73 10 13229 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 https://digitalcollections.lakeheadu.ca/files/original/e35ceec1dbed2f5f4680805765eddaaa.pdf dd07255052a20bd1b07f793d1b8cec30 PDF Text Text ����������������This page intentionally left blank ����������������������������������This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank �����This page intentionally left blank ���This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ������This page intentionally left blank ����This page intentionally left blank ��������This page intentionally left blank ������This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ���������������������������This page intentionally left blank ��������������This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ��This page intentionally left blank ����������This page intentionally left blank �������������� 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, 1975 Description An account of the resource Institute on Lake Superior Geology. Northern Michigan University, Marquette, Michigan. April 30-May 4, 1975. 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 1975 Contributor An entity responsible for making contributions to the resource D. Jay Johnson J.R. Mangham M.L. Cummings J. Wood Norris W. Jones Eugene I. Smith P.K. Sims Zell E. Peterman Frank W. Holcomb S.C. Nordeng B.M. Hamil A.M. Johnson Milton A. Gere Jr E. Wm. Heinrich David G. Meineke K.B. Rundman J.J. Mancuso M.S. Lougheed R. Seavoy R. Shaw Erich Dimroth Ronald F. Bacon G.E. Frantti Lloyal O. Bacon John H. Karl S. Chaudhuri D.T.A Symons L.J. Pesonen C. Patrick Ervin M.G. Mudrey Jr 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/82858b8f595b98020f0953e1a612ab90.pdf b1079fef31aa6fb4274a211f38225596 PDF Text Text �PROCEEDINGS TWENTY - SECOND SECOND ANNUAL ANNUAL INSTITUTE ON INSTITUTE ON LAKE LAKE SUPERIOR SUPER lOR GEOLOGY held at held RADISSON ST. ST. PAUL 11 East Kellogg Boulevard 11 St. Paul, Minnesota 55101 55101 Paul, Minnesota May May 3-7, 1976 1976 under the sponsorship sponsorship of Minnesota Geological Survey Survey IS11 l5jl University University of Minnesota Minnesota 1633 Eustis Eustis Street Street 1633 St. Paul, Paul, Minnesota Minnesota 55108 55108 G.B. and R.F. R.F. Beltrame G.B. Morey '\:\orey and Be1trame General Editors Editors p �SALES Please order from: Publications Geological Survey, Survey, 1633 Eustis St., Please Publications Sales, Minnesota Minnesota Geological 1633 Eustis St. Paul, Minnesota sales tax tax where where applicable. Minnesota 55108. 55108. Price Price$5.00 $5.00 (U.S.), (U.S.), plus 496 496 sales Make Make checks payable to Minnesota Minnesota Geological Geological Survey. Survey. Printed at: Printed University of Minnesota Minnesota Minneapolis, Minnesota 55455 Minneapolis, 55455 �TABLE OF TABLE OF CONTENTS CONTENTS v GENERAL INFORMATION V INSTITUTE INSTITUTE BOARD BOARD OF DIRECTORS v V LOCAL COMMITTEE COMMITTEE Vi vi SESSIONS CHAIRMEN SESSIONS Vi vi ANNUAL BANQUET SPEAKER ANNUAL SPEAKER Vii vii ACKNOWLEDGEM ENTS ACKNOWLEDGEMENTS VII vii CALENDAR OF EVENTS EVENTS AND PROGRAM PROGRAM VIII viii ABSTRACTS 3 FIELD TRIPS TRIPS 71 A. MINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY FIELD CONFERENCE CONFERENCE 73 B. B. ENGINEERING ENGINEERING AND AND PLEISTOCENE PLEISTOCENE GEOLOGY GEOLOGY IN IN THE THE TWIN TWIN CITIES AREA 75 111 iii �GENERAL INFORMATION GENERAL INFORMATION 22nd Annual INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Radisson Radisson St. Paul Paul St. Paul, Paul, Minnesota Minnesota 55101 5510 1 May 3-7, 1976 May 1976 by Sponsored by Minnesota Geological Survey Survey University of Minnesota Minnesota 1633 Eustis 1633 St. Paul, Paul, Minnesota Minnesota 55108 55108 INSTITUTE INSTITUTE BOARD OF DIRECTORS DIRECTORS RE. Giblin, of Mines, Mines, Ministry Ministryofof Natural Natural Resources, Resources, Sault Sault Ste. Division of P.E. Giblin, Ontario Division Marie, Ontario 1D. Hughes, J.D. Hughes, Department of of Geography, Geography, Earth Science and Conservation, Northern Michigan University, Marquette, Michigan Marquette, Michigan Michigan M.E. Geological and and Natural History Wisconsin Geological History Survey, Survey, Madison, Madison, Wisconsin Wisconsin M.E. Ostrom, Wisconsin *R.C. Reed (Secretary-Treasurer), (Secretary-Treasurer), Geological Geological Survey Survey Division, Division, Department of Natural Resources, Resources, Lansing, Lansing, Michigan Michigan M.S. Walton, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University Universityof of Minnesota, Minnesota, St. St. Paul, M.S. Walton, Minnesota *Permanent *Permanent Member Member vv �;; LOCAL COMMITTEE COMMITTEE Conference Chairman Chairman Matt Walton, Minnesota Geological Survey, University of of Minnesota, Minnesota, 1633 1633 Eustis St., St. Paul, Paul, Minnesota Minnesota 55108 55108 Eustis Technical Program G.B. Minnesota Geological Geological Survey, Survey, University University of Minnesota, 1633 G.B. Morey, Morey, Minnesota 1633 Eustis St., St. Paul, Paul, Minnesota Minnesota 55108 55108 Eustis P.W. Weiblen, Weiblen, Department Department of Geology P.W. Geology and and Geophysics, Geophysics, University of Minnesota, Minnesota, Minneapolis, Minnesota 55455 Minneapolis, 55455 Field Trips Trips Stanley E. E. Chernicoff, Department Stanley Department of of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minneapolis, of Minneapolis, Minnesota Minnesota 55455 55455 S.S. Goldich, Goldich, Department Department of Geology, S.S. Geology, Northern Illinois Illinois University, DeKaib, DeKalb, illinois Illinois 60115 G.B. Morey, Morey, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University Universityof of Minnesota, Minnesota, St. St. Paul, Paul, G.B. Minnesota 55108 55108 V.R. Murthy, Murthy, Department Department of Geology University of Minnesota, Y.R. Geology and and Geophysics, Geophysics, University Minneapolis, Minnesota 55455 55455 C.R. Nelson, C.R. Nelson, Department of of Civil Civil and and Mineral Mineral Engineering, Engineering, University of Minnesota, Minneapolis, Minnesota 55455 Minnesota, Minneapolis, Minnesota 55455 D.H. Yardley, Yardley, Department of Civil D.H. Civil and Mineral Mineral Engineering, Engineering, University of Minnesota, Minneapolis, of Minneapolis, Minnesota Minnesota 55455 55455 Physical Arrangements Physical i\rrangements Gordon J. 3. Amundson, Arnundson,Department Departmentofof Conferences, Conferences, Nolte Nolte Center for Continuing Gordon Continuing Education, University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 SESSION SESSION CHAIRMEN D.M. Davidson, Davidson,Jr., 3r., Department Department of Geology, University of Minnesota, D.M. Minnesota, Duluth, Duluth, Duluth, Minnesota Minnesota 55802 55802 S.S. Goldich, Goldich, Department Department of Geology, Geology, University of Northern Northern Illinois, Illinois, DeKaib, DeKalb, S.S. Illinois 60115 Department, 3M, Clare Goldsmith, Geology Geology Department, 3M, Bldg. Bldg. 526-2, St. Paul, Paul, Minnesota. Minnesota. Alan M. Goodwin, Goodwin,Department Department of of Geology, Geology, University University of of Toronto, Toronto, Toronto, Alan M. Ontario, Ontar io, Canada. vi �1C. Green, J.C. Green, Department Departmentof of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota 55802 55802 R.W. Marsden, Marsden, Department Department of Geology, University of Minnesota, R.W. Minnesota, Duluth, Duluth, Duluth, Minnesota 55802 55802 Z.E. Peterman, Peterman, U.S. Z.E. U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225 80225 F.i Sawkins, F.J. Sawkins, Department DepartmentofofGeology Geologyand and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis, Minnesota 55455 55455 Weiblen, Department Department of Geology Geology and Geophysics, Geophysics, University of Minnesota, Minnesota, P.W. Weiblen, Minneapolis, Minnesota 55455 55455 of Civil Civil and and Mineral Mineral Engineering, Engineering, University University D.M. Yardley, Department of of Minnesota, Minneapolis, of Minneapolis, Minnesota Minnesota 55455 55455 BANQUET GUEST GUEST SPEAKER ANNUAL BANQUET Prof. Eugene Shoemaker, Geology GeologyDepartment, Department, California California Institute of Eugene M. M. Shoemaker, of Technology, Pasadena, California. Technology, Pasadena, ACKNOWLEDGEMENTS The organizing committee committee of the The organizing the 1976 1976 Institute Institute on on Lake Lake Superior Superior Geology Geology gratefully acknowledge in typing typing the the final manuscript acknowledge the work work of 3o Jo Behm Behm in manuscript for for the Proceedings. Proceedings. Richard Richard Darling Darling prepared the cover cover illustration. illustration. vii �CALENDER OF OF EVENTS CALENDER EVENTS AND PROGRAM MONDAY, May 5, 1976 3:30 p.m. 3:30 Pre-Institute field Pre-Institute field trip tripA, A,1976 1976Minnesota Minnesota River River Valley Valley Field Field Trip and and Conference Conference departs from the Radisson Trip Radisson St. Paul Paul for for Donovan's Motel, Motel, Redwood Donovan's Redwood Falls, Minnesota. Minnesota. TUESDAY, May May 6,1976 6, 1976 TUESDAY, 8:00 a.m. 8:00 Minnesota River Valley Field Trip Trip departs from Redwood Minnesota River Valley Field Redwood Falls to Granite Falls Falls and and Montevideo. Montevideo. 5:00 p.m. Minnesota River Valley Field Trip Trip returns returns to Redwood Minnesota River Valley Field Redwood Falls. 8:00 8:00 p.m.10:00 p.m. 10:00 Discussion session, Minnesota Minnesota River River Valley Valley Conference, Conference, Z.E. Discussion session, Z.E. Peterman, Chairman. G.B. Morey Morey Introduction L'1troduction R.L. Bauer Bauer OF PRESTRUCTURAL STUDIES STUDIES OF CAMBRIAN ROCKS ROCKS IN IN THE MINNECAMBRIAN SOTA SOT A RIVER VALLEY VALLEY C.E. Hedge Hedge & & S.S. Goldich S.S. Rb-Sr GEOCHRONOLOGY GEOCHRONOLOGY OF THE THE MONTEVIDEO GNEISS, GNEISS, MINNESOTA MONTEVIDEO RIVER VALLEY VALLEY W. Wilson & w. & GEOCHRONOLOGY AND GEOGEOCHEMISTRY OF OF GRANULITE FACIES CHEMISTRY ROCKS NEAR NEAR GRANITE GRANITE FALLS FALLS IN THE MINNESOTA RIVER VALLEY IN VALLEY V.R. Murthy Murthy B.R. Doe B.R. Doe & & M.H. M.H. Delevaux LEAD ISOTOPE INVESTIGATIONS LEAD INVESTIGATIONS IN THE MINNESOTA IN MINNESOT A RIVER VALLEY VALLEY S.S. Goldich, J.L. Wooden, Wooden, PRECAMBRIAN HISTORY PRECAMBRIAN HISTORY OF THE THE MORTON-NEW ULM ULM REACH REACH OF MORTON-NEW THE MINNESOTA RIVER VALLEY VALLEY G.A. ]r. Ankenbauer, Jr. G.A. Ankenbauer, TM. T.M. Levy Levy & & R.U. Suda Suda P.W. Weiblen Weiblen,, P.W. K.3. K.J. Schulz Schulz & & B.V. B. V. Nielsen COMPOSITIONAL VARIATIONS VARIATIONS OF MINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY AMPHIBOLITE S.S. Goldich S.S. Summary viii 4 �F WEDNESDAY, May 5,1975 WEDNESDAY, May 8:00 a.m. 8:00 Minnesota River Valley Field Trip departs Redwood Minnesota River Valley Field Redwood Falls for for Morton and New New Ulm. Ulm. 8:00 a.m. 8:00 Field Trip on Engineering and Pleistocene Geology Trip B on Engineering and Geology in the Twin Cities area departs Twin Cities departs Radisson Radisson St. St. Paul. Paul. 5:00 p.m. 5:00 Field Trip on and Pleistocene Geology returns to on Engineering Engineering and Geology returns to Radisson Radisson St. Paul. Paul. 6:00 p.m.6:00 9:00 p.m. 9:00 Paul. Early registration, Minnesota Early Minnesota East, East, lower lower level, level, Radisson Radisson St. St. 8:00 p.m. 8:00 Conferences Smoker Smoker (cash bar) Capitol Ballroom, Ballroom, lower level Radisson St. Paul. Radisson 8:00 p.m. 8:00 Minnesota River River Valley Valleyfield field trip trip returns, returns, Radisson Minnesota Radisson St. Paul. THURSDAY, THURSDAY, May May 8, 1976 1976 7:30 7:30 a.m.9:30 9:30 a.m. Registration, outside outside Minnesota Minnesota East, Radisson Radisson St. Paul. Paul. 8:00 - General Chairman, 1976 Welcome, Matt \Valton, Walton, General 1976 Institute on on Lake Superior Super ior Geology. 8:10 8:10 SESSION I - SYMPOSIUM ON GEOLOGY AND SESSION AND GEOCHEMISTRY GEOCHEMISTRY PRECAMBRIAN ROCKS, ROCKS, 5.5. S.S. Go1dich Goldich and A.M. OF EARLIEST EARLIEST PRECAMBRIAN A.M. Goodwin, Co-Chairmen. Goodwin, 8:10 G.P. Beakhouse Beakhouse A REAPPRAISAL OF OF THE THE WESTERN WESTERN PORTION OF THE THE ENGLISH ENGLISH RIVER RIVER SUBPROVINCE, NORTHWESTERN SUBPROVINCE, ONTARIO AND SOUTHEASTERN ONTARIO MANITOBA 8:30 C.F. Gower Gower THE GEOLOGY GNEISSIC ROCKS THE GEOLOGY OF GNEISSIC IN THE IN THE KENORA DISTRICT, ENGLISH ENGLISH RIVER GNEISS RIVER G NEISS BELT BEL T 8:50 A.M. Goodwin LITHIC ELEMENT LITHIC AND MAJOR ELEMENT COMPOSITION IN IN THE THE SUPERIOR COMPOSITION GEOTRA VERSE, 0ONTARIO G EOTRA VERSE, NT ARlO 9:10 C.-L. Chou, Chou, N.B.W. & N.B.W. Harris, & ABUNDANCES OF RARE EARTH ABUNDANCES OF EARTH AND OTHER ELEMENTS. IN ARCHEAN ELEMENTS- IN GRANITIC AND GNEISSIC GRANITIC GNEISSIC ROCKS FROM THE THE ENGLISH ENGLISH RIVER RIVER GNEISS GNEISS BELT, ONTARIO A.M. Goodwin 9:30 G.N. Hanson Hanson & & S.S. Goldich 5.5. RARE EARTH EARTH ELEMENT ELEMENT STUDIES STUDIES OF THE THE ARCHEAN ARCHEAN GNEISSES GNEISSES OF THE MINNESOTA MINNESOT A RIVER VALLEY VALLEY ix �9:50 Welsh J.L. Welsh J.L. PETROLOGY PETROLOGY OF OF THE THE ARCHEAN ARCHEAN GNEISSES GNEISSES AT AT THE THE NORTHWEST CORNER CORNER OF THE SACRED HEART PLUTON; PLUTON; MINNESOTA RIVER VALLEY, VALLEY, MINNESOTA 10:10 10:10 W.R. Van &. W.R. Van Schmus & J.L. J. L. Anderson GNEISS GNEISS AND AND MIGMATITE MIGMATITE OF OF ARCHEAN AGE BASEMENT AGE IN IN THE THE PRECAMBRIAN BASEMENT OF CENTRAL WISCONSIN, WISCONSIN, U.S.A. 10:30 Z.E. Peterman, Z.E. R.E. Zartman, & R.E. &. P.K. Sims OLD W GNEISSES GNEISSES OLD PRECAMBRIAN W IN MICHIGAN IN NORTHERN MICHIGAN 10:50 M.M. Kehlenbeck M.M. NATURE THE QUETICO-WABIGOON QUETICO-WABIGOON NATURE OF THE BOUNDARY BOUNDARY IN IN THE THE de de COURCEYSMILEY SMILEY LAKES LAKES AREA, AREA, NORTHWESTERN WESTERN ONTARIO 11:10 D. Birk ELEMENTS IN THE ARCHEAN TRACE ELEMENTS IN THE GRANITOID GRANITOID DIAPIRS PIERCING WABIGOON GREENSTONE THE WABIGOON BELT 11:30 I.E. Smith, T.E. Smith, A. Turek, Turek, & &. C. Riddle THE THE GEOCHEMISTRY GEOCHEMISTRY OF THE GAMITAGAMA LAKE COMPLEX, GAMITAGAMA WAWA, ONTARIO WAWA, 11:50 E.C. E.C. Perry, 3r. Jr. SN. Ahmad S.N. Ahmad IN METAMORPHOSED METAMORPHOSED CARBON IN ISUA, WEST WEST SEDIMENTS FROM ISUA, GREENLAND THURSDAY, THURSDAY, May May 8, 1976 1976 8:10 8: 10 am SESSION SESSION IIII-- ENGINEERING ENGINEERING AND AND ENVIRONMENTAL ENVIRONMENTAL GEOLOGY, D.M. Yardley and and C. C. Goldsmith, D.M. Yardley Goldsmith, Co-chairmen. 8:10 H.O. Pfannkuch Pfannkuch SYSTEMS APPROACH TO TO ENVIRONENVIRONA SYSTEMS MENTAL GEOLOGY 8:30 8:30 D. Pollack Pollack & &. H.O. Pfannkuch IMPLICATIONS ENVIRONMENTAL IMPLICATIONS GROUNDW ATER-LAKE INTEROF GROUNDWATER-LAKE WITH LAND USE APPLICATION ACTION WITH 8:50 8:50 W. W. Rohrer & &. H.O. Pfannkuch Pfannkuch GROUNDW ATER SPREADING OF GROUNDWATER HYDROCARBON SPILLS SPILLS WITH WITH HYDROCARBON EMPHASIS ON MONITOR MONITOR SPECIAL EMPHASIS SYSTEM DESIGN DESIGN IN DRIFT SYSTEM IN GLACIAL DRIFT 9:10 9: 10 D.I. D.I. Siegel Siegel OF DISSOLVED OISSOL VED SOLIDS SOLIDS SOURCES OF IN GROUNDWATER GROUNDW ATER FROM SUPERIOR SUPERIOR IN AND RAINY RAINY LOBE LOBE TILL TILL AND xx �ji 9:30 S.!. S.I. Jacobsen THE TRACE ELEMENT THE ELEMENT GEOCHEMISTRY GEOCHEMISTRY OF PEAT PEAT BOGS BOGS OVER OVER DIFFERENT BEDROCK TYPES, TYPES, SOUTHERN BEDROCK HOUGHTON COUNTY, MICHIGAN MICHIGAN Coffee 9:50 10:10 10: 10 M.G. Mudrey, Jr. M.G. Mudrey, B.C. B.C. Parker, K. K. Cartwright Cartwright & &. L.D. McGinnis L. D. McGinnis DIAMOND DIAMOND DRILLING DRILLING IN ENVIRONENVIRONMENTALLY SENSITIVE SENSITIVE AREAS - ENVIRONMENTAL IMPACT: MONITORING MONITORING AND AND ASSESSMENT ASSESSMENT 10:30 E. Booy Booy & &. STRATIGRAPHIC STRA TIGRAPHIC VARIATION VARIATION IN IN MINERALOGY AND ENGINEERING MINERALOGY ENGINEERING CHARACTERISTICS OF ONTONAGON ONTONAGON CLAY NEAR A CLAY A MAJOR SLOPE SLOPE FAILURE, ONTONAGON ONTONAGON COUNTY, COUNTY, MICHIGAN S.). Dyl, S.J. Dyl, II II 10:50 A.M. A.M. Johnson Johnson & & H.O. Sorenson Sorenson ENGADINE DOLOSTONE OF OF MICHIGAN'S MICHIGAN'S EASTERN UPPER PENINSULA: PENINSULA: GEOLOGY AND RESOURCE EVALUATION GEOLOGY EVALUATION 11:10 E. Booy Booy & &. R.D. Harris SECONDARY MINERAL GROWTH SECONDARY OF THE THE WHITE WHITE PINE SHALE SHALE COMPARED WITH WITH CLASSIC "HEAVING" SHALES SHALES C.R. Nelson Nelson & &. D.H. Yardley D.H. MODIFICATION OF ENGINEERING MODIFICATION ENGINEERING PROPERTIES OF ST. ST. PETER PETER SANDSTONE SANDSTONE 11:30 12:10 12: 10 p.m.— p.m.1:30 p.m. 1:30 12:10 12: 10 p.m.1:30 1:30 p.m. 1:30 Lunch Informal meeting of of geologists geologists interested in Informal meeting in Precambrian Precambrian of of Wisconsin. Mudrey,Jr., Jr., convenor. convenor. All Wisconsin. M.G. M.G. Mudrey, All interested interested geologists geologists bulletin board board for for notice of location). are welcome. welcome. (See (See bulletin locaticn). SESSION III III - GENERAL GENERAL GEOLOGY, D.L. Southwick and R.W. SESSION GEOLOGY, D.L. R.W. Marsden, Co-Chairmen 1:30 R.W. R.W. Ojakangas ANATOMY OF OF A WELL-COVERED ANATOMY WELL-COVERED GREENSTONE BELT, NORTHWESTERN NORTHWESTERN MINNESOTA 1:45 D.L. Southwick D.L. HIGH-GRADE HIGH-GRADE METAMORPHISM METAMORPHISM ASSOCIATED WITH THE VERMILION ASSOCIA TED VERMILION BATHOLITH, MINNESOTA-ONTARIO BATHOLITH, 2:00 R.S. Maass Maass & &. L.C. Medaris, L.C. Medaris, Jr. PENOKEAN STRUCTURES AND PENOKEAN AND PLUTONIC ROCKS ROCKS IN PLUTONIC IN PORTAGE AND WOOD AND WOOD COUNTIES, WISCONSIN WISCONSIN xi �—— 2:15 G.L. LaBerge LaBerge & &. P.E. Myers Myers THE CENTRAL CENTRAL WISCONSIN WISCONSIN BATHOLITH BATHOLITH 2:30 P.E. Myers Myers THE WAUSAU SYENITE OF OF CENTRAL THE WAUSAU SYENITE WISCONSIN 2:45 E.J. Smith GEOLOGY AND AND GEOCHEMISTRY GEOCHEMISTRY OF THE PRECAMBRIAN PRECAMBRIAN MARCELLON RHYOLITE, COLUMBIA COLUMBIA COUNTY, WISCONSIN Coffee 3:00 3:15 P.K. Sims Sims MIDDLE PRECAMBRIAN PRECAMBRIAN AGE AGE OF MIDDLE VOLCANOGENIC MASSIVE MASSIVE SULFIDE DEPOSITS IN IN NORTHERN NORTHERN WISCONSIN WISCONSIN 3:30 W.C. W.C. Prinz CORRELATIVE CORRELA nVE IRON-FORMATIONS IRON-FORMAnONS AND VOLCANIC ROCKS OF OF PREAND VOLCANIC ROCKS CAMBRIAN X X AGE, AGE, NORTHERN CAMBRIAN NORTHERN MICHIGAN 3:45 M.S. Lougheed & &. 3.1. J. J. Mancuso ORIGIN OF LAMINAE ORIGIN LAMINAE IN IN PRECAMBRIAN IRON-FORMAION 4:00 T.-M. Han GEOCHEMICAL PROCESSES FOR GEOCHEMICAL THE FORMATION OF MAGNETITE MAGNETITE IN LOW-GRADE METAMORPHIC IN METAMORPHIC PRECAMBRIAN IRON-FORMATIONS IRON-FORMATIONS 4:15 W.F. W.F. Cannon & &. L.J. Drew Drew RESOURCES OF RECOVERABLE RECOVERABLE IRON ON THE THE MARQUETTE MARQUETTE RANGE, RANGE, MICHIGAN BY A MICHIGAN — - ESTIMATES BY MONTE CARLO SIMULATION SIMULATION MONTE CARLO METHOD 4:30 D.W. Snider D.W. A GROUND INVESTIGATION INVESTIGATION OF AN AEROMAGNETIC AEROMAGNETIC ANOMALY, ANOMALY, DICKINSON COUNTY, MICHIGAN MICHIGAN DICKINSON 5:30 p.m.5:30 6:30 6:30 p.m. SOCIAL HOUR HOUR(cash (cashbar) bar)CapitAL CapitAL Ballroom, Ballroom, Radisson Radisson St. St. Paul SOCIAL 6:30 6:30 p.m. ANNUAL BANQUET,Capital Capital Ballroom, Ballroom, Radisson Radisson St. St. Paul, ANNUAL BANQUET, Eugene M. Shoemaker, Shoemaker, Guest Guest Speaker. Eugene M. FRIDAY, FRIDAY, May May 9, 1976 1976 8:00 a.m. 8:00 SESSION IV GEOLOGY. P.W. P.W. Weib1en Weiblenand and J.C. J.C. IV - GENERAL GEOLOGY. Green, Co-Chairmen 8:10 8: 10 F.3. F.J. Sawkins Sawkins ORE DEPOSITS DEPOSITS IN RELATION TO TO HOTSPOT-GENERATED HOTSPOT-G ENERA TED INTRACONTINENTAL RIFTING RIFTING xii ~ �8:30 8:30 1M. Robertson J.M. GEOLOGY AND MINERALOGY GEOLOGY MINERALOGY OF SOME SOME COPPER SULFIDE SULFIDE DEPOSITS DEPOSITS NEAR MOUNT BOHEMIA, KEWEENAW MOUNT BOHEMIA, KEWEENAW COUNTY, MICHIGAN MICHIGAN 8:50 W.A. Bartlett, Bartlett, W.A. M.S. Lougheed, M.S. U.J.Mancuso J. Mancuso & & L.3. Walters L.J. DISTRIBUTION IN DISTRIBUTION OF OF SULFUR IN THE WEST KIERNAN THE WEST KIERNAN SILL, SILL, IRON COUNTY, MICHIGAN MICHIGAN 9:10 B. Bonnichsen & B. & R.I. Botto R.I. THE BEHAVIOR OR PRECIOUS BEHAVIOR OR METALS METALS AND AND OTHER OTHER TRACE ELEMENTS DURING ELEMENTS DURING THE FRACTIONAL CRYSTALLIZATION OF DULUTH CRYSTALLIZATION COMPLEX SULFIDES SULFIDES 9:30 LA. Vogel, T.A. Vogel, M.B. McBride & M.B. & R. Ehrlich Ehrlich SYNGENETIC MODEL FOR THE THE SYNGENETIC MODEL ORIGIN WHITE PINE ORIGIN OF THE WHITE PINE COPPER DEPOSIT 9:50 N. Scofield CHEMISTRY OF PRIMARY AND CHEMISTRY AND SECONDARY MINERALS OF SOME SOME SECONDARY MINERALS PORTAGE LAKE LAKE LAVAS, LAVAS, KEWEENAW KEWEENAW PENINSULA: PENINSULA: DEVELOPMENT OF MODELS OF MODELS OF DIFFERENTIATION AND LOW-RANK METAMORPHISM METAMORPHISM Coffee 10:10 10:30 1G. Grimes J.G. Grimes APPLICATION OF A A FLOW FLOW DIRECTION DIRECTION PORTAGE TECHNIQUE TO THE PORTAGE VOLCANICS, MICHIGAN MICHIGAN LAKE VOLCANICS, 10:50 C. Brumleve Brumleve FRACTURE PETROLOGY AND FRACTURE THE KINGSTON KINGSTON CHARACTERISTICS OF THE CONGLOMERATE,KEWEENAW CONGLOMERATE, KEWEENAW COUNTY, MICHIGAN MICHIGAN 11:10 B.E. B. E. Aaquist AN INTERPRETATION OF THE THE AN KINGSTON CONGLOMERATE AS AS KINGSTON IN THE THE PORTAGE PORTAGE A A RHYOLITE RHYOLITE TUFF lUFF IN LAKE LAVA LAVA SERIES, SERIES, KEWEENAW KEWEENAW PENINSULA, MICHIGAN MICHIGAN 11:30 3.M. J.M. DeGraff STRUCTURAL AND AND AGE AGE RELATIONRELATIONSHIPS AT THE LAC LAC LA LA BELLE BELLE SHIPS ANOMALY, KEWEENAW KEWEENAW MAGNETIC ANOMALY, COUNTY, MICHIGAN MICHIGAN 11:50 L.L. L. L. Babcock Babcock CONTACT RELATIONSHIPS RELATIONSHIPS BETWEEN BETWEEN CONTACT THE IACOBSVILLE SANDSTONE JACOBSVILLE SANDSTONE AND THE THE PORTAGE LAKE LAKE LAVA LAVA AND A PROGRESS PROGRESS REPORT GROUP: A xiii xiii ji �;;; 12:15 12:15 p.m.1:15 1: 15 p.m. Lunch 12:15 p.m.12:15 1:15 1: 15 p.m. Annual Business BusinessMeeting, Meeting,Institute Institute Board Board of of Directors. Annual 1:30 p.m. 1:30 SESSION V - GENERAL GEOLOGY, GEOLOGY, F.J. Sawkins Sawkins and and D.M. D.M. Davidson, Jr., Jr., Co-Chairmen. Davidson, 1:30 F.M. Swain, F.M. 1. Baysinger & J. & 3.M. J.M. Bratt HYDROCARBONS OBTAINED OBTAINED BY BY PYROLYSIS PYROLYSIS OF SOME SOME PRECAMBRIAN PRECAMBRIAN ROCKS OF MINNESOTA MINNESOTA 1:50 S.W. Stuhr & & S.W. E.N. Cameron E.N. GEOLOGY OF THE ROUND LAKE GEOLOGY INTRUSION, SAWYER INTRUSION, SAWYER COUNTY, WISCONSIN 2:10 R.M. Tyson Tyson & & B. B. Bonnichsen HORNFELSED BASALTS BASALTS IN THE THE DULUTH COMPLEX 2:30 1R. J.R. Burnell, Burnell, 3r. Jr. THE PETROLOGY AND AND STRUCTURAL STRUCTURAL RELATIONS OF THE THE LATER RELATIONS OF LATER PREPRECAMBRIAN BRULE LAKE LAKE INTRUSIONS, INTRUSIONS, COOK MINNESOTA COOK COUNTY, MINNESOTA 2:50 D.M. Davidson, Jr., D.M. Davidson, H. Halls & & 3.R. J.R. Burnell, 3r. Jr. PALEOMAGNETISM OF OF THE THE LATE PALEOMAGNETISM PRECAMBRIAN BRULE LAKE LAKE INTRUSION, INTRUSION, COOK COOK COUNTY, COUNTY, MINNESOTA Coffee. 3:10 3: 10 3:30 N.M. Pope N.M. PETROLOGY AND STRUCTURE STRUCTURE OF THE THE LATE LATE PRECAMBRIAN PRECAMBRIAN SILVER CREEK CLIFF AND SILVER CREEK AND LAFAYETTE LAFAYETTE BLUFF MAFIC INTRUSIONS, INTRUSIONS, LAKE COUNTY, MINNESOTA MINNESOTA 3:50 R.P. Meyer, Meyer, GEOPHYSICAL PROSPECTING OFF THE THE KEWEENAW KE.WEENAW PENINSULA 3.R. Moore, J.R. E.L. Nebrija Nebrija & & C.T. C. T. Young Young 4:10 H.C. Halls Halls THE SLATE THE CENTRAL THE SLATE ISLANDS: ISLANDS: THE UPLIFT OF OF A A METEORITE METEORITE IMPACT IMPACT CRATER? xiv �U) —1 C) -1 U) w ABSTRACTS • �I AN AN INTERPRETATION INTERPRETATION OF OFTHE THEKINGSTON KINGSTON CONGLOMERATE CONGLOMERATEAS ASAA RHYOLITE INTHE THEPORTAGE PORTAGELAKE LAKELAVA LAVASERIES, SERIES, RHYOLITE lUFF TUFFIN KEWEENAW KEWEENAW PENINSULA, MICHIGAN MICHIGAN B.E. Department of of Geology, Geology, University University of of Western Western Ontario, Ontario,London, London, B.E. Aaquist, Aaquist, Department Ontar io N6A N6A 5B7 5B 7 Ontario ABSTRACT The The rock rock type included included under under the the formation formation name nameof ofKingston Kingston Conglomerate Conglomerate within quadrangleisis interpreted interpreted as as having formed by by the fracturing within the Ahmeek Ahmeek quadrangle having formed fracturing and reworkingof of aa rhyolite rhyolite tuff. tuff. The and minor minor reworking The average average thickness thickness of of the the formation formation isis 10 layers, which which commonly commonlyare are lenticular lenticular in IO meters and individual individual layers, in shape and and cross cross bedded, range thickness from from 1I mm mm to to 65 65 cm. cm. Fragments Fragments consist consist entirely of of bedded, range in thickness rhyolite rhyolite having having quartz and and plagioclase plagioclase phenocrysts phenocrysts in a cryptocrystalline cryptocrystalline groundgroundmass. deep embayments embayments characteristic characteristic mass. The The phenocrysts phenocrysts have have vague vague boundaries boundaries and and deep parts of of the formation volcanic origin. origin. Sandy Sandy parts formation consist consist of angular angular quartz quartz and and of a volcanic feldspar feldspar crystals, feldspar feldspar laths, fine fine angular angular grains grains of cryptocrystalline cryptocrystalline material, and grainsofofhematite. hematite. Some and rounded rounded grains Some of the the poorly poorly sorted, sorted, coarse-grained coarse-grained layers layers have a texture indicative indicative of of in in situ situ fracturing fracturing of of fragments fragments with with separation separation the theonly only Also, sand around fragments in these layers appears movement of the fragments. Also, sand around fragments in these appears movement of fragments. to have have formed by by the breakdown breakdown of fragments. of adjacent fragments. The distribution of of the Kingston rhyolite plus plus similar similar rhyolitic rhyolitic facies facies in The distribution Kingston rhyolite in three other interflow interflow horizons horizons in the overlying overlying basaltic basaltic sequence sequence suggests suggests the source source of of the rhyolite rhyolite was was to to the the southeast, southeast, and and indeed, indeed, rhyolite rhyolite domes domes outcrop outcrop within within the lower part of from the the area lower part of the the Portage Portage Lake Lake Lava Lava Series Series from area of of the theAhmeek Ahmeek quadrangle to east end end of ofthe theKeweenaw KeweenawPeninsula. Peninsula. Native copper has has been been quadrangle to the east mined from from the the rhyolite facies of mined rhyolite facies of all all four four interflow interflow horizons horizons in in the the Ahmeek Ahmeek quadrangle quadrangle map map area. 3 �CONTACT RELATIONSHIPS RELATIONSHIPS BETWEEN BETWEEN THE JACOBSVILLE JACOBSVILLE SANDSTONE SANDSTONE AND THE THE PORTAGE LAVA GROUP: AND PORTAGE LAKE LAKE LAVA A PROGRESS PROGRESS REPORT Larry L. of Mineral Mineral Research, Research, Michigan Michigan Technological Technological UniverUniverLarry L. Babcock, Babcock, Institute of sity, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT Logs of of all theLaurium Laurium quadrangle quadrangle which which collar collar Logs all diamond diamond drill drill holes holes in in the between the Scales between Scales Creek Creek Flow Flow (PSc) (PSc) and and the the Jacobsville Jacobsville Sandstone Sandstone (JS) (JS) - Portage Lake contact were were officially Lake Lava Lava Group Group (PLLG) (PLLG) contact officially obtained obtained from from Universal Universal Oil Oil logs comprise 105 holes holes and Products. These These logs comprise 105 and represent represent 25,000 25,000 m m of of drilling. drilling. Stratigraphic correlation correlation between Stratigraphic between the southernmost southernmost four four field field sections sections along along the contact trace contact trace and and adjacent adjacent drill drill holes holes has hasbeen beencompleted. completed. These These sections sections are Gooseneck, Quincy, Oneco (ON), (ON), New New Gooseneck, Quincy, Dover, Dover, and and Dover Dover (north) (north) Creeks Creeks and and the Oneco (NB), and A) drill Baltic (NB), and New New Arcadian Arcadian (N (NA) drill holes, holes, respectively. respectively. The stratigraphic stratigraphic succession four The succession across across the the JS-PLLG JS-PLLGcontact contact zone zone in in the four field consists of of the the following following units, from from oldest oldest to to youngest: youngest: (1) (1) "typical" "typical" field sections consists (3) "contact" "contact" conglomerate, conglomerate, and and PLLG PLLG flat-lying JS, JS, (2) (2) basal basal PLLG PLLG melaphyre, melaphyre, (3) flat-lying lavas. However, However, an is present present between between (1) (1) and and (2) (2) in in the theQuincy Quincy an additional additional unit unit is Creek gravel quartzite Creek section: 35 35 to to 48 48 m m of of steeply steeply dipping dipping JS beach sand-beach sand-beach gravel conglomerate. The contact zone The JS-PLLG JS-PLLG contact zone on on Quincy Quincy Creek Creek was was mapped mapped in in detail. detail. An asymmetrical this asymmetricalbuttress buttresszone zoneextends extends250 250toto300 300mmacross acrossthe the contact contact at at this south%ast from PLL$ lavas, dip ste8pen in location. Proceeding Proceeding southeast from PLLG lavas, theth dip steepen3 in three three successivestages stagesfrom from15~290+ l5-29 + NW to 22-55 successive 22-55 0++ NW to 30 30 0++ NW÷-90 NW+-90 0—50 -50 ++ SE. The latter in the la tter stage stageisisan anantieinal anticlinalflexure flexureconsisting, consisting,-in thecrushed crushed axial axial portion, portion, of of large large quartzite blocks blocks (NW (NW limb) limb) and and sandstone sandstone blocks blocksand andslabs slabs(SE (SElimb). limb). Typical Typical flatflatlying JS JS is is encountered encountered immediately immediately southeast of this buckle. buckle. Results of field and diamond drill section correlations are are outlined outlined below: below: Results diamond drill (1) Interbedding between between the JS JS and and PLLG PLLG is is noted noted in in four four of ofsix sixNA NAholes holes Interbedding near Gooseneck Gooseneck Creek. Creek. Isopach maps constructed on on two two Isopach maps were were constructed successive, successive, essentially essentially flat-lying undisturbed undisturbed stratigraphic intervals interVals in in these four four holes: holes: volcanics volcanics (3-14 (3-14 m) m) and and sediments sediments (4-18 (4-18 m) m) which which these underlie underlie these these volcanics. volcanics. Two transport transport direction direction solutions solutions were were Two 0 computed0for each interval: computed for each interval: volcanics, volcanics, S27°E S27 E and and S45°E; S450E; sediments, sediments, both N15 E. The N150E. The latter direction direction is is identical identical to to those those measured measured on on "typical" JS JS exposed in the bed Creek and and represents represents the bed of of Gooseneck Gooseneck Creek "typical" exposed in "normal" JS JS transport transport direction direction in the "normaF' the Laurium Laurium quadrangle. quadrangle. Sediments Sediments exposed in the the bed bed of the the creek creek directly directly overlie overlie the theabove above mentioned mentioned exposed in volcanic interval. (2) The contact conglomerate conglomerate is is exposed exposed in all four four field field sections sections and and was was The intersected by by five five adjacent adjacent drill drill holes. holes. In In three of of these these holes, holes, 12 12 to 120 120 m m of lava lava separate separate this thisconglomerate conglomerate from from the theunderlying underlying Baltic Baltic No. conglomerate, i.e. i.e. the contact 4. No.33 conglomerate, contact conglomerate conglomerate is is No. No.4. (3) Between Creek section section and and the the nearest nearest dr!Hdrl holes Between the Dover Dover Creel< holes(0N9), (ON9),Nos. Nos. 3 and conglomerates exhibit exhibit identical identical dips, dips, 6.2 6.2 NW, NW, and and identical identical and 44conglomerates 4 �stratigraphic separation stratigraphic separation intervals, intervals, 120+ 120+44m. m. These These values values are are constant constant over aa horizontal horizontal distance distance of 2.3 km. over km. (4) (4) The uppermost The uppermost JS conglomerate conglomerate in Section isis in the the Dover Dover Creek Creek Section correlative with with the the Baltic correlative Baltic No. No. 33 of PLLG: the lowermost of the PLLG: the lowermost conglomerate, No. 2. conglomerate, No.2. (5) (5) A regionwide regionwideunconformity unconformityininthe theJS JSoccurs occursatatthe the top top of of the the uppermost A uppermost JS conglomerate conglomerate on JS on Dover Dover Creek Creek (Babcock, (Babcock, 1975). 1975). This This unconformity unconformity represents aa definitive at represents definitive rock-and rock-and time-stratigraphic time-stratigraphic break break (timeline) (timeline) at the top top of the Baltic 3 conglomerate which is present present in in both both the the Baltic No. No.3 which is JS the and PLLG. and the JS JS exposed exposed on These These correlations correlationsrequire requirethat that virtually virtually all all of of the on the Keweenaw Peninsula Peninsulaisistime time equivalent equivalent to to lowermost lowermost portions portions of of the PLLG. Keweenaw PLLG. REFERENCE Babcock, L.L., L.L., 1975 Babcock, 1975 The The Jacobsville Jacobsville Sandstone: Sandstone: Evidence Evidence for a Lower-Middle Lower-Middle Keweenawan Age: Age: Field Field Trip Trip 3, 3, Proc., Proc., 21st Inst. on Keweenawan 21st Ann. Ann. Inst. on Lake Lake Superior Superior Geol., Geol., pp. 87—123. 87-123. 55 �DISTRIBUTION DISTRIBUTION OF SULFUR SULFUR IN IN THE THE WEST WEST KIERNAN KIERNAN SILL, SILL, IRON IRON COUNTY, COUNTY, MICHIGAN MICHIGAN W.A. Bartlett*, M.S. iJ. Mancuso, W.A. Bartlett*, M.S. Lougheed, Lougheed, J.J. Mancuso, and and L.J. L.J. Walters, Walters, Department Department of of Geology, Green University, University, Bowling Green, Ohio Ohio 43403 43403 *Current address: Bowling Green, address: Geology, Bowling Bowling Green Lindgren Lindgren Exploration Co., Wayzata, Wayzata,Mn. Mn.55391 55391 ABSTRACT The West West Kiernan Kiernan Sill, located located in in eastern eastern Iron IronCounty, County,Michigan, Michigan, is is a The differentiated body body of of mafic mafic igneous igneous rock rock ranging ranging in in composition composition from from peridotite in age, and through gabbro gabbro to to granophyre. granophyre. It It is is Middle Middle Precambrian Precambrian in and has has been been through metamorphosed to greenschist facies. The The sill was intruded into the the Hemlock Hemlock metamorphosed to the the greenschist formation, and occupies an an outcrop outcrop area of and now now occupies of approximately 26 26 square square miles. miles. The The sulfur sulfur content content of of the the West West Kiernan Kiernan Sill Sill varies varies with rock rock type, type, but but in in general averages for for similar similar rocks. rocks. The general is low low as compared compared to published published averages The peridotitic rocks of sill average average 55 micromoles/gram sulfur, the gabbroic gabbroic rocks rocks average average 40 40 rocks of the sill micromoles/gram sulfur and micromoles/gram sulfur and the the granophyric granophyric rocks rocks average average 11 11 micromoles/gram micromoles/gram on statistical analyses sulfur. Based Based on analyses and and graphical graphical techniques techniques the the distribution distribution of of of sulfur. copper and copper and nickel nickel in in the the sill sill isis shown showntoto correlate correlate with with the distribution of Because copper and and nickel nickel ore deposits in Because copper in mafic mafic igneous igneous rocks are made made up up of concentrations of sulfide sulfide minerals, minerals,the the distribution distributionofof sulfur sulfur can can be be used concentrations of used as as aa in mafic prospecting tool to to indicate the prospecting tool the relative relative abundance abundance of of sulfide sulfide minerals minerals mafic igneous bodies. 66 �I STRUCTURAL STUDIES STUDIES OF PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS IN THE THE MINNESOTA MINNESOT A RIVER RIVER VALLEY VALLEY Robert L. L. Bauer, Bauer, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT ABSTRACT The The gneisses in the the Minnesota Minnesota River River Valley Valley between between Montevideo Montevideo and and Morton, Morton, Minnesota have been folded into a series of shallow, eastward-plunging Minnesota have been folded into a of shallow, eastward-plunging antiforms antiforms and synforms, (F2), (F2)' with wavelengths on on the order of of several kilometers major structures structures are are pre-dated (Himmelberg, 1968; 1968; Grant, 1972). 1972). These These major pre-dated in in the the (Himmelberg, Granite Falls Falls area area by, by, rare rare isoclinal, isoclinal, intrafolial intrafolia1folds, folds, (F1), (F 1)' which which are are coaxial coaxial with, with, but deformed deformed by by the F2 structures. structures. A third (F),), not third period period of folding, folding, (F notevident evidentfrom from aathe themapping mapping of of the themajor major structures, from aa det'ailed of the minor structures, is is deduced deduced from deiailed analysis analysis of minor folds folds and and mineral mineral Heart area area this third lineations lineations in the the gneisses. gneisses. In In the Morton-Sacred Morton-Sacred Heart third period period of of 0 folding yields minor minor folds trending trending about about N53°E, N53 0 E,plunging plunging 200 20 (Grant, (Grant, 1972). 1972). In the Granite area the orientations Granite Falls Falls area orientations of the the minor minor folds folds vary vary with with their their location location on on the Granite ). On the north of the antiform Granite Falls Falls antiform antiform (FJ). north limb of antiform the the folds folds have have an average average orientation orientation of of N6°E, N60 0 E, plunging plunging 30°. 30 0 • The The axial axial planes planes of of these these folds folds is very very close close to the generally with aa moderate moderate to steep generally trend NE-SW NE-SW with steep SE SE dip. dip. This This is the orientation ofof the the south orientation south limb limb of of the the Granite Granite Falls Falls antiform antiform and and the the foliation foliation near coincidence results in aa orientation orientation in the the outcrops outcrops near nearMontevideo. Montevideo. This This near coincidence results large variation in the F. to variation in F 3 fold fold axis axis orientations orientations in in these these areas, areas, ranging ranging from from NE NE to axial plane foliation defined by flattened quartz lenses is SE to SW-plunging. An SE SW -plunging. An 53 plane foliation defined by quartz lenses is locally well well developed developedon onthe the south southlimb limbofofthe theGranite GraniteFalls Fallsantiform. antiform. L. locally L 3 quartz quartz lineations defined by by the the intersection lineations defined intersection of of SS(compositional <Compositional banding) banding) and ana S3 S3 are are common in this this area, and show the the same same rangg range in in orientation orientation as as the F3 common in and show F 3 fold axes. A fourth generation A fourth generation of of minor minor folds, folds, (F4) (F4) is is common common only only in in the outcrops outcrops near near Montevideo. F, Montevideo. F 4..axial axialplanes planesgenerally generallytrend trendNW-SE NW -SE and and are are moderately moderatelyinclined0to inclined to 0 the northeast. northeast. The 1 heF4 F 4fold fold axes axes in in this this area areahave havean anaverage averageorientation orientation of of S80 S80 E, E, 4Q0 and generally occur as open warps of the gneissic banding with amplitudes 40° and generally occur open warps of the gneissic banding with amplitudes ranging from from 20-50 20-50cm. cm. A folds on onthe the north north limb limb of of the Granite ranging A few few NW-trending NW-trending folds Granite Falls antiform antiform have have orientations orientations which whichare are consistent consistent with with that that expected Falls expected of of F4 F 4folds superimposed superimposedon onthis this limb. limb. Unlike area, these folds Unlike the F4 F lJ. folds in in the the Montevideo Montevideo area, folds folds are concentric, concentric, parallel parallel folds folds with with wavelengths wavelengths ranging ranging from from 1-5 1-5 meters. meters. Both FF4 fold types types occur occur in in granitic granitic gneiss suggesting aa distinct distinct difference in the Both 4. fold gneiss suggesting the mechanical properties properties of of the the gneiss at the time of mechan'lcal gneiss at of folding. folding. A similar difference properties of of the A similar difference in in mechanical mechanical properties the gneiss gneiss is is suggested suggested by by the difference the difference in in the the character characterofofnarrow narrowNW NW and andNE-trending NE-trending shear shear zones zones which which The shear occur in both occur both the the Granite Granite Falls Fallsand andMontevideo Montevideo areas. areas. The shear zones zones near near Similarly oriented Granite Granite Falls Falls are mylanitic mylanitic and and have have aa cataclastic cataclastic microfabric. microfabric. Similarly zones in the the Montevideo area are are generally diktyonitic structures structures rather than zones in Montevideo area generally diktyonitic than shear shear zones, commonly commonlycontaining containingremobilized remobilizedgranitic graniticmaterial materialwithout without aa cataclastic zones, microfabric. REFERENCES REFERENC ES CITED CITED Grant, J.A., Grant, J.A., 1972, 1972, Minnesota Minnesota River River Valley, Valley, southwestern southwestern Minnesota, Minnesota, in Sims, Sims, P.K. P.K. and Morey, and Morey, G.B., G.B., eds., Geology Geology of Minnesota: A centennial volume; volume; Minnesota Minnesota Geol. Survey, Survey, p. 177-196. Geo!. 177-196. F-Iirnmelberg,G.R., G.R.,1968, 1968,Geology GeologyofofPrecambrian Precambrian rocks, rocks, Granite Granite Falls-Montevideo Himmelberg, Falls-Montevideo area, southwestern southwestern Minnesota; Minnesota; Minnesota Minnesota Geol. Geo!. Survey Survey Spec. Spec. Pub. Pub. Ser. 5, 33 33 p. 7 �I A A REAPPRAISAL REAPPRAISAL OF OF THE THE WESTERN WESTERN PORTION PORTION OF OF THE THE ENGLISH ENGLISH RIVER SUBPROVINCE, SUBPROVINCE, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO AND SOUTHEASTERN SOUTHEASTERN MANITOBA MANITOBA Department of Beakhouse, Centre Centre for Precambrian Precambrian Studies, Studies, Department of Earth Earth Sciences, Sciences, G.P. Beakhouse, University of of Manitoba, Manitoba, Winnipeg, Winnipeg, Manitoba, Canada. ABSTRACT ABSTRACT The River subprovince has been been considered consideredtoto be be a high The English English River subprovince has high grade, grade, Archean metasedimentary basin flanked by typical greenstone-granite terranes. Archean metasedimentary basin flanked by typical greenstone-granite Recent investigations, suggest that this investigations, however, however, suggest this is is an an oversimplification oversimplification and and that divisible into two units; a northern, the English English River River subprovince subprovince is is divisible into two units; a northern, largely largely sedimentary, gneiss belt) belt) and sedimentary, unit unit (Ear (Ear Falls-Manigotagan Falls-Manigotagan gneiss and aa southern, southern, mainly mainly plutonic unit River batholithic batholithic belt). unit (Winnipeg (Winnipeg River The gneiss belt belt comprises The Ear Ear Falls-Manigotagan Falls-Manigotagan gneiss comprises aa high high grade grade metagraymetagrayThe wacke-metasiltstone sequence intruded wacke-metasiltstone sequence intruded by by subordinate subordinate felsic plutons. distribution primary sedimentary sedimentary structures imply distribution of lithologies and and recognizable recognizable primary imply a major sedimentary basin basin with with sediment sediment deposited below wave wave base base from major sedimentary deposited below from turbidity turbidity sedimentationis, is, at at least least in part, flows. This This sedimentation part, aa distal distal facies facies of of volcanism volcanism in in the the Red subprovince to to the north. Red Lake Lake subprovince In contrast, the River batholithic batholithic belt belt is In the Winnipeg Winnipeg River is largely largely aa felsic felsic plutonic plutonic terrane comprising two major major suites; suites; an an earlier, massive comprising two massive to weakly weakly gneissic, gneissic, prepreand syn-tectonic trondhjemite-granodiorite-quartz diorite suite and a later, massive, post-tectonic granodiorite-quartz A complex massive, post-tectonic granodiorite-quartz monzonite-granite monzonite-granite suite. A complex assemblage of well assemblage of well layered, layered, felsic felsic orthogneisses orthogneisses with with subordinate subordinate interlayered interlayered remnants of recognizable metavolcanic and and metasedimentary metasedimentary rocks remnants of recognizable metavolcanic rocks occurs occurs on the the The southern southern flank flank of of this plutonic plutonic terrane. terrane. The origin origin of of the theWinnipeg Winnipeg River River are currently batholithic belt belt is problematic, problematic, and and several several possibilities are currently being being batholithic evaluated, includingthe the possibility possibilitythat thatthe the belt belt could evaluated, including could represent represent aa reactivated reactivated ancient crustal remnant. Regional geophysicalanomalies anomaliessupport support the the two-fold of the Regional geophysical two-fold subdivision subdivision of the gneissbelt belthas has aa thicker English subprovince. The The Ear Falls—Manigotagan Falls-Manigotagan gneiss thicker English River River subprovince. granitic crust, than the granitic crust, thinner thinner total curst, curst, and and higher higher Bouguer Bouguer gravity gravity values values than Aerornagnetic patterns also also are Winnipeg River batholitic Winnipeg River batholitic belt. Aeromagnetic patterns are disintincly disintincly different in In the two belts. 8 I �I TRACE AEAN GRANITOID TRACE ELEMENTS ELEMENTS IN IN THE THE ARCH ARCHAEAN GRANITOID DIAPIRS DIAPIRS PIERCING PIERCING THE THE WABIGOON WABIGOON GREENSTONE BELT BELT Dieter Dieter Birk, Birk, Department DepartmentofofGeology, Geology,McMaster McMaster University, University, Hamilton, Hamilton, Ontario OntarioL8S L8S 4Ml 4M1 ABSTRACT ABSTRACT Major and trace element element analyses analyses are are reported reported for for twelve twelve synkinematic synkinematic to to Major and late-kinematic granitoid granitoid diapirs diapirs intruding intruding Keewatin Keewatin greenstones greenstones of of the theWabigoon Wabigoon are included Greenstone Belt Belt of of northwestern northwestern Ontario. Ontario. Analyses Analyses are included of of associated associated Greenstone enclaves and aplitic dikes to evaluate the role of endomorphism and late diking. aplltic dikes to evaluate the role of endomorphism and late diking. Despite Despite a common common tectonic setting, setting, these thesediapirs diapirsrange rangefrom fromhomogeneous homogeneous granodiorites to concentrically zoned granodiorites to zoned plutons plutons or or complexes complexes of of granite-monzodiogranite-monzodiorite. The Therange rangeofofelement elementconcentraitons concentraitons(4.3>Na/K>O.9) (4.3>Na/K>O.9) is not compatible with a "late K K granite" granite" classification classification as required required by by current Archaean Archaean models models of secular secular of trace granitoid chemistry. chemistry. Each Each pluton pluton carries carries a distinctive distinctive "fingerprint" "fingerprint" of trace granitoid element abundances, but as a group abundances, but group these granitoids granitoids carry carry high high Sr Sr and and Ba, Ba, and and low low Th, and and U. U. Rb/Sr, Th, The The lensoid lensoid mafic mafic enclaves, enclaves, ubiquitous ubiquitous in these these plutons, plutons, have have undergone undergone basification and/or alkali alkali rnetasomatism, resulting in in trace element basification and/or metasomatism, resulting element abundances abundances markedly different different from from either their markedly their granitoid granitoid hosts hosts or orsuggested suggested metavolcanic metavolcanic sources. Strong Strong enrichment enrichment in in Rb, Rb, Ce and and Th Th can be be demonstrated, demonstrated, whereas whereas Sr Sr and and Although aa reciprocal reciprocal reaction process Ba values more erratic. Although process is is envisioned envisioned Ba values are are more between enclave enclaveand andhost, host,there there isis little little evidence of large scale between evidence of scale contamination contamination of Homogeneousgranodiorite granodioriteplutons plutons(such (suchasas the the Burditt the host plutons. plutons. Homogeneous Burditt Lake Lake the host Stock, Scattergood Stock) show heterogeneous heterogeneous enclave enclave distribution distribution without without noticeStock, Scattergood Stock) show able modal mineral or chemical effect. able modal mineral or chemical effect. Aplitic patches and and dikes show trace trace element of late Aplltic patches dikes show element contents contents typical typical of late core-to-rim zoning. differentiates complicated complicated by by strong strong core-to-rim zoning. Aplite Aplite apophyses apophyses cutting metavolcanic rocks rocks differ differ little little from metavolcanic from the intraplutonic aplites. 99 �THE BEHAVIOR BEHAVIOROF OF PRECIOUS PRECIOUS METALS METALS AND AND OTHER OTHER TRACE TRACE ELEMENTS THE ELEMENTS DURING THE THE FRACTIONAL FRACTIONAL CRYSTALLIZATION CRYSTALLIZATION OF OF DULUTH COMPLEX SULFIDES DURING Bill Bonnichsen, Bonnichsen,Department Department of of Geol. Bill Geo!. Sciences, Sciences, Cornell Cornell Univ., Univ., Ithaca, N.Y. N.Y. 14853 14853 and Robert I. and 1. Botto, Botto, Exxon Exxon Corp., Corp., Box Box 4255, Baytown, Texas 77520 77520 ABSTRACT In the Duluth the sulfide can be be described Duluth Complex, Complex, the sulfide mineral assemblages assemblages can described in In terms of the terms the high high temperature temperature phases phases that that crystallized crystallized from from sulfide sulfide melts. melts. The (1)(1)MSS three principal principal phases phases that thatformed formedfrom fromsuch suchmelts meltsare are MSS(monosulfide (monosulfide solid solid solution) which which cooled cooled to to pyrrhotite solution) pyrrhotite with with exsolved exsolved chalcopyrite-cubanite chalcopyrite-cubanite and and pentlandite, (2) ISS ISS (intermediate solid solution) solution) which pentlandite, (2) (intermediate solid which cooled cooled to to chalcopyrite chalcopyrite and cubanite (commonly in exsolution cubanite (commonly in exsolution intergrowths), intergrowths), and and (3) (3) BSS BSS (bornite-chalcocite (bornite-chalcocite solid solution), solution), which whichcooled cooledtotobornite-chalcopyrite bornite-chalcopyrite intergrowths. solid For normal For normal Fe-rich sulfide melts, melts, the the early early crystallization crystallizationofofMSS MSS leads to Cu Cu field enrichment in the the liquid. liquid. On Onthe theCu-Fe-S Cu-Fe-Ssystem systemliquidus liquidus surface surfacethe theMSS-ISS MSS-ISS field boundary not aa cotectic, but boundary isis not but isis aareaction reactionboundary, boundary, with with the the ISS ISS field on on the low temperature side. temperature side. Thus, continued crystallization crystallization of MSS MSS will will enrich enrich the the Thus, the the continued residual melt melt in Cu residual Cu until until its its composition composition migrates migrates into into the the ISS ISS field, field, causing causing the cessation of MSS andstart start of of ISS crystallization. The has aa lower lower CufFe Cu/Fe ratio ratio cessation MSS and ISS crystallization. The ISS ISS has than the melt melt so so that thatits itsremoval removalwill willcause causefurther furtherCu Cuenrichment, enrichment,which which can can lead lead to liquid compositions compositions reaching reaching the theISS-BSS ISS-BSS field boundary. boundary. In In the the Duluth Duluth Complex, Complex, the thesulfide—rich sulfide-rich basal segregations segregations crystallized crystallized as MSS, whereas MSS-ISS mixtures. MSS, whereas the the disseminated disseminated sulfides suifides crystallized crystallized as MSS-ISS mixtures. The Curich epigenetic sulfides which which percolated percolated into the footwall footwall and and inclusions, crystallized mainly and BSS. BSS. Fractional crystallization of mainly as ISS ISS and of sulfide sulfide liquids, liquids, as outlined above, is is one that may outlined above, one of several mechanisms mechanisms that may account for the the wide wide range range that characterize of compositions compositions that characterize the theDuluth Duluth Complex Complex sulfides. sulfides. Such Such a process process seems particularly applicable seems applicable to the Cu-enriched Cu-enriched epigenetic occurrences. Six samples, chosen chosen to to encompass the observed Six Duluth Duluth Complex Complex samples, encompass the observed range range of Cu/Fe CufFe ratios, were were analyzed analyzed by by neutron neutron activation, activation, spark-source spark-source mass mass spectrospectrometry, to further metry, and and atomic atomic absorption absorption to further examine examine the the fractional fractional crystallization crystallization process. The for fractional The results resultsare areininvery verygood good agreement agreement with with our predictions for crystallization During crystalliza tion trends. During sulfide sulfide crystallization, crystallization, Ni, Ni, Co, Co, and and Mo Mo were were incorporated into MSS MSS along whereas Ag, Ag, Au, Rh, Ir, Ir, selectively incorporated along with with Fe, Fe, whereas Au, Pd, Pd, Pt, Rh, Zn, Zn, Cd, Pb, TI, Se, Te, Te, Sb, Sb, Bi, Bi, W, W, and Sn were enriched enriched in in the theliquid liquid along along with with Cu, CU, to eventually in the eventually become become incorporated incorporated in the Cu Cu minerals. minerals. Our investigation investigation of of Our element indicates preferences preferences for for octahedral lattice element behavior behavior indicates lattice sites sitesininMSS, MSS, verses tetrahedral tetrahedral sites sitesininISS, ISS, which which largely largely governs governs element elementdistributions distributionsduring during sulfide sulfide liquid crystallization. crystallization. 10 10 �STRATIGRAPHIC VARIATION IN MINERALOGY MINERALOGY AND AND ENGINEERING ENGINEERING CHARACTERISTICS CHARACTERISTICS STRATIGRAPHIC VARIATION IN CLAY NEAR OF ONTONAGON ONTONAGON CLAY NEAR A MAJOR SLOPE FAILURE, FAILURE, ONTONAGON ONTONAGON COUNTY, COUNTY, MICHIGAN MICHIGAN Emmy Booy Booy and and Stanley Stanley J. Dyl, II, Department Geology and and Geological Geological Emmy Department of Geology Engineering, Michigan Engineering, Michigan Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT 45 for for approximately one mile mile north north and and south south of of the East U.S. 45 approximately one East Branch Branch of the OntonagonRiver River on on the Keweenaw Keweenaw Peninsula Peninsula of Michigan Michigan is is plagued plagued by by slope slope Ontonagon failures of of varying types and and sizes sizes along the road road cuts. cuts. The particular failures varying types along the The area area of particular interest for this the largest largest slide whichlies lies to to the the north interest this discussion discussion isis the slide which north of the East East Branchalmost almostatat the the crest crest of the Branch the hill. hill. The is one one in in which which the river river has has The area area is incised a valley about 200 feet feet deep deep into into aaflat flatglacio-lacustrine glacio-lacustrinedeposit depositofofthinly— thinlyincised about 200 layered red clays and silts. The particular is approximately The particUlar slide slide under under discussion discussion is approximately 700 700 feet long long and and 400 400 feet high. high. ItItisisimmediately immediatelyadjacent adjacenttotoHighway Highway 45 45 and and causes causes annual annual disruption disruption of the drainage the drainage on on the west west side side of of the theroadway. roadway. Both Bothmud mudflows flows and and block block gliding gliding contribute at various and in in different different areas to the slope various times and slope recession. recession. contribute Material of of the the slope was studied studiedatat 11 meter meter vertical intervals in the the as-yet intervals in Material slope was unfailed zones zones north north and and south south of of the the failed failed area area in in order order to to ascertain variability of unfailed the clay-silts of the clay—size fraction, Atterberg Atterberg Limits, the clay-silts in situ. situ. Mineralogy Mineralogy of clay-size fraction, Limits, shear strengths were determined. particle-size distribution, and vane vane shear The material, previously studied regional scale, scale, ranges ranges The material, like that previously studied on on a regional throughout the clay throughout clay and and clay-silt clay-siltregions regionsof ofthe theCorps CorpsofofEngineers Engineersand andU.S. U.S. Bureau Bureau of Soils Soils classifications. In In general, sand content isis less less than than5% 5%although although in in some some layers this is not true. The the layers, layers, in of the The mineralogy mineralogy ofof the in agreement agreement with with the the variability variability of the particle sizes, layer to layer. particle sizes, varies varies from from layer layer. However, However, itit may may be be accurate accurate to to state that the rock flour includes quartz and the rock flour includes considerable considerable quartz and feldspar feldspar in in the the clay-size clay-size fractions as as well fractions well as the the clay clay minerals minerals kaolinite, kaolinite, iiite, illite, and and mixed-layer mixed-layer material material which appears appears to to be be dominantly dominantly smectite. smectite. which Plastic limits limits vary vary in in the the general general range range of of24-30 24-30 and and liquid liquid limits limits vary vary from from 35 to 70 in particle size and clay mineral mineral content. content. The 35 to 70 reflecting variation variation in and clay The natural moisture content content of the moisture the material material generally generally approach approach the the plastic plastic limits limitsalthough although in in certain cases it is is higher higher than the plastic plastic limit. limit. This This moisture moisture content content increases increases in general the base general towards towards the base of the the hill, hill, but but not not atataauniform uniform rate. rate.Anomalously Anomalouslyhigh high values occur occur part way up higher clay content. values up the hill in zones of higher Shear strengths strengths are are extremely extremely variable, variable, generally generally in in the the4—25 4-25 tons/sq. tons/sq. ft. Shear region. This variability occurs occurs not only on up the the slope, slope, but region. This not only on aa scale scale of of tens tens of feet up within hole at vertical distances of of inches. inches. The vertical and and horizontal horizontal distances The variation variation within aa single single hole within hole may may be be as as much much as as 10 10 tons/sq. tons/sq. ft. ft. within a hole 11 11 U �SECONDARY MINERAL GROWTH OF OF THE WHITE SECONDARY MINERAL GROWTH WHITE PINE SHALE COMPARED COMP ARED WITH WITH CLASSIC "HEAVING" "HEAVING" SHALES SHALES Emmy Booy, Booy, Department Geology and Emmy Department of of Geology and Geological Geological Engineering, Michigan Technological Co., Technological University, University, Houghton, Houghton, MI, MI, 49931 49931and andRobert Robert D. D. Harris, Harris, Gillette Co., South Boston, MA. MA. ABSTRACT Workersinin the the eastern United Workers United States States and and Canada Canada have have observed observed secondary secondary mineral growth, particularly particularly gypsum gypsumand andaa variety variety of iron mineral growth, iron sulfates sulfates which which have have caused "heaving" of shales caused "heaving" of shales under under buildings. buildings. Because Because of of conditions conditions of similarities of (i.e. high oxygen (i.e. high oxygen contents contents and and presence presence of of moisture) moisture) between betweenshales shalesat at the the surface of the of the earth earth and and along along the the surfaces surfacesofofmine mineopenings, openings, the the possibility possibility that similar similar phenomena might might be the White phenomena be taking place in the White Pine Pine Mine, Mine, Michigan Michigan was was investigated. shales near In occurrences in shales near Ottawa, Ottawa, Ontario, Cleveland, Ohio, and Pittsburgh, substantial (up Pittsburgh, Pennsylvania, Pennsylvania, substantial (up to several several inches) inches) vertical verticalexpansion expansion has has taken place taken place in shales shales which which contain contain some some pyrite pyrite and and calcite. calcite. It has been been It has hypothesizedthat that the the reactions take place place in in the the shales hypothesized reactions which which take shales are catalyzed catalyzed by by oxidizing bacteria. oxidizing These would include include Thiobacillus Thiobacillus ferroxidans ferroxidans and and These bacteria would Ferrobacillus ferrooxidans. Repeated Repeated efforts to to grow grow such such bacteria in in cultures cultures of of Ferrobacillus ferrooxidans. proven unsuccessful. unsuccessful. Therefore, Therefore, a bacterial the White White Pine Pine Shale Shale have have proven bacterial mechanism mechanism growth on on White White Pine Pine shales shales has has been ruled out. for gypsum gypsum growth Samples ranging in in time of exposure exposure to the the mine mine atmosphere atmosphere from from 11 day day to to 10 10 Samples ranging years were years were collected collected from from the the mine mine roof roof — - most samples were from the the Brown Brown samples were Massive but several several were Massive but were from from the the Dark DarkGray GrayMassive. Massive. These contain These strata contain scattered nodules source for for Ca Ca in in the expected nodules of calcite calcite which which provide provide a logical logical source reactions. Microscopic 0.2 and and 0.4 0.4 Microscopicexamination examinationsuggests suggeststhe the presence presence of of between 0.2 percent pyrite coincideswith withdata data for for sulfur of the material. percent pyrite which which coincides sulfur analyses analyses of material. Therefore, the basic for the generation of gypsum are present. Therefore, basic chemicals needed needed for gypsum are Soluble sulfates in in the samples Soluble sulfates samples were were on the order order of of magnitude magnitude of of 10 10 ppm ppm or less. However, careful examination examination of of samples samples exposed exposed to to the mine However, careful mine atmosphere atmosphere showed some gypsum on surfaces of the the samples. samples. However, showed some growth growth of of gypsum on the the surfaces distribution throughoutthe the samples samplesstudied. studied. The The absence absence of of aa linear distribution was was random random throughout relationship between between time time of of exposure to the relationship exposure to the mine mine atmosphere atmosphere and and quantity quantity of of gypsum present isis attributed attributed to the gypsum present the anisotropic anisotropic distribution distribution of parent materials materials in in the mine. mine. Subsequently, Subsequently, similar similar gypsum gypsumgrowth growth was was observed observedon on the the surfaces of polished thin sections sections made made of of the the interior of the rock. polished thin rock. It has of the strata has been been concluded concluded that that possible possible weakening weakening of strataby byprogressive progressive growth does not not present present aa major growth of secondary secondary gypsum gypsum does major hazard at at the theWhite White Pine Pine Mine. However, some such such growth growthisis possible possibleand andisis concentrated concentrated at at the However, some the rock rock surfaces. Further, halite halite may may also also be be growing growing on on the the surfaces surfaces of of the theWhite White Pine Pine Shale. Shale. The The relatively relatively low low rate rateof ofgypsum gypsum growth growth in this this atmosphere atmosphere may may be due due to relatively high high pH pH (about (about 8) mine which which inhibits the relatively 8) in in the mine inhibits growth growth of of the the bacteria which elsewhere are are reported which elsewhere reported to catalyze catalyze the thechemical chemical reactions reactionsresponsible responsible for for shale deterioration. 12 12 �PETROLOGY AND AND FRACTURE FRACTURE CHARACTERISTICS OF THE PETROLOGY CHARACTERISTICS OF KINGSTON CONGLOMERATE, CONGLOMERATE, KEWEENAW KINGSTON KEWEENAW COUNTY, MICHIGAN MICHIGAN Charles Brumleve, of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Charles Brumleve, Department of Technological University, Houghton, Technological Houghton, Michigan Michigan 49931 49931 ABSTRACT The Kingston Kingston conglomerate conglomerate is is composed of subangular subangular to to subrounded subrounded clasts clasts of The composed of quartzy feldspar porphry. 60 quartzy porphry. These rhyolite gravels gravels make make up up approximately approximately 60 These red rhyolite percent of of the percent the total total rock. rock. The matrix is predominantly predominantly sand the same same The matrix sand of of the compositionasas the the clasts, of copper, composition clasts, with with secondary secondary mineralization mineralization of copper, hematite, hematite, calcite, and calcite, and chlorite, chlorite, in in order order of ofincreasing increasing abundance. abundance. The whole is is The unit unit as aa whole unsorted but is made up of bands bands or or lenses lenses of of poor poor to to well well sorted sorted clasts. up of unsorted The intensity intensity of of mineralization mineralization isis related related to the amount The amount of matrix matrix present present and and is an indication indication of the original original permeability permeability of the the rock. rock. The Thehanging hanging wall wall zone zone has has is the most the most matrix matrix and and received received the themost mostsecondary secondary mineralization mineralization whereas whereas the the has the the least matrix intermediate zone zone has matrix and the least mineralization. mineralization. Permeability tests tests using air demonstrated demonstrated the the tight cementation Permeability using compressed compressed air cementation of the rock. Conductivitytests tests were were used usedtoto determine determinethe the nature nature of of the the native of rock. Conductivity copper framework framework in elongate lenses parallel to copper to bedding. bedding. The The fracture characteristics characteristics of of the theconglomerate conglomerate are are controlled controlled by by the the degree degree of cementation cementation and and type type of of matrix matrix mineralization. mineralization. Silica cement produces produces a of Silica cement competent, nonfriable rock which tends to fracture competent, nonfriable rock which tends fracture transgranularly transgranularly across across clasts. clasts. Chlorite and in the matrix Chlorite and copper copper mineralization mineralization in matrix produces produces weak weak clast bonds. bonds. This This results results in failure failure by by intergranular intergranular fracturing fracturing of of matrix, matrix, clasts clasts and and native native copper copper masses. 13 13 �THE PETROLOGY AND STRUCTURAL RELATIONS RELATIONS OF THE LATER LATER PRECAMBRIAN PRECAMBRIAN BRULE LAKE INTRUSIONS, COOK COOK COUNTY, COUNTY, MINNESOTA MINNESOTA James R. R. Burnell, Burnell, Jr., Jr.,Department DepartmentofofGeology, Geology, University University of ofMinnesota, Minnesota, Duluth, Duluth, Duluth, Minnesota 55801 Minnesota 55801 ABSTRACT The splits into two tonguesatat its its eastern east-trending tongues eastern The Duluth Duluth Complex Complex splits two east—trending extent extent to to form form aanorthern northern and and a asouthern southernprong, prong, exposing exposing a strip strip of of older older Brule Keweenawan volcanic rocks rocks between between them. them. Brule Lake Lake is is located at the Keweenawan volcanic westernmost extent of of the strip westernmost extent strip of of volcanic volcanic rocks rocks just east east of of the the point point where where the the gabbro prongscoalesce. coalesce. The rocks are are intruded by aa series of large sillgabbro prongs The volcanic volcanic rocks intruded by like terminate against like bodies bodies which which terminate against rocks rocks of the the nearby nearby Duluth Duluth Complex. Complex. Thus, Thus, these intrusions, known informally as as the Brule Lake sills, sills, were were formed formed between the Brule Lake known informally time of of the theeruption eruptionofofthe thelocal localKeweenawan Keweenawanvolcanic volcanic rocks rocks and and the thesubsequent subsequent gabbroic intrusions. The the Brule Brule Lake Lake area, area, which which occur occur as as both both dikes dikes and and The intrusive intrusive rocks rocks of the non-porphyritic intrusions. intrusions. The sills, consist of porphyritic intrusions and subsidiary sUbsidiary non-porphyritic The porphyritic intrusionsform form the the most features at Brule most striking striking geologic geologic features Brule Lake. Lake. porphyritic intrusions These diabase porphyries are are approximately approximately 80 80 to to 300 300 meters meters thick and and extend for 22 diabase porphyries kilometers along along strike. strike. Most Most contain contain 50-60% 50-60% plagioclase plagioclase phenocrysts. phenocrysts. to 88 kilometers Mineralogy simple, consisting consisting of of plagioclase, plagioclase, augite, opaque opaque oxides oxides (magnetite Mineralogy isis simple, A typical mode and and ilmenite) ilmenite) with with minor minor quartz and and potash potash feldspar. feldspar. A mode includes includes plagioclase plagioclase 68%, 68%, augite augite (—uralite) (-uralite) 17%, 17%, opaque oxides oxides 9%, 9%, quartz quartz2%, 2%,K—feldspar K-feldspar chlorite-groundmass-epidote 3%. 1 %, chlorite-ground 1%, mass-epidote 3%. The units are are tabular tabular in in form The porphyry porphyry units form and and are tilted tilted totoform formsteep steepnorth-northfacing and more gradual south south slopes. slopes. Several sills are concordant facing slopes slopes and more gradual concordant with with the the trnd trendofofthe theintruded intrudedflows flows whereas whereas others others transect transect this this trend trend at at angles angles of of up up to to 0 30 • is dominated The texture texture of of the theporphyry porphyry units uni ts is dominated by by abundant abundant plagioclase plagioclase The Fine—grained groundmass groundmass phenocrysts textures poorly poorly developed. developed. Fine-grained phenocrysts with with subophitic subophitic textures occurs in the interstices of of the the plagioclase plagioclase laths, commonly commonly including including vermicular occurs in intergrowths of quarzt-plagioclase or quartz-potash feldspar. Small bodies bodies of of non-porphyritic diabase intrude intrude both both the volcanic Small non-porphyritic diabase volcanic rocks and the diabase intruded into into one diabase porphyries. porphyries. When When intruded one of the porphyritic porphyritic bodies, bodies, they are typically irregular in form thetrends trends of of the the larger larger intrusions. typically form and and cross—cut cross-cut the intrusions. When When intruded into into volcanic volcanic units, units, they they form form small small tabular tabular sills, sills, several several meters meters in intruded The mineralogy mineralogyofof these these smaller smaller intrusions intrusionsisis identical identical to to that that of the the thickness. The porphyries although, although, modally, modally, the the proportions porphyries proportions of plagioclase plagioclase are are less less (45-52%) (45-52%) and and of augite, more more (19-25%). (19-25%). Chemically the the Brule intrusions represent represent aa tholeiitic magma Chemically Brule Lake Lake intrusions magma saturated MgO is They are are characterized by with to silica. silica. They by values values of Si02 Si0 == 50%. MgO with respect respect to the2 non-porphyritic low, ranging ranging from from 2-3% 2-3% in in the low, the porphyry porphyry units, units, 5-6% 5-6% in in the non-porphyritic intrusions. Na20 NaZO isis particularly particularlyhigh high (>4% (> 4%in inthe theporphyries) porphyries) as as isis Ti02 TiO Z(2.25%). (2.25%). intrusions. Consideringthe the abundance abundance of of plagioclase phenocrysts inin the Brule Considering plagioclase phenocrysts Brule Lake Lake intrusions the bulk chemistry of of the intrusive intrusive melt melt closely closely approximates approximates the intrusions the bulk chemistry chemistry of several several Keweenawan Keweenawan basalts of of the the North NorthShore Shore Volcanic Volcanic Group. Group. 14 l~ �RESOURCES OF OF RECOVERABLE IRON ON THE MARQUETTE RESOURCES RECOVERABLE IRON MARQUETTE RANGE, MICHIGAN— MICHIGANESTIMATES BY BY A A MONTE MONTE CARLO SIMULATION MODEL ESTIMATES W.F. Cannon Cannonand andL.J. LJ. Drew, U.S. Geological Survey, Survey, National National Center, 12201 W.F. U.S. Geological 12201 Sunrise Sunrise Valley Drive, Drive, Reston, Virginia Valley Virginia 22092 22092 ABSTRACT The Negaunee Iron-formation, MarThe Negaunee Iron-formation,the the principal principal iron-bearing iron-bearingunit unitinin the the Marlong tons tons of material averaging quette Iron Range, contains about 205 205 billion billion long averaging about about 32 percent iron. About 49 49 billion billion tons tons are are within within 1,000 1,000 feet feet of the surface, 32 iron. About surface, which which we consider consider aa reasonable reasonable average depth for some present present we for open-pit open-pit mining, mining, although although some mines will probably be be deeper. mines will probably Three classes Three classes of iron-formation iron-formation are now now being being beneficiated beneficiated on on the the range. range. These are: These coarse-grained hematitic hematitic and 1) coarse-grained and magnetic magnetic iron-formation iron-formation beneficiated by by froth flotation, 2) magnetic iron-formation iron-formation beneficiated magnetically, and magnetic 3) fine-grained (less (less than than 0.05 0.05 mm) mm) nonmagnetic nonmagnetic iron-formation beneficifine-grained ated by selective flocculation and and flotation. We have have divided dividedthe the range range into into 1/4 square-mile We square-mile areas and and computed computed the the tonnage tonnage and characterized in each characterized the iron-formation iron-formation in each according according to its suitability for for and its suitability beneficiation by one one of these beneficiation by these processes, processes, using using a detailed detailed computerized computerized data bank bank developed by the the senior senior author. author. By By using using available available metallurgical data data and and by by means means developed by of by the the junior junior author, author, we we have have of aa Monte Monte Carlo Carlo simulation simulation model model designed designed by estimated the the total total amount amount of of metallic metallic iron iron recoverable recoverable from from the the Marquette Marquette range range by surface mining miningtoto 1,000 1,000feet. feet. The by each process, process, assuming assuming surface The model model considers considers the quality of concentrate, quality standards standards of of Fe Fe >60 percent quality of concentrate, using using quality percent and and Si09 SiO <10 < 10 percent; itit estimates estimatesthe theamount amountof ofiron-formation iron-formation that thatwill willmake makeconcentra4tes concentrates of this quality. empirical distribution distribution of of recoverable recoverable iron iron derived derived from from quality. From From the empirical many metallurgical tests, tests, the the total recoverable recoverable iron iron is is then then estimated. estimated. Figure 11 many metallurgical indicates that that ifif recoverable recoverable grades grades of of about about 20 20 percent percent Fe Fe are areeconomically economically indicates feasible, short tons 11 billion billion short tons of metallic metallic iron iron can can be be recovered recovered from from feasible, then then about about 11 iron-formation iron-formation that responds responds satisfactorily to to beneficiation beneficiation by by an an existing existing process. process. Most 7.2 billion billion tons-is tons—isininfine-grained fine-grained nonmagnetic nonmagnetic iron-formation. iron-formation. -about 7.2 Most of this this —about About tons is is in magnetic in About 3 billion billion tons magnetic iron-formation, iron-formation, and about 0.7 0.7 billion billion tons is in coarse-grained hematiticiron—formation. iron-formation. coarse-grained hematitic These These figures figures indicate indicate the the geologic geologic availability availability of of iron ironand andplace placemaximum maximum limits on on iron iron reserves reserves on on the the range range in in terms terms of ofcurrent currentmining mining and and beneficiating beneficiating technology. percentage of of this this iron iron that thatisisnow, now,or orever everwill willbe, be,economically economically technology. The The percentage available cannot cannot be estimated estimated without without much much more more detailed study. study. 15 15 �a "c0 30 ... ~0 7 S <II 6 C C ......~ 5 a 3 ::: 4 ~ a "a ".~S ~ 0 o 2 1 flocacion "0 <lJ '" 20 20 25 25 30 35 35 40 45 45 50 50 Recoverable (%) Recoverable Fe e (Z) Figure 1. — between estimated estimated tonnage - Relationship between tonnage of recoverable recoverable iron iron and and percentage of recoverable iron for three three beneficiating beneficiating processes. processes. 16 16 �ABUNDANCES OF RARE EARTH AND ABUNDANCES OF AND OTHER ELEMENTS ELEMENTS IN IN ARCHEAN GRANITIC AND AND GNEISSIC GNEISSIC ROCKS FROM FROM THE THE ENGLISH ENGLISH RIVER RIVER GNEISS GNEISS BELT, BELT, ONTARIO ONTARIO C.-L. Chou, Goodwin, Department Department of Chou, N.B.W. N.B.W. Harris, arid and A.M. A.M. Goodwin, of Geology Geology and and Erindale Erindale College, University of Toronto, Toronto, Canada Canada M5S M5S IAI. 1Al. ABSTRACT ABSTRACT The rocks in in the eastern The early early Precambrian Precambrian rocks eastern Lac Lac Seul Seul region region of of the the English English River River gneiss gneiss belt consist mainly mainly of tonalitic and and trondhjemitic trondhjemitic gneisses gneisses overlain overlain by by tonalitic migmatized migmatized metasedimentary rocks. rocks. Both Both are are intruded intruded by by granitic granitic plutons plutons and sills and and pegmatite pegmatite veins. veins. Smaller and sills Smaller bodies bodies of amphibolitic amphibolitic gneiss gneiss also are are found. found. Using neutron activation activation techniques techniques we have analyzed analyzed an amphibolitic amphibolitic gneiss, gneiss, two Using neutron tonalitic gneisses, gneisses, two granites, and and two pegmatites for for 24 24 elements elements (Na, (Na, K, K, Sc, Sc, Cr, Cr, Mn, Mn, Fe, Co, Ni, Ni, Zn, Zn, Rb, Rb, Zr, Zr, Sb, Sb, Ba, Ba, La, La, Ce, Ce,Nd, Nd, Sm, Sm, Eu, Eu, Tb, Tb, Yb, Vb, Lu, Lu, Hf, Hf, Ta Ta and and Th). Th). Scandium, Mn,and andCo Coare are positively positivelycorrelated correlatedwith with Fe, Fe, as as they they generally generally are are Scandium, Mn, concentrated in mafic minerals. The K/Rb ratios of three granitic rocks concentrated minerals. The K/Rb ratios of three granitic rocksare are290-. 290Slight variation Zr/Hf ratios ratios in in granitic granitic and and tonalitic tonalitic rocks rocks(32-28) (32-28) variation of of Zr/Hf 440. Slight contrasts contrasts with large variation variation of Hf Hi by by a factor of of 3. 3. AAfine-grained fine-grained amphibolitic amphibolitic gneiss has aa flat REE gneiss has REE pattern and and a total total REE REE content content of of 12X 12X chondritic chondritic abundance. abundance. It resembles basalts, suggesitng suggesitngthat that its its parent resembles Archean Archean basalts, parent is is basaltic, basaltic, formed formed by by partial melting old gray gray tonalitic gneiss melting of upper upper mantle mantle material. material.AA3.04—Gyr 3.04-Gyr old gneiss (74(74115) has aa smooth smooth and and steep-sloped steep-sloped REE REE pattern with with remarkable remarkable enrichment enrichment of of 115) has light REE REE and and depletion depletion of of heavy heavy REE REE (LaN (LaN == 71, and YbN Yb == 6.4). It has has a total total N REE and aa CeN/YbN REE content of about 2X 2X and CeN/Yb ratio ratio of of 0.5X 0.5X those those of of Saganaga Saganaga tonalites analyzed by Arth Arth and and Hanson Hanson(1975)'. (1975) ItIt i~isNlikely likely that that this tonalite analyzed by tonalite may may have have formed formed from from a granitic granitic melt melt which which has has been been significantly significantly contaminated by by mafic material. material. A secondtonalitic tonalitic gneiss gneiss (74-222B) (74-222B)has hasa atotal total REE REEcontent content 2X 2Xhigher higherthan than that that of A second 74-115 and and aa significant suggesting that that a plagioclase-rich 74-115 significant negative negative Eu Eu anomaly, anomaly, suggesting plagioclase-rich component was removed removedfrom fromthe themagna. magna. The REE patterns patterns of two component was The REE two granites granites have have very steep ratios are 160 steep slopes, slopes, their theirCeN/Yb..,J CeN/Yb N ratios 160 and and 85, 85, respectively, significantly higher than that of higher than of granitic granitic roèks roCks from from the the Vermilion Vermilion distirct. distirct. These These granites might have formed by by crustal crustal anatexis of might have formed of earlier earlier Archean Archean metasedimentary metasedimentary rocks. rocks. Two pegmatites show a strong positive Eu anomaly, but differ in total REE Two pegmatites show a strong positive Eu anomaly, but differ in REE and and other trace element contents reflecting that they are derived from different source element that they are derived from source materials. 17 �PALEOMAGNETISM PALEOMAGNETISM OF THE LATE LATE PRECAMBRIAN PRECAMBRIAN BRULE BRULE LAKE LAKE INTRUSIONS, INTRUSIONS, COOK COOK COUNTY COUNTY MINNESOTA MINNESOTA Donald M. Davidson, Davidson,Jr., Jr., Henry Henry Halls*, Halls*, and and James James R. R. Burnell, Jr., Department Donald M. Burnell, Jr., Department of of Geology, Geology, University University of Minnesota, Minnesota, Duluth, Duluth, *Department *Department of of Geophysics, Geophysics, University University of Toronto Toronto of ABSTRACT ABSTRACT Paleomagnetic involving ac ac demagnetization demagnetization up up to to 40 Paleomagnetic analysis, analysis, involving 40 oe, has has been been carried carried out out on onone onerhyolite rhyoliteflow flow(Keweenawan) (Keweenawan) and and two two porphyritic porphyritic intrusions intrusions which which flows in in the the Brule Brule Lake Lake area. area. These These flows flows and and intrusions intrusions are truncated truncated by by cut flows the Duluth Duluth Complex. Complex. of the various units of The The Brule Brule Lake Lake intrusive units units give indications of of primary reverse magnetizamagnetization which which has has been been altered by by normal normal intrusive intrusive activity, activity, probably probably associated associated with emplacement of of the theDuluth DuluthComplex. Complex. The Thenorthern northernintrusion intrusion(Fishbox (FishboxIsland) Island) shows shows a hard is closer closer to a reversed primary component component which which is reversed than than normal normal direction. The The hard primary southern intrusion (Jock (Jock Mock Mock Point) Point) exhibits exhibitsstable stable end end points points but but with with aa two southern intrusion two component responsewhich whichininatatleast least one one sample sampleindicates indicatesaa soft, soft, reversed reversed state. state. component response The rhyolite The rhyolite flow flow exhibits exhibits aa mixed mixed magnetic magnetic response response with with aa harder harder normal normal reversed components. components. and soft reversed Mean site determinations and paleo paleo pole pole positions positionsfor for these these sites sites are given Mean site determinations and given below: Paleo Pole Position Mean Mean Site 0 Intrusive- u No. No. Intrusive-u Intrusive-c No. No. Intrusive-c 139° 139 0 120 120° So. Intrusive-u Intrusive-c So. Intrusive-c So. 316 0 317 317° Rhyoli te Flow-u Rhyolite Rhyoli te Flow-c Rhyolite N N K <95 0<95 12 0 22° 22 3 3 3 35 35 35 4800 3 3 31 31 II D D 00 0 307.5 307.5°c 0 299 Lat. Long. 21 31 34.04N 145.41E 23 23 45.70N 173.35E 173.35E _66 -66°0 _75 -75°0 0 48 55 uu - uncorrected cc - corrected structurally Thus itit appears appears that that the southern Thus southern most most intrusion intrusion and adjacent flow flow unit more more Although the the clearly show show the the effects of clearly of remagnetization remagnetization than than the the northern northern sill. sill. Although results are consistent results consistent with with available available data data on on both both normal normal and and reversely reversely magnetized magnetized rocks of age, positive positive correlation between rocks of Keweenawan Keweenawan age, between the the Brule Brule Lake Lake intrusions intrusions and Logan sills and the the Logan sills does does not not appear appear feasible. feasible. 18 18 �STRUCTURAL AND AGE RELATIONSHIPS AT THE THE LAC LAC LA BELLE STRUCTURAL AND AGE RELATIONSHIPS AT MAGNETIC ANOMALY, COUNTY, MICHIGAN KEWEENAW COUNTY, MICHIGAN MAGNETIC ANOMALY, KEWEENAW James M. M. DeGraff, Department DepartmentofofGeology Geologyand andGeophysics, Geophysics, Michigan Michigan Technological Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT Along the Keweenaw Peninsulaof of Michigan Michiganthe thecontact contact between between the the Portage Keweenaw Peninsula Lake Lake Lava Lava Series and the Jacobsville Jacobsville Sandstone Sandstone has generally been considered considered to be thrust fault. fault.This ThisKeweenaw KeweenawFault Faultdescribes describesaasite sitealong alongwhich which the theMiddle Middle a great thrust KeweenawanPLLS PLLSononthe the north north has has been been thrust thrust southward southward over over the the Lower Lower Keweenawan Cambrian(?) Jacobsville Sandstone, Sandstone,with withaa possible possible vertical vertical throw throw of 10,000 10,000 feet feet Cambrian(?) Jacobsville (Bacon, 1966). 1966). Aeromagnetic maps (Bacon, maps for this this region region compiled compiled by by Baisley Balsley et et al al in in 1963 1963 delineate this regional well. However, However, an an earlier earlier map map comiTed compiled from from delineate regional contact quite well. the same data by shows that that a prominent magnetic anomaly exists along by L.O. L.O. Bacon Bacon shows this contact This anomaly anomalytakes takes the the form form of of a contact near near the site site of of Lac Lac La La Belle. Belle. This this magnetic "high" which which projects projects southward southwardfrom from the the nearly nearly east-west magnetic magnetic magnetic "high" lineations of of the PLLS by lineations PLLS into into aa region region of oflow lowmagnetic magnetic gradients gradients underlain underlain by Jacobsville Sandstone. Sandstone. Diamond has shown shown that that this Lac Jacobsville Diamond drilling and and field mapping mapping has Lac associated with with aa lobe La lava flows flows La Belle Belle magnetic magnetic anomaly anomaly is is associated lobe of of basaltic basaltic lava southward from from the PLLS into the Jacobsville Sandstone. PLLS into extending southward this project The purpose project was was to to investigate investigate the the structural structural and and age age The purpose of of this relationships of of the the PLLS, Jacobsville Sandstone Sandstoneand andbasalts basaltswithin withinthe thearea area of of the relationships PLLS, Jacobsville In order Lac Lac La La Belle Belle magnetic magnetic anomaly. anomaly. In order to accomplish accomplish this, the the following following four four field methods methods were were used: used: (1) ground magnetic magnetic work over the Lac La Belle magnetic anomaly, ground work over anomaly, (2) palaeomagnetic palaeomagnetic studies of basalts basalts in in the theanomalous anomalous zone zone in incomparison comparison with basalts of the PLLS immediately to to the north, PLLS immediately (3) geologic mapping mapping and and diamond diamonddrill drill hole hole correlations, correlations, and geologic (4) two regional PLLS—Jacobsville regional gravity gravity traverses traversesacross acrossthethe PLLS-Jacobsville Sandstone Sandstone contact, one contact, one on on either either side side of of the the Lac Lac La La Belle Belle magnetic magnetic anomaly. anomaly. Some conclusions conclusionswhich whichcan canbebedrawn drawnatatthe thepresent present time time are that: Some that: 1) 1) the flows rotated up up to to 45 flows within within the the anomalous anomalous zone zone have have b0een been rotated 45 degrees 0 counter-clockwise with with respect respect to to the N.70 N.70 E. E. strike of of the the PLLS PLLS to the counter-clockwise north, (2) faulting on both east and and west west sides sides of of the theanomaly anomaly has has been been very very faulting on both the east important in controlling the emplacement and rotation of of the the anomalous anomalous lavas, (3) the basalts associated associated with with the the anomaly are the the eastern eastern the exposed exposed basalts anomaly are extension of a larger larger block block of oflavas lavaswhich whichhas hasbeen beendowndropped downdropped on on the the west and and covered by Jacobsville Sandstone, (4) lavas in the lavas the lower lower section section of of the thePLLS PLLS and and within within the the anomalous anomalous zone zone 19 I �are not not reversely reversely magnetized, magnetized, and and therefore correlate correlate with with the theMiddle Middle Keweenawan rocks of of the Lake Keweenawan rocks Lake Superior Superior basin, basin, and and (5) in in this this area area the theevidence evidencepoints points totothe theJacobsville JacobsvilleSandstone Sandstone being being younger than the PLLS. PLLS. younger REFERENCES CITED CITED Bacon, L.O., 1966, 1966, Geologic Geologicstructure structure east and Bacon, L.O., and south of the the Keweenaw Keweenaw fault on on the basis of geophysical basis geophysical evidence, in The The Earth Beneath the Continents-A Continents-A Volume Volume of Geophysical Studies in in Honor A. Tuve: Tuve: Am. Am. Geophys. Geophys. Union of Geophysical Studies Honor of Merle Merle A. Geophys. Mono. 10, p. 42-55. Geophys. Mono. 10, 20 �LEAD ISOTOPE ISOTOPE INVESTIGATIONS INVESTIGATIONS IN IN THE MINNESOTA MINNESOT A RIVER RIVER VALLEY VALLEY B.R. and M.H. Delevaux, U.S. Geological Survey, Survey, Denver, Colorado 80225 B.R. Doe, Doe, and M.H. Delevaux, U.S. Geological ABSTRACT The isotopic systems systems have have been been investigated investigated for for whole-rock whole-rock and and The U-Th-Pb U- Th-Pb isotopic feldspar of the foliated feldspar samples samples of foliated and and also also more more massive massive phases phases of of the theMontevideo Montevideo Gneiss of Lund (1956),the the Sacred Sacred Heart Heart Granite, Granite, and Gneiss of Lund (1956), and the adamellite adamellite of of Section Section 28 28 near near Granite Granite Falls. Falls. We We have have not been been able able to to resolve resolve events events which which affected affected the the that time Montevideo Gneissprior prior to to 3.0 Montevideo Gneiss 3.0 b.y. ago. ago. At approximately approximately that time a thermal thermal event event reset reset the the U-Th-Pb U-Th-Pb system system in the the older, older, dark-colored dark-colored foliated foliated phase. phase. This event may by or or resulted resulted from from the introduciton of granitic may have been been accompanied accompanied by magma which formed the massive phase of of the gneiss. which formed gneiss. The age of Scared Heart Granite Granite has has aamicrolirie-whole-rock microline-whole-rock isochron isochron age of 2590 2590 The Scared m.y. The age is is in The feldspar feldspar isochron isochron model-lead model-lead age in excellent agreement at at 2560 2560 m.y., m.y., whereas the Pb-208/Pb204 age is is somewhat m.y. The Pb-208/Pb204 model model age somewhat younger younger at 2300 2300 m.y. The cause cause for this variation is not not understood understood at present. The adamellite of Section The epizonal epizonal adamellite Section 28 28 has has aa feldspar-whole-rock feldspar-whole-rock isochron isochron of of approximately 1850m.y., m.y.,determined determined by byan anacid-leach acid-leach method. method. The approximately 1850 The modellead modellead age is 2200 age is 2200 m.y., m.y., but the the Pb-208/Pb-204 Pb-208/Pb-204 model model age is in excellent agreement with with the the acid-leach, isochronatat 1850 1850m.y. m.y. The acid-leach, feldspar-whole-rock feldspar-whole-rock isochron The anomaly anomaly of about about 350 350 m.y. m.y. in the the model model ages ages isis similar similar to tothat thatfound foundininrejuvenated rejuvenatedcratons cratonswhere where Mesozoic and and Cenozoic Cenozoicigneous igneousrocks rockshave havepenetrated penetrated an 1800 Mesozoic 1800 m.y.-old basement. The m.y.-old adamellite adamellite of of Section Section 28 has penetrated penetrated an Archean The 1850 1850 m.y.-old 28 has Archean basement of 3800 m.y. m.y. in rocks ranging from 2600 rocks ranging from 2600 to 3800 in age. It is one one of the the few few Precambrian Precambrian examples displayingderivation derivationofof lead lead from from aa cratonzied examples displaying cratonzied continent and the the only only example as old old as as 1850 1850 m.y. 'V All rocks appear to have have lost about about half half of of their their uranium uranium fairly recently, recently, All the rocks but thorium thorium has hasbeen beenaffected affectedtoto aa lesser lesser degree. degree. These appear to be but These relationships relationships appear common in near-surface near-surface crystalline rocks and may may reflect reflect dilatancy. common in rocks and dilatancy. 21 �PRECAMBRIAN PRECAMBRIAN HISTORY HISTORY OF THE MORTON-NEW MORTON-NEW ULM ULM REACH OF THE MINNESOTA RIVER VALLEY THE MINNESOTA RIVER VALLEY S.S. Goldich, S.S. Goldich, 3.L. J.L. Wooden, Wooden, G.A. G.A. Arikenbauer, Ankenbauer, 3r., Jr., T.M. T.M. Levy, Levy, and and R.U. R.U. Suda, Suda, Northern Illinois illinois University, University, DeKaib, DeKalb, Illinois Illinois 60115 60115 ABSTRACT On the basis On the basis of current current research research on on the thePrecambrian Precambrian rocks rocks in inthe theMinnesota Minnesota River of events area is River Valley Valley aa tentative chronology chronology of events in the the Morton-New Morton-New Ulm Ulm area proposed. Time - M.Y. Time-M.Y. Event (?) Folding 1800 - 1200 (?) of the Sioux Deposition of Deposition Sioux Formation. Uplift and and erosion. 1900 - 1800 Emplacement of of diabasic diabasic dikes dikes and and small small granitic granitic plutons. Emplacement Thermal strong enough enough to to reset mineral Thermal metamorphism metamorphism strong mineral ages. ages. rv2600 rv 2600 Late tectonic emplacement emplacement of of aplitic aplitic and and pegmatitic pegmatitic dikes. dikes. Late tectonic or Late or syntectonic syntectonic emplacement emplacement of Sacred Sacred Heart and related adamellites. and (?) 2700 - 2550 2800 3000 ++ 150 3050 Deformation and and low-grade low-grade metamorphism. Deformation Emplacement of of granodiorite granodiorite and and adamellite. adamellite. Emplacement Deformation and and metamorphism metamorphism of of high-potash high-potashgranite, granite, basaltic basaltic Deformation rocks, and and gray gray tonalitic gneiss. rocks, gneiss. Possible Possible formation of of speckled speckled gneiss in shear zones. gneiss Emplacement of of high-potash high-potash granite granite and and pegmatite. Emplacement high- and and low-alumina low-alumina basaltic dikes Emplacement (?) (?) of highor sills. Deformation and metamorphism. 3550+ 125 - Extrusion and and intrusion intrusion of of trondhjemitic, trondhjemitic, tonalitic, and Extrusion and granodioritic Possiblybasaltic basaltic magma magmaalso alsoatat this this time. time. magma. Possibly 22 �LITHIC LITHIC AND MAJOR ELEMENT ELEMENT COMPOSITION COMPOSITION IN THE THE SUPERIOR GEOTRA VERSE, ONTARIO GEOTRAVERSE, A.M. Goodwin, Goodwin,Department Department of of Geology, Geology, University University of of Toronto, Toronto, Toronto, Toronto, Canada. Canada. A.M. ABSTRACT 2 The Geotraverse constitutes0 a a recta~ular rectanular area The Superior Superior Geotraverse constitutes area of of 24,610 24,610 mi2 mi 0 0 bounded by 90 90° and and 92°W longitudeand and 49 49° and and 52 52 N N latitude 92 W longitude latitude in in the the western western bounded by Superior Province Provinceofofthe the Canadian CanadianShield. Shield. The The area area crosses crosses or or includes Superior includes parts of six six major east-trending or belts belts which major east-trending subprovinces subprovinces or which in alternating alternating succession succession from from south to north south north are: are: Wawa WawaVolcanic, Volcanic, Quetico QueticoGneiss, Gneiss,Wabigoon Wabigoon Volcanic, Volcanic, English River Gneiss, Uchi and Berens Berens Plutonic Belt. River Uchi Volcanic, Volcanic, and Lithic proportions proportions (percent) in the Geotraverse Geotraverse are are as asfollows: follows: Granitic Granitic rocks rocks Metasedimentary rocks rocks - 5.3; Volcanic - 69.2; Migmatite - 10.5; Metasedimentary Volcanic rocks - 14.0; Mafic to ultramafic ultramafic intrusions intrusions - 0.5; and Syenite - 0.4. Granitic rocks rocks are are equally equally divided divided rocks comprise comprise mafic between gneissic (34.8) (34.8) and massive (34.6) (34.6) phases. Volcanic Volcanic rocks mafic and massive (12.8) and felsic (1.2) phases. The ratio of mafic to felsic volcanic rocks is 91.5 (12.8) and felsic (1.2) phases. The to felsic volcanic rocks is 91.5 to to 8.5. Lithic proportions in the the two gneiss Lithic proportions in gneiss belts differ significantly significantly with with the the English English River equally high high proportions proportions of of migmatite River Belt Belt containing containing equally migmatite (49.7) (49.7) and and granitic granitic gneiss (46.1) and negligible metasedimentary material, material, whereas gneiss (46.1) and negligible metasedimentary whereas the Quetico Quetico Belt Belt has has predominant predominant migmatite migmatite (64.8) (64.8) and and metasedimentary metasedimentary material material (29.0). (29.0). This contrast reflects reflects aa higher higher degree degree of of metamorphism metamorphism together together with with greater greater exposure exposure of older basement gneiss gneissdated datedto to be be at least of older basement least 3040 3040 m.y. m.y. old old in in the the English English River River Belt to to the north. Belt The three The three volcanic volcanic belts belts are are essentially essentially similar similar in in lithic lithiccompositon. compositon. A A salient feature feature is the of granitic in the two salient the high high proportions proportions of granitic rocks rocks especially especially in two northern Wabigoon - 77.1) equally northern belts belts (Uchi (Uchi - 65.0; Wabigoon equally divided divided between between numerous numerous latter appears massive plutons plutons and massive and adjoining adjoining gneissic gneissic rocks. rocks. The The latter appears to to represent represent foliated plutonic foliated plutonic rocks rocks intrusive intrusive into into nearby nearby volcanic volcanic rocks rocks which which would would imply imply aa post-volcanic age dated at 2750-2850 m.y. at 2750-2350 The weighted mean major major element element composition of the the Geotraverse is as The weighted mean composition of Geotraverse is as follows in in weight weight percent: percent: Si0 SiO,2 _-- 65.64, AL,O FeO (total) follows A1 2 0 3 -- 15.96, FeO (total) - 4.98, MgO MgO 2.32, CaO - 4.20, Na2O CO2 H20 - .88, CO Na 20 - 3.85,1C,O 3.85'£<.2° - 2.32, TiY2 Ti0 2 - .45, MnO MnO - .09, H....O 2 This compares c'losely with that of the Red compares closely with that Red Lake-Lansdown Lake-L~nsdownregion regIOn .09, P,O5 P 20 - .07. This 5 of northwestern Ontario (Shaw, (Shaw,et. et. a1.) a!.) as as well well as as both of northwestern Ontario both of of the theCanadian Canadian Shield Shield (Fahrig and Eade) and the the Ukrainian shield (Ronov, (Ronov,et. et. al.), (Fahrig and Eade) and Ukrainian shield al.), the the only only significant significant K20 and higher higher CaO CaO contents contents in in the Geotraverse. difference being being low low K Geotraverse. 0 and 2 tectonic development Although Although the the tectonic development of the Geotraverse Geotraverse crust remains uncertain, available available data data indicate of (1) uncertain, indicate some some blend blend of (1) spreading spreading of older older gneissic gneissic crust (older (older than than 3.0 3.0 b.y.) b.y.) with with (2) (2) accretionary accretionary growth growth of of ensimatic ensimatic volcanic volcanic belts belts (2750 -2900m.y.) m.y.)ininresulting resultingtroughs troughsand andbasins basinsrelative relativetotoaa metastable metastable craton to (2750 -2900 to the north. north. 23 �I THE GEOLOGY GEOLOGY OF GNEISSIC GNEISSIC ROCKS IN IN THE KENORA DISTRICT, DISTRICT, ENGLISH RIVER GNEISS RIVER GNEISS BELT. BELT. C.F. Gower, Gower, Department Department of of Geology, Geology, McMaster McMaster University, Hamilton, Hamilton, Ontario Ontario ABSTRACT ABSTRACT After After an an initial initial reconnaissance reconnaissance geological geological investigation investigation of of 2400 2400 sq. sq. km. in the southwest part part of of the the English English River River Gneiss Gneiss Belt, an area of of 100 100 sq. km. near near Kenora Kenora detailed study. study. was selected for detailed Most of the area range from from granitic granitic to Most of area is is underlain underlain by by gneissic gneissic rocks rocks which which range are best withthe the aid aid of of aa trianguiar untramaiic composition. composition. They They are best described described with "triangular untramafic diagram diagram" having having granitic granitic pegmatoid pegmatoid gneiss, gneiss, biotite biotite tonalite tonalite gneiss, gneiss, and and amphibolite amphibolite end members. members. as end BIOTITE BIOTITE TONALITE TONALITE GNEISS GNEISS 1 Mixed biotite tonalite —granitic pe~matoid gneiss, gneiss, granitic pegmatoid minor amphibolite minor arnphibolite . .. . Tonalite/leucotonalite gneiss, gneiss, minor minor amphiholite amphibolite and granitic gneiss Hornblende—biotite Hornblende-biotite tonalite tonalite gneiss, gneiss, common amphibolite enclaves enclaves . Amphibolite—leucotonalite gneissic Amphibolite-leucotonalite association, minor hornblende— association, hornblendebiotite tonalite gneiss Amphibolite, medium Amphibolite, medium grained, grained, network leucotonalite leucotonalite veins veins Granitic pep,matoid Granitic pegratoid gneiss Amphibolite, fine grained, Amphibolite, concordant leucotonalite, leucotonalite, uartz—epidote pods quartz-epidote pods GRANITIC PEGHATOID GNEISS GRANITIC PEGMATOID AMPHIBOLITE AHPHIBCLITE (1) much muchofof the the granitic Field studies suggest suggest that, (i) granitic material material represents represents Field studies pegmatite, (ii), represents both both mafic intensely Oi), the amphibolite amphibolite represents intensely deformed deformed intrusive pegmatite, (iii) do do not not assist assist in in determining protolith for for the the lavas and mafic mafic dikes, dikes, but but (iii) determining aa protolith lavas and biotite gneiss. biotite tonalite gneiss. isodilnal folds folds have have been The tectonic tectonic history The history is is complex. complex. FF isoclinal been refolded by by been used to define major F2 folds. iLve tight to open F2 folds. The minor F, folds open folds. The minor F?_ folds ~ave been used to F2 These major major structures have have been been re'folded rerolded by by an an F3 F fold which which appears to be a rim rim These 3 synformassociated associatedwith withthe the margin marginofofaalarge largetonalIte/granodiorite tonalite/granodiorite batholith. Two synform batholith. Two later (F4, also are are recognized. recognized. Mafic ter periods periods of of open open folding folding (F 4' FF5) 5) also Mafic dikes dikes which which have la with of the area which, been intruded throughout together with throughout the history of been intruded superimposed fold fold relationships superimposed relationships assist in in distinguishing distinguishing individual individual deforrnational deformational phases. 24 24 �APPLICATION OF A FLOW APPLICATION FLOW DIRECTION TECHNIQUE TO THE PORTAGE LAKE TO LAKE VOLCANICS, VOLCANICS, MICHIGAN MICHIGAN James G. James G. Grimes, Grimes, Department Department ofofGeology Geologyand andGeological GeologicalEngineering, Engineering, Michigan Michigan Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT A study study was was made made to to test ifif the theflow flow direction directiontechnique techniquedeveloped developed by by Elston Elston A and Smith Smith (1970) (1970)could couldbe be applied appliedto to the the Portage Lake in Michigan. Lake Volcanics Volcanics in Michigan. The The and technique, as as modified for basalts, basalts, presumes presumes that technique, modified by by Smith Smith and and Rhodes Rhodes (1972) (1972) for elongated will statistically align themself elongated fragments fragments (i.e. (i.e. crystals) crystals) will statistically align themseif in in the direction of flow. Samples were were collected collected from from various various locations locations within within the the series. series. The Samples majority of of samples were collected collected within majority samples were within the City City of of Houghton Houghton and and represent a rough stratigraphic section section through The remaining through the series. series. The remaining samples samples were were rough stratigraphic collected between South Range and Keweenaw Point. between South Range and Keweenaw The orientation orientation of of plagioclase crystals having havingaa length/breath length/breath ratio ratio greater plagioclase crystals The than three was in oriented oriented thin thin sections. sections. The than was measured measured in The results results were were then then submitted submitted for statistical statistical analysis. to a computer program program for analysis. Lineation values values all all had aa chi—square valueabove abovethe the90 90percentile percentile for for two two Lineation chi-square value degrees of of freedom. effect degrees freedom. Aximuth Aximuth was was determined determined by by imbrication imbrication and blocking blocking effect criteria. Two samples samples were were collected collected within withinfour four feet feet of each other Two other within within the the same same flow to to check the repeatability of the flow check the the method. method. In In addition addition to these these two two samples, samples, another thin section The difference another section was was measured measured twice. twice. The difference between between the two two flow flow directions were were 10.3 and 11.2 11.2 in in each each case, case, respectively. respectively. This This difference could could be directions 10.3 and mostly accountedfor for by bythe the ten ten degree degree intervals intervals that that the data data is is divided divided into for for mostly accounted analyses. The of the Scales Scales Creek Creek Flow Flow also also was was The upper, upper, middle, middle, and and lower lower portions portions of sampled to test the application of the method to some of the thicker flows in the application of the method to some of the thicker flows in the the sampled to sequence. Flow S35.OE,and andSO.6E S0.6Erespectively. respectively. The upper Flowaximuths aximuthswere wereS16.GW, S16.6W, S35.0E, and lower lower samples generally conform conform to to the aximuth aximuth directions directions of of samples samples above above and samples generally (S2.8W)and and below below (S9.DE) (S9.OE)the theScales Scales Creek Creek Flow. (S2.8W) Taken together, the results Taken together, results indicate indicate aa general general flow flow direction direction from from the the north. north. Within City of of Houghotn, Houghotn, the theflow flowazimuth azimuthwas wasS9.OE S9.0E for for the thelower lowerpart, part,S2.OW S2.0W Within the City for the for the the upper upper part part of the series. the middle middle part, part, and and S28.OW S28.0W for series. Individual Individual sample sample directions for the directions are areS17.OE S17.0E and and SLOE SLOE for the the lower lower part, part,S7.2W, S7.2W,S4.OE, S4.0E, and S4.5W S4.5W for middle and S33.7W S33.7Wfor forthe the upper upper part. part. middle part, and and S23.4W S23.4W and Further application application of the the technique technique could could demonstrate demonstrate regional regional patterns for for directions of of lava lava flow flow movements, movements, and and multiple multiple sampling sampling of long long strike lengths of of certain certain flows flows might might allow allow triangulation triangUlation of the source source area. area. 25 25 �REFERENCES REFERENCES Elston, W.E., flow direction of rhyolitic rhyolitic Elston, W.E., and Smith, 1970, Determination Smith, E.1., E.I., 1970, Determination of of flow ash-flow tuffs tuffs from ash-flow from fluidal fluidal textures: textures: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 81, 81, pp. pp. 3393—3406. 3393-3406. Smith, E.1., E.I., and and Rhodes, R.C., 1972, Flow direction direction determination determination of lava Smith, Rhodes, R.C., 1972, Flow lava flows: flows: Geol. Soc. Soc. America Bull., v. 83, Geol. 83, pp. 1869-1874. 1869-1874. 26 26 �I I THE THE SLATE SLATE ISLANDS: ISLANDS: THE CENTRAL UPLIFT UPLIFT OF OF A A METEORITE METEORITE IMPACT IMPACT CRATER? Department of of Geology, Halls, Department Geology, Erindale Erindale College, College, University University of of Toronto, Toronto, H.C. I-Jails, Mississauga, Ontario L5L 1C6 IC6 and Grieve, Earth Earth Physics Physics Branch, Branch, DepartDepartMississauga, Ontario L5L and R.A.F. R.A.F. Grieve, of Energy Energy Mines 'Mines and Ontario ment of and Resources, Resources, Ottawa, Ontario ABSTRACT ABSTRACT Shock metamorphic effects in in samples samples from from the the Slate SlateIslands, Islands,Lake Lake Superior Superior Shock metamorphic 0 (48°40'N, 87°OOW) suggest thatthetheislands islandsare arepart part of of aa meteorite (48 0 40'N, 87 00'W) suggest that meteorite impact impact structure. The The islands islands form form the the central central uplift upliftof ofaacomplex complex crater craterand andare areringed ringed by aa submerged trough and and annular annular ridge ridge with a dimater dimater of of 30 30 km. km. Precambrian Precambrian submerged trough bedrock units are are locally breccia dikes. bedrock units locally brecciated and and cut by by aliochthonous allochthonous breccia dikes. These These clasts of identifiable country country rock rock and and also also fragments fragments of of a dikes contain clasts sedimentary unit, in age, age, which is no longer present in unit, possibly possibly Upper Upper Keweenawan Keweenawan in which is no longer in of shatter The orientations orientations of shatter cones cones present present in in the the breccia breccia host host rocks rocks outcrop. The indicate indicate the interior interior of of the the islands islands as as the the approximate approximate shock shock centre. Microscopic Microscopic planar features, equivalent planar features, equivalent to those those described described from from other other impact impact sites, occur occur in in quartz and and piagiociase plagioclase and and the level level of of shock shock deformation deformation increases increases towards towards the the interior of of the the islands. islands. The The shock shock event postdates postdates Keweenawan Keweenawan igneous igneous activity interior (about 1.1. b.y. old) old) and on the basis basis of of the the erosion erosion level, level, may may be be early early Paleozoic Paleozoic in in (about and on age. 27 27 �GEOCHEMICAL PROCESSES PROCESSES FOR THE GEOCHEMICAL THE FORMATION FORMATION OF OF MAGNETITE MAGNETITE IN IN LOW-GRADE LOW-GRADE METAMORPHIC PRECAMBRIAN IRON FORMATIONS METAMORPHIC FORMATIONS Tsu-Ming Han, Han, The The Cleveland-Cliffs Cleveland-Cliffs Iron Iron Company, Company, Ishpeming, Ishpeming, Michigan Michigan 49849 49849 Tsu-Ming ABSTRACT A substantial substantial number number of of magnetite ores, magnetite-containing magnetite-containing specimens specimens and A collected from their oxidized equivalents collected from the low-grade low-grade metamorphic metamorphic iron iron formations in the Mesabi, Gogebic, and Marquette districts of the Lake Superior formations in Mesabi, Gogebic, and Marquette districts the Lake Superior region, and and the Lake region, Lake Albanel Albanel District of of the the Quebec Quebec Province, Province, Canada Canada have have been been study reveals reveals that the microscopically investigated. The microscopically The study the magnetite magnetite in in these these iron iron crystallinity, external formations not only varies formations not only varies in in grain grain size, size, crystallinity, external morphology, morphology, inclusion composition, composition,distribution, distribution,and and genetic genetic relationships inclusion relationships to its coexisting minerals but also also significantly significantlydiffers differsinininternal internalmicrostructures. microstructures. The minerals but The last variable was found to to be was found be the the most most useful useful key key to to the theinterpretation interpretation of of the thegeochemical geochemical processes of of the the magnetite formation. processes formation. These These internal internal microstructures microstructures are are normally normally not microscopically visible unless unless aa laboratory-induced oxidtion precedure not microscopically visible laboratory-induced oxidation precedure is employed. The sections were were heated heated at at about about 300 3000 C for three to employed. The well-polished well-polished sections to four four days and then then cooled days under under weakly weakly to moderately moderately oxidizing oxidizing conditions conditions and cooled to room room temperature for for reexamination. reexamination. The The most most important important internal microstructures microstructures in in by the the artificially produced this study, as outlined by produced hematite are are listed listedas asfollows: follows: 1. Lath-like, Lath-like, bladed, bladed, wedge-shaped, wedge-shaped, rhombhedral, rhombhedral, and and hexagonal hexagonal crystals crystals arranged or subparallel, arranged randomly, randomly, or subparallel, or in in such such forms forms resembling resembling druses druses and and inner inner linings of geodes crystals, clusters, geodes within within individual individual crystals, clusters, granules, granules, and and laminae laminae of of linings of magnetite. Irregular bodies Irregular bodies resembling resembling spheroids spheroids uniformly uniformly scattered throughout throughout granules, of magnetite. granules, clusters, and laminae laminae of 2. 3. Botryoidal Botryoidal structures structures in in clusters, clusters, laminae, laminae, and and granules granules of magnetite. magnetite. Zonal and and core-and-shell concentric structures structures in 4. Zonal core-and-shell concentric in individual individual magnetite crystals with of the the preexisting preexisting lath-like crystals. with or or without without inclusions inclusions of All of of the ore mentioned All the af afore mentioned internal microstructures microstructures have have been been found found in the the magnetite (b) hematite hematite and and chert, chert, (c) (c) carbonates carbonates and and magnetite coexisting coexisting with: with: (a) (a) chert, chert, (b) chert, chert, (d) (d) silicates and chert, and and (e) carbonates, silicates, and and chert. chert. The outlines of crystals, irregular bodies, and botryoidal masses masses are are apparently of of restored apparently restored preexisting preexisting hematite hematite which which was was probably probably deposited deposited as Fe(OH)3 gel. The Fe(OH)3 gel. The later later magnetite magnetitewas wasdeveloped developedby: by:(a) (a) nucleation nucleation followed followed by by one or several stages replacement of of hematite or stages of of enlargement, enlargement, and and (b) (b) pseudomorphic pseudomorphic replacement supplemented by by extensive overgrowth. overgrowth. Based onthe the ratio ratio of: of: (a) (a)the the size sizeofofthe the existing existingmagnetite magnetite crystals crystals to to that of Based on their initial nuclei, and and (b) (b) the the amount amountofof magnetite magnetitetoto that that of of the their initial magnetite magnetite nuclei, restored preexisting preexisting hematite, hematite, the thefollowing following conclusion conclusion is is drawn: drawn: The The migration migration of of in conjunction with the the redepositoin of iron iron as conjunction with redepositoin of as magnetite magnetite on on nuclei nuclei of of iron in magnetite or or preexisting magnetite preexisting hematite is is aa much much more more important important magnetite magnetite forming forming process than the simple process than simple reduction reduction of of hematite or or the the metamorphic metamorphic oxidation oxidation of the primary ferrous ferrous minerals like siderite and minerals like and greenalite. The The presence presence of of preexisting preexisting hematite hematite in in the the magnetite magnetite laminae, laminae, clusters, and and 28 �granules of the silicate granules of silicate and and carbonate carbonate iron iron formations formations indicates indicates that that some some iron iron formations normallyreferred referred to to as "silicate", fades formations normally "silicate", "carbonate", "carbonate", and and "mixed" "mixed" facies might fades prior might have have been been oxide oxide facies prior to topost-depositional post-depositional alterations alterations - silication, matter isis believed magnetitization, magnetitization, carbonatization, carbonatization, etc. Carbonaceous Carbonaceous matter believed to be be responsible for the facies change. responsible for change. On On the basis basis of the the results results of of these theseiron ironformation formationstudies, studies,one onecould could conclude conclude that the the magnetite magnetiteininthe thelow-grade low-grademetamorphic metamorphic Precambrian Precambrian iron iron formations formations of of the Lake elsewhere may may well well have have the the same same ancestry. Lake Superior Superior type found found elsewhere 29 �RARE RARE EARTH EARTHELEMENT ELEMENT STUDIES STUDIES OF OF THE THE ARCHEAN ARCHEANGNEISSES GNEISSES OF OFTHE THEMINNESOTA MINNESOTARIVER RIVERVALLEY VALLEY G.N. G.N. Hanson, Hanson, Department Department of of Earth Earth and and Space Space Sciences, Sciences, State State University University of ofNew New York, York and and 5.5. S.S. Goldich, Goldich, Department Department of Geology, Geology, Northern Northern York, Stoney Stoney Brook, Brook, New New York Illinois University, University, DeKaib, DeKalb, Illinois. Illinois. illinois ABSTRACT ABSTRACT Rare earth earth elements elements (REE) (REE) have have been been analyzed analyzed on on tonalitic tonalitic to to granodioritic granodioritic units units of of the the up up toto3800 3800m.y. m.y.old oldMorton Mortonand andMontevideo Montevideo gneisses, gneisses, mafic mafic and and ultramafic units units within within the the gneisses, gneisses, and and later later granitic granitic intrusions. intrusions. The Thesubparallel subparallel REE patterns along with similarities similarities inin other other geochemical geochemicaldata data suggest suggest that that the REE patterns along with upper upper amphibolite amphibolite to granulite granulite grade grade gneisses gneisses and and later granitic granitic intrusions intrusions have have aa similar origin resulting resulting from from partial partial melting of maf Ic quartz quartz diorite similar origin melting of mafic diorite or diorite diorite crust. sources, perhaps in the crust. Significantly Significantly different REE REE patterns for for K-rich K-rich pegmatoidal pegmatoidal veins veins and and zones zones containing hornblende within within the nebulitic containing porphyroblastic porphyroblastic hornblende nebulitic Morton Morton Gneiss Gneiss suggest suggest that tha t under under conditions conditions of recrystallization recrystallization and and major major element element mobilization, mobilization, the the REE REE mobilized on may have been mobilized on dimensions dimensions of of many many centimeters. centimeters. A relatively flat REE A relatively REE pattern for for aa tholeiitic tholeiiticamphibolite amphibolite is is similar, similar, although although slightly more more enriched enriched in in REE, REE, to to the 2700 m.y. old old Archean Archean basalts basalts in in aa greenstone slightly 2700 m.y. Hornblende belt in northeastern northeastern Minnesota Minnesota (Arth (Arth and and Hanson, Hanson, 1975). 1975). Hornblende rich, rich, komatiitic amphibolites have havepatterns patterns with with about about 30 30 times times chondrites komatiitic amphibolites chondrites for for Ce Ce and and about 8 times chondrites for Yb. This would suggest that if the REE have not been chondrites for Yb. This would suggest that if the REE have not been affected by the source (the mantle?) for this this rock affected by recrystallization, recrystallization, the source (the mantle?) for rock type type also also is is REE enriched. light REE 30 30 I �w Rb-Sr GEOCHRONOLOGY OF OF THE THEMONTEVIDEO MONTEVIDEO GNEISS, GNEISS, MINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY C.E. Denver, Colorado Colorado 80225 80225 and and S.S. 5.5. Goldich, Goldich, C.E. Hedge, Hedge, U.S. U.S. Geological Geological Survey, Survey, Denver, Northern illinois Illinois University, University, DeKaIb, DeKalb, illinois Illinois 60115 60 115 ABSTRACT Gneiss of of Lund Lund (1956) (1956)isis aa hybrid hybrid rock rock consisting consisting of biotitebiotiteMontevideo Gneiss The Montevideo quartz-feldspar gneissic, and granitic granitic phases phases of of different ages. gneissic, amphibolitic, amphibolitic, and ages. The biotite gneiss, gneiss, the the oldest oldest major majorphase, phase,was wasprobably probably derived derived from from volcanic volcanic material material of andesitic andesitic to to rhyodacitic rhyodacitic compositon compositon and and is is 3700 3700 ++ 100 100 m.y. m.y. old. old. Amphibolite Amphibolite clasts in represent basaltic basaltic lavas lavas or or dikes diks that in the gneiss gneiss may may represent thatwere were broken broken up. up. At approximately 3000 m.y. m.y. ago, ago, granitic granitic magma was intruded intruded in in the form of approximately 3000 magma was small irregular masses, masses, sheets, sheets, and and lit-par-lit lit-par-lit injections. small irregular injections. The The Rb-Sr Rb-Sr systematics systematics in in the at this the older older gneiss gneiss were were disturbed disturbed at this time. time. Failure Failure to recognized recognized the age age difference between the older foliated gneiss and the younger more massive difference between the older foliated gneiss and the younger more massive leucogranitic of the leucogranitic phase phase invalidates invalidates the earlier earlier geochronologic geochronologic investigations investigations of the Montevideo Gneiss. to lower metamorphism (upper (upper amphibolite amphibolite to lower granulite granulite facies) facies) High-grade metamorphism High-grade affected phase as as well well as as the the older but we we are are not certain affected the massive massive phase older gneiss, gneiss, but certain whether this occurred occurred shortly shortlyafter after emplacement emplacementofofthe theleucogranite leucogranite(N( 3000 m.y. whether this ago) or during the interval from ago) or during the from 3000 3000 to 2600 2600 m.y. ago. A 2600-m.y. 2600-m.y. event event isis represented represented in in the the emplacement of large granitic masses masses exposed inin the the Minnesota Minnesota River River Valley Valleysoutheast southeast and and northwest northwest of of the Montevideoexposed Montevideointensive cataclasis cataclasis affected the Granite Falls Granite Falls area. Locally Locally intensive therocks rocks approximately approximately These events events also also affected affected the the Rb-Sr in the older 2400 m.y. ago. These Rb-Sr systematics systematics in older 2400 m.y. ago. rocks. Small masses of of adamellite adamellite and numerous diabasic dikes dikes were were intruded intruded in in the Small masses numerous diabasic Montevideo Gneiss1850 1850m.y. m.y.ago, ago,and andlocally locallythese these intrusions intrusions affected affected the Montevideo Gneiss the Rb-Sr Rb-Sr system in the older older rocks. rocks. 31 31 I �I THE TRACE TRACE ELEMENT ELEMENT GEOCHEMISTRY GEOCHEMISTRY OF PEAT PEAT BOGS BOGS OVER OVER DIFFERENT BEDROCK BEDROCK TYPES, TYPES, SOUTHERN SOUTHERN HOUGHTON HOUGHTON COUNTY, COUNTY, MICHIGAN MICHIGAN Department of Jacobsen, Department of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Sue I.I. :Jacobsen, Sue Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT A investigation of of the feasibility preliminary investigation feasibility of of using using peat peat iningeochemical geochemical A preliminary prospecting was carried carried out using prospecting in in the Upper Upper Peninsula Peninsula of Michigan Michigan was using twelve peat peat to determine bogs bogs in in southern southern Houghton Houghton County. County. The The bogs bogs were were sampled sampled to determine if if difference type isis reflected in difference in in bedrock bedrock type in the the trace trace element element geochemistry geochemistry of the the peat layers layers above above them. them. The The bogs bogs were were selected selected to to provide provide as asmany many bedrock bedrock varieties varieties as as possible: possible: Portage Portage Lake Lake Lava Lava Series, Series, Copper Copper Harbor Harbor Conglomerate, Conglomerate, Nonesuch Shale, Freda Sandstone, and Nonesuch Shale, and 3acobsville Jacobsville Sandstone. Sandstone. Samples were weretaken taken at at sites 100 Samples 100 ft. apart along along at least least one one line line run run through through both the Davis each bog. bog. As As both Davis and and the Hiller Hiller peat peat samplers samplers proved proved inadequate, inadequate, a simple sampler was simple aluminum aluminum piston—type piston-type sampler was used. used. Peat samples samples 15 15 inches inches long long at depth intervals of depth intervals of 3 3 feet feet were were taken, taken,asaswell wellasassamples samplesofofthe theliving livingSphagnum Sphagnum moss mat and mineral material material where where possible. possible. Peat and the underlying underlying mineral Peat was was identified identified moss mat in the field field as as to to type type and and degree degree of of humification. humification. Maximum Maximum peat peat depth depth differed differed from to bog bog and and ranged rangedfrom from33feet feet to to 30 from bog bog to 30 feet. The pH was was0determined thelaboratory laboratoryand andranged ranged om 3.1 3.1toto 6.0. 6.0. After The pH determined ininthe from oven dryingatat 85 850 CC for ashedat at 500 5000 C oven drying for 24 24 hours, hours, the peat was was ashed C for for 22 hours. hours. Trace Trace the Atomic element concentrations are being being determined determined using using the Atomic Absorption Absorption Spectrometer. As peat profiles profiles are are not As element element distributions distributions inin peat not uniform, uniform, a study study of the the vertical distribution of trace elements vertical distribution of elements is is being being made. made. Spatial Spatial distributions distributions of of elemental concentrations concentrations and and pH pH are also also being being investigated. investigated. 32 I �ENGADINE ENGADINE DOLOSTONE OF MICHIGAN'S MICHIGAN'S EASTERN UPPER UPPER PENINSULA: PENINSULA: GEOLOGY GEOLOGY AND AND RESOURCE RESOURCEEVALUATION EVALUATION Allan M. M. 3ohnson,Institute Johnson,Institute of of Mineral MineralResearch, Research, Michigan Michigan Technological Technological University, University, Allan Houghton, and Harry Houghton, Michigan Michigan 49931 49931 and Harry 0.O.Sorenson, Sorenson,Michigan Michigan Geological Geological Survey Survey Division, Division, Department of of Natural NaturalResources, Resources,Stevens StevensT.T.Mason MasonBuilding, Building,Lansing, Lansing, Michigan 48926 48926 Michigan ABSTRACT ABSTRACT Results Results of of geologic geologic mapping mapping and and core-drilling core-drilling of of the theMiddle MiddleSilurian SilurianEngadine Engadine The work is part of a continuing cooperative project dolostone are reported. The work is part of a continuing cooperative project dolostone reported. between Geological Survey Surveyand andthe the Institute Institute of Mineral between the the Michigan Michigan Geological Mineral Research Research to evaluate limestone resources resourcesofof the the State. evalua te high-purity high-purity limestone State. Preliminary Preliminary results results of of similar work on the Fiborn limestone were reported last year at this similar work on the Fiborn limestone were reported last year this Institute Institute (Johnson and and Sorensen, Sorensen, 1975). 1975). (Johnson The Engadinedolostone dolostoneisisexposed exposedasasaa resistant resistant cuesta for massive Engadine for more more The massive 100 miles along along the northern northern margin margin of of the theMichigan Michigan Basin Basin from Manistique Manistique to to than 100 Drummond Island. Despite Drummond Island. Despite a thickness of only 200 200 feet the the shallow shallow regional regional dip dip of of 50 50 feet/mile south south allows allows the unit unit to to form form aa belt beltfrom from 55to to10 10 miles miles wide wide along along the the northern shores shores of of Lakes Lakes Michigan Michigan and and Huron. Huron. northern Three Three steel steel companies companies quarry quarry grade stone stone from from the the Engadine. Engadine. metallurgical grade Previously unpublished field work by by G.M. G.M. Ehlers, University of Michigan, Michigan, and and unpublished field establishe the following for the H.O. Sorenson, Sorenson, M.G.S., M.G.S., establishe following stratigraphic subdivisions subdivisions for H.O. Engadine dolostone: Engadine Name Descriotion Description . Thickness Bush Bush Bay Bay dolostone -massive, It. gray with cream -massive, mottling, med. med. to coarsely mottling, crystalline, porous porous 50' Swede Swede Road Road dolostone -massive (weathers (weathers thin), buff-massive brown, brown, finedly finedly crystalline crystalline 33' Prentiss Prentiss Creek dolostone -thinly bedded, bedded, gray to brown, brown, chert layers, med. crystalline chert 26' 26' Rapson Rapson Creek Creek dolostone dolostone -massive, It. It. gray-buff gray-buff with with -massive, lighter mottling, med-coarsely lighter crystalline, porous crystalline, porous 60' 60' Rockview Rockview dolostone dolostone -massive, gray, gray, med-coarsely med-coarsely -massive, crystalline, stromatolitic stromatolitic crystalline, at at base base TOTAL TOTAL 44' 44' 2flT 2TY 33 33 - ---~------------------- �These were established established from from field field mapping in the eastern These divisions divisions were mapping in eastern portion portion of of the Engadine. Examination of 16 cores drilled during 1975 spanning 100 miles of the the Engadine. Examination of 16 cores drilled during 1975 spanning Engadine, support these these stratigraphic subdivisions in the eastern Engadine, support subdivisions in eastern portion. portion. Cores Cores However, if the the western westernportion portionshow show some some inconsistencies. inconsistencies. However, the Engadine Engadine is is from the interpreted interpreted to to have have formed formed as as aareef reefororcarbonate carbonatebank bankalong alongaashelf shelfmargin marginwhere where minor minor onlap-offlap onlap-offlap fluctuations fluctuations occurred, occurred, these these inconsistencies inconsistencies can can be be resolved. resolved. Features Features of of the the Engadine Engadine dolostone dolostone supporting supporting this this origin origin include include its its massive, massive, porous porous structure, complete complete dolomitization, dolomitization, fossil fossil assemblage, assemblage, and and its position position in in relation to to other other shelf shelf formations formations and and to tothe theMichigan Michigan Basin. Basin. Core logs be employed employed to to evaluate evaluate the potential logs and and chemical analyses will will be potential of of Engadine as aa high high purity purity dolostone. dolostone. Results Results are are scheduled scheduled for for publication publication by by the Engadine the Michigan Survey inin 1977. Michigan Geological Geological Survey 1977. This This year year similar similar work work will will begin begin on on Traverse group in the the northern part of group limestones limestones (Devonian) (Devonian) in of the theLower LowerPeninsula Peninsula Michigan. of Michigan. REFERENCES Ehlers, and Kesling, R.V. Silurian rocks rocks of of the the Northern Kesling, R. V. 1957, 1957, Silurian Northern Peninsula Peninsula of Ehlers, G.M., G.M., and Michigan, Mich. Basin Basin Geol. Geol. Soc., 63 p. Michigan, Guidebook Guidebook Mich. Ehiers, G.M., 1973, 1973, Stratigraphy Stratigraphy of of the the Niagaran Niagaran Series Series of the the Northern Northern Peninsula Peninsula Ehlers, G.M., of Michigan, Univ. of Mich. Papers on Paleontology, no. 3, 200 Michigan, Univ. of Mich. Papers on 200 p. 3ohnson, A.M., and and Sorensen, Sorensen, H.O., H.O., 1975, 1975, Michigan Michigan Upper Peninsula Peninsula Middle Middle Silurian Johnson, A.M., Limestones: Geology Geologyand and Resource Resource Potential, Potential, (abs.), Limestones: (abs.), 21st 21st Annual Annual Inst. Lake Superior Geology, 16-17. Lake Superior Geology, p. 16-17. 34 34 on I �• NATURE NATURE OF OF THE THEQUETICO-WABIGOON QUETICO-W ABIGOON BOUNDARY BOUNDARY IN IN THE THE dE dE COURCEY-SMILEY COURCEY-SMILEY LAKES LAKES AREA, AREA, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO M. Kehienbeck, Kehlenbeck, Department Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Thunder Manfred Manf red M. Ontario Bay, Ontario Bay, ABSTRACT ABSTRACT In area, the boundary In the de de Courcy-Smiley Courcy-Smiley Lakes Lakes area, boundary between between the Quetico Quetico and and \Vabigoon Beltsisisexpressed expressedbybya asequence sequenceofof pelitic pelitic to semi-pelitic Wabigoon Belts semi-pelitic schists schists and and gneisses. At At the the present present level level of oferosion, erosion, these these metasedimentary metasedimentary rocks rocks are are in in gneisses. contact contact with with granodioritic granodioriticgneisses, gneisses, granites, granites,and and pegmatites, pegmatites,which which are areexposed exposed to to the south. south. the To To the north of of this this area, area,regional regional metamorphism metamorphism of of volcanic volcanic and and sedimentary sedimentary rocks rocks has has resulted resulted in in greenschist greenschist facies facies assemblages assemblages which which characterized characterized the Wabigoon Belt In the boundary boundary zone the metamorphic metamorphic grade grade increases increases Wabigoon Belt in in general. In de Courcey Courcey and and Smiley Smiley Lakes. Lakes. southward toward de Formation of of three distinct Formation distinct foliation foliation surfaces surfaces was was accompanied accompanied by by synsyntectonic as well well asaspost-tectonic post-tectonicrecrystallization recrystallizationproducing producingpolymetamorphic polymetamorphic tectonic as schists. In the boundary In boundary zone, zone, mineral assemblages comprising comprising andalusite, sillimanite, cordierite, garnet, biotite, biotite, and form aa facies fades series cordierite, garnet, and muscovite muscovite form series of of the theAbukumaAbukumatype. The boundary between Quetico Quetico and and Wabigoon WabigoonBelts Beltsinin this this area area is a complex The boundary between complex zone belts have have been been reconstituted reconstituted by bymultiple-phase multiple-phase zone in in which which rocks rocks of of both both belts metamorphism and melting. metamorphism and partial melting. 35 35 �J THE THE CENTRAL CENTRALWISCONSIN WISCONSIN BATHOLITH BATHOLITH Gene L. L. LaBerge, LaBerge, Geology Geology Department, Department,University UniversityofofWisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, Wisconsin 54901 54901 and and Paul Paul E. E. Myers, Myers, Geology Geology Department,Washington Department,Washington State State Wisconsin University, Pullman, Pullman,Washington Washington University, ABSTRACT ABSTRACT 1500 square miles miles in in Marathon Marathon County, County,Wisconsin, Wisconsin, Geological mapping of over 1500 Geological has has revealed revealed an an extensive extensive complex complex of of volcanic volcanic and and possible possible co-genetic co-genetic intrusive intrusive The volcanic volcanic rocks, as as pendants pendants and and xenoliths, xenoliths, are aresurrounded surrounded by by granitic granitic rocks. The intrusions showing an inward inwarddecrease decrease inin the the volume volume of of contaminant contaminant material. material. The showing an The volcanic "pendants" generally generally decrease decrease in in size and volcanic "pendants" and relative relativeabundance abundance westward westward across County, thus thus suggesting suggestingexposure exposureofofthe the eastern eastern portion portion of of a across Marathon Marathon County, convex batholith roof with its apex extending approximately along the west edge convex roof with its apex extending approximately along the west edge of of county. The The batholith batholith comprises comprises at least least twenty twenty separate separatestock-like stock-likeplutons, plutons, the county. which has has its own own contaminated contaminated margin. Mafic quartz diorites and and quartz each of which margin. Mafic monzonites grade inward inward to to a more monzonites grade more granitic core. core. The The younger younger plutons plutons are more more felsic. Gravity and Gravity and aeromagnetic aeromagnetic maps maps and and geological geological reconnaissance reconnaissance suggests suggests that Marathon County and and most most of of central are underlain Marathon County central Wisconsin Wisconsin are underlain by by granitic granitic rocks rocks containing scattered volcanic containing scattered volcanic roof roof pendants. We We suggest that that this this plutonic plutonic complex complex the "Central "Central Wisconsin Wisconsin batholith." be called the Aeromagnetic and geologic geologic mapping mappingshow showthat thatseveral several major majorstructural structural trends Aeromagnetic and intersect within within Marathon Marathon County. County. These These structural structural trends trends coincide coincide with with zones zones of intense cataclasis which intense which occurred before, before, during during and and after batholith batholith emplacement. emplacement. Most of of the six to date terminate Most six northeast-trending northeast-trending cataclastic cataclastic zones zones mapped mapped to terminate against or merge merge with with aa major major northwest-trending northwest-trending zone zone which which crosses crosses the the the cataclastic cataclastic zones locally acted acted as southwestern county. Although Although the zones locally as southwestern part part of of the county. conduits for for magmas, conduits magmas, most most of the the plutons plutons show show features features of of pervasive pervasive shearing, shearing, suggesting Available isotopic suggesting aa long long period period of of intrusion intrusionalternating alternating with withcataclasis. cataclasis. Available ages indicate the the batholith batholith was was formed formed during duringMiddle Middle Precambrian (Penokean?) (Penokean?) ages indicate time. 36 U �ORIGIN ORIGIN OF OF LAMINAE LAMINAE IN IN PRECAMBRIAN PRECAMBRIAN IRON-FORMATION IRON-FORMATION M.S. Lougheed Lougheed and and 3.1 J.J. Mancuso, Mancuso, Department Department of of Geology, Geology, Bowling Bowling Green Green M.S. University, Green, Ohio Ohio 43403 43403 University, Bowling Bowling Green, ABSTRACT ABSTRACT The original original particulate particulate constituents constituents of of Precambrian Precambrian iron-formation iron-formation are are The biogenic-carbonate minerals, opaline opalinesilica silica tests tests and biogenic-carbonate minerals, and organic organic material. material. These These constituents control control Eh Eh and and pH pH of of contiguous contiguous water water which which is is replenished replenished from an an open open sea source. source. Important Importantsecondary secondaryminerals, minerals, which which include include ferroan ferroan carbonates, carbonates, iron oxides, oxides, iron silicates, chalcedony-quartz, chalcedony-quartz, and and pyrite, pyrite, are are produced produced in in response response to environmental environmental factors factors affecting affectingthe theoriginal originalconstituents, constituents,and andwe wehave havediscussed discussed genesis over over the past past several several years years at at these these meetings. meetings. Typically, in in banded banded their genesis iron-formation, the thickness and lateral lateral extent of iron-formation, the thickness and of the the bands bands or or laminations laminations are are determined by the the presence determined by presence of of opaline opaline slurry slurry or gel. gel. An An exception occurs occurs when when grains of secondary carbonate constitute the bedload grains of secondary carbonate bedload during during current transport and and then deposited deposited as as thin thin laminae laminae of of nearly nearly pure pure carbonate, carbonate, (ex. (ex.Empire Empire mine, mine, are then however, laminae laminae are deposited Negaunee-siderite facies.). Most Most commonly, commonly, however, deposited from from Negaunee-siderite a bedload composed primarily of biogenic opaline gel or slurry which functions bedload composed primarily of biogenic opaline gel which functions as a medium iron-formation. medium of of support support for for any any combination combination of of the the other other constituents of iron-formation. Siliceous laminae, which whichmay maybe be more more than than one Siliceous laminae, one centimeter thick, thick, often often contain contain components such components such as flakes flakes and and shreds shreds of of algal algalhash, hash,which which commonly commonly show show evidence of having by laminar of having been been transported transported by laminar or or turbulent turbulent current current flow. flow. Commonly undulating bedded algal algal mats mats are inundated undulating bedded inundated by by an opaline opaline slurry mix mix to produce produce an an anoxic conducive to to the anoxic environment environment conducive the production production of of pre-greenalite pre-greenalite(greenaloid) (greenaloid) which the precursor precursor of of greenalite. greenalite. Beds Beds of of this this nature, nature, as as well well as as beds beds principally principally which isis the composed of greenalite granules, composed of granules, upon upon dewatering dewatering and and concomitant concomitant compression, compression, produce thin undulating laminae, notably notably in in "slaty" "slaty" facies, but produce thin undulating laminae, but when when oxidized oxidized they commonlyoccurs occurs in in chert produce iron-oxide iron-oxide chert laminae. laminae. Graded Graded bedding bedding commonly produce laminae containing particulate particulate material such laminae containing such as as granules. granules. The Thesuspended suspended load load was was apparently coming to to rest, rest, apparently transported in aa tenuous tenuous silica slurry slurry or gel, gel, which which upon upon coming is at at least allowed the load load to to gravitationally allowed the gravitationally settle into aa graded graded profile. profile. There There is least one case in one in which which chalcedonic chalcedonic laminae laminae were formed formed by by gravity gravity accumulation accumulation of siliceous tests tests of planktonic planktonic organisms. organisms. Normally Normally the tests tests would would be be comminuted comminuted siliceous to a slurry during bedloadtransport transport by bywater water currents. currents. These during bedload These few few genetic genetic examples examples of laminae in iron-formation, emphasize the complexities involved when we use the of iron-formation, emphasize the complexities involved when "banded iron-formation." term "banded 37 37 �• PENOKEAN PENOKEAN STRUCTURES AND AND PLUTONIC PLUTONIC ROCKS ROCKS IN IN PORTAGE PORT AGE AND AND WOOD WOOD COUNTIES, COUNTIES,WISCONSIN WISCONSIN Jr., Department R.S. Maass Maass and and L.G. L.G. Medaris, Medaris, Jr., Department of of Geology Geology and and Geophysics, Geophysics, R.S. University University of of Wisconsin, Wisconsin, Madison, Madison, 53706 53706 and W.R. W.R. Van Van Schmus, Schmus, Department Department of of Geology, University of Kansas, Kansas, Lawrence, Lawrence, 66044 66044 Geology, ABSTRACT ABSTRACT Three Three exposures exposures of Precambrian Precambrian rocks rocks along along the theWisconsin Wisconsin River River (Stevens (Stevens Point, Point, Conants Conants Rapids, Rapids, and and Biron Biron Dam) Dam) have been investigated in in order order to to establish establish the relative units and and to to characterize the relative and and absolute absolute ages ages of lithologic lithologic units the geometry geometry and age of folding. and age of folding. Relative Rela tive ages ages of of the the lithologic lithologic units units from from oldest oldest totoyoungest youngest are: are:banded banded quartzo-feldspathic quartzo-feldspathic gneiss gneiss and and amphibolite amphibolite (the (the Basal Basal Group Group of ofWeidman, Weidman, 1907); 1907); medium-grained tonalite; aa series series of fine-grained medium-grained tonalite; fine-grained tonalite dikes, dikes, less mafic mafic with with decreasing age of of intrusion; intrusion; maIic mafic dikes; dikes; and and diabase. diabase. All All these rock rock types types except except diabase have have been been recrystallized recrystallized under under middle middle grades grades of ofmetamorphism. metamorphism. for diabase Quartzo-feldspathic gneiss and and tonalites Quartzo-feldspathic gneiss tonalites contain contain quartz, quartz, microcline, microcline, plagioclase plagioclase (oligoclase to andesine), biotite, hornblende, epidote, sphene, sphene, and and opaques; opaques; amphibolite amphibolite and mafic mafic dikes dikes contain contain hornblende, hornblende, plagioclase plagioclase (andesirie (andesine to labradolabradoite and rite), and and sphene sphene +=blot biotite and epidote. rite), An early An early deformation deformation produced produced isoclinal isoclinal folds, folds, F1 F 1 ,' and a a penetrative penetrative foliation, SS,l' inin the is parallel to to compositoinal foliation, thebanded banded gneiss. gneiss. S S1 is parallel compositoinalbanding, banding, S0, SO' except in fold fold hinges, where So S0isistransected transected by by St' S1. A later deformation except hinges, where deformation produced producea broad open folds, folds, F2' F2, in the at aa high broad open the gneiss, gneiss, with with axial axial surTaces surfaces at high angle angle to to Sl' The gneiss contains a pronounced mineral lineation, L1, parallel to F1 and F2 fold F1 foW axes. gneiss contains pronounced mineral lineation, L l' The Ic dikes, dikes, although although intrusive intrusive mto into the gneiss The tonalites and and maf mafic gneiss and and discordant, at at least in least in part, part, to tostructures structuresininthe thegneiss, gneiss,contain containmineral mineral lineations lineations which which are parallel steeply to the parallel to the the linear linear elements elements in in the thegneiss, gneiss, plunging plunging steeply the southeast. southeast. In addition, S1 is medium-grained tonalite. is present in the medium-grained A A U-Pb U-Pb age of of 1900 1900 m.y. m.y. from from zircons zircons in in the themedium-grained medium-grained torialite tonalite (Van (Van Schmus, et et al, al, 1975) indicates that intrusion 1975) indicates intrusion and and deformation deformation occurred during during the Schmus, Penokean Orogeny. Orogeny. Although the banded gneiss may may be be Archean Archean inin age, age, itit was Penokean Although the banded gneiss was reworked during duringthe the Penokean PenokeanOrogeny, Orogeny,and andthe the predominant predominantstructures structures inin itit were worked produced produced during duringthat that event. REFERENCES REFERENCES Weidman, S., S., 1907, 1907, The The geology geologyofofnorth north central central Wisconsin, Bull. No. No. 16, 16, Wis. Wis. Geol. Geol. Weidman, Wisconsin, Bull. Na tural History Survey. Survey. Natural 1975, Geology Geology and and Rb-Sr Van Schmus, W.R., W.R., et Rb-Sr chronology chronology of Middle et al., aL., 1975, Van Schmus, Precambrian rocks Precambrian rocks in eastern eastern and and central centralWisconsin: Wisconsin: Geol. Geol. Soc. Soc. Am. Am. Bull. Bull. 86, 86, 1255-1265. 1255- 1265. 38 38 �GEOPHYSICAL PROSPECTING PROSPECTING OFF OFFKEWEENAW KEWEENAW PENINSULA PENINSULA Robert Robert P. P. Meyer, Meyer, 3. J. Robert Robert Moore, Moore, Edgardo Edgardo L. L. Nebrija Nebrija and and Charles Charles T. T.Young, Young, Department and Polar Department of of Geology Geology & &. Geophysics, Geophysics, Geophysical Geophysical and Polar Research Research Center, Center, University of of Wisconsin, Wisconsin, Madison Madison 53706 53706 University ABSTRACT With SeaGrant Grant sponsorship, sponsorship, we we have With NOAA-Wisconsin NOAA-Wisconsin Sea have been been conducting conducting experiments using using towed resistivity resistivity and andactive-source active-sourceaudiomagnetotelluric audiomagnetotelluric(AMT) (AMT) measurements measurements and and magnetic magnetic and and high-resolution high-resolution seismic seismic profiling profiling to explore explore for for copper copper deposits deposits offshore offshore of Keweenaw Keweenaw Peninsula. Peninsula. Among Among the areas areas studied studied were were Copper Copper Harbor Harbor and and Silver Silver Island Island where where there there are areknown known underwater underwater copper copper veins, veins, Great Sand Sand Bay Bay where where offshore offshore extensions extensions of of onshore onshore copper-bearing copper-bearing fissures fissures may may exist, Five-Mile Points where where we we searched searched for for a chalcocite deposit Five-Mile and and Seven-Mile Seven-Mile Points deposit within and Bete Bete Grise where aa potential placer Nonesuch Shale, Shale, and Grise Bay Bay where placer deposit deposit within the Nonesuch may exist. may Surface- and bottom-towed bottom-towed arrays arrays were were both both used used in in resistivity resistivityprofiling. profiling. In In 1975, AM AMT tests were were started started using 1975, T tests using a 150 150 m diameter circular circular loop loop of of wire wire laid laid on on the lake lake bottom bottom and and excited excited by by aa 400 400 Hz Hz AC AC generator generator as source. source. With With the the ship's ship's position regulated by by electronic electronic navigation, concentric arcs arcs were traversed about position regulated navigation, concentric about the loop the loop to to measure measure the the vertical vertical magnetic magnetic field, field, radial radial magnetic magnetic field, field, and and Both methods yielded distinct and reproducible anomalies field. Both methods yielded and reproducible anomalies tangential electric field. in apparent apparent resistivity resistivity and and E/H E/H ratios ratiosover overknown known copper copper veins veins at at Copper Copper Harbor Harbor A zone and anomalies over over expected expected lithologic lithologic contacts. zone of heavyheavyand correlatable anomalies mineral concentrations inside with towed towed resistivity mineral inside Great Great Sand Sand Bay Bay was was discovered discovered with The apparent and verified verified with with AMT. AMT. The apparent resistivity resistivity correlates inversely inversely with with the the and A heavy-mineral of the sands. sands. A probably probably underwater underwater vein vein was was also also heavy-mineral content content of At discovered in in this area. At Five-Mile Five-Mile and and Seven-Mile Seven-Mile Points, Points, the the offshore offshore discovered extensions of of the Nonesuch Shale were were mapped mapped and and structures structures favorable favorable to copper extensions Nonesuch Shale copper Both methods methods are are strongly delineated. Both strongly affected affected by by topography. topography. deposition deposition were were delineated. For For resistivity profiling, profiling, aa first-order first-order correction correctionfor fortopography topography has has been been developed developed and applied. High-resolution seismic seismic and and magnetic magnetic profiling profiling at at Bete Grise Bay Bay delineated a High-resolution basin off the Montreal Montreal River River characterized characterized from from grab grabsamples samples by byanomalous anomalous basin off the concentrations of of trace trace metals that decrease concentrations decrease outward outward from from the center of of the filled filled Within this this area area we also delineated offshore manifestation manifestation of of the basin. Within we also delineated aa logical logical offshore Keweenaw Fault. Fault. Whether Keweenaw Whether the anomalies anomalies represent the lake lake bottom bottom expression expression of a deeper hydrothermal deposit, a placer deeper placer deposit deposit formed formed during during lower lake levels from results from materials delivered by the Montreal Montreal River, or results from more more current current by the enrichment of of surficial sediments enrichment sediments is is not not presently presently known, known, and and this this question question awaits awaits the opportunity for physical sampling at at depth. depth. the opportunity for physical sampling 39 39 �DIAMOND DRILLING IN ENVIRONMENTALLY DIAMOND ENVIRONMENTALLY SENSITIVE SENSITIVE AREAS AREAS — ENVIRONMENTAL IMPACT: MONITORING MONITORING AND AND ASSESSMENT ASSESSMENT M.G. Mudrey, Jr., Wisconsin Geological and Natural Geological and Natural History Survey, 1815 University Avenue, Avenue, Madison, Madison, Wisconsin Wisconsin53706, 53706,Bruce BruceC.C. Parker, Parker, Department of University of Biology, Virginia Virginia Polytechnic Polytechnic Institute Institute and State Biology, State University, University, Blacksburg, Blacksburg, Virginia Virginia 24601, Keros State Geological Cartwright, Illinois Illinois State Geological Survey, Survey, Natural Natural Resources Resources 24601, Keros Cartwright, Building, Urbana, Urbana, Illinois Illinois 61801, 61801, and and Lyle Lyle D. Building, D. McGinnis, McGinnis, Department of of Geology, Geology, Northern illinois Illinois University, DeKaib, DeKalb, illinois Illinois 60115 60115 ABSTRACT A drilling program program can can be sophisticated exploratory exploratory diamond diamond drilling be mounted mounted to to A sophisticated moderate modera te depths, depths, and and environmental environmental disturbance disturbance minimized minimized in aa conscientious conscientious program involving impact impact assessment, assessment, training, training, and and real-time feedback program involving feedback among among all parties. Although not normally Although not normally the case case with with exploratory exploratory drilling, drilling, environmental environmental disturbance can occur occur in in sensitive sensitive areas areassuch suchas aswilderness wilderness areas, areas,public public park park lands, lands, and delicate, delicate, unique regions,such suchasasthe the polar polar regions. regions. One One factor, factor, of course, and unique regions, course, is the public public fear fear that thatthe theproposed proposedexploratory exploratorydrilling drilling program program might might irreversibly irreversibly disturb environmental conditions in areas noted for their recreational and disturb environmental conditions in areas noted for their recreational and scientific value. AA secondary value. secondary fear fear isis that thatexploitable exploitable natural natural resources resources will will be be found, found, and and that that they they will will be be developed developed causing major major impact to the the local local environment. environment. It is is important important to to recognize recognize that that the theconcept concept of of no no impact impact is is an an unrealizeable unrealizeable The objective objective of of all human goal. The human all impact impact statements statements is is to to minimize minimize or or reduce reduce potential adverse adverse impacts impacts to to the theenvironment, environment, whenever whenever and and as as far far as aspossible possible and and practical. We propose to to address address only only the the design design and and implementation implementation of of an an environmentWe propose ally exploratory drilling drilling program programinin aa sensitive sensitive area, area, the ally responsible responsible exploratory the dry dry valley valley From lanuary region of of Antarctica. region Antarctica. From January 1973 1973 until until December December 1975, 1975, aa comprehensive comprehensive diamond drilling drilling program program inin antarctic antarctic permafrost diamond permafrost and and under under severe severe environmental environmental Dry Valley Drilling Project restraints — restraints - the Dry Project— - was carred on. on. A A total total of of 13 13 months months of resulted inin the the recovery of over meters of of core of drilling drilling resulted recovery of over 2100 2100 meters core at 15 15 sites. sites. Although scientific scientific in in objectives, the Although the international, international, multidisciplinary multidisciplinary program, program, and and analysis are are applicable applicable to resource-oriented drilling its techniques techniques of of environmental environmental analysis drilling programs in other other areas programs in areas of of environmental environmental and and public public concern, concern, such such as as the the scenic scenic vistas of the Lake Lake Superior Superior region. The evaluation, after after identification of of the target of environmental environmental evaluation, target The first stage of sites, was was the the preparation preparation of of an anenvironmental environmental assessment, assessment, in in which which the theproposed proposed engineering operations plans, environmental impacts impacts were engineering operations plans, and and possible possible environmental were identified. These were were addressed addressed by by an an impact impact matrix which These which identified identified all projected projected actions extent, and Probability, areal extent, environment. and and all characteristics of the environment. significance were were assessed assessed atat this significance this time time by by an an impact impact committee committee consisting consisting of of environmentalists, project engineers, environmentalists, engineers, and and other other knowlegeable knowlegeable scientists. Potential environmental impacts impacts were were identified, identified, and environmental and revision revision of proposed proposed operations operations were made without without undue hardshiptoto the the environment environment or or to to the the drilling drilling contractor, contractor, in as made undue hardship much as no no operations operations had had yet yet started. started. much as Subsequently,appropriate appropriate documents documentswere weresubmitted submittedfor for review review to to governSubsequently, governQuestions raised raised were were addressed mental bodies. bodies. Questions addressed by by the environmental environmental committee. Pertinent documents Pertinent documents directly directly addressed addressed the proposed proposed program, program, and and the the language language Technical details details were were appended. appended. An was directed directed to the the general general public. public. Technical An effort was was made to to make make the the main was made main text of of the the document document readable readable and and concise. 40 �I In In the case case of of DVDP, DVDP, the antarctic antarctic soil soil and and lake lake ecosystems ecosystems are are particularly particularly delicate, and and consequently consequently vulnerable vulnerable to any any human human activity. activity. An An environmental environmental of each scientist scientist on on the the drill site, and and prior prior environmental environmental discussion discussion of each site by by scientists scientists and and drill drill team teampersonnel personnel comprised comprised the thebasis basis for forthe theDVDP DVDP environmental environmental An protection program. program. An operations operations procedure procedure and and monitoring monitoring scheme scheme was was implemented to detect implemented to detect and and control control environmental environmental impact. impact. Monitoring Monitoring before, before, during, during, and after after the thedrilling drillingoperations operationsidentified identifiedenvironmental environmentalchanges changescaused causedby by the activities at all all sites, sites, and and those those results results were were reported reported to to enhance enhance the accuracy accuracy of the the predictive predictive model, model, the Environmental Environmental Impact Impact Appraisal. Appraisal. One One objective was was to to prevent prevent or reduce reduce impacts impacts by by DVDP, DVDP, and and thus thus assist assist planning planning for any any future future projects in Antarctica. projects in Antarctica. For DVDP, critical environmental DVDP, critical environmental limitations included included no no surface transport, transport, minimal crew size, size, few few drilling options with with respect to minimal crew drilling options to equipment equipment and and circulating circulating fluids, fluids, an absolute absolute requirement requirement that that all all waste waste and and equipment equipment be be removed removed from from the be in site areas, areas, and and that that an aninteractive interactiveenvironmental environmental monitoring monitoring program program be in operation. constant operation. 41 �SYENITE OF CENTRAL THE WAUSAU WAUSAU SYENITE CENTRAL WISCONSIN WISCONSIN Myers, Paul Department of ofGeology, Geology, Washington Washington State State University, University, Pullman, Pullman, Myers, Paul E., E., Department Washington 99163 99163 ABSTRACT The Wausau syenite-quartzsyenite syenite pluton pluton inin two two segments and the more The Wausau syenite-quartz segments and more alkalic Stettin Stettin syenite syenite pluton pluton are areexposed exposed west westof ofthe theWisconsin Wisconsin River River near near Wausau Wausau in central These Middle plutons are in central Wisconsin. Wisconsin. These Middle Precambrian Precambrian (1650 (1650 ÷ + 50 50 m.y.) plutons concentrically zoned zoned and and show concentrically show a distinct distinct north-northeasterly north-northeasterly elongation. elongation. Each pluton has has a contact pluton contact metamorphic metamorphic zone zone of of fenitized fenitized wall wall rocks, rocks, an an alkalic, alkalic, laminated, xenolith-rich laminated, xenolith-rich wall wall zone, zone, an an intermediate intermediate zone, zone, and and a core. core. Silica content increases increases inward inward in each pluton. pluton. The southern southern segment segment of of the Wausau pluton isis circular circular in plan with a diameter Wausau pluton diameter The of eight miles. half of of this this caldera-like caldera-like structure were of miles. Although Although the core core and and south half were intruded the Ninemile preserved as as a intruded by by granite granite of the Ninemile pluton, pluton, its structure is preserved discontinuousring ringofoflarge largexenoliths xenolithsfive fivemiles milesinindiameter. diameter. The discontinuous The largest of of these these over two miles in the xenoliths xenoliths -- the Rib Mountain Mountain quartzite quartzite — - is over miles long. long. Bedding Bedding in The top top of xenolith dips very very steeply toward the the granite xenolith dips steeply southward southward toward granite core. core. The of the the xenolith has has been eroded xenolith eroded leaving leaving aa keel-shaped keel-shaped mass, mass, slightly slightly convex convex northward, northward, and surrounded at depth depth by by quartz quartz syenite and surrounded at syenite of the the crescentic crescentic intermediate intermediate zone. zone. Quartzite xenoliths xenoliths near near intrusive intrusive contacts contacts are aretypically typicallyveined veinedand and impregnated impregnated by by Pyroxene and amphibole syenite commonly containing volcanic K-feldspar. Pyroxene and amphibole syenite commonly containing volcanic xenoliths, form form a discontinuous outer rim rim (wall zone) of of the southern segment. discontinuous outer (wall zone) xenoliths, The northern northern segment segment of of the Wausau is semicircular The Wausau pluton pluton is semicircular in in plan plan with with its truncated southern southern edge edge along along the Rib Rib River. River. The TheStettin Stettinpluton plutonisiscontiguous contiguous with with it on internal structure are similar on the northwest. northwest. Although Although its size and and internal similar to that that of of the southern southern segment, segment, its intermediate intermediate zone zone consists consists of coarse coarse gray gray syenite, syenite, and and volcanic xenoliths xenoliths predominate. predominate. The probably represents represents aa The older older northern segment segment probably volcanic caldera caldera structure, structure, which which was was partially partially destroyed destroyed by by intrusion intrusion of of the the southern southern segment. The Stettin pluton The pluton is is oval oval in in plan plan with with dimensions dimensions of of 5.0 5.0 x 3.5 miles. Three major in mapping were: (1) major zones zones distinguished distinguished in mapping were: (1) a wall wall zone zone comprising comprising aplitic aplitic biotite syenite, an intermediate syenite, nepheline nepheline syenite syenite gneiss, gneiss, and "tabular syenite", (2) (2) an zone, zone, aplitic aplitic to to pegmatitic pegmatitic amphibole amphibole and and pyroxene pyroxene syenite syenite with with swirled swirled flow flow lineation, and and (3) (3) a circular circular core zone zone one one mile mile in in diameter diameter comprising comprising aa rim rim of of magnetite-rich nepheline-hedenbergite-fayalite nepheline-hedenbergite-fayaiite syenite,andandananinner inner core core of magnetite-rich syenite, pyroxene syenite. Both Both the Wausau Wausau and and Stettin Stettin plutons plutons possess possess strongly strongly metasomatized, metasomatized, but but Concentric cataclastic unassimilated xenolith-rich xenolith-rich wall unassimilated wall zones. zones. Concentric catac1astic lamination lamination was was developed by displacements accompanying accompanying the the forceful emplacement of developed by high-angle high-angle displacements of these plutons. plutons. Subsequently, Subsequently, more more passive passive intrusion intrusion of of the the Ninemile Ninemile granite granite caused caused a partial partial foundering foundering of the the southern southern part part of of the theWausau Wausau pluton. pluton. 42 �MODIFICATION MODIFICATION OF ENGINEERING ENGINEERING PROPERTIES OF ST. ST. PETER PETER SANDSTONE SANDSTONE C.R. C.R. Nelson Nelson and and D.H. D.H. Yardley, Yardley, Department Department of of Civil Civil and andMineral MineralEngineering, Engineering, University University of of Minnesota, Minnesota,Minneapolis, Minneapolis, Minnesota Minnesota55455 55455 ABSTRACT ABSTRACT The Peter sandstone sandstone is is aa formation formation of of major major geotechnical geotechnical importance importance in in The St. Peter the Twin Twin City Metropolitan Metropolitan area area as as well well as as elsewhere elsewherein inMinnesota Minnesota and and some some nearby nearby states. Nearly Nearly 200 200 miles miles of of tunnels tunnels and and other other openings openings have have already already been been constructed in it in in the the Metro Metro area. The The St. Peter Peter is is aa rather rathermassive, massive,weakly weakly cemented, cemented, very very pure pure sandstone sandstone of of 98.5% 98.5% - 99% 99% SiO2. Si0 2 • The compressive strength strength varies varies between between 670 670 and and 2800 2800 psi psi in in The compressive harder zones, zones, but but in In softer softer zones zones ititcommonly commonly varies varies from from less less than than100 100to to300 300psi, psi, hence some openings openings inin itit will hence while while some will support support themselves themselves most most need need some some type of of support. Because Because most most of of its strength strength is is aa result result of of compaction compaction and and grain grain is water-sensitive to the the degree that if water interlocking, interlocking, it is water-sensitive to degree that water agitates agitates the the grains grains St. Peter has much of the sandstone will deteriorate deteriorate r':!Jidly. raidly. The much of sandstone will The St. has aa porosity porosity of of per second. about 28% 28% and and a permeability permeability of 3.5 3.5 xx 10 10 cm cm per second. The The grains grains are quite quite about rounded, have aa frosted frosted surface and rounded, have and a diameter diameter of of 0.1 0.1 mm mm to to 0.5 0.5 mm. mm. A spray-grouting technique has has been been developed by the senior author, spray-grouting technique developed by author, using using a silicate-based liquid liquid that that can permeate for a few silicate-based permeate into into exposed exposed sandstone sandstone for few inches. inches. This forms aa hardened of sandstone with aa compressive strength on on the order This forms hardened shell shell of sandstone with compressive strength of 1500 psi in in the the soft zones. Test of 1500 psi Test patches patchesin inplace placefor for 33years yearsshow show no no evidence evidence of deterioration. This system of artificially for rehabilitaThis system artificially stengthening stengthening sandstone sandstone is being used used for It is also being used as the main excavation support tion tunnels. is also being used the main excavation support on on aa 10 10 tion of utility tunnels. foot tunnel where itit has the use at a foot tunnel where has replaced replaced the use of of steel steel rings rings and and oak oak lagging lagging at substantial cost reduction. substantial reduction. Elimination Eliminationof ofsteel steeland andwood wood support support makes makes itit possible possible to pour so that when to pour aa final final concrete concrete lining lining directly directly against against the sandstone sandstone so when the tunnel is is pressurized the resistance tunnel pressurized the resistance of of the the coupled coupled sandstone sandstone wall wall will will so so greatly decrease lining lining deformation deformation that that steel reinforcing decrease reinforcing is is not not required. required. Spray-hardening Spray-hardening also makes makesitit possible possiblefor forthe the first first time to the also time to apply apply shotcrete shotcrete to the St. St. Peter Peter sandstone in in this this area. sandstone It has has been estimated that that the thecost costsavings savings on on one one large large tunnel, tunnel, and and for for one one utility utility tunnel tunnel repair project, project, both both in in progress, progress, will will be be about about 1.3 1.3 million million dollars. dollars. Support funds funds of of less than from the NSF, program have have led led to the Support than $100,000 $100,000 from NSF, RANN RANN program the development. 43 �ANATOMY ANATOMY OF A WELL-COVERED WELL-COVERED GREENSTONE BELT, BELT, NORTHWESTERN MINNESOTA MINNESOTA Richard W. W. Ojakangas, University of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota55812 55812 ABSTRACT The rocks of of the Birchdale-Indus Birchdale-Indus area are part part of of aapoorly-exposed poorly-exposed volcanicvolcanicThe rocks sedimentary sequence sedimentary sequence within within the the Wabigoon Wabigoon Volcanic Volcanic Belt. Belt. The bedrock is Early Early The bedrock Precambrian in in age, age, and includes mafic mafic to intermediate Precambrian and includes intermediate flows flows and and intrusives; felsic dikes, dikes, agglomerates, agglomerates, tuffs and and volcaniclastic volcaniclastic rocks; rocks; iron-formation iron-formation and and associated associated metasediments; and granitic granitic rocks of Algoman age. All of these lithologies are cut metasediments; and rocks of Algoman age. All of lithologies are by by northwest-trending Middle Middle Precambrian mafic mafic dikes. dikes. The The area is is well-covered well-covered by by Pleistocene deposits. deposits. The volcanic-sedimentary sequence has has been been isoclinally folded; northeastThe volcanic-sedimentary sequence isoclinally folded; trending beddingand and foliations foliations are are generally generally steep steep to to vertical. trending bedding vertical. One One doublydoubly- plunging anticline and and one one syncline syncline have have been been mapped mappedwithin withinthe thearea. area. AA second plunging anticline second folding with with more folding more northerly-trending northerly-trending fold fold axes is is indicated indicated by by some some general general and and detailed relationships. sets of faults relationships. Three Three sets faults and and fractrures fractrures are aredocumented; documented; the the first set set trends trends east-west, east-west, the the second second northwest, northwest, and and the third third northeast. northeast. All of the Lower Lower Precambrian rocks rocks have have been been metamorphosed metamorphosed to amphibolite amphibolite grade. grade. Synthesis ofof the the geology of the Birchdale-Indus area with with that that of the Synthesis geology of Birchdale-Indus area the Emo Emo area in allows an an interpretation of in adjacent adjacent Ontario Ontario (Fletcher (Fletcher arid and Irvine, Irvine, 1954) 1954) allows of the the Mafic and and intermediate volcanic development of the volcanic development of volcanic accumulation. accumulation. Mafic volcanic and and intrusive rocks apparently apparently constitute constitute the lowest intrusive rocks lowest stratigraphic stratigraphic unit. unit. An An explosive felsic volcanic volcanic center, center, marked marked by by abundant abundant agglomerates, developed developed upon upon the mafic platform and Emo. Emo. Felsic tuffs, volcaniclastics, platform in the the vicinity vicinity of of Birchdale, Birchdale, Indus Indus and volcaniclastics, and iron-formation iron-formation were were deposited deposited outward outward from from this this center. center. and The Birchdale-Indus Birchdale-Indusarea, area, and and areas areas to to the west and The and south, have been actively explored for for base base metal for the past explored metal sulfide sulfide deposits deposits for past decade. decade. Thick Thick zones zones of of massive, sub-massive, sub-massive, and and dissemianted dissemianted pyrite and/or pyrrhotite have have been been penetrated at at several several localities, localities,but butcopper copperand andzinc zincminerals minerals have have not not been been found found Several of the drilled iron-sulfide bodies are associated in economic economic quantities. quantities. Several of drilled iron-sulfide bodies associated in with oxide iron-formation. REFERENCES CITED CITED Fletcher, Fletcher, G.L., G.L., and and Irvine, Irvine, T.N., T.N., 1954, 1954, Geology Geology of the Emo Emo area: area: Ontario OntarioDivision Division of of Mines 63rd annual annual report, report, V. V. LXIII, LXIII, part part5,5,3636p.p.plus plusmap mapNo. No.1954—2, 1954-2, scale scale 11 Mines 63rd inch to 11 mile. inch 44 �CARBON IN METAMORPHOSED SEDIMENTS CARBON SEDIMENTS FROM ISUA, ISUA, WEST GREENLAND WEST GREENLAND FROM Eugene C. C. Perry, Perry, 3r. Jr. and and Syed Syed Neaz Neaz Ahmad, Ahmad, Department Department of of Geology, Geology, Northern Northern Eugene illinois University, DeKaib, Illinois DeKalb, illinois Illinois 60115 60115 ABSTRACT ABSTRACT 0/00 ~. aphitic carbon carbon (S13 (6'3C vs. PDB) About 2.5% §aphitic C == -16.1 0100 PDB)occurs occurs in in aa specimen from the the 3.7 10 year year old at Isua, Greenland. The from 3.7 x 10 old supracrustal supracrustal sequence sequence at Isua, West West Greenland. The specimen, which whichcontains containsquartz, quartz,amphibole, amphibole,and andminor minormagnetite magnetiteand and pyrite, pyrite, is specimen, is associated with with a thick associated thick succession succession of of metamorphosed metamorphosed chert and and magnetite-bearing magnetite-bearing iron-formationand andwithin within2.4 2.4km kmacross acrossstrike strikeofof aa thick thick quartz-magnetite iron-formation quartz-magnetite unit unit containing sufficient sufficient iron iron to to be commercial significance. significance. Rocks in the the containing be of possible possible commercial Rocks in area have been metamorphosed to amphibolite facies and area metamorphosed to amphibolite facies and are sufficiently sufficiently sheared sheared so that that primary textures are are obliterated. so primary textures Carbonaceous organic organic matter matter is a common Carbonaceous common constituent of of iron-formation, iron-formation, and and it has has been suggested that the iron oxide of iron-formation been suggested that the iron oxide of iron-formation is aa biogeneic biogeneic facies ironprecipitate. Thus, Thus, the theassociation association of of carbonaceous carbonaceous material material with with oxide oxide facies for mationatat Isua Isua isis consistent with an gganic formation consistent with larganicorigin origin for1 for; this ancient ancient carbon. carbon. However, the the Isua Isua carbon carbon is However, is enriched enriched in in jc about 15 15 0/00 0 00 compared compared to C by about to later Precambrain material material of of known knownbiogneic biogneicorigin. origin. Since Since metamo~phism metamophism accompanied Precambrain accompanied /oo carbon reactions could by isotope-fractionating reactions could produce carbon isotope isotope produce a 15 0/00 fractionation, the stratigraphic fractionation, stratigraphic association association of of this this carbon carbon with with iron-formation iron-formation may may to its origin than is its present be a more reliable guide guide to present isotopic isotopic composition. composition. 45 45 I t �OLD PRECAMBRIAN W GNEISSES GNEISSES IN IN NORTHERN MICHIGAN OLD Zell E. ZeU E. Peterman, Peterman, Robert Robert E. E. Zartman, Zartman, and andP.K. P.K.Sims, Sims,U.S. U.S.Geolgoical Geolgoical Survey, Survey, Denver, Colorado Colorado 80225 80225 ABSTRACT dating of of gneisses in the western Radiometric dating gneisses in western part part of of northern northern Michigan Michigan has confirmedthe the presence presenceofof an an ancient ancient sialic sialic terrane terrane that formed confirmed formed more more than than 3400 3400 m.y. ago. An antiformal antiformal structure structure in in the the Watersmeet area contains contains aa core core of m.y. ago. An Watersmeet area of tonalitic to to granitic surrounded by by folded tonalitic granitic gneiss gneiss that that is surrounded folded and and metamorphsed metamorphsed Precambrian X graywackes. graywackes. The is cataclasitcal!y cataclasitcally deformed and recrystalPrecambrian X The gneiss gneiss is deformed and lized, and and geochronologic geochronologicdata datareflect reflectthe the effects effects of of severe tectonic and lized, and thermal thermal events. Whole-rock Whole-rock Rb-Sr Rb-Sr systems systems are are highly highly disturbed, disturbed, but but data datafor forsamples samplesfrom from two localities localitiesdefine definesecondary secondary isochrons of aut 00 m.y. two isochrons of 19ut m.y. AAsubstantially substantially older older age of the Sr/ Sr age the gneiss gneiss is is indicated indicated by by high high initial Sri 0.773 to 0.717 0.717 for Sr ratios of 0.773 These high high i~7ial int7ial ratios ratios resulted resulted from from local the two two isochrons. isochrons. These local redistribution redistribution of previously generated radiogenic Sr during the major previously radiogenic Sr during the major period period of of cataclasis cataclasis and and Metamorphismofof adjacent adjacent Precambrian X rocks recrystallization. Metamorphism Precambrian X rocks occurred occurred synchronouslywith withthe the reactivation and mobilization of the gneiss synchronously mobilization of gneiss as suggested suggested by 1810 m.y. m.y. isochron obtained on on four an 1810 isochron obtained four whole-rock whole-rock samples samples of graywacke of graywacke immediately adjacent adjacent to to the gneiss along the the northern northern contact. contact. immediately gneiss along U-Pb data obtained on zircon from the gneisses also reflect reflect the U-Pb data obtained on zircon separated separated from gneisses also complexgeology geologyhistory historybut butclearly clearlyplace placethe the time time of of primary crystallization at complex primary crystallization 90 rn~~b agoago or more. Three size fractions ofofzircon ~890 or more. Three size fractions zirconfrom froma atonalititc tonalititcgneiss gneiss have have Pb ages ages ranging ranging from from 3310 to 3370 m.y. and Pb/ Pb 3310 to 3370 m.y. and a primary primary age age of of about about 3500 3500 m.y. is is suggested. suggested. Zircon Zircon from from aa compositionally compositionally similar ~~t mU<i~&;10r20tj;or~ly m.y. defogpd aj recrystallized phase Pb! Pb! U, U, def02~d ~ recrystallized phaseofofthe thegneiss gneissyields yields Ph/ Pb/ Pb ages that are Pb/ Pb ages are concordant concordant at at 1760 1760 m.y. This This lower lower age age agrees agrees with with and Pb! Rb-Srages ages and andapparently apparently indicates indicates total total resetting or the whole-rock whole-rock Rb-Sr or perhaps perhaps even even crystallization of the zircon during this metamorphic episode. Data for two zircon crystallization of zircon during this metamorphic episode. Data two fractions from aa leucocratic phase of of the the gneiss gneiss plot plot on on aa chord fractions from leucocratic phase chord that intersects intersects concordia at about data may indicate the the presence concordia about 2600 2600 m.y. m.y. These These data may indicate presence of granitic granitic intrusions that were intrusions that were emplaced emplaced in in the the older oldergneisses gneisses during during the theAlgoman Algoman orogeny. orogeny. About 2710 m.y.—old About 20 20 km km northwest northwest of of the thegneiss gneissatatWatersmeet, Watersmeet,thethe 2710 m.y.-old Puritan Puritan Quartz Monzonite and Precambrian Quartz Monzonite and Precambrian W W metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks form aa greenstone-granite form greenstone-granite terrane that that evolved evolved in an ensimatic ensimatic environment. environment. The The presence of Algoman granitic rocks rocksininthe the older older gneiss gneiss terrane terrane may presence of Algoman granitic may indicate indicate that that both blocks blocks were in juxtaposition juxtaposition at at 2600 2600 to to 2700 2700 m.y. m.y. ago ago and and subsequently formed a continuous continuous and and coherent coherent sialic sialic basement basement to the the Precambrian Precambrian XX sedimentary sedimentary basins. tgOO 46 U �APPROACH TO A SYSTEMS SYSTEMS APPROACH TO ENVIRONMENTAL ENVIRONMENTAL GEOLOGY H.O. of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, H.O. Pfannkuch, Pfannkuch, Department of Minneapolis, Minnesota 55455 55455 ABSTRACT term "environmental geology" has has been been loosely loosely applied applied to to situations The term "environmental geology" situations ranging from pure problems to to those ranging from pure engineering engineering problems those of of traditional traditional general general geology. geology. The concept concept needs needs clarification clarification and and definition in order order to to provide the reference The definition in provide the reference space in in which solutionsfor for the the most most pressing pressing problems problemscan canbebeattempted. attempted. This space which solutions This is attempted attempted by by aa systems systems approach approach where where the the three three interacting interactingprincipal principalcomponents components are human on aa global human ecology, ecology, geology geology on global scale, and and clutural clutural anthroplogy anthroplogy from from aa socio-economic point of view. socio-economic The based on approach is based on an an The approach analogy argument, argument, that is that human analogy human ecosystems behave inin a similar ecosystems behave similar way way as as other otherecosystems. ecosystems. This This means means that ecosystem concepts concepts such ecosystem such as structure, structure, process process dynamics dynamics and and evolutionary evolutionary trends trends from to mature, from young young and and unstable unstable but highly highly productive productive to mature, complex complex and and stable stable systems can can be used systems used as parallels. The Theinterface interfacewith withgeology geologyisisprovided provided by by global global material cycles and energy flow processes. processes. The impact of material energy flow The impact of interaction is is measured measured in a first order simple mass mass change changeto to total total mass, in order approximation approximation by by simple mass, and and rate change change It has to geologic geologic rate relationships. relationships. It has to be refined to include include effects of of additivity additivity and accumulation, and those those of of stability and accumulation, and stability of of feedback feedback relations. relations. In In the the latter latter category fall the the triggering triggering effects effectsofofpossibly possiblysmall small temperature temperaturechanges changeson on world world Limitations of geological nature can be climatic changes. be expressed expressed by consumption or or use use rates, such as in resources where rate of consumption of formation formation is is compared compared to rate to rate of of consumption consumption or or with with the the carrying carrying capacity capacity of of the the earth earthwhere where loading loading or regeneration rates. rates are are compared compared to dissipation dissipation or In In the socio-economic socio-economic context, environmental environmental geology geology has two two contributions contributions to make. help make environmentally to make. On On a short short term term basis basis itithas hasto to help make environmentallysound sound compromisesthat that can can be be achieved achieved within within the the present present structure of time time and and space space compromises references in in the the decision decision making making process. process. This, This, however, however, is only only a temporary temporary and and transitional solution, solution, in in the end will have have to to provide transitional end environmental environmental geology geology will provide the the basis on on which new and and consistent consistent time time and basis which new and space scales will will have to be be developed developed for environmentally environmentally acceptable acceptable decision decision making making processes. processes. 47 I �ENVIRONMENTAL IMPLICATIONS IMPLICATIONS OF OF GROUNDW GROUNDWATER-LAKE ENVIRONMENTAL ATER-LAKE LAND USE USE APPLICATION INTERACTION WITH WITH LAND Dave Pollack Dave Pollack and and H.O. H.O. Pfannkuch, Pfannkuch, Department Department of ofGeology Geology and andGeophysics, Geophysics, University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT Many lakes, if not Many the majority, majority, have have to be viewed viewed as of and and an an not the to be as part part of expression of of local local and and regional groundwater flow flow systems. systems. Lake expression regional groundwater Lake level level variations variations are therefore are therefore strongly strongly related related to to watertable watertable fluctuations, fluctuations, especially especially in in lakes lakes Current methods without surface water inlets or outlets. Current methods of of establishing general lake lake water groundwater contribution to the general water balance balance only only give give net net contributions which whichare are insufficient insufficient to to calculate contributions calculate residence residence times of of chemical chemical or or biological inputs. An An areal areal flow biological flow net net method method is is discussed discussed to to calculate calculate absolute absolute amounts of of groundwater inflow and and outflow outflow and and its its spatial amounts groundwater inflow spatial relationships relationships with the the lake. Analysis of aa cross cross section section through through aa lake lake and and its its aquifer shows Analysis of shows that even with a fully lake bed of streamlines streamlines near fully permeable permeable and and uniform uniform lake bed there will will be crowding crowding of the shore, the shore, which which means means relatively relatively higher higher flow flow velocities velocities of of groundwater groundwater and and enhanced transport transport activity in enhanced in this this region. region. Analog Analogand and dimensional dimensional analysis analysis of some some very simple simple cases cases are carried very carried out out to to demonstrate demonstrate the thedependence dependence on on lake-aquifer lake-aquifer geometry and and toto define define the the critical critical parameters. geometry parameters. These These are are thickness thickness of of the the lakelakeaquifer, degree of depth penetration of the lake, and ratio of the aquifer flow aquifer, degree of depth penetration of the lake, and ratio of the aquifer flow section is given given by bythe the lake lake diameter. diameter. Further section to the the lake-aquifer lake-aquifer interface which which is Further increase of of flux large portions of the lake increase flux near near shore shore occurs occurs when when large portions of lake bottom bottom are are sealed by by impermeable sediments. sediments. The The direct environmental environmental implications implications are two two fold: fold: First First it is is necessary necessary to have a clear picture outflow ininorder ordertoto relate relate it to picture of of true true groundwater groundwater inflow inflow and and outflow the into the the total total lake lake budget, budget, this this provides provides insight insight into the relative relative importance importance of of groundwater groundwater carried pollution. pollution. Localization Localization and with high high and identification identification of areas with groundwater flow activity in groundwater flow in the thenear-shore near-shoreregion regionhave haveobvious obvious application application to to land land use planning and regulation regulation such such as as the the implacement of domestic sewage disposal planning and disposal or treatment facilities. The severity treatment facilities. The severity of impact impact depends depends on on length length of of flowpaths, flowpaths, residence time time of of pollutants, or regeneration capacity of of the residence pollutants, and and adsorption adsorption or regeneration capacity hydrogeologic Guidelines are are given given to to classify hydrogeologic unit. unit. Guidelines classify lakes lakes on on a semi-quantitative semi-quantitative basis to the expected basis according according to expected volume volume contribution of the the active activeflow flow region region near near shore. 