonnon— or weakly porphyritic Durfee Creek (Kadunce (Kadunce Creek Creek quad.). quad.). Pink, rhyolite K20) slabby jointing rhyolite or quartz latite (72% (72% SiO Si0 2 , 5.5% K 0) with with slabby jointing 2 Bushwhack?ng along old cliff to E and faint flow—banding. flow-banding. Bushwhacking E for 1/4 1/4 mile one eventually passes down down into into vesicular, vesicular, locally locally spherulitic spherulitic and flow banded top top of a porphyritic flow flow of of similar similar composition. composition. and flow These two two flows flows total total about about 1020 1020 feet feet in in thickness. thickness. Five Mile (Guano) Rock, Rock, aa mile mile out out in in Lake Lake Superior, Superior, is ~uano) is made of diabase. , 10.6 0.0 0.0 3.7 Track~. upstream Cross Devil Track River. This cuts a deep gorge just upstream felsite flow. flow. Continue on Hwy 61 into Grand Marais, or or in the upper felsite alternatively turn turn off just before rise on small side road alternatively road (Cook (Cook Co. Co. 87) Stop 11. 11. 87) toward toward lake lake to to Croftville settlement and optional Stop (off Hwy 61) 61) (off (1.3) _~~ (0.0) (0.0) (0.45) Stop 11. Spherulitic hasal phase, phase, Grand Marais rhyolite, Croftville Croftville Stop 11. (Grand quad.) Drive about 1.1 mile along Nipissing terrace terrace (Grand Marais Marais quad.) over (about 0.45 mi. from WWend this road). road). over Croftville Croftville basalts basalts (about mi. from end of this Private Property. ?roperty. Ask permission at at the the house hous~ in in birches birches on on lake lake side, beach-back. Slabby, Slabby, spherulitic spherulitic side, exwline examine outcrops outcrops at at modern modem beach—back. red rhyolite rhyolite is is exposed here (73.4% (73.4% SiO SiO , 4.65% K20) K20) that that contains contains red hedenbergie, ex—fayalite and magnetite andesine-oligoclase and rare hedenbergite, ex-fayalite and magnetite andesine—oligoclase and rare Nearby is cross—bedded, calcite—cemented interflow sand. phenocrysts. cross-bedded, calcite-cemented interflow sand. phenocrysts. Strata have been steeply tilted tilted by diabase diabase intrusions. intrusions. Continue on on road until until it it re—joins re-joins Hwy Hwy 61. 61. Croftville road , (0.45) (0.0) (0.0) (2.1) (2.1) Continue SW SW to to Grand Grand Marais. Marais. (off Hwy H'YY 61) 61) Stop 12. 12. Breakwater trachybasalt (Good (Good Harbor Bay Bay quad.). quad.). Drive to E end of Grand Marais harbor. harbor. Tombolo to Coast Coast Guard Guard Station at E here is is made by gravel bar connecting mainland to to resistant resistant island and and ledges ledges of of aa massive, massive, locally locally columnar-jointed, columnar—jointed, porphyritic porphyritic trachybasalt or basalt with small phenocrysts of of plagioclase, plagioclase, augite, augite, trachybasalt and rare olivine. olivine. It 360 feet feet thick. thick. It It is not known It is is about 360 this is is a big flow certain whether this flow or sill; to to the the west is is has has for certain aa sharp, sharp, chilled basal contact contact against against felsite felsite but but its its top top is covered. covered. It It becomes amydgaloidal and zeolitized zeolitized near near contact is �Going SW Going —90— -90- NE its to be be aa flow. flow. As can be seen seen from from its top and is assumed to point, it it forms forms one of the the major major strike—ridges strike-ridges of of vantage point, "Sawtooth Range" Range" to to the the west (as (as does the the big "thomsonite "thomsonite sta~ting Good Harbor Harbor Bay). Bay). The harbor at Grand Marais Harais starting at Good probably eroded from from rhyolite. rhyolite. 3.7 0.0 0.0 9.2 this this the the flm.," flow" is is lint Trail Trail Highway 61 passes corner corner of of harbor, harbor, near near start start of of Gunf Gunflint (Cook Co. Co. 12). (Cook Then highway rises rises to W W past a good norphyritic porphyritic rhyolite rhyolite cut cut (Breakwater trachybasa1t trachybasalt cuesta cuesta ahead), ahead), then then onto higher level (Breakwater down across the the Breakwater Breakwater trachybasalt trachybasa1t and and across across Fall Fall River River back down (Rosebush Creek). About 1 mile past this this creek, low low road road cuts cuts start start in two two thick porphyritic trachyandesite trachyandesite to to andesite andesite flows flows (55% (55% Si02, 5i0 , 2 phenocrysts and and 2.7% K K 0) 0) with small plagioclase and clinopyroxene phenocrysts 2 ahead is vesicular-rubble is held up by Terrace Point vesicuar—rubble tops. Big cuesta ahead Continue across thomsonite-bearing basalt basalt flow. flow. Continue across Cut Cut face (Good (Good thomsonite—bearing Harbor) Creek. Creek. 5.2 3.9 Stop 13.* Thomsonite—bearing low sediments (Good Stop Thomsonite-bearing basalt, basalt, interf interflow (Good Bay quad.). quad.). In this this large road cut one of the major cliff Harbor Bay formers (130') section of formers of of the the "Sawtooth "Sawtooth Range" Range" overlies a thick (130') interf low sediments. The Terrace Point basalt is dominantly a interflow sediments. The Point massive, massive, fine—grained, fine-grained, ophitic basalt that that characteristically characteristically contains contains thomsonite its lengthy exposure (including (including in thomsonite in amygdu1es, amygdules, but hut in its this cut) cut) several several flow units units of of varying character show complex this relations with the major, massive relations massive part part of of the the flow. flow. The interfiow interflow sediment Is is here mainly thin—bedded thin-bedded siltstone siltstone shale, but by walking up up the the bed of of Cutface Cut face Creek Creek at at and silty shale, the bottom bottom of of this hill one passes the this hill passes outcrops of the the basal contact contact the amygdaloidal—scoriaceous amygdaloidal-scoriaceous top top of of of the sediments resting on the an flow and wellan andesite andesite flow and eventually reaches large banks cut into well— bedded sandstone showing abundant ripple ripple marks. marks. 9.2 — 0.0 0.0 16.9 0.5 0 5 16.4 16 4 cuts of the the complex complex upper upper parts parts of of the the Highway 61 passes low cuts Terrace Point flow complex, complex, with big cuesta cuesta on this this flow flow visible visible ahead, ahead, then then at at jct. jct. of of Cook Cook Co. Co. 7 passes into coarse—grained coarse-grained olivine olivine passes into basalt of the the Lutsen Lutsen basalt basalt series. series. Cross Cross Cascade River in State Park. Park. Trail up W W side provides access to to good good river river outcrops outcrops of of Terrace Point thomsonite thomsonite basalt, basalt, the the underlying underlying sandstones, sandstones, and and several andesite flows flows of of the the Good Good Harbor Harbor Bay Bay series. series. Drive past Cascade Lodge. Lodge. Stop 14* Cascade (Deer Cascade olivine olivine basalt basalt of of Lutsen basalt basalt series (Deer Yard Lake quad.). 0.5 miles W. W. of of Cascade Cascade River. River. Shore outcrops of aa thick (100 more), relatively of (100 feet feet or more), relatively coarse—grained coarse-grained olivine basalt this Cascade—Lutsen Cascade-Lutsen area. area. basalt of a distinctive group in this Segregation cylinders cylinders up up to to 6" 6" or so so in Segregation in diameter and segregation lenses lenses or sills can can be be seen seen within within this this flow. flow. Highway continues continues on on long long straight straight stretch roughly parallel parallel to strike of Lutsen basalts, topmost series of the the North North Shore Shore to basalts, topmost Volcanic Group. Group. Pass Pass through Lutsen village (big (big ridges rid?,es to to W held up W up by Leveaux trachybasalt trachybasa1t sill), sill), to to Poplar River. Rive~, �—91— -91- Going SN SW 9.3 Going NE ---7.1 Stop 15. 15. Poflyritic Porphyritic olivine basalts of Lutsen series series (Lutsen (Lutsen Poplar River. River. Watch Hatch your step step -- dangerous. Private land. land. quad.), Poplar Several flows flows of a distinctive ophitic olivine basalt characterized characterized by abundant small small(1—3 (1-3nun) mm) blocky bytownite phenocrysts are are exposed exposed by the Poplar from Poplar River River at at Lutsen Lutsen Resort, Resort, up up through through an an frcrnthe the mouth mouth of the canyon to to the the highway bridge bridge and upstream to left bend impassable canyon (1/10 highway). Take fisherman's fisherman's trail trail on on WWside. side. This (1/10 mile nile from highway). flow Ilprimitive" composition composition (lowest (lowest K, K, highest highest Mg) Mg) ?low type type has has the the most most "primitive' Si02, 0.l2I K20). L bend in river , 0.12% K20). At of the North Shore lavas (1+7% (47% Si0 2 it overlies breccia-rubble breccia—rubble top of aa basaltic andesite andesite flow; flow; red red sand sand has been washed into all the interstices between the lava blocks, has lava a typical situation. situation. 12.3 4.6 Leveaux —- Onion HtIl=Stop 16. Leveaux_ porphyry !411. Eill (Tofte Mtn. trachybasalt trachlbasalt porphyry SWof of Poplar Poplar R.. at slight L quad. ) . 2.5 mi. R•..at L bend cross cross Rollins Rollins quad.). ml. SH Creek and irnediately immediately turn up U. U. S. S. Forest Service gravel road road (No. 336). Continue on it it as as it contours back to SW, then then cuts cuts up up (No. 336). OnionRiver Mvergap gapininbig big ridge ridge held held up up by by aa big big trachybasalt into Onion into porphyry sill. sill. This sill forms forms Leveaux Mtn., the high ridge ridge with a fire tower a fire tower on on it ittotothe theSW, SW, and and comes comes out to the lake lake shore shore to to form the islands at Taccnite Harbor SN of Tofte. Its contacts at Taconite Harbor SH .of Tofte. contacts are are not exposed but it it crosscuts crosscuts the the lavas. lavas. Park as near as as possible possible to the S S corner corner of of the hill hill on on the the NE NE side side of of the the gap, gap, and and bushwKack bush~ack a short distance N n to to· the the steeper, steeper, rocky rocky rise. rise. Here the lower lower part exposed fine—grained, pigeonite-augite pigeonite—augite trachytrachy— of the sill sillis is exposed—- a fine-grained, to trachyandesite. trachyandesite. Farther up up the Glope slope aa bit bit abundant abundant large large basalt to (1 blockylabradorite labradorite phenocrysts phenocrystsappearroruptly; appeartruptly; they appear to (1 cm) cm) blocky to floated. This porphyritic phase forms have floated. forms the upper part of of the the throughoutits its extent. extent. sill throughout 16.9 2.... 0.0 0.0 ---12.1 Continue SW svr past Tofte. pastSawbill SawbillTrail Trail (Cook (CookCo. Co.2)2)atat village village of Tofte. Town Town park park on on lake lake shore 0.3 0.3mi. mi.SW SW of ofEdgewater Edgewater Motel Motel has has good good exposures of of thin-bedded thin—beddedophitic ophiticolivine olivine basalts. basalts. DO DO NOT exposures NOT DESTROY DESTROY FEATURES. These the top top of the section section of the orth NorthShore Shore FEATI.ffiES. Theselie lie at at the Volcanic Group. 10.1+ 10.4 anorthosite in diabase (Tofte Stop 17. 17. Carlton Peak ?lloythosite (Tofte quad.) 1.7 1.7 mi. mi. jet., opposite opposite large large Superior Superior National National Forest Forest SW of Sawbill Trail jct., Sign, Sign, turn up road of Erie Mining Co. Co. to large quarry in in side side of of Carlton Peak, anorthosite xenoliths xenoliths in in Peak, which is held up by massive anorthosite intrusion. Private Property. Property. The The complex complex rela.tions relations a gabbroic intrusion. between the the anorthosite anorthosite and and various various phases phases of of olivine olivine gabbro gabbro are are well well 1.7 exposed. 2.5 9.6 Stop 18. Thin—bedded ophitic olivine tholeiites of Thin-bedded of Schroeder Schroeder 18. basalts, Temperance Temperance River River (Tofte (Tofte quad.). quad.). Park at State Park lots, lots, walk down down trail to bridge near near river river mouth. mouth. Note excellent erosional Several thin flows flows or flow units, with ropy ropy surfaces, surfaces, pipe pipe potholes. anygdules amygdules and lensing lensing shape shape are are well well exposed exposed here. here. If more time is is available, walk up NE side of river above available, above highway to to the the main main gorge gorge where the river river has has cut cut aa very very deep deep and and narrow narrow slot slot with with larger larger into thicker olivine olivine basalts. basalts. Warning: people have have been been potholes into Warning people killed trying trying to to jump jump across. across. Large joint joint columns colUmns visible visible on on trail trail killed cylinders are are present in in thicker thicker flows. flows. and overlooks, overlooks, and vesicle cylinders �—92— -92- Going SW SH Going 3.8 3.8 NE 8.3 8.3 9.14 2.7 Drive SW SI'! through Schroeder and and Taconite Taconite Harbor Harbor (power (power pellet shipping facility of plant and taconite pellet shipping facility of Erie Erie fining Mining Co.) Co.) with occasional occasional low low cuts cuts of of ariygdaloidal amygdaloidal or ophitic olivine olivine tholeiite. tholeiite. Stop 19*. 19*. Thin—bedded Thin-bedded ophitic ophitic olivine olivine tholeiite tholeiite of of Schroeder Schroeder basalts basalts at Sugar Loaf Point (Little at (Little Marais Marais quad.). quad.). Private property. property. Drive down side road (just (just opposite gravel gravel road road from from uphill) uphill) at at Consolidated Consolidated Paper Co. storage and and handling handling facility. facility. Drive down to cove, cove, Co. pulpwood pupwood storage end ask ask permission permission to towalk walk onpoint opoint at and at office. office. Notice great old Walk around pine boom—logs to raft raft pulpwood pulpwood across cross lake. boom-logs used to lake. Halk Excellent exarrioles Sugarloaf Point clockwise clockwise from from end end of of beach. Excellent examples up) and thicker flows flmv units units (6" (6" and up) flo1>ls of ophitic "olivThe " olivine of thin flow tholeiites ,It with ropy ropy surfaces, surfaces, bent bent pipe pipe amyvdules, amye:dules, and and clastic clastic tholeiites," dikes dikes where sand was washed into into open open ;oints joints in in the the tops tops or of flows. flows. not remove or destroy structures! On On the the sides sides of Please do not destroy these thes~_Et~.~ures! the high high knob at the end can the can be seen seen vertical vertical tube—like tube-like concentrations concentrations arnydules ("vesicle of amygdules ("vesicle cylinders") cylinders") in in the massive Massive Imler lower nart tart of the topmost flow. flo",. 11.77 11. 0.14 0.4 12.1 0.0 0.0 11.0 Cross Cook/Lake Cook/Lake County County line. line. Ophitic olivine!-holeii:~s, tholeiites, Ma! !-S.?-chY.Easalt., tracybasalt, and Qphiti c_ olivine ~If~it0l.! strike—fault, Caribou River River (Little (Little ~larais arais quad.) strike-fault, Caribou quad.) Park Caribou Park at Caribou Falls State Park 1°t side of the the hip-;h,.,ray highway and "Talk walk ut Falls lot on the HH side up the (Between the the highway highway and Lake Lake is is private property including trail. (Between typical ophitic falls over typical ophitic olivine olivine basalts). basalts). In In the river riverand and aiocg alonr; the trail are a few outcrops the outcrops of the red red volcanic volcanic breccia breccia and and basalt basalt that underly the "Manitou "lvlanitou trachybasalt," then then at at aa LL bend bend is is the the NE— NEmost outcrop of most of the the trachybasalt. trachybasalt. lis ap]Jroaches the falls falls As the trail anproaches the river has the has cut through aa thick section section of of volcanic volcanic breccia, breccia, nut but aa large strike-fault intervenes between this and and the the typical typical ophitic ophitic large strike—fault olivine thoeiites (flio2=5-.7%, oli vine tholeiites (Si02==45-47%, K the cli f f Torn tt:e :20=o.3_o.5z) 20"'0. 3-0.5%) that form over which the the river river fells. fa.lls. Several flovs, 10-30' each, Several flows, 10—30' each, are visible in the the cliff each with a massive lower part and in and an an amygdaloidal amygdaloidal and and slabbv-jointed top. slabby-jointed These nearly all allthe thelavas lavasbetween between Theseare are typical tynical of nearly 1:ittle arais Little Maraisand andLutsen, Lutsen, the uppermost sequence sequence of of tbe the North North Chore Shore the uppermost Volcanic Group. Group. Stop Stop 20. 20. cli' 2.2 8.8 8.8 Dri ve SW, 8\1, cross cross anitou ~ftanitouRiver, River,'.rhich lIhi ch has Drive has cut cut aa deep deep f!;orge aorge throup;h throu'h drift and olivine basalts (trail in State State Land Land accessible accessible drift (trail up up streaxn stream. in on SW S1:T side via via gravel gravel pit pit road), road). Commercialized has Cornniercializedgonre gorge dmmstrear'l downstrean has falls, sea arches. falls, Continue LW bend at at Little Little I·,farais Marais R. . SH almost to to I? H bend 14.5 4.5 6.5 6.5 Stop 21. 21. Manitou trachsasait (Little Stop !5~j.~.sm !-!_a~J1_x.:!?~a1.!-. (Littlei'larais Marais quad.). quad.). Turn 'I'urndo'.in down road at Ben Fenstad's Fenstad's Resort, Resort. Private ask permission Private nrqperty; property; ask for entry at for at office. office. Continue down to lakeshore, bearing bearinp. left left to to end of driveway dri vevay loop at at fishhouse. fishhouse. here here at B.t the the end end of of the the slit slin is is exposed the base of an 1arre larp,e flow flow of of granular granular trachvbasalt, trachybasalt, at at least least 300' rLles lonp" long, that forns ofth~SDreledges t1roreledges Croa 300' thick and 55 miles forms !'uch much of fro~ breakwater on, HE of M8ni this breaki-mter on, both SW G\l and and tIE tou FLyer. Pi vel". It contains contains Menitou Si022 and 2.3% about 52% 52;~ Si0 K2 (), and and has has labradorite. labradorite, augite, aup.;i te, and and 2.3 K20, and abundant ahundant KK feldspar feldspar and and altered rare olivine phenocrysts and pigeonite piGeoni te in in the the groundviass. groundmass. higher hip:,her in in the flow fIm, it it is is coarser— coarser- �—93— -93- Going SW Going SE HE grained, less less potassic and Its top is grained, and less less porphyritic. porph~ritic. Its is not exoosed. It overlies overlies aa sequence of interLedded eXDosed. It interbedded basalts and red red volcanic volcanic breccia breccia or or conglorierate. conglomerate. high ridge inland is held up by Continue Li ttle 'arais. ~1arais. High Continue S\J SW past Little a thick intrusive diabase sill containing a thick intrusive diabase containin~ some anorthosite blocks. blocks. 8.0 8.0 9.1 9.1 2.6 Stop 22.* .iartz tholeii tholejite—trachybasalt, Kennedy Landing 22. * QJ.artz te-trachybasalt, Kennedy (Finland quad.) quad.) Good cuts for for about about 1/3 mile through throu~h several several typical auartz quartz tholeiites tholeiites to to trachybasalts. trachybasalts. They show the the charcharacteristic fine-grained, fine—grained, aphyric anhyric texture, texture, oxidation lamellae, and acteristic and scoria-rubble feldspar scoria—rubble tops. They contain interstitial alkali feldspar and about about 51-53% 5l—53 5102 and Si02 and and up up to to 2% 2% K20. K20. Red sand, sand, locally cross— crossbedded, fills the interstices between fragments. fragments. Large knob knob bedded, fills is made of the thickest of of these flows. flows. overlooking the bay is 7.8 7.8 Stop 23. in ~y~nogllR..br~; syenoabbro; overturned Anorthosite in 23. ** An_,?rth,?sitE:. ove!:turned lavas l~vas (Illgen City quad.). quad.). After crossing crossing Kennedy Creek Creek come come to to deep deep vertical cut cut in an irregular discordant intrusion intrusion (part (part of of Beaver Beaver Bay complex) Day complex) of altered syenogabbro that contains contains aa great, great, massive massive of rather After examining this, walk block of rather pure pure anorthosite. anorthosite. After examining this, walk or drive SW drive SW downhill cut that sequence of of downhill to to lower cut that is is composed of a sequence several basaltic basaltic lavas lavas with an interflow sediment bed — several - all all of which which have been overturned, overturned, probably as as aa result result of of forceful forceful intrusion intrusion of nearby diabases. These basalts show show aa variety variety of of structures, structures, including at the NE end end some some including some some lobes lobes that that look like pillows and at red scoria,-rubble scoria—rubble that that is is characteristic of the top part of the red fine—grained tholeiites, tholeiites, basaltic andesites, fine-~rained andesites, and trachybasalts. trachybasalts. 11.0 42 0.0 0.0 0.0 It.9 ~ Continue to Ulgen lilgen City, City, ~ Lc•• •with Rte.ito Continue SW to Tith Minc. Minn. Rte. -.l to Ely. Ely. Just .Just to NE are cuts cuts in in quartz tholeiite flows, flows, to to SW SW cuts cuts in in altered rhvolite. rhyolite. 0.45 0.45 4.5 24.* Stop 21~. Palisade .!1~_a~ Head P.s>E1?-~)'Ti pohyritic Stop * ~~~isad~, tic:: rhyolite, rhyolite" Shovel Shovel Point Point (Illgen (Ingert City quad.3. quad.). 0.45 0.b5 mile SW SW of of Illgen Illgen City City jct., jet., or or 0.145 0.45 mile NE of Baptism River, River, search for NE for unmafled unmarked trail leading leading to to shore shore Here is at Shovel Point in at in Baptism Baptism 9. R. State State Park. Park. Here is well exposed the upper-middle upper—middle part of porphyritic rhyolite rhyolite the of the the thick thick (>300'? (>30d: porphyritic (quartz (quartz latite) latite) that that also also forms forms Palisade Palisade Head to to the the SW and the road cuts at at Tllgen III~en City. City. Take care on on clifftop. clifftop. View to SW over underlying lavas ("Baptism ( "Baptism basalts") basalts ") and and some some mafic mafic intrusive intrusive bodies, bodies, to Palisade Palisade Head. Head. Follow trail down dipslope to end end and and corner: view TIE toward overlying overlying quartz quartz tholeiite flows. NE corner: NE toward flows. Return on sa1Ie same trail trail _._----~ Drive Head (big (big hill hill with with Drive 811 SW across across Baptism !liver River to Palisade head radio beacon). 2.1 2.7 (Iliren joint (Tity quad.). quad.), Stop 25. 25. Palisade Drive up up Palisade Head Head rhvolite r1yaUiq. (Illgen City narrow, winding road--C,ju;t'" road (just past--Palisade past Palisade Creek) Creek) to to top top of of cliff cliff next to raOio careful — columns are radio beacon. beacon. ,9areful - joint colwnns are se-narating separating Excellent views from rest of of hill. hill. ~xcellent views to to .N, ~, NE, SE, SE, SW. SW. Ridges to �—94— -94- Goin,:?; GoinI SW Going NE "[IT, NE aie B,Te held up by intrusions intrusions of of Beaver Beaver Bay Bay complex. complex. Up Up N. lakeshore to NE is columnar—jointed columnar-jointed Shovel Point, Point, made made of of same same rhyolite flow, is smoke from Taconite Harbor flow, and far far beyond is plant and and Carlton Canton Peak power plant Peak anorthosite anorthosite knob knob at at Tofte. Tofte. To S across lake lake are are Apostle Apostle Islands Islands and Bayfield Peninsula, Wisc. across Wise. To SW is Reserve Mining Co. Co. taconite plant at at Silver Silver Bay Bay and and humpy humpy Palisades made of thick, por— topography of Beaver Beaver Bay Bay complex. complex. Palisades porrhyolite with quartz quartz and and feldspar feldspar phenocrysts, phenocrysts, flow— flowphyritic rhyolite banded at the base. Return to to highway. highway. 1.9 4.9 0.0 0.0 0.0 0.0 i1.8 14.8 0.4 l.3 14.3 0.14 at Silver Bay, 2.15 ml. mi. to traffic light light at Bay, site of Drive 2.75 Co. 's taconite plant where where about about 100,000 100,000 tons of ' Reserve Mining Co.'s rock from the eastern eastern Mesabi Mesabi Range Range are are processed per day. day. Stop 26. 26. Anorthosite in in diabase diabase of of Beaver Beaver Bay Bay complex, complex, Silver Silver (Silver Bay Bay 15' 15' quad.). quad.). Stop at road cut cut directly directly opposite opposite Bay (Silver the main building taconite plant (after building of of the the Reserve Reserve Mining Mining Co. Co. 's 's taconite (after Here several large blocks of anorthosite the' 2nd lights). anorthosite the traffic lights). 2nd are in the Beaver Beaver Bay Bay are included in diabase, a typical assemblage in complex. Large patches of of interstitital, interstitital, poikilitic poikilitic olivine olivine occur occur in anorthosite. No definite source source for for the the in some parts of the anorthosite. Small red red veins veins and and dikelets dikeletsofof"granoph~y'.(e" "granophe" anorthosite is is known. Small cut the diabase and and anorthosite. anorthosite. across Beaver Beaver River River to to Beaver Beaver Bay. Bay. Continue SW 2.8 miles across 3.2 3.2 11.6 Stop 27. St,up 27. Beaver Beaver Bay ferrogabbro and and Black Black_ Bay_ gabbro (names (names after y ferrogabbro Gebman) Gehman) of Beaver Bay Bay complex complex (Silver (Silver Bay Bay 15' 15' quad.). quad.), Drive or down to shore shore on on gravel gravel road road opposite opposite the the main main restaurant restaurant In tn walk down Beaver Beaver Bay. Bay. Walk E E through woods across little little point point to to shore shore ledges. These are well-foliated ferrogabbro of of the the Beaver Beaver Bay Bay well—foliated ferrogabbro Ferrogabbro, one one of of two similar similar plugs plugs in in this this area. area. On walking NE along the shore, the contact contact with an an enclosing enclosing ring—dike ring-dike of of Black Black Bay Bay Gabhro Gabbro is reached; reached; such rings rings surround both ferrogabbro is ferrogabbro plugs. plugs. It is rather It is inhomogeneous and locally contains very abundant apatite. inhomogeneous apatite. The The ophitic ophitic Beaver River Gabbro can can be seen farther shore below some some farther along the the shore cabins. Return to to highway. highway. - Continue SW through Beaver Bay complex; complex; most outcrop outcrop is of is of coarsely mottled, mottled, ophitic olivine gabbro ("Beaver ("Beaver River River Gabbrot' Gabbro" of of Gehman), Gehman), well well seen seen opposite opposite Kings's Kings's Landing 3 miles miles from from Landing Marina Marina 3 Beaver Beaver Bay. Bay. After 2.2 more miles road road branches to to Split Split Rock Rock Lighthous,buil on Lighthouse,built on anorthosite anorthosite in in diabase. diabase. At Day Hill Hill (parking (parking At Day and 1.0 mile beyond, is and trail), trail), 1.0 is last exposure of Beaver Bay Bay complex. Re—enter volcanics, continue 5.14 5.4 miles to to Gooseberry Gooseberry complex. Re-enter volcanics, continue Falls State Park. Park. 114.8 14.8 0.0 0.0 0.0 13.1 l3.i Stop 28. Stop 28. Smooth—surfaced Smooth-surfaced olivine olivine basalt, Gooseberry Falls Falls State basalt, Gooseberry State Park Park (Split Rock Point quad.). ~Split Rock P6int quad.). Below highway bridge are good exposures, highway bridge are good exposures, in. and between falls, of Columnar—Jointed olivine ln, and between falls, of columnar-jointed olivine basalt basalt lavas lavas with with ainygdalojdal tops, tops, and amygdaloidal and smooth, gently gently billowing billowing surfaces. surfaces. Continue SW through Castle Danger (2.L Continue (2.4 mi.), across Crow Crow Creek Creek ml.), across (a diabasic diabasic intrusion intrusion here (a returns soon soon to to SW SWat here returns at deeply deeply weathered weathered Lafayette Lafayette Bluff), Bluff), through through Encampment Encampment Porest owned old— oldForest(privately (privately owned growth forest with growth forest with summer to to Silver tni~~ summerhomes) homes) SilverCliff Cliff(anothp~ (anoth' +1I41- �Going NE Going SW SW —95— -95- intrusion) to outskirts of Two Harbors. gabbroic intrusion) 12.7 0.5 Stop 29. 29. Quartz tholeiite basalt, Two Harbors city park (Two (Two Stop Just before entering town, Harbors town, turn turn toward toward lake lake at at I:arbors quad.). quad.). Drive past Burlington Wa—Ke—Ya Motel. road to to city city camp camp ground and and Wa-Ke-Ya Burlington road Bay, and up up aa hill. hill. Park at hilltop picnic area, walk walk EE to to shore, shore, Bay, and then S. S. Well exposed contact between amygdaloidal, amygdaloida1, weathered weathered then (ex—laumontite) top of of one basalt and massive basal part of an (ex-laumontite) top analyzed fine—grained, fine-grained, aphyric quartz tholeiite tholeiite (50% (50% 5102, Si02, 0.6% K20). Local thin sand lenses near and and at at contact; contact; traces traces of of Cu have been been found. found. The tholeiite shows shows occasional small small quartz— quartzagate and chlorite amygdules amygdu1es and and typical typical incipient incipient sheeting— sheetingfractures with thin .of this this thick thick thin bands bands of of oxidation. oxidation. Upper Upper zonezone' ,of tholeiite can be examined to to S. S. toward toward power power plant; plant; it it becomes becomes rubbly, vesicular, brecciated, with abundant rubb1y, vesicular, abundant laumontite. laumontite. Return to Hwy 61. 13.1 0.0 0.0 20.6 20.6 20.6 0.0 0.0 0.0 5.9 (3.0) (3.0) (3.0) Continue SW to traffic light in in Two Harbors. Harbors. At west end of town town take express highway highway to to Duluth. Duluth. Many cuts cuts of basalts and minor diabase intrusions. At-about At- about 17.7 11.7 miles Moose Moose Mtn. is is seen seen inland, inland, held up by Lester River diabase sill. sill. At 20 20 miles jct. jet. with old old St. Louis Louis Co. Co. 61), 61), and and at at 20.6 20.6 miles miles Lester Lester River River Hwy 61 (now (now St. either continue continue straight on Hwy bridge. Just beyond, beyond,either Hwy 61 61 (London (London Rd.) Rd.) direct to downtown 6 miles ahead, ahead 9 or or turn turn uphill uphill on on Minn. Minn. 23 23 (60th Ave. Ave. E) E) across ItR tracks to to Superior Superior St; St; go left. (60th RR tracks left. Stop Stop 30. 30. Tischer Creek felsite felsite and and Endion Endion sill, sill, Congdon Congdon Park Park (Duluth quad.). Examine outcrops beneath bridge; then then walk walk up up on WWside side of of creek. creek. There are some some impassable impassable trail that starts on places where you must climb climb up up to to aa bank—top bank-top trail trail on on WWside. side. part of of section cuts cuts through orange, foliated foliated felsite felsite with with Lower part through orange, flow inclusions, Clut by two two flow structure, structure, quartz veinlets, occasional inclusions, out by or three basaltic basaltic dikes. dikes. Upstream at top of of steeper steeper part part of of gorge gorge the stream cuts down into red granophyre top top of of Endion Endion sill. sill. Upcuts gradually gradually down down into into intermediate, intermediate, then then gabbroic gabbroic stream the creek cuts rocks of main part of Endion sill. rocks of Endion sill. At Vermilion Road bridge (second (second bridge above Superior St.) St.) still still in in lower—middle lower-middle part part of of sill; sill; return via trail trail or Congdon Congdon Parkway Parkway on on W. W. side. side. See Ernst, Ernst, 1960. 1960. Continue SW on Superior St. St. over rise rise held held up up by by Endion Endion Sill. Sill. 5.0 5.0 0.9 0.9 5.9 5.9 0.0 0.0 0.0 0.0 11.2 11.2 Stop 31. 31. Basaltic-andesitic interflow sandstone, sandstone, Leif Leif Basaltic—andesitic lavas, interflow Erickson Park, Duluth Duluth (Duluth (Duluth quad.). quad.). At lath 10th Avenue E. E. turn turn off off Superior St. Road at at Leif Leif Erickson Erickson Park. Park. St. toward lake to London Road I Walk over footbbridge footbbridge near near "viking "viking ship" ship' to t shore. shore. Weakly por— porphyritic basalt or basaltic basaltic andesite andesite ledges ledges behind behind stage. stage. Rubbly Rubbly (weathered?) (weathered?) top top to to NE NE is is directly overlain by a thick thick cross—bedded cross-bedded sandstone, that is is cut cut by by aa small small dike dike at at NE NE sandstone, strongly epidotized, that more flows end of beach. Several more flows exposed along shore shore to to SW. SW. anc Superior Superior Street, Street, downtown downtown Duluth. Duluth. Lake Avenue and (approx.) ~approx.) 1L 11-22 approx.)) :approx. o. a 0.0 Drive SW on Hwy 61 past Point of Rocks Rocks through Duluth Complex Thomson Hill Hill to to Nopeming. Nopeming. Turn R R at (St. Douis 13), up Thomson at Midway Midway Road Road (St. Louis ~o. o. 13), drive uphill about 0.9 mi. mi. almost almost to to top top of of rise. rise. �—96— -96- Stop 32. 32. Basal (Puckwunge?) (Puckwunge?) sandstone, basal basalts of of Lower Lower Keweenawan Ke\veena\van ('Grandview ("Grandview Golf Course" locality, locality, Esko Esko quad.). quad.). Drive or walk E E on road toward toward Cloquet Cloquet city city water supply supply tank tank on on hill. Pass low outcrops of vertical Thomson slate slate and and graywacke graywacke (Middle Precambrian: more are exposed (Middle exposed on on rise rise and and roadcuts roadcuts to to N.). At slope, go either RR or LL along along base of of slope slope to to outcrops outcrops N.). At slope, of basal Upper Precambrian quartzite and and conformably conformably overlying mafic, porphyritic basalt with small augite mafic, augite and and altered altered olivine olivine to rocks rocks on Lucille Island Island at at Grand Grand Portage. Portage. phenocrysts identical to Note pillows subtly outlined by small vesicles and and color color zones. zones. �—97-. -97- TO THE GUIDE TO THE PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS OF NORTHWESTERN COOK COUNTY COUNTY AS EXPOSED ALONG ALONGTHE THE GUNFLINT GUNFLINT TRAIL AS EXPOSED Prepared by by Paul Paul W. \~. Weiblen Department of Geology and and Geophysics Geophysics University of Minnesota Hinnesota Minneapolis, Minnesota Minneapolis~ G. B. Horey G. B. Morey Minnesota Geological Survey Survey University of Minnesota Minnesota St. Paul, Minnesota '1. G. Mudrey H. G. Minnesota Geological Survey Survey University of of Minnesota Minnesota St. Paul, Paul, Minnesota �—98— -98- Geology of Northwestern Cook County, County, Minnesota INTRODUCTION An exceptionally complete complete Precambrian section is exposed in the vicinity of the the Cunf Gunflint County. lint Trail Trail in in northwestern northwestern Cook County. Rocks Precambrian age, age , represented by a volcanic Rocks of Early Precambrian succession and the the Saganaga Granite, are are unconformably unconformably overlain by by the the Middle Middle Precambrian Precambrian Animikie Animikie Group,coiLsisting Group, cOllsisting of of A low anglular unconformity the Rove Fotmations. Fo~ations. A the Gunflint and Rove separates strata from from the the nverlying f1verlying Puckwunge Puckwunge separates the t-1iddle Middle Precambrian strata Rocks Formation of Late Precambrian Precambrian age. age. The Logan Intrusive Intrusive Rocks and the Duluth Duluth Complex, Complex, which which intrude intrude and and truncate truncate the the Middle Middle Precambrian Precambrian the strata, strata, comprise comprise the the major major part part of of the the Upper Upper Precambrian Precambrian section. section. However, However, possible remnants remnants of the North Shore Volcanic Group occur at the top of Duluth Complex at Complex rocks. rocks. The geology of the area was summarized in 1959 by Grout and Because geologic mapping mapping since since 1962 has has considerably considerably reBecause revised the the geologic history of the the area, area, and because much of of this this work is is as yet unpublished, unpublished, aa comprehensive comprehensive summary summary is is presented here. This discussion is meant to to provide a framework for the the specific aspects of the the geology geology which which the the chosen chosen stops stops illustrate. illustrate. others. Lower Precambrian Introduction The Lower Precambrian rocks rocks in Cook County are the eastern extension of the Vermilion greenstone greenstone belt belt (Sims (Sims and and others, others, 1971, 1971, has shown that the district contains many in press). Gruner (1941) (1941) has major longitudinal longitudinal faults faults that that divide divide it it into into long long segments segments or or belts, belts, each with distinct distinct characteristics. characteristics. They cannot be connected stratigraphically with each other in in any any simple simple way. way. One segment segment extends from from Gabimichigami Lake Lake across across the the Gunflint Gunflint Trail Trail (Fig. (Fig. 1). 1). It It includes aa metavolcanic assemblage consisting consisting of of metabasalt, metabasalt, metaandesite, tuff, hornblende andesite porphyry, porphyry, metaandesite, agglomerate and tuff, metagraywacke and and slate. the Saganaga Saganaga and intercalated metagraywacke To the north, north, the slate. To Granite has has intruded and and metamorphosed metamorphosed the thevolcanic volcanicsuccession; succession; it it is overlaintotothe thesouth south youngerrocks rocksofofMiddle Hiddleand andLate LatePrecambrian Precambrian is overlain bybyyounger age. �-99—99— The metavolcanic assemblage constitutes constitutes aa homoclinal homoclinal sequence sequence towardwhat whatGruner Grtinerinferred inferredtoto be be the the axis \"hich dips dips southward southward toward which Pillow—topdirections directions of aa southeastward—plunging of southeastward-plunging synclinorium. Pillow-top indicate that thatthe thesequence sequence alsO also becomes becomes stratigraphically stratigraphically younger younger the south. However, However, some pillows pillm"s top top to to the the north north indicating indicating to the folding, but but poor exposure exposure precludes precludes detailed evaluation of the folding, structure. wasthought thoughttoto separate separate the Previously, an an unconformity unconformity was the mafic and rocks; thus thus the thesuccession successionwas was subdivided subdivided mafic and more morefelsic felsic rocks; metabasaltswere werereferred referredtoto as as part part of into two two formations. formations. The The metabasalts of the Ely whereasthe themore morefelsic felsicvolcanic volcanic and andclastic clastic the Ely Greenstone Greenstone whereas rocks \Vere placed placed within within the theKnife KnifeLake LakeGroup. Group. Recent mapping mapping rocks were (Fiorey andothers, others, 19(9) 1969) has has sho\Vn shownthese theset\VO twolithologies lithologies to (i-iorey and to be be other parts parts of district gradational, and gradational, an(~ nappin mapping in other of the the Vernilion Vermilion district (lorey 1968; 1971, (~Iorey and and others, others,1970; 1970;Green, Green, 1970; 107(); Sims Sims and and others, others, 1968; 1971, in press) has shown shm.;n that that specific specific rock rock types types are are not not diagnostic diagnostic particular strati~raphic stratigraphichorizon horizon—i.e., any particular - i.e., lithologic lithologic units units therefore no formal are formal stratigraphic stratigraphic are not not time-stratigraphic time—stratigraphic units units -— therefore used for for these nomenclature is is now no\V used these rocks. rocks. of Descriptive Stratigraphy Descriptive Stratigraphy Volcanogenic Rocks Volcano;;enic Detailed mapping in the Long Island Lake quadrangle, Detailed mappinR in the Lonfl Island Lake quadrangle, reconnaissance reconnaissance as far west \"est as Va>' Fay Lake Lake in the the Cillis GillisLake Lake quadrangle, quadrangle, and and as far Gruner's area have have indicated that the thevolcanigenic volcani8enicsequence sequence Grunerts Hark work in in the area indicated that of approximately 60 percent inetabasalt metabasalt and fragconsists of and associated frag— mental rocks, 30 percent netnandesitic agglomerate, conglomerate, tuff, mental rocks, 30 percent metaandesitic agglomerate, conglomerate, tuff, and flows, and and slate. slate. and flows, and 10 10 percent intercalated intercalatednetagraywacice metagraywacke and mappin rr.appin,~ IjuLLaaLs.st±1psis!; percent ofofthe :i.eta_~~i1.sa-h.~~_?.~(LQ.~sg ..0at~_~.t ro_c±,-s_: Over 95 95 percent themeta— metabasalt is basalt is extrusive; extrusive; there thereare areseveral severaltabular tabularbodies bodiesofofmetadiabase, metadiabase, rLall to too small at aa scale of to show shmv at of 1:24,000. 1:24,000. Nany Manyofof the the metabasalts exhibit pillow exhibit pillm-J structure. The pillows pillo\Vs are are as as much as as three three feet feet in in diameter, but many diameter, manyhave havebeen beendeformed deformedsosothat that they they are are now no\V two two or three three times times as as long lonf, as as they they are are wide. \"ide. Chilled rinds rindsare arewell—developed 1vell-developed and as much much I1Sasone-half inch thick: in and are are as one—half inch thick:typically typicallythey theyare are lighter lighter in color than interiors. Inter-pillm" color than the the dark dar:( green green or ordark darkgreenish—gray fJreenish-Rray interiors. Inter—pillow material locally material locally is iswell welldeveloped developed and and co!nists con~ists of of tuffaceous tuffaceous material material cEtert, chert, or or pillow—rind pillm,,-rind fragments. fragments. Themetabnsalts metaasalts shot: intense retrograde retrograde alteration; alteration; many The shoH intense many thin thin sections sections are nre nearly nearlyopaque. opaque. Recognizable Recognizable minerals include minerals includerelict relict augite augite and anu calcic cnlcic plagioclaso, plagioclase, and and secondary secondary sodic sodic plagioclase, plagioclase, actinolice, chlorite, actinolite, chlorite, epu'ote, epidote, calcite, calcite,quartz, quartz,leucoxene, leucoxene, and opaques. Property of oj C. C. Patrick Ervin Ervi n �—100— -100- The tabular bodies of metadiabase have have aa relict relict poikilitic poikilitic texture texture -— actinolite pseudomorphs after augite -— and a mineralogy much like that that of of the the metabasalts. Thin beds and mineralogically immature immature meta— metabeds of texturally and clastic rocks are locally intercalated intercalated with the the metabasalt. metabasalt. Several beds are crudely graded and have a texture suggestive of a pyroclastic a pyroclastic Most layers, layers, however, however, appear to be epiclastic with with pebblepebble— Most to be origin. to silt-size silt—size clasts of locally derived to derived metadiabase metadiabase in in aa finer—grained finer-grained matrix of chert, chert, plagioclase, plagioclase, hornblende, hornblende, chlorite, chlorite, and and sericite. sericite. Hornblende andesite prophyry and and related related rocks: rocks: There are two two types of hornblende-biotite hornblende—biotlte phenocryst bearing types bearing rocks. rocks. Both are light light greenish—gray greenish-gray in in color. color. One type type lacks lacks internal internal structure. structure. The ground plagioclase, lesser biotite, opaques opaques and and mass consists of plagioclase, lesser amounts amounts of biotite, rare secondary calcite. calcite. The other type type has similar rare quartz and secondary phenocryst and groundmass mineralogy mineralogy but but is is composed composed of of angular angular to to rounded, cobble—s,'ze clasts and and is is inferred inferred to to be be aa volcanic volcanic breccia rounded, cobble-s~ze clasts or agglomerate. Metagraywacke and and slate: slate: In the vicinity of Fay Fay Lake in in the the Gillis Lake quadrangle, quadrangle, the volcanic rocks inter— Gillis the felsic felsic volcanic rocks apparently interfinger, meta— finger, or are infolded with agglomerate agglomerate or conglomerate, conglomerate, metagraywacke, and and slate. slate. Amphibolites: The metamorphic effects of of the the Saganaga Saganaga Granite Granite metabasalts becomes becomes apparent apparent only only within within several several hundred hundred feet feet on the the metabasalts of the contact. contact. Away from from the the contact, contact, the the metabasalt contains incipient hornblende; hornblende; nearer the becomes granular granular incipient the contact, contact, the the rock rock becomes and consists of hornblende and and and calcic calcic plagioclase; plagioclase; at at the the contact, contact, the rock is strongly strongly schistose. schistose. The the The schistosity parallels the granite contact, contact, as does does a well—developed well-developed foliation foliation within within the the granite. granite. Saganaga Granite General General Statement: Statement: The Saganaga Saeanaga Granite Granite (A. (A. Winchell, Hinchell, 1888) 1888) (Fig. 1) 1) is is aa late-kinematic late—kinematic composite intrusion emplaced (Fig. arouno emplaced around 2,700 m.y. m.y. ago in older volcanic rocks rocks and and the the Northern Northern Light Light Gneiss. Gneiss. Inch— Inch- to foot—sized foot-sized inclusions inclusions of of both both rock rock types found in in the the types are are found granite. granite. The main phase, phase, which comprises comprises 85 85 percent of the the outcrop outcrop percent of area, "quartz—eye hornblende—bjotjte area, is is aa medium—graineci medium-grained "quartz-eye" hornblende-biotite tonalite. tonalite. Other Other phases phases include: include: 1) border phase, phase, found found along aloTIC' the the southern southern 1) a border margin of the the batholith margin of batholith and and along along the the base base of of a roof roof"pendant of pendant of the the Northern Northern Light Light Gneiss; Gneiss; 2) 2) aa younger younger fine—grained fine-grained tonali te which ,vhich tonalite lacks conspicuous lacks conspicuous tquartz_eyes?T; "quartz-eyes"; 3) 3) aa coarse—grained coarse-grained biotite—fluorite— biotite-fluoritebearing bearing granodiorite; granodiorite; and and 4) 4) aa quartz—feldspar quartz-feldspar pegnatite pegmatite which which occurs occurs as veinlets as three three feet as veinlets as as much much as feet wide wide in in the main phase. the main phase. �—101--101- Hain Phase: This "quartz eye"-bearing :iain This phase phaseisis aa "quartz eye"bearing tonalite containing 20 20 percent 1-6 percent percent percent quartz, quartz, 60 percent oligoclase, 1—6 microcline, up to 8 percent biotite, 6 percent hornblende, and microcline, to 8 6 percent hornblende, and 1-4 epidote. Other minerals include clino—pyroxene, clino-pyroxene, 1—4 percent epidote. muscovite, chlorite, muscovite, chlorite, sphene, sphene, apatite, apatite, zircon, zircon, calcite calcite and and opaque opaque oxides. Cataclastic deformation of the the tonalite tonalite· is is indicated indicated by by strong undulose extinction and granulation of strong of the the quartz quartz and and abunabundant mortar and mylonite mylonite zones. zones. dant Phase: The border phase is is aa quartz quartz bearing, bearing, hornblende hornblende Border Phase: diorite that that is gradational with the the "quartz—eye" "quartz-eye" tonalite. tonalite. This diorite is well developed along the phase is the southern southern edge edge of of the the batholith batholith in in feet wide, the is as much as as 1000 feet the Long Long Island Island Lake Lake quadrangle quadrangle where it is and Moose Bay area in Ontario where and in the Noose ,,,here it it is is found found along along the the roof pendant of the the Northern Northern Light Light Gneiss. Gneiss. Foliations Foliations underside of a roof rock are everywhere similar, in and in in the the country rock everYWhere similar, in the the border phase and and it is inferred that that the the border phase phase was was produced produced by by partial partial assimilation country rocks of mafic composition composition (Halford, (Halford, 1969). 1969). assimilation of of country Younger Tonalite: Tonalite: A A tonalite characterized characterized by by aa lack lack of of "quartz—eyes," aa fine—grained "quartz-eyes," fine-grained equigranular texture, texture, and and abundant abundant hornblende and biotite biotite crops out in the the Horseshoe Horseshoe Island Island area area of of hornblende crops out Saganaga Lake. Lake. This tonalite tonalite is is not not sheared sheared which ,,,nich indicates indicates that that it the main phase. phase. it was was emplaced after deformation of the Internal Structure: Structure: Linear structural elements marked by an an alignment "quartz eyes" and/or elongate hornblende grains grains are are alignment of 'quartz in the the border border phase. phase. Lineations in in the the border border well developed only in phase plunge gently southeastward. southeastward. In contrast, contrast, lineations in in the the main phase are are random. random. Structure All the minor structural elements elements in in the pre—Saganaga rocks rocks in in All the minor the pre-Saganaga the plunging the Long Long Island Island Lake Lake quadrangle reflect a southeasterly plunging synclinorium. synclinorium. In northwesterly-trending fault fault in addition, addition, a major, major, northwesterly—trending (Lookout Fault, Sims Sims and others, (Lookout Fault, others, 1969) 1969) separates rocks rocks showing showing no no metamorphic effect of of the the Saganaga SaganagaGranite Granitefrorn.those from;those that that do. do. The metamorphic effect fault is is marked marked by by aa topographic low fault 1m" developed in in aa breccia breccia zone zone as much as 50 feet as feet wide. wide. The breccia consists consists of highly sheared metabasalt in aa matrix of massive quartz quartz and and calcite. calcite. Fracture cleavage is is present present throughout the cleavage the area and and commonly commonly parallels parallels the the Fault. Southeastward Lookout Fault. formed by by bedding/ bedding/ Southeastward plunging plunging lineations lineations formed cleavage intersections developed. These lineations intersections are locally well developed. are consistent are consistent in orientation with mineral lineations lineations developed developed in in the amphibolites itself; obviously obviously all all of of these these the amphibolites and in the granite itself; structures tectonic event. event. structures are related to the same tectonic �—102— -102- related to to the the final final The Lookout Fault also apparently was related the Saganaga Saganaga Granite. Granite. Previously it was assumed emplacement of the (Grout, (Grout, 1936) 1936) that that the the granite granite was was emplaced emplaced into into its its present present position via a west\vard westward rotation rotation of about about 700 70° about about aa north—south north-south that the the eastern part part of of the the granite granite and and the the axis. This implies that represent roots roots of the Light Gneiss Gneiss represent the batliolith batholith that thatwere wereonce once Northern Light However,Goldich Goldichand andothers others (1968) as much as 25 miles deep. However, (1968) have have as much as 25 miles deep. that the granite was originally intruded at a shallow depth— suggested that the granite was at a depthan observation more consistent consistent with with the the regional regional Abukurna Abukuma greenschist facies (Mudrey, 1969) to its present present facies metamorphism metamorphism (Mudrey, 1969) -— and brought to relative position position by by dominantly vertical movements along several relative several westerly-trending border faults. faults. The granite—greenstone granite-greenstone contact contact westerly—trending border mapped by Harris (1968) (1968) on the the north shore shore of of Saganaga Saganaga Lake Lake was was interpreted to be the interpreted to be the northern border fault, fault, and it is here inferred inferred that the that the Lookout Fault is is its its southern southern analog. analog. The block block was was emplaced emplaced during during E8~ly E:ly Precambrian The Precambrian time, time, in in as as much as as detritus now found found in the the Knife Knife Lake Lake Group Group of of Gruner Gruner (1941) (19/+1) was derived there has derived from Granite. Although from the Saganaga Saganaga Granite. Although there has been been later t.,as movement on the the Lookout Fault, Fault, it it is is dominantly dominantly aa Lower Lower Precambrian Precambrian structure. MIDDLE ~UDDLE PRECAMBRIAN PRECANBRI!u~ Introduction Gunflint and and '\ove Rove Formations The Animikie Groun Group consisting of the the Gunflint comprises These rocks the entire this area. comprises the entire Middle :oliddle Precanibrian Precambrian inin this area. These rocks unconformably overlie Lower Lm.,er Precambrian rocks rocks and and in in turn turn are are intruded intruded and truncated truncated by gabbroic rocks rocks of Niddle i'·liddle Keweenawan KeweenaT,oJan age. age. The time time of Animilcie !mimikie deposition deposition has has not not been completely completely documented. documented. Hurley and iron— that deposition of the and others (1962) have have suggested suggested that the ironothers (1962) 6 io6 Although this years. formation around 1,900 1,900 ±± 200 xx 10 this K—A K-A formation occurred occurred around age includes age includes an an arbitrary and perhaps unnecessary unnecessary correction correction of of 20 20 percent assumed assumed argon argon loss, loss, it it nevertheless nevertheless has has been been widely widely quoted quoted In contrast, contrast, Faure Faure and and Kovacg Kovac (1969) in the literature. In (1969) obtained obtained aa Rb-Sr age of 1,685 ±± 24 x 10 years years from from the the Rb—Sr tvhole-rock whole—rock isochron age Gunflint Iron—formation. Iron-formation. They interpret interpret this this age age to to be be the the time time of diagenesis, however, similartotoother otherages agesobtained obtainedfrom from rocks rocks however,itit is similar Misra and Faure metamorphosed during the the Penokean orogeny. orogeny. Later Nisra Faure (1970) Iron-formation (1970) showed showed that that argillite argillite from from thr2e three Gunflint Gunflint Iron—formation . .1.7 localities Rb-Sr ages ages that that decrease from from "'.... 1.7 b.y. at the eastern localities have have Rb—Sr end to to 1.2 b.y. b.y. near... near ... the the western.. \vestern ... variation of of . this systematic variation apparent ages may be related to metamorphic effects caused by Keweenawan apparent ages may related to effects caused by Keweenawan . . ".'. Thus there diabase sills. sills •••• there is uriequivical depositional age for for is no no unequivical these rocks. b.y. at the eastern . �-103—10 3— Descriptive Stratigraphy Gunflint Iron—formation Iron-formation The Gunflint Iron—fori:iation crops out out in in aa northeasterly— Iron-formation crops northeasterlytrending belt Superior to trending belt that thatextends extendsfrom fromThunder Thunder Bay Bay on on Lake Lake Superior a point it is point in inMinnesota Minnesota 12 12 miles miles west west of Gunflint Gunflint Lake Lake where where it is truncated by the truncated the Duluth Duluth Complex. Complex. In Canada Canada the iron—formation is In the iron-formation is only slightly, slightly, if at at aF., al:_, metamorphosed and consists of silica, much of of which \"hich is is chalcedonic, chalcedonic, Consequently, Goodwin iron oxides, oxides, iron carbonates, iron carbonates, and and greenalite. greena1ite. Consequently, (1956) recognized six six sedimentary sedimentary facies facies which which serve serve to (1956) recognized to subdivide In Minnesota theoriginal oriina1 the iron-formation fourmembers. members. In Hinnesota the iron—formation into into four nature of metamorphism by the nature of the iron-formation is is -obscured obscured by TIetamorphism the the iron—formation Duluth Complex. The carbonates and greenalite are replaced by Complex. carbonates and greenalite are replaced by amphibole, amphibole, pyroxene, fayalite, and locally by garnet and pyroxene, fayalite, and and other silicates. In In addition, addition, many of the the small—scale small-scale sedimentary sedimentary textures textures have have been been almost completely completely destroyed; destroyed; however larger larger structures, structures, and especially complex bedding bedding relationships relationships are are still still preserved. preserved. Therefore the the four—fold nomenclatural nomenclatural scheme -— originally four-fold in the the Biwabik Biwabik originally outlined in Iron-formation (Wolff, (Holff, 1917) 1917) and and later later extended extended to to the the Gunflint Gunflint Iron— IronIron—formation retained by Morey and others formation (l3roderick, (Broderick, 1920) by 1'1orey and (1969) others (1969) 1920) -— ,vas was retained Accordingly, four because it it emphasizes various bedding aspects. aspects. Accordingly, members are recognized; members recognized; Lower Cherty, Cherty, Lower Lower Slaty, Slaty, Upper Upper Cherty, Cherty, Slaty. Although the do not and Upper Upper Slaty. the boundaries of of these these members members do coincide coincide witll those recognized recognized by by Goodwin Goodwin (1956), (1956) , the with those the two two schemes schemes can be equated equated \vith withonly onlyslight slight difficulty. difficulty. Lo\ver ChertLMemhe.r: Cherty Hember: Lower The Lo,ver is isthin, The Lower Cherty ChtertyNember Member thin, ranging in thickness Feldspathic quartzite quartzite that thickness from from 15 15 to to 45 45 feet. that contains contains feet. Feldspathic granite cobblesisis present present locally locally at at Lie granite and and greenstone greenstone cobbles the base base of of the the formation; these beds beds are are equivalent equivalenttotoGoodwin's CoodHin' s basal basalconglomerate conglomerate formation; member. AA persistent persistent magnetite-rich, magnetite—rich,silicate-bearing silicate—bearingunit unit five five to Feet thick occurs 15 feet occurs within IVithin this thismember member and an excellent and serves serves as as an marker—horizon. marl(er-horizon. :Iost commonly it liesdirectly directly uponbasement basement rocks, rocks, :c'st commonly it lies upon but loc<llly locaii.v it it overlies overlies either eitherthe thefeldspathic feldspathicqtiartzite quartziteorora chert— a chertcemented fragr.ents of cemented conglomerate conglomerate containing contctininr, frctgments algal structllres; in of algal structures; itit in is overlain overlainbyhya massive, a massive,chert—rich, chert-rich,magnetite—poor magnetite,-poor unit about about turn is 15 feet thick. 15 feet thick. ' \ Lower-,:,?-latY---l~~emher: Slaty Member: This This member memberisis8080toto 95 95 feet feet thick. The Lower lOHennost, magnetite-free 10 is a ablack, black,thin—bedded thin-bedded lowermost, nearly nearly magnetite—freo 10feet feet is argillitecomposed conlposcd dominantly dominantly of derived material. It argillite of volcanically volcanically derived It is equivalent equivalent to to the the intermediate InterPlcdi"tc slate slate on on the the 'esahi ;lesabi range range and and to to is the lower the lOh·er tuffaccous tuffaceous shale shale f,icies fD-cLcs ininCanada. l,<ln"da. The beds beds immediately aove the Intermediate .:1iJove tile IntenneJiate slate massive and clierty cherty and and resemble resemble slate are massive the upper upor aert the part of of the the lower LOIver Cherty ;'[e1l1her. This unit passes passes abruptly ahruptly Chcrty :-;ember. ipuird into cherty uith spilrse sparse inagnetite interuTl\!;]rd into cherty si.licate-hci1rini; beds ':lith magnetite inters iJ.icate— carjn beds calated calateJ with \vi til aa few fe\\' thinly—laminated tilinly-la:ninated silicate—rich silicate-rich beds. heels. The The remaining 50 feet is is ai1 thiin—bndciel laminatedrock rockcontaining containingvarious varioussilicates silicates thin-beJded totolill\linated and percent magnetite. and Cro from 20 2C to 35 35 percent map;netite. AA few fe'" cherty-silicate cherty—silicate beds, definitely amount are elefillitely subordinate subordinate in in illllount this interval. interval. are intercalated intercalated in in this �—104— -104- Upper Cherty Cherty Member: Member: There is is a complete complete gradation gradation between between The Upper Cherty the Lower Slaty and and Upper Upper Cherty Cherty Members. Members. Cherty Member, Member, the The lower as defined, is approximately 50 50 feet thick. thick. The 10loJer as presently defined, cherty layers part to lenticular lenticular cherty layers part consists of irregularly bedded to intercalated with thinly—laminated thinly-laminated silicate—rich silicate-rich layers layers that that increase increase in abundance abundance upward. upward. Thin irregular layers of magnetite are are common common in in the cherty beds near the the bottom of of the the member, member, but but become become less less abundant upward. upward. The top top of the the member—equivalent member-equivalent to to Goodwin's Goodwin's abundant upper algal chert facies—is facies-is characterized characterized by by several granular granular chert conglomerate fragments, fragments, chert beds beds containing algal structures, conglomerate and abundant magnetite. Upper Member: The Upper Slaty Slaty Member is is approximately approximately Upper Slaty S1ay Member: Thick lenticular chert chert beds beds with disseminated disseminated few tens tens of of feet, feet, but magnetite characterize characterize the the lower lower few but most most of of the the member consists consists of a thin—bedded thin-bedded to to laminated laminated quartz—silicate quartz-silicate rock rock thinly laminated layersofofgraphitir:: graphiticargillite, argillite, interbedded with with thinly laminated layers and pure chert. chert. The and one onetoto two twoinch inchthick thick beds bedsofof relatively relatively pure upper 10 feet feet is nearly magnetite free free and and consists consists of of limestone limestone and chert interbedded interbedded with with argillite. argillite. 150 feet thick. thick. 150 Rove Formation Rove Formation gradationally overlies The Rove overlies the the Cunflint Gunflint Iron— Ironformation and is intruded by Logan Intrusive formation Intrusive Rocks Rocks and and truncated truncated detailed description of Duluth Complex. Complex. A A detailed of the the formation formation by the Duluth is presented is presentedby byMorey Morey (1969). (1969). In In the the Long Long Island Island Lake, Lake, Gunflint Gunflint Lake, and Hungary Hungary Jack formation Lake, Southlake, and Jack Lake Lake quadrangles, quadrangles, the formation is characterized by by intercalated black to to grayish grayish black, black, locally locally is characterized intercalated black carbonaceous argillaceoussiltstone siltstone and fine-grained carbonaceousargillite, argillite, argillaceous and fine—grained gray\oJacke. In the silt silt sandstone beds becomecoarse— coarsegraywacke. In general the andand sandstone beds become formation. In grained, thicker, thicker, and and more more abundant abundant upward in the formation. tn are several addition, there are several lenses lenses and and irregular irregular bodies bodies of of limelimeaddition, there dolomite, and chert and a number of of calcite—dolomite calcite-dolomite con— constone, dolomite, cretions of of various shapes and sizes, similar cretions similar to to those those described described in the the formation by by Tanton (1931) (1931) and and Moarhouse Moorhouse (1963) (1963) scattered scattered near the the base base of the the formation. formation. Horey deep Morey(1969) (1969)has hassuggested suggestedthat thatdeposition depositionstarted started in aa deep basin in inwhich which fine—grained fine-grained sediment sediment accumulated accumulated under under reducing reducing conditions. The The siltstone siltstone and conditions. andsandstone sandstonebeds beds contain containmany many primary primary sedimentary structures indicative indicative of of turbidite sedimentary structures turbidite deposition. deposition. There is of this this type is also also evidence evidence of of an an increase increase infrequency infrequency of type of of deposition upward in in the the section. section. The graY\oJackes contain abundant abundant framework framework The graywackes grains grains of of quartz, quartz, feldspar feldspar and and Igranitici "granitic"rock rockfragments fragments indicative indicative of a granitic source area. source area. Sedimentary structures including cross— crossbedding and various kinds of of sole sole marks marks indicate indicate that that sediment sediment transport dominantly dominantly was \oJas from from north north to to south. south. These observations observations and the gray\oJacke mineralogy the the graywacke mineralogyled led Horey Morey(1969) (1969)toto conclude concludethat that the source terrane now exposednorth north of of the source area area was was the the Lower Lower Precambrian Precambrian terrane now exposed the outcrdp area of outcrop of the theRove Rove Formation. Formation. �—105— -105- Structure The Animikie SE Animikie strata strata form form aa homocline homocline that that dips dips 10°-15° 1O—l5° SE except where intrusive bodies and and secondary secondary structures structures have have disdisFor example, example, complex folding torted the beds. For torted or disturbed the commonly zones adjacent to to many of of the the Logan Logan commonly occurs occurs in narrow zones Intrusive is most likely related related to to the the forceful forceful ememIntrusive Rocks Rocks and and is the sills into into restricted restricted space. space. There is aa fairly fairly placement of the regular as much as 600 60° near the the Duluth Duluth Complex. Complex. regular increase increase in dip dip to as is most likely likely pre—Duluth pre-Duluth Complex Complex in in age. age. However, this structure is However, in the the Animikie Animikie strata strata inakestecognition makestEcognition of Lack of marker beds in faults northwesterly- and and northerly— northerlyfaults difficult; difficult; however, however, a number of northwesterly— trending faults have been mapped. mapped. trending faults faults have displacements displacements of of less less than than 50 50 feet; feet; however, however, Most faults the Lookout Lookout fault has aa displacement displacement in the the iron—formation iron-formation of fault has of at at least least 200 200 feet. feet. All All faults faults so sofar farrecognized recognizeddisplace displaceLogan Logan Intrusive rocks, Intrusive Complex; thus thus rocks, but but none extend into the Duluth Complex; movement apparently apparently occurred in Middle Middle Keweenawan Keweenawan time time prior prior to to movement of the the Duluth Duluth Complex. Complex. The fault fault pattern is similar emplacement of to 1960; Goodwin, Goodwin, 1960) 1960) near ,.,hat what can to that that in Canada (Moorhouse, (Moorhouse, 1960; be inferred inferred to to be the the northern the Lake northern hinge hinge of of the Lake Superior syncline. syncline. TIlis structure must have formed at least in prior to emplacement part prior to emp1acenen.t This must at least in of the Duluth Duluth Complex. Complex. Hovement during Keweenawan Keweenawan time time duplicates duplicates Movement on the Lookout fault during iron—formationwest westofofthe theGunflint Gunflint Trail, Trail, and the iron-formation and aanortherly— northerlytrending segment of fault separates separatesthe the iron-formation into two two trending segment of the the fault iron—Formation structurally distinct terranes. structurally terranes. East of the Gunflint Trail, Trail, the the rocks dip dip gently southward; southward; accordingly the outcrop area Animikie rocks of relatively wide most of of the apparent of the the iron—formation iron-formation isis relatively wide and and most apparent irregularities mappattern patternresult result fromthe the super-position irregularities ininthethemap from super—position of aa rugged rugged topography on gently—dipping gently-dipping strata. strata. The south side side of fault is is upthrown, upthrown, and and the the Anirnikie Animikie strata on this of the the Lookout fault side outcrop belt. belt. side dip dip steeply and thus form a narrow outcrop A also can can be be recognized. recognized. Just A number of smaller structures also east of Gunflint Trail Trail the the iron—formation iron-formation and of the Gunflint andthe thesills sills are folded into anticline with with a a steeply steeply into a southeasterly plunging anticline dipping north limb limb and a gently dipping dipping south south limb. limb. This structure post-Logan in age has an anticlinal axis which which is obviously post—Logan into the the trace trace of of the the Lookout Lookout Fault. Fault. projects into Metamorphism i'letamorphism In the the Animikie Animikie rocks no textural or or atineralogic mineralogic In rocksthere there is is no evidence for aapervassive metamorphism evidence pervassiveregional regional metamorphism beyond beyond minor minor of the the clay—size clay-size detritral frac'don. The The obvious recrystallization of detritral. fraction. the Animikie strata are are associated in the Animikie strata associated with with the the metamorphic effects in emplacement of the Duluth Complex and Logan Intrusive Rocks of Middle Ke,,,eenawan Keweenawan age. �—106— -106- The contact contact aureole aureole of of the the Duluth Complex has has not been studied in detail in in the the Gunflint Gunflint Trail Trail Area. Area. Preliminary work in in the the Gunflint Iron—formation shows there are a number of metamorphic Iron-formation there are a of facies similar to those those described from from the the Biwabik Bh\Tabik Iron—formation Iron-formation facies by French (1968) (1968) and and Bonnichsen Bonnichsen (1969). (1969). Unmetamorphosed iron— ironformation like that described by Goodwin Good\vin (1956) (1956) is is found found in in Minnesota Hinnesota lint and North Lakes. only in in aa small small area area between between Gunf Gunflint Lakes. There the the iron-formation consists of chert, chert, iron iron carbonates, carbonates, greenalite, greenalite, abundant abundant iron—formation amounts of finely disseminated hematite, and and traces traces of of magnetite. amounts However, lint Lake, Lake, the the iron-formation iron—formation has has been been metamorphosed metamorphosed However, west of of Gunf Gunflint and three three metamorphic zones zones have been distinguished distinguished by hy changes changes in in mineralogy along tI tie strike of the the formation formation toward tm'Jard the the Duluth Duluth Complex. Complex. Zone 1, 1, or slightly metamorphosed iron—formation, iron-formation, occurs occurs in in the the area immediately west of Gunflint Lake. It consists of quartz, iron of Gunflint Lake. It consists quartz, iron carbonates, greenalite, minnesotaite, and carbonates, and stilpnomelane. stilpnomelane. FinelyFinely— divided hematite hematite occurs occurs in the divided the east east end of the zone, ZOne, hut but disappears mid—way in mid-way in it. it. Disseminated Disseminated and and interlocking grains of magnetite are are abundant, especially as abundant, as rims rims around around granules. granules. This part of of the the iron— i ronformation is much like like that that described described by by French French (1968) (1968) in in 'unmetaniorphosed "unmetamorphosed" formation is Biwabik Iron—formation. Iron-formation. Zone 2, moderately metamorphosed iron—formation, Zone 2, or moderately iron-formation, is is about about 1.2 miles wide and extends to to within \vithin 0.3 0.3 miles miles of of the the Duluth Duluth Complex. Complex. GruneriteGrunerite— cummingtonite, hornblende and actinolite, cummingtonite, actinolite, as well as as quartz and magnetite map,netite As in characterize this this zone. zone. As in zone zone 1, 1, much of the the magnetite is is between hetHeen 0.002 and in diameter; and 0.02 0.02 mm in diameter; a a size—range size-range similar to to that that observed in various other other Lake Lake Superior Superioriron—formations. iron-formations. S:'1all-scale pre-metAmorphic Small—scale pre—metamorphic sedimentary structures such such as as granules granules and andoolites oolites are sedimentary structures are partly partly destroyed, destroyed, but primarystructures structuresand andbeddinr, bedding featuresarearelittle little but larger—scale larger-scale primary features affected. Zone 3, or orhighly highlymetamorpl-iosed metan,orphosed iron-formation, iron—formation,occurs occurs adjacent to the and is is characterized the Duluth Duluth Complex Complex and characterizedby bya awholly ",hollymetamorphic metamorphic fabric. The The rock composed chiefly quartz, magnetite, magnetite,iron—rich iron-rich fabric. rock is is composed chiefly of quartz, euliedraloror suhl1edral subliedral grains pyroxenes, and Very commonly, commonly, eultedral (.~rains pyroxenes, and fayalite. fayalite. Very of are poikilitically poikilitically enclosed 'Tithin large large silicate silicate grains; of magnetite magnetite are Ptlclose.d \orithin (~rains; they are of of essentially they are essentially the the same Si1Iile size size as in inthe thelower lOHer grade grade rocks. rocks. However a significantpart partofoftile themagnetite ragnetite is is extensively Hmvever a significant extensively recrystallized, recrystallized, .-:IS and grains as as aa millimeter and grains as much much <18 millimeter in in diameter diiwleter are arc concentrated concentrated along along Actinolite bedding planes. planes. Actinoli bedding te isiscommon cor:lJl1on in magnetite—rich rnagm~ti te-rich layers, layers, and and both prograde and retrograde cummingtonite :Ls±un(lantly oresent. In pro~rade and retro0rrtde cummin;>:tonitc is -:hundnntly nresent. In general this this zone zone is is very very similar similar to tothat thCltdescribed de~;cribedinin thetheJ)unka Dunka!~oiver Piver area on the the I'lesabi :olesabi range ranre by by Bonnichsen nonnicbsen (1)69). (l,)6~l). area on contactt aureole o0 fthe l\Tork on on the contnc theDuluth lluluthComplex Complex in Preliminary work RoveFormation Formationindicates indicates aa complex mixtureofof rock rock tyPes Rove complex mixture tyoes suggesting sUfgcstinR partial melting, and textural textural variations variations due to original original partial meltint, and and mineral mineral and due to Tue met"mop)!losed metamorphosedrocKs rocks :HC are netainorphilari. The inhornogenities and degree degree of of liletamorr1dsr,l. inhoinogenities and commonly layered Individual layers layers commonly layeredane! andhave haveil agranohlastic granoblastic texture. texture. Individual contain; 1) hiotite and contain; 1) cordierite corcJieriteand and Iyperstliene hynersthene with '\Tith minor loinor biotite and ilmenire, ilmenite, hiotite, and plagioclase, hiotite, and ilmanite, ilmenite, J) aur-ite, hypcrsthene, plagioclase, 3) augite, 2) hypersthene, plagioclase ±± minor olivine, ilmentte, or 1+) 4) hvperstliene, plagioclase olivine, biotite, biotite, and "at! ilmeni.t0., hypersthe.ne, contact plagioclase, K—feldspar, andbiotite. hiotite. Calcareous K-feldsrar, and Calcareous beds GeJs near ncar the contact have aa skarn—minera.logy consisting wollastonite,diopsi<le, diopside, tremolite, tremolite, have skarn-mineralogy consisting of of lvollastonitc, fromtile the contflct contact - and piece to and p:arn0.t. Away AI<7ay frol'l nnd from fron plnee to eLace Dlace and 8rossularite grossularite garnet. the the �—10 7— -107- distance varies varies from several tens to several hundreds of feet this from several feet — this distance or may most peletic rocks are are rich rich in in biotite, and and cordierite cordierite may mayor may not be present. present. The Logan Intrusive Intrusive Rocks Rocks also also have have metamorphosed metamorphosed the the Gunf Gunflint lint and Fonnations. The width of the metamorphic aureoles are related related and Rove Formations. to sill sill thicknesses and range from less than to than one foot foot to to more than than 30 30 Gunflint Iron—formation feet. In In the the Gunflint Iron-formation it is difficult difficult to to recognize recognize unique metamorphic assemblages mineral assemblages adjacent adjacent to to sills. sills. In zone 2, 2, mineral assemblages characteristic of zone 3 occurs in assemblages in aureoles around around the the sills. sills. Similarly In in zone zone 1, ininnesotaite, minnesotaite, which which is is characteristic characteristic of of zone 2 to the the sills. sills. metamorphism is found next to In the Rove Formation Fonnation thick thick sills have assemblages assemblages that that can can be be In the assigned to to the the pyroxene—hornfels pyroxene-hornfels facies facies whereas whereas thinner thinner sills sills have have assemblages characterisitc of the assemblages the hornblende—hornfels hornblende-hornfels facies. facies. Locally 1969) and chloritoid (Grant, andalusite (Morey, (Horey, 1969) (Grant, 1971) 1971) have have been been identified identified in certain beds. beds. UPPER PRECAMBRIAN Introduction In northeastern Minnesota two In two units are are recognized recognized in in the the Upper Upper Precambrian: the Lower Lower Keweenawan represented by the Puckwunge the Formation and and the Formation the Middle Keweenawan which consists consists of of the the Logan Logan Intrusive Intrusive Rocks, the the North Shore Volcanic Group (Green, Rocks, (Green, this this volume), and and the the Duluth Complex. Complex. Puckwunge Formation Fonnation The Puckwunge Formation consists consists of conglomerate conglomerate and and sandstone sandstone which unconformably North unconfonnably overlie the Rove Formation Fonnation and underlie the the North Shore Volcanic Group. The type locality was described by N. N. N. H. Winchell Winchell (1897) on Sec. 25, 25, T. T. 64 N., N., R. R. 33 B. E. where about about 18 18 (1897) on the the Stump Stump River in Sec. feet of section is feet is exposed. exposed. Exposures Exposures of of similar similarlithology lithologyare arefuund in frnind in the Grand Portage area (Grout (Grout and and others, 1959). 1959). the If these these isolated exposures are equivalent to to the the Sibley Sibley Series Series If in Canada (Tanton, in (Tanton, 1931) 1931) they represent represent aa period of sedimentation sedimentation around around period of 1376 *± 36 m.y. m.y. ago (Franklin Kustra, 1970) 1970) followed by possible possible 1376 (Franklin and Kustra, followed by uplift and erosion prior to to the the onset onset of of volcanic volcanic activity activity in in Middle Middle Keweenawan time. time. Intrusive Rocks Rocks Logan Intrusive The sills was was applied applied to intrusive The name name Logan Logan sills to tabular, tabular, diabase intrusive rocks in the Rove Formation rocks in the Rove Formation(Lawson,. (Lm"rson, 1893, 1893, p. 48). Similar intrusive p. 48). Similar intrusive in Animikie formations are Animikie and and Lower Lm.,rer Keweenawan Keweenawan formations are currently referred to as Logan referred to as Logan Intrusive Rocks. Rocks. As As now now defined, defined, they they include include sills and dikes of sills and dikes of diabasic diabasicgahhro gabbrowhich which range range in in measured measured age age from from rocks rocks 1300 n.y. ~300 m.y. (hanson (Hanson and and [alhotra, Ha1hotra, 1971) 1971) to to 963 963 m.y. m.y. (Franklin, (Franklin, cited cited Ln Hanless Wanless and In and others, others, 1970, 1970, p. 57). Thus the Logan Intrusive Rocks, Rocks, 57). Thus the Logan Intrusive p. �—108— -108- North Shore Shore Volcanic Group Group may may units of the Duluth Complex, Complex, and the the North have overlapping time—stratigraphic time-stratigraphic relationships. relationships. rocks In County the the predominant exposed volume volume of of the the Logan Logan rocks In Cook County from the sill-like, and and the the present sawtooth smvtooth topography topography results results from the is sill—like, The the inclined inclined sills sills and and Rove Rove Formation. Formation. The differential erosion of the feet sills and sills range range in in thickness thickness from from aa fe\v few feet feet to to over over aa thousand thousand feet and thick sills for several several miles. miles. In In three three sills can be mapped along strike for dimensions dimensions they they form form aa boXtVork boxwork pattern, pattern, their their emplacement emplacement having having been been ~ntro11ed fault plane connections connections between nntrolled by bedding, bedding, joint and possibly fault sills sills but but in in the the Grand Grand Portage Portage in in northeastern northeastern Cook Cook County County area area there there and extent are extent to to the the are major major northwest-trending northwest—trending dikes dikes comparable comparable in in size size and sills (Grout and Schwartz, Schwartz, 1933, P. p. 36—59). 36-59). sills (Grout Early detailed studies the Logan Intrusive studies of of the the petrogenesis petrogenesis of the Rocks were primarily restricted to to the the sill sill on on Pigeon Pigeon Point Point (Bayley, (Bayley, Reinvestigation of 1893; Daly, 1917; 1917; Grout Grout and and Schwartz, Sch\vartz, 1933). 1933). Reinvestigation of these these 1893; Daly, rocks currently in in progress follmving generalized descripdescriprocks is is currently progress and the the following textures, and is based the unpublished work of tion of of textures, and mineralogy mineralogy is based OIl on the of J. A. A. Grant, Grant, E. E. Mathez, Mathez, G. G. B. B. Morey, N. N. Mudrey and and P. P. Weiblen. Weiblen • J. margins, fine— .Texture: T exture: Rock types types include aphyric chilled margins, fine- to medium-grained diabase with ophitic clinopyroxene enclosing plagioclase, medium—grained diabase clinopyroxene enclosing plagioclase, porphyritic diabase with plagioclase plagioclase phenocrysts, phenocrysts, plagioclase plagioclase cumulates, cumulates, margins form sharp contacts and granophyre. Chilled margins contacts with with country country rocks. rocks. Clino— from fine fine to to medium medium toward toward the the center center of of sills. sills. ClinoDiabase grades from remains ophitic even though the the grain size changes changes and enclosed pyroxene remains plagioclase crystals rarely rarely exceed exceed 55 mm rom in in length. length. Plagioclase phenocrysts as 10 10 cms ems long long in in thick thick sills. sills. Diabasic crysts however however are as much as rocks with plagioclase plagioclase phenocrysts phenocrysts grade grade into into accumulations of essentially rocks with accumulations of Such accumulations are found coarse-grained plagioclase. Such found in in the the upper upper coarse—grained plagioclase. to the the parts of some large sills and their origin has been attributed to floating of of plagioclase (Grout floating (Grout and and Schwartz, Schwartz, 1933, 1933, p. p. 50). 50). M1neraly: Minor olivine is found Mineralogy: found in the the lower part of of some Plagioclase as small grains grains enclosed in Plagioclase both both as as phenocrysts phenocrysts and as pyroxene is generally highly highly seriticized. seriticized. Clinopyroxene is is altered altered to to amphibole within single oikocrysts. oikocrysts. The The remnant remnant pyroxene varies varies in composition from pigeonite through augite and has a mottled birefringence which resembles resembles that that of of the the complex complex lunar lunar pyroxenes. pyroxenes. Ilmenite lirnenite and and minor minor magnetite appear at distinct horizons in in some some sills. sills. The is The ilmenite is commonly skeletal. skeletal. Minor interstitial interstitial quartz quartz is is characteristic characteristic of of much of of the the diabase. diabase. Biotite is is ubiquitous ubiquitous in the diahase diabase and texturally appears to appears to be of both igneous and and metamorphic metamorphic origin. origin. Granophyric intergrowths the diabase \vhere intergrowths are are common common in in the the upper upper part part of of the where they impart a pink mottling which can can be be recognized recognized In in hand hand specimen. specimen. Separate impart a Separate o~currences of granophyre in mappable units are rare, rare, except for for the the occurrences Pigeon Point sill (Mudrey P~geon (Hudrey and and Weiblen, Weib1en, 1971). 1971). sills. sills. �-109—10 9— Structure: In Structure: the Duluth Complex truncates the the various various In plan view the along strike strike at at aa low low angle angle (Fig. (Fig. 3). 3). Where exposed, the the Logan sills along base of the Duluth Complex dips gently southward, southward, whereas whereas both both the dips gently country rocks rocks may may dip dip as as much much as as 60° 60° to the south. south. Logan sills and country Drilling in in the the vicinity vicinity of of the the contact contact indicates indicates that that the the base base of of the the Drilling Complex steepens to as much as 60° and levels levels off off to to about about 30° 30° 11 km. km. This structural structural configuration configuration is i down-dip (Johnson, 1970, 1970, p. p. 82). 82). This down—dip (Johnson, zuch like that Mancuso and Dolence (1970) the East much that described by Hancuso (1970) in the ?Iesabi district. They suggested that Mesabi district. that the the emplacement emplacement of the Duluth that area was in part controlled controlled by by aa pre—Complex pre-Complex structure. structure. Complex in that :1inor hydrothermal hydrothermal mineralization mineralization is is found found within within >inera1ization: Mineralization: Hinor the Logan Intrusive Rocks. The mineralization is probably similar similar to to the the important occurrences occurrences the Thunder Thunder Bay Bay silver silver deposits, deposits, but nO no commercially important Island where where aa shaft shaft was was sunk have been found found in in Minnesota. Minnesota. On Susie Island along a fracture zone filled with calcite-barite and lesser amounts along a fracture zone filled with calcite—barite and lesser amounts of of quartz, bornite, bornite, chalcocite, chalcocite, chalcopyrite, chalcopyrite, pyrite, pyrite, covellite covellite and and quartz, malacite, malacite, ore was recovered which which contained 6.22 percent copper and At Loon trace trace amounts of silver silver (Grout (Grout and 1933, p. p. 64). 64). At and Schwartz, Schwartz, 1933, Lake, R. S. Blankenburg Blankenburg has has investigated investigated aa prospect prospect in in aa quartz-calcite quartz—calcite Lake, vein that that contains arsenopyrite with minor cobalt cobalt (Johnson, (Johnson, 1968). 1968). Duluth Complex consists of a variety The Duluth Complex consists of a variety of of anorthositic, anorthositic, troctolitic, troctolitic, granodioritic, and and granophyric granophyric rocks rocks which which crop out in in an an arcuate arcuate belt belt granodioritic, crop out A brief review from the Gunflint Trail (Fig. (Fig. 1). 1). A review of of from Duluth Duluth to to east east of of the the early literature literature and and recent work up to to 1969 1969 is is given given by by Phinney Phinney the of subsequent subsequent mapping and study of of the northeastern (1969). The results results of limb of the the Complex Complex are are presented by by Nathan Nathan (1969), (1969), Morey Horey and and others (1969), Johnson Q970), and Davidson Davidson (1970). (1970). (1969), Johnson a970), and Nathan (1969) mapped aa layered series of sheet—like (1969) mapped sheet-like intrusions intrusions across across the Gunflint, and Hungry Hungry Jack Lake quadrangles (Fig. (Fig. 2). 2). To the Gunflint, South Lake and the west, west, in in the the the Long Island quadrangle, Nathan's Nathan's layered layered series series is is truncated the Tuscarora Intrusion and and other other associated associated rocks. rocks. truncated by by the Nathan Layered Series of Nathan The layered layered series series extends extends from from the the east east edge edge of of the the Hungry Hungry Jack The Jack Lake quadrangle across across the South Lake quadrangle and into into the Gunflint \vhere it it is is truncated truncated by by the the Tuscarora Tuscarora Intrusion. Intrusion. This Lake quadrangle where truncation is is marked by an irregular northwest trending trending scarp scarp (Fig. (Fig. 3). 3). truncation For the most part, part, the the series series consists consists of of aa sequence sequence of of conformable conformable For the most The sheets thicken sheets 15-25° to to the the south. south. The sheets having having a regional dip of 15—25° to west and and are are locally locally interrrupted interrrupted by by minor minor crosscutting stockstock— to the the west and dike—like dike-like bodies. bodies. On the the east side of the Hungry Jack Lake Lake quadrangle aa nortlnvest northwest trending trending fault fault offsets offsets the the series series with with an an unknown unknown quadrangle amount of amount of displacement, displacement, but but as as much much as as 140 140 feet feet of of vertical vertical displacement displacement northeast side side is is inferred of the the northeast inferred (Fig. (Fig. 3). 3). �-110—110— The series consists consists of of troctolitic, troctolitic, gabbroic, gabbroic, and and associated associated felsic rocks. rocks. Several of the major units represent represent uniqud unique occuroccurrences in the the Duluth Complex of oxide—rich rences oxide-rich gabbros gabbros and and two—pyroxene two-pyroxene gabbros. For the most part, fine—grained fine-grained rocks rocks are are not not chilled chilled margins but occur principally as or inclusions inclusions as separate intrusions intrusions or of mappable size. size. Planar orientation of of minerals is is common, cornman, indicating flow flow or or crystal crystal setting. setting. Differentiation resulting resulting from from these processes can be demonstrated within some some units, units, however however the the layered series does not form form aa regular regular stratigraphic stratigraphic sequence. sequence. Intrusive relationships for 27 different units were established for 27 different units established using cross-cutting cross—cutting structures, structs, fine—grained using fine-grainedmargins, margins, inclusions inclusions and thermal effects, effects, the latter being principally aa development development of dark clouded plagioclase near intrusive intrusive contacts, contacts, Nathan (1969, (1969, p. 99). On the basis of field field relationships, relationships, mineralogy, and and composicomposip. 99). tion, tion, Nathan concluded the 27 27 units could could be be combined combined into into eight eight cogenetic cogenetic groups. groups. Detailed rock descriptions and interpretations interpretations are are given given by by Nathan (1969, (1969, p. p. 38—185) 38-185) and are are summarized summarized here here using using his his nomennomenclature. The descriptive rock rock names have have several several textural textural prefixes prefixes clature. that that characterize the primary mineral assemblages. assemblages. AA size size classclassification for these rocks, rocks, based on on visually—estimated visually-estimated mean mean grain grain diameters, is: diameters, is: >10 mm, mm, very coarse—grained; coarse-grained; 4—10 4-10 mm, rnrn, coarse—grained; coarse-grained; 1—4 mm, mm, medium-grained; medium—grained; 1/2—1 1-4 1/2-1 mm, fine—grained; fine-grained; <1/2 <1/2 mm, mm, very very fine— fineA 'granular' grained. fabrics are are recognized. recognized. A "granular" rock has Four basic fabrics grained. If elongate elongate grains grains are present and only equidimensional equidimensiona1 minerals. minerals. If are randomly oriented, the the rock is is "decussate," "decussate," if if the the grains grains define define aligned, the a plane, plane, the rock rock is "foliated," "foliated," and and if if the the grains grains are are aligned, the rock l'lineated. II All rocks rocks are named by the the characterizing characterizing rock is is "lineated." primary mineral assemblage, assemblage, in in order order of of increasing increasing abundance; abundance; the the primary mineral assemblage assemblage refers refers to to early early crystallizing crystallizing phases phases in in Modes are indicated by sub— contrast to to late late interstitial interstitial phases. phases. Modes subIf scripts. If a significant part of the the primary assemblage assemblage was was scripts. transported in the magma the rock rock is is referred referred to to as as an an allocrystallate, allocrystallate, aa cumulate cumulate being a special special case case in in which gravity gravity settling settling has has occurred. occurred. being a Rocks formed formed by crystallization in in place place are are called called autocrystallates. autocrystallates. Rocks Thus a Subscripts are used to to indicate modal composition. composition. Thus a descriptive descriptive Subscripts fine— rock name name for for aa troctolite troctolite formed formed by by gravity gravity settling settling could could he he aa fineinter— grained foliated olivine20—plagioclase70 cumulate with minor 01ivinezo-plagioclase70 cumulate \-lith minor interstitital augite5and augitesand oxides5. oxides S • Group 11 da The oldest unit (da) (da) in in the the layered layered series series now now appears appears in the upper part of the the section section as as dilated dilated septa septa as as It is is 8a fine-grained fine—grained foliated much as as 200 200 feet feet thick. thick. It much cumulate with with minor minor pigeonite9 —plagioclase63 cumulate 01ivine~s-plagioclase63 pigeonite 9 olivine which are and aug1te are also also cumulus cumulus in in the the middle middle of of and aug?e the unit. unit. ~his unit grades grades into into aa 1,000 foot—thick foot-thick his unit the sheet of foliated augite15—pigeonite26 augiteIS-pigeonite26of medium-grained, medium—grained, foliated A very fine—grained piagioclase cumulate (dh). (dh). A fine-grained plagioclase59curnulate S9 ollvine1 —augite27—plagioclase61 rock olivine o-augite27-plagioclaseGl rock (dc) (de) occurs occurs as as sizes near the base of masses o9 ~f various shapes and Slzes of masses the layered layered series. series. Nathan speculated that that it might the represent aa chilled margin of the represent the Group 1 intrusive intrusive rocks. - db db dc de �-111—111— Groip22 Group dg the major part of of the group comprises comprises the major oxide—rich oxide-rich part the This group The main unit layered series. unit (dg) (dg) is a a coarse—grained coarse-grained series. —augite —olivine foliated ilmenite—titanomagnetite foliated ilmenite-titanOmagnetitell-augitel~-olivineI4­ plagioclase cumulate. Within tff~s unit unit fe efollowing followrng plagioclase S66crystallization appears: (1) (1) ilmeniteilmenite— sequence of of5crystallization olivine-plagioclase; (Z) ilmenite—titanomagnetite—olivine— ilmenite-titanomagnetite-olivineolivine—plagioclase; (2) augite—plagioclase; and finally augite-plagioclase; finally (3) (3) apatite—pigeonite— apatite-pigeonitetitanomagnetite-ilmenite-olivine-augite-plagioclase. titanoinagnetite—ilmenite—olivine—augite—plagioclase. dd de Very fine—grained fine-grained foliated foliatedolIvine—oxide—augite—plagioclase olivine-oxide-augite-plagioclase Very plagioclase (dd) and (dd) and fine—grained fine-grained granulo—decussate granulo-decussate augite augite— - plagioclase (de) rocks occur in in unit (de) rocks occur unit dg dg as as inclusions inclusionsasasmuch much as as 400 400 A number of mappable units are across. A are gradational gradational feet across. with (1) at at the the base base of of the the complex, (1) complex, a fine— fine- to coarse— coarsegrained decussate decussate augite—olivine—plagioclase augite-olivine-plagioclase autocrystallate autocrystallate (df) grades into rocks rocks having a texture texture and and mineralogy similar (df) to that unit dg,and may may be the to that in unit the base of the the cumulates cumulates of of Unit df unit dg. dg. Unit df shows sulfide mineralization mineralization similar similar to to unit ttf ttf of of the the Tuscarora Tuscarora Intrusion Intrusion (Johnson, (Johnson, 1970, 1970, p. p. 68). 68). unit dg: dg: unit df df di dj dj dk Groyp3 dm din (2) A fine-grained, fine—grained, olivinezo-plagioclase66-olivine20 olivine2Q—p1agioclase6—o1ivine90 (Z) A cumulate with minor miner augite5-oxide4-pigeon~te4-apatiEel augite —oxide4—pigeonie —apatite1 cumulate with within unit * fine—grained, as aa thin thin sheet sheet ,vitfiin unit dg. dg. (3) (3) A fine-graine4, occurs as autocrystallatee decussate, oxide2 —augite28—plagioclase decussate, oxideZ3-augite2S-plagioclase45 autocrystallat 5 containing minor livine2 olivine and and apatite2 apatite tntrudes intrudes unit dg and and Z z is (4) Unit Unit dg is presumed to to be aa late late differentiate differentiate (di). (di). (4) grades upward into 100—200 grades 100-ZOO foot—thick foot-thick discontinuous discontinuous sheets sheets of coarse—grained, foliated pigeonite4—titanomagnetite4— of coarse-grained, foliated pigeonite -titanomagnetite 4 4 augite6—plagioclase83 cumulatescontaining minor potass~um potassium augite -p1a gioclase cumulates containing minor S3 6 feldspar2 fine—grained granular feldspar and and quartz1 quartz (dj). (dj). A fine-grained granular 2 l plagioclase, quartz, orthoclase orthoclase rock rock (dk) (dk) occurs occurs as as dikes dikes cutting rocks. cutting other Group 22 rocks. Unit din, the upper upper part part of the dm, the the layered layered se•:ies, se~ies, is a 2,000 foot—thick 2,000 foot-thick sheet of coarse—grained coarse-grained decussate decussate pigeonite11—augite24--plagioclase59 pigeonite13-augite24-~lagi~clase59autocrystallates and cumu1aes cumulates containing conta~n~ng minor nanor oxides2, oX~desZ' quartz2 quartz 2 and potassium potassium feldspar1. feldspar . This unit is thought thought to to This unit l have been emplaced along along foliation planes planes and thus thus to have dilated dilated the the earlier earlier units. units. Variations in in grain grain size and and modal mineralogy suggest suggest th.t that this this unit unit may be a multiple intrusion. intrusion. A A related related intrusion intrusion may be be dl c..ll dn do do geonite unit dl, aa inedluin—grained medium-grained decussate decussate pi pigeonite17— 17 augite20—plagioclase50 rock containing augite20-plagioclase60 containing minor oxide, oxide, quartz, which occurs occurs as quartz, and and potassium feldspar, feldspar, ''''hich as a small stock about 1—1/2 1-1/2 miles stock about milesacross acrossininthe the central central part of the Hungry Jack quadrangle. quadrangle. Another related related intrusive granular oxide19— oxide intrusive unit unit is is aa fine-grained fine—grainS granular 19 plagioclase41—augite4 rock (dxi) which occurs occurs as aa plagio~lase4l-a~gite40 rocl~ (dn) 1vhich sheet 6 sheet 6 feet thick tlack anI and 4 mlles the northern miles long in the the part of Souti of the South Lake quadrangle. quadranp;le. Felsic dikes which intrure were given given aa separate separate designation intrude unit unitdcL dm \vere designation (do) (do) and may represent a a late—stage late-stage differentiate of of unit unit dj dj or partially fused fused country country rock rock (Nathan, (Nathan, p. p. 115). 115). �-112—112— Group 44 dp dq Group 55 dr ds Group 66 dt du dw The next intrusive unit unit (dp) (dp) occurs occurs as as aa concordant concordant as 1,200 feet feet thick thick between bet'}7een units units dg dg and and sheet as much as It is is aa fine—grained db. It fine-grained foliated augite32—plagioclase58 augite32-plagioclaseS8 andtrace trace amounts cumulate with olivine3—hypersthene.7 olivine -hypersthene"? and amounts of oxides. Plagioclase augite occur in aa granular oxides. Plagioclase and ~nd augite occur in granular fabric, hyperstheneas as as pheno— hypersthene as oikocrysts, oikocrysts,and andolivine olivine phenocrysts. of late-stage late—stageinterstitial interstitial material crysts. The absence absence of material suggests the suggests the unit unit formed by flow flow or or crystal crystal settling settling with exchange exchange between between the the magma magma and andthe the inner cumulus cumulus melt. Near melt. Near the the top top of of unit unitdp, dp,a 100—foot—thick a 100-foot-thick sheet of medium—grained foliated olivine17—plagioclase83 of medium-grained foliated olivine17-plagioclase83 cumulate gradational with with unit dp. dp. cumulate(dq) (dq)isis gradational In the southwestern lint Lake southwestern part part of of the the Gunf Gunflint Lake quadrang!le quadrangiLe pyroxene-plagioclase and and aa heterogeneous assortment of pyroxene—plagioclase olivine-plagioclase olivine—plagioclase rocks rocks possibly possibly related related to to unit unit tta tta of the Tuscarora Intrusion truncate truncate the the layered layered series. series. of the A typical example is a medium—grained A medium-grained decussate decussate tironals5— tironals S ollvine5—augite 5—plagioclase75 autocrystallate (dr). olivines-augitelS-plagioclase75 autocrystallate (dr). Near the the base base of o the layered series a medium-grained Near medium—grained foliated augite1 —plagioclase77 rock foliated augite17-plagioclase77 rock with minor minor oxide3— oxide 3 pigeonite and olivine oivine (ds) pigeonite? and (ds) is is intruded intruded as as aa sheet sheet 300 feet feet chick hick between 300 between units units df df and and dg. dg. Unit ds ds is is highly altered with montmorillonite montmorillonite after after plagioclase, plagioclase, and and amphibole amphibole and chlorite after after pyroxene. pyroxene. Locally chalcopyrite and and bornite occur within interstitial, chalcopyrite interstitial, altered pyroxene. pyroxene. A number of oxide—rich A oxide-rich stock— stock- and and dike—like dike-like bodies bodies 3/4 miles miles across the Complex Complex across occur near the base of the in the South Lake Lake quadrangle. quadrangle. Nathan recognized recognized four four varieties: varieties: (1) olivine (1) medium-grained medium—grained granular olivine16— oxide73 rocks oxide amount of of plagioclase plagioclasel6 and and 73 rocks with a minor amount augite (dt). augite (dt). The ilmenite andtitanomagnetite anddtanomagnetite occur occur as the latter generally has has exsolved exsolved as primary primary phases; phases; the coarse ilmenite lamellae with intra—titanomagnetite coarse intra-titanomagnetite granules which have in in turn turn exsolved exsolved to to a a fine fine reticulate reticulate intergrowth of magnetite magnetite and and hercynite.(')On hercynite.C)On Little Iron Little Iron Lake in the South Lake quadrangle quadrangle aa medium-grained mediunv-grained granular plagioclase 1—oxide24—olivine gra~ular,plagioclase 1-oxide -olivine (du) rock rock (du) 24 49 having minor hypersttene hyperstLne and hav1ng m1nor 1/2 mile mile and augite augite forms fogs aa 1/2 long composite sheet long sheet within unit dt.G)A coarse--grained coarse-grained unit dt.(3)A granular plagioclase8—oxide23_pjgeonjt2, granular plagioclase -oxide -pigeonite -augite —augite '· i nor8 olivine I' ,23 44 rock rock containing minor m 0 1Vlne occurs as as 24small con t a1n1ng inalldisdi cordant cordant masses in the the South South Lake Lake quadrangle. quadrangle. UI) (4) Two Two occurrences of a coarse—grained occurrences coarse-grained decussate decussate oxide oxide —_ augite31_p1agioc 't l ' 1ase 10mapped a~g1,e3l-~ ag10c autocrystallate (dw) (dw) were wer0mapped S5 autocrystallate within wlth1n unit unlt dg. dg. This unit exhibits an amphibole an amphibole alteration alteration similar similar to to that that in in unit unit ds, ds but but is is conconsidered sidered to to be be part part of of group 5 rocks b;cause of its its group 5 rocks because of large oxide content. content. �-113—113— Groupj dx dy dy dz Group 88 daa dmaa Several fine—grained Several fine-grained decussate rocks occur as as discontinuous thin sheets discontinuous sheets along the base of the the comcomand dikes dikes higher higher in in the the plex and as small stocks and section. represent either either fused fused fractions fractions section. They may represent country rock rock or contaminated contaminated melts, but but all all are are of country They consist to be intrusive. They consist of: of: (1) (1) fine— finethought to grained -augite 2-plagioclase66 grained decussate decussate oxide oxide7—augite2plagioclase66 7 olivine -quarrz and and potassium1 potassluffi 1 rock having minor olivine2—quartz2 2 (2) fine-g~ained fine—grained decussate decussate oxide oxideçfeldspar (dx); (dx); (2) —augite31—plagioclase55 autocrystallate hypersthene -augite -plagioclase autocrystal1ate hypersthone SS (dy); and and (?Y (~t fine—grained fine-g1~inedaugite3—oxide9 augite -oxide g decussate 3 quartz10—orthoclase15—hornblende29—plagioclase34 rock quartzlO-orthoclaselS-hornblende29-p1agioclase34 rock (dz).. (dz) The youngest intrusive unit within the layered series 1—1/2 miles dikes and and stocks stocks as as much much as as 1-1/2 occurs as dikes across the Hungary Jack Lake quadrangle. This unit, unit, across in the inedium-grained granular granular quartzls-alkali quartz18—alkali feldspar feldspar77 aa medium-grained oxide2 (daa), rock ,vitl, (daa) , truncates truncates rock with minor augite and oxide 2 1 unit din. unit dm. Across an an interval at the the inerval over a mile wide at there is is aa prog,ressive progressive increase in end of of unit unit din, dm, there in east end the amount amount of of late stage interstitial material that the that has has a composition similar to to unit unit daa. daa. This unit unit (dmaa) (dmaa) might be aa late late stage stage differentiate differentiate ofofdin. dm. Nathan found however that hm-lever that unit unit dx dx has has been been intruded intruded and and altered altered by by daa. daa. n Therefore, unit daa Therefore, it itisispresumed presumed that thatdin dm was \Vas cold cold when ,vhen unit daa was intruded and that that the the gradational zone zone represents represents melt from daa daa that that was introduced introduced into into unit unit dm. dm. Intrusion and and Associated Associated Rocks Rocks Tuscarora Intrusion In the Long Island quadrangle (Fig. the Long (Fig. 2) 2) a a sequence of rock types common to to other appear in in the other parts partsofofthe theDuluth DuluthComplex Complex appear the following following succession away succession away from the base: (1) (1) aa fine-grained augite from the fine—grained poikilitic augite gabbro (tp), (tp), (2) (2) aa fine-grained (hornfels) (th), (th), fine—grained granoblastic gabbro (hornfels) (3) (ttf-ttm), (4) (4) interlayered interlayered (3) aa finefine— to to medium-grained medium—grained troctolite (ttf—ttm), troctolite and troctolite and poikilitic gabhro gabbro (tta), (tta), (5) (S) anorthositic anorthositic gabbro gabbro (ag), (ag), (6) ferrograndiorite ferrograndiorite (tg), (6) (tg), (7) (gr), and (7) (7) metamorphosed (7) granophyre granophyre (gr), flows (:mv). (kmv). Although the the outcrop pattern suggests aa simple differentiated differentiated layered sequence, the stratigraphic position of units tp, tp, ag, tg and gr layered sequence, the of units ag, tg have not been unequivocally established. established. Hm.;rever, ttm, and and However, units ttf, ttn, are clearly clearly parts a separate troctolite intrusion that that truncates tta are parts of of a part layered series series (Fig. (Fig. 3). 3). part of of Nathan's layered ynits ttm,tL,ad ttf, and tta: The unit of the Tuscarora Intrusion The main unit Units tta: is aa niedium—grained medium-grained troctolite (ttm, Fig. is troctolite (ttrn, Fig. 2), 2), consisting consisting of of 6S-70 65—70 percent and 10-lS 10—15 percent cumulus percent cumulus plagioclase (An (An 56 S-60)' and cumulus divine amouns 09 ol~vine (Fo0). (F~50). Relative amoun~s of poikilitic augite and iron—titanium iron-titanium oxides oXldes varies varles locally. locally. Orthopyroxene mantles olivine and and occurs occurs in in simplectic plagioclase. Biotite biotite is associated with sitaplectic intersrowth intergrowth with plagioclase. tile oxides. Planar orientation of of plagioclase and modal— modalthe iron-titanium iron—titanium oxides. layering are are locally locally well—developed well-developed and and mutually concordant. concordant. mineral layering poikilitic �-114-114— The troctolite grades into The into an an upper upper unit unit which which consists consists of of interlayered poikilitic augite gabbro and and troctolite (Fig. 3). 3). troctolite (Fig. The poikilitic augite augite consists consists of of about about 70 70 percent percent plagioclase plagioclase 15—20 percent augite, (An SO - 60 )' 15-20 augite, 5—10 5-10 percentilmenite percent ilmenite and and is is medium— med1um- to coarse—grained coarse-grained with withwell well developed developedaugite augite orthocrysts orthocrysts as much as 1—1/2" across. The as much as 1-1/2 across. The troctolite \vithin the the layered layered troctolite within interval interval is similar to to that that in in unit unit ttm. ttm. Contacts Contacts between between layers layers are generally generally sharp sharp and and in in general gener& conformable are conformable with with layering layering in in the the troctolite. troctolite. Interlayering of several several inches inches Interlayering occurs on a scale of to to several feet, feet, and is undulatory with wave lengths lengths of of ten to twenty twenty ten to feet feet and amplitudes of two two to to three three feet, but the the gross gross structure structure feet, but is nearly flat—lying. is flat-lying. 11 A belt of fine—grained Unit ttp; ttp: A fine-grained rocks rocks occur occur beneath beneath unit unit ttf. It ttf. It consists consists of fine— fine- to medium—grained medium-grained augite augite troctolite troctolite with 60—70percent percentcumulus cumulusplagioclase plagioclase (An50), with 60-70 (An ), 5-10 cumulus 5—10 percent cumulus 50 olivine percentpoikilitic poikilitic augite, .5—10 ~livin~ (Fo35), (F~35)' 15—20 ~5-20 perce~t augite, 5-10 percent . iron—titanium oxides, minor orthopyroxene-plagioclase orthopyroxene—plagioclase simplect1te. simplecite. 1ron-t1tan1um oX1des, and mlnor As yet the upper contact As contact of tins this unit unit has has not not been been observed observed and and it it is not clear from outcrop data is data if if it it is is aa separate separate intrusion intrusion or the the basal unit of the the overlying overlying rocks. rocks. Johnson (1970, (1970, p. p. 76) 76) concluded concluded from from drill drill core data that that it is is aa separate separate intrusion. intrusion. Unit th: th: Several areas of fine—grained, fine-grained, granoblastic granoblastic gabbro gabbro consisting of 50 to 60 percent short tabular tabular plagioclase, plagioclase, 30 30 to to 40 percent rounded rounded augite, augite, minor minor subhedral subhedral iron—titanium iron-titanium oxides, oxides, olivine, and and blades of biotite are olivine, are exposed exposed on on topographic topographic highs. highs. These rocks however rocks may be a remnant remnant capping over the the troctolite; troctolite; hOlvever there is no noticeable chilling of of the the troctolite troctolite next next to to the the there is hornfels and they they more likely likely represent represent large large inclusions. inclusions. Unit ap; ag: A break in in plagioclase plagioclase content content separates separates A distinct distinct break units tta tta and and ag. ago Unit ag ag — - an anorthositic gabbro— - contains 75 units anorthositic gabbro 75 to contrast to the 85 (in to the 50 50 to to 70 70 percent percent S5percent percentplagioclase plagioclaseAnAn5560 ( 55 60 Plagioclase is phase, and and interinterof is the the only only cumulus cumulus phase, of unit unit tta). tta). Plagioclase stitialminerals, minerals,occurring occurring in invarious various proportions proportions are are augite, augite, stitial olivine, and iron texture. Orthopyroxene olivine, and iron oxides oxidesinin aa poikilitic poikilitic texture. occurs in in siciplectic occurs sil:lplec tic intergrowth intergrm-Jth with W'i th late—stage late-stage plagioclase. associatedwith \'liththe theiron—titanium iron-titanium oxides. oxides. Planar Biotite isisassociated orientation of orientation of plagioclase plagioclase is is developed developed locally. locally. At At the the top top of of unit ag, quartz quartz and and potassium potassium feldspar unit ag, feldsparoccur occurinterstitially. interstitially. Tue flat—lyingoutcrop outcroppattern patternofof the the ferrogranodiorite ferrogranodiorite (tg) The flat-lying (tg) and granophyre concordant with \vithin the the and granophyre(gr) (gr) isis concordant with the the structure structure within troctolite (ttm) troctolite (ttm) and and the the anorthositic anorthositicgalibro gabbro could could be be just just another another part of the layered intrusion. IImvever some field evidence contrapart of the layered intrusion. however some field evidence contradicts this interpretation. interpretation. llornfels Hornfels inclusions inclusions and and sulfide sulfide mineralmineraldicts this ization are are found found in at several several localities localitiesalong along the the contact contact ization in unit unit tta tta at with unit ag. ago Thus the troctolite may be intrusive into the the Thus the intrusive into anorthositicgabbro gabbro as asininthe the GabbroLake Lake quadrangle quadrangle (Green (Green and and anorthositic Gabbro Phinney (1969) (1969)has hasextended extendedthe theolder older anorthositic anorthositic others, 1966). 1966). Phinney gabbro from from the Gabbro Lake quadrangle eastward the Gabbro eastward and and this this extension extension projects toward toward unit unit ag. ago Thus TIluS unit ag ag may be aa thin thin wedge wedge of of an an In this anorthositic gabbro. gabbro. In this case, units units areally extensive older anorthositic fg to the the troctolite troctoliteand and intruded intruded fg and and gr gr could could be either related to the ancirthositic gabbro or or aa differentiated differentiated part into the anorthositic gabbro part of of the the anorthositic gabbro. gabbro. anorthositic �-115—115— Unit f: This unit is restricted Unit fg: restricted to to aa topographically topographically high high area in the southwest corner of the the Long Long Island Island Lake Lake quadrangle quadrangle southwest corner (Fig. 3). 3). It medium-grained ferrogranodiorite which contains (Fig. It isisa amedium—grained ferrogranodiorite which 50 to 60 percent cumulus plagioclase, 10 to 15 percent amphibole, 50 to 60 percent cumulus plagioclase, 10 to 15 percent amphibole, minor clinopyroxene, amounts of potassium minor clinopyroxene, and and varying varying amounts of quartz, quartz, potassium anorthositic feldspar, and magnetite. Contacts with the underlying anorthositic gabbro and overlying granophyre are are gradational gradational over over tens tens of of feet. feet. The former former could replacement by by intrusive intrusiveferrograno— ferrogranocould represent replacement diorite or or differentiation differentiation within within the the anorthositic anorthositic gabbro. gabbro. Further diorite study is needed to the stratigraphic stratigraphic relationships. relationships. is needed to clarify clarify the i the Unit Unit gr: The ferrogranodiorite grades grades into into and is cut The ferrogranodiorite and is cut by by It consists It consists of of quartz, quartz, The texture texture ranges plagioclase, potassium plagioclase, potassium feldspar and and magnetite. magnetite. The ranges from from granophyric granophyrictoto granitoid. granitoid. fine- to medium—grained medium-grained granophyre. fine— granophyre. Unit kmv: kmv: The The granophyre granophyre intrudes intrudesblack black fine-grainedmeta— metafine—grained volcanic rocks whch whch are remnants of ofMiddle Middle volcanic rocks are interpreted interpreted totobeberemnants groundmassisishighly highlyaltered. altered. Acicular Keweenawan The groundmass Keweenawan flows. flows. The blades of ilmenite and plagioclase plagioclase phenocrysts blades ilmeniteare arecommon common and phenocrysts are are clouded similar intruded rocks rocks in layered series. clouded similar to to intruded it'. the the layered series. the the Mineralization: Two Two types types of mineralization are found in Duluth Complex 1m., grade gradecopper—nickel copper-nickel Duluth Complexininthis this area: area: (1) (1) low concentrations are associated associated with with the the basal basal rocks concentrations are rocks of of the the Tuscarora Intrusion and Tuscarora the layered series series intrusions intrusions and several of the (Johnson, 1970), (2) Ilmenite— and and titanomagnetite-rich titanomagnetite—rich rocks (Johnson, (2) Ilmeniterocks occr occur in in several several units units of of Nathan's Nathan's layered layered series. series. With \-lith regard regard to to the the mineralization, the the unpublished unpublished Ph.D. Ph.D. thesis (1970) warrants warrants special special mention. mention. The thesis thesis thesis of of Johnson (1970) summarizes the the results results of summarizes of an an exploration program conducted by the Cleveland—cliffs the Cleveland-Cliffs Iron IronCompany Company and and the Amerada-Hess Amerada—Hess Corporation Company from from 1966 1966 to to 1969. 1969. This program ass~ssed This assessed the economic potential of the base of the Duluth potential of the base of the Duluth Complex in in aa 38 38 km corridor along the Gunflint Trail adjacent adjacent to to the the Boundary Boundary Waters Waters Canoe Canoe Area. Area. The drilling program (10 (10 holes) holes) provides provides an unique opportunity opportunity to to assess assess the the effects effects of of drilling drillingononthe thearea area comparison with with other other inin comparison activities activities such such as as logging logging and and recreation. recreation. More importantly the the rereMore importantly lease lease of of geophysical, geophysical, drill drill core, core, and assay data, data, along along with Johnson's Johnson's study represents represents a study a major contribution by by aa mining company company to to the the concern for for the the environment of the the area. area. The The correlation correlation of of geogeophysical and physical and drill drill core core data, data, discussed below, makes makes possible possible aa discussed below, more accurate accurate evaluation more evaluation of of mineral mineral resources adjacent areas areas resources in in adjacent and in other and in other areas areas of of similar similargeology geology using using less less expensive expensive and and disruptive disruptive preliminary preliminary investigations. investigations. Coç—Nicke1_Iinera1izatjon: ~0J?E.£!:.-Nickel ~'lineralization: Discontinuous gossan Discontinuous areas areas of gossan and visible sulfide and visible sulfide mineralization min~r-;li~-ation ,.,ithin have been been mapped mapped within unit ttf ttf have across the across the Long Long Island Island quadrangle. quadrangle. Similar Similar isolated isolatedexposures exposures have have been found in in unit tta atat the been.found unit tta thecontact contact with with anorthositic anorthositic gabbro. gabbro. The The sulfide assemblage, consisting sulflde assemblage, consisting of pyrrhotite and and minor minor of chalcopyrite cI:alcopyrjte,pyrrhoi, pentlandjte occurs occursinterstitially interstitially to plagioclase pentlandite plagiocla~e and and olivine. Because Because of the size of of the of the smaller smaller grain grain size the troctolite troctolite a a distinct distinct interstitial interstitial texture, texture, like like that thatfound found in the sulfide sulfide mineralization mineralization in in the Kawishiwi in the the iCawishiwi area in the Gabbro area in tQe Gabbro Lake Lake quadrangle, quadrangle, is not apparent apparent ininhand handspecimen. specimen. is not �-116—116— Drilling across across the the quadrangle quadrangle (Johnson, 1969) has has indicated indicated aa Drilling (Johnson, 1969) tabular, tabular, possibly continuous volume of of low low grade grade ore ore (0.3% (0.3% combined combined copper-nickel) about 50 feet thick thick in in the the unit unit ttf. ttf. A A thinner thinner 10—20 10-20 copper—nickel) foot-thick zone, 50—100 50-100 feet feet above above the the lower lower mineralized mineralized zone, zone, has has foot—thick zone, aa higher combined copper—nickel copper-nickel content content that that approaches approaches one one percent percent 84). The mineralization can be correlated3with correlated with a (Johnson, p. 84). the order of 700 x 10 3 ohmcentimeters detectable resistivity anomaly on the in the troctolite (ttf, (ttf, ttm). ttm). Mineralization: The primary titanium titan1um oxide oxide phases phases Titanium Mineralization: ) and titanomagnetite are i].menite ilmenite solid 0 -MgTi0 solid solution solution (Fe (Fe20 —MgTiO -FeTi0 —FeTiO3) 3 3 2 3 (Fe304—Fe (Fe 0 -Fe 2TiO Ti0 4). ). Subsolidus exsoLtion exsolution as fiasresulted resulted in in the the complex complex 3 4 intergrosAhs âescribed intergrowEhs described above. Johnson (1970, (1970, p. p. 87) 87) estimates estimates that that Ti Ti recovered recovered from from ilmenite ilmenite in In unit unit ttf ttf in in the the Tuscarora Intrusion Intrusion could add $1.50 per ton to to sulfide ore ore from from this this unit. unit. The largest titanium concentrations at Little Little Iron Iron Lake Lake in in the the Gunflint Gunflint Lake Lake at exposures in the the South South Lake Lake quadrangle. quadrangle. do not exceed occurrences at the surface do however are in units dt and du quadrangle quadrangle and and other other isolated isolated Unfortunately, most of these Unfortunately, these about 35 feet feet in maximum about dimension. A large low—grade A low-grade titanium titanium resource also is contained within unit dg (Fig. unit (Fig. 3). 3). Oxide—rich Oxide-rich layers as much as as 5 feet feet thick are common, common, although individual layers seem seem too too thin thin and and discontinuous discontinuous to be mined separately. Unit dg should he to be considered considered in its its entirety for commercial evaluation with the the potential of of developing a very large tonnage tonnage of of low—grade low-grade ore. ore. The unit is very heterogeneous and and exposures are scarce and discontinuous, so only widespread field exposures and discontinuous, systematic drilling will reveal reveal which which parts parts have have the the greatest greatest promise. promise. �_____ _____, -117—117— References Cited Bayley, Bayley, W. W. S., S., 1893, The eruptive and and sedimentary rocks on Pigeon Point, their contact contact phenomena: phenomena: U. U. S. S. Geol. Geol. Point, Minnesota, Minnesota, and their Survey Bull. Bull. 109, 109, 121 121 p. p. Bonnichsen, Bill, 1969, 1969, Metamorphic Metamorphic pyroxenes pyroxenes and and amphiboles amphiboles in Bonnichsen, Bill, the Biwabik Iron—formation, Iron-formation, Dunka Dunka River River area, area, Minnesota: Minnesota: Mineralog. Soc. Soc. 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N. lveiblen, Weiblen, 1971, Reinvestigation in the in the Pigeon Point area, area, Minnesota (abst.): (abst.): in 17th Ann. Ann. Inst. on Lake Superior lnst. Superior Geol. Geol. Nathan, Nathan, Ii. H. D., portion of of the the Duluth Duluth Complex, Complex, 0., 1969, 1969, The geology of aa portion County, unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Dniv. of of Ninn., Minn., 198 198 p. p. Cook County, Phinney, W. C., 1969a, the Gabbro Phinney, W. C., 1969a, The The Duluth Complex in the Gabbro Lake quadrangle, 11innesota: Minnesota: Minn. quadrangle, Minn. Geol. Geol. Survey Survey Rept. Rept. trw. lnv. 9, 9, 20 20 p. p. Phinney, N. W. C., C., 1969h, 1969b, Geology Geology of of Central Central part part of of Duluth Duluth Complex; Complex; Phinney, P. K. in Summary of Fieldwork Fieldwork 1969: 1969: P. K. Sims and and I. I. Westfall, Westfall, eds.: eds.: t-~inn. Minn. Geol. Geol. Survey Survey Inf. Inf. Circ. Circ. 7, 7, p. 2 18. Sims, P. P. K., B. Morey, R. Sims, K., G. G.B. R. w. l.v. Ojakangas, and N. W. L. L. Griffin, 1968, 1968, Preliminary geologic map of the the Vermilion Vermilion district district and and adjacent adjacent areas, northern ttinneso ta: lirin. Geol. areas, Ninnesota: ;1inn. Geo1. Survey Survey Misc. Map Hap N—S. H-5. Sims, Sins, P. P. 1(., K., G. C. B. B. Morey, Morey, and and J. J. C. C. Green, Green, 1969, 1969, The The potential potential for for ne~v in Minnesota: Ninnesota: 30th Ann. Ann. Mining Hining Symposium, Symposium, new mineral discoveries in Univ. of Uinn., Dniv. ~1inn., p. p. 75—87. 75-87. Tanton, Tanton, T. T. L., L., 1931, 1931, Fort Fort William and and Port Port Arthur, Arthur, and and Thunder Cape mapmap— areas, district, Ontario: Ontario: Geol. CeoI. Survey Survey Canada Canada Mem. Mem. areas, Thunder Bay district, 167, 222 1G7, 222 p. p. Wanless, IL hlanless, R. K., K., IL R. U. D. Stevens, Stevens, G. G. R. and R. R. N. N. Dalablo, Da1abio, 1970, 1970, R. Lachance, Lachance, and Age ages, z\gedetenninations determinations and and geological geological studies studies K-Ar K—Ar is6topic istopic ages, Report 9: 9: Geol. Geol. Surv. Surv. Canada Canada Paper Paper 69—2A, 69-2A, 78 78 p. p. Report Winchell, 1888, Report Winchell, A. A., 18$8, Report of of aa geological survey in ~linnesota Minnesota during the season of 1887: the season of 1887: tlinn. Minn. Geol. 16th Ann. Ann. Geol. Nat. Nat. Hist. lust. Survey, 16th Rept., p. 336—337. 336-337. Rept., p. , 1897, Some· Some new features _____ , 1897, features in the the geology of northeastern northeastern Minnesota: Minnesota: Amer. v. 20, 20, p. p. 41—51. 41-51. Amer. Geologist, Geologist, v. Wolff, \-101ff, J. J. F., F., 1971, 1971, Recent Recent geological geological developments on the the Mesabi Mesabi iron iron developments on range: Amer. Inst. Inst. Min. Mm. Engs., range: Trans. Trans. Amer. Engs., V. 56, p. p. 142—169. 142-169. v. 56, �-120—120— FIELD FIELD TRIP TRIP GUIDE GUIDE TO TO THE THE PRECAMBRIAN PRECAMBRIAN ROCKS, ROCKS, ~UL' i'u.._ •• _ .. _ COOK COUNTY ALONG THE GUNFLINT TRAIL Stop 1 End of Trail Campground -- Main Phase of Saganaga Granite the Saganaga Granite Granite at at this this stop stop is is aa The main phase of the medium—grained medium-grained hornblende—"quartz—eyet' hornblende-"quartz-eye" tonalite tonalite having quartz2o— quartZ20plagioclase (An27)60_lO—hornblende6—microljne3_5 (An27)60-70-hornblende6-microline3_S and and accessory accessory biotite, chlorite, chlorite, epidote, epidote, sphene, sphene, apatite, apatite, allanite allanite muscovite, biotite, and magnetite. magnetite. The apparent lineation of of the the "quartz—eyes" "quartz-eyes" is is 25_300 ENE. 25-30° ENE. This structure is is parodied in in the the hornblende—biotite hornblende-biotite inclusions. inch-sized inclusions related to to These inch--sized inclusions are are probably related the the south south of of Seagull Seagull Lake. Lake. the greenstones to the The bay leading north to Saganaga Lake was The Has considered considered by by Grout (1936) (1936) to to be aa shatter shatter zone. zone. It It is here interpreted as as a fault in the granite. fault the granite. At this stop, aa minor secondary secondary east— eastnortheast and epidote epidote northeast trending foliation is marked by shears and veinlets, and and may be related related to to faulting. faulting. veinlets, Stop 22 Gunf lint Trail Trail near near the the Campground —- Lamprophyre dike in Saganaga Gunflint Granite larnprophyre dike at this stop is is 50 SO feet feet wide, tv-ide, and and can can be be The lamprophyre traced to to the north shore of Saganaga Lake where it it is is found found to to cut cut the northern boundary fault fault (Harris, (Harris, 1968, p. p. 21). 21). This observation the sets aa 10lv-er lower age sets age limit for faulting and uplift uplift to to the the west Hest for for the the Goldich and others (1961, p. 52) date the biotite Saganaga Granite. Granite. (1961, p. S2) date the biotite (KA—70B)fromasmall (KA-70B)from a small island island to to the the north north at at 1.75 1. 