48 �PETROLOGY AND AND STRUCTURE STRUCTURE OF THE LATE PETROLOGY LATE PRECAMBRIAN PRECAMBRIAN SILVER CREEK CREEK CLIFF AND LAFAYETTE BLUFF BLUFF MAFIC MAFIC SILVER INTRUSIONS, LAKE LAKE COUNTY, MINNESOTA INTRUSIONS, MINNESOTA Neil M. M. Pope, Pope, Department Department of of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Neil Minnesota, 55801 55801 ABSTRACT Approximately4-1/2 4-1/2 Miles Miles northeast northeast of Two Approximately Two Harbors, Harbors, Minnesota, Minnesota, the North North Shore Volcanic VolcanicGroup Groupisisintruded intrudedby bythe the Silver Silver Creek Creek Cliff Cliff sill sill which which trends trends northnorthShore northeast from Cliff for for 66 miles. northeast from Silver Silver Cliff miles. The The Lafayette Lafayette Bluff Bluff sill, sill, approximately approximately 61/2 miles northeast of 1/2 of Two Two Harbors, Harbors, intrudes intrudes the theNorth NorthShore ShoreVolcanic VolcanicGroup Group and and trends north toward the Silver Silver Creek Cliff sill. sill. The Silver Silver Creek Creek Cliff sill The sill is is dominantly dominantly olivine olivine diabase diabase with thin layers layers and and lenses of of olivine-free diabase. lenses diabase. Commonly Commonly aa plagioclase plagioclase - augite pegmatitic pegmatitic facies borders the lenses lenses or or an an entire entire lens be pegmatitic. pegmatitic. The borders the lens may may be The Silver Silver Creek Creek Cliff Cliff sill sill is is approximately approximately 200 200 feet thick thick and and is is conformable conformable with with the the lava lava flows flows throughout throughout most of of its its extent. In In the Encampment Riverarea area the the contact contact of of the sill is steep most Encampment River and crosscuts the flows. This area may represent the feeder zone and crosscuts the flows. This zone for the the sill. sill. The The Lafayette Bluff Bluff sill sill isis an anamygdaloidal amygdaloidal porphyritic porphyritic olivine olivine diabase diabase with with plagioclase phenocrysts which which average average 22 cm plagioclase phenocrysts cm in in length. length. The The sill is is approximately approximately 600 600 feet thick thick and and isisdeformed deformedinto intoa south-plunging a south-plunging syncline syncline and and anticline. anticline. Subsidence of the the underlying flows into into the magma Subsidence of underlying flows magma chamber chamber is is proposed proposed for the the origin of of this deformation. The mineral mineral compositions compositionsof of the the sills sills are similar. The The The olivine olivine diabase diabase of each sill sill normally normally consists consists of an an average average of of66% 66% plagioclase, plagioclase, 12% 12% olivine, olivine, 16% 16% augite, 2% Ca-poor pyroxenes, pyroxenes, 2% 2% altered altered interstitial interstitial material, 2% Ca-poor material,2% 2%opaques opaques (ilmenite (ilmenite and and magnetite), magnetite), and and trace amounts amounts of apatite and and aa interstitial interstitialgranophyric granophyric intergrowth of quartz and alkali feldspar. Field evidence does does not not support support any any definite definite structural relation Field evidence relation between between the the sills. The The Lafayette LafayetteBluff Bluff sill sill isis poorly poorly exposed exposed where it appraches appraches the the Silver Silver Creek Creek Cliff contact between them. AA Cliff sill, and and there there are are no no outcrops outcrops which which show show any any contact between them. whole rock analysis analysis (by (by 5.5. S.S. Goldich, Goldich, 1939) 1939)ofofthe the diabase diabase from from the the Lafayette Lafayette Bluff Bluff whole rock 4.7% MgO. MgO. An An average of of sill shows 46.9%Si0 SiO2, 21.0%A1Al2O, 8.8%total total Fe, and 4.7% sill shows 46.9% , 21.0% 0 , 8.8% 2 2 3 three new new whole whole rock rock analyses analyses of' of the the Silver Silver Creek CreekCliff Cliffolivine olivinediabase diabase shows shows 47.8% Si02, AL,03, 11.2% total Fe, and 6.5% MgO. The Fe/Mg is 1.73 for 0 , 11.2% total Fe, and 6.5% MgO. The FelMg 1.73 47.8% Si0 , 17.5% 17.5% A1 2 3 2 the Silver Silver Creek Creek Clift Clift sill SIll olivine olivine diabase diabase and and 1.86 1.86 for for the the Lafayette Lafayette Bluff Bluit sill sill olivine diabase. Both Both sills sills contain contain normative normative hypersthene. hypersthene. The The olivine diabase diabase olivine diabase. from the Silver indicating the diabase is Silver Creek Creek Cliff Cliff sill sill has has 7.1% 7.1 % normative normative olivine indicating an olivine of the Lafayette olivine tholeiite. tholeiite. The The diabase diabase of Lafayette Bluff Bluff sill sill has has 0.2% 0.2% normative normative quartz the diabase diabase isis on on the border or of quartz suggesting suggesting the border of of oversaturation oversaturation or of being being a quartz tholeitte, tholeitte, despite despite the themodal modal olivine. olivine. 49 �CORRELATIVE IRON-FORMATIONS IRON-FORMATIONS AND AND VOLCANIC VOLCANIC ROCKS ROCKS CORRELATIVE OF PRECAMBRIAN X AGE, AGE, NORTHERN NORTHERN MICHIGAN MICHIGANj J OF PRECAMBRIAN X C. Prinz, William C. Prinz, U.S. U.S. Geological Geological Survey, Survey, National National Center Center -— Stop Stop 954, Reston, Virginia 22092 ABSTRACT The Ironwood, Ironwood, Vulcan, Vulcan,and and Neguanee NeguaneeIron-formations Iron-formations have have long long been been accepted accepted The as correlative. They, along slate and as correlative. They, along with with immediately immediately underlying underlying slate and quartzite quartzite (Palms, Felch, Feich, Siamo, and Ajibik), are sandwiched sandwiched between between shallow-water shallow-water quartzite quartzite (Palms, Siamo, and Ajibik), are and dolomite and dolomite below, below, except where where locally locally absent absent because because of of erosion erosionor ornondeposinondeposition, and tion, and eugeosynclinal eugeosynclinal graywacke graywacke and and slate slate above above (Michigamme, (Michigamme, Copps, Copps, and and Volcanicrocks rocksofof the the Hemlock Formation in in Iron Tyler). Volcanic Hemlock Formation Iron County, County, the Emperor Emperor Volcanic Complex Complexofofthe the eastern eastern Gogebic Gogebic range, range, and and possibly possibly the the volcanic volcanic rocks rocks at Volcanic Blair Lake near Watersmeet also occupy this stratigraphic interval. Except for the the Blair Lake near Watersmeet also occupy this stratigraphic interval. Except for eastern end eastern end of the the Gogebic Gogebic range, the distribution distribution of the the iron-formations iron-formations and and the the volcanic units units is mutually volcanic mutually exclusive. exclusive. Volcanic Iron Volcanicunits unitsare are centrally centrally situated situated in Iron and eastern eastern Gogebic Gogebic Counties, Counties,whereas whereasthe theiron-formations iron-formationsare aretoto the the east east in the the and Marquette and and Menominee Menomineedistricts districts and andtoto the the northwest northwest in in the the Gogebic Gogebic range. range. The Marquette The ironformationsare are relativley relativley thin compared ironformations compared with with the the highly highly variable variable and and locally locally great thicknesses of the volcanic volcanic units. Volcanic rocks of of the Volcanic rocks the Emperor Emperor Volcanic Volcanic Complex Complex are interbedded interbedded with with and and overlie the upper in the the eastern Gogebic upper part part of of the theIronwood Ironwood Iron-formation Iron-formation in Gogebic range, and tuff tuff beds and beds are present in in the the lower lower part part of of the theIronwood Ironwood in the main main part of of the the and the Ironwood range. Thus, Thus, the Emperor Emperor Volcanic Volcanic Complex Complex and Ironwood Iron-formation are, are, at least at least in in part, part,equivalent equivalent in in time. time.Hemlock Hemlockvolcanics, volcanics, on on the the other other hand, hand, have have been been thought thought to be be younger younger than than the the iron-formations. iron-formations. This This isis based based on on correlation correlation of ferruginous conglomerate conglomerate beneath Hemlock with Goodrich Quartzite, Quartzite, of ferruginous beneath the the Hemlock with the Goodrich which suggest here here that that this conglomerate which overlies the Negaunee Negaunee Iron-formation. Iron-formation. I suggest conglomerate is not Goodrich, and that Hemlock rocks correlate correlate with the Emperor, is Goodrich, and Hemlock volcanic volcanic rocks Emperor, and and thus, at at least leastininpart, part,with withthe theIronwood, Ironwood,Vulcan, Vulcan, and and Nagaunee Nagaunee Iron-formations. Iron-formations. I postulate postulate that the the iron-formations iron-formations were were deposited deposited in relatively relatively stable and and slowly subsiding areas areas bordering bordering aa tectonically unstable slowly subsiding unstable and and rapidly rapidly subsiding subsiding basin basin series of troughs in in which or series of basins basins or or troughs which large large volumes volumes of volcanic volcanic material material accumulated. near the eastern accumula ted. The The northwestern northwestern margin margin of the volcanic volcanic basin basin was was near end of the the Gogebic Gogebic range, range, probably probably striking striking west-southwest west-southwestinto intoWisconsin Wisconsin south south of of the main main iron iron range. range. The Theeastern easternmargin margin of of the thebasin basin lay lay approximately approximately along along the boundary between Dickinson and Iron IronCounties. Counties. The may have have extended extended south boundary between Dickinson and The basin basin may and to include and the and southwest southwest to include the the volcanic volcanic units units in in north-central north-central Wisconsin Wisconsin and volcanogenic base-metal The extension extension of of the the basin basin to to volcanogenic base-metal deposits depositsthat that they they contain. contain. The the north north is is uncertain. /Work the Geological /Work done done in cooperation witfE with the Geological Survey Survey Division, Division, Michigan Michigan Department of of Natural Natural Resources. Resources. 50 50 �GEOLOGY AND MINERALOGY GEOLOGY MINERALOGY OF SOME SOME COPPER SULFIDE DEPOSITS NEAR NEAR MOUNT MOUNT BOHEMIA, BOHEMIA, KEWEENAW KEWEENAW COUNTY, MICHIGAN MICHIGAN James M. M. Robertson, Robertson, New New Mexico Mexico Bureau Bureau of of Mines Mines & & Mineral Mineral Resources, Resources, Socorro, Socorro, New Mexico 87801. 87801. ABSTRACT Copper sulfides, in in interesting amounts, have been recently discovered Copper sulfides, discovered in in the the Keweenaw Peninsula Peninsula of of northern northern Michigan, Michigan,aa district district long long famous famous for for its deposits Keweenaw deposits of of The sulfides occur extensively native copper. copper. The sulfides occur extensively in the the vicinity vicinity of ofMount Mount Bohemia, Bohemia, chiefly flow tops, chiefly as open-space open-space fillings fillings and and replacements replacements in in amygdaloidal amygdaloidal flow tops, aa of occurrence of native copper in the the region. traditional mode mode of copper in region. An An andesite dike dike (or (or dikes), almost almost invariably associated with with the mineralized invariably associated mineralized flow flow tops, tops, typically typically dikes), carries at least trace traceamounts amounts of of sulfides. sulfides. The The present present study study indicates indicates that that both both copper copper and and sulfur sulfur have have been been added added to to dikes and flow tops in the dikes and flow the Mount Mount Bohemia Bohemia area, area, probably probably by by hydrothermal hydrothermal solutions solutions moving upward along along zones zones of of structural structural weakness, moving upward weakness, and and outward outward along along relatively permeable flow flow tops tops and and broken broken dike dike margins. margins. The permeable The sulfur sulfur and and most most of the the copper copper are most most likely likely of of direct direct magmatic magmatic origin, origin, although although some some copper copper may may have have been been derived der ived at depth from pre-existing pre-existing flows. flows. Microscopic studies, studies, supplemented supplemented by by X-ray Microscopic X-ray fluorescence fluorescence analyses, analyses, have have defined aa zonal defined zonal pattern pattern of of total totalcopper, copper,sulfur, sulfur,and andsulfide sulfideminerals mineralsdeveloped developed about the Bohemia Fault, a northwest-trending break on on the the northeast about Bohemia Fault, northwest-trending break northeast flank flank of of Mount Chalcocite predominates predominatesnearest nearest the the fault, with bornite, Mount Bohemia. Bohemia. Chalcocite fault, with bornite, chalcopyrite, and chalcopyrite, and finally finally pyrite pyrite becoming becoming increasingly increasingly abundant abundant with with increasing increasing distance from from the break. break. The sequence developed developedinin the the Mount area is: The chronologic chronologie sequence Mount Bohemia Bohemia area is: dike dike emplacement and and alteration, faulting and fissuring, and sulfide sulfide mineralization. mineralization. At emplacement fissuring, and At least some least some of the the faulting faulting isis related relatedtotoregional regionaldeformation deformation thought thought to to have have occurred in in later Upper time. Regionally, is occurred Upper Keweertawan Keweenawan time. Regionally, native native copper copper deposition deposition is also believed to have followed this period of deformation and preceded copper have followed this period of deformation and preceded copper also believed sulfide mineralization. sulfide Mineralization in in the Mount several chemical trends Mineralization Mount Bohemia Bohemia area followed followed several trends during the the period with each each point point in in a mineralized during period of of sulfide sulfide deposition, deposition, with mineralized dike dike or flow top top undergoing at least part flow undergoing at part of ofa ageneralized generalizedsequence sequencewhich whichincluded: included: (1) (1) solutions whose whose initial initial Cu/S Cu/S ratios introduction of solutions ratios were were relatively relatively low; low; (2) progressiveincrease increaseinin the the Cu/S progressive Cu/S ratios ratios of of the theore-forming ore-forming solutions; solutions; and and (3) (3) 022 of the progressive increase in the ff0 the solutions. solutions. 51 �GROUNDWATER SPREADING OF HYDROCARBON GROUNDW ATER SPREADING HYDROCARBON SPILLS SPILLS WITH WITH SYSTEM DESIGN DESIGN IN IN GLACIAL GLACIAL DRIFT SPECIAL EMPHASIS EMPHASIS ON MONITOR MONITOR SYSTEM W. Rohrer Rohrer and and H.O. H.O. Pfannkuch, Pfannkuch, Department of W. of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minneapolis, Minneapolis, Minneosta Minneosta 55455 55455 ABSTRACT The introduction introduction of immiscible immiscible hydrocarbons hydrocarbons into the the hydrogeologic hydrogeologic environThe ment by accidental spills ment spills or or subsurface subsurface pipeline pipeline breaks breaks presents aa class class of of problems problems that is is different different from from miscible miscible leachate leachateor or soluble soluble contamination contamination propagation. propagation. The mechanisms of subsurface spreading comprise comprise three three distinct The mechanisms of subsurface spreading distinct stages; stages; downwardmovement movementofof the the free hydrocarbon downward hydrocarbon phase phase through through the unsaturated unsaturated zone, zone, spreading on on the the groundwater table and spreading groundwater table and through through the capillary capillary fringe, fringe, and and finally finally transport of transport of the the dissolved dissolved hydrocarbon hydrocarbon phase phase vertically with infiltrating recharge recharge water and horizontally in the groundwater flow field. Each one of these processes water and horizontally in the groundwater flow field. Each one of processes is characterized by is by different material material constants. constants. For Forthe thedownward downward movement movement it it is is the retention capacity capacity of of the the unsaturated unsaturated zone zone that determines determines the total amount amount of hydrocarbonphase phase reaching reachinggroundwater, groundwater,the the capillary capillary characteristics characteristics of of the hydrocarbon capillary fringe fringe system system defines defines the the extent capillary extent of of spreading spreading on on the watertable, watertable, and and hydrodynamic dispersion the dissolved dissolved hydrodynamic dispersioncoefficients coefficients delimit delimit the the shape shape and and extent extent of the phase spreading. about these these material phase spreading. Very Very little is is known known about material constants constants in in drift drift material, since material, since most most reported research research has has dealt with with alluvial alluvial deposits. deposits. This This work work presents results for for retention capacity presents experimental experimental results capacity of of glacial glacial drift drift and and hydrocarhydrocarbon depth depth in in the capillary bon capillary zone zone of of spreading. spreading. The The retention capacity capacity depends depends on on grain size size distribution, distribution,initial initialwater watersaturation, saturation,and andsurface surfacecharacteristiss characteristis of the grain the liquids invol~ed. invol'ed. The liquids The values values for for outwash outwash sands sands are on on the the order order of of 20 20 1/rn 11m and for tills 80 80 1/rn 11m.. Furthermore some some preliminary preliminary values values of hydrocarbon hydrocarbon thickness in in is given givenfor for the the same same material. the capillary fringe of equilibrium equilibrium is The design design of of aa monitoring system deals deals with with the the recognition of the the spatial The monitoring system recognition of distribution of of the free phase ininthe the subsurface subsurfaceafter after the distribution free and and dissolved dissolved hydrocarbon hydrocarbon phase spill, spill, the reconstruction reconstruction of inflitration inflitration site site and and infiltration infiltration mechanism mechanism (intergranOntergranular or or preferred path), the determination determination of of general general flow pattern and and emplacement emplacement of interceptor wells, and the establishment of background noise, well interceptor wells, and the establishment of background noise, well sampling sampling and analytical methods. techniques and methods. 52 �ORE DEPOSITS DEPOSITS IN IN RELATION RELATION TO TO HOTSPOT-GENERATED ORE INTRACONTINENTAL RIFTING INTRACONTINENTAL 3. Sawkins, Sawkins, Department Department of of Geology Frederick J. Geology and and Geophysics, Geophysics, University University of Minnesota, Minneapolis, Minnesota, Minneapolis, Minnesota 55455 ABSTRACT ABSTRACT It can be demonstrated It demonstrated that the the tectonic, tectonic,igneous, igneous, and and sedimentary sedimentary processes processes associated with associated with subcontinental subcontinental hotspot hotspot activity activity provide provide favorable favorable environments environments within which whichore-generating ore-generating systems systems can can operate. operate. within In particular particular certain certain tin deposits In deposits are associated associated with the products products of crustal melting during during the the early early stages stages of hotspot melting hotspot activity. Copper Copper mineralization mineralization is is in some cases cases closely some closely associated with with hotspot hotspot controlled controlled geologic geologic regimes, regimes, and and both both hydrothermal and and stratiform stratiform copper hydrothermal copper deposits deposits can results. results. Copper-nickel Copper-nickel mineralization in some rocks isis also to be be aa product zation some layered layered mafic igneous igneous rocks also considered considered to product of hotspot-associated basaltic basaltic magmatism. magmatism. Other Other metal metal deposit deposit types types that, that, at least in hotspot-associated some instances, instances, appear appear to to bear bear a relationship to hotspot stratiform some relationship to hotspot activity include include stratiform in shales shales and and lead-zinc lead-zinc replacement replacement deposits deposits in in carbonate carbonate rocks. rocks. lead-zinc deposits deposits in Two major continental fragmentation Two major continental fragmentation events events related to subcontinental subcontinental hotspot activity, activity, have in the geologic hotspot have occurred occurred in geologic past and and aa number number of of important important metal deposits deposits can can be be correlated with metal with each. each. This age This approach, approach,that that relates relates the age and geologic environment of intracontinental ore deposition to hotspot activity, and geologic environment of intracontinental ore deposition to hotspot holds holds significant promise for exploration geologists. geologists. 53 53 �KOMATIITES AND AND THEIR CHEMICAL KOMATIITES CHEMICAL VARIATIONS VARIATIONS K.3. K.J. Schulz, University of of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT komatiites from from South South Africa, Canada, Australia and Examination of komatlites Minnesota (Vermiliondistrict) district)shows showsthat that distinct distinct chemcial Minnesota (Vermilion chemcial suites can can be be defined defined which, while showing showingaageneral generalsimilarity similarity also also have have notable notable differences differences (Fig. which, while (Fig. 1). 1). A A striking difference difference isis the the CaO/Al203 ratio of the striking CaO/ Al 0 ratio the South South African African ( :> 1, Fig. 1a) > 1, Fig. la) 2 3 versus the the Australian Australian and and Canadian Canadian (generalIy1, (generally $1, Fig. Fig. ib, 1b, c) c) komatiites. komatlites. Vermilion Vermilion versus samples are relatively high Fe, Fe, Ti (Thisisis also also true true of of the samples are relatively high Tl and and PP (Fig. (Fig. 1d). the id). (This Minnesota River Valley low Al Al2O. amphibolites, see Weiblen and others, this Minnesota River Valley low amphibolites, see Weiblen and others, this 0 2 meeting). Work Workinin progress progresssuggesis suggest'sthat thatononaa global globalscale scaleat at least least two two distinct distinct Archean komatiite suites may Archean komatlite may exist, exist, distinguished distinguished not not only only by by CaO/A1203 CaO/ Al 0 ratio but 2 3 In Minnesota, appears that the also by FeO/MgO and AL,03/TiO.,. also by A1203 Al 0 vs vs FeO/MgO and Al 03/TiO. In Minnesota, itit appears that 2 3 unique occurrence occurrenceofof komattites komattites witi witi norrnar tholeiites isis repeated repeated in unique normJ tholeiites in time in in the the Lower and Upper Upper Archean Archean and and the Keweenawan. Lower and Keweenawan • .;:1° 10 .1\ .4+ ~ .J t .3 t '. • ,-,' i ? TI ._ .2+ 1 • L : .6 .5 SOUTH ~F~ICRN qFHICRN KOMATIITES SOUTH KOMRTIITES .2 ·1 I T t .0 .1 •1 .2 .3 • .33T~ .5 .5 •.1<1 .5 .6 l T I 1 .6++ .6 .55 1 C .; t . ~~ ,,' t ~\\ .6- ORNROIRN ITES CRNRDIRN KOMRTI KOMRTIITE5 .:J A .1 I .0 .11 t! d • t + / + / .1 + .2 + .2 .3! .3 1 + t .1 I L .00 + l j VErMILION VERMiLIC~ KOMRTIITES <OMRTIITES i .2 t .1 .;.i. .2 i '3 + '" T • .J r .t .2 PUSTRRLIRN I TES RUSTRRLIRN OMRTI KOMRTIITES .3 \ .0 .1j_ .1 T .21 .2 ~ 4. b .<1 '. .._,. / // \\ 'I I " X t .1 .J + .5 .6 .5 .0 .;. MS RL SI MG FE FE MN MN OR CR AL 51 TI iI P NR NR ' cCi " T t MGFE FEMN MN~RCRRLL St MG Sf II TI K K .11 40 + 23 P NR NR F 38 27 ~ 1. Log Fig. 1. Log plots plots of komatilte komatilte compositional compositional normalized normalized to Hawaiian Hawaiian tholeiite (as (as oxides, right to left: left: 8.1, 8.1, 10.04, 10.04, .17, .17, 10.9, 10.9, 13.4, 13.4, 50.4, 50.4, 2.7, 2.7, .28, .28, 2.3, 2.3, .53). .53). Numbers oxides, right below 0 have have negative negative values. values. Data Data from from various various sources. sources. below a 54 �CHEMISTRY OF OF PRIMARY PRIMARY AND AND SECONDARY SECONDARY MINERALS OF SOME CHEMISTRY MINERALS OF SOME PORTAGE LAKE LAKE LAVAS, KEWEENAWPENINSULA: PENINSULA: DEVELOPMENT OF PORTAGE LAVAS, KEWEENAW MODELS OF OF DIFFERENTIATION AND MODELS AND LOW-RANK LOW-RANK METAMORPHISM METAMORPHISM Nancy Scofield, Scofield, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Nancy Technological University, Houghton, Technological Houghton, Michigan Michigan 49931 49931 ABSTRACT Minerals from from the the Scales Scales Creek Creek flow flow (SCF) (SCF) and and two thinner thinner (40', (40', 55') 55') basalt Minerals flows above above SCF SCFwere were analyzed analyzedby byelectron electron microprobe. microprobe. The interior of flows The interior of the the SCF SCF shows some some igneous igneous differentiation differentiation as shows as evidenced evidenced by by increases increasesofofFe/Fe-s.Mg Fe/Fe+Mg (9%) and Fe/Fe+Ca Fe/Fe+Ca (14%) an increase of and (14%) in augite and and an of Na/Na+Ca Na/Na+Ca (6%) (6%) in in plagioclase. plagioclase. plag (ZAn) (%An) (40—702modal) aodal) (40-70% Drill—hole Drill-hole depth depth cpx (20—402 da1) cpx (20-40: modal) Wo En Pa \00 la Fsl0* Fe203* MgO HgO CaO <:40 Na20 K20 Je20 10.3 10.5 11.1 11.1 2.06 7.83 18.8 18.8 6.9 6.9 0.07 0.07 4.30 0.02 0.02 0.07 0.07 85 85 180 180 (3) (3) 12.0 12.0 (J) (3) 11.7 11.1 (2) (2) (2) (2) 12.2 12.2 12.3 12.3 12.3 5,b4 5.04 7.75 7.75 7.43 7.45 7.80 3.90 5.90 8.2 8.2 9.9 9.7 9.1 10.4 10.4 8.4 3.90 3.90 2.26 2.26 2.15 2.15 2.32 2.90 0.30 0.27 0.30 0.31 2.10 2.10 455 455 130 130 110 110 150 130 420 420 puap 081-1832 081—1832 pWllp ab 081—1839 081-1839 055—1185 055-1185 5C 1233 SCF 1233 1285 1285 200' 1320 1370 1310 2—3 2-3 (6) (6) 42— 4239 39 42 38 62— 1616— 4239 22 38 20 44 44 18 34 44 22 14 44 16 40 44 42— 43— 15— 4243- 1538 39 23 2—3 (5) (5) 2-3 48—80(11) (U) 48-80 50—82 (8) (8) 50-82 65—80 (5) 65-80 (5) 43—30 (3) 43-30 (5) CII (p"lII) Cu (pptu) (5) (5) (8) (8) a. Mumthr analyses in in parenthessu. "uaber ofotanalyae. parentheae•• Pump pupsL1yits•••tadolll&1n astadosaln Pump —• p~.llyit *Total iron *Total iron am 1e203, 1e203' albitized ba.aalt ab basalt ab —• albit1zed C4EMICAL TRENOS IN SC..LES CREEK FLOW 0.4 0.5 Fe/Mg F'/M9 0.& *— .mi.$ry • -llulIl .....' " OJ 0.4 0.5 0.6 BOTiOY 0—.9ts; peq .dçsa I 2 3 .. NoICo FuCo D—cflnft. Q-c/lIOIit.; pIaqcoss plaqc:or.. A—oiyi 0.05 Q.l 0.15 0..$ Ci X/Ne K/Nn C'!·;:J-4lt...... The basalts basalts are are altered by by low-rank low-rank metamorphism metamorphism of the prehnite-. prehnitepumpeilyite of secondary pumpellyite facies. facies. The The proportion proportion of secondary minerals, minerals, as alteration alteration products products and in and in veins veins and and amygdules, amygdules, increases increases toward toward flow flow tops. Augite Augite is replaced replaced by by chlorite chlorite and and plagiodase plagiodase is is albitized. The Ca thus thus released released is is available available for for The Ca pumpellyitization pumpellyitization of plagioclase, plagioclase, which which occurs occurs concurrently concurrently and and subsequently subsequently to to a.Ibitization, releasing albitization, releasing Na. Na. However, aa closed-sytem closed-sytem model model demands demands overall overall However, participation of the participation of the relatively relatively unaltered unaltered flow flow interiors interiors by by a depletion depletion of of aa few few percent of the the Na Na present, present, but but this this isis not notobservable observable petrographically. petrographically. Pyroxene in in pumpellyite metadomains isis altered altered to pumpellyite pumpellyite metadomains pumpellyite and/or and/or epidote. epidote. The Mg Mg thus thus mobilized augments the the Mg content of chlorite mobilized augments Mg content chlorite and and results results in in higher Mg Mg values in in chlorite chlorite than than in in augite augite from from which which chlorite chlorite isis derived. derived. Both Both pumpellyitized pumpellyitized and and albitized are depleted in K K relative relative to less albitized zones zones are depleted in less altered altered parts of of flows, flows, and and K K is is concentrated concentrated in in the the base base of of the SCF, SCF, where where sericitization sericitization of of plagioclase plagioclase isis extensive. extensive. . 55 55 �SOURCES OF DISSOLVED GROUNDWATER DISSOL VED SOLIDS SOLIDS IN IN GROUNDW ATER FROM SUPERIOR AND RAINY FROM RAINY LOBE TILL Siegel, Department of Donald I. Siegel, of Geology Geology and and Geophysics, Geophysics, University of Minnesota, Minnesota, Minneapolis, Minnesota 55455 ABSTRACT Preliminary study study of of recent analyses Preliminary analyses of water water quality quality shows shows that groundwater groundwater within surficial aquifers aquifers related related to Superior within surficial Superior and and Rainy Rainy lobe lobe deposits deposits contains contains significantly less less sodium than is found significantly sodium than found in bedrock bedrock aquifers aquifers within within igneous igneous rocks rocks of central and northeastern Minnesota. Minnesota. Inasmuch Inasmuch as as Superior Superior and Rainy Rainy lobe lobe deposits consist mainly of materials consist mainly of materials derived derived from from these these and and similar similar igneous igneous rocks, rocks, the the observeddifference difference in in sodium sodium content content between between groundwaters groundwaters within within the the surficial observed surficial and bedrock and bedrock aquifers aquifers may may be be considered considered anomalous anomalous assuming assuming that that groundwater groundwater most influenced Possible mechanisms chemistry is most influenced by by aquifer mineralogy. explaining the the differing sodium values and and gross gross water water chemistry chemistry are suggested, explaining sodium values suggested, in particular, by theoretical reconstructions of surficial particular, by using using theoretical reconstructions of surficial and and bedrock bedrock waters. waters. Initial results results highlight Initial highlight the importance importance of of compositional compositional differences within aquifers in local local and and small, small, intermediate intermediate flow flow systems systems as as the the dominant in dominant control of both both gross gross groundwater chemistry chemistryand and ultimately ultimately the the gradual gradual evolution evolutionofof water water types groundwater types as as deduced by by Chebotarev and deduced and others. 56 56 �MIDDLE MIDDLE PRECAMBRIAN AGE OF VOLCANOGENIC VOLCANOGENIC MASSIVE MASSIVE SULFIDE DEPOSITS IN NORTHERN NORTHERN WISCONSIN WISCONSIN P.K. Sims, U.S. Denver, Colorado Colorado 80225 80225 U.S. Geological Survey, Denver, ABSTRACT The copper-zinc at the copper-zinc massive massive sulfide sulfide deposits at the Flambeau Flambeau mine, mine, near near The Ladysmith and at Pelican River, east of Rhinelander, Wisconsin, have model lead Ladysmith and Pelican River, east of Rhinelander, Wisconsin, have model ages of 1,830+150 m.y. (J.S. (iS. Stacey, ages 1,830+150 m.y. Stacey, B.R. B.R. Doe, Doe, and and L.T. L. T. Silver, Silver, written written commun., commun., Inasmuchas as the the deposits 1976). Inasmuch deposits are considered considered as as being being of of submarine submarine volcanic volcanic exhalative also are interpreted exhala tive origin, or igin, the associated volcanic rocks rocks also interpreted as as being being middle middle Precambrian (Precambrian X) X) in age. The analytical analytical data on The on the leads leads from from the the two two ores, ores, provided provided by by Stacey, Stacey, Doe, Doe, and Silver, Silver, are tabulated tabulated below. below. 206 Pb 204 Pb 207Pb 204 Pb 204 208Pb 204 Pb Model Model age in m.y. Flambeau 15.323 15.167 35.016 1,820 Pelican River 15.688 15.359 35.202 1,835 Deposit The isotopic composition compositionofof the the leads leads is is similar to the the least least radiogenic radiogenic leads leads from from The isotopic The model model lead lead ages the massive massive sulfide sulfide deposits deposits at Flin Flin Flon, Flon, Manitoba. Manitoba. The ages are and granitic grartitic rocks rocks consistent with with zircon zircon U-Pb U-Pb ages ages of of 1,800-1,900 1,800-1,900 m.y. on volcanic volcanic and in and adjacent Michigan, in northeastern northeastern Wisconsin Wisconsin and Michigan, determined determined by byW.R. W.R. Van Van Schmus Schmus and his and his associates in in 1975. 1975. The volcanic volcanic rocks rocks in in the the Ladysmith-Rhinelander Ladysmith-Rhinelanderbelt belt are are interpreted interpreted as The as being being approximately correlative correlative with with the the dominantly submarine volcanic volcanic rocks rocks that that are approximately dominantly submarine are interbedded with with turbidite-like the upper of the interbedded turbidite-like sedimentary sedimentary rocks rocks in the upper part of the Marquette northern Michigan. Apparently these these rocks Marquette Range Range Supergroup Supergroup in in northern Michigan. Apparently rocks accumulated in in a eugeosynclinal environmentininthe the southern southern part part of the accumulated eugeosynclinal environment the middle middle Precambrian basin basin in the the Lake Lake Superior Superior region. region. 57 �GEOLOGY AND GEOCHEMISTRY GEOCHEMISTRY OF THE THE PRECAMBRIAN PRECAMBRIAN MARCELLON MARCELLON RHYOLITE, RHYOLITE, COLUMBIA COUNTY, WISCONSIN COLUMBIA WISCONSIN Smith, Divsion Divsion of Science, Science, University University of ofWisconsin-Parkside, Wisconsin-Parkside, Kenosha, Kenosha, Eugene I. Smith, Wisconsin 53140 531ltO ABSTRACT The inlier isis formed formed by by four four mineralogically mineralogically and and chemically chemically distinct distinct The Marcellon Marcellon inlier rhyolite tuffs which rhyolite flows flows and and ash-flow ash-flow tuffs which are folded folded into into aa northeast-striking, northeast-striking, asymmetric arjifom. Rhyolite asymmetric antiform. Rhyoliteononthe thewestern westernlimb limbofofthe theantiform antiformstrikes strikesN.N..50 50 0 0 E. and E. and dips dips 50 50 -85 _85 to the the northwest. northwest. The The units units on on the the eastern eastern limb limb also also strike strike N. N. 0 50 50 E., E., but dip dip steeply (80° (80 to vertical) vertical) to to the the southeast. southeast.Two Twochemically chemicallydissimilar dissimilar greenstone dikes intrude the rhyolite flows. dikes rhyolite flows. The The core of the the antiform antiform isisformed formedby bya aquartz quartz(2%), (2%),plagioclase plagioclase(15%), 05%), and and alkali (2%)rhyolite rhyolite with with well well preserved preserved shard shard outlines outlines in in the matrix alkali feldspar feldspar (2%) matrix (unit (unit unit probably is an Structurally above It). This unit probably is an ash-flow ash-flow tuff. Structurally above unit 4It is: is: (a) (a) well well 4). This banded, plagioclase-bearing Olt-18%) (14-18%)rhyolite rhyolite with with local local spherulitic spherulitic lenses (unit banded, plagioclase-bearing (unit 3); 3); (6%), alkali feldspar feldspar (4%), (It%), plagioclase (1%) 0 %) rhyolite (unit 2); (b) flow (b) flow banded, banded, quartz (6%), and (c) (c) quartz quartz (296), (296),alkali alkalifeldspar feldspar (2%), (2%),plagioclase plagioclase0(1%) rhyolitecharacterized characterized by %) rhyolite and spherulites up up to 15 15 cm in diameter diameter (unit (unit 1). 1). The rhyoliteisis one one of of ten major The Marcellon Marcellon rhyolite major rhyolite rhyolite and and granite granite inliers inliers in in south-central Wisconsin. Chemicallymost mostofof the the rocks form the inliers Wisconsin. Chemically rocks which which form inliers can can be divided divided into into three threegroups: groups:(1) 0)high high CaO CaO(1.48-1.68%), (1.48-1.68%), high high TiO, Ti0 2(0.30-0.42%), (0.30-0.42%), and and low rhyolitesand andgranites granites(Observatory (ObservatoryHill HillRhyolite hyolite dikes dikes and and low Rb/Sr Rb/Sr (0.37-0.79) (0.37-0.79) rhyolites the Baxter Baxter Hollow Hollow Granite); Granite); (2) (2) intermediate intermediateCaO CaO(1.28#O.32%) (1.28+0.32%) and and Rb/Sr Rb/Sr (1.09+ 0.09+ 0.29) rhyolite rhyolite (unit (unit 33 at Marcellon 0.29) Marcellon and and the the Marquette Marquette Rhyolite); Rhyolite); and and (3) (3) low low CaO Cad Rb/Sr (159) (0.37+0.14%), (0.37 +0.14%), high Rb/Sr 05~) rhyolites rhyolites and and granites granites (Observatory (Observatory Hill, Hill, Berlin, Berlin, Utley, and rhyolites, and and granophyric granophyricgranites granites at at Moritello Utley, and Endeavor Endeavor rhyolites, Montello and and Red Red Althoughunit unit 33 at Marcellon falls into chemical 2, the other Granite). Although Marcellon falls chemical group group 2, other Marcellonunits, units,along alongwith with rhyolites rhyolitesinin the the Baraboo area, are transitional Marcellon Baraboo area, transitional in chemistry chemistry between between groups groups 2 and and 3. 3. For For example, example, units units 1 and 22 are are more more closely closely related to to group group 33 in in terms termsof oflow lowCaO CaO(0.29-0.36%), (0.29-0.3696), but but differ differ by by having having lower lower Rb/Sr (2.27+0.57). Unit 44 isis similar similar to group 2 because of intermediate Rb/Sr (2.27+0.57). Unit intermediateCaO CaO(0.94%) (0.9lt96) and but it isis higher and Rb/Sr (1.32), 0.32), but higher in in K2O/Na20 K 0/Na 0 and and lower lower in in Ba Ba than than typical typical group group 22 2 2 rocks. Rocks of the three with the the transitional Rocks of three chemical chemical groups, groups, along along with transitional types, types, fall along aa trend along trend typical typical of of aarock rockseries seriesshowing showing strong strong caic-alkaline calc-alkaline affinities. affinities. Rhyolites are are cornagmatic, and the granophyric Rhyolites comagmatic, and granophyric granites granites are apparently apparently the the subvolcanicequivalents. equivalents. These chemical data along subvolcanic These chemical along with with available available U/Pb dates (1.8 (1.8 b.y.) confirm that that these rhyolites the last stages of rhyolites and and granites formed formed during during the of the the b.y.) confirm Penokean Orogeny. 58 �THE GEOCHEMISTRY GEOCHEMISTRY OF THE THE GAMITAGAMA GAMITAGAMA LAKE COMPLEX, COMPLEX, WAWA, WAWA, NORTHERN ONTARIO I.E. Smith, T.E. Smith, A. A. Turek, Turek, and and C. C.Riddle, Riddle, Department Department of ofGeology, Geology, University University of of Windsor, Windsor, Windsor, Ontario, Canada Canada ABSTRACT The The Gamitagama Gamitagama Lake Lake Complex Complex is is aa calc-alkaline calc-alkaline stock stock (Ayres, (Ayres, 1969), exposedwithin within the the Abitibi volcano-plutonic exposed volcano-plutonic belt in in the the Superior Superior Province Province of of Canada, south Canada, south of of Wawa Wawa in in Ontario. It penetrates penetrates a a series series of regionally metamorphosed felsic and and mafic mafic volcanic volcanic rocks metamorphosed felsic rocks interbedded interbedded with metasedimentary metasedimentary rocks with aa variety variety of of other plutons. rocks and and iron-formation, iron-formation, and and is associated associated with plutons. The The metamorphic gradevaries variesfrom from greenschist greenschisttoto amphibolite amphibolite facies facies within within the metamorphic grade the area area and is overprinted by contact metamorphic aureoles adjacent adjacentto to the the plutons. plutons. The and is overprinted by metamorphic aureoles The plutonic rocks plutonic rocks include include cataclastic cataclastic and and gneissose gneissose trondjhemites, trondjhemites, gabbros, gabbros, norites, diorites, dior ites, syenites, syenites, and and granites. Major Major and and trace elemental elemental contents contents of the the volcanic volcanic and and plutonic plutonic rocks rocks are are usedtoto identify identify the igneousrock rocksuites suitesofofthe the area, area, to to follow used the various various igneous follow their their evolution and Comparisonswith with recent evolution and to determine determine which which are are co-magmatic. co-magmatic. Comparisons recent igneousrock rock suites suitesare areused usedtotoreconstruct reconstructthe the development developmentof of the the Archean Archean crust crust in in igneous this this area area and and to to identify identifythe thetectonic tectonicenvironments environments ininwhich whichthe themagmas magmas were were generated. 59 �A A GROUND GROUND INVESTIGATION INVESTIGATION OF AN AN AEROMAGNETIC AEROMAGNETIC ANOMALY, ANOMALY, DICKINSON DICKINSON COUNTY, COUNTY, MICHIGAN MICHIGAN David Snider, Geology and Minerals David W. W. Snider, Geology and Minerals Research Unit, Unit, Geological Geological Survey Survey Division, Division, Michigan Department of Natural Natural Resources, Resources,Lansing, Lansing, Michigan Michigan 48926 48926 Michigan Department ABSTRACT ABSTRACT During the the latter latter part of of September, September, 1975, 1975, the the Geology Geology and and Minerals Minerals During Research Research Unit Unit of the the Michigan Michigan Geological Geological Survey Survey conducted conducted a ground ground reconnaisreconnais- sance of aa small, sance investigation investigation of small, closed closed aeromagnetic aeromagnetic anomaly anomaly in in north-central north-central Dickinson County. The The purposes purposes of of the the study were two-fold: (a) Dickinson County. study were (a) to determine determine what what geologic feature caused geologic feature caused the the aeromagnetic aeromagnetic anomaly anomaly and, and, (b) (b) to to investigate investigate any any mineral resource potential associated with the area in and around the anomaly. mineral resource potential associated with the area in and around the anomaly. Nearly Nearly all of of the the closed closed anomaly anomaly lies lies within within an an east-west east-west trending trendingswamp swamp covering covering an area of of nearly nearly three three square square miles. miles. The of investigation consisted of sampling The methods methods of sampling outcrops for petrographic and chemical chemical analyses, analyses, ground ground magnetic magnetic surveys, surveys, and andaaVLF-EM VLF-EM survey. The results of of the the study indicate that The combined combined results that the theclosed, closed, airborne airborne anomaly anomaly peridotite that was caused caused by by the the near-surface near-surface occurrence occurrence of of serpentinized serpentinized peridotite that was contains appreciable of magnetite. This appreciable amounts amounts of This ultrarnafic ultramaficbody body underlies underlies most most of of the northern northern portion portion of of the the swamp swamp area, area, strikes strikesN75°-80°W N750 -800 W and and dips dips to the the south. south. The relative position positionofof the the body body with with respect respect to to metasedimentary rocks to to the The relative metasedimentary rocks south and and southwest southwest suggest suggest that that this this ultramafic unit south unit was was emplaced as a sill. The results of the The the chemical chemical analyses analyses show show no no anomalous anomalous Ni-Cu-Co values. surveyshow showthe the presence presence of of two The results of the the VLF-EM VLF-EM survey two separate separate The results first is anamalous zones within withinthe the project project aera. The anamalous zones The first is caused caused by by the the relatively relatively magnetic, serpentinized peridotite peridotite that crops magnetic, serpentinized crops out within within the the swamp. swamp. This This area produced aa high high ground ground magnetic magnetic response response as as well well as as aa VLF-EM response. However, produced VLF-EM response. However, the combined geophysical, geological, and chemical evidence indicate that the the combined geophysical, geological, and chemical evidence indicate that the surface exposures of the the magnetic, surface exposures of magnetic, serpentinized serpentinized peridotite has has limited limited ecomonic ecomonic potential. The feature responsible The responsible for for the thesecond secondVLF-EM VLF-EM anomalous anomalous zone zone does does not not express itself itself at at the express the surface, surface, nor nor does does ititcorrespoind correspoind with with any any ground ground magnetic magnetic anomalies. All of of the anomaliesgenerated generatedinin the the project All the major major VLF-EM VLF-EM anomalies project area were were correlated with with the the serpentinized correlated serpentinized peridotite peridotite and and showed showed aa reverse reverse cross-over cross-over to anomaly was determined determined that that the theVLF-EM VLF-EM instrument instrument was was responding responding to anomaly form. It was It was the magnetic permeabilityofof the the rock the magnetic permeability rock rather rather than than its itsconductivity. conductivity. It was survey yielded yielded no no reliable therefore concluded concluded that the the VLF-EM VLF-EM survey reliable data concerning concerning the the conductivity conductivity of of the the serpentinized serpentinized ultramafic. ultramafic. The VLF-EM VLF-EMinstrument instrumentused usedininthis thisstudy studyisisa arather rather restrictive, restrictive, reconnaisThe reconnaissance tool, tool, and and as as such be used sance such cannot cannot be used for for detailed detailed interpretation interpretation of of buried buried conductive bodies, bodies, especially especially when when those those bodies bodies possess possess high high magnetic magnetic permeabilpermeabilconductive this occurrence of ultramafic therefore suggested ity. suggested that this occurrence of ultramafic rock rock be be ity. ItIt is therefore investigated in in more investigated more detail by by those those using using a more more discriminating discriminating EM EM method method which which wouldbetter better determine determine its economic economic potential. would 60 60 �HIGH-GRADE HIGH-GRADE METAMORPHISM METAMORPHISM ASSOCIATED ASSOCIATED WITH WITH THE THE VERMILION VERMILION BATHOLITH, MINNESOTA-ONTARIO MINNESOTA-ONTARIO David L. L. Southwick, Southwick, Department Department of of Geology, Geology, Macalaster Macalaster College, College, St. Paul, David Minnesota. ABSTRACT Aluminous, magnesianschists schistsalong alongthe the north north contact Aluminous, magnesian contact of of the theVermilion Vermilion batholith contain various combinations combinationsofofsillimanite, sillimanite,cordierite, cordierite, staurolite, staurolite, garnet, contain various is rarely and and sapphirine sapphirine along along with with biotite, biotite, oligoclase, oligoclase, and and quartz. quartz. Muscovite Muscovite is rarely So far as present; tourmaline is a common and sometimes abundant accessory. present; tourmaline is a common and sometimes abundant accessory. So as known, this is the first reported occurrence of sapphirine in Minnesota or western known, this is the reported occurrence of sapphir ine in Minnesota or western Ontario. Ontario. Staurolite-bearing assemblagesappear appeartoto represent represent the the highest Staurolite-bearing assemblages highest metamorphic metamorphic grade. grade. There There is is excellent excellent textural textural evidence evidence that the the reaction reaction garnet garnet ++ staurolite + taken place. Experimental quartz-cordiertie has has taken Experimental work work indicates that this this reaction reaction quartz—cordiertie is with lower lower pressure pressure favoring favoringthe the formation formation of of cordierite. is pressure-controlled, pressure-controlled, with cordierite. Sapphirine occurs together together with with staurolite staurolite in some Sapphirine occurs some rocks, rocks, indicating indicating formation formation at the highest metamorphicgrade. grade. There is no no clear-cut evidence as to the reactions highest metamorphic There is evidence as reactions governing sapphirine formation. governing sapphirine Field relations indicate that the Field relations the high-grade high-grade schists are the the product product of of thermal thermal assemblages inin the the schists metamorphism by adjacent batholith. batholith. Observed Observed assemblages schists metamorphism bythe the adjacent 0 suggest maximum suggest maximum temperature and and pressure pressure in in the theneighborhood neighborhood of of 600-700°C 600-700 C and and This environment environmentisiscompatable compatablewith withthe the inferred inferred temperature temperature and pressure 3-5 kb. This at crystallization crystallization of of the the major major part partof ofthe theVermilion Vermilion batholith. batholith. Detailed investigations investigations of of the phase chemistry currently are are underway. underway. 61 �GEOLOGY OF THE ROUND GEOLOGY ROUND LAKE LAKE INTRUSION, INTRUSION, SAWYER COUNTY, WISCONSIN SAWYER WISCONSIN S.W. Stuhr and and E.N. S.W. Stuhr E.N. Cameron, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT enclosed in in Archean rocks aa short The Round Round Lake Lake intrusion intrusion is enclosed Archean rocks short distance distance southeast of the edge southeast edge of of the theLake LakeSuperior SuperiorSyncline SynclineininSawyer SawyerCounty, County,Wisconsin. Wisconsin. Geophysicaldata dataindicates indicatesthat that the the intrusion intrusion isis at at least five Geophysical five miles miles long long but but less less The intrusion intrusion may maybe be aa derivative than than one one mile mile wide. wide. The derivative of aa gabbroic gabbroic magma. magma. Diabasic gabbro gabbro occurs occurs as as inclusions inclusions inin the the outer outer portions Diabasic portions of of the oxide-rich oxide-rich core. core. Magnetite-troctolite, and mafic pegmatite Magnetite-troctolite, magnetite, anorthositic anorthositic olivine olivine gabbro gabbro and form the troughshaped form troughshaped core of the intrusion. intrusion. The dominant dominant minerals minerals are olivine, and titanomagnetite titanomagnetite in The olivine, plagioclase and in various various In the core of the intrusion, olivine and plagioclase crystallized early proportions. In the intrusion, olivine and plagioclase and the iron-titanium oxides crystallized crystallizedlate. late. At and the iron-titanium oxides At the the base base of of the thenarrow narrowintrusion intrusion of magnetite magnetite troctolite was aa thick zone zone of was formed. formed. The The iron-titanium iron-titanium oxides oxides became became enriched in the the residual liquid and andaalarge largezone zoneofofmagnetitite magnetitite formed formed in in the the central central enriched in residual liquid part of the intrusion. intrusion. As As differentiation differentiation proceeded, proceeded, additional additional magnetite-troctolite magnetite-troctolite clusters accumulated formed toward the the top formed toward top of of the the intrusion. intrusion. Plagioclase Plagioclase clusters accumulated into lenses of anorthositic olivine gabbro gabbro inin the the lower of the lenses of anorthositic olivine lower and and middle middle portions portions of the intrusion. Finally, Finally, mafic mafic pegmatites, pegmatites, consisting consisting of of plagioclase, plagioclase, perthite, augite, augite, iron-titanium oxides and apatite apatite as major oxides and major minerals, minerals, developed developed in the upper upper portions portions of the intrusion. intrusion. Chemical variation variation of of specific Chemical specific minerals minerals is is a function function of both both the the oxide/silioxide/silicate ratio cate ratio and and cryptic cryptic changes changes related related to to position position in the the intrusion. intrusion. Olivine, plagioclase plagioclase and and iron-titanium oxides oxides show show slight but consistant consistant chemical chemical changes. changes. Cryptic variations variationsare are most most pronounced pronouncedininthe the portion portionofof the the intrusion Cryptic intrusion that crystallized last. The oxides were were concentrated concentrated in in the The iron-titanium iron-titanium oxides the residual residual liquid liquid under under the intrusion the product conditions of low conditions of low oxygen oxygen fugacity. fugacity. If the intrusion is the product of of iron enrichment of basaltic magma, it must have migrated migrated from from the site of differentiation. After After the the iron-rich iron-rich magma magma was was intruded, intruded, itit followed followed aa "normal" "normal" path of differentiation in in place. place. 62 U �HYDROCARBONS HYDROCARBONS OBTAINED OBTAINED BY BY PYROLYSIS PYROLYSIS OF OF SOME SOME PRECAMBRIAN ROCKS OF MINNESOTA* PRECAMBRIAN ROCKS OF MINNESOTA* F.M. :i. Baysinger, and 1M. F.M. Swain, Swain, J. Baysinger, and J.M. Bratt, Bratt,Department DepartmentofofGeology Geologyand andGeophysics, Geophysics, of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 University of ABSTRACT ABSTRACT Drill Drill core samples samples of of 42 42 Precambrian Precambrian sedimentary, sedimentary, igneous, igneous, and and metamorphic metamorphic rocks partial vacuum rocks were were analyzed analyzed by by heating heating under under partial vacuum at 100°C 1000C and and at 400°C 400 0 C to to release hydrocarbons and other volatile products. hydrocarbons and products. The yielded methane methane inin amounts amounts ranging rangingfrom from traces traces to to 33 The core core samples samples yielded way of comparison, but averaged averaged much much less. less. By By way comparison, samples of microliters per gram, but Middle Marcellusblack black shale, shale, from Middle Devonian Devonian Marcellus from Pennsylvania, Pennsylvania, yielded yielded methane methane in in am ounts up to 77 ul/g. ul/g. amounts Other up to to C11 were Other straight straight chain chain hydrocarbons hydrocarbons up C were found found in the the volatile volatile ll o products, especiall' especiallj: those those obtained obtained atat400°C; 400 C;benzene benzenealso also was was aacommon common product, product, mainly in the the 400 mainly in 400 C C experiments. experiments. Carbon Carbon dioxide dioxide and and nitrogen nitrogen appear appear to form form aa large part of of the the non-hydrocarbon non-hydrocarbon volatiles in at least least some some of of the the samples. samples. Spectral data data indicate of the Spectral indicate that the the straight straight chain chain pyrolysis pyrolysis products products of Precambrian rocks are mainly alkenes, whereas those of the Devonian rocks, Precambr ian rocks are mainly alkenes, whereas those of the Devonian rocks, to above, above, are are aamixture mixture of ofalkanes alkanes and and alkenes. alkenes. Alkanes Alkanes were however, however, referred to Available obtained from from several several algae-bearing algae-bearing Middle Middle Precambrian Precambrian argillites. argillites. obtained evidence indicates, indicates, although not conclusively, conclusively, that that the alkenes evidence although not alkenes were were contained contained in the rock rock rather ratherthan thanbeing beingproduced produced from from alkanes alkanesduring during pyrolysis. pyrolysis. The writers believe believe that surface contamination The writers contamination in most most of the drill drill cores cores was was minimal owingtotothe the low lowpermeability permeabilityofofthe the rocks rocks studied, studied, and and that that contamination minimal owing by drilling was also minimal. by not formed that the There is aa reasonable reasonable possibility possibility that the volatiles, volatiles, if not formed from from There is kerogeri residues residues by bythe the pyrolysis pyrolysisexperiments, experiments, are are in in part juvenile kerogen juvenile igneous igneous gases gases or or are substances substances that that were were distilled distilled out out of of the thedeeper-lying deeper-lying rocks rocks during during intervals intervals of of folding and and metamorphism, metamorphism, and and subsequently subsequently accumulated accumulated at at higher higher levels. folding *The paper paper isis scheduled scheduled for for publication publication in in July 1976 "Origins of of Life." Life." *The 1976 "Origins 63 63 �—- HORNFELSED BASALTS BASALTS IN THE THE DULUTH DULUTH COMPLEX COMPLEX Department of of Geological R.M. B. Bonnichsen, Bonnichsen, Department Geological Sciences, Sciences, Cornell Cornell R.M. Tyson Tyson and and B. Ithaca,New NewYork York14853 14853 University, Ithaca, ABSTRACT ABSTRACT Two typesofof hornfelsed basalt (see (see figure) figure) occur occur in compositional types hornfelsed basalt in the the Two compositional Babbitt-Hoyt of the Duluth Babbitt-Hoyt Lakes Lakes region region of Duluth Complex. Complex. The The Erie Erie Hornfels Hornfels (Sec. (Sec. 18, 18, T.59N., Dunka Railroad Railroad Hornfels T.59N., R.13W.), R.13W.), Dunka Hornfels (Sec. 33, 33, T.60N., T.60N., R. R. 12W.) 12W.) and and Reserve Reserve Hornfels (Sec. 32, (Type1)I) are are olivine Hornfels (Sec. 32, T.60N., T.60N., R.12W.), R.12W.), (Type olivine tholeiites tholeiites consisting consisting of of plagioclase augite (16-45%), olivine (0-2196), (0-21%),and and inverted inverted pigeonite plagioclase (40-62%), (40-6296), augite 06-45%), olivine pigeonite (018%). 1896).- The The Reserve Reserve body body has less than than 1% 1% opaque opaque oxides and more than than 10% 10% olivine, whereas whereas the others others have have 1-3% 1-396 opaque opaque oxides oxides and and generally generally less less than than 10% 10% olivine. olivine. The range from from granoblastic granoblastic in in the theDunka Dunka Railroad Railroad and and Reserve Reserve bodies, bodies, The textures range which are surrounded surroundedby byintrusive intrusiverocks, rocks,totoaabetter-preserved better-preserved basaltic fabric in which are in the This type contains plagioclase-two Erie Hornfels at the base of the complex. Erie Hornfels at base of the complex. This contains plagioclase-two pyroxene and plagioclase pyroxene metamorphosed metamorphosed amygdules amygdules and plagioclase phenocrysts. phenocrysts. The The Colvin Colvin Creek Hornfels and T.59N. T.59N. R.13W.) R.13W.)isisan an example example of of Type Hornfels (T.58N. (T.58N. and Type H, II, and contains contains (28-34%), equant plagioclase (52-56%), irregular to locally poikilitic augite (28-3496), hypersthene mantling augite, and hypersthene (1-6%) 0-6%) mantling and magnetite magnetite(10-20%). (10-2096). It represents represents an an type has oxidized basalt which which has has been been metamorphosed. metamorphosed. This This type has aa granoblastic granoblastic oxidized basalt texture texture and and contains contains zoned zoned plagioclase plagioclase phenocrysts phenocrysts and and metamorphosed metamorphosed amygdules amygdules . composed composed of of augite enclosing plagioclase. \Ve believe believe these these hornfels hornfels bodies bodies were were originally originallyflows flowsthat that were were part of the We the Their metamorphism to the pyroxene North Shore Volcanic Volcanic Group. Group. Their metamorphism to the pyroxene hornfels hornfels or North Shore sanidinite facies was thermal in sanidinite facies was predominantly predominantly thermal in nature. Devolatilization Devolatilization was one one major major effect as as shown shown by by the the anhydrous anhydrous minerals minerals now now constituting the the amygdules amygdules and the the scarcity scarcityofofhydrous hydrousminerals mineralscommon common in inunmetamorphosed unmetamorphosed North North Shore Shore and Volcanicrocks. rocks. Partial Partial melting locally occurred occurred with with the the formation melting locally formation of syenite and Volcanic Such dikes, dikes, composed composedofof Na-plagioclase, Na-plagioclase,quartz, quartz, chlorite chlorite and local dikes. Such granite dikes. biotite and occur in in the Dunka and tremolite, tremolite, conspicuously conspicuously occur Dunka Railroad Railroad- Horniels Hornfels and and have have been observed many other been observed at at many other localities. The volcanic volcanic horfelses horfelsesatat the the base base of of the lie above only aa few The the complex complex lie above only few hundred feet of of Virginia VirginiaFormation. Formation.This Thisisismuch muchthinner thinnerthan thanfarther farther to to the the west. hundred feet suggests the the Virginia was eroded eroded prior prior to extrusion Virginia was extrusion of of the the volcanic volcanic rocks. rocks. It suggests Perhaps this this accompanied preceeding the Keweenawan Perhaps accompanied regional regional doming doming preceeding Keweenawan episode episode of continental continental rifting rifting.• .... L 01 + . /I pi px 40 so 64 64 60 70 �I SYNGENETIC SYNGENETIC MODEL MODEL FOR THE THE ORIGIN OF OF THE THE WHITE WHITE PINE COPPER COPPER DEPOSIT DEPOSIT Thomas Geology Department, Department, Michigan Thomas A. A. Vogel, Vogel, Geology Michigan State University, University, East East Lansing, Lansing, Michigan 48824; M.B. M.B. McBride, McBride, Department Department of Agronomy, Michigan 48824; Agronomy, Cornell Cornell University, University, Ithaca, New New York York 14853; 14853; and Robert Robert Ehrlich, Ehrlich, Geology Geology Department, Department, University University of of South Carolina, Carolina, Columbia, Columbia, South South Carolina Carolina29208. 29208. South ABSTRACT ABSTRACT The syngenetic model model for the the mineralization mineralization of of the thelower lowerNonesuch Nonesuch Shale Shale at at The syngenetic White Pine, Michigan depends upon copper entering the basin complexed White Michigan depends upon copper entering the basin complexed to clay clay In order order for this this model model to to be be viable viable for for the the White White Pine Pine deposit, deposit, it it isis minerals. In necessary to demonstrate necessary to demonstrate that significant significant copper copper can can be be complexed complexed to clay clay minerals and that that these in the source minerals and these minerals minerals can be be produced produced in source terrane for for the the lower Shale. Furthermore, if copper lower Nonesuch Nonesuch Shale. copper entered entered the the basin basin complexed complexed to clay minerals, the clay clay mineral mineral fraction fraction present presentininthe thelower lowerNonesuch Nonesuch Shale Shale may may record occurrence. its occurrence. Basalts and andesites are extensively exposed inin the the rocks Basalts and andesites are extensively exposed rocks of of the theMiddle Middle Keweenawan and all all workers workers agree agree that that the sediments Keweenawan and sediments of of the the Nonesuch Nonesuch Shale Shale are derived from weathering of these rocks. derived predominantly predominantly from rocks. In In most environments, the first clay clay mineral mineral to to form form from from weathering weathering of of basalt basalt isismontmorillonite. montmorillonite. The dominant clay mineral mineral assemblages assemblagesthat that exist exist in Shale are are aa dominant clay in the the lower lower Nonesuch Nonesuch Shale complex intergrowth of of chlorite chlorite and and illite. illite. AA probable for these intergrowths complex intergrowth probable origin for dlagenetic alteration of of montmorillonite. montmorillonite. Many Many workers workers have is due to a diagenetic have traced the change from from montmorillonite montmorillonite to chiorite-illite chlorite-illite intergrowths intergrowths in in the thegeologic geologiccolumn column and the alteration to chlorite-illite and experimentally, experimentally, the alteration of of montmorillonite montmorillonite to chlorite-illite is is well well known. It It is is reasonable reasonable that that the thechlorite-illite chlorite-illiteintergrowths intergrowthsininthe thelower lowerNonesuch Nonesuch known. Shale been diagenetically Shale represents represents montmorillonite montmorillonite that that has been diagenetically altered. their ability One of of the One the characteristic characteristic features features ofofmontmorillonite montmorillonite is is their ability to to adsorb cations, and and considerable considerableresearch researchhas hasbeen been devoted devotedtoto the the study adsorb cations, study of the the adsorption and exchange exchange properties properties of of copper adsorption and copper and and clays. clays. Heydemann Heydemann (1959) (1959) 1959, 1959, was the first firstworkers workers totoshow showexperimentally experimentally that that copper copper could could be be was one one of of the In addition, selectively adsorbed from copper selectively adsorbed on on montmorillonite montmorillonite from copper ions ions in in solution. solution. In well-knownthat that organic-clay organic-clay complexes complexeswill will adsorb adsorb copper copper from from dilute it is well-known dilute Steger has suggested aqueous solutions solutions (Kaufherr, (Kaufherr, et. et. al., 1971; aqueous 1971; Steger, 1973). 1973). Steger suggested that organic-clay complexes complexes could could be be used used to to remove remove trace amounts organic-clay amounts of of copper, copper, zinc zinc and and Many workers workershave have shown shownthat that copper copper is is bound lead from from water. water. Many bound preferentially lead over on organic-clay complexes. over other divalent cations on A study study of of the clay A clay fraction fraction of of samples samples from from aa copper-rich, copper-rich, black black shale shale was was undertaken determine if some some of the the copper copper was was structurally structurally bonded bonded in undertaken in in order order to determine the clay lattice and state of the the clay mineral mineral lattice and also also to determine determine the oxidation oxidation state the iron iron in in order to to better of formation of these these minerals. minerals. The order better understand understand the the environment environment of formation of The original samples samplescontained contained4.75% 4.75%copper copperand andthethe <<22 micron micron (clay) (clay) fraction fraction original micron fraction After leaching leachingthe the << 2 micron fraction with contained 0.96% copper. copper. After with sodium sodium contained 0.96% no Cu Cu II was removed, chloride (NaTPB NaC1), no tetraphenyl boron - sodium (NaTPB - NaCl), II was removed, thus tetraphenyl boron sodium chloride A indicating that that the copper indicating copper is is not not present present as as interlayer interlayer Cu Cu IIII or or soluble soluble Cu Cu II. II. A detailed electron microscopeand and microprobe microprobestudy studyofofthe the <<22 micron detailed electron scanning scanning microscope micron fraction failed failed to show the presence presence of of any any free free native native copper copper or or chalcocite grains. fraction show the grains. Electron Spin Resonance studies studies of of these samples Electron Spin Resonance samples show show Fe Fe III III (G (G about 4.0) 4.0) in octahedral sites sites in in the the clay of Fe III is octahedral clay minerals. minerals. Abundance Abundance of III in in the clay day minerals minerals is 65 65 �probably about 2-3% probably about 2-3% (determined (determined by by comparing comparing the spectrum spectrum with with known known clays). clays). The presence of of Fe Fe III HIininthe the octahedral octahedral sites sites must result The presence result from from the themontmorillonite montmorillonite having formed in an an oxidizing oxidizing environment. environment. These These data are are consistent consistent with withaamodel modelininwhich which montmorillonite montmorillonite formed formed in in the weathering and copper probably as as a copperweathering environment environment and copper was was complexed, complexed, probably coppercopperinin the the <<22 micron organic complex. complex. The The insoluble insoluble copper micron fraction fraction indicates indicates that that when broke down, some of of the copper when the copper-organic-montmorillonite complex complex broke down, some copper was was forced forced into into the octahedral octahedral sites sites of of the theresulting resulting chiorite-illite chlorite-illite intergrowth. intergrowth. However, most of of the the copper copper was was released released and and provided provided the the source source of of copper However, most copper for for the mineralized mineralized zone. zone. REFERENCES CITED CITED Heydemann, A., 1959, Heydemann, A., 1959, Adsorption Adsorption ans sehr sehr verdUnnten verdUnnten Kupferlösungen Kupferlosungen an reinen reinen Tonmineralen; Geochim. Geochim. Cosmochim. Cosmochim. Acta. v. 15, 15, p. p. 305-329. 305-329. Kaufherr, N., N., Yariv, Yariv, S., S., and and Heller, Heller, L., L., 1971, 1971, The The effect effectof ofexchangeable exchangeable cations cationson on the sorption by montmorillonite; montmorillonite; Clays Clays and and clay clay minerals, v. sorption of chiorophyllin chlorophyllin by 19, p. 193-200. 193-200. Steger, H.F., the mechanism of adsorption adsorption of of trace copper Steger, H.F., 1973, 1973, On On the mechanism of copper by bentonite; Clays and clay minerals, minerals, v. v. 21, 21, p. p. 429-436. 429-436. 66 �GNEISS AND AND MIGMATITE MIGMATITEOF OF ARCHEAN ARCHEAN AGE AGE IN IN THE THE PRECAMBRIAN GNEISS BASEMENTOF OF CENTRAL CENTRAL WISCONSIN, BASEMENT WISCONSIN, U.S.A. W.R. Van Van Schmus, Schmus, Department of Geology, University University of of Kansas, Kansas, Lawrence, Lawrence, W.R. of Geology, Kansas, 66045, 66045,and and J.L. 1L. Anderson, Department of of Geological Kansas, Anderson, Department Geological Sciences, Sciences, University University of Southern Angeles, California California 90007 of Southern California, Los Los Angeles, 90007 ABSTRACT Many of of the the southernmost of the the Precambrian in central southernmost exposures exposures of Precambrian shield shield in central Many Wisconsinconsist consistofofgneiss, gneiss,migmatite, migmatite, and/or amphibolite with associated younger Wisconsin younger intrusive rocks rocks ranging ranging in in compositon compositonfrom from tonalite tonalite to granite. Rb-Sr intrusive Rb-Sr whole-rock whole-rock analyses and U-Pb zircon analyses show that analyses and U-Pb zircon analyses show that the migmatitemigmatite- and and gneiss-forming gneiss-forming events occurred events occurred about about 2.8 b.y. b.y. ago. ago. Ages Ageson onminerals minerals and and younger younger plutonic plutonic rocks rocks indicate that older indicate older gneiss gneiss and and migmatite migmatite were were intruded intruded and and locally locally metamorphosed metamorphosed during major major events events 1.5 during 1.5 to 1.9 b.y. ago. Rb-Sr isochrons for for the the migmatite have Rb-Sr isochrons have elevated initial initial Sr87/Sr86 Sr 87 /Sr 86 ratios (ca. 0.710), suggesting suggestingthat that the the migmatites migmatites formed formed from from crustal rocks 0.710), rocks of intermediate intermediate to granitic were themselves themselves formed formed more more than than 3.0 b.y. ago. granitic composition composition arid and which which were 3.0 b.y. ago. If this If this is true, true, then then the thegneissic gneissic and and migmatitic migmatitic rocks rocks inincentral centralWisconsin Wisconsin may may represent an an eastward extension of of the the ancient represent eastward extension ancient ( >> 3.3 3.3 b.y. b.y. old) old) Minneosta Minneosta River River Valley Valley Terrane. 67 �COMPOSITIONAL VARIATIONS VARIAnONS OF MINNESOTA RIVER VALLEY VALLEY AMPHIBOLITES AMPHIBOLITES P.W. K.3. Schulz, Schulz, and and B.V. B. V. Nielsen, Nielsen, Minnesota Minnesota Geological Geological Survey, Survey, St. P.W. Weiblen, Weiblen, K.J. Paul, Minnesota Minnesota 55108 55108 ABSTRACT Studies of Archean at Morton, reveal that hornStudies of Archean amphibolites amphibolites at Morton, Minnesota Minnesota reveal horn- blende-plagioclase enclaves(two (twometers meters inin size) size) contain contain only blende-plagioclase enclaves only rare rare clinopyroxene, clinopyroxene, whereas larger enclaves Both types types are whereas larger enclaves (20 (20 meters long) long) contain contain up up to to 30%. 30%. Both rimmed by biotite. biotite. Except rimmed by Except for for K, K,compositional compositional variations variations within within and between between the two types types reflect reflectigneous igneous processes processes and and resemble resemble northern northern Minnesota Minnesota greenstones greenstones (Figs. la & & b). Some Some amphibolites amphibolites from from near near Delhi Delhi and and Montevideo Montevideo contain contain -<< 10 10 wt, % Al2O.. wt. Al 20 j • Their Their compositions compositions mimic mimic komatilte-like komatlite-like greenstones greenstones (Figs. (Figs. Ic lc & & d). d). The data that magmas data 'uggest suggest that magmas of of igneous igneous precursors precursors of of certain southwest southwest The Minnesota amphibolites and and northern northern Minnesota greenstones were were generated generated from Minnesota amphibolites Minnesota greenstones similar source rocks in comparable tectonic regimes. regimes. .6 .5 to ta 1• .4 .4 .33 MINN l'lINN ' .6 .EttI .5 + b T\iC;::l RVEP VRLlEY TH TH MPHI60LITES • '. L. \ RLLEY RMPHI80LITES ; i ! .4 ! .3 t r .1 T 1.2 .2 .1 .2 .2 .1 :L t t .0 + .1 • i .0 EN—S 9N-S SN—7 5N-7 ... .4 .il c. .5 (!) CD .:J t ;9 m 19 17 • : T '!' CD <:> c. ! .b .~ i I .5Ir iCJ .6+ d , .6 .5 Td .6'- PVE9 \IPLLEY MI~·j~. Fl:VER W,U_EY HEL HBlPMPHISOL1TES RMPHI80LITES .34- cC MINr\ .4 .3 .3 17 15 IS 1d 13 12 x 12 ÷3 + 32 :~.4 ~ 8N-3 3N-2 EN—i 8N-I 36 'A 32 20 y 20 t 1.3 .6 1 VERMILION KOMRTIITES VERMiLION KOMRTI ITES I I .~ T .2 :~ ~ .11- i .0 .0+ . ~ .2 .2 <:> CD .3 .3 + . 1 TiI EN—S '" 8N-6 SN-S 3N-5 8N-4 xx SN—4 I .2 + t O-F,EENSTONE VERMILION GREENSTONE __ '" t .1 •.2 2 ~I' .3 ~b-I~1 j .; K56-75 ' x 56-756 i- 56-754 to 56-665 .• J T (!) 56-66:J i .5 cD 1- .3 + . -1- T .5. .o- ~ I' -i. W MO FE .I1N MN CR OP Rl PL SI MS FE SirIII PNR P NR T (!) CD 39 35 38 37 I .,. i K K j 40 6. t 1 <:> xX CD MG FE MN OP RL TI MG MN CR Rl SI 5 I TI PNP P NR K i< Log plots plots of of compositions compositions normalized normalized to Hawaiian tholeilte (as Fig. 1. 1. Log Hawaiian tholeiite (as oxides, oxides, right right to left: 8.1, 8.1, 10.04, 10.04-, .17, 10.9, 10.9, 13.4, 13.4-, 50.4, 50.4-, 2.7, 2.7, .28, .28, 2.3, 2.3, .53). .53). Numbers Numbers below below 00 have negative values. negative values. (Data (Data from Nielsen, Nielsen, in in prep., prep., Sims, Sims, P.K., P.K., 1972, 1972, and and Green Green and and Schulz, in prep). REFERENC ES REFERENCES Sims, P.K., 1972, Metavolcanic and associated Metavolcanic and associated synvolcanic synvolcanic rocks rocks in in Vermilion Vermilion Sims, P.K., 1972, district, in district, in Sims, Sims, P.K. P.K. and and Morey, Morey, G.B., G.B., eds., eds., Geology Geology of of Minnesota: Minnesota: A A Centennial Volume, Volume, Minnesota Geological Survey, p. 632. 68 �Rb-Sr GEOCHRONOLOGY AND TRACE ELEMENT ELEMENT GEOCHEMISTRY GEOCHEMISTRY OF GRANULITE FACIES ROCKS NEAR FACIES NEAR GRANITE GRANITE FALLS, FALLS, IN IN THE THEMINNESOTA MINNESOTA RIVER RIVER VALLEY VALLEY Wendell E. E. Wilson Wilson and and V. V. Rama Rama Murthy, Murthy, Department of of Geology Geology and andGeophysics, Geophysics, Wendell University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT Sr- isotopic isotopic composition compositionand and the the trace-element trace-element abundances abundances of K, Rb, Rb, Sr, Sr, The Srand Ba Ba have have been been determined determined in in several several whole and mineral and whole rocks rocks and mineral separates from from four lithologic four lithologic units units in the the Minnesota Minnesota River River Valley, Valley, near Granite Granite Falls, Falls, Minnesota. Minnesota. The sampled units units are are the inner The sampled inner and and outer units units of of hornblende-pyroxene hornblende-pyroxene gneiss, gneiss, the biotite-garnet gneiss, gneiss, and and the the metagabbro metagabbro originally originally included included in in the the"hornblende"hornblendepyroxene gneiss" of Himmelberg Himmelberg (1968). (1968). Rb-Sr data give The The whole whole rock rock isochron isochronages ages (T) (T) obtained obtainedfrom from the the Rb-Sr data are give below; ages ages obtained obtainedfor for metamorphic metamorphic events, events, as as determi~ed determiied by below; by mineral mineral isochrons isochrons are given giveni21;ra8~ets. ibraets. All All ages areare in inunits yrs); all all errors errorsare are 20-. 2-. are ages unitsofofaeons aeons (10 (10 yrs); The initial Sr/ Sr ratios ratios (I) refer to the Sri Sr (I) refer the whole whole rock rock isochrons. isochrons. The Garnet-.Biotite gneiss Garnet-Biotite 0.14 (1.81); (1.81); I == 0.7008 +÷0.0009. 0.0009. T == 3.54 ~÷0.14 I-Iornblende-Pyroxene Gneiss Gneiss (outer (outer unit) Hornblende-Pyroxene T == 3.31 ~÷0.26 0.26 (1.78); (1.78); I == 0.7011 :-÷0.0012. 0.0012. Gneiss (inner Unit) Unit) Hornblende-Pyroxene Gneiss Data Data scatter precludes precludes attempts at dating. dating. Meta-gabbro of of Himmelberg Himmelberg (1968) (1968) T ==2.68 :+ 0.20 (l.80); (1.80); I == 0.7037 :-÷ 0.0001. Interpretations of the the above Interpretations of above data data are are subject subject to to the theusual usualambiguities ambiguities in in discussions ofgeochronological geochronologicalproblems problemsofofearly earlyArchean Archeanterranes. terranes. The discussions of The simplest simplest explanation seems to be that the combined section of hornblende-garnet-pyroxene explanation seems be that the combined section of hornblende-garnet-pyroxene granuLitefacies faciesrocks rocksatat Granite age of granulite Granite Falls Falls has has aa minurnum minumum age of 3.55 3.55 AE AE with with a pronounced metamorphism at at 1.8 1.8 AE. AE. The element patterns patternsofofthe thehornblende-pyroxene hornblende-pyroxene gneisses gneisses and and garnetgarnetThe trace element biotite gneisses graywackesofof island-are-alkali island-arc-alkalibasalt basalt affinities affinities and gneisses resemble resemble graywackes and the metagabbros resembles aa low-K metagabbros resembles low-K tholeiite. tholeiite. The rocks at Granite Granite Falls Falls The granitic rocks therefore represents aa very very old old layered sequence of of basaltic therefore probably probably represents layered sequence basaltic rocks rocks and and graywackes intruded by by the the Montevideo Montevideo Gneiss. Gneiss. 69 69 t �I PETROLOGY OF THE NORTHWEST CORNER OF PETROLOGY OF THE ARCHAEAN ARCHAEAN GNEISSES GNEISSES OF NORTHWEST CORNER THE SACRED HEART THE HEART PLUTON; PLUTON; MINNESOTA MINNESOTA RIVER RIVER VALLEY, VALLEY, MINNEOSTA MINNEOSTA lames L. Welsh, James Welsh, Department of of Geology Geology and and Geophysics, Geophysics, University Universityof ofWisconsinWisconsinMadison, Wisconsin ABSTRACT Approximately 66 miles miles south south of of Sacred Sacred Heart, Minnesota, Approximately Minnesota, along along the Minnesota Minnesota River Valley, the Sacred Sacred Heart Heart quartz monzonite River Valley, the monzonite is intrusive intrusive into into an an older older gneissic gneissic complex. Detailed in the the gneisses along the the northwestern Detailed mapping mapping in gneisses along northwestern portion portion of the the outcrop outcrop belt reveals reveals four four structurally structurally concordant concordant lithologies, lithologies, which which are are described described below from from south south to to north. below The southern part part of of the the area consists of the Sacred The southern consists of Sacred Heart Heart pluton. pluton. To To the the north, the pluton is in in gradational, gradational, but but apparently apparently intrusive intrusive contact contact with a salmonnorth, pluton is salmonpink clinopyroxene clinopyroxene syenite, syenite, which which contains contains abundant, nebulitic, mafic pink abundant, commonly commonly nebulitic, Manyofof the the larger inclusions inclusions. Many inclusions are zoned, zoned, consisting consisting of of pyroxene-rich pyroxene-rich rinds and rinds and hornblende-rich hornblende-rich cores. Separated Separated from from the syenite syenite by by aa sill-like sill-like body body of of quartz monzonite is aa sequence of interlayered tonalitic monzonite is sequence of tonalitic gneisses gneisses and and amphibolites, amphibolites, which are are in in turn which turn separated separated by by another another sill sill of quartz quartz monzonite, monzonite, from from a layered layered gneiss consisting consisting of of alternating alternating pink leucogranitic gneiss pink microcline-rich microcline-rich bands bands and and yellow yellow plagioclase-rich bands. bands. Numerous inclusionsofof tonalitic tonalitic gneiss gneiss are are contained contained in in the the plagioclase-rich Numerous inclusions quartz monzonite quartz monzonite monzonitelies lies toto the the north, monzonite sills. sills. More More quartz north, with with tonalitic tonalitic gneisses again again cropping cropping out out across across the the river. gneisses The represent the oldest The interlayered interlayered tonalitic tonalitic gneisses gneisses and and amphibolites amphibolites represent oldest Isoclinal folding foldingand andshearing shearingwithin withinthe the unit unit indicate rocks exposed exposed in in the the area. Isoclinal rocks deformation and probable probable metamorphism metamorphismprior priortoto the the intrusion intrusion of of the quartz deformation and quartz monzonite. Field monzonite. Field relations relations and and modal modal data suggest suggest that that the theplagioclase-rich plagioclase-rich bands bands of are part of the the layered layered leucogranitic leucogranitic gneiss gneiss are part of of the thetonalitic tonaliticgneiss gneisscomplex. complex. Mineral textures and Mineral textures and modal modal data also also suggest suggest aa possible possible relationship relationship between between the microdine-rich microcline-rich bands bands of of the the layered layered leucogranitic leucogranitic gneiss gneiss and and the thepyroxene pyroxene syenite. syenite. Although the the microcline-rich microcline-rich bands bands of of the layered leucocratic Although leucocratic gneiss gneiss are are somewhat somewhat the syenite more more quartz-rich quartz-rich it is thought thought that desilication desilication of of the syenite occurred occurred by by conversion of of aa former former amphibolite conversion amphibolite to aa pyroxene-rich pyroxene-rich rock, rock, during during the intrusion intrusion of a potassium-rich potassium-rich magma. This This reaction reactionisisevidenced evidenced by by the the zoning zoning of of the the inclusions inclusions within the the syenite. within The following sequence sequence of of events events is is thought to have The following have occurred: (1) (1) deformation and metamorphism and metamorphism of a volcanic pile forming forming the the tonalititc gneisses and amphibolites; (2) dilatation dilatation of of the gneiss followed by by infiltration infiltration of of a amphibolites; (2) gneiss sequence sequence followed potassium-rich magma magma into into the the rupture zones, forming potassium-rich forming the pyroxene pyroxene syenite and the layered leucogranitic gneiss; intrusion of of the the quartz monzonite. gneiss; (3) (3) intrusion 70 �FIELD TRIPS �I FIELD TRIP A FIELD MINNESOTA RIVER VALLEY MINNE50TA VALLEY FIELD TRIP AND FIELD AND CONFERENCE No formal formal guidebook for the the Minnesota No guidebook for Minnesota River River Valley Valley Field Field Trip Trip has has been prepared prepared at the been the specific specific request request of ofS.S. 5.5. Goldich, Goldich, convenor. convenor. Abstracts of talks talks given given at at the theTuesday Tuesday evening evening discussion discussion at RedwoodFalls Fallsare areincluded includedasasa apart partofof these these Proceedings. Proceedings. A Redwood A collection collection of of reprints pertaining reprints pertaining to the the geology geology of of the theMinnesota Minnesota River River Valley Valley and and an an informal set set of stop informal stop descriptions descriptions will will be be provided provided to the the participants. participants. However,inasmuch inasmuchasasthe thelatter latter are not However, not quotable quotable for for publication publication they are not included included here. 73 73 I �• FIELD TRIP BB ENGINEERING GEOLOGY, PLEISTOCENE GEOLOGY AND ENGINEERING GEOLOGY, GEOMORPHOLOGY IN THE THE TWIN TWIN CITIES AREA AREA INTRODUCTION INTRODUCTION 8:00 May 5th 5th St. Paul 8:00 a.m. Wednesday, Wednesday, May Paul Radisson Radisson Hotel, Hotel, St. St. Paul. cost parking parkingisis available available just just across across the the river river from Paul. Low Low cost from the the hotel, hotel, immediately west of the immediately west the first firstexit exitfrom fromthe theWabasha WabashaAvenue Avenue bridge. bridge. Field Field clothes are recommended for underground construction inspection. inspection. Bring recommended for underground construction Bring aa hard by bus bus to to the hard hat if if you you have have one. one. Transportation Transportation by the University University of of Assemble: Assemble: Minnesota pus. Minnesota cam campus. a.m.,back of Pillsbury Optional Optional Assembly Assembly Point: Point: 8:30 8:30 a.m.,back Pillsbury Hall, Hall, University University of of Minneosta campus. Near-by opportunities are are limited. Those who Minneosta campus. Near-by parking parking opportunities who find it convenient may join join the the field field trip trip at this point rather than find convenient to do do so so may than going Paul. going to to St. Paul. MORNING ITINERARY MORNING The will divide divide into into two two equal at the The excursion excursion will equal groups groups at the University University of of Minnesota campus. One One group groupwill willbebetransported transportedtoto site site A A by by bus bus for for the Minnesota campus. on foot foot to site B. first half half of of the the morning. morning. The The second second group group will will proceed proceed on B. In mid-morning mid-morningthe the two two groups groups will willexchange exchangesites sites via via bus bustransportation. transportation. In Site A; Site A; Como Como Avenue Avenue Storm Storm Sewer Sewer Tunnel. Tunnel r City City of ofMinneapolis: Minneapolis: Ralph Rabus and Ray Ray Sterling; Sterling; guides) guides) The The portal portal of of the the tunnel tunnel isis located located at the Rabus and the foot of the River on on the the northeast bank foot the bluffs bluffs along along the the Mississippi Mississippi River bank about The site site affords view of of the half a mile half mile below below St. St. Anthony Anthony Falls. The affords aa good good view incised gorge gorge of of the Mississippi, carved since since the the end incised Mississippi, carved end of of the the Pleistocene Pleistocene glaciationasas St. St. Anthony AnthonyFalls Fallsretreated retreatedfrom fromits its original originalsite site at at the glaciation confluence of of the Minnesota and Mississippi Riverstotoits its present present site, confluence Minnesota and Mississippi Rivers about 88 miles miles upstream. upstream. The about The falls falls is is now now stabilized stabilized by a lock lock and and dam dam as facilities for control and well as water control and diversion facilities for the experimental experimental operations of of the St. operations St. Anthony Anthony Falls Falls Hydraulic Hydraulic Laboratory of the University University of Minnesota. Abovethe the falls falls the the river river flows flows on on aa pavement pavement of of hard, hard, slabby slabby Above Platteville Limestone. Limestone. The Platteville Platteville Limestone is underlain by two two to The Limestone is underlain by 75 �three feet feetofofsoft softshale, shale,known knownasasthe theGlenwood Glenwood Formation, Formation, beneath beneathwhich which is the St. St. Peter PeterSandstone, Sandstone, aa light light yellow yellow to to almost almost white, white, medium-grained medium-grained to fine-grained, fine-grained, friable friable sandstone sandstone composed composed almost entirely entirely of of well well rounded rounded but of quartz sand or two but frosted grains grains of sand with with one one or two percent of of clay clay binder. binder. The is very The sandstone sandstone is very massive, massive, and and in in many many exposures exposures appears appears to to have have almost no no bedding. bedding. It is is about about 150 150 feet thick thick in in the theTwin Twin Cities Cities basin. basin. These formations are are well exposed inin the the river These formations well exposed river bluffs bluffs visible visible from from the the portal site. A storm sewer A storm sewer tunnel, tunnel, 10 10 feet in in diameter, diameter, is is being being excavated excavated in in the St. Peter Sandstone by hydraulic hydraulicmining miningmethods. methods. AA jet jet of of water directed Sandstone by directed at the the St. St.Peter PeterSandstone Sandstoneloosens loosensthe theclay claybinder binderand andthe therock rockdecomposes decomposes into a slurry into slurry of of incoherent incoherent sand. sand. The The properties properties of the the sandstone sandstone which which allow it to allow it to be be mined mined by by this this method method also also allow allow the the rock rock to to ravel ravel upon upon exposure, especially especially where where skin skin stresses exposure, stresses are are developed developed ininunderground underground at the The Department Department of of Civil Civil and and Mineral Mineral Engineering Engineering at the openings. The University of Minnesota has developed University of Minnesota has developed aa sodium sodium silicate based based chemical chemical grout which grout which penetrates porous porous rocks rocks and and hardens hardens to consolidate consolidate the rock rock into aa strong, strong, durable durable material. material. The is sprayed sprayed on on the the surface surface of of the into The liquid liquid is tunnel to form tunnel form aa strong strong skin, skin, which which supplies supplies all of the the support support needed needed where where has not not been the St. Peter Peter Sandstone Sandstone has been adversely adversely affected by by fracturing and and In weaker weaker zones decomposition. In zones shotcrete and and epoxy-cemented epoxy-cemented rock rock bolts bolts are used used for additional support. Research Research by by Walter Walter Parham Parham of of the theMinnesota Minnesota Geological Geological Survey Survey has has shownthat that the the primary primary clay clay minerals minerals inin the the St. St. Peter Sandstone are illite shown Sandstone are and montmorillite, montmorillite, which which form form an an effective effective binder, and binder, even where present in in where these clays very small quantities. In very small In zones zones where clays have have been been converted converted by by diagenesis toto kaolinite, kaolinite, the the kaolinite diagenesis kaolinite tends tends to occupy occupy interstices between between sand grains, grains, rather rather than than coating sand coating the grains, grains, and and much much of the intergrariular intergranular slight change cohesion This slight change in in mineralogy mineralogy greatly weakens weakens the St. cohesion isis lost. This Peter Sandstone and has has strongly strongly affected underground Sandstone and underground construction locally locally This phenomenon phenomenondoes doesnot not appear appear to to have in the Twin in Twin Cities Cities area. This have been been encountered encountered in in the the present tunnel. Experimental Tunnel Tunnel and and Test Site B; Test Chamber: Chamber: (Donald (Donald Yardley Yardley and and 13; Experimental Charles Nelson, guides). The Charles Nelson, guides). The Department Department of of Civil Civil and and Mineral Mineral Engineering Engineering at the at the University University of of Minneosta, Minneosta, aided aided by by aa grant grantfrom from NSF-Rann, NSF-Rann, is is construting an an experimental experimental tunnel tunnel and and large underground chamber beneath construting underground chamber 76 �I the University University of Minnesota Minnesota campus campus to develop develop construction construction methods methods and and structural parameters spaces. One parameters for the the design design of of large large underground underground spaces. One of of the primary is to take advantage primary purposes purposes is advantage of of the the very very large largeenergy energy savings savings that may may be be achieved achieved through through the the better better use useofofunderground underground space. space. Underground space also also provides provides opportunities opportunities for for relieving relieving urban urban congesconges- tion tion and and mitigating mitigating the the environmental environmental impacts impacts of many many transportation, transportation, industrial and and utility facilities. The will be The experimental experimental excavation excavation will be entered entered through through an an existing existing steam tunnel tunnel of the the University University heating heating system system (The (The temperature temperature is is high. high. steam Be to shed prepared to shed your your jacket). jacket). At At one one point point in in the the passage passage through through the Be prepared concrete-lined steam tunnel there is is an an intersection intersection with with an an unlined unlined tunnel. tunnel. This tunnel, excavated excavated in in the the St. This tunnel, St. Peter Peter Sandstone, Sandstone, exhibits exhibits a persistent, persistent, vertical crack or fissure in its crown which makes makesitit appear appear that that the crown which the tunnel tunnel follows aa vertical joint joint zone. zone. In In fact, the the fissure fissure has has developed developed as as the the follows result of the tensional characteristically develops tensional stress which which characteristically develops in in the crown crown of a circular circular arch archininan anunderground underground structure structure when when the the overlying overlying load load is is of shifted from the the rock that was to the the rock on either either side side of of the shifted from rock that was removed removed to rock on tunnel in arch. tunnel in the the abutments to the arch. The stratigraphic stratigraphic succession successionatat the the site consists The consists of: Glacial Glacial drift, 45 45 St. Peter Platteville limestone, 30 ft.; ft.; Glenwood shale, 44 ft. ft. to 55 ft.; ft.; Platteville limestone, 30 Glenwood shale, ft.; St. Peter sandstone, penetrated penetrated 99 ft. ft. to 10 ft. at sandstone, 10 ft. at invert invert elevations. elevations. The experimental tunnel and and chamber chamber isis partly partly excavated The experimental tunnel excavated in weak weak shale of the Glenwood Formationand andpartly partly in in St. St. Peter shale of Glenwood Formation Peter Sandstone. Sandstone. The roof the chamber chamber is is formed formed by by hard, hard, slabby slabby limestone roof of the limestone of of the Platteville 100feet feet of of unlined access tunnel tunnel isis traversed Formation. About About 100 unlined access traversed in the the GlenwoodFormation, Formation,a ashale shaleunit, unit,two twototo three three feet thick, Glenwood thick, characterized characterized by aa persistent by persistent soft mud mud seam seam about about one one inch inch thick thick containing containing pyrite pyrite The shale severe deterioration and air crystals. The shale shows shows severe deterioration and air slaking slaking due due to to exposure. About 70 70 feet feet of excavated in in St. St. Peter About of the access access tunnel tunnel have have been been excavated Sandstonewhich whichhas hasbeen been grouted grouted by by spraying spraying with with the the sodium Sandstone sodium silicate compound A. compounddescribed described under under Site Site A. Another 70 70feet feet of of the the tunnel Another tunnel in in St. Peter Sandstone Sandstone has has been beenleft left untreated as a control. The test test chamber is in of excavation. excavation. A The chamber is in the process process of A drift drift has has been been driven the the full full length lengthofof 100 100feet, feet, and and aa cross cross drift has been driven been driven driven the full width of of 50 50 feet. feet. The in one one section section to to 20 20 feet. feet. width The long long drift drift has has been been widened widened in Thecompleted completedchamber chamberwill willbebe100 100byby5050feet, feet,8 8feet feethigh. high. The The Platteville Platteville The 77 77 I �Limestone will form form the the roof roof of of the the chamber. Limestone will chamber. The The invert invert will will be be in in the the St. St. Peter Sandstone. from the the roof will cut cut about Sandstone. The The walls walls from roof down down will about 4 feet of of Glenwood shale and andabout about 44feet feet of of St. Peter Glenwood shale Peter Sandstone. Sandstone. Excavation of the the access tunnels Excavation of tunnels and and chamber chamber has has been been entirely entirely by by hand using pneumatic pneumatic drills drills and and spades hand operations, operations, using spades and and hydraulic hydraulic rock rock splitters. This This has has been been necessitated necessitated by by the small small size of the access access tunnels both the the St. Peter (4 (4 feet wide wide by by 6.5 feet feet high). high). However However both Peter Sandstone Sandstone and and the Glenwood shale are are readily readily excavated excavated in in this Glenwood shale this way. way. The The hydraulic hydraulic rock rock splitters have very useful useful in in spalling spallingoff off the the shale splitters have proved proved very shale to the the bedding bedding surface in the surface the overlying overlying Platteville Platteville Limestone Limestone which which has has been been chosen chosen to to form form the roof. As As construction construction proceeds, proceeds, the the underground underground chamber is being being thoroughly instrumentedtoto determine determine rock rock deflections, deflections, stresses, stresses, and thoroughly instrumented and the influence of an an overlying overlying perched perched water water table on structure. influence of on the underground underground structure. Instrumentation includes six-point extensometers, extenso meters, two-point extensometers, and the roof meters, and inverted inverted piezometers piezometers installed installed from from below below through through the roof into the perched into perched water water table table above above the the Platteville PlattevilleLimestone. Limestone. A boresupport for for the roof scope is being used to to examine drill being used dr ill holes. Principal Pr incipal support roof is is provided by epoxy-grouted rock bolts provided by epoxy-grouted rock bolts which which consolidate consolidate the the overlying overlying Platteville Limestone Limestone into a rigid rigid plate. Noon: Box lunch picnic. Noon: Box AFTERNOON ITINERARY ITINERARY Stanley Chernicoff, Field Leader Stanley Leader the Twin The surficial geology geology of of the Twin Cities Cities Metropolitan Metropolitan Area Area is is The surficial dominatedby bythe the effects effects of of the late dominated late Pleistocene Pleistocene glaciation glaciation of of Minnesota. Minnesota. The glacial glacial events events that modified are reconstructed The modified the regional regional landscape landscape are by interpreting the deposits of glacial by interpreting the deposits of glacial materials materials and and their their associated associated landforms. landf or ms. In the Metro In Metro area, area, glacial glacial deposits deposits from from two two points points of of origin origm have have been identified. identified. Approximately years ago, ago, an an ice lobe accumulating been Approximately 20,000 20,000 years basin advanced in the Lake Superior basin advanced along along aa bedrock bedrock conduit conduit (the MinneapolisLowland) Lowland)totoaa terminal Minneapolis terminal position position topographically topographically expressed expressed locally as as the St. Croix locally Croix moraine. moraine. This This land land form, characterized by by hills hills and and is composed of poorly depressions ice-block lakes, lakes, is composed of poorly sorted sorted depressions dotted dotted with with ice-block traversed eastern mineral constituents constituents entrained entrained by by the the glacier mineral glacier as as it traversed eastern 78 �Minnesota. The quantities of red The bedrock bedrock supplied supplied quantities red sandstone, sandstone, basalt, basalt, and and red that impart impart the the characteristic red granophyre granophyre that characteristic red red hue hue to to Superior Superior lobe lobe drift. drift. Approximately 16,000 years years ago, Approximately 16,000 ago, ice ice originating originating in in southeastern southeastern Manitoba and northwestern northwestern Minnesota Minnesota advanced advanced along along the the Red River Manitoba and River valley valley toward a terminal terminal position position near near Des Des Moines, Moines, Iowa. Iowa. A A short-lived short-lived extension extension of the the Des Des Moines Moines lobe lobe (the (the Grantsburg Grantsburg sublobe) sublobe) entered entered the the Minnesota Minnesota lowland from the the southwest across the northwest lowland from southwest and and proceeded proceeded across northwest corner of the metropolitan the recently metropolitan area overriding overriding the recently deposited deposited red red glacial glacial drift. The of the Grantsburg are markedly different from The deposits deposits of Grantsburg sublobe sublobe are markedly different from the Superiorlobe lobematerials. materials. A long its its route route of of advance, advance, the the ice ice traversed Superior A long traversed a sedimentary sedimentary terrane terrane incorporating incorporating fragments fragments of of Paleozoic Paleozoic limestone, limestone, The and the dolomite, dolomite, and and siliceous siliceous shale. The carbonate carbonate composition composition and the diagnostic grey grey color color (yellow (yellow or tan tan in in oxidized oxidized exposures) exposures) easily easily distinguish distinguish sublobe drift from Grantsburg sublobe from the thereddish—colored reddish-colored Superior lobe sediments. A field review review of the the geology geology of of an an urban urban center centershould should describe describe the the geologic character character of of the area and, geologic and, wherever wherever possible, possible, relate the the observed observed physical conditions conditionstoto their their land-use land-use potential. potential. The The object object of of this part of physical of the excursion to introduce the salient features excursion isis to introduce the features of of the thelocal localgeology geology and and promote discussion regarding responsible responsible urban urban development development within within the promote discussion regarding geologic framework. ace: Stop Grey Till Till - Red Till Till Interf Interface: Stop C; C; Grey New New Brighton Brighton Quadrangle Quadrangle - N. The stratigraphic relationship and Matterhorn Matterhorn Drive. Drive. Danube Road Road and Danube till and between the the red between red Superior Superior lobe lobe till and the theoverlying overlying grey grey Grantsburg Grantsburg of red red till have sublobetill till isis demonstrated demonstrated at at this sublobe this locality. Masses Masses of have been been incorportated into into the the grey till creating the thin incorportated grey till thin interlaminations. interlaminations. Stop D; Anoka Anoka Sandplain: Sandplain: Stop ID; New Brighton Quadrangle-County Road Road I and New Brighton Quadrangle-County and Lexington Ave. Ave. Sand-charged Sand-chargedmeltwaters meltwatersassociated associated with with the the wastage Lexington wastage of of the Grantsburg sublobe constructed constructed this this extensive extensive sandplain. sandplain. The the Grantsburg sublobe The plain is characterized by characterized by ice-block ice-block depressions depressions and sand sand dunes. dunes. The high The high water of the relatively table is a consequence consequence of relatively low low transmissivity transmissivity of of the the underlying underlying glacial till. glacial River; Abandoned Valley Valley of the Mississippi Stop Ej Mississippi Riverj E; Abandoned Quadrangle—WheelockParkway Parkwayand and Nebraska Nebraska Ave. Quadrangle-Wheelock Ave. 79 Paul East St. Paul East Alongthe the route Along route of of �travel travel from from the theAnoka Anoka Sandplain Sandplain to this locality, the the alignment alignment of of ice-block ice-block lohanna, Josephine, Josephine, McCarron) McCarron) represents represents a lakes (Round, (Round, Valentine, Johanna, lakes former course course of of the theMississippi Mississippi River. River. The The bedrock bedrock valley valley is buried buried by by deep deposits of glacial drift. drift. Stop Park: St. Paul Stop F; Fi Indian Indian Mounds Mounds Park: Paul East East Quadrangle Quadrangle -- Warner Road. This This site affords affords aa view view of of the theMississippi Mississippi River River floodplain. floodplain. The The geological and and environmental elements of environmental elements of the floodplain floodplain management management issue issue (ie. the construction of dikes dikes at at the Holman construction of Holman Field Field airport airport and and the Pig's Pig's Eye Eye coal coal terminal) are visible. visible. Stop Stop G; G; Perched Lake Lake Plains Plains within within the the St. St.Croix CroixMoraine:White Moraine:White Bear Bear Lake Lake This This level level plain plain represents reversalofofaa glaciated glaciatedterrain. terrain. At represents aa characteristic topographic topographic reversal At one byice ice that that fed one time, time, the plain plain was was surrounded surrounded by fed meitwater meltwater into into an an East Quadrangle East Quadrangle - County Highway Highway 99 and and 115 115 St. St. The subsequent subsequent wastage wastage of of the surrounding enclosed basin. basin. The surrounding ice resulted in in the perching perching of basin basin sediments sediments above above the surface surface previously previously covered covered by by ice. Stop Hi H; Land-Use Land-Use Planning PlanningininaaGlaciated Glaciated Terrain: Terrain: Marine Stop Marine on on the St. Croix This This site was was one of of several proposed County Sanitary Sanitary Landfill. Landfill. The proposed for the the Washington Washington County The glacial glacial drift of the drift the locality locality includes includes a mantle mantle of of bess loess(windblown (windblown silt) and and dense dense red till. The red The suitability suitability of of this this site sitefor foraalandfill landfillwill will be be discussed. discussed. 81 (May Ave.) and and 155 Quadrangle - County Road 81 Quadrangle (May Ave.) 155 St. 80 �1 tr ?fkt? \ N '\\\ III 1ri4 I —- . I - L i FL 'Lii NJI\. ------—------ .... -- :- 1111 - • 1-94 to 1m -... -~ 0 sr . F - - / IF F-r-irt r7—1 rr-i / .5 .s- IL. .. \.Jr =-T: — ... S 0 ___ :: Pa -- LJiiEijF IJ JUf r1Jc?tLTi1JA1)o 1 —.-.i[ '- ii . N CAMPUS ..- z.4 I - ,/ 4.. J _ J i V. __ I r:: .... � 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, 1976 Description An account of the resource Institute on Lake Superior Geology. St. Paul, Minnesota. May 3-7, 1976. 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 1976 Contributor An entity responsible for making contributions to the resource B.E. Aaquist J.L. Anderson G.A. Ankenbauer Larry L. Babcock W.A. Bartlett Robert L. Bauer J. Baysinger G.P. Beakhouse Dieter Birk Bill Bonnichsen Emmy Booy J.M. Bratt Charles Brumleve James R. Burnell, Jr. Keros Cartwright E.N. Cameron W.F. Cannon C.L. Chou Donald M. Davidson, Jr. James M. DeGraff B.R. Doe M.H. Delevaux L.J. Drew Stanley J. Dyl Robert Ehrlich S.S. Goldich A.M. Goodwin C.F. Gower James G. Grimes N.B.W. Harris Henry Halls Tsu-Ming Han G.N. Hanson C.E. Hedge Sue I. Jacobsen Allan M. Johnson Manfred M. Kehlenbeck Gene L. LaBerge T.M. Levy M.S. Lougheed R.S. Maass J.J. Mancuso M.B. McBride Lyle D. McGinnis L.G. Medaris, Jr. Robert P. Meyer, Jr. Robert Moore M.G. Mudrey, Jr. Paul E. Myers Syed Neaz Ahmad Edward L. Nebrija C.R. Nelson B.V. Nielsen Richard W. Ojakangas Bruce C. Parker Eugene C. Perry, Jr. Zell E. Peterman H.O. Pfannkuch Dave Pollack Neil M. Pope William C. Prinz V. Rama Murthy C. Riddle James M. Robertson W. Rohrer Frederick J. Sawkins K.J. Schulz Nancy Scofield Donald I Siegel P.K. Sims Eugene I. Smith T.E. Smith Harry O. Sorenson David W. Snider David L. Southwick S.W. Stuhr F.M. Swain R.U. Suda R.M. Tyson A. Turek W.R. Van Schmus Thomas A. Vogel L.J. Walters P.W. Weiblen James L. Welsh Wendell E. Wilson J.L. Wooden D.H. Yardley Charles T. Young Robert E. Zartman 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/4d5f21876dae8187655f5bdd3788714d.pdf 68bc6e24596e10eeea5abbcd8bbaf56f PDF Text Text I INNESOTA i' ;i �I I 1 2 1 3 I I I I 1 I. 1. THREE SYMONS SYMONS55 1/2' 1/2' SHORT-HEAD, THREE SHORT-HEAD JAND ANDTWO TWOSYMONS SYMONS I 1/14' STANDARD 4 1/4' STANDARD CONE CONE CRUSHERS CRUSHERS OPERATING OPERATING AT /4 BLYVOORUITZICHT GOLD MINE MINE, BLYVOORUITZICHT GOLD CARLETONVILLEJ J CARLETONVILLE, TRANSVAAL, REPUBLIC AFRICA, TRANSVAALJ REPUBLIC OF OF SOUTH SOUTH AFRICA. 2, 2. P & H MINING ~ MINING SHOVELS, SHOVELS J BUILT BUILT ININMILWAUKEE MILWAUKEE BY BY HARNISCHFEGER., HARNISCHFEGER J HAVE HAVE BEEN BEENWORKING WORKINGYEAR—ROUND YEAR-ROUND REMOVING OVERBURDENAND ANDMINING MINING IRON REMOVING OVERBURDEN IRON ORE ORE AT AT I I 1 DOFASCO'S ONTARIO J DOFASCO'S ADAMS ADAMSMINE MINEAT AT KIRKLAND KIRKLAND LAKE LAKE, J ONTARIO, CANADA SINCE IT IT BEGAN IN 1964k CANADA SINCE BEGAN OPERATIONS OPERATIONS IN 1964. 3. 3, ROTARY KILN KILN COMPLETES INDURATION OF OF IRON ROTARY COMPLETES INDURATION IRON ORE ORE PELLETS AT AT 2400°F 2'400°F IN PELLETS INTHIS THISGRATE—KILN ~ PELLETIZING PELLETIZING PLANT IN PLANT IN MINNESOTA. MINNESOTA. I �PROCEEDINGS Twenty Fourth Twenty Fourth Annual Annual Meeting Meeting INSTITUTE ON LAKE INSTITUTE LAKE SUPERIOR SUPERIOR GEOLOGY HELD AT HELD AT THE THE PFISTER HOTEL PFISTER HOTEL MILWAUKEE r~IlH,~UKEE WISCONS IN WISCONSm MAY9-14 9-1I4 1978 MAY 1978 J SPONSORED BY BY THE SPONSORED THE DEPARTMENTOF OF GEOLOGiCAL GEOLOGICAL SCIENCES DEPARTMENT SCIENCES UNIVERSITY OF UNIVERSITY OF WISCONSIN-MILWAUKEE WISCONSIN-MILWAUKEE 53201 MIlWP\UKEE WISCONSIN \JI SCo;~S IN 53201 MILWAUKEE, G, MURSKY C,A, SAlOTTI AND ANDW1H. W,H,SCHRAMM SCHRAMM G1 MURSKY) C.A1 SALOTTIJ GEiJERAl IT Ji"{S GENERAL ED EDITJRS J J J I �1 I I I I I 1 I I I I I SALES I Department of Geological Sciences, Please order from: from: Department Sciences, Univer— University of of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin, Wisconsin, 53201. sity 53201. Price Make checks checks payable payable to to Institute on Lake Lake Superior Superior $5.00 (U.S.A.). Make Institute on $5.00 (U.S.A.). Geology, Wisconsin. Geology, Milwaukee, Wisconsin. I I I I I �TABLE OF OF CONTENTS CONTENTS GENERAL INFORMATION GENERAL INFORMATION . . . . . . . . . . . . . . vv INSTITUTE BOARD OF DIRECTORS . INSTITUTE . . . . . . . . . . . . v . LOCAL COMMITTEE . . . . . . . FIELD TRIP COMMITTEE COMMITTEE . SESSIONS CHAIRMEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. vi vii vii ANNUAL BANQUET KEYNOTE SPEAKER . . . . . . . . . . . ix ACKNOWLEDGEMENTS . . . . ix . . . . . . . . . . CALENDAR OF EVENTS AND PROGRAM . . . . . . . . . . . . . . POSTER SESSION . . .. xv ABSTRACTS OF OF PAPERS PAPERS . . . . . . . . . . . . . . . . . . . 1 1 FIELD TRIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX OF OF AUTHORS AUTHORS . . . . . . . . . . . . . . . . . . x . . .. 43 49 �GENERAL INFORMATION INFORMATION 24 TH 214TH ANNUAL ANNUAL INSTITUTE ON INSTITUTE ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY PFISTER HOTEL PFISTER HOTEL MILWAUKEE, MILWAUKEE) WISCflNSIN WIsrn~SIN MAY 9-1 9-14LL 1978 ~1AY SPONSORED BY BY THE SPONSORED THE DEPARTMENT OF OF GEOLOGICAL DEPARTMENT GEOLOGICAL SCIENCES SCIENCES UNIVERSITY OF UNIVERSITY OF WISCONSIN-MILWAUKEE WISCONSIN-MILWAUKEE MILWAUKEE, MILWAUKEE) WISCONSIN WISCO:~SIN INSTITUTE BOARD OF DIRECTORS Giblin, Ontario Division of Mines, P.E. Giblin, Mines, Ministry of of Natural Natural Resources, Ontario. Resources, Sault Ste. Marie, Ontario. J.D. J.D. Hughes, Hughes, Department of Geography, Geography, Earth Science and Conservation, Northern Michigan University, Conservation, University, Marquette, Michigan. Marquette, M.M. Kehienbeck, Department Department of of Geology, Geology, Lakohead Lakhead UniverM.M. Kehlenbeck, University, Thunder sify, Thunder Bay,. Bay" Ontario. G. Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University University G. of'Wisconsin-Milwaukee, Milwaukee, Wisconsin. Wisconsin. of Wisconsin—Milwaukee, Milwaukee, R.C. Reed (Secretary-Treasurer), R.C. (Secretary-Treasurer), Geological Survey Survey Division, Division, Department of Natural Natural Resources, Resources, Lansing, Lansing, Michigan. Michigan. M.S. M.S. Walton, Walton, Minnesota Geological Survey, Survey, University of Minnesota, Minneapolis, Minnesota, Minneapolis, Minnesota. Minnesota. v b �LOCAL COMMITTEE Conference Chairman Gregory Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University University of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin. Wisconsin. Organizing Committee Committee Richard Bains, Corporation, Milwaukee, Milwaukee, Wisconsin. Bains, Rexnord. Rexnord Corporation, Frank J. Qf Geological Geological Sciences, J. Charnon, Charnon, Department Of Sciences, University of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin. Wisconsin. John Erb, Milwaukee, Wisconsin Erb, Allis-Chalmers Corporation, Co~po+ation, Milwaukee, Robert E. E. Gernant, Gernant, Department of Geological Sciences, Sciences, University of Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin. Wisconsin. Donna McElroy, McElroy, Department of of Geological Geological Sciences, Sciences, University University of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Mill·'aukee, Milaukee, Wisconsin. of Wisconsin. Katherine G. G. Nelson, Nelson, Department of Geological Geological Sciences, Sciences, Milwaukee, Wisconsin. Wisconsin. University of of Wisconsin, Wisconin, Milwaukee, Mervin Nelson, Nelson, Mervin Nelson Nelson and and Associates, Associates, Milwaukee, Milwaukee, Wisconsin. Wisconsin. A. Paull, Richard A. Paull, Department of Geological Sciences, Sciences, University University Wisconsin-Milwaukee, Milwaukee, Wisconsin. of Wisconsin-Milwaukee, Wisconsin. Gordon R. R. Pirie, Pine, Department Gordon Department of of Geological Geological Sciences, Sciences, University University Qf Wisconsin-Milwauk~e, Wisconsin-Milwaukee, Milwaukee, of Mi~waukee, Wisconsin. Wisconsin. Charlene Ryder, Ryder, Harnisch~eger Harnischeger Corporation, Charlene Corporation, Milwaukee, Milwaukee, Wisconsin. Wisconsin. Charles A. A. Salotti, Salotti, Department Department of of Geological Geological Sciences, Sciences, University University Charles Wisconsin—Milwaukee, Milwaukee, Wisconsin. of Wisconsin-Milwaukee, Wisconsin. Department of of Geological Sciences, University University William B. Schramm, Department Geological Sciences, William }. of Wisconsin-Milwaukee, Milwaukee, Wisconsin. of Wisconsin—Milwaukee, Milwaukee, Wisconsin. Robert W. W. Taylor, Taylor, Department Department of of Geological Geological Sciences, Sciences, University Robert Wisconsin'. of ~visconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Wisconsin. Carol Taylor, Cedarburg, Cedarburg, Wisconsin. David E. E. Willis, Willis, Department Department of of Geological Geological Sciences, Sciences, University of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Wisconsin. Wisconsin. vi �FIELD TRIPS Chairman, R.A. Chairman, R.A. Paull, Paull, Department of of Geological Geological Sciences, Sciences, UniverUniverof Wisconsin-Milwaukee, Wisconsin-Milwaukee, Milwaukee, sity of I1ilwaukee, Wisconsin. Trip II -- Southwestern Southwestern Wisconsin Zinc Zinc — - Lead District W.A. Broughton, W.A. Broughton, University of Wisconsin-Platteville, Platteville, Platteville, Wisconsin. A.V. A.V. Heyl, Heyl, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia. Virginia. M.G. M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Madison, Wisconsin. Madison, Wisconsin. W.S. West, West, U.S. W.S. U.S. Geological Survey, Platteville, Platteville, Wisconsin. Wisconsin. Trip II Mineral Extraction and Processing II -- Mineral Equipment Manufacturers in the Greater Equipment Milwaukee Area C.A. Salotti, C.A. Salotti, Department of Geological Sciences, Sciences, University University of of Wisconsin—Milwaukee, Milwaukee Wisconsin. Wisconsin-Milwaukee, Trip III -- Precambrian Rhyolite and and Granite Granite Inliers in South—Central Inliers South-Central Wisconsin. E.I. Smith, Wisconsin—Parkside, E.I. Smith, Division rf nf Science, University of Wisconsin-Parkside, Kenosha, Kenosha, Wisconsin. SESSIONS CHAIRMEN A.T. A.T. Broderick, Broderick, Manager, I1anager, Mineral Mineral Development, Development, Inland Inland Steel Steel Company, Company, Ishpeming, Michigan. Ishpeming, J.D. Hughes, J.D. Hughes, Chairman, Chairman, Department of ~f Geography, Earth Earth Science Science and Conservation, Conservation, Northern Michigan University, University, Marquette, Marquette, Michigan. J.O. Kalliokoski, Kalliokoski, Chairman, Chairman, Department Department of of Geology, Geology, Michigan Michigan J.O. Technological University, Houghton, Houghton, Michigan. Michigan. vii �M.M. M.M. Kehienbeck, Kehlenbeck, Chairman, Chairman, Department of Geology, Geology, Lakehead University, Thunder Thunder Bay, Bay, Ontario. Ontario. E.R. May, Senior Geologist, E.R. May, Geologist, Exxon Exxon Company U.S.A., U.S.A., Rhinelander, Rhinelander, Wisconsin. Rachel Rachel K. K. Paull, Panll, Department of Geology of Wisconsin-Madison, Madison, Madison, and and Geophysics, Geophysics, University University Wisconsin. Wisconsin. P.K. P.K. Sims, Sims, U.S. U.S. Geological Survey, Denver, Denver, Colorado. Colorado. M.S. M.S. Walton, Walton, Director, ~irector, Minnesota Minnesota Geological Geological Survey, Survey, Minneapolis, Minneapolis, Minnesota. viii �ANNUAL BANQUET BANQUET KEYNOTE KEYNOTE SPEAKER SPEAKER Congressman James James Santini, Santini, House House of of Representatives, Representatives, Washington, Washington, Member, D.C. Member, Committee Committee on on Interior Interior and and Insular Insular D.C. Affairs; Affairs; Subcommittee Subcommittee on on Oversight Oversight of of Public Public Lands Mines Mines and and Mining. Mining. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The organizing committee for for the the 24th 24th Annual Annual Meeting Meeting on on Lake Lake Superior Geology gratefully gratefully acknowledges acknowledges the the support support of of the the followfollowing corporations in in the the Milwaukee Milwaukee area: area: Allis-Chalmers Corporation Corporation Harnischfeger Corporation Rexnord Corporation Ix ix �CALENDER OF EVENTS CALENDER AND PROGRAM Tuesday Tuesday 9, 9, 1978 1978 May ~lay Pre—Institute Field Trip I Pre-Institute I — - Southwestern Wisconsin Zinc-Lead District, departs Zinc-Lead departs from Madison, Wisconsin to Platteville, from Madison, to Platteville, Wisconsin at 12:30 12:30 P.M., P.M., and and return return to to Milwaukee, Wednesday May 10, 1978 Milwaukee, 10, 1978 about about 6:00 P.M. P.M. Wednesday May 10, 10, 1978 1978 Pre—Institute Mineral Pre-Institute Field Trip Trip II II —- Mineral Extraction and Processing Equipment Processing Equipment Manufacturers in the facturers the Greater Milwaukee Milwaukee Area, Area, departs from from the the Pfister Pfister Hotel Hotel about about 8:30 A.M., and return 8:30 A.M., return about about 4.30 4:30 P.M. P.M. 1:00 -- 3:30 3:30 P.M. and 6:00 —9:00 -9:00 P.M. P.M. Early Registration, Registration, near the the Imperial Imperial Ballroom, Pfister Hotel Ballroom, Hotel 7:30 -- 10:00 P.M. Conference 'Smoker", "Smoker", Henry Henry && Louis Louis Room, Room, Pfister Hotel. Hotel. Thursday May Hay 11, 1978 1978 7:00 —- 8:00 A.M. 7:00 Early Registration near near the the Imperial Imperial Ballroom, Ballroom, Pfister Pfister Hotel. Hotel. 8:00—11:55 8:00-11:55 A.M. A.M. Morning Session, Session, Imperial Imperial Ballroom, Ballroom, Pfister Hotel. Hotel. 9:00 A.M. A.M. -- 4:50 P.M. Poster Session, Session, Henry and Louis Room, Room, Pfister Hotel 1:30 —- 4:50 P.M. Afternoon Session, Session, Imperial Imperial Ballroom, Ballroom, Pfister Hotel. 6:00 P.M. P.M. Cocktail Hour Hour (cash (cash bar), bar), Henry Henry and and Louis Louis Room, Room, Pfister Pfister Hotel. Hotel. 7:00 P.M. P.M. Annual Banquet, Banquet, Imperial Imperial Ballroom, Ballroom, Pfister Pfister Hotel. Keynote speaker: Congressman James speaker: Congressman James Santini. Santini. xx �Friday Friday 12, 1978 1978 May 12, 8:10 A.M. A.H. —- 12:10 12:10 P.M. P.M. Morning Morning Session, Session, Imperial Imperial Ballroom, Ballroom, 8:10 Pfister Pfister Hotel. Hotel. 4:10 P.M. P.r-!. 1:30 —- 4:10 Afternoon Afternoon Session, Session, Imperial Imperial Ballroom, Ballroom, Pfister Pfister Hotel. Hotel. 6:30 P.M. P.M. 6:30 Post—Institute Post-Institute field field trip trip III III —Precambrian Precambrian Rhyolite Rhyolite and and Granite Granite Inliers Inliers in in South-Central Wisconsin departs from from the Pfister Hotel, Hotel, for for Oshkosh, Oshkosh, Wisconsin. Wisconsin. This field field trip trip will will return return to to Milwaukee, Milwaukee, Saturday, May 13, 13, 1978 1978 about about 6:30 6:30 P.M. P.M. xi xi �TECHNICAL PROGRAMS A.M. 8:00 —- 11:55 11:55 A.M. Thursday, May 11, 11, 1978 1978 Morning Session Session -- Co-Chairmen: Rachel Rachel K. K. Paull Paull and and Paul Paul K. K. Sims Sims 8:00 8:00 Opening Remarks Remarks 8:15 8:15 Smith, E.I. E.I. A A New Precambrian Surface Contour Map for for South-Central South-Central Wisconsin. Wisconsin. 8:35 Zietz, I. I. A A New Detailed Detailed Aeromagnetic Map Covering Most of of the the Precambrian Precambrian Shield Shield in in Wisconsin. Wisconsin. 8:55 Sims, P.K. P.K. Peterman, Z.E. Z.E. Precambrian Geologic Framework of Northern Wisconsin. Wisconsin. 9:15 Cannon, W.F. W.F. A A Middle Middle and and Late Late Precambrian Precambrian Fault System System in Northern Wisconsin and Northern Michigan. 9:35 Jones, D.G. D.G. Geology of the Iron Formation and Associated Rocks of the the Jackson Jackson County County Iron Iron Mine, Mine, Jackson Jackson County, Wisconsin. Wisconsin. 9:55 -- 10:15 COFFEE BREAK 10:15 Van Schnius, Schmus, W.R. Woronick, R.E. R.E. Egger, N.L. N.L. Geochronologic Relationships Relationships in in the the Carney Geochronologic Lake Gneiss Gneiss and other Basement Gneisses Gneisses in in Dickinson County, County, Upper Michigan. 10:35 DuBois, J.F. J.F. Van Schxnus, Schmus, W.R. Petrology and Geochronology of Archean Gneiss in the Lake Arbutus Area, Area, West-Central West-Central Wisconsin. 10:55 R.D. Hammond, R.D. Van Schmus, W.R. W.R. Geochronology of Archean Rocks Rocks in Marquette County, County, Upper Michigan. Michigan. 11:15 Peltonen, D.R. D.R. Salotti, C.A. Salotti, Taylor, R.W. Taylor, R.W. Relations Between Soil Geo9hemistry Geochemistry and Bedrock Geology, Iron Iron County, County, Wisconsin. Wisconsin. 11:35 11:35 Cummings, M.L. M.L. Myers, P.E. P.E. Petrology and Geochemistry of Amphibolites, River, Eau Claire County, Wisconsin. Eau Claire River, Wisconsin. 11:55 — - 1:30 LUNCH xii �1:30 1:30 —- 4:50 4:50 P.M. P.M. Thursday, Thursday, May May 11, 11, 1978 1978 Afternoon Session Session -- Co-Chairmen: Co-Chairmen: A.T. A.T. Broderick Broderick and and J. J. Kalliokoski Kalliokoski 1:30 1:30 Ojakangas, R.W. R.W. Criteria Criteria for for Alligator Alligator River River Type Type Uranium Uranium Deposits Deposits in in the the United United States. States. 1:50 1:50 Kalliokoski, J. J. Kalliokoski, The Unconformity-Type Unconformity-Type Proterozoic Proterozoic Pitchblende Ore Body Model and and Its Its Application to to Northern Northern Michigan. Michigan. 2:10 2:10 Peterman, Z.E. Z.E. Peterman, P.K. Sims, P.K. Baseline Uranium and Thorium in Archean and Lower Lower Proterozoic Proterozoic Rocks Rocks of of the the Marenisco—Watersmeet Marenisco-Watersmeet Area, Area, Michigan. Michigan. 2:30 2:30 D.G. Meineke, D.G. M.K. Vadis, M.K. Klaysmat, A.W. A.W. Pilot Exploration Geochemical Survey of Uranium Uranium in in Organic-Rich Organic-Rich Lake Lake Sediments, Sediments, Northeastern Northeastern Minnesota. Minnesota. 2:50 J. Trow, J. Possibilities possibilities for for Uranium-Gold Uranium-Gold QuartzQuartzPebble Ores in the the Lake Superior Region in the Light of a New Model for for Elliot Elliot Lake—Witwatersrand Lake-Witwatersrand Genesis. Genesis. 3:10"3:l0 - 3:30 COFFEE BREAK 3:30 W.S. Meddaugh, W.S. Salotti, C.A. Mursky, G. G. The Distribution of Uranium and Thorium in the Wolf Wolf River River Batholith, Batholith, Northeastern the Wisconsin. 3:50 Heinrich, E.W. E.W. Industrial Sand and Sandstone Resources of of Michigan. 4:10 Nebrija, E.L. Welkie, Welkie, C,J. CJ. Meyer, Meyer, R.P. Gere, Jr. Gere, M.A. Jr. Offshore Sand and and Gravel Gravel Exploration Exploration Offshore in Western Lake Michigan. 4:30 4:30 Economic Mineral Mineral Production in in Michigan Michigan Economic Past and Present. Present. xiii xiii �8:10 8:10 —- 12:10 12:10 A.M. A.M. Friday, Friday, May May 12, 12, 1978 1978 Morning Morning Session Session -- Co-Chairmen: Co-Chairmen: M.M. M.M. Kehienbeck Kehlenbeck and M.S. M.S. Walton 8:10 Molling, MoIling, P.A. P.A. Tyson, Tyson, R.M. R.M. Chang, I..L.Y. L.L.Y. Chang, A iA Petrographic Petrographic Guide Guide for for Unit Unit Identif Identification River Troctolite, cation of of the the Partridge River Duluth Duluth Complex, Complex, Minnesota. Minnesota. 8:30 8:30 Foose, M.P. M.P. Cooper, R.W. R. W. Faulting in in Part Part of of the the Duluth Duluth Complex, Complex, Northeastern Northeastern Minnesota. Minnesota. 8:50 8:50 Bauer, Bauer, R.L. R.L. Polyphase Deformation Deformation in in Archean Archean Schists Schists of the the Western Lake Lake Vermilion Vermilion Area, Area, Minnesota. Minnesota. 9:10 9:10 Cambray, Cambray, F.W. F.W. Plate Tectonics Tectonics as as aa Model Model for for the the EnviEnvironment of of Sedimentation Sedimentation the the Marquette Marquette Super group and the Subsequent Supergroup Subsequent Deformation Deformation and Metamorphism Metamorphism Associated Associated with with the the Penokean Orogeny. Orogeny. 9:30 Larue, D.K. D.K. Problems in in Paleogeographic Paleogeographic ReconstrucReconstruction of the Chocolay and and Lower Lower Menominee Menominee Group Sedimentation, Marquette Range Range Supergroup , Lake Superior Region. Supergroup, Region. 9:50 -- 10:10 COFFEE BREAK 10:10 Massey, N.W.D. N.W.D. The Geochemistry of Keweenawan Keweenawan Lavas Lavas of of the Mamainse Point Formation, Formation, Ontario. Ontario. 10:30 Jirsa, M.A. M.A. The Petrology and Tectonic Tectonic Significance Significance of the Interf low Sediments Sediments in in the KeweeInterflow nawan North Shore Volcanic Group of Northeastern Northeastern Minnesota. Minnesota. 10:50 10:50 West john, D. D. Westjohn, Cambray, F.W. Cambray, F.W. Finite Strain in the Precambrian Kona Formation Formation of of the the Marquette Marquette Synclinoriuxn. Synclinorium. 11:10 11:10 Strakele, A.E. A.E. The Geology and and Petrology Petrology of of the the Wine wine Lake Intrusion, Lake Intrusion, Cook County, County, Minnesota. 11:30 11:30 Cambray, F.W. The Origin and Timing of Cleavage FormaThe Formathe Siamo Siamo Slate Slate of of Precambrian Precambrian tion in the X X Age, Marquette County, County, Michigan. Michigan. 11:50 11:50 Hughes, J.D. Hughes, J.D. A A Post Two Creeks Buried Forest in in Michigan's Northern Peninsula. 12:10 — - 1:30 LUNCH xiv �1:30 —- 4:10 P.M. Friday, May 12, Friday, 12, 1978 Afternoon Session Session -- Co-Chairmen: J.D. J.D. Hughes and E.R. E.R. May May 1:30 Banaszak, K.J. K.J. The pH of Ore Ore Fluids of of Mississippi Mississippi Valley Type Deposits. Type Deposits. 1:50 Cummings, M.L. M.L. Stratigraphy and Mineralization, Mineralization, Quinnesec Formation, Northeastern Northeastern Wisconsin. 2:10 Aaquist, B.E. B.E. Hodder, R.w. R.W. Microstylolites—An Microstylolites-An Indicator Indicator for an Early Stage of Native Copper Deposition in a Phyolite Tuff, a Rhyolite Tuff, Keweenaw Peninsula, Peninsula, Michigan. Michigan. 2:30 Scofield, N. N. Native Copper Deposits Derived from from Keweenawan Basalt by by Combined Nearby Keweenawan Igneous, Igneous, Deuteric, Deuteric, and Metamorphic Processes. 3:10 2:50 -- 3:10 COFFEE BREAK 3:10 Johnson, A. A. Scofield, N. N. Doane, V. V. Geology and Mineralogy of Northern Michigan Phosphorites. Phosphorites. 3:30 Shanabrook, D. D. Precambrian X X Paleopoles from the Upper Peninsula and a a New Method for Remanent Vector Determination. Determination. 3:50 Luther, F.R. F.R. The Geology of of the the Gore Gore Mountain Mountain Garnet The Deposit, Southeastern Adirondacks, Deposit, Warren County, County, New New York. York. END OF TECHNICAL SESSIONS SESSIONS POSTER SESSION Thursday, May ii, Thursday, 11, 1978 4:50 P.M. 8:00 A.M. A.M. -- 4:50 M.G. Mudrey, M.G. Aereomagnetic Map Map of of Northern Northern Wisconsin. Wisconsin. Sims, P.K. Sims, Cannon, W.F. W.F. Mudrey, M.G. M.G. Preliminary Geologic Map of Northern Wisconsin Wisconsin. Shaffer, N. N. Possibility of Mississippi Valley-Type Ore Deposits in in Indiana. Indiana. xv �h I �MICROSTYLOLITES-AN MICROSTYLOLITES-AN INDICATOR INDICATOR FOR FOR AN EARLY STAGE STAGE OF NATIVE NATIVE COPPER COPPER DEPOSITION DEPOSITION IN IN AA RHYOLITE RHYOLITE TUFF, TUFF, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN B.E. B.E. Aaquist, Aaquist, American American Copper Copper && Nickel Nickel Co., Co., Milwaukee, Milwaukee, Wi, Wi, 53226 53226 and and R.W. R.W. Hodder, Hodder, University University of of Western Western Ontario9 Ontario p London, London, Ont. Onto N6A N6A 5B7 5B7 ABSTRACT Microstylolites Microstylolites are are contact contact surfaces surfaces between between clasts clasts in in aa rhyolite rhyolite tuff tuff hosting hosting native native copper copper in in the the Kingston Kingston mine. mine. The microstylolites conform conform to to Pettijohn's Pettijohn's (1949) (1949) definition: definition: "a stylolite seam seam is is aa surface surface of of contact contact marked marked by by interlockinterlockor mutual mutual interpenetration interpenetrationof' of the two sides. sides. The teethteething or like projections projections of of one one side side fit fit into into the the sockets sockets of of like like on the the other." other." The microstylolites are are mostly mostly dimensions on chlorite grains grains with with their their long long axis axis parallel parallel to to the the contact contact surface. Some fine fine grained grained hematite hematite is is also also present3 present. Quartz and feldspar phenocrysts terminated terminated by by aa microstylolite microstylolite are are Fluid inclusions in neither neither fractured, fractured p nor nor stressed. stressed. in pheno— phenocrysts are similarly similarly terminated terminated by by microstylolites. microstylolites. Depth of burial is the the single single most important factor factor in microstylolite development. development. In sandstones, sandstones p microstylolites microstylolite have been been recorded recorded at at depths depths of' of burial burial of of 1250 1250 to to 1650 1650 meters meters (Trurnit 1968). Tuft Tuff in the Kingston mine is overlain overlain by by (Trurnit,p 1968). about 1700 1700 meters of of lavas lavas and and sedimentary sedimentary rocks rocks of of the the Portage Portage Lake Lava Series, Series, sufficient sufficient weight to induce induce formation of microstylolites. micro stylolites. native copper copper is common in white white rims rims on In the the tuff, tuff p native These rims are white where potash rhyolite clasts. clasts. These reddish rhyolite feldspar grains in clasts clasts are are clear clear and and lack lack disseminated disseminated hematite of of reddish reddish grain grain interiors. interiors. Microstylolites terminate terminate This suggests deposition of the white, white p copper-bearing copper-bearing rims. rims. This the native copper and whiting of the rims of clasts clasts prior prior to to native the rims microstylolite formation and, and, hence, hence, before before lithification of microstylolite the tuff'. tuff. the References Pettijohn, F.J. (1949); (1949); Sedimentary Sedimentary rocks: rocks: Pettijohn, F.J. Brothers,p New and Brothers New York, York, 526 526 p. p. Publ. by Harber Publ. (1968); Pressure Pressure solution phenomena phenomena in detrital Trurnit, P. p. (1968); Sed, Geol., Geol., vol. rocks: vol. 2, 2, p. p. 89—114. 89-114. rocks Sed. —3— -3- �The pH of Ore Fluids of Mississippi Valley Valley Type Type Deposits Deposits by Konrad J. J. Banaszak Department of Geology Indiana/Purdue University at at Indianapolis Indianapolis 925 W. Michigan Michigan,t Indianapolis, 925 w. Indianapo1is t Indiana Indiana 46202 of the solutions responsible responsible for for Mississippi Mississippi Valley The pH of the ore solutions type deposits is critical chemical chemical variable variable in the the discussion type ore deposits is aa critical musthave havebeen been acid, acid, based based of the origin of of these these deposits. deposits. This p1-I pH must curves,t equilibrium relations relations with with silicate on zinc zinc dispersion curves minerals of "modern "modern ore fluids", fluids", and the absence of magnesium silicates in the paragenetic sequences sequences of of the the deposits. deposits. Zinc and dispersion curves were recreated recreated in the the laboratory by Lavery and Barnes (1971) buffered to to aa pH of of 6 at at (1971) with model ore solutions solutions buffered 0 basic did did not not reproduce 100 C. C. The model ore solutions that that were basic the curves. have both aa low partial curves. Modern "ore fluids" fluids" appear to to have acidic pH, pH, and are probably in pressure of carbon dioxide and an acidic equilibrium equilibrium with with silicate silicate rocks. rocks. The composition of fluid fluid inclusions inclusions in an assumed equilibrium with K-spar, K—spar, albite, albite, quartz, quartz, muscovite, muscovite, and 0 montmorillinite indicates of 5 for at 150 150° montmori11inite indicates an approximate pH of for brines at to 200°C. minerals in the 200 0 C. Other evidence is is the the absence of silicate minerals the paragenetic sequence sequence (See (See Drever, Drever, 1974.). 1974.). In Mississippi Valley type deposits, deposits, the the absence of sepiolite, sepio1ite t an easily crystallized others,t 1973)t 1973), especially restricts restricts the phase (Christ (Christ and others the pH of the ore solution to acidic values. In the presence of a silica silica phase, phase t quartz or opa11ine opalline silica, and at at the the magnesium activities either quartz si1ica t and of the ore fluid must have been indicated by fluid fluid inclusions, inc1usions t the the pH of the ore fluid must no greater greater than than 66 at at 100°C 1000 C and and 55 at at 150°C. 1500 C. Christ, C. C. L. L.,t Hostet1er Hostetler,t P. P. B. B.,t and and Siebert Siebert,t R. R. M. M.,t 1973 1973,t Studies Christ, Studies in the system MgO —- Si02 -— C02 -— H20 (III): The activity product of sepiolite: sepiolite: Amer. Amer. Jour. Jour. Sci., Sci. t v. v. 273, 273 t p. p. 65—83. 65-83. Drever,t J. J. I., 1974,t Geochemical Geochemical model model for of Precambrian Drever I., 1974 for the origin of Bull. Geol. banded iron iron formations: formations: Bull. Geo1. Soc. Soc. Amer., Amer. t v. v. 85, 85 t p. p. 1099—1106. 1099-1106. Lavery, N. N. G., G., and and Barnes, Barnes, H. H. L' L., 1971, Zinc Zinc dispersion'in dispersionin the LaverYt the t 1971, Econ. Geol., Wisconsin zinc—lead zinc-lead district: district: Econ. Geo1., v. v. 66, 66 t p. p. 226—242. 226-242. Wisconsin —4— -4- �POLYPHASE DEFORMATION IN POLYPHASE IN ARCHEAN SCHISTS SCHISTS OF THE THE WESTERN WESTERN LAKE VERMILION VERMILION AREA, MINNESOTA* MINNESOTA * Bauer, Department Robert L. Robert L. Bauer, Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minneapolis, Minnesota Minnesota, Minneapolis, Minnesota 55455, 55455, and Department of Geology, Macalester College, College, St. St.Paul, Paul,Minnesota Minnesota55105 55105 ABSTRACT A and structural structural study study has has been been initiated detailed petrologic petrologic and initiated in in the the A detailed Norwegian Bayquadrangle quadrangleand andparts partsof of adjacent adjacent quadrangles quadrangles in in the western Norwegian Bay western Lake The rock Lake Vermilion Vermilion area. The rock exposures exposures consist consist of of Archean Archean schists schists and and lamprophyres metamorphosed metamorphosedto to the the middle middle amphibolite amphibolite facies facies and and intruded by lamprophyres quartz monzonite monzonite stock stock(Wakemup (Wakemup Bay Bay stock). stock). The The stock and and adjacent adjacent aa quartz schists are bounded on the the north north by by the the Vermilion fault, on on the southeast schists are bounded on Vermilion fault, southeast by by the Frazer the Frazer Bay Bay fault, fault, and and on on the the south south by by the the Haley Haley fault. fault. The The structural studies reported on on here studies reported here indicate the the schists schists have have undergone undergone four periods periods of deformation The most evident evident structural structural feature in The most in the the area areaisisaaprominent prominent foliation foliation which wraps around around the the Wakemup WakemupBay Baystock. stock. This This foliation foliation (S (si) which wraps 1) is axial planar planar parallel to to bedding to rare rare isoclinal isoclinal F1 F 1 folds folds and and is is parallel bedding (S(Sj r in in the the schist. schist. Numerous thin Numerous thin lamprophyre and granitic veins cutting 0 the schist are boudinaged or folded folded by by the the flattening flattening normal boudinaged or normal to S 5l' F2 F 2 folds folds are are the the most mostcommon common minor minor structures structures preserved preserved and and are are commonly accompanied accompaniedbybyaa weak weak to to strong commonly strong axial axial plane plane foliation foliation (S,). (S). The distribution of of minor distribution minor F2 F 2 folds folds indicates indicates the thepresence presenceofofa amajor majorsou'Thwestsou1hwestaxes of plunging FF,2 antiform south of of the plunging antiform partially partially exposed exposed south the stock. stock. The The axes of the the minor F, 'Tolds show aa systematic variation inin orientation orientation to to the minor F lolds show systematic variation the west, west, northwest and olding (F.) northwes~ and north of the the intrusion intrusion as as aa result result of ofref refolding (F 3) of of the the major major F, structure stoc1. Despite F2 structure around around the the western western end end of of the theWakemup Wakemup Bay Bay stOCK. Despite the la1ge-sca1e F3folding foldingaround aroundthe thestock, stock,minor minorF'3 F folds large-scale F3 folds are are rare rare and and occur occur only only Th'se folds along the western margin of the along the margin of the intrusion. intrusion. The-se folds are are open, open, westwardwestwardplunging warpsof ofthe the foliation foliation with with near near vertical axial plunging warps axial planes. planes. The shallow shallowdips dipsofofthe the schist schist near near the the contacts contacts of of the stock The stock and and the presence of a flat-lying roof pendant of of schist and lamprophyrenear near the the center center and lamprophyre of the stock's stock's exposure, exposure, suggest suggest the surface surface exposures exposures are very very near the the top top of of the stock. stock. Evidence for for an an Fh is restricted to Evidence F 11. deformation deformation is to kink kink bands, bands, up up to 55 cm cm wide, which whichdeform deformthe theS2 2 foliation. wide, A similar similar sequence sequence of of structural structural events has been recognized north of of the A recognized north Vermilion fault. Further study lead to the Vermilion fault. study of the the area area isis in in progress progress which which may may lead of major correlation of major structural features across across the the fault. fault. *Research supported by by the the Minnesota Minnesota Geological Geological Survey Survey -5- —5— �PLATE TECTONICS PLATE TECTONICS AS AS AAMODEL MODEL FOR FOR THE THE ENVIRONMENT ENVIRONMENT OF OF SEDIMENTATION SEDIMENTATION THE AND THE SUBSEQUENT THE MARQUETTE MARQUETTE SUPERGROUP SUPERGROUP AND SUBSEQUENT DEFORMATION DEFORMATION AND AND METAMORPHISMASSOCIATED ASSOCIATED WITH THE METAMORPHISM THEPENOKEAN PENOKEANOROGENY OROGENY CAMBRAY, William,Department Departmentofof Geology, Geology, Michigan Michigan State CAMBRAY, F. F. William, University, East University, East Lansing, Lansing, Michigan Michigan 48824 The Marquette Supergroup Supergroupof of Precambrian Xage agehas hasbeen beendivided divided into into The Marquette Precambrian X three groups. This sequence can be be compared comparedtoto the the one one which which forms forms on on groups. This sequence can plate margin suchasasthe theAtlantic. Atlantic. The aa passive passive plate margin such The Chocolay Chocolay Group Group represents anepicontinental epicontinentalshallow shallowsea seafollowed followedbybythetheinitiation initiation of represents an rifting thethe beginning of of Menominee riftingatat beginning Menominee times. times. The The doming doming associated with rifting would thethe unconformity rifting wouldaccount accountforfor unconformitybetween between the thetwo twogroups groups and the the separate separate basins basins in in which the banded iron formations formations and andturbidites turbidites and which the banded iron were depositedformed formedasasa aresult resultof of rifting rifting producing were deposited producing local localdepressions depressions such as the the Marquette, Republic and andIron Iron River/Crystal River/Crystal Falls such as Marquette, Republic FallsTroughs. Troughs. This extensional wasaccompanied accompanied intrusionofoftholeiite tholeiite dykes This extensional phase phase was by by intrusion dykes parallel to Troughand and intrusion sills into parallel to the the Marquette Marquette Trough by by thethe intrusion ofofsills the sediments within the Subsequently the area the sediments within the troughs. troughs. Subsequently area underwent underwent subsidence and accumulated accumulatedthe the large large thickness subsidence and thickness ofofBaraga BaragaGroup Group sediments sediments which compare comparefavourably favourablywith withthe the turbidites turbidites which which which formed formed on on the the subsubshelf edge edge of ofthe themodern modern Atlantic AtlanticOcean. Ocean. siding shelf In this interpretation proposed In interpretation ititis is proposed that thatthe theIron IronRiver/Crystal River/Crystal which includes includes the the Riverton Riverton Iron Formation, Falls area area succession, succession, which Formation, is contemporaneous with the the Menominee Groupofof the the Marquette and that contemporaneous with Menominee Group Marquette Range Range and Greenstonesrepresent representsubmarine submarine extrusionsrelated related to to the the Badwater Badwater Greenstones extrusions the of the the troughs troughs referred referred to rifting which at this time. rifting which isisproposed proposed at time. Each Each of are which are are found found today today on on constructive plate plate margins. margins. are likened likened to to those those which Subsequent to deposition was Subsequent to depositionthe thearea area wascompressed compressedand andmetamorphosed metamorphosed It isisproposed Orogeny(1.85 (1.85- - 1.9 1.9 Ga B.P.). It in the the Penokean Penokean Orogeny Ga B.P.). proposed that that during during this episode Archean this episode deformation deformation ofofthe theunderlying underlying ArcheanBasement Basement occurred occurred by by particularly the ductile shears shears along along pre-existing weaknesses, weaknesses, particularly the mafic mafic dykesreferred referred to to above, producingeast-west east-westfolding folding in in the dykes above, producing the overlying overlying Marquette Supergroup. During this phase Marquette Supergroup. During phase troughs troughs are thought thought to to have have beenthe the locii locii ofofgreater andand that weaknesses been greaterstrain strain that weaknessesdeveloped developed during during the were utilised to narrow them andandproduce the earlier earlierrifting rifting were utilised to narrow them producea amore more intense folding. The seeminglyanomalous anomalous orientationsofoffolds folds in the intense The seemingly orientations the troughs as the the Republic are thought thought to have controlled troughs such such as Republic Trough Trough are have been been controlled by the stress stress distribution distribution across troughswith withvariable initial orientaby the across troughs variable initial orientations. history of the The deformation deformation was The was accompanied accompanied by by metamorphism. metamorphism. The The history the region has manyfeatures featuresinin commonwithaplate commonwithaplatetectonic tectonic cycle cycle involving region has many followed byby subsidence aa continental continental rift rift followed subsidenceatatthe themargin marginof,ofananexpanding expanding ocean followed followed by movement, ocean by reversal reversal ofofplate plate movement, subduction, subduction,compression compression and metamorphism. Thefact fact that that all the cited is situated and metamorphism. The the evidence evidence cited situated on on crust does older Archean Archean crust does not negate negate the hypothesis. hypothesis. All the themore more recent recent examplessuch suchasas the the Appalachian Appalachian and andAlpine Alpine Orogeny are underlain underlain by examples Orogeny are by continental crust. All this thethe supposed continental thismeans means isisthat that supposedocean oceanwas was comcompletely andcontinental continentalcollision collision resulted. The suture zone pletely subducted subducted and resulted. The zone associated with with this weare are left left totodebate associated this event event has has not not been been located located and and we debate whether whether itit is is present present but but cryptic cryptic ororthat thatProterozoic Proterozoictectonics tectonicswas was similar in in all allother otherrespects respects to to plate plate tectonics. tectonics. —6— -6- �THE IN THE THE ORIGIN ORIGIN AND AND TIMING TIMINGOF OFCLEAVAGE CLEAVAGE FORMATION FORMATION IN THE SIAMO SIAMO SLATE SLATE OF OF PRECAMBRIAN X AGE, MARQUETTE PRECAMBRIAN X MARQUETTE COUNTY, COUNTY, MICHIGAN MICHIGAN CAMBRAY, William, Department Departmentof of Geology, Geology, Michigan CAMBRAY, F. F.William, Michigan State State University, University,East EastLansing, Lansing,Michigan Michigan 48824 48824 In the the previous previous work work (Powell, (Powell, C. C. McA; McA; 1969, 1969, Bull. Bull.Geol. Geol.Soc. Soc.America) America) itithas cleavage formed hasbeen beensuggested suggested that thatthethe cleavage formedpenecontemporaneously penecontemporaneously with the of sandstone sandstonedikes dikes and andthe the origin origin of theemplacement emplacement of ofboth bothwas was ascribed ascribed to to dewatering dewatering during during late latediagenesis diagenesisororlow lowgrade grademetamormetamorphism. In the the outcrop outcrop referred referredtotobybyPowell Powellthe thedikes dikescan canbebeshown shown to tohave have been emplacedbefore beforedeformation deformation and and to to have undergonerotation rotation as been emplaced have undergone as rigid rigid bodies bodies prior priortotothe theformation formationofofthe thecleavage. cleavage. The The cleavage cleavage cuts cuts acros thedikes dikesand andthe thehost hostsediment, sediment,and anditit is across the theboundary boundary between between the not deformed folds in in the bedding whichare arerelated related to to the the rotation deformed bybyfolds bedding which The sense of this rotation is consistent with of the the dikes. dikes. The sense of this rotation is consistent with the the shear shear magnitude however couple on the the limbs limbs of of the couple on the major major fold. The The magnitude however is greater than one than that thatpredicted predictedif if oneassumes assumes the the dikes dikes originated originatednormal normal to bedding and were deformed by flexural slip or flexural flow folding. bedding and were deformed by flexural slip or flexural flow This can can be introducing aa flattening This beexplained explainedbyby"additional "additionalstrain" strain" introducing flattening can across as the across the bedding bedding as the fold fold develops. develops. The The flattening canbebedemondemonstrated strated by by the the variation ininbed bed thickness thickness as as a function function of of distance distance from the rigid from the rigidsandstone sandstone dikes. dikes. The cleavageisisdefined definedbybythin thin laminae laminaeofofoptically optically irresolvable The cleavage material areascontaining containing quartz, quartz, chlorite, material separated separated by by broader broader areas chlorite,muscomuscoquartz, chlorite vite and and aa carbonate. carbonate. The The quartz, chloriteand andmuscovite muscovite show show features features vite which suggestthe thecleavage cleavageoriginated originatedbybyrecrystallisation, recrystallisation, possibly which suggest possibly in conjunction conjunction with with pressure pressure solution. solution. All the theevidence evidence points points totocleavage cleavage forming forming late late inina asequence sequence of of deformation and metamorphism which involvedrotation rotation of the deformation and metamorphism which involved thesandstone sandstone dikes, flattening and and rec~ystallisation. dikes, recrystallisation. —7— -7- �middle and and late late Precambrian fault system A middle Precambrian fault system and northern Michigan in northern Wisconsin Wisconsin and by W. F. Cannon W. U. S. Geological Survey Survey Reston, Virginia 22092 Reston, 22092 Interpretation Interpretationofofaeromagnetic aeromagneticand and gravity gravitymaps mapsof ofnorthern northernWisconsin Wisconsin and and northern Michigan that major regional faults Michigan suggests suggests that faults are are much much more more abundant abundant than previously previously believed. believed. The newly identified identified faults abrupt linear than The newly faults appear appear as as abrupt scale aeroaerotruncations of aeromagnetic aeromagnetic patterns patterns on on aa newly newly compiled compiled 1:250 1:250 000 000 scale (U.S.G.S.map mapMF MF888). 888). Some Somefaults faults also also coincide coincide with with steep magnetic map map (U.S.G.S. gravity gravity gradients. gradients. Many Manyfaults faultsproduce producelateral lateraloffset offset(some (someasasmuch muchas as 20 20 km) km) of magnetic magnetic anomalies anomalies caused caused by by middle middle Precambrian Precambriansupracrustal supracrustaland andPenokean Penokean indicates that that large-scale large-scale lateral adjustment intrusive rocks; rocks; this evidence evidence indicates adjustment took took place orogeny(-1,800 (-1,800m.y. m.y.ago). ago). Other Other faults, faults, place in the area area after the the Penokean Penokean orogeny especially in northern Michigan, hadlarge large vertical vertical displaceMichigan, are known known to have have had ments during during the the Penokean Penokeanorogeny. orogeny.Some Somefaults faultscut cutrocks rocksofofthe the Wolf Wolf River River ments batholith intrusive and and flow flow rocks (-1,100 ('1,100 batholith 4-1,500 ~1,500 m.y. m.y. old) old) and and Keweenawan Keweenawan intrusive m.y. old). old). Some m.y. Some east-trending faults and and fractures fractures contain contain lower lower Keweenawan Keweenawan diabase diabase dikes. Although the the age age at at which which it it began is unknown, unknown,the the faulting faulting is at least Although began is least as as old as orogeny,and anditit continued continued until until at least as the Penokean Penokean orogeny, least 1,100 1,100 m m y. y. ago, ago, probably probably episodically. Some, most, lateral Some, and and perhaps perhaps most, lateral movement movement isis of ofKeweenawan Keweenawan age. age. Much of of the the map map pattern pattern in in northern northern Wlsconsin Wisconsinreflects reflectsmajor majorlateral lateral fault fault moveMuch movements; ments; it may may be be aa reflection of of intraplate intraplatetectonics tectonicsduring duringthe theopening opening of of the the Keweenawan rift, as Keweenawan rift, as the the older older Precambrian Precambrian rocks rocks ininMichigan Michiganand and Wisconsin Wisconsin were caught between the somewhat opposed opposedopening openingdirections directions of of the midconwere tinent arms of of the the rift rift system. tinent and and mid-Michigan mid-Michigan arms system. AApre-Keweenawan pre-Keweenawan fault fault and and fracture fracture system system probably probably controlled the the location location and and orientation orientation of of the the KeweenKeweellawan rift and of pre-existing awan rift and associated associated transform faults, faults, so so that that some some segments segments of faults behaved as transform transform faults during rifting, behaved as rifting,whereas whereas other other segments segments shifted so as to to alter the the Wisconsin-Michigan Wisconsin-Michigan plate plate as as it it moved so as the shape shape Of of the moved generally southward. Regardless of its its origin origin and and history, history, the the fault system Regardless of system is important important geologically geologically because its control control on on the the regional regional map mappattern. pattern. Additional faults because ofofits faults having having displacements displacements too small to resolve resolve by by means means of existing existing aeromagnetic aeromagnetic data data probably probably are also also abundant abundantand andwill willbe beimportant important in in interpreting interpreting the map map pattern on a a larger scale. scale. —8— -8- �I Petrology and and Geochemistry of Amphibolites, Amphibolites, Eau Petrology Eau Claire Claire River, River, Eau Claire Claire County, County, Wisconsin Wisconsin Eau M. L. L. Cummings, Cummings, Dept. M. Dept. of of Geology Geology and and Geophysics, Geophysics, LJW UW -- Madison P. E. Myers, Myers, Dept. Dept. of of Geology, Geology, UW Claire - Eau Claire P. E. Precambrian amphibolites, amphibolites, mica schists, Precambrian schists, and intrusives intrusives crop crop out out for for 12 km km along along the the Eau Eau Claire Claire River River in north—central Eau Claire 12 in north-central Claire County. County. Massive Massive and and banded. banded. mafic mafic amphibolites, amphibolites, with with more more than than 40 40 percent percent hornblende local mineral mineral assemblages: hornblende-garnet--plagiohornblende, have local hornblende-garnet-plagioclase-quartz, and and hornblende-cummingtonite-garnet-plagioclase-quartz clase-quartz, hornblende-cummingtonite-garnet-plagioclase-quartz with accessory apatite, and opaques opaques as as sulfides and with apatite, sphene, sphene, biotite, biotite, and sulfides and oxides. amphibolites, oxides. Feldspathic amphibol ites, with 10 10 to to 25 25 percent percent hornblende, hornblende, are are characterized by dominant plagioclase. characterized plagioclase. Accessory epidote, quartz, quartz, sphene, and and garnet garnet show show variable variable abundance. abundance. Banding Banding and and hornblende hornblende 1inunsphene, eation are Hornblende analyses analyses from from amphibolites amphibolites show show eation are indistinct. indistinct. Hornblende Al203 15.7 weight weight percent with in 1.05 1.05 to to 1.81 between 9.8 Al 203 between 9.8 and 15.7 with Al Al in 1.81 tetrahedral sites. 100 Mg/(Mg Mg/(Mg + Fe) vary from hedral sites. 100 from 20 20 to 70 70 with values below with values 50 dominant. 50 dominant. , Mica schists schists with assemblages: assemblages: biotite-hornblende—epidote-plagioclasebiotite-hornblende-epidote-plagioclasequartz, and subordinquartz, and muscovite-biotite-epidote—plagioclase-quartz muscovite-biotite-epidote-plagioclase-quartz and subordinate amphibolite layers layers composed composed of hornblende, hornblende, biotite, biotite, plagioclase and quartz underlie the 100 Mg/(Mg + Fe) of quartz the eastern half half of of the the area. area. 100 of hornhornthese amphibolites amphibolites ranges ranges from from 47 47 to to 52. 52. Epidote in blende in. in. these in both both assemblages contains contains 11.5 11.5 to to 13.0 13.0 weight weight percent percent Fe203. Fe203' An intrusion intrusion breccia 0.75 km south of Big Falls Falls contains amphibolite xenoliths in in strongly foliated foliated granodiorite(?) granodiorite(?) composed of biotite, biotite, muscovite, epidote, epidote, plagioclase, plagioclase, and and quartz. quartz. AA second intrusion intrusion breccia breccia at at county highway highway KK 1.5 1.5 km km east of Big Big Falls Falls contains mafic amphibolite xenoliths corase—grained, flow-laminated flow-laminated tonalite(?) tonalite(?) matrix. matrix. The xenol iths in in a, a corase-grained, The rocks rocks described above are cut cut by by granite granite pegmatite pegmatite and and diabase diabase dikes. dikes. The following, following, tentative tentative chronology chronology is is based based on on petrochemistry, petrochemistry, structure, structure, and and regional regional geology. geology. The oldest rocks rocks -- mica schists schists and and amphibolites amphibolites -- representing volcanic sediments sediments and mafic flows(?) flows(?) were intruded by aa gabbro which differentiated into intruded by into mafic mafic and and anorthositic anorthositic layers. layers. Metamorphism of these these rocks rocks to to garnet amphibolite amphibolite grade grade accomaccompanied intrusion intrusion of tonalite, tonalite, trondhjemite trondhjemite and adamellite north north of the the panied area. area. AA second second metamorphism produced produced coarse coarse hornblende hornblende and and plagioclase plagioclase in in the the amphibolites amp~ibolites , while while compositional compositional layering layering was ~as transposed transposed by by strong strong compressional compressional stresses. stresses. Synkinematic Synkinematic intrusion intrusion of tonalite tonalite (1850 (1850 ++ 50 m.y.) produced produced the the breccias breccias east east and and west west of of Big Big Falls, Falls, and and was was 50 m.y.) followed by by postkinematic postkinematic intrusion intrusion of of granite granite pegmatite pegmatite dikes. dikes. ShearShearing ing with contemporaneous contemporaneous formation formation of of epidote epidote and and chlorite chlorite was was followed followed by by prolonged prolonged erosion erosion after after which east—northeast-trending east-northeast-trending olivine 01 ivine diabase diabase dikes dikes were intruded intruded (1100-900 (1100-900 m.y.). m.y.). Weathering and and erosion erosion continued continued until until marine marine deposition deposition of of Upper Upper Cambrian Cambrian sandstones. sandstones. , This chronology chronology implies implies an an Archean Archean age age for for the the mica mica schists schists and and This layered layered gabbro gabbro sequence. sequence. —9— -9- �Stratigraphy Stratigraphy and and Mineralization, Mineralization, Quinnesec Formation, Formation, Northeastern Wisconsin Wis cons in M. M. L. L. Cummings, Cummings, Dept. Dept. of of Geology Geology and and Geophysics, Geophysics, 13W UW —- Madison Madison Volcanogenic semi—massive semi-massive to to massive sulfide zones zones occur at several stratigraphic stratigraphic levels levels in in the the Quinnesec Quinnesec Formation Formation in in Narinette Marinette County, County, Northeastern Northeastern Wisconsin. Wisconsin. The Quinnesec Quinnesec Formation Formation includes includes basic basic to to felsic felsic flows, flows, tuffs, tuffs, iron iron formation formation and and clastic clastic sediments, sediments, that that were were intruded intruded by by quartz diorite to to quartz quartz monzonite monzonite at at about about 1850—1900 1850-1900 m.y. m.y. Two Two types types of of conformable conformable massive sulfide sulfide deposits occur occur in in the the Quinnesec Formation. Formation. 1) 1) 2 to 10 cm cm beds with up up to to 70% 70% sulfide sulfide in in iron iron Quinnesec formation, formation, and and 2) 2) 33 to to 20 20 meter meter sulfide sulfide zones zones characterized characterized by by subangular subangular quartz clasts clasts and and rounded rounded graphitic graphitic muscovite—chlorite muscovite-chlorite clasts clasts supported supported in aa sulfide sulfide matrix. matrix. Two Two main zones zones have been defined at at stratigraphic stratigraphic in levels levels separated by approximately approximately 300 300 meters meters of of basalt basalt flow, flow, tuffs tuffs and and iron formation. formation. The lower deposit overlies overlies graphitic, graphitic, sulfide—bearing sulfide-bearing felsic felsic tuff and is overlain by garnetiferous garnetiferous iron iron formation formation and and biotite— biotiteThe upper deposit overlies a 30 to 60 meter amphibole metasediments. overlies a 30 to 60 meter iron formation and is capped capped by thinly thinly laminated, laminated, graphitic, graphitic, siliceous siliceous sediments that grade upward into into fine fine grained, grained, well—bedded well-bedded siltstones. siltstones. Both main sulfide sulfide deposits deposits overlie overlie and and are are interbedded interbedded at at the the base base with with tremolite and anthophyllite—bearing assemblages, possibly representing anthophyllite-bearing assemblages, possibly representing alteration zones. zones. The sulfide mineralogy of of the the massive massive sulfide sulfide deposits deposits alteration Sphalerite and is simple, simple, with monoclinic pyrrhotite pyrrhotite predominant. predominant. is chalcopyrite occur throughout throughout the the deposits deposits with with sphalerite sphalerite forming forming loloPyrite is generally secondary, associated with fracthin beds. beds. is generally secondary, associated with fraccalized thin tures, however, however, some pyrite may be part of the tures, the metamorphic metamorphic sulfide sulfide Highest Zn and and Cu concentrations concentrations are are 1.0% 1.0% and and 0.1% 0.1% respecrespecHighest assemblage. tively. Iron formation formation is is represented by the assemblage Iron assemblage grunerite—quartz, grunerite-quartz, grunerite—ferro—actinolite—quartz, grunerite—ferro—hornblende—ferro— grunerite-ferro-actinolite-quartz, grunerite-ferro-hornblende-ferroactinolite—quartz, and gruneritegrunerite— actinolite-quartz, grunerite—ferro—hornblende—garnet—quartz grunerite-ferro-hornblende-garnet-quartz and Grunerite— All assemblages can contain calcite. stilpnomelane-quartz. contain calcite. Gruneritestilpnomelane—quartz. ferro—actinolite—garnet—quartz occurs in ferro-actinolite-garnet-quartz in high Mn bulk bulk compositions. compositions. phase with with magnetite magnetite and and ilmenite locally Pyrrhotite is is the main opaque phase locally Sphalerite occurs either or pyrrhotite, abundant. Sphalerite occurs with magnetite or pyrrhotite, abundant. chalcopyrite tends tends to be restricted to to pyrrhotite—bearing pyrrhotite-bearing samples. samples. The formation that that underlies the upper main massive sulfide iron formation sulfide zone zone is is divided into into upper upper and and lower lower units units separated separated by by aa sulfide sulfide rich rich zone zone divided unit is containing 0.5% Cu and and 0.5% 0.5% Zn. Zn. The lower unit is characterized by The upper unit numerous sulfide-rich beds. beds. upper unit is is characterized by numerous thin sulfide—rich Base metal ions garnetiferous beds, beds, some of which are garnetiferous are highly graphitic. graphitic. Base were available periodically during iron formation deposition with precipitation controlled controlled by by local local Eh-pH Eh—pH conditions conditions and and intensity intensity of of hydrothermal hydrothermal pitation activity. Metamorphic conditions conditions were were in in the the epidote epidote amphibolite amphibolite facies facies of of Metamorphic Primary textures are well preserved with penetrative amphibolite facies. Primary textures are well preserved with penetrative amphibolite facies. deformational features features weakly weakly developed. deformational developed. —10--10- �PETROLOGY AND GEOCHRONOLOGY OF OF ARCHEAN ARCHEAN GNEISS GNEISS IN THE LAKE ARBUTUS AREA, AREA, WEST-CENTRAL WEST—CENTRAL WISCONSIN THE James F. F. DuBois DuBois and W. W. R. James R. Van Schmus Department of Geology University of Kansas Lawrence, Kansas 66045 Lawrence, 66045 The gneiss of of central out along the Black central Wisconsin crops out The basal gneiss River in in Clark Clark and and Jackson Jackson counties counties and and is is particularly particularly amenable amenable to to River detailed study at at a detailed a series of exposures below below Arbutus Arbutus Dam Dam near near Hatfield, Hatfield, gneiss has has aa heterogeneous heterogeneous composition, composition, ranging from Wisconsin. The gneiss granite to granite to tonalite, tonalite, and contains interlayered inter layered amphibolite amphibolite units. units. There is considerable considerable scatter scatter of of the the Rb—Sr Rb-Sr geochronologic geochronologic data, data, but an upper age limit limit can can be be defined defined by by aa 2.8 2.8 b.y. b.y. isochron. isochron. This age presumably dates the time of upper amphibolite to granulite facies metamorphism. Later open system conditions are probably due either to Rb metasomatism or to loss of to Rb of radiogenic radiogenic Sr. Sr. The former former may be be explained as an an effect effect from from intrustion intrustion of of Penokean Penokean granite granite (1830 (1830 m.y. m.y. old) old) 33 k.m. k.m. north of of the the study study area. area. Two models are proposed for the structural relationships between between the the gneiss gneiss and and granite. granite. The granite may be a small body intruding continuous and extensive gneissic terrane, terrane, or the gneiss may be present as a a roof pendant within a large Penokean batholithic batholithic complex. complex. Due to limited exposure it may be difficult to prove either either model. model. U—Pb U-Pb data on zircon from the the gneiss yield a concordia intercept intercept corresponding to The lower concordia to an an age age of of 2.9 2.9 b.y. b.y. concordia intercept intercept of 1.0 b.y. b.y. is too high to be interpreted by a simple diffusion model. model. It may, may, however, however, be explained by U U and Pb diffusion affected by a second second metamorphic metamorphic event event about about 1.8 1.8 b.y. b.y. ago. ago. —11— -11- �FAULTING IN PART OF OF THE THE DULUTH DULUTH COMPLEX, COMPLEX, NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA FAULTING IN PART FOOSE, Michael S. Geological Geological Survey, Survey, Reston, FOOSE, Michael P., P., U. U. S. Reston, Va. Va. 22092, and and COOPER, Roger W., W., Minnesota Geological COOPER, Geological Survey, Survey, University University of of Minnesota, Minnesota, St. St. Paul, Paul, Minn. Minn. 55108 55108 faulting and and fracturing Intense faulting fracturing in in part part of the the Duluth Duluth Complex, Complex, northnortheastern Minnesota, Minnesota, has eastern has been documented by by detailed detailed field field mapping. mapping. Faulting is Faulting is recognized principally by by the the displacement displacement of of mappable, mappable, mineral graded layers mineral layers that that were were probably probably formed formed in in aa manner manner analagous analagous to that to that of of sedimentary sedimentary turbidites. turbidites. Recognition of the the faulting, faulting, fracturing, and depositional fracturing, depositional environment establishes establishes aa basic basic geologic geologic style that that may have significant regional regional implications. implications. The area mapped in Lake Lake County, County, approximately approximately 23 23 km southeast mapped is is in of Ely, Ely, Minn., Minn., near near the the basal basal part part of of the the Duluth Duluth Complex. Complex. It It is is between Birch Lake, between Lake, the the Tomahawk Road, Road, and and Minnesota Minnesota Highway Highway 1. 1. Two distinct rock sequences were identified. distinct identified. The lower lower sequence is is prepremedium—grained troctolites 10 percent dominantly medium-grained troctolites that that contain contain 33 to 10 intercumulus pyroxenes and/or oxides; oxides; the intercumulus pyroxenes the upper sequence sequence is is mediummediumto to fine-grained fine-grained troctolites troctolites that that contain contain little little or or no no intercumulus intercumulus pyroxenes or or oxides. oxides. Well-defined and mappable layering layering is is best best developed in in these these upper upper troctolites. troctolites. Most common are layers layers that that have have abundant cumulus cumulus olivine olivine at at the the base base and and decreasing decreasing amounts amounts of of olivine olivine abundant upward. Contacts of layers layers are sharp, sharp, but but inclusions inclusions of of olivine-poor olivine-poor clasts clasts occur within the the olivine-rich basal basal part part of of overlying overlying layers. layers. The olivine-poor top of one layer is approximately 10 m thick top layer is approximately 10 m thick and and provides a distinctive marker horizon provides horizon that that can can be be traced traced through through much much of the the study study area. area. Layers Layers appear to to have been been formed formed by by density density currents currents carrying olivine and and plagioclase plagioclase grains. grains. Faults and fractures are the Faults fractures the most abundant abundant and and important important strucstructures recognized in the area. They are identified principally tures in the area. identified principally by by the the off—setting off-setting of mappable layers, layers, but also by variations in in the the orientation mineral laminations, occurrence of of gouge, gouge, and and the tation of mineral laminations, the the occurrence the presence of marked topographic the study area are three topographic lineaments. lineaments. In In the three major major directions of faulting. direction trends trends N30-40E, N3O—OE, and faulting. The principal principal direction and less prominent faults less prominent faults are usually oriented N-S N-S and and N35W. N35W. However, However, virtually any direction of of faulting faulting may may be be observed observed locally. locally. Rarely, minor folds folds are are observed observed in in association association with with some some major major faults. faults. Previously, Previously, only a few few faults faults have have been been identified identified by by groundgroundcontrolled mapping, largely owing to great difficulty difficulty of of detailed detailed controlled mapping, largely owing to the great field field mapping in in the the Duluth Duluth Complex. Complex. However, However, the the intense intense faulting faulting documented area defines defines aa structural structural style that may be documented in in this this small small area that may common to to much of of the the region. region. Certainly, Certainly, the the possibility possibility of of intense intense faulting and fracturing fracturing must must be be considered considered in in any any further further work work and and interpretation of the the Duluth Duluth Complex. Complex. —12— -12- �ECONOMIC MINERAL PRODUCTION ECONOMIC MINERAL PRODUCTION IN MICHIGAN MICHIGAN PAST PAST AND AND PRESENT PRESENT Milton Milton A. A. Gere, Gere, Jr. Geological Geological Survey Survey Division Michigan Michigan Department Department of Natural Natural Resources Resources Box 30028, Lansing, Michigan Box 30028, Michigan 48909 48909 ABSTRACT ABSTRACT Michigan's mineral production production statistics statistics have compiledeither either in Michigan's mineral have been been compiled whole or in part whole or part from from 1845 1845 to the the present. present. In 1877 1877 Act Act 99was was passed passed which created the the position of MineralStatistics. Statistics. The which created of Commissioner Commissioner ofofMineral The duty of wastoto give give the of the theCommissioner Commissioner was the governor governor an an annual annual report report about the yearly mineral about the mineral production production statistics statisticsand andthe thedevelopment development of of the smelting industries. industries. Part the mining mining and and smelting Part of Act Act 99 required required all all mining mining companies submittheir their production companies toto submit production figures figurestotothe theCommissioner. Commissioner. In 1911 the duties duties of weretransferred transferred to to the 1911 the of the theCommissioner Commissioner were the Geological Geological Survey, Survey, now now aa Division of ofthe theMichigan MichiganDepartment Department of of Natural Natural Resources. Resources. Presently, receives most mostof of the the yearly mineral mineral Presently, the the Geological Geological Survey Survey receives production statistics, exclusive production statistics, exclusiveofofpetroleum petroleum and and natural natural gas, gas, through through understandingwith withthe the U.S. U.S. Bureau a memorandum memorandum of ofunderstanding Bureau of Mines. Mines. Company data submittedto to the the U.S.B.M. sent on on to to the data submitted U.S.B.M. isis sent the State. State. Oil and and gas gas silver production is collected by directly. Copper, production is by the the State State Survey Survey directly. Copper, silver and iron iron ore ore figures figures are for taxation and are also also received received separately separately for taxation as as well well as through the the U.S.B.M. U.S.B.M. as through Tabulationsof of the the value value of of nonmetallic, Tabulations nonmetallic, metallic, metallic, and and fuel fuel minerals minerals from 1910toto present present show showthat thatuntil until 1977, from 1910 1977, the the fuel fuel minerals mineralswere were always the the smallest smallest group group with with the metallics always metallics and and nonmetallics nonmetallics switching switching leading leading places places several several times. times. In 1977 1977 the the fuels fuels formed formed the the middle middle group group for the first time. the first time. Michigan's 1977 mineral production production value, value, according 1977 mineral according to the the U.S.B.M. U.S.B.M. Michigan's 1976total total value annual, preliminary preliminary report, report, was $1.51billion. billion. The annual, was $1.51 The 1976 value it was million. record at $1,543.5 $1,543.5 million. 1910 it was $80.5 $80.5 million~ set a record million. In 1910 Everyone the8383counties countiesininthe theState Statecontribute contribute to to the the total mineral Everyone ofofthe mineral However,all all of the value. However, the metallic metallicminerals minerals and and aa large large amount amount of the the high value high value for nonmetallic nonmetallic minerals minerals isisproduced produced ininthe theUpper Upper Peninsula. Peninsula. The balance balanceofofthe the nonmetallics nonmetallicsand andall all of of the The the fuel fuel minerals minerals are are derived derived from the the Lower Lower Peninsula. Peninsula. from —13— -13- �GEOCHRONOLOGY GEOCHRONOLOGYOFOFARCHEAN ARCHEANROCKS ROCKSIN IN MARQUETTE COUNTY, COUNTY, UPPER MICHIGAN MICHIGAN Roger D. D. Hammond Hammond and and W. W. R. R. Van Schmus Roger Department of Geology University of Kansas Lawrence, 66045 Lawrence, Kansas 66045 According to Morey and and Sims Sims (1976) the Archean Archean basement basement of of the Lake According to Morey (1976) the the Lake is composed of two two different different terranes, gneiss terrane Superior region is composed of terranes, aa gneiss terrane dnd aa granite-greenstone granite—greenstone terrane, terrane, which which differ differ in age, and type, strucstrucage, rock type, tural style, and metamorphic grade. tural style, and metamorphic grade. They extend the boundary between these two two terranes these terranes through the central part of of Marquette Marquette County, County, Michigan, Michigan, beneath the middle Precambrian rocks of the Marquette Range rocks of the Marquette Range Supergroup. Supergroup. Locally, the north of the boundary, which which are are part part of the Locally, the Archean rocks rocks north the boundary, the granite—greenstone terrane, are known as as the and those granite-greenstone terrane, are the Northern Complex and those south boundary, which which are are part of the gneiss terrane, are known south of the boundary, part of the gneiss terrane, are as as the Southern Southern Complex. Complex. If Morey and Sims' Sims' model is is correct, correct, rocks rocks m.y. should be present in the gneiss older than 3,000 m.y. gneiss terrane, terrane, and the rocks of of the the granite-greenstone granite—greenstone terrane terrane should should not not be be older older than than about about rocks 2,800 A geochronologic study was was done 2,800 m.y. m.y. A done on the the rocks of of the Northern and on on aa granite granite body body of of the the Southern Southern Complex Complex which which had had yielded yielded Complex and anomalous Rb—Sr Rb-Sr age age systematics systematics with with one one sample sample giving giving aa 3,200 3,200 m.y. m.y. Woolsey, 1975), 1975), to model age (Van (Van Schmus and Woolsey, to verify or revise Morey and Sims' Sims' model. The Northern Complex Complex consists consists of of granitic granitic to to tonalitic tona1itic gneisses, gneisses, with lesser lesser amounts amounts of of granites, granites, amphibolites, amphibo1ites, and and volcanics, volcanics, that that extend extend approximately 80 80 kilometers kilometers east—west east-west and and 40 40 kilometers kilometers north—south. north-south. The eastern part part of of the the Complex Complex includes includes aa greenstone greenstone belt. belt. U—Pb U-Pb isotope isotope studies on zircons from samples of the gneisses and volcanics do not indicate an age any greater than 2,750 m.y. m.y. for rocks of the Northern Complex. Complex. The rocks of the Southern Complex are primarily granitic gneisses with lesser lesser amounts amounts of granites, granites, mafic gneisses, gneisses, and and amphibolites, amphibo1ites, which extend approximately 75 75 kilometers east—west east-west and 50 kilometers north— northsouth. body, 1.5 by 4 kilometers in size, south. One granite body, size, was mapped about 8 kilometers south south of of Ishpeming. Ishpeming. It is a medium-grained medium—grained granite which appears gray gray in in outcrop outcrop in in the the western half half and and red red in in the the eastern eastern half. half. Parts of of the the granite granite body are are quite quite porphyritic porphyritic with with aligned aligned feldspar feldspar phenocrysts. phenocrysts. Although Although no no direct direct contacts contacts were observed, observed, the the presence presence of gneissic inclusions suggest that the granite was intruded intruded into into the the surrounding surrounding gneiss. gneiss. Rb—Sr Rb-Sr isotope isotope data data on on wholerock wholerock samples samples from from the the granite define a 2,400 m.y. m.y. isochron with a Sr87/Sr86 Sr 87 /Sr 86 intercept intercept of 0.7200. U—Pb V-Pb isotope studies on zircon Zircon from from the the granite do do not indicate indicate an an age age any any greater greater than than 2,600—2,700 2,600-2,700 m.y. m.y. The The granite granite is is possibly possibly remobil— remobilized crustal crustal material material as as indicated indicat~d by by the the high high initial initial Sr87/Sr86 Sr 87 /Sr 86 ratio. ratio. Ages Ages of of the the rocks rocks studied studied from from both both these these complexes complexes conform conform with with Morey Morey and 5j? Sims'model, model,even eventhough thoughprimary primaryages agesininexcess excessofof2,800 2,800 m.y. m.y. have have yet yet to to be be found found from from the the Southern Southern Complex. Complex. —14— -14- �INDUSTRIAL INDUSTRIAL SAND SAND AND AND SANI)STONE SANDSTONE RESOURCES RESOURCES OF OF MICHIGAN MICHIGAN E. E. Wm. Heinrich Heinrich Dept. Dept. Geology and Mineralogy The The University University of of Michigan Michigan Ann Arbor, MI 48109 MI 48109 Michigan's silica, silica, sand sand and and sandstone sandstone deposits, deposits, which range range in in age from Middle Precambrian to to Quaternary, Quaternary, embrace a considerable diversity of geological types types and have a remarkable diversity of technological applications. applications. Historically, Historically, Michigan sandstones were famous for for two two pur- poses: poses: 1) 1) the the Jacobsville sandstone (Cambrian) (Cambrian) used as a colorful dimension stone in the construction of of larger larger buildings buildings (churches, (churches, courthouses, courthouses, breweries), breweries), mainly in in the the Upper Peninsula and 2) 2) the the Marshall sandstone (Devonian), (Devonian), utilized in the last half of the the 19th 19th century century for for abrasive abrasive (Grind Stone Stone City, City, Huron Huron Co.). Co.). wheels (Grind The spectrum of deposits and and poten— poten- tial deposits, deposits, by formation, tial formation, age and application, includes: includes: 1. 1. Sunday, Sturgeon, Middle Precambrian quartzites: quartzites: Sunday, Mesnard, Ajibik, Ajibik, and Goodrich Mesnard, Goodrich quartzites: quartzites: aggregate; the Ajibik Ajibik may be of potential value for the for ferrosilicon. ferrosilicon. 2. 2. Munising sandstone (Late (Late Cambrian): Cambrian): 3. 3. Sylvania sandstone (Lower (Lower Devonian): presently exploited glass—sands of the near Rockwood as one of the premier glass-sands United States; States; also also abrasive abrasive sand sand and and silica silica flour. flour. 4. 4. Napoleon sandstone (uppermost Napoleon (uppermost Devonian): quarried near Jackson for for flagging, flagging, riprap riprap and and sandstone-bituminous sandstone—bituminous Jackson hot hot mix for pavement. 5. 5. Pleistocene till, till, glaciofluvial deposits, deposits, and and lakebeds: lakebeds: fill fill sands sands and aggregate. 6. 6. Dune sands in southwestern Michigan Michigan (Quaternary): (Quaternary): active mining for for molding molding sands sands (considered mining (considered the industry industry standard for such such sands); sands); also also evaluated as glass—sand. for glass-sand. —15— -15- glass—sand potential. glass-sand potential. �A POST POST TWO TWO CREEKS CREEKS BURIED FOREST A IN MICHIGAN'S MICHIGAN'S NORTHERN PENINSULA IN John D. D. Hughes, Hughes, Department Department of of Geography, Geography, Earth Earth Science Science and and John Conservation, Northern Northern Michigan University, Conservation, University, Marquette, MI MI 49855 9855 ABSTRACT In 1976-77, 1976—77, spruce spruce and and tamarack tamarack trees trees in in growth growth position position In were exposed exposed between six and eleven meters below the were eleven meters the surface surface during construction construction of the tailings basin for during the Gribben Gribben tailings for the the Cleveland—Cliffs Iron Cleveland-Cliffs Iron Company. Company. The The site, site, located sixteen kilometers southwest southwest of Marquette, Marquette, Michigan, Michigan, lies kilometers lies within the the outwash apron of the outer Marquette Marquette moraine. moraine. Throughout the excavation, excavation, there there is no evidence that glacial glacial override the is ~o evidence that override occurred following following the the period of growth such as presence occurred as the the presence of distorted strata, strata, sheared sheared trees, trees, or or intercalated intercalated till. till. + 1he outer parts parts of two trees yere dated at + 14he treesl~ere at 9780 . —250 C.y.a., C.y.a., W3904 W3901 and and 98509850± 300 300]C.y.a., -250 C.y.a., W3866 W3866 (N. (M. Rubin). Rubln). Spruce needles needles from the Spruce the upper pars part of the the buried A0 Ao soil horizon were dated dated at at 10,230±3001 10,230~3001 C.y.a., C.y.a., W3896 W3896 (M. (M. Rubin). Rubin). The largest tree collected has a diameter of sixty centimeters largest has sixty centimeters and 150 growth rings. and rings. Most trees trees suffered a severely severely reretarded growth growth rate rate during their final tarded final thirty thirty or forty forty years years of growth, growth, a a condition that is is attributed to climatic climatic deterideterioration accompanying accompanying the the glacier's glacier's return. return. Evidence in in the Gribben Gribben tailings tailings basin indicated indicated aa minimum period of of plant plant growth growth of of 150 150 years years following following recession of the Valders (Great (Great Lakean) Lakean) Stadial. Stadial. Tree growth in the the basin was terminated by local local ice-marginal ice-marginal ponding caused by glacial glacial readvance readvance into into the the area. area. Deposition of lacustrine sediment capped capped by outwash gravel gravel and and sand occurred during building of the Marquette-Munising moraine Similar dates have moraine system. system. have been obtained from from detrital detrital spruce and hemlock found found in red till and and red red clay clay till in Michigan's westernmost westernmost county county and and near near Ashland, Ashland, Wisconsin at elevations elevations 400 00 to Wisconsin at to 600 600 feet feet above above present present Lake Lake Superior. Superior. It It appears that a a glacial glacial advance advance climaxed climaxed slightly slightly less less than 10,000 years years ago, ago, and and at at that that time, time, almost almost all, all, if not not all, all, of the Lake Superior Superior basin was occupied occupied by by glacial It glacial ice. ice. It is is proposed that the name Marquette Stadial Stadial be adopted adopted for for the the period period of of glacial glacial advance advance and and Gribben Gribben Interstadial for for the the preceding preceding time time of of retreat. retreat. —16— -16- �THE THE PETROLOGY PETROLOGY AND AND TECTONIC TECTONIC SIGNIFICANCE SIGNIFICANCE OF OF THE THE INTERFLOW INTERFLOW SEDIMENTS SEDIMENTS IN IN THE THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANIC VOLCANIC GROUP GROUP OF OF NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA Mark Mark A. A. Jirsa Jirsa University University of of Minnesota—Duluth Minnesota-Duluth Duluth, Duluth, Minnesota Minnesota 55812 55812 Interfiow Interflow sediments sediments occur occur as as lenticular lenticular bodies bodies between between and. and crevice cre~ce fillings, fillings, within, lavas lavas of of the the North North Shore Shore Volcanic Volcanic Group. Group. Their Their structure, structure, texture, texture, and composition composition offer evidence of the the depositional/erosional relrelationships ationships between between the the volcanic volcanic and and sedimentary sedimentary accumulations accumulations and and the the borderland during during Keweenawan Keweenawan rifting. rifting. surrounding borderland The The majority majority of of the the 380 380 (total) (total) of of interflow interflow sediments sediments occur occur as as bedded bedded interflow interflow sandstones, sandstones, conglomerates, conglomerates, and and minor minor shaly shaly sediments. sediments. Tabular Tabular and and trough trough cross—bedding, cross-bedding, planar bedding and lamination, lamination, and ripple marks are the the most most prevalent prevalent primary primary structures. structures. Other deposits include include sediment—filled sediment-filled flow—top flow-top breccias, clastic clastic dikes, dikes, and and sedimentary/volcanic sedimentary/volcanic breccias. breccias. Nearly Nearly Most clastic all interflow interflow beds beds lie lie on on uneroded uneroded flow flow tops. tops. Most clastic dikes dikes are are the the result result of sediment filling filling fractures in upper lava surfaces; surfaces; however, however, some were were filled filled by by sediment sediment injected injected into into lava lava fractures fractures from from underlying underlying clastic. clastic. Mud cracks, slump structures, and convolute laminations occur in cracks, structures, in deposits. most types types of of deposits. deposits. most These volcanogenic arkosic sediments are reddish—brown reddish-brown to to buff, buff, and consist of predominantly fine—to well—sorted grains fine-to medium—grained, medium-grained, subrounded, subrounded, well-sorted of plagioclase, clinopyroxene, clinopyroxene, magnetite, magnetite, and and various various rock rock fragments. fragments. The The dominant rock fragments fragments are volcanic; volcanic; however, however, agate, agate, chert, chert, shale, shale, and glass Minor constituents shards also occur. occur. Actual tuff tuff beds beds are are rare. rare. Minor constituents are are potpotGrains are fresh assium feldspar, quartz, and accessory heavy minerals. feldspar, quartz, and accessory heavy minerals. Grains are fresh to to altered, and in many cases, altered, cases, replaced replaced by by various various zeolites, zeolites, chlorite, chlorite, calcite, calcite, and potassium feldspar. In In addition to silica and hematite, these these minerals minerals potassium feldspar. form the major chemical chemical cements. cements. Paleocurrent indicators show predominant current flow sourhward and southeastward towards the the present Lake Lake Superior Superior Basin. Basin. These data imply imply a a fluvial environment of deposition, and sedimentary structures support this fluvial environment of deposition, and sedimentary structures support this Several deposits deposits may may reflect reflect influences influences of of fluvio-lacustrine fluvio—lacustrine implication. Several and eolian environments. The response response of of the the Keweenawan Keweenawan terrain terrain to to rifting rifting and and basinal basinal developdevelopThe and ment is interpreted from a combination of sedimentological, sedimentological, petrographic, petrographic, and In general, sediment bodies are thicker clastic dike orientation orientation analyses. analyses. In general, sediment bodies are thicker and more more variable variable in in lithology lithology in the the area area from from Tofte Tofte to to Grand Grand Portage Portage than than and This may suggest more ponding and/or longer in the area from Duluth Duluth to to Tofte. Tofte. This may suggest more ponding and/or longer periods of of volcanic volcanic quiescence quiescence in in the the northeasternly northeasternly portions portions of of the the basin. basin. periods Petrology indicates indicates predominantly predominantly local local (Keweenawan) sources for for sediments; sediments; Petrology (Keweenawan) sources however, several several deposits deposits had had variable variable sources sources which which may may include include some some prepre— however, The presence of agate fragments some Keweenawan sediments and intrusions. intrusions. The presence of agate fragments in some deposits implies implies mineralization mineralization of of lava lava prior prior to to erosion, erosion, and and thus earlier deposits thus an earlier Data obtained obtained from from cycle of of volcanism, volcanism, burial, and uplift cycle uplift in in the the source source area. area. Data clastic dike dike orientations orientations is is significant significant because because sediment sediment filling filling (by whatclastic (by whatdating the the stress stress ever process) process) occured occured near near the the time time of of lava lava deposition, deposition, thus thus dating ever Although many of these orientations are scattered and patterns at that time. Although many of these orientations are scattered and patterns at time. reflect cooling cooling fractures fractures filled filled with with sediment, sediment, some some conjugate conjugate orientations orientations reflect occur stresses. occur which which may may reflect reflect regional stresses. This study study was was partially funded This funded by the Minnesota Geological Geological Survey. Survey. —17— -17- �Geology and and Mineralogy Mineralogy of of Northern Geology Northern Michigan Michigan Phosphorites Phosphorites Scofield and Allan Johnson, Johnson, Nancy Nancy Scofield and Virginia VirginiaDoane Doane Institute ofofMineral Institute MineralResearch Research Michigan Technological Technological University University Michigan Houghton, Michigan 49931 Houghton, Widespreadoccurrences occurrencesofof Middle Middle Precambrian Precambrianphosphate-bearing phosphate-bearingstrata strata in Widespread in the werefirst first reported the central part partofofthe theUpper Upper Peninsula Peninsula of Michigan Michigan were reported by by Cannonand andKlasner Klasner (1976). Surface Surface exposures Cannon exposures of the the bedded bedded phosphorites phosphorites were were found of several basins near near the the contact contact with with older found at margins margins of several sedimentary sedimentary basins older Archean crystalline rocks. The thickest thickest known phosphorite section section (100 Archean crystalline rocks. The known phosphorite (100 m) m) is the eastern eastern margin margin of of the in Section Section 15, 15,T49N T49N R28W, R28W, ononthe the Dead Dead River River Basin Basin 17 17 miles northwest The rocks rocks here here strike strike NS miles northwest of of Ishperning, Ishpeming, Michigan. Michigan. The NS and and dip steeply to the Early in 1977, wascollected collected for steeply the west. west. Early 1977, aa bulk bulk surface surface sample sample was mineralogical study studyand andpreliminary preliminarybeneficiation beneficiationtests testsbybythe theInstitute Institute of mineralogical Mineral Research During the the summer 1977,the theupper, upper,richest richest section Research (IMR). (IMR). During summer ofof1977, was diamonddrilled drilled by in cooperation was diamond by IMR IMR in cooperation with the theMichigan Michigan and and U.S. U.S. Geological Geological Surveys. Results the apatite to thiswork work showed showed the to be be present present as as pebbles, pebbles, oöids ooids Results of this andasasfine finecrystallites crystallites in aa quartzitic the apatite apatite is is in and quartzitic matrix. matrix. Most Most ofof the in length. Aphanitic apatite dark, elongate elongate pebbles pebbles 1-30 1-30 mm mm in apatitecomprises comprises75-80% 75-80% Submicrongraphite, graphite, pyrite pyrite euhedra, of the the pebbles. pebbles. Submicron euhedra, quartz quartz and and stilpnomelane stilpnomelane are also present. This apatite has identified by francolite, the are present. This has been been identified by XRD XRD asasfrancolite, the carbonatefluorapatite. fluorapatite. carbonate Someofofthe the rich surface P205,but but the the bulk Some surfacebeds beds contained contained as as much much as as 15% 15% P205, However, the drill drill core However, ininthe coreapatite apatitedecreased decreased zones with depth, depth, although although intermittent intermittentricher richer zoneswere wereencountered. encountered. Calcite Calcite was was observed with depth replaced some apatite. observed to be be more more abundant abundant with depth and and may may have have replaced some apatite. Several pyrite-rich pyrite-rich zones Several zoneswere were encountered, encountered, but but surface surface weathering weathering had had oxidized The conglomerate conglomeratecontaining containing the the apatite muchofof the the pyrite pyrite in much inthe theupper upper 55meters. meters. The pebbles appears appearsto to have shale-pebble origin origin and pebbles have aa shale-pebble and the theoccurrence occurrencemay may be be aa channel channel deposit. surface 6.95% P205. P205. surface sample sample averaged averaged 6.95% The bestresults resultsofof initial initial beneficiation fatty acid The best beneficiationtests testsusing using aa standard standard fatty acid float produced float produced aa27% 27% grade grade P205 P205 at 60% 60% recovery. Reference F. and Kiasner, J. J. S. ApatiteCannon, W. W. F. and Klasner, S. (1976), (1976), Phosphorite Phosphorite and and Other Other ApatiteBearing Rocksinin the Precambrian of Northern Bearing Sedimentary Sedimentary Rocks Precambrian of Northern Michigan, Michigan, U.S.G.S. U.S.G.S. Circular 746, 746, 66 p. p. —18— -18- �GEOLOGY OF OF THE THE IRON IRON FORHATION FORMATION AND ASSOCIATED ROCKS GEOLOGY OF THE THE JACKSON JACKSON COUNTY COUNTY IRON IRON MINE, MINE, JACKSON COUNTY, OF COUNTY, WISCONSIN WISCONSIN David G. C. Jones, Jones, Department Department of of Geology Geology and Geophysics, David Geophysics, University University of Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 Wisconsin, AB STRACT ABSTRACT Precambrian Precambrian magnetite magnetite iron iron formation formation crops crops out out as as low low hills hills in in Jackson County, Jackson County, Wisconsin. Wisconsin. The pit The Jackson Jackson County Iron Company's open pit taconite mine mine was was opened opened in in the taconite the largest of the the hills. hills. The The ore ore body body mined mined strikes northwest northwest and and dips dips 70—80 degrees southwest. strikes 70-80 degrees southwest. The The ore ore body body is is aa lens 915 915 meters meters in length and 150 meters in lens in width. It It averages averages about about 35% magnetite. magnetite. Dominant the iron iron formation formation are: Dominant mineral mineral assemblages within the are: 1. magnetite-quartz-grunerite-ferroactinolite magnetite—quartz—grunerite—ferroactjnolite 1. 2. magnetite-quartz-cummingtonite-biotite magnetite—quartz—cummingtonjte_bjotite 2. 3. magnetite-quartz-garnet-Ca-rich magnetite—quartz-.garnet—Ca—rich hornblende-ferroactinolite-grunerite hornblende—ferroactinolite—gruneritc 3. Amphiboles commonly contain visible exsoiution Amphiboles exsolution features. features. Ca-rich Ca—rich hornblende (hastingsite) replaces garnet. (hastingsite) garnet. Southwest of Southwest of the the iron formation formation is is aa highly highly weathered weathered siliceous siliceous schist schist as the of quartz, and mapped as the hangingwall hangingwall schist. schist. It It is composed of quartz, biotite, biotite, and sericite. Weathering decreases sericite. decreases with depth. depth. The schist, northeast The footwall footwall schist, of the ore body, of the ore body, is is identical identical to to the the unweathered unweathered hangingwall hangingwall schist. schist. Both are composed mainly of three are three assemblages: assemblages: 1. quartz-chlorite-muscovite-andalusite quartz—chlorite—muscovite—andalusje 1. 2. quartz—biotite—chlorite_stauroljte_garnet_andalusjtemuscovite 2. quartz-biotite-chlorite-staurolite-garnet-andalusite-muscovite 3. quartz-biotite-oligoclase-muscovite quartz—biotite--oligoclase—muscovite 3. Phase relations relations suggest suggest that rocks attained attained chemical chemical equilibrium at at Phase that the the rocks staurolite—grade metamorphism. staurolite-grade metamorphism. Texturally the the footwall footwall schist ranges from from a a highly foliated foliated coarse—grained coarse-grained schist schist to to aa nearly nearly granular granular schist. schist. Interlayered with the pelitic schist schist are are zones of grunerite-garnet-quartz grunerite—garnet—quartz Interlayered with the pelitic zones of iron iron formation and poorly foliated, foliated, dark dark green green amphibolite. amphibolite. A A lenticular zone zone of talc talc schist about 350 meters long and 40 meters wide is is situated within the the iron iron formation formation in in the the eastern portion of the the mine. mine. The assemblages taic-garnet—andalusite, talc-garnet-andalusite, talc—biotite, talc-biotite, and talc—cummingtonite talc-cummingtonite are locally locally present. present. the Compositional banding of quartz and magnetite is prominant within the iron iron formation formation and and provides provides the the contrast contrast necessary necessary for for viewing viewing minor minor structure. structure. The rocks rocks have been isoclinally isoclinally folded folded around nearly vertical axes and and sheared sheared into into boudins. boudins. Features Features observed observed include: include: 1) 1) small small boudins boudins and and isolated isolated and and rotated rotated fold fold hinges hinges of of minor minor isoclinal isoclinal folds, folds, 2)transposed, 2)transposed, bedding, 3) 3) prominent prominent lineation lineation of of amphiboles amphiboles developed in in the the plane plane parallel bedding, of compositional compositional banding, banding, and and 4) 4) distinct thickening thickening and and thinning thinning of of iron iron formation formation along along strike. strike. Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone unconformably unconformably overlies overlies the the PrePrecambrian cambrian terrane. terrane. Within Within the the Mount Mount Simon Simon aa basal basal conglomerate conglomerate containing containing clasts clasts of of angular angular hematitic hematitic iron iron formation formation is is well well developed. developed. The The congloconglomerate merate grades grades rapidly rapidly upward upward into into well well sorted, sorted, poorly poorly indurated indurated sandstone. sandstone. The The deposit deposit has has not not been been dated, dated, but but structural structural and and metamorphic metamorphic style style indicate indicate that that it it may may be be Archean. Archean. —19— -19- �U The The Unconformity-Type Unconformity-Type Proterozoic Proterozoic Pitchblende Pitchblende Ore Ore Body Body Model Model And And Its Its Application Application to to Northern Northern Michigan Michigan J. J. Kalliokoski Kalliokoski Michigan Michigan Technological Technological University University Houghton, Houghton, Michigan Michigan 49931 49931 Previous Previous studies studies establish establish that that this this class class of ofore orebodies bodieshasP has aa characcharacteristic setting: setting: aa short short distance distance below below an an unconformity, unconformity, in in almost almost any any teristic kind kind of of host host rocks rocks that that have developed developed permeability through either physical or chemical chemical ground ground preparation preparation (or (or both). both). This This chemical chemical ground ground preparapreparaor tion tion is is represented represented in in the the viscinity viscinity of the the ore ore body also also by various types of of low low temperature temperature alteration, alteration, none of which need to to be a a direct direct effect or the deposition deposition of of the the pitebblende. pitchblende. The The quantity quantity and and intensity intensity cause of the of of alteration alteration cannot cannot be related related to to the the size size of of the the pitchblende deposits. deposits. In In a similar similar coincidental coincidental fashion, fashion, pitcbblende pitchblende ore ore bodies bodies can can adjoin adjoin also economic concentrations concentrations of of nickel—cobalt nickel-cobalt arsenides arsenides and and gold. gold. By By contrast, graphite graphite and and pyrite pyrite are are interpreted interpreted to to be be related related more more directly directly the ore ore body body and and to to the the mineralization mineralization process. process. to the An evaluation of the geochemical system indicates indicates there to be be adequate adequate major outstanding sources and and uranium uranium transport transport mechanisms. mechanisms. The The major outstanding uranium sources problem concerns the locus locus and manner in which uranium is deposited deposited as as pitchblende. There is some indirect geological evidence to suggest that uraniferous fluids the precipitation results results from the mixing mixing of of oxidized oxidized uraniferous the from the fluids methane and with those containing containing large quantities of such reducants as methane and within are capable capable of precipitating precipitating pitchblende pitchblende within H2S, These substances substances are H2S. remaining of of their low little evidence remaining their low temperature systems, systems, with very little previous existence. existence. thick the model model to to northern northern Michigan Michigan one one can note note that that aa very very thick Applying the sandstone body of young Precambrian continental rests continental redbed redbed Jacobsville Jacobsville sandstone rests Thus, unconformably on a a floor floor of middle and and lower lower Precambrian Precambrian rocks. rocks. Thus, oxidized system the first first requirement requirement of of the the model model is is met, met, that that of of an an oxidized the system The basement is cut by aa series series of of situated a more reduced reduced one. one. The basement is cut by situated above a These provide the easterly faults and diabase dikes. dikes. These provide the easterly trending trending major faults The second requirement, requirement, that of secondary permeability second permeability in in the the basement. basement. The Jacobsville grade metasedimentary metasedimentary rocks rocks below the the Jacobsville middle Precambrian low grade It is is proposed proposed that because of their are are quite quite carbonaceous and pyritic. It the gaseous gaseous hydrohydrolow low metamorphic metamorphic grade grade these these rocks rocks could could have have provided provided the precipitate carbons carbons or or possibly possibly HH2S that are are required required by by the the model model to to precipitate 2 S that pitchblende zones of of mixing. mixing. pitchblende in and along the permeable zones —20— -20- �Problems in in Paleogeographic Reconstruction of the the Chocolay and lower lower Menominee Group Sedimentation, Sedimentation, Marquette Range Supergroup, Supergroup, Lake Superior region Larue, D. D. Knight, Knight, Northwestern University, University, Evanston, Evanston, Il. Larue, II. 60201 60201 Due to structural complications and few outcrops, outcrops, little is to structural complications and is known about the regional sedimentary facies and source areas of the Chocolay about facies and areas of and Menominee Groups and their Groups of the Marquette Range Supergroup and their Animikian equivalents. In structurally deformed areas isopachous areas isopachous and and paleocurrent data are equivocal (Ramsay, 1961, 1966), 1966), but have have been used used (Ramsay, 1961, Trends in in previous previous reconstructions (Taylor, in (Taylor, 1972, Sims, Sims, 1976). 1976). regional mineralogy are are employed employed by by others others (Morey, (Morey, 1973, 1973, Gair, Gair, 1975). 1975). Data bearing on paleogeographic reconstructions reconstructions of the the Chocolay 1) an increase in feldspar and grain size Group include: include: 1) size in in basal basal quartzites toward toward the the Lake Lake Mary Mary Quadrangle Quadrangle (Bayley, 1959, Gair Gair and and quartzites (Bayley, 1959, to weakly weakly unimodal NE — Weir, 1956); Weir, 1956); 2) 2) strongly unimodal NW — - SE to - SW orientations of of symmetric—ripple symmetric-ripple mark crests crests in in quartzites; quartzites; 3) 3) regional regional decrease in basal quartzite thickness toward the west (excluding (excluding the poorly understood understood Trout Trout Lake Lake Formation) Formation) (Sims, (Sims, 1976); 4) 4) local local westerly westerly thinning of quartzite quartzite in the the Gogebic Gogebic Range; Range; 5) 5) restriction restriction of of large large thinning of domal stromatolites stromatolites to Kona Dolomite Dolomite (Marquette area); 6) 6) greater greater domal to the the Kona (Marquette area); volume of intercalated clastic silica in the the Kona Dolomite than than strati— stratigraphic equivalents; equivalents; 7) 7) presence presence of of subrounded subrounded quartzite quartzite and and chert chert graphic Symmetric— pebbles in channel deposits of of the the Randville Randville Dolomite. Dolomite. Symmetricripple spacing in quartzite indicates indicates short short period period waves. waves. Evaporite casts (Taylor, 1972) with mud mud cracks cracks in dolomitic dolomitic units units indicate indicate mineral casts (Taylor, 1972) aa semi—arid semi-arid to to arid environment with with periods periods of of subaerial subaerial exposure. exposure. facies transition in North — - south facies in the the lower lower Menominee Menominee Group Group continues into Iron Iron Formation Formation sedimentation sedimentation (Gair, (Gair, 1975). 1975). Available of the paleocurrent data suggest flow parallel to to the the trend trend of the transition (E -— W). (E data, though obviously scant, scant, support the interThese available data, pretation of aa shallow basin deepening gently to to the south, south, with aa major detrital source source to to the the north, north, and a local source for feldspar feldspar and subrounded pebbles pebbles near near the the Lake Lake Mary Mary Quadrangle. Quadrangle. Shorelines possibly extended NW NW —- SE during deposition of Chocolay Chocolay sediments. sediments. Water depth varied from intertidal (possibly (possibly supratidal) supratidal) to to shallow subtidal for for the entire area, area, thus thus the significance of the term "shoreline" for for the dolomitic units is is questionable. questionable. The Wewe Slate may represent aa still deeper—water deeper-water phase of sedimentation (Puffett, (Puffett, 1974, Gair and Thaden, 1968). 1974, 1968). Lower Menominee Group Group sedimentation was similarly influenced influenced by by aa northern northern source source (Morey, 1973) and and by by mean mean similarly (Morey, 1973) water depths increasing southward, southward, but the contribution of local faulted uplifts is indicated faulted indicated (Gair, (Gair, 1975, 1975, James, James, 1954). 1954). —21— -21- �THE GEOLOGY OF THE GARNETDEPOSIT, DEPOSIT, THE GEOLOGY OF THE GORE GORE MOUNTAIN MOUNTAIN GARNET SOUTHEASTERNADIRONDACKS, ADIRONDACKS, WARREN WARREN COUNTY, COUNT!, NEW SOUTHEASTERN NF.W YORK YORK Frank R. Luther, Department of Geological Sciences, Sciences, Lehigh University, Frank R. Luther, of Geological Lehigh University, Bethlehem, Pa. Pa. (now University of Bethlehem, (now at Department Department of Geography-Geology, Geography-Geology, University Wisconsin -- Whitewater, Whitewater, Wis.) Wisconsin deposit, aa garnet amphibolite, amphibolite, is The garnet deposit, is located on the north slope of Gore Mountain Mountain in slope in the the southeastern southeastern Adirondack Adirondack Highlands. Highlands. The 1) rocks rocks of of charnockitic affinity, 2) major rocks rocks of of the the area area are: are: 1) 2) ananorthosite, gabbro; all of these rocks are orthosite, and 3)corona-bearing olivine gabbro; metamorphosed to the the upper amphibolite or hornblende granulite facies. facies. The garnet amphibolite contains euhedral to anhedral garnet porphyroblasts which which are are commonly commonly 10-20 10-20 cm in in diameter diameter (some range up up to to 30 30 roblasts (some range cm). These garnets are surrounded oy a surrounded by 1-2 mm ~u rim of plagioclase (an52) (an52) em). and biotite, biotite, a thick (up (up to to 10 cm) em) shell of hornblende, hornblende, and often a pressure shadow of plagioclase (an40) and orthopyroxene sure (an 40 ) and orthopyroxene (en67). (en67). Electron microprobe analyses show the composition of microprooe of the garnets to be remarkably uniform for for garnets of this this size. size. To the north, north, the garnet amphibolite grades through a 2 m m transition transition zone into aa layered layered gabbro containing igneous olivine, olivine, pyroxenes, pyroxenes, and and plagioclase plagioclase and and corona corona structures structures of of igneous metamorphic pyroxenes, pyroxenes, garnet, garnet, and and plagioclase. plagioclase. This contact is is charcharacterized by major changes in mineral proportions and texture texture while the the 3 /Fe+ Z change Fe+3/Fe+2 Change in bulk chemistry is small (an (an increase in H2O HZO and Fe+ toward toward the the garnet amphibolite). amphibolite). Electron microprobe analyses show that that compositional compOSitional variations between minerals occurring in the the garnet ampnibolite and gabbro are very small; small; compositions are: are: plagioclase (p1)-an39, (pl)-an39, garnet -ai47py40gr1sp1, orttiopyroxene garnet (g) (g)-a147PY40grl2sPl, orthopyroxene (opx)-en68, (opx)-en b8' norublende hornlJlende (h)(h)paragasite, clinopyroxene clinopyroxene (cpx)—augite, (cpx)-augite, and and magnetite magnetite (mt). (mt). These two two rocks are surrounded surrounded by by anorthosite anorthosite on on the the west, west, north, north, and and east. east. Tne gabbro contains contains xenoliths xenolithS of of deformed deformed anorthosite. anorthosite. To the the south, south, there there is with syenitic granulite granulite (mangerite); patches of ananis aa sharp contact with (mangerite); patches orthosite up up to to 55 mm thick thick occur occur along along this this contact. contact. The following A hot dry gabbrolc follOWing geologic geologic history history is is proposed. proposed. A gabbroic magma was intruded intruded along the the contact of already deformed mangerite and anorthoanorthosite. The magma crystallized slowly slowly without tectonic tectonic disturbance to to proproduce the was absorbed absorbed by the layered layered gabbro. gabbro. Water from from an external source was by the of the the margin of the gabbro during subsolidus subsolidus cooling causing aa transformation from gabbro to trom to garnet garnet arnphibolite amphibolite following tollowing tne the reaction: reaction: 19 p1++ S8 cpx+ opx+4 mt+ - 66 h+ 19 pi cpx +1.0 10 0px + 4 oi+ 01 + I. l rot + 66H20 HZO ~ h + 9Y p1+4 pi -:- 4 g+ g +1 1opx. opx. A A petrogenetic petrogenetic grid grid suggests suggests that that aa temperature temperature of of about about 800°C BOUoC and and aa load load pressure of of large large garof 77-~kb kb isisconsistent consistent with with this this reaction. reaction. Growth Growth of nets consumed piagioclase yielding aa hornblende shell around around each garnet. consumed plagioclase garnet. Later detormation produced pressure shadows garnets and shadows around the the.garnets and aa weak weak toliation foliation through through the the garnet garnet amphibolite. amphibQlite. Reference Luther, Frank R., 1976, 1976, The petrological evolution evolution of ot tue the garnet garnet deposit deposit at at Gore Mountain, Warren Warren County, County, New New York; unpublished unpublished dissertation, dissertation, Lehigh Lehigh University. University. —22— -22- �THE GEOCHEMISTRY GEOCHEMISTRY OF KEWEENAWAN LAVAS LAVAS OF OF THE THE MAMAINSE MAMAINSE POINT POINT THE FORMATION, ONTARIO FORMATION, N.W.D. N.W.D. Massey, Massey, Dept. Dept. Geology, Geology, McMaster McMaster Univ., Univ., Hamilton, Hamilton, Ont. Onto The Mamainse Point Formation Formation outcrops outcrops at at Mamainse Mamainse Point, Point, about 80 about 80 km north of Sault Ste. Ste. Marie, Ontario. Ontario. It consists of tholeiitic flood flood basalts with rhyolites rhyolites and conglomeratic sediments, and and spans spans the the palaeomagnetic palaeomagnetic reversal reversal normally normally sediments, regarded as the boundary between Lower Lower and and Middle Middle Keweenawan. Keweenawan. The The flows flows consist of olivine-phyric melaphyres melaphyres at at the the base base which pass up up into into feldspar-phyric feldspar-phyric melaphyres melaphyres and and ophites. ophites. The Alona Bay Bay sequence is is also also olivine-phyric olivine-phyric and The thin Alona with the basal section of the Mamainse probably correlative with the basal the Mamainse Point sequence. sequence. Low—grade, burial burial metamorphism has has caused zeolite—grade Low-grade, zeolite-grade secondary minerals minerals to develop, both both within within the to develop, the rock rock and in veins and vesicles. vesicles. Although laumontite occurs throughout, throughout, a a crude metamorphic zoning zoning is is developed developed with with epidote epidote occuroccurring mainly mainly in in the the basal basal section section and and stilbite stilbite in in the the upper upper ring Heterogeneity, with the development of parts. Heterogeneity, of epidote-, epidote-, chlorite— chlorite- and albite—rich—metadomains, albite-rich-metadomains, is is restricted restricted to to feldspar-phyric melaphyres in lower feldspar-phyric lower parts of of the the section. section. The metamorphism was was accompanied by increases in The in Na, Na, K, K, Rb, Rb, Li, Li, Ba, Ba, Fea/Fe2, Fe3/Fe2, H2O+ H20+ and and C02, C02, and and increases increases or or decreases decreases in Ca, Ca, Sr and in and Cu. Cu. Al, AI, EFe, ~Fe, Ti, Ti, P, P, Y, Y, Zr, Zr, Nb, Nb, ?FeOT/MgO ?FeOT/MgO and ?MgO appear to be immobile or little and little affected affected by by the the The immobile trace elements confirm the tholeialteration. The confirm the tholeiitic nature of the itic the lavas and suggest an an ocean—floor ocean-floor to to within-plate character. within-plate character. The occurrence of a suite of of flows flows of of distinctive distinctive chemchemical type beneath the "Great Conglomerate", but ical type the "Great but not not repeatrepeated above, above, would suggest the triple triple reversal reversal in the the palaeo1 magnetic stratigraphy of Mamainse Point' is real and not Point due to strike strike fault fault repetition. repetition. (1970) Paleomagnetism Paleomagnetism and and correlation correlation of of some Ipalmer, H.C. (1970) 'Palmer, H.C. Can. Jour. Middle Keweenawan rocks, rocks, Lake Lake Superior. Superior. Can. Jour. Earth Sci., 7, I, 1410—1436. 1410-1436. —23— -23- �THE DISTRIBUTION DISTRIBUTION OF OF URANIUM URANIUM AND THORIUM IN THE THE WOLF WOLF RIVER RIVER BATHOLITH, IN BATHOLITH, NORTHEASTERN WISCONSIN Meddaugh, t-leddaugh, W. \.J. S.; S.; Salotti, Salotti, C. A.; and and Mursky, Mursky, G. G. Department of Geological Geological Sciences Sciences University of Wisconsin —- Milwaukee Milwaukee, Milwaukee, Wisconsin 53201 53201 Measurements of outcrop radioactivity radioactivity at at over over 175 175 locations locations and and wholewholerock and thorium analyses rock uranium and analyses by gamma spectroscopy have have revealed revealed significant differences differences in in the the radioactive radioactive character character and and radloelement radioelement distribution of several several of the the lithologic lithologic units units that that comprise comprise the the Wolf Wolf River Batholith. is aa large Batholith. The batholith, batholith, dated about about 1500 1500 m.y., is large epizonal anorogenic composite pluton consisting epizonal consisting mainly of of quartz quartz mon— monzonite and and granite granite with much lesser lesser amounts amounts of of monzonite, monzonite, syenite, syenite, and and rhyolite. For the the purposes purposes of of this For this study the the batholith has has been been arbiarbitrarily divided trarily divided into into a southern section and and aa northern northern Section. section. In the the southern southern section, section, the the Red monzonite, the In Red River quartz monzonite, the most radioradioactive unit of the entire batholith, active unit of batholith, is is considerably considerably more more radioactive radioactive than than either the Wolf River quartz monzonite or or the the Waupaca Waupaca quartz quartz mon— monzonite. Two somewhat some~"hat anomalous anomalous areas, areas, one one east east of of Tigerton Tigerton and and the the other near near Big Big Falls, Falls, have have been been located located within within the the more more radioactive radioactive interior region of the monzonite. Preliminary analyses interior region of the Red Red River quartz monzonite. analyses of typical yield average values of oF typical samples samples of Red River quartz quartz monzonite yield average values 37 and 10 10 ppm ppm UU (Tb/U (Th/U == 3.7) 3.7) while while samples of mafic—rich mafic-rich material material 37 ppm Th and yield individual individual values values as as high high as as 150 150 ppm ppm Tb Th and and 190 190 ppm ppm U. U. Peripheral areas of the areas the Wolf River quartz monzonite, particularly particularly near near its its contact contact with the the Tigerton anorthosite, anorthosite, are are more more radioactive radioactive than than central central areas. areas. The \1aupaca Waupaca quartz monzonite and The and the the Wolf River River quartz quartz monzonite monzonite have have similar average outcrop radioactivities. radioactivities. The Belongia Wolf River Belongia granite, granite, slightly more radioactive radioactive than the Wolf is the the most most radioactive quartz monzonite, is radioactive unit unit in in the northern section of the the batholith. batholith. Marginal l-larginal regions regions of of the the granite granite tend tend to to be be more more radioactive than inner inner areas. areas. Typical Typical samples of Belongia Belongia granite granite yield yield preliminary average values of 27 27 ppm ppm Th Th and and 6.3 6.3 ppm UU (Th/U (Th/U == 4.3). Average outcrop radioactivity radioactivity of of the the Hager Hager rhyolite rhyolite is is slightly slightly less less than than that of the the Belongia Belongia granite. granite. Samples of the the Peshtigo Peshtigo monzonite, monzonite, the least least radioactive radioactive unit unit of the the entire entire batholith, batholith, yield yield preliminary preliminary the 5.14). ftverage 114ppm ppm Th Tb and and 2.6 2.6 ppm ppm U U (Th/U /verage outcrop radio— values of of 14 (Th/U == 5.4). radioactivities activities of of the Hager feldspar feldspar porphyry porphyry and and the the Hager Hager syenite syenite are are intermediate between that that of the the Belongia Belongia granite granite and and Peshtigo Peshtigo monzonite. monzonite. intermediate —24— -24- �PILOT EXPLORATION GEOCHEMICAL SURVEY OF URANIUM IN ORGANIC—RICH ORGANIC-RICH LAKE SEDIMENTS, NORTHEASTERN MINNESOTA D.G. Meineke, M.K. M.K. Vadis and A.W. A.W. K1aysmat, Klaysmat, Minnesota Department of D.G. Meineke, of Natural Resources, Minerals, Hibbing, Hibbing, Minnesota 55746 Resources, Division of Minerals, ABSTRACT As part of the National Uranium Resource Evaluation Program (NURE (NURE Program) Carbide—Nuclear Program) of the the U. U. S. S. Department of Energy (DOE), (DOE), Union Carbide-Nuclear Division, Division, the DOE contractor responsible for for geochemical exploration surveys, decided to surveys, to investigate investigate the the use use of of organic—rich organic-rich lake lake sediments sediments for for the NURE Program Program in in Minnesota. Minnesota. This study was done in conjunction NDNR with the the Minnesota Minnesota Department Department of of Natural Natural Resources Resources (MDNR). (MDNR). The MDNR had previously applied organic—rich sediment to various areas of organic-rich lake 1ake'sediment northern Minnesota for for the the evaluation evaluation of of base base metal metal potential. potential. The observations and and conclusions conclusions described described here here are are those those of of the the MDNR MDNR and and observations do not necessarily represent those those of of Union Union Carbide—Nuclear Carbide-Nuclear Division. Division. Organic—rich lake sediment samples samples were were selected selected to to represent represent five five Organic-rich lake sediment major geologic geologic formations formations from from previous sediment surveys conducted by the MDNR in the the Western Vermilion Vermilion District District of of northeastern northeastern Minnesota. Minnesota. The objectives of of this this study study were: 1) 1) to determine whether or not uranium in the various various rocks is reflected reflected in the sediment, and and 2) 2) to to rocks is the sediment, determine if of the raw data was was necessary in order order to to if any treatment treatment of use this information for for evaluation evaluation of of uranium uranium potential. potential. of the bedrock is Results indicate that the uranium content content of is reflected in in the the sediment. sediment. The uranium concentrations in in sediments sediments over the Vermilion Massif Massif are about twice those over over other rocks; rocks; which compares with with the the difference difference in in relative relative radioactivity radioactivity levels levels of of the the compares same rocks rocks as reported by Ojakangas (1976). (1976). Examination of the data suggests that uranium may be concentrated in the inorganic fraction of the the sediment. sediment. Although the reflection of the uranium content content of of the the bedrock is is discernible discernible by by basing basing the the uranium the unignited unignited (total) sample weight, weight, the the distribution distribution concentration on the (total) sample of uranium based on on the the ignited ignited sample sample weight weight (inorganic fraction) more more of (inorganic fraction) reflects the bedrock bedrock geology geology because because of of loss-on-ignition loss—on—ignition varivariclearly reflects ation between samples. samples. No significant relationships were observed for for or manganese, manganese, which which would would suggest suggest that that uranium is is not not uranium and iron or preferentially preferentially adsorbed adsorbed by by iron—manganese iron-manganese hydroxides hydroxides and, and, therefore, therefore, does not create elevated uranium uranium values values unrelated unrelated to to the the bedrock bedrock geology. geology. REFERENCE Potential ininPrecambrian 1976, Uranium Potential Ojakangas, R.W., R.W., 1976, Precambrian Rocks Rocks of of Report to U. Minnesota: Report U. S. S. Energy Research and Development Administration, Contract ContractAT(O5—l)—1652, AT(05-1)-1652, 259 259 pages. —25— -25- �A PETROGRAPHIC PETROGRAPHIC GUIDE GUIDE FOR UNIT UNIT IDENTIFICATION OF THE THE PARTRIA IDENTIFICATION OF DGE RIVER TROCTOLITE, TROCTOLITE, DULUTH COMPLEX, COMPLEX, MINNESOTA MINNESOTA DGE Molling, Philip Philip A., A., Tyson, Tyson, R. R. Michael, Michael, and and Chang, Chang, Luke Luke Molling, L. Y., Y., Department of Geology, Geology, Miami University, L. University, Oxford, Ohio 45056 Oxford, The partridge Partridge River River Troctolite Troctolite (PRT) has aa lithology lithology simisimiThe (PRT) has lar to to that that exhibited exhibited by by the the south South Kawishiwi Kawishiwi Intrusion Intrusion lar However, the the units units recognized recognized in the SKI SKI do do not not (SKI). However, in the extend into extend into the PRT (Bonnichsen (Bonnichsen and Tyson, Tyson, 1975). 1975). The The PRT does exhibit exhibit aa cryptic-like cryptic—like layering layering as as it it becomes becomes more more does However, there is no distinct distinct variabimafic with depth. depth. However, is no lity in the mafic mineral species which thus thus provides provides aid in the definition of correlatable units. little aid units. This study of one drill core has concentrated on on the the silicate silicate and oxide mineralogy and their their relationships relationships with with depth. depth. Five specific petrographic relationships relationships used in conjunction have been determined as indicators indicators of units: units: (1) (1) Some This epitaxial bio— biotite grows epitaxially epitaxially to to augite. augite. This biotite is is characteristic of the lower lower portion of of the the drill drill (2) Inclusions Inclusions of of biotite biotite aligned aligned in core studied. (2) in paralin the the upper upper half half of lel arrays arrays within within augite augite are arecommon cornmon in of is believed believed to to be aa rethe drill core. This This occurrence occurrence is (3) Oxide Oxide inclusions, inclusions, reddish—brown placement texture. texture. (3) reddish-brown rutile and and opaque opaque ilmenite, appearing in in augit augit as as minute minute rutile ilmenite, appearing blebs and rods are arranged in rows, rows, locally throughout the drill core and may represent gradational contact contact zones. zones. (4) The texture texture and and amount amount of of exsolved exsolved oxide inclusions in (4) The in the plagioclase crystals varies consistently with depth and is believed believed to to be be the the most most diagnostic diagnostic feature of differenis feature of tiation. (5) wormy, symplectitic symplectitic intergrowth Gf of plagio(5) AA wormy, clase and orthopyroxene similar to Taylor's (1964) (1964) mymer— mymerkite is is evident. evident. This This fine fine grained grained symplectite symplectite appears appears to to have set up have set up its itsown own plagioclase plagioclasedomain domain wherein wherein the the opx opx blebs blebs exist. Another symplectite, symplectite, coarser coarser in in grain grain size, size, appears as an earlier phase relative to the fine grained symplectite and does does not not exhibit exhibit aa separate separate domain. domain. Of the the petrographic relationships relationships used, used, only two two appear to be representative representative of of the the primary primary conditions conditions of of the the magma; magma; the oxide inclusions inclusions in in augite augite and and in in plagioclase. plagioclase. The The others appear appear to to be due due to to later later stages stages of of crystallization crystallization or deuteric deuteric alteration. alteration. The use of these these relationships relationships will allow allow for for the the definition definition of of crystallization crystallization units units which heretofore heretofore have have not not been described described for for the the Partridge Partridge River River Troctolite. Troctolite. the drill core. —26— -26- �AEROMAGNETIC MAP MAP OF OF NORTHERN NORTHERN WISCONSIN WISCONSIN AEROMAGNETIC (Poster Session) Session) (Poster M. G. G. Mudrey, Mudrey, Jr., Jr., Geological Geological and and Natural Natural History History Survey, Survey, University University of M. of Wisconsin—Extension, 1815 University Avenue, Madison, Wisconsin Wisconsin-Extension, 1815 University Avenue, Madison, Wisconsin 53706, 53706, and J. J, H, H, Karl, Karl, Department Department of of Physics, Physics, University of Wisconsin—Oshkosh, and Wisconsin-Oshkosh, Oshkosh, Wisconsin 54901 Oshkosh, Wisconsin 54901 ABSTRACT In 1973, In 1973, the the Geological Geological and and Natural Natural History History Survey Survey and and the the Department of Physics, University of Wisconsjn—Oshkosh, initiated aa detailed of Physics, University of Wisconsin-Oshkosh, initiated detailed aeroaero— magnetic survey survey of of northern northern Wisconsin Wisconsin with with primary primary funding funding from from the the Upper Upper magnetic Great Lakes Lakes Regional Great Regional Commission. Commission. The is a a color compilaThe map map on display is tion at at 1:250,000 1:250,000 by Zeitz, Zeitz, Karl tion Karl and and Ostrom (1977) (1977) published published as U, S. as U, Geological Survey Survey Open-file Open—file Report Report 77-598, 77—598, and and is is available available in in black black and Geological white as white as U. U. S. S. Geological Survey Miscellaneous Miscellaneous Field Field Study Study MF—888. MF-888. The map is derived by photographic The reduction of 86 aeromagnetic aeromagnetic survey survey maps published at a scale of 1:62,500 maps 1:62,500 by the Geological and and Natural Natural History History Survey with a a standard line line spacing spacing of of 0,8 kilometers flown flown north—south north-south at at an an elevation of 150 meters (48,000 (48,000 square square kilometers of of coverage), coverage). The process of construction of the the maps maps consisted consisted of removing the the regional regional magnetic magnetic varivariation of the the earth's total total magnetic magnetic field field as determined by by Fabiano Fabiano and and Peddie (1969), (1969), and and contouring contouring the the reresidual at at 20 20 gammas. gammas. If the regional regional variation is is not not removed, removed, aa severe severe banding banding effect, effect, which which •is .is not related related to the geology, geology, subdues subdues the the magnetic magnetic pattern caused by by the the geology, geology. An additional 3,400 square square kilometers kilometers were were flown flown in in 1977. 1977. An obvious obvious correlation correlation when the the map map is is compared compared to to a a geological map map (Sims, (Sims, Cannon and Mudrey, Mudrey, 1978, and and presented presented at at this this Institute Institute on on Lake Lake Superior Superior Geology Geology meeting) meeting) in in addition addition to to the the parallelism parallelism of of magnetic magnetic and and geological geological trends trends is is that that the the broad broad magnetic magnetic "low" "low" areas areas coincide coincide very very well well with with regions regions of of predominantly predominantly metasedimentary metasedimentary and and metavolcanic metavolcanic rocks, rocks, and and their their gneissic gneissic equivalents. equivalents. The The magnetically magnetically "high" "high" areas, areas, on on the the other other hand, hand, correlate correlate well well with with more more extensively extensively granitized granitized terranes, terranes. The The Gogebic Gogebic Iron Iron Range, Range, other other iron iron formations, formations, and and Middle Middle and and Late Late PrePrecambrian cambrian gabbroic gabbroic plugs plugs are are readily readily discerned discerned as as magnetic magnetic highs highs of of over over 7,000 7,000 gammas. gammas. —27— -27- �OFFSHORE IN SAND AND GRAVEL EXPLORATION EXPLORATION WESTERN LAKE MICHIGAN Edgardo L. L. Nebrija, Nebrija, Carol Carol J. J. Welkie, Welkie, and and Robert Robert P. P. Meyer Meyer Geophysical and Polar Research Research Center Center Lewis Weeks Weeks Hall, Hall, University University of of Wisconsin Lewis 1215 W. W. Dayton Dayton St., St., Madison, Madison, Wisconsin Wisconsin 53706 53706 Offshore sand and gravel deposits are are potentially potentially important resourgravel deposits important resources, near high-use high—use urban centers centers which which usually usually lack nearby nearby ces, especially near land sources and, of this low—cost, high-bulk high—bulk and, thus, thus, require transport transport of this low-cost, commodity from aa distance. Conventional acoustic acoustic profiling and and coring coring distance. Conventional of these deposits however, because because the high acoustic acoustic imdeposits is is difficult, difficult, however, the high impedance of sands and and gravels and because because concongravels inhibits inhibits sound penetration and ventional coring is is generally generally inapplicable. inapplicable. off Kewaunee, At three three test test areas in in Western Western Lake Lake Michigan Michigan —- off Kewaunee, Mani— Manitowoc, and Rawley Point towoc, Point —- experiments experiments to to determine the lateral extent extent and thicknesses of sands and gravels were conducted conducted using using combined combined sands and gravels were acoustic and Schlumberger resistivity profiling, profiling,resistivity Schlumberger resistivity resistivity sounding from the the water water surface, surface, and selective surficial surficial sediment sediment sampling. sampling. PrePrevious detailed sediment sampling by other workers workers showed showed temporally temporally changing sediment patterns off Kewaunee, Kewaunee, and and laterally laterally uniform, uniform, well— wellsorted, fine sorted, fine sands off Rawley Point. Point. Knowledge of of the the apparent apparent resisti— resistivities obtained over these sediments was used used to offshore exsediments was to determine offshore extensions of of known onshore gravels at Manitowoc. tensions Initial testing of of this this integrated integrated geological-geophysical geological—geophysical approach approach Initial testing shows that: that: (1) Where Where surficial surficial sediments sediments are thin, (1) thin, there is is low low correlation correlation between the and the sediment type inferred the observed apparent apparent resistivity and inferred from acoustic profiles or physical samples. samples. Instead, Instead, the the contours contours of of apparent resistivity resistivity reflect reflect the the trends trends in in the the till till and and glaciolacustrine glaciolacustrine apparent clays beneath beneath the the thin thin sediments sediments and and point point to to prospective prospective areas, areas, such such as as clays probable buried channels channels or or ancient ancient shorelines. shorelines. (2) In In areas areas where where acoustic acoustic profiles show thick the ob(2) thick sediments, .the observed apparent resistivity is correlatable served correIa table with with the the type type and and distribudistribution of of the tion the sediment. sediment. The lateral uniformity of of the the acoustically—impenetacoustically-impenetrable sands sands off off Rawley Rawley Point, Point, for for example, example, is is reflected reflected in in the the relativerelativerable ly constant apparent resistivity over most of ly of the the area. area. (3) Given Given the the water water depth depth from acoustic profiles, (3) profiles, the the water resisresistivity from independent independent specific-conductance specific—conductance measurements, measurements, and and the the tivity from resistivity ranges ranges of the sands sands and underlying till till from resistivity profiling elsewhere, yields aa resistivity— elsewhere, then, then, resistivity sounding yields resistivitydepth structure structure which which is is helpful helpful in in estimating estimating thicknesses. thicknesses. The The electrielectridepth cal pseudo-section pseudo—section also also aids aids in in interpreting interpreting the the lateral lateral changes changes in in sand sand cal thickness. (4) gravel deposits deposits (4) The The offshore offshore extensions extensions of of the thick thick onshore gravel are mappable mappable on on the the basis basis of of their their relatively relatively high high resistivity resistivity and and potenpotenare tial tial subsurface deposits undetectable from from surficial surficial samples samples are are inferinferred from the resistivity red resistivity data. data. —28— -28- �CRITERIA CRITERIA FOR FOR ALLIGATOR ALLIGATOR RIVER RIVER TYPE TYPE URANIUM URANIUM DEPOSITS DEPOSITS IN IN THE THE UNITED UNITED STATES STATES Richard Richard W. W. Ojakangas Ojakangas Department Department of of Geology, Geology, University University of of Minnesota, Duluth, Minnesota 55812 55812 Three Three geologically geologically similar similar uranium uranium subprovinces—-Rum subprovinces--Rum Jungle, Jungle, South South AlliAlligator River Valley, Valley, and Alligator Rivers——are Rivers--are present in the top end of the Northern Territory Territory of of Australia. Australia. Pitchblende Pitchblende deposits, deposits, with with minor minor secondary minerals, minerals, are found in a specific, specific, generally carbonaceous carbonaceous and chloritic horizon of of Lower Lower Proterozoic Proterozoic metasedimentary metasedimentary rocks. rocks. This This horihorizon consists of the presumably equivalent Golden Dyke, Dyke, Koolpin, Koolpin, and Cahill Formations Formations in in the the three three respective respective subprovinces. subprovinces. In the Rum Jungle and Alligator Rivers Rivers subprovinces, subprovinces, Archean Archean basement basement rocks rocks are are also also exposed. exposed. The The ore ore bodies generally generally occur occur at relatively relatively shallow shallow depths, depths, and most intersect the the eroded Lower Lower Proterozoic Proterozoic surface. surface. The grade grade of of ore ore genergenerally ally ranges ranges from from 0.25 0.25 to to 0.40 0.40 percent U308, with short short lengths lengths of of core core as 72 72 percent. percent. Structural preparation of of the host rocks rocks is is evias rich as dent dent in in each each deposit. deposit. Remnants of of aa hematite—quartz hematite-quartz breccia are associassociated with many ore ore deposits, deposits, and and may may represent represent aa Proterozoic Proterozoic regolith. regolith. Throughout the eastern part of of the region, region, the Middle Proterozoic (1500 (1500 m.y.?) Kombolgie Formation Formation of conglomerates, conglomerates, quartzose quartzose sandstones sandstones and and volcanics, overlies overlies the the Lower proterozoic metasedimentary rocks rocks with Rivers subpro— unconformity. All ore bodies in the Alligator Rivers subproangular unconformity. vince occur near this this unconformity. unconformity. In the South Alligator River River Valley Valley subprovince, Volcanics and the overlying Kombolgie Formasubprovince, the Edith River Volcanics deposits occur tion overlie the the Lower Proterozoic rocks, rocks, and all ore ore deposits In the the Rum Jungle Jungle subprovince, subprovince, the the Depot Depot Creek near this this unconformity. unconformity. In m.y.) may may have had essentially Sandstone of Upper Proterozoic Proterozoic age age (<1400 ~1400 m.y.) the same same relationship relationship to to the the Lower Lower Proterozoic Proterozoic and and to to the the ore ore deposits deposits the as do the Kombolgie and and Edith Edith River River Volcanics Volcanics in in the the other other subprovinces. subprovinces. Evidence can be amassed for for both both syngenetic syngenetic and and supergene supergene origins. origins. Most workers seem to prefer a Australian workers a syngenetic origin with initial deposition of uranium in Lower Proterozoic geosynclinal rocks rocks during sedimentation. Additional enrichment is is attributed to anatexis and metamorphism, with later morphism, later local local supergene supergene enrichment. enrichment. The original sources sources of the uranium are generally generally thought thought to to be be the the Archean Archean complexes. complexes. Some River Volcanics Volcanics as as the source rock in the workers suggest the Edith River Alternatively, a South Alligator subprovince. Alternatively, a strong case can be made for aa dominant dominant supergene supergene origin, origin, with with oxidizing oxidizing waters waters having having carried carried for eroded Lower Proterozoic surface either before, before, during uranium along the eroded or after after deposition of the overlying rock or rock units. units. What is the What the applicability of these criteria to exploration in the United Regardless of of the hypothesis hypothesis of of origin, origin, the major field States? Regardless field criteria The presence presence of of aa major major unconformity unconformity is is of of remain essentially the the same. same. The primary importance, importance, as as is is the the reducing nature of the structurally preThe significance significance of of the the relative relative ages ages of of the the rock rock units units pared rocks. The pared host rocks. beneath and above the the unconformity unconformity is is not not clear. clear. —29— -29- �Relations Between Between Soil Soil Geochemistry and Bedrock Geology, Relations Geology, Iron County, County, Wisconsin Iron Peltonen, D.R., D.R., Salotti, Peltonen, Salotti, C.A., C.A., and and Taylor, Taylor, R.W. R.W. Department of Geological Sciences Wisconsin—Milwaukee University of Wisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin 53201 heavy metal metal geochemical geochemical soil soil (B horizon) and and biogeochemical biogeochemical (aspen A heavy (B horizon) (aspen twigs) survey survey was was completed completed over over approximately approximately 100 100 square square miles miles directly directly twigs) south of the the Gogebic Gogebic Range Range in in aa granite-greenstone granite—greenstone terrain terrain in in Iron Iron south County, Wisconsin. County, Soil samples samples were were dry dry sieved, sieved, the the -80 —80 mesh mesh fraction fraction Soil and taken taken into into solution solution using aa lithium metaborate metaborate fusion fusion collected and technique. The twigs The twigs were ashed and dissolved in in 2M 2M HC1. HCl. 3000 Nearly 3000 elemental analyses were made using using atomic atomic absorption absorption spectrophotometry. spectrophotometry. These results were processed by by computer computer and statisttcal statistjcal parameters parameters These results were assigned to to all anomalous anomalous values. values. indicates there there is is communication between the the B Geochemical data indicates soil horizon in in the the glacial glacial till till and and the the underlying underlying bedrock. bedrock. Nickel and and copper are distinctly lower lower in in soils soils overlying overlying "granites" "granites" than than in in soils soils the underlying rock rock types be disdisoverlying greenstones, greenstones, and allow the types to be tinguished with greater than than aa 97.5% 97.5% confidence confidence level. level. In two areas where Zn Zn concentrations are known to be greater than 0.1% in parts of the bedrock, bedrock, anomalous values values of of Zn Zn in in the the overlying overlying soil soil samples samples occur. occur. —30— -30- �BASELINE URANIUM URANIUM AND AND THORIUM THORIUM ININARCHEAN ARCHEANAND ANDLOWER LOWER PROTEROZOIC PROTEROZOIC ROCKS OF OF THE AREA, MICHIGAN ROCKS THE MARENISCO-WATERSMEET MARENISCO-WATERSMEET AREA, MICHIGAN E. Peterman K. Sims Z. E. Peterman and and P. P. K. Sims U.S. Geological U.S. Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225 80225 Radiometric dating in area, northern Radiometric inthe theMarenisco-Watersmeet Marenisco-Watersmeet area, Michigan, has Michigan, has delineated delineated aalower lowerArchean Archean (Precambrian (Precambrian W) W) gneiss gneiss terrane at least terrane least 3,400 3,400 m.y. m.y. old old adjacent adjacent to to and and south south of aa greengreenstone-granite terrane terrane (2,600 to 2,700 m.y. old). old). Both stone-granite (2,600 to 2,700 m.y. Both terranes formed the basement basementfor for the the lower formed the lower Proterozoic Proterozoic (Precambrian (Precambrian X) X) sedsedimentary Marquette imentary and and volcanic volcanic rocks rocks ofofthe the MarquetteRange RangeSupergroup. Supergroup. The gneisses were were involved involved in folding during the The gneisses foldingand andmetamorphism metamorphism during Periokeanorogeny orogeny (1,750 m.y.ininthis this area). Analyses Analyses of UU Penokean (1,750 ++ 5050 m.y. and Th Thin in samples samplescollected collectedfor for radiometric and radiometric dating dating provide provide basebaseline data line data for forevaluating evaluatingradioelement radioelement mobility, mobility, and and possibly possibly enenrichment, during richment, during reactivation reactivation ofofthe theancient ancientbasement basement rocks. rocks. The lower Archean gneiss at Watersmeet contains 1.4 to lower Archean gneiss Watersmeet contains to1414ppm ppm UUand and 99 The available available data to 35 35 ppm ppm Th. Th. The data suggest suggest UUand and Th Th enrichment enrichment in in more highly cataclasized cataclasizedfacies fades of the more highly the gneiss. gneiss. A leucogranite dike in the dike the gneiss, gneiss, provisionally provisionally related related totothe thelate lateArchean Archean event, contains and6868ppm ppm fieldscintillometer scintillometer event, contains 18 18 ppm ppm UUand Th,Th, andand field measurements suggestthat that these these high high values in the measurements suggest values are are common common in granite near nearThayer ThayerofofFritts Fritts (1969), dikes. The The granite (1969), also thought thought to be reactivated Archean gneiss, has has U Uand andThThcontents contentssimilar similar to be Archean gneiss, those of the leucocratic phase of this those the gneiss gneiss atatWatersmeet. Watersmeet. A leucocratic phase of The Puritan Puritan Quartz rock contains contains2121ppm ppm UUand and 29 29 ppm ppm Th. Th. The Quartz MonzoMonzonite, aalate nite, lateArchean Archean intrusion intrusion ininthe thegreenstone-granite greenstone-granite terrane, terrane, is higher Th/U ratio. ratio. Uranium higher than than average average in Th Th content content and and Th/U ranges from from 2.5 to ranges to 88ppm ppm and and Th Th from from 17 17 to to 62 62ppm. ppm. In In all the the crystalline rocks, crystalline rocks,K Kand and UUvary vary independently, independently, aa feature feature suggestsuggestof the ing post-crystallization movement post-crystallization movement of of U. U. Metagraywackes Metagraywackes of Marquette Range RangeSupergroup Supergroup consistentlylow low in in both Marquette areare consistently both UU and and Th, Th, These values values are are simiwith averages averages of of2.6 2.6ppm ppmUUand and 6.6 6.6ppm ppm Th. Th. These with lar mayreflect reflect a lar totothose thoseofofother othergraywackes graywackes and and may a high high volcanic volcanic componentininthe thedetritus. detritus. component —31— -31- �NATIVE COPPER COPPER DEPOSITS DEPOSITS DERIVED DERIVEDFROM FROM NEARBY NEARBY KEWEENAWANBASALT BASALTBY BY COMBINED COMBINED IGNEOUS, KEWEENAWAN DEUTERIC, DEUTERIC, AND ANDMETAMORPHIC METAMORPHICPROCESSES PROCESSES NancyScofield, Scofield, Institute Mineral Research Nancy Instituteof of Mineral Researchand andDepartment Department ofofGeology Geology and and Geological Engineering, Technological University, University, Houghton, Geological Engineering, Michigan Michigan Technological Houghton, Michigan, Michigan, 49931 ABSTRACT flow) from A thick (60 (60 m) m) basalt basalt flow flow (Scales (Scales Creek Creek flow) from the the middle middle of the the Portage LakeVolcanics Volcanicswas wasintensively intensivelystudied studiedpetrographically petrographically and and its its conPortage Lake conIn the stituent minerals stituent mineralsanalyzed analyzed by by electron electronmicroprobe microprobe techniques. techniques. In the interior chemically: 1) 1) whole rock CuCuabundance of the the flow, flow,which whichisisnearly nearlyunaltered unaltered chemically: whole rock abundance is 110-150 ppm;2)2) microscopically-visible microscopically-visible native 110-150 ppm; native Cu Cu isispresent presentwithin withinpseudopseudomorphsafter after olivine; olivine; and morphs and 3) 3) Cu Cu concentrations concentrations in oxidized oxidized titanomagnetite titanomagnetite (2-3 modal modal %) %) are are2000-2500 2000-2500ppm. ppm. With With increasing degree degree of deuteric deutericand and metametamorphic alteration, alteration, Cu morphic Cu was was released released from from primary primary minerals, minerals, disseminated, disseminated, and and mechanismsofof Cu Cuconcentration concentration incorporated into incorporated into secondary secondary minerals. Dominant Dominant mechanisms 1) igneous differentiation by transfer within after extrusion extrusion are: are: 1) igneous differentiation by gaseous gaseous transfer the flow, 2) the 2) release release of ofnative nativeCu Cu during during deuteric deuteric oxidation oxidation of ofFe-Ti Fe-Ti oxides oxides and Fe-Mg Fe-Mg silicates, and and3)3)mobilization mobilization and andredistribution redistribution by and silicates, by later latermetametamorphic fluids. morphic fluids. Extrusion of the Extrusion the flow flowonto ontoaawet wetsurface surfaceproduced produced aa basal basal zone zone of high high oxygenand andvolatile volatile activity, accompanied oxygen activity, accompaniedbybygaseous gaseous transfer transferdownward downward of of Cu, Cu, This zone, Cu by by this this gaseous transfer, was Fe, and and Ti. This zone, enriched enriched to to 420 420 ppm ppm Cu gaseous transfer, was Fe, immediately abovethe thevesicular vesiculartop top of of the immediately above the underlying underlying flow, flow, and and provided provided aa source of Cu Cufor for later later circulating source of circulatingmetamorphic metamorphic fluids which which followed followed the the perperIf this within meable flow-top flow-top channeiways. meable channe1ways. If thisprocess processwas was repeated repeated elsewhere elsewhere within the volcanic pile, belowthe the basal basal zones zonesofof thick thick flows the pile,channelways channe1ways below flows may, may, in some cases, have haveunusually unusually high high Cu some cases, Cu concentrations. —32— -32- �POSSIBILITY OF OF MISSISSIPPI MISSISSIPPI VALLEY-TYPE VALLEY-TYPE ORE ORE DEPOSITS DEPOSITS IN IN INDIANA INDIANA POSSIBILITY Shaffer, Nelson Nelson R., R., Indiana Indiana Geological Geological Survey, Survey, Bloomington, Bloomington, Indiana Indiana Shaffer, The midwestern midwestern United United States States is is recognized recognized as as aa lead-zinc lead—zinc metallmetall— The ogenic province due to the occurrence there of low—temperature ogenic province due to the occurrence there of low-temperature ore deposits deposits of the the Mississippi Valley-type. ore Valley-type. Such Such deposits deposits commonly rocks on on the the flanks flanks commonly occur within within Paleozoic dolomite host rocks of structurally high areas of areas far from from regions regions of of igneous igneous activity. activity. They are are characterized by simple mineral suites, They suites, usually usually sphalerite, sphalerite, fluorite, galena, galena, or or barite, barite, that that are are believed believed to to have have formed formed fluorite, at moderate moderate temperatures temperatures from strong brines. at brines. One One explanation of the origin and characteristics characteristics of of Mississippi Mississippi Valley-type Valley—type of the origin and deposits suggests that they formed as a natural consequence of deposits suggests they formed as a natural consequence of when sedimentary sedimentary connate connate waters, waters, the the metalmetalbasin development when brines, migrated migrated updip from the basin basin and precipitated bearing brines, from the ore minerals upon encountering encountering sources sources of of reduced reduced sulfur. sulfur. Indiana lies lies near near this Indiana this general province and and contains contains many many geologic geologic features that appear suitable for the development of Mississippi features development of Mississippi Valley-type deposits. A structurally high high region collectively deposits. known as the Cincinnati and Kankakee Arches, crosses Indiana and as the Kankakee Arches, crosses separates the Michigan and Illinois Basins. separates the Paleozoic carbonates occur in the Knox Dolomite (Cambrian Ordovician); Black River (Cambrian and Ordovician); and Trenton Limestones Limestones (Ordovician); Salamonie, Louisville, Louisville, and (Ordovician); Salamonie, Wabash Formation (Silurian); Muscatatuck Group (Devonian); (Silurian); (Devonian); and Salem, St. Louis, and Ste. Genevieve Limestones Salem, St. and Ste. Genevieve Limestones (Mississippian). (Mississippian). Unconformities Knox, Trenton, Trenton, and Wabash Unconformities exist at the the tops tops of Knox, Formations. Numerous occurrences of of sphalerite, sphalerite, fluorite, fluorite, barite, barite, and galena galena have have been been noted noted in in Indiana Indiana in in the the past, past, and and more more than than and 60 new but generally minor occurrences have been found found during this recent recent study, study, many many in in the the Black Black River—Trenton River-Trenton section, section, especially in northern Indiana where extensive dolomitization has occurred. occurred. The dolomitized reef facies facies of the Wabash Formation had many mineral occurrences in northern Indiana as did the overlying lying Devonian Devonian limestones. limestones. Limestones of the the Salem Salem and and Ste. Ste. Genevieve also had occurrences of sphalerite and fluorite fluorite in southern southern and and southwestern southwestern Indiana. Indiana. Limited information information from from fluid fluid inclusions inclusions in in sphalerite, sphalerite, barite, barite, and fluorite fluorite indicates indicates that that some some samples samples have have formed formed from from brines brines in the range of temperatures reported from Mississippi Valleytype deposits. deposits. Minor elements in 80 sphalerite specimens from Indiana Indiana included included cadmium cadmium (.03 (.03 to to 6.9 6.9 percent), percent), iron iron (.01 (.01 to to .61 .61 percent), percent), and lesser amounts of gallium, gallium, germanium, germanium, copper, copper, and manganese. Silver was not not detected detected in in sphalerite sphalerite samples. samples. Due to favorable favorable geology, geology, occurrence of minor amounts of ore minerals, arid tentative evidence that that fluids fluids of the ore—forming and tentative evidence ore-forming type passed through suitable host rocks, rocks, a real possibility exists exists that that undiscovered undiscovered Mississippi Mississippi Valley-type Valley-type ore ore deposits deposits may occur in Indiana. occur in Indiana. —33— -33- �PRECAMBRIAN X PALEOPOLES THE UPPER PRECAMBRIAN X PALEOPOLES FROM FROM THE UPPER PENINSULA PENINSULA AND AND AANEW NEWMETHOD METHOD FOR REMANENT VECTOR DETERMINATION FOR REMANENT VECTOR DETERMINATION SHANABROOK, David, Department Geology,Michigan Michigan State State SHANABROOK, David, Department ofofGeology, University, University, East EastLansing, Lansing, Michigan Michigan 48824 A method methodwill will be which makes makesitit possible possible to use be described described which use the the three-dimensional modelingprogram programofofWhitehill Whitehill modified three-dimensional magnetic magnetic modeling modified so so as magneticvector vectorinto intoaccount account thatitit is as to take take the the remanent remanent magnetic soso that possible the declination declination and inclination of possible to determine determine the and inclination ofaabody's body's remanentvector vector directly directly from remanent fromobserved observed magnetic magnetic data. This This is is done done by SHALOCI writtenbybyWilliam William Ciolek, Ciolek, by using using aacomputer computer program program named named SHALOCI written Mark Locher,and andthe theauthor authortotocalculate calculate the the induced field due Mark Locher, induced field due to to This induced field isisthen the body. body. This induced field thensubtracted subtractedfrom fromthe theobserved observed data data to yield yieldthe themagnetic magnetic field fielddue due totothe thebody's body'sremanent remanent vector. vector. SHALOCI thenused used againtotocalculate calculate the the magnetic magneticfields fields due SHALOCI is isthen again due to to various vectors various vectors in inorder ordertotomatch matchthe theobserved observed anomalie. anomalie. This method method is accurate of the the vector's vector's true accurate to within within 10 10 degrees degrees of true declination declination and44degrees degreesofofits its inclination. inclination. Because this, the the results results of and Because ofofthis, are often often useful this method method are useful in in determining determining the the age age of aa body body which which is very very helpful ininPrecambrian Precambrian shield areas areas like likethe theUpper Upper Peninsula Peninsula of of Michiganwhere wherethere thereare aremagnetic magneticbodies bodiesofofdifferent different ages. Michigan ages. At Present, this computer-oriented approachisislimited limited to bodies present, computer-oriented approach bodies with fairly strong fairly strongremanent remanentmagnetic magnetic vectors vectorsand and which which have have not not been been metamorphosed very severely,but butfuture futurework workmay maybebeable abletotoalleviate alleviate metamorphosed very severely, these problems. problems. Paleomagnetic work done done on on samples samplesfrom from aa metadiabase metadiabase dyke dyke of of Paleomagnetic work PrecambrianXXage ageinin connection connection with the of supposed supposed Precambrian themagnetic-modeling magnetic-modeling described hasyielded yieldedsome some interestingresults. results. Thermal described above above has interesting Thermal dedemagnetization hasestablished establishedaapaleopole paleopolethat that falls falls on magnetization has on the the apparent apparent polar wandering curvefor for North Americaeither either at 2.04 wandering curve North America 2.04 bybp bybp or 1.84 1.84 bybp depending dependingononwhether whetheritit is is normal bybp normal or reversed. reversed. Further work work is being undertaken clarifythe thesituation, situation,but butitit is is clear being undertaken to to clarify clear that the the long long held held idea idea that thatthe themany many positive positivemagnetic magnetic anomalies anomalies in the the Upper Peninsula of of Michigan were due due to to "normally" Upper Peninsula Michigan were "normally" magnetized magnetized PrePrecambrian metadiabases have revised lightofof the the fact cambrian XXmetadiabases willwill have to to be be revised in in light that they Southern they yield yieldnorth-seeking north-seekingpaleopoles paleopolesininthethe SouthernHemisphere. Hemisphere. —34— -34- �Precambrian geologic geologic framework framework of northern Wisconsin by P. K. Sims Sims and and Z. Z. E. E. Peterman U.S. u.S. Geological Geological Survey, Survey, Denver, Colorado Colorado 80225 80225 Northern Wisconsin contains rocks belonging to each of the three major major subdivisions subdivisions of of the the Precambrian. Precambrian. Lower Precambrian Precambrian (Archean (Archean or or Precambrian W) rocks rocks constitute constitute the the basement. basement. Except for the the Gogebic Gogebic Range and vicinity, vicinity, which is underlain by 2,700—m.y.—old 2,700-m.y.-old greenstone— greenstonegranite complexes, complexes, the the basement rocks are dominantly gneisses and amphibolite. m.y. have amphibolite. Minimum ages for the the gneisses of 2,800—3,000 2,800-3,000 m.y. been obtained at a few localities in central Wisconsin (by W. R. (by W. R. Van Schmus) Schmus) and near Morse, south south of of Nellen. Mellen. Middle Precambrian Precambrian (Precambrian (Precambrian x) X) supracrustal rocks occur on the the Gogebic Range, Range, in in a 75—km—wide belt across across northern Wisconsin, Wisconsin, and and in 75-km-wide east—trending east-trending belt Marathon Marathon County County and and vicinity vicinity in in central central Wisconsin. Wisconsin. The proportion proportion of volcanic rocks rocks Increases that of of sedimentary increases southward relative to to that rocks; rocks; these volcanic rocks contain the valuable massive sulfide deposits known at at Crandon, Crandon, Ladysmith, Ladysmith, and and Pelican Pelican River, River. near near Monico. Monico. Abundant granitic m.y. old) granitic rocks (1,800—1,850 (1,800-1,850 m.y. old) intrude intrude the the volcanic rocks. As known previously, the the youngest rocks are local platform quartzite deposits m.y. old, l,500—m.y.— deposits more than 1,500 m.y. old, the large 1,500-m.y.old Wolf River batholith and associated syenite, syenite, and the approximately l,l00—m.y.—old 1,100-m.y.-old (Keweenawan) (Keweenawan) volcanic volcanic and and sedimentary sedimentary rocks rocks related related to to the midcontinent rift the rift system. system. The middle Precambrian rocks that overlie Archean gneisses, gneisses, together basement, were folded m.y. ago, with the basement, folded and metamorphosed about 1,800 m.y. ago, and were cataclastically cataclastically deformed deformed locally locally about about 1,600 1,600 m.y. m.y. ago. ago. In In contrast, strata overlying overlying the the greenstone-granite greenstone—granite basement basement on the the Gogebic Gogebic contrast, Range were not deformed deformed during during this this interval. interval. At least three three major high—angle high-angle fault fault sets sets have have been been recognized. recognized. The youngest, related related to to the the midcontinent midcontinent rift rift system, system, consists consists of of N. N. 50—55 E. E. faults faults that that were were formed formed in in late late Keweenawan Keweenawan time; time; they they probably probably 50-55 produced most of of the the northward northward tilting tilting of of strata strata on on the the Gogebic Gogebic Range. Range. North—northeast—trending North-northeast-trending faults faults that had repeated movements and that that typically have wide wide zones zones of of mylonite mylonite bound bound the the middle middle Precambrian rocks rocks in the Marathon County area, as as described described earlier earlier by by G. G. L. L. LaBerge. LaBerge. Probably the the oldest set consists of long, long, northwest—trending northwest-trending faults that reactivated and and have have apparent apparent right-lateral right—lateral movemovethat were repeatedly reactivated f— ments; the the major fault, fault, the the Mineral Mineral Lake Lake fault, fault, is is interpreted interpreted to to of offset Archean rocks about 160 160 km km and and middle middle Precambrian Precambrian rocks, rocks, 10—15 10-15 km. km. —35— -35- �A NEW PRECAMBRIAN PRECMIBRIAN SURFACE SURFACE CONTOUR CONTOUR MAP MAP FOR SOUTH-CENTRAL WISCONSIN, Eugene I. I. Smith, Smith, Division Division of of Science, Science, Univ. Univ. of of Eugene Wisconsin-Parkside, Kenosha, Wisconsin-Parkside, Kenosha, WI 53141 A new surface su~face contour map for for the the buried Precambrian Precambrian basement of south-central Wisconsin was constructed constructed using using data from from 200 200 deep water water and oil test wells, wells, geophysical data studies, and and previously published Precambrian surface studies, contour maps of of Wisconsin. The new map shows that that (1) (1) the the Precambrian surface Precambrian surface slopes slopes gently to the the east, east, southeast southeast and south off the and the Wisconsin arch. arch. Standing above this this surface are are numerous numerous ridges ridges and knobs of resistant rhyolite, surface granite and quartzite, quartzite, many of which protrude through granite through the the Paleozoic and Pleistocene cover as inliers (e.g., (e.g., at Waterloo, in in the loo, the Fox River Valley, and and at at Baraboo). Baraboo). Buried knobs of Precambrian rock occur occur at at Ripon Ripon (granite), (granite), BrotherBrothertown (quartzite), Waupun (quartzite), town (quartzite), Waupun (quartzite), Whitewater (quartz(quartzite) ite) and Rosendale (rock (rock type type unknown) unknown) . Both the the exposed knobs rise abruptly from and buried knobs from the the peneplained peneplained PrePrecambrian surface; surface; for for example, example, the the rhyolite knob at at Berlin stands stands over 600 feet feet above this this surface, surface, and that that at at Marcellon, 470 470 feet. feet. The change in in elevation elevation in in both both cases cases occurs occurs over a a lateral lateral distance of less less than than 11 mile. Other knobs have The eastward plunging have similar similar relief. relief. (2) (2) The Waterloo syncline syncline is is revealed revealed by by an an arcuate arcuate ridge ridge that that in in places stands 700 700 feet feet above the the level level of of the the surrounding surrounding Precambrian surface. surface. This ridge ridge is is only only exposed exposed in in the the area to the east of Waterloo, near Portland. to the east of Waterloo, near Portland. The nose of of the Waterloo Waterloo fold is the is in in the the Portland Portland area. area. The north limb limb extends as a ridge from from Portland Portland to to near Hartford Hartford in in WashWashington County, aa distance distance of of 30 30 miles. miles. The south south limb limb extends as aa continuous continuous (?) (?) ridge as far as Fort Atkinson and then then continues as a series series of of quartzite quartzite knobs knobs into into central Walworth County, aa distance distance of of 45 45 miles miles (( a buried quartzite knob is is located located at at Whitewater, and and quartzite quartzite is is found Delavan). (3) found beneath Delavan). (3) The subsurface subsurface data data is is supsupportive portive of a northeast trending trending fault fault extending extending from from near near Sheboygan to to central central Walworth Walworth County County (( as shown shown on onmaps mapsby by Thwaites, and Dutton and and Bradley), but but the the presence presence of of other other faults faults in in the the Precambrian Precambrian basement basement of of south-central south-central Wisconsin Wisconsin is is uncertain. uncertain. . —36— -36- �THE GEOLOGY AND PETROLOGY OF OF THE THE WINE WINE LAKE LAKE INTRUSION, INTRUSION, COOK COOK COUNTY, COUNTY, MINNESOTA by Andrew E. E. Strakele, Strakele, Jr. Jr. University of Minnesota, Duluth Duluth, Duluth, MN 55812 Exposures of of granophyric granite and associated associated felsic felsic intrusive rocks Exposures granophyric granite intrusive rocks of the eastern part part of the Duluth Complex form form an east-west east—west trending belt of the eastern the Duluth trending belt which parallels the the northern or basal contact of the North Shore Volcanic Group in Cook County, County, Minnesota. Minnesota. Along the western limit limit of of this this belt, belt, where it begins to to trend trend southwestward near the county line, line, there there exist several bodies of medium—grained medium-grained diorite diorite and and quartz quartz diorite. diorite. The largest body of these bodies, together with these dioritic rocks and some smaller satellite bodies, an adjacent adjacent unit unit of recrystallized recrystallized rhyolite rhyolite and and granite granite have have been been informally informally an designated as as the Wine Lake Intrusion Intrusion by Grout, Grout, Sharp, Sharp, and and Schwartz Schwartz in in 1959. 1959. Coarse—grained gabbroic gabbroic anorthosite anorthosite underlies underlies this this general general area to to the Coarse-grained the north and west, west, being locally overlain by a fine medium—grained gabbro. fine to medium-grained gabbro. dioritic rocks rocks also also occur above above the the gabbroic gabbroic anorthosite anorthosite as as bodies bodies of of 1 The dioritic to to 5 km2 km 2 in in area. area. Both gradational and intrusive contacts appear to exist between these these three three rock rock units. units. The rhyolite and granite unit of the Wine Lake Intrusion has an outcrop pattern pattern suggestive suggestive of of aa subhorizontal subhorizontal sheet. sheet. locally contains contains both both irregular cuspate cuspate and and sometimes sometimes angular The granite granite locally inclusions inclusions of fine—grained fine-grained quartz quartz diorite diorite near near the the granite—diorite granite-diorite contact. contact. Large xenoliths xenoliths of amygdaloidal amygdaloidal basalt basalt and and some some late-stage late—stage basaltic basaltic dikes dikes Large have also also been observed observed in in the the Wine Wine Lake Lake area. area. Field relationships, relationships, petrography, petrography, chemistry, chemistry, and modelling of chemical trends by by aa least least squares squares approximation approximation program for for crystal crystal fractionation fractionation trends and magma mixing support the derivation of gabbro by fractionation of and support the derivation gabbro by fractionation of plagioclase from gabbroic anorthosite. The gabbro was apparently altered from gabbroic anorthosite. The altered by the addition of the components of albite, albite, quartz, quartz, orthoclase, orthoclase, and H2O H20 to produce the diorite and quartz to quartz diorite diorite phases. phases. The evidence also suggests that the components were were derived derived from the the remelting of of that the granitic granitic mineral components xenoliths of of rhyolite rhyolite composition. composition. This model is in conflict with the the model of Weiblen and Morey (1975) (1975) which states that the the felsic felsic series rocks rocks were the differentiation differentiation of of gabbroic gabbroic anorthosite. anorthosite. produced by the —37— -37- �POSSIBILITIES POSSIBILITIESFOR FORURANIUM-GOLD URANIUM-GOLD QUARTZ-PEBBLE QUARTZ-PEBBLE ORES ORES IN IN THE THE LAKE LAKE SUPERIOR SUPERIOR REGION IN IN THE REGION THE LIGHT OF AANEW NEW MODEL ~lODEL FOR ELLIOT IAKE-WITWATERSRAND lAKE-WITWATERSRAND GENESIS James Trow, Thow, Department of Geology, Michigan Michigan State State University, University, East Lansing,Michigan Michigan 48824 L882 East Lansing, Gibbs free-energy calculations support support a new model for the the formation of quartz-pebble tion quartz-pebble oresg oresl 1) 1) a typically granitic, granitic, alkaline, alkaline, or metamorphic source area was exposed to to 2) 2) oxygenated atmospheres during mamorphic jar C02—impoverished episodes jor glacial C02-impoverished episodes since zince the the Early Early Precambrian. Precambrian. Lower PC02 P002 and related higher pH pH of rain rain and and runoff runoff inhibited the the dissolvdissolvirig oxidizeduranium uraniumasasU020~, UO20},U0 UO2CO°, UO2(CO3)2(H2O) to ing ofofoxidized C0 0, and U02(C01)2(H20)2 to propro2 3 duce some some clastic clastic hydrated hydrated uranyl uranyl oxide oxide pseudomorphs seudomorphs arter duce after uraninite, uraninite, some water-soluble U02(HP04)i u02(HP0) complex some water-soluble complexions, ions, and and possibly possibly (if (if not not exposed exposed too long) long) some uraninite clasts 3) 3) which were transported by streams along with with magnetite magnetite and and hematite hematite clasts, clasts, ferric ferric hydroxide hrdroxide hydrosols, hydrosols, nuggets, and and ilmenite ilmenite clasts, clasts, among among others. others. 4) ) These materials were gold nuggets, where hydrated uranyl uranyl oxide oxide clasts clasts were were carried to aa steep Eh gradient where re-reduced to to uraninite uraninite pseudomorphs, pseudomorphs, where whereU02(HP04)Z UO2(HPO) complex complex ions ions were were reduced to interstitial uraninite, uraninite, where where magnetite and hematite hematite clasts were reduced to pyrite "clasts", "Clasts", where where ferric ferric hydroxide hydrosols were were reduced to interstitial pyrite, lost their their clastk clastc pyrite, and where gold nuggets lost Au5 (to precipitate much much later as as non-clas~ non-clastt character by dissolving as AuS(to precipitate gold), gold), all by reactions paradoxically requiring 02 as well as anticiHS, the pated H2S or HS-, the latter latter two two from from interbedded interbedded and and underlying underlying sulfidic sulfi~ from the the reaction of botanic botanic sugars sugars upon upon S04. SOC. Quartz quartz pebbles pebbles basalts or from indicate the the sedimentary environment and and imply the the availavailindicate the vigor of the ability elastic ilmenite resulted in ability of of reactant reactant air. air. Sulfurization of clastic iron sulfide sulfide (later to to become become pyrrhotite) pyrrhotite) and and Ti021 T102; the the latter latter then then endure as ore, joined U02 to form brannerite. 5) To endure ore, the reduced system from renewed renewed oxidation under under post-glacial highhighwas sealed and preserved from A 55,000-miles er PC02 climates, climates. A 55,OOO-miles Jeep reconnaissance reconnaissance in the Basin and Range, Mountains, and the Range, the Rocky Mountains, the Appalachians has discovered five five of further Late Precambrian targets worthy worthy of further study, study,ofof Late Precambrianand andEocambrian Eocambrian ages. ages. Additional glacially-related glacially—related terranes terranes to be Additional be reconnoitered reconnoitered include include Late Late and Pliocene-Pleistocene. Pliocene-Fleistocene. Ordovician-Early Silurian, Permocarboniferous, and Late Precambrian possibilities in the Lake Superior region inviting examination include i) Mt. McCaslin NcCaslin (Wis1) the parent ledge ledge from which the Nt. (Wisconsin) consin) pyritic-quartz-pebble conglomerate boulder was wrenched during the Pleistocene, Pleistocene, 2) 2) conglomerates conglomerates at at the the base base of of the the Keweenawan, Keweenawan, ininthe cluding the the Bessemer Bessemer Conglomerate Conglomerate (Wisconsin), (Wisconsin),Nopeming Nopemingand andPuckwunge Puckwunge Conglomerates (Minnesota),and andcorrelatives correlativesalong alongthe the northern northern and and easteastConglomerates (Minnesota), ern shores of of Lake Superior Superior (Ontario), (Ontario), and and 3) 3) the southwestward continuation of the pyritic quartz-pebble conglomerate conglomerate at at the the base base of of the the Fond du Lac Lac Formation (Minnesota) (Minnesota) particularly where it overlies the St. Cloud Granite, Granite, and the St. the correlative top of the the Copper Harbor Conglomerate (Michigan). (Michigan). AA Pleistocene possibility possibility beneath beneath lake—bottom lake-bottom U ppb Ste. Marie (Michigan), (l'iichigan), suggested by 37 37 U in in well well clays near Sault Ste. source as Elliot Lake ores. water, may have been derived from the same source as Elliot Lake ores. water, may have been derived from the same —38— -38- �GEOCHRONOLOGIC RELATIONSHIPS RELATIONSHIPS IN GEOCHRONOLOGIC THE IN THE CARMEYLAKE LAJCEGNEISS GNEISS AND AND OTHER CARNEY OTHER BASEMENT BASEMENT GNEISSES GNEISSES IN DICKINSON DICKINSON COUNTY, COUNTY, UPPER MICHIGAN IN W. R. R. Van Van Schmus, Schmus, R. R. E. E. Woronick, Woronick, and N. W. N. L. L. Egger Egger Department of Geology Department of of Kansas University of Lawrence, Kansas Kansas 66045 66045 Lawrence, The Carney Carney Lake Lake Gneiss Gneiss and and other other granitic granitic gneisses gneisses exposed exposed in The in the the Feich trough trough region, region, Dickinson Dickinson County, County, have have generally generally been been assumed Felch to assumed to be Archean Archean (Lower be (Lower Precambrian) Precambrian) in in age. age. According According to to the the model model of of Morey Morey and Sims Sims (1976), gneisses belong belong to to aa terrane and (1976), these these gneisses terrane that is in in part older than older than 3.0 3.0 b.y. b.y. We are carrying out total—rock total-rock Rb—Sr Rb-Sr and zircon U—Pb analyses analyses from from these rocks in in order order to to determine determine their primary age U-Pb these rocks their primary age and to to evaluate effects of post—Archean and post-Archean metamorphic metamorphic events. events. for the Carney Lake Lake Gneiss Gneiss indicate indicate that that this unit has has aa Data for the Carney this unit of about about 2.8 2.8 b.y. b.y. and and has has undergone undergone extensive extensive redistribution primary age of of Rb Rb and Sr of Sr during during aa metamorphic metamorphic event event about about 1.8 1.8 b.y. b.y. ago. This event event was probably regional metamorphism associated with emplacement of the the during the the Penokean Orogeny northeastern Wisconsin plutonic complex during about Orogeny about 1.83 b.y. 1.83 b.y. ago. ago. Feich Trough region continue to reflect the Data from the the Felch to reflect the complex geochronologic relationships relationships reported on previously by Banks and Van Schmus (1971, Schmus (1971, 1972). 1972). There is is clear clear evidence for for a major event 2.1 2.1 b.y. ago that that caused caused extensive Rb—Sr Rb-Sr re—equilibration re-equilibration in in the the basement gneisses. gneisses. Our preferred interpretation interpretation is is that that the the event was high—grade high-grade metamorphism, perhaps with minor anatexis, affecting 2.8 2.8 b.y. b.y. old old gneisses. gneisses. Alternatively, Alternatively, it it is is possible that that much of the the gneiss has has primary primary ages of about about 2.l 2.1 b.y., b.y., but have have incorporated incorporated substantial substantial amounts amounts of of older older radiogenic radiogenic Sr87. Sr 87 • Finally, Finally, even even though though the the age age systematics systematics are quite quite complex, complex, there there is is no clear clear evidence evidence that that any any of of the the units units studied studied to to date date are are older older than than 2.8 2.8 b.y. b.y. —39— -39- �FINITE THETHE PRECAMBRIAN FINITESTRAIN STRAININ IN PRECAMBRIANKONA KONAFORMATION FORMATIONOFOFTHE THEMARQUETTE MARQUETTE SYNCLI SYNCLINORIUM NORIUM WESTJOHN, Davidand andCAMBRAY, CAMBRAY, William,Department Department of of Geology, WESTJOHN, David F. F. William, Geology, Michigan State University, Michigan State University, East EastLansing, Lansing, Michigan Michigan 48824 Slates ininthe thePrecambrian Precambrian Kona Kona Formation Formation of the the Marquette Marquette SuperSupergroup contain ellipsoidal reduction spots and deformed group contain ellipsoidal reduction spots and deformed veins. veins. Each Each feature has independently in other has been been used used independently other areas areas as as aameans means of measuring finite strain measuring finite straininduced induced in in rocks rocks during during tectonic tectonicdeformation. deformation. However, the strain values obtained from either However, the strain values obtained from either of these these indicators are open open to questions questions because because the the following followingassumptions assumptionsmust mustbebemade; made; the werepredeformational predeformationaland and initially spherical, the reduction reduction spots spots were initially spherical, and the veins veins were were predeformational predeformationaland andinitially initially had and the had aa wide wide range range of presenceofof these these features features in planar planar orientations. orientations. The The presence in the thesame same lithology provided an opportunity opportunitytoto test test the the validity validity ofofsuch provided an such assumptions. Both Both indicators occur occur ininthe thesame same strain straindomain, domain, and and should show showthe thesame same strainstate stateif if the are valid. valid. should strain the assumptions assumptions are In this and thisstudy, study,reduction reductionspots spots anddeformed deformedveins veinsfrom fromthe thesame same strain domain are used to determine the orientation strain domain are used to determine the orientation and and dimensions dimensions of the minimum finitestrain strain ellipsoid. ellipsoid. the minimum finite In using the two methods it is possible test is valid to In using the two methods it is possible to to test if ifitit is to use them independently as a measure of finite strain. use them independently as a measure of finite strain. Preliminary suggests that that there are differences which Preliminary work work suggests are some some differences which indicate that the veins may have developed after some increment strain that the veins may have developed after some increment ofof strain and that they record only part of the strain history and that the and that they record only part of the strain and that the rereduction spots provide a more complete record. spots provide a more complete If this may If thisisisthe thecase caseit it maybe be possible possible to to plot plotpart partofofthe theincremental incremental strain history of the region and to record both magnitude and history of the region and to record both magnitude and orientation orientation of strain thethe Penokean strainatatseparate separatetimes timesduring during PenokeanOrogeny. Orogeny. The reduction spots indicate a minimum finite strain ininwhich The reduction spots indicate a minimum finite which Orientations Orientations of Principle Axial Ratios Ratios k value value Extensions Principle Axes Axes V Z (a-i/b—i) V X Z X : YY :: ZZ (a -1/ b-l) XX Y Z XX Y Z Reduction +58% +7% -43% 82°/O93° 8°/273° 10/0030 1.5:1.1:0.6 0.50 Spots : —40— -40- �— AA new new detailed detailed aeromagnetic aeromagnetic map map covering covering most most of of the the Precambrian Precambrian shield shield in in Wisconsin Wisconsin by by Isidore Isidore Zietz Zietz U.S. U.S. Geological Geological Survey, Survey, National National Center, Center, Reston, Reston, Virginia 22092 22092 ABSTRACT ABSTRACT A A detailed aeromagnetic survey, survey, having a flight flight separation of ½ ~ flight altitude of 500 feet, feet, has been made over most of mile and a flight the Precambrian shield shield in in Wisconsin. Wisconsin. The survey survey was under under the the direction ofofJohn direction John1-1. H. Karl Karl of the University of of Wisconsin Wisconsin at at Oshkosh. Oshkosh. An aeromagnetic aeromagnetic map, map, published published by by the the U.S. U.S. Geological Geological Survey Survey in in 1977, 1977, was prepared at was at a scale of 1:250,000 by photographically reducing and compiling 86 maps that that cover cover areas areas shown on standard 86 aeronlagnetic aeromagnetic maps standard U.S. U.S. Geological Survey 15' IS' quadrangles. quadrangles. In addition, addition, a colored colored aeromagnetic aeromagnetic and at the same has been map of the the same area and at the same scale (1:250,000) (1:250,000) has prepared and placed on on open-file open-file by by the the U.S. U.S. Geological Geological Survey. Survey. By using using these these two two aeromagnetic aeromagnetic maps, maps, together together with with the the existing existing By regional gravity data, regional data, available available outcrops, outcrops, and and existing existing isolated, isolated, sparse geologic geologic mapping, mapping, Paul Paul Sims Sims and and William William Cannon Cannon have have prepared prepared sparse aa regional regional geologic map. In the the main, main, the In the uncolored aeromagnetic map was was used used for for structural analysis, analysis, whereas whereas the the colored colored version version of of the the map map on on which which structural the differences differences of magnetic magnetic intensity intensity are are conspicuous conspicuous was was used used for for the inferring inferring lithologic variations. —41— -41- �— — — — —; ——— I- m -Fl — �FIELD FIELD TRIP TRIP II SOUTHWESTERN SOUTHWESTERN WISCONSIN WISCONSIN ZINC-LEAD ZINC-LEAD DISTRICT DISTRICT LEADERS: LEADERS: M.G. M.G. Mudrey, Mudrey, Jr., Wisconsin Geological and and Natural Natural History Survey, Survey, W.A. W.A. Broughton, Broughton, University University of of Wisconsin-Platteville, Wisconsin-Platteville, Walter Walter S. S. West, West, U.S. U.S. Geological Geological Survey, Survey, and and Allen Allen V. V. Heyl, Heyl, U.S. U.S. Geological Geological Survey. Survey. DATE: DATE: 1978. May 99 —- 10, 1978. This trip will visit the Wisconsin part of the historic Upper Mississippi Mississippi Valley Valley Zinc-Lead Zinc-Lead District. District. Stops Stops at at quarries and and roadcuts roadcuts will provide a a background on the ore—bearing ore-bearing Paleozoic rocks before going underground at a historic mining site, site, and and aa producing producing zinc-lead zinc-lead mine. mine. 1. 1. Assemble in in Madison, Wisconsin, Wisconsin, at at 12:30 12:30 p.m. p.m. on on Tuesday, Tuesday, May May 9, 9, 1978, and proceed to to Platteville, Platteville, Wisconsin Wisconsin for for overnight overnight lodging. lodging. Tour southwest southwest Wisconsin, and and journey journey to to Milwaukee Milwaukee on on Wednesday, Wednesday, May 10, 10, for for the the evening evening festivities. festivities. 2. 2. The cost is is $40.00 $40.00 and and includes: includes: a) a) b) b) c) c) d) d) Overnight accommodations accommodations (double (double occupancy) occupancy) at at Platteville. Platteville. Bus transportation from Madison to Platteville with a a return trip trip to to Milwaukee. Milwaukee. An evening banquet in Platteville on Tuesday, Tuesday, May 9, 9, and lunch on Wednesday, May May 10. 10. Guidebook. 3. 3. participants. Limited to a a maximum of of 36 participants. 4. 4. The guide materials designed for for this this field field trip trip are: are: a) a) b) b) c) c) d) d) Geology of Upper Mississippi Valley Zinc-Lead Zinc-Lead District, District, Information Circular Number 16, 16, 1970. 1970. ($3.00) Upper Mississippi Mississippi Valley Valley Base Base Metal Metal District, District, Field Trip Trip Upper Guidebook Number Number 1. 1. ($4.00) If purchased purchased together, together, the cost is $6.00. If $6.00. Available from: from: Natural History Survey Wisconsin Geological and Natural 1815 University University Avenue Avenue 1815 Madison, Madison, Wisconsin 53706 608-262-1705 608—262—1705 —45— -45- �FIELD TRIP II II FIELD TRIP MINERAL MINERAL EXTRACTION EXTRACTION AND AND PROCESSING PROCESSING EQUIPMENT EQUIPMENT MANUFACTURERS MANUFACTURERS IN THE GREATER GREATER MILWAUKEE MILWAUKEE AREA AREA LEADER: LEADER: Charles Charles DATE: DATE: May 10, 10, 1978 1978 A. A. Salotti, Salotti, University University of of Wisconsin-Milwaukee. Wisconsin-Milwaukee. This tour will visit a number of major manufacturing plants where mineral and and solid solid fuel fuel extraction and processing equipment is fabrifabricated. Milwaukee is is a world center center for for this activity, activity, and much of the equipment used in the the Lake Superior Region originated in southeastern Increased coal utilization, utilization, coupled with rapidly changing Wisconsin. Wisconsin. technologies processing, are are reflected in technologies in mineral and solid fuel fuel processing, the dynamic character character of this this industry. industry. 1. 1. Depart from the the Pfister Hotel, Hotel, downtown downtown Milwaukee, Milwaukee, on Wednesday morning about about 9:00 9:00 a.m., a.m., May May 10, 10, 1978. 1978. Return to the Pfister Hotel Hotel about about 4:00 4:00 p.m. p.m. 2. 2. There is no guidebook for for this this trip. trip. —46— -46- �FIELD FIELD TRIP TRIP III III I PRECAMBRIAN PRECAMBRIAN RHYOLITh, RHYOLITE, GRANITE, GRANITE, AND QUARTZITE INLIERS INLIERS IN IN SOUTH-CENTRAL IN SOUTH-CENTRAL WISCONS WISCONSIN LEADER: LEADER: Eugene Eugene I. I. Smith, Smith, University University of of Wisconsin—Parkside. Wisconsin-Parkside. DATE: DATE: May May 12 12 -- 13, 13, 1978 1978 This field trip will visit rhyolite ash—flow ash-flow tuff and granite of Middle Precambrian age age (1765 (1765 + ~ 20 20 m.y.), which are are inliers inliers on the the southern southern margin of of the the Precambrian Precambrian shield. shield. These rocks are younger than than granite granite margin and rhyolite in the Wausau area of central Wisconsin (1900 m.y.), and (1900 m.y.), older than the Wolf River River batholith batholith of of northeastern northeastern Wisconsin Wisconsin (1500 (1500 m.y.). m.yJ. the Wolf Stops are are designed designed to to illustrate illustrate stratigraphic stratigraphic and and structural structural relations relations interesting province. province. in this interesting 1. 1. Depart Milwaukee on Friday evening, evening, May 12, 12, 1978, 1978, at at 6:30 6:30 p.m., p.m., and proceed to Oshkosh, and Oshkosh, Wisconsin for for overnight overnight lodging. lodging. Tour south—central south-central Wisconsin on Saturday, May May 13, 13, and and return return to to Milwaukee Milwaukee about about 6:30 6:30 p.m. p.m. 2. 2. The cost is $35.00 $35.00 and includes: includes: a) a) b) b) c) c) d) Overnight accommodations accommodations (double occupancy) at at The The Pioneer Pioneer Overnight (double occupancy) in Oshkosh, Oshkosh, Wisconsin. Bus transportation from Milwaukee to to Oshkosh Oshkosh and and return return Bus from Milwaukee to Milwaukee. Lunch on May May 13. 13. Guidebook. 3. 3. No limit on number of participants. No 4. 4. The guide materials designed for for this this trip trip are: are: a) a) b) b) c) c) d) d) Introduction, Introduction, Geochronology, and and Engineering Engineering Geology Geology of of Precambrian Rocks Rocks in South-Central South-Central Wisconsin, Wisconsin, Geosciences Geosciences Precambrian Wisconsin Number 2. 2. ($4.00). ($4.00). Wisconsin Number Wisconsin, Field Precambrian Inliers Inliers of South-Central Wisconsin, Trip Guidebook Guidebook Number Number 2. 2. ($5.00). ($5.00). If purchased purchased together, together, the cost is If is $8.00. $8.00. Available from: from: Natural History Survey Wisconsin Geological and Natural 1815 1815 University Avenue Madison, Madison, Wisconsin Wisconsin 53706 608-262-1705 608—262—1705 —47— -47- �U INDEX OF AUTHORS AUTHOR PAGE • • • • 3 Aaquist, B. B. E. E. Banaszak, K. K. J. J. · 44 • • • • • • • • • 55 Bauer, R. R. L. L. 6, 6, 7, 40 40 Caxnbray, F. F. W. Carnbray, . Cannon, W. Cannon, W. F. F. . 8 26 • 26 Chang, L. L. L. L. Y. Y. Cooper, R. R. W. W. . . . 12 Cummings, M. M. L. L. . . 9, 10 . 9, Doane, v. V. 18 DuBois, DuBois, J. J. F. Egger, . . . . 11 11 L. 39 Foose, N. Foose, M. P. P. 12 · 12 Gere, N. 13 M. A., Jr. M. Jr. Hammond, R. R. D. D. . . . • . 14 Heinrich, E. E. W. W. . . . . . 15 15 3 Hodder, R. R. W. W. . Hughes, J. J. D. D. . . . . . . . . . 16 17 · 17 Jirsa, M. Jirsa, M. A. A. Jonnson, A. A. 18 Jones, D. D. G. G. 19 19 • • • . 20 J. Kalliokoski, J. Klaysmat, Klaysrnat, 25 A. W. W. A. 21 Larue, D. K. D. K. • R. F. R. Luther, F. W. D. D. N. W. Massey, N. W. S. S. Meddaugh, W. e. • • • • • • • • • • • • • 22 · 23 23 • • • • • • • • • • • • • • • • 24 -49-49- �AUTHOR PAGE Meineke, D. D. G. G. 25 · 25 Meyer, R. R. P. P. 28 Molling, MoIling, P. P. A. A. . . . . . . . . . . . . . 26 Mudrey, Mudrey, M. M. G., G., Jr Jr. 27 • 27 Mursky, G. G. 24 Myers, P. P. E. E. 9 Nebrija, E. E. L. L. 28 Ojakangas, R. R. W. W. 29 Peltonen, D. D. R. R. 30 Peterman, Z. Z. E. E. 31, 31, 35 35 Salotti, C. C. A. A. 24, 24, 30 30 Scofield, N. N. 18, 32 32 Shaffer, N. N. 33 Shariabrook, D. Shanabrook, D. 34 Sims, P. Sims, P. K. K. · 31, 31, 35 35 Smith, E. E. I. I. • . Strakele, A. A. S., Strakele, E., Jr Jr. . . . . • • . . . • 36 37 • 37 Taylor, R. R. W. W. 30 Trow, J. J. 38 • 38 Tyson, R. R. M. M. 26 Vadis, M. M. K. K. 25 Van Van Schmus, Schmus, W. R. W. R. 14, 39 11, 14, 39 Welkie, C. C. J. J. 28 Westjohn, West john, D. D. • • 40 Woronick, R. R. E. E. 39 · 39 Zietz, I. I. 41 —50— -50- �TWENTY—SEVENFIRMS FIRMS IN IN THE TWENTY-SEVEN THE GREATER GREATER MILWAUKEE MILWAUKEE AREA AREA EITHER EITHERMANUFACTURE MANUFACTURE OR SUPPLY FOR MINERAL OR SUPPLY COMPONENTS COMPONENTS FOR EXTRACTION EXTRACTION AND AND PROCESSING PROCESSING MACHINERYI MACHINERY, THEIR SALES IN IN 1977 THEIR AGGREGATE AGGREGATE SALES 1977WAS WAS 9.5 BILLION 9,5 BILLIONDOLLARS. DOLLARS, �2,51O,000'E §+ OZAUKEE CO. OZAUKEE CO. '7 LEGEND 2,590,00~E 2.5+00' +§ R·21-E Port~ c.m.nL-----J U.S... STATE ~ Bitum. J.. Concret. COUNTy Bilumilo<ls a u « ::J: Vl """_".._ 6'0"1 =--==-_ Eo""- =====> ·T~n R~ ========= Fire Lont ========== W '" « :::> 3' Multilane Oivided ==:=1== Freeway ;::;;;;;::;;;;:=;::;;;;= Intorchol\9' """"~'*'~== H~hwoy S.porotion T-B·N ==='t'~T~== Int.rstat. Hi9t!woy Nq. - - - - - - - - Gj3 U.S Hipoy No. @ Stott Highway NO. Counly Hwy. L,tter- - - IAl Roilrood ~~~ Dom .. ¢2_ _~~~~-"" •• _ •• _ Co""ty Boundory ._._._._ _ mm.@U%G15 Corporol. Limits "0 Not. T·)·N ..... ...... ~ o o a Stot. Forests G1't:U:i Airport ~ Fi5h Hatchery .... ~ Game Form ..... CO Counly SeOL @ UnincOfp. VilloQl O Schools- • Public Hl.Ilt.or Fi$h.Grds. ~. Hospilol + RO"9"Stotioft _ Public Camp 8 Picnic Grdl. State Pork + Without COmPllt•• .~ Without Focilltle Woyside A With Compllt., County Pork __W1th Focllitl.. T·6·N __ Stole Bwndory C;,il Town Boundory --' (]) C€§) • 0 With FOcllltl.. A Without Fociliti.' 6 -Surface types on town roods not shown. T·5-N a u « Bi w '" « :::> MILWAUKEE CO. 3' -1 Town of Raymond 2,510,DOO'E RACINE CO. ~ 2,550,000' ~~ PopulalrorL Co. Seat ~_ 239 SQ. MI. 1,046.268 . . Ililwaukee ~+ Town of Caledonia R·22-E R·21-E Land Area + § 2,590,000'E RACINE CO. 254 83 2278 0 Grid based on Wisconsin coordinate system, south zone TOTAL FOR COUNTY DEPARTMENT OF TRANSPORTATION ') DIVISION OF HIGHWAYS STATE OFFICE BUILDING Madison, Wisconsin o I , SCALE ~:::::::J MILES MILES OF HIGHWAY asofJan.I,1975 STATE COUNTY.. . LOCAL ROADS OTHER ROADs.. r .... 2615 COflected for ¢41 JAN. 1976 ~ Compiled frcrn U.S.G.S. Quad/angles Based on Aerial Photographs MILWAUKEE 40·9 � https://digitalcollections.lakeheadu.ca/files/original/cdb7e5f2759e322eb662e91633befa43.pdf 8b8cb45be09f5be9ace0f0580c35e58a PDF Text Text UNIVERSITY OF WISCONSIN-EXTENSION GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostrom, State Geologist and Director UPPER MISSISSIPPI VALLEY BASE-METAL DISTRICT Prepared for: TWENTY-FOURTH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY UNIVERSITY OF WISCONSIN-MILWAUKEE MILWAUKEE, WISCONSIN MAY 9—14, 1978 FIELD TRIP GUIDE BOOK NUMBER 1 1978 �Field Trip Guide Book Book Number Number 11 University University of of Wisconsin—Extension Wisconsin-Extension GEOLOGICAL GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith Meredith E. Ostrom, Ostrom, State Geologist and and Director UPPER MISSISSIPPI MISSISSIPPI VALLEY BASE-METAL DISTRICT DISTRICT (companion volume to Information volume to Information Circular CircularNumber Number 16) 16) With contributions contributions by With by W. A. A. Broughton, A. A. V. V. Heyl, Heyl~ M. M. G. G. Mudrey, Mudrey, Jr., Jr., M. M. E. E. Ostrom, Ostrom, Rachel K. A. Paull, W. S. K. Paull, paull, Richard A. Paull, and W. S. West Edited by M. M. G. G. Mudrey, Mudrey, Jr. Jr. Natural History Survey Geological and Natural Prepared for Annual Meeting Twenty-Fourth Annual INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY University University of ofWisconsin, Wisconsin,Milwaukee Milwaukee Milwaukee, Milwaukee, Wisconsin May 9-14, 9-14, 1978 Richard A. A. Paull, Chairman, Field Trip Committee PaUll, Chairman, University of Wisconsin-Milwaukee Available from the the Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, of Wisconsin-Extension, Wisconsin—Extension, 1815 University of 1815 University University Avenue, Avenue, Madison, Madison, Wisconsin 53706 53706 1978 �CONTENTS OONTENTS Page INTRODUCTION INTRODUCTION by by M. G. G. Mudrey, Mudrey, Jr Jr. • • • • • • • . • • • • • • . • • • • • 1 TUESDAY, MAY MAY 9, 9, 1978 1978 TUESDAY, Geologic Road Road Log Log for for U. U. S. S. 151 151 from from Madison, Madison, Wisconsin Wisconsin (U. (U. S. S. 12 12 and and 14 junction) junction) to to Platteville, Platteville, Wisconsin Wisconsin (Wisconsin (Wisconsin 80 80 and and 81 81 junction) junction) by by Richard Richard A. Paull Paull and and Rachel Rachel K. K. Paull Paull • • • • • 77 • Geologic Road Road Log Log for for Grant Grant County County by by M. M. G. G. Mudrey, Mudrey, Jr., Jr., W. W. A. A. 14 Broughton, Broughton, A. V. V. Heyl, Heyl, and and W. W. S. S. West West • • • • • • • • WEDNESDAY, MAY MAY 10, 10, 1978 1978 WEDNESDAY, Geologic Road Road Log Log for for Lafayette Lafayette County County by by M. M. G. G. Mudrey, Mudrey, Jr., Jr., W. W. A. A. Broughton, Broughton, A. V. V. Heyl, Heyl, and and W. W. S. S. West West . • • • • • • • • • • • • • • 16 16 Geologic Road Log for for Madison Beltline, Beltline, 1—90, 1-90, and and 1—94 1-94 from from Madison, Madison, Wisconsin Wisconsin (U. (U. S. S. 12 12 and and 14 14 junction junction with with U. U. S. S. 18 18 and and 151) 151) to to Milwaukee, Milwaukee, Wisconsin Wisconsin (1—94 (1-94 junction junction with with 1—43 1-43 and and 1-794) 1-794) by by Rachel Rachel K. K. Paull and and Richard Richard A. Paull Paull • • • . • • • . • • • • • • • • 17 17 SlOP DESCRIPTIONS GFXHl>GICAL S1UP DESCRIPTIONS GEX)LOGICAL Stop 11 Stop Stop Stop Stop Stop 22 33 44 55 — ——-—- ...3228 M. E. Hoadley Hill by M. E. Ostrom • • • • • Section 22 Quarry by M. Section M. G. G. Mudrey, Mudrey, Jr Jr .• Hill by M. M. E. E. Ostrom Ostrom. • . • • • Potosi Hill St. John Mine by M. St. M. G. G. Mudrey, Mudrey, Jr Jr . • • Industries Shullsburg Mine by Shullsburg by Staff, Staff, Eagle—Picher Eagle-Picher Industries (not (not attached to road road log) log) . . . 28 32 33 37 37 ILLUSTRATIONS Figure 1. 1. Figure 2. 2. Figure 3. 3. 4. Figure 4. Map of main part of Upper Mississippi Valley Valley zinc—lead zinc-lead district district. . . . . . . . . . . . . . . . . . . . . Highway map showing route route of of field field trip trip • • . • • • • • Detailed stratigraphic column column of of Platteville, Platteville, Decorah, Decorah, and and Galena formations in in zinc—lead zinc-lead district district • . • • • • • • • • • Simplified stratigraphic column column showing showing relative relative quantitative quantitative . stratigraphic distribution of zinc and lead in Wisconsin. stratigraphic Stalactites in Cave Cave of the the Mounds Mounds near near Blue Blue Mounds Mounds. • Cross section through Blue Mounds Cross Mounds from west to east • • Blue Mound viewed viewed from from west • • • • • • • • • • . • • • • • • . . •. of glacial glacial deposits Photograph of deposits of southeast Wisconsin polished Precambrian Waterloo Quartzite . • Glacially polished • Intensively farmed Intensively farmed drumlin near Sullivan • • . • . • • • • • • Scenic overview of the southern Kettle Interlobate Scenic Interlobate Moraine. Moraine • • . Figure Figure Figure Figure Figure Figure Figure Figure 5. 5. 6. 6. 7. 7. 8. 8. 9. 9. 10. 10. 11. . . i :i. 22 3 4 5 9 10 11 18 20 22 23 �I NTRODUCT ION INTRODUCTION M. G. G. Mudrey, Jr.' M. Jr.1 The zinc zinc and and lead mines of of southwestern Wisconsin Wisconsin are are part part of of the the oldest oldest The lead mines producing zinc-lead zinc-lead mining district district in the the United United States, States, the continuously producing The largest and most most productive parts Upper Mississippi Valley District. The largest and parts of of this district district extend extend across across five five Wisconsin Wisconsin counties counties and and into into small small areas areas in in this Illinois and and Iowa (Fig. Over 1.2 1.2 million million tons tons of of zinc zinc and and nearly 100,000 Illinois (Fig. 1). 1). Over tons of of lead lead have have been been recovered recovered from from the Wisconsin portion of tons of the the Upper Upper MissMississippi Valley Valley district district from 1910 to issippi to 1974, 1974, with with aa combined combined value value in in excess excess of of Heyl and and others others (1959) suggest that an an additional additional 250,000 tons $267 million. Heyl (1959) suggest tons of zinc zinc and and 350,000 to 400,000 tons of lead were produced produced in the Wisconsin part of tons of lead were the Wisconsin of of the district in in the the period period following following 1800. 1800. The text that accompanies this this field trip (Heyl and others, others, 1970) 1970) covers covers the of the region, and field (Heyl and the early history of the region, the the geologic controls on ore ore mineralization. mineralization. In (1976) In addition, addition, West West and Weeks (1976) provide additional information information on on the the district district and and its its production. production. The field field trip commences commences in Madison, Madison, proceeds The proceeds to Platteville for for an overnight stop, examines the formations directly related related to the horizons, and night stop, examines the formations the ore horizons, visits an historic lead Mine) and and an operating zinc-lead mine visits lead mine (St. (St. John Mine) near Shullsburg Shullsburg (Fig. (Fig. 2). 2). The returns to Madison where private The field field trip returns vehicles can be picked up, up, and vehicles and terminates terminates in downtown Milwaukee prior to the 25th Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. Potosi and Shullsburg 7.5Geologic stops will be in in the the Dickeyville, Potosi In addition, addition, the the route leads through minute topographic quadrangles. In through the the Platteville, Platteville, Cuba City, and and New New Diggings Diggings 7.5-minute 7.5-minute topographic topographic quadrangles. quadrangles. Geologic (1963); Dickeyville, Geologic quadrangle references references are Cuba City, City, Agnew (1963); Dickeyville, Whitlow and West (l966a); Diggings, Mullens Mullens (1964); Potosi, Whitlow and West (l966b); (1966a); New Diggings, (1964); Potosi, (1966b); Shullsburg, Mullens (1964). and Shullsburg, (1964). cuts and a The trip starts with two road cuts a quarry that include units of the the The first Sinnipee Group (Figs. (Figs. 33 and and 4). 4). The first day ends ends with a a visit to an early lead mine (St. (St. John Mine), Mine), that that may well have been the the first operating mine in in Wisconsin. The second day the the Shullsburg Mine Mine of of Eagle Eagle Picher Picher Industries, Industries, Inc. Inc. will be be visited. visited. After a lunch lunch stop stop in in Shullsburg, Shullsburg, the the route leads leads back to to cultural tour along back roads, roads, and and then returns Platteville via aa cultural returns to Madison and Milwaukee. This year marks the the 125th l25th anniversary anniversary of the the first Wisconsin geological survey. Under an act of of the Legislature approved March 25, 25, 1853, 1853, a a State Geological Survey was created, created, with an annual annual appropriation appropriation of of $2,500 per per year year for four years. years. Edward Daniels was appointed appointed State Geologist by Governor Leonard J. J. Farwell. Daniels' Daniels' instructions instructions were to to "complete his his survey survey of of that that of the state known as mines' before commencing the survey of portion of as the 'lead 'lead mines' the remainder of of the the state." state." We welcome you you to to the the Zinc-Lead Zinc-Lead District, and and hope that that you you find find the the geology, geology, companionship, and and tour tour rewarding! rewarding! 1 Wisconsin Wisconsin Geological Geological and and Natural History Survey, Survey, Madison Madison 1 1 �Pb \ "'" "ALLAMAKEE Cu ) RICHLAND * Pb* CRAWFORD / * COLUMBIA SAUK Pb* Cu ( River Pb* I' Pb Madison * * DANE Zn *Pb o Pb Zn * 0 Pb CLAYTON -- Belmont • ·Calamine .Darlington Platteville _ IOW4 "\ LAFAYETTE ~ Dubuque • Shullsburg ~ Pb --~bO--- "ol'ol' . '-"ol'ol'/ DELAWARE ~O WISCONSIN -ILLINOiS - - .,~-.- - ~.o.... DUBUQUE • Galena STEPHENSON Cu Zn PbOAu Freepo·rt -Opb ~...t.. -..!?....-...-.- JONES --I-_=-----,:---------j JACKSON Pb A. CARROLL o Pb 0o 10 I I I I Pb Lead Zn Zinc Cu Copper Au Silver Silver 0o Miles 20 Miles I I I EXPLANATION OGLE I I I io 10 20 Kilometres * * Mine or or prospect prospect inin dolomite dolomite of Mine Silurian age age o Mine or prospect Mine·or prospect in in Galena, Galena, DecoDecorah, and and Platteville Platt~ville formations formations A prospect in in Prairie Prairie du du Mine or prospect Chien group Boundaryof of main main part part of of district Boundary Figure 1. 1. Figure Map of main part of the the Upper Upper Mississippi Valley Valley zinc—lead zinc-lead district, district. 2 �Route from Madison t. Platteville and return via U.S. Hwy 151 (69 miles) iH?E HHHr \ P iiNL - 'I lmH fl0 1HRRI - i-t )JTF F- -I \ (ELMON LAIi _=i__ , S -4=4 --S ' I /11/ \V F TN ' : )Jf — r (Ii 1 k 1ff S—f— -7L ij I• Figure 2. 2. hul Isburg 1k WHITEII F- RI-N STATE OF STATE OF ILLINOIS ILUNOIS ---- j / )SHUL/UR j MON R-2•W ........ I k-2 O( Jj 7L oi - ENONç L — — T'1JL/ ,/ I '- ELKVE 1- - / - /L J 17 '— t R.2E Tuesday May May 99 Route Route Tuesday Wednesday May Route Wednesday May 10 10 Route Scheduled Stops Scheduled Stops Highway map map showing showing route route of of field field excursion. excursion. 3 3 Of TRANSPORTATION TRANSPORTATIClH DEPARTMENT OF D1VI~0t4 . SCALE? SCALE O' MIG"",AYS , .1Lf:S MILES �System System Series Group Upper Unner Devonian Devonian Member Kenwood Kenwood (55') (55' \ Milwaukee (80') (80') Thiensville Thiensville (65') (65') Lake Lake Church Church (35') (35' ) Middle Cayugan Silurian Formation Waubakee (30') (30') Racine Racine (100') (100' ) Manistique Manistique (150') (l50' ) I1endricks Hendricks) (110')) (1l0' Byron Bvron Mayville (175') (175' ) Niagaran Alexandrian Alexandrian Cincinnatian Sinnipee Sinnipee Champlainiao Champlainian Ordovician Neda (55') (55') Maquoketa (240') (240' ) Galena 230' Galena (230') (25') Decorah Decorah (25') Platteville (100') (lOO' ) St. St. Peter Glenwood (13') (13' ) Tonti ) Tonti 332')) (332' Readst own Readstown Shakopee Canadian Prairie du Chien Chien Willow Willow River River (50') (50' ) New Richmond Richmond (25') (25') Oneota (200') (200' ) Jordan Trempealeau Trempealeau Cambrian St. Lawrence St. (50 )) (50' St. Croixan St. . Tunnel City City (200' (200')) Lone Rock Lone Mazomanie Maz~ Wonewoc (100') (100' ) Sunset Point Point Van Oser Oser) Norwalk j (60') .Black Black Loch Lodi < -. Earth Earth < Reno Tomah Birkmose Ironton (40') Ironton (40') Galesville Bonneterre (20') (20') ~onneterre Elk Mound (250')Eau Claire (250') Mt. Mt. Simon (500') (500') Figure 3. Detailed stratigraphic column of Platteville, Detailed Platteville, Decorah, Decorah, and and Galena formations Galena formations in the Upper Mississippi Valley Valley zinc—lead zinc-lead district. 4 �I Known]ECIl relative Quantities -1:<;0 • • I ~ t;, Q) _-'-';~- i~I' ~ ' G roup or formation In Dolomite, buH, cherty; Ptllt4mtru, at lop, ~~; I ~ ~~~ 0( ~ Average thickness. Description 90 fLjP-=A--o-o,-om-,-..-.-"-11-.-oh-'-ff'-;-'-"-i1-,,-,,-o,-,-n-.-,,-,-,-,.---t-- -jO 200 II DolomIte. yellowlsh·buff. thln·bedded, snaly_ I Dolomite. yellowlsh.buff, thiCk. bedded :.Rt. f!ptucullt1!S In middle 225 105 Dolomite. drab to butt: cherty; Rrclpta.cutiU. near base limestone and doIOI'T"te. brown and grayish: green, sandy shale and phosphatic nO(lules at base DISCONFORMITY 40 80 Galena dolomite St. Peter sandstone I I 108=l Shale, blue. dolomitiC: phosphatic depauperate fauna <1t base Maquoketa shale I feet_I 55 75 40 ~ Sandstone. quartz, coarse. rounded . , f - - - - - - - D1SCONF'ORMITV------f---I 280- -f". Dolomite, Iight·buff, cherty; sandy near base and Prairie du ChIen group ~:~ .~:, ~:".~".~.~.' lundifferentlated) Trempealeau formation FranconIa sandstone Sandstone and Siltstone. glaucoroitlc Dresbach sandstone Sandstone f.------l';;:±8-----------Eau Clai,e sandstone Siltstone and sandstone 0- I 320 I ---~ 110· 140 ~o l 70 330 1050 I 700 I I Mount Simon sandstone Figure Figure 4. 4. Sandstone 440 780 I __J Simplified stratigraphic stratigraphic column column shOWing showing relative relative quantitative quantitative Simplified stratigraphic distribution distribution of of zinc zinc and and lead lead in in the the Wisconsin Wisconsin stratigraphic district. district. 55 �References Cited Agnew, Agnew, A.F., 1963, 1963, Geology Geology of of the the Platteville Platteville quadrangle quadrangle Wisconsin: Wisconsin: U.S. U.S. Geol. Geol. Survey Bull. l123—E, 1123-E, p. p. 245—277. 245-277. Heyl, A.V., Jr., Heyl, A.V., Jr., Agnew, Agnew, A.F., Lyons, Lyons, E.J., E.J., and and Behre, Behre, C.H., C.H., Jr., Jr., 1959, 1959, The Geology of the the Upper Upper Mississippi Valley valley Zinc—Lead Zinc-Lead District: District: U.S. U.S. Geol. Geol. Survey Prof. Paper 309, 309, 310 310 p. p. Heyl, A.V., Ay., Jr., Heyl, Jr., Broughton, Broughton, W.A., W.A., and andWest, West, W.S.,, W.S., 1970, 1970, Guidebook Guidebook to to the the Upper Mississippi Valley Geol. and valley base base metal metal district: district: Wisconsin Geol. Nat. Nat. History Survey Inf. Inf. Circ. No. No. 16, 16, 49 49 p. p. Mullens, T.E., City, New New Diggings, Diggings, and and Shullsburg Shullsburg Mullens, T.E., 1964, 1964, Geology of of the Cuba City, quadrangles, Wisconsin U.S. Geol. Geol. Survey Wisconsin and and Illinois: Illinois: U.S. Survey Bull. 1123-H, 1123-H, p. 437-531. p. 437—531. West, W.S. West, W.S. and and Weeks, R.A., R.A., 1976, 1976, Zinc Zinc and and Lead Lead in in C.E. C.E. Dutton, Dutton, ed., ed., Report prepared by the Mineral and and Water Resources Resources of of Wisconsin: Wisconsin: Report U.S. Geol. Geol. Survey in U.S. in collaboration with the the Wisconsin Wisconsin Geol. Geol. and and Nat. Nat. History Survey for the Committee on Interior Interior and and Insular Insular Affairs, Affairs, United States Senate, p. p. 132—145. 132-145. Whitlow, J.W., West, W.S., W.S., l966a, Geologic map of of the Dickeyville Whitlow, J.W., and West, 1966a, Geologic the Dickeyville quadrangle, Grant County, quadrangle, County, Wisconsin: Wisconsin: U.S. U.S. Geol. Geol. Survey Survey Map Map GQ-488. GQ-488. Whitlow, Whitlow, J.W., J.W., and and West, W.S., W.S., 1966b, 1966b, Geology Geology of of the the Potosi Potosi quadrangle, quadrangle, County, Wisconsin, Wisconsin, and Dubuque County, Iowa: U.S. Geol. Geol. Survey Grant County, Iowa: U.S. 1123-1, p. p. 533—571. 533-571. I Bull. 1123—I, 6 �Tuesday, Tuesday, May 9, 9, 1978 1978 for U.S. U.S. 151 151 from from Madison, Madison, Wisconsin Wisconsin (U.S. (U.S. 12 12 and an 14 Geologic Road Road Log for Geologic 14 junction) junction) to Platteville, Wisconsin (Wisconsin to platteville, (Wisconsin 80 80 and and 81 81 junction) jUnction)* A. Paull Richard A. 11 and Rachel K. K. Paull and 2 2 U.S. U.S. 151 from Madison to to Verona traverses traverses aa recently recently glaciated glaciated (Woodfordian) (Woodfordian) part of the Eastern Ridges and and Lowlands Lowlands physical physical province. province. Since the the drift in in this area was was deposited deposited near near the the ice margin, it it is and the the this ice margin, is generally thin, thin, and exerts considerable considerable influence on the the character of of the landunderlying bedrock exerts influence on the landFrom the scape. the western edge of the the Wisconsinan (Woodfordian) (Woodfordian) terminal moraine just west west of of Vernoa to the River, the route crosses crosses aa thin sliver of of older the Sugar River, the route (Illinoian) drift. drift. The remainder of the route lies within the the classic Driftless Area of of the the Western Western Uplands Uplands physical physical province. province. and Mt. Mt. Horeb, Horeb, rock exposures exposures along along the Between Madison and the highway are mainly dolomite assigned to to the the Lower Ordovician Ordovician Prairie Prairie du du Chien Chien Group. Group. However, The bedrock from Mt. some younger rocks are are also also present. present. The Mt. Horeb to to Platteville Plattevil1e is predominantly Middle Ordovician limestone is limestone and and dolomite dolomite of of the the Platteville, Platteville, Decorah, and Galena formations, formations, although the the Middle Middle Ordovician St. St. Peter Sandstone Decorah, is also exposed along along the the highway highway in in aa few few places. places. Several isolated mounds (outliers) of Upper Upper Ordovician Ordovician Maquoketa Maquoketa Shale Shale capped capped by by resistant, resistant, Silurian Silurian (outliers) of dolomite are present near U.S. of Blue Mounds Mounds and Platteville. U.S. 151 in the vicinity of and Platteville. Mileages 0 o (69) U.S. 12 and 14 on the southwest Junction U.S. U.S. 151 and 18 with U.S. The road road log edge of Madison, Madison, Wisconsin. Note: The log from from Madison Madison to Milwaukee Milwaukee provided provided for for Wednesday Wednesday May May 10, 10, 1978 1978 also also begins begins to at this this intersection. intersection. 1.5 (67.5) Gravel pits pits to the southeast southeast are in glacial outwash that fills fills aa preglacial bedrock bedrock valley. valley. 2.5 (66.5) Rock exposures exposures along the valley sides sides are red and yellow St. Peter Sandstone capped by Middle Ordovician weathering St. Platteville-Galena dolomite. 8 (61) Verona, Wisconsin and Verona, and junction junction with with Wisconsin Wisconsin 69. 69. The thin thin drift cover here was deposited near the margin of Wood— of the Woodfordian ice. ice. 9 (60) Moraine, the terminal moraine of Wisconsinan Cross the Johnstown Moraine, (Woodfordian) glaciation in (Woodfordian) in this this area. area. *This road road log is is published pUblished with permission permission of of Kendall/Hunt Kendall/Hunt Publishing Publishing Co., Co., Dubuque, Iowa and it should not not be be duplicated duplicated by by any means means without without written Dubuque, permission. 11 The University of WisconsIn—Milwaukee Wisconsin-Milwaukee Alverno College, 22 The The University University of of Wisconsin-Madison and Alverno College, Milwaukee Milwaukee Wisconsin-Madison and 7 �Mileages Mileages 10 10 (59) (59) Cross the the Sugar River. River. The of the Sugar River, The upper upper course of which flows flows south and which and southeast to to join the the Rock River, developed along along the developed the western margin of the the Woodfordian glacier. glacier. This broad, broad, terraced terraced valley once carried great quantities This quantities of of meltwater and outwash southward southward from from the the wasting wasting ice ice front, front, which lay immediately east of of here. The Sugar River defines the the edge of of the the Driftiess Driftless Area Area here. here. The outer edge edge of of the the Woodfordian Woodfordian terminal terminal moraine moraine forms forms the the The partially wooded wooded ridge ridge on the east side of the partially the valley. The deposits between the Sugar River River and and the the terminal terminal moraine moraine deposits the Sugar probably include include aa thin strip of Illinolan probably Illinoian glacial deposits. deposits. River, the the route route gradually gradually ascends ascends toward toward aa From the the Sugar River, ridge crest which marks marks the the edge edge of of the the Middle Middle Ordovician Ordovician ridge crest Platteville-Galena upland Platteville-Galena upland surface. surface. 15 (54) Junction County County P. P. Friable St. St. Peter Sandstone is is quarried quarried just north of of here here at at Kievenville. Klevenville. A thin layer of overlying Middle Middle Ordovician Platteville Platteville Dolomite Dolomite is is stripped stripped away, away, and and the poorly poorly consolidated consolidated quartz sandstone below is the is mined for for foundry and and refractory refractory sand. sand. 18 (51) Mt. Mt. Horeb, Wisconsin Wisconsin occupies occupies aa ridge ridge top. top. Originally settled settled Swiss farmers, farmers, its its heritage heritage is recalled by by by Norwegian and and Swiss is recalled commercial establishments along along the the route. route. 20.5 (48.5) (48.5) Junction with with County County JG. JG. This steep, steep, wooded road road descends descends one one mile north to to Little Norway, Norway, a a restored Norwegian pioneer homestead. The side ttV?i side road road follows follows a anarrow, narrow,deeply—cut, deeply-cut, "V"shaped valley that is is typical typical of of the the upper upper reaches reaches of of drainages drainages in the Driftless Area. The Tyrol Ski Basin, 22 miles miles north north of of Little Norway, Norway, takes takes advantage advantage of of these these steep steep valley valley walls. walls. 20.8 (48.2) Entrance to to Cave Cave of of the the Mounds Mounds is is north north of of the the highway, highway, off off County County F. F. This cave is developed in the the Middle Ordovician Galena had no no natural entrance, Galena Dolomite. Dolomite. It It had entrance, and was accidently accidently discovered by by quarry quarry blasting blasting in in 1939. 1939. The cave, cave, which which features features aa variety variety of of intricate intricate dripstone dripstone deposits, deposits, is is open open for for tours tours during the the summer summer months months (Fig. (Fig. 5). 5). Brigham Brigham County County Park, Park, on on East Blue Mound, is is aa short short distance distance beyond beyond the the cave cave on on County County F. F. 21 21 (48) (48) The wayside park park north north of of the the highway highway is is developed developed in in an an old old quarry quarry in in the the Galena Galena Formation. Formation. 88 �Figure 5. 5. Dripping Dripping stalactites stalactites hang hang from from the the ceiling ceiling of of this this narrow passageway in in Cave of the the Mounds near near Blue Blue Mounds, Wisconsin. Photo courtesy of Cave of of the the Mounds. Mileages 22.7 (46.3) village of Mounds, nestled beneath Village of Blue Mounds, beneath the the west west and and east east summits of of the Blue Mounds (Fig. summits (Fig. 6). 6). The summits summits of East and West Blue Mounds are The are about about 1.6 1.6 miles miles apart (Fig. (Fig. 6). 6). The East Mound, Mound, site of Brigham Brigham County County Park, Park, has aa broad flat has flat top top developed on the the Upper Upper Ordovician Ordovician led Silurian Silurian Maquoketa Shale. However a a few blocks blocks of of silicif silicified 9 �Mileages dolomite are are found found on the crest and flanks. dolomite flanks. The The elevation of the West West Mound Mound is the is 1716 feet, feet, some 230 feet higher higher than than its its neighbor to the east. This mound has a the This a smaller, smaller, more rounded rounded led Silurian Silurian summit area, area, and it it is is capped capped by by 85 85 feet feet of of silicif silicified dolomite. Thus, Thus, West Mound is is an outlier of of the the Silurian escarpment, which has has retreated about 50 miles to escarpment, to the the southwest southwest as aa result of downdip as downdip erosion. erosion. Iowa Co. Dane Co. EAST WEST W MOUND Silurian dolomite O~I--------il o 1.6 Mil. Km E. MOUND U. Ord. Maquoketa Shale M. Ord. Plalteville-Goleno dolomites Figure Figure 6. 6. section through through Blue Blue Mounds Mounds from from west west to to east. east. Cross section Elevation in in feet is indicated along the the right margin. After Black, 1970. 1970. Blue Mounds State Park, Park, on West Blue Mound, Mound, is is reached by a well—marked well-marked road road that that goes goes north north through through the the village. village. At the the mound top, top, observation towers towers are located located at both the the east and and west ends ends of of an an old old racetrack. racetrack. The towers towers provide an opporthe Driftless tunity to view the Driftless Area Area to to the the west, west, the the glaciated Madison, and and the the Precambrian Baraboo Baraboo Range Range countryside toward toward Madison, to the north. Indians reportedly used used the mound top as as an an north. Indians reportedly the mound led cap rock into observation post, post, and and fashioned fashioned the the silicif silicified projectile points. points. They attributed the blue haze, haze, which often veils these wooded mounds when viewed from below, below, to the the pipe smoke of Wakanda, the the Earth—maker. Earth-maker. The Upper Ordovician Maquoketa Shale, Shale, which makes up East Mound the Silurian on West Mound, forms the the upper part and underlies the Mound, forms of the the gently sloping sloping sides sides of of these these wooded wooded mounds mounds (Fig. (Fig. 6). 6). The Platteville—Galena Platteville-Galena formations formations are the basal foundation for both mounds, mounds, which are perched perched on the edge of the the Middle Ordoviclan Ordovician cuesta cuesta called called Military Military Ridge. Ridge. To the north, north, steep drainages flow toward toward the the Wisconsin River valley, valley, about 11.5 away. The headwaters of one of these north-flowing miles away. streams forms the separation separation between between the the two two mounds. mounds. 22.9 22.9 (46.1) (46.1) Dane/Iowa County County line. line. Enter Iowa Iowa County in in an an area where Dane/Iowa roadcuts expose thin—bedded, thin-bedded, nodular nodular Middle Middle Orcovician Orcovician dolomite. dolomite. Several small quarries quarries along the highway between here and Barneveld also also provide provide exposures of of the the Middle Ordovician Platteville—Galena Platteville-Galena formations. formations. 10 10 �Mileages 26 (43) Barneveld, Wisconsin. Wisconsin. The Blue Mounds, the the most northeasterly northeasterly of of the Silurian outliers, outliers, are are visible visible to to the the east east (Fig. (Fig. 7). 7). Figure 7. Figure 7. A A view east east to to the the gently—sloped, gently-sloped, wooded wooded Blue Blue Mound, Mound, from a a quarry developed in in the the Middle Ordovician Ordovician Galena Dolomite. The route westward from Barneveld to to Ridgeway Ridgeway passes passes numerous numerous roadcuts in the Middle Ordovician Ordovician Platteville-Galena Platteville-Galena formations formations as as it traverses Military Military Ridge. Ridge. 31 31 (38) Ridgeway, named for the Town of Ridgeway, the Middle Ordovician Ordovician cuesta cuesta of of Military Ridge, Ridge, upon upon which which it it is is perched. perched. 35 35 (34) Wayside to for to north of the the highway has a a historical marker for Military Road". Road". This road was completed in 1835 to link "Old Military Fort Howard Howard at at Green Green Bay Bay to to Fort Fort Crawford Crawford at at Prairie Prairie du du Chien. Chien. In this this area, area, the the route route followed followed the well-defined, well-defined, broad, In treeless ridge crest at the the northern edge edge of of the the Middle Middle Ordovician Ordovician Platteville-Galena cuesta. Platteville-Galena cuesta. Since this this ridge forms the the drainage divide between the the Wisconsin River to to the the north north and and the the Platte, Platte, Galena, and Pecatonica rivers Galena, rivers to to the the south, south, it it is is not not dissected dissected by streams. This aided aided road road construction construction by by eliminating eliminating the the need for bridges. bridges. Besides army traffic, thousands of of pioneers pioneers passed passed this this way way to to Besides traffic, thousands the booming booming lead lead mining area, the area, the early territorial territorial capitol of of Wisconsin, and and the the thriving thriving port port cities cities on on the the Mississippi Mississippi River. River. This same route was utilized utilized later later by by the the Chicago Chicago and and NorthNorthwestern Railroad. 11 �Mileages Mileages 39 39 (30) (30) Junction with with U.S. U.S. 18 18 and and State State 23. 23. U.S. Junction U.S. 18, 18, west west from from here, here, continues continues along along the the route route of of the the historic historic army army road road along along Military Ridge. Ridge. Military Governor Park, located 3 miles north north of of this this Governor Dodge Dodge State Park, intersection intersection along along Wisconsin Wisconsin 23, 23, embraces embraces two two lakes lakes formed formed by by impounding Mill Mill Creek, Creek, aa tributary to impounding to the the Wisconsin River. Bedrock exposures exposures in in the the park park include include roadcuts roadcuts through through the the Bedrock Platteville-Galena Platteville—Galena upland upland surface, surface, and and scenic, scenic, natural natural outcropoutcrop— pings pings of of the the underlying underlying Middle Middle Ordovician Ordovician St. St. Peter Peter Sandstone Sandstone along the floor of the the valleys. valleys. Turn south on U.S. U.S. 151 into Dodgeville, Wisconsin. U.S. Turn U.s. 151, from here here to Platteville, Platteville, generally follows an from an historic historic cutoff cutoff from the the Military Military Road to the lead mines, from mines, and and the the river river ports ports along the Mississippi. 395 39.5 (29.5) (29.5) Dodgeville, Wisconsin. The The city was was named named for for Henry Dodge, Dodge, an early lead miner and Indian Indian fighter fighter in in this this district. district. Since avid supporter of of President Andrew he was well-liked and an avid Jackson, he he was was appointed appointed as as the the first first territorial territorial governor governor Jackson, of Wisconsin in in 1836. 1836. 43 43 (26) (26) Silurian outliers of Belmont outliers of Belmont Mound Mound and and Platte Platte Mound are are visible to the the southwest, southwest, as as the the highway highway crosses crosses the the rolling, rolling, partiallypartiallyto dissected, Middle Ordovician dissected, Ordovician upland upland surface. surface. Roadcuts provide of Middle Ordovician dolomites this part of of the exposures of dolomites along this route. 47 47 (22) (22) of the commemorates the The historical marker north of the highway commemorates early days of of Mineral Mineral Point. Point. 48 48 (21) (21) Mineral Point, Point, Wisconsin. This part of the the zinc—lead zinc-lead district was settled settled in in the the l820t5 1820's and 1830's by miners from other mining regions in the U.S., U.S., and and by by Cornish Cornish immigrants. immigrants. A A short short side side trip into this historic town, town, with with its its narrow, narrow, steep steep streets, streets, is interesting. Here, Here, on Shake Shake Rag Rag Street, Street, the the Cornish Cornish miners miners their small small homes from local local dolomite along the side side of of built their aa narrow narrow valley valley across across from from the the mines. mines. The street street received received its name because the the miners' miners' wives waved waved dish dish rags rags to to call call the the menfolk menfolk home home when when dinner dinner was was ready. ready. As aa carry—over carry-over from from these these days, local local restaurants and bakeries still make pasties pas ties (meat (meat days, pies), pies), the the traditional, traditional, hearty hearty lunch lunch of of the the Cornish Cornish miner. miner. Part of Shake Rag Street contains a a complex of of restored Cornish Cornish cottages cottages from from the the 1830's 1830's and and 1840's, 1840's, that that includes includes Pendarvis Pendarvis House. House. This This site site is is operated operated by by the the Wisconsin Wisconsin Historical Historical Society Society for for the the public. public. The The Mineral Mineral Point Point Historical Historical Society Society has has aa museum at at Pine Pine and and Davis streets that contains excellent mineral mineral samples samples from from local local mines. mines. 49 49 (20) (20) The The highway highway south south of of Mineral Mineral Point Point follows follows aa narrow narrow ridge ridge that that forms forms aa drainage drainage divide divide overlooking overlooking numerous, numerous, small, small, steep—sided steep-sided valleys valleys on on either either side. side. 12 12 �Mileages Mileages 52 52 (17) (17) The The wayside wayside park park north north of of the the road road provides provides another another view view of of Platte and and Belmont Mounds, as as the the route route traverses traverses the the dissected dissected Middle Middle Ordovician Ordovician highland highland surface. surface. 54 54 (15) (15) Iowa/Lafayette Iowa/Lafayette county county line. line. Enter Enter Lafayette Lafayette County. County. Within Within one mile mile the the highway has has crossed crossed Mineral Point Point Branch Branch and and the the upper upper reaches reaches of of the the Pecatonica Pecatonica River. River. The valleys valleys formed formed by by these these drainages drainages cut cut through through the the Middle Middle Ordovician Ordovician PlattevillePlattevilleGalena formations into into the the underlying underlying Middle Middle Ordovician Ordovician St. St. Peter Peter Sandstone. The contact between between these these formations formations is is exposed exposed west west Sandstone. of the the highway highway near near the the county county line. line. 61 61 (8) (8) Belmont, Wisconsin. Wisconsin. Enter Belmont, dolomite. 61.5 (7.5) Junction Junction with with County County GG in in Belmont. Belmont. A A short short side side trip trip along along this this highway highway provides provides access access to to two two interesting interesting state state parks. parks. Three Three miles northwest northwest on on County County GG (and (and B) B) is is First First Capitol Capitol State State Park, Park, the restored site of the the first Wisconsin Territorial Territorial Capitol Capitol in in This apparently remote 1836. remote location location was was in in the the booming booming lead lead 1836. mining district, district, and and consequently consequently at at the the population population center center of of this this territory when Governor Henry Dodge called called the the Territorial Territorial Legislature to to order. order. They met here for 46 46 days in in 1836 1836 to to Madison, then essentially develop aa constitution. Eventually Madison, uninhabited and undeveloped, undeveloped, was selected selected as as the the permanent permanent capitol. Roadcuts Roadcuts expose expose Middle Middle Ordovician Ordovician Less than aa mile mile east east of of First First Capitol Capitol State State Park Park on on County County G G Less Here, a scenic parking area is is Belmont Mound State State Park. Park. Here, a parking area is is This is another Silurian located on the the south south side side of of the the mound. mound. This outlier, as evidenced by abandoned outlier, abandoned quarry quarry exposures exposures of of thin— thinbedded Lower Silurian Silurian dolomite. dolomite. An observation observation tower tower affords affords a a panoramic view that includes includes numerous numerous mounds, and and the the distant distant edge of of the Silurian escarpment to to the the south south and and southwest. southwest. Both the mounds and the the escarpment are are capped capped with with resistant resistant dolomite, and and once once were were part part of of aa continuous continuous bedrock bedrock Silurian dolomite, surface that that sloped sloped gently to the southwest. surface southwest. There are several old lead and zinc mines in old in this this area. area. U.S. 151 turns west here. U.S. here. 62 (7) Junction of Wisconsin 126 126 in in Belmont. Belmont. 66 (3) Platte Mound, Mound, north of of the highway, rises to an elevation Platte the highway, elevation of of Locally, this 1430 feet. feet. Locally, this wooded hill is is called "M" "M" Mound, because because of the the letter letter formed formed of of white white painted stones that is of is maintained annually by by mining mining engineering students from the University annually University of of This feature, feature, and Little Platte Mound to Wisconsin-Platteville. to Wisconsin—Platteville. This the east, east, are are capped capped by resistant, the resistant, cherty Lower Silurian Silurian dolomite. dolomite. The nonresistant nonresistant Upper Ordovician Maquoketa Shale underlies The underlies the the Silurian (cap rock), rock), and forms forms the gradual slopes that Silurian that rise rise These isolated isolated upward upward from from the the Middle Middle Ordovician Galena surface. These hills are are remnants remnants (outliers) (outliers) of of an an extensive extensive Silurian upland hills The edge of of this surface, which which eroded downdip to surface, to the the southwest. southwest. The highland is is low low located located in in northwestern northwestern Illinois highland Illinois and east—central east-central Iowa. Iowa. 13 13 �Mileages 67 (2) (2) Lafayette/Grant county line. line. 69 69 (0) Enter Platteville and pass a a large quarry developed in in the the Middle Ordovician Galena Galena Dolomite Dolomite to to the the north of of the highway. Middle the highway. Wisconsin 80 Junction U.S. U.S. 151 with Wisconsin 80 and and 81. 81. Enter Grant County. The University University of of Wisconsin-Platteville, Wisconsin—Platteville, with its The its long history of training engineers and and geologists, geologists, is located in this of training mining engineers is located this The Mining Mining Museum, Museum, on on Main Main Street Street in in Platteville, Platteville, provides city. The provides an opportunity for for tourists tourists to to tour tour uiilerground underground in the historic Bevan lead mine, mine, and to to view relics from the the early days of the the lead rush. rush. MADISON—PLATTEVILLE LOG END OF U.S. U.S. 151 MADISON-PLATTEVILLE Geologic Road Log for Grant County 3 l , W.A. W.A. Broughton1'2, M.G. Mudrey, Broughton l ,2, A.V. A.V. Heyl3, Hey13, W.S. W.S. West3 west M.G. Mudrey, Jr. Jr., Continuation of Tuesday, May May 99 Continuation This leg of of the visits four four localities localities that Middle This the trip visits that illustrate the the Middle Ordovician succession of southwestern Wisconsin, Wisconsin, and a a tour of a vintage 1830 lead mine now operated as as aa tourist tourist attraction. attraction. After the the visit visit to to the the mine, mine, we will return return to to Platteville Platteville for for the the evening. evening. Lodging and dinner this this evening follow the the Individual stop descriptions follow are covered by by the the field field trip trip fee. fee. road logs. logs. Mileages 1 2 33 0.0 Governor Governor Dodge Dodge Motel. Motel. on U.S. U.S. 151 and proceed proceed right right (southwest) (southwest) Leave motel and 6.1 Stop Stop 11 —- Hoadley Hill. Hill. Excellent exposure exposure of of St. St. Peter, Peter, Platteville, and Decorah formations. Continue west on Platteville, on U.S. U.S. 151. 151. 7.4 Right turn turn onto onto Church Church Road Road (gravel). (gravel). 7.8 Bear left, left, at at YY in in road. road. 8.1 2 quarry in upper part part of of Platteville Formation Stop 2 -- Section 2 stop and Decorah Formation. Quimbys Quimbys Mill Mill Member of of Decorah Decorah Formation is especially especially well well exposed. exposed. Middle Ordovician Ordovician fossil fossil locality. locality. Turn around around at at top top of of hill, hill, and and return return to to U.S. U.S. 151. 151. Continue Continue west on on U.S. U.S. 151. 151. Wisconsin Wisconsin Geological and and Natural Natural History History Survey Dept. of Geology, IJW—Platteville Dept. of Geology, UW-Platteville U.S. U.S. Geological Survey Survey 14 14 �Mileages 11.7 11. 7 Enter Dickeyville. Enter 12.0 12.0 Right turn (north) Right (north) onto U.S. U.S. 61 and State 35. 35. 15.9 15.9 Cross Platte River. Cross River. 16.1 16.1 Base of of Potosi Potosi Hill Hill roadcut. roadcut. 16.6 Stop 3 Potosi Hill. Excellent exposure of upper part stop - Potosi part of of Platteville Formation, Shale,an.d lower part part of of the the Formation, Decorah Shale, axd lower Galena Formation. Continue north on U.S. U.S. 61 and and State 35. 35. 18.5 Enter Tennyson. 19.1 Turn left left (west) (west) on on County County 0. O. 19.7 Enter Potosi. Potosi. 20.3 sign. Proceed straight ahead (south) Stop sign. (south) on State 133. 133. 20.5 Stop 4 -- St. St. John's Mine. Mine. Old lead lead mine from the the 1830's. 1830's. Retrace route to to intersection intersection State State 133 133 and and County County 0. O. 21.9 Intersection with U.S. U.S. 61 61 and and State State 35. 35. County County 0. O. 27.6 Enter Cornelia. 31.5 Junction with with U.S. U.S. 151. 151. 34.7 Governor Dodge Dodge Motel. Motel. Turn left left (north) (north) toward toward Platteville. Platteville. END OF LOG 15 15 Continue east on �Wednesday May 10, 1978 1978 Geologic Road Road Log Log for for Lafayette County Hey13, W.S. 1 , W•• A Broug h ton 1,2 , A.V. Broughton1'2, d rey, Jr. M.G. Mu Mudrey, Jr.', LA. M.G. A.V. Heyl3, W.S. West3 West 3 of the trip visits the Shullsburg Mine of of Eagle-Picher Industries, This leg of Industries, the only only operating operating zinc-lead zinc—lead mine mine complex complex in in the the Upper Upper Mississippi Mississippi Valley Valley base base the metal district. Participants are are reminded reminded to to wear wear appropriate appropriate safety safety equipment; equipment; including hard hat, hat, light, light, self—rescuer, self-rescuer, safety safety boots boots and and glasses. glasses. In the afternoon afternoon we we will will return return to to Platteville, Platteville, Madison Madison (where private In the (where private automobiles can be be picked picked up), up), and and Milwaukee. Milwaukee. Historical and cultural cultural stops stops may be made en en route. route. We plan plan to to arrive arrive in in Milwaukee Milwaukee about about 6:00 6:00 P.M. P.M. Morning, Morning, May 10 10 Mileages 11 2 3 0.0 Leave Governor Dodge Motel and and proceed proceed left left (east) (east) on on U.S. U.S. 151. 151. 0.2 Turn right (south) (south) on on State State 80 80 and and State State 81. 81. 6.8 Buildings and tailings pond of of abandoned New Jersey Zinc Company's Elmo Mine can can be be seen seen in in left left distance. distance. 9.4 Enter Cuba Cuba City. City. 9.7 Turn left on County County H (best route). left (east) (eas~on 10.9 Junction with County County J. J. Turn right, right, proceed proceed south south on on County County J. J. 11.9 Vinegar Hill Acid Plant, Plant, closed in 1948, 1948, was located south of road. 13.6 Enter Benton. 14.0 14.0 Join State 11. 11. Turn left left (east). (east). are along this this road. road. 21.8 Shullsburg. Enter Shullsburg. 23.1 Right turn (south) (south) on County 0. o. 24.7 Tailings area of of Eagle-Picher Industries, Mine Tailings Industries, Inc. Inc. Shullsburg Mine on left. left. 25.1 Left turn turn (east) (east) on on County County W. W. Numerous abnadoned abnadoned mines mines Wisconsin Geological and Natural History Survey Dept. of of Geology, Geology, TJW—Platteville UW-Platteville U.S. Geological Survey U.S. 16 �Mileages Mileages 25.8 Left Left Stop Stop hat, hat, mine mine 29.8 About noon; noon; return to to Shullsburg Shullsburg for for box box lunch. lunch. turn (north). (north). Entry to Eagle-Picher property. property. Shullsburg Mine. You 55 -— Shullsburg You are are reminded reminded to to have have on hard light, self-rescuer, self—rescuer, safety boots, light, boots, and and glasses. Tour complex with company geologists. geologists. Afternoon, Afternoon, May May 10 Scenic return to Scenic to Platteville. Historical sights en route via via W, include County W, include towns towns of of New New Diggings, and and Hazel Hazel Green. Green. Right turn (north) turn (north) on State 80 and 11 to to Cuba City and and Platteville. Platteville. 57.1 Enter Platteville. Return to Madison. Stop to pick up private Bus will will continue continue to Milwaukee, arriving arriving about about automobiles. Bus to Milwaukee, 6:00 P.M. Geologic Road Road Log for Geologic for Madison Madison Beitline, Beltline, 1—90, 1-90, and and 1-94 1-94 from from Madison, Madison, Wisconsin Wisconsin (Junction (Junction U.S. U.S. 12 12 and and 14 14 with with U.S. U.S. 18 18 and and 151) 151) to to Milwaukee, Milwaukee, Wisconsin (Junction (Junction 1—94 1-94 with 1—43 1-43 and and I_794)*. 1-794)*. 2 Rachel K. K. Paull' paull l and and Richard A. Paull2 paul1 Milwaukee is within the Eastern This route from Madison to Milwaukee is entirely within the Eastern Ridges and at right right angles angles to to the the Ridges and Lowlands physical province, province, and and it it trends trends at general strike of the the Paleozoic Paleozoic formations. formations. Consequently, Consequently, the the bedrock along the route, route, although largely obscured by Woodfordian the Woodfordian glacial glacial deposits, deposits, ranges ranges from Upper Upper Cambrian Cambrian formations formations on on the the west west to to Silurian Silurian dolomite dolomite on on the the east. east. The glacial geology encountered encountered along along 1—94 1-94 is is spectacular. spectacular. As shown shown in in Figure 8, 8, the the interstate interstate cuts most of these these glacial features features essentially at right angles. angles. From From west to to east, east, these these include include well-developed well-developed drumlin drumlin fields, fields, outwash plains, plains, the the Kettle Kettle Interlobate Interlobate Moraine with numerous scenic lakes, lakes, and recessional moraines of of the the Lake Lake Border Border morainic morainic system. system. Other significant significant attractions along this this route route include: include: the Lapham Peak Peak overlook overlook high high in in the the Kettle Moraine and the the subcontinental subcontinental divide divide that that separates separates drainage drainage destined destined for the the North North Atlantic Atlantic via via the the St. St. Lawrence Lawrence from from that that which which reaches reaches the the Gulf Gulf of Mexico Mexico via via the the Mississippi. Mississippi. *This *This road road log log is is published pUblished with with permission permission of of Kendall/Hunt Kendall/Hunt Publishing Publishing Company, Company, Dubuque, Iowa, means without written Iowa, and and it it should should not be duplicated by any means permission. permission. 1 1 University University of of Wisconsin—Madison Wisconsin-Madison && Alverno Alverno College, College, Milwaukee Milwaukee 22 University of Wisconsin-Milwaukee University of Wisconsin-Milwaukee 17 17 �1/ f 1\ .........- I /I ; ' l c•• 3m.1 I "I I II I II ,I II 'pm. ~ GLACIAL LAKE DEPOSITS I ,\ \ ~----<16km ~ ~VALDERAN DRIFT I i-T7@;--.---\fij.+:.w 1._...... I I I II" UE££E1!..S~ Whit_atr- G> ~ I WALWORTH I I I I R.cine r - -++·~4)H+.:f>{ I i--- ..... I I (WOODFORDIAN) IT] RECESSIONAL MORAINE 'i ~ L..nG_..... Figure 8. Figure 8. ::...... ;:. I I I 1·...:·.. :·:1 LAKE BORDER MORAINE rn D TERMINAL MORAINE WOODFORDIAN DRIFT [l] INTER LOBATE MORAINE [Z[] DRUMLIN TRENDS • AL TONIAN DRIFT KENOSHA Glacial deposits deposits of Wisconsin, including of southeast Wisconsin, glacial lake lake deposits, the the Kettle Kettle Interlobate Interlobate Moraine, Moraine, drumlin patterns, patterns, and and the the Lake Lake Border Border morainic morainic system. system. The Altonian drift shown shown in in Rock Rock and and Walworth Walworth counties, counties, Wisconsin Wisconsin also also includes includes drift that that is is older than than Interstates 94, 43, and 90 are also Wisconsinan. Interstates 94, 43, also indicated. Generalized from numerous numerous sources, sources, including Thwaites, 1956. 1956. Mileages Mileages o 0 (83) Intersection of U.S. U.S. 12 and 14 14 with U.S. U.S. 18 18 and and 151 151 on on the the southeast edge of of Madison, Wisconsin. Wisconsin. Turn east on the Madison Beltline (U.S. (U.S. 12, 12, 14, 14, 18, 18, and and 151). 151). Note: This was the the starting point point for for the the U.S. U.S. 151 151 Madison Madison to to Platteville Platteville roadguide roadguide starting provided for Tuesday May 9, 9, 1978. 1978. 11 (82) The wooded tracts on both sides of the highway are parts of the 1,240 acre University of Wisconsin Arboretum. Although primarily aa research and study area, area, hikers are are permitted permitted on on 24 24 miles miles of of extends north from here to foot trails. trails. This nature preserve extends the south shore of of Lake Lake Wingra. Wingra. 3 3 (80) Intersection of of U.S. U.s. 12 and and 18 with U.S. Intersection U.S. 14 and and 151. 151. east on U.S. U.S. 12 12 and and 18. 18. 4.5 (78.5) Monona, north of the Lake Monona, the highway, highway, is is the the second second largest largest of of Madison's four four lakes. lakes. These lakes are the result of Pleistocene erosion and deposition along the the Yahara Yahara River River drainage. drainage. 5.5 (77.5) wooded, irregular ridge visible visible to the the south over over the the flat flat The wooded, irregular ridge part of of the Woodfordian Johnstown-Milton outwash surface surface is is part the Woodfordian terminal moraine system. terminal 6.2 (76.8) Cross the the Yahara River, River, which which connects connects Madison's Madison's four four lakes. lakes. flows southeasterly to to join the the Rock River north The Yahara flows The relatively flat flat land surface of Janesville, Janesville, Wisconsin. The of south of of the the highway highway is is probably probably an an outwash outwash deposit deposit (valley south (valley train) formed formed during the complex Pleistocene history train) history of of the the Yahara River. 18 18 Continue �— Mileages 7.5 (75.5) of U.S. Junction of U.S. 12, 12, 18, 18, and U.S. U.S. 51. 12 and 18. 18. east on on U.S. U.S. Continue east 9.2 (73.8) and 18 with 1—90. Junction of of U.s. U.S. 12 and 1-90. Turn north (left) (left) on on 1—90. 1-90. 12. 12. (71) Interstate 90 90 traverses traverses rolling, rolling, morainal countryside. Interstate 13.7 (69.3) Junction of 1—90 1-90 with with 1—94. 1-94. Turn east on 1—94 1-94 to to Milwaukee. Southeast of of this this intersection, intersection, crushed crushed stone stone is is produced produced from from theMiddle Ordovician Platteville Formation. The underlying St. Peter Sandstone is also exposed in St. in this this quarry. quarry. 18 (65) (65) Exit County NN to to Sun Sun Prairie Prairie and and Cottage Cottage Grove. Grove. Well-developed drumlins, trending southwesterly, rise drumlins, rise above above rolling rolling ground ground moraine, moraine, and and are are cut by by the the interstate. interstate. The irregular, irregular, hilly ridge on the skyline to the the south is is the the Woodfordian Woodfordian MiltonMiltonJohnstown terminal moraine system of the the Green Bay Bay lobe. lobe. 21 (62) Area of poorly poorly drained, drained, peaty peaty soil soil in in an an interdrumlin interdrumlin area. area. A commercial sod sod and mint farm is is north of the the highway. highway. This region is drained by Koshkonong Creek, which crosses This crosses This stream flows into beneath the interstate at Baxter Road. This into Lake Koshkonong to the south, Lake south, after draining aa vast, vast, marshy marshy area. area. 24 (59) Exit Wisconsin 73 Southwest—trending 73 to to Marshall and and Deerfield. Deerfield. Southwest-trending drumlins form islands between swamps within the drumlins the rolling rolling countryside. countryside. Just east of this junction, junction, a a large large number number of of glacial glacial erratics erratics are present. These are part of of the the boulder boulder train train derived derived from from exposures of exposures of the Precambrian Waterloo Quartzite northeast northeast of of here. here. 27 (56) Goose Lake Lake and the swamp to the Goose the south south are are remnants remnants of of aa much much larger shallow lake that once existed between between drumlins drumlins in in this this area. Much of the the land land here here has has been been ditched ditched for for drainage, drainage, but but drumlins still rise as wooded islands some drumlins islands surrounded surrounded by by swamps. swamps. Fossil remains of of aa mastodon mastodon and and aa giant giant beaver beaver dated dated at at 9,000 9,000 to 10,000 years years B.P. B.P. were found in to in shallow peat peat deposits deposits nearby. nearby. 28 (55) Dane/Jefferson county county line. line. Enter Jefferson Jefferson County, and and aa specspectacular array of drumlins. An excellent swarm swarm occurs occurs where where County 0 crosses crosses the the interstate. interstate. The extensively tiered tiered roadcut roadcut at the at the county line provides a a transverse section section through through aa drumlin. Erratic boulders are common in in the the drift drift in in this this area. area. 33 (50) Exit Wisconsin 89 to to Lake Lake Mills and and Waterloo. The rough country immediately west of of here consists of pitted pitted outwash outwash between between patches of of the Lake Mills recessional moraine system. patches system. Rock Lake, Lake, .25 mile mile to to the the southwest, southwest, occupies occupies aa very large kettle. .25 kettle. There are also many small ice stagnation features in are in this this area. area. Most of these are are sandy deposits, of deposits, some of which lap lap onto onto the the margins margins of drumlins. of 19 �Mileages Exposures of Precambrian quartzite exist north and east of Waterloo, where they form low hills waterloo, hills and ledges which protrude through thin thin glacial glacial drift drift (Fig. (Fig. 9). 9). Most of these these outcrops outcrops are polished and striated by glaciation. are Figure 9. 9. Exposures of glacially polished, polished, gently eastwarddipping, Precambrian Waterloo Waterloo Quartzite Quartzite near near dipping, Hubbleton, Wisconsin. Milwaukee Public Museum Hubbleton, Museum photo. photo. This quartzite quartzite is similar to to that exposed in the the BarabooBarabooThis is similar that exposed Devil's Lake Lake area. area. A basal conglomerate is is present between the quartzite quartzite and and the the the overlying Paleozoic sandstone. sandstone. Small Small potholes are scoured scoured on on some some quartzite quartzite surfaces, surfaces, and and bedding bedding potholes are planes are occasionally ripple marked. planes The main outcroppings of of Waterloo Quartzite are about a a mile east of Portland, of Waterloo Creek and Portland, and at the junction of the Crawfish Crawfish River. River. These exposures occur occur on on the the borders borders of of connect4d series series of of marshes, marshes, which which mark mark aa preglacial preglacial valley valley aa connect4d that was was a that a tributary to to the the Rock Rock River. River. 35 (48) Eastbound rest area in in an an area area of of rolling rolling ground ground moraine. moraine. 37 (46) 1-94 crosses crosses the 1-94 the Crawfish River, River, a tributary tributary to to the the Rock. Rock. miles south on the west bank of of this Aztalan State Park is is 1.5 1.5 miles the west this river. In Late Woodland Indian In addition to Late Indian effigy mounds, mounds, this park park contains contains aa two-tiered two-tiered pyramidal pyramidal mound, mound, and and aa partly partly this restored stockaded led with with the the Middle Middle Mississippi stockaded village village identif identified culture. When the the site was first described in in 1837, 1837, it it was named Aztalan in the hope hope that the cultural cultural remains remains preserved here were were those here those of of the Mexican Aztecs. Aztecs. To reach the the park, park, use use the Lake Lake Mills Mills exit and then turn the turn east on on County County B. B. 38 (45) Westbound rest area, area, in in an area of ground moraine and low—lying low-lying drumlinoid hills. hills. 20 �Mileages Mileages 39 39 (44) (44) 1-94 crosses crosses the the Rock Rock River. River. The The Rock Rock marks marks aa general general 1-94 vegetation vegetation divide divide between between native native hardwood hardwood forests forests to to the the east, east, and and oak oak savannas savannas and and prairies prairies to to the the west. west. Some Some think think the the river river formed formed a a barrier to to prairie prairie fires, fires, thus thus preserving preserving the the on the the east. east. forests on Jefferson, Jefferson, 6.5 6.5 miles to to the the south at the the junction junction of of the the Crawfish Crawfish and and Rock Rock rivers, rivers, experienced experienced aa short—lived, short-lived, geology-related, geology-related, land boom boom about about 1840. 1840. A A federally-assisted federally-assisted project project was was planned planned land to to construct a a canal from Lake Michigan at Milwaukee to to the the Rock River River near near Jefferson. Jefferson. Some Some construction construction was was actually actually Rock accomplished accomplished before before the the million—dollar million-dollar project project was was abandoned. abandoned. Meanwhile, Meanwhile, land land values values had had sky—rocketed sky-rocketed in in Jefferson Jefferson as as the the prospect prospect of of a a connection between the the Mississippi River and and Lakes seemed seemed imminent. imminent. Land promoters promoters arrived, arrived, and and the Great Lakes a a steamboat made it it up up the the Rock Rock River River from from St. St. Louis. Louis. Tracts Tracts of of swampland swampland were bought bought by local local residents residents and and newcomers newcomers at at inflated prices, prices, in the hope that great profits would result when· the the canal canal was was completed. completed. The land land promoters promoters left left town town when with well—laden well-laden carpetbags, carpetbags, before before news news of of the the abandonment abandonment of of reached southern southern Wisconsin. Wisconsin. the canal plans reached 40 40 (43) (43) Exit Wisconsin 26 26 to to Watertown, watertown, Johnson Johnson Creek, and and Jefferson, Jefferson, within the the Jefferson Jefferson County County drumlin drumlin field. field. Where the the interstate interstate within drumlin, the roadcuts cuts through a a drumlin, roadcuts have been carefully sodded over to conceal the internal character of the sandy and clayey till. However, However, at the the northwest northwest corner corner of of this this intersection, intersection, behind the service station and restaurant, restaurant, an excavated drumlin is exposeq. is exposed. 46 46 (37) Irregular ground ground moraine moraine assumes assumes symmetry symmetry and and order order as as the Irregular the highway traverses traverses aa classical classical drumlin drumlin field, field, produced produced by by the the highway Green Bay lobe lobe of the the Woodfordian Woodfordian ice ice advance advance (Fig. (Fig. 10). 10). These drumlins trend essentially north-south north—south in in this area, but but nearer nearer drumlins trend essentially this area, to Madison Madison the orientation was southwesterly. to southwesterly. Poorly drained drained areas areas and and tamarack tamarack swamps swamps flank flank many many of of the Poorly the drumlins this area. area. drumlins in this 50 50 (33) (33) Wisconsin 135 exit. 52 52 (31) (31) Enter Waukesha Waukesha County. County. The Jefferson/Waukesha county line. Jefferson/Waukesha line. Enter drainage in this rolling countryside is poor, and farm fields fields drainage in this rolling countryside is poor, and farm Numerous tamarack swamps with red osier must must be ditched. ditched. Numerous tamarack swamps with red osier dogwood are are lingering lingering evidence evidence of of the the boreal boreal climate climate of of the the dogwood Pleistocene. Pleistocene. 21 21 �Figure 10. 10. An intensively—farmed, intensively-farmed, north—south north-south trending drumlin Sullivan, in Jefferson County, Wisconsin. In near Sullivan, this this area, area, these streamlined hills hills are are so so numerous numerous that they are termed a a drumlin swarm swarm or or field. field. Milwaukee Public Public Museum Museum photo. photo. Mileages 55 (28) (28) Wisconsin Wisconsin 67 67 exit exit to to Oconomowoc Oconomowoc and and Dousman. Dousman. The interstate interstate now traverses outwash and proglacial lake lake sediments sediments in in an an area area once occupied by the the Green Bay lobe during the the Woodfordian Woodfordian ice ice advance. To the the east, east, the the view view of of the the Interlobate Interlobate Moraine Moraine looming above the flat outwash surface surface is is impressive. impressive. A A few overgrown kettles are adjacent to to the the highway on on the the south south side. side. To the the north, north, rising rising above above the the flat flat outwash outwash plain, plain, is is an an inconincongruous gruous landform that that resembles the the classic moulin moulin kames kames of of the the northern northern Kettle Kettle Moraine. Moraine. This is is an an artificially—created artificially-created ski ski hill near Oconomowoc. 59 (24) (24) provides a a side trip to to view the the Kettle An exit on County CC provides Kettle Interlobate Moraine from the the observation observation tower tower on on Lapham Lapham Peak Peak (Fig. This tower (Fig. 11). 11). tower provides provides an an excellent excellent overview overview from from the the highest vantage vantage point point in in the the southern southern Kettle Kettle Interlobate Interlobate Moraine. Moraine. To the the west west is i~ Genesee Genesee Flat. Flat. To the the east is is the the glacial spill— spillway described described at at Mile Mile 61. 61. Several scenic scenic glacial glacial lakes lakes are are also visible. visible. 22 22 �Figure 11. 11. Kettle Interlobate A scenic overview of of the southern Kettle Interlobate Moraine from the the observation tower tower on on Lapham Lapham Peak. Peak. Photo by Professor R.F. Black, University of University of Connecticut. To reach Lapham Peak, To Peak, go south on County CC (Kettle (Kettle Moraine Moraine Scenic Drive) Drive) about 1.8 miles to a crossroad. Scenic crossroad. Turn left (east) (east) onto Government Hill Hill Road. Road. Continue about 0.7 mile to to a a small small The tower park that that includes includes the the Lapham Peak observation tower. park tower. The A marker at 1233 for state station WHAD is also located for located here. A feet of of elevation, elevation, on a feet a glacial erratic boulder boulder in in the the park, park, is is dedicated to one of Wisconsin's earliest geologists dedicated geologists and and "Increase A. A. Lapham, Lapham, Eminent scientist and naturalists: and useful naturalists: "Increase citizen". citizentt. The route ahead crosses a a region of pitted pitted (kettled) (kettled) outwash outwash Nagawicka deposits, and and many many kettle kettle lakes dot the deposits, lakes dot the landscape. landscape. Nagawicka Other Lake, immediately immediately north of of the highway, is such a Lake, the highway, a lake. lake. Other examples are are Upper Upper and and Lower Nemahbin lakes, examples lakes, which sandwich the the 23 23 �Mileages interstate about 1 mile west west of of here. here. The The ice ice blocks blocks which formed these lake basins basins were were derived derived from from the formed these lake the Green Bay lobe lobe along the the western western edge of of the Interlobate Moraine. along 60 (23) The interstate approaches the The the crest crest of of the the Interlobate Interlobate Moraine. Moraine. A small ski area south of the highway utilizes part of this this slope. From the crest of this this ridge, ridge, the radio tower tower and observation tower on Lapham Peak Peak are are visible visible south south of of the the highway. highway. The Kettle Kettle Interlobate Moraine, whi.ch which trends trends northeasterly northeasterly across across The Interlobate Moraine, miles, from Walworth to Wisconsin for about 130 miles, to Kewaunee counties is the premier glacial feature in is in Wisconsin. It It is is probable that the the resistant Silurian that the position Silurian dolomite dolomite influenced influenced the of the deposits in in this area, by by retarding retarding the of the interlobate interlobate deposits this area, the spread of the the Green Green Bay Bay lobe. lobe. Within this this morainal complex, complex, the country is rolling and rugged, rugged, with abundant abundant knobs knobs and and kettles. kettles. This feature formed during the the Woodfordian glacial advance by a a juxtapositioning of the the terminal terminal moraines of of the the Green Green Bay Bay and and Lake Lake Michigan Michigan lobes. lobes. Between these icy walls, walls, complex complex drainageways drainageways developed, developed, and and meltwaters meitwaters these icy reworked some of the morainal materials. The resultant resultant deposits deposits are a a mixture of of sand, sand, gravel, gravel, boulders, boulders, and and clayey clayey till. till. Much of the coarser material was derived from of from the the Silurian Silurian dolomite, dolomite, but igneous and metamorphic metamorphic rock rock types from far far to to the the north but igneous and types from are also present. present. 61 (22) Wisconsin 83 Wisconsin 83 exit. exit. This'highway This/highway follows follows low ground along an agandoned drainage drainage channel channel which which carried carried the the last last meltwater meltwater agandoned that drained southward southward through through this this part part of of the the Kettle Kettle Inter— that drained Interlobate Moraine. Water drained drained down down this this .25 .25 mile mile wide wide valley valley until it reached Wales, Wales, about about 33 miles miles to to the the south, south, where where it until it reached cut through the Interlobate Interlobate Moraine to to flow flow west. west. Gravel flank this this drainage, drainage, and and aa remnant remnant of of aa high outwash terraces terraces flank terrace is is visible on the the east side side of of this this valley. valley. 62 62 (21) Pewaukee Lake Lake lies lies to to the the north. north. The church at Holy Hill, Hill, a kame high on on the the Interlobate Interlobate Moraine, Moraine, is is also also visible visible kame perched perched high to the north on aa clear clear day. day. Pewaukee Lake occupies a a pre— preglacial river valley which was scoured into the Upper Ordovician Maquoketa Shale. Shale. This ancient valley was Maquoketa was blocked by morainal debris deposited along its eastern margins by the the Lake Michigan lobe during the Woodfordian ice ice advance. advance. 63 63 (20) Ground moraine deposits deposits in in this this area area are are thin. thin. North of the the highway on the west edge edge of of the golf course, course, there the west the Tumblebrook golf there is is a a small quarry quarry in in Silurian Silurian dolomite. dolomite. Glacial striae striae on on bedbedrock in this area indicate indicate that that ice ice movement movement was was west—southwest. west-southwest. South of the the Valley), and and character of road, names of of aa subdivision (Pebble road, the the names a farm (Stoney (Stoney Hill), Hill), bear testimony testimony to to the the the morainal material. the 24 �Mileages 65 (18) Exit County GG to to Pewaukee. Pewaukee. A A drumlin field lies lies south of the the highway for the the next next several several miles. miles. These east-west trending trending drumlins abundant drumlins are composed of of sandy clay till till that that contains contains abundant boulders. 68 (15) Exit County County F. F. West of of this this intersection, intersection, the the route route crossed the Pewaukee River, River, which is the is tributary tributary to to the the Fox. This valley valley is paralleled by outwash terraces, is terraces, which are are commercial commercial sources sources of sand sand and and gravel gravel in in this this area. area. 69 (14) Exit Wisconsin 164 164 to to Sussex Sussex and and Waukesha. Waukesha. East—west East-west trending trending drumlins are north and and south south of of the the highway. highway. Dunbar, while visiting Waukesha in 1869, Colonel Dunbar, 1869, drank from from some of of the springs which issue some issue from the the glacial glacial drift drift in in this this area with high amounts of dissolved calcium area calcium magnesium magnesium bicarbonate. bicarbonate. Upon deciding that the local Upon local mineral waters had had eliminated eliminated his his !tincurable ailments", ailments", he he began began to to advertise advertise his his cure cure nationwide, nationwide, "incurable and Waukesha Waukesha soon became a and a fashionable health health spa. spa. Although this fad waned after about 30 this fad 30 years, years, bottled bottled spring spring water water is is still a Waukesha product. product. Waukesha is is located located on on the the Fox Fox River. River. Outwash terraces terraces along along this this river are important commercial sources sources for for sand sand and and gravel. gravel. Since the glacial drift drift is quite thin in this this region, region, Silurian dolomite is extensively quarried along the the valley oC of the the Fox from the from the Waukesha area northward to to Sussex, Sussex, Lannon, Lannon, and and Menomonee Falls. Falls. 71 (12) Road) to Waukesha and Wisconsin State Exit U.S. U.S. 18 (Blue (Blue Mound Road) Patrol headquarters. headquarters. 74 (9) Moorland Road. Road. The flat terrain here is is poorly poorly drained, drained, Exit Moorland clay—rich ground moraine. Ditching and clay-rich and channelization channelization were required for for the extensive development of required of the the land land north north of of the highway. The golf course to to the the south south represents represents aa more more intelligent land land use. use. A A few few isolated isolated patches patches of of moraine, moraine, and and east—west trending drumlins rise several east-west rise above above the the generally generally swampy ground. The route ahead ahead descends descends aa prominent prominent ridge, ridge, which which is is part part of of the Woodfordian Woodfordian Lake Border recessional the recessional moraine system. system. Sunny Slope Road traverses this forms the drainage drainage divide divide this crest, crest, which forms between Lake Michigan Michigan and and the the drainage drainage basin basin of of the the Fox Fox River. River. The Fox flows southward southward parallel parallel to to the the Woodfordian Woodfordian moraines moraines to to reach the Illinois River, River, and and ultimately ultimately the the Gulf Gulf of of Mexico Mexico via the Mississippi. 76 (7) Milwaukee/Waukesha county county line. line. 78 (5) Exit 1—894 45 north to 1-894 (U.S. (U.S. 45) 45) south to Chicago and and U.S. U.S. 45 du Lac. Lac. The Milwaukee County Zoo Zoo is is northwest northwest of of this this Fond du intersection. 25 Enter Milwaukee County. County. �Mileages 79 79 (4) (4) Wisconsin State Exit Exit Wisconsin Wisconsin 181 181 (84th (84th Street). Street). The Wisconsin State Fair Fair Park grounds and an Olympic-size Olympic—size outdoor outdoor ice are southeast grounds and ice rink are of of this this junction. junction. The interstate traverses traverses Wisconsinan (Woodfordian) ground moraine and recessional moraines of (Woodfordian) ground of the the Border system. system. The highway here is essentially parallel Lake Border to the east—west direction of of ice movement, and and consequently the east-west ice movement, the inorainic ridges trend north-south. About 100 morainic ridges 100 feet feet of of glacial glacial deposits, deposits, primarily primarily a boulder clay till, till, overlie Silurian dolomite in in this this area. area. 81 (2) U.S. u.S. 41 exit (north (north and and south). south). Milwaukee Milwaukee County County Stadium, Stadium, home home of the the Milwaukee Brewers and also the the site of the the Milwaukee games of the the Green Bay Packers, Packers, is is just just west west of of this this junction. junction. The large large hill southwest of the the stadium is a Silurian dolomite of the Veterans Administration exposure on the the grounds grounds of the U.S. U.S. Veterans Hospital. 82 (1) Route parallels parallels the the industrial industrial complex complex along the the east—west east-west Menomonee River River valley. valley. Three large, large, glass glass domes in in trending Menomonee Mitchell Park Park are are visible visible to to the the south. south. One contains aa display of vegetation native to a desert environment, environment, another features features a desert tropical houses local flora and is often tropical plants, plants, and the last houses local flora used for special special flower flower shows. shows. 83 (0) Junction 1—94 1-94 with with 1—43 1-43 (U.S. (U.S. 141) 141) and and 1—794. 1-794. The Milwaukee Harbor is is to to the the woutheast, toward toward the the high—rise high-rise Harbor Freeway bridge along along the the lakeshore. lakeshore. Three rivers rivers merge at the Milwaukee Harbor, Harbor, the Menomonee west, the Milwaukee River comes River flows flows from the the north and west, from the the north, north, and the Kinnickinnic Kinnickinnic River originates to the west and and south. south. Milwaukee grew from three settlements that were originally separated by these these rivers. rivers. Walker's Point, Point, east east of of the the Kinnickinnic River, River, is now dominated by the towering towering clock of the Allen Bradley Company. Company. The Milwaukee River flowed between Kilbourntown on the west and Juneautown Juneautown to to the the east. east. The high smokestack to the the east is part of of the Jones Island Island Here, sewage sludge is dried and Sewage Plant. Plant. Here, and Metropolitan Sewage Milorganite, aa commercial converted to Milorganite, commercial fertilizer. fertilizer. Jones Island, Jones Island, an artificially breached breached peninsula, peninsula, also also contains contains aa tanker pier, pier, cargo terminals terminals and and aa heavylift heavylift wharf, wharf, and and is is headquarters for the the Port of of Milwaukee. Milwaukee's inner harbor was was developed developed by by an enlargement enlargement of of the lower Kinnickinnic Kinnickinnic the lower River, and it serves serves as as the and wintering wintering area for for part River, the service service and part of U.S. U.S. Steel's Steel's iron ore carrier fleet. of fleet. END OF LOG through downtown Milwaukee to the Pfister Proceed through Pfister Hotel; Hotel; headheadquarters for for the the 24th 24th annual annual meeting meeting of of the the Institute Institute on on Lake Lake quarters Superior Geology. We hope you enjoy enjoy your your stay stay in in Milwaukee! Milwaukee! 26 �— GX)LOGICAL GIDLOGICAL STOP SIDP DESCRIPTIONS DESCRIPTIONS Page Stop Stop 1I —- Hoadley Hill Hill Hoadley 28 28 Upper Upper part part of of the the St. St. Peter Peter Sandstone, Sandstone, the the Glenwood Glenwood Formation, Formation, aa complete complete section section of of the the Platteville Platteville Formation, Formation, and the the lower lower part part of the the Decorah Formation Stop 22 —- Section Section 22 Quarry Quarry Stop 32 32 QUimby's Mill Mill (upper (upper part part of of the the Platteville Platteville Quimby's Formation) Formation) Stop 33 —- Potosi. Potosi Hill Hill Stop 33 33 Upper part of the Platteville Formation, Formation, the Decorah Formation, Formation, and the lower part of the Galena Galena Formation (Snake Cave) Cave) Stop 44 —- St. John Mine (Snake Dunleith Member (cherty (cherty (non-cherty upper (non—cherty upper unit) unit) 37 37 lower unit) and and Wise Lake Lake lower of the Galena Formation Formation 27 27 �Title: Title: Hoadley Hill Hill Hoadley Location: Exposure Exposure in in roadcut roadcut at at north north side side of of U. U. S. S. Highway Highway 151 151 about about 6.5 6.5 miles southwest of of Platteville Platteville in in the the NW!, NW, NWI, Sec. Sec. 12, 12, T.2N., T.2N., R.2W., R.2W., Grant Grant County (Dlckeyville (Dickeyville 7.5—minute 7.5-minute topographic topographic quadrangle, quadrangle, 1972), 1972). Author: NWt, M. M. E. E. Ostrom (modified (modified from Agnew et. al., al., 1956) 1956) section for for the the Platteville Platteville Formation. Formation. Description: This is the reference section exposed qere lere are are the the upper upper part part of of the the St. St. Peter Peter Sandstone, Sandstone, the the The strata4 strat~exposed Formation, a Formation, and the Glenwood Formation, a complete section of of the Platteville Formation, the lower et. al,, al., (1956) (1956) lower part part of of the Decorah Formation. Description from Agnew et. is: ORDOVICIAN SYSTEM Decorah Formation Spechts Ferry Shale Member Member (+1.0 (+1.0 feet) feet) 62.9' - 63.4' 62,9' — 0.5'+ Shale, bluish—green. Shale, bluish-green. 62.7' — 62.7' - 62.9' 0.2' Bentonite, white; Bentonite, white; weathers weathers orange orange brown. brown. 62.7' 62.5' — 62.5' - 62.7' 0.2' Shale, yellowish-green yellowish—green above above to bluish-green below. below. Shale, 28 �62.4' —- 62.5' 62.5' 62.4' 0.1' 001' Shale, Shale, brown brown and and olive, olive, soft. soft. Platteville Platteville Formation Formation (54.3 (54.3 feet) feet) Quimbys Quimbys Mill Mill Member Member (0.3 (0.3 —- 0.5 0.5 feet) feet) 62.0' —- 62.4' 62.4' 62.0' 0.4'+ 0.4'± Limestone, Limestone, conchoidal conchoidal dark—brown dark-brown parting parting at at dark dark purple, purple, fine—crystalline, fine-crystalline, dense, dense, fracture; fracture; very very wavy wavy upper upper surface; surface; thin, thin, to to black, black, fossiliferous fossiliferous platy platy shale shale base. base. McGregor McGregor Limestone Limestone Member Member (30.9 (30.9 feet) feet) 61.1' —- 62.0' 62.0' 0.9' 0.9' Limestone, Limestone, light—gray, light-gray, very fine fine crystalline, crystalline, very very dense, dense, conchoidal fracture like like "glass rock" rock" above, above, fairly massive, massive, very very fossiliferous; fossiliferous; wavy upper upper surface. surface. 60.4' —- 61.1' 61. l' 60,4' 0.7' 0.7' Limestone as next above above but less less dense, medium— mediumbedded above to to thinthin- bedded below, fossiliferous; fossiliferous; wavy upper surface. surface. 58.8' —- 60.4' 1.6' Dolomite, light Dolomite, light olive drab, drab, fine fine crystalline, crystalline, "sugary", argillaceous, argillaceous, very very thin—bedded; thin-bedded; molular, molular. 55.8' —- 58.8' 3.0' Dolomite as above above but thick—bedded; thick-bedded; calcite calcite near near middle. 55.2' —- 55.8' 55.2' 2.6' Limestone, thin—bedded Limestone, thin-bedded yet stands massively as one unit; light greenish unit; greenish gray gray brown; brown; weathers weathers brown, brown, with a a few argillaceous streaks; streaks; sparingly fossiliferous, ferous, but with fossils fossils and and fucoids fucoids on on top top surface. surface. 51.8' — - 55.2' 55.2' 51.8' 3.4' Limestone, Limestone, thin—bedded thin-bedded as above but the the beds are a~e distinct; modular beds and shaly partings; distinct; partings; argillaceous is is upper 0.3 feet, ceous feet, which which is is very very fossiliferous, fossiliferous. 48.2' - 51.8' 51.8' 48,2' — 3.6' 3,6' Limestone, light buff ish gray, gray, in in medium medium to to thick Limestone, buffish beds; in places beds; places gradational gradational into into above above unit, unit. 44.3' - 48.2' 48.2' 44,3' — 3.9' 3,9' Limestone, light light greenish to to bluish gray, gray, in massive Limestone, beds but but composed composed of of thin thin beds beds which are are not sepabeds rated; ample ample shaly shaly material material in in wavy wavy bands; bands; fairly fairly rated; fossiliferous, argillaceous; argillaceous; aa peculiar mottled fossiliferous, light gray gray and and darker darker gray 0,1-foot light O.l-foot zone, zone, 11 foot foot below top, top. 40.3' 44,3' 40.3' -— 44.3' 4.0' 4,0' Limestone, light light gray, gray, very very fine fine crystalline, crystalline, very very Limestone, dense, sublithographic, sublithographic, in. in extremely extremely thin thin and and modumodudense, lar beds beds with with thin thin calcareous calcareous shaly shaly partings partings which which lar become thinner thinner below; below; the the shale shale beds beds are are light light become grayish blue,mottled, blue,mottled, very very fossiliferous; fossiliferous; weathers weathers grayish slightly recessed. recessed, slightly 29 29 �36.7' —- 40.3' 40.3' 36.7' 3.6' 3.6' Limestone, Limestone, as as above, above, but but beds beds are are not not quite quite as as thin; thin; fossiliferous; fossiliferous; poor poor gastropod gastropod zone zone 1.7 1.7 feet feet above above base; base; shaly shaly zone zone at at base, base. 33.1' —- 36.7' 36.7' 33.1' 3.6' 3.6' Limestone, Limestone~ dolomite, dolomite, light—gray, light-gray, fine fine crystalline, crystalline, very very slightly slightly argillaceous, argillaceous, very very fossiliferous, fossiliferous, medium—bedded; medium-bedded; Indistinct indistinct argillaceous argillaceous partings, partings, not not wavy; wavy; calcite calcite and and limonite, limonite, especially especially In in basal basal 0.6 0.6 feet. feet. Pecatonica Pecatonica Dolomite Dolomite Member Member (21.5 (21.5 feet) feet) 28.3' —- 33.1' 33.1' 28.3' 4.8' 4.8' Dolomite, Dolomite, light light grayish grayish brown, brown, very very coarse coarse crystalcrystalline and vuggy, vuggy, upper 2 feet a mixture of of lithology lithology and a somewhat argillaceous fine crystalline "sugary" "sugary" laminated dolomite; dolomite; a 1-foot I-foot bed of very very vuggy vuggy dolomite dolomite from from 1.8 1.8 to to 2.8 2.8 feet feet above above base; base; shaly shaly in lower part; part; stylolitic partings 1 foot above above base. base. 21.4' —- 28.3' 21.4' 6.9' DolomIte, gray, laminated, laminated, somewhat argil— Dolomite, mediuin medium-gray, argillaceous, laceous, fine—crystalline fine-crystalline "sugary", "sugary", fossiliferous, fossiliferous, especially in lower 0.9 feet; feet; medium— medium- to to thick— thickbedded; shaly at top; bedded; top; weathers brownish in in lower lower 2.5 feet. 17.8' —- 21.4' 3.6' Dolomite, medium medium gray, gray, laminated, laminated, argillaceous; argillaceous; very fossiliferous partings. partings. 16.4' 17.8' 16.4' —- 17.8' 1.4' 1.4' Dolomite, light light grayish grayish brown, brown, very very coarse coarse crystalcrystalline and and vuggy; vuggy; thin thin brownish gritty dolomitic line and platy shaly parting at top. and top. 13.6' 16.4' 13.6' -— 16.4' 2.8' 2.8' Dolomite, medium gray, Dolomite, gray, laminated, laminated, somewhat argillaceous, fine crystalline. laceous, H.6' 13.6' 11,6' -— 13.6' 2.0' 2.0' Dolomite, medium gray, Dolomite, gray, laminated, laminated, argillaceous, argillaceous, silty and and sandy sandy with with fine fine to to coarse coarse quartz quartz grains grains silty similar to to those those of of the the St. St. Peter Peter Sandstone, Sandstone, phossimilar phate nodules nodules abundant (especially phate (especially in in two two zones, zones, one at at base, base, the the other 1 foot above one above base). base). Glenwood Formation (1.5 (1.5 feet) feet) 11.2' 11.6' 11.2' -— 11.6' 0.4' 0.4' Shale, sandy with rounded quartz grains, Shale, grains, khaki to to drab, soft; drab, soft; phosphate nodules. H.O' 11.2' 11.0' -— 11.2' 0.2' 0.2' Shale, sandy, sandy, olive olive to to grayish grayish brown; brown; mottled mottled Shale, yellowish brown, brown, friable. friable. yellowish 10.4' 11,0' 10.4' -— H.O' 0.6' 0.6' blocky, Shale, sandy, sandy, mediummedium— to dark—gray, Shale, dark-gray, olive, olive, blocky, very hard, very hard. 30 30 �10.1' — 10.1' - 10.4' 0.3' Shale, medium-gray, medium-gray, blocky; blocky, hard, Shale, hard, sandy; sandy; streak of carbonaceous material at at top. top. St. Peter Sandstone Formation St. Formation (÷10,2 (+10.2 feet) feet) 10.0' — 10.1' 10.0' - 0.1' Sandstone, red and white; white; rounded; Sandstone, rounded; frosted, frosted, coarse to medium-grained. medium—grained. 9,8' 9.8' —- 10.0' 0.2' Sandstone, gray, Sandstone, gray, pinkish, pinkish, very very friable. friable. 9.7' 9.7' —- 9.8' 0,1' 0.1' Sandstone, brown, Sandstone, brown, iron—stained, iron-stained, hard. hard. 8.4' — 8.4' 9.7' 9.7' 1.3' 1. 3' Sandstone, yellow to gray, Sandstone, gray, very friable, friable, with irreirregular lower lower surface. surface. 8.3' — 8.3' - 8.4' 8.4' 0,1' 0.1' Sandstone, light—gray, Sandstone, light-gray, very very friable. friable. 8,1' — 8.1' - 8,3' 8.3' 0.2' Sandstone, yellow to Sandstone, to dark—brown, dark-brown, laminated, laminated, hard, hard. 7.0' 7.0' —- 8.1' 8.1' 1.1' 1.1 ' Sandstone, gray and yellow; Sandstone, yellow; hard irregular lower lower surface. - 7,0' 7.0' 7.0'+ Sandstone as above, above, but but medium— medium- to to fine-grained; fine-grained; spoils. 0.0' 0.0' — EXPOSURE BASE OF EXPOS URE Significance: This is the reference section section for for the the Platteville Platteville Formation. Formation. The contact relationships and lithologies of the St. St. Peter, Peter, Glenwood, Glenwood, Platte— Platteville, and Decorah Formations can be examined. yule, and Note the lithology, mineralogy, and structure of the St. Formation, lithology, mineralogy, St. Peter Formation. What direction did it it come from? Does it contain evidence of life? How do for its mineral homegeniety? What was the you account for the environment environment of of deposideposiit change toward toward the the top? top? What is is the the significance significance of of no no change? change? tion? Does it of of change? What is is the the relationship of of the the St. Peter Peter to to the the Glenwood? Glenwood? Note the various beds beds of of the the Glenwood, Glenwood. What is is their their significance? significance? If If they could for long distances distances of of several hundred miles, miles, what would be the signibe traced for ficance? What is is the the nature and and significance significance of of the the Glenwood/Platteville conconlithology, i.e. i.e. phosphate nodule beds, beds, tact? Note the variable Platteville lithology, fossil etc. What is is their their significance? significance? What would be be the the fossil beds, beds, sandy beds, etc. significance if if they could be be traced several.hundred several. hundred miles? References: Dapples, Dapples, 1955; 1955; Agnew et. et. al., al., 1956; 1956; Templeton Templeton and and Willman, 1963; 1963; Ostrom, 1964 and Ostrom, and 1970. 1970. 31 �Title: Title: Section 2 Quarry Section Location: Abandoned Abandoned quarry on west side of gravel road Location: road about about 0.7 0.7 miles miles north north of U. S. Highway 151 about 0.3 miles west of Piddington Cementary in the the SW!, SW, of U. S. Highway 151 about 0.3 miles west of Piddington Cementary in SW, SE, Sec. 2, T. 2 N., R. 2 W., Grant County (Dickeyville 7.5—minute SW!, SE!, Sec. 2, T. 2 N., R. 2 W., Grant County (Dickeyville 7.S-minute topographic quadrangle, quadrangle, 1972). Map location location on Hoadley Hill Hill description. topographic description. See Hoadley Hill Hill description. description. QUimby's Quimby's Mill Mill Member of Decorah Description: See ,Formation is is well well exposed. Excellent Excellent Middle Middle Ordovician Ordovician fossil fossil locality. "Formation locality. 32 32 �Title: Title: Potosi Hill Hill Potosi at east east side side of of U. U. S. S. Highway Highway 61 61 in inthe theSW!, SW, NW!, NW, Sec. Location: Location: Roadcut Roadcut at Sec. 7, 7, R.2W., Grant Grant County. County. (Potosi (Potosi 7.5-minute topographic topographic quadrangle, quadrangle, 1972), 1972). T.2N., R.2W,, Author: M. E. E. Ostrom Ostrom (modified from Cline dine et M. (modified from et al, aI, 1956, 1956, Kruse, Kruse, 1970). 1970). in Description: The lower part of the section exposed here can be examined in The major major emphasis emphasis here here is is focused focused closer detail at the the Hoadley Hill Hill Stop. Stop. The uppör part wh~ch which includes Ferry, Guttenberg, Guttenberg, and Ion on the the upper includes the Spechts Ferry, Ion Members of of the bers the Decorah Shale Formation and and the the lower part of the Galena Dolomite The Quimbys Quimbys Mill Mill Member consists consists of purplish gray-brown, Formation. The gray-brown, sublitho— sublithographic, thick-bedded, thick—bedded, conchoidally fractured fractured limestone graphic, lilnestone with uneven upper surIt is is called called the the "Glass "Glass Rock" Rock" locally locally because because face base. It face and and shale at its base. when broken, broken, and and when broken pieces pieces are are shaken together, when together, it sounds like broken glass. The Quimbys Quimbys Mill Mill is is overlain overlain by by the the Spechts Spechts Ferry Ferry Member Member which which consists consists The of fossiliferous, fossiliferous, gray-brown gray—brown limestone limestone with with green green shale shale interbeds. interbeds. At this of this Metabentonite exposure two thin beds of "metabentonite" occur near its its base, base. Metabentonite The metametais of volcanic volcanic ash ash dust. dust. The is believed believed to to be be the product of alteration of bentonites are are orange orange to to light light reddish brown and about 2 inches thick. bentonites thick. The The Spechts Spechts Ferry Ferry is is overlain overlain by by the the Guttenberg Guttenberg Limestone Limestone Member Member which which 33 �consists of of hard, hard, finely consists fossiliferous, light light brown, brown, finely crystalline, crystalline, thin-bedded, thin—bedded, fossiliferous, limestone with with brown brown carbonaceous shale interbeds, limestone interbeds. The The presence presence of of these these interbeds has has led led to to the the member member being being referred referred to to as as the the "Oil "Oil Rock" Rock" in in the interbeds the southwest Wisconsin Wisconsin zinc-lead zinc—lead mineral district, southwest district. The Ion Dolomite Dolomite Member overlies the The the Guttenberg. Guttenberg. It It is is aa gray gray to to blue dolomite, medium-crystalline, medium—crystalline, and and medium-to medium—to thick-bedded thick—bedded with with green dolomite, green shale shale interbeds, It It is is locally called interbeds. called the the "Bluet'. "Blue". The Galena Dolomite Formation overlies the The the Ion, Ion. It It is is aa light light buff buff to drab, cherty, cherty, thick-bedded, thick—bedded, vuggy vuggy dolomite dolomite with with medium medium to drab, grains. to coarse coarse sugary grains, The basal basal contact is gradational. gradational. A zone of of Prasopora insular The is Ulrich marks insularis marks the top top of of the Ion Member in some areas. the areas. It It is is absent here. here, Good fossil hunting in in the the Spechts Spechts Ferry Ferry and and Guttenberg Guttenberg Members. Members. Near the north end of of the roadcut there is is a a quarry in which can be seen seen an example of is the main site of of zinc and of "pitch-and-flat" "pitch—and—flat" structure which is lead mineralization mineralization in the district, lead district. Here Here there there is is no mineralization. mineralization, Description of outcrop follows: follows: ORDOVICIAN SYSTEM Galena Dolomite Formation Cherty Unit 45.8' — 45.8' - 65.8' 65.8' 20.0' Dolomite, yellowish-buff, yellowish-buff, medium—to medium-to coarse—grained, coarse-grained, Dolomite, vuggy, chert in in upper upper 10', 10'. vuggy, abundant white chert Decorah Decorah Formation Formation (43,8 (43.8 feet) feet) Ion Dolomite Member Member (19,5 (19.5 feet) feet) (Gray unit) 38 3' —- 45 8' 38.3' 45.8' 7,0' 7.0' buff, thick-to thick-to massive—bedded, massive-bedded, vuggy, vuggy, Dolomite, buff, green shale shale partings throughout, throughout, sparry sparry calcite calcite present. present. 33,8' 33.8' —- 38.3' 38.3' 5.0' 5.0' Covered Covered interval, interval. 32,8' 32.8' —- 33.8' 33.8' 1.5' Dolomite, buff, buff, medium—grained, medium-grained, medium—bedded, medium-bedded, with with green green shale shale partings, partings. (Blue unit) unit) 27.2' 27.2' —- 32.3' 32.3' 5.1' 5.1' Dolomite, purplish purplish gray, gray, medium—grained, medium-grained, slightly slightly Dolomite, fossiliferous. fossiliferous. Green Green shale shale present present as as partings, partings, and as as a 05' 0.5' bed bed 0.8' 0.8' below below the the top top of of the the interinterand val, val, calcite calcite present. present. 26.3' 26.3' —- 27,2' 27.2' 0,9' 0.9' Shale, green. green. Shale, of of interval, interval. 0.3 green green dolomitic dolomitic shale shale in in middle middle 0.3 Guttenberg Guttenberg Limestone Limestone Member Member (15.3' (15.3' feet) feet) 34 34 �21.7' 21.7' —- 26.3' 4.6' Limestone, Limestone, purplish brown, brown, fine-grained to to sublithosublithographic, graphic, fossiliferous, fossiliferous, upper 1' l' fine—to fine-to medium— mediumgrained, grained, brown shale shale present as as partings, partings, calcite calcite and limonite after iron iron sulfide sulfide present present in in small small amounts. 21.6' —- 21.7' 21.6' 0.1' Metabentonite, brownish brownish orange, orange, crumbly, crumbly, sticky sticky when when wet. wet. 12.0' -- 21.6' 9.6' 9.6' Limestone, Limestone, purplish brown, brown, sublithographic, sUblithographic, thinthinwavey—bedded, wavey-bedded, fossiliferous, fossiliferous, brown brown carbonaceous carbonaceous shale present as thin thin beds and partings, partings, calcite calcite and limonite limonite present. present. 11.0' - 12.0' 12.0' 11.0' — 1.0' 1.0' Limestone, Limestone, brown—gray, brown-gray, Line—grained, fine-grained, thick-bedded. thick-bedded. Spechts Ferry Shale Shale Member Member (9.0 (9.0 feet) feet) 11.0' 10.2' —- 11.0' 0.8' Shale, Shale, orange—gray, orange-gray, calcareous, calcareous, and and limestone, limestone, tan— tangray, gray; fine—grained, fine-grained, limestone limestone 0.4' 0.4' to to 0.7' 0.7' from from base of of unit. unit. 9.6' —- 10.2' 9.6' 0.6' Limestone, gray, gray, fine—grained, fine-grained, thin-bedded. thin-bedded. 6.4' 6.4' —- 9.6' 9.6' 3.2' 3.2' Shale, Shale, gray, gray, green, green, brown, brown, fissle, fissle, some some beds beds fossi— fossiliferous, limestone limestone present as thin lenses near liferous, middle of of the the interval. interval. 5.6' 5.6' —- 6.4' 08' 0.8' Limestone, Limestone, tan, tan, with iron iron oxide mottlings, finefinegrained, thin—bedded. thin-bedded. 