7S h.y. b.y. Sundeen (1936) (1936) reviewed reviewed the the petrography petrography of of the the larnprophyre lamprophyre dikes the Saganaga Lake are.a and found biotite, biotite, hornblende, dikes in the Lake area and the mafic phenocrysts in a groundmass of of either either and pyroxene pyroxene as as the plagioclase or This dike dike contains contains plagioclasesoplagioc1ase5— plagioclase or "orthoclase. "orthoclase"11 This pyroxenel5_20—pyroxenei5_20—biotite513 pyroxenelS-20-pyroxeneI5_20-biotiteS_IO and and hornblende5. hornblendes. Accessory Accessory minerals include minerals include quartz, quartz, apatite, apatite, magnetite, chlorite, chlorite, carbonate, carbonate, sphene, pyrite, pyrite, zircon, sphene, zircon, serpentine, serpentine, talc talc and perovskite. perovskite. Stop 3a Stop Saganaga Saganaga Granite Granite -— Border Phase The strongly foliated foliated hornblende diorite diorite exposed exposed at at this this stop stop is typical typical of the border phase of the the Saganaga Granite. Granite. The foliation is of the is defined defined by by aa layering characterized by various proportions is proportions of of dark dark and light minerals; it is is nearly vertical and strikes N70°W. N70oW. Elongate and light minerals; it the foliation foliation plane plane define define an an elongate elongate hornblende needles within the ilneation lineation that that plunges gently gently to to the the east. east. A A transition from the border to the the main phase involving involving an an 'quartz—eye' structure structure increase in quartz - with tv-ith the the development development of of "quartz-eye" -— and aa decrease in hornblende can be seen in in a number of of outcrops outcrops lint Trail Trail to to the on either side of of the the Gunf Gunflint the north of of this this stop. stoP. �—121— -121- Stop 3b 3b Ietabasalt and associated rocks Netabasalt rocks vicinity of of this this stop, stop, vaguely pillowed meta— metaIn the general vicinity basalt thin-bedded to to laminated pyroclastic pyroclastic material material typical typical basalt and thin—bedded of the the mafic the volcanic succession succession are are exposed. exposed. Layering of nafic part of the is is nearly vertical and strikes in in aa northwesterly northwesterly direction. direction. Fracture Fracture cleavage direction cleavage also also is is near near vertical and strikes in a northeasterly direction parallel to to the the trace of the the Lookout Lookout fault. fault. The mafic cut by byconformable conformable layers layers of offine—grained fine-grained mafic rocks rocks are cut graphic feldspar granite. Locally graphic feldspar a thin layer of iron-formation Locally a thin layer of iron—formation overlies the older composed and chert chertunconformably unconformably overlies composedofof magnetite magnetite and rocks. Iron-rich the lower lower part the Cunflint Gunflint Iron—richstrata stratatypical typical of of the part of the Iron—formationare are exposed exposedon on the the steep north—facing Iron-formation north-facing slope immediately immediately to the to the south south of of these theseexposures. exposures. Stopj4 Stop lint Iron-formation Iron—formation Rock Trail Trail—- metamorphosed Gunf Gunflint Along Magnetic Rock Along of Zone 22 Thin-bedded, Thin—bedded, fine—grained, fine-grained, chert—axnphibole—inagnetitebearing chert-amphibole-magnetite-bearing strata assigned to to the upper part of of the the Lower Lower Slaty Slaty member member are are exposed along Magnetic Rock Rock Trail Trail at at this this locality. locality. These exposures are the transition between moderately and and strongly strongly metamorphosed metamorphosed are near the iron-formation; small, poorly developed developed pyroxene pyroxene porphyroblasts porphyroblasts iron—formation; small, can be be seen,pecially seen,especiallyinin moremassive massive beds beds at the the top of of the the thethemore member. Along to the thesouth, south,the theiron—formation iron-formation is Alongthe thepower powerline linetrail trail to locally with beds at 15°. locally deformed deformed with beds dipping dipping northward northward at 15°. Approximately7575feet feetfarther farther to Approximately to the thesouth southa anorthwesterly— northwesterlytrending, medium-grained medium—grained diabase diabase sill sill cuts cuts slaty slaty iron—formatin. iron-formatin. Approximately 200 feet the slaty to Approximately 200 feet to to the the south south the slaty beds beds again dip dip to the south south and coarse-grained, magnetite-rich the and are are interlayered interlayered with with coarse—grained, magnetite—rich cherty beds. beds. On the same knob, knob, algal chert—bearing chert-bearing beds characteristic of the Upper Cherty Member also of also are are exposed. exposed. Stop 55 Along the Kekabeic Kekabeic Trail Trail—- Metamorphosed Gunflint Iron—formation Iron-formation at at Zone 3. The Kekabeic oror less base of of the the Gunflint Gunflint The KekabeicTrail Trailmore more lessparallels parallels the the base Iron—formationand andthe thenorth-facing north—facing slopeimmediately immediately southofofthe thetrail trail Iron-fornlation slope south The iron—formation contains exposures exposures of ofthe theLower Lower Slaty SlatyMember. Hember. The iron-formation everyhas been extensively metamorphosed and now consists where in this this area has of various quartz—cummingtonite—grunerite—fayalite— various assemblages assemblagesofof quartz-cun~ingtonite-grunerite-fayalite­ magnetite and magnetite andquartz—cummingtonite—grunerite—pyroxene—magnetite. quartz-cummingtonite-grunerite-pyroxene-magnetite. �-122—122-are in Test along the the Trail. Trail. IIost Host are iI:. the the lowe.: 10HE;:: Test pits can be seen along magnetite-rich the Lower Lower Cherty Cherty Member. Member. Various sulfides, sulfides, magnetite—rich part of the especially pyrrhotite, the magneti:e. magnetL:e. pyrrhotite, also are associated with the Stop 66 rail cut -— Basal Contact of the dIe Duluth Along the Paulson Mine Mine railcut Complex. Complex The Paulson Mine railcut railcut exposes exposes the the base base of of the the Duluth Duluth Complex Complex from the from the Kekabeic Trail to to the Tuscarora Lodge Lodge road, road, aa distance distance of of about 1—1/4 1-1/4 miles. Contacts between bet\veen beds of of the the Upper Upper Cherty Cherty Memhe: Hembe:.: of the Gui-if Gunflint Iron-formation lint Iron—formationand andfine-grained fine—grained poikilitic poikilitic augite augite troctolite, troctolite, unit unit tp tp of the Duluth Complex, are are exposed exposed at at the the west west end of the the railcut. railcut. Also at the the west end end truncation truncation of of aa thin thin sill sill of the Logan Intrusive Intrusive Rocks Rocks can can he be seen. seen. About half—way half-l'1ay along along the the railcut, railcut, argillite and graywacke of the the Rove Rove Formation Formation are are in in contact contact The contact aureole here is ,-lith the the base base of of the the Duluth Duluth Complex. Complex. The is with narrow with no visible recrystallization recrystallization of of Rove Rove Formation Formation rocks rocks except within a few few feet feet of of unit unit tp. tp. This is inferred to to be aa 100—1,000 feet. reflection of the the thickness thickness of unit unit tp tp 100-1,000 feet. The dip lint and and Rove Rove Formation Formation varies varies from from 15-60° 15—60° to to the the south of the Gunf Gunflint along this part of of the the contact. contact. Stop 7a 7a Scenic overlook overlook on on the the Gunf Gunflint lint Trail above above Gunf Gunflint lint Lake -— Copper— Coppernickel mineralization at at the the base base of of the the Tuscarora Tuscarora Intrusion Intrusion The base of unit unit ttf of the the Tuscarora Intrusion Intrusion is is exposed exposed on on the northeast side lint Trail Trail at the side of of the the Gunf Gunflint the overlook. The fine— fineto mediuin—grairied troctoliteshows shows no no regular regular increase increase in grain medium-grained troctolite grain size size away away from a contact with unit tp tp and and the the upper upper part part of of aa Logan Logan sill. sill. Visible chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, pentlandite occur occur interstitial interstitial and olivine olivine in in the the troctolite. troctolite. This is a typical typical to plagioclase and of the example of the copper—nickel copper-nickel mineralization of of unit unit ttf, ttf, which which was was found by by Cleveland-Cliffs Cleveland—Cliffs Iron Company (in found (in five five holes holes along along the the base base of the Complex) to of the Complex) to occur constantly in aa 150 feet feet thick thick interval interval near near the base of unit unit ttf. ttf. The combined nickel—copper nickel-copper content content is is about about the 0.3 percent in this this interval. interval. A A slightly richer richer zone zone 10 10 to to 20 20 feet feet thick was was intercepted about about 50—150 50-150 feet above the the lower lower zone. zone. Stop7b Stop 7b 2000 feet northeast Rocks and 2000 feet northeast of of Stop 7a -— Logan Intrusive Rocks the the Rove Formation Thin bedded argillite is is exposed exposed on on the the north north face face of of aa ridge ridge capped by diabase. diabase. The argillite is recrystallized recrystallized to to aa biotite— biotitean interval interval of of aa few few inches inches at at the the contact. contact. bearing hornfels over an is typical typical of fine— fine- to to medium—grained medium-grained diabase diabase in in thin thin The diabase is sills the lower lower parts parts of of thick thick sills. sills. sills and in the �—123— -123- Stop 88 Northwest arm of Poplar Lake on the the Gunflint Trail At this stop stop typical exposures and and intrusive intrusive relationships relationships of of At this four of Nathads Nathans units units will be be examined. examined. On the the north north side side of of the the unit unit df, df, a fine—grained fine-grained decussate augite—olivine—plagioclase augite-olivine-plagioclase rock rock the Tuscarora Intrusion intrudes (troctolite) similar to unit ttf ttf of the intrudes (troctolite) unit dc, aa very veryfine—grained fine-grained granular granularolivine—augite—plagioclase olivine-augite-plagioclase rock whichmay mayrepresent representa achilled chilled margin marginofof the the oldest rock (gabbro) (gabbro) which unit of About 50 feet (da). About feet north of the the Trail Trail of the layered series (da). at the east end of the northwest arm of Popular Lake, at the east the north~vest Lake, a small small mass of unit dt, dt, aa medium—grained medium-grained granular granular olivine olivine oxide oxide rock, rock, occurs occurs within unit unit dc. dc. A A small isolated exposure of of unit unit ds ds with with uncertain uncertain contact contact relationships occurs occurs between units dc dc and and df df about about 500 500 feet feet Lake and and 400 400 feet feet north north of of the the Gunflint Gunflint Trail. Trail. northwest of Popular Lake South of of the the Gunflint Gunflint Trail there are exposures of of the the large large oxide— oxiderich sheet sheet unit dg (coarse—grained, foliated oxide, augite, olivine, dg (coarse-grained, foliated oxide, augite, plagioclase rock). plagioclase Stop 9 Sto2j Gunflint Trail Trailsouth southofofBear BearClub ClubLake Lake— - Late granitic granitic rocks rocks Cunflint of the theDuluth DuluthComplex Complex Unit daa, daa, a medium-grained quartz-feldspar rock, rock, is is medium—grained granular quartz—feldspar as aa dike on the the north north side side of exposed as dike in in unit unit dm dm on of the the Gunflint Gunflint Trail. Trail. The mainmass massofofdaa daaoccurs occurssouth southofofthe th Trail 1—1/2 The main Trailasasa astock stock 1-1/2 miles miles across. Unit dm, across. dm, aa cumulate cumulate sheet sheet ofofpigeonite—augite—plagioclase pigeonite-augite-plagioclase rockhas hasvisible visibleinterstitial interstitial quartz rock quartz and and alkali alkali feldspar feldspar in in an an This interinteraureole much as wide around daa. This aureole as much as 11 mile mile wide aroundthe the stock stock of daa. stitial material is interpreted as as replacement associated with the intrusion of unit daa. daa. stitial �This page intentionally left blank �"-"'; ADA ~ N A D A c '''L, . ./I '1''''-,t-'-"~)(. _/ <.~~,;t? x" I 'bJ I u : ST. LOUISI St LOUIS ' x. >. )( Ely. xLAKEx Marais X r AN AT ON P LANATION E E XP IKg XX I [+++ + +++J K xx )( xx xx Duluth Duluth Compte. Complell . O~ so' +)" ~~{ SlIver '" ~ '\. Bo.y ~V 0"" .c: U, '9'" <I)", to -" ~~ -c C ..r="c Zo 4? .!:! > 'C :'2 ::;; y.,e a. a :::> ""'" :.;;; 'E E 'c C <X cr INDEX MAP Figure 1 L 0 o 1 I 10 1O 20 ! I C A A L E if s S e 3Orniles 30 miles I ~{ 4? C 2 N V'1 Mci ic intrusive nt, usive rocks Mafic rocks ci rIrirt Shore of North Shore I , 1/7"-: N I // I ? Ettrus,ve Extrusive rocks rocks rongrnq ranging in from olilJine diem. in Composition composition from bosolr totile and basalt to quartz Quartz lotite local rhyolite tocot rt.yolite [02 4cg lite and Argillite cnd Groywocke Groywacke in Cook Rove Fm. includes Rove Fm. in Cook County County C ~ to ond and Vrginio Virginiaand andI horneon Thomson Fm. Fms. St. Louis Louis County .. in in St. County VO S/ I /-' I Lrl ~ ron —Fottitoijon Iron - Formation ncluces Gunflint C u,f tilt in Cook includes Cook County and B'wo bitt in in St. cnd Biwabik Louis County County SI. Louis o l'iitiu Undiv dod ided >lap showing the geologic 1ap of of northeastern northeastern Hinnesota Minnesota showing settinE of Cook County setting County and and the the location location of of Figure Figure 2. 2. C c: ,,=! n .0 E "'C" 4? .t'" a- �I ~) SAGANAGA ISAGANAGA GRANITE 4800730 —H— CANADA ~ + 0 CMATION AN ROVE FORMATION ANO INTRUSIVE ROCKS LOGAN INTRUSIVE ROCKS df L ds — I i-a I-' Gunflint dq tta I dp db dm -~ ag ~f9+ DULUTH WLUTH COMPLEX LAYERED SERIESOF OF NATHAN NATH\ LAYERED SERIES dm + da DIAGRAM BLOCK 0 dgL--------- DULUTH COMPLEX TUSCARORA INTRuSION '~f\ N 0' Trail BLOCK A DIAGRAM DIAGRAM + B • dm + do Quadrangles Studied Field trip hip stop Field stop seA L E Contact o Fault 3 2 4 = t> ~ ~ 5 mi. .~'*'tl) ~~ ",0", " " ~<b s-v G.:J BWCA boundary boundary BWC.A ~ .'" V ~'(§q, c§'t:: ;§ %o3T•3O' Figure 22 Figure I I Generalized geologic map map of part of of northwestern northwestern Cook Cook County. County. The The Gunflit-it Gunflint Iron-formation is is stippled. stippled. Only the the major units units of of the the Layered Layered Series Series of of Iron—formation in the the Duluth Duluth Complex Complex are are shown. shown. The area designated designated df df also also includes includes Nathan in dc,de,dk,ds,du,dy,dx, and dz; similarly ds dc,de,dk,ds,du,dy,dx, ds includes includes dc,de,dg,dk,dt,du,dv,dw; dc,de,dg,dk,dt,du,dv,dw; dg includes dc,dd,dh,di,du,dv,dt, dc,dd,dh,di,du,dv,dt, and dz; dz; dp dp includes dg,dj,and dg,dj,and dq; dq; db db includes includes (Nathan, 1969). da,dd, da,dd, and dm; dm; and and dm dm includes includes da,dd,de,dn,do, da,6j,de,dn,do, and dx. dx. (Nathan, I I I I I I I I I I I I I I I I I -,'" '" "-~~ ","''I 0/' �SAGAN.GA &EANtTS\ MET *VOLC ANICS LGI.JNFLINT lION FM. M El A V Ot C A N I C S FL I N1,\ .106 A N .IOVE ff N. M. dy I t-' tv ---J I in a \ \ 'I.-~-"'----- \\ \ \\ \ , Ii iJlm,l 0 o md 9r \ ------- -, .)l Figure 33 'I ,fg ' , II \ ~ lmile I dm —1900 -1900 / og 1900 C190° 1100 1700 1700 db 1500 I Soc 1500 A B 300FEET FEET 1300 ~1 FfET L_L-----------.... 1 300 300 EE1 diagrams showing showing the the irif inferred Block diagrams erred geologic geologic relationrelationships of of rock units in the ships the Long Island Lake and Gunflint Gunflint Lake quadrangles quadrangles (location Lake (location of diagrams shown in Figure 2). 2). f �-128—12 8— Mesabi Range Magnetite Hesabi Nagnetite Taconite 8, 1971 1971 May 8, by by R. R. W. W. Narsden Harsden Minnesota, Duluth University of Hinnesota, Duluth, Ninnesota Hinnesota �—129— -129- MESABI RANGE RANGEFIELD FIELD TRIP MESABI INTRODUCTION at the Mineinin Virginia, Virginia, The MesabiRange Rangefield fieldtrip trip starts at The Mesabi the Auburn Auburn Mine Minnesota andproceeds proceedsto to the Erie Minnesota and Erie Mine Mine near near Aurora, Aurora, the theReserve ReserveMine Mine at Babbitt and and ends ends at at the the Dunka Dunka Pit theeast eastend endofof MesabiRange Range at Babbitt Pit atat the thethe Mesabi near Birch trip isisdesigned show near Birch Lake. Lake. The The trip designedtoto showthe themetamorphic metamorphic changes changes the Biwabik iron iron formation formation caused caused by by the the intrusion intrusion of of the the Duluth Duluth in the Complex. The trip plan is shown on the index index map. The Mesabi esabi Range The Range trip trip is is made made possible possible by by the the cooperation cooperation of of the the Minnesota Ore Operations, United United States States Steel Steel Corporation, Corporation, the the Erie Erie other inforMining Company and Reserve Mining Company. Maps and and the Reserve and other Leaders for each part of furnished by the the mining mining companies. companies. Leaders mation were furnished the trip are are shown in the trip trip log. log. Stop 1. 1. Stop AUBURN MINE Leader: Wayne L. L. Plummer The accompanying map, section section and description description of the The accompanying map, stratigraphic sequence gives the geologic geologic setting setting of of the the Auburn Auburn Mine. Mine. The unit numbers shown shown on on the the stratigraphic stratigraphic sequence sequence are are painted on on the the rock rock to to aid recognition recognition of the the horizons. The upper part of the Pokegama quartzite and the Cherty, Lower Lower Slaty and 145 3*5 feet feet of the the Upper Upper Cherty Cherty Lower Cherty, members of the Biwabik formation members formation are are exposed. exposed. Oxidized and partly partly leached Biwabik formation is exposed on on the the west west pit wall wall and the Upper Slaty member and leached Virginia pit formations are exposed in north are exposed in the the slump slumpstructure structure at at the north end end of of the the pit. pit. �44 E S C' RESERVE <4 CQ(\ -1 0÷ I I-. f-' w o0 #9 I 1- Os ,Figure .Figure 11 INDEX MAP INDEX MAP OF THE OF THE MESABI DISTRICT DISTRICT,, MINNESOTA MESABI I I �---ex---• I f-' GRANITE Figure 22 Figure MESABI RANGE RANGE IRON FORMATIONS IRON ( BLACK BLACK AREAS AREAS ARE ARE DIRECT—SHIPPING DIRECT-SHIPPING ORE ORE BODIES BODIES)) U) W I-s f-' I �-132—132— AUBURN MINE MINE AUBURN The is isone the The Auburn AuburnMine Nine oneofofa agroup groupofofopen openpits pits located located near the city of Virginia, Minnesota. It city of Virginia, Minnesota. It was was originally developed as asan anunderground underground originally developed mine by the during the and promine by the Minnesota Minnesota Iron IronCompany Company durin?, theperiod periodfrom from1894—1902 1894-1902 and duced 2,143,000 2,143,000tons tons of of ore prior 1902 duced prior totoclosing closingin in 1902when whenownership ownership passed passed to the Oliver Iron Mining Nining Company, Steel 'Cor'CorOliver Iron Company,a asubsidiary subsidiaryofof United United States States Steel poration. Reopened as an poration. an open by Oliver in in 1951, 1951, the mine produced an openpit pit by 11,219,000 tons tons of of ore ore by by the the end end of of 1969 1969 when whenthe themine minehecirne became additional 11,219,000 inactive because the remaining ore is is under under the the approach approach traccs tracks totothe theViridrtia Virr,inia rescreening plant plant located located just just west west of of the the nine. mine. Most of the the crushing and rescreening open pit ore was loaded loaded by by electric electric shovels shovels into into side side dump dump cars cars and and hauled hauled to to the plant by electric locomotives, but in the plant in the the last last few few years, years, ore ore from from the the lower benches benches was was loaded loaded into into trucks, trucks, hauled hauled to to aa stockpile stockpile beside beside the the track track lower in the the upper part of the in the pit and reloaded into into railroad railroad cars. cars. The Auburn Auburn Nine and other former Oliver Iron }Iining Mining Company mines mines on the Mesabi Ran?,e Rance are are the Mesabi Mine now operated by U. S. S. Steel Steel Corporation, Corporation, Minnesota Minnesota Ore Ore Operations. Operations. The rocks rocks exposed in the the mine starting startin~ at at the the bottom bottom are arc the the the lower lower three three members members of of the the Biwabik Biwabik iron iron formation: formation: Pokegama Quartzite and the Lower Cherty, Cherty, Lower Slaty Slaty and and part part of of the the Upper Upper Cherty. Cherty. These dip dip from from degrees to to 20 20 degrees degrees to to the the northwest northwest as as the the formation formatcy lies north 5 degrees lies on on the the north side of the gently southwestward plunging Eveleth anticline and the center center fold known as the fold the Virginia Virginia Horn. Horn. formed in the Biwabik formation formation by removal The Auburn ore body was formed leaving less less of silica from iron bearing rock by leaching ground waters, waters, leaving soluble iron iron Oxides. oxides. The The ore body follows formation for ore body follows drnvn downthe thedip dipof of the the formation for fissure scarcely 50 about 3000 feet. as a aSlr::. small fissure 50 feet feet about 3000 feet. Beginning as at the the southwestern southwestern part part of of the the mine, the the ore ore body gradually gradually widens wide at toward the the northwest into a larger larger trough trough with with aa maximum maximum width width of of about about toward 500 feet. feet. In the the vertical walled fissure fissure at at the the southwestern southwestern end end of of the the mine, mine, the ore the ore extends extends from from slightly slightly above above the the Quartzite Ouartzite (here (here reduced reduced to to aawhite wite sand) feet of the Lower sand) through through 115 115 feet of the Lower Cherty Cherty member, memher, whereas whereas near near the the west west end end of the mine, the ore extends extends to depth of of about about 260 260 feet feet from from the the surface surface of the mine, the ore to aa depth Duetoto the the leaching to contact. Due leaching of to the the Lower Lower Cherty-Lower Slaty contact. silica, ore zones zones are commonly slumped into structures resembling synclinal structures resembling folds. folds. Where slumping occurs adjacent to to taconite taconite walls, walls, sltnp slump faults faults may ii silica, occur. Glacial deposits deposits consisting of reddish—gray—brown reddish-fray-brown till containing containinff numerous boulders boulders of of granite granite and and greenstone greenstone covered covered the the entire entire area area to numerous to aa depth of 10 to to 35 35 feet. feet. years An earth slide in the northwestern bank of the mine several years was stabilized stabilized with with aa rock fill which now covers covers much much of of previously ago was fill which previously exposed exposcd formation formation in in this this area. area. �-133—13 3— I I I I I I I I ROUCHLEAU MINE VIRGIJ1IIA I --l-- I ------ I I I I -j-----t---- ! i I I I " \/Jf'~O~ ~Oo @ V CRUSHER SCREENING -L __ PLANT --- \ \ RIqQ: \ .::>(( \ \ \---_--I \ Figure 33 Figure ~ II1- GEOLOGIC MAP AND VICINITY VTCINITY GEOLOGTC MAPOF OF AUBURN AUBURNMJr~E M:rE AND �-134-134— Table 11 Table STRATIGRAPRIC SEQUENCE G'mATIGRAPHIC SEQUENCE IN THE THEBIWABflC BIWABIK ThON IRONFORMATION FORMATION AUBURN ICIE AUBURN KmE Thickness 'l'h1ckness in feet1 in teet l UPPER CHERTY MEMBER 16.22 Jaspery, algal chert (G 16. Jaspery, conglorieratic conglomeratic and and algal submember I) (a and S $ submember x) 15. 14. 14. 13. 13. 12. 10 (eat.) (est.) Covered Covered interval interval 10 (est.) (eat.) Nodular hematitic chert chert. beds interbedded interbedded with with laminated hematite-eilicate-magnetite beds hematite-silicate-magnetite 48 48 +1' +f Laminatedhematite-uilicate-magnetite heniatite-ailicate-magnetite beds with subordinate Laminated jaspery chert beds Jaspery beds and and lenses 31 Jaspery, conglcaneratic chert beds with subJaspery, conglomeratic chert beds interbedded interbedded with ordinate laminated laminated heinatite-ailicate-magnetite hematite-silicate-magnetite beds beds 28 liberty taconite taconite with magnetite Cherty with thin thinirregular irregular magnetitebeds, beds,mqgfl* magneanddisseminated disseminated 'retite tite mottles mottles and mBgnetite 16_ _--=~ ....,;;1;;,;;6 143 LUiQER $LATY MEMBER3 11. U. 10. silicate magnetite Laminated silicate magnetite taconite taconite with withsubordinate subordinate silicate chert chert lenses lenses silicate Laminated non-magnetic silicate taconite, part. Laminated non-magnetic silicate taconite,fissile fissile in in part. 6' of fissile fissile"intermediate "intermediate slate" slate" at atbottom bottan (a (G and S 6' of submember Q) 6ubmember Q) 101 .....37 3;.;7_--=~ 138 ER LC1WER CHERTY MEMBER LO CHERTY Cherty with irregular irregularrnngnetite magnetite beds. Upper Upper 10' liberty taconite taconite with has silicate rich has dark-colored dark-colored silicate richbeds beds instead instead of ofmagnetite magnetite beds, ng base of lower indefinite beds, mak4 making lower slaty slatysomewhat somewhat indefinite 37 37 8. Mottled with chert "pebbles" and and Mottled silicate-magnetite silicate-magnetite chert with abundant coarse coarse granules. abundant U 11 7. 7. Cherty taconite with with thick thick (i"±) (1 t)magnetite magnetite beds beds and and mottles mottles liberty 84 9. 9. 6. 1f Mottled cherty very irregular irregularmagnetite magnetite Mottled cherty taconite taconite with with thin, thin, very beds. 14 5." Thick jaspery chert beds beds interbedded interbedded with with varying varying proporproporThick 5. tions of of thin, thin,regular regularlaminated lBDlinatedinngnetite-hematite-. magnetite-hemat1te-s1l1cateilicate- carbonate carbonate beds beds.• 66 �-135—135— Thlckneoo Thickne on l feet1 in feet (ConYd) Ldwer Cherty Member Member (Cont'd) Lover Cherty Fflyft, 'rhi c k henicstitic hem~~ti tic chert beJa beis with witb subordinate sulJordinate laminated laminated zonos. Seineclastic elastic sand sand grains grains near zones. Some near bottcn. bottan. Much carbonate. 8a Jaspery, ehert with subordinate Jaspery, conc'lomeratic conglomeratic and algal chert subordinate laminated zones. lnminnted zonea. Sand graino graino common. common. 4:4 2. z. l'lassivechlorit1c chioritic (or (or hematitic) hematitic) sandstone sandstone l-lilsslve 8 8 1. 1. Jaspery, Juapcry, conglomeratic and algal algal 4.. 3. chert 4 4: 236 Total thickness exposed Total, 5I7 Base not exposed Base exposed P0iGAl4A QUARTZ ITE ** ** * ** * * * ** 1. 1. Units 15 and onbank bankbetween betweentruck truckroed road,and andrailroad railroad near entrance Units and 16 measured measured on entrance to pit. pit. Units measured on on SW bank, at at BE end end,ofof pit. pit. Remainder measured. to Units 11 - 5 measured S\rl bank, measured above railroad. above railroad. 2. Unit correspondtoto numbers numberspainted paintedon onthe the walls walls of the Unit nwubers numbers correspond theAtthun Auburn Mine Mine and and are not Intended intended to be a new stratigraphic stratigraphic system. system. 3. 3. exists The lower lower slaty-upper slaty-upper cherty cherty contact contact is 1s not not well—marked, well-marked and and disagreement disagreement exists to its its position. position. as to ** ** ** ** ** * * orebody bodyisis of of the fissure or The Auburn Auburn ore or trough trough type type and and its and its location and 0 W, 400 W, nearly nearly appear to be controlled controlled by set striking strikingabout aboutNN 40 orientation appear to be by aa fracture set at right At the SE of the the mine at right angles angles to to the the strike strikeofofthe theiron ironformation. formation. At SE end. end. of mine the trough is only from the the quartzite quartzite through trough only 50' 50' wide wide and and the theore oreextended extended upward upward from through about about U5' ofofthe At the the northwest end the the trough trough 1s is 500 115' theLower LowerCherty Chertymember. member. At northwest end 500 feet feet wide wide and and ore ore occurs occurs for about about 260 Z60 feet feetfrcmt fran the the Lover Lower Slaty-Lcwer Slaty-Lower Cherty Chertycontact contact to to the Exceflent examples examplesofofore oreslump slumpstructures structurescan canbebeseen seenin in the the ends of the outcrop. Excellent eDds ot pit, pit, especially especiallyatatthe thenorthwest northwestend.. end. �-136— -136- Mine sLown ERIE MINE MINE —- The stops in inthe theErie Erie Mineare are shownon onthe theaccompanying accompanying map. The Erie geologists designate units in in the the Biwabik Biwabik formation formation as follows: A—F A-F G-O G—O P—Q P-Q R—W R-W Leader: Stop 2. 2. Upper Upper Lower Lower Slaty member — - .av. 110' 110' av. Cherty member - avo 185' 185' Slaty member — - av. avo 105' Cherty member — - av. avo 125' Forrest W. W. Boyce Bovee Erie —- Pit 1 West This stop the upper part part of the the Lower Lower Cherty member This stop is is in the (units are are designated TT and and SS layers layers by by Erie). Erie). The Biwabik (units formation is is composed composed of of tine fine Stilpnomelane, Stilpnomelane, I!innesotaite, Minnesotaite, magnetite and cherty quartz and contains bands, mottles quartz and contains bands, mottles and and blotches blotches of' of pink to yellow carbonate. carbonate. Stop 3. 3. Erie Pit 2 West This stop stop is is in in middle to to upper upper part part of of the the Upper Upper Cherty Cherty with the the member and the lower part of the Upper Slaty member (F) (F) with in this this pit pit are algal layer (I) (I) well exposed. exposed. (Units (Units in are designated (Upper Slaty), G, G, H, H, I, I, JJ and and KK by by Erie). Erie). A A diabase sill about about F, (Upper feet in thickness occurs near the bottom of 33 feet of the the exposed exposed iron iron formation in the KK layer. layer. Some green green mottles mottles of of cuminingtonite cummingtonite occur in the I J layer layer and and carbonate carbonate mottles mottles in in the the KK layer. layer. Stop Stop 4. . Erie Pit Pit 33 This stop is in in the western part part of of Pit Pit 33 in T, S. S. and BR of the the Lower Lower Cherty Cherty member. member. The layers in the middle part of rock is a cherty, silicate silicate taconite taconite with with layers layers of of cummingtonite. cummingtonite. Stop 5. Stop 5. Erie Pit Pit 33 This stop stop is is in the the eastern part of pit 33 in the T, CS and R F in about about the the same same stratigraphic stratigraphic layers of the Lower Cherty member in zone as as stop stop 4. 4. Much of the chert in the Biwabik formation formation has has gone to form form actinolite actinolite and and cumniingtonite. cummingtonite. The rock is termed taconite. Locally pyrrhotite occurs occurs in in the the a magnetite-silicate magnetite—sflicate taconite. iron formation. formation. �ERIE MINING COMPANY COMPANY ERIE MINING Of MAP OF E-1835.2 E— 1835 • 2 PLANT 8 MINE AREAS AREAS & MINE LEGEND o CRUSHER CDCOAR COARSE CRUSHER ®FINE FINE CRUSHER CRUSHER ® @ CONCENTRATOR CONCENTRATOR ® .j)PELLET @ PELLET PLANT ® ® ® LOADING LOADING POCIET POCKET ®STOCKPILE STOCKPILE ® CD GENERAL SHOPS SHOPS .1; ADI.IINISTRATION AOMINISTRATION BUILDING S I I-' La) LV ....... I AREA I S Figure 44 Figure Plan of of Erie Pit Plan Erie Pit — �—138— -133- RESERVE MINING COMPANY COMPANY Minil1g Company Company mine mine is is situated situated in in aa zone zone with ~vith aa The Reserve Miniqg considera~le considerable range in mineralogy and texture texture shown shown by by the the Biwabik Biwabik formation. formation. The The Reserve Reserve geologists geologists designate designate units units of of the the Biwabik Biwabik formation as follows: follows: A—G A-G 11—0 H-O P—Q P-Q R-V H—V Stop Stop 6. Upper Upper Lower Lower 100130 av.—120 Slaty member member -— 100'-130' av.-120 Cherty 120—160' av.—140 Chertymember member—- 120-160' av.-140 Slaty member —- 75—120' 75-120' av.'90 av.-90 Cherty member — - 30'-50' av.-30 30'—50' av.—30 Reserve Mine Mine (Peter Mitchell HitcheEMine) Hine) Leader: James James i1. W. Emanuelson Emanuelson This sstop is in This top is in the the western ~ves tern part part of of the the mine, mine, northwest of of Crusher No. No.22 in the the middle middle part partofofthe theUpper UpperCherty Chertymember member in in the J, KK and rock is silicate taconite with J, and L L zones. zones. The The rock is aamagnetite magnetite—- silicate abundant cuznnhingtonite. cummingtonite. Stop Stop 7. 7. Reserve Mine Mine This stop is in same general stratigranhic stratigraphic zone zone as as stop stop 6. 6. with Hith The rock rock is layers from from FF to 00 exposed. exposed. The is aamagnetite—quartz—silicate magnetite-quartz-silicate taconite with and garnet. garnet. There taconite with hedenbergite, hedenbergite, ferro—hypersthene, ferro-hypersthene, and There are local local areas areas of of pegmatite. pegmatite. Stop 8. 8. Dunka Pit The Dunka Erie ['lining Mining Company Company isissituated Dunkapit pit of of the Erie situated near near the eastern end of the Rangewhere wherethe the Bhvabik Biwabik formation formation is eastern end of the Hesabi Nesabi Range by the theDuluth DuluthComplex. Complex. This Hill show show the upper upper This stop will, intruded by part of the part Upper Cherty the Upper Upper Slaty Slaty the Upper Cherty member, member,the thelower lowerpart part of of the member,and and gabbro gabbro of of the member, the Duluth DuluthComplex. Complex. The is composed composed of magnetite, hedenbergite, hedenbergite, The taconite taconite is of quartz, quartz, magnetite, fayalite with with andradite andradite garnet garnet and and locally locallysome some hessingerite hessingerite fayalite The contains suiphides, sulphides, chalcopyrite chalcopyrite and and Thegabbro gabbroininthis this area contains pyrrhotite with pyrrhotite with pentlandite. pentlandite. The iron iron formation formation and andgabbro gabbrowill willbe be observed observedinin the the pit pit and The and in north of of the the pit. pit. in outcrops outcrops north �— -' __I / / ea _I - —— __i SCALE SCALE IN IN MILES MILES —11 4 0 5 2Z 5 / / / / / I I tO / / 'sTrOe,. stnva / I /8 /& 8/~ "E i/l '7 '2OA f/~ STAfiC) "I<c 0: I~ " "/>c / 460 400 / I I I I I (.0 '0 / I I / / / / / - -&try / p -— 2C • 0 SCA.E SC --' AtFtPC i.E iS 5ØS StS?iOeiCO AT iJJ) FT iNT€vSiS SIRS DPI ROADS C IAD DPI F Lint STh YISG co-s5i0$i SHO_ O&nI. ms •PT OLJTLIIA • S Off _ _N PIT Oln'LJNE,I.S - ';"b6 ZC = SCALE ,", 2000' JAN 196~ JQ'I . . . . 10A- I Figure Figure 55 Plan of Plan of Reserve Reserve Mine Mine �lL ERIE ERIE MINING MINING COMPANY COMPANY HOYT PLANT HOYT LAKES LAKES PLANT PLANTSITE TO TO DUNKA DUNKA PIT PIT AREA AREA Figure 6 U, DUNKA PIT BABBITT / ¶ '\ y/ ~ --- C -- 01 \J c:> I I-' ...... o0 .pI RESERVE MINING co. CRUSHER No.2 AREArJ ,, . ., , . , r-. :' ~ l P P L SIT E r-- ) ~ ( I I �—141— -141- of the Metavolcanic— Geology of the Vermilion MetavolcanicMetasedimentary Belt, Belt, Northeastern Minnesota May 8, 1971 Prepared by R. R. \v. U. Ojakangas, Ojakangas, University University of of Ninnesota, iinnesota, Duluth, Duluth, and and Ninnesota Geological Survey P. P. K. Sims, Sims, Minnesota Geological Survey, K. Survey, Minneapolis, Minneapolis, Minnesota C. G. B. Norey, Morey, Hinnesota Minnesota Geological Survey B. Survey Minneapolis, Minneapolis, Minnesota J. J. C. C. Green, Green, University University of of Minnesota, Minnesota, Duluth, Duluth, and Minnesota Geological Survey �—14 2— -142- Guide to Metavolcanicto the the Geology of of the Vermilion Metavolcanic— Belt; Northeastern Minnesota Metasedimentary Belt; INTRODUCTION The The Vermilion district is is a a belt of metavolcanic-metasedimentary metavolcanic—metasedimentary rocks rocks more than 100 100 miles long long and and as as much much as as 20 20 miles miles wide. wide. It is is bordered on on the the north north and and south south by by younger younger granitic granitic batholiths batholiths (Fig. (Fig. 1) 1) of Algoman Algoman (Kenoran) (Kenoran) age. age. The region is typical of Lower Precambrian (>2,500 greenstone—metasediment--granite complexes complexes of of the the Superior (>2,500 m.y.) greenstone-metasediment-granite province. metavolcanic—metasedimentary sequence constitutes a complex The metavolcanic-metasedimentary volcanic pile, pile, characterized characterized by interfingering of lithologies and local local volcanism. Most of the the metasediinents metasediments are composed of of repetitions of volcanism. volcanic detritus, detritus, and probably include volcaniclastic and and epiclastic rocks. Numerous Numerous coeval and younger igneous rocks rocks occur locally within the sequence. sequence. The stratified sequence was metamorphosed and and deformed deformed before before and and during emplacement of the bordering granitic rocks rocks of the the Giants Range and the the Vermilion Vermilion batholith. batholith. Pervasive greensehist greenschist facies facies batholith and assemblages were developed except adjacent to the the intrusive bodies where metamorphism attained aniphibolite amphibolite grade. Deformation consisted consisted of of two two metamorphism attained major foldings foldings and and of of later later faulting faulting on on aa major major scale. scale. STRATIGRAPHY ST RATIGRAPHY The metavolcanic and metasedimentary rocks rocks are are assigned assigned to to five five The oldest oldest formation, (Morey and and others, others, 1970). 1970). The formation, the the Ely formations (Morey is overlain Greenstone overlain Creenstone -— composed mainly of mafic mafic metavolcanic metavolcanic rocks rocks -— is stratigraphically in the west by the Lake Vermilion Formation and locally, locally, the Soudan Iron—formation, Iron-formation, and in the central part by the the Knife Lake Group (Figs. (Figs. 22 && 3). 3). Both the Lake Vermilion Formation and the Knife Lake Group Group are composed mainly of intermediate—felsic the Knife intermediate-felsic pyro— pyroand volcanogenic volcanogenic sandstones. sandstones. The Newton Lake Formation, Formation, clastic deposits and a younger mafic to to intermediate-felsic unit, overlies the a intermediate—felsic metavolcanic unit, Knife Knife Lake Lake Group Group in the the central part part of of the district and interfingers with it to the east (Fig. it (Fig. 3). 3). A A generalized and idealized pre—deformational pre-deformational stratigraphic sequence the western part part of the district is shown in sequence for for the figure 4. 4. Ely Greenstone Greenstone Ely Greenstone, Greenstone, as as redefined redefined (?Iorey (Horey and others, 1970), 1970), is is an The Ely an elongate body of dominantly mafic metavolcanic rocks, rocks, on the the average 2—4 2-4 miles miles wide, wide, that that extends from the vicinity of Tower eastward to to distance of of about about 40 40 miles miles (Figs. (Figs. 22 && 3). 3). Pillowed or or Moose Lake, aa distance lavas and metadiabase dominate dominate the the formation. formation. massive metabasaltic lavas pyroclastic Pillowed lavas of andesitic comnosition, composition, interinediate—felsic intermediate-felsic pyroclastic �-143—14 3— ic—intermediate epiclastic epiclastic deposits, deposits, chert chert and banded deposits, maf mafic-intermediate iron-formation, tuff (?) (?) comprise comprise the the iron—formation, and siliceous carbonaceous tuff remainder. Andesite and and dacite dacite porphyry porphyry are are conmion common hypabyssal hypabyssal intrusive rocks. rocks. The green color of most of of the the rocks rocks is is due due to to abundant secondary chlorite and green amphibole. abundant amphibole. at about The ruaxinul maximum exposed estimated at about exposedthickness thicknessofofthe the Ely Ely is is estimated feet; the are consistently to the 15,000 feet; the tops tops of of separate separate flows flows are consistently to the north, north, as indicated by by pillows. pillows. as indicated Soudan Iron—formation Iron-formation The The Soudan Iron—formation, Iron-formation, the the thickest thickest and and most most continuous continuous banded iron-formation iron—formation in in the the sequence, sequence, extends extends from from Tower Tower and and Soudan Soudan eastward eastward for a a distance of about 16 miles (Fig. (Fig. 2). 2). for In In the the Tower-Soudan Tower—Soudan area area it it is is ov~rlain overlain directly directly by by intermediate— intermediatefelsic volcaniclastic rocks of the felsic the Lake Lake Vermilion Vermilion Formation, Formation, whereas whereas east east (Fig. 2) 2) it it is is overlain directly by at least 7,000 7,000 feet feet of Armstrong Lake (Fig. of metavolcanicrocks rocks with with lenses of mafic—interinediate mafic-intermediate metavolcanic lenses ofofbanded bandediron— ironThus, the formation, which are are assigned assigned to to the the Ely Ely Greenstone. Greenstone. Thus, the Soudan, Soudan, which represents a time—stratigraphic time-stratigraphic unit, unit, is is a useful indicator of the the essential contemporaneity contemporaneity of of intermediate-felsic intermediate—felsic volcanism in the west west essential in the (Lake Vermilion Vermilion Formation) Formation) and and mafic mafic volcanism in the east (Ely (Lake (Ely Greenstone). The Soudan Iron—formation, as redefined 1910), The Iron-formation, as redefined (Morey (Morey and others, others, 1970), consists of several several types of ferruginous ferruginous cherts cherts that consists of types of that are interbedded meta— with fine—grained fine-grained carbonaceous carbonaceous and and sericitic sericitic tuffs tuffs (?) (7) and local metabasalt; all are are intruded intruded by by metadiabase metadiabase and and dacitic dacitic porphyries. porphyries. The thickness thickness of of the the formation formation has has not not been been determined determined accurately accurately because because probably is of complex folding, folding, but probably is less than 1,000 feet. feet. It It should be noted that the in the Ely the iron—formation iron-formation in Ely trough trough (Reid, (Reid, 1956), 1956), which which has has yielded hematite iron iron ore, ore, probably yielded large quantities quantitiesofofhigh—grade high-grade hematite probably is is not equivalent equivalent to to the Soudan Iron—formation. Iron-formation. The high—grade high-grade hematite ores that that were the Soudan Iron—formation Iron-formation at at Soudan (Klinger, (Klinger, ores were mined in the 1956) and and in in the the banded banded iron-formation iron—formation at at Ely Ely (Machamer, 1968) are are 1956) (Machamer, 1968) considered to to have been formed formed by by hydrothermal hydrothermal processes processes (Gruner, (Gruner, 1926). 1926). FO~lation Lake Vermilion Formation In the extreme the district ~Fig. 2), 2), the Lake In the extreme ~~estern western part part of of the district (Fig. Vermilion Formation Formation overlies theEly ElyGreenstone Greenstone or orthe theSoudan Soudan overlies either either the Iron—formation. Until recently these strata were assigned to the Iron-formation. the Knife Lake Lake Group. Group. They were reassigned (Morey (Morey and others, 1970) to to the Lake Vermilion Formation because they the they are not demonstrably concontinuous the Knife tinuous with with strata strata exposed exposed in in the the type type area of of the Knife Lake, Lake, in the eastern part part of of the the district. district. formation which has has been The Lake Vermilion is aa heterogeneous formation divided (Morey (Morey and and others, others, 1970) into four fourinformal informal members — - a fe1dspathic 1910) into members feldspathic quartzite member, member, member, a metagraywacke-slate metagraywacke—slate member, member, a volcaniclastic member, and a mixed metagra~vacke-felsic metagraywacke—felsic conglomerate conglomerate member. member. �—144— -144- The feldspathic quartzite member, member, composed dominantly of -ts volcanogenic minerals and and rock rock fragments fragments of of dacitic dacitic composition, composition, is in at the the fold fold nose nose southwest southwest of of Tower Tower in contact contact with with the the Ely Ely Greenstone Grenstone at (Fig. 2), than the the metagraywacke-slate as indicated indicated (Fig. 2), and and is is older than metagraywacke—slate member, as by graded graded beds. beds. The metagraywacke-slate metagraywacke—slate member, member, which Is is areally area11y the most extensive member, overlies the the Ely Greenstone locally, locally, as as member, directly overlies the south south limb limb of of the the fold fold at at Tower, Tower, but but for for the the most most 'part ,part Is is in in contact contact on the with the the older quartzite. The graywacke graywack~generally generally are well bedded and commonly are are graded; graded; like like the the feldspathic feldspathic quartzite, quartzite, they they consist consist mainly mainly commonly of volcanogenic volcanogenic debris. debris. A A chioritic chloritic facies occurs on on the the shores shores of of the the fades occurs eastern part part of of Lake Lake Vermilion, Vermilion, but but aa biotitic biotitic facies, fades, containing containing scattered scattered amphibole, amphibole, is is dominant dominant elsewhere. elsewhere. The member contains several interbedded lenses of metabasalt that that are are sufficiently sufficiently large large to to be be shown sho\vu on on figure figure 2. 2. The volcaniclastic member is is of interest because it was interp:eted inter~~eted previously to 1903) related to to be mainly aa conglomerate (Clements, (Clements, 1903) to the the Laurentian orogeny. Instead, it it is orogeny. Instead, is dominantly tuff tuff and and agglomerate agglomerate of of dacitic composition, with lesser lesser dacitic dacitic lavas, lavas, banded banded iron—formations, iron-formations s and euxenic black black slates. slates. Locally, Locally, dacite porphyry intrudes the the various rock types. The agglomerates, agglomerates, which which are are interbedded with tuffs, types. The interbedded with tuffs, consist consist cobbles and boulders in a of sub—rounded sub-rounded felsite felsite to to felsite felsite porphyry cobbles and boulders txotic rock fragments, fine-grained matrix of similar similar composition. composition. Exotic fragments, mainly fine—grained iron-formation and greenstone, constitute constitute only only one one or or two two percent of the the iron—formation rock. metagraywacke—felsic conglomerate member, member, which occupies The mixed metagraywacke-felsic occupies an of about about 30 square miles miles on the south limb of the of an area of 30 square the south limb of the fold fold south of Tower, interfingers with and and is is stratigraphically stratigraphically overlain overláin by the meta— Tower, interfingers with the metaIt consists consists of of a graywacke-slate member member (Fig. (Fig. 2). 2). It a maximum of about graywacke—slate 10,000 feet feet of to mafic rocks, felsite felsite flows, flows, several several of felsic felsic to mafic volcaniclastic volcaniclästic rocks, types and metagraywacke metagraywacke (Griffin, (Griffin, 1969; 1969; types of of cong1.omerates conglomerates and agglomerates, and Griffin and Morey, 1969). 1969). The thickness thickness of the the Lake its constituent constituent Lake Vermilion Formation and its members is poorly known because of complex complex folding and faulting faulting and and rather poor exposures. exposures. In the the Tower quadrangle, quadrangle, the quartzite member is estimated to to be the volcaniclastic member is be 1,500-2 1,500—2,000 feet thick and the t OOO feet metagraywacke—slate to be a maximum of about about 4,000—5,000 4,000-5,000 feet feet thick. thick. The metagraywacke-slate to is at at least least 3,000 3,000 feet feet thick thick and and is is probably probably much much thicker. thicker. member is Knife Lake Group Rocks of the Knife Knife Lake Group directly overlie the Ely Greenstone Rocks from the vicinity of Ely, Ely, where the the Knife Knife Lake Lake terminates terminates against against aa fault, fault, from The Knife Group, as eastward to to Moose Moose Lake Lake (Fig. (Fig. 3). 3). The Knife Lake Group, as redefined eastward (Morey consists dominantly of graywacke, gra~vacke, slate, slate, and and (Morey and and others, others, 1970), 1970), consists lava phyllite but includes includes substantial amounts amounts of pyroclastic rocks, rocks, lava flows, and and conglomerates. conglomerates. Gruner (1941, (1941, p. p. 1624) estimated that that the the flows, 15,000 the eastern end of the district district is about 15,000 feet feet Knife Lake near the thick, but this figure may be conservative. conservative. thick, but this �—145— -145- Newton Lake Formation The Newton Lake Lake Formation Formation was was mapped mapped earlier earlier (Clements, (Clements, 1903) 1903) as Ely Greenstone, but has been renamed (Morey as Ely Greenstone, (Morey and and others, others, 1970; 1970; Green, Green, l970)because it is stratigraphically younger 1970)because younger than than the the Knife Knife Lake Lake Group Group (Fig. the north north by by the the Vermilion (Fig. 3). 3). The formation formation is is truncated truncated on the fault and and along along strike to fault to the the northeast by granitic rocks rocks of of the the Vermilion batholjth. batholith. At its its western extremity, extremitYt near near :olf Wolf Lake, Lake, the the is truncated truncated by by aa fault fault (Fig. (Fig. 2). 2). formation is The western western part part of of the Lake formation formation is is composed principrinciThe the Newton Lake pally of of mafic mafic volcanics volcanics and and the the eastern eastern part part of of intermediate-felsic intermediate—felsic pally members,t which interfinger in volcanic members in the the vicinity vicinity of of Newton Newton Lake. Lake. volcanic member member consists consists dominantly dominantly of of metabasalt metabasalt and and metameta— The mafic volcanic andesite and fine—to—coarse—grained fine-to-coarse-grained andesite lavas lavas,t some some of of which are pillowed, and metadiabase and tuff tuff or tuff—breccia. tuff-breccia. Several small bodies of serpen— serpentinized peridotite are are associated spatially with the tinized the metabasalt metabasalt and and metadiabase. Small Small lenses lenses of of siliceous siliceous marble marble and and banded banded iron-formation iron—formation in the the formation. formation. The felsic member, east east of of Newton Newton Lake, Lake t occur locally in is composed composed of of felsic—intermediate is felsic-intermediate volcanics, dominantly dominantly tuff—breccia tuff-breccia deposits and and lesser lesser flows. flows. At places, metabasalt is is interbedded interbedded with the dominantly felsic volcanics. the Intrusive Rocks Five activity are are recognized recognized in in the the Five distinct distinct episodes of intrusive activity region. In In order age, from from oldest to to youngest, youngest, these these are are order of of inferred age, (1) synvolcanic have aa (1) synvolcanic bodies, bodies, including including hypabyssal porphyries, which have metadiabase and and metagabbro, metagabbro, and serpentinized wide range of composition, composition, metadiabase serpentinized peridotite (2) lamprophyres and related related hornblende—bearing hornblende-bearing rocks, rocks, (3) (3) peridotite,t (2) plutonic plutonic rocks rocks of of the the Giants Giants Range Range and and Vermilion Vermilion batholiths, batholiths, which which are are syntectonic, (4) altered diorite—gabbro diorite-gabbro which forms forms large large dikes dikes that that are are syntectonic, (4) post-tectonic, (5) basalt, basalt, which forms forms small, small, discontinuous, discontinuous, scattered scattered post—tectonic, and (5) dikes. In the Saganaga Granite of Winchell (1888) (1888) at at the the eastern eastern In addition, addition, the end of the district (Fig. end (Fig. 1) in age age to to the the 1) is is approximately equivalent in rocks of the rocks the two two batholiths batholiths and and intrudes intrudes the the older older rnetavolcanics metavolcanics (Grout, (Grout, 1929; and Goldich, Goldich, 1970). 1970). 1929; Hanson and The rocks of The plutonic plutonic rocks of the the Vermilion Vermilion and and Giants Giants Range Range batholiths batholiths proprofoundly affected the the volcanic—sedimentary volcanic-sedimentary sequence. sequence. Granitic rocks rocks of of the the foundly on the the south, south, irregularly irregularly intrude intrude the the composite Giants Range batholith, on sequence or are in fault contact contact with it, it, and and have have cut cut out out an an unknown unknown amount amount of section at Where the granite is at the the base base of of the the Ely Ely Greenstone. Greenstone. ~~ere is not in in fault with the the lower-grade lower—grade volcanic-sedimentary volcanic—sedimentary rocks, rocks, it it has has normal normal fault contact contact with to the the older older strata, strata, with with the the development development of of intrusive relationships to amphibolite-facies to the the contact. contact. The Vermilion amphibolite—facies assemblages adjacent to batholith, on on the the north side the district, transects the the upper side of of the district, transects upper stratistrati— graphic part of the the supracrustal sequence. sequence. This leucocratic biotite biotite granite granite includes wide wide zones of abundant inclusions of biotite schist includes zones of schist and and amphibolite amphibolite STRUCTURE The metavolcanic metavolcanic and rocks dominantly constitute a and metasedimentary rocks homoclinal, northward—younging homoclinal, northward-younging sequence sequence in in the the central central part part of of the the district, district, �-146—146-whereas they are faulted in in the the western western and and are both complexly folded folded and and faulted eastern parts. parts. Deformation was not pervasive, pervasive, and and primary primary structures structures Graded bedding and other primary features remain in most of of the the rocks. rocks. Graded features remain in the the graywacke—slate gray\vacke-slate successions, and and pillow pillow structu:es structu::es and and variolites are remarkably well preserved in the mafic metavolcanic remarkably preserved in the mafic metavolcanic rocks. rocks. At places, however, hmvever, a penetrative penetrative deformation, deformation, mainly mainly shearing, shearing, has has obliterated the the bedding. bedding. the western part of the area the the rocks rocks are are complexly complexly folded folded as as In the aa result two distinct episodes of deformation. deformation. The younger folds folds and and result of of two aa pervasive accompanying cleavage largely largely obscure obscure the the older older folds, folds, alalthough though the the older folds folds were important in in determining determining the the distribution distribution of the rocks. rocks. Detailed studies in in the the Tower quadrangle quadrangle and and adjacent adjacent areas areas (Hooper and Ojakangas, Ojakangas, 1971) 1971) indicate that (Hooper and that the metasedimentary strata, strata, and to to aa lesser degree the metavolcanic rocks, rocks, first first were ,,,ere folded folded on on west'iVestThese (F1) folds were tight to isoclinal, had northwest-trending axes. axes. (fo ) folds tvere tight to isoclinal, had northwest—trending l steep axial axial planes, planes, and probably had gentle or steep or moderate moderate plunges. plunges. Major ~lajor fold axes, axes, as as determined by consistently facing fold facing or or opposing opposing tops tops of of beds, beds, were spaced from from 700 700 to to 1,500 1,500 feet feet apart. apart. The younger (F2) (F ) folds, folds, which 2 most of comprise most of the mappable ones, ones, are are strongly strongly asymmetric asymmetrlc and and have have In most most of of the area the (F2) steep axial planes that that trend trend eastward. eastvlard. In (F ) folds folds 2 are dominantly Z—folds, are Z-folds, and the the northwest—trending northwest-trending limbs limbs are are two two or or more more times longer than the southwest—trending southwest-trending limbs; limbs; plunges plunges are are generally generally times of aa pervasive, pervasive, mild, mild, axial axial plane plane cleavage cleavage with with steep. The intersection intersection of In biotitebiotite— and higher—grade to F2 fo fold fold axes. axes. In higher-grade rocks, rocks, bedding is parallel to 2 to the the cleavage—bedding cleavage-bedding intersection. intersection. new minerals minerals are aligned parallel to In joints, In the the Tower Tower area, area, several several nearly nearly vertical vertical structures structures -— faults, faults, joints, and third deformation deformation displace displace the the cleavage cleavage of of the the F2 F and kink bands of a third 2 deformation. High—angle faults High-angle faults of two two trends, trends, longitudinal longitudinal and and transverse, transverse, break break the metavolcanic—metasedimentary sequence the metavolcanic-metasedimentary sequence into into aa number number of of blocks blocks or or segments and separate it in part from from the the marginal batholithic batholithic rocks. rocks. segments The Vermilion fault fault (Sims (Sims and and others, 1968), 1968), aa longitudinal longitudinal fault fault with with an inferred length of 300 300 miles (Sims, (Sims, 1970) 1970) generally generally separates separates the the Vermilion batholith and associated amphibolite facies facies schists schists from from lower— lm"ergrade rocks of of the the district. district. The directioncl the the horizontal horizontal The amount and directionof component of of movement component movement is not known, known, but but possibly possibly is is several several miles. miles. The vertical displacement is inferred to be on the order of a mile, bring displacement is inferred to on the order of a mile, to to bring higher-temperature-facies higher—temperature--facies rocks rocks on on the the north north against against lower-temperaturelower—temperature— facies facies rocks rocks in in the the district. district. Other longitudinal faults, faults, some some of which ,,,hi-ch appear to to be be strands strands from from the the Vermilion fault, fault, slice the the northern part part of the district into of into separate separate segments. segments. The transverse transverse faults faults trend trend northeastward or north—northeastward north-northeastward and have have dominantly dominantly left left lateral lateral displacements; the principal faults displacements; faults of this this Set set have have measureable measureable displacements 3-4 miles (Griffin (Griffin and and Morey, ~1orey, 1969). 19(9). displacements of of about 3—4 The The major faults faults of the area are expressed expressed commonly commonly as as narrow, narrow, Where exposed, linear topographic depressions. depressions. I,'here exposed, they are are seen seen to to of wide zones of crushed crushed and and altered altered rock rock or or of of intensely intensely consist either of silicified and altered altered rocks. rocks. �-147—14 7— Selected References Clements, J. ri., U., 1903, C1e~ents, J. 1903, The Vermilion iron—bearing iron-bearing district district of of Minnesota: Minnesota: U. S. U. S. Geol. Geol. Survey Survey Mon. Hon. 45, 45, 463 463 p. p. Coldich, S. S. S., S., Nier, Nier, A. A. 0., 0., Baadsgaard, Baadsgaard, Ha1fden, Halfden, Hoffman, Hoffman, J. J. H., H., and and Goldich, Krue;er, H. U. The P:ecambrian geology and geochronology Krueger, H. IV., 1961, The P::ecambrian and geochronology of of ilinnesota: dinnesota: [inn. Hinn. Geol. Geol. Survey Survey Bull. Bull. 41, 41, 193 193 p. p. , Green, C., 1970, 1970, Lower Precambrian rocks rocks of of the the Cabbro Gabbro Lake Lake quadquadGreen, J. J. C., rangle, rang1e, northeastern northeastern Minnesota: }1innesota: :--1inn. Geol. Survey, Survey, Spec. Spec. Pub. Pub. Minn. Geol. ser., ser., SP—10, SP-10, 96 96 p. p. Griffin, L., 1969, Embarrass quadrangle, quadrangle, St. St. Louis Louis County, County, Minnesota: Minnesota: Griffin, ,~. U. L., Minn. Ceol. ~Hnn. Geol. Su—vey Su-vey Misc. Misc. Map Hap Sec., Ser., MaD Map M—6. 1'1-6. Griffin, Griffin, U. IV. L., L., and and ?torey, !'forey, G. C. B., 8., 1969, 1969, The The geology geology of of the Isaac Lake Minn. Geol. Survey, quadrangle, quadrangle, St. St. Louis County, County, Minnesota: Hinn. Survey, Special Pub. SP-8, 57 57 p. p. Pub. Ser., SP—B, Grout, F. Grout, F. F., F., 1929, The Saganaga Saganaga granite granite of of Minnesota—Ontario: Minnesota-Ontario: Jour. Jour. Geology, Geology, v. v. 37, 37, p. p. 562—591. 562-591. Gruner, .3. Gruner, J. W., The Soudan Formation and a new suggestion as to to the the U., 1926, The Econ. Geol., v. 21, p. 629—644. oriign of the the Vermilion iron iron ores: ores: Econ. 21, p. 629-644. Cruner, .3. Gruner, J. W., W., 1941, 1941, Structural geolony geology of of the Knife Lake area of northeastern Minnesota: Geol. Soc. Hinnesota: Geol. Soc. America Bull., Bull., v. 52, 52, p. p. 1577—1642. 1577-1642.' Hanson, G. G. N. N. and and Go1dich, Goldich, S. Hanson, S. S., S., 1970, Early Early Precambrian Precambrian geology geology of of the Saganaga-Northern Light Inst. the Saganaga—r4orthern Light Lakes Lakes area, area, Minnesota-Ontario: Minnesota—Ontario: Inst. Sup. Geology, Geology, Proc. 16th 16th Ann. Ann. Mtg., Mtg., Thunder Thunder Bay, Bay, Ontario, Ontario, Lake Sup. p. 18. p. 18. Hanson, C. R., 1971, 1971, K-Ar K—Ar ages ages of of mafic mafic dikes and Hanson, G. N. N. and and >Lalhocra, Nalhotra, R., evidence for low—grade lOVT-grade regional metamorphism metamoJ.Tphism in in northeastern northeastern evidence for :linriesota: Hinnesota: Geoi. Soc. Soc. America Bull. Bull. (in (in press, press, March March issue). issue). Ceol. Hooper, Vermilion [looper,Peter Peter and and Ojakangas, Ojakangas, R. R. W., U., Multiple Multinle deformation deformation in the Vermilion district, Minnesota: district, Hinnesota: Can. Can. Jour. Jour. Earth Earth Sci. Sd. (in (in press, press, April April issue). issue). Klinger, Klinger, F. F. L., L., 1956, 1956, Geology Geology of of the the Soudan Soudan mine mine and and vicinity; vicinity; Guide Guide book book Series, Series, Precambrian ef of northeastern Minnesota: Geol. Geol. Soc. Soc. America, America, Ninneapolis, Heeting, p. p. 120—134. 120-134. Minneapolis, Minnesota Meeting, iachmner, J. F. Machamer, J. F., 1968, Geology the iron are the Geology and and origin of of the ore deposits deposits of of the mine, Vermilion district, Minnesota: Zenith mine, Ninnesota: Minn. Minn. Geol. Geol. Survey Survey Spec. Spec. Pub., SP—2, Pub., SP-2, 56 56 p. p. , Ojakangas, Ojakangas, 11. R. U., W., Sims, Sims, P. & Hooper, P. K., K., & Hooper, Peter, Peter, 1971, 1971, Geology of the Tower Tm.,rer Quadrangle: Quadrangle: !'linn. Geol. Survey Survey (In (In preparation). preparation). Minn. Geol. Reid, 1. I. L., L., 19 1956, l:Zeid, S6, Ceolo1y Geo1of-y of the the Ely Ely Trough: Trough: Guidebook Series, Series, Precambrian of northeastern Minnesota: Geol. of Soc. America, Minneapolis Hinneapolis meeting, meeting, Geol. Soc. i,. 135—148. TJ. 135-148. �—14 8— -148- Sims, P. 1970, Geologic Geologic map map of Minnesota: P. IC., K., 1970, Minn. Geol. Survey Survey Misc. Map Set., Misc. Ser., Map M—l4. M-l4. Sims, Morey, C. Sims, P. P. K., K., Morey, G. B., B., Ojakangas, R. R. W., W., and and Griffin, Griffin, N. W. L., L., 1968, 1968, Preliminary geologic map of of the the Vermilion Vermilion district district and and adjacent adjacent areas, areas, northern Minnesota: Minn. Geol. Geo1. Survey Survey Misc. Misc. Map Map Ser., Ser., Map Map M—5. M-5. Sims, Morey, G. Sims, P. P. K., K., Morey, G. B., B., Ojakangas, R. R. N., W., and and Viswanathan, Viswanathan, S., S., 1971, 1971, (in press), press), Geologic Map of Minnesota, Hibbing (in Hibbing Sheet: Sheet: Minn. Geol. Geol. Survey. Survey. Winchell, H. H. V., V., 1888, 1888, Report Report of of observations observations made made during during the the summer summer Winchell, Minn. Geol. (northern Minnesota); Minnesota): Minn. Geol. Survey Survey Ann. Ann. Rept. Rept. v. v. 16, 16, of 1887 (northern p. p. 395—478, 395-478, map. map. �F L A NJ ATION EXPLANATION cc o C, ~ c~ "-' -'=' ~ E D ° :::) 0C l::~~:1 3: { cC, 0 V ~ 0 ill U "-' ill 3: Duluth Duluth 0:::'" ~f N I Complex a. CO o ~ ~ -0 E -o-'=' -o ::J 0 Virg1nia Vrqinio <..? "'~'l Q... and Formations Rove ill I f-' C « Bv,::uk and Biwabik and Gunflint Gunflinl fornialions Iron — - formations ~ C co o ~+++++J Gions Giants r:''",; ;->~, 'I '] "::~;::::'7·{~::/,--- Range Range Granile Granite Vermilion GronLte Granile , / t,/~'-J = co o — -'=' E Saganaqa Sagona go o S u ~ Granite Q... Q; 3: o ---.J ~Sif epiclastic, volconiclastic undivided epiclastic, volcaniclastic sedlmenlary rocks, extrusive mafic sedimentary rocks, extrusive rocks, and and lhe te igneous rocks, Soudan Iron Iron -—formation tormotion (sit), (sit) mainly greensch;st focies greenschist facies o0................ jO '0 IIoowiiIl 20 I SCALE 5 CAL E 30 Miles 3OMiies J5 E o u 1: "-' & 0::: '0 I �-\0 92°00' 92°45' 90°45' -«) o o co co CANADA "" Area. of <:r p1a.te I I-' lJl o0 °Cook. I + + + + + + + + + + + + + cr + + + + + + + + + + + + Location + + ,'i' ,.'" Map ~qj~ + 'vI;;) (:)~ .",o," ~"r.o~' ~<> ~(:) ",,'0 ::<,,<6 <0(:) 'vC::; ~r:'JQ., 4..':::J'::;''v~ + T + + ., L- ..., L < ,.. "7 .t.. ~ L ? V A 7 90°45' 7 7 1\ ~'" ;, 1'\ \'" L r I< ,o,<> r- ~ L 'e- ~$"~ " "," <§> ~C?it' C)<..J,9.; .~ '<f -,J ,} v'" ~ "o,~ .,.. «J~ ~ ~ ,>'> ,o, »' '" 92°45'00" ~ 92°00' ,,<I;> o,<> ,,1$ '0'" <'¢~~~ ~l>~'v 'v~& <Q~~ J> "", ,'> o,'> ,,«. .J,.<:i <¢",,, o," . . . e,r::),.,."<> .. v'" -~ 'e- '" 92°00'00" ~ Index I "," v'" ~;§' '\:t''''' + Figure 1. 1. Figure 92°00'00" to quadrangles stud ied Generalized the Vermilion (Morey & 1970) Generalized geologic map map of of the Vermilion district, district, Minnesota Minnesota (Morey & (thers, cthers, 1970) i I I I i I I i I I I �C PL LA AN NA ATTI10 N E )C XP ON foijli North of at Vernii/ioii Vermilioll foull I'..... ... '1 Range Granite Range Grande G,onis Glonts Ver ni lion Gronile Bionic Biollle Schisi 5chiSl Newton Lake Lake Farmolion Formal ion Newton undivided undivIded Vif.:::: . ~v.gs. vii Amphibolile Amphibolite —7-———-—vmv vmv vgv YQ vq c LLake oice .2 .D E 3 ~ Q.. 5 .':'.':'." :"> . Verm,tion Vermilion Knit Knife Lake Lake vVm vvm Group (undivided) For molio n Formation vgs, meiagroywocke metagraywacke member member quorrziie vg. quartzite member member v q, vgv, mi xed metogroywacke metagraywacke - felsic felsic vg v, mired I I-' conglomerate member conglomerate member vvtn, vaiconicMsic member member vvm, volcaniclastic bonded iron -- formation vif > banded vlf cmv. dominantly dominantly melobasoli metabasalt and and vmv, metod i a baaso S8 meladiab V1 I-' I - format On Soudan Iron Iron -formation Soudon dominantly domlnontly jaspiiite jospilite, jasper, and cherl chert osper and -- cit Ely Greenstone Greenstone e9, domlnontly menobosoltic metabasaltic eg, dominantly p i ilowed flows and metaandesitic meiaandesitic pillowed and 'nlern,ediate composition and Intermediate composi lIon pyrociostic pyroc lost\c depOsits deposits elf, banded bonded Iron Iron -formation - formation 9it, Corroci, dotled where wiere inferred nte- 'Cd Contact, dotted Vault Faull,• oared dotted where where o '"' 22 inferred 4 5S 6 8 CAL E CAL E loMites �-g 92'30' 92°3 H '7 W R~7W' 9j '45' 92'00' H IS W R~-4VV B. '3"W -0 o Zoo ooZ II"'" "'"II (j) (j) ID f-< f-< Z I'l ton (j) f-< ..4 ,v_t —c a Z zZ (II C -. (j) ID (II Jwtfl okes (j) / I-f-< log1e' b V1 N: t-: 1 'V '< c-..Lake z z (H ft 6 ... : : : Z o(j) · · b H W R t~ 7 7"'V\T Z ,/ ri7' · ·. . . . . .. . .. . . . . . . . . . . · · ·· Figure 2. 2. I .. .. . . . .. . ... .. . . .. .. .. . ............................................................... . 92*30 92'30' I ::::..................... :::::::::::::::: ::::::: ~ . . . .. . 0 a is w 16VV R 0 0 0 -J ~-~-= R . .. 91045 of the the western western part part of Geology of of Vermilion Vermilion district, district, Minnesota Ninnesota (Norey (Norey &&others, others, 1970). 1970). j I I I b -J 92' 92° 15' '5 p o(j) 0 0 n law 8W ~5""N I I I II-' LI I �I I C L AN AT S ON Sc P L A N A T I O N E E X Ou'''''' 1 Cornplt. '-'-' -', - ' , -'" Sno"~OA'" Lo_" "e,,"""O~ StOel und,·•• ded ,,,,I"don Lii LLL G'Qn,'e o~~'O'ed ~(~,~,~ ro. .... ,on La •• formot,on molK: ,Olcon,e nm" mtmatl nh, Itl$,(· ,nl.rmed·"·" .....x:on..: mem!>e< oom'l'Io<"ly fe pyroelau,e (nf,) of ~.c:-"",ermed>o'. ond ,oc.~ ~,m,lc, I.~~.' lIo .. ~ eompc~",on Kn,lt 'm~. dom,nonlly mtlO\l,ay .. o~'. 0"<:1 $101., 'm~. ~m'l'Ianuy m.,'otO~O,1 dom.non", .okon.elo~"t 'oe. 01 '0 ,nr.rmtd,ol. tompo~,"OI'l Ow. Ely .\!. Itl~,~ Gr.el'l~lol'le dJm,nonl" ..,.lotlO$Olh( p,llo".d and .... 'e'm.d'O'. (O""O'O$,I,on Oy'OCIO$I..: d.PO~,I$ ""eloonde~,''': SC £ seA L S. = ~ : 4 t . . . . ;} . . - - 2 - o..._.__ • ~ Ofl<l £E I f-J Ui lJl I G,o"p S.—. La~e hi W ~.,~~...tl - I - F _~M,l~ �- 4 ,e; - - / - - —— — t\ - —— c — —- N .--.--- / / -:- -- 'F !)y/ - / / / 7 Figure 3. 3. I I / G eology of the the central Geology central part part of of the th e Vermilion district , Minnesota M'l.nnesota (Morey Vermilion district, (Morey & & others, others , 1970). 1970). I — I I I �—155— -155- E E w W 0 - C? ...... z::::;. 13 ./ '- /=:::> " ~ / " L:) c=r ' ,;' .. . .• 12 / "/ "- I \ ,;' " .... / / ....... ,;' " "- / / .. j . . .. 0[77: 00 00 .,j . . o 0 " "- "- "/ "- / I 0I- 1. 0 .,.. .,.. ..... •Q ,;' " 6 ..... I' "- ./ ...... Fe1dspathic quartzite quartzite Feldspathic agglomerate Dacite agglomerate I' \. Graywacke-slate Graywacke—slate I I " / / ,;' ./ ... ,;' \. / / \. , " / I' .... Dacite tuff Daci te porphyry Dacite Iron—formation Iron-formation Basalt—andesite Basalt-andesite GENERALIZED AND IDEALIZED IDEALIZED PRE—DEFORMATIONAL PRE-DEFOID1ATIONAL VOLCANIC VOLCANIC PILE, PILE~ WESTERN VERHILION VERMILION DISTRICT of \. / Figure 4. 4. (Not (Not to to scale. \. 3 ,;' ,- \ / \. \ '- \. ,;' 0 0 " Numbers indicate approximate stratigraphic stratigraphic positions positions Numbers field trip stops.) stops.) field trip 2 " �—156— -156- VERMILIONDISTRICT DISTRICT FIELD FIELD TRIP VERMILION INTRODUCTION This field field trip trip is is designed to be a one—day one-day trip, trip, starting starting near near Ely Ely Representative outcrops of most and ending aa few miles west of Tower. few miles west of Tower. of the the major rock rock types types in in the the Vermilion Vermilion district district are are included. included. Most stops are in in the the Lake Vermilion Formation, Formation, the the Ely Ely Greenstone, Greenstone, and and the the Soudan Iron—formation. Iron-formation. None are in the the Knife Lake Lake Group because because good good exposures are not easily accessible; accessible; however, however, the the Knife Knife Lake Lake rocks rocks are are to those those in in the the Lake Vermilion Formation. Forma.tion. similar to Stop 1 Any several roadcuts Any of several roadcuts 2—10 2-10 miles South of Ely Ely on Hwy. Hwy. 1. 1. Giants Range bathalith batholith Most abundant facies in in this this area area ('Farm C'Farm Lake Fades' Facies" of of Green, Green, 1970) 1970) is is medium—grained, medium-grained, porphyritic porphyritic hornblende—biotite hornblende-biotite quartz—poor quartz-pooradainellite adamellite with K-spar phenocrysts. phenocrysts. Hornblende and K—spar K-spar are are commonly con~only aligned aligned in in flow flow pink K—spar structure. Monzonitic, granodioritic, granodioritic, and and dioritic dioritic phases phases also also occur; occur; all all have been cut by shear shear zones zones locally. locally. Stop 22 South of Ely on Hwy 1. Outcrops under powerline pmverline on EE side of Hwy 1, l, 1.4 1. 4 Outcrops under mi. mi. S of junction junction with Hwy Hwy 169. Ely Greens Greenstone tone of a within the Dacitic to to andesitic, andesitic, pillowed lavas characteristic characteristic of a zone zone within the Ely trendsE—W E-W south shapes show show tops face face Greenstone that that trends south of of Ely. Pillow shapes Ely Greenstone are cut These volcanics volcanics are north, as as in in most most of of the the formation. formation. These cut by aplitic north, dikes to the the Giants Giants Range Range batholith; the hidden hidden contact in related to batholith; the contact lies lies in dikes related the the slope slope to to the the southwest, southwest, and and granite granite outcrop outcrop can can be be seen seen near near the the base base of the slope. slope. of Ely. 14. at curve about 0.25 Stop 3 Roadcuts Roadcuts on on Hwy Hwy 169, at 0.25 ml. mi. W. of Ely. StoRj Ely Ely Greenstone of the Creenstone Pillmved metabasalt that that is is typical typical of of the the màflc mafic lavas lavas of the Ely Ely Greenstone Pillowed The pillow structures is exposed in road road cut cut on on north north side of highway. higlmay. The pillow structures have have side of is exposed in somewhat drawn smoothly tops, nearly flat flat bases, and and are are somewhat drawn out out in in smoothly rounded tops, of an vertical an inch inch thick. thick. The The Thechilled chilled rinds rinds are are aa fraction of vertical dimension. The and SE and face U., dip pillmv structures strike strikeapproximately approximately N.20° N. 20° Eo, dip 800 80° SE., face pillow , southeastward. southeastward. The long subparallel to to the the The long dimension dimensionofofthe the pillows pillows is is subparailel in~ersection cleavageand andbedding beddingand andplunge-s plunges steeply steeply northeastward. northeastward. intersection ofofcleavage �—15 7— -157- The exposures are on the the northwest limb limb of of aa tight tight syncline, syncline, the the axis axis The Ely trough contains an through the the Ely Ely trough. trough. trough contains an of which passes through iron—formation that was largely altered to hematite, and which was iron-formation that was was aa substantial source of of direct—shipping substantial direct-shipping hematite ore. ore. On the the south side of highway, fine—to—medium—grained fine-to-medium-grained metadlabase metadiabase is is exposed in road cut and on on hill to to south. south. The metadiabase intrudes and and crosscuts the the pillowed metabasalt. AA contact can can be seen seen in in the the southern southern part part of the tile crest crest of of the the hill. hill. 4. About 2.5 mi. \oJ of Stop 33 on Hwy Hwy 169, turn turn NN (right) (right) on on road road to to Burntside Burntside Stop 4. ml. W Lodge (Co. 88). Continue on road past bridge over Burntside River (Co. 88). Burntside River and and About 1.4 miles past Van Vac road (on (on left). left). About past junction with Van Vac road Stop in about 0.2 miles road, (on curve) curve) on on private private road. road. Stop road, turn left (on north on private road, road, at at curve curve to to right. right. Newton Lake Formation Formation Serpentinized metaperidotite metaperidotite and and associated associated gabbroic gabbroic rocks rocks are are exposed exposed Serpentinized from base of hill northward to from to crest. crest. It is about 150 Serpentinized peridotite is is exposed at base of hill. It 150 feet thick, is nearly black, black, and contains some feet thick, is some poikilitic poikilitic augite. augite. Iniinediately northofofserpentinized serpentinizedperiodite periodite and and apparently apparently gradational gradational Immediately north into it it is is aa coarse-grained coarse—grained hypersthene (?) into (?) gabbro, which grades in turn into a gabbro (higher The gabbro appears to into (higher on on hill). hill). The to have some some crude crude compositional layering and is in part diabasic. diabasic. On crest of hill, hill, part of the the gabbro (or (or diorite) diorite) contains contains coarse, coarse, radiating radiating pyroxene pyroxene crystals, crystals, as much as an as an inch inch long. long. There is some interstitital quartz and feldspar granophyric material in this this phase of the the rock. rock. Pyrite is widely scattered through the the gabbroic gabbroic rocks. rocks. ultramafic-mafic body at this stop is near the the southwestern end of an The ultramafic—mafic at this stop is intrusive sheet that that is about 3.5 3.5 miles long long and and 1,000 1,000 feet feet or or more more thick, thick, and which underlies little little Long Long Lake. Lake. The sheet appears appears to be a differbody, from peridotite at entiated body, at the the base base to to gabbro gabbro at at the the top. top. North of the eastern end end of of Little Little Long Long Lake, Lake, aa small small body body of of serpentinized serpentinized of the eastern peridotite, peridotite, within within metadiabase, metadiabase, is is exposed exposed in in aa roadcut roadcut along along the the Echo Echo Trail. The top top of the body is truncated truncated by by the the Vermilion Vermilion fault. fault. Stop 55 Roadcut about Roadcut about 13.0 13.0 miles miles W W of of Ely Ely and and about about 2.5 2.5 mi. ml. W W of of Eagle's Eagle's Nest Nest Lake road (Co. (Co. 408) 408) on on Hwy H\vy 169. 169. Other outcrops of of similar similar rocks rocks are are also also present along the the highway. highway. Soudan Iron—formation Iron-formation and cross—cutting cross-cutting dacite. dacite. Roadcut Roadcut in Soudan Iron—formation. Iron-formation. A quartz—feldspar quartz-feldspar (dacite) (dacite) A porphyry dike and Ely Creenstone Greenstone are exposed exposed at at east east edge edge of of outcrop. outcrop. The iron-formation is The iron—formation is composed composed of of interlayered interlayered red red and and white white chert chert and and opaque iron iron oxide that plunge oxide layers; layers; it it is is deformed into into drag drag folds folds that plunge 0 500_600 50 -60 0 N.E. Beyond a covered interval interval of of 0.1 0.1 miles miles to to the the east, east,the the �-158iron-formation thin to thick, thick, black, black, red and and white chert chert iron—formation consists consists of of thin beds interlayered with black black argillaceous argillaceous beds beds that that contain contain abundant abundant veins, veins, stringers, and and beds beds of of euhedral euhedral pyrite. pyrite. The beds trend trend about about N.85° and W. N.85° W. and dip dip 80°N. 80 o N. This is representative of the This dacite the felsic felsic volcanic volcanic rocks rocks which apparently provided the the detritus detritus for for most most of of the the sedimentary sedimentary and tuffaceous tuffaceous rocks rocks of the the district. district. Stop 66 Outcrop just W W of Stuntz Bay road road at at crest crest of of Soudan Soudan Hill, Hill, at at the the N, N. edge edge Soudan, 1,000 ft ft E. E. of Soudan Soudan mine. mine. Conserve this this outcrop. outcrop. of village of Soudan, Soudan Iron—formation Iron-formation This is much—visited classic This is a much-visited classic exposure exposure of of folded folded Soudan Soudan Iron—formation Iron-formation comprised of alternating beds of hematite and and jasper. jasper. The nearby Soudan mine was opened opened in in 1884, 1884, and and operated operated continuously continuously until until 1962. 1962, when when it it was was deeded to to the the state state by by U. U. S. S. Steel for for the development of of Tower—Soudan Tower-Soudan State State It was was the the first first iron ore mine in Minnesota; 15.5 million tons Park. It tons of of high grade grade ore ore (63—66% (63-66% Fe) Fe) were were shipped. shipped. Most of the small folds Host folds are the the result result of of the the second second deformation deformation in in the area, and these (F2) the area, (F ) folds folds plunge to to the the east east at at steep steep angles. angles. However, 2 evidence of an earlier set of folds is is provided provided by by structures structures such such as as these in the the sketches below. below. F1 fold axis Fl /" F2 F fold axis axis 2 F F INTERFERENCE INTERFERENCE PATTERNS PATTERNS F1 AND AND F2 l 2 Approximate F1 F FOLD MODIFIED BY BY F2 F 1 DEFORMATION 2 N N 1 H One Foot Foot Approximate Scale Scale �-159—159— Stqpl Several outcrops outcrops on peninsula in Lake Vermilion, east of Several of McKinley Bay, I Bay, E and W W of development development road. road. Lake Vermilion Formation, Lake Formation, Volcaniclastic Member White Hhite dacitic tuff, tuff, white dacitic dacitic agglomerate, agglomerate, black black carbon— carboniferous (?) slate graywacke, all all of of the the volcani— volcaniiferous (?) slate and minor chloritic graywacke, clastic member, are interbedded interbedded in in this this area. area. The westernmost exposures member, are of the the Soudan Iron—formation Iron-formation also occur here. here. Good exposures of the the agglomerate are best reached by boat; therefore, agglomerate boat; therefore, we shall shall only only see see some some large glacial glacial erratics of this rock rock type type which are are virtually virtually in in place. place. The dacitic tuff tuff is is very very difficult difficult (arid (and commonly commonly impossible) impossible) to distinguish from from dacite dacite flows. flows. Study of thin sections is is usually necessary to to resolve resolve the the question. question. It comfort to know that It is is some some thmfort (1903) and numerous other workers had had similar similar difficulties. difficulties. Clements (1903) three main components components —- dacitic The tuff is composed of three dacitic volcanic rock fragments, and volcanic volcanic quartz. quartz. Recrystallization Recrystallization causes causes fragments, plagioclase, and the volcanic volcanic rock fragments the fragments to appear as a fine—grained fine-grained quartz— quartzplagioclase plagioclase matrix. matrix. stop Stop 88 Large mi. WW of of Tower Tower on on Hwy Hwy 169, 169. roadcuts 0.3 mi. Lake Vermilion Fornation, Formation, Felds feldspathic athic Quartzite Quartzite Member Member This is a a limonite—stained limonite-stained exposure of the the conglomeratic conglomeratic facies facies This is of the the feldspathic feldspathic quartzite quartzite member. member. Bedding and clasts clasts are are best observed on the the glaciated surface at at the the western end end of of the the south south roadcut. Pyrite and pyrrhotite are are the the major major sulfides sulfides present, present, and and to have replaced replaced slaty slaty fragments fragments .in ,in the the conglomerate. conglomerate. Most appear to clasts clasts are volcanic rocks, rocks, probably mostly dacitic. dacitic. The matrix is is the strong Stop 10. 10. Note the similar to the feldspathic quartzite of Stop development development of F2 lineation which ~vhich plunges easterly easterly at at about about 600. 60°. ~t.-<?.p_J_ 5t229 Small outcrop SS of thvy Hwy 169, 169, in and across ditch, ditch, 1.1 mi. WW of of Tower. Tower. (optional) Lake Vermilion Vermilion Formation, Lake formation, FeljIiicQuartzite feldspathic ~uartziteMember Member feldspathic quartzite Lapilli (?) in the basal part of of the the feldspathic Lapilli tuff tuff (?) This is the This is the only exposure of this this rock rock type type in in the the immediate immediate it appears appears to area; it to be transitional in in texture texture between between the the dacitic dacitic tuffs and dacitic agglomerates. tuffs ap,glomerates. newiber. melilber. �-160- Note: Stop 10 South of the highway in the woods on West Two Rivers is tte folded western end of the Ely Greenstone. The fold nose points W but the fold plunges E at about 55°. This is an antiformal mass cored by older, mafic volcanics whose fold axis plunges toward the older rocks the wrong way. Some small folds at Stop 11 exhibit the same structure. Roadcuts N & S of Hwy 169, 1.85 mi W of Tower. Lake Vermilion Formation, Feldspathic Quartzite Member Feldspathic quartzite is an unfortunate choice of field terms, as the rock is largely composed of plagioclase and volcanic rock fragments with only minor large quartz grains (see below). Faint bedding and lamination are visible on some parts of the outcrop, and a sericitic phyllite band occurs on the north cut. At the east end of the south cut, felsic volcanic fragments up to an inch in diameter are visible. The 20 ft.-thick dike of diabasic gabbro at the tvest end of the outcrop is the youngest rock in the area. It has a minimum K-Ar age of 1570 m.y., and similar dikes a few miles away have ages of 1520 and 1685 m.y. (Hanson & Malhotra, 1971). The dike exhibi~s excellent chilled contacts and some inclusions of the quartzite. The feldspathic quartzites contain 20-30% plagioclase; 15-30% felsic volcanic rock fragments; 30% fine recrystallized quartz and plagioclase which probably represents, in large part, recrystallized volcanic rich fragments, plagioclase and quartz; 5-10% micaceous matrix; and 5-10% quartz, including some quartz which is definitely of volcanic origin. �—161— -161- -.l1.Long Long roadcut roadcut SSof of Hwy H\vy 169, 169, 2.5 Z. 5rid. mi. WW of Tm.]er. Conserve these these folds. folds. Tower. Conserve Stp_11 _~t...2.E .. jjrwacke—Slate Vermilion_Formation Lake Vermilion Formation, Metagraywacke-Slate Member (The composition Strongly and slate. slate. (The Strongly folded biotitic metagraywacke and this rock is is described at at Stop Stop 12, lZ, where the rocks of this where the rocks are are evenly evenly bedded folding results from two and relatively undeformed.) The The complex folding two deformations, as described in in the the text text accompanying accompanying this this tions, as sketched below and as described Some geologists have speculated that field trip trip log. log. Some that the the folding folding is is soft soft sediment deformation, deformation, rather than than tectonic. tectonic. However, these these stnictures structures are are unique unique in in the the area, area, this this exposure exposure is is located located near near aa major major anticlinal anticlinal axis, well—preserved sedimentary structures axis, and well-preserved structures nearby nearby are are not not chaotic. chaotic. the excellent excellent grading. grading. Note the Approximate N i One Foot F1 F fold fold axis l Approximate Scale ·····e 5Q0 50° axial plunge OVERTURNEJ) F2 FOLD FOLD OV ERTU R.:\IED F2 F1 FOLD F2 CLEAVAGE FOLD ANT) A..~D FZ P2 cleavage fold axis 1 / -7 F F FOLD 1ODIFIED BY fOLD MODIFIED HY FF Z 2 1 DkFORMATION. DEFORMATION. F2 Cleavage FZ ~ o• F 2 cleavage --"EYE STRUCTURE" t1EYE STRUCTURE" DUE DUE TO TO EROSION EROSION OF FOLDS WHICH OF FFI FOLDS I-.THICH WERE I-.TERE DEFOR1€1) DEFORMED BY FOLDS. BY FF FOLDS. Z �-162—162— 'I •. -. C Stop 12;Lposure ExposureNJNWof of bridge bridge across across Pike Pike 169. .r:S'Y (Junction of of Co. Co. 77 Hwy 169. (Junction 77 and ... this outcrop. Please conserve conserve this River on Co. Co. 77, 77, 0.55 0.55 mi mi NN of of River an Hwy 169 is 2.4 miles W of Tower). Hwy 169 is 2.4 miles W of Tower). .;: Lake Lake Vermilion Formation, Formation, Metagraywacke—s]ate Metagraywacke-Slate Member Member This This is is an an exposure exposure of of biotitjc biotitic metagraywacke metagraywacke and and slate, slate having having excellent grading. excellent grading. Two-thirds the 200 200 graywacke beds beds on Two—thirds of the on ~his this exposure are are graded and nine percent of the exposure the 100 beds are are 100 siltstone siltstone beds graded. Beds here here are are thin, graded. Beds thin, but graywacke beds beds are are as as much much as as 12 12 feet feet thick. North—trending kink North-trending kink bands bands were formed formed by by the the latest latest (F (F )) deformation. Small Small scale scale faults faults are are common. A NNE-trending fault with 1000 feet feet A NNE—trending fault with aiout aout 1000 of of left—lateral left-lateral displacement displacement forms the S side forms the side of the river channel at this locality, locality, and extends for this for several several miles miles to to the the north north and and south. south. The biotitic biotitic graywackes graywackes contain contain 10-20% l0—20 plagioclase; The plagioclase; 15-25% 15—25% felsic felsic volcanic rock fragments; 30—50% fine recrystallized rock fragments; 30-50% fine recrystaliized quartz and and plagio— plagioclase which probably represents, clase which represents, in large large part, part, recrystallized volcanic volcanic rock fragments, plagioclase, and rock fragments, and quartz; quartz; 2-5% 2—5% quartz, quartz, and and 10-15% lO—15 biotitic matrix. matrix. Stop 13 Exposures N of Hwy 169 on Co. Co. 77, 77, at Gruben's Resort Resort on Exposures about 10 mi N (Optional) (Optional) Arrowhead Point. Point. Best exposures are are just just EE of of wooden wooden bridge bridge to to Isle Isle of Pines. Pines. Lake Vermilion Vermilion Formation, Formation, Hetagr~acke-Slate Metagrywacke—Slate Member Lake i'lember Exposures Exposures of chloritic graywackes of this locality, pillowed greenstones of this locality, slate. This is near the axis This locality is is an ENE—trending (F2) is an ENE-trending (F 2) anticline, anticline, the the the west although the beds at the fold the west the beds at fold and slates. Both east and west are are interbedded interbedded with the the graywacke— graywackethe Arrowhead Point Point fold. fold. This of the axis axis of of which ,,,hich plunges plunges steeply steeply to to nose are younger to the are younger to the east. east. The 40-50% plagioclase (albite—oligoclase), (albite-oligoclase), The chloritic gra~vackes graywackes contain 40—50% 20—25% felsic volcanic rock fragments, 20-25% felsic volcanic fragments, 10—20% 10-20% chioritic chloritic matrix, matrix, 2—6X 2-6% quartz, quartz, some of of which which is some is definitely of volcanic origin. origin. Roadcuts bet\veen between lanes of Hwy 169 on "Confusion Stop 14 Roadcuts "Confusion Hill" Hill" (the (the Continental Continental (Optional) Divide) N of Virginia and about 23 23 miles WW of of Tower. Tower. (Optional) Divide) about about 3 mi N Giants Giants Range Granite the south edge of the This the complexity complexity of of the the south This exposure illustrates the Giants Range A gray gneiss contaLning containinh ailiphiholite amphibolite gray granite granite gneiss Rangebatholith. batholith. A inclusions cut by by diorite, diorite,and andminor minor pink pink granites granites cut cut the theabove above rocks. rocks. inclusions is is cut At top of of the the exposure exposure between het\\'een the tHO lanes of of the thehichway higlmay are At the the top the ttro remnants of mafic remnants of LOvIer LowerPrecanlHian Precanl,rianthinly thinly bedded bedded sediments sediments (tuffaceous?), (tuffaceous?), mafic lapilli tuffs (?y, and massive massive amphibolites. lapilli tuffs (fl, �� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1971 Description An account of the resource Institute on Lake Superior Geology. University of Minnesota, Duluth, Minnesota. May 5-8, 1971. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1971 Contributor An entity responsible for making contributions to the resource R.N. Annells P.O. Banks W.R. Van Schmus Bill Bonnichsen Donald M. Davidson Jr Erich Dimroth Jean-Jacques Chauvel William H. Duhling Jr J.C. Green H.C. Halls G.F. West R. Roy Harold A. Hubbard H. King Huber Eric Frodesen Wayne T. Jolly Richard L. Kellogg William J. Hinze George deVries Klein Gene L. LaBerge M.S. Lougheed J.J. Mancuso Roger C. Malan David A. Sterling Allen F. Mattis Joseph T. Mengel Jr Ronald A. Hendrickson G.B. Morey J.S. Mothersill M.G. Mudrey P.W. Weiblan Wallace Darwin Myers Norbert W. O'Hara L.A. Prince G.N. Hanson W.A. Robertson W.F. Fahrig A.P. Ruotsala R.J. Shegelski G. Spencer F.C. Tan E.C. Perry Jr P.K. Sims S. Viswanathan T.A. Vogel T.J. Rohrbacher W.S. White Robert F. Johnson E.R Brooks J.T. Wilband Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/3ecd85424de1d35eb6f0359af1235823.pdf 916dcba45175acb8a04524d427dc4144 PDF Text Text �18th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY MAY 3-6, 1972 MICHIGAN TECHNOLOGICAL UNIVERSITY HOUGHTON, MICHIGAN PART I. TECHNICAL SESSIONS AGENDA and ABSTRACTS Edited by W. I. Rose, Jr. �AGENDA Tuesday May 2, 1972 8:00 a.m. Field Trip A leaves Michigan Tech Memorial Union Wednesday May 3, 1972 6:00 p.m. 7:0010:00 p.m. Field Trip A arrives back in Houghton. Institute Registration, St. Albert the Great Student Parish, MTU Campus Thursday May 4, 1972 7:3010:00 a.m. 8:00- Registration, Fisher Hall Foyer 12:00 noon General Session I, 135 Fisher Hall 1:305:00 p.m. General Session II, 135 Fisher Hall 7:00 p.m. Banquet and Address, Onigaming Supper Club Friday May 5, 1972 8:0011:00 a.m. 1:30— Penokean Session I, 135 Fisher Hall 4:45 p.m. Penokean Session II, 5:30 p.m. Departure of General Session III, 135 Fisher Hall. Field Trips B and C. from MTU Memorial Union. Saturday May 6, 1972 8:00 p.m. Departure of Field Trip D from MTU Memorial Union 6:00 p.m. Field Trips B, C. and D. arrive back in Houghton. �7 8-12 Paper No. GENERAL SESSION MAY 4, 1972 TECHNICAL SESSIONS I. Time 8:15 a.m. 34 8:0.0 a.m. 8:35a.m. 10:40 a.m. 10:20 a.m. 10:00 a.m. 18 10 8 15 9:00 a.m. 11:00 a.m. 17 6 11:20 a.m. 11:40 a.m. Co-chairmen: Ehrlich 0. Lewan M. G. Mudrey W. Weiblen J. C. Green K. G. Books P. M. T. A. Vogel R. Author(s) Robert C. Reed and Donald M. Davidson, Jr. 135 Fisher Hall (Building #15, See Map) AM Title Introductory remarks, Announcements Based on Lithologic Variation Deposition Model for the Lower Nonsuch Shale Weathering and Metasomatism of the Presque Isle Serpentinized Peridotite, Marquette County, Michigan Break for coffee Petrologic and Structural Aspects of the Gabbro Sill on Pigeon Point, Minnesota Keweenawati Lavasin Minnesota Peleomagnetic Evidence for the Extent of Lower Dimroth W. O'Hara J. Hinze Oray A. Robertson J. A. Kilburg E. N. W. E. W. Upper Precambrian Ely's Peak Basalts Petrology, Structure and Correlation of the Magnetic Reversals and Polar Shifts as Markers in a Proterozoic Time Scale The Eastern Terminus of the Lake Superior Syncline The Labrador Trough — not a Precambrian Plate Boundary �II. GENERAL SESSION 1:30 p.m. 13 4 E. Brown Author(s) Randall J. Weege and Gerald Anderson Title B. Lou gheed Co-chairmen: Iron Segregation in Precambrian Iron Formations: Effects on Sedimentary Compositions S. Geologic compilation and Nonferrous Metals Potential , Precambrian Section, Upper Michigan M. w. w. J. LeAnderson M. Lahr A. Bodwell J. J. Mancuso The Newly Compiled Geological Map of the Precambrian of Upper Michigan P. W. Ojakangas Waupee Volcanics R. Smith H. McNutt Kal 1 iokoski A. Bodwell The Geology of the Garlic River Greenstone Belt R. D. R. P. M. Clifford Cuddy' P. M. Clifford G. Nature Effect of a Rigid° Ultrebasic Sill on Deformation R. Archean Salic Volcanic Rocks at Kakagi Lake, NW Ontario - Their Physical and Chemical J. Lower Precambrian Metavolcanic-Metasedimentary Sequence, Rainy River, Northernmost Minnesota J. L. Berkley Precambrian Geology of a Greenstone Belt in Oconto County, Wisconsin, and Chemistry of the The Geology of the Deer Lake Gabbro-Peridotite Complex, Itasca County, Minnesota Formations Morphology of Magnetite in Precambrian Iron M. 1:30- 5PM Paper No. 1:50 p.m. 2 Time 2:10 p.m. 9 12 2:30 p.m. 3:10 p.m. 16 11 3:30 p.m. 2 2:50 p.m. 3:50 p.m. 19 5 4:10 p.m. 4:30 p.m. In Adjacent Rocks, Kakagi Lake, NW Ontario �III. IV. BANQUET 9:55 •a.m. 27 23 J. Naldrett, University of Toronto 7:00 p.m. May 4, 1972 Relation of Penokean Polyphase Deformation to Regional Metamorphism In the Western Marquette Range, Northern Michigan The Penokean Orogeny Title W. J. S. A. Trent F. Cannon S. S. Goldich Author(s) Co-chairmen Carl E. Dutton and Stephen C. Nordeng Penokean Tectonics in Northern Michigan V. G. G. W. B. Morey L. LaBerge R. Van Schmms Kiasner Three-phase Deformation Associated with the Penokean Orogeny, East Gogebic Range, Michigan 0. Banks Coffee and Discussion Precambrian Rocks in Minnesota Stratigraphic and Tectonic Framework of Middle Lineaments and Mylonite Zones in the Precambrian of Northern Wisconsin Dickinson Counties, Michigan, Part II Chronology of Precambrian Rocks of Iron and Short Break (10-15 minutes) P1. 8-11 A.M. Archean Ultramafic Lavas and Their Associated Nickel Suiphide Deposits" A. Onigaming Supper Club (U.S. 41 South, Houghton) ADDRESS MAY 5, 1972 PENOKEAN SESSION .1 Paper No. 25 Time 8:00 a.m. 24 26 8:50 a.m. 20 8:30 a.m. 9:20 a.m. 10:15 a.m. 28 9:40 a.m. 10:35 a.m. 11:00 a.m. �V. ____ PENOKEAN SESSION 2 and GENERAL SESSION 3 1:30-5:00 p.m. Author(s) J. W. Avery and Robert Seasor Title Geochronology of Precambrian Rocks in the Penokean Fold Belt Subprovince of the Canadian Shield Regional Relationships in the Penokean Province Stratigraphy and Sedimentation of the Espanola Formations an Early Aphebian (Middle Precambrian) Carbonate Unit. Granitic Plutonic Rocks of the Southern Province of the Canadian Shield J. T. Mengel M. E. W. H. G. Haddadin. Booy R. Van Schmus B. Stonehouse M. Young J. A. Robertson S. Goldich J. S. Stuckless Structured Clay Products Industry, Keweenaw Peninsula, Michigan J. Warren S. lvii nnesota-Wi sconsi n E. G. Winter Glacial On ft on the Mesabi Iron Range, Minnesota, Its Characteristics, Origin and Hydrologic Bedrock Morphology in the Vicinity of Portage Subsurface Geology of the Duluth Superior Area, Potential Sources of Raw Materials for the Lake, Keweenaw Peninsula, Michgan 1. Minnesota Ages of Some Precambrian Rocks in East Central Co-chairmen: 31 Paper No. 1:30 p.m. 29 Time 1:50 p.m. 33 30 2:10 p.m. 2:30 p.m. 32 3 2:50 p.m. 3:20 p.m. 21 14 4:00 p.m. 22 3:40 p.m. 4:20 p.m. Signi ficance. p �Paper THE GEOLOGY OF THE DEER LAKE GABBRO—PERIDOTITE COMPLEX ITASCA COUNTY, MINNESOTA John L, Berkley University of Missouri, Columbia ABSTRACT The Deer Lake Gabbro—Peridotite Complex is located in northern Itasca County, Minnesota, three miles southwest of Big Deer Lake. It is intruded into a terrane composed of quartzofeldspathic, tuffaceous metasedimentary rocks and pillowed metabasalts of Lower Precambrian age (Sims, et. al., 1971). In recent years the area has been investigated by several mining companies as a possible source of exploitable nickel deposits. Detailed mapping has revealed that the complex is composed of five, separate, sheet—like, basaltic intrusions, averaging approximately 700 feet in thickness, each, Magma was supplied to the area in chronologically, widely dispersed episodes, allowing time for earlier intrusions to differentiate and lithify before the emplacement of a later sheet above those already present. Observed contacts between any two sills are character— Ized by chilled dolerite against a thin zone of amphibolite, The chilled do].erite is thought to represent the parent magma, while the amphibolite is probably a result of contact metamorphism by the magma, For any given sill within the complex, a sharp contact separates the chilled dolerite from the layered sequence above which consists of, from stratigraphic bottom to top, an augite—hornblende peridotite, diopsidic or augitic pyroxenite, and gabbros of varying compositions. This layered series of rocks is a result of selective crystallization and gravity settling of phases, Typical cumulate—intercumulate textural relations as described by Jackson (1961) from the Stllwater Complex of Montana may be seen in rocks from the peridotite up to and including certain lower gabbro units. Small scale layering structures may occassionally be observed in pyr— oxeniteg and lower gabbros. Figure one shows the ideal sequence of rock types for any particular intrusion within the complex and gives the expected cumulate and intercuinulate phases for each unit, The peridotite is composed of rounded to elongate olivines surrounded poikalitically by augite, hornblende, or both, Evidence of reaction rims may be seen surrounding some olivine crystals. The peridotite grades sharply into a pyroxenit., usually composed predominately of subhedral to euhedral diopside 1 �Paper enclosed by plagioclase, diopsidic overgrowth, or oikocrysta originally of pyroxene composition but now completely altered. With increasing cumulate plagioclase content, the pyroxenite grades gradually into an augite gabbro. Upper units may exhibit a significant quartz content and micrographic intergrowth. Micro— pegatite veins cut many gabbro exposures and pegmatitic material has been observed in certain pyroxenite units as well. Post—intrusive folding in the area has deformed the formerly horizontal sills into a sequence of tightly folded anticlinee and sync].ines with axial traces trending N4OE. The complex plunges to the southwest at an undetermined magnitude. Exposure of the intrusive units is now restricted to a narrow band six miles long and a maximum of about one and one half miles wide. Metamorphic grade does not surpass lower amphibolite or hornblende hornfels facies in the rocks of the complex with most assemblages, including those of the adjacent country rocks, falling into the greenschist fades, REFERENCES CITED Jackson, Everett D.,, 1961, Primary textures and mineral associations in the ultramafic zone of the Stiliwater Complex Montana, U. S. G, S. Prof. Paper 358, 106 pp. Sims, P. K., Morey, G. B., Ojakangas, R. W., and Viswanathan, S., 1971, Geologic Map of Minnesota, Hibbing Sheet: Mimi. Geol, Survey. 1 �FIGURE I. -— — ZONE CONTACT . ZONE ULTRAMAFC ZONE GABBRO ZONES — SINGLE NONE I4ORNBLENDE AUOITE/ PLAGIOCLASE AUGITE OLIVINE- PYROXENE OIKOCRYSTS DIOPSIDE QUARTZ PYROXENE OIKOCRYSTS PLAGIOCLASE PY ROXENE AUGITE QUARTZ PHASES CUMULATE PLAGIOCLASE N ONE N ONE PHASES CUMULATE INTER — INTRUSIVE SHEET. DEER LAKE AMPHIBOLTE DOLERITE PERIDOTITE PYR OX ENI T E GABBRO CUMULATE LOWER GABBRO AUGITE GABBRO AUG ITE BEARING MEMBERS QUARTZ IDEAL STRATIGRAPHIC COLUMN FOR A COMPLEX, MINNESOTA. ETAMORPHICFAdES CONTACT FACIES BORDER SERIES LAYERED GENETIC FACIES �Paper 2 GEOLOGIC COMPILATION AND NONFERROUS METALS POTENTIAL PRECAMBRIAN SECTION, NORTHERN MICHIGAN W. A. Bodwell Michigan Technological University ABSTRACT The geology and nonferrous metal occurences of the PreCambrian section, Northern Michigan, have been compiled at the scale of 1:250,000. The map incorporates considerable new data which has become available since the previous regional map of 1936. Review of the regional geology and mineral associations indicates several geologic environments or conditions considered to have potential for mineral deposition. 1) The effective coverage of past exploration drilling in the Michigan copper district was assessed. From this data, it appears that as much as 80 - 85% of presumed favorable ground is yet to be penetrated by drilling according to criteria developed herein: a) The strata-controlled ore deposit sought has a minimum strike length of 2000 feet. b) Maps showing drill holes were reviewed and all strike segments with 2000 feet or more between drill holes were outlined. These areas were measured by planimeter and compared to total area of the favorable strata. c) All strike segments of greater length constitute untested ground. 2) A series of small felsic porphyry intrusives occurring near the base of Portage Lake lava series appear to have potential for copper sulfide deposits based on analogous features with mineralized felsic porphyry bodies on north limb of the Lake Superior syncline in Ontario. 3) A greenstone belt northwest of Marquette, Michigan exhibits certain characteristics of mineralized greenstone belts of the Canadian shield. The presence of numerous base metal occurrences and one small gold deposit suggest that significant base metal or precious metal depsoits may yet be found. �Paper 3 POTENTIAL SOURCES OF RAW MATERIALS FOR THE STRUCTURAL CLAY PRODUCTS INDUSTRY KEWEENAW PENINSULA, MICHIGAN EMMY BOOY AND MUSA S. HADDADIN Michigan Technological University ABSTRACT The Keweenaw Peninsula of Michigan was explored for potential sites for the establishment of a structural clay products plant. The most favorable location for the establishment of such an industry was in Ontonagon County, in the southwestern portion of the Peninsula. The sedimentary cover overlying the Precambrian to possibly Cambrian bedrock varies rapidly both laterally and vertically because of the conditions of deposition during the Pleistocene. In general, the average particle size decreases from North to South. Otherwise, no consistent variations were observed. Most sediments having suitable properties for raw materials for the structural clay products industry have been mapped as glacial lake sediments. An attempt was made to identify distinctive flora which might provide a mapable criterion for distinguishing between sediments for structural clay products manufacturing and those unsuitable. Although there is variation in floral assemblage with topography (e. g. well vs. poorly-drained areas) there was no distinguishable variation with sediment size. suitable Requirements for suitable materials for structural clay products include good workability, low drying and firing shrinkage, good dry and fired strengths, and good fired color. Most of the samples studied met all criteria for most structural clay products. The mineralogy of the samples did not vary appreciably in major constituents throughout the area sampled. Illite, expandable vermiculite, and chlorite were the dominant clay minerals. Quartz and feldspar were ubiquitous, while minor kaolinite, calcite, and dolomite were present in many samples. Certain fundamental soil mechanics tests were run on the materials in conjunction with the ceramiô tests performed. In general, the samples tested were relatively stable clays to silty clay soils. �Paper 3 In the area studied the most desirable location from the view- points of volume of material available and ease of transportation to markets would be in the area around Ontonagon. Most of the samples studied from this area would be useful for all types of structural clay products. �Paper 4 IRON SEGREGATION IN PRECAMBRIAN IRON FORMATIONS: EFFECTS ON SEDIMENTARY COMPOSITIONS BRUCE E. BROWN Department of Geological Sciences Milwaukee, Wisconsin ABSTRACT According to Ronov's (1964) estimates, cherty iron formations of the pre-Cambrian type were present in the amount of 15% of the total sedimentary rock volume during the time period around 2 b.y. ago. The segrega- tion of iron to this degree would seem to require significant shifts in the iron contents of other types of sediments, particularly shales. A sample mass balance calculation after the manner of Garrels and Mackenzie (1971, p. 242) illustrates this. Using a present day "average igneous rock" (Brotzen, 1966) as a source for limestone, sandstone, and shale, and considering just the total iron percent we have, after Garrels and Mackenzie (1971, p. 242): Average igneous rock Fe oxides in gms/kg 62 limestone shale sandstone 62 4 if one considers a situation where 15% by weight of the sediments are of iron formations containing 30% iron oxides, we must subtract 45 grams of iron oxide to supply this source, leaving only 17% to go into shales and sandstones. The assumption is made that iron normally going into shales (such as might happen during the weathering of a basalt today) has been diverted into iron formations. If this assumption is valid, shales formed during times when iron formations were a significant portion of the sedimentary column, should contain less iron than might otherwise be expected considering possible igneous sources. Since iron is the heaviest common element this might have implication regarding the composition, density and isostatic relationships ofrocks such as granitic gneiss formed by metamorphism of shale. �Paper 5 EFFECT OF A "RIGID" ULTRABASIC SILL ON DEFORMATION IN ADJACENT ROCKS, KAKAGI LAKE, NW. ONTARIO by R. G. Cuddy, P. M. Clifford Department of Geology, McMaster University, Hamilton, Ontario ABSTRACT The greenstones of Kakagi Lake consist of about 7500 metres of basic to acid volcanic rock, and some associated sedimentary rocks. Embedded within this assemblage are "sills" of ultrabasic material Study of the western portion of the Kakagi Lake area shows that the ultrabasic sills have a fold form of class 1-B or 1-C (cv. Ramsay; 1967 pp. 365 ff.), as revealed by thickness, measurement and isogon plots. Petrographic study of one sill (Ridler, 1966) suggests that very little strain has occurred within the sill. The rocks in contact with the sills are with very few exceptions, acid pyroclastic volcanics. They lack significant primary layering and, mechanically, form thick, rather homogeneous units. Cleavage density rises, as does consistency of orientation of cleavage, in the vicinity, and along axial surface continuationsof tight folds in the sills. Conversely, open folds in the sills are adjacent to areas of low cleavage density and locally variable cleavage orientation. In addition, fragments in the pyroclastic rocks, though flattened to lie roughly parallel to cleavage, are poorly oriented within the cleavage, a situation which suggests rather low strains within the cleavage plane compared to the high strains across it, or alternatively, a fluctuation of pyroclast long axes over 1800 in the pre-strain state. Fold axes, few in number, are everywhere of moderate to steep plunges. These features are the product of an early phase of deformation. Subsequent deformation has produced kink folds and en echelon quartz-filled gash arrays. These suggest local orientations of principal axes of stress or strain, apparently not of regional value. It is not clear from our data, or any other data available whether the granites surrounding these rocks are fully responsible for the deformation, or have merely modified a prior fold array whose axial surfaces were aligned east-west. What is clear is the marked effect of the sills with their low ductility compared to the pyroclastic rocks in which they occur. Ramsay, J. G. (1967) Folding and Fracturing of Rocks. Ridler, R. H. (1966) M.Sc. thesis (unpublished) Univ. of Toronto. �Paper 6 THE LABRADOR TROUGH - NOT A PRECAMBRIAN PLATE BOUNDARY Erich Dimroth, Service d'Exploration gologizue, Mjnistre des Richessea naturelles, Qubec ABSTRACT The boundaries between the Precambrian age provinces are the natural location where to look for Precambrian plate boundaries. This is specifically so for the .junction between the Superior and Churchill Provices, which are separated by the Circum-Ungava geosyncline. Deep erosion has removed the whole of the original geosynclinal filling in the sector between Labrador trough and Cape Smith belt, and the relations between the geosynclinal filling and its basement can be studied. Other segments of the Labrador trough are deeply enough eroded to infer the presence of a basement. At the level of the basement (that is between the Labrador trough and the Cape Smith belt) the contact between the Superior of Churchill Provinces appears to be gradational. The Archean gneisses are continuous to Ungava bay, but they give Hudsonian K-Ar ages east of line indicated in Wanless (1969). The Archean gneisses east of the age front appear to have suffered Hudsonian deformation, as indicated by the folded outline of the contact between the basement and the Lower Proterozoic sequence. Beau et al. (1963) noted that the Hudsonian biotite isograd intersects the basement-cover contact, and retrograde metamorphism has been noted in a few basement outcrops visited. It appears therefore that a Hudsonian tectonic, metamorphic and age (K-Ar) front, intersects a uniformly Archean terrain between the Cape Smith belt and the Labrador trough. The northernmost Labrador-trough and the easternmost Cape Smith belt are synclinoria plunging south-southeast and west-northwest. The Lower Proterozoic sequence of both belts, which includes very voluminous oceanic tholeiites rests on the basement gneiss with an absolutely sharp contact (Hardy, 1969; Schimann, 1972). �Paper 6 -2- In the centre of the Labrador trough a very thick sequence of oceanic tholeiite rests on continental red beds and on shallow water sediments (for example sandstone with coarse current cross-bedding, stromatolitic dolomite). Units of stromatoljtjc dolomite, of oolitic iron formation and similar shallow-water deposits is continuously exposed across the whole trough, and, in its east, mantles domes of basement gneiss. There is not a trace of a sheeted gabbro complex, and in fact the source of the basalts is still enigmatic. Only very few and generally thin gabbroic dykes intersect the sedimentary sequence and are the only possible conduits known at present. In the extreme east of the Labrador trough a metamorphosed meta-pelitic sequence, comprising interbeds of orthoquartzite, dolomitic sandstone (now diopsidequartzite), para-aniphibolite, is exposed. Arkoses, arkosic conglomerates, are present here and there and perhaps indicate the presence of occasionally emergent source areas east of the trough. According to Wanless (1970) granitoid gneisses east of the trough give at one locality a K-Ar age of 2160 m.y., that is somewhat older than the Rb-Sr age of the Labrador trough rocks (Fryer, 1971). This seems to confirm the basement nature of at least some granitoid gneisses east of the trough. There appears little doubt that the Labrador trough formed by differential subsidence and that it is not related to a continental margin existing at Lower Proterozoic time. REFER EN C ES Beall, G. H., Hurley, P.M., Fairbairn, H.W., and Pinson, W.H., Jr. (1963), Comparison of K-Ar and Rb-Sr dating in New Quebec and Labrador. Am. J. Sci., V. 261, p. 511-560. Fryer, B. J. (1971), Rb-Gr whole rock ages of Proterozoic Strata bordering the eastern part of the Superior Porvince, Canada. Geol. Soc. Amer., Abs with programs, 3, p. 574-575. �Paper 6 -3- Hardy, R.1(1969), Gologic de la re9ion du lac des Chefs, These de maitrise, non publiee; Ecol Polytechnique. Travaux sur le Department of Natural Resources, Quebec, Report S-126AF, p. 7-10. Schimann, K. (1972), Wakeham Bay In: terrain 1971. Wanless, R. K. (1969), Isotopic age map of Canada. Geol. Surv. Canada, Map No. 1259A. Published with the permission of the Minister of Natural Resources, Quebec. �Paper 7 I DEPOSITIONAL MODEL FOR THE LOWER NONESUCH SHALE BASED ON LITHOLOGIC VARIATION Robert Ehrlich and Thomas A. Vogel Geology Department Michigan State University 48823 East Lansing, Michigan ABSTRACT The White Pine copper deposit is one of the classic strata—bound Not only is the mineralization restricted to a small lower portion of the Nonesuch Shale but the vertical succession of lithologies within the mineralized section is remarkably similar in all parts of This striking similarity in vertical succession has in the the mine. past been used as a basis for assuming wide scale lateral continuity of subunits within the Lower Nonesuch Shale. This in turn led to models of deposition, diagenesis, and ore emplacement in which the layercake The aspect of the lower Nonesuch stratigraphy played a key role. purpose of this report is to integrate the observed lithologic variation into an overall depositional model for the Lower Nonesuch Shale. deposits. The lower fifty feet of the Nonesuch is composed of numerous textural modes such as graded, well—laminated, crudely laminated, fragmental, blebby, massive, etc. Various combinations of these textural elements can be found in varying proportions in each of the formal stratigraphic units and each of these (Domino, Brown Massive, etc.) have extensive lateral continuity whereas the individual textural elements included within each unit are not persistent. These lateral changes arise in three principal ways: (1) abrupt changes apparently resulting gradual and (2) from slumping and sliding of plastic sediments, and continuous changes in lithology within a major stratigraphic unit such as massive units becoming crudely laminated and then graded. Similar lateral variations can be seen with major elements within one formal stratigraphic unit varying laterally into a lithology which is a characteristic of an adjacent stratigraphic unit above or below. Most of the textural elements can be seen in varying proportions in the massive units. When observed in detail, it can be seen that there is a non—random juxtaposition of the elements; that is, certain elements tend to be adjacent to certain others. Figure 1 shows the most probable �Paper 7 PAGE 2 associations between textural elements. Elements adjacent in the diagram tend to be intimately associated with each other on a hand sample scale. Elements far apart on the diagram are rarely seen juxtaposed. Figure 1 Mutual Occurrence of Textural Elements in Massive Units Textural elements relatively closer on diagram occur together more often. ,Massive ———— Crudely Laminated ———— Graded ———— Laminated Fragmental' "Blebby ———— Crudely Laminated In these massive units the textural elements on the left side diagram (e.g., fragmental, massive, blebby) are more abundant than on the right. Because each of these elements, except those on the extremes, is associated with two others, these inter—relationships the basis for the pattern of vertical and lateral variation within massive units. of the those are the A characteristic vertical succession is from bottom to top; massive, crudely—laminated, fragmental, scoured surface, massive, blebby, crudely— laminated, graded, well—laminated. A section such as this is composed of two depositional units, each beginning with a massive textural variety Within each and terminated by a fragmental or laminated variety. depositional unit there are no sharp boundaries as one proceeds from one textural element to another, indicating that the sequence of textural elements arose from a single genetic event. The textural varieties and lateral and vertical relations observed are consistent with a depositional model involving progressive infilling of a depositional basin with coarse, denser materials being deposited over materials of low specific gravity that are mechanically weak. The pattern seen here can be understood if the effects of lateral migration and loci of sedimentation are considered as well as general infilling in the basinward direction. In general terms, the dynamic model consists of coarse—grained material deposited on muds, triggering its accompanying flow components. In the Nonesuch two modes of deposition and transport were involved in most slumps. The uppermost, least consolidated materia],, generally (1) hematite—rich, moved rapidly, partially as suspended material, partially as bonafide turbidity flow, and fanned out into a roughly lobate deposit. �Paper 7 PAGE 3 (2) The slightly more consolidated material underlying this zone, in a more reduced condition, either flowed plastically, more slowly, down the depositional slope with relatively little rotation or, if it was reasonably coherent, behaved as a rotational slump with a well—developed concave upward slip surface. Sediment that has moved further downslope is more laminar and less rotational in nature. This, coupled with longer time involved in transport, allows the previously homogenized sediment to differentiate itself with respect to grain size. The sequence, updip to downdip, is thickest, but of least lateral extent at the updip end, and thinnest (perhaps only one graded bed thick) but most laterally extensive at its downdip extremity where it fans out in an unrestricted fashion. This process model can explain the three dimensional pattern of rock variation and provides an important framework for a discussion of the origin of the other geochemical and petrological variations in the Lower Nonesuch Shale. �Paper 8 PALEOMAGNETIC EVIDENCE FOR THE EXTENT OF LOWER KEWEENAWAN LAVAS IN MINNESOTA by John C. Green Geology Department University of Minnesota, Duluth and Minnesota Geological Survey Kenneth G. Books U. S. Geological Survey Silver Spring, Maryland ABSTRACT Most of the North Shore Volcanic Group of Gehman (1958), from central Duluth northeastward to the diabase complex at Hovland (Fig. 1), is now known to be middle Keweenawan on the basis of its normal magnetic polarity (Books, 1968; Palmer, 1970; new data). Beneath (north of) the Hovland diabase and the southern prong of the Duluth Gabbro Complex in Cook County is a series of lavas, approximately 8,000—10,000 feet thick (the Hoviand and Grand Portage lavas of Green 1971) that were extruded during an earlier period of reversed polarity, and are therefore lower Keweenawan. These two units can be traced for at least 25 and probably 50 miles westward, where they are intruded by the Duluth Gabbro Complex. The Hovland lavas include many porphyritic basalts with platy plagioclase phenocrysts. These two lava units thus correlate with the lithically similar reversed "Traps of the South Range" in the Ironwood area, Michigan—Wisconsin, (Books, 1968) and with the Osler Series of Ontario (Palmer, 1970). The Grand Portage lavas are cut by a dike swarm of basalt and porphyritic basalt that also show reversed polarity and may have been feeders for the porphyritic Hovland lavas. The Grand Portage lavas rest disconformably on the Puckwunge Formation of Schwartz, 1942, an orthoquartzite that overlies the middle Precambrian Rove Slate. Although the samples showed only weak magnetization, new determinations give an unequivocal reversed polarity for the Puckwunge, and support its correlation with the lithically similar Sibley Series sandstones of the Thunder Bay district, Ontario. At the southwest end of the basin also, the Duluth Gabbro Complex intruded between lavas of normal and reversed polarity, i.e. between middle and lower Keweenawan volcanic rocks. New determinations show that most or all of the basalts at Ely's Peak (the wedge of lavas that underlie the Duluth Gabbro Complex west of Duluth) have reversed polarity, and thus correlate with the flows at Ironwood and Grand Portage. The basal pyroxene—porphyritic lavas in this unit bear a very close resemblance to the basal lavas on Lucille and Magnet Islands east of Grand Portage, further supporting this correlation; such lavas are not known from anywhere else in the North Shore Volcanic Group. Samples from the conformably underlying "Nopeining sandstone" and from the lowest flow at the "Grandview Golf Course" locality show weak magnetization and considerable scatter, but normal polarity. What is believed to be the same flow (certainly part of the same unique pyroxene—basalt flow group) 3/4 mile to the south shows reversed polarity. Although these normally polarized samples were taken at least 500 to 800 feet (structural distance) from the base of the Duluth Gabbro Complex and are not visibly recrystallized, even in thin section, it appears likely that the basalt's polarity has been inverted to �Paper 8 normal during contact metamorphism by the Duluth Gabbro Complex. No conclusions can yet be made regarding the original polarity of the sandstone; it may have been normal, thus correlating with the Bessemer Quartzite of Seaman, 1944, beneath the lowest Keweenawart flows at Ironwood, or it may also have been changed from an original reversed state, thus correlating with the Puckwunge and Sibley. Further investigations will be carried out. References Books, K. G., 1968, Magnetization of the lowermost Keweenawan lava flows in the Lake Superior area: U. S. Geol. Survey Prof. Paper 600—D, p. D248—D254. Gehman, H. M.,, Jr., 1958, The petrology of the Beaver Bay Complex [Minn.J [abs.], in Institute on Lake Superior Geology, Apr. 21—22, 1958: Minneapolis, Univ. Minn. Center Continuation Study [19581, p. 1. Green, J. C., 1971, Stratigraphy of the North Shore Volcanic Group northeast of Silver Bay, Minn. [Summary]: Inst. on Lake Superior Geology, May 5—8, 1971: Duluth, Univ. of Minn., Duluth, 1971, p. 20—22. Palmer, H. C., 1970, Paleomagnetism and correlation of some middle Keweenawan rocks, Lake Superior: Can. Jour. Earth Sd., v. 7, No. 6, p. 1410—1436. Schwartz, G. M., 1942, Correlation and imetamorphism of the Thomson Formation, Minnesota: Geol. Soc. America Bull., v. 53, no. 7, p. 1001—1020. Seaman, W. A., 1944, Summary of the geology of the Marquette iron range [Mich.]: Michigan Geol. Survey Prog. Rept. 10, p. 11—17. �a II ntrusjve rocks a L owes af Keene.wen teuas tt44t Kewn.n u&s ktween&u,an Kilo", ee's S )s _______ �Paper 9 THE NEWLY COMPILED GEOLOGICAL MAP OF THE PRECAMBRIAN OF THE UPPER PENINSULA OF MICHIGAN J. Kalliokoski and W. Bodwell Department of Geology and Geological Engineering Michigan Technological University Houghton, Michigan With the retirement of the older staff, the Department of Geology and Geological Engineering found itself in a position of requiring a mechanism whereby it could refamiliarize itself with the Precambrian geology of the Upper Peninsula, in order to identify good field-thesis problems and to become knowledgeable about the mineral potential of the region. The most direct approach seemed to be in compiling all geological data on the most suitable scale. With the help of the Institute of Mineral Research (M. T. U.) and the full cooperation of the Michigan Geological Survey, the U. S. Geological Survey, various mining companies, and land owners, this task has now been completed. The resulting map, "Precambrian Geology of the Upper Peninsula" (M. T. U. Press, Geological Series, Map 2, 1972) is on a scale of 1:250, 000. A second map "Geology of the Marquette-L'Anse Region, Michigan", (M. T. U. Press, Geological Series, Map 1, 1972) shows the available outcrop data for the "Northern Complex" on a scale of 1:62, 500. Both maps, uncolored, show the location of known base metal and precious metal showings. The 1:250, 000 map (released April, 1972) is priced at $3. 00 and the 1:62, 500 map (released in late August, 1972) is $5. 00, both including postage, prepaid. They are available from the Department of Geology and Geological Engineering, Michigan Technological University, 49931. Although the maps are complete in themselves, they represent part of the documentation for an M. S. thesis by W. Bodwell, entitled "Geologic Compilation and Non-ferrous Potential, Precambrian Section, Northern Michigan". Copies of the thesis may be obtained from the Department for the cost of reproduction. �Paper 10 PETROLOGY, STRUCTURE, AND CORRELATION OF THE UPPER PRECAMBRIAN ELY'S PEAK BASALTS JAMES A. KILBURG University of Minnesota, Duluth ABS TRACT The Upper Precambrian Ely's Peak basalts crop out in a north—south trending, wedge shaped belt in the area around Nopeming, southwest of Duluth, Minnesota. These Lower Keweenawan flows overlie the basal Upper Precambrian quartzite in the southwestern portion of the Lake Superior basin. There are about 18 individual flows totaling some 1,200 feet of thickness, the thickest flow being 125 feet thick while the thinnest is less than 10 feet thick. Many of the flows show lateral continuity, for example, one flow is traceable for about three miles along strike. Petrographically, there are three main types of flows. Five of the first six that form the basal portion are dark gray, porphyritic basalts. Of these, four contain euhedral, zoned, single and glomerophorphyritic augite phenocrysts up to 5 mm in diameter. Some ilmenite phenocrysts and some olivine pseudomorphs are also present. The groundmass contains altered plagioclase, magnetite, augite, actinolite, chlorite, and sphene. The sixth flow up from the base is a dark gray, porphyritic basalt with single and glomeroporphyritic plagioclase phenocrysts up to 7 mm in diameter; there are also occasional augite phenocrysts. The groundmass contains altered plagioclase, augite, actinolite, ilmenite, sphene, epi— dote and chlorite. The third type of flow is a dark gray, commonly ophitic, altered basalt. It consists of plagioclase, occasional olivine pseudo— morphs, actinolite after augite, augite, ilmenite, magnetite, epidote, sphene, and chlorite. Structures within the flowsinclude ropy surfaces, vesicular and amygdaloidal tops, straight and bent pipe vesicles, straight cylinder vesicles, columnar joints, and pillows in the basal flow. Several northeast trending basalt dikes cut the flows and have been deeply eroded leaving pronounced lineaments. The whole sequence has undergone regional hydrothermal metamorphism to the high zeolite—low greenschist fades. Minerals present which demonstrate this are actinolite, chlorite, and epidote. The only zeolite present is wairakite which has been discovered probably for the first time in the Lake Superior region. It is the highest temperature zeolite. Intrusion of the Duluth Complex is thought to be responsible for elevating the geothermal gradient and thus, permitting the formation of wairakite. The gabbro intrusion also contact metamorphosed the lavas to a medium grained pyroxene hornfels for a distance of up to one—fifth of a mile from the contact. �Paper 10 Pressures of metamorphism are thought to have been around 2,000 bars, although a range of pressures between 1,500—2,500 bars seems feasible. This pressure was produced by the weight of up to 30,000 feet of overlying Upper Precambrian lavas and Duluth Complex which underlie the North Shore of Lake Superior; however, as little as about 16,000 feet of overburden could have produced the minimum pressures of about 1,500 bars needed for metamorphism. Based on their distinctive petrology and reversed magnetic polarity (Green and Books, 1972), the Ely's Peak basalts appear to correlate with the basal flows at Grand Portage, Minnesota. This implies that the time of deposition at these localities was approximately the same, and the source area from which these lavas were derived was probably the same. �Paper 11 PRECAMBRIAN GEOLOGY OF A GREENSTONE BELT IN OCONTO COUNTY, WISCONSIN, AND CHEMISTRY OF THE WAUPEE VOLCANICS. Melvin M. Lahr University of Wisconsin, Madison, Wisconsin ABSTRACT Detailed mapping has been carried out in the northern half of the Mountain Quadrangle in order to establish the geologic history and evolution of a Precambrian greenstone belt and to determine the nature of volcanism. The sequence of Precambrian events was the following (oldest to youngest): 1. Deposition of the Waupee formation, including flows, agglomerates, tuffs, volcaniclastic sediments, and sandstones. 2. Emplacement of the Macauley intrusive (granodiorite to quartz monzonite). 3. 4. 5. Deformation and regional metamorphism. Deposition of the Baldwin conglomerate. Intrusion of the Hager granite and contact metemorphism of the older rocks. The Waupee formation trends approximately N450E and has a steep dip. Relic graded bedding and cross-stratification indicate that tops of beds are to the northwest. Three lithologic units have been distinguished in the Waupee formation: a basal member consisting of massive flows, volcaniclastic sediments, and minor agglomerates; a middle sandstone member with a subordinate amount of massive flows; an upper thin-bedded tuff member. Pyrrhotite mineralization is concentrated along the boundary between the basal and middle members of the formation. Sedimentary features and volcanic textures have been preserved in the Waupee formation, but recrystallization under conditions of the amphibolite facies has produced the following mineral assemblages: basic volcanic flows: plagioclase-hornblende-clinopyroxene. p1 agi ocl ase-hornbl ende-cummi ngtoni te. quartz-biotite-hornblende-plagioclase+ sedimentary rocks: epidote. quartz -microcline-biotite-mu scovite+ p1 agiocl ase. Contact metamorphism due to intrusion of the Hager granite has been superimposed on the regional metamorphic assemblages, resulting in the appearance of garnet, vesuvianite, scapolite, clinopyroxene, hornblende, and plagioclase in the metavolcanic rocks. In the aluminous metasedimentary rocks the assemblage quartz-plagioclase-alkali feldspar-muscovitebiotite-andalusite+ sillimanite has developed. �Paper 11 Eighteen samples of massive volcanic flows from the Waupee formation were fused and analyzed for nine elements (Si, Al, Ti, Fe, Mn, Mg, Ca, Na, K) by means of an electron microprobe. The majority of samples are basalts (Sio2, 46 to 51%) containing 15 to 20% A1203 and 2.0 to 5.8% Na20 + K20; a few samples are andesiEic, containing up to 6T% Si02. If the chemical compositions of the massive flow rocks have not been modified during regional metamorphism, then the Waupee volcanics can be classified as high-alumina and alkalic basalts. As yet, no tholeiitic basalts have been recognized in this area. The chemistry of the metavolcanic rocks and the nature of associated metasedimentary rocks suggest that the Waupee formation originated in an island ac environment. �Page 12 THE GEOLOGY OF THE GARLIC RIVER GREENSTONE BELT P. James LeAnderson Queen's University, Kingston, Ontario ABSTRACT The Garlic River Greenstone Belt is the Archaen greenstone belt northwest of Marquette, Michigan. It consists of a series of basalt flows, tuffs, greywackes, arkoses and iron formations formerly referred to as the "greenstone" or as Mona Schist. The belt is twenty miles wide along the southern boundary, at the contact with the Marquette Synclinorium, and extends ten miles to the north (See Fig. 1). Discernable tectonic history indicates gentle folding of the flows and sediments, followed by intrusion of quartz monzonite pegmatites, large diabase dikes and finally granodiorite pegmatites.. The flows and sediments were metamorphosed to chlorite schists and amphibolites. The chlorite and chloritic amphibole schists may represent greywackes and/or reworked or waterlain tuffs. The amphibolites are thin bedded or massive; some of the latter have pillows or relict plagioclase laths, indicating a volcanic origin. Felsic volcanics are uncommon, but form a zone of sheared rhyolitic at the east end of the Dead River Basin. Small extrusive bodies of porphyritic dacite are found throughout the chlorite and amphibole schists. tuffs (?) The Arkoses (Gar) occur commonly as thin units in the chlorite and amphibole schists, but are the dominant rock type in two areas near the northwestern boundary of the belt. Iron formation (IF) consists of thin discontinuous lenses of Neither carbonate nor sulfide facies iron formation ntagnetite in arkoses. were found. Two synclines have been mapped trending northwest—southeast and plunging southeast, one in the northwest corner of the belt and the other some six miles to the south in the central part. Additional detailed mapping may reveal other folds. Two large downfaulted basins with lower (Ar) and middle and upper (Amu) Animikie Sediments, partially covered with thick deposits of Pleistocene sand, truncate the northern and western boundaries of the belt. A third smaller basin occupies the center of the belt. In the northern part of the area two ages of felsic intrusives can be distinguished, but this distinction cannot be made southeast of the Dead River Basin. The younger intrusives are predominantly quartz monzonites, and are cut by the second set of intrusives which are weakly metamorphosed, non— porphyritic granodioritea. The felsic intrusives in the southern part are porphyritic granodiorite pegmatites. Diabase dikes consisting of unoxiented subhedral hornblende and plagioclase crystals trend east—west across the regional foliation but are not folded. They appear to belong to one set, intermediate in age between the quartz monzonite and the granodiorite. �2 Paper 12 TFie uniformity of mineral composition of the greenstones and the ubiquitous and commonly complete alteration to chlorite and sericite, makes However, the trend, from determination of the metamorphic grade difficult. predominantly pale green amphiboles to dark blue—green amphiboles, from the center to the margins of the belt, indicates that the metamorphic grade increases in the same direction from the greenschist to the amphibolite facies. Although stratigraphic and time relationships in the belt are unknown the following generalizations can be made, 1) the sediments, tuffs and lavas were deposited in shallow water, possibly subaerially, as indicated by the pillow lavas and oxide facies iron formations, 2) the series of thick and extensive metabasalts, tuffs, greywackes and rhyolites south of the Dead River Basin indicate continuous and voluminous outpourings of lava and pyroclastics, and 3) the thin discontinuous layers of basalt, greywackes, tuffs, dacites, arkoses and iron formations to the north, suggest local eruptions of short duration with frequent erosional breaks. After folding of the greenstones, magma intruded and assimilated the lower units, leading in turn to first stages of development of the The magma spread further into the greenstone and lit—par—lit gneisses (Gu), formed pegmatite dikes and sills in the nose of the northwestern syncline. This was followed by the intrusion of a series of diabase dikes; at this time the metamorphic grade reached it's peak. The area was then covered by Animikie sediments which were folded by the Penokean Event, when the structural basins were formed. The intrusion of Keweenawan dikes, followed by deposition of the Jacobaville sandstone in late Precambrian or early Cambrian times, closed the geological record, with the exception of that attributed to the Pleistocene glaciation. �GENERALIZED GEOLOGIC MAP OF THE GARLIC RIVER GREENSTONE BELT AND of Michigan. PCg Lower Precambrian Garlic River Greenstone Belt Oneiss Complex Pgn, Lower Precambrian where approximately located where approximately northern peninsula Dotted Shoet dashed located complex in the Location map of the Lower Precambrian Garlic River Greenslone Belt and the Gneisx Geologic contacts Faults VICINITY* �Paper 12 COLUMN' GEOLOGIC GENERALIZED C .00 a NE Sandstone Jacobsviile 2 a--I unconformity Dikes Diabase Keweenowan Middle and tAmu) Upper 0 Lower and N (A) Animikie (Aim) Middle 2 Reony Lower 0 Creek (Ar) Formation — Serpentinized Peridotites 2 2 Granodiorites Intrusive contact Metadiabase Dikes Intrusive contact Quartz Monzonites Intrusive contact Gu Gar — IF Z Garlic River 3 Greenstones Gri GIpa GI Gm (G) U Gneiss and Intrusive Complex (Gn) �Paper 12 Based in part on maps by Case, J.E. and Gair, J.. (i5), Gair, J.E. and Thayden, R.E. (1968), Puffett, w.P. (1969) and LeAnderson, P.J. (1969). 1Units with symbols are included on the map with Units without symbols descriptions in the text. are not included on the map due to the scale involved. 2The age is uncertain. They may be post—Anamikie and pre—Keweenewan. 3The stratigraphic succession of the units of the Garlic River Greenstone is indeterminate. BI BLIOG.APHY Case, J.1. and Gair, J.E., 1965, "Aeromagnetic Map of parts of Marquette, Dickenson, Baraga, Alger, and Schoolcraft Counties, Michigan, and its Geo1o'ic Interpretationt', U.S. Geological Survey Geophysical mv. Map GP—467 Gair, J.E. and Thayden, R.E., 1968, "Geology of the Marquette and Sands Quadrangles, Marquette County, Michian", U.S. Geological Survey Professional Paper397 LeAnderson, P.J., 1969, "The Pre—Animikie Greenstone Complex of a small area in Narquete County, "ichignn", Unpub]Jsed Msc. Thesis, Michian State University Puffett, W.P., 1969, "The Reany Creek Formation, Marquette County, Michigan", U.S. Geologicl Survey Bull. 1274—F �Paper 13 MORPHOLOGY OF MAGNETITE IN PRECAMBRIAN IRON FORMATIONS M. S. LOUGHEED and J. 1. MANCTJSO Bowling Green University, Bowling Green, Ohio ABSTRACT The morphology of magnetite in all metamorphic fades of unoxidized Precambrian iron formations in the Lake Superior region is remarkably similar. Particularly noticeable are discrete symmetrical or distorted octahedral crystals of magnetite disseminated within individual lamina of chert. Several other features are noteworthy: 1) the crystal diameters range from sub—micron to over fifty microns; 2) the concentration of crystals in a particular lamina can range from a fraction of a percent to aggregates constituting the entire lamina; 3) the invariant associate of magnetite is chert; 4) the variant associates are iron carbonate and/or iron silicate minerals; 5) the minor but not uncommon associates are minute hematite crystals as disseminated spherical clusters, and pyrite as fram— boids, octahedra, and crystal aggregates generally within laminations of digital stromatolites or in laminations of mat algae. The morphology of magnetite, its variation in grain size, and its relationship to chert (quartz) siderite, iron silicate minerals, pyrite and/or hematite indicate that it is primary and that no chemical interreactions took place during diagenesis or metamorphism even to extremely high grades. �Paper 14 SUBSURFACE GEOLOGY OF THE DULUTH-SUPERIOR AREA, MINNESOTA-WISCONSIN J. T. MENGEL, JR. University of Wisconsin, Superior ABSTRACT Study of about 300 borehole records for the Wisconsin Geological Survey indicates that the Quaternary succession in the western end of the Superior lowland consists of glacial, lake, and river deposits which record stages in the development of Lake Superior which are not presently evident in the high-level shore deposits around the rim of the basin to the west or in deeper water lake deposits to the east. Preliminary interpretation of the sequence suggests two times of deep water red clay accumulation separated by a low water stage during which sands and gravels were laid down across an unconformity. A prominent boulder bed overlies the youngest red clay deposit, suggesting a late pulse of ice development during about Nippissing time. The Duluth Complex forms the north wall of the lowland in the Twin Ports area and is found in borings along St. Louis and Superior Bays, where wells encounter the same lithologies known from surface exposures. Fluvial red clastics - mainly quartzose sandstones with limited amounts of conglomerate and shale - of the Bayfield group are unconformable on the Complex and subcrop beneath most of the plain. Throughout the subcrop the Bayfield Group is identified as a "sandstone" or "brownstone" and an aquifer. Similar red clastics underlie most of the western end of the Superior Basin and are the principal source from which the Ouaternary sediments were derived. Along the base of the South Range the red clastics are cut off by the Douglas Fault which brings the Keweenawan basalt sequence of the St. Croix Horst upward and northward over the sandstones. Basalts crop out locally along the crest of the South Range and subcrop beneath the Quaternary succession southward to the Lake Duluth beaches (elevation about 1070) and beyond. The most notable feature about the configuration of the erosion surface on which the Quaternary succession lies is the buried western extension of the major depression along the northerly shore of Lake Superior (cf. Farrand, 1969). Twenty-five to 50 feet of local relief is present on the bedrock One local high forms a prominent outcrop along the bay front at the foot of 27th Avenue West in Duluth and a belt of subsurface surface everywhere. bedrock highs are known in the northern half of 48N-13W, extending westward into the center of 48N-14W in Wisconsin. �Paper 14 2 A maximum thickness of about 600 feet of sediments are present along the axis of the north shore depression between Fond du Lac and Superior Bay and 100 to 300 feet are present under the plain as far south as the crest of the South Range. Less than a hundred feet of glacial drift overlain by clays and/or sands is present along the crest of the South Range. Glacial drift everywhere overlies the bedrock of the plain. Typically about 25 feet is present except toward the bottom of the north shore depression, where as much as 200 feet is known. The drift ranges from a silty or sandy clay to an argillaceous sand and generally contains gravel and erratic boulders. Clean sand/gravel lenses are presently locally most commonly at or near the base of the drift, and are an important source of ground water when encountered. Lake deposited stiff red clay overlies the drift and is more or less gradational with it. Along the northerly side of the St. Louis River in West Duluth, and beneath the plain to the south of Superior almost the entire Ouaternary succession is medium to stiff red brown clay containing scattered ice rafted pebbles and cobbles. Silty, sandy/gravelly layers, some of which contain small amounts of water are encountered in the clays, most comonly at depths of about 20 to 50 feet below the general level of the plain. At higher elevations i.e., about 900-1000 feet the clays are gradational with sandy materials representing shore reworking of the underlying drift and materials introduced by small tributary streams. Locally the sandy materials extend to lower elevations-lying on top of the clay sequence. Along the St. Louis River the clays are largely replaced in the stratigraphic succession by brown, poorly permeable dense argillaceous silty to sandy deposits which become coarser and cleaner and may contain gravels toward the top of the sequence. These deposits, which reach a maximum thickness of about 200 feet lie on a stiff red clay unit, which in turn rests on glacial drift deposited in the north shore depression. Deep engineering bore control is not adequate to define lateral relationships with the middle part of the clay sequence. It presently appears that there is little or no interbedding of sand and clay either in West Duluth or in Superior, suggesting the possibility of introduction of the sandy materials by ice or in part by turbidity flow or river deposition along the general trend of the north shore depression. The coarseness of the upper part of the sandy sequence, its considerable degrees of sorting, and prominent cross bedding indicate the existence of high energy conditions at the Lakehead prior to deposition of the 15 to 50 foot thick red clay which overlies the sandy unit, forming the surface of the Superior plain. The uppermost clay layer lies on an undulating surface having up to a few tens of feet of relief. Contours on the base of the clay define the north shore depression and indicate slopes toward the depression and toward Lake Superior. The clay dips beneath present water level in Howards Bay and is known beneath the younger sands and gravels of Connors Point and the outer end of Rice's Point. Both of these points are built along �Paper 14 3 the erosional zero edge of the clay as it subcrops under St. Louis Bay, suggesting that this fact may have influenced their construction. The same red clay subcrops beneath the outer end of Minnesota Point and under Wisconsin Point. This uppermost clay rests on a thin sandy or gravelly unit which overlies the main clay sequence in West Duluth and Morgan Park and conditions are similar in Superior. Prominent develop- ment of clays to elevations of about 700 feet on the Duluth hillside may indicate flooding of the plain to this level during development of the clay layer. A later very low water stage, perhaps Ferrand's (1969) Houghton Stage, allowed deep incision of drainage along the north shore depression, exposing the sandy sequence and initiating the present drainage system. A general rise in lake level toward a maximum of about 610 feet during the Nippissing Stage caused the deeper parts of the drainage to become aggraded with sandy materials and subjected the upper red clays to strong wave attack. The rise of the uppermost clay away from the north shore depression made it particularly subject to wave erosion, causing steep bluffs from the central part of the Superior Bay waterfront eastward to the present shore line of the lake. A prominent clay platform was developed offshore from the bluffs. This platform is the floor on which Minnesota and Wisconsin Point are built. It is presently blanketed by twenty to at least 70 feet of clean fine to coarse sand containing small amounts of gravel. A greater thickness of such sandy deposits may lie below present control depth under the central part of Rice's Point and the northerly third of Minnesota Point. A great number of large crystalline rock boulders occur at or near the base of these young sandy deposits under Superior Bay. Maximum boulder size recorded so far is 5 x 6 x 7 feet for one recovered during construction of the Cloquet water line. Large boulders are known throughout the length of the Superior Front Channel and the open lake shore to the southeast, their number, size and wide distribution, together with the existence of a higher lake level more or less following their deposition may suggest a late pulse of ice development. An alternative view is that they are developed by exposure of the top of the sandy unit beneath the upper red clay. This unit is known to contain boulders locally, as in the vicinity of the local bedrock high at the foot of 27th Avenue West in Duluth. However, the fact that boulders lying on a few feet of sand overlie the top of the young red clay under Connors Point suggest that ice transport may be involved. It is quite possible that some of the sand present on south shore beaches comes from exposure of the underlying sands. Much of the modern south shore sand is derived from reworking of the underlying till which is exposed along several drainages as the bedrock surface rises to the east of the Twin Ports. A period of declining lake levels during which water levels dropped from about 610 to perhaps 590 feet, witnessed the sequential development of the lake-head barriers of Grassy Point, Rice's—Connors Points, and Minnesota-Wisconsin Points (cf. Loy, 1963). All are built primarily from materials derived by the erosion of the sandy sequence of the north shore depression by the St. Louis River and by lake activity during the high waters of the Nippissing stage. The eventual decline in water level during the subsequent Algoma stage was low enough �Paper 14 4 to permit development of spruce woods rooted in the sands of what is now Allouez Bay. Later flooding, which is apparently continuing at present (cf. Moore, 1948), has led to development of organic-rich mucks, locally capped by peats as the main sediments above the most recent harbor sands. The upper parts of the organic deposits often contain sawdust, wood fragments and horse manure, a legacy of late 19th century activities in the harbor. Slag, wood derivatives, etc. of more recent origin are also present. Dredging for harbor development and slip construction have largely altered the natural stratigraphic sequence of the young sands and organic materials but the natural bottom contours, sediment types, and shore features can still be studied on the excellent 1861 chart directed by Captain G. C. Meade for the Army Corps of Engineers. REFERENCES Farrand, W. R., 1969, The Quaternary history of Lake Superior: Proc. 12th Ann. Conf. Great Lakes Res., International Assoc. Great Lakes Res., p. 181-197. Loy, W. G., 1963, The evolution of bay-head bars in western Lake Superior: Pub. No. 10, Great Lakes Res. Dir., Univ. Michigan, Ann Arbor. Moore, Sherman, 1948, Crustal movements in the Great Lakes area: Bull. Geol. Soc. Amer., 59, pp. 697-710. �Paper 15 PETROLOGIC AND STRUCTURAL ASPECTS OF THE GABBRO SILL ON PIGEON POINT, MINNESOTA M. G. Mudrey, Jr. and P. W. Weiblen Minnesota Geological Survey and University of Minnesota, Minneapolis Detailed mapping on Pigeon Point, Cook county, Minnesota, discloses petrologic and structural complexities heretofore not reported. The sill on Pigeon Point ranges in composition from a tholeiltic olivine gabbro to ilmenite gabbro, to quartz gabbro, and to potassium feldspar-bearing gabbro. The red granitoid rock above the sill is intrusive in the upper parts of the gabbro, but the origin of these red rocks by differentiation of the gabbro or fusion of the Rove sedimentary rocks is not clear. Analyses of coexisting phases in the gabbrô indicate iron— enrichment during the differentiation history of the sill. Analysis of phases also sets limits on petrogenetic relations to the Logan Intrusive Rocks, and to the Pigeon River Intru— sions of Geul. The Pigeon River Intrusions appear to have a simple direct relation; however the Logan Intrusive Rocks of Geul cannot be directly related by simple fractional crystallization to the sill on Pigeon Point. Since emplacement and cooling of the sill, faulting and fracturing on northwest and east-west trends has occurred. The northwest faulting is marked by barite—calcite veins, and the east—west direction by late olivine diabase dikes. �Paper 16 Lower Precambrian metavolcanic—metasedimentary seguence, Rainy River, northernmost Minnesota Richard W. Ojakangas University of Minnesota, Duluth ABSTRACT A thick metavolcanic—metasedimentary sequence is exposed in northernmost Minnesota, south of the Rainy River and about midway between International Falls and Baudette. The previously undescribed volcanic rocks range In composition from basalt to rhyodacite. Intermediate—felsic tuffs and agglomerates and dacitic flows and hypabyssal intrusions apparently are the dominant rock types. These rocks are intermittently exposed along the edges of two younger 200—400 ft wide diorite—gabbro dikes that trend nearly perpendicular to the northeasternly regional strike of the steeply dipping country rocks. Stratigraphic top determinations are limited to a few pillowed metabasalts. However, the scanty data indicate that the sequence may be as much as 25,000 feet thick. Massive suif ides are present in prospect pits and in drill holes in the western part of the area. References: Fletcher, G. L., and Irvin, T. N., 1955, Geology of the Emo Area: 63rd Annual Report, Ontario Department of Mines, part 5, 36 p. Ontario Department of Nines, 1967, Kenora—Fort Frances Sheet, Geological Compilation Series, Map 2115. �Paper 17 THE EASTERN TERMINUS OF THE LAKE SUPERIOR SYNCLINE ERDOGAN ORAY W. S. HINZE N. W. O'HARA Michigan Purdue University West Lafayette, Indiana Naval Weapons Center China Lake, California State Univ. East Lansing, Michigan ABSTRACT A regional gravity Investigation of the eastern portion of the Northern Peninsula of Michigan was conducted and combined with previously observed gravity stations in the Southern Peninsula of.Michigan, Beaver Island, northern Lake Huron, northern Lake Michigan and the Sault Ste. Marie area of Canada to investigate the eastern terminus of the Lake Superior syncline. The Bouguer gravity anomaly map of the eastern portion of the Northern Peninsula shows three major positive gravity anomalies. One of these anomalies trends southeast from Grand Island in Lake Superior and can traced orthwestby magnetics to the Middle Keweenawan volcanics of This anomaly represents the margin of the western limb of the Lake Superior syncline. Another positive anomaly trends south from Whitefish Point on the south shore of Lake Superior be the Keweenaw Peninsula. and is interpreted as a horst of basalts which can be traced magnetically to the Middle Keweenawan volcanics outcropping on Mamainse Point, Ontario. The eastern limb of the syncline near the eastern edge of the Northern Peninsula is also defined by a positive gravity anomaly. These three positive gravity anomalies which are associated with positive magnetic anomalies merge in the vicinity of Beaver Island in Lake Michigan and mark the termination of the Lake Superior syncline. South of Beaver Island, the Keweenawan basalts continue in a south—trending narrow belt and are expressed by the "Mid—Michigan gravity high". The Bouguer anomaly map indicates two local gravity minimums in the Whitefish Bay area on the south shore of Lake Superior. These are interpreted to result from a thick accumulation of Upper Keweenawan clastic sediments. The results of two dimensional model studies suggest that the Lake Superior syncline in the eastern portion of the Northern Peninsula consists of up to 12,000 feet of basaltic flows overlain by Upper Keweenawan clastic rocks. Two geological models can be fitted to the observed anomalies of the northern tip of the Southern Peninsula of Michigan. The basalts either extend throughout the northern tip of the Southern Peninsula where they are highly faulted into a series of horsts and grabens or they are confined to the Grand Traverse Bay area in which case pre—Keweenawan extrusives and intrusives make up the basement of the northern tip of the Southern Peninsula. �Paper 18 MAGNETIC REVERSALS AND POLAR SHIFTS AS MARKERS IN A PROTEROZOIC TIME SCALE W. A. ROBERTSON Geomagnetic Laboratory Earth Physics Branch Department of Energy, Mines and Resources Ottawa, Canada A B STRACT The construction of a useful Precambrian time-scale Fossils are scarce. Sedimentary basins are widely separated, and deposition rates may have been different from today. Small errors in radiogenic age determinations represent many millions of years. Geologists should consider the help that is presents great difficulties. becoming available from paleomagnetic sources when attempting to divide Precambrian time into useful time units. Difficulties using paleomagnetic methods of dating so far back in time are no greater than those of other methods, and have one unique advantage. The pattern of reversals of the earth's magnetic field is world-wide; it is not diachronous, and any identifiable marker horizon occurs at the same point in time wherever it is found. This is not true of polar-wandering curves, however, which apply only to their own continent. The figure shows a hypothetical reversal pattern for the earth's magnetic field, with time as abacissa. Above and below it are hypothetical movement rates, on the same time scale, of two continents, EG and AS. It is hypothetical for the Proterozoic due to lack of data, but is based on patterns emerging from Phanerozoic time. M intervals are ones of mixed polarity, whereas N and R. are of wholly normal and reversed polarity respectively. Reversal nodes marked X, between wholly normal and wholly reversed polarity intervals provide unambiguous, universal marker horizons. G nodes, where one double polarity inversion took place, give good marker horizons but may be hard to find in rock sequences. The F nodes also yield marker horizons, but may be harder to identify precisely. �Paper 18 -2— At the first and third polarity node the continents are shown as accelerating sympathetically at the time of change of reversal frequency. Further back in time they are shown as independent of each other, and more indern.dent of the polarity rhythm. Whether there are links between motions at the earth's surface and reactions at the core-mantle boundary is still an unsolved problem. In any case, the location of a pole position on the polar wandering curve of the same continent will be a measure of its age. The accuracy will be highest for rocks formed at times of rapid polar movement: conversely if a conti- nent is static relative to the pole for a long interval pole positions will not differentiate ages of rocks formed in that interval Working out the polarity scheme for a Precambrian period is a very big task. Unconformities will leave gaps that have to be filled in from elsewhere. Nevertheless a pattern is : beginning to emerge in the Hadrynian and Helikian (880-1640 m. Y.) of the Canadian Shield, although large gaps remain to be filled. An older normal interval ( 1400 m.y.) appears to be followed by a mixed interval. Then a second normal interval is succeeded by a reversed interval about 1100 m.y. ago (a potential X node). A possibly longer normal interval then appears to be followed by one of mixed polarity. It is still too early to use paleomagnetic nodes as boundaries to help form a Proterozoic time-scale, but new polar wandering and reversal pattern data are accumulating fast, and we would be wise to consider the possibility of using them to help to split the Precambrian into time strati graphic units of wide application. �Ic' 1¼. rr, WORLD -WIDE POLARITY fl C C; 4 S tt. —4 C) fl hi N 1,, z -x *3 �Paper 18 'vv'ORLJ) —WIDE C.Di /tr POLAR IT z rr —4 C) t-j N C' �Paper 18 -2SELECTED REFERENCES Cox, Allan, 1968, Lengths of geomagnetic polarity intervals. J. Geoph. Res. V. 73, p. 3247-60 Cox, A., Doell, R. R., and Dairymple, G. B. 1964, Reversals of the earth's magnetic field, science, V. 144, p. 1537-43. Gough, 0. I., Ondyke, N.D., and McElhinny, M. W., 1964, The significance of paleomagnetic results from Africa. J. Geoph. Res. V. 69, p. 2509-2519. Heirtzler, J. R., Dickson, G. 0., Herron, E.M., Pitman III, W. C., and Le Pichon, X., 1968, Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents, J. Geoph. Res. V. 73, p. 2119-36. Irving, E., and Robertson, W. A., 1969, Test for polar wandering and some possible implications. Res. V. 74, p. 1026-36 J. Geoph. McElhinny, M. W., 1971, Geomagnetic reversals during the Phanerozoic. Science, V. 172, p. 157-9. Minkovitch, D., Opdyke, N.D., Heezen, B. C., and Foster, J. H., 1966, Paleomagnetic stratigraphy, rates of deposition and tephrachronology in North Pacific deep-sea sediments. Earth and plan. Sci. 1st. V. 1, p. 476-92. Robertson, W. A., and Fahrig, W. F. 1971, The Green Logan Paleomagnetic Loop -- the polar wandering path from Canadian Shield rocks during the Neohelikian Era. Can. J. Earth Sci. V. 8, p. 1355-72. Vine, F. J.., 1968, Magnetic anomalies associated with Mid-Ocean Ridges. The History of the Earth's Crust. Ed. R. A. Phinney, p. 73-89. �Paper 19 ARCHAEAN SALIC VOLCANIC ROCKS AT KAKAGI LAKE, NW ONTARIO - THEIR PHYSICAL AND CHEMICAL NATURE by D.R. Smithl R. H. McNutt P. M. Clifford? ABSTRACT At Kakagi Lake, and Archaean (older than ca. 2500 my) supracrustal assemblage has, for its upper portion, salic volcanic rocks, approximately two thousand metres thick. These rocks are somewhat unusual , being almost devoid of outcrop-scale layering in rhyodacitic and andesitic scoriaceous breccias and having limited or crude layering in crystal tuffs. Within the fragmental rocks, there is only poor sorting of size fractions. Moreover, in any given outcrop, the accessory fragments which make up the bulk of the framework are monolithologic. Analysis of variation of maximum fragment size, and framework - matrix ratios reveal a "cryptic° macroscopic layering, not visible in individual outcrops. In addition, there are two, possibly three, areas having both large values of maximum fragment size, and a high framework matrix ratio. These areas are interpreted as projections of emission centres into the present day outcrop plane. Chemical analyses of 23 pairs of fragments and adjacent matrix show that, in general, the fragments are the richer in Si02 and perhaps Na20, with matrix the richer in total Fe and MgO. Discriminant function analysis of our data, using the four oxides mentioned, properly identifies fragments from the matrix in 80% of the samples. These pyroclastic rocks have rather strong caic-alkaline affinities, and tend to be normal or low in K)O. Normatively, matrix is: 33% basaltic, 48% andesiti, 19% dacitic; fragments are: 29% basaltic,29% andesitic, 42% dacitic. These chemical differences are echoed in thin sections. Fragments commonly have polycrystalline quartz aggregates and felspar phenocryst in a felsic background: matrix is markedly chloritic. Alteration is ubiquitous. There are no discernible chemical trends along "strike or upwards through the volcanic pile. This reinforces the evidence from physical properties-considerable thickness, lack of layering, poor sorting, monolithologic fragment 1. Texaco, Calgary, Alberta. 2. Department of Geology, McMaster University, Hamilton, Ontario. �Paper 19 —2- character locally - which indicate a pyroclastic flow origin for these rocks. Presence of a fabric possibly pseudomorphic after shard structure is further support for this interpretation. �Paper 20 Three-phase deformation associated with the Penokean orogeny, east Gogebic Range, Michigan-' by Virgil A. Trent U.S. Geological Survey, Washington, D.C. Abstract Three phases of deformation in the east Gogebic area resulted in tight folding of Precambrian X (Marquette Range Supergroup) strata followed by folding and block tilting of the Precambrian Y (lower Keweenawan) and Precambrian X (Animikie) phase of orogeny. sections during the last The deformationa]. periods are marked by coeval volcanism and by three angular unconforniities. Although the deformations may be widely spaced in time, lithology and structural morphologlj suggest that they are separate phases of a single orogenic episode. Near the east end of the Gogebic Range, Precambrian X (Marquette Range Supergroup) strata lie between tilted metamorphosed Precambrian Z volcanic rocks (lower Keweenawan) to the north and strongly meta- morphosed Precambrian W or X gneiss complex, Algoman Granite of Lawson (l9lL), and volcanic rocks (Keewatin) to the south. Three defoniiational phases can be identified in Precambrian X rocks of the eastern Gogebic Range: -'Work done in cooperation with the Geological Survey Division of the Michigan Department of Natural Resources. 1 �Paper 20 i) The earliest was folding of the Sunday Lake Quartzite, Bad River Dolomite, Palms Formation, and Ironwood Iron- Formation. Mafic lava flows intercalated with the Ironwood Iron-Formation indicate that extrusive volcanic activity preceded folding. The large Wolf Mountain anticline began to form, followed by erosion and Copps Group of Allen and unconformable Barrett (191S) and deposition of the the Tyler Formation. 2) The strongest deformational phase, the Penokean orogeny, as defined by Goldich and others (1961, p. 120-122, i6-i6o), took place at the end of Precambrian X ("Animikie") The this time. Wolf Mountain anticline was more tightly folded during event. Mafic sills, also intercalated with the Ironwood Iron-Formation were intruded syntectonicafly. The northernmost thick sill truncated by the pre-Keweenawan unconformity (Prinz, 1967), appears to be genetically related to flow breccia cropping out along its eastern margin. Erosion of these volcanic rocks, parts of the Tyler and Copps, and older rocks preceded the unconformable deposition of the oldest Keweenawan strata. 3) Post-lower Keweenawan deformation, upon which Blackwelder 638) based his original definition of the Penokean orogeny, warped and the whole Precambrian succession (191)4, p. tilted except for the Jacobsville Sandstone. folding seems to mimic major Penokean The last phase of trends of the preceding folding, especially in the area close to Lake Gogebici. Torsional basement movements related to block tilting probably contributed to the assymetry of the Wolf Mountain anticljrie. 2 �Paper 20 A large Wolf Mountain in the area. flat-lying niass of (T. 147 N., R. 1414 eflipsoidal basalt north of w.) may be the youngest volcanic rock It lies athwart the Precambrian X (.Animikie) structural trend and has not been blocktilted. The youngest major fracture in the area passes nearby, and to the southwest the fracture is filled by a thick mafic dike which I interpret to be the feeder. Two miles to the northeast, this fracture truncates the lower Keweenawan ridge. This field evidence suggests that these ellipsoidal lavas were extruded in post-early Keweenawari time and were perhaps associated with the terminal phase of folding. 3 �Paper 20 References cited Allen, R.C., and Barrett, L.P., l9l, A revision of the sequence and structure of the pre-Keweenawan formations of the eastern iron range of Gogebic (Geol. Michigan: Michigan Geol. Survey Pub. 18 Ser. l), p. 33-61; in part, Jour. Geology, v. 23, p. 689—703. Blackwelder, geologic Eliot, l91L, A summary of the orogenic epochs in the history of North America: Jour. Geology v. 22, no. 7, p. 633-65)4. Goldich, Samuel S., Nier, John H., and Krueger, Alfred 0., Baadsgaard, Halfdan, Harold W., Hoffman, 1961, The Precambrian geology and geochronology of Minnesota: Minnesota Geol. Survey Bull. 141, 193 p. Lawson, A.C., 191)4, A standard scale for the pre-Cambrian rocks of North America: Internat. Geol. Cong., 12th, Canada, 1913, Comptes rendus, p. 31i.9-370. Prinz, W.C., 1967, Pre-Quaternary geologic and magnetic map and sectioriLs of part of the eastern Gogebic iron range, Michigan: U.S. Geol. Survey Misc. Geol. mv. Map 1-1497. 14 �Paper 21 BEDROCK MORPHOLOGY IN THE VICINITY OF PORTAGE LAKE, KEAW PINSULA, MICHIGAN E. J. WARREN Department of Geology and Geological Engineering Michigan Technological University ABSTRACT Portage Lake stretches across the Keweenaw Peninsula of Michigan between Keweenaw Bay and Lake Superior. This circumstance was put to good use by the Indians and later by French voyaguers and Jesuits who used the long sinuous lake as a shortcut in their travels along the south shore of Lake Superior. Modern shipping uses the same shortcut, now known as the Keweenaw Waterway. Portage Lake has a maximum depth of about 50 feet located On the other hand, Torch in the main body of the lake. Lake, which is connected to Portage Lake by Torch Bay and a dredged ship channel, was once 170 feet deep before it was partially filled by mill tailings from various copper recovery operations. Several geologists have speculated about the origin of these unusual lakes (Martin, 1911; Scott, 1921; Hughes, 1963). However, they were handicapped by their lack of knowledge of the bedrock morphology around and under the lakes. The bedrock morphology was determined from water well and diamond drill logs and by geophysical methods. Seismic refraction profiles were run on land and on the mill tailings in Torch Lake. On the lakes, sparker and air-gun surveys were performed. Unfortunately the sparker survey lacked penetration and the air-gun profiles were rendered nearly useless by excessive reverberation. Gravity profiles were then run over Portage Lake, on ice, in an attempt to extrapolate the land based information. Interpretation of the gravity surveys, now being performed, is hampered by the large regional gravity gradient due to the Keweenaw fault (Bacon, 1966). Preliminary results indicate that both Portage and Torch Lakes lie in a complicated network of buried bedrock valleys. A water well next to the narrow northwest arm of Portage Lake reaches a depth about 380 feet below lake level and a diamond drill hole east of Hancock Michigan reaches bedrock about 280 feet below lake level. Of course, there is no assurance that either of those wells have reached the deepest part of the bedrock valley. �Paper 21 Torch Lake lies in a bedrock valley with a floor 250 feet This valley underlies the pre-. below present lake level. sent Traprock River valley to the north and continues south of Torch Lake into Portage Lake under Torch Bay. The bedrock valley under Torch Lake is also connected to Portage Lake by a bedrock valley 200 feet below lake level which parallels the Keweenaw fault and passes under the town of Dollar :ay. bedrock valley about 150 feet below lake level extends from the southeast part of the main body of Portage Lake out through Portage Fh-itry, curving to the east of the present channel. The deepest bedrock valley, however, extends south of the main body of Portage Lake under the present Sturgeon River valley where a depth L50 feet below present Lake Superior level was found. The southern extension of this deep It is interesting valley still remains to be explored. that this valley has bedrock depths on the same order as the depth of Keweenaw Bay. A bedrock valley 200 feet below lake level branches off the west side of the Sturgeon valley and passes under Otter Lake. It is probable that these buried bedrock valleys were originally a product of stream erosion. It is possible that some glacial overdeepening has taken place also, but this cannot be detexmiined until all the data is compiled and a contour map of bedrock elevations is completed. At any rate, it is apparent that the base level for stream erosion was once considerably lower than the present Lake Superior level. This discovery may have some bearing on the controversy about whether Lake Superior is mainly a result of subaerial erosion, of glacial scour, or of some combination of the two. References Bacon, L. 0., 1966, Geologic Structure East and South of the Keweenaw Fault on the Basis of Geophysical Evidence: The Earth Beneath the Continents, A.G.U. Mon. 10, pt2—55. Hughes, J. D., 1963, Physiography of a Six Quadrangle Area In the Keweenaw Peninsula North of Portage Lake: Unpublished Ph.D. Dissertation, Northwestern Univ., Evanston, Ill., 228 pp. Martin, L., 1911, Physical Geography of the Lake Superior Region: Chapt. IV in U.S.G.S. Mon. LII, The Geology of the Lake Superior Region, p85-l17. Scott, I. D., 1921, Inland Lakes of Miohigan: Mich. Geol. and Biol. Survey, Lansing, Mich., 383 pp. �,, 4/ / / I / / I F I / / ,, 6, LAKE SUPERIOR -¼ SCALE :250000 OF MICHIGAN THE KEWEENAW PENINSULA �Paper 22 GLACIAL DRIFT ON THE MESABI IRON RANGE, MINNESOTA ITS CHARACTERISTICS, ORIGIN, AND HYDROLOGIC SIGNIFICANCE'! THOMAS G. WINTER U. S. Geological Survey ABSTRACT Glacial deposits in the Mesabi Iron Range area consist ments. The basal till occurs in only a small number of mines, but they are scattered across the entire Iron Range. The is dark gray to dark greenish gray and brownish gray, sandy, silty, and is calcardous. The middle till unit, a of three major till units and associated glaciofluvial sedi- till bouldery till, is the thickest and most widespread of the three tills. It is grey, yellow, red, orange or brown, sandy, silty, contains abundant cobbles and boulders, and is non-calcareous. The till was depsoited by the Rainy lobe, which has a minimum age of 14,000 to 16,000 years before present. The surficial till was deposited contemporaneously by two minor sublobes of the same ice lobe about 12,000 years ago. The brown silty till occurs in the western and north-central part of the area. It is light to medium brown, sandy, silty, and calcareous. Red clayey till the south-central part of the area is red to reddish brown, clayey, silty, and calcareous. Stratified fluvial sediments occur within the glacial drift at many places in the Mesabi Iron Range area. These sediments, which are important aquifers, occur extensively between the three main till units. The thickest and most extensive aquifer consists of glaciofluvial sediments that lie between the surficial till and the bouldery till. The thickness of the glaciofluvial sediments is greater than 50 feet in much of the area, and the transmissivity is greater than 100,000 gallons per day per foot at a number of localities. Glaciofluvial sediments underlying the bouldery till occur largely in the western half of the area. These sediments are generally less than 50 feet thick and their transmissivity is generally less than 50,000 gallons per day per foot. Surficial glaciofluvial sediments are a source of ground water for high yield wells only in the eastern part of the area in the general vicinity of the Biwabik bedrock valley. Thickness of these sediments is greater than 100 feet in some places, but their transmissivity is generally less than 50,000 gallons per day per foot. �Paper 22 -2- The glacial drift aquifers can yield as much as 40 mgd (million gallons per day). Assuming that the ratio of area underlain by aquifer to total area is constant for the study area (about 20 percent where mapped in detail), it is concluded that as much as 80 million gallons per day could be developed from glacial drift aquifers without causing excessive water declines and depleting streamfiow. Publication authorized by the Director, U.S. Geological Survey �Paper 23 CHRONOLOGY OF PRECAMBRIAN ROCKS OF IRON AND DICKINSON COUNTIES, MICHIGAN PART II P. 0. Banks Department of GeologyCase Western Reserve University, Cleveland, Ohio 44106 and W. R. Van Schmus Department of Geology University of Kansas, Lawrence, Kansas 66044 Ertensive K-Ar, Rb-Sr, and U-Pb data available for the Precambrian rocks of Iron and Dickinson Counties, Michigan, permit considerable clarification of the chronologic development of this area. The following ares are considered well established (rounded to nearest 25 m.y.): Peavy complex 1900 m.y., Hemlock volcanics 1950 m.y., and Porphyritic Red Granite 2100 m.y. A U—Pb concordia intercept ago of 2575 ni.y. for the Norway Lake gneiss is considered minimal for this unit because of probable multiple secondary events. The pre—Animikie post—Dickinson Granite Bluffs gneiss gives an apnarent Rb—Sr whole rock age of Ca. 2700 m.y. whereas its apparent zircon U—Pb concordia intercept age is ca, 2100 m.y. This anomaly can be explained either by urusual migration of radiogenic Sr or by multi-stage Pb loss. Additional mineral analyses are in progress to resolve the issue. Our previous conclusion (Banks and Van Schmus, ILSG 1971) remains unchanged that the Animikie Series of James et al. is bracketed between 1900 and 2100 m.y. and therefore is not correlatable with the original Huronian of Ontario. Resolving the ae of the Granite Bluffs gneiss will determine whether the Dickinson Group Is or is not a candidate for correlation with the original Huronian. Additirnal data of interest include a Pb/Pb age of 2900 m.y. for detrital zircon from the East Branch arkose, and a suggestion from K—Ar h.ornblende and U-Pb apatite and sphene data that the last major metamorphism in the area occurred 1500—1600 m.y. ago. �Paper 24 PENOKEAN TECTONICS IN NORTifERN MICHIGAN by W. F. CANNON U. S. Geological Survey Washington, 2O242 D.C. ABS TRA CT The major Penokean deformation in northern Michigan occurred between 1.9 and 2.0 b.y. ago. Lower and. middle Precambrian rocks were deformed independently of, and mostly before, regional metamorphism; the deformation took place at low temperatures. The subsequent metamorphism was a low-pressure type in which andalusite was stable over a wide temperature range. The maximum confining pressure is set by the aluminosilicate triple point at about 5 kilobars (about 13 miles burial depth), but the true pressure may have been much less. Structural interpretations must be consonant with mechanisnis of rock deformation possible at low temperatures and low to moderate confining pressures. Lower Precambrian granitic rocks form the basement for the Marquette Range Supergroup in much of northern Michigan. granitic Experimental rock deformation indicates that rocks have very high strength and very low ductility under probable conditions of Penokean deformation, and kinematic interpretations of Penokean deformation must consider the probability of a strong nond.uctile basement; interpretations requiring a weak ductile basement are difficult to reconcile with the probable physical environment of deformation. The first-order regional structures in northern Michigan are uplifts of lower Precambrian rocks with middle Precambrian rocks of the Marquette Range Supergroup in intervening synclinorial basins. A wide divergence of trends for these structures suggests vertical tectonism rather than regional horizontal compression. The lower Precambrian cores of many uplifts are cut by diabase dikes. These dikes are older than the Penokean orogeny, and many are probably associated with mafic intrusive and extrusive rocks in the middle Precambrian section, yet these dikes were not externally deformed during Penokean folding; they remain planar and. largely massive. These relationships substantiate inferences from experimental rock deformation of a strong nonductile basement and strongly suggest that the lower Precambrian rocks remained rigid and were not penetratively deformed d.uring Penokean deformation. The uplifts are interpreted, as fault- bounded blocks of lower Precambrian rocks which were uplifted V The Gogebic Range is excluded from this discussion because of cnp1ications introduced by younger deformation. �Paper 24 along steep faults, many of which are steep reverse faults. The blocks may have moved either as single units or, more likely, with internal adjustments occurring along relatively narrow shear zones and parallel to dike margins. During this phase of deformation, middle Precambrian rocks were passively draped over the fault blocks, forming the presently preserved synclinal structures which occupy the relatively dow'nfaulted segments of the basament. Second-order and, smaller folds in middle Precambrian rocks indicate that these rocks have undergone substantial horizontal shortening, whereas the underlying lower Precambrian rocks have not. Furthermore, the trends of second-order and smaller folds are mostly in west and west-northwest directions and are much more uniform than trends of first-order structures (block uplifts). In some areas, second-order folds cross the trends of first-order structures at high angles. Many of these smaller folds seam to have formed independently of first-order structures, and their genetry requires a thin-skinned compressive deformation which has affected. only the middle Precambrian rocks and not the lower Precambrian basament. Many of these folds may be due to gravity sliding or spreading which, because of relatively uniform fold trends, appears to have occurred in response to a region-wide gradient. This phase of deformation must have occurred before block faulting produced sithstantial structural relief on the contact of lower and middle Precambrian rocks. The suggested sequence of events is: 1) Regional gravity sliding which produced folds in middle Precambrian rocks with west and west-northwest trends but did not deform the lower Precambrian basament rocks. This event was probably associated with early uplift of the depositional basin. 2) Uplift of fault-bounded basament blocks with widely divergent trends, accompanied by passive draping of middle Precambrian rocks and earlier gravity folds into basins or tight synclines between the uplifts. A second set of folds formed in middle Precambrian rocks in areas marginal to the uplifts. �Paper 25 THE PENOKEAN OROGEM S. S. Goldich Northern Illinois University DeKalb, Illinois 60115 ABSTRACT The Penokean orogeny (Blackwe1der, 1914) was redefined by Goldich arid others (1961) as Middle to Late Precambrian event that involved the Anuinikie Group of Minnesota and Ontario and similar rocks that were formerly assigned to the Huronian in Wisconsin and Michigan. Time limits from 1600 to 1800 ni.y. were set for the orogeny; however, Peterman (1966) showed that the metasedimentary rocks of the Cuyiina district were folded 1850 n.y. ago. New data for the Thomson Formation of east-central Minnesota give a minimum age of the folding and metamorphism of 1900 n.y. ago (Stuckless and Goldich, 1972). Thus, the Penokean orogeny is a Middle Precambrian event, using 1800 m.y. as the time boi.]ndary between the Middle and Late Precambrian (Goldich, 1968). Limiting ages have been placed on the type Huronian rocks by dating of the Nipissing Diabase in the Blind River—Bruce Mine area (Van Schmus, 1965) and of the Nipissing Diabase and Gowganda Formation at Gowganda (Fairbairn and others, 1969). The type Huronian rocks are at least as old as 2280 n.y. (Gow— ganda Formation) and were folded at least 2160 m.y. ago (Nipissing Diabase). Fryer (l97l has reported ages of 1800, 1870, and 1790 m.y. for volcanic and metasedimentary rocks from the Belcher Fold Belt, the Labrador Trough, and the Mistassini Lake area. Rb—Sr ages, however, must be used with caution. They do not necessarily date the time of deposition or of a specific metamorphic event. In Minnesota, for example, isochron ages on Aniniikian rocks range from 1900 to 1660 n.y., but all were probably deposited at essentially the same time. Considerable radiometric dating of Middle Precambrian rocks is now in progress. Until the new data from a number of laboratories are published and can be assessed, it is premature to correlate the rocks of widely separated areas of North America. References For references prior to 1969 see Goldich (1968). Fairbairn, H. W., P. M. Hurley, K. D. Card, and C. J. Knight (1969) Correlation of radionietric ages of Nipissing Diabase and Huronian metasedinients with Proterzoic orogenic events in Ontario: Canadian Jour. Earth Sci., v. 6, p. 489—497. Fryer, B. J. (1971) Rb—Sr whole—rock ages of Proterozoic strata bordering the eastern part of the Superior Province, Canada (abs.): Geol. Soc. America Abstracts with Program, v. 3, p. 574—575. Goldich, S. S. (1968) Geochronology in the Lake Superior region: Jour. Earth Sci., v. 5, p. 715—724. Canadian Stuckless, J. S. and S. S. Goldich (1972) Ages of some Precambrian rocks in east-central Minnesota: 18th Annual Institute on Lake Superior Geology, Houghton, Michigan. �Paper 26 RELATION OF PENOKEAN POLYPI-IASE DEFORMATION TO REGIONAL METAMORPHISM IN TI-fE WESTERN MARQUETTE RANGE, NORTHERN MICHIGAN John S. Kiasner Michigan Technological University Houghton, Michigan ABSTRACT Recent work at Lake Michigamme at the western end of the Marquette Trough suggests that some metamorphic minerals began to form during the early stages of Penokean deformation contrary to previous studies (Powell 1970) that suggest that regional metamorphism almost completely postdates deformation. The new studies indicate that metamorphism peaked late in the deforrna.tional sequence as shown on figure 1. F F1 F2 F Deformational events Andalusite Garnet S t.au ro lit e Actinolite Grunerite Biotite Sericite Thermal metamorphism ically shown Chlorite Fabric elements Time Figure 1, Kinematic relationship of metamorphism to deforrnationQ The deformational sequence, characterized by four phases, started with regional soft sediment deformation (F that produced a penetrative N 75° W trending foliation, th8 early stages of which can be identified as slaty cleavage (S ). Selective migration of silica (Williams 1972) during continued deformation (F1) along the early formed slaty cleavage enhanced this cleavage an formed the numerous quartz veins. The F -F1 deformational couplet produced the regional S foliation. ° ) �Paper 26 Crenulation folding (F2) of S1 foliation resulted in the formation of S2 fracture cleavage and formation of lineations (L2) due to the intersection of S1 and S2. The L2 lineations are flat lying because the strike of S2 and S1 are nearly parallel. Kink—banding (S) that affects S0, Si, 2 and L2 characterizes the last eformationai event in the area. Regional thermal metamorphism accompanied the sequence of deformation. The growth of pre-F1 andalusite porphyroblasts (figure 1) indicates that metamorphism started early in the deforinational sequence. It probably peaked between F2 and deformation as indicated by the growth of post-, pre-F2 staurolite porphyroblasts and post-F2 brown biotite and grunerite. Abundant retrograde metamorphism is shown by andalusite and staurolite porphyroblasts that have been replaced by sericite, and by garnet porphyroblasts that have been replaced by chlorite. References James, H. L., 1955, Zones of Regional Metamorphism in the Precambrian of Northern iviichigan, Bull. Geol. Soc. Am., v. 66, p. 1Li55_1483. Powell, C. McA., 1970, Relict Diagenetic Textures and Structures in Regional lVletarnorphic Rocks, Northern Michigan, North- western University Report 20, N.A.S.A. Geol. Test Site No. 126, 35 p. Williams, P. F., 1972, Development of Metamorphic Layering and Cleavage in Low Grade Metamorphic Rocks at Bermagui, Australia, Am. Jr. Sci., v. 272, p. 1—7. �Paper 27 LINEAMENTS AND MYLONITE ZONES IN THE PRECAMBRIAN OF NORTHERN WISCONSIN Gene L. LaBerge Wisconsin Geological and Natural History Survey and University of Wisconsin-Oshkosh ABSTRACT Recent geological mapping in Marathon County by the Wisconsin Geological and Natural History Survey has shown that a number of major zones of shearing cross central Wisconsin. At least 3 directions of major shearing have been recognized: N300_350E, N60°E, and N800E. The N300_350E trend is best developed in the area mapped, but reconnaissance indicates that other directions are impor- tant in other parts of the county. The major shear zones are represented by zones of mylonite and variously sheared rocks up to a mile wide. Because a number of different rock types, ranging in composition from granite to greenstone, have been granulated, mixed, and recrystallized to varying degrees to form the mylonite, the zones are lithologically variable both along and across the strike. However, they are structurally rather uniform, displaying a lensoidal structure on all scales from map scale to thin section. Indeed they seem to be composed of a myriad of overlapping lenses which show different degrees of flattening. Excellent examples of the progressive shearing of a granitic rock to produce a mylonite were observed along several of the shear zones. The best example of a mylonite zone mapped is that along the Eau Claire River in northeastern Marathon County. It has been mapped for a distance of approximately 20 miles, and almost certainly continues an additional 15 miles across the county. Furthermore, it is on a topographic lineament which can be traced across Wisconsin for at least 120 miles. At least 4 other major N300_35oE shear zones cross Marathon County, and some of these also occur on topographic lineaments 100 miles or more long. Numerous stream valleys and other topographic lineaments in northern Wisconsin are oriented approximately N30°E, and these may also represent shear zones. Significantly, the N600E and N80°E directions of shearing are also common trends of topographic lineaments. �Page 27 -2- The origin of these major shear zones is not yet certain; however, the lithologic associations in the area mapped coupled with the major shearing suggest that northern Wisconsin be part of a Precambrian subduction zone. Whatever the explanation of the shear zone, it is evident that they represent a major feature in the Precambrian of the Lake Superior region which has not previously been recognized. �—' • ,1 N ) '\ /-1e N 11 Jv 'F ' r$tt cerJf } i/f woo Fe L'.n /' • I 1r - T1 5 I. L. i11tth1r\ I - / S ibar,) -I 1! I s1o -::; ---(U 'Y t / ZL -I Po (TI ___ I 99 I I L4 Witt41 0)__fl ,NorthJ Lp (r7 aieik / _ f/ : _I LINEAMENTS AND'S POSSIBLE SHEAR ZONES IN MARATHON COUNTY T. L / / U L.—Th&/-T/r /i 7 7--MariTi1a _c) r&rrU 4:;j 29 I :; ____ �Page 27 00 C LIMIT OF OLDER DRIFT —......—LIMIT OF YOUNGER DRIFT S10. LINEAMENTS AND POSSIBLE ShEAR ZONES IN NORTHERN WISCONSIN �Paper 28 STRATI GRAPHIC AND TECTONIC FRAMEWORK OF MIDDLE PRECAMBRIAN ROCKS IN MINNESOTA G. B. MOREY Minnesota Geological Survey St. Paul, Minnesota ABSTRACT Sedimentary strata of Middle Precambrian age in Minnesota predominantly consist of argillite and graywacke with lesser amounts of iron—formation, quartzite, quartzose siltstone, limestone, and dolomite. These strata unconformably overlie folded metasedimentary and igneous rocks approximately 2,700 m.y. old; locally they also appear to unconformably overlie diabasic gabbro or diorite dikes that may be approximately 2,000 m.y. old (Hanson and Malhotra, 1971). Except for an older unnamed dolomite unit in east—central Minnesota, all the sedimentary rocks are assigned to the Animikie Group, a wedge-shaped body that thickens from less than 100 feet in the northern part of the State to at least 15,000 feet in areas 100 miles to the south. The Animikie Group comprises a single depositional event that began with well— sorted clastic detritus characteristic of a stable shelf —— Kakabeka, Pokegama, and Mahnomen Formations ——, passed through a phase of iron—formation deposition —— Gunflint, Biwabik, and Trommald Formations ——, and ended with deposition of fine sand and mud characteristic of a "deep" basin with poor circulation —— Rove, Virginia, Rabbit Lake, and Thomson Formations. Locally, the "deeper" water clastic rocks contain intercalated lava flows, thin to thick beds of pyroclastic material, and layers of carbonate— to sulfide—facies iron—formation. During or subsequent to the time of deposition, the sedimentary rocks in east—central Minnesota were folded —— perhaps more than once —— into numerous large antic lines and syndines that have many second-order folds on their limbs. The major folds are asymmetric, with steeply—dipping to locally overturned north limbs and more gently—dipping south limbs. Fold axes trend within 300 of east, and plunge from horizontal to 300 east. In addition, a part of the Thomson Formation was regionally metamorphosed to at least the lower range (staurolite and garnet) of metamorphic grade in the amphibolite facies; however, definable metamorphic isograds are not everywhere parallel to recognizable structural trends, suggesting that deformation and metamorphism were independent variables in the orogenic scheme for this region. The time of folding is unknown, but the metamorphism on the Cuyuna range has been dated at 1,850 m.y. ago (Peterman, 1966). The Animikie strata in northern Minnesota also were deformed about northeast-trending axes, although the degree of deformation and the metamorphic grade is less pronounced. In addition, these rocks appear to have been subsequently folded about north-northwest—trending axes. Available isotopic data cluster around an age of 1,650 m.y. and these data may reflect a period of mild deformation and metamorphism at that time. A variety of igneous rocks also were intruded into the sedimentary pile in east—central Minnesota. Several discrete events can be recognized, which together with the deformation and metamorphism comprise the Penokean Orogeny. These include (Woyski, 1949; Goldich and others, 1961): (1) pre—tectonic emplacement of small mafic intrusions; (2) syntectonic emplacement (1.78 — 1.63 b.y.) of intermediate—size intrusions of tonalitic to granodioritic composition -- the quartz monzonites at Warman, Isle, and Pierz, the tonalites near Hillman and Freedhem, and the gray granodorite at St. Cloud; and (3) late-tectonic to post—tectonic emplacement (1.73 1 .68 b.y.) of Woyski's "Stearns Magma Series" consisting of the augite—hornblende (red) granite at St. Cloud, the porphyritic quartz monzonte at Rockville, and other similar intermediate to silicic rocks. Lastly,rocks of the Stearns Magma Series are cut by basalt dikes which may have been emplaced during a single period, at least 1,570 m.y. ago (Hanson, 1968). — �Paper 29 GRANITIC PLUTONIC ROCKS OF THE SOUTHERN PROVINCE OF THE CANADIAN SHIELD James A. Robertson Division of Mines, Ontario Ministry of Natural Resources, Toronto *paper presented by permission of the Director, Geological Branch. AB STRACI In Ontario granitic rocks associated with the eastern portion of the Penokean fold belt comprise: (1) Archean basement; (2) early post-Huronian intrusives (= Penokean of Church, 1968), and (3) late post-Huronian intrusive ( Hudsonian of Church). Other authors eg. Stockwell (1964) have used Hudsonian and Penokean interchangeably and have not named the earlier orogenic event. The individual granitic bodies are named on Figure 1. Algoman = Archean (Robertson, 1960) granitic rocks may be divided into massive quartz monzonite and gneissic to migmatitic Bodies of quartz monzonite were formed during the terranes. Early workers placed these Kenoran orogeny circa 2,500 MY. Overprinting bodies with the "young" post-Huronian granites. of age dates becomes pronounced as the Penokean fold belt is approached (Van Schmus, 1965). 1) The Creighton and Murray Granites (Card, 1968; Ginn, 1958) They were intruded prior lie south of the Sudbury Irruptive. to the irruptive and local anomalous cutting relationships The reflect remobilisation of the granite (Hawley, 1962). granites pre-date the regional metamorphism and deformation. Gibbins et al (1971) have obtained 2,200 MY, which suggests that they are earlier than the Nipissing Diabase (2,155 MY Whether they are synchronous with the Van Schmus, 1965). earlier post-Huronian orogenic cycle or with early Huronian volcanism remains an open question (Card et al, 1972). 2) �—2— Paper29 3) The Cutler Batholith (Robertson, 1969; 1970a; Cannon, 1970) lies some eighty miles west of Sudbury and intrudes folded and metamorphosed Huronian sediments and Nipissing Diabase and is itself foliated. Age-dates (Wetherill et al, 1960; Van Schmus, 1965) indicate a minimum age of 1,750 MY with some thermal resetting at 1,350 MY. The Cutler granite is clearly synchronous with the Hudsonian orogeny. The granite is intrusive but may have been derived from Huronian rocks at depth and metasomatism may have been an important factor (Cannon, 1970). The Croker Island Complex (Card, 1965; Robertson, 1970) lies some twelve miles southeast of Cutler and comprises a circular complex of comagmatic mafic to granitic rocks accompanied by a marked magnetic anomaly. The complex postdates regional metamorphism and folding. Age-dates (Van Schmus, 1965) and paleomagnetism studies (Palmer, 1969) indicate 1,445 MY. The complex is clearly late Hudsonian. Similar magnetic anomalies under Manitoulin Island were drilled by Union Carbide. Core of granitic rock resembling that at Killarney was obtained and submitted to Van Schmus for dating. 4) Grenville Front Granites (Card et al, 1971; Frarey and Cannon, 1969; Hnderson, 1967; Quirke and Collins, 1930) are intrusive bodies in the Southern Province adjacent to the Grenville Front. To the northwest these bodies are intrusive but to the southeast they become strongly mylonitised passing into the deeper crustal granite-gneiss complex of the Grenville Province. The mylonite zone marks the Grenville Front. 5) 5a*) The Killarney batholith featured in the classical work of Quirke and Collins (1930) with a minimum age of 1,585 MY comprises porphyritic quartz monzonite. 5b*) The Lake Panache and Eden Lake Intrusives, (Card et al, 1971) range in composition from gabbro-granite with a minimum age of 1,430 M.Y. from mica. 5c*) The Chief Lake Batholith comprises quartz diorite to quartzonzonite marking the northeast continuation of the Killarney granite. Near Coniston, Phemister (in Grant et al, 1962) interpreted the rock as feldspathised sediment. Krogh (1971) indicates an initial age of 1,730 MY with some granites at 1,590 MY - 1,460 MY reflecting early movement on the Grenville Front. *Individual bodies not shown on Figure 1. �Paper 29 — — Conclusion The granitic rocks of the Ontario Sector at the Southern Province may be classified with respect to petrography, mineralogy, chemistry, isotopic composition and they can be fitted into the historical and structural scheme established by regional mapping (Robertson et al, 1969; Card et al, 1972). However, much detailed work on individual bodies remains to be done. References CannQn, W.F. (1970) Plutonic Evolution of the Cutler Area, Ontario; G.S.A., Vol. 81, p. 81-94. Card, K.D. (1965) The Croker Island Complex; No. 14. Bull. Ont. Dept. Mines, Geol. Circ. Card, K.D. (1968) Geology of Denison-Waters Area, District of Sudbury, Ont. Dept. Mines G.R. 60. Card, K.D., Palonen, P.R., and Siemiatkowska, K.M. (1971) Geology of the Louise-Eden Area, District of Sudbury; Ont. Dept. Mines and Northern Affairs, Open File Report 5065. Card, K.D. et al (1972) The Southern Province in Canada in Structural Styles in Canada, in press. Geol. Assoc. Can., Contribution to 24th mt. Cong. Montreal 1972. Church, W.R. (1968) The Penokean and Hudsonian orogenies in the Great Lakes region and the age of the Grenville Front, 14th Annual Ints. on Lake Superior Geology, p. 16-18. �Paper 29 —4— Frarey, M.J., and Cannon, R.T. (1969) Notes to accompany a map of the Geology of the Proterozoic Rocks of Lake Panache. Collins Inlet Map Areas, Ontario. Geol. Surv. Can. Paper 68-63 Gibbons, W.A., McNutt, R.H., and Adams, C.J.D. (1971) Rb-Sr Isotopic Studies of the Murray Granite, Geol. Assoc. Can. Abstracts, Sudbury 1971, p. 27-28. Ginn, RM. (1958) A Study of the Granitic Rocks in the Sudbury Area. Unpublished M0Sc. Thesis, Queen's University. Ginn, R.M. (1961) Geology of Porter Township, Ont. Dept. Mines, Geol. Rept0 No 5. Grant, J.A., Pearson, W.J., Phemister, T.C., and Thomson, J.E. (1962) Geology of Broder, Dill, Neelon and Dryden Townships District of Sudbury, Ont. Dept. Mines GR 9. Hawley, J.E. (1962) The Sudbury Ores: Their Mineralogy and Origin, Can. Mm. Vol. 7, part 1, 1962. Henderson, J.R. (1967) Structural and petrologic relations across the Grenville Province-Southern Province boundary, Sudbury, District of Ontario. Ph.D. Thesis, McMaster University, Ontario. Krogh, T.E. (1971) Isotopic ages along the Grenville Front in Ontario. Assoc. Can. abstracts Sudbury 1971. Geol. Palmer, H.C. (1969) The Paleomagnetism of the Croker Island Complex, Ontario, Canada; Can. Jour. Earth Sci., Vol. 6, p. 213-218. Quirke, T.T., and Collins, W.H. (1930) The Disappearance of the Huronian; Geol. Surv. Can. Mem. 160. Robertson, J.A. (1960) The General Geology of Part of the Blind River Area; Thesis, Queen's University, Kingston. Robertson, J.A. (1969) Geology of the Cutler Map-Area; File Rept. 5026. Robertson, J.A. (l970a) Geology of the Spragge Area; M.Sc. Ont. Dept. Mines, Open Ont. Dept. Mines, Geol. Rept. 76. �—5- Paper 29 Robertson, J.A. (1970) Geology of the Massey Area, Districts of Algoma and Sudbury; Ont. Dept. Mines Open File Rept. 5043. Robertson, J.A., Card, K.D., and Frarey, M.J. (1969) The Federal-Provincial Committee on Huronian Stratigraphy Progress Report; Ont. Dept. Mines, M.P. 31, 26p. Van Schmus, R. (1965) The Geochronology of the Blind River-Bruce Mines Area, Ontario Canada; Jour. Geol., Vol. 73, p. 755-780. Wetherill, G.W., Davis, G.L., and Tilton, G.R. (1960) Age Measurements on Minerals from the Cutler Batholith, Cutler, Ontario; Jour. Geophys. Research, Vol. 65, p. 2461-2466. Structure, metamorphism and Post-Huronian granitic intrusions of the eastern Southern Province. Fig. 1. �Paper 30 REGIONAL RELATIONSHIPS IN THE PENOKEAN PROVINCE H. B. STONEHOUSE Michigan State University ABSTRACT Investigations over the last few years in that area of the Southern Province of the North American Shield known as the Penokean Fold-Belt Subprovince, allow some of the following conclusions to be made:1. 2. Similar sequences of sediments deposited over a period of about 600 my (roughly 2.2 by to 1.6 by ago) are of predominently shallow water origin. Local tectonic activity occurred during deposition of these sediments. 3. Intrusive igneous activity during this period resulted in basic dikes and/or sills; acid intrsives are minor. 4. The regional E-W folding increases in intensity to the 5. Older geological events tend to occur in the eastern part of the region and younger ones in the west. 6. Regional tectonism was most intense at some time before south. the end of the period. Events which took place within this region during this time period are pit into the context of cause-effect relationships and a regional-time pattern; a better geological understanding results. The evidence strongly suggests that the area be re- designated as "The Penokean Province" and that the term "Penokean Orogeny" be replaced by "Penokean Tectonic Sequence". �Paper 31 AGES OF SONE PRECAi4BRIAN ROCKS IN EAST-CENTRAL NINNESOTA J. S. Stuckless Department Northern and S. S. Goldich of Geology Illinois University Illinois 60115 DeKaib, ABSTRACT The McGrath Gneiss, formerly assigned to the Penokean orogeny, l6Oo-lOO m.y. ago, was actually emplaced in a Lower Precambrian terrane during the Algoman orogeny, approximately 2700 m.y. ago. Locally the gneiss is intensively sheared. This phase of the deformation is related to epeirogeny that followed the regional metamorphism of the Middle Precambrian formations. Rb—Sr isochron studies of igneous rocks that were emplaced following folding and regional metamorphism place a minimum age of 1900 m.y. on the Mid- This age is somewhat older than the 1850 m.y. age obtained by Z. E. 'Peterman for the metasedimentary rocks of the Cuyina district and is considerably older than the previous K-Ar and Rb-Sr mica age determinations. The McGrath Gneiss appears to be extensive in east-central Minnesota; hence, it is likely that the Middle Precambrian rocks of Minnesota were all- deposited on an erosion surface developed on an Archean continental crust rather than on oceanic crust. dle Precambrian Thomson Formation. �Paper 32 GEOCHRONOLOGY OF PRECAMBRIAN ROCKS IN THE PENOKEAN FOLD BELT SUBPROVINCE OF THE CANADIAN SHIELD W. R. Van Schmus Department of Geology University of Kansas Lawrence, Kansas 66044 ABSTRACT The Penokean Fold Belt subprovince is that part of the Southern Province consisting of the folded and metamorphosed Middle Precambrian rocks which occur in an E-W trending belt running south of Lake Superior and north of Lake Huron. Included within this belt are strata of the Huronian, Marquette Range, and Animikie supergroups and associated economic deposits. For many years these rocks have been considered possible corre- latives, and the folding, metamorphism, and intrusive activity have been referred to as the Penokean Orogeny. Recent and current field and laboratory studies now show that the orogenic history of this region can not be represented by a single major orogenic episode. Instead, this portion of the North American continental plate was affected by a succession of events over the interval 2.7 to 1.1 b.y. ago. The oldest Proterozoic rocks are apparently those in Ontario, north of Lake Huron. In this area Huronian strata overlie a 2.7 b.y. old basement and are intruded by the 2.16 b.y. old Nipissing Diabase. To the west, in Upper Michigan, the Proterozoic sedimentary and volcanic rocks, the Marquette Range supergroup, are apparently younger, being between 1.90 and 2.05 b.y. old, and thus not correlative with true Huronian rocks. Farther west, in Minnesota, the Animikie rocks may be partly correlative with and partly younger than those in Michigan and Wisconsin. There have been multiple periods of intrusive, metamorphic, and tectonic activity. The oldest Proterozoic deformation apparently occurred about 2.15 b.y. ago in Ontario, affecting the Nipissing Diabase and Huronian rocks. A major episode of igneous, metamorphic, and tectonic activity occurred about 1.9 + 0.1 b.y. ago, affecting most, if not all, of the E-W trending belt from Minnesota to Ontario. This event would appear to be the one most representative of a uPenokean Orogeny.' Subsequent to the main orogenic activity several intrusive and! or metamorphic episodes have occurred, about 1.65, 1.5, and 1.3 b.y. ago. Several of these younger events may be correlated with the Middle Precambrian history of Wisconsin and the rest of the Midcontinent. Finally, much of the area was affected by Keweenawan igneous activity and associated metamorphism 0.9 to 1.2 b.y. ago. �Paper 32 -2- On the basis of present geologic and geochronologic data, it appears reasonable to interpret the Penokean Fold Belt as an orogenic belt developed along the southern edge of the Superior craton about 1.9 billion years ago. The exact nature of this structural belt and its possible relation to arc-trench sequences of present models of plate tectonics must await further work. �Paper 32 SELECTED BIBLIOGRAPHY Aldrich, L. 1., Davis, G. L., and James, H. L., 1965, Ages of Minerals from metamorphic and igneous rocks near Iron Mountain, Michigan: Jour. Petrology, v. 6., p. 447-.472. Banks, P. 0., and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: 77, 208-220. Jour. Geology, R. , 1971, Chronology of Precambrian rocks of Iron and Dickinson Counties, Michigan (Abs.). 17th Annual Institute on Lake Superior Geology, Duluth, Minn., May. Banks, P. 0. and Van Schmus, W. Bass, M. N., 1959, Mineral age measurements --Wisconsin: Inst. of Washington Year Book, 58, 246-247. Carnegie Dickinson, W. R., 1971, Plate tectonic models of geosynclines: Earth Plan. Sci. Letters, 10, 1965-174. Dott, R. H., Jr., 1969, Isotopic dating of the Baraboo and Waterloo quartzites. 15th Institute of Lake Superior Geology, Oshkosh, Wisc., p.15. Dutton, C. E. , and Bradley, R. E. , 1970, Lithologic, geophysical, and mineral commodity maps of Precambrian rocks in Wisconsin. U. S. Geol. Surv. Map set 1-631, with accompanying pamphlet (15 pp.). Fairbairn, H. W., Hurley, P. M., and Pinson, W. H., 1960, Mineral and rock ages at Sudbury-Bling River, Ontario: Geol. Assoc. Canada Proc., 12, 41-66. Fairbairn, H. W., Hurley, P. M., Card, K. D., and Knight, C. J., 1969, Correlation of radiometic ages of Nipissing diabase and Huronian metasediments with Proterozoic orogenic events in Ontario. Can. J. Earth Sci., 6, pp. 489-497. Faure, G., and Kovach, J., 1969, The age of the Gunflint Iron Formation of the Animikie Series in Ontario, Canada. Geol. Soc. America Bull., 80, 1725-1736. Goldich, S. S., Nier, A. D., Baadsgaard, H., Hoffman, J. H., and Krueger, H. W. , 1961 nology of Minnesota: Krogh T. E. , , The Precambrian geology and geochro- Minnesota Geol. Survey Bull. 41. and Davis, G. L. , 1971, the Grenville Front inter- preted as an ancient plate boundary: Washington Year Book, 70,. 239-240. Carnegie Inst. of Peterman, Z. E., 1966, Rb-Sr dating of middle Precambrian metasedi- nientary rocks of Minnesota. 1031-1044. Geol. Soc. America Bull., 77, Van Schmus, R., 1965, The geochronology of the Blind River-Bruce Mines area, Ontario, Canada: J. Geol., 73, 755-780. Woolsey, L. L., 1971, A Rb-Sr geochronologic study of the Repi.iblic metamorphic node, Republic, Michgn. Unpub. M. S. Thesis, Univ. of Kansas, Lawrence. �Paper 33 STRATIGRAPHY AND SEDIMENTATION OF THE ESPANOIA FORMATION, AN EARLY APHEBIAN (MIDDLE PRECAMBRIAN) CARBONATE UNIT GRANT M. YOUNG Department of Geology University of Western Ontario London, Ontario ABSTRACr The Espanola Formation is unique among Huronian formations in its high carbonate content. It forms part of the Quirke Lake Group, lying between the Bruce Formation (beneath) and the stratigraphically higher Serpent Formation. The Bruce Formation is mainly unstratified sandy polymictic paraconglomerate (tillite) whereas the Serpent Formation consists mainly of cross bedded felspathic quartzites. In the Quirke Lake area the Espanola Formation is divisible into three units, here called, in ascending order, limestone member, siltstone member and dolostone member. Some fifty miles to the southeast these three members can still be recognised but the central, dominantly terrigenous clastic unit, is much thicker. In the southern area there is also an additional thick upper member which displays fining upwards cycles (from conglomerate to mudstone) similar to those attributed to fluvial deposition. In the Quirke Lake area the Espanola Formation contains both intraformational and intrusive breccias. The intrusive breccias are later than some faulting and transect clastic dykes. They are considered to be downward intrusions caused by release of high pore pressure in watersaturated sediments along fissures in the already lithified Espanola Formation. The triggering mechanism for the breccias may have been earth tremors associated with early (pre-Gowganda) earth movements for the breccias appear to be spatially related to areas where there is evidence of disconformable/unconformable relations between the Gowganda Formation and older Huronian rocks. Cross bedding studies, mainly from the highest member of the Espanola Formation in the southern part of the Huronian outcrop belt, reveal a bimodal pattern with dominant modes in the south-west quadrant and towards the E.S.E. Microprobe analyses of the carbonates of the dolostone member showed that the rusty-weathering dolostones are composed of ferruginous dolomite. The Espanola Formation is interpreted as a post-glacial transgressiveregressive cycle (Fig. 1). The limestone and dolostone members are thought to be shallow water deporits while the siltstone member represents a deeper water facies (involving some turbidite transportation). The sandstone member of the southern region is thought to have been laid down from meandering streams which initiated sedimentation of the thick prograding fluvial sequence of the Serpent Formation. �0 .,-4 C. S S SQ '.4 00 00 '0 5 0 FIG. 1, F- LU 0.0 ,-l us C w C. .0 '0 NW I I (turbidite facies) SERPENT FORMATION SPACE - TINE RElATIONSHIPS DURING SEDIMENTATION OF THE ESPMTOLA FORMATION TRANSPORT DIRECTION DOMINANT SEDIMENT UPLIFT AND EROSION REGION OF CONTEMPORANEOW UPLIFT — ESPANCLA Southern limit of SUBS! DEN CE REGION ZONE OF TECTONIC Northern Limit of preserved Huronian ZONE OF TECTONIC TECTONIC HINGE ORMATION SE III • �Paper 34 WEATHERING AND METASOMATISM OF THE PRESQUE ISLE SERPENTNIZED PERIDOTITE, MARQUETTE COUNTY, MICHIGAN M. D, LEWAN Michigan Technological University ABSTRACT Presque Isle Park, Marquette, Michigan is underlain by a mass of peridotite, probably cut by Archean granite and definitely cut by a diabase dike of probable Keweenawan age. The three rock types grade upward into a complex altered zone that has variable thickness and mineralogy, depending upon the rock type it occurs on. This zone is comprised of a lower zone of dolomite-silica. and an upper zone rich in silica, which in turn is unconformably overlain by Jacobsville Sandstone. Data from major element analysis of 42 rocks, qualitative mineralogy determinations by X-ray diffraction, and field observations indicate that the peridotite has undergone three periods of alteration; 1 )early s erpentinization, 2)carbon dioxide meta somatism after emplacement, and 3)weathering after the area was exposed to surface conditions. The granite has also undurgone the same sequence of alteration with the exception that the first period of alteration was illitization. On geological and geochemical grounds the serpentinization and illitization processes could not have been contemporaneous. The forming of the silica rich weathered zone, which is best developed over the granite, is the result of weak acidic meteoric waters dissolving dolomite out of the dolomite-silica zone. Chemical and mineralogical profiles show that the removal of dolomite results in the upward concentration of residual minerals such as quartz, rutile, hematite, chlorite, and illite. The weathered zone was searched for nickel concentrations such as garnierite, but none were found. Field evidence indicates that the weathering and metasomatic alteration post-dates the intrusion of the probable Keweenawan dike and pre-dates the deposition of the Jacobsville Sandstone. Jacobsvifle Sandstone p Basal Conglomerate 8 Silica-Rich weathered zone c ° -— Dolomite-Silica zone , Diagramatical sketch(not to scale) showing the relationship between the rock units on Presque Isle.. � https://digitalcollections.lakeheadu.ca/files/original/a4db2f602031c8a408c608d8cb354236.pdf d677645b5be965a820d9bca69a888cc9 PDF Text Text ������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/b5f4086c9db7eb5ddf6d4f37b1ce7c16.pdf b1d42fe2b6fcf5b2fb62b0815cc007f1 PDF Text Text �---'--------......;;===================----------=====--------------==================.,......------'.. i" Michigan Technological University University /- ..-..;// ....::>' /tPl;SID~8;t;.~ /' ~ H'QH~A . _.'~ / ~7'" .:- .-":-'Y._~;---;;;r-;;.,.-;~--?~'-:~ - ----. --:..-- Y.~==-.:,- - _=_ -. ---._ __ HOUGHTON MI 49931 • -2< ' '1'~1J - rf'I 0'">" ~ III! :r::£'(P~ .- _.._. . . . . - .--- - ..- - . - . - . ,{'(}-(~.,c?". 'J<'£:: .f\ --' / (',{,!~,-- -~ .,~~ './ ---~. - -_. - . _ . ' - . N'-c.A ~ ~\ Seaman c···.· -' ••/ / ! --; , . .~r: ~; Mineral Museum . . .. --- (5th (5th floor) Memorial Union Union .. .,~=-'~" ::~::::-~':"'~~~:. .'.~' ~:-- - ----,- ...->--'-" / ~ —- - 1 (3rd floor) \\ / / // / r--. .. - ~f1Y- -. Geology -.—- ~~-::.~;,::;:~:~,:, * -.:• ,/ ..' ~C~ 0 ~.-:_-- - .. --7'- - " " . .. . -.., _ ...:>c.....- ~- // /' --;;.,;-. ---;.. - _~'~..rg;~.'~~~: ~_.-ifi,~.:.'~-': ~-F'i:rPJl' -~... ..e;- . ' ~ ... ?- • -~I)<0.rr - / PORTAGE LAKE / Commuter & DHH -) - _ ... - rv-l\l:rd- ~ (l"ri_,y,> 0 "'-0,,r ~ ( ,'."" f\,:,''''''- Qr4 'b-97? ?•j(4?it ,/7 r-5.jfy ,,, 5' //' - //.'/, /j1'J. HARONAVE' " - - clf i—__._ —__-'" = - - / J/ / ( /— — ,,, 5- --5 —'-_ \ -= 5J( 'n\\ \ 11 v'— r (" r -y"y' AdmInistration BuIlding Administration Building 4 ROTC ROTC BuildIng Building 5 Academic Academic Offices Offices BuIlding Building Electrical Energy Resources Resources Center Center ElectrIcal Energy 7 EERC-AE. Seaman Seaman Mineralogical Mineralogical Museum EERC·A.E. Museum (5th (5th Floor) Floor) 9 Alumni AlumniHouse-MT House-MT Fund Fund Humanities Center Center Arts and Humanities InstItute of of Mineral Mineral Research Research (Benedict (Benedict Lab) Lab) ,39- 'i\ '(! . 12 Institute CivIl-Geology Building Civil·Geology Hall 15 Fisher Hall library Forestry·lnstitute of Wood Research 19 ChemistryMetaurgyBuiing Chemistry·Metaliurgy Building MechanicalEngIneering-Engineering Engineering-Engineering Mechanics 20 Mechanical -3(Y- 24 Student Development Complex Student Development Complex Douglass Houghton Hall (DHH) Daniell Heights Housing -r4-,c' 34 Memorial Union Memorial UnionBuilding Building 37 Wadsworth Wadsworth Hall Hall \L7 -— - - I - - // rr-w-- fç,7 - FOOTBALL FIE LD -, / k/ 1 ' 9c'?1i-' /) J 14 (1 38 West West Coed Coed Hall Hall 38 39 Coed Coed Food Food Service Service 39 East East Coed Coed Hall 4t Central Heatmg Healing Plant 41 42 Physical Physical Plant Plant Storage Storage Building Building 42 Lakeside Laboratory 43 Lakeside 43 44 Storage-Service Storage-Service Building Buiiding (Pool (Pool Cars) Cars) 44 50 Gates Tennis Tennis Center Center 50 Gates 58 U.S. Forest Engineering Laboratory U.S. Forest Engineering A Visitors'Parking Parking Ares Area A Visitors )L. ç- - 9 - 40 Not appearing on on map map: Experimental Mine, Hancock Hancock Ford Forestry Center, Alberta Ford Alberta Keweenaw Research Center Center, Memorial Memorial Airport Airport Mont Ripley Ski Hill, Ripley Portage Lake Golf Course, Course, Houghton Houghton I ',S (\C'l(') '()r l ' r- (( .,.... .-,_ -( ,CY C �FIELD GUIDE TO THE GEOLOGY GEOLOGY OF OF THE THE KEWEENAW PENINSULA, PENINSULA, MICHIGAN BY J. Bornhorst Theodore J. William I. I. Rose, Rose, Jr. Jr William James B. B. Paces Department of of Geology and Geological Engineering Michigan Technological University University Houghton, Houghton, Michigan 49931 FOR SALE SALE AT: AT: E. R. R. Lauren Bookstore, Bookstore, Memorial Union E. Michigan Technological University Houghton, Michigan 49931 Houghton, Prepared as field trip trip guide guide for for the the 29th Annual Institute as aa field Annual Institute on Lake Superior Geology held held at at Michigan Michigan Technological Technolo~ical University on May 11—14, 11-14, 1983. 1983. FIRST EDITION May, 1983 May, COVER PHOTO: Miners Miners at at the the Mine(?) circa circa 1910. 1910. Baltic Mine(?) Michigan Technological University Archives and Copper Country Historical Collections. Collections. �PREFACE — It is presumptuous presumptuous for for us us to put together is based based mainly mainly on on the the work work It is to put together aa book which is of others. We have done so because hundreds of people come to of to the Keweenaw each year to to look look at at geological geological features features and and many many of of them them ask ask us us for for advice. advice. So we've tried to tried to communicate with people people who who are are doing doing serious serious geological geological field field trips. trips. This is is a first first draft of an evolving document, document, which we expect to to continually rerePlease help help us us make make it better by by suggesting changes, changes, finding finding mistakes mistakes and and Please it better vise. telling us what we've we've left left out. out. Starting with Douglass Douglass Houghton almost almost 150 years years ago, ago, dozens dozens of of geologists geologists have have contributed aa mountain of of geological on the the Keweenaw Keweenaw which which makes makes it it contributed geological information information on aa real challenge to to compile this this book. book. The greatest greatest contribution by far far has come come from from Walter Walter S. S. White, White, who who devoted devoted much of of his his professional professional career career to to Keweenawan Keweenawan whose impact geology and whose impact can can be traced traced to to virtually virtually every every page page of of this this book. book. of his his We hope that that we have faithfully faithfully transmitted his his ideas with a a fraction fraction of enthusiasm. ingenuity and enthusiasm. Houghton Houghton 30 March 1983 i1 �TABLE OF CONTENTS Page i PREFACE iii HOW TO USE THIS GUIDE GUIDE iv LIST OF OF STOPS STOPS vlii viii LIST OF MAPS ix LIST OF FIGURES xi LIST OF OF TABLES TABLES INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA 11 17 17 ROAD LOG AND STOP DESCRIPTION INDEX TO GEOLOGY ON NAPS MAPS IN IN THE FIELD FIELD GUIDE GUIDE 111 111 112 112 REFERENCES 11i i �HOW TO USE THIS GUIDE To make all the the stops stops listed listed in in this this guide guide would would take take three three days. days. If If you wish to to emphasize certain types types of of stops, stops, we we recommend recommend the the following following subsets: subsets: Suggested Stops Stops Sediments Sediments Volcanic Rocks Mineral Deposits Broad Coverage 5, 6, 8, 8, 9,. 16, 17, 17, 19, 19, 20, 20, 24 24 10, 13, 13, 16, 5, 6, 9, 10, 1, 15, 16, 16, 17, 17, 18, 18, 21 21 1, 3, 3, 11, 11, 12, 12, 13, 13, 14, 14, 15, 2,3,4,7,11,13,17,22,23 2, 3, 4, 7, 11, 13, 17, 22, 23 3, 6, 10, 10, 11, 11, 13, 13, 16, 16, 18, 18, 19, 19, 20, 20, 24 24 3, 6, Be imaginative and make up up your own own subset subset of of stops. stops. stops are are on on or or near near private private land. land. Please respect private property. property. The preMany stops Sent problems of access are minimal, but obviously we could ruin we don't don't sent problems of access are minimal, but obviously we could ruin things things if if we use low profile outdoor principles. principles. AA few few stops stops are are located located ot on old mine dumps. dumps. These can be hazardous, hazardous, especially especially where where bad bad ground ground occurs. occurs. Use common sense. sense. - have north north to to the the top top and and are are 1:24,000 1:24,000(4(4cmcmtoto1 Ikin). km). All maps have road log route on the the maps, maps, while while stars stars mark mark the the stops. stops. follow the the Dots follow Mineral collectors have long long flocked flocked to to the the Keweenaw to to collect its its unusual minerals. minerals. One of the best in the world located at this best mineral museums in world is located at the starting point point of of this field trip. trip. The Seaman Mineralogical Museum, Museum, open from 9:00—4:30 9:00-4:30 weekdays, weekdays, is is housed housed in the the EERC EERC Building, Building, Fifth Floor, in Floor, on on the the Michigan Michigan Tech Tech Campus. Campus. The mineralogical over the the Keweenaw and is collection includes includes samples samples from from all over is aa must for for all all rockhounds. rockhounds. 111 iii �STOPS LIST OF STOPS The following used to to help help you you design design your your own own field field trip trip following list of stops can be used to to see the geology of the the Keweenaw Peninsula. Peninsula. The location location of of stops stops are are shown shown in Figure la. la. The appropriate maps for for each stop and trip trip route are located in Figure Figure lb. lb. — — STOP MAP) (APPROPRIATE MAP) STOP DESCRIPTION STOP 11 (1) (1) Ophitic Scales Creek basalt flow and Keweenaw view, 7th 7th St., St., Houghton. Houghton. Waterway view, 2 2 (1) (1) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Isle Royale Mine, Dodgeville. Dodgeville. '-" 3 (2) (2) Section through a lava lava flow flow at at South South Range Range quarry. quarry. ....---4 (2) (2) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Baltic Mine. Mine. 5 5 (3) Glacial deposits on M—26 M-26 south south of of Houghton. Houghton. 6 6 (4) (4) Overlook of Keweenaw Waterway, Waterway, Houghton and the Range towns; towns; Quincy Quincy Hill, Hill, Hancock. Hancock. 7 7 (4 ) (4) Secondary minerals of amygdaloid at at dump dump of of Quincy Quincy Mine. Mine. 8 (6) (6) Flat—lying Flat-lying Jacobsville Jacobsville Sandstone Sandstone along along M—26, M-26, near Dollar Dollar Bay. Bay. 9 9 (7) (7) Hungarian Falls, Falls, near near Hubbell. Hubbell. Keweenaw Fault at Hungarian 10 10 (8) (8) Keweenaw Fault at at Natural Wall Wall Ravine, Ravine, near near Laurium. Laurium. 11 (9) (9) Secondary minerals in amygdaloid at at dump dump of of Wolverine Wolverine Mine. Mine. 12 (9) (9) Ophitic Scales Creek basalt flow, flow, at Scales Creek near Copper City. City. —- 13 ...../13 (9) (9) Lava flows flows of Portage Lake Volcanics and mineralized conglomerate with an excellent ized excellent view view of of the the central part of of the the Keweenaw Keweenaw Peninsula, Peninsula, Bumble— Bumbletown Hill. 14 (12) (12) Ophitic Greenstone flow and vein mineralogy at dump of Phoenix Mine. 15 15 (12) (12) part of of the Portage Lake Lake Section through through the the upper part the Portage Volcanics along along Eagle Eagle River. River. 16 (12) Contact between Portage Lake Volcanics Volcanics and Copper Contact Harbor Conglomerate Conglomerate at at Eagle Eagle River River Falls. Falls. ~. t/ iv �STOPS (Cont'd.) (Contld.) LIST OF STOPS STOP DESCRIPTION STOP (APPROPRIATE MAP) 17 17 (13) through the the upper upper part part of of the the Portage Portage Section through Lake Volcanics along Owl Owl Creek Creek and and amygdaloid! amygdaloid/ vein mineralogy at dump dump of of Copper Copper Falls Falls Mine. Mine. v"J.8 "18 (16) (16) Lava flows of the the Lake Shore Shore Traps Traps at at Esrey Esrey Park. Park. V19 \/19 (17) Overlook of Lake Superior Superior and and the the eastern eastern end end of of the Keweenaw Keweenaw Peninsula and outcrops of Copper the Harbor Conglomerate at at Brockway Mountain. Mountain. flO (17) (17) Copper Harbor Conglomerate Conglomerate at at Dan's Dan's Point. Point. 21 (20) (20) Diorite and granophyre stock stock at at Mt. Mt. Bohemia. Bohemia. 22 (21) Secondary mineralogy of of veins and and conglomerate conglomerate at Delaware Delaware Mine'. Mine~ The Delaware Mine is is open to to tourists for for aa fee. fee. 23 (28) Amygdaloid mineralogy of of dumps dumps at at Osceola Osceola Mine. Mine. 24 (30) at Hancock Hancock campground campground quarry. quarry. Nonesuch Shale at v �I ( I . ···i·9*··..······..·····;:;: ; ~ "'-~'L"'"alre Bailey . Eagle . . . f~~;I~.·.:::::::···:< . . . ""C~~r~·I La e M.,!dO'~ C ............ Delawar~.~.,2 ..'····· ....····· Copper Harbor 20 \ 0 " fifo" 5 IJ Eagle H ...r-nnr :._. _ - .~ .-:--~"::::~tS ~-~. Lak e Fanny Hooe Schlstter('.., •....1 (? ········\···'>... 21 = LakeV ~ Manitou Island Island ........ Phoenix .-:,., <f.2 .~.' i-~ Lake .../ "to A:::;!l\(~~:,..• o Kearsargei..,.J 1 ..i '···12 -< ~. McLain State Park McLain Park .rC"aiun;-~t·'· .f .-.,1.0... ~~ ~~ ~\ o~ C, Laurium 23*/ . Lake Linden ..... .... Scale Scale 1 0o M I 1 1 2 3 4 miles 4miles ~ Freda Atlantic South ~ ~ly ~ '" Painlsdale Pa in ed a le 12 Stopnumber number •2 Stop Figure Figure 1A: 1A: Route Route and and stop stop map map �SU ~~ \\ \ 17 o o~ 13~ ~ 23 o 12 'I-~ ... '" _0_" 27 ./' <~ t-<t-<. -.)~ ~ ~ \ o ~ c., 8 SCALE in in miles 01234 ,.... ji"Wiij o 1 2 ....., 3 p> 4 Dil2 Map number 12 ,.*" I'l + ~ " Figure 1B: 18: *'2 number Stop number Index of of 1:24,000 Index 1:24,000 scale scale maps maps �LIST OF OF NAPS MAPS Page MAP MAP 1 18 MAP MAP 2 22 MAP MAP 33 26 MAP MAP 44 31 MAP MAP 5 35 MAP MAP 6 39 MP MAP 77 42 MAP MAP 88 46 MAP MAP 9 49 MAP 10 MAP1O 60 MAP MAP 11 63 MAP 12 MAP 64 MAP13 MAP 13 71 MAP 14 MAP 74 MAP15 MAP 15 76 MAP 16 MAP 77 MAP17 17 MAP 79 MAP 18 MAP 82 MAP MAP 19 86 MAP2O t-1AP 20 87 MAP MAP 21 88 MAP 22 MAP 91 MAP MAP 23 95 24 MAP24 MAP 96 MAP25 MAP 25 98 MAP26 MAP 26 99 NAP MAP 27 100 MAP MAP 28 104 MAP MAP 29 106 MAP MAP 30 109 viii viii �LIST OF FIGURES Page vi Vi Figure 1: 1: Index map map of of route, Index route, stops and 1:24,000 scale scale maps. maps. Figure 2: 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. 2 2 Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and strati— stratigraphic column, column, western western Lake Lake Superior Superior region. region. 3 3 Generalized geologic geologic map of of the the western western Upper Upper Peninsula and stratigraphic stratigraphic section section of of the the Portage Portage Lake Volcanics. 4 4 Columnar stratigraphic Section section of of rocks rocks northwest northwest of of the Keweenaw Fault in the Calumet—Ahmeek the Calumet-Ahmeek area. area. 66 rocks Location of silicic to to intermediate intrusive rocks the Portage Lake Volcanics. in the Volcanics. 8 8 Figure Figure Figure Figure 4: 4: 5: 5: 6: 6: 7: 7: Schematic diagram showing interrelationships between northwest of of the major stratigraphic units units northwest the Keweenaw Fault in the the Keweenaw Peninsula. 10 Geologic and structure structure maps of of the the Keweenaw Keweenaw native native copper district. district. 13 and paragenesis of of secondary minerals Distribution and secondary minerals in Volcanics. in the the Portage Lake Volcanics. 14 14 Elemental mobility in in an an idealized idealized lava lava flow flow and and diagrammatic diagra~matic regional model for for metamorphism metamorphism of of the Portage Lake Volcanics. the 16 16 Figure 11: 11: Geologic cross—section cross-section for for Map Map 1. 1. 20 Figure 12: 12: Geologic profile of South Sou~h Range quarry. quarry. 21 21 Figure 13: 13: Speculative ice—marginal ice-marginal positions positions during during the the Wis— Wisconsin ice retreat. retreat. 27 Figure 14: 14: End moraine of the End the Keweenaw Bay Lobe glacier. glacier. 27 Figure Figure 15: 15: Enlarged view of ice—marginal ice-marginal positions. 28 Figure Figure 16: 16: High level drainage drainage through through the the Portage Portage Gap. Gap. 29 29 Figure Figure 17: 17: View from from Portage overlook overlook facing facing south. south. 32 32 Figure Figure 18: 18: Structures of the the Quincy Mine location. location. 36 Figure 19: 19: Geologic cross section section for for Maps Maps 4, 4, 5 and 30. 30. 37 37 Figure Figure 8: 8: 9: 9: Figure 10: 10: ix �Page Figure 20: 20: Relationships of of Jacobsville Sandstone. Sandstone. 40 21: Figure 21: Geologic sketch map of of Hungarian Falls Falls area. area. 44 Figure 22: 22: Wall Ravine. Ravine. Geologic sketch map of of Natural Wall 47 Figure 23: 23: Geologic Geologic map map and cross section, Wolverine Mine and and section, Wolverine arid cross vicinity. 51 Figure 24: 24: Thickness of of the the Kearsarge Kearsarge flow. flow. 52 Figure 25: 25: Paragenesis of secondary minerals in in the Kearsarge amygdaloid. 52 Cross section section of of Kearsarge Kearsarge amygdaloid amygdaloid showing showing the Cross the banding of of mineral assemblages. assemblages. 54 Distribution of quartz, quartz, microcline and high grade ore in in the the Kearsarge Kearsarge amygdaloid. amygdaloid. native copper ore 55 Figure Figure 28: 28: Outcrop map of of the the Allouez—Bumbletown Allouez-Bumbletown Hill Hill area. area. 57 Figure 29: 29: Map and section of the Greenstone flow between Seneca and the the Cliff Cliff Mine. Mine. 61 Figure 30; Figure 3O Map and section section of of the the Greenstone Greenstone flow flow near near Phoenix. Phoenix. 66 66 Figure Figure 31: 31: Stratigraphy of the Portage Lake Volcanics Volcanics above above the the Greenstone flow. flow. Greenstone 68 68 Plot of K20 and P205 content of 106 individual individual Portage Lake Volcanic flows flows in in stratigraphic stratigraphic order. order. 69 69 Schematic cartoon cartoonofdepositional Schematic of depositional environment environment of of the the Copper Harbor Conglomerate. Conglomerate. 83 83 Measured section of Copper Harbor Conglomerate at Dan's Dants cartoon of of the the depositional depositional environment. environment. Point and cartoon 84 84 Geologic map showing andesitic dikes near Mount Bohemia and occurrence occurrence and and paragenesis paragenesis of of secondary secondary and and opaque opaque and in the the dikes. dikes. minerals in 90 90 map and development of Sketch map of the the Keweenaw Keweenaw Fault Fault in in of Deer Deer Lake. Lake. vicinity of 93 93 Figure 26: 26: Figure 27: 27: Figure Figure 32: 32: Figure Figure 33: 33: Figure 34: 34: Figure 35: 35: Figure Figure 36: 36: Figure 37: 37: Figure 38: 38: Schematic illustration of the the funnelling effect on on Schematic illustration of funnelling effect fluids, Kingston Kingston conglomerate. conglomerate. mineralizing fluids, 102 102 Results of gravity gravity measurements across the Bear Lake on Map Map 29. 29. traverse plotted on 108 108 x �LIST OF TABLES Page Table 1: 1: Secondary minerals found found within within the the Portage Portage Lake Volcanics. Volcanics. 11 Table 2: 2: Major—element Major-element composition composition of of the the Kearsarge Kearsarge flow. flow. 51 Table Table 3: 3: Volume percent amygdule minerals from mapped assemblages shown in in Figure 26. 26. 54 Average major—element major-element composition of the the Scales Creek Creek flow. flow. 57 57 Table 4: 4: Table xi �INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA PENINSULA General Background The Mid-Continent Mid—Continent Rift Kansas to Lake Superior Superior Rift System extends northeasterly from Kansas to Lake It was was formed and then southeasterly through and through lower lower Michigan Michigan (Fig. (Fig. 2). 2). It formed about 1.1 1.1 to 1.2 b.y. b.y. ago ago (Keweenawan age) by by extensional extensional thinning of the the rigid rigid Precambrian Precambrian to 1.2 (Keweenawan age) thinning of Superior crustal block (Kiasner (Klasner and and others, others, 1982). 1982). Present day crustal thickness thickness the Lake Superior region, region, however, however, is is between between 40 40 and and 50 50 Km, Km, which which is is thicker thicker in the than than adjacent areas areas (Halls, (Halls, 1982). 1982). -— Peninsula is is located located on on the the margin margin of of the the Lake Lake Superior Superior Basin, Basin, The present Keweenaw Peninsula one of of the one the basins within the the Mid—Continent Mid-Continent Rift Rift System System (Fig. (Fig. 3). 3). The volcanic and sedimentary rocks rocks on the northwest side side of of the the Keweenaw Keweenaw Peninsula Peninsula generally generally dip dip toward Lake Superior and include the Portage Lake Volcanics, moderately toward Volcanics, Copper Copper Conglomerate, Nonesuch Shale Shale and and the the Freda Freda Sandstone. Sandstone. The Jacobsville Sand— SandHarbor Conglomerate, stone stone occupies the southeast side side of of much of of the the Keweenaw Keweenaw Peninsula Peninsula and and is is in in fault along the the Keweenaw Keweenaw Fault. Fault. The Jacobs— Jacobsfault contact contact with the Portage Lake Volcanics along ville Sandstone is however, it it is probably slightly younger than the the Freda Sandstone, Sandstone, however, is still most most likely upper Keweenawan in is still in age age (Kalliokoski, (Kalliokoski, 1982). 1982). At some time after the deposition of basin filling filling sediments, sediments, the Lake Superior region was was subjected to compression roughly region roughly normal normal to to the the basin basin axis. axis. These stresses in the the Keweenaw Keweenaw and and Isle Isle Royale Royale Faults, Faults, both both high high angle reverse reverse stresses re~ulted reulted in faults faults near near the margins of the the Lake Superior Superior Basin Basin (Fig. (Fig. 3). 3). This faulting steepened the dips the Peninsula Peninsula and and on on Isle Isle Royale. Royale. Definite age the dips of of strata exposed on both the relationships between between reverse reverse faulting faulting and and deposition deposition of of the the Jacobsville Jacobsville Sandstone Sandstone relationships are unclear: unclear: faulting syn- or wholly post—depositional. post-depositional. faulting may may be partially syn— The Lake Superior Syncline was affected affected by aa regional regional burial metamorphic and/or hydrothermal event. event. Remobilization of many elements, elements, particularly within the the Portage Lake Volcanics, Volcanics, caused lava flow caused strong alteration of of lava flow tops tops and and interbedded interbedded concon— glomeratic units. units. Native copper deposits of the the Keweenaw Peninsula are believed to to formed wholly or in in part the deposition of of the the Freda SandSandhave formed part after after the of much or all of stone (White, (White, 1968). 1968). Paleozoic geologic geologic processes processes were were largely largely atectonic. atectonic. Sediments associated with the the Michigan basin probably once covered the the Keweenaw Peninsula, Peninsula, as evidenced by the the isolated limestone at at Limestone Limestone Mountain Mountain and and Sherman Sherman Hill, Hill, isolated occurrence of of Ordovician limestone about 20 miles south about south of Houghton. The present day landscape of the the Keweenaw Peninsula is strongly strongly influenced by Pleistocene glaciation. is glaciation. Stratigraphy The bedrock geology of the the Keweenaw Peninsula consists of five major stratigraphic units. Portage Lake Volcanics, Volcanics, Copper Harbor Conglomerate, Conglomerate, Nonesuch Shale, Shale, Freda Sandstone and Jacobsville Sandstone Sandstone (Figs. (Figs. 33 and and 4). 4). The accumulated maximum thickness of of these these units units is is over over14,000 14,000in. m. The bedrock in the Keweenaw Peninsula is unconformably capped by a variety of is of glacial glacial deposits. deposits. �2 2 A. o0 -= KM t000 1000 KM ORIENTATIONS ORIENTATIONS OF SEGMENTS SEGMENTS OF THE MIDCONTINENT RIFT RIFT B. ---1\ l. I "----... N670,E N67 E "~ f, , 1. ----,j--, , ~ 0 N38 E( i---~~ ;:'-3~'E \ , 1 j 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. A. Major Proterozoic A. Figure 2: rifts of of North North America America (from (from Burke, Burke, 1980). 1980). B. B. Orientation of and Paleozoic rifts individual the Mid—Continent Mid-Continent Rift Rift System System (from (from Kiasner Klasner and and others, others, individual segments of the 1982). �r- lie i ~ " II iA*' I 0 - Nipigon Sand,,,,",,. o JACOBSVILLE-BAYFIELD UP UPTO TO5000'+ 500O I f Cambrian &nd _ latesa: Kewc:etUlwu 49. '9" ONTARIO '\ Coppc:r Harbor Conalomcf1ue -/'-'-, '\;Z~'-S~10' /",-, - ""~O'~';ES o Kewecnaw&.l'l voleank: s.cquence, including Portage Lake Voleanic;s ,- __ ~ FREDA SANDSTONE SANDSTONE UP TO UP 70 12,000'+ 2000+ -1030 Ma (m,n.) IO30Mo(n,n.) 0:: W 0.. 0.. 0 MINNESOTA =:l .,. aa.. :3 :::> 47. 0 o 0:: (.!) (0 « WISCONSIN o I 50 I I o 45~ 45- I .,. I 93" I i ... 10(1 0:: I~"",""ES 100 I $0 ill , I ::2: \~')(Il(')Ll£"1RES I I .,. J 85" « C-) u LU w 0:: aa.. LAKE SUPERIOR REGION—distribution of of selected selected rock units. SUPERIOR REGION-distribution units, o0 —• :° .nç•0 .0 zz I— I- z Z COPPER HARBOR CONGLOMERATE 350' 350 -7000' -7000 zz « ~ I040Mo -1040Ma zz LU w UJ w 3: LU w 0:: o0 0:: 0 o Y: LU W aa.. 11 a.. PORTAGE LAKE PORTAGE VOLCANICS 9000' 9000 -15,000'. -(5,000. ::J I (include unnamed ufl0med (Include formation in west UP) formation west U.P.) VW ·YW ThUNDER BAY THUNDER REGION REGK>N KEWEENAW 1Sl..£ ROYALE [,lK£ SUPt.RIOR S£ ct jjjp LU W 1 .J P£HIN$ULA o co :E~ VERTICAL SCALE VERTICAL EXAGGERATED EXAGGERATED SOUTH RANGE RANGE SOUTH VOLCANICS (North Shore ~ Volcanics) Volconics) G]J t'ostvolcanic rrvludrg Poslvolcamc sodimenbo sc:dimenUry rocks. rocks. including the Copper Copper Harbor Harbor Conglom.::rale Conglomerate the tntrrbnddnd volcanic sedimentary ro<:h. rnck,. InltrbeJded VOIcMic and and seJimcntary nolading the the Portage Portage Lake Lake VolcanICS 'olratncs Including Prevolcanic Pynvolcanic rocks rock, a: indrcale relative relative directions directions Arrows indicate of movement along faults BESSEMER & BESSEMER B BARRON BARRON QUARTZ lIES QUARTZITES LU w ~ LAKE LAKE SUPERIOR SUPERIOR BASIN—cross BASIN--cross section. MIDDLE - I BASEMENT PRECAMBRIAN ,v•°°: I Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and stratigraphic stratigraphic column column of of upper upper Precambrian rocks in the western Lake Superior region (map and cross—section from rocks in Lake Superior region (map and cross-section from Huber, column from from Daniels, Daniels, 1982). 1982). Huber, 1975; stratigraphic column w �4 NE SW NATIVE COPPER < aw 2 0 2 •° . .4 EEl > wo 0a—a- .4 F MINES — 2000 —, oo —1 1000 2000 3000 — 4000 5000 €000 — Location at onion within atratigraphic anc lion Aanraalmnln upFnn limIt at apiaatn & aaa'tn Approalmate Figure lawn, lion It at A. Generalized geologic map of upper Precambrian rocks of western Upper 4: B. GeneralPeninsula, Michigan. Hatched area is represented in cross—section in B. ized stratigraphic section of the Portage Lake Volcanics from Victoria to Copper Harbor (modified from Stoiber and Davidson, 1959). The major marker horizons and mines are shown. The dashed and dotted lines represent the approximate stratigraphic limits of secondary epidote and quartz and prehnite respectively. �Portage Lake Volcanics The Portage Lake Volcanics is a succession of more than 200 individual basaltic lava flows with a total thickness of 2500 m to 5200 m (Butler and Burbank, 1929; Huber, 1973; White, 1968) (Fig. 4). White (1960) recognized these volcanics as a thick pile of subaerial tholeiitic flood basalts. They are the product of rift zone magmatism and are comparable to the rift zones of East Africa and Iceland (Basaltic Volcanism Study Project, 1981; Chase and Gilmer, 1973; Green, 1977 and 1982; White 1960 and 1972). Volcanism was apparently controlled mainly by eruptions from fissures located under Lake Superior. The Portage Lake Volcanics are others, 1982). about 1,100 m.y. old (Van Schmus and Most of the lava flows are difficult to follow laterally with confidence. The Scales Creek, Kearsarge and Greenstone flows are the best documented laterally continuous flows. The Greenstone flow can be correlated to Isle Royale (Huber, 1975; Longo, 1982). There are thin conglomerate and sandstone beds throughout the section and these are excellent marker horizons (Fig. 4). The sediment inter— beds in all but the uppermost part of the Portage Lake Volcanics have been given names and are shown on the maps included in this field guide (Fig. 5). The inter— bedded sediments make up approximately 3 to 8% of the formation (White, l971a). The conglomerates of the Calumet area the host rocks for large native copper deposits. The lithology of the conglomerates is dominated by clasts of rhyolitic volcanic rocks (Merk and Jirsa, 1982). The frequency of interbedded sediments increases in Eventually volcanism waned and sediment deposition the upper part of the formation. became dominant, the overlying Copper Harbor Conglomerate. The dominant composition of the lava flows of the Portage Lake Volcanics is tholeiitic basalt. Dikes of mafic and intermediate composition cut the volcanic pile but are as unconmion. a whole Silicjc. volcanic and subvolcanic rocks comprise less than 1% by volume of the exposed Portage Lake Volcanics (Bornhorst, 1975; Grimes, 1977; Robertson, 1974; Robertson and others, 1979). They tend to be in the lower part of the stratigraphic section in the Keweenaw Peninsula (Fig. 6). The composition of volcanic rocks of the Portage Lake Volcanics was affected by both Primary magmatic differentiation has long been igneous and metamorphic processes. recognized both within and between tholejitic flows (Broderick, 1935; Broderick and For example, the Greenstone flow, the thickest Hohl, 1935; Cornwall, l95la and b). individual flow in the formation (Figs. 4 and 5), is chemically stratified due to Copper may have conceninternal differentiation (Cornwall, l951b; Longo, 1983). differentiation trated in the pegmatitic and more importantly in the flow tops. Work by Scofield (1976) demonstrated that copper can also be concentrated in the Rose and Grimes base of individual flows by gravitational setting of magnetite. (1979) showed the existence of three magmatic cycles within the Portage Lake Vol— canics which initiate with basalts that have high incompatible element abundances. The degassing of volatiles during and after eruption in an oxidizing subaerial environment was also important in that it allowed degassing of SO2 (Cornwall, 1951c). This created a sulfur deficient environment which favored the later deposition of native copper. A third pre—metamorphic process was deuteric or diagenic alteration of olivine and glass to hydrous minerals, the most important of which is chlorite. Ljvnat and others (1976) used '3D and '3180 to show that the basalts have undergone extensive isotopic exchange with low—temperature meteoric waters prior to metamorphism/hydrothermal mineralization. After emplacement the volcanic pile was subjected to extensive low—temperature, low—pressure hydrothermal/metamorphic alteraThe Portage Lake Volcanics on the Keweenaw Peninsula are in fact a classic tion. �6 Feet FR EDA SANDSTONE ci ,.,', Lava unit 0 AND fn .. COPPER HARBOR 0 NONESUCH SHALE CONGLOMERATE 0 06 0.-A 0 00 0 12,000 c a 15,000 =- - Lava unit c 000 o — QO 4 00 0 0 0 0-0 •0 0 o00 000 00 0 •2.0 . 00 . 0 0 0 11,000 c 14,000 1. .: PORTAGE LAKE LAVA SERIES Lava unit ci :0 10000 c 13,000 . Figure Columnar stratigraphic section of rocks northwest of the Keweenaw 5: Fault in the Calumet—Ahmeek area (from White and others, 1953). The labels for units within the Portage Lake Volcanics are consistent with those used on the maps in the field guide. �C phc paf T Hancock conglomerate (No. 17) Ashbed flow pp 9000 — -— Pewabic West conglomerate (No. 16) pk Kearsarge flow pv Wolverine sandstone (No, 9) 4000- poc Old Colony sandstone (unnumbered) 3000pg Greenstone flow pa Allouez conglomerate (No. 15) 4 orta - Lak 'r,Icanics ph Houghton conglomerate (No. 14) 7000 pi Scales Creek flow psc 2000 - Iroquois flow —— = pc - conglomerate TI (No. 13) 1000P0 pkc flow Kingston conglomerate (No. 12) Pcc Copper City flow PS 5000 St. Louis conglomerate (No.6) Figure 5 continued. �8 STUDY AREA Lake Superior COPPER HARBOR INDEX MAP OF NORTHERN MICHIGAN EAGLE RIVER Fish Cove I..: LacLo_ atiot Lake Cambrian Jacobsvil le Sandstone Upper Keweenawan Precambrian loge - .-.•. . . 10 Miles Figure 6: Portage Lake Lava Series Intrusive or extrusive body Bedrock geology of the Keweenaw Peninsula showing the location of silicic to intermediate volcanic and subvolcanic rocks (from Robertson, 1975). �9 locality of abundant and widespread low temperature alteration minerals (Table 1). Penetrative deformation did not accompany the metamorphic episode and primary textures are preserved even in the most intensely recrystallized areas. Copper Harbor Conglomerate The Copper Harbor Conglomerate conformably overlies and locally interfingers with the Portage Lake Volcanics (Fig. 3). It varies in thickness from about 100 m to 1800 m. The Copper Harbor Conglomerate is a red—brown basinward—thickening wedge of volcanogenic clastic sediments. These clastic sediments fine distally and up— section. Sandstones are lithic graywackes and conglomeratesare composed of volcanic clasts with a ratio of mafic to intermediate + silicic composition of about 2:1 (Daniels, 1982). Daniels (1982) has interpreted the Copper Harbor Conglomerate as Mafic to intermediate lava flows are a prograding alluvial fan complex (Fig. 7). interbedded in the exposed Copper Harbor Conglomerate (Fig. 5). These lava flows are termed the Lake Shore Traps and occur predominantly within the middle section of the formation. Nonesuch Shale — The Nonesuch Shale is a succession of gray—black siltstone, shale and sandstone which overlies and interfingers with the Copper Harbor Conglomerate (Fig. 3). The Nonesuch has a thickness of between 40 m and 215 m. The Nonesuch was deposited in a reducing, rift—flanking lacustrine environment initiated through disruption of drainages (Fig. 7) (Daniels, 1982). This differs from the over and underlying redbeds that formed in an oxidizing environment. Freda Sandstone The Freda Sandstone is a cyclic succession of red—brown, ferruginous, sandstone The Freda and mudstone overlying and gradational with the Nonesuch Shale (Fig. 3). It is dominantly fluvial in origin with has a maximum thickness of over 3700 m. The top of this greater compositional maturity than the Copper Harbor Conglomerate. formation is not exposed. Jacobsville Sandstone The Jacobsville Sandstone is a red to bleached white succession of coarse—to—fine— grained feldspathic and quartzose sandstone with varying amounts of siltstone, shale and conglomerate which rests in fault contact with the Portage Lake Volcanics in the Keweenaw Peninsula. Elsewhere it can be found overlying Middle Precambrian basement. Jacobsville is probably slightly younger than Freda Sandstone. Jacobsville has a Sandstones are fluvial in origin whereas conmaximum thickness of over 3,000 m. glomerates are believed to be alluvial fan deposits (Kalliokoski, 1982). Structure Structure of the Keweenaw Peninsula is dominated by the Keweenaw Fault (Fig. 4), a high angle reverse fault where older Portage Lake Volcanics are thrust to the Both units are affected by this major northeast over younger Jacobsville Sandstone. the normally flat—lying Jacobsville Sandstone is often strongly tectonic feature: deformed by drag folding near the fault contact and the Portage Lake Lavas are often highly fractured. The Keweenaw Fault cuts off the base of the Portage Lake Volcanic Series along its entire strike length so that the total stratigraphic thickness �__ 10 NONESUCH SHALE DEPOSITION POSSIBLE "LAVA-DAMMED LAKE" MODEL FOR SANDSTONE FREDA STREAM BRAIDED FLUVIAL BASIN MA IN BASIN CENTRAL FLUVIO-DELTAIC 0 00 0 O - LUVIQ°Th 0 o 00 0 o° x0 x 0 0 0 0 PORTAGELAKExVOLCxANICSxxX x O 0 0 x x _— o0xxXxx XXX 0 CONGLOMERATE 0 o_—T 0 ALLUVIAL°PLAIN OCOPPER HARBOR 0 0 x 00 x - x - x : x x tINTERFLOW 0 0 SEDIMENTS X -------- ±±± RELATIVE PAL ED F LO W DIRECTIONS Figure 7: Schematic diagram showing the interrelationships between major stratigraphic units found northwest of the Keweenaw Fault in the Keweenaw Peninsula (from Daniels, 1982). x �:ii Table 1: Secondary minerals found within the Portage Lake Volcanics, Keweenaw Peninsula, Michigan (from Butler and Burbank, 1929; Stoiber and Davidson, 1959; Jolly and Smith, 1972). Widespread Minerals Locally Important Minerals Rare Minerals Laumontite Analcime Apophyllite Prehnite Sericite Atacamite Pumpellyite Orthoclase /Nicrocline Bowlingite Quartz Chalcedony Brucite Epidote Thompsonite Chlorastrolite Albite Natrolite Chrysocolla Chlorite Chabazite Cuprite Hematite Native Silver Faujasite Sphene Sulfides Fluorite Calcite Arsenides Powellite Native Copper Datolite Serpentine Heulandite Stilbite Ankerite Tenorite Sulfates Tourmaline Clay Minerals Whitneyite Wairakiite �12 The regional tectonic as well as the total displacement along the fault is unknown. context of the compressional stresses which caused development of major reverse faults is unknown at the present time, although it is probably unrelated to processes which formed the Mid—Continent rift. — The Keweenaw strata dip moderately northwesterly toward the centr of the Lake This Superior Basin and their dip angles increase toward the base of the section. is in part due to modification attributed to the Keweenaw Fault, but White (1960) has demonstrated syn—depositional downwarpage of the basin. Thus, lava flows and sediments formed wedge—shaped beds thickening basinward such that a relatively constant horizontal datum level was maintained throughout the life of the basin. Smaller scale, post—depositional folds are also present as broad synclines and anticlines (wavelengths from 5 to 10 miles) (Fig. 8). The regional context of these folds is not clearly understood, however, they appear to predate major reverse Late high angle faulting occurred throughout the area and produced several faulting. major offsets of the Keweenaw Fault. This type of fracturing and faulting is partiSignificularly abundant in the upper portion of the section northeast of Mohawk. cant deposits of massive native copper later filled many of these cross—cutting channelways (summarized from White, 1968). Mineralization and Alteration The Keweenaw Peninsula is the location of a dormant billion—dollar copper mining district. From 1845 to 1968 the mines of the Keweenaw native copper district produced about 11 billion lbs. of refined copper (Weege and Pollack, 1971). The major ore producing horizons are geographically restricted to a 45Km long belt within the Portage Lake Volcanics in the Keweenaw Peninsula (Fig. 8a). There is a close relation— ship in both time and space between native copper mineralization and alteration in the Native copper, the principal ore mineral in the Portage Lake Volcanics (Fig. 9). Keweenaw Peninsula, occurs in amygdaloidal and brecciated flow tops, interflow conglomerate units, and fracture systems (Butler and Burbank, 1929; White, 1968 and 197la). The predominant native copper deposits are lenticular blanket—like ore bodies that are found along certain stratigraphic horizons such as the tops of lava flows and conWeege and Pollack (1971) estimated that 58.5 percent of the district glomerate beds. copper production came from flow top ore bodies and 39.5 percent came from conglom— erate ore bodies. The remaining 2 percent of copper production was from fissure (or vein) ore bodies. There are three main varieties of lava flow top recognized in the Keweenaw native 1) fragmental or flow top breccia; 2) nonfragmental! cellular copper district: or vesicular basalt; 3) "scoriaceous" or flow top breccia with a sandy or silty White (1968) estimated that 21 percent of the lava flow tops in the Portage matrix. Lake Volcanics are brecciated (fragmental). These flow tops consist of a rubble of The interstices between fragments and the vesicles are vesicular and massive lava. commonly filled with secondary minerals. Most of the major flow top (amygdaloid) copper ore bodies are of the fragmental type. White (1968) has estimated that uppermost 5 to 20 percent of most individual lava flows is vesicular and contains between 5 and 50 percent vesicles which are commonly filled with secondary minerals. The abundance of amygdules decreases downward and the middle and lower parts of flows The tops of these flows are locally termed cellular are amygdule—free massive basalt. Cellular amygdaloid may have traces of native copper but and often have smooth tops. �1968). White, (from district copper native Keweenaw B. the of Folds amygdaloids. in quartz of limit northwest approximate the is line dotted The amygdaloid. (ashbed) Atlantic 7) and amygdaloid; Royale Isle 6) amygdaloid; Osceola 5) amygdaloid; Pewabic 4) amygdaloid; Baltic 3) amygdaloid; Kearsarge 2) conglomerate; Hecla and Calumet 1) production: of order in number, bold the by identified are deposits Major 1968). White, (from district copper native Keweenaw the of map Geologic A. 8: Figure 3 •l �14 Eagle Harbor Section • o,f4 FEET Top of Portage Lake Lava Seriea I Hancock Congl. 2000 I-Il I Greenstone Flow Allouez Congl. — Houghton Congi. Calumet & Hacla Congl. 0 I - I - 2000 King8ton Congl. PUMPELLY lIE ZONE Kearaarge Amyg, 4000 Scale8 Creek Amyg. 8000 Upper Limit of Zone at Dehydration Gratlot Flow Bohemia Congl. 8000 10,000 Keweenaw Fault - I EPIDOTE ZONE 12,000 Micwcline — Chlorite —— — Epidote — — — — Pumpellyite — — — Prehnite — — — Copper — — — — Datolite — — — — Silver — — — — Ankente — — Quartz — — — — — - Sericite — — — — Colcte — — Arsenides — Sulfides — .-_ — — — — — Albite — — .._ Aduloria — — — — Saponite — — — Laumontite — — Analcime — — Sulfates(barite,anhydrrte, gypsum) Figure 9: A. Distribution of secondary minerals in the Eagle Harbor section of the Portage Lake Volcanics (compiled from Butler and Burbank, 1929; Jolly, 1974; Jolly and Smith, 1972; Stoiber and Davidson, 1959; White, 1968). Location of section is between Copper Falls and Delaware Mines shown in Figure 4. B. Paragenesis of secondary minerals in the flow tops and veins (from White, 1968). Solid black symbols are the more abundant minerals. Secondary minerals shown here are nonmagmatic and not of supergene origin. �15 — A few smooth topped flows show a tendency no ore deposits are only of this type. forming what are locally for the amygduies to be laterally interconnected in bands, important host rock for ore termed "coalescing cellular amygdaloid". This is an "ScoriaceouS" amygdaloid is used locally for flow top breccia at the Quincy Mine. filled with sandy or silty in which interstices between vesicular fragments are mineralized example of The Ashbed amygdaloid is the onl-y significantly detritus. this type. — native copper deposits, Conglomerates interbedded with lava flows are host for major of copper distrifundamental control The particularly in the vicinity of Calumet. Permeability is decreased by conglomerate. bution is the permeability of the host greatly on sedimen— Localization of ore depends abundant fine detrital material. which might bedrock topography tological and environmental factors, such as the conglomthickness of influence location of a stream channel resulting in differing erate. — right deposits are tabular and commonly crosscut the bedding at nearly Large masses of native copper weighing many tons were first angles to strike. the fissure deposits. These deposits are economically much less discovered in types. important than the other Fissure Copper sulfides are a minor constituent of the system, and are found as small veins cutting the flow top native copper deposits, joint—coatings in the conglomerate units, and in association with Mt. Bohemia intrusive (Butler and Burbank, 1929; Copper sulfidesandarsenides are paragenetically Broderick, 1931; Robertson, 1975). Significant copper sulfides with minor late in flow tops and conglomerates (Fig. 9b). native copper also occur at the base of the stratigraphically higher Nonesuch Shale and top of the Copper Harbor Conglomerate (Brown, 1971) at White Pine, approximately 70 Km southwest of most of the discovered mineralization in the Keweenaw Peninsula. The solutions that formed the White Pine deposit may have been related to those which formed the deposits in the Keweenaw Peninsula (Ensign and others, 1968). Vesicular and fragmented flow tops of the Portage Lake Volcanics were prevasively altered by hydrothermal fluids, producing low temperature metamorphic mineral associations occurring as amygduie and vein fillings as well as whole rock replacements in the most permeable hOrizons. The systematic metamorphic zoning varies vertically within the volcanic pile and is equivalent to zeolite, prehnite—pumpellyite facies (Jolly and Smith, 1972; Stoiber and Davidson, 1959), and possibly lower greenschist facies (Fig. 9a). The copper deposits lie stratigraphically within the pumpellyite The copper, in the deposits, may have been leached from dehydrated lava flows zone. (epidote zone) in the deep parts of the pile and migrated up dip and precipitated in the zone of hydration where conditions were sufficiently reducing (Jolly, 1974; Scofield, 1976; White, 1968). These workers and Cornwall and Rose (1957) suggest that most of the copper was probably initially tied up in Fe—Ti oxides and their oxidation released the copper. The oxidation reactions of magnetite to hematite and pumpellyite to epidote may occur along with native copper deposition (Jolly, 1974). The intensity and degree of alteration varies as a function of position within individual flows, position in the volcanic pile, and proximity to cross—cutting fractures (Jolly and Smith, 1972). Local controls, such as pre—alteration composition, appear to govern the assemblages of final alteration products and their major—element compositions. Figure 10 shows a summary of known elemental mobilities and a schematic picture of alteration conditions. �PERMEABILITY LITHOLOGY DIA GNOSTIC MINERALOGY Added to flow top Redistributed within flow Hgh '''''' e'°r : FLOW TOP - FLOW INTERIOR Low , None —r---- Pumpellyite Epidote Metadomain - Ca Al f .. Albitized Basalt Albite Chlorite Unmetamorphosed Basalt Ca—Plagiociase 16 ELEMENT MOBILITY from Outside flow - 114 Na Clinopyrosepe Olivme Si - - 1 H2 Lost from flow top Remained Immobile — K, Fe, Ti, Mg, Zn Cu —w- Cu(s) HO—*-HO 2 (p) 2 Ni Ce) Elements Remained Immobile I. DEPTH 4. TEMPERATURE I Basal chill zone ii Least—altered flow interior lIE Amygdular flow top Arrows denote tluid movement Figure 10: A. Possible elemental mobility pattern in an idealized lava flow in the pumpellyite and epidote zones within the Portage Lake Volcanics (based on chemical data of Jolly and Smith, 1972; Jolly, 1974; Scofield, 1976; Stoiber According to Jolly (1974) Cu and H20 were derived from and Davidson, 1959). the epidote (dehydration) zone and deposited in the pumpellyite (hydration) zone. Diagrammatic regional model for the Portage Lake Volcanics showing local B. thermal/chemical gradients superpositioned on the regional geothermal gradient and showing the movement of fluids along flow tops and bottoms and through frac— tures (modified from Jolly and Smith, 1972; Scofield, 1976). �17 ROAD LOG AND STOP DESCRIPTION Mileage MAP 1 0.0 Assemble at the Memorial Union on University. Begin the field trip the northeast side of the Union. on a kame terrace to the south of the campus of Michigan Technological from the circular drive lqcated on The Michigan Tech campus is located the Portage Lake. 0.1 Right turn. 0.2 Immediately after there is a right turn on to Townsend Drive. Left turn. The Quincy Mine can be seen on the ridge on the skyline. 