3.9' 3.9' —- 5.6' 5.6' 1.7' Shale, gray-green—brown. gray-green-brown. Fissle, with with thin thin lenses lenses Shale, of gray fine-grained fine—grained limestone. of limestone. 3.2' 3.2' —- 3.9' 0.7' Limestone, Limestone, dark to light gray, gray, thin-bedded, thin-bedded, fossilfossilif erous. iferous. 2.7' —- 3.2' 2.7' 3.2' 0.5' Shale, Shale, brown—green-orange—gray, brown-green-orange-gray, brown carbonaceous carbonaceous shale parting at top, top, metabentonite metabentonite near near middle. middle. 2.2' —- 2.7' 2.2' 2.7' 0.5' Limestone, Limestone, purplish-brown, purplish-brown, fine-grained, fine-grained, thin— thinbedded, bedded, very fossiliferous, fossiliferous, fucoids at at base. 2.2' 2.0' —- 2.2' 2.0' 0.2' Metabentonite, orange, Metabentonite, orange, sticky when wet, wet, with with brown brown shale partings. Platteville Formation Quimbys Mill Member Member (1.2 (1.2 feet) feet) 2.0' 0.8' — 0.8' - 2.0' 1.2' Limestone, purplish gray-brown, gray-brown, sublithographic, Limestone, sUblithographic, thick—bedded, conchoidal fracture, fracture, irregular upper thick-bedded, surface, shale at surface, at base. base. 35 �McGregor Limestone Limestone Member Member (0.8 (O8 feet) feet) 0.' -- 0.8' 0.8' 0.' 0.8' O8' Limestone, purplish gray-brown, medium— Limestone, gray-brown, fine—to fine-to mediumgrained, thick-bedded. grained, thick-bedded. Spechts Ferry and Metabentonite beds beds are Significance: The Spechts are not present everywhere. In addition, addition, in in the the district district mineralization mineralization it it quite quite often often occurs occurs In where the the Spechts Spechts Ferry Ferry is is thickest0 thickest. could one one account account for for the the local absence of of the How could local absence the Spechts Ferry Member? one account for for the the thickening of of the The metabentonite beds? How could one Spechts Ferry Shale coincident coincident with mineralization? for Spechts for the location and mineralization minerali'zation of "pitch—and—flat" "pi tch-and-flat" structures? References: Cline et al,, Wiliman, 1963; al., 1956; 1956; Templeton and Willman, 1963; Kruse, Kruse, 1970. 1970. 36 �Title: Title: St. John John Mine Mine (Snake (Snake Cave) Cave) St. Location: Opening Opening is is in in valley valley wall wall on on the the north north side side of of State State Highway Highway 133 133 Location: about about 0.2 0.2 miles miles south south of of intersection intersection of of County County Highway Highway "0" "0" and and State State Highway in Potosi Potosi in in the the swi, SW, NW, SW, Highway 133 133 in swi,Sec. Sec.34, 34,T.T.3 3N., N., R.R. 2 2 E,, E., Grant County County (Potosi (Potosi 7.5—minute 7.S-minute topographic topographic quadrangle, quadrangle, 1972), 1972). Grant NW!, M. G. G. Mudrey, Mudrey, Jr., Jr., (Modified St. John Mine brochure, Author: M. (Modified from St. brochure, L.C. L.C. Ihm, Ibm, owner, 1966). owner, and and Whitlow Whitlow and West, West, 1966). This mine mine is is aa natural natural cave cave that that was was extensively exploited for Description: Description: This By 1843, 1843, it it had had yielded yielded 2S0,000 250,000 pounds of lead, lead 1870. By lead. The lead prior to 1870, Potosi sub-district sub—district produced produced 21,300 21,300 tons tons of of 80 percent lead from 1862 to Potosi to 1876, 1876. The vein strikes Galena joints. The Galena occurs occurs in in gash gash veins veins and and openings openings along minor joints, N. its length and N. 6So 65° W., W., and and is is noted noted for for its and continuity. continuity. Host rock rock is is Ordovician Ordovician Galena Dolomite, Dolomite, with Maquoketa Shale on the Host the ridge ridge to the west. 37 37 �The floor floor of of the the cave cave is is in the Dunleith Member (cherty The (cherty lower iower unit) unit) of of the Galena Dolomite. In most most outcrops, outcrops, it it is is aa pale-yellowish-brown pale—yellowish-brown to the Galena In light-olive—gray and and grayish-orange finefine- to medium~grained medium—grained vuggy light-olive-gray vuggy fossiliferous fossiliferous dolomite containing abundant chert as nodules or or as as nearly nearly continuous continuous layers. layers. Chert in the Dunleith Member is nodular and and distributed parallel parallel to to the the bedding. bedding. Near mineralized mineralized zones zones chert is Near is selectively mineralized and contains microscopic microscopic grains of of disseminated disseminated iron iron sulfide sulfide that that color color it it bluish bluish gray gray and and locally locally very very grains dark gray. gray. The top of the cherty unit is is marked by by two two discontinuous discontinuous layers layers of of chert chert odulea separated from the main cherty section by 6—9 feet of non—cherty odulesnseparated section by 6-9 feet of non-cherty dolomite., dolomite. The roof of the cave is in in the Wise Lake Member (non—cherty (non-cherty upper upper unit) unit) of the Galena Dolomite. The strata of the non-cherty unit are pale—yellowish— of The of pale-yellowishbrown to yellowish— yellowish- and grayish-orange fine—grained fine-grained porous porous fossiliferous fossiliferous dolomite. The minerals minerals of of the zinc and and lead lead deposits deposits in in the the Potosi Potosi quadrangle quadrangle are are the zinc mostly simple suif ides, carbonates, and sulfates, simple sulfides, carbonates, sulfates. The primary sulfide sulfide minerals are sphalerite, sphalerite, galena, galena, pyrite, pyrite, marcasite, marcasite, chalcopyrite, chalcopyrite, and and digenite. digenite. Galena is fairly fairly stable and persists the others others are are commonly is persists above above the the water water table.; table.; the altered. These include smithsonite, smithsonite, cerussite, limonite, limonite, melanterite, melanterite, malachite, malachite, azurite, azurite, and erythrite, erythrite. Mine, originally a natural cave, History: St. St. John Mine, cave, was first first named named LaSalle LaSalle Cave, de La Salle, Salle, an an early early French French explorer explorer in in Cave, after Robert Cavelier Sieur de North America, America, who traveled with his company on on an an expedition expedition through through the the upper upper Mississippi River Valley Valley in in 1679 1679 and and again again in in 1687 1687 after after King King Louis Louis XIV XIV names names him Viceroy of North North America. LaSalle is is the man who claimed and and named named" Louisiana Province Province for for the the French French king. king. St. John Min~ Mine was worked by the St. the Indians Indians many years years before before white white pioneers pioneers arrived in the the 1827 1827 "lead "lead rush". rush". Drifts of of the the old old mine follow follow the the natural natural crevices filled with with stalactites. stalactites. The foxes who used used it it for for dens dens are are said said to to have have uncovered uncovered the the rich rich lead lead deposits near near the the entrance entrance by by digging digging and and running running in in and and out out the the natural natural cave cave crevice. The Indians mined galena for barter but but it it was left left to to the the white white men to to extensively develop develop these these diggings, diggings. The first white man John Mine man known known to to have have worked worked St. St. ·John Mine and and who who gave gave it it the the name it still bears was Willis St. St. John, John, who made aa small small fortune fortune from from this this mine between between 1828 1828 and and 1870. 1870. In the Upper Mississippi Valley, valley, lead lead seems seems to to have have been been discovered discovered about about noted in in 1700 1700 by by LeSueur, LeSueur, who who 1692 by Nicholas Nicholas Perrott. Perrott. This metal was als,o als.o noted took lead out of a place which we believe from the the description description must must have have been been Snake Hollow, Hollow, now now Potosi, Potosi, Wisconsin, Wisconsin. In 1766 John Carver brought to to St. Louis Louis aa 500 pound hunk of lead lead he had received from barter barter with with the the Indians Indians who who mined mined a a cave on the eastern Mississippi bank somewhere somewhere between between the the mouth mouth of of the the Grant Grant and Platte Platte Rivers. Rivers. This 500 pound pound piece of lead lead may have have been been taken taken from from St. St. John Mine, Mine, which which points points to to the the importance importance St. St. John John Mine Mine played played in in bringing bringing settlers to to the the lead lead region. region. 38 38 �With With the the arrival arrival of of permanent permanent settlers settlers in in 1825, 1825, the the Winnebago Peace Treaty and and "lead "lead rush rush of of 1827", 1827", the the convening convening of of the the first first Wisconsin Wisconsin Territorial Territorial Legislature in in 1836, 1836, Potosi Potosi and and its its suburbs suburbs (La (La Fayette, Fayette, Van Van Buren, Buren, Dutch Dutch Hollow, Hollow, British Hollow, Hollow, Buena Buena Vista, Vista, and and Rockville) Rockville) flourished. flourished. Potosi Potosi in in 1838 1838 was was British hoping hoping to to become become the the capital capital of of Wisconsin; first first state state capitol capitol was was Belmont, Belmont, but Madison Madison won won out. out. The The Mexican Mexican War War of of 1847; 1847; the the Gold Gold Rush Rush of of '49 '49 and and the the but cholera cholera epidemic epidemic in in 1854 1854 depleted depleted its its citizens citizens for for aa few few years; years; but but by by 1859 1859 when the the Civil War broke broke out, out, production production of of lead, lead, and and with with it it the the growth growth of of the the village of of Potosi, Potosi, was was on on an an upswing. upswing. village Well Well over over two—thirds two-thirds of of all all lead lead for the the North was supplied during the . Civil War by by the the Galena, Galena, Benton, Benton, New New Diggings, Diggings, Shullsburg, Shullsburg, Mineral Mineral Point Point and and mines. The The remainder remainder was was furnished furnished by by mining mining towns towns called called Platteville, Platteville, Potosi mines. Hardscrabble, Hardscrabble, Yuba, Yuba, and and Meeker's Grove, Grove, all all in in the the southwestern southwes~ern Wisconsin Wisconsin zinc-lead region. region. zinc—lead W. S., References: Whitlow, Whitlow, J. J. W., W., and and West, west, W. S., 1966, 1966, Geology of the Potosi References: quadrangle, Grant Wisconsin, and Dubuque County, Grant County, Count~ Wisconsin, County, Iowa: Iowa: U.S. Geol. Geo!. Bull. 1123—I, 1123-1, p. p. 533—571. 533-571. Survey Bull, Heyl, Heyl, A. A. V., V., Jr., Jr., Agnew, Agnew, A. A. F., Lyons, Lyons, E. E. J., J., and and Behre, Behre, C. C. H., H., Jr., Jr., 1959, Zinc-Lead District: U.S. 1959, The The Geology of of the Upper Mississippi Valley Zinc—Lead Geol. Survey Survey Prof. Prof. Paper P~per 309, 309, 310 310 p. p. Geol. Ibm, L. undated, St. Brochure, Potosi, Wisconsin. Ihm, L. C., C., undated, St. John Mine Brochure, It N I Flowstone ST. MINE MAP ST. JOHN JOHN MINE Grant County, County, WI. WI. March, March, 1967 By By Norm Norm Frater, Frater, Mike Mike Wopat, Dome to Surface and Priscilla Wilson Wilson and Priscilla Length, Length, 1050 1050 ft. ft. o0 , 25 I 50 50 I 39 39 500-3J8T026-78 500-3J8T026-78 � https://digitalcollections.lakeheadu.ca/files/original/84e51458c8021c67351733b42c3176a9.pdf 9836a92afb4f6a9e8da7322e3a3cdf9c PDF Text Text LU~ UN IVERSITY OF UNIVERSITY OFWWISCONSIN-EXTENSION IS CO NS IN -E XT EN SI ON GE OL OG IC AL AN D NA GEOLOGICAL AND NATURAL HISTORY SURVEY TU RA L HI ST OR Y SU RV EY M er ed ith E. Os tro m I St Meredith E. Ostrom, State and Director at e Geologist Ge ol og ist an d Di re ct or PRECAMBRIAN INLIERS PRECAMBRIAN INliERS IN IN SOUTH-CENTRAL W SOUTH—CENTRAL WISCONSIN ISCONSIN Prepared Pr ep ar ed for: fo r: TW EN TY -F OU RT ANNUAL MEETING TWENTY-FOURTH H AN NU AL ME ET IN G IN ST IT UT E ON ON LAKE INSTITUTE LA KE SUPERIOR SU PE RI OR GEOLOGY GE OL OG Y UN IV ER SI TY OF UNIVERSITY OF WISCONSIN-MILWAUKEE W IS CO NS IN -M IL W AU KE E MI LW AU KE E, WISCONSIN MILWAUKEE, W iS CO NS IN M AY9—14, MAY 1978 9_ 14 ,1 97 8 FI ELD TR IP FIELD TRIP GU ID E BO OK GUIDE BOOK NU M BE R 22 NUMBER 19 78 1978 �Field Trip Trip Guide Guide Book Book Number Number 22 University of Wisconsin-Extension Wisconsin—Extension GEOLOGICAL GEOLOGICAL AND AND NATURAL NATURAL HISTORY HISTORY SURVEY SURVEY Meredith E. Ostrom, Ostrom, State Geologist Geologist and and Director Director PRECAMBRIAN PRECAMBRIAN INLIERS INLIERS IN IN SOUTH-CENTRAL SOUTH-CENTRAL WISCONSIN WISCONSIN (companion volume volume to Geoscience Wisconsin Wisconsin Volume Volume 2) 2) With With contributions contributions by by Rachel K. A. Paull, K. Paull, Paull, Richard A. Paull, and Eugene I. I. Smith Edited by by Eugene I. I. Smith, Smith, University of Wisconsin-Parkside of of Wisconsin-Milwaukee A. Paull, Paull,University University Wisconsin-Milwaukee Richard A. G. Mudrey, Mudrey, Jr., Jr., Geological and Natural History Survey M. G. for Prepared for Twenty—Fourth Twenty-Fourth Annual Meeting INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY University of Wisconsin, Milwaukee Milwaukee Milwaukee, Milwaukee, Wisconsin May 9—14, 9-14:, 1978 A. Paull, Paull, Chairman, Chairman, Field Trip Committee Richard A. University of Wisconsin—Milwaukee Wisconsin-Milwaukee Available from the Wisconsin Geological and Natural History Survey, Survey, of Wisconsin—Extension, 1815 University University Avenue, University of Wisconsin-Extension, 1815 Avenue, Madison, Madison, Wisconsin 53706 1978 �CONTE NrS CONTENTS Page Page INTRODUCTION by Eugene I. I. Smith Smith. • • • • • • • • • • • • • • • • • • • • • 11 FRIDAY, FRIDAY, MAY MAY 12, 12, 1978 1978 Geologic Geologic Road Road Log Log for for U.S. U.S. 41 41 from from the the Intersection Intersection of of Wisconsin Wisconsin 74 74 Menomonee Menomonee Falls Falls at at the the North North Edge Edge of of Waukesha Waukesha County County to to Oshkosh, Oshkosh, Wisconsin Wisconsin (junction (junction Wisconsin Wisconsin 21) 21) by by Richard Richard A. A. Paull Paull and and Rachel Rachel K. Paull Paull K • . . . . . . . . • • • . . • • . . • . . . . . 5 . SATURDAY, MAY 13, 13, 1978 1978 SATURDAY, to Precambrian Rhyolite and and Geologic Road Log for aa Field Excursion to Granite Inliers Inliers of South—Central South-Central Wisconsin by Rachel K. K. Paull Paull A. Paull • • • • • • • • • • • • • and Richard A. 11 11 GEOLOGICAL STOP STOP DESCRIPTIONS by Eugene I. I. Smith Stop 11 —- Granite Granite at Flynn's Quarry Quarry County Park. Park • • • Stop Stop 2 —- Rhyolite Rhyolite at Observatory Hill Stop 33 —- Rhyolite at Marcellon Marcellon.• • • • • Stop 4 -- Rhyolite at Marquette • • • • • . . • . • • • . •• Supplemental Stop —- Rhyolite • Rhyolite at Ingall's Knob • Stop 5 —- Quartzite Portland. Quartzite at Portland . • . 33 49 49 57 68 76 83 88 REFERENCES REFERENCESCITED. CITED. • •• . . ILLUSTRATIONS Figure 1. 1. Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 2. 2. 3. 3. 4. 4. 5. 5. 6. 6. 7. 7. 8. 8. 9. 9. 10. 10. 11. 11. 12. 12. 13. 13. 14. 14. 15. 15. Figure Figure Figure Figure Figure Figure Figure Figure 16. 16. 17. 17. 18. 18. 19. for the Lake Superior Institute field Route for field trip to the south— southcentral Wisconsin Precambrian rhyolite and granite inliers •. • Flynn's Quarry County Park • • compass map of of Flynn's Pace and compass Contact between granite porphyry dike and granite • • • Metabasalt dike cutting cutting granite. granite. • • • • • • • • • Route map from Redgranite to to Montello. Montello. ~ • •. •. • . . • • . Elemental concentrations for for rhyolite rhyolite groupings groupings • • • Geologic map of Observatory Observatory Hill Hill • •. • • • • • • • • sandstone outcrops on Observatory Hill. Cambrian sandstone Hill. • . . . • • in Cambrian Cambrian sandstone Conglomerate in sandstone • • • • • • • • • • . . . Contact between rhyolite dike and rhyolite • of contact of Close-up of rhyolite dike and and rhyolite. rhyolite. Close—up of • Route map for for traverses on the Marcellon exposures • • • • • Geologic map map of of the the Marcellon Marcellon inlier inlier • • • • • • • Geologic Photomicrograph of of Marcellon Marcellon rhyolite rhyolite ash-flow ash—flow tuff tuff • • • • • • • Photomicrograph Stratigraphic variation in in elemental elemental concentrations concentrations for for Stratigraphic the Marcellon Marcellon rhyolite rhyolite • • • • • • • • • • • • • • • • • • the • • . •. •• . .. Weathered spherulites in the Marcellon rhyolite. rhyolite • • of spherulitic spherulitic texture texture in Marcellon Marcellon rhyolite Photomicrograph of of spheroid spheroid with with concentric concentric bands bands • • • • • Photomicrograph of Photomicrograph of of spheroid spheroid with with aa core core of of coarse coarse quartz quartz Photomicrograph and epidote. and • . . . . . . • • . • . . • . • . . . • . . . epidote. • •. • . • . . • • i1 22 32 32 33 35 35 36 37 48 49 49 50 50 53 53 56 56 58 58 59 59 59 59 60 62 62 62 63 63 �Page Figure 20. 20. Pumice Pumice and and shard shard fragments fragments in Marcellon Marcellon rhyolite rhyolite • • Figure Figure 21. 21. Lineation formed formed by by stretched stretched pumice pumice in in the the Tertiary A. A. L. L. Figure Tuff, San San Mateo Mateo Mountains, Mountains, New New Mexico Mexico • • . • . • Peak Tuff, . ••••••• Figure 22. 22. Folds in the Marcellon rhyolite rhyolite. • • • • • • • • • • • ••• Figure 23. 23. Sketches Sketches of of folds folds in the the Marcellon Marcellon rhyolite rhyolite• • • • • • . • . •. • Figure Figure 24. 24. Route Route map map for for traverses traverses at at the the Marquette Marquette exposures exposures • •. •. •. • Figure Figure 25. 25. Geologic map of the Marquette inlier • • • • • • • • Figure 26. 26. Rb/Sr-Na Rb/Sr—Na20/K20 plot for for Marquette Marquette rhyolite rhyolite • • • . • . . • Figure 0/K 0 plot 2 2 Figure 27. 27. Photomicrograph Photomicrograph of of shards shards in in Marquette Marquette rhyolite rhyolite • • Figure . Figure 28. 28. Photomicrograph of shards in Marquette rhyolite. rhyolite • • • • • • • Figure 29. 29. Sketch map of breccia on Ingall's Ingall's Knob • • . . ••• Figure 30. 30. Detailed map of of the Portland quartzite quarries. quarries • • . . . . . . . Figure 31. 31. Photomicrograph of of the Waterloo Quartzite • • • • • Figure 32. 32. Detailed route map through the Waterloo Quartzite area area. Figure 33. 33. View of phyllite layer in quartzite quartzite. • • • • • ••• Close—up of foliated Figure 34. 34. Close-up foliated Waterloo Quartzite • • • • • • • •. . . . . 65 65 66 67 68 6969 70 76 77 79 82 84 85 87 87 TABLES TABLES Table 1. Table 1. for Central Wisconsin inliers and igneous Chemical analyses analyses for rocks in in the the Baraboo area area. • • • • • • • • • • • • • • • • • 39 �INTRODUCT ION INTRODUCTION Eugene I. Smith1l Eugene I. Smith v years very little attention has has been paid to the For the the past seventy years At the well known igneous rock in in the the Fox Fox River River Valley. Valley. At the turn of the the century well geologists Chamberlin, Weidman. Weidman. Leith and Hobbs described geologists such as as Irving, Irving, Chamberlin, and Hobbs these isolated these isolated exposures of Precambrian rock. rock. Between 1907 and 1972 few The last geological studies studies were were initiated. initiated. The last major field field trip to visit these was conducted by A. A. Leith in 1935 for Precambrian rocks rocks was for the the Kansas Kansas Geological While the will be be shown to you on this Society. While the geology that that will this Lake Superior Institute field trip is based for Institute field for the the most part part on on geological geological studies studies comcom1972, descriptions descriptions of the Hill rhyolite pleted since 1972, the Observatory Hill rhyolite and and the Waterloo This field trip Waterloo Quartzite Quartzite rely rely considerably considerably on on the the earlier earlier work. work. This trip is intended intended to to introduce introduce you you to to the the rock rock types types and and the the rock rock fabric fabric formed formed is post—Penokean igneous event (1765 m.y. ago) ago) and during a a major post-Penokean igneous event (1765 m.y. and to demonstrate the structural structural style of a post—Penokian The the post-Penokian deformation deformation (1650 (1650 m.y. m.y. ago?). ago?). field trip stops oldest to youngest field stops are are arranged arranged in stratigraphic stratigraphic order from from oldest youngest (fig. 1). 1). Since the the exposures are are on on the the flank flank of of the the Wisconsin Wisconsin Arch, Arch, (fig. travelling to the travelling the southeast off the the crest of of the the arch arch conveniently conveniently exposes exposes younger units. units. Here fine—grained The first first stop is is at at the the Flynn's Granite Granite Quarry. Quarry. Here fine-grained granophyric granite is is cut cut by by granite granite porphyry porphyry and and metabasalt metabasalt dikes. dikes. The granite probably is the equivalent of of the rhyolites to be the subvolcanic subvolcanic equivalent the rhyolites 3, and viewed at at stops stops 2, 2, 3, and 4. 4. Hill (stop by a sequence of of steeply dipping Observatory Hill (stop 2) 2) is is formed formed by a sequence porphyritic rhyolite which erupted erupted from from source source chambers chambers now porphyritic rhyolite ash—flow ash-flow tuffs tuffs which represented by granite cropping out to represented to the the northwest northwest (Flynn's (Flynn's Quarry, Quarry, The rhyolite rhyolite is cut by by finefine— and coarse—grained Montello and and Redgranite). Redgranite). The is cut and coarse-grained rhyolite dikes and and is is surrounded surrounded by by exposures exposures of of Cambrian Cambrian sandstone. sandstone. Stops 33 and Marcellon and and Marquette Marquette rhyolites) rhyolites) display the fabric Stops and 44 (The (The Marcellon the fabric and and mineralogy of the the texturally texturally variable variable rhyolites. rhyolites. In In the the volcanic volcanic section sparsely-porphyritic sparsely—porphyritic plagioclase-bearing plagioclase—bearing rhyolite rhyolite commonly alternates alternates with with quartz, plagioclase, porphyritic quartz, plagioclase, alkali alkali feldspar feldspar rhyolite. rhyolite. The rocks rocks show show fabrics common common to ash-flow ash—flow tuffs have undergone undergone compaction, compaction, welding welding and and fabrics tuffs that that have late—stage primary laminar flowage (eutaxitic and spheruloidal spheruloidal textures late-stage laminar flowage (eutaxitic and textures and and large flow folds). folds). The Waterloo Quartzite Quartzite (stop 5), the youngest exposed exposed Precambrian Precambrian rock The (stop 5), the youngest in south-central south—central Wisconsin, Wisconsin, is is folded folded into into a broad eastward eastward plunging synsyn— a broad dine. The The nose nose of of the structure lies lies in the Portland Portland area area near near the quarry cline. the structure in the the quarry visited during Stop stop 5. 5. 1'Division Division of of Science, Science, University University of of Wisconsin—Parkside, Wisconsin-Parkside, Kenosha, Kenosha, Wisconsin Wisconsin 53141 53141 1 1 �Red granite Redgranite S TO p'1)!e!.---.oE::-----I CD Flynn's Quarry County Park STOP Du Lac @) Marquette Rhyolife Rhyolite Hill Marcellon R hy o life / z C, Waterloo Quart zite I \ '::')"""----~+--~I Mllwaukee\ o o 0 10 20 30 30 C-) w uJ ~ <t -J ...J 40 MIles 40 Miles SCALE Figure 1. 1. Route for the Lake Lake Superior Superior Institute the south— Route for the Institute field field trip to to the southcentral Wisconsin Precambrian rhyolite and granite inliers. central rhyolite and granite inliers. 2 �I thank Pattie Pattie Fields-Troha Fields—Troha for for typing typing draft draft copies copies of I thank of these these stop descriptions and Jill Ann Hartnell for for drafting drafting the the figures. figures. Diane Pyper made many useful editorial corrections corrections that that helped helped smooth smooth out out the rough spots. many useful editorial spots. also thank thank Frank Frank Luthur Luthur (University (University of of Wisconsin-Whitewater) Wisconsin—Whitewater) for for an an II also informative discussion on on the the metamorphic metamorphic rocks rocks from from Waterloo. Waterloo. Participants on this trip will traverse Participants trip will traverse the the scenic, scenic, glaciated countryside side of southeastern and and south—central south-central Wisconsin to study isolated exposures of Precambrian granite, granite, rhyolite, quartzite that rhyolite, and and quartzite that project through a cover of Paleozoic rocks of rocks and Pleistocene drift (Fig. (Fig. 1). 1). Board bus at 6:30 P.M. P.M. sharp on Friday May 12, 12, 1978 in in the front of the the Pfister Hotel (Headquarters (Headquarters for for the the 24th 24th Annual Annual Lake Lake Superior Superior Institute). Institute). of travel will follow U.S. Our route route of travel will U.S. 41 41 to to Oshkosh, Oshkosh, Wisconsin. Wisconsin. A A geological roadguide for for this this part part of of the the trip trip is is provided. provided. Overnight accommodations accommodations will will be at at the Pioneer Inn, Inn, on the west shore of Lake Winnebago in in Oshkosh 8:00 trip This 6:30 On Saturday Saturday May May 13, 13, 1978, 1978, board board the the bus bus in front of of the the Pioneer Pioneer at at On in front A.M. A.M. sharp. sharp. The guidebook includes includes a a geologic roadguide for the field field route, route, as well as as detailed information information on on each each of of the the geologic geologic stops. stops. field field excursion will terminate at the Pfister Hotel in in Milwaukee about about P.M. P.M. A companion volume to this Geoscience Wisconsin Volume 2, 2, contains papers papers by Smith (1978c), Van Schmus (1978) (1978c), Van (1978) and Haimson (1978) (1978) on the the geology, geology, ages, ages, and and engineering properties of of the the granites, granites, rhyolites rhyolites and and quartzites. quartzites. 3 �Friday, Friday, May May 12, 12, 1978 1978 Geologic Geologic Road Road Log Log for for U. S. S. 41 41 from from the the Intersection Intersection of of Wisconsin Wisconsin 74 74 Menomonee Menomonee Falls Falls at at the the North North Edge Edge of of Waukesha Waukesha County County to to Oshkosh, Oshkosh, Wisconsin Wisconsin (junction (junction Wisconsin Wisconsin 21) 21) 1 2 Richard Richard A. A. Paull1 Paull and and Rachel Rachel K. K. Paull2 Paull U. U. S. S. 41 41 trends trends north—northwesterly north-northwesterly through through the the glaciated glaciated Eastern Eastern Ridges Ridges and Lowlands Lowlands Province Province of of Wisconsin. Wisconsin. The The orientation of this this route route is is such such and that that it it cuts cuts obliquely obliquely across across the the strike strike of of the the Paleozoic Paleozoic formations. formations. From From south—southeast south-southeast to to the the north—northwest, north-northwest, these these units units include include Silurian Silurian dolomite, dolomite, Tipper Ordovician Maquoketa Maquoketa Shale, Shale, and and the Middle Ordovician Upper Ordovician Ordovician Platteville— PlattevilleGalena formations. formations. However, However, the the bedrock bedrock along along the the highway highway is is largely largely obobGalena scured scured by by Wisconsinan (Woodfordian (Woodfordian and and the the younger younger Valderan) Valderan) glacial glacial deposits. deposits. exception exists exists along along the the crest crest of of the the prominent prominent Niagaran Niagaran (Silurian) (Silurian) An exception escarpment, where where glacial glacial deposits deposits are are thin. thin. escarpment, Included Woodfordian glacial glacial features features are are well—displayed well-displayed along along U. U. S. S. 41. 41. Included are a a recessional moraine related to retreat of the Lake Michigan lobe, lobe, kames kames and kettles kettles associated with the spectacular Kettle Interlobate Interlobate Moraine, Moraine, and and well—formed well-formed drumlins drumlins within the area occupied by the the Green Bay lobe. lobe. Deposits Deposits that accumulated accumulated in in Glacial Glacial Lake Lake Oshkosh Oshkosh when when retreat retreat of of the that the last last Wisconsinan (Valderan) ice ice tongue tongue blocked northeastward drainage (Valderan) drainage into into Green Green Bay Bay are are also also traversed. Details on the the geology geology encountered encountered along along U. U. S. S. 41 are provided provided in the Details 41 are the geologic road log that that follows. follows. We hope this this will help to make your your enjoyable. Mileages in in the the road road log log are are cumulative, cumulative, with journey more enjoyable. mileage increments between each each entry entry included included in in brackets. brackets. Mileages o 0 (2.0) (2.0) Con— 74 exit exit from U. U. S. S. 41 Wisconsin 74 41 to to downtown Menomonee Falls. Falls. Continue northwest on U. U. S. S. 41 Oshkosh, the tinue northwest 41 and and 45 toward toward Oshkosh, the location of tt our "watering our watering hole" hole " for for this this evening. evening. Lime Kiln Village Village Park is mile west west in the Lime is about about one mile the heart heart of Here, the the business business district district of Menomonee Falls. the Falls. Here, the Silurian Dolomite dolomite forms a small falls on the dolomite forms a small falls the Menomonee River. River. was quarried here for lime production as early as the 1850's, was quarried for lime as as the 1850's, and Glacial three historic historic kilns three kilns are preserved within the the park. park. striae on on the the Silurian bedrock in striae in the the vicinity vicinity of of the the kilns kilns establish an an east-west east—west flow flow direction direction for for advance advance of of the the Lake Lake establish Michigan glacial glacial lobe during the Michigan the Woodfordian. 2.0 2.0 (5.0) (5.0) Enter Washington Washington county county in an Waukesha/Washington county line. Waukesha/Washington line. Enter area of of foIling folling countryside, countryside, on on the the northwestern northwestern edge edge of of the the intensely intensely area lThe 1The University University of of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin University of of Wisconsin-Madison, Wisconsin—Madison, Madison, 22The The University Madison, Wisconsin; Wisconsin; and and Alverno Alverno College, College, Milwaukee, Milwaukee, Wisconsin Wisconsin 55 �Mileages Mileages urbanized, greater greater Milwaukee Milwaukee area. area. This urbanized, This region region was was last last glaciated glaciated during the the Woodfordian Woodfordian by by the the advance advance of of the the Lake during Michigan Lake Michigan lobe. lobe. The outermost outermost (oldest) (oldest) of of a a series series of of three, three, major major ridgeridge— The forming recessional recessional moraines moraines (Lake Border Moraines), Moraines), which forming (Lake Border which parallel parallel the shore of Lake Michigan in the Milwaukee the shore of Lake Michigan in the Milwaukee area, area, trends trends through through this area. area. this To the the west, west, one one catches catches glimpses glimpses of of the the irregular irregular hills To hills of of the the Woodfordian interlobate moraine that developed Woodfordian interlobate moraine that developed between between the the Lake Lake Michigan lobe lobe on on the the east east and and the the Green Green Bay Michigan Bay lobe lobe on the west. This This is the Kettle Interlobate Moraine, which trends is the Kettle Interlobate Moraine, which trends north-northeast from Walworth Walworth County County to to Kewaunee Kewaunee County County to from to form form the the glacial glacial backbone of eastern Wisconsin. bone of eastern Wisconsin. Northwest-trending Northwest—trending u.s. U.s. 41 41 is is on on aa collision course course with with this this prominent prominent topographic topographic feature. collision feature. 7.0 7.0 (1.0) (1. 0) 8.0 8.0 Wisconsin 167 167 (Holy Hill Road) Road) exit; exit; continue continue on Wisconsin (Holy Hill and 45. 45. on u.s. U.S. 41 41 and Holy Hill, aprominentkame topped by Holy Hill, a prominent kame by aa picturesque picturesque church, church, is located about about 77 miles miles west west of of here here within within the the heart of the Kettle located Interlobate Moraine. U.S. u.s. 45 exit exit to to West West Bend; Bend; continue continue north north on U.S. 45 u.s. 41. 41. (4.0) (4.0) 12.0 12.0 (1.0) (1. 0) 13.0 13.0 (lO) (1. 0) 14.0 14.0 (0.4) (0.4) 14.4 14.4 (0.9) (0.9) The highway highway ascends ascends the the eastern eastern edge edge of the the Kettle The Kettle Interlobate Moraine, and leaves the lowland occupied by the Lake Michigan lobe Moraine, during the Woodfordian advance. advance. This This country is is higher and more more irregular,with with kettles kettles and and abundant abundant locally locally derived derived erratics irregular, of erratics of light—colored Silurian light-colored Silurian dolomite. dolomite. Wisconsin 60 exit to Slinger and Hartford within the Kettle Inter— Interlobate Moraine. Moraine .. The Hilltop Restaurant on the west side of the highway is is well well named, named, for for it it occupies occupies the the crest crest of of the the Kettle Kettle Interlobate Interlobate Moraine. Moraine. The The scenic scenic kettle kettle and and kame kame topography topography that that characterizes characterizes this this region region formed formed when the Green Bay and Lake Michigan glacial lobes lobes stagnated stagnated along along their their junction junction during during the the Woodfordian. Woodfordian. As As the the ice ice at at the the melting edges edges of of these these juxtaposed juxtaposed lobes lobes began began to to thin, thin, sedimentsedimentladen meltwater meltwater •flowed flowed down in the the ice ice to to provide provide laden down cracks cracks and holes in aa source source for for subglacial subglacial streams. streams. Meltwater Meltwater also also cascaded cascaded over over the the ice ice surface surface into into the the widening abyss abyss between the the tongues. tongues. Here, Here, large large chunks chunks of of ice ice were buried in in the the outwash outwash sands sands and and gravels. gravels. The The resulting resulting maze maze of of crevasse crevasse fills, fills, moulin moulin kames, kames, eskers, eskers, outwash outwash fans, fans, and and kettles kettles is is superimposed superimposed on on aa dual dual complex complex of of ridges ridges which which had had previously previously formed formed as as lateral lateral moraines. moraines. Little Switzerland Switzerland Ski Ski Hill, Hill, to to the the west west of of the the highway highway at at the the edge edge Little of of Slinger, Slinger, utilizes utilizes aa prominent prominent moulin moulin kame. kame. The The internal internal makeup makeup of of aa similar similar kame kame is is revealed revealed in in an an abandoned abandoned sand sand and and gravel gravel operation operation about about 0.1 0.1 mile mile north north of of the the ski ski hill. hill. The The gravel gravel in in this this kame kame is is well—stratified, well-stratified, and and it it includes includes an an abundance abundance of of lightlightcolored Silurian Silurian dolomite dolomite cobbles cobbles and and aa few few large large boulders. boulders. Other Other colored well-formed well-formed kames kames are are present present east east of of the the highway. highway. 66 �Mileages Mileages 15.3 15.3 Junction Junction U.S. u.s. 41 41 and and Wisconsin Wisconsin 144. 144. Continue Continue north north on on U.S. u.s. 41. 41. (1.7) (1.7) 17.0 17.0 (0.8) (0.8) 17.8 17.8 (3.5) (3.5) Junction Junction U.S. u.s. 41 41 and and County County K. K. The The highway highway descends descends from from the the Interlobate Interlobate Moraine toward toward the the lowland lowland area area occupied occupied by by the the Green Green Bay lobe lobe during during the the Woodfordian Woodfordian ice ice advance. advance. Bay The sand sand and and gravel gravel pit pit west of of the the highway highway is is on on the the northnorthwestern western edge edge of of the the Kettle Kettle Interlobate Interlobate Moraine. Moraine. This This is is one one of of many many such such operations operations that that exploit exploit the the abundant abundant resource resource of of waterwaterwashed washed sand sand and and gravel gravel within within this this unique unique morainal morainal complex. complex. The route poorly—drained ground route ahead ahead traverses traverses gently gently rolling,, rolling, poorly-drained moraine. Tamaracks Tamaracks flourish flourish in in some some of of the the wetter wetter areas. areas. moraine. 21.3 21.3 (1.7) (1.7) 23.0 23.0 Junction Junction U.S. u.s. 41 41 and and Wisconsin 33; 33; continue continue north north on on U.S. u.s. 41. 41. The The route route crosses crosses aa recessional recessional moraine that that formed formed as as the the Woodfordian Woodfordian Green Bay Bay lobe lobe paused paused during during its its retreat. retreat. Green Wayside east east of of the the highway is is in in an an area area of of swampy, swampy, rolling rolling ground ground (4.0) (4.0) moraine. moraine. 27.0 27.0 (2.5) (2.5) This high area provides an excellent overview of scenic, scenic, irregular irregular abundance of of erratics erratics in in the the till till here here is is documented documented countryside. An abundance by by stone stone fences fences that that line line some some fields, fields, and and by by rock rock piles piles in in others. others. 29.5 (0.6) (0.6) u.s. 41 41 and and Wisconsin Wisconsin 28. 28. Junction U.S. 30.1 (1.9) (1.9) county line. line. Enter Dodge County in in an an area area dominated dominated Dodge/Washington county large, well—formed well-formed druinlins. drumlins. Erratics in in fence fence rows rows and and farmyards farmyards by large, the stony stony nature nature of of this this till. till. testify to the 32.0 (0.4) (0.4) Wayside east of of the the highway. highway. 32.4 (1.6) (1.6) Wayside west of of the the highway. highway. 34.0 34.0 (2.4) (2.4) The Junction 67. Continue north on U.S. u.s. 41. 41. The Junction u.s. U.S. 41 and Wisconsin 67. route ahead ahead gradually gradually climbs climbs the the gentle gentle (2°-5°), route (2°-5°), easterly dipslope However, the the bedrock in this of resistant Silurian Silurian dolomite. dolomite. However, of the theresistant region is is covered covered by by aa swarm of broad, broad, low drumlins drumlins that create region aa gently gently rolling landscape. 36.4 36.4 (1.0) (1.0) Junction 49. Junction u.s. U.S. 41 41 and and Wisconsin 49. 37.4 37.4 (1.4) (1.4) Fond line. Fond du du Lac/Dodge Lac/Dodge county line. 38.8 38.8 (0.5) (0.5) highway utilize utilize a Sand and and gravel gravel operations operations on on both both sides sides of of the the highway Sand a local local area area of outwash deposits. 39.3 39.3 (2.7) (2.7) Roadcut on on the the west west side side of of the the highway highway exposes exposes Silurian Silurian dolomite dolomite Roadcut The proximity proximity of of bedrock bedrock to to the the where thin. The where glacial glacial deposits deposits are thin. 77 Continue north north on on U.S. u.s. 41. 41. Continue north north on on U.S. Continue u.s. 41. 41. Enter Fond du du Lac County. Enter County. �Mileages Mileages surface has has facilitated facilitated the the development development of of numerous numerous dolomite quarries surface in this this general area. This rock rock is is an excellent dimension in area. This dimension stone, stone, but most most of it it is is crushed for but for agricultural lime and road building. building. However, some some is is kilned to produce chemical However, chemical lime. lime. This high high point point provides provides aa good good view view of of the the north-northeasterly This trending Kettle Kettle Interlobate Interlobate Moraine Moraine along along the the skyline skyline to to the the east. east. trending A lowland region, nonresistant Middle Middle region, developed on relatively nonresistant and Upper Upper Ordovician rocks, and rocks, lies lies to to the the west. west. 42.0 42.0 (0.6) 42.6 42.6 (2.0) Large Large quarries quarries in in Silurian dolomite are located east and west of U.s. 41. U.S. 41. This is is the the edge of the the Silurian (Niagaran) This (Niagaran) escarpment, escarpment, and it provides a fine view of the Ordovician lowland ahead. provides a fine the ahead. This excarpment (or ment (or cuesta) cuesta) is the the most significant bedrock feature in eastern Wisconsin. It It emerges emerges from from aa thick thick cover cover of of glacial glacial deposits deposits aa few miles miles northeast northeast of of Milwaukee, Milwaukee, and and trends trends north-northeast north—northeast as few as aa prominent cliff along the the east side of Horicon Marsh and Lake Winnebago. From here, here, the the escarpment persists northeastward to form the the rocky rocky spine of the Door Peninsula. It continues across form Lake Michigan as as a Lake a string of bedrock islands before it rises rises as the the rugged Garden Peninsula of of Upper Upper Michigan. Michigan. The route descends toward the Ordovician lowland through route ahead descends through an an area of gently rolling ground moraine. rolling ground moraine. 44.6 44.6 (0.6) The highway in this vicinity crosses the ill—defined The ill-defined terminal terminal moraine of the latest Wisconsinan (Valderan) (Valderan) ice advance of the the Green Bay Bay lobe. The wooded edge of the Silurian escarpment is is visible visible along along the the skyskyline to to the the east. east. 45.2 (1.8) Junction U.S. U.S. 41 and Wisconsin 175 to Fond du Lac, Lac, at at the the south south end end of Lake Winnebago. Winnebago. Continue northwest northwest on on U.S. U.S. 41. 41. Lake Winnebago, Winnebago, with a surface area of 215 215 square square miles and and aa maximum maximum depth depth of of 21 21 feet, feet, is is the the largest largest inland inland lake lake in in Wisconsin. Wisconsin. It sprawls for for 28 28 miles along the west edge of the the Silurian Silurian escarpment, escarpment, and is situated in an area underlain by relatively relatively nonresistant Middle Middle and and Upper Upper Ordovician Ordovician rocks. rocks. This lowland lowland extends extends from from Green Bay southwestward through through Lake Winnebago, Horicon Horicon Marsh, Marsh, and over a a low low drainage divide into into the the broad valley valley now now occupied occupied by by the the Rock Rock River. River. During the the Pleistocene, the the Green Green Bay Bay lobe lobe advanced and and retreated retreated along along this this route route numerous numerous times. times. The ice, ice, in part confined by the the resistant resistant Silurian Silurian escarpment, escarpment, scoured scoured the the Ordovician bedrock and deposited aa variety variety of of glacial glacial landforms. landforms. During northeastward regressions regressions of of the the Woodfordian Woodfordian and and Valderan Valderan glaciers, glaciers, drainage along along the the lowland lowland into into Green Green Bay Bay was temporarily temporarily blocked blocked by by the the retreating retreating wall wall of of ice. ice. A A vast vast lake, lake, termed termed Glacial Glacial Lake Lake Oshkosh, formed impounded behind behind the the youngest youngest formed from from the the meltwaters meltwatersimpounded (Valderan) (Valderan) of of these these icy icy dams. dams. At At this this time, time, the the site site of of Fond Fond du du Lac Lac was was under under 40 40 to to 60 60 feet feet of of water. water. Eventually Eventually Green Green Bay Bay became became ice ice free, free, and Glacial Lake Oshkosh drained into Lake Michigan via via the the 88 �Mileages Mileages Winnebago remnantofofthis this feature, feature, surviving Fox River. River. Lake Lake Winnebago is isa aremnant surviving Fox in a shallow irregularity on the floor floor of of this this ancient ancient water water body. body. in a shallow irregularity on the Cross Cross east east branch branch of of Fond Fond du du Lac Lac River. River. 47.0 47.0 (1.8) (1.8) 48.8 48.8 (4.2) (4.2) Junction Junction U.S. U.S. 41 41 and and U_S. U.S. 151. 151. Continue Continue north north on on U.S. U.S. 41. 41. The The route route ahead ahead traverses traverses aa relatively relatively subdued subdued area area underlain underlain by by sediments sediments deposited deposited in in Glacial Glacial Lake Lake Oshkosh. Oshkosh. Junction U.S. U.S. 41 41 and and Wisconsin Wisconsin 23. 23. Junction Continue Continue northwest northwest on on U.S. U.S. 41. 41. The The wooded wooded Silurian Silurian escarpment escarpment continues continues to to dominate dominate the the horizon horizon to to the east. east. the 53.0 53.0 Wayside Wayside west west of of the the highway, highway, as as U.S. U.S. 41 41 curves curves northward. northward. (4.0) (4.0) 57.0 (1.7) (1.7) 58.7 58.7 (3.2) (3.2) ascends to to reddish, reddish, rolling rolling Valderan Valderan ground ground moraine moraine at at Highway ascends the western western edge edge of of Glacial Glacial Lake Lake Oshkosh. Oshkosh. the Winnebago County Fond du du Lac/Winnebago Lac/Winnebago county county line. line. Enter Enter Winnebago County in in an an area area Fond rolling ground ground moraine. moraine. There is a good view to to the the east east of of the the of rolling Silurian escarpment escarpment along along the the far far shore shore of of Lake Lake Winnebago. Winnebago. The The sediments deposited deposited route from here to Oshkosh traverses reddish sediments Lake Oshkosh. Oshkosh. in Glacial Lake 61.9 61.9 (0.7) (0.7) of the the highway. highway. Wayside east of 62.6 62.6 (2.7) (2.7) U.S. 41 Junction U.S. U.S. 41 and Wisconsin Wisconsin 26. 26. Continue north on U.S. through aa subdued subdued area underlain by flat-lying glacial lake through deposits. 65.3 65.3 (2.9) (2.9) Continue north north Junction U.S. U.S. 41 and Wisconsin 26 26 and and 44 44 to to Oshkosh. Oshkosh. Continue Oshkosh, on on the west shore Winnebago, is on U.S. U.S. 41. 41. Oshkosh, shore of Lake Winnebago, developed on the ancient floor floor of of Glacial Glacial Lake Lake Oshkosh. Oshkosh. 68.2 68.2 The geologic geologic roadguide roadguide for Junction U.S. U.S. 41 and Wisconsin 21. 21. The for intersection, the Precambrian Precambrian inliers inliers field field trip trip begins begins at at this this intersection, the and 21. and continues continues westward on State 21. A PLEASANT PLEASANT EVENING: EVENING HAVE A END - HAVE END OF OF LOG - 99 �__________ __________ Saturday, Saturday, May May 13, 13, 1978 1978 Geologic Geologic Road Road Log Log for for aa Field Field Excursion Excursion to to Precambrian Precambrian Rhyolite Rhyolite and and Granite Granite Inliers Inliers of of South—Central South-Central Wisconsin Wisconsin l 2 Rachel Rachel K. K. Paull' Paull and and Richard Richard A. A. Paull2 Paul1 This This road road log log starts starts at at the the intersection intersection of U. U. S. S. 41 41 and and Wisconsin 21 21 on on the the northwestern northwestern edge edge of of Oshkosh, Oshkosh, Wisconsin, Wisconsin, and and terminates terminates in in Milwaukee, Milwaukee, 'Wisconsin "Wisconsin at at the the junction junction of 1—94 1-94 with 1—43 1-43 (U. (U. S. 141) and and 1—794 1-794 (see (see Fig. i). 1). Fig. The The route route of travel travel on this this trip trip is is due due west from from Oshkosh for for 26 26 miles miles to Redgranite, Redgranite, and then then south—southwest south-southwest nearly nearly to to Portage Portage (Marcellon (Marcellon inlier). inlier). to Since Since we detour to to look look at at two two Precambrian Precambrian inliers, inliers, this this leg leg involves involves about about 50 50 we proceed northeast miles of of travel. travel. From here, here, we northeast to to a a rhyolite inlier near miles Marquette; aa distance distance of of 20 20 miles miles by by road. road. After After aa 5 mile segment segment to to the the east, east, Marquette; our route route trends trends south south for for 40 40 miles. miles. From immediately immediately north north of of Waterloo, Waterloo, our we travel travel eastward eastward for for 7 7 miles miles to to the the Waterloo Waterloo Quartzite, Quartzite, and and then then south south for for we to reach reach Interstate Interstate 94 94 at at Lake Lake Mills. Mills. After aa fast fast 50—mile 50-mile run run to to 8 miles to In all, all, we we will will cover 206 east, we are are back back in in Milwaukee. Milwaukee. 206 miles, miles, make make the east, 5 geologic stops, and even stop stop for for lunch lunch (Fig. (Fig. 1). 1). It will be be aa busy busy day day: 5 geologic stops, This odyssey through east—central east-central Wisconsin traverses traverses parts of two two of However, the four four major physical provinces provinces recognized recognized in in Wisconsin. Wisconsin. However, in in the the the provinces are area the features are area covered covered by by this this field field excursion, excursion, the features of of both both provinces The Eastern Ridges and by young young glacial glacial deposits. deposits. The and Lowlands Lowlands parallels parallels masked by This province province contains contains aa sequence sequence of of generally generally north—south north-south Lake Michigan. This striking, Ordovician Ordovician through through Devonian formations, formations, with with the older rocks striking, the older rocks to to the the Differences in in resistance resistance of of these units result west. Differences these units result in broad, broad, subdued subdued ridges alternating with lower lower areas. areas. The Central Plain is is aa lowland lowland region, region, ridges developed on Upper Upper Cambrian sandstones, sandstones, that west of of the developed that lies lies to to the the west the Eastern Ridges and Lowlands. Lowlands~ Ridges Within the the general region of the the Central Central Plain covered by this this trip, trip, there are are ten localities localities where where Precambrian granite granite and and rhyolite there rhyolite project project through through aa cover cover of of Lower Lower Paleozoic Paleozoic rocks rocks and and unconsolidated unconsolidated Pleistocene Pleistocene The igneous igneous rocks rocks in these inliers deposits. The inliers are dated dated at at 1765 1765 m.y. m.y. old, old, and they they probably probably formed and formed during the waning stages stages of of the the Penokean Penokean orogeny. orogeny. Although Granite inliers inliers lie lie northwest Granite northwest of the the area area where rhyolite rhyolite is is exposed. exposed. Although the field field relations relations are are not not established established at at present, present, the the rhyolite rhyolite and and granite granite the If so, so, the the granite granite is are comagmatic. If is a a subvolcanic are generally generally believed believed to be comagmatic. equivalent of the extrusive rhyolite. equivalent of the rhyolite. After accumulation of of the sequence of of Precambrian quartz After the rhyolite, rhyolite, a a thick sequence After deposition, these sandstone deposited. After deposition, sandstone and and other other sedimentary rocks was deposited. rocks and and the the underlying underlying rhyolite rhyolite were were subjected subjected to to an an intensive intensive episode episode of of rocks Detailed information information on on the the Precambrian Precambrian folding, m.y. ago. ago. Detailed folding, possibly possibly 1650 m.y. history of of this this region region is is provided provided by by Eugene Eugene I. I. Smith Smith in in the the next next section section of of history this this guidebook. guidebook. The five five stops stops on on this this field field excursion excursion provide provide an an opportunity opportunity to to examine examine The However, rhyolite rhyolite each types described above. above. However, each of of the the major major Precambrian rock types receives the the most most emphasis, emphasis, with with three three stops stops devoted devoted to to an an examination examination of of this this receives diverse diverse rock rock type. type. 11 11 1 1University of Wisconsin—Madison, Madison, Madison, Wisconsin; and Alverno College, University of Wisconsin-Madison, Wisconsin; and Alverno College, Milwaukee, Wisconsin Milwaukee, Wisconsin 2University of of Wisconsin-Milwaukee, Wisconsin—Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin 2University �The glacial glacial geology geology of of east-central east—central Wisconsin Wiscctisin is is also also spectacular, spectacular, and and The quite varied. The trip trip begins begins in in an an area area occupied occupied by by the the youngest youngest Wisconsinan Wisconsinan quite varied. The (Vanderan) ice ice advance, advance, and and by by lakes lakes which which formed formed during during the the retreat retreat of of this this (Vanderan) ice. However, However, most most of of the the route route traversed traversed is within the ice. is within the region covered by an older older Wisconsinan Wisconsinan (Woodfordian) an (Woodfordian) advance of of the the Green Green Bay Bay lobe. lobe. Deposits Deposits formed by by this this icy icy tongue tongue include large expanses of formed of glacial glacial lake lake sediments, sediments, recessional moraines moraines related related to to the the retreat retreat of of this this lobe, lobe, outwash outwash sands sands and and recessional gravels, scenic scenic kettle kettle lakes, lakes, and and some some of of the the best best drumlin drumlin swarms swarms in in the the gravels, world. All All of of these these features features combine combine to make make this this region region a glacial showworld. a glacial case, and a most pleasant place to case, a most pleasant,place to spend spend aa field field day. day. We hope hope the the geologic geologic roadguide roadguide that that follows follows makes makes your trip more We enjoyable. Mileages Mileages are are cumulative, cumulative, with with mileage mileage increments enjoyable. increments between each entry provided in in brackets. brackets. Detailed for each stop is Detailed geologic geologic information for provided by Eugene I. provided I. Smith in in the the next next section section of of this this guidebook. guidebook. It It would would be beneficial beneficial if if you you would would read read the the detailed detailed descriptions descriptions of be of each area area before we stop. we stop. Mileages Mileages o0 (2.2) (2.2) Start of of Geologic Geologic Road Road Log Log at at intersection intersection of of V.. S. 41 Start 41 and Wisconsin 21 at the the northwestern edge of of Oshkosh, Oshkosh, Wisconsin. Wisconsin. west on State Highway Proceed west Highway 21. 21. is located located on on the west shore shore of of Lake Lake Winnebago, Winnebago, the largest Oshkosh is the west inland lake in in Wisconsin. This shallow lake lake is is aa remnant remnant of of Glacial Glacial Lake Lake Oshkosh, Oshkosh, a much larger larger Pleistocene water body formed formed when the the retreating retreating Valderan ice blocked northeastward northeastward drainage drainage along Valderan ice blocked along the the Green Bay lowland into into Lake Lake Michigan. Michigan. The route ahead traverses lacustrine lacustrine sediments that that accumulated in in Glacial Glacial Lake Lake Oshkosh. Oshkosh. 2.2 2.2 (2.6) Enter an an area area of of higher, higher, gently gently rolling rolling countryside. countryside. This is ground moraine moraine and is a a Valderan ground and outwash complex that that once stood stood as as an an island island in in Glacial Glacial Lake Lake Oshkosh. Oshkosh. 4.8 4.8 (2.2) (2.2) the flat floor of of Descend from the morainal "island" onto the Glacial Glacial Lake Lake Oshkosh. Oshkosh. Here, Here, the the lake lake sediments sediments are are well-drained to to be be intensively intensively farmed. farmed. sufficiently well—drained 7.0 7.0 (0.7) (0.7) This This subdued subdued ridge ridge is is the the western western edge edge of of the the gentle, gentle, east—dipping, east-dipping, Middle Ordovician Ordovician (Platteville—Galena (Platteville-Galena formations) formations) cuesta. cuesta. The route route ahead ahead descends descends through through the the Ordovician St. St. Peter Peter Sandstone Sandstone onto onto aa relatively relatively Middle Ordovician flat surface surface developed developed on on dolomites dolomites of of the the Lower Lower Ordovician Ordovician flat Prairie Prairie du du Chien Chien Group. Group. However, However, the the bedrock bedrock in in this this area area is is obscured obscured by by glacial glacial deposits. deposits. 7.7 (0.3) Enter Enter Omro Omro on on the the Fox Fox River. River. The The Fox Fox flows flows northeasterly northeasterly to to join the the southeasterly southeasterly flowing flowing Wolf River River drainage drainage in in Lake Lake join Butte Butte des des Morts. Morts. This This shallow shallow lake lake is is another another remnant remnant of of Glacial Glacial Lake Lake Oshkosh, Oshkosh, and and it it drains drains into into Lake Lake Winnebago Winnebago at at Oshkosh. Oshkosh. 12 12 �Mileages Mileages The The Middle Middle Ordovician Ordovician St. St. Peter Peter Sandstone Sandstone is is quarried quarried for for foundry foundry This sand sand a few miles south of here near Waukau. sand a few miles south of here near Waukau. This sand is is trucked trucked to to Berlin Berlin for for processing, processing, but but from from 1870-1878, 1870-1878, the the St. St. Peter Peter in in this this area supplied aa glass factory in Omro. glass factory in Ornro. 8.0 8.0 (0.5) (0.5) The The park park on on the the south south bank bank of of the the Fox Fox River River represents represents Unfortunately, use use of of the the flood flood plain. plain. Unfortunately, such such foresight foresight exercised exercised when when downtown downtown Omro Omro was was developed. developed. intelligent intelligent was was not not 8.5 8.5 (2.5) (2.5) Junction Junction Wisconsin 21 21 and and 116 116 at at the the west west edge edge of of Omro. Ornro. Continue Continue on on State State 21, 21, and and cross cross the the Fox Fox River. River. The route ahead ahead parallels the north side of the swampy Fox River valley for for the the next next few few miles. miles. 11.0 11.0 (2.8) (2.8) Another Another area area of of rolling rolling Valderan Valderan moraine moraine that that once once stood stood as as an an island island in Glacial Glacial Lake Lake Oshkosh. Oshkosh. 13.8 13.8 (2.0) (2.0) Intersection Wisconsin Wisconsin 21 21 and and County County K. K. The gentle gentle ridge ridge just just east east of this intersection is the easterly—dipping, western edge of the easterly-dipping, edge of the Lower Ordovician Ordovician Prairie Prairie du du Chien Chien escarpment. escarpment. As such, such, it it serves serves to define the boundary between the Eastern Ridges Ridges and and Lowlands Lowlands and and Central Plain. Plain. the Central The bedrock underlying the the Central Plain is is predominantly predominantly sandstone sandstone Late Cambrian Cambrian age. age. However, the the bedrock in in this this vicinity vicinity is is of Late covered by glacial lake lake sediments. sediments. A A quarry developed developed in in the the Prairie Prairie du du Chien Chien dolomite dolomite is is immediately immediately intersection. The glacial deposits here are are thin thin southeast of this intersection. edge of of the the cuesta. cuesta. along the edge 15.8 15.8 Waushara/Winnebago WausharajWinnebago county county line. line. Enter Waushara Waushara County. County. (1.3) (1.3) 17.1 (2.0) (2.0) 19.1 (1.8) (1.8) bogs, like the one north of the highway, Tamarack bogs, highway, are common common in in poorly— poorlydrained localities throughout throughout this this region. region. The truck-farming area south of the road was a former The former tamarack tamarack bog. When drained by ditching, ditching, the peaty bog soils are highly productive. A remnant of the former habitat still exists along the west edge edge of of the tilled tilled land. land. The prominent line of northeasterly trending ridges about about 33 miles here is northwest of here is part part of of the the Woodfordian Woodfordian morainal morainal complex. complex. These ridges, ridges, which which mark mark the the western western edge edge of Glacial Lake Oshkosh, These Oshkosh, are older older than than the the patches patches of Valderan Valderan till previously traversed. are traversed. Continue west west on on 21. 21. 20.9 (0.3) (0.3) Junction of Wisconsin 21 21 with 49. 49. 21.2 21.2 (5.2) (5.2) Good view view to to the the northwest of the hilly Woodfordian Good Woodfordian drift. drift. The soils adjacent adjacent to the road are lacustrine sediments pinkish to red soils Poor drainage drainage and that accumulated in Glacial Lake Oshkosh. that Oshkosh. Poor numerous tamarack tamarack swamps swamps are are characteristic characteristic of of this this lowland area. numerous area. 13 13 �Mileages Mileages 26.4 26.4 (1.3) (1. 3) Enter Redgranite Redgranite and and Junction Junction with with County N. N. Enter County NN toward toward Lohrville. Lohrville. County Proceed Proceed west west on on Redgranite was was once once the the site site of of aa thriving thriving quarry quarry operation operation and and Redgranite pickle factory. factory. The aa pickle The pickle pickle factory factory might might prosper prosper again, again, but but the quarry quarry is is permanently permanently abandoned. abandoned. Now the Now flooded, flooded, it it is is the the focus focus of aa city city park. park. of This This quarry, quarry, adjacent adjacent to to Wisconsin Wisconsin 21 21 aa few few blocks blocks northwest northwest of of here, employed employed about about 260 260 workers workers in in 1909 1909 to to produce produce hand-trimmed here, granite paving paving blocks blocks for for aa few cents apiece. granite apiece. With With the the average average trimmer producing producing up up to to 300 300 blocks blocks per per day, day, four four trains trains were trimmer were required required to to haul haul the the daily daily output output southward southward to to the the booming booming towns towns of of Milwaukee, Chicago, Chicago, and St. Milwaukee, St. Louis. Quarrying Quarrying declined declined rapidly rapidly after 1915, 1915, when when concrete concrete became became the the preferred road building after material. However, material. a more modest However, other other uses uses of granite granite allowed a operation to continue until the the pit pit was was closed closed in in 1931. 1931. By this time, the the quarry quarry occupied occupied 77 acres acres and extended downward to aa depth time, depth of 200 of 200 feet. feet. As the name of the town indicates, indicates, the rock rock exposed here is a reddish granite. reddish granite. It is and granophyric granophyric in in texture, texture, is fine-grained and and leucocratic leucocratic in in composition, composition, with quartz quartz and alkali feldspar and feldspar comprising 90% to 98% of the the rock. rock. Subordinate minerals include biotite (altered (altered to to chlorite), chlorite), sphene, muscovite, and sphene, hornblende, hornblende, muscovite, zircon. zircon. This granite, granite, like others exposed in in this this general general area, area, is is dated dated at at 1765 1765 m.y. m.y. old. old. A A well-exposed, well-exposed, greenish-black, vertical vertical dike of fine—grained fine-grained metabasalt trends trends northeasterly across across the the lake. lake. This dike is about 5 feet feet wide, wide, and it it has sharp sharp contacts contacts with with the the granite. granite. The Precani1rian bedrock at at this locality Precambrian bedrock locality was polished polished and and striated striated by by westerly westerly moving moving Woodfordian Woodfordian ice. ice. 27.7 27.7 (0.3) (0.3) 28.0 28.0 (0.1) (0.1) 28.1 28.1 (0.1) (0.1) 28.2 28.2 (0.1) (0.1) 28.3 28.3 Enter Enter the the village village limits limits of of Lohrville, Lohrville, once aa thriving thriving center center for for granite granite quarrying. quarrying. County NN turns turns south. south. County County NN turns turns west. west. An An abandoned, abandoned, small small quarry quarry north north of of the the road road exposes exposes aa medium—to medium-to coarse—grained, coarse-grained, reddish reddish granite. granite. The The Lohrville Lohrville Stone Stone Company Company north north of of the the highway highway occupies occupies aa building building constructed constructed from from local local granite. granite. The The piles piles of of glacial glacial erratics erratics gathered gathered together together by by this this firm firm suggest suggest that that these these are are aa more more important important commodity commodity today today than than the the local local bedrock. bedrock. County County NN turns turns south. south. The The large, large, glacially-smoothed glacially-smoothed knob knob of of granite granite north of the highway establishes that Pleistocene deposits north of the highway establishes that Pleistocene deposits are are thin thin in in this this area. area. Depart Depart Lohrville Lohrville as as County County NNturns turns westward. westward. (0.8) (0.8) 14 14 �Mileages Mileages 29.1 29.1 (0.6) (0.6) STOP STOP 11 at at Flynn's Flynn's Quarry Quarry County County Park Park south south of of the the highway. highway. This This park, park, like like the the one one at at Redgranite, Redgranite, is is developed developed around around aa flooded flooded granite quarry. quarry. The The park park road road is is an an old old quarry quarry road, road, which which loops loops granite around around the the lake lake before before returning returning to to County County Highway Highway N. N. Details Details on on the the geology geology at this stop are described by Eugene Smith Smith in in the the next next section section of of this this guidebook. guidebook. Unfortunately, Unfortunately, only only 30 30 minutes is is available available to to examine examine this this interesting interesting locality: locality~ After After stopping, stopping, continue continue westward westward on on County County N. N. The The route route ahead ahead passes passes through through aa low low area area occupied occupied by by tamarack tamarack bogs bogs before before ascending ascending to to higher, better-drained, better-drained, Woodfordian Woodfordian ground ground moraine. moraine. 29.7 29.7 (0.5) (0.5) County County N N turns turns southward southward along along an an irregular, irregular, rolling rolling morainal morainal ridge. ridge. The The till till is is studded studded with large, large, locally—derived locally-derived granitic granitic erratics. erratics. 30.2 30.2 (0.2) (0.2) Enter community community of of Spring Spring Lake. Lake. Enter 30.4 30.4 (0.3) (0.3) Junction County County NNand in Spring Spring Lake. Lake. Junction and FF in 30.7 30.7 (4.1) (4.1) County NN turns turns west. west. Turn northward northward on on N. N. County NNand Z. Turn southwesterly on N N and and leave leave Spring Spring Junction County and Z. Lake, Lake, through an area of rolling sandy till till within the the Woodfordian complex. Large glacial erratics of of local local derivation derivation are are morainal complex. common in the fields fields adjacent to the highway, highway, and and several several kettle kettle lakes general area. area. lakes are present in this general The attractive countryside between here and and Neshkoro is is part of of As such, Green Lake Lake recessional recessional moraine. moraine. As such, it it has the Woodfordian Green little value value for agriculture, but but it is little for agriculture, is highly prized as recreational land for city dwellers who want to be land for city dwellers who want to be weekend "tree farmers." farmers." The The pine plantations that enhance this landscape are the are the result result of of their their endeavors. 34.8 (0.5) (0.5) Pine Bluff Bluff Enter Marquette County. Pine Waushara/Marquette county county line. line. This prominent landmark is located about 33 miles west of is of here. here. landmark is is a glacially-smoothed, elliptical knob of coarse-grained, a glacially-smoothed, elliptical knob coarse-grained, gray to pinkish granite granite that that rises rises more more than than 100 feet above the swampy pinkish feet above The granite of this lowlands River. The this inlier is lithlowlands along the White River. related to the granites exposed in in the the ologically and genetically genetically related to the granites exposed Redgranite-Lohrville and Montello areas. Redgranite-Lohrville areas. Glacial striations striations on on the the bedrock bedrock at at this this locality locality trend trend about about Glacial N65°W. 35.3 35.3 (0.7) (0.7) in an an area area Turn west west on on County County Nand N and E in Junction Nand E. Turn Junction County N and E. where sand sand dunes dunes formed where formed on top of the the sandy Woodfordian drift. drift. 36.0 36.0 (0.5) (0.5) Junction County County Nand N and E with Wisconsin 73. Junction 73. and E. and County County E. 36.5 36.5 (0.7) (0.7) Cemeteries on on both both sides sides of of the the highway highway provide provide ample ample evidence evidence of Cemeteries the monument-quality monument-quality of central Wisconsin granites. the granites. 15 15 Turn south south on on State State 73 73 Turn �Mileages Mileages 37.2 37.2 Cross White White River in downtown Neshkoro. Cross (0.4) (0.4) 37.6 37.6 (1.3) (1. 3) 38.9 38.9 Junction Wisconsin 73, Junction 73, and County E E and and N. N. Turn west on EE and and N. N. The route route ahead ahead leaves leaves the the lowland lowland occupied occupied by by the the White White River and The traverses aa scenic, scenic, rolling rolling upland upland within within the the Woodfordian Woodfordian morainal traverses complex. complex. and E. Junction County County NNand E. Continue west on E. Continue E. (1.6) (1. 6) 40.5 40.5 (2.6) There are are several kettle lakes There lakes of various sizes developed nearby in in sandy, glacial outwash. This This is is another another region region with with low agriculagriculsandy, tural potential, potential, which which is is rapidly rapidly being being converted to to recreational tural recreational !Ifarms "farms." 43.1 43.1 (0.4) Junction County E and and Wisconsin Wisconsin 22. 22. 43.5 43.5 (0.6) Wisconsin granite granite headstones headstones dominate the cemetery east of Central Wisconsin the highway. 44.1 44.1 (0.3) Junction County E and Wisconsin Wisconsin 22. Continue south south on on 22. 22. The route ahead ahead traverses traverses sandy, sandy, rolling, route rolling, Woodfordian ground moraine. moraine. 44.4 44.4 (4.0) (4. 0) 48.4 (2.9) (2.9) 51.33 51. (1.6) (1. 6) 52.9 52.9 Turn 22. Turn south on E and 22. Cross Mecan River, River, one of many fine fine trout trout streams streams in in central central Wisconsin. Peat swamps along the highway were drained and and developed developed as as muck muck farms. The route traverses a The route ahead traverses a stony till formed into broad, broad, low drumlins with aa general general east—west east-west orientation. orientation. This better— betterdrained land supports aa growth of pine and land supports and cedar. cedar. The sand and gravel pit east of the the road road is is developed developed in in Woodfordian Woodfordian outwash. outwash. Kettles are are also also present present in in this this area. area. Enter the the city city of of Montello. Montello. (0.5) (0.5) 53.4 53.4 (0.3) (0.3) 53.7 53.7 (0.1) (0 .1) Junction of of Wisconsin Wisconsin 22 22 with with 23 23 in in Montello. Montello. 22 22 and and 23. 23. Turn west on Wisconsin Quarries north of the the highway exploited aa ridge ridge of of finefine- to to mediummediumgrained, red to grayish—red granite to produce monument stone, grained, red to grayish-red granite to produce monument stone, paving paving blocks, blocks, building building stone, stone, and and crushed crushed rock. rock. When When this this granite granite was was selected selected for for the the tomb tomb of of U.S. u.s. Grant Grant in in New New York York City, City, business business boomed. activity peaked, peaked, with with some some 200 workers employed. boomed. By 1910, 1910, activity employed. In In later later years, years, business declined until the the last last quarry quarry closed closed in in 1976, 1976, after nearly nearly 100 100 years years of of operation. operation. The The longevity longevity of of operations operations at at this locality locality was facilitated facilitated by well—developed well-developed vertical vertical joints joints that that allowed the the rock rock to to be be removed removed in in large large "precut" "precut" blocks. blocks. The granite of this this inlier is granophyric and leucocratic like area and and at at Pine Pine Bluff. Bluff. It It those those exposed in in the the Redgranite-Lohrville Redgranite-Lohrville area is is also also of of the the same same age age (1765 (1765 m.y. m.y. old). old). Several Several near-vertical near-vertical dikes dikes 16 16 �Mileaqe of of greenish-black, greenish-black, fine-grained fine-grained metabasalt metabasalt up up to to 55 feet feet thick thick cut cut the the granite, granite, and and are are well well exposed exposed in in the the quarries. quarries. Well monadnock Well drilling drilling adjacent adjacent to to the the granite granite ridge ridge discloses discloses that that this thismonadnock stood stood more more than than 200 200 feet feet above above the the general general level level of of the the Precambrian Precambrian surface surface prior prior to to transgression transgression of of the the Late Late Cambrian Cambrian sea sea (see (see article article by by Eugene Eugene I. I. Smith Smith in in this this guidebook). guidebook). Glacial Glacial striae striae on on the the bedrock bedrock surface surface indicate indicate ice moved westerly westerly across across this this area. area. ice 53.8 53.8 (0.5) (0.5) 54.3 54.3 (0.4) (0.4) Junction Wisconsin Wisconsin 22 22 and and 23. 23. Junction that that the the Woodfordian Woodfordian Turn Turn south south on on State State 22. 22. Cross the the Fox Fox River River once once Cross again. again. The The Fox flows flows northeasterly northeasterly to to reach reach Lake Winnebago, Winnebago, and and ultimately Lake Lake Michigan at at Green Green Bay. Bay. We We first first crossed it it about about 46 46 miles miles ago, ago, at at Omro. Omro. The Fox was part of the historic canoe canoe highway highway across across Wisconsin. Wisconsin. Although used used by by Indians Indians for for centuries, centuries, it it was was "popularized" "popularize& by Marquette and and Joliet on their their historic journey journey from from Lake Lake Michigan Michigan A flood of explorers, missionaries, trappers, Mississippi. A flood trappers, to the Mississippi. The Fox is dammed just and traders traders soon soon paddled paddled after after them. them. just upstream and and enlarge enlarge Buffalo Buffalo Lake. Lake. Thelocks The locks visible from from here to deepen and the highway were part of of a a navigation scheme scheme originally originally designed designed to link the the North Atlantic (via the Great Lakes) with the Gulf of (via Lakes) Shifting Mexico (via the Wisconsin River and the Mississippi). (via the Wisconsin River and the Mississippi). Shifting sandsandbars along the shallow Wisconsin River ruled against this the River ruled against this plan plan from from the beginning. 1.5 A canal at Portage, Wisconsin was started in 1838 to eliminate the at Portage, the 1.5 mile land bridge between the headwaters of the Fox and the Wisconsin mile This project was finally completed in 1876, River. 1876, but the cost of maintaining a a channel in the Wisconsin River proved prohibitive, prohibitive, and and soon abandoned. abandoned. the project was soon 54.7 (1. 8) (1.8) 56.5 (1. 7) (1.7) 58.2 58.2 (1. 5) (1.5) into an an Leave Montello and Leave and the the lowland lowland along along the the Fox Fox River, River, and proceed proceed into area ground moraine. moraine. area of rolling, rolling, Woodfordian ground The prominent, prominent, wooded wooded hill hill about about 44 miles miles to to the the southwest southwest is is The Observatory Hill, Hill, the highest point in with an an Observatory in Marquette Marquette County, County, with This will will be the locale of our elevation feet. This our second second stop. stop. elevation of 1080 feet. deposited in The in aa The truck truck farms farms in in this this flat flat area area utilize utilize fertile fertile soils soils deposited glacial lake, lake, which which formed formed when when northeasterly northeasterly drainage drainage was was blocked glacial by ice. by the the retreating Woodfordian ice. 59.7 59.7 (0.2) (0.2) We will will return return to this Junction B. We this interJunction Wisconsin 22 and County B. loop. section in in aa few few hours, hours, and and go go east east on on BB after after making making aa large large loop. section outwash. Continue south south on on State State 22 22 in in an an area area of of pitted pitted sandy sandy outwash. Continue purity of of Gravel Gravel pits pits in in this this area area are are testimony testimony to to the the water-washed water-washed purity these these deposits. deposits. 59.9 59.9 (0.9) (0.9) Our Turn east on Gem Road. Junction 22. Turn Road. Our Junction Gem Gem Road Road and Wisconsin 22. southwest immediate destination destination is is Observatory Observatory Hill, Hill, about about 22 miles miles southwest immediate 17 17 �Mileages Mileages of here. here. To To of and approach and approach reach our our objective, objective, we we must must circle circle this this promontory, promontory, reach from the the west. west. A small small kettle is located northwest northwest of of the the highway. highway. 60.8 60.8 (1.4) (1.4) Large glacial glacial erratics erratics of of local local derivation derivation litter the field north of Large the road. the road. 62.2 62.2 (0.2) Junction 14th Road and Gem Road. Junction Road. 62.4 62.4 (1.0) Junction 14th Road and 13th Road. Turn Junction (left) on 13th Road Turn south (left) in an an area of rolling ground moraine. At long last, in last, we are closing in on Observatory Observatory Hill! in Hill~ 63.4 63.4 (0.5) An irrigation well west of the road encountered Precambrian Precambrian porphyritic rhyolite, rhyolite, lithologically identical to to exposures exposures on on Observatory Hill, Hill, at a a depth of of 300 300 feet. feet. 63.9 63.9 (0.4) (0.4) 64.3 64.3 (1.1) (1.1) Turn (left) on 14th Road. Road. Turn west west (left) - Junction 13th Road and Gillette Ave. Ave. Proceed southeasterly (straight (straight ahead) on on Gillette Gillette Ave. Ave. and ascend the ahead) the flank flank of Observatory Hill. Hill. STOP 22 for for Observatory Observatory Hill rhyolite. STOP rhyolite. This bedrock hill, hill, which rises rises about 250 above the level of the surrounding landscape, about 250 feet feet above the level landscape, has aa core of resistant core resistant rhyolite rhyolite flanked by medium—to medium-to coarse—grained, coarse-grained, friable, friable, iron-stained Upper Upper Cambrian Cambrian sandstone. sandstone. Locally, Locally, this sandgrades into a stone grades a conglomerate that contains clasts derived from from the Precambrian bedrock. the bedrock. Glacial striae on the rhyolite vary from N45W to N74W, Glacial N74W, and record record the movement of ice over and around this resistant knob. the knob. A A detailed description of the the rocks rocks at at this this locality locality is is provided provided by by Eugene Smith Smith in in the the next next section section of of this this guidebook. guidebook. Since only 60 60 minutes is is allocated for for this this stop, stop, we should should proceed proceed with with enthusiasm: enthusiasm~ NOTE: Since this road dead ends ends about about 0.4 mile ahead, backtrack northwesterly to to the the intersection intersection of of Gillette Gillette Road Road and and 13th 13th Road. Road. The logged mileage that follows follows' assumes a turn—around turn-around at the the dead end end of Gillette Gillette Road Road after after this this stop. stop. a 65.4 65.4 (0.7) (0.7) 66.1 66.1 (0.2) (0.2) 66.3 66.3 (0.4) (0.4) 66.7 66.7 (1.5) (1.5) Intersection of Gillette Road Road and and 13th 13th Road. Road. The bedrock bedrock of of the the high, high, wooded hill west of of this this intersection intersection is is Upper Cambrian Cambrian sandstone sandstone with no no rhyolite rhyolite exposed. exposed. Turn south south on on 13th 13th Road. Road. 13th 13th Road Road turns turns sharply sharply to to the the west west in in an an area area of of rolling rolling countryside countryside formed by aa Woodfordian Woodfordian recessional recessional moraine. moraine Pine plantations, cedars, cedars, and oaks accentuate accentuate the the beauty beauty of of this this glacial glacial landscape. landscape. Junction Junction 13th 13th Road Road and and Gillette Gillette Drive. Drive. Continue Continue west west on on Gillette. Gillette. NOTE: NOTE: It It seems seems that that the the Gillettes Gillettes are are important important in in this this country! country~ AA low low bedrock bedrock ridge ridge north north of of the the road road is is the the Taylor Taylor Farm Farm rhyolite rhyolite locality. porphyritic rhyolite exposed here locality. The The well-jointed, well-jointed, porphyritic here is is 18 18 �Mileages Mileages similar similar to to that that found found on on Observatory ObservatoryHill. Hill. However, However, the the high high bedbedrock rock hill hill of of sandstone sandstone northeast northeast of of here here separates separates these these two two localities. Glacial Glacial striae striae on on this this rhyolite rhyolite document document aa general general localities. N70W N70W direction direction of of ice ice flow flow for for the the Green Green Bay Bay lobe lobe of of Woodfordian Woodfordian ice at at this this locality. locality. ice Turn Turn south south on on County County F. F. 68.2 68.2 (0.2) (0.2) Junction Junction Gillette Gillette Drive Drive and and County County F. F. " 68.4 68.4 LUNCH STOP STOP at at John John Muir Muir County County Park Park on on Ennis Ennis Lake. Lake. LUNCH (1. 4) (1.4) John John Muir, Muir, aa distinguished distinguished naturalist naturalist and and aa prime prime mover mover in in the the establishment establishment of of our our national national park park system system in in 1890, 1890, was was born born in in His family came to Wisconsin to farm the land Scotland in 1838. His family came to Wisconsin to farm the land Scotland in 1838. he was only a boy of across the lake from this memorial park when he was only a boy of across the lake from this memorial park when Fountain Lake 11. He grew up on this beautiful kettle lake (called Fountain Lake He grew up on this beautiful kettle lake (called 11. ingredient in the in those days), and it proved to be a significant ingredient in the in those days), and it proved to be a significant development of his love of nature. development of his love of nature. The The importance importance of of this this lake lake to to Muir Muir is is well well documented documented on on page page 96 96 Youth" (University of his autobiography, autobiography, "The "The Story of My Boyhood Boyhood and and Youth" (University Press, 1965). 1965). of Wisconsin Press, "Our beautiful beautiful lake, lake, named Fountain Lake by father, father, but Muir's Muir's Lake Lake lakes by the neighbors, neighbors, is one of the many small small glacier glacier lakes that that adorn adorn It is Wisconsin landscapes. landscapes. is fed by twenty or thirty meadow the Wisconsin surrounded by by springs, is is about about half a mile long, wide, and surrounded springs, a mile long, half as wide, meadows low finely-modeled hills dotted with oak and hickory, and finely-modeled hills hickory, meadows and ferns. full of grasses ferns. full grasses and and sedges sedges and many beautiful orchids and First there a zone rushes, and just just beyond beyond the the there is is a zone of green, green, shining rushes, fifty or or sixty rushes sixty feet feet rushes aa zone zone of of white white and orange orange water-lilies fifty On bright days, forming aa magnificent magnificent border. border. days, when the lake wide forming sun—spangles danced together together breeze, the lilies lilies and and sun-spangles danced was rippled by a breeze, between in radiant radiant beauty, beauty, and and it it became became difficult difficult to to discriminate discriminate between in them. them. and Bible-lessons, Bible—lessons, On chores and sermons and On Sundays, Sundays, after or before before chores especially in lily time, we the lake lake for for hours, hours, especially in lily time, we drifted about on the ducks, getting finest finest lessons lessons and and sermons sermons from from the the water water and flowers, getting flowers, ducks, In particular particular we we took took Christ's Christ's advice advice and and fishes, fishes, and and muskrats. muskrats. In they grow grow up up in in beauty beauty out out how they devoutly devoutly "considered the lilies" -- how ideglOri0USlY among the breezy sun-spangles." of of gray gray lime lime mud, mud, and and ride gloriously among the breezy sun-spangles." of rolling, rolling, After lunch, lunch, continue continue south south on on County County FF through through an an area of After Immediately to to the the west, west, the the north-flowing north-flowing Fox Fox River River sandy sandy drift. drift. Immediately parallels parallels the the highway. highway. 69.8 69.8 (1. 7) (1.7) The rolling, rolling, sandy, sandy, Turn east east on on County 0. Junction O. Turn o. The Junction County County F and 0. Differences ground moraine moraine contains contains large large erratics erratics scattered about. ground about. Differences with tamaracks tamaracks in in drainage drainage are are clearly clearly reflected reflected in in the vegetation, vegetation, with the higher, well— in in swampy swampyplaces, places,and andoaks oaksand andplantation plantation pines pines on on the higher, welldrained drained soils. soils. 19 19 �Mileages Mileages 71.5 71. 5 (1.4) (1. 4) 72.9 72.9 Junction County County 00 and and 13th 13th Road. Road. Junction Turn Road. Turn south south on on 13th Road. Knights Lake, Lake, on on the the east east side side of of the the road, road, occupies occupies aa small Knights small kettle. kettle. (0.7) (0.7) 73.6 73.6 (0.4) (0.4) Junction 13th Road and 14th Road. Junction Road. Turn (right) on 14th Road. Road. Turn south south (right) This road road curves curves eastward immediately ahead. This ahead. 74.0 74.0 (0.9) (0.9) Junction 14th 14th Road Road and and Dalton Dalton Road Junction Road at at the the Marquette/Columbia Marquette/Columbia county line. Turn south south (right) on Dalton Dalton Road Road and and enter enter Columbia County, County, line. Turn (right) on through rolling rolling country country with with some some land land suitable suitable for agriculture. through for agriculture. 74.9 74.9 (0.2) (0.2) Junction Dalton County CM. CM. Junction Dalton Road Road arid and County Turn (right) Turn southwesterly (right) County CM CM in in an an area with abundant erratics. County erratics. We will backtrack We will this intersection after Stop 3. this 3. 75.1 75.1 (0.4) (0.4) well on on the the A. A. Uchtung farm on the right side of the road reached A well Precambrian rhyolite at at aa depth depth of of 390 390 feet. feet. Drilling continued 170 feet into the rhyolite. feet into the rhyolite. 75.5 75.5 (0.6) (0.6) 76.1 76.1 (0.1) (0.1) 76.2 76.2 (0.7) (0.7) Junction County CM and and Monthey Monthey Road. Road. Road. Road. on to Turn south (left) (left) on Monthey Exposure road. Exposure of Middle Middle Precambrian Marcellon rhyolite east of the road. This is is one one of four This four isolated exposures of rhyolite in this immediate immediate area. area. STOP 33 at Marcellon rhyolite locality. STOP locality. This scenic exposure is is aa 70 feet feet above above glacially rounded and polished knob that rises nearly 70 the surrounding surrounding countryside. countryside. Glacial striae indicate aa westerly direction for for Woodfordian Woodfordian ice ice flow flow at at this this locality. locality. A A detailed description of of the geology geology to to be be observed observed here is is supplied supplied by Eugene Smith Smith in in the the next next section section of of this this guidebook. guidebook. only 45 45 minutes for for an an examination examination of of this this Unfortunately, we have only interesting interesting exposure. exposure. After studying studying the the rock rock here, turn turn around around and and backtrack backtrack northward northward along along Monthey Monthey Road. Road. 76.9 76.9 Junction Junction Monthey Monthey Road Road and and County County CM. CM. Turn northeast northeast (right) (right) on on CM. CM. Turn (0.6) (0.6) 77.5 77.5 (2.7) (2. 7) 80.2 80.2 (0.6) (0.6) 80.8 80.8 (0.2) (0.2) Junction Junction CM CM and and Dalton Dalton Road. Road. Continue Continue northeastward northeastward on on CM CM through through rolling, rolling, glacial glacial countryside. countryside. Junction Junction County County CM CM and and Wisconsin Wisconsin 22. 22. Turn .=T:.. :u:.::r:..:.n=-.north . :n.:.:o::..:r=.t.=.h:..:. . .(left) --'(.=1:.. :e:.. :f::..:t"-'):.. .-o::.on .:n:..:. . . =State S:.. :t:..:.a::..:t::..:e::.. . .22 . :2::..:2=. and and cross cross Columbia/Marquette Columbia/Marquette county county line. line. Enter Enter Marquette Marquette County County once once again. again. State State Historical Historical Marker Marker on on the the east east side side of of the the highway highway is is entitled entitled "John "John Muir Muir Country," Country," and and it it describes describes his his sojourn sojourn in in this this area. area. It It also also includes includes this this meaningful meaningful quote quote of of Muir's: Muir's: 20 20 �Mileages Mileages "Everybody needs beauty as well as as bread; bread; places to play in and places to pray to in and to pray in, in, where nature may heal heal and and cheer, cheer, and and give give strength to body and and soul soul alike." alike." 81.0 (1. 2) (1.2) The house house west of the fieldstone, the trade 82.2 (3.6) Wisconsin 22 22 climbs climbs onto a a highland littered littered with with glacial glacial erratics. erratics. 85.8 (3.5) road name is a a showplace for samples of Wisconsin for for glacial glacial erratics. erratics. Junction Wisconsin Wisconsin 22 22 and and County County B. B. Turn east on County B, in in a a region of sandy outwash outwash occupied occupied by by gravel gravel pits. pits. The route ahead is is numerous swamps, characterized by numerous swamps, some of which are drained for muck farming. Higher areas support support pine pine plantations. plantations. 89.3 (0.7) Marquette/Green Marquette/Green Lake Lake county county line. line. Enter Green Lake Lake County. County. 90.0 (3.1) (3.1) The poorly drained lowland lowland north of of the the road road is is part part of of the the extenextensive Grand River Wildlife Area. Area. When the retreating Woodfordian ice dammed the the northeastward flowing flowing drainage drainage of of the the Fox Fox and and Grand Grand rivers, rivers, In time, time, it filled with meltaa glacial lake formed formed in in this this area. area. In water, westward into water, and overflowed westward into the the Wisconsin River. River. However, continued retreat of the Green Bay lobe lobe of the Woodfordian ice redrainage, and this lake was emptied. However, Lake stored northeasterly drainage, emptied. However, Puckaway and and Buffalo Lake Lake exist exist as as remnants remnants of of this this ancient ancient water water body. body. 93.1 Junction County and H.. Junction County BBand H. Continue northeasterly (left) (left) on on BBand H. and H. (0.3) 93.4 (2.4) 95.8 (0.5) (0.5) 96.3 (0.3) and H. Junction County B Band H. Turn north north on on County County H. H. The high, high, wooded hill to the northeast of this this intersection intersection is is Bartholomew Bartholomew Bluff. Bluff. It It is a is a bedrock feature feature composed of Upper Cambrian formations formations capped by resistant Lower Ordovician dolomite dolomite of of the the Prairie Prairie du du Chien Chien Group. Group. The route ahead traverses the the east east edge edge of of an area of of poorly—drained, poorly-drained, glacial lake deposits now occupied by the Grand River Marsh. glacial lake deposits Marsh. The bedrock hill immediately northwest of the the road road is is one of several isolated rhyolite exposures, exposures, which trend northwestward from from here for for about one mile. about one mile. In In all, all, there there are are seven rhyolite knobs knobs in this general area. area. These features features stood several hundred feet feet above above the the general general Precambrian erosional level as monadnocks,prior to transgression of of the the Upper Cambrian sea (see (see article by Eugene I. I. Smith in this guidebook). guidebook). STOP 4 STOP 4 at an exposure of the the Marquette Marquette rhyolite. rhyolite. The cedar-covered, cedar-covered, glacially-smoothed, bedrock bedrock knob west of the highway rises about glacially-smoothed, 100 feet above poorly-drained tamarack swamps to the north. 100 feet above north. A A similar exposure lies immediately east east of of the the road. road. Glacial striations and chatter marks on the bedrock indicate indicate that that the the Woodfordian ice generally moved westward at this locality. locality. However, measurements vary vary from from N57W N57W to to N86W. N86W. analysis of of the the rhyolite rhyolite at at this this stop stop is is provided provided by by Eugene Eugene Smith An analysis in the next section section of of this this guidebook. guidebook. About 60 60 minutes are available to study the the exposures exposures at at this this locality. locality. 21 �Mileages After examining the rhyolite, rhyolite, continue northeasterly on County H. H. 96.6 (1.0) (1. 0) 97.6 (3.8) KK. Turn Turn east (right) and KK. Junction County H H and and KK. (right) on H Hand KK. The route ahead traverses traverses rolling rolling ground ground moraine moraine studded with with numerous numerous erratics. erratics. ahead The shape of the east—west east-west trending drumlin south of the road road estab— establishes that ice movement in this area lishes area was was to to the the west. west. Junction County H, Continue straight ahead (east) H, KK, KK, and and B. B. Continue (east) on County H. The route ahead traverses scenic, County scenic, glacial countryside countryside with some agricultural potential. some potential. Lake Lake Puckaway, Puckaway, an an enlargement of the Fox River, River, is occasionally occasionally visible visible to to the the north. north. 101.4 (2.1) Junction County HH and Wisconsin 73. Turn south (right) and Wisconsin (right) on State State 73. 73. The route ahead traverses traverses rolling rolling agricultural agricultural land. land. 103.5 (0.3) Junction Wisconsin 73 73 and and 44. 44. 103.8 (0.6) Enter Manchester, Manchester, a a hilltop community astride the the Green Lake Lake recessional recessional moraine. This prominent glacial feature, feature, which trends trends north-northwestnorth-northwestward and south—southeastward south-southeastward from from here, here, formed formed as as the the Green Bay Bay lobe lobe of the Woodfordian ice paused paused during during retreat. retreat. 104.4 104.4 (0.4) Leave Manchester in an an easterly easterly direction. direction. The boundary between two major physical provinces trends trends northeast—southwest northeast-southwest through through this this area. area. The Central Plain, Plain, to the northwest, is a The the northwest, a subdued region characterized by Upper Upper Canibrian Cambrian bedrock. The Eastern Ridges and Lowlands, Lowlands, with younger bedrock, occupies the the region region to to the the east east and and southeast. southeast. However, this However, this division is ill—defined ill-defined here because of the thick cover cover of young glacial glacial deposits. deposits. 104.8 (0.4) (0.4) Junction Wisconsin 73 73 and and 44. 44. rolling agricultural agricultural land. land. 105.2 105.2 Cross Grand River. River. Continue south on 73 73 and and 44. 44. Turn south on State 73 in an area area of (1.6) (1. 6) 106.8 106.8 (0.7) (0.7) The highway intersects intersects aa drumlin drumlin that that trends trends east-west. east-west. The blunter, east—facing east-facing nose of this drumlin indicates westerly ice ice movement in in this area. area. 107.5 107.5 Lake Maria, Maria, east of the highway, highway, lies lies along the trend of the the Green Lake recessional moraine. moraine. (1.8) (1. 8) 109.3 (0.6) (0.6) Green Lake/Columbia Lake/Columbia county county line. line. Enter Columbia County in in an an area area where intensively farmed farmed drumlins stand stand above above flat, flat, low low areas areas that that are poorly poorly drained. drained. When drained, drained, these lowlands lowlands are are productive muck farms. farms. 109.9 109.9 (2.9) (2.9) Several roadcuts the next 0.5 mile expose thin-to medium-bedded roadcuts in the Lower Ordovician Ordovician dolomite dolomite of of the the Prairiedu Prairie du Chien Chien Group. Group. Some of of these bedrock exposures form form the the cores cores of of drumlins. drumlins. 112.8 112.8 (2.0) (2.0) The high-voltage power lines crossing the highway come come from from aa large, large, coal-fired power plant plant at at Portage. Portage. This facility facility utilizes Wisconsin River water water as as aa coolant. coolant. 22 22 �Mileages Mileages 114.8 114.8 (0.5) (0.5) Junction Junction Wisconsin Wisconsin 73 73 and and 33. 33. 115.3 115.3 (1.0) (1.0) Enter Randolph. Randolph. Enter 116.3 116.3 (0.2) (0.2) Leave Leave Randolph. Randolph. '116.5 ll6.5 (13.0) (13.0) Continue Continue south south on on 73. 73. Cross Cross Columbia/Dodge Columbia/Dodge county county line, line, as as Wisconsin Wisconsin 73 73 turns turns east, east, and and then south. south. Enter Enter Dodge Dodge County. County. The route route ahead ahead traverses traverses rich rich agricultural land land developed on a swarm swarm of broad, well—formed, well-formed, southsouthwesterly-trending drumlins. drumlins. westerly-trending 129.5 129.5 (1.3) (1.3) Junction Wisconsin 73 73 and and U.S. u.s. 151. 151. 130.8 130.8 (0.9) (0.9) Dodge/Columbia Dodge/Columbia county county line. line. Enter Columbia County and and the the city city of of Cross southeasterly flowing Crayfish River. Columbus. southeasterly flowing Crayfish River. Columbus. 131.7 131.7 (0.6) (0.6) Junction Wisconsin Wisconsin 73 73 and and 89 89 in in Columbus. Columbus. Wisconsin 89. Wisconsin 89. 132.3 132.3 (3.0) (3.0) Leave Columbus. Columbus. The route route ahead ahead traverses traverses intensively intensively farmed, farmed, rolling, rolling, glacial countryside. countryside. 135.3 135.3 (4.8) (4.8) Columbia/Dane county county line. line. Enter Dane County. County. drumlins here trend trend southwesterly. southwesterly. 140.1 (1.4) (1.4) Dane/Dodge county county line. line. drumlins. 141.5 (0.7) (0.7) Stop sign at junction junction of of Wisconsin Wisconsin 89 89 and and County County T. T. (east) on on Dalman Dalman Road. Road. ahead (east) 142.2 (1.0) (1.0) Junction Dalman Road Road and and County County I. I. 143.2 (1.0) (1.0) village of Portland and junction with Wisconsin 19. Village 19. 19, and and leave leave Portland. Portland. on State 19, 144.2 (0.3) (0.3) Cross Maunesha Maunesha River. River. 144.5 (0.1) (0.1) Knobs of of glacially-smoothed, glacially-smoothed, Middle Middle Precambrian Precambrian Waterloo Quartzite Knobs These exposures exposures are are two of lie lie north north and south of the highway. These about aa dozen dozen quartzite quartzite knobs knobs that that protrude protrude through the the glacial drift about All of the the exposures exposures are are smoothed by glacial in area. All in this general area. action, and and some some have have small potholes developed action, developed on on the the upper upper surfaces. surfaces. This quartzite quartzite is is quite quite This Baraboo syncline, syncline, about Quartzite, ripple ripple marks marks Quartzite, also present present within within the also Continue south south on on State State 73. 73. Turn south south (left) (left) on on Broad, Broad, well-shaped Enter Dodge County in an area with occasional Proceed straight Turn south (right) (right) on County County I. I. Turn northeast to that that exposed in the well-known similar to Like the the Baraboo 35 35 miles to to the the northwest. northwest. Like cross bedding, and conglomeratic beds are cross bedding, thick quartzite sequence sequence in in this this area. area. 23 23 �Mileages The structure here is an easterly plunging The plunging syncline. syncline. as at at Baraboo, Baraboo, may have occurred 1650 as 1650 m.y. m.y. ago. ago. This folding, folding, Measurements of glacial striae indicate that the ice flowed Measurements flowed about S2OW at at this locality. S20W locality. 144.6 (0.3) STOP 5 at at the the abandoned abandoned John John O'Laughlin O'Laughlin quarries quarries in in the the Waterloo Waterloo STOP Quartzite. The quartzite quartzite at this stop is described by Eugene Smith in the next The at this minutes Is section of this this guidebook. guidebook. About 30 30 minutes is allotted to assimilate the geology at at this this locale. locale. 144.9 144.9 (1.7) Junction Wisconsin 99 99 and and Hubbleton Hubbleton Road. Road. 19. Proceed east on Wisconsin About 1 mile north along along Hubbleton Road, Road, in in the the ditch ditch along along the the eastern edge edge of the the road, eastern road, an isolated exposure of Paleozoic conglomThis conglomerate, erate is is present. present. This conglomerate, which contains rounded Waterloo Quartzite boulders boulders up to 66 feet across, is probably a Quartzite feet across, a local facies facies of the Middle Ordovician St. St. Peter Peter Sandstone. Sandstone. It is is also one of the few Paleozoic exposures in in this this general general area. area. About 0.5 0.5 mile mile straight north of the St. About St. Peter conglomerate locality, locality, at the at the junction of Maunesha Creek and the Crawfish River, River, is is Stony Stony Island. This is This is another glacially rounded mass of Waterloo Quartzite. Here, several pegmatite dikes dikes up to 3.2 feet thick intruded the Here, quartzite after after folding. folding. These dikes were dated by L.T. L.T. Aldrich and and others in 1959 as as 1444 1444 m.y. old. old. The route more drumlin county, The route ahead traverses traverses more county, although the agricultural potential is not as good as it was is as good as it was east east of of Portland. Portland. 146.4 146.4 (0.4) Easterly dipping Middle Precambrian Waterloo Quartzite adds dipping ledge ledge of Middle adds interest to Interto the lawn of the the farmhouse farmhouse south of the highway. highway. mittent exposures indicate indicate that that this this ledge ledge persists persists southward southward along along strike for almost a mile. for almost a mile. 147.0 (0.3) (0.3) Another exposure of Waterloo Quartzite is is visible visible about about 100 100 yards yards north north of the highway. the highway. 147.3 (0.5) (0.5) Junction Wisconsin Wisconsin 19 19 and and County County GG (north). (north). Continue east east on on 19. 19. Exposures of brecciated Waterloo Quartzite cemented cemented by by milky milky quartz quartz are located about 0.75 0.75 mile to to the the north. north. Additional exposures of quartzite are present in in the the vicinity vicinity of of Mud Mud Lake, Lake, about about 55 miles miles north—northeast north-northeast of of here here along along County County G. G. 147.8 147.8 (0.5) Dodge/Jefferson Dodge/Jefferson county county line. line. Enter Jefferson County. County. 148.3 148.3 (2.4) Hubbleton Hubbleton and and junction junction Wisconsin Wisconsin 19 19 and and County County G. G. Turn south south (right) (right) on GG in a a broad area of flat, flat, poorly-drained muck soils soils located located between between intensively intensively farmed drumlins. drumlins. Where ~ihere ditched, ditched, the muck soils soils are also also cultivated. cultivated. 24 24 �Mileages Mileages 150.7 150.7 (2.1) (2.1) County county GG continues continues southward southward through through drumlin drumlin country. country. 152.8 152.8 (1.4) (1.4) The The low low ridge ridge of of Waterloo Quartzite Quartzite in in the the field field about about 150 150 yards yards east of the highway is sometimes referred to as the Lake east of the is sometimes referred to as the Lake Mills Mills here is is light light blue blue to gray in exposure. exposure. The The quartzi-te quartzite here in color, color, and and it is composed almost entirely of coarse, interlocking quartz it is composed almost entirely of coarse, interlocking quartz grains grains with with rare rare mica. mica. Primary Primary foliation foliation (bedding) (bedding) strikes strikes N. 500 W. and dips 70° northeast on the south N. 50° W. and dips 70° northeast on the south limb limb of of the the Waterloo syncline. syncline. Waterloo 154.2 154.2 (2.0) (2.0) Junction Junction County County GG and and Wisconsin Wisconsin 89. 89. through good good drumlin drumlin country. country. through 156.2 156.2 (1.8) (1.8) Junction Junction Wisconsin Wisconsin 89 89 and and Interstate Interstate 94. 94. Milwaukee. 1 Milwaukee.1 Turn south on Wisconsin 89 89 Turn east on 1-94 I-94 toward toward The 1-94 I-94 route from from the Lake Mills-Waterloo interchange interchange to to Milwaukee is entirely within the Eastern Ridges and and Lowlands physical province, and the highway trends at right angles to the the general general strike strike of of the the Paleozoic Paleozoic formations. formations. Consequently, Consequently, the bedrock along along the the route route ranges from from Middle Ordovician formations formations on the the west to to Silurian Silurian on the the east. east. However, However, these rocks rocks are are largely largely obscured obscured dolomite on glacial deposits. deposits. by Woodfordian glacial The glacial geology encountered along along 1-94 I-94 between here and and Milwaukee Milwaukee spectacular. The orientation of the the route route is is such such that that the the interinteris spectacular. state cuts cuts most glacial glacial features state features essentially at right angles. angles. From west to east, east, these include well—developed well-developed drumlin drumlin fields, fields, outwash outwash plains, plains, the Kettle Interlobate Interlobate Moraine with numerous scenic scenic lakes, lakes, and recessional recessional moraines moraines of the the Lake Lake Border morainic system. and system. Other significant attractions along along this this route route include: include: the Lapham Peak overlook high in the Kettle Moraine, Moraine, and and the subcontinental subcontinental divide, divide, which separates drainage destined for for the North Atlantic via via the the St. Lawrence Lawrence from that that which flows to the St. flows to the Gulf of Mexico via the Mississippi. 158.0 (2.0) (2.0) Eastbound rest area in in an area area of rolling rolling ground ground moraine. moraine. 160.0 (1.0) (1.0) 1-94 crosses the Crawfish River, I-94 River, aa tributary tributary to to the the Rock. Rock. Aztalan In State Park is is 1.5 miles miles south on the west bank of this river. State river. In addition to to Late Late Woodland Woodland Indian Indian effigy effigy mounds, mounds, this this park park contains contains addition two—tiered pyramidal mound, mound, and a aa two-tiered a partly restored stockaded village identified with the the Middle Middle Mississippi Mississippi culture. culture. When the site was was first first described described in in 1837, 1837, it it was was named named Aztalan Aztalan in the the hope hope site that the the cultural cultural remains remainspreserved here were were those those of Mexican Mexican Aztecs. Aztecs. that preserved here To reach reach the the park, park, use use the the Lake Lake Mills Mills exit exit and and then then turn turn east on To County B. County B. 161.0 161.0 (1.0) Westhound rest rest area, area, in in an an area area of ground ground moraine moraine and low—lying Westbound low-lying drumlinoid drumlinoid hills. this geologic guide published with with permission ofofKendall/ 1ndof The remainder of this road geologic roadis guide is published permission Kendall/ be duplicated duplicated by by any any means means Hunt Publishing Company, Company, Dubuque, Dubuque, Iowa, Iowa, and and it should not not be Hunt without 25 without written permission. permission. 25 �Mileages Mileages 162.0 162.0 (1.0) (1.0) 1—94 crosses the Rock The Rock Rock marks marks aa general general vegetation I-94 Rock River. River. The divide between between native native hardwood hardwood forests forests to to the the east, east, and and oak oak divide savannas and prairies to the west. Some think think the the river river formed savannas west. Some formed barrier to to prairie prairie fires, fires, thus thus preserving preserving the the forests forests to to the the aa barrier east. east. Jefferson, 6.5 miles miles to Jefferson, to the south at the junction of the Crawfish and Rock Rock rivers, rivers, experienced experienced aa short-lived, short—lived, geology-related, geology—related, land and boom about about 1840. 1840. A federally—assisted federally-assisted project was planned to to construct aa canal canal from from Lake Lake Michigan Michigan at at Milwaukee Milwaukee to to the the Rock River construct Some construction construction was was actually actually accomplished before near Jefferson. Jefferson. Some the million-dollar million—dollar project was was abandoned. abandoned. Meanwhile, Meanwhile, land land values had sky—rocketed sky-rocketed in Jefferson as as the prospect of a connection the Mississippi Mississippi River River and and the the Great Great Lakes Lakes seemed seemed imminent. iminent. between the Land promoters arrived, arrived, and a a steamboat made it up the Rock River River from St. St. Louis. Tracts of swampland were bought by local residents residents and newcomers newcomers at at inflated inflated prices, prices, in in the the hope hope that that great profits profits and would result when the the canal canal was was completed. completed. The The land promoters left town town with with well-laden well—laden carpetbags carpetbags before before news news of the the abandonabandonleft ment of the canal plans plans reached reached southern southern Wisconsin. Wisconsin. 163.0 (6.0) Watertown, Johnson Creek, Exit Wisconsin 26 to Watertown, Creek, and Jefferson, Jefferson, within the Jefferson County County drumlin drumlin field. field. Where the interstate interstate cuts through a a drumlin, drumlin, the roadcuts have been carefully sodded sodded over to conceal the internal character of the sandy and and clayey clayey till. till. However, However, at the northwest corner of this intersection, behind the the service station and restaurant, restaurant, an excavated drumlin is is exposed. exposed. 169.0 (4.0) moraine assumes assumes symmetry and order as Irregular ground moraine as the highway traverses a classic drumlin field, field, produced by the the Green Green Bay Bay lobe lobe drumlins trend essentially of the Woodfordian ice ice advance. advance. These drumlins north—south, north-south, but nearer to Madison the the orientation is southwesterly. Poorly drained areas and tamarack tamarack swamps swamps flank flank many of of the the drumlins. drumlins. 173.0 (2.0) Wisconsin Wisconsin 135 135 exit. exit. 175.0 (3.0) Jefferson/Waukesha Jefferson/Waukesha county county line. line. Enter Enter Waukesha Waukesha County. County. The The drainage in this rolling rolling countryside countryside is is poor, and and farm farm fields fields must must be ditched. ditched. Numerous tamarack tamarack swamps swamps with red red osier osier dogwood dogwood are are lingering evidence of the the boreal boreal climate climate of of the the Pleistocene. Pleistocene. 178.0 (4.0) Wisconsin 67 67 exit exit to to Oconomowoc Oconomowoc and and Dousman. Dousman. The interstate now traverses traverses outwash and proglacial lake sediments in an area once occupied by the the Green Bay Bay lobe lobe during the the Woodfordian Woodfordian ice ice advance. advance. To To the the east, the the view of the the Interlobate Interlobate Moraine Moraine looming looming above above the the flat flat outwash surface surface is is impressive. impressive. A A few few overgrown kettles are are adjacent to to the the highway highway on on the the south south side. side. To the north, north, rising rising above the flat flat outwash plain, plain, an incongruous landform landform resembles resembles the classic moulin kames kames of of the the northern northern Kettle Kettle Moraine. Moraine. This is is the artifically—created artifically-created ski ski hill hill near near Oconomowoc. Oconomowoc. 182.0 182.0 (1.0) (1.0) An An exit exit on on County County CC CC provides provides aa side side trip trip to to view view the the Kettle Kettle 26 26 �Mileages Mileages Interlobate Moraine Moraine from from the the observation observation tower tower on on Lapham Lapham Peak. Peak. This This tower tower provides provides an an excellent excellent overview overview from from the the highest highest vantage vantage point point in in the the southern southern Kettle Kettle Interlobate Interlobate Moraine. Moraine. To To the the west west is is Genesee Genesee Flat. Flat. To the east is is the the glacial glacial spillway spillway described described at at mile mile 184. 184. Several scenic, scenic, glacial glacial lakes lakes are are also also visible. visible. To reach Lapham Peak, Peak, go south south on County CC (Kettle (Kettle Moraine Scenic Scenic Turn left (east) onto Drive) about 1.8 miles to a crossroad. Drive) about 1.8 miles to a crossroad. left (east) onto Government Government Hill Hill Road. Road. Continue about 0.7 0.7 mile to to aa small small park that includes includes the the Lapham Lapham Peak Peak observation observation tower. tower. The The tower tower for for state station station WHAD WHAD is is also also located located here. here. A A marker at at 1233 1233 feet feet of elevation, elevation, on a a glacial erratic boulder in in the the park, park, is is dedicated dedicated to one of of Wisconsin's earliest earliest geologists geologists and and naturalists: naturalists: "Increase A. A. Lapham, Lapham, Eminent scientist scientist and and useful useful citizen." citizen." The route route ahead ahead crosses crosses a a region region of of pitted (kettled) (kettled) outwash outwash deposits, and and many many kettle kettle lakes lakes dot dot the the landscape. landscape. Nagawicka Nagawicka Lake, Lake, immediately immediately north north of of the the highway, highway, is is such such aa lake. lake. Other examples examples are are Upper and Lower Nemahbin lakes, lakes, which sandwich the interstate west of of here. here. The ice blocks which formed formed these lake lake about 1 mile west basins were derived from from the the Green Green Bay Bay lobe lobe along along the the western western edge edge of the Interlobate Interlobate Moraine. Moraine. 183.0 183.0 (1. 0) (1.0) The interstate approaches the crest of the Interlobate Interlobate Moraine. Moraine. A small ski area south of the highway utilizes A small ski area south of the highway utilizes part part of of this this slope. slope. From the crest of this ridge, ridge, the radio tower and and observation tower tower on Lapham Lapham Peak are are visible visible south south of of the the highway. highway. The Kettle Interlobate Moraine, Moraine, which trends northeasterly across across Wisconsin for for about 130 miles, miles, from from Walworth to to Kewaunee Kewaunee counties, counties, It is is probable that the is the the premier glacial feature is feature in in Wisconsin. Wisconsin. It resistant Silurian Silurian dolomite dolomite influenced the the position of the inter— resistant interlobate deposits deposits in in this this area, area, by retarding the spread of the Green lobate Bay lobe. lobe. Within this morainal complex, complex, the country country is is rolling rolling and and rugged, rugged, This feature formed with abundant knobs knobs and and kettles. kettles. formed during the Woodfordian glacial advance by a a juxtapositioning juxtapositioning of of the the terminal terminal inoraines of the the Green Green Bay Bay and and Lake Lake Michigan Michigan lobes. Between these moraines of walls, complex drainageways drainageways developed, developed, and meltwaters reworked icy walls, some a some of the morainal materials. The resultant deposits are a Much of the mixture of sand, mixture sand, gravel, boulders, and and clayey clayey till. till. material was was derived from the Silurian dolomite, coarser material dolomite, but igneous and and metamorphic metamorphic rock rock types types from from far far to to the the north north are are also also igneous present. 184.0 184.0 (1. 0) (1.0) This highway highway follows an Wisconsin 83 83 exit. exit. This follows low ground along an abandoned drainage drainage channel channel which which carried the the last meltwater that abandoned drained southward southward through through this this part part of the the Kettle Kettle Interlobate drained Water drained drained down down this this .25 mile wide wide valley valley until until it Moraine. .25 mile Moraine. Water reached Wales, Wales, about about 33 miles miles to to the the south, south, where where it it cut cut through through the the reached Gravel outwash outwash terraces terraces flank flank Interlobate Interlobate Moraine Moraine to to flow west. west. Gravel this drainage, drainage, and and aa remnant remnant of aa high terrace terrace is this is visible on the east east side side of this valley. 27 27 �Mileages 185.0 (1.0) (1. 0) Pewaukee Lake Lake lies lies to to the the north. north. The church at at Holy Holy Hill, Hill, on on aa kame kame perched high on the Interlobate Moraine, is also visible to the north Interlobate is also visible to the north on aa clear clear day. day. Pewaukee Lake occupies aa preglacial river river valley valley which which was scoured into the Upper Ordovician Maquoketa Shale. This Shale. This ancient valley was blocked by morainal debris deposited along along its its eastern eastern margins by the Lake Michigan lobe during the Woodfordian ice lobe the ice advance. advance. 186.0 (2.0) Ground moraine deposits in in this this area area are are thin. thin. North of the highway on the west edge of the Tumblebrook golf golf course, course, there there is is aa small small quarry in Silurian dolomite. Glacial striae on bedrock in this in Silurian dolomite. area indicate that ice ice movement was was west—southwest. west-southwest. the road, road, the the names names of a South of the a subdivision (Pebble (Pebble Valley), Valley), and Hill), bear testimony to the character of the aa farm (Stoney (Stoney Hill), the morainal material. material. 188.0 (3.0) Exit County GG to the highway to Pewaukee. Pewaukee. A drumlin field lies south of the for the next several several miles. miles. These east—west east-west trending drumlins are composed of sandy clay till till that contains abundant boulders. boulders. 191.0 (1. 0) (1.0) Exit County County F. F. West of this intersection, intersection, the the route route crossed crossed the the Pewaukee River, River, which which is is tributary tributary to to the the Fox. Fox. This valley is is paralleled by outwash terraces, terraces, which are commercial commercial sources sources of of sand sand and gravel gravel in in this this area. area. 192.0 (2.0) Exit Wisconsin 164 164 to to Sussex Sussex and and Waukesha. Waukesha. lins are ,north north and and south south of of the the highway. highway. East-west trending drum- Colonel Dunbar, Dunbar, while visiting Waukesha in 1869, drank drank from from some some of of the springs the springs which issue from the glacial drift, drift, with high amounts amounts of of dissolved calcium calcium magnesium magnesium bicarbonate. bicarbonate. Upon deciding that the local local mineral waters had eliminated his "incurable "incurable ailments," ailments," he he began to to advertise advertise his cure cure nationwide, nationwide, and and Waukesha Waukesha soon soon became became aa fashionable health spa. fashionable spa. Although this fad fad waned after about about 30 30 years, years, bottled spring water is still a Waukesha product. spring is still a Waukesha product. Waukesha Waukesha is is located located on on the the Fox Fox River. River. Outwash terraces along along this this river are important commercial sources for for sand and and gravel. gravel. Since the glacial drift is quite thin in this region, the region, Silurian dolomite is is extensively quarried along the valley of the Fox from from the the Waukesha area area northward to to Sussex, Sussex, Lannon Lannon and and Menomonee Menomonee Falls. Falls. 194.0 (3.0) U.S. 18 (Blue Exit U.S. (Blue Mound Road) Road) to Waukesha and WiscOnsin Wisconsin State Patrol Headquarters. 197.0 (2.0) Exit Moorland Moorland Road. Road. The flat terrain here is is poorly drained, clayclayground moraine. moraine. Ditching and channelization were required required for for rich ground the extensive development development of of the the land land north north of of the the highway. highway. The golf course to the south represents a more intelligent intelligent land land use. use. A few few isolated patches of moraine, moraine, and several east—west east-west trending trending drumlins rise rise above above the the generally generally swampy swampy ground. ground. The route route ahead descends aa prominent ridge, The ahead descends ridge, which is part of the 28 �Mileages Mileages Woodfordian Woodfordian Lake Lake Border Border recessional recessional moraine moraine system. system. Sunny Sunny Slope Slope Road Road traverses traverses this this ridge ridge crest, crest, which which forms forms the the drainage drainage divide divide between between Lake Lake Michigan Michigan and and the the drainage drainage basin basin of of the the Fox Fox River. River. The The Fox Fox flows flows southward southward parallel parallel to to the the Woodfordian Woodfordian moraines moraines to to reach reach the the Illinois Illinois River, River, and and ultimately ultimately the the Gulf Gulf of of Mexico Mexico via via the Mississippi. Mississippi. the 199.0 199.0 (2.0) (2.0) Milwaukee/Waukesha Milwaukee/Waukesha county county line. line. Enter Milwaukee Milwaukee County. County. Exit Exit 1-894 1-894 (U.S. 45) south south to Chicago and U.S. (U.S. 45) U.S. 45 45 north north to to Fond Fond du du Lac. Lac. The The Milwaukee Milwaukee County County Zoo Zoo is is northwest northwest of of this this intersection. intersection. 202.0 202.0 (2.0) (2.0) Exit Wisconsin Wisconsin 181 181 (84th (84th Street). Street). The The Wisconsin State State Fair Fair Park Park Exit grounds and an Olympic-size outdoor ice ice rink rink are are southeast southeast of of this this Wisconsinan (Woodfordian) junction. junction. The interstate traverses traverses Wisconsinan (Woodfordian) ground moraine moraine and and recessional recessional moraines moraines of of the the Lake Lake Border Border system. system. The The highway highway here here is is essentially essentially parallel parallel to to the the east-west east-west direction direction of ice ice movement, movement, and and consequently consequently the the morainic ridges ridges trend trend north— northsouth. About 100 100 feet feet of glacial glacial deposits, deposits, primarily primarily aa boulder boulder south. clay clay till, till, overlie overlie Silurian Silurian dolomite dolomite in in this this area. area. 204.0 (1.0) (1.0) U.S. U.S. 41 41 exit exit (north (north and and south). south). Milwaukee County County Stadium, Stadium, home home of of the Milwaukee Brewers and also the site of the Milwaukee games and also the site of the Milwaukee games of of the Green Green Bay Bay Packers, Packers, is is just just west west of of this this junction. junction. The large large hill southwest of the stadium is a Silurian dolomite stadium is a Silurian dolomite exposure exposure on on the grounds of the the the U.S. U.S. Veterans Veterans Administration Administration Hospital. Hospital. 205.0 (1.0) (1.0) Route parallels the the industrial industrial complex complex along along the the east-west east-west trending trending Three large, glass domes in Mitchell Park River valley. valley. large, Menomonee River are to the the south. south. One contains a a display of vegetation are visible to native to a desert environment, another features environment, another features tropical tropical plants, plants, and the the last houses houses local flora and is used for special flower shows. shows. 206.0 Junction 1—94 1-94 with with 1-43 1-43 (U.S. (U.S. 141) 141) and and 1—794. 1-794. The Milwaukee Harbor is to the southeast, toward the highrise Harbor Freeway bridge along is to the southeast, the the lakeshore. Three rivers merge at at the the Milwaukee Milwaukee Harbor. Harbor. flows from from the the north north and and west, west, the the Milwaukee Milwaukee flows north, and the north, the Kinnickinnic River originates The Menomonee Menomonee River The River comes comes from the the to the west and south. south. Milwaukee grew from three settlements that were originally separated Walker's Point, by these rivers. rivers. Walker's Point, east of the Kinnickinnic River, River, is now now dominated dominated by by the the towering towering clock clock of of the the Allen Allen Bradley Company. Company. is The Milwaukee River flowed between Kilbourntown on the west and The Juneautown to to the the east. east. The high high smokestack smokestack to to the the east east is is part part of the the Jones Jones Island The Here, sewage sewage sludge sludge is is dried and Metropolitan Sewage Plant. Metropolitan Plant. Here, converted to Milorganite, Milorganite, aa commercial converted commercial fertilizer. fertilizer. Jones Island, Island, an an artificially artificially breached breached peninsula, peninsula, also contains Jones contains tanker pier, pier, cargo cargo terminals terminals and and aa heavylift heavylift wharf, wharf, and is aa tanker is Milwaukee's inner harbor headquarters for the Port of Milwaukee. Milwaukee's headquarters 29 �was developed by an enlargement of the lower Kinnickinnic River, was River, and it it serves serves as as the the service service and and wintering area for and for part of U.S. Steel's iron ore carrier fleet. u.s. fleet. END OF OF LOG END Proceed through downtown Milwaukee to Proceed to the the Pfister Pfister Hotel. Hotel. 30 30 �,/ * N I o0 NE NE QUARRY QUARRY A A ,,- \\ \I / '\ '\ rn 1! 200 FEET FEET Flynn's SW QUARRY QUAR RY QUARRY -- — \ / , , / -:.- \I I " \ "'/ ,"- '\, [J I " -V,-. \ \ / .::: N ~ A' \ \ ./ E X P L A N AT I 0 N EXPLANATION METABASALT METABASALT DIKE DIKE STRUCTURE RELATED RELATED TO TO I• STRUCTURE QUARRY OPERATION OPERATION QUARRY J o DEBRIS DEBRIS PILE PILE D [Tj GRANITE PORPHYRY r,o "0) GRANITE PORPHYRY DIKE DIKE l'v I GRANITE GRANITE AT AT REDGRANITE REDGRANITE Figure Figure 2. 2. ! y' 1' QUARRY WALL OR STEEP STEEP QUARRY WALL OR SLOPE SLOPE Pace Pace and and compass compass map map of of Flynn's Flynn's Quarry Quarry County County Park, Park, Waushara Waushara County. County. 32 32 �Geologic Geologic Stop Stop Descriptions Descriptions . 11 Eugene Eugene I. I. Smith Smlth STOP 11 -- GRANITE GRANITE AND AND RELATED RELATED INTRUSIONS INTRUSIONS AT AT FLYNN'S FLYNN'S QUARRY QUARRY COUNTY COUNTY PARK PARK STOP Location: All All exposures exposures at at this this stop stop are are reached reached by by an an easy easy walk walk from from the the ParkParkLocation: ing area area (Fig. (Fig. 2). 2). ing Description: Description: Granite Granite Fine—to Fine-to medium—grained medium-grained red red (granophyric) (granophyric) granite with micropegmatitic micropegmatitic and and myrmeketic texture texture is is exposed in in three three quarries within the the boundaries boundaries of of Flynn's Flynn's County Park Park (Fig. (Fig. 2). 2). Quartz and and alkali alkali feldspar feldspar compose compose 90 90 to to 98 98 perperQuarry County cent cent of of the the rock, rock, with biotite biotite (partially (partially or or wholly altered altered to to chlorite), chlorite), sphene, sphene, muscovite and and zircon zircon as as subordinate subordinate minerals. minerals. The granite for for the the hornblende, muscovite most part part is is texturally texturally homogeneous. homogeneous. Locally Locally however, however, grain grain alignments alignments and and fine— fineThe mineralogy and texture of the granite grained bands (dikes?) (dikes?) are are observed. observed. (especially the intergrowths intergrowths of of quartz quartz and and alkali alkali feldspar) feldspar) suggest suggest that that it (especially the it is is a a shallow intrusion. shallow intrusion. Granite Porphyry Dike Dike In northeast quarry, quarry, the the granite granite is is cut cut by by aa 200 200 m wide wide east east trending In the the northeast granite porphyry dike dike (strike (strike east—west, east-west, dip dip 75° 75° to to the the south). south). The dike rock rock is characterized by by large large (5 mm) alkali alkali feldspar feldspar phenocrysts phenocrysts set set in in aa fine— is characterized (5 mm) fineof quartz, quartz, biotite biotite and and chlorite. chlorite. The finely disseminated chlorite grained matrix of gives the matrix of the the dike rock a a green color, color, thus thus making it easily distinguishable from from the the red red granite. granite. The contact between granite and dike rock is is clearly visible visible on on aa ledge ledge on on the the north north wall wall of of the the northeast northeast quarry quarry (Fig. (Fig. 3). 3). In detail, the the contact contact bends bends in in and and out, out, suggesting suggesting some some assimilation assimilation of granite In detail, of granite during intrusion. intrusion. Fragments (xenoliths) (xenoliths) of of granite are found found within the the dike near the the contact; contact; also also feldspar feldspar phenocrysts phenocrysts are are concentrated concentrated and and weakly weakly aligned aligned near in the granite mornhvrv porphyry dike at at the the contact. contact. in the Figure 3. Figure View of of the the contact contact between between the the granite granite porphyry porphyry dike dike and and granite granite View Note in Flynn's Flynn's Quarry Quarry County County Park (dashed in (dashed line traces traces contact). contact). that the the feldspar feldspar phenocrysts phenocrysts are are concentrated concentrated and and weakly weakly aligned aligned that in the the dike dike rock near the in the contact. contact. of Science, Science, University University of of Wisconsin-Parks Wisconsin—Parkside, lDivision ide , Kenosha, Kenosha, Wisconsin Wisconsin 53141. 53141. Division of 33 33 �Chemically, the the dike dike is is aa less less differentiated differentiated phase phase of of the granite. It It is Chemically, the granite. lower in SiO , and K K20 and higher higher in in Al A1203, Fe20 and CaO when when compared to lower 0 and 0 , FeO + Fe 0 and 2 3 uarry granite 1, an~lyses analyses 18 18 and and 31). 3). In terms terms of trace the Flynn's auarry g~anite (Table (Table 1, In elements the the dike dike is is higher higher in in Ba, Ba, and and has has aa lower lower Rb/Sr Rb/Sr ratio than the granite. elements the granite. , Metabasalt Dike Dike On the the north north wall wall of of the the main main quarry, quarry, the the granite granite is cut by a m wide) wide) On is cut a thin (2 (2 m 0 metabasalt dike striking striking N. N. 80 80 E. E. and and dipping dipping 700 70 to to the south (Fig. (Fig. 2). 2). The dike rock is is fine fine grained grained and and has has aa distinctive distinctive green color color on both weathered and fresh ~ock fresh surfaces. In thin section, the metabasalt displays intergranular texture with In thin section, the metabasalt displays intcrgranular texture with laths of of plagioclase enclosing mats of laths of epidote, epidote, clinozoisite clinozoisite and and iron iron oxide. oxide. The contact between the metabasalt and granite is clearly observed on a contact between the metabasalt and granite is observed a ledge just above Here lenses lenses of of granite granite are above water level level (Fig. (Fig. 4). 4). Here are completely enclosed by stringers of metabasalt. Except for these lenses, no granite fragments lenses, fragments were noticed within dike rock. These contact relationships suggest that rock. that the the meta— metabasalt intruded primarily by the dilation of country rock. intruded primarily by the dilation of country rock. Comparison of of Flynn's Flynn's Quarry Quarry Granite Granite to to Granite Granite in in Nearby Nearby Areas: Areas: Redgranite to to Pine Bluff— Bluff- Granites and Dikes Granites similar in Granites in mineralogy and and texture texture to that that at at Flynn's Flynn's Quarry are exposed in discontinuous discontinuous outcrops Redgranite to Pine Bluff exposed outcrops from from the the city of of Redgranite (Fig. (Fig. 5). 5). Dikes of of metabasalt trending east—west east-west and and approximately approximately N. N. 45E. 45E. cut cut the One of the most easily visited of the granite in in many many localities. localities. One the most of these dikes forms distinct ridge ridge jutting into the forms aa distinct the quarry lake lake north of S.T.H. S.T.H. 22 in downtown Redgranite Redgranite (just (just north north of of Griffs' Griffs' Cafe). Cafe). A A coarse—grained coarse-grained diorite dike cuts granite in in a small small quarry in in the the N N 1/2, 1/2, Sec. Sec. 27, 27, T.18 N. N. R. R. 11 11 E. E. (Fig. 5). The The dike dike is about 5 m (Fig. 5). m thick thick and and trends trends N. N. 40 40 E. E. (dip vertical). In thin section, section, flow—aligned flow-aligned plagioclase plagioclase laths laths surround surround clots clots of of chlorite chlorite and and epidote. epidote. Montello Granite Granite Another granite similar in in lithology to to that that at at Flynn's Quarry and and at at Red Red Granite is located in the city of Montello (Buckley, 1898). in the city of Montello (Buckley, 1898). There is is also also an an exposure to the the east of Montello in in the the SE SE 1/4, 1/4, Sec. Sec. 9, 9, T. T. 15 15 N., N., R. R. 10 10 E. E. This granite granite was was extensively extensively quarried quarried from from 1880 1880 to to 1976. 1976. President Grant's sarcophagus in in New York City is is carved carved from from Montello Montello Granite. Granite. The rock in in the the Montello quarry is is a a red granite composed of of intergrown intergrown quartz and and alkali alkali feldfeldspar crystals (myrmeketic (myrmeketic and and micropegmatitic textures textures are common) common) with chlorite, chlorite, biotite, biotite, and and euhedral euhedral zircon zircon as as accessory accessory minerals. minerals. Attempts to to date this this rock rock by the the fission—track fission-track technique technique failed because an an insufficient insufficient number of of zircon zircon grains were separated separated and and most most of of the the separated separated zircons zircons were were metamict. metamict. The Montello granite is is cut by thin thin metabasalt dikes (plagioclase (plagioclase and and sausserite sausserite as as dominant minerals) Quarry minerals) which which trend trend northeast, northeast, north—south north-south and and northwest. northwest. faces faces at Montello are are commonly commonly bounded bounded by by these these dikes. dikes. The metabasalt metabasalt dikes dikes are closely sheared at at their their margins; margins; several several dikes dikes are are sheared sheared throughout. throughout. The granite commonly shows shows aa dark red red bake zone zone extending 22 to to 5 5 cm em inward inward from from the the intrusive contacts, contacts, also small more common in granite near small grains grains of of pyrite are more metabasalt metabasalt than than farther farther away away from from the the granite—dike granite-dike contacts. contacts. 34 34 �Figure Figure 4A. 4A. View of a a thin metabasalt metabasalt dike that that The dike in this view County Park. County Park. in this view dips about southern southern contact contact (left) (left) dips about Granite (G) to the north of line). (G) in the dike rock rock (D). (D). Figure 4B. Figure 4B. Close—up of the contact between the Close-up the metabasalt dike dike and and granite. granite. Basalt intruded granite along Basalt along closely closely spaced spaced joints. joints. 35 cuts cuts granite in Flynn's Quarry is is 22 meters mete~s thick. thick. The 10° to the north north (dashed the dike appears appears as as a window �Lohrville Lohrville Quarries Redg ranj.t(f~~---/' .c-"~edgranite Quarry —2'FIynns Spring Lake, Lake"", /_Jf\. Flynn's Quarry (STOP (STOP I) I) Spring Quarri es Quarries I" WAUSHARA COUNT COUNTY WAUSHARA -MARQUETTE COUI COU .YY ;,.' - Quarry Quarry with with Diorite Dike Dike — T;-- GREEN GREEN LAKE LAKE COUNTY COUNTY 00 Berlin Gran ite Berlin Pine Pine Bluff Granite I I I o I I "--1 ~ Granite Montello Granite Buffalo Lake Figure 5. 5. 3:iiii~ 2 3 4 5 Miles 0 .Oiii32• 3iE! Mil es SCALE SCALE I I Princeton EXPLANATION ... C.J Granite Exposures ~ Quarry 00 City Field Trip Trip ~ Field Route Route Detailed route route map map from from Redgranite Redgranite to to Montello Montello showing showing granite granite Detailed exposures and and locations locations of important quarries. exposures quarries. 36 36 �_____________ _________ Chemical Comparisons: The granite at at Redgranite (and (and presumably Flynn's Quarry) Quarry) is is similar in in chemistry, mineralogy and age to that chemistry, that at Montello, Montello, except for noticably higher higher amounts of of Cu and Cr in amounts in the the Montello Montello Granite, Granite, (Table (Table 1, 1, analyses analyses 14 14 and and 18). 18). These similarities indicate that the granites are comagmatic and and that that they they formed during the same intrusive formed intrusive event. event. Studies of cuttings from from deep deep wells wells show that that granite lithologically similar to to that that exposed at at Redgranite and and Montello occurs in the basement over a a large area of south—central south-central Wisconsin. Wisconsin. These rocks rocks probably probably form form aa large large late—Penokean late-Penokean or or post—Penokean post-Penokean (1765 (1765 m.y. m.y. old) old) composite batholith which is exposed only in in the the Redgranite area area and and at at Montello (Smith, 1978c). (Smith, The similarity of the the granites at Montello and and Redgranite was noted noted long long ago by Weidman (1904) who labelled these rocks the Waushara Granite. (1904) labelled these rocks the Waushara Granite. Emmons (1940) also also suggested the presence of aa large (1940) large batholith batholith in in central central Wisconsin. Wisconsin. However, he did not distinguish between the older Penokean aged granites However, the aged granites in in central Wisconsin (Wausau area) area) and and the younger granites granites in south—central central the younger south-central Wisconsin. - 44 -- 3 -- - -- - -- - - 2 -- - 0. Co :::J 0 (I o I I I I I I o0200500400500600 200 300 400 500 600 0 10 Zr 20 - - - • ~I I I 3040 30 40 50 50 I 0 50 I I 10015020 100 150 20 3040 30 40 Cu Cr I --I 0) 50 Pb I I 100150200250 100 150 200 25 o Zn Zn 4— 4 3 -3 2 0. Co :::J 0 o1 ~I I 0 o 000 1000 500 Ba Ba ao 2.0 I I 50 50 00 100 I I 150 150 00 200 Sr La tOO 150 50 200 100 200 Rb 10 10 30 50 I I I 70 70 90 90 ItO 110 V Y (ppm) Figure 6 6. chemical groups groups (from Some elemental concentrations for for the four four chemical (from elemental concentrations for Smith, l978a). 1978a). Bars indicate indicate the the range range of of values values for each each chemical chemi~al Smith, group. Dot indicates that data point is is based based on on one one analysis. analysls. that the the data Dot group. 37 �Relationship of Granites to to Rhyolite: Rhyolite: The Redgranite Redgranite and and Montello Montello Granites Granites are are similar similar in in major major 8nd cnd mino~ minor element element The chemistry and and age age to to the the rhyolites rhyolites exposed exposed to to the the south south (stop for example) example) chemistry (stop 22 for (see table analyses 4-29; 4—29; and and Fig. Fig. 6; 6; and Smith, (see table 11 , analyses Smith, 1978c by Van Van Schmus, Schmus, 1978. 1978. These similarities similarities strongly strongly suggest suggest that that the the granites granites and and rhyolites rhyolites are are comagThese comag— matic. In other other words, words, the the granites granites may may represent represent the the magma magma chambers chambers from from matico In which the which the rhyolite ash—flow ash-flow tuffs tuffs were erupted. erupted. Later, its Later, granite intruded its own volcanic volcanic cover engulfing much of 9wn of the the rhyolite. rhyolite. Surviving Surviving rhyolite exists as roof roof pendants within as within the the granite. granite. , 38 38 �Table 1. 1. NEW CHEMICAL ANALYSES FOR CENTRAL WISCONSIN INLIERS AND IGNEOUS ROCKS ROCKS IN THE BARABOO BARA~OO AREA AREA 11 2 2 3 3 4 4 5 5 6 6 w CA, °t.O BB Ba Ba Co Co Cr Cr Cu La La Mo Ni Ni V Y Y Zr Pb Pb Rb Sr Zn Zn Sc Sc 20 20 1300 1300 33 32 32 30 30 49 10 10 12 12 77 32 32 320 28 165 165 210 210 55 70.61 0.37 14.29 0.92 2.03 0.34 1.61 4.45 3.78 0.92 0.04 0.08 99.55 70.26 0.30 14.10 0.86 2.66 0.10 1.02 1.48 4.29 3.69 1.32 1. 32 0.04 0.17 100.29 71.79 71. 79 0.28 14.46 1.40 0.86 0.07 0.30 1.34 3.48 4.63 1.25 1. 25 0.09 0.08 100.03 24 1350 33 15 20 55 10 10 10 33 38 440 22 22 154 212 190 55 25 1200 33 25 50 31 31 10 10 66 15 15 320 22 22 120 324 110 55 28 690 33 55 120 35 10 10 66 30 200 40 40 152 105 130 0.11 O.ll 8 8 99 10 GROUP 22 GROUP 11 69.28 Si02 0.42 Ti02 TiO2 A1203 13.90 Fe203 1.37 2.89 FeO 0.14 MnO 0.90 MgO CaO 1.68 Na20 4.17 K20 4.33 H20+ 0.92 0.07 H20H20— 0.18 P205 P205 TOTAL 100.25 7 7 71.81 71. 81 0.26 14.29 1.57 1. 57 0.90 0.06 0.20 1.15 4.14 4.54 1.09 0.05 0.09 100.15 33 650 33 10 55 40 10 10 88 22 230 30 125 97 70 72.95 0.25 13.77 13.77 1.69 0.72 0.06 0.26 0.91 3.88 4.46 0.73 0.04 0.04 99.76 71.11 71.11 0.28 14.68 1.67 0.84 0.06 0.26 1.11 4.00 4.35 1.21 1. 21 0.06 0.09 99.72 20 590 33 11 60 35 10 10 99 28 210 45 137 97 145 20 650 33 10 45 45 10 10 10 30 240 30 134 137 105 73.07 0.28 14.65 1.60 0.69 0.06 0.06 0.13 0.94 3.78 4.21 0.78 0.06 0.05 100.30 28 690 33 11 II 55 47 10 10 6 30 210 40 138 95 105 72.85 72.85 0.27 0.27 13.88 1.13 1.09 1. 09 0.05 0.05 0.27 0.27 1.09 1.09 3.58 3.58 4.53 0.96 0.05 0.05 0.10 99.85 71.85 71. 85 0.29 14.32 14.32 0.68 0.68 1.82 1. 82 0.09 0.09 0.26 0.26 1.25 1. 25 3.68 3.68 4.52 4.52 0.78 0.78 0.08 0.08 99.70 99.70 22 630 33 10 55 40 10 10 88 22 230 35 35 130 130 130 130 70 70 20 20 720 33 12 12 45 42 10 10 10 10 55 30 200 200 45 116 116 150 150 115 115 �Table 1. 1. (Continued) (Continued) 11 11 12 12 13 13 14 14 15 15 16 16 17 17 GROUP 22 Continued) GROUP (Continued) Si02 Si02 Ti02 A1203 A12O3 Fe203 FeO MnO MgO CaO GaO Na20 K20 H20+ H20P205 71.22 0.24 0.24 14.15 14.15 1.53 0.70 0.12 0.12 0.15 0.15 2.03 2.03 3.14 4.66 1.94 0.05 0.07 TOTAL 100.00 71.64 71.64 0.28 14.36 14.36 1.84 1.84 0.65 0.07 0.28 1.37 1. 37 4.07 3.74 1.50 0.09 0.10 99.99 18 18 19 19 20 20 GROUP 33 72.27 72 .27 0.30 13.83 13.83 1.51 1. 51 1.08 1.08 0.08 0.24 1.61 1. 61 3.87 3.72 1.51 1. 51 0.07 0.09 72.33 72 .33 0.28 13.62 1.94 1.94 0.68 0.07 0.29 1.27 4.70 3.73 1.16 0.05 0.10 75.83 0.21 11.92 11. 92 1.08 0.98 0.07 0.06 0.53 3.43 5.45 0.54 0.01 0.01 75.09 0.21 12.33 12.33 1.08 1.12 0.08 0.04 0.39 3.76 5.58 0.49 0.00 0.01 100.18 100.22 100.12 100.18 25 25 20 73.73 0.29 12.09 12.09 1.83 1.83 1.34 0.11 0.04 0.36 3.50 6.03 0.36 0.01 0.01 0.00 99.69 76.14 0.24 11.79 11. 79 1.10 1.10 0.88 0.02 0.09 0.45 3.16 5.65 0.58 0.01 0.01 0.01 0.01 100.12 75.30 0.19 0.19 12.04 12.04 1.04 1.04 1.04 1. 04 0.06 0.06 0.04 0.04 0.33 0.33 4.65 4.65 4.63 4.63 0.33 0.33 0.03 0.03 0.00 0.00 99.68 99.68 75.60 75.60 0.17 0.17 12.59 12.59 0.99 0.99 0.71 0.71 0.03 0.03 0.04 0.04 0.13 0.13 4.46 4.46 4.95 4.95 0.47 0.47 0.02 0.02 0.00 0.00 100.16 100.16 A o B B Ba Co Co Cr Cu La La Mo Ni Ni V yy Zr Pb Pb Rb Rb Sr Zn Zn Sc Sc 29 29 730 33 11 11 55 55 45 10 10 10 10 77 27 27 190 50 50 155 155 126 120 26 26 26 26 20 20 630 3 3 9 9 55 55 35 35 10 10 10 12 12 28 200 40 116 126 126 115 750 33 88 72 37 37 10 10 10 10 12 12 22 22 210 40 102 102 135 135 85 - - - 650 3 3 77 50 37 37 10 10 10 10 10 27 270 35 75 106 106 120 120 - 440 3 3 38 23 78 10 10 10 10 5 5 70 420 22 190 190 25 55 55 33 410 3 3 23 22 90 10 10 10 5 5 71 590 23 152 152 31 125 125 33 20 20 390 33 27 26 120 10 10 55 85 550 22 152 11 115 33 20 20 390 33 88 9 95 10 10 10 55 65 590 28 202 21 65 3 22 22 22 22 115 115 545 545 3 13 13 22 22 72 10 10 10 10 55 49 450 19 19 117 117 55 105 105 33 33 16 16 25 25 65 10 10 10 10 55 49 480 480 28 120 120 28 28 95 95 33 �Table Table 1. 1. (Continued) (Continued) 21 21 22 22 23 25 25 24 24 26 26 27 27 28 28 MARCELLON Si02 Si02 Ti02 Ti02 A1203 A1203 Fe203 Fe203 FeO FeO MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 H20+ H20+ H20H20P205 P205 TOTAL TOTAL B B oJ:>. Ba ,.... Co Cr Cr Cu Cu La La Mo Mo Ni Ni Co V V Y Y Zr Zr Pb Pb Rb Rb Sr Sr Zn Zn Sc Sc 75.68 75.68 0.12 0.12 12.46 12.46 0.68 0.68 1.09 1.09 0.13 0.13 0.12 0.12 0.36 0.36 3.66 3.66 5.00 5.00 0.57 0.57 0.04 0.04 0.07 0.07 99.98 99.98 78.25 78.25 0.11 0.11 11.05 11.05 0.95 0.95 0.84 0.84 0.07 0.07 0.16 0.16 0.29 0.29 3.66 3.66 3.72 3.72 0.70 0.70 0.09 0.09 0.09 99.98 75.55 75.55 0.14 0.14 12.21 12.21 0.42 0.42 1.71 1.71 0.17 0.17 0.29 0.29 0.45 0.45 2.82 2.82 5.16 0.85 0.04 0.06 99.87 76.63 0.12 11.38 11.38 0.97 0.97 1.13 0.12 0.12 0.13 0.62 3.16 4.66 0.59 0.01 0.06 99.58 40 40 240 240 33 54 54 95 95 47 47 10 10 55 55 50 50 200 200 22 22 131 131 72 72 100 100 55 25 25 160 160 33 44 44 115 115 35 35 10 10 11 11 55 42 42 180 180 19 19 108 108 61 61 130 130 55 20 20 180 33 62 62 160 160 50 50 10 10 55 55 52 52 200 180 180 165 165 61 61 105 105 55 35 35 240 33 41 80 45 45 10 10 55 55 50 50 190 190 14 14 130 130 46 110 55 , 29 29 BARABOO BARABOO 71.99 71. 99 0.26 0.26 13.57 1.93 1. 93 0.88 0.11 0.37 1.10 4.34 4.91 1.20 1. 20 0.08 0.03 100.77 . 30 970 5 5 15 15 40 90 10 10 55 88 60 150 22 102 95 95 102 102 77 71.80 0.32 13.74 1.30 1.72 0.11 0.58 0.85 4.43 4.49 0.60 0.04 0.13 100.11 100.11 20 1050 3 3 58 105 52 10 55 55 35 220 18 110 176 135 135 77 73.77 0.14 0.14 12.35 1.01 1.81 1. 81 0.13 0.13 0.39 0.94 3.26 4.92 1.25 0.04 0.07 100.08 100.08 22 22 410 3 3 58 58 110 42 10 55 55 38 160 19 108 82 82 110 55 73.83 73.83 0.16 0.16 13.33 13.33 0.96 0.96 1.21 1. 21 0.07 0.07 0.31 0.31 0.43 0.43 2.51 2.51 5.28 5.28 1.43 1.43 0.05 0.05 0.08 0.08 99.65 99.65 27 1100 1100 3 3 25 25 42 42 49 49 10 10 10 33 31 240 55 205 110 110 35 35 55 72.76 72.76 0.22 0.22 13.34 13.34 1.77 1.77 0.72 0.72 0.12 0.12 0.18 0.18 0.45 0.45 4.39 4.39 5.25 5.25 0.77 0.77 0.08 0.08 0.01 0.01 100.06 100.06 35 35 950 950 5 5 22 22 45 45 80 80 10 10 55 55 33 33 140 140 25 25 115 115 62 62 115 115 77 I �Table 1. 1. (Continued) Table (Continued) 30 31 32 33 34 35 35 36 36 37 37 DIKES Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO CaO Na20 1(20 K20 H20÷ H20+ H20— H20P205 P205 TOTAL >l:> t'V B B Ba Ba Co Co Cr Cr Cu La La Mo Mo Ni Ni V V Y Zr Zr Pb Pb Rb Sr Zn Sc 63.92 0.94 0.94 15.65 15.65 1.92 1. 92 4.38 0.20 1.40 1.40 1.58 1.58 4.71 4.71 3.34 3.34 1.51 0.11 0.11 0.31 0.31 99.97 99.97 72.10 0.30 12.74 1.06 2.21 0.12 0.09 1.08 3.12 6.12 0.73 0.03 0.04 99.74 20 20 20 1050 1050 1170 3 3 3 3 12 12 65 65 26 16 16 88 88 10 10 10 10 5 5 63 590 19 180 56 110 33 40 10 10 10 10 15 15 25 25 200 30 30 113 218 218 75 75 - 60.59 0.93 16.47 1.61 1.61 4.50 0.18 1.77 3.86 4.27 3.27 1.50 0.11 0.48 99.54 50 1200 4 4 16 70 68 10 10 6 6 92 28 28 220 25 25 105 514 180 20 48.94 0.99 17.84 2.21 6.56 0.19 6.57 9.59 3.25 1.11 2.97 0.12 0.31 100.29 25 660 24 42 50 10 10 10 24 24 240 11 11 75 75 28 28 38 642 180 27 49.47 0.94 14.77 1.46 7.42 0.19 7.05 6.54 4.59 1.09 5.57 0.18 0.36 99.63 52.02 1.27 15.84 2.66 7.72 0.21 4.78 7.87 3.23 1.66 1.96 0.10 0.34 99.66 15 680 20 155 77 21 10 19 240 14 86 15 15 55 55 270 170 25 25 33 950 20 27 27 75 75 29 10 10 270 31 31 180 180 20 20 154 154 419 190 24 24 60.72 0.99 15.72 1.13 5.86 0.19· 0.19 1.89 1. 89 3,94 3.94 3.90 3.31 1.43 0.10 0.46 99.64 56.21 1.33 1.33 13.20 13.20 1.95 1. 95 6.66 6.66 0.14 0.14 5.10 6.01 3.09 2.56 2.34 0.14 0.98 99.71 22 22 1250 77 20 32 32 33 33 10 16 55 55 32 32 240 22 22 155 155 420 220 16 16 70 70 1100 37 150 80 95 95 10 10 51 51 260 260 45 620 21 21 75 75 625 160 160 23 23 I �Table 1. 1. (Continued) (Continued) Si02 Si02 Ti02 Ti02 A1203 A1203 Fe203 Fe203 FeO FeO MnO MnO MgO MgO CaO Na20 Na20 K20 K20 H20+ H20+ H20H20P205 P205 TOTAL TOTAL ..,. w B B Ba Ba Co Co Cr Cr Cu Cu La La Mo Mo Ni Ni V V yY Zr Zr Pb Pb Rb Rb Sr Sr Zn Zn Sc Sc 38 38 39 39 40 40 69.76 69.76 0.37 0.37 13.77 13.77 0.76 0.76 2.25 2.25 68.44 68.44 0.50 0.50 14.20 14.20 1.46 1.46 2.99 2.99 0.17 0.17 0.62 0.62 2.02 4.78 4.78 3.06 1.11 1.11 0.04 0.13 99.52 70.22 70.22 0.35 14.26 14.26 0.94 2.47 2.47 0.19 0.34 0.34 1.30 4.48 3.76 1.07 0.06 0.09 99.53 17 17 990 990 33 28 28 135 135 40 40 20 20 10 10 55 22 22 280 280 25 25 105 105 205 205 97 97 20 20 1250 1250 55 15 15 110 110 29 29 20 20 55 22 22 29 29 260 260 20 20 1400 55 25 25 90 40 20 55 55 30 270 ----- ----- --- 10 55 0.13 0.43 0.43 2.30 2.30 . 3.95 3.95 3.55 3.55 2.12 2.12 0.03 0.03 0.11 0.11 99.53 99.53 ----- ----- 72 72 420 84 84 275 275 41 41 42 43 43 71.20 71.20 0.47 0.47 14.90 1.72 1.60 67.60 67.60 0.44 0.44 15.10 1.75 1. 75 2.24 2.24 76.17 76.17 0.17 0.17 12.05 0.96 0.96 1.00 0.03 0.11 0.26 3.76 4.27 0.63 0.07 0.06 99.53 ----- --- 0.72 0.71 0.71 1.70 1. 70 5.98 0.70 0.40 1.10 2.10 1.95 1.95 4.95 1.60 0.90 100.38 100.62 ----- 18 550 33 45 410 33 20 10 10 40 20 220 220 10 190 190 26 110 66 --- 25 25 450 25 17 370 35 20 17 35 20 220 40 40 180 79 205 66 16 16 165 165 33 45 45 155 55 20 10 17 26 340 16 95 26 120 55 �Table 1. 1. Number Sample Number Explanation Description. Description 1. 1. 179 Coarse-grained rhyolite dike on Observatory Hill. 2. 2. 180 Contact zone of coarse-grained rhyolite dike on Observatory Hill. on Hill. 3. 3. 183 Baxter Hollow Hollow Granite. Granite. 4. 89 5. 5. 102 Marquette rhyolite rhyolite (unit (unit G). G). 6. 6. 106 Marquette rhyolite rhyolite (unit (unit G). G). 7. 7. 101 Marquette rhyolite rhyolite (unit (unit F). F). 8. 8. 100 Marquette rhyolite rhyolite (unit (unit E). E). 9. 9. 103 Marquette rhyolite rhyolite (unit (unit D). D). 10. 104 Marquette rhyolite rhyolite (unit (unit D, D, massive massive phase). phase). 11. 91 Marquette rhyolite rhyolite (unit (unit C). C). 12. 92 Marquette rhyolite rhyolite (unit (unit B). B). 13. 98 Marquette rhyolite rhyolite (unit (unit B). B). 14. 99 99 Marquette rhyolite rhyolite (unit (unit B). B). 15. 15. 107 Montello Granite. Granite. 16. 16. 108 Observatory Hill Hill rhyolite. rhyolite. 17. 17. 109 Endeavor rhyolite. rhyolite. 18. 110 Granite at Redgranite collected collected in in Flynn's Flynn's Quarry. 19. 19. 112 Berlin rhyolite. rhyolite. Marquette rhyolite (unit (unit C) G) from from Noble's Quarry. Samples 4-14 are are keyed keyed to to figure figure 45. 45. 44 �Table Table 1. 1. Explanation Explanation (Continued) (Continued) 20. 20. 114 114 Utley Utley rhyolite. rhyolite. 21. 21. 173 173 Marcellon Marcellon rhyolite rhyolite (unit (unit A). A). Sample Sample numbers 21-27 are keyed to figure numbers 21-27 are keyed to figure 33. 33. 22. 22. 176 176 Marcellon Marcellon rhyolite rhyolite (unit (unit A). A). 23. 23. 174 174 Marcellon Marcellon rhyolite rhyolite (unit (unit B). B). 24. 24. 161 161 Marcellon rhyolite rhyolite (unit (unit B). B). 25. 25. 145 Marcellon rhyolite rhyolite (unit (unit C). C). 26. 26. 175 175 Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). 27. 27. 178 178 Marcellon rhyolite rhyolite (unit (unit D). D). 28. 28. 182 182 Caledonia Church rhyolite rhyolite (south (south limb limb of the the Baraboo Syncline). Syncline). 29. 29. 147 Baraboo rhyolite from the the NE NE ~, , sec. 23, rhyolite from T. 12 T. 12 N., N., R. R. 7 E. 30. 30. 105 Marquette andesite andesite dike dike (figure (figure 45). 45). 31. 31. 111 111 Granite porphyry dike from from Flynn's Quarry County Park. Park. 32. 32. 148 Marcellon andesite andesite dike dike (figure (figure 33). 33). 33. 33. 177 Marcellon basalt dike dike (figure (figure 33). 33). 34. 34. 153 Netabasalt dike Metabasalt dike at Montello (collected (collected from from 23). quarry just north north of of S.H. S.H. 23). 35. 35. 154 154 Metabasalt dike at Redgranite (from (from quarry city of Redgranite). 36. 36. 155 dike from granite quarry near Diorite dike from granite 11 E.). E.). 27, T. T. 18 N., R. Spring Green Green (NE (NE ~,, sec. 27, Spring R. 11 37. 37. 184 Denzer diorite 45 45 �Pable 1. 1. Table Explanation (Continued) (Continued) Explanation 38. 38. 192 192 Dacite dike dike at at Marquette Marquette (figure Dacite (figure 45). 45) . 39. 39. 190 190 Dacite dike dike at at Marquette Marquette (figure Dacite (figure 45). 45) . 40. 40. 191 191 Dacite Dacite dike dike at at Marquette Marquette (figure (figure 45). 45) . 41. 41. 210 210 Dacite Dacite dike dike in in the the Utley Quarry. Quarry. 42. 42. 211 211 Andesite Andesite dike dike in in the the Utley Quarry. Quarry. 43. 43. 193 193 Taylor Farm rhyolite. Taylor rhyolite. major element element analyses analyses on on Table Table 6 (except All major #41 and (except 'ft4l and 42) 42) were made made using conventional wet-chemical methods were methods (K. (K. Aoki, Aoki, analyst). Major element analyses 41 and 42 were analyst). were done done by 0. Joensuu. Joensuu. Trace element analyses (Rb, O. (Rb, Sr, Sr, Pb Pb and and Zn) Zn) by atomic absorption spectrometry (0. (0. Joensuu, analyst). analyst). All other trace trace elements by optical emission spectrography spectrography (0. Joerisuu, analyst). (0. Joensuu, analyst). The for Zr Zr are are accurate accurate to to The result~ result for ± 107g. Sr and Rb are accurate to ± 10%. Sr and Rb are to -- 5% the amount present present 5% of of the xcept for ~xcept for low low Sr Sr (less (less than than 20 20 ppm) ppm) which which is is accurate accurate to to 1070 of -- 10% of the the amount amount present. present. 46 46 �') ( .5 MILES 0 zz <{ a:: CD EXPLANATION rn :E <{ containing rounded Friable quartz sandstone, locally containing rounded rhyolite fragments C) u zz <{ a:: CD :E <{ C) u Ui lLI a:: LII E3 t"(\/] 0 ~ I Fine-grained Fine - grained rhyolite dike Coarse-grained rhyolite dike Coarse-grained rhyolite rhyolite Hill rhyolite Observatory Hill Q. a- Location of Location -+- Figure 7. Figure 7. field fi eld trip stops Quarry Vertical banding Geologic Hill adapted adapted from from Hobbs Hobbs and and Leith Leith (1907). (1907). Geologic map of Observatory Hill Approximate locations of field field trip Stops stops are superimposed. Contour interval 20 20 feet feet between between 800 800 and and 960 960 feet; feet; above above 960 960 feet feet the the interinterinterval val is val is 10 feet. feet. Contour Contour lines lines between between 900 900 and and 960 960 feet feet are are approxapproximately located. located. 48 �STOP 22 -- RHYOLITE RHYOLITE AT AT OBSERVATORY OBSERVATORY HILL HILL STOP Location: Location: Observatory Observatory Hill Hill (Hobbs (Hobbs and and Leith, Leith, 1907) 1907) is is one one of of five five porphyritic porphyritic rhyolite inliers inliers in in south—central south-central Wisconsin Wisconsin (others (others are are at at Endeavor, Endeavor, Taylor Taylor rhyolite Farm, Utley Utley and and Berlin). Berlin). The The hill hill is is formed formed by by steeply steeply dipping dipping flows flows of of Farm, quartz—and quartz-and alkali alkali feldspar—bearing feldspar-bearing rhyolite rhyolite tuffs, tuffs, cut cut by by coarse—grained coarse-grained and and fine-grained rhyolite rhyolite dikes. dikes. Observatory Observatory Hill Hill is is surrounded surrounded by by outcrops outcrops of of fine—grained Upper Cambrian Cambrian sandstone sandstone and and conglomerate conglomerate (Fig. (Fig. 7). 7). Upper The traverse traverse to to the the summit summit of of Observatory Observatory Hill Hill will will follow follow an an easy easy but but The It is Please stay together during the climb. sometimes indistinct trail. Please stay together during the climb. It is sometimes indistinct trail. Observatory Hill. quite easy to become lost on the slopes surrounding Observatory Hill. quite easy to become lost on the slopes surrounding Description: Description: Stop 2A 2A Stop The climb climb to to the the summit summit of of Observatory Observatory Hill Hill begins begins at at exposures exposures of of Cambrian Cambrian The sandstone just just to to the the east east of of the the bend bend in in Gillette Gillette Road Road (north (north side side of of road) road) sandstone of rhyolite The outcrop at this stop is about 300 m to the south (Fig. 7). outcrop at this stop is about m to the south of rhyolite (Fig. 7). outcrops on Observatory Hill and and is is composed composed of aa friable friable reddish—brown reddish-brown quartz quartz No fragments of rhyolite are found here; they are quite common, sandstone. fragments of rhyolite are found here; they are quite common, sandstone. however, in in sandstone sandstone exposures exposures closer closer to to the the rhyolite ledges. ledges. however, Stop 2B 2B Stop Walk from from stop stop 2A 2A to to the the northwest over over the the low low rise rise to to the the first first northnorththe outcrops of sandstone and east trending valley (Fig. 7). Note the outcrops Cambrian east valley (Fig. 7). A conglomerate conglomerate on the southeast side side of of the the valley valley (Fig. 8). 8). A conglomerate thick and and contains contains rhyolite bed in this exposure is approximately 40 cm thick cropping m to fragments to rhyolite rhyolite cropping out out 200 200 m to the the north. north. fragments lithologically similar to rounded and reach 10 cm in size The fragments within the conglomerate are rounded and reach 10 cm in size The fragments are pebbles in Occasionally, quartzite quartzite is is found found as as small small rounded rounded pebbles (Fig. 9). OCcasionally, in the the (Fig. 9). of quartz— The source of these clasts may be in the large area conglomerate. The source of these clasts may be in the large area of quartzconglomerate. (Smith, 1978c) 1978c) or or from from vein vein quartz quartz ite ite to to the the northeast northeast of of Observatory Hill (Smith, within the rhyolite. Figure Figure 8. 8. View of of Cambrian Cambrian sandstone sandstone outcrops outcrops at at stop stop 2B 2B on on the the south south flank flank View of 49 of Observatory Observatory Hill. HIll. �Figure 9A. Figure 9A. Figure Figure 9B. 9B. Close—up of of aa conglomerate conglomerate layer layer interbedded interbedded with with Cambrian sandClose-up stone at stop stop 2B. 2B. In fragments are angular (compare (compare In these these bands, bands, fragments with Fig. with Fig. 9B). 9B). Most Most of the fragments fragments are are porphyritic porphyritic rhyolites rhyolites similar to to those cropping out on Observatory Observatory Hill. Hill. View View of of large large rhyolite rhyolite fragments fragments (up (up to to 10 10 cm cm in in size) size) in in aa conconglomerate glomerate layer layer at at stop stop 2B. 2B. In In this this band, band, fragments fragments are are rounded rounded (compare (compare with with Fig. Fig. 9A). 9A). 50 50 �o On On Observatory Observatory Hill Hill exposures exposures of of conglomerate conglomerate containing containing rhyolite rhyolite pebbles pebbles are are usually usually restricted restricted in in occurrence occurrence to to aa zone zone 55 to to 20 20 mm wide wide about about the the rhyolite rhyolite ledges. The The conglomerate conglomerate layer layer at at Stop Stop 2B 2B is is located located an an unusually unusually large large distance distance ledges. from from rhyolite rhyolite exposures exposures (200 (200 m), m), and and its its deposition deposition probably probably reflects reflects aa relatively relatively short lived lived and and highly highly energetic energetic event. event. In In the the Baraboo Baraboo region region Dott Dott and and Dalziel Dalziel short (1970) (1970) reported large large boulders of of Baraboo Quartzite entrapped within Cambrian sandstone. They They envisaged envisaged transport transport of of cobbles cobbles and and boulders boulders by by waves waves and and strong strong sandstone. currents currents generated generated by by violent violent tropical tropical storms storms that that pounded pounded the the Baraboo Baraboo islands islands during Cambrian Cambrian time. time. Observatory Observatory Hill Hill probably probably existed existed as as aa small small island island in in during Strong late Cambrian time and was probably also hit by violent tropical storms. late Cambrian time and was probably also hit by violent tropical storms. Strong currents currents generated generated during during these these storms storms are are probably probably responsible respon$ible for for the the transtransport port of of rhyolite rhyolite fragments fragments away away from from the the Observatory Observatory Hill Hill island, island, thus thus forming forming the conglomerate band observed at Stop 2B. the conglomerate band observed at Stop 2B. Stop 2C 2C Stop From Stop Stop 2B 2B climb climb the the ridge ridge above above the the sandstone sandstone exposure exposure and and join join aa trail trail Follow this trail to where it running along along the the crest crest of of the the ridge. ridge. Follow this trail to where it joins joins the the running main main trail trail and and then then continue continue up up the the hill on on the the main trail trail (Fig. (Fig. 7). 7). Note the the first first outcrops outcrops of of rhyolite rhyolite to to your your left left and and straight straight ahead. ahead. There There vicinity is at least 500 feet feet of relief on the Precambrian surface in in the the vicinity of of is Observatory Hill. Hill. Just ahead rhyolite exposures are are at an elevation of of 1080 1080 Observatory northwest of of Observatory Observatory Hill, Hill, rhyolite rhyolite was was enfeet. About About 1200 1200inm to the the northwest feet. countered in in an irrigation irrigation well at a depth of 300 feet feet (480 (480 feet above above sea sea level). level). Cross into into the the rhyolite exposures and and continue to to the the trail trail junction. junction. the trail trail to to the the right right (south). (south). The fork to the the left left (north) (north) goes goes to to Follow the 1920's the summit summit where where aa lookout tower was was once once located located in the the lookout tower the early 1920's The ruins ruins of of the the tower can still still be be observed observed along along the (Fig. 7). The tower can the inscriptions (Fig. 7). carved into the rhyolite by by several several of of the the workers workers who manned manned the carved the rhyolite the tower. tower. Follow the trail (south) to aa large large area area of of bare bare rock rock which forms Follow the trail (south) to forms the bluff). sharp the south bluff). sharp southern southern edge edge of of Observatory Hill Hill (hereafter called called the rhyolite exposures exposures (20 From the south bluff bluff the the Marcelloii Marcellon rhyolite (20 km to to the the south) clear and the the Baraboo Baraboo Hills Hills (30 (30 km km to to the the southwest) southwest) can can be be easily easily seen seen on on aa clear and At this stop, we we will will examine examine the Hill rhyolite rhyolite and a day. At this stop, the Observatory Hill a day. coarse-grained dike. coarse—grained rhyolite dike. Observatory Observatory Hill Hill Rhyolite Rhyolite rhyolites exposed exposed The Observatory Observatory Hill Hill rhyolite rhyolite is is typical typical of of porphritic porphritic rhyolites The It contains contains phenocrysts phenocrysts of of quartz quartz (< 1 mm in in (~l in size size in south-central south—central Wisconsin. Wisconsin. It in size) size) set set in and in a a and rounded) rounded) and and pink pink to to white white alkali alkali feldspar feldspar (1 (1 to to 55 mm mm in On close close examination, examination, the the matrix matrix of of the the rhyolite rhyolite dark dark gray to black matrix. On and pumice pumice fragments. fragments. shows shows faint faint flow flow structure structure formed formed by flattened shards and o 50°E. The rhyolite rhyolite is In E. The is an an In general, general, these these bands bands dip dip steeply steeply and and strike strike N. N. 50 the entire entire hill. ash-flow hill. ash—flow tuff tuff and and is is remarkably remarkably texturally texturally homogenous homogenous over over the pheno—crysts Petrographic studies studies indicate indicate that that the the rhyolite rhyolite is is composed composed of of pheno-crysts Petrographic The devitrified ground-mass. ground—mass. The of of quartz quartz and and alkali alkali feldspar feldspar set set in in aa coarsely coarsely devitrified 51 51 �quartz is is anhedral anhedral and quartz and is is usually usually strained strained (7%). (7%). Some Some of of the the quartz quartz is is deeply deeply embayed. Alkali Alkali feldspar feldspar (23%) (23%) is is probably probably orthoclase orthoclase and and may may display display carlscarlsembayed. bad twinning. twinning. Accessory Accessory minerals minerals are are chlorite, chlorite, biotite biotite (?), bad epidote, iron (?), epidote, iron oxide and and zircon. The matrix matrix commonly commonly contains contains aligned aligned and and flattened flattened Y Y shaped shaped oxide zircon. The and cuspate cuspate shards. and shards. o In terms terms of of major major and and minor minor element element chemistry, chemistry, the the rhyolite rhyolite belongs belongs to to In chemical group group 33 (Table 1, analysis analysis 16; 16; Fig. Fig. 6), 6), of of Smith Smith (1978a) and is chemical (Table 1, (1978a) and is therefore similar similar in in chemistry chemistry to to granophyric granophyric granites granites and and porphyritic porphyritic rhyorhyo— therefore lites in the Fox River Valley. The group group 33 rhyolites rhyolites and and granites granites are are lites Valley. The distinguished , distinguished from from other other south-central south—central Wisconsin Wisconsin igneous igneous rocks rocks by by high high Si0 Si02, 2 K20/Na20, La, Zr, Y and Rb/Sr; and low CaO, A1203 and Ba (Table 1). K 0/Na 0, La, Zr, Y Rb/Sr; and low CaO, A1 0 and Ba (Table 1). 2 2 3 2 Coarse—Grained Rhyolite Coarse-Grained Rhyolite Dike coarse—grained rhyolite dike strikes north south across Observatory A coarse-grained rhyolite dike (Fig. 7). The dike is about m wide wide at (Fig. 7). The about 70 m at the south bluff but pinches out to to the north. m thick) dike of similar coarse—grained the north. A thin (15 (15 m thick) dike coarse-grained rhyolite strikes N. N. 50 E. E. across the strikes the southeast southeast slopes slopes of of Observatory Observatory Hill. Hill. These dikes were were originally identified by Hobbs and Leith (1907) dikes (1907) who referred referred to to them as as granite dikes. them The contact between the the dike and the Observatory Hill rhyolite is well displayed on the east edge the edge of of the the south south bluff. bluff. The contact shows complex interfingering of of dike dike rock rock into into Observatory Observatory Hill Hill rhyolite rhyolite (Fig. 10) and and in interfingering (Fig. 10) in locality a a rhyolite zenolith is is found found in in dike dike rock rock close close to to the the contact. contact. Locally the Hill rhyolite is intensely fractured near the the Observatory Hill the contact contact (Fig. 11). Also, quartz veins are concentrated on either side of the (Fig. 11). Also, the contact. contact. Extending 55 to to 10 10 m m into into the the dike from from the the intrusive intrusive contact contact is is aa fine— finegrained contact zone (chill zone?). grained contact zone zone?). The rock in this zone is is gray—green gray-green in in color and and contains large large plagioclase plagioclase phenocrysts. phenocrysts. Petrographic Petrographic studies studies of of the the dike rock rock of of the the contact zone zone reveal reveal sub— subhedral hedrHl zoned zoned plagioclase phenocrysts (30%) (30%) with cores altered to to sausserite sausserite and unaltered unaltered rims, rims, subhedral alkali feldspar feldspar (5%), (5%), fractured and broken quartz (3%) (3%) and and small small subhedral subhedral feather—like feather-like grains grains of of biotite (1%). (1%). The matrix is a microbreccia containing fragments of fine—grained is a fragments of fine-grained rhyolite, rhyolite, basalt and and eutaxitic eutaxitic rhyolite. rhyolite. At this this locality locality also also notice notice the the glacial glacial polish polish and and grooving. grooving. glacial striations trend N. 70° W. glacial striations trend N. 70° W. Here Here Walk Walk to to the the east east of of the the south south bluff bluff to to the the first first major major outcrop. outcrop. Here Here rhyolite in the central part of the dike is well exposed. rhyolite in the central part of the dike is well exposed. This This rhylite rhylite is is similar similar in in mineralogy to to that that of of the the contact zone, zone, but differs by by having having aa coarser—grained coarser-grained matrix matrix than than the the contact—zone contact-zone rock. rock. Also, Also, it it is is pink pink to to red red in in color color in in outcrop, outcrop, not not green green in in color color like like the the contact—zone contact-zone rock. rock. Petro— Petrographic graphic examination examination indicates indicates that that plagioclase is is the the dominant phenocryst phenocryst (46%). (46%). Alkali Alkali feldspar feldspar is is present present in in micropegmatitic micropegmatitic intergrowths intergrowths with with quartz quartz (21%). (21%). Quartz, Quartz, in in addition addition to to its its occurrence occurrence in in alkali alkali feldspar—quartz feldspar-quartz 52 52 �Figure 10. 10. Figure View of the contact between the coarse—grained coarse-grained rhyolite dike (below), (below), Hill rhyolite rhyolite (above). (above). Note Note the the fingers fingers of of and the Observatory Hill coarse—grained rhyolite rhyolite extending extending into into the the Observatory Observatory Hill coarse-grained Hill rhyolite rhyolite Also noteworthy are the numerous veins of quartz (dashed line). line). veins that the contact. contact. that roughly parallel the Figure Figure 11. 11. Close—up view view of of the the shattering shattering of of the the Observatory Observatory Hill Hill rhyolite rhyolite Close-up at dike. at the the contact contact with with the the coarse-grained coarse—grained rhyolite dike. 53 53 �intergrowths, intergrowths, (10%) include include (10%) oxide. These oxide. These is present present as as small small anhedral anhedral phenocrysts is phenocrysts (2%). (2%). Accessory Accessory minerals minerals chlorite in in irregular irregular clots, clots, epidote, epidote, clinozoisite, clinozoisite, and chlorite and iron iron minerals are set led groundmass groundmass (21%). set in in aa finely finely devitrif devitrified (21%). This dike dike and and aa fine-grained fine—grained granite at This at Baxter Hollow Hollow (Gates, (Gates, 1942) 1942) are are similar in chemistry, and form chemical group 1 of Smith (1978a) similar in chemistry, group 1 of Smith (1978a) (Table (Table 1, 1, analyses 11 and The rocks rocks are are distinguished distinguished from from the the other other analyses and 2; 2; and and Fig. Fig. 6). 6). The granites and rhyolites in the the Fox Fox River River Valley Valley and and Baraboo Baraboo area area by by higher higher granites and rhyolites in Ti02,, CaO, CaO, Ba, Ti0 Ba, V V and Sr Sr and and by by lower lower Si02 Si0 and and Rb.Sr Rb.Sr ratio. ratio. Both Both the the ObserObser— 2 2 vatory Hill Fox ovatory Hill rhyolite rhyolite and and the the Baxter Baxter Hollow Hollow Granite are younger than the the Fox River Valley Valley and and Baraboo Baraboo rhyolites. Baxter Hollow Hollow Granite Granite intrudes rhyolite River rhyolites. Baxter intrudes rhyolite (Gates, 1942) 1942) but but its its relationship relationship to the overlying Baraboo (Gates, Baraboo Quartzite Quartzite is is unclear (Dott Daiziel, 1972). unclear (Dott and and Dalziel, 1972). This This stratigraphic stratigraphic and and chemical chemical evidence evidence suggests that that the the intrusion intrusion of of the the Baxter Baxter Hollow Hollow Granite Granite and and the the Observatory Observatory suggests Hill rhyolite rhyolite was was a discrete igneous event that occurred after the emplacement Hill a discrete igneous event that occurred the emplacement and folding folding of of the the widespread rhyolite ash—flow and ash-flow sheets. sheets. The for aa short short time time at at the turn The coarse-grained coarse—grained rhyolite rhyolite dike dike was was quarried quarried for of the the century. century. This This opera~ion operation is evidenced by by aa large of is evidenced large area area of broken dike rock located just just below and and to to the the east east of of the the south south bluff. bluff. Labradorite Porphyry Dike Dike Hobbs and east—trending "labradorite porphyry" Hobbs and Leith (1907) (1907) reported reported an east-trending porphyry" dike just to to the the north north of of the the south south bluff. bluff. A for this this dike dike A careful search for revealed an east-trending east—trending fine—grained quartz—feldspar rhyolite dike about fine-grained quartz-feldspar 5 5 m m in in width. width. This This dike is is truncated by the north—trending north-trending coarse—grained coarse-grained rhyolite rhyolite dike as as is the "labradorite porphyry" porphyry" dike described by Hobbs and Leith. In terms terms of of location, location, orientation orientation and and stratigraphy, stratigraphy, it almost Leith. In it is is almost certainly the the same same dike dike mapped mapped by by them. them. In In thin thin section, section, this rock contains rounded rounded and embayed quartz phenocrysts phenocrysts (2%) (2%) and alkali feldspar with perthitic texture (altered (altered to to sericite sericite and and dusted dusted with with iron iron oxide) oxide) (3%). (3%). These minerals occupy a a fine—grained fine-grained matrix (devitrified) (devitrified) with iron oxide accentuating a a crude evidence of crude banding banding (95%). (95%). The only evidence of metabasalt on Observatory Hill is found found on on the the south south bluff. bluff. Here aa green metabasalt that that occurs occurs in in an an outcrop outcrop only 3 m m long long and and 0.3 0.3 mm wide wide may may intrude intrude rhyolite. rhyolite. Other Other Exposures Exposures of of Porphyritic Porphyritic Rhyolite: Rhyolite: Other Other exposures of of porphyritic porphyritic rhyolite rhyolite (Endeavor, (Endeavor, Utley, Utley, Berlin, Berlin, and and Taylor Farm) Farm) are are mineralogically, mineralogically, texturally, texturally, and and chemically similar similar to to the the rhyolite rhyolite at at Observatory Observatory Hill. Hill. However, However, common common in in the the Utley rhyolite rhyolite are are zones zones of of spherulites spherulites and and lithophysae, lithophysae, also also disk—shaped disk-shaped coarse—grained coarse-grained inclusions inclusions may may represent represent recrystallized recrystallized collapsed collapsed pumice. pumice. Rhyolite is is locally locally sheared sheared at at Berlin (Weidman, (Weidman, 1898) 1898) and and slickensided slickensided surfaces surfaces are are found found at at Utley Utley (Gram, (Gram, 1947). 1947). Rhyolite at at Utley Utley is is intruded intruded by by rhyolite, rhyolite, dacite dacite and and metabasalt metabasalt dikes. dikes. 54 54 �1/ / o / CC ~_ ~ I ~~v'1'\:Y N t4 /' .>.. ~ t J ~ ( --- -/ ) / (A/ (AI J ~< ~4 ~ /' EXPOSURES EXPOSURES /OF WELL BANDED WELL BANDED ?/ UNIT C ---- "---.,,, ~ -- ~ UW DEEP HOLE HOLE ) WAYNE / BUSH FARM BUSH FARM SPHEROIDS) I / f ~/u,,~ / (~~~~ ---- ,..- L BOX - PARK HERE WELL BANDED UNIT B QUARTZ VEINS EXPLANATION --- -o O .. 200 200 400 400FEET FEET I 4 4- CONTACT STRIKE AND AND DIP DIP OF OF STRIKE FLOW BANDING BANDING FLOW PLUNGING ANTICLINE ANTICLINE PLUNGING PLUNGING SYNCLINE SYNCLINE PLUNGING FIELD TRIP TRIP ROUTE ROUTE ,,~;~ FIELD I'' -+-+-+- FENCE FENCE Figure Figure 12, 12. Route Route map map for for traverses traverses at at the the Marcellon Marcellon rhyolite rhyolite exposures, exposures. Letters Letters A, A, B, B, CC refer refer to to Marcellon Marcellon rhyolite rhyolite unit unit numbers numbers (see (see text text and and Fig, Fig. 13). 13). 56 56 �STOP 33 -- THE THE MARCELLON MARCELLON RHYOLITE-SPHEROIDAL RHYOLITE-SPHEROIDAL TEXTURES TEXTURES STOP Location: Location: To To reach reach the the outcrops outcrops of of spheroidal spheroidal rhyolite rhyolite we we will will walk walk into into the the woods woods at at the the mail mail box box located located across across Monthey Monthey Road Road from from the the Wayne Wayne Bush Bush Farm. Farm. This This traverse traverse requires requires aa bit bit of of climbing climbing on on bare bare rock rock that that becomes becomes quite quite slippery during during wet wet weather. weather. Wear Wear proper proper field field boots boots and and take take considerable considerable slippery care while while on on this this traverse. traverse. care (west) (west) This This stop stop will will illustrate illustrate several several of of the the textural textural types types of of rhyolite rhyolite in in the the Marcellon inlier. inlier. See Figure Figure 12 12 for for the the traverse traverse route. route. The The rhyolite rhyolite exposures exposures Marcellon to to the the east of of Monthey Monthey Road Road are are described described in in aa supplemental supplemental stop. stop. Introduction to the the Marcellon Rhyolite: Rhyolite: The The Marcellon Marcellon inlier inlier (Hobbs (Hobbs and and Leith, Leith, 1907; 1907; Smith, Smith, 1978a) 1978a) is is composed of texturally texturally variable rhyolites rhyolites similar similar in in chemistry and and lithology lithology to to rhyolites at the the Marquette exposure (Stop (Stop 4), 4), and and in the Baraboo Baraboo area. area. The Marcellon inlier inlier is is formed by four four mineralogically and and chemically distinct ash—flow ash-flow tuffs tuffs folded into into aa northeast striking striking asymmetric asymmetric (and possibly overturned) overturned) antiform antiform (Fig. (Fig. 13). 13). The western limb limb of of the the antiform antiform (and N. 500 50° E. E. and and dips dips 50—85° 50-85° to to the the northwest. northwest. The eastern limb limb also also strikes N. strikes strikes N. N. 50° 50° E. E. but dips dips steeply steeply (80° (80° to to vertical) vertical) to to the the southeast. southeast. The The rhyolite are cut cut by a northeast trending andesite dike and by an east rhyolite flows flows are a northeast (Table 1, 1, analyses analyses 32 32 and and 33). 33). The andesite andesite dike dike cuts cuts trending basalt dike (Table and is is therefore therefore younger. younger. the basalt dike and The structurally highest A) at Marcellon Marcêllon is a The highest unit unit (unit (unit A) a sparsely porphy— porphyritic ritic plagioclase (1%), (1%), quartz (2%), (2%), alkali feldspar feldspar (2%) (2%) rhyolite characterized diameter) composed of radiating by abundant abundant large spherulites spherulites (up (up to 15 cm in diameter) On the fibers of alkali feldspar and quartz. On the eastern flank of the the fold, fold, fibers alkali feldspar and quartz. spherulites are are less less distinct and and smaller, smaller, but but still still conspicuous. conspicuous. Structurally below unit unit A is is a a rhyolite (unit (unit B) (6%), alkali B) which contains sparse quartz (6%), feldspar (4%) feldspar (4%) and plagioclase (1%) (1%) phenocrysts in a a banded matrix with Several samples samples show show perlitic perlitic cracks cracks in occasional occasional faint faint spherulitic growths. Several characteristically well banded and contains plagioclase the Unit Unit C is the matrix. Bnnding in unit as (14-18%). B~nding unit C is is continuous and as the the dominant phenocryst (14—18%). 0 relatively consistent in orientation (N. 50°E.) but locally broad westward westward relatively consistent in orient~tion (N. 50 E.) but locally broad Several lenses of spherulitic rhyolite plunging exposed. Several lenses of spherulitic rhyolite lie lie plunging flow folds folds are exposed. Unit C parallel sharp contacts contacts with with nonspherulitic nonspherulitic rock. rock. C parallel to banding and have sharp mineralogy to rock on on the on the on the the eastern eastern flank flank of of the the fold fold is is similar similar in in mineralogy The core core of the antiform is western flank, flank, but it it lacks lacks conspicuous conspicuous banding. banding. The is (2%), formed (unit D) formed by by aa rhyolite rhyolite (unit D) which which contains contains phenocrysts phenocrysts of of quartz quartz (2%), plagioclase (15%) and alkali alkali feldspar feldspar (2%) in aa fine-grained fine—grained devitrified devitrified plagioclase (15%) and (2%) in groundmass with numerous shards, flattened pumice and perlitic fractures groundmass with numerous shards, flattened pumice and perlitic fractures All units at are interpreted as ash—flow tuffs. (Fig. 14). All Marcellon ash-flow tuffs. (Fig. 14). Marcellon includes: Evidence at Marcel10n includes: Evidence for for the the northeast northeast striking striking antiform at (b) geologic map (Fig. (a) (Fig. 13); 13); (b) (a) the the symmetric symmetric pattern pattern of of lithologies on the geologic map rhyolite) which indicates structural (orientation of structural data data (orientation of banding banding within within the the rhyolite) which indicates 50° E. E. and and dips dips to to the the that N. 50° that the the western western part part of of the the structure strikes N. but dips steeply to the the northwest; the eastern part also also strikes northeast, northeast, but dips steeply to northwest; the rhyolite The chemical chemical correlation correlation of of lithologically lithologically similar similar rhyolite southeast. (c) The (c) southeast. Similarities in structure. Similarities from the eastern flank of of the the structure. in from the the western western flank flank to the 57 57 �o0 250 500 1000 250 500 750 750 1000 2000 FEET 250 250 o0 500 METERS N 1 :j ':·1 ~ l:{:. Basalt DIke Baaalt Dike 'f",$#!) Quartz Plagloclase Alkali Feldspar Quartz·- Plavlacla .. -- Alkali Feldapar Rhyolite Rhyolite .' I, .......,/ :j176 YII76 ::.::::rr-——, ....~';T ,.::. :':.:::.) )•_• ,,, ....~:.y EXPLANATION ':6~ '/ Andesite grained And..lte Andesite Dike And..lte Dike Dike,• Coarse Caar.. -—vralned Dike I, '- Unit Unit D D Plagloclase Plav1acla.. RhyolIte Rhyolite banded and flaw flow folded banded and folded Unit Unit C C Quartz— Plagloclese Alkali Feldlper Feldiper Rhyollte Quartz - Plavlacla .. • -Alkali Rhyolite Unit Unit B 8 Spheruiitlc Spherulllic Rhyellte Rhyeille U,dt Utit AA 45 Strike Strike and and Dip Dip .f efBanding Bandlnv ~+- Vertical Vertical Banding BandlllV -_ .. +- ~+- Contect, whereInferred, lnf.rred, dotted Contact, dashed daahed where dotted where where I4 burled burled Flow Flow Foldln Faldln, Trace of of axIal axial Diane ,lane of orrow indicates Indlcat .. Trace of anticline, enticllne, arrow direction direction of ofplunge plunve Trece of axialplane plane of of syncline, Iyncllne, arrow arrow indicates Indlcat.. Trace of xlal direction direction of of plunge plunve Sample Location Location Sample Antlcllne, trace of Anticline, showing Ihowlnv trace of azlal axial plane plane Figure Figure 13. 13. Geologic Geologic map map of of the the Marcellon Marcellon inhier inlier (adapted (adapted from from Smith, Smith, 1978a). 1978a). 58 58 �Figure 14. 14. Figure Photomicrograph Photomicrograph of cuspate and Y—shaped Y-shaped shards shards in in the the Marcellon rhyolite ash—flow ash-flow tuff tuff (unit (unit D). D). Bar scale scale is is 11 mm mm long. long. rhyolite the ratios of of lithologically lithologically similar similar units units (Table (Table 1, 1, analyses analyses 21—27) 21-27) the Rb-Sr Rb—Sr ratios For example, both spheru— s.tratigraphically suggest that they are &tratigraphically equivalent. For example, both spherusuggest that they are Similar groupexposures (unit (unit A) A) show similar Rb/Sr Rb/Sr values. values. Similar grouplitic rhyolite exposures Unit D D (Quartz_plagioclaSe—alkali ings for units units B Band (Quartz-plagioclase-alkali feldfeldings are apparent for and C. Unit quartz—bearing rhyolites by a spar) can be distinguished from from the the other other quartz-bearing rhyolites by a lower lower spar) (2.82% as as compared compared with with a Fe20 Rb/Sr and higher 0 (2.82% a Rb/Sr ratio and higher Ba, Ba, CaO, CaO, and and FeO ++ Fe 2 he other rhyolites by having a 1.77-2.13 %). Also, C from ~he other rhyolites by having a unit is different from 1.77—2.13 %). higher Ba content content (Fig. (Fig. 15). 15). higher Ba Bt- DtD- • • • S • • • S • CtC Bha. B o0 Cf> A CD :> I 100 100 ~oo 500 Ba Ba Figure Figure 15. 15. 1000 30 40 50 ~o 60708090 60 70 80 90 00 0003040 La La I ~o 50 100 00 50 I~O Sr Sr HI 00 100 ISO I~O Rb Rb 2000 1.00 2.0 2.0 Rb/Sr Rb/Sr 0) 0.5 O.~ 1.0 1.0 CoO CaO .20 I.~O 0.5 Stratigraphic variation variation in in elemental elemental concentrations concentrations for for the the MarMar— Stratigraphic Ba, La, La, Sr Sr and and Rb Rb are are in in ppm; ppm; CaO CaO and and MgO MgO are are cellon cellon rhyolite. rhyolite. Ba, For comparison, elemental concentrations for in in weight weight percent. percent. For comparison, elemental concentrations for (from Smith, 1978a). the Baraboo rhyolites (B) are also plotted the Baraboo rhyolites (B) are also plotted (from Smith, 1978a). 59 59 O.~ MO MgO �Marcellon Traverse: Walk into into the the woods woods to the the west west Marcellon Traverse: Walk Monthey Road from the Wayne Bush Farm. See Figure 12 Monthey Road from the Wayne Bush Farm. See Figure 12 at the the mailbox located at located across across for the traverse traverse route. for the route. Unit B B Unit Note the the well-banded well—banded unit unit BB rhyolite rhyolite to to your your right right in in the exposure just Note the exposure just to the west of Monthey Road (Fig. 12). The bands bands are are discontinuous discontinuous and to the west of Monthey Road (Fig. 12). The and are are formed by by collapsed pumice fragments and formed and shards. shards. At At this this exposure, exposure, bands bands strike N. N. 50° 500 E. E. and and dip dip to to the the northwest northwest at at 50° 50° to to 70°; 70°; thus thus indicating indicating the the strike orientation of orientation of the the west limb of the the Marcellon Marcellon antiform. antiform. Band is Band orientation orientation is remarkably consistent consistent in in this this area, area, but but several several broad broad folds folds interrupt this remarkably interrupt this pattern. In several several places unit B is pattern. In is spherulitic. spherulitic. Walk to the southwest along along the the margin margin of of the the bluff. bluff. Cross Cross the barbedbarbed— wire fence and wire and climb to to the the crest crest of of the the bluff bluff (Fig. (Fig. 12). 12). As ascend, As you ascend, note the grooves in differentially weathered unit B rhyolite note the lichen lichen growing in grooves (the grooves grooves are are parallel parallel to (the to the the banding described desc~ibed above). above). At the crest of At the the bluff bluff notice notice the the glacially glacially polished polished and and striated striated surface surface (striations the (striations trend trend N. 70° of milky quartz on the N. 70° W.). W.). Also noteworthy are are the the large large veins veins of south flank of of the the bluff. bluff. One is 20 cm wide and and over over 66 mm long. long. One quartz quartz vein is Cross the the summit the hill hill and descend descend to its base (you Cross summit of of the (you should now be on the the west west side on side of the hill and almost at at its its end) end) (Fig. (Fig. 12). 12). Notice that that as hill is east to west west the as the the hill is traversed traversed from east the banding so common in in unit B disappears and and that the rock becomes becomes highly charged charged with spheroids (characterdisappears that the (characteristic istic of of unit unit A). A). This the contact between between unit unit BB and and unit unit A. A. This change marks the Spheroidal Spheroidal Texture Texture Unit A is a a poorly—banded poorly-banded ash—flow ash-flow tuff with a a spheroidal texture texture (Figure (Figure 16). 16). Banding trends trends N. N. 20°E. 20 0 E. to to N. N. 30° 30° W. W. and and may may swirl swirl about about spheroids or may be truncated truncated by by them. them. Three important types of spheroids are are present present in in this this exposure. exposure. Figure Figure 16. 16. View Vi~w of of weathered weathered spherulites spherulites in in the the Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). These These spheruljtes spherulites are are identical identical to to those those observed observed in in unit unit A. A. 60 60 �Spherulites Spherulites composed composed of of radiating radiating fibers fibers of of quartz quartz and and alkali alkali feldspar feldspar A small alkali feldspar crystal may be present in the (Fig. 17). A small alkali feldspar crystal may be present in the core core of of the the (Fig. 17). Spherulites In outcrop they appear massive and may be broken. spheroid. In outcrop they appear massive and may be broken. Spherulites spheroid. commonly commonly form form by by the the devitrification devitrification of of volcanic volcanic glass, glass, and and commonly commonly occur occur in in the densely welded vitric basal zone of an ash—flow cooling unit. the densely welded vitric basal zone of an ash-flow cooling unit. (1) (1) Spherulites Spherulites are are also also quite quite common common in in felsic felsic lava lava flows. flows. Spheroids with with concentric concentric bands. bands. In thin section they they are are composed composed of of Spheroids alternating led glass alternating concentric concentric bands bands of of coarsely coarselyand and finely finelydevitrif devitrified glass (Fig.l8). (Fig.18). "Thesespheroids spheroids may may be be concretionary concretionary lapilli lapilli (??). (??). These (2) (2) (3) Lithophysae Lithophysae with with hollow hollow cores cores and and in in many many cases cases with with drusy drusy quartz quartz lining lining (3) In thin the cavity cavity wall. wall. These These spheroids spheroids may may not not have have aa central central cavity. cavity. thin the section many of of them them have aa core core of of epidote, epidote, and/or and/or quartz quartz (Fig. (Fig. 19). 19). The The spheroids spheroids have have cross sections sections that that are are nearly nearly circular circular (average (average ratio ratio ± 0.11). of minor to to major major axis axis == 0.71 0.71 ~ 0.11). The cross sections of of these these of length of spheroids may be regarded as strain ellipses, ellipses, and their their nearly circular suggests that that these these rhyolites rhyolites were were not not strongly strongly deformed. deformed. Also Also supportsupportshape suggests ing this this suggestion is is the the overall freshness of the the rhyolites rhyolites (there (there is is little little evidence for medium— medium- or high—grade high-grade metamorphism, metamorphism, and and original textures textures are are in the the matrix). matrix). Also considering considering their their age, age, these these rocks rocks are are preserved in remarkably fresh fresh in in terms terms of of their their chemistry chemistry (Smith, (Smith, l978a). 1978a). Deep Well: Well: Return Return to to Monthey Monthey Road. Road. Walk from from the the Bush Farm Farm to to the the tree tree Deep covered hill just to to the the north north of of the the farm farm (Fig. (Fig. 12). 12). The outcrop of well— wellbanded unit at the base of of the hill was was the banded unit C at the base the hill the site of a a deep hole drilled by B. Haimson and students students from the the University of of Wisconsin—Madison. Wisconsin-Madison. Two B. ninety—seven feet of core core was was recovered hundred and ninety-seven feet of recovered before drilling had to hundred and The 1978). be stopped because of of the the extreme extreme hardness hardness of of the the rock rock (Haimson, (Haimson, 1978). The hole penetrated banded banded unit C. and hole unit C. and then then entered a a poorly banded rhyolite C. This This poorly banded banded rock is most probably mineralogically identical identical to unit unit C. separate ash-flow ash—flow cooling aa textural textural variant variant of of unit unit C. C. and and may may represent represent aa separate Also, a 1 m thick dike trending trending N. N. 26°E. 26°E. was was intersected intersected unit. Also, aIm thick inetabasalt metabasalt dike unit. at feet in in the the hole. hole. at aa depth of 132 feet 61 61 �Figure 17. Figure 17. Figure Figure 18. 18. Photomicrograph of spherulitic texture in the Marcellon rhyolite unit These spherulites spheruljtes are are composed composed of of radiating radiating fibers fibers of of unit A. A. These quartz and and alkali alkali feldspar. feldspar. Bar scale in in 11 mm mm long. long. Photomicrograph Photomicrograph of of aa spheroid spheroid with with concentric concentric bands. bands. Core Core is is composed composed of of coarse—grained coarse-grained quartz and and alkali alkali feldspar; feldspar; rim rim is is formed formed by by fine—grained fine-grained quartz quartz and and alkali alkali feldspar. feldspar. Several Several spheroids spheroids show show alternating alternating bands bands of of coarse— coarse- and and fine—grained fine-grained material. material. Bar Bar scale scale is is 11 mm mm long. long. 62 62 �Figure Figure 19. 19. and Photomicrograph of of aa spheroid spheroid with with aa core core of of coarse coarse quartz quartz and Photomicrograph Quartz grains grains are are interlocking interlocking and and probably probably grew grew in in aa epidote. epidote. Quartz surrounded The core core is is off-center off—center within within the the spheroid spheroid and and is surrounded cavity. cavity. The Many of the the by aa band band of of fine-grained fine—grained quartz quartz and and alkali alkali feldspar. by feldspar. Many of fine— and spheroids are are more more intricate intricate and and have have alternating alternating bands bands of of fine- and spheroids These coarse—grained alkali alkali feldspar feldspar and and quartz quartz about about the core. These coarse-grained Bar scale scale is is 11 mm mm long. long. structures structures may may be be lithophysae. lithophysae. Bar 63 63 �Supplemental Stop Stop -— Flow Flow Structures Structures in in the the Marcellon Marcellon Rhyolite: Rhyolite: Supplemental This stop stop illustrates illustrates structures structures and and textures textures in in unit unit C. This From C. From the the Bush Bush Farm walk walk to to the the north north on on Monthey Monthey Road Road to to the the tree tree covered covered knob Farm (Fig. knob (Fig. 12). 