0.55 Left turn on Agate Street, where we go up the steep hill on the south side of the Portage. We are climbing off of the kame terrace. 0.8 Right turn on Seventh Street. 1.0 STOP 1. Scales Creek flow on Seventh Street, City of Houghton. This stop is marked by a prominent ridge of ophitic basalt, which is an outcrop of the Scales Creek flow, one of the great Keweenawan flows, which can be traced continuously for a strike length of more than 160 Km along the Peninsula. It is about 70 m thick, with an amygdaloidal top which is typically not resistent and a prominent, ridge—forming, ophitic core. The ridge at this site can be followed down hill all the way to Shelden Avenue, where it is covered by glacial deposits. It can be traced across the valley, where it passes through the Ripley School, a prominent brick building across the Keweenaw Waterway. This bearing, about N3OE, is the regional strike of the Portage Lake Volcanics which dip about 500 to the NW. Another clue to the attitude of the rocks is given by the Quincy #2 shaft house on the horizon which heads up an inclined shaft down dip along the amygdaloidal ore bodies of lava flows just over 2000 m higher in the Portage Lake section. Throughout the Portage Lake section between Baltic and Mohawk, most amygdaloidal and conglomerate zones show well developed zeolite and prehnite—pumpellyite facies metamorphism and native Cu mineralization. At this site the amygdaloids just below the Scales Creek flow are strongly mineralized. One mine, the Sheldon Columbian, operated just a few hundred m to the east in the early 1900's. This same horizon is exploited by a series of shafts called Isle Royale Mines, for several km to the SW. Stop 2 is at one of these mine dumps. The most obvious geomorphological feature here is the Keweenaw Waterway, The waterwhose origin was thoroughly investigated by Warren (1981). way formed in a fault zone like many which crosscut the Portage Lake stratigraphy. A bedrock valley, more than 200 m deep formed along the fault as a result of stream superposition through a cover of flat—lying This valley, like others on the Keweenaw, was deepened and sediments. widened by glacial erosion, in a fashion similar to the finger lake The complex glacial deposits, consisting of region of New York State. moraines, terraces, varved clays and gravels were the result of the pattern of ice retreat from the region, which had profound and complex effects on the drainage patterns. �/ 71! /, )- - II 55 NJ/' C ft7 D— G N I - -. IStOP 2• -. // / J /1 /11 i// /1 9SGIS1eYaChASHAFT —/ / Li -- d \\\\ P L - 12 p /_ - K E C •==- — I / I ' H San ds1;i one ••°' - _ji _____ C0LL6E OF MINING AND YE CN0L0G \_y' __________________ 46' SSa 907 si _________ _____ \/ I A 1/ 1059 4 +1 /1 R2 Jdevii1e - - -: . 1M7 --- L . --;•: //r '-4 / A ______ T -- — 10 II /R 567/ -7 0 607 .4- - />7) // -/ t.• I - // - H - — NC - Map4 - , — - •MAP 1 �19 1.1 Left turn on Portage Street. 1.25 Grand Portage Mine dump on left. 1.45 At this spot the Scales Creek ridge is Near the Houghton water tower. slope exposed higher on the south of the Keweenaw Waterway. There are many bald knobs with more or less east—west trending deep glacial grooves on them. To the east of the prominent ridge, there are many mine oprIings from the series of Isle Royale shafts. The Adams Township takes its water supply from these Isle Royale mines which are now filled with water, and this is the source of water for Hancock and several other towns. 1.55 Cross Sharon Avenue and continue on Portage Street east of the City of Houghton fire station. 2.15 Right turn immediately followed by a left turn so we are now on Bridge Street heading south. 3.0 Entering Dodgeville. On the right hand side of the road is one of the prominent Isle Royale mine dumps. 3.2 Center of Dodgeville. If you turn on the road to the right through the Trailer Park, there is access to the Isle Royale mine dumps from Shaft No. 4 and 5. The Isle Royale Mine is described at Stop 2, continue ahead. 3.6 Junction to the Green Acres Road and make 3.7 STOP 2. Isle Royale Shaft No. 6 a right turn. mine dump on the Green Acres Road. The Isle Royale mine worked the top of the Isle Royale flow. Production from the Isle Royale amygdaloid began in 1855, the mine closed in 1948. A total of about 350 million lbs. of refined copper was removed from this mine (Weege and Pollack, 1971). The Arcadian Mine (see Map 4) may also work the Isle Royale amygdaloid. The Isle Royale flow varies in thickness but is about 70 to 150 ft. thick and lies just below the Scales Creek flow discussed in Stop 1. It dips about 50 to 60° to the northwest (Fig. 11). A gentle fold accounts for the curvature of the flow (see Map 1), Isle Royale syncline. The flow from the top down is characterized by fragmental zone, banded amygdaloid, foot inclusion zone, The fragmental zone consists of irregular fragments and massive main trap. of amygdaloid and fine—grained basalt ranging from small grains to tabular The vesicles and spaces between the blocks several feet in long direction. secondary minerals. The banded amygdaloid is an fragments are filled with considerable area. Amygdules are commonly abundant unbroken rock body over zone a banded appearance. Below the fragat certain horizons giving this amygdaloid is the foot inclusion zone which is indemental zone or banded foot inclusion The finite patches or inclusions of amygdaloid basalt. devoid of amygdules (summarized zones grades into massive basalt practically from Butler and Burbank, 1929). �L_, I. _J —, - - Le Vc ific Ss S iac 11: Cross section A—A' on Map 1 (from White, 1956). Labels are as follows for the Pewabic West conglomerate (pp), Creenstone Portage Lake Volcanic Series (P) and its subunits: flow (pg), Allouez conglomerate (pa), Calumet and Mecla conglomerate (pc), Kingston conglomerate (pkc), National sandstone (pn), Kearsarge flow (pk), Wolverine sandstone (pw), Scales Creek flow (psc), Bohemia conglomerate (pb), St. Louis conglomerate (ps), Baltic conglomerate (pbc), and Unnamed conglomerate (pu). Figure P ...vIIIe A' �21 Butler and Burbank (1929) recognized two distinct periods of alteration. The earliest alteration was oxidation which caused the development of This oxidation could essenhematite, which produced reddened basalt. alteration shortly after eruption. tially represent deuteric The second after the period of alteration was probably flows had been tilted. This period was complex and resulted in deposition of native copper. This stage :L divisible into three substages: 1) An early stage of deposition of epidote, pumpellyite quartz, calcite, most of the native copper and minor prehnite, alkali feldspar, and laumontite; 2) an intermediate stage characterized by the development of sericite with quartz, calcite, anhydrite, gypsum and minor barite; 3) a final stage of copper sulfides and arsenical copper accompanied by calcite, sericite, quartz, chlorite, and specular hematite occurring in numerous veinlets. Stoiber (unpubthe following estimate of the lished data) made percentage of alteration the Isle Royale Mine: quartz, 26— minerals on dumps from four shafts of 59; calcite, 5—39; prehnite, 6—32; pumpellyite, 1—17; epidote, 1—10; sericite, 0—12; chlorite, 0—3; K—feldspar, 0—trace. This dump and the ones near Dodgeville are freshly reworked and good specimens of native copper and alteration minerals can be found. 3.9 Junction M—26 at the Copper Country Mall and you are going to make a left turn. MAP 2 5.6 Entering Atlantic Mine. 6.9 Right turn at the sign that says South Range Village Limit and drive about 150 yards into the road and walk to the right through a notch up the hill another 60 meters to Stop 3, the South Range Quarry. NW SE Felsite bed 9 IEE Fragmental amygdaloid i Non-fragmental amygdaloid 190 FEET F(a) Masve basaft PegmatEte layer (a) and zone of thin Figure 12: Geologic profile of the South Range quarry along the northeast wall (from Cornwall, 1951; White, l97lb). Location of the quarry is shown in Map 2, Sec. 17, T54N, R34W. �22 C ;: 52 // p —q w• • . njflfe San .one I �23 STOP 3. South Range Quarry. South Range quarry provides an excellent cross sectional view of a massive to amygdaloid lava flow (Fig. 12) of the Portage Lake Volcanic Series. The base of the section is a conglomerate bed, about 4 m thick; it is exposed This is overlain by an 18 m thick fine— on the main path to the quarry. grained basalt flow, followed by a 42 m thick ophitic basalt flow and finally the lower 17 m of another ophitic basalt flow. The conglomerate is well indurated and consists mostly of pebbles and cobbles of rhyolite with subordinate clasts of basaltic lava set in a sandy matrix of similar composition. The clasts are subangular to sub— The overall character is similar to the Copper Harbor Conglomrounded. This conglomerate is erate which will be seen later in the field trip. one of a number of sedimentary beds which are interbedded with the Portage This particular bed is correlatable with the National Lake lava flows. Sandstone, a marker bed in the Nass—Rockland area. The basalt flow that occupies most the quarry face has features which The characterize the thicker flows of the Portage Lake Volcanics. lower half of the flow is massive basalt, overlain by a zone with progressively smaller pegmatitic layers, topped with cellular amygdaloidal basalt, and at the top a discontinuous layer of flow top breccia (called fragmental amygdaloid). A typical pegmatitic layer, consists of 4 cm to 1.3 m core of green amygdaloidal lava surrounded by a 4—9 cm border zone at the top and bottom. The border zone is composed of a medium to coarse grained aggregate of albite/oligoclase, augite, ilmenite, and magnetite. Pegmatitic layers toward the top of the zone are more amygdaloid. Quartz, prehnite, and a green or red cherty substance occurs in flattened vesicles The pegmatitic layers are products of cooling at the top of the layer. and differentiation as it cooled (description of pegmatitic layers from Cornwall, 1951). Amygdules and interfragmental spaces are filled with Locally the basalt is quartz and prehnite containing traces of copper. intensely epidotized or prehnitized. Outside of the Quarry and to the north are a series of glacially grooved outcrops in which the exposures of the pegmatitic zones are spectacular. Take a right turn on M—26, going into the town of 7.9 Return from Stop 3. South Range. 8.4 At stop sign in South Range, take a left turn. 8.6 Right turn at the church and immediately foiJowed by a left turn as the whole road jogs to the left. 8.7 Entering the town of Baltic. 8.8 Right turn. 9.2 The main road turns to the left, we go to the right on a small paved road driving past a concrete building towards some very large mine dumps. �24 9.4 STOP 4. Baltic Shaft No. 3 Mine Dump. The Baltic, Champion, and Trimountain mines worked the Baltic amygdaloid. Total proThe Baltic Mine opened about 1898, the others opened in 1902. duction from the Baltic amygdaloid was about 1.85 billion lbs. of refined copper which was the third largest producer in the Keweenaw native copper district (Weege and Pollack, 1971). The amygdaloid was developed for about 7 Km along strike and to the 38th level in the Baltic Mine. The Baltic flow is an ophite that varies considerably in thickness but The Baltic amygdaloid in many places is 17 m is around 50—70 m thick. or more in thickness and is composed of fragmental amygdaloid, the average stoping width is about 5—8 m. However, like all fragmental amygdaloids of the district, there are significant variations, e.g. the lode can thin to only a few feet thick composed of trappy or cellular amygdaloid. The lode dips at about 70°NW (summarized from Butler and Burbank, 1929). The abundant minerals associated with copper in the Baltic amygdaloid are Copper sulfides are unusually quartz, pumpellyite, epidote and carbonate. The sulfides characteristically occur in fissures that dip 75 abundant. Most of the copper sulto 900 and strike nearly parallel with the lode. fide in the lode is chalcocite associated with iron—bearing carbonate, there is some bornite and rare chalcopyrite. Native copper is irregularly distributed through the amygdaloid ranging from minute specks to masses weighing several tons. Native copper occurs at the margins of sulfide veins and it may occur with quartz in the center of veins. Sulfides are in general paragenetically late (Fig.9h Introduction) (summarized from Butler and Burbank, 1929). The majority of the dump at this stop is amygdaloid basalt. R. E. Stoiber (unpublished) made the following estimate of the percentages of the seconcalcite, 91; quartz, 5; epidote, 3; dary minerals in the dump as a whole: Paragenetically epidote and chlorite were early minerals; chlorite, 1. calcite, quartz and native copper were intermediate; and copper sulfides Excellent specimens of chalcocite and iron—bearing carbonate were later. can be found on this dump as well as native copper. 9.4 Retrace route in Baltic. 9.9 Stop sign in Baltic, make a left turn to go back in the direction of South Range. 10.1 Right turn, immediately followed at the church by a left turn. 10.3 In the center of South Range, right hand turn off M—26. 10.8 Passing the South Range Quarry, Stop 3. 12.5 M—26 jogs to the right at the center of Atlantic Mine �25 MAP 3 14.7 STOP 5. Glacial Deposit Near Pamida The Keweenaw Peninsula has probably been modified by all of the major glacial episodes of the Pleistocene. During maximum glaciation the entire Keweenaw Peninsula is believed to have been overridden by around 3000 m of ice. The present form of Portage and Torch Lakes is related to the final retreat of the Laurentide ice sheet in the Lake Superior The final glacial advance and stillbasin (shown in Figs. 13 and 15). stand over the Keweenaw Peninsula was made by the Keweenaw Bay Lobe, marked by an end moraine of Wisconsin stage (Fig. 14) (summarized from Warren, 198]). The earliest recognized channel cut by drainage through the Portage Gap area is the Huron Creek channel (Nap 3). The channel is waterworn bedSince there is no delta at the southern end rock due to southward flow. of this channel perhaps the source of water was a large lake where glacial The drainage sediments had time to settle before the water was removed. in Fig. 16 (summarized from pattern through the Portage Gap is shown Warren, 1981). A delta kame is just west of the Huron Creek channel and is the location The sediments, in this dissected knob, show strong of Stop 5 (Map 3). evidence of being deposited by a braided stream closely associated with Extreme variations in grain size and sorting occur within a a glacier. This suggests differing flow regimes during distance of a few meters. Poorly to well—worked unconsolidated sands predominate but deposition. Numerous cut—and poorly sorted pebble conglomerates are also present. Large striated boulders of basalt within fill structures are present. from a nearby glacier. This the gravel and sand must have originated large exposure is capped by a thin (less than one meter) poorly sorted clay till which thickens rapidly to the south; it is about 7 meters thick The later unit may be a flow till(?) at the top of the nearby hill. which slumped off the nearby glacier (description by S. Beske—Diehi and S. Nordeng, Dept. of Geol. & Geol. Engrg., MTU). 15.75 Between Junction of M—26 and US—4l, so turn right on US—4l past the Mobil and Erickson gas stations. 16.2 Excellent outcrop of basalt with exposed amygdaloid on both sides of the road. 16.35 Make a left U—turn back onto US—4l going one way back through the City of 1—loughton. 16.45 Amygdaloidal basalt with pegmatitic zones at Burger King Restaurant, Shelden Avenue, Houghton. This stop is an alternate to the South Range Quarry Stop. Excellent exposures of the cellular amygdaloid and pegmatitic interior of a thin Portage Lake lava flow are found to the west of the restaurant and along Montezuma The flow top is strongly metamorAvenue, just a few steps to the north. phosed with a variety of amygdule minerals of the prehnite—pumpellyite The green color of the basalt is due to the abundance of epidote. facies. Below the amygdaloid the basalt is virtually unmetamorphosed except where thin pegmatite zones cross it. �1I 4 0 6O7 R A T ) —. 4 I '',;ee1cii:.! 1 I 4 G 26 L E — ., �1981). Warren, 1976; Kalliokoski, 14: Figure (from glacier Lobe Bay Keweenaw the of moraine End / / e 80 Kilometers es ii M 0 F 0 Prest, 1975; Huber, (from America North central from retreat ice Wisconsin the during positions ice—marginal Speculative 13: Figure 1969). 46) (Fig. 1257A). Map Canada of Survey Geological 1969, Prest, K. V. (from basin Superior Lake the readvance, or surge, ice major Note Amenca. North central from RETREAT ICE WISCONSIN in H P H B NJ' y,.,. ,.4k,.,b,,,, Sh,,..,,d. K "fl". F 40 U j' ,)" L .• •' 27 �L-\' ii) o 5t - -- - -, - - - -?-- -- S — "0A P E - ( - -' - - .— T -"i /5S5 - S jS ji - !j ' - S -- I _\ S. S SI 5—- - QS.AUL -S-j - -- S - f I -- 1 S -' '< S S I \ /55( S ) - S7 sS S - - // HURP - ( ' )•J / - / At KE - /, .S\ 55 - - : S \_S . I / S 55 / - S S MUWAUKEE - 1 5 / S q S mo0/ S - - S. I :/fj'S.S ,jS/ :-r- S - /5 - \55 I - s - / /- S -S. _S___SS S 5CHICAGO Figure 55 S S S 55S\ /,/ ...5 I 5S / / —-S Enlarged view of ice—marginal positions during Wisconsin ice retreat 15: (from Prest 1969) . Note the major ice readvance in the Lake Superior Basin and withdrawal pattern over the Keweenaw Peninsula. S. �29 LAKE / WfSHBURN // / -.5 / I/ Figure 16: High level drainage through the Portage Gap during the Washburn Stage (from Warren, 1981). �30 16.9 Right turn on US—41/M—26 and crossing the Portage Lake Lift Bridge into Hancock. The bridge was built in 1957, and is designed to accommodate Great Lakes ore boats, who prefer the Keweenaw Waterway route to rounding Keweenaw The present bridge abuts the Hancock side of point in stormy weather. the canal at approximately the site of the old Quincy Mill where the tramway descended Quincy Hill from the mines. MAP 4 17.15 Left turn on TJS—41 into Hancock. 17.35 Right turn and immediately followed by US—41 going to the left but we go straight at 17.4. 17.5 Bear to the left on White Street. 18.0 Junction between White Street and Lincoln Drive which is US—41, we take a right turn. The fenced ground near this locality surrounds an area of recently caved ground, which is thought to be related to shallow stopes of the Hancock Mine. The detection and distribution of such openings is a problem of considerable concern to local authorities, since many mines had shallow workings, since towns grew up adjacent to mines and since maps of the underground workings are incomplete and/or inaccurate. 18.3 Turn off US—41 to the right to the overlook of the Keweenaw Waterway or Portage Lake which is Stop 6. STOP 6. Keweenaw overlook near Quincy Mine. This overlook, near the crest of Quincy Hill, allows a broad overview of all the previous stops and also the best general view of the Keweenaw The features which can be seen are, from east to west (left Waterway (Fig. 17). to right): 1) On the skyline, the knobby terrane of the Huron Mountains, which lie across Keweenaw Bay. The mountains are underlain by the Archean gneisses and granites of the Northern Complex, and are the main source 2) In the forearea for the extensive deposits of Jacobsville Sandstone. ground, underlying the flat topography of Jacobsville Sandstone is clearly The Jacobsville extends from the Keweenaw fault, which crosses visible. the Waterway just east of the Michigan Tech campus, across the Keweenaw The formation is genBay and under the Huron Peninsula (Pointe Abbaye). erally flat—lying, while all of the other rocks of the Peninsula dip north3) Within the town of Houghton several westward toward Lake Superior. ridges of basalt can be traced downhill, the most prominent being the The attitude of the Scales Creek flow horizon, where Stop 1 was made. Portage Lake flows and the alternation of resistent flow interiors and interflow conglomerates with less resistent flow tops makes site investigation work critical for construction projects, to accurately determine For example, depths to bedrock and to make hydrologic interpretations. site investigations of the extensive area south of the main campus, where the Michigan Tech Student Development Complex (visible from the overlook) is now located, provided the focus of several Masterts theses for students in Geological Engineering (Stevens, 1971; Hase, 1973). A �7 dVV i / 28 fl\ / I I // 4 _0 / i I / - 0 "HH< L -' / •/ -- - R - 2Z71L 7t z / r iA .•'.<;:Ir..r /1 // (( I _,_ t! II - r • G I / •0 - / / —: / \\ I. - / I I / • // 2? // / / Wewabic h(' / -.. // ---- / NA2 I II NA6 (CH!GAN 4N/ // A2!,'ll .fl. 1/ 2 A2/ /k' / // P -___-J ;LAK/E / 1 5 !s'c , \/ // , lI i//11 !r/z"v/ >1 - • _ wJI .1 L ./.7:E MaF5 - �View from Portage overlook facing south. Notable features include: 17: 1) Huron Mountains, 2) Flat—lying Jacobsville terrain, 3A) Scales Creek flow ridge, 3B) Student Development Complex, 4A) Houghton water tower at Isle Royale Shaft #1, 4B) Isle Royale dump 114, 4C) Isle Royale dump 115, 4D) Wheelkate Bluff (Trimountain, 5) Highway M—26, 6) Contact between the Portage Lake Volcanics and the Copper Harbor Conglomerate, 7) Houghton County Courthouse, 8) Quincy Smelter, 9) Michigan Technological University Main Campus. Previous stops are located with stars and stop numbers are prefixed with an S. Figure w �33 general map, showing the detailed bedrock geology of the City of Houghton (Holcomb, 1975) is used routinely by developers in the area. 4) On the skyline on the opposite side of the Waterway, beginning at the Houghton water tower a series of mine dumps representing the Isle This marks the Royale lodes can be seen extending into the distance. approximate route of the road between Stops 1 and 2, and shows the The knob on the skyline is Wheel— strike of the Portage Lake Lavas. kate Bluff near South Range which is one of several residual bedrock 5) The divided M—26 highhighs and is located just south of Stop 3. way is visible, traversing the glacial deposits described at Stop 5. 6) To the right, the Waterway traverses the upper contact of the Portage Lake Volcanics and the Copper Harbor conglomerate, Nonesuch Shale and Freda Sandstone. The Stop is the best single locality to observe the Keweenaw Waterway. The Waterway and the peninsula are named for an Indian word for Portage route, but to make the Waterway accessible to Lake Superior shipping, This canal work was necessary at both the northern and southern shores. The geological history of the Waterway was investwas completed in 1873. igated in detail by Warren (1981). This and other major bedrock valleys were formed by stream superposition as ancient rivers eroded through flat— But the valleys lying Paleozoic rocks into the tilted Keweenaw strata. Then the Pleistocene. were greatly deepened by glacial erosion during as the Keweenaw Bay sub—lobe retreated at the end of the Wisconsin glaciation, the Waterway allowed eastward drainage across the Peninsula to lower First, drainage occurred in the Portage Gap lake levels to the east. (between Houghton and Hancock) while a tongue of ice remained in what is As the ice retreated further, the valley now nowwestern Portage Lake. occupied by Portage Lake was formed by eastward drainage of successively Torch Lake was formed lower proglacial lakes in western Lake Superior. by a trapped block of ice which later melted in place to form the lake Warren's study includes a complete bedrock topographic map of basin. the Keweenaw and a series of maps showing the pattern of ice retreat, based on the distribution of glacial deposits. Houghton was named for Douglass Houghton, the geologist who sparked the Michigan copper mining boom by publishing his Michigan State Geologist Houghton was settled in 1852 and is the site of several Report in 1841. historic buildings, the most important of which is the Houghton County Courthouse (1887), a prominent yellow brick building with Jacobsville Sandstone facing and copper roof and a flag pole, on the hill above the main part of town. Hancock was settled in 1859. Across the road and just slightly up hill is Quincy Hill House (1871), the mine manager's house for the Quincy Mine. The Quincy No. 6 mine shaft house dominates the skyline behind the viewpoint. A map of the Quincy operations in its heyday are given in Figure 18. The inclined No. 2 shaft descends at about a 45° angle more than 3 Km (1.7 Km below the surface) making this one of North America'a deepest mines. The surface projection of the area mined is shaded on Map 4. 18.35 Right turn back on US—4l going up the hill. 18.75 Prominent outcrop of basalt with glacial grooves. �34 18.85 Right hand turn would lead to the Quincy Steam Hoist, we're in the center The Quincy Steam Hoist can be now of the Quincy Mine area (Fig. 18). visited during the summer months for a small admission charge. Inside is the largest steam mine hoist in the world. This great machine, invented by Bruno Nordberg and installed in 1920, could lift a 10 ton ore load at a rate of more than 1000 m per minute. The hoist is still in pristine condition and a full museum of the Quincy Mine is maintained inside as well. MAP 4 or 5 On the left hand side, immediately after 19.3 Turn right on Arcadian Road. the turn are some of the Quincy mine dumps, nearest Shaft No. 1. This will be Stop 7. Please respect private property signs and stay within the public right—of—way. STOP 7. Quincy Mine Dumps. The Quincy Mine worked the Pewabic amygdaloid. Production from the Quincy Mine began in 1856 and ended in 1967. Total production from the Pewabic amygdaloid was about 1 billion lbs. of refined copper, ranking fourth in the district (Weege and Pollack, 1971). Lankton and Hyde (1982) give an outstanding illustrated historical account of the history of the Quincy Mining Company which earned the name "Old Reliable" because it paid dividends so regularly. The Pewabic amygdalLoid deposit consists of a group of relatively thin flows. These basaltic flows are A geologic cross section is shown in Figure 19. Some texturally distinctly porphyritic with large feldspar phenocrysts. of the thicker flows have an ophitic texture. The tops of flows in some places are cellular whereas thick flows may be either cellular or fragmental. The amygdaloids of Pewabic flows are characteristically of a type Flows of this type typically have smooth termed ].ocally as coalescing. tops in which individual vesicles are larger than average, reaching an inch or more in diameter. VesiciLes in the same layer may coalesce to form a A series thin, jagged gash with a lateral extent of up to 12 feet or more. of such openings provided an almost continuous path for the flow of mineralizing hydrothermal solutions. Several such layers may occur in the same flow top. Where coalescing is well developed in the Pewabic amygdaloid there may be 2 to 10 layers from 3 to 5 feet thick. There is every gradation from coalesced layers of vesicles to those that show only a moderate tendency to collect in layers (summarized from Butler and Burbank, 1929). quartz is the most abundant secondary mineral assoCalcite is also abundant. ciated with native copper. Pumpellyite, epidote Laumon— and chlorite are common but not abundant and prehnite is present. tite and datolite are common in upper levels but not lower levels (summarized from Butler and Burbank, 1929). In the Pewabic lode, The majority of the dump at this stop is amygdaloidal to massive basalt. Secondary minerals in this dump are mostly quartz and calcite with lesser amounts of pumpellyite followed by epidote. Paragenetically epidote and pumpellyite seem to be early whereas quartz, calcite and native copper formed later. �__ 35 zz .../ ... V I _/ • / V ; /t \ \0. 3/ S Jl 0 I • •90:•.• — —-1 -I - - rj z / z N 7 NM j" , 4 - .v__ /' \ / I �I I J I I I :tI J ''j!J QUill~(CY MJINJE QUIENCY MI[NIE JLOCA1rJION LOCAT lION \ \ I _ ~...:r~, " HOU§JING AND HOUS]LNG AND COMMllJ:NJITY COMMUNIITY§TR1UC1r1UR1E§ STRUCTURES Co C0 f 92O R920 J 4 ClrXi5 Pdence C/zrko ~t.(Jence , 11 ff Metf,adtt Methodi.:;tG'7urd7 07urch 5tootom £7ce Mine O{flce (4 14 frank/in Franklin ichooL ochool. 7 Captaur.5 /ejidence Captalf1'.5 Re.5idence franklin Franklu7 .5dJool, icJ700l; Franklin (5 Old 1.5 Ola FranklU7 FrenkWi Franklif? (r~tl)~?) 1/. -" \..r f6 Pewdbic YcJioal ochoa, 15 Pewabic Qurncy ichoo/ QUI ncy SChool Mesnard" •••• Megn.-d -11' ~~.~~~_'~_'_~I._:-:"~"J' U~ '- ---:, \~~ r::~-,'c?::>' , .LI\D~ r;,~~:::/;:~cpJ I\~ J-1~(" G~' <S-' ;: \ .. /' '';\ '/ b;l ~' / \'1:1\ .. " ',,','1,/, \ .. '\ '~ ,~..- \ L.xe (" ,)'v , 9(8) VI \\,'I ,.~, . ~ :", ~ '\ ,®' ', . . '-<::\::i{,::;::: \ " ;. ';- .-;::~ -~_/. ." ~_. =--" ~ "'Ir)!~;'~~::[ • "' t.-" • "{"l'r J'\ : • ':". '" , "'-I' ~.~·:•. :t :, .~ •. '.. ..y~';" ;.~ ~,,"~ .~'. ~ J ',,- ~~ \0t"\' \", (/. 8 \"~ - • ""'. /\, ~.~., /' ~~. r ;' J 5inir: ,;:.O@ • ~ ••,. : ~~"~ / . .":./ ' ••• 0 ,', .. ';: . 'i' ~.- ---~ -J ' ' : . ' ' \VEl tV _ -- "'';'.', ~I)('I)'''' ~ Z ")~~ [1' •~ ,,' \: % ~~ ,~'-- ,.,~ - "I" ~ ,t; ~~ '~.~~",..~.~ ~ ~'f? ~.~ -':_. , 0®' R, .. , \Uti .. , . \ , ') fiu / " .",.. , j. 1'iin !'~inp ® #~:;~'s;ng- ~ .,. ,I Structures StructuH'.S of the the Quincy quincy 'A~G' .. h ';: ~ 'O6~/-,. '·~., ,., • .. /- • Figure 18: 18: ., . h'. i,; #.. . ~~---;- • II---~' J,:. ~, , •.•" . , . " ,®I'I. • ~ :---.-J.... ~ •. t. .... :;.:( ';:'~:\, ·1 " ~; '0\..;.), "~' " ~~i \.',' ~.~~~'i:::'--~., _~ --' .. i (~,",\~ .. /~.;/~~~,.~~I ,1r,-"\r .. ~,:,./... I -;:'1'" 'i'" . '''i;';~';cl:'' • , ',Ii', l'UI Franklin . , . , - ~ ,I, i/···' d,..... " " -![?'~' ..,.t .... ;l:~ '~~'-i.,~-",:~~"""... 6 -- , ~"" Pr I'is.,J)ir ,I .. >or ", ••h,c c- - - -. ~ (Y~'0'~0\ /~!e ,'" ',' u~ 8~~ _;t:,:~~'c~lL, N~6 ; _ , ' ~', @ ) . . W I Z . - ; - : - N 0 ? '~ -.----"'Cl.\ •• • .•~ . '"".•• , ~i~fr .. r '1'/" "J'II .. P~8bl('. •• ,-b~ ......, ~ ·~".I:.. ,I.', - ~ ,:_~. '~II '\!2~).J .... JuP<V,or"$~ '-~~> J!I ~ -______. ,;.,--::~ r'..... lt~ .•_, ~~_.:.- \ ~ ,\. ,'/ ~.~.~ ..••••·1".::"f! 4-ro CalumBt 4—eoca(umr "J,;t. ..... ~...",~" "~\"'':~'')\~;' ~. ,) , (,/",~ ~:;>{( \ :" ". ~ ':', \.-. " .... .., .. ', 5ord flaije 800rdinq ttouse /lhrth!5 OOX otDre 8. Abrth5 . Ii >;,,~/' (3. Jomei /1 Oa9r and i2w77pany fJ James, H ueaq8r cmcJ Wmp.'3ny Abrths /?;!..5ldence O<zorqe wr7e North::> .iderice •.~ -'9-~_ '., "0'., 6 =- .... ; ••-~ .,. , {i? IS Cat/)olle Olurcfiand arid Priest~ Prtest5 C.ti?olc 07urch /?Q.5idencØ R.e.:;ldence 5 9, :1' .. '. ~ . P<.-~ '.. 10 Clubhouse(öathhou5e) (l3athhouse) (0 Clubh,ue Ooctor:J Lbctcr f(e:,t.(Jence Rejtdene Dipetary DI,::;,oe=ary A9cnt5 f?e.5ldence idence k;Jent::> Z ,~ '. ~ I '----------:.~. ~;J: ~:h ~il!i t:/"2Ie' 1l: ~;H ica(e: ~ :~: 11T .~ "¥' '"F'""'C 'iIi: TT 4a:)}.~ i :1; 1um·:¥:-'.lf-----¥'-------, : r;11.. !I': Vl.U(1 • II] - , .\ I - 0 '~~•• ~ or, 'H~lJof A180 of C,e fuxaon me QlHncyMV74 kocy l.t:>cdctOn.,.no Locacror, a,ri Vte<nuy'(noC1dll} ------....... J0cation (['rom Lankton Lankton and and Tyde, Eyde, 1.982). 1982). location (crom Vnnty ( ~ ! 3 n~ a , l.v 0'> �s S' B- I I n ~l·(!,,.1 7""""- s .., c ~ 7/ 'N' J ~'C' ~ ~ "n",~ " .. .'!>'"<" ~teOa ~~ .".'_ L~ . I .J(VJ ' ~~,~eSUC; p ~ c -''' .c:= <' Copper Harbor Jacobsville -4000' I ., <P: ./ Figure 19: 19: Geological cross cross sectionfromB section from Bto to B' B' on on Map Map 30, 30, B' B' to to B" B" on on Map Map 4, 4, B" B" to to B"' B'" on on Map Map 5. 5. This This cross section section illustrates illustrates the the general general geologic geologic relationships relationships of of the the Keweenaw Keweenaw Peninsula. Peninsula. The successively by the the Copper Harbor Conglomerate, Conglomerate, the the Nonesuch Portage Lake Volcanics are overlain successively Shale and the the Freda Freda Sandstone. Sandstone. The Portage Portage Lake Lake Volcanics Volcanics are are in in fault fault (reverse) (reverse) contact contact with with the the Introduction). Labels for Jacobsville Sandstone Sandstone (see (see Fig. Fig. for the the Portage Portage Lake Lake Volcanics Volcanics (P) (P) younger Jacobsville are follows: Hancock conglomerate (phc), (phc) , Pewabic Pewabic West West conglomerate conglomerate (pp), (pp), Greenstone Greenstone flow flow (pg), (pg), are as follows: Allouez conglomerate Kear— canglomerate (pa), (pa), Calumet and and Hecla Hecla conglomerate conglomerate (pc), (pc), Kingston conglomerate conglomerate (pkc), (pkc), Kearsarge flow flow (pk), sarge (pk), Scales Creek flow (psc), (psc), Bohemia Bohemia conglomerate conglomerate (pb), (pb), St. St. Louis Louis conglomerate conglomerate (ps). (ps). W --.J �38 38 MAP 55 19.5 Entering Coburntown. Coburntown. This is is another one of the the communities that that sprung up around the the Quincy operations, operations, most of the the houses built and owned by by up Several ethnically distinct neighborhoods existed the company. Several existed "on "on the the hill" in in the the early early 1900's. 1900's. In lived on on the the In all all more than 6,000 people lived hill in in 1905. 1905. 20.45 Y in There is a Y in the road, road, we take the right hand branch which is essentially aa straight tially straight road with a sign sign saying saying Arcadian Arcadian Scenic Scenic View. View. 20.7 Passing a radio radio tower tower on on the the right. right. We are now crossing the the Scales Creek flow the top top of the small small ridge ridge (see (see Map Map 5). 5). The Arcadian Mine worked flow at at the an amygdaloid just just below below the the Scales Scales Creek Creek flow. flow. The amygdaloid may corcoran relate with the the Isle Isle Royale Royale amygdaloid discussed discussed at at Stop Stop 2. 2. North of the the road is is Shaft Shaft No. No. 11 of Mine. Stoiber (unpublished (unpublished date) date) of the Arcadian Mine. estimated the percentages of of non—metallic non-metallic secondary minerals in in the dump calcite, from Shaft No. No.11 as: calcite, 43; 43; prehnite, prehnite, 25; 25; quartz, quartz, 16; 16; K—feldspar, K-feldspar, 8; 8; epidote, epidote, 6; 6; pumpellyite, pumpellyite, 1; 1; chlorite chlorite 1; 1; and and laumontite, laumontite, trace. trace. 21.4 see the the largest largest part part of of Portage Portage Lake, Lake, Down to to the the right of of the the road road you you can can see of view is the field field of is basically Keweenaw Bay and the the Huron Huron Mountains. Mountains. Much of the flat—lying flat-lying Jacobsville terrane. terrane. 21.6 Road turns turns to to the the right right and and changes changes to to gravel. gravel. 21.8 descending off off the the Portage Lake Volcanic Volcanic Series Series across across the the Keweenaw We're descending Fault onto Jacobsville Sandstone. Sandstone. 23.0 have aa view of of the the Isle Isle Royale sands sands We are descending the the hill and and we have across Portage Lake in in Houghton. Houghton. These are tailings from the Isle Royale out and and into into Portage Portage Lake. Lake. dumps (Stop (Stop 2) 2) which were brought brought out 23.15 Junction with M—26 M-26 and and take take aa left left turn turn at at the the Portage Pottage Lake Lake Coal Coal Dock. Dock. 23.6 Entering Dollar Bay Bay on on M—26. M-26. MAP 66 25.2 of flat—lying Exposure of flat-lying cross—bedded cross-bedded redbeds of the Jacobsville Sandstone on the left hand side side of of the the road road (northwest (northwest side). side). STOP 8. 8. Jacobsville Sandstone. Sandstone. The Jacobsville Sandstone is a a fluvial fluvial succession of feldspathic feldspathic and quartzose quartzose sandstones, sandstones, conglomerates, conglomerates, siltstones, siltstones, and shales shales up to 1,000 m m thick (Fig. (Fig. 20a). 20a). There are no interbedded lava flows flows or cross—cutting cross-cutting dikes. The Jacobsville Sandstone is separated from the Portage Lake Valcanics Volcanics by the Keweenaw Fault, Fault, aa reverse reverse fault. fault. The Jacobsville Sandstone is is probably upper upper Keweenawan in in age and and may may be slightly younger than the the, Freda Sandstone. Sandstone. Current the Keweenaw Peninsula are to the northeast and east east Current directions directions in the suggests transport transport to to deeper parts parts of aa basin located located northeast of of which suggests Keweenaw Keweenaw Bay Bay (Fig. (Fig. 20b). 20b). West of Lake Gogebic thickness thickness and and current direc— directions tions suggest another deep deep part part to to the the basin. basin. East of Calumet, Calumet, near the the Keweenaw Fault (Stop (Stop 10) 10) the the Jacobsville Sandstone contains boulders of basalt which suggests a topographic topographic high in the the Portage Lake Volcanics north north of the the fault fault during during this this period period of of Jacobsville Jacobsville sedimentation. sedimentation. Metamorphosed �/ / / / ,0 /~(" / / // / .I,/""!' ... /Ci' ,;:"00' / , / /'pP .~ // /' ~ 56 / '-~~~ ..... / -....;,:~. / '086 • /// / //' // 39 // ." // II II II 1070 1070 , -I [ II II II II II II II II H \\ ,\ z , " \ 1068 ,__L_ — . II / / p- \\ H \' \\ \\ ,\. H "\\ ". —--•• , L ' p~~// ~\~. H... if] :=:;\ fr-- t1 16 II II r p N 0~ I~ 0 ,:;1'Q , '....... 0, NA/5Q .............. " II NAI3' II "'NA/5Q "" NA/3' " C'~ II :~<? H 1/ 1 0~ ....... .,,00 933 l ' ':O~ ....... CJO C, / 4, cL '\ 21 / ')0 -"',--- ""'--: ...... , . . . . ; /i /1 ~ ~\ \. 1 "( II II I I-=-- 4 A ~0 ...0 b~ --'~ , NAI7 NAI7 N-,~ Il /I It II J e~ ,~ ,000 ___ OFFSET _— OFFSET -4":t- ~0 14 i-- / KEWEENAW KEWEENAW FAULT FAULT c• \\ II .-:-1r;o.f6=====.=~ 15 N83 22 23 • 630 • : H Mill I,- 1 884 I, 'I ii I II" 'I. 913 / - "'-" '", / \. L )8 s. -T , --"J". /_-9_/ \ Stop8 602 602 \• \ "', - 0 V - II ii I, ou II * , H,;" II ,,'I; / CJ~ / ~O'" // 'so / / j .: // 668 ~ 11~ .~ /;:.~=J- ..--"--1-~~==-~;:./~ -: -- II JI-ij . - - If//// • -, ,... .~ .,;.: -:-- // // II /1I, // '1/ II // II /? /-::-~==;!/ 1, II ,726 26 / "// 11/ /,/ ,,/ ij "7 'l~' ,y 1- . 'l /,'l // 7, ~. /.1 ,'/ /1' ,,;1 ",' - "/ //' 800 :- H •- -j 4-\ Aap5 // / *0 ~0 27 62 // 26 ---- H >, \ "''-\ ,,----"'\ _ _ ;;:."'::- _F1_ \\ '\ \. '. 0,", "1L-B9~ --- ' , _ _ ,Q!=D_ M on pv, '\ ,--- ....—.. —'-.. 7 35 • 1 6 .. . MAP6 ~AAP ,,",, • �____ 40 Sandstone Thickness Current Directions 9400 Geophys. est. (ft.) 597 Weillft.l o 50 I j Km. B. A. I rocks Iron ranges 0 - 0 km mi 30 I 50 so N --...... ,. \ c. C. Figure 20: 20: Relationships of Jacobsville Sandstone Sandstone (from (from Kalliokoski, Kalliokoski, 1982). 1982). of Jacobsville Jacobsville Sandstone with minimum thickness denoted Thickness of denoted by +'. '+'. B. Current in the the Jacobsville Jacobsville Sandstone. Sandstone. C. Location of of Current directions in C. possible source areas iron formation staurolitic metasedimentary possible source areas of of iron formation and and of of staurolitic metasedimentary rocks. A. A. �41 iron-formation quartz-staurolite pebbles pebbles suggest suggest aa source source from from the the iron—formation and quartz—staurolite jacobsville Jacob sville sedimentation sedimentation was was preceded preceded by by aa long period of cratonic stability stability with with little little or or no no volcanic volcanic activity. activity. Erosion was was apparently initiated by late Keweenawan warping along the the mid—continent mid-continent rift rift system. system. The major movements on on reverse reverse faults faults were were after deposition (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). after Jacobsville deposition southeast southeast (Fig. (Fig. 20c). 20~. sandstones varies from from subarkose subarkose to to quartz quartz sublithic sublithic Lithology of sandstones arenite. There are some some beds of of arkose arkose and and quartz quartz arenite. arenite. Grain size size varies from from fine fine to to coarse. coarse. Quartz grains show show evidence evidence of of volcanic volcanic and and metamorphic origin. origin. Microcline is relatively relatively unaltered unaltered and and plagioclase is is unaltered to to highly altered. altered. Other clasts clasts include: include: volcanic rocks, rocks, schist, the minerals epidote, epidote, biotite, biotite, muscovite muscovite and and chlorite. chlorite. schist, shale and the Sandstone varies in in color color from from red red to to aa cream—white cream-white or or purplish—red purplish-red color. color. The color depends on on the the alteration of of ferromagnesian ferromagnesian minerals minerals and and the the amount of iron oxide deposited deposited as as rims rims on on feldspar feldspar grains. grains. Ripple marked amount of bedding surfaces surfaces and and cross—bedding cross-bedding are are common common in in some some localities. iocalities. Sandstones are fluvial stones fluvial and conglomerates probably represent represent alluvial fan fan deposits (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). At this this stop stop the the character character of of the the Jacobsville Jacobsville Sandstone Sandstone can can be be seen seen in in The exposures here can be the exposures on the left side of the road. the left side of the road. exposures here can be compared and contrasted to to Jacobsville that that will be seen at Stop 99 and Stop 10. 10. 25.9 the small small town town of of Mason. Mason. Mason was the the site site of company housing Entering the for for the Quincy mill operations operations from from 1890. 1890. 26.5 On the the right right hand hand side side of of the the road road is is an an old old dredge dredge which is is stuck stuck in in in Torch Torch Lake. Lake. This is the the C&H dredge #1, #1, built in in 1913, 1913, bought tailings in by Quincy in by in 1955 1955 and and used used until until 1967. 1967. 26.7 Now we pass pass the the remains remains of of the the main main buildings buildings of of the the Quincy Quincy Mill, Mill, built built in 1890 1890 to to accommodate accommodate steam stamps, required when when the Quincy operation operation in stamps, required the Quincy expanded to to the the Pewabic Pewabic Lode. Lode. 27.0 Along the road on the the left there there are more outcrops of flat—lying flat-lying Jacobsville Sandstone. 27.3 On the right, right, Torch Torch Lake. Lake. 27.7 On the right hand side of the the road road are tailings tailings which have been revegetated. revegetated. These tailings tailings now as we are entering Tamarack City are part of the the mill operation of the the Calumet && Hecla company mines and the the Calumet region region which have major mills located located at at Tamarack Tamarack and and Hubbell. Hubbell. 28.15 On the left hand side of the the road road are the the footings footings from from one of the the Tamarack Mills. MAP 7 28.6 On the right right hand side of the the road road are the the remains remains of a steam steam stamp stamp mill. mill. 28.7 Left turn, turn, going going up up the the hill hill toward toward Stop Stop 9. 9. Follow the paved road road which jogs a little little to to the the left left and and goes goes up up the the hill. hill. �__ _______ p 28 c/ / 5 \\ // ___ __ ___________ // i ''s / / //\ ;o367 /\' // TL 7 TL5 FaLls + 31 f I HIL / -LLVARY EM / 1 \ 36\ 42 MaD88 42 • J Cr C - Lake n en / 'S 'I I, ii' . T I \\\ \ II II II II /7 // 959 'I \ \ \ 12 1Ltp,9 . / mrs 1 \ &çubbell —;: -N ---- .. — •••S" 'so —\N ___--1-_ MapG ( MAP77 MAP \ �43 28.85 Cross the the old Copper Range Range railroad railroad grade. grade. 29.0 Sign indicating indicating Hungarian Hungarian Falls. Falls. This is is the the lower lower part part of of the the falls. falls. Continue going up the the hill, hill, straight straight ahead. ahead. 29.25 Junction of a a four—wheel four-wheel drive drive road road to to the the left. left. Stop and walk Stop here here and towards towards Tamarack reservoir/Hungarian reservoir/Hungarian Falls Falls upper upper part part where where excellent excellent exposures of of Jacobsville Jacobsville Sandstone Sandstone are are found found near near the the Keweeriaw Keweenaw Fault. Fault. STOP 9. 9. Hungarian Falls. Falls. The Keweenaw Hungarian Falls is is located located near near the the Keweenaw Keweenaw Fault Fault (Fig. (Fig. 21). 21). The Fault is reverse fault Volcanics and and Fault is aa reverse fault that that juxtaposes older older Portage Lake Volcanics the In this the younger Jacobsville Jacobsville Sandstone. Sandstone. In this locality, locality, the the Keweenaw Fault presumably dips dips at at a west similar to presumably a high angle to to the west to that that illustrated illustrated in Figure 19, in 19, Stop Stop 7. 7. The The Keweenaw Fault Fault at at the surface surface varies varies from from aa single fault single fault plane to to aa more complex complex fault fault zone, zone, such such as as described described hear near Structural relationship Lac La Belle. relationship of of beds beds near near the the fault fault also varies varies from steepened also steepened dips dips to to folds. folds. In general the the dip of the the In Portage Lake Volcanics and Jacobsville Sandstone Sandstone steepen steepen appropriately appropriately as one approaches the the fault. fault. as At Hungarian Hungarian Falls the At the fault fault contact causes very little little deformation of the Jacobsville Sandstone, the Sandstone, which which is is only only tilted tilted slightly. slightly. To To the west of of the fault fault at this this site site the the Portage Lake Volcanics are unusually shallow shallow If not not viewed in the If the context of of many many other other localities, localities, the the fault fault dipping. might not might not be recognized as such such a a profound feature, feature, and could appear as a a conformable contact. contact. The the fault fault exposure The contrast contrast between between the exposure here here and and that at at the the next next stop stop (Stop 10) at at Hungarian Hungarian Falls Falls is and illusthat (Stop 10) is striking striking and illustrates of rocks rocks along along this this major major feature. feature. trates the the structural variability of The Portage Portage Lake Volcanics near the The the Keweenaw Fault at Hungarian Falls conInterbedded sists of of basaltic lava flows sists flows with interbedded interbedded conglomerate. conglomerate. sediments make make up up aa small small part part of of the of the Portage sediments the stratigraphic stratigraphic section section of the Portage Lake Volcanics Volcanics and and are found found as relatively thin thin widely separated separated beds. beds. However, in the the Keweenaw Peninsula conHowever, here and at some other localities in glomerates glomerates within the Portage Lake Volcanics are either near or at the the fault contact. fault Walking downstream downstream along along the the stream stream to to the the upper upper and and lower lower falls falls allows allows examination of good exposures of Jacobsville Sandstone with cross bedding, of Sandstone bedding, interbedded shaly shaly and and conglomeritic conglomeritic horizons horizons and and many many typical arkosic redred— interbedded typical arkosic bed sedimentary features. features. 29.25 Turn around and and go go back back down down the the hill hill to to Tamarack Tamarack City. City. 29.8 Stop sign. sign. 29.9 Entering Hubbell 30.5 On the right are Calumet & & Hecla mill buildings which have recently recently been taken over over by by Michigan Michigan Tech Tech Ventures Ventures as as aa pilot pilot plant plant location taken location for for small small industries. Torch Lake is is still on the the right with many of the the tailings tailings out in in the the lake. lake. Stamp mill mill remains are straight Stamp straight ahead. ahead. Turn left left on on M—26. M-26. �Ta arack reservoir metal gra Jacobs yule sands tone 100 feet -.- z — fIIs D fault basalt c Ong!omer Figure 21: Geologic sketch map of the Hungarian Falls area (by J.M. Robertson, 1973). Basalt and conglomerate are part of the Portage Lake Volcanics. Note that north is toward the left margin of the page. �45 31.4 Entering the town of Lake Linden. The Houghton County Historical Museum is on the right hand side of the road. The building (1917) was donated by the C&H Company to the Houghton County Historical Society in 1963. Among the best displays are scale models of underground mines and a rich photographic record of the boom copper days. 32.2 Right turn on Ninth Street (the so—called Bootjack Road) in Lake Linden. 32.35 Follow the signs to the Lakes Left hand turn at two blocks after 32.2. This is Gregory Street. Drive—In Theatre. MAP 8 33.3 On the left hand side of the road is the Lake Linden cemetery. The road heads north along the Trap Rock River Valley. On the left hand side of the road at the top of the steep slope is the Keweenaw Fault. On the right hand side of the road is a flat—lying Jacobsville terrane. The Trap Rock River follows another of the glacially eroded, deep bedrock valleys described by Warren (1981). 34.5 Pavement ends. 34.6 The gravel road bears to the right. 34.9 Cross a bridge over the Trap Rock River. 35.0 Left turn at the Trap Rock Schoolhouse. 35.0 Cross the Trap Rock River again. 35.7 Left turn on to another dirt road that begins to go up hill. 36.1 Access to the Cross the railroad grade of the Copper Range railway. Natural Wall ravine for mapping purposes can be gained by walking a couple hundred yards to the left along this railroad grade and then walking along the stream valley up toward the fault line. 36.2 Poor exposures of flat—lying conglomerate beds within the Jacobsville Sandstone on the left hand side of the road. 36.4 Stop by an old wooden sign on the left hand side of the road. 200 meters to the left (south) to the Natural Wall ravine. STOP 10. Walk about Keweenaw Fault at Natural Wall Ravine. The Natural Wall is a bed of sandstone within the Jacobsville which has a near vertical attitude and because it is more resistant, it forms a On the sides of wall which extends outward from the walls of the ravine. the ravine the lithology of the Jacobsville here includes conglomeritic The attitudes of beds in the creek beds, sandstones and shaly horizons. flat—lying to the bottom change from east, to vertical and even locally overturned as the fault is approached. An anticline in the Jacobsville trends parallel to and 300 m east of the fault. West of the fault the Portage Lake Volcanics dip to the WNW at 35—40° (Fig. 22). �__ ______________ 7- II =" 46 -': '-,-; •=/_ rN. '/ - - -- - // _.>c I 0, /ö• - 0 -o ' Co 1 0 ' -, • - (,' I \Pj II '- (O' Cog,' ,,' ,< ' -Co " ,d/ ,-; d' / C 0 // / N' 0- N LU /12'i NN "N\ N • - - p\ -, F / ,,/, - /,,' -\ \\ ci 1 // , MI I, I, - e //4' / ,,,i'</ {7iiir ,,// \-" ,/\ / /IL[=== ci C ' \ —4 'C N ' " I -> (z,I4' , ,,\ k ," ". ,/,, =====' - ) -';tiiiiit V/11 __\\ — , 0- \ i I 17 -I ;3S? __WZZ ii4t - I ' P I - < - - r"N(N - ._:;:_ 4. ITC. - ,, ' 4- 0 - ci / .7 , il? -( _o— Sly) 07 I • — 1 : -I/,wI 0- —_. II 7___ /1/1/7- Co 'C I - ;r' 0 ,/ / - - \. \ ) - -/ // - I t - , NQN ci 0 - �47 . • : -. D / N -V l 'Ii 1 SC LE n thousmds of feet 1) // GN : I CL" HEA G.. 13Wfl1V — I I 11111! 1111 1-II 1111111 U II 111111 Figure 22: Geologic sketch map of the Natural Wall Ravine. Note that north is toward the right margin of the page. 2 �48 37.95 The beginning of pavement, we are entering the town of Laurium. 38.7 Left turn which is followed immediately by a right hand turn at the next stop sign on School Street. 38.8 Turn right. Junction of School Street and Calumet Avenue, which is US—41. This is Calumet, Michigan, the center of the Michigan Copper District, and a site of the Calumet & Hecla headquarters. Here Edwin Huribut discovered the Calumet conglomerate load in the early 1860's and this Greater became the most important ore body in the whole district. Calumet (including Red Jacket, Blue Jacket, Yellow Jacket, Laurium and Among many historic Rambaultown) had a population of 33,000 in 1910. buildings here are the Calumet Theatre (1900) and the C&H Community Library Building (1898). MAP 9 40.0 Entering Centennial 40.3 On the left hand side of the road you can see the Centennial Mine After closing in 1968, this mine was dewatered in the Shaft No. 6. This operation has since been abandoned. mid—l970's by Homestake. The Centennial Mine Shaft Nos. 3 and 6 worked the Calumet and Hecla The ore body lies up dip and northeast from the main ore conglomerate. body in the C&H conglomerate mined by the Calumet and Hecla Mine in the The C&H conglomerate yielded about 4.2 billion lbs. of Calumet area. refined copper, the largest lode in th district and is over one—third of the total production from the Keweenaw native copper district (total district production of about 11 billion lbs.). The C&H lode had the highest average grade in the district of 57 lbs. of Cu per ton of rock treated (Weege and Pollack, 1971). The Calumet and Recla conglomerate can be followed along strike for more Along most of this length it is less than about 1 m thick. than 65 Km. In the Calumet area it averages over 3 m thick and tends to thicken with The bed consists of north trending thicker and thinner zones depth. representing channels. At the Centennial Mine Shaft Nos. 3 and 6 thickness is often less than 3 m and the C&H conglomerate was deposited in The pebbles in conglomerate at Centennial a tributary stream channel. The pebbles in are almost all quartz—feldspar phenocrystic rhyolite. the main channel conglomerate are a quite varied suite of rhyolite and Main and granophyre with some quartz—feldspar phenocrystic rhyolite. tributary channel conglomerates tend to be coarser and contain less fine Outside of the 5—foot thickness contours the material where thicker. bed is usually shaly or sandy. At Centennial, copper mineralization tends to occur in bands with the bed and the intensity is related to the type and amount of interstitial material and location of pinch—outs or Higher grade areas are related to conglomerate with coarse barriers. sand or small pebbles as interstitial material, especially when pebbles Evidence and sand grains are quartz—feldspar phenocrystic rhyolite. also strongly suggests that the mineralized areas follow the axis of stream channels and grade is highest adjacent to the 5—foot thickness contour where the conglomerate bed increases greatly n thickness down These pinch—outs localized ore deposition from mineralizing soludip. Sedimentological relationships are tions that were migrating up—dip. �S. Q. -.7 4i 'J. idO I I, N N k-j: IC 7 /5 "4 -'-—--- —, I( - H I, C. dew b7 �50 important in exploring the conglomerate ore bodies (summarized from Wee and Pollack, 1971). 40.6 Entering Kearsarge, Michigan. 41.1 Stone boat on the 41.3 Right turn onto Water St1 .t just before the Wolverine Market. straight ahead on the main paved road. 41.5 STOP 11 is the Wolverine Mine dumps. There are dumps both on the right and left hand side of the road. The oner on the righL hand side of the road (south), just on the other side of some old buildings, ar somewhat dangerous because of bad ground. Mining in this are.a waS Very shallow (Shaft No. 3). The dumps on the left hand side of the road appear to be (Shaft ice. 2). much safcr Park along the road and walk about 100 in to right hand side of the road. Continue the north. The Wolverine Mine is one of seven different mines that worked the Kear— Centennial, South Kearsarge, &orth Kearsa rge, Ahneek. sarge amygdaloid: Allouez, Mohawk, and Seneca. Production of copper from the Kearsarge amygdaloid began in 1887 and stopped in 1967. About 2.3 billion lbs. of ref -i:ied copper Were produced frccn the Kearsarge amygdaloid making it the second largest producer of the Keweenaw native copper district (Weege and Underground workings are continuous far more than 12 Km Pollack, 1971). and extend down dip as much as 2500 m. The Kearsarge amygdaloid is one of the best documented ore bodies in the district. The Kearsarge flow has been recognized for a distance of around 55 Kit along strike, it lies directly above the Wolverine sandstone. The flow dips between 35 and 40 degt-ees to the northwest (Fig. 23). The interior of the Jt flow is a well developed ophite with a compositi:irI shown in Table 2. has an amygdaloid top that ranges from near zero up to 10 in in thickness. Just below the amygdaloid there is a zone in which the glow is distinctly Abundance and size ol porphyritic with tabular plagioclase phenocrysts. the plagioclase phenocrysts in this zone is variable but they can make up a large percentage of the rock and can be up to 2.5 cm in length. This zone. is probably the result of plagioclise floating during in situ crystallization of the flow. The stratigraphic and textural relRtionships makes this flow wore easiiv recognized than most. The near—surface thickness of the Kearsarge flow clearly shows that the most productive area is where it is thickest (Fig. 24). The flow top in the productive ares is Individual fragments mostly a fragmental amygdaloid (flow top breccia). are generally less than 15 cm in greatest dimension and contain nwnerous small amygdules. The fragmental amygdaloid makes up the uppermost part of the flow grading downward into banded cellular atnygdaloid with arnygdules This grades downward into a zone with fewer abundant at certain horizons. and large amygdules with less tendency to be found in bands and stilt further The amygdaloid top of the Kearsarg flow in downward into massive basalt. the mined area has an average thichness of around 2 rn (summarized from Butler and B'jrbsnk, 1929). �51 I A' A C ln,IIe 4000t1 Figure 23: Geologic map and cross section showing Mine and vicinity (modified from White and others, me Mine Shaft No. 2 dump (see Map 9). Labels are (pi); Calumet and Hecla conglomerate (pc); Osceola merate (pkc); Wolverine sandstone (pw); Old Colony conglomerate (ps). Table 2: Major—element composition of the Kearsarge flow (from Stoiber and Davidson, This is a weighted average exclu1959). sive of the top 12 feet and thus represents a close approximation to the original composition of the flow. the Kearsarge flow, Wolverine 1953). Stop 11 is the Wolver— Iroquois flow, as follows: flow (po); Kingston conglo— sandstone (poc); St. Louis Weight Percent Si02 A1203 Fe203* MgO CaO Na20 1(20 Ti02 MnO H20+ H20— CO2 Total ppm Cu 48.55 16.51 11.54 6.68 9.44 2.82 0.58 1.49 0.18 0.16 2.06 0.63 0.15 100.79 90 �52 300 Thickness 200 feet 100 Top of Wolverine sandstone C) CD 0 CD 0 a CD CD Butler and Burbank, 1929). Figure 24: Thickness of the Kearsarge flow (modified from from This is the near surface thickness along a strike distance of around 35 miles directly to Mandan (Map 20). The thickness is relative to the Isle Royale (Map ) underlying Wolverine Sandstone which is arbitrarily shown as horizontal. Th Chlorite Epidote Microcilne Hematite Prehnite Pumpellyite Quartz Sericite Native Copper Calcite early — TIME late Figure 25: Paragenesis of secondary minerals in the Kearsarge amygdaloid at the Wolverine Mine Shaft No. 2 (Paces and Bornhorst, unpublished data). The relationships are based on a limited megascopic and thin section study of samples from the Shaft No. 2 dump and may be modified slightly as research proceeds. The exact timing of the later minerals are difficult to determine because they do not occur together. �interior. flow Kearsarge the of outcrops find can one dumps 3 and 2 Nos. trace. quartz, and 1; Shaft the of vicinity the In prehnite, 10; epidote, 38; microcline, 51; calcite, minerals: of percentage following the estimated data) (unpublished Stoiber whole, a as dumps 2 and Nos. Shaft the For found. be can copper native with specimens Excellent 1 relationships. paragenetic their and assemblages mineral of variety a see to opportunity the have will you dump 2 No. Shaft Mine Wolverine the At trict. dis- copper native Keweenaw the in bodies ore amygdaloid of complexity the of illustration excellent an is amygdaloid Kearsarge the of area ductive pro- the within minerals amygdule of variation spatial and temporal The Bornhorst). and Paces of data unpublished of addition with 1959 Davidson, and Stoiber from summarized (mostly zones regional the within islands free prehnite and quartz are there that suggests data detailed zones. prehnite and quartz the within lies amygdaloid Kearsarge the Thus, scale regional a On mineralization. copper significant of limit the mark also may microcline of limit The boundary. zone quartz the straddle to appears ore copper richest The zones. mineral the than irregular more much is present copper native of amount The absent. is it until depth with irregularly decreases microcline of amount The depth. increasing with zone quartz the within content quartz in increase irregular an is There zone. quartz the within percent 15 about averages whole a as and depths shallower at percent 10 than less considerably is Quartz 27). (Fig. depth with vary mineralization copper native of grade and minerals amygdule the However, mineralization. copper native of grade the and banding between correlation strict no is There 25). (Fig. samples individual in seen relationships paragenetic the with consistent is This openings. remaining the in calcite of deposition finally and channel the of center the in epidote and quartz by followed channel solution the of parts outer the along first deposited been have would microcline and Chlorite channel. permeable a along moving solution hydrothermal a from minerals secondary of deposition by explained be may banding The 26). Fig. in corner wall hanging (north flow overlying the of base the in found is assemblage last The microcline. ± chlorite—calcite and epidote; ± calcite—microline calcite—epidote; quartz—epidote; microcline; ± calcite ± chlorite layer: amygdular the of top to bottom the mineral major five are from assemblages There bedding. to parallel roughly are bands The Table and 26 (Fig. 3). amygdaloid Kearsarge of bottom to top from minerals amygdule of arrangement banded a is there 3 No. Shaft Mine Ahmeek the In 25). (Fig. chlorite and calcite, copper, native quartz, are minerals formed latest the and minerals formed early are prehnite and microcline epidote, chlorite, Paragenetically spatially. and temporarily both vary assemblages mineral secondary The 1959). Davidson, and Stoiber from (summarized minerals amygdule secondary the with associated occurs copper Native sericite. and laumontite, pumpellyite, prehnite, chlorite, K—feldspar, epidote, calcite, abundant): of amounts lesser and quartz least to (most are whole, a as amygdaloid Kearsarge the in minerals filling space interfragmental and amygdule The plagioclase. replacing pseudomorphically pumpellyite fine—grained of consists basalt lyitized Pumpel— groundmass. cryptocrystalline to fine—grained a in set laths albite euhedral percent 60 about is basalt Albitized pumpellyitization. and albitization alteration: of types two by affected been has basalt top flow The oxidized. well is amygdaloid Kearsarge the in basalt The 53 �54 NORTH SOUTH Ii chlorite-mlcrocline-calcite SCALE Eli:; 10 0 3Oleet 20 copper ,, Contact between Kearsarge amygdaloid and overlying flow bottom Figure 26: Cross section of the Kearsarge amygdaloid showing the banding of amygdule mineral assemblages, Ahmeek Mine, 35th level, 399 to 500 feet south of Shaft No. 3 (from Stoiber and Davidson, 1959). The footwall is the bottom of the Kearsarge flow. Data from the back and walls are projected to a horizontal plane. In one mapped locality Stoiber and Davidson (1959) found a laumontite—quartz—calcite zone. Amygdule mineralogy of the various zones are given in Table 3 below. Table 3: Volume percent of amygdule minerals from mapped assemblages shown in Figure 26 (from Stoiber and Davidson, 1959). Mineral Assemblage Band Chlorite Chlorite— Microcline— Calcite Microcline— Calcite Quartz— Epidote Calcite— Epidote 0—3 45—82 0—47 5—10 0—trace 0—8 0 0 Volume Percent Amydule Filling Chlorite Microcline Calcite Epidote Pumpellyite Quartz 100 0 trace 0 69—74 15—25 0—5 0—1 0 0—6 0—5 1 2 0 2 0 0—1 90—96 0 87 12 0 trace 4—9 1 2 1 �copper SCALE 2 27: 4 SENECA N K (thousands of feet) W Distribution of quartz, microcline and high grade native Microcline present on hachured side of line only -" Lower limit of microcline l?igure A Over 10% quartz on hachured side of line Upper limit of quartz Very high grade copper ore NORTH KEARSARGE AHMEEK MO H ore in the Kearsarge amygdaloid (modified from Stoiber and Davidson, 1959). The Calcite and epidote are present in all zones. Kearsarge amygdaloid dips about 35 to 40 degrees to the northwest. Data from the incline are projected to a horizontal plane. CENTENNIAL WOLVERINE SOUTH KEARSARGE �56 41.5 Continue on the same road and in the same direction as before (.isr), away from Kearsarge. 42.1 There is a dirt road junction to the right, stop here. We are now in the vicinity of Scales Creek, which is the type section of the Scales Creek flow. This Is the sane flow seen at Stop 1, about 14 miles to the south, in Houghton. STOP 12. Scales Creek. This stop gives one an opportunity to look at the Scales Creek flow, a regionally extensive basaltic flow. This is the same unit observed at Stop 1, and it has been traced for more than 150 Km along the Keweenaw. There are outcrops of the Scales Cteek flow on both sides of the main road and along Scales Creek, just to the north and paralleling the road. The Scales Creek flow Is characteristically ophitle. This flow was studied, from drill core northeast of here, by Scofield (1976). The Scales Creek The massive flow has an amygdaloidal top and base and a massive interior. interior of this flow is believed to be for the most part geochemicallv unaltered (Table 4). Mineralogically primary and secondary minerals are present. Modes estimated for the massive interior are plagioclase, 40 percent; pyroxene, 48 percent; olivine, 10 percent; and opaque oxides, 2 percent. Primary plagioclase, pyroxene, and opaque oxides can be found but olivine is pseudomorphically replaced by talc, serpentine, and/or chlorite. In the amygdaloidal flow top no primary minerals are present but all have P]agioclase is been replaced by a suite of secondary alteration products. now albite with some replacement by sericite, chlorite, and puinpellyite; clinopyroxene is replaced by chlorite; olivi.ne is replaced by chlorite, epidote and pumpellyite, and opaque oxides are altered to hematite and sphene. Scofield (1976) has studied these changes in some detail. 42.1 Turn around and retrace route back to US—4l. 42.7 Passing the Wolverine mine dumps, Stop 11. 42.9 Right turn on 115—41 at Wolverine Market. 44.2 Entering the Village of Allouez. We have an excellent view of the southeast side of a prominent ridge. This ridge is held up by the Greenstone flow which is the thickest and volumetrically Largest single flow within the Portage Lake Voicanics. It wili be seen at Stop 14. 44.4 Left turn on a paved road called Bumbletownkoad, just before a Standard gas station. 44.6 Stay on the paved road, bearing right. 44.75 STOP 13. Allouez Conglomerate and flumbletown Hill (Fig. 28). The description of this stop is modified onj.y slightly from White (1971b). The stop begins with a survey of the dumps of the Allouez conglomerate mine (1869—1392, 1300T Cu). �Table 4: Average composition of three samples from the massive part of the Scales Creek flow (from Scofield, 1976). Weight Percent 5i02 47.57 A1203 16.10 Fe203* 12.54 MgO 7.67 CaO 10.00 Na20 2.24 K20 0.29 Ti02 1.43 97.84 Total 0 1000 L Figure 28: Outcrop map of the Allouez—Bumbletown Hill area (White, 197lb). 2000 FEET �58 The lithology of the conglomerate is best studied in the dumps. The largest boulders in this conglomerate are about 2 feet in diameter, and the median size is about 3 inches. A pebble count of boulders mafic rock, more than 8 inches across gave the following results: mostly amygdaloidal, 16 percent; quartz porphyry, 36 percent; feldspar porphyry, 11 percent; granophyre, 37 percent. The greater heterogeneity of this assortment suggests a less restricted source terrane than the one that supplied the Kingston and Houghton Conglomerates in this area; the Kingston, in particular, is made up almost entirely of fragments of quartz porphyry. These dumps are well known to rockhounds as a chryso— colla locality. Thin black veinlets cutting the conglomerate are calcite full of chalcocite dust. From the dump, it is a short walk to the top of the hill, which is an area of exceptionally good exposure and provides an opportunity to see several key units of the Portage Lake Lava Series. One has a unique view of both an area of intensive mining activity and of the general physiography of the Copper Range. From here, on a very clear day, one can see Isle Royale to the northwest. The Huron Mountains lie beyond Keweenaw Bay to the southeast. Bumbletown Hill is on the southwest side of Allouez Gap, a saddle crossing the Copper Range, similar to, but much less prounounced than, the valley at Houghton—Hancock. At this gap, the strike of the lava flows swings, going northeast from about N35°E to N50°E. Fractures and minor faults associated with this bend are probably the reason for the gap. To the northwest, the land slopes off very gradually toward Lake Superior, The southeast as it does through most of the length of the Copper Range. flank of the Copper Range has a steeper slope at the skyline, more or less along the line of the Keweenaw Fault. The low—lying plain between the fault and Keweenaw Bay to the southeast is underlain by flat—lying Jacobs— ville Sandstone. Looking northeast along the strike of the Copper Range, one can see the At Bumbletown cuesta form of the ridge upheld by the Greenstone Flow. Hill, this flow is only 85 m thick; it thickens abruptly to more than 300 m at the near end of the cuesta ridge. To the right of the Greenstone ridge, the more distant hills are upheld by lavas much lower in the section; dips of bedding are steep, and cuesta forms are less pronounced. The amygdaloidal top of the Kearsarge Flow has been the principal producer in this area. The line of shafts along its outcrop is a little more than a mile southeast of Bumbletown Hill, and the bottom levels are almost vertically below the surface trace of the Houghton Conglomerate (see outThis immediate area is unique in that five different and widely crop map). separated layers have been at least modest producers, suggesting a common Stratigraphically highest is the Allouez Conglomerate; plumbing system. dumps of the old Allouez mine (1869—1892, l3,000T copper) lie along the A small headframel200m N65°E of the foot of the hill, 300 m southeast. hilltop is the Allouez No. 3 Shaft, which produced (1944—1964) about l7,000T of copper from the Houghton Conglomerate (No. 14) and 2000T copper from the Iroquois Amygdaloid, 170 m stratigraphically beneath; The large headframe 6200 feet due both were found by diamond drilling. �59 east of the hilltop serves the shaft of the Kingstone Mine; this deposit, discovered in 1962 also by diamond drilling, is in the Kingston Conglomerate (No. 12), 300 m stratigraphically above the Kearsarge Flow. The outcrops on the top and upper slopes of Bumbletown Hill represent a series of andesite flows, some slightly porphyritic. The flows range Unlike the basaltic flows found below the up to 20 m in thickness. Houghton Conglomerate, these flows are not individually very extensive; the map shows two flows pinching out within this small area. As a group, the hilltop are stratigraphically equivalent the flows in the vicinity of whose and lithologically similar to those tops were mined at the Quincy Mine, just north of Hancock. The Greenstone Flow is exposed in a series of outcrops 160—300 m southIts thick amygdaloidal top is exposed at the end east of the hilltop. of a private roadway 200 m south—southeast of the hilltop. Columnar fine—grained basalt and ophitic basalt can be seen in exposures farther down the slope. 45.05 Take a left turn on US—4l and cross into Retrace route back to US—4l. Keweenaw County from Houghton County. 45.9 Entering Ahmeek. 46.25 Junction to Cliff Drive. MAP 10 47.65 49.5 Turn left on Cliff Drive. Passing Seneca Lake on the right hand side of the road. We are driving Along the road are along strike, near the base of the Greenstone flow. several small basalt outcrops mostly on the left side of the road, At this point the Greenstone Flow abruptly thickens to nearly 400 m. It dips northward at about 25° toward the Lake Superior Syncline. This lava flow can be traced along much of the Keweenaw and has been stratigraphically and geochemically correlated with a similar unit on Isle Royale, 90 Km away on the other side of the syncline (see Fig. Thus the areal extent 3a). of this great flow exceeds 5000 and its volume is of the order of 800— 1500 Km3 according to White (1960) and Longo (1983). It rivals the composite Roza flow (Columbia R.) as the largest known lava flow on earth, The Greenstone typically shows spectacularly developed pegmatites, ophitic horizons and columnar jointed areas. A cross section of the Greenstone Flow at this locality and a map of the zone where the flow thickens rapidly The pegmatoid zone is unusually thick in the northern are in Figure 29. part of this map. The ophitic zones of the flow are relatively unaltered portions and Longo (1983) has shown that the composition of these zones are remarkably constant and demonstrated the great chemical similarity of the composition of the Isle Royale and Keweenaw ophitic exposures of The rapid thickening of the Greenstone here was sugthe Greenstone Flow. gested by White (pers. comm., 1982) to be caused by the separation of the upper part of the flow into multiple flow units, which appear to be separate flows. To the north the flow may be a continuous, single flow unit, while to the south it may have been made up of many flow units. �—_ . ,.// ! • • ,•//Moh /7 0 ) / ( - / •1' 2 Io / ) ) �10 I EM 0 7 SCALE 1 mile Figure 29: Map and cross section showing vertical zones within the Greenstone flow between Seneca and the Cliff Mine (from Longo, 1983). I 92 1 2 20 15 225 285 680 (feet) Thickness Vertical Scale: 1"=200' Sub-ophite Pg: 2nd Pegmatoid Zone -Sub-ophite Pg: 1st Pegmatoid Zone LOp: Lower Ophite Pg: 3rd Pegmatoid Zone UOp: Upper Ophite Mel anophyre EM: Columnar Jointed Top of Flow Vesiculated Flow Top �62 MAP 10 and 11 50.0 Crossing the Cratiot River MAP 11 50.6 52.5 We are now driving on the southeast side of a prominent ridge which is held up by the Greenstone Plow. We are at the site of the Cliff Mine which was the first mine in the district. The dumps ind old footings for the mine building are mainly on the 1.eft hand side of the road and the townsite, of which little remains, is on the right hand side of the road. optional stop where one can look at the Greenstone Flow and the Cliff Mine dumps. In this region the Creenatone Flow is mainly ophitic basalt and sometimes shows quite well dev.loped coarse columnar jointing. The Cliff Mine worked the Cliff fissure. The mine operated discontinuously from 1845 to 1887. It produced a tote] of abcwt 38 million The productive portion of the fissure lies under lbs. of refined copper. the Creenstone Flow. The Cliff fissure is nearly at right angles to the attitude of bedding and dips steeply to the east. Most of the mineralization was confined to the fissure although SOL1C amygdaloids were mineralized (Cliff Mine suinmarizedtromsutler and Burbank, 1929). Many large masses of native copper were mined from the Cliff Mine and larger masses weighed up to 100 tons. The large 100 ton mass had to be cut, by hand, into smaller pieces, it could not be blasted (Clarke, 1976). Among the fissures rhr Cliff was the In addition to native copper and silver the followmost productive of silver. caling minerals are found at the Cliff Mine (not in order of abundance): cite, epidote, chlorite, laumontite, prehnite. datolite, thomsonite, chlora— strolite, apophyllite, adularia, gypsum, sphalerite, galena, pyrite and surface oxidation minerals. This is zir 53.1 Tunction of U5—41/M—26. Turn left (north). MAP 12 53.4 Entering Phoenix 54.5 Turn left on a dirt road just before (0.1 mile) the junction between US—41 It is about 100 meters from the paved road to the base of the and M—26. Phoenix Nine dump which is Stop 14. STOP 14. Phoenix Mine and Greenstone Plow. At this stop one can look at the Phoenix Mine dump and the lower ophite of The Phoenix Mine worked numerous veins below the the Creenstone Flow. Greenstone Flow. Like the Cliff Mine discussed at mileage 52.5, the Phoenix t'Iine was one of the. eatltet mines in tze d.Lstrict and opexattd off and cc'. from 1849 to 1917. It produced a total of about 17 million lbs. of refined The Phoenix Mine also worked the Ashbed copper (Butier and Burbank, 1929). ainygdaloid where it is mineralized in the vicinity of vein copper occurrences. The Phoenix Mine dump is notable for halfbreedS (native copper plus native silver) and for spectacular secondary analcite. Other minerals reported in the Phoenix Mine ares (Clarke, 1974a) include: pumpellyite, chlorite, natrolite, chlorastrolite, and apophyllire. �It I -t- /1 -iii - I I - 'I (/ If.-r: V- - I -/2 - // // 'i \ /_ 1;' FJ 'T 'ii L7 I - - C - L -.-. - - -c C: --- - - - // - - -:--- Efri /2- - -- r - -- / -: - • / - : '\-. = — — .1 / (r / . /9GOI H ,/ /7 - - // /I- , / I /2 --r - I ' -I \ C9 �_ oo __ - - 0 '. "/ - ' w. ta - '.;:.' Phoenix Ashbed1.. - Workings ! LI9 -- 0 / - /; 4 - / - r A9i-PhoenIx Mine - K Stop 11' MAP 12 -- �54.6 Flow. Greenstonie the cross and strike to perpendicular drive River. Eagle towards M—26 on left Turn 55.0 flow. the in middle cooling slower the represent which exposures, these on found be can cm 5 to up pyroxenes individual with texture, ophitic coarse Exceptionally road. the of left the to Flow Greenstone the of Outcrops 55.4 River. Eagle along traverse a begin also can one road, the up just 15, Stop At spring. the of periods water high the in done be can't This contacts. flow many at looking River Eagle to way the all here from downstream river the follow can You pools. deep many are there locality this in and road the of site the from m 25 about is River Eagle River. Eagle along seen be can Flow Greenstone the above flows the where stop optional an is This road. the of side hand right the on pull—out a is There 55.7 downstream. or upstream either River Eagle along traverse a begin to possible is it stop this At flow. Ashbed the of north River Eagle in bend sharp very a is There flow. Ashbed the crosses River Eagle locality this In right. the on pull—out road dirt maintained poorly a is There to begin and River Eagle Cross l951b). (l951a, Cornwall by papers in described was Flow Greenstone the of differentiation of petrology and chemistry The Sn Sc 28 Zr Zn Y V Sr 195 259 92 84 14 wt.% ppm 0.14 1.2 0.4 2.1 9.9 7.8 12.8 15.1 46.7 214 104 6 8 186 1680 11 66 Rb Ni Mn La Cu Cr Ba Ti02 K20 Na20 CaO MgO FeO* A1203 Si02 is: (1983) Longo of study from determined Flow, Greenstone unaltered the of composition average The 1877—1887. from 1,000 of population a had which Phoenix, of townsite the of and flow great the of strike the of view a is there Ridge Greenstone the of top the From observed. be all can zones ophitic and subophitic pegmatoid, the cliff the along exposures the following By 30. Figure in shown ophitic lower the is zone ophitic The Flow. Greenstone the of portion ophitic the of exposure spectacular a is there where hill the of top the to climb and ahead Proceed shaft. the above just zones fissure the of one pass then and dump the over up climb must you Flow Greenstone the at look To 65 �1 mIle PHOENIX (Longo, 1983). Figure 30: Section and map of the zonation of the Greenstone flow near Phoenix, Michigan SCALE I 78 540 5 62 8 170 35 25 250 (feet) Thickness I ____. ______ Lower Ophite Vertical Scale: 1"200' Bottom of Flow LOp: Sub-ophite Pg: Pegmatoid Zone _—Pg: Pegmatoid Zone Sub-ophite C' a.' Pegmatoid Lenses with intercalated lenses of ophites and sub—ophites Sub-ophite Pg: Pegmatoid Zone Pg UOp: Upper Ophite Ml: Melanophyric Zone Top of Flow �67 STOP 15. Eagle River Eagle River, Jacobs Creek and Owl Creek each make excellent stream traverses which are regularly mapped as an introductory exercise in the Michigan Tech field camp. At this point, approximately at the Ashbed amygdaloid, a traverse along the stream north to Eagle River allows excellent observations of the upper stratigraphy of the Portage Lake Volcanics. The Ashbed is a very distinctive fragmental amygdaloid traced over a distance of almost 100 Km in outcrop and drill holes. It is the second flow top below the Hancock Conglomerate (Fig. 31 and Map 12). The amygdaloid is a jumble of amygdaloid fragments and interstitial brown, fine—grained detrital material. The secondary minerals filling the amygdaloid are calcite quartz, chlorite and minor epidote. Some vesicles contain minute Exposures of the Ashbed are found both in flecks of Cu (White, 197lb). Small mines were found along this horiroadcut and within the streambed. zon in many places, from Atlantic Mine (near Stop 3) to Copper Falls (Stop 17) The stream traverse to Eagle River traverses the section shown in Figure 31. Among the features seen in the traverse are: 1) excellent sections through individual lava flows showing amygdaloidal tops, and massive melaphyric, 2) Interbedding of sediments glomeroporphyritic or ophitic lower portions. with the lava flows, which becomes more prevalent up section. 3) The occurrences of several dikes which cut the section at low angles. These dikes make up a very small portion of the volume of the section and may be analogous to the dikes described in the Tertiary lavas of eastern Iceland by Walker (1975). If you decide to take this traverse, it's best to to wet feet and the traverse is not advisable in the just resign yourself water. spring because of high The flows just above the Greenstone Flow are compositionally different from Although they are tholeiitic basalt like most of the Portage Lake Lavas. nearly all the PLy, these rocks are distinctly higher in K20 and other inLower in the stratigraphy below the Gratiot compatible elements (Fig. 32). flow another zone of K—enriched basalts occur. This caused Rose and Crimes (1979) to divide the PLV into three cycles of basaltic lavas each of which The cycles may reflect different begins with relatively K—enriched basalts. It is interesting to note that degrees of partial melting or fractionation. one of these cycles begins after emplacement of the Greenstone Flow. 55.9 There is an outcrop of amygdaloidal basalt on the left side of the road. Further off of the road is a rock dump from the Phoenix Ashbed workings (1855—1862, 1913—1917, 400T Cu). 56.6 Entering Eagle River. On the left is the road to Five Mile Point. The stone monument is a memorial to Douglass Houghton who was the first State He did pioneering geologic studies in the Keweenaw Geologist of Michigan. He drowned off Eagle River in 1845. Peninsula. 56.8 Cross Eagle River on the Eagle River Bridge. Park NE of the bridge. �COPPER HARBOR CONGLOMERATE 68 14000 Stratigraphy of Figure 31: the Portage Lake Volcanics above the Greenstone flow in the vicinity of Eagle River and Phoenix, Michigan (from Cornwall and Wright, 1954). Melaphyre Tongue of Copper Harbor conglomerate MelophyreS 13000— Ophihc flows; thickest flow pegmatific Melaphyres flows; thickest flow pegmatitic Melaphyres; thicker flows slightly glorneroporphyritic and ophitic 12000— —Hancock conglomerate (No. 17) gygaloid}t egrained rnelaphyreo, Ashbed porphyritic Melaphyres; thicker flows glomeroporphyritic and pegmatitic melaphyres, porphyritic lomeroporphyritiC flows Upper chill zone Greenstone flow PORTAGE LAKE LAVA SERIES �• .S •5 S .•• S • • • S. S • S S I • S S S. •• S • S •S S S S. S •. •S ::, S S. S. ••S. S • S • •S • S • • 2 S S S • 1(20 3 ' S M-O 5wt% 75 50 - 25— No. S •• • S S :. S S S S S . S • S :S. S. •5 S S • S S S • S S S S • S •:. S 55S • S S S S S S. • .2 S S S S • S .3 P205 I .4 .5 GS wt% top) sampled Figure 32: Plot of K20 and P205 content of 106 individual PLV flows in stratigraphic order (1 in drill holes across the section in the vicinity of Delaware by W. S. White (pers. comm., 1976) and reported GS represents the Greenstone flow horizon, M—0 represents the melaphyre—ophite line, by Rose and Grimes, 1979. a texturally traceable line in the PLV below the Gratiot flow in this area. The stratigraphic position is plotted by flow no. and is not to scale. 75. 50 25 No. S S 1 I �70 STOP 16. Eagle River Falls. The falls occur at the contact between the top of the Portage Lake Volcanics and the base of the Copper Harbor Conglomerate. There are some spectacular If the water is low, like it is potholes that have developed on this face. sometimes in the summer, you can see ropy surfaces on flows at the top of The contact dips about 30° NNW. The contact the Portage Lake Volcanics. relationships suggest very little erosion between the flow and deposition Under the bridge one of the basalt beds of the Copper Harbor Conglomerate. can get a good view of the lithology of the lower part of the Copper Harbor It consists of mostly rhyolite pebble conglomerates but inConglomerate. cludes many sandstone and even some shaley beds. There is an optional route to Eagle Harbor via Sand Dunes Drive given after the Garden City road log. NOTE: Eagle River to Eagle Harbor via Garden City Road MAP 12 56.85 Go straight after crossing the bridge. M—26 goes to the left which is the optional route. Passing in front of the Keweenaw County Courthouse and offices. 57.1 Gitche Gumee Bible Camp, continue on paved road. 57.2 Pavement ends. MAP 13 60.2 This is the Garden City Road. Junction with paved road. Turn left towards Eagle Harbor. 60.3 Cross Jacobs Creek. 60.5 Junction of a dirt road on the left. Continue ahead on paved road. From this road, a short distance to the west, there is access into Jacobs Creek, at the site of the Arnold Mine, along the Ashbed amygdaloid. This is the end of a traverse one can make across the upper part of the Portage It is recommended to begin the traverse at the lower end Lake Volcanics. of Jacobs Creek where it crosses M—26 (Sand Dunes Drive optional route to This is a very tough traverse with many steep and dangerous Eagle Harbor). There are excellent exposures of many individual lava points within it. At the Arnold Mine, one of the nearly conformable flows along Jacobs Creek. Geologic traverses made along massive dikes is exposed in the streambed. ahead), and Jacobs Creek allow Eagle River (Stop 16), Owl Creek (Stop 17 lateral variations in the upper part of the Portage one to look in detail at Lake Volcanics. �\\\\\ 71 — 1 :,, '' \" 'I J• I \\; ' lHwtl 0 . . 4. £L - Coooer Harbor Corg!omes an k ( ' \\ i \\ - MAP 13 I - 11 k I; �72 61.2 On the left is a roadside park with a tower. From the top of this tower there is an excellent view of Isle Royale on a clear day. You can also see some of the ridge—valley topography due to the dipping lava flows and conglomerates in this part of the section. 61.9 Dirt road that slants to the right goes to the old townsite of Copper Falls. Copper Fails was settled in about 1846 and had a population of 500 in 1877. Today there are a handful of residents. 62.2 Cross Owl Creek. 62.3 Road to the right goes upstream to the dumps of the Copper Falls Mine which is part of Stop 17 described below. 62.4 If you follow this road several hundred Road to the left goes downhill. meters, you will reach the 30—mile stampsands which are the tailings dump from the Copper Falls mining operation. From this stampsand you can gain access to the bottom of Owl Creek and can begin a one—hour traverse upIf you continue upstream beyond stream to the bridge along this road. the bridge, you will reach poor rock dumped along Owl Creek from the Copper Falls mining operation. By climbing out of the creek bed, to the east, one can reach a dirt road which will come out on the main road at 62.3 STOP 17. Owl Creek — Copper Falls Mine. Owl Creek is another one of the streams that cut across the upper part of The traverse begins downstream where the base the Portage Lake Volcanics. of the Copper Harbor Conglomerate and top of the Portage Lake VoiLcanics interfinger. There are excellent exposures of interbedded conglomerate! There are sandstone and lava flows along the bed and sides of Owl Creek. several well exposed amygdaloidal flows. The Copper Falls Mining Company worked several fissures and the Ashbed The mine operated from 1847 to 1893. It produced about 18 amygdaloid. million lbs. of refined copper from the Ashbed amygdaloid and about 9 Copper Falls million lbs. from fissures, mostly the Owl Creek fissure was the only mine in the north end of the district above the Greenstorie flow that paid dividends but was not a profitable venture (summarized from Butler and Burbank, 1929). The Owl Creek vein starts near the base of the Copper Harbor Conglomerate and extends through the Portage Lake Volcanic Series, probably into the Greenstone flow. The vein was productive only in the vicinity of the Ash— bed amygdaloid. The Ashbed flows are distinctly porphyritic. The amygda— bid is scoriaceous with a notable clastic component. In some localities The mineralpebbles and boulders of amygdaboid are set in a sandy matrix. ization of the Ashbed amydgdaloid is similar to that found in other amygda— bids in the Keweenaw Peninsula. At the Copper Falls Mine the more abundant minerals are: calcite, quartz, epidote, and pumpellyite. Datolite is abundant in the Ashbed near fissures. Datolite is abundant in fissures Native copper was more abundant toward the top part of such as Owl Creek. the deposit. Other minerals reported in the Copper Falls area include: �73 laumonitite, prehnite, native silver, adularia, analcite, apophylite, faugasite, natrolite, stilbite (summarized from Butler and Burbank, The Copper Falls Mine is stratigraphically one 1929; Clarke, l974b). highest in the Keweenaw native copper district and is near the top of the pumpellyite zone (see Figs. 4b and 9a in the Introduction). MAP 14 63.75 63.85 Crossing Eliza Creek There is a dirt road that goes off to the right. From this dirt road just a few hundred meters up hill you can begin a traverse upstream on Eliza Creek to get the exposures of the Portage Lake Lava flows of this region. 64.9 We are at Eagle Harbor where we join back up with M—26. Turn right on M—26. Eagle River to Eagle Harbor via Sand Dunes Drive (M—26). MAP 12 o At Eagle River Bridge make a sharp left turn, follow M—26. 0.1 Sharp right turn. MAP 13 3.05 Jacobs Creek Falls. From this point one can begin a traverse up Jacobs Creek that ends near the Arnold Mine on the Garden City Road (mileage There are excellent exposures of the upper part of the Portage 60.5). For those who are hardy, the stream Lake Vol.canics along Jacobs Creek. offers virtually continuous exposures through thin pahoehoe flows, especially in the first several hundred meters. This is a steep and rough traverse, and should not be attempted in high water periods. 4.9 Great Sand Bay. 5.9 The Lake Shore Traps form the offshore ridge. The Lake Shore Cat Harbor. Traps are mafic lava flows interbedded with the Copper Harbor Conglomerate. MAP 14 7.8 Right hand turn by the Eagle Harbor Store. 8.0 We are at the Junction of M—26 and Garden City Road Route. Return to Main Road Log Mileage. Stay on M—26. �/ - ( I - - - C..-;. *i . etC r Lake Superior - - '"1 it /// .. ( . / ci' iI - 41" 63gke ':yh ff \ ag H / I 8/AST GUARD O8 \..( GLE HARBOR (32 S ____ - . z-- .. �75 65.0 65.75 MAP 15 66.9 67.5 67.65 The harbor at Eagle Harbor is controlled by the occurrence of units which These are basalt flows which are inter— are called the Lake Shore Traps. bedded with conglomerates of the Copper Harbor Conglomerate and form typiThere are excellent exposures of the Lake Shore cally resistant ridges. Traps that occur at the Eagle Harbor Marina and continuing along the shore through Grand Marais Harbor and into Agate Harbor and eastward through small boat from the Copper Harbor. These are accessible by canoe or winds are on—shore. Marina, but don't try it if the Junction to the left to the Eagle Harbor Marina. Continue ahead on M—26. On the right hand side you can see the offA view of Grand Marais Harbor. shore islands and ridges which are controlled by the occurrence of the Lake Shore Traps. We are driving along a conglomerate ridge. this Road passes along the shores of Lake Bailey on the right hand side of Harbor Conglomerate conglomerate ridge. The ridges throughout the Copper the valleys are underlain by the tend to be held up by the conglomerates, On conglomerate. and shaley members within the more easily eroded sandy The (on the right) is Mount Lookout. the opposite side of Lake Bailey Vol— contact between the Copper Harbor Conglomerate and the Portage Lake canics runs through the back side of Mt. Lookout. sandstone On the left hand side of the road there are exposures of the members of the Copper Harbor Conglomerate. NAP 16 69.1 69.2 69.7 70.0 Crossing the Silver River there are excellent exposures of the Copper Brock— Harbor at this locality and along the left hand side of the road up look at the Copper Harbor way Mountain. This is an optional stop to At Eagle River Falls (Stop 16) one had the opportunity to Conglomerate. At this locality look at the basal beds of the Copper Harbor Conglomerate. of the formation, just bewe are stratigraphically in the more central part (20) one low abundant interbeds of Lake Shore Traps. At an upcoming stop The formation. will get the opportunity to look at the upper part of the of other stops. lithology of the sediments here can be compared to those the summit On the south side of the road at this stop a 3 Km trail leads to in the of Mt. Lookout (Map 15), one of the most spectacular viewpoints contact The summit is located on conglomerate, but very near the Keweenaw. with the Portage Lake Volcanics. Allow at least 1½ hours. this Junction to Brockway Mountai1 Drive. We are going to come back to Go to Park. point but we are going to first take a side trip to Esrey the left on M—26. shallow dipping We are now at the shore of Lake Superior where there are approxilava flows of the Lake Shore Traps. The road follows the shore mately parallel to the strike of the lava flows. STOP 18. Esrey Park. �___ ti del4f SI. dVV\I - - _; 3 3 - I p O4 • . —:- - .. ---— - —-I i20° - — - - _- ____________ — C- ——- S I - .. -. - )) Th of magflet .— Approxtmate posItlOfl °I/ .D - 1ff yi pa qtl V �- /_ \ * I r copper Copper L - _i_=-i j' - _ : - -— rbOr. -- - - - 4-.••• - 20 ,.:—.--—:- — ., Shore TrapS. _—- ,— -A Ashbed I T1ZH hc -.-- e -TiLak •:. ! ngtOmC rate ——-— - catedbY2lrb0 _____ tl / _______ - - _ �78 The rocks cropping Out at Esrey Park are lava flows of the Lake Shore Traps. The Lake Shore Traps consist of a number of lava flows interstratified within the Copper Harbor Conglomerate. The Lake Shore Traps extend from the tip of the Keweenaw Peninsula west and south to just north of Hancock. They lie stratigraphically near the middle of the Copper Harbor Conglomerate. They consist dominantly of mafic flows similar to those of the Some intermediate compositions have also been Portage Lake Volcanics. reported. The Lake Shore Traps represent the waning stages of Keweenawan volcanism in the Keweenaw Peninsula. Several of these flows have been traced offshore by prominent magnetic anomalies. The large outcrop between the parking lot and the lakeshore is the massive interior of a fine grained basaltic flow which strikes approximately parallel to the shore. The flow's amygdaloidal top can be observed along the lakeThe metamorphic grade of these rocks is substantially shore to the east. lower than that of the Portage Lake Volcanic Series, i.e. within the zeolite zone. Note the "fresh" appearance of massive interior basalt (with olivine phenocrysts) and the low temperature amygdaloidal minerals (in order of calcite, chlorite, laumontite quartz, adularia decreasing abundance): and analcite. 70.1 Turn around and head back towards the junction of Brockway Mountain Drive. 70.9 Sharp left turn onto the Brockway Mountain Drive followed by some more exposures of the sandy conglomerate zones within the Copper Harbor Conglomerate. We will drive for several kilometers along a conglomerate ridge with many conglomerate exposures. MAP 17 75.9 At the summit of Brockway Mountain we take a right turn a short distance to the observation site. STOP 19. Brockway Mountain Viewpoint. This high conglomerate ridge reaches an elevation of over 1300 feet and is one of the best known tourist stops in the whole Keweenaw. Excellent views of the ridge and valley topography of the northern shore of the Keweenaw can be had here, because the scrub vegetation allows a 360° panorama. The conglomerate here dips at about 20° to the north. To the west the Lake Shore Traps form prominent drowned ridges in the vicinity of Esrey Park. Lake Bailey (with the small island) and Lake Upsom occupy a topographically low valley of finer grained clastic sediments within the Copper Harbor Conglomerate. Just to the south of Lake Bailey the conglomerate ridge of Mt. Lookout can be seen, marking the contact between The inland the Copper Harbor Conglomerate and the Portage Lake Volcanics. lake almost directly south is Lake Medora, and just beyond the lake is a prominent ridge which marks the stratigraphic position of the Greenstone flow. In the distance, farther to the south across Lake Medora, Mount To the southBohemia (Stop 21) with a fire tower on top can be seen. west a distant ridge with white Air Force tracking buildings on it, marks Gratiot Mountain, which is underlain by andesitic dikes and small rhyolite bodies. To the east, Copper Harbor is visible and Lake Fanny Hooe (see Map 18) which occupies the same stratigraphic horizon as Lake Bailey. Beyond Copper Harbor to the east, East Ridge, a conglomerate ridge, is To the north, on the skyline 65 Km the prominent hill on the skyline. away is Isle Royale, easily visible on a clear day. The skyline of Isle �8- Map 16 _ —-- er — -- —--- i_ I 9 ( - Dans P9int N. _J I Lake Shore Tr,ps 26 __-1 —-- — -—--—- (3 — —c- - — et L - Stop 20 —= - - I /077 — Harbor — - — : 26 - - —- 4 Su;_5Or ILake —t . — ••- -- I -- -i_s -e I'.. —. .---.. - '''c —— — p /1) ( i— ) — -I --_----- ——. — --- - '.— —— —- .•1. .f.. .••\ '.4—.. 2! ..ii&' ) :jt .SM.c14— •Q=__ aSr.'; t .-..'—- — "••• SV,.fl -—__75 :nrftt - —-;. — _ ____ �80 Royale is the Greenstone Ridge, underlain by the Greenstone flow, which is apparently a continuous unit all the way from one side of the syncline to the other. It may be the largest single lava flow on earth, with a volume of more than 1500 Km3 (Longo, 1983). 75.9 MAP 18 79.45 80.5 MAP 17 81.7 83.35 We turn to the right and follow the road straight ahead toward Copper Harbor now going downhill and continuing along the ridge with excellent views all the way down. There is a pull—out on the right hand side of the road to give an excellent Copper Harbor is controlled by view of Copper Harbor and Lake Fanny Hooe. The islands offhsore including the occurrence of the Lake Shore Traps. Porters Island are underlain by lava flows. From the Copper Harbor Marina, with a small boat you can have access to excellent exposures of the Lake Shore Traps along the edges of Copper Harbor. There are exposures of the Copper Harbor Conglomerate along the road descending into Copper Harbor. Junction at M—26, turn left. We come to the shore of the lake again at a place called the Devil's Washtub. If you stop here by the right hand side of the road and take a short walk along the conglomerate along the shore, you come to wave washed exposures of the conglomerate at the Devil's Washtub. STOP 20. Dan's Point. There is a small gift shop observation tower on the right hand side of the road. Walk just a few yards down to the shore of Lake Superior to look at the lithology of the Copper Harbor Conglomerate and the occurrence of stromatolite in well exposed and wave washed exposures. Dan's Point consists of a lakeshore outcrop of Copper Harbor Conglomerate that is characteristic of the upper two—thirds of the formation (sometimes called the Outer Conglomerate). As a whole, the Copper Harbor Conglomerate is a red—brown, basin—ward thickening wedge of volcanogenic clastics which attains a maximum thickness of 1830 m (Daniels, 1982). A coarse conglomerate facies consisting of well—rounded, poorly sorted clasts of mafic to silicic volcanic rock fragments directly overlies and locally interfingers with the lavas of the Portage Lake Volcanics (Elmore, 1981). The conglomerate facies is generally clast—supported and contains a ratio of mafic to silicic intermediate clasts of about 2:1. The Copper Harbor Conglomerate fines both distally and upsection so that sandstone interbeds become more frequent in the upper two—thirds of the formation. Sandstones are predominantly subangular to angular lithic graywackes which exhibit current—ripples, festoon trough—cross beds, parting lineations and dessica— tion features. Laminated crystalgal carbonate horizons are interbedded within the conglomeratic and sandstone facies in the upper two—thirds of the formation. Stromatolites occur as laterally—linked drapes over cobbles, as laterally—linked contorted beds in mudstone—siltstone lenses and as poorly developed mats in coarse sandstone (Elmore, 1981). �81 The depositional environment of the Copper Harbor Conglomerate has been interpreted as a prograding alluvial fan complex (Fig. 33) with proximal— to—distal braided stream and sheet flood facies on coalesced alluvial fans and sand flats (Elmore, 1981; Daniels, 1982). Isolated cryptoalgal carbonate and ooid lenses formed in shallow, medial fan lakes receiving very low rates of sediment influx (temporarily abandoned stream channels) (Elmore, 1981). Paleocurrent indicators suggest sediment transport was from the southeast to northwest indicating that a basin was located toward the center of the rift zone (Daniels, 1982). The stratigraphic section of the "Outer Conglomerate" (that part of the Copper Harbor Conglomerate above the Lake Shore Traps) exposed at Dan's Point consists of about 80—90 ft. of interbedded conglomerates and sandPredominantly clast—supported conglomerate beds consist stones (Fig. 34). of rounded, cobble—to—small boulder—sized clasts with a matrix of coarse sand—sized sub—angular grains cemented with iron oxides. Conglomerate clasts are predominantly felsic volcanics (approx. 70%) with sub—ordinate basalt, pyroclastic, plutonic and metamorphic lithic fragments. Several silty—sandstone interbeds higher in the exposed section exhibit cross— bedding, current lineations, ripple marks, parting lineation and (reduction spots along bedding. In particular one should note the white stromato— lite (genus Colleria) horizon draping cobbles about one—third of the way up the exposed section. Algal growth occurred during a period of depositional quiescence and was halted by an influx of silty material followed by renewed conglomerate deposition. Please do not remove stromatolite from the outcrop. Good specimens can be found in the pebble beach. 83.35 MAP 18 86.65 87.1 Turn around and go back toward Copper Harbor on M—26. To the left is the junction Junction, again, to the Brockway Mountain road. to the Copper Harbor Marina. Continue straight ahead on M—26 to Copper Harbor. Junction between M—26 and US—4l in Copper Harbor. out of Copper Harbor. Turn right on US—41, south Copper Harbor was suddenly a boom town in 1843, following the discovery of Porter's Island was the site of the first governcopper in the vicinity. ment land office and in 1844 Fort Wilkins was built on the shores of Lake Fanny Hooe, to protect the miners from potentially hostile Indians. The lighthouse was built in 18o6. Fort Wilkins is now a state park with campMuch exploration activity took place in the ing facilities and a museum. fort and there are shafts and exploration pits immediate vicinity of the all along the land between Lake Fanny Hooe and the Harbor, mostly from In 1853 and for several decades thereexploration in the 1843—46 period. after mining activity took place south of the fort in a series of workings called the Clark Mine. The mineralization is of the fissure and amygdaloid type and consists of prehnite, epidote, analcite, quartz, laumontite, adularia, microcline, chlorite, datolite, calcite and several copper minerals including chalcocite, cuprite and tenorite as well as native copper. Agates are conspicuous in the amygdaloids here, and the area is well known for datolite collecting. One occurrence of manganese minerals in a fissure The manganese minerals found accounts for the name of Manganese Lake. brannite and manganite, orientite. The Estivant here were pyrolusite, of the Clark Mine lands which were deeded to Pine tract represents a part are now a nature preserve, containing some of the C&H Company in 1942 and Upper Peninsula. the last virgin pine tracts in the �L — -S. Cover P'-.. •.. . •• 963 W.AW __ -S ••. • ••- • . Copper :' - LL$i :;/ I• I /* • -, Shore p-----: •; - Lake tTTTTT+ Copp.r H - 4. • erJiarbr Lake Superior J z. HAYS — .) EXPLORATION Copper I 1 Copper Hao< _ '- .) --- ---- . !/ ;,j. �1982). Daniels, from (modified deposits stromatolitic containing lakes ephemeral shallow and deposits plain flood and stream braided fans, alluvial coalescing showing Conglomerate Harbor Copper the of environment depositional of cartoon Schematic 33. Figure — BAStNwARD 83 �I I I I I — IJj i: (T\ ; oooo00oqo;.ooy %o6,°fJ.. 0o:0 P ooj°Q4 ! I Ili. 9# I t'•' C' T rt CD C) CD CD- CD-. H- H. rtt)Q 0 o CD CD I H.t) H- t CD rl- CD CD H H- Fij 0 H. C -1 CD L) -C-- CO '-'1 CD C) CD CD- CD-. CD o '-1 oCDo CD- d 0 H. C 0 H- H- rrDrtCD '—j H- !10 00 H. H. (I) H- OC) H. rt H C o-r CD CD 0(J) H.H CD- CD CC rtH 00CC CD CD- 0HCD H- H- H- 0 0 rt H. C Hrt rt CDC) C) oCDCDCD CD CC H. 0 o o C)CDH H 0(000 0 C) CD CD OH CQ 0 H. CDHCD CD (I) H. CD rt HO -0 oCD 0 o- H. o H H H. HO 0C) 0 H- CI)—. CD c 00 (DrtC) H H. CD CCCD C CD-. C) CD CD H.CD 0 0 rt rt H- H. CD �85 Keweenaw Point, Horseshoe Harbor, East Bluff and other points of interest can be reached by taking an unmarked dirt road which goes eastward from the end of US—41. This road is rough and poorly maintained and may be followed around to Mandan. Horseshoe Harbor has excellent exposures of the Copper Harbor Conglomerate (Fig. 34). 88.2 MAP 19 91.45 MAP 20 94.3 94.55 MAP 21 97.3 MAP 20 101.4 101.6 Nice exposures of the Copper Harbor Conglomerate to the left of the road as we are going up the hill. Lake Medora on the right hand side of the road, Junction to the left to Mandan. Mandan now is only a few houses, it had 300 residents in 1910. Continue ahead on IJS—41. Road to the left. This is the entrance to the outer portion of the Keweenaw Peninsula, all on poorly maintained dirt roads. To visit Mount Houghton and Keweenaw point, you may exit here. Junction of the road to Lac La Belle, Turn left and continue to Stop 21 at Mt. Bohemia. If you wish to skip this stop, you may jump ahead to mileage 105.45. On the left hand side of the road is a large outcrop of amygdaloidal basalt of the Portage Lake Volcanics. These exposures are flows in the lower part of the formation below the Scales Creek flow (see Fig. 4 and in the Introduction). Dirt road turning off the main road to the left. This is STOP 21 at Mt. Bohemia, It is about one half mile walk up this road to. the summit of Mt. Bohemia; this is a four—wheel drive vehicle road. STOP 21. Mt. Bohemia. An intrusive body of diorite and granophyre crops out on the south slope of Mt. Bohemia. The majority of the intrusive body is a massive, medium— grained, miarolitic diorite. The major constituents of the diorite, are oligoclase and hornblende with lesser amounts of orthoclase, magnetite, uralitized augite, apatite, sphene, quartz, sericite, epidote, chlorite, and calcite. The later are alteration products or are introduced secondary minerals. The central core is a fine— to coarse—grained, miarolitic granophyre. The major constituents of the granophyre are albite, quartz and granophyric intergrowths of quartz and feldspar with lesser amounts of orthoclase, sericite, hornblende, apatite, sphene, magnetite and chlorite. Miarolitic cavities are lined with quartz, albite, calcite, chalcopyrite, and chalcocite (summarized from Cornwall, 1954). The Mt. Bohemia intrusive body yielded a Rb—Sr age of 1,130 ± 35 m.y. (Chauduri and Faure, 1968). The diorite and granophyre at Mt. Bohemia intrude basaltic lava flows of The basalts are slightly the lower part of the Portage Lake Volcanics. metamorphosed at the contact. The intrusive body is cut by the Lac La Belle This fissure is mineralized with fissure which trends north—northwest. copper sulfides, mostly chalcopyrite and bornite and in gangue of calcite, chlorite, and quartz (summarized from Juilland, 1965). �P —— _ ( Dl / 4r? 4 — / p 6 \ / - 'P E4 ' p \ai\ L0 ON pg - - • 0 .•, ) /- .5, - /000 S — J/ .• Map 18 �''' p — • -- :TI 'I -; I ,;.. - - • '------—4\1— _j '/ K __\ / 3Yk. - Flow Sci K * Stop 21 :...' ...P 20 7 — �MAP 21 -— = - - - I —___ I V = 1 = — - -I — E) ) MF35N / —- Rv er // • ' - — t/ I 7-IS --- • • ap23 •• 'P24 Map 20 I a \ I --:- / t Ifft /080/P\ \ ---------- - :\i - .-;: - _ (1 �89 Andesitic dikes are found in the vicini.ty of Mt. Bohemia (Fig. 35a). They average about 5 m in thickness. The dikes intrude flows of the Portage Lake Volcanics, two flow tops are shown in Figure 35a as alpha and beta. The dikes and amygdaloidal flow tops carry copper sulfides. Copper sul— fides in other parts of the district are found typically as fracture fillings. Native copper is typical of amygdaloids. A variety of secondary The and opaque minerals are found in the dikes and flow tops (Fig. 35). paragenetic sequence is consistent with that for the other deposits in the district (compare Fig. 35c and Fig. 9b in the Introduction). Copper sul— The copper and sulfur in this occurrence fides are paragenetically late. is believed to be of direct magmatic origin related to the magma source that produced the andesite dikes and Mt. Bohemia intrusive body. The emplacement of flows, subconcordant faulting and chronologic sequence is: fracturing, dike emplacement, renewed movement along subconcordant breaks, regional low—grade metamorphic/hydrothermal alteration, minor folding and faulting, and sulfide mineralization (summarized from Robertson, 1975) The road Up to the summit of Mt. Bohemia crosses flows of the Portage Lake Volcanics. The diorite and granophyre intrusive complex crops out to the southeast of the summit. Intrusive stocks are not common in the Keweenaw Peninsula, Most of these occur in the lower part of the Portage Lake Vol— canics and are rhyolitic in composition. Mt. Bohemia is the only occurrence of a diorite stock in the Keweenaw Peninsula. OPTIONAL SIDE TRIP TO Lac La Belle Discussion of complex relationships along the Keweenaw Fault and the Keweenawan rhyolite bodies, Go straight ahead (south) towards Lac La O At turnoff to Mt. Bohemia. Belle down hill. O4 Junction of roads to left and right at Lac La Belle. MAP 21 To Bete Grise turn left. (See Map 22) Bete Gi se is located on the shore of Keweenaw Bay on the Keweenaw Fault. Along the shoreline east of the point where the road reaches the shore are several exposures of the Keweenaw Fault which crosses on and off These may be visited in canoe or small boat. Also shore several times. to the east are several of the rhyolite bodies which are chiefly found in the lower part of the Portage Lake Volcanics. Three tenths of a mile north of Bete Grise, four—wheel drive road continues east of the paved road to Smith's Fisheries. The road intersects the Bare Hill Rhyolite body, a shallow Beyond the end of the road at Smith's Fisheries a trail continues intrusive. eastward along the shore to the mouth of the Montreal River. From here one may traverse up river to several falls over fine outcrops of basaltic flows or continue along the shore to the Fish Cove Rhyolite, a compositionally zoned shallow intrusive (Bornhorst, 1975). Inland and not far from Bete Grise is the Mt. Houghton Rhyolite. This is an extrusive rhyolite dome �14 55 495I 18 I /48\ 43/31 \ 'i2 47 32' 46 ._—-- 34 22A7flh777/' _____jB 36< 37 6 I g8 7 25 ffflaTImffl1/7"° 4 50 Lac La Belle Fissure - 60 0 EM DIIHe —-.40 Amygdaloid - °jk \-c'-\ v-s, <j r--,1 64 I 7___2t1 Mt. Boheiat'\ .Oiorite,>vt\ \ __-c 56.54 — 61 FIRE TOWER \ 0 loo2oo Amyqdoloids and dike projected to 1300 elevation - )iogy and drQ hole locations in the Mount Bohemia area (modi - from a preliminary Calumet and ilecla Mining Company map). Secondary minerals MINERAL Chlorite Vesicle- Frocture- fillings fillings in dike matrix 0 Epio'ote Quartz 0 0 0 0 ca/cite 5cr/cite Pumpe//y/te Microc/ine o 0 - o Hem Pyri 1, Cc, su/fides Noth Copper - Common o G Minor Nonpyrogenic 0 Rare 0 —Absent Minerals in the DPis MINERAL Pyrogenic I Deuteric Hydrothermal Supergene Magnet/fe Chlorite Pumpe//ylte 3cr/cite .- 'ucrt Microc/ine Su/idj Cha/capyr,te Ga/eva 5p/,o/er,fe ——— Epidote Colch Hei I, Hematite Z Pyrite —— —— — —— ti ——-—— ——— —— P2 ietic sequence of secondary minra1s in the dikes. Pink born,te Purple born/fe Diqenife Ojucleite Cha/coc/te Hematite I.E Cove/life —-— Paragenesis of opaque minerals in dikes and flow tops at Mount Bohemia. Figure 35: Geologic map showing andesitic dikes near Mount Bohemia and occurrence and paragenesis of secondary and opaque minerals in the dikes (from Robertson, 1975). �Y) 1 I I FauI.' Creek e I', r0 Houghton ,. ,iJ \'_ �92 with prominent flow banding and block and ash flow deposits on its flanks. Mt. Houghton is best approached from the Mandan Road (Map 19). Rhyolites make up less than 1% of the mass of the Portage Lake Volcanics Considerable textural variety of as seen in outcrop on the Keweenaw. rhyolites are found including intrusive and extrusive rhyolite and even But the abundance and variety of rhyolitic boulders small ignimbrites. and cobbles within the interflow conglomerates demands that a large number of rhyolitic source areas must underly the Jacobsville south and east of the Keweenaw Fault. To Gratiot River. Turn right and proceed ahead 1.2 miles on paved road. At the west end of Lac La Belle, in the vicinity of Deer Lake, the rocks south of the Keweenaw Fault are Portage Lake basalts (Fig. 36). These rocks may represent the lowest stratigraphic horizons exposed in the The area has been studied by geological and Portage Lake Volcanics. geophysical methods by DeGraff (1976) and his model for the development It is still of this unusual feature is shown graphically in Figure 36. another example of confusing deformation which is typical of this great A traverse down the Little Gratiot River from the Lac La Belle— thrust. Gay Road crosses many outcrops of the basalts. The fault—bounded, tilted body of Portage Lake Volcanics was defined by dense array of magnetic and gravity profiles and a few key drillholes, The attitude of the beds was altered by the faulting, but the rocks, like the rest of the Portage Lake Volcanics, have normal magnetic polarity. AFTER OPTIONAL SIDE TRIP to Lac La Belle return to main road log. MAP 21 101.6 At Mt. Bohemia turnoff. 105.45 Back at the junction of US—4l, 106.5 Dirt road to the right goes to Stop 22 at the Delaware Mine. on the dirt road and follow the signs to the Delaware Mine. 106.2 STOP 22. Turn around and retrace route back to US—41. Make a left turn towards Mohawk. Turn right Delaware Mine. The Delaware Mine, first known as the Northwest Mine, has had a long and It was operated by various companies from about unprofitable history. The mi:ie mostly worked veins for mass copper. Three shafts 1847 to 1887. were opened in 1881 to mine copper from the Allouez Conglomerate (#1, #2, The Allouez Conglomerate was seen at Stop 13. Total production from #3). the Delaware Mine was about 7.5 million lbs. of refined copper. As with other vein deposits in the Keweenaw, the Delaware Mine is a notable locality for datolite. Other minerals reported from the Delaware Mine poor rock piles include (not in order of abundance): chlorastrolite, prehnite, calcite, laumontite, analcite, chlorite, epidote, native copper and native silver (summarized from Clarke, 1975; Zelenka, 1978). �± \ -L Portage Lake VolcaflaS -o \ •Ro Gay Lee LaBeIle To sete Bo8e N N S S S llasalts and sandstones in a block south of the fault are exposed and overturned. l3asalts and sandstones in a block south of the fault are exposed and dip to the south. Classical fault contact between basalt and sandstone. Sandstone still exposed north of the IKeveenaw Fault. Sketch map of part of the Keweenaw Fault in the vicinity of Deer Lake, where the Figure 36: Portage Lake Volcanics are found south of the Keweenaw Fault. At right successive cross sections show stages in the development of the Keweenaw Fault at Deer Lake as envisioned by DeGraff (1976), P = PLy, J = Jacobsville. 11 \ Portage Lake VolcanicS 1' Mt Bohenja N Prior to faulting. �94 The Delaware Mine is open to tours for tourists during the summer months. It is owned and operated by Jack and Tom Poynter. At this stop one has the opportunity to look at the dumps from the Delaware Mine and to visit (for a fee) the underground workings. 106.35 MAP 23 109.0 Junction of Delaware Mine and US—4l. ahead towards Phoenix. Left turn on TJS—4l and continue Ahead we can see cliffs of the Greenstone flow. contact of the flow. Road nears the basal 110.3 Exposure of one of the flows beneath the Greenstone flow. 111.1 In the To the right one can see the Greenstone ridge in the background. foreground is the ghost town of Central and its associated dump piles. 111.45 Junction of paved roads to the right and left. Continue ahead on US—4l. The road to the left goes to Gratiot Lake and an Air Force Base; road to the right goes toward the ghost town of Central and the Central dump piles. The Central Mine worked a fissure vein striking nearly at right angles to bedding and dipping steeply to the east. The mine operated from 1854 to 1898 and produced about 52 million lbs. of copper. The fissure extends from just below the Greenstone flow to the Kearsarge Conglomerate. A strike fault at the Kearsarge Conglomerate offsets the vein to the west and below this it is not mineralized. The town of Central, settled in 1854, was settled mainly by Cornish immi— Although the area was mostly abandoned after the mine closed, grants. the descendants of these immigrants now living all across the country, hold a yearly reunion in July at the townsite. Later immigrant groups to the copper mining towns included: Italian, German, Croatian and Finnish people. MAP 24 112.8 Continue ahead on US—41. The road to the Junction of road to the right. right connects with an earlier part of this field trip at Jacobs Creek (mileage 60.3). 113.9 Another view of the ENE striking Greenstone flow holding up the prominent ridge. 114.6 Again another excellent view of the Greenstone flow ridge. MAP 12 115.4 Junction of M—26 and US—4l at Phoenix. There is an optional route from Phoenix to Ahmeek via US—41/M—26 given after the Five Mile Point road log. �- - - — ( I (L/ C4 ----i-I - - — .- —::; p- H. p p I 7 -- I I - 07 IL 1 ,. . - —y 24 — jge I — L — '7 :-fi0 L 2O' - J. - 1— y./ :' •O- c. . I 1 �_ ____ ___I de, • •-1-•r ,4. -— ".? ii /ç/)/11 \ I, ( // • ( - I \'\ •H \'\ .i • 1 —--\-- -, __ C _\ \\\ \\ \\ \\ \\ - -- \\ D — i4 i--, - I N -f I j 2 (fl ) \c \ LU — 1 copt 1 2 1 / ( - - C — /7 -- — - ••/// - 1 \\ '.1 1 -. - Map 1. �97 Phoenix to Ahmeek via Five Mile Point (a scenic route along the Lake Superior shore). MAP 12 115.4 Right turn toward Eagle River. 117.4 Left turn on to the road to Five Mile Point. MAPS 25 and 26 On the right hand side of the road is a turn—off to the Five Mile Point 112.2 In the front You must get permission to enter this area. lighthouse. yard of the lighthouse, there is a thin lava flow of the Lake Shore Traps with the Copper Harbor Conglomerate bed above and below it 121.5 MAP 27 126.9 Five Mile Point beach turn—off at the right hand side of the road. Along this beach there are many exposures of the Copper Harbor Conglomerate. Cross the Gratiot River. 128.45 A thin basalt flow, from a position just above the Greenstone flow, forms an outcrop here which displays a well—developed columnar jointing. The Greenstone flow itself shows spectacular columnar jointing in some areas, most notably along the Palisades shown on Isle Royale where columns 2 m In a few areas the colonade/entablature or more in diameter are found. jointing pattern described in Columbia River flood basalts is well— developed in the Greenstone. On the Keweenaw columnar jointed exposures in thin flow sequences are rare, probably because the underlying horizons were not water—saturated when covered by the next lava flow. 128.7 Stop sign. 128.8 Another stop sign. 130.0 Right turn which is immediately followed by a stop sign in front of a Join US—4l with a right turn. Directly ahead at about 11:00 church. This is a shallow mine that worked the Kingston is the Kingston Mine. Total proConglomerate. The Kingston ore body was discovered in 1962. duction was about 20 million lbs. of copper until mining stopped in 1968 The mine was left open as a research operation (Weege and Pollack, 1971). in the late 1970's. Go straight ahead. Turn left followed in block by a right turn. The Kingston Conglomerate is stratigraphically about midway between the It is overlàirt by a Calumet Conglomerate and the Kearsarge amygdaloid. A bedding plane fault separates the over60 m thick ophitic basalt flow. The conglomerate rests on a lying basalt from the Kingston Conglomerate. The Kingston Conglomerate can be traced along scoriasceous amygdaloid. strike for over 100 Km and ranges in thickness from 0.3 to 30 m. In vicinity of the ore body it averages about 13 m. Where the bed is thick it consists of a lower layer of shale and siltstone, 10—15 cm thick and an upper congloineratic layer (summarized from Weege and Pollack, 1971). �MAP 25 M — .', ór 5 :; %0 r - - - 07/ / - / i - V ' 4 ,<' /\ �99 Fivemile Poini 6NDH / TcUAR 'I / / —- I I J Sevenmile / /• !Point V I. '1 C7 7f q Map4-'7 MAP 26 r/ �100 : 2 I? Lake Shon I,> J7 • • ( MAP 27 Ma, •./. / �The Kingston Conglomerate is typical of rhyolite pebble conglomerates. Pebbles are largely subangular to subrounded quartz—feldspar porphyry. Quartz—free porphyritic and nonporphyritic rhyolite pebbles, common in Interstitial sand other conglomerates, are not present in the Kingston. Sandstone composition is similar to the peb— and sand lenses are common. The intensity of mineralization is related to the amount of matrix bles. present which is an indication of the original permeability. The main alteration minerals are kaolinite and chlorite. Introduced calcite and copper are found as fillings in healed fractures, interstitially filling A few individual pebbles are replaced voids and replacing the matrix. Economically important copper is found as rims around clasts by copper. Matrix filling takes place along and as matrix replacement or filling. texture bands parallel to bedding. Epidote and quartz are also found as introduced minerals. Bleached rock is commonly associated with mineralization in the Keweenaw native copper district but is not present in the Kingston ore body. The abrupt thinning of the conglomerate bed localized the ore body with high grade ore nearest the pinch—out (Fig. 37) (summarized from Weege and Pollack, 197; Brumleve, 1976). PHOENIX TO AHMEEK VIA US—4l/M—26. MAP 12 O Continue straight ahead on US—4l/M—26. 0.5 Bear left on US—41/M—26. Junction of US—41 and Cliff Drive. excellent view of the Greenstone flow ridge. Another MAP 10 5.2 Lumber mill on the left side of the road. 6.0 Entering Mohawk. 6.1 On the left hand side of the road are mine dumps from the Mohawk Mine. The Mohawk Mine worked the Kearsarge amygdaloid which is described at Stop 11. 7.0 MAP 9 The hill on the skyline with the four towers on it is Bumbletowfl Hill, the location of Stop 13. 7.9 Junction of US—41/M—26 and Cliff Drive in Ahmeek. 8.0 Junction of US—4l/M—26 and the road from Five Mile Point. RETURN TO MAIN ROAD LOG MILEAGE. 130.0 Junction of US—41/M—26 and the road from Five Mile Point. 134.1 Junction of US—41/M—26 and M—2O3. �-- - - -..-, .— contact - .' ore body footwall -..' N N N N N N N N N N N N - N ' contact ha ngwall •' N N Schematic illustration of the funnelling effect on mineralizing 37: fluids causing localization of ore deposition (modified from Butler and Burbank, 1929 by Brumleve, 1976). Figure basalt ridge -— r .YfJ FI :- I! C �103 There is an optional route from Calumet to Hancock via M—203/Mctain State Park given after the TJS—41/M—26 road log. Calumet to Hancock via US—4l/M—26. 134.1 Continue straight ahead on US—41/M—26. MAP 28 134.8 Flashing light 135.7 Continue straight ahead. center of Calumet. A right turn leads to the The Osceola Mine Shaft No. 13 can be seen on Southern edge of Calumet. Follow the right hand side of the road behind the Holiday gas station. Mileage is not logged the roads on Map 28 if you wish to go to Stop 23. to this stop. STOP 23. Osceola Mine Shaft No. 6. ProThe Osceola Mine worked the Osceola amygdaloid in the Calumet area. duction from the Osceola amygdaloid began in 1879 and continued until 1920 when mining activity stopped. The mine reopened between 1925 to 193L A total of The mine reopened in 1925 and production continued until 1968. about 600 million lbs. of refined copper was removed from this mine which The amygdaloid was ranks fifth in the Keweenaw native copper district. developed for about four miles along strike and to a depth of 4,500 ft. along incline (2,700 ft. vertically) (summarized from Weege and Pollack, 1971). The Osceola flow is an ophitic basalt and varies in thickness from 35 to The thickest part of the flow, near Calumet, has been the most 210 feet. The Osceola flow has been traced from the Cliff Mine to the productive. In the Calumet area the flow strikes N35°E and dips around Arcadian. The top of the flow is a well developed fragmental amygdaloid 37°NW. consisting of well oxidized, reddish, angular fragments of vesicular lava which typically range in size from a few inches up to a foot in diameter. The lode ranged in thickness from 1 ft. up to and sometimes greater than Amygdules and the voids in the brecciated flow top are filled 60 ft. mostly with calcite, epidote, K—feldspar, chlorite, and native copper. Quartz is present in certain areas and there is also minor amounts of The fragmental amygda— prehnite, pumpellylte, laumontite, and analcite. bid is frequently interrupted by sill—like layers of dense basalt which may have been emplaced by injection of lava from the interior of the flow into the solidified, brecciated crust. These dense basalt layers proNative copper vided barriers to the movement of mineralizing solutions. in the Osceola ranges from disseminated to small masses up to an inch in diameter to large masses weighing hundreds of lbs. (summarized from Weege and Pollack, 1971; Butler and Burbank, 1929). The Osceola Shaft No. 6 is at the southwest end of the ore body and was A barrier zone is believed to have the richest part of the deposit. funnelled mineralizing solutions moving up dip resulting in the high Textures and colors characteristic of fragmental copper contents. Stoiber (unpublished data) made amygdaloid can be seen in this dump. secondary minerals in the dump as a an estimate of the percentages of �Map. - S N 104 N -1 I. .H.. t. :: ,'I -- - .1 - I' •r- - I.- •- '\_ &__ - --- - -L /\ . /Q — :1: c-.- , '1 -/1 .1 N s 42 — 1 1 L-4y'-*- - _s / /-N / ' -- -— 5/ --- /ss 0 5, 'r' -x tL - / 7l, — / H -' /,- 26- k_ __,; -I' 'V 081 A LS34 p LS33 5/5 — '3 N Q33 /: A II 1&J - :', — L312 P28 — I �105 whole: calcite, 59; microcline, 29; prehnite, 4; epidote, 1; quartz, 1; These and pumpellyite, laumontite and native copper can be chlorite, 5. found on this dump. Bleaching of the basalt in vicinity of native copper can be seen in individual specimens. 135.7 Continue ahead on US—4l/M—26 towards Hancock. No Maps Until Hancock Turn left on White Street. 145.45 Junction of White Street on the left. 145.9 Right turn on Tezcuco 146.0 Stop sign at Quincy Street. Go straight ahead through this stop sign one more block to Hancock Street where you make a left hand turn. 146.55 Middle of the Portage Lake Lift Bridge. 146.8 Junction of US—4l/M—26. Stay left on US—4l to the left past the Mobil and Erickson gas stations. 148.1 Left hand turn off Townsend Drive back into the Michigan Tech Campus. Street in Hancock. CALUMET TO HANCOCK VIA M—203/McLain State Park. O Junction US—41/M—26 and M—203 on the edge of Calumet. turn on M—203. Make a right hand No Maps Until Near McLain State Park. 0.5 Village Limit of Calumet. 2.5 Junction of road to Calumet Township Waterworks Park. 4.2 Bear right on Y 4.6 Nice view of Lake Superior. MAP 29 6.7 with Continue straight ahead. another paved road. Continue on M—203. Road to the right is Lakeshore Drive which goes to Calumet Township Waterworks Park; road to the left is Salo Road to the Bear Lake Rhyolite. The Bear Lake Rhyolite cuts the Freda Sandstone bedrock. It is the youngest known igneous activity in the Keweenaw Peninsula. The Bear Lake Rhyolite is a minimum of 1054 ± 34 m.y. years old based on a K/Ar age date (White, 1968). 7.0 Exposures of sand dunes on the right. 7.5 Bear Lake on the left hand side of the road. glacial Bear Lake Channel. Cross on top of the filled �_ __ __ 106 /('i2 (/ F •... LVA A K E T;_ r I654 eøx COAST \GUARD 7( -' 715 2 792 ( 77 Lily Pond I' I' IIv,i )_i. = TO Hahc MAP 29 1J 26 . T BI 9 i ---V( / TTi N _ af n== c/ : 25 �107 The Bear Lake Channel (Map 29) represents a deep bedrock valley, the Although the Waterway was dredged extension of the Keweenaw Waterway. to the west of McLain Park, because the distance was less, the Bear Lake Channel is a much more profound feature, with more than 600 feet The definition of this and other similar bedrock valleys to bedrock. is shown by gravity data. One such traverse, plotted on the map, is See also the discussion of the origin of the displayed as Figure 38. Keweenaw Waterway under Stops 1, 5 and 6. 8.4 Entrance to McLain State Park and the other edge of the Bear Lake Channel. Camping facilities are located here. 9.2 Continue on M—203. Road to the right is to the Coast Guard Station; road to the left is the Bear Lake Road, location of gravity traverse. 10.6 Access road to Lily Pond. At this point the End Moraine of the Keweenaw Lobe, a great mass of glacial ice which was stabilized here during the Wisconsin glaciation, is crossed. The The regional distribution of this moraine is plotted in Figure 14. positions of lobes as they retreated at the end of the Wisconsin period are shown in Figure 15. 13.5 High Point Road, continue ahead on M—203. NAP 30 16.1 Cross Swedetown Creek. To the northeast along Swedetown Creek there are If one is interested in looking in more expcsures of Freda Sandstone. detail at the Freda Sandstone, excellent exposures can be found elsewhere. In the local area excellent exposures of Freda Sandstone are present along Redridge/Freda can the shore of Lake Superior between Redridge and Freda. be reached by following the Houghton Canal Road which begins on the west side of Houghton (see Fig. 17). 16.55 Access to Hancock Campground. The Nonesuch Shale is exposed in an abanThis is Stop 24 and doned quarry located just NE of the boat launch. mileage is not logged from the main road to the quarry. STOP 24. Hancock Campground. As a whole, the Nonesuch Shale consists primarily of siltstone with subordinate amounts of shale and sandstone. It can be distinguished from the formations above and below by its generally grayish color. Most Nonesuch Lithologically is a rippled, laminated siltstone with reddish—gray partings. siltstones and sandstones of the Nonesuch are composed of around 30 to 40 The rock fragpercent rock fragments and 60 to 70 percent mineral grains. ments are mostly volcanic with a 2:1 ratio of mafic to silicic + intermediate The Nonesuch is stratigraphically between the composition (Daniels, 1982). Copper Harbor Conglomerate and Freda Sandstone (Fig. 5). It is The Nonesuch crops out around the margin of the quarry at this stop. a fine— to medium—grained, gray to reddish brown sandstone with subordinate interbedded, reddish—brown laminated siltstone and shale (Cornwall and The attitude of bedding here is about N30°E, 25°W. Wright, 1956). �108 BEAR LAKE 9 8 7 6 5 4( I 2 I I 4 6 8 0 12 14 x 0 2 -3 Q) S a) Li Results of gravity measurements across the Bear Lake Figure 38: traverse plotted in Map 29. At top is Bouguer anomaly with regional In the middle the regional trend is subtracted to get the trend. solid line which is compared with the modelled topography (X's). Below is the model of the valley and the density difference of the bedrock (Freda Sandstone) and the valley fill (Warren, 1981). �109 n 'I - • McI31fl State Park / I V I t , .,, -I - .4 • // - -- ( ; c, '-.' / 'ir •i• 0 r -• -•• —;• I• • 30 JI_1_ - - �110 16.7 Hancock Beach. 16.85 Sharp left hand turn on M—203. 17.9 Turn right on the one—way road. Junction M—203 and US—41. US—4l back to the Michigan Tech Campus Edge of Hancock. Follow south �111 INDEX TO GEOLOGY ON MAPS IN THE FIELD GUIDE Map No. — — — Quadrangle Reference 1 Chassell White, 1956 2 South Range, Chassell White & Wright, 1956; White, 1956 3 Chasseli Warren, 1981 4 Chassell, Hancock White, 1956; Cornwall & Wright, 1956a 5 Chasseil, Hancock White, 1956; Cornwall & Wright, 1956a 6 Laurium Cornwall & Wright, l956b 7 Laur ium Cornwall & Wright, l956b 8 Laur ium Cornwall & Wright, 1956b 9 Ahmeek White & Others, 1953 10 Mohawk Davidson & Others, 1955 11 Mohawk Davidson & Others, 1955 12 Phoenix Cornwall, 1954a 13 Eagle Harbor Cornwall & Wright, 1954 14 Eagle Harbor Cornwall & Wright, 15 Delaware Cornwall, l954b 16 Delaware Cornwall, l954b 17 Lake Medora Cornwall, l954c 18 Lake Medora, Fort Wilkins Cornwall, l954c; Cornwall, 1955 19 Lake Medora Cornwall, l954c 20 Delaware Cornwall, 1954b 21 Delaware Cornwall, l954b 22 Lake Medora Cornwall, l954c 23 Eagle Harbor Cornwall & Wright, 1954 24 Eagle Harbor Cornwall & Wright, 1954; Cornwall, l954a 25 Phoenix Cornwall, l954a 26 Phoenix, Mohawk, Ahmeek Cornwall, l954a; Davidson & Others, 1955; White & Others, 1953 27 Ahmeek White & Others, 1953 28 Laurium Cornwall & Wright, 1956b 29 Hancock Cornwall & Wright, 1956a; Warren, 1981 Hancock Cornwall & Wright, 1956a MTU Campus Map (Cover Page) White, 1956; Hase, 1973 1954 �____________ _____________ 112 REFERENCES Basaltic Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets: Pergamon Press, Inc., New York, 1286 p. Bornhorst, T.J., 1975, Petrochemistry of the Fish Cove rhyolite, Keweenaw Peninsula, Michigan, U.S.A.: Chemical Geology, v. 15, p. 295—302. Broderick, T.M., 1935, Differentiation in lavas of the Michigan Keweenawan: Geological Society of America Bulletin, v. 46, p. 503—558. Broderick, T.M. and Hohl, C.D., 1935, Differentiation in traps and ore deposition: Economic Geology, v. 64, p. 342—346. Brown, A.C., 1971, Zoning in the White Pine copper deposit, Ontonagon County, Michigan: Economic Geology, v. 66, p. 543—573. Brumleve, C., 1976, The petrology and fracture characteristics of a native copper bearing conglomerate, Kingston Mine, Keweenaw County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 97 p. in Studies in Geophysics, Burke, K., 1980, Intracontinental rifts and aulacogens: Continental Tectonics, National Academy of Sciences, Washington, D.C., p. 42—49. 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Cornwall, H.R. and Wright, J.C., 1954, Bedrock geology of the Eagle Harbor quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 36. 1956a, Geologic map of the Hancock quadrangle, Michigan: U.S. Geolo— gic'al Survey Mineral Investigations Field Studies Map MT 46. 1956b, Geologic map of the Laurium quadrangle, Michigan: gical Mineral Investigations Field Studies Map MT 47. U.S. Geolo- Oronto Group, MichiDaniels- P.A., Jr., 1982, Upper Precambrian sedimentary rocks: gan—Wisconsin: Geological Society of America Memoir 156, p. 107—133. Davidson, E.S., Espenshade, G.H., White, W.S. and Wright, J.C., 1955, Bedrock geology of the Mohawk quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 54. DeGraff, J.M., 1976, Structural and age relationships of rocks associated with the Lac La Belle magnetic anomaly, Keweenaw County (M.S. thesis): Michigan Technological University, Houghton, 130 p. Elmore, R.D., 1981, The Copper Harbor Conglomerate and Nonesuch Shale: Sedimentation in a Precambrian intracontinental rift, Upper Michigan (Ph.D. dissertation): University of Michigan, Ann Arbor, 192 p. Elmore, R.D. and Van der Voo, R., 1982, Origin of hematite and its associated rema— nence in the Copper Harbor Conglomerate (Keweenawan), Upper Michigan: Journal of Geophysical Research, v. 87, p. 918—928. Ensign, C.O., Jr. White, W.S., Wright, J.C., Patrick, J.L., Leone, R.J., Hathway, D.J., Trammell, J.W., Fritts, J.J. and Wright, T.J,, 1968, Copper deposits in the Nonesuch Shale, White Pine, Michigan: in Ridge, J.D., ed., Ore Deposits of the United States, 1933—1967: American Institute of Mining, Metallurgy and Petroleum Engineering, p. 462—488. Fritts, C.E., 1952, A petrologic study of the Mount Houghton felsite, Keweenaw Peninsula (M.S. thesis): Michigan Technological University, Houghton, 42 p. Green, J.C., 1977, Keweenawan plateau volcanism in the Lake Superior region: Geological Association of Canada Special Paper No. 16, p. 407—422. �_____________ ____________ Green, J.C., 1982, Geology of Keweenawan extrusive rocks; of America Memoir 156, P. 47—55. Geological Society 114 Grimes, J.G., 1977, Geochemistry and petrology of Keweenaw rhyolites and associated rocks, Portage Lake Volcanics, Michigan (M.S. thesis): Michigan Technological University, Houghton, 80 p. Halls, H.C., 1982, Crustal thickness in the Lake Superior region: of American Memoir 156, p. 239—243. Geological Society Hase, H.W., Jr., 1973, Geological—geophysical site investigation of a portion of the Student Development Complex, Michigan Technological University, Houghton County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 35 p. Holcomb, F.W., 1975, Urban Geological Map of the Eastern Half of the City of Houghton, Michigan (M.S. thesis): Michigan Technological University, Houghton, 87 p. Huber, N.K., 1975, The geologic story of Isle Royale National Park: Survey Bulletin 1309, 66 p. U.S. Geological Jolly, W.T., 1974, Behavior of Cu, Zn, and Ni during prehnite—pumpellyite rank metamorphism of the Keweenawan basalts, Northern Michigan: Economic Geology, v. 69, p. 1118—1125. Jolly, W.T. and Smith, R.E., 1972, Degradation and metamorphic differentiation of the Keweenaw tholeiitic lavas of northern Michigan, U.S.A.: Journal of Petrology, v. 13, p. 507—531. Juilland, J.D., 1965, Mineralization of the Mount Bohemia intrusive, Keweenaw County, Michigan (M.S. thesis): Michigan Technological University, Houghton, 78 p. Kalliokoski, J., 1976, End moraine map of northern Michigan—Wisconsin: Technological University Press, Geologic Map Series, Map hA. 1982, Jacobsville Sandstone: 156, p. 147—155. Michigan Geological Society of America Memoir Klasner, J.S., Cannon, W.F. and Van Schmus, W.R., 1982, The pre—Keweenawan tectonic history of southern Canadian Shield and its influence on formation of the mid— continent rift: Geological Society of America Memoir 156, p. 27—46. Lankton, L.D. and Hyde, C.K., 1982, Old Reliable — an illustrated history of the Quincy Mining Company: The Quincy Mine Hoist Association, Inc., Hancock, Michigan, 159 p. Livnat, A., Rye, R.O. and Kelly, W.C., 1976, Stable—isotope and fluid inclusion studies of the Keweenaw copper district, northern Michigan (abs.): Geological Society of America Abstracts with Programs, v. 8, p. 980—981. Longo, A.A., 1982, A geochemical correlation, with correlative inferences from petro— graphic and paleomagnetic data, of the Greenstone flow, Keweenaw Peninsula and Isle Royale, Michigan (abs.): Proceedings of the 28th Institute on Lake Superior Geology, p. 22—23. 1983, A geochemical correlation, with correlative inferences from petrographic and paleomagnetic data, of the Greenstone flow, Keweenaw Peninsula and Isle Royale, Michigan (M.S. thesis): Michigan Technological University, Houghton. �_______________ 115 Merk, G.P. and Jirsa, M.A., 1982, Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks: Geological Society of America Memoir 156, P. 97—105. Prest, V.K., 1969, Retreat of Wisconsin and recent ice in North America: Survey of Canada Map 1257A. Geological Robertson, J.M., 1974, Major and minor element geochemistry of some late Precambrian dikes, Keweenaw County, Michigan (abs.): Proceedings of the 20th Institute on Lake Superior Geology, p. 27. 1975, Geology and mineralogy of some copper sulfide deposits near Mount Bohemia, Keweenaw County, Michigan: Economic Geology, v. 70, p. 1202— 1224. Robertson, J.M., Grimes, J.G. and Rose, W.I., Jr., 1979, Intermediate and silicic volcanic and subvolcanic rocks of the Portage Lake Volcanics, Michigan (abs.): Geological Society of America Abstracts with Programs, v. 11, p. 255. Rose, W.I., Jr. and Grimes, J.G., 1979, Cyclical compositional changes within flood Geological Society of basalts of the Portage Lake Volcanics, Michigan (abs.): America Abstracts with Programs, v. 11, p. 255. Scofield, N., 1976, Mineral chemistry applied to interrelated albitization, pumpel— lyitization and native copper redistribution in some Portage Lake basalts, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 144 p. Stevens, A., 1971, A study of subsurface analysis of the proposed outdoor instruction area, Student Development Complex, Michigan Technological University, Houghton Michigan Technological University, Houghton, County, Michigan (M.S. thesis): 58 p. Stoiber, R.E. and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250—1277, 1444—1460. Van Schmus, W.R., Green, J.C. and Halls, H.C., 1982, Geochronology of Keweenawan rocks of the Lake Superior region: A summary: Geological Society of America Memoir 156, p. 165—171. Walker, G.P.L., 1975, Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland: Journal of the Geological Society of London, v. 131, p. 143—161. Warren, E.J., 1981, The bedrock topography of the Keweenaw Peninsula, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 169 p. Weege, R.J. and Pollack, J.P., 1971, Recent developments in the native—copper district of Michigan: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 18—43. �__________ ___________ ____________ _____________ White, W.S., 1956, Geologic map of the Chassell Quadrangle, Michigan: gical Survey Mineral Investigations Field Studies Map MF 43. U.S. Geolo- 1960, The Keweenaw lavas of Lake Superior, An example of flood basalts: American Journal of Science, v. 258—A, p. 367—374. 1968, The native copper deposits of northern Michigan: ed., Ore Deposits of the United States, 1933—1967: Metallurgy and Petroleum Engineering, p. 303—325. in Ridge, J.D., American Institute of Mining, l971a, Geologic setting of the Michigan copper district: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 3—17. 1971b, Field Trip A—2 —— Houghton to Calumet via South Range quarry and Society of Economic Geologists, Guidebook for Field Conference, Eagle River: Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 68—75. 1972, Keweenawan flood basalts and continental rifting: Geological Society of America Abstracts with Programs, v. 4, p. 732—734. White, W.S., Cornwall, H.R. and Swanson, R.W., 1953, Bedrock geology of the Ahmeek quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 27. White, W.S. and Wright, J.C., 1956, Geologic map of the South Range quadrangle, Michigan: U.S. Geological Survey Mineral Investigations Field Studies Map MF 48. 1960, Lithofacies of the Copper Harbor Conglomerate, northern Michigan: U.S. Geological Survey Professional Paper 400—B, p. B5—B8. Zelenka, B.R., 1978, The history of the Delaware Mine: Local Publication, 20 p. �i: r 2' V r 25 1. 4 14 Figure 1B: 15 r 1. 2 in mites SCALE 0 17 I r i 3 4 k12 18 12 i Stop n!Jmher Map number Index of 1:24,OOC caIe 'naps 0 r I 2 29 r 1 �'Freda McLain State Park Atlantic South Painesdale p4 Chassell Eagle rm 4 C, 0 1 4 Scate 2 o4? 3 + 4miteS Copper Harbor 12 Manitou Island Stop number Figure 1A: Route and stop map Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1972 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 3-6, 1972. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1972 Contributor An entity responsible for making contributions to the resource John L. Berkley W.A. Bodwell Emmy Booy Musa S. Haddadin Bruce E. Brown R.G. Cuddy P.M. Clifford Erich Dimroth Robert Ehrlich Thomas A. Vogel John C. Green Kenneth G. Books J. Kalliokoski James A. Kilburg Melvin M. Lahr P. James LeAnderson M.S. Lougheed J.J. Mancuso J.T. Mengel Jr M.G. Mudrey Jr P.W. Weiblen Richard W. Ojakangas Erdogan Oray W.J. Hinze N.W. O'Hara W.A. Robertson D.R. Smith R.H. McNutt Virgil A. Trent E.J. Warren Thomas G. Winter P.O. Banks W.R. Van Schmus W.F. Cannon S.S. Goldich John S. Klasner Gene L. LaBerge G.B. Morey James A. Robertson H.B. Stonehouse J.S. Stuckless Grant M. Young M.D. Lewan Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/11c9d1d86b50e5a7348f083a877476c3.pdf 671b46482ec80859cddc170b04d8d1d3 PDF Text Text C O O P E R A T I V E EXTENSION E X T E N S I O N PROGRAMS PROGRAMS COOPERATIVE I University U n i v e r s i t yofo fWisconsin—Madison Wisconsin-Madison U n i v e r s i t y of o fWisconsin—Extension Wisconsin-Extension University Nineteenth Annual Annual Nineteenth Lake Superior Superior Geology Geology Institute on Lake May 3-6,1973 3-6,1973 Madison, Madison, Wisconsin Wisconsin I P1 ERTS-1 satellite Photo Far infrared band photographed on August 12, 1972 Sponsored Sponsored by the the Geological and and Natural Natural History History Survey Survey Wisconsin Geological Extension Wisconsin - Extension University of Wisconsin and the Departments of the theUniversity University of of Wisconsin WisconsinSystem System Departments of of Geology of - �Technical Program Program and Abstracts ffor or tthe h e 19th Annual GEOLOGY INSTITUTE ON LAKE SUPERIOR GEOLOGY held held at at Sheraton Inn Inn Madison, Wisconsin May May 3—6, 3-6, 1973 1973 �MADISON PRAIRIE Central South South --Central MADISON, MADISON, WISCONSIN WISCONSIN OREGON OREGON 4 0 SHERATON SHERATON INN INN 1 1 MADISON MADISON INN INN 22 MAYFLOWER MAYFLOWER MOTEL MOTEL 33 44 NATIONAL NATIONAL MOTOR MOTOR INN INN 55 QUALITY QUALITY INN INN 66 Short Short Course Course Dorms: Dorms: 77 MURPHY'S MURPHY'S 88 99 POOLE'S POOLES PARK PARK MOTOR MOTOR INN INN HUMPHRY HUMPHRY HALL HALL JORNS JORNS HALL HALL RESTAURANT RESTAURANT CUBA CUBA CLUB CLUB ROHOE'S ROHDES STEAK STEAK HOUSE HOUSE 10 107777SIRLOIN SIRLOIN STRIP STRIP 11 DEPARTMENT DEPARTMENT of of GEOLOGY GEOLOGY 11 and and GEOPHYSICS, GEOPHYSICS, SCIENCE SCIENCE HALL HALL 12 GEOLOGICAL 12WISCONSIN WISCONSIN GEOLOGICAL and and NATURAL NATURAL HISTORY HISTORYSURVEY SURVEY �19th 1 9 t h Annual Annual Institute I n s t i t u t e of Lake Superior S u p e r i o r Geology Geology Sheraton Sheraton Inn, Inn, Madison, Madison, Wis. Wis. May May 3—6, 3-6, 1973 1973 Sponsored Sponsored by by the t h e Wisconsin Geological & Natural History Survey Survey and and Departments of of Geology, Geology, the t h e University U n i v e r s i t y of of Wisconsin Wisconsin System. System. Individuals Individuals from from the t h e U.S. U.S. Geological Survey, Survey, Department of Geology Geology of of the t h e University University of of Kansas, Kansas, and and the t h e Inland Inland Steel S t e e l Corporation Corporation also a l s o contributed c o n t r i b u t e d greatly g r e a t l y to to arranging arranging the t h e program program and and field f i e l d trips. trips. INSTITUTE BOAFZI OF OF DIRECTORS DIWCTORS INSTITUTE BOARD * J.W. J.W. * * * Avery Avery (Treasurer), ( T r e a s u r e r ) , Jones Jones && Laughlin Laughlin Steel S t e e l Corp., Corp., Negaunee, Negaunee, Michigan. Michigan. R.D. R.D. Reed Reed (Secretary), ( S e c r e t a r y ) , Michigan Michigan Geological Geological Survey, Survey, Lansing Lansing Michigan. Michigan. M.E. M.E. Ostrom, Ostrom, Wisconsin Wisconsin Geological Geological && Natural Natural History H i s t o r y Survey, Survey, Madison, Madison, Wisconsin. Wisconsin. J. J. Kalliokoski, K a l l i o k o s k i , Michigan Michigan Technological Technological University, University, Roughton, Houghton, Michigan. Michigan. D.M. D.M. Davidson, Davidson, Jr., Jr., Dept. Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota Minnesota at a t Duluth, Duluth, Duluth, Duluth, Minnesota. Minnesota. M.W. M.W. Bartley, B a r t l e y , Thunder Thunder Bay, Bay, Ontario, Ontario, CANADA CANADA * Permanent Permanent members members * LOCAL LCZALCOMMITTEE CWITTEE M.E. M.E. Ostrom, Ostrom, Conference Conference Chairman Chairman Technical Technical Program Program C. C. Craddock, Craddock, Chairman Chairman B. E. Cameron Cameron C. C. Dutton Dutton G. G. Medaris Medaris G. G. Mursky Mursky Field F i e l d Trips Trips M. M. Roshardt, Roshardt, Coordinator Coordinator W. W . Broughton Broughton C. Dutton C. Dutton A. A. Heyl Hey1 H. H. Klemic Klemic G. G. LaBerge LaBerge G. G. Medaris Medaris P. P. Myers Myers G. G. Mursky Mursky J. J. Ohlson Ohlson L. L. Weis Weis W. W. West West ft. Van Schmus R. Van Schmus 11]. iii Physical P h y s i c a lArrangements Arrangements P. P. Olcott, O l c o t t Chairman , Chairman Short Short Course Course Office Office College College of of Agricultural Agricultural and and Life L i f e Sciences Sciences U n i v e r s i t y of of Wisconsin— WisconsinUniversity Extension Extension �CARL APPRECIATION CARL E. E. DUTTON DIJTTON -- AN APPFZCIATION Carl Dutton's career half C a r l Dutton's c a r e e r in i n geology extends through nnearly early h alf a century, and most of this time his headquarters have been in Science century, of t h i s h i s headquarters in Hall H a l l on the t h e Madison campus campus of of the t h e University U n i v e r s i t y of of Wisconsin. Wisconsin. H has Ree has worked extensively Michigan, Wisconsin, Wisconsin, and Minnesota, Minnesota, and he is e x t e n s i v e l y in i n Michigan, is well Precambrian geologists Superior w e l l known to t o Precambrian g e o l o g i s t s throughout throughout the t h e Lake S uperior meeting, h his t h e occasion of of this t h i s meeting, i s ccolleagues o l l e a g u e s and friends f r i e n d s in in area. On the Madison extend this t h i s appreciation a p p r e c i a t i o n for f o r his h i s many many contributions. contributions. iv �Carl C a r l was was born born in i n Dunkirk, Dunkirk, Ohio, Ohio, on on January January 24, 24, 1904. 1904. H Hee was educated DePauw University University (LA., aatt DePauw (B.A., 1926), 1926), the t h e University U n i v e r s i t y of of Illinois I l l i n o i s (M.A., (M.A., 1928), 1928), and tthe University and he U n i v e r s i t y of of Minnesota (Ph.D., (Ph.D., 1931). 1931). Carl C a r l and and Val Val Dutton Dutton have have two sons professor sons — John, a meteorology p r o f e s s o r at a t Pennsylvania Pennsylvania State S t a t e University, University, and Robert, Robert, aa physician in i n San San Francisco Francisco — and ffive i v e grandsons. They have have H i l l s , just j u s t west w e s t of of the t h e Madison Madison campus, campus, since s i n c e 1946. 1946. llived i v e d in i n Shorewood Shorewocd Hills, Carl C a r l has divided his h i s life l i f e between various v a r i o u s academic positions p o s i t i o n s and the the U.S. Geological Geological Survey, Survey, and and he he iis widely respected respected aas s widely s a tteacher e a c h e r and a ffield ield U.S. geologist. Assistant g e o l o g i s t . He was aa Teaching A s s i s t a n t at a t Illinois, I l l i n o i s , an an Instructor I n s t r u c t o r at at Minnesota, Assistant Minnesota, and and an an A s s i s t a n t Professor P r o f e s s o r at a t Wayne State S t a t e University U n i v e r s i t y and and at a t the the University Hee joined U n i v e r s i t y of of Michigan. Michigan. H joined the t h e U.S. U.S. Geological Geological Survey Survey in i n 1943, 1943, becoming Regional Geologist in i n 1946 1946 and and Research Research Geologist Geologist in i n 1962. 1962. Since has p participated Mineral Resources Resources ccooperative coming to t o Madison he has a r t i c i p a t e d in i n tthe h e Mineral ooperative program of History i s t o r y Survey and the the of the t h e Wisconsin Geological & Natural H U.S. Geological Survey, Survey, he has taught some cclasses e c t u r e d in i n tthe he U.S. taught sane l a s s e s & llectured Department of Geology and and Geophysics, Geophysics, and and he has been a valued counselor and friend f r i e n d to t o many professors p r o f e s s o r s and and students. students. During his Carl h i s stay s t a y at a t the t h e University U n i v e r s i t y of of Minnesota C a r l was introduced intrcduced geological problems of of tthe Canadian S Shield Professors tto o tthe he g e o l o g i c a l problems h e southern Canadian h i e l d by P rofessors Grout, John Gruner, His doctoral dissertation Frank Grout, Gruner, and and George George Schwartz. Schwartz. H is d octoral d issertation on the t h e conglomerates and and structure s t r u c t u r e of of the t h e Ensign Ensign Lake Lake area, a r e a , Cook Cook County, County, Minnesota, Minnesota, under Professor P r o f e s s o r Gruner was the t h e beginning of of his h i s life—long life-long Hee also ffascination a s c i n a t i o n with with the t h e Precambrian. Precambrian. H a l s o became interested i n t e r e s t e d in i n iron iron formations and llater Michigan, eeventually formations a t e r began a rresearch e s e a r c h program in i n Michigan, ventually achieving achieving international i n t e r n a t i o n a l rrecognition e c o g n i t i o n as a s an authority a u t h o r i t y on on iron i r o n ores. o r e s . He He paper on U.S. U.S. iiron ore deposits att tthe Geological gave a paper ron o re d eposits a h e International I n t e r n a t i o n a l Geological Algiers U.N. Committee on Iron Ore Congress in in A l g i e r s in i n 1952, 1952, served on tthe h e U.N. Resources in 1953-54, and spent spent ssix weeks sstudying deposits Resources i n Geneva in i n 1953-54, i x weeks t u d y i n g iron iron d eposits AID I D program in i n Yugoslavia Yugoslavia in i n 1961. 1961. Carl C a r l is i s aa Fellow Fellow of of the the with the the A Society of America America and and sserves Membership S Secretary Geological S o c i e t y of e r v e s as a s tthe h e Membership e c r e t a r y ffor or tthe h e Society S o c i e t y of of Economic Economic Geologists. Geologists. Through the papers and t h e years y e a r s Carl C a r l has has produced prcduced many many papers and geologic geologic maps, maps, has worked worked ffor many y years and only aa few few can can be be mentioned mentioned here, here. lie H e has o r many e a r s in in the district of Michigan Michigan and Wisconsin, Wisconsin, and is co—author t h e Menominee iron iron d i s t r i c t of i s GO-author of USGS P.P. i s also a l s o co—author co-author of of USGS Maps MF—99 MF-99 of P.P. 513 513 and and Map Map 1—466. 1-466. He is MF-l81 on the He and MF-181 t h e bedrock geology geology of of the t h e Cuyuna Cuyuna district, d i s t r i c t , Minnesota. Minnesota. He iis s widely known for f o r aa series s e r i e s of of papers on on iron i r o n ore o r e resources r e s o u r c e s of of the t h e U.S., U.S., some foreign f o r e i g n countries. c o u n t r i e s . He is i s co—author co-author of of USGS USGS P.P. P.P. North America, and and some MF—225 on the ore deposits of tthe River— 570 and Map MF-225 t h e geology and o re d e p o s i t s of h e Iron I r o n RiverCrystal C r y s t a l Falls F a l l s district, d i s t r i c t , Michigan. Michigan. A very important contribution c o n t r i b u t i o n is i s aa series series of llithologic, geophysical, and mineral mineral commodity commodity maps of of Precambrian rocks of i t h o l o g i c , geophysical, Wisconsin, published as These maps are iin n Wisconsin, a s USGS USGS Map Map 1—631. 1-631. a r e aa complete of a available Wisconsin Precambrian, Precambrian, including compilation of v a i l a b l e information on tthe h e Wisconsin including previously unpublished d data numerous field many p r e v i o u s l y unpublished a t a ccarefully a r e f u l l y eextracted x t r a c t e d from numerous field Carl notebooks on hand in i n the t h e files f i l e s of of the t h e State S t a t e Survey. Survey. IIn n aaddition, ddition, C a r l has has written has served as w r i t t e n papers ffor o r several s e v e r a l guidebooks and has a s a leader l e a d e r on many ffield i e l d trips, t r i p s , both formal formal and and informal. informal. Carl i s indeed indeed a gentlemen and aa scholar s c h o l a r in i n the t h e highest highest C a r l Dutton is and aa wonderful wonderful man man tto have aas ttradition, r a d i t i o n , and o have s aa cco1league o l l e a g u e We W e thank thank him him for for his h i s long service s e r v i c e and and numerous contributions c o n t r i b u t i o n s to t o our our profession, p r o f e s s i o n , our our state, state, and our u university; his n i v e r s i t y ; for for h i s enduring interest i n t e r e s t and ccareful a r e f u l work in i n the the Precambrian; for his patient his Precambrian; for h i s generous and p a t i e n t assistance a s s i s t a n c e to to h i s ffellow ellow geologists g e o l o g i s t s in i n the t h e classroom, classroom, the t h e office, o f f i c e , the t h e laboratory, l a b o r a t o r y , and and the t h e field; field; and for his We for h i s cheerful c h e e r f u l optimism, optimism, quiet q u i e t modesty, modesty, and and gently g e n t l y dignity. d i g n i t y . We having C Carl us campus, and w wee hope enjoy and appreciate a p p r e c i a t e having a r l among u s on tthis h i s campus, he remains with with us u s for f o r many many years. years. - - v �TABLE TABLE OF OF EVENTS EVEWTS Wednesday, May 2, 1973 May 2, 1973 7:00—9:00 7:OO-9:OO p.m. p.m. Registration R egistration Conference Smoker (Cash Conference (Cash Bar) Bar) Mezzanine Mezzanine Ballroom North Registration Registration Technical Session S e s s i o n 11 Luncheon Technical Session S e s s i o n 22 Happy Hour (Cash Happy (Cash Bar) Bar) Banquet Mezzanine Ballroom North Ballroom South South Ballroom North Ballroom South South Ballroom South South Technical Session S e s s i o n 33 Luncheon Technical Session S e s s i o n 44 Business Meeting Buses for f o r Field F i e l d Trips T r i p s 22 && 33 leave Sheraton Inn leave Inn Parking Parking Lot Lot Ballroom Ballroom Ballroom Ballroom Thursday, May Thursday, May 3, 3, 1973 1973 8:00—10:00 8:OO-1O:OO a.m. a.m. 8:30—12:00 noon 8:30-12:OO 12:00—1:00 p.m. 12:OO-1:OO p.m. 1:30—5:10 1 ~ 3 0 - 5 : l Op.m. p.m. 6:00—7:00 6:OO-7:OO p.m. p.m. 7:00—8:30 p.m. 7:OO-8:30 p.m. Friday, F r i d a y , May 4, 4, 1973 1973 8:30—12:00 noon 8:30-12:OO 12:00—1:00 12:OO-1:OO p.m. p.m. 1:30—4:45 1:30-4:45 p.m. p.m. 4:45—5:00 4~45-5:00 p.m. p.m. 7:00 p.m. 7:OO p.m. Saturday, Saturday, May 5, 5 , 1973 1973 7:30 a.m. a.m. 6:00 p.m. 10:00 p.m. Bus for leaves f o r Field F i e l d Trip T r i p 11 leaves Sheraton Inn Parking Lot Bus ffor Field or F i e l d Trip Trip 1 1 returns returns Sheraton Inn Parking Lot Field Trip Bus ffor or F ield T r i p 2 returns returns Sheraton Inn Inn Parking Parking Lot Lot Sunday, May 6, 6 , 1973 1973 7:00 7:OO p.m. p.m. Bus for f o r Field F i e l d Trip T r i p 33 returns returns Sheraton Inn Inn Parking Lot vi North South South North North �TECHNICAL TECHNICALPROGRAM PROGRAM - SESSION SESSION 11 — Morning, Morning, Thursday, Thursday, May May 3, 3, 1973 1973 Co—chairmen: Co-chairmen: Alan Alan T. T. Broderick Broderick and and L. L. Gordon Gordon Medaris, Medaris, Jr. Jr. 8:30 M.E. M.E. Ostrom Ostrom Welcoming Welcoming Remarks Remarks 8:40 P.K. P.K. Sims Sims Tectonic Tectonic history h i s t o r y of of Early E a r l y Precambrian Precambrian rocks in the Vermilion district, rocks i n t h e d i s t r i c t , northnortheastern e a s t e r n Minnesota. Minnesota. p. 34—35 34-35 p. 9:05 Edward Edward M. M. Ripley Ripley & & ' Donald Donald M. M. Davidson, Davidson, Jr. Jr. Structural Structural ultramafic ultramafic 9:25 M.S. M.S. Lougheed Lougheed && J.J. J. J. Mancuso Mancuso 9:50 Discussion Discussion of of papers papers evolution e v o l u t i o n of of the t h e Deer Deer complex, Minnesota. complex, Minnesota. p. p. Lake Lake 29 29 The The biogenic biogenic origin o r i g i n of of primary primary minerals minerals in i n Lake Superior Superior Precambrian Precambrian ironironformation. formation. p. 21—22 21-22 p. 10:00 Coffee Coffee break break 10:30 Klaus J. Schultz S c h u l t z && Klaus J. Edward Edward M. M. Ripley Ripley Petrology Petrology of of some some Early E a r l y Precambrian Precambrian differentiated d i f f e r e n t i a t e d ultramafic u l t r a m a f i c bodies bodies in in northeastern n o r t h e a s t e r n Minnesota. Minnesota. p. 32—33 32-33 p. 10:50 M.G. M.G. Mudrey, Mudrey, Jr. Jr. && A.L. A.L. Geldon Geldon AA Lower Lower Precambrian Precambrian lamprophyre lamprophyre pluton pluton near n e a r Ely, Ely, Minnesota. Minnesota. p. 25 25 p. 11:10 John John S. S. Klasner Klasner && Thomas Thomas R. R. Turner Turner Precambrian Precambrian north—south north-south oriented o r i e n t e d faults faults in the western Marquette i n t h e western Marquette district, district, northern n o r t h e r n Michigan. Michigan. p. 17—18 17-18 p. 11:30 Jens F. Touborg Touborg Jens F. 11:50 11:50 Discussion Discussion of of papers papers 12:00 12:OO Adjourn Adjourn 12:00 12:OO Luncheon Luncheon Structural S t r u c t u r a l and and stratigraphical s t r a t i g r a p h i c a l analysis analysis of of the t h e Geco Geco sulphide s u l p h i d e deposit d e p o s i t in in Manitouwadge, Manitouwadge, northwestern northwestern Ontario. Ontario. p. 38-39 38-39 p. Ballroom Ballroom South South vii vii �- SESSIII SESSION 22 — Afternoon, Thursday, May May 3, 3, 1973 1973 Co—chairmen: Co-chairmen: Paul G. G. Schmidt Schmidt and and Greg Greg Mursky Mursky Paul 1:30 M.D. Lewan M.D. Lewan Geochemistry Geochemistry of the the calcium-carbon calcium—carbon dioxide metasomatism dioxide metasomatism at a t Presque Presque Marquette, Michigan. p. 19—20 19-20 IIsle, s l e , Marquette, Michigan. p. 1:50 D.M. Mickelson D.M. Summary l a c i a l geology of of Summary of g glacial north—central Wisconsin. p. 24 24 north-central p. 2:15 E. Wm. Wm. Heinrich E. A n unusual manganese manganese deposit in in An Keweenawan lava, lava, Copper Copper Harbor, Michigan. p. 12 p. 12 2:35 Thomas A. A. Vogel & & Nancy Alyanak "Framboidal" "~ramboidal" chalcocite from White Pine, Michigan. Pine, p. 42 42 p. 2:55 Discussion of papers 3:05 Coffee break 3:35 Roger W. W. Cooper Cooper The Keweenawan volcanics north of of Gogebic range range in i n Wisconsin. Wisconsin. the Gogebic p. P. 99 3:55 John C. C. Green Progress report Progress report of of the t h e Coimuittee Committee on Keweenawan Keweenawan Stratigraphy. Stratigraphy. p. 11 11 p. 4:15 R.J. R. J. Stevenson Stevenson A Keweenawan Keweenawan layered layered mafic intrusion intrusion Finland, Lake near Finland, Lake County, County, Minnesota. Minnesota. p. 36 36 p. 4:35 W.F. W.F. Cannon Cannon High grade magnetite magnetite deposits deposits at High grade at Republic, Michigan: Their bearing Republic, Michigan: Their on the genesis genesisof ofMarquette MarquetteRange Range hard ore. 6-8 hard ore. p. 6—8 5:00 Discussion of papers 5:10 Adjourn 6:00 Happy Ballroom South South (cash (cash bar) Happy hour Ballroom 7:00 Banquet Ballroom South Address by Dr. Cameron Dr. Eugene Cameron ANIM&L, VEGETABLE, VEGETABLE, OR OR M MINERAL? ANIMAL, INERAL ? viii v iii �- Friday, May 4, SESSION SESSION 33 — Morning, Friday, 4, 1973 1973 Co-chairmen: Co—chairmen: Ralph W. Carl E. Dutton Ralph W. Marsden Marsden and and C a r l E. 8:30 Richard Berger Richard and oothers and thers Environmental Environmental geology geology and and land land use planning, Chassel planning, Chassel quadrangle, quadrangle,Houghton Houghton p. 3—4 County, Michigan. p. 3-4 8:50 Ennny Booy & E mmy B00y Ruth J. J. Sobanski Sobanski Engineering geology of of the t h e Military Military Hill H i l l landslides, l a n d s l i d e s , Ontonagon Ontonagon County, County, Michigan. P. 5 p. 5 9:10 C.R. Bentley C.R. Magnetotelluric evidence for f o r lateral lateral variations v a r i a t i o n s of of ccrustal r u s t a l structure s t r u c t u r e in in northern n o r t h e r n Wisconsin. P. 2 2 p. 9:30 F. Touborg Jens F. The Atikokan Iron I r o n Range Range and and its its iron-copper m mineralization. iron-copper ineralization. p. p. 40 9:50 Discussion of Discussion of papers 10:00 Coffee break 10:30 G. G. Mursky Mursky and others others Mineralogical and and chemical studies studies of greenstones in 26-27 of i n Wisconsin. Wisconsin. p. p. 26—27 10:50 W.R. Van W.R. Van Schmus Schmus Geochronology of of Precambrian Rocks iin n eeastern a s t e r n Wisconsin. p. 41 41 p. 11:10 L.G. Medaris, Jr. L.G. Jr. and others others late b a t h o l i t h — a late The Wolf River batholith massif in Precambrian rapakivi r a p a k i v i massif in northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. p. 23 23 p. 11:30 J.L. J.L. Anderson Graphical analysis a n a l y s i s of of portions p o r t i o n s of of the granite the g r a n i t e system with application application biotite—bearing tto o b i o t i t e - b e a r i n g granitic g r a n i t i c melts melts and gneisses. and g neisses. P. p. 11 11:50 Discussion of of papers 12:00 Adjourn 12:00 Luncheon - Ballroom South South ix �- SESSION SESSION 44 — Afternoon, Friday, Friday, May 4, 4, 1973 1973 Co—chairmen: Co-chairmen: Paul C. Paul C. Tychsen Tychsen and and Perry P e r r y Olcott Olcott The ppetrology e t r o l o g y and geochemistry of Round Lake Lake iintrusion, n t r u s i o n , northwestern Wisconsin. p. 30 30 p. 1:30 D.L. D.L. E.N. E.N. Roder & Cameron Cameron 1:50 J.E. Thresher J.E. The formation of of the t h e Pittsville Pittsville (Wisconsin) migmatite. 37 (Wisconsin) p. 37 p. 2:10 Robert A. A. Jenkins Jenkins The geology of of Pembine and and Beecher townships, Marinette townships, M a r i n e t t e County, County, Wisconsin. p. 15—16 15-16 p. 2:30 John M. M. Ohlson Ohison The iron i r o n ore o r e deposits d e p o s i t s at a t Black River Falls, F a l l s , Wisconsin, Wisconsin, geology operations. p. 28 and o perations. p. 28 2:50 Discussion of of papers papers 3:00 Coffee break 3:30 0.H. Dury G.H. Southwest Wisconsin as a s aa duricrusted duricrusted pediplain. p ediplain. p. 10 10 p. 3:50 A.V. A.V. Ileyl Hey1 Mississippi Upper M i s s i s s i p p i valley v a l l e y lead—zinc lead-zinc district. d istrict. p. 13—14 13-14 p. 4:10 S.B. Romberger S.B. Upper Mississippi M i s s i s s i p p i valley v a l l e y base base metal metal deposits: d e p o s i t s : experimental solutions s o l u t i o n s to to p. 31 problems of ore genesis. p. 31 problems of o r e g e n e s i s . 4:30 Discussion of of papers 4:45 Business Meeting Business 5:00 Adjourn 7:00 from parking parking lot. Buses for f o r field f i e l d trips t r i p s 22 and and 3 3 leave l e a v e from lot. x �GRAPHICAL ANALYSIS OF OF PORTIONS GRAPHICAL ANALYSIS PORTIONS OF OF THE THEGRANITE GRANITESYSTEM SYSTEMWITH WITH APPLICATION TO BIOflTE—BEARING GRANITIC MELTS AND GNEISSES APPLICATION TO BIOTITE-BEARING GRANITIC MELTS AND GNEISSES Department of Geology and Anderson, Department of Geology J. LL.. Anderson, Wisconsin, Madison, Wisconsin Wisconsin. Madison, Wisconsin 53706 53706 Geophysics. University University of Geophysics, of ABSTRACT ABSTRACT - phase relations in biotite—bearing modelto to describe describe phase granitic melts ite-bearing granitic melts model analysis SiOy - KA1Si3O8 analysis of ofthe thesystem system SiC2 KAlSi30g NaA1Si1OS — FeO Fe2O3 provides a tentative Hz0 - K2MgSiAL20 1120 provides KgMgfiSifiAlzOzo Graphical Graphical CaAl2Si2O8 CaAl SigOg — — — gneisses. Defining and gneisses. Defining 'FeO' 'FeO' as as an an arbitrary arbitrary combination combination of of FeO FeO and Moreover,it it has specifies the and Fe20 theoxygen oxygen fugacity. Moreover, has been been and Fe20 specifies split the system system into three four comoonent comoonent subsystems necessax necessary to split to of the the components components 110, KMgSi6fl2G20, to evaluate evaluate separately separately the effect of and Quartz, alkali feldspar, and CaAl2Si2Op on the the rest rest of of the the system. system. Quartz, CaAl Si 0 on plagioclase, iotite, magnetite, plagioclgse: !?iotite, magnetite,granitic granitic melt, melt, and and vapor vapor are are the the considered phases. considered phases. Application Apolication of of Schreinemakers' Schreinemakers' rules rules combined combined biotite — magnetite magnetite with with experimental experimental data data on on alkali alkali feldspar feldspar — biotite and of topologies. topologies. The The and crystal—melt crystal-melt equilibria equilibria generates generatesan. an array of system system is is characterized characterized by by degenerate degenerate equilibria, equilibria. - - In In application, application, several several conclusions conclusions can can be be made made which which are are as as 1) degrees of 1 ) Dependent Dependent on on the the number number of of degrees of freedom, freedom, the the KK/Na /N~ Fe/Mg ratios in biotite can and ~ e/~ ratios g in biotite can be be aa function function of of temperature, temperature,total total pressure, potential of water, water, oxygen fugacity, and the pressure, chemical chemical potential oxygen fugacity, the bulk fugacity is buffered and fluid fluid If oxygen oxygen fugacity composition composition of of the the rock. rock. If pressure equals equa total totalpressure, pressure,divariant divariant assemblages assemblages (with (with respect respect to to F) have T and and P) have fixed fixed biotite biotite compositions. compositions. Such Such assemblages assemblages become become T trivariant H20 is not in in excess such as in %O H2O - undersaturated trivariant if if HgO undersaturated additional degree of freedom allows only one of of the two melts, melts. One additional ratios will vary with ratios (i.e., (i.e., Fe/Mg ~e/Mgor or K/Na) K/N~)to to be be fixed. fixed. The other other will the bulk composition the composition of of the the rock, rock. As to which of of the the two two ratios ratios will Another degree degree of of freedom freedom will this is is depends depends on on the the assemblage, assemblage. Another Biotite allow ratiosto tovary varywith withthe thebulk bulkcomposition, composition. 2) 2) Biotite allow both ratios follows: follows: - stability can of partial stability canstrongly stronglyinfluence influencethe thecomposition composition of partialmelts melts derived assemblage quartz—plagioclase—biotite— quartz-plagioclase-biotitederived from from gneisses gneissesofofthe the assemblage of partial partial Ifthe thebiotite biotiteremains remainsstable stablebeyond beyond conditions conditions of magnetite. magnetite. If melting onlytonalitic tonalitic melts can result. result. 3) melting only melts can Alternatively, this this 3) Alternatively, coexist in assemblage assemblage cannot cannot coexist in equilibrium equilibrium with introduced granitic granitic south of Stevens melt. A possible example is an injection gneiss south Point, Wisconsin, where the Point, Wisconsin, the alkali alkali feldspar feldspar in in the granitic granitic veins veins isolated from to is isolated from the the host host rock rock by by plagioclase. plagioclase. LiV) 4) Application Application to ranakivi massifs, such batholith of ranakivi granite granite massifs, such as as the Wolf River River batholith of Topological changes Wisconsin, Wisconsin, is is possible, possible. Topological changes suggesting suggesting feldspar feldspar mantling and replacementofofalkali alkalifeldsoar feldsparby bybiotite biotite exist. exist. mantlinc and the the replacement The feasibility of is being The feasibility ofsuch such explanations explanations is being studied, studied. 1 �MAGNETOTELLURIC EVIDENCE FOR FOR LATERAL LATERAL VARIATIONS OF MAGNETOTELLURIC EVIDENCE OF CRUSTAL STRUCTURE CRUSTAL STRUCTURE IN NORTHERN NORTHERN WISCONSIN WISCONSIN C. R. R. Bentley, Bentley, Department Department of Geology and of Geology and Geophysics, Geophysics,University University of of C. Wisconsin—Madison,Madison, Madison, Wisconsin, Wisconsin, 53706. Wisconsin-Madison, 53706. ABSTRACT ABSTRACT IIff two-dimensional two-dimensional inhomogeneity inhomogeneity iis s the reason reason ffor o r apparent apparent anisotropy anisotropy studies, then of the the pair of iinn magnetotelluric magnetotelluric studies, then one one of of curves curves at a t each each site site should be close to t o that t h a twhich whichwould would be be observed observed over over aa one-dimensional one-dimensional earth. should be close Ontthis On h i s basis, sites s i t e sini nWisconsin Wisconsin can can be be divided divided into i n t o three three geographically geographically The systematic systematic distinct w i t h decidedly decidedly different d i f f e r e naverage t average curves. curves. The d i s t i n c tgroups groups with grouping implies tthat grouping ofof ssites i t e s implies h a t the the differences differences rreflect e f l e c t real real differences differences justvariations variationsin in local near-surface conditions. conditions. the crust, crust, not notjust within the thethe local near—surface That implication boundary That implication isi sstrengthened strengthenedby bythe thefact f a cthat t t h one a t one boundarybetween between groups correspondstto groups corresponds o an an abrupt change change iinn structure structurededuced deduced completely completely independently from from seismic seismic and andgravity gravity data in independently data alone alone (Ocola (Ocola and and Meyer, Meyer, in The two-dimensional two—dimensionalassumption assumption alsoimplies implies tthat press, J.G.R.). press, J.G.R.). The also h a t the the c o r r e c t " curve curve of of each each pair corresponds corresponds t otocurrent t o the the "correct' currentflow flow parallel parallel to current direction directioncorresponding corresponding to t o the the two-dimensional boundary. two-dimensional boundary. Plotting current acceptedcurve curveaat eachs site accepted t each i t e reveals reveals a a parallelism parallelism with withcontours contours ofofBouguer Bouguer gravity anomalies, controlling gravity anomalies, suggesting suggesting tthat h a t the the two—dimensionality two-dimensional i t y control 1ing the the tensor orientation isi snot notnear—surface near-surface aatt all, a l l ,asashas haspreviously previouslybeen been tensor assumed, associatedinstead insteadwith withgross grosscrustal crystal structure. t i sis associated assumed, b ubut 2 �ENVIRONMENTAL GEOLOGY GEOLOGYAND ANDLAND LAND U USE ENVIRONMENTAL SE PLANNING, CHASSELL QUADRANGLE, COUNTY, MICHIGAN QUADRANGLE, HOUGHTON HOUGHTON COUNTY, CHASSELL Richard M. Hamil, Hamil, Department Department of of Geology Geology Richard Berger, Berger, Eniny Emy Booy, Booy, and and Brenton Brenton M. and Geol ogi cal Engineeri ng, Michigan Technol ogi cal University, and Geological Engineering , Mi chi gan Techno1ogi cal University, Houghton, Mi chi gan 49931. Houghton , Michigan ABST RACT ABSTRACT The Chassell ChassellQuadrangle Quadrangle locatedinin the the southeastern southeasternquarter quarter of of the The i s islocated It formerly uutilized I t includes includes land land which which was was formerly t i l i z e d for f o rcopper copper area iiss sparsely o r agriculture. The The area sparselypopulated populatedand andmay may mining as aswell well as as ffor mining evaluation of geological be developmenti ninthe the future. future. An An evaluation geological be expected expected tto o undergo undergo development factors affecting such development factors affecting such developmenthas hasbeen beenmade. made. Keweenaw Peninsula. Keweenaw Peninsula. About 85 85 percent percentof of the the land has About has a a slope less less than than 15 15 percent, percent, with withmore more About one one quarter quarter than than half of of that t h a thaving having aaslope slope less less than than 55percent. percent. About of the the land land ininthe thequadrangle quadranglehas has more more than than 50 50 feet f e e t of ofoverburden, overburden, another another quarter (mostly (mostly overlying overlying the the Jacobsville Jacobsville sandstone sandstone in the the eastern eastern area) area) 30 tto 30 o 50 50 ffeet, e e t , and and the the rest r e s t (mostly (mostly in in the thewesterly westerly areas areas overlying overlying the the Portage Lake Lake Lava Lava flows) flows) between and 30 30 ffeet Portage between 00 and e e t of of overburden. overburden. Most of of these Most these soils loam s o i l s are are classified c l a s s i f i e dasassilty s i l tto y sandy t o sandy loam(USDA (USDA cclassification) l a s s i f i c a t i o n )oro rSM SM or or SC (Unified Soil Soil Classification) SC (Unified Classification)having havinga alow lowshrink—swell shrink-swell potential potential and and There iiss aa prevalent prevalent hardpan hardpan layer good permeability permeability (about (about 2.2 2.2 inches/hour). inches/hour). There good pHofof the the soils s o i l s isi ssomesomeThe pH at a t variable variabledepth depth which which isi sa asandy sandyloam loam or o rSC. SC. The The corrosion corrosion hazard hazardf for metal and andconcrete toncrete iiss low. - 55 ttoo 6.6. The o r metal low. what acid — what 10 percent percentofof the the land There generally aa thin thin topsoil. About There iis s generally About 10 land area area is is Theseare aremostly mostly on on the the floodplains underlain organic ssoils. underlain by by alluvium and and organic o i l s . These of wouldseverely severely thepotential potentialf ofor of rivers rivers which which would r e restrict s t r i c t the r uutilization. tilization. areas are generally classified areas are c l a s s i f i e dasasmarshland. marshland. These Underground water supply providedbybythe theglacial glacial ddrift Underground water supply i sisprovided r i f tand andbedrock. bedrock. Wherethe theglacial glacial ddrift Portage Where r i f tisi sdeep deepand and ini nparts partsofofthe the PortageLake LakeLava Lava series series Jacobsville The Jacobsvi l l esandstone sandstone there there is i s sufficient s u f f i c i e n water t waterfor f o domestic r domestic supplies. supplies. The There are some problemswith with Fe has some problems Fe content has ssufficient u f f i c i e n twater water for f o rdomestic domestic use. use. There in water water from from the the glacial glacialand andJacobsville Jacobsvillesources; sources;septic s e p t itanks c tanksmay maycontaminate contaminate some the shallow shallow aquifers. some ofof the About 80 80 percent percent of of the land theChassell ChassellQuadrangle Quadrangleisi swell—drained. well-drained. About land ini nthe There The Pilgrim, Pike, The Pilgrim, Pike, and and Sturgeon Sturgeon Rivers Rivers drain drain the thearea area tot oPortage PortageLake. Lake. There and during during spring spring thaw flooding permanent marshland marsh1 and and thaw temporary temporary flooding iiss substantial substanti a1permanent occurs iinn many uplandareas areasdue duet otothe theimpermeability impermeability of of the the underlying many upland underlying bedbedoccurs areasdirections directions of of surface drainage ddiffer rock. In some some areas surface drainage i f f e r from from the the drainage drainage patterns at bythe the glacial glacial patterns a t depth depth due due to t o the thepresence presence of of bedrock bedrock ridges ridges masked masked by ddrift. rift. Old mine openings openingsdodonot notappear appeart otobe beaamajor majorhazard hazardinin future planning, Old mine planning, bbut u t shaft locations locations will willhave have to t obe be taken taken into intoaccount. account. 3 �About 20percent percentofof the the land land iiss currently About 20 currentlyowned owned by by large private private organorganExceptffor holdings, most of the land izations. Except o r small small state s t a t e and and municipal municipal holdings, most of land of the the quadrangle quadrangle iis s held held by by small small individual individual landholders. landholders. Current forestryand andfarming fanningwith w i t hpotatoes, potatoes, Current uutilization t i l i z a t i o n isi smostly mostlyini nforestry There iiss less less strawberries, and and dairy dairy products products being being the thedominant dominant crops. crops. There commercial and g h t industrial industrial purposes. purposes. than used ffor o r connnercial than 10 10 percent percent of of the the land used andl ilight Recreational useofof the the land, land, e.g. e.g. hunting snowmobilingi sisf afairly hunting and and snowmobiling irly Recreational use usewill will probably widespread. Future Future use probably include include mining mining and and recreation as as well well as agriculture. Development Development industry willbebep partially as of of industry will a r t i a l l y controlled by by access water which which iiss abundant along the the shores of Portage u t less less access tto o water abundant along shores of Portage Lake Lake bbut accessible in major majorquantities quantities further inland. accessible in inland. 4 �ENGINEERINGGEOLOGY GEOLOGY THEMILITARY MILITARYHILL HILL LANDSLIDES, ENGINEERING OFOFTHE LANDSLIDES, ONTONAGONCOUNTY, COUNTY, MICHIGAN MICHIGAN ONTONAGON EmmyBooy Booyand andRuth RuthJ.3.Sobanski, Sobanski, Department Department ooff Geology Geology and and Geological Geological Emmy Engineering, Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. Engineering, Michigan Michigan Technological ABSTRACT The vvalley The a l l e y of o fthe t h eEast EastBranch Branchofo the f t hOntonagon e OntonagonRiver, River,Ontonagon Ontonagon County, County, Michigan i is throughaat hthick Michigan s downcut downcut through i c k sseries e r i e s of o f glacial g l a c i a lake—deposited l lake-deposited clays, clays, Thesecclays have proven provenaa hazard hazardt to tthe h e Ontonagon Ontonagon clays. These l a y s have o construction c o n s t r u c t i o n and and maintenanceoof 45because becauseo foft hthe numerous slopef afailures maintenance f tthe h e U.S. U.S. Highway Highway 45 e numerous slope i l u r e s ooff various sizes are rrepetitive These f afailures i l u r e s are e p e t i t i v e in in various s i z e s abutting a b u t t i n g on on the t h ehighway. highway. These nature, rreflecting nature, e f l e c t i n g variation v a r i a t i o n ini nmoisture moisture content content with w i t h precipitation p r e c i p i t a t i o nand and snowmelt. snowmel t. The nature ooff the clayscauses causes The llayered a y e r e d nature t h e Ontonagon Ontonagon clays s usubstantial b s t a n t i a l v avariability riability in i n the t h e physical p h y s i c a l properties p r o p e r t i e s of o f the t h e mass mass bboth o t h l alaterally t e r a l l y and and vvertically. e r t i c a l l y . IInn general tthe material be cclassified general he m a t e r i a l can can be l a s s i f i e d as as clays c l a y s and and clay—silts c l a y - s i l t s with w i t h fine f i n esand sand percent to contents ranging contents ranging from from less l e s s than than 11 percent t o 14 14 percent. percent. Atterberg those ffor A t t e r b e r g LLimits i m i t s of o f these these materials m a t e r i a l s range range from from those o r inorganic i n o r g a n i c clays clays P l a s t i c limits l i m i t srange range from from of o f low low pplasticity l a s t i c i t y to t o those those of o f high high pplasticity. l a s t i c i t y . Plastic 24 50,.liquid limits l i m i t sfrom from 27 27 to t o 100, 100, and and pplasticity l a s t i c i t yindices i n d i c e s from from 12 12 to t o 58. 58. 24 tto o 5O,Jiquid There appearst otobebenonoc oconsistent of physical There appears n s i s t e n t p apattern t t e r n o of f vvariation a r i a t i o n of p h y s i c a l properties properties of (e.g. at o f the t h e material m a t e r i a l wwith i t h llocation o c a t i o n wwithin i t h i n iindividual n d i v i d u a l sslides l i d e s (e.g. a t toes toes of o f slides slides or o r on on the t h e failure f a i l u r eplace placeata the t t h escarp) scarp)nor n owith r w i t helevation e l e v a t i o above n abovea adatum datum nor nor along along the t h e general general north—south north-south ttrend r e n d of o f the t h ehighway. highway. The nnatural moisture content content ooff these The a t u r a l moisture these failure-prone f a i l u r e - p r o n e materials m a t e r i a l s ranges ranges from from 18 tto percent iin takeni nint hthe 18 o 41 41 percent n samples samples taken e l late a t e Fall F a l l of o f1972. 1972. This T h i s approaches approaches water has observed aatt various times the Free water has been been observed times t h e pplastic l a s t i c llimits i m i t s of o f the t h e soils. s o i l s . Free of water ttable o f year y e a r on on these these slides s l i d e s and and the t h e ground ground water a b l e is i s frequently f r e q u e n t l yextremely extremely close close to Averagep rprecipitation e c i p i t a t i o n i in n tthis h i s area area is i s 34 34 inches, inches, much much oof f iitt t o the t h e surface. surface. Average meltwater iinn the t h e form form of o f snowfall s n o w f a l l whose whose meltwater i s isa as isignificant g n i f i c a n t ffactor a c t o r in i n the the frequent frequent occurrence occurrence ooff Spring Spring sslides. lides. IIttisi sextremely extremely uunlikely n l i k e l y tthat h a t chemical chemical o or r e electrical l e c t r i c a l sstabilization t a b i l i z a t i o n ooff these slopes wwill Surface drainage drainage appears i l l prove prove useful. u s e f u l . Surface appears tto o be be the t h e most most these slopes economic formo fofslope slopec ocontrol economic form n t r o l i in n tthis h i s instance. instance. 5 �HIGH-GRADE MAGNETITE HIGH-GRADE MAGNETITE DEPOSITS DEPOSITS AT AT REPUBLIC, REPUBLIC, MICHIGAN: MICHIGAN: THEIR BEARING ON THE GENESIS O F MARQUETTE RANGE HARD ORE* ORE* OF U.S. Geological Survey, Survey, Washington, D.C. D.C. 20244 20244 W.F. Cannon, U.S. W.F. ABSTRACT ABSTRACT Hard ore (60—65 (60-65 percent Fe) in i n the Marquette Iron Range consists c o n s i s t s of I t characteristicalcharacteristicalconcentrations of specularite, s p e c u l a r i t e , magnetite, and and martite. martite. It thethe Negaunee lly y occurs at a t the thetop topofof NeqauneeIron—formation Iron-formation and and over over a few feet feet grades grades llaterally a t e r a l l y and downward into i n t o jaspilite j a s p i l i t e (30-35 (30-35 percent percent Fe). Fe). Van Hise Hise classic and Leith (1911) (1911) developed the now c l a s s i c concept tthat h a t tthe h e ore was formed by surface weathering and leaching of silica s i l i c a from from the iron-formation iron-formation prior prior to deposition of the unconformably overlying Goodrich Quartzite, and the t o deposition of the unconformably overlying Goodrich Quartzite, and the ore produce tthe o r e was was later l a t e rdeformed deformed and and metamorphosed metamorphosed t to o produce h e present present specularite— speculariterich "This hypothesis hypothesis has has withstood withstood critical c r i t i c aexamination l examinationby bymany many r i c h rock. rock. This geologists; evidence in its support is especially compelling in the eastern geologists; evidence i n i t s support i s especially compelling i n the eastern part p a r t of the t h e Marquette Marquette Range. Range. Boyum (1964) (1964) and Anderson (1968) (1968) have suggested suggested that concept, although although probably probably valid, v a l i d , is i snot not adequate adequate tto o explain explain aall ll t h a t this concept, ffeatures e a t u r e s of of the the ore ore bodies. bodies. M y own leadsme me My ownreexamination reexaminationofofthese these deposits deposits leads to support conclusions. II believe to supportBoyum's Boyum's and and Anderson's conclusions. believe that t h a tmuch much of of the the ore, o r e , especially e s p e c i a l l y specularite—rich s p e c u l a r i t e - r i c h ore, ore, has formed as suggested suggested by Van Van Hise and Leith, magnetite-rich ore (commonly Leith, but that t h a t magnetite-rich (commonly greater g r e a t e r than than 90 90 percent magnetite) has has aa different magnetite) d i f f e r e n t origin. origin. - At the Republic open pit, the jaspilite unit at the top of the Negaunee A t the Republic open p i t , the j a s p i l i t e u n i t a t t h e t o p of the Negaunee Iron-formation Iron-formation iiss presently presentlybeing beingmined. mined. The The jjaspilite a s p i l i t e is i s the the host h o s t rock rock The ffor o r magnetite-rich magnetite-rich hard hardore, o r e which , whichwas waspreviously previouslymined minedunderground. underground. The piti t provides p provides exceptional exceptionalexposures exposures of ofthe t h ehigh—grade high-grade magnetite magnetite ore ore bodies bodies and and ttheir h e i r contacts contacts with with the the surrounding surrounding j jaspilite. aspilite. Three ccritical r i t i c a l features features Three common hard—oredeposits deposits iinn the common t otoaall l l magnetite—rich magnetite-rich hard-ore t h e Marquette Marquette Range Range and and difficult d i f f i c u l ttot oexplain explainby bythe theweathering weathering hypothesis hypothesis are a r e shown shown tthere h e r e bbetter e t t e r than than at other a t any any o t h e r locality. locality. 1) Although Althoughsspecularite alll lhard—ore bodies, magnetite 1) p e c u l a r i t e is i scommon common tto o a hard-ore bodies, magnetite i s the thepredominant predominant mineral n many, a r t i c u l a r l y in i n higher higher grade grade is mineral iin many,pparticularly metamorphic rocks toward toward the the west west end end of of the the Marquette Marquette Range. Range. The magnetite-rich magnetite-rich ore ore contains contains ttextural The e x t u r a l evidence evidence iindicating n d i c a t i n g tthat hat formedaafter it has formed f t e r regional regional deformation. deformation. it a) a) The ore iiss massive, textures are massive, deformational deformational textures a r e absent, absent, and and "The ore magnetite grains aare magnetite grains r e largely l a r g e l y euhedral euhedral and and undistorted. undistorted. b) b) Bodies of massive massiveore ore sharply sharply truncate truncate schistose Bodies of s c h i s t o s e and and crenulated specularite—rich crenulated specularite-rich jjaaspilite. spilite. c c)) The magnetite-rich oreis icommonly s commonlysomewhat somewhat vuggy vuggy and porous, porous, The magnetite-rich ore containing sspecularite, containing p e c u l a r i t e , dolomite, dolomite, and and quartz crystals c r y s t a l s in i n vugs. vugs. 6 �2) 2) Magnetite—rich Magnetite-rich ore ore is i s characteristically c h a r a c t e r i s t i c a l l y associated associated with w i t h quartz quartz veins. (+ dolomite, s u l f i d e ) veins. dolomite, sulfide) ±. ± 3) 3) Although ~ l t h o u g hthe the magnetite—rich magnetite-rich ore ore invariably invariably occurs occurs in i n hematitic hematitic iron—formation iron-formation (jaspilite), ( j a s p i l i t e ) , the the ore o r e bodies are a r e surrounded surrounded by by narrow narrow haloes haloes in i n which which jasper jasper was was converted converted to t o gray gray chert c h e r t or or milky milky quartz quartz and and some some specularite s p e c u l a r i t e was was reduced reduced to t o magnetite, magnetite, i s associated associated i n d i c a t i n g that t h a t the the formation formation of of magnetite-rich magnetite-rich ore ore is indicating with w i t h aa reducing reducing process process rather r a t h e r than than an anoxidizing oxidizingprocess process such such as as weathering. weathering. + The magnetite—richore oreiis s probably probably of of hydrothermal hydrothermal origin o r i g i nand andbecause because The magnetite-rich s the only only recognized recognizedpost postiron—formation iron-formation Penokean regional metamorphism iis Penokean regional metamorphism the fluids f l u i d swere wereprobably probably derived derivedby by dehydration dehydration and and dedethermal event, event, the thermal carbonatization carbonatization of ofthe theiron—formation iron-formation and and underlying underlying rocks rocks during during progressive progressive regional metamorphism metamorphism which which reached reached sillimanite s i l l i m a n i t e grade grade at a t Republic. Republic. regional topt oof thethe Negaunee l o c a l i z a t i o n of of the t h eore o r eatathe t the p of NegauneeIron-formation Iron-formation The localization The might be explained explained through throughthe the buffering buffering aaction might be c t i o n of of the theiron-formation iron-formation on on A s fluids f l u i d s(considered (consideredhere hereasa sF120 H20 for for the oxygen oxygen fugacity h e fluids. f l u i d s . As the fugacity of of tthe CO2 rrich) i c h ) are a r e expelled expelled during during metamorphism metamorphism s i m p l i c i t y but but probably probably also a l s o CO2 simplicity w i l l contact contact first f i r s t the the and pass pass upward upward through through the t h e rock rock section, s e c t i o n , they they will and magnetite-silicate and r e l a t i v e l y reduced reduced magnetite-silicate andmagnetite—carbonate magnetite-carbonate uunits n i t s iin n the the relatively lower lower part p a r t of ofthe theNegaunee Negaunee and and will w i l ltend tendtoward towardan anequilibrium equilibriumoxygen oxygen fugacity determined on figure f i g u r e1,1, determined by by aa buffer b u f f e r curve curve fugacity (f02), ( f o 2 ) ,such such as a s point p o i n t 11on such as curve curve A, A, and and will w i l l contain contain concentrations of ferrous ferrous and and ferric f e r r i c iron iron such A s fluids f l u i d spass passupward upward and and species appropriate appropriate for f o r that t h a tf02 f o 2and andtemperature. temperature. As species contact the jaspilite, whichthe thej jaspilite contact the j a s p i l i t e , a aredox redoxreaction reaction must must occur occur iin n which a s p i l i t e is is partly of sspecularite p a r t l y reduced reduced by by the the conversion conversion of p e c u l a r i t e to t o magnetite magnetite and and the the fluids fluids are bybythethe hematite— a r e oxidized oxidized to toachieve achievean anf07, f o such suchasa point s p o i n2, t 2determined , determined hematiteThe increased increased f02 f of of the t h e fluids f l u i d sand andconsequent consequent B). Tfie magnetite buffer magnetite buffer fcurve urve B). 02 lower species lower ssolitility o l u b i l i t yofofferrous ferrousiron iron speciesand andthe theoxidation oxidationofofsome some ferrous ferrous iron i r o n to t o less l e s s soluble soluble ferric f e r r i c species species results r e s u l t s in i n the the precipitation p r e c i p i t a t i o n of of Textures clearly clearly magnetite. Textures magnetite. indicate i n d i c a t e that t h a t silica s i l i c a was removed removed during during the the wasp precipitated its hydrothermal activity a c t i v i t yand and the themagnetite magnetite presumably presumably was r e c i p i t a t e d iin n its hydrothermal Because t the h e equilibrium equilibriumff02 of the buffered assentlages is of the buffered assemblages i s very very place. Because small atmffor the02 probable small small (10-40 (10-40 to t o10—20 10-20 atm o r the probable conditions conditionsof ofmetamorphism), metamorphism), small volumes of l a r g e volumes volumes of l u i d , and and the t h e system system can can volumes of rock rock can can buffer buffer very very large of ffluid, buffered until u n t i l all a l l hematite hematite in i n the the jaspilite j a s p i l i t e is i s converted converted to t o magnetite. magnetite. remain buffered I propose that t h a t the the magnetite—rich magnetite-rich ore ore has has formed formed by: by: 1) 1) the reduction reduction of hematite to t o magnetite magnetite during duringa ahematite—magnetite hematite-magnetite b u f f e r reaction; reaction; 2) 2) buffer of the precipitation p r e c i p i t a t i o nofofmagnetite magnetitefrom fromhydrothermal hydrothermal (metamorphic) (metamorphic) ffluids l u i d s as a s the the the fluids oxidized during duringt that reaction and and tthe f l u i d s were were oxidized h a t bbuffer u f f e r reaction h e ssolubility o l u b i l i t y of of i r o nwas was decreased. decreased. ferrous iron 7 �2 t HEM. 1 Fe—SILICATE T Figure Figure 1.-— I.-- T—f0 T-f diagram showing e l a t i v e positions p o s i t i o n sofof hematite-magnetite diagram showingrrelative hematite—magnetite 02 buffer buffer curvi curveand and aabuffer buffercurve curvedetermined determined by by the the equilibruim: equilibruim: quartz magnetite == Fe—silicate. F e - s i l i c a t e . Points Points 1 1 and and 22 iillustrated l l u s t r a t e d difdifquartz ++ magnetite ference ference in i n f02 f o2 controlled controlledby by the thebuffered bufferedassemblages assemblages at a t constant constantT. T. The formation ore t oto require e s t r i c t e d set set The formationofof magnetite-rich magnetite—rich oreappears appears requirea ar restricted of of conditions: conditions : 1) must reach 1)Metamorphism Metamorphism must reach a t at l eleast a s t bbiotite i o t i t e grade, grade, although although most most l l large l a r g e ones ones are a r e in i n garnet garnet or o rhigher higher grade. grade. ore bodies bodies and and aall ore 2) 2 ) Iron-formation Iron-formation with mostly ferric f e r r i c iron, i r o n , such as a s jaspilite, j a s p i l i t e , must be physically physically above above iron-formation iron-formation with w i t h abundant abundant ferrous ferrous iron. iron. 3) 3) A stratigraphic s t r a t i g r a p h i c or o r structural s t r u c t u r a l trap t r a p capable of concentrating concentrating the the flow flow of of fluids f l u i d s must must be be present. present. The The Goodrich Goodrich Quartzite Quartzite and and metadiabase metadiabase sills s i l l s and and dikes dikes were were apparently apparently relatively r e l a t i v e l y impermeable, impermeable, and the Negaunee—Goodrich Negaunee-Goodrich contact contact near near anticlinal a n t i c l i n a l crests c r e s t s and and dikedikeand the quartzite q u a r t z i t e intersections i n t e r s e c t i o n s were were favorable favorable loci l o c i for f o rore o r eformation. formation. The absenceofofany anyofof these these tthree The absence h r e e conditions conditions iinhibits n h i b i t s the t h eformation formation of of magnetite-rich magnetite-rich ore. ore. References References Paderson, G . J . , 1968, 1968, The The Marquette Marquette district, d i s t r i c t , Michigan, Michigan, in i n Ridge, Ridge, J.D., J.D., Anderson, G.J., (ed.), (Graton-Sales (ed. ) , Ore deposits of the t h e United United States, S t a t e s , 1933—1967 1933-1967T~raton-Sales Volume), V. 1: 1:New New York, York, Pat. Am. Inst. I n s t . Mining, Metall., Metall., and and Petroleum Petroleum Volume), V. Engineers, Engineers, p. p. 505—517. 505-517. Boyum, B.H., 1964, 1964, The The Marquette Marquette mineral mineral district, d i s t r i c t , Michigan: Michigan: Inst. I n s t . on on Boyum, B.H., Lake Lake Superior Superior Geology, Geology, 10th, l o t h , Ishpeming, Ishpeming, Mich., Mich., May May 1964, 1964, Guidebook, Guidebook, 13 13 p. p Van C.R., and and Leith, Leith, C.K., C.K., 1911, 1911, The The geology geology of of the the Lake Lake Superior Superior Van Hise, Hise, C.R., region: region: U.S. U.S. Geol. Geol. Survey Survey Mon. Mon. 52, 52, 641 641 p. p. * Work Work done doneinicooperation n cooperation with Geological Survey Division, with Geological Survey Division, Michigan Dept. * of of Natural Natural Resources Resources 8 Michigan Dept. �THE VOLCANICS NORTH THE KEWEENAWAN KEWEENAWAN VOLCANICS NORTH OF OF THE THE GOGEBIC GOGEBICRANGE RANGE IN I NWISCONSIN WISCONSIN Roger W. W. Cooper, Cooper, Department Department of o fGeology Geologyand andGeophysics, Geophysics, Roger U n i v e r s i t yofoWisconsin—Madison, f Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin 53706 53706 University ABSTRACT ABSTRACT The sequencennorth The Keweenawan Keweenawan v ovolcanic l c a n i c sequence o r t h of o f the t h eGogebic GogebicRange Range has has aa total t o t a lthickness thicknessofo more f more than than 35,000 35,000 feet f e e t and and an an attitude a t t i t u d e ofo fabout about This sequence of volcanic flows was investigated NW. T h i s sequence o f v o l c a n i c f l o w s was i n v e stigated N65-75 E, 70-80 N65—75 70—80 NW. to t o determine determine iiff aa stratigraphic s t r a t i g r a p h i c division d i v i s i o nofothe f t h eflows f l o w sinto i n tmappable o mappable units units Four units have been defined on the basis of texture, Four u n i t s have been d e f i n e d on t h e basis o f t e x t ure, c o u l d be be achieved. achieved. could petrographic characteristics, c h a r a c t e r i s t i c s ,and andchemical chemi c a l analyses. analyses. petrographic Unit U n i t 1, 1, which which is i s the t h e basal basal unit, u n i t , consists c o n s i s t s of o fabout about 5000 5000 ffeet e e t of of p i l l o w basalts b a s a l t sand and subalkaline subal k a l i n e basalts. basalts. The The basalts b a s a l t sare aremedium— medium- to to pillow The ttextures e x t u r e s most most common common i nint hthis i s unit unit f i n e - g r a i n e d and and grayish—green. grayish-green. The fine—grained are are intergranular i n t e r g r a n u l a r and and subophitic, s u b o p h i t i c , with w i t hophitic o p h i t itexture c t e x t u rless e l e scommon. s common. Unit U n i t 22 is i sabout about 20,000 20,000 ffeet e e t thick t h i c k and and consists c o n s i s t s of o f flows flows more more alkaline alkaline are aaphanitic The fflows l o w s are p h a n i t i c tto o fine-grained, fine-grained, than those those found U n i t 1. 1. The than found iinn Unit most common common The most t e xtextures t u r e s a are r e i nintergranular tergranular b l u i s h - g r a y to t oreddish-brown. reddish-brown. The bluish-gray Flows ooff rather r a t h e r basic basic and iintersertal n t e r s e r t a l with w i t hmicrophenocrysts microphenocrysts of o f plagioclase. plagioclase. Flows and composition neart hthe bottomo of and f felsic composition near e bottom f t hthe e uunit n i t give g i v e way way tto o intermediate i n t e r m e d i a t e and elsic flows upward. upward. flows Unit p o o r l yexposed exposed but b u t estimated estimated to t o be be 2000 2000 tto o 4000 4000 ffeet e e t thick. thick. U n i t 33 isi spoorly ItI tisi scomposed composed o of f pporphyritic o r p h y r i t i c f felsic e l s i c flows flows that t h a t have have aa ppink i n k t to o sslightly lightly purple abundantphenocrysts phenocrystsoof p u r p l e groundmass groundmass wwith i t h abundant f ffeldspar e l d s p a r and and quartz. Unit by gglacial U n i t 44 is i swidely w i d e l y covered covered by l a c i a l drift d r i f but t b uestimated t estimatedtot obe beabout about The flows appear to be mainly mafic, gray, and usually The flows appear t o be m a i n l y m a f i c , gray, and u sually 10,000 ffeet e e t thick. thick. 10,000 The flows are highly vesicular; pipe The flows are h i g h l y v e s i c u l a r ; p i p e n o t more more than than 20—25 20-25 f efeet e t tthick. hick. not amygdules and e s i c u l a rtops topsare are common. Interbedded Interbedded wwith i t h these these flows f l o w s are are amygdules and vvesicular common. The pebbles pebbles found found sedimentary rocks ranging from sedimentary rocks from conglomerate conglomerate ttoo shale. shale. The interbedded flows and These interbedded and i n these these beds beds are are predominantly predominantly f felsites. e l s i t e s . These in sedimentary beds beds pass pass upward upward into i n t othe t h eCopper CopperHarbor HarborConglomerate. Conglomerate. sedimentary The sequenced idisplays general compositional The Keweenawan Keweenawan v ovolcanic l c a n i c sequence s p l a y s aa general compositional trend upward t r e n d from from subalkaline s u b a l k a l i n e ttholeiitic h o l e i i t i basalts c b a s a l tat s athe t t hbase e base upwardthrough through After the extrusion o f these these the t h e porphyritic p o r p h y r i t i c felsic f e l s i c flows flows of o f Unit U n i t 3. 3. A f t e r t h e e x t r u s i o n of f e l s i cflows flowsthere t h e r eappears appears to t ohave have been been iintermittent n t e r m i t t e n t volcanism volcanism of o f aa felsic more alongwwith more mmafic a f i c nnature a t u r e along i t h eerosion r o s i o n o of f t the h e ffelsic e l s i c flows. flows. 9 �SOUTHWEST WISCONSIN PEDIPLAIN SOUTHWEST WISCONSINAS ASA ADIJRICRIJSTED DURICRUSTED PEDIPLAIN Dury, Departments of GG. . HH. . Dury, o f Geography and and Geology, Geology, The The University U n i v e r s i t y of o f Wisconsin-Madison, Wisconsin-Madison, Science S c i e n c e Hall, H a l l , Madison, Madison, Wisconsin Wisconsin 53706. 53706. ABSTRACT ABSTRACT The Driftless D r i f t l e s s Area of of Southwest Wisconsin and and adjacent adjacent parts p a r t s of of Minnesota, Iowa, Iowa, and and Illinois I l l i n o i s consists c o n s i s t s of o f dissectdissected e d plateau p l a t e a u country c o u n t r y traversed t r a v e r s e d by by the t h e Wisconsin Wisconsin and and MississMississhas iippi p p i Rivers. R i v e r s . IIn n tthe h e ppast, a s t , the t h e area area h a s been described d e s c r i b e d in in terms o of orr more more ppeneplains, terms o of terms f one o e n e p l a i n s , aand/or n d / o r iin n terms f a sseries e r i e s of o f cuestas. cuestas. IIn n aactuality, c t u a l i t y , it i t is i s recognizable r e c o g n i z a b l e as a s aa dissected d i s s e c t e d pedipedithe few residuals that have escaped plain: p lain: the residuals t h a t e s c a p e d planation p l a n a t i o n rise rise ssharply h a r p l y from the t h e summit surface s u r f a c e and and exhibit e x h i b i t typical t y p i c a l pedipedii s widespread, widespread, ment profiles. p r o f i l e s . Evidence of o f deep deep weathering w e a t h e r i n g is On carbonates, the rregardless e g a r d l e s s of o f lithology. l i t h o l o g y . On c a r b o n a t e s , t h e deep deep weatherweathering i n g pprofiles r o f i l e s consist c o n s i s t of o f rotted r o t t e d rock r o c k and and red r e d residuum; residuum; but but part p a r t of o f the t h e latter l a t t e r may have been introduced i n t r o d u c e d subsequently subsequently weathering. tto o deep w e a t h e r i n g . On On arenites, a r e n i t e s , the t h e profiles p r o f i l e s are a r e varyingly varyingly horizonated h o r i z o n a t e d into i n t o pallid, p a l l i d , mottled, m o t t l e d , and and duricrusted d u r i c r u s t e d zones, zones, tthe h e ppallid a l l i d zones zones frequently f r e q u e n t l y showing tthe h e rresults e s u l t s of o f attack attack on q quartz grains, and the crusts ranging from highly uartz grains, the c r u s t s ranging highly fferruginous e r r u g i n o u s to t o highly h i g h l y siliceous. s i l i c e o u s . Crust C r u s t texture t e x t u r e can can be be Ferruginous nodules rreplicated e p l i c a t e d in i n Australian A u s t r a l i a n samples. s a m p l e s . F e r r u g i n o u s n o d u l e s in in Wisconsin pprofiles widely have developed tthe h e Wisconsin r o f i l e s aappear ppear w i d e l y tto o have within w i t h i n bedrock. bedrock. On O n eeither i t h e r side s i d e of of the t h e lower lower Wisconsin river, r i v e r , the the deeply-weathered d e e p l y - w e a t h e r e d and and d.uricrusted d u r i c r u s t e d ssurface u r f a c e defines d e f i n e s aa wide wide of which tthe glacial sshallow h a l l o w vvalley, a l l e y , iinto n t o tthe h e ffloor loor o f which he g lacial ssluiceway l u i c e w a y is i s incised. i n c i s e d . IInvestigation n v e s t i g a t i o n of o f ppossible o s s i b l e comparcompari s in i n proproaable b l e rrelationships e l a t i o n s h i p s for f o r the t h e Mississippi M i s s i s s i p p i trench t r e n c h is Ass could c o u l d bbe e expected, e x p e c t e d , there t h e r e is i s evidence e v i d e n c e that t h a t the the ggress. ress. A weathering was, to deep w e a t h e r i n g was, t o some extent e x t e n t at a t least, l e a s t , aa groundgroundwater and some some thin t h i n crusts c r u s t s appear a p p e a r to t o have have been been w a t e r phenomenon; and ddeposited e p o s i t e d under carbonates c a r b o n a t e s in i n the t h e subsurface. subsurface. Outstanding problems include O u t s t a n d i n g problems i n c l u d e the t h e distribution d i s t r i b u t i o n of o f the the deeply-weathered d e e p l y - w e a t h e r e d surface s u r f a c e in i n glaciated, g l a c i a t e d , in i n addition a d d i t i o n to t o ununglaciated, g l a c i a t e d , areas; a r e a s ; the t h e relationship r e l a t i o n s h i p of o f some some ferruginous ferruginous ccrusts r u s t s tto o ssuiphide u l p h i d e deposition d e p o s i t i o n or o r translocation; t r a n s l o c a t i o n ; and the the off the ttime-stratigraphic i m e - s t r a t i g r a p h i c pposition osition o t h e latest l a t e s t local l o c a l episode episode off deep weathering. o weathering. 10 �PROGRESS REPORT PROGRESS REPORT OF OFTHE THECOMMITTEE COMMITTEEON ONKEWEENAWAN KEWEENAWAN STRATIGRAPHY STRATIGRAPHY C. Green, Green, Geology Department, Department, University of of Minnesota, Minnesota, Duluth, John C. Duluth, Duluth, Duluth, Minnesota 55812 and Minnesota Geological Survey ABSTRACT A BSTRACT An A n informal Committee on Keweenawan Stratigraphy was formed in in February 1973 of p participants 1973 in i n response to t o tthe h e wishes of a r t i c i p a n t s at a t the Symposium Symposium on Late Precambrian Geology of of the t h e Lake Superior Area at a t the Annual Meeting members are a r e George V. V. Cohee, Cohee, Campbell Campbell t h e G.S.A. G.S.A. in i n Minneapolis. Minneapolis. Its members of the Craddock, H. Dott, A. Hubbard, Hubbard, Craddock, Robert H. Dott, John C. C. Green (chairman), (chairman), Harold A. Wm. H. Vs. H. Mcllwaine, McIlwaine, Glenn Glenn B. B. Morey, Morey, and and Walter Walter S. S. White. White. Some Some rather r a t h e r wide differences of of opinion and usage aare by tthe differences r e represented by h e members and because of s i n c e its i t s organization, organization, few few areas a r e a s of complete of the short s h o r t time elapsed since consensus have developed by the t h e mid—March mid-March abstract a b s t r a c t deadline. deadline. name "Keweenawan" The name "Keweenawan" appears appears to t o be be widely widely considered considered as a s applying to, to, not formally defined as, as, aa p provincial supergroup, a ass iif f not r o v i n c i a l llithostratigraphic i t h o s t r a t i g r a p h i c supergroup, part well as a s to t o that that p a r t of of geologic time t i m e when the Keweenawan Supergroup was being formed. formed. It would then be composed composed of of various groups and formations, formations, but many of these stratigraphic s t r a t i g r a p h i c units u n i t s have yet y e t to t o be formally formally defined. defined. An An attempt will w i l l be be made made to t o clarify c l a r i f y their t h e i r stratigraphic s t r a t i g r a p h i c relationships. relationships. wrestling with with tthe of tthe most appropriate The Committee is aalso l s o wrestling h e problem of h e most which tto of the sstratigraphic t r a t i g r a p h i c llevels e v e l s aatt which o define the base and tthe h e top of Keweenawan, the assumption that t h a t there there should be some some unifying geotectonic geotectonic Keweenawan, on the many respects respects tthe Disturbance" coherence implied implied by by the t h e name. name. IIn n many h e "Keweenawan Disturbance" could be compared with with tthe of Late T Triassic h e Palisades Disturbance of r i a s s i c time, time, and 8, "Keweenawan" rocks could be defined a as of tthis Keweenawan" rocks s those formed aass a result r e s u l t of his event ofevents eventsiin the area Mid—Continent Gravity High event or o r complex complex of n the a r e a of of tthe h e Mid-Continent High or o r aatt least l e a s t the the Lake Superior Superior District. District. 11 �AN AN UNUSUAL UNUSUAL MANGANESE MANGANESE DEPOSIT IN I NKEWEENAWAN KEWEENAWAN LAVA LAVA COPPER HARBOR, MICHIGAN COPPER HARBOR, MICHIGAN E. Heinrich, Department E. Wm. Wm. Heinrich, Department of o f Geology Geology and and Mineralogy, Mineralogy, U n i v e r s i t y of o fMichigan, Michigan, Ann Ann Arbor, Arbor, Michigan. Michigan. University ABSTRACT ABSTRACT One ooff the t h e rare r a r enon—cupriferous non-cupriferous mineral mineraldeposits depositsin iKeweenawan n Keweenawan lava lava One i s the t h emanganese manganese occurrence occurrence just j u s teast e a sof t oManganese f ManganeseLake Lake and and about about one one is m i l e south south of o fCopper Copper Harbor Harbor in i n sec. 58N,R.R.26W. 26W. Butler sec. 4,4, T.T.58N, mile B u t l e rand andBurbank Burbank (1929, p. p. 59) 59) rrefer e f e r to t o that t h a t deposit d e p o s i t as t h e Manganese Manganese mine" tate as "... the mine" and and sstate that t h a t "... some some ore was was shipped t h e mine." mine. " shipped from from the "... "... The ddeposit e p o s i t is i s aacalcite—rich c a l c i t e - r i c hreplacement replacement lens lensini nananamygdaloid amygdaloid The t h a t is i sstratigraphically s t r a t i g r a p h i c a l lay short a s h odistance r t d i s t a n cbelow e belowthe t h ebase baseofo fthe t h eCopper Copper that Harbor Harbor ("Great") ("Great") Conglomerate. Conglomerate. Old workingsi nindicate Old workings d i c a t e tthat h a t the t h e mineralimineral iz a t i o n extends extends east-west along t h ethe s t strike r i k e oof f tthe h e amygdaloid amygdaloid f ofor r aatt least least zation east—west along a few few hundred hundred ffeet. e e t . The The replacement o n s i s t s ooff material m a t e r i a l grading grading replacementrock rockcconsists from nearly n e a r l y pure pure coarse—grained coarse-grained wwhite h i t e ccalcite a l c i t etot ohigh—grade high-grade black black from manganese oxide ore. The manganese oxide The manganese manganese minerals c l u d e hypogene hypogene brauni te, mineralsi ninclude braunite, o r i e n t i t eand andmanganite manganiteand andsome some supergene supergene ppyrolusite. yrolusite. A orientite A trace t r a c e of o f chalcochalcocite c i t eand and very very minor minor goethite g o e t h i t eare arethe t h eonly o n l other y o t h ehypogene r hypogene species, species, and and l i m o n i t e , chalcedony chalcedony and and opal opal ini nsmall smallamounts m o u n t sare aresupergene. supergene. The The limonite, manganese minerals i n and ace t hthe e ccalcite. alcite. manganese mineralsv evein andrep1 replace T h i s occurrence occurrence of o f orientite, o r i e n t i t ea, hydrous a hydrous calcium-manganese s silicate, ilicate, This calcium—manganese i s believed b e l i e v e d to t obe beonly o n l ythe t h esecond second recorded recorded ffor o r the t h e world. world. (The is (The type type locality l o c a l i t yisi in s i Oriente n O r i e n t Province, e Province,Cuba.) Cuba.) The mineral appears as gglistening The mineral appears as listening copper-red needles forming minute minute rradial exceedingly copper-red need1 es forming a d i a l aggregates aggregates and and exceeding1 y ffineine- grained matted matted lenses. lenses. The amygdaloid,oother than being beingeextensively replaced by by ccalcite, The hhost o s t amygdaloid, t h e r than x t e n s i v e l y replaced alcite, which which aalso l s o f fills i l l s the t h e vesicles v e s i c l e s eentirely n t i r e l y alone, alone, iis s relatively r e l a t i v e l y fresh. f r e s h . Neither Neither native n a t i v e copper copper nor n o r the t h e characteristic c h a r a c t e r i s t i suite c s u i of t e accompanying o f accompanyingsecondary secondary s i l i c a t e sisi present, s present,although althoughnative n a t i v ecopper coppermineralization m i n e r a l i z a t i o nofothe f t hcross— e crosssilicates f i s s u r e type type occurs occurs at a t the t h e Clark Clark mine mine a short s h o r t distance d i s t a n c e to t o the t h e south. south. fissure The ddeposit e p o s i t is i s believed b e l i e v e d to t obe bepenesyngenetic penesyngenetic and rigin. The and volcanogenic volcanogenici nin oorigin. 12 �UPPERMISSISSIPPI MISSISSIPPI VALLEY UPPER VALLEY LEAD—ZINC LEAD-ZINC DISTRICT DISTRICT A. V. V. Heyl, A. Heyl, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225. ABSTRACT ABSTRACT The UpperMississippi MississippiValley Valley ddistrict The Upper i s t r i c thas hasbeen been the the source source of of about about aa billion bi 1 liondollars do1 l a r (present—day s (present-day prices) worth worth of of zinc zincand and lead, lead, and and minor minor amountsofof copper copper and and barite. barite. Ore amounts Ore deposits deposits are are chiefly chiefly ininlimestone limestone and and dolomite of of the Galena, Decorah,and andP lPlatteville dolomite Galena, Decorah, a t t e v i l l e Formations, Formations, aall l l of of Middle Middle Locally, small of lead, Ordovician age. age. Locally, small deposits deposits of lead, zinc, zinc, and and iron iron sulfide s u l f i d ehave have been mined mined from from underlying underlying Lower been Lower Ordovician Ordovi cian dolomite do1 omi t eand andUpper Upper Cambrian Cambrian sandstoneand andover1 overlying UpperOrdovician Ordovicianshale shale and andSiSilurian sandstone yi ng Upper 1uri an dolomite. do1 omi t e . No No post—Precambrian igneous rocks known theregion, region, and andggranitic post-Precambrian igneous rocks areareknown in in the r a n i t i c and and metasedimentaryPrecambrian Precambrian basement rocks unconformably underlie metasedimentary basement rocks unconformably underlie thethed idistrict strict at algal reefs a t depths depths of 1,500 1,500 to t o 2,000 2,000 feet. f e e t . No No algal reefs are are known known in the the Middle Middle Ordovician rocks, rocks, and b u t not not an an unconformity, unconformi t y , separates separates these these Ordovician and a diastem, di astern, but rocks rocks from from Upper Upper Ordovician Ordovician shale. The The sstrata t r a t a are are gently gently flexed and and faulted, probably largely largely the probably the result r e s u l tofofgentle gentlecompressive compressive and and rotational rotational adjustments adjustments in the along the underlying underlying crystalline c r y s t a l l i nbasement, e basement,especially especially alonglineaments lineamentsbetween between basement blocks. blocks. Folds basement Folds of three three orders orders ofofmagnitude magnitude are are recognized, recognized, and and many relatedjoints joints and reverse, sstrike—slip, normalf faults of small many related and reverse, t r i k e - s l i p , and and normal a u l t s of small to to moderate displacements displacements are are present. moderate The zinc—leaddeposits depositsrange rangei ninplan plan from fromllinear The zinc-lead i n e a r through through arcuate arcuate to to Theyare areepigenetic epigeneticand andp opostlithification Most ore eelliptical. l l i p t i c a l . They s t l i t h i f i c a t i o n deposits. deposits. Most and vugs, i n fractures, fractures,breccias, brecci as, and vugsbut , b usome t someimpregnated impregnated openspaces spaces in ffilled i 11edopen and replaced replaced wall wallrock. openspace spacei is along shears, small reverse and rock. The The open s a1 ong shears, reverse and and bedding—plane joints re1 related bedding-pl ane f a ufaults, l t s , joints ated tto o intermediate intermediate tto o small small folds, folds, and and within structures. Sphalerite and galena are are the the principal within solution—slump solution-slump structures. and galena ore minerals, and ore and the the general general sequence sequence of deposition depositionofofmain mainore oreand andgangue gangue minerals was: quartz, iillite, was: quartz, l l i t e dolomite, , dolomite, pyrite, pyrite,marcasite, marcasite, cobaltite(?), cobal t i t e ( ? ) , sphalerite, galena, chalcopyrite,mmillerite, sphalerite, galena, chalcopyrite, i l l e r i t e , barite, b a r i t e , and and calcite. c a l c i t e . Wallrock Wall rock rocks,ssilicification, aalterations l t e r a t i o n s include include solution of the the carbonate carbonate rocks, i l i c i f i c a t i o n dolomiti— , dolomititype of of clay, zation, changes changes i in n type clay, addition additionofoftrace traceelements, elements, and and sanding sanding of dolomite. Country rock between orebodies bodiesiis Country rock between ore s unaltered. Oxygen-isotope, carbon-isotope, lead-isotope, Oxygen-isotope, carbon-isotope, lead-isotope, sulfur—isotope, sulfur-isotope, and and Bubbles in sphalerite—stratigraphy studies studies are or in progress. sphalerite-stratigraphy are completed completed or progress. Bubbles sulfide and mineralsare are ffilled sulfide and gangue gangue minerals i l l e dwith withconcentrated concentratednear—neutral near-neutral chloride brines that lead iinn the brines t h a t have have filling f i l l i n temperatures g temperaturesofof1200 120' tot o40°C. 40°C The The lead the galena iiss notably galena notably radiogenic. radiogenic. Themetals metals and andsulfur sulfur are postulated The postulated to t o be be derived derived from fromheated heated basin basin brines that were later diluted by meteoric waters. magmaticf lfluid brines t h a t were l a t e r diluted by meteoric waters. A A magmatic u i d contribution possible, but b u t iti tisi snot notsupported supported by by present present ffluid l u i d inclusion inclusion data. data. bution is possible, magmatichearth hearthinin the the basin basin areas AA magmatic areas ttoo the the south south and and southwest southwest is i s the themost most possible heat possible heat source. source. AA large lateral l a t e r a component l component of of flow flowthrough throughpermeable permeable Cambriansandstone sandstone updip from basinsi sisprobable, probable, bbut u t available available evidence evidence Cambrian updip from thethebasins 13 �the ddistrict Within the istrict suggests flow through fracture zones. suggests some some flow through basement basement fracture zones. Within the ore from tthe aquifers through ore solutions solutions flowed flowed upward upward from h e aquifers through available fracture fracturesystems systems into i n t oMiddle MiddleOrdovician Ordovician strata s t r a t awhere wherethey theyleached leachedcarbonate carbonate physicalrrestraints properties of of the rocks. rocks. Changes Changes i ninphysical e s t r a i n t s and and chemical chemical properties the ore ore solutions n andnear nearopen openspaces spaces solutions allowed allowed ore ore minerals minerals tot obebedeposited depositedini and derived from from leaching. leaching. derived 14 �THE THE GEOLOGY GEOLOGY OF OF BEECHER BEECHER AND AND PEMBINE PEMBINE TOWNSHIPS TOWNSHIPS MARINETTE MARINETTE COUNTY, COUNTY, WISCONSIN WISCONSIN Robert A. Jenkins Jenkins Robert A. Department of of Geology Geology and and Geophysics Geophysics Department University of of Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin University Four Four metavolcanic metavolcanic formations, formations, separated separated by by major major faults, faults, occur occur in in Beecher Beecher and and Pembine Pembine townships townships in in northeastern northeastern Marinette County, County, Wisconsin. Wisconsin. The formations formations are are the the Quinnesec Quinnesec Marinette Formation, the the Mc Allister Allister Formation, Formation, the the Beecher Beecher Formation, Formation, Formation, the Pemene Pemene Formation. Formation. The relative relative ages ages are are uncertain uncertain and the but but the the order order of of naming naming is is suggested suggested as as the the order order of of decreasing decreasing age. All All the the formations formations have been been folded folded and and regionally regionally metametaage. morphosed morphosed to to greenschist greenschist facies. facies. In In general general the the rocks rocks have have not not been been strongly strongly sheared sheared or or altered, altered, and and primary structures structures volcanics have been been intruded intruded by by are well well preserved. preserved. The The volcanios are granite, granodiorites,quartz quartzdiorites, diorites,and andultrainafics. ultramafics. granite, granodiorites, The The Quinnesec Quinnesec Formation, Formation, over over 10,000 10,000 ft. thick, thick, consists consists predominantly predominantly of of tholeiitic tholeiitio metabasalts metabasalts and and cala-alkaline cala-alkaline metametaandesites. The formation formation is is isoclinally isoclinally folded; folded; axial axial planes planes andesites. of the the folds folds are are vertical vertical and and strike strike east. east. The The andesites andesites are are of of of two two types, types, one one nonporphyritic nonporphyritic and and pillowed, pillowed, having having its its source to the west and the other, other, porphyritic porphyritic and mainly agglomeratic, 100 to to 1,000 1,000 agglomeratic, having having its its source source to to the the east. east. AA 100 ft. thick is interlayered interlayered with with the the thick porphyritic porphyritic rhyolite rhyolite flow flow is andesites. andesites. The Mc Allister Formation, Formation, 1,000 1,000 to to nossibly ~ossibly10,000 10,000 ft ft The thick, consists consists of of metamorphosed metamorphosed tholeiitic tholeiitio basalt basalt agglomeragglomerthick, ate. alps vertically, vertically, and and faces faces ate. The The formation formation strikes strikes east, east, aips south. Fragment Fragment size in in the formation formation increases increases from from west west to to south. east, suggesting suggesting aa vent vent to to the the east. east. east, The Beecher Beecher Formation, Formation, at at least least 10,000 10,000 ft. thick, thick, strikes strikes N50°W, N~O'W, dips dips vertically, vertically, and and faces faces north. north. The The lower lower 9,000 9,000ft. ft. consists mainly mainly of of rhyolite rhyolite and and rhyodacite rhyodacite flows. flows. The The upper upper consists 1,000 ft. of the formation rhyformation is is an an alternation alternation of of bedded bedded rhy— olitic olitic tuffs tuffs and and acidic acidic fragmentals. fragmentals. The lower lower part part of of the the formation formation is is more highly sheared sheared and and altered than than other other formformations ations in in the the area. area. This This may be be due due to to intrusion intrusion of of the the Amberg Amberg granite granite into into the the lower lower part part of of the the formation. formation. Formation consists consists of 7,000 ft. of microspher— The Pemene Formation of microspherulitic ulitic soda soda rich rich rhyolite rhyolite and and rhyodacite rhyodacite flows. flows. The The flows flows are interlayered units and interlayered with a few few thin thin sedimentary sedimentary units and were Individual flows apparently apparently extruded extruded subaqueously. subaqueously. Individual flows are are 500 500 to 1,200 1,200 ft. thick and traceable traceable laterally laterally for for over over four four miles. miles. the The formation formation is is folded folded into into an an east east trending trending asemmetric asemmetric on the north limb limb dip dobly doublyplunging plunging syncline. syncline. The units on 55 SS and and those those on on the the south south limb limb are are vertical. vertical. 55 Thin various rock rock types Thin sections sections of the various types have been been examined examined 15 �ffor o r primary structures s t r u c t u r e s and to t o determine determine metamorphic metamorphic grade. grade. Whole rock major element analyses a n a l y s e s have have been been run r u n using u s i n g the the eelectron l e c t r o n microprobe. microprobe. These analyses a n a l y s e s have been used to to iidentify d e n t i f y rock types o determine h e petrochemical types and and tto determine tthe petrochemical c h a r a c t e r i s t i c s of the t h e voloanios. volcanics. characteristics t r e n d s indicate I n d i c a t e that t h a t the t h e rocks r o c k s of of the the The petrochemical trends aarea r e a may be the t h e products of several s e v e r a l cycles c y c l e s of of volcanism. volcanism. Each formation is i s chemically chemically distinctive. d i s t i n c t i v e . The Qtxinnesec Quinnesec the n north Formation grades from f r o m tholelitic t h o l e l i t i c bbasalts a s a l t s Iin n the o r t h to to ccab-alkaline a l c - a l k a l i n e andesites a n d e s l t e s in i n tne tne south, south, suggesting suggesting that t n a t it It may have formed at a t the t h e edge edge of of an an island i s l a n d arch a r c h enviornment. enviornment. Mc Ablister Preliminary analyses a n a l y s e s indicate i n d i c a t e that t h a t the the M c A l l l s t e r Formation basaLts. It may therefore t h e r e f o r e correlate correlate cconsists o n s i s t s of ttholeittic h o l e l l t i c basalts. Formation oor may rrepresent with part p a r t of of the t h e Quinriesec Quinnesec Formation r Iit t may epresent a sseparate e p a r a t e volcanic v o l c a n i c cycle. c y c l e . The Beecher Formation Formation rhyolites rhyolltes and rrhyodacites are typical cab—alkaline h y o d a c i t e s a r e t y p i c a l c a l c - a l k a l i n e acidic a c i d i c vobcanics. volcanlcs. They may tie be the of the t h e aacidic c i d i c end product of t h e Quinnesec The pemene Pemene Formation rrhyolites volcanism. h y o l i t e s aare r e characterized characterized These These by higher h i g h e r Na20 Na20 and lower lower K20 K20 than t h a n normal normal rhyolites. rhyolites. volcanios are distinctly different from the rocks of the volcanics are d i s t i n c t l y d i f f e r e n t the rocks the Beecher Formation and therefore t h e r e f o r e probably rrepresent e p r e s e n t a separate separate period of volcanism. volcanism. The age of of the not t h e volcanism in i n the t h e area a r e a is is n o t positively positively known b but Rebelbo (1969) U-Pb d date z i r c o n U-Pb ate (1969) rreport e p o r t a zircon u t Banks and Rebello for a rhyolite just to the west of the area of 1905 (+30 for r h y o l i t e just t o the of a r e a of 1905 (+30 to to -10) m.y. This rrhyolite -10) m.y. h y o l i t e probably correlates c o r r e l a t e s with the the Beecher If this correlation is correct then the acidic Formation. cidic Formation. I f t h i s c o r r e l a t i o n i s correct then the a possibly volcanism and p o s s i b l y tthe h e mafic volcanism in In the t h e area a r e a is is upper Middle Precambrian in age. Middle Precanbrian i n age. 16 �PRECAMBRIAN PRECAMBRIAN NORTH-SOUTH NORTH-SOUTH ORIENTED ORIENTED FAULTS FAULTS IN IN THE THE WESTERN WESTERN MARQUETTE MARQUETTE DISTRICT, DISTRICT,NORTHERN NORTHERNMICHIGAN MICHIGAN John S. S. Klasner Klasner John Western Illinois W e s t e r n Illinois University University Macomb, Macomb. Illinois Illinois Thomas Thomas R. R. Turner Turner Michigan Michigan Technological Technological University University Houghton, Michigan Houghton, Michigan ABSTRACT ABSTRACT Recent has R e c e n t mapping mapping in in northern n o r t h e r n Michigan Michigan h a s indicated indicated the the presence p r e s e n c e of of prominent 100W W to t oNN 200 20' E E faults, faults, many many of of which which offset offset east-west east-west prominentNN100 T h e s e faults faults are a r e expressed e x p r e s s e d as a s shear shear trending Keweenawandiabase Keweenawan diabase dikes. dikes. These trending zones zones in in lower lower Precambrian P r e c a m b r i a n granites, g r a n i t e s ,offsets offsetsininthe thecontact contactbetween between middle middle and anddiscontinuities discontinuities and lower lower Precambrian P r e c a m b r i a n rocks, r o c k s , topographic topographic lineaments, l i n e a m e n t s ,and in aeromagnetic a e r o m a g n e t i c trends. trends. in Regionally Regionally tthese h e s e faults f a u l t s are a r e on on trend t r e n d with with major m a j o r lineaments l i n e a m e n t s observed observed ontthe Hinze and and others o t h e r s (1966) (1966) on h e bbasis a s i s of of aaeroeroby by other workers w o r k e r s in in the the area. a r e a . Hinze magnetic studies in eastern Lake Superior show a major north-northeast a m a j o r n o r t h n o r t h e a st magnetic studies i n e a s t e r n Lake S u p e r i o r show trending trending fault fault extending extending nnorth o r t h aacross c r o s s the the lake l a k e just just east e a s tof of the the tip t i pof of the the in nnorth Keweenaw Peninsula. Peninsula. La L a Berge B e r g e (1972) (1972) in o r t h central c e n t r a l Wisconsin Wisconsin has has Keweenaw mapped These mapped major m a j o r northeast n o r t h e a s t trending trending shear s h e a rzones zonesup u pto t oone onemile m i l eininwidth. width. These features f e a t u r e s coupled coupled with with major m a j o r lineations lineations on on psuedo psuedo radar r a d a rphotographs photographs suggest suggest that t h a t aa major m a j o r fault fault zone zone bisects b i s e c t s the the arcuate a r c u a t eshaped shapedarea a r e aoutlined outlinedby by the the midmidcontinent continent gravity gravity high high and and proposed proposedKeweenawan Keweenawan rift. rift. With movement, studies With rregard e g a r d to to the the timing timing of of movement, studies in in the the western w e s t e r n part part of near of the the northern n o r t h e r n complex complex n e a r Herman, Herman, Michigan Michigan suggest s u g g e s t that that at a t least l e a s t some some of the faults may m a y have have been r i o r tto o Penokean e t a m o r p h i s m . For For of been active active pprior Penokeanmmetamorphism. example, north-south fault example, aa body body of of gabbro gabbro occupies occupies aa north-south fault tthat h a t cuts cuts granite granite gneiss, g n e i s s , and and the the gabbro gabbro is i sinterpreted i n t e r p r e t e dtot ohave havebeen beenmetamorphosed m e t a m o r p h o s e d by by Penokean oorr some s o m e earlier e a r l i e r thermal t h e r m a levent. event. Penokean In places dikes aare In many many p l a c e s east-west e a s t - w e s t Keweenawan Keweenawan dikes r e offset offset at a t the the northnorthhas found ffor the dikes No evidence evidence h a s been been found o r sshearing h e a r i n g of of the d i k e s at a t these these south faults. No faults faults and and in in some s o m e instances i n s t a n c e sthe theKeweenawan Keweenawan dikes dikes have have been been found found to t o intrude intrude N e v e r t h e l e s s , the the conclusion conclusion seems s e e m s inescapable inescapable that that along the fault f a u l tzone. zone. Nevertheless, along the numerous occurrence of offset dikes at the north-south faults must denote the n u m e r o u s o c c u r r e n c e of offset dikes a t the north-south faults m u s t denote post-Keweenawan post-Keweenawan fault fault movement. movement. 17 �References Hinze, Wrn. O'Hara, N. W., Trow, Wm. J., O'Hara, N. W., Trow, 3. J. W. W. and and Secor, G. G. B., 1966, 1966, Aeromagnetic Studies Studies ofofEEastern Lake Superior, Superior, in the the EEarth Aeromagnetic a s t e r n Lake arth Beneath the Continents, G. U. U. Geo& Smith, ed. ed. ,, A. G. Beneath the Continents, Steinhart Steinhart & physical physical Monograph Monograph 10, 10, pp. pp. 95-110. 95-110. La Zones in in the the PPreL a Berge, G. G. L., L . , 1972, 1972, Lineaments Lineaments and and Mydonite Mydonite Zones re1: 18th 18th Ann. Ann. Inst. Inst. on on Lake Lake ccambrian a m b r i a n of of northern n o r t h e r nWisconsin Wisconsin [abs. [abs,}: Superior Geology, Michigan, ppaper 27. Superior Geology, Houghton, Houghton, Michigan, a p e r 27. 18 �- GEOCHEMISTRYOF OF THE THE CALCIUM GEOCHEMISTRY CALCIUM - CARBON CARBON DIOXIDE DIOXIDEMETASOMATISM METASOMATISM AT PRESQUE MICHIGAN PKESQUE ISLE, ISLE, MARQUETTE, MICHIGAN M. D. Lewan, Lewan, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, M. Michigan Michigan Technological Technological University Presently With Shell Presently With Shell Oil Oil Company, Company, New New Orleans, Orleans, Louisiana Louisiana 70160 70160 ABSTRACT ABSTRACT A highly veined rock rock composed of of dolomite dolomite and quartz quartz with with peridotite at minor hematite, hematite, overlies overlies the the Presque Presque Isle Isle serpentinized serpentinized peridotite Marquette, Michigan. Marquette, Michigan. Petrographic Petrographic and field observations observations clearly clearly indicate indicate that that this this rock rock was was originally originally highly highly serpentinized serpentinized peridotite peridotite which has since since been been subjected subjected to to metasomatic metasomatic solutions. solutions. which has The The author author (Lewan, (Lewan, 1972) has interpreted interpreted this this dolomite-quartz dolomite-quartz rock as originally being a peripherial shear zone which which developed during the tectonic tectonic intrusion intrusion of of the the peridotite. peridotite. Either during during or or after after its its emplacement water water from the surrounding country rocks circulated through emplacement this highly fractured fractured peripherial peripherial zone zone causing causing extensive extensive serpentinizaserpentinization tion to the the still still warm warm but but cooling cooling peridotite. peridotite. Following Following the the period of of serpentinization a potash rich granite was was emplaced and and was was apparently serpentinization illitized by late late stage stage magmatic along its its outer outer boundary boundary where where illitized magmatic water water along it contact with with the comes in contact it comes the peridotite. peridotite. Both the the highly highly serpentinized serpentinized peridotite and illitized metasomatic soluperidotite illitized granite were susceptable susceptable to metasomatic soluwhich resulted in the formation of the now now existing existing dolomite-quartz tions which rock. objective of this was to investigate rock. The objective this study was investigate the chemical conditions which may may have induced this period parameters and prevailing conditions of metasomatism. of metasomatism. Comparative analysis of the chemical chemical composition composition of the Comparative the dolomite-quartz rock dolomite-quartz rock with the serpentinized peridotite and illitized granite indicates were introduced into granite indicates that calcium and carbon dioxide were system with with partial removal the system removal of of silica silica and and magnesium. Experimental Experimental work by Gordon with free work Gordon and and Greenwood Greenwood (1970) (1970) and Ellis (1959), (1959), along along with free metasomatism probably never energy calculations calculations suggest suggest that that the metasomatism exceeded 300°C. Luce (1972) has has shown shown that that serpentine serpentine is is most most soluble soluble 300°C Luce exceeded waters which which gradually become become more more basic basic as as the serpentine in acidic waters dissolution continues. dissolution continues. This increase in in pH probably also accompanied metasomatic solutions serpenthe metasomatic solutions during during the the dissolution dissolution of of the the highly highly serpenperipherial zones which which eventually eventually resulted resulted in tinized and illitized peripherial mobilization of silica the mobilization silica released released from from the the serpentine serpentine lattice lattice and and the the precipitation of precipitation of dolomite. dolomite. pre-Jacobsville This period of metasomatism has been dated as pre-Jacobsville peridotite sandstone and post-granite sandstone post-granite illitization. illitization. The occurrence of the peridotite greenstone terrain offers offers an-attractive anattractive hypothesis in greenstone hypothesis that that this this metasomatism may may have been a result somatism result of of the the expulsion expulsion of of fluids fluids from from neighneighboring rocks rocks during during the the regional regional metamorphism metamorphism of of the the area. area. 19 �REFERENCES REFERENCES CITED CITED Ellis, Carbon Dioxide (1959), The The Solubility Solubility of of Calcite Calcite in in Carbon Dioxide Ellis, A. J. (1959), Solutions, Am. 3. Sci., 257, pp 354-365. Solutions, Am. J. 257, pp 354-365. Cordon, M., and and Greenwood, Greenwood, H. H. 3. J. (1970), (1970), The The Reaction: Reaction: Dolomite Dolomite Gordon, T. T. M., + Quartz + Water == Talc +Quartz +Water Talc + Calcite Calcite + Carbon Carbon Dioxide, Dioxide, Am. Am. 3. J. Sc!., Sci., 268, 268, pp 225—242. 225-242. pp + + Lewan, and Weathering Weathering of the Lewan, M. XL D. (1972), (1972), Metasornatism Metasomatism and the Presque Presque Isle Isle Serpentinized Serpentinized Peridotite, Peridotite, Marquette, Marquette, Michigan, Michigan, Michigan Michigan Technological Technological University, University, unpublished unpublished M.S. M.S. Thesis, Thesis, 55 55 pp. pp. Luce, Luce, R. R. Kinetics Kinetics W., Bartlett, W., and Parks, Parks, G. 0. A A. Dissolution W., Bartlett, R. R. W., . (1972), (1972), Dissolution of Magnesium Silicates, Geochim. Cosmochim. Acta, of Magnesium Silicates, Geochim. Cosmochim. Acta, 36, 36,pp pp 35-50. 35-50. 20 �THE BIOGENIC ORIGIN THE ORIGIN OF OFPRIMARY PRIMARY MINERALS MINERALS IN IN LAKE LAKE SUPERIOR SUPERIORPRECAMBRIAN PRECAMBRIAN IRON-FORMATION IRON-FORMATION M. Lougheed and 7. J. Mancuso, Department M. S. S. Lougheed and J. J. Mancuso, Geology, Department of of Geology, Bowling Bowling Green University, University, Bowling Bowling Green, Green, Ohio Ohio 43403 43403 ABSTRACT ABSTRACT Primary Primary minerals minerals in in the the Lake Lake Superior Superior Precambrian Precambrian ironironformations formations are are the the direct direct products products of of the the life life processes processes of of a melange of filamentous filamentous and and unicellular unicellular organisms organisms together together with minerals so with associated associated bacteria. bacteria. Primary Primary minerals so formed formed are are aragonite Pyrite is aragonite and/or calcite, calcite, magnetite, magnetite, and and opal. opal. Pyrite is formed formed during decay decay of of organic organic material material with with attendant attendant sulfate sulfate reducing bacteria and is therefore later in origin than reducing than the the above above three three minerals although although it it too too is is of of biogenic biogenic origin origin and may be Hematite occurs be considered considered primary. primary. Hematite occurs as as an an alteraalteration product of earlier earlier formed minerals and is not considered a primary mineral. a primary mineral. bacteria and is therefore later in Aragonite Aragonite or or calcite calcite crystals crystals are are biogenically deposited deposited structural structural elements elements occurring occurring as as submicron submicron width width prisms prisms oriented normal to an algal mat, mat, and producing in turn a carbonate mat. carbonate mat. A succession succession of of algal algal and carbonate carbonate mats (laminae) occurs occurs in horizontally horizontally banded banded iron-formation; iron-formation; in in domical or columnar domical columnar stromatolites; stromatolites; as as coatings coatings on on granules granules (pellets); or forming forming micro—oncoliths. micro-oncoliths. Micro-oncoliths Micro-oncoliths are are typically 0—50 microns microns in Calcium carbonate typically 220-50 in diameter. diameter. Calcium carbonate can can be dolomitized, dolomitized, sideratized, sideratized, or or silicified. silicified. Magnetite initially occurs subMagnetite occurs as as a a diffuse diffuse cloud cloud of of subwithin the micron sized sized crystals crystals within the protoplasm of unicellular unicellular Too plants. plants. Too high aa concentration concentration of of oxygen oxygen produced produced by by photosynthesis in photosynthesis in these these unicellular unicellular plants can can be lethal lethal to them; they therefore therefore oxidize oxidize iron iron that that is is dissolved dissolved in in the the water to to produce magnetite, thereby attenuating attenuating a a lethal lethal buildup of oxygen. oxygen. During During deposition deposition and and early early diagenesis diagenesis buildup of magnetite may may be be recrystallized to the submicron crystals of magnetite form Diagenesis may subseform coarser coarser octahedra octahedra of of magnetite. magnetite. Diagenesis subsequently produce quently produce megascopic megascopic subhedral subhedral masses masses of of magnetite. magnetite. Some magnetite is produced by oxidation of siderite during the depositional depositional stage, stage, which which subsequently subsequently may may be be recrystalrecrystallized during diagenesis diagenesis in in aa similar similar manner manner to to that that of of primary primary biogenic magnetite. biogenic magnetite. Siliceous Siliceous tests tests of of microorganisms microorganisms yield yield the the hydrous hydrous silica, which during deposition is almost invariably comminuted to an an opaline opaline slurry. slurry. This slurry slurry readily readily dehydrates dehydrates during during diagenesis to diagenesis to chalcedony chalcedony or or more more often often to to chert. chert. From From five five to seven seven types types of siliceous siliceous tests tests of of unicellular unicellular organisms organisms 21 �occur. occur. Usually Usually the t h e cavities c a v i t i e s are a r e filled f i l l e d with w i t h organically organically stained s t a i n e d chalcedony, chalcedony, and and often o f t e n submicron submicron sized s i z e d anhedra anhedra of of carbonate c a r b o n a t e are a r e present. p r e s e n t . The The test t e s t walls w a l l s are a r e not n o t organically organically stained; clear. Occasionally O c c a s i o n a l l y the t h e core c o r e and and s t a i n e d ; they t h e y are a r e water w a t e r clear. test t e s t are a r e recrystallized r e c r y s t a l l i z e d to t o an an optically o p t i c a l l y oriented o r i e n t e d sphere s p h e r e or or ellipsoid e l l i p s o i d of o f quartz. q u a r t z . The The tests t e s t s range range in i n width w i d t h from from 55 to to 25 microns although a l t h o u g h aa few few may may exceed exceed 50 5 0 microns. microns. PreservaPreservation t i o n of o f siliceous s i l i c e o u s tests tests occurs o c c u r s only o n l y when when they t h e y were were deposited deposited in n e v e r when when water w a t e r current c u r r e n t activity a c t i v i t y prevailed. prevailed. i n quiet q u i e t water, w a t e r , never They therefore t h e r e f o r e are a r e not n o t found found in i n association a s s o c i a t i o n with w i t h granules granules or o r stromatoljtes. stromatolites. P y r i t e may be thought t h o u g h t of o f as a s primary in i n the t h e sense s e n s e that that Pyrite it results r e s u l t s from from iron i r o n in i n the t h e water w a t e r reacting r e a c t i n g with w i t h sulphur sulphur produced produced by sulfate s u l f a t e reducing r e d u c i n g bacteria b a c t e r i a during d u r i n g decay decay of of organic o r g a n i c debris. d e b r i s . Pyrite P y r i t e occurs o c c u r s as a s discrete d i s c r e t e octahedrons o c t a h e d r o n s or or octahedrons o c t a h e d r o n s modified m o d i f i e d by aa cube, cube, as a s framboidal f r a m b o i d a l octahedra, o c t a h e d r a , or or as a s framboidal f r a m b o i d a l mats mats or o r spheres. s p h e r e s . Secondary Secondary replacement replacement pyrite pyrite formed during d u r i n g diagenesis d i a g e n e s i s is i s ubiquitous. ubiquitous. 22 �-- THE WOLF RIVER BATHOLITH BATHOLITH -- A L LATE THE WOLF RIVER ATE PRECANBRIA1 PRECAMBRIAN RAPAKIVI MPAKIVI MASSIF I NNORTHEASTERN NORTBBASTERN WISCONSIN WISCONSIN MASSIF IN L. G. G. Medaris, . Nyles, Medaris, Jr., Jr., J. L. L. Anderson, Anderson, and J. J. R B. Myles, Department of Geology Wisconsin, Madison 53706 Geology and Geophysics, Geophysics, University of of Wisconsin, 53706 ABSTRACT AESTRACT Anorogenic, epizonal batholith, epizonal ggranitic r a n i t i c rocks rocks of of the t h eWolf Wolf River River b atholith, covering an aarea of approximately 3600 square miles, miles, represent a major covering r e a of element of the t h e Precambrian Precambrian terrain t e r r a i n in i n northeastern northeastern Wisconsin. Wisconsin. This batholith, 1500 m. m. y. y. iin age, has llithologic, n age, i t h o l o g i c , mineralogic, mineralogic, b a t h o l i t h , 11150 1450 tto o 1500 chemical, and structural respect to that are a r e similar similar in i n every every respect to chemical, s t r u c t u r a l ffeatures e a t u r e s that those those of of the t h e classic c l a s s i c rapakivi rapakivi massifs massifs in i nFinland. Finland. A vvariety been distinguished, distinguished, including including ggranite, A a r i e t y of of rock rock types types have have been ranite, quartz monzonite,r rhyolite, trachyandesite, but quartz monzonite, monzonite, ssyenite, y e n i t e , monzonite, h y o l i t e , and and trachyandesite, but quartz monzonite of tthe monzonite iiss predominant, predominant, accounting accounting for f o r 87% 87% of h e exposed exposed area. A porphyritic porphyriticttexture of aalkali A e x t u r e iis s characteristic, c h a r a c t e r i s t i c , ini nwhich which phenocrysts phenocrysts of lkali feldspar f e l d s p a r and, and, to t o a lesser l e s s e r extent, e x t e n t , plagioclase and quartz quartz are a r e set s e t in i n aa medium— tto mediumo fine—grained fine-grained matrix of quartz, quartz, two feldspars, f e l d s p a r s , and mafic minerals. Rapakivi texture t e x t u r e is i s extensively developed in i n the t h e Waupaca Waupaca quartz monzonite and and occurs occurs in i n minor minor amounts amounts throughout throughout the t h e batholith. batholith. Quartz iis many llithologic units; s euhedral iin n many ithologic u n i t s ; bbiotite i o t i t e and hornblende are Quartz generally anhedral and interstitial i n t e r s t i t i a l to t o feldspars f e l d s p a r s and quartz. quartz. The The granitic g r a n i t i c rocks rocks of of the t h e batholith b a t h o l i t h tend tend to t o be be rich r i c hini nSiO SiO and alkalies, , CaO, and and MgO. TLg batho— andpoor poor in i nAl20 A120 , MgO. ~ bathoe a l k a l i e s , particularly p a r t i c u l a r l yKK0,0,and 11th l i t h has has alkaline a l k a l i n e affiniies, a f f i n i z i e s , although only only eraluminous Jeraluminous and metaluminous metalminous types have been recognized recognized so so far. f a r , Values of of normative Q—Ab—Or Q-Ab-Or for for representative r e p r e s e n t a t i v e specimens specimens plot p l o t close c l o s e to t o a low low pressure thermal trough and and minimum minimum for f o r the t h e experimental experimental "granite" "granite" system, system, with with aa slight s l i g h tdisplacement displacement towards normative Or. Or. towards Perthitic P e r t h i t i c alkali a l k a l ifeldspar feldsparisi the s t hpredominant e predominant mineral mineral in i n the t h e bathoJ.ith, batholith, accompanied quartzand andplagioclase, plagioclase, ranging accompanied bybyquartz ranging in i ncomposition composition from from An An 3 to to )tO, An Iron—richbbiotite 40, with most values falling f a l l i n g between A n 10 1 0 tto o 25. 