12). Turn right right (east) on the dirt road road (just Turn (east) on the dirt (just south south of of the the hill). hill). Walk the Walk~st st the drilling site site (described (described in in Stop Stop 3) 3) and and continue continue walking walking for for about drilling 70 m about 70 m (Figure 12). 12). Turn Turn left left (north) (north) into into the the trees trees and and follow follow the the "canyon" "canyon" to (Figure to the the bare steep steep exposure exposure on on the the right right (a (a distance distance of of about about 50 50 m, bare on the way, m, on the way, you you should pass pass aa large large red red granite granite erratic). erratic). The should The textures textures described described below below are are located on on this this exposure. exposure. located Unit CC is is aa well-banded well—banded rhyolite rhyolite containing containing plagioclase plagioclase (15-25 (15—25 %) Unit as the the %) as dominant phenocryst. The unit unit strikes strikes N. N. 30° E. and dips steeply dominant phenocryst. The 30° E. steeply 500 50° to to 80° 80° to the the northwest northwest (this exposure is to (this exposure is on the west limb limb of of the the Marcellon antiform). Marcellon antiform). Bands are discontinuous and are in general lighter—colored Bands are discontinuous and are in general lighter-colored than than the the matrix matrix (Fig. 20). 20). Many Many bands bands have have aa dark dark medial medial line, line, and and in in places places they they are (Fig. are observed to bend bend about about phenocrysts. phenocrysts. The to The bands bands were were formed formed during during primary primary flowage flowage and and compaction of an ash-flow ash—flow tuff tuff by by shearing shearing and and compaction compaction of compaction of an shards. of pumice and shards. Banded ash-flow ash—flow tuffs tuffs similar similar to to those those observed observed here here are Banded in are quite quite common in outflow deposits about Tertiary volcanic centers (Schmincke outflow deposits about Tertiary volcanic centers (Schmincke and Swanson, 1967; Deal Deal and 1967; and Rhodes, Rhodes, 1976). 1976). When viewed perpendicular to the foliation plane, these Tertiary ash—flow tuffs tuffs display display strong strong lineation formed plane, these Tertiary ash-flow formed by flattened pumice (Fig. 21). flattened pumice (Fig. 21). The be 20 20 to to 11 on the The axial axial ratio of pumice may be on the flow plane, plane, and flow and as as high high as as 200 200 to to 1 1 on to the the flow flow surface surface on the the plane normal to and parallel parallel to and to the the direction direction of of flow. flow. Where pumice shows a a high degree of stretching and flattening the rock and the rock may may resemble resemble aa flow-banded lava, but the the flow—banded lava, presence of glass shards shards and the discontinuous nature of the bands suggests suggests instead that that the the rock rock is highly foliated foliated ash-flow ash—flow tuff instead is aa highly (Smith, 1978b). 1978b). tuff (Smith, The banding at this locality is is folded folded into aa series anticlines series of broad anticlines and synclines that plunge steeply (50° that plunge steeply (50° to to 80°) 80°) to the the west. west. Fold amplitudes amplitudes are as great as as 30 30 mm and and wavelengths wavelengths vary vary up up to to 10 10 m. m. In most most cases where aa fold nose is observed, the plunge of the fold fold is observed, the plunge of the fold axis parallels the the dip dip of of unit unit C C as as aa whole. whole. Fold Fold limbs limbs are are themselves themselves folded folded into antiforms and synforms synforms that plunge steeply steeply to to the the west west (Fig. (Fig. 22). 22). These minor minor folds folds have amplitudes amplitudes of up to 10 m and wavelengths that of up to 10 m and wavelengths that vary vary from from several several centimeters centimeters to to several several meters. meters. Flow Flow bands bands on on fold fold limbs limbs may may truncate truncate each each other, other, also fold crests may may not not completely completely close, close, forming forming fanning fanning patterns patterns (Fig. (Fig. 23). 23). The ae interpreted The folds folds:re interpreted as as ramp ramp structures structures formed formed during during the the flowage flowage of of an an ash—flow tuff. ash-flow tuff. In In detail detail they they are are formed formed by by compressional compressional buckling buckling and and thrustthrusting ing of of the the upper upper part part of of an an ash—flow ash-flow cooling cooling unit unit over over aa more more fluidal fluidal interior interior (Smith, 1978b). In Tertiary ash—flow (Smith, 1978b). In Tertiary ash-flow tuffs tuffs ramp ramp structures structures are are broad broad warps warps in in the the flow flow foliation foliation that that resemble resemble large large folds folds in in felsic felsic lavas. lavas. Amplitudes Amplitudes are are up up to to 50 50 mm and and wavelengths wavelengths vary vary from from several several meters meters to to tens tens of of meters. meters. Many Many are asymmetric with gentle limbs dipping 10° to 30° sourceward, are asymmetric with gentle limbs dipping 10° to 30° sourceward, and and are are convex convex upward upward (Schminke (Schminke and and Swanson,l967). Swanson,1967). 64 f14 �20. Figure 20. Highly flattened and sheared sheared pumice pumice and and shard shard fragments flattened and fragments forming forming a a pronounced lineation lineation in in the the Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). The The bands bands colored than are discontinuous and and are are in in general general lighter lighter colored than the the matrix. matrix. Note that that several bands bands trend trend to to form form about about cavities cavities and and phenocrysts. phenocrysts. Figure Figure 21. 21. Close—up of of lineation lineation formed formed by by highly highly flattened flattened and and stretched stretched Close-up pumice in in the the Tertiary Tertiary A. A. L. L. Peak Peak Tuff, Puff, San San Mateo Mateo Mountains, Mountains, New New pumice The strong lineation formed during the late—stage laminar Mexico. The strong lineation formed during the late-stage laminar Mexico. Also note note the the numerous numerous rotated inclusions. flowage flow. Also inclusions. flowage of of the the ash flow. 65 65 �Figure Figure 22A. 22A. A large steeply plunging flow fold fold in the Marcellon rhyolite The fold fold axis axis strikes strikes N. N. 50° 5Ø0 W. W• and and plunges plunges 8So 85° to to (unit C). C). The The plunge of the fold axis the west. The axis parallels parallels the the dip dip of of unit unit as aa whole. Dashed line traces C as Dashed traces the limbs limbs of of the the fold. fold. Figure Figure 22B. 22B. AA small small fold fold in in the the Marcellon Marcellon rhyolite rhyolite (unit (unit C). C). This This structure structure probably probably formed formed during during primary primary flowage flowage of of the the ash—flow ash-flow tuff. tuff. Its Its axis axis strikes strikes east—west east-west and and plunges plunges 60° 60° to to the the west. west. 66 66 �I 23A. Figure 23A. I foot Sketch of a fold fold in in the Marcellon rhyolite unit C C where does not completely close producing a fanning pattern. not completely close producing a fanning pattern. truncation of of banding. banding. fold fold Also Also crest crest note note O.5m 0.5 m Figure 23B. Figure 23B. Sketch of of aa large large fold Sketch fold in Marcellon rhyolite rhyolite unit unit C. C. steeply (left). steeply to to the the west west (left). 67 67 Fold plunges Fold plunges �STOP 44 -- THE THE MARQUETTE MARQUETTE RHYOLITE RHYOLITE(NORTH (NORTh OF OF COUNTY COUNTY HIGHWAY STOP HIGHWAYH) H) Location: The The stratigraphy stratigraphy and and fabric fabric of of the the Marquette Marquette rhyolite rhyolite to Location: to the the north north of of County Highway H will be examined at this stop. County Highway H will be examined at this stop. AA supplemental supplemental stop stop views views banding, pumice pumice lenses lenses and and aa block-flow block—flow breccia breccia in in exposures banding, exposures to to the the south south of of County HH on on Ingall's Ingall's knob. knob. See See Figure Figure 24 24 for for traverse traverse routes. routes. County EE -- r N t4 STOP 400 FEET 400 FEET = /) I z- UNIT B —, ' — FIAMME BR EC CIA EXPLANATION CEJ GEOLOGIC GEOLOGIC UNIT UNIT .--- CONTACT CONTACT _——-- ~ Figure Figure 24. 24. -+--t-+- see see text text for for xpI an at ion '3xplanation PLUNGING PLUNGING ANTICLINE ANTICLINE —-----. ' - GATE GATE ~ TRAIL TRAIL --:yo PLUNGING PLUNGING SYNCLINE SYNCLINE FENCE FENCE FIELD TRIP FIELD TRIP ROUTE ROUTE Route Route map map for for traverses traverses at at the the Marquette Marquette rhyolite rhyolite exposure. exposure. Introduction Introduction to to the the Geology Geology of of the the Marquette Marquette Exposure: Exposure: The The rhyolite rhyolite at at Marquette Marquette (Pretts, (Pretts, 1895; 1895; Hobbs Hobbs and and Leith, Leith, 1907; 1907; Smith Smith and and Hartlaub, Hartlaub, 1974; 1974; Smith Smith l978a) 1978a) occupies occupies seven seven small small hills hills surrounded surrounded by by PleisPleistocene tocene sediments sediments and and Paleozoic Paleozoic sedimentary sedimentary rocks rocks (Fig. (Fig. 25). 25). The The extensive extensive cover cover prevents prevents reliable reliable field field correlation correlation of of units units from from hill hill to to hill, hill, and and since most contacts are obscured, relative since most contacts are obscured, relative age age of of the the Marquette Marquette units units can can only only be be inferred inferred by by noting noting their their stratigraphic stratigraphic position position within within major major folds. folds. CorreCorrelations lations depicted depicted on on the the geologic geologic map map (Fig. (Fig. 25) 25) are are based based primarily primarily on on chemical chemical 68 68 �"'J fool· I-'. (J'q — 'i CD CD ~ l!..:I U1 . ~ .... C'l CD El 2 ll> "0 'i .c t: ffi CD CD C"t C"t CD CD 1-4 H ::s .... I-S fool· i-a. CD CD '"i Plagioclose Rhyollte Plagioclase Rhyolite Volts EE and Units and C C V.~~;ij Breccia Breccia ILI'/- E$KtFJ C. Strike and dip of of contact Strike and dip contact Normal fault, fault, dashed Normal' dashed where where ,~ approximately located, approximately located, UUD .... ""U upthrown upthrown side, side, D-downthrown D-downthrawn ,,"" Antlcllne, trace of Anticline, showing showing trace of axIal plane directIon axial plane and and direction )'7 ,,"" Syncline, trace of Syncline, showing showing trace of axial dIrection axial plane plane and and direction of plunge of plunge Overturned Anticline, Overturned Anticline,showing showing trace trace of of axial axial plane plane and and direction of direction of plunge plunge c' Overturned ","" Overturned Syncline, Syncline, l' showingtrace trace of of axial showing axial plane and and direction direction of plane of plunge plu n g e ) I I I I I — Sample SampleLocation Location I I I I Quarry ,. 1 .1. .1 I I. ,2 4'KK)" / ~, , ,, .•I. \ ll> c-lC"t CD CD y ""y ~..., Andeslte C?) Andesite (f) Dikes Dikes Fine- Gralned Rhyolite Rhyollte Dike Fine-Grained Dike 8 ':• • ll> "" C. "0 Vertical Vertlcol banding bonding of plunge of plunge Very fine-grained rhyolite. coarsely porphyritic rhyolite H> ~ StrIke and Strike and dip dip of of banding bonding s side side [2] L Very fine—gralned rhyollte, rn coarsely porphyritic rhyollte 0 CD CD Quartz Quar t z- Plagloclase P 10 g I ocla se - AlkalI AI ka II Feldspar Feldspar Rhyollte Rhyolite ,'/ ' 1/oils B,O,F 8,O,F and Units and A A (J'q o.q fool· i-S. C"t Porphyritic Quartz-Alkali Porphyritic Quartz-Alkali FeldFeldspar Rhyollte with spar Rhyolite with interbedded Interbedded flne-gralned rhyollte flow fine-grained rhyolite flow (Jolt 6 Unit G D 0 0 I-. 0 ::r Contact, dashed where where InInContact. dashed (erred, ferred, dotted dolled where where burled burled -. ~' EXPLANATION t: I N N , \ t ..CLUPPER1S CLUPPER1"S HILL H, H> 'i 0 0 2 El '60 C/) El 2 I-a. fool· HC"t .... 0 ....I-I 1.0 0 . ::r ....:t —1 00 a, OJ '-' ~O 250 !SOO 500 7'0 750 10'00 000 2000 20'00 FEET FE ET • INGALLS KNOB 2.!50 250 xoo METERS !SOO METERS i �________________ and petrographic petrographic similarities. and similarities. The inlier inlier is is formed formed by by seven seven mineralogically mineralogically and and chemically chemically distinct distinct The volcanic flows, ash—flow tuffs, and breccias. volcanic flows, ash-flow tuffs, The The units units lettered lettered A A to to G from from southeast to to northwest northwest are are broadly broadly folded folded into into aa series series of of normal normal and and oversoutheast overturned anticlines anticlines and and synclines synclines with with an an average average wavelength wavelength of of 300 300 m. turned The m. The fold axes axes strike strike N. N. 200 N. 400 fold 20° to N. 40° E. E. and plunge plunge to to the the northeast. northeast. These These folded rhyolite rhyolite units units are are cut cut by by aa 100 100 m m thick thick andesite andesite dike dike (Table 1, analysis analysis folded (Table 1, 30) which was intruded along a northeast trending normal fault. 30) which was intruded a trending normal fault. The The fault fault is downthrown downthrown to to the the north, north, and and the the displacement, displacement, calculated calculated by by estimating estimating the is the amount of of structural structural shortening, shortening, probably probably does does not not exceed exceed 600 600 m. amount The m. The structures structures to the the north north of of the the fault fault have have aa one one to to one one correspondence correspondence to to those those to to the the to south, except except that south, that they are displaced to to the the southwest. southwest. While the the map shows map shows simpler structural structural patterns patterns to to the the north north of of the the fault fault then then to to the the south, south, this this simpler difference is probably due due to poor poor structural structural control control to difference is probably to the the north of the fault. fault. The youngest youngest rock in northeast trending fine—grained The in the the inlier inlier is is aa northeast fine-grained massive dacite dacite dike, dike, 35 35 m m thick, which cuts cuts the fault and dike massive thick, which the fault and the the andesite andesite dike (Table 1, 1, analyses 39 The dike dike is unit C in lithology (Table 39 and and 40). 40). The is similar to unit (fine—grained with with plagioclase plagioclase as as the dominant phenocryst), (fine-grained phenocryst), but but it it is is disdistinguished from unit unit C C on on chemical chemical grounds grounds (Fig. (Fig. 26). 26). 89 "ioo G—.-•\ \106\ 'I98 !1194 —II 10 10 i'92.—B I / ' 9 Rb! Rbi /Sr I Sr 97 'I — jP5 !e'P5 191 (i ', , 191 (....... Rhyolite Rhyolite dike dike , \ \ "Andesite" \ \ dOk ..... .... \ \ \dike I e ~ \ 190' \ \ ..... I9O \, \ , ~.J 189 189 0 0 l.a 1.8 Na20/K20 Figure Figure 26. 26. ° Rb/Sr—Na20/K Rb/Sr-Na 2 0/K 0 plot plot for for Marquette Marquette inlier inlier samples. samples. This This plot plot de~ de monstrates monstrates tat t5at mineralogically mineralogically similar similar rhyolites rhyolites can can be be distindistinguished guished on on the the basis basis of of Rb/Sr Rb/Sr and and Na20/K20 Na O/K ratios. Also Also note note the the ratios. cyclic cyclic change change in in Rb/Sr Rb/Sr ratio. ratio. Plagioclase_bearing Plagi~cla~e-bearingrhyolites rhyolites (unit (unit CC and and E) E) have have Rb/Sr Rb/Sr greater greater than than 1, 1, whereas whereas quartz—plagioclase_ quartz-plagioclasealkali alkali feldspar feldspar rhyolites rhyolites (units (units B, B, D, D, and and F) F) have have Rb/Sr Rb/Sr less less than than 1. 1. Unit Unit GG is is the the quartz—alkali quartz-alkali feldspar—plagioclase feldspar-plagioclase rhyolite rhyolite (from (from Smith, Smith, l978a). 1978a). ° 70 70 �unit GG is is aa thick thick (1000 (1000 m) m) quartz quartz (10 (10 %), %), alkali alkali feldspar feldspar (commonly (commonly perth— perthUnit Except for minor porphyry. rhyolite thitic) (16 %) and plagioclase (7 %) rhyolite porphyry. Except for minor plagioclase (7 %) and thitic) (16 %) variations variations in in phenocryst phenocryst abundance abundance and and faint faint banding, banding, the the unit unit is is texturally texturally Shard—like forms were observed in the matrix of unit G, homogeneous. Shard-like forms were observed in the matrix of unit G, indicating indicating homogeneous. it is is an an ash—flow ash-flow tuff. tuff. AA fine—grained fine-grained rhyolite rhyolite is is interbedded interbedded with with that it unit unit G, G, and and crops crops out out near near the the south south end end of of the the unit unit GGexposure. exposure. The The 66 units units lying lying to to the the southeast southeast of of unit unit GG are are texturally texturally variable, variable, with with banded, banded, fine—grained fine-grained and and porphyritic porphyritic varieties varieties common. common. Most of of the the units units show show evidence ~vidence of of brecciation brecciation and and micro—brecciation. micro-brecciation. Coarse Coarse breccia breccia is is found found on on the the southeast southeast margin of Ingall's Ingall's Knob where clasts of of porphyritic porphyritic and and fine—grained fine-grained red to to black black rhyolite rhyolite exceed exceed 10 10 mm in in size. size. Unit D D on on Cluppert's Hill is is also also Eutaxitic texture is well displayed in several of extensively brecciated. brecciated. texture is displayed in several of the the extensively units. units. Each unit unit in in the the Marquette inlier inlier has distinguishing chemical chemical and and mineralogical characteristics which are used to correlate units between are used to correlate units between (Fig. 46, 46, Table Table 1, 1, analyses analyses 4—14). 4-14). Units Units A, A, B, B, D, D, and and FF are are porphy— porphyexposures (Fig. ritic ritic plagioclase (18 (18 to to 27%), 27%), quartz (2 (2 to to 8%), 8%), and and alkali alkali feldspar feldspar (1 (1 %) %) 20 to to 36 36 % % total total phenocrysts. phenocrysts. Unit B is is distinguished from from rhyolites with 20 the other quartz bearing rhyolites by Na Na20/K20 0/K 0 greater than 1.0 and and low low Rb/Sr 2 2 0.92). Unit D D and Unit F P are similar in in both major and and minor element (0.64 —- 0.92). however, contains in its upper part aa 100 m D, however, m thick thick massive chemistry. Unit D, phase; similar massive masive rock phase; aa similar rock is is not not associated associated with with unit unit F. F. To date, date, no Units C and E are I ine--grained been made made on on unit unit A. A. Units C and E are fine-grained chemical studies have been (10 to 15 15 %% phenocrysts) with plagioclase plagioclase as as the the dominant dominant phenocryst. phenocryst. Unit E (10 is C by lower lower CaO. CaO. is distinguished distinguished from unit C Noteworthy is the cyclic change from phenocryst—poor phenocryst-poor plagioclase rhyolite (units E) to phenocryst—rich (units C and E) phenocryst-rich three—mineral three-mineral rhyolite (units (units B, B, D, and F). F). This cyclic variation in mineralogy is is also reflected in in trace trace D, and element chemistry (Table (Table 1, 1, analyses 4—14); 4-14); for example, example, Rb/Sr ratios ratios vary vary from 1.45 1.45 to to 1.23 1.23 for for units units EE and and C and and from from 0.71 0.71 to 1.0 for from for units units F, F, D, D, and B (Fig. (Fig. 26). 26). Chemical and flow direction data (Smith, (Smith, 1978a) 1978a) show that that all all of of the the Marquette units are comagmatic and that all flows flows erupted from from aa source source to to This evidence evidence suggests the outcrops. This suggests that that cyclic the northwest of the present outcrops. variation in chemistry, mineralogy, mineralogy, and texture reflect reflect eruption from a variation in chemistry, and texture a differentiating source. source. Fine—grained Fine-grained units probably represent eruption eruption from from On the the other other hand, hand, more more highly porphyritic fractionated crystal-poor magma. On fractionated crystal—poor varieties may may represent represent eruption from from zones zones of of crystal crystal accumulation within varieties The lower lower Rb/Sr Rb/Sr ratios ratios in phenocryst phenocryst and the source chamber. chamber. The and feldspar rich units (F, and B) B) may may be be explained explained by aa model model where where Sr is units (F, D and is concentrated into As a the crystallizing feldspar and the and Rb Rb is is enriched enriched in in the the liquid liquid phase. phase. As a consequence phenocryst phenocryst and rich units would have have lower Rb/Sr than the consequence and feldspar feldspar rich units would the fine—grained, feldspar-poor feldspar—poor varieties varieties (units (units C C and and E) E) which which formed formed from from fine-grained, fractionated, crystal- and and feldspar—poor feldspar-poor magma. magma. fractionated, crystal— Alternately, fine—grained Alternately, fine-grained and and phenocryst—rich phenocryst-rich pairs pairs may represent compositionally zoned zoned ash-flow ash—flow sheets sheets with with the the phenocryst-rich phenocryst—rich unit unit at at the compositionally the Zoned ash-flow ash-flow tuffs tuffs commonly commonly top at the the base. base. Zoned top and and the the fine-grained unit at show an an upward upward increase increase in in MgO, MgO, CaO, CaO, A1 Al203, TiO2 and and Sr/Rb Sr/Rb and and may may vary vary in 0 , Ti0 show 2 3 2 71 71 �from quartz quartz latite latite at at the top to rhyolite rhyolite at composition from the top at the the base (for (for example see Smith, Smith, 1960; 1960; Ratte Ratte and and Steven, Steven, 1964; 1964; Smith Smith and and Bailey, Bailey, 1966; 1966; Noble Noble and and see Hedge, 1969; 1969; and Phenocryst abundance, abundance, and and xenolith xenolith abundance abundance Hedge, and Rhodes, Rhodes, 1976). 1976). Phenocryst and size size usually usually increase increase upward, upward, with with pumice pumice commonly commonly showing showing reverse reverse zonation zonation and (Sparks, 1976). ash—flow sheet sheet the (Sparks, 1976). Within one one ash-flow the transition from phenocryst—poor phenocryst-poor to phenocryst-rich phenocryst—rich tuff tuff can can be be abrupt abrupt (Noble, 1970). Marquette Marquette units units FF and and EE to (Noble, 1970). may together represent a single compositionally zoned ash—flow sheet with unit may together represent a single compositionally zoned ash-flow sheet with unit B the differentiated fine—grained base and unit F the less differentiated pheno— E the differentiated fine-grained base and unit the less phenocryst-rich top. Grouping of of units units D D and and C C is is doubtful doubtful since since they they are are separated separated cryst-rich top. Grouping . by a a fault fault and by an an andesite andesite dike. dike. More More detailed detailed field field and and chemical chemical data must be obtained before this be this model model can can be be properly properly evaluated. evaluated. The Marquette Rhyolite Traverse: The Stop 4A — Unit CC Stop - Unit Walk due then turn to to then turn north from the the locked locked gate on the woods (east) the woods (east) to the the first first the the north side side of County Highway H, H, exposure (see exposure (see Fig. Fig. 24 24 for for the the route). route). This exposure exposure is formed by by a plagioclase—bearing rhyolite rhyolite ash—flow This is formed a plagioclase-bearing ash-flow tuff tuff (unit C). It contains contains small small (up to 55 mm mm in in size) size) anhedral anhedral to to subhedral subhedral plagioplagio— C). It (up to clase laths set in a fine—grained matrix matrix that brown. clase laths set a black fine-grained that is is streaked reddish brown. Unit C is well banded, banded, and and may may also also display spherulitic and Unit is commonly well and brecciated texture. texture. At this this locality, locality, bands stand out prominently due to to differential erosion. The bands form the erosion. the reddish—brown reddish-brown streaks, streaks, and and under under careful scrutiny scrutiny they are observed observed to be be composed composed of discontinuous lenses lenses of collapsed pumice they are o£ discontinuous and shard fragments. fragments. The banding trends trends N. N. 60 E. E. and dips 85° south south or or is is vertical. Since this exposure is on the flank of of a northeast plunging vertical. Since this exposure is on the south flank a northeast syncline, syncline, aadip dip to to the the north north is is expected. expected. This is probably due This deviation is due to flow folding folding in the ash—flow tuff supplemental stop at flow the ash-flow tuff (see (see the the supplemental at the Marcellon rhyolite for for further further discussion discussion of of flow flow folding). folding). Stop 4B 4B —- Unit Unit B B This stop is is just to to the the west of an old stone fence (Fig. (Fig. 24) 24) constructed about 1900 as about as part of of the the old old Driblow Driblow farm. farm. Unit B is is a a porphyritic quartz, quartz, plagioclase, plagioclase, alkali feldspar—bearing feldspar-bearing rhyo— rhyolite with aa reddish—brown reddish-brown to to black black matrix. matrix. Quartz is is rounded and and clear and and may may be be up up to to 33 mm mm in in size. size. Plagioclase is is pink to to white in in color and and occurs in in laths up up to to 66 mm mm in in size; size; some some grains grains show show prominent prominent albite albite twinning. twinning. Alkali Alkali is is difficult difficult to to identify identify in in hand hand specimen. specimen. On weathered surfaces surfaces faint faint banding banding and and minor minor brecciation brecciation are are observed. observed. This quartz—bearing quartz-bearing rock is is distinguished from other quartz—bearing quartz-bearing rhyolites in in the the Marquette inlier inlier by its its higher ratio. higher Na20/K20 Na 0/K ratio. Unit B is is the the only sodic rhyolite in in the the inlier inlier 2 (Fig. (Fig. 26). 26). Unit ufiit B changes in in lithology lithology laterally. laterally. On Ingalls Ingalls Knob Knob (south (south of of Highway Highway H) H) quartz quartz is is small small and and rarely rarely observed observed in in outcrop outcrop whereas quartz quartz is is large and and easily identified identified in in unit unit BB exposures exposures to to the the north north of of HighwayH. HighwayH. ° The The contact contact between between unit unit BB and and unit unit C C trends trends No. No. 10° 10° W. and and passes passes to to the the south south and and east east of of this this stop. stop. Many Many of of the the large large blocks blocks observed observed just just to to the the south of our present position are breccias with an assortment of fragment fragment types. types. It It is is doubtful, doubtful, however, however, whether whether these these blocks blocks are are in in place. place. 72 72 �Stop 4C 4C —- Small Small Andesite Dike Intruding Intruding Unit C C Rhyolite Stop Traverse due north north from from Stop Stop 4B to to the the low low outcrops outcrops across across the the field field in in the trees (just (just to to the the north north of of ihe the Bee Bee Hives) Hives) (Fig. (Fig. 24). 24). At this this stop stop aa fine—grained unit C is fine-grained variety of unit is cut by a a thin andesite dike (an (an off—shoot off-shoot trending dike). dike). The andesite andesite and and rhyolite rhyolite are are at at first first of the main northeast trending difficult The following difficult to to distinguish distinguish from from one one another another in in the the field. field. following characteristics will aid aid in in their their identification. identification. Unit C C rhyolite rhyolite breaks breaks irregularly irregularly with with aa splintery splintery surface. surface. Sparse small plagioclase laths laths are are the the dominant phenocryst. ,dominant phenocryst. Jointing produces straight breaks and angular angular corners rock. The andesite contains small plagioclase laths (1/2 (1/2 mm) mm) set in in a a in the rock. fine—grained fine-grained matrix with with aa characteristic characteristic greenish greenish hue. hue. Jointing Jointing produces produces irregular breaks and and rounded corners corners in in the the dike dike rock. rock. A A fresh fresh surface surface of of the rhyolite reflects when reflects light light from from numerous numerous planes, planes, and and thus thus "twinkles't "twinkles" when rotated in in direct direct sunlight. sunlight. Partially Partially separated separated splinters splinters of of rock rock are are lighter lighter in color than unbroken rock rock and and form form grooves grooves on on the the broken broken surface. surface. In concontrast, trast, the andesite has aa smooth smooth and and dull dull freshly freshly exposed exposed surface. surface. In several several places, places, aa very fine fine banding is observed in the is observed the andesite and (N. 450 45° E.) obliquely to to the the strike strike of of the the dike. dike. These bands may may be be trends (N. flow bands sheared into into this this orientation orientation after after dike dike emplacement. emplacement. Alternately they may reflect aa rock rock cleavage cleavage formed formed during during the the folding folding of of these these rocks. rocks. Stop 4D (Optional) (Optional) — - The Contact Between the the Andesite Dike and and Unit Unit C C Rhyol ite Rhyolite Since the exposure is small, it will not not be be visited on the the size of this this exposure is small, it will It is is of of considerable considerable interest, interest, however, however, because because it it displays displays one one field trip. trip. It of the few exposed contacts contaots in in the the inlier. inlier. east across From Stop 2C walk to the east across the the field field to the the gap in the north— northThe exposure exposure (piled trending fence fence (Fig. (Fig. 24). 24). The (piled with rock) rock) encountered on the way is composed of of unit unit C C rhyolite rhyolite cut cut by by numerous numerous quartz quartz veins. veins. After passpassing through through the ing the gap in the fence proceed through through the the forest forest (bearing (bearing N. N. 10 10 E.) E.) The contact contact between rhyolite rhyolite and to the the first first rock rock ledge. ledge. The and andesite is is exposed on top of has toppled exposof this this ledge where a a juniper tree tree with shallow roots roots has ing aa fresh fresh rock roák surface surface (the tree was was uprooted uprooted during during aa major major ice ice storm storm in in ing (the tree April, 1976). 1976). The intrusive contact trends trends N. N. 87° 87° E. E. and and dips dips 60° 60° to to the the north. north. This dip dip probably reflects reflects the northeast—trending normal This the inclination of of a a northeast-trending normal fault fault (later (later intruded intruded by the the dike) dike) (Fig. (Fig. 25). 25). The difference between rock rock types types is subtle (see (see discussion discussion under under Stop Stop 4C). 4C). The contact is is sharp; sharp; no no are found dike and and no contact contact effects effects are xenoliths of of rhyolite rhyolite are found within the the dike in the the rhyolite. rhyolite. This dike is is fine—grained fine-grained and and shows shows little little change observed in In thin thin section, section, the in grain size from ôontact in contact to to center. center. In the texture of the the dike rock is intergranular to ophitic of sausseritized plagio— dike ophitic with aa framework framework of plagioclase laths clots set in aa patchy matrix of epidote—clino— clase laths and clots of iron oxide oxide and and epidote-clinozoisite. Both andesite and and rhyolite rhyolite are are jointed jointed with with N. N. 60° 60° E. E. and and N. N. 40° 40° W. W. as as important directions. displays the contact contact between the dike and Another exposure that displays the andesite dike unit C rhyolite can be reached by walking through the the trees trees from Stop 4C (bearing N. N. 10° 10° W.) W.) to to an an exposure piled with rock (Fig. (bearing (Fig. 24). 24). The contact here trends N. N. 80 E. and and dips dips 65° 65° to to the the north. north. Piled on top of the the exposure exposure 73 ..., �are rocks rocks moved moved to to this this location location from from the the cleared cleared field field to to the the north. north. Most Most of of the are the blocks are massive unit D rhyolite. This rock is similar in outward appearance blocks unit D rhyolite. This to unit unit C, C, but but it it can can be be distinguished distinguished quickly in the field from the other fine— to the field finegrained units grained units by the bell-like sound sound emitted emitted when when hit hit by by aa hammer. hammer. Also the rock breaks with aa distinctive "breaking "breaking glass" glass" sound. sound. Stop 4E — Massive Unit Unit D, D, and Unit E - Massive See Figure 24 for directions from See from Stop Stop 4D 4D to to this this locality. locality. at point 4E* 4E* (see Fig. 24) For orientation stand at (see Fig. 24) and and look to the northwest; northwest; the contact contact between between unit unit D D and and unit unit EE trends trends N. N. 30° 300 E. E. through through the the grassgrass— the Unit E lies on the covered depression before you. you. Unit the rock rock ledge ledge to to the the northwest. northwest. Massive unit rhyolite is fine grained near near its Massive unit D rhyolite is very fine its contact with unit E, E, but becomes noticeably coarser in in grain size to to the the south. south. Plagioclase altered to sausserite sausserite occurs occurs in glomeroporphyritic glomeroporphyritic clots and altered and is the the dominant dominant Phenocrysts are set in a devitrified matrix that phenocryst. Phenocrysts are set a devitrified that contains coarser— coarsergrained pod—shaped pod-shaped areas areas (pumice (pumice fragments?). fragments?). Broken spherulites are also Unit D locally displays displays fine fine striations that observed in in the the matrix. matrix. Unit that are similar to those in in the the andesite andesite dike dike (see (see description description of of Stop Stop 4D). 4D). These 0 striations strike (N. 30°E.) contact between units D striations (N. 30 E.) parallel parallel to the the contact D and E but dip obliquely to it striations as dip it (80° (80° south for for the the striations as compared to 60° 60° north for the the contact). Unit D at at this Unit this location is is similar in lithology to the the fine—grained fine-grained variety of of unit unit C observed at Stop 4C; 4C; it however, splinters like glass glass.when at Stop it however, .. when This fine-grained broken and commonly rings rings like like aa bell bell when when hit hit by by aa hammer. hammer. has chemical chemical characteristics characteristics that rock has that distinguish it it from other fine—grained fine-grained Marquette rhyolites (Fig. (Fig. 26). 26). Walk across across the the grass covered depression to to the the low low rock rock ledge ledge of of banded banded unit E rhyolite. rhyolite. The contact between unit unit D D and unit unit E trends trends northeast northeast through this this depression. depression. Banding in in unit unit E is is formed formed by discontinuous white to pink streaks pumice fragments fragments and streaks that that represent represent pumice and shards sheared and compressed during late—stage late-stage primary flowage and and during post—depositional post-depositional compaction compaction and welding. Bands may be up to to 50 cm long, long, but are are usually usually less less than than 55 mm mm in in width. Commonly they they bend bend about about phenocrysts. phenocrysts. Bands strike N. N. 53°E. 53°E. and and dip 47° to to the the west. west. On the southwest corner of of the near the On the southwest the outcrop near the base of the the unit, unit, unit E grades into into aa spherulitic spherulitic rhyolite. rhyolite. Spheruites Spherulites are are as as large large as as 33 cm cm in in diameter. diameter. To the the west, west, the the outcrops are are covered by aa drumlin elongated in in an an east— eastwest direction. direction. This orientation reflects the the movement of the the Green Bay Bay Lobe Lobe (Woodfordian) (Woodfordian) from east east to to west west in in this this area. area. Stop 4F 4F (Optional) (Optional) —- Porphyritic Porphyritic Unit DD From From Stop 4E walk north north to to the the east—trending east-trending fence, fence, then then follow follow the the fence fence eastward (300 (300 m) m) to to the the north—south north-south fence fence (Fig. (Fig. 24). 24). Outcrops encountered to to the east—trending fence fence are are of of unit the north north of the the east-trending unit E rhyolite, rhyolite, blocks in the field field 74 74 �to to the the south south are are fine—grained fine-grained unit unit DD rhyolite. rhyolite. Continue Continue walking walking Note the angular blocks fence to to the the first first exposure. exposure. Note the angular blocks of of rock rock to to fence of the the fence. fence. Here aa wide wide assortment assortment of of rhyolite rhyolite lithologies lithologies is is of blocks blocks were were probably probably transported transported by by ice ice aa short short distance. distance. along along the the the the north north found. found. These These Unit Unit DD is is gray gray on on weathered weathered surfaces surfaces but but pink pink on on freshly freshly broken broken fractures. fractures. In In hand specimen abundant abundant phenocrysts of rounded quartz up up to to 3 3 mm in in size size and and subhedral feldspar (plagioclase and alkali feldspar) up to 5 mm in length (plagioclase feldspar) up to in length are are -easily identified. identified. In In thin section the rock contains large large rounded rounded and and embayembayeasi1y ed quartz (10%), (10%), subhedral grains of sausseritized plagioclase (8%), (8%), and and ortho— orthoperthitic texture texture (14%). (14%). Banding in in unit D D at at this this locality locality is is clase with perthitic faint; faint; band trends trends vary vary from from N. N. 7° 7° E., E., 70° 70° east east to to N. N. 500 50° E, E, 85° 85° southeast southeast (deviation due to to flow flow folding?). folding?). (deviation Unit D D is is easily distinquished from unit B, B, particularly by differences in Na20/K20 ratio (the greater than 11 for for unit (the ratio is is greater unit B and and less less than 1 for unit D). D). Also, Also, unit D D contains a 100 m m thick thick massive phase (stop (stop 4E); 4E); aa unit similar similar massive phase phase is is not not associated associated with with unit unit BB (or (or in in fact fact with with unit unit F, F, the other quartz, plagioclase, alkali alkali feldspar—bearing feldspar-bearing rhyolite rhyolite unit). unit). the quartz, plagioclase, 75 75 �SUPPLEMENTAL STOP STOP -- MARQUETTE MARQUETTE RHYOLITE RHYOLITE ON ON INGALL'S KNOB SUPPLEMENTAL INGALL'S KNOB Highlights of of this this stop stop include include the the well-banded well—banded unit unit C, C, and and pumice pumice Highlights lenses and and breccia in lenses in unit unit A. A. Unit C — Banding: Park Park at at the the entrance entrance to to the the Ingall's Knob gravel gravel pit pit (see Unit - Banding: Ingall's Knob (see Fig. 24). Walk along along the the dirt dirt road road toward toward the the gravel gravel pit pit and and then then bear bear right right Fig. 24). Walk (south) to to the the outcrops outcrops of of dark rhyolite clearly visible (south) visible on on the the flanks flanks of of Ingall's Knob. These These outcrops outcrops are are composed composed of of well well banded banded unit unit C C rhyolite rhyolite Ingall's (Fig. 27) • (Fig. Figure Figure 27. 27. Photomicrograph of highly highly flattened flattened and and crenulated crenulated shards shards in in the. the. Marquette rhyolite rhyolite (unit (unit C). C). Flattening probably occurred during during primary movement of the Folding may have occurred during the ash ash flow. flow. during flowage or during during later later deformation. deformation. Bar scale scale is is 11 mm mm long. long. The bands are discontinuous and are formed by sheared and collapsed pumice fragments. Banding strikes strikes N. N. 50°E. 50 0 E. and dips 700 70° to to 800 80° to the the south; south; bands are locally folded. The rock in this locality also contains lenses of breccia locally folded. in this and spherulitic spherulitic rhyolite. rhyolite. Unit AA —- Fiamme Fiamme (Pumice Lenses): Lenses): Walk Walk to to the the end end of of Ingall's Ingall's Knob Knob (see (see Fig. Fig. 24) 24) and and climb directly directly up up the the rock rock face. face. The The rock rock forming forming the the bluff bluff on on the the southeast end of Ingall's Knob is a porphyritic quartz, orthoclase, plagio— Ingall's is quartz, orthoclase, plagioclase—bearing ash—flow tuff tuff showing showing nicely nicely developed developed fiamme fiamme (the black clase-bearing rhyolite rhyolite ash-flow (the black lens—like features in the rock). The fiamme are collapsed pumice fragments lens-like features in the rock). The fiamme are collapsed pumice fragments and and are are elongated elongated parallel parallel to to the the strike strike of of unit unit AA (N. (N. 50°E.). 50 0 E.). They They have have an an average average axial axial ratio ratio of of 12 12 ++ 8/1 8/1 (based (based on on the the measurement measurement of of 50 50 fiamme). fiamme). In thin section, section, unit A A rhyolite rhyolite contains contains rounded rounded and and embayed embayed quartz quartz (10%), alkali feldspar with perthitic (10%), feldspar perthitic texture texture (8%), (8%), partially partially sausseritized sausseritized 76 76 �plagioclase and iron plagioclase (5%), (5%)"and iron oxide oxide (tr). (tr). The The matrix matrix is is finely finely devitrified devitrified but but contains bands bands that that are are more more coarsely coarsely recrystallized. recrystallized. Flow Flow texture texture is is common common contains with with shard—like shard-like forms forms aligned aligned and and locally locally bent bent about about phenocrysts phenocrysts of of quartz quartz Ic xenolith xenolith was was identified in and feldspar feldspar (Fig. (Fig. 28). 28). One One small small maf mafic in thin thin and sections. sections. Figure 28. 28. Figure flattened shards shards in the Marquette rhyolite Photomicrograph of flattened rhyolite ash-flow tuff tuff (unit (unit A). A). Shards are are aligned and locally ash—flow locally bent bent about about quartz and and feldspar. feldspar. Bar scale is phenocrysts of quartz is 11 mm mm long. long. The change in slope above the rock face face marks the contact Unit A A —- Breccia: The between the top of unit unit A ash—flow ash-flow tuff tuff (below) (below) and and the base of unit A A breccia o contact varies in orientation between N. 40°E. and N. 30°W., (above). This in orientation between N. 40 E. and N. 30 o W., (above). o The wavy nature of this trends N. N. 50°E. 50 E. The this contact suggests that that but in general trends it is an unconformity. it is It is Unit is poorly sorted and and is is approximately approximately 50 50 mm thick. thick. It is Unit A breccia is o 50°E. banded with large clasts and crudely banded and matrix matrix fragments fragments elongated elongated in in aa N. N. 50 E. Along the the route of this direction (parallel to the the strike of of unit unit A). A). Along this traverse, traverse, direction (parallel concentrated toward toward the aa crude is observed with large fragments concentrated the crude size size sorting sorting is This size size sorting, sorting, however, however, is is not not characteristic characteristic of of upper part of the the unit. unit. This In other locations, large of rhyolite are the unit as a whole. In other locations, large fragments rhyolite are the unit On our our route, route, breccia breccia near near the the base base of of the the unit unit found the unit. unit. On found throughout the contains (less than contains small small (less than 30 30 cm cm in in size) size) dark-colored dark—colored porphyritic porphyritic rhyolite rhyolite Toward fragments. are quartz—bearing quartz-bearing rhyolites. rhyolites. Toward Only aa few few of of the the fragments fragments are fragments. Only the top top of of the the unit unit the the fragments fragments become become huge; huge; one one block block is is 33 33 m m long long in in aa the o Most of of the the larger larger fragments fragments are E. direction and is is 12 m m wide. Most are similar N. N. 50 50°E. However, three in lithology to the quartz-bearing unit A ash-flow tuff. However, three other in lithology to the quartz—bearing unit ash—flow tuff. rock types types are are present;l)banded present;.l)banded rhyolite rhyolite with with small small white white feldspar, feldspar, 2) 2) banded banded rock rhyolite with with large large (5mm) (5mm) white white feldspar, feldspar, and and 3) 3) massive massive rhyolite rhyolite with with small small rhyolite The matrix matrix of of the the breccia breccia is is gray gray in in quartz phenocrysts. The quartz and and alkali alkali feldspar feldspar phenocrysts. 77 77 ------------------------------------------..., �color on on weathered weathered color with crystal, rock with crystal, rock surfaces. In thin thin section section the the matrix matrix is is microbrecciated microbreccjated surfaces. In o and angular angular shard shard fragments fragments aligned aligned in in the the N. and E. direction. N. 50 50°E. direction. Breccia Exposure Exposure at at the the Summit Summit of of Ingall's Knob: Details Breccia Ingall's Knob: Details of of the the relationship relationship between fragments and matrix are revealed in an exposure between fragments and matrix are revealed in an exposure at at the the summit summit of of Ingall's Knob Knob (Fig. The largest largest fragment fragment at at this this location location is is aa porphyporphy— Ingall's (Fig. 29). 29). The ritic (black (black in in color) color) rhyolite rhyolite composed composed of of quartz quartz and and alkali alkali feldspar feldspar phenoritic pheno— o crysts. It is 5 in wide and over over 10 10 m m long long in in the the N. N. 50 50°E. direction. Contacts crysts. It is 5 m wide and E. direction. Contacts between it it and and the the breccia matrix (gray between (gray in in color) are are sharp. sharp. Note Note the the smaller fragments of of black black rhyolite rhyolite in in the the matrix matrix on on both both sides sides of of the the larger fragments larger blackblack— colored rhyolite rhyolite fragment. colored fragment. These These fragments fragments probably probably are are pieces pieces of of rhyolite rhyolite that broke broke off off the the larger larger fragment fragment during during transport. that transport. Just Just to to the the north north there is a large red fragment impregnated is a large red fragment impregnated with quartz veins. veins. The fragThe size size of of this this fragment is is difficult difficult to estimate because of extensive cover. ment cover. Notice Notice the the smaller smaller red—colored fragments fragments in in the the matrix matrix just just to to the the south south of of the the red red-colored red clast. clast. The The red fragment fragment is is aa porphyritic porphyritic rhyolite rhyolite similar similar in in mineralogy mineralogy to red to the the black black fragments. Both Both fragment fragment types are similar similar in mineralogy to to the unit A ashfragments. types are the unit ash— flow tuff. flow tuff. Origin of Origin of the the Breccia: Breccia: In this breccia in in the the In order order to to explain explain the origin of this following observations observations must be accounted for: following for: 1. The matrix matrix of of the the breccia breccia may may show a crude layering that 1. The a crude that resembles resembles a flowage a flowage texture. texture. Smaller and shards aligned in the the Smaller fragments, fragments, crystals crystals and shards are are aligned N. 50°E. N. 50 o E. direction. direction. Many of of the the larger clasts have unequal dimensions in in section and have have section and their long axes oriented in in the the N. N. 50°E. 50 o E. direction. direction. 2. 2. There are are aa wide variety variety of of clast clast types. types. Many of the the larger larger fragfragments are are similar in in lithology to to the unit A A ash—flow ash-flow tuff. tuff. 3. 3. 4. 4. There is is only a a slight suggestion of size sorting in in the the deposit. deposit. 5. 5. Many of of the the fragments fragments are are very very large large (up (up to to 33 33 mm long). long). The unit unit is is similar similar in in overall overall fabric fabric to to mud—flow mud-flow breccias or or lahars lahars commonly tuffs and lavas in commonly interbedded interbedded with with ash—fLow ash-flow tuffs in Tertiary Tertiary and and Holocene Holocene volcanic volcanic piles, piles, in in terms terms of of poor poor sorting sorting and and fragment fragment size size (Parsons, (Parsons, 1968; 1968; Smith, Smith, 197Gb). 1976b). However, However, mud—flow mud-flow breccias breccias usually usually do do not not contain contain elongated elongated or or oriented oriented fragments, fragments, and and the the matrix does not show show flow flow structure. structure. The The unit unit may may instead instead represent represent aa pyroclastic—flow pyroclastic-flow breccia breccia (that (that is, is, aa block block avalavalanche anche or or block—flow block-flow deposit). deposit). Modern Modern examples examples of of this this type type of of deposit deposit are are described described by by Aramaki Aramaki (1963) (1963) and and Parsons Parsons (1968) (1968) from from Asama Asama Volcano Volcano in in Japan. Japan. Modern Modern block—flow block-flow deposits deposits may may erupt erupt initially initially as as ash ash flows flows and and then then during during emplacement emplacement may may pick pick up up large large fragments fragments from from the the surface surface over over which which they they travel. travel. Also, Also, fragments fragments from from the the walls walls of of the the vent vent and and cognate cognate pumice pumice are are often often incorporated. incorporated. The The matrix matrix of of the the Holocene Holocene block—flow block-flow deposits deposits around around Asama Asama Volcano Volcano may may be be crudely crudely banded banded and and is is commonly commonly composed composed of of fine fine ash ash and and dust. dust. These These breccia breccia units units extend extend as as far far as as 18 18 km km from from Asama Asama Volcano Volcano and and vary vary in in thickness thickness from from 40 40 cm cm to to 10 10 mm (Parsons, (Parsons, 1968). 1968). There There are are many many similarities similarities between between the the Holocene Holocene pyroclastic—flow pyroclastic-flow breccias breccias about about Asama Asama Volcano Volcano and and the the unit unit AA breccia; breccia; consequently, consequently, II suggest suggest that that the the 78 78 �Matrix Matrix NN 0 : o \/ I— Ii Cover Cover quartz veins veins quartz k~~v~:'~>:"? _ ~~ ~ \N? . /" '. . ~/ . .,; 0 — o() oO 00 o "" \ " - 0 0 - / "", ?... '" ......."" ",......... ---/ 00 —7-Matrix oo~ ~ 7 7- --~/ Matrix \ " I - / \ ' ./ ./,r-. -~/~. /. -=- /. ......... -::: . : \ - / .r -. ? • ~ ?:;:~/- \ ~ °/....-- / ...... • ?/ / C/. ct:1/.· . 7/ ' / 110 T Tree Tree feet _I 00 0 00 00 . ?"- - ? /1' / .. • _ . Tree ?"2? ree 7' .. Matrix Matrix Stump EXPLANATION fH Black r::I Red Red rhyolite rhyolite rhyolite Small of rrhyolite Sma II ffragments rag men t s of hy 0 lit e in matr ix in matrix o11 Figure Figure 29. 29. Matrix, microbreccia Matrix, microbreccia Sketch map map of of an an exposure exposure of of unit unit A breccia Sketch breccia on Ingall's Ingall's Knob. Knob. 79 79 �unit A A breccia breccia is is aa pyroclasticpyroclastic— or or block-flow block—flow breccia breccia and and not not aa mud-flow mud—flow unit deposit. deposit. Unit A-Unit A—Unit B Contact Unit The contact contact between between unit unit A A and and unit unit B B on on Ingall's Ingall's Knob Knob is is gradational. gradational. The The basal basal part part of of unit unit B B contains contains numerous numerous beds beds and and lenses lenses of of breccia breccia that that The grade into unit A Just to to the the northwest northwest of of the the outcrop outcrop of of unit unit A grade A breccia. Just detail above) good exposure exposure of brecciated unit breccia (described (described in detail above) is is a a good This lens of breccia is separated from from massive massive unit B by a B (Fig. (Fig. 24). 24). This lens of is separated a thin (2 m m wide) wide) sheared zone. Unit B breccia at (2 zone. Unit at this this exposure is is monomictic. monomictic. This is contrast to other other unit lenses, and This is in contrast unit B breccia lenses, and the the unit A breccias that are are polymictic. that 80 80 �N WATE RTOWN WATERTOWN t+ IUNCTION TO WATERLOO STOP 5 - POLISHED EXPOSURE NORTH QUARRY SOUTH QUARRY SOUTH QUARRY UW DRILLIN DRILLING SITE .5 MILES 0 CONTOUR INTERVAL CONTOUR INTERVAL 10 FEET 10 FEET EXPLANATION — ====ROAD ROAD • BUILDING BUILDING QUARRYWALL WALL JVQUARRY Figure Figure 30. 30. Detailed map of the Portland Portland Quarries. Quarries. Field trip Stop 55 is is in in the the north quarry. quarry. South quarry should should be be entered entered from from the the east. east. 82 82 �QUARTZ ITE NEAR NEAR PORTLAND PORTLAND STOP 5 -- WATERLOO QUARTZITE This stop illustrates quartzite, the This illustrates the the lithology of the the Waterloo quartzite, the youngest major Precambrian rock est rock unit unit in in south—central south-central Wisconsin. Wisconsin. These outcrops are at at the the extreme extreme southeastern southeastern edge edge of of the the exposed exposed Precambrian Precambrian shield shield in in are Wisconsin. gate on the 19, walk south Location: From the the locked gate the south side side of of S.T.H. S.T.H. 19, toward ~oward the the John John O'Laughlin O'Laughlin Quarries Quarries (this (this area areaisis-a -a Department Department of of Natural Natural Resources hunting hunting preserve). preserve). At the the road road junction junction take take the the left left fork. fork. The right of the Wisconsin's two deep drill drill right fork leads leads to the the site site of the University of Wisconsin's holes, about 900 feet of holes, of core core was was obtained obtained from from one one of of them. them. Drilling was terminated before intersecting the base of quartzite (see Haimson, guide terminated before the base of the the quartzite (see Haimson, Walk past the large corrugated iron building and then turn 1978). the large iron and then turn west (right) (right) 1978). and walk walk about about 70 m m through the and the trees trees to to the the quarry quarry (see (see Fig. Fig. 30 30 for for route). route). The Waterloo Quartzite is Introduction: The is probably stratigraphically equivalent to the the Baraboo Baraboo and and Barron Barron Quartzites Quartzites in in Wisconsin Wisconsin and and to to the the Sioux Sioux Quartzite Quartzite to In south—central in Minnesota Minnesota and South Dakota (Dott in (Dott and and Dalziel, Dalziel, 1972). 1972). In south-central Wisconsin the quartzite quartzite sheet lies lies stratigraphically above late—Penokean late-Penokean aged rhyolites rhyolites and and granites granites and and is is mainly mainly preserved preserved as as infolds infolds into the aged the igneigneThe absolute age ous basement. basement. The age of the quartzite can only be determined by indirect means. At Baraboo Baraboo the the quartzite overlies overlies rhyolites rhyolites that that are are similar similar in chemistry to those rocks in the Fox River Valley dated at 1765 m.y. in in the Fox River Valley dated at 1765 m.y. old. old. This date is This is the the maximum maximum age age of of the the quartzite. quartzite. Both the rhyolite and overlying quartzite quartzite were were deformed deformed during an event suggested by Smith (1978a) (1978a) to to Rb—Sr apparent age of the have occurred 1650 1650 m.y. ago. ago. This date is the Rb-Sr the Fox River Valley igneous igneous rocks rocks (Van (Van Schmus Schmus and and others, others, 1975). 1975). These data suggest suggest that Baraboo—Waterloo Quartzite was was deposited on an eroded rhyolite—granite that the the Baraboo-Waterloo rhyolite-granite basement between 1765 1765 and and 1650 1650 m.y. m.y. ago. ago. A pegmatite dike with with coarse coarse quartz, quartz, feldspar and muscovite crystals crystals that feldspar and muscovite that cuts the Waterloo Quartzite (on (on Rocky T. 9N., R. l3E.) has been dated at 1440 m.y. Island —- NW Sec. 27, 27, T. 9N., R. l3E.) has m.y. old by the Rb—Sr method (Aldrich Also, muscovite from a phyllite the Rb-Sr (Aldrich and and others, others, 1959). 1959). Also, bed in the Quartzite has has been dated dated at m.y. old by the K—Ar bed the Waterloo Quartzite at 1410 m.y. K-Ar technique (Goldich dates place a (Goldich and and others, others, 1966). 1966). These dates a minimum age on the the deposition of of the the quartzite. quartzite. , t, At Waterloo, Waterloo, the the dominant rock rock is a a red to to gray vitreous vitreous quartzite comcomposed of 75 to 98% Si02. Quartz is present as interlocking posed to 98% Si02' is interlocking and and strained strained sand—sized grains (Fig. sand-sized (Fig. 31). 31). Muscovite in in the the matrix of the the quartzite commoncommonly displays displays lepidoblastic lepidoblastic texture, with increasing amounts ly texture, and and with amounts of mica the Occasionally, thin phyllite layers rock may grade into aa foliated foliated quartzite. quartzite. Occasionally, are found found interbedded with the Bands of are the quartzite. quartzite. Bands of andalusite andalusite schist were identified in core core recovered recovered from from the the deep deep well well drilled drilled just to the identified in the east of the quarries quarries (Haiinson, (Haimson, 1978). The andalusite is is partially partially altered altered to to sericite. sericite. The assemblage andalusite—muscovite—quartz andalusite-muscovite-quartz suggests that that the the quartzite was locally, if not regionally, regionally, metamorphosed metamorphosed to the part of the locally, if not the upper upper part the greenschist facies. An amphibolite dike was also encountered in in the the well (Haimson, (Haimson, 1978). 1978). In the the Waterloo Waterloo area area the the quartzite quartzite forms forms aa broad broad east-plunging east—plunging syncline syncline In (Buell, 1892, 1892, Warner, Warner, 1904, 1904, Sumner, Sumner, 1956) 1956) which which is is almost almost entirely entirely buried buried (Buell, by Ordovician and and Cambrian sedimentary sedimentary rocks rocks (Fig. (Fig. 32). 32). Outcrops to to the the north of -h-, Sec. 25, T. 8N., 8N., R. R. l3E.) define the north of Lake LakeMills Mills(NE(NE 25, T. l3E.) define the south limb of the structure. structure. Here bedding dips dips to to the the north north at at 500. 50°. The apparent nose t, 83 �of the of the fold fold is in the Portland area area (the (the area area of of Stop Stop 5). 5). Here the strike o of bedding changes from N. 30°W. (in the the south) south) to N. N. 30°E. of bedding from N. 30 W. (in 30 o E. (in (in the the north) north) defining a a broad concave eastward arc; arc; the the nose nose of of the the syncline. syncline. Strike and dip dip measurements measurements are are a bit erratic erratic in this area suggesting that and a bit this area that the the structure in the nose of the syncline is complex. The north limb of of the syncline is complex. The of the the syn— syndine is cline is exposed exposed near near Mud Mud Lake Lake where where quartzite quartzite strikes strikes N. N. 80°E. 80 o E. and and dips dips The north north limb limb may may extend extend as as far far to the east as steeply to the the south. south. The the east as Hartford in Washington County (Sumner, ford (Sumner, 1956). 1956). Figure Figure 31. 31. Photomicrograph of of the the Waterloo Waterloo Quartzite Quartzite from from the Photomicrograph the Portland Quarry. Quarry. Interlocking and strained quartz grains grains are are interrupted interrupted by aligned laths of laths of muscovite. muscovite. With increasing increasing amounts of muscovite the the rock rock grades into into aa foliated foliated quartzite quartzite and and finally finally aa phyllite or schist. grades Bar scale scale is is 11 mm mm long. long. The quartzite at at Waterloo is well jointed jointed with N. N. 40°E. 40 o E. and N. N. 80°E. 80 o E. o directions common (also (also N. N. 70°W. 70 W. as as aa minor minor direction). direction). However no no detailed studies of of the rock fabric in studies in the the Waterloo Waterloo area area have have been been undertaken. undertaken. Thick Thick layers of of phyllite, layers phyllite, so common in in the the upper upper part part of of the the Baraboo Baraboo Quartzite, Quartzite, are lacking in the Waterloo Quartzite. Phyllite beds at Waterloo are thin are thin (rarely thicker thicker than than 25 25 cm) cm) and and commonly commonly pinch pinch out out over over aa lateral lateral distance distance (rarely of 10 to to 20 20 m. m. Primary structures such as bedding planes, planes, cross bedding and and conglomerate beds are common, common, and ripple marks are occasionally observed. observed. The unravelling of the structural history of the Waterloo Quartzite is is crucial to the understanding understanding of of the the 1650 1650 m.y. m.y. old old event. event. The Waterloo Waterloo Quartzite Quartzite is is overlain overlain by by Cambrian Cambrian sandstones sandstones that that locally locally contain large large rounded rounded boulders boulders of of quartzite. quartzite. About 3 km north north of of Stop Stop 55 (Fig. (Fig. 32), 32), blocks of quartzite 1 meter in size are embedded in Cambrian sandstone sandstone close to the quartzite exposures; exposures; the size of the the clasts decreases rapidly until just 700 m m from the the sandstone—quartzite sandstone-quartzite contact the the Cambrian sandstone is fine grained and friable and is fine and contains contains no no quartzite quartzite fragments fragments (Buell, (Buell, 1892). 1892). 84 84 �PORTLA D SHIELDS 19} - . . - - - - - - l 1 WATERTOWN o 2 MILES WATERLOO N MILFORD t EXPLANATION E X P L A N AT I ON o0 QUARTZITE QUARTZITE EXPOSURE EXPOSURE DIP OF OF BEDDING AND DIP BEDDING STRIKE STRIKE AND -®—i--— f -.-...;:)~ H.R. H.R. ROAD ROAD RAILROAD TRACK RAILROAD TRACK FIELD ROUTE TRIP ROUTE FIELD TRIP HUBBLE TON HUBBLETON ROAD ROAD Stop 55 Figure Detailed route route map map through through the the Waterloo Waterloo Quartzite Quartzite area. area. Stop Figure 32. 32. Detailed Map adapted adapted from from Buell Buell (1892). (1892). is is at at the the Portland Portland Quarries. Quarries. Map 85 85 �If the the Paleozoic Paleozoic sedimentary sedimentary rocks rocks and and the the Pleistocene Pleistocene sediments If sediments were were stripped from the Waterloo area, the quartzite would stripped from the Waterloo area, the quartzite would stand stand as as an an arcuate arcuate ridge (concave (concave to to the the east) east) 500 500 to to 900 900 feet feet above above the ridge the surrounding surrounding Precambrian Precambrian surface. For example, to the north of the city of Waterloo, Waterloo, quartzite surface. For example, to the north of the quartzite is is intersected in in deep deep wells wells at at 135 135 feet feet above above sea intersected sea level. level. Just Just 22 miles miles to to the the east, quartzite quartzite is is exposed exposed at at the the Portland Portland quarries quarries at east, at an an elevation elevation of of 860 860 feet (see (see Smith, Smith, 1978c). l978c). feet Only one one deep deep well well has has penetrated penetrated quartzite. quartzite. This Only This well well located located near near Reesville in western Dodge County penetrated 500 feet feet of of quartzite Reesville in western Dodge County penetrated 500 quartzite before before entering aa mica-rich mica—rich rock described by Thwaites (1940) entering (1940) as as aa gneiss gneiss or or aa schistose quartzite. schistose quartzite. Studies of of well well cuttings cuttings show show that that the the Waterloo Waterloo Quartzite Quartzite is Studies is part part of of aa large area of quartzite extending from Waterloo to Milwaukee large area of quartzite extending from Waterloo to Milwaukee and and north north to to Fond du du Lac Lac (Smith, Fond (Smith, l978c). 1978c). Thwaites Thwaites (1940) (1940) reported reported iron-bearing iron—bearing shale shale interbedded with this large quartzite sheet. interbedded with this sheet. Stop Description: Description: After Stop its steep south wall. After entering entering the the quarry, quarry, walk to its south wall. The rock this quarry quarry is typical of of Waterloo Waterloo Quartzite Quartzite in The rock in in this is typical area. in the the Portland area. It is is coarsely coarsely recrystallized and is It is rich in in muscovite. muscovite. Bands Bands of conglomerate are common and and contain quartzite quartzite fragments fragments up up to to 33 cm in are in size. size. Conglomerate Conglomerate bands strike N. 35°E. and dip 42° to the south. bands N. 35°E. and 42° to the south. On the western part of of the the quarry wall a 25 cm thick thick phyllite phyllite lens lens is is exposed exposed (Fig. (Fig. 33). 33). The phyllite The phyllite thins thins to to 3 3 cm cm and and eventually eventually pinches pinches out out to to the the west. Color banding that that represents primary bedding parallels conglomerate represents parallels conglomerate layers. layers. Cross is Cross bedding bedding is observed just above the the phyllite lens lens (Fig. (Fig. 33). 33). Dott and Dalziel (1972) (1972) report report a a mean current direction of of 165 165 degrees degrees (S. (S. l5°E.) 15°E.) for for the Waterloo Quartzite based on measurements of 38 Quartzite based on measurements of 38 cross sets. sets. This compares with aa direction of 171 degrees measured for the Baraboo Quartzite Quartzite (Dott (Dott and and Dalziel, Dalziel, 1972). 1972). Common current directions for these two quartzites strongly strongly suggest suggest that that the the Baraboo Baraboo and and Waterloo Waterloo Quartzites Quartzites are correlative. correlative. In In outcrops just to the the south south of of the the quarry, quarry, foliated foliated quartzite quartzite is is highly polished and grooved (due to highly polished and grooved (due to glaciation). glaciation). Grooves Grooves trend trend N. N. 20°E. 20 o E. Foliation Foliation and and cross cross bedding bedding (?) (?) impart impart aa swirl—like swirl-like pattern pattern to to the the outcrop. outcrop. In places the foliatedquartzite In places the foliated quartzite has has weathered weathered out in in aa series series of of low low ridges ridges each each about about 11 cm cm high high (Fig. (Fig. 34). 34). 86 86 �Figure 33. 33. Figure View of aa thin thin phyllite phyllite layer layer (between (between arrows) arrows) interbedded interbedded with with quartzite at at the the Portland Portland Quarry Quarry (Stop (Stop 5). 5). Note Note the the crossbedding crossbedding in the quartzite just just above above the the phyllite phyllite bed. bed. Figure Figure 34. 34. located just just to to the the Close-up Close—up view view of of foliated foliated Waterloo Waterloo Quartzite Quartzite located Foliation planes planes are are south south of of the the quarry quarry visited visited at at Stop Stop 5. 5. Foliation each about about 11 cm cm high. high. weathering out out here here into into aa series series of of low low steps steps each weathering 87 87 �References Cited Cited References Aldrich, LL, T., Wetherill, Wetherill, G. G. W., W., Bass, Bass, M. Aldrich, o T., M. No, N,, Compston, Compston, W., W., Davis, Davis, G. G. 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Weidman, S., Weidman, S., 1898, 1898, Precambrian Precambrian igneous igneous rocks rocks of of the the Fox Fox River River Valley, Valley, Wisconsin: Wjsc. Wisconsin: Wisc. Geol. Geol. and and Nat. Nat. History History Surv. Surv. Bull. Bull. 3, 3, 63 63 p. p. Weidman, S., district of Wisconsin: Wisconsin: Wisc. Wise, Weidman, S., 1904, 1904, The Baraboo iron—bearing iron-bearing district Geol, and and Nat. Geol. Nat. History Surv. Surv. Bull. Bull. 13, 190 190 p. p. 89 1 000-3K8T007-78 1000-3K8T007 -78 �OMISSIONS OMISSIONS South-Central Wisconsin Wisconsin Precambrian Inliers Field Field Trip Trip Guide Guide Book Book Number Number 22 -- Precambrian Inliers in in South-Central off the bar scales In preparation publication, the the bar scales were were inadvertently inadvertently left left off the In preparation for for publication, following figures. figures. Figure 14 14 (p. (p. 59) 59) Photomicrograph Marcellon rhyolite Photomicrograph of of Marcel10n ash-flow tuff. tuff. Marcellon rhyolite ash-flow Horizontal dimension, 3.3 mm. Horizontal dimension, 3.3 rom. Figure 17 17 (p. (p. 62) 62) Photomicrograph of Marcellon rhyolite Photomicrograph of Marce1lon rhyolite spherulitic spherulitic texture0 Marcellon texture. Horizontal dimension, 6.4 mm. Horizontal dimension, 6.4 rom. 62) Figure 18 18 (p. (p. 62) bands. Photoinicrograph of of aa spheroid spheroid with with concentric concentric bands. Photomicrograph Horizontal dimension, Horizontal dimension, 6.4 6.4 mm. rom. Figure 19 19 (p. 63) (po 63) (p. and Photornicrograph of of aa spheroid spheroid with with aa core core of of quartz Photomicrograph quartz and Vertical dimension, 11.2 mm. epidote. Vertical dimension, 11.2 rom. epidote. Figure 27 27 (p. 76) (p. 76) in the Photomicrograph crenulated shards Photomicrograph of of flattened flattened and and crenulated crenu1ated shards in the Marquette rhyolite. dimension, 6.6 Marquette rhyolite. Horizontal Horizontal dimension, 6.6 mm. rom. Figure 28 77) 28 (p. (p. 77) Photomicrograph of of flattened Marquette in the Photomicrograph flattened shards shards in the Marquette Horizontal dimension, rhyolite ash-flow rhyolite ash-flow tuff. tuff. Horizontal dimension, 6.6 6.6nun0 rom. (p. 84) Figure 31 31 (p. 84) Photomicrograph Quartzite. Photomicrograph of of the the Waterloo Waterloo Quartzite. Horizontal dimension, 6.6 Horizontal dimension, 6.6nun. rom. Figure 33 33 (p. (p. 87) 87) View em thick. View of of thin thin phyllite phyllite layer, layer, about about 40 40 cm cm thick. in middle middle of in of layer. layer. Pen lies Pen lies � 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, 1978 Description An account of the resource Institute on Lake Superior Geology. Milwaukee, Wisconsin. May 9-14, 1978. 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 1978 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Contributor An entity responsible for making contributions to the resource Aaquist, B. E. Banaszak, K. J. Bauer, R. L. Carnbray, F. W. Cannon, W. F. Chang, L. L. Y. Cooper, R. W. Cummings, M. L. Doane, v. DuBois, J. F. Egger, N. L. Foose, M. P. Gere, M. A., Jr. Hammond, R. D. Heinrich, E. W. Hodder, R. W. Hughes, J. D. Jirsa, M. A. Jonnson, A. Jones, D. G. Kalliokoski, J. Klaysrnat, A. W. Larue, D. K. Luther, F. R. Massey, N. W. D. Meddaugh, W. S. Meineke, D. G. Meyer, R. P. MoIling, P. A. Mudrey, M. G., Jr. Mursky, G. Myers, P. E. Nebrija, E. L. Ojakangas, R. W. Peltonen, D. R. Peterman, Z. E. Salotti, C. A. Scofield, N. Shaffer, N. Shanabrook, D. Sims, P. K. Smith, E. I. Strakele, A. E., Jr. Taylor, R. W. Trow, J. Tyson, R. M. Vadis, M. K. Van Schmus, W. R. Welkie, C. J. Westjohn, D. Woronick, R. E. Zietz, I. https://digitalcollections.lakeheadu.ca/files/original/0b9bd71e6ea5d2bd92035b333128d0ca.pdf de6d723232fadd49a8389d502051a921 PDF Text Text DULUTH, MINNESOTA INNESOTA MAY 8-13,1979 MAY 8-13, 1979 •e 25th ANNUAL ANNUAL INSTITUTE ON ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY ___;_• ,. �TECHNICAL SESSIONS and ABSTRACTS for the the 25th ANNUAL 25 th AJ.\lNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY Sponsored by Sponsored UNIVERSITY OF OF MINNESOTA, MINNESOTA, DULUTH DULUTH held at DULUTH, MINNESOTA Joint Session with the in Joint the North Central Central Section Section Geological Society of America May 8 —- 12, 1979 Donald M. M. Davidson, Davidson, Jr., Jr., Program Chairman Chairman David G. G. Darby, Darby, Field Trip Chairman Moss, Technical Editor Carol Moss, Editor �TABLE OF CONTENTS Page Page No. No. INSTITUTE DIRECTORS AND LOCAL COMMITTEE 1 1 PROGRAM 22 ABSTRACTS OF OF TECHNICAL TECHNICAL SESSIONS SESSIONS 8 8 ** COVER DRAWING: large anticline. anticline. View from the the east east bank of of the the The large St. bridge, St. Louis Louis River, River, just south of the highway bridge, looking west. Thomson Dam Area, near near Thomson, Thomson, Minnesota. Minnesota. W. Wilson, Wilson, May 30, W. 30, 1968 �-1—1— 25th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY Sponsored by University of of Minnesota, Duluth Duluth at at Duluth, Minnesota Duluth, May 8 —- 12, 1979 1979 INSTITUTE BOARD OF DIRECTORS DIRECTORS Donald M. M. Davidson, Davidson, Jr., Jr., Department of of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota* Minnesota* J. J. D. D. Hughes, Hughes, Department of of Geography, Geography, Earth Earth Science Science and and Conservation, Conservation, Northern Michigan, Michigan, Marquette, Marquette, Michigan M. F. M. F. Kehlenbeck, Keh1enbeck, Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, Ontario G. G. Mursky, Mursky, Department of Geological Sciences, Sciences, University of of Wisconsin, Wisconsin, Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin R. C. C. Reed, Reed, Geological Geological Survey Division, Division, Department of R. of Natural Resources, Resources, Lansing, Lansing, Michigan M. Walton, M. Walton, Minnesota Geological Survey, University of of Minnesota, Minneanolis, Minneapolis, Minnesota *Present address: address: Department of Geological Sciences, Sciences, University of of Texas, Texas, El Paso, Paso, El Paso, Paso, Texas Texas �—2— -2- PROGRAM Tuesday, May 8, 8, 1979 8 a.m. Field Trip 1 leaves Hotel Radisson Duluth Duluth Wednesday, May 9, Wednesday, 9, 1979 8 a.m. a.m. Field Trip 2 leaves Hotel Radisson Radisson Duluth Duluth 12 noon opens, Superior Superior Foyer, Foyer, Hotel Hotel Registration opens, Radisson Duluth p.m. 5 p.m. return Hotel Radisson Radisson Duluth Duluth Field Trips 1 and 22 return 7-10 p.m. 7—10 p.m. Smoker poolside, poolside, Hotel Radisson Duluth Duluth Thursday, May 10, Thursday, 10, 1979 7:30 —12 a.m. Registration, Registration, Superior Foyer, Hotel Hotel Radisson Radisson Duluth �—3— SESSION 1 Morning Thursday, May 10, 1979 Early Precambrian Co—chairmen; Manf red Kehienbeck, Paul Meyers 8:45 D. H. Davidson, Jr. Opening Remarks 9:00 John Klasner and Paul Sims Geologic Interpretation of Gravity Data in the Marinesco, Thayer and Watersmeet Quadrangles, Michigan 9:20 K. Howard Poulsen Polyphase Deformation of Archean Rocks at Rainy Lake, Ontario 9:40 Elizabeth Palmer and Donald Davidson Paleostrain Analysis - Across a Shear Zone, Northwestern Marathon County, Wisconsin 10:00 Stephanie Wurdinger Structural Geology of Amphiboliric Gneisses, Northeast Chippewa County, Wisconsin 10:20 Coffee Break 10:40 Hanfred Kehienbeck Structural Interpretations in the }Iazelwood Lake Area, Thunder Bay, Ontario 11:00 Paul Sims and David Southwick New evidence on the stratigraphy and structure of the Soudan area, Western Vermilion district, Minnesota 11:20 Bruce Brown Deformational History of Arehean Creenstone Terrane, Eastern Lake of the Woods, Ontario 11:40 Thomas Waggoner and Thomas Mroz Palmer Gneiss Update 12:00 Noon. Adjourn for Lunch Luncheon Meeting of Board of Directors — location to be announced. �—4— SE S SI ON 2 Afternoon Thursday, May 10, 1979 Middle Precambrian Co—chairmi: Ralph W. Marsden, Glen Morey 2:00 David Larue and F. William Cambray Cross folding in the eastern part of the Marquette Trough, Michigan 2:20 Roy Shegelskl. Stratigraphy of the Cunflint Formation, Kakabeka Falls Area, Ontario 2:40 Karen Kimball Coexisting Ainphiboles in the metamorphic iron formation, Jackson County, Iron Mine, Wisconsin 3:00 Mike Cutmnings Phase relations of oxide—free iron formation in the Amphibolite Facie 3:20 Coffee Break 3:40 Mark Kirstein Contact Metamorphism of iihe Virginia Fonna— tion in the Minnamax Deposit, St. Louis County, Minnesota 4:00 Jesse Dann Comparative najor element variations within the Emperor Igneous Complex, and the Hemlock and Badwater Volcanic Formations, northern Michigan 4:20 C. Bennett and 0. C. Innes Stratigraphy and Petrochernistry of Huronian Volcanies, North Shore of Lake Huron, Ontario 4:40 Discussion Session 5:00 Adjourn **** ****** *** Even ln& 7:30 Banquet with North Central Section GSA — Speaker: Dr. Vincent McK'lvey For"ie r Di e I: t United States Geological Survey Hot1 Normandy �—5— -5- SE ON 33 S E S SSI ION Morning Friday, May Friday, ~fuy 11, 1979 Late Precambrian Late Co—chairmen: Co-chairmen: Foos Stan Watowich, Mike Foos 9:00 William Matlack Geology of of the Duluth Complex-Virginia Complex—Virginia FormaFormaGeology the Duluth tion Contact, Contact, Minnamax Deposit, Minnesota tion 9:20 George Lehman and and Donald Davidson Petrology Aspects of the the Troctolite—Olivine Troctolite-Olivine Gabbro Series, Series, Duluth Duluth Gabbro Gabbro Complex (Late Gabbro (Late Precambrian), Northeast Cramer Cramer Quadrangle, Quadrangle, Minnesota 9:40 James Hahnenberg James Petrology and a~d Geochemistry of Keweenawan Diabase Dikes in Michigan's Western Upper Peninsula 10:00 Coffee Break Coffee 10:20 John Green Green Bedrock Geology of the Milepost 7 Area, Area, Silver Bay, Bay, Minnesota 10:40 Stephen Cuggenheim, Guggenheim, Peter Wilkes and S. hT. W. Bailey S. The Nature of Greenalite Greenalite 11 :00 11:00 Discussion Session 11:20 Adjourn for Lunch �—F.— SESSION 4 Afternoon Friday, Nay 11, 1979 Ceneral Session Co—chairmen: Cedric Iverson, Mike Mudrey 1:40 Business Meeting of the Institute 2:00 William Cannon and Dennis Kostick Ronchi Filtering — an easy, inexpensive tech— nique for linear enhancement of many kinds of Geologic Data 2:20 Elizabeth King and William Cannon Results of a Truck Magnetometer Survey of the Southwestern Quarter of the Iron River 20 sheet 2:40 Jim Trow DOE-Bendix—Michigan Geological Survey Diamond— Drilling for and Geologic Information in Marquette Iron Counties 3:00 Coffee Break 3:20 Maurice Brock, Jo Kalliokoski and Richard Ojakangas Status of USGS Uranium Studies in Michigan's Upper Peninrula 3:40 Tom Evsns State Legislation Affecting Mineral Development in Wisconsin 4:00 End of Technical Session Saturday, May 12, 1979 Field Trips 3, 4, 5, 7, 8 Depart Leave 0800 Normandy Inn �—7— -7- POSTER PAPERS Morning Friday, Friday, May 11, 1979 1979 9:00 to to 12:00* 12:00* Room, Radisson Duluth Duluth Hotel Hotel Explorer Room, Glenn R. R. Bruck Glenn A for the Origin of the Horse A new Proposal for Creek Channel, Channel, in in Polk Polk && St. St. Croix Croix Counties, Counties, Wisconsin Jeff Greenberg and Bruce Brown Preliminary Geologic Geologic Interpretation lnterpretation of the the Northeastern Wisconsin 1:250,000 Geologic Geologic Map Frank Karner and and John T. T. Ray The Precambrian Basement Basement of of North Dakota M. P. M. P. McKenna and L. L. W. W. Gladen and and Mineral Potential of Cook Mineral Survey and County, Minnesota County, Nancy Scofield and David B. B. Jorgenson Pink and Green Albite Phenocrysts from the the and Green Mohawk Mine, Mine, Michigan--Indicators Michigan——Indicators of Changes in Hydrothermal Fluids D. tv. N. Snider D. and B. B. K. K. Parker copper—sulfide potential of several igneous The copper-sulfide plugs in Michigan's Keweenaw Peninsula G. G. Bennett and D. D. G. G. Innes Innes Huronian Volcanic Volcanic Rocks, Rocks, North Shore of Lake Huron, Ontario Huron, *Authors to 12:00 *Authors will will be be present present 11:00 to �—8--8- HURONIAI'TVOLCANIC VOLCANIC ROCKS, NORTH SHORE HURONIAN SHORE OF OF LAKE HURON, ONTARIO HURON, ONTARIO G. Bennett G. Innes Bennett andand D. G.D. Innes Ontario Ministry of Natural Ontario Ministry ofResources Natural Resources ABSTRACT distribution, petrochemical and The distribution, and stratigraphic stratigraphic relationships relationships of volcanic and and clastic clastic formations formations at at or or near near the the base base of of the the Huronian Huronian of Supergroup of the the Southern Structural Structural Province Province of of Ontario Ontario permits permits the the following following reconstruction of of Middle Precambrian Precambrian events events in in terms terms of of rift tectonics. tectonics. 1. 1. Sands Sands and gravels of the the Livingstone Creek Creek Formation Formation are deposited on on Archean Archean basement. basement. 2. 2. Thermotectonic uplift centered east east of of the the present present Elliot Elliot Lake area (probably (probably in the the Sudbury Sudbury area) area) causes causes an an easteastward erosional erosional beveling beveling of of the the Livingstone Livingstone Creek Creek Formation. Formation. 3. 3. The andesitic member of the The the Thessalon Formation Formation erupts erupts from central vents and fissures in in aa subsiding subsiding basin basin or or graben. The study of of 110 110 chemical chemical analyses analyses indicates indicates that that in spite of local spilitization, these these oldest oldest vol— volcanics included (tholeiitic) canics (tholeiitic) basaltic andesite, andesite, icelandite, icelandite, rhyolite; rhyolite; and (mildly (mildly alkalic) alkalic) hawaiite, mugearite mugearite and and ankaramitic flows. flows. 4. 4. The of compositionally uniform uniform tholeiitic tholeiitic flood flood The eruption of basalt forms the upper (basaltic) member of the Thessalon forms the (basaltic) Formation. 5. 5. Reoccurrence of of uplift in in the the Sudbury Sudbury area area results results in in of the upper member of the erosion of the Thessalon Thessalon Formation Formation east of of Thessalon and its complete removal east removal east east of of the the Elliot Lake area. area. 6. 6. In the Sudbury area the the thick thick accumulations accumulations of of tholeiitic tholeiitic In the basalt (Elsie erupt from (Elsie Mountain and Stobie Formations) Formations) erupt fissures basin or or graben. graben. Increasing subsubfissures in a subsiding basin sidence and/or waning volcanism causes causes much intercalated intercalated Formation; while in wacke and conglomerate in the Stobie Formation; the Massey area (80 the Massey (80 km to the the west), west), basalt to to rhyolite rhyolite of of the the Salmay Lake Formation is is erupted on on aa surface surface in in part part of exhumed, exhumed, layered gabbro—anorthosite of gabbro-anorthosite which was probably probably emplaced during the Thessalon volcanic event. event. Coarse Coarse sands sands and and uraniferous gravels of the the Matinenda Matinenda Formation are on the the eroded surface of of the are laid laid down down on eroded surface the Thessalon Formationinin the the Elliot Thessalon Formation ElliotLake Lake area areaand andwestward; westward; but in the but are are intercalated intercalated with with the the younger younger volcanics volcanics in the Massey and Sudbury areas areas to to the the east. east. 7. 7. The eruption of the the predominantly predominantly rhyolitic rhyolitic Copper Copper Cliff Cliff the Sudbury area marks the final Formation of of the marks the final Huronian Huronian volcanic episode. episode. 8. 8. Cessation of volcanism in in the the Sudbury—Massey Sudbury-Massey area area is is folfoland the deposition of the lowed the lowed by by prolonged subsidence and thick thick turbidite turbidite sequence of the the McKim Formation. �-9—9— STATUS OF USGS URANIUM STUDIES IN MICHIGAN'S UPPER PENINSULA U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225, 80225, Richard Richard Maurice Brock, U.S. W. Ojakangas, Ojakangas, University of Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 55812 W. and Survey, and J. J. Kalliokoski, Michigan ~1ichigan Technological Technological and U.S. U.S. Geological Survey, University, Houghtor, Houghton, Michigan 49931 49931 and and U.S. U.S. Geological Geological Survey Survey University, ABSTRACT The U. U. S. S. Geological Survey is is conducting work work related related to to uranium uranium Lower, Middle, Middle, and Upper Precambrian Precambrian rock rock units. units. Randomly potential of Lower, selected samples from all units are being being analyzed analyzed for for uranium uranium content. content. In knowledge is is In general, general, base-level base—level data data are being generated where such knowledge lacking. Possible enrichment enrichment of shear zones zones is is one focus focus of of the the study. study. Mylonitic shear zones containing radioactive biotite biotite and and chlorite chlorite pods pods cut granitic rocks; rocks; some Some of these these porphyritic or or porphyroblastic porphyroblastic rocks rocks A number of primary are 3—5 3-5 times times more radioactive than than other granites. granites. A radioactive occurrences are present in in the the granitic granitic terrane terrane (see (see Kallio— Kalliokoski, 1976). koski, 1976). All the the major Middle and and Upper Precambrian Precambrian sedimentary sedimentary units units of of the the Cogebic Range in Michigan and Wisconsin, and other units Cogebic and Wisconsin, units to to the the east, east, are are in the the process of being being studied. studied. Paleocurrent patterns have been been determined determined (largely on cross--bedding) cross—bedding) for for the the Sunday Sunday Quartzite (72 (largely on (72 readings——bimodal readings--bimodal WNW I~l and ESE), ESE), the the Palms Formation Formation (102 (102 readings——bimodal ceadings--bimodal W~ and and E), E), the the Bessemer ENE and and W), W), and and the the Jacobsville Jacobsville Bessemer Sandstone Sandstone (105 (105 readings—--biniodal readings--bimodal ENE Formation (150 (150 readings——local readings--local variability). variability~ Field data are of primary importance, but but drill drill core core samples importance, samples of the the Jacobsville are also being studied. studied. Paleogeographic—depositional Paleogeographic-depositional models are are being being constructed; constructed; these these should should be be of value in determining sources and and transport transport directions directions of of radioactive radioactive However, to date abnormal radioactivity mineral grains grains and/or and/or solutions. solutions. However, radioactivity has only been found has found in detrital monazite of of the the Goodrich Goodrich Quartzite Quartzite (Vickers, (Vickers, 1956) in phosphatic zones zones of of the the Michigaimni Michigammi Formation (Cannon and 1956) and in Formation (Cannon Kiasner, 1976). Klasner, 1976). There are a number of minor radioactive radioactive occurrences occurrences which which may be related to the sub—Jacobsville sub-Jacobsville unconformity unconformity (Kalliokoski, (Kalliokoski, Langford Langford and Ojakangas, 1978). 1978). References Cannon, W. W. F. Klasner, J. Cannon, F. and Klasner, J. S., S., 1976, Phosphorite and and other other apatite— apatitebearing sedimentary rocks rocks in in the the Precambrian Precambrian of of Northern Northern Michigan: Michigan: U.S. Geological Geological Survey Survey Circular Circular 746, 746, 66 p. p. U.S. Kalliokoski, Kalliokoski, J., J., (with (with C. C. Johnson), 1976, 1976, Uranium Uranium and and thorium thorium occurrences occurrences in Precambrian rocks, rocks, Upper Upper Peninsula of Michigan and northern in Wisconsin, with thoughts Wisconsin, thoughts on other possible possible settings: settings: U.S. ERDA, ERDA, Grand Junction, BJX—48(76), BJX-48(76), 294 294 p. �-10- Kalliokoski, J., J., Langford, F. F. F., F., and and Ojakangas, Ojakangas, R. R. W., W., 1978, 1978, Critera Critera Kalliokoski, guides to to for uranium cccurrences occurrences in Saskatchewan and Australia as for as guides favorability for for similar deposits deposits in the United States: fsvorability States: U.S. D.O.E., D.O.E., Grand Junction, Junction, CJBX—1l4(78), Grand CJBX-114(78), 480 480 p. p. Vickers, 1956, 1956, Geology and monazite content content of of the the Goodrich Goodrich Quartzite, Quartzite, Vickers, Palmer area, area, Marquette County, County, Michigan in in Contributions Contributions to to the the U.S. Geological Survey Bulletin geology of uranium, 1955: 1955: U.S. Bulletin 1030, 1030, p. p. 171-185. �-11-· —11.-DEFORMATIONAL HISTORY OF AN ARCHEAN ARCHEAN GREENSTONE GREENSTONE TERRANE: TERRANE: EASTERN LAKE OF THE WOODS, WOODS, ONTARIO ONTARIO A. Brown* Bruce A. Department of Earth Sciences University of of Manitoba, Winnipeg Winnipeg ABSTRACT ABSTRACT A A structural and stratigraphic study study has has been been completed completed in in the the east— eastcentral part of the the Lake Lake of of the the Woods Woods region. region. The rocks of this this area area conconstitute aa typical greenstone assemblage of volcanic and stitute and sedimentary sedimentary litho— lithologies. The greenstones occupy an east—to—west east-to-west trending trending belt belt bounded bounded on on the the north, north, south, south, and east by granitic batholiths in in the the study study area. area. The results this study indicate that that the the greenstones have have undergone undergone aa comcomresults of of this can be be related related to to the the diapiric diapiric emplacement emplacement plex deformational history which can of the large bordering plutons of the large plutons and several smaller stocks stocks within the the belt. belt. features of of the the area area are are aa series series of of major major The earliest structural features east-west trending isoclinal folds folds (F1) (F I ) with horizontal to to shallow shallow plunging plunging east—west trending axes. F1 folds FI folds have an associated axial axial planar planar foliation foliation and and are are well well defined by top defined top reversals reversals within the the volcanic—sedimentary volcanic-sedimentary section. section. These folds are are aa regional folds regional feature feature and can be traced traced beyond the the area area of of study. study. facies distribution distribution as as well well as as structure structure supports supports Evidence from sedimentary facies their early early origin. origin. Deformation which accompanied emplacement emplacement of of the the granitic granitic plutons plutons produced folds folds (F2) (F 2 ) and aa complex complex pattern pattern of of faults faults and and shear shear zones. zones. Axial planar cleavages, cleavages, penetrative mineral lineation, lineation, and and aa complex complex set set of of F2 folds and related fabrics crenulations are associated associated with with the the F2 F2 folds. folds. F folds fabrics 2 show a consistent style throughout throughout the the area, area, but but their their orientation orientation and and degree of development is is variable depending depending on on their their location location relative relative to to the deformational deformational and and metamorphic regime surrounding the the the plutons. plutons. Where pluton contacts parallel the the structural structural grain grain of of the the greenstones, greenstones, F1 FI folds folds were tightened tightened and and flattened, flattened, and and shear shear zones zones developed developed along along litho— lithologic boundaries. Vertical displacement occurred occurred along along these these zones, zones, causing causing repetition of section and development development of of cataclastic cataclastic textures. textures. Where the the structural grain met a pluton contact contact at at aa high high angle, angle, shear shear zones zones acted acted as as detachment faults faults to to accommodate flexural flexural folding folding of of bedding bedding and and F1 F I axial axial planes around steeply steeply plunging plunging F2 F 2 axes. axes. In In the late stages of deformation, deformation, a set set of of northwest— northwest- and and northeast— northeasttrending kink kink bands bands was was overprinted on rocks trending rocks with strong planar fabrics. fabrics. Kinks grade into crenulation cleavage Kinks cleavage in in fine fine grained grained pelitic pelitic rocks rocks and and fine fine grained cataclastic cataclastic rocks. rocks. The latest latest structures are a series of northwest—trending northwest-trending faults faults into into diabase dikes dikes were intruded intruded in in Late Late Proterozoic Proterozoic time. time. which diabase *Present address: address: Wisconsin Geological and Natural History Survey, Survey, Madison, WI 53706 Madison, �—12— -12- A PROPOSED SOUTHERN SOUTHERN SPILLWAY SPILLWAY FOR FOR GLACIAL GLACIAL LAKE LAKE GRANTSBURG GRANTSBURG A Glenn R. R. Bruck and Earth Earth Science Science Department of Plant and The University of Wisconsin—River Wisconsin-River Falls Falls 54022 River Falls, WI 54022 ABSTRACT In 1935 W. W. S. S. Cooper described Glacial Lake Grantsburg Grantsburg which which was was formed when the Mississippi and St. St. Croix Croix Rivers Rivers were dammed dammed by by the the glacial advance of of the the Grantsburg Grantsburg Sublobe. Sublobe. Lacustrine sediments sediments indiindicate that the lake occupied an area of of approximately approximately 11,500 11,500 km2 km 2 mi 2 ). The estimated geographic center center of of this this body body of of water water (4,500 mi2). lies within Burnett County, County, Wisconsin. Wisconsin. Lacustrine sediments also indiindicate that the lake maintained a level level between 305 305 mm (1002 (1002 ft) ft) and and 325 325 mm (1070 ft) a possible maximum maximum at at 335 335 mm (1100 (1100 ft). ft). (1070 ft) with with a Cooper's the lake includes includes aa southern southern limb limb of of water water Cooper's description of the This limb was extending to the vicinity of St. St. Croix Croix Falls, Falls, Wisconsin. This confined on the west by the the Grantsburg Sublobe Sublobe and and on on the the east east by by the the St. Croix Moraine, Moraine, which was deposited about St. about 1,300 1,300 years years earlier earlier by by the the Superior Lobe. Lobe. The present investigation investigation suggests suggests that that the the lake's lake's southern extension terminated near St. St. Croix Croix Falls Falls and and Dresser, Dresser, Wisconsin; Wisconsin; this this location being determined by evidence evidence indicating indicating that that the the Grantsburg Grantsburg was pinned against the Sublobe was the St. St. Croix Moraine in in this this area. area. Although Cooper's most detailed of the the Cooper's study is is the most detailed investigation investigation of lake to date, date, he was unable to to find aa drainage drainage spiliway spillway associated associated with with its highest highest level. level. As a result, result, he hypothesized that that the the lake, lake, at at its its highest stand, stand, might have drained over over the the Grantsburg Grantsburg Sublobe. Sublobe. A A topographic topographic examination examination of of the the St. St. Croix Croix Moraine Moraine near near Dresser, Dresser, Wisconsin, reveals reveals a gap that lies lies at at the 304 304 m (1,000 ft) level, fully Wisconsin, m (1,000 ft) level, fully (180 ft) ft) below the the morainal ridge ridge it it divides. divides. During the the glaciation, 55 m m (180 this gap gap was was low enough enough so so that this that it was penetrated by outwash outwash from from the the marks the beginning of of a 42 km nearby Grantsburg Sublobe. Sublobe. The gap also also marks the beginning a 42 (26 mi) is clearly defined by the the 304 304 m m (1,000 (1,000 ft) ft) contour. contour. (26 mi) channel channel which which is The channel trends trends southward and and merges with the the Apple Apple River River near near HuntingHuntington, Wisconsin. From here it follows ton, follows the Apple River to to a a point point 6.5 6.5 km (4 it finally the St. St. Croix (4 mi) mi) WNW WNW of of Sommerset, Sommerset, Wisconsin, Wisconsin, where where it finally joins the River. This route describes a course which bypasses aa 26 This 26 km km (16 (16 mi) mi) stretch of the the St. St. Croix Croix River. River. The present study suggests suggests that that this this bybypass represents a southern spillway spillway for for Glacial Glacial Lake Lake Grantsburg Grantsburg which which facilitated the the lake's lake's drainage drainage during during the the maximum maximum advance advance of of the theGrants-' Grants~ burg Sublobe. Sublobe. Evidence in support of this this hypothesis consists consists of of two two major major observaobservations: First, the altitude altitude of of the the channel channel First, the close correlation between the and the level of of Glacial Lake Grantsburg; and the level Grantsburg; and and secondly, secondly, the the outwash outwash from from the the gap gap at at Dresser Dresser indicates indicates that that the Grantsburg Grantsburg Sublobe found east of the from the the ice ice flowed flowed through through the the gap. gap. drainage from �—13— -13- RONCHI FILTERING--A FILTERING——A RAPID INEXPENSIVE TECHNIQUE TO AID IN THE DETECTION OF LINEATIONS LINEATIONS IN PHOTOGRAPHS, PHOTOGRAPHS, MAPS, MAPS, ROCKS, ROCKS, AND THIN SECTIONS F. Cannon and Dennis Kostick William F. U.S. Geological Survey U.S. Survey Reston, Virginia 22092 Reston, 22092 ABSTRACT Ronchi filtering filtering is is a simple visual technique that that can aid in identifying linear trends trends in in Landsat Landsat images, images, aerial aerial photographs, photographs, geologic geologic identifying linear maps, aeromagnetic and gravity maps, maps, and topographic maps; maps; it can also be maps, It may used to to detect subtle subtle linear linear features features in in rocks rocks and and thin thin sections. sections. It sometimes be be an an adequate adequate substitute for for more more expensive expensive and and time—consuming sometimes time-consuming computer enhancement enhancement of of data. data. A A Ronchi parallel thin thin width of each parent area. area. filter is a type type of linear diffraction opaque stripes stripes are are arranged arranged on on aa clear opaque opaque stripe is equal to to the the width of The filter used in our work contains contains 88 grating in in which so that plastic so that the the the adjacent adjacent transtransstripes stripes per per millimeter. millimeter. filter is held about about 10-30 10—30 cm in front front of of the eye, The filter is held eye, and the object to be studied, studied, for for example, aa Landsat Landsat image, image, is is viewed viewed through through the the filter. filter. when viewed viewed in this way is Any small object when this way is seen as as multiple images images aligned to the the direction direction of of stripes stripes on on the the filter. filter. For example, example, aa perpendicular to dot dot appears as a line line of of several several individual individual but but closely closely spaced spaced dots. dots. This property can be used to to enhance enhance subtle subtle linear linear trends. trends. For example, example, by viewing aa Landsat image image through through the the filter filter and and slowly slowly rotating rotating the the filter filter 0 , a through 180 1800, a user user performs performs aa rapid rapid linear linear enhancement enhancement in in all all possible possible through directions. Subtle linear trends, not easily visible to the untrends, commonly not aided eye, eye, may become readily visible through the filter when it is is stripes on the grating is is perpendicular oriented so that the direction of of stripes to the to the trend on the the image image or or object. object. This technique has has been useful in regional tectonic studies in the the Lake Superior region by helping us us to identify linear trends trends in Landsat images, maps. images, aeromagnetic, aeromagnetic, and gravity maps. �—14— -14FOR~ATION IN THE AMPHIBOLITE FACIES FACIES PHASE RELATIONS OF OXIDE-FREE IRON FORMATION M. L. M. L. Cummings Department of Geology University of of Wisconsin Eau Claire, Claire, Wisconsin 54701 54701 ABSTRACT Iron Iron formation formation units, units, up up to to 50 50 m m thick, thick, occur occur in in the the Precambrian Precambrian Quinnesec Formation, Formation, west central central Marinette Marinette County, County, Wisconsin. Wisconsin. The iron formations metasediments and formations are associated with basalt flows, flows, graphitic metasediments and sub-economic sub—economic massive sulfide. sulfide. The iron formation well—bedded gray quartz and iron silicate formation contains contains well-bedded Locally, are Locally, quartz beds beds are fractured fractured and in some cases cases fragments fragments are separated by thin septa of iron silicates. Some sections are charactercharacterized by by rounded, ized rounded, 1 to to 2 cm, em, quartz nodules. nodules. Oxides and/or sulfides are are disseminated in iron silicate beds with beds or occur as as thin layers layers interbedded interbedded with iron silicates. Ilmenite is the oxide phase, phase, but magnetite is is locally locally Ilmenite is abundant. Monoclinic pyrrhotite is is the the main main opaque opaque phase. phase. Sphalerite grains interstitial to to iron silicates or associated associated with occurs as isolated grains with pyrrhotite. only in in pyrrhotite—bearing pyrrhotite-bearing beds. beds. Chalcopyrite occurs only beds. sequences can be determined by the the The metamorphic grade of of volcanic sequences iron silicate assemblages in oxide—free iron oxide-free iron iron formation. formation. Iron silicate assemblages in oxide—free oxide-free samples samples from from the Quinnesec Formation include include grunerite/quartz, grunerite/stilpnomelane/quartz, grunerite/stilpnomelane/quartz, grunerite/ferro—hornblende/ grunerite/ferro-hornblende/ stilpnomelane/quartz, grunerite/garnet/ferro—hornblende/quartz, grunerite/garnet/ferro-hornblende/quartz, grunerite/ grunerite/ ferro—actinolite ferro-actinolite ± ± ferro—hornblende/quartz. ferro-hornblende/quartz. Calcite is a common accessory accessory mineral. Stilpnomelane, Stilpnomelane, restricted restricted to to grunerite grunerite and and grunerite/ferro— grunerite/ferrohornblende assemblages, assemblages, is is more more iron—rich iron-rich than than associated associated amphiboles. amphiboles. grunerite in garnet-free garnet—free Manganese is preferentially partitioned into grunerite samples. samples. Magnesium is is preferentially partitioned into into ferro—actinolite ferro-actinolite in in Ferro—hornblende is grunerite/ferro—actinolite grunerite/ferro-actinolite assemblages. assemblages. Ferro-hornblende is the the silicate phase containing containing the the highest highest concentration concentration of of titanium. titanium. The iron silicates can be represented in the simplified system FeOFeO— A1203—CaO—Si02—H20. Na2O in stilpnomelane, MgO, MnO MnO and and Ti0 TiO2 A1203-CaO-Si02-H20. K2O K20 and Na20 stilpnomelane, MgO, in 2 in amphiboles remove remove the the system system from from the the ideal ideal simplified simplified system. system. Iron silicate assemblages assemblages in the Quinnesec Formation indicate that that the the assemblage assemblage hornblende/grunerite/quartz is approxiis stable under metamorphic conditions, conditions, approximated from associated associated metasediments, metasediments, at at 5200 520 0 CC and and 1.5 1.5 to to 3.5 3.5 kb. kb. Actinolite/ high—manganese bulk garnet/quartz is is stable at at higher temperatures temperatures or in in high-manganese compositions. �—15— -15- MAJOR-ELEMENT VARIATION WITHIN THE EMPEROR IGNEOUS COMPLEX AND THE HEMLOCK AND BADWATER BADWATER VOLCANIC FORMATIONS FORMATIONS Jesse C. C. Dann Department of Geology && Geological Engineering Engineering Michigan Technological University Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT Major—element variations variations within the Emperor Igneous Major-element Igneous Complex, Complex, and the the Hemlock and Badwater volcanic formations formations of of the the Lower Lower Proterozoic Proterozoic of northern Michigan were studied studied to to determine determine the the magma magma series series type. type. Fifty-two Fifty—two new new analyses analyses indicate indicate that that continental continental tholeiite tholeiite dominates dominates and that most of of the the less less abundant abundant calcalkaline calcalkaline rocks rocks are are not not really really and that most distinguishable from from those those associated associated with with aa Lower Lower Proterozoic Proterozoic Cu-Zn Cu—Zn distinguishable massive sulfide deposit in in Wisconsin. The Emperor Emperor Igneous Igneous Complex Complex in in the the East East Gogebic Gogebic Range Range consists consists of of The two two distinct suites: suites: calcalkaline volcanic rocks and and tholeiitic tholeiitic sills. sills. The the Ironwood The volcanic volcanic rocks, rocks, interbedded interbedded with with the Ironwood Iron-formation, Iron—formation, consist consist mostly of andesite breccia with minor lava flows; flows; they they are interpreted to to S1O2 increases upward from represent a subaqueous volcanic apron. apron. Si0 increases upward from 2 54 to to 62 62 percent with FeO remaining remaining at at 99 to to 11 11 percent. percent. The sill comcomintruded the iron—formation in in three stages which which show aa FeO FeO increase increase plex intruded the iron-formation three stages from 12 to to 19 19 percent. percent. Formation north north of of Crystal Falls Falls displays displays tremendous The Hemlock Formation tremendous Rhyolite lava lithologic and geochemical variety. variety. Rhyolite lava and/or volcaniclastic deposits occur at three horizons the formation formation which is dominated deposits at three horizons within within the which is and volcaniclastic sediments sediments (pillow breccia, flow by basaltic lavas lavas and (pillow breccia, breccia, hyaloclastite, and and turbidites). turbidites). The lowermost basalts, deposited deposited breccia, hyaloclastite, about b.y. ago, ago, are are poorly poorly differentiated oceanic basalts, basalts, perhaps about 2 b.y. perhaps in aa fault—bound fault-bound basin; ironerupted in basin; these are are overlain by slate and iron— formation. continental tholeiite The succeeding lavas, lavas, composed composed of. of. continental basalt, subcycles of of FeO FeO and and Ti02 Ti0 2 enrichment. enrichment. The upperbasalt, display several subcycles high-iron basalt (up (up to to 25 25 percent percent FeO) FeO) is is most unit of extraordinarily high—iron immediately overlain by by iron—formation. iron-formation. The rhyolites do do not not occur occur at at the top the top of volcanic cycles. cycles. The Badwater Greenstone outcropping along the north margin of the Iron Iron River-Crystal River—Crystal Falls Falls basin basin consists consists of of several several different different sequences sequences of of dominantly tholeiitic tholeiitic volcanic volcanic rocks. rocks. Exposures on the south limb of the basin exhibit a close relationship between high iron tholeiite basalts and iron-rich iron—rich sediments; sediments; these these rocks rocks are are interpreted interpreted to to belong belong to to the the Hemlock Hemlock Formation. It is is clear clear that that lavas lavas associated associated with with the the Ironwood Ironwood Iron-formation Iron—formation It are not not enriched in are in iron. iron. However, is some evidence which leads one However, there is to suspect to suspect aa relationship relationship between between iron-rich iron—rich lavas lavas of of the the Hemlock Hemlock Formation Formation and the and the overlying Amasa Iron—formation. Iron-formation. �—16— -16- STATE LEGISLATION AFFECTING AFFECTING MINERAL MINERAL DEVELOPMENT IN IN WISCONSIN WISCONSIN Thomas J. J. Evans Evans Geological and Natural History Survey Survey University of of Wisconsin Wisconsin —- Extension 1815 University University Avenue 1815 Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT development in Wisconsin has has stimulated stimulated Proposed metallic mineral development wide—ranging wide-ranging legislative legislative activity activity by by the the State State of of Wisconsin. Wisconsin. The new legislation, 1977 and and 1978, 1978, also also has has impact existlegislation, passed in 1977 impact on the the two two existing metal mines in Wisconsin. ing metal in to Metal mining operations are subject to new laws concerning concerning (1) (1) taxation taxation of of mineral mineral revenues revenues (Chapters (Chapters 31, 31, 185, and (2) controls controls on on operating operating procedures procedures and environmental 185, and 423), 423), (2) impacts from from the exploration (drilling) impacts (drilling) phase phase through through actual actual mine mine propro(Chapters 377, 377, 420, 420, and and 421), 421), (3) (3) controls controls on on metallic metallic mineral mineral duction (Chapters exploration lease terms procedures (Chapter and terms and and recording recording procedures (Chapter 253), 253), and (4) submittal submittal of of metallic metallic mineral mineral exploration information of (4) of geologic geologic interest to the the State State (Chapter (Chapter 422). 422). Some of will be be of the background leading to to the the recent recent legislation will reviewed with with aa brief discussion of the reviewed the current current status status of of each each law, law, its its impact the mining industry, industry, and subsequent regulatory regulatory activity. activity. impact on the Potential modifications of of the the laws laws will will also also be be noted. noted. Proposed legislation in the the 1979 long1979 legislative sessions sessions concerns concerns long— term of mining companies and and registration registration of of severed severed mineral mineral term liability of interests. Prospects for and ramifications ramifications of this additional Prospects for of this additional legislative legislative addition, the activity will will be be examined. examined. In addition, the work of of the the Legislative Legislative Council Council Mining Committee's Committee's Subcommittee Subcommittee on on Reclamation of Nonmetallic Mining will be reviewed. �—17— -17- BEDROCK GEOLOGY AREA, SILVER BAY, BAY, MINNESOTA GEOLOGY OF OF THE MILEPOST 7 AREA, C. Green Green John C. Geology Department University of Minnesota Duluth, Duluth, Minnesota 55812 55812 ABSTRACT tailings disposal disposal area area lies lies in in the the Reserve Mining Company's new tailings broad valley of the the Thirty—nine Thirty-nine Creek Creek tributary tributary to to the the West 'vast Branch Branch of of the Beaver River about five the five miles miles west west of of Silver Silver Bay. Bay. The basin basin is is underlain by lavas of the the North Shore Shore Volcanic Group Group whereas whereas the the high high the southeast side is is held up up by by diabase diabase of of the the Beaver Beaver Bay Bay ridge along the complex. The the northwest flank flank is is also also underunderThe more more gradual slope on the by mafic mafic intrusive intrusive rocks. rocks. All of of the the bedrock bedrock is is of of lain predominantly by Keweenawan (Late (Late Precambrian) Precambrian) age. age. During the summer of 1978 the the bedrock geology of the the area was studied by field field mapping and and examination examination of of drill cores obtained obtained for for dam dam foundation foundation testing. testing. The lavas The lavas in the basin and along strike to to the the south south can can be assigned assigned to of Green Green (1942). (1942). They dip gently (about (about to the the Gooseberry River basalts of 90) 9 0 ) to to the southeast, southeast, and consist of roughly roughly 700 700 feet feet of of intergranular intergranu1ar andesites andesites and basaltic andesites overlain by about about 850 850 feet feet of of ophitic ophitic olivine basalts. basalts. The later tend tend to to hold up low low hills within the the southsoutheast part of of the the basin. basin. The high ridge along the the east east side side is is made predominantly predominantly of of ophitic ophitic olivine diabase, diabase, but but a olivine a few anorthosite xenoliths and and thick thick screens screens and and blocks of basaltic hornfels are are also also present present as as well well as as minor minor interflow interflow volcanic sandstone sandstone and and breccia. breccia. The main diabase intrusion intrusion appears appears to to have been localized localized along along aa major NNE—trending NNE-trendin8 fault fault which which also also divides divides the lava succession into two the lava two separate structural and stratigraphic blocks; blocks; the flows east east of of the ridge the flows ridge strike WNW and dip south whereas those those to to the the west strike NE NE and and dip dip SE. SE. Some also occurred occurred since since intrusion, intrusion, Some faulting faulting has also producing breccias and topographic topographic cross—valleys cross-valleys and and juxtaposing juxtaposing unmeta— unmetamorphosed sediments sediments next next to to diabase. diabase. morphosed The intrusive rocks rocks of the the western flank flank are are more diverse diverse and and are are probably interdigitated with lavas lavas but exposures exposures are are too too poor poor to to show show contact relations. relations. The uppermost unit is is aa ridge—forming, ridge-forming, fine—grained, fine-grained, iron—rich trachybasalt iron-rich trachybasa1t sill, sill, probably probably with with two two branches. branches. The other major units the west side of the the area are are mostly ophitic ophitic olivine olivine diabase diabase units along the and gabbro of various types; types; some have highly zeolitized zeo1itized roof roof zones. zones. This the Minnesota Geological Survey Survey with This project was was supported by the the cooperation cooperation of of Reserve Reserve Mining Mining Company and Klohn Leonoff Consultants, the Consultants, Ltd. �—18— -18- INITIAL PROGRESS AND INTERPRETATION OF GEOLOGICAL MAPPING IN IN NORTHEASTERN NORTHEASTERN WISCONSIN WISCONSIN J.K. J.K. Greenberg and B.A. B.A. Brown Brown and Natural Natural History History Survey Survey Wisconsin Geological and Madison, Wisconsin Madison, ABSTRACT Initial results Initial results from reconnaissance—scale reconnaissance-scale bedrock geological geological mapping mapping in (an area bound by 45°N, 45 0 N, 90°W 90 0 W and the the state state border) border) in northeastern northeastern Wisconsin Wisconsin (an suggest the presence of four distinct tectonic tectonic regions regions separated separated by by three three structures which which are are best best defined defined by by their their geophysical geophysical signasignamajor boundary structures tures. Available age data data indicate indicate that that most, most, if if not not all, all, of of the the observed observed rock units are Middle Precambrian. Precambrian. The three The three boundaries extend approximately east east to to west across across the the map map area. The northern one is is nearly parallel with and and just just north north of of the the of Vilas County and just just south south of of the the Wisconsin—Michigan Wisconsin-Michigan southern border of border in Forest and Florence Counties. Counties. The central boundary extends from from the northern border of Lincoln County County in in the the west, west, across across central central Forest Forest The southern boundary County, and through Amberg in in eastern Marinette County. County. The County, continues from northern Marathon County County east—northeast east-northeast through through Merrill Merrill and and across southern Forest County before swinging across swinging to to the the south south along along the the eastern eastern border of Oconto County. County. The northernmost tectonic tectonic region region consists consists of of Michigamme Michigamme and and equivalent equivalent sedimentary rocks including iron iron formation formation and and small small volumes volumes of of volcanic volcanic rocks, rocks, all of of aa wide range range in in metamorphic metamorphic grade. grade. The next region to to the the is separated from from these these rocks rocks by by the the northern northern boundary, boundary, aa complex complex south is series of of fault fault zones. zones. This region is is characterized characterized by by isolated isolated areas areas of of migmatitic gneisses gneisses associated associated with with foliated foliated granitic granitic intrusions. intrusions. These areas areas of of felsic felsic rocks are surrounded on on the the north north and and east east by by predominantly predominantly mafic volcanic volcanic rocks, including the the Quinnesec Quinnesec Formation, Formation, and and are are apparently apparently mafic rocks, including However, late truncated on on the truncated the south by the central geologic boundary. boundary. However, late to to post—kinematic post-kinematic plutons, plutons, ranging ranging in in composition composition from from gabbro gabbro to to granite, granite, the regions to to the the north north and and south south of of the the boundary. boundary. Much of of intrude both the the immediately to to the the south south is is typical typical ofofa at!greenstonelt "greenstone" terrane the region immediately terrane composed of metavolcanic and and metasedimentary rocks rocks which which are are the the hosts hosts for for major major massive sulfide sulfide mineralization. mineralization. The southern boundary between between the the greenstone greenstone terrane and and rocks rocks including the McCaslin Mountain Quartzite terrane Quartzite and and Wolf Wolf River River intrusives to to the the south south is is expressed, expressed, at at least least in in part, part, as as aa major major Batholith intrusives shear zone. zone. All of of the tectonic tectonic features in in the the map area area will will be be better better understood as future future work extends extends mapping mapping coverage coverage to to the the west west and and south. south. �—19— -19- THE NATURE OF OF GREENALITE GREENALITE Stephen Guggenheim, Guggenheim~ Department of Geology, Geo1ogy~ University of of Illinois Illinois at at Peter Wilkes, Wi1kes~ Department of of Metallurgical Metallurgical and and Mineral Mineral Engineering, University of Wisconsin—Madison, Engineering~ Wisconsin-Madison~ and and S. S. W. w. Bailey, Bai1ey~ DepartDepartment of Geology Geology and and Geophysics, Geophysics~ University University of of Wisconsin—Madison, Wisconsin-Madison~Madison, Madison~ Wisconsin Chicago, Illinois, Chicago~ I11inois~ ABSTRACT Pure samples of greenalite, greena1ite~ including including aa single single crystal, crysta1~ have have made m&de detailed structural structural characterization characterization than than before. before. All possible a more detailed samples studied consist of an intimate lntergrowth samples intergrowth of of aa predominant predominant trigonal trigonal phase and and a a minor monoclinic phase, phase~ even even down down to to the the smallest smallest in the the electron electron microscope. microscope. Specific polytypes cannot cannot particles visible in 3n reflections, be assigned because of absence absence of of the the diagnostic diagnostic kl I 3~ ref1ections~ but the mode of layer layer stacking stacking differs differs in in the the two two phases. phases. The single crystal allows allows the crystal the sense of the axes to to be established and and leads leads to to the the conclusion that that the monoclinic phase is is in in a fixed fixed orientation orientation relative relative to the trigonal trigonal host~ layers. Tetrahedral inversion inversion to the host, but but with inverted layers. is for relief of the the lateral misfit anticipated anticipated due due is aa known known mechanism for 2+-rich octahedral to Si—rich tetrahedral tetrahedral sheet sheet and and aa Fe Fe2—rich to aa Si-ric~' octahedral sheet. sheet. As in in antigorite, antigorite~ it it causes elimination elimination of of octahedral octahedral cations cations and and surface surface OH OH groups at at the groups the inversion loci, loci~ thus thus simulating an excess excess of of Si Si upon upon con— conventional allocation of chemical chemical analyses analyses assuming assuming aa full full complement complement of of anions. Hexagonal arrays of satellite spots spots around around sharp sharp kl I 3n 3~ spectra on hkO hkO electron diffraction nets are interpreted spectra interpreted as as due due to to multiple diffraction caused by the the coherent coherent intergrowth intergrowth of of the the mono— monoclinic phase scattered as islands islands throughout throughout the the matrix matrix of of the the trigonal trigonal 2+-rich and Mn2+_rich host. and its its abundance abundance increases The is Mn Thc monoclinic phase is with fromgreenalite greenalitethrough through the the species species tosalite tosalite to to caryc— carycwith Mn2+ Mn2+ cont conttntfrom pilite, pilite~ the the Mn ~ill or-analogue grecnalite~ where the the monoclinic phase phase is is —analogue of of greenalite, predominant and the the trigonal trigonal phase phase is is minor. minor. predominant 2 �—20— -20- PETROLOGY AND GEOCHEMISTRY OF KEWEENAWAN DIABASE DIKES ONTONAGON, ONTONAGON, GOGEBIC, GOGEBIC, IRON AND DICKINSON COUNTIES, COUNTIES, MICHIGAN James J. J. Hahnenberg Hahnenberg Department of of Geology Geology Western Michigan University Kalamazoo, Kalamazoo, Michigan 49008 Keweenawan diabase dikes in Michigan's Upper Peninsula Peninsula are are being being trace element element (Rb, (Rb, Sr, Sr, Ba) Ba) concenconcenanalyzed for major and selected trace trations compositions. Specifically, techniques techniques trations and bulk mineral compositions. microscope, x—ray using the the petrographic microscope, x-ray fluorescence, fluorescence, atomic atomic absorption absorption spectrographic analysis analysis and and the spectrographic the magnetometer are being used to to accurately define mineralogical and and chemical chemical trends trends and and magnetic magnetic Sample distribution is character of the the dikes. dikes. Sample is spaced as uniformly as possible on a trend trend roughly perpendicular to to the the Keweenawan Keweenawan "rift "rift trend". The dikes dikes will be compared to to other Keweenawan igneous igneous units, units, in the the region region (the (the Powdermill Powdermill specifically lower Keweenawan flows in Group, formerly the Group, the South South Trap Trap Range). Range). Correlation with chemical trends in more recent trends recent rift rift systems systems will will be be attempted. attempted. The larger dikes are composed of subophitic subophitic plagioclase plagioclase and and pyroxene (augite (augite and and pigeonite). pigeonite). Opaque minerals are a minor, minor, but minerals are orthoclase and ubiquitous, constituent. constituent. Interstitial minerals quartz which occur locally locally as micropegmatitic intergrowths intergrowths associated associated with needles of of apatite. apatite. Some altered, being Some dikes dikes are only slightly altered, uralitized and chioritized, chloritized, while others others consist consist of of 15—25% 15-25% secondary secondary minerals. In In small small dikes, dikes, mineral grains are microcrystalline to to cryptocrystalline. The dike~ have narrow chilled margins The larger dikes abruptly changing to to phaneritic texture texture toward toward their their centers. centers. �—21— -21- INTERPRETATIONS IN THE HAZELWOOD STRUCTURAL INTERPRETATIONS AREA, THUNDER THUNDER BAY, ONTARIO ONTARIO LAKE AREA, M.M. Keh1enbeck Kehienbeck M.M. Department Department of Geology Geology Lakehead University University Lakehead Bay, Ontario Ontario P7B P7B SB1 5l Thunder Bay, ABSTRACT The Hazelwood is underlain by Hazeiwood Lake area is by Archean stratified sedimentary rocks rocks and and fragmental fragmental volcanic volcanic rocks. rocks. Primary structures, structures, particularly graded bedding, bedding, are well in most most outcrops. outcrops. Pillow lava lava flows flows occur occur sporadisporadipreserved in cally interlayered inter1ayered with agglomerates and and tuffaceous tuffaceous units. units. All rocks possess a well developed cleavage which appears parallel to axial surface surface of of observed observed minor minor folds folds in parallel to the the axial in the the sedimentary sequence. sequence. Applying the the technique technique of structural facing to to the the rocks rocks gives the sense of of younging younging of of the folded stratigraphic stratigraphic gives the sense the folded succession. Results from from Hazelwood Hazelwood Lake Lake indicate Results indicate that that a a significant the stratigraphic sequence down prior to to portion of of the sequence was was upside upside down the last last folding event the event in in the the area. area. �—22— -22- COEXISTING AMPHIBOLES ANPHIBOLES AT AT BLACK RIVER FALLS, FALLS, WISCONSIN WISCONSIN Karen Kimball Department of Geology and and Geophysics University of Wisconsin Madison, Wisconsin Madison, Wisconsin 53706 S3706 ABSTRACT Extensive outcrops outcrops of of iron iron formation formation are are present present seven seven miles miles west west of of Extensive Black River Falls, Falls, Wisconsin. Wisconsin. The dominant mineral assemblages in The in the the iron iron formation are: are: 1) 1) magnetite—quartz-.grunerite—ferroactinolite magnetite-quartz-grunerite-ferroactinolite 2) magnetite—quartz—cummingtonite—biotite magnetite-quartz-cummingtonite-biotite 3) 3) magnetite—quartz—garnet—hornblende—ferroactinolite—grunerite magnetite-quartz-garnet-hornblende-ferroactinolite-grunerite The amphiboles amphiboles in in the iron formation formation are are products products of of aa metamorphic metamorphic event event The the iron which reached reached lower lower amphibolite amphibolite facies. facies. Coexisting amphiboles amphiboles occur occur as as disdis- grains in in contact contact with with each each other, other, as as coarse coarse intergrowths, intergrowths, or or occaoccacrete grains sionally as as 20—25 20-2S micron blebs of of one one amphibole amphibole in in another. another. are not are not altered and and not not exsolved. exsolved. The amphiboles Individual amphibole grains are are homogeneous. homogeneous. Multiple electron microprobe analyses show that that compositional variations are less than than two two percent. percent. The amphibole assemblage hornblende—ferroactinolite—grunerite hornblende-ferroactinolite-grunerite is is the only three amphibole assemblage found found in in the the iron iron formation. formation. three quartz this assemblage quartz assemblage is is invariant. invariant. In the In the presence of of The chemical formulas formulas for for these these amphi— amphi- boles are (Na,K) 2Ca9(Mg,Fe,Al)5Si75023 for 9Mg1 4Fe4 boles are (Na,K) .2Ca.g(Mg,Fe,Al)SSi7.S023 for the the hornblende, hornblende, Ca1 Cal.9Xgl.4Fe4 Si7 . 8023 for the ferroactinolite and 7Si7 7023 for Si and (Mg,Fe)6 (Mg,Fe)6.7Si7.7023 for the the grunerite. grunerite. 7 8 0 23 for are abundant abundant and and include: include: Amphibole pairs are (Na,K)1Ca19Mg3Fe11Al29Si5023 grunerite—hornblende Mg14Fe57Si77023 —- (Na,K)lCal.gMg3Fel.lAlZ.gSiSOZ3 grunerite-hornblende Mgl.4FeS.7Si7.7023 grunerite—ferroactinolite Mg18Fe57Si79023 —- Ca19Mg14Fe39Si78023 grunerite-ferroactinolite Mgl.8FeS.7Si7.9023 Cal.gMgl.4Fe3.9Si7.8023 cummingtonite—gedriteMg4.SFe2.lSi7.SAl.4023 Mg48Fe21S178A14023 —- Mg12Fe47A12Si56A115023 cummingtonite-gedrite Mgl.2Fe4.7A12SiS.6All.S023 cummingtonite—actinoliteMg3.7Fe3.8Si7.9023 Mg37Fe38Si79023 — cummingtonite-actinolite - Ca19Mg32Fe15Si8O23 Cal.gMg3.2Fel.SSiS023 �—23— -23- Ferroactinolite coexisting with with grunerite grunerite has has higher higher Mg/Mg+Fe Ng/Mg+Fe and and Ferroactinolite Ca/Mg+Fe ratios than ferroactinolite coexisting with with grunerite grunerite and and hornhorn— Ca/Mg+Fe ratios than ferroactinolite blende. Grunerite Gruncrite in the two two phase assemblage assemblage has has lower lower MgIMg+Fe Mg/Mg+Fe ratios ratios and higher Ca/Mg±Fe Ca!Mg+Fe ratios than than in in the the three three phase phase assemblage. assemblage. Cumming— Cumming- tonite with gedrite gedrite has has higher higher Mg!Mg+Fe Mg/Mg±Fe and and lower lower Ca/Mg+Fe tcnite coexisting coexisting with ratios ratios than cummingtonite cucrmingtonite coexisting coexisting with with actinolite. actinolite. The the chemistry the The composition composition of of the the amphiboles amphiboics is is related related to to the chemistry of of the rocks. The in magnetite sections of the The Fe-rich Fe—rich amphiboles amphiboles occur occur in magnetite deficient deficient sections of the iron formation. formation. The magnetite. The Fe-poor Fe—poor amphiboles occur with magnetite. The !1g-rich Mg—rich The amphiboics occur in a transition amphiboles transition zone zone surrounding surrounding aa talc talc schist. schist. �—24— -24- PRELIMINARY RESULTS OF A A TRUCK-MOUNTED MAGNETOMETER SURVEY OF THE THE SURVEY OF THE SOUTHWEST QUARTER OF IRON QUADRANGLE, MICHIGAN AND AND WISCONSIN WISCONSIN IRON RIVER 10x2° l°x2° QUADRANGLE, R. King and and William William F. F. Cannon Cannon Elizabeth R. U.S. Geological Survey U.S. Survey Reston, Virginia 22092 22092 Reston, ABSTRACT In August August of of 1978, 1978, the U.S. U.S. Geological Survey In Survey made made aa survey survey of of the the southwest quarter of the southwest the Iron River l°x2° 10x2° quadrangle, quadrangle, Mich.—Wis., Mich.-Wis., using using a truck—mounted This work, work, which is part truck-mounted magnetometer. magnetometer. This part of of aa mapping resource-evaluation program in in the the Iron Iron River and resource—evaluation River quadrangle, quadrangle, was was done done over poorly exposed Proterozojc Proterozoic and and Archean Archean terrane, terrane, which which is is covered covered by a thick thick layer layer of glacial alluvium. alluvium. The survey consisted of 470 miles traverses generally of nearly 470 miles of of traverses generally The traverses in aa north—south north-south direction. direction. The traverses were done over over oriented in selected unpaved forest forest roads roads to to minimize minimize the the effects effects of of heavy heavy traffic traffic and of steel in in the the roadbed. roadbed. The system used a fluxgate fluxgate magnetometer magnetometer on aa boom on the the top top of the the truck, truck, and the the variations in the the mounted on total field were recorded in in both analog analog and and digital digital form. form. total magnetic magnetic field The purpose of the the survey survey was to to augment augment existing existing aeromagnetic aeromagnetic coverage, which which was was flown coverage, flown at a 1/2—mile 1/2-mile line line spacing spacing and and at at an an elevation elevation of 500 ft. above the surface, with with ground-level ground—level magnetic magnetic data data to aid in in of ft. above the surface, to aid detailed geologic geologic interpretations. interpretations. A A number of domal domal uplifts uplifts have have been been both mapped and inferred inferred from from sharp sharp linear linear magnetic magnetic anomalies anomalies that that outoutline them. them. The Archean Precambrian gneisses in in the the cores cores of of these these domes domes have relatively low magnetic relief, relief, as as do do the the metasedimentary metasedimentary rocks rocks of of the overlying overlying Michigamme Michigamme Formation, the Formation, and are not readily readily distinguishable distinguishable on the aeromagnetic aeromagnetic map. map. However, However, there there are subtle differences differences in the magnetic signatures between the Michi— the almost magnetically featureless featureless Michigamme rocks. These differences gainme slates slates and and the the more more variable variable gneissic rocks. can be observed on the the detailed detailed ground ground magnetic magnetic profiles profiles and and permit permit more more accurate interpretation of the the aeromagnetic aeromagnetic map. map. complex system system of of faults faults having having predominant predominant The The area has has been cut by a complex northwest and northeast trends, trends, some some with considerable horizontal horizontal and and vertical displacements, of displacements, which are apparent from the magnetic pattern of the the contoured contoured aeromagnetic data and the the ground profiles. profiles. The magnetic profiles also also detect detect relatively relatively low amplitude, amplitude, sharp sharp negative negative magnetic magnetic profiles anomalies anomalies associated with a series series of of reversely reversely magnetized magnetized Keweenawan Keweenawan diabase dikes djabase dikes striking approximately east. east. �~25- FORMATION CONTACT METAMORPHISM OF THE VIRGINIA FORMATION MINNAMAX DEPOSIT, ST. ST. LOUIS LOUIS CO., CO., MINNESOTA Mark Kirstein Department of Geclogy Geology University of Minnesota—Duluth Minnesota-Duluth Duluth, Minnesota 55812 Duluth, 55812 ABSTRACT Calc-silicate Calc—silicate bodies occur in the Virginia Formation Formation and and as ns xenoliths xenoliths in metadiabase dikes near the contact with the the base of of the the Duluth Duluth Complex Complex in the Minnamax Deposit, Deposit, St. St. Louis County, County, Minnesota. The rocks of of the the footwall footwall have been matamorphosed to to the the pyroxene pyroxene hornfels hornfels facies. facies. Later sulfide mineralization is present in in all metamorphic rocks. rocks. The calc—silicate calc-silicate bodies are are ellipsoidal ellipsoidal to to spherical spherical and and range range in in length from 4 inches to to 44 feet. feet. They are generally generally light light gray gray and and are are fine to fine to medium grained grained granofels. granofels. There are are three three types types of of bodies: bodies: (a) (a) homogenous, (b) (b) layered, layered, with alternating alternating layers layers of of leucoxene leucoxene or or diopside, diopside, homogenous, and (c) concentric' two distinct mineral layers. layers. The most and Cc) concentric showing at at least two common mineral assemblages are diopside and wallastonite with either common mineral assemblages either grossularite or or anorthite. anorthite. Accessory minerals include include ilmenite, ilmenite, sphene, sphene, and leucoxene. Later sulfide replacement occurs with chalcopyrite, and chalcopyrite, exsolved exsolvcd cubanite, and Associated with cubanite, a~d minor magnetite. with the the sulfide sulfide mineralization mineralization is the the development development of of poikiloblastic quartz, is quartz, calcite, and and apophyllite apophyllite with minor anhydrite, and laumontite. laumontite. minor anhydrite, fluorite, fluorite, humite, humte, and The Virginia Formation, Formation, a pelitic hornfels, hornfels, and and later later metadiabase metadiabase dikes look almost identical in in hand sample. sample. They are fine fine grained, grained, massive, massive, and dark dark gray. gray. Relict bedding, bedding, when seen seen in in the the hornfels, hornfels, is is highly highly concontorted and discontinuous. The hornfels consists dominatly torted dominntly of of equigranular equigranular plagioclase, cordierite, and hypersthcne hypersthene with with minor minor quartz, quartz, untwinned plagioclase, apatite, and and graphite. graphite. Biotite and orthoclase orthoclase occur occur locally. locally. Black "reacticn" "reaction" rims rims exist for for 3 inches into into the the hornfels when in in contact contact with with calc—silicate bodies. calc-silicate bodies. The rima rims consist of plagioclase, plagioclase, hypersthene, and and poikiloblastic augite. augite. The metadiabase dikes dikes consist consist primarily primarily of of lathy lathy interstitial hypersthene hypersthene and and augite. augite. Ilmenite, quartz, quartz, labradorite with interstitial and apatite occur as accessory accessory minerals. minerals. Sulfides in the the hornfels consist consist of pyrrhotite with exsolved pentlandite, pentlandite, chalcopyrite, chalcopyrite, and and minor minor magnetite magnetite and ilmenite. ilmenite. Sulfides Sulfides in the metadiabase are restricted restricted to to fractures fractures and and are dominatly composed of are of pyrrhotite. pyrrhotite. The calc—silicate calc-silicate bodies show metasomatic effects effects with aa gain gain of of aluminum and and aa loss loss of of calcium. calcium. This is responsible for for the the formation formation of of the "reaction" rims. the rims. Some the bodies may bc the top top of the the Some of of the be from the that were brought up up by by the the intrusion intrusion of of the the Duluth Duluth Biwabik Iron Formation that Complex. The to have originated as concretions in in the the The majority appear to Virginia Formation. Formation. The sulfides and associated silicates silicates are are related related to to a a later retrograde retrograde metamorphic metamorphic event. event. �—26— -26- GEOLOGIC INTERPRETATION OF GRAVITY DATA DATA IN IN THE THE MARENISCO-WATERSMEET AREA, AREA, NORTHERN MIGHIGAN J. S. Kiasner, Klasner, U. U. S. University, J. S. S. Geological Geological Survey Survey and and Western Illinois University, S. Geological Survey, Macomb, Illinois Illinois 61455, 61455, P. P. K. K. Sims, Sims, U. U. S. Survey, Denver, Denver, Macomb, Colorado, Colorado, 80225, 80225, and S. S. A. A. Jankowski, Jankowski, Department of of Geology, Geology, Western Western Illinois 61455 Illinois University, University, Macomb, Macomb, Illinois Illinois 61455 ABSTRACT Geophysical studies have been conducted in in the the western part part of of northern Michigan to aid in determining the the geology geology of of the the tectonic tectonic zone zone marking the the boundary between between two two Archean Archean terranes terranes recognized recognized in in the the Lake Lake Superior region;.a region;. a greenstone—granite greenstone-granite terrane terrane on on the the north north and and aa gneiss gneiss terrane on the the south. south. A the area having aa 22 milligal milligal contour contour A gravity map of the interval stations. The map interval was was prepared prepared using using data data from approximately 310 stations. includes gravity readings obtained includes obtained along along 33 profiles profiles with with 300 300 in m station station spacing to to aid in in interpretation interpretation of of the the data. data. The gravity anomalies generally are in The in good agreement agreement with the the mapped mapped geology. Pronounced lows coincide coincide with the the large large pluton pluton of of Archean Archean Puritan Quartz Monzonite west of Lake Gogebic and and the the Archean Archean gneiss gneiss dome dome Small positive anomalies anomalies coincide with synclinal basins near Watersmeet. Small of the lower Proterozoic Formations and and with magnetic of Proterozoic Copps Copps and and Michiganmie Michigamme Formations anomalies interpreted as being caused anomalies caused by lean lean iron—formation iron-formation and and associated associated rocks. Amphibolitic layers layers in in both the the quartz quartz monzonite monzonite and and the the gneiss gneiss also have positive gravity gravity anomalies. anomalies. A A relatively steep steep (approximately (approximately 5 milligals per km) km) north—sloping north-sloping gradient coincides coincides with the the inferred inferred position of of the the boundary zone zone between the the Archean greenstone greenstone and and gneiss gneiss terranes. A two—dimensional A two-dimensional gravity model consistent consistent with mapped geologic geologic units units and measured rock densities suggests that that the the synclinal synclinal basin basin within within the the greenstone terrane which involves involves the the Copps Copps Formation Formation is is about about 2.0 2.0 km km deep, deep, whereas the gneiss terrane which includes Michigamme the basin within the gneiss terrane which includes the the Michigamme Formation may be approximately 33 km deep. deep. A north-sloping north—sloping regional gravity gradient extrapolated A extrapolated from from data data outoutside the study area corresponds with the the boundary zone zone between between the the two two basement terranes and reflects an increase increase in in density density from from north north to to south south rocks of the the upper crust and perhaps also also in in the the lower lower crust crust and/or and/or in rocks upper mantle. �—27— -27- CROSS FOLDING IN THE PRECAMBRIAN CROSS PRECAMBRIAN X STRATA STRATA OF OF THE THE EASTERN EASTERN MARQUETTE MARQUETTE TROUGH, TROUGH, MICHIGAN MICHIGAN D. D. K. K. Larue Larue F. F. W. W. Cambray Cambray Michigan State University Michigan State Northwestern University Evanston, Illinois 60201 East Lansing, Lansing, Michigan 48824 ABSTRACT X Chocolay and Menominee Group strata The Precambrian X strata in in the the eastern Marquette trough trough of Michigan show evidence evidence of of two two episodes episodes of of deformation. The first and major nlajor deformation deformation CD1) (Dl) folded folded the the strata strata E-W slaty slaty cleavage cleavage (S1). (Sl). The second, second, less less intense intense and formed vertical E—W deformation (D2) (D2) locally formed cross cross folds of of bedding bedding and and folded folded cleavage. The major synclinal fold fold in the the trough, trough, termed termed the the Marquette syn— synclinorium, was Dl deformation. Macroscopic D1 Dl folds folds are are clinoriuni, was formed formed by by the D1 confined to the the hinge region of this this synclinorium (e.g., (~.£., Harvey Harvey Quarry, Quarry, Marquette). Minor Dl fold axes plunge gently gently to to the the EE or or WW in in vertical vertical E—W E-W axial planes. planes. At localities, the Enchantment Lake Formation along along U.S. U.S. 41 41 in in At two localities, Negaunee and the Kona Formation in Sec. Sec. 32, T48N, T48N, R26W, R26W, Negaunee, Negaunee, the the quartzose beds beds exhibit minor folds folds with steeply plunging plunging axes, axes, F2, F2, and and aa vertical NW—SE NW-SE axial axial plane, plane, S2. S2. These minor folds folds have an an S—shaped S-shaped profile profile and can be shown to to deform deform Sl. Sl. Similar features features of minor folds folds can be (northeast shore of of Teal Lake), Lake), in in the Mesnard observed in the Siamo Slate (northeast Marquette), and in Quartzite (shore (shore of Lake Superior, Superior, Marquette), in the the Negaunee Negaunee Iron Iron Formation (New (New Richmond Mine, Palmer, and on Jasper Knob, Knob, Negaunee). Negaunee). These Mine, Palmer, lithologies rarely develop cleavage so it it is is not possible to to determine determine the the sequence of folding directly. directly. However, However, minor folds folds showing showing steeply steeply plunging plunging fold axes fold axes are thought to have been superimposed on the the already already steeply steeply dipdipping limbs of In addition, addition, small intrafolial of the the Marquette Marquette synclinorium. synclinorium. In folds in bedding with an E—W folds E-W axial surface and steep plunge can can be seen seen on on an island in Teal Lake and are attributed to to the the D2 episode. episode. folds in the Marquette synclinorium exhibit aa somewhat The major folds variable fold—axis fold-axis orientation orientation from from south south of of west west to to north north of of west, west, as as exhibited by the Goose Lake syncline and the the folds folds associated with the the Isabella syncline in in the the Palmer Palmer area. area. These major folds folds may be either refolded D1 Dl folds or or both both D1 Dl and and D2 D2 folds. folds. Absence of a pervasive slaty cleavage makes assignment assignment difficult. difficult. The sequence of events is is consistent consistent with aa north—south north-south compression compression to to D1 structures, structures, followed by a NE—SW produce Dl NE-SW compression to to form form the the D2 D2 structures. The NE—SW NE-SW compression could could be induced induced by aa left—lateral left-lateral strike— strikeslip movement on the Marquette trough in the the late late stages of of D1 Dl compression. compression. Such displacement shortening displacement would would be expected if the regional directions of shortening during Dl D1 were were not not precisely orthogonal to during to the the trough. trough. It is interesting interesting to note that It is to note that the the regional regional shortening represented by D2 has a similar orientation to to that that represented represented by the the folds folds in in the the Republic trough. trough. �—28--28- PETROLOGY OF THE TROCTOLITE—OLIVINE TROCTOLITE-OLIVINE GABBRO SERIES, SERIES, DULUTH DULUTH GABBRO GABBRO COMPLEX COMPLEX (LATE (LATE PRECAMBRIAN) NORTHEASTERN NORTHEASTERN CRAMER CRAMER QUADRANGLE, LAKE AND AND COOK COOK COUNTIES, QUADRANGLE, LAKE COUNTIES, MINNESOTA MINNESOTA George Lehman Dames and Moore Co. Co. Lakewood, Colorado Colorado 80401 and Donald M. Davidson, Davidson, Jr. Jr. Donald ~. Dept. Dept. Geological Sciences Sciences University of Texas, Texas, El Paso El Paso, Paso, Texas Texas 79968 in the the northeast quarter quarter of of the the Cramer Cramer quadrangle, quadrangle, MinneMinneAs observed in sota, textures, the orientation of igneous igneous laminations, laminations, systematic systematic sota, rock textures, in modal abundances abundances of of minerals as as well well as as the the chemical chemical comcomvariations in of major minerals Indicate position of indicate that that the the troctolite—olivine troctolite-olivine gabbro gabbro series series in the Duluth Gabbro Complex (Keweenawan) differentiated differentiated in situ situ as Complex (Keweenawan) as a a result of crystal crystal settling. settling. Here, Here, the the troctolite—olivine troctolite-olivine gabbro gabbro series series is is exposed as as a southwest—northeast trending band of outcrops approximately exposed a southwest-northeast approximately two two km in in width which lies lies between two two distinct distinct terrains. terrains. The area to to the the northwest is is dominated by rocks rocks of of the the anorthosite anorthosite and and felsic felsic series series while while the area to southeast contains flow units of the the area to the the southeast the North North Shore Shore Volcanic Volcanic Group. The general orientation of igneous igneous laminations laminations (N6OE, (N60E, 15SE) lSSE) within within the the troctolite—olivine gabbro gabbro series troctolite-olivine series is interpreted to to be be the the result result of of gravity gravity settling, suggesting that that the the unit has has tilted tilted approximately approximately 15 IS degrees degrees toward toward settling, the southeast since solidification. The general strike of the of the the troctolite troctolite unit is parallel to to a well defined defined lineament lineament which which occurs occurs along along the the northnorthwestern contact contact of of the the unit. unit. Textures Textures of of the troctolitic troctolitic and and gabbroic gabbroic rocks rocks indicate indicate that, that, in in general, general, plagioclase and olivine are are cummulate, cummulate, while pyroxenes pyroxenes and and oxides oxides are are interinterstitial. stitial. Modal analyses show that rocks rocks of troctolitic troctolitic affinity affinity (P1 (PI -— 70%; Cpyx —- 10%; 01 — - 16%) are the northwest boundary (base?) (base?) are abundant abundant along the is the the most abundant while olivine gabbro (P1 (PI —- 68%; Cpyx —- 22%; 01 —- 8%) is lithology along along the the southeastern southeastern contact contact (top?). (top?). Interstitial ilmenite is is the major major oxide oxide component and occurs as 1—1.5% the 1-1.5% of the the rock rock unit. unit. Electron microscope analyses of of plagioclase, plagioclase, olivine, olivine, and and pyroxene pyroxene mineral grains from rocks of the troctolite series vary vary nearly continuously and systematically in in composition composition upward upward through through the the column. column. These compositional variations are: are: An77 to to An58 AnS8 (plag), (plaf,), Fo70 Fo 70 to to Fo50 FoSO (01), (01), and and Wo41 En45 Fs14 to Wo38 En36 Fs26 (Cpyx). W0 4l En4S FS 1 4 to W038 En36 FS 26 (Cpyx). the troctolite—olivine troctolite-olivine gabbro gabbro series series as as calculated calculated The bulk composition of the from modal abundance data data and and individual individual mineral mineral compositions compositions suggests suggests that that the could have been derived from aa magma with aa composition composition identical identical the series series could to that of the chilled margin of the the Pigeon Point Point sill. sill. The results of of this this to that of the investigajion support the investigation the model proposed by Weiblen which indicates indicates that that units units the Duluth Complex Complex (other (other than than the the anorthosite anorthosite and and felsic felsic series) series) have have of the been derived from from aa late late stage, stage, high—Al high-Al magma, magma, the the composition composition of of which which is is compatable with the the Pigeon Pigeon Point Point sill. sill. �—29— -Z9- GEOLOGY OF THE DULUTH COMPLEX-VIRGINIA FORMATION CONTACT MINNAMAX DEPOSIT, MINNAN.AX DEPOSIT, MINNESOTA MINNESOTA William Matlack Department of Geology University of Minnesota-Duluth Minnesota—Duluth Duluth, Minnesota 55812 Duluth, 5581Z Deposit, near Babbitt, Babbitt, Minnesota, is is aa large, large, low— lowThe Minnarnax Minnamax Deposit, sulfides at at the of the grade deposit deposit of of iron—copper—nickel iron-capper-nickel sulfides the contact contact of the and the the Virginia Formation. Formation. Mineralization is is primarily Duluth Complex and disseminated disseminated in in troctolitic troctolitic rocks rocks of of the the Duluth Duluth Complex, Complex, and and is is locally locally massive at the the contact and in the immediately adjacent Virginia Formation. tion. ° In In the the Minnamax test shaft area, area, the the contact contact dips dips 0 to to 35 35 degrees degrees is highly irregular. irregular. Apophyses Apophyses of the the Duluth Complex intrude SE and is the Formation and and xenoliths xenoliths of of the the Virginia Virginia Forrna— Formathe underlying Virginia Formation tion, feet in dimension, dimension, occur occur in in the the complex. complex. tion, ranging ranging upwards upwards of of 150 feet primarily of of argillic argillic hornfels hornfels with with The Virginia Formation consists consists primarily calc-silicate concretions. concretions. Minor lithologies include include graphite abundant calc—silicate Bedding, schist, schist, and calcareous argillic argillic hornfels. hornfels. Bedding, schist, biotite schist, where visible, for a a few feet feet and is locally locally conconvisible, can only be traced for and is torted; concretions appear randomly oriented. oriented. Metadiabase dikes dikes and and torted; concretions sills, metamorphosed metamorphosed by by the the Duluth Duluth Complex, Complex, occur occur in in the the Virginia Virginia sills, Formation. The Duluth Complex consists primarily of a mineralized phase which is characteristically troctolitic. troctolitic. Near the the contact contact it it is is commonly noritic. Here it contains cumulus cumulus plagioclase and intercumulus hypersthene, olivine, olivine, and and augite, augite, and and is is highly highly variable variable in in composition, composition, hypersthene, texture, Sulfides are primarily interstitial texture, and sulfide sulfirle content. content. Sulfides interstitial to to Xenoliths of of an an unmineralized unmineralized phase, phase, ranging ranging upwards upwards of of 100 100 silicates. Xenoliths feet in dimension, dimension, occur in in the the mineralized mineralized phase. phase. These xenoliths feet range from olivine olivine gabbro gabbro to feldspathic peridotite, peridotite, and and range in composition composition from to feldspathic Fractures and cumulus olivine olivine and and plagioclase. plagioclase. are characterized by cumulus breccia zones, zones, both in in the the Virginia Virginia Formation Formation and and the the Duluth Duluth Complex, Complex, commonly contain ides and and granitic granitic veins veins and veinlets. contain massive massive sulf sulfides Sulf ides locally locally replace replace hornfels, hornfels, particularly particularly at at the Duluth Complex Sulfides Complex contact. Field relationships and and petrography petrograhy indicate Field relationships indicate that that the the Virginia Virginia and metamorphosed to pyroxene hornfels Formation was was highly highly deformed deformed and metamorphosed to hornfels facies facies by the the Duluth Duluth Complex. Complex. The common cornmon pelitic mineral assemblage assemblage of of plagioclase—hypersthene—cordierite plagioclase-hypersthene-cordierite suggests suggests substantial substantial loss loss of of Si02, SiOZ, Na20, from the the Virginia Virginia Formation Formation (Bonnichsen, NaZO, K20, KZO, and and 1120 HZO from (Bonnichsen, 1971). 1971). These constituents constituents contaminated contaminated the the base base of of the the mineralized mineralized phase phase of of the the comcomplex. formed from a residual fluid of Granitic vein material may have formed the the mineralized mineralized phase, phase, or or by by direct direct partial partial melting melting of of the the Virginia Virginia Formation. of unmineralized metadiabase dikes and sills in Recognition of the Virginia Formation explains many complexities complexities in in the the petrology, petrology, the structure, of the the contact contact zone. zone. Massive sulfides sulfides structure, and mineralization of appear to to have formed formed by: by: 1) 1) migration of a sulfide—rich sulfide-rich fluid into into and along fractures, and fractures, and and 2) Z) local the Virginia Formation. Formation. local replacement of the �-30MINERAL SURVEY MINERAL SURVEY AND MINERAL POTENTIAL OF COOK COUNTY, COUNTY, MINNESOTA M.P. and D.G. M.P. McKenna, McKenna, L.W. L.W. Gladen, Gladen, M.K. M.K. Vadis, Vadis, and D.G. Meineke Resources, Division Division of of Minerals Minerals Department of Natural Resources, P.O. 567 P.O. Box 567 Hibbing, 55746 Hibbing, Minnesota 55746 ABSTRACT ABSTRACT This This study was was conducted to to obtain and compile information on on the the mineral potential potential of of Cook Cook County, County, Minnesota. Minnesota. This This information will be used to the Minnesota Department of Natural Resources Resources (MDNR) (MDNR) in in making making to assist assist the decisions in in relation to to mineral lands it land management management decisions mineral lands it administers administers and and to to provide provide information which may lead to to further further leasing leasing and and exploration exploration of of MDNR administered administered lands. lands. The study included included various various informatfon information gathering gathering activities. activities. Initially, aa literature survey was conducted to to determine determine the the existence existence and and location location of of reported economic mineral occurrences. This was followed by reported by aa field field examinexamination, during during which which outcrop outcrop samples samples were were collected collected for for assay assay and and microscopic microscopic ation, study study in in order order to to determine determine the the nature nature and and extent extent of of mineralization mineralization and and the the host rock rock geology. geology. A A compendium was prepared on past mineral exploration activity in in Cook Cook County; County; it it includes includes available available drill drill logs logs and and assays, assays, geologic, geologic, geophysical, and geochemical In some some cases, cases, where drill logs and assays geophysical, geochemical data. data. In were not available, the the cores cores were were logged logged and and assayed. assayed. An organic'-rich organic--rich lake sediment e~~loration exploration geochemical reconnaissance sediment reconnaissance survey survey was was conducted conducted concurconcurthe field field examination examination of of mineral mineral occurrences. occurrences. rently with the A report will contain all derived A report is is in preparation which will all information derived from this study. study. It It also describes the the various models models which which were were used used in in models are are based based on the mineral potential potential of of the the area. area. These models determining the economic mineral occurrences occurrences found Minnesota and and in similar environ— economic mineral found in Minnesota similar geologic geologic environments in other parts of ments of the the world. Results Results of of this this study indicate indicate that that significant significant vanadium concentrations concentrations exist in titaniferous magnetlte magnetite deposits deposits occurring occurring within within the the Duluth Duluth Complex. Complex. Disseminated low grade grade Cu-Ni in the the more Cu—Ni mineralization also also occurs occurs in more mafic mafic units of the the Duluth Duluth Complex. Complex. Ag—Cu—Zn Ag-Cu-Zn fissure—vein fissure-vein mineralization occurs in the Rove Formation where the the Rove Rove is is intruded intruded by by Logan Logan sills. sills. The lake lake sedisedithe ment geochemical geochemical survey survey indicates indicates anomalous values in in certain areas which have potential for for economic economic mineralization. mineralization. survey did did not not include include the the Boundary Boundary Waters Waters Canoe Canoe Area Area (BWCA); (BWCA); This survey however, however, some some of the the highest mineral potential areas in Cook County were added added to to the BWCA after the the field field surveys surveys were were completed. completed. �—31— -31- PALEOSTRAIN ANALYSIS ACROSS AA "SHEAR "SHEAR ZONE", ZONE", NORTHWESTERN MARATHON COUNTY, COUNTY, WISCONSIN Elizabeth Palmer Department of Geology University of Minnesota Duluth, Minnesota Duluth~ and N. Davidson, Jr. Donald M. Jr. Department of of Geological Geological Sciences Sciences University of of Texas Texas El Paso, Paso, Texas Texas ABS TRACT ABSTRACT The boundary between two major trending Precambrian terranes between two major northeast northeast trending Precambrian terranes (superbelts?) is is structurally structurally concordant concordant with geological units which (superbelts?) which trend trend approximately 750 approximately 75 0 through Athens, Athens, Wisconsin vTisconsin in in northwestern northwestern Marathon Marathon County. County. This 0.75 to width, generally, generally, though not This belt or "shear" "shear" zone, zone, 0.75 to 4 km in width, though not uniquely, gneissic amphibolites amphibolites of of the uniquely, separates separates gneissic the Chippewa Amphibolite ComCom(Archean?) to to the north from volcano-plutonic (greenstone-granite plex (Archean?) north from volcano—plutonic (greenstone—granite units (PG (P8 x?) on on the the south. south. Foliations within the host host rock strike 50_700 50-70 0 and dip dip 50—75° 50-75 0 N N while 0 0 lineations trend trend 230_2500, 230-250 , and and plunge plunge 65—75°. 65-75 . The zone itself has gradational gradational boundaries and is is composed of of cataclasized equivalent greenstone and amphibo— amphibolite units showing showing mortar mortar texture, texture, feldspathic feldspathic porphyroclasts, porphyroclasts, comminution comminution lite units and structure, and varying degrees degrees of of recrystallization. recrystallization. Discrete and fluxion fluxion structure, fault fault planes have also been recognized recognized within within the the zone. zone. Paleostrain Paleostrain analysis analysis was was carried carried out out on on samples samples from from each each host host unit unit at at distances up up to km from from the the shear shear zone zone as as well well as as on on samples samples located located distances to 99 km within the the zone zone itself. itself. At least 50 strain indicators, indicators, usually deformed fragments, were measured from 3 sets of orthogonal mineral grains or volcanic fragments, faces cut on to the the principal faces cut on each each sample sample as as well well as as the the angle angle relative relative to principal directions directions (foliation, (foliation, lineation lineation and and right right angles angles to to both) both) in in the the rock parallel to to which cuts cuts were were made. made. Strain was the methods of of was analyzed using the Ramsay (Rf/Q), Ramsay (Rf/8), Elliott's polar polar plot plot and and the the Hsu Hsu plot. plot. A fit strain A best best fit for each each sample sample using using the the Pase Pase 55 program program of of Siddans. Siddans. ellipsoid was was calculated for Error the best Error limits limits on on the the dimension dimension and and orientation orientation of of the best fit fit strain ellipsoid and its its orientation orientation were were calculated calculated at at less less than percent for for each each soid and than 2 percent sample. Results indicate that that both the gneiss Results indicate both the gneiss and and volcano-plutonic volcano—plutonic regimes regimes are characterized by fabric (V=+O.16, (V=+0.16, 0.19, characterized by aa flattened flattened fabric 0.19, 0.3; 0.3; K=0.4) K=O.4) with with generally low strain values (G5=O.75, (8 s =0.75, 1.29, 1.29, 0.5). 0.5). As the the shear shear zone zone is is approached, (V=-0.5; K=2.4) is approached, aa strong strong linear linear fabric fabric (V=—O.5; K=2.4) is is developed developed which is generally one order of magnitude greater greater in in €s value than than is is flattening flattening in in the host host rocks. the rocks. This This linear linear fabric fabric cannot cannot have have developed developed from simple shear alone. alorre. The lineation appears to have as aa result The lineation appears to have developed developed as result of of ductile deformation along the the deformation which, which, though though regional regional in in scope, scope, appears appears localized localized along zone. zone. A consistent with the strain A strong strong vertical vertical stress stress component component appears appears consistent pattern. �—32— -32- POLYPHASE DEFORMATION DEFORMATION OF OF ARCHEAN ARCHEAN ROCKS ROCKS POLYPHASE AT AT RAINY RAINY LAKE, LAKE, ONTARIO ONTARIO K. K. Howard Howard Poulsen Department of Geology Geology Lakehead University Thunder Bay, Bay, Ontario ABSTRACT The Archean geology geology of of the the Rainy Rainy Lake Lake area area has has been been the the subject subject of of considerable study study for considerable for nearly a a century. century. A.C. A.C. Lawson Lawson mapped mapped the the region region (1888, 1913) 1913) and and interpreted the (1888, the stratigraphy. stratigraphy. He placed aa sequence sequence of of metasedimentary metasedimentary biotite schists schists (the (the Coutchiching Group) Group) beneath beneath aa sequence sequence He further of metavolcanic schists schists (the (the Keewatin Keewatin Group). Group). He further recognized a second sequence of metasedimentary rocks (the of largely largely congloineratic conglomeratic metasedimentary (the Seine Seine Group) which he placed unconformably above Group) above the the Keewatin. Keewatin. Various workers re-studied the the area applying the the techniques techniques of a a number of geological have re—studied subdisciplines. Some of the the Coutchiching Coutchiching Group Group Some have have disputed the existence of and have placed it above the and the Keewatin as as aa lateral lateral equivalant equivalant of of the the Seine Seine Group. Others have have upheld upheld Lawson's Lawson's original original interpretation interpretation and and the the conconOthers flicting points the Seine-·Coutchiching flicting points of of view view have have become become referred referred to to as as the Seine-Coutchiching problem. proble~. present study re—examines re-examines the the significance of the Keewatin— KeewatinThe present boundary in in light light of of detailed detailed structural structural investigation investigation of of two two Coutchiching boundary type localities. At Rice Bay, and geometric analysis of of fabric At Bay, lithological mapping and geometric analysis fabric reveals the the presence presence of of aa major major antiform antiform with with moderate moderate plunge. plunge. elements reveals Observed younging information (graded (graded bedding and and pillow shapes) shapes) does does not not to this this simple simple interpretation interpretation and and part part of of the the sequence sequence is is recognized recognized conform to as having a downward structural structural facing facing with with respect respect to to the the major major fold fold closure. closu~e. This implies that that the the sequence sequence was was overturned overturned by by an an episode episode of of folding folding (F1) (F l ) predated the the development development of of the the major major closure closure (F2). (F 2 ). which predated At Bear Passage, Passage, structural structural elements elements similar similar to at Rice Rice Bay Bay are are At to those those at Fold axes axes (F2) axial surfaces surfaces (S2) no longer have systematic systematic exposed. (F2) and and axial (S2) no longer have orientations, however, however, and and appear appear to be complexly due to orientations, to be complexly redistributed redistributed due to the the intrusion of a quartz monzonite pluton. The crest of this pluton conforms pluton. The conforms to to a a broadly antiformal antiformal structure structure (F3). (F 3 ). The rocks rocks of of the the Bear Bear Passage Passage area area are are transected by by aa penetrative crenulation cleavage S4 transected S4 which which is is axial axial planar planar to to minor folds folds (F4). (F4). While simple stratigraphic interpretations interpretations are precluded precluded by this this polyphase deformation, deformation, a a key exposure at at the the Keewatin—Coutchiching Keewatin-Coutchiching contact reveals the contact the presence of of structurally structurally overturned overturned strata. strata. These strata appear to appear to have a a downward structural structural facing facing with with respect respect to to each each of of the the observed fold observed fold phases and hence overturning overturning is is assigned assigned to to F1. Fl. The documentation of polyphase deformation The deformation in in the the Rainy Rainy Lake Lake area area makes makes clear the clear the reason for for previous conflicting conflicting stratigraphic stratigraphic interpretations. interpretations. The of structurally overturned strata recognition of strata favours favours the the stratigraphic stratigraphic supersuper" Fold nappes (F1) position of the the Coutchiching Coutchiching upon upon the the Keewatin. Keewatin. (FI) may have responsible for for inverting inverting part part of of the the sequence. sequence. It It is not clear clear whether whether been responsible this and subsequent deformations were unique this and unique events events or or merely merely progressive progressive episodes in in a a continuous continuous sequence sequence of of deformation. deformation. �—33 -33- THE PRECAMBRIAN PRECf~BRIAN BASEMENT OF NORTH DAKOTA John T. T. Ray Ray and John and Frank R. R. Karner North Dakota Geological Geological Survey Survey and and University of North Dakota Grand Grand Forks, Forks, North Dakota Dakota 58202 58202 ABSTRACT Information on on the Information the Precambrian basement of of North North Dakota Dakota is is based based on on cores and and cuttings cuttings from 132 drilling tests cores tests (Lidiak, (Lidiak, unpublished; unpublished; Muehiberger Muehlberger and others, 1967; Moore, unpublished), unpublished), 11 age age determinations determinations (Peterman and and ethers, 1967; Moore, (Peterman and Hedge, data and and correlation correlation with with surrounding areas areas of of Hedge, 1964), 1964), geophysical geophysical data exposure. The North North Dakota Dakota Precambrian Precambrian consists consists of of several several types of Archean Archean The types of Superior Province Province and and possibly younger terranes Superior terranes in in the the east, east, often often with with deep deep profiles, and and much much less less well well known known terranes in the west, including weathering profiles, terranes in the west, younger rocks, rocks, possibly aa southern southern extension extension of of the the Churchill Churchill Province. Province. The Williston basin, basin, centered centered in northwestern ~orth North Dakota, Dakota, is is the dominant strucstrucWilliston in northwestern the dominant tural that determines the depth to to the the Precambrian. Precambrian. From aa depth of tural feature feature that determines the approximately 200 m the Precambrian approximately 200 m in in eastern eastern North North Dakota, Dakota, the Precambrian surface surface slopes slopes The distribution of 3 rn/kin m/km totoa adepth of radiometric radiometric age age S depthof of 5100 5100 m m in in the west. dates and dates and a pronounced break in in the the trend trend of of geophysical geophysical features features suggests suggests that the the Superior/Churchill Superior/Churchill Provincial boundary transects that transects central central North North Dakota. The Precambrian Precambrian basement basement of of east2rn eastern North North Dakota Dakota has has been been divided divided into into The five terranes terranes based based on on predominant predominant petrographic character five character and and r2gional regional gravity gravity features (Lidiak, unpublished). Amphibole Amphibole schist schist terrane is characterized by features (Lidiak, belts of belts of low and medium grade grade metamorphic rocks rocks with with associated associated gravity gravity highs. highs. The predominant predominant rock rock types types are arc actinolite actinolite and and hornblende hornblende schists schists with with occuroccurThe rences rences of of retrogressive quartz—biotite—feldspar quartz-biotitc-feldspar gneiss, gneiss, serpentinite, serpentinite, stretched stretched lithic lapilli tuff, lithic tuff, massive and porphyritic porphyritic basalt basalt and and banded banded iron iron iron iron formaformaThe Ramsey Ramsey gneiss tion. The gneiss tërrane terrane consists of of silicic silicic to to intermediate intermediate rocks rocks with aa persistent The characteristic lithology persistent gneissic gneissic fabric. fabric. The lithology is is layered layered gneiss metamorphosed metamorphosed to amphibolite facies gneiss facies and and fine— fine- to to medium—grained medium-grained gneiss gneiss with subordinate foliated foliated plutonic plutonic rocks. rocks. The three terranes terranes are are The remaining three characterized by silicic silicic to to intermediate intermediate massive massive plutonic plutonic rocks rocks with with associated associated gravity gradient and are are distinguished by by location. location. The Grand Grand gravity lows lOWS of of gentle gradient terrane (east—central), (east-central), McIntosh ~1cIntosh granite granite terranc terrane (southeast), (southeast), Forks plutonic terrane and Towner terrane (north—central) (north~central) all and Towner granite granite terrane all contain contain occurrences occurrences of of amphiamphi— bolite facies faci2s gneiss. gneiss. The generalized pattern of large l3rgc plutonic plutonic areas ureas within gneissic terranes terranes and intervening intervening greenstone greenstone belts belts is is consistent consistent with with the the gneissic exposed 2XpOSeG Archean rocks rocks to to the the northeast. northeost. ~ew information infor~ation on the Precambrian of eastern North Dakota Dakota was New was added added by the Red River River Valley Valley drilling drilling program program of of 1977 1977 (Moore, (Moore, unpublished) unpublished) which which propro the Red vided 26 26 cores. ceres. Preliminary petrographic results results suggest suggest that that the the concept concept of the amphibole schist schist terrane terrane be be ret&ined retained and and the the distinction distinction of of the the remainremainof the amphibole ing tcrranes on the ing terranes on the basis of rock fabric fabric ha b2 abandoned. abandoned. Amphibole schist schist tcrrane terrane is is characterized charactGrized by ty low low to to medium mediu~ grade grade metasedimentary ~et3sedimentaryand and tnetavolcanic metavolcanic rocks sever. cores which included included the the following following rock rock types; types; rocks and and was was penetrated penetrated by seven pillowed basalt, basalt, porphyritic porphyritic basalt, basalt, stretched stretched lithic lithic lapilli l&pilli tuff, tuff, mica mica schist, schist, talc-chlorite schist, (with graded graded beds), beds), and and meta—graywacke. meta-graywacke. The talc—chlorite schist, phyllite (with remaining cores cores pen2trated penetrated fine— re~aining fine- to to coarse—grained coarse-grained igneous igneous rocks, rcck8, gneiss, gneiss, and and �—34— -34- banded gneiss. gneiss. The intcrpretation interpretation of the the dominant igneous igneous character of banded the Grand Grand Forks Forks plutonic plutonic terrane terrane is is revised revised by the occurrence of of rocks the the occurrence rocks with aa gneissic-migmatitic gneissic-migmatitic fabric fabric in in six six of of seven seven cores. cores. Accordingly, the distinction of the the remaining terranes terranes by predominant fabric fabric may be misleading and will be be eliminated. eliminated. Subdivision of these these gneissic gneissic and and the basis of rock rock chemistry and plutonic terranes is being attempted on the petrographic character. character. Lidiak, E. G., G., Buried Precambrian Rocks of North Dakota: Dakota: unpublished Lidiak, E. manuscript. Moore, W. W. L., 1978, AA Preliminary Preliminary Report Report on on the the Geology Geology of of the the Red Red River River Valley Drilling Project, Project, Eastern North Dakota and Northwestern Minnesota: unpublished manuscript. manuscript. Muehlbergcr, Muehlberger, W. W. R., R., R. R. E. E. Denison, Denison, E. E. G. G. Lidiak, Lidiak, 1967, 1967, Basement Rocks in in Interior of of United United States: States: AAPG Bull. v. 51, 51, no. no. 12, 12, Continental Interior p. 2351-2380. p. 2351—2380. Peterman, Z. Peterman, Z. E., E., and and C. C. E. E. Hedge, Hedge, 1964, 1964, Age of Basement Rocks from the the Basin of of North North Dakota Dakota and and Adjacent Adjacent Areas: Areas: USGS Prof. Prof. Williston Basin Paper, 475—D, Paper, 475-D, p. p. Dl00—D104. DlOO-Dl04. �—. -I — -35- PINK AND GREEN ALBITE PHENOCRYSTS FROM THE MOHAWK MINE, - INDICATORS OF CHANGES IN IN HYDROTHERMAL HYDROTHERMAL FLUIDS FLUIDS MINE, MICHIGAN - Nancy Scofield Institute of Institute of Mineral Research and and Department of Geology and and Geological Engineering Michigan Technological University Houghton, Houghton, Michigan 49931 49931 B. Jorgenson David B. Department of of Geology Geology Central Michigan University Mount Pleasant, Pleasant, Michigan 48859 ABSTRACT Albite phenocrysts phenocrysts with with green green rims and pink interiors Albite rims and interiors are are present in samples of altered altered basalt basalt taken from the and known to be presamples of taken from the Mohawk mine and In the #3 and and #4 #4 mines. mines. In the collected samples, samples, phenocrysts are sent in Ahmeek #3 5-20 rom long and and 1—10 1-10 mm mm wide. wide. Some the smaller phenocrysts are green 5—20 mm long Some of of the only. Microscopically, the green portion consists Microscopically, the green consists primarily of of pumpellyite with some white to to light light green green remnant remnant albite. albite. Some of the the pumpellyite pumpellyite extends into into the the pink pink interiors interiors which which are are predominantly predominantly albite albite with with an an extends abundance of of sericite as an alteration product. abundance product. Under high power, power, small amounts of of red red iron iron oxide oxide are are apparent apparent in in the the phenocryst phenocryst interior, interior, appearappearamounts ing as as clouds clouds or clots of dust—like ing dust-like particles. particles. Albite twin lamellae lamellae are are continuous through through the the green green and and pink pink portions portions of of the the phenocrysts phenocrysts although continuous masked by alteration in in the the pink pink portion. portion. Flat stage extinction angle measurements on albite albite twins twins suggest suggest a composition of about An5. AnS. X—ray X-ray diffraction analysis analysis of the phenocrysts verifies the the mixture of of albite and and pumpellyite pumpellyite in in the the green green rims, rims, with with albite albite showing showing up up as as the only albite Structural differences differences between between the pink and phase of of the the pink pink interiors. interiors. Structural green albite were not not detected. detected. Electron microprobe microprobe analyses analyses show pumpellyite compositions Electron compositions in green and pink portions portions to to be identical identical with total total iron, iron, calculated calculated as as FeO, FeO, about about 5%. 5%. in major element element compocompoAlbite compositions are near AnO with no difference in sition between the exception of of a range of K K between pink pink and and green green albite albite with with the (0—3% in pink albite. (0-3% 1(20) K20) in albite. The suggests its its presence in The distribution distribution of of K K suggests alternation products. products. Measurement of minor Mg and Fe concentrations concentrations in in albite revealed that that incipient incipient pumpellyitization pumpe11yitization is is common. common. But only pink pink albite showed showed minor minor Fe Fe (up 0.7% Fe203) Fe203) unaccompanied by Mg, Mg, consistent albite (up to to 0.7% with the the red red iron oxide microscopically observed as as aa possible possible source source of of the the pink coloring. coloring. Because cross-cuts albite, to be Because pumpellyite pumpellyite cross—cuts albite, pumpellyite is assumed to paragenetically paragenetica11y later later than than albite. albite. The of sericite suggests The distribution of control by the original calcic calcic interior interior of of plagioclase. plagioclase. But whether sericitization preceded preceded or contemporaneous with albitization is is unclear. unclear. sericitization or was was contemporaneous At least two two stages fluids of of different comAt least stages of of alteration alteration by by hydrothermal hydrothermal fluids comare inferred. inferred. position and/or conditions are �—36— -36- AREA, ONTARIO STRATIGRAPHY OF THE GUNFLINT FORMATION, FORMATION, KAKABEKA FALLS AREA, J. Shegeiski R. J. Shegelski Lakehead University Thunder Bay, Bay, Ontario ABSTRACT total of ten stratigraphic stratigraphic sections sections of the Gunflint For.mation A total of ten of the Gunflint Formation have been measured measured over a distance of a lateral distance of 3.6 3.6 kilometers kilometers in the the From the m Kaministikwia River River gorge. gorge. the study, study, a a composite section 57 57 m Kaministikwia thick was was found found to to contain six distinct distinct lithostratigraphic lithostratigraphic members. members. These members members are, These are, in ascending order: order: 1. (3 meters) 1. basal basal member (3 composed of of conglomerate, composed conglomerate, quartzite, quartzite, stromatolites, stromatolites, taconite taconite or or pyritic, pyritic, black chert—carbonate; meters) composed of chert-carbonate; 2. 2. lower shale member (7 (7 meters) of fissile carbonaceous shale; fissile shale; 3. 3. lapilli lapilli member member (4 (4 meters) meters) composed composed of of felsic quartz—feldspar felsic quartz-feldspar lapilli—tuffs; lapilli-tuffs; 4. 4. middle middle shale shale member member (22 (22 meters) meters) composed of of fissile fissile carbonaceous carbonaceous shale; shale; 5. 5. chert-carbonate chert—carbonate member member (11 composed (11 meters) meters) composed composed of of alternating alternating layers layers and and lenses lenses of of chert chert and and siderite; siderite; 6. (at least least 10 10 meters; top top not not exposed) exposed) composed composed of of 6. upper shale member (at fissile carbonaceous shale. shale. The composite section section therefore therefore contains contains 70% fissile 70% fissile carbonaceous shale, 20% 20% chert—carbonate, chert-carbonate, 7% 7% lapilli—tuff lapilli-tuff and 3% diverse lithologies of of the the basal basal member. member. and 3% Primary in the the various Primary sedimentary sedimentary structures structures are are well well preserved preserved in various strata. Well rounded, rounded, well sorted sorted sand sand grains grains in in the the basal basal quartzites, quartzites, in association with taconites taconites and and stromatolite stromatolite mounds mounds suggest suggest aa shallow, shallow, littoral environment. environment. The presence presence of of accretionary accretionary mudball mudball lapilli, lapilli, graded ash-fall ash—fall tuffs and large large scale scale crossbedding crossbedding in in the lapilli—tuffs graded tuffs and the lapilli-tuffs indicate subaerial derivation and and shallow shallow water water reworking reworking and and deposition. deposition. Dessication Dessication features features and and soft soft sediment sediment slumpage slumpage and and brecciation brecciation occur occur within chert chert carbonate carbonate layers layers and and lenses. lenses. The The lenticular geometry of of chert chert carbonate beds as well as as their their intimate intimate interlayered interlayered relationrelationships with with ripple-marked, ripple—marked, and and mud-cracked mud—cracked carbonaceous carbonaceous shales shales suggest suggest aa ships The entire strati— shallow water origin for for both both of of these these lithologies. lithologies. The stratigraphic is therefore therefore considered to have in aa graphic section section is considered to have been been deposited deposited in shallow water environment environment at at the the margin margin of of aa large large restricted restricted basin. basin. �—37.-37- NEW EVIDENCE ON THE STRATICRA2HY STRATIGRAPHY AND AND STRUCTURE STRUCTURE OF OF THE SOUDAN AREA, AREA, WESTERN VERMILION MINNESOTA VEmlILION DISTRICT, DISTRICT, MI~mESOTA P. P. K. K. Sims Sims U.S. Geological Survey U.S. Survey Denver, Colorado 80225 80225 Denver, and D. D. L. L. Southwick Minnesota Geological Survey Survey St. St. Paul, Paul, Minnesota ~innesota 55108 55108 ABSTRACT southeast of of Soudan, Soudan, Minnesota at scale Recent geologic mapping southeast 1:24,000 has has further further clarified clarified the the stratigraphy stratigraphy and and structure structure of of the 1:24,000 the western Vermilion Vermilion district. district. Numerous top—indicators top-indicators confirm the the major structure the area to be structure of of the area to be aa broad, broad, steep-limbed, steep—limbed, southward-overturned southward—overturned anticlinorium, the axial trace trace of of which trends trends about about N.70° N.70 o W. W. The core core anticlinorium, the of the anticlinorium is is metabasalt metabasalt belonging belonging to of the of the anticlinorium to the the lower member of the Ely Greenstone. On the the upright north limb of the fold, fold, the the stratigraphic succession succession above above the the lower lower member member is is as as follows: follows: Soudan Soudan Iron—formation Iron-formation Member of Ely Greenstone, Greenstone, upper member of Ely Greenstone, Greenstone, and and Lake Vermilion Formation. Although the the Soudan Member is is characterized characterized by the the presence of of cherty iron—formation, stratigraphy is iron-formation, its its internal. internal stratigraphy is complex and and more more than than half of it is composed half composed of of volcanic and and volcaniclastic volcaniclastic rocks. rocks. Felsic volcanic and and volcanogenic rocks of of the the Lake rest volcanogenic sedimentary sedimentary rocks Lake Vermilion Formation rest directly Soudan Member in the directly on the the Soudan the Soudan quadrangle, quadrangle, but pinch out out toward the east beneath a tongue toward the east tongue of pillow pillow breccia, breccia, mafic mafic aquagene aquagene tuff, tuff, iron—formation, and and pillowed pillowed metabasalt metabasalt belonging belonging to to the the upper upper member member of of the the iron-formation, Ely Greenstone. The iron—formation iron-formation at at Jasper Peak is a lenticular body member; it within the the lower Ely member; it is is stratigraphically beneath the Soudan Iron—formation Member. Iron-formation The stratigraphy of of the overturned south limb of the the anticlinorium is as as follows: follows: lower lower member member of of Ely Ely Greenstone, Greenstone, member member of of Ely Ely Greenstone Greenstone near near Two Rivers, Rivers, upper member of of Ely Ely Greenstone, Greenstone, and and Lake Lake Vermilion Vermilion Formation. Formation. The member near Two Two Rivers Rivers is is aa heterogeneous heterogeneous sequence sequence of of pillowed pillowed basalt, basalt, tuff, felsic felsic porphyry, porphyry, felsic tuff, tuff, and cherty iron—formation iron-formation that that basalt tuff, appears to be slightly slightly below the stratigraphic position position of of the appears to be the stratigraphic the Soudan Iron— Ironformation connect with with it. it. formation Member and does not connect lower and upper members of the the Ely Greenstone are distinct in in terms terms The lower of of primary structures, structures, textures, textures, and and bulk bulk chemical chemical compositions compositions (Schulz, (Schulz, 1977). The lower member the form The lower member consists consists chiefly chiefly of of calc-alkaline caic—alkaline basalt basalt in the of massive massive and and pillowed pillowed flows; flows; the pillows typically of the pillows typically are irregular irregular in size and shape and are highly highly amygdaloida1, amygdaloidal, indicating and shape and are indicating deposition in shallow water. The tholeiitic basalt the form of of pillowed The upper upper member member is is chiefly chiefly tholeiitic basalt in the flows. The The pillows pillows are are regular regular in in size size and and shape and and are generally non— nonamygdaloida1, indicating deposition deposition in in deep deep water. water. amygdaloidal, indicating The stratigraphic record clearly clearly indicates indicates a a highly mobile vo1canostratigraphic record volcano— tectonic environment that may a smaller scale to to the tectonic environment that may have been been analogous analogous on a modern volcanic arc arc and and back—arc back-arc basin. basin. REFERENCE Schulz, K.J., K.J., 1977, Schulz, 1977, The petrology petrology and and geochemistry geochemistry of of Archean Archean volcanics, volcanics, district, northeastern Minnesota: Minnesota: Unpublished Ph.D. Ph.D. western Vermilion district, Dissertation, p. Dissertation, University University of of Minnesota, Minnesota, 349 p. �-38—38— GEOCHEMICAL AND GEOPHYSICAL ANOMALIES ASSOCIATED WITH THE BEAR LAKE INTRUSIVE, INTRUSIVE, SECTIONS 24 24 AND AND 25, 25, T56N, T56N, R34W, R34W, HOUGHTON COUNTY, SECTIONS COUNTY, MIGHIGAN D. D. W. W. Snider and and B. B. K. K. Parker Michigan Geological Survey Survey Geology and Minerals Research Research Unit Unit Lansing, Lansing, Michigan Michigan ABSTRACT The Bear Lake Intrusive Intrusive is is aa nearly circular circular felsic felsic igneous igneous body body which appears to to have intruded intruded the the Freda Freda Sandstone. SQndstone. The The body is roughly 1.3 km km in diameter and is 1.3 is located about 11.2 km (7 (7 miles) miles) north north of of the the city of of Hancock, Michigan. Michigan. The work at the the Bear Lake body was part part of of aa larger larger investigation investigation that was designed to that was to test test a a model based upon the the copper copper sulfide sulfide mineralimineralization at at Mt. Mt. Bohemia (Section zation (Section 29, 29, T58N, T58N, R29W, R29W, Keweenaw Co., Co., Michigan). Michigan). Basically, Basically, the the model model suggests suggests that that several, several, isolated isolated intrusive/extrusive intrusive/extrusive bodies of Keweenawan age distributed throughout throughout the the Keweenaw Keweenaw Peninsula Peninsula may represent exploration targets targets for for copper copper sulfide sulfide mineralization. mineralization. Both the soil geochemistry and the soil and the ground geophysics tend tend to to support support this this idea idea at the Bear Lake body. at body. The results of the the field mapping, mapping, geochemistry geochemistry and and geophysics geophysics indiindicate the following: following: 1. 1. The predominantly felsic body displays displays an an easily easily recognizable recognizable magnetic signature. signature. 2. 2. There are two two relatively strong conductors conductors (VFL—EM) (VFL-EM) associated associated with the the body. body. 3. The body has has potassic rock rock chemistry, chemistry, averaging averaging 6.43% 6.43% K20, K20, with with a high K20 Na20 0 ratio averaging 3.4. K2 0 : Na 3.4. 2 Trace element analyses indicate indicate that that the the copper copper values values for for the the felsic felsic body average 190 ppm ppm which is is anomalous anomalous when when compared compared to for that that rock type type (15—3Oppm). (15-30ppm). to the the published published averages averages for : 4. 4. 5. 5. The results results of a soil geochemistry survey survey indicate indicate aa pattern pattern of of anomalous copper values that that appears appears to to be be associated associated with with the the anomalous location of of the VLF—EM VLF-EM conductors. conductors. development of of aa model model or or "type" "type" deposit deposit based based upon upon the the Although the the development Mt. Bohdmia sulfide mineralization mineralization is is still still in in its its early early stages, stages, we we Mt. Bohemia copper sulfide hope that chemistry studies studies as as well well as as geophysical geophysical and and case case that further further rock rock chemistry history studies studies from history from several several other other known known areas areas of of similar similar copper copper sulfide sulfide the idea that Michigan's Copper mineralization will confirm or refute the Country may may have have another type Country type of of mineralization for for which to to explore explore in in addition to addition to the the native copper and White Pine—type Pine-type copper copper settings. settings. �—39--39- DOE-BENDIX-MICHIGAN GEOLOGICAL SURVEY DIAMOND-DRILLING DIAMOND-DRILLING DOE-BENDIX-MI CHIGAN GEOLOG ICAL SURVEY INFORMATION IN MARQUETTE AND IRON COUNTIES, FOR GEOLOGIC FOR GEOLOGIC INFORMATION COUNTIES, MICHIGAN James Trow Department of Geology Michigan State University East Lansing, Lansing, Michigan Michigan 48824 East ABSTRACT Many Precambrian XX argillites argillites and and slates slates are are carbonaceous carbonaceous and and pyritic, and some contain pyrrhotite, chalcopyrite, pyritic, chalcopyrite, sphalerite, sphalerite, and and galena. PrecambrianW metabasalt Precambrian.W metabasalt (1059—1148') (1059-1148') at at DL—5 DL-5 contains contains strata—bound ides with with 130-2010 130—2010 ppm Cu and 20—50 strata-bound suif sulfides 20-50 ppb ppb Au. Au. Maximum uranium content in holes occurs in a 2"—thick conglomerate in a 2"-thick conglomerate at at 3011' 3011' at DL—4, with 130 ppm U U (nitric/perchloric) at DL-4, (nitric/perchloric) or or 260 260 ppm ppm UU (hydro— (hydroW metarhyolite fluoric/nitric/perchloric acid acid digestion). digestion). Precambrian W fluoric/nitric/perchioric at DL-S (997-1059') with 72—76 72-76 ppm U U is is aa possible possible source source rock rock for for at DL—5 (997—1059') uranium in in Precambrian Precambrian XX strata. strata. In Marquette County, County, age Y dikes and minor gravity gravity faults faults In Y diabase dikes appear in E-.W, vertical, vertical, and and 2) 2) parallel parallel to in two two orientations: orientations: 1) 1) E-W, to SW— SWE—W vertical faults Precambrian XX slaty slaty cleavage. cleavage. Such E-W faults at at DL—1 DL-l dipping Precambrian and DL—7 have downthrown north sides; and DL-7 sides; SW—dipping SW-dipping faults faults at at DL—3, DL-3, DL—5, DL-5, and DL-4 DL—4 have downthrown SW sides, and sides, suggesting the the possibility possibility of of age age YY horst and graben structure in horst in the the region, region, in in harmony with Cannon's Cannon's north—south tension enunciated at 1978 Institute north-south Institute on on Lake Superior Superior Geology. Epigenetic X rocks Epigenetic sulfide remobilization in Precambrian X appears to be structurally related to to the the post—Penokean post-Penokean faulting, faulting, which appears to drags drags slaty cleavage cleavage as as well well as as bedding. bedding. Lower dip of Penokean slaty cleavage at DL—5 is at DL-5 is thought thought to to reflect post—Penokean post-Penokean rotation rotation of of Clark Clark Creek block. block. �I DL—l: DL-l: DL—3: DL-3: DL—7: DL-7 : DL—5: DL-5: DL—4: DL-4: DL—6: DL-6: NWk-4, NW¼, SW~, Sw¼, NW~, NW¼, NW~, NW¼, SW!t;, NE~, SW¼, NE¼, NW~, SE~, NW¼, SE¼, NWk-4, NE¼, NE~, NW¼, 28W, Section 5, 5, TT 50N, 50N, RR 28W, 29W, 14, TT 50N, Section 14, 50N, RR 29\01, Section 4, T SON, 50N, RR 28W, 4, T 27W, Section 16, 16, TT 49N, 49N, RR 27\01, 2, TT 48W, 48N, RR 28W, Section 2, 30, TT 46N, 46N, RR 33W, NE~, NE~, Section 30, NE¼, NE¼, Hole number -- DL—l DL-l 2148' Terminal depthdepth. ............ Terminal 2148' Maximum deviation deviation 56~0 from vertical ............ 56½0 Overburden ................ 0—71' 0-71' Age Y Y diabase diabase ............. --X strata Age X Dip of bedding ........... 30°SE— 30 0 SE3 0 m'1 Dip of cleavage cleavage .......... 37°—65°SW 37 0 -65 0 SW (Argillite, (Argillite, slate slate, ...... 71—2148' 71-2148 ' (turbidite, marble, marble, (algal stromatolite (algal Cherty carbonate,...) carbonate, ... ) --)) clastics, algal clastics, )) stromatolite, stromatolite, )) "iron—formation" "iron-formation" (Argillite (Argillite and ....... --(g r aywacke (graywacke Quartzite ............... --Age W W basement ............ --- O I 0 --r I Shallowest phosphate ...... --- I I East Baraga Basin, Marquette County East Baraga Basin, Marquette County East Baraga Basin, Marquette County Clark Creek Basin, Marquette County Dead River Basin, Marquette County NW of of P.masa Amasa Oval, Iron County DL-3 DL—7 DL-7 DL—5 DL-5 DL—4 DL-4 DL-6 1634' 697' 697' 1148' 3176' 1093' 1 4½0 l41P 0—243' 0-243' 0 330 0-320' 0—3 20' 523—602' 523-602' 12° 0-76' 0—76' 2286—2358' 2286-2358' 2825-2827' 2825—2827' 41.,,,0 4½0 2 0-236' 0—2 36' 0 SW1 55°—70° -70 0 S1' 0 l5 -45 0 S\-7 l5°—45°SW O -40 0 NE 55°—40°NE 55° S— 55 S- 0 -65 0 SW 37°—65°SW 37 243—569' 243-569' 20°—40°SW 20 0 -40 0 sw 320-523' 320—523' 0 -6S o SW 3 5°—6.5°SW 35 76—2966' 76-2966' 569—659' 569-659' 660—714' 660-714' 2966-3019' 2966—3019' 440 44 0 0—163' 0-163' 1545—15 51' 1545-1551' 20 0°NE— NE0 SW 0.T. 60°SW 60 O.T. 40 0-55 0 SW 40°—55°SW 163—1634' 163-1634' --- --- 0 vertical 0 65 65 °NN ? --- --- 714-884' 714—884' ----- --- 884—997' 884-997' 997—1059' 997-1059' metarhyolite 1059—1148' 1059-1148' metameta— basalt 514' 514' --- ) ) 236-1903' ? --- 659—697' 659-697' granite 490' 3019—3119'' 3019-3119 3119—3176' 3119-3176' tonalite 2810' 421' 421' �—41— -41- PALMER GNEISS UPDATE Thomas Waggoner and Thomas Mroz Thomas Cleveland-Cliffs Cleveland—Cliffs Iron Company Ishpeming, Ishpeming, Michigan Michigan 49849 49849 ABSTRACT The Palmer Palmer Gneiss Gneiss is The is somewhat of a misnomer for for an an Early Early Precambrian Precambrian formational unit composed primarily of quartz quartz chiorite—sericite chlorite-sericite schists. schists. The unit unit contains The contains thin beds of orthoquartzite and and slate, slate, along along with with aa typical typical Archean magnetite/pyrite chert iron—formation. iron-formation. The gneiss has been intruded intruded by granite with small small amounts amounts of of calcite, calcite, ankerite, ankerite, pyrite pyrite and and chalcopyrite. chalcopyrite. The preference of the intrusive granites for for foliation foliation planes planes indicates indicates deformation prior prior to to the the granitic granitic episode. episode. In Sections Sections 25, In 25, 26 and 27, 27, T47N, T47N, R27W, R27W, the the northern limit limit of of the the Palmer Palmer 0 Gneiss the east-west to Gneiss is is the east—west Palmer Palmer Fault Fault that that dips dips fairly fairly uniformly uniformly at at 58 580 to the north. north. The gneiss is is in in direct direct contact contact with with the the middle middle and and upper upper portions portions of the Negaunee Iron—Formation. of Iron-Formation. Both the Palmer Gneiss and and the the Negaunee Negaunee Iron— IronFormation have been offset by northwest—trending northwest-trending near—vertical near-vertical faults. faults. The terminus of the Palmer Gneiss is is gradational gradational into into the the pegmatitic pegmatitic southern terminus granite. Assimilation of of the Palmer Gneiss into into granite granite has has produced produced comcomthat make determination determination of of the the original original rock rock extremely extremely positional variations that difficult. The Palmer Gneiss contains numerous east—west The east-west vertical vertical faults faults that that further confuse the further the lithologic lithologic sequence. sequence. The foliation trends N N 700_800 70 0 -80 0 W W with northerly northerly attitudes attitudes varying varying between between Where bedding was observed, was N N 720 W with a observed, the trending was 72 0 W a northeasterly dip dip of of 610. 61 0 • 3500 35 to 85°. 85 0 • The Palmer Gneiss is is a Lower Precambrian Precambrian meta—sedimentary meta-sedimentary sequence sequence that that has by Lower Lower Precambrian Precambrian pegmatitic pegmatitic granite granite whose whose abundance abundance has been intruded by increases to to the the south. south. Assimilations and and post—intrusion post-intrusion progressively increases shearing have caused extensive silicification, shearing silicification, carbonization carbonization and and sericitization. sericitization. �—42--42- STRUCTURAL GEOLOGY OF OF AMPHIBOLITIC AMPHIBOLITIC GNEISSES, GNEISSES, NORTHEAST CHIPPEWA CHIPPEWA COUNTY, COUNTY, WISCONSIN WISCONSIN Stephanie Wurdinger Wurdinger Department of Geology University of Minnesota Duluth, Duluth, Minnesota, 55812 ABSTRACT ABSTRACT Precambrian amphibolites, amphibolites, hornblende schists and and intrusive intrusive units units are exposed along the the Chippewa and Fisher rivers rivers near near Holcombe, Holcombe, Wisconsin. Wisconsin. the northern boundary of of the the Chippewa Chippewa These rock formations occur near the Amphibolite Complex and are judged judged to to be Archean Archean (?) (?) in in age. Exposures of in order order to to determine determine the the stages stages of of of the rocks were investigated in deformation and and their their relative relative ages. ages. The major rock units units in the the area are quartz—biotite quartz-biotite amphibolite amphibolite at at Holcombe dam, dam, and interbanded amphibolite gneiss gneiss and and tonalite tonalite along along the the Fisher River. River. Intrusives into into the quartz-biotite include Intrusives quartz—biotite amphibolite include dikes, and and aa hypabyssal hypabyssal coarse grained granodiorite and associated dikes, andesite intrusive. intrusive. The two two amphibolite units are are separated separated by by aa zone zone of mylonite mylonite at at least least 300 300in m wide. Banded gneiss gneiss along the the Fisher River displays displays three three periods periods of of An early phase of folding. of deformation, deformation, Fi, Fl, produced produced isoclinal isoclinal folds folds in in A tonalite banding banding and and aa mineral mineral lineation in zones of amphibolite. tonalite amphibolite. A penetrative axial planar foliation, foliation, S1, Sl, trending trending east—west east-west was was also also During FI F1 deformation, deformation, ptygmatic folds During folds formed in in response response to to produced. the closely spaced spaced S1 Sl foliation. foliation. During aa later later deformadeformathe development of closely tion, F2, F2, large large folds, folds, possibly possibly isoclinal, isoclinal, refolded earlier mineral tion, lineations and along aa great great circle circle distribution. distribution. and minor minor fold fold axis axis lirieations lineations along The axial planes of F1 Fl and F2 are believed to to be be coplanar. coplanar. A A third third fold fold deformation, F3, deformation, F3' produced broad, broad, open open folds folds with north—south north-south axial axial planes planes at a a high angle angle to to earlier earlier fold fold axes. axes. At Holcombe dam the the first and third third fold fold deformations deformations can can be be Late synkinematic granitic in the the quartz—biotite quartz-biotite amphibolite. amphibolite. Late observed in intrusives foliation parallel parallel to to S1. Sl. The hypabyssal andesite andesite intrusives show a faint foliation intrusive faint intrusive exhibits exhibits aa strong, strong, steeply-plunging steeply—plunging lineation and a faint foliation which also also parallels parallels S1. Sl. The quartz—biotite quartz-biotite amphibolite was later later converted converted to to hornblende hornblende A schist along a shear zone zone which is is exposed exposed along along the the Chippewa Chippewa River. River. A penetrative lineation plunges plunges moderately to to the the west. west. Late movements along the zone zone formed formed small pods pods of of brecciated mylonite along along foliation foliation along the planes. the rocks in in the the area area were crosscut crosscut by by aa series series of of closely—spaced, closely-spaced, All the steeply-dipping faults. Strike separation along the the faults faults is is dominantly steeply—dipping faults. right lateral, right lateral, and offset offset does does not not exceed exceed ten ten feet. feet. � https://digitalcollections.lakeheadu.ca/files/original/29d12afcf47b7c5708ec5c269de2bd74.pdf 7ce48d615fb442ba698f3fd3d1fd53cb PDF Text Text u.a.eX UNIVERSITY OF WISCONSIN-EXTENSION GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostrom, State Geologist and Director MIDDLE PRECAMBRIAN GEOLOGY OF NORTHERN WISCONSIN Prepared for: TWENTY-FIFTH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY UNIVERSITY OF MINNESOTA-DULUTH DULUTH, MINNESOTA MAY 8-13,1979 FIELD TRIP GUIDE BOOK NUMBER 4 1979 �-{ffr _____ Tuesday May 8 Route .......... Wednesday May 9 Route 5 I " 0 " I 10 I I miles 20 I I �Field Trip Guidebook Number 4 University of Wisconsin-Extension GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostrom, State Geologist and Director MIDDLE PRECAMBRIAN GEOLOGY OF NORTHERN WISCONSIN Road Log and Geological Stop Descriptions Gene L. LaBerge and M.G. Mudrey, Jr. Edited by M.G. Mudrey, Jr. Geological and Natural History Survey Prepared for Twenty-Fifth Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY University of Minnesota-Duluth Duluth, Minnesota May 8 - 13, 1979 (meeting concurrently with the Thirteenth Annual Meeting, North-Central Section, Geological Society of America) David G. Darby, Chairman, Field Trip Committee University of Minnesota-Duluth Available from the Wisconsin Geological and Natural History Survey, University of Wisconsin-Extension, 1815 University Avenue, Madison, Wisc.onsin 53706. 1979 �CONTENTS INTRODUCTION by M.G. Mudrey, Jr. ........................................................................ 1 TUESDAY, May 8, 1979 Geologic Road Log for Ashland, Bayfield, Iron, and Vilas Counties .... 6 WEDNESDAY, May 9, 1979 Geologic Road Log for Oneida, Price, and Sawyer Counties .......•..... 9 GEOLOGICAL STOP DESCRIPTIONS Stop 1 - Grand View Quarry by G.L. LaBerge ..•••.•.•.....••..•....... Stop 2 - Mount l~itt1esey by G.L. LaBerge . Stop 3 - Pence by G. L. LaBerge ....•....••........................... Stop 4 - Hurley Overpass by G.L. LaBerge ...•.........•.•............ Stop 5 - Bear River by G.L. LaBerge .............•................... Stop 6 - Monico East by M.G. Mudrey, Jr . Stop 7 - Monico Gravel Pits by M.G. Mudrey, Jr . .....•............... Stop 8 - Witte Farm by M.G. Mudrey, Jr . Stop 9 - Monico West by M.G. Mudrey, Jr ...•......................... Stop 10 - Beck Tower Wayside Park by M.G. Mudrey, Jr . Stop 11 - Jump River at Big Falls County Park by G.L. LaBerge ......•. Stop 12 - Arpin Dam in Radisson by M.G. Mudrey, Jr . 12 15 20 23 27 30 32 34 36 38 40 43 ILLUSTRATIONS Figure 1. Figure 2. Table 1. Map of northern Wisconsin showing distribution of various lithologies in the Middle Precambrian ................•.... Schematic cross sections showing inferred lithologic -structural relations during the "Penokean event of Middle Precambrian age ........•......................•.... Time-stratigraphic framework of Precambrian rocks in Wisconsin ............•..•................................. Highway map showing route of excursion 5 2 inside front cover SPECIAL EVENT TUESDAY, May 8, 1979 - Evening Field trip banquet at Holiday Acres, Rhinelander, t..Jisconsin After dinner addresses: Discussion of Massive Sulfide Deposits by J.M. Franklin Discussion of the Crandon Deposit by E.R. May and Paul G. Schmidt i 4 �INTRODUCTION M.G. Mudrey, Jr. l Northern Wisconsin is blessed with an abundance of sand and gravel resources deposited by the last major glacial advance. This is a mixed blessing, in that bedrock exposures are few and far between. A fair average would be about one small outcrop per township. Since the 1920's and extensive exploration for iron deposits, bedrock studies in northern Wisconsin have been few. In the late 1960's, Gene LaBerge and Paul Myers working for the Geological and Natural History Survey initiated detailed-reconnaissance mapping in the central part of the state. Renewed interest in the Precambrian geology of northern Wisconsin was spurred in 1968 with the discovery near Ladysmith in Rusk County of a small, but rich massive sulfide ore body. Additional discoveries since then include the Pelican River deposit near Rhinelander in Oneida County, and the Crandon deposit in Forest County. In addition, numerous theses and dissertations have studied the various Precambrian and Pleistocene units. Although present detailed coverage is sparse (less than five percent of Wisconsin is mapped in any detail), the general framework and distribution is known or can be inferred from geophysical studies. This trip is designed to show the lithologies which illustrate changing environments in the Middle Precambrian, with predominantly sedimentary rocks in the north, and extrusive and intrusive igneous rocks in the south. Classical localities of Middle Precambrian iron-formation, conglomerates within the Middle Precambrian, the environment of volcanogenic massive sulfide accumulation and granitic plutons will be visited in road cuts, quarries, and natural exposures. To cover the terrane, we must travel over 500 miles. Some of the exposures are well studied, whereas others are having been identified in the past few years. Because of the non-ferrous base-metal interest in northern Wisconsin, several of the stops will concentrate on the general rock types infue volcanic pile, and their relation to known ore deposits. In addition, at the field trip banquet Tuesday evening in Rhinelander Jim Franklin of the Geological Survey of Canada will give a general summary on Precambrian massive sulfide deposits and their enclosing rocks and Ed May and Paul Schmidt of Exxon, U.S.A., will present their observations on the largest zinc-copper find to date in Wisconsin, the Crandon deposit near Little Sand Lake in Forest County. The weather this time of year can be nasty, but usually is crisp and invigorating. Stops will not be particularly strenuous. We will assemble for prompt 8:00 a.m. departure on Tuesday, ~fuy 8, 1979, and proceed with field stops to Rhinelander, Wisconsin, for an overnight stop, and journey back to Duluth with field stops the next day. We plan on returning to Duluth about 6:00 p.m. on Wednesday, in time for you to join the activities of the Twenty-Fifth Annual Institute on Lake Superior Geology and the Thirteenth Annual North-Central Section of the Geological Society of America. Monday evening, before the trip, an informal technical/social gathering is scheduled in Duluth. The geologic framework will be discussed, and all participants will have the opportunity to get acquainted before the Tuesday morning departure. WELCOME TO BADGER LAND! 1 �Table 1. Era System Paleozoic Time-Stratigraphic Framework of Precambrian Rocks in lVisconsin Stratigraphic Units Intrusive Rocks Approximate Age -----------------------------::-:::7':::-~::::_::_;:_"i:'_:;;:_~::::1;'~------------------66O:T:"iiDO-;;~;_:_ semimature at base grading 600-1,100 m.y. Bayfield Group upward to mature clastic rocks deposited mainly in shallow water Oronto Group immature clastic rocks deposited mainly in shallow water Upper Keweenawan ·--disconformity-- Middle Keweenawan c co N Lithology and Depositional Environment ... .0 E co t) Q) ... 0- Lower Keweenawan Portage Lake and Powder Mill volcanics south of Lake Superior and Chengwatana volcanics in northwest and along St. Croix River --disconformity-Bessemer Quartzite along Gogebic Range mafic and intermediate lavas and interbedded sedimentary rocks 600-1,100 m.y. gabbroic and granophyric complexes near Mellen and Mineral Lake south of Lake ~uperior immature clastic rocks deposited mainly in shallow water 1,120 m.y. 1,200 m.y. Q) +-' rapakivi massif and associated granite, syenite and anorthosite in northeast (Wolf River area) co ....J --unconformity?-Quartzite at Baraboo, Barron and as isolated outliers in north --unconformity-- clastic rocks deposited mainly in shallow water rhyolite inliers in south subaerial tuffs and breccias --regional unconformity-- 1,500 m.y. 1,765 m.y. epizonal, Dost-tectonic granite in south and isolated plugs in north 1,765 m.y. epizonal to mesozonal, syntectonic granites 1,880-1,820 m.y. 1,800 m.y. �positions uncertain - - - - - - - - - - - - - - - - - - - - - - - - - - - - - basaltic to felsic volcanic and volcaniclastic rocks in north c eo ..... ..a E eo submarine flows, tuffs, and volcanic sediments model lead ages from massive sulfide deposits are l,830 m.y. Physical correlation with other units is difficult at best. May correlate with Tyler Formation in north. metamorphic studies suggest 685 0 C at 7.5 RDars. This area has been correlated with the Gogebic Range. kyanite-staurolitegarnet bearing schists and associated quartzo-feldspathic gneiss near Park Falls to Mercer (including Powell kyanite locality) u Q) ..... a. ~ "'C "'C ~ basaltic to felsic volcanic and volcaniclastic rocks in extreme northeast (Florence area) submarine flows, tuffs, and volcanic sediments uranium-lead ages on zircon from gneisses are around l,850-l,900 m.y. Some volcanic rocks (Quinnesec) have been correlated with the Lower Precambrian and with the Middle Precambrian. Stratigraphic relations in this area are not clear. Tyler Formation on Gogebic Range clastic rocks deposited mainly in deep water (=Baraga v.> ~roup of Michigan) 0. :l >. I: 0,.... l-i <1l c.:J .u --local unconformity?-- (1) ..... Ironwood Iron-formation on Gogebic Range iron formation Palms Formation on Gogebic Range immature clastic rocks deposited in shallow water (=Menominee Group of Michigan) 1.1'\ 00 (1) ..::< e ..... e S ..... ."<1lC ,..,I <t<.u (1)0 ."e ::;:: II ....... 0 ~ .uo ~I.I'\ U ~ eN :l >. (1)"" --regional unconformity?-Bad River Dolomite on Gogebic Range o o (/J cc..o stromatolitic dolomite C1l (=Chocolay Group of Michigan) <1l ..0 ---------::~~::~::~.::::~----------------~ --regional unconformity-- 2,600 m. y. c eo ..a E eo u volcanics and associated sediments south of Gogebic Range submarine flows, tuffs and agglomerates ..... >- ..... eo L.LJ epizonal granite south of Hurley 2,710m.y. --unconformity?-- Q) a. gneiss, migmatite and amphibolite in south and western end of Gogebic Range o l-i 0. high-grade migmatites 2,800 m.y.+ �---------~---~-~~- MIDDLE PRECAMBRIAN ROCKS IN WISCONSIN Geology modified from Sims 11976) Figure 1. IX'ii'l Granitic Rocks Ii>! Metasedimentary Rocks [:,/:',:::':] Metavolcanic Rocks Map of northern Wisconsin showing distribution of various lithologies in the Middle Precambrian. Metasedimentary rocks include slates, conglomerates, iron-formations, and carbonates. These rocks are least deformed and metamorphosed in the extreme northwest. To the south, these rocks contain kyanite and various other higher metamorphic grade minerals. The metavolcanic rocks include mafic to felsic lavas and associated pyroclastic and epiclastic materials. The granitic rocks include epizonal granodiorite to granitic plutons, and alkali-rich post-tectonic granites. 4 �WAUSAU . .. ". " 1900 m·y· LAKE SUPERIOR m.y. ... .'. ... tsJ B MIDDLE GLL PRECAMBRIAN GRANITIC ROCKS SEDIMENTARY ROCKS EARLY PRECAMBRIAN ~ 15?:1 ~ ~I"GREENSTONE" ~ VOLCANIC ROCKS ~ DOLOMITE, ETC. Figure 2. GRANITIC ROCKS Schematic cross sections showing inferred lithologic -- structural relations during the "Penokean" event of Middle Precambrian age. The upper diagram illustrates a north (right-side) -- south (leftside) section from Lake Superior to central Wisconsin near Wausau during the Middle Precambrian about 1,900 m.y. ago. To the north, platform sediments including carbonates and iron-formation were deposited, while to the south, deeper water sediments and volcanics were accumulating. The lower diagram illustrates the cross-section after cessation of tectonism about 1,800 m.y. ago. To the north the sequence is little deformed, whereas to the south the sequence is folded, and in the extreme south the sequence was moved to shallow structural levels along major faults or shear zones in an apparent host-graben arrangement. 5 �Tuesday, May 8, 1979 Geologic Road Log for Ashland, Bayfield, Iron, and Vilas Counties This leg of the trip visits the dominantly sedimentary part of the Middle Precambrian. The first stop is about two hours after starting. Lunch will be at Stop 2 on Mt. Whittesey. The last stop will be about 4:00 with a 90 minute deadhead trip to Holiday Acres in Rhinelander. Mileages 63 Follow U.S. 2 from Superior to the intersection with U.S. 63 turn right (south) on U.S. 63. 14 Proceed on U.S. 63 to intersection with Bayfield County D in Grand View. Turn left (south) on County D. Note: There are several approaches to stop 1. Directions are given for the best route, however roads may be closed by washouts. The alternate direction given below is longer, but is generally a better maintained road. 3.2 Proceed on County D to intersection with U.S. Forest Rd. 377 at Chequamegon National Forest Sign. Turn left (east) on Forest 377. 2.6 Proceed on Forest 377 to intersection with Forest 378. right (south) on 378. 3.1 Proceed on Forest 378 intersection Forest 198 (straight ahead) and 202 (cross road). Continue straight ahead (east) on Forest 198. 1.3 Proceed on Forest 198, crossing Marengo River and then turning right onto unmarked road parallel to Forest 198. 0.2 Proceed on unmarked road to bridge with gate over Marengo River. Park vehicles in area left (north) of road. 1900 ft. Cross bridge on foot, entering private land. Follow quarry road, keeping to right at branches of road, into quarry. Stop 1. 10.4 Turn Grand View Quarry -- Bad River Dolomite Return to Grand View. 6 �Alternate Route From Grand View to Stop 1 4.8 Proceed on County D to intersection with Forest 201 (Atkins Lake Road). Turn left (east) on Forest 201. 4.0 Proceed on Forest 201 to intersection with Forest 202. left (north) toward Marengo Lake on Forest 202. 1.5 Proceed on Forest 202 to intersection with ~orest 198 (right) and 378 (left). Turn right (east) on Forest 198. 1.3 Proceed on Forest 198, crossing Marengo River and then turning right onto unmarked road parallel to Forest 198. 0.2 Proceed on unmarked road to bridge with gate over Marengo River. Park vehicles in area left (north) of road. 1900 ft. Cross Bridge on foot, entering private land. Follow quarry road, keeping to right at branches of road, into quarry. Stop 1. 11.8 Turn Grand View Quarry -- Bad River Dolomite Return to Grand View. 4.8 Follow U.S. 63 north from Grand View to intersection with County E. Turn right (east) on County E. 7.4 Proceed on County E to intersection with Ashland County C (E turns left). Continue straight ahead on County C. 1.3 Proceed south on County C to crossroad intersection with Midway Road. Turn left (east) on Midway Road. 2.3 Proceed east on Midway Road and rejoin County C. straight ahead (east) on County C. 2.4 Proceed east on County C to intersection with State 13. Turn right (south) on State 13. 9.9 Proceed south on State 13 to intersection with State 77 in Mellen south of railroad tracks. Turn left (east) on State 77. 0.4 Proceed east on State 77 to intersection with County P (Lake Drive). State 77 turns left (north) over railroad tracks. Continue straight ahead on County P (Lake Drive). 1.6 Proceed on Lake Drive. Road jogs left. Stay on Lake Drive. Road jogs left. Stay on Lake Drive towards Camp Galike. Turn left on third dirt road to left (east). This may be marked "Mellen Fire Tower Road." 7 Continue �1.5 Proceed on dirt road to flagged area. Hike 100 yards north of road into cleaning. Note: There is a locked gate on the Fire Tower Road. The key is available from the Head Ranger, Copper Falls State Park, about 3 miles northeast of Mellen on State 169. Stop 2. Mt. Wittlesey. Ironwood Iron formation Afternoon, May 8 3.1 21 Return to County P and State 77 in Mellen. Follow State 77 east from Mellen to Pence (mileage that follows is calculated from sign on west city limits of Pence. 0.4 Proceed into Pence on State 77 to intersection with Spruce St. Proceed south one block, and park on Whiteside Street. Out crop is located on south side of Whiteside Street, at the intersection with Spruce Street, under a large tree. 5.1 Return to State 77, and continue east towards Hurley. Enter Hurley. Stop sign at intersection of State 77 and Fifth Ave. Turn left (north) onto Fifth Avenue. 0.5 Follow Fifth Avenue to intersection with U.S. 51. (west) onto U.S. 51. 1.1 Follow U.S. 51 northbound, taking overpass towards U.S. 2 westbound. Stop at large outcrop on right (east) side of road immediately after crossing the overpass. 2.5 Return to southbound U.S. 51 by taking U.S. 2 westbound to cross-over (about 0.5 miles) and reverse direction to eastbound U.S. 2, and taking the exit ramp to southbound U.S. 51. Next leg of trip mileage is measured from intersection of U.S. 51 and State 77 in Hurley. 26.6 Turn left Proceed south on U.S. 51 to intersection of U.S. 51 and State 47 in Manitowish. Turn right (south) on State 47. 3.9 Follow State 47 to intersection with State 182. (west) on State 182. 1.2 Follow State 182 to large outcrops on both sides of road. Stop 5. 1.2 50 Turn right Bear River - Powell Kyanite Return to State 47. Turn right (south) on State 47. Follow State 47 southbound towards Rhinelander and intersection U.S. 10. 8 �Wednesday, May 9, 1979 Geologic Road Log For Oneida, Price and Sawyer Counties This leg of the trip visits the dominantly volcanogenic part of the Middle Precambrian basin near Monico in Oneida County, with incidental stops at granite localities. We will start with a short trip to Monico and examine volcanic rocks, and spend the last half of the morning deadheading to our lunch stop in Price County. One afternoon stop will be made in Sawyer County. We plan on arriving in Duluth - Superior around 6:00 p.m. Morning, May 9 Mileages 14 1.0 Follow U.S. 8 east from Rhinelander to the intersection with U.S. 45 and U.S. 47 south in Monico. Continue east on U.S. 8, crossing on bridge over Chicago and Northwestern Railroad tracks and U.S. 45 to north. About 0.2 miles east of intersection of U.S. 45 to north, take. County V to the right, and park. Outcrop is located at intersection of U.S. 45 and County V. Stop 6. Monico East - Mafic Pillow Basalt. 0.2 Return westbound on U.S. 8 to intersection with U.S. 45 north. Turn right (north) on U.S. 45. 0.5 Proceed to Lake Road, and turn left (west) onto Lake Road. 0.6 Proceed on Lake Road, crossing Baade Road and stopping behind house on left (south). Stop 7. Monico Gravel Pits (Baade and Lake Roads)--Intermediate to felsic pillow lavas. 0.6 Return to U.S. 45 and turn left (north) on U.S. 45. 0.9 Proceed to small, abandoned farm on right (east) side of road. Stop 8. Witte Farm - Coarse Felsic Agglomerate. 1.4 Return south to U.S. 8. 2.4 Proceed west on U.S. 8 to intersection with old U.S. 8 and Leith Road. Proceed on old U.S. 8. 0.7 Proceed to flagged area. road. Stop 9. 0.7 Turn right (west) on U.S. 8. Small outcrops on both sides of Monico West -- Section 26 - pyritic tuff. Return to U.S. 8 and proceed east on U.S. 8. 9 �1.6 Proceed east on U.S. 8 to intersection U.S. 45 (southbound). Turn right (south) on U.S. 45. 2.5 Proceed to Wayside on west (right) side of highway. in wayside. Stop 10. 2.5 Outcrop Beck Tower Wayside Park - Late red granite. Return north to U.S. 8. Turn left (west). 14 Proceed on U.S. 8 west to Rhinelander. 44 Continue west on U.S. 8 to Prentice. 18 Continue west on U.S. 8 to junction with Price County N near Kennan. Turn left (south) on County N. 10.2 Proceed on County N to junction with road to Big Falls County Park road. Turn right (west). 1.0 Proceed on park road to park entrance and turn left (south) into park. 0.2 Proceed to pavillion. Outcrops in river west of pavillion. Stop 11. Big Falls County Park on the Jump River, Price County - Granite and Pyritic tuff. Afternoon, May 9 11.9 0.9 Return to Kennan and junction of County J and N. (west) on County J. Follow County J to U.S. 8. Ladysmith. Turn left Turn left (west) on U.S. 8 to 27 Follow U.S. 8 through Ladysmith to intersection with State 77. Turn right (north) on State 27. 23 Follow State 27 to Ojibwa to intersection with State 70. Turn left (west) on State 70. 4.4 Follow State 27 and 70 west. road. 0.7 Proceed on gravel road. cross bridge. 0.4 Proceed to junction with Swede Road. Turn right. 0.25 Proceed to junction with Birch Lane. Turn right. 0.6 Follow Birch Lane. Turn right crossing bridge and park. Walk 350 feet along trail to river. Stop 12. Turn left (south) on gravel Turn left (east) on asphalt road, Arpin Darn in Radisson - Late Porphyritic Granite. 10 �1. 25 Return to intersection 1 Continue west on asphalt road into Radisson and intersection with State 40. Turn right (north) to intersection with State 70 and 27. with asphalt road. 29 Follow State 27 to Hayward. 77 Follow State 77 to Minong and U.S. 53 to Duluth. 540.2 mi. End of Log GEOLOGICAL STOP DESCRIPTIONS Page Stop 1 - Grand View Quarry - Bad River Dolomite ..........•......... 12 Stop 2 - Mount Whittlesey - Ironwood Iron-formation ...........•.... 15 Stop 3 - Pence - Basal Palms Formation ........•.................... 20 Stop 4 - Hurley Overpass - Tyler Formation Stop 5 - Bear River - Powell Kyanite •.............................. 27 Stop 6 - Monico East - Mafic Pillow Basalt 30 Stop 7 - Monico Gravel Pits - Andesite Pillow Lava 32 Stop 8 - Witte Farm - Coarse Felsic Agglomerate 34 Stop 9 - Monico West - Section 26 Pyritic Tuff 36 Stop 10 - Beck Tower Wayside Park - Jennings Granite 23 , 38 Stop 11 - Jump River at Big Falls County Park - Granite 40 Stop 12 - Arpin Dam in Radisson - Late Porphyritic Granite 43 11 �BA 44/5W/22 Title: Grand View Quarry -- Bad River Dolomite Location: Johnson & Johnson Quarry, Grand View. NW~, NW~, NW~, Sec. 22, T.44N., R.5W., Bayfield County. (Chequamegon National Forest, 1 mile, 1968) ~ inch o Author: Gene L. LaBerge (1978) Description: This quarry provides one of the largest and most excessible exposures of the Bad River Dolomite in IVisconsin. The formation was named by Van Rise and Leith (1911) from exposures along the Bad River at Penokee Gap southwest of Mellen. According to Aldrich (1929), it unconformably overlies the Lower Precambrian greenstones and granites to the south. In the eastern part of the Gogebic Range the Sunday Lake Quartzite conformably underlies the dolomite, but both the dolomite and quartzite are missing in the central part of the district, presumably due to erosion prior to deposition of the overlying Palms Formation (Irving and Van Rise, 1892). Thus, there appears to have been gentle folding or arching along a north-south axis causing erosion of the Bad River Dolomite and Sunday Lake Quartzite prior to deposition of the Palms Formation, the basal unit of the Animikie Series (James, 1958) in this area. 12 �BA 44!5W!22 (2) The exposures in the quarry are fairly typical of the formation. The bedding dips 35 0 - 75 0 north, along with all other Middle Precambrian units on the Gogebic Range in Wisconsin. Komatar (1972) estimates a minimum thickness of 550 feet in this area, thinning to about 310 feet eight miles to the east. Aldrich (1929) reports that the lower part of the formation is mainly a dolomitic limestone with a much more siliceous upper part. The silica occurs as lenses of sandy dolomite or cross-bedded sandstone (now quartzite), and as beds, pods and irregular masses of chert (Komatar, 1972). The chert ranges in color from light gray to black, presumably due to included organic matter. Algal structures up to nearly 1 meter in diameter, some with black chert layers alternating with dolomite, are present in the formation (Figure 1). Figure 1. Algal structures in the Bad River Dolomite. Photo is of a large glacial erratic near Clam Lake, about 10 miles southeast of Grandview. Several mafic dikes striking N.80oE. and dipping 84°S. are exposed in the quarry (Komatar, 1972). These are presumably Keweenawan diabase dikes. Mineralogically, the formation consists of medium-grained granular carbonate with lenses, pods and patches of quartz. A reaction rim of pale green tremolite typically occurs between the quartz and carbonate. The tremolite is also present in layers of massive, randomly oriented crystals and as radial aggregates several inches in diameter. The mineral assemblage in the Bad River Dolomite and associated Palms and Tyler Formation indicate that the area was metamorphosed to greenschist facies during the Penokean orogeny about 1700 m.y. ago (Komatar, 1972). He reports that the metamorphic grade increases from quartz-albite-muscovite-chlorite subfacies on the east to quartz-a1bite-epidote-almandine subfacies in the Grandview area. This metamorphism was associated with only slight deformation. 13 �BA 44/5W/22 (3) Intrusion of the Mellen gabbro produced widespread contact metamorphism superimposed on the earlier regional metamorphism. K/Ar ages (Komatar, 1972) date this event at 1050±40 m.y. Discussion: The Bad River Dolomite was deposited on an erosion surface of Lower Precambrian greenstones and granites. The presence of algal structures, sandy dolomite and interbedded layers of sand indicate deposition in a shallow marine environment. The increase in sand content upward in the formation suggests either a shallowing of the basin or a change in source area providing more coarse clastics to the basin. The unit is similar in all respects to the Kona and Randvi11e dolomites in the Marquette and ~1enominee districts of Michigan respectively, with which it is generally correlated. The absence of the Bad River Dolomite in the central part of the Gogebic suggests a gentle upwarp in that area resulting in erosion of the formation prior to deposition of the overlying Palms Formation. Gentle folding and greenschist facies metamorphism occurred during the Penokean orogeny. The major northward tilting of the units and contact metamorphism associated with emplacement of the Mellen gabbro occurred during Late Precambrian time. References Citied: Aldrich, H.R., 1929, The geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 71, 279 p. Irving, R.D., and Van Rise, C.R., 1892, The Penokee Iron-bearing Series of Michigan and Wisconsin: U.S. Geo1goical Survey Monograph 19, 534 p. James, R.L., 1958, Stratigraphy of Pre-Keweenawan rocks in parts of northern Michigan: U.S. Geological Survey Professional Paper 314-C, p. 27-44. Komatar, F.D., 1972, Geology of the Animikian metasedimentary rocks, Mellen Granite, and Mineral Lake Gabbro west of Mellen, Wisconsin: Unpub. M.S. Thesis, University of Wisconsin-Madison, 70 p. Van Rise, C.R., and Leith, C.K., 1911, The geology of the Lake Superior Region: U.S. Geological Survey Monograph 52, 641 p. 14 �AS 44/2H/9B Title: Mount Hhittlesey - Ironwood Iron-formation Location: Author: Berkshire Mine, SH\, SW\, sE\, Sec. 9, T.44N, R.2W., Ashland County. (Mt. Hhittlesey 7~-minute topographic quadrangle. 1967) (Get key from Ranger at Copper Falls State Park) Gene L. LaBerge (1978) Description: The Ironwood Iron-formation ranges from about 450-950 feet in thickness and extends for approximately 60 miles across Michigan and Hisconsin in a west-southwesterly direction from west of Lake Gogebic, Michigan, to west of Mineral Lake in Wisconsin. It lies conformably between the Palms Formation and the Tyler Formation. The prominent hill here (Mt. Whittlesey) results from the resistant nature of the exposed metamorphosed iron-formation. The lowlands west and east of the hill are the result of cross-faults of Late Precambrian age that offset the Middle and Upper Precambrian strata (Aldrich, 1929). The iron-formation exposed here shows the bedding characteristics typical of Middle Precambrian iron-formations of the Lake Superior region. Two basic styles of bedding are readily apparent -- one is a laminated rock consisting of alternating layers about 1 cm thick of recrystallized chert and iron oxides. This is commonly referred to as "banded" or "even-bedded" or "slaty" ironformation. The other bedding type present is a thick and irregularly-bedded variety with beds up to 15 cm or more thick. The thicker beds are cherty with abundant sand-size clasts (granules or oolites) of chert in a chert matrix. The clasts commonly are somewhat ferruginous, whereas the matrix is more pure 15 �AS 44/2W/9B (2) :oj ~ .., <1J . 0 o o ~. o o .... .., _ . - , - 6 - - --l - -~ - Volcanics along Powder Mill Creek Intermediate to felsic lava flows unco!Or1Ol1 basdlt flows;except in I Lower 5000 ft thin basalt flows with a few intermediatG flows . Pillow lavas at base ~ N .n a. S a. ~ :l 0'-' ..,:.J o o 0.. Bessemer Sandstone of Seaman (1944) Quartz arenite with abundant matrix; congLunLeratic at base '" C1l ~~_---.-f-..-~/'-r---u-"1""-':"';;"~~~"--~~--+------------------------1 f-.- a. £i :l 0 .., -.-; Cl >< :l E C1l - C1l If) (:Q - -- - S C1l 00 C1l .., - 0 0 - - a-. - - - ---- - Tyler formation Light - to dark - gray pl&gioclaserich fine-grained sandstone, argillaceous siltstone, and argillite. --Lowermost 1000 [t is partly ferruginous and has len~es of lean cherty iron-formation - ~~= 0. :l X C ..,0 C1l ..-4 r--. <lJ Cl -< .n "0 «> .., E C1l u ..,<lJ 0.. "U -.-; E '-' ~ C -aor, a-. -a I If) ~ -.-; E 0 c <lJ ?-: 0. :l ..,o Cl I -0 0alf) ',-..'-_ Anv il"M~~be~ ..:::.:;--\ Ironwood Iron-Formation .....- -- -_...:.---.;.. ==-=:=-'?ence Membcl- ~-'--:'~MostlY thin-bedded cherty carbonate ~ ;:-" - -_- ::.. -, "." -.. =,-;; i.ron- forma t ion --::'-Norr ie Member ~ ~ ~~":>l" fj er---I ~-': Mostly thick wavy bedded cherty iron----.a .: ..---.-- - -e - r'Cr1 - .. " '. ~ ,,"'~' forma tion :- ~ym-;:;uth M~m:,~r ./ Palms Formation Sericitic argillite; red-brown '"~ ~-~~.*~~~~~~ quartzite at top Bad River Dolomite / Gray to buff dolomite and cherty doloo mite. Stromatolitic structures common. a in both east and west parts of Found '" Gogebic district, absent in center ':-~-=- - ~ '-- -=---- --- >. C1l --i o u o ..c: u a If) rl .... Sunday Quartzite Mainly white, gray, and red vitreous quartzite, and conglomerate at the base. Known only in the eastern Gogebic Precambrian W(lower)complex Sedimentary-volcanic ("greenstone") sequence, partly metamorphosed to foliated hornblende gneiss, intruded by quartz monzonite and pegma t i te Figure 1. Generalized stratigraphic section in central and western Gogebic Range (from Schmidt and Hubbard, 1972, p. A3). 16 �AS 44/2W/9B (3) chert. These cherty units are highly irregular in shape and are separated by layers composed mainly of iron oxides. Intra-formational conglomerates are relatively common in the "wavy" or "irregularly" bedded or "cherty" ironformation. These different bedding styles represent different intensities of wave action in the basin during iron-formation deposition. Or alternatively, they represent alternately shallow and deep water conditions, with the thin-bedded variety representing deep (quiet) waters and the wavy bedded units indicating shallow (agitated) waters. These bedding differences were used by Hotchkiss (1919) as a basis of subdividing the formation into five members based on the dominant bedding style. He recognized three units with dominantly wavy bedding (Plymouth, Norrie, and Anvil) separated by two units of mainly thin-bedded iron-formation (the Yale and Pence). These units can be recognized over much of the 60-mile length of the range, and are roughly correlative with the lower cherty, lower slaty, upper cherty and upper slaty members of Biwabik Iron-formation in Minnesota. The iron-formation here has been metamorphosed to grunerite grade, and consists of quartz, grunerite, magnetite and minor hematite and garnet, with minor dolomite, ankerite and siderite co-existing with the grunerite (Laybourn, 1979). Minnesotaite is the stable iron-silicate present in the iron-formation east of Ballou Creek (about 2 miles east of here), and iron-rich pyroxenes (ferrohypersthene and ferroaugite) appear from Mellen westward (Laybourn, 1979). The metamorphic facies are produced by contact metamorphism related to the Mellen and Mineral Lake gabbro complexes. Economic Geology: Iron ore was discovered on the Gogebic Range at Bessemer, Michigan in 1873, and over 300 million tons of natural ore was mined before operations ceased in 1966 (Schmidt and Hubbard, 1972). Most of the mining operations were done ,between Hurley, Wisconsin, and Wakefield, Michigan, on the eastern part of the range. Natural ores that are economically exploitable have been worked out. Marsden (1978) reports that major reserves of taconite ore in the Ironwood Iron-formation remain on the western end of the Gogebic range where the rocks have been more highly metamorphosed. The intensity of metamorphism increases progressively westward from biotite grade to pyroxene grade (Marsden, 1978). The area of interest for development of magnetite taconite extends from near Upson southwestward for 21~ miles to just west of Mineral Lake. Outcrop width of the iron-formation is 1000-1500 feet over much of this length, but folding in the }1t. vfuittlesey area produce an outcrop width of 2500 feet locally (Marsden, 1978). Marsden (1978) estimates the total reserves of magnetic taconite in Wisconsin to be 4,171,000,000 metric tons, of which 3,711,000,000 metric tons are in the Ironwood Iron-formation of the Gogebic Range. The other taconite reserves are the Agenda deposit (Sec. 22, 23, 24, T.42N., R.IE.), 160,000,000 tons; the Butternut deposit (Sec. 20, 21, 28, 29, T.49N, R.1W), 48,000,000 tons; and the Pine Lake deposit (Sec. 21, 22, 23, 26, 27, 28, T.44N, R.3E.), 184,000,000 tons. The latter three deposits are not in the Ironwood Ironformation, but appear to be in lateral equivalents (Allen and Barrett, 1914). 17 �AS 44/2W/9B (4) Thus, the Middle Precambrian of northern Wisconsin contains one of the largest undeveloped taconite reserves in North America. Discussion: Mineralogically, the iron-formation is generally referred to as "oxide facies," implying that it was deposited as oxides with the chert. LaBerge (1964) showed that the magnetite is almost entirely secondary. Dimroth (1975) points out that the mineral facies are diagenetic (or metamorphic) and do not reflect the depositional environment. Thus, unless we can prove that the present mineralogy is the original mineralogy, there is no basis for interpreting the depositional environment from the mineralogy. The Facies concept of James (1954) should be restricted to a descriptive rather than interpretative concept. The present mineralogy of iron-formations is the product of the depositional, diagenetic, metamorphic, and in many cases, the weathering environment; it should not be assumed that the present mineralogy is the original mineralogy. The subdivision of the Ironwood into members based on the dominance of granular (cherty) or laminated (slaty) iron-formation (Hotchkiss, 1919) works well in the eastern two-thirds of the Gogebic. However, subdivision of the formation into the various members in the western third of the district is difficult. In part, this may be due to the highe~ metamorphic grade in the western end of the district, but there seems to be a real change in the stratigraphy as well. Morey (1972, p. 209) shows a similar relationship for the western Mesabi, where subdivision into the cherty and slaty members is difficult. This may suggest a change in the Animikie Basin to the southwest. The presence of a thicker succession, interbedded clastics and volcanic rocks in iron formation in the Cuyuna district (Marsden, 1972) may indicate a change from platform to deeper basin to the southwest. References Cited: Aldrich, H.R., 1929, The Geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 71, 279 p. Allen, R.C., and Barrett, L.P., 1915, Contribution to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geological Survey Publication 18, Geologic Series 15, p. 13-164. Dimroth, E. 1975, Paleo-environment of iron-rich sedimentary rocks: Geologischen Rundschau, v. 64, p. 751-767. Hotchkiss, W.O., 1919, Geology of the Gogebic Range and its relation to recent mining developments: Engineering/Mining Journal, v. 108, p. 443-452, 501-507, 537-541, 577-582. James, H.L., 1954, Sedimentary facies of iron-formation: v. 49, p. 235-293. Economic Geology, LaBerge, G.L., 1964, Development of magnetite in iron-formations of the Lake Superior Region: Economic Geology, v. 59, p. 1313-1342. Laybourn, D.P. 1979, Geology and metamorphism of the Ironwood Iron-formation, Gogebic Range, Wisconsin: Unpub. M.S. Thesis, University of MinnesotaDuluth, 223 p. , s:l �AS 44/2W/9B (5) Marsden, R.W., 1972, Cuyuna District: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (G.M. Schwartz Volume): Minnesota Geological Survey, p. 227-239. Marsden, R.W., 1978, Iron ore reserves of Wisconsin -- A Minerals Availability Systems Report: in Proceedings of the 51st Annual Meeting, Minnesota Section AIME and 39th Annual Minnesota Mining Symposium, p. 24-1 -- 24-28. Morey, G.B., 1972, Mesabi Range: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (G.M-.-Schwartz Volume): Minnesota Geological Survey, p. 204-217. Schmidt, R.G. and Hubbard, H.A., 1972, Penokean Orogeny in the central and western Gogebic Region, Michigan and Wisconsin: Field Trip A, 18th Annual Institute on Lake Superior Geology (Roughton, Michigan). 19 �Ir 46/2E/32 Title: Pence--Basal Palms Formation Location: Author: Intersection of ~~iteside Street and Spruce Street in Pence, Wisconsin. SE~, SW~, Sec. 32, T.46N., R.2E., Iron County. (Iron Belt 7~-minute topographic quadrangle, 1956). Gene L. LaBerge (1978) Description: The Palms Formation is the basal unit of the Middle Precambrian Animikie Group (James, 1958), and unconformably overlies the Bad River Dolomite and Sunday Lake Quartzite of the Chocolay Group (Cannon and Gair, 1970). According to Aldrich (1929), the Palms is continuous throughout the Gogebic range, averages about 450 feet in thickness, and contains a basal conglomerate, a "quartz-slate" unit, and an upper quartzite unit. At this locality the basal Palms rests on Lower Precambrian granite, the older Bad River Dolomite and Sunday Lake Quartzite evidently having been removed by post-Bad River - pre-Palms erosion. Both west and east of here the Bad River Dolomite and Sunday Lake Quartzite are present between the Palms and the underlying Early Precambrian granite and greenstone. The following generalized description is taken mainly from Aldrich (1929). The basal conglomerate of the Palms is up to about six feet thick and appears to be derived mainly from the immediately underlying rock types (Aldrich, 1929). It was deposited on an uneven erosion surface, and thus varies in thickness locally. The larger clasts are well rounded at some localities, and very angular 20 �Ir 46/2E/32 (2) at others according to Aldrich (1929). Here the clasts consist of quartz, chert, granite, and felsic and melfic volcanics, are moderately well rounded and range up to about 8 cm in ~iameter. The outc~op is slightly phosphatic. Overlying the basal conglom~rate~ and comprising about 400 feet of the formation is the thin-bedded "quartz-slate" unit characteristic of the Palms. It consists of alternating quartz-rich and argillaceous beds 1-3 cm thick with ripple marks, cross-bedding and scour-and-fill features common. The quartz-rich beds are composed mainly of quartz, although some are quite feldspathic. 0uartz grains range from angular to well rounded, with the larger grains generally the most rounded (Aldrich, 1929). Argillaceous layers consist mainly of fine sericite, chert, ~hlorite and magnetite. A general coarsening of grain size of argillaceous materials and the appearance of octahedra of magnetite west of the Tyler Forks River is evidently due to contact metamorphism produced by the Upper Precambrian Mellen Gabbro. The uppermost 50 feet of the Palms consists of a vitreous quartzite composed of medium-grain, well-rounded quartz. Minor mica is present on bedding planes. The quartzite varies from white, green, brown to red (Aldrich, 1929). The Palms is overlain conformably by the Ironwood Iron-formation. This represents an abrupt transition from clastic sedimentation in the Palms to chemical sedimentation (with virtually no clastics) in the Ironwood. A similar abrupt transition is present throughout most -- but not all -- of the Lake Superior region. Discussion: The Palms Formation is an important part of understanding the geometry of the Animikie Basin. It is genetally correlated with the Pokegama and Kakabeka Formations of the Mesabi and Gunflint districts respectively on the north shore of Lake Superior, and the Siamo and Ajibik Formations of the Marquette district (Cannon and Gair, 1970). The Kakabeka Formation is mainly a conglomerate and generally only a few feet thick (Goodwin, 1954). The Pokegama is mainly a quartzite and up to 167 feet thick (Morey, 1972). These formations underlie the iron-formation in their respective districts. The general thickening of the clastic sequence beneath the iron-formation suggests a deeper (or older) basin to the south, or alternately that the sea was transgressing northward onto the craton at the onset of iron-formatin deposition. In the ~1arquette district, the Siamo Slate and Ajibik Quartzite are 1,000 feet thick in the Neguanee area, but thin markedly to only about 100 feet near Michigamme at the western end of the district (Boyum, 1970). Thus, the nature and thickness of the formations underlying the major iron-formation differs from place to place within the basin and must reflect local differences in the pre-iron-formation history of the Animikie basin. In the Gogebic district, the Palms has some features typical of shallow water deposition, and some (the quartz-slate) which appears to have similarities to deeper water deposition, perhaps transitional into a graywacke-type environment farther south. References Citied: Aldrich, H.R., 1929, The geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 71, 279 p. Boyum, B.H., 1970, the Marquette Mineral Range, Michigan: Geological Society of America, Field Trip to Marquette Iron Range, }1ichigan, 21 p. 21 �Ir 46/2E/32 (3) Cannon, W.F., and Gair, J.E., 1970, A reVlSlon of stratigraphic nomenclature for Middle Precambrian rocks in northern Michigan: Geological Society of America, Bulletin, v. 81, p. 2843-2846. Goodwin, A.M., 1954, Facies relations in the r,unflint Iron-formation: Geology, v. 51, p. 565-595. Economic James, H.L., 1958, Stratigraphy of pre-Keweenawan rocks of northern Michigan: U.S. Geological Survey Professional Paper 3l4-C, p. 27-44. Morey, G.B., 1972, Mesabi Range: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (G.M. Schwartz Volume): Minnesota Geological Survey, p. 204-217. 22 �IR 46/2E/14B Title: Hurley Overpass. Location: Tyler Formation. Junction U.S. Highway 2 and U.S. Highway 51 north of Hurley, Wisconsin. SE~, SE~, NE~, Sec. 14, T.46N., R.2E., Iron County. (Ironwood 7~-minute topographic quadrangle, 1975) 77 Author: Gene L. LaBerge, 1978 Description: This exposure is characteristic of most of the Tyler Formation which conformably overlies the Ironwood Iron-formation, and is the youngest Middle ~re­ cambrian unit recognized on the Gogebic Range. The unit is generally referred to as the Tyler "slate," although Alwyn (1976) reports that the formation is about one-third slate and two-thirds graywacke sandstone. Alwyn (1976) reports that the Tyler formation is approximately 7,000 feet thick in this area, but increases in thickness westward to about 12,000 feet near Mellen. Schmidt and Hubbard (1972) report that the Tyler has been completely removed by pre-Keweenawan erosion to the east. Because of its stratigraphic relations, the Tyler is generally correlated with the Virginia and Rove formations in Minnesota and with the Michigamme formation in Michigan (Leith, Lund, and Leith, 1935; James, 1960). Sedimentological studies led Alwyn (1976) to conclude that the Tyler formation was derived mainly from a granitic terrane and that sediment transport was northward into the Animikie basin. Thus, he postulates a granitic landmass south of the Gogebic range shedding abundant clastics. The presence of probable Middle Precambrian submarine volcanics near Mercer approximately 20 miles to the south 23 �IR 46/2E/14B (2) PREeM"R IAN Y ROCKS r- I PRECAMflRIAN X ROCKS SOUTH + 2000 FEET + + + + + + + + + + 2000 FEET + + ... ... + + + ... + ... + + + + + ... ... + + + + + + + + +- + ++ ... + + + ... + + + + + + + + + + PRECAMBRIAN W ROCKS Generalized diagram of the relationship of Precambrian rocks in the central Gogebic district EROSION SURFACE NORTH SOUTH + 1- + + + + 1- +. + + ... + <- + 1- +- + +. + ... + ++ t- + + + ... + + + +- + +. + + + + + + + + + + + + + t ++ + Hypothetical post-Penokean pre-Keweenawan cross-section on same surface as front of block diagram above 24 + + �IR 46/2E/14B (3) (Allen and Barrett, 1914; Dutton and Bradley, 1970) suggest that the granitic landmass must have been narrow. Assuming that the volcanics near Mercer are correlative with those in the Ironwood Iron-formation in the eastern Gogebic range (Aldrich, 1929), limits on the size of the landmass would suggest that it must have been tectonically uplifted to continue to provide the source of sediments for the Tyler Formation. The dip of the Tyler Formation at this location is 70 0 N\~. Graded beds and other primary structures indicate that the beds are right-side up (Schmidt and Hubbard, 1972). Cleavage in the shaly layers dips less steeply than the bedding (about 30 0 NW). According to Schmidt and Hubbard (1972), this cannot be a Keweenawan axial plane cleavage because that cleavage would dip more steeply than the bedding. If this is an axial plane cleavage, it must have formed during an earlier deformation, presumably the Penokean Orogeny. Discussion: Schmidt and Hubbard (1972) point out that the basal Keweenawan dips more steeply northward than the Middle Precambrian Tyler and Ironwood Formations, suggesting that the Middle Precambrian was dipping south'during early Keweenawan time. The cleavage to bedding relationship at this stop also suggests that the Tyler Formation was dipping south at the time the cleavage formed. Thus, the present orientation of the units is a result of subsidence of the Lake Superior syncline during Keweenawan time, as shown for most of the Gogebic range, suggesting that a block approximately 60 miles long and perhaps 10-15 miles wide rotated northward nearly 90 0 with no obvious internal deformation. The tilting of this block occurred after deposition of the Oronto Group (of early Late Keweenawan time (Craddock, 1972)) because of the Freda sandstone dips near vertically along the Montreal River on the Michigan-Wisconsin border. This suggests that the Tyler and other Middle Precambrian rocks were buried beneath at least 12 miles (20 kms) of Keweenawan basalts and sandstones during the Late Precambrian. However, the low metamorphic grade of the Tyler at this locality is difficult to reconcile with the interpretation of having been buried to a depth of 12 miles. Either an unusually low geothermal gradient of burial was too short to affect much recrystallization, or heretofore unrecognized structures in the Keweenawan sequence give an exaggerated apparent depth of burial. The last alternative seems most likely. Most recognized faults (and the most obvious ones) on the Gogebic are cross-faults; however, mine mapping (Hotchkiss, 1919) has demonstrated the presence of bedding faults and strike faults in the Ironwood Iron-formation. The strike faults duplicate the section in places. I suggest that strike faults (or perhaps thrust faults) exist in the Keweenawan duplicating the section to give an exaggerated thickness of Late Precambrian rocks and therefore an exaggerated apparent depth of burial for the Tyler Formation in this area. Perhaps the question should be raised whether the cleavage may be related to these postulated thrust faults, and therefore of Keweenawan age. Resolution of this problem is pertinent to an understanding of both the Middle and Late Precambrian geology of the Lake Superior region. References Cited: Aldrich, H.R., 1929, The geology of the Gogebic Iron Range of Wisconsin: Wisconsin Geological and Natural History Survey Bulletin 71, 279 p. 25 �IR 46/2E/14B (4) Allen, R.C., and Barrett, L.P., 1915, Contributions to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geological and Biological Survey, Publication 18, p. 65-129. Alwyn, B.W., 1976, Sedimentation of the Middle Precambrian Tyler Formation of north-central Wisconsin and northwestern Michigan: Unpub. M.S. Thesis, University of Minnesota-Duluth, 175 p. Craddock, C., 1972, Late Precambrian - Regional geologic setting: in P.K. Sims and C.B. Morey, editors, The Geology of Minnesota (C.M. Schwartz Volume): Minnesota Geological Survey, p. 281-291. Dutton, C.E., and Bradley, R.E., 1970, Lithologic, geophysical and mineral commodity maps of Precambrian rocks of Wisconsin: U.S. Geological Survey Miscellaneous Geological Investigation Map 1-631, 1:500,000, 6 sheets, separate text. Hotchkiss, W.O., 1919, Geology of the Gogebic Range and its relation to recent mining developments: Engineering/Mining Journal, v. 108, p. 443-452, 501-507, 537-541, 577-582. James, H.L., 1960, Problems of stratigraphy and correlation of Precambrian rocks with particular reference to the Lake Superior Region: American Journal of Science, v. 258-A, p. 104-114. Leith, C.K., Lund, P.J., and Leith, A., 1935, Precambrian rocks of the Lake Superior Region: U.S. Geological Survey Professional Paper 184, 34 p. Schmidt, R.G., and Hubbard, H.A., 1972, Penokean Orogeny in the central and western Gogebic Region, Michigan and Wisconsin: Field Trip A, 18th Annual Institute on Lake Superior Geology (Houghton, Michigan). 26 �IR 42/4E/28B Title: Bear River-Powell Kyanite Location: On State Hwy. 182 approximately 1 mile west of State Hwy. 47. SE\, SW\, Sec. 28, T.42N., R.4E. (Wilson Lake, 7Yz-Minute Topographic Quadrangle, Vilas County). 47 Author: Gene L. LaBerge (1978) Description: This exposure is part of a sequence of upper amphibolite facies gneisses and schists that occur as widely scattered outcrops along the Flambeau River flowage. Magnetic surveys and diamond drilling suggest that this sequence of rocks continues eastward into northern Michigan, and the occurrence of iron-formation, pellitic rocks and volcanics has served as a basis for correlating these rocks with the much lower-grade rocks on the Gogebic range (Allen and Barrett, 1915). James (1955) includes this area in the core of his "Watersmeet node," an elongate area of high-grade regional metamorphism, and Dutton and Bradley (1970) show that metamorphic intensity decreases in directions from this high-grade center. l1ain lithologies present include amphibolites, quartzo-feldspathic gneisses and schists, some of which contain staurolite and kyanite ±sillimanite (Black, 1977). Exposures here are mainly garnet-staurolite-kyanite-bearing schists, although sillimanite is present in small amounts. The sillimanite occurs as incipient crystal clusters in the kyanite. Black (1977) concluded that 27 �IR 42/4E/28B (2) the mineral assemblage kyanite-staurolite-muscovite + sillimanite suggests metamorphism at 685 0 C and a pressure of about 7.5 Kb. This indicates that the rocks were metamorphosed at a depth of 25 kilometers and at temperatures at or near minimum melting range (Black, 1977). The rocks have been intensely folded about an east-northeast trending fold axis with a prominent east-northeast foliation. Quartz boudins, intrafolial folds, disconnected fold hinges and limbs, and augen and other features of transposed bedding are common and obliterate most primary features of the rocks (Black, 1977). The sequence probably represents a highly deformed and metamorphosed pile of mafic to felsic volcanic rocks and graywackes. The high-grade rocks are bounded on the north by a sequence of less deformed, and less metamorphosed mafic-intermediate volcanics, iron-formation and slate (Allen and Barrett, 1915; Black, 1977). The boundary between these sequences contains a prominent zone of electrical conductivity called the flambeau Anomaly (Sternberg and Clay, 1977). The anomaly is evidently produced mainly by highly graphitic rocks that extend a minimum of 17 kilometers into the crust. The conductive zone extends west-southwesterly more than 100 km to near Couderay in Sawyer County. Discussion: Allan and Barrett (1915) interpreted the boundary between the greenstones on the north and the high-grade rocks on the south as an unconformity. Black (1977) interprets the boundary as a major fault with the south side uplifted. The proposed fault may correlate with Sims' (1976) postulated boundary between a 2650-2700 m.y. old granite-greenstone terrane to the north and an older gneiss terrane to the south (Black, 1977). The Flambeau Anomaly appears to be in-folded or in-faulted along the boundary between the greenstones (of unknown age) and high-grade metamorphic rocks (also of unknown age). Thus, the more recent interpretations of the geology in this area raise the question of whether the high-grade metamorphic rocks exposed here are really correlative with the Tyler Formation of the Gogebic. The stratigraphic position of the greenstones to the north is also debatable. Alwyn's (1976) interpretation of a granitic landmass south of the Gogebic as a source area for the Tyler coupled with the recent recognition of major faults and the Flambeau Anomaly suggests that the geology may be far more complex than heretofore recognized. References Citied: Allen, R.C., and Barrett, L.P., 1915, Contributions to the pre-Cambrian geology of northern Michigan and Wisconsin: Michigan Geological and Biological Survey, Publication 18, p. 65-129. Alwyn, B.W., 1976, Sedimentation of the Middle Precambrian Tyler Formation of north central Wisconsin and northwestern Michigan: Unpub. M.S. Thesis, University of Minnesota-Duluth, 175 p. Black, F.M., 1977, The geology of the Turtle-Flambeau area: Iron and Ashland Counties, Wisconsin: Unpub. M.S. Thesis, University of Wisconsin-Madison, 150 p. 28 �IR 42/4E/28B (3) Dutton, C.E., and Bradley, R.E., 1970, Lithologic, geophysical and mineral commodity maps of the Precambrian of ~~isconsin: U.S. Geological Survey Miscellaneous Geologic Investigation }1ap 1-631, 1:500,000, 6 sheets, separate text. James, H.L., 1955, Zones of regional metamorphism in the Precambrian of northern Michigan: Geological Society of America Bulletin, v. 66, p. 1455-1487. Sims, P.K., 1976, Presidential address - Precambrian tectonics and mineral deposits, Lake Superior Region: Economic Geology, v. 71, no. 6, p. 1092-1118. Sternberg, B.K., and Clay, C.S., 1977, Flambeau Anomaly: Ahigh-conductivity anomaly in the southern extension of the Canadian Shield: in J.G. Heacock, editor, The Earth's Crust: American Geophysical Union Monograph 20, p. 501-530. 29 �ON 36/llE/29 Title: Monico East - Mafic Pillow Basalt Location: Intersection of U.S. 8 and County V, center of Sec. 29, T.36N., R.llE., Oneida County (Monico 7Yz-minute topographic quadrangle, 1965). 45 8 & 8 47 Author: M.G. Mudrey, Jr. (1978) Description: A large outcrop is in the southwest corner of the intersection. The rock consists predominantly of sulfide-bearing, gray-green, chloritic pillow basalt trending N. 85 0 E., and dipping 80 0 SE. The two-foot thick by three-foot long pillows are slightly stretched and top to the south. Original pyroxene has altered to hornblende and chlorite. Plagioclase is extensively altered. The southeast edge of the outcrop is a ten-foot thick massive flow or sill. Diabasic texture in this unit is well developed. Discussion: Two supracrustal sequences characterize the Middle Precambrian succession in northern Wisconsin and Michigan, a dominantly sedimentary unit including iron formations to the north, and a dominantly volcanic sequence including massive sulfide deposits to the south. Inasmuch as bedrock exposures are poor south of the Gogebic Range area, geologic maps of northern Wisconsin are based dominantly on geophysical interpretation. Units defined in the few areas of outcrop are extrapolated into the poorly exposed areas. The belt of rocks from Ladysmith on the west to Pembine on the east appears to be dominantly volcanic, with few intrusives. The volcanics in the Monico area are among the least deformed and better exposed in this belt. Pillows and other indicators of subaqueous deposition are evident in the volcanic rocks exposed in the Monico area. These features are well preserved because of the low metamorphic grade. The sequence around Monico appears 30 �ON 36/llE/29 (2) to young to the south, and the sequence is known to be repeated by faulting that trends east-northeast. This particular outcrop appears to lie stratigraphically above the massive sulfide deposit at Pelican River to the west, and possibly above the Crandon deposit to the east. It is representative of the basaltic rocks in the Monico area. �ON 36/llE/30 Title: Monico Gravel Pits - Andesite Pillow Lava Location: Exposures are at the top of the hill behind houses on Baade and Lake Roads, and on the north side of the gravel pit to the west, NE~, NE~, Sec. 30, T.36N., R.llE., Oneida County (Monico 7~-minute topographic quadrangle, 1965). Author: M.G. Mudrey, Jr. (1978) Description: The outcrops consist of pillowed. fine grained. light gray andesite with sparse to abundant quartz and plagioclase phenocrysts. The pillows appear to top south. Schriver (1973, p. 25) describes the rocks as amygdaliodal basalt. In the gravel pit, the amygdule fillings have weathered out, leaving a pockmarked vesicle texture. Amygdules constitute up to three percent of the rock. range in size up to three mm, and have a ~lobular shape, but are generally undeformed. A chlorite rim encloses the amygdule filling of epidote or epidote and quartz. The groundmass consists predominantly of epidote and actinolite less than 0.05 mm in size. Plagioclase phenocrysts are largely altered to epidote and calcite and appear to be around AnZ5-30' Schriver (1973, p. SO, no. 16) reports the following chemical data: SiO Z TiOZ Al Z0 3 FeO T MuO 53.5 0.7 14.0 9.3 0.1 Molecular Norm (Irvine-Baragar) Q ZO.5 Or 0.3 Ab 10.1 An 15.3 Ho 12.9 3Z �On 36/llE/30 (2) MgO CaO Na20 K20 6.9 10.6 2.1 0.1 Total 97.3 En Fs Mt II 25.5 12.0 2.1 1.3 Other analyses of this unit several miles to the southwest contain more silica and potassium, and might more properly be termed dacite. Other outcrops of this unit may be found on the hills to the southwest and to the northeast. Mapping in 1978 by Mudrey suggests that this unit can be traced along an east-northeast strike about 3/4 mile. Mapping also suggests that this unit overlies the tuffaceous agglomerate unit to the east and south. Discussion: Intermediate to felsic Middle Precambrian volcanism characterizes the northern Wisconsin volcanic belt. May (1977) describes the host rocks associated with the Flambeau deposit near Ladysmith, and Schmidt and others (1978) describe similar rocks associated with the Crandon deposit. Recently, Bowden (1978) described a similar sequence of rocks at the Pelican River deposit. Present mapping and geophysics suggest that the sequence of volcanic rocks immediately around Monico are close to the same stratigraphic position as the rocks at Pelican River. This exposure probably lies stratigraphically beneath the Pelican ore body, although definitive mapping has not been completed. References Cited: Bowden, D.R., 1978, Volcanic rocks of the Pelican River massive sulfide deposit, Rhinelander, Wisconsin: A study in wallrock alteration: Unpub. M.S. Thesis, Michigan Technological University, 62 p. May, E.R., 1977, Flambeau - A Precambrian supergene enriched massive sulfide deposit: Geoscience Wisconsin Vol. 1, p. 1-26. Schmidt, P.G., Dolence, J.D., Lluria, M.R., and Parsons, G., III, 1978, Geology of the Crandon massive sulfide deposit in Wisconsin: Skillings' Mining Review, v. 67, no. 18, p. 1, 8-11. Schriver, G.H., 1973, Petrochemistry of Precambrian greenstones and granodiorites in southeastern Oneida County, Wisconsin: Unpub. M.S. Thesis, University of Wisconsin-Milwaukee, 83 p. 33 �(00 Title: Witte Farm - Coarse Felsic Agglomerate /"" ON 36/11E/2l "'~ Location: 1.4 miles north of intersection of U.S. 8 and U.S. 45. Outcrop located 400 feet east of highway behind abandoned house. SE~, NW~, Sec. 21, T.36N., R.llE., Oneida County (Monico 7~-minute topographic quadrangle, 1965). Author: M.G. Mudrey, Jr. (1979) Description: Three-foot long, angular, dacite clasts range in size from inches to several feet are set in an amphibole-bearing tuff or graywacke. Within the clasts, sparse euhedral plagioclase phenocrysts (An20) up to 1.8 mm in maximum dimension are set in a flow banded matrix which wraps around the crystals. The rock is intensively altered, and sericite extensively replaces plagioclase. The groundmass consists predominantly of quartz, muscovite, and calcite. Blood red hematite is present, along with local concentrations of epidote and chlorite. The matrix for the clasts consists of altered mineral grains 0.3 to 0.4 rnrn in size. A few relict (? pyroxene (?) and amphibole crystals remain, but the grains in the matrix consist predominantly of epidote-chlorite-muscovite-quartz granules. Calcite occurs abundantly as granules and in veins. Blood red hematite is sparse, and reflict glass shards can be seen in thin sections. The trend of bedding is N. 70 0 -75 0 W. and dips 85 0 SW. About 700 feet to the northeast, intermediate pillow lavas appear to top south, however the bedding trend at this locality is N. 60 0 W. This is the only area of the quadrangle in which folding has been suggested. 34 ) �ON 36/llE/2l (2) A small body of intrusive granodiorite can be found about one thousand feet north. Discussion: Sangster (1972) noted the close spatial association between felsic agglomerates (or coarse pyroclastics) and massive sulfide ores, and that these agglomerates were a characteristic feature of many mining regions. Sangster (1972, p. 3) remarks that "the author L-Sangster=/ once remarked to his colleagues that whenever he stood on the outcrop containing the largest fragments of acid pyroclastic in any given mining camp, he could invariably hear the mine mill nearby. His colleagues immediately dubbed this distinctive lithology 'millrock' and since then, 'millrock' has been observed close by most massive sulfide deposits in Precambrian volcanic rocks." The interpretation of this distinctive lithology is still open. Millrock is generally found in, or close to volcanic units in which the massive sulfides occur. The belt of rocks from the Pelican deposit, about 7 miles west, to several miles east of this locality has been extensively explored since the early 1970's. Although only the Pelican deposit has been announced as a possible massive sulfide deposit, the intensity of exploration attests to the favorable terrane. References Cited: Sangster, D.F., 1972, Precambrian volcanogenic massive sulfide deposits in Canada: A review: Geological Survey of Canada Paper 72-22, 44 p. 35 �ON 36/10E/26 Title: Monico West - Section 26 Pyritic Tuff Location: Old U.S. 8 west of Monico, SE~, NW~, Sec. 26, T.36N., R.IOE., Oneida County (Monico 7~-minute topographic quadrangle, 1965). 8 & 47 8&47 Author: M.G. Mudrey, Jr. (1978) Description: The low outcrop on the north side of the road is a fine, light-gray, pyritic, indistinctly bedded lithic-crystal tuff which trends N. 60 0 -70 0 E. and dips vertically. The crystals consist of millimeter-sized, sericitized plagioclase. Most of the crystals are euhedral and embayed and corroded. Less altered lithic fragments contain minor amphibole. Actinolite, chlorite, and epidote are the dominant alteration minerals. Prehnite (?) and hematite are sparse. The low ledge on the south side of the road consists of beds of gray, finegrained, chloritic crystal tuff and bedded, light gray, aphanitic ash. The tuff is similar to the tuff on the north side, but matrix is more abundant, and the crystals sparser. Chlorite in the ash is berlin blue in thin section. This volcaniclastic unit varies considerably from fine tuffs and ashes to lapilli tuff. The unit is 3,000 to 4,000 feet thick and can be traced along strike at least three miles. Discussion: Massive sulfide are bodies consist mainly of sulfide-rich tuff, and grade distally into pyritic tuffs. These lithologies usually do not crop out because the sulfides weather readily. Therefore, the sulfide-rich outcrop here is unusual. It illustrates the general lithology and composition of the distal ends of a massive sulfide are body. Some outcrops in the area contain more 36 �ON 36/l0E/26 (2) sulfide than this One. A recent road cut in Sec. 21, T.36N., R.llE. contains abundant sulfidic and sericitic schists, and may represent the lateral equivalent of the mineralized zones at Little Sand Lake. The trend of bedding at this locality and at the Crandon deposit near Little Sand Lake in Forest County is slightly north of due west, and on projection this locality could be essentially the same stratigraphic horizon as that at Little Sand Lake. Intervening between the two, however, is the granite body at Jennings (exposed at Beck Tower Wayside). Wisconsin aeromagnetic data suggest a northwest-trending fault immediately west of the Little Sand Lake deposit, therefore, this particular exposure probably is not directly correlatible with Little Sand Lake, but does illustrate many of the rock types spatially associated with the host rocks for the massive sulfide deposit. 37 �On 35/llE/6 Title: Beck Tower Wayside Park - Jennings Granite Location: 2~ miles south of Monico on U.S. 45 and State 47 S\V~ SEY. Sec 6 T.35N., R.llE., Oneida County (Monico 7~-minute topographic'qua~;ang;~, 1965)~ Author: M.G. Mudrey, Jr. Description: This outcrop is a coarse, red, biotite granite and exhibits spheroidal weathering. Another outcrop is present 500 feet to the northeast in a railroad cut. Fresher outcrops of the same granite are found near Jennings, about 6 miles east. According to Venditti (1973, p. 46), the rock contains euhedral orthoclase, microcline and microperthite (40 percent), subhedral to euhedral oligoclase (An27, 23 percent), anhedral quartz (31 percent), and minor amounts of interstitial biotite (3 percent). The biotite is pleochroic and light brown to dark brown, is sagenitic, and altered to chlorite. The grain size is 4-5 mm and shows no cataclastic textures at this outcrop, although outcrops near Jennings show narrow, well developed mylonitic zones. Venditti (1973, p. 90, no. 24) reports the following analysis: 73.1 tr 15.5 1.5 tr tr Si02 Ti02 A1 2 0 3 FeaT MnO MgO 38 �On 35/llE/6 (2) CaO Na 2 0 1.5 3.0 4.3 Total 98.9 K2 0 Van Schmus and others (1975, p. 1259, no. D1356) report a Rb-Sr age of 1,580 m.y. from this locality. Van Schmus (in press) reports a U-Pb zircon age of 1,765± 10 m.y. from this locality. Discussion: The potassic granitic intrusives in the Middle Precambrian of northern Wisconsin are all post-tectonic, and their ages cluster around 1,765 m.y. The younger 1,600 m.y. Rb-Sr age represents a wide-spread alteration of Rb-Sr ages that is not fully understood. Van Schmus (in press) has divided the Middle Precambrian igneous activity into two pulses. The older one began with mafic to felsic volcanism 1,850~ 20 m.y. ago, and was followed immediately by tonalitic to granitic plutonism 1,840 1,820 m.y. ago. Structural studies by Maas (1977) indicate that these rocks were emplaced during the main phase of the Middle Precambrian thermotectonic event. The second pulse consisted predominantly of phyolitic and granophyric granite and occurred about 1,765± 10 m.y. ago. No plutonic units have been found so far with zircon ages in excess of 1,850, nor have any been found with ages on the order of 1,615 - 1,630 m.y., the time of widespread alteration of the Rb-Sr isotopic systems in the region. After emplacement of the late granites, major faulting occurred (LaBerge and Myers, 1976 and LaBerge, 1977), and has been recently studied to the south in Marathon County. Late faulting is recognized in north-central Wisconsin as seen in the mylonitic samples from Jennings. Extent and magnitude of the faulting in north-central Wisconsin is not known. References Cited: LaBerge, G.L., 1977, Major structural features in central Wisconsin and their implications to the Animikie Basin (abs.): 23rd Annual Institute on Lake Superior Geology (Thunder Bay, Ontario). LaBerge, G.L., and Myers, P.E., 1976, The Central Wisconsin Batholith (abs.): 22nd Annual Institute on Lake Superior Geology (St. Paul, Minnesota). Maas, R.S., 1977, Structure and petrology of an Early and ~iddle Precambrian gneiss terrane between Stevens Point and Wisconsin Rapids, Wisconsin: Unpub. M.S. Thesis, University of Wisconsln-Madison, 128 p. Van Schmus, W.R., in press, Chronology of igneous rocks associated with the Penokean orogeny in Wisconsin: Geological Society of America Memoir. Van Schmus, W.R., Thurman, E.M., and Peterman, Z.E., 1975, Geology and Rb-Sr chronology of Middle Precambrian rocks in eastern and central ~visconsin: Geological Society of America Bulletin, V. 86, p. 1255-1265. Venditti, A.R., 1973, Petrochemistry of Precambrian rocks in southeastern Oneida County, Wisconsin: Unpub. M.S. Thesis, University of WisconsinMilwaukee, 93 p. 39 �Pr 34/2W/20 Title: Jump River at Big Falls County Park Location: Along the Jump River in NE~, NE~, Sec. 29, and SE~, Sec. 20, T.34N., (Jump River Fire Tower, Topographic Quadrangle, R.2W., Price County. 1970). N N Author: Gene L. LaBerge Description: The main rock type exposed here is a weakly foliated quartz monzonite of presumed Middle Precambrian age. Foliation strikes approximately east-west and dips vertically. Late stage aplite dikes along with minor pegmatite and vein quartz cut the main quartz monzonite body. DO\Vllstream from the main park area the rock has been extensively sheared to f1aser gneiss and mylonite. The main catac1astic foliation is oriented approximately east-west with a vertical dip and is about one-half mile wide. Within the catac1astic zone are smaller mylonitic zones that strike N.30 o E. and about 40 o SE. Pyritic tuffaceous andesitic(?) greenstone crops out at the major bend in the river approximately three-quarters of a mile downstream from the park. ~ood preservation of primary textures suggests the rocks have undergone only greenschist or lower amphibolite facies metamorphism. A number of exposures of mafic rocks are present along the river between the tuffaceous greenstone and quartz monzonite. They appear to be somewhat metamorphosed and sheared. 40 �Pr 34/2W/20 (2) Discussion: This exposure is along a major structural feature in Wisconsin, the "Jump River lineament" (Myers, 1974). The lineament is expressed topographically and on both the Bouguer anomaly gravity map (Ervin and Hammer, 1974), and the aeromagnetic map (Zietz, Karl, and Ostrom, 1978). Where exposed, the lineament consists of cataclastic rocks. North of the lineament of the rocks are dominantly volcanic rocks in the greenschist and/or lower amphibole facies with numerous more or less foliated granitic plutons. This forms a major east-west volcanic belt of Middle Precambrian rocks across Wisconsin from the Michigan border westward to the Keweenawan overlap (Sims, Cannon, and Mudrey, 1978). (Note that the "Jump River Fault" of Sims, Cannon, and Mudrey (1978) does not coincide with the "Jump River lineament" of Myers (1974).) South of the lineament, gneisses, amphibol~tes, schists and migmatites are the predominant rock types for nearly 30 miles. Relatively unmetamorphosed volcanic and plutonic rocks are common in Marathon County and are in fault contact with the gneisses (LaBerge, 1977). Little or no work has been done on the high-grade rocks; however, they appear to be mainly amphibolite grade with few, if any, primary features preserved. Cummings and Myers (1978) and Myers (1977) have studied similar rocks in the Eau Claire area that are evidently part of this terrane, and they concluded that the rocks are at least in part Early Precambrian. Probable Middle Precambrian granitic rocks intrude the highergrade rocks, and isolated patches of low-grade metavolcanic and metasedimentary rocks are present in places (Myers, 1978a, b). The low grade metamorphic rocks are probably Middle Precambrian in age, but no age determinations are available on the higher grade rocks. Thus, we do not know whether the high-grade rocks represent an Early Precambrian basement on which simply more highly metamorphosed Middle Precambrian rocks. The "horst-graben" pattern in Central Wisconsin is suggestive of basin and range structure. The implications of this structure, as well as its timing, has important bearing on our interpretation of the tectonic development of the Animikie Basin. As indicated here, the emplacement of at least some of the granitic plutons occurred prior to final displacement along the fault zones. If this is a Penokean age pluton, the faulting must be either late Penokean or post-Penokean in age. References Citied: Cummings, M.L., and Myers, P.E., 1974, Eau Claire River at Big Falls: Wisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 27/8W/13, 10 p. Evin, C.P., and Hammer, S., 1974, Bouguer anomaly gravity Map of T..visconsin: Wisconsin Geological and Natural History Survey, scale 1:500,000, 2 sheets, separate text. LaBerge, G.L., 1977, Major structural features in central Wisconsin and their implications on the Animikie Basin (Abs.): 23rd Annual Institute on Lake Superior Geology (Thunder Bay, Ontario), p. 23. Myers, P.E., 1977, Eau Claire River at Little Falls: Wisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 27/8W/19, 6 p. Myers, P.E., 1978a, North Fork of the Eau Claire River at Knight Pool: lJisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 26/5W/lO, 2 p. 41 �Pr 34/2W/20 (3) Myers, P.E., 1978b, Eau Claire River at Confluence of North and South Forks: Wisconsin Geological and Natural History Survey, Geology of Wisconsin Outcrop Description EC 26/5W/29, 2 p. Sims, P.K., 1976, Presidential address - Precambrian tectonics and mineral deposits, Lake Superior Region: Economic Geology, v. 71, no. 6, p. 1092-1118. Sims, P.K., Cannon, W.F., and Mudrey, M.G., Jr., 1978, Preliminary geologic map of Precambrian rocks in part of northern Wisconsin: U.S. Geological Survey Open-file Report 78-318, scale 1:250,000, 2 sheets. Zietz, I., Karl, J.H., and Ostrom, M.E., 1978, Preliminary aeromagnetic map covering most of the exposed Precambrian terrane in Wisconsin: U.S. Geological Survey Miscellaneous Field Study MF-888, scale 1:250,000. 42 �SW 38/7W/23 Title: Arpin Dam in Radisson - Late Porphyritic Granite Location: River channel downstream from Arpin Dam, one mile southeast of Radisson, NW\, SE\, Sec. 23, T.38N., R.7W., Sawyer County (Radisson 7~-minute topographic quadrangle, 1972) Author: M.G. Mudrey, Jr. (1978) Description: Outcrops are reasonably abundant in the vicinity of Radisson. The bedrock consists of a coarse, hornblende-granodiorite with inch-sized microcline megacrysts generally aligned N. 50o~E. Medium-granied aplite dikes up to onefoot wide trend N. 15 0 -35 0 E. The granodiorite consists of subhedral to euhedral microcline set in a groundmass of sutured quartz grains, subhedral plagioclase (An 15-20), minor brown biotite slightly altered to chlorite, and green hornblende with trace amounts of apatite, epidote and zircon are found. The aplite dikes consist of equal amounts of subhedral plagioclase (An 20), microcline, and anhedral quartz. Trace quantities of muscovite, chlorite and zircon are present. Van Schmus (in press) reports an U-Pb zircon age of 1,765 10 m.y. for a sample from Grimh Flowage, about 0.6 miles west of this locality. Discussion: This granodiorite, the Jennings granite, other alkalic granites, and the rhyolites of south-central Wisconsin are all late Penokean and yield ages around 1,765 m.y. For the most part, the granitic rocks are little deformed, but all yield Rb-Sr ages around 1,600 m.y. The 1,600 m.y. age is widespread. However, there appears to be no rock units or major structures related to this resetting in northern Wisconsin. Smith (1978) has determined that the Baraboo 43 �SW 38/7W/23 (2) Quartzite and the rhyolites of southern Wisconsin were metamorphosed and deformed about this time. The 1,600 m.y. age is pre-Wolf River and associated rapakivi granites, syenites and anorthosites. Some of the faulting in the area may be related to this 1,600 m.y. thermal event. The Radisson granodiorite is similar to the Rockville Granite of Minnesota, both in petrography and in age (Keighin and others, 1972, p. 240). References Cited: Keighin, C.W., Morey, G.B., and Goldich, S.S., 1972, East-Central Minnesota: in P.K. Sims and G.B. Morey, editors, The Geology of Minnesota (C.M. Schwartz Volume): Minnesota Geological Survey, p. 240-255. Smith, E.I. 1978, Precambrian rhyolites and granite in south-central Wisconsin: Field Relations and geochemistry: Geological Society of American Bulletin, v. 89, p. 875-890. Van Schmus, W.R., in press, Chronology of igneous rocks associated with the Penokean orogeny in Wisconsin: Geological Society of American Memoir. 44 600-3 J 9T025-79 � https://digitalcollections.lakeheadu.ca/files/original/eec5ad95f486276a3fc18dd307239f9b.pdf 8d0703cdf8c8bf578aa79690dfd9c0ec PDF Text Text DEPARTMENT OF GEOLOGY, UNIVERSITY OF MINNESOTA AT DULUTH QUATERNARY GEOLOGY OF THE DULUTH AREA BY CAROL M. MOSS, RANDEE J, ZARTH CHARLES L. MATSCH AND --------- I PREPARED FOR FIELD TRIP N0.3 OF GEOLOGICAL THE NORTH-CE:·!TRA.L SECTIO~! SOCIETY OF AMERICA 13TH ANNUAL MEETING AND INSTITUTE OF LAKE SI.IPERIOR GEOLOGY MAY 3-12, 1979 DULUTH, MINNESOTA MAY 12, 1979 25TH i'1EETING THE �DEPARTMENT OF GEOLOGY, UNIVERSITY OF MINNESOTA AT DULUTH QUATERNARY GEOLOGY OF THE DULUTH AREA BY CAROL M. MOSS, RANDEE J, ZARTH AND C!1ARLES L. MATSCH CHARLES L. MATSCH, FIELD TRIP LEADER PREPARED FOR FIELD TRIP N0.3 OF THE NORTH-CENTRAL SECTION GEOLOGICAL SOCIETY OF AMERICA 13TH ANNUAL MEETING AND THE INSTITUTE OF LAKE SUPERIOR GEOLOGY 25TH MEETING MAY 12, 1979 ��1 PHASES OF GLACIAL ¾; ACTIVITY IN NNESOTA .,_ 1 1-------,;i;_ ·--·T-.i.., ! \. j r,.c\i>- i ·-·- ""o -- 4ss,~ ---=- · lae•c" ~_,_.__.,,,__, ~•-T£.-~,· ~ 4o I, ,s.. r· . ,. • • ! I -- LAKE '----·-·-\ ~ :-=-=== ,. .--;ro~ , . b -- R LAKE DULUTH LEGEND AGE OF ICE •Dc~rOldHI □ ~ I] • ■ ~ - SCALE ,o v......,. ,. -WUN Source: Geology of Minnesola: A Cen1t,nn1 ■ f Volume Frontispiece drafted by Mark Zwaschka; reproduced through the courtesy of the Department of Geography, UMD. ��QUATERNARY GEOLOGY OF THE HEAD OF LAKE SUPERIOR REGION Regional Setting Bedrock The northwestern shore of Lake Superior lies generally parallel to the strike of a southeastward dipping sequence of lava flows and mafic intrusive rocks emplaced about 1.2 b.y. ago (Fig. 1). This Keweenawan volcanic pile called the North Shore Volcanic Group is composed mainly of basalt, but includes significant volumes of rhyolite and lavas of Fig. 1. General geologic map of Minnesota and adjacent states. 1 �intermediate composition. The flows are estimated to be over 20,000 feet thick (Green, 1972). The largest of the associated intrusive bodies is the Duluth Complex, a meld of mafic material, mainly gabbro and anorthosite, but including the felsic rock granophyre. Smaller intrusions in the form of dikes and sills lace the entire section. Geophysically, rocks of similar density are traceable as a gravity high southwestward as far as Kansas, region (Fig. 2). and elsewhere in the Great Lakes The belted configuration as well as the composition of the rocks suggests that the entire sequence represents an episode of crustal rifting and insipient sea-floor spreading. That the process aborted is indicated by the insignificant width of the mafic rock belt. 0 0 Miles 250 Kilometers 400 Minnesota \ Wisconsin Nebraska Fig. 2. The mid-continent gravity high outlines the distribution of basaltic rocks emplaced during a rifting event about 1. 1 b. y. ago. 2 �Following the cessation of volcanic activity, the last to occur in this part of the earth's crust, subsidence of the area resulted in the tilting of the entire sequence gently eastward. sediments accumulated in the subsiding basin. A thick wedge of elastic These Late Precambrian sediments include the arkosi.c Fond du Lac Formation and the Hinckley Sandstone. Paleozoic marine transgressions either did not reach the western Lake Superior region, or the sedimentary record of such activity has been completely removed by erosion since deposition. Atop the Precam- brian, and separated from it by a profound unconformity, is the Quaternary System. Quaternary Geology The structure and differential erosion of the Precambrian bedrock in the Lake Superior region resulted in the development of a pre-glacial lowland which had a direct effect on ice movement in northeastern Minnesota. The lowland channeled ice from the Laurentide Ice Sheet into individual lobes which periodically invaded the western Lake Superior region from the north and northeast. Multiple glaciation of ~he region is evident from stratigraphic, geomorphic, and lithologic relations. The Superior Lobe generally moved southwest along the axis of the Lake Superior basin and west onto the upland, transporting sediment derived from the North Shore Volcanics, Duluth Complex, and Precambrian sandstones. Another ice mass, the Rainy Lobe, invaded from the north-northeast and deposited fragments of Precambrian crystalline rock (granite, gneiss, and gabbro), meta-sedimentary rocks, and iron formation. 3 �Four main advances during the Wisconsin Glaciation are recognized and shown in Figure 3 (Wright, 1972). The earliest, or St. Croix Phase, involved concurrent movement of the Rainy and Superior Lobes in a southwesterly direction, with deposition of a sandy-matrixed till and formation of the St. Croix moraine in south-central Minnesota. The formation of the Toimi Drumlins in northeastern Minnesota, composed of gray to brown sandy till with a large percentage of gabbroic fragments, is attributed to this phase of the Rainy Lobe. A period of glacial retreat followed, and a vast system of tunnel valleys was eroded in the glacial drift by subglacial streams flowing in a southwesterly direction. 100 Miles 0 100 Kilometers 0 A Silver Say I St. Croix Phase ' ·..... •· '\ Automba Phase . Split Rock Phase \ @ Nickerson \ ' Fig. 3. Phase '' . Minneapolis~.···. ' , ...... . . Outline of ice margins during successive phases of the Superior Lobe during Late Wisconsin glaciation. (From Wright, 1973.) 4 �The second, or Automba Phase, brought a readvance of the Superior Lobe out of the basin, this time in a more westerly direction. Movement continued as far west as the Mille Lacs Moraine, which borders the west and south sides of Mille Lacs Lake. The Automba drumlin field in western Carlton County is associated with this advance, as is the Highland moraine, which marks the northernmost extent of the lobe as it moved laterally out of the basin. The Rainy Lobe again advanced across the upland from north- east to southwest, forming the Vermilion moraine. After this phase, the Superior Lobe retreated far enough into the Lake Superior Basin to allow proglacial lakes to form around its margins. These lakes were sufficiently deep to allow deposition of silt and clay which was incorporated into glacial till during the next advance, or Split Rock Phase. The third, or Split Rock Phase of Wright (1969) is marked by the advance of a small tongue of ice which moved southwestward in the Denham area, depositing a discontinuous-layer of red clay-rich till on some of the eskers and tunnel valleys associated with earlier phases. A small field of drumlins was also formed in the Split_ Rock River Valley near Barnum. Late-glacial and early postglacial activity- is represented by extensive glaciolacustrine deposits and shoreline features at various levels, which developed during successive glacial lake stages as the Superior Basin was uncovered by melting of the Laurentide Ice Sheet. Winchell (1901) distinguished three lake levels in the western Lake Superior region: (1) "Glacial Lake St. Louis" at 345 m, (2) a lower, but more distinct level, Glacial Lake Nemadji (324 m), and (3) Glacial Lake Duluth 4 m lower than Glacial Lake Nemadji. 5 Glacial Lake Nemadji �was recognized from lacustrine clays, beach features, and a channel at roughly 321 m, which drained by way of the Kettle and St. Croix River systems. In Winchell's view, Glacial Lake Duluth covered approximately the same area as Glacial Lake Nemadji but had an outlet at 316 m and drained by way of the Brule-St. Croix River system. Leverett (1929) in addition to mapping Superior Lobe moraines, discussed the development of proglacial lakes. In his view, Glacial Lake 2 Nemadji was a small lake, covering a maximum area of 130 km, at an elevation of 321 m. It was bound on the northwest by the Thomson moraine and by the ice margin as it stood at the Fond du Lac moraine (Leverett, 1929). With further ice retreat, Lake Nemadji merged with several other small, proglacial lakes and eventually stabilized as Glacial Lake Duluth. Beach elevations at the western part of this lower lake range from 305 m to 318 m (Leverett, 1929). G. M. Schwartz (1949) delineated strandline features of Glacial Lake Duluth at elevations of 325 m. He also noted the extensive clay and silt deposits associated with the lake plain, especially the varves found at the Wrenshall clay pits. W. R. Farrand (1960) integrated much of the earlier shoreline data and added new observations in an attempt to correlate strandlines basinwide. His results are shown in Table 1. Farrand considered the shorelines of Glacial Lake Nemadji, as described by Leverett, to be associated with Glacial Lake Duluth. The term Glacial Lake Duluth was modified " ... to include all those major water bodies which occupied the southwestern part of the Lake Superior basin and which discharged into the St. Croix River system via either the Moose Lake outlet or the Brule-St. Croix outlet or both." (Farrand, 1960). 6 �TABLE 1--LAKE STAGES. (after Farrand,· 1960). LAKE STAGE ELEVATION AGE OUTLET (B.P,) (ft) Sault Lake Superior Sub-Sault Sault Beach 1000 2000 602 602 602 St. Marys River St. Marys River St. Marys River Algoma 3200 595-596 St. Marys Strait Ni pissing Great Lakes 4100 605-607 St. Marys StTait Houghton Low Stage 8500 360 Post-Minong series 90008500 ? Minong Post-Duluth Beaver Bay Manitou Washburn 9200 proto St. Marys R. St •. Marys Str,:lit : I St. Marys Strait &Au Train-Whitefish Strait . 420? 470? I 650 765 850 Au Train-Whitefish I Strait? Marquette Marquette 10,000 ' 870 Moquah Highbridge Sub-Duluth Duluth Epi-Duluth 10,220 920 955 1007 Marquette Huron Mts. Huron Mts. 1035 1060 1070 1085 Brule-St. Croix R. 1100 10, 700. 10,500 Moose Lake and Brule-St. Croix Moose Lake; Brule-St. Croix Recent work by H. E. Wright has contributed to working out stratigraphic sequences and relationships among ice lobes. In his interpre- tation of the development of glacial lakes following ice wastage, Wright supported the sequence proposed by Leverett: (1) the highest lake level of Glacial Lake Nemadji (318 m) and (2) the lower level of Glacial Lake Duluth near 305 m (Wright, 1972). 7 �Quaternary Stratigraphy, Sedimentology and Geomorphic Features Introduction Surficial sediments in the western Lake Superior region can be broadly grouped into three types: those deposited during advances of the Superior Lobe, those resulting from retreat and stagnation of the glacial ice, and and sediments associated with the formation of Glacial Lake Duluth. Lodge- ment till, deposited by actively advancing glacial ice is exposed in, or underlies, most of the region. In a generally NE/SW-trending belt roughly parallel to- Lake Superior, ice disintegration features of till and interbedded or associated sands and gravels predominate. A similarly trending belt of ground moraine parallels the present shoreline along the southern edge of the stagnant ice features. Lake clays with varying amounts of pebbles and boulders cover much of the remaining southern parts of the region. Tills Two tills of different ages, representing· separate advances of the Superior Lobe are extensively exposed along the Lake Superior shoreline and in some of the deeper stream valleys. Visually and texturally, the tills are very similar, and unless seen in their stratigraphic sequence, it is difficult to distinguish the two. The contact between the ~Jo tills is generally sharp and commonly a stone line or a gravelly or sandy layer separates them. Lower Till The lower till is generally dark reddish-brown, silt-rich, stony and very compact. Fissility is developed locally. 8 Although texture �varies, most of the samples analyzed fall into the loam category (U.S. Department of Agriculture Soil Classification). Analysis of 9 samples from exposures northeast of Duluth averaged 36% sand, 46% silt, and 18% clay. Basalt fragments comprise greater than 50% of the 1-2 nnn sand fraction, with gabbro and "red rock" fragments being the only other rock types of significance. boulder size. Up to 25% of the clasts by volume are cobble or This till is correlated with the St. Croix phase of the Superior Lobe as described by Wright (1969). Upper Till The upper till is the predominant surface material in upland areas away from the lake plain, including the Highland moraine. Its color is similar·to the lower till, although in many exposures it appears to be more red-brown. Compactness varies among localities; in places, the sediment is as highly compacted as the lower till, while in other areas, the material is easily disaggregated by the fingers. Although the same Lake Superior region rock fragments are present (basalt, gabbro, "red rock" sandstone, etc.) and in the same general percentages as in the lower till, this till varies considerably in the amount of pebbles, cobbles and boulders which are present from locality to locality; some sections are extremely stone-poor. Although variable in texture, the younger till is generally somewhat siltier than the lower till. Analysis of 28 samples from the Duluth vicinity shows an average composition of 30% sand, 50% silt and 20% clay (Fig. 4). Clasts of cobble or boulder size comprise at most 20% of the volume of the sediment. The textural variability may be due in part to the position of this till in the stratigraphic section; it 9 �CLAY Figure 4 Grain Size Disf ribuf ion in Tills I I \ @ Upper till average ... Lower f i II average 0 \ A I \ clay I ("'\ silty clay I I-' 0 sandy clay sandy clay \ \ \ \tlty clay loam clay loam O ("\ a._O mcf' ?o I /~ loam 6. J. sandy 1oam I \ ~ ~ 0 e - 0 0 0 silty loam 00 00 I I). I SAND 0 A I 0 .I s i It 0 SILT �was probably partially derived from the various sediments left by the preceding glacial advance. Thus, reworked older drift of varying composition may comprise most of this till rather than material eroded directly from bedrock sources. Th_is till has been attributed to advance of the Superior Lobe during the Automba phase (Wright, 1969). Stratigraphic Type Sections Although the two tills can be seen superimposed at many locations, probably the two best exposures are on McQuade Road in the French River quadrangle and in the City of Duluth along the shoreline at Leif Erikson Park (Stop No. 1 on the road log). At Leif Erikson Park the lower till is a sandy, dark brown to dark red-brown, fissile sediment with abundant boulders. the Superior Lobe are present. Clasts typical of The upper till is more red-brown in color, more silt-rich, and at this location more cohesive than the lower till. A discontinuous boulder line marks the generally sharp contact between the two tills. This may represent an erosional surface developed between glacial advances. At this location the textural difference between the two tills is easily distinguished. Along McQuade Road at the Sucker River, the same sequence is again exposed, although less textural difference is apparent between the two tills. The lower till at this location lacks the fissility of that at the Leif Erikson exposure; both tills at the McQuade location are compact and stony. Fabric Studies Orientation of the long axis and dip of elongated stones were measured for both tills at the McQuade Road location (Fig. 5). 11 The majority of �oo 00 f--' N 0 A. 1so FIGURE 5: B. 1so 0 Orientations of longest axes of elongated stones in McQuade Road exposure. Each circle equals one stone. A) Upper till, B) Lower till; average regional striation direction associated with the deposition of this till is approximately N65°E. �elongated stones dip in an upglacier direction. In general, the long axes of stones in the lower till tend to lie approximately 45° from the direction of ice flow as inferred from the regional striation pattern. In the upper till, a similar pattern is evident, with a large concentration of stones lying nearly transverse to ice flow as inferred from regional features such as the Highland flutes. Both tills also show a slight concentration of elongated stones in the direction parallel to inferred direction of ice flow. Clast Composition At both the Leif Erikson Park and McQuade Road exposures, grain counts of three size ranges were studied: clasts larger than 2 mm (up to and including roughly 4 cm), the 1-2 mm fraction, and the fraction less than 1 mm (Figure 6). Basalt is the predominant rock type in the 1-2 mm fraction as well as in the greater than 2 mm fraction. This is due in part to the abundance of basalt as the predominant bedrock type at and upglacier from the sample site. rock are also important. Physical characteristics of the bed- The abundance of joints and vesicles makes the basalt flows more susceptible to breakdown by abrasion, plucking and grinding during a glacial advance. The gabbro and diabase with their more widely-spaced joints and fractures are more resistant to plucking and crushing. abundant. The less than 1 mm fractions show quartz to be extremely Granite from sources still farther northeast as well as sand- stone from within the Lake Superior Basin are probably the source. little sandstone in the larger size range is an indication of its "crushability." 13 Very �80 BO LE 2 60 60 i/ 40 40 20 20 I :~:=:: / ,/{ /f~-, R,G B LE 6 GB 0 Q,F R,G B GB 0 I-' +' 80 60 ' 40 1\}:: ! 80 N25-1 N25-2 60 :::::: (ti~ 40, ,, .·.·-· 204::: 20 •••••••• B .-.·.· It? 1-:-:-:-: R,G GB Q,F ss 0 FIGURE 6: Percent composition of sand fractions in lower (LE 2, N25-l) and upper (LE 6, N25-2) tills. B=basalt, R,G= red rock or granite, GB=gabbro, QF= quartz or feldspar, SS=sandstone, O=other. B □ < l mm R,G GB □ 1-2 mm ss Q,F [ill ' ' > 2 mm 0 �Ice Disintegration Features In the areas west of the broad band of lacustrine clays, most of the topography reflects ice-marginal deposition of material from active as well as stagnant ice. A distinctive geomorphic feature, the Highland moraine, marks the northernmost edge of the Superior Lobe at its maximum advance during the Automba phase, and the Thomson moraine developed in the later Nickerson phase. Both features display great variability in sediment types over very short distances, and the landforms also indicate varying environments of deposition. The following studies of a part of the Thomson moraine near Wrenshall, Minnesota are presented as an introduction to terrains originating from ice disintegration. The moraine is a hulIDllocky complex of kames, kettles, disintegration ridges, and eskers. to 20 m. Local relief is varied but may be up These features are typical of an ice-disintegration environment. Ice-disintegration describes the processes involved in the break-up of a stagnant, wasting glacier. Ice-disintegration features are of two maj.or types: (1) controlled ice-disintegration and (2) uncontrolled ice-disintegration (Gravenor and Kupsch, 1959). Uncontrolled ice-disintegration results from equal forces acting in all directions forming unoriented features, such as kames, kettles, and general hummocky terrain. Controlled ice-disintegration occurs when there is break-up along fractures in the ice and when deposition is localized to form linear disintegration ridges and eskers. Uncontrolled Ice-disintegration Features Karnes Kames are conical hills or mounds of any size consisting of stratified sand and gravel. Kames are abundant in the northwest portion of 15 �the Wrenshall quadrangle and are associated with the Thomson moraine. There they are generally small, reaching maximum dimensions of up to 0.5 km in length and 20 min elevation. They have flat to rounded tops and varying slopes according to the texture of the underlying material. The kames are found to occur both as single, isolated hills and as composite hills which merge to produce ridge-like landforms. Texturally, these kames consist of poorly to moderately sorted, stratified sand and gravel, with boulders. The sand and gravel is in some places capped with fine sand to silt. Kettles Kettles are small basins created by the ablation of buried ice. Kettles found in the Thomson moraine area vary in size but are generally small, less than 1 km in diameter. Some display irregular shapes but most kettles tend to approach circularity. Kettles that are associated with kames tend to give a "pitted" appearance to the landscape and this "kettle and kame" topography is characteristic of ice-disintegration complexes. F. G. Driscoll (1976) in a study of moraine lakes at the Klutlan Glacier, Yukon Territory, suggests lake development may be the result of (1) the melt-out of ice containing differing amounts of debris, resulting in an irregular depositional surface; or (2) uneven surface debris accumulations due to topographic reversals, resulting from slumping of sediment. Superglacial lake development on a stagnant debris-covered surge lobe proceeds in five distinct stages as the buried ice melts (Driscoll, 1976): (1) accumulation of meltwater in low areas on the moraine; (2) expansion of the lake basin by both lateral and vertical melting, and the establishment of inlet and outlet streams; (3) accumulation of melt-out debris along lake perimeter, vegetation cover, and mass-wasting along steep shore areas; 16 �(4) stabilized slopes, rounded lake bottom, areal expansion ceases, significant life in lake; (5) reduction in enclosing slopes, heavy vegetation on periphery, decrease in lake depth and areal extent, final melt-out of buried ice, increase in biomass. Controlled Ice-disintegration Features Linear Disintegration Ridges The term linear disintegration ridge pertains to a ridge that originates during ice stagnation (Gravenor and Kupsch, 1959). Ridges of varying sizes, up to 12 min height and several kilometers in length, are found within the Thomson nroraine. Although these ridges are related to controlled disintegration, they appear gradational with uncontrolled features and are found with kettles and kames. The linear ridges vary in composition from medium and fine sand to sandy gravels, although the latter is predominant. The stratified nature of the drift contained in these ridges suggests that they were open crevasses in the stagnating ice which provided a site for the accumulation of stratified sediments. Sedimentology The sediments associated with ice-disintegration in the Duluth area exhibit a wide variety of textural characteristics, geometries, and sedimentary structures. The sediments are generally poorly to moder- ately sorted, stratified sand and gravel. The geometry of the units varies from sheet deposits to pods and lenses. The grain size distri- bution shows abrupt changes and an extreme range of sizes from boulders to clay. The sediments are thin to thickly bedded, with some cross- bedding, faults, current and gravity structures. 17 The clasts,generally �surrounded, are composed of Precambrian sandstone, basalt, rhyolite, gabbro, granite, gneiss, iron formation, slate, and graywacke. The sediments can be divided into five units based on their internal and external characteristics. These are (1) gravel, (2) horizontally- bedded sand, (3) cross-bedded sand, (4) silt and clay, and (5) diamicton. A gravel pit along West Alcohol Road, SW½, SE½, Sec. 19, T48N, RJ.6W, (Stop in road log) reveals good exposures of these sedimentary units and their structures. The exposures generally show abrupt vertical changes with an overall fining upward sequence in most sections. One locality in the pit near the entrance shows fine to medium sand overlain by very coarse sand, gravel, and boulders, occasionally with mudballs. These units are overlain by laminated silt and clay which show discontinuous beds that are gently contorted in the lower 0.5 m. Lobes of overlying fine sand protrude downward into the silt and clay unit. The fine sand shows small scale cross-laminations with sets 2 cm in thickness. The sand is overlain by another silt and clay unit which shows load structures into an overlying medium to fine sand. Another location, approximately 75 m to the northwest, shows the gravel to be the predominant sediment with lesser amounts of crossbedded sand, horizontally-bedded sand, and diamicton. gravel occurs in the basal 4.5 m of the section. The The unit shows crude cross-bedding with sets to 0.5 min thickness and often containing interstratified sand, less than 0. 3 min thickness. Overlying the gravel are ' the horizontally-bedded and cross-bedded sand units. bedded with gravel-boulder lenses. These are inter- Horizontally-bedded sand has bed thicknesses from 2-3 cm to 2 mm and the cross-bed sets are up to 0.5 m 18 �thick. The sand exhibits scour and fill features in some localities, in addition to normal faults. Cross-bedding measurements, from both the cross-bedded sand and the gravel unit, show that paleocurrent directions (n=l2) for the WestAlcohol Road Gravel Pit are generally to the northwest, but there is a considerable amount of scatter in the orientations. Depositional Environment The ice-disintegration complex west of Wrenshall is characterized by hummocky, kettle-kame topography, consisting of a wide range of sediment types and structures. The extreme range of grain size along with abrupt changes in texture and slump structures indicate that these • sediments were deposited in close contact with stagnant ice (Flint, 1971). Sediment supplied to the complex originated from the stagnating ice mass. The abundance of granite and iron formation clasts (typical of Rainy Lobe sediment) suggests that there has been reworking of the older, underlying drift. The depositional environment of the sediment was one of large velocity fluctuations of the meltwater, which must have varied considerably as indicated by the rapid change in grain size. In the west central portion of the Wrenshall quadrangle, the very hummocky terrain was the result of deposition in ice-walled basins and later wastage of the sediment-covered ice. There was abundant meltwater available which allowed the sorting and stratification of the sand and gravel. An esker depositional environment is also observed. The esker was probably formed in a tunnel in the stagnant ice as evidenced by a single, steep-sided ridge containing longitudinally continuous sedimentary units 19 �(Banerjee and McDonald, 1975). Current flow appears to have been to the southeast with the esker terminating in a delta in a lacustrine environment. The sediments of the West Alcohol Road gravel pit may have been deposited in an ice-walled, fluvial environment, possibly by braided streams. The fining upward sequence, sand and gravel lenses, apparent channeling, scour and fill features, and floodplain silt and clay tend to support this hypothesis. Paleocurrents indicate major flow N60W with some directional variations which would be expected in a braided stream environment. Another possibility is that the sediments were deposited in a large ice-walled basin. The predominance of gravel and boulders indicates the need for a proximal source of sediment. Slump structures, faults, and a diamicton support an ice-contact origin. The laminated silt and clay would have been deposited in a quiet water pool or lake, with an increase in current velocity or loading from overlying material causing convolutions. In general, these sediments were deposited on, against, or under stagnant, wasting ice, and according to R. F. Flint (1971): "In such a place (ice-contact environment) anything can happen and it often does." 20 �GLACIOLACUSTRINE ENVIRONMENT The western tip of the Lake Superior Basin contains geomorphic features and sediments associated with a glaciolacustrine environment. The morphology, stratigraphy, and spatial occurrence of various sedimentary facies are ascribed to the activities of Glacial Lake Duluth, which had a high-stand above 1100 feet. Geomorphic features and sedimentary deposits of Glacial Lake Duluth are well-displayed in the Wrenshall and Frogner 7-1/2 minute quadrangles, and the following discussion is largely concerned with that area. Geomorphology The lacustrine environment in the Wrenshall and Frogner quadrangles is characterized by well-developed beach landforms and extensive lake plains. These features may be compared to the marine shoreline profile typical of sandy, mainland coasts. Coastal areas are divided into three morphologic zones: (1) mainland, (2) nearshore, and (3) offshore. The mainland area consists of older features, such as ancient strandplains, alluvial plains, lagoons (or shallow, restricted bodies of water), or bedrock. Dunes are common, as a result of a large supply of loose sand, and are found bordering the beach. The nearshore area, in a marine environment, extends seaward from the mainland and consists of two main zones: (1) backshore and (2) shoreface. The backshore is the area which is subjected to wave action only during extreme high water, usually generated by storms. ward, the profile shows the shoreface zone. 21 Continuing sea- The shoreface is defined as �a submerged zone which extends to a depth where sand size material is not moved by normal currents (Harms and others, 1975). It is the shoreface that is affected by swash and backwash, breakers, and longshore currents, which transport sand across the entire zone. The offshore area is not affected by normal wave action. Coarse sediment is transported into the offshore zone only under extraordinary conditions, such as storms or density currents (Harms and others, 1975). The lacustrine complex in Wrenshall and Frogner quadrangles is divided into two main morphologic groups: (1) nearshore and (2) offshore, which are separated by a narrow transition zone. shows two zones, the backshore and the shoreface. usually less than 120 min width. The nearshore profile The backshore is narrow, This merges with the hummocky terrain of the ice-disintegration complex previously discussed. The backshore is relatively flat, but in some places is marked by small discontinuous beach ridges. The shoreface in these quadrangles is expressed as a north- east trending belt, approximately 1.8 km in width. The shoreface here is basically a surface of no relief, sloping gently, 3 to 8 degrees, to the southeast and east. The shoreface zone is influenced by current action which is reflected in the presence of beach scarps, spits, an offshore bar, and a delta at elevations near 330 m. Wave-cut beach scarps in the shoreface dip 5 to 8 degrees to the southeast and are underlain by medium to fine sand with boulders and gravel concentrated at the base of the slope. The largest spit trends north-south and is located at the center of Sec. 1, T47N, Rl7W. It is 1.3 km in length and 0.5 km in width with side slopes of 3 degrees. The spit curves to the southwest indicating longshore currents flowing to the southwest. Several smaller spits are located in section 2. 22 �An offshore bar, with up to 6 m of relief is found in SW¼, Sec. 11, and W½, Sec. 4, T47N, Rl7W. It generally lies parallel to the former shore- line, 0.8 km lakeward, and extends for 2.4 km. Paleocurrent directions (four measurements) to the northwest indicate shoreward growth of the bar. A fan-shaped form, located in Sec. 31, T48N, Rl6W, is interpreted to be a delta. It is roughly 2.6 km 2 in area, relatively flat-surfaced in the north portion, with a foreset slope of 4 degrees to the southeast. A former ice tunnel, now containing an esker found to the northwest in the ice-disintegration complex, appears to have supplied the delta with meltwater. Lakeward of the nearshore area nearshore and offshore environments. is a transition zone which separates The transition zone occurs as a northeast trending scarp between 300 and 309 min elevation which slopes 3 degrees to the southeast. The sediments of this zone are transitional in nature between the nearshore sands and the offshore clays, with the sands and clays interfingering. This feature was misinterpreted by Leverett, Farrand, and Wright to be a strandline feature of Glacial Lake Duluth. It appears instead to be a depositional feature associated with the higher (330 m) elevation of Glacial Lake Duluth. The offshore environment is represented by an extensive lake plain that covers the southeast quarter of the Wrenshall quadrangle and most of the Frogner quadrangle. southeast A profile of the offshore from northwest to shows it to be gently dipping to the east-southeast at less than 3 degrees. Two weak scarps are seen on the profile at elevations of 288 and 264 m, which may represent lower lake levels of the Highbridge and Washburn stages respectively (Farrand, 1960). 23 The offshore area has �been deeply dissected by the Nemadji River and the Red River, a tributary of the St. Louis River. These streams have downcut as much as 42 m into the offshore sediments. Extensive slumping is very common along the stream valleys, indicating the instability of the underlying material. Sedimentary Units The sediments of the glaciolacustrine environment may be divided into four units: (1) horizontally-bedded sand, (2) cross-bedded sand, (3) laminated silt and clay with dropstones, and (4) massive clay with dropstones. Horizontally-bedded Sand This sand occurs widely throughout the nearshore zone as a sheetlike deposit, with a minimum thickness of 6 m. The grain size distri- bution shows moderately sorted sand with gravel and a mean grain size of 20 (O.25 mm, medium-fine sand). Sedimentary structures are not abun- dant in the horizontally-bedded sand. nated to medium bedded. The sand varies from finely lami- The bedding planes are faint and difficult to recognize, giving a massive appearance to the sand. Heavy mineral laminae are present and help to distinguish bedding planes. Slightly inclined bedding at one locality gives a general paleocurrent direction to the south-southwest. The only other direction indicator available is a general fining of the sand on the shoreface from medium to very fine sand, suggesting currents flowing to the south. The presence of a plane bed structure associated with the medium to fine grained, horizontally-bedded sand indicates an upper flow regime (Reineck and Singh, 1973). In the upper flow regime the main mode of 24 �sediment transport is via continuous rolling of grains in sheets several grains thick (Reineck and Singh, 1973). Accordingly, the sediment trans- port is large. Cross-bedded Sand The cross-bedded sand occurs as ribbon type deposits. These deposits are generally small, less than 1.5 km in length and 0.5 km in width. The grain size distribution for cross-bedded sand shows that this is moderately sorted. The mean grain size is 1.50 (0.35 mm, medium sand), although there is locally coarse sand and gravel. sedimentary structures found in this unit. Cross-beds are the main These occur as planar or tabu- lar forms with sets up to 0.5 min thickness. The cross-beds show good topset, foreset (inclined 25 degrees), and bottomset beds with laminae comprised of gravel, fine sand, or heavy minerals. Paleocurrent directions indicate (1) current flow to the east-southeast (lakeward) and (2) current flow to the northwest (shoreward). The shore- ward current direction is observed in the area of the offshore bar and indicates a shoreward growth of the bar. Bedforms of small ripples and mega-ripples associated with the crossbedded sand indicate transport and deposition in the lower flow regime (Reineck and Singh, 1973). The cross-bedding developed as a result of the migration of small current ripples and megaripples. In the lower flow regime, the resistance to flow is large and the sediment transport is small. Laminated Silt and Clay The laminated silt and clay occurs as extensive sheet-like deposits which are also associated with massive clay. nated silt and clay varies from 0.5 to 15 m. 25 The thicknesses of the lami- �Texturally, two distinct populations are observed: high silt content and high clay content. The silt layer is moderately sorted with a mean grain size of 5.80 (0.02 mm, medium silt). The unit is pale brown (Munsell color: 10 YR 6/3, dry) and consists of greater than 55 percent silt. The clay layer is reddish brown (Munsell color: 5 YR 4/4, dry) is ang_/composed of greater than 75 percent clay, with silt generally less than 10 percent and sand Oto 2 percent. In a few locations, carbonate concretions are found within the clay layers. The sedimentary structures associated with the silt and clay are very thin to thin bedding, discontinuous and distorted bedding. The silt and clay beds vary from several millimeters to several centimeters in thickness, and change considerably within a stratigraphic section. Discontinuous bedding is contorted, showing small scale recumbent folds and lenses of silt. The laminated silt and clay are rhythmites, alternating layers of different compositions, which may be varves if each couplet represents a single year of deposition (Reineck and Singh, 1973). These appear to have been deposited in the quiet water, deep portion of the basin. The abundance of clay indicates that the main mode of deposition was from the falling out of fine particles from suspension. The presence of silt would indicate more competent currents or turbulence, possibly during the summer thaw, which would periodically transport and deposit the silt. Massive Clay The massive clay, with the laminated silt and clay, comprises the major portion of the lake basin. Massive clay appears as a thick, sheet- like deposit which has lateral continuity. 26 The exposed thickness of the �clay is up to 20 m. Texturally the clay content is greater than 75 per- cent with several samples showing greater than 90 percent. prises the remaining 10 to 25 percent of the sediment. Silt com- The clays are reddish brown (Munsell color: 5YR 4/4, dry) to dark reddish gray (Munsell color: 5YR 4/2) where unoxidized and have a general massive appearance. There are no visible laminae of coarser or different colored material, however in some exposures, the clay does show minor fissility, indicating an internal structure. The presence of massive clay suggests quiet, deep water deposition without apparent current activity. Drops tones Scattered within the massive clay and laminated silt and clay are individual clasts up to 10 cm or more in length. These stones are thought to have originated as ice-rafted material as evidenced by their sporadic occurrence, in addition to their large size which would otherwise require a competent current for transport. Clay Mineralogy Four samples from the laminated silt and clay and massive clay were analyzed by x-ray diffraction. These include a red clay lamina, a gray silt lamina, reddish gray massive clay, and reddish brown massive clay. There is little difference in composition, other than peak intensities, among these samples. The samples contain (1) quartz, (2) calcite, (3) dolomite, (4) plagioclase, (5) k-feldspar, (6) montmorillonite-illite mixed layer, (7) chlorite, and (8) possible hematite. This mineral group is consistent with those determined by Mengel and Brown (1976) for other clay samples in the Wisconsin portion of the lake basin. 27 �These minerals were derived from the underlying weathered bedrock and older glacial sediments. The abundance of calcite and dolomite indicates a source in the drift of the St. Louis Sublobe to the northwest of the study area. Calcite is commonly found as vein fillings and amygdules in the flows of the North Shore Volcanics and could have been incorporated into the drift of the Superior Lobe. Another possible source for the carbonates is the Hudson Bay area with glacial transport of the sediment into the Wrenshall and Frogner area (Mengel and Brown, 1976). Stratigraphy Exposures along roadcuts and stream valleys in the lacustrine complex allow the stratigraphic relationships of the sedimentary units to be worked out. Subsurface data are available only for the area near Wrenshall and show the drift to be up to 115 m thick. Various sections are summarized in a schematic north-south cross-section (Figure 7 ). The section shows the basal unit as older drift or bedrock. These older units are overlain by (1) moderately sorted, probable nearshore sand, (2) massive clay with laminated silt and clay, and including dropstones, and (3) moderately sorted, fine to medium grained, horizontally- and I cross-bedded sand. The presence of shallow water sand over deepwater silt and clay suggests progradation resulting in nearshore facies over offshore facies. Depositional Environment As shown on a surface plot of the sediments (Fig. 8 ), the mean grain size distribution changes depending on the distance from the shoreline. The nearshore facies is shown to be composed primarily of medium sand. The sand consists of both horizontally-bedded and cross-bedded units. Shoreface activity includes upper and lower flow regimes, as indicated by 28 �w m ,'1 i i 'f j J: . ~ ~ •• ~ ~ ~ I r :z 0 1-1 E--< r--r--- u CJ\ .--l V'") ..c .j.J tU I Cl) ti) H (1j N ,~ ., 0 0- u µ~ (/J I ;'!: z u I-< I ,-.. ~ '-' l I ~ I E:-< ii «:: f ;::;..: IJ.l ~ ct :.e • u ·¥ t/J t l ~ ,-... : • ~ lJ 4> k ;: i ::; "1• t,;(j •T"l Gt. i 1 1 j ·'ii ~ i Cl I ::z: < E- ....:1 s2 '!i ';l 0 z < CJ) I $, 1l ;;, 1~: ~ i:i I i: $ ill i f 1': ,:: 29 J.... t .!'/ i �H I I I I I ! i' I Y"\r~ • ,. ! 1 /] / H : • ' .¼ . i I ! ~ I : /. fI ~ -~ 1 1 m·1 ~: I · . --~ -,-- -- ---•-,· - -- - ... L ~ -· : : I ' [I ' : f I ~ ~~ : , .. I ~:::.,..,,r ~ I . r-,""~--f .... ,..,,.. • .,. .. I I ! 3 ~ 4 I I 4 1 _,,.., ~.....---...i-6 , 3;)· • ! I · ~--- ~ ~ ! A ' I I I I I ! ~-~_.. - / ~ - ..... t: _ _..,_nn-1,---n--.,~ .. I ~?'I I I e 1 I I U )/,#' f : D IQ ,P--1 • I I, : I 3 H: I r. 1 I I II l I I 1/, I I I _, ~ I )efjY #r ~~ 1 I 3g : I I __ I lJ - I I : I I • llot I I . . 0, l I I 14 , I I <:'lii~OV---,,.,_C'C'- I 1 1,I I I !l I I f I I . ·an : 1 I · I f91 t : l II t l l ~ ' 'vsM{.I ~ - - .;:- ........... ~ ~-'I., .... ~ ., ...~~ -: I I • I : . I ,,,.. , .cJ__j I II I . , ' I "d I /:I ti I AA · - I' M n I . (.'I • ...... ,.. .... "' ..,, ,.., .., ... " .., ... ,., - - - ..,. I I · . I ., • +,:I •rl ~ I . @ {h ·1 j t! 1 LI I 1 II fI I !l a, ' ! 1 :I I' I :.~ / , ,, I I I i I JI • I I I I t j II • : D I ' 1 I ' ·1 M I - - - ... - " ... I :1 f I I 2,0=,25mm J,0=., 125mm 4%~o062.5mm j;J= ') OJ1 Jmm 6f1cn01,56mm 7Jo=,,0078mm i l I ~ I 4 - - - - .. - - ...... ~ - . . . - - - - .I' I ,:i. I 1 1jli:::; ~ 5mm. --1-"""t'l'lt"I"" I I lI.........,.~, - ) . .· ~ ' I l I I . .., • I im 0%::::lmm I • A "I - - - - I l'.tl~- A3 I I I , l ao .. a~ o - I I I I' ...,.J _ _.. ,,._.,.. __ 1--ll'la""""''"--11"'1"'..,.. ___ i:-,,J._,,_::::rT __ ~/._yJ-' H 111 II i I ... I Shoreline Contour Interval:1% I t .J"""' ...,,..._r.)_,..., s.. • r.o, 1' II I I I I U-1...-l....W I I I ~n'7.,.~ I •a " ,~ MEAN GRAIN SIZE DISTRIBUTION :--= . . . . . .,,.-r .. ----r . . ~~ . ., ~1-==--.-"'-:~- --~1~~- -~-I I -----,-. ,iI' I I I ~ I ~ I - .. -:~ - _., - ~ ' I I .~ 1· I IJ G :1.,- "''"n,:, ~l"Y\()~:--..":') ~.., --"""'-.-'-"" ..,.,~-j11"'!1 .... ,.... ..... ~-- o;; I C I . = I A i '" • I I I I I ; f.11 II : l l 1 w I -'t---~~-,,,. -'"Y'~ r- - -----1•~M-- .. --r---~--:-n-•fl·---L.------ :I ~-I~~: :I II ____ _.,~. . , __ .,.,.,._~, - -- ..-.-~--,...---··t- ___ ,. __ - ..J,. .. 0 I 1 • . , 1 I ai I ,.,,,..---;. ~~ ~11.\1. 1 ....__--,..__-,--..;r _.-,,_ le, : ' I I I U 0 ' " J lL 10 1111 m I II , -•r'"•. r ~ ~ 4 I -r--, 1.',, ; • • • I• , I , 1 •t-------~..,.,_•r.tJIID-1•_,.,.,_ ... m.L•-•••• I I m ,... n- • I .--.,.,,,_= 1 llln P ~ 31! 1 ,_.,r.-•1.-.,.,..o• '1 f"ltl)'lar-o- . . • I t I I iI M I I ~ .,J, ' i 'j_f,J~ ..... ..... ! M~ f0j -,Wt•t•r.tct•c.-ee-,.•, . :· ,' a A I I A:! 0 ,· lfJ • l I I I •n--,-ro..,.c:"»•-"""'• nt <"a ! : ,, . ,. • -c n ~ .,. - . I Rt i I Ir"' ,. .. f/ JV u ~ I ·-•• ... •'--~--.., ; n~ ~ "' • = .... ., ~ ......... Figu:re 8 --DISTRIBUTION OF MEAN GRAIN 0 l1 mile size;· f J (R.J.· Zarth, 1977) M,!,tih;~J,-~iy-,X',.b/ ',"'°' a;,,.,;.~t 1 ~•,-+''4 , , 1,1, •<~•·.1.1,. •-· ... _.,, ,, .. ,:,~ ,., ~.•. , ~,/ L..,-, ,;, ,t• .,• ....., .... ,.,,:.,...,.t, ...\>-&.1h:...1-•".,h;,.-,.i,.~L~~lc.biW,4r.,)·,~1~il•t',,/ll~h.-H.. ''•~,;: .- ,ih\1:.c,"'..t':;(~.r,.-\~•,.i,~1-,9i'.rn,,J,1d"J,,-4,1...,,v.,,,;,.1.,-J. ..,1,.;;,,. ,,,.., .,, ,•... •• • �f._ 1? ·i ' '~ -.~ ' -~ ,....__ r-• r-~ O'\ <,...; :;: ~ f.() '.5 1-4 Ci) tJ'.J ;... ~ _,j i i{ ' .i C) N ' -< t.t., '"1 'l ...J~ < ~ ~ :z ~ C,!l O"\ Q h ;:l bQ ...: '""' 31 i! l J ''' �bedforms. The current directions to the southwest parallel the shoreline, causing the formation of spits (Figure 9 ). The offshore bar formed sub- aqueously and paleocurrents show a shoreward growth, possibly due to storm waves. The north-central portion of the study area has very fine sand and silt relatively close to the shoreline, suggesting lower current strength. Deltaic sedimentation shows an upper surface of sand, with very fine sand and silt on the prodelta slope. and west from the feeding esker. Two narrow valleys radiate south These may represent remnant distributary channels cut into the delta, with the silt and fine sand as floodplain deposits, as suggested by their standard deviations (Folk and Ward, 1957). -There is an abrupt grain size change in the lake basin from predominantly sand to predominately silt and clay (Fig. 8). This boundary, which can be traced laterally, occurs between 300 and 309 min elevation and is represented by a northeast trending scarp, The zone shows varying textures with interfingering sand, silt, and clay. The variety in sediment type reflects the changes in current strength. This abrupt change in slope and sediment type is here interpreted to represent the depositional front of a coarse grained shelf of Glacial Lake Duluth. The offshore facies occurs south and east of the transition zone (Fig. 8). It is composed of laminated silt and clay, massive clay, and dropstone deposits. These sediments were derived from the wasting ice lobe and meltwater streams draining the ice-disintegration complex. Offshore sedimentation must have occurred primarily as the settling of sediment from suspension as evidenced by massive appearing clays. 32 �The rhythmite couplets (silt and clay layer) are not gradational but occur as distinct layers. This would suggest deposition by two sedimentation pulses and modes of deposition (Ashley, 1975). The normal suspension sedimentation may have been periodically interrupted by density currents as underflows, interflows, and overflows. These flows result from the high suspended sediment content of meltwater streams from the ice-disintegration complex and ice lobe entering the lake. These flows have been described in present day Glacial Lake Malaspina, Alaska, by Gustavson (1975). These currents provide a mechanism for the deposition of the silt layers of the rhythmites during the summer months. This would result in clay being deposited continuously in areas not reached by current flows, and massive clays would form (Gustavson, 1975). In add~tion, offshore occurrence of dropstone deposits, interbedded with silt and clay, suggest ice rafting of sediments as a depositional mechanism. The ice dammed Glacial Lake Duluth,with calving of the ice front,would produce massive icebergs which would release sediment over the lake basin as the ice would melt. Vegetational History Cores from bogs and lakes contain a history of plant succession in the form of pollen and macro-fossils, including seeds, woody fragments, and leaves. Studying quantitatively the contents of such cores at a particular site allows the determination of the time of arrival of plant migrants, as well as the reconstruction of the fabric of the plant communities at different times. All of these studies lead to the fuller view of the vegetational history within the time represented by the sediment core. As a data proxy for climate, the pollen record is 33 �then transcribed into a history of climatic change. Sampling along the proper traverses allows the monitoring of the march of vegetation in the wake of retreating glaciers. Most ponds and lakes in glaciated terranes deep enough to accumulate a significant sediment record originated as kettles on ice-cored end moraines. The vagaries of down-wasting of buried stagnant ice decree a complex natural history for the surface features of such a terrane. Topographic reversals are common because the hillslopes are extremely unstable: debris flows and slumps denude sediment-mantled slopes, fill depressions with colluvium, and thereby redistribute the insulation on the stagnant ice surface. slopes and hilltops. Melting proceeds more rapidly on the bared Differential melting transforms ice-cored hills into holes, and vice versa. In such an unstable environment lakes and ponds are ephemeral. Sediment, including pollen and plant macro-fossils is not collected into a continuous and permanent record until a stable basin is formed, generally near the demise of the ice core. Melting to that point in the moraine's history may take thousands of years. Therefore, radiocarbon dates on bottom sediments in such lakes can be significantly younger than dates obtained from beneath basal till in the same moraine. For the same reason, cores contain an incomplete record of revegetation-generally the earliest part is missing. It follows that the best lakes for pollen studies are those that formed early in the history of deglaciation and that continued as stable catchments to the present. In broad outline, the pattern of plant succession in Minnesota during the Late Wisconsin and post glacial is similar to that of the 34 �entire Great Lakes region (Wright, 1976). Minnesota (see Fig. Wolf Creek in central for location WC) and Weber Lake in northeastern Minnesota are two sites that have been especially useful to reconstructing the vegetational history • . ·1. i r.. ,, ti \ .. . .. \. 0 KILOMETERS Figure 10. Major phases in the Wisconsin glaciation in M:lnnesota. Approx1rrate dates 1n thousands of yeal's. Note the non-synchronous maxima of the SL1perior and ~s 1·-:0ines lobes. Locations of Wolf Cr~~k .:ind Weber I,'1.lw al.'c sho~m. The oldest pollen zone at Wolf Creek represents an herb tundra, which prevailed from 20,500 yr BP until about 14,700 years ago. was followed by shrub tundra and forest tundra. This Spruce expanded into the area about 13,600 years ago and was the dominant species for about 35 �4,000 years. Then, spruce was replaced by pine about 10,500 years ago. Cores from Weber Lake, situated farther northeast in the Toimi drumlin field, indicate that herb tundra persisted there until about 11,000 yr BP, with a rapid transition to shrub tundra and then spruce and finally pine. A summary of the changes in major vegetation types and their relationships to glacial phases is shown in Figure NORTH 2000 RAINY 20 0 !:J Stagnant ice Figure 11. 40 ♦ LOBE SUPERIOR LOBE 60 ,co 80 ,20 Ro.c.iacarbon do.le, wit!\ one <10.nd<1t"d c!ev1<11ion 14() 160 180 ZOOmdtt • Rejected r<1d10c<1rbon d.<11e Transect from north to south in eastern Minnesota, showing times and areas of ice-lobe advance, as well as the changes in major vegetation types since glaciation, as inferred from pollen and seed analyses of lake sediment cores. (Courtesy. H. E. Wright). 36 �Glacial Materials and Soil Profiles by Royce Lewis, Soil Conservation Service The kind of soil horizons and their sequence formed on well drained sites in the Duluth area generally can be correlated with the kind of glacial materials. as examples. The Ahmeek, Duluth and Ontonagon soils may be used See Figures 1 through 6 for some physical and chemical properties of these soils. The Ahmeek soils are formed in noncalcareous, reddish brown, sandy loam till. Their sequence of horizons may be interpreted as A , A , 2 1 Bhir, B, and C. X X The Duluth soils are formed in noncalcareous, reddish brown, loam till and have a sequence of horizons of A , A , Bhir, A , BT, 2 2 1 and C. The Ontonagon soils are formed in calcareous reddish brown, lacus- trine sediment and have a sequence of horizons of A , A , BT and CCA' 2 1 The A horizons of these soils have higher accumulation of organic 1 carbon, lower bulk density and higher porosity than other horizons in the pedon (area of about l square meter). They are higher also in available water capacity (1/3 minus 15 bar water). They generally are higher in base saturation and pH than the horizons immediately below. They cotmnonly are black. The A2 horizons generally are discontinuous within a pedon of Ahmeek and Duluth soils and are continuous in the Ontonagon soils. They are horizons of maximum removal of clay, iron or aluminum, which results in a concentration of quartz or other resistant minerals in the sand and silt size. They are lighter in color than the underlying B horizons. The Bhir horizons have significant accumulations of organic carbon, iron and aluminum coatings on sand and silt particles. 37 They are low in �bulk density, base saturation and pH. They have also a higher cation exchange capacity per unit of clay than the underlying horizons. They are commonly reddish brown. The BT horizons have appreciable accumulations of translocated silicate clay particles as contrasted to the B horizons (in the Ahmeek X soils); however they have higher bulk density and lower porosity than BT horizons. The base saturation of the B horizons, and content of clay range widely among these soils. They seem to be a mark of the kind of glacial materials along with the properties of the C horizons. The C horizons are presumed to be relatively little affected by biological activity and include accumulation of calcium and magnesium carbonate (CCA horizons) and high bulk density (Cx horizons). 38 �.&IIKEEJ:l'ElXJ11' J'art:l.oJ.. Siu Dutz:1.bution ('6) 2 l)optb so ail1: l'vtiolA Sue D1atr..bution ('6) 2S 50 75 l!ue S&turation JO 50 Co) 70 pf! (~0) 6,6 7.0 .4 2S Sill: Clq so lllJLll'm PEllOI hrt:l.olA Siu ll1atribut1on (1') 2 0 7, .. l)optb 2S so olq 1111: llua· S&tun.tian (1') 10 50 70 pf! (CaCl) .4 �REFERENCES CITED Ashley, G.M., 1975, Rhythmic sedimentation in Glacial Lake Hitchcock, Massachusetts-Connecticut, in Glaciofluvial and Glaciolacustrine Sedimentation, A.V. Jopling and B.C. McDonald, eds.: SEPM Special Pub. 23, Tulsa, p. 304-320. Banerjee, I. and McDonald, B.C., 1975, Nature of esker sedimentation, in Glaciofluvial and Glaciolacustrine Sedimentation, A.V. Jopling and B.C. McDonald, eds., SEPM Special Pub. 23, Tulsa, p. 132-154. Driscoll, F.G., 1976, Formation and wastage of neoglacial surge moraines of the Klutlan Glacier, Yukon Territory, Canada, Unpub. PhD Thesis, U of Minnesota, 309 p. Farrand, W.R., 1960, Former shorelines in western and northern Lake Superior Basin, Unpub. PhD Thesis, U. of Michigan,. Ann Arbor, 226 p. Flint, R.F., 1957, Glacial and Pleistocene Geology, Wiley and Sons: New York, 553 p. Folk, R.L., and Ward, W.C., 1957, Brazos River bar: a study in the significance of grain size parameters, Jour. Sed. Pet., Vol. 27, p. 3-26. Gravenor, C.P., and Kupsch, W.O., 1959, Ice-disintegration features in western Canada, Jour. Geol., Vol. 67, p. 48-64. Green, J.C., 1972, General geology, northeastern Minnesota and North Shore Volcanic group: in Geology of Minnesota: A Centennial Volume, Minnesota Geological Survey, p. 291-332. Gustavson, T.C., 1975, Sedimentation and physical limnology in proglacial Malaspina Lake, southeastern Alaska, in Glaciofluvial and Glaciolacustrine Sedimentation, A.V. Jopling and B.C. McDonald, eds., SEPM Special Pub. 23, Tulsa, p. 249-263. Harms, J.C., Southard, J.B., Spearing, D.R., and Walker, R.G., 1975, Depositional environments as interpreted from primary sedimentary structures and stratification sequences, Short Course #2, SEPM, Dallas, 161 p. Leverett, F., 1929, Moraines and shorelines of the Lake Superior basin, U.S. Geol. Survey, Prof. Paper 154-A, 72 p. Mengel, J.T., and Brown, B.E., 1976, Final report: red clay slope stability factors, Little Balsam Creek drainage, Douglas County, NW Wisconsin, U.S. E.P.A. and Red Clay Project# G-005140-01. Moss, C.M., 1977, The Surficial and Environmental Geology of the French River Quadrangle, St. Louis County, Minnesota: unpub. MS Thesis, University of Minnesota, Duluth, 69 p. 40 �Reineck, H.E., and Singh, I.B., 1973, Depositional Sedimentary Environments, Springer-Verlag: New York, 439 p. Schwartz, G.M., 1949, The geology of the Duluth metropolitan area, Minn. Geol. Survey Bull. 33, 136 p. Winchell, N.H., 1901, Glacial lakes of Minnesota, Geol. Soc. Amer. Bull., Vol. 12, p. 109-128. Wright, H.E., Jr., and Watts, W.A., 1969, Glacial and vegetational history of northeastern Minnesota: Minnesota Geological Survey, Spec. Publ. SP-11, p. 1-23. _ _ _ _ _ , 1972, Quaternary history of Minnesota, in The Geology of Minnesota: A Centennial Volume, P.K. Sims and G.B. Morey, eds., Minn. Geol. Survey, p. 515-547. Ice retreat and revegetation - - -Area, - - , in1976, Quaternary Stratigraphy of North in the Western Great Lakes America, W.C. Mahaney, Editor: Dowden, Hutchinson, and Ross, Inc., Stroudsburg, Pa. Zarth, R.J., 1977, The Quaternary geology of the Wrenshall and Frogner quadrangles, northeastern Minnesota: unpublished M.S. thesis, University of Minnesota, Duluth, 93 p. 41 �II! \ Ill I I I I Ii i ) 0 l\l Ol 1I111 \1111'. -.... ' s. c·. A. ,L, 'i'. 111 \I\ 111111111111 I11 \ ci 2 4 6 b-3 b-3 I;....., E-3 b3 j i\\ !\lli\\1\11. 111I L .. .. . ......... I ii I , B 10 MILES \ '\ □ -J DenhClJll.', s I I I I ' llll i l\llltl \ l!,., . 0 N (JI l\1AP OF A PART OF NORTI1 ~42 �' ,/ . ~- ,., ,, ...... ' ' ' ~~, ~ II ,. ," # I ... J11 47• io· ' &., . ,(o/ ..) ~v QI I Ol ,-. ..!..~~•:=~~ ~· •~ 1TASCA ca.f I l I ' I :f" QI p..i I 0 e: .~--.., :.,.-;::;_.;f...,,a..-i-:-..c_4-+_ _-,.._ _..,....--,-~f,;''7'-__; I S C A. L E ,o...,.,..,.;o.,.._..•0==20;..._.,;3.;0==40 m,1.. INDEX TO QUADRANGLES :,A STERN MINNESOTA SHo,vING l\'IAJOR GEOIVIORPHIC FEATURES From: Wright, H.E., Jr., and Watts, W.A., 1969, Glacial and Vegetational History of Northeastern Minnesota, Minn. Geol. Survey Special Publication No. 11, 59 p. 43 STUDIED �ROAD LOG AND STOP DESCRIPTIONS Mileage o.o 0.0 Start. Normandy Village, Superior St., Downtown Duluth. Proceed to 3rd Ave. W., turn right. Proceed 2 blocks to 2nd St. W. Turn right. Proceed to 10th Ave. E. Turn right and continue to London Rd. Turn left and proceed to Viking ship at Leif Erikson Park on Lake Superior. 1.5 1.5 STOP 1. Leif Erikson Park. Exposures along the waveeroded shoreline of Lake Superior show two different tills atop the striated and polished Keweenawan lava flows and interflow sediments. The unconformity between the Precambrian and Quaternary Systems encompasses over one billion years. Continue east on London Road 4.7 6.2 Lester River. Rocks are lava flows. A wellstriated whaleback is exposed at the mouth of the stream. The river is popular with smelt and steelhead fishermen. 0.5 6.7 Turn right onto Lake Superior Scenic Drive. Many miles of shoreline were given to the City of Duluth by the Congdon family to be developed as public recreational areas. Notice the effects of recent wave erosion. 2.3 9.0 City of Duluth Water Supply Plant. On the left is the newly constructed filtration plant necessitated by the high amounts of fine-textured fibrous amphiboles suspended in the lake water. Source of the minerals is a taconite (low grade iron ore) processing plant at Silver Bay, which disposes of tailings into Lake Superior. 0.5 9.5 STOP 2. Turn right into scenic pull-out near Duluth Tent and Trailer Camp. Proceed along path to Lake Shore. A variety of glacial sediments, including tills and possibly glaciolacustrine sediments, is exposed along the shore, resting atop lava flows of the North Shore Volcanics. Continue east on Scenic Drive 1.7 11.2 Turn left onto McQuade Rd. (St. Louis Co. Rd. 33) 44 �0.6 11.8 Intersection with Hwy 61 Expressway. Continue north on McQuade Rd. Exposures along the route are pebbly mud deposited in Glacial Lake Duluth. The road transects several flat benches that may be shoreline features. 2.9 14.7 Junction with Lismore Rd. McQuade Rd. 0.7 15.4 Continue north on STOP 3. Gravel pit on the right exposes a complex of cross-bedded outwash interpreted to be a delta constructed by a meltwater stream at its junction with Glacial Lake Duluth's highest stand in the area. Thin diamictons may be debris flows from high-standing ice-cored topography near the shoreline. Continue north on McQuade Rd. 0.9 16.3 STOP 4. Sucker River. Two tills exposed in the stream bank correlate with those along the Lake Shore. Here the upper, fine-textured till is far above the level of Lake Duluth, eliminating the possibility that it is of glaciolacustrine origin. Both tills contain a fabric resulting from the preferred orientation of elongate clasts. See general text for details. Make a U-turn carefully and return south on McQuade Rd. 3.5 19.8 Turn right onto Lismore Rd. 2.9 22.7 Outcrop on right is a coarse-textured felsic intrusive called "granophyre". In one view this rock type, which is common in the Duluth Complex, is a late-stage magmatic differentiate derived from basaltic magma during the crystallization of the Duluth gabbro. 3.4 26.1 Turn left onto Jean Duluth Rd. 5.2 31.3 Large outcrop of granophyre on right. 1.3 32.6 Intersection with Glenwood Ave. Duluth Rd. and Skyline Pkwy. 1.0 33.6 Turn left onto Woodland Ave. 0.1 33.7 Turn right onto Arrowhead Rd. 1.5 35.2 Turn left onto Kenwood Ave. 45 Continue on Jean �1.1 36.3 0.7 37.0 Turn right onto Skyline Pkwy. STOP 5. Turn left into parking lot of First Methodist Church. View of Duluth-Superior harbor. The outer natural barrier at the head of Lake Superior, called Minnesota and Wisconsin Point, is the largest fresh water bar in the world. Sand derived from till bluffs to the east along the south shore is moved to the lakehead by beach drifting. It began to form about 3,000 years ago. Segments of an inner bar are also visible. This feature was constructed during the slightly higher Nipissing level of the lake about 4,000 years ago. Continue west on Skyline Pkwy to Hwy 2. Numerous outcrops of gabbro along the route. 8.3 45.3 0.3 45.6 Junction Hwy 2. Proceed through intersection to Thompson Hill Information and Rest Area. Gabbro bedrock along Hwy 2 is abraded and plucked into whaleback forms. STOP 6. Thompson Hill Rest Area and lunch stop. Good views of the estuary of the St. Louis River. Very accessible are outcrops of the so-called layered series of the Duluth Complex, the result of episodic crystallization of different minerals in the magma chamber. Remember Bowen's reaction series? Exit on northeast side to Hwy 2 and Interstate 35 North. 2.1 47.7 Exit right onto Central Ave and Hwy 2. 0.2 47.9 Turn right onto Central Ave. 0.3 48.2 Stop sign. Turn right onto Raleigh St. 0.6 48.8 Stop sign. Turn left onto Grand Ave, and Hwy 23 8.0 56.8 Fond du Lac village limit. French fur traders were the first white men to see the "head of the lakes" region, about 1659. Twenty years later Daniel de Greysolon Sieur de Lhut raised the French flag on the shores of Lake Superior. In 1817 John Jacob Astor established one of his fur trading posts on the banks of the St. Louis River at Fond du Lac. 0.5 57.3 Junction Hwy 210. 0.5 57.8 Excavation on right exposes glaciolacustrine sediments associated with Glacial Lake Duluth. 46 Keep left on Hwy 23. �2.3 60.1 STOP 7. Turn right into scenic overlook. The St. Louis River and its tributaries have entrenched deep valleys into the sediments of Glacial Lake Duluth. Mass-wasting of the fine-grained sediments results in a distinctive rounded topography. Watch for bald eagles--an active aerie is a few miles upstream. Continue south on Hwy 23. (Following road log is approximated from topographic maps.) 1.7 61.8 Turn right onto Carlton Co. Rd 18 to Wrenshall. The route crosses the nearshore "continental shelf" of Lake Duluth. 2.2 64.0 Turn right into Wrenshall. 0.5 64.5 Turn left onto West Alcohol Rd. The route will climb gradually across nearshore glaciolacustrine sediments onto a hurmnocky bounding stagnation moraine, a part of the Thomson moraine. 1.3 65.8 STOP 8. West Alcohol Rd. gravel pit. Exposures show the sedimentary complexities of a moraine resulting from the stagnation and melting of dirty glacier ice. Return to Wrenshall 1.3 67.1 Turn left to Carlton. The lake plain narrows to a long embayment. Outcrops are Thomson Formation, a Middle Precambrian metasiltstone-slate. 4.2 71.3 Carlton. Continue north on Hwy 45. Numerous outcrops of Thomson Formation striking generally east-west in the form of miniature hogbacks (piggy backs?). 2.4 73.7 Junction Hwy 45 and I-35. Hwy 45. 0.3 74.0 Stop sign. Continue to Scanlon on Turn left on Hwy 45 toward Cloquet. Prepare for sharp left turn 0.3 74.3 Turn left onto Washington Ave. (Carlton Co. Rd. 16) 1.4 75.7 Junction Hwy 33. lane. 47 Turn right and proceed into left �0.3 76.0 Turn left onto service road fronting National Guard Armory, then right toward Armory entrance. 0.1 76.1 Stop sign. 0.4 76.5 Turn left into City of Cloquet Public Works Dept. gravel pit. 0.1 76.6 STOP 9. Cloquet esker. Gravel pit exposes the internal structure of the highest esker in Minnesota. See the Wrenshall Quadrangle topographic map. Mixed bedrock lithology suggests erosion of older tills before final deposition of esker gravel. Turn left to Pine Valley Park. Retrace route to Armory 0.5 77 .1 Turn left to Hwy 33 via service road to Pizza Hut. 0.2 77 .3 Turn left (north) onto Hwy 33. 0.7 78.0 Junction Hwy 33 and Hwy 45. Hwy 33. 0.1 78.1 St. Louis River. 0.9 79.0 Turn right onto North Rd (Carlton Co. Rd. 2) 1.7 80.7 STOP 10. Pit on left exposes the southeast end of a drumlin-like landform ascribed to the Automba phase of the Superior Lobe. Reworked clay displays slickensides produced by "drumlin-forming processes." Continue north on Continue east on County Rd 2 7.0 87.7 Junction Midway Rd (St. Louis Co. Rd 13). right to I-35. 1.9 89.6 Junction I-35. Turn left to I-35 northbound to Duluth. Rock outcrops are lava flows near the bottom of the North Shore Volcanics, of Late Precambrian age. 9.9 99.5 Exit from I-35 onto Superior St. in Duluth. 0.6 100.1 Normandy Inn. End of field trip. 48 Turn �DIAGRAM SUPPLEMENT TO ROAD LOG 8·12" LAKE CLAY 6• 10' UPPER LE t3 LE 5 TILL LC 4 LE 3 5-s' LOWER TILL LE 2 LE 1 lava flows Stratigraphic section at Leif Erickson Park; Duluth,Minnesota. S]%, S\'l¼, Sec. 23, T5ON, Rl4W. Textural composition of samples: LE 1, 34% sand, 45% silt, 21% clay; LE 2, 49% sand, 42% silt, 9% clay; LE 3, 39% sand, 43% silt, 18% clay; LE 4, 23% sand, 74% silt, 3% clay; LE 5, 20% sand, 65% silt, 15% clay; LE 6, 24% sand, 47% silt, 29% clay. c~ M., Moss, 1977 HIGHLAND MORAINE 1400' f ICI DISINTIOaAr I O N - - - - - - . flATUUS LAKI SUPERIOR ------? ---UPPU TIU LACUSUINI 7 Dll'OSITS ,===---------- ? =-----' DIAGRAMMATIC CROSS SECTION LOWU JILL IIDaOCIC • 49 FRENCH RIVER QUADRANGLE 1200' ? -- 1000' aoo' ooo' £LIV. C. M. Moss, 1977 �O lacustrine clay or silt Figure 12 • average, 22 samples Cl ccmpaci, pebbly clay Grain Si%e Oistri but ion in Lacustrine Deposits 0 0 □ □ Cl (C. M. Moss, 1977) 0 LO 1.1 1.2 0 1.3 A 0 0 Cl 0 C A A A A A 1. 4 1.5 l. 6 1.7 1.8 1.9 2.0 Bulk Density; g/cc FIGURE 14: Comparisons of bulk den3ities of glacial sediments: □ = pebbly, compact clay O= laminated or massive pebble-free clays A= sand- or silt-rich. till (C.M. Moss, 1977) 50 �INLAND AREAS L. SUPERIOR BASIN GLACIAL LAKE DULUTH PEBBLE•FREE CLAY DEPOSITION ICEBERGS -0- -- ------... , •o " a·· .. _ .- - RETREATING ICE ' DROPSTONES DEBRIS WASHED OR SLUMPED FROM ICE A M I XE D P £ 8 BL E • f REE CLAY & DROPS TONE DEPOSITS I RETREATING ICE DEBRIS SLUM PED ,FROM ICE .t B Model for deposition of clay facies in Glacial Lake Duluth. (A) earliest stages of deposition with material supplied from icebergs and retreating ice. Clays are carried away from the ice and are deposited in deeper water. (B) later stages of deposition; pebble-free clays continue to settle over slumped debris and icebergs drop coarser material over scattered areas. (Moss, C.M., 1977) 51 �FIGURE 15: Composite stratigraphic section for locations below 115or in French River quadrangle. {C. M; Moss, 1977) 0 360 I 0 270- Measurements of planar cross bedding in deltaic sands and gravels. Section 31; 'I'52N, Rl2W; 24 observations. (C. M. Moss, 1977) 52 �N25-2 N2S-1 Stratigraphic section, McQuade Road at Sucker River; SW 1/4, NW 1/4, Sec. 30, T 52 N, R 12 W ~d SE 1/4, NE 1/4, Sec. 25, T 52 N, R 13 W. Textural composition of samples: N 25-1, 32% sand, 44% silt, 24% clay; N 25-2, 26% sand, 46% silt, 28% clay. (C. M. Moss, 1977) ·"· . BAY-HEAD. BARS IN LAKE -SL'PERIOR Tilll La ke Superior DULUTH Aerial oblique map of the Duluth-Superior Harbor (From Loy, W. G., 1963, The Evolution of Bay-head Bars in Western Lake Superior, Publ. No. 10, Great Lakes Research Di¥ision, Univ. of Michigan) 53 �29? 1:1 295 m SILT-FINE SANO 290 m CLAY SILTY CLAY WITH SILT LAYERS 285 nt CLAY, MASSIVE 280 m CLAY WITH SILT LAYERS 275 m SANDY GRAVEL GRAVELY CLAY SANO 270 CLAY WITH PEBBLES Ill SANO, i-lEDIUM 265 m SILT-;INE SAND WITH CLAY LAMINAE 260 m f,AMINATEO CLAY AND SILT ~55 m HNE SAND 250 m ----------------------------------------------------- CLAYEY SILT SILTY CLAY WITH PEBBLES Wayside Rest, Esko Quadrangle, SW 1/4, SW 1/4, Sec. 13, T 48 N, R 16 W. (Zarth, R. J., 1977) \ ' I ~ \'-----. ..___ Striated bedrock from I-35 Thomson Fm outcrop. Sketc- =C from photograph. North is towards to~ of figure; scale ~s approx. 1.5. --- J ~fi / ) Y,1 1 (A. Norton) � 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, 1979 Description An account of the resource Institute on Lake Superior Geology. University of Minnesota, Duluth, Minnesota. May 8-12, 1979. 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 1979 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/47fb6d5d027e7e529543644a84d9e3f3.pdf 2e63fed116258cab9c6032555b496100 PDF Text Text �PROCEEDINGS AND AND ABSTRACTS ABSTRACTS PROCEEDINGS the for the 26th 26th ANNUAL ANNUAL INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY held held at THE DAVIES CENTER CENTER THE DAVIES UNIVERSITY UNIVERSITY OF OF WISCONSIN WISCONSIN -- EAU EAU CLAIRE CLAIRE May May 66 -- 10, 10, 1980 1980 sponsored by sponsored by The University University of Wisconsin The Wisconsin - Eau Eau Claire E. Myers Program Paul E. Myers Program Chairman Chairmanand andEditor, Editor, Paul Activities Chairman, Nancy Nancy Jo Activities Chairman, Jo Pickett Geology Geology Department Department University of of Wisconsin Wisconsin - Eau Eau Claire �SALES SALES Proceedingsand andAbstracts Abstractsand andfield field trip Proceedings tripguidebooks guidebooks may be purchased purchased (@ (@$5.00 $5.00each eachU.S.) U.S.) from may be from the the Depart-. Depart- ment of Geology, University of Claire, ment of Geology, University of Wisconsin-Eau Wisconsin-Eau Claire, Eau Claire, Claire, WI checks or money Eau WI 54701. Make Make checks money orders payable to to 26th Institute on payable 26th Annual Annual Institute on Lake Lake Superior Superior Geology. Field trip tripguide guidebooks booksmay may also also be be purchased purchased from from the the Wisconsin History Survey, Survey, PubPubWisconsin Geological Geological and and Natural Natural History lications Sales lications Sales Division, Division,1815 1815University UniversityAvenue, Avenue,MadMadison, WI WI 53706. i-Ili �Of' COTTS TAL Or Dedi cati on Dedication • General Information Informationand andAcknowledgments Acknowledgments General iv iv Vi vi Directors Board Board of Directors 11 SessionChairmen Chairmen Technical Session 2 2 Activity ActivitySchedule Schedul e 3 3 Schedule Schedu 1e of Papers Papers 4 4 Abstracts 9 9 Poster Papers Papers 65 Index 75 111 iii �DEDICATION DEDICATION Ralph will thismonth, month, May May 1980, 1980, as as Professor Professor of of Ralph W. W.Marsden Marsden willretire retire this only his Geology atat the ofMinnesota, Minnesota, Duluth. Duluth. Duluth Duluth has has been been only Geology the University of most recent long career careerdevoted devoted totomining miningand and geology. geology. Because most recent stop stop in aa long Ralph on Lake Lake Superior Superior Ralph has haslong long been beena astaunch staunchsupporter supporterofofthe the Institute Institute on Geology sinceits its inception friend of Geology since inception in in 1955, 1955, and and because because heheisisaa friend of every every geologist geologist in in the the Lake Lake Superior Superior region, region, this this volume volume is is dedicated dedicated to to him. him. Ralph geology degrees of Wisconsin, Wisconsin, Ralph received received his his geology degreesfrom fromthe the University University of He then thenwent wenttoto the the Philippines as completing his graduate graduate work work in 1939. 1939. He as completing a as Chief Chief of of the Geological Division of the a geologist and and served served as Geological Survey Survey Division the Unfortunately, the the last Philippine Bureau Bureau of ofMines Mines from from 1940 1940 to to 1945. 1945. Unfortunately, Philippine three years in this role were served in civilian internment camps three years this role were served in civilian internment campsunder under guidance of of the theJapanese. Japanese. the guidance After aa few few years years with with the theJones Jones &&Laughlin Laughlin Steel Steel Corporation, Corporation, he he moved to the United States Steel Corporation. He became manager of Geomoved to the United States Steel Corporation. He became manager of GeoInvestigations in in 1953, 1953, aa post post he he retained retained for 11 11 years years until he he logical Investigations became manager of ofU.S. became manager U.S.Steel·s Steel 'siron iron ore ore operations. Ralph has haslong long had hadaa love love for Ralph for academia, academia, having having taught taught at atWisconsin Wisconsin while student, at the while aa graduate graduate student, the University UniversityofofOklahoma Oklahoma for one one year, and the Internment Internment Camp Camp School 1967 the and even evenin in the Schoolininthe the Philippines. Philippines. In 1967 University of of Minnesota, Minnesota, Duluth, Duluth, was was able him back back to the uniuniable to to entice him to the versity vers ity environment. envi ronment. He He served the Geology Geology Department Depa rtment for served as as head headof of the for 77 years, leading it italong along aa path path of ofspecialization specializationininPrecambrian Precambrian studies. studies. years, leading Ralph has as one one of ofthe themost mostknowledgeable knowledgeable "iron "ironmen" men" Ralph has aa reputation as Foreign governments, the United Foreign governments, the United Nations and foreign companies companies have have sought advice. His knowknowNations and several several foreign sought his his advice. ledge ores, and and especially especially those those of of the theLake Lake Superior Superior region, region, ledge of of iron ores, is encyclopedic. encyclopedic. His His latest latest major major undertaking undertaking was was aa review reviewof of the the iron ore Wisconsinfor for the U.S. ore reserves reserves of of Minnesota Minnesota and and Wisconsin U.S. Bureau Bureau of Mines, Mines, aa knowsRalph Ralphrealizes realizes that project recently recentlycompleted. completed. Yet, everyone everyone who who knows his expertise is far broader broader than he is inhis expertise is far, far than his his specialization, specialization, for for he is indeedaageologist geologistinIn all all respects. deed respects. the world, world, and and is widely widely traveled. traveled. in the He served the AIN1E AIME and asaswell He has has long long served andSEG, SEG, wellasasother other professional perspective, his organizations, in in aa number number of His broad broad perspective, his organizations, of capacities. His unimpeachable integrity, and his steady hand hand are unimpeachable integrity, and his steady are appreciated appreciated by by all. all The fortunate Ralph's prespresThe ILSG ILSGhas hasbeen been fortunatetotohave havehad hadthe thebenefit benefit of of Ralph's ence and entireexistence, existence,and andwe weknow know we we shall enjoy enjoy ence andsupport supportfor for its its entire that benefit benefitforfor manymore more years years totocome. come. Remember, Remember, Ralph, many Ralph,that that with an ILSG volumededicated dedicated you,you youcannot cannoteasily easilyforget forget this this unique an ILSG volume to toyou, unique We thank thank of which which you you have have long been been an organization of an important important part. We you! iv �Dr. Ralph Ralph W. W. Marsden Marsderi v V �GENERAL INFORMATION GENERAL INFORMATIONAND ANDACKNOWLEDGEMENTS ACKNOWLEDGEMENTS We welcome This is our first, first,but buthopefully hopefully not not We welcomeyou youtoto Eau EauClaire. Claire. This is our Wehope hopeyou youenjoy enjoy yourselves and attempt at at playing playing host host totoILSG. ILSG. We and last attempt return with others others to tohelp helpususcontinue continue our ourstudies studiesofofthe thePrecambrian Precambrian return geology the region. region. geology of of the We haveattempted attemptedtoto make makeyour yourstay stay here here as as convenient convenient as as possible. We have The excellent conference facilities ofof thethe Davies The excellent conference facilities DaviesCenter Centerhave havebeen been gengenerously provided provided by by the the University of erously of Wisconsin Wisconsin - Eau Eau Claire. All arrangements arrangements for space, space, food, food, and and transportation transportationwere werehandled handled by Nancy Pickett. Students by Nancy JoJo Pickett. theGeology GeologyDepartment Department Students and arid faculty faculty ofofthe have donatedmuch muchtime timeand andeffort effort to assure have donated assure the the success success ofofthe theconfer— conference. Manuscripts were typed typed by Hoitomt and and Gail Gail Wirz. Coordinator Manuscripts were by Penny Penny Hoitomt visual aids aidsisisDr.Dr.James James Wilson. Wilson. of visual of WisconWisconConference Conferencevehicles vehicles have havebeen beenprovided providedbybythe theUniversity University of - Oshkosh, Survey, the the sin — Oshkosh,the the Wisconsin WisconsinGeological Geologicaland andNatural Natural History History Survey, University Center Valley, at andby by the the University University Center System, System, Fox Fox Valley, at Menasha, Menasha, and of Wisconsin Special thanks thanksare aredue due thefield field trip trip Wisconsin - Eau Eau Claire. Special to tothe leaders: Randy Maas, Manmohan leaders:Michael MichaelCumings, Cummings, Randy Maas, ManmohanSood, Sood,Randy RandyVan Van Schmus, Schmus, and Stephanie Wurdinger. and Wurdinger. have had had the enthusiastic support support ofofcolleagues colleagues and and ILSG ILSG friends I have the enthusiastic havehelped helpedmake makethe thejob throughout the and region. region. You You have ..job easier. throughout the state and Thankyou you a11 all Thank ~ E. Myers Paul E. Myers Conference Director Conference Director vi �26th 26thANNUAL ANNUAL INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY sponsored by sponsored by University of ofWisconsin Wisconsin - Eau Eau Claire Eau Claire, WI Eau Claire, WI 54701 May 10, 1980 1980 May66 -- 10, INSTITUTE INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS D. D. M. M. Davidson, Davidson, Jr., Jr.,Department Department of ofGeological Geological Sciences Sciences University of Paso, Texas ofTexas, Texas, El El Paso, Paso, El El Paso, Texas (1979) (1979) M.F. Kehlenbeck, M.F. Kehlenbeck, Department Department of of Geology Geology Lakehead University, Thunder Bay, Ontario (1977) Lakehead University, Thunder Bay, (1977) G. of Geological G. Mursky, Mursky, Department Department of Geological Sciences Sciences University University ofofWisconsin, ~Iisconsin,Milwaukee, Milwaukee, Wisconsin t~isconsin (1978) (1978) P.E. Myers, Myers, Department Department of of Geology Geology P.E. University University ofofWisconsin, Wisconsin, Eau Eau Claire, Claire,Wisconsin Wisconsin (1980) (1980) R. C. Reed, Reed, Geological Survey Division R. C. Geological Survey Dept. of Dept. ofNatural NaturalResources, Resources,Lansing, Lansing,Michigan Michigan(Permanent (PermanentMember) Member) M. M. Walton, Walton, Minnesota Minnesota Geological Survey Survey University ofofMinnesota, University Minnesota, Minneapolis, Minneapolis,Minnesota Minnesota (1976) (1976) 1. �TWENTY-SIXTH ANNUAL MEETING MEETING TWENTY-SIXTH ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY -- 1980 1980 INSTITUTE TECHNICAL SESSION CHAIRMEN CHAIRMEN TECHNICAL SESSION Bruce Brown Brown Dr. Bruce Wisconsin Geological History Survey Survey Wisconsin Geological and and Natural Natural History 1815 Avenue 1815 University University Avenue Madison, WI WI 53706 Dr. Dr. William William S.S. Cordua Cordua Department of and Earth Earth Sciences Sciences Department of Plant and University of ofWisconsin Wisconsin River River Falls, Falls, WI WI 54022 Dr. I. Smith Dr. Eugene Eugene I. Smith Division ofofScience, Science,Earth EarthScience ScienceProgram Program University of of Wisconsin Wisconsin - Parkside Parkside Kenosha, WI Kenosha, WI 53141 53141 Dr. Donald Davidson, Jr. Jr. Dr. Donald M. M. Davidson, Departmentof of Geological Department Geological Sciences Sciences University of ofTexas Texas at at ElE1 Paso Paso El E1 Paso, Paso, TX TX 79968 Dr. Jeff Dr. JeffGreenberg Greenberg Wisconsin Geological and and Natural Natural History HistorySurvey Survey Wisconsin Geological 1815 University University Avenue 1815 Avenue Madison, WI WI 53706 Dr. Gene Gene LaBerge LaBerge Department of Geology Department of Geology University University ofofWisconsin Wisconsin Oshkosh, WI WI 54901 Dr. Michael Michael Mudrey Mudrey Dr. Wisconsin Survey Wisconsin Geological Geological and and Natural Natural History Survey 1815 University Avenue 1815 University Avenue Madison, WI WI 53706 Richard Ojakangas Ojakangas Dr. Richard Geology Department Department of Geology University of ofMinnesota Minnesota Duluth,MN MN 55812 55812 Duluth, 2. �TWENTY-SIXTH TWENTY-SIXTH ANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY ACTIVITY ACTIVITYSCHEDULE SCHEDULE TUE, MAY 66 TUE, MAY a.m. 8:00 a.m. FIELD TRIP TRIP #1, CHIPPEWA VALLEY: Departurefrom from north north FIELD CHIPPEWA VALLEY: Departure entrance, entrance, Davies Davies Center, Center, University UniversityofofWisconsln-Eau Wisconsin-Eau Overnight in in Eau Eau Claire Claire(accommodations (accommodations not Claire. Overnight included included in in fee). WED, MAY 77 WED, MAY 8:00 a.m. a.m. FIELD CHIPPEWA VALLEY--DAY 2: 2:Departure FIELD TRIP TRIP #1, CHIPPEWA VALLEY--DAY Departure from north entrance, entrance, Davies Davies Center. Center. Return Return at 5:30 5:30 p.m. p.m. 7:00 a.m. a.m. THU, MAY 88 THU, MAY FRI, MAY MAY 99 FIELD TRIP TRIP #2, #2, BLACK RIVERVALLEY: VALLEY: Departurefrom fromfront front FIELD BLACK RIVER Departure Return Return by by entrance, Midway Midway Motor Motor Lodge, Lodge, Eau Eau Claire. Claire. 6:00 p.m. p.m. 4:00 p.m. p.m. REGISTRATION BEGINS: WillowLounge, Lounge,Davies Davies Center, UWREGISTRATION BEGINS: Willow UWEau closes at at 10:00 10:00 p.m. p.m. Eau Claire. Claire. Registration closes p.m. 7:00 p.m. SMOKER: SMOKER: 8:15 a.m. a.m. TECHNICAL SESSIONS I AND Council Fire Fire Room, TECHNICAL SESSIONS I AND II: II:Council Room, Davies Davies Center, 8:15 8:15 a.m.-12:O0, a.m.-12:00, and and 1:40-5:00 1:40-5:00 p.m. p.m. Center, 8:45 a.m. a.m. POSTER SESSIONS: Alumni Room, Davies Center, p.m. POSTER SESSIONS: Alumni Room, Davies Center,toto 5:00 5:00 p.m. 7:00 p.m. p.m. CASH BAR: Blackhawk Lounge, Davies Center,until until 7:00 CASH BAR: Blackhawk Lounge, Davies Center, 7:00 p.m. p.m. 8:00 p.m. 800 p.m. ANNUAL Council Room, Davies Davies ANNIJALINSTITUTE INSTITUTEBANQUET: BANQUET: CouncilFire Fire Room, Dr. Ralph Marsden,University University of Center. Speaker, Speaker, Dr. Ralph Marsden, Minnesota -- Duluth. Minnesota Duluth. 8:00 a.m. a.m. TECHNICAL SESSIONS AND Council Fire Fire Room, TECHNICAL SESSIONS III III AND IV:IV:Council Room, Davies Davies Center, 8:00-12:00 and and 1:20-5:00 1:20-5:00 p.m. p.m. Center, 8:00-12:00 8:45 a.m. a.m. POSTER POSTER SESSIONS: Ojibwa Room, Davies Center, UW-EC Ojibwa Room, Davies UW-EC toto 10:00 p.m. p.m. Alumni DaviesCenter Center to to 3:00 Alumni Room, Room, Davies 3:00 p.m. p.m. 12:15 p.m. p.m. SYMPOSIUM LUNCHEON LUNCHEONFOR FORAUTHORS AUTHORSAND ANDCOORDINATORS: COORDINATORS:PresPresSYMPOSIUM ident's Room ($2.00) ($2.00) ident's Room 3:20 p.m. p.m. PRESENTATION PAPER AWARD: Council PRESENTATIONOFOFBEST BESTSTUDENT STUDENT PAPER AWARD: CouncilFire Fire Room, Room, Davies Davies Center. 6:00 p.m. p.m. CARAVAN DEPARTURE WAUSAU--FIELD AND 4: 4: CARAVAN DEPARTUREFOR FOR WAUSAU--FIELDTRIPS TRIPS33 AND Entrance, Davies DaviesCenter, Center,UW-EC UW-EC North Entrance, — SAT, MAY 7:30 a.m. SAT, MAY 10 10 7:30 a.m. 8:00 a.m. a.m. FIELD TRIP WAUSAU SYENITE: Departure Boy FIELD TRIP #3, WAUSAU SYENITE: Departurefrom from Big Boy Restaurant ofRoutes Routes 29 29 and and U.S. U.S. 51. 51. Restaurant near near intersection intersection of Return restaurant for lunch lunch at at noon. noon. Participants Returnto to the the restaurant will return the trip. trip. will returntotothe therestaurant restaurantupon upon completion completion ofof the FIELD TRIP TRIP #4, COUNTY: Departurefrom from Holiday Holiday FIELD #4, MARATHON MARATHON COUNTY: Departure Inn, Wausau, Wausau, WI. WI. Return Returnthere thereatat end endofof trip. trip. Shuttle bus will be available to to take take participants participants toto Centrdl Centil bus will be available Wisconsin Airport Airport at Wisconsin atMosinee. Mosinee. 3. �SCHEDULE OF OF PAPERS PAPERS SCHEDULE SESSION SESSION II Thursday, May Thursday, May 8, 1980 1980 Morning ~rning Session Session PRECAMBRIAN GEOLOGY GEOLOGY Co—chairmen: Co-chairmen: 8:15 8:20 8:40 D.M. D.M. D<lvidson. Davidson,Jr. Jr. and and R.R. Ojakangas Ojakanq P.E. Myers Myers Opening remarks Opening remarks *B. Van Van de de Voorde Voorde && *6. P. P. Ervin Ervin N.M. M.M. Kehienbeck Kehlenbeck Geophysical study of aaPrecambrian Precambrian Geophysical study of boundary in Minnesota boundary Minneso~ Regional structure,metamorphism metamorphism and and Regional structure, stratigraphy of of the theQuetico Quetico Gneiss Gneiss Belt, Thunder Bay, Ontario Thunder Bay, 9:00 *R.S. Maass, Maass, 9:20 *J.'; . Goodge Migmatites from Granitic Migmatites from the the Vermilion Vermilion Granitic Complex, Minnesota CompleK, Minnesota 9:40 9:40 A. Fleming, Fleming, A. M. "C. Heinz, Heinz, R. Lee R. Lee && H. H. Woodard Wloodard Geology of the southeastern Geology of southeastern contact contact zone zone of the the Vermilion Vermilion batholith, batholith,Minnesota Minnesota *K.H. Poulsen Poulsen && M.M. Kehienbeck "I,M. Kehlenbeck Overturned Archean Archean successions successionsand andtheir their Overturned significance 10:00 10:00 • Medaris, J, L.G. Jr.. & L.G. Medaris, W.R. Van W.R. Schmus V" Schmus 10:20 Coffee Break Break 10:40 10:40 *C.N. Brandon, Brandon, EoI. Smith smith && E.I. F.R. F.R. Luther Luther Archean andEarly Early Proterozoic Proterozoic tectonic Archean and ofnorth—central north-central Wisconsin history of isconsin The Precambrian PrecambrianWaterloo Waterlooquartzite, quartzlte, The southeastern southeastern Wisconsin: Wisconsin: evolution evolution and and significance 1l:00 11:00 E.t. Eo!. Smith Smith Rare earth element the elementdistribution distribution in the Rare Precambrianrhyolites rhyolites and and granites granites of Precambrian south—central Wisconsin Wisconsin south-central 11:20 1l:20 M.L. Cummings Cunmings Geochemistry andvolcanic volcanicstratigraphy stratigraphy of Geochemistry and of west-central ~est·central Marinette MarinetteCounty, County, Wisconsin Wisconsin 11:40 11:40 W.F. W.F. Cannon Cannon && M.G. M.G. Mudrey Mudrey Where Where isis the the source sourceof of Wisconsin Wisconsindrift drift diamonds? di amnds? There ~ill be aaluncheon luncheon r:eetjng meeting of of the theBoard Board There will be of Directors Directorsininthe theHeritage HeritageRoom, Room, Davies Davies Center Center * student student paper paper 4. �SESSION SESSION III! May 8, 1980 1980 Thursday, May Thursday, Afternoon Session Session PRECAMBRIAN GEOLOGY GEOLOGY Co-chairmen: 1:40 1: 40 Greenberg and and 6. G. LaBerge LaBerge J. Greenberg V.W. V.W. Chandler Chandler Correlation of and ofgravity gravity andmagnetic magneticanomalies anomalies in east-central east-centralMinnesota Minnesota and and northwestern northwestern Wisconsin <Ii sconsi n 2:00 2:00 *R.S *R.S. Maass Maass &~ L.G. L.G. Medaris, Medaris, Jr. Metavolcanic rocks rocksat at Eau Claire Dells, Eau Claire Oells, Metavolcanic Marathon MarathonCounty, County,and andananevaluation evaluation of the zone" hypothesis hypothesis infnWisconsin :.Iisconsfn the "shear "shear zone" 2:20 ILL. LaBerge G.L. LaBerge Were there two Middle Mfddle Precarthrian Precambrian orogenies orogenies Were there two 2:40 2:40 MA.. M.L. CurFillings Ctlllt1lings Volcanic plutonic rocks Volcanic and and plutonic rocks ofofthe theJump Jump and and Yellow River Valleys, north-central Yellow River north-centralWisconsin Wisconsin 3:00 Coffee Break Break 3:20 *1. *T. Ernst, Ernst, J. Markert Markert &to M. M. Montz Montz In the the Lake lake Superior Superior region? region? in Heavy ofPrecambrian Precambrian rocks rocks Heavymineral mineral analysis analysis of in Rusk Rusk County, County, Wisconsin Wisconsin 3:40 P.A. P.A. Daniels Daniels &to Depositional setting of Depositional ofaastromatolite— stromatoliteacute alluvial fan oolite facies faciesonona aKeweenawan Keweenawan alluvial fan 4:00 R.J. Shegelskl R.J. Shegelski Stratigraphy Stratigraphy of the the Gunflint GunflintFormation, Formation, Current River River area, area, Thunder Thunder Bay 8ay 4:20 N.W. N.W. Jones Jones Petrology of some Logandiabase diabasesills sills from Petrology some LOgan from Cook Minnesota Cook County, County, Minnesota D.R. D.R. Elmore EllOOre 4:40 *P. Morton 5:00 Adjourn sills Differentiating ultramafic ultrall\lfic flows flows from from sills in the Mine area, area, northwestern theShebandowan Shebandowan Mine northwestern Canada Ontario. Ontario, Canada 5. �SESSION III SESSION III Friday, Friday, May May 9, 9, 1980 1980 Morning Session SYMPOSIUM BASIN - -AA REVIE~ SYMPOSIUM- -TECTONIC TECTONICHISTORY HISTORYOFOFTHE THELAKE LAKESUPERIOR SUPERIOR BASIN REVIE Coordinator: Co-chairmen: ~. W. Richard Wold Richard J. Wold Cordua Smith Cordua and and E. E. Smith 8:00 J, . Dii. D.M. Davidson, Oavj dson, Jr. Geological evidencerelating relatingtoto the the interpreGeolo9ical evidence tation of of the theLake Lake Superior Superior basin basin structure 8:20 J.S. asner, J.S, Kl Klasner, The Pre-Keweenawan tectonichistory history of of the The Pre-Keweenawan tectonic the north-central United and central central United States States and Canada andhow how influenced formation formation of Canada and it itinfluenced Mid-Continent Rift the Mid—Continent Rift W.r. Cannon && W.F. Cannon W.R. W.R. Van Schnius Schmus 8:40 8:40 J.C. Green Green Keweenawan volcanism Keweenawan volcanismand andthe thenature nature of of Keweenawan rift Keweenawan rift tectonics tectonics 9: 00 9:00 R.W. R.W. Ojakangas, ~ak.angas , Upper Precambrian the Upper Precambriansedimentary sedimentaryrocks rocksof of the Lake Superior region region Lake G.B. G. B. Morey, rey, P.A. .A. Daniels && P Kalliokoski J. Kal1iokosk.i 9:20 Geochronology of Keweenawan rocks: Geochronology of Keweenawan rocks: aa review W.R. Van Schmus, M. R. Van Schmus, Green && J.C. J. C. Green H.C. Hallss Hall 9:40 Break Coffee Break 10:00 10:00 W.J. W.J. Hinze, Hinze, R.J. Wold Wold && and magnetic magnetic anomaly anomaly studies Gravity and studies of Lake Superior Lake 10:20 10: 20 V.W. V. W. Chandler, P.L. P.L. Boman, Boman, W.J. Hinze && W.J. Hlnze N.W. N. W. O'Hara Long wavelength gravity gravity and Long wavelength and magnetic magnetic anomalies anomalies of the theLake Lake Superior SuperiorRegion Region of 10:40 J . H. Luetgert Luetgert && J.H. R.P. Meyer Meyer Seismic refraction studies Seismic refraction studies of ofLake Lake Superior Superior structures crustal structures 11:00 ll:OO R.J. R,J. Wold, Wol d, D.R. O. R. Hutchinson Hutchinson & T.C. Johnson Johnson Topography and surficial structure of Topography and surficial of_ake lake Superior basedononseismic seismicreflection reflection Superior bedrock bedrock based profiles 11:20 J.H. Karl, J.H. Karl, M.P. M. P. Bernardin, R.P. R. P. Meyer, Meyer, M.E. M. E. Bengtson Bengtson & H.C. H. C. Halls Hall s Geophysical studies Islands, Geophysical studiesof of the the Slate Slate Islands, Lake lake Superior N.W. N.W. O'Hara O'Hara , • 6. �SESSION III III (CONTINUED) SESSION (CONTINUED) 11:40 12:00 12:15 12: 15 Lake Superior Superior red clay l6ke clay niineralogy: mineralogy:car— cor· relation relationwith withmechanical mechaniC61 behavior behavior J.T. J. T. Mengel Mengel && B.E. B.t. Brown Brown P61eomagnetism of ofKeweenawan Keweenawan rocks rocks Paleomagnetism I#J.C. t1 •• C, Halls && L.J. L.J. Pesonen Pesonen Adjourn lunch Adjourn for for lunch There Symposium Luncheon 6nd coordinators coordin6tors There will will bebea aSymposium Luncheonfor for 6uthors authors and at 12:20 the Davies 0avis Center 12:20 p.m. p.m. in in the the Presidents Presidents Room Room ofof the Center ($2.00) ($l.OO) I'd SESSION IV Friday, May May 9, 9, 1980 1980 Afternoon Session Session GENERAL GENERAL Co—chairmen: Co-chairmen: 8. B. Brown Brown and and M. M. Mudrey Mudrey 1: 20 1:20 *T.J. Grundi, Grundl, E.C. Perry, Perry, Jr. && LC. R.H. R.H. Gilkeson Gllkeson Stable isotope tracer Stable tracerstudies studiesIninthetheCantro— Cambro· Ordovicianaquifer aquiferofofnorthern northernIllinois Illinois Ordovician 1:40 1: 40 *L.I. Kelley & *L.I. Kelley" F.R. F.R. Karner Kamer Kaoliniticweathering weatheringzone zoneononPrecambrian Precambrian Kaolinitic basement of southeastern North North Dakota Dakota and and basement of western Minnesota Minnesota 2:00 W.R. ifI.R. Rehfeldt Hydrogeologic investigationsatataalandfl'l landfill Hydrogeologic investi~6tions site in in the the red red till till(Valderan) {Valderan) region region of eastern Wisconsin Wisconsin 2:20 T.D. Vick T.O. Vick Seismic survey surveyofof aa i:lJried bjried river Seismic riverchannel channel 2:40 3:00 *W.M. Lucko &" kW.M. S.A. S.A. Kissin Kissin The Quetico gneiss The pegmatites pegmatitesofof the the Quetico gneiss belt, belt, northwestern Ont6rio, and their theiruranium uranium northwestern Ontario, and potential COffeeBreak Break— also - also BEST STUDENT PAPERAWARD AWARD Coffee BEST STUDENT PAPER CASH PRIZE PRIZE $200 CASH SYMPOSIUM SYMPOSIUM -—URANIUM URANIHfl IN IN WISCONSIN WISCONSIN AND AND THE THE UPPER UPPER MIDWEST [DWEST CD\ I INUED ON CONTINUED ON NEXT NEXT PAGE PAGE 7. 7. �SYMPOSIUM URANIUMIN IN WISCONSIN SYMPOSIUM·—URANIUM WISCONSIN AND AND THE THE IPPER UPPERMIDWEST MIDWEST Coordinator: M.G. M.G. Niudrey, Mudrey, Jr. Jr. 3:20 G. Mursky G. Mursky Relationship of ofCanadian Canadian uranium uranium deposits deposits to to the the geologic geologic setting settingofofWisconsin Wisconsin 3:40 J.K. J. K. Greenberg Greenberg Uranium provinces: Uranium provinces:enrichment enrichmentinin granitic granitic rocks relations totoWisconsin rocks and and relations Wisconsin 4:00 W.B. Coker && W.B. Coker J.M. J.M. Franklin Franklin Regional Regional geochemistry geochemistry and and metallogeny metallogeny 4:20 J.J. J.J.Mancuso Mancuso && R.H. Motten R.H. Motten Geology of the Geology of the NicCaslin McCaslin Range, Range, northeastern Wisconsin 4:40 T.J. T.J. Evans, Evans, J.K. Greenberg Greenberg && M.G. Mudrey, Mudrey, Jr. M.G. isconsin Wisconsin interest interestin1nradiological radiologicalimpacts impacts from uranium uranium exploration resulting from exploration(drilling) (drilling) 5:00 5:00 Adjourn lake Superior, Ontario Ontario north shore shore of Lake north 8. �This page has no number in original. Appears between 8 and 9 ABSTRACTS �GEOPHYSICAL STIJDY GEOPHYSICAL STUDY OF OF AAPRECAMBRIAN PRECAMBRIANBOUNDARY BOUNDARY IN MINNESOTA MINNESOTA IN Barbara VanDeVoorde aridC.C.Patrick Patrick Ervin Barbara VanDeVoorde and Department of Geology Department Geology Northern University NorthernIllinois Illinois University DeKaib,Illinois Illinois 60115 DeKalb, West-central West-central Minnesota Minnesotaisis divided divided by by aa northeasterly northeasterly trending trendingboundary boundary an older older gneiss terrane to the separating two Early Early Precambrian Precambrian terranes: an gneiss terrane the separating two south south and and aa younger youngergranite-greenstone granite.-greenstoneterrane terranetoto the the north. The The nature, location, and and origin of ofthis thisboundary boundary is is aamatter matter of ofconjecture. conjecture. During of 1979, 1979, COCORP a deep-crustal,sei seismic reflecDuri ng the summer summer of COCORP ran ran a deep-crustal, smi c refl ecMinnesota Geological Survey tion profile profileacross acrossthe theboundary. boundary. The The Minnesota Survey conducted conducted a gravity survey utilizing the a concurrent concurrent gravity survey utilizing theelevation elevationpoints pointssurveyed surveyed by by the the crew. A corresponding should be be completed completed seismic crew. corresponding aeromagnetic aeromagneticprofile profile should before meeting. before this meeting. This discuss only This paper paperwill will discuss only the the modeling modelingofofthe thegravitational gravitationalfield, field, which is bei-ng using a two-dimensional modeling algorithm. algorithm. which being done done using two-dimensional modeling 9. �REGIONAL STRUCTURE, AND STRATIGRAPHY REGIOI~AL STRUCTURE, METAMORPHISM METAMORPHISM AND STRATIGRAPHY OF OF THE THE QUETICO GNEISS BELT, THUNDER QUETICO GNEISS THUNDER BAY, ONTARIO ONTARIO M.M. Kehienbeck M.M. Kehlenbeck Fold axes Structurally therocks rocksform formaacomplex complex domical domical feature. Fold axes plunge plunge Structurally the gently andaxial axial surfaces surfacestrend trendparallel parallel to the gently to the the east east or or west, west,and the long long axis axis of the thedome. dome. Metamorphic mineralsare aredistributed distributed in zones which parallel the Metamorphic minerals zones which thedomindominant planar gradeincreases increases from from greenschist greenschist facies ant planar structures, structures,and and metamorphic metamorphic grade on the margins granulite fades on the margins toto granulite facies near near the the center centerofofthe thedome. dome. In several several places places near near the center of the the structure structureevidence evidence indicates indicates In the center that rocks rocks become become younger and south. south. younger toward toward the the north and Boundarieswith with the Wabigoon Belt to the Belt to Wabigoon Belt the north northand andShebandowan Shebandowan Belt Boundaries the south south are are transitional. transitional. the 10. �ARCHEAN AND AND EARLY EARLY PROTEROZOIC TECTONIC HISTORY ARCHEAN PROTEROZOIC TECTONIC HISTORY OF OF NORTH-CENTRAL NORTH-CENTRAL WISCONSIN WISCONSIN R.S. Maass Maass and R.S. andL.G. L.G. Medaris, Medaris, Jr. Department Geology and and Geophysics Geophysics Department of Geology University ofWisconsin Wisconsin University of Madison, WI 53706 53706 Madison, WI W.R. Van W.R. Van Schmus Schmus Department Department of Geology Geology University Kansas University ofofKansas Lawrence, Kansas Kansas 66044 Four field seasons anddetailed detailedstructural structural studies Four field seasons of reconnaissance reconnaissance and studies cocoordinated with geochronologic in portions investigation have have been been undertaken undertaken in ordinated geochronologic investigation of Waupaca, Waupaca, Portage, Wood, Jackson, Eau Claire, Claire,Chippewa, Chippewa, Marathon, Marathon, Portage, Wood, Jackson, Clark, Clark, Eau Lincoln, and and Price Price counties counties ininan an attempt attempttotodecipher decipherthe theArchean Archean and and Early Early Proterozoic tectonic history of ofnorth-central north-centralWisconsin. Wisconsin. Proterozoic tectonic Archean gneisses been identified in Portage, Portage, Archean gneissesand andmiqmatites migmatiteshave have been identifiedsosofar far in Wood,Jackson, Jackson,and andClark Clark counties. Gneisses Wood, Gneisses containing in containingsimilar similar structures structures in Waupaca Claire countiesare arealso alsobelieved believed to to be in age, Waupaca andand EauEau Claire counties be Archean Archean in age, although although zircons from the Eau Claire county countylocality locality yield from the Eau Claire yieldan an Early Early Proterozoic Proterozoic age. age. zircons This This unit isis one one of of the the most most thoroughly thoroughly recrystallized recrystallized rocks rocks in the the terrane terrane and weare aretherefore therefore considering consideringthe the possibility possibility that and we thatthe thezircons zirconshave havebeen been reset. The The Archean Archeangneisses gneissesare areofofvolcanic, volcanic, plutonic, plutonic, and and sedimentary sedimentary origin, and and generally generally exhibit exhibitstructures structuresindicative indicativeof of polyphasedeformation. deformation. origin, polyphase Theoldest oldest recognized recognizedEarly Early Proterozoic Proterozoic rocks rocks in Wisconsin are mafic mafic to The Wisconsin are felsic volcanicswhich whichwere wereextruded extruded atatthe thebeginning beginningof of PenokeanOrogeny, Orogeny, felsic volcanics thethe Penokean about Conipressionaldeformation deformationfollowed followedshortly shortly thereafter thereafter 1860 m.y. m.y. ago. ago. Compressional about 1860 resulting resulting in in vertical vertical and and near near vertical vertical dips dips for forthese these rocks. rocks. Medium-grained granitic tona1itic plutons were emplacedthroughout throughoutthe theterrane terranebetween between granitic tototonalitic plutons were emplaced 1840and and1830 1830 m.y. ago, followed finer-grained granitictototonalitic tonalitic 1840 m.y. ago, followed by by thethe finer-grained granitic plutons along between plutons along the the southern southern margin margin ofofthe theterrane terrane between1830 1830and and 1820 1820 m.y. m.y. these plutonic plutonic rocks rocks contain contain aapronounced pronounced lineation ago. The The vast vast majority majority of these lineation which is commonly, but not always, weaktotomoderate moderatefoliation. foliation. which commonly, but always, accompanied accompanied bybyaaweak Catac1astic textures textures are are present present in in all alldeformed deformed rocks, rocks, but butthey theyare aresubordinate subordinate Cataclastic to recrystallization textures. textures. Cataclasis Cataclasis occurred occurred simultaneously simultaneously with to recrystallization recrystallizationduring during Penokean deformation deformation and and amphibolite amphibolite facies facies metametarecrystallization Penokean morphism regionalextent, extent, rather rather than being restricted totolocalized morphism ofofregional than being localizedzones zones of shearing. shearing. The plutonic rocks are generally synkiriematic synkinematic toto late kinematic, kinematic, but but aa The plutonic rocks are generally the basis basis of radiometric few kinematic. On On the radiometric ages ages ititappears appears that thatsome some few are are post kinematic. the undeforrned undeformed units are older than than deformed deformed units elsewhere, thus thus defordeforof the units are units elsewhere, mation terminated at different the terrane. terrane. mationmay mayhave have terminated at differenttimes timesin indifferent different parts parts of of the However, thisconclusion conclusionmust must viewed caution lightofofthe the level level of However, this be be viewed withwith caution in in light precision the radiometric radiometric ages, ages, especially especially when when attempting precision of the attempting to to distinguish events so closely spaced events so spaced in time. time. Penokean the emplacement emplacement of 1760 m.y. old Penokearideformation deformationhad hadended endedprior prior to to the of 1760 m.y. old Subsequently these these rocks and rhyolites rhyolites ininsouthern southernWisconsin. Wisconsin. Subsequently rocks were were granites and folded, whereas rocks the state state were were folded, whereas rocksofof the the same sameage ageininthe thenorthern northernhalf half of the 11. �(Maass, continued) (Maass, Medaris Medaris and and Van Van Schmus, Schmus, continued) Throughout the the Lake Superior region, not. Throughout Lake Superior region, Rb-Sr Rb-Srsystematics systematicshave havebeen been reset at at approximately approximately 1630 1630 to to 1615 1615 m.y. m.y. It It appears appears likely that this this likely that event responsible for forthe thefolding folding metamorphism of the the southern southern event is responsible andand metamorphism Wisconsingranites, granites, rhyolites, rhyolites, and and quartzites, quartzites, but buthad had only only aathermal thermal Wisconsin expression in northern northern Wisconsin. Wisconsin. expression 12. �MIGMATITES FROM THE VERMILION MIGMATITES FROM THE VERMILION GRANITIC GRANITICCOMPLEX, COMPLEX,MINNESOTA MINNESOTA John ~J. Goodge Goodge John W, Carleton College Carleton College Northfield, Minnesota 55057 Northfield, Minnesota Archean migmatiticrocks rocksdated datedatat 2.7 2.7 b.y. b.y. from Archean migmatitic from the the Big Biq Falls, Falls,Minnesota Minnesota area were wereinvestigated investigated in in order Vermilion Graniarea order to to further furtherknowledge knowledge of the the-Vermilion Granitic tic Complex, Complex, particularly particularlyininthose thosewestern westernportions portionswhich whichhave have been been less less The Vermilion Vermilion Granitic Granitic Complex lies in in north-central extensively studied. The Complex lies north-central extensively studied. Minnesotaand andisiscomprised comprisedprimarily primarilyofof pink pink leucogranite leucogranite with with substantial substantial Minnesota rocksofof the the Vermilion Vermilion Distportions of migmatite migmatite throughout. throughout. Volcanogenic Volcanogenic rocks portions of rict ofofMinnesota parent rocks rocks for for the rict Minnesota are arebelieved believedtotobebethe themetamorphosed metamorphosed parent the regional scale scale rocks migmatites in the the Vermilion Vermilion Granitic GraniticComplex. Complex. On On aa regional rocks in migmatites the Big Big Falls Falls area are grouped groupedasasmigmatites, migmatites, locallydistinct distinctdifferdifferthe area are butbut locally encesinin structure structure and andfabric fabric permit permit the the subdivision subdivisionof of the the rocks rocks into into four ences four gneiss, mixed and units: tonalite, tonalite,garnet-biotite garnet-biotite gneiss, mixedtonalite tonalite andgneiss gneissand and grangranitic dikes. itic dikes. Structurally, Structurally,the thegneissic gneissicportions portionsappear appear as as rafts raftsupuptoto2Oni 20m size which which are are enclosed enclosed by by both the tonalite tonaliteand and mixed mixed rock. rock. Orientations in size both the of foliation one raft raft to foliationand andbanding banding in in the the gneiss gneiss are are consistent consistent from from one to another, another, which thatthey theyhave have not notbeen been extensively extensivelymoved moved during migniatization. migmatization. which indicates that The tonalite tonalite exhibits the form of n.ebulitic The exhibits compositional compositional inhomogeneities inhomogeneities inin the form of nebulitic structures shown shown bybydifferences concentrations. The structures differencesinin biotite biotite concentrations. Themajority majority of migmatite appears and gneiss, migmatite appearstotobebea amixture mixtureofoftonalite tonalite and gneiss, displaying displaying aa variety o-F structures including including complex folds and andswirls, swirls, boudinage, dilation and of structures complex folds boudinage, dilation and to nebulitic nebuliticstructures structures indicative of high-grade metamorphismand and schlieren to indicative of high-grade metamorphism Several pegmatitic pegmatiticdikes dikescutting cutting both both the the tonalite severe deformation. Several severe plastic plastic deformation. and gneiss represent represent the the youngest youngestrocks rocks in in the area. dikes are and gneiss area. The The dikes are up up to meter in in cross section, straight 1 meter cross section, straight and and in in sharp sharp contact contact with with the the gneiss. gneiss. 1 The tonalite isiscomposed The tonalite composed of ofmediummedium- to coarse-grained coarse-grained (3-7mm) (3-7mm) plagioclase, quartz quartz and and biotite biotitewith withminor minormicrocline microclineand andmuscovite, muscovite, and and accesaccessories of In several sories of zircon, zircon,sphene, sphene, apatite apatiteand andananopaque opaque mineral. mineral. In several samples, samples, plaqioclase of microcline. The gneissisis well-foliated, well-foliated, plagioclase contains contains small small patches patches of The gneiss medium-grained (0.5-2.0mm)and and composed plaqioclase,quartz quartzand andbiotite biotite medium-grained (0.5-2.0mm) isiscomposed of of plagioclase, with minor Plagioclase, biotite biotite and cordierite (?) minor garnet garnet and and microcline. Plagioclase, and cordierite (?) have replaced replaced subhedral subhedralgarnet garnetto to form form fine-grained aggregates, have aggregates, and and replacement grades from from minor minor to complete. granitic dikes ment grades complete. The The granitic dikes contain contain coarse-grained coarse-grained (4-6mm) microcline,quartz quartz and andmuscovite muscovitewith withminor minorplagioclase plagioclaseand andbiotite. biotite. ~-6mm) microcline, Plagioclase and gneiss oligoclase. The Plagioclase composition compositionininboth bothtonalite tonalite and gneiss is is oligoclase. gneissic of the therocks rocks and and composition composition of plagioclase indicate gneissic fabric of of the the plagioclase indicate that metamorphism reached amphibolite facies, thethebiotite, garnet and and niicrocmicrocmetamorphism reached amphibolite facies,and and biotite, garnet line content metamorphic content isisconsistent consistentwith withthis this metamorphic grade. grade. Modal Modal mineral mineral analysis of these these rocks rocks reveal reveal that that the the tonalite tonaliteand and gneiss gneiss are are similar similarinincomposicomposisis of content (average tion, despite despite aa significant significantdifference differenceininthe thebiotite biotite content (average15% 15% in tonalite; tonalite;28% 28% in in gneiss). gneiss). 13, 13. �(Goodge, continued) (Goodge, Models genesis of the the migmatites migmatites near near Big Big Falls Falls must must consider consider Modelsfor for the the genesis the following: the the strong structures in in the the strong fabric of of the the gneiss, gneiss, complex complex structures the mixed and gneiss, mixedrock, rock,mixing mixingofofthe thetonalite tonalite and gneiss,aa late-stage late-stage injection injection of granitic granitic material, material,compositional compositional similarities similaritiesbetween between the the tonalite tonaliteand and gneiss gneiss and consistencies the plagioclase plagioclase composition. composition. Further petrographic petrographic and and and consistencies in In the geochemical analysis willlead leadtotoananinterpretation interpretation of of the geochemical analysis will the relationship between the tonalite tonalite and between the and gnelss. gneiss. 