25. Iron-rich i o t i t e and hornblende are minerals, although olivine, a r e the t h e predominant mafic minerals, o l i v i n e , clino— clinopyroxene, and pyroxene, and orthopyroxene orthopyroxene occur occur in i n monzonite monzonite and and trachyandesite. trachyandesite. Fluorite Fluorite is batholith, i s tthe h e most widespread accessory mineral in i n tthe he b a t h o l i t h , and a halogen— halogenrich biotite i s reflected r e f l e c t e d in i n high Cl C l and F F contents of of b i o t i t e and r i c h environment is hornblende. Wolf River b batholith The Wolf a t h o l i t h may have crystallized c r y s t a l l i z e d from from relatively r e l a t i v e l y dry dry granitic partial off pre-existing pre—existing g r a n i t i c magmas tthat h a t were derived by p a r t i a l melting o crustal materials, basaltic volcanics, v volcaniclastic crustal m a t e r i a l s , consisting c o n s i s t i n g of of b a s a l t i c volcanics olcaniclastic sediments, and quartz dioritic sediments, d i o r i t i c to t o granodioritic g r a n o d i o r i t i c plutonic plutonic rocks. rocks. , 23 �SUMMARY WISCONSIN SUhMkRY OOF F GLACIAL GEOLOGY GEOLOGY OF OFNORTH—CENTRAL NORTH-CENTRAL WISCONSIN D. M. Department of M. Mickelson, Mickelson, Department of Geology Geology and and Geophysics, Geophysics, University University of Wisconsin, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT ABSTRACT The The Pleistocene glacial g l a c i a lchronology chronology of of central c e n t r a land andnorthern northernWisconWisconnot not well well established. established. Early Early workers workers (Owen, (Owen, l8t7; 1847; Chamberlain, Chamberlain, 1907) outlined o u t l i n e d the t h e distribution d i s t r i b u t i o n of of glacial g l a c i a l deposits deposits and and 1882, Weidman, 1907) recognized aa presumed older o l d e r drift d r i f t outside the t h e terminal moraines of of WisWisconsin consin age. age. Hole Hole (1943) (1943) and and Thwaites (l913) (1943) concluded that t h a t the t h e older older d r i f t (Border order Drift) rift) was of of one one age age and and was deposited deposited in i n the t h e pre—Cary pre-Cary drift (pre—late ( p r e - l a t e Woodfordian) woodfordian) time. time. Radiocarbon Radiocarbon dates d a t e s (Black (Black and and Rubin, Rubin, 1968) beneath beneath the t h e Border Border Drift D r i f t in i n Wood Wood County County are a r e >>i5,O00 45,000 years years B.P. B.P. 1968) In I n southern southern and and western Wisconsin wood wood from from an an old o l d till till possible possible B. P. P. c o r r e l a t i v e with with the t h e Border Border Drift D r i f t is i s dated dated at a t about about 30,000 30,000 years B. correlative and and is i s considered considered Rockian Rockian (late ( l a t e Altonian) Altonian) age. age. The The Border b r d e r Drift D r i f t may may actually a c t u a l l y consist c o n s i s t of of 22 tills t i l l s of of differing d i f f e r i n g age. age. The till was was The lower lower till deposited by by ice i c e moving moving from from the t h e west in i n Marathon County County (LaBerge, (~a~erge, deposited 1972) 1972) and and the t h e upper upper till till by by ice i c e moving moving from from the t h e northwest northwest in i n southern southern Lincoln Lincoln and and Langlade Langlade Counties. Counties. sin s i n is is Three Three ice i c e lobes lobes built b u i l t terminal terminal moraines moraines in i n Lincoln Lincoln and and Langlade Langlade Counties Counties during during late—Woodfordian late-Woodfordian time. time. The The Wisconsin Wisconsin Valley Valley Lobe Lobe advanced advanced from from the t h e northwest northwest depositing depositing aa reddish—brown, reddish-brown, sandy sandy basal basal till. To the t h e east, e a s t , the t h e Langlade Langlade Lobe Lobe deposited deposited aa dark dark reddish—brown reddish-brown till. To basal b a s a l till till as a s ice i c e flowed flowed from from the t h e northeast. northeast. Further Further east, e a s t , the t h e Green Green Bay Bay Lobe, Lobe, advancing advancing from from the t h e east e a s t and and southeast, southeast, deposited deposited aa brown, brom, sandy, sandy, dolomitic dolomitic till. till. No No absolute absolute dates dates are a r e available, a v a i l a b l e , but but stratigraphic s t r a t i g r a p h i c and and geomorphic geomorphic evidence evidence suggests suggests that t h a t the t h e advance advance of of these t h e s e lobes lobes to t o their t h e i r terminal terminal moraines moraines was was not not contemporaneous contemporaneous as a s reported reported by by Thwaites Thwaites (1943). (1943). At At the t h e junction junction of of the t h e Wisconsin Wisconsin Valley Valley Lobe Lobe and and Langlade Langlade Lobe Lobe no no strati— stratigraphic till graphic sections s e c t i o n s showing showing 22 tills t i l l s are a r e available. a v a i l a b l e . Relationships Relationships of of till fabric f a b r i c azimuths, azimuths, moraine moraine alignments alignments and and drainage drainage features f e a t u r e s indicate i n d i c a t e an an early e a r l y advance advance of of the t h e Langlade Langlade Lobe Lobe and and the t h e formation formation of of the t h e Parrish Parrish Moraine. This was was followed followed by by an an advance advance of of the t h e Wisconsin Wisconsin Valley Valley Lobe Lobe Moraine. This and was followed followed shortly shortly and the t h e formation formation of of the t h e Harrison Harrison Moraine Moraine which which was thereafter t h e r e a f t e r by by aa readvance readvance of of the t h e Langlade Langlade Lobe Lobe to t o aa position p o s i t i o n 66 miles miles short and tthe short of of its i t maximum s maximum advance advance and h e formation formation of ofthe t h eSummit SummitLake Lake Moraine. Moraine. Stagnant Stagnant ice i c eofofthe t h Wisconsin e WisconsinValley ValleyLobe Lobemay may have have been been present present during during this t h i sreadvance. readvance. To To the t h e east, e a s t , the t h e Green Green Bay Bay Lobe Lobe advanced advanced to t o its i t s maximum maximum position position and and retreated r e t r e a t e d at a t least l e a s t 20 20 miles miles before beforethe t hmaximum e maximum advance advance of of the the Langlade Bay Lobe till is stratigraphically beneath Langlade Lobe. Lobe. Green that Green Bay Lobe till i s s t r a t i g r a p h i c a l l y beneath that of of the t h eLanglade Langlade Lobe Lobe aat t lleast miles in i~from from the t h e margin margin of the the e a s t 55 miles Langlade Outwash streams h e Langlade Langlade Lobe Lobe iice c e cut c u toutwash outwash streams from from tthe Langlade Lobe. Lobe. Outwash and thet hGreen Bay and till tillofof e Green BayLobe. Lobe. 24 �A PLUTONNEAR NEARELY, ELY, MINNESOTA A LOWER LOWER PRECAMBRIAN PRECAMBRIAN LAMPROPHYRE LAMPROPHYRE PLUTON MINNESOTA M. G. M. Mudrey, ~ r .and and ' A. L. Geldon, Geldon, University U n i v e r s i t yofoMinnesota f Minnesotaand andMinnesota Minnesota G. Mudrey, Jr.1 A. L. Geological Survey. Survey. ABSTRACT ABSTRACT Oneoof bodies ooff lamprophyre One f tthe h e bbetter e t t e r exposed exposed bodies lamprophyre wwithin i t h i n tthe h e Early E a r l y PrePrecambrian Vermilionddistrict cambrian Vermilion i s t r i c t of o fMinnesota Minnesota is i s located l o c a t e d88km km northwest northwest ooff Ely, Ely, on tthe on h e north n o r t h side s i d e of o fBurntside Burntside Lake. Lake. The The ccrudely r u d e l y e elliptical l l i p t i c a l pluton, p l u t o n , about about by0.5 0.5 km, km,i is Lower Precambrian 1 km km by s situated s i t u a t e d in i nthe t h ecore coreofo a f afold f o loutlined d o u t l i n eby d by Lower Precambrian migmatizedb ibiotite amphibolite; howevert hthe migmatized o t i t e sschist c h i s t and and amphibol i t e ; however e p lpluton uton i sisvvitually itual l y 1 unmetamorphosed unmetamorphosed andand i s is d i sdiscordant c o r d a n t t otot hthe e sstructure. tructure. The has aa narrow, narrow, discontinuous discontinuousborder borderzone zoneo fofuuralitized The ppluton l u t o n has ralitized phlogopite-bearing These two two phlogopite-bearing pyroxenite p y r o x e n i t e and and an an inner i n n e r zone zone of o flamprophyre. lamprophyre. These rock types based relations, petrography, f i efield 1 d re1 a t i o n s ,petrography, rock types are a r e considered considered comagmatic comagmati c based on on Both the t h e pyroxenite p y r o x e n i t e and and the t h elamprophyre lamprophyre are are cut c u tbybynumerous, numerous, and and chemistry. Both thin adamell i t i composition, c composition,which whichcontain c o n t a i nxenocrysts xenocrysts t h i n dikes dikes of o fmonzonitic monzoni t i c to t oadamellitic of mafic minerals tthat o f the t h e same same m a f i c minerals h a t occur occur in i nthe t h epyroxenite p y r o x e n i t eand andlarnprophyre. lamprophyre. The The dikes representa al alate dikes are a r e probably probably comagmatic, comagmatic, b ubut t c ocould u l d represent t e ppink i n k lleucocratic eucocratic phaseoof adjacent VVermilion phase f tthe h e adjacent e n n i l i o n ggranite. ranite. The lamprophyre lamprophyrei is Approximately213 2/3 ooff the The s a melanocratic porphyry. porphyry. Approximately the exposed lamprophyrei sisaa bbiotite—bearing hornblendes spessartite; exposed lamprophyre i o t i t e - b e a r i n g hornblende p e s s a r t i t e ; the t h e remainremainThe sspessartite byuuralitized ing 113 is i s augite a u g i t e inokersantite. i n o k e r s a n t i t e . The p e s s a r t i t e iiss dominated dominated by ralitized i n g 1/3 with subordinatec hchloritized ddiopsidic i o p s i d i c aaugite ugite w i t h subordinate l o r i t i z e d bbiotite, i o t i t e , sericitized s e r i c i t i z e dandesine, andesine, andi interstitial and n t e r s t i t i a lpotassium potassium feldspar; feldspar; the t h e relatively re1 a t i v e l yunaltered u n a l t e r e d inokersantite inokersantite is by ddiopsidic i s dominated dominated by i o p s i d i c augite a u g i t e and and biotite b i o t i t ewith w i t hsubordinate subordinateandesine andesineand and interstitial crude subhorizontal subhorizontal llayering i n t e r s t i t i apotassium l potassium feldspar. feldspar. A A crude a y e r i n g within w i t h i n both both types ooff lamprophyre byananupward upward increase types lamprophyre i is s marked marked by increase i ning rgrain a i n ssize i z e oof f the the groundmassand and decrease phenocrysts; an groundmass decrease i n in s i size z e o of f tthe h e phenocrysts; an increase in i n amount amount of of potassiumf efeldspar potassium l d s p a r aatt the t h e expense expense ooff total t o t a l ferromagnesian ferromagnesian minerals; minerals; and and aa change change iinn the t h e compositions compositionsofo the f t hferromagnesian e ferromagnesianminerals——mainly minerals--mainly an an increase increase in i n the t h e iron/magnesium iron/magnesium rratios. atios. Calculated compositions Calculated compositions for f o r the t h erocks rocksbased basedon onmodal modal data data and and microprobe microprobe analyses analyses oof f cconstituent o n s t i t u e n t phases phases i nindicate d i c a t e tthat h a t this t h i s pluton p l u t o nmay may be be related r e l a t e d to to an alkali an an uncommon b a s a lparent, t parent, uncommon petrochemical petrochemical type type ini nLower LowerPrecambrian Precambrian a1 k a l ibasalt an terranes. terranes. The wasemplaced emplaced cooled rrapidly. The ppluton l u t o n was i nina as esemicrystalline m i c r y s t a l l i n e sstate t a t e and and cooled apidly. byeearly IInitially n i t i a l l yhigher h i g h e roxygen oxygen ffugacity, u g a c i t y , as as indicated i n d i c a t e d by a r l y ccrystallization r y s t a l l i z a t i o n of of magnetite andapparently apparently magnetite and h i ghigh h f e ferric/ferrous r r i c / f e r r o u s rratios a t i o s in i n biotite, b i o t i t e decreased , decreased Disequilibrium i s e q u i l i b r i u m ttextures e x t u r e s iindicate n d i c a t e that that somewhat somewhat d uduring r i n g c rcrystallization. ystallization. D crystallization c r y s t a l l i z a t i o nbegan beganata depth t depthand andconcluded concluded at a t shallower, shallower, synvolcanic synvolcanic depths. depths. 1Nowa tatDry DryVValley INOW a l l e y DDrilling r i l l i n g Project, P r o j e c t ,Department Department of o f Geology, Geology, Northern Northern Illinois University, DeKaib, Illinois 60115. I l l i n o i s U n i v e r s i t y , DeKalb, I l l i n o i s 25 �Mineralogical Mineralogical and and Chemical Chemical Studies Studies of Greenstones in i n Wisconsin by G. G. Mursky, G. G. Schriver S c h r i v e r and and A. A. R. R . Venditti Venditti Department of o f Geological Geological Sciences Sciences University U n i v e r s i t y of of Wisconsin—Milwaukee Wisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin ABSTRACT Central, C e n t r a l , northern n o r t h e r n and and northeastern n o r t h e a s t e r n parts p a r t s of o f Wisconsin contain volcanic—sedimentary c o n t a i n numerous belts b e l t s of of Precambrian volcanic-sedimentary sequences sequences which which are a r e commonly commonly referred r e f e r r e d to t o as a s greenstones. qreenstones. The The units u n i t s appear appear to t o be chiefly c h i e f l y of of middle Precambrian age aye and and they they have been been included included by Stockwell Stockwell (1970) (1970) in i n the t h e Southern Southern Province Province have B e l t which forms forms the t h e southern s o u t h e r n extension e x t e n s i o n of of the the o r Penokean Penokean Fold Fold Belt or 2.5 2.5 to t o 2.7 2.7 b.y. b.y. old o l d Superior Superior Structural S t r u c t u r a l Province Province of of the the Canadian Canadian Shield. S h i e l d . The The volcanic v o l c a n i c rocks in i n Wisconsin have chemical chemical c h a r a c t e r i s t i c s similar s i m i l a r to t o Archean volcanic v o l c a n i c assemblages a s s e h l a q e s of of the the characteristics S u p e r i o r Province Province and and these t h e s e similarities s i m i l a r i t i e s are a r e reflected r e f l e c t e d by the the Superior following following trends: trends: (1) The alkali—lime a l k a l i - l i m e index, index, as a s proposed proposed by by Peacock Peacock (1931), (19311, The f o r Wisconsin's v o l c a n i c rocks has a range from 59 to to for Wisconsin's volcanic 64 and and thus t h u s parallels, p a r a l l e l s , very v e r y closely, c l o s e l y , the t h e alkali—lime alkali-lime index of volcanic v o l c a n i c rocks rocks from from the t h e Superior Superior Province Province index which show show aa range ranqe from from 56 56 to t o 64 6 4 (Wilson (Wilson and and others, others, which 1965). 1965). (2) volcanic Volcanic rocks rocks from from Wisconsin Wisconsin are a r e potassium—poor potassium-poor and and compare to t o Goodwin's (1968) (1968) trend t r e n d of of potassium-poor potassium-poor compare volcanic v o l c a n i c rocks rocks in i n the t h e Superior Superior Province. Province. (3) The The Niggli N i g y l i silica s i l i c a and and total t o t a l alkali a l k a l i values v a l u e s for f o r volvolcanic c a n i c rocks rocks from from Wisconsin, when plotted p l o t t e d in i n relation relation to t o Wilson's Wilson's (1965) (1965) standard s t a n d a r d curve curve drawn drawn for f o r oceanic oceanic alkaline and orogenic calc-alkaline suites, plot alkaline c a l c - a l k a l i n e s u i t e s , p l o t on on t h e orogenic o r o q e n i c calc—alkaline c a l c - a l k a l i n e side s i d e of of the t h e standard s t a n d a r d curve curve the nearly same region r e g i o n as a s the t h e plots p l o t s for f o r the t h e volvoln e a r l y in i n the t h e same canic c a n i c suites s u i t e s from from the t h e Superior S u p e r i o r Province. Province. The greenstones ureenstones have have been been metamorphosed metamomhosed to t o greenschist areenschist facies ~ k o n n a i s s a & z eand and f a c i e s or o r -lower l o w e r amphibolite amphibolite facies. f a c i e s . Reconnaissance detailed s u l p h i d e mineralization mineralization d e t a i l e d work work has has not n o t revealed revealed any any sulphide except e x c e p t for f o r some some disseminated disseminated pyrite. pyrite. 26 �References References Goodwin, Goodwin, A. A. M., M., 1968, 1968, Evolution Evolution of of the t h e Canadian Canadian Shield: Shield: Geol. Assoc. Can. Proc., v. 19, P. -01. Assoc. Can. Proc., v . 1 9 , p. 1—14. 1-14. Peacock, Peacock, M. M. A., A., 1931, 1931, Classification C l a s s i f i c a t i o n of of Igneous Igneous Rocks: Rocks: Geology, V. 39, p. 54—67. Geology, v. 39, p. 54-67. Jour. Jour. Stockwell, Stockwell, C. C. H., H., 1970, 1970, Geology Geoloqy of o f the t h e Canadian Canadian Shield Shield (Introduction), Chapter IV in Geology (Introduction), I V i n Geology and and Economic Economic Minerals Minerals of of Canada, Canada, 5th 5 t h Ed., Ed., Department Department of of Energy, Energy, Mines, and Resources, Ottawa, Canada, p. Mines, and Resources, Ottawa, Canada, p. 44—54. 44-54. Wilson, H. D. D . B., B., Andrews, Andrews, Peter; P e t e r ; Moxham, Moxham, R. R. L., L . , and and Ramlal, Rarnlal, Wilson, H. K., 1965, Archean Volcanism in the Canadian Shield: K., 1965, Archean Volcanism i n t h e Canadian S h i e l d : Can. Can. Jour. J o u r . Earth Earth Sci., S c i . , v. v. 2, 2 , no. no. 3, 3, p. p. 161-175. 161-175. 27 �TEE IRON OREDEPOSITS DESITS AT TIE IMN ORE ATBlACK BUCKRIVER WJER FALlS, WISCONSIN, FALLS, WISCONSIN,GEOlOGY GEOLOGYAND ANDOPERA.TIONS OPEFATIONS John M. Ohison, Inland John M . Ohlson, Inland Steel S t e eCompany, l Compsw, Ishpeniing, Ishpeming, Michigan Michigan h498h9 W9 ATBAC'P Thepresence presenceofofiron iron bearing bearing rocks rocks iin the Black River Falls Falls area The n the Black Mver Attempts ttoo known since since 1839. 1839. Attempts of west-central nest-centralWisconsin Wisconsinhas hasbeen beenknown wereunsuccessful. unsuccessful. u t i l i z ethis t h i sresource resourcebefore beforethe theturn turnofofthe the centumwere utilize century 1nlandts facility, f a c i l i t y ,which whichopened opened iin n 1969, 1.969, u t i u z e s standard standard grinding grinding Inland's utilizes and nagnetic separation and mgnetic s e p m t i o n techniques. techniques. The rocks of of the the area are The rocks are aa sequence sequence of of steeply steeply dipping dipping highly highly metaaorphased sedimentsincluding includingaa thin-banded thin-banded mgnetite-quartz nagnetite-quartz metamorphased sedkmnts iron fornation. iron formtion. The The ssediments e d h e n t s l lie i e on a granite granitegneiss gneissbasement basement and intmded by by both both acid acidand and basic bssicdikes dikes.• The and are intruded %e eentire n t i r ePrecambian Ft-ecambian sequenceiis sequence s overlain w e r l a i n by by flat flatlying lyingC*mbrian Cambrian sandstones. sandstones. Water Water iiss obtained wells iinn aa concealed disobtained from from wells concealed Pleistocene Pleistocene valley valley which which was n s discovered by by geo@ysical geoaysical methods. covered methods. Plant water water circulates circulates in Plant i naaclosed closedsystem. system. Experimental Experimental ttree r e e and and grass Wisconsin gmss planting planting with with the t h ehelp helpofofthe the WisconsinDepartment Ceprixent of Natural Natural Resources, the University of ExtensionService, Service, and and the the SSoil Resources, the of Wisconsin Wisconsin Extension oil conservation Service Servicewwas started on on the the waste waste ddisposal Conservation as started i s p s a l ppiles i l e s within within a year and aa half half of of plant plant startup. %e a year and The plant plant and and waste waste disposal disposal areas were designed designed from from the the outset environmentaleffect. effect. were outset to t ohave havea aminimum minimum environmental 28 �STRUCTURAL EVOLUTION O OF STRUCTUm EVOLUTION F TEE THE DEER DEER LAKE LAKEULTRAMAFIC ULTRAMAFIC COMPLEX, COMPLEX, MINNESOTA MINNESOTA M. Ripley Ripley and Donald N. M. Davidson, Davidson, Jr., J r . , Geology Department, Department, Edward M. Edward University of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812. 55812. ABSTRACT ABSTRACT Lake Ultramafic Ultramafic Complex Complexisislocated located 6.5 6.5 kilometers The Deer Deer Lake kilometers southsouthThe The magnetic magnetic anomaly anomaly associated a s s o c i a t e d with with this this Effie, E f f i e , Minnesota. Minnesota. The east e a s t of of Archean Complex Complex is is 13 13 kilometers long long and and 33 kilometers wide wide and and trends S. 45W.from the of Deer Lake to just n northeast o r t h e a s t of the the S. 45W.from t h e south tip t i p of t o just town of of Big Big Fork. Fork, The stratigraphic within s t r a t i g r a p h i c succession w i t h i n this t h i s Complex Complex consists c o n s i s t s of two stratiform s t r a t i f o r m differentiated d i f f e r e n t i a t e d gabbroic sills, one nonstratiform gabbroic s t r a t i f o r m sills sills s i l l and and two two locally l o c a l l y discordant discordantultrainafic u l t r a m a f i c lenses. lenses. The stratiform sill (700-1,100 m. m. thick) t h i c k ) are a r e composed composed of: of: basal b a s a l peridotite p e r i d o t i t e (160—330 (160-330 m.), m.), (700—1,100 orthopyroxene m.), gabbro 450—650 m.) 450-650 m.) orthopyroxene clinopyroxenite (less ( l e s s than 160 160 m.) plus medium— to p l u s or o r minus mediumt o fine—grained fine-grained differentiated d i f f e r e n t i a t e d felsic f e l s i c cap cap rock. rock. Zones of plumose texture all t e x t u r e have been observed o b s e ~ e dalong contacts contacts between all zones are a r e interpreted i n t e r p r e t e d as a s spinifex—like s p i n i f e x - l i k e chill c h i l l contacts contacts mafic mafic units. units. These zones r a t h e r than sequential s e q u e n t i a l contact contact metamorphic metamorphic effects. effects. rather , Deformation of the t h e Complex Complex commenced commenced with a period of of folding f o l d i n g which The axial The a x i a l plane plane produced two anticlines with an intervening syncline. two a n t i c l i n e s with an i n t e ~ e n i n gsyncline. trends of of these upright, nonpiunging, isoclinal N. 45 E. E. with upright, nonplunging, i s o c l i n a l folds f o l d s is N. Folding a a wavelength of of 1200 1200 meters meters and and an an amplitude amplitude of of 400 400 meters. meters. Folding was produced in response to the emplacement of the Zeisser's Island i n response t o t h e the Zeisser's Island Pluton located located just j u s t southeast southeast of the t h e central c e n t r a l portion p o r t i o n of the t h e Complex. Complex. Local bending of the Complex to an east—west trend around bending of t h e Complex t o an east-west t r e n d around the t h e north north end of the t h e Pluton also a l s o occurred occurred at a t this t h i s time. time. Conjugate Conjugate shear shear fractures fractures trending N. N. 20 W. W. and N. N. 80 W. W. developed in i n response to t o the t h e same NW—SE NW-SE stress s t r e s s system system which which produced produced folding. folding. The The second second stage s t a g e of deformation deformation resulted r e s u l t e d from from extensional extensional release release The with The ffaults a u l t s trend trend with the t h e development development of of normal normal faults f a u l t s and and joints. joints. W. and have minimum minimum dip dip separations separations on on the t h e order o r d e r of of 400 400 meters. meters. N. 45 W. Faulting produced 800 Longi800 meter—wide meter-wide graben graben and and horst h o r s t structures. s t r u c t u r e s . Longitudinal W.) (N. 45 W. ) release r e l e a s e joints j o i n t s are a r e believed t u d i n a l (N. (N. 45 E.) E.) and traverse t r a v e r s e (N. to t o have developed under the t h e same stress s t r e s s orientation o r i e n t a t i o n as a s the t h e normal faults. faults. Strike N. 45 E. E. trend t r e n d characterizes c h a r a c t e r i z e s the t h e final final S t r i k e slip s l i p faulting f a u l t i n g along a N. U g h t - l a t e r a l strike s t r i k e separation s e p a r a t i o n displacement offset offset s t a g e of of deformation. deformation. Right—lateral stage Renewed movement along this t h i s fault f a u l t preprenormal faults f a u l t s about about 300 300 meters. meters. Renewed sumably produced an additional a d d i t i o n a l 100 100 meters strike s t r i k e separation displacement displacement Precambrian diabase diabase dikes. dikes. of middle Precambrian 29 �THE CHEMISTRY OF THE THE PETROLOGY ETROLOGY AN]) AND CHEMISTRY THE ROUND ROUND [AKE L A E INTRUSION, INTRUSION, NORTHWESTERN NORTIMESTERN WISCONSIN WISCONSIN D. L. Roder Cameron Roder and E. N. Cameron Department of Department of Geology Geology and Geophysics Geophysics University University of of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT The The Round Round Lake Lake intrusion intrusion is is aa northeast-trending northeast-trending Precambrian Precambrian mafic layered intrusion by subsurface subsurfacedrilling drilling of mafic layered intrusion found found by of an an area area ten ten miles east miles east of Hayward, Hayward, Wisconsin. Wisconsin. The The body may may be as as much much as as eight eight miles long long and two miles magnetitemiles and two miles wide. wide. Portions Portions drilled drilled consist consist of of magnetitetroctolite troctolite with with anorthositic anorthositic gabbro gabbro layers layers that that range range from from threethreefourths fourths inch inch to to more more than than eighty eighty feet feet in in thickness. thickness. Diabase Diabase interintersected sected by the the drill drill holes holes appears appears to to form form later later intrusions. intrusions. Mineral Mineral assemblages assemblages in in the the magnetite-troctolite magnetite-troctolite and and anorthositicanorthositicgabbro gabbro are are the the same, same, the the two two rock rock types types differing differing only only in in mineral mineral proportions. ilmenite, and and proportions. Plagioclase, Plagioclase, olivine, olivine, titanomagnetite, titanomagnetite, ilmenite, apatite apatite are are cumulus cumulus minerals. minerals. Clinopyroxene, Clinopyroxene, biotite, biotite, and and plagioclase plagioclase are minerals. The are intercumu.lus intercumulus minerals. The magnetite-.troctolite magnetite-troctolite averages 28 averages 28 volume volume per per cent cent plagioclase, plagioclase, 36 iron36 per per cent cent olivine, olivine, 33 33 per per cent cent irontitanium oxides, oxides, 33 per per cent cent augite augite and and biotite, biotite, and and aa trace trace of of titanium anorthositic gabbroaverages averages 66 66per per cent cent plagioclase, plagioclase, apatite. The anorthositicgabbro 22 22 per per cent cent olivine, olivine, 88 per per cent cent iron-titanium iron-titaniumoxides, oxides, '-t 4 per percent cent augite, augite, and and less less than than one-half one-half per per cent cent apatite. apatite. Titanomagnetite in in these these rocks rocks is is an an irregular irregular microintergrowth microintergrowth Titanomagnetite of ulv%pinel. of magnetite magnetite and and ulv1spinel. Ilmenite Ilmenite occurs occurs as primary granular granular aggregates, (111) lamellae lamellae in in titanomagnetite, titanomagnetite, and and as as granular granular aggregates, as as (111) aggregates aggregates around around titanomagnetite titanomagnetite grains. grains. Hercynite Hercynite is is found found as as tiny tiny "dots" "dots" in in titanomagnetite. titanomagnetite. Magnetite appears appears to to have have settled settled as as euhedral euhedral crystals. crystals. Anhedral Anhedral aggregates aggregates are are thought thought to to be be due due to to enlargement or partial recrystallization recrystallization of touching crystals after settling. settling. Only Only small-scale small-scale cryptic cryptic layering layering is is displayed displayed by by the the intrusion. intrusion. Plagioclase ranges ranges from from An51 AnS1 to to Anits, An~r,, but chemical Plagioclase but no consistent consistent chemical trend trend is is evident. evident. In X-3, anorthositic•gabbro In core core from from drill drill hole X-3, anorthositic gabbro and and magnetite-troctolite are interlayered; olivine magnetite-troctolite olivine in in anorthositic-gabbro anorthositicgabbro ranges from from P053 FoS3 to to Fo56, FoS6, whereas whereas olivine olivine in in magnetite-troctolite magnetite-troctohte ranges ranges from Fo5, Fo57 to to Fo Fo2. 2 . In In core core from from drill drill hole hole X-2, X-2, anorthositie anorthositic gabbro developed. In gabbro layers layers are are poorly poor y developed. In this this core, core, olivine olivine ranges ranges from from Fo57 of Ca4$lg3,Fel8. CaqMg37Fe18. FoS7 to to Fog1. FoS1. Augite Augite has has an an average average composition of Microprobe analysis analysis of of titanomagnetite titanomagnetite gives gives the the following followmg range range of of Microprobe composition: composition: total total iron iron as as FeO FeO 65 65 to to 7'-!74 weight 20 to to weightper percent, cent, Ti02 Ti02 20 21l per cent, cent, MgO MgO 0.5 0.5 to to 3.8 3.8 per per cent, cent,A1203 A12O3 2.3 2.3 to to 3.9 3.9 per per cent, cent, V203 V03 24 per 1.0 to to ]J3 L.3 per per cent, cent, and and Cr203 Cr203 0.1 0.1 to to 1.2 1.2 per per cent. cent. Primary Primary ilmenate ilmen~te has an an average average composition composition of of Ilmg8Hem2 Ihg8Hem2 and and contains contains up up to to S5 weight weight has per per cent cent MgO. MgO. !? Information Information at at hand indicates indicates the the presence of of sizeable sizeable concentraconcentrations tions of of iron-titanium iron-titanium oxides, oxides, but but further further exploration exploration will will be be necessary necessary to determine determine their their form, form, extent, extent, and and relations relations to to the the Round Round Lake Lake to intrusion intrusion as as aa whole. whole. 30 �UPPER MISSISSIPPI VALLEY EXPERIMENTAL UPPEX MISSISSIPPI VALLEYBASE BASEMETAL MET& DEPOSITS: DEF'OSITS: FXPERIMEIiTAL SOLUTIONS TO PROBLEMS OF ORE ORE GENESIS GENESIS SOLUTIONS TO mOBLEMS OF' B. Romberger, Romberger, Department of of Geology and Geophysics, Geophysics, University of S. B. Wisconsin, Madison, Madison, wisconsin Wisconsin 53706 Wisconsin, 53706 ABSTRACT A BSTRACT Chemical models for of base metals f o r tthe h e ttransport r a n s p o r t and deposition of in Mississippi Valley Type Deposits are studied experimentally using i n Mississippi Valley Type Deposits a r e using object is i s tto o supply evidence tto o a mineral synthesis synthesis approach. approach. The obJect support tthe hypothesis tthat have been been deposited deposited from metalmetal— support h e hypothesis h a t tthese h e s e oores r e s have containing, sulfur—deficient, chloride—rich solutions containing, s u l f u r - d e f i c i e n t , chloride-rich s o l u t i o n s entering a sulfur—containing reducing environment. Copper, iron, sulfur-containing i r o n , lead, l e a d , and and zinc zinc were synthesized together together iin molal sodium chloride chloride ssolutions olutions ssulfides u l f i d e s were n 3 molal between 200 20' and and 200°C 200° under the t h e vapor vapor pressure pressure of of water. water. Copper, iron, iron, lead, barium, and calcium were introduced a ass solid l e a d , zinc, zinc, barium, s o l i d carbonates or or The amount amountofof ssulfur soluble chlorides soluble chlorides along along with with elemental elemental ssulfur. u l f u r . The ulfur The of tthat added a l l metal. metal. The added was iin n excess excess of h a t necessary necessary tto o rreact e a c t with with all products depended dependedonont hthe of tthe products e sstarting t a r t i n g composition composition of h e experiments, experiments, but pyrite, galena, digenite, barite, were generally covellite, covellite, p y r i t e , sphalerite, s p h a l e r i t e , galena, digenite, b arite, Morphology of of some some of tthe he anhydrite, anhydrite, and and aa second second generation generation calcite. c a l c i t e , Morphology composite m metallic e t a l l i c sulfide s u l f i d e grains g r a i n s suggest suggest initial i n i t i a l rreaction e a c t i o n occurred above the indicated by by t h e melting temperature temperature of of sulfur. s u l f u r . Nonequilibrium iiss indicated with of unreacted unreactedssulfur tthe h e presence presence of u l f u r iin n tthe h e cores cores of of grains g r a i n s together with metal concentrations concentrations in i n the t h e co—existing co-existing solutions. solutions. No No metal high metal carbonates remained in i n the t h e run products. products. The sulfides s u l f i d e s showed a regular zonation in in rrelation e l a t i o n to t o the t h e un— unzoningiin terms of reacted ssulfur u l f w and and ccalcite. a l c i t e . Summarizing S m a r i z i n g t hthe e zoning n terms of paragenesis, c o v e l l i t e is i s early, e a r l y , followed followed by by galena galena and and sphalerite. sphalerite. paragenesis, covellite Pyrite F y r i t e forms before galena and s p h a l e r i t e but i t s r e l a t i o n s h i p t o s unclear. Barite B a r i t e and anhydrite form independently of of the the ccovellite o v e l l i t e iis ssulfide u l f i d e zoning, zoning, however the t h e second second generation c a l c i t e i s t h e l a s t phase galena and sphalerite but its relationship to generation calcite is the last phase whichappear appeart otocause causep precipitation, ttoo form. form. The The ffactors a c t o r s which r e c i p i t a t i o n , iin n order order of of activity, sulfur a c t i v i t y , increasing increasing pH pH of of solution, solution, importance, are: a r e : increasing sulfur and decreasing temperature. temperature. To aid a i d in i n determining tthe h e chemical conditions underwhich sulfide sulfide precipitation p r e c i p i t a t i o n took place, p l a c e , tthe h e aqueous solutions s o l u t i o n s were analyzed for f o r copper, zinc, llead, barium, and concentration of of the t h e metals metals zinc, e a d , iron, i r o n , barium, and calcium. calcium. The concentration with decreasing temperature temperature and increasing time; time; and barium decreased with that t h a t of calcium either e i t h e r increased or o r decreased, depending on the t h e starting starting variation i s a ttypical ypical v a r i a t i o n of the t h e molar ratio ratio conditions. The following is Cu:Fe:Pb:Zn iin of l1.0:1.0:1.0:1.0: .O:l.O:l.O:l.O: aatt Cu:Fe:F'b:Zn n solution s o l u t i o n aafter f t e r aa starting s t a r t i n g rratio a t i o of 200°C, 1.0:0.114:1140:360; 120°C, ~1.0:1.0:830:2280; 20O0c, ~ . 0 : 0 . ~ & : ~ 4 0 : 3 6a0at t ; 12O0C, . 0 : ~ . 0 : 8 3 0 : 2 2 8 0 and ;and at a t 25°C, 25OC, 1.0:0.15:3.3:150. The copper concentration ttypically y p i c a l l y dropped from from a few few 1.0:0.15:3.3:150. 200°C, to l000ppm t o less less 100Oppm in i n the t h e starting s t a r t i n g solution s o l u t i o n to t o less l e s s than than 55 ppm aatt 20o0C, v a r i a t i o n s are a r e consistent with the t h e paragenesis than than 11 ppm ppm at a t 25°C. 2F°C These variations not established observed in observed i n the t h e minerals. Because equilibrium was not e s t a b l i s h e d tthe he major significance s i g n i f i c a n c e of of these t h e s e data is i s to t o demonstrate relative r e l a t i v e tendencies ffor o r metal sulfides s u l f i d e s to t o precipitate p r e c i p i t a t e under under the t h e conditions conditions of of the t h e experiment. experiment. 31 �PETROLOGY OF PETROLOGY O F SOME SOME EA1LY EARLY PRECAMBRIM PRECAMBRIAN DIFFERENTIATEDULTRAMAFIC LlLTRAMAFIC BODIES BODIES DIFFERENTIATED IN I NNORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA Klaus J. Schulz Schulz and and Edward Edward M.H.Ripley, of Minnesota, Minnesota, Duluth, Duluth, Klaus 3. Ripley, University of Duluth, Minnesota Minnesota 55812. 55812. ABSTRACT Mapping iin n the t h e Newton Newton Lake Ely, Minnesota Minnesota and and Mapping LakeFormation Formationnorth north of of Ely, the t h e Deer Lake Lake Area n northern I t a s c aCounty, County, Minnesota Minnesota has l o c a t e d aa Area iin northern Itasca has located number number of of mafic—ultramafic mafic-ultramafic bodies of of Early Early Precambrian age, many many of which which are a r e differentiated. differentiated. Detailed mapping mapping of of these t h e s e bodies bodies has has shown shown Detailed that t h a t they they are a r e conformable conformable to t o the t h e surrounding surrounding country country rocks, rocks, indicating indicating they are either sills or flows. that t h a t they a r e e i t h e r sills o r flows. Country Country rocks both areas a r e a s conconrocks iinn both sist of of medasedimentary medasedimentary and r g e l y pillowed metavolcanic metavolcanic rocks. rocks. No andl alargely No sist evidence evidence for f o r contact contact metamorphism metamorphism has been been observed observed between between the t h e bodies bodies and the country rocks. and t h e country rocks. The bodies o 1,000 e e t in i n thickness thickness and and have have The bodies range range from from400 400t to 1,000ffeet lateral miles. The l a t e r a lextents e x t e n t sfrom from aa mile mile to t o several s e v e r a l miles. The rocks t h eDeer Deer rocks of the Lake Areahave havebeen beenf afaulted andt itightly while those north of Lake Area u l t e d and g h t l y folded folded while of Ely Ely are a r e faulted f a u l t e dand and only only broadly broadly folded. folded. Serpentinization S e r p e n t i n i z a t i o n and t h e r aalterlterand oother isextensive extensiveini nalla lthe l t hbodies e bodies with metamorphism generally generally of the the a t i o n is ation with metamorphism green—schist green-schist facies. facies. I n both areas, areas, bodies composed composed solely s o l e l y of of gabbro gabbro or o r peridotite p e r i d o t i t e exist, exist, In however however most most appear appear to t o be be differentiated. d i f f e r e n t i a t e d . The The typical t y p i c a l sequence sequence in i n the the is peridotite, p e r i d o t i t e , pyroxenite, pyroxenite, d i f f e r e n t i a t e d ones, ones, from from bottom bottom to t o top, top, is differentiated porphyritic p o r p h y r i t i c gabbro, gabbro, gabbro. gabbro. The The peridotite p e r i d o t i t e is i s composed composed of of rounded rounded to to euhedral euhedral olivine o l i v i n e and and rare r a r e chromite chromite surrounded surrounded by o i k i l i t i cpyroxene pyroxene by ppoikilitic and and amphibole. amphibole. At A t least l e a s t some some of of the t h e peridotites p e r i d o t i t e s contain contain both both ortho— orthopyroxene h e r z o l i t e . The The pyroxene and and clinopyroxene clinopyroxene and a s s i f i e d as andwould wouldbebec lclassified as IIherzolite. pyroxenite contains sub— pyroxenite is is in i nsharp sharpcontact contactwith withthe t h eperidotite p e r i d o t i tand e and contains subhedral h e d r a l diopsidic d i o p s i d i c augite a u g i t eand and in i nsome some cases cases also a l s o contains contains bronzite. bronzite. With Plagioclase, Plagioclase, in i nvarying varyingamounts, amounts, forms forms the t h e intercumulate i n t e r c u m d a t e phase. phase. With increasing increasing plagioclase p l a g i o c l a s e content content the t h e pyroxenite pyroxenite grades grades into i n t o porphyritic porphyritic gabbro composed composed ofofaaugite, u g i t e , plagioclase p l a g i o c l a s eand andpyroxene pyroxene phenocrysts, phenocrysts,which which gabbro are gabbro contains contains pplagioclase, a r e now now completely completely aaltered. l t e r e d . The The gabbro l a g i o c l a s e , augite, augite, t e r s t i t a l quartz quartz and and and secondary secondary aactinolite c t i n o l i t e with with varying varying amounts and amountsofofi ninterstital micrographic micrographic intergrowths. intergrowths. Cumulate Cumulate t textures e x t u r e s in i n the t h eperidotite, p e r i d o t i t epyrox— , pyroxandporphyritic p o r p h y r i t i cgabbro gabbro along along with with minor minor layering layering and and size s i z e grading grading e n i t e , and enite, i n d i c a t e that t h a t selective s e l e c t i v e crystallization c r y s t a l l i z a t i o nand and gravity g r a v i t y settling s e t t l i n gofofphases phases indicate were the the main main mechanisms mechanisms ofofddifferentiation. i f f e r e n t i a t i o n . Many Many of t h e bodies bodies examinexaminwere of the ed ed were were also a l s o found found to t ohave have complex complex chilled c h i l l e dmargins. margins. A of sulfide A ddetailed e t a i l e d study study of s u l f i d e mineralization m i n e r a l i z a t i o n in i n the t h e bodies bodies of of the the Deer Areashows showst hthat copper, and and iron i r o n sulfides s u l f i d e s are a r e conconDeer Lake Lake Area a t nnickel, i c k e l , copper, The centrated centrated in i n the t h e chilled c h i l l e d margins, margins, making making up up 22 to t o 3% 3%of of the t h e rock. rock. The 32 �basic b a s i c sulfides s u l f i d e s appear to t o have formed formed from from an immiscible Immiscible sulfide— sulfideof intrusion, oxide lliquid, i q u i d , which aatt the t h e time of i n t r u s i o n , coexisted with the the of ssulfide also silicate s i l i c a t e magma. A general llayering a y e r i n g of u l f i d e phases was a l s o found to t o exist e x i s t through through the t h e bodies bodies with with nickel n i c k e l sulf s u l f iides d e s concentrated concentrated in i n the the peridotite, pyroxenite and p porphritic p e r i d o t i t e , copper sulfides s u l f i d e s in i n the pyroxenite o r p h r i t i c gabbro gabbro u l f i d e s appear to t o have and iron i r o n ssulfides u l f i d e s in i n the t h e upper gabbros. gabbros. These ssulfides magma, p precipitating i l i c a t e magma, r e c i p i t a t i n g aass late l a t e phases been in i n solution s o l u t i o n in i n the ssilicate with the t h e intercumulus intercumulus minerals. chemical analyses of of samples from tthe bodies north north of Chemical analyses samples from h e bodies of Ely Ely show show a a bodies appear appear to The bodies t o be be general withddifferentiation. general iron i r o n enrichment enrichment with i f f e r e n t i a t i o n . The ttholeiitic h o l e i i t i c in i nnature n a t u r e and and very ssimilar i m i l a r to t o differentiated d i f f e r e n t i a t e d ultramafic ultramafic bodies age in i n Canada, Canada, Africa, Africa, and and Australia. Australia. bodies of Early Precambrian age 33 �TECTONIC HISTORY HISTORY OF OFEARLY EARLY PRECAMBRIAN PRECAMBRIAN ROCKS THE TECTONIC ROCKS IN IN THE VERMILION DISTRICT, DISTRICT, NORTHEASTERN NORTHEASTERN MINNESOTA VERMILION MINNESOTA P. P. K. K. Sims, Sims, Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul,Minnesota Minnesota55108 55108 ABSTRACT ABSTRACT The Vermilion district, ini nnortheastern The Vermilion northeasternMinnesota, Minnesota, contains contains aa sequence sequence of of complexly complexly bordered on on the the north north by by the the intertonguing volcanic volcanic and and volcaniclastic volcaniclasticrocks rocksthat thatisi sbordered intertonguing Vermilion granite—migmatite granite-migmatite massif massif and Vermilion andon on the the south southby by the the Giants Giants Range Rangebatholith. batholith. The supracrustal rocks adjacent to rocks dominantly dominantlyhave havegreenschist—facies greenschist-facies assemblages; assemblages; adjacent to the intrusive they have amphibolite—facies intrusive granitic graniticrocks rocks(Ca. (ca. 2700 2700m.y. m.y. old) old) they hove amphibolite-focies assemblages. assemblages. The supracrustal rocks rockstrend trendgenerally generally eastward, eastward, are are steeply steeply inclined, and The supracrustal andhave have and faulted. Two Twogenerations generationsofoffolds foldshave havebeen beendistinguished distinguished been complexly folded and in part of of the i n the the western western port the district. The older generation is i s represented represented by to by tight tight to that trend trend northwestward northwestward and axialsurfaces surfaces close folds that and have have planar, planar, steeply steeply inclined inclined axial and axes. The and gently—plunging gently-plunging axes. Theyounger younger generation generationfolds foldsare aresuperposed superposed on on the the older older folds of the district. folds in i n the the extreme extreme western western part of district. These These folds trend eastward eastwardand and folds trend axialsurfaces surfacesand andsteep steep plunges; plunges; they they are are accompanied accompanied by by ao have planar upright upright axial have pervasive steep steep cleavage cleavage and and associated associated lineations lineationsthat thatobscure obscuremost moststructures structures pervasive related relatedto tothe theolder olderdeformation. deformation. Judged Judgedfrom fromthe thedivergent divergenttrends trendsofofstructures structuresand and generally steep steep plunges the rocks rocks in i n the the eastern eastern part of the the district district the generally plungesof of lineations, lineations, the also also were were folded folded during during two two or or more more periods periods of deformation. deformation. Three steep fault fault systems, systems, each each of of which whichhas hasassociated associatedmylonite, mylonite,post—date post-date the the Three folding. folding. The The oldest (2) (?) faults faults have haveaa dominant dominant vertical verticalcomponent componentof ofmovement. movement. The The major major fault faultini nthis thissystem systemoccurs occursat atthe theapproximate approximateboundary boundarybetween betweenthe thelow— lowgrade supracrustal supracrustal rocks and the Vermilion Vermiliongranite—migmatite granite-migmatite massif; massif; another fault fault grade separates separates the eastern part of the the Giants GiantsRange Range batholith batholithand andassociated associatedamphibolite— omphibolitefacies facies rocks rocks from from the the supracrustal supracrustal rocks. rocks. These These faults probably have vertical movements faults probably have vertical movements of 3,000 3,000 to to5,000 5,000 feet, feet,and andappear appeartotohave havedeveloped developedlargely largelyini nresponse response to to isostatic isostatic of adjustments between crustal crustal blocks blocks having having different different rock adjustments between rock densities. densities. The younger (?) represented mainly mainly by straight, steep, (?) system system iiss represented steep, north—northnorth-northThe next younger east trending trending faults that cut cut both both the the granitic graniticrocks rocksand and the the volcanic volcanicrocks rocksand and have have east left—lateral miles. These These faults locallyare areabundant abundant left-lateral displacements displacementsof ofas asmuch much as as 44 miles. faults locally and and closely closelyspaced. spaced. Some Someofofthem themappear appeartotodisplace displacesupracrustal supracrustalrocks rocksmore more than than the the intrusive intrusiverocks, rocks,suggesting suggestingthat thatthey theypre—date pre-dote emplacement emplacementof ofatatleast leastsome some of of the the granitic granitic rocks. rocks. The youngestfaults faultsare aretranscurrent transcurrentfaults faultshaving havinghorizontal horizontalright right lateral displaceThe youngest ments. this system this systemisi sata least t least250 250miles mileslong longand andtransects transectsseveral several ments. The Themajor majorfault faultini n greenstone—granite greenstone-granite complexes. complexes. In I n northwestern northwestern Minnesota Minnesota iti tappears appears to to have have disdisplaced distinctive distinctivegravity gravityanomalies anomalies aa distance distance of about about 35 miles; miles; in i n the the Vermilion Vermilion placed district,where whereit iconsists t consistsofofseveral severalstrands, strands, iti thas hasdisplaced displacedthe the upper upper part part of of the the district, volcanicpile p i l ea adistance distanceofofabout about1212miles, miles,distorting distorting i t from a thick almond-shaped volcanic it from a thick almond—shaped lens lens to toaatenuous tenuouseast—trending east-trending mass. mass. Metamorphism, folding, and andemplacement emplacement of the the granitic graniticrocks rockswere werebroadly broadly Metamorphism, 34 �synchronous, and andoccurred occurredduring during the the Algoman Algomanorogeny. orogeny. The synchronous, The foldng foldingofofthe thesupra— supraresulting from from the the relative relative upwelling crustal rocks is attributed to to compression compression resulting upwelling convergence of of the the flanking batholiths, experiand convergence batholiths, aamechanism mechanism demonstrated demonstrated experimentally by Romberg (1967). The Vermilion massif andat at least least aa part part of of the Giants Ramberg (1967). The Vermilion massif and Giants Range batholith continued continued to rise because becauseofof their their buoyancy buoyancy after after crystallization crystalUzation Range batholith of the the granitic rocks. rocks. The Thetranscurrent transcurrent faulting faultingtook took place placeduring during aa fate latestage stage of of the orogeny, orogeny, after after the the crust crust had had attained attained sufficient sufficient strength strength to to transmit transmit regional regional related to the fracturing can compressive compressive stresses. stresses. Cataclasis Cataclasis related can account account for the the disparity between andmineral mineral ages agesi n in the the Giants Range batholith between whole—rock whole-rock and Range batholith (Prince and Hansen, Hansen, 1972). 1972). 35 �LAYEREDWMAPIC INTRUSION A KEWBENAWAN KEWEENAWAN LAYEmD I C INTRUSION NEAR NZAR FINLAND, FINLAND,LAKE LAKECOUNTY, COUNTY,MINNESOTA XIRXTSOTA R.J. R.J. Stevenson, Department Department of Geologys Geology, University of Stevensons Minnesota-Duluth, Duluth, Ninnesota-Duluth, DuLuth,Minnesota Kinnesota55812 55812 ABSTRACT ABSTRACT and one The NNE The Sonju Sonju Lake h k e Intrusion, Intrusion, four four and one half halfmiles milesNN3 Finland, has an Finland, Minnesota, Minneeota, has an exposed exposed area area of of one one and and one one intrusion isissurrounded miles • The intrusion half two and and one one half half miles. The surrounded half by two granite ,of the granophyric granite,of on three sides on three sidesby by diabase diabase and and granophyric the side is Beaver Beaver Bay Bay Complex, Complex, and and the the western western side isobscured obscured by by lamination, cryptic cryptic layering, glacial. drift. It Itshows shows igneous igneous lamination, layering, and layering, and and rhythmic rhythmic layering, and has has a a stratigraphic stratigraphic thickness thickness of of dip of approximately 3500feet feet based basedon onthe the strike strike and approximately 3500 and dip of the the rock units units comprising the intrusion intrusion igneous igneous lamination. lamination. The The rock comprising the picrite; are, from the base to the are, from the base to the top top respectively: respectively: basal basal picrite; troctolite; a gabbro; an a gabbro; an an apatite-rich ferrogabbro; an a troctolite; olivine-hedenbergite quartz-bearing diorite; diorite; a hedenbergite hedenbergite olivine-hedenbergite quarts-bearing The ferrogabbro granodiorite; granodiorite; and and a a hedenbergite hedenbergite adamellite. adamellite. The ferrogabbro contains 43.50$ SiC2. Si02. contains 19.26% 19.26s FeC FeO and and 43.50% of of glacial drift. The The compositions compositions of the the major major minerals minerals vary vary with with strati— etratigraphic height; height; they have been studied by electron electron microprobe plagioclase varies varies from An33 in and optical optical methods. methods. The plagioclase from An in the the and The piorite to to An An ininthe thehedenbergite hedenbergite adamellite. adame~lite?~ The basal picrite basal picrite to in to Fo12 3'0 in the the divine ?07 in in the basal olivine varies varies from froml#o 12 uppermost uppermost apatite—rich apatite-rich7$errogabbro. The cumulus cumulus clinopyroxene d~nopyroxene hrrogabbro. The ranges ranges from from Ca Ca Mg Ng 6Fe Fe 1 in the lowest gabbro to Ca 0Mg Mg Fe Pe injrmjiatg5ana The int?%ne%!atJ5and ferrogabbro. in the uppermoM upperno@ jatite-rich &ti&rich ferrogabb~o. The in the felsic rocks rocks have hedenbergites hedenbergites clustered felsic clustered around around Ca49Mg03Pe43. Ca49Mg03Fe48* lamination, cryptic layering, The The igneous igneous lamination, layering, and and rhythmic rhythmic P extreme iron—enrichment layering the and the extreme iron-enrichment 3' layering and establish this this intrusion trend all establish intrusion as as a a differentiated, tholeiitic intrusion of the differentiateds Skaergaard type. type. Skaergaard trend all tholeiitic intrusion of the A 36 N �THE THE PITTSVILLE PITTSVILLE (WISCONSIN) THE FORMATION FORMATION OOF F THE (WISCONSIN) MIGMATITE MIGMATITE J. E. Thresher, Department Department ooff Geography Geography and niversity o E. Thresher, andGeology, Geology,UUniversity off Wisconsin—Extension, W i scons i n-Extens ion, Madison, Madison, Wisconsin Wisconsin 53706. ABSTRACT The Pittsvi The P i t t s v ilie l l emigmatite m i g m a t i t ewas was formed formed during d u r i n g the thePrecambrian PrecambrTan by by the the iintrusion n t r u s i o n of o faahydrous hydrous granitic g r a n i t i cmagma magma into i n t o aa series s e r i e s ofo fdiabases diabases and and Duet to the hydrous hydrousnnature spatially extensive extensive b a s a l t s . Due o the a t u r e o of f t the h e ggranite, r a n i t e , spacially basalts. transport of magma into the country rock took place which hasbeen been t r a n s p o r t o f magma i n t o the c o u n t r y rock took p l a c e whichhas recordedbybyppoikiloblasts off quartz potash ffeldspar e l d s p a r wwithin i t h i n the t h e older older recorded oikiloblasts o q u a r t z and and potash rocks, and and the the presence presenceo of the ggranite. rocks, f ooriginal r i g i n a l hydrous hydrous mminerals i n e r a l s wwithin i t h i n the ranite. The observedl ilithologic The observed t h o l o g i c layering l a y e r i n g ini nthe t h emigmatite migmatitehas has formed formed axial axial planar p l a n a r to to a a series s e r i e s of o f subisoclinal s u b i s o c l i n a lnorthwest northwest plunging p l u n g i n g folds. f o l d s . Contemporaneous( (or so) w with was raneous o r nnearly e a r l y so) i t h this t h i sfolding folding wasthe t h edevelopment development of of almandine-amphibolitef afades minerals wwithin almandine-amphibolite c i e s minerals i t h i n the t h e migmatite. migmatite. Later Later more openeast-west east—west were i imprinted on tthis more open t r etrending n d i n g s usubhorizontal b h o r i z o n t a l f ofolds l d s were m p r i n t e d on his ffabric, a b r i c , and and this t h i swas was followed f o l l o w e dby bya agreenschist g r e e n s c h i s tfacies f a c i e smetamorphic metamorphic event, event, apparently a p p a r e n t l y uunrelated n r e l a t e d tto o tthe h e folding. folding. Two episodes wererecorded recorded therocks, rocks,the thef first irst Two episodes o fofj ojointing i n t i n g were w i within t h i n the of o f which which effected e f f e c t e d only o n l ythose thoseofo fPrecambrian Precambrian age. age. The The llater a t e r episode episode also also sandstonesand andi sisthus thus aatt least ffractured r a c t u r e d the the overlying o v e r l y i n gupper upperCambrian Cambrian sandstones least thesej ojoints lower Paleozoic Paleozoic in lower i n age. age. Many Many o fofthese i n t s aare r e f filled i l l e d with w i t h quartz, quartz, granite and/or cchlorite. hlorite. g r a n i t e and/or The rnigmatiteswere werel alater byaaggranitic The migmatites t e r i nintruded t r u d e d by r a n i t i c pluton p l u t o n which which is is considered be rrelated considered tto o be e l a t e d to t o the the greenschist g r e e n s c h i s t facies f a c i e smet met and and possibly possibly Several youngerggranitic Several younger r a n i t i c and and bbasaltic a s a l t i c dikes dikes tthe h e ffilling i l l i n g of o f the t h e joints. joints. crosscut the ccrystalline c r o s s c u t the r y s t a l 1 i n e rocks rocks locally. locally. The eentire The n t i r e sequence sequence is i s unconformably unconformably overlain o v e r l a i nby byupper upperCambrian Cambrian sandstones andconglomerates conglomerates which sandstones and which a r are e e sespecially p e c i a l l y pprevalent r e v a l e n t in i n the the southern the PPittsville area. southern ppart a r t oof f the i t t s v i Il earea. 37 �STRUCTURALAND ANDSTRATIGRAPHICAL STRATIGRAPHICALANALYSIS ANALYSIS OF STRUCTURAL OF THE GECO GECO SULPHIDE DEPOSIT DEPOSIT IN I N MANITOUWADGE, MANITOUWADGE, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO Jens Geology, U University Jens F. F. Touborg, Touborg, Department Department oof f Geology, n i v e r s i t y of o fOttawa Ottawa and and Departmentoof Geology,UUniversity Department f Geology, n i v e r s i t y of o f Toronto, Toronto, Ontario, Ontario,Canada. Canada. ABSTRACT ABSTRACT In area hhigh rocksc oconsisting I n the t h eManitouwadge Manitouwadge area i g h grade grade metamorphosed metamorphosed rocks n s i s t i n g ooff metavolcanic—and metasedimentary downfoldedi in metavolcanic-and metasedimentary s e rseries i e s l i lie e downfolded n a northeast northeast plunging ssyncline, plunging y n c l i n e , the t h e core core of o f which which is i soccupied occupied by by aa granodiorite g r a n o d i o r i t ebody. body. Regionalssuiphide occurs wwithin Regional u l p h i d e mmineralization i n e r a l i z a t i o n ooff stratabound stratabound nnature a t u r e occurs i t h i n aa quartz-muscovite schist quartz-muscovite s c h i s t horizon h o r i z o nalong alongthe t h econtact c o n t a coft metasedimentary—and o f metasedimentary-and ooverlying v e r l y i n g metavolcanic metavolcanic sseries e r i e s iinn the t h e upper upper part p a r t of o fthe t h esequence. sequence. The GecoCopper-Zinc-Silver Copper-Zinc-Silvers usulphide beingl located The Geco l p h i d e ddeposit e p o s i t being o c a t e d wwithin i t h i n aa synclinal s y n c l i n a l dragfold d r a g f o l d on on the t h e northeast n o r t h e a s t limb l i m b ooff the t h e syncline s y n c l i n e consists c o n s i s t s of o f aa ttabular a b u l a r body body of o f massive massive sulphides sulphides enveloped enveloped by by a a haloe haloe of o f disseminated disseminated pyrite—pyrrhotite—chalcopyrite mineralization. p y r ite-pyrrhoti te-chalcopyri t e m i n e r a l i z a t i o n . A discontinous d i s c o n t i nous zone zone ooff disseminated chalcopyri chalcopyrite—pyrrhotite—sphalerite—gahnite disseminated te-pyrrhotite-sphalerite-gahni t e mmineralization ineralization The occurs along tthe occurs along h e north n o r t h contact c o n t a c t of o fthe t h equartz—muscovite quartz-muscovite sschist c h i s t horizon. horizon. The south ccontact mineralization south o n t a c t ooff this t h i s contains contains disseminated disseminated ssphalerite phalerite m i n e r a l i z a t i o n in i n aa discontinous by magneti magnetite-chert discontinous zone zone ffollowed o l l owed by t e - c h e r t iiron r o n formation. f o r i n a t i on. The massives suiphide bodywhich whichs tstrikes east-west and andddips The massive u l p h i d e body r i k e s east-west i p s ssteeply t e e p l y to to the elongatedlenses lensesbecoming becoming successsuccesst h e north n o r t hisi scomposed composed of o f aastring s t r i n of g o5—6 f 5-6elongated plungeo of thesepparallels iively v e l y smaller s m a l l e r towards towards the t h e east. east. The The plunge f these a r a l l e l s tthe h e aaxis x i s of of the t h e dragfold. dragfold. IIn n detail d e t a i l the t h emassive massive sulphide s u l p h i d e body body cconsists o n s i s t s oof f 33 pprincipal rincipal rock types: coarseggrained rock types: 1) 1) compact compact ore: coarse r a i n e d p pyrite y r i t e rrich i c h sphalerite s p h a l e r i t e ore. ore. coarsegrained grainedppyrrhotite-chalcopyrite-sphalerite-pyriteayered ore: coarse yrrhotite-chal copyrite-sphaleri te-pyri te22)) 1layered Mg schistose ore: 3 ) schistose ore: ffine i n e grained g r a i n e dkneaded kneaded ('durchbewegte") ("durchbewegte") Mg ssilicate i 1i c a t e rich r i c h ore. ore. 3) ore These33 types types ddefine o r e of o f similar s i m i l a rcomposition composition to t o the t h e layered l a y e r e d type. type. These e f i n e aa mineralogical-textural-compositional zoningppattern the m i n e r a l o g i c a l - t e x t u r a l - c o m p o s i t i o n a l zoning a t t e r n wwithin i t h i n tthe h e lenses; lenses ; the compacttype typei siscconfined andt hthickest compact o n f i n e d t otot hthe e ccentral e n t r a l and i c k e s t ppart a r t of o f the t h e lenses, lenses, the the layered l a y e r e d ore o r e is i s arranged arranged along along the t h e north n o r t h contact c o n t a c tand and increases increases in i namount amount with with decreasingwwidth decreasing i d t h ooff the t h e lens; lens; the t h eschistose s c h i s t o s eore oredominates dominates in i nthe t h epinch—out pinch-out areas. W Within i t h i n the t h e compact compact oore r e sphalerite s p h a l e r i t e rich r i c hzones zonesare aredeveloped developed towards towards the t h e south south contact. contact. Textures iindicate Textures n d i c a t e aa metamorphic metamorphic r erecrystallization c r y s t a l l i z a t i o n of o fsulphides sulphides and and Annealingf fabrics Annealing a b r i c s exist e x i s t ini nmonomineralic monomineralic aggregates; aggregates; ppyrite yrite porphyroblasts reveal reveal aacomposite composite aggregate aggregate structure s t r u c t u r eand andare a r ecomposed composed of of 2 2 varieties v a r i e t i e s of o f pyrite; p y r i t e ; microfold m i c r o f o l dstructures s t r u c t u r e s are are characteristic c h a r a c t e r i s t i c of o f the t h e layeredlayeredand sschistose massivetypes types as aswwell and c h i s t o s e massive e l l as as the t h e disseminated disseminated types. types. silicates. silicates. 3 sets s e t s of o fsynkinematic synkinematic dyke dyke intrusions i n t r u s i o n semplaced emplaced as as Dyke chronology: chronology: 3 Dyke q u a r t z ddiorites, i o r i tes, 2) 2 ) amphibolites amphi b o l i t e s and, and, 3) 3) granodiorite g r a n o d i o r i t e and and ffollows, o l l o w s , 1) 1 ) quartz granite showdiscordant discordantr erelationships g r a n i t e pegmatites pegmatites show l a t i o n s h i p s tto o the t h e layered l a y e r e d rocks rocks None ooff these dyke dyke generageneraiincluding n c l u d i n g all a l lthe t h edisseminated disseminatedmineralized m i n e r a l i z e dzones. zones. None Dykes ooff ttions i o n s transect t r a n s e c tthe t h massive e massiveore—quartz—muscovite ore-quartz-muscovite sschist c h i s t contact. Dykes 38 �1) and and 2) 2 ) generations generations occur occur as as highly highly folded foldedboudinaged boudinaged fragments fragments wwithin i t h i n the the Significant metamorphic reaction zones are present present massive sulphide ore types. massive sulphide types. Significant metamorphic reaction zones are in-and as follows: follows: niagnetite-sulphide in-and around around the fragments fragments and and appear appear as magnetite-sulphide impregnated zones thes isilicate rock and andsphalerite sphalerite rich rims impregnated zones in inthe l i c a t e rock rims up up to t o 5" 5" rims, Zinc Within the the sulphide sulphide rims, Zinc rich around the the boudinaged boudinaged fragments. fragments. Within wide around sphalerite nearthe thessilicate sphalerite zones zones are are concentrated concentrated near i l i c a t e contact, contact, Iron Ironrich richsphal— sphale r i t ezones zones away away from his. erite from tthis. In conclusion as as a metamorphosed conclusion the thesulphide sulphidemineralization mineralizationis regarded i s regarded a metamorphosed lithological zoning in in thethe boudin—shaped The lithological zoning boudin-shaped bedded sulphide deposit. bedded sulphide deposit. The massive sulphide massive sulphideore orerepresents representsaaprimary primarystratigraphical stratigraphical configuration, Stratigraphical tops tops have have not not although although accentuated accentuated during the the deformation. deformation. Stratigraphical thedistribution distribution of However the of been determined in been determined in the theManitouwadge Manitouwadge area. area. However relatively r e l a t i v e l ycopper copper rich zones zones tto o the the north, zinc zinc rich richzones zones to t o the the south south followed by by magnetite-chert magnetite-chert iron iron formation formationdefines definesa abroad broadpattern patterncomparable comparable I tisi sproposed proposed to othersynvolcanic synvolcanicsulphide sulphidedeposits. deposits. It t o the the vertical verticalzoning zoningini nother that syncline represents represents the the refolded limbs t h a t the theManitouwadge Manitouwadge syncline limbs of ofan anoverturned overturned nappe structure with w i t hananeast—west east-west axis. axis. nappe structure 39 �THE ATIKOKAN THE ATIKOKAN IRON IRON RANGE RANGE AND AND ITS ITSIRON—COPPER IRON-COPPER MINERALIZATION MINERALIZATION dens. F. F. Touborg, Touborg, Suite S u i t e1006, 1006, 77 77Howard Howard St., St., Toronto TorontoM4X M4X IJD, lJD, Ontario O n t a r i oCanada. Canada. Jens. ABSTRACT The Atikokan Atikokan IIron The r o n Range Range iin n northwestern northwestern Ontario O n t a r i o contains containswidespread widespread magnetite—basemetal suiphide whichi sissspatially magneti te-basemetal sulphide m i mineralization n e r a l i z a t i o n which p a t i a l l y associated associated with w i t h lensoid l e n s o i dbodies bodies ofo ultrabasic—basic f u l t r a b a s i c - b a s i cigneous igneousrocks rockscomposed composed ooff pyroxenites, gabbros, amphibolites and and pperidotites. gabbros, amphibolites eridotites. The lenses, lenses, having The having a strong s t r o n g geophysical geophysical response, response, are are concordantly concordantly enclosed enclosed iinn metavolcanic metavolcanic rocks rocks of o f basaltic—andesitic b a s a l t i c - a n d e s i t i c composition composition and and 16 mmile zoneo of strikes ddefine e f i n e aa 16 i l e llong o n g zone f sstratigraphical t r a t i g r a p h i c a l continuity. c o n t i n u i t y . IItt strikes uniformly andddips The zone zonel lies i e s aa few few u n i f o r m l y eastnortheast eastnortheast and i p s ssteeply t e e p l y tto o the t h e north. n o r t h , The hundredso of whichi in hundreds f f feet e e t nnorth o r t h ooff the t h e Quetico Q u e t i c o Shear Shear S&tructure, t r u c t u r e , which n tthis h i s area area separates Archean Archeanmetavolcanic metavolcanicsseries e r i e s to t o the t h enorth n o r t hfrom fromSeine Seinemetasedimentary metasedimentary separates The impact impact ooff metamorphism area iiss low. metamorphism i nint hthe e area low. sseries e r i e s to t o the t h e south. south. The Concentrations occuri in Concentrations ooff Iron—Copper Iron-Copper m imineralization n e r a l i z a t i o n occur n ttabular a b u l a r deposits deposits up Examples are: The The Atikokan Mines-, Mines-, up ttoo 3000 3000 feet f e e t long l o n gand and50-250 50-250 wide. wide. Examples SapaweLake-, Lake—,Archibald-, Archibald—,Pattison-Roberts Pattison—Roberts and and Mark Mark prospects. Sapawe rospects. IIn n detail detail the disseminated t h e mineralization m i n e r a l i z a t i o n consists c o n s i s t sofo lenses f lensesdominated dominated by by 1) 17 massive—or massive-or disseminated magnetite minor sulphide sulphide vveinlets massive—or disseminated disseminated magnetite wwith i t h minor e i n l e t s and and 2) 2) massive-or ppyrrhotite, y r r h o t i t e , lesser l e s s e amounts r amounts of o f pyrite—chalcopyrite p y r i te-chal c o p y r i t e (.3-.6% (. 3-. 6%Copper) Copper) and and trace trace mineralized amountsoof Nickel—Cobaltbearing bearing sulphides. sulphides. The amounts f Nickel-Cobalt The m i n e r a l i z e d lenses lenses are are characterized by aa banded bandeds tstructure concordanti nintercalations c h a r a c t e r i z e d by r u c t u r e wwith i t h concordant t e r c a l a t i o n s ooff the the zonest the mineralization ultrabasic—basic host rock. u l t r a b a s i c - b a s i c host rock. Within W i t h i n pinch—out pinch-out zones he m i n e r a l i z a t i o n and and interbandedwwith tthe h e host h o s t rocks rocks become become hheavily e a v i l y interbanded i t h tthe h e surrounding surrounding volcanic volcanic rocks. Geometrically Geometrically the t h e ruagnetite-and magneti te-and ssulphide u l p h i d e lenses lenses are arranged arranged in in en—echelon sometimesw with aa complex complex en-echelon s t rstructure, u c t u r e , sometimes i t h t hthe e ssulphide u l p h i d e rich r i c hzones zones confined c o n f i n e d tto o tthe h e ffootwall o o t w a l l side; side; this t h i sfeature f e a t u r emay may be be a a possible possible iindicator ndicator ooff stratigraphical s t r a t i g r a p h i c a l tops. tops. Preliminary P r e l i m i n a r y microscopic microscopic work work reveal reveal the t h epresence presence of primary of primary magmatic magmatic ttextures e x t u r e s in i n both both the t h eoxide-and oxide-and sulphide s u l p h i d ephases. phases. Origin Available t h e mineralization mineralization O r i g i n of o f mineralization: mineralization: A v a i l a b l e data data suggest suggest 1) 1 ) the forms an an i Integrating forms n t e g r a t i n g part p a r t of o f the t h eultrabasic—basic u l t r a b a s i c - b a s i c host h o s t rocks. rocks. 22)) there t h e r e is is no evidencet to no evidence o iindicate ndicate a a possible p o s s i b l e relationship r e l a t i o n s h i p to t othe t h ebedded bedded iron i r o n formations formations Wall rock rock contained within w i t h i nthe t h eSteep SteepRock—and Rock-and Caland Caland deposits nearby. nearby. 3) Wall alteration a l t e r a t i o n isi slacking l a c k i n gapart a p a r from t fromminor minorquartz-carbonate quartz-carbonate vveining e i n i n g ooff the t h e host host There i is 4) There s no no ddirect i r e c t relation r e l a t i o nbetween between the t h e mineralized m i n e r a l i z e d uultrabasicltrabasicrock. 4) synvolcanic i intrusive! A synvolcanic ntrusive/ bbasic a s i c series s e r i e s and and the t h e Quetico Q u e t i c o shear shear sstructure. tructure. A extrusive e x t r u s i v e origin o r i g i n isi sproposed proposed for f o rthe t h estratabound stratabound ultrabasic-basic u l t r a b a s i c - b a s i c series s e r i e s and and iits t s associated associated mineralization. mineralization. 40 �GEOCHRONOLOGY PRECM4BRIANROCKS ROCKSIN IN EASTERN WISCONSIN GEOCHRONOIAGY OFOFPRECAMBRIAN WISCONSIN W. Schxnus,Department DepartmentofofGeology, Geology,University University of . Van Van Schmus, of W. RR. lawrence, Kansas, 66044 Kansas, Lawrence, Kansas,66024k Kansas, geochronological studies studies by the author, in Recent geochronological in Recent conjunction with other published and unpublished data, now conjunction permit the the delineation delineation of of major major chronologic chronologic units units for for Precambrian rocks Precambrian rocks in in eastern eastern Wisconsin. Wisconsin. The The oldest oldest rocks rocks in in the the eastern eastern part part of of the the state state are the metavolcanics, gneisses, gneisses, and intrusive rocks rocks in northeastern corner, the northeastern corner, including including the the Quinnesec Quinnesec Fm., Fm., Dunbar Gneiss, Dunbar Gneiss, Hoskin Hoskin take Lake Granite, Granite, Newingham Newingham Granodiorite, Granodiorite, and AtheLstane Athe-"Sane Quar'z QuaiJ%Monzonite. Monzonite. These These rocks rocks are are about about 1900 m m.y. whole-rock data and 1850 1850 to 1900 .y. old based on Rb-Sr whole-rock published U-Pb U-Pb zircon zircon data. data. Apparently the bulk of of the the state state is is made made up up of of metametavolcanics and volcanics and granitic granitic rocks rocks that that yield yield ages ages of of 1650 1650 to to rocks in Waushara 1700 1700 m.y. m.y. The The author author has has analysed analysed such such rocks in Waushara Co. (granites) (granites) and and to to the the south south (rhyolites), (rhyolites), and and other other workers workers have have reported reported similar similar ages ages from from near near Monico, Monico, Wausau, Wausau, and Baraboo. Baraboo. Intrusive into the 1650—1700 m.y. 1650-1700 m .y. old complex complex is is aa Intrusive large large plutonic plutonic assemblage assemblage that that is isabout about12450 1450 to to 1500 1500 m.y. m.y. old and is is now now referred referred to to as as the the Wolf Wolf River River Batholith. Batholith. It It includes a wide variety of includes of rocks rocks from from Mountain, Mountain, to to Wausau, Wausau, Point, to Waupaca and apparently is to Steven's Steven's Point, is the last major major plutonic plutonic or or metamorphic event event in in the the state, state, except except for for the the Keweenawan Keweenawan rocks rocks in in the the far far northwest. northwest. absolutely dated are Not yet absolutely are gneissic gneissic and and related related rocks in Published rocks in the the Steven's Steven's Point-Wisconsin Point-Wisconsin Rapids Rapids area. area. Published mineral ages from these rocks rocks suggest suggest they may be related mineral ages from to Resolution to the the northeastern northeastern Wisconsin Wisconsin complex, complex, or or older. older. Resolution of this problem, plus extending extending our our knowledge knowledge westward westward and and northwestward, is currently currently in northwestward,is in progress. progress. 41 �"FRMIBOIDAL" WHITEPINE, PINE, MICHIGM "ERAMBOIDAL" CHAJJCOCITE CHALCOCITE FROM FROM WHITE MICHIGAN Thomas A. A. Vogel and and Nancy Nancy Alyanak, Alyanak, Geology Geology Oepartment, Department, Michigan 48823 Michigan State S t a t e University, University,East EastLansing, Lansing,Michigan Michigan48823 ABSTRACT ABSTRACT Chalcocite with nnuclei Chalcocite with u c l e i occurs occurs throughout throughout the t h e mineralized mineralized zone zone aatt White White Pine, Pine, Michigan. Michigan. They They are a r e more more abundant abundant in i n the t h e well—laminated, well-laminated, black, black, fine—grained fine-grained lithologies l i t h o l o g i e s than than in i n the t h e massive massive lithologies. l i t h o l o g i e s . In In polished section nuclei s e c t i o n these n u c l e i are a r e either e i t h e r circular, c i r c u l a r , ellipsoidal e l l i p s o i d a l or o r con— cont o the t h e shape shape of of the t h e grain, g r a i n , with with aa median median circular c i r c u l a r diameter diameter of of four four fform on to microns microns and and aa median median ellipsoidal e l l i p s o i d a l long long axis a x i s of of eight e i g h t microns. microns. Microcrysts Microcrysts at a t least l e a s t as as small small as as 0.2 0.2 microns microns are a r e found found in i n each each nucleus. nucleus. The The nuclei nuclei are pyrite a r e similar s i m i l a r to t o the t h e framboidal texture t e x t u r e commonly observed in in p y r i t e assoassociated c i a t e d with with sediments. sediments. The The chalcocite chalcocite nuclei n u c l e i can can only only be be observed observed after after the t h e polished section s e c t i o n has been etched and stained s t a i n e d with a weak hydrochloric acid acid and and potassium ferrocyanide solution——a s o l u t i o n ~ astain s t a i n very sensitive s e n s i t i v e to t o low concentrations concentrations of of iron. iron. e l e c t r o n microscope shows that The scanning electron t h a t the microcrysts within c i r c u l a r or o r ellipsoidal e l l i p s o i d a l nucleus are a r e densely packed, a well-defined well—defined circular packed, with a few scattered s c a t t e r e d microcrysts in i n the t h e surrounding surrounding grain. grain. However, the t h e micro— microfew crysts c r y s t s are a r e less l e s s densely densely packed packed where where the t h e nucleus nucleus occupies occupies the the entire e n t i r e grain. grain All A l l gradations between between dispersed dispersed and and densely densely packed packed microcrysts a r e found. found. microcrysts are Preliminary microprobe d i c a t e s t hthat a t the u c l e i aare r e higher iron, Preliminary microprobedata datai nindicates the nnuclei higher iinn iron, potassium and carbon carbon than than the the surrounding potassium and surrounding grain. grain. Two Two origins o r i g i n s are a r e possible possible for f o r the t h e framboidal framboidal chalcocite: chalcocite: 1.) 1.) replacement of 2 . ) formation of primary framboidal framboidal chalco— chalcoof framboidal framboidal pyrite p y r i t e and 2.) cite. c i t e . We We are a r e currently c u r r e n t l y evaluating evaluating these these alternative a l t e r n a t i v e genetic models and and their t h e i r implications. implications. 42 �WISCONSIN OF LANDFORMS Na .., ii: Or- tLJ ni story irvey FII rrF F F. Su Unoron I rd Geolo irsi Hanson. Dirnotor and Stoto Genlngiot L'Fur UNIVERSITY ESTENSION, UNIVERSITY OF WISCONSIN 1971 30 Ti __ 0 UCALE OF VILEU EU �A A' lie Cassai Racine boo too 002 455 StiLES IS SCALE iuniuue Fat it] A S imL HOtFrtFTs - id 200 SL Or) _c 10 - 0 - 203 400 25 boo 500 Jr loon, In Leoal cool Sea boo Peat Fr F 'a Fr sri "r ron taboo and Adaoe toFu Eieoatian GriP Gla(n D!der at trio (OrryF (Otto) dssnsnsin V2snirainn ci oi Hordes -. DriP r data) (sisarne Seeks Mntantrri and tgnenes Boors 0rorphie imenLated ii and Graean UndiffererrlLFud h r -tamest iF Marc and Ugeenas irks toeke .1 is miii ndiI UrFjfersrtiarnd and Granite [E a - - BasalE and Gabbrn 'c P r Oornraii000 'chin For tree and Ps' 0mm Graaneitc senptnmerale) 'rotc ncr-rninuodir wirb (sandstones I-crrn',c"s tlnwennerrrn Formutioos Upper a-rd - corns with (sandstones nrA. aed shale) a-ri 5dolomite dotoir snore _55 °oncrr Oncbrinr' air Cumb i_poor Formations Jeo (dolomin) iso "mine dr Pr Ar,a? Chine Group Crrhs none and shale (snrho,crs doreen in usutnF rrsrcrr torrreratr-( ruEd rFFr Parer Fm) '0nr StS (mainly 'usr, Group Aneell Oscs'l F,rtr r--ssils some rune )dclsrnitcoirh shale) oh5 sF and ccc lanresroon with (dolomite Group Sponipea dtu, 'F dolomrtn) srd arrd (ehuls irrein Oct. Forrtiati °rrnurrorr iolrntn Mc,, S'iapaiokr--lu hdcLoortn; (oolomitu( sir Is, Si Formations lurian Furoariors II 1— a a skis' shale) dod O'i (doloroipsin rho Forrrratronn Dovoniuo S LEGEND - -1- I Co L SilLhd GO SCALE 30 1971 1)JF[°lVflLjyj1 WISCONSIN Fj• OF UNIVERSITY )s:H EXTENSION. UNIVERSITY an Geologist State and Director h( F. George 1rr::ni Hanson. 'r :r-:.n. Forli' History 'ir Geological Survey Natural s:•-•j and !YF: F WISCONSIN iF'fl In::) MAP GEOLuGIC fl-il' )l S ,.'f:s d �SHORT GEOLOGIC GEOLOGIC HISTORY HISTORY OF OFWISCONSIN WISCONSIN The bedrock separatedinto intotwo twomajor majordivisions: divisions:(1) (1) older, older, predominantly predominantly crystalline crystalline rocks rocks of of the bedrock of Wisconsin Wisconsin isisseparated Precambrian Precambrian Era; and and (2) ( 2 )younger youngerrelatively relativelyflat-lying flat-lyingsedimentary sedimentaryrocks rocksof of the thePaleozoic Paleozoic Era. Era. The Precambrian Precambrian Era Era lasted lasted from from the the time time the theearth earthcooled, cooled,over over4,000 4,000 million million years years ago, ago, until until the thePaleozoic Paleozoic Era Era which began began about 600 million years ago. ago. During During this vast period which million years period of of 3,400 3,400 million million years yearssediments, sediments, some some of of which which were rich rich in iron iron and and which which now now form formiron ironores, ores,were weredeposited depositedinin ancient ancient oceans; oceans; volcanoes volcanoes spewed spewed forth forth ash and and lava; mountains were built built and and destroyed, destroyed,and and the the rocks rocks of of the upper crust mountains were crust were were intruded intruded by by molten molten rocks rocks of of deepdeepseated origin. Only a fragmentary fragmentary record record of of these these events events remains remains but, but, as as tree treestumps stumpsattest attesttotothe thepresence presenceofofformer former forests, forests, the rocky rocky roots roots tell tell the thegeologist geologist of of the thepresence presenceofofformer formermountains. mountains.Nowhere Nowhere does does any trace trace of of the the original original crust remain, remain, and and the theoldest oldest rocks rocks yet yet found found in inthe thestate stateare areabout about2,000 2,000million millionyears yearsold. old.With Withthe theexception exception of ofthe the Upper Keweenawan formationsthat that outcrop outcrop in in the northwest, northwest, all of of these these rocks rocks have havebeen beenextensively extensively deformed, deformed, Keweenawan formations and in altered that their in many many areas areas they they are are so so highly highly altered their original original nature and and origin origin are are extremely extremely difficult difficult to interinterpret. I n the the north-central north-central part partof of the thestate statesurface surfaceoutcrops outcrops are areso sosparse, sparse, due due to to aa cover cover of of glacial glacial deposits, deposits, that In that details of the bedrock bedrock are are obscured. obscured. In In such such areas areasthe theonly onlyclues clues to t othe theunderlying underlyingrocks rocksare areobtained obtainedindirectly indirectlyby bysuch suchgeogeophysical methods as as airborne physical methods airborne magnetics. magnetics. IIn n the the past past much muchhigh-grade high-grade iron iron ore ore was was produced produced from the Precambrian Precambrian rocks of of northern northern Wisconsin, Wisconsin,and andmuch muchlow-grade low-gradeore ore("taconite") ("taconite") awaits development. work indidevelopment. Recent Recent geologic geologic work cates that that the the area areahas hasa ahigh highpotential potentialfor forfinding findingores oresofofother othermetals metalssuch suchasascopper. copper. At the the close close of of the the Precambrian Precambrian Era Eramost mostofofWisconsin Wisconsinhad hadbeen been eroded eroded to to aa rather ratherflat flatplain plainupon uponwhich which stood stood hills of more resistant rocks as those now exposed in the Baraboo bluffs. There were still outpourings of basaltic exposed in still basaltic lava lava in the the north north and and aatrough troughformed formed in inthe thevicinity vicinity of ofLake LakeSuperior Superiorininwhich whichgreat greatthicknesses thicknesses of of sandstone sandstone were were deposited. deposited. The Paleozoic Era began began with with the the Cambrian Cambrian Period, Period, the rocks Paleozoic Era rocks of which which indicate indicate that that Wisconsin Wisconsin was was twice twice subsubmerged beneath the sea. Rivers draining the land carried sediments which were deposited in the sea to form merged the sea. Rivers draining the land carried sediments which were deposited in the sea to formsandsandstone and plants plants living in the sea stone and shale. shale. Animals Animals and living in sea deposited deposited calcium calcium carbonate carbonate and built built reefs reefs to toform formrocks rocks which are magnesium-rich continued into the dolomit-a magnesium-rich limestone. limestone. These same same processes processes continued the Ordovician Ordovician Period Period are now now dolomite—a during which, was submerged submergedthree three more more times. times. Deposits Depositsbuilt built up up in in the sea which, as indicated indicated by the the rocks, rocks, Wisconsin Wisconsin was sea when when the land land was was submerged submerged were partially or or completely completely eroded eroded at at times times when when they theywere weresubsequently subsequently elevated elevated above sea level. level. During During the the close close ofof the the Ordovician Ordovician Period, Period, and and in the above sea the succeeding succeeding Silurian Silurian and and Devonian Devonian Periods, Periods, Wisconsin is believed Wisconsin is believed to have remained remained submerged. submerged. The youngest youngest rocks rocks outcropping in in Wisconsin Wisconsin are of of Devonian Devonian age age and and are areabout about350 350million million years years old. old. Absence Absence of The of If the thedinosaurs dinosaurs younger rocks makes makes interpretations interpretations of post-Devonian post-Devonian history in Wisconsin Wisconsin aa matter of of conjecture. conjecture. If younger roamed Wisconsin, as well well they they might might have some 200 million million years years ago, no trace Wisconsin, as trace of of their theirpresence presenceremains. remains.AvailAvailevidence from from neighboring neighboring areas, areas, where whereyounger youngerrocks rocksare arepresent, present,indicates indicatesthat thattowards towardsthe theclose closeof of the the PaleoPaleoable evidence some 250 million present. DurDurzoic Era, perhaps some million years years ago, ago, aa period period of of gentle uplift began which which has continued to the present. ing ing this this time time the the land land surface surface was was carved carved by rain, wind wind and and running running water. water. The final final scene scene took took place place during million years when glaciers glaciers invaded invaded Wisconsin Wisconsin from north and and The during the last million years when from the north sculptured thevalleys valleysand andleft leftaadeposit depositof ofdebris debris over over all all exexsculptured the the land land surface. surface.They Theysmoothed smoothed the thehill hilltops, tops,filled filledthe cept the southwest southwest quarter of of the theState Statewhere wherewe wemay maynow nowstill stillsee seethe theland landasasititmight mighthave havelooked lookedaamillion millionyears years ago. ago. �fI;Director si;p 5Hanson,j J•!U]%9#IC State and Geologist :' Survey,, History Natural !4[c au 'FiJOG-> d 'ge !tñJiS% Geological .!IHCOIISIfl i]1.y of University Wisconsin )I.Ii1 PtisIt uqen ds n 'H irf 'tjsoap0 pitted SLft LJSDaiflfl unpitted ne 1t)15.tJ Morn ptrnOJ9 4 or,es .YY;_JOW p'q L r ,• tR: OF dç SCALE MILES 40 p -. iHFI.Jj after 1956 Tliwaites, q Hi 1 'i• _r' n 1] DEPOSITS GLACIAL WISCONSIN F L �I SHORT S HORT HISTORY OF OF THE ICE AGE IN I N WISCONSIN WISCONSIN U 1,000,000 years ago The Pleistocene Epoch or o r "Ice "Ice Age" Age" began about 1,000,000 ago which, which, in f o u r separate separate s h o r t time time ago. ago. There were four i n terms of of geologic geologic time, time, i s a very short g l a c i a l advances advances iin n tthe h e Pleistocene Pleistocene each each followed followed by by an an inter—glacial i n t e r - g l a c i a l period period glacial is whent the The ffourth o u r t h gglacial l a c i a l stage s t a g e is i scalled c a l l e dthe t h Wisconsin e Wisconsin Stage Stage when h e iice c e receded. receded. The because wasi nint hthis that it was first studied detail. because itit was i s SState tate th a t it was first s t u d i e d iin n d etail. The gglaciers snow The l a c i e r s were were formed formed by by the t h e continuous continuous accumulation accumulation of of snow. snow. The snow i n t o ice i c e which reached a maximum maximum thickness of of almost almost two two miles. miles. The The turned into sheet spread spread over over Canada and ppart of it it flowed flowed iin general southerly southerly iice c e sheet a r t of n aa general direction d i r e c t i o n toward Wisconsin and neighboring states. states. f r o n t of the t h e advancing advancing iice c e sheet sheet had had many many tongues or o r "lobes" "lobes" whose whose The front direction wereccontrolled by tthe of tthe d i r e c t i o n and and rate r a t eofofmovement movement were o n t r o l l e d by h e topography topography of h e land land surface over by tthe surface over which which they they flowed flowed and by h e rrates a t e s of of ice i c e accumulation in i n the the different d i f f e r e n t areas from which they were fed. fed. sheet transported transported aa great rockddebris "drift". The ice i c e sheet g r e a t amount amount ofofrock e b r i s ccalled a l l e d "drift". was was "Drumlins" p i l e d up up aatt the t h e margins margins of of the t h e ice i c elobes lobestot oform form"end "end moraines". moraines". piled are of ddrift byt the a r e elongated elongated mounds mounds of r i f t which which were were molded molded by h e iice c e passing passing over over them them and hencei nindicate and hence d i c a t e tthe h e ddirection i r e c t i o n of of ice i c e movement. Some "ground Some ofoft this h i s was was deposited deposited under under the t h e ice i c etot form o form "groundmoraine" moraine"and andsome some pattern of end moraines, moraines, iin red, shows tthe was occupied occupied The p a t t e r n of n red, h e pposition o s i t i o n tthat h a t was advanced down down the t h e basin basin of of Lake Lake Michigan, Michigan, by four f o u r major ice i c e lobes. lobes. One lobe advanced Green Bay, Bay, aa third another another down down Green t h i r ddown down Lake Lake Superior and over the t h e northern peninsula The Michigan and yet a fourth of Michigan fourth entered entered the the state s t a t e from from the t h e northwest northwest corner. corner. The of "Kettle Moraine" well-known "Kettle Moraine" was was formed formed between between the t h eLake LakeMichigan Michigan and andGreen Green Bay Bay well—known lobes. As A s tthe h e ice i c e melted melted the t h e drift d r i f was t wasreworked reworked by by the t h e running running water. water. Large amountsofof sand sand and andgravel gravel were weredeposited deposited tto "outwashplains"; plains"; ppits amounts o form form "outwash i t s were were formed iin whereburied buriedblocks blocks of of ice of these are formed n tthe h e outwash outwash where i c e melted melted and and many many of are now now occupied occupied by by lakes. lakes. The action profoundly modified tthe landscape, smoothing o off a c t i o n of of tthe h e ice i c e profoundly h e landscape, f f tthe he places ititchanged changed I n some some places of hills ccrests r e s t s of h i l l s and ffilling i l l i n g the t h e valleys v a l l e y s with with ddrift. r i f t . In the of tthe Wisconsin t h e course of rivers r i v e r s forcing them to t o cut new channels such aass tthat h a t of h e Wisconsin River at a t tthe h e Dells; Dells; elsewhere it it dammed dammed the t h e valleys v a l l e y s to t o create c r e a t e lakes lakes such such as a s those those of tthe of h e Madison Madison area. area. During rrecent e c e n t years there t h e r e have been intensive i n t e n s i v e studies s t u d i e s made made of of the t h e polar polar caps, and methods have been developed for iice c e caps, f o r dating glacial g l a c i a l events events from from the the of tthe wood, bones, bones, eetc. which aare found iin many of of rradioactivity a d i o a c t i v i t y of h e carbon iin n wood, t c . which r e found n many of these these sstudies previously accepted e s u l t s of t u d i e s aare r e causing many previously tthe h e deposits. deposits. The rresults concepts to t o be changed changed or o r challenged. challenged. We thought tthat were rrather extensive gglacial W e once thought h a t tthere h e r e were a t h e r extensive l a c i a l ddeposits e p o s i t s oolder lder than Wisconsin age age in i n the t h e State, S t a t e , but but age age determinations determinations do do not not support support this. this, It was aalso thought that It l s o thought t h a t the t h e ice i c e left l e f t Wisconsin some some 20,000 20,000 years years ago ago but but aa Countywas wasburied buriedunder under an an advancing advancing iice fforest o r e s t aatt Two Creeks in i n Manitowoc Manitowoc County ce i s accumulating accumulating to t o indicate i n d i c a t e that t h a t ice ice 11,000 years ago. tongue tongue only 11,000 ago. Evidence is may have occupied the Area" of of tthe southwestern p part of t h e so—called so-called "Driftless " D r i f t l e s s Area" h e southwestern a r t of the t h e State S t a t e which hitherto h i t h e r t o has has been been held held to t o be be unglaciated. unglaciated. Most sscientists believe Most c i e n t i s t s now b e l i e v e that t h a t the t h e cause of the t h e Pleistocene "Ice "IceAge" Age" was duet to was due o vvariations a r i a t i o n s in i n the t h e solar s o l a renergy energyreaching reaching the t h eearth, e a r t h ,but buthow howthese thesemay may We haveoccurred occurredisissstill have t i l l aa matter matter of of conjecture. conjecture. W e a are r e sstill t i l l in i nthe t h eIce I c eAge Age and and it anybody's guess whether future millenia it is anybody's future m i l l e n i a will w i l l see s e e the t h e melting melting of of cities, or the regrowth coastal caps and the slow drowning of our t h e slow our c o a s t a l c i t i e s , o r t h e regrowth and and oftthe more tthe more h e inexorable inexorable advance advance of h e gglaciers. laciers. the t h e ice ice once once Prepared by tthe Natural History HistorySurvey, Survey, August August Prepared by h e University University of ofWisconsin Wisconsin Geological Geological £& Natural 19641 1964' �WiSCONSIN OF unIVERSITY A A U II Al IA OAR ._<__,1<., Spruce White Fir, Balsam FOREST BOREAL Cedar Tamarack, Spruce, Black SWAMPS CONIFER —— •—fl.l- Maple, <r— Birch Yellow Hemlock, N FOREST MESIC NORTHERN i:_ t' .', F —. Pine Red Pine, White FOREST PINE Grasses Prairie pine, Jock BARRENS PINE — r 4/ 'C<L<.. Joint, Blue Sedges, Cordgrass MEADOWS SEDGE L___J • r— <Willows, Ash Maple, Soft - HARDWOOD LOWLAND Elm - -c - Stigar Basswood, Maple, FOREST MESIC SOUTHERN Oaks Red ond Block White, FOREST OAK SOUTHERN 1 LI±J 7 t Bluestem Oak, White Oak, Bur I SAVANNA OAK -, -1";,;] Composites Bluestem, -< PRAIRIE a LEGEND 6 I r a / a S C C a L Miles at Scale 80 40 0 1965 Wisconsin of University Director L L:s4 Hanson, G.E. Survey History Natural and Geological Wisconsin 1I\L H j ccc WISCONSIN OF VEGETATION EARLY -. I f pi �INTERPRETATION OF OFTHE THEVEGETATION VEGETATIONOF OFWISCONSIN WISCONSIN about the the middle middle of of the the llast This map map iiss based on the original original land land survey survey conducted conducted about a s t cencenSurveyorswere wererequired requiredtotoplace placeaa stake stake eachhalfmile, tury. Surveyors eachhalfmile, identified identified by by notation notation of of nearby nearby trees, and and to to note note briefly briefly the the general general plant plant cover cover of of each each quarter quarter section. These records records have have been used to been to reconstruct reconstruct the the presettlement presettlement distribution distribution patterns patterns of ofplant plantcommunities communities shown shown on on the map. map. The plant communities recognized,however, however,are arebased basedon on systematic systematic studies studies of presentThe communities recognized, presentday vegetation. vegetation. The day The results results of of these these studies studiesare aresummarized summarized in a recent recent book book (J. T. Curtis, Curtis, The The Vegetation of Wisconsin, University of Wisconsin Press, 1959) in which each community, with Vegetation of Wisconsin, University of Wisconsin Press, 1959) in which each community, its history, history, location, location, and and relationship relationship to toother othercommunities communities and tothe tothe environment, environment, iiss considered considered Since some of the factors determining vegetation vary gradually, the vegetation vegetation itself itself in detail. in Since some of the factors determining vegetation vary gradually, the varies gradually and boundaries on the map are somewhat arbitrary. gradually and boundaries on the map are somewhat arbitrary. The vegetation vegetation of of the the state floristic provinces The s t a t e is is divided divided into into northern northern and southern southern floristic provinces by by aa line that runsinans-curve runs in an S-curvenorthwest northwestfrom fromMilwaukee MilwaukeetotoHudson. Hudson.North Northofofthis this line line the vegetation vegetation Southwest of of the the line, abroadleaf forest containing containing conifers—pines, conifers-pines, hemlock, is abroadleaf hemlock, spruces, spruces, and fir. Southwest conifers are are much much lless andare are replaced replacedby byforests forests with with several several species species of conifers e s s important important and of oaks, and by the the prairies—areas dominatedby bygrasses grasses and and tall herbs. by prairies-areas dominated herbs. Fire has has been been important important in in determining determining almost all of of the the plant plant communities communities and and their their lolothe coming of white white man, man, the the prairies (1) (1) and and the the open open woodlands woodlands burned burned almost almost cation. Before Before the coming of every year. year. Thus every Thus most most of of the the southern southern part part of of the the state s t a t ewas was covered covered with with prairie prairie or or oak oak savanna savanna (2), an orchard-like withaa few few large large bur bur or or white white oaks oaks growing in fields fields of (2). orchard-like community community with growing in of grass. grass. Only in in the the more more protected protectedplaces places did did forests forests survive. (3) but but many many were were Only survive. Some Some of of these these were were oak oak(3) sugar elm forests (4). sugar maple-basswood-slippery maple-basswood-slippery elm (4). The The lowlands lowlands were were occupied occupied by by river river bottom bottom Withsettlement, settlement, the the fires fires were (51, and and sedge sedgemeadow meadow (6). ( 6 ) . With were stopped, and the oak oak savannas savannas forest (5), of the prairies grew up dense white white oak-black oak-black oak oak forests forests found found today. today. Most Most of prairies have have been been grew up to to the dense cultivated, andat and a tpresent, present,with withthe theoak oaksavannas, savannas,are areamong amongthe therarest rarestofofour ourplant plantcommuaities. communities. In part of of the the state, aa combination In the northern northern part combination of fire and and poor poor soil resulted resulted in in the the develdevelopment of pine barrens (7) on the sandy soils, and pine forests (8) on somewhat better soils. In (8) on somewhat better soils. opment of pine barrens (7) on the sandy soils, and pine the the absence absence of of fire, fire, the the white white pine pine forests forestsgradually gradually changed changed to to the thenorthern northern equivalent equivalent of of the the sugar forests, aa community sugar maple-basswood maple-basswood forests, community containing sugar sugar maple, maple, yellow yellow birch birch and and hemlock, hemlock, with beech beech added added in in the the eastern eastern counties counties (9). (9). Also Also present present in in the the north north were were large large tracts tracts of of lowlowwith land, with with tamarack tamarack and andblack black spruce spruce bogs bogs in in the the wetter wetter areas, areas, and white cedar swamps land, swamps in drier, but still still very very moist moist habitats habitats (10). (10). In In the extreme extreme north north are local local occurrences occurrences of of the thenorthern northern but conifer by fir and spruce. conifer forest forest (11) (11) dominated dominated by A comparison comparisonofof this this map map with with maps maps ofof climate, climate, soil, and A and glacial glacial deposits deposits shows shows many many The correspondences, indicating relationships between correspondences, indicating many many relationships between vegetation vegetation and the the environment. environment. The original vegetation vegetation was was thus by the the distribution of both original thus determined determined by distribution of both climatic climatic and and soil soil factors, factors, modified modified by fire. fire. 0. G. Cottam, Cottam, 0. 0. L. L. Loucks Loucks Department of Botany Department The University of of Wisconsin Wisconsin � https://digitalcollections.lakeheadu.ca/files/original/ac9dd9c98d82d2009fc6fa2432059ff8.pdf cc4f1f23c1fae5b8a1976c91c2b31a0d PDF Text Text University of Wisconsin—Extension GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostroin, State GeoIogSt and Director GUIDEBOOK TO THE PRECAMBRIAN GEOLOGY OF NORTHEASTERN AND NORTHCENTRAL WISCONSIN 18th Ausnuul Institute on Luke Superior Geology Madison, Wisconsin, 1973 �UNIVERSITY UNIVERSITY OF OF WISCONSIN-EXTENSION WISCONSIN-EXTENSION GEOLOGICAL AND AND NATURAL GEOLOGICAL NATURAL HISTORY SURVEY SURVEY E. Ostrom, Ostrom, State State Geologist Geologist && Director Director Meredith E. GUIDEBOOK TO TO THE PRECAMBRIAN PRECAMBRIAN GEOLOGY OF NORTHEASTERN NORTHEASTERN AND AND NORTHCENTRAL WISCONSIN with Special Papers on Chronology of Precambrian Precambrian Rocks Rocks in in Wisconsin Wisconsin W.R. Van Van Schinus Schmus The Wolf River Batholith——a Batholith--a Late Late Precambrian Precambrian Rapakivi Rapakivi Massif in in Northeastern Wisconsin Wisconsin L.G. L.G. Medaris, Medaris, Jr., Jr., J.L. J.L. Anderson, Anderson, and and J.R. J.R. Myles Myles Precambrian Geology of Marathon County G.L. LaBerge LaBerge and and P.E. PE. Myers G.L. Field Trip Committee Committee C.E. C.E. Dutton, Dutton, U.W. U.W. Geological Survey Survey G.L. LaBerge, LaBerge, UW—Oshkosh; mV-Osh~osh; Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Sur. Sur. L.G. L.G. Medaris, Medaris, Jr., Jr., UW—Madison UW-Madison G. G. Mursky, Mursky, UW-Milwaukee P.E. P.E. Myers, Myers, UW-Eau mV-Eau Claire; Claire; Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Sur. Sur. W.R. Van Schmus, W.R. Schmus, University University of Kansas L.W. L.W. Weis, Weis, UW Center System-Fox Valley Valley printed in in limited limited quantities quantities for for the the 19th 19th This guidebook was printed Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. Madison, Wisconsin Madison, 1973 Available from from the the Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Wisconsin—Extension, 1815 University University of Wisconsin-Extension, University Avenue, Madison, Madison, Wisconsin Wisconsin 53706. 53706. Price: $5.00. �DEDICAT I DEDICATION This guidebook is is dedicated to to Carl E. E. Dutton Dutton in in appreciation appreciation for for his continual encouragement and and advice advice to to us us all all and and in in recognition recognition of of toward an an understanding of the the Wisconsin Precambrian. his contributions toward I �INTRODUCTION I NTRODUCT ION With the exception of early bulletins of of the the Wisconsin Wisconsin Geological Geological and Natural Natural History Survey produced between about about 1900 1900 and and 1930 1930 little little had been published on the Precambrian geology of of Wisconsin Wisconsin until until the the appearance appearance in in 1970 of of "Lithologic, "Lithologic, Geophysical, Geophysical, and Mineral Commodity Maps of of Precambrian Rocks Rocks in in Wisconsin" by by Carl Carl E. E. Dutton Dutton and and Reta Reta E. E. Bradley, which was the product of aa cooperative effort of Bradley, of the the State State Survey and and the the U.S. U.S. Geological Geological Survey. Survey. That publication is is aa compicompilation which drew together in in concise form at at aa scale scale of of 1:500,000 1:500,000 all all that was generally known about Precambrian geology of of Wisconsin Wisconsin and, and, thus, thus, served to focus focus attention on the the mineral potential of of Wisconsints Wisconsin's Precambrian rocks and and to indicate the inadequacy inadequacy of of available available geological geological and information. As aa direct consequence of the the publication publication and geophysical Information. company exploration activity increased increased markedly and and the the interest interest of of university and and survey survey geologists geologists was was revived. revived. As aa part part of of this this revival revival the the Wisconsin Wisconsin Geological Geological && Natural Natural History History Survey has initiated a program to survey and and map the the Precambrian geology geology of the state in cooperation with geologists on the the faculty faculty of of the the UniverUniversity of Wisconsin System System at at its its various various campuses. campuses. At the the present time time L. LaBerge (UW—Oshkosh), Professors Gene L. (UW-Oshkosh), Paul Myers (UW—Eau (UW-Eau Claire), Claire), and and Joe Mengel (UW-Superior) are supported by the Survey on aa part—time part-time Mengel (UW—Superior) basis during summer months to map Precambrian geology in in Wisconsin. Wisconsin. Other university geologists contributing to the program have obtained support from from various grant programs including the University—Industry University-Industry Program, the Wisconsin Alumni Research Foundation and Research Program, and from Industry. industry. The Survey will soon soon publish aa bouguer bouguer anomaly anomaly gravity gravity map map of of the the state prepared by Professors C. C. Patrick Ervin (formerly state (formerly UW—Madison, UW-Madison, now Northern Illinois (UW—Madison) at at a scale Illinois University) University) and and Sigmund Sigmund Hanuner Hammer (UW-Madison) of 1:500,000, 1:500,000, utilizing over of over 16,000 16,000 stations. stations. In In addition, addition, the Survey has begun aa program under the the leadership leadership of of Prof. Prof. John John Karl (Department (Department of Physics, Physics, UW—Oshkosh) UW-Oshkosh) to to produce an an aeromagnetic aeromagnetic map of of the the northern northern two—thirds of the the state at north—south flight two-thirds at a a north-south flight line spacing of one—half one-half mile. This study was initiated initiated by aa grant from from the the Upper Great Lakes Lakes Regional Regional Commission and has been strongly supported by aa substantial substantial grant from NL Industries Industries and and by aerial aerial photograph prints prints provided provided by by INCO. INCa. This field field guide and accompanying accompanying maps, maps, printed for the the 19th 19th Annual Institute on on Lake Lake Superior Superior Geology, Geology, will will be included in what what is Institute is hoped be aa complete series series of of Precambrian Precambrian field field guides guides and and will eventually be maps for Wisconsin Wiscsin atata ascale maps for scaleofof1:250,000, 1:250,000, published published as as Geological Geological and and Natural History History Survey Survey Information Information Circulars. Circulars. When used in in combination with the the bouguer gravity anomaly anomaly map and and the the aeromagnetic aeromagnetic map map they they will will provide aa basis for identification identification of of areas areas of of above above average average mineral mineral popotential in Wisconsin which can then be made the subject for detailed tential in Wisconsin study. M.E. Ostroin Ostrom & Director State Geologist & �SPECIAL PAPERS Chronology of Pncainbrimn Rocks by W.R. Van Schaus Wolf River Satboiith——a Lst• Precabrian Rspakivi Kant! La Wcrtheasten Wisconsin The by b.C. Medaris, Jr., J.L. Anderson, and J.R, kyle. Ptecnibrtan Geology of Marathon County by G.L. Laflerge and P.E. Myers �Superior Lake Superior u o N ....o --' "" Q Waupaca River Falls Map Symbol Age Im.y.) Chronologic Unit PALEOZOIC Keweenawan COVER 1115 .:20 Wolf River Batholith gr • •rhy• • 1500 .:50 rhy • >1500 Quartzite <1675 1675 .: 50 Central Wisconsin Complex o ~ ~ > 1500 TIgerton Anorthosite < NE Wisconsin Complex ?? o 1875 .:50 Metavolcanics and metasedi ments 1900 .: 50 Archean Complex >2500 Age uncertain or unknown I. Figure 1. Madison Miles 0 0 Kilometers Milwaukee 40 50 • = Primary age determinations Primary age WRVS 2/73 Generalized geochronologic geochronologic map mapofatPrecambrian Precambrianrocks rocksin in Wisconsin Wisconsin and Michigan. Generalized and Upper Upper Michigan. I �11 Chronology of Precambrian Rocks Rocks in in Wisconsin by W.R. Van Schmus* W.R. Geochronologic data for Precambrian rocks rocks in in Wisconsin have have existed existed for for more than aa decade, decade, but until recently the the data were limited limited to to analyses of of separate separate minerals minerals and distributed, so that analyses and were widely distributed, that exact interpretation of primary formational ages ages and and delineation of of chronologic chronologie provinces was not possible. possible. These early data were summarized summarized by by Dutton Dutton and (1970) and will not be be reviewed reviewed in in detail detail here. here. and Bradley Bradley (1970) In terms of of obtaining primary ages In terms ages of Precambrian rocks, rocks, as opposed to metamorphic ages, ages, the geochronologic methods most likely likely to to yield yield reliable results are the Rb-Sr whole-rock isochron isochron method and and U-Pb U-Pb analyses on cogenetic suites suites of of zircons. zircons. Application of these these procedures procedures to Precambrian rocks rocks in Wisconsin has recently been done by P.O. p.O. Banks (Banks (Banks and and Cain, Cain, 1969; 1969; Banks and and Rebello, Rebello, 1969; 1969; and and unpublished unpublished data), data), by Z.E. Z.E. Peterman (unpublished (unpublished data), data), Dott Dott and and Daiziel Dalziel (1972), (1972), and and by by the author Schmus, 1972, the author (Van Schmus, 1972, 1973; 1973; Thurman and and Van Schmus, Schmus, 1973; 1973; and and unpublished data). data). A A summarization summarization of of these these data data is is presented presented in in Table Table 1. 1. unpublished Based on the the available available geologic geologic and and geochronologic geochronologic data, data, aa genergeneralized chronologie alized chronologic map map has has been prepared for Precambrian rocks of Wisconsin and and Upper Upper Michigan Michigan (Figure (Figure 1). 1). A the various various A few comments on the chronologic brief discussion discussion of of their their significance significance is: is chronologie units units and and a a brief presented below, below, but space does not jermit permit detailed detailed description description or or disdiscussion. The "Pb The "Precambrian X", etc. terminology terminology used below below refers refers to to the the Xt, etc. current U.S. U.S. Geological Survey subdivisions of of Precambrian time: time: Precambrian Z, Z, base base of of Cambrian Cambrian to to 800 800 m.y. m.y. ago; ago; Precambrian Precambrian Y, Y, 800 800 to to 1600 m.y. m.y. ago; X, 1600 to ago; Precambrian X, to 2500 2500 m.y. m.y. ago; ago; and and Precambrian Precambrian W, W, oldçr than old~r than 2500 2500 m.y. m.y. Archean Complex (Precambrian (Precambrian W) The oldest rocks rocks in in the the area area are are exposed exposed in in the the northern northern part. part. In In Upper Michigan these have been shown to be 2.5 to to 2.7 2.7 b.y. b.y. old or or older older (Aldrich, 1965; Woolsey, Woolsey, 1971; 1971; Banks Banks and and Van Van Schmus, Schmus, 1971, 1971, (Aldrich, and and others, others, 1965; 1972), 1972), but no dates have been reported reported as as yet yet from from presumed presumed Archean Archean rocks rocks in northwestern Wisconsin. in These latter units unconformably underlie the metasediments metasediments and the and metavolcanics of the Gogebic Range (Aldrich, (Aldrich, 1929) 1929) and there seems little doubt that and that they they are are in in fact fact Archean. Archean. However, the southward extent of these these rocks is is not well known, known, as as outcrops outcrops are are widely scattered throughout the the area area and and lithologic lithologic correlation correlation of of PrePrecambrian crystalline rocks rocks is is risky risky at at best. best. ** Department of University of of Kansas. Kansas. of Geology, Geology, University �2 T&bl.1. 1. 'fable Sury of Primary Gscohronologio S~ of PJ-1aaI7 GeoohronologioData Datafor torPreoeabrisn PNoaabrianRocks Boob in inWisconsin. Vlnouin. Northea.tern Wisconsin Visoonsin COmplezl Compl.xz 1. Northeastern P. (rhyoiit.) Quinnl.. o VIa. (rhyolite) Quinnissc 1906 ~ 25 1805 25 11.7. ..y. Ho skinLake Iske granite granite Hoskin 1880 15 (z) (Z) Banks Banks and Cain, 1969. 1969. Dunbar .iss Dunbar gneiss 1880 2~ 15 1880 15 (Z) Bank8 and Cain, 1969. 1&69. (z) Banks 1860~ 21~l 1880 (2) Banks and Cain, Cain, 1969. (Z) BanD and 1969. 1930 2 o (Z) Aldrioh and and others, 1965. 1965. (z) Aldrich 1810 : 50 (R) Van Sebmus, Unpub.° N.vinghamgranodiorite granodiorit. Newingham "*mb.rg pink "Jllberg p1nk graniti' granit'" (Ath.lstan. quartz (Athel8tane quartsmonzonit.) IIOMOnitlO) }3 ainstte quartz JIuoinett. quartz diorits diorite Atbelatane quartz quarts monsoniti lIOn&onit. Athelotano Hoskin Lake lake granite Hoskin granite } Overall oo.slt. oompo.it..estimate: Ove1"&ll .t1lrate I :t (Z) Banks and RebellO, Rbello, 1909. (z) Bank8 and 1969. 1875 50 1875 ±~ 50 VisooMlnComplex: COmpleZI Central Wisconsin 2. Central Baraboo rWolite Baraboo rI'o1ite 1840 lMO :2 40 m.y. a.,y. (R) Dott and DaIziel, Dalziel, 1972. 1972. So, Wisconsin rbyolit.s So. Wisoonsln rbJo1ites 1665 4D 1666 :2 40 (a) (R) Wausau-Mbnioo voloanios Wausan—bnioe volcanic. 1640 4D 1840 2~ 40 (R) Petel'llllUl,Unpub.° Unpub.* (a) P.t.rman, Co. granites granites Waushapa Co. Waushera ~ 70 70 1846 1646 ± andVan VanSohlllU., Sobmus,19'7a.* 1975. 'l'hurman and (R) Thurman Vausau area Waumau areagranites granite. 1600 :t 85 85 1600 ± CR) (R) Jackson JacksonCo. Co.granit.s granite. 1690 CR) Overall composite OOIlPOsite estimate: e8t1Jla'te I 3. llna.* Thurman and Van Van SobIua, Sobaus, 1975 .'' '!'hU!'lllUl and P.t.rman, Petel'lllU'1,Unpub.* Unpub.* and P-'-run, P.teruan, 1972. 1972. (a) nKismia ..io and 1675 ± 16715 : 50 Volt Wolf River River Batholiths Batholith: Wolf Volt River-Bad River-a.d River quartz quartz monsonites IIODSOnit.s 1450 :± 30 50 lI.y. a.y. 1450 (R) Van Sobmus, Unpub. Belongia Belongia gNnite granite 1~ 1500 :t2 20 (Z) Banks, Banks, Unpzb.' Unpub.** (z) 1480 2 (a) Onpub.** CR)Van VanSohlllU., Sciu5, Unpub.' Wolf River batholith Wolt River batholithoombinad oombined Wolf River River quartz Volt quarts monzonits lIOn&onite a.d River quazo1;s monzonits lIOn&onite Red River quartz Hager complex oomplez B.longla Belongia granite viborgit. granite Vaupaca wiborgite granite Waupeoa Big Palls Big Yells med-gr. m.d-gr. granite Stevens gNnite Stevens Point Point grq gray granite Wausau oomplez Wausaueyenite syenit. complex St.tin iyenit. complex St.tin ~nite oollPlez Hogvty Hogarty hornblende hornblende granite granite Overall Overall oolllpOsit. compositee8tiDate .stimatsI 1500 ± 50 (Z) denote. zircon Zircon U-Pb U-Pb oonoordia age; (R) (R) denotes denote. tho1e-rock whole-rcok (z) denotes oonsordiaintercept intsrc.pt age; Rb-Sr Rb-Sr isochron isoobron a.gs. ~. in preparation. Sohmus, ThtmDan, Thurman, and and Peterman, ** Van Sohmus, 'etel'lDan, 1n preparation. and Banks, *" Van Sohmu., ** Medari., and 1laDU, in in preparation. preparatlon. ScLnu5, Madaris, �3 No Archean rocks rocks are are conclusively present present in in northeastern northeastern Wisconsin. Wisconsin. Although the the Quinnesec metavolcanics metavolcanics have have often often been been referred referred to to as as pospossibly being Archean, Archean, it it now seems seems probable probable that that they they are are much much younger, younger, as mentioned below. below. The lack lack of of Archean rocks rocks in in this this area area is is as will will be mentioned major geologic geologic problem, problem, for for they are exposed just to aa major to the the north in in Michigan (James, (James, and and others, others, 1961). 1961). Recent maps of of the the area area (Dutton, (Dutton, 1971, Dutton and and Bradley, Bradley, 1970) show show the the presence presence of of aa major major east—west east-west 1971, trending Formation trending fault fault system system separating strongly deformed Quinnesec Formation rocks on the south from much less less deformed Badwater Greenstone Greenstone on on the the rocks north; and this fault system may therefore north; therefore coincide coincide with with or or be be part part of of an an old old major tectonic boundary. remaining problems problems are are to to determine determine how how far far Some of the other major remaining south Archean Archean rocks rocks can be be recognized, recognized, to determine their south their ages, ages, and and to to determine the the nature of their their disappearance (burial, (burial, faulting, faulting, orogenic orogenic destruction, etc.). d~~truction, etc.). "Animikie" Metasediments and Metavolcanics (Precambrian (Precambrian X) Metagediments and These rocks represent the the major units of of sedimentary sedimentary and and volcanic volcanic origin in the northern part of of the the area area and and include include the the economically economically vital sedimentary sedimentary iron iron formations. formations. Geochronologic data (Aldrich, (Aldrich, and and others, others, 1965; 1965; Banks and and Van Schmus, Schmus, 1971, 1971, 1972) 1972) indicate indicate that that these these rocks rocks in the the Iron Iron Mountain Mountain area area are are about about 1900 1900 m.y. m.y. old. old. Banks and and Rebello (1969) obtained a 1900 million year age age for zircons from a a Quinnesec (1969) obtained a Formation rhyolite in Wisconsin, and in Wisconsin, and the the author author regards regards these these rocks rocks as as approximately, if if not not exactly, exactly, equivalent equivalent to the units approximately, units in Michigan (for (for example, the example, the Badwater Badwater Greenstone). Greenstone). No direct data exist exist for for similar similar rocks rocks from the northwestern part of the the state, state, namely the the Gogebic Range, Range, but but with the lack of any evidence to to the the contrary, contrary, the the commonly commonly used used correcorrelation with rocks rocks to to the the east east is is accepted accepted here. here. Clearly, Clearly, however, however, direct direct analytical is required. required. analytical confirmation is As with the the Archean rocks, rocks, the the maximum maximum southern southern extent extent of of these these rocks is is unknown. unknown. Northeastern Wisconsin Complex (Precambrian (Precambrian X) are exposed several gneissic gneissic In the northeastern corner of the state are and plutonic units units which are and plutonic are younger than the the Quinnesec Formation, Formation, and and in in places intrude it it (Cain, (Cain, 1964). 1964). U—Pb U-Pb ages on zircons zircons and and Rb-Sr wholerock isochrons (Table (Table 1) 1) show show that that these these rocks rocks are are about about 1875 1875 m.y. m.y. old. old. They can be traced traced southward southward for for more than than 50 50 Km. Km. south south of of the the MichiganMichiganWisconain border, Wisconsin border, but their their maximum southern southern limit limit is is not not known. known. Although these rocks rocks are important in Wisconsin, only small plutons these are important in northeastern Wisconsin, of this age exist in in Michigan (Peavy (Peavy Complex and and scattered scattered dikes dikes and and area; Aldrich, and others, others, 1965; 1965; Banks Banks and and pegmatites in the Felch Trough area; Aldrich, and Again, it Van Schmus, Schmus, 1971, 1971, 1972). 1972). Again, it appears appears that that the the E—W E-W fault fault system system be part part of of aa major major boundary. boundary. may be The westward extent of these these 1875 m.y. m.y. old rocks rocks is is also also not not known, known, but it it is is quite possible possible that that many many of of the the rocks rocks in in the the northern northern part part of of the state (north the (north and and west westof of Rhinelander) Rhinelander)are are similar similar in in age. These and and the older older rocks rocks are truncated on the south by the the the volcanic—plutonic volcanic-plutonic rocks rocks of the Central Wisconsin Wisconsin Complex, but exact the Central Complex, butthethe exactnature natureofofthe the transition transition is also unknown (intrusive, is (intrusive, fault, fault, suture suture zone?). zone?). �4 4 Central Wisconsin Complex (Precambrian (Precambrian Y) Rocks which yield Rb—Sr Rb-Sr whole—rock whole-rock ages ages of of 1650 1650 to to 1700 1700 m.y. m.y. appear appear to make up the the bulk of the the Precambrian basement basement of of Wisconsin, extending extending from Rhinelander in in the the north to to at at least least as as far far south south as as Baraboo Baraboo and and for for at least least 150 Km. Km. in at in an an east—west east-west direction direction (Figure (Figure 1). 1). These rocks rocks are are mainly volcanic, volcanic, volcaniclastic, volcaniclastic, and and associated associated granitic granitic intrusives; intrusives; the the exposures of these rocks in the the Wausau area area are are described in in aa later later section section of this guidebook. guidebook. Other areas areas of these these rocks rocks are are the the Monico area, area, the the granites granites of Waushara County and and the rhyolites to to the the south, south, the the rhyolites rhyolites underlying the quartzite at Baraboo, Baraboo, and and some of of the the rocks rocks in in the the Black Black River Falls area area (Table (Table 1). 1). Although several types types of of rock rock are are represented, represented, outcrop control control is outcrop is presently insufficient for purposes of of major correcorrelations. The full full extent of of these these rocks rocks is is unknown, unknown, particularly particularly to to the the south and west, and represents a major problem in south and west, in Midcontinent Precambrian geology. The geochronologic control on on this this complex complex to to date date is is only only by by Rb—Sr Rb-Sr whole-rock isochrons, isochrons, and and it it is is possible that that the the 1675 1675 m.y. m.y. age age given given here is a time of widespread alteration alteration of of slightly slightly older older rocks. rocks. U-Pb U—Pb zircon ages will for many of these units in the the near future future zircon ages will be be measured measured for in order order to to get get a in a better handle on the true age of these rocks and and to to look for any resolvable age age differences within the the complex. complex. Quartzites (Precambrian (Precambrian Y) Y) Dott and Dalziel (1972) (1972) have recently recently extensively extensively summarized summarized the the Precambrian quartzites in in Wisconsin. Wisconsin. The age of the quartzites is is bounded by by the the underlying underlying 1675 1675 m.y. m.y. old old rhyelite rhy~lite at at Baraboo Baraboo and and 1450 1450 to 1500 m.y. m.y. old intrusive rocks at at Waterloo (pegmatite) (pegmatite) and and at at Wausau Wausau (syenite intruding Rib Mountain Quartzite). (syenite Quartzite). (Precambrian Y) Y) Wolf River Batholith (Precambrian The youngest youngest plutonic plutonic event event in in the the state state was was the the formation formation of of aa large large It complex referred to in this guidebook as as the the Wolf River batholith. batholith. includes includes a a large variety of felsic intrusive intrusive rocks rocks which occur occur from from Mountain to to Wausau to to Stevens Stevens Point Point to to Waupaca Waupaca and and are are all all about about 1500 1500 m.y. old old (Table (Table 1; 1; Figure 1). 1). This complex is is described in in detail in in m.y. later sections of this guidebook and later and will not be elaborated on on here. here. Published mineral mineral ages ages from from several several localities localities (Bass, (Bass, 1959) 1959) indicate that this event event was was the last major thermal event in that this in Wisconsin except except for the Keweenawan activity for activity to to the the north. north. This complex is is relatively relatively well well defined defined as as to to its its areal areal extent, extent, and and it on all all sides sides by by older older units. units. However, However, the the exact exaot shape shape it is is surrounded on still needs to to be better defined, defined, and and more more U—Pb U-Pb ages ages on on zircons zircons will will have to to be determined on on individual individual units units to to fully fully tie tie down down their their absolute absolute age(s). age ( s). �5 Keweenawan Rocks Rocks (Precambrian (Precambrian Y) y) Keweenawan volcanics, volcanics, sediments, sediments, and and intrusive intrusive rocks rocks occur occur in in the but will will not not be discussed here. the northern part part of of the the area, area, but here. The age age of 1115 1115 m.y. m.y. for of for these rocks (Figure (Figure 1) 1) is is primarily based on on the the U-Pb (1963, 1972). 1972). Chaudhuri (1972) (1972) U—Pb zircon data of Silver and Green (1963, and Chaudhuri and Faure (1967, and Chaudhuri (1967, 1968) 1968) have also also reported reported Rb—Sr Rb-Sr ages ages on on similar rocks in Michigan. in Michigan. Miscellaneous The major rocks rocks included included in in this this category category are are the the granites, granites, gneisses, schists, and migmatites in central Wisconsin, gneisses, schists, Wisconsin, extending extending westward from Waupaca to Stevens Point—Wisconsin from Waupaca to Stevens Point-Wisconsin Rapids, Rapids, and and west. west. These rocks have apparently apparently been been intruded intruded by by the the 1675 1675 m.y. m.y. old old complex, and Bass Bass (1959) complex, (1959) has obtained some mineral ages ages as as old old as as Thus, it would appear 1900 m.y. these rocks. rocks. Thus, appear that that these these rocks rocks m.y. from these exact are are at at least 1900 m.y. m.y. old old and and may may even even be be Archean. Archean. Clearly, Clearly, exact determination of of the the primary ages ages of of these these rocks rocks is is important important since since it will will help help define define the minimum southern limit of sialic rocks it rocks younger than 1900 m.y. m.y. in in North North America. America. Regional Significance Significance Several major discrete igneous, Several igneous, metamorphic or sedimentary periods or events can now be recognized in in Wisconsin and and Upper Upper Michigan. Michigan. The 2500 m.y. m.y. and older rocks rocks represent the southern edge of the 2500 and older the Superior m.y. old rocks Province of of the the Canadian Canadian Shield. Shield. The 1850 to 1900 m.y. represent aa major major period period of of sedimentation, represent sedimentation, volcanism, volcanism, and and orogeny and and is considered considered by by the represent the so—called is the author to represent so-called "Penokean Orogeny" in the area Orogeny" area (Van (Van Schmus, Schmus, 1972). 1972). The 1650 to to 1700 1700 m.y. m.y. old rocks can be correlated roughly with rocks rocks of of similar similar age age in in the the Rockies and the Southwest, Rockies Southwest, although although exact correlations will need need to to await further data. In case, it await data. In any any case, it appears appears that rocks with ages ages of 1650 to 1750 m.y. m.y. comprise a a major structural structural belt from from Arizona Arizona to to Wisconsin. The 1500 m.y. m.y. old complex correlates well in in age, age, litholithologic character, to 1500 m.y. m.y. old old logic character, and tectonic setting with 1450 to plutons throughout the Southwest and plutons and volcanic and and plutonic plutonic rocks rocks in in Missouri. These rocks probably are are part of another another structural structural province province of and south of and partially overlapping the 1650 to to 1750 m.y. m.y. old old rocks rocks (Bickford and Van Schmus, Schmus, 1973). 1973). In summary, summary, it it now now appears appears that that the the various various chronologic chronologic units units In recognized in Wisconsin can be related to other rocks throughout recognized throughout North America, America, and and these these correlations may ultimately ultimately provide provide the the framework upon upon which we we can determine the detailed evolution of the framework the continent during during Precambrian Precambrian times. times. �6 Acknowledgements This work has has been largely supported by National Science Science Foundation Foundation The author gratefully acknowledges the Grants GP—1362 GP-1362 and and GA—15951. GA-15951. The cooperation of all all his his colleagues who are are mapping and and carrying carrying out out petro— petrologic studies in the area and logic studies and whose work provides the the base base necessary necessary for for sample collection and and data data interpretation. interpretation. I �7 References Aldrich, Aldrich, H.R., H.R., 1929, 1929, Geology Geology of of the the Gogebic Gogebic iron iron range range of of Wisconsin: Wisconsin: Wisconsin Geol. Geol. and and Nat. Nat. History Survey Survey Bull. Bull. 71, 71, 279 279 p. p. Aldrich, Aldrich, L.T., L.T., Davis, Davis, G.L., G.L., and and James, James, H.L., H.L., 1965, 1965, Ages Ages of of minerals minerals from metamorphic metamorphic and from and igneous igneous rocks near Iron Iron Mountain, Mountain, Michigan: Michigan: Jour. Jour. Petrology, v. v. 6, 6, p. p. 445—472. 445-472. Banks, P.O., P.O., and Cain, J.A., J.A., 1969, 1969, Zircon Zircon ages ages of of Precambrian Precambrian Banks, and Cain, Jour. Geology, granitic rocks, rocks, northeastern northeastern Wisconsin: Wisconsin: Jour. Geology, v. v. 77, 77, p. 208-220. p. 208—220. Banks, P.O., Banks, P.O., and and Rebello, Rebello, D.P., D.P., 1969, 1969, Zircon Zircon ages ages of of aa Precambrian Precambrian Geol. Soc. rhyolite, Soc. Amer. Bull., Bull., rhyolite, northeastern Wisconsin: Geol. v. 80, p. 907—910. v. 80, p. 907-910. Banks, Banks, P.O., P.O., and and Van Van Schmus, Schmus, W.R., W.R., 1971, 1971, Chronology Chronology of of Precambrian Precambrian rocks of Iron and and Dickinson Dickinson Counties, Counties, Michigan Michigan (abs.): (abs.): 17th rocks of Ann. Inst. on Lake Superior Geol., Duluth, Minn., May, p. Ann. Inst. on Lake Superior Geol., Duluth, Minn., May, p. 9-10. 9-10. Banks, P.O., Banks, P.O., and and Van Schmus, Schmus, W.R., W.R., 1972, 1972, Chronology of of Precambrian Precambrian rocks of of Iron and rocks and Dickinson Dickinson Counties, Counties, Michigan. Michigan. Part II II (abs.): (abs.): Ann. Inst. 18th Ann. Inst. on Lake Superior Geology, Geology, Houghton, Houghton, Mich., Mich., May. May. Bass, M.N., M.N., 1959, Bass, 1959, Mineral age age measurements—Wisconsin: measurements-Wisconsin: Inst. of of Washington Year Book Inst. Book 58, 5~, p. p. 246—247. 246-247. Carnegie Bickford, M.E., M.E., and Bickford, and Van Schmus, Schmus, W.R., W.R., 1973, 1973, Possible Middle and and Late Precambrian igneous arcs arcs in in the the Mid—continent Mid-continent region region of of North America America (abs.): (abs.): Program, Program, North-Central North-Central GSA GSA Meeting, Meeting, Columbia, Mo., Columbia, Mo., April. Cain, Cain, J.A., J.A., 1964, 1964, Precambrian Precambrian geology geology of of the the Pembine Pembine area, area, northeastern Wisconsin: Acad. Sd. northeastern Wisconsin: Mich. Mich. Acad. Sci. Arts, Arts, and and Letters, Letters, Papers, v. Papers, v. 49, 49, p. p. 81—103. 81-103. Chaudhuri, Chaudhuri, S., S., 1972, 1972, Radiometric Radiometric ages ages of of Keweenawan Keweenawan intrusions intrusions and extrusions in in Michigan Michigan and and adjacent adjacent areas areas (abs.): (abs.): Geol. Soc. Amer. Amer. Abstracts with Programs, Soc. Programs, v. v. 4, 4, p. p. 470. 470. Chaudhuri, S., Chaudhuri, S., and and Faure, Faure, G., G., 1967, 1967, Geochronology Geochronology of of the the Keweenawan rocks, rocks, White Pine, Pine, Michigan: Michigan: Econ. Geology, Geology, 62, p. v. 62, p. 1011—1033. 1011-1033. Chaudhuri, S., Chaudhuri, S., and and Faure, Faure, G., G., 1968, 1968, Rubidium—strontium Rubidium-strontium age age of of the Mt. Bohemia intrusion, the Mt. intrusion, Michigan: Michigan: Jour. v. 76, 76, Jour. Geology, Geology, v. p. p. 488—490. 488-490. Dott, R.H., Dott, R.H., Jr., Jr., and and Dalziel, Dalziel, I.W.D., I.W.D., 1972, 1972, Age and and correlation correlation of the the Precambrian Precambrian Baraboo Baraboo Quartzite Quartzite of of Wisconsin: Wisconsin: Jour. Geology, v. Geology, v. 80, 80, p. p. 552—568. 552-568. �8 Dutton, C.E., C.E., 1971, 1971, Geology Geology of of the the Florence Florence area, area, Wisconsin Wisconsin and and Dutton, Michigan: U.S. U.S. Geol. Geol. Survey Survey Prof. Prof. Paper Paper 633, 633, 54 54 p. p. Dutton, Bradley, R.E., Dutton, C.E., C.E., and Bradley, R.E., 1970, 1970, Lithologic, Lithologic, geophysical, geophysical, and and mineral commodity maps of of Precambrian Precambrian rocks rocks in in Wisconsin: Wisconsin: U.S. Geol. Survey Map set Geol. set 1—631, 1-631, with with accompanying accompanying pamphlet pamphlet (15 (15 p.). p.). James, H.L., C.L., and and Pettijohn, Pettijohn, F.J., James, H.L., Clark, L.D., L.D., Lanley, Lamey, C.L., F.J., 1961, 1961, U.S. Geol. Geology of of central central Dickinson Dickinson County, County, Michigan: Michigan: U.S. Survey Prof. Prof. Paper Paper 310, 310, 176 176 p. p. Kiemic, H., H., and Klemic, and Peterman, Peterman, Z.E., Z.E., 1972, 1972, in in Geological Survey Survey Research Research 1972. Chapter A: U.S. Geol. Geol. Survey Prof. Paper 1972. Chapter A: U.S. Paper 800—A, 800-A, p. p. 3. 