14. �GEOLOGY OF THE GEOLOGY OF THE SOUTHEASTERN SOUTHEASTERN CONTACT CONTACT ZONE ZONE OF OF THE THE VERMILION VERMILION BATHOLITH, BATHOLITH, MINNESOTA MINNESOTA Anthony Dion Heinz, Heinz, Anthony Fleming, Fleming, Dion Lee and and Henry HenryWoodard Woodard Robert Lee Department Geology Department of Geology Beloit Be1oit College College Beloit, Beloit, Wisconsin Wisconsin mapping in in the theFourtown Fourtown Lake Lake quadrangle quadrangle and and reconnaisreconnaisDetailed geologic geologic mapping sance mapping mappinginin the Friday sance FridayBay, Bay,Iron IronLake Lakeand andAngleworm AnglewormLake Lake quadrangles quadrangles was was 1979field field seasons order to to better carried out out during during the the 1978 1978 and and 1979 seasons inin order better underunderstand the complex natureof of the the southeastern contact zone of the stand the complex nature southeastern contact zone of the Vermilion Vermilion Batholith. The The oldest schist oldest rock rock units units are are layered layered amphibo1ites, amphibolites,biotite biotite schist and aa complex complexunit unit which which may mayhave haveoriginally originally been and been aa volcanic volcanic agglomerate. agglomerate. These rocks by hornbJende hornblende adamellite andmigmatized migmatized by by an an These rocks are are intruded by adamellite sills sills and early episode episode of anatexis. anatexis. These These processes processeshave haveobscured obscuredthe thestrati9raphic stratigraphic relationships theearlier earlier rock relationships between between the rock units. This wasregionally regionally folded folded to This entire entire assemblage assemblage was to produce produce the the northeastnortheastThe detailed detailed mapping in the trending outcrop outcrop belts belts that thatare arenow now observed. observed. The mapping in the trending Fourtown Lake confirms that on the the southern southern Fourtown Lakequadrangle quadrangle confirms thatmost mostofofthe thearea arealies lies on limb of aa major 'major synform. synform. The of the the Friday FridayBay Bay quadrangle quadrangle probproblimb of The southern southernhalf half of The entire ably is underlain by the northern limb of this same structure. ably underlain by the northern limb of this same The entire region was subjected to to passive the Vermilion Vermilion Batholith and region was subjected passive emplacement emplacement ofofthe and the contact zone, zone, which the contact whichisis several several miles miles wide, wide, appears appearstotobebethe theresult result of aa second intense migmatization migmatization and and anatexis. secondstage stageof of intense The then cutcut by by a giant horsetail-like Theregion regionwas was then a giant horsetail-likesplay splayofofleft left lateral faults extending extending northeastward northeastward fro'm zone to the south. south. fromthe theVermilion Vermilionfault fault zone to the The episode episodeof of faulting faulting was hydrothermalalteration alteration of the The was accompanied accompanied bybyhydrothermal the fault fault zone zone rocks rocks and and by by the the development development of of quartz quartz and and epidote epidote veins. veins. mapping will extend both both north north and and east east from from Future Future detailed detailed structural mapping will extend the Fourtown the Fourtown Lake Lake quadrangle. quadrangle. Petrologic studies of of the the contact contactzone zone rocks rocks Petrologic studies are now now in progress. progress. Many Manyimportant importantquestions questionsconcerning concerningthe theorigin origin of these these are be answered answered by rocks remain to be rocks remain by these these continuing continuing studies. 15. �OVERTURNEDARCHEAN ARCHEANSUCCESSIONS SUCCESSIONS AND THEIRSIGNIFICANCE SIGNIFICANCE OVERTURNED AND THEIR K.H. Poulsen Poulsen and and M.M. M.M. Kehienbeck Keh1enbeck K.H. Lakehead University Lakehead University Thunder Bay, Thunder Bay, Ontario Nunerous separated Nunerousexamples examplesofofoverturned overturned Archean Archeansuccessions successionsfrom from widely widely separated Recognition of these cratons have these cratons havebeen beenreported reportedininthe therecent recentliterature. literature. Recognition phenomena in in North America is is still limitedtototwo twosuch suchexamples examples from from the the phenomena North America still limited Superior structural province; province; one one near near Red Red Lake, the other other at at Rainy Rainy Superior Lake, Ontario, Ontario, the Lake, In the the latter latterexample, example,the theoverturned overturnedsuccession succession includes includes Lake, Ontario. In strata which which have have been long standing standing controversy: controversy: the beenthe the subject subject of aa long it can and Keewatin Keewatin Groups Groups of of A.C. A.C. Lawson. Lawson. At At Rainy Rainy Lake Lake it can be be Coutchiching and demonst~ated succession is overturned overturned for for distances distances demonst'atedthat thatthe the stratigraphic stratigraphic succession 15 km km and the deformation deformation which which produced produced the took place place of 15 and that that the the inversion inversion took relatively early ininthe thedeformational deformational history history of of the the region. region. relatively early The thatthe thesequence sequence at at Rainy Rainy Lake Lake isisoverturned overturnedhad had not notbeen been The fact fact that recognized that two two fundamentally fundamentally difThe reason reasonfor forthis this is that difrecognized previously. The ferent approaches approaches totostructural and stratigraphic interpretationhave havebeen been structural and stratigraphic interpretation mapped largeantiforma1 antiformal folds which applied in the the past. past. A.C. A.C. Lawson Lawson mapped large which he he applied assumed totobebeanticlines. As aa result, he interpreted interpretedthe theCoutchiching Coutchiching assumed anticlines. As result, he metasedimentary forms toto be metasedimentaryrocks rocksnear nearthethecores coresofofthese theseanti antiforms be the the oldest in the the region. region. Observations Observations of younging younging using primary primary sedimentary sedimentary strata in and andvolcanic volcanicfeatures featuresatatkey keylocalities localitiesindicate indicatethis this stratigraphic stratigraphic interpretation to be be incorrect. incorrect. F.F. F.F. Grout, Grout, on on the the other hand, hand, interpreted the the pretation stratigraphy from from observations observations of of younging younging in graded graded beds beds near nearstratigraphic stratigraphic result,heheplaced placedthe theCoutchiching Coutchichingmetasedimentary metasedimentary rocks rocks contacts. As As aa result, much stratigraphiccolumn. column. In addition, addition,however, however, Grout Grout used used muchhigher higherinin the the stratigraphic the younging the structure. structure. Anticlines and and synclines synclines the youngingcriteria criteria to to interpret the mapped observed minor such as mappedininthis this manner mannerconflict conflict with observed minor structures structures such as fold It is only by the integrated symmetry and bedding-cleavage relationships. It is only by the integrated symmetry and bedding-cleavage relationships. application of of both both structural structuraland andprimary primaryyounging younging data data that that an an extensive extensive inverted sequence sequence can can be be recognized. recognized. Widespread Archean terranes Widespreadoverturning overturningin in Archean terranes has has mainly mainly been beenattributed attributed structures are to the the existence existence of of large large fold foldnappes. nappes. Such Such structures are normally normally assocassocwith the the concept concept of compressional compressional tectonics the iated with tectonics generally generally related related to the the other other hand it has c10siilg of primitive primitivevolcano-sedimentary volcano-sedimentary basins. basins. On On the hand it has closing of been that in the the developdevelopbeenproposed proposed thatgravity gravitydriven driventectonics tectonics might mightalso also result result in ment of instability near boundariesbetween between ment of nappes, nappes,either either due due to to crustal instability near thethe boundaries Each of of sub-provinces the buoyant buoyant emplacement emplacement ofofgneissic sub-provinces or or to the gneissic diapirs. diapirs. Each these be supported supported by from the Rainy Rainy Lake Lake region. these models modelsmay mayinin part part be by data data from Further documentation documentation ononthe and timing of ofthe thedeformation deformation Further thelateral lateral extent and will be be required required before before a a critical criticalappraisal appraisalofofthese thesemodels models will will be be possible. possible. will 16. �THE THE PRECAMBRIAN PRECAMBRIAN WATERLOO WATERLOO QUARTZITE, SOUTHEASTERN SOUTHEASTERN WISCONSIN: WISCONSIN: EVOLUTION AND AND SIGNIFICANCE EVOLUTION Clifford I. Smith CliffordN.N.Brandori Brandon and and Eugene Eugene I. Smith Division of ofScience Science Wisconsin-Parkside Univ. ofofWisconsin—Parkside Keriosha, WI Kenosha, WI 53141 Frank R. R. Luther Frank Dept. of Dept. ofGeography-Geology Geography-Geology Univ. Univ. of ofWisconsin-Whitewater Wisconsin-Whitewater Whitewater, WI WI 53190 The The Waterloo Waterloo Quartzite Quartzite forms forms aa broad broad asymmetric asymmetric eastward-plunging eastward-plunging syncline that isisa aprominent prominent structural structuraland andtopographic topographicfeature featureofofthethePrecambrian Precambrian basementof of southeastern Wisconsin. basement Wisconsin. If Ifthe thePaleozoic Paleozoic and and Pleistocene Pleistocene overoverburdenwere werestripped stripped from from the the Waterloo area, the the quartzite burden Waterloo area, quartzitewould would stand stand as as an an arcuate ridge arcuate ridge 150 150 toto275 275mmabove above the the surrounding surrounding Precambrian Precambrian surface. surface. A detailed structural structural study studyofofquartzite quartziteexposures exposures reveals reveals two two important important 60 EEwith with variable dip, vertical , The joint joint directions: directions: N 60 dip, and and NN30-40 30-40 W, W, vertical, N 60 interpreted as as the the axial axial plane plane direction for for the the syncline; syncline; 60EEjoint joint set set is interpreted the variable variable dip dip is probably duetoto stress stress refraction refraction in the the probably due the quartzite. quartzite. The N30-40 N30-40Wdirection W direction roughlyperpendicular perpendicular thehinge hingeline lineofof the the fold. The is isroughly to tothe These joint directions are similar to those described by Dalziel and Dott These joint are similar to those described by Dalziel and Dott (1970) (1970) For the Baraboo Quartzlte (which crops crops out out 60 to the The copfor the Baraboo Quartzite (which 60 km km to the northwest). northwest). The lanar attitude thethe Baraboo lanar attitudeofofthe theaxial axialplanes planesof of Barabooand andWaterloo Waterloo synclines synclines suggests thatboth both structures structures formed during the tectonic event. sugge~ that formed during the same same tectonic event. Andalusite wereidentified identified by by petrographic petrographic and and X-ray X-ray Anda1usite porphyroblasts porphyroblasts were diffraction studies diffraction studies ininbeds beds of ofschist schistinterbedded interbedded with with quartzite quartzite (near (near the the nose of the reported nose of the syncline synclineatatGlascow1s G1ascow ' s Farm). Farm). This This is the the first first reportedoccurence occurence medium grade index the Waterloo Waterloo area area of aa medium grademetamorphic metamorphic indexmineral mineralininoutcrop outcrop in in the (Haimson, 1978,identified identifiedandalusite andalusiteinin core core from fromdeep deepwells wellsdrilled drilled into the (Haimson, 1978, the assemblegeandalusite-muscovite-quartz andalusite-muscovite-quartz suggests suggeststhat that the quartzite). The The assemblege quartzite was upper greenschistfacies fadesoror to to the quartzite was metamorphosed metamorphosed to to thetheupper greenschist the lower lower amphibolite facies. In contrast, contrast,the themetamorphism metamorphism of the the Baraboo Baraboo Quartzite amphibolite only reached the facies ony reached thelower lowergreenschist greenschist fades(pyrophyllite (pyrophylliteisis found foundinin phyllite phyllite that either beds interbedded This suggests suggests that either the the thermal thermal beds interbeddedwith withthe the quartZite). quartzite). This event responsible for for andalusite restricted totothe event responsible andalusite growth growth was was restricted theWaterloo Waterloo area area at a deeper level in the or that that the the heat heat source source (intrusive (intrusivebody?) body?) was was at deeper level the Baraboo region. Baraboo ~Je Wesuggest suggestthe thefollowing following scenario scenay,oio involving involvingthree threeepisodes episodesofofmetamormetamorphisni for the phism for the development development of the the Waterloo Waterloo area: area: (1) Deposition Deposition ofofthe theWater-fl Waterlao volcanic-plutonic terrain between loo sediments sediments on on an an eroded eroded volcanic-plutonic terrain between1760 1760and and1630 1630 1630m.y. m.y.ago agoforming formingthe the syncline m.y. ago. m.y. ago. (2) Folding Folding and and metamorphism metamorphism 1630 (3) An and An intrusive event event affecting affectingthe theWaterloo Waterloo andmajor majorjoint joint directions. (3) 17. �(Brandon, Smith Smith.and andLuther, Luther, continued) (Brandon, The andalusite andalusite porphyrob1asts porphyroblasts probably probablyformed formedatatthis this time. Quartzite. The This event haveoccured occuredsoon soon afterthe thefolding folding episode or possibly as This event may may have after episode or as late as as 1500 1500 m.y. the Wolf Wolf River event). The ni.y. ago ago(related (related to to the River intrusive event). pegmatite dike well pegmatite dike on onRocky RockyIsland Islandand andthe theamphibolite amphiboliteidentified identified in in aa well (4) AAretrograde core probably probably formed stage. (4) retrogrademetamorphic metamorphic event event core formedduring during this this stage. producingaaweak weak penetrative foliationthat that is is revealed by aligned aligned sericite sericite producing penetrative foliation revealed by grains within the the andalusite anda1usite porphyroblasts. porphyrob1asts. grains 18. �RARE EARTH EARTH ELEMENT ELEMENTDISTRIBUTION DISTRIBUTION IN RARE IN THE THEPRECAMBRIAN PRECAMBRIAN RHYOLITES RHYOLITES AND AND GRANITES GRANITES OF SOUTH-CENTRAL OF SOUTH-CENTRAL WISCONSIN WISCONSIN I. Smith Smi th Eugene 1. Division of ofScience Science University University ofofWisconsin-Parkside Wisconsin-Parkside Kenosha, WI Kenosha, WI 53141 53141 The rhyolites and The rhyolites and granites granites ofofsouth-central south-centralWisconsin Wisconsin resulted resultedfrom fromanorogenic anorogenic igneous activity 1760+ igneous activity 1760~10 10 m.y. m.y. ago. ago. This This event event occurred occurred after afterthe themagmatic magmatic activity thethe Penokeari activityofof PenokeanOrogeny Orogeny (1850 (1850 m.y.) but but before beforethe theemplacement emplacement of the the Wolf River River Batholith (1500 earth and Wolf (1500 m.y.). Rare Rare earth and trace element element data data suggest suggest that two typesformed formedduring during this this event, two major major magma magma types event, but butpreclude precludea acomagmatic comagmatic The magma types are: are: a peraluminous relationship relationship between between the the type type types. types. The magma types peraluminous suite characterized characterized by bylow lowBa/Sr, Ba/Sr,Rb/Sr Rb/Srand andhigh highCaO CaO and and Al Al?Ol (the Marcellon Marcel10n 0 and Marquette Marquetterhyolites-groups rhyolites-groups22and arid44ofof Smith, Smith, 1978); 1978); aa metaluminous mt1urninous suite suite and characterized by andA1Al 03 (the quartz-aklali characterized by higher higher Ba/Sr, Ba/Sr, Rb/Sr Rb/Sr and and lower lower CaD CaO and 03 (the quart7.-ak1ali feldspar Utley,Berlin, Berlin,Endeavor, Endeavor, 0bservator Observatory2 Hill, Hill,and and Taylor Taylor feldspar rhyolites rhyolites at Uley, Farm; Montello and and Redyranite; Redgranite; and Farm; the the granophyric granophyric granites granites at Montello arid aa porphyritic porphyritic granite dike dike at atFlynn's Flynn'sQuarry-group Quarry-group 33 of of Smith, Smith, 1978). 1978). Both Both suites show light suites show light REEenrichment enrichment(La/Yb-4.7-8.6) (La/Yb-4.7-8.6) and REf and prominent prominent negative negative Eu fu anomalies anomalies (Eu/Eu*= (Eu/Eu*= 0.15-0.4), butthethemetaluminous metaluminous suite suitedisplays displaysuniformly uniformly higher REEabundances. abundances. 0J5-0.4), but higher REE The and granite of of the the metaluminous metaluminous suite the northwest northwest of the The rhyolite rhyolite and suite occur occur to to the of the Thesesuites suites in general rhyolite of ofthe theperaluminous peraluminous suite. These general correspond correspond to those those proposed by J\nderson, Schmusand andCullers Cullers (1978). proposed by Anderson, Van Van Schmus Within the peraluminous peraluminous suite the Marcellon Marce110n rhyolite rhyolitemay mayhave have formed formed from from the the Within the suite the Marquette rhyolite plagioclase, orthoclase orthoclase Marquette rhyolite by bythe thefractional fractional crystallization crystallization ofofplagioclase, and biotite. Within Within the the metaluminous suitethe thequartz-alkali quartz-alkali feldspar feldspar rhyolites and biotite. metaluminous suite and granophyric granites may may have have formed formed from from aa magma magma having and granophyric granites havingthe the composition composition of the Flynn1s Quarry involving two two feldspars, feldspars, the Flynn's Quarrygranite granitebybyfractional fractional crystallization crystallization involving biotite and biotite and hornblende. hornblende. fractional crystallizaEven due to fractional Eventhough thoughthere thereisis wide wide compositional compositional variation variation due the two two suites suites remain remain compositionally compositionally distinct. This indicates indicates differences differences tion, the distinct. This Modelstudies studies suggest suggest that that the suite in crustal crustal source source materials. materials. r~odel the peraluminous peraluminous suite was was generated generatedby by21% 21%nonmoda1 nonmodal fractional fractionalmelting meltingof of aa crustal source source having having an an model source source is intermediate The model intermediatecomposition composition(quartz (quartzdioritic dioritic or or andesitic). The remarkably similar in in composition to the the andesite anddacite dacite dikes dikes that that cut the remarkably similar composition to andesite and the sourcefor for the the metaluminous metaluminous suitewas was difficult to rhyolite exposures. The The source suite difficult to rhyolite exposures. model, since since the the undifferentiated undifferentiated member thissuite suite could could not not be be identified identified model, member ofofthis the source sourceisis rriost probably an an intermediate intermediate rock, rock, but with confidence. confidence. However, However, the most probably but The major abundancesthan thanthe thesource sourcefor for the the peraluminous suite. The with higher higher REE REE abundances peraluminous suite. igneous suites of south-central probably formed formedbybypartial partial fusion igneous suites south-central Wisconsin Wisconsin probably fusion of of The crust was probably tectonically different partsofofa aheterogeneous heterogeneous crust. The crust was probably tectonically different parts thickened during duringthe thePenokean Penokean Orogeny. Orogeny. 19. �GEOCHEMISTRY WEST-CENTRAL GEOCHEMISTRYAND AND VOLCANIC VOLCANIC STRATIGRAPHY STRATIGRAPHY OF OF WEST-CENTRAL MARINETTE COUNTY, COUNTY, WISCONSIN WISCONSIN MARINETTE M. M. L. Cummings Cummings Department of Earth Sciences Sciences Department of Earth Portland State University Portland State Portland,OR OR 97207 Portland, The volcanic volcanic pile The pile ininwest—central west-central Marinette Marinette County, County, Wisconsin, Wisconsin, includes includes mafic to felsic felsicflow flowand andpyroclastic pyroclasticunits, units,and andclastic clastic sedimentary,massive massive mafic sedimentary, The volcanic volcanic belt isisapproximately and iron formation formation units. The approximately 88km km sulfide and wide and is bounded on the north by the Dunbar gneiss and on the south by wide and bounded on the north by the Dunbar gneiss and on the south by the Atheistane quartz North ofGe-l-emn—Lake thebelt belt is is approximately Athelstane quartz monzonite. monzonite. North of~olernan-Lake the approximately 2 km wide where the Twelve Foot Falls quartz diorite occurs to the km wide where the Twelve Foot Falls quartz diorite occurs the north north and and betweenvolcanic volcanic units the Atheistane Athelstane quartz monzonite monzonite to the south. south. Contacts Contacts between the to the are steeply strike north are steeply dipping dipping and and strike north to tonorthwest. northwest. felsiccenter centernorth northofof Coleman Lake Lake contains contains interlayered interlayered andesite andesite A felsic Coleman and massiverhyolite rhyolite flows. and massive flows. Fragmental Fragmental units have not not been been observed. observed. Plagiounits have clase phenocrysts occur in in the quartz and clase phenocrysts occur the andesite andesite flows flows and and abundant abundant quartz and plagiorhyolite clase sparse plagioclase flows. The The rhyolite clase or or sparse plagioclase phenocrysts phenocrystsoccur occurininrhyolite rhyolite flows. flows contain 70 70 to to77% 77% S102 Si0 2 and flows contain contain 57 57 toto60% 60% Si02. Si0 2 , flows contain and the the andesite andesite flows The northwestern underlain by by porphyritic The northwesternportion portionofofthe thevolcanic volcanicpile pile is is underlain dacite and and rhyodacite rhyodacite flows. flows. Basalt flows are are present present locally. Basalt and andrhyolite rhyolite flows locally. The southeastern area is underlain underlain by by clastic clasticmetasediments, metasediments, The southeasternportion portion of of the the area formation, massive massive to semi-massive semi-massive sulfide, and basalt and and dacite flows. flows. iron formation, sulfide, and The composition differenThe compositionofofthe theflows flowsdefine definea adistinct distinct calc-alkaline caic-alkaline differenThe composition compositionof of the tiation trend. trend. All units units are are subaikalic. subalkalic. The the volcanics volcanics suggests island island arc suggests arc volcanism. volcanism. The volcanic volcanic units units of The of westcentral westcentral Marinette Marinette County County are are chemically chemically disdistinct from the thevolcanic volcanicunits units-inineastern easternand andnortheastern northeasternMarinette MarinetteCounty County tinct from includingthe theQuinnesec, Quinnesec,Beecher, Beecher,and andPeniene Pemene Formations. Formations. The The flows the flows in the including study area in general study area general are are higher higher in in TiO TiO?,, K20, K20, A1203 A1 203 and and CaO, CaD,and and lower lower in Na20 and FeO FeOthan than Quinnesec, Quinnesec, Beecher Beecher ana an Pemene Na 20 and Pemene Formations. The The volcanic piTe ininwestcentral westcentral Marinette MarinetteCounty County should should not be be considered considered part the pile part of the Quinnesec Quinnesec Formation. 20, 20. �WHEREIS IS THE WHERE THE SOURCE SOURCE OF OF WISCONSIN WISCONSIN DRIFT DRIFT DIAMONDS? DIAMONDS? W. F. Cannon Cannon W. U.S. U.S. Geological Geological Survey Survey Reston, Virginia Virginia 22092 Reston, M. G. G. Mudrey, Mudrey, Jr. M. Wisconsin Geological and and Natural Natural History Wisconsin Geological History Survey Survey Madison, Wisconsin Wisconsin 53706 Madison, Between 1876and and 1903, dIamonds found in at leastseven sevenlocalities localities Between 1876 1903, diamonds werewere found in at least southern and and central central Wisconsin. Wisconsin. All were were found found in Pleistocene Pleistocene glacial in southern The bedrock bedrockkimberlite kiniberlite source source for for the deposits Holocene river the deposits or or Holocene river gravel. The diamonds but to tobebeininnorthern Canada, the diamondsisis unknown unknown buthas hasbeen beenpresumed presumed northern Canada, the only area north of contain kimberlites. Recently, area north of Wisconsin Wisconsin previously known known toto contain That find a kiniberlite kimberlite pipe pipehas has been been found found in in Iron IronCounty, County, Michigan. Michigan. That causedusustoto consider considerthe the possibility possibility that diamonds caused thatWisconsin Wisconsin drift drift diamonds have have come fromaamore morelocal local source--kimberlites source--kimberlites ininnorthern come from northernMichigan Michigan and and Wisconsin. Wisconsin. The very poorly poorly exposed, exposed, but strong positive The Iron Iron County Countykimberlite kimberlite is is very but aa strong magneticanomaly anomaly indicates thatitit is roughly magnetic indicates that roughly circular circularininplan planand and200-300 200-300 meters meters in diameter. diameter. Although Althoughthe the kimberlite kimberlite is is entirely entirelysurrounded surrounded by by Precambrian rocks, it contains abundant inclusions of fossiliferous limestone, Precambrian rocks, it contains abundant inclusions of fossiliferous limestone, probably from Ordovician Black Black River River Group Group that overlaid the thearea areawhen when probably from the the Ordovician that overlaid the The post-Ordovician post-Ordovicianage ageofof the the kimberlite leads the kimnberlite kimberlite was was intruded. The leads us to suspect that other possible possible cryptovolcanic cryptovolcanic structures in in Paleozoic Paleozoic us to suspect that other rocks overkimberlite kimberlite pipes pipes that are rocks in the the region region were were formed formed over are not not yet yet exposed exposed by by erosion. Such Such structures structures include includeLimestone LimestoneMountain Mountainand andSherman Sherman and Baraga BaragaCounties, Counties,Michigan; Michigan;Glovers GloversBluff Bluff in Hill in Houghton Houghton and in Marquette Marquette County, south of County, Wisconsin; Wisconsin;and andpossibly possiblyan anarea areaalong alongthe the Brule Brule River River south Iron River, Iron River, Michigan. Michigan. No diamonds known IronCounty County kimberlite,but butitit has No diamonds areareknown in in thethe Iron kimberlite, has not not cryptovolcanic structures structures could been been adequately sampled. sampled. The The cryptovolcanic could not not be be the the source of the becauseeven evenifif they source the Wisconsin Wisconsin diamonds diamonds because they are are caused caused by by kimberlites, those kimberlites, those kimberlites kimberliteshave havenot notyet yetbeen beenexposed exposed by by erosion. Elsewhere occur as isolated Elsewhereininthe theworld, world, kimberlites kimberlites rarely rarely occur as aa single single isolated body; bodiesare aremore more common, common, and body; clusters ofofbodies andthe the presence presenceofof one onekimberlite kimberlite makes suspectthat that others others exist nearby. makes usussuspect nearby. The discovery discoveryof of additional additional kirnberlites be very very difficult difficult because The kimberlites may may be because coverof of glacial glacial drift of the the extensive extensive cover driftand andthe theprobable probable small small size of of If all are magnetic, they might be found by detailed kimnberlite bodies. If kimberlite all are magnetic, they might be found by aeromagnetic However, the County kimberlite aeromagnetic surveys. However, the magnetism magnetismofofthe the Iron Iron County kimberlite appears to be by secondary secondarymagnetite magnetiteformed formedduring duringserpentinization serpentinization appeal~s to be caused caused by of olivine, olivine,sosoananunserpentinized unserpentinized kimberlite kimberlitemay may not not be be strongly stronglymagnetic. magnetic. We We suggest suggestthat that one one or or more more diamond-bearing diamond-bearingkimberlites kimberlites may mayexist exist in northern northern Michigan Michiganoror \~isconsin, Wisconsin,but butthe the discovery discoveryof of sLich suchbodies bodiesisis unlikely unless is undertaken. undertaken. unless a a very very thorough thorough search search is 21. 21 �CORRELATION OF OF GRAVITY CORRELATION GRAVITY AND AND MAGNETIC MAGNETIC ANOMALIES ANOMALIES IN EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTAAND ANDNORTHWESTERN NORTHWESTERN WISCONSIN WISCONSIN V.W. Chandler V.W. Minnesota Geological Survey Minnesota Geological Survey 1633 Eustic Eustlc Street 1633 St. Paul, st. Paul,MN MN 55108 55108 Similarities andand magnetic Similaritiesiningravity gravity magneticanomaly anomaly patterns patternsinineast—central east-central Minnesota andnorthwestern northwestern Wisconsin Wisconsinimply imply that that several Minnesota and several Precambrian Precambrian rock rock A broad niagnetic may be between the the two two areas. areas. A magneticmaximum maximum units may be correlative correlative between that isisbounded bounded to the the south south by by east-trending east-trendinglinear linearmagnetic magneticmaxima maxima is an an anomalypattern patternthat that exists exists in anomaly in both both central central Aitkin AitkinCounty, County,Minnesota, Minnesota, and and areas are are characterized characterized by northern Sawyer Sawyer County, County, Wisconsin. Wisconsin. Both Both areas by regional regional gravity maxima. gravity maxima. In Aitkin AitkinCounty, County,Minnesota, Minnesota,the thebroad broadmagnetic magneticmaximum maximum is is associated with the linear associated with the theArchean Archean McGrath McGrath Gneiss Gneiss whereas whereas the linearmagnetic magneticmaxima maxima are apparently related totobelts beltsof of early Proterozoic metavolcanic metaare apparently early Proterozoic metavolcanic andand meta— sedimentary rocks. Similarly, sedimentary Similarly,ininSawyer SawyerCounty, County, Wisconsin, Wisconsin, the thebroad broadmagnetic magnetic maximum associatedwith withArchean Archean graniticand andgneissic gneissicrocks rocks and andthe the linear linear maximum is isassociated granitic magnetic maxima areare believed to to bebe related Proterzoic magnetic maxima believed relatedtotobelts belts of of early Proterzoic east-trendingbelt belt of of irregular metavolcanic and and metasedimentary metasedimentary rocks. An An east-trending metavolcanic magnetic minima minima and Lacs and and Kanabec Kanabec Counties, Minnesota, magnetic and maxima maximainin Mille Mule Lacs Counties, Minnesota, resembles Barron and and Rush Rush Counties, Counties, Wisconsin. Wisconsin. Both resemblesaa magnetic magnetic terrane terrane in Barron regions are characterized characterized by by regional regional gravity gravitymaxima. maxima. This This magnetic magnetic terrane regions are Minnesota corresponds Proterozoic granites granites and and minor minor volcanic volcanic in Minnesota correspondstotoearly early Proterozoic rocks rocks of similar similar age. age. In In Wisconsin, Wisconsin, the the corresponding corresponding niagnetic magnetic terrane terrane is associated with exposures of Barron Quartzite and early associated with exposures of middle middle Proterozoic Proterozoic Barron Quartzite and Proterozoic and volcanic rocks. rocks. Proterozoic granites and In order to to shift shiftthe thediscussed discussed magnetic magnetic terranes terranes of east-central east-central In order Minnesota Minnesota to to match match corresponding corresponding terrances terrances in northwestern northwestern Wisconsin, Wisconsin, aa This distance southeastward transposition 60 km km is required. This distance southeastward transpositionofof at at least 60 is required. is consistent consistentwith withsome some estimates estimates ofofcrustal crustal separation during Keweenawan separation during Keweenawan riftingbut butloss lossofoftypical typical magneticsignatures signatures near near the the rift rift zone,where where riftirig magnetic zone, the Keweenawan clastic make this estimate somewhat somewhat tentative. the Keweenawan clasticrocks rocksare arethick, thick, make this estimate tentative. Clearly, quantitative quantitativeanalysis analysisof of gravity magnetic anomaliescombined combined with gravity andand magnetic anomalies further geologic geologic studies studies Isisrequired requiredbefore beforethe themodel model presented presented in this paper paper in this can be tested. The The results of this thispaper, paper,however, however, demonstrate demonstrate the the results of can be fully fully tested. potential utility gravity magneticdata data ininunraveling unraveling and and correlating correlating potential utility of of gravity andand magnetic complex now separated separated by by the the Keweenawan Keweenawan rift system. complexgeologic geologic features now rift system. 22. �METAVOLCANIC ROCKS ROCKSAT AT EAU EAU CLAIRE DELLS, METAVOLCANIC DELLS,MARATHON MARATHON COUNTY, COUNTY, AND AND AN EVALUATION OF THE AN EVALUATION OF THE SHEAR "SHEAR ZONES' ZONE" HYPOTHESIS HYPOTHESIS IN IN WISCONSIN WISCONSIN R.S. andL.G. L.G. Medaris, Medaris, Jr. R.S. Maass Maass and Department of Geology Department of Geology and and Geophysics Geophysics University of ofWisconsin Wisconsin Madison, WI WI 53706 53706 In years the the interpretation interpretation as of rocks In recent recent years as niylonites mylonites of rocks at the the Dells Dells R1OE) of the the Eau Eau Claire ClaireRiver River(sec. (sec.7, T29N, 7, T29N, R10E)ininMarathon MarathonCounty CountyWisconsin Wisconsin has wide acceptance acceptanceamong amonggeologists geologistsworking workinginin the of has gained gained wide the Precambrian Precambrian of this interpretation interpretation and the Lake the Lake Superior Superior region. region. Based Based ononthis and geophysical geophysical data, data, numerous numerousauthors authors have have drawn d'awn aa major major N2SE N25E to to N3OE N30E trending trending "s 'shear hear zone" zone Therocks rocksatat the the Dells Dells are are aa mafic to felsic through through this this locality. locality. The mafic to felsicmetametavolcanic sequence, sequence, probably probably Early Early Proterozoic Proterozoicininage, age,which whichwas wasdeformed deformed and and metamorphosed amphibolite facies during metamorphosed totoamphibolite duringthe thePenokean Penokean Orogeny. Orogeny. The The inequiinequigranular textures in in these representrelict relict porphyritic granular textures these rocks rocks represent porphyriticfeatures features and and are not the result of of cataclasis. cataclasis. The The metavolcanics, metavolcanics, 'trending ~endingN35E N35E totoN45E N45E are not the with vertical verticaldips, dips,are arebounded bounded on on the the west west and and north north by by the the Kalinke Kalinke quartz quartz monzonite, deformed during thethelater the monzonite, which which was wasemplaced emplacedand and deformed during later stages stages of of the Penokean undeformed 1500 PenokeanOrogeny, Orogeny,and andononthe theeast eastby by the the undeformed 1500m.y. m.y.old old Wolf Wolf River Sa thol ith. Batholith. ll The volcanic sequence sequence theDells Dellsranges ranges from basaltictotorhyolitic; rhyolitic; The volcanic at atthe from basaltic the including feldspar feldspar porphyries, porphyries, quartz quartz porphyries, the latter latter including porphyries,and andlapilli lapilli tuffs. In the feldspar feldspar porphyries porphyries many many of the the feldspar feldsparphenocrysts phenocrysts remain remain In the subhedral to to euhedral, euhedral, and and aa significant significant number not been rotated into subhedral number have have not been rotated the plane planeofof the the foliation. foliation. Some Someofofthe the quartz quartz phenocrysts phenocrystsinin the the quartz the quartz porphyries have beenflattened, flattened, but porphyries have been but others others have have not, not,and and none none are are as as granugranuIn addition, some contain relict lated as as would would be be expected expectedin in a mylonite. In addition, some contain relict embayment unitsare arenow now amphibolites amphibolites containing containingsubhedral subhedral embaymentfeatures. features. Basaltic units euhedral hornblende, hornblende, while contain to euhedral while compositionally compositionally intermediate intermediate units contain subhedral garnet. subhedral Compositionallayering layeringvaries variesinin thickness thickness from frommillimeters millimeters to to tens tens of Compositional distinctive lithologies lithologies down to the meters. Numerous Numerous distinctive down to the millimeter millimeter scale scalecan can be traced across acrossthe theoutcrop outcropwith withlittle little orornonochange be traced change in in thickness. thickness. Crosscutting mafic andfelsic felsic veinlets cutting mafic and veinlets are are tightly tightlyfolded, folded,but butthere thereisisnonoevidence evidence of isoclinal isocJinal folding, folding,and and attenuation attenuation of of fold fold limbs limbs isisminor. minor. Both Both the the micromicroscopic and features of these scopic and mesoscopic mesoscopic features these rocks rocks were were produced produced by by deformation deformation associated middle grades grades of metamorphism associated with with middle metamorphism without withoutsubstantial substantial transpositransposltion tion of of layering. layering. ThroughoutWisconsin, Wisconsin,rocks rocksolder older than than the the 1765 m.y. old old granites 1765 m.y. granites and and Throughout rhyolites rhyolites have have been been subjected subjected to to a widespread widespread brittle brittle deformation deformation event event in nature during the thePenokean Penokean Orogeny. Orogeny. This This deformation deformation was was regional regional in nature rather rather than zones of intense intense cataclasis. cataclasis. We many of the than localized localized in zones Wesuggest suggestthat that many of the localities previously localities previouslydescribed described as as mylonites, mylonites, are are either eithermetavolcanics, metavolcanics, or rocks affected by this thisregional regionalevent, event,and andshould should be be reevaluated reevaluated with with these these rocks affected by alternatives inin mind. mind. 23. �WERE THERETWO TWOMIDDLE MIDDLEPRECAMBRIAN PRECAMBRIANOROGENIES OIOGENIESIN IN THE THE LAKE WERE THERE LAKE SUPERIOR SUPERIOR REGION? REGION? Gene LaBerge Gene L. L. LaBerge Geology Department Department Geology University ofofWisconsin-Oshkosh University Wisconsin-Oshkosh Oshkosh, Wisconsin 54901 Oshkosh, WIsconsin Precambrianrocks rocksinin Central Central Wisconsin Wisconsinoccur occurasaslarge, large, discrete areas Precambrian areas of gneisses, areas of of greenschist gneisses, amphibolites amphibolites and and migmatites, migmatites, and and areas greenschist facies facies Countyisis underlain underlain mainly volcanic volcanic and and plutonic rocks. rocks. Marathon Marathon County mainly by by greengreenfacies volcanic volcanic and and plutonic contact with with gneissic gneissic schist facies plutonic rocks rocks inin fault contact ages suggest suggestthat that both rocks rocks on on the the north, north, west west and and south. south. Radiometric Radiometric ages both the the gneisses and greenschist greenschist facies fades rocks gneisses and rocks are areMiddle MiddlePrecambrian. Precambrian. Fold axes, axes, mineral mineral lineations Fold lineations and and elongated elongated fragments fragments in the the gneisses gneisses However, comparable plunge to the west west at at 200_600 20 0 -60 0 over the region. region. However, comparable plunge to the over most most of of the thegreenschist greenschistfades faciesvolcanic volcanic rocks in MarathonCounty Countyplunge plunge lineations ininthe rocks in Marathon east to northeast Near the fault boundary between east northeast at at 500 50 0 to to near near vertical. Near the fault boundary between vertical. gneissic and andgreenschist greenschistfacies fadesrocks, rocks,the thelineations lineations are are nearly nearly vertical. vertical. gneissic Lineations in greenschlst(?) Lineations greenschist(?) fades faciesvolcanic volcanicrocks rocksIninRusk, Rusk,Price Priceand andOneida Oneida Counties the east. east. Therefore, appears to be a consisconsisTherefore, there appears to be Counties also also plunge plunge to to the tent relationship relationshipbetween between direction directionofoflineations lineations metamorphic grade. grade. andand metamorphic This that the rocks beensubjected subjectedtotodifferent different stresses, This suggests suggests that rocks have have been stresses, and and these these stresses stresses may maybebeofof different different age. age. Myers (1978) rocks folded folded about about Myers (1978)reports reports greenschist greenschlst facies facies volcanic rocks east-plunging axes axes restihg restiHg unconformably unconformably on on gneisses gneisses in western western Clark Clark County. County. Thus, aa period of formation of of the Thus, of erosion erosionmust must have have occurred occurred between between formation the gneisses and rocks. gneisses anddeposition depositionof of the the volcanic rocks. If the If thegneisses gneisses (and (and the thedeformation deformation ininthem) them)are areMiddle MiddlePrecambrian Precambrian and and the the greenschist greenschlst facies fades rocks rocks are are also alsoMiddle Middle Precambrian, Precambrian, then then there must be be two two periods periods of of Middle deformationinIn the the region. These must Middle Precambrian Precambrian deformation two postulated deformations deformations may may be Lake Superior two be recognized recognized elsewhere elsewhereinin the the Lake region. Mild Mild flexuring on the the iron iron ranges after flexuring and and erosion erosion occurred occurred on ranges after deposition of ofthe theChocolay ChocolayGroup Group ofofthe theMarquette MarquetteRange Range Supergroup. Supergroup. Conceivably the gneissic gneissic rocks Conceivably the rocks In in Central Central Wisconsin Wisconsin represent represent aamore more intense intense metamorphi sm associ ated with is unconformity. unconformity. The II Penokean Orogeny," Orogeny, II The 'Penokean metamorphism associated withththis which which occurred occurred after afterdeposition depositionof of thethe Menominee Menomineeand and Baraga Baraga groups, groups, would would then be then be represented represented by by the thegreensch-Ist greenschist fades faciesmetamorphism metamorphism and and widespread widespread ofgranitic graniticrocks rocksIn in muchofofnorthern northernWisconsin. Wisconsin. intrusion of much 24. �VOLCANIC OF THE VOLCANIC AND AND PLUTONIC PLUTONIC ROCKS ROCKS OF THE JUMP JUMP AND AND YELLOW YELLOW RIVER VALLEYS, VALLEYS, NORTH-CENTRAL WISCONSIN WISCONSIN NORTH-CENTRAL M. L. M. L. Cummings Cummings Department of of Earth Department Earth Sciences Sciences Portland State State University Portland Portland, OR Portland, OR 97207 Metavolcanic Metavolcanic rocks rocks are are exposed exposed along along the the Jump Jump River ininsoutheastern southeasternRusk Rusk Countyand andlocally locally along County along the the Yellow Yellow River Rivernear nearGilnian, Gilman, Wisconsin. Wisconsin. Plutonic rocks rocks crop crop out south south of of the theJump Jump River River arid and along along the the Yellow Yellow River. River. The The metavolcanics and and some some plutonic plutonicrocks rockshave havebeen beendeformed deformedand andmetamorphosed metamorphosed under under upper greenschist greenschisttoto lower lower amphibolite amphibolitefacies fades conditions. upper conditions. Schistosity Schistosity is weakly to to strongly developed andisis subparallel subparallel to bedding in the weakly developed and bedding in the volcanics. volcanics. Stratigraphic tops Stratigraphic tops indicate that that the thevolcanics volcanics are are overturned overturned to the the south south and appear have been fold axes. axes. and appearto to have beenfolded folded about about northeast northeast trending trending fold Quartz monzonlteplutons plutonscrop cropout out south south of of the River and and locally locally the Jump Jump River Quartz monzonite The plutons plutons are are weakly weakly foliated foliated and can can be be shown showntotointrude intrude the the volcanics. volcanics. The and quartz monzonite pluton also crops locally display display cataclastic cataclastic textures. textures. A quartz monzonite pluton crops out along north of out along Main Main Creek Creek north of the theJump Jump River. River. The displaysa agrano— granoThe pluton displays phyric texture and phyric and euhedral euhedralquartz quartzcrystals crystals occur occur as as inclusions inclusions in feldspar feldspar crystals. crystal S. A strongly foliated foliatedpluton plutoncrops cropsout out2½ 2~miles miles south south ofofthe theJump Jump River River and similar sirnilarplutonic and plutonic rocks rocks crop crop out out along along the the Yellow Yellow River. River. The The composition of the the plutons plutons Is is granodlorite, granodiorite. An intermediate intermediatecomposition corripositionvolcanic volcaniccenter centercrops cropsout outeast eastofofthe the village village An of Jump Jump River. Volcanic Volcanic blocks blocks to one one foot foot diameter diameter form form massive massive units associated bedded tuffs and massive flows. associatedwith with fine-grained fine-gralned bedded tuffs and massiveporphyritic porphyritic flows. Crystal-lithic tuffsand andintermediate intermediate totobasic basic flows flows crop crop out out at atapparently apparently Crystal-lithic tuffs similar stratigraphic similar, stratigraphic levels levelseast eastand and west west of the the volcanic volcanic center. center. A A prophy.prophyritic with plagloclase phenocrysts riticfelsite felsite with plagioclase phenocrystsoccurs occurs totothe thesouth south ofofthe themain main fragmentalunits units of of the the volcanic volcanic center center and andisis believed believedtoto be bestratigraphically stratigraphically fragmental abovethe the volcanic volcanic center. above The geologic geologic evolution evolution of The of the the area area suggests suggests volcanism volcanism followed followed by by or or Deformation of the Deformation of the area area produced axes. Quartz monzonite monzonite produced recumbant recumbantfolds folds about about Northeast Northeast trending axes. iritrusives were alongthe theaxial axial zones zonesofof the the folds folds producing intrusives were emplaced emplaced along producing linear The metamorphic grade may increase to the south plutonic toward the plutonic belts. The metamorphic grade may increase to the south toward Yellow This interpretation interpretationsuggests suggests that thatthe theproposed proposed northern northern Yellow River. This boundary of the Amphibolite complex and the the Jump River Fault boundary of the Chippewa Chippewa Amphibolite complex and Jump River Fault Zone Zone need to to be need be reconsidered. reconsiderea. associated with, intrusion intrusion of granodioritic associated with, granodioritic plutons. plutons. 25. �HEAVY MINERAL ANALYSIS OF OF PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS IN IN RUSK RUSK COUNTY COUNTY HEAVY MINERAL ANALYSIS * Tom Ernst, cohn Tom Ernst. John Markert, Melissa Melissa Montz Montz * UniversityofofWlsconsln-Oshkosh Wisconsin-Oshkosh University Department Department of Geology Geology Oshkosh, Oshkosh, Wisconsin 54901 The bedrock bedrockin -InRusk RuskCounty County consistsmainly mainlyofofgranitic granitic and The consists and metavolcanic metavolcanic rocks of middle quartzite bodies are believed middle Proterozoic Proterozoic age. age. Several Several quartzite bodies are believed to rocks The age ageof of the various unconformably middle Proterozoic rocks. rocks. The various unconformablyoverlie overlie the the middle quartzltes isisnot quartzites notknown, known, but but they theyhave have been been correlated correlated with with the the middle middle Proterozoic QuartzitebybyDott Dott and andDalziel Daiziel (1970) (1970) and andwith with the the late Proterozoic Baraboo Baraboo Quartzite late Proterozoic Sioux Sioux Quartzite QuartziteofofMinnesota MinnesotabybyCraddock Craddock (1972). (1972). The study determine whether siliceous The study was wasundertaken undertakentototry try to determine whether the the various various siliceous rocks have the same origin and whether Four units rocks have the same origin and whether they they may maybebecorrelative. correlative. Four were sampled sampled for study,the theBarron Barronand andFlambeau Flambeau Quartzites Quartzitesand andtwo twounnamed unnamed were for study, units informally units. informallyreferred referredtotohere hereasasthe theBruce Bruceand and Broken Broken Arrow Arrow units. The BarronQuartzite Quartziteisisnearly nearlyflat-lying flat-lying and The Barron and forms forms aa ridge ridge in the the Petographic show well-rounded, northwestern part the county. county. Petographic studies show northwestern part of the To the south, south, the theFlambeau Flambeau well-sorted grains grains with with quartz quartzovergrowths. overgrowths. To In contrast to the Quartzite forms another contrast to the flat-lying flat-lyingBarron, Barron, Quartzite forms another resistant resistant ridge. In Flambeau Quartzite as as a steeply dipping tightly the the Flambeau Quartziteoccurs occurs a steeply dipping tightly folded folded unit. unit. Thin section similar totothe theBarron Barron although although sorting sorting section analysis analysis reveals reveals aa lithology lithology similar is not not as as complete. complete. Heavy Heavy minerals to toboth minerals common common bothbodies bodiesinclude include apatite, apatite, zircon, corundum, corundum, and and ubiquitous hematite hematite and and niagnetite. magnetite. In In addition addition the the Barron has some some siderite, while the theFlambeau Flambeau Quartzite contains contains Barron Quartzite Quartzite has siderite, wh1e sphene. Between thetwo twoquartzite quartzite ridges ridges lie Between the liethe theBroken Broken Arrow Arrow and and Bruce Bruce units. Examination of These massiveunits unitsare areboth bothfine-grained fine-grained splintery splintery cherts. These massive cherts. Examination thin have undergone shows small small serrated serratedquartz quartzgrains grainsthat that have undergonesome some thin sections sectionsshows Heavyminerals minerals of of metamorphism butbut show no no evidence of aofdetrital metamorphism show evidence a detritalorigin. origin. Heavy the Broken Arrowunit unit include include grossularite, the Broken Arrow grossularite,zoned zoned hematite hematite and and possibly possibly spesspessartite. The very ferruginous ferruginous and and contains contains zircon zircon (malacon), (malacon), The Bruce Bruceunit unit is very and schorl. analcite and We haveestablished establishedthat that the the metacherts metachertsare arenot not detrital detrital and We have and thus thusmay may be related to the the older oldervolcanic volcanicsequence sequence rather than than the the younger younger quartzites. be related to quartzites. Petroqraphic andheavy heavymineral mineralstudies studiesindicate indicateaaseparate separateorigin origin for for the Petrographic and the respective and the metacherts. respective quartzites quartzites and the metacherts. ** Student Paper Paper 26. �DEPOSITIONAL SETTING OF OF STROMATOLITE-OOLITE STROMATOLIIE-OOLIIE FACIES DEPOSITIONAL SETTING FACIES ON ALLUVIAL FAN ON AAKEWEEAWAN KEWEEAWAN ALLUVIAL FAN Paul A. Pau1 A. IJaniels Da ni e1s Dept. Dept. of of Natural Natural Resources, Resources, Geological Geological Survey Survey Division P.O. P.O. Box Box 30028 30028 Larising MI Lansing, MI 48909 48909 R. Douglas Douglas Elniore Elmore R. Dept. Dept. of ofGeology Geology and and Mineralogy Mineralogy The University University of The ofMichigan Michigan Ann Arbor, MI Ann MI 48109 48109 The predominantly consists heavily The Copper CopperHarbor HarborConglomerate Conglomerate(~ (' 1 B.Y.) B.Y.) predominantly consists of of heavily andboulder boulder conglomerates conglomerateswith with subordinate subordinate volcanics oxidized immature immature sandstones sandstones and The unit unit is withthe the volcanics volcanics in in the The is aafining finingupward upwardand and basinward basinward sequence sequence with the lower lower portions. The The sediments (basinward) flowing sedimentswere weredeposited depositedbybynortherly northerly (basinward) streams alluvialfan fanenvironment environment off offthe thebasin basin margin. margin. streamscreating creatingaaclassical classical alluvial 1 Sedimentary structuresand andassociated associatedfeatures, features, including including current crescents, crescents, Sedimentary structures parting lineation, tabular tabular and and trough trough cross-stratification, intraformational parting cross-stratification, intraformational conglomerates, mudcracks,oolites, oolites, cross-stratified cross-stratified boulder conglomerates, mudcracks, boulderconglomerate, conglomerate, large boulders boulders ('-S (~ 70 extensive oxidation, oxidation, and and 70 cm), cm), micro-crass-stratification, micro-cross-stratification, extensive calcite pseudomorphs after probably arid, calcite pseudomorphs after gypsum; gypsurri;allall combine corribirietotoindicate indicate aa probably periodically subject to large periodically dessicated, dessicated, shallow shallow water water environment environment that was was subject large variations variations in in flow flow regime. regime. Seeminglyenigmatic, enigmatic, in in regard of such such an an environment, environment, Is is Seemingly regard to the the harshness harshness of the fan occurrence occurrenceofof algal algal stromatolites. The stromatolites are the medial medial fan The stromatolites arenow now represented laminated carbonates carbonates intercalated intercalatedwith withmudstone mudstone and and represented by by thinly thinly laminated stromatolites are sandstone, and and as as drapes drapes on sandstone, on conglomerate. conglomerate. These These stromatolites are well-preserved well-preserved with the original original depositional early diagenetic with much much ofof the depositional and and early diagenetic fabric being being retained. retained. Various micro-structure Various micro-structuretypes typesand andcements cements can can be be recognized. recognized. Stromatolite morphologiesinclude includelaterally laterally linked morphologies linkedhemispheroids hemispheroids (LLH), (LLH), horizontal horizontal mats, mats, Thin beds and oncoids, and beds containing hematitic hematiticsingle single andcompound compound oncoids, and intraclasts. intraclasts. Thin (grapestone) exhibiting primary radial cortical (grapestone)ooids, ooids,some some exhibiting primary radial corticalfabric, fabric, occur occur interinterbeddedwith withthe the stromatolites. stromatolites. bedded This cyclic three This carbonate carbonatedepositional depositional environment environmentwas was cyclicwith withat at least three thin (< « 25 25 cm) cm) biostromes biostromes present of about about four four presentthrough througha astratigraphic stratigraphic interval interval of meters. Discontinuous exposuresencompass encompass a lateral extent extent of approximately Discontinuous exposures a lateral approximately algal encrusted boulders, up 13 kilometers. Overturned 13 Overturned algal encrusted boulders, up to 50 50 cm cm in diameter, diameter, occur about two two meters rrietersstratigraphically stratigraphically below occur about belowthe thelowest lowestobserved observed biostrome, biostrome, attesting of this facies attesting to to the the exlstance existance of facies at at an an earlier earliertime, time, and and in in aa position position still stillcloser closertotothe thebasin basinedge. edge. The existanceofof the the stromatolite/oolite stromatolite/oolite facies The existance facies indicates indicatessome some of the the complexities should be complexities that that should be addressed addressedininany anyinterpretation interpretation of of the the overall depositional in particular, depositional system, system, in particular,how how aa cyclic cyclic"quiet "quietwater" water"environment environment related totoboulder boulderconglomerates. conglomerates. 27. �STRATIGRAPHY OF THE GUNFLINT GUNFLINT FORMATION FORMATION, STRATIGRAPHY OF THE CURRENTRIVER RIVER AREA, THUNDER CURRENT THUNDER BAY BAY R.J. Shegeiski Shegelski R.J. Department Geology Department of Geology Lakehead University Lakehead University Thunder Thunder Bay, Bay, Ontario OntarioP78 P7B 5E1 5El A total of offourteen fourteen stratigraphic stratigraphicsections sections ofofthe theGunflint GunflintFormation Formation have beenmeasured measured along Current River resultinginin aa section section with aa have been along thethe Current River resulting The composite compositesection sectionfrom fromthis this study lateral extent extent of of 2.6 2.6 kilometers. kilometers. The study thick and containsfive five distinct members. is 43 43 meters meters thick and contains distinctlithostratigraphic lithostratigraphic members. The base baseof of the the Gunflint The Gunflint Formation Formation has has not not been been observed observed in these these sections sections and is is probably below the the level level of and probably below of Lake Lake Superior Superior but there there isisa aconformable conformable contact with overlying asas Rove contact with overlying fissile fissileblack blackshale shaleinterpreted interpreted RoveFormation. Formation. fissile black The are, blackshale shale(450 (450cm, cm, base base The members members are,inin ascending ascendingorder: order: 1. fissile not 2. micrite-siliceous not exposed); exposed); 2. micrite-siliceousgrainstone grainstone (taconite) (taconite)association associationcapped capped by 11 meter of algal algal chert cm); 3. 3. fissile meter of chert (1450 (1450 cm); fissileblack blackshale shale(1250 (1250 cm); cm); grainstone (920 (920 cm) cm) and breccia siliceous grainstone and4.4. an analgal algal chert-intraformational breccia At least association (200 which is overlain association (200 cm) cm) which overlainby bythe theRove Rove Formation. Formation. At 50% this composite thicknessisis fissile 50% ofofthis composite thickness fissileblack blackshale shalebecause because black black shale shale interfingers with and forms a matrix to grainstone lenses as well as occurring with and forms a matrix to grainstone lenses as well as occurring as separate remainderisis predominantly predominantlysiliceous siliceous grainstone. as separatemembers. members. The The remainder grainstone. Micrite and and siliceous grainstone grainstone occur occur as as lenticular lenticulardeposits deposits which which exhibit tabular exhibit tabularand and trough trough cross cross bedding. bedding. The The grainstones contain containsmooth smooth and pustular pustular algal algal laminae, feriestrae and andpisolites pisolites and are locally locally overand laminae, fenestrae and are overlain by by flat-pebble flat-pebbleconglomerates, conglomerates, intraformational breccias breccias and and stromatolite mounds. The The grainstone-algal association isisa achert-carbonate chert-carbonatechemical chemical grainstone-algal association sedimentwhich whichwaswas reworked a littoral-intertidal depositional sediment reworked in ainlittoral-intertidal depositional environenvironmentand andisis analogous analogoustoto the the deposits deposits of Shark Australia. Flatment Shark Bay, Bay, Western Western Australia. pebble conglomeratesand andintraformational intraformatlonal breccias breccias are pebble conglomerates are high-energy high-energy deposits deposits which formed during during periodic storms. fissile shales which formed storms. The The fissile shales associated associated with with these deposits deposits likely likely represent waterdeposits depositsofof clastic clastic these represent lagoonal lagoonal and and deeper deeper water contemporaneouslywith withthe the chert carbonate. debris which which accumulated accumulated contemporaneously carbonate. 28. �PETROLOGY OF SOME SOME LOGAN LOGAN DIABASE SILLSFROM FROM COOK COOK COUNTY, COUNTY, MINNESOTA MINNESOTA ETROLOGY OF DIABASE SILLS Norriss W. Norri W. Jones Jones Department of Geology Department Geology University ofofWisconsln-Oshkosh University Wisconsin-Oshkosh Oshkosh, Wisconsin 54901 Oshkosh, 54901 Four Lower Keweenawan Logan diabase sills between between South South and and Birch Birch Lakes, Four Lower Keweenawan Logan diabase sills Lakes, South Lake Lakequadrangle, quadrangle,northeastern northeasternMinnesota, Minnesota,are arestratified stratified as South as shown shown in Figure ~ (thickness Althoughfabric fabric isis variable, meters). Although variable, the the following following (thickness in meters). general sequence ofof textural general sequence textural zones is is recognized: zones recognized: lower lower chilled, lower chilled, lowerfine—grained, fine-grained, " f}?~~. medi um-grai ned, course—grai ned medium-grained, course-grained :: ~RTIX (except in sill C) (except in sill C), porphyry , porphyry or porphyritic, upper fine-grained, porphyri tic, upper fi ne-grai ned, I::'i'<. upper chilled. upper chilled. ';/--" . r;~ I-~~~~~~~:.~;[)· ~ '62 -,..~ '"! 1S6 ,:,;.-" ..:::•. - lSI ;ooLo. [1.1. B SilL. A CHILLEO MA!tqf,: AND rtNE-r.RAINI::U PORPIlYRY. INTERC.R. ;~2;~~ lJ9 FINt:- to MEDTUM-CRO •• INTER(:R. Ij"-/} -' /I T- lOS~ .. ' — ?IFO.—C,00, OPIIITIC pT:. .' ','-, "','.- ,'.. 'I .. :-tf.OIt'!'<.-<'RA1NFTI, -." SlLl -Ol'HITlC TO I ~: : .. n SURorH IIle . ," ~(lR!-'HR '. ",,' ~ POYrOT,TODIUMAOCO. .':',;<" ;/" ~ ..., ~ :' , ;') 07 99 ~ t) F!NE-CRALNET,OPOITXC nSF.-cR.\[NF.f),nPIlITIC — TO ~TO SUa00000!c SU80PHlTlr /'/ -CIHI.U:O'V.Rc:lN 66 SILl.C .,.... 5) 51 50 __ CHlLl.F.O l(Ml.(:fN 10C-P., IOrERO., ~ ..;. . . ', ~HlE-r.!U)., tNf£R.GR .•FTOP1F909. f[\,' f'lIE~O$. TOO TOO..• 0001TIc. '.',: .~~ ......... I-'EO.-r.RO oPII1TlC. p007IiOoTrTr PORPIIYRITlr ~'~_~".'I _ :<if.DIUl'l-f:RA!':r.n, OPHITIC '" . Both chilled margins Both chilled margins contain contain scattered phenocrysts of plagioscattered phenocrysts of clase in aa matrix clase matrix of of plagioclase, plagioclase, amphiboleand/or and/orbiotite, biotite, quartz, amphibole quartz, and acicular,ororskel skeland granular, granular, acicular, — etal ilmenite. etal ilmenite. The and The finefine- and mediumgrained zones zonesconsist consist of medium-grained plagioclase, augite, plagioclase, augite,interstitial interstitial quartz, acicular quartz, acicul~rapatite, apatite,some some K-feldspar, and and eniLayed, embayed, skeletal or lath—shaoed lath-shaoed ilmenite; ilmenite;pegeo— pegeoEn 2Fs nite Fs nite (ave. (ave.Wo Wo DEn and ) and partially —resbe i n— rich partially-res6rbe~, i~§n-rich, olivine (2 samples, samples, Fo F0 2 and ol i vine (2 in2Oe Fo33 .) are present F0 ~) are present in ~6~esamples. samples . 33 F0TOUFOPOIPLrTO. = Cour—grained zonesare are distingdistingCour~e-grained zones uished by the the abundance abundance and uished by and variety variety of inter-growths inter-growthsbetween between quartz quartz and K-feldspar K-feldspar and/or and/or sodic sodic plagloand plagio1igure Fi gure 1 clase; pyroxene is typically pyroxene is typicallymore more Porphyry zones zones contain contain plagioclase phenoaltered altered than than in in finer-grained finer-grainedzones. zones. Porphyry phenocrysts appeartoto be beslightly slightly more calcic than crysts which which appear more calcic than the the matrix matrix plagioclase; plagioclase; thethe rnedium-grained other aspects aspects of of the the mineralogy mineralogy are are similar similarto to medium-grained zones. zones. Deuteric~lteration alteration was wasextensive extensivein inallall zones, zones,but butthe theintensity, intensity, distribution, distribution, Deuteric andexact exactnature natureofofthe the alteration alteration are the scale scale of of a thin and are variable, even even on on the thin section. ,'.- ~ ... : ~'.'; ~ -:~ :~; ~ 8 :.... :'•. ".:;.;. _ o rI.'l(-r;RAINF:Il. POIKIUTlt' -UlII.U;o ,'lAllf:IN -Q'iF-t:II.O •• I~Tr.RI:'t,. YORl'lIr:. 0 -CHILl,rr} 'Ullt;J~ Fourteen rock ana analyses for major and and microprobe Fourteen rock lyses for major oxides oxi des from from sills sill A s A andB Band m; croprobe analyses of feldspars, analyses of feldspars, pyroxene, pyroxene, and and olivine olivinefrom from1313samples samples (mostly (mostly from from sills AAand B) show showthat: that:(1) (1)there thereisislittle little variation sills and B) variation ininbulk bulkorormineral mineral chemistry zones;(2) (2) chilled chilled margins chemistry in the the finefine-and andmedium—grained medium-grained zones; margins are are notably richer ininSi02 alkalis than notably Si0 2and and lower lower ininCaO CaD and and alkalis than other other zones; zones; porphyry zones zones (based (based on on one one analysis) analysis)are arelower lowerin in FeD, MgO,and andCaO CaD (3) porphyry FeO, MgO, and richer in alkalis, high and richer alkalis,reflecting reflectingthethe highpercentage percentage of ofplagioclase; plagioclase; (4) coarse-grained are enriched enriched in in Si02 alkalis, depleted (4) coarse-grained zones zones are 5i0 2 and and alkalis, depleted ininCaO CaO 29. �(Jones, continued) (Jones, continued) — and MgO,have havehigh highFe20~/FeO Fe2O/FeO ratios,and andcontain containplagioclase plagioclase which which is is notably and MgO, ratios, notably are similar similar throughout, more sodic (5) augite compositions compositions are throughout, more sodicthan thanother otherzones; znes; (5) (6) the of cores mostly in 0En3 - Es WO~O_40En35_4~Fs?n_3n; (6) the composition composition of cores of mostly in the therange rangeWo ; except in the plagioclas~ crystals (excluding pneno~rysts) is An 45 _52 , except the plagioclase (xcudin enryts) is An45_52, course-grained course-gralned zones. zones. These suggest emplacement emplacement of magma containing phenoThese data data suggest of aa magma containing plagioclase plagioclase phenominor assimilation assimilation of ofadjacent adjacent Rove Rove Formation, minerals, crysts, minor Formation,crystallization crystallization minerals, and migration alkalis, water towardthe thecoarse-grained coarse-grainedzones, zones, and migration of of silica, silica, alkalis, andand water toward which werethe thelast lasttoto solidify. solidify. which were 30. �DIFFERENTIATING ULTRAMAFIC FLOWSFROM FROMSILLS SILLS IN IN THE DIFFERENTIATING ULTRAMAFIC FLOWS THE SHEBANDOWANr~INE MINEAREA, AREA, NORTHWESTERN ONTARIO, CANADA SHEBANDOWAN NORTH~~ESTERN ONTARIO, CMADA Penelope Penelope Morton Morton Department of Geology Geology Department Carleton University Carleton Ottawa, Canada Canada Shebandowan Ni-Cu Mine Chico Metals, Ltd.)isisspatially spatially associated Shebandowan Ni-Cu Mine (Inca Metals, Ltd.) associated with ultramafic sill which is is intrusive intrusive into intovolcanic volcanic rocks rocks of with aa thin thin ultramafic sill which A Belt, Superior Province,northwester~ northwester Ontario. A the Shebandowan-Wawa Shebandowan-Wawa Belt, Superior Province, study study of the the volcanic volcanic statigraphy statigraphy ininthe themine minearea area (32 (32 km km )) has has revealed revealed ultramafic the presence ofof conformable the presence conformablelens-like lens-like extrusive extrusive and and intrusive intrusive ultramafic rocks. These These are arenow nowserpentinites serpentinitesand andtalc-carbonate talc-carbonateschists, schists, but but in many instances, relict relict textures many instances, textureshave havebeen been preserved. preserved. In In the the field, field, flows flows are are differentiated differentiatedfrom from sills sinson on the the basis basis of of rock rock association. Ultramafic Ultramafic flows and genetically (?) flows are are spatially spatially and genetically (?) related to related to black black and and white, white, magnetite-chert magnetite-chert iron iron formation formation and and dark dark Youngingdirections directions green, green, iron iron rich rich basaltic basaltichyaloclastite hyaloclastite(17.8% (17.8%FeO). FeO). Younging indicate that that hyaloclastite indicate hyaloclastite sits sits on on top top of ofthe the iron ironformation formation which which in turn Sills, however, relationship however, show show no no such such relationship turn tops tops the the ultramafic ultramafic flows. flows. Sills, and can canbebeintrusive intrusiveinto into either basalts felsic pyroclastic and basalts or more more felsic pyroclastic rocks. rocks. Typical petrochemical plots al.,1977; 1977; Muir, Muir, 1979) 1979) do do not not Typical petrochemical plots (Arndt (Arndt et et al., differentiatethese theseultramafic ultramaficrocks rocksbutbut disseminatedchromites chromites have have differentiate disseminated markedlydifferent different chemical chemicalaffinities. affinities. Chromites Chromitesfound foundinin flows markedly flows are are generally generally lower lowerininA12O A1 0 and Ti0 2 and and MgO MgOcontents, contents,higher higher in TiO and have have higher +2 +2 +Mg and Fe +3 2 3+3 . . Fe /Fe +Mg and Fe /Fe +Al+Cr +Al+Cr ratios than those those chromites chromltes found found in 1n ratios than sills. sills. Analyses Analysesof of chromites chromites from from consecutive consecutivesamples samplesfrom froma athin thinsill sill (every 20 20 feet) and 03 decreases (every and from from a thin thin flow flow(10 (10feet) feet)show showthat thatCrCr?03 decreases and Fe203 Fe2O3increases increasestowards towards topofof both both units. units. But case of and thethetop But in he the case the sill , chromites the siTl, from the immediate immediate top and and bottom bottom have have exactly the chromites from exactly the same Fe203and andCrCr7O2 contents whereas thoseininthe the flow flow are ~ame Fe?03 contents whereas those are markedly markedly differelit, This different. This 8ifferent chemical trend trend might might well be attributed ifferent chemical well be attributed to different cooling cooling histories flows and and sills. histories for flows sills. ° Arndt, Naldrett, A.J., Arndt, N.T., N.T.,.~a~drett, A.J., and and D.R. D.R. Pyke, Pyke, 1977, 1977, Komatiitic I<omatiitic and and FFe Rich Rich e Tholeiit-ic Tholel1t1cLavas Lavas ofofMunro Munro Twp., Twp., Northeastern Northeastern Ontario. Journal of Petrology, Journal Petrology, Vol. Vol. 18, 18, pp. pp. 319-369. 319-369. Muir, T.L., Archean Muir, T.L., 1979, 1979, Discrimination Discrimination Between BetweenExtrusive Extrusive and and Intrusive Intrusive Archean Ultramafic Rocks Rocks in in the theShaw Shaw Dome Major and and DomeArea AreaUsing Using Selected Selected Major Trace Elements. Trace Elements. Can. Vol. 16, 16, pp. 80-90. Can.Jour. Jour.of of Earth Earth Sci., Sci., Vol. pp. 80-90. 31 31. �GEOLOGICAL EVIDENCE EVIDENCERELATING RELATING TO TO THE THE INTERPRETATION GEOLOGICAL INTERPRETATION OF OF THE THE LAKE SUPERIOR LAKE SUPERIOR BASIN BASINSTRUCTURE STRUCTURE Donald M. M. Davidson, Davidson, Jr. Jr. Donald Department of Sciences Department of Geological Sciences University Uni versity of of Texas, Texas, El El Paso The configuration the Lake Lake Superior Superior Basin Basin coincides the regional regional The configuration of the coincides with with the geologic structure and and is isprimarily primarilycomposed composed of of rock rock units unitsofof LakePrecambrian Precambrian geologic Lake (Y) age overlie older (Y) age which which unconformably unconformably overlie olderassemblages. assemblages. Evidence of poorlydeveloped developedininpre-Keweenawan pre-Keweenawan (late Evidence of basin basin formation isispoorly (late Precambrian) and geologic units region. Precambrian) andlower lower Keweenanwan Keweenanwan geologic unitsinin the the Lake Lake Superior Superior region. However,middle middle Keweenawan Keweenawan intrusives,lava lava flows, and However, intrusives, and associated associatedsediments sediments display primary features features such such as flow thickness, thickness, and and crosscrossdisplay primary as mineral mineral layering, layering, flow bedding, whichdirectly directly indicate at that that time. bedding, which indicate basin basin development development. at time. Upper Keweenawan sedimentational patterns delineatethe thebasin basin outline. outline. Keweenawan sedimentational patterns delineate Penetrative and foliation, are well well Penetrativestructures, structures,particularly particularly folds folds and foliation, are developed in Archean and Middle Precambrian rocks, but are generally rare in develvped in Archean and Middle Precambrian rocks, but are generally rare Late Precambrian faults and and joints joints are Precambrian sequences. sequences. Nonpenetrative Nonpenetrative faults are prevalent prevalent allPrecambrian Precambrian rocks rocks in in the the Lake Lake Superior Superior region. region. Curvilinear Curvilinear faults in all east-west trends, trends, prevail prevailin in Archeanand andMiddle Middle Precambrian Precambrian units, units, with east-west Archean although other other trends trends are are to to be noted, particularly particularly ininWisconsin. although be noted, Wisconsin. Northeast-and northwest-trending fractures Northeast-and fracturesare arecommon common in in Late LatePrecambrian Precambrian Faults of units although although regional regional data data are are incomplete. incomplete. Faults of late latePrecambrian Precambrian age age have been the region. region. have beenreported reportedtotooccur occurlocally locally in in the summary, Archean, Archean, Middle Middle Precambrian Precambrian and and pre-Keweenawan pre-Keweenawan geologic In summary, geologic units render little direct over that that time time interinterunits render little directevidence evidence of of basin basin formation formation over val. The The basin basin structure structure appears initiated ininmiddle appears to have have been been initiated middleKeweenKeweenawantime timeasasa acrustal crustalrift. rift. Rifting in awan in the thebasin basin proper proper was was very very likely likely enhancedbybyeast-west east-west structuraltrends trendswithin within older older units. enhanced structural 32, 32. �THE PRE-KEWEENAWAN TECTONICHISTORY HISTORY OF OF THE THE NORTH-CENTRAL THE PRE-KEWEENAWAN TECTONIC NORTH-CENTRAL LINITED UNITED STATES STATES AND AND CENTRAL CANADA CANADAAND ANDHOW HOWITIT INFLUENCED OF THE THE MIDCONTINENT CENTRAL INFLUENCED FORMATION FORMATION OF MIDCONTINENT RIFT u.S. Illinois University J.S. Kiasner, Klasner, Western Western Illinois Universityand andU.S. U.S.Geological Geological Survey Survey Macomb, Illinois 61455 Macomb t Illinois W.F. W.F. Cannon, Cannon, U.S. U.S. Geological Geological Survey Survey Reston, Reston, Virginia Virginia 22092 W.R. Van Van Schmus, Schmus,University University of W.R. ofKansas Kansas Lawrence, Kansas Kansas The Midcontinentrift rift formed about1.1 1.1 b.y. b.y. ago in crust The Midcontinent formed about ago in crust that thathad had aa long long and complex block for for several several hundhundand complexhistory historybut butthat that had hadbeen beena arigid rigid crustal crustal block red million years beforethe therifting. rifting. The rift formed red million years before The rift formed at aa high high angle angle to the the general ENE ENEstructural structural grain of general of older olderrocks rocksand and crossed crossed aaboundary boundary that sepseparates two very different different geologic arates two very geologic terranes terranes near near the the southern southern edge edge of the the Superior Province. Province. North North of crust typical typical of the the boundary, boundary,thetherift rift is is within crust of Superior Superior Province Province that that had had been been deformed deformed only and gentle gentle warpwarponlyby byfaulting faulting and ing 2.6 b.y. b.y. ago; ago; south southofofthe theboundary, boundary, riftisis in in crust that ing after about about 2.6 thethe rift that had longer and more complex complexhistory. history. There, had aa much much longer and more There, rocks rocks as as old old as as 3.8 3.8 b.y. have b.y. (Kenoran (Kenoran have u'ndergone undergonerepeated repeatedtectonism; tectonism;major majorevents eventstook tookplace placeat at 2.6 b.y. orogeny), 1.9 b.y. b.y. (Penokean (Penokean orogeny), (theemplacement emplacement of orogeny), 1.9 orogeny), and and 1.5 1.5 b.y. (the of the Wolf River Wolf River batholith batholithand andsynchronous synchronous volcanism). volcanism). The boundary boundarybetween'the between theSuperior SuperiorProvince-type Province-typecrust crust and and rocks rocks to to the The the south effect the Midcontinent Midcontinent south seems seemstoto have havehad hada apronounced pronounced effectononthe thenature natureof of the rift. Where rift. Where the is ininSuperior Superior Province-type Province-type crust, ititisisabout about150 150km km therift rift is wide andisis complex; whereitit is in terrane to the wide and complex; where in rocks rocks ofofthe themore more complex complex terrane the Its width south, ititisisabout south, about9090kmkmwide wideand and has has aa simpler simplershape. shape. Its widthchanges changes abruptly at the the contact contact of of the the two two terranes. terranes. abruptly Lithologic and/or may Lithologic and/or tectonic tectonicboundaries boundaries within withinthe theSuperior SuperiorProvince Provincemay have the Superior Superior Province, Province, haveaffected affectedthe theextent extentofof the the Midcontinent Midcontinentrift. rift. In the the riftlies lies entirely within the confines of Shebandowan the Shebandowan granite-greengranite-greenthe rift entirely within the confines of the stone belt except 'stone except for for the thepoorly poorlydefined definedarm arm that thatextends extends to toLake Lake Nipigon. Nipigon. Changes composition, structure,ororthickness thicknessofof the the crust crust at the Changes inincomposition, structure, the north north edge of the beltmay mayhave have inhibited the the northward extension of edge of the Shebandowan Shebandowan belt inhibited northward extension of the the.ririft. ft. Orientations arms are are probably probably controlled Orientations of of the the rift rift arms controlled by by older older faults faults or analysis of fractures. Lineament Lineament analysis of gravity gravityand ~ndaeromagnetic aeromagneticmaps maps and and Landsat Landsat images presence of linearzones zones that thatare aremore more than than 1000 1000 km km long. imagesindicate indicate the the presence of linear l~any known faults or zones zones of of crustal crustalweakness. weakness. Manyofof the the lineaments lineaments coincide coincide with with known faults or Geologic data indicate indicate that these Geologic data thes features features formed formed before before 1.1 1.1 b.y. b.y. ago. ago. Conspicuous directions N. 65 65 b W., W., N. N. 45° 45 0 W., W., N. N. 35° 35 0 E., and and N. N. 65° 65 0 E., E., Conspicuous directions are N. the thoseofofindividual individual segments segments therift. rift. the same same asasthose ofofthe 33. �(Klasner, Cannon and and Van Van Schmus, Schmus, continued) (Kiasner, Cannon continued) A large large elliptical elliptical gravity gravitylow, low,more more than than -60 -60 milligals milligals ininamplitude, amplitude, lies ininpart partabove above granitic graniticrocks rocks inincentral centralWisconsin. Wisconsin. This low low suggests suggests the presence of large large volumes subjacentgranitic granitic rocks the presence of volumes ofof subjacent rocks throughout throughout this area. The subsurface granite granite IninWisconsin Wisconsin may may have have played played aa role role The inferred subsurface in localizing because of the the rift rift symmetrically localizing the the rift rift becausethe thearcuate arcuate shape shape of symmetrically of encircles encircles the the gravity gravity low. low. It It may may be be that the the granite graniteformed formed an an area area.of unusually strong strong crust crust through throughwhich whichthe therift rift could unusually could not not form. form. 34. �KEWEENAWAN NATURE OF OF KEWEENAWANVOLCANISM VOLCANISMAND AND THE THE NATIJRE KEWEENAWANRIFT RIFT TECTONICS KEWEENAWAN TECTONICS John C. Green Green John C. Geology Geology Department Department University of ofMinnesota, Minnesota, Duluth Duluth Duluth, Minnesota Minnesota 55812 55812 Since theearly earlyinklings inklingsinin the the '60's '60's of aa rift—tectonic origin for Since the rift-tectonic orlgln for the the Mid-Continent Gravity High, High, aanumber Mid-Continent number of of more more detailed detailedconcepts concepts have have developed. developed. These These include include that of ofWhite White (1972) (1972) who who proposed proposed the the existence existence of of several several separate basins of accumulation of lavas along a tensional zone, contrasting separate basins of accumulation of lavas along a tensional zone, contrasting with modern modern examples such as as thethe East African Rift central graben graben examples such East African Riftwith with its its central and Gilmer Gilmer (1973) and relatively thin and relatively thin volcanics. volcanics. Chase Chase and (1973) subsequently subsequently proposed proposed widens aa strictly strictlyrigid-place rigid-placemodel, model, ininwhich which the the rift rift widens totothe thenorth northfrom from aa pole New pole of of rotation rotationin in NewMexico Mexico and and in in which which mafic mafic mantle-derived mantle-derived rock rock completely completely fills the to widths 80-90 fills therift rift to widthsof of 80-90km. km. Weiblen Weiblen and press) have have since since and Morey Morey(in (in press) suggested Duluth Complex, Complex, and the suggestedthat that the the Duluth andbybyextrapolatio~ extrapolation,other otherparts parts of of the structure, of normal normal faulting faulting ininwhich structure, developed developed through through aa sequence sequence of whichdowndowndropped, rotated blocks wayfor for the the great dropped, rotated blocks of of crust crustunder under tension tensionhave have made made way great volumes intrusions leaving leaving an an intact, intact, horizontal volumes ofofintrusions horizontal carapace carapace of volcanic volcanic rocks. rocks. Green (1977) (1977)elaborated elaborated on on LoJhite's White's model model of of broad Green broad volcanic "pl plateaus." ateaus. 1I The following evidence mapped volcanics tends tends to to The evidence within withinthethe mappedKeweenawan Keweenawan volcanics minimize, thoughnot noteliminate, eliminate,the therole roleof of normal normalfaulting, faulting, particularly particularly minimize, though grabenformation, formation, and andmega-dikes mega-dikes withinthe theLake LakeSuperior Superiordistrict. district. 1. 1. Nograben within No- where are the pre-Keweenawan where are the lavas 1avas seen seen to tobe befaulted faultedagainst aga i nst pre-Keweenawan rocks. rocks. 2. With the exception exception of the the Osler Osler Group Group in Thunder Thunder Bay-Nipigon the basal basal the Bay-Nipigondistrict, district, the Keweenawan lavas erupted onto area relief that was either an Keweenawan lavas areare erupted onto an an area of of lowlow relief was either an erosion surface surfaceoror the the site site of cratonic erosion cratonic deposition deposition of water-laid water-laid quartz quartz arenite. arenite. At of the conglomerate reflect localfault faultrelief. relief. 3. The At the the base base of the Osler Osler aa conglomerate maymay reflect local The stratigraphy thevarious various Keweenawan plateau accumulations is is ininmany many stratigraphy ofofthe Keweenawan plateau lava accumulations cases remarkably remarkablycontinuous, continuous,showing showingboth botha asurface surfaceofoflow lowrelief relief on cases on which which flows could spreadout outfor for many manytens tensofofkilometers, kilometers,and andthe thelack lackofof faulting faulting flows could spread within The major major faults faults now evident show reverse, not not normal within sequences. sequences. The now evident show reverse, normal displacement. 4. Normal Normaldisplacement displacementisis rarely rarely observed rocks on on either either observed between between rocks side of basaltic dikes within andand beyond Keweenawan ~ide ofKeweenawan Keweenawan basaltic dikes (feeders?) (feeders?)both both within beyond Keweenawan volcanic areas. areas. If normal faults faults had had been been prevalent, prevalent, the the feeder feeder dikes dikes could could If normal The small be expected expectedtoto have havefollowed followedthem thempreferentially preferentially or vice be vice versa. versa. 5. The percentage (2-3%) (2-3%)ofof interflow interflow sediments percentage sediments in in most most of ofthe me major major plateau-lava plateau-lava sequencesargues arguesagainst againstlarge large normal-fault normal-fault displacement sequences displacement during during volcanism. volcanism. 6. The The fanning of dips dipsand and down—dip down-dip thickening the Portage Portage Lake Lake Volcanics Volcanics fanning of thickening of the imply warping, warping,not notfaulting, faulting, at at the the edge edge of the the lava lava basin. basin. 7. If mafic imply If mafic magma supply gravityanomaly anomaly were were dominated dominated by by half-graben half-graben magma supplytotothe the crustal crustal gravity faulting leading totointrusions, intrusions, surely manysuch suchfaults faultswould wouldhave havereached reached faulting leading surely many the surface are they? Where are they? 8. The anomalies the surface through through the the lavas. lavas. Where The gravity gravity anomalies (at least leastininwestern westernLake LakeSuperior Superiorwhere wherethe theattempt attempthas hasbeen beenmade: made: White, 1966) can can be be adequately adequately modeled modeledbybythe the known knownlava lavabasins basins without without any 1966) any major major separation of ofmany many tens kilometers. 9. Chase Chase and model crustal separation tens of kilometers. and Gilmer1s Gilmer's rriodel ignores basalts of of Ontario. ignores the thick thickOsler Oslerand and Mamainse Mamainse basalts This of Keweenawan basicallysupports supportsa view a view of Keweenawanniagmatism magmatism in This evidence evidence basically oval basins basins (such (such as as the the Columbia Columbia Plateau sma ler extent extent large, oval Plateaubasalts basalts but but of smaller 35. �(Green, continued) (Green, and thicker) which and thicker) which gradually graduallysubsided subsidedbybywarping warpingwhile whilekeeping keepinga more-or—less a more-or-less level surface. The models of Chase and Gilmer and of Weiben and do not riot level surface. The models of Chase and Gilmer and Wei ben and Morey Morey do fit the the rocks fit thegeology geology ininthe theLake Lake Superior Superior area area where where the rocks actually crop crop out. out. 36. �UPPER PRECAMBRIAN PRECAMBRIAN SEDIMENTARY SUPERIOR REGION REGION UPPER SEDIMENTARY ROCKS ROCKSOF OFTHE THE LAKE LAKE SUPERIOR Rich.rd ofMinnesota, M"lnnesota,Duluth, Duluth,MN MN55812 55812 Richard W. W. Ojikangas, Ojdkangas, University University of G.B. Morey, Minnesota Minnesota Geological St., St. St.Paul, Paul,MNMN55108 55108 GB. Morey, Geological Survey, Survey, 1633 1633 Eustis Eustis St., Paul A. A. Daniels, Daniels, Michigan Michigan Geological Geological Survey, Survey,Box Box 30028, 30028, Lansing, Lansing, MI MI 48909 48909 Paul J. Kalliokoski, Houghton, Kalliokoski,Michigan MichiganTechnological TechnologicalUniversity, University, Houghton,MIMI49931 49931 Quartzose sandstoneunits units which which represent represent parts of Quartzose sandstone ofone oneorormore moresand sand sheets sheets a few few hundred hundred feet in thickness thickness include includethe theBessemer Bessemer Quartzite in a feet or or less in Quartzlte in Michigan Group in Ontario Michigan and and Wisconsin, Wisconsin,the the Pass Pass Lake LakeFormation Formationofofthe the Sibley Sibley Group in Ontario near Thunder Bay, the the Puckwunge Formationininnortheastern northeastern Minnesota, Puckwunge Formation Minnesota, and and the near Thunder Bay, is present Nopeming Quartzite Duluth. A basal basal conglomerate conglomerate is present at at each each Nopeming Quartzitejust just west west of Duluth. localityabove above the the subjacent subjacent unconformity. unconformity. Lava Lava flows succeed succeed the the sandstones sandstones locality except in Ontario overlie the except Ontariowhere where red redmudstones mudstones and and carbonates carbonates overlie thesandstone sandstone and and are in turn are turnoverlain overlainbybyflows flowsand andsedimentary sedimentary rocks rocks of ofthe theOsler OslerFormation. Formation. The immediately overlying overlyingthetheBessemer Bessemerand andNojeming Nopellling are arecommonly commonly pillowed pillowed and and flows immediately the sandstone sandstone appears to tohave been un1ithified volcanism the appears have been unlithifiedatatthe thetime timeofofinitial initial volcanism whereas the Puckwunge Puckwunge appears to have lithified(e.g. (e.g. Mattis, Mattls, 1972). whereas the appears to have beenbeen 1ithified 1972). There is paleomagnetic andradiometric radiometricevidence evidencethat thatthe the lower lower Sibley Sibley is older paleomagnetic and older (1340 (1340 m.y m.y.) (Wanless andLoveridge, Loveridge,1977) 1977)than thanthe thelatter latter two be closer closer to (Wanless and two units units which which may may be to 1100 m.y. m.y. old. Paleomagnetic evidence(e.g. (e.g. Books, 1100 Paleomagnetic evidence Books, 1968, 1968, 1972; 1972; Halls Halls and and Pesonen; inin prep.) thatthe theBessemer Bessemer and are normally normally Pesonen, prep.) indicates that and the the lower lower Sibley Sibley are polarized theother otherunits units are are reversely be interinterreversely polarized polarized and and thus thus can can be polarized whereas whereas the preted to Thequartzose quartzosesandstones sandstones pre-tectonicinin origin, origin, preted to be be younger. younger. The areare allallpre-tectonic although the Sibley although Sibleyrocks rockswere were deposited depositedupon upon aadown-faulted down-faulted block blockwhich whichmay may have been beena afailed failed arm armof of aa 1300 m.y. old old rift effect have 1300 m.y. riftwhich whichcould couldhave have had had some some effect in press). on on sedimentation sedimentation(Kustra (Kustraeteta1., al., 1977; 1977; Franklin Franklin et et al.,, a1., in press). During During many many pauses pausesinin Keweenawan Keweenawan volcanism, volcanism,compositionally compositionally immature immature gravels, gravels, sands, silts, silts, and sands, andmuds, muds, dominantly dominantly derived derived from from intra—basinal intra-basinal volcanic volcanic sources sources but were moved but locally locallyfrom fromextra-basinal extra-basinalolder olderterranes terranesasaswell, well, were moved toward toward the the of the the volcanic volcanicbasin basinbybystreams streams and and deposited deposited -in in stream stream valleys, on on center of alluvial and lakes White, 1970; alluvial plains, plains,inindeltas, deltas, andin in lakes(e.g., (e.g., White, 1970;Merk, Merk,1972, 1972, 1979; 1979; Jirsa, 1979, 1979, 1980). 1980). Jirsa, When volcanism ceased over most area,tectonic tectonicactivity activity associated When volcanism ceased over most of of thethe area, associated with the with the rifting-volcanic rifting-volcanicevent eventcontinued. continued. In In response, response, dominantly dominantlyfluvial fluvial 'redd bed' in the "re bed sedimentation sedimentation began began in the tectonic tectonicbasin basinwhich whichdeveloped developed on on the the site of pfLake Lake Superior, Superior, with with streams streams flowing flowing into intothe thebasin basinfrom frommarginal marginal site portions of of the the basin basin and and from from adjacent adjacent highlands. highlands. The The oldest sedimentary sedimentary portions sequence, the the Oronto Shale, and Group (Copper (Copper Harbor Harbor Conglomerate, Conglomerate, Nonesuch Nonesuch Shale, and sequence, Oronto Group Freda Sandstone present in in northern northern Wisconsin, Wisconsin, western western Freda Sandstoneininascending ascendingorder) order)isis present Upper Michigan, and and on on Isle Royale. Upper Michigan, Royale. The The Copper (to(to7000 ft ftthick) CopperHarbor Harbor 7000 thick) is dominantly fining upward alluvial fan-fluvial fan-fluvial clastic The gray dominantly aafining upward alluvial clasticwedge. wedge. The pyritiferousand andcarbonaceous carbonaceous Nonesuch is isananargillaceous cupriferous, pyritiferous Nonesuch argillaceoussiltsiltstone reducing conditions, conditions, stone unit unit (250—750 (250-750 ftft thick) thick) which which accumulated accumulated under under reducing probably lacustrine(and (anddèltaic) d~.aic)environment. environment. The The Freda Freda(12,000+ (12,000+ftft thick) probably in aa lacustrine is aa fluvian f1uvian and and lacustrine?) lacustrine?) unit. The The source source rocks rocks for for the theOronto Oronto Group Group included both Keweenawan Keweenawan volcanics andand older rocks, with included both volcanics olderbasement basement rocks, withthe thelatter latter most important in the most important the Freda. Freda. - ll 37. �(Ojakangas, Morey,Daniels Danielsand andKa11iokoski, Kalliokoski, continued) (Ojakangas. Morey, continued) In Wisconsin, the the more more steeply dipping Dronto Oronto Group Group is (unconIn Wisconsin, steeply dipping is overlain (unconformably?) by mature (e.g., (e.g., Hite, formably?) by the more more mature Hite,1968; 1968;Myers, Myers,1971; 1971;Craddock, Craddock, 1972), 1972), subhorizontal Bayfield Bayfield Group whichincludes, Includes,inin ascending ascendingorder, order, the the fe1dfeldsubhori~onta1 Group which and the spathic Orienta Orienta Sandstone, Sandstone, the quartzose quartzose Devils Devils Island IslandSandstone, Sandstone, and Chequamegon Sandstone. Sandstone. Geophysical suggests the group group fe1dspathic feldspathic Chequamegon Geophysical evidence evidence suggests may beasasmuch muchasas7000 7000 thick (Mooney, (Mooney,etet a1., al., 1970). The Devils Devils Island may be ft ftthick 1970). The Island (300 ft thick) (300 ft thick) isisapparently apparently the the result result ofofthe thelacustrine lacustrinereworking reworking of of Orienta fluvial detritus in tectonic tectonic activity. Orienta fluvial detritus during during aa significant significant pause pause in The source theBayfield BayfieldGroup Groupwere were dominantly dominantlypre-volcanic pre-volcanicbasement basement The source rocks rocks for the Oronto detritus detritusmay may also also have have been been important. important. rocks, although reworking reworking of Oronto rocks, although In threeformations formationsare arepresent--the present--thefeldspathic-lithic feldspathic-lithic red In Minnesota Minnesota three red Church Formation thered redfeldspathic fe1dspathicFond Fonddu du Lac Lac Solor Solor Church Formation(to (to3200 3200ftft thick), thick), the Formation and the the buff buffquartzose quartzose Hinckley Hinckley Sandstone Sandstone (to Formation(400-1200 (400-1200ftft thick), thick), and (to 500 ftft thick). The the subsurface subsurface (Morey, (Morey, 1972, 1972, 500 The Solor Solor Church, Church, found found only only in the In the 1974) zone. In the 1974) was wasdeposited depositedsouthwest southwestofofLake LakeSuperior Superioralong alongthe therift rift zone. basins flanking the St. St. Croix CroixHorst, Horst,the theSolar SolorChurch Church isisoverlain overlainunconformunconformbasins flanking the ably by duLac Lacwhich whichininturn turnisis gradationally gradationally overlain by ably by the the Fond Fond du by the the contrast the the Solor Solor Church Church conformably conformably overlies rocks Hinckley. In In contrast overlies basaltic rocks on top top of the and in in turn isis unconformably overlain by by the the Hinckley; Hinckley; at at on the HUrst Horst and unconformably overlain places aa regolith regolith separates separates the the two two formations. formations. The The hiatus represented represented by by places this regolith beenofof significant significant duration, regolithmay may have have been duration, for forthe theSolor SolorChurch Church was indurated by by diagenetic or processesprior prior to was indurated or very verylow lowgrade grade metamorphic metamorphic processes to the deposition of ofthe theFond Fond du du Lac. Lac. The The Solor Church Church Formation Formation can can be be correcorrethe deposition lated with du Lac Lacwith with the the Orienta, with the theOronto Oronto Group, Group, the the Fond Fond du Orienta, and and the the Hinckley with the Devils Island. The Solor Church and the Fond Hinckley with the Devils Island. The Church and the Fond du du Lac Lac were were deposited stream-floodplain environment, deposited in aa meandering meandering stream-floodplain environment, whereas whereas the Hinckley Hinckley appears to have beenformed formedbybythe thereworking reworkingofof Fond FondduduLac Lacdetritus detritus in the have been the appears to same lacustrine environment same lacustrine environment in which which the the Devils DevilsIsland IslandSandstone Sandstonewas was formed formed (Tryhorn (Tryhorn and and Ojakangas, Ojakangas, 1972). 1972). In Michigan the feldspathic In Michigan the fe1dspathic to toquartzose quartzose Jacobsville JacobsvilleSandstone Sandstone is aa northward-thickening, fault-borderedwedge wedge regionallyvariable variablefluvial fluvial northward-thickening, fault-bordered ofofregionally sedimentary rocks. The maximum drilledthickness thicknessisis 2845 ft and sedimentary The maximum drilled 2845 ft and the the geogeophysically is 10,000 ft. Most of the physically inferred thickness thickness is 10,000 ft. Most of the conglomerate conglomerate clasts can be be correlated correlated with areas to to the can with deeply deeply weathered weathered source source areas the south south and and southsoutheast, east, confirming confirming paleocurrent paleocurrent data data near near the the base base of of the the section. section. Northeast coarse conglomerate conglomerate(clasts (clasts to near the of Houghtori Houghton aa coarse to 36 36 cm) cm) exposed exposed near KewnawanFau1t interbed highly angular angular basalt basalt fragments KewenawanFault andand an an interbed ofofhighly fragments in the the sandstonewere werederived derivedfrom fromthe the Portage PortageLake Lakefelsic felsic and sandstone and mafic mafic lavas lavas northwest northwest from basement of the the present present fault faultor or from basementhighs highsnow now buried buried under under the the sandstone. sandstone. TheJacobsville Jacobsville is is also found on the the east of Lake Superiorand andisis interinterThe found on east end end of Lake Superior preted to be present a deep deep drill hole ininthe themiddle middleofofthe theMichigan Michigan preted to be present in in a drill hole Basin (Fowler and Basin and Kuenzi, Kuenzi, 1978). 1978). Correlation with with the theBayfield BayfieldGroup Groupremains remains uncertain. Sedimentologicaland andstratigraphic stratigraphic analysis analysis in progress progress will willexpand expand Sedimentological upon earlier work on the the causal upon earlier work (e.g.. (e.g., Fowler Fowler and and Kuenzi, Kuenzi, 1978) 1978) on causal tectonic events and and the the resultant sedimentational within the events sedimentational events events which which occurred occurred within the mid-Continent rift system system in in the theLake Lake Superior Superior region. region. mid-Continent rift 38. �GEOCHRONOLOGY KEWEENAWANROCKS: ROCKS: A A REVIEW GEOCHRONOLOGY OFOF KEWEENAWAN REVIEW W.R. Van Van Schmus, Schmus,Dept. Dept. of of Geology, W.R. Geology, Univ. Univ. Kansas, Kansas,Lawrence Lawrence J.C. Green, Green, Dept. Dept. of ofGeology, Geology, Univ. Univ.Minnesota-Duluth Minnesota-Duluth J.C. H.C. Dept. of of Physics, Physics, Univ. Univ. Toronto, Toronto, Ontario Ontario H.C. Halls, Flails, Dept. There have have been beenmany manyU-Pb, U-Pb,Rb-Sr, Rb-Sr,and andK-Ar K-Argeochronologic geochronologicstudies studies of of There U-Pbdata data of of Silver that most U-Pb Silverarid and Green Green show show that most of the the igneous igneous activity (by activity (byvolume) volume) occurred occurred lllO 1110++10 10m.y. m.y. ago ago ininthe theLake Lake Superior Superior region. region. This age includes rocks of the the upper upper normal normal magnetic magnetic polarity as well well as as upper upper This age includes rocks polarity as polarity sequence, thus dating dating that of the theunderlying underlying reversed reversed magnetic magnetic polarity sequence, thus units of reversed-to-normal reversed-to-normal change change atat1110 1110-1-~ 10 10 m.y. m.y. ago. ago. Keweenawan rocks, Keweenawan rocks. Many results are conconManyofof the the Rb-Sr Rb-Sr and and K-Ar K—Ar resultsononthe the1110 1110m.y. m.y.old old units units are cordant, although in many many instances cleardiscordance discordance with with the theRb-Sr Rb-Sr cordant, although instances there there is clear and ages being too young. young. Many not yet yetdated datedbybyU-Pb U-Pb methods, methods, and K-Ar K-Ar ages being too Manyother other units, units, riot also give give young young ages, ages, suggesting suggesting that thatupper upperKeweenawan Keweenawan igneous may igneousactivity activity may However, review review of paleomagnetic have as young young as as 900 900 m.y. m.y. ago. ago. However, paleomagnetic have extended extended to to as pole positions for such youngcrystallization crystallization forsuch such units unitsshows shows no no evidence evidence for such young pole positions for ages; the data are are consistent consistent with all ages; the paleomagnetic paleomagnetic data allyounger youngerages ages being being about about 1100 m.y. m.y. old. 1100 K-Ar of 1150-1250 m.y.for for older older units (e.g., K-Ar results suggest suggest ages ages of 1150-1250 m.y. (e.g.,Logan Logan Sills) ofofthe and, along along with with Rb-Sr results, for Sills) thereversed reversedsequence sequence and, Rb-Sr results, for riornial normal polarity pole positions positions are polaritydikes dikesofofthetheSudbury Sudburydike dikeswarm. swarm. Paleomagnetic Paleomagnetic pole are also also consistent igneousactivity activity occuring consistent with withearly earlyKeweenawan Keweenawan igneous occuring about about 1200 1200 m.y. m.y. ago. Thus, we conclude concludethat that Keweenawan riftingand andassociated associatedigneous igneousactivity activity Thus, we Keweenawan rifting began began1200-1225 1200-1225m.y. m.y.ago, ago,peaked peakedatat1110 1110m.y. m.y.ago, ago, and andceased ceasedshortly shortly thereafter. 39. �GRAVITY STUDIES OF GRAVITY AND AND MAGNETIC MAGNETIC ANOMALY ANOMALY STUDIES OF LAKE LAKE SUPERIOR SUPERIOR William 3. J. Hinze, Purdue University, West Lafayette, Lafayette, Indiana Indiana47907 47907 Hinze, Purdue University, West Richard Richard J. J. Wold, Wold, U.S. U.S. Geological Geological Survey, Survey,Denver, Denver, Colorado Colorado 80225 80225 Norbert W. W. O'Hara, Inst.ofof Technology,Melbourne, Melbourne, Florida Florida32901 32901 Norbert O'Hara, Florida Florida Inst. Technology, Gravity and magnetic Gravity and magneticanomalies anomaliesininLake LakeSuperior Superiorare areuseful usefulprimarily primarily in out the the extent extentand and near—surface near-surface structure igneous rocks rocks that crop crop tracing out structure of igneous out around the lake lake or or on on islands islands within within the out around the the lake. lake. The the The data data show showthat that the LakeSuperior Superiorstructural structural basin with the the shoreline shoreline of the Lake basin generally generally conforms conforms with the lake. The The limbs the basin basin are aredelineated delineatedbybygravity gravity magneticmaxima maxima limbs of the andand magnetic which occur occur over over the the outcropping and buried buried mafic mafic volcanic volcanic rock. which outcropping and rock. The The limbs coalesce at at the andsoutheastern southeasternends ends thelake lake into into the coalesce the southwestern southwestern and ofofthe the midcontinent and and mid-Michigan mid-Michigan geophysical geophysical anomalies. anomalies. These These geophysical data geophysical data indicate several several faults faults that roughly parallel the indicate roughly parallel the outline outline of of the the basin basin or or transect the the anomaly anomalymaps mapsprovide providenonoindication indication of transect the basin. basin. However, However, the of an an axial graben. Rather, the the inferred inferred axis graben. Rather, axis of of the the basin basin isisgenerally generallyaamagnetic magnetic minimum reflecting the increased minimum reflecting increased thickness thickness of ofsedimentary sedimentary rocks rocks having having low low magnetic susceptability. magnetic susceptability. Gravity and and magnetic magnetic anomalies arecaused caused anomalies locally locally are by and variation variation in by structural deformation deformation and in thickness thickness of of volcanic volcanic and and sedisedimentary rock related relatedtotopre-Keweenawan pre-Keweenawan topography topography and and Keweenawan Keweenawan fault mentary fault blocks major north-northeast north-northeast trending that strike strikeinto intothe thebasin basinfrom fromthe themargins. margins. A major trending fault divides fault divides the thebasin basin into intocontrasting contrastingeastern easternand and western western units. units. By comparisonwith withthe thewestern westernunit, unit, the the eastern eastern unit unit is comparison is characterized characterized by by relatively subdued due to to a combination of relatively subdued gravity gravityand and magnetic magnetic anomalies anomalies due combination of less diastrophism, of volcanic rock, less diastrophism, decreased decreased volume volume of rock, and and more more extensive extensive sedimentary sedimentary cover. cover. Modeling ofofthe constraintsprovided provided by by the the Modeling thegravity gravity data data utilizing utilizing constraints geologic, magnetic, magnetic, and andseismic seismicdata dataindicates indicatesthat that volcanic volcanic units units overlain geologic, by relatively nonmagnetic low-densityclastic clastic sedimentary sedimentaryrocks rocksfill fill the by relatively nonmagnetic low-density the Lake Superior basin. This model showsthe theentire entire crust to Lake Superior basin. This model shows to be be abnormally abnormally This density dense beneath both both eastern eastern and western Lake and western Lake Superior. This density is dense beneath as the the result resultofofextension extensionalong along an an axial axialzone zone associated associated with with interpreted as also indicates aa broad pervasive the mantle. mantle. This This modeling modeling also broad pervasive intrusions intrusions of the thickening the axis thickening of the the crust crust by by aa few few kilometers kilometers along along the axis of of the the basin. basin. W.S. overlapping volcanic volcanic W.S. White Whitedivided divided the the Lake LakeSuperior Superiorbasin basininto into six overlapping basins whose whoseboundaries boundaries closely followfaults faults and andother other structural structural features basins closely follow features Removingthe thegravitational gravitational identified identifiedbybygeologic geologicand and geophysical geophysical data. data. Removing effects of the surficial sedimentary rocks of the Bayfield Group of the surficial sedimentary rocks of the Bayfield Group and and Jacobsville Sandstone gravity anomaly results Jacobsville Sandstone from from aa smoothed smoothed Bouguer Bouguer gravity anomaly map map results mapthat that shows showsonly onlyminor minorvariations variations from from the the original original map. in an an anomaly anomaly map map. The maxima maximaofofthe theanomaly anomalymap map correlatewith withthe the lava lava basins The correlate basins of of White. White. The eastern Lake Lake Superior and have have aa lesser thickness The basins basins of of eastern Superior are are smaller smaller and lesser thickness of volcanic volcanic rocks rocks than than the the basins basins in in the the western western part part of the the lake. lake. These differences differences reflect reflect aa major major division in in the the midcontinent midcontinent rift rift system. system. The of anomalies anomalies extending extending from from central Lake Superior Superior southeast southeast into pattern of central Lake This may Michigan Michigan is is subdued subdued compared compared to tothat thatof of the the western western limb. This may represent aa fundamental fundamental difference limbs with the differenceinin the the degree degreeofof extension extensioninin the the limbs with the eastern subjected to extension, igneous igneous activity, anddiastrophism. diastrophism. eastern limb limb subjected to lesser extension, activity, and 40. �(Hlnze, (Hinze, Wold Wold and and O'Hara, O'Hara, continued) continued) These interpretations of data in the These interpretations of the thegravity gravityand andmagnetic magnetic anomaly anomaly data the Lake Superior Superior basin basin are are consistent with Lake with the theconcept conceptthat thatmid-America mid-America was was subjected time concurrently concurrently with the subjected to tensional tensional forces forcesininKeweenawan Keweenawan time the Grenville These forces forces caused extension of of the Grenville orogeny. orogeny. These caused extension the crust crustwhich whichcaused caused of igneous activity and in aa igneous activity and diastrophism diastrophism that today today is observed observed in aa range range of more dense denseand andperhaps perhapsthickened thickenedcrust crustoverlain overlain by more by volcanic volcanic and and sedimentary sedimentary rock basins basins that rock movements. that have have been been disturbed primarily primarilybybyminor minorvertical vertical movements. 41 41.. �LONG GRAVITY AND LONG WAVELENGTH WAVELENGTH GRAVITY AND MAGNETIC MAGNETIC ANOMALIES ANOMALIES OF THE OF THE LAKE LAKE SUPERIOR SUPERIOR REGION REGION V.W. Chandler, Minnesota Geological Survey, V.W. Chandler, Minnesota Geological Survey, St.Paul, St. Paul ,MN MN P.L. Boman, Boman, Exxon Exxon Corporation, Corporation, Houston, Houston, TX TX W.tJ. Hinze, W.J. Hinze, Purdue Purdue University, University, West West Lafayette, IN IN N.W.O'Hara, O'Hara,Florida Florida Institute N.W. InstituteofofTechnology, Technology,Melbourne, Melbourne, FL FL and particularly particularlymagnetic magneticanomaly anomaly maps maps of the the Lake Lake Superior Superior region region Gravity and are by short short wavelength anomaliesthat that originate originate from are dominated dominated by wavelength anomalies from near-surface near-surface sources country rock. rock. As sourceswhich whichhave havestrong strongphysical physicalproperty propertycontrasts contrasts with with the country a broad, deep deepsources sourceswith withlimited limited physical a result result anomalies anomalies which which have have broad, physical property property This problem contrasts can be bedifficult difficult totodiscern contrasts can discernininthe theanomaly anomaly pattern. pattern. This problem can can be alleviated by upward upward continuation of ofgravity gravityand andmagnetic magnetic data datatotoemphasize emphasize be alleviated by long wavelength wavelength anomaly anomaly components. components. Gravity and and magnetic magnetic data data compiled compiled over over the Superior region continuedtoto levels levels of the Lake Lake Superior region were were upward upward continued of 50, 50, 150, 150,and and 350 350 km km and long wavelength wavelength anomalies and the the resulting long anomalieswere wereinvestigated investigatedfor for significance significance to to crustal crustal structure. structure. '1 ,1 The long wavelength wavelengthgravity gravity anomalies of the The long anomalies of the 50 50 (Figure (Figure 1), 1),150 150and and350 350 km km level data data define define aa continuous, continuous, arcuate arcuate belt beltofofmaxima maxima that that extends extends along along the the St. Croix St. Croix Horst, Horst, into intothe theLake LakeSuperior SuperiorSyncline, Syncline,and andsouthward southward across across the the Michigan Basin. This arcuate Michigan Basin. This arcuate belt reflects reflectsthe theextensive extensiveemplacement emplacement of mafic mafic The 50 50 km rocks into the rifting event. rocks the crust crustduring duringthe theKeweenawan Keweenawan rifting event. The km level concentrationsalong alongthe thearcuate arcuaterift rift gravity data data indicates indicates that thatprimary primary mass mass concentrations occur slightlyoffset offset segments along along the the St. St. Croix CroixHorst, Horst,the theMinnesota Minnesota occur in in slightly segments shore shore of Lake Lake Superior. Superior. The The Keweenaw Keweenaw Peninsula, Lake Michigan, Peninsula,northeastern-most northeastern-most Lake and the central The intense intense gravity and the central Michigan Michigan Basin. Basin. The gravityminima minima which which commonly commonly flank the central the central rift riftanomaly anomaly in in low-level low-level data data are are not notapparent apparent at least leastas as aa concontinuous zone are no tinuous zone in the the upward upward continued continued data. data. There There are no long long wavelength wavelength anomalies whichdirectly directly connect connect with with either eitherthe theNipigon NipigonPlate PlateororthetheKapuskasing Kapuskasing anomalies which feature. In along the the rift rift zone In addition, addition, the thelong longwavelength wavelength gravity gravity maxima maxima along zone do do not display not display aachange change in in character characterupon upon crossing crossingthe theGreat GreatLakes Lakes Tectonic TectonicZone. Zone. Other long long wavelength wavelengthanomalies anomaliesoccur occurinin the the Lake Lake Superior Superior region region that are Other are these anomalies anomalies are are aa apparently not related related totoKeweenawan Keweenawan rifting. Among these apparently rifting. Among : northeast-trending northeast-trendingmaximum maximum over Wisconsin, aa northeast-trending northeast-trending maximum over northern Wisconsin, maximum across Bast, and across the the southern southern Michigan Michigan BasiW, and north-trending north-trendingmaxima maxima over over the the Long wavelength wavelength gravity gravity minima Kapuskasing feature and the the Moose Moose River Basin. Long minima Kapuskasing feature and River Basin. reflecting rocks occur over reflecting aa thickening thickening of offelsic felsiccrustal crustal rocks occur overthe theWisconsin Wisconsin Arch Arch and over over the the Superior Superior Province Provinceadjacent adjacenttoto the the Grenville Grenville Front. and Front. Upward continuationofofthe themagnetic magneticdata datatotolevels levelsof of 50 50 (figure 2) Upward continuation 2) and and 150 km kmreveals revealsseveral several long long wavelength wavelengthanomalies anomaliesthat thatlocally locally show rela150 show aa relationship to to the the corresponding corresponding gravity data. data. The The 50 50 km km level level magnetic magnetic data data reveal an arcuate belt of alongthe therift rift zone reveal an arcuate of maxima maxima along zone which which in in gross gross form form corresponds arcuate gravity gravitymaxima. maxima. However, However, in in the the Lake Lake Superior Superior corresponds to to the arcuate Syncline, the north of of Syncline, the axis axis ofofthe themagnetic magnetic maxima maxima lies approximately approximately 100 100 km km north the gravity gravitymaxima. maxima. The The 50 several 50 and and 150 150 km kmlevel level magnetic magnetic data data reveal reveal several long wavelength wavelength anomalies anomalies that long that are are believed believedtotobebeunrelated unrelated to Keweenawan to Keweenawan rifting. Among theseanomalies anomaliesare are aa regional maximum in northern rifting. Among these maximum in northern Minnesota Minnesota and maximaalong alonga abelt belt extending and maxima extending from from northern northern Lake Lake Huron Huron to to southern southern Upward continued intermediate in these these Wisconsin. Upward continuedgravity gravityvalues valuesare arelow lowto to intermediate areas implying these areas areas is dominated bybyfelsic, but highly highly areas implying the the crust crust in these is dominated felsic, but magnetic, magnetic, rocks. rocks. Long Long wavelength correspond to wavelength magnetic magneticminima minimagenerally generally correspond regional gravityminima minima over over the the eastern eastern Superior Superior Province Province and and over over the the regional gravity 42. �(Chandler, Boman, Hinze (Chandler, Boman, Hinze and and O'Hara, O'Hara, continued) Wisconsin Wisconsin Arch. The 50 and magnetic magnetic data The 50 km kmlevel level gravity and data were weresubjected subjectedtoto quantitative quantitative correlation and analysis indicated indicated that that the correlation and modeling. modeling. Correlation Correlation analysis the majority majority of anomalies inin the related to to long long anomalies the long long wavelength wavelengthgravity gravitydata dataare aredirectly directly related wavelength magnetic magnetic anomalies, anomalies, although although exact wavelength exact spatial spatialcorrespondence correspondencebetween between Keweenawan anomaly peaks notcommonly commonly observed. observed. Poisson Poisson analysis analysisalong alongthethe Keweenawan anomaly peaks is not rift zone rift zone yields yieldsmagnetization magnetization to to density density contrasts contrasts consistent consistent with with mafic mafic Modelingresults results of igneous rocks into intermediate rocks. rocks. Modeling igneous rocksemplaced emplaced intofelsic felsic to intermediate long wavelength anomalydata data along along the the Keweenawan rift zone zoneare are consistent consistent long wavelength anomaly Keweenawan rift with emplacement of ofmafic rocks into the continental continental with emplacement maficigneous igneous rocks intoallall levels levels of the crust. 52 50 4e. 46 44. 42' 40' — — — — CONTOUR CONTOUR Figure 1. INTERVAL INTERvAL'• 55 MILLIGALS "'LLIGALS 0 o 500 500KM KM Central Central North North America America Bouguer Bouguer gravity gravity anomaly upward continued continued to to 50 0 km, anomaly upward km, data data 20 km (flat (flat earth earth asswnption). assumption), interval = 20 43. 43. CONTOUR INTERVAL INTfRVAL' 50GAMMAS GAMMAS CONTOUR • 50 Figure 2. 2. o 0 500 KM ~OKM Central North North Ameri~a America total Central total magnetic intensity anomaly, reduced to the intensity anomaly, the pole, pole, upward continued data interval continued to to 50 50 kin, km, data interval = 20 (flat earth aseumption). assumption). 20 km km (flat �SEISMIC REFRACTION REFRACTION STUDIES STUDIES OF OFLAKE LAKESUPERIOR SUPERIORCRUSTAL CRUSTALSTRUCTURE STRUCTURE J.H. Luetgert J.H. Luetgertand and R.P. R.P. Meyer Meyer Geophysical and Geophysical and Polar Research Research Center Center Department Department of Geology Geology and and Geophysics Geophysics University ofofWisconsin-Madison University Wisconsin-Madison A series series of seismic seismic refraction lines linesshot shotininLake LakeSuperior Superior (Figure (Figure 1) 1) has inversiontechniques techniquesextended extended has been beenanalyzed analyzedusing usingsimple simpletravel-time travel-time inversion Thelines lines were wereshot shotbybyaasingle singleship shipfiring firing by generalized generalized ray by ray tracing. The airguns and and explosives, explosives, with with radio-controlled airguns radio-controlled buoys buoys as as receivers. receivers. The have been been modeled, The upper upper 12 12 km kmofof crust crust have modeled,showing showingthe thevelocity velocity distribution down distribution down to toand and including includingthe theUpper Upper Refractor, Refractor,anananomalouslyanomalouslyshallow, (6.4-6.9 km/sec) km/sec) suite refractors underlying underlying shallow, high high velocity velocity (6.4-6.9 suite of refractors the Lake Superior Basin. Basin. the Lake Profiles inin the thewestern western end end of the lake lake confirm confirm the the essentially synclinal synclinal structure structure ofofthe thecrust crustsuggested suggested by by the the geology geology of the the lake lake margins and by previous previous seismic seismicmeasurements. measurements. margins and Travel-time offsets of the the profiles offsetsobserved observed on on many many of profilesprovide providemore more precise definition crustal faulting faulting inferred inferredfrom from extrapolation extrapolation of precise definition of crustal knownfaults faults on known on land land and and frorri from gravity gravityand andaeroniagnetic aeromagnetic surveys. surveys. Evidence is shown for extension extensionofof the the Isle Royale fault to shown for Royale fault to the the west, west, for forextension extension faulttotothe the east, east, and arid for for the Keweenaw fault the existence existence of the the postulated postulated of the the Keweenaw Thiel fault of Keweenaw faultroughly roughlybetween betweenthe thetiptip of Keweenaw Peninsula Peninsula and and the Slate Slate Islands. 1::= ~ b---. Figure 11 44. 1 -.... 7A �TOPOGRAPHY ANDSURFICIAL SURFICIAL STRUCTURE TOPOGRAPHY AND STRUCTURE OF OF LAKE LAKE SUPERIOR SUPERIORBEDROCK BEDROCK BASED ON REFLECTION PROFILES PROFILES BASED ON SEISMIC REFLECTION Richard J. Wold, Wold, U.S. U.S. Geological Geological Survey, Survey,Denver, Denver,Colorado Colorado 80225 80225 Richard Deborah U.S. Geological Geological Survey, Survey,Woods Woods Hole, Hole, Massachusetts Massachusetts 02543 02543 DeborahR.R. Hutchinson, Hutchinson, U.S. Thomas Minnesota, Minneapolis, Minneapolis,Minnesota Minnesota 55455 55455 ThomasC.C.Johnson, dohnson,Univ. Univ. of of Minnesota, Thickness unconsolidated sediment sediment and underlying Thickness of of the unconsolidated and topography topographyof of the the underlying bedrock surface Lake Superior from 8000 8000 km of bedrock surface of of Lake Superior were were interpreted interpreted from km(kilometers) (kilometers) of high-resolution seismic taken 1966 A seismic reflection reflectionprofiles profiles takenduring during 1966and and1967. 1967. A map was isopach map map of unconsolidepth-to-bedrock depth-to-bedrock map wasconstructed constructed by by combining combining the the isopach of unconsolidated sediments sediments(from (fromour ourprofiles) profiles) with the of the dated the bathymetric bathymetric map map of the lake lake (Canadian 885, 1973). 1973). (Canadian Hydrographic HydrographicService Service Chart Chart 885, Lake Superior Superior can can be be divided divided into Lake into three threemorphologic morphologic regions regionsbased based on on bathymetry region composed longlinear linear bathymetry and and underlying bedrock: bedrock: aa western western region composed ofoflong valleys and gentle changes changesininrelief, relief, aacentral of aa single valleys and gentle centralregion regioncomposed composed of broad depression, and and an an eastern eastern region regioncomposed composed of of aacomplex complex broad bathymetric bathymetric depression, pattern lineartroughs troughsand and shoals. shoals. pattern of linear The western western region region is dominated or less The dominated by by a a more more or less continuous continuous bathymetric bathymetric and bedrock bedrockvalley valley paralleling paralleling the Bay, Ontario, Ontario, to and the north north shore shore from from Thunder Thunder Bay, Duluth, Minnesota, Minnesota, which which reaches reaches depths depths of ofmore more than than 800 800 m m (meters) (meters) below below lake m of of overlying lake level level near nearSilver SilverBay, Bay,Minnesota, Minnesota,and and has has more more than than 500 500 m sediments. This probably resulted unconsolidated sediments. This valley valley probably resulted from fromdifferential differential glacial erosion erosion where where the the relatively relativelyerodible erodible sandstoneofofthe theOronto OrontoGroup Group sandstone comes relativelyresistant resistant underlying Keweenawan volcanic volcanic comesinin contact contact with with the relatively underlying Keweenawan rocks second basement basementvalley valley to to the rocks and and gabbro gabbro of the theDuluth DuluthComplex. Complex. A second southeast the north north shore shore valley valleyand and probably probably represents represents the the contact contact southeast parallels parallels the betweenthe the Oronto Oronto Group Groupsediments sedimentsand andthe theoverlying overlying Bayfield between BayfieldGroup Group sediments. sediments. Thethickness thicknessof of the the Oronto Groupisisabout about1.5 1 .5kmkm thisarea areaof of the the lake, lake, The Oronto Group in inthis linear valley using an assumed the southeast. southeast. Another Another linear valley using an assumedregional regionaldip dipof of 8° 8° to the occurs Isle Royale Royale which close to the the possible possible occurs south southofof and andparallel parallel to to Isle which isis close location thecontact contact betweenthe theFreda FredaFormation Formationand andCopper Copper Harbor Harbor location ofofthe between Conglomerate Conglomerateand andthe theoverlying overlying Bayfield Bayfield Group Group and and Jacobsville JacobsvilleSandstone. Sandstone. The central region The central region is isseparated separated from from the the western western region region by by aa north-south north-south basementridge ridgeand andconsists consistsofofaa broad broadvalley valley with with only only 8-15 8-15 m m of unconsoliunconsolibasement dated bedrock surface. dated sediments sedimentsoverlying overlying the bedrock surface. The complex complexpattern patternofof troughs troughs and andshoals shoalsof of the the eastern The eastern region region form form aa north-south north-south dendritic pattern pattern with withvalleys valleysasasmuch much as as 100 100 km km long, long, but but only The bedrock bedrocksurface surfaceisis more than 600 600mmbelow belowlake lake12vel level in 5 to to 10 10 km km wide. wide. The more than some by 300 300 mmof of unconsolidated unconsolidated sediments. sediments. These someplaces placesand andisis overlain by features are stream erosion, erosion, followed followed by by glacial glacial features are probably probablythe theresult result of of initial initial stream The stream stream erosion erosion may maywell well have scour. The have followed aa system system of of shear shearzones zones which have have been shore exposures exposures of the underlying underlying sediments sediments which beenobserved observedinin the the shore of the of the the Bayfield BayfieldGroup Group and and Jacobsville Sandstone Sandstone to the south. south. All these these bedrock bedrock to the valleys are are truncated truncated about about 15 15 km km north the south south shore shore where valleys north of of the wherethe thelake lake floor floor rises abruptly abruptly to to the the coastline. coastline. rises 45. �(Wold, Hutchinson (Wold, Hutchinson and and Johnson, Johnson, continued) In general of the the bedrock surface in Lake general,, the morphology morphology of bedrock surface Lake Superior Superior probablyreflects reflects the the result of of glacial glacialscour scouralong along pre-existing pre-existing stream stream probably valleys which, which, in in turn, contacts, pre-existing turn, were were controlled controlled by by formation formation contacts, valleys topography, and topography, and shear shear zones. zones. Over theacoustic acousticimpedence impedence contrast across across the the Over most mostof of the the lake, the unconsolidatedsediment-bedrock sediment-bedrockinterface interfaceisis high sothat that the seismic high enough enough so seismic unconsolidated energy energyisis reflected reflected back backwith with little little orornonopenetration penetration into intothe thebedrock. bedrock. Despite this, this, there Despite thereare aresome some places places where where layering within within the thebedrock bedrock can can be be thestructural structural trends trends that identified identifiedand andapparent apparent dips dipsdetermined. determined. Among Among the have have been beendetermined determinedfrom fromthese thesedips dipsare arethe the following: following: aa southwest-plunging southwest-plunging synclinal feature synclinal feature bordering bordering the the Bayfield Bayfield Peninsula; Peninsula; a syncline syncline lying lyingbetween between the Apostle Peninsula, which which probably probably represents represents the the the Apostle Islands Islands and and the theKeewenaw Keewenaw Peninsula, center of center of the the Lake Lake Superior Superior depositional depositional syncline; syncline;a asouth—plunging south-plunging syncline syncline located between between Michipicoten Michipicoten Island and and Superior Superior Shoals; Shoals; and and an an apparent apparent dip dip to the south south of to the region of the of the the bedrock bedrock in the the southeastern southeastern region the lake. lake. 46. �GEOPHYSICAL STUDIES ISLANDS, LAKE LAKE SUPERIOR SUPERIOR GEOPHYSICAL STUDIESOF OFTHE THE SLATE SLATE ISLANDS, J.H. Karl,and andM.P. M.P. Bernardin, Bernardin,Department Department ofofPhysics Physicsand andAstronomy, Astronomy, J.H. Karl, University ofofWisconsin, University Wisconsin,Oshkosh, Oshkosh, Wisconsin Wisconsin 54901 R.P. Meyer, R.P. Meyer, and and M.E. M.E. Bengtson, Bengtson, Geophysical Geophysical and and Polar Research Research Center, Departm~nt of of Wisconsin Wisconsin Department of Geology Geologyand andGeophysics, Geophysics,University University of 53706 Madison, Wisconsin Madison, Wisconsin H.C. of Geology, Geology,Erindale ErindaleCollege, College, University University of Toronto, H.C. Halls, Department Department of Toronto, Mississauga, Ontario, Ontario,Canada Canada L5L1C6 Discussion of origin ofofshock shock features features found found ininthe theCanadian Canadian shield shield Discussion of the the origin has existed the literature literaturefor forperhaps perhaps 20 20 years. years. Several Several well well known known has existed in in the crypto-explosion structure typify typifythis this debatebetween between meteorite meteorite impact impact and and crypto-explosion debate endogenous process such as as thethe Charlesvoix structure, the endogenous process such Charlesvoix structure,the theBrent Brentcrater, crater, the all, Sudbury the Clearwater Clearwatercomplex complex and and the theManicouagan Manicouagan caldera. In In all, Sudbury basin, basin, the The Slate Slate Islands Islands of northern about 79 79 such suchstructures structures have have been beenidentified. identified. The about northern Lake Superior Superior exhibit Lake exhibitshock shockmetamorphic metamorphic features features inincommon common with many many of these these as shatter-cones shatter-conespresent presentlocally locally in host intrusive sites such such as host rocks rocks and and intrusive brecciated clasts, deformation lamellae lamellae in in quartz and brecciated clasts, and and show show deformation and plagioclase grains. In In addition, the central central uplift uplift ofofa acomplex addition, the the islands islands form form the complex crater morphology whichisis ringed ringed by troughand andannular annular ridge ridge with aa morphology which by aa submerged submerged trough diameter of diameter of about about30km. 30km. On the active On the other other hand, hand,the theislands islandsare are located locatedinin aa once oncetectonically tectonically active region associated associatedwith withthe theMichipicoten Michipicoteritriple triple junction and at the region and at the intersecintersection of controls the the location location of late of two two major major regional regional faults, one one of which which controls late Precambrian alkalic magmatism. Precambrian alkalic magmatism. The and deformation deformation The shatter-cone shatter-cone structures and lamellae may be associated associated with with diatreme relatedto to these these regional lamellae may be diatreme emplacement emplacement related features; and thus the the Islands astrobleme-diatreme features; and thus Islands fall fallinto intothethe astrobleme-diatreme controversy. controversy. However, thelocation location of of the However, the the Slate Slate Islands Islands ininthe theLake Lake Superior Superior Basin Basin region the recent recent water water cover cover may may have region with the have reduced reducederosion erosionofof the the structure structure fargreater greaterextent extentthan than for formany many of the the other other cryptoexplosion cryptoexplosion sites. In to aa far addition the the lake lake presents presents the the opportunity opportunityfor formarine marinegeophysical geophysical techniques techniques are not not available available for other other sites. sites. Currently, we we are capitalizing on on that are are capitalizing situationbybyusing using aavariety varietyofofmarine marinetechniques techniques in in association association with with this situation airborne magneticstoto help help identify identify the airborne magnetics the geological geological process process responsible responsible for the the formation formation of the the Slate Slate Islands. Islands. During During July, July, 1979, 1979,we we conducted conducted an an aeromagnetic aeromagnetic survey survey over aa 30 30 XX60 60 km km area over overthe the Islands Islandsusing usingactive activeradar radarpositioning positioningatat1000 1000yard yardflight flight line line area This aeromagnetic data shows clear spacing 1500 surface. This aeromagnetic data shows clear spacing 1500feet feet over over the the lake surface. linear features features which which have have been and linear beenpreviously previouslyinterpreted interpreted as as regional regional faults and long wave-length arcuate apparently related related totoa adeep-seated deep-seated source source long wave-length arcuate trends trends apparently sourcesininthe thevicinity vicinity of centered the Islands. Islands. Shallow Shallow sources centeredatat the the location location of the the Islands centered in in the the Islands produce produce short short wavelength wavelength anomalies anomalies centered the long long wavelength wavelength magnetic magnetic depression. depression. 47. �LAKE SUPERIOR SUPERIOR RED RED CLAY CLAY MINERALOGY: MINERALOGY: LAKE CORRELATION WITH MECHANICAL BEHAVIOR BEHAVIOR CORRELATION WITH MECHANICAL E. Brown T. Mengel Mengel and and B. B. E. Brown J. T. IDS, Minnesota and and IDS, Minneapolis, Minnesota Department of Geological Sciences Sciences Department of Geological University Wisconsin-Milwaukee University ofofWisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin Wisconsin In threetypes typesof of stratigraphic stratigraphic In the the red red clay clay area area of ofDouglas Douglas County County three successionare areobserved observed from bore hole data: clay(~(c25' 25 thick) thick) over succession from bore hole data: redred clay over older red red clay, clay, red redclay clayover overbrown brown or or gray gray clay, clay,and andred redclay clayover overbrown brown sand. The mean meancontents contentswith withstandard standarddeviation, deviation, of The of sand sand (>44u), ( >44u),silt silt (44-2u), clay (2-O.2u), (44-2u), coarse coarse clay (2-0.2u), and and fine clay clay (<O.2u) «0.2u) of of red red clay clayfrom from 28 28 borehole samples samplesisis 3.5+2.5, borehole 3.5~2.5, 25.6+12.4, 25.6~12.4, 39.8±8.4, 39.8~8.4, and and 28.8+8.2. 28.8~8.2. Smectite clayisisdominant dominant fineclay clayfraction; fraction;illite illite and Smectite clay in in thethe fine and chlorite are dominant in the the coarse are dominant in coarse clays, and and quartz; feldspars, feldspars,and and carbonates, carbonates, Particle size are dominant the silt silt and and sand sand fractions. Particle size distribution are dominant ininthe The equations: and mineral mineralcontents contentscorrelate correlatewith with the the Atterberg Atterberq limit limit values. and values. The limit==10.0 10.0++0.78 0.78 (% (% coarse coarse ++ fine clay) clay) and and Liquid limit Liquid Plasticityindex index == 0.1 0.1 ++0.51 0.51 (% (% coarse coarse ++ fine clay) Plasticity fine clay) have of 0.76 0.76 and and 0.84 this body body havecorrelation correlation coefficients coefficients of 0.84 respectively respectively for this of data. data. The dominant mode inin the LittleBalsam Balsam Creek Creek drainage drainage south The dominantfailure failure mode the Little south of Superior andinin other other similar locales Superior and locales involves involves drying drying and and cracking cracking of of aa surficial layer surficial layerofofclay claywhich whichthen then slides slides as as aadcollement decollement sheet sheet over over the the underlying clay. This failureappears appears totohave havebeen been promoted promoted by This failure by deforestation underlying of the the area. area. 48. �PALEOMAGNETISM PALEOMAGNETISM OF OF KEWEENAWAN KEWEENAWAN ROCKS ROCKS H.C. H. C. Halls Hall 5 Erinda1e College College Erindale Mississauga, Ontario,Canada Canada Mississauga, Ontario, L.J. Pesonen L.J. Pesonen Geological Survey of Finland Geological Survey of Finland Espoo, Espoo, Finland Keweenawan paleomagnetic polesoccur occuralong along aa broad trendingline line Keweenawan paleomagnetic poles broad NW-SW NW-SW trending Stratigraphic and the north north central central Pacific. Pacific. Stratigraphic and radiometric radiometricevidence evidence suggests suggests in the that within within this this polar polardistribution distributionthere thereis is a hairpin-shaped path, path, open open to that a hairpin-shaped the (the so-called so-called Logan Loop)along alongwhich whichthere thereisis aa progressive the SW SW (the Logan Loop) progressive antiThis path clockwise movement poleswith with time. This clockwise movement ofofpoles path which which is only only about about 100 100 of arc in width, afterfiltering filtering ofofthe arc width, emerges emerges after thepole polepopulation population using using certain certain reliability criteria, andthus thusthe the scatter scatter of ofdata data about about this path is reliability criteria, and this path is attributable to uncertainties not to to variations variations in in paleofield table uncertainties in the the data data and and not pa1eofield direction. Late Precambrian poles North America, America, together Late Precambrian poles from from elsewhere elsewhereinin North Keweenawan paleointensity with Keweenawan paleointensityand andpaleosecular paleosecularvariation variation (PSV) (PSV)studies studies further Keweenawan support apparent apparent polar polarwander wander(APW) (APW) as as the theunderlying underlyingcause causeof of Keweenawan There are problems paleopole distribution. problems however: however: more 90% of paleopole distribution. There more than than 90% Keweenawan poles alongthe the western western arm armof of the the Logan Loop; its its apex Keweenawan poles lieliealong Logan Loop; apex remains remains undefined and from aa steeply-dipping steeply-dipping volcanic volcanicsequence sequence define define undefined andonly only two two poles poles from the eastern Furthermore,almost almosthalf halfthe thetotal total length the eastern arm. arm. Furthermore, length of the the loop loop lacks lacks data because Keweenawan igneous unitscontain containasymmetric asymmetricreversals reversals with data because Keweenawan igneous units with inclination differencesaveraging averaging about about 25°, 25 0, across which there across which inclination differences there are are no no interintermediate directions. There are possible explanations explanations of the the reversal reversal mediate directions. There are three three possible (1) APW, (2) regionalsecondary secondary magnetization magnetizationcomponent component superasymmetry: (1) APW, (2) aa regional 0) reversals imposedononoriginally originally symmetric (1800) reversalsor or (3) (3) some intrinsic imposed symmetric (180 some intrinsic property Paleomagnetic, paleointensity andPSV PSV data data propertyofofearth's earth's internal internal field. field. Paleomagnetic, paleointensity and are generally ininaccord accordwith with(1), (1), although volcanic sequenceis isknown knownwhere where are generally although oneone volcanic sequence successive situationthat that posesproblems problemsforforAPW. APW. successive asymmetric asymmetricreversals reversals occur, occur, a situation poses Of Of the the two two remaining remaining explanations explanations (3) (3) cannot cannot be be discounted discounted while while (2) (2) is con con~ sidered the Local overprinting overprinting events events have have recently recentlybeen been sidered the least least likely. likely. Local demonstrated but have different differentages agesand andcauses. causes. They They may may be be demonstrated but they they appear appear to to have due igneousactivity, activity, burial Keweenawan due to Late Late Keweenawan Keweenawan igneous burialof the of the Keweenawansequence, sequence, meteorite impact. impact. emplacement ofofcopper-bearing emplacement copper-bearingores, ores,and andinin one oneinstance instance to to meteorite These Paleozoic or very very late latePrecambrian Precambrian Thesemagnetic magneticoverprints overprints appear appeartoto be be Early Early Paleozoic (500-900Ma) Ma)ininage ageand and arearethus thusimportant importantasasthey theylie lie in in an an age age interval interval poorly poorly (500-900 represented in North represented North American American paleomagnetic paleomagnetic data. data. 49. �STABLE ISOTOPE STUDIES IN STABLE ISOTOPE TRACER TRACER STUDIES INTHE THECAMBRO-ORDOVICIAN CAMBRO-ORDOVICIAN AQUIFER AQUIFER OF ILLINOIS OF NORTHERN NORTHERN ILLINOIS T.J. Grundi Grundl Northern Illinois University Northern Illinois University Dekaib, Illinois Dekalb, Illinois E.C. Perry, Jr. E.C. Perry, Northern University NorthernIllinois Illinois University Dekalb,Illinois Illinois Dekalb, R.H. R.H. Gilkeson Gilkeson Illinois State Illinois StateGeological GeologicalSurvey Survey Oxygenand andhydrogen hydrogen (deuterium) isotoperatios ratios for for water Oxygen (deuterium) isotope water of ofthe theCambroCambro- Ordovician aquifer closelyapproximate approximate the in Ordovician aquiferof of northern northernIllinois Illinois closely the ratios ratios in meteoric water, implying that thatlittle little isotope exchange occuredbetween between meteoric water, implying isotope exchange hashasoccured 180 ofofgroundwater cSlSO groundwaterin in the system groundwater system groundwaterand androcks rocksofofthe the aquifer. aquifer. 0 0/00 (vs. ranges from , characteristic ranges from about about -7 %0 SMOW), characteristic of of modern modernprecipitation precipitation (vs. SMOW) precipitation in in Illinois, in Illinois,totoabout about -12 0/ 00 , characteristic of of modern modern precipitation The implication implication considerably considerablycolder colderclimates climatesthan thanthat thatofofnorthern northernIllinois. Illinois. The some Cambro-Ordovician of of this this Isisthat that someofofthe thewater waterininthethe Cambro-Ordovician aquifer system system of northern Illinois Illinois has northern hasbeen been stored stored since since the the Pleistocene. Pleistocene. oxygenisotopes isotopesininsulfate sulfate of of northern and oxygen northern Illinois Illinoisgroundwater groundwater Sulfur and establish this this sulfate establish sulfate to a mixture ofof2 2end-member end-member compositions. compositions. One One +20, 0IbO0 = = +16) is derived end-member +16) presumably presumably is derived from from Paleozoic Paleozoic end-member( ( 034S 34S = +20, sulfate miners The other other sulfate sulfate miner~!sininrocks rocksassociated associated with the the aquifer. aquifer. The S = 2.6, ol8o component (0 S 018 0 = 1.5) presumably results 1.5) presumably results from from oxidation oxidation of ( pyrite pyrite in in the the glacial glacial drift driftoverlying overlying the the aquifer. aquifer. 9g The presence in the thegroundwater groundwater of northern northern The presenceofofnatural natural isotope isotope tracers tracers in Illinois andadjacent adjacentareas areas should should prove prove useful useful in in establishing establishing recharge recharge Illinois and and flow patterns patterns in in this important and flow important aquifer. aquifer. 50. �KAULINITIC WEATHERING KAOLINITIC WEATHERING ZONE ZONE ON ONPRECAMBRIAN PRECAMBRIAN BASEMENT BASEMENT OF OF SOUTHEASTERN SOUTHEASTERN NORTH NORTH DAKOTA DAKOTA AND AND WESTERN WESTERN MINNESOTA MINNESOTA Keiley Lynn I.I.. KeJley Lynn and and Frank Frank R. R. Karner Karner Department of Geology Geology Department University of ofNorth NorthDakota Dakota Grand Forks, North Grand Forks, North Dakota Dakota 58202 Detailed petrologic petrologicand and geochemical geochemical studies studies have have confirrried confirmed the existence existence weathering profile profile developed deep weathering developed uniformly on on aa variety varietyofofPrecambrian Precambrian of aa deep suite of 26 drill cores basementrocks rocksinin the the southern River Valley. A suite basement southern Red Red River 26 drill cores from aa drilling drilling program from program ininthe theRed Red River RiverValley Valley(Moore, (Moore, 1978), 1978), has has provided provided new information on new information on the the basement basement of eastern eastern North North Dakota Dakota and and western western Minnesota. Minnesota. The Precambrian PrecambrianisIs penetrated penetrated at at an depth of approximately The an average average depth approximately 300 300 m m in The surface dips 5-10 rn/km toward the north and west. the Red River the Red River Valley. The surface dips 5-10 m/km toward the north and west. Different rock mafic metasedimenDifferent rock types types ininthe thecores coresinclude includeintermediate intermediateto to mafic metasedimentary and metavolcanic schists, and intermediate to felsic coarse-grained and metavolcanic schists, and intermediate to felsic coarse-grained Precambrianrocks rocksofofthe the region region are are interpreted massive or rocks. The The Precambrian interpreted massive or gneissic gneissic rocks. to be aa buried buried extension extension of the the Superior Superior Province, Province, and and are to be are divided divided into terranes granitic rock rock and and mafic mafic schist, on on the the basis basis of of patterns patterns seen seen in terranes of of granitic Superior Province rocks which crop out to the east, and regional geophysical Superior Province rocks which crop out to the east, and regional geophysical data (Lidiak, data (Lidiak,unpublished; unpublished;Muehlberger Muehlberger and and others, others, 1967; 1967; Ray Ray and and Karner, Karner, 1979). 1979). In the In the southern southern part part of ofthe theRed Red River River Valley, Valley,aathick thickweathering weatheringresiduum, residuum, up 75 m thick, isisdeveloped developed on on the the upper upper surface surface ofofthe thePrecambrian, Precambrian, up to to 75 wherever it isisimmediately wherever it immediately overlain overlainbybyCretaceous Cretaceous rocks. rocks. Where Where the the deepest, least-weatheredrocks rocksare arefoliated, foliated, ghost-like ghost-like traces traces of the the structures structures can can least-weathered often be be followed followed up up through through all all but butthe themost mostextremely extremely weathered weathered material. Weathered numerous sand-size Weatheredmafic maficand andintermediate intermediaterocks rocksoften often contain contain numerous sand-sizesiderite siderite nodules. The uppermost few meters of some cores is bauxitic in appearance, The uppermost few meters of some cores is bauxitic in appearance, but but aluminum oxides are generally absent. aluminum oxides are absent. Scanning microscope/microprobe Scanning electron electron rnicroscope/microprobe studies that feldspars micas are are altered altered to studies show show that feldspars and and micas to kaolin-group kaolin-group minerals. minerals. rock type, type, the the end end product product of weathering weathering is Regardless Regardlessofoforiginal original rock is generally white to containing suspended aa white to greenish greenish kaolinitic kaoliniticclay clay containing suspended angular angular quartz quartz grains. Trends those reported reported by by Trends in major element in major elementchemistry chemistryare aresimilar similar to those Goldich (1938) Goldich (1938) and and Harriss Harrissand andAdams Adams (1966). (1966). Calcium the early early Calciumisislost lost in in the stages of weathering, stages weathering, followed followedbybysodium sodium and and potassium. potassium. Silicon lost in in Silicon isis lost the parts of of some profiles. Iron values the uppermost uppermost parts some profiles. values are arehigh highwhere wherealuminum aluminum values This is apparently function of of original values are are low low and and vice-versa. This apparently aa function rock type. rock type. The this study study support support evidence evidence for aa pre-Cretaceous pre-Cretaceous kaolinitic The results results of this kaolinitic weathering episode on on the the southwestern part of weathering episode southwestern part of the the Canadian Canadian Shield. This study, variety ofofrock rocktypes types subjected subjected to to identical identicalweathering weathering study, involving aa variety conditions, shows thatdifferent different rock conditions, shows that rock types types alter to to similar similarweathering weathering products. The The pathways pathwaystaken takenbybyfelsic felsic and and mafic mafic rocks rocks may niaydiffer. differ. This study study has has been been supported supported ininpart partbybyananHEW HEW administered administered Domestic Domestic Mining and and Mineral and and Mineral Mineral Fuel Fuel Conservation Conservation Fellowship the Mining Fellowship granted granted to the senior author. author. 51 51. �(Kelley and and Karner, Karner, continued) continued) Reference Cited Reference Goldich, S.S., 1938, A Study Study of of rock rock weathering. weathering. J.3. Geol., Geol., V. V. 46, 46, p.p. 17-58. 17-58. Goldich, 5.5.,1938, Harriss, and Adams, Adams, J.A.S., 1966, Geochemical Geochemical and studies 1-larriss, R.C., and J.A.S., 1966, andmineralogical mineralogical studies Sci,, V. on rocks. Amer. Amer. J.3. Sci., V. 264, 264, p.p.146-173. 146-173. on the the weathering weatheringofof granitic granitic rocks. Lidiak, E.G.,Buried BuriedPrecambrian Precambrian rocks rocks of ofNorth North Dakota. Dakota. unpublished unpublished manuscript. manuscript. Lidiak, E.G., Moore,Walter WalterL., L., 1978, A preliminary preliminary report on Moore, 1978, A on the the geology geology of of the the Red Red River River Valley DrillingProject, Valley Drilling Project, eastern eastern North North Dakota Dakotaand andNorthwestern Northwestern Miflnesota. Minnesota. Prepared for Bendix Prepared for Bendix Field FieldEngineering EngineeringCompany, Company, subcontract subcontract 77-059-E. 77-059-E. 292p. Muehiberger,W.R., W.R., Denison, Denison,R.E., R.E., and Lidiak, E.G. rocks in Muehlberger, and Lidiak, E.G. 1967, 1967, Basement Basement rocks United States. States. A.A.P.G. V. 51, p. 23512351continental continental interior interior ofofUnited A.A.P.G. Bull., Bull., V. 51, p. 2 380. 2380. Ray, and Karner, Karner, Frank Frank R., R.,1979, 1979,The ThePrecambrian Precambrian basement basement of North North Ray, John John T., T., and Dakota(abs.) (abs.) Proceedings, 25th Inst. Inst. Lake Dakota Proceedings, 25th Lake Superior Superior Geol., Duluth, Duluth, p. p. 33-34. 33-34. 52. �HYDROGEOLOGIC INVESTIGATIONS LANDFILLSITE SITE II1 HYDROGEOLOGIC INVESTIGATIONS ATAT A ALANDFILL IN THE THE RED TILL (VALDERAN)REGION REGIONOF OFEASTERN EASTERN WISCONSIN WISCONSIN RED TILL (VALDERAN) Warren R. Rehfeldt Warren R. Donahue&&Associates, Associates, Inc. Donahue 53081 Sheboygan, Wisconsin Sheboygan, The practice practice of of landfllllng thethe most of solid The landfillingis is mostwidely widelyused usedmethod method of waste disposal in waste disposal in Wisconsin. Wisconsin. The The most landfill mostacceptable acceptable landfillisis the the "sanitary sanitary landfill whichrefuse refuseisisplaced placedInintrenches trenches or or other other specific specific locations, locations, , in landfill',"in which then compacted compacted covered daily ordertotoisolate isolate the then andand covered daily withwith soilsoilininorder the solid wastes from the environment. wastes from environment. Evaluation Evaluation ofof the potential of of aa the pollution pollution potential land disposal solid waste management. land disposal site siteisisananimportant importantaspect aspectofof solid waste management. hydrogeologicinvestigation investigation was undertakenatatan anexisting existing sanitary A hydrogeologic was undertaken landfill, located to determine determinethethefeasibility feasibility of of inlandfill, locatedinineastern eastern Wisconsin, Wisconsin, to creasing the the depth site is creasing depth of the the present present operation. operation. The The site is licensed licensed to to operate operate under the the condition that than 10 10 feet feet thattrenches trenches cannot cannot be be excavated excavated deeper deeper than under until an completed until anengineering engineeringstudy studyis is completedand andapproved approvedbybythe theWisconsin WisconsinDepartment Department of Natural Natural Resources. Resources. In eastern which is is underlain In eastern Wisconsin, Wisconsin, which underlain by by sedimentary sedimentary bedrock, bedrock, glacial erosion produced producedtill till that erosion thathas has considerable considerable silt siltand andclay clayand and therefore thereforehas has low permeability. The coefficient of of permeability permeabilityofofthe thesilty silty clay low The coefficient clay soil soil on on the the laboratory as the site sitehas has been been measured measured inin the as being being 22 to to 66XX10-8 10- 8cm/sec. em/sec. the site siteisisunderlain underlainbybymore more than than Analysis geologic borings Analysis of of geologic borings indicate indicate that the 30 metersofofglacial glacial drift 30 meters driftwhich which isisconsidered considered to to function function as as an an aquitard. aquitard. Groundwater the upper upper few few feet, feet, perched perched upon upon the underlying underlying Groundwateroccurs occurseither eitherin in the silty clay, occasional sand silty clay,ororin in occasionalsilty silty sandseams seams or or pockets pockets that are are found found in thetill. till. An evaluation of of the conditions indicates indicates that there the An evaluation the hydrogeologic hydrogeologic conditions there is no no hydraulic hydraulicconnection connection between between the the surface surface and and underlying underlying bedrock bedrock aquifer. aquifer. A thorough hydrogeologic investigation investigation and thorough hydrogeologic and aagroundwater groundwater monitoring monitoring program are of oflandfill program areessential essentialininlocation locationand andoperation operation landfill sites. In addition to. hazards addition to identifying identifying potential potentialpollution pollution hazardsassociated associated with withwaste waste we should should apply knowledge ofof hydrogeologic disposal, we apply our our knowledge hydrogeologicconditions conditions to to promote sitffi andenvironments environments for waste waste disposal disposal where where there safemote sit and there are are natural natural safeguardsthat that will will assure guards assure protection protection ofofhealth healthand and resources. resources. 53. �SEISMIC SURVEY SURVEY OF OF AABUR:[ED BURIED RIVER RIVERCHANNEL CHANNEL Timothy D. 0. Vick Timothy Vick Department Department of Geology Geology Carleton College Carleton College Northfleld, Minnesota, Northfield, Minnesota, 55057 seismic refraction refraction survey River valley A seismic survey of aa portion portion of ofthe theCannon Cannon River cut into Northfield,Minnesota Minnesota revealed revealed a sizable buried buried channel channel cut in Northfield, Prairie du Prairie du Chien Chien bedrock. bedrock. The The buried channel channel begins begins on on the the Carleton CarletonCollege Collegecampus. campus. It It is is cut cut into dolomite dolomite which which varies varies markedly markedly in in hardness hardness from from place place to place. place. The The modern modernriver river channel isis filled withlayers layersofof loam,sand sand and and gravel. gravel. The channel filled with loam, flood courseofofthe the river river is flood plain plain overlies overlies the the buried buried valley; valley; the themodern modern course is offset from offset from the the buried buried channel. channel. the slope the portion portion ofofthe thechannel channel mapped mapped in detail,, the slope of the the chanchanIn the in detail nel is one buried channelbegi begins in a "wa "waterfall' ne1 one to eight ei ght percent. percent. The The buri ed channel ns ina terfa 11 about meters high, then continues continues north north 250 250 meters meters with aa about one one and andaahalf half meters high, then depth of of up depth up to six sixmeters meters and and aa width width ofofalmost almost100 100 meters. meters. The channel The channel the study study area, area, from from wide wide and and changes changescharacter charactermarkedly markedlyininthe the center center of of the gently-sloping to steep narrow;inin this section gently-sloping steep and and narrow; section itithas hasa achannel channel slope slope It then of eight and has hasvertical vertical sides. eight percent, percent, isisabout about 20 20 meters meters wide wide and sides. It then wider (150 (150meters) meters)at at the the end levels off offatat1818meters metersdeep deepand and becomes becomes wider end of the survey tributary buried the survey area. area. A tributary buriedchannel channel joins joinsthe themain main channel channel near near end of the the study study area. area. the the end 1 ' thechannel channelincreases increasesinin depth depth to over A mile downstream downstream the over 30 30 meters. meters. A slope slope of 30 per mil mile 30 meters meters per e is indicated i ndi cated for forthe theburied buri edchannel channel;; the modern slopeofofthe theriver river is modern slope is only onlytwo two meters meters per per mile. mile. Buried channels channelsare arefound foundinInother otherparts partsof of the the Mississippi Buried Mississippi River River Such MinneapolisSuch channels channelshave havebeen beendescribed describedinin the the metropolitan MinneapolisSt. Paul Countyasaswell well as as under under the the Mississippi Mississippi River Paul area area and and in Dakota Dakota County River itself. The buried channel in Northfield may be related in itself. The buried channel Northfield may be related inage ageand andmode mode of formation formation to other other buried buried channels channels in the region. region. in the system. Techniques used survey included included computer computer processing processing of seismic seismic Techniques usedinin the the survey results permitting permitting interpretation interpretation ofofdata data under under conditions conditions of refraction results extremely bedrock topography. topography. extremely irregular irregular bedrock 54. �THE PEGMATITIES OF OF THE THEQUETICO QUETIeoGNEISS GNEISSBELT, BELT, NORTHWESTERN ONTARIO ONTARIO THE PEGMATITIES NORTHWESTERN AND URANIUM POTENTIAL POTENTIAL AND THEIR URANIUM W.M. Lucko Luckoand andS.A. S.A. Kissin W.M. Department of Geology Department of Geology Lakehead University Lakehead University Thunder Bay, P7B 5E1 5El Thunder Bay, Ontario P7B Reconnaissance studiesalong alonga aroughly roughlynorth-south north-south traverse traverse across Reconnaissance studies across the Quetico Gneiss GneissBelt, Belt, utilizing Ontario Highway Quetico utilizingroad-cuts road-cutsin in Ontario Highway527, 527,have havebeen been made inin order characterize uranium-bearing uranium-bearing pegmatites pegmatites in and and adjacent adjacent made order to characterize Analyses of samples to the Gneiss Gneiss Belt. Analyses samples by by the the Geological Geological Survey SurveyofofCanada Canada to the revea 1ed uranium urani urn contents ng from<l:O from < 1:0 ppm ppm UUtoto 36.3 ppm inin the pegmatites. revealed contents rangi ranging 36.3 ppm the pegmatites. The pegmatitesare areofoftwo twodistinct distinct types: The pegmatites types: a granitic graniticpegmatite pegmatiteshowing showing intrusive relationships relationships to to all allother otherrocks rocksininthe thearea areaand and an an anatectic anatectic granitic pegmatite intimately the gneisses gneisses of the the Quetico Quetico Belt. The The granitic pegmatite intimately related related to the pegmatitesare are located located near near the the north and pegmatites and south south margins margins of the the Gneiss Gneiss Belt Belt and Wabigoon andand Shebandowan-Wawa Greenstone Belts. Belts. and extend extend into intothe theadjacent adjacent Wabigoon Shebandowan-Wawa Greenstone The pegmatitesoccur occurasasdikes dikesororlensoidal lensoidal bodies bodiesofof plagioclase-perthiteplagioclase-perthiteThe pegmatites quartz varying amounts amounts of and muscovite. muscovite. Accessory Accessory minerals quartz with varying of biotite biotite and include include zircon, garnet, garnet, tourmaline, tourmaline, and and rare rare hematite. hematite. Apatite occurs in Apatite occurs the most most uranium-rich uranium-rich sample. sample. The pegmatites occur as as lenses lenses and and niigniatite migmatite bands bands most The anatectic anatectic pegmatites most strongly strongly The pegmatites pegmatitesare are feldspar-rich feldspar-rich (ca. in the the center center of of the the Quetico Quetico Belt. The (ca.75%) 75%) consisting of oligoclase consisting oligoclase with with microcline microcline exsolutions, exsolutions,quartz, quartz,muscovite, muscovite, and and Accessoriesinclude includezircon, zircon,cordierite, cordierite,sillimanite, sillimanite, minor corroded minor corrodedbiotite. biotite. Accessories garnet, and chlorite. The garnet, and chlorite. The latter suggests that thatthese thesepegmatites pegmatiteshave have been been latter suggests andptygmatic ptygmatic foldingofof small small dikes dikes is also metamorphosed. Boudinage Boudinage and folding also rrietarriorphosed. observed. Uranium the anatectic anatectic pegmatites pegmatiteswas was fairly uniformly uniformly distributed distributed Uranium ininthe fairly in the the range range of 2-7 2-7 ppm, ppm, but ranges to 36.3 ppm ppm inin the but ranges to highs highs of 36.3 the granitic granitic pegmatites. No No uranium identified, the uraniummineralization mineralizationwas was identified,but but zircon zircon is is the The high high value value was was found foundin in an probable host in most most rocks. rocks. The an apatite-bearing probable host In rock, and andthis this mineral mineral isis a rock, a likely likelyhost host for foruranium, uranium, as as well. well. The The pegmatites pegmatites do not seem likely prospects for for economic economic deposits uranium, owing owing to aa do not seem likely prospects deposits of uranium, lack lack of identifiably identifiablymineralization mineralizationand andlow lowconcentrations. concentrations. They They may, may, howhowever, be ever, be the the ultimate ultimatesource source ofofdisseminated disseminated uranium uranium in the the Sibley SibleyGroup Group sandstonesand andunconformity-vein unconformity-vein type type uranium deposits in sandstones uranium deposits in the theGreenwich Greenwich Lake Lake area. 55. �RELATIONSHIP RELATIONSHIP OF OF CANADIAN CANADIAN URANIUM URANIUM DEPOSITS DEPOSITS TO THE TO THE GEOLOGIC GEOLOGIC SETTING SETTING OF OF WISCONSIN WISCONSIN Gregory Mursky Mursky Departmentof of Geological Department Geological Sciences Sciences University ofofWisconsin-Milwaukee University Wisconsin-Milwaukee Milwaukee, Wisconsin Wisconsin 53201 53201 One analyzing the the uranium uranium potential of Onelogical logical and and preliminary preliminary step step in In analyzing potential of aa region region Is is totoaccess access one one area area against against another, another~ based based on on geological geological data data and the the periods periods of of mineralization. An and An important relates importantcriterion~ criterion, asas it it relates to Wisconsin, Wisconsin, is the the geochronological geochronological position position of of Precambrian Precambrian rock rock units units in in the the Canadian Canadian Shield. Wisconsin Wisconsinand andthe theperiods periodsof of uranium uraniummineralization mineralization in The The overwhelming overwhelmingnumber numberofof Precambrian Precambrianuranium uraniumdeposits deposits and and occurrences occurrences in North the Canadian Canadian Shield often North America Americaare aredistributed distributed within the Shield which which is Is often designated throughoutthe the world world as as distinctive distinctive uranium uranium metallogenetic metallogenetic designated throughout Major uranium uraniumdistricts districts tend province. Major tend totobebeconcentrated concentrated along along the themargins margins the Canadian Canadian Shield (Figure 1) 1) and and include, include,among among others,: others,: the Great Bear Bear of the Shield (Figure the Great Lake area, area, the Great Lake Great Slave Slave Lake Lake area, area, the the Beaverlodge Beaver10dge area, area~ the theAthabasca Athabasca basin basin area, area, the the group of occurrences within the area, the the Wollaston Wollaston Lake Lake area~ group of occurrences within the southern southern part part of the the Churchill Churchill Structural StructuralProvince, Province, the thegroup group of ofoccurrences occurrences within the the western part part of the the Superior Superior Structural Structural Province, Province, the thePort PortArthur Arthur(now (nowThunder Thunder western Bay) area, the Bay) area, the Elliot ElliotLake Lake area, area,the thegroup groupofofuranium uranium occurrences occurrences within the the southeastern part of of the Structural Province distributed near southeastern part the Superior Superior Structural Province distributed near the the Grenville Lake area area and and the the deposits depositsand andoccurrences occurrences Grenville Front, Front,the theMakkovik-Seal Makkovik-Seal Lake within the within the Grenville Grenville Structural Structural Province. Province. Uranium Mineralization and Events within within the Uranium Mineralization and Orogenic Orogenic Events the Canadian Canadian Shield, Shield, the absolute absolute age the age determinations determinations of of the the host host rocks, rocks, and and the the periods periods ofofuranium uranium mineralization revealedaadefinite definite pattern have revealed pattern and and a certain degree degree of mineralization have correlation with with orogenic orogenic events: events: In the Elliot ElliotLake Lakearea area ofofthe theSuperior SuperiorStructure StructureProvince, Province,the theuranium uranium In the m.y. events events and the mineralization belongs to 2,500 to 2,600 m.y. mineralization belongs to 2,500 to 2,600 and relates relates to the Huromian sedimentation~ the Kenoran Kenoran Orogeny, Orogeny, that Huromian sedimentation,which whichclosely closely followed the according to the time according to postasslum-arqon postassium-argon ages ages on on micas micas spans spans the time between between 2,230 2,230 to to 2,730 m.y., with frequency at at 2,480 maximum frequency 2,480 m.y. m.y. 2,730 witha amaximum Within Churchill Structural Structural Province Province during during the the interval intervalbetween between the the Within the the Churchill Kenoranand andHudsonian HudsonianOrogenies Orogeriies(approximately (approximately1,859 1,859and and2,200 2,200 m.y.) m.y.) two Kenoran two periods of of uranium mineralization are are evident, evident, both periods uranium mineralization both of which which correspoid correspond to first period, the periods of the periods ofgranitization, granitization~ metamorphism, metamorphism,and andmetasomatism. metasomatism. The The first period, embracesthe thetime time interval interval around embraces around 2,200 2,200 rn.y., m.y.,and andthe thesecond secondone one around around 1,920 1,920 m.y. m.y. The uranium uraniummineralization mineralization in in the with aa highest highest peak peak at at about about 1,735 1,735 m.y. m.y. The the Beaver10dge Lake northernSaskatchewan, Saskatchewan, took took place placearound around1 1,780 m.y. Beaverlodge Lakearea, area, in northern ,780 m.y. During the interval intervalbetween between the theHudsonian Hudsonian and and Grenville GrenvilleOrogenies Orogenies and and During with Stockwell's Stockwell ISproposed proposed Elsonian E1sonian Orogeny Orogeny (about (about 1,370 1,370 m.y.) coinciding with theGreat GreatBear BearLake Lakearea areashow showaarange rangebetween between 1,200 1,200 uranium uranium mineralization mineralization ininthe to 1,450 1,450 m.y. m.y. 56. �(Mursky, (Mursky, continued, page page b) b) At the the time time of Grenville Grenville Orogeny Orogeny which the time time interval At whichfalls falls within within the of 800 800 to 1,100 1,100 m.y. m.y. and and aa mean mean age 955 m.y., uranium mineralization ageof of 955 m.y., uranium span between between 880 by the occupies aa time time span occupies 880and and1,100 1,100m.y. m.y.and andisis exemplified exemplified by deposits in Lake area, area, Saskatchewan; Saskatchewan; Great Great Bear Bear Lake Lake region, deposits in the theBeaverlodge Beaverlodge Lake N.W.T.; and Ontario. The The uranium Bancroft N.W.T.; and Bancroft Bancroft region, region, Ontario. uraniumdeposits deposits in in the Bancroft area are similar age age as as the the granitic graniticIntrusions intrusionsand andthus thuscorrespond correspond to area are of similar 950 and 950 and1,070 1,070m.y. m.y. interval. interval. Geochronologic results, and geological geological data data show show that thatPrecambrian Precambrian rocks rocks Geochronologic results, and can be begrouped groupedinto intoseveral severaldistinct distinct categories in Wisconsin Wisconsin can categories and and age age patterns: patterns: (1) The 2,500 2,500 m.y. and older orthogneisses, andgranitic granitic The m.y. and orthogneisses, paragneisses, paragneisses, and rocks rocks which which occur occur in in the the western western and and northern northern part of of Wisconsin. Wisconsin. The The gneiss gneiss terraine terraine isiscomposed composed of of several several types types of of migmatic migmatic gneisses, gneisses, including amphibolite related mafic and related mafic rocks, rocks, granitic graniticgneisses gneisses and and including amphibolite and peliticgneisses gneissesand and hybrid hybrid rocks. rocks. The The assemblages assemblages seem seem to granite, pelitic correspond the Kenoran Kenoran Orogeny Province correspond to to the Orogenyininthe the Superior Superior Structural Structural Province Shield and andcoincide coincidewith with the the 2,500 of the the Canadian Canadian Shield 2,500 to 2,600 2,600 rn.y. m.y. old old uranium mineralization region. uranium mineralization in in that region. (2) The 1,850 1,850 to to 1,900 m.y. old volcanic The 1,900 m.y. volcanicand and plutonic plutonicrocks rockswhich whichmake make up up most the basement basement complex and northeastern Wisconsin. Wisconsin. most of of the complexof of northern northern and This suite suite consists consists of of granitic granitic to to dioritic dioriticplutonic plutonicrocks rockswhich which are are This intrusive contemporaneous intrusive into intoa acomplex complexofofessentially essentially contemporaneous volcanic volcanic rocks. The agesand anddistribution distribution of these The ages these rocks rocks suggest suggest that they they directlyrelated relatedto to Penokean Orogeny Orogeny (1,850 1,900 m.y.) m.y.) which, which, are are directly Penokean (1,850 to 1,900 thethe Hudsonian in time, time,coincides coincidesroughly roughlywith with HudsonianOrogeny OrogenyininCanada Canada and and its period its period ofofuranium uranium mineralization mineralization (1,920 (1,920 m.y.) m.y.) as as represented represented in the Churchill Structural Structural Province. Province. the (3) The1,780 1,780toto1,800 1,800m.y. m.y.old oldgranitic granitic and rhyolitic rocks The and rhyolitic rocks which which apapparently constitute constitute most most of ofthe thePrecambrian Precambrian terraine in insouthern southern rocksconsist consistprimarily primarily of of rhyolites Wisconsin. These These rocks rhyolites and and granites. granites. The TherhY81itic rhyolitic units units occur occur in in southern southern Wisconsin, Wisconsin,asasin1iers inliers in in the the Paleozoic rocks, whereas whereasthe theqranitic granitic rocks into central Paleozoic rocks, rocks extend extend into central and and northern Wisconsin. Wisconsin. These These rocks have been deformation rocks have beensubjected subjected to to deformation and whichappears appearstoto be be related related totothe and low-grade low-grade metamorphism metamorphism which thePenokean Penokean In time, Hudsonian Orogeny. In time, these these rocks rocks relate relatetotothethe HudsonianOrogeny Orogeny in in Canadaand andthe the1,780 1,780m.y. m.y.uranium uraniummineralization mineralization which which is represented Canada represented by the the Beaverlodge Beaverlodge area area ofofSaskatchewan. Saskatchewan. by (4) The rocks in central central and and east-central east-central Wisconsin. Wisconsin. The 1,500 1,500m.y. m.y. old old plutonic rocks Some rocks are are composed composed of quartz monzonite monzonite and and show show aa Someofof these these rocks of quartz striking similarity rapakivi massifs Scandinavia striking similaritytotothethetypical typical rapakivi massifsin in Scandinaviaand and in the the Great Great Bear Bear Lake Lake region region ofofCanada, Canada, where where the the associated associated uranium uranium mineralization, and and particularly the isotopic isotopicdata data on on pitchblende, pitchblende, are are mineralization, particularly the grouped m.y. mark. mark. grouped around around 1,400 1,400 m.y. It isistherefore, that thethe considerations thethe Precambrian It therefore,quite quiteclear clear that considerationsof of Precambrian age Wisconsin and the age patterns patterns in in Wisconsin andthe theperiods periodsof of uranium uraniummineralization mineralization in in the CanadianShield Shield would would suggest suggest abundant abundant reason reason to to investigate investigatePrecambrian Precambrian Canadian 57. �(Mursky, continued, page (Mursky, page c) mostlikely likely types terrain ininWisconsin Wisconsin for foruranium uranium as as well as as thorium. thorium. The The most types of deposits deposits Ininthe thePrecambrian Precambrian terraine terraineininWisconsin Wisconsin would would be: be: (1 ) (1) deposits associated associated with igneous igneous rocks. rocks. deposits (2) deposits Precambrian basins. basins. deposits In in clastic clasticsediments sediments ininPrecambrian (3 ) (3) igneouscomplexes. complexes. vein and/or replacement vei nand/or replacement deposits deposits near nearigneous (4) pegmatite pegmatite deposits deposits which whichwould wouldhave havea agenetic geneticrelationship relationship to igneous bodies. igneous bodi es. LaceND , LGo.l"'"HC AND IIU.AflU 1"""'" 0... AI.. ~otr""_., . I,OI,'H O'4'C ..... _ . CONOlOIo4(IMtlC _.-.. . .....'-"), AiH.~'...-('." • ••••• 0 IUl/f'N DC'~"""' . . . T'trc •. , . . . . . . . .'::t~r Ckf...,.., • • .-- ..... , ... ,.---"" ... ~" known Di6tribution of ofpresent prQscntand uncJformer fOrlnururanium uro)niUlll mines mines and oJnd known lyore 11 Distribution occurronces tho Canadian Ciln.JcHcan Shiold Il\ftQr A. h. II. II. Lang. Lung, 1570) 1970). occurrences in in the shield (Cite: I'ltJUfC 58. �URANIUM ENRICHMENT IN IN GRANITIC URANIUM PROVINCES: PROVINCES: ENRICHMENT GRANITICROCKS ROCKS AND AND RELATIONS RELATIONS TO TO WISCONSIN WISCONSIN JeffreyK.K.Greenberg Greenberg Jeffrey Wisconsin Geological Geological and and Natural Natural History Survey Wisconsin Survey Most uranium uraniumdeposits, deposits,but butparticularly particularly granitic Most graniticigneous igneous ones, ones, are are bound by closely bound bytime time(geologic (geologichistory) history) and and space space(tectonic (tectonicsetting) setting) into 'provinces". These "provinces". These provinces original uranium uranium provincesare areproposed proposedasasthe thesites sites of of original No concentration early but but evolved evolvedsialic sialic crustal crustal nuclei nuclei (shields). No concentration ininearly major in inrocks years. major uranium uraniumdeposits depositsare areknown known rocksolder olderthan thanabout about2.8 2.8billion billion years. Since Precambrian time, shieldareas areas have have undergone undergone major Since early Precambrian time, shield major modification, modification, Throughout thermo-tectonic thermo—tectonic events events (orogeny, particularly along along their theirmargins. margins. Throughout particularly etc.), etc.),uranium uraniumbecame became mobilized mobilized and and consequently consequently reworked reworked during each each progresprogressively The enrichment enrichmentofof uranium uraniumand andits its concentration concentration into into sively younger younger event. event. The deposits is an deposits an Important important product product of the the tectonic tectonicreworking reworking and and chemical chemical difdifferentiation ferentiation of of the the crust. crust. The Colorado Colorado Front Front Range Rangeand andEgyptian EgyptianRed RedSea Sea Hillsare are two two plutonic The Hills uranium alkaline uranium provinces. In each each case, case, progressively progressively younger younger and and more more alkaline plutons plutons are are enriched enriched in in uranium. uranium. The The Pikes Pikes Peak PeakBatholith Batholith in inColorado Colorado and and the Younger Granitesofof Egypt Egyptasaswell well as as highly highly urariiferous the Younger Granites uraniferous bostonite bostonite dikes dikes two provinces provinces also also possess in both typify these both areas areas typify these intrusions. intrusions. The The two possess radioIt can genically enriched enriched older older"basement" "basement" rocks. rocks. It can be be concluded concluded that that an an originaluranium uranium concentration concentration ininthese theseareas areaswas wasenhanced enhanced through through tectonic tectonic original and and magmatic magmatic reworking. Many of same rock and geologic environments environments which which are are hosts hosts Many of the the same rock types types and RedSea SeaHills Hills exist exist in for uranium uranium deposits deposits in the the Front FrontRange Range and and Red in Wisconsin. Wisconsin. However, even no However, evenunder underapparently apparentlyideal ideal chemical chemicaland andtectonic tectonic conditions, no major deposits are This absence maybebeinin part major uranium uranium deposits are known known in Wisconsin. Wisconsin. This absence may a it isismost a function function of thick thick glacial glacialblanketing blanketingofofthe thebedrock; bedrock; however, however, it most likely that did not likely thatthe theearly earlyparental parentalcrust crustforforwhat whatisisnow nowWisconsin Wisconsin did not Muchofof that that provide an abundant abundant source eventual uranium uranium enrichment. enrichment. Much provide an source for for eventual enrichment may north in in Canada Canada and Wyoming, but enrichment maybebepresent presenttoto the the north and west west in in Wyoming, but it it decreases the south east away form the the nuclear nuclear shield. decreases toto the south and and east away form shield. 59. �REGIONAL REGIONAL GEOCHEMISTRY GEOCHEMISTRY AND AND METALLOGENY, METALLOGENY, NORTH SHORE SHOREOF OF LAKE LAKE SUPERIOR, NORTH SUPERIOR, ONTARIO ONTARIO W.B. Coker Coker and andJ.M. J.M. Franklin W.B. Geological Survey Canada, Ottawa Ottawa Geological Survey of ofCanada, Ontario, Canada The Proterozoic Proterozoic and Archeanterranes terranes of of the northern The and Archean northern Lake Lake Superior Superior area area include exceptional variety variety of an an accompanying include an an exceptional of lithologles, lithologies,with with accompanying array array of Regional lake sediment water surveys mineral types. Regional sediment and and water surveys were were underundermineral deposit types. taken to obtain the distribution and concentration of selected taken to obtain information information on on the distribution and concentration of selected elementsinin lakes lakes lniiiedlately elements immediately north north of ofLake Lake Superior. Superior. The principal principal Archean lithologic domains, The Archean lithologic domains, with attendant attendant deposit deposit types types are: and examples and examples 1) Supracrustal "greenstone" with massive sulphide Supracrustal "greenstone" sequences, sequences, with massive sul phide (Manitou(Manitouwadge), gold vein and iron formation wadge), gold vein (North (NorthShore Shore Gold) Gold) and iron formation(Wawa (Wawa and and Schreiber areas) types. types. Schreiber areas) 2) intrusions,with with Cu-Moporphyry porphyry type typeoccurrences occurrences (Priske (Priske Twp. Twp. Felsic intrusions, Cu-Mo occurrence) and occurrence) and uraniferous pegmatites pegmatites (Greenwich (Greenwich Lake). Lake). 3) Mafic Intrusions, intrusions,with withCu-Ni Cu-Ni(Nicopor) (Nicopor)and andZn-Cu Zn-Cu(Zenmac) (Zenmac) types. types. Mafic and intrusive units units with with major major Principal Proterozoic stratigraphic and Principal Proterozoic deposit types, and and examples, examples, are: deposit types, 1) Aphebian Gunflint iron formation. Aphebian Gunflint formation. 2) Apheblan Roveshale, shale,with with Ag veins (Creswel). Aphebian Rove Ag veins (Creswel). 3) SibleyGroup Group red-beds, red-beds, with with Pb-Zn-Ba Pb-Zn-Ba veins veins (Dorion) (Dorion) and and Helikian Sibley U+Cu veins(Greenwich (GreenwichLake, Lake,Little Little Bear). U~Cu veins Bear). 4) Heliklan volcanics, with native Helikian Osler Osler Group Group volcanics, native Cu-chalcocite Cu-chalcocite veins veins and and amygdule fillings. amygdule fillings. 5) Helikian He1ikian gabbroic gabbroic intrusions, intrusions,including includingunniineralized unmineralizedLogan Logan diabase diabase sills, and mineralization (Great sills, andthe theCrystal CrystalLake Lakegabbro gabbrowith withNi—Cu Ni-Cu mineralization (Great Lakes Nickel). Lakes Nickel). 6) He1ikian alkalic alkaliccomplex complex (Port (PortColdwell) Coldwell)with witha amagmatic magmatic Cu eu (Ni, Pd, Pd, Helikian zone, Pb-Zn-Ag Pb-Zn-Ag veins veins in in the themetamorphic metamorphic halo, halo, and and UUzones zones near near Pt) zone, the the northeast northeast contact. contact. 7) 7) Prairie Lake) Helikian carbonatite (( Prairie Lake) with with U, U, Nb Nb and and rare earths. earths. Helikian carbonatite Trace element elementpatterns patterns in in lake andwater waterclosely closely relfect'the reirect the Trace lake sediment sediment and chemicalcharacteristics characteristics of the chemical the major major lithologic lithologicdomains, domains, although although glacial overburden andvarying varyinglimnologic limnologicconditions conditions clearly clearly modify overburden and modify the the elemental elemental distributions. The The trace trace element patterns in element patterns in the thelake lakesediments sediments and and waters waters may divided into into three may bebedivided three groups: groups: 60. �(Coker and Franklin, Franklin, continued, (Coker and continued, page page b) b) 1) 2) Patterns related to to bedrock bedrock features, features, as as indicated indicated by byour ourbedrock bedrock Patterns trace element data, which which have haveonly onlymarginal marginalore oredeposit depositsignifisignifitrace element data, cance: (I) (i) Rove shaleisis characterized Rove shale characterized by by elevated elevated Zn, Zn, Ni, Ni, Ag, Ag, As As and and The Ag Ag deposits Hg sediments and lake waters. waters. The Hg in in lake sediments and FF in in lake are not not specifically outlined. are outlined. (ii) (i;) Port Coidwell Alkalic Complex reflected by by FF in in lake Port Coldwell Alkalic Complex isisreflected lake waters sediments; Pb waters and and by by Zn Znand andNiNiinin lake lake sediments; Pbinin lake lake sediments form halo around around the theComplex. Complex. ments form a halo (iii) (iii) Logandiabase diabase sillsare areclearly clearly identified identified by Logan sills by high high Cu Cu levels lake sediments; sediments; Fe in lake Fe ahd ahd Ni Ni levels levels in in the thelake lakesediments sediments reflect the the sills sillstotoa alesser lesserdegree. degree. (iv) In the the Sibley Sibley Group Group the the Kama Kama Hill Formation, and In Hill Formation, and to to aa lesser extent the are reflected the Rossport Rossport Formation, Formation, are reflected by by elevated elevated As As contents contents in the the lake lakesediments. sediments. (v) Wawaarea areavolcanic volcanicand andsedimentary sedimentary strataare are reflected reflected by Wawa strata by elevated Ni Ni in lake lake sediments; sediments; elevated elevatedMn, Mn, Fe, Fe, As, As,Co Co and and Pb in lake reflect the Pb in lake sediments sediments reflect the major major iron formation formation within this thisArchean Archeansequence. sequence. In addition iron formation, formation, certain deposit In addition to to the theWawa Wawa iron deposit types types are are morespecifically specifically reflected more reflectedbybysome some of of the thelake lakesediment sediment and and water water data. For example: example: (1) (i) Manitouwadgemassive massivesulphides sulphidesare arereflected reflected by Manitouwadge by Cu, Cu, Zn Zn and and Pb lake Pb lake sediment sedimentdata, data, as as expected, expected, although althoughin in addition there is significant significantFFininthe thelake lakewaters waters and and U U in the the lake lake there sediments,possibly possibly reflecting reflecting the sediments, the pegmatites pegmatites present present in the the area. area. ((ii) ii) Zenmac are by the the Gabbro-hosted Gabbro-hostedzinc zincdeposits deposits at at Zenmac arereflected refiected by Zn lake sediment Zn and and Co Co lake sediment data. data. (iii) Mo—Cu-bearing felsicintrusions intrusions are are identified MO-Cu-bearing felsic identifiedbybyMoMoand andCu Cu lake sediment sediment data. data. (iv) Pb-Zn-Ba veinsassociated associatedwith with the the Sibley the Port Pb-Zn-Ba veins Sibley Group Group and and the Port Coldwell Alkalic Alkalic Complex are indicated by Coldwell Complex are by the the Pb Pb and and Zn Zn lake sediment sediment data. (i i 1) (v) 3) 3) The zonesofof uraniferous uraniferous pegmatites north of Dorion, The zones pegmatites north Dorion, which which are associated with unconformity are associated with unconformity - related relateduranium uranium occurrences, occurrences, are distinctly distinctlyoutlined outlinedbybythe thelake lake sedimentand and water water UUdata. data. are sediment Finally, under specific specificphysicochemical-limnological physicochemical-limnological conditions conditions an an Finally, under individual trace traceelement, element, ororgroup group ofoftrace traceelements, elements,may may be be conconThe scavenging scavengingeffect effect of centrated to unexpectedly unexpectedly high centrated high levels. The both iron iron and and manganese manganese hydroxide on trace metals metals both hydroxideprecipitates precipitates on (mainly Zn, this area. area. (mainly Zn, Co Coand andNi)Ni)ininlakes lakesisis evident evident in in this hl. �GEOLOGYOF OF THE THE MCCASLIN GEOLOGY MCCASLIN RANGE, RANGE, NORTHEASTERN NORTHEASTERN WISCONSIN WISCONSIN Joseph J. J. Mancuso, Joseph Mancuso, R.H. R.H. Motten* Motten* Bowling Green Bowling Green University University Bowling Green, Ohio Ohio Bowling Green, The McCaslin McCaslinRange Range locatedininportions portions of Forest, The is islocated Forest, Oconto, Oconto, Marinette, Marinette, and northeastern Wisconsin. Wisconsin. It forms forms a a ridge ridge two two to and Lang1ade Langlade Counties Counties in in northeastern to five wide extending an east-west east-west direction. The The major miles wide miles extending 25 25miles miles in in an major geologic thearea areainclude include Lower PrecambrianWaupee Waupee volcanics, volcanics,McCauley McCauley units ininthe thethe Lower Precambrian Granite, and and Hines Hines Quartz Quartz Diorite, Diorite,and andthe theMiddle MiddlePrecambrian PrecambrianBaldwin BaldwinConglomerate, Conglomerate, McCaslin Granite. McCaslinQuartzite, Quartzite, Hager HagerRhyolite, Rhyolite, Belongia Belongia Granite Granite and and High High Falls Falls Granite. On On the the McCaslin McCaslin Range, Range,the the Middle Middle Precambrian PrecambrianMcCaslin McCaslinformation formationconsists consists of of massive red-grey and quartz-pebble quartz-pebble conglomerates conglomerates similar those massive red-grey quartzites quartzites and similar to those found in in the River uranium uraniumdistrict district in found the Elliot ElliotLake—Blind Lake-Blind River in Ontario. Ontario. It It rests rests unconformably unconformably on on Lower LowerPrecambrian Precambriangreenstones, greenstones,granites, granites, and and gneisses. gneisses. The dominant the region region isisthe theMcCaslin McCaslin Syncline Syncline which which trends trends The dominantstructure structure in in the to close close to the approximately east-west. It It plunges plunges 50 5° to to the the west west and and appears appears to the approximately east—west. east but is disrupted east but disrupted by by the the intrusive High High Falls Falls granite. granite. The The northern northern limb and nose of of the McCaslin and nose the syncline synclineare arerepresented representedbybythethe McCaslinRange Range and and Thunder Thunder Mountain, respectively, while Mountain, respectively, while the the southern southern limb limb isisrepresented represented by by the the Baldwin Baldwin Conglomeratewhich whichisis exposed exposednear near the the town town of Mountain, Conglomerate Mountain, Wisconsin. Wisconsin. well-developed metamorphic metamorphic aureole relatedtotothe the High HighFalls Falls granite A well-developed aureole related intrusion can be be traced tracedthrough throughprogressive progressivemetamorphic metamorphic changes changes in the Hager, Hager, intrusion can in the McCaslin, and formations. The metamorphicmineral mineral assemblage indicates McCaslin, and Waupee Waupee formations. The metamorphic assemblage indicates temperature approximatelylOO°C 700°C adjacent thegranite granite intrusion intrusion aa maximum maximum temperature of ofapproximately adjacent to tothe where sillimanite occurs,and andgrades gradeswestward westward through through zones zones of andalusite andalusite and and where sillimanite occurs, muscovite at the theextreme extreme western western end end of the the range. range. muscovitedown downtotosericite sericite at The The lithology lithology and and stratigraphic setting settingofofthe theMcCaslin McCaslin formation formation on on the the McCaslin Range Rangeare aresimilar similar to to those McCaslin those of of uranium uranium producing producing basal basal Proterozoic Proterozoic sedimentsinin Canada, Canada,South South Africa,Brazil, Brazil, and Africa, and Australia. sediments Comparisons with known uraniferous conglomerates: Comparisons with known uraniferous conglomerates: I. Similarities and Similarities and indications indications ofofuranium uranium mineralization: mineralization: A. The McCaslin McCaslin formation formation occurs The occurs immediately immediately above above the the unconunconatthe thebase base ofofa aMiddle MiddleProterozoic Proterozoicsequence. sequence. formity at B. B. The basal basal member member theformation formation is is a quartz-pebble The ofofthe quartz-pebble conconglomerate which is overlain overlainbybya asequence sequence ofofcross-bedded cross-bedded glomerate which and ripple-marked sandstones. and sandstones. C. C. cobble of ore-grade ore-grade conglomerate conglomerate was found in in A cobble was reportedly reportedly found the the drift driftononMcCaslin McCaslinMountain. Mountain. (Wisconsin (Wisconsin Geological Geological Survey) Survey) *Kennecott *Kennecott Exploration, Inc., Inc.,Casper, Casper,Wyoming Wyoming 62. �(Mancusoand andMotten, Motten, continued) (Mancuso D. D. Anomalous concentrations of of uranium Anomalous concentrations uranium were were reported by by NURE NURE inin the McCaslin Hydrochemical& &Stream StreamSediment SedimentSurvey, Survey, Iron McCaslin area. (NURE (NURE Hydrochemical Iron Mountain Mountain Quadrangle; Quadrangle; 1978) 1978) II. dissimilarities: II. Apparent Apparent dissimilarities: A. Uraniferous conglomerates conglomerates Ontario,Brazil, Brazil, Australia, and Uraniferous in inOntario, and South Africa are dated dated at at 2150 2150 to to 2800 2800 m.y. m.y. (Robertson, (Robertson, 1974). 1974). South Africa are The McCaslin reportedly1900 1900m.y. m.y.(Van (VanSchmus, Schmus, 1976). 1976). The McCaslinformation formation is reportedly B. Accessory apparently lacking lacking inin outcrops outcrops ofofthe theMcCaslin McCaslin Accessorypyrite pyrite is apparently formation, but isisaamajor majoraccessory accessory in in the theknown known deposits. deposits. formation, but C. C. Hematite is major accessory accessory in the McCaslin McCaslin formation Hematite is a major in the formation but but is lacking in in the theknown known deposits. deposits. 