3. Silver, L.T., L.T., and Silver, and Green, Green, J.C., J.C., 1963, 1963, Zircon Zircon ages ages for for middle Keweenawan Keweenawan rocks of the Am. Geophys. Geophys. Union the Lake Lake Superior Superior region region (abs.): (abs.): Am. Union Trans., Trans., v. v. 44, 44, p. p. 107. 107. Silver, L.T., L.T., and Green, Green, J.C., Silver, J.C., 1972, 1972, Time constants for for Keweenawan igneous activity activity (abs.): (abs.): Geol. Geol. Soc. Amer. Abstracts Abstracts with with Programs, Programs, v. 4, v. 4, p. p. 665. 665. Thurman, E.M., Thurman, E.M., and and Van Schmus, Schmus, W.R., W.R., 1973, 1973, Rb-Sr Rb-Sr age age of of Precambrian Precambrian volcanic and and plutonic inliers inliers in in southeastern southeastern Wisconsin Wisconsin (abs.): (abs.): Program, Program, North—Central North-Central GSA Meeting, Meeting, Columbia, Columbia, Mo., Mo., April. Van Schmus, Schmus, W.R., W.R., 1972, 1972, Geochronology of of Precambrian Precambrian rocks rocks in in the the Penokean Fold Belt subprovince subprovince of of the the Canadian ~anadian Shield Shield (abs.): (abs.): Program, Program, 18th Ann. Ann. Inst. 1nst. on on Lake Lake Superior Superior Geology, Geology, Houghton, Houghton, Mich., May. May. Van Schmus, W.R., 1973, Schmus, W.R., 1973, Chronology of of Precambrian Precambrian igneous igneous and and metamorphic metamorphic in eastern Wisconsin and and Upper Upper Michigan (abs.): (abs.): Program, events in 1973 Ann. Ann. Meeting Amer. Amer. Geophys. Geophys. Union, Washington, D.C., April. 1973 Union, Washington, D.C., April. Woolsey, Woolsey, L.L., L.L., 1971, 1971, A A Rb—Sr Rb-Sr geochronologic geochronologic study study of of the the Republic Republic metamorphic node, node, Republic, Republic, Michigan: Michigan: Unpub. Unpub. M.S. M.S. Thesis, Univ. Univ. of Kansas, Kansas, Lawrence. Lawrence. �9 t33:ir JTh f4 i:tc 2LTY y 2j; 2GIC1 1f1:i--= ii-i 4jLj yEa WOLF RIVER BATHOLITH--A LATE PRECMvIBRIAN RAPAKIVI MASSIF IN NORTHEASTERN WISCONS IN -. \2 TIlE by --:, a:: 2L J.L. Anderson*, Jr.*, 2' rf- Medaris, L.G. Myles** and J.R. C- iEE.CJL.JZINTRODUCTION LL-- aLa-aU .-: co tf •- 1L!• Classic rapakivi texture, in which grains of ovoidal alkali feldspar are mantled by plagioclase, has been described from several localities of Precambrian granite in northeastern Wisconsin (Gates, 1953; Elders, 1968), but until the present time, the regional distribution and petrologic significance of these rocks have not been Our investigation, in conjunction with chronologic fully appreciated. studies by W.R. Van Schmus (this guidebook), has established that an extensive rapakivi massif, the Wolf River batholith, underlies an area of at least 3600 square miles and represents a major feature of the This anorogenic, Precambrian terrain in northeastern Wisconsin (Fig. 1). epizonal batholith, 1450 to 1500 million years in age, consists predominantly of reddish, hypersolvus quartz monzonite and granite. In addition to the widespread occurrence of rapakivi texture, the Wolf River batholith has textural, mineralogical, chemical, and structural features that are similar in every respect to those of the classic rapakivi massifs in Finland. L t •-i&;t Li' k:y.a 4121 2 tt flCTh rjp 2!71fl ©1i -rt ras;-- tia #e :2 -it ut a?-. faa, rfl t 2UU r, :ytLr, : C:KCLiliCT.CCCiI i-Li'CfCt.CC. i-; L2tL :1r:yCiia 1j :y;,itL;y:j. r;1iC1i1C t!LtcL -LiC-r--CLi'J.c. ca aqiy-: La€'L -t iiE '5iTh-yrC aU '-U EiC LiiTT eJ' :caCyL& a1€TTICi'-2 y'iñk;I L1ra. lyai;Lt. 2ii,<: 'LirJL Ct C;iag:f, :':C'iTCtC LtC.. ::,J'.tCi'irt:C2.CCIIi, EyLa? 'i:r. flI •'CY-fl:C, 1\ t!f2T7 2T'jir :;MiC:i. C2C ta- I CCC ix rc'L;-c 2€ 1O29Lfl bxü iTnat 'Li]. ntUi C—tt2 nct- I •b - f;aLi CLE -u. -. . - UU- -z-i j•aditiCtL-• t€ CICCitC CtCiitti:LCC! LCI k.CiLC ITCaC tfi- lit 1 fr L5LitiCC.iL., 'iir:ic:a. :11Z"'2t11";f TC ;.;CT : ::rol,: :iZi1 .;yji g:aiUL'ii i:,J ii4cJsiucLi 45{j ?:U-UUL. cJ T7,r,::At :.a'::i:d •U t:: C •: t]TLC'2 : T-Lj .-Ci irCaLi? :,y., ----2 ICoILt'i C€C tttat 1'---, --, C'axiLal. aa. - L.,' LITHLOGY rtCr ±..1i.:1L'::::s€ ih- -— - - 't]'. CCC' General Characteristics liLVtJC 1ACC Cxii •iiy 'k:.C' ECliTcJ. lCJhra; ny;]i Lta'y,Li 7ç1;'T' ;-CCLi A variety of rock types have been recognized in the Wolf River batholith, including granite, quartz monzonite, monzonite, trachyandesite, syenite, and rhyolite. Quartz monzonite and granite are by far the most abundant rock types in the batholith, adcounting for 94% The predominance of alkali of the exposed area (Table 1, Fig. 1). feldspar over plagioclase in the batholith is illustrated by a plot (Fig. 2) of modal quartz, alkali feldspar, and plagioclase for representative specimens, obtained by point counts of both thin sections and stained polished surfaces of hand specimens. 2 1li-li ii-c t-a niii1 iL U a:c--.xli Li €lufrCI CE ix -uCla titi )Ei 1.. r LaU-uUSL lila t:IC.Jliuii U pta U. €L-€L 'yiyfl -. cr.. cE 2B12 1s,i'fT I tCli, - C-CT xAs?IT'r2' 'Liii i1.ii iLiT-ii ' - ] a1kaL- tzau€E Lii- ',j-c 'It,-: ar tL.2iCiiCT ruT-fT x lixvxuia, 'JL'i.- :uc'J-€l :1- iL:s uf lifC-iULihtiii.. ')2vt.1€Th p.. I 1R La TLi1--R,g-IC-9€ tu..-C C.çi-Cr xr).dt •-a :tp€E t P b.u-t:x Li'U LExy Cli ',yc.t'h •.:i -u-TxxuT'tx. CCCL. i'--n.ix 1 ILJC Cxli :xfJ.Jt '-zr:'.LiCibla-ii c-C 3€ -CT.C. itiyii:C iLiH 'r' auuTi-iCL ccxL L€Tituic Rapakivi texture is one of the most characteristic features of being most extensively developed in the Waupaca quartz monzonite, but occurring in minor amount in all of the other granite and quartz monzonite units. Equally characteristic is the development of porphyritic texture in all lithologic units of the batholith. Typically, phenocrysts1 of alkali feldspar, and to a lesser LLi&:•iuiLci 7 JULia.U. Lii" x--.,cy.i-Cl,li-: lyxaiTta ir-vrut .'UCa U: C2itT'-xfJT4T tI-LIt et311C Li-U 11CC- 'C b-a iit rCttlii,i J.CLfl.fTl rxcii,.E CIxe xrit.ciE .1LC?LiiC I I J'IZIl =itlL'L- -L . t:;rtaaa' p-CTiU.j:it:lC iLL .xj.:,f nuuiiaaCC'---ixx--- -.---.j- :€-l'1TF itl -c -i, - h-iiuci-xca.2.t- ,,.I,Cxeyftxi :t-r CE CCJ-f ui''1r 4p.iiii .iHc- :ii-.7tnt_-i irE lkui 1 -i-U; -CILL xxix- Def of Geology & Geophysics, University of Wisconsin—Madison of Geological Sciences, Univ. of California—Santa Barbara A non—genetic descriptive term, such as megacryst, might be more appropriate to describe the large alkali feldspar grains, but since phenocryst is still the term accepted by Finnish geologists, this convention will be followed here. -filL'. WLiifT 'c-a .e:''Lt :CT. 'Ii -_' Li 1 C--- aL.' -c-Sf -C it I- U-fl" fx-x.tC-x, ,LL:xi'a;y C.€-LilgiCtl. CL-Cf ,j 7: Li.. u'xlx .., taL:-Cxx€ trti., IJ'.raul. •:$p2Y vniiui xixi i.-.LL 2:Li.'litf lIC'iLC'i'C CE--x C '-,e-Li --C -a--€ fit lrxiac. Lc--ii-II E1 Ix: 'IcC ttxx Ut-Il .CC-€1Lib-iU If aiaza'n trLC-T,:J.Cs1. -'' cliaUca ** 1 Department Department . :11 :CL ** I * It_i the Wolf River batholith, �P.- 89 - 0 - ':*-- - LjLi - /F: LIMITED EXPOSURE us / - —0 / LIMITED EXPOSURE EXPLA NATION IsLofls5 granite Belongia i LtC1Ctj% 5 Wolf River granite and sd C11oT quartz monzonite 0* Red porphyritic r5CiRiser ru-p0-i:: quartz monzonite it;C- Waupaca J!&Ci wiborgite r7 CEJiUt Stevens Poist grey granite I Hay Creek C!Cifr-C:cI1CC9. quartz monzoriite, T rIi ::rIi F Hsç!s! rfr:c1Cis Hager rhyolite Hager feldspar -]-sQsC -ici5ir porphyry bxsspi'y k{wsr Ci$Clci Hager syenite Peshtigo 1q:-liL nlonzonite CiC and -:sch-'is5Ci trachyandesite i-:i!(I :i-CIIC High Falls51CiCittCi granite 1 H THE WOLF RIVER ?rk•,:BATHOLITH -4—IH1iI1H GEOLOGIC MAP OF Anorthosite :-iIC, rii5PscN], i4C tLG BY G. MEDARIS. JR J L ANDERSON, 01] [j y-y__ ':UJs AP-II Mi_t WA VANVi SCHMUS. AND J,jI:. A. MYLES 10 6 10 Ci 20 22 30 2t MILES Precambrian rocks older than 1450 —- Contact, dashed where C'6C365. 16232 46 approsimaie — Fault Mylonite 1500 M Y �4214 11 Table 1 Proportions of lithologic units in the Wolf River batholith areas only) and key to symbols used in Figures 1—7. I7717'!110 11,1rcp:4rl 21.21:. 20's. 2 :7172 07203111120i '7:'i -fl :10012. 202171:11 22; Areal extent, % .47!',47t1 :212-21:7 o Belongia • Belongia granite, coarse—grained £ Wolf River granite fine-grained 7122 71!-.1'7-'-12-!-"4.; granite, 2 7 '' 1-210,27 2120-2120 '7:2.7020 21-27207 '171 ";fl C'' and quartz monzonite 51.0 2t"'3i.101 -::'a'fl'3 21 72721172102-021,1024: (14.- Red River porphyritic quartz monzonite 20.6 Waupaca quartz monzonite (wiborgite) 10.5 721: 24 (77,1.71' 07-212110 21017; • Hager rhyolite 3.6 57 Hager feldspar porphyry 0.2 - 3-CT': 27212 11204:0177 ,!C14J 221:-i - - Hager syenite 1.9 Hay Creek quartz monzonite 0.1 '6- 21:72021'.';317. C1.-.4? 4:i$-10. •2 • • 0 '17 ";-fl:7-73:..-3 141 0114 4212'. Unit y- :r 74,7o ;lj '4' - Symbol (exposed Peshtigo trachyandesite 2'0c20T'710'2'? 0 4 32424:!370 -'4-, Peshtigo monzonite J -2041002112110 •U-31,1W7, Not Shown Stevens Point grey granite 5.0 Not Shown High Falls granite 4.0 7212 ,' 21 .102121 4: 0140)1 707102-2;- '24i l- 24 ;411'TP 21.27.121 extent plagioclase and quartz, are present in a medium— to fine—grained granitic matrix, consisting of quartz, microcline, plagioclase, and mafic minerals. In all cases, matrix plagioclase is more sodic than plagioclase phenocrysts. Quartz is interstitial to feldspars in some units, but in others, particularly in granite and some varieties of quartz monzonite, quartz displays a distinctive idiomorphic habit and apparently was one of the earliest phases to crystallize. '71100 2 — 7;; I :12:; 272-721 21-724.: 117 3-10 71721.211171 115:21123-; '2021212' TT FL p0'; 102121,1-77:21077 A-trocoao-fw 4,,•;I_1rT; - :c;:-1-:-20.1i;'o-- 212)03 1)1 1'-.r.'327:;720-07 723-0421122 421 '21if;t2152 07712!! 21JL2---L22L SI ;cnr-o$ -n .LjJ720;0 0 ,10207077> s—p ','7c7-Jt- •-0 ,L2 Z:'20J' 7!::214r44:1014 A;10:A-•: 171 10- 2121:22; 277371 274710'7721l 2-4 1112 02 21-42022 72111210('7.A:! 7:107.417 7 24Ti,; -'-,m-. - ',:'''' .',- — .-.• 7 Iron—rich biotite and amphibole are the most common mafic minerals in the batholith, although orthopyroxene, clinopyroxefle, and olivine Biotite and occur in some of the darker rocks, such as monzonite. to subhedral and occur in areas interamphibole are anhedral typically Such an occurrence stitial to feldspar and quartz. suggests that in the biotite and amphibole appeared relatively late crystallization sequence of the granitic rocks. 21 2."-0- 0100 '1:31 .02 ':20'. TI -1021. 21:1120 -:4211-.. 21 - •3o©1coosI:jf 0 --':: 20t-207044.Z0I 2-117:170 C 114q77:.12761. '3 '10 7; 0,FL0lPOl 2-20 2412" TA. 4,' 2-021 2120: 214 2-20-1 1-4 $"7--1 1ir ;7-'71211214201 -1133-11221! '20741271724214:121 34:1 217 21121 21 2021 -ro'31::-'a li 1:;':-2-c;7 1)212124 410 7024-20720 -0:. 202 aCIC-Ip 1021721 21:217717121 21212 -4, -14. 1$ 'ccoo: J, 1422 -174- 37 202101:1223 20:20 12011221! 4:i;::10 P 10111-27 Descriptions of the Lithologic Units IT Twelve lithologic units have been distinguished in the Wolf River batholith, and the following descriptions are intended to summarize only the most salient features of each unit. Actually, some lithologic units are quite heterogeneous with respect to variations in texture and grain size, and the brief descriptions given here are not intended to encompass every conceivable variant that might exist within each of the twelve units. 21321:7 41-221 1t:2a'y-:p.a21;i 202321,2121212; 2I'' 2(12:-I pL1-Lt $4 )C'1 %21';#210' 22-f • -.'- 04: --.; ç0ccJ2;E-- i4J2 IlL 211 -- 14:2 C- -21-rn4:-ap. 7t.'7TL5 421221 21.-I! 4- LIII 21-21,'. -21'tL 221 2 21 flEC 1ç42r11-2 CC -:72)121!. 01CC.L -Ca210 214 1,141 T4 flt21 7212111 2111 flafl ifl;'. ai2a'-21 2•L21 I 114212-2 21.21;t21tCC12fl 17-114-; .72-Li �12 Quartz Fl 2E / 50 50 2,• I!- /• A ----- 10 ;CttT ___ — -— T feldspar eOD[J 10 Plagioclase Figure 2. 2 Wolf Modal analyses of lithologic types from the &q;4 TP°N Xyen? :;bTLflhi. sñ2( CJ rig River batholith. u':t7cCC44q 2°-f i22 (Sbo1s listed in Table 1) -T E bCCjUAA$ ;j'it:.fl1. . This coarse—grained quartz Waupaca quartz monzonite (wiborgite). 21 CCfl resembles z2=:.;:'n rapakivi texture and closely monzonite has abundantly developed I-)ç. Approximately 70 to 80% of the:tCe;1 pink the classic wiborgite in :T Finland. pL(Civtv.I 5U2 ;L: 4i, 21i 5.0 cm in length) are mantled with ovoidal grains (1.5 to ]:i%-r:A;) alkali feldspar .tthCVTC& LCçP-J2 common. 1 to 6 mm thick, and multiple layers are a layer of 4C plagioclase LCfl (rjtC, :2 The thicker a plagioclase mantle•Ci is, the smaller and more rounded is the )LJ texture is characteristic, alkali feldspar the [ 2T- Ci in Cfl core. A porphyritic .s#_1_plagioclase, and idiomorphic quartz with the mantled feldspars, Cfl large [ <•:.LdTs microcline, plagioclase, quartz, set in a medium—grained matrix ::±:t:1 of ;o; 1U Ibiotite, and amphibole. :i C LE 4 LLifl i'an2 :i ;r p cr ]tYL : (k; fIYIii ar 5i:; IL: ro-t r. 'v: iij;•t : .D':t Wolf granite and quartz monzonite. The Wolf River granite and '! River ::.Y12;. quartz monzonite in being coarse— quartz monzonite resembles the Dt Waupaca <crIL: ovoidal alkali feldspars (1 to grained and prophyritic with prominent c :2 texture is much less abundant, 3 cm in length), except that rapakivi L f ';i ;r1TI the alkali feldspar ovoids. plagioclase rims occurring on only 3 to 10% of 2: r:• 2L1J r;zcq - ;dtr :c1 I r;icP :i rr i;fl �.11 -:1 1. 1J a 1:.4Ti1 and groundmass. fine—grained in Yi4':7CC. phenocrysts olivine feldspar — li iii L1 .. a is trachyandesite 4 40% with monzonite, the of equivalent porphyritic ::tIiI?t interstitial of traces and opaques, biotite, amphibole, The quartz. -'E•I:LYL!rC and tL1' r;:T•+:1i: clinopyroxene, orthopyroxene, olivine, amounts TP'::.'1' in subequal feldspar :):j.'jL;::o.c I slightly vp-: L and (IrU alkali and plagioclase 4;yic1 containing porphyritic, mm) (3 ?;TTiio •."° t1.1fl*.1i.] relative 11 medium-grained isT monzonIte 1J[ The minerals. Ic maf of abundance yii Zi11t1.. and quartz, of paucity color, to grey dark brown their by guished 4:. are rocks These trachyandesite. and 1° distinmonzonite Peshtigo I — T I 1 L 11R1.:i4i.Z flt.1l . : Tin.1ar7i1 T.i..T°tfl ..lt:1:t.i i:i.1 c11t 12.1r JT1 41 /-. core. the in that iJ i111:r1z) :1I9944L.trw r °T with continuity optical in is rim granophyric the in feldspar alkali °7Th II cores occur The feldspar. alkali of euhedral around quartz and spar 1j J_L ° L,C1 .4 texture, granophyric presence feld- alkaliE. of intergrowths which in of Ii 1'Lf'L CII grains LC 41 ° 1r the is granite this of feature 1.4L14..' characteristic A matrix. the in 7'ji 7't occurs ':71 r'r' n°U aInriI IC '7CILC .present. IC17rCI IC? ECIçLIIr jr'i as .j of IC clusters mineral only the is and mafic Biotite iICCI2I:LCI:t421cIcJrI:.7CI is texture rapakivi of amount minor a and boundaries, resorbed show U °0iFk-U r .3 — commonly phenocrysts quartz The in cm) 24 matrix. mm) (1 fine—grained a çL;r0 It: ; In £11 •,•0nLI7I :tM50C: IC CI°4 to (0.5 feldspar alkali ovoidal and rum) 5 to (3 quartz idiomorphic of :riLIJ is I.I "nhLn1t .11iC I-i: ii:; :CIrTrmfl of up made phenocrysts granite Inr0r':.P.=t1:I 20%) to (15tI7. fine—grained The C ' I .,1 1 1 irflll'l oi.f rOr'?). T7(,j 'oLi' 11 I't1 .:?i I 47 :° rI'4 &. t ' 1 7 Tt.tl c 4i1 CrIC IlITTI C: 1CIC are texture granophyric present. and '.: rapakivi of amounts Small — 14 IC' 21 a are in set to quartz and feldspar mm). (2 matrix medium—grained 45%) (35 sr c7IC0'CCc7II'.Ii? ICIlilfi. 21 1r0::vr.Cc7 oL1.:.rrJl a CI',ig'ICCI °LIL. alkali of phenocrysts which in texture porphyritic acquires unit zI1:1 IC',:, rT"7T some as biotite I this however, localities, mafic sole the mineral. Jt ' I ,:CI I. 41.'1; U.CIC.t 4 quartz, and feldspar and plagioclase of amounts small with idiomorphic C'AcLI floiIir'1i of [CII U subhedral .:cCc1In mm), :'IC mainly consisting to (3 even—grained alkali 5lIlT, I yi I I l::t rt7r 4.rCt4C4 1W '- U,:' ir :.J].: 7'' itiriCi CIiICt ,T7ii7t pink, i-c'rTCI7.IilThe ilc :::U°t'CVCCJLl: 5r477 €7 predominantlyT1Ct and massive, isal7CTrrrTC'I granite coarse-grained ?LIni. 0iC:iSJInr€2CY1? 07T:Irn [,.IInIC7LCi €ICC'ICLt'Iz'la variety equigranular grained variety. porphyritic fine-grained and lIt ICBelongia JICl"7'oofIn types ffCiiL €74 coarse— a exist: granite Two granite. Belongia liT tI I lIC 7111 CI'liltCJ[°'Ia 114C rock. the to fabric planar imparting ':r'Ti4 [--1iJ !71:njTIrfr'5 C' ,17 l4:2'i Xiiii.I)41 . are aligned, commonly phenocrysts feldspar The slabs. stained in 0' ,i*r_ : 417 to up n' rC.ç.', 1il1I.inCCl on 4 IlL,' the of 15% apparent are phenocrysts feldspar alkali mantles U Yr' not 4C171 €4 plagioclase discontinuous thin, although conspicuous, is texture ' ICCCt: ILU mineral, 01 4. IC '' CIT II 71141 il'27L l7CI5I 111111711 although CI CII T?1 some at Rapakivi localities. present is amphibole mafic sole the as biotite usually and predominant, is plagioclase 40 L1! C' _T "—r'l CI "11 which of feldspars, two quartz, anhedral to idiomorphic of matrix iL'Ino'1iC 1 1i C. m91Tcir: .L,IUTW.C101. 2 with mm) 2 to '14 (1 medium-grained a of consisting 80% remaining the 7jTi: 'sTh'cC ri €17 11' I0 InTL cm 14''1 rock, the of 20% about constitute size) in 2.0 to phenocrysts (0.5 o.loo1oooocrr: feldspar K%cc no L'T1CIT74404J[ ZC2t!7t alkali t411 Typically, IC:l subhedral phenocrysts. feldspar alkali t.Cl1j[CtCii i::,ti Ti .1771 :fl 711104:j::C'Ti'.T° 717 phenocrysts rather angular, and to in ovoidal, ICCITI'l than ,nT.'zo!Uj matrix proportion .'01..t CCI riI00 quartz .r,I,; Wolf and .0C'CIl; River UTL4.CI 411:711 1€174 111 contains nyCv" '1 LI Waupaca fewer unit this monzonites, 'T:i;°7rLo€ quartz porphyritic River Red LC,LiiLLCI1 In the to comparison ThJ monzonite. 0 llTr 'I • 10 Fn', CT7C CT. L I p'4 4ltt4'L 1 '€': ;4.:Tlt CC IttTIC' l. 4 .1 I::-,:.Cc:: 2 nt t'1:. In lT'r i41 r'o ., . .iiTit C: 7:711 predominant 4:11-ri 71717 CI: I 1144 11 C€1CC4 granite II 417.714 type. rock the becomes 0C1CrI.4. 'C01:nx 1c714 IC '1777141. it, 1 t'€ rr" 1411 as appearsI quartz and grains, idioblastic iron, in richer becomes r:ç'T -- TLC .121:? :,rc2€I.rnCI 1141. In 7111171 4:717111 it; .7:, :U amphibole C'1,:°° 141,': -. ;c:T14 :amount, biotite inIcdecrease and plagioclase northeast, the to Yto171I ?.;LI: monzonite, ICC..n:CUJ€Cr: quartz '7,711:2: is ff':0y$-r7114 71111 711111742 granite Belongia the with Xl'TiiiICI contact *11 the towards but 0;: :..Th:nr..LIiIIU: 2r'i'''n plagioclase, iln41C.nIT 4111.the I,14 of CI .i'0U unit River Wolf bulk The amphibole. and LI biotite, .71t.LCC:L;I IC'Ct, :mi,'C:2t °tn: l,7f.:cl:'4LrICC: interstitial 'ircTCI71IC.':I:c:I.40CIiT microcline, quartz,4lIC]71'4rli1 anhedral to subhedral of matrix grained :1 feldspar .1 €JIC7fr'[l and 'To,., Alkali Jr II'C set1111': 1'.ilrCsC 14 plagioclase CI1 a 'IL I 1L11 are phenocrysts mediumin 0 --': 1 r' CCCI 13 �14 :-:cirL:r&10154122:?1'1 222111Lc'-l'ZIIOSLI idiomorphic 0C:.*-2, I'll conspicuous The Illoco:Hager rhyolite t'-L'a-L--rlL:Lt-r contains 'L1''1L,-h2, 131-to Hager rhyolite. 1110L112112112' 51220130772101. IlSoc ;oc.:lI-.ILO-co, :1121(1 less quartz phenocrysts mm) and prominent feldspar phenocrysts -50to to 44 co] :'0311.01 1F'.,Lo :--' 0110 (3 7-tn-:.]rcrcc: :1* quartz, 701911011. feldspar, 11121.0.221.221 f1 11101 ll--15L1.-O-0 matrix (4 to mm) 170 in a '1111-f very ULIOIIfine—grained (0.1 mm) of --14 to-i5 too) '01: -:11-too The pheno— 01111,11.511713. ortcc 11-0 8/00211. con:21 7-: -- and and fL' clusters of li-tc-:. biotite, to ac I] lesser extent, amphibole. ;ooo o:f 120 "1122€: '4201911. :r7ycLito, commonly :2211201-00 0 3322111 crysts, constituting 30 CUL 0' of±2222 the rhyolite, show resorption 37 to 45% 1. :10112.lt,101 t-:-'i4I,-?11t1 of -cd 02101011102 evidence :.o2:22.(112t.80101, without : tO is The 1-105221:: rhyolite cool] homogeneous, 111 massive .1--'-12,11011 and 5-:att 11-:;:; features. :1001: is tS-co:'otto to lot; IrSc-oO:': brecciation or573112-12' pyroclastic 01- thought be intrusive, ir.ot thus 0,122 -It'f.to- and 911180 010 01' :11:1,10 activity, -1'31.1,2iD112S'1-22, rather 1-ftc-ac-c- extrusive. 1201,52112 than 111112211 0711fine— fi'-o ' :1-12.101' 100 03.0.822431 121.1 the "Cr0701111 somewhat In :ccy;f hand op8o?4-1112. specimen the Hager-- rhyolite resembles In 2212 ort c]h-oHager ,1]:cc rhyolite oIlo'o' 0 to has Sac ac much grained Itoh the :'-c±- that to-Il cicpzl-ogranite, : ---.01 ic, except :21 cOol-Il Belongia ,7119 pink, 110221111., 71I-IOF. .C'at.012:' 001be 028 101.12k-I, 4-11-411 to finer grained pii. :ish—grey, rather than 10-: tends 40'2ILILL1O-1. groundmass 3C-912.In.r111123,'211 and jlb:i:-o-':' o 5.'-I,.1-9 ci,rtc::: on a fresh surface. or- 2222220 (11Y1011'l:lIc, f.'-O-.'t I'712'51 is al somewhat The '1:10/ ' feldspar Oolon IC' porphyry '3702 Hager j;111'5.: 5ti1-7-t1ifl50 Hager feldspar porphyry. 22 o..'(' 00, I is ':3111 12210 10511-5021 -p-202t74-' :-o similar to the rhyolite, differing in that the feldspar porphyry t4.tf.:-oI22c€9* :"ft-,-OJIL.:--:, 12:12001110 0-c- 'Lbo feldspar 407 .01,5 t.1'12t110'C221-'-c1111112 001-C, >71'- n:-o o1J11lt;.tlld1 more abu:Ldant darker grey00in color and -woC contains and conspicuous 01cc-Icr .t2211 0011:22.-to LIc :-oc- ol Or is the0cr13' only oo,i-c mafic:01 mineral in 714-1:;: 1 0035' 0?1:1.' phenocrysts to1730000 quartz.- Biotite p54: -01:5122 iL-: compared 71.42-1.0porphyry. :oo.c2 705 the feldspar 11*1:1.1 Scm' SOtO and r11122011.o&, .522'07', foliate, The isOL'-217grey to 12-0 reddish—grey, 111401010 Sw 117.1"dtlt-O 131. syenite Hager syenite. 1971214.011feldspar 7-01 C o: 11:' fCctSl :0 11 Lo:lm-f porphyritic, with aligned phenocrysts (25%) of anhedral alkali >a2L I :00011 pL>cocm c-51.to C2-1"% :td7-15h5--,'v:o1t -In-I tI: SOo000: feldspars, biotite, oil Solic: rco.'c, Jr;11-015:;. -,:. 5'.l.oo=-If.'coi.clrCand 1:25cm-cr minor plagioclase 1111 a fine—grained matrix of t1b077.L11t 0011 in 01101 C-? Granophyric iL103Di'9*7'0t't'011 of '7c1,c-cochdc: . intergrowths wo-r:-:cc- rJ: 81,3121: c,:.L amounts amphibole, small of1111811011quartz. c131:11 702 1.1: and alkali feldspar 0-3102 01010 ±122 12-0111102 a.'1Y22:-38IC to some qua.tz and alkali 1142110,1.110 occur adjacent 01111:0.'- 1 feldspar 5'-,t::r:-.4l01-. 77-s'1307'C"o: 22, phenocrysts. ¶ 11 massive icr-nA :1011111.IL'-iir and This quartz monzonite is 5.100 1112,122 Id lltItC1.7'coStLO ,-1071.1-;:0i -1 Hay 17ClLc Creek quartz monzonite. ]1I1,'L .111111:123,8101': 0 (1 cm) in a 7)2:3:52210 ' 0111 14 5112 -0051212' 11017.:C-.'D 437 ..'fl'11L40 porphyritic, pink alkali feldspar'phenocryStS -1-oOp°-y'2' '21I, containing 70-0121±.--:', 'oS -.lcp.c' cc, biotite, 7711112:' 12, two too feldspars, :-00clcJo'.rtl.t 11'-fl,l medium—grained matrix mm) of anhedral quartz, :12.11101.12121*. -950-4] 401, 801011 (2 1-5111lIlkt amphibole, 01022 sphene. 'l'c-,Lct , and - 2110 1.011-LI unit *1.14- in 71,101.00-37 this have not yet studied -not 5114 '>O '.5001-:c..:' ,572 We granite. -to 5082' :,oL,OILIL1V" actually a grey 31.1:1 -x;t.o-'inorth ocr-IS Ifof ,7002201:.1:o1:,o0 50One Stevens Point is ::-01:711d collected 71.c sample detail. tloc-c.Oi., 11-c.] -21 op to-' alkali feldspar 22 Ltao'n: 17% 122c1h111t122L2-aa porphyritic quartz 10% subhedral ,1,iL:s1:1 '-cttrt about 12210:211(1 022 with 0±11 -110': 12 monzonite o:_r1 iI allotriomorphic 'IL 0 1100101 in a fine—grained pJenocrysts (0.5 to 1 cm in length) I :750 tOot-Otto , This and biotite. 711! ,:c:-±oU 1.11-1.,, 0111L7 '3:011:: c-oitsc:, plagioclase, .-.:-i1 quartz, granular 1111.1&1lCit1c matrix of '-ttc-0o. microcline, 41'20C.'91.5F' 'I,0.72 '41-123 finer grained varieties :1::f5o-o.cc'',0-.11cI 1.12 some 11.0111,of of the rocktois lithologically 2-111.111,11,1 to rook, 11'1411c.1C-J.4 cc 113' similar .'-Io-'111c1:1.t3 flo-7,"lil-T-:OlCci quartz 0,8111 River 1111.02712' porphyritic 110S12'L-S monzonite. of the -1-221 Red 0" '1'.oIt:-1h:11-'a-: 5':81911100 Stevens Point grey 21 ',i 21 ca"c. -151-1.- hetero1151125 granite High 0:1-cool t.: is rather 1-c a :'s;- 5i oil: Falls .:&-c: t-:, The High 42-S'LS,: Falls granite. 5(122: .lJ0;:1.1..771.1222I12':cLllt-I0 oo'-i22 1911, '12013,-I,1-l allotriomorphic geneous mainly ofdt medium—grained OCI'SI 01LT9* 11.01:174 011111 unit, 12227 -1 consisting octorw': oIl-Ill Shear zones 011are extensively 51.12.0 2103.01 9*-L-02011*o.1 wt1oor.. of :7.'911'1712 granular granite and quartz(19-3>1101.0-0, monzonite. 11711 other units 11 the oLir1 11111 -il:':211t 10305-1111 absent developed It'll? 0021,2107:01 outcrops, a1- feature from 12-1510 22222:1.1,0 of 18: '211.1' -1: in some -lb rcr'0" :7110024±22: Eau '-IILOOIci Claire River mylonite :0 '11c-'o,..'.7f 1712,11: :'r50 11:11 of -11.':L'klt the Wolf River exception the 11:::, catrl-:clLlLibI, with 1i',tmr batholith 'i&3,:77oo1, It is ::,.1.o1c150V uncertain 1;, .0 11? this guidebook). 1770-1'. .015 122/11121.1117zone (LaBerge, field trip locality 8, :1' -015 1210: (1 a17c1-cbS-.. 7t-I1'1:,11L11-' It' whether of the 1,12.1 batholith 022000121 I'Ll]: or lIlt" 114r I.½0:C '1-;: truly n"mCft ilL granite 01 II;111l'1.' is whether the 4111911'? High Falls part 122 :.137L&1t1b,1€02011;1 to ItoIn the 1.> '1"°111i12:. 3ii:1"11'32212.2L111-4 terrain. 0' 480- surrounding 71.0 older, it represent :5' the 1211:11 of 11 might mtgkb 0017 .c10IL::, part -: >s tac-]]' assigned to the bath— it. SOS tOlctO: 1 021-10 3:30 oso L,oliac to absence of isotopic dates it has tentatively been ooto-ptc 1,0120110 21201-so cooS tçlOIolti -.150 ol' and is spatially .10:1 1:c-cr:,'-lllm' 01-8 cool-cIlo': ,1T:8.'11L'.tO olith because it intrudes the Macaslin quartzite dli;:1,I'5bl 0-1-30:1012 -'tC-OLCIO. Ito. -oob :101410 monzonite. and Peshtigo ::l -19-12 .1, . -110.: 11c5 Ct29ttl: granite, i'oç'to..*tl- , Belongia 7;: the 1(14 —cr1 : rhyolite, related -o Hager c-tm .al,e-21 to '1 21111 �/t c-'5c-,, at.1; c-y cc;c cc'C:Ic'C'cc6 cCEcIICECcZ /Ld:,LLL -cc:. :c;:ccicc cc ,.C1 ::cc-:cc---5- To illustrate the chemical compositions of the granitic rocks, mesonorms have been calculated after the method suggested by Parslow (1969) (Fig. 4). Such a calculation takes into account the amount of potassium incorporated in biotite, thereby reducing the amount of normative Or and presumably providing a more realistic comparison of normative Q-Ab-Or with experimental data in the "granite" system. SJc-ccCc..,.C: ccL?c:.,lcccp cc,c. ic. c :c-iaccc :1;-: 2cc,:-,cccj 22-c--cU'. /p:p cc: ptc;ccc-T:cccr c::ccccct.c-i cc -'' P :1 cc-C-S -I ci 1•:as I :;:cvccc- 'cy 1c2JIC:cC,'5 cci;: cccfl c-cc::' ILL.Ii;,6;5 Ct fClC:-cC:;f.c.Lc :;c-:cc: cc-i. ,;IC:'1'. 31.;-ccc ccCci C'PL rv,cc.,mc I:; 1CTC6ttc-:e 'CC!. —25:cc:cll c,; 'c2cp.; ..:I3_':L:CC:ci. 'ZLj cc '— I cccc,irc,Li cp'.:cc;cc: L.ttXI6 c-'2J cc' ccc-: :ca'TLt:ccaci; riS4 c; "iccic ! Icc. cc: I!TCiL p,cITC. cc-.;. CttEC PLC:,' Cp; ;C:LC:C: (IN CSLC:LCC:5 l'Lc1, cclcc c['ci A Peacock plot of analyzed specimens (Fig. 3) illustrates the alkalic or aikali—calcic nature of the Wolf River batholith. Despite the alkalic affinities of the batholith, all of the lithologic units so far recognized are peraluminous or metaluminous. However, syenite and associated nepheline syenite in the Wausau area yield isotopic ages of 1450—1500 m.y. (Van Schmus, LaBerge, and Myers, this guidebook) and may represent the peralkaline complement to the peraluminous granitic rocks of the Wolf River batholith proper. PILc.cccc cc cc:' cc-c 'cYs,ccc-rm :':f'c;1C:;';c-C'c-LcccC: c; C.:LI ccc' C C:/L,IIL1'L:ciiP'JL ci ;'--;, ;'.:: 'fltcc CC:C: C:CtcL .Jccc-'C:6L .C-1; iC:177ci1: c:L:JC: clC:;1l..iC::.Ic I 'C:CJ cc:; "IL 6F1'i:C:ciYTl ccc ;c CC.IL'i C:ii,c-,L c',;:CCL.c.=.T'\a,[T PC: Cc-c Lc'ff'Ct5 I'5.c.15 5Cc S':.L °Zji TCC:LC:UtC:915' iC2-CISL" .1c. "ccc :1:'c:ccc1J PLC: cWUCJVL"1: 51 :1:5, a/c-c' ic. Bulk chemical analyses of specimens from the eastern part of the batholith, including Wolf River quartz monzonite, Belongia granite, Peshtigo monzonite, and Hager rhyolite, feldspar porphyry, and syenite have been obtained by electron probe analysis of fused rock samples, following the method described by Gulson and Lovering (1968). From the analyses listed in Table 3, it is evident that these rocks are relatively rich in Si02 and alkalies, particularly K20, and poor in A12O3, CaO, and MgO, features shared by the Finnish rapakivi granites (Sahama, 1945). ccc'.CCP leST .Y'CC'i"CI' cci "5 I-i 'ctc-c, 2C:J'. c-C: : 'CC:CPTIcC T ( C. — I L cccc'c.'.c C H' C:'c-Cc- 'C:'.'; '"1'EIP6/ 'ci cli;'; 'c--Cc sic- LT -I LI c.'-c-Ii:-', cc; IL -.1 ' cc :ccc c.c.cc.:ccpr cc-C c-CRc-c- (c c-ac-.ac-c;cc. pc'pc'c. 2L S r,,c,.Cc-1' ccc5ct'S' :C: çc6"csc-'c 'ccci: c'c' ' ;cI PC ;!.cLT'Ccrc cctccci:' ;cn 'c-cc"; tTc: c--c 5;; 5,5 Thp 'lrI.Tc-c ti i-;":.CC: ccicl.'Lc .'C: cc 'C7"Z' 'Ci-c1'fl p-C:, C:'cTC.i LC.'CC.ilT :6;Ipr'::z'c-; C'IC:PC:']C' Ic c3?SCIC7CCS Ec'PCC:IC.1L :'ctc- : 'cc-; cc 4.rCI 'ccc ic-Cc : '.5': c-cc;.i:c si:cc ROCK CHEMISTRY From published descriptions of rock types in the Finnish rapakivi massifs (Vorma, 1971) and from examination of rapakivi specimens in the petrology collection at the University of Wisconsin, it is apparent that each of the lithologic units in the Wolf River batholith corresponds to one of the distinctive rock types recognized in the Finnish occurrences. A correlation of rock types from the two regions, based on textural, mineralogical, and chemical characteristics, is given in Table 2. The only dubious correlation is that of the Hager rhyolite and feldspar porphyry with granite porphyry and quartz porphyry dike rocks. Texturally, the correlation seems to be valid, and perhaps the only difference is a higher level of emplacement for the Hager rhyolite and feldspar porphyry compared to the rapakivi dike rocks described by Vorma. p'6,:',::: p 'ip ciTc: cc- '2,TC:c-'2c- .,''ccj ','; cci. cccccPC cc "155 "S i. cc'; :,'Irc.cc':'c'.i:c' 1."cr: - C: H; ;,L',,L,'.cm 'IC Cc- ,' C:C:U'C'STC CL2tit S ic c-c. C P':.: CC:c-? (-7 I I cc- PC cc-cc "ccc:'ClCl-ccctc c-Er c': cc " A,c:T-cP,c': cc cc p PTLC:c-Cc:C:cc'c.c"- 't cc- s. :c'i-icC:'c- ccc': pip;' C:T'1cc,-: cc-c cc .,,: :1Cl;C:2cc7- p,'c,;'"c-,l' '2 -c' 'C"l." ;c-r' c-c L'icC 6):PC57 '-;'::':c'c',, 'I'P rIct'L,.6L i'' L"c- C:'pr—c-ici; Lit. 'aciccC:",ccc;c-;XL1 I'C' icc-i I1c..J'15 :'1Cc-C i'L ,,,''.:'c'Tc-cr.,,:te '1 c',. c-.:ctc,ci cc, ',Th -c-c- 'LC,-cTCPP'C:LL' P1 ]'ci',1C I/c cci L.,:m:cp.p' L..(CiPC.: cij; PC c" cc :'c.:;L; cc-cc c':c-cIcP'C ' WE c-Cc-C ci ,?,Lc;/ pc L::6;:c6 cc, ccI-cc- C: P':tJ'ic-'i icc-lIT,' '.,5 'CIT, 'c cc :cc ,,r6Cc ccc-: lcC:c';: :rc-y -'l:: c-Si. cc; ciT ccc, : 'cc-, 1,6:1:! ,;1:CCc .. cc'c'c ic-'J L'JC:c:,:cl: Sc-c-cia ic"cc: c c-Cc' ::_SIP :LlcC:1C:c 1cc'p.r c-i' P 'ccc '.. .,c- rpcp7;:i,;i:r'p':L5c. I :7PIH HH'.i sic's; ccc-.. cci fc;:mlcic-c-c:c- ;c,ii":7:ccx: c LITHOLOGIC CORRELATION OF THE WOLF RIVER BATHOLITH AND FINNISH RAPAKIVI MASSIFS LcI'Si2C:J111L 1::C:::ici Pc-c' :cac''1 pccc.:c-'.Ic-cc :tc;G1E:.ir 5,'c-'p' c'S a Cicc cc C:-i':"lC:c.C.PL :P'i"c-UC:r CfCui 'ic-C:4 Anorthosite. Anorthosite, containing plagioclase of about An 50 composition, occurs within the batholith, where it is intruded by granite (Fig. 1 and Weis, field trip locality 7, this guidebook). Interestingly, anorthosite of similar nature is associated with Finnish rapakivi, where it is also intruded by granite. A genetic relation between anorthosite and rapakivi has been suggested by Kranck (1968), among others, but some Finnish geologists believe that the spatial association is simply fortuitous and that there is no direct genetic connection (Savolahti, 1956). c:';": CC c-cc-pp 6:flC:C:'C':cIlC'C: c-i'll. cc-'PCic c-c- ,_F.cL 1'C:. i;-cc-:ci' P cc-';ccAPc ccc , ia,C PC'cUC"l c-CC:' CT,, c—-c—— " ctwc- C:T'Ic-PH A? :ci, .ccc.:cccc ucic-ciCC; nctp'-ccP I'c- J C " 6',c 'icmL,L..-,,'_Lc_', ''.2'-. 1—c—_c, - Si ClC .1CC:;' 'p c: :cc-c,'CL"P' 4-"':"'c--''4 ,•,—. C-'1'.1 ccccc' .-— 'cc-it-C.' c-nc (..'la SCCC'ST,JC.i Ic-SIC ::.cCc;c..6I ,;12T75:1',r 5:. PJ' Lc-cc'c-/ C 'p, C:.Tc-,,cC:i'iIk. 'f;CC'i'ic''' c-c ?'-'I'CLC:;''i cc-p •" ii's 4. Lj', C: "1 . cic-'c- ' L 6/'— in 15 �16 Table 2 tC.i! Correlation units in the Wolf River with onrc: those 2ar-o:- batholith rrntr O:r'-cLrct Ui -ifof1. lithologic t.n01['J-f .' nyt+ in the i5rr9t Wiborg rapakivi massif in Finland. Et n1ri :irn Er at1i :''!tAL. Wolf River batholith '.ai Wiborg rapakivi massif cr;a•r:te Peshtigo 27&II'C' monzonite Tirilite 1Ckt2C3flI :8 Waupaca quartz monzonite 'i Wiborgite -t Wolfr River izt1'C granite ;c&-t.. and quartz monzonite Pyterlite L1i 1/rL ri: Red quartz monzonite r\ct! River porphyritic Porphyritic granite :: t-•i rrttt L•L.Z'c9 -pL1T_:;r' Belongia crsgL granite, coarse—grained lilt Even—grained granite 3Jis 7 *1Ci: biotite Belongia aririCt granite, fine—grained Porphyry aplite rg aIL1c rrqy1 ( iCrp Dike granite porphyry rr:c2asaa a .e- rocks; and quartz porphyry grL';Q ja( r.rirr' Hager rhyolite and arci feldspar Z&T.t' porphyry ac Na 1: Na20 + K20 -p Ilt 2.- I lU 52 56 - CaO -— 58 6o 2 76 Sc , wt. % Si02 Fl.gur igure 3. 3' ncco1ith River atholith cloif 1ri'nz torn Ure forhpec:iraens specimenc from the Wolf grapb ftc Peaconk Peacock graph �1 17 Table 3 Bulk Chemical Analyses 66.14 0.68 1.13 13.112 51.8 1.145 r 71.14 7, o.6i :i 0.28 iy:'- nC'": '"3: 0.20 'F'"' ".cr's -A-; 0.39 69.6 %9i 'r6.2 714.5 7 6 5 9L2. Tb2 14 5: 69.6 Si02 3 :5'; 2 1 3:-c 12.1)4 1'9°J 99° IJI -r' -Sc 1)4.33 s:. i6.6 14.18 2.53 3_I 2.29 3.72 11.29 6.31 io.8 MnO o.o6 0.03 1—" 0.02 0.02 3 0.02 ;i1F.;. 0.03 ::.-:, 0.12 MgO 0.33 0.13 c_'I'-3 0.08 :5ri3 0.18 51°11 0.37 7".:;' 0.90 1.36 CaO 1.69 0.58 0.58 L 1.111 F[ 2.39 24.07' Na20 L 1.38 3.83 3.13 3.22 11.142 CI 3.3)4 3.611 11.119 1(20 5.83 5.85 5.56 6.02 '"fl-'j ., 6.28 ..-.;3 5.111 T':° .-..i 24.35 100.21 99.09 100.03 100.31 100.9)4 100.5)4 101.0)4 1- F' c-A :4. I —- ii Cc c.w 3% Wolf River ciuartz monzonite 2 ? Belongia granite, coarse, average of four analyses 3 Belongia granite, fine, average of five analyses 14 1T Hager rhyolite 5 Hager feldspar porphyry, average of three analyses ,T'31.33II33. •c;11;'rx 6 Hager syenite, average of three analyses 7 Peshtigo monzonite (c° ci: 1 11 -- Fe as Fe203 ',o. :7 F"" Total IF — * I Total CIT 1)4.3 31 "ii A" Fe203* 11.80 ti: 111.3 991 A1203 3333) .D:3,T? 9-3 73,1: :13 J:33:3 ':.3'i.73 7,33.:F3'3J,?3 tFnL;cToca 1:7 ?32c-' :cc;,cT, CiX313 co7'Fc:i: ?17700:19 5'3ç1':f33ci OX1i9t j3 :9co±935301. •33Y.3 r3v'i,:iO; Jo LI- 3F .9 �18 Q i o--:JorL8!a fC&OAt Belongia granite -5 tatr hcres granite Wolf River granite and quartz c-rr7onlt-e monzonite and 4uartz A feldspar ris cii he • feldspar Hager ffac;-er rhyolite, raritcporphyry, n-or piriTy. and syenite / -- ii- L-— - L2 Or Figure 4. . ilivar compositions of Pull of specimens spec incas from from the ih-c Wolf boll River Bulk c-orapos;tLcns hr. bat-holith in p. Ab, lb. and Or. batholith in t-crzss terms of of mesooornotI-Vi mesonormative Q, 8ourxdarycurve c-ursafor for P11 P1 BounOary = bars shown -shon: for for 1030 hu 1000 2 comnant son. comparison. batals fist-cd (Symbols listedIn inTable Table 11) - I �; TCC -'.-"Yt( 7-it F k-CELl -'C to up determined. been have 1.5% -Ci -'-'-I Cl (CCCI 11.12 7 CC CLCtLCLILI7'fliC( of ,,LIC; '7C'.If a is 7LCiLI'ICC-C- high ITT- (CT.' VCL.C:'L,.T'CkI and to up contents -IC, -Cl) 1.8% of far, So halogens. content ILCI',LCC, River C-Il. L'21fl'C7 CL characteristic ;TCLiI, the "I 7-s77[ of C 'C-CCI.C;-I 11 C!.IITL'.t .7L1112 III '- CI A '-(1 1'-CC.i Wolf batholith from biotite feature 11 - granite. Belongia YC:.7C7.i7.lL'L t(C' .T 5 IT c"CCC-Ci-'-'C YI'LIC"C 1147 IC-' .2C.1LCC-),,'C SIC, - 71121 2(9-112(12Fe+++ 4 -.1! coarse—grained the of biotite in Al octahedral for substituting 5' LkIC'Ct.CI1l of may granite 'C to -LII due iDI1Li,1)';-;'LCL. 7.7 '74t C-Cl) be -CI'4, 7-1(220 11757 CI- 7L2100;.CICY.X1Li1LI711.IL amount larger a of varieties two the from LLL7-.L7.CT'C (CC 2,'C€'2.ii'I1OI- LLI,(ILlCi7IL.CT1Li 71; C-C,C'-I'CC',.,, 4. CC' 11511C-cC"P-&, 'C3C.Tfl,-.CI Belongia biotite of content aluminum in difference The granite. :(.7,, 7,'C2;'7i2ucL11-C-LI? C-CC- T515 C '1 octahedral CLIC.CCT& IC-C CCIII 9-7.r.CCTL'C 21'L,-'0--C fine-grained the from compared when biotite with Al, C'7,IIC 'CC7TCC1C-i "II5CC5CLIL'-CC C?-CCLICCIC I '21201111 C2.(1i1'4 CL? but 'lLCI'.Ci?I[2-? 5.121 particularly aluminum, amounts small relatively of contains ' 7711L'i. LL.TCLCL '-"I' ('7 1:20 71 5,L7:.u.t I(C 2CC-c O' "CL 7'1C-0C 'C.' CC.CCcIzi.. -'CL mineral mafic sole the is which in granite, Belongia biotite grained ,p.7f -coarse— 1111-112111? 1l)C-'C.LC ('11 '1-" '1','C'5.CCCCC - LII CCII. ' River hI'7 216 P 'CCC 'CC the by is rule to exception I TI provided this An granite. Ii '0. the '1(177. 7721.'CC Hager .I-.5.7I'(' the TIC-47 C)JL7ICL.CC IC"?, LI-CCItT:' C CCI? rhyolite, quartz Wolf and monzonite, porphyritic River CC"IC(I 7217':CICCCCCC.'5r7 LIt'IC 7?- -CC' 1.i:I1Ci'2-CJCLCCCLI7,:ICILC7I some as CLI' Red the of members granite, Belongia fine—grained the such C'C5'C-711'C7. 74 211T-1,1.LILI'C.CL- 2177117CC LYfiC 'LI ?1i.I-77'C'C'l' '((PCI! lithologies k-Camphibole—free in occurring biotite aluminous most the .-i4.'7 'C'L7'YC River 'C-C,(CC-.,! I 7(7 12 .1 -CC, followed (It CLCCCCJ C.L5I,c.C-T':t:L is 117,74? ('71 by batholith, Wolf the from biotite pattern 22Tt7 This CIII CI '-21,1? a t'-. 5(C CC'? c:L' 75. "...L'LI. 7'fC"--'- as -W't-C(C 1(1-717 'C'CCIEC C-C.yC.-C21'i, well. amphibole containing rock from biotite than aluminous CCCIII CI more a as 2"CC occurs 1127 97 iCi-"kCs 177 CCC'. CC 1'?'-'? ;C( '"1(121.1 C-711'ICUIL -C' LI-CC be to tends it rock, in mineral L'-""CI-'mafic sole the C-IC?-.(1947), -2.77, 45971.C,CC-k.i 7,Cl7CI37l-iC-'CCL previously .IL2'CC.-C'C"J As 211 biotite where Nockolds C'S, by recognized L 7Cr pis 'C'I11:LkiC,C7 per C11-CCCIC LI 2,,, CI C'CC;SL!CCLI1 CLLI'CI 'CCC' formula CI?'. C-Y"' to unit. atoms 0.5 than less amounting low, '7mT ''.LLcI'©YIICC( ,i1PCC- 7L7'lç..ICCIC-ZCC ,12ITLILZ C' LI' -CTI'7?7 in :(CCIC7,CCLTCVC '11-7 01Cr Ci Al biotite octahedral monzonite, quartz porphyritic River Red and 1-1. ('1111.7? Belongia "41'CTCTLIC(l C171t CL't 3.2 'CI' C' 12192 9CS-CCICC- the "-kkC.C-'CILL .1"CII With '114; .2 - C tI 1 with granite the IL? of exception atoms. Al 3.5 to 1TI-IL'Ci1LI2-t-1Lk2 C-c'9i1C -1.1211117. CLC7CIC cl- fine—grained CSLCIC-TC,, 2CCC'L'II.C-Lbiotite contain 1721717-'. which 7.' of pecimens most granite, Belongia ranges oxygens, 0,IC.LC117 I'IC,C7 2232' 721111 CLI. 2.35 2172117-CC 11 7 -CL to 7.uCL'CI units 1all 'V .1-4,1 1,7 '7 about the 7except from CC'211C2'LCL for 3.10 C an 11 CIII- ;'H-172121 ul uCIlLfiCC,LC The 7-C basis LCICI'C'Cl anhydrous Itl?"CI.- 'LI:.CI4'k 'CCj' on7-1217 "CCLI I?.. of 22 calculated atoms, Al of number -. (CCI (:,7,IC 71-11211 'C'ICC'7 River. ;i,9.? the 41 portion 97--. granitic and '2.1.2011,,'! granite, '12'?'CL"C7 Belongia Wolf 'CCI. of Cl CILI,177213'.LC' L-1'7C -.2:117-I ,(1C1 219-C! consistently 67 -nICIT -CCCLII being CCII-177 than U&LI7C'rLIi 'Cl-CC rhyolite, Hager the (17-51 greater for -:i 90 about -7127-f':: silica—rich '7.20 C.II'CiC'Y' CCLI. ?'7175L_12-217777most 1CC-ILthe (1.7 1i, I'I'4:Y'(1 L4CC-4 'ILITt.'t :1,1 are rocks, in highest ratios Fe—Mg expected, CuI-wC39I(C,'r 11Cit..C,.CC!i'TC7'CI° IL, values 10'.." 01-25221, ..;i'CC(C 2CI,,,)"21.,L, ';"I'II(c( As to 70.1 from ranging be might 98.6. lOOxFe/Fe+Mg of 3iLI"li'"CI with ""'.CT.-LC'CLp.Ci'7. 011.772217 1 The 'TL'I'.u,, in 71121' .77 biotite '517 siderophyllite --'37(11017 tIC -C"7, 1'',I-C,JC'iLL':C and '217 C1 i' eastonite, iron—rich, is 5.7 Fig. C'.CLIT,..10T1LL-'5L 011.731 have C CLfl'LI-iC,-"T-CC'C of 1-1151111 9i-!'f( analyses 73- terms LII ,C'I-"l phlogopite, 'ICC TILCIIIC (Il)'-[ end—member 'CC plotted H -2(1,771 been in annite, ..L(', elements L1 C'4L I'7IC:"T'C'7.I eleven 122111 '97' C1'21C4' I.C means 7"ILC1'UP by 'CC-' 12277? J1f_.LE1T 'k'3,1J. analyzed the and probe, electron the of for 01(117-CC CC -22I'I'c''CC'-?C,2', 1i-.C(1''ILCCL'CCCCC'pC 47 'i'-IC(4 , CCCI! Biotite Biotite. been have specimens representative from CCII'C'C-.7, - 2 11 C.u'CCL!LC.,:p, CC:Ck19C.C-I-3 the accessory minerals. 1!1LC'. :111 and 011772'(C"Y-' 121421177 and 777' widespread 1-CC' C7-1.'I5'-k.:-1 —' most 74??' 'CCC. LIt 'CL pyroxene. 7(7, .LCCI'.i,i Fluorite of characteristic the is 7771)207 iron—rich ''Ilk and 'i..71170u7 1IY''7-C, (CC'!.-'' C'C.C CC.C..fl.,2u74'.Li(I 112.77 biotite olivine locally, and amphibole, plagioclase, (120.1(1CC-CC- smaller .L:-:L-7 :s -:sl fl'"7'-',Q' 77- 42t -11-1.2171-1-C.;: C:'.'L7 73sodic of amounts with quartz, and feldspar alkali perthitic up made are batholith 'CI 1771 (1507 C'" 1'171'T-2111k7-1'2 7r-, 717- 7721.,I1"-L,River C&,"71 .Wolf 11-I' (IT' of predominantly the ,of Rocks , 7. (9C t MINERALOGY CCLI. 219:9771 47,7. 'C17.l C' 1120 -- -1'.7--I (Luth, to respect withj7ILII7JCI21C-: saturated 1969). (12113-1120" could -_.Cc72LEC1 magma aP in -'c;11-I'C'['CC , CIa-7CC C'C..,IC 4LCI-'I72'-i conceivably under— 'CCC7LC"ci equilibria crystal—melt reflect C1"'.7C, -'ic LCL1TIC 7'ICC-CLCnLL' [ -71C77 a '1 41C5'C LCt'7''L-- 'Cs-I- rapakivi 7121>7211.15' IffCt7lLICCCl (('4121 '1;, displacement Such granites. Finnish the by 721.771711 shared -7feature ,-: 13122120 L',,'C,1-"'-C1C'C 71.112 a1 12177.21,21 corner, Or 2194. 11,21217711: -: still 917 from TI .5-C are the toward LL'1I20.'-LL'1CCL minimum C7''I:'I.C;-C granite the displaced (1Y-c' C/-C -7-TI 1 .2,'C Hager IC 7i'Ii,C.'LlC.cLI the Ci313':'c-CC'21-'of 7C calculation '('977114(7(1!,') 310117"'.-! Belongia mesonorms, rhyolite and granite 1,5-C "[(7 CC. 4C':'CIC'(L'LLIO.LLithe 1177. in 0115-77' (''2777: despite C' C feature 7 712110515 'II of C 1174 is 112117-) i3'C IC CCI amount that, by Or normative reduction .C'.77 toward 177191117 \''7'7) IC-It)-?,, 1721CC' 'C1CC' Ab—Or II along extend 'C7'Iti the significant A join. trough thermal the "7)5771 79((15C;the I'll near '017.:-?..: granitic u'C.C,,'11-7LI, -317-k-IC- 711.-'-' '17';. '7-I7- 7.1 and minimum (Cc granite plot rocks the(1-77 for Mesonorms 1121 - , 19 �Al 20 atoms 1002 1OUx 3 90 80 •4 Hager Hay Creek Peshtigo 10 100 90 • A • AAI •A As A 80 o A A Belongia S1 A A Wolf River 10 U K2Fe5A1Si5Al3020(0H) K2Fe6Si6A12020(0H) V 80 vvV V Waupac a Red River 60 40 23 20 gA •OH K2Mg5A1Si53020(0H) (.M-SA1 1:(DH).4 KMg6Si6A10000(0EI) Figure 5. FiRure a of Cumpos'Y cf Comuosition hatholith. tTL frcn from biotite cL:River Fir the Wolf ir LL7L (Symbols listed in Table 1) �21 fr i-i-U li-U)- fli- 15Ui-1 tci ThTZti'-i-iitUp Ut ; Ti-I [-i-U)-'P Si-U -Ui- _..t Ui-ill U4 .U'LJitLU the Biotite from the Wolf River batholith is similar to that Finnish rapakivi granite in displaying high Fe—Mg ratios, relatively low Al contents, especially octahedral Al, and enrichment in halogens (Simonen and Vorma, 1969). i-C Li- i-lU f7' U)lIUi-Ui5Ufl LU U r; •Q:U)i-,i-J 5 r-: -•l i-li-C Ti- U iLiSU)cU3-SlL-U) Lii-U) i--i-2 I?*81 c)iir.a U5U)UUl)'i-U LI k-i-- I i-IHLUTtC U i-i-J-U2 )fl TtitU)i U U U)flj'.L U)I2. Lii- itLUI: t-p ioi-i- ri-i- UI -U-li-f UU)UUU U -i-I 4fl2 Li-a.., Ui-U U -i-T-U U 4€LU2:UU U2t1iUU)L 'i-U Ut i-i-i- 2rim '--rU 1 LU'ti-UL ,-LLJ i-C- S A ubiquitous textural feature exhibited by the Wolf River rocks of biotite and alkali feldspar wherever phases are in contact. Configuration of the contact suggests these two at the expense of alkali feldspar, perhaps rethat biotite has grown of intensive variables during or after crystallization, flecting a change in equilibria among alkali feldspar, biotite, with a resultant change and magnetite, as studied experimentally by Wones and Eugster (1965) and Rutherford (1969). fl 'flU li-I) 5i".'i- UUU .xU:UQ :i-j. i-U)21it\J[3L • L---.1ff5 an intimate intergrowth UU[l-i-2 is i-• I -; 4liUi-U 1U)iI t.1Ul :U): U)li-i_ Cri-IlLi[ i-riI iii- :yi- SUU( i- i-i- LUlL. i-i- -TTLi-1 1Y ir&-; 1-i-) U)Uc i-UUU:flU)U2 i-U LI: 1 U'i-i-ti i-i-i-CLkçU):U)J Ui-U)fl[U iur -U ;-tp-; ;1i.U lit I _U))L2 i-i li-U E -CTU cC-fl flfl- i-U- atcLU.I.t- 14 U)ifl'i- UTU:U€ ''L 11 1 - U)li- ii: p-i-t i-i-i-i- i-.7$v- :c p Amphibole. Electron probe determinations were made for ten elements in amphibole from eleven specimens. According to the classification proposed by Leake (1968), most of the amphibole Is a hasting— sitic hornblende, with values of Ca+Na+K ranging from 2.54 to 2.71, Si from 6.33 to 6.50, and lOOxFe/Fe+Mg+Mn from 77.3 to 93.4, calculated on an anhydrous basis of 23 oxygens. In a few samples Si values around 6.6 were obtained, indicating ferroedenitic hornblende, according to Leake's classification. Like biotite, amphibole contains appreciable amounts of halogens. —r;a L.i-U)L iiC4Ui-i- - Ui-. iI[U.i- •_' U) LCi-U1I :—, rt;: Ifl:-I-:r42 i-U) .S. ii.: •1 U a:r U I. 1. U) U)12Ur •qr[U.Ui): i—U Li- U rii- zY2 - T:L4c acITr y - -U)-1 - -U)Uç ç-- i-LU) lifihili-. :JtU) Si- li-Ui U)U)ui.U)i,U 'U IEi.[U:L: cUll—Ut t' .CflU)1r )CI; Ui-1.:.fU fl UITltl CLJçJ U) iiU -IUYUU ri. TU);UUL U)'UiLU)LU- UUrU) 1jiy2t-4- Lii- i-JU) fl-l:v :i- i-•5'j1- Ui- LU atL1i-: :2.U)ILL LtYL u1it-* U)c:cUiLUU)JU) U4UkOL1 T LcL i3t nr; For comparative purposes the analyses have been plotted in terms of atomic Ca, Fe, and Mg (Fig. 6). Amphibole from the more silica—rich rocks tend to have higher Fe—Mg ratios than that from syenite and mon— zonite. Coexisting amphibole and biotite have similar Fe—Mg ratios, but generally the Fe—Mg ratio in amphibole is slightly higher than that in biotite. :1.: 11 L :_rU -UU)rL I tiIj \_41 — T1- •L;:. 2UCLL1Lt LyU [U( L SL EE U)) i-iIi--: C.U:;Uç. ULU) r; U) 1JQZtU r 21 1tyu2T':u 1i iv- 2 ) 12 çtt:. Ii(:.3U) UT.LUL I [U)UU)IU —e r-.r - cn Ca 20 Fe 80 Mg 0 Ca [U-ti 0 U Composition of amphibole from the Wolf River ct;:- (Symbols listed in Table 1) LU J -[& L {Ct t LY'; k LUT1 u: batholith. 3Tft1: a: PUETt U 6. Ca 20 Fe 50 Mg 30 c I Figure uc Ca 50 Fe 50 Mg flhc �22 41-3'5' The (13] hastingsitic hornblende in Wolf River batholith is closely '57 the 501, ;-,-. 05(17'] i 5751'. similar in chemical composition to ferrohastingsite i'7135145: 7(17:5175 1(3 41.315155555:35. from 55/57 Finnish '4530-5353/ rapakivi 'ç',7./512t*z described :.o'/ Vorma UVL(1."', and 51,551 (1969). 415375513i1 by Simonen 301137 17 'i Olivine, Anhydrous mafic minerals. 1114 '(4-414213 4144 (317(3 clinopyroxene, [0 57(I5'5513.'OU/L I orthopyroxene, 7"/3"55:../'13 /i5775; amphibole, and biotite occur in the Peshtigo 10415117513 sos 7 '5411' (151354- '13(7 .511(1, :4135(07 monzonite 4'55 trachyandesite, 57,03 (I': and 3/15113/3 and where generally surrounded pyroxene amphibole, .3775504 olivine ':7753 51/I is 04', 5(15% .5' .13/ -'13557/415,0 by 3041375 or 35111 (1't5( hiIS 21: Electron probe analyses have only been completed pyroxene, by amphibole. 0 ci:5/43(l'(; : 75/453-[5' 345-51. 3173 13221/ 53:2.3 441310 13553 (15(0' 13'(1.53 Fa for olivine one specimen, yielding an iron—rich composition 5413 L( from 115(11 01/101, 5 T31—5(1' 5 of ,,5( L'•lk'L21• 1321:ss However, it is evident from optical properties that olivine 92.2 toi1, 92.8. 'V '27' -7. 7.30751 (17 4(s-t 'IrlO,37 4101'S/D 130410 57 iron—rich from and pyroxenes as well, will prove to be 3:/3( 'sojs-ss.17: •/k•[ other 354:.': specimens, sssur.. 57trs #n 5:3 3 (1170, '241. 545(5(1.14 when analyzed 114(1' by '5717051 probe. 5 :32 electron 4'7''," ''/51, s C 17(3 '1 '2 3 C Similar olivine from green and gray varieties of Finnish 55157:414, iron—rich 5C4(11--'13t1[l53k :(11[/ 35 (15[ 5041's 1551312155 4(2.4151(1: 41 353544 rapakivi have Simonen 513 -(1553 been 1/5(41 described S1531E (1961). 414155555' by 1 416' :3.4 s The Wolf by Alkali feldspar. 441 4 River 55541. batholith ('55557 is characterized "413 1.5J:5 çsrxs13 41 1::T-1;:4; perthitic hypersolvus S and [:5113 quartz 55 which pink, 5ft/1(A554 granite (:1113 54541 monzonite, (I5,ic3/13.s in 21c:2 3/515 of perthitic alkali feldspar predominant mineral. A variety 41 5L-/k 35 is 47 the s-s :/:4513cc5C513r-1'. js:its13ci .2- LI #;T13L' patch as textures are including sss exhibited, 2147TI41 vein, and 41 tssis:21 perthites, 415 film, qLCS2 433541 i?t1 In general, alkali feldspar in granite well 7113(1 as 41 combinations 31535 51:13 55i 5/I of 13 these. 55557 1755 :/) contains larger amounts of extensively 313125 5'11133 a331431 L4/I(V 5'. perthite and 413 more i:/133 '3515 fl5.(1çi5 developed 5:4.: 553I grid r.'t:.21 twinning does alkali feldspar monzonite. 15134141 5(541135/4 35 quartz 13t41' in /i71i21T/5I than /415.13(14 311r:riy'(AL -5 513- ' ',s5. - - '13 21 i-tI— L from only To date, feldspar ''1-l21 alkali 41 'L5 /113 has 13131 been 54135 examined 41 detail 414335 13, ttXS/ 135531(5 in Hager feldspar four units, including Belongia granite, Hager rhyolite, — 141 " 'F study of porphyry, and River granite :. 45 Wolf V s:s X-ray "2112141/ 11r/' s-41s.41 and quartz 1v-: 141:15 s• sJszC2 monzonite. and Stewart nine specimens, utilizing the method described by Wright J —1 (IL _5 4 1155. 53 feldspar (1968), reveals that the host portion of peithitic alkali 41(1 41- 21 C5oiLL 53 Th7 st;-(:yssC 51415 312fl 5' in 314 these 13241 units 53P1 consists 51551335 of 27 maximum i55(7'15( microcline AYA11321 5c with 4>:• compositions ofr Or 99 22 to that yielded values of Or 95 and (1 100, ... except for (13/ two 5:/k specimens 443 97. 7 (155(215 71!3 t35735 s21 13' T35V3..•; s' — 13 i5/ 1 '1 t 11 I tt5tft5 21 . 2© samples and Perthitic 3•-. 54.55 alkali:- feldspar 12 -S1i; was hand picked L,. 5(3 four 5Tht%t TiAS Tu5 sA:cTs from for K, Na, analyzed by means of atomic absorption spectrophotometer : "55 ;5 The and Ca. -m bulk compositions of s perthite obtained lfl this fashion are -pITASISS in Or 83, 77, 76, and 72 (Fig. 7). 3Vi 0/ 54 :t32'}3 444J ?.:1;4 sits . f4; tt5554 ir . Orthoclase, and feldspar with intermediate /55k Y (:tV alkali 212,713 2T5 A7(5751L2. microcline, rapakivi (Vorma, structural states have been described from Finnish 0' 21 3.1C355/ i12121:'.:: VJUSC::..; from the Wolf River 1971), but has not Vt 1 557 yet ILAA4 1$ 15 i55J orthoclase 55 been V353(A identified However, alkali feldspar from batholith. &_,. only the more silica—rich 1[T JV•% °5JL5 lithologic units has been date, and orthoclase, :35 2154. jtes•. examined .rr((!;:p to (1:1. ic çi5 if present, would probably ::2 occur in C7 units 55 the 51; Waupaca quartz monzonite SCCCL such as 21 (wiborgite) and Peshtigo monzonite (tirilite). (V c1n/k1fl:ri t11 Li 3i.A3 L 21. s /lIAA'( 5T.ZLk Plagioclase in Plagioclase. 57 the •54 batholith 1 is relatively sodic, ,5 .y.T:5-% i:s7fl:21 ranging in composition from sodic andesine to £. albite (Table 4), 4.5 r:iç Li as 215 Within each determined by universal stage measurements. L lithologic Iw1 i1 composition on the order of unit T 4•'r::; is a3 variation tWt.:-J/kc, in plagioclase ;irv' there L2uiytL and phenocrysts are consistently more calcic anorthite, 5 to 15 mol % 2 COAC cicvJr. Act21 Slight normal zoning of phenocrysts than 1/k associated matrix grains. :.2Tzoning has2'Ttcti7 only occurs in allr units, but rL4 oscillatory 21t :L o[1t been observed in the Red River porphyritic quartz monzonite. ;:V"CW1 — I fl ncrla t ci qiz'i I L L Cz lA: irç �' ti iTii11Zi.L7ci zoned iiii ;;:c)jirc1i4 Li -LnLzr4 '[:J4ciiLLN cores. roundedzUriU enclosing overgrowths subhedral o-c to euhedral of 1c1;rtJ 11 'I'7 consisting malacon the is Zircon 1940), others, and (Tyler, variety iiff. cJ.1Ir-çci7iJ2. ' Yi'TTTLiC also I,ccI3 is ix mineral, accessory granites. rapakivi Finnish the in common btWci 'V :VtFTi. J&cj L©Lithe c€ij in Ti tions ubiquitous most the Lqc Fluorite, batholith. River Wolf cr,'-j are I TV'' ILt apatite, rutile, iT combinavarious in present sphene and allanite, i:iiTitT? magnetite, zircon,'t Fluorite, minerals. Accessory ILL I' I I - iriti1-:T TitIt •TV. - cIs'.iii 3n'ri • ilmenite, • ijh .crc:ii ij'f - • - • i' iY'TiC4ii, rapakivi LT 21ii 7..L. texture. of development i:-- LCDi iic L L'i Li may plagioclase flCtt1('7 the in role a •:iic play by feldspar alkali replacement of ti mantles of growth IL" IT pin 1ti1Cli1 c2 TSU.L yi'2 related genetically are ii that and and perthite [i -c&L:ii2-uc ic;Tj. 'i2 rLcI':PL 1 'ir.:Iic:2 that suggests observation patch of formation This plagioclase. •1Ti with continuous rjii i niair:i: tiCi r'1ii2c mantle the to similar compositionally and optically it •2i'q!cLTL 7 •nplagioclase situation this In feldspar. is perthite 1'i1I,l1i parch the in i'1iiJC •"TitTJLi P 'L1TDDL alkali mantled of core the within occurs commonly perthitebT'LIL',i Patch • Ti•c'i ic'iitIii i-i? £L. 4L i-i' "'- --- ct--irp. I :C' iiii i:pci ciit tI'I Lint L'f:CT that Lt—ic specimen. 1.7: 115d1I2iIi in fr-iiL2LL'-I phenocrysts iTiz;i'TL:c plagioclase the of part sodic most the to corresponds 9-iii77 specimen J-'iHT77,tt .97'i'27 any L:' in YM7-composition iPtitiTci' 79a has TiTit7';iri7ii that plagioclase mantle individual 'I17? tT2TT c-cLLT1Ci t2ciiTL i: 17(7 979 ii fliclIiI but Furthermore, quartz Waupaca in 23 An about (wiborgite). monzonite t2777 in ri 7XL17Xf7I -PCi 7'a has .T 9 An TIL( plagioclase ri Ci' Li' Li granite, Belongia the about ofii 1iC7tJ.t7 composition p174.9 exaniple, 'i Lc17?kFor unit. that yn-. ; '1i ULi 7-1bulk :T1 the 7C1LJC. mantle of i-:pt chemistry reflects clase IL:lJ: " ";(? lithologic c;S14c:7 ''7'1799c117 'i2 a Within l7t' IL IcLY'9LL477C the 'i given plagio— mantle of9 composition unit 9'i:L'L79''7iT 217 1717'Y it2iT:. /7 ETi13 774 TCi ' Table in listed (Symbols y-j(;9L 1);c ?1i1 i' p17Li1' C" granite porphyry. feldspar Hager and i17Ot7 WC79 4C)Composition UiTiIi'LiL4C'9 the from nPcDtej feldspar of BelongiaiL', 14 — Or -' • 'c • • •: - Figure 1. ' • Ab 23 �24 Table plagioclase from the Composition Coepoiition otofpi.agiocJ aee .Cooii the 1$ Wolf River Rrvoo batholith • -. iThcC ielc:oi.r P°l°WW i .-—-• = =_ - - - j E.oiIetdt9 3e-J.oo1oI1&. - =--•=-r••••= — — T:T'.l = .LdOt}cJ P•:loer ra,mto 1uoI1. çrot?1 IrDroo.,Io = - jFzt_ttJfl 1j Ij = = I L 0 10 30 20 )ThL rnol % •R•:riT. i±oro ?orpIh..vrLh14 Or:tIThflTO 40 Anorthite or larto graln tetrtt gfl1O Phenocrysts -oiemoero1:e or large grains Matrix grains 4 �:33114 .191' 1. 113113 :1,1c:,tL.:1111 111 131114 773.1-31 31 2.21437, 33J, 'in 1171' 1313;.: 13..$1133.9: cI7111.4, '1471 :141147.313351 155 u7--T17 71 311- 131 c31311414;lc 053.1721173:33'.- -17- 147112.3:14 1111111 14.137- :1133371317-7-353,3 2. A foliated, gradational zone about six inches thick occurs between the Hager rhyolite and feldspar porphyry. The feldspar porphyry is believed to represent a border phase of the rhyolite. 3. Dikes of Red River porphyritic quartz monzonite intrude the Wolf River quartz monzinite at several localities along the Wolf River. 4. The contact between the Wolf River quartz monzonite and Belongia granite is inferred to be gradational, because of the change in lithologic and mineralogic character displayed by the Wolf River quartz monzonite in proximity to the Belongia granite, as summarized previously. :0:3f3 32373 7 4113: tT21 2141.1211111 '11 1T1113-;'l: 31,li%1'JC5 13314 ff: 7-111 14331 1114'. :., 11 2313111 2:ThtrvlIl21l; 111 1 14117- 2111 07 111413-21141113 13 12211-171i1 3111L%;.21141 17','1131113 721 1111137-117227. 3.311112113 121 11::7c3311::6:ar T21-1313 313.1 0111L'0'2 14l,11131113 11 7-121 Ilt.131 l 41 ,L I: 121.31 :1t7 14:1' '131151: 4'15l9 11-31 14 ::14'.13721.: 1314 in 3;. 7-2212-1733 13,cll':i111 .-cin7- 72133111; :1911113313 1:11-7-3111 1117- -Lin- 71 7-' 1T. 31(4 3117 5.3113-1433) 132-143,1131 311-11L'71 111? 2'l '11 17-215313; T143T1: 12111111:1,124 '1: 7-14. 27-' :1:.%331323 cIt 3147-115 1414-l31lj 31 7121114141321 CC 1114 -lt*3(313;147 114:;:;t11. I,11& 247 c-23'7-L .317-371 23-4 1313 :312351 71.11 114.11143715 çç7-1 1:131733: 133 24 11-131:1:17- Peshtigo monzonite and trachyandesite have been intruded by dikes of Belongia granite at High Falls reservoir on the Peshtigo River and on the Oconto River near Mountain. cr;: 17 213:. 17137- -c112.711"1:lI 311; 1-::1:1113:14 :1:17-: Internal contacts of the batholith. Contacts between different lithologic units within the batholith have been found so far in only a few places, with the following relations: 514 1211 3-13371 511 22.21 31 '3111-114:; 113113 4112:-) '111111T747-'1117 .C:i'1V731141 3114, 1-33-13.2131157-211 211133.71131 ii' ,l 31 1 71:4 14:3:7-11: 3)11311 14Ll21:21: 11 7 -1:1451:3 p111c314Ii !114 '7-33l4C-247-- .tl2A1%_1l:1111434,331:r:. The second feature of importance is found at the northeastern end of the batholith, where the Belongia granite, Hager rhyolite, Hager feldspar porphyry, and Peshtigo monzonite are arranged in an arcuate pattern, perhaps reflecting their emplacement in a ring complex. Such an interpretation is supported by the distinctly por— phyritic textures and high—level characteristics of the lithologic units involved. In addition, metasedimentary rocks that occur in the postulated ring complex dip steeply and have strikes that are concordant to the arcuate arrangement of the enclosing igneous rocks. (Ring structures occurring in rocks of similar age occur in the Wausau area, N LaBerge and-Myers, this guidebook.) - _ 1 3311 5 133 2111c 21.7-. 11 1-c.31C0 p213 1147311.3111 1111. 113157-' s. inii 21 7:33 111411. 1141111 2*:2i7-.11r1437 3;3133311.1'311'3 '131111211 141,1233 : 31-7 117;:tl%-:33 43173 :21 2. 33143:' 33114111214-1' 25137.133' 2331 'Cl,clL1: y11c1T1.#c51rb-:1 721- 43-'11'': :7-: 'r :11:1211: .;-2111'13133:1331a1 112-: 11-33112i 1414 3; 11 1:.t1;14%112'J 111:31521 1(7-,.73,1117 C1413% 77- ''11:1113,3131n 1121 73 :11: 33:; L3 ..1'33'&43 7- 6314331' 7-913 21331341311,. 91432142 0-7110 .13:-i31 11:c:7115141131 J1414-7-33 112 1731; ' 3111111117-.: '11 'cii 41'1u1421'cIci1s ' 13,3373.213 1111:321:14 4 S'1:1:31: 7-311 1111-c',3$:13 41'l : r1r1n713:cj2.21z1131o 7'f"'l31r: 13; 7141311 3 73,212113 :3:-' -311111 17124:1114 l 1414113112; 127 1r::11)31,2, .3131') : 13 31; 7321114 173214 411333 114733,1314 1'.71- 17 13C.:'1-11 34 221111.11; 3737-1117213 214 2-1314 41731:12 141 1314.427- 1131131537 7133!.'131 2113111)511 14441111131414 :7-11:1:; 3123', .111723113 433'1J1!L33: 111 31,7 ,C17111'3. '77-4-141 ,141.31413', 121 321'1'137- 54111117111 ':3117-rI-Ic' 11417 137-3111111 1131:'113;1114 1214 7-3133141113317 1:1s:'t 113211 1': 1 14172 .71:13117 7-1151 . '313j% a.T13121' 1'373 212 14111311111 P*1 '$131111414 tIlt II, in 1131,k'117t I 1u211317-133'7-,L3 31"7 4;,311.ff.1'3;L :47- 7; 1131 _12412111 14-14L311 -371i3121 37 :-'lljl 41i3 331347 4131175'7"l37 4." 1111I1,.1 132113 '11413233231 322 33,13 11.11" Although structural studies of the batholith are still in progress, In two major features are readily apparent from the map (Fig. 1). the south—central portion of the batholith, the distribution of the Waupaca, Red River, and Wolf River quartz monzonites defines a major ENE trend that was previously recognized on a more local scale by Borst (1958). The contact between gneiss and Waupaca quartz monzonite probably represents the southern margin of the batholith. 1 .144:15111-53111. 1,c3::. ::( ::' sIll -12 _'&11 14 3-31 14117 14 2311 c—, ,&31 '17 r 113147- '1 1 " '113 1 '77 i11'5L147. 1121lC7-.'1,11-'331"t' 3313,' lf%-:rl,©1r, ; ,' 7-24221-2 .51411 3;':' Many of the granitic rocks in the batholith are Structure. massive, but within some units, in dikes, and near contacts, feldspar phcnocrysts may have a planar or linear orientation, presumably due Shearing is confined to well defined zones along to magmatic flow. Some of this the eastern and western borders of the batholith. emplacement of shearing may be related to the batholith, but some may be later than, and unrelated to, emplacement of the batholith (LaBerge, field trip locality 8, this guidebook). 11t13217-1374137 14;1 312-23:135333 '31,17-3r;37; '437 111'7, 'F;.,;, 314:213313 321: t'%'7-711117- "11 5151113 .14213 1331 73121713 31111-7 'c'- :113tT,) —$ LH11.34 3312 13312 37147314113 15:31 5:721-41411137 13 111 :12375 742 14 -32: . 31143 '.1311111": 11 31:111131*31111 07 5114.11113.lI113111414J21 33111 31r12115 :14:;; 7114 3111343 1.11.1 117,1 .1 r33.1.1t...23 31:; 2.112%:. 133' 12Cr,: 53' 31213,.: 32311 111 141:3191111I:111 11111111 44 11117-1137114 21' 11)51711 7-7137131:11111. 111.323-1 ''i'11 113,:53.3111:'.. 3313 -33-14;: 174311114' 111113 14 7,141:c7, 711'433311 '3' .7. :1:131116 L111'T131411-31 '?l51i'11l1114'3.in1 c.:1c1:, 14113111,231: 3113113 - 11317-17-1 .3:1: '1:1 31141s317'll 7 '1541113 14411 111 STRUCTURE AND CONTACT RELATIONS OF THE BATI-{OLITH 711,71 17, :7-171.1 1113 31747-11111737- ,1741 '077 3J1 l31tTl'7- III1I 111 37: 25 cia �26 ocarI o 070t2 of Lt bab- J! tio m::rL1.i,et: pt of In the northeastern part of External contacts of the batholith. ::.c Lcowl a the Belongia coo ac:0 a±cr•t several well exposed contacts where tioa :ttJ 0 .00 afoot a are the there 0 t batholith tLtkLc. U1t- tLOtOO.OtX0000 metasedimen—OO0 09L2 2'; and 0 LU0Z ptoP 7200 intrude metavolcanic granite and porphyry coo Hager feldspar to 2 1o!flal;1; act ri):-' sharp and discordant, and In all cases the contacts are tary rocks. 000t'0'0000 present in the intrusive rocks. ot oc3anCc1o chilled oar0ta margins are commonly 7t000ff't cotlttO : 0.11 oa iJ : fl :ia fotrof ca rco 010.0 00. the assemblages, much of &c 0 L'0rl0 WOO, basis0± oftEa000Ot textures and mineral 'o1.00o ocoka cat ha intrusion of the granitic rocks can be CO tjo ft rW 'rI 'o tooof bya contact metamorphism induced o-c,tatt totorcoçO :'f too iftiacotacy However, the discovery of 012:01 footca -. facies. fob :01-i hornblende WC coolo ltoot',i: assigned hornfelS to' the f000ti to ;a.bcLOt00 201 1.0=2010001 cto -oct o assemblage, quartz_biOtite_mUsC0vitePota5 .bbo co01t1 the lcTos;'WOtlf apparently stable tOo 0001 ;:ota2Jat410'L;;,0 rock pelitic a; specimen 01 aco'onof of ;a L 0200 metasedimentary feldspar_afldalUsite, in a folIo-pat •cLJ oootC La 0010 01W-. have been the pyroxene hornfels facies may of flo ooo.u;002sO 010it:0' .co-.oo O07 suggestsfathat conditions 0.77010 foot .o.o'01It f.o:a of roT at 07007 r:.;r Ic tO-a •ocoi'Occ 0 in the contact Scapolite to ,:cf: :; 01 is relatively abundant f cro]'L. attained 01. locally. 7114 i-ccbatholith. Ltfocf ttI; 2W the 0:; I.:oo'000,1%010102W:;at:tr-0 of metamorphic rocks,21012W attesting the halogen—rich nature t tCC00, a-ac to 0.0010: On the fiLo Co 1 2 CONCLUS IONS of cotta cot 0 oafaIltat000 been fo to point out1;the existence of toot oat till paper The7';.i purpose of this has Loot 7t ct 00201t0 tic and to describe its Woo: '0.0 zn:1 northeastern :02LI10Lmassif 701 :.:Lincart OFt4 01W- WisconSin , a major rapakivi c ;aojo-r 2W Ot 001711 o01o-7rI o in It seems appropriate, 101 characteristics. crcrcI.o?tZ ;-ofmineralOgic iLt 000ta.0200 petrologic and ffn batho— hypothesis for the origin of this 100 fLo 001 Carl of r2.cifaC-0'± i-- offer -141401NJ 01' conclusion, to o±'tr- aa working :1cn.cl aol ct: frfuture 2Woo studies. c';tai i to, direction of too-loot tO 0712W too tOo lith and to outline the blob Ci I must talCi take 7 r7' t-atLo'I I ;t coot of 0017 the Wolf batholith of 'oi.I River too- scheme 14-iY01W; Oc 0origin cot: Any forIcrthe features: 11170 'cc LC11/ into accounttOo the toOl following !. 1) 1) 2) bulk c.: of 'L 7-Abc constitute the 01,1 granite f 010Ci1 0010 05t:: 1 ocota 11' 1200-00 ,0 and hypersolvUS monzonite oct quartz the batholith, in0027102W nature, 7. c!'ZCP-IL ot 10 epizonal the batholith is io :oo,1vobtti; a'•ooa tOO batholith the tOo ta:Tho) ' oft plot itt-ct near ;!!rto. of oti the granitiC members otOfl7t a,:ft A the compositions of 00000 displaced 01 normative . 4:Q—Ab--Or, =001o1- but tot toO are Ic, terms too: a of granite minimum in t-a;ott•o o!oLo!L!lilr .0,0020 7-c toward Or, :0111 0 t'ob-t7fli feldspar by cI' alkali andratreplacement to 002202 of fcc::- to is -cct0'-011. 25- 012 c;,00c of. there extensive mantling 'P.', oligoclase, aflbote to -clILIfot 000. composition from albite to It ooocol01050I0 plagioclase 017,01200 ranging in respect 02W010t oa_with :2 -7; talc o:t to to be interstitial :ik.ill020 00010)100hydrous tend to co 001010012 mafic 177,t-tc minerals IL! quartz and feldspar, and on fo1tIo0Y 007012003 of Ltz:0 biotite ;' I cthe expense O1717'AP growth noCiCi -A .11 at Oil act.a:0101 apparent late-stage there Ut:---: is to rn-i of alkali OOILO17LIO feldspar. oil. ' 3) 4) -fl ,fl 5) P 6) t'rocoriginated from laothcJ,Of:2 may coo hoc: Wolf?:t River havecooL1oL0-lC1 or '7c'o cOt batholith ±00 oogo.ot that tcti'f the We suggest H20, initially undersaturated with :n çMtc ct0.0 0-C parent jJOi'tct magma, 01101 monzonitiC a 0 pquartz taboO 0 crustal material. .1700,12170 700=-0 i.atcaig 0117-octalpartial melting of00pre_existiflg -70l derived :'AOSd 00 .21t that was by J0L'."I1OLJ. batholith precludes I (87Sr/86Sr)0 in the 01 1002 An average of 0.705 for 0100 value Cii origin 00 000 1 0 i20tat.i 1410 with an crust but is compatible lOt :lcI1tlt 5 01, from focat older r hO 70 lOiittl,C 0' derivation granitiC ott: 50.071012 :':-OcOJOi volcanic and plutonic * atatmood° basic 0701 and intermediate lifor: .Ci,O.t!: (10 0001-0 )77 older from an terrain of 01001 --i't For example, partial Nil' eo0J-c. ±:folotllIfl. northeastern Wisconsin. 110010. 00aa in It ;1.Ot000000717'O material, as09that :oat01. 01 such 1090071 101140 (mean 020-0 granite or :7'10!L0t) Hoskin Lake 2,tLhc,000170Lc co,ast-zmonzonite 0110 -01 10 01 melting of Athelstane quartz trIo IJI cci. LII). years 141110 ,, million rIit a c:oA 10, (87Sr/SGSr)0, 0.7021) after a period of 350 , ,01" 0 Rb/Sr, 2.5; 55, ftC. ratio of 'OtCf.r 001701 of 0.714. strontium 01!.initial tot I 01 0,0-otti .710 isotope :11 07 an would produce aa :7112 rock with nIl 7 pt-cl'017' oh-ct oortaltt an abunMo northeastern 'ocotfcae$°' Wisconsin!, contains c'ao-::aiia in 'to: terrain However, the toto older fb-o'o-000T1, chemically equivalent oI-::amtsooi :01701 17th. intermediate volcanic rocks and dance of -c-I basic La boo tocO.0'lr0k'5.CL000 0100- tcfit material would 01015 tx'IlCta 00-0 'i'col .1 be of :2W,'o Rb/Sr for b-c this crustal 0101values 01200 os: plutonic rocks, 01010 00 and o'tcro f and Ot!0OI0 others, 1970). 01171 ETC.Oc 01C'I I Hart, and 1967; c.'.'21020: 00.11 others, ACt-0 17fl0fl 'jless :C than tOol 2.5t (Peterman, OIL: 77 much irtta2.Hy oa1t1J.'i toat I'll 3 ,i I I - 1702, �27 i the mean value of Rb/Sr were 0.6 or less in such crustal material, partial fusion after a period of 350 million years would yield a rock with an initial strontium isotope ratio like that in the Wolf River j .4c. icc I[ L1 ctr ccl I L-tn ic IL cc1 I N L. I cc' Ii Il') ci I 1111 1 1y '' cccc flycSc r cccc 1 I batholith. c" Lh1 If nYc cc. Future investigation of the Wolf River batholith will include: 'LCcIP.2Fc c1cS1cc ccc O©_LJ1L=iccc cic7IccnLIr -r9 F) Wc1. ccZcc4cc additional mineralogical studies that should enable us to evaluate intensive parameters, such as T, Total' H20 O2 TNcEcicccTcpcc lI -- 1j In cc1 F, and tc.n-iccFcIcL-cc and detailed chemical studies of major, minor, and trace element contents in the batholith that should provide constraints on the mode of origin of this rapakivi massif. ;cci;c;iT1zi yi iic -c *cLcr cccL-- ccjl cYtc icicc cci cIcccc1 ccc i:q,: cc 4iJfliL 1ELI c'7qI' cP4©IF: cj j:-crc2 Lc1cLc 2) Lptccc 1) �28 REFERENCES of Big Falls, ':-pc:c9.c. cC W7 Ccl 2424.1958, 12 The Granites Borst, R.I., !lm/.c,,2 9.7 4Wisconsin, •lcLc Madison. Univ. Wisconsin: 12,2. Thesis, M.S. :) 24. Wisconsin: 21cm granites of from the :2 c14c4w' -cm-22 ".2. ir242c2 Elders, \V.A., 1968, Mantled feldapars 24 .c 11 cmLc:::: 2-i 37—49. 2c2- V.- 76, p. Jour. Geol., -. ,1'.c-citccPtIL'$ of :4 perthite, p. 55—70 in c-:L. :24cc.) 7: significance 12.4. 1953, Petrogenic 2iCi] R.M., Gates, cl plagioclase: c.cm42'cHcrelationships re ccm2L. cc-; of 2c1.cc:i[ ppetrogenic .241-; Selected :r-nLcmcm (ed.) R.C. Emmons 20... ?9'2l 52. dC :ciirr0 Mem. Geol. Soc. Ccc Amer. - "• dL'AElectron .c,2:t.c', 2;; -cd: ij,ctc-: using the ,E-cm-L analysis J.F., iccmcmr.1..cS Qi21968, .24. Rock Gulson, B.L. and Lovering, LJ 2)i27 C2 cm p. 119—122. Geochim. et Cosmochim. Acta, v. 32, >22121:2:" Probe: 2. a volcanic rocks: ccm2cmcmcmcULcrC.'c2Cc:2r 'cct an modern .24'::;4 1970, cl:2- 2:Ancient cm-C. others, Hart, S.R., 52 and Lett., v. 10, p. 17—28. Earti. Plan. Sc trace element model: .:..:j2I:Lt(1y4.'24 .c.:flcwi.!cJ-r >2.7cJ..;1.- c lower I ccc' -2:24 :ccIcm-d AnorthositeS and magmas from the ;'-5. rapakivi, :124. H'C5 Kranck, E.H., 1968, k:'uct2'c72'.9d Rcc..'.:dc:. :244.7 Origin of anorthosite and 7cccmcccc (ed.) '7244 Isachsen crust, p. 93—98 :1:': inY.W. 18. C':--C i24c -l12c Univ. State New York, Mem. 11: cm .fl.,i;; cC :ncy.r:ccd.t: cc:2cc related rocks: and subcalciieroUS ccm:cm 224, .i'cm;:). calciferoUS cc of analyzed cm dcit2I'i cC Leake, B.E.,,lc:2?. 1968, A2. catalog c22;'d, Paper 98. Geol. Soc. Amer., Spec. Ccci, C..c..'t'r-. amphiboles... tR:i - 2. iidc.'\i = Si02 to NaAlSi3O8 — Si02 and KA1S13O8 —.24224 .. 'it> systems Luth, -c,. 1*22). 1969, The ..LniC, W.C., cc betweenc H2O content, p1-120, and Tota1 ' 9 t1' the relationship 20 kb and 267—A, p. 325—341. 12227 ,24'; Amer. Jour. Sci., v. in granitic magmas: '' L ).21-'' .' [ - .-,i-cc'c:cCLcomposition ccm,-:c,24tic'c and ccC >c2cccz chemical relation 241'cL•c:-. between 2-cm Nockolds, S.R., 1947, The Amer. Jour. igneous rocks: !:-244r221 cuiT:1 cI r4dL2lLkiLC2'c :: the biotite micas of '12922 in paragefleSiS c--'. 242,c., 2422, p. 401—420. -. 245, Sci., v. 224 ;u24c, 24':-24,1y Mineral. 12 Mag., cc :2.t7' 'cmiTanalyses: mJ.24cm ccc.crcm'1' c; of granitic rock '2:224 Mesonorms Parsiow, ';y>2-di"- G.R., 1969, 2. 22). 37, p. 262—269. c24-2424 v. . ].'C' >2:19 eugeosynclinal Li some 5::>'>I: -: ratios in ...]:2447', 87Sr/86Sr .2,'2i'9 1967, 2 Peterman, and others, 24±; )i9iy' Z.E., 22::'::magma 24cc dc)". cd bearing on the origin of granitic tac ic Ccc'.: 424 cr24.> and iriS their sedimentary 92CiJ'P3i].2.24 rocks . : 4.21 2; 2, p. 433—439. 2-cm24 Lett., V. '4o ccc' 2-Plan. 24:, Sc 24 rcmicc iCc belts: ':cmtc - Earth in 24. orogenic ., lIlt.". . iron biotite — ,cccmcmc2cmc'7,J1> determination of'>d2 c;2) Rutherford, M.S., 1969, An experimental 2 L, 10, 1:,,.:,. p. 381—408. cccmcmcm.449 Jour. Petrology, V. equilibria: -jC-241feldspar icm±:1;,c'''rhi:lcJ;"' alkali t'r,::24'124 4* 'cr22 its -9L'U'I'.7-1- rapakivi the chemistry of the east Fennoscafldian Cc ±2cc d%2:c!:C'7 24 ?:"'d On Sahama, T.G., 1945, 2424 136, p. 15—67. J1'.2,.'L22d. v. c;c":i Finlande, 24472, comm. ccrcm geol. >; ciC24c: Bull. graniteS 'ill,, .. Savolahti, Icr ci.'::'':l, A., Finlande, , 211'.,L ccl:. 2cm Finland: AhvenistO massif Cc: 24 :c'dtcrd ;ccc 24.' in 1214 The 1956, 114, p. 1—96. v. c 174, from rapakiVi :2cc I'cmc:224;' :7: CL Simonen, A., 1961, Olivine 2-I SN. .26. p. 371—376. v. 196, 2424 Bull. :.c"ir, geol. FcC , comm. ' FcrCHcC22 2411. •c2c,' -. Finlande, Bull. comm. ccc" geol. I �29 I 'J >? c and Vorma, A., 1969, Amphibole and biotite from rapakivi: Bull. comm. geol. Finlande, v. 238, p. 1—28. cL lEE Simorten, A., cL - c C,.71)ClfrTVEE5r 07 11) 1 ¶-c,c5 cwLc3 rTr. 1971, Alkali feldspars of the Wiborg rapakivi massif in southeastern Finland: Bull. comm. geol. Finlande, v. 246, LC::1).çY.I2., LlCC I)2t:) cdwf:L !J5LLLC7 caE: I II 1—72. 1flL '1): l_I ©ICLL p. cC7I7CCEEE L.tC[tcd5IC Vorma, A., Wones, D.R., and Eugster, H.P., 1965, Stability of biotite: Amer. Mineral., v. 50, experiment, theory, and application: 1228—1272. p. I 7)EEI diTcl.AlJ1l CilCt51)cL CLIEC d•dSl1)LCdi C CcC 1i 1Ih' I &tEEEi;IEEIk'EL I L?1) C? 7 3T57d cdi Wright, T.L.,, and Stewart, D.B., 1968, X—ray and optical study of alkali feldspar: Amer. Mineral., v. 53, p. 38—87. 51) LJiCcst rtld:;ditl 713: lJIlTl-l C 77&;J=d c,C, Cc-r.1: .1 . c1 C .cc c• L7CllC;C.1)liJ :cT df 13f0 �This page intentionally left blank �51'4.i?'71 11113132.33 >'1"" >, LI? 3fl 331 24.141111 •1'1c University of WiSCOflsln—Oshkosh University of Wisconsin—Eu Claire 1,,' '•,•i2.:327'7 324.3 of Geology, of Geology, 4121733123 377.12113131 /:. 13>33- '1 131 111)51 .17%:T :3::: Department Department '3' 23 11411201111: * 23411321113 0311 3313111413 ** Some of these problems are included as stops on this field trip. Tentative interpretations of the geology of some of these areas are presented below. However, we emphasize that the interpretations are based almost entirely on field relations, with little petrographic work, and almost no chemical or isotopic studies. Therefore, the interpretations presented here may be subject to change as additional field and laboratory studies are completed. 12143 3.'- .2'12121 4-1241 'C 111>1 133n2 4. 7151> '51,1> "1341S3 '35" :131312L .1313'' 313 (337113 133: 7,21031332733, 1132 1110102,3 14-271 ' 51-13121. 3.3" >11.14 7. (3.1 132.1711:12::: - 31 1 7.1'53 , :-n), ,'l lilt' 7.323; • 0:3:731143 773773231 37 1131 121371.73311' 7>1,2111(13' 7'1T3 '2./Cit1S''?-). 143:: 34' 117 13371233 4.113134.8 79711313 2111174-2 71 rI' 13 37.: 17713171:51 "1' 7:13 73151317135 '-1%. '1212.. 11321273. 7121273372 >' 322' 3-33.212 '3 4-'341'21j11'SL. 1211) '.591'11)732 ' 3174 '21133512121 31317 132fl33"23411 51.;'171h1.'34., 3212 172711o,21) 71217"4L ,s7 '3-13310 111111 327733127 11 42'lll32l3i'1167, .1711 "377. '31.33) '717.21: (.1%413I'711 '4 1711 '..'11,.311% 3131111 117.5 '1512117 3714; (33131'3 ',1414 133732131 41<73:; 31'31,'4313'< '251" i>7.1L71j11 16.11377 7.141 -4-1', 73314 7.721 1130 451:111.1 "11132 41211171 In 1969 the W.G.N.H.S. initiated a program of regional mapping of Approxithe Precambrian in Marathon County at a scale of 1:24,000. mately twelve minute quadrangles (about half of Marathon County) have been mapped to date. Progress reports and data maps of this work have been placed on open file by the Survey (LaBerge 1969, 1971, This field work has provided much new LaBerge and Myers 1972, 1973). data and has identified a number of problems in the area. >3>31323 1)723, 2)23)2.. 1:0 115153 1131371 '(13212273 33273312,1251 310 .33,3113,317323 732cc1J:'.': .51 i351"7',4'3) (1)" "'7.223 7 4-lfl 1'- 3, '<7121334 71,,.33131,:i 5x31%''15557f 711 333f32733<j33'17 E:3211112 :'1., '771)3312 135133175::Y 1121's17'13737(1 3122 1111:17.2, 17351772,,I713 7>7313 ;r 13 11313 77111,) 1113 '1113 33 '33251 m3 '31. ' 4i)027211Yi 1131331 2 7:73 ,i( C'23312 7 ln%2511'12':1'17. ("32. [: 1) (6<3,7 313211)33711712713' 1131 1211)7 The only comprehensive account of the regional geology of north central Wisconsin, including Marathon County was published by Weidman He recognized many of the major aspects of the geology, although (1907). his work was mainly reconnaissance in nature. The geology of the Wausau—Wisconsin Rapids area was examined in 1917 to 1921 as part of a land classification survey of the Wisconsin Geological and Natural History Survey (W.G.N.H.S.). These data are on file in Madison. An unpublished W.G.N.H.S. report by Enunons and Snyder (1944), and geo— physical studies by Vickers (1956), Allingham and Bates (1961) and Henderson, Tyson, and Page (1963) cover parts of Marathon County. Selected aspects of the geology in cntral Wisconsin were presented as the topics for field trips by Emmons (1953), LaBerge and Weis (1968) Theses prepared at the 13W—Madison and and Weis and LaBerge (1969). at 13W—Milwaukee have also dealt with certain aspects of the geology. Recent cooperative work by the U.S.G.S. and the W.G.N.H.S. to compile the geological and geophysical data on the Precambrian of Wisconsin was published by Dutton and Bradley (1970), and Dutton (1971) showed some volcanic—sedimentary belts and sulfide occurrences in Wisconsin. 1', :133211211132 112111517112 113 '.•4.l1[' 32714711' '1 .,acl '2313 13'l 31, 342123271 1P "7111L'311'1:31 "32cl. '.3 172.74 :71321) 1: 2:1"47'±5 117711 7 42t513° :1131 1.2 :' 34113: '1, 51'13'31, 71'3, L .1-141 37712 71')> 21,34',13" 713::, 31331773i '4, C 'o337- 1') i>321 2)21-' 1 74513311127 1y: 13111 >151 51:313 1 13144- ''23173.3.111711.7< 3323,131< '4 42 33123 132318 14,7: '331'3',3113'l1 4151':,1231'43.1113. ''17'4514' 13. 117.11011932 3322313104.33, ,3,,7734j(',7 Los.113.'7 .33:3371;3'3331$2371 321T :i,33,431$ .3. 3. 12:1:'. 7331131 p 1)3)3' 131>713 '33 1-'<' :1333 '213 .1)11' 77: '17.311>1): 3('312327'4 i1T' 3112111125 773 :4183 771'? 111232 233133 171.7 ±1:4 1 '4143231 14.3131 .127L1 '14 .31733'125 '71:7141s1323232 7'42113133rlhc4 23313 '3$(-' 1113231151 £311. 02'' 4.: :4. 32114$: 2.13: "L74r::r:cc'l.slIl,.''t 1.1'111'132 7)47 23113' 132 113 71132 51'1'7';,3315 >74 313332 17' '32132' 31111.7 13I1,.:''",15111123.± :I7s11c'1'E: 4)13, 3>4733 J' .1 6"3321325'4 3213'I'3(3 32'51: '133711 12.2"11 821.534 ,-,3211,11111,J ,31.•3'3314 9.1$: 711 317321313.331 3)5 I332'.13'I3lfl 2'31; 3113:3 1333 '"'1 ,,311LI1 I ';Q'33 32333213' ''1jI1It 332 71(3' 'i';,,'4 113 ';73 11:1513123 ' 13 .32 '.'7:2s37 1)1:3'l7',1$.771: —733 13.3 13'T3'1121,$ • 1$ 13713311171'323g331'l'4611517 311 '1±SLII4LI$21 14 3711.11137:32' .1370133 32:11472132 3'113 11313733. 372 .J32Jc '3312±" 3.32 - 4732313:13 1 S'co':r31i 37332 117 3'.L.127% $31351111 3'43: 41 32i"'., 4.1313711130)1.73 (13 733111111'3'3 '"tI 2'332.'71'.'l'L '%:3'"8 '1.11/' 3:313321131741 1) ,'.',119L'73113'314 117121 '1C".3333 1.1: 13" 11113(1119 33:7 ill 37) £':: 71 -- 4131:3.4-753. <10724. 121, i21231272s'1l :121::7'::c.13. "3 3273113,,7$'37 3241132 321111 '7'>(4 3013311.11 .n-62:o'c:vp' 1331-li The Wisconsin River Valley in central Wisconsin constitutes the southernmost extent of the continuously exposed Canadian Shield. Available radiometric ages indicate that these rocks are mainly of late Middle Precambrian age (Dutton and Bradley, 1970, and Van Schmus, this guidebook), yet the character of these rocks, their relationship to one another and to Precambrian rocks of other parts of the Lake Superior region has been largely unknown. '1J',,'1)7"1:3710: 52611 7:114 337 13'l 717 122(4' 33721111117174)3 311331 '333. '11112 43 14131:13 32i41712u3 72"< 327' 1:'1T4717 )'711',, 1:13111532-3334 :21230232 3111 24 323234 733') 341121- 31(30 3: 1377771.33 3312';'3' 33' 13 .l1121113321247 (1-2'$. 421-st ' :.11:%1s143113111"13 'I 134: '17131' '1331 31711) 11713111232; —>321) 31117343)12(11.2.32 11 1[11'7'; '.'4 .311121 '172321: 71313, 21151"'37I111 '131"" 7'3,<'.':2311)1:1)1323 '1" 4 '14.12/271 - 32307221' 3(33'7'251"% 2'3(32331113131151111 7721'; 4"112Th'7t 311434' 41' 11' 31'1773'34. 134227:7-1331 7>7133':14'44-,c13t113 '11214 137 3 ".7122313 '2'1'11171'211oT1371'1 32'51';5 :713111311:4131 13?:,.:, '74.33 7)1: 311,3 INTRODUCT I ON 513121331.111 Ill' Gene LaBerge* and Paul E. Myers** [7.123 7,324.211311723 751'5 11711' by 341321" PRECAMBRIAN GEOLOGY OF MARATHON COUNTY 131131'.41, M7113.;31i11'.13..'131,1 711 31 �32 General Geology .ici:' dfl!, River ifl Wolf 'fl'Y granite Q the ci;ii 'Cciatflt TLcci The Wausau region in Marathon County west of ciici1 Thi. ci.cc3. and c1 Tbv flcifltThS11%t .;:d kci4 pfl;fl:twccrc batholith is characterized by a.t. northeast—trending patchwork cci of folded hn :•a been flEfla intruded cci: cicii which have flE tc. felsic volcanic block rocks tid (?) maficci. to bjiflcflci faulted Ji ci tI cifltLfl •.c.fl.Ec events. aj:i1 deformational )fii3citfl and :cces]IflTh plutonic and :ccJ1 mylonitized during succeeding 1 iciZflL ci tJh ciciri (1) gabbro— -jC.,::Ycici generalized sequence: :i:flLfl.: The plutonic rocks were intruded in the Tkci p 'o.ci1: Li cy: i t.?'• .iwtc tti•ci i (3) quartz monzonite, flul.LCr .2 anorthosite(?), (2) diorite—quartz diorite, fl 3fl cirtflcj7cilci dia— L- Eci fiLciL by The granite isv cut ENE—trending cci and (5) granite. (4) syenites, 1flflk.3tci CtTL.JH,fl grcinit3 3S ttit; filotci Some granitic intrusions, such as the Granite Heights granite, cic.LIvfl rsTh1 ccie base cijfl.flF dikes. tflL3Lt: OLJLO fci' as indicated JL.t•C3JH•l by the fact that it has .J flfltflflflti ;icttIci b'S evidently predate this1flJ,:flfl-• sequence, t, i'h rcitz ,T-.clcirci.ci:-- plutons werefl t5.s younger :_ cicicicici been in zones along which some of the flflOi. mylonitized rfllLlbi.b .fl-fl1 y'cii- the tcici Granite flOO for O2flb' 0 cicir1i :'u -. Peterman (1970) established a 1600 m.y. age )Ci iflfrrijfl! Pcit•JLLr ficib intruded. Ibiccis TEtiui1'? 91L)3flJf rcitrci Thus, these ages ",cci' i Heights granite, and 1450 m.y. for the Wausau pluton. Ccci mci ci f0nt ton: ci! Some of the plutonic units are citLotorat 0rt , !1acJ ciiat sm are consistent with the field relations. 51'q'ci ::ii: ouiiut' cici.: contaminated and fil C'1.L' i-iltcicij cci cocii-uicibci intru.ve breccias; their contacts tend to be highly ocicot— cifluflt well— 0Th:,alflccontacts, fiCaicitci, abundant, a Strongly discordant cc zcfl:t li-yl: are cic:cic::L:: commonly mylonitized. !i&tfluit..citciflfl d1ci fl' cOcci21 , ta, t 1 ciJL metamorphic aibi- flflici of middle to high grade SflXkCI absence oriented :cEfl ru 1:Jti, and iflThtci' xenoliths, ciplcccii- cucit. icH crlitcc epizonal emplacement. cit 1Cm suggests ci ':ci: cu rafted xenoliths wallrocks except as lower nrccicicixcc: ci LJc e in a broad mylonite NE and ENE—trending shear zones appear to converge !c.flOcii' L'C a! margin to t1'c cci::r.:M ci of the Hogarty hornblende oacacJ i-iL to c:,.i1 parallel zone rc'ar near and the cciatr: western 1i.c.' bci2::JJoib) granite (Wolf River batholith). : ±C 1 'c. a- ciii -ra1- gr:tttc it: ti: !trily C rJC ' 1, flL3. ccc I 7u1] tnni-c'- Rocks L.ciC0 Volcanic i-i-X'1 i'by shear LvCL0.masses, cifliF3 generally separated boiccici2ci rccH4lfl cic cci as large Volcanic rocks occur 03JLi i-ira taaflTciLci ic air iitLl '1 Ti ci. and 'ci accici are basaltic to rhyolitic The rocks Ii-'fl volcanic ' cicici.or fihicirci, 20rci3 and/or zones plutons. nub. ra1c7-iciciLiC. and fragmental ircici- include crc. Ii-ir',pillowed, r:t Iciccic,,massive, ccci TLs The rabta mafic'7Cc: volcanics trachytic. 'ccc. less 1 i-nc. ci' Oi-ILCiLi are 'ticifldii-,. 3fr, volcanics The intermediate ctv.cc cci. iThi-i i-ccitt acicicic 1 i-Oct sediments. unitscat and associated cc ,uI ci'. Ui-i-i-, the "basaltic" varieties. rncty rEutflflTa1t chloritic and cucac more commonly fragmental than fl1 ii'CLbiat ti-cc Lob tuffOs, s, welded cclcioci'.tcifl include :CcLcsC 0 volcanics ;"i-riC cti- 0, felsic The predominantly ,,j, pyroclastic, cici'.J'Ll.fl •iThacc Ttr: nit bbas Eastt of the lJcc':.fl-' tuffs, laharscci,23.cfl'Oitu'fl and associated volcaniclastic sediments. irtilu, 'k,-:rc 3' seg00: ci'fluicilfl the volcanic i-b. cio -atciw ti- contact) in-c western.c batholith 'rC,u nrciu: the Rb."c'ci (nearer Wisconsin - £ciOci'uci 1fi1. River 'r''cflci,fl ciuci-il cdaiciii-cLbycolithologic Li'bt',j ci trends and i-fl '1evidenced chicir,t i-c' ci i-na.. .ti-2 have ments 0 ai-i northeasterly strike as :cMa:cc ''4i Land Ci1,.itOciiacci Classification Maps). Ii. b.- tacit c baciu'FlCtp WL.L1:uC cci on magnetic "lines" township maps (W.G.N.H.S. 1 -? icni:J-i-bc.-:'Ly. No 7i-• 000n'.River northwesterly. 1-4: b1ticO" trend cci'fl'ocJ is more tort: their tI—i- Wisconsin West of the i—cd, bcthe 'to volcanics cC L:i1, Tci'c nabbeen iranrecognized. ;ncntacd, stratigraphic 1Cm base to has yet 1 ci' — - .1' circcitici' a. :1 ''" i' "' '1 'lJrcrS' i-H ofcc1oan:o volcanic rocks 'Ca-ti-r :0the cnscit'tcc:u Hi cict It notycit yettcz:'cic known whether various "blocks" at is a' aoccci-n.ir. once—continuous sequence (a volcanic— :Lci,cccic' cnan.=c0'fl cci-'c. rf are segments of a ic'.adt at i-t represent different 1u000fl.iJciTit&i-Y 'Jr iTciJ to sedimentary "greenstone" belt) or whether they incicluci': occc.md1c'a'ci ni Ccc at work -T,ccic-ttccc"i,5.; c, from ci-'i-ci-' The answer may3-H not',te be forthcoming field i--i-C 0 ci'. "Ce i-fl tt't.ciLc episodes. volcanic ;J'cn'a;rtfi dismembered CLaim.alone. licor.'c: it:, Rocks Plutonic cit plutonic c. (Stop 8) 'P11: The largest mass of •tt-Lcip fl,•' :Hjifluflfl "ti-' flood Li-iCc Cflrcc1.;;ci1 Hogarty Hornblende Granite: i'nCi anCrLitt ciacoorcic acinulaL granite" to which underlies eastern itiaçc: s rccjci'ritiLe:rCc tb.: "Hogarty hornblende rocks cciatn;sci mapped isc the '-cob..': 'r t.o rnir Tigerton u-c•.u ciciZat lucc'ni-mOi-This pluton probably extends eastward to the '21:., a pLat -ci' rCca:.or Marathon Cci;:oty County. 'fltci 'ti-i-cc. to 'Ii'2H.nlcap9 lihologically coLic ccitc.a'' indistinguishable Cc.: act, 'i-r'ci- County, Anorthosite mass in Shawano is cc:a'r ibrc -H :c&at. quartz monzonite (Medaris, M uJ.[b.'mr oiccrba cicrcicin.L:1-r ci ci Wolf River ott the i-i'm ractc.' part oar-b of from the coarser 2 '-cii ticiac:'oj Itti-ccdla. locally intrudes volcanic cub :11001 L:y flTJcLi-0CL14i-? Ortu ci guidebook), and b..' .["fi,, this Anderson, and i-tb Myles, ,.ci Ti-ac :c tati-. 0': cc-l at It is nj,ri-u myionitized along the lc.ni-' Little Eau .mnaafrcErTh o.ircifit In western rocks &Uoucg its margin. cci. along 21L011'c? b.bva: Claire River. icc tn . r' ft cai �icc'!, ci.jcc'cc I', ' [1Li'i "ccc. rc' c LLTh ci' ci, 'i,ccci:.ic.ccC ,iT:' Diorite, quartz diorite, and quartz monzonite intricately intrude volcanic rocks in the region northwest of Marathon City. Alignment of metavolcanic xenoliths is northeasterly. '-cccl , ccc i", ic':' .'4.tccc.'. ccc: cISr,Sii cL,"1"c i,,., L[ccl'cLit 4LL :tLiCR: zcic',i cci' Tccii'ciccccic.;"cci ccc'.iici's'iic 5c1c tic. t,cc c'iccc'cclc Lc L.ir:ccn,cc:,.ci 'rrcicca'.i cc.'c',icc.cc,rcc,.c'cccc.c:ciL'{cc ti5 i;'i2ii c cc''.'c.cicc':ccc iccic,crclcC c2c'ci cA'c'ccccc c''[ccctui s-tic' t!C4 ccco.cc'ccci 'c1'Ei Mafic Intrusive Masses: Several small mafic bodies separated by granitic rocks occur southeast and south of Wausau. The largest mass is a gabbro body which interrupts the Eau Claire River mylonite zone near Callon. Smaller blocks of quartz diorite, gabbro, hornblendite, altered pyroxenite, and anorthosite enclosed mainly in leucogranite extend southwest from the Callon gabbro. Inclusions of pyroxenite and layered gabbro occur in diorite—quartz diorite southwest of Mosinee. It is possible that these mafic rocks are uprafted fragments of an older, subjacent, differentiated gabbro—anorthosite pluton. (Stop 11). ',LL!L cciii. cii 'c'. itc"i't cii ti,'lci'.cic'i :cc 54.c.ci'c:;c ,','T,c",yccc c,.scica 'cci5cciJ,,'cc. c cc':. c"s.q,'tccciC TO' c5'ifci. "Si,, ii". Tic: L'T 'ci:i' ccci ;C,Tccc:cc' ccc" cc'iccscTCtc7c.t UI_ ' '2Tc c.ciI:. [itci' .I'c'":c'.'A'S c .L'c'ccc,ct1t icc:' 'i''i.T_l'ictft ,dc,i'c,C .ji 'c.4't't'C it'. *"; c,:,s'c'.'c V:it's..t" '!n.:',ccct cii'St"ccc cctc'c-ccc iiccc?,_cci: ccccczcct cç..Zt r,crn.cIL"< LII c'.tt,Tc.ci :'i',SL ,c,c:c'c '4 ccc cc.tcc.c cc'. '''ccc' s'' scIc. tic::": 'cii.c'2 ,,.c!LI c4.ccC..cci "ccci "L'uii.'2.S. ic ;'- ccc' c,:5ttc 'ccii'c'i c,T;'rcc— ,,;',cRci i—4cic2cc 'tii'IctL li"l'.'ci [2 'ci'i'',ct Itcccc'briI'[C;ctc'ci .'.,c'Cl'LL ccc ii:'IIL L',,Ii',I''ccL,:'','5 Although elongated northeasterly these two alkalic plutons interrupt several major shear zones, and appear to have been "punched up" through rocks having a pronounced northeast structural grain. They are probably the roots of volcanoes, and their concentric structure must be due in part to caldera collapse. 'yccick"sic''c cc'c .c'c cccrL':,c: c'icI.cccicic..cc.cc.c ciii:': ':c;ci;ccc'.cIci, ,:. 'cc'rc.ccccc.:e'cc ',.ccTh .,c'_ cI.cc"cc ci'ccici-i ic'T' ic"cc'Lc'It' ,cirtcci'c,'icci S.t :c1'Jj(. 'C iifi'Jci tjiic.cc.[ r;',ci" :cicccL cci, i'cccidct ccct' [ccclii's .c',,cc:i?ci .1cc,!,,,, csiiyccy't ctc'I'ccH5t tic ;tccrcc ccc'.sci.'.'.c'cc oc'ci':cO.ci'Lc 1,1cic.i. ''5 'c'c'ccjcc'r'c ,.'cccc: c,.,':: The nearly contiguous, smaller (5 x mile) Stettin pluton (Stop 10) to the northwest is more alkalic and has more pronounced concentric structure. A border zone comprises gneissic nepheline syenite. A more massive intermediate zone of syenite and tabular The coarse amphibole—bearing syenite has swirled flow structures. core margin (1 mile diameter) of nepheline syenite is donut—shaped, rich in magnetite, and encloses a core of massive, gray pyroxene— amphibole syenite. .""[.cc''c [2 l]'tci"i.'CciciSL' c' Cccii c"citccl[c"-cctc:tii ci: ciit ccc''c.'cc',Ci :c ,s"is cc':: 'c,: ::,ccc.c:c :)i, i-cc'st"icc.::.3 ii 'jc •cicrcLL;.,'lcc 'ccci ccl :Pc',ic.'ccccij'c.. 'ii' cc 'cicfct'ccc cc;cCcc c5r',"c]i c'Hc cit'c'.cLl2 C'hciui.:fl.tc'cci'Tctc.,cc:-tcJcc lc:i['.c': 'cc'; ';,'1:"C'5 c..-,c"cicc .,t'-' 1:4]. SiIL. cicr'c.'t'ccc"ccuc, 'c cc =c"cccc'z' ccc ''c,c' tc[tc:'i"c C' 3 c''c4ci'c'.r ccc"' ccc cicc:'cc:cc'::ci ;' ci' c' "'cs'IRcc.ic,ci:'Li ,t'c.c4,.;L'2.cc"r ;ccIc2ci'c'c.ts ccicc,.cc'c: 1c'ci1 ii Jc t' L:,ccc,t :]L:II:L C '' ci; 'cc':: icc's cii ii'. c ' ct.Ii'.c't'i [2 The larger (17 x 8 mile) Alkalic Plutons; Wausau, Stettin: (Stop is elliptical in plan and comprises: (1) a Wausau pluton 9) hornblende-biOtite granite (Ninemile granite), core of younger intermediate zone of quartz syenite containing (2) a semicircular large lensoidal quartzite and schist xenoliths, and (3) a crescentic The southwest north rim of xenolith—rich pyroxene—amphibole—syenite. rim of the pluton is breached by the Ninemile granite which "spills out" to form a nearly circular mass to the southwest. Abundant xenoliths are found in the granite where the "xenolith circle" should Although the Ninemile granite intrudes the syenite, the contact close. In general, where the syenite intrudes between the two is gradational. it is alkalic, and where it intrudes more mafic volcanic rocks it siliceous volcanics and sediments is granitic. cs.: i.c .'-ccc.cs cc..cccc cc': "',. c..cciicc.'H1 .cs.çLcl.,.'lIc.'l iCC, cc.. cii"il:i:. ci' 'c':'c'cc.c 'it,JtLT ccci'. cclj'"cic"Icsc ',' '.' C'5 'ccc's:, ccii cccii '2" ccitT '[2. cc, 1'.'ci'C Pc ciSc" ci2icc;cc"cci': cc. cic'(VLcicCE.T ic]".'Tlt:'.it' c'Pc'.c'cc ccc.': L""i,c"tc [2.": ',c[2 ic.2jcc"ic' 'vcic:c'c.c-Lstci" 'ci ':cilI:L!:"c ciC,ci.tr ttcc'tLc";c: '.'c',i'i:: cci ;.ict, cc4c t':riC;;: tc',cci. :.;':t,,O ciSc', ut '":cc[2, [2 ciccs:i cccc'I.":c'cc'ccci ,c!,L'cii'c cc . .cuiiccc'c,$ cc . ccs.1.ç'cc cciii: ccco ci ALt' Ccci rI"cp'cc1.c'!c.'c.'i[ 'c[ccccic' ""1"'"' f -"S 'ciC,cic,','ccc: ci ,Ic ccu1cc "cc' cc.: ci,.,t'S ccr.;c', 14 .c:cc c.'flc iic';c,L'ici C iI[2Lt"V"c- .c"Itccc'tI Ci-''i[ iici..'l,c'c c-icc ci ccc. 7"c;'cCIci";..l'.Tt ccic'.cc5': 'ccici[ 'r'c,'cccc,cica:'cc' ''ccC',c'icic':.'Cci cc.' ccc; :91 cr'rc'cccc Ii ti, 'ii 'ccIccccccc.tJxc.c ii iccc':c'ci'c ccC'ii.:JY ocr 2.lfc Ac c',c,"cct ccci ccc 'cic',''ric]: Several other felsic plutons have been Other Felsic Plutons: They include the Kalinke quartz intruded into the volcanic complex. monzonite, the Granite Heights granite, which intrude volcanics north A granite and east of Wausau, and are cut by several shear zones. aplite intrusion of, as yet, undetermined size extends southwest from Marathon City. A leucocratic granite, which interrupts the Eau Claire mylonite zone and cuts gneissosity in the Hogarty hornblende River occurs south of Callon. granite, .Te,Tccci.i ccv. S :.LiT'[2cic'c'.c c',,iic cc 'c 0' 'c"' .1cc"cir-'ccccc', ,ccc.c .'Ii;cc;;':cc :'cccc'.ccc.ccrc1c,c ccc'cccc's 'cc' I,cc.,iccii c,ccc:ciic'ciJic ,"c-ci; cc,c'.cc, ':c'c'c'Ccc.,ic;'c ccii .' 4"c-n- rIicicici'Cc':c 1c2 ii4c ccccc 'c'; ''ci'c'.'ciT'c'L:] p;rccc cc. ci ccc.ccc cit 'ccc 'cc"cLt'cc'L c,t',,'.Jliccc.7S:l cA,t,.,c 'cc' ci:'c'c.[cc it'Lci cc",,cc;c:tcc'cici' cc's'cc-c c"ciicc,.,c:c' .ci[ ccccLcc,cc ccccics;cc:'c "cc" '. cicc'c'nc cc,"c:'"ci; a", 'cccc'cl "i ccci cLccii [ccc ccc:ccci,'cci': r"hii,C', ,: l'cc'ccic'ci ccc cc'cf'c'tic Ccci 'ccc'cccci ;c1i.c21'cct c.rrc'ccc''cc,c'cPci)'c cL'ci"'c,,c"C" LIt cc; 'mc,' c' ccc'ic cc:.cciccctc'L .':ccC",',c'C, cc]c1s,c,c cc', A' J,'I[ Ci's:: c'c:'r[.cc cic'cc'sccccc 33 �34 Structural i-->>'*i sn.i - Geology :575y5515c1'j, >>LCIC,naa. fcs.rsra a'. C i,1955'slfi-35-7 ti-::>> dominant Shear are the feature in Marathon County. daawdr'ar" structural 'sa' as ar-a Isls sa::- zones rocks, including 'nani:55 5535-Cit The major zones wide variety of sheared-s-sac> -> s.csan'r aa :1 si-i-is-s comprise lads si-:-ssc :aaa->>,a,s- these Nature displacement i-nt dCa; :>a.aaisaa'Ss across 1:55s3'axa of 'n-'5 can' -i-si-i. n-sal mylonites. gneisses, schists, s-s'SiaXa- and i-i-laX atlh'sa: 5-aC51-ai-i Marathon Several zones extend completely Lssi-si1-u"i-c-CCC C-Cad-a-CS. - across s-s-tiG->>--,-sasiCi shear -5 C-fti--Xzones is, :551kin'ThT's, unknown. —'cs'ss.d-sal: zone liLa. laS'S most555a557511-51a' conspicuous shear 5:55-C-Is' CiCts,>55a' :JC-1n1i-151*Lu:d County and an distancea555735ad-. beyond. The a:-. unknown which >55 155 .171: ':5: Ca' 'Jh.nis-an CLn>sr sari-a' mapped thus far is the N30°S Eau Claire River zone (Stop 8) S LIsa daC 5: 51n>5 -5-" a,t.-c3-3 marginasof ad the tdu -:'- 'Sd the -"a>>-as-- i-tugS ad-n, western is 555155 i-jars'. with, parallels, places is coincident tin plsc->>-a ,a-i-si in 355>>- and inns,>> Other C-'. h_Cr shear >neR : zones l>>55jfRiver 5551-tnPluton). lIla 59.; Hogarty hornblende 'Ksgarty dais:?-: n-Crs'agranite ;raa 55, (Wolf in Marathon -.---ar5 Ca: 55a-tdss west n-.:i-a-sc-",-- farther ;15i ta'nnd a::, present approximately trend are -s this aasnTCn:aci-a i-al.:' parallel pa's-a. -a-I to r55 sc-as: aS La-s ad an the lisa of rock affected to It vCL-::i-:r :;';a,nS County, but none appears to be equal in volume llla.sai-1:a, 5-sn: awn- n-nsa's-as-- to 5: t. Sn-annasS-a ,>>-a-arn,s Thus, intensity of >>a'>>siT">>' shearing seems to diminish C-C a5TLL,a ' 55' 'l'i' Cs ic-nC-, Cl sic--n: River d.s-ar- zone. Eau Claire 55na:l. lbs 5:Cc ' '-s front. i:lC-s batholitic westward away from tic--sri- the ::'aarrarC :;a.ay :- - 1 I - 1. and across n-i-Cc-SC las 5±1:35 Lithology rocks Ii: in s55'nr shear nsasea, zones, —a55C''j. which i-i-n-s varies along s-nC iIlssa51Lss557 of ad :sa.:'C': texture of the original Cast-inn cl tn-s an--i-CL-ass 515: -'3>5S,c 5.'>ra ristrike, is-srss" probably controlled -aiaJiy carat -:'-c-TLsic.s- by mineralogy and C ts-d li-a, is partial pressure of H2O as:: sar-ial saass -s ad 51Ctsr>>si-:'s:'ftassc rock, intensity ci> shearing, sdass--lsnS:, temperature and tntasa-S 55s' of a-s-sd, 5555 Mafic rocks are 5f-i-n ?-ssILa iSCCC_C the rock. :'a-i-i-I:n> c-as-sshiars-ns; C lsCc'i->-iad during shearing, ar.d post—shearing history of .dsrS's'g a'baa::::>> and 155: ->>'i'-sa Granitic 015.555>>' convertedCs toI sad-CL banded as amphibolites oranchioritic phyllonites. cssvsx'::-d SitS n-as: I"Cnalislc'r:tis -51111 From and CL mylonites. icnj',n-a,, Th5'35 gsan.aaan-> ;;-lha.JLcsain-aa as' a-is-a' rocks are converted to augen gneisses, phyllonites, and -ar's CsrrC-rt-n-'3 :>:-slica' I nan--5:r115'sn5553' characterized by interlensing a':,saa arssi an -u-i-rnstarts-ed :; 'n-anti--sn-i, shear zones are map scale to >ck'in: thin section, si-aL-c Cc ti-ni-cjill an-s-s-a'> slip as planes. - c-s'-- example, 5ui5'siQsS shear alIas-a zones. a':sas> For IFS-Si-n intruded Several small plutons i155>>t'uiiS have nn-ni-'-C>>i C;'., In-' Claire River zone i53':r'i- near Callon. 5' -s-S. CCI s-iar i--a' Eau gabbo and leucogranite 5c'51a"->>J-,d 5.51,,5557'alffltainterrupt 275.35 ''CL the sn-33C sass as--cl trend also occur northeast and i_Can a-; srann - -',n-sahythe 515; same 55CC - Ta'S Shear aaitln approximately s->-v n-n- with 151-a' as zones a-r'as'9 ha The'-.iraza-la Granitefls.t:.ls Heights Ida 1,5- granite s>> 'an-cadtS:'.-i"-- pluton. -Isl.s-u-o-:->::ac-s Stettin southwest -alar- discordant -CL the a,-y', -i-la--n-cc of ass-c ca--> sheaied and therefore tibaaT--n-SCaare proascii-h CC_CC-C: 5 i-;have n-2t lan-a',:: and Kalinke quartz monzonite been ulc-,an,'i--sI s-nd dali >sr,'C -55555_Ca ::r—a- lI-sasis.tC-', >a :ra-pre—shearing). 5-n-i-5'5JC5-5CL' bably (or cs.l:'1- pre—kinematic ion's:' repeatedly have been '_C 57 isas-aC 'n-5-n--as19-3lf 15 i-a tin-ass-C SOs- County aaa'Cs in Most of the Precambrian rocks Marathon 31' '5a-s Miss-isoji-;;,cali!'sc'ss: 55-.-? The differing -n-s-all.>>> :is:.iI-san.5 compositions. -s-S widely t—;s'rs"n-ar sheared and magmas of is:5'ar-'s'd -s>.l by an- l intruded a'Ca'ss'nnti ;53LsC:--?tCl'X-> aca'i-2 of 75 3135I the intrusions. 'as some -51- san:: for nibs—i as-s -5>1-s-i- channeiways ::,-.--i-Css,siCIn provided shear au-Si-Si-I evidently alCoa>>: zones -ad of the an"':. many as: asi small 51, 5 plutons 5-n t;as--a::'d and :5.>> s-1Ci-5C55I.S'i?'753'>>-'>>' cn-'355t:'C' The relationship of shearing to intrusion sad all' sn--o5isa s-ui-i(Hogarty hornblende granite) Sd -cICL5s 55 1:5' .i":ttarIs 'asn-t,t) 5,-s-ad-sI 3tti-'-n-s si--I'd the emplacement of a-I the Wolf River batholith i-he si-C 51115'? n--n-s'iPrecambrian geology ICC-a a,iss1a-:si at a>n-all JTof 5" Marathon C am—is s'f Ida -aa,>:'C ;n-rciCl>s-n-C remains one of the major problems in the resun&a.a cat: -- >55._CC u5i, County. i—:-SidLs:; -: Major 55aJa' Problems s-ca In-ma's- sCant anai-s Some the i-an morea important ones are anI 51—c Sara's of '—s-":aaa> ad- can- remain. Many major si-CL a-a problems -rcsn-n--s-Ci-r':.. discussion and sn-sal research. 5 .bsanasa:C-ta: ratIaa':L'Lasas Class :>,:>, sr's. -'>i5ai iS'-s' listed below in the hope that they may stimulate i-it ba-S balsa- S's Li Cataclasis: -i'- Lan-IS: Shear Zones — Cr: - - - 1. 5, and mapped? 'l'ci, -an-lan sacS's sariSclassified -staaaiiiIas- ars: How ass areaa-aa-c71 cataclastic rocks best 2. 5, 1155-1-35" CC dated? Can mylonites be dais: vsssLc:cflin&n-s 3. determined? .>>I5lII aaes:a,s:: c-:ot n-rrrr: 3-55 si--saC- 51 How i-sad amount of displacement 55155 and -3T5- type ia-" are 13 44. Class'? How? -, i-i- -isas-bs:nsa'fl p-': tcdcs':st'ia:dp:- between csdlsnc'n-s What, if any, are and space relationships avisthe j'e time it: nsa. Wl'at, atsiasas; a-n? ,'i-s5:'i9a,aBt'5 shearing magmatic intrusion? cbacvrlsa; and �s? ane err t older subjacent of samples ted upraf they Are variation? fC =— xenoliths Cji, 1t2At4v and orientation (:ICC ofjC Significance lithologic iCZ [ r:• ft$CCEY:1 <%-Y9 C Subvolcanic? — syenite (e.g. 7i;T !ttZ i)r,; When ' ?Ji-•i ci?1j lILCrCYqISC Ccnj intruded? syenites the were f.CtCR how and volcanics Brokaw)? near C CC 5. C 4. trachyte 7 I i—C It— and plutons between Relations comagmatic? are plutons Which iCCCCIV emplacement? of mechanisms and Depth 3. 2. C 1. i:t:C7 Geology: Plutonic 35 I �1! 36 atrSW Bates, •fl0 R.G., fl'. 1961, geophysical data and Allingham, J.W. Xfl '3Ut - "Use 34) of *t.tss%•;o. t'Zflfl ';'r geology i4tç to 4•1 interpret in Precambrian rocks of central Wisconsin": !fliS'V1'13 £.Ptrctl bV $%Y wea 1> U.S.G.S. Prof. Paper rn-cs — D—296. zt •IrJ. .(%',.; 424—D, p. °' D—292 SELECTED REFERENCES 5tF:SS.a'ffi 't1. j , L, ' %.'f Dutton, G.E., 1971, "Volcanic—sedimentary belts and sulfide —rae occur87Ps fl1'r7rC2L StCt C4fl(U U.S.G.S. Prof. Paper 750—B, p. B96—Bl00. rences in Wisconsin": r, r.oswç,s, tr : ;c.a.y rcb.a '—,;çj OtZ tn. • '°q.' •. t"i ';a'tIrtnrxrc;s Dutton, C.E.,. and '..'73SZ Bradley, R.E., 1970, geophysical, and >.E 'char "Lithologic, DLC'4Ln32 mineral commodity maps of the Precambrian of Wisconsin": U.S.G.S. 1c w:42L Arxa•nu ..f,q'g ;ta Misc. Geol. mv. Map •4gfl -15ee •"flf 1—631, :%.I4... 6C sheets. -:rj ;r ru :'wt:.jtn(, pUtfla V $ () r.qe;.p at; Emmons, R.C., Annual Tn—State3 Geological O'eQ 1953, Guidebook for 17th v, :ia( .t$q, flD4tC Field sv,.'-.xarr Conference, 11 yr p.. ,t0Ij rt4'7ii.'9 !rag r' Emmons, and F.G., fl•j Snyder, c'& 1944, y€L "A 'Ii, Structural Study of the cç Cztc.,&a R.C., xq,:iz ta•a Unpublished rept. in the files of the Wisconsin Wausau Area": i1SW% WV ;qa 4 aj; t,Wt47tttft ;'etBr.tV14 ';de.. Geol. 'TU. Survey, 'it&flS 16 p. C 'ba( a:;: t •,'( 'CT, "g'g t:\ttsc. tj) .j •. :, ': i t:b Henderson, J.R., Tyson, N.S., and map P%7I Page, 'at 'o.Qwj J.R., 1963, "Aeromagnetic rr.,:i4'rney U.S.G.S. Geophys. mv. Map GP—40l. of the Wis.": jo :qt Wausau :'sa.rajç, area, SM 49' 'SS't 'ts1 ,. :sfljr "It v' ar LaBerge, G.L.. 1969, report on P.tnnrEsJ. .acSe.t uz' the geology ".ZiGT "Preliminary a5 ma of the northern part of the en Wausau East quadrangle, .nacsfl :tth 'c,2as. Wisconsin Wis. Geol. Nat. Hist. Survey, Open File Rept., 13 p., '2s.C?3 "C map. iee ;* rnas ;ntj i:'t. t.jff f'L •'vc'- LaBerge, on mapping of i1 Precambrian geology :.qh? 1971, s25v.; Report s.r'sg co SZ'LWS$ 'GW4e.q G.L., 'ca1t "Progress Wis. Geol. Nat. in t7flcW Marathon County, Wisconsin": ELf a-a • Survey, :::Tt•sIflr3J4 'tu,c list. Open fli.J File Rept., 27 !Z p., maps. '4rc3 '?3 C.1 'Ai. L0 '.r. 'craet't, vx nrnc4w r taCaaST& tfli: UC'4Ojq n;i 4flc; '1.2? 'flL 5 LaBerge, G,L., sv 1972, "Lineainents and Mylonite Zones in the Precambrian of Wisconsin" (Abstract):t North Central Section Meeting, T2 G.S.A., DeKaib, *e.q.n.z) '•ezoa Ill. U::z*r1 't' •t .trj ts 't.St3 ''O LaBerge, G.L., "1971 %eclSord Progress t•.dej Report on .:,. Mapping t1.3E TL€T,; 4"u'f and Myers, P.E., 1972, Wis. Geol. Nat. Hist. of Precambrian Geology of Marathon County: 1;b C4taPN.Ls: J.$2t->' &.O %'.at1 fl '&.1C1s5 Survey, Open File Rept., 28 p., illus., maps. &j nd'ag bw4, c.çg 'd 4-aç "!na :. 1Ltui VII .vc flo rt LaBerge, G.L., P.E., 1973, "Precambrian Geology of tr)4flflfr( Marathon nrn..*twse. 1an and Myers, Lard sue. Wis. Geol. Nat. Hist. Survey, County; 1972 Progress Report": Sp.4 1.C-) 20.aC 4Z'a.t1 Open fl%C File Rept. (in C;) progress). 'cs.azs.c5 )T "djj 'fly W flr: ;r•i fl.1a3 ?rr, LaBerge, Ci Central ..:.t; and Weis, k"! 1968, "A• Greenstone fltLrj%S'LVaTh Belt in 'I3J4(i. G.L., '.t!Cr4 L.W., Guidebook for 32nd Annual Tn—State Field Wisconsin?": Yt33—(aZ1 ,.4t1.i.CCfliVTk )OtOflt3 aC$ t.LV, Conference, 42 p. .3 4DrdXtat) c'rq ' ''re: 'c;si Vickers, ra part of UJSttCs R.C., 1956, "Airborne .a'q.r:y,, ':t and pfl ground 1WdCUCte.F' of ;n4>s1 reconnaissance U.S.G.S. the syenite 0cm rie.I Wausau, ;utsI'r.JCT c c°u 'p Bull. nit.ts s.a complex near rgnip. Wisconsin": 1042—B, d p. 32—33. xwgna 'tn'ab1 a Weidman, bTId... geology 'Z4ni Central u4TLBt Wisconsin": çu:w.CCCTa. Cktz'ia of North t•::....;#'.•-q S., 1907, '.a.cr "The Geol. Nat. Hist. 697 p. •t$ •V1J! Survey r..t..s Bull. •IrR 0 16, 09 ;I . 'TZ '*1t 'h°1 Wis. '3;j.4 "Central Wisconsin Volcanic Weis, L.W., and Z.1Ct LaBerge, .n)'ja;s G.L., 1969, '44%tJ_ zu:awc,, 4.3VCr.s' Guidebook for 15th Annual Superior Belt": I.?:.2t.p;a3 :'a.it.t Institute rj-4n(fl w on Lake dOfl Geology, Oshkosh, Wisconsin, 30 p. VØ (.j tSo ".atcers ;•1t -— .n; ft 'u;snt: ae a... .. a ..j4uQ �This page does not have a number 1 1:500,000 scale, Wisconsin, northcentral and northeastern in terrain Precambrian the of map geologic and itinerary trip Field 2 1:250,000 scale, Wisconsin, Sheet, Mountain Iron the of map geologic Preliminary 3 1:250,000 scale, Wisconsin, Sheet, Bay Green the of map geologic Preliminary Plate Plate Plate pocket In LaBerge G.L. leucogranite and Masses Gabbroic Locality: Additional Myers P.E breccla intrusive diorite quartz Sheared 11: LocalIty Myers PE. zone pluton—wall syenite Stettin 10: Locality PE Myers Institute Technical syenlte-.Old quartz Wausau volcanics mafic 9 Locality LaBerge G.L. Rivr Wolf between Contact 8B: Park County Dells Claire Eau 8A: Locality and batholith LW Weis anorthosite Tigerton The Scftnus Va.n Schmus Van W•R• and Anderson, J.L. Jr., Medaris, R Schmus Van 7: 6: monzonite quartz porphyritic River Red The and Jr., Medaris, LG Locality LG. 5: W and Anderson, JL. Jr., Medaris, L.G monzonlte quartz River Wolf The WR Locality Locality MM Lahr, area Mountain the 3 Anderson JL. and Mylés, JR. Jr., Medaris, L•G trachyandesite Peshtigo and granite Belongia 4: of geology and porphyry feldspar and rhyolite Hager The Locality Locality JL and Myles, JR. Anderson Lahr, M.M Schmus, Van W.R. Jr.,, Medaris, L•G• monzonite quartz gray Amberg and monzonite quartz pink Athelatane 2: Locality G Hall G.I and Mursky Wisconsin northeastern in volcanics Quinessec 1: Locality Wisconsin Northcentral and Northeastern of Geology Precambrian the to Guide Field �37 L CI'C,':'i 7TCHJ Field Trip Locality 1 TITLE: Quinessec Volcanic.J in Northea;t rn Wisconsin (l'I-7J!,I C C3'CSI CC-XCk? 7 St .7;:; 'T'y CICCC,IYC.,C,:4 LOCATI( MC.: T.37N., RJOE., Marinette County IJ, " "na sec. 1, LI7tC 7',;aa.;:7t7r; Centr, AUTHORS: t,c;:'?L± .CCi. 7':,';ai,r, i"C[ 'a fI:r.17; ,;:a,1 ,'r• C"Ca. ''Ii; I,7C,C"7M: L,uZ77 Gregory Mursky, Department of Geological Sciences, UW—Milwaukee George I. Hall, Hudson Bay Mining & Smelting Ltd., Calgary '7CC, I ;:a CC KtI• ":H':aaf"7 1yT7', DATE: February 1, 1973 't 2C7'C'i1S SUMMARY OF FEATURL$: part oi Marintte County in northeastern Wisconsin Northeastern is underlain by Quinessec volcanics which consist of pillowed and •;:;: :;r,:CZJC '7., '77CC "CThCC "TC'taCQ C'C7 Cc "IC,:': :7';: CC 'CJ . ,C13C S$LCNCI, aT'tC [ YI' iC1P'4"t 1CC 'C7CL i'" •,7C [':'C '!tC '1 t 'Y'CJ' )':ICIL3E1 aC"<tIitC'T,C,C' rLiC'Ci7C I1C'CQ1C,4 S.'.ICCC' C4 vi"CC",LC1CC1a a . fragmental basalt, massiv basalts, amygdaloidal basalts, myrmekitic basalts and a very small percentage of tuffs and rhyolites (Fig. 1). The volcanics display shearing as a dominant structural feature with two distinct trends at N60°E and S6O°E and signs of regional metamorphism which varies from quartz—albite—epidote—chlorite subfacies, away from the granitic intrusions to quartz—albite—epidote—almandine subfacies near the Hoskin Lake granite (Hall, 1971). C' r 1Ia '.';:aa. •a/;!.:zc•Z. wa474t1ir2-. I'C.':z1I,:, 7C CI C': [::;:"L'1 C,7;,;,LC ., ;3,'IC'T'zJi. CICLC VT7CTCLC 'a : :;;:;: 'a C'C1 'E1?C:,,Cd Titt7 'CC'' il;: 1ia 'C CCt's''a: J7117 7 C';: C" L1• cs• '1' C'C1C tCi CcC'7XtY ;:''aI ;:,C:,;:. c_.;:01©.'11 ;,1:a::C ''' ':' a. •aicaa ttp17 'CCC17::. '.C'Ck",a,I] CLt I'i7-ç m',7 'C=; lP' 'flC1ICC "ai 7T4COLL '-'T'1 C12 jrcr'; The Quinessec volcanics have chemical characteristics comparable t:7Y'J1 ICCICfC :3CLC4C a:'7'q 'C 7u7CCvI-'. y{I• CY',TY' tI;, •'•'• C JU .CCL v'ç 'flit; CCC. :? Ct7 CC a a Y' f:a'j,,Cu;:;:CtI C4 7C7t'T'17 IaaR12T71 C'5. C' . CT'7I to the Archean volcanic assemblages from the Superior Province o the Precambrian Shield in Manitoba, Ontario, and Quebec, and thus show the WCZJ '- 'St L silica: alkali values from Quinessec volcanics, when plotted in refernce oceanic alkaline and orogenic calc— alkaline curve of Wilson (1965), plot in the same orogenic calc—al :aline wield as suites from the Superior Province (Fig. 2). iwa;: o —pa ';:'y'a '17a7 'n ©;:: I : CLL± •;:rL •.':q °9.jj7 C'CIiC_C"z.ç[ •:s-C'CCL' CT1C cY'1; i'.'C•4-'1.C cCC:iicti' ,;:,Cat ''JC7 JC iC''LC ""CiCVI,''y C'Cj, JC j :i t;1r7.C'Ja The c tion equivalent percnt of An—Ab—Or for Quinessec volcanics is quite similar to Goodwin's (1968) Archean assemblages from th Superior Province (Fig. 3). t/I'i,L7LCC 'Ci ;:tir:;r:'a IJiI;77ji C c:e Y"1 JC I II,7":i CY'R1; ?i'C;fl :,Li a;: ,c-:7t'r a CCjj (2) t'C Nili ii "c.'qa CTçi ;;t (1) 4't following similarities: : A plot o.. oxide ratios relative to stratigraphic thickness (Fig. 4) does not show any pronounced chemical trends although there appear to be three separate zone within the pillowed and fragmental basalts. c: Ca:ttc1:; :T7hCTYI,flL ::4 L: :CCC; apCC:C :::,1aCa ac.r.i. :: aiqC 7CL7 '.. L•;'..Lta, ;- .,'.CC 3C'''i' •C.:C:. :,Th:,c.'.:ia, a'p.aac. 'nz .'i'c•,.:; pc:',:C.::;:'.,ri ira tu'çc .-;r ''i C' �ii 38 -Ii 8800 7'07 - --., -- Nocra 1 177 \ 1_ £ rriC:,,, T' / — 2 — — — ,.'NtMrnet C'HIIT C ,STUDr' 'N / -) * / A 7 L_ y—1'-,, a 7\ t, toN 'N 4.*4*47* AA A A'\\,7'.-.it'- — 7-' '1H'c221J.t'C —-;,,--._ .AAT3N II 4—"ii 'Ni cons N H-— 27 - A -- - 7 7- CL 1 - ',,,_ a—-—-- - 'N—- -, -- - _1-L--7--.- Jfl=cn - - *-'7 —- -- - 10 ,L_-r-- —I — ' N' - - ;- - - 27 1— -. P.. 7-1 ;0'''7-°"--- -Nt--H, 7—- rrmI n (1 r '.j.-[\ C fl7-_° 77-- 7, 21 '- 1 i-n Li e 't,,oCit'li,'. - - 'N — -- - (7a / - -*4 2_ — 7 -"N t'Nt.,q —-_a,t Y.-:---. / 7 -t ,-i.;, lot (/ 'N N,' 27 0 '/ — 'N I - 1''N';*,/ 0 of -b • oN 17 a.- 1 N oCt— ' .-!'NL ,fi -'27-7—-- N 0.1t&_,t " A -A : s,,b —'t,-"S — A a r - r >, c I '. ( 07 'S 7- I / 'N'" 7-pLOt - - /1 17 . 'S — -- Ca-21 AREA — / 77 I là CA L4 a- 45•45- - * —---- 7--''S 'N /21. - -.7*7--f - ' 'Nk. i-'7-%_ - a VI 7-N. I LEGEND 1- Precambrian mt rusive —' L rocks 70, - - '7-.-'o 21 7-— 1i .1Fraqmenta1 7-4 I 'I volcanics 1Arnygdaloidal /LjJ basalt ara:J 6-I!77If 721/'CJIN I 0 7,-;.J-1 p o— '' "N I Myekitic C • - H —- I a -''S-— - - •.. '1d basalt -L * - - - Chr-'Nt 1-731---c' rk.,0i'Nu:.,elco Acidic volcanics 7- 0 7. 7 LCCAON MAP CE o_jbasalt U) . (1 r1 - - 0 -o Luny >, - i/f,-,ç Wi •-ns',-- — 12 -' -- Mo r,,.?te -* ---- k,om.er - - �'r\ LI I. 3',j 'C[' ''Th' C.C' Hall, 1971) 3' (After 7—U- Canadian 3 '1 the of Province Superior the in Shield. 13'22IOft J37;1-C-l,-" assemhlaes7 volcanic Archean 3'23'2L;c. three ;.122;, for trend 'uT1-2/3'33'T-C curve ri:Cj3'crr Dashed Wisconsin. (1968) Goodwin's is 333'1'.3' 3':.,-'''7 acidic County, Marinette NE in rocks volcanic -= '— 2:1523 Cation :.3'7.-( in 23' .2:1 13'-3'--23'[2percent 11,12.322 equivalent Ic 3' basic and ith—An-Or C , I 22; /\ \ \ ' I: 3. Figure \ 0 3 /C II Number Sample ,z C An /-,1'V"Ci T., G. '3'3'1;121i :1:3''121 caic—alkalifle rocks. p33'.A1 'ri13:_: (Mter Hall, :: 1971) rocks3' alkaline oceanic separating orogenic from _l 3' with made is curve standard (1965) Wilson's County, Marinette NF c WiscOnSin. — r' '1 I cI' I_ : C--— comparison 1721/ :!C " C— -'' aniilyzed and basic )'C acidic ci volcanic rocks in 3'/ ofci Plot 3'003, I3'.3' ':• I13'Gr;2. Niqqli :17 :511123:' values silica-alkali of - - - - , — —C VLj c 400 500 12' 2. 5172.3' Figure CO 4gI Sit 300 00 200 7 l0 I 7/ 4 / / /7 / / // / 20 12 > 0 / 12 CALCALKALNE ," OROGENIC 12 7-V 39 0: - 30OCEANIC ALKALINE 40- �40 40 V Si/I.E N,crn.H .: i 54- . Cl — / -. 25 0.23. 50 .5, — 75 H\ 'N'1;\l .7' 01 - I -. — N,1 - ------! 1/ : 0.3 ,0',, C .04 A' 10. / ..' H — -1 xA — C .4. /1/ /,/ A ,.' .Jo1 - - /A H / // r Ceo 0332 L.tSiUI I . 20 (I; t P. nu5' i I it .- t II -— -1 7. fly 04-." 7 --- / 00 —- 0 I '4- I c '4- 0 :: ((S 3 C. :; 5-—.,. I. •1 -o 1A C - ' I-.. C 0 // •1 0 -c /7 /7 'I 10- 7 7 —.. — 1 a.'-C'-. -' '. " • .'0.' I: -- 5 -- .7' T 1 / JL.' 0 H -- - ,±J1 Bottom Bc -1-L_ Ir tr'Sit' dItIIn 5. 5, .:''H''sv,-,I,''12 ('IL.' — - l(C7 Figure 4. ' 0)01 /I'fl( t'kr' - —- -. Tt1 0.5 0.3 V sc. Bottom '3's A55 (ion l..I ", I -t FeC) ) J '3 A 1515504: Plot of chemical 5555c/:t c- with stratigraphic d0457nS,2.C .sjI. variation 4 04552044335533555504/04 04"r:5e33335 in Ni Marinette :;1;t-5-.t Cocsit.y.. thickness 7555 hasalts NIE County, bsc/c.5T.tS ins.c '55 shows: Wisconsin. ,55..'(-5,33j/5r5 5550 JL07 zhz': 001 Generalized qeoloqv r->. Si 550455355.555 sc1s' scs's d5Ct??04*5 3 qrain size -4555.5.04 75.5,55; increase; grain size decLse; -.-- hcsc4 (i55 7 i r (EnrpBc'cT L.':3 basalts; isis Bc 55' Ct /4 shearing; porphyritic (.4 2"?'10455.a"''(S 55: basalts; CtjiL55557L 045575.A 55555 q fragmental modal StC'. iLL auartz. 55-75, 'JcS"I' (AfterssBcI, Hall, '.'s. G. I., Bc, 1971) .5 c. " Wi, I, ,_,-_., 5_ A'.' Si �41 DESCRIPTION: U l/ce n:cYk t,jc 14i.V a'oci' ri' 'u :a:aL :xn vi 'UU Massive basalts crop out to the north of myrmekitic (1) Massive basalts: basalt and comprise one unit within which there are three quartz—rich zones containing up to 10 percent of quartz grains measuring 0.15 mm in Massive basalts contain varying proportions of albite, epidote, diameter. Most of these minerals clinopyroxene, chlorite, actinolite and leucoxene. average 0.2 mm in size. Clinopyroxene is commonly altered to actinolite and plagioclase to epidote. Pyrite constitutes up to 1 percent of the rock but may occur in greater quantities in the quartz—basalt zones. :1L c : tecc1 tsa I I cLa: cc Ui tr ci c21i Ct F3eELcL1 S. - Xccii p I 'U cc. rJ c cccc/. a1: cctt'cUL UJ"c/RLtc cU eca Pitci tititre L±i-UILI. 'U a i Mctcc c'tkcc.tQ L& :crc k nc - c. :rr a-cc-i e•:c:'c cay cc.YCLC:ic ftS 134L1 irL 'U aft aagc .fctc0 cc cr .ccJLaSe i caL act iic.: c-c cUr r--eUicd cii 2eachae g cc - chsaccic sL'trect ii: cU-fl.. ratrcc tibia calLer icaci lice cc fl iL fS;.-iIi-Lf.IL-- 5rtt ataice c cc Ltii a cc U 'Ucr I rca -cc cc lUC cciiai a cc -L c'c:•H ate Ifcar UI U Ucac'U cc a a ';Lcc-c ccii at. - calU iniic-U; a'cc.ab cc;: ticac cc aa.lian cii a -racial Ha t UcccU ccc ti T1LL JUic -.leTh tS±L ace C/c. CccThL' :- cmi- icc ccc a-ta - cc-rat a t'U 1tJR -ar: t'a. 1Li ccc as::.: ;c'Ua ic: ii i;ufl9L cc :c:a cc- cit cL:-r 1: - -cc ccc cccc p1 cc-I- crit.trL cccci--: ccc- c' a iii:;' i-c U Urit ii:, hit-cc Ui 'U ccl cc-i :cycLnta_ iliac-. LL ci (2) Pillowed and fragmental basalt: Rocks to the north of massive basalts are fragmental and pillowed with well developed shearing and flow structures. The fragments are mostly angular, at times elongated, The pillows, where present, are and measure up to 5 inches in length. deformed. These rocks are made up of plagioclase phenocrysts and a groundmass consisting of epidote, actinolite, some chlorite and dm0pyroxene and occasional grains of quartz. ,- ccii :;1ccctth i-cc-cpa-c H rath -ira pUL:c-i1 aiU ci ecai'vccc ccc ar-ella (Y:i/Lc'IL_ 'IL ccalc.c ccciii ic-eU ccci i-rca i: ci cci 'U ccl -ci CC.' La.. SLLC !CtiC atiLcag --crc a cci ytmic-cacctr ccc ;PL-rgtcU -f cc Lie c cciL -cciiti :ci:ci hiU ccc L UIL 1ccckSct. t'ca-a tTI 11 LltJc -a iia'hccc iitt& I C --j.c-ac dcci :i.ILc 'Up-aL ILLC7 Ce 'U IL tm3i TLC (cjCC.?:ILtS - r:-i - cccl a1 2/c Ui iT iciacla ti-al arc etacitcaca kcic'cL La -cica lea icaraIra criiaJ. Tic (3) Amygdaloidal basalts: These rocks in hand specimen are uniformly fine grained, massive, gray in color, and contain up to 20 percent of disseminated dark green chlorite grains which measure up to mm in size. In thin sections the chlorite grains form amygdules which are Plagioclase in the form of surrounded by a fine mosaic of quartz. laths averaging 1—2 mm in length forms about 30 percent of the rock. The groundmass is composed of a fine mass of chlorite and epidote. cc Ii. cc ccc ccc ccc- icc icc ••- aac - 'c -ii- cc-. aca)r.ci/L'c aca7 yr LC-H-H c-c-ct teucia elite culcrt-cc cha acce cci cc Ian uccancre greca -U ilaccc the hr.: -ccc taLc-Ui cc Iii- claciccicita- :L.r.caJ'U'U ctcbc-clai i 1 1ccttc- nnr:ccc icuc a cacic -rtcc a CI :-ecci can a- a I Ic ccU aJjuJ:jIcc u-Y 1 - cia -ci eccacat era cicica it-c n,air,ec-LaI.. yrea:Urc nrccniti-ci-i cci La ac-a ca:cLcca-lla ecnii 'Li'; inacicica] 'U :cuut.cuThflil'l ycceacca n-cc 'U ccc arc-scec.a ::acc-L.i.-z cci c-ac- aUcta1 iat'U j:Iapa-.:cIea-e cc.tc1 ci: -ccci ace c-c-ai-acl --aria tiatacig a .lcrr.nti ear ccc "C•Cti'U a: ci i-cf cc-ecU a: 'I-c. Ua-i iac ccc rn'-: car -:r'ar a ccci c•ihc rljtflfl'Ulitcarccc cc J lr -ii (4) Myrmekitic basalts: To the north of amygdaloidal basalts the volcanics become slightly coarser grained and do not show the abundant chlorite amygdules. Under the microscope the rocks are composed of myrmekitic intergrowths of plagioclase and quartz, plagioclase laths, quartz, chlorite, epidote, and actinolite. Clinopyroxene may be present occasionally and some carbonate minerals are to be found as interstitial groundmass material. The southern contact of the myrmekitic basalts with the amygdaloidal basalts is gradational. c t cc ccc 'rica ct:ia 'C c1/.'tj c)'J1CU tU SU 'U tLcr:O Massive basalts contain isolated patches of welded ash flow tuffs and rhyolites which indicate acidic variety of volcanism in this region. The The thickness of tuffs and rhyolites is estimated at 400 feet. tend clastic with rounded quartz tuffaceous rocks to show appearance grains up to inch in diameter and cherty fragments up to 1 inch in size embedded in fine grained chloritic matrix with distinct shards which have devitrified to quartz and feldspar. The rhyolites are dark gray to black and very fine grained and contain quartz, orthoclase, cherty material and plagioclase. icc -a J ala c-cia 1 arcifc;r. bIl -b-c :r 11cr cc a -ccccL.r-ci ccc ic-acita lU i aia;yca,1c:a2.-c!L Air ccciii. tcc TcaU ccc ccci:: cii; �42 42 SELECTED BIBLIOGRAPHY 8'Liv:.t Goodwin, A.M., A0M., 1968, J!S% Evolution 'o1t'.ionof*2the •b Canadian .AU1 W4Shield: Oucihilti. 7 19, P. Canada Proc., v. Cer.&Ss .L; . 1—14. T"r.; Ct.C. Geol. Assoc. t9fl. G.I., A Study of the 'r.z?Precambrian fl3x,brtt1 Greenstones in Northeastern 6xsy a2 0,1, a 1971, J. Unpublished£.t? M.S. Thesis, tr:i.r, 'fl:t,g.Jv, Univ. Marinette County, Wisconsin: V:.nctctt; I':'jjj.b* flrcgotce Wisconsin—Milwaukee, ¶Mt' watuxMt, Wise., 'n4, ac. 80 p. kaecariu-kUvriks. Milwaukee, Hall, '*3.3, l:.tt MacDonald, Gtsj of Hawaiian rbra'.w T•cvn; Lavas: tact Origin Cct.a.ceit:.cct and Jor.z'.Id G.A., 2.JL. 1968, Composition II. In ic C1A.. Studies in R.R., Hay, R.L., Anderson, C.A., Li L., and im3 PZ'13't1D, .ntR; E.3.., 13 Volcanology, Coats, Geol. Amer. Memoir 116, ..1. p. !Lrtc.t' ed.: p. 477—522. 41''.-.t. C... . Soc. Ln td..,. 5c. A ?i3 tflTlti Wilson, H.D.B., and Archean Volcanism in the Canadian s'td others, 3*h1b. 1965, £racar. 4ssct, '1fl,fl., TIC?,3, & p. 161—175. Can..c."r Jour. Earth ttr1tt Science, ¼c1tfl?G, v. 7- 2, no. Shield: (!a isiC ', �'111101-32072quarries. rinP0Ni'L-lI: are monzonite 11:0,' (CLI 11110 0 - n:ioAmberg ,12375' of o'coon .049 0-23 areasS.1--401001-,C exposed:420 quartz extensive east, the 70. 1 7'LTU -4- About 17>77:010dates. _.t (1- isotopic 07 40701' by' indicated LJ'>--'7 70-4 UZ'LOLIO 2370: these -040;.1of. age to mile types rock 107 OLE,1101L7 I 101009 grey 4,04 i[0--0 901: 2oii::.o>oo,o:'- ,0Ci 1o .17 2,177011027175 22 relative the confirming thus monzonite, quartz Amberg of dikes 217 intruded po°i:coi:ii 0> "i÷11:,CL2i.E0TiJ C"C703177 07110. At to by is monzonite quartz 1'1tJLI pink 1tTht.7'100'[:7 Athelstane .02110017:. locality this -o%io in 't'I m.y. age. ill CLY 2o':o-p ':,[1723100LL 1670 to 0070:1 1640 being possibly ICY 04 01,1.11711711, 0:01,0-1 .$1t,:$1 younger grey 10.01117 1t10 Jon 'to0 23o' '0 .0':.is quartz monzonite Amberg the that suggest data isotopic '7700 .r7010E0 .21 10170. 2 m.y. 770' with 141-704.171 1110 0, o;17 the )SCm: 023C and Preliminary Cain Banks by given 2. ->24fl 18604-C of age (1969). 70: 171>41101 I Co7j,i407'01- (111110' 9:. 17'7 232 0 agreement 1 9IL2 good in monzonite, quartz pink Athelstane the for C 2017101>2" obtained sJtI}fr (Rb-Sr, 'UJCY'l[LO'ILOlL '1--Il-,: 7001-'> has - " '707 -1210 An m.y. 3011 isochron) CI' 0.17 age 70-0, >. been rock whole 50 ± 1810 "[2 of - '1 - ' op grey tro7artL monzonite. quartz :,co2 Amberg the ((10077017 be L14401-r2Zt1i!quartz Y.O&ol5 ¶'7"J J.04236y '7070' grey31the .iool0o?' '1. and (7-71- monzonite 92( variety, pink71170 the called Athelstane oN 0" 20'. 701-LI 971. 0.0144 -oo''rNj2 c-c L1277017'J'L177 1-4 ICLO';71'1 2>[ CoO 0211. propose we variety pink the that two the lithologies, of distribution [013 1 (Plates 79 -°Oi'0170[j 0-0107010345.1 9'; 0" 0t'7'([71]'1area geographic the of Because '2). '17 and Atheistane -7 the in in :-',-ntI being 4"-0, variety ,Costot:, pink '.distribution, 11 141171.' 101711 501>O '0 has t!C72J'1112-I 4111 U 9'. 231 of 11101 abundant ,7'.:ctc particularly wide a the 411 J'1 1042' I 04, and 1173 plutons, "OIJ O'ji'14,; 02,-2,O'n300 -'>4702711:1 7.110. 17° 0.1 -230.01: 2 270 that distinct four in occurring Amberg, of vicinity the in 4LITOTJ'011,10"-ilCo c'9 110 the oioo01mm grey 0o:o 05o11104:NL 99 040 %"4(",,'IIIL(U 10,> predominant €0is variety that established has mapping L7[0"4,;1 Field 7 were I(grey?) 0'. 1-14 ,n'c'L711012 2-0074LL'y 11047.2) 417(1 -distinguished. c'71II1I":0071194[: .0o-1 granodiorite Amberg S703L117110 separate atO 1770 and (pink) ite 10 granuI,,11.o 4L1 map a 'm:'fl'170:1,c4 .jo,74 which 0017 granite 23 170,% 27:3 t04' 711017I 1023 2Amberg on IJ.'00, presented and pink >0 of sample Amberg 't'rp 0427±701: 011:0, 4,0 103 2347--i';o (U—Pb, a ,00:: m.y. an pc'ooccoo :237:1:: Cain for zircon) 15 ± CCCI 1860 of age reported (1969) 4173 Banks .f0704" Beckman tLJ01"JG'?1110.01 ;7102,.$([4'141.1.''4114j,itN .lOfOO(1 "200112779 ((140 ,211 recognized were subsequently and (1964). and '1400 Cain by i.17'33by '- .21."OJ.2 ,:OILO.1t 710':. opo0 and (1963), so: '(Efn.C. .24227 grey '7-vo:7.1-707- Cain name the granite2oop1: varieties and pink Amberg 13,0 $:c04w-'0'7290'. originally 0d200in 70 1727fl..j LI'I'J17'>[-°' 13777> area rocks Granitic given:5 were Athelstane—Amberg1 the ' L41 DESCRIPTION: '$'L41.E-'-i-'2-2ltt 0.071372 quartz771.701 pink monzonite. 170131.1' 14 17704>023 40.7 0170.4. Atheistane into intrusive C: '7307414 41 11040,701.1 quartz are 0.'.II7 1%' grey -J1,0070'0'1'1' of 970.' monzonite Amberg Dikes 217>274-, '0 23 >7,47077(27,0 FEATURES: OF SUMMARY 1'00 1973 4,4:41 24 1972 700>07070 to March, '>C001111'25 Summer, DATE: 04 707 '1LIIO..:I5''o0 J.L. 011,207(2117,1Santa '0,1144 11(10:11270(1 -1771 Anderson, UW—Madison and Barbara; '"12077Cotter 722,73 0,70'j ''4>01 ,174'12°0Jy Corp., Lahr, M.M. 111>1" California- of 'opcq Univ. "o"7707; Myles, J.R. Colorado; 0.7 Medaris, 4"1VtC1(. 74 Van €L7.O 0007123 7-2 ':l7C'94[17'o4i o.fl Jr., - 41-123471 -"oLIlO L.G. '417 :1> UW—Madison; Kansas; of Univ. Schmus, W.R. 0 ' - AUTHORS: ., 1230 '720 sec. SW, 72 '7019,1171, R.20E., T.35N., ''741 C'T 10, County Marinette C *lUi: NW-&, LOCATION: °-: nol 01070 11111000 I 1.1110.,:Coo3ik.4 17-CO 012101-c quartz 9' :7041171: quartz 2310 2 >-fofl grey Amberg pink Athelstane monzonite and OIL monzonite TITLE: 17 2 i7'7"J7-[14137'7 Trip 171 Field Locality 43 so �44 to cra'n-g: tnc8, The Atheistane •' ?ti.rtar.squartz qta rmonzonite mennritehasana amedium— .tdtt- to coarse—grained, allotriomorphic granular contains tnC1 both biotite hornblende, grnttiisc texture, cazte, aotlafla blit.t: n:and !ctDbJSilfl4, and laSt has a a distir4ctivs distinctiveappearanze appearancedts due the;?4aGtLcS presence of pink perthitic toto VSe tH from five specimens tve pasine .i microcline and white plagioclase :L%4iC41dZiP(An fLu23—28). 2ti- 2E. Biotite ttog yielded values of lOOxFe/Fe+Mg from 71 to 78, but two other samples gave free '1 tc 10:. but ti., gavu y.eideC 'mpiUte aisSrhastingsitic iaorsgatzt'hornblende hrLh 'nieorr magnesian values of 85 said and 91. of 3? SI. Amphibole "aluts Foliation is common in this as are 'atit. as an hastingsitic hornblende. .yaattcr So acts's 4, tbta unit, recrystallization textures, such as aggregates of quartz grains aoryista.IUnt lea tn'.'a.'t, eush as s.srnstt'v e. 'vact endnmwith 'nts Saussuritizationof of;1.gtoe1.wsc plagioclase is is widespread, ''S'ep,d and a..J mosaic outlines. wunic c.t :.taa a*ssaLtrezcc epidote is usually bpdct9 43'S Jy associated with biotite and hornblende. tat flontc*rrp.nc n4.trocive •n 'stit. -/aluc. o 1cCflefZkt ot $.ct tbi sai;In hntsti: iorcts&e. ii aErcJx!? ittib bloti.u rx1 'bunfl.su's. The greyntet' quartz monzonite has a medium— kcdL'r'totc'fine—grained, fuav.znaad, ?ns Amberg 3btng rns nnvzcut.e PSLS Although hornblende few J) tto4L bovir twtdt occurs catynj in ft c.a ...fl hypidiomorphic hypi5 cnrfl to granular :'saaigir texture. tO Values of sinisrsl. Vctun samples, L1o;ite biotite is the most a4teant waCts mafic mineral. 'c. by 'ayfar tn t)as sol abundant martin. tn lOOxFe/Fe+Mg of 67 69 have been obtained C?and rn E3 Jte.ve t#sn ctcwkfor i'vrbiotite ?Co:ictfrom trri two i3 the ji, ..tflstit ;uac vcctv'.ib", toLiecSn Atheistane quartz monzonite, foliationsad and specimens. As saetnon. 4.c: in recrystallization textures common in the Amberg. Plagioclase tat nbov,. P\'aioo3 we ita.tt ! tmcn@'. tezttns b.ry,are CC!14vfl n' IJ, slip nd (An fl 22—39) is sxartrc extensively saussuritized, bsat.tt biotite is Li partially altered 39) iu y gna:c:ttzcci, to chlorite, and epidote plagioclase and with is, iS 0p2.*t* 14iis1 present t'bSift.t in :r p134.CtSta* satassociated 6rcctttsti R±1. tO CLLtZi biotite. blDt ito - I �,V 45 REFERENCES CJ[.idul! .CC r! y:' Banks, P.O., and Cain, J.A., 1969, Zircon ages of Precambrian granitic Jour. Geol., v. 77, p. 208—220. rocks, northeastern Wisconsin: T-'C ça&; - a a 3ZaC iRi1&t VVvrVy-:: :•L1.fC citA:C -: .J: - 7—14. J.A., and Beckman, W.A., 1964, Preliminary report on the Precambrian geology of the Athelstane area, northeastern Ohio Jour. Sci., v. 64, p. 57—60. Wisconsin: c:V. wViyr2;i:J t3-.r) aw V a L7V-7VVC p. #cl;lJ'C, r p.ct 3cn1V:.Cavr 1 or :.fc.TraC3Cr7 CICC C.. VVCC Cain, C C- 1963, Some problems of the Precambrian geology of a review: Ohio Jour. Sd., v. 63, northeastern Wisconsin: Cain, J.A., a �This page intentionally left blank �I 47 Field Trip Locality :771177 3 7 4Ci . 7217. . TITLE: .1:177,7.1 Belongia granite and Peshtigo trachyandesite : [7777717777177 77 774777' 77 1 777]7 '- 's771:p 774 1" LOCATION: T.32N., R.18E., Marinette County, west end of '.713? 77i:L'3.1": 77' 5r.: ,fl]7: 1, .777777, sec. 77" NW, .774 High Falls Dam 17,7] :1 t 1777 AUTHORS: Medaris, Jr., UW—Madison; J.R. Myles, Univ. of California— Santa Barbara; and J.L. Anderson, UW—Madison 77177771 °1f 7,7 .1"":77',.7] 11771"[7t7,! L.G. "7'77.I7i7.7]] 1' 7 5777777t3 DATE: 1971 and 1972 Summers, SUMMARY OF FEATURES: fl.:"" Peshtigo trachyandesite has been intruded by Belongia granite. A syenitic border phase of the Belongia occurs at contacts between granite and trachyandesite and as veinlets in the trachyandesite. .77'773 1777,7 .4,7 1"177177711.11 : '7711 77. 074(7!!I'777'7777L :7711 _•.••.1"7'[71.i77i7:7P77 2rc "l' 13:77 777 IL )7S,77:11. .72 77:77 .1777:11777.771 ''1"" 1 2777' 77 777777137717721377 7:77 '1771, .11'37i777 DESCRIPTION: Belongia granite and Peshtigo trachyandesite are in contact at but we were initially puzzled by the rather ambiguous However, after examination of thin sections, relations displayed here. chemical analysis of rock and mineral specimens, and discovery of more explicit Belongia—PeshtigO outcrops near Mountain, we believe that the Belongia granite has intruded the Peshtigo trachyandesite and that the syenitic rocks occurring here are a border phase of the Belongia. I 1'! '771.74 7771715'r.:]1i711 -'7 ''1"' .7 .1::.:. 7:7 1" L:771477727117 :714 777: .7 1:7117]. 77'I )hif' %7'.:''7r 1:) 72277 --"i"-j-L77.77 fl 71 717717717777: 17r1':ln ..7277i777...171,'7717.cL7:7'C€ .1:177.7 7)1 .7777777 57,777:7 '7'":'7c 7.777 1' 3.277]. 41 7'r.7] 71.7717 , 77 7777 577's 7772'71117771:1C1 7772 :7;7. this locality, 4"" tO.€ :r71"j0 7777." 13771 771" 7Y77 17'1]Z1.i7 7771 7717': 7 In thin section the Belongia granite is typical in appearance, consisting of euhedral to subhedral phenocrysts of alkali feldspar and quartz in a fine-grained matrix of biotite, quartz, and feldspar. Granophyric texture, a characteristic feature of the fine—grained Belongia granite, is present at the margins of alkali feldspar pheno— crysts. In contrast, the Peshtigo trachyandesite clearly shows evidence of recrystallization. Relict feldspar phenocrysts are set in a fine—grained granoblastic matrix, and the phenocrysts are surrounded by a well—defined rim that is intergrown with minerals of the matrix. In addition, anhedral poikiloblastic hornblende and biotite are scattered throughout the matrix. Thus, thin section study suggests that the Peshtigo has been recrystallized, presumably due to intrusion by the Belongia. Th7.T177': 1171:17. "775fl[ 7717 77 71773177112 7777:1777 L77 :fl 777".5.7 7["'777 .1]]; " )74fl14177 "i::7flfl 72.7.177 77 7 7771[:7 7 "L"' 7:7717 .77177'777j' 77777 13 21 27712772 7:.] 71" " 773.i77771771: :7L 71777.7777* L :777. 71.7:1fl7> . [77 :7 .777 1.7777 7: 1]: L,7]17711111717; 7 11277777 1 W.%' 77:'7.1 1]7:'77 7:2 71752 .17 •'1 771: J3.:'777 771". 777 1-:j7..;71.)7 ]77.t. c..11-:1tse.J Cc::"777]i T.7771":1 :7 ::71, .7"7L)777TI"".177#' 47 77111 :7,Ltl '77 1)7771277 17 2 :7777 5)771 •70777a'!l 777 77.7: 7. 7271] 7!1$ILTZJT'73 .771 7]12777]LItflLl7. 777 L"p: 7j7 77127.21477 c'77 711'1 771r!717"1:771.I. "1,7 57177C71321.'717T.77T7]77]1.:17:7777t 7771 777777 177,772' 2 7777 7157: 1:.7 177": 77.] 77,)*" -ij 777] 71 71717247 ,:7117'71$.C7]1 7717 751 1T\77.1.777 :7c.477t? 13 .717 ]717 7i:17"77'.121*" 7.17777.771 :]771]7ifliJ7,77, '• I LI 1177)77771 7.127 F*"V 247711€ 1.! 777 1<"L 777 7,1' LI £2 �48 If sooolttc con'ca'o to Do Lweaothe th: tctcocgla The occurrence syeniteatat contacts between Belongia ot'oi. and 5l,o(1''3'i1Ct of 33,0 1130 ?'aootlg'c. o:gc,rthat tool the Ito Peshtigo and as Peshtigo, suggest :'sii,I 543 :ijcutting ','to'nc the at- veinlets PSOJt ig'IcLc" 31 soil ai coct'iaco; t%o Fir 'Loll :a Chemical syenite phase cS of the Belongia. analyses-'o,,,:-cio'a":'o±o demonstrate 'a border to,'1oo ;l,ooo to' a 371 33 Ic is t'Ic,t of i,'30j nie4!,r::e between teI-'co-a' that ,:3 granite tYct I to La that composition ofI syenite is intermediate to'a ocopcoTttitoia tin— '1 the laic na!c'ci: , 3 Lilt Tot I -oo 0 of E' biotite t1"aI amphibole I:' 433,'a' and and trachyandesite analyses -L a tO 1), but ai'aca'noD'aioitirJ 1,9 (Table to-,':- mafic t',3333c 3:01375330 (Table reveal that To Fe—Mg St :aL:Lco ratios acoare 'Li (1.':(1,ir higher for minerals from coal 'toao 1,3 jilT:- 2) iD 101 cAlthough i,'Oli oc'aOI::'a1013o I .; granite and syenite for those from trachyandesite. 300 tiJti" .3 to than Inca :Fctr'.ooov't 010'tlL71liOtaiOili o'aY3been toot due coo ppartly cool4 to contamination development ofaDo thest-coin syenite could have cçco'at 33 :c' COOLO. 40::3 in the it': '000lL-:icof granite by in':' reaction i"ac",3or 'ttL with i33--oij5i,'o'ac't1:atotrachyandesite, perhaps reflected 00 47-0233 :' oco (1969) have occi '['.4': '-orb. a 'ta'o;tatvc :3"a:c(J,o 1: Ti02 content of the syenite (Table 1), Luth and Tuttle TaL 3Iii"L/i'ji_ :looo, in a granite DLI 'a 7 cici'S flO: shown experimentally that a syenitic border phase may form 3,1:3233 3:0303 tool: 333t4- tl"at a rot' tiC bcc'do:'t margin of '1, t'ova, 'lino cov'c,'a1iotto 5'ai'içO, 04 113(133 taicc,:'o :3 m:at,a33al, due to '.0 vapor transport of material between the crystallized 'cot' olcJLly a:-' -, to. still partially molten. 3 1-111 33:3. '30 Theinterior attot' ci.' portion, an intrusive body and the otto- oat:": 1:33: ., 113Th : fl331 53123'i'34 other o':'oi"c, Belongia iIOiL'Cv' 'a 1 coal 1,':i:t where :441301 localities Syenite hasU'o'co been observed 'ja'aor'co:I at 3-' several St-a'otts tao 03713231(1 to-i 0? 'Di':,t3o alliLlOl' 4001111 40' 1PC'(1'0'flL 'to, granite40has intruded either Peshtigo monzonite or Waupee volcanics. 030'L3' 30: 'Il,tflhiilo',I Doctirltig'; lco'30 monDi,: _.a Peshtigo on.:4L4' intrusive oa o'ic'CLT?t into For example, a clearly 1T33J'cI1.2 'a granite 03:7(1(10 to is JILt:' co:'o'pl c'. Belongia t:'at-ooc:t 33310, tiT 3 037'L':to' ''at ((1311 0307' 1:130:175 - (at the boundary between sees. zonite Mountain 133. a a arailroad aOL -i,-.ti cut near '':'tc'c.t'o in o"o.II:',,. over -ova:: -33-toogranite 7aznt to grades ::co)a::: :113,T.31N., 3 2a - R.l6E., toar'lc County), 14 and 23, 5, 1411, -' Oconto where 44 an'S " 14 sharp that lb-ta :':."icoo several inches into aa ot-a':.ita syenite zone 11 inches thick that has a "-'23,0' 18 L,n too :co,,c orCosi. contact against monzonite. 00(1,3107 0-33--o- Peshtigo Foahtig'o acoacasi,'ne . - - - :1 os:: 32' 23 7110 Jtra--O IT, Electron probe analyses of331 Belongia granite, -o'ot'o-ta 37:130and Poolct:t 1(1:03 •o:ctoco-to Belongia border phase, and Peshtigo trachyandesite 117230 Do: cog La 3-o'--do" Table 1'fc:lo 1. : - 1 31133 Si02 Ti02 1144 153' Al203 76.8 2 65.2 3 .68.3 4 57.8 0.21 0.70 0.64 '3-14 1.45 11.62 13311 15.31 141,43 14.28 16.60 Fe203* 3.20 :- . 6.67 4.48 10.80 MnO 0.03 0.02 0.05 0.12 MgO C, 13 0.10 0.57 0.63 1.36 CaO 0.75 1.52 1.74 4.07 Na20 3.16 3.66 11,13 3.76 41,434.49 K20 TO 5.15 6.69 5.73 4.35 101.02 130, 4 100.40 99.61 101.04 331,331 Total * 1 1 2 :j 3 Iii l-i' as Fe203 Total FtFe151 Total Belongia TM' 2C 7-si cng1s granite, g"iaou' <.0', tb TM 2B ,': ar in iic Po,3c'' <ki<:.Y-i,?3-.,.,0a113 Syenitic veinlet Peshtigo trachyandesite, 'TI 44-',ji,-' 'at LcOAi±,.Yc,'0 localities Ji'0335 at In-oi"co: border o':'tii,-' phase Average two coca:yooo.. analyses, Belongia '3 433 7.7 '23135 of iLt'i - 33 and 331-3 M2 near cr4 69 '1va:c. 507'L, 171.2G :0: Mountain, -S 4 33-4 Po:t'cSoci Peshtigo traco'H'ctd-oo'' trachyandesite, to, PP3 �r ;ratictf. rnn.tt: 513—548. 115, 144S. Mem. Amer. 513-tk4 p.p 113, magmas: ra4xnc granite and cqut Soc. Geol. 'wti granite with -v..tl' equilibrium in phase 't p)tas vapor hydrous Thc The 1969, o.',, 0.F., Tuttle, sa and W.C., Luth, 'c4., u.ctb, b.1. 'rico: hynct Lr br RENCE FE RE Tfl PP1 ittu. trachyandesite, Peshtigo hyeztlc tr Psuitico 2B ai e •nvhth: frar from Amphibole iii 33 from toltts Biotite i?n 44 TM nttD)et, veinlet, syenitic nctatti o's from1 Amphibole te.ptf'ace trachyandesite, Peshtigo psgi; t.1'v&&Sp' 'r ytr2.sj, PP1 13.07 3$' 8.81 33.18 32.07 32.eV 28.91 0.95 t\t LT4 0.74 ..Jt 1.06 3.85.r —— . 9.76 :.. 10.00 .0 —— l.fl 1.75 1.76 •,fl 1.33 1.45 98.18 98.51 94.5 80.8 95.1 •—-. - z ''.3 Mg + Fe Fe x 100 t caE Total a; Fe LeO as FeO • 1.59 8.37 t • 22 2B TM CL veinlet, syenitic M\I&).tfrkl from trON Biotite g:aat, granite, 85.2 93-4 96.4 0.92 3.72 3.tt 2.81 2.3' 1.92 40.97 41.40 96.22 93.54 43.4 95.72 9.12 .aC CaO MgO 0.74 —- MnO 34.96 541S6 34.4 34.98 '* Total Na20 -— —— 1.02 ipr ItS 3.23 K20 8.59 8.61 —— —— t —— —— 14.26 13.22 2 3 1•,• 5 1 Belongia Biotite lainsgLt from fr3u' igtite 2C TM 2 ts.' '5.i 34.07 34 34.17 .fl.fl 37.81 4 5 FeO* A1203 Ti02 TiG Si02 FtC2 .1 1 Peshtigo svt granite, Belongia Bc1cv.hs trachyandesite kcsht.7. tp.cl';'w&lsssatu and tw.e, phase, border :cndc: Belongia $,1tvtga gns:.ts.. amphibole and btuu.tr, Electron ¾, 2. Table Yc,tle 'ca from açb±ao.s biotite of a! PaL:flS analyses ;tct* probe :O4v,n 49 �This page intentionally left blank �ICnI CCiT 4. 201CC C of rocks. older CI:o--otcCoo:: CC. contact CC diorite quartz Hines the of Emplacement T CCC 505 and metamorphism 5. p1Cc gneiss, Macauley quartzite. and I51!C q11CC. Waupee 50CC coo and CI:;:cLt-o of i 'n5-5 CjC C-C clasts contains metasediments, metavolcanics which conglomerate, Baldwin the of deposition subsequent and Erosion Ill I 1 ::LncF -C v. s> iir.y contemporaneous). IC5Ci 2:CIT been have may 1. -;:Yr;o os:TzCCpL C5=-C4 5505 rocks. sedimentary quartz—feldspar "Cp;C1Ci:tCnCoiC:. pooo CC53I5.0CCC !4TN pzoo agglomerates and volcaniclastic, and 3P5:17 "0C0CJbCfi0C I?C'IP"Ss the t? 1531 001;. of Deposition formation, Waupee 2. rCLiCTCCCIFICrC CCCIILYIC 1:*.CCJI-:;J:L1. metamorphism. contact attendant with TC7CC5 CC0CC quartz to 5CJr2;0C2C2(C gneiss ;;CLCtCVC Macauley t5]5 the of Emplacement monzonite) (granodiorite 55050: 3. CC.OUI101111C55.C cCCCCJ Ccn ECO metamorphism andpC1 Deformation (Events 3 CCC and IF 2 T CI?C-lC;1CUC •Pco "OCCOCCOSS tuffaceous, and calcareous, s-si: , o::coopJ.. o500CCC flows volcanicC — of consisting i: CCC;: CCss5 CIIICn-5-I 1o youngest: to oldest from events, following the including "00CC 5105 CQ:CC5 515. 05 [CCC C C area, 03. preserved CC SCC0s Pis s'; history CC T :oo 0C3[inCCcC. Mountain the in Precambrian complex A AREA MOUNTAIN THE OF GEOLOGY DESCRIPTION: 5Th CC C yocovos:siffare 0CCarea 5525 Mountain 5055 •5fljp 55 theC10 of history geologic presented. j%05 " iTs I? p5±5:05-C: C 5CC are 001. 0iIL map iIT:iiT55 outlineIbCC sketch A this at illustrated the C ofr:rT1[1s,t and iCtC locality. T20,.tC.ssclfeldspar .5005 ç;- Hager and rhyolite, C5'5C.C..:C 5503 Baldwin 1: l:10flp --F po Hager iCStsy:3 conglomerate, Th; porphyry 115100551 c CCC0?2Ci CC 0111 the soI1C.1CC.54:L ;cs member upper :51 Waupee Cs:. between formation, the of Relations 5-: C .JX5. :1 Th FEATURES: OF SUMMARY 0±1:31 C3 C53, "CCSummers, 515 0151 1972 and 1971 DATE: Kansas; of Univ. ChlC" I"C"1 Lahr, "1.soo; Cotter C CT and M.M. Colorado -Corp., ''I iS0CICi5iC1I._L33L ":— Medaris, 1To_ -"_y; L.G. Schmus, Van W.R. UW—Madison; Jr., AUTHORS: .05:550 R.l6E., T.31N., 505 Oconto P110:3 County 1,- "51511 sec. OilS SE, NE-, LOCATION: 5525 15Mountain area C51CCC1 5I5 rooTs and 5i-i'5j: The 55 of geology :'o:c: P5511550:3 CS and ". 1:50.10. Hager rhyolite the porphyry 3"Ci1±5:5 feldspar TITLE: ;-iIs 55±:13[ 4 Locality •P-sp Trip P1 Field 51 �52 ". 6. H7495707)f,aJ:Ci .7,5', o'ios.t batholith OItco.asIs"Th (1450—1500 cf"1sc of the4aosf Wolf River m.y.), including H, .5nc1s0J, 7.57l5y7$),L5, 1's-Is'S Igo ,)ç71(33t Ott Hager 51'051'," syenite, Oju'tlfS. feldspar the Peshtigo monzonite, and :t'IJ .137 '.7" porphyry, 9,00 )159551:17ç0755:7,351 of xa0 Ool 0777.0 granite, son's tO with rhyolite, Belongia '2, and 75. lOs contact 1c)ltol, S metamorphism .1:)' older ..dcicr ,&557'J.Kt9'77:,51'5 Emplacement 11 : rocks. r"77''3'1 1' and 11153. steeply 2713 Waupee 0'1157'55',t.'sOi dips The 'l1710'cs formation '.111 strikes N55E. M15)507•O' about '55ss011't Ot.o':, 7-oH sot Relict llTGaO cross-stratification -3)77)3'- 555333711 '1' 370- :1' 3111W '1.7 cccfs.Loss.g ¶959 155a55'3 that graded bedding and consistently indicate 'I,7ll'075'1,0'I'L' 17'a'lst tops llTs 0: of1150053:9 beds are to to tilt the.5-cotio; north; there 1't$9. is no evidence repetition "16 01531. )1a955' for ''01 '25197:5 Hc:is of of. beds 3159 '90101199 15. 0571115 the within Waupee formation. C'r'flt CI'S, 5 15 /Ot. 51531191 has 11751 Waupee l'a'ITJSOOI formation ,sLo-a9 units ooc'ossI,s.tLrs'. The fIlLS. been i35,t")5757'5 divided offosSinto fo'•:a three (Fig. 1): 1)5 1195107 ot.55:1i3. of SI'S' metavolcanic a basal member consisting 17I1''ois aIl91a1:f'9$ £9.;-5.."OsLC-2.111.5: and llat'95. volcaniclastic 10 0jIt,L3'jLI4111-'1O meta— 1s-tS5-' 0 and sedimentary 1701 rocks, .s. .i:r: .L 515517 .9075 '91317 :o'o 1115719 1:71)517' 2'3t1J510'LsttiO'7 3,' a :nmiddle metasedimentary member, IsIS. an Ii's upper 505,105 577, the 1•''hP'S'a9omo 97i5'31-,9'.1. 995'"a,Y'T member. Within 7155711] tuffaceous metasedimeutary 0)19 'bas,sT. basal member, .111-:'5JLY-157 basalt 7r)t),51.f"7'1i75777,7 7:7357, but 71j'95j577l977.90al5 type is tHe the predominant of volcanic rock, andesite39 and so 553,'5.7171,55,9, 95,7 rhyolite 7'575:.7J 17553 LL77of 3-"'11M 53'H. occur toward the IsIt top the unit. '0091a5)5L. ll,rt5719 505 Chemical analyses of 18 specimens fo:..caa,r1c 7'''-L1' belong )1 calc—alkaline 'S's a 'IL's.volcanic 'loScolt: rocks demonstrate that :la57', the 5505)7259, to :::li053&1OI,5L.i1S sequence 61'.7617101100 )1.Ja-5 7"t9.?aO 'lOs 7,15:7 setting 7 15571,5 '1717 (Lahr, '7755 and 55557:J could have originated in an Ifs island si 1010 arc 0511:57:7 - 1972). 15 ., flC."')071,079 in formation have not been '50aup:c' .ls:-as 1395 11513'I '.1 the 'LOso Waupee IICIiU.tO 75377' evaluated 091.955077: 73 L 55S .e.1700 of completely yet because 0.1 complexities '3 lo.ç'I357._ '0.5555 introduced 5517 1710'7953050 by over11' 9523.' lapping ro),.esn0:s'caJI',:ot.'oaotlll metamorphic events. 02551 Most ,ss.jsocoLccoI specimens cOOT) display 2157710 :)0'9t7'107 9' assemblages 119515 :.os05bs.s5-os.., but characteristic of amphibolite 775555a'l 1a1'OT :3 facies '9) 57's metamorphism, ffl'.,'I:,'esso 5253 505 s :05 S:,'I garnet, 99251r17:IL, idocrase, 951-7','s occur 5j05'51,']0i05 :7'): of .a5.,7.2:0i1rs)Ls7o origin 07 contact 1:50795' .15371757 in scapolite, and 917551 andalusite 1c5715515535 metamorphic 151. rocks 11052.957rhyolite 05120112:07 a-'.1'.'.':112 ' S LOs, .11,93,1 51'-55 1591.Ca1s7'lOsSI Hager i05"15'7i 719 and of15i.lr-a7-si:5:''so.as appropriate composition near the Belongia 11 granite '2 91507 191519315's porphyry. poJ1o1'-a-r7. and feldspar 54.5tss,j/:1''701H1s Metamorphic assemblages sC71i07.,L1,a-535I' - I .Yo' 0505137'rIrtf FIELD TRIP LOCALITY Oi' '12 57t11&5.' W are 9552 tuffaceous In the woods south ofofCounty :17025 outcrops '3'S '15' '5152 of oco51 S'a.a53'j, Ccor Highway Jo. 255-1 3'S:. the upper :sLseWaupee 'Ozcspeo formation. I scoaost)'oRl , Cot On .sp,o"— member co-s 5500of c2 the :),',5 r,"i1a'J5711 a 7H50'1a9 15i517'N3,.,9 rr 351L75o1Tll 015 232 the north side 95) of the highway ", are outcrops of Baldwin conglomerate. 155' 571111 '5550 1,i,a 1 :1195'i.99 t'LaI of isiS Hager 7:55:95 consists 7150151105:112 00,'I1t1:. in .,5sli05751' 10959, prominent The highest, most outcrop area 1I.osOOr feldspar 071 this 51513.51517':53'9 porphyry, and between porphyry s7157 Baldwin iOssl7,'sr 305. '9 S l91:1tt fa57']feldspar 2T1515 10071950.) fl:. and -170-a an 501 intrusive contact l'07a55211 ,.$j)07JL base 7J115 5 '),995':' Ca.JI1L/ii0'7 On conglomerate is 9-97,1,35,7 exposed along of the '571.9 outcrop. f37,5 the 7,75'55 5' IsO a95to'10 the 1.150 southern 3a-1,-,j,,'7, :55 7'7';:177:711'5'.7551 S a,'505a5751117 97 55515s5.t 3117.11 1':571,Wf90 15157,955 north side istot)' '5577,1 of the 171 prominent outcrop a gradational contact between Hager 513:571555775115 is exposed. 512,25,'s'4'955, rhyolite feldspar porphyry Cf 'Ccilooosao' "Jr fl I SLISO and 55) 1sot1.rl.aio'rocks "3/3171]inr, metasedimentary .579 55'- : REFERENCE 77:111715.153'? of a greenstone a:o Oconto 7:173,j1595'S.'1 a lbol.. in Lahr, M.M., belt i0'1k, Precambrian .51]39s95.5'5 95, geology .1,19.: 1972, '.i1,57'.715'çj'iT eoa;c-- ''3L7;5J115O. 93'0)'i95!'s'11,17',: of County, Wisconsin and isiS the 117,15 Waupee volcanics: on'I geochemistry -50155117; ')'b"cO' Univ. i'a'yl 797j'sis,, 505555 M.S. Thesis, Wisconsin, '55'H.s')'1n7 LI, Madison. 'a I �P4/ // -. . ' 1? / P. / Jp \j r4 ( "/ /7/ \4 . A /i '-I ( - ILI 1 i-i;-' 7 ILk .1'<• - '4/ ) LL L.G.MedarJr&MJviLahr Baldwin conglomerate bc Macauley gneiss WI wm wu mgn Hines quartz diorite hqd JUM ['?IL¼ 4 LI bg Peshtigo morizonite pm 1 metasedimentary rocks metavolcanic and metasedimentary rocks ::;. tuffaceous metasedimentary rocks Waupee formation ' fl4LA!1.. ../ 4..I/;1'. i :-.-'I bg Hager feldspar porphyry Hager syenite hs hfp /)7I:4.75 Ii5r! L_ '/.fl/II/1,lp J4I., T"L4//J A/. H a..' 7 1//—/-. ://j// Mountain Hager rhyolite hr 4/'.'' J11 [7 tiar'I•t I [7 d I4/iiA] /1// 1/4 —117 hr Belongia granite bg EXPLANATION ±iL j *¼-; C,T R / 7 \/ 7:; /1/4/ I mile iL ¼ijI(4// ri 4/ 17/ If•; Tij 1 A S J. I//v hs I'.. j(( / -. / L A" j ,; ;.f/.:/,H LdhiJI.% 'I 1kv\/ D.cH (T. ¼' GEOLOGIC MAP OF THE MOUNTAIN AREA 1• j I i �This page intentionally left blank �55 Field Trip Locality 5 [17 TITLE: The Wolf River quartz monzonite t1ILL_JJT C:tCHH[1 I_• L LOCATION: Menominee County, on the 11° IL — -t IT VT — Z,? — H:. _— SE*, L sec. 22, T.28N., R.15E., of the Wolf River west bank NEQ, V IZ"'I]°( AUTHORS: L.G. Medaris, Jr., UW-Madison; W.R. Van Schmus, Univ. of Kansas; J.L. Anderson, mv—Madison; and J.R. Myles, Univ. of California- •1Ii C! H HHF4 <Jj 'C ° HL1 I ° c-HTrI - — I I — Santa Barbara l1J&flL H >(j(! j DATE: and 1972 1971 1LIIC [L 4IT°'I HHTI Summers, FHHU1H SUMMARY OF FEATURES: 1;2 (FFjj!i' Exposure of typical Wolf River quartz monzonite. rT4I ;i HLT DESCRIPTION: VJHCcYi The Wolf River quartz monzonite is the most extensive lithologic unit in the Wolf River batholith, accounting for 51% of the exposed area (see Fig. 1, page 10, this guidebook). :cc çT :I I TI .T1FIHTJH H i :• L — The quartz monzinite consists of large, pink, ovoidal alkali feldspar grains (1 to 3 cm) with a medium—grained interstitial matrix of quartz, two feldspars, biotite, and hornblende. The quartz mon— zonite is massive to slightly foliated and is cut by aplite dikes, some of which contain scattered, subhedral alkali feldspar phenocrysts. 'yHT-H[iE i1 H=1I3 C)CCI JTflT1 ''HH TcH Z:tC cq 4T'L©H t= 2Hi)II He;C5 c(qI HHItJ:HI .CCI HIP 'IHI L.V :H !F L H4 I C L ;4Q p' tJ L — II F' :H -( At several localities along the Wolf River the quartz monzonite has been intruded by dikes that resemble the Red River porphyritic quartz monzonite. Two such occurrences are well exposed at Beartrap Falls on the West Branch of the Wolf River (sec. 4, T.28N., R.l5E.) arid at Ducknest Falls on the Wolf River (sec. 27, T.30N., R.l5E.). F 1PE I (C ° ( °]i 1 IF Cc 4j1 — t7• :.:Z '1J :__L: 1 I Tj )14V C CvI&L i:;: 1 IH T1? �This page intentionally left blank �57 l.it:c Field Trip Locality T: TITLE: 6 The Red River porphyritic quartz monzonite LV' VeEV' n!I41.V'iSLVt eL'ç LOCATION: :;l :.*T1Ti °fl R.14E., Shawano County, T.27N., 2, V sec. on the Red River )çy) LV' 3IV'C Lyi; SE-, aL •IpLVI:. SW-, 37 AUTHORS: UW—Madison; W.R. Van Schmus, Univ. rV)Vi IV' L.G. Medaris, Jr., and J.L. Anderson, of Kansas; 13W—Madison 3: 3 -3rL-t uTmfl )JV DATES: Summer, 1972 LLZ1 SUMMARY OF FEATURES: V'J Exposure of typical Red River porphyritic quartz monzonite IL c:V'VLVV'I ty r)1[ V'L TT. fl.d:c r DESCRIPTION: IV' The Red River porphyritic quartz monzonite constitutes 20.6% of the exposed area of the Wolf River bgtholith and is located in an ENE-trending belt between the Wolf River quartz monzonite and the Waupaca quartz monzonite (see Fig. 1, page 10, this guidebook). ')t ç •iV' i ThLV' t)L7- V':tJ V11:rL LVV' 1V'V tT LV'4'Fli i ir — - Fl I1 —ft VD& :: j VS Cif1V2 'LIL7 4•II.E '11 1> tcCL7 At this locality the quartz monzonite consists of 10 to 20% subhedral alkali feldspar phenocrysts (0.5 to 2.0 cm in length) in a medium-grained matrix (1 to 2 mm) of idiomorphic to subhedral quartz, two feldspars, and biotite. The quartz monzonite displays a prominent foliation due to alignment of feldspar phenocrysts. çJ t. ;"zV':i' 2QVSLLtIL tLY- zci rzc1; LV') ° C)51 I i i —n nj:tccri cj ' LI I $3 'I TTi3i. LTfl- LJ H7Q7f 1'4.T 7Lta1V'fiIflC LC TL6I;=LY c 11 I €4 i)v&: �This page intentionally left blank �Dissertation. i iv .pcc...Lc I cli7Vl LiC/, 447, 4I - 1965, The Origin of the Tigerton Anorthosite. IITIL W., Cl-1c41J, L. C-.Il-: unpubi. Ph.D U. ci ycv Weis, Wis., fill-a,.- (IL.fl Reference -ccr-aiI avccc-vcc E NY. y'cc 1s14.; The most common twin is the Aibite twin. Pericline and Carlsbad twins are common, the latter has reentrant angles. External optical scatter occurs. Grain size reflects cataciastic deformation, with some outcrops, e.g. SW-, Sec.11, T27N, R11E, appearing almost layered. - --21 a- 1,1:1cc1 ILsCflacc C-nt-C-I c Ct d-yC- 411'tL)CC-Ll IltILl I Ill-till :?fii.a-fl ILl cca(a II4Cfi\C vral3cc c mc,ff'lvaw.;. cc-vt tc-;fl,; cat- rcrt-ntc'c c-cc- crr.a-: ma- t'r d-a 'cacc:ca1 - - 1fl'- l-714kC)ll 111 -q. [I 'C - 1t11-:cO1'ILLclnCI :ccw cn4 ccc a, La-trcitczcc JlaC(.)© 1-ILl The composition of the plagioclase by outcrops has a median value of An53, with only one outcrop having an average over An56 (An60). The larger common inclusions in the plagiociase are hematite, hornblende, biotite, ilmenite and magnetite. Very fine rods of these plus rutile also occur commonly in the 010 plane. C -1:15 ;fi-- 11117 CCflV II c-4;4c-a]aiI fill 9hiT .. -----Cr r'CCccc-accrC I41( 1,ji .11-I-1141".LT flC.'-iiftL)tCCll.iCCrIlr 1.-I Ti Ic'.: fl1-cr ar-;a 511:5-Il pa 71 ccv caaltC- cat iall: tilcIlla SILL l4t1c cccync city CLLLCa-l .- I aCvcc'-.'L-rcr-- a-y1 a-ILL - - 72-rn C--m:ig c- Lid pita- fill-cl cia: 111:,ILlfl t 14 a-fl TIc c-c 4p1fi.1471: 4 Tdll The Tigerton anorthosite outcrops always include granitic material. The anorthosite exposures generally are small with the largest continuous The contact with the Wolf masses exposed only about 35 meters long. River batholith is sharp, both megascopically and microscopically. C- l.-L1IL C 4llIIlLlli s-1 Cr1: 1ILfitilT1 4-c- -fit-IL? .111 pat.-: mc --fl icy c--cc -r-;nt 7ia-a-- ccc Sr Lccr;-:c-5- CCr.L!-C,IC.S, I4cc)I1IJtLcI LCt -? ll1-rcill cLttcc ducc-ca:-c cc macc-Cr ,Lt c- -I-Li- cU I cct—aa;caac 1111 'i'jj .clcCnrczv 4( ififi 'wIIc C_i.4jL :c'ca [IICLS The Tigerton anorthosite may cover 125 sq. ml. in western Shawano Most exposures are anorthosite, hornblende anorthosite, biotite anorthosite, or gabbroic anorthosite; a few are anorthositic gabbro. The plagioclase ranges from An32 to An64, with most of it An4 to An56. Grain size of the plagioclase is riab1e; 5 cm. grains are common and There is local foliation. grains up to 20 cm. occur in porphyritic parts. Biotite is second. Hornblende is the most conspicuous mafic mineral. At some localities pyroxene occurs as cores within hornblende, occaIlmenite/magnetite are common, with ilmenite sionally it is discreet. Locally, as in the SW-, NE-, Sec. 33, far more abundant than magnetite. T.28N RilE, these affect the compass. - 1'C--Pfi-dP 'lftT -cCL C 0147 C '- cc-a-c1::' c:n-::--c4crn 1r1k1 a1.c71rcL-c CflC:rT fit c-fl ?cuvfi 1tcc flalcILa -mir cc -s- CL3r1:c-; ca-c-i 71 I .rrjrcLflcC, 1 fl1 imLad I.- 71 --••c•'.1,T-fi ;ICL :1111-ca- II .11 40 lIla 47 v-IL-v1- I;LIc 711LC:L. It l- 'ta- - fl Tha-LLa-..Lr.plc :2 -: IL11 v; 1OCT11 iv 'my H ;1:;l1caifl: cc-co'rcicaa'Crl a.CflILc-1 cc Cfl l.t iltrI.II. IL? 1-IL -ca-; 1i-filc.1iCi ct-cl pcc---J- C'IfiL di -cPU Cm II- iIL-0I- ILL/v a-; l'1fi-c-LJlJtC..,-lc- It -ILlIC d-ll-t.' 11: C., I CCCII Ii CJyII13 tt:tdt.IL-'c9 ca--n vcc: -Il 210 c-ala-crap wcc-. alIt .1 : ma-arc :ra-171IL-.:l? --cc 7. c-t7 v5rycrcrcc -c-laIr 1:1: lift —flIc fl -I-fl 7a- F I?P 1a--A5.IIL am cap-ct s. 3111ilyfitLcilfl SI-Il iccr:ILC Or? Ca-a-la- I71ui cmiv Cq ILI-i'.-p Co. acILCLICL4 DE SCR I PT ION: '-c-c cLLcaI-zccrcrcc r-;r-c-c3y, - p :l.l?lIlfll- Lt--[ a-c Contact relationship of the Tigerton anorthosite. - ?S'7cfl,,:cc £4 SUMMARY OF FEATURES: -,,- 1, 7.S4aJJOIS Summers, 1962, 1963, 1972. DATES: ::cy-=crv-aw-14- ::.r,,-1l- . dd?IC/ -c a W. ;a--Il1. L. UW Center System—Fox Valley Weis, AUTHOR: pcc-c a::.:ip-[ cva-vc.xct1ta5 7'IlL.I-J 1C Art 50i1, SW--, sec. 23, T.27N., R.l2E., Shawano Co., Middle Branch Embarrass River & Co. Road J. CrC -cT m4fl Cr1a' Cram m.-ra-1rv iafi 4c NW, SW, LOCATION: 0711104 211?' iti J(?lirtj, a-kr. The Tigerton Anorthosite TITLE: Lcc-mca- -rfl;a- p407,1 Field Trip Locality 7 59 1 �This page intentionally left blank �61. 61 ;' r:iLca ctr:L,o '1 Field Trip Locality 8A TITLE: Ec1. :9.e 1 au b Eau Claire Dells County Park LOCATION: CR sec. T.29N., 7, R.1OE., Marathon County c SW-, AUTHOR: LFLtirg; UW-Oshkosh ]1 Gene L. LaBerge, DATE: i61TL iTa\ 31.1b721 Summers 1970, 1971, 1972 k ''..J1i1S J.5l AH1A: A SUMMARY OF FEATURES: i2]7s; bt izA1I ti2 D:1L :Laite Ia •iL9.:g;, Eau Claire Dells is on the western margin of the Wolf River batholith, consisting of a large expanse of relatively homogeneous "granite". This is in marked contrast to the volcanic rocks with a myriad of small plutons and large scale shearing which characterizes the geology of Marathon County mapped by LaBerge and Myers. ti;i 2' Ai Ian©b Ja ct eTk aag 1xaa a; g$gj ;a-& iLt:.ny riA by i2t :-J tztiL L(C) :tLCJ .CCRH ;cauaacti.c th;. I bt]huA ijc1i ThISCZ ra' IaL'Ltari±n C,oaarA •f gaagy a.:atEcat a3tcrc tXT CBC a arIact A major shear zone which strike approximately N30°E occurs at or near the western edge of the Wolf River batholith (informally called This shear zone is the Hogarty hornblende granite by LaBerge, 1971). particularly well exposed at Eau Claire Dells, where it is more than However, the zone has a mile wide and consists mainly of mylonite. been mapped for about 30 miles along strike, and reconnaissance to the southwest indicates that it probably continues for at least another A number of other shear zones parallel to this trend have 10 miles. The magnitude and been recognized farther west in Marathon County. number of these shear zones thus constitute a major aspect of the Precambrian geology of central Wisconsin. Cl AIaL9©11 V .t 72i icr: race Ltaa :cccta it b isad ArAc: c'c. c:'.rc;r CL raiUj La icl.IrcI•de LjC I Ac blacaIb-ci Ia; -cc-el; arAbic: I ciA re:ecIgi7i.: beea icrccc Are-i .-; cc! 1ircbac *. Ire.- at IA air. LId cIt asp-c-cl c-rIce a :c11 C I-rrAL.i-cc 1Iae at cc;iele I - 11 cr jCHCcTiHcUJ7 Eta ci; S.t$yO€;Sdl wthta- yc tcrabI3Tc2e c.cCcty tIAa : Able lad 9 ]a:JLCcga Ia ccntc 1JL -c ;cA . LTz I Ia7 il; —r bare Tb CR ciA acre Lcccc c ride-Al tbviic Re-s aç•9 ccii elI tic ceec 1 cc! JPU.c:aci-lLeIaa -cieiLcyy cC; DESCRIPTION: maccc-rely •rGii ttccccidy iii; IlIad cartacci, dcc ci:;; Li ;icii 'rr-4 Al irL Ac ?LaIcI At Eau Claire Dells county park the exposed rocks are moderately to well banded. The banding dips vertically and strikes approximately N30°E. At the Dells proper (just downstream from the highway bridge) the rocks are relatively fine grained, felsic, and homogeneous, and CL-fluid —U c1.LCRc ip Idri iCc 1 cc A It d cc bT1 f-c ,CRiLHC Icac D y-ç -j Cj91[ — AIcr; be c-:acum i:Incd ccrccc Ac ;clc-;w]c LCRLL. l 1 Irpli A caR 1-I___ cccl; Ac do not display conspicuous banding. However, further downstream (near the foot bridge) the rocks are more mafic and are more banded. Upstream from the highway bridge the rock is well banded with alternating mafic and felsic lenses and well developed quartz lenses (boudinage structures) evident near the dam. Small garnets are abundant in several zones immediately below the dam on the north side of the river. East of the swimming and picnic area are outcrops of banded amphibolite. Thus, cicpriic 1R-cCCIVelrhtdLii U cci i lb izerc;i-cl elcuic bccrAiw4igc 'ii L 11411 c Ic clIcL eCu; 4 I LLi tK2 :iJi'Gii'CClCR :i jiij lrcc-c-c-: i51C_it re tic 4 44i Lw ci cc—' C I rcuurc; la-c'c-:--iiia!,, c ICc_ 1 cc airi Ii 4uiliLc2,H - -r — I 1 — IcceciLl IcLL _c U-1i 'ci 11 TiItdV 1' i1 l111l eccA L I Ll1' -_-' it II �62 EXPLANATION FOR MAPS OF EAU CLAIRE DELLS AREA, MARATHON CO. II Scale 1:24,000 — L cd Cary drift; terminal moraine. m 2 Mylonite- and related cataclastic rocks. kqm Kalinke quartz monzonite. '1± LI'J hhg [ dJ mvJ k',j?'J,j,'2, granite. JJt,.:L' hornblende Hogarty Diabasic intrusions. 1.25 '''1 1' :":1., '±:2 and Maf Ic volcanics (locally metagabbro amphibolite). Outcrops, or outcrop areas Geological 0i'jc2'; contacts Rockpiles ' Quarries I �— 2J N6 I. — — 1 F r i ¶1 _________ I /--" , U - - 5-' - ,_" - :- LU - / 4' —— ——— —— I -' ,k7e 4':—... F ' I' I US 5' U,: U —F' ' -:; —' - II -U - 1 : I, - It/I // -s -- - - 4 - t114q -':4 ':1], Il • 44-- IC t—-_ I: - 4si - •1 • / I z 2\J - C' -I - - - �64 J1 Figure 1. j-• l3 and lens-structures in Eau Claire Delic Ba ding LÀ • - upstream fjAL. ±'om the t1t Licge brdg on CTH—Y Light gray iense% al Larker gray banded materifl 1± i rt prcb1 v boudin. quartz, i babl areqatz :;mjH Park •fic rich. :: Ltthth mafth is rrelatively structures a- aoth the banding and the lens t P fJ- tearing. thrmed as a result of sh thg hct are believ 1 to ihave L D Figure 2. Ba1d. CnJin!.g mc' ltns structures in fe]sic mylonite ±L_tJ. just downstrE?arr from dir bridge on CTH-Y. Where the rock is i more homogt --meous, the I L. banding and lens structures are less obvious, hut they are still a common featureS ktl - - I - �Lcturestru flow groundrass. ndirr - f surrou the tH of and feldspars the of most fof shape lens the :- the grained Not matrix. Felc 4. Figure fine a in "eyes" flJrkspar L .1 - ce p fracturec the that Y1 sir'± irrdu ua rt'1air pc overall or Cl De S L'ie from 'tevct' au&rtz formed lens-shaped taller grain, z River LC2 ç the f nt. JJTh t7±. Eau 'e lens . - - 30 X31 X fragments. also note and i. zone. shear Figure - - Jhe iote Nc u 3. 65 �66 tti the n-Itt IT: 'IL'aaicittlct' on the composition range from cc,'lr,'S 4ILy of nIL' the cir'n mylonitic L ciaci i'arocks :'4m- :"a4ILa ttam "basaltic" east nan C 4" the LitmCenter 'L'a'vI:';'Dells tam Inarea tans taIL Itt ti"basaltic" mta,t a a to "granitic" in and'ILant back to 'ct 'gamin ,, - j ci,r::;:m ttS':L2 Compositional acmIncn i'll' 'nau4nci ' I' downstream alongrhthis cross—section of tin the ci,caama" shear zone. ILcirn,a: tt"na'n: attiama LaS tat a'of I-isa 4' a.; 'r;:r,lmn. Inca? are variations inca. common both andacitacts across talUs thea strike the shear cltit:i:iCLL 1,t tact,": anal ". maalong , 'r,' appearance alt: character 'tint aa,ncnic' 'tr:ar"aan-m'.c':a'a and with the LIt':: result variation in I' the :a'Tata' 1 of zone nIL aa -'a:'ttti.'nLr' zcanni,LL cof the 1:'am zone. Variations aa'ci,aaadepending ILanami - na 'W4t'? upon cU whether Ct,Rt> t hydrous act-n :Yr C, 7am a an lcra also tItan' arise a ant' , eat' anhydrous ;acrla',L,:c:,m minerals Lan'aILt during i'iaairL4: ', t,,p'aJ,,, (feldspars) yam tna'tra'ti formed minerals (micas, etc.) or cn:i',r,'tatILai'a:i,tac1 'tamIli an,tIL'an, recrystallization. alt. taIL 5t 5çc laSt along it, and aititaL::the tic: Most of the Dells elsewhere act Eau tat CIClaire :- a' Cal cl,:, Itbanding itt; c-IL? ac'aaIta tIg at acatactal and 'actc atic'a,it,S' of aiRvariously -'nainacs" ILflattened Eau Claire River actually Fain, :lcIrt F. ''a' zone ?a';ta;tlIa? ,s consists IL: length IT ttgn aILS ni'::range cnsct in ft nit, material elongated ::tt,:t of na .-hrla which caL mafic tInt" canand IL' felsic at at;:rzm'a:d lenses Snnclr. Figures ansi 22 Fi':na'te 1IL and mci a ':-rtc:',c:Th'aof cL aim from more than a fraction an inch. f;ncc accca tacta amile Lit' to Microscopically cataclastic mnymlJiaja lenses. lcanams ott the ant smaller illustrate some 'l'l';raenco; - aaiLLI' oanaTLca,atI,n a: of Thus, "tb-as: maIL4 4are art tcnaa'-features, such inifS Figures 4:t'i'5t 31 and common. at SU:as asillustrated i,, tt.ttitdI La IL anti a cia ?'ni;Tc:5[ tectonically. ,,:,itt :tr}n,:c tt,i 1 i, a have 'tarn formed 'a'n Ut! t-a'agt to the rocks in this zone believed ,,cy'c are 'itt rc,nlUaL::ltmt' a-n 9::crnags: Shearing ttai7 may ;'acmctt:t produce the banding (as well as ar, cataclasis) ta:cacilaaai R't'ji from an tI't 4anILiLf aa 'antI a:c'ac zone stint ap;;:ci,aILan a: crosses 'actitac aa shear initially L,'n',o'gaa':a't''as homogeneous rock, maIL' when approaches or t,it:,mLam,,l.:: "cot-, and raIL, a cattaIL 4at,c'nc:'i '$.":nai '5 'n "L:tl,t:j:aaia,, Inca at's Lam contact between:tacontrasting lithologiesLas thetam banding may be r:na'i'nna pronounced. -Its ILLs rocks r';tim ILn'tk'c'n'n*'c This situation is ta 14::, II represented ac.,cr-'caicadT by 4; the between the ti-n evidently '"a "a latter !a'nls " ittaiat;':Ta tim-n hut tin''' road bridge damLa; upstream. anaL the titan 'IL: ''caaa and - I - �67 Field Trip Locality 8B :811 1IC'I"7j 1)1011. )ITS1I TITLE: Contact between Wolf River batholith and mafic volcanics !Y1II CtI 111 it IFi11i,1I CIlUlCIf 1C'070U 'C 11111 OCII-0L.fCtCTI k1ao': II LOCATION: I P1) IL -'r T.29N., R.1OE., Marathon County 18, sec. oqLCC1I:Ip Ct0-flUC$UII't I ej C;-. 5j3 I I N, N4, NE, AUTHOR: Gene L. LaBerge, UW-Oshkosh DATE: Summers 1971, 1972 s OF FEATURES: SUIVUVIARY The locality is typical of the contact between the Wolf River batholith (Hogarty hornblende granite) and mafic volcanics. Near the granitic rocks the greenstone has been converted to an amphi— bolite and, as at this locality, when shearing occurs the amphibolite may be well banded. Although lack of outcrops prevents determining the width of the contact metamorphic effects with certainty, it is recognizable in the field in a zone 'about one half mile wide. J.LU'0.i — CU-CI =-p•P;:: —I _ : - 8flU RC{i 1111 : ItO —' , r,_ . t"— T L-CI41 OCIl 1- I 1 St CICIL ' 4 jV •lfl :8 1 zIr;I1C'jr,J:CCplTII 1U111LIT18t- ICC -: 11C U' E C P:ICi,CIU'C 'I.lU' 8C'U-iIiCU p3 U L '—'- CII ,-CCCOfl 0€- CU' j :11 I1tI;_.CI TIll ILIfUtCI -CIp (1 71:1:111 Ci €17412 :-: TiI.11I L IC tq CCII-C I --c iwIr 1r.;iPT-173*V 1I) L1 Although the contact between the "granite" and greenstcne is poorly exposed, it was mapped on the basis of lithology of rockpiles. Rockpiles along what is believed to be the contact consist of a mixture of amphibolite (meta—greenstone), granite (commonly pegmatitic), vein quartz and in places metagabbro. Small dikes and veins of granite vein the amphibolite blocks were observed at a and quartz cutting east of the "contact zone" consisted number of places. Rockpiles granitic rocks, whereas west of the almost entirely of porphyritic "contact zone" the rockpiles and small float in fields consisted almost This change in rock entirely of slabby amphibolite and greenstone. 40 type was generally restricted to a acre (-- mile) width or less, and at least locally the change in lithology takes place on opposite sides of a creek bed. Thus even without outcrops one can locate bedrock contacts quite closely in many (but not all) areas on the basis of the lithology of rockpiles and/or float. Trenches dug for burying telephone cables were especially useful in providing information on underlying bedrock. ,I7'C7 CIIIZ CIT - I j - - TUU'"U' s- U':Ux,7UJ r' - (U' UU-L— t8IL LU U 11 ::81t 8)U't r& '1118. OCL. -y - I' - U EU1I-i UICICIU 1 tJL"I:I?cA 1 5U'1 - 1_t •3f1 — 1t tL 8 t I 7cU1:.:j: U-J1ETh:::U±DIT1t I L CI T I $Illt. —T :1i c li ;Lcn Cc::t 811711 Vfi :155I8 T &[ -Cit ;xirU tJ.E7 UI -f 'YI)i c3;ILz 1ifLt; -. 5t I r•:r i3 - 1tL ¼'LrL1CtJJI ,CU' ' 8IU7 I- 93T;dItcC-- I .CyC.! rF71I2!t2 — C' ¶1-I C i'31:c7U:15i;U214-IIi Ui Y:oU:CUvU L - L-C ;CIiLi4 1fr:c 118 8I1Ut t:1:I t5';icIv:i-:I :I7rrI 11 6Ut r- C ::: t:LX ct: rzt L;:: it if I Tr;Lez: i1ir:i:i89 :-: r a:rq z �68 '<if•'i FOR MAPS c) EXPLANATION ?.c0 :L,:J 'q AREA, fJA'SJEu1 ILP<J<2.L DELLS OF EAU CLAIRE MARATHON CO. <2<J ,i-•;<2 LIi Scale 1:24,000 5:.< <21?L7h SL moraine. Cary drift; terminal cd 1 m <2T<2 Mylonite and related cataclastic rocks. 'UT<2 kqm Kalinke quartz monzonite. hhg Hogarty hornblende granite. :i:Y•y i'l'c,v±c.. dj JD* L.1L"1<2: my .:&J=.l1 and • L i.<2.'L;< Mafic:i't2z1; volcanics (locally metagabbro amphibolite). 1 L Diabasic H intrusions. <j:c1HH ''<2<2 <22' outcrop Outcrops, or areas ,-'..- <2 Geological ':•1 c" 2' XL<2<22contacts Rockpiles ' Quarries I �1' R.IOE. I - - I0 M / hhg - my k , 19 .. V - I •1 - , I — d / — - — — C. / I / 1. d - / / '•-•-- r •,' ,' my hhg / / 29 I / m I- /1 C. — : / I. hg h i• I. ,Tr r It. 1 / , 'I I I. I 'I , i,i , , I .1. • / I,. Ir / A m / / m, — —I m '.4 / / A / A A' A 0 / A my, .-— - C- // .1••' my / / ,mv / / 1L) m m / 4- A l, (iI -- 'p — / C / / qm / A 'A , - —— / ,/ I I rtitt• .tii—z. C I PV -4 K Th 4 / f I ,1 'I K —— /' / I -I • .— C. C .• 'K : III I / •_—\ Q tr Cc 4 C I i.)C •--:-. ,;; N. R.9E. -J i1es F' / / C. •, — C -- C, N - -T-J .-- Cj CtJ I. cd ¼ It •• K S -.—- '-.4 JJ 1' "'C •\C / a::H ,$/ - A , / N. / kqm / A 1 '1 N-- - 7—. "C �70 DESCRIPTION: 5cL iLSS' au f!/ @5the Sbc contact .lLc.rttc- @rs cc ccl are coarse Outcrops of "granite" within 100 feet of St.: :1. cc cc-lcc712 ctc:c "granite" for several miles to the east. Sc N•ciT-S of the cc.c grained tcU ccitt and typical 4111 ir icc to "granite" throughout much Indeed the rock is strikingly similar T'ti fltLtt lt.TSiT-tc c::Jcc and Menominee counties to the east. 1ftIllJ .ctt. lIt cc. - valley in Shawano ck.c 55.? River of the Wolf @5 of : -. l - ' ii L- ' lcici -I con@t:,i is itiL1l1SC'f', but ? IN cit tcc' The contact hasc,:ct notb3i,fl beenLCICI@ found inci outcrop, I'!lcift cc,'i-c/ itself c:.c?r ccl itc:LI191 Y Along this valley one can -.j:citcac swamp. c'ccif.t•r under •rcrciLiLl; or Sift. a ri. valley veniently in :;c&ct icc,ccc: ::;cinc'sIlc -'c-IfS granite with abundant mafic inclusions. .iIij:Cc1.lc 11@cY¾ find blocks @5 of the tcccciiccit1 :L—i-: numerous Vi:LIV narrow liTil rsrc'cc zone evidently frccr form a very 5c"-•ct@, cy1.i±-itijJ 5 :.:- Ctc-,, however, 'ctiii ¶-5,cJ1 blocks, • -c5. The inclusion—rich -'ciii Ic-cd S t-c rcnSc@ tI,cc tcic' @'Iit. 'I and the granitic rocks on 55cr west cc the between Sc '.-iittr.ithe 55 amphibolitic ' iic.Ttiti IS : rocks on - .- r1,•c *311 5 the east. :'c'c-ticmapped ccpcJ1 all r15 rocks '?-cc'iplutonic cIt5cc. :ct± the '5t ct•cs t if also : C$flLT'J This stop is typical&cin that itt7 -,-,c5.cr.r:i'-i',r oiLcttcc-' Sr.,c :-45.:- the intrude older volcanic sequence. I 121-il is the ;L itT' iccgeneral dLfl''da area Ic this cccI dccl ci: cit. '.c,ia in 5 important ,i9cTcft1 and An interesting problem Sc-•:jt •c@;3 uc&jnrci: of :5 cS@ the Il-SLI Wolf River :1* [i; the cSc@z SI'.a shearing relationship to emplacement cr5 c± crlI.. of the 5?LciccLJ,c-cr1 cccc crc cii:' cc 'clcflcc:IS of here one can demonc:? localities ccc': S 5cc At a number of southwest ;tt, 5wi5kircJt'S?' batholith. cd'rclu21ti-I 55cdiL5lI hcti rdrcT'lT'-ji hornblende granite) has :.'i'r-.r- batholith Sn:ccS ± :1: (Hogarty -cc:t ttct 55cca' River strate that theWcI Wolf clLc:: Sc nc-c: 1cim:crgneiss, -:'.Ccc - mylonite and granite, i.ct.-i5cc gcrcc5. 51, augen ;-L.cccC ar1. gneissic -Ic produce been c,;i-ccic'cC! sheared to 'c-cic. c@iL-cill. will :-: if -R This Iproblem 123511cataclastic c-cd---?,ocd:,r-j.c i:cScon cc a¾ rather 1 -aIccI large scale. other rocks c.cclclcifL and512cc-nINatural 1:--the t@ Wisconsin :crcrcc GeologicalticS -ccc tc.c by ea mapping --:--c- as be @zclitrcl@ examined further Lnt pr.'c ccci:-:, The presence tibitI cd southwest along zone. LL:-LtLS-± this dc-ic 101 -cc History Survey continues to the c: c.'rcc' c.-.'c-tb7 1515' crocks r dcc may ct c 15115 of the batholithiC icc S'rcrii.: c±L:c.cof major s;cc-,.cT'rL.t shear zone along the front @5? @2 a ¾ cii c-tc-cticd c-c Cit-I batho— the c-cc emplacement 5la3ftLlt-tL-t of the ccJ ncc.2 cc ccinftncirc,gT'T'I indicate that cISc', the shearing is related to ccilT' crits cc-icr, cf-ic-cf which i-SlitS Lt1TT,CnCI@ along 1,-.,r,U1L L.J ±'l-ck- as iii a buttress behaved ,l' 5-ltIitlfltL 51 lith, or perhaps itc&t that 'Tcd the batholith Ni:- t@•1¾L.SL. the shearing occurred. - 1 -". �71 Field Trip Locality i±CC 9 J, iji TITLE: L-'UI Wausau quartz syenite — Old Technical Institute c- 'U-2:'CTioC.:'ojt. :iTcC0C,c',1Lc-itCIt' :i-r -'=r LOCATION: Marathon County T.29N., R.7E., 'U'U- 'U 35, 'U sec. !:fl_' NE*, 'U AUTHOR: UW—Eau Claire 0—C1T:2: Ltc-Uc- : Paul E. Myers, "I'U,:OOUiYO 'U DATE: 2:-fl February, 1973 .TTt7tJEt€.C SUMMARY OF FEATURES: c;crIIU 7n'q(U! An early, medium—grained pyroxene—amphibole quartz syenite containing NW-oriented quartzite, schist, and volcanic xenoliths is cut by coarser-grained, flow-lineated quartz syenite of similar composition (Figure 1). Average xenolith orientation here is structurally continuous with the concentric lamination of the Wausau syenite pluton whose granite core is in Ninemile Swamp 5 miles southwest of here. "Rootless", lenticular pegmatite with walls of coarse K—feldspar and cores of quartz were probably differentiated from the nearly crystallized syenite at places of greatest quartzite assimilation. Thin screens of biotite schist and quartzite were raf ted up(?) and brecciated in the viscous syenite magma (Figure 2). —"CCC IlçU4'UU.c-I CCCC1C TC05TCthC.=c-QCCCCfC CC'C'çCC2:-=TO'C'0Ci Tj ijC C i'C,C T flTh TOC2: CC t ri ' r ; tiiI ki 3'4 CCC CC CiCi:2t" tk' i J(il =ur 0 TiQi :4Io2:T i::'TCC LL 'Ito r:;mitt. i'Itt1ci ,i,'l; &\trli UC,0CCii 2:1L7 WT(1' CC - CX4TX'v22'0'L ,2: 000 ii:•::c-rc 104.T1!iX U' Lc — fl'IL''tT00ii c:iz,o.Lni0t o:2 2:0 CT:7 r,4,,)itiic-l t ''•rC',C 7CC C''Ct Ut c- I I 4 i20U,k Ci O,c-c-i[ YT'0tiit± F.T.04 'Ti C tian DESCRIPTION: 4iTP TI' fi ' 1T'1r cf iLi 4"1[I According to Weidman (1907, p. 203—208) the "Wausau-type" quartz syenite is composed of alkali feldspars (orthoclase, microcline, albite, and microperthite), barkevikite, hedenbergite, fayalite, biotite, and quartz. Accessories include fluorite, apatite, magnetite, zircon, and allanite(?). L'.tlc-.[ '--r T ti Ir ]0Iic--0act ::ti2L 0 S' c-i viJI3p;4: 0 r I iT - <) 1JT : tcCL :1 - I i(iflT0t1flT ;Y:B 4i;$ Structures and cross—cutting relations of the syenite phases exposed here typify those seen throughout the crescentic northern rim of the Wausau syenite pluton. They are listed and described below in order of decreasing age. [)1L4 0c-Ti. ..1-c- 00 ?f0T.an:1- c-c-OfI. 0.:ThflI!Jc-;t&:4= uii-ic--•o ThJDL ji4c :4: :j. r2Ii7. o-rot (LLtt -iT-i OLIL fC• c-i i0C TJ.1 i1i �72 -: II .4 I- — 1 5- 4 5 I — -5- — — ,_zl., -A" A L,:;-' --r • 1 j V ' -A I *I•-••_ • - - '-21 - — ' - I At — ' - 4- ---S -• - - C— - •'-" '1— 4A -- _••__IA - • -" - — _•', 1' -1' — - - - _•1, I -' -- -- - , / •• - - 5- : -' ' -' ': -II, -- - I - •• —- ,'4' ':4 - - ': ''4/' - '.-: ' 1, - 5-:' I-I- - --5-_k -, 15s'I -A •,, s,'I 'hi . 45-', , , — A A — I '•,5A-42-'_ - / — -, -- ' — -''2- • - I' 1 • '/4 2- -— - _;A -- - -_ - -h //5_ - - A • • 5-5- A - '—S 5- - - ' — - l.'\',', 41' • I 5- ,, '-'5- 5,5 • - - L - -• '5. • . I"1 -lw',' 4'',5-:5-5' — ' - çt5 5-ç I - I, • - I . • - 4- - '4 - • -- '-,-T:_ • -l - - ::4' : - — I — '• 7 5- I - ,::-'- • II5I 5- • ft J,_ -• •• I — -• I - 1" - -: ,-• - ' -•,•,' ••- ,. ' - I: • k ,. I T I' --. - H- -5- A_I' '.1 I,,2121'IA_ A '- :2_' ' • 9' A I 5 ''-'''-" C- - • 1 A -A5-5-' --'- P 'I 2- I 55- - -----—I A - •21:--- ---2s. .1 ' - •, '_&••*, - fl5-:4s": seams 5-2-slt4.,::LElj:l,L:5-.2-2-1I with swirled lineation and thin Amphibolite (a) xenolith •:lc:.JA,._i'1421L1b1,A,42Figure 1 Lenticular veins with - ;- A.534'P2-'5Thf"ftL-1'2- 1 1'' '11 of syenite is 'El cut by coarse pyroxene syenite (psy). c:'1,-.1tatQ ; ,,— t1LZ4-1L'-1L1_'i EHsIJA mutually crossq-:2-r- (q) show walls of K—feldspar-: (Kf) and cores of quartz 2(ICI_ Joint f'!VLt'rhI:2-Ifl',s1 intervening offset a small fault. 111 W _'-2-_ along cutting relations an1Th,C2-'VL1'2*1'th'1 15-21? '-'15- with 24 115-Al I' -1,11 amphibole. 1_s. A"' i'i- 5-s' coatings are of coarse, sodic Ah- 'f2-- 5' 4Ui - I 151,5- •, - 1. 1. 21---1H41:;2 syenite. They in2-12-il i-La xenoliths in 2-21 the :c: X'lh,!IA1'L".2i5 The oldest 15.5- cAt :'::5cIftt,: rocks :1:4::': here are '.'2 ILC21 *1 2-4,IC I meta— -:-c1,t1t-21151 amphibolitiC 1-2-21.112 4121 -: -lr,-J, schistose, clude recrystallized, 212FA!41214442 :121.1.4 thoroughly L*2-1AV' ±2,15*12-S tuff(?). unaltered felsic 5-1-2-211:5'-.L,fll22-2t45-2l 4*1*1 volcanics(?), quartzite, 'I222-2-5-A/flH' and virtually 2CsJ.A!1_i:,2-LI4)IC-I parallel to xenoliths tend 2-14: to - be .r2I1-•1*1ltl -T5-± aer,:: 5.2-2-2 of Note that long dimensions it1'2 ::i4 disparity, despite lithologic 211-152-45441 21% tIal15471.4%:, lamination and/or foliation and that, *1124121 i-Cl :*14:.6j4)Ic,1I-: -s 1:4211%' :5"a.L "grain" to distinct structural a ã.2-tlLCC ,—:ar i: -Lka±r c:52-tkP: 1117:5:2their mutual alignment imparts a 21.? :::s21.21j2, considerable 2-21 of tCi- be factor believed 14211-2112- to fa:'.tc:2, tlLc 1:2- — a the21'rJCL*1%21 enclosinghIyE21LI syenite *1l1it21L5 4' this 11545-LI pluton. rnechanisma 55-2--2122- 1:2154 :15 for '5,2-,1a-iI-211412t 42-151221 45I:215--ICç I significance in working out emplacement 2-I 2-' l-- 14 5-4 rai , 2-'- 22. ilyllIl-ib I 4.1? .-: 2-: syenite flow—laminated -1-2-C :; 21.-I quartz - -E'It1i5.5424' lensoidal 41:csm15rair.L?2- - '152-121 An early, fine—grained, .-IrC phase. —. chilled -.m15!lal 2155-2242-. may represent Ta-'--Y,C 45-Al/-C_I a I - �'3I,3L'1$ 'UI'? 377$i'35(7'3'7573 Segmented metadiabase(?) screen in flow—banded, quartz syenite. 117' 4- L4"712337—11A7-"[ 36 - 'y77'.e33-: '' 357-:cI'316P'75-17 r7nam,, rr-,---', -' — - — — 2 Of,4f • 7": Figure 7/ - — "4- 8 N - ,84 8. N • A A- — A-I — 1 t ' I '4-4 - - 8 j '4-- 4-"4-54 — a_A-' 24- -- :4 8 : -I,; :44 '448- A- —4 - 4-4 -4 x 2 -. eA— 'I :4 ' A A 41 — 2 - '4 A- A — — A — , 1 - Ar - — 31 A -- A- - 4-' 71 H : - '"'8'.I7'LJC, 33,%1. 'L31[t :7823_H'TA':A531.:Y-c':y.'':-:',':PTS- -=A-A-A--" Coarse, sodic amphibole crystallized along joint surfaces. '7/'31!, 7'7': 7'31:':L:18(:73 '' 5. 2323331':? 3. 4-5- Coarse—grained, flow—lineated pyroxene—amphibole quartz syenite cuts the fine—grained phase with sharp discordance. This unit contains irregular, lensoidal and tabular inclusions of amphi— bolite, schist, and quartzite most of which show little assimilation. Although most of these inclusions show northwesterly elongation, the enclosing quartz syenite displays highly discordant flow—lineation with swirls and eddies suggesting considerable turbulence and viscosity in the quartz syenite magma. After gaining access to the xenolith along its banding or schistosity, the magma pulled loose segments from its surface. With increasing magma/xenolith ratio the xenoliths became plastic and were strongly deformed in the flowing magma. Quartzite xenoliths appear to have been more readily plastiA screen of cized presumably because of lower melting point. schistose metadiabase(?) crosses the south end of the outcrop. Its thin western end shows plastic deformation and "pull—outs", whereas its more brittle eastern end is segmented into many angular fragments (Figure 2). '74 Late—stage, lenticular granite pegmatite veins with quartz cores probably represent residual liquid segregations along incipient contraction fractures in the already crystallized syenite. They appear to be "rootless" and of local derivation perhaps from zones of abnormally high quartzite assimilation. — — 77t11'3 8(8771-31A ,(,7'%:7 P-331'Efl': (4485 71773 "718 L'S.7'3'L811-1':': ('(In-I ç4-7171.,( '- 75 T1'871 73317 - 7'-; 3.8(17 'L571 717'445 : 357 87'71':33115 31— 33-75-1':-' :Th-i:ï. 37337' 5(4-8 -73'',':—:' 73,7131(1-5-3 .1- Th'r,l - 4-127-V-lI''1Ctt- 3:iAL3T7 37733" '174Y 'V/,J 5,877) 3T75'1Yi"L-7J ':':4d5731--114' J- L137'43 '5',:[',-'1(3 753371. 7;'PL-3': fl7, .771717 ,237331- '5 4-7'.318j8'72 -:4 :-77': 11-'73'4': '753715 1231 (81'i',1s'4'3.53 — [3-13773 53371 -3313SF ':': 7)8(t-U7 3-, 2377 75 375'7": 3'1331;3 (173 -1'& 71,7(3:44 423,.33.-3S,[717 Y'3 ':'78:-4713-37;- 1': 37" 7'3": i 37 75 -1 $771 473 -:I,3.3-$11:1M 513.1-34 3.3 33%'77'472333€': '35 3471-"':(4-' 4717 -J'U'':' --751172343 4. '3133''. 3's-s-cs,: 77:11 —:-3":x, 23823373: ,:-123721814-,': 23 4(173'A5LL 337573(757 5-34 '8718, 3-7,'!,,A-3348788 '(1'j('3-771':-_-1t7'':237'5- 5-3177 1575-Tr''33'3371'(,$ 7711":2 1323341331 731'4'C7513 (5157' '5,33 5:" °i':-:H'.: ;1-L3--'2'•':-(33.'; ,575%[771,'14- "171'%:131- ,77' C'5. 3(7-AC,- •ThtT$71'.8.33"1"4 ':711,7 23-731-'. ;38771:37(;::; 175, t,334-',7 '337733 1571', 1311-1 Sx':3 7'7'7-4'7'-131,3':'5(35 --C: ':"-k7"1":-x71- 3'l 3'317':41,?,'23 ii1i175—2 -1311 -7,31,it 73 'i771315'( 3—':-'fl 731313333:4 'I73 51 4771171' 3,7354373' 7::."iICi)'I A-r,A17'3-5 731'3271 1'i15$ 51i1J1 - C."I1375477 :':'-' 3,33, 1172171 :377758-73 48733 ;t-:-- ':':-: 175433-77'17'75 '735233-: 317(13-? --31373-5? (-Y''7' 714 ,'731-::': 71,[)-':Aç; ''5 :7'.733': ;5337735718'7'7. 4'7''5P -3: 1:15' '315 734T?j2. '73443135- :337317 ''13"73.5-53':':5 77 3313734 pa;3-7'4 a': 2317 373(3 - '7 - I - ".314-ICY 3153.73 731 L1513- — 731,11':17.'7317'I3 t,:7,'' 34 '74137 8 7'813f5 473.5 A'7'71'-'3-)'3iAA 7773 (5''337Y, 'c7L'ç83D - 5551_-1-3 7517583 73 �74 a ih* the syttitea syenites eM and It is '.s suggested that many of the structures in itt San1v. Sntfr L,.&zbr3cn .Liin1' indicate forceful, subvolcanic stS3L*a •( t? ii Ytuasu. quartz syenites of the Wausau pluton 4trIN,tULa1 aftt."'tlS .! Careful structural analysis may '22e-ILL o trz w5.uclrJs avafltt V3$tVjection of dry, viscous syenite magma. of magma flow and xenolith mixin rithi:. 1i themchanism5 ;wasntnt in time time s'ts'WRl reveal the twc instance, traLtrce, nC ?t&t' t fn.çcmwrcs fnt 1.a Do the xenoliths, for represent fragments from the magma. thvtM'vJ g :salttr& eM ta;;;. aatl J aflr during caldera collapse and later invaded fault breccia formed initially a:rLt -asvnn? by ticw,fllflA upwelling syenite magmas? t,q cvg..;tz;'rl :tat nr 2! the 3tflfl4rfl the marjn D the ntc] t;o. f wit brte3. i £:sst atE anz f;nv efl r: ,t; tt':tg *itt'D 2rrY tJJ! RE FERENCE a*rth of north iTLoraw, g..tcsL, w,The fl' nalts: Weidman, Sanluel, 1907, geology cS 'Faaa3L3Lr: central Wisconsin: £'C. Bulletin c7taat and ax! Natural Fsti..nl' History £4tctcfl Survey, !wtey1 BCLsttft XVI. Geological tV::cscs.':D Wisconsin I �uiclrYrkJ,, south. the to tc FuNiclgJNtcuru volcanics 1 ru t j Ncontiguous from derivation suggest iN mafic syenite nepheline the in auruiuui ui lenses and INuruNuisur; bands ft'NYI7 tAtut1] Mafic vr'I;rur, pluton. the of ciLL ucuuru)7113U1cuucuruizt emplacement urvt duringi-il itization itttRrNutiNiN mylon— by segmented and lenticulated locally were crystals feldspar -5 ' 2. ICL'I C contorted: strongly is syenite nepheline the in banding positional 54) ui,:iUuiLuii))YN) and clinochlore(?) iC lirY'lui JUNNNNN1L 1117 cancrinite, c-r-irNrr::Nrr tJtcu7cuuiu-I'Nb5'u Comallanite(?). thorogummite, uruyIu. (red) (N WL N apatite, r' here), cu5 fluorite, abundant (unusually I_ Yui_t zircon include Accessories Jj (lepidomelane). 1— mica brown, and (arfvedsonite) amphibole sodic ±± sodalite at::riuiuia nepheline, uiNil rc:rjoNtir1 vNINiii composed aegirine, Ltak:r±LNuj1il1r-i microperthite, anorthoclase, of mainly &NCYçJ.YiP1Nr1 is :t4a nepheline o'7N:di7-Nug here syenite k-iNN 7i2iiil Dvrrriel the N17N 235—264) T'7'7N) p. (1907, Weidman '7aaz1 '7 to According I 4 't[ 5Ni ±' c' UYTY I I t,fl .i - L ,_ 1 NI U [ '- _i2 t: l'7I :r NY location. this at N tI across east—northeasterly strikes property mine N:1a zircon tN17 abandoned the syenite N$IriN77N trtLN,JT: tabular and syenite N'7GiJZr nepheline brirrNarr contact r1ccN1tazu The !Tjr,_ LiliN ttrryrl banded J1iFilri. b between 7UN It:'ly DESCRIPTION: i:r, rI5Ier7 : (Nt$Z; ivN1:1i2lI NJJNN, near zone wall the :crrr ibe 1J. ILJ stop in is t.zNyr This pluton. the INI of edge south the 1 pyroxene s Ii (psy). syenite anorthoclase—rich of core a and 235—245) p. tite—rich 1907, (Weidman, syenite nepheline—hedenbergite—fayalite 1L magne1 Nil, -:r: caa 1:: in of rim a comprising diameter 7:i, atIl2 mile a zone core circular a (3) ' > pyroxene and amphibole vu t and lineation, flow swirled with syenite —RH — I' an (2) (lsy), syenite LjCL' pegmatitic to aplitic of zone intermediate aplitic lensoidal, La and (tsy) syenite tabular (nsy), syenite nepheline banded comprising zone wall a (1) mapping: field in distinguished were zones yr major Three zoned. concentrically a2d and northeasterly, 1L!• is J! elongate ]1LL)t. in oval pluton 'JLi.7c syenite ;7v(J!c1f Stettin S.tit7tz, The JL2tcL L:a1, 1) (Figure plan, 1,TJ 1 r lIV 1rl_ i :iaKair Ii c at 1 I i7 L ' 1b JL — 7_I' N17i=/Jcrv FEATURES: OF SUTvIMARY February, 1973 DATE: \ib,Lf1 UW—Eau Myers, E. Paul Claire AUTHOR: t>/ County Marathon XCaJtJrYs R.6E., T.29N., 22, sec. SE--, corner, NW C.T.H. '7 & Rd. Stettin7 0: LOCATION: zone 'wall tr'ita, tt!t; Stettin It• — pluton :L':N syenite TITLE: j-1!IJ Trip -H 1: I' Locality 10 jc7,r'7 Field 75 �Figure FF'/ .7/ I 76 '4-' 4-"" - ,: /7 " SYv 4--" my "4- .7/' 4-——. 'F'- tsy 1 F•" F / 7r / - / 1,7-Ft -'7 4/ 7.7.- '>' '',7 C4--- 7- -".- -' 1 1 --i-i-" 4- / / , '1/ ' 44- 1_F '/ 7-", -: 1/4- 1,, '4- 4---' i, , - , '' 4-4 2 ''j''i ,-'_f / - -. - /_ F'-. F ' F/$&f, .,. 4-''" - 4-' F" /./ ' F- -F 'FFF4- '4 / '-"F 4-7 4-' ,_e/4' /7/ '4 4/ -- 4-4- -4-' / 4/ 'F' - .4/ 4./' j ' \ /L 4-' 4-- F,4/4-f -"'"- — 4-'--F4--V4--F- ->ç4-74- - -- - -. —9 4/ "-' /4- 1 ''fl- .- -I 1.1 7' '-4- - y':- .—--",-,--.4- - 4- ' 4-—" - F' F, "7' '27"- - - - -S_,4__-,,_., '4-'F'7'4-I 7- '-74-' .# 4-1 7' 4- /4- 1/4' ,t,,,, 4. '"-F -4- cii - - - '1 —-F 4-4-,4/ -, my — '-"iFt7-,- /4-1 IF-_>,, 74- 5TTTIN L'-17'TT"7'' 7-7 4- / C 4-> 4- 77/7/ - .4-4 '"l c '.4-'..->- ,•_,,,.. - 1 ' "'-,. F .'F'47 .1 r•f$F - 1-' -' ,".77'i .; '-4-'/',.'/I - Ii ' 4-V -- —/4- 1 fv ,.' 4,,. I -' IL / /ts / -— / I C F 4- ——-—4- : 1 4 • - , :. / / 4, / 71 - - F I 7/v 7' I / ._ 4-F7. I: 4' /' ' , I - 1, >4- F.4 / 'C ,,, - ''v-1"'" /.- / F,-..: I ' F I ilL ri N / t Ii STETTIN H LIT I PWTON 4-'- " 1 I - 4/' F . 1" OF THE 4- / - ,,,,, F c7- my F H 4-/F 4-p).' MAP '.! • ,, — 'F /7 "•'-"• "S - /fr/LE - - '44/ ,,0 F I.- 4- 4-' ',, ,,/ by PE.Myers '1 ,_ Geology F'—. '4/174/4 p:'!,1,1 111:1 IF/-F) Nil '. Survey Wisconsin Geol. & Nat. Hist. 4-i I I I I 4- 973 >Hi-.ft1 Li,yI4711C EX7>PLAN ATION Qal ; LL'II r Lii tsy 1f L/4-V!U-•) A]]uvum :: (U C L I) i-fl Qgt n sy TM] p UNCONFORM TY C gr • F •I Syenitized vo]canics :'."ti,itispyroxene syenite - —7 rsyap ic/Fr /74/ .j,4, 5- 5/fl Lensoida] syenite V Granite Amphibole syenite Svenite 5'2i'- 4-/i ap]ite t-> - - 3/4/i/i Nepheline syenite 7sy - :4--n' Tabular syenite r mvb --'--F-,--. ,,F_1 is -' -½ '-,' , vo]canics Brecciated mafic 4-, F4-F., fv Felsic vo]canics'I mv I Mafic F,,• • - • volcanics a �77 2 . L.... Figure 2B Figure 2A Porphyroblastic(?) tabular syenite with mafic lenses (Fig. 2A) in a matrix of alkali feldspar and interstitial sodic pyroxene and amphibole. With increase in mafic content, the tabular syenite becomes poikil— itic (Fig. 2B) H.. -.-' ;4= 'H :•.. IJ_, ='H H' 'H' 'H 'H H'. H•'-- -'H H—•-=-'' ==; 'H -;-=. H: Ci . _;'H 'H 'H 'H E 'H H.- ii 'H "H — 'H 'H 'H- 'l 'H 'H 'H Li: 'H-: Figure 3 —— Tabuar syenite with abundant mafic lenses. Note para alignment of feldspars in maf Ic lenses and serrated margins. (3/14 x) L (A 1/ H-- 'H 'H H) - .;-..' I 'H 'H 'H 'H 21 'H Ci; amphi bole. 'Hr. 'H 1.4 'H 'H 'H -'H C') 'H 'H I,L 14 H-. H. 'H Figure —— Detail of mafic tabular syenite from NE Sec. 22, T.29N.,R 6 E, Porphyroblasts(?) of microperthite (white) Black crystals are sodic �78 ii cr Zircons ''C CL'ICCCC and I'C% some IRiCS thorogummite (C'C,C L3ltrIC II, may C collected 'CtCC :13(113 from hit: be hiitCC. pegmatitic tC).ClCIZliL'C phases of the nepheline syenite along the pit wall and west of the •C' C.. Ict-I :CC.C:LC Ctfli just iCac' (LII C.CC Please mill headframe, where a jig table was set up to separate zircons. YC(". 7ZIL.ICC,.I:j iiC'i-iizz e iiCCCIj,C iCr C-C'; it CLSAC 'ikit Cc ci r:3Ii'CC'3 'g3C(3 stay out of the building as it is very dilapitated. CCC CC. .L?.dlt:.. Lila (CC '3:3 ].:CIC C.:: ,L3 aq: liiTC':I.1 s: s ': 1 ;3 The tabular syenite itniCt a: at i.E this location (Weidman, ILIC p. 255—264) auCrLL: 1907, is pale orange with long, slender porphyroblasts (?) of zi1tCi C$cCtL: (Lilt r14 .Y&Ci'HLiC HEICYLICC(C5 ii4 C.-" HI gray micro— Smaller perthite and 2A). Ct mafic r.itti ii lenses C:31C5: (Figure :1iiCLhii1 felcspar t,:,( aadii:' laths 'C'ykLC are a,ra CLCLCiT:,I The feldspar crystals show considerable size variation pinkish. Th ii,'i- SCCC 2t1 Cm: 1a3 CcaitlI'cCtCC CC in 'Lr this All are in planar array so that the rock is banded but not Why? i1Vi.,i Cit CII, ,J5Ii71C •CiXC,CL 3:3 ThIEC.. II1[1 CacC rock. .Ctt•Ci LI' 2t31iC Some of the microperthite porphyroblasts(?) conspicuously lineated. °?CCLCdCYI (CIII'', 5C' CCIC.L (TiTiiCCi.CflCC:,l 14 iCCLLtLiCiCtC, (L1HE-i contain zoned mafic have rims. Concordant (C :3 licCi inclusions ICC. C tt[' CCC ' and tiuC'ii. some ICC C4LTCCII mafic CCC mafic lenses (altered mafic volcanic xenoliths) ciCaTiicc 131:1 are ,za composed ;c sodic atçiCa çC'CCtCE-C't: of amphibole, brown mica, and and contain perthite porphyro— i,Lt CILC't hit (-tiC green pyroxene Pfl 'CCC IlL CTC::iC.. ci-)XCL.C1 C blasts(?) of to CC similar 1LPI C'' size, L 'lE-C shape, CC and 3IC orientation CLC'IC Ci those iiCC.i4 in u:.1 the C1CC. enclosing 2ciiCtp:::C suggesting pink syenite — aii feature strongly t33CCCrL HE5r origin of ;C the Cfl7 iS r;2CCLC Ct metasomatic Tabular syenite l-mile east of here consists dominantly microperthite. C HIJ ii JargC. CiCC!CC &ii:a2c At another of crJCi'1 poikilitic and Pt33 , pyroxene 4.j c-:l sodic ;YI'C amphibole C.nj:: ti,cLnrs çoaj - (Figure 'C'tc; €1 2B). riCiJ d location 0.8 north—northwest contains C)L.LCC a°c mile i-IP CCC ::CCCCCLC of here C-C.L the LCH tabular FCCYF-C syenite C.c rCC_: Some C much more 'HEflCi C,ii( abundant: maf Ic lenses (Figure ELLcL 3). 3CCC boulders at CC this Cli. ii same location irT are composed entirely this mafic rock (Figure -i Cc 4). •2LCiC C $CCi- taL1 CCC iCLCtCC of '' - C,. L a' , e-ic 1f:"14C CC !c'-t iatty C rii Itt L j-Iir3C3ij ii rica 'CCtiC C C cfa It CC is suggested shearing C3.,th5eiFL that CViC iiUIS mylonitization J[C:C i. TC3tLZ accompanied -.rTli3..C333 CCL and Fragments forceful injection of pluton. TaTZi.tiJ subvolcanic aCCflC .:CaC ;.- the j.L Stettin XstsJ,-, syenite c:tuiitE-E iC of ?3if; mafic volcanic loose C,t7TL rocks 33CC broken rct.2C SiiCCtI from )EC2![ the €CC walls were EJ3- rafted up ZiL along £(art These fragments locally acted as them in the magma. 3C viscous C37C 'it syenite cii1t,j c4!Taa; c.rCaLii cia-iit nuclei L-4 crystallization SL1 ICc of 1:3 the C./1C syenite, itLCC to CC. have IIL2iICutt for C&itii r-. although thqy appear Considerable metasomatic alteration been resistant to assimilation. LJC%QJ T CL znC ufl54 C fl1C of the early wall zone complex Cti at ni emplacement Lii followed 1i...:.Ir7 its ri original J.: çrc;:;: as evidenced by the coarse, euhedral microperthite porphyroblasts(?). ')Cfld: 1'.th: ::1c€ Textures in poikilitic phases of the tabular syenite suggest nearly Cç7$ TC.L izCc CC.LI7 ;tc.J simultaneous crystallization of feldspars and CC2iS'LLiC 52EZC ..Ei C5TTT C Y(fl mafic minerals, :ir- although T1 the amphibole is 2L:ruDi. younger than the pyroxene. xyj. 7 iC F24. •CC !'- t :•:j ittn;9Ji a >Ij : j 1? I. :c Your ideas are solicited! These CLJL tentative SricFGC conclusions [CLCC ?7 are CC presented to stimulate discussion and debate. C. CcCt TX RE FE HENCE S L' X'S ST Emmons, R.C., V Wausau ':1: and Snyder, F.C., 1944, A structural study of the Wisconsin Geological & Natural History Survey, unpub. report. area: iC icc;1rL rj$)CrCr igxt'Q .C1t J. EZ dci :qtu Geisse, Elaine, 1951, The petrography L AF!T of the syenites, nepheline C1 sye— M.A. Thesis, nites and related rocks west of Wausau, Wisconsin: 'T t&r:u piTc; iiE7CSJ L4CC;L CC•k ICt i'&.'P Smith 4LL( College. :JC;. rr ;. C' i Turner, D.S., 1948, minerals tt- Heavy accessory t'T radioactive CQC3 511CifL and LE1PCTP13T studies of Ph.D. Dissertation, Univ. the igneous Croi rocks in the Wausau area: of IC Wisconsin. t':i* ''J1 u Weidman, Samuel, 1907, The of North Central Wisconsin: JIL geology tC1 1.ZC Geological and Natural aj, jttJi1I History j(.. EStJjI1 Survey Bulletin XVI. TLkityD .•&![• Wisconsin i ii- 2tcr;iz �l fl -.344 4747) ,4i217L 247-417.' low 2112 Ii '444 bridge -"=" 77 water. at only of times C1 . west the from it 117, 210 location this 1 the of end reached be may Note: gabbro. t1:21I17r214i.21212 :1421,17:171 ;141:7,T[4?1! 'I11'11117147 1242 4171: 171113'111I12121171L11$11 the of consolidation complete before stratification of disturbances 17 " 1717 the 11 inI layers I t121 clase r212LI in represent probably 2) Figure detail (see gabbro ij4 114'' 211 1 '44 I Di plagio- ¶ strong I 21 in crenulations discordance. with gabbro "Stair—step" $42134 2 7 1 —The c211JL IL the in banding the into cuts diorite quartz NE. strike planes 311212 3717174214 -14'2'117. 1-211) axes '21: 41274 quartz 211211? fold - 1'-1-7'44 2444444 7112)1' The are axial their and vertical, nearly diorite. 1r_ 4411714 14T77442. 2 271 11?,.i 3 was xene '247 the in incorporated then and open—folded xenolith gabbro 21214417 a in pyro— large 221274121141 At 111-1 :1: 211.prLln banding compositional I,: 3':' tl-L#. '47 1) 2-411311412: (Figure #1, Location 1 I I L14 i 1 I 'Ii1 I I 4 - 1 I 101 — 1 1-1 37.4?.' r' magma. 47 24414114412 quartz diorite 14242 —1Pj vertical AL 1414 '1 the in 4447' xenoliths of transport considerable suggests This east. 1447'(1711111 71:1:15 -441241114.7172 212I['71I14 1 4441144 411 74412 171112217 12, -- 1111444.it[2. 2412117 northat least at :7 miles 2 least and here from southwest miles 4 extends 4711112237 '11 4711171. 2711-1114 hIlt 17111:1121: 11741'5%' 121:42121714 447.1212,14 1t2444'± 371. probably which body, diorite quartz the around place in found is them of J4i44274337 4444:14.. :,L7iIt1LIrw:p 7i47'3- I none 174217 2: -.14-Tc11:l5.14 as 2141 .2412 '311 .4423115 and are 121-12±1 121442. 17242 yet xenoliths, here found types rock dominant the quartz 3-1 774T_42 17 schist, chlorite—epidote metapyroxenite, banding, showing depositional(?) 7112 in- 22 some gabbro, PyroxeneC $122 - 421 2 outcrops here. of east mile exposed 2126 are 141211440 :1141'047ItI11'444 '147424-2.2. 114441117411 21111i117 2242271721-41117 117114' 1 i-'211''2'which rocks, volcanic and diorite quartz hornblende taminated $1224471211014 2371437. 14'14.:71j1 con- 11212212224 11241211422I10 excellent between1713144211124 contact 412112122'22 sheared 1477747 the near is outcrop This 'ccl5Il 11 111L12i2H[— rir1 'It?"" 17 j'' [47117 [1717 7J.r1411A72127J[1' DESCRIPTION: 5 .17411:41714414 of .1r 2lt[11:4.147-71t:17712 stress. shearing conditions '[1714,7 different 7444±11 1l$44771i12177114 :1.1110:c41:7-1 rare 12a 1410-f.111i-liltl.±1 [1212..'.171. i-;17[2'24121t_d!C 4424 1l-7s'['L['.[i[714 compare under types rock specific of behavior to opportunity a 1 142/'7[3' branching, 1i17 zone, shear ENE.-trending :1 ' T''H ii affording thus along mylonitized 1.17-44 .[4773fl%1_ '4751741114471 :11t1 'ii:424n '42.4122112 771121: 3724 was quartz 37 747242-2 pyroxenite, gabbro, banded and schist xenoliths angular of 514,-,fl4-:44:14 221 7i=121 21114111424421344 127.174421114 quartz :3117142:i,47:71 44514'$1-41417' '14237,4 abundant, containing diorite hornblende Flow—lineated 'i,1 ' TA A 1 2717±U.L 14172 OF SUMMARY 174151444474417174 FEATURES: ;i7417i '1%:-nj--t;tFebruary, 1717-1717 1973 DATE: 4111.115 -47422s171s:ir Myers, E. Paul 211113151 Claire 1)[274'-'[4417 UW—Eau AUTHOR: R.7E. :47.4411)7 771,4 '4:444 '07sec. T.27N., 29, SE--, [1 4:110 u&14111'31 ®211'$172 at Mosinee: River 7412411'1"-111171) Wisconsin LOCATION: 7442.1(111124147 [31,fl57'711' Sheared 51t,111'112 quartz 2114127 intrusive 425-. '1.214:144.111171 breccia diorite 74 22 41 TITLE: 5i1J[. Field 37M7 Locality Trip 11 79 �1 -- LOcat°' �/ , / Ill , diorite. quartz ' / / / 1 \ " ' / in / / '' 1 i, / / I I' / _ I I '- / i / / ' NI / / , I / I v / / f \ / /1 / 'S / - / I — / 3 " / 1" / / Figure /\ I' / — I t /__.: — — / / •- :- / 'I t/ /\ / (Detail.) crenulated locally Banding quartz in gabbro pyroxene Folded — — it': U• / — r / / /, 1 / ' / diorite. Figure 2 • U_U :, •. U: 4 S / S — t I ' --- - —=-- ir— / 1; I / , , / \ maic :/ / T— i '•I 44 I U - 44 54' US — '5 '\ 4, ',,.'lI 5, .5 'S. I •• / o I / — - I A Epidote—chiorite /'L_____________—J /5incs ' — — __ U -:,-eQ / // xenolith schist I '/ I ' -—-=-- -: — ' •/,i 'A -A A I, ' 5-.-44(5-.; I 5 ) • •-•:• U, U -.c,-'4 :h-.?-H',' I I " UI s1I / U,, • •' U, 5/ A 'U •. • —4 A U ç Ii I.! I •, —,., ..A . H '.: SI U: c.,,.4' rI H '-S • - 4,, U -. •<, .tA/",,' 44- '4,2171, '4•1A -1 U- 1 U U - U •;•_•i :1 54 5- —U' 54' --U AT 45 .5-A •'"•'' • 'I . 5, U,'4 4 1* '.:- H H .. -. A - • ,U S -I A U •• • • 2 •- —I / 5, / '1 V 44. * 544'— / US. • 1': / —I 12'' 5, — I -1- 5,.,.. 4', .±... / -' U — •' I I — AlE_ TA/1 LE L 81 �82 7 H :;' L i'ittntditw Pitcc'cisa brecciatsi'tct withq!ciartc:; quartz 3tctctht intrusive Figure 4 —— Sheared alL ILLquartz wnaztc cars 'c-at I with tic-. contact lenses (cross—ruled) (crcna= ratia:2 I along aJLc'ic: the Criasas tc'wcJt 2 "Pt a, tHr!c:;te acm ccc ±;tti-,cggabbroic gt5. 'ci' it xenoliths. diorite containing ac±lPa,t criica—ra-a i.ir:li;.$ schist xenolith cc' of rtial chiorite—epidote LttItLt4@W #2(Figure 'FCUris 1) L: a dttLL'tmt-itt\ AtIt Location #2, vxlittct,:; are i:c: truncated rUt I rt,acattt4 tc; pl.a.cnttzt which is segmented ;.C.(+t cciii by shear planes by the :r.tntrJLttttgi; a2iria'r ii;:; interlensing Ia! awl ath.t'ari.nrlP (and It clear tinalP that shearing ,;,It therefore tt.ttriiftrtt claw':; 5-t. is UlLitic'r 3). 2) ±t!±Ks:ritii (Figure quartz 3;anr-ta- diorite tr,rst episodes .tmt±cn&taIt 2caw two th'crcncri - Thus, wcvl Lttintrusion. çrttittttittctquartz qiticir diorite metamorphism?) preceded 3a2r'nrcrp1i2aaU) ccc the tle snibiat cawtsainp crn..cc:;cw. development of schist contemporaneous S i t '25Iw'!LC;!ISL,i:;t:; ni:;:svalidated, rat I C atarI, Was Its.iddtcLt3 are cii shearing of r,n iLl the cit ii in The a absence -"°- cc of syenite xenoliths riP the gabbro? Ciii with folding of nii: two 'Wti 'Its 'c"t" units :Tw'Ltiiti'tage aa of the ticS PwUsy quartz diorite only cncdcc.,:;.scti indicationsciF of relative its the Lc'rJcc-c3 is qinartc satin:; it:; ctiatiStt seen in contact. nit twit snLca'nncLcs n' yt 'Pccan been since they have not yet n arc £ it'itsltw Lrwcni,i.a tact itria;t :; the intrusive breccia has been rcaran'titlP converted :.gccra 1) i 21w Lcccttcnr #3, #3, (i Figure ci Location At itt:; 'w c _ig tnt by shearing to a lensoial gneiss showing differential lenticulation 1. xenoliths with resultant length/width ratios largely litha with racai't-aicnt m:LIq'cIh!cticta ccaicicsc acacacit cclP cci cai.crvcc,ca'cjw' and segmentation of lr.awtcta, Several tt1tt crc-alLintermediate :1wcr,a.c:; St ' texture. ccc ir ic c!iofrcenctL ittI tflt.tLttdd.i Ll" and xenolith mineralogy a function Lilt a mLacc;ati,©h, Cit ctsac"acd at erc1H'Incs!. car:; stages cf of tracali xenolith Ut attenuation can be observed at this location. There stct-;ac Liatcancri. intrusive thtcctiaiLvc:3aLlitcLa!Kti between as is throughout titia thisragiani regiona ac'urizci'tc curious association It tJcct!CJlfTtitt?Jt' gmindtt 4. miia See Figure 4. aTc.Lat..i' l,tLic I -nUt tcstititi'ci' (rich (a-Icc in Ic ac-cal contacts xenoliths) and shear zones. ij'itwt 1c l' itit. bci4 mma;:'a.racl gabbro naL±tzc body ani-iccitic a ni'-fcjitcttat'it CUrl the subjacent layered cp:ca'ctz diorite .2±ctr:'te intrude lists quartz Did r' L:;1 4 j !LIt,i is this body related Li. If so, Ce H ii cvii,, and raft the xenoliths up to this level? atj,crtttosttc' :;li-'st:;.-srtcicc ± the to Tigerton anorthosite? F F - �83 Additional Locality iC L ttctYT'L'T'iiu'21 119-C TITLE: Gabbroic masses and leucogranite iiL.ILIttU .11'L7?11'T:'C '- IITTI LOCATION: sec. 31, T.28N., R.9E., Marathon County. Low and CTH J southeast of Callon. outcrops float along TLLYL. 'c:.cctL11LLCtcE'.'TI 'ZPL,IL ,: it W-, W-, '-ccc 1, L '.iLYii Cf'' C H-TC 1:-c mc 'i'i•• cTc: c'i',w AUTHOR: :: UW—Oshkosh LaBerge, L. $ DATE: Summers 1970, cr Gene 1972 SUMMARY OF FEATURES: T:T These exposures will not be visited on this trip but constitute an interesting part of the overall geology along the trend of the Eau Claire River shear zone. .3Ct:j9y I' CC T-:-'IL'H Ct ;c i'9-c LLi-.',?C1Ct2 In -Tc:-- :ttL22 "c:Ln;c 1111 iLçu,.qcT:.j- ;!:L - 1-i '3'u- IL 'iY T-:11C,: fl The Eau Claire River mylonite zone is interrupted in the vicinity of Callon by a gabbroic mass, at lest some of which appears metamorphosed (mg). Although the gabbro mass lies athwart the shear zone, it is substantially unsheared, and it contains inclusions of banded Thus amphibolite (sheared meta—greenstone?) and other sheared rocks. this mass seems to be younger than the major shearing in this area. Tc1 "11;Cti .111117111 ..L';Lm; 3CrL. :c'ti'111'tt 1-UEC CUEIa 11c.li.E ccci; , 11.i:tlc -cc TLTC1TL,TJ1LL3 3r' 1Ic'cc C-9T :±-cT, -r. -ccyç ii uLLcc: tt:LcuJ.I,L p-nL: Lr,L.c, t-Ec-:c:E U11t' 11 !TE'.c' u-.E :'•I', Ct " :;:T) '1H• T:ICI TTTIY5L I -L1 iT1'9c: ' IL:&ct_c:'J 61 611cc-cc .-Ur:uT TT1i t.t11'-.LLi.&7LLf .t'c:Ic:C EL:. ic. ,,.t- .,-rIc:tt cc tiL •'C'C CCt:4t''iYE .';,7)uC:q.:cI11CCX :-- LL! :—c ": cut': 1132. -nq u97' '1' I Southwest of the Callon area are numerous blocks of mafic rock The surrounded and intimately intruded by leucocratic granite (lg). maf Ic rocks have a range in composition, including hornblendite, gabbro, cliorite, quartz diorite; the leucogranite contains much pegmatite and graphic granite. A small altered pyroxenite (now talc-serpentine— actinolite, etc.) (ts) which outcrops near the N* corner, sec. 10, T.27N., R.8E. and a number of probably indigenous blocks of anorthosite near the SE corner sec. 8, T.27N., R.8E. may also be related to the gabbroic masses. And inclusions of pyroxenite and what appears to be layered gabbro are present in the dioritic rock in the Wisconsin River Valley at Mosinee (NW, SE-, sec. 29, T.27N., R.7E.). If all these rocks are related, it would indicate the presence of a well— differentiated mafic intrusion which was subsequently segmented and intruded by granitic rocks, mainly the leucogranite. An additional piece of this maf Ic jigsaw puzzle may be the large roadcut of grano— phyre just north of the intersection of U.S. 51 and WIs. 153 at Mosinee (near the center of SW*, sec. 28, T.27N., R.7E.). :19111 iiLi2I 'L :1:,'1'C '1'' L .''•'" flL E- ,',,bCT ,-T; 'CT T1CL. L;;ci:'.c.l1. fiI:L,i,L>n c;c c<1 )c9i:"Lm - cu -Ic: T9,IiLLT' .Lr t-L:Tii9 .JL2 C:,sL1cT :Izm i-TcUETE'.n ',.c.,m:uc .':,'€iLi'LLC:,iILI ;—cc:cct- :c; -;n Eu' ttt .n-c ;CLCIityQ T.:c:: . L9L"?LL' cTc.;cuc:. E: c-,.9c.J pc)Cc' L(T'CLL L.t' EL L'-L'.\''Li 1cLLt cci. CL pcnLc :.'1 .,nL icn C:T. i-; jCC.Li C :-Y7--L C,:Ls TUE C.'L 2tEL iTT JI i'4 -c:::Etrt, :Yi 'c-nc-cc :c-;cZ - ;i;-ci 2[P Cj- :tcI. CLt :1(J TT :Cr ju ct.' cT c<-. 'C:Iitc tTyTht. 'LLY ;TrULLt.tTLCL cu- Ti titl1-T. -1t• : )i LT tIt9tCiL- rIcv-:J ii 1 ccc:- u-nc 71,. tl'mL ': E.tCtT'V'tEL?[LtCLcCCtLr Tm f' iLH 'I .TT • uin ccLclJIYT -1I)auI uu pcLcuLtC... L .L9tO kz- I L2,itL c4LL. Li9 ?LV ; ct:cc .QYj:T tLCL. L [ccacr i99- Cc LLL H:,'41:y,, r •9u c; Ii :t �84 ,y EiE EXPLANATION JLk*17 i.711 AREA MAP FOR ict1l CALLON gal Quaternary alluvium ss Lower iLc;: PaleozoiC sandstone ig LeucocratiC granite mg 117 gabbroMetagabbro and related(?) ±7j1t• 7:Hr: diorite rocks ts Talc-Serpefltiflite m 1tL.(I :1h:iH Mylonite and:1related sheared rocks g Small granitiC bodies hhg :fl[:i.X.1 granite HogartyF, hornblende qd Quartz diorite - fv Felsic volcanics and associated volcano-genic sediments my Mafic volcanicS and associated volcano•?I& sediments jd:J-iir±b? genic 1 • granodiorite tH masses 7:.-r 'fli1 ii9: j:jTi Geologic contact Shear zone �'f"%. 31 Th! qal P - - T.28N. F IS ft 2'- 1 -, I I -. -"ml I - if! ft P ((ft "2 2 ' / I 121 / -P qI qal mg - Jl /7 - :7i[ — 2 I 2 — - 2 I 2 - "2 3 i1! -'. 7 Ig / qal( — I. itilIt -ft - 12 - t - '— ( /1 1._I 2 — 2 '1 '1k — -L / —-. "2 —. -P K- C J I ---I — . J I £ -( ig — L A -__..__m_ I / 1 - I c-s -- — - I 7 - — - I? - 2 -L'1" ç 'I 1$, - Miles — . Ig C 2 ft / / / 1. hhg 1 / I 7.. .1 I "-- LI — 11/71 SS (2( -'- : _.—-c' PU2TILI" d 1') qal -'/H 1/2TPJ -- --- T.28N. - IC mg hhg 2 - --;:. _' Jv ICI I). --='---71'---'---"=', -._i_--' -1 .1 qd / '( _4-P.1tL;._t 1 -'1-71 - —-- i7't L ,/' rng —— ILi:'& '1.41 ;Yi-..'-' a4:- 2-P ft ,/, m 7 h- . ,1-1 _D-P 'A' ¶2H ..- " ' ] - •'• 1 12 C k—I i'L .)hh94 -? (),-' ,/ '(2 p--'/' I-P - —1 ±A,;i _.71-S.LJ Ig 731 /5Ii"2 l9 :-———— —— ' — -1 lID m' ,1 '/211 1' P2 .1 / hhg '(U l\ I[o / I — —__=—tC41E —— AT Ig 1/fl -J 'U.'1 . Ig \ '9 J mg /1' 7o7'17' mg\ .' .—'----''-- '1.: 1 [ mg J 2 ft :11.11 qal — m r. — mg 2 4icti)Ec. '-.4, ,t;t+_.I_I.+4.+4* - — / '3 I -. — 11 7 A 11• 1/' ní2 ...7(2 ? my ' / /?/ ____ ___ ____ ____ ___ ____ _______ _____ E. R. C_i1Iory_\ - -— ' -' mg, .k%.:.L—II ', '11 \ 1- - Sç. - 26 25 2 - L cI9-L\ .1_i - -' qc nI \Ig) '1'tJx(/ - Alt2 / - H — ii , -- 4"—1 jH qal ,7') - — ft1 ft' 1-; " 33—-' H. - "21---'' / 15 —jI jr ft/I •.pft;q77 t1/1 -:' ' ft V - — -' — i-P'—i ii , I 1. (1 28??,/ -. 21 —--- - — —ç-—--.- T4 \m4 '- - - / A IL I'I,L I . _,Ig / 1_—- — / 11 TT — Ig I (x) 29 J-.------ ... — I" 'r - , J uit— ,LJL. /fi L' _1- ' fv —— L' 17 Li T I — " c/iT1V/ L • al 1 'N tL__—,Ia 1 / r - - ____ ________ �'c:c;y&at the -t'ii- cLL-cin. ac-c-u-scccs ccm-rcc-tc 'Ii tk F Field Ld ccc] relations a-c',ILc• suggest following sequenceccof events in the cc-: Hogarty -)d the ccc; a,;:•r1 of cc ;t-c .cc. 1) clb-c'ic'' on iY emplacement area shown theacccy;-iccc:5CLcr accompanying map: cc-cc. )iLr-cc 31 T3'ccJ-m.y. ,c-c;into the mafic volcanic hornblende granite l5OO ago vcJtcaccLc sequence; cccc-ca;cccii :C'JrJLILF uii3.@:;i9jd,.i -s: ltc-a- mylonite a-tc]cc vi: zone scc-:c 'L:c 3L:irZ 2) c;Fc•ca::L shearing 33 to t;cctcu.cFcproduce the Eau Claire River (the shearing LlFricict,acrcc:c:-i. ilL iL::F ficil:-:: rcJ ct-cd c d'-dcif't3' may be at least in part related to the emplacement of the Hogarty 3ist-L-ldd.' L c-c:• cci ,:c-cii;.5 t:.cct5 of :tc '.-i ' ,c Lac4 -c hi--c gabbroic hornblende 3) intrusion (and differentiation?) the c-iccclls granite); ccc'ca-c'ci-: d-c.r:,cb is:iLc? 'CI'') 3 iccis;s: ;"rv-:Isc:--3 ci' Fr3ii-5ThI3F5 :1, ct -u:cc mass; 4) intrustion of the leucogranite with segmentation of the &'St sr- a_ri :5,,, subsequent to emplacement I) has L -icc place Minor shearing taken gabbroic ,,3 mass. ti-s ac :gxzt.t.c ic—c the tici youngest Thus seems -Ic to be "hac the leucogranite -cccc -- cr-c cyvtcvic,ii of c the leucogranite. 3; iF tC'33 igneous rockmapped Yc2c-iic.F-t. in this FFTiL area. • iii Li? ijcc c "3 '- I P ' P : DESCRIPTION: Iiic,u-3 c-ct maf .c ,scStrvtc-3 and Low -cr' outcrops cc:,'ir-'rp aid and3iLFFs-t float of Ci leucogranite ic -'cc--S rocks c-c-icc occur Icrfor :ti,.iIic -;.c.;c ;'-J,;rc the ciclll tIc-: fields and woods along approximately a mile along c :1. in the c 1iL-cac-csCTH t3 J and xc:-c-:ic of JEt IdE5. ftJ_iLaii'cttc- zones Alternating -:31 maf c ciIc rocks -EL, T.28N., -:7. tic-iLL -;j:3zc; edge of sicsec. iiiis 31, western R.9E. iii the tci. Leucogranite is cr'.ccB&ciialong cio•ccthe lix ccroad. -cidi- iL-xsr5u;-i-c-'tx-c present and leucogranite are W1 :33ofit granite predominant rock type 2:3cvc:c1c-it-3-'t cic ii-',,'-i: in the cccc, area, cad and veins and dikes '-Zi s'cc cutting the mafic rocks were seencc atcccra1 several;Ic-ccaplaces. Lack of outcrops tIc tI--c---: :1FLi3 :tar— cc F idF- and precludes shape of the mafic zLstc-cr :3 sii the size '3lC ;Iii4, accurately 2c c—ic:-'. IF-Li.- determining I -is leucogranite. ciLa;-. 32 I3j-J.I)SU by the No clear c-c5c-c-ccc:'t a] seem to be surrounded masses, but Il-ct all tccscia. 15 ]clFcit Is ic-c--c -t.;;--'.-s-i iii.-: cc cc-Itt33 the occurrences of maf Ic rocks cutting granite were ccc-c seen. cd the c-tt - ;'i - ,Lcca il u': :/ci scr'c' c-lIt: the icc-c Ii ccccQL—ICat t-'c EL with -F--cc,:,:AIL.L- have ii :rcr-g-c The ccxc mafic rocks evidently range in composition, 1ccicc a '-cc :cccccic 5-r ;5r33r Biotite differences reflected Fr in the ferromagnesian minerals present. FtDcdWiLt, and lbLcci—lIcLtcbdIs is '3- abundant, cct -3i--Fr--! Is 7--t,-clt:1?ar-t predominant in ccc:c samples, others hornblende 3-cii iF5. in ii some iccctc iiiscc-icc5 commonly present Iiinc-Iothers Lac-ci :--t r--c'cvsca accl icc:-cfl-c-c-c1c both pyroxene and hornblende c-cc'uic occur. Quartz -"tc:Li.L,,'tCI it-c cccxc: cccLUt;usEL c'c;cc. variation Lit-c The c:-:5ctcccc extent to which cc; the compositional 'tctctcc:.,c itt-icc--c It; In the phases. 'ic-b-S blotitic fxc_'ic S.F 11cc to 1-c- partial it-aft cclc original -r-i1.c:ill cCtccFc t-i:-- ej in vii: the cc, maflc rocks reflects compositions orIs-; is due F,-s ax-sic cc-i: known. No it2cc'c;c-ac±ic petrographic work $itlc Fcc has yet c:ca-v. tV "digestion" by the Ilta ic;cxf'..-s granite is it not L77"'2cJ1c Cii -. c-cplagioclase rc;t :';,t cc: cccccsb I dcxc are arc Lcc' been done on these so compositions largely unknown. c2i,i,cc rocks, c--cctcc 'FLisi 'ccc I - i_3 3 ���� https://digitalcollections.lakeheadu.ca/files/original/e490e5cc4d21cd046bce02006cfdf9de.pdf dce4b4bbbee755b78cfd691154fc6c7f PDF Text Text University of Wizcensir,—Extsnsien GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E.Ostrom, State Geologist and Director GUIDEBOOK TO THE GEOLOGY AND MINERAL DEPOSITS OF THE CENTRAL PART OF JACKSON COUNTY AND PART OF CLARK COUNTY, WISCONSIN Prepared in cooperation with the U.S. Geological Survey and the Inland Steet Company tor the 19th Annual Institute on Lake Supetior G.otogy Madison, WisconsIn, 1973 �UNIVERSITY OF WISCONSIN-EXTENSIa1 GEOLOGICAL Afl NATURAL HISTORY SUit flY Meredith E. Ostrcn, State Geologist & Director GUIDEBOOK TO THE (ZOLOGY AND MINERAL DEPOSITS OF TH CENTRAL PART OF JACKSON COUNTY AND PART OF CURE COUNTY, WISCC*ISIN by Harry Alemic, U.S. Geological Survey, Washington, D.C. 20244 John M. Ohisan, Chief Geologist, Inland Steel Co., Ishpeming, Michigan This guidebook was printed in limited quantities for the 19th Annual Institute on Lake Superior Geology. Madison, Wisconsin Publication authorized by the Director, U.S. Geological Survey. Available from the Wisconsin Geological and Natural History Surveys University of Wisconsin—Extension, 1815 University Avenue, Madison, Wisconsin 53706. price $1.50. �GUIDEBOOK THE GUIDEBOOK TO TO THE AND MINERAL MINERALDEPOSITS DEPOSITS OF PART OF GEOLOGY AND OF THE THE CENTRAL PART OF JACKSON COUNTY COUNTYAND ANDPART PARTOF OF CLARK CLARKCOUNTY, COUNTY,WISCONS WISCONSINJJ JACKSON INlI by Harry and John Harry Klemioa" Klemi~/ and John M. M. Oh1son/ Ohlso~ IINTRODUCT NTRODUCT ION This field field trip is designed to provide an introduction to the general central part of of Jackson general geology and the economic geology of the central It includes includes aa visit visit to the Jackson County and part of Clark County. It magnetic taconite mine and County Iron Company's modern magnetic taconite mine and agglomeration plant, examination of plant, of outcropping Precambrian features, features, Upper Upper Cambrian strata, strata, and various local local physiographic physiographic features. features. will include Stops 1 through 9 (Figure 1), if if The trip will include visits visits to Stops (Figure 1), time permits. Additional places of interest interest are are shown as as localities 10 through 27 on the the maps and and are are described described briefly briefly in in the the text. text. general geology of of the northern part part of of this this area and of the The general the northern and of the the north has been been described described by by Wiedman Wiedman (1907). (1907). adjoining area to the Ostrom, Davis, Davis, and and Cline Cline (1970) have made made excellent excellent Ostrom (1966) (1966) and and Ostrom, (1970) have descriptions and correlations descriptions and correlations of of the the Upper Upper Cambrian Cambrian strata that that cover cover much of west—central west-central Wisconsin and and extend into into Jackson Jackson and and Clark (1961) discussed the clastic sedimentation Counties. Potter and Pryor (1961) of the the Paleozoic rocks of this general area of area and and noted noted the the presence presence of of phosphatic material in in the the Cambrian Cambrian rocks. rocks. The modern mining and and beneficiation facilities the Jackson facilities of of the County Iron Iron Company have have been been described described by by Skillings Skillings (1970). (1970). An occurrence of wavellite in Jackson County was described rence described by by Klemic Klemic and and Mrose Mrose (1972). The senior author is indebted to the Jackson County Iron Company for information information concerning concerning the the iron iron deposits. deposits. The cooperation and access access to their their property of many others in providing information and is gratefully acknowledged. is acknowledged. Much unpublished information information concerning the local local geology was was also also obtained from the the Wisconsin Geological Geological and and Natural History History Survey. Survey. Most of Jackson Jackson County and and parts of Clark County are in the "drift— "driftless area', but thin thin gravel gravel deposits deposits interpreted interpreted to to be be glacial glacial drift drift less area", but or outwash from glacial glacial deposits are present in many places east of the Black River. River. 11 Publication Publication authorized authorized by by the the Director, Director, U.S. U.S. Geological Geological Survey. Survey. ~/ U.S. U.S. Geological Survey, Survey, Washington, Washington, D.C. D.C. 20244. 1/ Chief Geologist, Inland Inland Steel Steel Co., Co., Ishpeming, Ishpeming, Michigan. Michigan. �2 9O0Os I1r d N (P I r 2 it S ho rtv ill e /J1c(T _ 141 rrc 1 \ atfi 1 6- eth7 2Q__. KSON / I c'°cT'r1 if 0 -18 41oj 'lL 1 23 IT Figure 1. 1. Figure S4 I I887 7 IJI (77) N Ti I i -o \ milee _44°15t=4 Field trip etops end other localities of geologic interest stops and in Jackson Jackson and end Clark C1rk Counties, in Counties, Wisconsin,. Wisconsin .. Base by U.S. Claire, 1964. 196)i. Eau Geological Survey, 1:250,000, Claire, l:2S0,000, Geological Survey, �r r 3 Exposures of Precambrian rocks in Jackson County and in the southern part part of of Clark Clark County County are are largely largely limited limited to to the the valley valley of of the the southern Black River and and its its tributaries. tributaries. A A few few mounds of Precambrian iron— ironformation and and associated associated schists schists and and some some quartzite quartzite knobs knobs occur occur as as windows in the Upper Cambrian sedimentary strata which form the the bedrock over most of of the the area. area. The exposed Precambrian rocks rocks consists consists mainly mainly of of paragneisses, paragneisses, schists, schists, phyllites, phyllites, quartzites, and, and, locally, locally, iron—formation. iron-formation. Granite and associated rhyolite and and aplitic aplitic dikes, dikes, and and gabbroic, gabbroic, dioritic, dioritic, and and doleritic dikes are are exposed in in many places. places. gneisses are are mostly mostly of of granitic granitic to to granodioritic granodioritic composition, composition, The gneisses and volcanic volcanic rocks. rocks. Thin chloritic and are metamorphosed sedimentary and layers of greenstone in in the the gneisses gneisses may may be be sills sills or or volcanic volcanic rocks. rocks. The foliation of the gneisses generally dips steeply and in some places In most most places the the gneisses are highly contorted migmatites. In the the weathered zone zone at at the the top top of of the the Precambrian Precambrian rocks rocks is is relatively relatively shallow, shallow, and or no no saprolitic saprolitic zone zone at at the the top top and it appears that there was little or of the the Precambrian Precambrian at at the the time time of of deposition deposition of of the the basal basal Upper Upper Cambrian Cambrian of sediments. age, totaling more Sandstone strata of Late Cambrian age, more than than 400 fe~t feet in thickness thickness in in places places in in Jackson Jackson and and Clark Clark Counties, Counties, rest rest unconformably unconformably in on the Precambrian Precambrian rocks. rocks. In most of the area area east of of the the Black Black River, River, however, however, the the sandstone cover cover is is less less than than 200 200 feet feet thick. thick. In In ascending order, the formations include include the Mount Simon and and Eau Eau Claire Claire order, the Cambrian formations the Mount Sandstones and and the Wonewoc and and Lone Lone Rock Rock Formations Formations of of Ostrom Ostrom (1966). (1966). units are are described described in in Figure Figure 2. 2. These units The Cambrian formations formations dip dip very very gently gently (less (less than than 10) 1°) southwest. southwest. or minor minor features features related related to to the the sedimentary processes involved Except ffor involved gradual transgression and in gradual and regression regression of of seas seas in in aa marine—shelf marine-shelf sediment zone, zone, these formations are are conformable conformable with with each each other. other. Most of the rocks cemented, very porous porous rocks are quartz arenites arenites which are weakly cemented, and permeable, permeable, and which have been intensively and intensively leached. leached. Loose sand accumulated by the disintegration of the accumulated the sandstone sandstone mantles mantles large large areas areas and conceals conceals formational formational contacts in and in most places. Deposits of river gravel derived largely from glacial deposits of the few tens of feet feet thick thick on some some terraces terraces along along north of the area are are a a few tens of the Black Black River. River. STOPS OF GEOLOGIC INTEREST STOPS STOP 1: STOP 1: Upper part of Mount Simon Sandstone. Sandstone. Location: quadrangle. West side of U.S. Black River Falls quadrangle. U.S. Rte. Rte. 12 about 500 feet north of Interstate about Interstate Rte. Rte. 94 94 (Figure (Figure 3). 3). The roadcut exposes flat—lying, medium—bedded, cross— flat-lying, thick— thick- to medium-bedded, crosslaminated, poorly poorly cemented, cemented, pale-gray pale—gray to to buff, buff, mediummedium- to to fine-grained fine—graiñed laminated, quartz sandstone with a few thin, white, clayey partings partings and thin, white, and minor �4 Upper Cambrian Cambrian formations Lone Rock Rock Formation 1966). Sandstone Sandstone Formation (Ostrom, (Ostrom, 1966). buff to to greenish-grey; greenish-gray; sandstone, sandstone, and shale, shale, huff and thinto medium-bedded, thinly crossbedded, thin- to medium-bedded, thinly crossbedded, some layers ripple ripple marked, medium- to to finesome layers marked, mediumgrained, glauconitic end grained, and micaceous, micaceous, fossiliferous; shale, buff to gray, mostly in very to gray, mostly in very thin thin erous; shale, exposed in borrow borrow pits on on layers. Unit is is well well esoosed ridgetops FEET FEET ~·~·;.:i:;;:{f~~t~:~~.ji~:~·i·;·:::: 200 ·,;':":::::;"'W.,,\(.l!II.!t~·.?\;.::> ·..·.·...::"i' .. ~·zone .:.,::.."...... Wonewoc Formation (Ostrom, 1966). Wonewoc 1966). Sandstone, white, pale-yellow to light-yellowish-brown, white, light-yellowish-brown, thick- to thicktomedium-bedded, medium-bedded,crossbedded, crossbedded, some some thin layers layers and and shalay shaley partings. partings. PredomiPredomiranges from coarse nantly medium grained, grained, but but ranges grained silty; weakly weakly cemented cemented escept except for grained to silty; thin zonesthat thatare arecemented cemented by by brown brown thin irregular irregularzones Unit forms forms bluffs iron osides. oxides. Unit Eau Eau Claire Claire Sandstone. Sandstone. Sandstone and and shale; shale; sandstone, pale-yellow-brown pale-yellow-brown to to buff, mediumsandstone, to thin-bedded, croasbedded, medium- to very ~wtjA2)i~~lJ/jJ~I\1~:lil;~~~~{~::~~:~~!~~~~~~~~i~:J,~;~~~~ fine grained, some thin coquinoid layers of ·:,::•.···..,;·;,;,··:·..... :·c>::"... :.:· small brachiopods, weakly cemented, friable, except for thin irregular megular zones zones that are are locally escept cemented by iron osides; shale, light-greenish- ~~ltl'~ §ig~i~·Y:5.:;~~~:r:i:~l~.:.;: gray to buff, generally in thin partings, but locally more than 1 foot thick. Unit generally poorly esposed o C • • • • ••• .. '~ " Mount Simon Simon Sandstone. Sandstone. Sandstone and shale; shale; sandstone, pale-yellow-brown pale-yellow-brown to to white. white, thickthicksandstone, to thin-bedded, thin-bedded, crossbedded, crossbedded, mainly mainly mediummediumgrained, but ranging from grained, from pebble pebble conglomerate conglomerate in basal layer layer to to very very fine fine grained grained and and in thin basal silty, weakly weakly cemented, cemented, friable; friable; shale, shale, lightlightgray, greenish-gray, locally locally red, red, mostly mostly gray, buff, greenish-gray, foot thin partings, partings, but but locally locally more more than than 11foot in thin bluffs along along streams. streams. Unthick. Unit forms bluffs conformity at base at base -:!.f":: ;'-':~/~"~~~\to ',' ,'. ',',:: \ ; I_'~ ,-, " < ", -I: ~ A • ;, _', \,' ~ ~, ., " ,', ,,-;. ~,- ~"... , -, - < '" < v Precambrian metamorphic and igneous igneous rocks Figure 2.—Generalized stratigraphic section aection of Paleozoic 2.-Generalized stratigraphic Paleozoic aedisnentary sedimentary rocks near near Black Black River River Falls, Falls, Jackson Jackson County, CoWlty, Wia., Wis., showing showing the approximate position position of of the the wavellite wavellite occurrence. occurrence. Data from Klemic DRtA 1972. Kiemic end and Mroa8, l4roee, 1972. �5 Figure 3. Blsck Rivsr Fall. area: Stop. 1, 2, 4, 6, and localities 11, and 25. Base by U.S. Geological Survey, Black River Falls nuadrangle, 1968, 1:62,500. 10, �6 partings stained by iron oxide. The Cross—beds dip southeast. No fossils noted here. this outcrop is typical of exposures of the upper part of the Mount Simon Sandstone west of the river. These beds are about 100 the Black to 120 feet above the base of the formation as exposed near River to the northeast and to the south. The lower part of the formation in most areas has thicker bedding and in average grain size. is slightly coarser The forested mound 3. mile to the east is Tilden Mound or section u Mound. It is a motadnock of Precaubflan iron-formation, schist, and phyllite. The relief on the Precambrian surface between the top of the mound sad the surface of the Precambrian rocks on the west side of Black River is 170 feet in a horizontal distance of about 400 feet. Unfoliated Precambrian granite crops out in the river valley locally between Tilden Mound and Interstate Rte. 94. Castle Mound, $ miles to the south—southeast is Upper Cambrian sandstone. STOP 2t Precambrian monadnock of iron—formation. Location: Black River Pails quadrangle in the NE sec. 12, T. 21 N., R. 4 W. near the junction of Levis Creek Road and West Bottom Road (Figure 3). Precambrian iron-formation flanked and partially capped by remnants of the Upper Cambrian Mount Simon Sandstone extends 50 feet above the surrotmding plain that is underlain by the Mount Simon Sandstone. The surf icial part of the iron—formation contains both itagnetite and martite. The strong magnetic anomaly associated with the mound of iron—formation extends both northwest and southeast of the mound. The extent to which the magnetic anomaly at the crest of the mound has been altered by lightning strikes is an interesting question. STOP 3: Jackson County Iron Company magnetic taconite mine and agglomeration plant. Location: Hatfield SW 71—minute quadrangle, SE fr, sec. 15, P. 21 74., R. 3 W. (Figure 4). The open pit mine is at the site of iron Mound, a nonadnock of Precambrian iron—formation that fornierty extended about 150 feet above the surrounding plain. Eron Mound was flanked and partly capped by the Mount Simon Sandstone. The uppermost part of the mound was approtiraately at the altitude at which the Lau Claire Sandstone (which overlies the Mount Simon Sandstone) formerly occurred. Iron—formation here dips about iV SW and is in an interval as much as 350 feet thick. This thickness may represent an isoclinally folded unit or it may be a faulted segment of a thick formation. It extends to below 650 feet above sea level. Quartz—chlorite schists border the iron— formation. Magnetite is the predominant iron-rich mineral, but some thin layers contain abundant specular hematite. The iron—formation has Mat Sc dikes, granitic been metamorphosed to garnet—actinolite grade. or aplitic dikes, and quartz veins cut the iron—formation. A zone of tRic schist parallela the layering of the iron—formation near the center of the pit. �7 '-I I' S �S The ore averages 20 to 23 percent in recoverable iron. About 3 of crude ore are required to produce 1 ton of pellets containing 63.5 percent iron and 1 percent silica. The nagnetite and gangue minerals are so finely interlocked that in order to obtain suitable iron ore concentrates, a final grind is made to a size at which 93.5 percent of the ore will pass through a 325—mesh screen. The Tnagnetite t€ separated from the gangue minerals by magnetic separators. Twenty pounds of hen— tonite clay is added per ton of concentrate in a mixer. The nixture is fed to a balling mill in which the powdered concentrates are converted to pellets, about 85 percent of which are 3/8 to 5/8 inch in diameter, The pellets are dried and preheated and then are heated to 2500 degrees F. In this process, the nagnetite is converted to hematite, and the finished pellets become hardened enough to withstand a compression of 800 lbs. tons Pellet shipments in 1972 were 887,000 long tons. More details concerning the iron deposit and the mining, beneficiaticrn, and pelletizing of the ores, tailings disposal, water supply, and environmental factors will be discussed at stop 3. ST4W 4: Eau Claire Sandstone and Wonawoc Formation of Ostron (1966). Black River Falls quadrangle, SW fr, sec. 24, T. 21 N., Location: R. 4W. Esst end of Castle Mound, 500 feet west of U.S. Rte. 12 on Castle Mound Road (Figure 3). Castle Mound is an elongate ridge capped by the lower part of The upper part of the Mount Siron Sandstone forms the basal part of the ridge from about 880 to Wonewoc Formation of Late Cambrian age. 995 feet above sea level, and, except at the eastern end of the ridge, it is largely concealed by talus and soil derived from the overlying rocks. The Eau Claire Sandstone, which includes fossiliferous tedium— to fine—grained sgndstone, forms the strata at altitudes of 995 to 1025 feet above sea level. The fossils in the Ea Cl.tre Sandstone are snail white phosphatic brachiopod shells composed of fluorapatite. These distinctive white shells are chars.cteflstic of the Lao Claire Sandstone In the area west of the Black River. East of the river the formation has been intensively leached, and although the fossiliferous zones are present, the fossil shell remnants are generally stained by iron oxides. Commonly the shells have been coaipletely removed and are represented by empty molds in the sandstone. A noticeable anount Of glauconite is generally present in the formation. Close exaninstion Of specimens of the coquina of phosphatic brachiopod shells reveals that quartz grains in contact with the shell mates-ia]. have been partially dissolved, leaving flat surfaces that conform to the adjoining smooth shell surfaces. Empty molds of fossils also show this modification of the innermost layer of quartz grains. Remnants of the Esu Claire Sandstone capping low hills in the area to the ecist are generally stained and cemented by brown iron oxide and weather out as small platy fragments that contrast with the pale—colored and weakly cemented and nonfossilt— lerous rock of the underlying Mount Simon Sandstone. The Mount Simon sad the Wonewoc, however, also contain iron oxide—cenented layers, but these are generally inedium—grained s andstane s. �9 STOP 5: STOP 5: Lone Rock Formation of of Ostrom Ostrom (1966). (1966). 1 Black River Falls quadrangle, NW NW 4' , sec. 10, 10, T. Location: River Falls quadrangle, T. 21 21 N., N., Borrow pit on south side of Pine Creek Road Road near R. W. (Figure (Figure 5). 5). pit of R. 5 W. crest of of hill. hill. The Lone Lone Rock Formation of of Late Late Cambrian age extends from from near near the The age extends the 1120 foot foot contour to to the the crest crest of of the the hill. hill. The formation formation consists consists mainly of light brownish—gray, brownish-gray, medium— medium- to to thin—bedded, thin-bedded, medium fine— fine- to fine—grained cross—laminated fine-grained cross-laminated sandstone sandstone and and thin thin layers layers of of shale. shale. The sandstone is argillaceous and and glauconitic. glauconitic. Some beds are are abundantly abundantly fossiliferous, and trails, ripple ripple marks, marks, and and mud mud cracks cracks are are well well fossiliferous, and worm trails, in thin thin sandstone sandstone layers. layers. The rock exposed here here is is typical typical preserved in of the rock in the of the the Lone Lone Rock Rock Formation at at other "shale "shale pits" pits" near near the the crests of ridges in both the the Black Black River River Falls Falls and and adjoining adjoining quadrangles. quadrangles. The environment of deposition of the Lone Rock Formation was similar It was was one in which shallow seas to that of the the Eau Eau Claire Claire Sandstone. Sandstone. It seas transgressed over over lagoonal lagoonal areas areas and and in in which which marine marine life life flourished flourished in in transgressed Local concentrations of brachiopod the littoral and the and neritic neritic zones. zones. Local shells in coquinalike layers resulted from from the the winnowing winnowing of of sediments sediments containing abundant abundant shells shells and and shell shell fragments. fragments. chitinous The rocks have been extensively leached of calcareous and and chitinous material, leaving fossil molds. Phosphatic brachiopod shells, material, shells, however, however, have been more more resistant leaching, as white resistant to leaching, as indicated by the the remaining white brachiopod shells. shells. The sandstone and and shale of the the Lone Rock Formation are extensively used for for surfacing dirt dirt roads and for for fill fill at bridges and and culverts culverts in used roads and at bridges Jackson County because they are to erosion because they are more more cohesive cohesive and and resistant resistant to the readily than is is most most of of the readily available available rock rock of of the the underlying underlying Cambrian Cambrian sandstones in in this this general general area. area. Soil developed on on the the Lone Lone Rock Rock ForFormation is rich in potash because of the presence of glauconite and clay and is and is rich in phosphorus from marine organisms. organisms. In In comparison, comparison, poor soils occur occur on the the Wonewoc Wonewoc and and the the Mount Mount Simon, Simon, which which consist consist largely largely soils of quartz quartz sand. sand. STOP 6: STOP 6: Wonewoc Formation Formation of of °strom Ostrom (1966). (1966). Location: Black River River Falls Falls quadrangle, quadrangle, SE SE sec. 31, T. 22 22 N., N., 31, T. W. (Figure R. 5 W. (Figure 3). 3). On south side of Wisconsin Rte. Rte. 27, 27, at at roadside roadside rest area and dirt road leading leading up up hill hill to to shale shale pit. pit. t, The Wonewoc Formation is well well exposed in large roadcuts on the Rte. 27 and south side of Rte. and on the the north side side of of Interstate Interstate Rte. Rte. 94. 94. More than 100 100 feet feet of of beds beds of of the the Wonewoc Wonewoc Formation Formation are are visible visible in in the the face face than of the the large large roadcut roadcut to to the the north. north. The top top of the the formation formation is near altitude altitude 1210 1210 feet feet and and is is approximately approximately at at the the top top of of the the exposed exposed rock rock formation is is below road face. The base of the formation road level level and and is is probably near altitude 1040, 1040, at at the the base base of of the the steep steep slope slope of of the the ridge. ridge. �1.0 Figure . Creek Rod ere!* Stop . Base by U.S. Geological Survey, Black River Falls cuadrangle, 1968, 1:62,500. Pine �11 white, pale yellow to The sandstone of the Wonewoc Formation is white, to thick thick bedded, bedded, cross-laminated, cross—laminated, and and predominantly predominantly light light brown, brown, medium to coarse— to very fine—grained medium grained, grained, but includes coarsefine-grained sand and and minor amounts of of clay. clay. Some thin zones are are cemented cemented by by brown brown iron iron oxides. oxides. A large large chamiel channel in in the the sandstone sandstone is is exposed in in the the lower part of the the A The rock here here is of that Wonewoc Formation The is typical typical of that in the the Wonewoc roadcut. In some some places, places, iron—oxide throughout this general general area. area. In iron-oxide cement is is more fossils were were found found at outcrop, but but in some some places places abundant. No fossils at this this outcrop, vertical tubular markings may represent represent burrows burrows made made by by marine marine creatures. creatures. At Wildcat quadrangle, and quadrangle, and and cemented cemented by by and has been called has Humbird, in in the the southern part of Fairchild Mound east of Humbird, at several other localities, localities, variegated variegated sandstone sandstone colored colored at several iron oxide oxide is is very very distinctive distinctive in in appearance appearance and and locally locally iron "Zebra rock" rock" because because of of the the pattern pattern of of its its markings. markings. Although the the Wonewoc Formation forms bluffs and and cliffs, cliffs, the rock is is generally only weakly cemented, and and bedrock bedrock on on the the lower lower slopes slopes of of ridges hills underlain underlain by by this formation is is commonly commonly concealed concealed by by ridges and and hills this formation loose sand and and rubble from flom overlying overlying beds. beds. STOP 7: 7: Eau Claire Sandstone Sandstone and and Wonewoc Wonewoc Formation Formation of of Ostrom Ostrom (1966). (1966). STOP 35, T. Black River Falls quadrangle, SW -, sec. Falls quadrangle, SW~, 35, T. 23 23 N., N., Location: R. 55 W. (Figure (Figure 6). 6). At Silver Mound and in the field field on the southwest R. of Silver Mound. of Fossiliferous and glauconitic sandstone beds of the Eau stone stone are are well well exposed exposed in in aa small small excavation excavation on on aa prominence prominence field Mound, and loose fossiliferous fossiliferous Eau field southwest of of Silver Mound, stone occurs occurs at at an an altitude altitude of of 1025 1025 feet feet on on the the south south tip tip of of stone near the the highway. highway. Claire in in the the Claire Silver Silver SandSandMound Mound Silver Mound is is an an important important archeological archeological locality. locality. The mound is is capped by the the Wonewoc Wonewoc Formation. Formation. The lower lower part part of of the the formation formation is is largely concealed. concealed. The uppermost 100 feet or so of beds, beds, however, however, is thoroughly cemented by silica, silica, and and the the rock rock is is aa brittle brittle quartzite. quartzite. This rock was was extensively extensively used used by by prehistoric prehistoric Indians for the manufacThis Indians for the manufacture of tools tools and and weapons. weapons. Artifacts are numerous in the fields fields surrounding the part of of Silver Mound, Mound, and artifacts and and whitish whitish rounding the southern part and artifacts flakes of quartzite from this flakes this locality locality are are widespread widespread in in Jackson Jackson County. County. Similar quartzite occurs in lesser amounts miles amounts on a ridge several miles northwest of of Silver Silver Mound. Mound. The source of the the silica that that cemented the sandstone sandstone and and the the conditions conditions under under which which it it was was deposited deposited in in the the formation formation of the quartzite in this this almost isolated occurrence require require an explanation. Upper Cambrian strata of this There is no lack of silica in the the Upper this general but most most of of it form of of quartz quartz general area, area, but it is is in the the relatively inert inert form sand. Therefore, Therefore, some some local chemical environment that that differed from the the general conditions must have made silica general silica available available in in solution. solution. Perhaps the chemical the the chemical environment environment of of the the fossiliferous fossiliferous beds, beds, particularly of of the coquina layers, layers, may have been the the source source of of the the silica. silica. As previously described, the the quartz sand grains in contact with the phosphatic brachiopod described, shells have have been been partially partially dissolved dissolved into into hemispherical hemispherical forms forms having having their their shells �·OO$'G9:! '996! 'a!~ue~penu r'uadrangle, s!!ed Falls 1:62,OO. 1968, l:iw~:20!OalJ U.S. fleological ·S"n Aq by aseg Base "L 7. dOlS Stop ~ooH Rock ~oe!g Black 'AaAInS Survey, :a~.Ia pree: punai'{ Silver Mound .leAHS "9 Figure 6. e.:nj,:.!I (';1 12 �13 flat against the the shell shell surfaces. surfaces. The chemical environment environment that that flat surfaces against produced this result in the Eau Claire Claire and the Lone Lone Rock, Rock, both both of of which which produced this result the Eau and the are are fossiliferous and and contain phosphatic phosphatic brachiopods, brachiopods, would would have have made made available large quantities of of silica silica in in solution. solution. Such silica—bearing silica-bearing waters percolating from the fossiliferous fossiliferous Lone Rock Formation may have the silica silica cement cement in in the the Wonewoc Wonewoc Formation Formation at at Silver Silver Mound. Mound. deposited the Small zones of silicified sandstone a few inches thick, thick, in the Mount Simon Sandstone near its contact with the Eau Claire Sandstone have been noted in in several several places places in in Jackson Jackson County. County. STOP 8: 8: STOP Exposure showing complexities complexities of of Precambrian Precambrian rocks. rocks. This stop also provides an opportunity to also to examine examine some some economic economic uses uses of of local local geologic features problems and possibilities arising features and some of of the problems and possibilities from the pressures of demands demands for for their their use. use. Hatfield 7-i-—minute quadrangle, SE -, Location: Hatfield 7!-minute quadrangle, ~, sec. 3, 3, T. T. 22 22 N., N., R. W. At Black River, River, north of County Rte. Rte. K K and and south south of dam at at R. 33 W. Lake Arbutus (Figure (Figure 7). 7). Because of of load load limitations limitations at at the the bridge bridge over over the the canal canal at at Hatfield, Hatfield, it will be necessary to to walk about about 11 mile mile to to the the large large exposure exposure of of PrePrecambrian metamorphic immediately below the at the metamorphic rocks rocks immediately the unconformity at the the Upper Upper Cambrian Cambrian sandstone. sandstone. base of the Lake Arbutus is an an artificial artificial lake impounded behind a dam built bedrock in in the the valley valley of of the the Black Black River. River. Water level upon Precambrian bedrock in the the dam dam is is maintained maintained at at or or near near the the level level of of the the unconformity unconformity at at the top of the the the Precambrian. A A canal canal aa little little more than than 22! miles long long has been cut in the Upper Cambrian sandstone to carry water to the penpen— stocks of aa small small electrical electrical power power plant. plant. The hydraulic hydraulic head at the power plant is is nearly 100 100 feet. feet. This power plant is is an an important important local local nonpolluting source source of electric energy. energy. Lake Lake Arbutus Arbutus has has a a surface area of of slightly more more than two square miles and and is is aa popular recreation center, center, having two two county parks and and aa State campsite on its shores. on its shores. Hatfield, Hatfield, aa small resort community on the the west west side side of of the the lake, lake, is is in an an area in in which which only only about about 10 10 to to 30 30 feet of of beds beds of of Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone overlies overlies the the metametafeet morphic and and igneous igneous Precambrian Precambrian basement basement rocks. rocks. The community obtains obtains its water supply largely from wells in its in the the sandstone. sandstone. A A few wells extend into into the the Precambrian Precambrian basement basement rocks. rocks. disposed into the surficial mantle of Sewage from the the community is is disposed surficial mantle of sand and in the the upper layers layers of of the the sandstone sandstone strata. strata. Thus the the possipossibility exists for pollution of of the the water water supply. supply. Should the local local substantially, both the the amount amount of waste redemand for water increase substantially, quiring disposal and and the the possibility possibility of of pollution pollution of of the the local localgrc*ind ground waters would would also also increase. increase. Alternative sources sources of of water water and and improved improved facilities eventually be be needed. needed. facilities for sewage disposal will eventually - �14 'U . JAO CO 21 T. 22 N. 25' C" C" 0 ; 19 i- J9 \)./.;iç;// y 4O- -, HatfI) eld O7 / fl9• I /l-o ( Backw \'\ C' ) JiVt\ jJJ/ (fl I'? 1Y U(1 ¼) 18 II OA 0 OLD 897 LA V 93 ,/ 0 I 895 0 11 I Loca],i'- 200000 FEET HIGH BANK 1jii 889112$ i7,ei Pits 16 440 Locality 25 - 22'30" 900 45' Pigure Figure mile 7. 680 1810000 FEET I c.1ty 17 ° 4.2 MI. To WIS. 54 '23J 42' 30" localities 17, 17, 24, 24, and and 25. 2. Stop 8 and and localities Hatfe].d quadrangle, 1970, Base from U.S. Geological Survey, Hatfield 1970, ].: 214,000. 1:24,000. Lake Arbutu8 area: area: Lake Arbutue �15 1 The contact between the Mount Simon Sandstone and the underlying west end of the bridge where Precambrian rocks rocks is at road level level at the west mile southwest County Rte. southwest of of the the dam dam at at Rte. K K crosses the Black River Lake Arbutus. A A thick thick bed of of coarse—grained coarse-grained cross—laminated cross-laminated sandstone sandstone is is exposed exposed on on the the west west side side of of the the road, road, and and Precambrian Precambrian granitic granitic gneiss gneiss the east side side of of the the road. road. The channel of the the Black River crops out on the has been cut about about 50 50 feet feet into into the the Precambrian Precambrian rocks rocks at at the the bridge. bridge. t -' Rte. K, K, then go northeast northeast on Clay School School Proceed east on County Rte. Road about 0.2 mile to to aa dirt dirt lane lane on on the the west west side side of of the the road. road. Follow woods and dirt lane to clearing in woods and turn north on path leading down into valley. Proceed northeast northeast toward toward the the foot foot of of the the dam. dam. the river valley. This large large exposure of bedrock shows shows some some of the the complexity of the the basement rocks. rocks. Granitic and and chloritic chloritic gneisses, gneisses, schists, schists, Precambrian basement A large and greenstones trend trend northwest and and dip dip steeply steeply northeast. northeast. A northeast—trending metagabbro dike dike at east end end of of the the dam cuts cuts the the northeast-trending at the the east gneisses. Another large dike on the west side of the east channel of the river is more dioritic in in composition. composition. The intervening granite the gneisses and chloritic sills sills are are contorted contorted in in sinuous sinuous forms forms on on which which gneisses and chloritic there is is well-developed well—developed quartz quartz rodding rodding or or slickensides slickensides that that dip dip to to the the there A feet southwest of the dam a prominent siliceous east. A few hundred feet metarhyolite(?) and the adjoining gneiss are cut by a contorted mass of metarhyolite(?) dipping mafic dike or or sill. sill. An east—trending east-trending swarm of narrow steeply dipping' unfoliated siliceous siliceous and and chloritic chloritic dikes dikes cut cut all all the the other other rock rock types. types. Minor quartz—filled quartz-filled fractures fractures cut the younger dikes and the other rock units. At one place on the west side of the river a quartz vein is more than three three feet feet thick. thick. Minor amounts amounts of of pyrite pyrite are are evident in in the the rocks, and fine—grained pyrite is abundant in the youngest dike. rocks, and fine-grained pyrite is abundant in the youngest dike. STOP 9: STOP 9: Wavellite occurrence occurrence in in the the Eau Eau Claire Claire Sandstone. Sandstone. quadrangle, SW Location: Black River Falls Falls quadrangle, SW -, sec. 23, 23, T. T. 22 22 N., N., R. (Figure 8), 8), roadcut roadcut on on East East Snow Snow Creek Creek Road. Road. R. 4 W. W. (Figure t, Wavellite (Al3(P04)2(OH)35H20) (A13(P04)2(OH)3'5H20) occurs occurs as as thin thin botryoidal botryoidal crusts, erusts, small masses, and cement in the the sandstone sandstone at outcrop small spherical spherical masses, and as as cement at this this outcrop and at several other places where where this this stratigraphic stratigraphic unit unit is is exposed exposed in this general general area. area. The source of the phosphorus is believed to have been phosphatic phosphatic fossil fossil material material such such as the phosphatic phosphatic brachiopod brachiopod shells shells as the in the Eau Claire Sandstone. Sandstone. The Wonewoc Formation which crops out on the west side of the road is weakly cemented, is cemented, very porous and and permeable permeable sandstone. sandstone. It It is is coarser in grain size than the underlying rock in grain rock and and is is thoroughly thoroughly leached. leached. The Wonewoc-Eau Claire contact zone zone is is favorable favorable for the the development of aa Wonewoc—Eau perched water table in places is abundant abundant in in the the places where where shale or clay is Claire. Eau Claire. in many places in Wisconsin where the Eau Wavellite probably occurs in Claire Sandstone is is present and where conditions for movement of ground water were comparable comparable to to those those in in this this area. area. In addition, similar conIn addition, ditions for occurrences of wavellite in association with the Lone Rock Formation may exist. Wavellite, however, may may be be readily readily overlooked, overlooked, Wavellite, however, particularly icial stains of particularly in in cases cases where where it it contains contains surf surficial of iron iron oxides. oxides. �16 -I ZLji *_—:•1: - °• -.-i---- 19• 25 F IF LocalY 24 Locality 23. I 23N Ei 928 1 ' cc; 25 O1I 96 III\ EVERG EEN :T -3 'p23 \ ,** - o T.22N — M 48 13 889 f OF - POWERHO LOcZty 16 17 GreI I 21 Fj \1],'?'Locality iave1 15 .x-= Figure 8. 8. localities 12, Merrillan ares: area: Stop Stop 99 and localities 12, 15, 1', 19, 19, 20, 20, 21, 21, 22, 22, and and 27. 27. Base Base by by U.S. U.S. Geological Survey, Geological Black cuadrangle, 1968, 1968, 1:62,500. l:62,O0. Black River Falls Falls quadrangle, �17 ADDITIONAL LOCALITIES OF GEOLOGIC INTEREST INTEREST of Precambrian Precambrian rocks. rocks. Exposures of Falls 15-minute 15—minute quadrangle, quadrangle, SE SE ~, , sec. 15, Locality 10: Black River Falls Locality 10: T. 21 21 N., N., R. R. 44 W. W. (Figure (Figure 3). 3). North of U.S. U.S. Rte. Rte. 12 at Black River T. Falls. Accessible from from east east end end of of bridge bridge crossing crossing Black Black River. River. Unfoliated jointed granite granite at at the Falls below the the dam dam appears appears Unfoliated the Falls fresh, but much of the fresh, the hornblende is is altered altered to to chlorite. chlorite. Similar granite cuts cuts iron-formation iron—formation and rocks adjoining adjoining the the iron-formation iron—formation in granite and rocks Z.E. Peterman Peterman of of the the U.S. U.S. Geological Geological Survey Survey has has deterdeterthe subsurface. Z.E. mined that that the the rubidium—strontium rubidium-strontium ratios in these granites indicate an age of years (U.S. (U.S. Geol. Geol. Survey, Survey, 1972). 1972). age of about 1,690 million years Locality 11: 11: Black River Falls Falls 15—minute 15-minute quadrangle, quadrangle, NE NE -, ~, sec. 22, the valley of Black River at T. 21 21 N., N., R. R. 44 W. W. (Figure (Figure 3). 3). In the at the the base base T. On south side of river. of river. of bluff of Mount Simon Sandstone. On Granitic gneiss and gray chloritic gneiss are cut by dolerite In In contrast to the deep channel cut cut by by the the Black Black River River in in the the Precambrian rocks Arbutus, the-channel rocks below the dam at Lake Arbutus, the· channel here here is only about only about 10 feet feet down into into the the Precambrian Precambrian rocks. rocks. The outcrops here may be concealed if if water water level level is is high. high. dikes. 15—minute quadrangle, quadrangle, NE NE ~, , sec. 30, Locality 12: Black River Falls Falls 15-minute Locality 12: T. N., R. R. 33 W. W. (Figure (Figure 8). 8). West side side of Black River near junction junction T. 22 N., Creek and and river. river. Readily accessible by road road to to canoe canoe landing. landing. of Hall's Creek bluffs leads leads to exposures exposures of of phyllite phyllite and gneiss Path to south along bluffs and gneiss beneath unconformity at at base base of of Mount Mount Simon Simon Sandstone. Sandstone. Weathered schist and and phyllite at at the the base of cliffs of Mount Simon Sandstone are are exposed a short exposed a short distance distance upstream from from the the mouth of of Hall's Hall's Creek; Creek; chloritic chloritic mafic mafic intrusive intrusive rocks rocks also also occur occur in in the the creek creek valley. valley. t, Locality Falls 15-minute 15—minute quadrangle, quadrangle, SE SE , sec. 17, Locality 13: 13: Black River Falls T. W. (Figure (Figure 8). 8). West side side of of Black River River about about 0.4 0.4 mile T. 22 22 N., N., R. R. 33 W. quarry near near river. river. southwest of power plant. plant. Abandoned quarry Strikingly contorted dark gray and and white hornblende gneiss of and a fine—grained fine-grained intrusive rock granitic to granodioritic composition and of gabbroic composition are present are exposed in the the quarry face face and and are are present in loose blocks. blocks. The composition of of feldspar feldspar augen augen in the the gneiss gneiss has has not been determined. Locality -, sec. 25, 25, T. Locality 14: 14: Hatfield 15—minute 15-minute quadrangle, quadrangle, NW NW~, T. 23 23 N., N., R. R. 33 W. W. (Figure (Figure 9). 9). West side side of of Black Black River River near near French French Island. Island. Pink granite typical of that in several several localities along along the Black River north of of Lake Lake Arbutus is is well well exposed exposed along along the the river. river. The basal beds of the the Mount Simon Simon Sandstone Sandstone crop crop out out on on the the west west side side of of the the road. road. Similar granite crops crops out out at the abutment of the abandoned bridge on the east side of of the Black River 0.2 mile mile south of Wisconsin Rte. Rte. 95 95 in the NW , in the NW~, sec. 19, 19, T. T. 23 23 N., N., R. R. 22 W. W. �18 15 17 Levis Mound I Sch . ·r l own Hall ~ 2~ ,, . ·., .~ I "Locality .. 14 ~.:~:;.' "-29 \ /. / "-/ 34 I( (, If /I If figure Figure 9. '-< .. -< L I II•• v· t.ke Arbutus Arbutu area: L.ke ( .l'Gravel Pit - ( I Localittea 14 and 15. 1. Base Locelities 14 and Baseby by U.S. U.S. Geological Geo1op,ica1 Survey, Hatfield Hatfield planimetric l98, l:1L8,000. Survey, planimetric map, map, 1958, 1:48,000. �19 Locality Locality 15: 15: Hatfield 15—minute 15-minute quadrangle, quadrangle, R. 2 W. (Figure 9). North side of of East Fork R. W. (Figure 9). east of of the the bridge. bridge. t, NW 4, T. T. 22 NW -, sec. 4, 22 N., N., of Black River River 250 feet of 250 feet Large outcrop of of granitic granitic and and migmatitic migmatitic gneiss gneiss cut cut by by maf mafic and ic and aplitic dikes. During periods of normal or low water level this outcrop is is well exposed. exposed. Quartz rodding or slickensides on minor folds folds in the the gneiss gneiss is in is similar to that in the the outcrop near near the the dam dam at at Lake Lake (Stop 8), 8), but but the the rodding rodding here here plunges plunges east east at at aa low low angle. angle. Arbutus (Stop of the mafic and aplitic dikes dikes at at this this locality locality have have The relative relative ages ages of the mafic and aplitic not been determined. Pink granite and and small aplitic dikes crop out at several several other places along along the the East Fork Fork of of the the Black Black River. River. t, 20, T. T. 23 Locality 16: 16: Hatfield 15—minute 15-minute quadrangle, quadrangle, SW SW -, sec. 20, 23 N., N., R. 1 W. (Figure (Figure 10). 10). Brushy Ridge Road. Road. R. Quartzite, a small Quartzite, probably of Precambrian age, age, is exposed in ina small roadcut tributary of of Rock Rock Creek. Creek. Quartzite roadcut on the south side of aa tributary zones in in the the Mount Mount Simon Simon Sandstone Sandstone occur occur in in aa small small knob knob on on the north zones the north side of the east-trending east—trending road 0.8 mile north side north of of this this roadcut. roadcut. t, Hatfield 15-minute 15—minute quadrangle, quadrangle, NE NE , sec. 22, Locality Locality 17: 17: Hatfield 22, T. T. 22 22 N., N., R. R. 3 W. W. (Figure (Figure 7). 7). Morrison Creek at at County Rte. Rte. K. K. Granite gneiss cut by mafic dikes is is exposed beneath the the bridge during periods of of low low or or normal normal water water level. level. Bluffs of of the the basal basal beds beds of the Mount Simon Sandstone and metamorphic and outcrops outcrops of of the the Precambrian metamorphic rocks and mafic maf Ic and and granitic granitic intrusive intrusive rocks rocks are are exposed exposed along Morrison rocks Creek to the the east of of this this locality. locality. 15—minute quadrangle, quadrangle, NW NW t, , sec. 9, 9, T. T. 21 Locality 18: Hatfield 15-minute 21 N., N., Locality 18: R. W. (Figure (Figure 11). 11). On north side of Battle Point Road. Road. R. 2 W. Precambrian quartzite is is exposed exposed in in aa small small quarry. quarry. The quartzite is is brecciated and recemented by by silica. silica. Basal sandstone of the Mount fragments of of the the quartzite quartzite at the unconformity unconformity includes fragments at the Simon Sandstone includes between the Precambrian and and the the Cambrian Cambrian rocks. rocks. Exposures of of Cambrian Cambrian rocks. rocks. t, Locality Black River -h-, sec. 19, Locality 19: 19: Black River Falls Falls 15—minute 15-minutequadrangle, quadrangle,SE SE 19, T. T. 22 22 N., N., R. R. 33 W. W. (Figure (Figure 8). 8). At bridge on on County Rte. Rte. E E crossing crossing Hall's Creek. Creek. Basal beds of Mount Simon Sandstone Sandstone are are exposed exposed near near stream stream level. level. bedded, cross-laminated, cross—laminated, medium to very coarse coarse The sandstone is is thick bedded, grained, and has at the the base the grained, has a thin pebbly layer at base in places places along the creek. �20 NEILLSVILLE 1S.4 MI. MI. TO WIS. 91S ~.~ r-ri-''l. ) / _.~~l~le Sch . "I / _. -'"- . " .1/-;... ~ _. "":' l..~ '. \, @. . 73 ........... R1W rf'o '' 44°30' 1 660000 FEET 6 5 0. BM 1005 ShortviIle 9 'v" 16 13 1--....·. '- 24 9 ",:-~,;";"",,,.lL'·~~ I •• I "--,. ":-,------.--- .. Figure 10. 10. Figure } -:- .. ,,'- mile ---.. by U.S. 3bortville Shortville area: area: Locality Locality 16. 16. Base by U.S. plazimetric map, Geologieal map, Survey, Hatfield Hatfield planimetrie Geological Survey, 1958, 1:48,000. l98, l:1.i8,000. �21 , F'1inmak r ',Flowage 36 ,.r:..-;-" ~~\~:.:. , ,-- / J f!t>:3,) .......\ \1 L I: Ii II II ft II II II II 1/ II .. ~ ~~~~~:.:_;~ f~~( "' )' vp , " /1 (~~/ / ,, >dk'2 . --' /.-9~. /; /' r, /I. ::~ l \'./ / - - :;', , ~ .... ..... _ _ :', /" ... ~ ';' 1\, \\~ 1 ~~~ {3 . t \{} ....... , ,\\.'-..,'~'.~,\ \" \.\; { \\. I.' {~ ~- ....."'\.,-:-. "- {\. '" ....... t. '.:= ~"~~~ .. .' <~ ~-, \~:-..\ /'" ;.'): . -" . 1/ /'~}/. ~ I~;~:~~~-'') :. ......._- ,\("~ ~')~~2,~ "- 5 v . I' .... ' Figure 11. 11. • Town Line Flovege area: Locality F1owge area: 18. Base by U.S. Geological Locality 18. 1958,l:Ii8,000. 1:48,000. Survey, Hatfield Hatfield planimetric planimetric map, map, 19S8, �22 Locality 20: ?, sec. 26, Locality 20: Black River Falls Falls 15—minute l5-minute quadrangle, quadrangle, NW NW~, 26, T. T. 23 23 N., N., R. R. 44 W. W. (Figure (Figure 8). 8). At park on west side of U.S. U.S. Rte. Rte. 12 at at south edge of Merrillan. Thick-bedded sandstone of the Mount Simon Sandstone is well well exposed at on Hall's Hall's Creek Creek where where there is aa scenic at the darn dam on scenic waterfall. waterfall. Locality 21: Locality 21: Black River Falls 15—minute 15-minute quadrangle, quadrangle, sec. sec. 30, 30, T. T. 23 23 N., N., R. R. 3 W. W. (Figure (Figure 8). 8). At Bruce Mound, in in Clark Clark County. County. Prominent cliffs of the Wonewoc Wonewoc Formation are are strikingly exposed exposed along the southwestern side side of of the the mound. mound. The Lone Rock Rock Formation Formation caps caps the mound at at the the lookout lookout tower. tower. The Eau Claire and and Mount Simon Sandstones stones are largely concealed on the the lower lower slopes slopes of of the the mound mound but but are are partly exposed exposed near near the the ski ski resort resort facilities facilities on on the the east east side side of of the the mound. Locality River Falls Locality 22: 22: Black .River Falls 15—minute 15-minute quadrangle, quadrangle, sec. sec. 22, 22, T. T. 22 22 N., N., R. R. 4 W. W. (Figure (Figure 8). 8). Along road following the top of ridge leading from West Snow Creek Road Road toward toward radio radio tower. tower. Shale pits in Lone Rock Formation have have excellent exposures exposures of of the the fossiliferous glauconite sandstone sandstone and and shaly shaly strata. strata. Locality 23: 15—minute quadrangle, quadrangle, NW~, NW , sec. 29, Locality 23: Black River Falls Falls 15-minute 29, T. N., R. R. 44 W. W. (Figure (Figure 3). 3). Roadcut on east side of Moss Hill Hill Road. Road. T. 21 N., Exposures of upper part of Mount Simon Sandstone are are capped at at an an altitude of 940 feet by the the Eau Eau Claire Claire Sandstone Sandstone which which has has thin thin layers layers of brachiopod shells. shells. A of coquina consisting of white brachiopod A similar occurrence is miles to the west. is at an altitufe altitufe of of 940 940 feet feet along along Wold Wold Road Road l-- miles Note the concentration of brachiopod shells along some of the cross It laminae. 14, T. T. 22 Locality Hatfield 15-minute 15—minute quadrangle, quadrangle, SW~, SW , sec. 14, Locality 24: 24: Hatfield 22 N., N., On northwest northwest side side of of Mollies Mollies Creek, Creek, at at sharp sharp bend bend R. R. 33 W. W. (Figure (Figure 7). 7). On about about 1000 feet feet northeast northeast of of junction of of Mollies Mollies Creek Creek and and Morrison Morrison Creek. Thin basal beds of the Mount Simon Sandstone have a thin basal basal layer of acts. The underlying Preof quartz quartz pebbles pebbles that that resemble resembleventif ventifacts. cambrian gneiss and schist is is deeply weathered to greenish—gray greenish-gray clay at the the unconformity unconformity between between the the Precambrian Precambrian rocks rocks and and the the Cambrian Cambrian at sandstone. Locality Locality 22, T. T. 22 N., Hatfield 15-minute 15—minute quadrangle, quadrangle, NE NE ~, , sec. 22, Hatfield N., On south bank of Morrison Creek about 1600 feet R. (Figure 7). 7). of feet R. 3 W. W. (Figure mouth of of Hay Hay Creek. Creek. southwest of mouth 25: 25: the Mount Simon Sandstone is is cemented Basal quartz conglomerate of the by pyrite in small about 6 inches inches thick a few feet small lenticular zones zones about feet above normal water water level. level. The streambank is is slightly overhanging in in places, places, and and careful search may be required to to find the the pyritic conglomerate. conglomerate. 1 �23 Locality 15—minute quadrangle, quadrangle, NE NE ~, , sec. 33, Locality 26: 26: Hatfield Hatfield 15-minute 33, T. T. 22 22 N., N., R. 1 W. (Figure 12). 12). Saddle Mound, Mound, north north of of Wisconsin Wisconsin Rte. Rte. 54. 54. R. W. (Figure The crest of the mound at at the lookout tower is capped by about 60 feet feet of the Lone Rock Formation. Glauconitic sandstone 60 sandstone is is well well exposed in a small small abandoned quarry near the foot foot of the tower, tower, and Ostrom's Ostrom's (1966) (1966) Birkmose Birkmose Member Member of of the the Lone Lone Rock Rock Formation Formation is is exposed exposed near the the guard rail rail several several hundred hundred feet feet east east of of the the tower. tower. steep southern slopes slopes The Wonewoc Formation is well well exposed on the steep the mound. mound. Minor amounts of weathered fossiliferous fossiliferous sandstone, sandstone, of the probably of the Eau Claire Sandstone, Sandstone, can be found found on the the spur on the northwestern side side of the the mound near near an an altitude altitude of of 1100 1100 to to 1130 1130 feet. feet. Most of of the the Eau Claire Sandstone, Sandstone, however, however, is is concealed by debris from the overlying formations, formations, and of the loose fossiliferous fossiliferous rock on and some some of the loose the lower slopes is is talus talus from from the the Lone Lone Rock Rock Formation. Formation. Holocene river river gravels. gravels. Locality 27: Falls 15-minute 15—minute quadrangle, quadrangle, SE SE ~, , sec. 20, Locality 27: Black River Falls T. T. 22 22 N., N., R. R. 33 W. (Figure (Figure 8). 8). Gravel pit on on west west side side of of Black Black River. River. gravel deposits deposits at this locality are are on aa wide wide terrace terrace Sand and and gravel at this about 20 feet feet above above river river level level and and cover an area of of more more than than one one square square about mile. The gravels include aa wide variety of siliceous igneous and rock types types and and minor minor amounts amounts of of sedimentary sedimentary rock. rock. Most of metamorphic rock the gravel gravel is is outwash from from glacial glacial deposits deposits that that are are abundant abundant to to the the the north. gravel deposits occur on the west side of the Black Similar gravel River in Clark County north of Wisconsin Rte. Rte. 95, 95, and in Jackson County as indicated on on both sides of the river south of Black River Falls, Falls, as the of these these areas. areas. the topographic maps of During construction of these deposits of Interstate Rte. Rte. 94, 94, these deposits were were important sources of sand and gravel, important gravel, and and they they currently currently supply supply local local needs. �r 24 ~(~4 Figure 12. .\ Saddle Mound: Locality 26. Base by U.S. Geological Survey, Hatfield SE quadrangle, 1970, 1:62,500. I �25 25 REFERENCES Klemic, Harry, Harry, and Mrose, Mrose, M.E., M.E., 1972, 1972, Geologic relations and X-ray X—ray Klemic, crystallography of of wavellite wavellite from from Jackson Jackson County, County, Wisconsin, Wisconsin, U.S. Geol. Geol. Survey and implications: U.S. Survey Prof. Prof. and their geologic implications: Paper 800—C, BOO-C, p. p. C53—C62. C53-C62. Ostrom, M.E., 1966, Ostrom, M.E., 1966, Cambrian stratigraphy stratigraphy in in western western Wisconsin: Wisconsin: Wisconsin Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Inf. Inf. Circ. Circ. 7, 7, 79 79 p. p. Ostrom, M.E., M.E., Davis, Davis, R.A., R.A., Jr., Jr., and Cline, L.M., L.M., 1970, 1970, Field Field trip trip Ostrom, and Cline, guidebook for Cambrian-Ordovician Cambrian—Ordovician geology geology of of western western Wisconsin: Wisconsin: Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Inf. Inf. Circ. Circ. 11, 11, 131 131 p. p. Potter, P.E., P.E., and Pryor, W.A., W.A., 1961, 1961, Dispersal Dispersal centers centers of of Paleozoic Paleozoic Potter, and Pryor, and and later clastics of the the Upper Upper Mississippi Mississippi Valley Valley and and adjacent adjacent areas: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 72, 72, no. no. 8, B, p. p. 1195—1250. 1195-1250. Skillings, DN., Jr., Skillings, D.N., Jr., 1970, 1970, Jackson Jackson County County Iron Iron Co.: Co.: Mining Rev., Rev., v. v. 59, 59, no. no. 24, 24, p. p. 1, 1, 10—14. 10-14. Skillings U.S. U.S. Geological Survey, 1972, 1972, Iron—formation Iron-formation in in Jackson Jackson County, County, Geol. Survey Prof. Wisconsin: U.S. U.S. Geol. Prof. Paper Paper 800—A, BOO-A, p. p. A3. A3. Weidman, Samuel, 1907, 1907, The The geology geology of of north north central central Wisconsin: Wisconsin: Weidman, Samuel, Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Bull. Bull. 16, 16, Sci. Sci. ser. ser. 4, 4, 697 p. p. 697 — � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1973 Description An account of the resource Institute on Lake Superior Geology. University of Wisconsin, Madison, Wisconsin. May 3-6, 1973. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1973 Contributor An entity responsible for making contributions to the resource J.L. Anderson C.R. Bentley Richard Berger Emmy Booy Brenton M. Hamil Ruth J. Sobanski W.F. Cannon Roger W. Cooper G.H. Dury John. C. Green E. Wm. Heinrich A.V. Heyl Robert A. Jenkins John S. Klasner Thomas R. Turner M.D. Lewan M.S. Lougheed J.J. Mancuso L.G. Megaris Jr J.L. Anderson J.R. Myles D.M. Mickelson M.G. Mudrey Jr A.L. Geldon G. Mursky G. Schriver A.R. Venditti John M. Ohlson Edward M. Ripley Donald M. Davidson D.L. Roder E.N. Cameron S.B. Romberger Klaus J. Schulz Edward M. Ripley P.K. Sims R.J. Stevenson J.E. Thresher Jens F. Touborg Thomas A. Vogel Nancy Alyanak Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/eddbd61b970180849763678b02b3769c.pdf 1ac2e8ab662d00b13fc5c7262915a1e8 PDF Text Text ������������������������������������������������������������������������������������������������������������������������������������������������������������������������ Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1974 Description An account of the resource Institute on Lake Superior Geology. Sault College of Applied Arts and Technology, Sault Ste. Marie, Ontario. May 1-5, 1974. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1974 Contributor An entity responsible for making contributions to the resource L.L. Babcock Ronald F. Bacon R.L. Bauer Emmy Booy Theodore J. Bornhorst W.F. Cannon B.A. Carlson W.J. Hinze Jeffery L. Clarke A.R. Coyner K.J. Freeman T.A. Vogel Gene L. LaBerge John C. Green H.C. Halls J.B. Heslop W.M. Tupper D.G. Innes J. Kalliokoski William H. Listerud M.S. Lougheed J.J. Mancuso P.R. Mainwaring A.J. Naldrett S.C. Nordeng David I. Norman R.V. Oja Richard W. Ojakangas James M. Robertson A.P. Ruotsala C.A. Salotti D. Weirauch R.W. Sersor P.C. Thurston N.F. Trowell M.A. Vos P.I. Wallace J.W. Cosgrove P.M. Clifford David H. Watkinson Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English