63. �WISCONSIN WISCONSIN :[NTEREST INTEREST IN RADIOLOGICAL RADIOLOGICAL IMPACTS IMPACTSRESULTING RESULTINGFROM FROM URANIUM EXPLORATION EXPLORATION(DRILLING) (DRILLING) URANIUM Thomas K. Greenberg, Greenberg, and and M.G. M.G. Mudrey, Mudrey, Jr. Jr. ThomasJ.3. Evans, Evans,Jeffrey Jeffrey K. Wisconsin Geological History Survey Survey Wisconsin Geological and and Natural Natural History Recenturanium uraniumexploration explorationactivity activity in Recent in northeastern northeastern and and central central Wisconsin Wisconsin has stimulated assessing potential radiological impacts impacts resulting has stimulatedinterest interest in assessing potential radiological In the from intoa uranium a uraniumorebody. orebody. In the midst midst of far-ranging far-ranging claims claims of from drilling drilling into significantly harmful impacts impacts on on one one hand hand and assertions of of zero zero significantly harmful andthe theflat flat assertions impact on on the the other hand, impact hand, an an informal informal technical technicalworking workinggroup groupwas was formed formed as as a request order to determine a result result of ofaalegislative legislative requestin in order to determinewhat whatfacts factsare areknown known aboutthe theexploration explorationactivity. activity. The about The objectives of ofthe theworking workinggroup group have have been (1) identify been toto (1) identifyexisting existinginformation informationononuranium uraniumexploration explorationimpacts impacts available in in the reliable state, federal, international literature; literature; available the reliable federal, and and international (2) consult (2) consult state, state, federal, federal,and andinternational internationalagencies agencies having having some some experience with issues surrounding uranium drilling impacts; (3) if possible, ience with issues surrounding uranium drilling impacts; (3) if possible, prepare "wors "worst case"estimates estimatesofofradiological radiological impacts ondrillers drillers and prepare t case" impacts on and exexploration geologists, geologists, and and(4) (4)investigate investigatethe thefeasibility feasibility of ploration of low-level low-level radiation monitoring monitoring of of uranium uranium drill sites areas having knownuranium uranium drill sites at at areas having known deposits, exploration sites ininWisconsin. deposits, as as well well as as atatproposed proposed uranium uranium exploration Wisconsin. The report reviews reviewsthe the public public policy policy aspects of investigating potential The report aspects of potential radiological radiological impacts impacts ofofuranium uranium exploration explorationand and the thegeneral general methodology methodology of the working group's approach approachtotoevaluating evaluatingthese thesepotential potential radiological the working group's impacts. Results dateindicate indicate (1) (1) the the literature literature dealing Results toto date dealing with with radiological radiological impacts from drillingisis limited, limited, (2) impacts from drilling (2) interest of of local, local, state, state, ororfederal federal government in in this the governmentagencies agencies thistopic topic ranges rangesfrom fromtotal total indifferences indifferences to the of drilling drillingactivity activity (moratorium),(3)(3) perceivedradiation radiationexposure exposure prohibition of (moratorium), perceived to the driller appears minoratat this this point, to the exploration exploration geologist geologist and and driller appears minor point, and and (4) (4) monitoring of of actual actual drill may monitoring drillsites sites mayprove prove totobe bethe themost most direct directapproach approach to resolving uraniumexploration explorationactivities. activities. The resolving the the issues issues surrounding surrounding uranium The status of the the informal -informal technical technical working working group's group's investigations as as of of early early May, May, 1980will will be 1980 be presented. presented. 64. �GEOLOGIC IN NORTHEASTERN NORTHEASTERN WISCONSIN: AN UPDATE UPDATE GEOLOGIC MAPPING MAPPING IN WISCONSIN: AN B.A. Brown B.A. Brown and and J.K. Greenberg Greenberg Wisconsin Geological and and Natural Natural History Wisconsin Geological History Survey Survey Madison, Madison, Wisconsin Wisconsin Continued reconnaissance reconnaissancemapping mapping reinterpretation of andand a a reinterpretation of geophysical geophysical Continued data signigicantly improved our understanding of the Precambrian data have have signigicant1y improved our understanding of the Precambrian geology geology conceptofoffour four distinct distinct tectonic of northeastern northeastern Wisconsin. Wisconsin. The The concept tectonic regions regions separated west trending boundary boundary structures has not separatedby by three three major major east east to to west structures has changed, boundaries and types present present changed,however howeverthe thenature natureofof the the boundaries and the the rock rock types within the three regions better known result of the southernmost southernmost three regions are are now now better known asasaaresult of exextended mapping and new gravity map. tended geologic mapping and aa new gravity map. The new newgravity gravity data data have haveenabled enabledestimation estimationofof the the extent extent of The of several several known part of ofthe thearea areaand and suggest suggest the the presence presence of knownplutons plutonsinin the the central central part several parts of the several granitic granitic and and mafic mafic plutons plutons in in the thesouthern southern and and western western parts the sheet. The Batholith is and eastern eastern boundaries boundaries of the the Wolf Wolf River River Batholith The northern northern and resulting interinterdelineated by by its itsgravity gravitysignature signatureand andrecent recentmapping. mapping. The The resulting delineated rocks of of the pretation indicates indicates aa sharp sharp contrast contrast between between rocks the Batholith Batholith and and the the granitic graniticterrane terraneofofthe theAmberg-Athelstane-High Amberg-Athelstane-High Falls area. area. The southernmostboundary boundary zone, which followsthe theWolf WolfRiver Rivercontact contact in in The southernmost zone, which follows the to be rilajor fault fault zone This zone the east appears appears to be aa major zone in in the thesouthwest. southwest. This zone truncates northeast trending cates trending cataclastic catac1asticzones zonesknown known from from previous previous mapping mapping in Marathon County. The The central central boundary zone is is marked by east-west east-west trending Marathon boundary zone marked by and cataclastic catac1astic zones zones in the the east, east, but buttotothe thewest westofofthe theCavour Cavourarea area faults and becomesless lessdefined definedand andisischaracterized characterizedbybyaadistinct distinct class becomes class ofofhornblendehornblendebearing intrusions,ranging rangingfrom from gabbro gabbro to granodiorite. granodiorite. These bearing dioritic dioritic intrusions, rocks crop out out in aa band from east east to to west west in in near rocks crop band for over over 100 100 km km from near proximity the central centralboundary. boundary. to the Field work thethe unmapped work in in 1980 1980 will willconcentrate concentratein in unmappedand and poorly poorlyexposed exposed northwestern the sheet. sheet. A program planned northwesternportion portion of the programofoftest testdrilling drilling isisplanned for problem problem areas areas throughout and aa geochronological geochronological study throughout the the area, area, and study of of important rock types important rock types is is now now in progress. progress. 65. �ANALYSIS OF ANALYSIS OF AANEW NEW GRAVITY GRAVITY MAP MAP FOR FOR THE MERRILL-RHINELANDER AREA, AREA, WISCONSIN WISCONSIN THE MERRILL-RHINELANDER C. Ervin and and Kelly Kelly Tuftee Tuftee C. Patrick Ervin Department Geology Department of Geology Northern Illinois University Northern Illinois University DeKalb, DeKalb,Illinois Illinois 60115 The History Survey Survey and and Northern Northern The Wisconsin WisconsinGeological Geological and and Natural Natural History IllinoisUniversity University havecompleted completeda anew new gravity gravitymap map ofofnortheastern northeasternWisconWisconIllinois have sin. Data Data east east of 89 89 degrees degrees longitude and and in in Vilas VilasCounty County were were recompiled recompiled from earlier earlier surveys, from surveys,using usingthe thenew newGeodetic GeodeticReference Reference System System - 67 67 formula formula and the the International International Gravity 71 datum. and Gravity Standardization Standardization Net Net - 71 datum. The The remainder remainder of the the map, map, including including Oneida, Oneida, Lincoln, Lincoln,western westernLanglade, Langlade, and and northern northernMarathon Marathon counties, consists of ofnew new data data on on approximately approximately aa one-mile counties, consists one-mile grid. grid. Preliminary interpretation Interpretation of that a rather ofthe thenew new data data suggests suggests that rather simple, simple, Preliminary qualitative analysis is sufficient totodelineate delineate the the regional regional variations variations in in qualitative analysis is sufficient The gravity gravity data, rock data, used used in conjunction conjunction with with the the aeromatic aeromatic data, data, rock type. The are valuable guide guide for for and and constraint constrainton on the thegeologic geologicmapping mapping of the the hidden hidden are a valuable Precambrian rocks. Precambrian 66. �PETROLOGYOF OFTHE THE BEAR BEAR LAKE LAKE INTRUSIVE, PETROLOGY INTRUSIVE, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN Institute ofofMineral Allan Johnson, Johnson, Institute MineralResearch Research Michigan Technological Technoloqical University, University, Houghton, Michigan Houghton, Michigan Michigan 49931 Boyd Parker, Parker, Michigan Michigan Geological Geological Survey Boyd Survey Division Department of Natural Natural Resources, Department of Resources, Lansing, Lansing, Michigan Michigan 48906 David Snider, Michigan David Snider, Michigan Geological Geological Survey Survey Division Department of Resources, Lansing, Lansing, Michigan Michigan 48906 Department of Natural Natural Resources, Jack Van Van Alstine, Alstine, Michigan Jack Michigan Geological Geological Survey Survey DNR, DNR,Marquette, Marquette, Michigan 49855 The Bear BearLake Lake intrusiveisisaanearly nearlycircular circular felsic The intrusive felsicplug plugwhich which intrudes intrudes It Keweenaw Itisislocated locatedin the in the KeweenawPeninsula Peninsula miles (13 (13 km) km) north north ofofHoughton, Houghton, Michigan. Michigan. eight miles the Upper Freda formation. formation. Upper Keweenawan Keweenawan Freda Earlier work work on on the the Bear Bear Lake Lake intrusive intrusivebybythe theMichigan Michigan Geological Geological Earlier Survey designed to test aa model model of Surveywas waspart partofofaa larger larger investigation designed to test copper mineralization. Basically, the copper mineralization. the model model suggested suggested that that the the several, isolated isolated intrusive/extrusive intrusive/extrusive bodies bodies of Keweenawan of Keweenawanage ageininthethe Keweenaw Keweenaw Peninsula Peninsula may maybebethe thesource sourcefor for copper coppersulfide sulfide mineralization (Snider (Snider and and Parker, 1979). 1979). The The Bear BearLake Lakeintrusive intrusive appeared appearedtotooffer offer an an opportunity to test test this thismodel. model. Geological Survey Survey in in 1978 indicated the Field work work by by the the Michigan Michigan Geological 1978 indicated poss"ibi1ity coppermineralization mineralizationassociated associated with with the the Bear Bear Lake Lake intrusive. possibility ofofcopper intrusive. Anomalous copper values ofof190 in inthe the presence presence of of two two Anomalous copper values 190ppm ppm theintrusive, intrusive, the VLF-EM conductorsand andanomalous anomalous copper values soil over over these VLF-EM conductors copper values in inthethesoil these conconductors supported this hypothesis. ductors supported this hypothesis. In 1979 1979 the Mineral Research Research joined project. A verIn the Institute Institute ofofMineral joined the the project. The 208 208 feet feet tical diamond drill hole was was put put into into the the largest largestconductor. conductor. The tical diamond drill hole (63 m) deep deephole holepenetrated penetrated8686feet feet (26 (26m)m)ofof glacial glacial overburden, (63 m) overburden, 30 30 feet iii) (9 m) of highly altered 25 feet feet (7.6 (9 m) of altered fragmental fragmental rocks rocks (volcanoclastic?) (vo1canoc1astic?) and and 25 (7.6 m) of clastic clasticsediments sediments ranging ranging from from siltstones siltstones totocoarse coarsearkoses. arkoses. The The bottom bottom 67 feet (20 (20 m) m) cored cored the the intrusive intrusivewhich whichbecame became more with 67 morecoarsely coarselycrystalline crystalline with depth. The The intrusive intrusive has andotherwise otherwisealtered altered the has apparently apparently metasomatized metasomatized and overlying overlying sediments. sediments. These Theseoverlying overlying sediments sediments have have not not been been found found in in outcrop. outcrop. Minor Minor amounts amountsofof native native copper copper were were present present as as finely finely disseminated disseminated grains grains in in quartz quartz veinlets vein1etsbetween between 162 162 and and 180 180 feet (49 (49 and and 55 55 m) m) of of depth. depth. Reference Snider, D.W., D.W., and and Parker, Parker,B.K. B.K.(1979) (1979)Geochemical Geochemical and andGeophysical Geophysical Anomalies Associatedwith with the the Bear Lake Intrusive, Intrusive, Sections Anomalies Associated Bear Lake Sections2424and and 25, 25,TS6N, T56N, R34W, Houghton County, Michigan, on Lake Lake Superior Superior Geology, Geology, R34W, Houghton County, Michigan,25th 25thAnnual AnnualInstitute Institute on Duluth, MN, May p. 38. Duluth, MN, May8-13, 8-13, Abstract, Abstract, p. 67. �THE COSUNA PROJECT -- AANEW THE COSUNA PROJECT NEW CORRELATION CORRELATION CHART CHART FOR FOR THE THE NORTHERN NORTHERN MID-CONTINENT REGION REGION G.B. arid D.J. Bergstrom G.B. Morey Morey and Bergstrom Minnesota Survey Minnesota Geological Geological Survey 1633 Eustis Street 1633 Eustis St. Paul, Paul, Minnesota Minnesota 55108 Late Association of of Petroleum Geologistsinitiated initiated Late in 1976, 1976, the the American American Association Petroleum Geologists North aa national national project project called called 'Correlation "CorrelationofofStratigraphic StratigraphicUnits Unitsofof NorthAmericafl America" (COSUNA), afterward gained officialsupport supportinin this this country (COSUNA), andand soonsoon afterward gained official country from from the the United States and numerous numerous otherprofessional professionalsocirties. socirties. It United States Geological Geological Survey Survey and other It beaaproject project of of voluntary voluntary effort, effort, and is designed designed toto be and the the objectives objectives are are (1) (1) to to develop seriesofof stratigraphic stratigraphic charts charts correlating rock rock units units of of both both the the develop aaseries surface subsurface across acrossgeologic geologic provinces provinces of of the United surface and and subsurface United States, States, and and (2) to thethickness thicknessand and lithologyofofeach eachlithostratigraphic lithostratigraphic unit (2) to summarize summarize the lithology throughout the geologic geologiccolumn, column,asaswell wellasastoto identify identify pertinent throughout the pertinentpaleonpaleonthe data data base basewill will conform and radiometric radiometric data. data. Although Although the conform insofar tological and as possible possible to to the the standards standardsset setforth forth in in the Stratias the International International Code Code ofofStratigraphic Nomenclature Nomenclature will be include information information not not formally formally graphic it itwill be necessary necessary toto include as possible possible for specified within within the theCode Code to to insure insure as as complete complete a data data base base as country. the the entire country. For the the purposes this project, For purposes ofof this project,the theUnited UnitedStates Stateshas has been been divided divided The Minnesota MinnesotaGeological Geological Survey Surveyhas hasvolunteered volunteered to to coorinto 20 20 regions. regions. The dinate the program in the dinate program in the states states ofofMinnesota, Minnesota, Wisconsin, vlisconsin, northern northern Michigan Michigan and eastern eastern South NorthernMid-contintent Mid-contintent and South Dakota, Dakota, which which comprise comprise the theCOSUNA COSUNA Northern Region. The The stratigraphic stratigraphic succession succession in this thisregion regionisissummarized summarized in in approxapproximately 40 columnserected erectedtotorepresent representmajor majorlateral lateral changes changesininlithology, lithology, imately 40 columns structure, This correlation the the other COSUNA structure, and and age. age. This correlation chart, chart,asaswell wellasasallall other COSUNA charts, has constructed following following the for the has been been constructed the general general format format used used for the charts charts of western (Douglas and andothers, others, 1970). Canada (Douglas 1970). The COSUNA charts western Canada The COSUNA chartshave haveaa vertical time units chronostratigraphically. tical timescale, scale,with withthe theArchean Archean and and Proterozoic Proterozoic units Thus they from the the correlation correlationcharts chartspreviously previouslypublished published by by the the Thus theydiffer differ from Geological Society Society of of America depictsstratigraphic stratigraphic Geological America inin that each each column column depicts relationships among rocksofofall all ages among rocks ages rather than than rocks rocks of of only only one one geologic geologic system. Because rocksranging ranainginin age agefrom fromearly early Archean Archean(> (>3,600 m.y.) to Because rocks 3,600 m.y.) Holocene «10,000 Northern Mid-continent Mid-continent Region, Region, aa mixture mixture Holocene (<10,000years) years)occur occurin in the Northern of chronometric andchronostratigraphic chronostratigraphiccriteria criteria of chronometric and ofvarying varying degrees degrees of of acacvery complex complex stratigraphic curacy curacy and andprecision precision were wereused usedtotoportray portray what what is is a very stratigraphic has resulted ininmany many stratigraphic stratigraphicand andcartographic cartographicproblems problems This has succession. This ProjectDirector, Director, that have have not yet yet been been resolved. resolved. Nonetheless, Nonetheless, the the COSUNA COSUNA Project Childs (University of Dr. Orb Orlo Childs of Arizona), Arizona), has has invited invitedany any interested interestedgroups groups or individuals to participate in the review of the geologic or individuals to participate in the review of the geologiccolumns columns ininareas areas Therefore, as as part part of this in which which they they have have expertise. Therefore, thisreview review process, process, weactively actively solicit solicit assistance evaluationofof this this chart. we assistance in in preparation preparation and and evaluation 68, 68. �(Morey and (Morey and Bergstrom, Bergstrom, continued) Reference Reference Cited Douglas, R.J.W., 1970, Geotectonic R.J.W., and and others, others, 1970, GeotectonicCorrelation Correlation Chart Chart for for Western Canada, Douglas, R.J.W., R.J.W., ed., ed.,Geology Geologyand andEconomic Economic Western Canada,inin Douglas, Minerals of ofCanada: Canada: Geological Survey Survey ofofCanada, Canada,Economic Economic Geology Geology ReportNo.1, No. 1,Chart ChartIII. III. Report 69. �MINERALOGY GRANITIC PLUTONIC PLUTONIC MINERALOGYAND ANDCHEMISTRY CHEMISTRYOF OFMIDDLE MIDDLE PRECAMBRIAN PRECAMBRIAN(Xg) (Xg) GRANITIC ROCKS ROCKS FROM FROM NORTHERN NORTHERN WISCONSIN William L. L. Petro* Petro·"" Geology and and Geophysics Geophysics Department Department of Geology University of ofWisconsin Wisconsin Madison, Wisconsin Wisconsin 53706 Madison, study of Middle igneousintrusive intrusive rocks A study Middle Precambrian Precambrian igneous rocks from from northern northern Wisconsin is in progress thethe Penokean Wisconsin is progress to to gain gainfurther furtherunderstanding understandingofof Penokean orogeny. The The rocks rocks are are separated separatedinto into two two suites suites by by radiometric radiometric dating. dating. Van Van Schmus Schmus(in(inpress) press)and andSims Simsand andPeterman Peterman (in(inpress) press)estimate estimatethat that the suite is 1800-1900 m.y. old. The The range rangeof of rock rock types types is older (Penokean) (Penokean) suite 1800-1900 m.y. The older older suite granite-granodiorite-tonalite (IUGS (rUGS classification). classification). The suite has has primary igigPrice,Rusk, Rusk, and and Sawyer Sawyer counties. The The common common primary been been studied studied in Price, neousmineral mineralassemblage assemblage quarz + plagioclase + biotite++alkali alkali feldspar neous is is quarz + plagioclase + biotite feldspar + hornblende. Van Schmus Schmus(in (in press) rocks appear appearto to be be syntectonic. Van hornblende. These These rocks estimates that the suite is 1765 estimates that the younger younger suite 1765 m.y. m.y. old. This This suite suite ranges ranges from toquartz quartzmonzonite, monzonite, and and has has been been studied studied ininSawyer, Sawyer, Oneida, Oneida, from granite to and Marinette Niarinette counties. The primaryigneous igneous mineral mineral assemblage The common common primary assemblage is and quartz feldspar ++ biotite biotite+ +hornblende. hornblende. The quartz ++ plagioclase plagioclase ++alkali alkali feldspar estimates by by powder powder difdifyoungersuite suite appears to be be post-tectonic. From younger appears to From estimates fraction methods,K-feldspars fraction methods,K-feldspars from from both both suites suitesappear appear totobebeordered ordered(between (between Preliminary results of microcline). Preliminary intermediate and and maximum maximum microcline). of mineral mineral chemistry have have been been obtained microprobe. In In the the older older suite, suite, chemistry obtained by by electron microprobe. biotites (total iron determined biotiteshave have0.65-0.73 0.65-0.73wt.% wt.%FeO/FeO+MgO FeOjFeO+MgO (total determined as as FeO), FeO), 0.61-0.76 wt.% wt.% FeO/FeO+MgO, FeOjFeO+MgO, plagioclases normally hornblendes have have 0.61-0.76 hornblendes plagioclases are are normally zoned and have have 31-49 31-49 mole% mole%An, An,and andalkali alkali feldspars feldspars have have 87-92 87-92 mole% mole% Or. Or. zoned and In An,and andalkali alkali fel dIn the the younger younger suite, suite, plagioclases plagioclaseshave have 30-36 30-36 mole% mole% An, feldhave 84-89 84-89 mole% mole% Or. Or. Two geothermometry yields temperatures spars have Two feldspar feldspar geothermometry yields temperatures Major element of 600-800°C 600-800°C (range element rock chemistry chemistry has has (rangefor for both both suites). suites). Major glass beads beads (sample (sample fused fused with been determined been determinedby bymicroprobe microprobeanalysis analysis of of glass Both suites flux). have been been determined determined by by INAA. INAA. Both flux). Some Sometrace trace elements elements have may have have been beenmetamorphosed metamorphosed duringa a1600-1650 1600-1650m.y. m.y.old old regional metamorphic may during metamorphic event which which reset reset Rb-Sr systematics in east-central event Rb-Sr systematics east-central Wisconsin Wisconsin and and the the Fox Fox with Mesozoic-Cenozoic River Vally Vally (Van (Van Schmus Schmus etetal., 1975). Comparison Comparison with Mesozoic-Cenozoic River al., 1975). intrusives ofofknown bebemade known tectonic tectonic setting settingallows allowsinferences inferencestoto made about about the the settingininwhich whichthe theMiddle MiddlePrecambrian Precambrian intrusives intrusiveswere were generated. generated. tectonic setting Chemicaldata dataareareconsistent consistent with(but (butnot notcriteria criteria for) generation Chemical with generation of the the older suite older suite during during plate platesubduction, subduction, and and generation generation of the the younger younger suite This seems be in general related to aa subsequent subsequent collision event. This seems toto be general agreeagreerelated to collision event. ment with with the ment the geologic geologicmodel model presented presented by byCambray Cambray (1978). ** Student Student paper 70 70. �METALLIC MINERALS OF ISLET,LAKE LAKESUPERIOR SUPERIOR METALLIC MINERALS OF SILVER SILVER ISLET, Nancy Scofield Nancy Scofield Institute MineralResearch Research Institute ofofMineral Michigan Michigan Technological Technological University University Houghton, Michigan 49931 Houghton, L.L. Babcock Babcock Tucson, Arizona 85711 Tucson, Isletisislocatedin locatedtn Thunder Bay Bay near near the ofthe the Sibley Sibleypeninsula. peninsula. Silver Islet Thunder the tip of The general Between thetheSilver veinproduced produced $3,260,000. $3,260,000. The Between1869 1869and and1922 1922 Silver Islet Islet vein Themain mainSilver Silver Islet Islet geology of the island island was was described described by by Franklin (1970). (1970). The geology of the vein vein strikes N35°E, N35 QE, dips dips 70 70 to to 80 80 degrees degreestotothe theeast, east, occupies occupiesa afault fault cutting It has widthof of 20 20 feet the Rove formation and a gabbro gabbro dike. It has aamaximum maximum width the Rove formation and (7 whichnarrows narrowstoto8 8toto10 10feet feet (3 (3 meters) in the dike (7 meters) meters) which meters) in dike and and 2 to 44 (1 meter) meter) ininnearby nearby shale, shale, and and has has been been traced depth of 1200 1200 feet feet (1 traced to to aa depth (400 (400 meters). In the In the present present study, study, the the metallic metallic minerals minerals in in polished polished sections sections from from 55 samples (#1-5) from from the the Silver Silver Islet Isletvein veinwere wereanalyzed analyzed by by electron electronmicroprobe. microprobe. samples (#1-5) The presenceofof the the following previously-reported The presence previously-reportedminerals mineralswas was confirmed; confirmed; galena (gn), galena (gn),sphalerite sphalerite(sl), (sl),chalcopyrite chalcopyrite(cp), (cp),nicco1ite niccolite (nc), (nc), gersdorffite gersdorffite (gf), (#3) pink pink dolomite dolomite is cut and native native silver silver (Ag). and (Ag). In one one sample sample (#3) cut by by aathin thin(1(1mm) mm) vein vein of of pyrrhotite pyrrhotite(po) (po)and andpentlandite pentlandite(pn) (pn)which whichappear appeartotoshow showmutual mutual exexsolution Anothersample sample (#5)hashas safflorite (sf) (sf) closely relationships. Another (#5) safflorite closely solution relationships. associated anothersample sample (#1) (#1) associatedwith with Fe-gersdorffite Fe-gersdorffite (Fe-gf). Gersdorffite ininanother Compositional ranges ranges of of major is near near the theNiNiend endmember member (Ni—gf). (Ni-gf). Compositional major and and minor minor elements are are shown in Table shown in Table 1. 1. elements TABLE I1 TABLE Rangesof of Analyses Ranges Analyses (Atomic (Atomic percent) po P0 Fe9S F~95 Fe Fe S S NI Co Co As As Ag Cu Cu Zn Zn Pb Sb Hg Hg Cd 47 47 53 53 po pn (Fe,NI)S (Fe,Ni )5 sf (Fe, Co)As2 Co)As2 - 30—33 30-33 50—52 50-52 14-18 23-26 22 — - 6-7 66-68 - - - 1-2 - — - - — - - — — - - - - - Fe-gf Ni-gf Ni -gf fNi,Co,Fe)AsS Thi,Co,Fe)AsS 24 24 32 32 - 8 36 36 0.5-2 O. :"2 cp CuFeS2 CuFe52 25 51 51 31—35 31-35 25-30 1-3 33-35 0-2 1-2 1-2 — - nc /liAs NiAs Ag Ag Ag Ag - - 05 0-5 - 5-9 43-47 - 50-54 0-0.1 - 13 0.3-4.4 4046 40-46 23 - - - - - - - - - - - - — — — 0.7-2.9 - - - 96-98 - 24 2-4 - 51 si lnS ZnS - "- gn gn PbS PbS - - 44-4A - - 87 87 - - - - (0.5 - The paragenesis is isnot are The paragenesisofofthese theseminerals minerals notsimple, simple,but butthe thepossibilities possibilities are constrained by the analyzed analyzed compositions minerals involved. involved. constrained by the compositionsof of the the minerals REFERENCE REFER E N CE Franklin, J.M., J.M., 1970, 1970, Metallogeny Metallogeny of the the Proterozoic Proterozoic Rocks Rocks of the the Thunder Bay Bay District,Ontario; Ontario;Ph.D. Ph.D.Thesis, Thesis,Western I~estern University, University,London, London, Ontario, Ontario, District, 17 3- 175. pp. 173-175. 71. �GROUNDWATER WATERGEOCHEMISTRY GEOCHEMISTRYASASAN ANAID AID TO GROUND TO GEOLOGIC GEOLOGIC MAPPING OF DRIFT-COVERED MAPPING OF DRIFT-COVERED AREAS: AREAS: TEST TEST CASES CASES ININWESTERN WESTERN MINNESOTA MINNESOTA D.L. and R.S. R.S. Lively Lively D.L. Southwick Southwick and Minnesota Survey Minnesota Geological Geological Survey St. Paul Paul,, Minnesota 55108 Ground water anomaly anomalymaps mapshave havebeen been used decadesasastools tools for for Ground water used forfordecades mineral mineral exploration. In conjunction conjunction with withregional regionalgeophysical geophysicalmaps maps and and whatever direct direct subsurface data are variwhatever subsurface data are available, available,maps maps of of geochemical geochemical variations also appear to be be useful useful for determining ations in in ground ground water water also appear to determining structural structural and lithologic trends beneathglacial glacialdrift. drift. Contoured maps and lithologic trends in in bed bed rock rock beneath maps of alkalinity, alkalinity,specific specific conductivity, dissolved oxygen,and anddissolved dissolved conductivity, dissolved oxygen, radon in ground ground water can be modest cost from from data data radon water can be made madeatatrelatively relatively modest fieldequipment. equipment. Other geochemical geochemical species species such such acquired portable field acquired with with portable as helium, helium, the the metals, metals, and and sulfate sulfate are as are useful useful also, also, but but have have the the disaddisadanalysis. vantage vantageof of requiring requiring laboratory analysis. Because between ground-water ground-water geochemistry geochemistry Becausethe the complex complexrelationship relationship between and bed bedrock rockinvolves involvesgeologic geologicand andhydrologic hydrologic variables thatare aredifficult difficult and variables that to assess, interpretation interpretationofofground-water ground-watergeochemical geochemical maps maps isis rarely to assess, factorsinin interpretation are straightforward. Significant poorly poorly known known factors are drift thickness, thickness, drift drift driftcomposition, composition, and and the the degree degree of hydrologic hydrologic interconinterconHowever,the the coincidence coincidence in in trend nection between drift and bed bed rock. rock. However, trend nection between drift and observed partsofofwestern westernMinnesota Minnesotabetween betweengeochemical geochemical anomalies anomalies and and observed in in parts geophysical anomalies, and, and, less lesscommonly, commonly, between between geochemical geochemical anomalies anomalies geophysical anomalies, and mapped on the and mappedgeologic geologiccontacts contactsstrongly strongly suggest suggest bedrock bedrock influence influence on details of of this influence hydrogeochemical system. The The details influence warrant vlarrant further hydrogeochemical system. investigation and we we intend to to study study the thehydrogeochemical hydrogeochemical interactions investigation and interactions amongground ground water, rock, drift, especially especially as as they they apply among water, bedbed rock, andand drift, apply to the the manyimportant important questions questions remain, distribution radiumand and radon. radon. Though Though many remain, distribution ofofradium maps ofof geochemical help maps geochemicalvariations variationsinin ground groundwater waterhave havethe thepotential potential to help with the the vexing vexing problem problem of of mapping mapping bed bedrock rock beneath beneaththe thevast vast drift-covered drift-covered tracts tracts ofofthe thesouthern southern Lake Lake Superior Superior region. region. 72. �INDEX E.I.,E.I., Luther, F.R., THE PRECAMBRIAN WATERLOO QUARTZ— Brandon, C.N., C.N.,Smith, Smith, Luther, F.R., THE PRECAMBRIAN WATERLOO QUARTZITE, SOUTHEASTERN ANDSIGNIFICANCE, SIGNIFICANCE,p.p. 17. ITE, SOUTHEASTERN WISCONSIN: WISCONSIN: EVOLUTION EVOLUTION AND Brown, B.E., B.E.,Greenberg, Greenberg, GEOLOGIC MAPPING IN NORTHEASTERNWISCONSIN: WISCONSIN: J.K.,J.K., GEOLOGIC MAPPING IN NORTHEASTERN AN (poster 65 AN UPDATE UPDATE (posterpaper), paper), p. p. 65 Cannon, W. W. F., F.,Mudrey MudreyJr.,Jr., M.G., WHERE IS THE SOURCEOFOFWISCONSIN WISCONSIN DRIFT DRIFT M.G., WHERE IS THE SOURCE DIAMONDS?, p. p. 21 DIAMONDS?, 21 Chandler, CORRELATION OF OF GRAVITY AND MAGNETIC Chandler,V.W, V.W., CORRELATION GRAVITY AND MAGNETICANOMALIES ANOMALIES ININEAST-CENTRAL EAST-CENTRAL MINNESOTA WISCONSIN, 22 MINNESOTA AND AND NORTHWESTERN NORTHWESTERN WISCONSIN,p.p. 22 Chandler, V.W., W.J., O'Hara, N.W.,N.W., LONGLONG WAVELENGTH V.W.,Boman, Boman, P.L., P.L.,Hinze, Hinze, W.J., OIHara, WAVELENGTH GRAVITY AND 42 GRAVITY AND MAGNETIC MAGNETICANOMALIES ANOMALIESOFOFTHE THELAKE LAKESUPERIOR SUPERIORREGION, REGION,p.p. 42 Coker, J.M., REGIONAL GEOCHEMISTRY AND AND METALLOGENY Coker, W.B., W.B.,Franklin, Franklin, J.M., REGIONAL GEOCHEMISTRY METALLOGENYNORTH NORTH SHORE 60 SHOREOF OFLAKE LAKESUPERIOR, SUPERIOR,ONTARIO, ONTARIO,p.p. 60 GEOCHEMISTRY Cummings, M.L., M.L., GEOCHEMISTRYAND ANDVOLCANIC VOLCANICSTRATIGRAPHY STRATIGRAPHY OF OFWEST-CENTRAL WEST-CENTRAL MARINETTE COUNTY, 20 MARINETTE COUNTY,WISCONSIN, WISCONSIN,p. p. 20 VOLCANIC Cummings, M.L., M.L., VOLCANICAND ANDPLUTONIC PLUTONICROCKS ROCKSOFOFTHE THEJUMP JUMPAND ANDYELLOW YELLOW RIVER RIVER RIVER VALLEYS, NORTH-CENTRAL WISCONSIN, p. 25 RIVER VALLEYS, NORTH-CENTRAL WISCONSIN, p. 25 Daniels, Elmore, D.R.,D.R., DEPOSITIONAL SETTING OF STROMATOLITE-OOLITE Daniels,P.A., P.A., Elmore, DEPOSITIONAL SETTING OF STROMATOLITE-OOLITE FACIES KEWEENAWAN ALLUVIAL FAN, FACIES ON ON A A KEWEENAWAN ALLUVIAL FAN,p.p. 27 Davidson Jr., Jr., GEOLOGICAL EVIDENCE RELATINGTOTOTHE THEINTERPRETATION INTERPRETATION OF OF Davidson D.M.D.M. GEOLOGICAL EVIDENCE RELAT:[NG THE LAKE THE LAKE SUPERIOR SUPERIOR BASIN BASIN STRUCTURE, STRUCTURE, p. 32 p. 32 Ernst, Ernst,T.,T., Markert, Markert, J., Montz, J., Montz, M., HEAVY M., HEAVY MINERAL MINERAL ANALYSIS ANALYSIS OF PRECAMBRIAN OF PRECAMBRIAN ROCKSININ RUSK RUSKCOUNTY*, COUNTY*,p.p. 26 ROCKS 26 Ervin, C.P., Tuftee, K., ANALYSIS OF A OF NEW GRAVITY MAP FOR Ervin, C.P., Tuftee, K., ANALYSIS A NEW GRAVITY MAP FORTHE THEMERRILLMERRILLRHINELANDER AREA, WISCONSIN (poster 66 RHINELANDER AREA, WISCONSIN (poster paper), paper) , p. p. 66 Evans, T.J., Mudrey Jr.,Jr., M.G.,M.G., WISCONSIN Evans, T.J.,Greenberg, Greenberg,J.K., J.K., Mudrey WISCONSININTEREST INTEREST IN IN RADIOLOGICAL IMPACTS RESULTING RESULTING FROM FROM URANIUM 64 RADIOLOGICAL IMPACTS URANIUM EXPLORATIONS EXPLORATIONS(DRILLING) (DRILLING) ,, p. 64 D., Lee, R., Woodard, H., GEOLOGY OF THE SOUTHEASTERN Fleming, A., A.,Heinz, Heinz, D., Lee, R., Woodard, H., GEOLOGY OF THE SOUTHEASTERN CONTACTZONE ZONEOFOFTHE THEVERMILION VERMILIONBATHOLITH, BATHOLITH,MINNESOTA*, MINNESOTA*, p. p. 15 CONTACT Goodge, J.W., J.W.,MIGMATITES MIGMATITESFROM FROM THE THE VERMILION VERMILION GRANITIC GRANITIC COMPLEX, COMPLEX, MINNESOTA*, Goodge, MINNESOTA*,p.p. 13 13 Green, J.C., KEWEENAWAN Green, J.C., KEWEENAWANVOLCANISM VOLCANISMAND ANDTHE THENATURE NATUREOFOFKEWEENAWAN KEWEENAWAN RIFT RIFT TECTONICS, p.p. 35 35 TECTONICS, Greenberg, J.K., URANILIM Greenberg, J.K., URANIUMPROVINCES: PROVINCES: RELATIONS TOWISCONSIN, WISCONSIN,p.p. 59 RELATIONS TO 59 ENRICHMENTIN IN GRANITIC ENRICHMENT GRANITIC ROCKS ROCKS AND AND Grundi, T.J., Jr.,Jr., E.C.,E.C., Gilkeson, R.H., STABLE ISOTOPE TRACER Grundl, T.J.,Perry Perry Gilkeson, R.H., STABLE ISOTOPE TRACER STUDIES THE CAMBRO-ORDOVICIAN CAMBRO-ORDOVICIAN AQUIFER OF OF NORTHERN ILLINOIS*, p. . 50 50 STUDIES IN IN THE AQUIFER NORTHERN ILINOIS*, Halls, Pesonen, L.J., PALEOMAGNETISM KEWEENAWAN ROCKS, 49 Halls, J. ~. C., C., Pesonen, L.J., PALEOMAGNETISM OF OF KEWEENAWAN ROCKS p. p. 49 *Student paper paper 73. �Hinze, W.J., W.J.,Wold, Wold, O'Hara, N.W., GRAVITY AND MAGNETIC ANOMALYSTUDIES STUDIES Hinze, R.J.,R.J., O'Hara, N.W., GRAVITY AND MAGNETIC ANOMALY OF LAKE LAKE'SUPERIOR, 40 OF SUPERIOR,p. p. 40 Johnson, 4Johnson,A., A., Parker, B., B.,Snider, Snider,0., D., VanVan Alstine, Alstine, 3., PETROLOGY J., PETROLOGY OFOF THE THEBEAR BEAR LAKE LAKE INTRUSIVE, INTRUSIVE, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN (poster (poster paper), paper),p.p. 67 Jones, N.W., PETROLOGYOFOFSOME SOMELOGAN LOGAN DIABASE DIABASE SILLS SILLSFROM FROMCOOK COOK COUNTY, COUNTY, Jones, NW., PETROLOGY MINNESOTA, p.p. 29 29 MINNESOTA, J.H., Bernardin, Bernardin, M.P., M.P., Meyer, Meyer, R.P., R.P., Bengtson, Bengtson, M.E., H.C., Karl, 3.H., M.E., Halls, H.C., GEOPHYSICAL GEOPHYSICAL STUDIES STUDIESOFOFTHE THESLATE SLATEISLANDS, ISLANDS,LAKE LAKESUPERIOR, SUPERIOR,p. p. 47 47 Keh1enbeck, Kehlenbeck, M.M., M.M., REGIONAL REGIONAL STRUCTURE, STRUCTURE, METAMORPHISM METAMORPHISM AND AND STRATIGRAPHY STRATIGRAPHY OF OF THE THE QLIETICO GNEISSBELT, BELT, THUNDER THUNDERBAY, BAY,ONTARIO, ONTARIO,p. p. 10 QUETICO GNEISS 10 Kelley, Kelley,L.I., L.1., Karner, Karner, F.R., KAOLINITIC F.R., KAOLINITIC WEATHERING WEATHERING ZONEZONE ON PRECAMBRIAN ON PRECAMBRIAN BASEMENT OF OF SOUTHEASTERN NORTHDAKOTA DAKOTAAND ANDWESTERN WESTERNMINNESOTA*, MINNESOTA*, p. 51 BASEMENT SOUTHEASTERN NORTH 51 K1asner, J.S.,Cannon, Cannon,W.F., W.F.,Van VanSchmus, Schmus, W.R. W.R.,, THE THE PRE-KEWEENAWAN PRE-KEWEENAWAN TECTONIC TECTONIC Kiasner, J.S., HISTORY HISTORY OF OF THE THE NORTH-CENTRAL NORTH-CENTRAL UNITED UNITED STATES STATES AND AND CENTRAL CENTRAL CANADA CANADA AND AND HOW FORMATION THE MID-CONTINENT RIFT,p.p. 33 HOW ITIT INFLUENCED INFLUENCED FORMATION OFOFTHE MID-CONTINENT RIFT, 33 LaBerge, WERE THERE TWO LaBerge,G.L., G.L., WERE THERE TWOMIDDLE MIDDLEPRECAMBRIAN PRECAMBRIAN OROGENIES OROGENIES IN THE THE LAKE LAKE SUPERIOR REGION?,p.p. 24 SUPERIOR REGION?, 24 Lucko, W.M., S.A.,S.A., THE PEGMATITES OF OF THE W.M.,Kissin, Kissin, THE PEGMATITES THEQUETICO QUETICOGNEISS GNEISS BELT, BELT, NORTHWESTERN ONTARIO THEIR URANIUM POTENTIAL*,p.p. 55 NORTHWESTERN ONTARIO ANDAND THEIR URANIUM POTENTIAL*, Luetgert, J.H., Meyer, SEISMIC REFRACTION STUDIES LAKESUPERIOR SUPERIOR Luetgert, J.H., Meyer, R.P.,R.P., SEISMIC REFRACTION STUDIES OFOF LAKE CRUSTAL CRUSTALSTRUCTURE, STRUCTURE,p.p. 44 Maass, R.S., R.S.,Medaris Medaris METAVOLCANIC ROCKSATATEAU EAUCLAIRE CLAIRE DELLS, DELLS, Maass, Jr.,Jr., L.G., L.G., METAVOLCANIC ROCKS MARATHON COUNTY, ZONE II HYPOTHESIS HYPOTHESIS IN IN MARATHON COUNTY,AND ANDANANEVALUATION EVALUATIONOF OFTHE THE IISHEAR 'SHEAR ZONE" WISCONS:N*, WISCONSIN*, p.p. 23 23 Maass, L.G., Van Schrnus, W.R., ARCHEAN Maass, R.S., R.S., Meclaris MedarisJr., Jr., L.G., Van Schmus, W.R., ARCHEANAND ANDEARLY EARLY 11 PROTEROZOIC p. 11 PROTEROZOICTECTONIC TECTONICHISTORY HISTORYOF OF NORTH-CENTRAL NORTH-CENTRALWISCONSIN*, WISCONSIN*, p. J.S., Motten, GEOLOGY OF MCCASLIN THE MCCASLIN RANGE, NORTHEASTERN Mancuso, J.S., Motten, R.H., R.H., GEOLOGY OF THE RANGE, NORTHEASTERN WISCONSIN, p. 62 WISCONSIN p. 62 Brown, B.E.,B.E., LAKE LAKE SUPERIOR REDRED CLAY MINERALOGY: Mengel, J.T., J.T., Brown, SUPERIOR CLAY MINERALOGY: WITH MECHANICAL MECHANICAL BEHAVIOR, WITH BEHAVIOR,p.p. 48 CORRELATION G.B.,Bergstrom, Bergstrom, THE COSUNA PROJECT - A NEW CORRELATIONCHART CHART Morey, G.B., 0.3., D.J., THE COSUNA PROJECT - A NEW CORRELATION FOR THE THE NORTHERN NORTHERN MID-CONTINENT REGION (posterpaper), paper), p. FOR MID-CONTINENT REGION (poster 68 p. 68 Morton, DIFFERENTIATING ULTRAMAFIC FLOWS THETHE SHEBANDOWAN Morton,P.,P., DIFFERENTIATING ULTRAMAFIC FLOWSFROM FROMSILLS SILLSIN IN SHEBANDOWAN MINE AREA, ONTARIO, CANADA*, MINE AREA, NORTHWESTERN NORTH~ESTERN ONTARIO, CANADA*, p. 31 31 p. RELATIONSHIP OF Mursky, Mursky, G. G.,, RELATIONSHIP OF CANADIAN CANADIAN URANIUM URANIUM DEPOSITS DEPOSITS TO TO THE THE GEOLOGIC GEOLOGIC SETTING SETTING OF OF WISCONSIN, WISCONSIN, p. 56 p. 56 *Student paper paper 74. �Ojakangas, Ka1liokoski,J.,J., UPPER Ojakangas,R.W., R.W.,Morey, Morey,G.B., GB., Daniels, Daniels, P.A., P.A., Kalliokoski, UPPER PRECAMBRIAN ROCKS OF OF THETHE LAKE SUPERIOR REGION, p.p. 37 PRECAMBRIANSEDIMENTARY SEDIMENTARY ROCKS LAKE SUPERIOR REGION, 37 Petro, W.L., MINERALOGYAND ANDCHEMISTRY CHEMISTRY OF OF MIDDLE MIDDLE PRECAMBRIAN PRECAMBRIAN (Xg) GRANITIC Petro, W.L., MINERALOGY (Xg) GRANITIC PLUTONIC ROCKS FROM NORTHERN WISCONSIN* (poster paper), PLUTONIC ROCKS FROM NORTHERN WISCONSIN* (poster paper),p.p. 70 Poulsen,K.H., K.H., Keh1enbeck, OVERTURNED ARCHEAN SUCCESSIONS AND AND THEIR THEIR Paulsen, Kehienbeck, M.M., M.M., OVERTURNED ARCHEAN SUCCESSIONS SIGNIFICANCE, 16 SIGNIFICANCE, p. p. 16 Rehf1edt, W.R., HYDROGEOLOGIC INVESTIGATIONS INVESTIGATIONS AT LANDFILL SITE IN INTHE THE RED RED Rehfledt, W.R., HYDROGEOLOGIC AT A A LANDFILL TILL (VALDERAN) (VALDERAN) REGION REGION OF OF EASTERN EASTERN WISCONSIN, 53 TILL WISCONSIN,p. p. 53 Scofield, Scofield, N.,N., METALLIC METALLICMINERALS MINERALS OF OF SILVER SILVER ISLET, ISLET, LAKE LAKE SUPERIOR SUPERIOR (poster (posterpaper), paper), p. p. 71 71 Shege1ski, R.J., STRATIGRAPHY GUNFLINT FORMATION,CURRENT CURRENT RIVER RIVER AREA, AREA, Shegeiski, R.J., STRATIGRAPHY OF OF THETHE GUNFLINT FORMATION, THUNDER BAY, p. THUNDER p. 28 28 Smith, E.I., RARE EARTH ELEMENT THETHE PRECAMBRIAN Smith, E.I., RARE EARTH ELEMENTDISTRIBUTION DISTRIBUTIONIN IN PRECAMBRIANRHYOLITES RHYOLITES AND GRANITES GRANITES OF OF SOUTH-CENTRAL SOUTH-CENTRAL WISCONSIN,p.p. 19 AND WISCONSIN, Southwick, Lively, R.S., GROUND WATER GEOCHEMISTRY Southwick,D.L., D.L., Lively, R.S., GROUND WATER GEOCHEMISTRY AS AS AN AN AID AID TO TO GEOLOGIC DRIFT-COVERED AREAS: AREAS: GEOLOGIC MAPPING MAPPING OF OF DRIFT-COVERED MINNESOTA (poster 72 MINNESOTA (posterpaper), paper), p. p. 72 TEST CASES TEST CASES ININWESTERN WESTERN Van Van De De Voorde, Voorde,B.,B., Ervin, Ervin, P., GEOPHYSICAL P., GEOPHYSICAL STUDY STUDY OF AOFPRECAMBRIAN A PRECAMBRIANBOUNDARY BOUNDARY :[N IN MINNESOTA*,p. p. 99 MINNESOTA*, Van Schmus, Schmus, W.,R., W.R., Green, Green,J.C., J.C., H.C., GEOCHRONOLOGY OF KEWEENAWAN Van Halls,Halls, H.C., GEOCHRONOLOGY OF KEWEENAWAN ROCKS: ROCKS: A REVIEW, REVIEW, p. 39 A p. 39 Vick,T.D., T.D., SEISMIC SURVEYOF OF AABURIED BURIED RIVER RIVER CHANNEL, CHANNEL, p.p. 54 54 Vick, SEISMIC SURVEY Hutchinson, D.R., Johnson, T.C., T.C., TOPOGRAPHY ANDAND SURFICIAL STRUCTURE Wold, R.J.,, Hutchinson, D.R., Johnson, TOPOGRAPHY SURFICIAL STRUCTURE Wold, R.J. OF LAKE SUPERIOR SUPERIOR BEDROCK ONONSEISMIC 45 OF LAKE BEDROCKBASED BASED SEISMICREFLECTION REFLECTIONPROFILES, PROFILES,p.p. 45 *Student paper paper 75. � https://digitalcollections.lakeheadu.ca/files/original/f7ae80e1a840559c070a2a1da82925c6.pdf da285056eb25e07a79f0e273fc6f4f63 PDF Text Text 26th 2 6th Annual InstitUteon on Lake Lake Superior SuperiorGeology Geology Institute FIELD TRIP TRIP 1 FIELD 1 Precambrian Geology Geology of the Ohippewa Valley, Chippewa Valley Wisconsin Wisconsin GENERALIZED PRECAMBRIAN GEOLOGY OF THE EAU CLAIRE REGION gO - Di abase I...,! I-,, • I, Gabbro to+ Tonolite tr Trandhjemite I','—,— Volcanics and sediments Amphibolites 4 Shear zone May May 6-7, 1980 1980 Universily Claire University of Wisconsin-Eau Wisconsin-Eau Claire —— - - - — — �PRECAMBRIAN GEOLOGY GEOLOGYOF OF THE THE CHIPPEWA PRECAMBRIAN CHIPPEWA VALLEY VALLEY FIELD GUIDE GUIDE P. E. E. Myers, R. Wurdinger M. L. L.Cummings, C m i n g s , and and S. S. R. Wurdinger P. Myers, M. Prepared ffor Prepared or Twenty-Sixth Annual Twenty-Sixth Annual Meeting Meeting INSTITUTE ON INSTITUTE ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY University of Claire University o fWisconsin-Eau Wisconsin-Eau C laire Eau CClaire, Eau l a i r e , Wisconsin Wisconsin May 6—11, 1980 �26th ANNUAL 26th ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SULLRLORGEOLOGY GEOLOGY FIELD TRIP #1 #I May May 6—7, 6-7, 1980 1980 STOP STOP + - DAY DAY Dies. Tues. 5/6 516 LOCATION LOCATION LEADER LEADER SUBJECTS SUBJECTS PAGE PAGE 1 Big B i g FFalls alls Cummings C mings Geochemistryand andPetrology Petrology ooff Geochemistry metamorphosed, layered mtamrphosed, layered gabbros gabbros deformational hhistory deformational istory 23 !3 22 Little L i t t l e Falls Falls Myers Myers Tonalitic T o n a l i t i c intrusion i n t r u s i o n breccia breccia 35 35 3 3 Confluence, Confluence, N. N. Side Side Myers Myers Amphibolite-volcãnic Amphibolite-volcanic contact contact 45 44 Knight Knight Pool Myers Myers Metabasalts, i l l o w breccias(?) b Metabasal t s , ppillow 55 55 Rock Rock Dam Dam Myers Myers Mylonitized rhyol ite 59 59 66 County County Hwy Hwy MM Myers Myers Metasediments. 63 7 7 Confluence, Confluence, S. S. Side Side Myers Myers Younger(?) and volcanics volcanics Younger(?) sediments sediments and 47 88 "Big Bend" Bend" Yellow Yellow River River Myers Myers Cataclastic "dikes" in metadiorite Catacl 67 67 9 9 Cadott Cadott Bridge Bridge Myers Nyers Cataclasis—intrusion—folding Cataclasis-intrusion-folding sequence; multiple sequence; mu1 t i p l e deformations deformations 71 71 75 75 RETURN EAU CLAIRE RETURN TTO O EAU CLAIRE Wed. Wed. 10 10 Wissota WissotaDam Dam Myers Myers IIntrusion n t r u s i o nsequence: sequence: trondh,jemitetrondhjemitetonalite—pegmatite—diabase, etc. etc. tonalite-pegmatite-diabase, 11 11 Jim Jim Falls Falls Myers Myers Amphibolite—granite contacts, Amphi bol ite-grani t e contacts, shearing, cataclasis, cataclasis, folding shearing, folding 5/7 517 12 12 Cornell Cornel 1Dam Dam Myers Myers 13 13 Fisher River River 14 14 81 Relations between Relations between garnet garnet amphiboamphibolite l i t eand andflaser f l a s e rgneisses gneisses 89 89 Myers Myers Tectonic Tectonic oorr Intrusion(?) breccia breccia 93 Holcombe Hol combeDam Dam Wurdingér Wurdinger Intrusion-deformation Intrusion-deformationsequence sequence 97 15 15 Shoulder Shoulder Creek Creek Cummings Cumings Intermediate andf felsic Intermediate and e l s i c volcanics vol canics 1133 11 16 16 Jump River (N. (N. Side) Side) Cuttinings Cumings Jump River ~ntermediatefragmental fragmental volcanics volcanics Intermediate 115 115 17 17 Jump River: Hwy Jump River: Hwy 73 73 Cumnings Cumi ngs Contact metamorphism o foff efelsite lsite Contact metamorphism 117 117 18 18 Sec. Sec. 22, 22,T33N, T 3 3 ,R4W R4W Cumnings Cummings Intermediate c rcrystal-lithic y s t a l - l i t h i c ttuff uff Intermediate 119 119 . * Not Not aall l l of o f the the stops stops described h i s guidebook guidebook w will i l l be i s i t e d . Their inclusion describedi nin tthis be vvisited. inclusion is i s to t opermit permit the theuse use of o fthis t h i sguidebook guidebook after a f t e rthe theconference. conference. , ,,~ >... ,. ..-,',,. , ~,?:.;! L �—1— PRECAMBRIAN GEOLOGY OF THE CHIPPEWA VALLEY - AN INTRODUCTION P. E. Myers Exposures of Precambrian Exposures of Precambrian rocks ini nwest—central west-central Wisconsin Wisconsin are confined confined mainly Valleyand andi tits majort tributaries, mainly to t o the the Chippewa Chippewa Valley s major r i b u t a r i e s , the Yellow, Yellow, Jump, Jump, and Eau Claire rivers, which drain the southwestern and Eau C l a i r e r i v e r s , which d r a i n the southwestern edge edge ooff the the Canadian Canadian Shield Shield in i nWisconsin. Wisconsin. From the Eau Claire dips southFrom the Eau C l a i r e area, area, the thePrecambrian Precambrian basement basement dips south- west west at a t 10 10 feet feet per permile m i l ebeneath beneath aa thickening thickening cover cover of o f lower lowerPaleozoic Paleozoicsandsandstones, shales, and.carbonates. stones, shales, and carbonates. To To the north north and and east, east, the thePrecambrian Precambrian rocks rocks are are overlain o v e r l a i nby byglacial g l a c i adeposits l depositsand andoccasional occasionaloutliers o u t l i e rof s oCambrian f Cambriansandstone. sandstone. Owing outcrop and and sstructural Owing tto o sparseness sparseness oof f outcrop t r u c t u r a l complexity complexity of o f the the rocks, rocks, traditional traditional mapping methods have proven inadequate. mapping methods have proven inadequate. However, However, aaf fair a i r approximation approximation ooff the the regional regional geology geologyhas hasbeen been gained gain through a combination of detailed studies of outcrops outcrops with w i t hpetrographic petrographicand andgeochemical analyses, aeromagnetic and gravity mapping and radiometric radiometric dating. mapping and dating Following of the region by Dutton, I began field Following iinitial n i t i areconnaissance l reconna work with the major problems and working out the work w i t h the the objective o b j e c t i v eofo defining f def geologic geologic history h i s t o r yofo fthe theregion. regionSubsequent publication of Dutton and Bradley's geologic northern Wisc Wisconsin (1970) provided a starting point. Additional geologic maps maps oof f northern specialized specialized studies studiesby bystudents student (Cumings, 1974, 1975, 1978), Maercklein (1974), Piotruscewicz (1979) have greatly accelerated the study (19781, and and Wurdinger kiurd Piotruscewicz (1978), of o f the the region. region. This This guidebook guidebook i is s aa synthesis synthesis ooff available available information information on on the the Precambrian supplementary information Precambrian hhistory i s t o r y of o fthe theChippewa Chippewa Valley. Valley. Relevant, Relevant, supplementary information isi sdrawn Anderson, drawnfrom f r o mimportant importantworks worksbyby Anderson,Van VanSchrnus, Schmus, and and Medaris Medaris (1975), (1975), LaBerge LaBerge (1972, (1972, 1980), 1980),Maass, Maass, Medaris, k d a r i s ,and andVan VanSchmus Schmus (1980), (1980),Maass Maassand andVan Van Schmus Schmus (1980), (1980), Sims Van S i n s (1976), (l976), Smith Smith(1978), (19781,and and VanSchmus Schmus (1974, (1974, 1976 1976 ,, 1980). 1980). Aeromagnetic mapsbybyKarl Karl and and Friedel Friedel (1974-1976) and by by United United States Steel Aeromagnetic maps (1974-1976) and Steel Corp. Corp. (1973) (1973) and and Bouguer Bouguer ggravity r a v i t ymaps maps by by Ervin Ervinand and Hamer Hanrner (1974) (1974)have havebeen been most most useful useful in between i ninterpolating i n t e r p o l a t i ncontacts g contacts betweenwidely widelyseparated separatedoutcrops. outcrops. The The geologic geologic map map presented presented in i n Figure Figure 1is i saa"best "bestapproximation" approximation" of o f the the Precambrian rock uunits Precambrian rock. rock units u n i t sini nthe theChippewa Chippewa Valley. Valley. The The rock n i t s are are ttypically ypically heterogeneous, sot hthat generalize uunits was necessary necessary t to o generalize n i t s by selecting the the heterogeneous, so a t iittwas predominant predominant unit. unit. Its I t spurpose purpose is i s to t oportray portraybroad broad regional regional patterns patterns of o frock rock distribution. d i s t r i b u t i o n . Quality.of geologicinformation informationgenerally generallydiminishes diminishesaway away from fro Qua1i t y o fgeologic the the rivers. rivers. 1 It is emphasized that the interpretations and conclusions in this guidebook are tentative, It is our hope that you will assist us in clarifying the history of these phenomenally complicated rocks. The geologic map (Figure 1) also shows stop locations. Those in parentheses. are optional, ut are included because of their relevance. You are encouvaied to stay and continue your field trip after the conference or to return to Eau Claire soon with your own field trip. t r i p .There Thereremains remains aa large l a r g enumber number oof f tthesis h e s i and dissertation topics. I may be able able to t o assist a s s i s tyou you in i nthe theselection selectionofo fone. one �—2— ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS - We areindebted indebtedt oto the the U University EauCClaire M e are n i v e r s i t y of-Wisconsin Of .Wisconsin — Eau l a i r e ffor o r general general Undertwo tworesearch researchgrants, grants,t hthe sponsorshipooff this e UUniversity n i v e r s i t y aalso lso sponsorship t h i s conference. conference. Under provided M. M. L. L. Cummings Cummings w iwith t h s sumer u m r f ifield e l d and and lab l a b assistants, assistants, and andP.E. P.E. Myers Myers provided chemicalanalyses analysesand andt hthin sections Of of 50 The Wisconsin Wisconsin Geological and 50 rocks. rocks. The chemical i n sections and Natural H History assistedUSusgreatly, greatly, both both through throught htheir e i r pprovision r o v i s i o n of of Natural i s t o r y Survey Survey assisted time, base maps asas well encouragement tthin h i n sections, sections,probe probeanalysis analysis time, base maps w eas l l much as much encouragement throughoutt the termooff tthe We thank Northern throughout h e term h e project. project. W e thank Northern States StatesPower PowerCompany Company the ffor o r permission permission tto o study study and and vvisit i s i ttheir t h e iproperties r propertiesalong along t h Chippewa e Chippewa River River and ffor as possible, possible, outflow and o r consenting consenting tto o reduce, reduce, as outflow from from reservoirs r e s e r v o i r s during during our our visits Holcombe. v i s i t sataLake t LakeWissota, Wissota, Jim JimFalls, F a l l sand , and Holcombe.The TheUniversity U n i v e r s i t yofoWisconsin— f WisconsinOshkoshand andt hthe generously Fox Valley, Val.ley, Menasha Menasha have have generously Oshkosh e UUniversity n i v e r s i t y of o fWisconsin Wisconsin — Fox allowed us the use of their vehicles for the trip. allowed us t h e use of t h e i r vehicles f o r t h e t r i p . - We thank those those ooff our have ooffered W e eespecially s p e c i a l l y thank o u r colleagues colleagues and and students students who who have ffere suggestionsconcerning concerningo uour ttheir h e i r many many hhelpful e l p f u l ideas ideas and and suggestions r i ninterpretations t e r p r e t a t i o n s ooff the th geologyoof Students, as as wwell geology f tthis h i s region. region. Eau Eau CClaire l a i r e Students, e l l as as students students from from other other universities time,t talent, u n i v e r s i t i e s have have generously generously ccontributed o n t r i b u t e d time, a l e n t , and and ideas ideas tto o our our often often Field Mike Mudrey, Weis, ffrustrating r u s t r a t i n gwork. work. F i e l d trip t r i pdrivers d r i v e rare s are Mike Mudrey,Len Len Weis,Gene GeneLaBerge, LaBerge and A1 Al Sun. NanPickett, Pickett, Penny Hoitomt, and andGGail Wirz devoted devoted l long hours tto t and Sun. Nan Penny Hoitomt, a i l Wirz o n g hours o the preparation of Carlson aassisted o f the t h e guidebook, guidebook, and and Diane Diane Carlson s s i s t e d in i n plotting p l o t t i n geochemical g geochemi data. Many Manystudents, students, past past and and present, present, have beeni ninvolved have been v o l v e d wwith i t h various aspects aspe of field and lab preparations. We thank you all sincerely. o f f i e l d and l a b preparations. We thank you a l l sincerely. �—3— - Precambrianrock rockunits units in Distribution of of major Figure 11 —— Distribution major Precambrian in the theChippewa, Chippewa, Yellow, Jump, and Eau Claire river valleys and their major tributaries Yellow, Jump, and Eau Claire river valleys and their major tributaries as as inferred from inferred fromaastudy studyofofsparse sparseoutcrops outcropsand andfrom fromaeromagnetic aeromagneticmapping. mapping. �-4-4- . - GENERAL GEOLOGY GENERAL GEOLOGY (Myers and andothers, others, 1974) The Precambrian Precambrian "Chippewa "Chippewaamphi amphibolite The bol i t e complex' complex" (Myers 1974) iiss megagneissconsisting consistingofof steeply-dipping, steeply—dipping,lensoidal lensoidal screens, aa megagneiss screens, enclaves, enclaves, and and xenolith and schist xenol it h trains t r a i n sofo amphibolitic f amphi bol i t i gneiss c gneiss and s c h i sembedded t embedded subconcordantly subconcordantly iin n (Figure 11). younger, synkinematic syrrkinematicand andl alate kinematictonal tonalite ). younger, t e kinematic i t e and and trondhjemite trondhjemite (Figure The Chippewa amphibolite complex (CAC) forms the core of an eastward-plunging The Chippewa amphibol i t e complex (CAC) forms the core o f an eastward-pl unging Penokeanorogen, orogen,which whichi is and metamorphosed Penokean s overlain overlaineastward eastwardbybyless l e sdeformed s deformed and metamorphosed volcanic and sedimentary rocks of the Flambeau volcani—sedimentary province ttoo volcanic and sedimentary rocks o f t h e Flambeau volcani-sedimentary province the north and the Black River .volcani-sedimentary province to the southeast. the north and the Black River volcani-sedimentary province t o the southeast. Within the region, these these volcanic volcanic and rocks are are represented Within the Chippewa Chippewa region, and sedimentary sedimentary rocks represented by the South Fork volcanic and sedimentary assemblage in the headwaters by South Fork and sedimentary assemblage i n the headwaters oof f the Eau Claire River and the Jump River volcanic rocks to the northeast. The Eau C l a i r e River and the Jump River volcanic rocks t o the northeast. The block diagram(Figure (Figure2)2)i is a generalized representation ooff the the types diagram s a generalized representation types of o f rocks rocks and and structures occurring occurringi in structures n tthis h i s region. region. This This pattern pattern is i s similar s i m i l a rtot oone oneby by Glikson Glikson (1957, p.p. 21) 21) ffor tonalite-trondhjemitessialic (1957, o r Archean Archean tonalite-trondhjemite i a l i c nuclei, nuclei, which which contain contain attenuatedre1 relics xenoliths. GGlikson's i c s of o f supracrustal supracrustal enclaves enclaves and and xenoliths. I ikson's diagram diagram iiss attenuated included pattern to included (Figure (Figure 3) 3) for f o rcomparison. comparison. Probably Probably the the most most conspicuous conspicuous pattern t o be. be seen on onthe the generalized generalized geologic geologic map the region Z—shaped seen map oof f the region (Figure (Figure1)1)is i the s the 2-shaped pattern produced byamphibol amphibolitic mayrepresent representl alarge plunging ffold pattern produced by i t i c enclaves, enclaves, which which may r g e plunging old remnants. Although Althoughthe the ggranitic r a n i t i c rocks, rocks, as asrepresented represented mainly mainly by by trondhjemite, trondhjemite, tonalite, adamellite, tonal i t e , and and subordinate subordinate adamell i t e , llocally o c a l l y intrude i n t r u d e the t h eamphibolites, amphibol i t e s , the the contacts contacts Cataclasis has hascclearly majorr role comnonly sheared. sheared. Cataclasis l e a r l y played played aa major o l e iin n the the are most most commonly deformation and andmetamorphism metamorphism rocksthroughout throughoutthe theregion regi.onduring duringaat deformation o f of thethe rocks t lleast east catathree major major deforniational d e f o m t i o n a l events, events, one oneofo which f whichwas wasthe thePenokean. Penokean. IIn n the CAC, CAC, cata(1)) bending, crushing, and andl elenticulation bending, crushing, nticulation cclasis l a s i s isi smost mostconspicuously conspicuously manifested manifested by: by: (1 development ooff feldspars feldspars with w i t h simultaneous simultaneous development o f of a cahcharacteristic a r a c t e r i s t i c i ninterlensing t e r l e n s i n g f foliaolia(2) laminar transposition ooff originally ttion. i o n . (2) laminar transposition o r i g i n a l l ydiscordant discordantstructures structuressuch such as as dikes, dikes, dikes, and and xenoliths, xenoliths, into mechanical dikes, i n t o the the plane plane of o f cataclastic c a t a c l a s t i cfOliation, f o l i a t i o n(3) , (3) mechanicalhomohomogenizationooff contiguous contiguousrock rocku nunits withoutr recrystallization, genization i t s wwith i t h oor r without e c r y s t a l l i z a t i o n , (4) (4) detachdetachSince tthe ment andtransposition transpositionoof as ttectonic ment and f ffold o l d fragments fragments as e c t o n i c xenoliths. Since h e proper proper off cataclastic iinterpretation nterpretation o c a t a c l a s t i c features features affects a f f e c t s the the interpretation i n t e r p r e t a t i o n of o f geologic geologic sequence, and andsince since there remains sequence, remains considerable considerable debate debate as as tot othe t h mechanisms, e mechanisms, some some goodexamples examples them have included in several stops (mainly 8-ll). good o f of them have beenbeen included i n several o f tof h ethe stops (mainly #8-11). Whereasthe thevolcanic volcanicrocks rocksoof the Jump JumpRiver Riverarea area(Cunnings, (Cumings, p103) p103)have haveaat Whereas f the t l least east locally been metamorphosed to the lower amphibolite grade, those of the South l o c a l l y been metamorphosed t o the lower amphibolite grade, those o f t h e South Fork Fork area (SFVS) (SFVS)are areo of lowermetamorphic metamorphic grade indicatedbybythe theprevalence prevalence area f lower grade as as indicated of ofc hchlorite, lorite, epidote, River volcanics volcanics (JRV) comprisemainly mainlybbasaltic epidote. and and garnet. garnet. The The Jump Jump River (JRV) comprise a s a l t i c tto o One andesitic flows fragmentalvolcanics volcanicso of andesitict to f andesitic o rrhyolitic h y o l i t i ccomposition. composition. One andesitic flows and and fragmental The higher eruptive center was found in the area just east of the town of Jump River. eruptive center was found i n the area j u s t east o f the town o f Jump River. The metamorphic gradeo fofthe theJRV JRVmay may theproximity proximityt oto the the south metamorphic grade be be duedue t o to the south of o f several several large ggranitic Top iindicators large r a n i t i c plutons. plutons. Top n d i c a t o r s in i n the t h eJRV JRV indicate i n d i c a t e the t h esequence sequence iiss overoverthe JRV rocks wwill i l l be beseen seen turned with w i t h beds beds facing facing (younging) (younging) southward.Examples southward.Examples oof f the JRV rocks att stops a stops 15-18. 15-18. Myers Myersand andothers others(1974) (1974)i identified d e n t i f i e daamajor major geophysical geophysical lineament lineament along the Jump River. Sims andMudrey Mudrey(1978) (1978)placed placeda amajor majorf afault along Jump River. Sims and u l t in i n the t h esame same area. area. Cummings (this Cunnings ( t h i s rreport) e p o r t ) suggests suggests that t h a t the thelineament lineamentsimply simplymarks marksthe theboundary boundarybetween between volcanic rocks rockst to the north north and andg granitic rockst to the south, south, and andt hthat i sprobably probably volcanic o the r a n i t i c rocks o the a t iitt is not a fault SFVS rocks mainly andesitic, andr hrhyolitic not f a u l t zone. zone. The The SFVS rocks areare mainly andesitic, d adacitic, c i t i c , and y o l i t i c pyropyroconglomerates, micaceous eclastics l a s t i c s interstratified i n t e r s t r a t i f i ewith d w i tuffaceous t h tuffaceous conglomerates, phyllites, p h y l l i t e sand , and micaceous quartzites. They They have have been beenr regionally uppergreenschist greenschist facies e g i o n a l l y metamorphosed metamorphosed t otoupper and compressed compressed series ooff open open ffolds and i n into t o a aseries o l d s which which plunge plunge gently east-northeastward. east-northeastward. Except where wherethese theserocks rockshave havebeen beensheared, sheared,primary primaryminerals mineralsand andstructures structuresare are wellwellExcept preserved. These Theserocks rocks wwill preserved. i l l be beseen seen at a tstops stops3—7. 3-7. Although Although bedding bedding within w i t h i nthe theSFVS SFVS unit angles,i its u n i t dips dips at a t moderate moderate angles, t s contact contact (at ( a t stop stop 3) 3) with w i t h amphibolitic amphibolltic and and plutonic plutonic Thebest bestt tentative hypothesisi is rocks of CAC is i saahigh—angle high-angle shear shear zone. zone. The e n t a t i v e hypothesis s tthat hat o f the theGAG �F/atnbeaa P/age /1 0 S c. tr;'J L r.i Trondhjemite Shear zone zone FIGURE FIGURE 22--Volconics and sediments Amphibolites GENERALIZED PRECAMBRIAN PRECAMBRIAN GEOLOGY OF THE THEEAU EAUCLAIRE CLAIREREGION REGION �-6- the.SFVS rocksr rest on aa folded, folded, locally uncon— t h e SFVS rocks e s t on l o c a l l ysheared shearedand andrecrystallized r e c r y s t a l l i z eangular d angular uncon-, formity. more detailed field mapping, petrographic and geochemical formity. Considerably Considerably more d e t a i l e d f i e l d mapping, petrographic and geochemical analyses are needed neededt otowork worko uout and genetic genetic rrelationships analyses are t t hthe e s structural t r u c t u r a l and e l a t i o n s h i p s of o f these these rocks. s clear c l e a r that t h a t this t h i sarea area(stops (stops33and and 7) 7) isi sone oneofo fconsiderable considerable rocks. However, However, i tit iis significance. Whereast hthe amphiboliteswweredeformed and significance. Whereas e amphibolites e r e deformed and r e crecrystallized r y s t a l l i z e d aat t lleast east twice before trondhjemite intrusion (Van m.y.ago ago (VanSchmus, Schmus, 1980) 1980) before tonalite t o n a l i tand e and trondhjemite i n t r u s1842—1830 i o n 1842-1830m.y. The amphibolites andvolcanics volcanicswere weresynkinematically synkinematicallyand andl alate The amphibol i t e s and t e kkinematically inematically intruded by trondhjemite, tonalite, gabbro, and adamellite (quartz intruded by trondhjemite, t o n a l i t e , gabbro, and adamell i t e (quartzmonzonite). monzonite). The mostabundant abundant rock type i sisf afaint1yfoliated i n t l y - f o l i a t e dleucotrondhjemite. leucotrondhjemite. At A t Wissota Wissota The most rock type Dam (Stop# #10) Cadott(Stop (Stop#9), #9),and andFisher FisherRiver River (Stop (Stop#13) #13)t hthe trondhjemite iiss Dam (Stop l o ) Cadott e trondhjemite intruded intruded by by hornblende-biotite hornblende-biotite ttonalite. o n a l i t e . At At other o t h e r localities, l o c a l i t i e s ,however, however, the the reverse trondhjemites and and ttonal reverse relationship r e l a t i o n s h i pcan canbe beobserved. observed. The The trondhjemites o n a l i ites t e s are proprobably Thet otonalites bably coeval coeval and and comagmatic. comagmatic. The n a l i t e s ddisplay i s p l a y closer c l o s e r chemical chemical and and mineralogical mineralogical similarities which s i m i l a r i t i e stot the o t hamphibolites e amphibolitesfrom from whichthey theywere were probably probably derived. derived. The The gabbros formpplug—like intrusions, and and although althoughthey they are are younger youngerthan thant hthe gabbros form l ug-1 i k e intrusions, e t otonalites, nal ites, they beeninvolved involvedi in adamellite #8). The they have have been n ccataclastic a t a c l a s t i c deformation deformation (Stop (Stop #8). The adamellite is with i s complexly complexly iintergradational ntergradational w i t h the t h e trondhjemite trondhjemite and and iin n some some l olocalities c a l i t i e s (e.g. (e.g. North North Fork of Eau Claire River) intrudes the trondhjemite. Like the other granitic Fork o f Eau C l a i r e River) intrudes t h e trondhjemite. L i k e t h e other g r a n i t i c rocks, rocks, however, has also a l s o been been cataclastically c a t a c l a s t i c a l l ydeformed. deformed. however, iitt has Almost regardlessoof Almost regardless f oolder l d e r structures, structures, granite g r a n i t epegmatite pegmatite dikes, dikes, usually usual 1y concontaining along aa ppersistent garnet were were iintruded n t r u d e d along e r s i s t e n t east-northeast-northt a i n i n g biotite b i o t i t eand andmuscovite muscovite ++ garnet east east trend t r e n d as as exemplified exemplified aatt Little L i t t l Falls, e F a l l sWissota , WissotaDam, Dam, and and Jim Jim Falls F a l l s as as well w e l l as as many otherplaces. places.Many Manyo foft hthe dikes are are texturally many other e l alarger r g e r dikes t e x t u r a l l yand andcompositionally compositionallyzoned zoned with w i t h quartz quartz cores. cores. At Jim Jim Falls F a l l s(Stop (Stop11—A) 11-A) the t h e pegmatite pegmatite dike d i k e contains containsen enechelon echelon quartz veins as as gash gashf rfracture quartz veins a c t u r e f fillings. i l l i n g s . Microcline Microcline crystals c r y s t a l sini nthese thesedikes dikeshave have been severely bent, broken, and lenticulated. At several locations the dikes been severely bent, broken, and l e n t i c u l a t e d . A t several l o c a t i o n s t h e dikes have beencompletely completely truncated truncated by shearing. Falls have been shearing. At At Jim Jim F a l l s at a t least l e a s t three t h r e e ages ages of of pegmatite pegmatite iintrusion n t r u s i o n can can be be seen. seen. The The older o l d e r dikes dikes are areboudinaged boudinaged in i n the t h e compositional compositional layering pegmatite dikes dikes have been ooffset l a y e r i n g of o fthe t h ebanded banded amphibolite amphibolite host host rock. rock. The The pegmatite have been ffset by Precambrian by north-northwest-trending north-northwest-trending faults f a u l t sofo Late f Late Precambrian age. age. Late Precambrian gabbro—diabase dikes rockswwith Precambrian gabbro-diabase dikes c u t cut a l lallt hthe e o other t h e r rocks i t h strong disdiscordance. chilled (Stop 10) 10) iindicate cordance. Their l e d margins margins (Stop n d i c a t e shallow shallow intrusion intrusion T h e i r conspicuously conspicuously chi1 after The a f t e r aaprolonged prolonged erosional erosional interval i n t e r v a l(1600-1100 (1600-1100 m.y.). my.). The dike d i k e at a tWissota WissotaDam Dam contains large, partially resorbed fragments very coarse—grained contains p a r t i a l l y resorbed fragmentsofo labradorite f l a b r a d o r i tand e and very coarse-grained norite. n o r i t e . This This dike d i k e is i sintruded intrudedby byaathin t h i nleucotrondhjemite leucotrondhjemite dike, dike, which which displays d i s p l a y san an unusual type of crush texture where it is involved in a small fault zone. unusual type o f crush t e x t u r e where i t i s involved i n a small f a u l t zone. The basement was deeply saprolitized (Cumings and and Scrivner, 1980) The Precambrian Precambrian basement was deep1 y saprol i t i z e d (Cutmnings 1980) in timewwith formationooff kkaolinite—rich i n Late Late Precambrian Precambrian time i t h formation a o l i n i t e - r i c h ssoils. o i l s . A distinctive distinctive illitic clay rocks(as (asseen seen i l l i t green i c green c l adeveloped y developedon onthe t h ehornblende—rich hornblende-rich rocks a tatL Little i t t l e Falls). Falls). The clays form markeras ast the EauCClaire River repeatedly crosses The clays form a conspicuous conspicuous marker h e Eau l a i r e River crosses the the unconformity Lak Eau Eau CClaire M t . Simon Simon unconformity between between Lak l a i r e and and Lake Lake Altoona. Altoona. Late LateCambrian Cambrian Mt. Sandstone, which ooverlies knob— Sandstone, which v e r l i e s the t h ePrecambrian Precambrian rocks, rocks, occurs occursabundantly abundantlyasasridge r i d gand e and knobshaped shaped ooutliers u t l i e r s throughout throughout the t h eChippewa Chippewa Valley region. region. Clay Clay and and feldspar content content decrease upwardi nint the formation owing owing tto decrease upward h e formation o reworking reworking of o f the t h esands. sands. Glacial till andand outwash till outwashofot.he f t h Chippewa e Chippewa lobe l o b eofo Wisconsin f Wisconsin glaciers g l a c i e r sare areexposed exposed in Valleynortheast northeasto fofEau Eau Claire.AtAtL Little i n the t h e Chippewa Chippewa Valley Claire. i t t l e Falls F a l l s (Stop (Stop #2) #2) the the tills highly and an oolder t i l l are s are h i g h weathered l y weathered andmay may represent represent an l d e r glaciation. g l a c i a t i o n . Silicified Silicified Cretaceous EauCClaire Cretaceous ttree r e e fragments fragments found found in i noutwash outwash downstream downstream ffrom r o m Eau l a i r e suggest suggest that that Cretaceous sedimentary rocks may underlie deposits iinn the Cretaceous sedimentary rocks may l o clocally a l l y under1 i e g glacial l a c i a l deposits t h e northern northern part p a r t of of the theState, State, oro that r t h aCretaceous t Cretaceousfossil f o s s wood i l woodfrom fromMinnesota Minnesota was was ccarried a r r i e d into into Wisconsin duringanane aearlier Wisconsin during r l i e r gglaciation l a c i a t i o n and and llater a t e r redeposited redeposited iin n this t h i sregion regionduring during Late Lste Wisconsin Wisconsin time. . . �—7— xroiith-gMissmigmatit. zoo. Block Block diagram diagram illustrating illustrating the the concept concept of ofcâivai coevalrelations relation*between between Archaean Archaean gra_nite—greenstone andhigh& high-gradeterrains. terrains. Thà The d diagram represents aa tilted g c 8 n i t ~ ~ t ~ e ntmaina fterrains t o ~ and i i represent> tilted crustal crustal synclinorium (about segment allowing observation observation of of aa major segment allowing major greenstone gneiutonesynclinorium (about mid-way) mid-way)and and aa ultramaflc—mafic high-grade terrain (front left part). Domal tonalites intrude relics of an hiih-gnde terrain (front left part). Domal tonalitec intrude relics of an ultramafic-mafic volcanic volcanic crust crust (early (earlygreenstones) greenstones) (black). (black). The Thetonalites tonalitesbecome becomeincreasingly increasingly gneissose gneisscde (dashed patterns) both toward their margins and with depth. Late greenstone depositories fdsshed oatternst both toward their margins and with depth. Late gmenstone depositories and (hatched (dotted) form (hatched patterns) pattern*) and and sedimentary d i e n t u y sequences se&enc~ (dotted) form unconformably uocoufonnably and parsparalate supraconformably above the tonalites and the early greenstones. L.oci of maximum eonfonnablv abcw the tomtità and the early gmeiutoncs. h i of maximum late supra.. . of crustal synclinoria. Deep-seated crustal deposition deposition coincide coincidewith withinterdomal interdoma1 synclinoria. Deep-seatedgneiss gneissroot rootzones zones of of supracrustal batholiths by aa linear batholiths are are characterized characterized by linear structural structural grain, grain. attenuated attenuated relics relics of supracrustal enclaves andxenoliths. xenoliths, maficÑultramafi mafic—ultramafic intrusion* intrusions and anorthosites. enclaves and and anorthosites. - ~ , .Figure Figure f - 3 Block diagram from GGlikson, 21 3 -— Block diagram from l ikson, 1957, 1957, p. 21 DESCRIPTIONS OF OF MAJOR MAJOR ROCK ROCK UNITS UNITS Introduction Introduction Rocks amphibolite complex complex(CAC) (CAC)consist consistmainly mainly ooff plagioclase Rocks ooff the Chippewa Chippewa amphibolite plagioclase ), amphibole, quartz and biotite. Conron accessory minerals amphibole, quartz and b i o t i t e . Common accessory minerals are are K—feldK-feldspa-, idote, chlorite spa?-!-$dote, c h l o r i t e and and iiron r o n oxides. oxides. Granitoid Grani t o i dcomponents components contain contain the thesame same (An (An essential as the the amphibolites amphibolitesbut buti in essential minerals minerals as n ddifferent i f f e r e n t proportions. proportions. The The apparent mineralogical simplicity of CAC rocks suggests regional metamorphic equilibration, mineralogical s i m p l i c i t y o f CAC rocks suggests regional metamorphic e q u i l i b r a t i o n , following Penokean m.y.j. following the t h emajor majorplutonic p l u t o n iphases c phasesofothe f the Penokeanorogeny orogeny (1840-1830 (1840-1830 m y . ) . By By contrast, the rocks contain contain abundant abundantcchlorite, (JRV) and and South South Fork Fork (SFVS) (SFVS) rocks hlorite, theJump Jump River River (JRV) epidote, and garnet, and andshow show greater 1lithologic epidote, and garnet, s i significantly g n i f i c a n t l y greater i t h o l o g i c and and chemical chemical ddiversity. iversity. (See (See Figures Figures 66 and and 88 ). Amphibolites Amphi bol ites Mafic, intermediate, plutonic Mafic, intermediate, and and feldspathic feldspathic amphibol-ites amphibol-ites ooff volcanic and and p lutonic derivation structures, fabrics, att least derivation contain contain structures, fabrics, and and minerals minerals indicating indicatin a l e a s t three three deformations and (See Stop Stop ##1). and as as many many episodes episodes of o f metamorphism metamorphism (See I . In I n outcrop outcrop the the amphibolites are medium darkgray, gray, commonly comonly laminated laminated and andlineated, lineated, and amphibolites are medium t otodark and cut c u t by by 7 numerous numerous ggranitoid r a n i t o i d veinlets, veinlets, many many of o fwhich whichhave havebeen been strongly stronglydeformed. deformed. The The dominant dominant minerals are Subordinatequartz, quartz,bbiotite, andhornblende. hornblende. Subordinate iotite, are plagioclase plagioclase(An2555) (Annss5 )and �-8trace minerals Common trace minerals are are dd 10 10 percent percent each. each. Comon epidote, and cc epidote, The coarse— sphene,i rand iron oxides,pyrite, pyrite, garnet, garnet,zircon, zircon, apatite, apatite, and coarsesphene, o n oxides, and aallanite. l l a n i te. The grained mafic mafic and andfeldspathic feldspathic amphibolites amphibolitespossess possessstructures structuresi nindicating grained d i c a t i n g dderieriand 2). vation from gabbroicand andanorthositic anorthositicpprotoliths r o t o l i t h s (stops (stops 1 and 2). Textures Textures in in vation from gabbroic fine—grainedmafic maficand andintermediate intermediateamphibol amphibolites indicatet htheir derivation mainly fine-grained i t e s Indicate e i r derivation mainly from basalt basalt flows andesite pyrocl pyroclastics. from flows and and andesite astics. Associated Associated biotite—hornblende— b i o t i te-hornbl endechlorite—epidote schists (Figure 8) probably represent chlorite-epidote schists (Figure 8 ) probabl represent sedimentary sedimentary pprotoliths. rotoliths. The banded bandedamphibolites amphibolitesa tatBig BigFFalls 1) were derived from The a l l s (Stop (Stop 1 were probably probably derived from a a layered layered Although relict garnets occur sparsely throughgabbro (Curnings and Myers, 1979). Although r e l i c t garnets occur sparsely throughgabbro (Cumnings and Myers, 1979). out the the large large hornblendized garnetporphyroblasts porphyroblastsaat Big FFalls CAC, the hornblendized garnet t Big a l l s are are unique. unique. out the CAC, Laminatedamphibolites amphibolites 2) contain Laminated a t at L i Little t t l e FFalls a l l s (Stop (Stop 2) contain ultramafic ultramafic inclusions inclusions (autoliths?). (auto1 i t h s ? ) . Garnetiferous Garnetiferous amphibolites amphibol i t e s ooff the the Cornell Cornell area area are are richer r i c h e r ini nalumina a1 umina The garnets in these amphibolites than those elsewhere in the CAC. than those elsewhere i n the CAC. The garnets i n these amphibolites are are fresh, fresh, show show Plagio— no rotation, and no rotation, and engulf engulf older older laminations laminations produced produced iin n part p a r t by by shearing. shearing. Plagiolaminaeare areaxial-planar axial—planar clase + quartz quartz laminae t ototitight, ht, iisoclinal s o c l i n a l shear shear folds folds(F—l), (F-I), which which clase were locally compressed into small open folds (F—2) with oblique axial trends. were l o c a l l y compressed i n t o small open f o l d s F-2) w i t h oblique a x i a l trends. 1 ! ? Chemical compositionso of the amphibolites amphibolites are are included Chemical compositions f the i n c l u d e din i nTables Tables 1—3, 1-3, and and iinn Figure 5 Figure 5 . Volcanic and and Associated Associated Sedimentary SedimentaryRocks Rocks Volcanics ooff the River area Volcanics the Jump Jump River area (stops (stops 15-18) 15-18) comprise comprise mafic mafic and and intermediate intermediate Relict (basaltic and andesitic) flows flows and andandesitic andesitict otorrhyolitic ict (basaltic and andesitic) h y o l i t i c pyroclastics. pyroclastics. Re1 sedimentary and porphyritic textures are well preserved despite local metamorphism sedimentary and p o r p h y r i t i c textures are well preserved despite l o c a l metamorphism The JRV JRVwere wereintruded intruded by by Penokean(?) Penokean(?)g granitic tto o lower lower amphibolite amphibolite grade. grade. The r a n i t i c plutons plutons along the south side of the Jump River. along the south side o f the Jump River. Basaltic(?) andesitic, andesitic, and andr hrhyolitic volcanic rocks rocksi ninterstratified Basaltic(?) y o l i t i c volcanic t e r s t r a t i f i e d with with siliceous volcaniclastic sediments p h y l l i t e sconglomerates, , conglomerates,and andmicaceous micaceous siliceous volcaniclastic sediments— phyllites, quartzites - are Fork ooff the areexposed exposed along along the the North North Fork Fork and and South South Fork the Eau Eau Claire Claire quartzites River (Stops (Stops 3-7, 3-7, Figure Figure 21). 21). Although Although bedding bedding in i nthe thetuffaceous tuffaceoussandstone sandstone and and conglomeratedips dipsaat moderateangles anglest otothe theeast east and andsoutheast, southeast, contacts contacts w with conglomerate t moderate ith contiguous amphibolite and andplutonic plutonic rocks rocks are steeply dipping contiguous amphibolite dipping and and strongly stronglysheared. sheared. Numerous small exposures of andesitic to rhyolitic volcanic rocks crop Numerous small exposures o f andesitic t o r h y o l i t i c rocks crop out out in EauClaire ClaireRiver River and andJump Jump Riveri ninthe theeast eastside side ooff the region. i n the the area area between between Eau River region. The SFVS Thus is is inferred that the two terranes contain correlative rocks. SFVS Thus i s i s i n f e r r e d t h a t the two terranes contain c o r r e l a t i v e rocks. The ), and rocks show and ttheir heir show a "normal "normal" calc—alkaline calc-alkaline ddifferentiation i f f e r e n t i a t i o n trend trend (Figure (Figure 66 ), compositions areclose closet to those ooff nearby nearby ttonalite compositions are o those o n a l i t e and and trondhjemite. trondhjemite. The The possibility Penokean trondhjemitic and and ttonalittc o n a l i t i c plutons plutons intruded intrudedtheir t h e i rown own b i l i t ythat t h athe t the Penokean trondhjemitic volcanic beexamined, examined, especially volcanic ppiles i l e s should should be especially i ninl i light g h t ooff the the closeness closeness i in n ttheir heir ages (1860m.y. m.y.f ofor the SFVS SFVSand and l840m.y. ages (1860 r the 1840 m y . f oforthe r the plutonic plutonicrocks rocksaccording according to t oVan Van Schmus, 1980.) 1980.) Schmus, - - Plutonic Rocks Plutonic Rocks The ttonalites essentially ooff plagioclase The o n a l i t e s of o fthe theChippewa Chippewa region are composed composed essentially (Ançç),),quartz, Compositionalvariations variations are quartz,hornblende, hornblende, oor r bbiotite, i o t i t e , or o r both. both. Compositional are (An exprsed expressedmegascopically megascopically as as differences differences in i nthe thehornblende—biotite hornblende-biotite ratio r a t i oand andthe the abundanceoof quartz. Mafic tonalites, with abundance f quartz. Mafic tonalites, w i t h total t o t a mafics l maficsini nexcess excess of o f35 35 percent, percent, tend to andare arecommonly comonly associated associatedwwith t o be be hornblende—rich hornblende-rich and i t h mafic amphibolites. Biotite, younger than thethe hornblende, B i o t i t e , which whichisi sinvariably invariably younger than hornblende,produces producesa awell—defined well-defined foliation. weatheredoutcrops, outcrops, iitt f o l i a t i o n . Although Although ffoliation o l i a t i o nmay may not notbe beconspicuous conspicuous on on weathered is i s invariably invariablypresent. present. All A l l tonalites t o n a l i t e sseen seen ini nthin t h i nsection sectionshow show some some eeffects f f e c t s of of cataclasis, mostly and mostly as as interlensing interlensingshear shearsurfaces surfacesalong alongwhich which plagioclase p là i"; .?.' *'9 yas . ".z,*.. i'-,;<*,-. .,*&\.> , t. . :: �—9— quartz Biotite quartz are a r e mylonitized. mylonitized. B i o t i t eflakes f l a k e sare arecrenulated crenulatedbybydisplacements displacements along along shear surfaces during post-metamorphic catashear surfaces d u r i n g cataclasis, c a t a c l a s i s ,a afactor f a c t osuggesting r suggesting post-metamorphiccata— Tonalite cclasis. lasis. T o n a l i t e contacts c o n t a c t s are a r e typically t y p i c a l l ysheared sheared with w i t h considerable considerable mixing m i x i n g ooff contiguous rock rock uunits. contiguous nits. The trondhjemites trondhjemitesaare composed quartz, and andbbiotite. The r e composed e s sessentially e n t i a l l y o f of o loligoclase, i g o c l a s e , quartz, iotite. Epidote, K—feldspar, muscovite, iiron Epidote, K-feldspar, muscovite, r o n oxides, oxides, and and sphene sphene are a r e ubiquitous u b i q u i t o u s accessory accessory minerals. The Thetrondhjemites trondhjemitest etend and minerals. n d t otobebel eleucocratic u c o c r a t i c and o nonly l y f afaintly i n t l y ffoliated. oliated. Theyaare adamellites byaasslight 1i t e s by l i g h t increase increase in in They r e ccontinuously o n t i n u o u s l y i nintergradational t e r g r a d a t i o n a l wwith i t h adamel K-feldspar. The trondhjemites trondhjemitesas asseen seeni nint thin K-feldspar. The h i n section s e c t i o n contain c o n t a i n large, l a r g e , subhedral subhedral margins owing ggrains r a i n s ooff plagioclase p l a g i o c l a s e with w i t h untwinned untwinned margins owing i n in p apart r t t otos tstructural r u c t u r a l ddisisordering under conditions of cataclasis. Quartz ggrains lamellar, o r d e r i n g under c o n d i t i o n s o f c a t a c l a s i s . Quartz l a r , undulatory undulatory r a i n s show show lame1 occuri in eextinction, x t i n c t i o n , are a r e finer f i n e rgrained g r a i n e dthan than the t h e plagioclase, plagioclase, and and comonly commonly occur n cclots lots or ribbons. In contact with K-feldspar grains, the plagioclase is myrmekitic. o r ribbons. I n c o n t a c t w i t h K-feldspar grains, t h e p l a g i o c l a s e i s myrmekitic. Muscovitei is Biotite B i o t i t e isi sconinonly commonly altered a l t e r e d to t o green green chlorite+ c h l o r i t e +muscovite. muscovite. Muscovite s iinvariably nvariably a late mineral , probably formed during retrograde metamorphism of the region. a l a t e m i n e r a l , probably formed d u r i n g retrograde metamorphism o f t h e region. The best exposure exposureo of Dam(Stop (Stopl o10), wherei tit i iss cut cut ) , where The best f t trondhjemite r o n d h j e m i t e i is s at a t Wissota Wissota Dam by dikes and irregular masses of gray tonalite containing amphibolite by dikes and i r r e g u l a r masses o f gray t o n a l i t e c o n t a i n i n g amphibol i t e xxenoliths. enoliths. The aadamellites simply ccontain moreK-feldspar K-feldspar((microcline) than the The d a m e l l i t e s simply o n t a i n more m i c r o c l i n e ) than t h e trondhtrondhjemites. Whereas most of the K-feldspar in the trondhjemites occurs as regular jemites. Whereas most o f t h e K-feldspar i n t h e trondhjemites occurs as i rirregular as ddiscrete occursmore more comonly commonly as i s c r e t e ggrains r a i n s in i n the the iinclusions n c l u s i o n s in i n the t h e plagioclase, plagioclase, iti toccurs adamellites. E a r l y kinematic kinematic veins veins and and dikes dikes of o f adamellite adamell i t e showing showing folding f o l d i n g and and adamell i t e s . Early boudinage, indicate that the sequence of intrusion was complex and not boudinage, i n d i c a t e t h a t t h e sequence o f i n t r u s i o n was complex and n o t confined confined to t o aa single s i n g l e differentiation d i f f e r e n t i a t i o nsequence sequence (as (as at a t Jim Jim Falls, F a l l s , Stop Stop 11). 11). Several as to Several plug-like p l u g - l i k e gabbro gabbro bodies bodies were were seen, seen, but b u t so so poorly p o o r l y exposed exposed as t o render render However,aagabbro gabbrobody bodyi sis wwell along tthe them unmappable. unmappable. However, e l l exposed exposed along h e Yellow Yellow River River The gabbro gabbro has has aa bbrecciated near Stop 88 about about 22 m miles r e c c i a t e d margin margin i l e s eeast a s t of o f Cadott. Cadott. The near Stop Relict against amphibolitic and volcanic(?) rocks in intermediate composition. ict a g a i n s t a m p h i b o l i t i c and v o l c a n i c ( ? ) rocks i n i n t e r m e d i a t e composition. Re1 clinopyroxene clinopyroxene ggrains r a i n s aare r e thickly t h i c k l ymantled mantled by by hornblende, hornblende, which which iiss in i nturn t u r nrimmed rimmed gabbroonont hthe YellowRRiver with (Ans5), The gabbro e Yellow i v e r ccosists o s i s t s ooff plagioclase p l a g i o c l a s e (An55), w i t h brown brown bbiotite. i o t i t e . The hornblende,bbiotite quartz, ppyrite, hornblende, i o t i t e and and accessory accessory quartz, y r i t e , magnetite, magnetite, sphene, sphene, zzircon, ircon, The rock rock is apatite, i s cut c u tby bynumerous numerous shear shear zones, zones, and and ddisplays isplays l l a n i t e t ? ) The a p a t i t e , and and aallanite(?) a TheThe gabbro appears a subtle s u b t l e cataclastic c a t a c l a s t i c foliation f o l i a t i o in n ithin n t hsection. i n section. gabbro appearstot obe beyounger younger than than tthe h e ttonalite o n a l i t e or o r trondhjemite t r o n d h j e m i t e - late l a t ekinematic. kinematic. - Chemical analyseso of Chemical analyses f t the h e pplutonic l u t o n i c rocks rocks are a r e included i n c l u d e d ini ntables t a b l e s5 and 5 and6.6.AnAnAFM AFM diagramf ofor rocks iiss given v a r i a t i o ndiagram diagramshowing showing diagram r t the h e pplutonic l u t o n i c rocks given in i n Figure Figure 77.. AA variation well-defined aa w e l l - d e f i n e d iinterrelationship n t e r r e l a t i o n s h i p of o f the t h e plutonic p l u t o n i c rocks rocks is i s given given in i n Figure Figure 4 . Thessignificance K20curve curvei sisn not exceptt hthat The i g n i f i c a n c e oof f tthe h e double double K20 o t f ufully l l y understood, understood, except a t iitt probably represents representstwo twod distinctly series, which whichaare otherwisei nindistinguishprobably i s t i n c t l y uunrelated n r e l a t e d series, r e otherwise distinguishIt isi ssuggested Morechemical chemicaldata dataa rare needed able. More It suggested that that e needed t o to v everify r i f y t this h i s trend. trend. ont the ffuture u t u r e studies s t u d i e s should should concentrate concentrate on h e aalkali l k a l i ratios r a t i o sini plutonic n p l u t o n assemblages i c assemblages in i n the t h e plutonic p l u t o n i crocks rocksofo the f t h eChippewa Chippewa Valley. �-10- '—S so 60 70 00 •7s;Ot - Variation diagram showingv avariation Figure diagram showing r i a t i o n ooff various various oxides oxides Figure 4 -—Variation in relation to weight.percentage of silica for tonalites, i n r e l a t i o n t o weight ,percentage o f s i l i c a f o r tonal i t e s ,adamellites, adamell i t e s , and Bulkchemical chemical and trondhjemites in i nthe t h eChippewa Chippewa amphibolite amphibolitecomplex. complex. Bulk analyses by Technical Service Laboratories, Mississauga, Ont. analyses by Technical Service Laboratories, Mississauga, Ont. �—11— F AMPHIBOLITES (Fe203+FeO) 0 0 05 0 0 00 0 M (MgO) A (Al 203-Na20-K20) -- Figure 5-Figure 5 AFM AFM diagram diagram f for o r amphibolites.omafic aaphfbolites. o m a f i c amphibolites1 0 intermediate amphibol iites, t e s , and and amphibolites, 0 intermediateamphibol • feldspathic feldspathic amphibo4ites.Plotted amphibolites. - P l o t t e d in i nmolecular molecular proportions. proportions. Total iron i r o noxide oxideexpressed expressedas asFe203 Fe203 F SOUTH FORK SOUTH FORK VOLCANIC AND AND METASEDIMENTARY METASEDIMENTARY ROCKS ROCKS 0 0 A (A1203-Na20—K20) 0 (Fe2O3+FeO) . • NI Figure 66 -— diagram ffor -- AFM AFM diagram o r metavolcanic metavolcanic and and associatedsedimentary sedimentary rocks, •andesite associated rocks, andesite t tuffs, uffs, 0 dacite(fl, d a c i t e ( ? ) , ootuffaceous t u f f a c e o u s conglomerate, conglomerate, o o rhyolite, 0 r h y o l i t e ,Amuscovite—biotite A muscovite-biotite quartzite. quartzite. (MgO) �—12— F (Fe203+FeO) PLUTONIC ROCKS PLUTONIC ROCKS o Trondhjemite 0 Trondhjemite • Tonalite £ A Adamellite Adamel 1i t e Gabbro • Diorite oo a U o AA (Al203—Na20—K20) (A1 n03-Na,0-K,0) M (MgO) -- Figure CompositeAFM AEM p l oplot t o of f pplutonic l u t o n i c rocks rocks Figure 77 -— Composite amphibolite complex, complex,pplotted iinn the t h e Chippewa Chippewa amphibolite l o t t e d in in and 66 ffor molecular proportions. proportions. See o r desdesSee t tables a b l e s 5S and molecular ccriptions r i p t i o n s of o f rocks. rocks. COMPOSITE COMPOSITE PLOT PLOT F - (--C (Fe2O3+FeO) Plutonic P l u t o n i c rocks rocks South Fork volcanic volcanic South Fork O and and sedimentary rocks C__ .— •1 Amphibol ites A (Al 203-Na20—K2 -- (MgO) Composite AFM AFM pplot l o t showing showing compositional compositional Figure 88 -- Composite llimits i m i t s ofo fplutonic p l u t o n i crocks, rocks,South SouthFork Forkvolcanic volcanicand and sedimentary rocks, rocks, and Average ttrend sedimentary and amphibolites. amphibol i t e s . Average rend shownwwith heavyblack black lline. shown i t h aa heavy ine. �—13— - 1 J- - TABLE BULK CHEMICAL CHEMICALCOMPOSITIONS COMPOSITIONS I'FIC AMPHIBOLITES* TABLE I1 — BULK OFOFMAFIC AMPHIBOLITES* 7336 A 7425 177132 77138 77155 7902 A B A B A8 98 52 r28 7927 7908 N-I A 4&30 7941 7950 A A 986609 SiC2 49.06 A1203 15.61 17.12 14.88 13.16 13.30 13.51 19.95 11.06 14.66 13.86 Fe203+ 12.40 11.16 11.12 14.46 13.51 11.59 13.24 11.62 11.09 11.93 1 FeC 9.65 10.90 9.02 9.69 11.87 11.47 12.34 12.10 14.75 5.21 3.19 5.57 7.31 10.85 3.08 2.32 2.32 2.93 1.32 1(20 0.77 0.68 0.85 1.04 0.68 0.31 0.78 Tb2 0,77 öT1 1.01 1.13 MnO 0.19 0.18 0.56 0.14 0.21 P205 0.14 0.12 0,19 0.29 CaD 10.04 MoO 6.60 'rJa2O LOI TOTAL Soec. No. 7336—A 0.64 0.75 1.99 0.60 5.52 15.28 8.11 7,66 2.57 1.18 2.23 1.64 0.70 0.19 0.58 1.00 0.71 0,34 0.90 0.96 0.18 0.21 0.21 0.20 0.19 0,21 0.17 0.00 0.27 0.09 0.08 0.15 0,71 0.37 0.42 0.26 0.56 0.66 0.60 99.28 100.2 100.3 98.28 100.31, 98.31 100.0 99.35 100.1 100.01 Location Eau Claire R. Desc rip U on H—P—8—E—C schist with contorted granitic SE¼S%% Sec.l8; T26N, R5W veinlets in isoclinal folds; banding cut discordantly by granitic veinlets,dikes 7425—B Cornell CornellDam Dam SW¼SE¼Sec.18; T3IN, R6H SMiSEdSec.18; T31N, R6 H—C schist; strongly lineated; isoclinal folds of P 77132 Eau Claire R. Eau Claire R. SW¼Sk SWiSlfc Sec. Sec. 20; 20; T27Nç T Z 7 kRJW R fine—grained schist; stronaly strongly fine-grained H—P H-P schist; 77138—A 771384 Eau Claire R. Eau Claire R. NE¼SE¼ Sec.29; T27N, NWEk Sec.29; T27N. R7W R H—P schist, lineated; lineated; associated H-P schist, associated with with 77155—B Knight Knight Pool; Pool; North North Fork. For 7902—A 1 ineated banded gneiss. banded P—H P-H gneiss. Fine—grained H—P schist (H—60%); thinly Eau Eau Claire ClaireR.R. NW¼SE¼ Sec.IO; T26N. R N W E k Sec.10; T26N. R7W banded with lensoidal lensoidal masses of feldspar banded with masses of felds Little L i t t l eFalls, Falls,Eau EauClaire ClaireR. R. H—rich inclusion of of lineated H-rich inclusion lineatedhornblendite hornblen SW¼NW¼ Sec.19; T27N, S U W Sec.19; T27N. R7W R7W very very tight t i g h t isoclinal i s o c l i n a l folds folds of of PP locally loca 0—B bearing gneissic gneissic H H ttonalite o n a l i t e intrusion intrusion breccia; breccia- H has a pronounced green color color ini nspecimen pronounced green spe and and iinn thin t h i n section. faction. 7908—A 7927—N—i 7941—A Fisher R. Bridge Bridge Fisher R. SWgSW¼ Sec.4; T3IN, SMiSMi Sec.4; T31N. R6W R6H H—P schlst—looksl i like gneissic HHgabbro; H-P schist-looks k e gneissic gabb cut cut by by pegmatite pegmatite veinlets veinletsand andmylonite mylonit 'veinlets" veinlets" with withright—lateral right-lateraldisplacement displac Little L i t t l eFalls, Falls,Eau EauClaire ClaireR. R. Lineated Lineated horrblendite hornblendite xenolith xenolithIn iH— n H- 5W¼NW¼ Sec.19; 19; T27N, SHWIfa Sec. T27B. R7W B71b tonalite t o n a l i t e intrusion intrusionbreccia breccia Knight S. Fk. Fk. Knight Pool; Pool; S. Medium fine—grained H—P schist Hedium fine-grained H-P schist NW¼SE¼ Sec.l0; NUkSEk Sec. 10; T26N, T26N. R7W R7H 7950—A Jim Falls, Falls,Chippewa ChippewaR. R. SW'iE¼.Sec.30; SwaiEii.Sec.30;T3ON, T30N.R8W RBH Medium—grained H—P schist withPPi nIn ttight Mediuei-grained H-P schist with ight isoclinal i s o c l i n a lshear shearfolds, folds,whose ihose limbs limbs impart impart aa pronounced layering iinn the pronounced layering the rock rock * Chemical Chemical analyses analyses by by Technical Technical Service Service Laboratory, Laboratory, Mississaugua, Mississaugua, Ontario, Ontario,Canada Canada ** Mineral hornbiende; Q = quartz; plagioclase-H r a l Abbreviations:P Abbreviati0ns:P ==plagioclase; B == biotite; E = epidote; C = chlorite; biotiteK ; = K K—feldspar; = K-feldspar; NM == muscovite; uu S == sericite; sericite; 6 6==garnet garnet �-14- TABLE 2 — BULK CHEMICAL COMPOSITIONS OF INTEIE0IATE NIPHIB0LITES* 7830 A 5th2 Al203 Fe203+ 7830 — B 7830 7830 6 H 7830 I C . 5.42 4.55 6.13 6.13 MgO 6.10 4.51 3.47 Ma20 3.66 3.16 3.96 3.31 2.69 K20 0.72 1.36 1.89 1.18 0.99 1.00 flO2 0.46 0.61 0.34 0.27 0.22 '1.70 MnO 0.14 0.14 0.06 0.06 0.02 0.13 0.08 0.23 0.11 P2°s 0.03 0.00 0.25 LOI 1.17 1.61 1.53 1.19 0.71 0.80 TOTAL 7830—A 78a-A — 57.08 57.24 57.5k 63.0i 68.42 63.39 15.87 14.89 17.74 l4.3r 14.37 17.22 8.68 9.75 5.80 6.64 3.77 5.28 FeO CaO Spec. & g,g&&NO. 7904 4.94 5.18 1.14 2.20 3.02 4.17 98.41j98.85 98.73 98.94 98.22 !22d - Location Location Confluence off NN&6 SSForks Confluencm o Forts of the of the Eau Eau Claire Claire R. R. 12611, SE¼NE¼SbDS Sec.15; SEkNESR k . 1 6 ; T26N. R5W endoof RW NENEand f outcrop OUtCnIP Descr1otion ~ criotimLineated P—H gneiss withlensoidal lensoidalPPclots. clots, gneiss with Lineated P-H Interlensing shear Interlensing shear surfaces surfaces with with —C E-C laminae; Segmented, lenticulated PP && H. laminae; +nted, lenticulated H. 7830—B 7833-0 2 2 meters meters west westofof7830—A 7833-A Feldspathic gneiss. ~with Feldspathic H—P H-P gneiss, 4 t subhedral hsubhedral PP lineation; Large && H H lineation; Largefl—P Q-P bands bands form f o m bandbanding; EE (10%) layerino. ing; (10%)along along and and across across H—P H-P layerinq. 7830—C 78304 33 meters westof west.of7830—8 7830-8 P—Hgneiss gneissccomposed bent and and crushed P-H w s e d ofofbent crushed lensoldal PP &6 H; lensoidal H; both bothshow show undulatory undulatory extinction and fragmented crystal extinction a d f r a m n t e a c w s t a l bounboundaries; crvss-cuttiig cross—cutting shear shear planes daries d a m s are are E—rich. E-rich. 7830—6 7833-6 15 meters 15 meters west west ofof7830—F 7833-F Medlum—coarse—grained feldspathic P—H gneiss Medim-coarsegrained feldspathic P-H gneiss with lenticular with l m t i m l a rH, H. P. P..and and- subordinate subordinate ffine ine -~~ - - - - -~~ grainS grained(J. 0 . PP wnearly a r l y aall l l altered altered to t o 5; 5 ; HH grains mestly m s t l y converted converted to t o oreen green C. C. H H grains segmented,broken broken{nto into sigmoidal sepented. s i m i d a l lenses lenses which wrap around coarser P lensolds. h i c h wrap a m d coarser P lensoids. Cataclastic lamination N400W, vertical. Cataclastic lamination NW%. vertical. ~ ~ 7830—H 7830-H 5 meters meters west west ofo 7830—6 f 7830-6 Bands P—H gneiss;contains contains abundant abundantpyrite. pyrite. 8anded P-H gneiss; Broken and and bent bent P and P porphyroclasts wr@~ymclasts andlen— lenEmken ticulated, bent, H iin ticulated. bent.segmented semented H na a matrix matrix altered tto E. and ooff fi, Q, E. and P. P. P P altered o 5; S; H H partly partly altered toto C-PE. Tension fractures fractures across altered WE. Tension acms cataclastic laminatio.i, are filled filled with l&aimtim arc withC#E. C+E. cataclastic 7830—I 7830-1 Same location asas7830—6 Sam location 7830-6 Felsic layer fi, less less HH Felsic layerini 7830—G; n 7820-6; more more 0, than 7830—6; muchmylonitization. mylonitization. 7830-6; mch 7904—C 79044 Yellow River, east Yellow River, east of of Cadott Cddott Volcanic (?) (?)Now Now aa fine—grained fine-grained H—B H-E t tonalite onalite or trondhjenite. layering oarallel parallel to or trondhjmite. H H layering to foliation. N No evidenceo of volcanic oriqin. oriqin. 8B foliation. o evidence f volcanic - - - - analysis by * Chemical Chemical analysis by Technical Technical Services Sewices Laboratories, Laboratories, Nississaugua. Mississaugua, Ontario, Ontario.Canada Canada - plagioclase; HH — hornblende; hor,iblende; 0Q quartz quartz Mineral Abbreviations: P P —plagioclase; Uineral chlorite; B biotite;K — K K—feldspar; K-feldspar; P1 tl = muscovite; mscovite; EE = epidote; epidote; C C == chlorite; 8 = biotite; S sericite; 6G = garnet S *= sericite; �—15- - TABLE 33— BULK OF N.IPHIBOLITES* TABLE BULKCHEMICAL CHEMICAl COMPOSITIONS CLWOSXTIONS O F FELDSPATHIC FELDSPATHIC PMPHIBOLITES* 7711 77105 77119 77128 A 5i02 M203 Fe203+ C 48.36 50.51 49.69 57.54 28.48 26.71 24.89 18.80 3.05 3.48 4.18 7.15 FeO CaO 6.72 1.92 0.68 2.94 Na20 3.11 1.67 2.91 4.34 <20 0,28 0.26 0.44 0.25 0.31 MnO 0.18 0.04 0.26 0.49 0.05 P205 0.02 0.06 0.09 0.08 0.12 LOl 0.52 0.02 0.40 0.60 0.60 TiC2 TOTAL Spec. Swc. No. No. 12.99 14.46 13.31 Mg0 2.87 98.96 98.48 99.43 98.96 Location Description Description Strongly P—H—G schist; ragged Stronglylineated lineated P-H-G schist; ragged S G iinn layers. layers. 7711 7711 Cornell NI NE¼ CornellDam D m Nlk N& Sec. Sec. 19; 19; T3IN. T31t1,R6W MU 77105—A 77105-A Eau Claire R. Eau Claire R. ata Nine— t Ninemile Cr. MR NEkSW Sk%Sec. Sec. m i l e Cr. 15; T27N, R8W 15; T27N. RW Strongly lineated gneiss with with folded lineatedP—H P-H gneiss lineatlon lineatim 77119—C 771194 Big B i g Falls, Falls, Eau Eau Claire Claire R. SR Sec. R. 44i4 Wa S& Sec. 13; 13; T27N, R8W T27N. R8U Lineated gneiss ssimilar Lineated P—H P-H gneiss i m i l a rtot 77105—A o 77105-A Eau Claire R. Eau Claire R. Intermediate P—H gneiss; I n t e m d i a t e P-H gneiss; t i gtight h t i sisoclinal oclinal folds folds of o fPPbands bands 77128 77128 * Nlk NW¼ NE¼ Sec. 19; 19; T27N, T27N.R7W R7W NEk Sec. Chemical analysis Services Laboratory, Laboratory, Mississaugua, Mississaugua, Ontario, Ontario,Canada Canada Chemical analysis by Technical Services -- Mineral * ~ i n e r aAbbreviations: 4bbmviations: l - - P == plagioclase; HH = hornblende; hornblende; 0Q = quartz; quartz; BB == biotite; biotiteK ; = K K—feldspar; = K-feldspar; M= nI!scovite; EE epidote; w iwscovite: epidote; C C = = chlorite; chlorite; SS— sericite; sericite;S G—= garnet garnet �-16- - TABLE ROCKS TMLE 44 . BULK SULKCHEMICAL CHWICMCOMPOSITIONS CWOSITIfflSOFOMETAVOLCANIC F M€rAVOLCANAND A MMETASEDIMENTARY IETASEDIMEWARY WCS FROM SOUTHFORK FORKOOF THE EAU EAU CCLAIRE FKU SWTH F THE L A M RIVER* RIVERg ===== == 6 .4l 4 fl6 Y8 fl 7829 7829 A 5102 A1203 B 7829 7830 F E 7831 7832 B 56.84 59.48 48.19 61.76 61.60 75.89 82.64 8.51 6.03 4.08 10.40 UO 1.33 1.33 0.76 0.76 '%a 3.43 3.43 3.10 3.10 Fe203+ 7830 C 7.14 6.80 1.22 2.60 FeO Feo CeO MgO Na20 Ma-0 K2O flO2 0.51 MnO 0.05 P205 0.21 L0I LU TOTAL Spec. No. 7.44 7.44 T7T 7.77 7.77 0.60 0.60 3.65 3.65 4.06 4.06 0.06 0.06 0.00 0.00 8.10 8.10 2.03 2.03 2.25 2.25 0.22 0.22 2.23 2.23 4.68 nnn 4.m 3.29 3 . 8 3.38 3 . 2 ~0.16 0.16 0.08 t26 TT t2 t11 tfl tfl t t 0.49 0.65 0.56 0.51 0.24 0.10 0.04 0.09 0.07 0.00 0.01 0.10 0.27 0.21 0.08 0.25 0.00 0.00 & L80 Th 11 98.11 99.39 99.50 100.1 99.74 96.77 99.72 Location Descriotion Description* (7329) (7323) Confluence N. &&S.S. Forks Forks Confluence of of N. of of Eau Eau Claire C l a i mRiver River 5E¼ T26N.R5W R5U SE4 5E¼ SE4 Sec. Sec. 16; 16;T26N. Chioritized, Chloritized. sericitized s e r i c i t i z e d vitric v i t r i andesite c andsite 7829—A 7829-A Same S m as as 7329 7323above above Feldspathic Feldswthic andeslte(?) a n d s i t e ( ? ) tuff tuff 7829—B 7829-6 Same Sme as as 7329 7323above above Coarse feldspathlc tuff Coarse feldspathic 7829—C 7829-C Same Sam as as 7329 7329above above Coarsest. Coarsest, H—bearing, H-Unring. feldspathlc f e l d s w t h i c andesite andesite tuff; P is and tuftClastic Clastic P ibroken s broken andbent; Wt;rocks mcks have have been been strongly strongly sheared, sheared. locally l o c a l l cata— y cataclasis clasisproduced produced interlensing interlensingshear s h n rsurfaces surfaces along fonTled. alongwhich e t c hC C f o W . Fragmented FragmntedH.H. 7830—E 78%-E tuff tuffwith withlensoidal lensoidalP Pand andclasts clastsini fine— n finegrained graiced tuffaceous tuffaceous matrix; thinly t h i n l ylaminated, laminated. bedded. bedded. (Thin (Thin section sectiononly) only) Eau NE¼ 5W& Eau Claire ClaireRiver: River: NE4 S& Gray Way meta—agglomerate mta-agglomerate ( ?(?) ) ssimilar i m i l a rtot oC C Sec. ovoid clasts clasts of strained Sec. 16; 16;T26N, T26N.R5W; R5U; 44meters meters Rounded, Rounded! ovoid strainedQ, Q,P.P , CC (pennine); (wnnine); devitrified & v i t r i f i e d glass(?) glass(?) Matrix meshwork MdtrixIsi as laminated a laminated m s b r kofoffine— finegrained g n i n eQ+P+E—C. d WM-C. west westofo7830—0 f 7830-0 7830—F 78%-F 55meters 7830—E meterswest westof of 7830-E Coarse, Coarse. sheared sheared dacite(?) dacite(?) with' with. bent, bent, broken matrixooff interlensing broken PP and and Q Q In i n E—C E-C matrix interlensing folla, fine—gralned folia,very very fine-gratned crush crushdebris. debris. Some angular fragments S m angular fragnents of strongly stronglyzoned zoned - P.P. Van — U—Pb VanSchnmjs Schms sample s a w l e for forzircon zircon u-Pb dating m.y.) sample 74—VS—ic. dating(1859±20 (1859220 my.) sample 74-vs-lo. Metatuff? Ntatuff? 7831—B 7831-8 Hay Rock Dam HayCreek Cmekbelow belw Rock Dam 7832 7832 County County Hwy. W . HM at a tEau fau Claire Claire H—C quartzite and andpphyilite M-C quartzite h y l l i t e with w i t h kink kinkfolds folds River NE¼ RiverNENEk NE4Sec. Sec. 1:1: on on the the hats l i n b sofofa small a smallanticline a n t i c l i nwhich e which T26N, ~ 2 6R4W ~R .~ U plunges ENE at about 400 plunges ENE a t about m0 * - 514¼ Sec. 15; S& NE¼ NE4 Sec. 15;T26N, T26N.R4W R4U - Sheared Sheared rrhyolite i t y o l i t e (?) (?Icontains containspolygranular polygranula~ lenses matrix of Q4K+M lensesofo Q f Qini an laminated a laminated matrix of WKM - - Chemical memical Analysis Analysis by by Technical Technical Services Services Laboratory, Laboratory, Mississaugau, Mississaugau, Ontario, O n t a ~ i oCanada , Canada Mineral MineralAbbreviations: Abbreviations P P plagioclase; plagioclase;H — H hornblende; hornblende;Q Q =quartz; quartz; B8==biotite; b i o t i t eK; =KK—feldspar; = K-feldspar; N M= =muscovite; mscovite; E E= epidote; epidote;C C =chlorite; chlorite; SS ==sericite; s e r i c i t e0 ; = G garnet garnet �—17— - TABLE BULKCHEMICAL CHEHICALCOMPOSITIONS CtXPOSITIONS OF OF TONALITES* TWALITES* TABLE S5 - BULK 7906 A 5402 A1203 Fe203+ == 7922 7923 A 7927 7927 0—2 N—2 7952 —— B 64.52 64.71 56.79 61.05 66.81 64.79 16.39 16.56 16.73 16.00 15.18 16.69 4S8 8.40 7.18 tTh FeO 5.93 6.48 4.91 MgO 4.28 2.27 3.43 3.81 1,74 1.82 Na20 3.79 3.89 2.93 3.34 3.98 4.52 (20 T402 2.29 2.11 2.10 1.37 1.23 1.41 0.62 0.43 0.67 0.68 0.06 0.06 0.14 0.11 0.53 0.05 0.36 0.04 9 0.25 0.18 0.11 MnO 0.20 P205 L0I TOTAL 5 0.17 fl 0.19 ] 100.3 99.14 98.23 100.5 100.2 98.07 Wissota Uissota Dam, Dm. Chippewa C h i p w a R. R. NE¼ Sec. 3; NEk NIJJ¼ w% k. 3; T28t1 T2&i 7906—A 7906-A T2 ..ucation a Spec. Swc. No. No. 4.05 4.28 2.24 CaD Description Description ** * B—H tonalite flow lineation; lineation; 6-H t o n a l i t e w with i t h s slight l i g h t flow not not sheared sheared WN R8W Fisher Fishev River River Sec. W . 4; 4; T31N, 131N. 7922 7922 SW¼ Sk% Sl.P Sh R6N R6W Fisher Fisher River River 5W¼ Sec.4; 4; T31N, S+! SSW¼ Uk Sw. T31N. 7923—A 7923-A R6W R6W 7927—0—2 79274-2 Gneissic Gneissic 6B ttonalite o n a l i t e protorriylonite p m t m y l o n i t e with w i t h fljIl blebs (20%); (20%); contains contains occasional occasional xenoliths xenoliths of o f feldspathic feldspathic rock rock (adamellite?) ladamcllite?) - Banded, gneissic H-B H—B tonalite; xenolith xenolith tonalite; Banded, gneissic ( ? ) BB == 10%; 10%; i n adamellite adamellits or o r granodiorite granodiorite (?) in 15%; E = 2% E 2% H = 30%; 30%; P P == 35%; 35%; 0Q matrixf ofor Little L i t t l eFalls, Falls,Eau EauClaire Claire Gneissic Gneissic P—H—B P-H-B t o ntonalite a l i t e matrix r iintrusion ntwsion H— River Sec. 19; River SW¼ Sbh ti%W4 Sec. 19; breccia brecciacontaining containingabundant, abundant,elongated elongated HT27rJ, T27tl. Rib! R7U rich r i c h xenoliths xenoliths - 7927—N—2 7927-N-2 Little ( 7 ) PP L i t t l eFalls, Falls,Eau EauClaire Claire Massive tkssive HHt otonalite n a l i t e or o r trondhjemite t m n d h j m i t e (?) matrIx (63%) not twinned; twinned; QQ = 21%; 21%; H = 13%; 13%; matrix (63%) River River SW¼,NbP, Sec.l9, T27N,R7W W.W, Sec.19. T27N.R7M for f o r H—rich H-rich xenoliths xenoliths 7952—B 7952-6 gnelssic H-B H—B tonalite; llocally Jim Jim Falls; Falls;Chippewa Chippewa River River Sheared Sheared gneissic tonalite; o c a l l yconcontainslenses lensesand andbands bandsofofH—schist H-schist and anddike— dikeME¼,NEk. NE¼.Sec. Sec. 30; N&, 30; 13CM, TDN, tains pegmatite p e g m t i t emasses musses Ren R8W * Chemical analyses Sewice Laboratory, Laboratory, Mississaugua, Mississaugua, Ontario, Ontario,Canada Canada Chemical analyses b.v by Technical Technical Service ** * Mineral Abbreviations: Abbreviations: P P = plagloclase; plagiwlase; HH==hornblende; hornblende; 0Q = quartz; quartz; B = bbiotite: i o t i t e : KK == Kfeldspar; K.fe1dspar; NI4 == muscovite; muscovite; EE epidote; epidote; C C = chlorite; S S = sericite; sericfte; SG= garnet garnet -- - - �-18- - TABLE OF TABLE 66— BULK BULKCHEMICAL CHCNICAl ANALYSES PNALYSES O F TRONDHJEMITES, TROtJDtUEMlTES,, ANDDlQRlTE* DI0RITE* ADNIELLITES. XMELLITES.GABBRO • AND ~~, — — — — 'a aaaa——a AOMLLITE TRONOHJEMITES 7335 7337 77131 7713617830 7905 Al203 Fe203+ 70.22 13.85 70.97 7901 7942 A D C 5102 7906 7425 A GABBRO & DIORITE 7904 A 7945 A 5i 70.62 72.36 71.18 78.27 65.66 72.20 49.45 52.33 15.50 14.10 15.13 13.75 15.52 14.59 15.54 12.00 16.69 14.02 16.30 20.27 3.12 2.09 2.97 2.17 2.49 2,54 2.11 1.68 3.S 2.04 9.11 6.75 FeO Cia 2.95 1.12 2.71 MgO 1.03 Na20 4.39 0.56 4.57 0.96 4.59 3.11 1.34 fl 1.51 K20 7107 Ibt 0.05 P205 0.06 ti 05 29 0.03 0.04 0.01 0.04 1.44 2.61 2.90 2.56 2.56 2.6 2.04 0.42 0.97 0.81 0.71 0.44 2.l 0.68 9.53 8.45 3.05 4.45 4.62 4.84 3.33 4.Of 3.07 2.88 3.59 4.33 1.43 1.45 2.39 tY 1.22 4.05 3.96 0.86 0.96 0.04 0.03 0.03 0.02 0.10 0.02 0.05 0.09 0.09 t fl fl Th Th i fl 0 fl fl Th tä o.3 tTh 0.01 0.05 0.03 0.16 0.00 0.25 0.05 0.25 9.86 5.13 0.24 LOl Th TOTAL 99.57 100.2 99.44 98.54 99.30 100.0 100.0 99.99 100.2 99.01 98.75 100.2 Location Spec. Mo. 0.21 0.59 Descri pti 0n TROMD}43EMITES 7335 Eau Claire River Ew Claire Rivernear m a rmouth mth of d *ippoonqill lhiPPMlWfl1Creek Creek Sit W 5E¼ SE& kSec.18; . 1 8 ; T26M, T2ffl. R5W R5U Gnelssic Leucotonal I te; gteissosity gneissoslty Gneissic LeucotoMlim produced by elmgation elongation of Pmduced by o fAb—rim,*d A b - r i m d PP 7337 Eau Claire River Eau Claire River at a tmouth muth of t.thippoorwill of lhippoolWfl1Creek CNek St Mt Sec.18; T26N, R5W SWa N!& *.I& , l fn f Rm Highly sheared, chloritized, gneissic Highly s h ~ m d .chloritized. gneissic trondhjauite; mcct m m i h j a i t e ; banded. b a M . nylonitized, aylonitized, mechanically intermixed with H—P schists. hanically intemixed with H-P schists. 771 31 EauClaire Claire River Eau River Foliated, Foliatsd, fine—grained, fine-grained, aaplitic p l i t i c BR mu SR Sit WS SPASec.20; SSC.~;127N, 1 2 7 ~RTh . trondhjemi te. tmndhjmite. Eau Claire River Eau Claire River Foliated. H—B Foliated. n-B ttrondhjemite mndhjmite Eau Claire River Eau Claire 0.5 meters 0.5 m t m of of 7830-C 78244 HR SWa St Sec.l6 Ek b . 1 6 west west T26t1. R5W Rm m. Coarse, feldspathic trondhjemites ((Oligoclase O l i w l a s e porphyroclasts p r ~ h m l a s in ~ fine—grained - fim-grained i n matrix m t r l x of of strained strainedQ; Q; laminated) I d n a t e d l Feldspars Feldswrs bent, broken, and Intruded by Q—rich mylonite. h t , bmken. and i n t M by Q-rich aylonite. Cadott Bridge, Yellow Riv. W tt Bridge, Yellan Riv. St MR SWI NEkSec.31; Sec.31;T29N 12%R6W R6U Trondhjnite protomylonite with pmtcwlmite gneiss gndss w ith Trnrdhjcmite E+M+B. and N H altered alteredtoto E m . ovoid PP and Wissota Dam, Riv. Dam. Chippewa Chippea Riv. Uissota trondhjemite: nmjor major rock Gneissic B—H B-M tmndhjmite: rack ttype mbelow belcuWissota MissotaDam. Dm. 7907 Fisher River Fisher River Nit Nit NWa N!&Sec. Sec. 9;9;T3IM, T31N.R6W R6U Gnelssic h e i s s i c M-leucotrondhjmnite. ble!4cotmndhjmite. Accessory Accessory B and andE£ ffort, throughgoingfoliation; foliation; cono m throughwing conB tains round zircons. tains mund zircons. 7942—A Knight Pool, Pool, North off might Nwth Fork Fork o Eau Claire River M u Claire SR NE Sec.l0; SEk See.10; T26H. TZffl.R5W Rm 8—trondhjrclte or granodiortte geiss. 77136 MR St m s!& Sec.20; Sec.20; T27N, n7NR7W . R7U 7830—0 7905-C 7906—D MR N P' Nt nw' Sec.3; sec.3; T28M, T r n ,R8W m m ADAJIELLITE A MLLITE 742S-A Cornell Dam, 7425-A Come11 Dam. Chippewa Chippewa Riv. SR MR SEk NEkSec.l8; See.l& T31M, T31N.R6W MU GAB8i0 W B R O AMU AfiD DIORITE DIDRITE 7904—A Big Bend, 7904-A Bend, Yellow Yellow River River NR NEkSE¼ S& Sec.33; Sec.33; T29H, T29N.R6W R6U LLittle j t t l eFalls, Falls,Eau Eau Claire Claire River SWaNit NWaSec. See. 19; 19: River St T27N. R7W T27N. R7U 7945—A 7945-A * * B—H flaser gneiss gneiss oorr mylonite E M a dadamellite a m l l i t e maser mylonite gneiss with lensoids gneiss lensoid* of of PPand and KKini nQ—rich Q-rich mylonitic matrix; withwith H—P—C mylonitic matrix;interlensed interlensed H-P-6 gneiss and and schist schist gneiss Sheared,foliated, foliated, cataclastic Sheared, cataclasticH—dlorite H-diorite with w i t h B ffoliation o l i a t i o ncut cutbybycataclastic cataclastictone— h a llite i t e"dikes 'dikes. B—H quartzgabbm; gabbro; pmbably probably aa contaminated 0-H quartz antaminat& for,,, ?om of o f H—tonalite. H-halite. chemical analyses by Technical Technical Sewices Services LLaboratories, Ontario, ~ m i c aanalyses l by & x a t o r i e s , Mississaugua, Missjssaugua, Ontario, Canada Canada Mineral Abbreviations: P == plagiwlase; plagioclase; HH = hornblende; quartz; Abbmviations: P hornblende; Q Q == quartz; muscovite; EE a epidote; CC = cchlorite = =K—feldspar; BB == bbiotite; i o t i t e ;K K K-feldspar; NM = mscovite; hlorite sericite; BG •= garnet sS = sericite; garnet - .- �-19— GEOPHYSICS GEOPHYSICS Aeromagnetic quadranglemaps mapsbybyKarl Karl and and Friedel Friedel (1974-1976) Aeromagnetic quadrangle (1974-1976) have have not not been been published published i in n ffinal i n a l form. form. However, maps show However,the the preliminary preliminary maps showimportant important trends, trends, and the patterns patterns help help ttoo identify and the i d e n t i f yand andcorrelate c o r r e l a t eaeromagnetic aeromagnetic signatures signatures with with mapping on the ground. Steep-sidedridges ridges and andtroughs troughselongate elongatepparallel mapping on ground. Steep-sided a r a l l e l to to sstructural t r u c t u r a l grain graincharacterizes characterizesareas areasunderlain underlainbybyscreens screensand and enclaves enclaves of of amphibolite. The The amphibolite amphiboliteterranes terranesare arei in sharp contrast contrast wwith n sharp i t h the splotchy splotchy contour patterns and andlow lowr relief by ggranitic contour patterns e l i e f of o f areas areas underlain underlain by r a n i t i c rocks. rocks. These maps maps were considerable help i n compiling compiling the the generalized generalized geologic geologic map map iin n Figure Figure 1. 1. were ooff considerable help in portion off Wisconsin AA p o r t i o n of o fthe theBouguer Bouguergranity g r a n i t yanomaly anomalymap map o Wisconsin by Ervin Ervin and and Hamer Hamner (1974) has been included included (Figure g )) ffor Note the pronounced (1974) has been (Figure 9 o r reference. reference. Note pronounced ggravity ravity Extendedalong alongi its the "lineament" slope along the t h e Jump Jump River. Extended t s trend trend southwestward, southwestward, the "lineament" follows the t h enorth n o r t hshore shoreofoLake f LakeHolcombe Holcombe and and along the south south side sideofo Flambeau f Flambeau Ridge, whereBarron-type Barron-typeqquartzite are thrown thrown iinto Ridge, where u a r t z i t e conglomerates conglomerates are n t o large l a r g eopen open folds The Barren Barronquartzites quartzites northwest northwest ooff f o l d s which which plunge plunge northwest northwest at a t about about 55°. 55O. The Flarnbeau Ridgeare aret typically Flambeau Ridge y p i c a l l yundeformed. undeformed. lineament trending trending northwesterly AA strong aeromagnetic aeromagnetic lineament northwesterly across across the themouth mouth ooff the the Yellow Yellow River Riveron on the theeast eastend endofo Lake f LakeWissota Wissota isi smatched matched by by aa major major shear shear zoneoof (1976) shows showsseveral several major major northzone f ssimilar i m i l a r trend t r e n d in i n the the rocks rocks there. there. Sims Sims (1976) west-trendingf afaults The Bouguer Bouguer ggravity west-trending u l t s ooff similar s i m i l a r trend. trend. The r a v i t yanomaly anomalymap map shows shows aa maybe bef afaultultllarge a r g e "positive" " p o s i t i v e "anomaly anomaly just j u s t east eastofo Lake f LakeWissota. Wissota. This anomaly anomaly may bounded on tthe bounded on h e west. GE OC H RON OL OGY GEOCHRONOLOGY Major events events iinn the Major the geologic geologic history h i s t o r yofothe f t hChippewa e ChippewaValley Valleyregion regionhave havebeen been compiled Itisi semphasized emphasized t hthat a t t this h i s is is compiled iin n the the chronology chronology presented presented iinn Table Table 7. 7. It Only those thoseage agerelationships relationshipsf ofor whichthere therei sis ffield a tentative t e n t a t i v echronology. chronology. Only r which ield evidence have been included. Zircon U/Pb UIPb dates dates have have been been published published(Van (VanSchmus, Schmus, evidence have been 1980 and Maass Maassand andVan Van Schmus, 1980) rocksi in Valley: (1) 1980 and Schmus, 1980) f o rfor f o four u r rocks n tthe h e Chippewa Chippewa Valley: (1) sheareddacite(?) dacite(?) from volcanic and sedimentaryrocks rocksaatt llocation sheared from the South South Fork Fork volcanic and sedimentary ocation 7830-F (SeeTable Table4 4f ofor description). Age ± 20 m.y.; (2) 1860 + 20 my.; (2)banded banded amphibolite amphibolite 7830-F (See r description). Age == 1860 Age==1850 1850+ +20 m.y.;(7) (3) ffoliated Stop 1. from Big Falls, Stop f r o m Big 1. Age 20 my.; o l i a t e d hornblende hornblende ttonalite onalite Age == 1847 1847+ 10 m m.y.; ffrom r o m LLittle i t t l e Falls, Falls, Stop Stop 2. 2. Age + 10 y . ;and and (4) (4) trondhjemite trondhjemiteataChippewa t Chippewa Age == 1830 Falls 1830 j^± 15 m.y. m.y. F a l l sDam. Dam. Age amphibolite( u(unit Cumings)i sis only only 1850 1850m.y. m.y.old, old,iitt IIffthe t h e banded banded amphibolite n i t ##1 l oof f Cuimn'ngs) whenwhen two two episodes of metamorphism wwill i l lbe bevery verydifficult d i f f i c utol texplain t o explain episodes o f metamorphismand and deformation deformation Van Schmus Schmus(1980, (1980, p. 3) precedingi nintrusion the LLittle preceding t r u s i o n oof f the i t t l eFp.lls F a l l s Tonalite Tonalite took took place. place. Van states that, "In theBig BigFFalls thep opossibility states that, " I n the the case case oof f the a l l s z zircon i r c o n the s s i b i l i t y s still t i l l exists exists m.y. ago tthat h a t they theyare aremetamorphic, metamorphic, formed formedduring duringthe thePenokean PenokeanOrogeny Orogeny about about 1850 1850 m.y. ago (Van Schmus, Schmus,1980) 1980)and and thegneiss gneiss iis (Van t hthat a t the s Archean, Archean, bbut u t for f o rthe thepresent presenta Penokean a Penokean are iinclined We are n c l i n e d from from abundant abundant ffield i e l devidence evidenceata many t many primary age agei is preferred." We primary s preferred." other places places tto o support support the contention contention tthat h a t the t h e age age of o f the the amphibolites amphibolites at a t Big Big Falls F a l l s - and andelsewhere elsewhere throughout throughout the the CAC CAC - is i sArchean. Archean. - - - BIG FALLS LITTLEFALLS FALLSAREA AREA- INTRODUCTION - INTRODUCTION FALLS - LITTLE generalized geologic geologic map mapo of the Big Big FFalls—Little AA generalized f the a l l s - L i t t l e Falls F a l l sarea area(Figure (Figure10) 1 0 )shows shows that the rock units occur in bands trending west—northwest. It is suggested t h a t the rock u n i t s occur i n bands trending west-northwest. It i s suggested t hthat a t iiff the mafic mafic hornblende hornblende sschist c h i s t underlies the the feldspathic feldspathichornblende hornblende gneiss gneiss (layered (layered gabbro), the symetry of the units indicates an overturned anticline gabbro), the symnetry o f u n i t s indicates an overturned a n t i c l i n e cored cored iin n part part by the hornblende tonalite intrusion breccia. Later faulting has modified this by the hornblende tonal i t e i n t r u s i o n breccia. Later f a u l t i n g has modified t h i s The biotite-hornblende-epidote-chlorite biotite-hornblende-epidote-chlorite schists structure. The schistsmay may be be the the substrate substrate for f o r the thelayered layeredgabbro. gabbro. - �0 -- - - - IA C F(amo au R /1/ d N r1 }4 • '[ P-2- E-W-CA -l • ::\- tesafs __ç'.- TEt C1T r / L2) /• A /çL•.Zt_C Figure 9 —--—( • R E \N // -__ -__ / -:\ , } 2O ) 7 •7/ /r7, -- Bouguer anomaly gravity map of the Chippewa Valley region from Ervin and Hamer, 1974. �—21— - TABLE TABLE 77 - TENTATIVE CHRONOLOGY THE CHIPPEWA TENTATIVE CHRONOLOGY FFOR OR THE CHIPPEWA VALLEY VALLEY REGION REGION ———UNCONFORMITYUNCONFORMITY— Erosion, regional Erosion, j o i n t ijointing, n g , regional up1uplift ift —————--——--'-———"— I Fourth Deformation, Deformation,Block Blockf faulting Fourth a u l t i n g along along northwest-trending northwest-trending faults. Holcombe Taults. HolcombeDam, Dam, Lake Lake Wissota. Wissota. - IIntrusion n t r u s i o n of o fleucotronchjemite leucotronchjemiteveins, veins, Lake LakeWissota ~issota 1100mm.y. IIntrusion n t r u s i o n of o fgabbro-diabase gabbro-diabase dikes dikes throughout throughout region; region; ENE ENE trends trends (?) 1100 y . (?) C.UNCONF0RMITY Erosion — removal severalkilometers kilometers of Erosion removal o f ofseveral o f rock UNCONFORMITY —.r IThird T h i r d Deformation, Deformation, Cataclasis, Cataclasis,and andGreenschist GreenschistFacies FaciesMetamorphism Metamor~hism Largescale scale open openf ofolding ancfTical drag ffolding associated with Large l d i n g a n d x c a l drag o l d i n g a s s .------mylonitization; formation s t r i ke-sl i p faulting f a u l t i n gand and widespread widespread mylonitization; formation of andSouth South o f garnet, garnet, chlorite, c h l o r i t e ,and andepidote epidoteini amphibolites n amphibol itesand P Fork, Jump River volcanic volcanic and sedimentary series. series. I Fork, Jump River and sedimentary Aplite pegmatited idike A p l i t e and and pegmatite k e i nintrusion t r u s i o n ( L(Little i t t l e Falls, F a l l s , Jim Jim Falls) Falls) 25 m.y.* 1824 Fa1I sWissota , WissotaDam Dam (dikes) (dikes) IIntrusion n t r u s i o n of o f "Lineated "Lineated tonalite", tonal i t e " ,Jim JimFalls, Late Kinematic Kinematici intrusion Late n t r u s i o n of o f gabbro, gabbro, Yellow Yellow River River (Stop (Stop 8) 8) S 1830 ± 15 p•y* IIntrusion n t r u s i o n of o f trondhjemite, trondhjemite, granodiorite, granodiorite, adamellite, Lake adamel 1ite, Lake Wissota, Chippewa ChippewaFa1 Falls, Fisher River River (leucotrondhjemite) Wissota, l s , Fisher (leucotrondhjemi t e ) Main Main Cpulse ooff pplutonic pulse l u t o n i c aactivity. c t i v i t y . Intrusion I n t r u s i o nofo composite f composite batholiths batholiths along the axis along axis ofo the f thePenokean Penokean orogen. orogen. .4 CBreccia, LLittle 1842 ± 20 m.y.* Intrusion I n t r u s i o n ooff "Foliated "Foliated Tonalite" Tonalite" Breccia, i t t l e Falls, Falls, Cadott. Cadott. Synkinematic intrusion under high compression and the prepreSynkinematic i n t r u s i o n under compression and i nin the sence of a steep geothermal gradient. Formation of Little sence o f a steep geothermal gradient. Formation o f L i t t l e Falls Falls and Fisher Fisher River River breccias, breccias, and and possibly possibly the the breccia breccia aatt Cadott. and Cadott. 20 m.y.* Volcanism Volcanism and andSedimentation: Sedimentation: deposition deposition of 1860 o fSouth SouthFork Forkand andJump Jump River volcanic volcanic and and sedimentary sedimentary rocks rocks as as part p a r t of o fthe theFlambeau Flambeau and Black Black River River volcanic volcanic provinces. and provinces. - 0 - a UN CONFORMITY SecondDeformation, Deformation, Cataclasis, and Second andRegional RegionalMetamorphism Metamorphism Strike—slip S t r i k e - s l i ~f afaulting, u l t i n g . iocaliized l o c a l l i z e d cataclasis, cataclasis. formation formation ooff tectonic open (F-2) (F-2) open open folds, folds, development development oof fte ctonic ttight, i g h t , open breccias by differential breccias d i f f e r e n t i amovement l movement along along shear shear planes; planes; iintrafolial n t r a f o l i a folds.Subsequent l folds.Subsequent erosion. erosion. IIntrusion n t r u s i o n of o f trondhjemite trondhjemite (Cadott, (Cadott, Jim Jim Falls) F a l l s )and and Granite Granite ((Little L i t t l e Falls) Falls) First F i r s tDeformation Deformationand andMetamorphism Metamorphism w i t haxial a x i aplane l planeshearing, shearing, displacement; displacement; IIsoclinal s o c l i n a l folding f o l d i n g(F—i) (1-1 ) with formation ooff garnet (Big FFails). formation garnet porphyroblasts porphyroblasts (Big alls). Intrusion I n t r u s i o n and and ggravity r a v i t y ddifferentiation i f f e r e n t i a t i o nof o fBig BigFalls F a l l sgabbro gabbro For details, see For see Table Table 8. 8. —1 * Van Van Schmus, Schmus , 1980 1980 Basaltic Volcanism Basaltic Volcanism and and Sedimentation Sedimentation �IA ib '7 b 1'. A 9 P. E. Myers Mat Ic hornblende schist ? Kilometers BiotUe - hornbIende — epidote—chiorite schist Feidspothlc hornblende gneiss Hornblende tonolite Intrusion breccia Pegmotite Diabase EXPLANATION Figure 10-- Geologic map of the Eau Claire River including the Big Falls and Little Fans areas. thg SI N) N) �-23- —23— STOP STOP #1 fl :\T: TITLE: TITLE: - GEOLOGY BIG FALLS GEOLOGY OOF F BIG FALLSCOUNTY COUNTY PARK, PARK, EAU EAUCLAIRE CLAIRECOUNTY, COUNTY,WISCONSIN WISCONSIN LOCATION: LOCATION: Eau Claire ¼, SEC. SEC.13, 13, T. T. 27N., Claire Eau C l a i r e River, River,NW NH ¼, %, SE SE \, 27N., R. R. SW, 8U, Eau Eau C laire County County I935 - 925 ..Tiii 1 1' \:. :f t—\ / \C AUTHOR: AUTHOR: M.L. M.L. Cumings Cunnings DATE: DATE : - March, March, 1980 1980 -/———r i / - / - -— - — — — -r - SUMMARY OF SUIWARY O F FEATURES: FEATURES: The rocks aatt BBig Falls Parkare areppart The rocks ig F a l l s County County Park a r t oof f aa ddifferentiated i f f e r e n t i a t e d mafic mafic intrusive igneous compositional compositional banding banding i n t r u s i v eofo Early f E a r lPrecambrian y Precambrianage. age. Primary igneous is Rocks iinn the thearea areahave havebeen beendeformed deformed and and metametai s present present iin n aall l l units. u n i t s . Rocks morphosed three times times producing producing complex morphosed three complex rrelations e l a t i o n sbetween between primary primary igneous igneous structures structures and and structures structuresformed formed by by tectonic t e c t o n i cprocesses. processes. INTRODUCTION: INTRODUCTION: The outcroppings ooff Precambrian rocks aatt Big northThe outcroppings Precambrian rocks B i g Falls F a l l sCounty County Park Park ini nnorth— central Eau Claire County, Wisconsin, record a complex geologic Eau C l a i r e County, Wisconsin, record a complex geologic h history i s t o r y ffor or the west-central west-central Wisconsin Wisconsin area. area. Although Although on on ffirst i r s tinspection, inspection, the thegeology geology seems seems r erelatively l a t i v e l y straightforward, aacloser closerexamination examination reveals reveals evidence evidence ffor or possibly three periods of deformation and metamorphism and three possibly three periods o f deformation and metamorphism and three llate a t e stage stage apparentlong longgeologic geologichhistory recordedi inthe fault f a u l t sets. sets. The The apparent i s t o r y recorded n t h e rocks rocks sugsuggests that the Big Falls area and at least parts of the west-central gests t h a t the B i g F a l l s area and a t l e a s t p a r t s o f the west-centralWisconWisconsin s i n area area are are underlain underlainby byrocks rocksofo Archean f Archean age, age, possibly possiblyearly e a r l yArchean Archean age. age. �Figure 11 -- Outcrop geologic map of the Big Falls area, Eau Claire County, Wisconsin 6' 4Oteet transitional gnelss teldspathic gneiss omphlboflte schlst diobose dike bonded ntIbd lie gneiss EXPLANATION I a �-25- The outcrops aatt Big The outcrops B i g Falls F a l l sare arethe themost mostextensive extensiveand andbest bestexposed exposed outcrops of a differentiated mafic intrusive of unknown size. o ~ t c r o p so f a d i f f e r e n t i a t e d mafic i n t r u s i v e o f unknown size. Outcrops Outcrops of 3.5 km km up up river r i v e rfrom from Big Big of the the intrusive i n t r u s i v eare arefound foundfor f o approximately r approximately 3.5 Falls F a l l s tot oapproximately approximately44km kmdown down river r i v e r(Cumings (Cumingsand andMyers, Myers, 1978). 1978). The The intrusive contains anorthosites, gabbroic anorthosites, gabbros i n t r u s i v e contains anorthosi tes, gabbroic anorthosi tes, gabbros and and mafic mafic cumulates. cumulates. Mostly Mostly anorthositic a n o r t h o s i t i c rocks rocks crop crop out out down down rriver i v e r from from Big Big Falls; Falls; Besides representing gabbroic to mafic cumulates crop out upstream. gabbroic t o mafic cumulates crop out upstream. Besides representing the the best the intrusive, include examples best exposures exposures oof f the i n t r u s i v e , the theBig BigFalls F a l loutcrops s outcrops include examples of rock uunits o f the the major major rock n i t s ooff the the intrusive. intrusive. PREVIOUS PREVIOUSWORK: NORK: Big studied in west—central B i g Falls F a l l swas was one one of o f the the first f i r sareas t areas studied i n west-centralWisconsin Wisconsin mappedi ninddetail (Cummings, (Cumings, 1971). 1971). The The area area was was mapped e t a i l and and preliminary preliminarychemical chemical data data was was presented presented by byCumings Cumingsand andMyers Myers(1974) (1974)and andCummings Cummings (1975). (1975). An An expanded studya1along theEau EauC Claire RiverVal Valley the extent expanded study ong the l a i r e River 1ey iin n which which the extent of of exposure mapped, exoosure ooff the differentiated d i f f e r e n t i a t e dintrusive i n t r u s i vwas e was mapped, was was reported reportedby by these eearlier Cummings and Myers Myers (1978). This Cumings and This paper paper has has drawn drawn ffrom r o m these a r l i e rworks works but b u t also also presents presents new new interpretations i n t e r p r e t a t i o n sand andreexamines reexamines eearlier a r l i e r conclusions. conclusions. ROCK ROCK UNITS: UNITS: The byf four lithologies The ddifferentiated i f f e r e n t i a t e d intrusive i n t r u s i v e is i srepresented represented by o u r 11 thologies at at Big Big Falls F a l l s (Figure (Figure11). 11).The Theunits u n i t sare arerecognized recognizedby bythe thepercentage percentage of of hornblende and pplagioclase, hornblende and l agiocl ase, and and the the prominence prominence of o f compositional compositional banding. banding. hornblende—rich alternating Unit t e r n a t i ng U n i t 11 is i sdistinctly d i s t i n c t banded l y bandedwith with hornblende-rich bands bands a1 with The unit u n i thas has been been called c a l l e daabanded banded amphibolite amphibolite w i t h plagioclase-rich plagioclase-richbands. bands. The gneiss Myers, 1974) emphasized gneiss (Cumings, (Cumings, 1975, 1975,Cummings Cumings and and Myers, 1974) but b u t iti must t mustbebe emphasized that to tmetamort h a t the the banding banding is i s inherited i n h e r i t e dfrom from the the protolith p r o t o l i t and h andisi not s n odue t due o metamorphic differentiation. f r o m local local phic d i f f e r e n t i a t i o n . Unit U n i t one one is i s found found only only at a t Big Big Falls F a l l sand and from relationships bei ninf fault with the other other three three uunits r e l a t i o n s h i p s appears appears t otobe a u l t contact contact w i t h the n i t s at at garnet porphyroblasts porphyroblastsare areprominent prominenti nin the the uunit Big Coarse garnet n i t occurring occurring Big Falls. Falls. Coarse both both in i nhornblende—rich hornblende-rich and and plagioclase—rich plagioclase-rich compositional compositional bands. bands. Units Units 2, 2, 3, 3, and and 44 are are stratigraphically s t r a t i g r a p h i c a l lcontinuous y continuousand andare arerepresenrepresen- tative compositional banding t a t i v eofoapparent f apparentmesoscopic mesoscopicand andmegascopic megascopic compositional banding iinn the the intrusive. intrusive. Unit i sdark dark green green to t o black, black, finely-banded finely-banded amphibolite amphibolite sschist c h i s t of OT U n i t 22 is unit The tthird h i r d unit u n i t is i s .2.3 2.3 m m thick thick unit 2 2 to t o an an anorthositic a n o r t h o s i t i c uunit n i t in i n unit u n i t 4. 4. The and has sharp sharp contacts contacts against against units and has u n i t s 22 and and 4. 4. The The uunit n i t isi sbest bestexposed exposed on on the island i.suniform uniform along along sstrike, t r i k e , however however iitt isi sabsent absent i s l a n d where where i its t s width is or greatly disrupted on the north and south banks of o r g r e a t l y disrupted on the north and south banks o f the river r i v e rbecause because of of faulting. faulting. The The tthird h i r d unit u n i t is i stransitional t r a n s i t i o n a lfrom fromthe the amphibolite amphibolite sschist c h i s t ooff unit u n i t 22 to t o an an anorthositic The tthird h i r d unit u n i tisi s2.3 2.3m mthick t h i c and k andhas hassharp sharp concona n o r t h o s i t i c uunit n i t in i n unit u n i t 4. 4. The on the the island The uunit n i t is i sbest bestexposed exposed on i s l a n d where where iits ts tacts t a c t s against against units u n i t s 22and and 4. 4. The width i sabsent absent or o r greatly g r e a t l ydisrupted disrupted on on the the width is i s uniform uniform along along sstrike, t r i k e , however however iitt is north and south banks banksoof the rriver and south f the i v e r because because oof f ffaulting. aulting. The The ffourth o u r t h uunit, n i t , previously previously referred r e f e r r e d to t o as as aa feldspathic feldspathic gneiss, gneiss, is i san an The uunit n i t ranges ranges anorthositic a n o r t h o s i t i c unit u n i tthat t h adisplays t displaysdiffuse d i f f u scomposition e compositionbanding. banding. The from anorthosite to from aa gabbroic gabbroic anorthosite t o an an anorthosite. anorthosite. Oneo of themajor majord idifficulties Big One f the f f i c u l t i e s in i n interpreting i n t e r p r e t i n g the the geology geology oof f B i g FFalls a l l s iiss deciding which which structures structures and andtextures texturesare aremetamorphic metamorphic and and which which are are primary primary igneous featuresformed formed during andd idifferentiation f f e r e n t i a t i o n ooff the the intrusive. intrusive. igneous features during c r ycrystallization s t a l 1i z a t i o n and �—26- IGNEOUS FEATURES: PPRIMARY. R I N A R Y . IGr4EOUS FEATURES: The most prominentigneous igneousfeature feature iiss compositional All The m s t prominent compositional banding. banding. All rock units display such banding and each of the rock units is, in rock units display such banding and each o f the rock u n i t s i s , i n i titself, self, a compositional layer layer ooff the a compositional the larger l a r g e r intrusive. intrusive. Individual horn— Compositional bandsare arebest bestdisplayed displayedi ninuunit hornCompositional bands n i t 1. 1. Individual blende-rich bands range from 0.6 cm to nearly 20 cm thick and alternate alternate blende-rich bands range f r o m 0.6 cm t o nearly 20 cm t h i c k and Bandsare are generally generally with plagioclase-rich thick. Bands with plagioclase-rich bands bands 0.6 0.6 cm cm tto o 30 30 cms cms thick. uniform in thickness along strike but individual bands cannot be uniform i n thickness along s t r i k e but individual bands cannot be traced traced the crude mesoscopic inesoscopic the length length ooff the the outcrop outcrop because because o fofl alate t e ffaults. a u l t s . AA crude banding is also present; feldspar—rich bands are prominent nearthe ther river, banding i s also present; feldspar-rich bands are prominent near iver, but thickness of but the the number number and and thickness o fhornblende—rich hornblende-rich bands bands increases increases away away from from the river. the r i v e r . Compositionalbanding banding not as as obvious obviousasasi ninuunit Compositional i n in u nunit i t 2 2i sis not n i t 1, 1, but but Fine—scale banding (<.5 cm) may be metamorphically iiss nonetheless nonetheless present. present. Fine-scale banding (< .5 cm) may be produced, however howeverbands bands greaterthan than15 15cm cmt hthick are believed primary. i c k are primary. The The produced, greater more mafic layers, possibly representing clinopyroxene olivine m r e mafic layers, possibly representing clinopyroxene o l i v i n ecumulates, cumulates, contain 60 contain 60 to t o 90 90 percent percent hornblende. hornblende. Cumingtonite—garnet—hornblende Cumningtoni te-garnet-hornblende layers may represent olivine, m y represent olivine, orthopyroxene orthopyroxenecumulates. cumulates. The The mesoscopic inesoscopic Someoof compositional bands can be easily traced through the park. f the compositional bands can be e a s i l y traced through the park. Some mesoscopic bands are characterized by fine-scale bands of plagioclase msoscopic bands are characterized by fine-scale bands o f plagioclase Suchfine-scale fine—scale bands alternating bands areare d i fdifficult f i c u l t tto o trace trace a1 ternating with w i t hhornblende. hornblende. Such becauseooff deformation. because deformation. - The percentage percentage ooff hornblende The fourth fourth unit The u n i tisi sweakly weaklybanded. banded. The hornblende varies varies from band bandt to band, generally generally composing less than than 15 15 percent percent ooff aa given from o band, composing less given band. band. The contact contact zone zonebetween betweenu nunit anduunit The i t 22 and n i t 3 is i sremarkable remarkable for f o raanumber number During crystallization of the intrusive of apparently primary features. During c r y s t a l l i z a t i o n o f the intrusive o f apparently primary features. blocks ooff already already ccrystallized to the the ffloor blocks r y s t a l l i z e d material material apparently apparently dropped dropped t o loor by crystals accumulating there. of the intrusive and were buried by the c r y s t a l s accumulating there. Three Three i n t r u s i v e and were buried o f the exampleso of blockshave havebeen beenfound. found.Figure Figure1212i sisaafeldspar-rich feldspar—richcclast examples f blocks l a s t that that The iinternal displays internal displays i n t e r n a lcompositional compositional banding. banding. The n t e r n a l banding banding iiss truncated truncated by banding bandingi in the more moremafic maficenclosing enclosingrock, rock, folds folds in by n the i n the theclast c l a smay t mayhave have Two examples examplesoof hornblende—richcclasts been produced producedbybyl alater been t e r deformation. deformation. Two f hornblende-rich lasts casethe the cclast have been been discovered. discovered. IInn each have each case l a s t is i s clearly c l e a r l ymore m r e mafic mafic than than the enclosing rock. banding iiss not n o t present present in i neither e i t h e rsample. sample. the rock. Internal banding Although the clasts clasts have havebeen beenf l aflattened in the the plane planeooff sschistosity Although the ttened i n c h i s t o s i t y they they can can of be recognized recognizedas asclasts clasts formed formed during during magmatic magmaticc rcrystallization. Blocks of be y s t a l l i z a t i o n . Blocks earlier r o m ddifferent i f f e r e n t sstratigraphic t r a t i g r a p h i c units u n i t s of of e a r l i e r crystallized c r y s t a l l i z e d materials materials ffrom differentiated differentiated mafic maficintrusives intrusiveshave havebeen been noted noted in i nmajorcomplexes, m j o r complexes, including including the Bushveld the Stillwater Bushveld Complex Complex (Willemse, (Willemse, 1969 1969 )) and and the S t i l l w a t e rComplex Complex (Hess, (Hess, 1960). 1960). Anotherfeature featurenear nearthe thecontact contactbetween between and Another u nunit it 2 2 and u nunit i t 3 3i sisi illusllusstrongly contorted trated 3. AA strongly contortedband band approximately approximately 0.3 0.3 mm wide wide can. can t r a t e d in i n figure f i g u r e 3. be traced across the island. The width and andthe ther relative be traced across the The width e l a t i v e stratigraphic axesoof approximately uniform. uniform. The level of o fthe theband bandare areapproximately The axes f ffolds o l d s in i nthe theband band are apparently random,and andlimbs limbsare arecomnonly comonlytruncated truncated against against limbs limbs of are apparently random, of other folds. The other The ffold o l d axes axes do do not coincide coincide with w i t h any any deformation d e f o m t i o n features features observedi in the enclosing rocks. Apparently Apparently the the material material represents soft observed n the reoresents soft sediment thecrystals crystals tthat thef lfloor sediment ddeformation e f o m t i o n o fofthe h a t accumulated accumulated ononthe o o r ooff the the magma chamber during crystallization. magma chamber during crystal1 ization. Slumpage Slum~ageo of f eearly a r l y formed formed ccrystals rystals on havebeen beentriggered triggeredby by convection convection iin n the cooling cooling on the chamber chamber f lfloor o o r may may have magma earthquakes during the intrusive. magma o r or earthquakes during c r ycrystallization s t a l l i z a t i o n oof f the �-27— The apparentlyprimary primary cclasts features in The abundance abundance o of f apparently l a s t s and and slump slump features i n the the contact betweenu unit anduunit lack of n i t 33 and and the the apparent apparemt lack o f such such features features contact zone zone between n i t 22 and in outcrop i n the the rest r e s tofo the f the outcroparea areasuggests suggests either e i t h e raaslow slowrate r a t eofoaccumulation f accumulation of o f crystals c r y s t a l sononthe thechamber chamber floor f l o o rallowing allowingsuch suchfeatures featurestot appear o appearconcenconcen- trated off tect r a t e d over over a a thin t h i n stratigraphic s t r a t i g r a p h i c zone, zone, or o r might might indicate i n d i c a t e aa period period o tectonic t o n i c instability i n s t a b i l i tduring y duringwhich whichblocks blocks of o fcrystalline c r y s t a l l i n material e materialdropped dropped to t o the the floor chamber f l o o rofo the f the chamberand and slumpage s l umpage ooff unconsolidated unconsolidated ccrystals r y s t a l s occurred. occurred. TECTONIC TECTONIC FEATURES: FEATURES: Polymetamorphism and make the geologic p opolydeformation l y d e f o m t i o n make i n t interpretation e r p r e t a t i o n oof f the geologic Polymetamorphism and the rocks evolution evolution oof f BBig i g FFalls a l l s ddifficult. i f f i c u l t . The The response response ooff the rocks to t odeformation deformation and metamorphism under varyingconditions conditionshas hasproduced produceda awide widev variety and metamorphism under varying a r i e t y ooff structural s t r u c t u r a land and mineralogical mineralogical features. features. One the important features of One oof f the important features of the the rock rock is i s that t h a t the the intensity i n t e n s i t yofo dislocative f d i s l o c a t i v edeformation deformation is i snot n o tconstant constant rocks are are adjacent throughout throughout the the area. area. Intensely Intensely deformed deformed rocks adjacent to t o rocks rocks conconThe deformational and metamorphic taining primary igneous features. t a i n i n g primary igneous features. The deformational and metamorphic history h i s t o r yofo fthe thearea areahas hasbeen been reconstructed reconstructed from from tthin h i n section section analysis analysis coupled with interpretation of structures observed in l e d w i t h i n t e r p r e t a t i o n o f structures observed i n outcrop. outcrop. The features are are the the coarse garnet porhe oldest apparent apparent metamorphic metamorphic features coarse garnet phyroblasts whichoccur occuri nin uunit prominentlyi in The garnets garnets and prominently n uunit n i t 1. 1. The phyroblasts which n i t 2 and are are believed believed to t obe beoldest oldestbecause because they theyappear appear to t ohave have been been present present while while younger structures and mineral textures were developing in the younger structures and mineral were developing i n the rocks. rocks. have formed formed aatt the Highly elongatedi sisoclinal Highly elongated o c l i n a l ffolds o l d s in i n unit u n i t11 may may have the same same time. time. The The aaxial x i a l planes planes of o f such such folds f o l d s are are typically t y p i c a l l ysheared sheared(Figure ( ~ i g u r14.) e14. )Some Some of the structuresfound foundi ninu unit the well—developed well-developed f o fold l d structures n i t 2,2, pparticularly a r t i c u l a r l yon on the the island, island, may may be be of o fthe thesame sameage. age. Folding preceded preceded f faulting. a u l t i n g . The The ffaults aults cross lowangle angle(probably (probablyemphasized emphasized by by cross the the compositional compositional banding banding at a taalow later l a t e r flattening) f l a t t e n i n g )producing producing aa pattern pattern that t h a t resembles resembles ccross-stratification r o s s - s t r a t i f i c a t i on (Figure features appear appeart oto be bethe the remnants remnantso of theeearliest (Figure 15). 15). The The above above features f the arliest deformation Deformation, although although intense intense deformation and and metamorphism metamorphism oof f the area. area. Deformation, and pervasive, ddid not features iinn the main and pervasive, id n o t destroy destroy primary primary features the rock. rock. The main deformational features are are found found iin with deformational features n rocks rocks w i t h aa relatively r e l a t i v e l yhigh highpercentage percentage gradeapparently apparentlywas wasi nin the the garnet garnet amphibolite of o f plagioclase. plagioclase. Metamorphic Metamorphic grade a more morebbrittle Faulting late l a t eini nthe thedeformational deformational period period suggests suggests a rittle facies. facies. Faulting behavior behavior iinn the the rock rock after a f t e rhaving havingbehaved behaved in i n aa ductile d u c t i l emanner manner during during the the peak peak of o fmetamorphism. metamorphism. The metamorphism-deformationd idid develop as as extensive aa The second second metamorphism-deformation d nnot o t develop main structures structures appear The main appear to t o be be associated associated suite s u i t e of o fdeformational deformational features. features. The with and eearly w i t h flattening f l a t t e n i n gasasindicated indicatedbybycompositional compositional banding bandin9 and a r l y ffault a u l t planes planes zonesooff ddislocation wrapped aroundgarnet garnet porphyroblasts. Major wrapped around Major zones i s l o c a t i o n are are aa occurs iinn unit minor minor feature of o f the thedeformation; deformation; one one occurs u n i t22where where aashear shear zone zone zonepresents presentsan anexcellent excellent .example exampleoof cuts f ttransposition ransposition The zone cuts the schist. schist. The of compositionally banded o f foliation, f o l i a t i o nwhere , wherepre-existing pre-existing compositionally bandedrocks rocksoccur occuras as tectonic tectonic inclusions inclusions oorr rootless rootless intrafolial i n t r a f o l i afolds l f o l d sin ian strongly a s t r o n g ldeformed y deformed deformational zone meters wide. wide. Locally Locally matrix. The The deformational zone iiss approximately approximately 22 meters matrix. and 2 and foliation some openf ofolds havedeveloped developedi in units some open l d s may may have n u n i t s 11 and 2 and f o l i a t i o ndeveloped developed under amphibolite amphibolite The rock rock was was metamorphosed metamorphosed under particularly p a r t i c u l a r l y in i n unit u n i t 2. 2. The producedaacoarse coarse grained plagioclase— The metamorphism metamorphism produced plagioclasefacies conditions. conditions. The hornblende assemblage and recrystallization of the hornblende assemblage and r e c r y s t a l l i z a t i o n o f the f afault u l t planes planes ooff earlyI n unit u n i t 11 coarse coarse garnet porphyroblasts porphyroblasts apparently apparentlybecame became formed ffaults. a u l t s . In formed �-28- unstable unstable in i n the thepresence presence of o f plagioclase plagioclaseunder underthe thenew newmetamorphic metamorphic conditions conditions and reaction rims of a highly aluminous hornblende developed and reaction rims o f a highly aluminous hornblende develooedbetween between the the two ~ W Ophases. phases. Similar Similar alteration a l t e r a t i o nofo fgarnet garnettot ohornblende hornblende also also occurs occurs iinn unit unit 22 but but is i snot n o tas asreadily r e a d i lobserved y observedini noutcrop outcropbecause because of o fthe thehigh highpercentage percentage of o f amphibole amphibole iin n the the rock. rock. The sequencei sis associated associated w with The tthird h i r ddeformatlonal—metamorphic d e f o m t i o n a l - m e t m r p h i c sequence i t h developdevelopment ment ooff intense intense zones zones ooff deformation defonnation that t h a t occur occur on on the the south south bank bank and and island island and the development weaksschistosity and the development oof f aa weak c h i s t o s i t y oriented orientedNN55 55W. !4. The The main main deformdefomation beenbefore beforer erecrystallization a t i o n appears appears tto o have have been c r y s t a l l i z a t i o n since sinceshear shear zones zones that that developed onthe thei island and south south bank bankare arethoroughly thoroughlyrrecrystallized developed on s l a n d and e c r y s t a l l i z e d and and fine f i n e pervasive pervasive shear shear zones zones iin n unit u n i t11 are are not not only only recrystallized r e c r y s t a l l i z e dbut b u tserved served Although deforas the locus for crystallization of fine—grained garnet. as the locus f o r c r y s t a l l i z a t i o n o f fine-grained garnet. Although deformation features are are not not prominent, prominent,recrystal recrystallization mation features 1i z a t i o n textures textures are areextensive. extensive. The coarse grained The main new mineral to appear was euhedral epidote. The grained The main new mineral t o appear was euhedral plagioclase that t h a thad hadformed formed during during the thesecondmetamorphism second metamorphism r recrystallized e c r y s t a l 1ized grains tthat to clusters ooff fine t o form form clusters f i n e polygonal polygonal grains h a t preserve preserve the the outline o u t l i n eand and recrystallized twinning twinning ooff the original o r i g i n a l plagioclase plagioclase grains. grains. The The recrystal 1ized plagioclase plagioclase is as 10 10 percent percent aanorthite i s variable variableini ncomposition compositionranging rangingas asmuch much as n o r t h i t e content content within I n unit u n i t22the thedevelopment development of of w i t h i n aa single single relict r e l i c tplagioclase plagioclase grain. grain. In prismatic was prismatic hornblende hornblende and and locally l o c a l l yeuhedral euhedralepidote epidote wasaccompanied accompanied by by crystallization c r y s t a l l i z a t i o nofo ffine—grains fine-grains of o f ilmenite ilmenite in i nrelict r e l i ccoarse t coarsehornblende hornblende ilmenite inclusions inclusions are are hhighly the old crystals. Such Such ilmenite i g h l y concentrated concentrated i in n the old grains but but aanarrow narrow inclusion—free inclusion-free band band surrounds surrounds each each grain. Apparently Apparently the third metamorphism occurred under epidote amphibolite facies conditions t h i r d metamorphism occurred under epidote amphiboli t e facies conditions that extensiver recrystallization t h a t produced produced extensive e c r y s t a l l i z a t i o n but b u tdid d i dnot n o completely t completely destroy destroy the coarse second metamorphism. coarse grained grainedtextures texturesproduced producedduring duringthethe second metamorphism. All with A l l younger younger sstructural t r u c t u r a l features features in i nthe therocks rocks are are associated associated w i t h late late casethe thef fault are nnot faults. In I n each each case a u l t planes planes are o t recrystallized r e c r y s t a l l i z e d and and are are the the sites s i t e s of o f alteration a l t e r a t i o n of o fthe therock. rock. A deformation and metamorphism theBig Big FFalls A sunuiary s u m r y ooff deformation and metanmrphism f ofor r the a l l s outcrops outcrops groupingoof deformationalfeatures featuresi sis different different is The grouping f deformational i s presented presented in i n Table Table 1. 1. The than the interpretations presented by Cunrings (1975) in that growth than the interpretations presented by C m i n g s (1975) i n t h a t growth of of garnet porphyroblastsand and therock rock garnet porphyroblasts f o lfolding d i n g o f of the i n into t o t i tight g h t i isoclinal s o c l i n a l folds folds Also the second deformation are included in the first deformation. the second deformation is is are included i n the f i r s t deformation. interpreted more as aa fflattening more as l a t t e n i n g event event than than an an intense intense folding f o l d i n g event event as as previously. the interpretation threemajor majordeformational deformational I n any any case, case, the i n t e r p r e t a t i o nof07three previously. In and metamorphic events has m e t m r p h i c events has not n o tchanged. changed. Relating the events recorded recorded aatt Big the deformational deformational and and metamorphic m e t m r p h i c events Big Falls frameworko fofregional regionaltectonic tectonicaactivity F a l l s to t o the the broader broader framework c t i v i t y is i s not not an an Penokean easy easy task. The The tthird h i r ddeformation deformationisi sapparently apparentlyyounger youngerthan thanthe the Penokean zonesand andr erecrystallization found aatt Big Falls Orogeny. Cataclastic Cataclastic zones c r t a l l i z a t i o n found F a l l s are are also also present present aatt LLittle i t t l eFalls F a l l s(stop (stop2),2 one , onemile m i l east, e east,where whereaa1842 1842 ±2 10 mm.y. 1980)t otonalite y . (Van (Van Schmus, Schmus, 1980) n a l i t e intrusive i n t r u s i v ehas hasexperienced experiencedthe thesame same the tthird deformation andr erecrystallization. deformation and c r y s t a l l i z a t i o n . Possibly Possibly the h i r d event event coincide coincide with with widespread low-grade m.y. (Van widespread low-grade metamorphism metamrphism at a t 1650—1700 1650-1700 m.y. (Van Schmus, Schmus, 1976, 1976, structures Sims, Sins, 1976 1976 i nthe theLake LakeSuperior SuperiorRegion. Region. The The structures )) reported in developed developed aat t tthat h a t time, time, as as seen seen at a t Big BigFalls, Falls,may maynot n obe t beprominent prominentand and shear zones, although althoughpreserving preservingcataclastic cataclastic textures shear zones, textures ini nhand handsample sample are are Big FFalls thoroughly recrystallized. Structures thoroughly recrystallized. Structures produced produced aat t Big a l l s during during the the third be eeasily without great great aattention t h i r d deformation deformation could could be a s i l y overlooked overlooked without t t e n t i o n to to ? �—29— TABLE TABLE 1: 1: Chronology Chronology ffor o r Big Big Falls F a l l sCounty CountyPark Park Intrusion I n t r u s i o n and and ddifferentiation i f f e r e n t i a t i o n of of a a mafic mafic intrusive. intrusive. Slump structures develop developon onthe thef floor Slump structures l o o r of o f the the magma magma chamber chamber and autoliths are produced by tectonic activity. and a u t o l i ths are produced by tectonic a c t i v i t y . First and metamorphism F i r s deformation t deformation and metamrphism Crystallization Crystal1i z a t i o nofofcoarse coarsegarnet garnet porphyroblasts porphyroblasts iinn units units 1 1 and and 2. 2. Isoclinal I s o c l i n a lfolding f o l d i n gand andshearing shearing of o f axial a x i a l planes planes of o f the the developing d e v e l o ~ i n afolds. folds. Faulting. Second Second defdrmation deformationand andmetamorphism metamorphism Flattening F l a t t e n i n gand and development development ooff local l o c a l intensely intenselysheared shearedzones. zones. Minor Minor open open folds f o l d sproduced. produced. Crystallization C r y s t a l l i z a t i o nofofcoarse coarsegrained grainedhornblende hornblende and and plagioclase. plagioclase. Alteration to tan aluminous A l t e r a t i o nofogarnet f garnet o an aluminoushornblende hornblendebecause because of of incompatability between plagioclase p l agiocl ase and and earlier e a r l i e rformed formed garnet. garnet. incompatabil itybetween Third metamorphism T h i r ddeformation deformationand and metamorphism Local deformation,c crystallization Local intense intense cataclasis cataclasis and and deformation, r y s t a l l i z a t i o n of of NS5W N55W s schistosity. chistosity. Growth euhedralepidote, epidote,r erecrystallization Growth oof f euhedral c r y s t a l l i z a t i o n of the the rock rock but but textures are not destroyed. texturesproduced produced during duringthe the2nd 2ndmetamorphism metamorphism are destroyed. Late Late faulting faulting Development lens shaped, fault—boundedstructures structuresi in Development oof f lens shaped, fault-bounded n unit u n i t11 as as unit u n i t11 is i sfaulted f a u l t e dinto i n t oplace placeagainst against unit u n i t2.2. Right—lateral Right-lateral faults faults Left-lateral L e f t - l a t e r a l faults faults �-30- the ffine The second deformation and the i n e details d e t a i l s In i n the the rock. rock. The second deformation and metamorphism metamorphism aatt Big Falls plutonism and metamorphism Big F a l l s coincides coincideswith w i t hregional regional plutonism and metamorphism associated associated with the with thePenokean PenokeanOrogeny. Orogeny. Intense Intense folding folding does does not n o tappear appear to t ohave have occurred occurred aatt Big Big Falls F a l l s at a t this t h i s time. time. Instead Instead aa pronounced pronounced f lflattening a t t e n i n g and and the the developdevelopment The ffirst ment ooff local l o c a lshear shearzones zones are are recorded. recorded. The i r s tdeformation deformationproduced produced 'the the pervasivei sisoclinal pervasive o c l i n a l folding f o l d i n g at a tBig B i gFalls F a l l sand andappears appears tto o represent represent llate ate Archean deformation. Thus Thusthe thei nintrusion andddifferentiation Archean deformation. t r u s i o n and i f f e r e n t i a t l o n of o f the the mafic mafi c intrusive appears to have been an earlier Archean event. i n t r u s i v e appears t o have been an e a r l i e r Archean event. SUMMARY: S UMMARY : The outcropsa at BigFFalls areppart The outcrops t Big a l l s are a r t oof f aa ddifferentiated i f f e r e n t i a t e d mafic mafic intrusive intrusive Claire The iintrusive tthat h a t crops crops out out along along the the Eau Eau C l a i r e River. River. The n t r u s i v ewas was emplaced emplaced during the Archean. Differentiation Archean. D i f f e r e n t i a t i o nproduced produced compositional compositional layering layering and and possible possible tectonic tectonic activity a c t i v i t yduring duringcrystallization crystal 1i z a t i oproduced n producedslump slump structures structures and and autoliths. Three deformational and and metamorphic metamorphic, periods resultedi ninfolding, folding, autoliths. Three deformational periods resulted The first deformation appears faulting and recrystallization of the rocks. f a u l t i n g and r e c r y s t a l l i z a t i o n o f the rocks. The f i r s t deformation appears beenArchean Archean ageand and produced structuresi in ttoo have have been i ninage produced i s o cisoclinal l i n a l f ofold l d structures n aalll l The second deformation occurred during the Penokean Orogeny rock units. rock units. The second deformation occurred during the Penokean Orogeny and The tthird and i is s primarily p r i m a r i l y associated associated wwith i t h fflattening l a t t e n i n g of o f the the area. area. The h i r ddefor— deformation is with regional low—grade i spossibly possiblyassociated associated w i twidespread h widespread regional low-grademetamorphism metamorphism iinn the theLake Lake Superior SuperiorRegion. Region. �—31— I I 2.'.' -- Figure 12 Anorthositic cclast schist. Figure 12 -—Anorthositic l a s t enclosed enclosed iin n amphibolite amphibol i t e schist. betweenuunit and uunit on the the island. island. between n i t 22 and n i t 33 is i s exposed exposed on Contact zone zone I -- 13 -- Possible Figure 13 structure iinn amphibolite Figure Possible slump slump structure amphibolite schist in i n the the contact contact zone zone betweenuunit and uunit as exposed exposedon onthe the island. island. between n i t 33 and n i t 44 as �—32— C Ifl - hornblende— Figure fold structure structure from Figure 14 14—- Sheared Sheared fold from unit u n i t 1. . Black Blackareas areasare are hornblendeporphyroblast rich bands and round object in lower right corner is a garnet rich bands and round object in lower right corner i s a garnet porphyroblast 1 a—- —a- — — w_ — - -c 1.d - -- 15 cn, . Note the similarity similarityto tcross— o crossFigure Earlyformed formedf afault in unit u n i t 1 . Note Figure 15—— 15-- Early u l t in has s t r a t i f i c a t i o nfound foundinin sediments. The The fault f a u lplane t plane hasbeen beenwrapped wrappedaround around stratification sediments. garnet blackroughly roughly circular circular features. garnet porphyroblasts porphyroblasts shown shown asasblack features. 1 �—33— ACKNOWLEDGEMENTS: ACKNOWLEDGEMENTS: The presenti ninterpretation the geology geologyoof BigFFalls The present t e r p r e t a t i o n oof f the f Big a l l s iis s the the result result of with o f years years ofofwork workand anddiscussions discussionswith w i t hmany many people. people. Discussion P. Myers, Myers, Discussion w i t h P. R. Maass, 3. Grant, D. Davidson and participants on several field trips R. Maass, J. Grant, D. Davidson and p a r t i c i p a n t s on several f i e l d t r i p shave have influenced thinking. influenced my my thinking. REFERENCES REFERENCES CITED CITED Cummings, M.L., 1971, 1971, Geology Geologyoof Cumings, M.L., f BBig i g Falls, F a l l s , Wisconsin: Wisconsin: Guidebook, Guidebook, 3rd 3rd Annual Wisconsin State University Geology Field Conference, Annual Wisconsin State University Geology F i e l d Conference, p. p. 13—20. 13-20. Cumings, Cutmnings, M.L., M.L., Myers, Myers, P.E., P.E., 1974, 1974, Geology Geology ooff the the Big Big Falls F a l l sArea: Area: book, Tn-State Geological Conference. book, 38th 38th Annual Annual Tri-State GeologicalField F i e l d Conference. , GuideGuide- Cummings, M.L., 1975, 1975, Petrology Petrology and and sstructure Cumings, M.L., t r u c t u r e of o fPrecambrian Precambrian gneisses gneisses at at Big thesis, University B i g Falls, F a l l s ,Eau EauClaire C l a i r eCounty, County,Wisconsin: Wisconsin: M.S. M.S. thesis, U n i v e r s i t y of of Minnesota, Minnesota, Duluth. Dul uth. Cummings, M.L., Myers, Myers,P.E., P,E., 1978, Cumings, M.L., 1978, Petrology and and geochemistry geochemistry ooff Amphibolites, Amphibolites, Eau Claire Eau C l a i r e River, River,Eau EauClaire C l a i r eCounty, County,Wisconsin: Wisconsin:Cabs) (abs)24th 24thAnnual Annual Institute Lake I n s t i t u t on e on LakeSuperior SuperiorGeology. Geology. Hess, America, Hess, H.H., H.H., 1960, 1960, Stillwater S t i l l w a t eIgneous r IgneousComplex: Complex: Geological Geological Society Society of of America, Memoir 80, p. Memoir 80, p. 225. 225. Sims, 1976, Precambrian Precambrian Tectonic Tectonic and and Mineral Mineral Deposits, Deposits, Lake Lake Superior Superior Sims, P.K., P. K., 1976, Region: Geology, V.V. 71, Region: Economic Economic Geology, 71, p.p.1092-1118. 1092-1118. Van Schmus,1976, 1976,EEarly andMiddle MiddleProterozoic Proterozoic hhistory Van Schmus, a r l y and i s t o r y of of the theGreat GreatLakes Lakes Area, Area, North NorthAmerica: America: Phil. P h i l .Trans. Trans. R.R. Soc. Soc. Long. Long. A. A. 280, 280, p.p.605-628. 605-628. Van 1980, Geol. Geol. Soc. Paper, #180, #180, Goldich GoldichVolume. Volume. Soc. Amer. Amer. Spec. Spec. Paper, Van Schmus, Schmus, 1980, Willemse, J., 1969, 1969,The Thegeology geology ofo fthe theBushveld BushveldIgneous Igneous Complex, Complex, the largest largest Willemse, 3., repository of magmatic ore deposits in the world: in Magmatic repository o f magmatic ore deposits i n the world: i n Magmatic ore ore deposits: GeologyPublishing Publishing Co. Co. p. 1-22. Economic Geology 1-22. deposits: Economic �-35-35STOP STOP #2 #2 TITLE: TITLE: - LITTLE LITTLEFALLS FALLSBRECCIA BRECCIA LOCATION: LOCATION: County HighwayKKaat EauCClaire 1/4, NW 1/4, Sec. t Eau l a i r e River; SW SW 114, NW 114, Sec. 19, 19, County Highway T27N, Fall Creek 77 1/2' T27N. R8W R8W Fa1 1 Creek 1/2' Quadrangle Ouadranal e - T - J' '7. - • AUTHOR: Paul E. Myers DATE: February, 1980 SUMMARY OF FEATURES: Archean basalt, vo.lcanogenic sediments,and andgranite, granite, aafter ? ) basalt, volcanogenic sediments, f t e r being being Archean ((?) deformed andr erecrystallized deformed and c r y s t a l l i z e d aatt least l e a s t twice, twice, were were synkinematically synkinematically intruded intruded by hornblende tonalite about 10m.y. m.y. hornblende tonal i t e tto o form form the t h e Little L i t t l eFalls F a l lbreccia s breccia about1842 1842++10 A f t e r intrusion i n t r u s i o nofo fgranite g r a n i t epegmatites, pegmati t e s , tthe h e rocks rocks ago ago (Van (Van Schmus, Schmus, i in n press). After were again: deformed deformedbybyshearing, shearing,wwith widespread development developmento of were again i t h widespread f ccataclastic atacla s t ic rocks narrow, interlensing,'ENE Most ooff these these rocks and and narrow, i n t e r l e n s i n g , ' ENE to t oWNW-trending WNW-trending ffaults. a u l t s . Most Shallow iintrusion n t r u s i o n of o fdiabase diabase about about faults f a u l t s at a t Little L i t t l eFalls Fa11s are are right-lateral. r i g h t - l a t e r a l . Shallow 1100 m.y. ago agofollowed followedprolonged prolongedup1 uplift the erosion erosion ooff several kilometers 1100 m.y. i f t and and the several kilometers green cclay remaining i in on tthe Pockets oof f green l a y remaining n low low places places on h e amphibolitic amphibolitic o f rocks. rocks. Pockets of terrane were were buried during during marine marine deposition deposition of o fthe t h eMt. Mt.Simon SimonSandstone Sandstone in in Deeply weathered till and outwash southwest the Cambrian time. Deeply weathered t i l l and outwash southwest ooff the Late Cambrian bridge bridge aatt Little L i t t l eFalls Fa11may s mayrepresent represent aa pre-Wisconsin pre-Wisconsin g glaciation l a c i a t i o n oof f tthis h i s region. region. DESCRIPTION: DESCRIPTION: The complexstructures structuresand and texturesi nint hthe The complex textures e L Little i t t l e Falls Fa11s breccia breccia are are mainly a manifestation of a variation in the proportions of plagioclase, mainly a manifestation of a v a r i a t i o n i n the proportions o f plagioclase, B i o t i t e , epidote, epidote,and andchlorite c h l o r i t eare aresparse sparseaccessories. accessories. and hornblende. hornblende. Biotite, quartz, and �-36- Banded amphibdilte, amphibdiite ,composed composed of of45-70% 45-70% hornblende hornblende and and 20-40% 20-40% pl agi ocl a s e plagioclase Banded e xenoliths t h e breccia. breccia. Many make up make upabout about90% 90%ofoft hthe xenol.iths in in the Many of the t h ebanded banded amphibol i t e xenoliths xenoliths contain contain folds foldswhich whichwere were detached detached dduring u r i n g tonalite tonal i t e amphibolite intrusion. However, mostofofthe thexenoliths xenolithsaare elongatedparallel parallel tto intrusion. However, most r e elongated o ttheir heir lamination. ItI tisisnoteworthy xenoliths aat noteworthy that t h a t the t h e amphilolite amphilolite xenoliths t LLittle i t t l e Falls Falls lamination. do not not contain contain garnets, garnets, although a1 though garnetiferous garnetiferousamphibolite amphibol i t eisi sexposed exposed 1/4 1/4 mile mile do enveloping r a r eini the n t h xenoliths e xenoliths(<5%) ( 4 5%)as as iti tisi in s ithe n the enveloping downstream. Biotite B i o t i t eisisrare downstream. tonal i t e tonalite. . U l tramaficxenoliths, xenol i ths,which whicharea rcomposed e composed ofofover over90% 90%greenish greenish gray gray Ultramafic Mg-rich hornbiende hornblende wwith i t h accessory accessory epidote-cl inozoisi t e , and and plagioclase, plagiocl ase, Mg-rich epidote-clinozoisite, make up e s s than t h e breccia. breccia. Their make upl less than 5% 5%ofofthe the xenoliths xenoliths iinn the Theirangular angularshape shape l u s t e r s indicate fragmentation fragmentation and a r t i a l dispersal dispersal of of and occurrence and occurrencei nin cclusters andppartial d u r i n g ttonalite o n a l i t e intrusion. intrusion. This This feature f e a t u r e of of fragmentation fragmentation is is l a r g e r blocks blocks during larger we1 1-displayed at a t Location Location 7927-D 7927-D (Figure 1Q. Some Some ofof tthe h e ultramafic u l tramafic well-displayed (Figure1. xenol i ths show show relict re1 i c tgabbroic gabbroictextures textureswith w i t hprimary primarypyroxene pyroxene apparently apparently xenoliths 7927-N-1) rep1 aced by by metamorphic metamorphic hornblende. (Tab1e 11,,7927-N-i) replaced hornblende. (Table tabular xenolith xenol i t h (?) ( ? ) of offine-grained, fine-grained, foliated f o l i a t e dhornblende hornblende tonalite tonal i t e AA tabular (Table 55 , , 7927-N-2). occurs just east e a s t of ofthe thebridge. bridge. (Table 7927-N-2). occurs aatt the location just AA large of -foliated, bliated, porphyroblastic large fragment fragment of porphyroblastic biotite b i o t i t egranite graniteis iexposed s exposed wasmapped mapped a t Location Location7927-V. 7927-V. The The fragment fragment was i n ind edetail t a i l (Figure 4). 4 ) . The The at granite granite contains contains 1-3 1-3cm cm porphyroblasts porphyroblasts of K—feldspar K-feldspar i nin aa ffoliated o l i a t e d granoblastic granoblastic Sodic piagioclase plagioclase isi s matrix matrix of of microcline, microcline, quartz, quartz, and and brown brown bbiotite. i o t i t e . Sodic Lenticular Lenticular form form of ofthe theK-feldspar K-fel dsparporphyroblasts porphyrobl a s t s indicates indicates The gradational contact contact recrystallization beforeand/or and/or during during cataclasis. catacl asi s . The recrystal 1 i z a t i onbefore between the fragment fragment and andenclosing enclosing breccia breccia iiss marked by an an inward inward substitution substitution marked by between the of of K—feldspar K-feldspar ffor o r plagioclase plagioclase and and bbiotite i o t i t efor f ohornblende r hornblendeand and by by an an increase increase in in gradational contact contact along along aatt lleast abundance of quartz. The The gradational e a s t the the west west side s i d e of of abundance of quartz. the indicatest hthat i s aa xenolith xenolith and and not not aa ffault a u l t slice, s l i c e , although although its its the fragment fragment indicates a t iitt is shape andposition position were probably modified modified by by post-intrusive post-intrusive shearing. shape and were probably shearing. accessory. accessory. about30% 30% The tonalite plagioclase (An_5), ),about The tonal i t eisi composed s composed of 35-40% 35-40% plagiocl ase (An bluish quartz,5-101 5-10% Id aaccessory bl u i s h green green hornblende, hornblende, 25-30% 25-301 quartz, b i biotite, otite, % 5 a c c e ~ ~ epidote, ~epidote, ry is displaysanani nindistinct i sflow-laminated, flow-laminated, and and commonly commonly displays d i s t i n c t lineation 1ineationproduced produced plagioclase/hornblende Large variation ini nplagiociase/hornblende mainly by by hornblende hornblende alignment. a1 ignment. Large mainly The plagioclase plagiocl ase ratio r a t i oindicates indicatesconsiderable considerablecontamination contamination by by amphibolite. amphibol i t e . The commonly displays bent albite twin lamellae, while associated, polygonal commonly displays bent a l b i t e t w i n lame1 l a e , while associated,polygonal crude, transgressive B i o t i t ecommonly commonly produces produces aa crude, transgressive quartz grains grains are a r e unstrained. unstrained. Biotite quartz The biotite may have formed from hornblende during ater f o l i a t i o n . The b i o t i t e may have formed from hornblende during aa llater foliation. deformation. deformation. �—37- EXPLANATION EXPLANATION Hornbrnnd. tonolits QMiS$ Gnsissic tonalit. bmcclo Ultromofic brenda Linuoldal ompitibolite Porpflyroblasllc gmnit• gnslos Bonded oinphibolits Trace of vertical flow lamination Shear zone ihowing dl1acament Plunge of minor fold P E. Myers Figure 16-- Geologic map pointsoof Figure 16-Geologic map o foft hthe e L Little i t t l e Falls F a l l s area area showing showing points f iinterest nterest �:: .,- L ' S , —. -,- \ '- " - 0' -: : — - — — — - .- — -. - - - --.--— - - - — 5— S — — - . -• ,c• - - o — -- - - — ——-—S. - - - -- -O• — — _c. — - —r -_ 0 - — -— . a— - 00 - - .— --:: - -2 - — — - — -- - —\ tonalite biotite granite gneiss in hornblende Figure 17 -- Deformed xenolith of porphyroblastic drag along both in the xenolith shows intrusion breccia (Location 7927-W on Figure 16). Foliation relative Porphyroblasts to the xenalith. edges; indicates north-northeast flowage of tonalite magma are microcline. .. 4r '0 �-40STAGES STAGES IN I N BRECCIA BRECCIA FORMATION: FORMATION: study ooff outcrops showst hthat intrusion AA study o u t c k p s 1like ike that t h a t ata tLocation Location7927-C 79274 shows at in t r u s i o n ooff haveinvolved involved anatexis anatexis i in ttonalite o n a l i t etook tookplace placeunder under stress stress and and may may have n the amphibolite amphibol it e wwith i t h formation formation ooff aa mobile mobile phase phase oof f ttonalite o n a l i t e composition. composition. The following sequence is suggested: The f o l 1owl ng sequence i s suggested : 1) 1) Formationooff veined amphibolitic Formation veined amphibol i t i c gneiss gneiss by bysegregasegregattion i o n (?) ( ? ) of o ffeldspathic feldspathic lamlnae laminae subparallel subparallel to to 7927—C) ooriginal r i g i n a lbanding banding ini nthe theamphibolite amphibo1it (Location e (Location 79274) with w i t h local l o c a l accumulation accumulation ofoft otonalitic n a l i t i c clots c l o t s and and dikedikellike i k emasses, masses, blocks blocks ofo famphibolite amphibol i t became e becamedetached. detached. 2) 2) Partial P a r t i a l fusion fusion of of quartz—feldspar quartz-feldspar ffraction r a c t i o n to t o form form aa tonalitic t o n a l i t i ccrystal c r y s t amush l mushwhich which intruded intrudedacross across ooriginal r i g i n a l layering l a y e r i n gtot oform formbreccia brecciadikes dikes(Location (Location7927-C, 7927-C, Figured 18-A). Figure1'8-A). 3) 3) Detachment,r orotation, and mixing mixing ooff blocks; blocks; throughDetachment* t a t i o n y and throughgoing flowage* flowage,l elenticulation, and ppartial a r t i a l assimilation assimilation going n t i c u l a t i o n * and of Fluidization o f xenoliths xenoliths(Figure (Figure18 18CC and and D). D). F l u i d i z a t i o n of of the xenoliths-rich stress rresulted xenol i t h s - r i c h mixture mixture under under stress e s u l t e d in in development steeply p1 plunging development o of f steeply unging fflow 1ow ffolds. olds . AGE AGE OF OF THE THE BRECCIA BRECCIA A A rrelatively e l a t i v e l yxenolith-free xenol it h - f r e esample sample of o fhornblende hornblende tonalite tonal it efrom f r o m Location Location 7947 was recently recently dated 7947 was datedusing usingU—Pb U-Pb methods methods by Van Van Schmus Schmus ((1980) 1900) . at at If gneissi sis ttruly 1842 ++ 10 m.y. 1842 m.y. I fthe t h e porphyroblastic porphyroblastic gneiss r u l y a xenolith x e n o l i t h in i n the the breccTa, breccTa and and episode episode of o fgranite g r a n i templacement e emplacementand andsubsequent(?) subsequent (?)metamorphism metamorphism must have have preceded precededt hthis The ggranite therefore represent represent aa fragmust i s date. The r a n i t e may may therefore mentoof Archeanc rcrust upfrom fromaaggranitic thetonal tonalite ment f Archean u s t c carried a r r i e d up r a n i t i c basement basement i ninthe it e magma. This This could could indicate i n d i c a t e that t h a t granitic g r a n i t i crocks rocksmay may underlie underliethe theamphibolites amphibolites at a t Little L i t t l e Falls. Falls. PEGMATITE DIKES PEGMATITE DIKES Blotite-muscovite K-feldspar B i o t i te-muscovi t e ggranite r a n i t e pegmatite pegmatite wwith i t h K-fel dspar ccrystals r y s t a l s up up tto o 30 n maximum dimension c u tcut a t at nearly g h t angles 30 cm cmi in maximum dimension nearlyr i right angles across across flow flow lamination in i n enclosing enclosing breccia. breccia. Orientation of o f the the dikes d i kessuggests suggests. that t h a t they theywere were intruded during stress stress release and/or thermal thermalcontraction contractionooff the the intrusion intruded during release and/or intrusion Quartzveins veinsand andlenses lenseso of breccia. Quartz f ssimilar i m i l a r oorientation r i e n t a t i o n and and oorigin r i g i n are are exposeda tatthe theeast eastend endo fofthe theoutcrop outcrophere here Falls. The exposed a tatL iLittle t t l e Falls. The best pegmatite exposurei is where the the one one tto pegmatite exposure s aa Location 7927-Z, 7927-Zy where o three-meter three-meter dike dike contains very contains very large, 1arge bent bent and and marginally marginal 1y crushed crushed K-feldspars. K-fe1 dspars Although A1 though not vvisibly i s i b l y offset o f f s e tby by shear shear zones zones aat t LLittle i t t l e Falls, F a l l s ythe theinternal i n t e r n a deformation l deformation not iinn the the dike' dike indicates indjcates it i twas was intruded intruded prior p r i o rtot omajor majorshearing shearing in i nthe t h eMiddle Middle Precambrian. . , �B. C. D. -- Figure showing textures and theLLittle Figure 18 18 -- Outcrop Outcrop photographs photographs showing textures and s t rstructures u c t u r e s i ninthe ittle Falls Fa11s breccia.(A) breccia. (A) Tonalite Tonal it e breccia breccia dike d i k e cutting c u t t i n g lamination lamination in i n amphibolite amphibol it e at at Location seedetailed d e t a i l e dgeologic geologicmap map in i nFigure Figure19. 19. For detail, detai 1 ,see Location 7927-C. 7927-C. For (B) andsegmented segmented mafic byminor minorfa,ult fault along (B) Sheared Sheared and mafic x exenolith n o l i t h c cut u t by along which which quartz quartz later l a t e r crystallized. c r y s t a l l i z e d . View View east at a tLocation Location7927-W. 7927-W. (C) (C) Mafic Mafic amphibolite amphibolite xenoliths xenoliths in tonalite 7927-W. i n flow-laminated flow-laminated hornblende hornblende tonal it e20 20feet feetnortheast northeastofoLocation f Location 7927-W. XenoXenoliths feldspar content commonly l i t h swith wita h higher a higher feldspar content commonlyshow show more more plastic p l a s t l cdeformation deformationand and veining. beenfolded foldedpprior veining. The The llarger a r g e r xenolith x e n o l i t h appears appears tto o have have been r i o r to t o its i t sengulfment engulfment in suggestsddifferential We1 1 developed developed f1flow ow 1lamination aminati on suggests i f f e r e n t i a1 i n the thetonalite tonal itmagma. e magma. Well movement between magma xenoliths bedofre and detachment. (D) (D) Mafic and movement between magma andand xenoliths bedofre and a fafter t e r detachment. and u l tramafic xenoliths l a t i v e l y 1i t t l e assimilation a s s i m i l a t i o n in i n the the tonalite. tonal ite.Mixing Mixing ultramafic xenoliths show showr erelatively little of suggests 1itho1ogi es suggestsconsiderable considerable turbulence t u r b u l ence and and vvertical ertical o f diverse d i verse xenolith xenol it hlithologies flow within high proportion proportion of w i t h i nthe t h etonalite t o n a l i tmagma, e magma, which which probably probably contained contained aa high of Location 7927-X. 7927-X. xenocrystic as we1 well xenocrysti c hornblende hornblende as 1 as as xenoliths. xenol iths. Location �-42- SHEAR ZONES ZONES invol v i ngmodest, modest, I n t e r 1ensing, west-northwest-trending west-northwest-trendi ngshear shearzones zones involving Interlensing, r i g h t - l a t e r adisplacement l d i s p l acement andconspicuous conspicuousdrag dragfolding f o l d i n(Locations g (Locations 7927-X right-lateral and 7927—X have segmented segmented and flow and Figure 22. have andtransposed transposed primary primary flow and Y,Y, Figure lamination small shear 1amination iin n the t h e intrusion i n t r u s i o n breccia. breccia. Where Where small shear zones zones converge, converge, the breccia is with i sconverted converted to t oaazoned, zoned, laminated laminated dike—like d i k e - l i k e body body w i t h walls of hornblende core of of quartz-epidote hornblende sschist c h i s t and and aa core quartz-epidote mylonite mylonite up up tto o 1.5 1.5 meters wide. this wide. If If t h i ssmall smallscale scaletransposition transposition ofo fprimary primary lamination lamination is is expanded mapscale, scale, one one can can rreadily expanded t oto map e a d i l y see see how how primary layering 1ayeringmay may be be ami nation para1 1e l to to t o t a l l yobliterated obl i t e r a t e dand andreplaced rep1aced by by aa secondary secondary 1lamination totally parallel shear dislocation iinn the the iinterlensing shear dislocatton the rock. rock. Many Many o of f the n t e r l e n s i n g structures structures of of the Precambrian terrane of of west-central Wisconsin represent 1largePrecambrian terrane M i sconsin may may represent argescale scale tectonic transposition transposition by byshearing. shearing. • The The ffault a u l t seen seen at a tLocations Locations7927-X 7927-X and and Y Y probably probably ooffsets f f s e t s pegmatites pegmatites but not not the the diabase diabase dikes. dikes. Its I t sage age isi stherefore thereforeprobably probablyLate LateMiddle Middle Precambrian Precanbrian (Penokean?) ( Penokean?) A mucheearlier producedi sisoclinal A much a r l i e r deformation deformation produced o c l i n a l folds f o l d s and and banding banding in in the amphibolites before iintrusion +10 10m.y. m.y. ago. ago. atnphibolites before n t r u s i o n of of the thetonalite t o n a l i t e1842 1842+DIABASE DIKES DIKES East-northeast-trending, Late Precambrian basaltLate Precambrian(Keweenawan?) (Keweenawan?) basalt~ast-'northeast-trending , diabase dikes ccut Q. Their Their chilled chilled diabase dikes u t the the breccia breccianear near locations, locations,7927-Z 7927-Zand andQ. margins shallow iintrusion margins i indicate n d i c a t e shallow n t r u s i o n after a f t e rconsiderable considerable erosion. erosion. THE THE PRECAMBRIAN-CAMBRIAN PRECAMBRIAN-CAMBRIANUNCONFORMITY UNCONFORMITY A and erosion erosion wwith A surface of o f deep deep weathering weathering and i t h about about 20 20 meters meters ooff relief gently west—southwest Cambrian re1i e dips f dips gently west-southwestbeneath beneathLate Late CambrianMt. Mt Simon SimonSandstone Sandstone throughout Eau CClaire throughout the region. region. The The Eau l a i r e River River flows flows approximately approximately down down the the dip d i p of o f this t h i smajor majorunconformity. unconformi t y . Chemical weathering of of underlying Chemical weathering underlyingampamphibolitic impermeable green, hibol i t i crocks rocksengendered engendered aahhighly i g h l y impermeable green, i l l illitic i t i c clay. clay. Some this mayhave haveoccurred occurreda fafter deposition ooff the Some o of f th i s weathering weathering may t e r deposition t h e sandsandstone by reaction of stone by o fcirculating c i r c u l a t i ngroundwater g groundwaterwith w i t hferromagnesian ferromagnesian minerals mineral s in through the Mt. Groundwater ccirculating i r c u l a t i n gdownward downward through Mt i n the the amphibolites. amphibol ites. Groundwater Simon Sandstone flows along theclay Simon Sandstone flows l a t laterally e r a l l y along the c l a y l alayer y e r uuntil n t i l iti tcomes comes out out at a t the the surface surface as as aa spring. spring. Since the the Precambrian-Cambrian Precambrian-Cambrian unconformity unconformity is the llevel i s generally generally just j u s t above above or o r below below the e v e l ofthe of theEau Eau Claire C l a i r e River, River, the the river's r i v e r ' smajor majordischarge dischargeisi major s majorfrom fromgroundwater groundwatersystems. systems. Its I t sdischarge discharge varies .only •only sslightly, l i g h t l y ,even evenduring duringprolonged prolonged periods periods of o f drought. drought. . . �'979 Felsic LI mylonite amphibolite folds q - C • • 5Feet i bo% Figure 19 -- GEOLOGIC MAP OF LOCATION 7927-C, LITTLE FALLS Bonded Ultramof Ic, hornblendlte xenoflths Veined and lensoldal omphibolite Hornblende tonolite gnelss Breccia Quartz L1. EXPLANATION E. Myers (A) �-44CHRONOLOGY CHRONOLOGY FOR LITTLE FALLS FOR LITTLE FALLS AREA AREA 1. 1. Basaltic Basal t i cvolcanism volcanismand and sedimentation sedimentation 2. Intrusion I n t r u s i o n of o f Big B i g Falls F a l l s gabbro; gabbro; ddifferentiation i f f e r e n t i a t i o n with w i t h deposition deposition of o f ultramafic u l tramafic autolfths. auto1 i'ths. Mineralogical Mineralogical and and chemical chemical ssimilarity i m i l a r i t y of o famphibolites amphi bol ites at a t Big Big Falls thoseaat F a l l s (Unit (Unit 2) 2) and and those t LLittle i t t l eFalls F a l l ssuggest suggest their t h e i r close close relationship. relationship. 3. Isoclinal ~ s o c l i n afolding lf o l d i n gand andshearing shearing 4. Intrusion 7927W) I n t r u s i o n of o (porphyritic?) f ( p o r p h y r i t i c ?granite ) g r a n i t(Location e (Location 7927W) 5. Catalasis folding. Catalasis and and regional regionalmetamorphism, metamorphism, folding. 6. Intrusion +20 m.y. to tVan Schmus, I n t r u s i o nofo fhornblende hornblendetonalite t o n a l i t(1842 e (1842 + 20 m.y.according according o Van Schmus, 1980) 1980) 7. Intrusion I n t r u s i o nof o fgranite granitepegmatite pegmatite(Location (Location7927Z) 79271) 8. Strike—slip trend) and and1locallized S t r i ke-sl ip faulting f a u l t i n g(WNW (WNW trend) ocal 1ized cataclasis catacl a s i s 9. 9. Prolonged erosionwwith formationoof surface ooff low relief Prolonged erosion i t h formation f aa surface low topographic topographic re1 i e fand and aa soil s o i l rich r i c hini green n greenclay c l a yononthe themafic maficamphibolites amphibolites I 10. 10. Intrusion ?) I n t r u s i o nofo fdiabase diabase dikes dikes(Location (Location7927R) 7927R) (1100 (1100 m.y. m y . ?) 11. 11. Erosion Erosion 12. 12. Marine Marine deposition deposition ofo fMt. Mt.Simon SimonSandstone Sandstone - Late LateCambrian Cambrian - �-45- -- THE FORK AREA AREA -- INTRODUCTION THE SOUTH SOUTH FORK INTRODUCTION Figure2l Figure21 is i s aa geologic geologic strip s t r i pmap map of of the theSouth South Fork Fork area area in i n eastern eastern Eau Claire Claire and Eau and western western Clark counties counties (Stops (Stops3—7). 3-7). An An examination examination of of the map should reason forfor d i difficulties f f i c u l t i e s in interpolating interpolatingbedrock bedrock units units map shouldreveal revealone one reason between exposuresinint hthis between exposures i s region. If cataclastic I f the theexposed exposed contact contact betweeh between catacl astic gneiss and and metatuff a t Stop Stop 33 is i s representative representativeofofconcealed concealed feldspathic gneiss metatuff at contacts iin n the the area, area, iti tcan can be be inferred inferred that thatcontacts contacts are are typically typicallysheared sheared contacts andnearly nearly vertical vertical and lensoidal fault and and that t h a t they they enclose enclose lensoidal f a u l t slices s l i c e swhich which have have been juxtaposedmainly mainlybybystri strike-slip ke-sl i p displacement displacement (Figure 20). 20). Although A1 though the the been juxtaposed metavolcanic and and metasedimentary South Fork Fork area area (SFVS) (SFVS) are are metavolcanic metasedimentaryrocks rocks of of the South commonly foliated foliated(as ( aat s aRock t RockDam Damand and Mead Mead Dam) l l show show excellent comonly Dam)they theya all excellent Garnet, chlorite, chlorite, preservation preservation of primary primary minerals mineral s and and sedimentary sedimentary textures. Garnet, epidote, and muscovite indicate indicate attainment and muscovite attainment of upper upper greenschist greenschist fades faciesmetametamorphismunder underconditions conditions of of moderate SFVSrocks rocksa are interlayered morphism moderate stress. SFVS r e interlayered aatt Stop Stop 33 with w i t h sheared sheared mafic mafic and and feldspathic feldspathicplagioclase-hornblende plagioclase-hornblende gneisses gneisses contactsaare nearlyvvertical, of the theChippewa Chippewa amphibolite amphibolitecomplex complex (CAC). (CAC). The The contacts r e nearly ertical, northwest-trending. In contrast northwest-trending. contrast with w i t hthe theCAC CAC rocks rocks which were were deformed deformed and and metamorphosed threetimes, times,the theSFVS SFVS rocks Stop displayre1 relict metamorphosed a t at l e aleast s t three ro.cks a t atStop 7 7display ict upright SFVS upright bedding bedding which which dips dips ata tmoderate moderate angles. angles. It I t isi sbelieved believedthat t h athe t the SFVS rocks were were deposited deposited unconformably unconformably upon upon eroded, eroded, twice-deformed twice-deformed and andmetamormetamormetatuff from phosedArchaen Archaenamphibolites amphibolites about 1860 phosed 1860 m.y. m.y. ago. ago. Andesite Andesite metatuff from the confluence area (Stop 3, Station 7830-F), as dated by Van Schmus (1980), is confluence area (Stop Station 7830-F), as dated by Van Schmus (1980), is greenschistgrade grademetamorphism metamorphism and these After greenschist and some somefolding, folding, these 1860 m.y. After 1860 + m.y. rocks wereimbricated imbricatedbybystrike-slip strike-slip displacement alongnearly nearly vertical, vertical, rockswere displacement along trondhjemi t i c The imbrication i t i cand and trondhjemitic interlensing imbrication also also involves involves tonal tonalitic interlensing faults. The intrusive m.y. old old but b u t not not intrusive rocks rocks about about 1840 1840 m.y. Present Erosion Surface Surface faults Figure 20 Figure 20 --Block Blockdiagram diagramshowing showing hypothetical hypotheticaldisplacement displacementmechanism mechanism which which best explains of SFVS and best explains the distribution distributionand andspatial spatialrelations relations of SFVS andCAC CAC rocks rocks in the the South South Fork Fork area. area. �EXPLANATION EXKANATION Gneissic granodiorite granodiffite Gneissic wj Foliated Foliated ml biotite biotite tonolite tondite Foliated trondhjemite trondhjemite w Volcanics [ Voicanics wl Metasedirnents m g A5 Metasediments Mafic omphibolites amphiMites Mafic Reid Field trip trip stop stop 2 milss Fairchild, 6 mi. ,p Figure -- Geologic Fork of 0f the Figure 21 21 -Geologic strip s t r i pmap map of of the t h eNorth North Fork Fork and and South South Fork t h e Eau Eau Claire River River in ineastern eastern Eau Eau Claire Claire and western Clark counties. and western counties. �-47-47STOPS #3 and #7 STOPS #3 #7 TITLE: CONTACT BETWEEN BETWEEN CHIPPEWA AND SOUTH SOUTH FORK FORK VOLCANIC VOLCANICROCKS ROCKS CONTACT CHIPPEWA AMPHIBOLITES AMPHIBOLITES AND LOCATIONS: LOCATIONS: Stop #3, T26N, #3ÂSE SE 11/4, / 4  SE SE 1/4, 114 Sec. Sec. 16, 16 TZ6N,R5W: R5W: Field F i e l d Loc. LOC.7830 7830 Stop #7, NE 1/4, Sw 1/4, Sec. 16, T26N, Stop #7, NE 114, SW 1/4 Sec. 16, T26N9R5w: R5W: Field Fie1d Loc. LOC.7329 7329 AUTHOR: AUTHOR : P. P. - March, March, 1980 1980 DATE: DATE : E. E. Myers Myers SUMMARY SUMMARY OF OF FEATURES: FEATURES: The The llithology i t h o l o g y and and contact contact relations r e l a t i o n sofo fsheared sheared metatuffs, metatuffs, tuffaceous tuffaceous sedimentary rocks and and pplagioclase-hornblende gneiss are are well-exposed, sedimentary rocks l a g i o c l ase-hornbl ende gneiss we1 1-exposed9 but but difficult d i f f i c u l ttot ointerpret i n t e r p r e at t a Stop t Stop 3. 3. Tuffaceous Tuffaceous conglomerate, conglomerate9sandstone, sandstone, and and s f 1 tstonewith w i t hwell-preserved we1 1-preservedprimary primarydepositional depositionalfeatures features l p 45-60 SSW siltstone dipd45_600 SSW at a t Stop Stop 7. 7. DESCRIPTION: DESCRIPTION: Stop Stop 3: 3: Four Four nnearly e a r l y vvertical e r t i c a l rock rock units u n i t s here here (Figure (Figure 22) 22) are are listed 1i s t e d from from northeast northeast to t osouthwest southwest : : (1) (1 ) banded, banded, mafic, mafic, hornblende-plagioclase hornblende-plagioclase gneiss Table88 (#7830-A (#7830-Aand andB),B),(2) (2)andesite andesitet tuff u f f and and quartzo-feldspathic quartzo-feldspathic gneiss and and Table volcaniclastic v o l c a n i c l a s t i csedimentary sedimentary rocks rocks (#7830-D,E, (#7830-D9 E, and and F), F) (3) ( 3 )mafic mafichornblende hornbl ende tonalite tonal it e (no (no analyses), analyses), and and (4) ( 4 ) feldspathic f e l dspathi c tonalite tonal it egneiss. gneiss. Discordant Discordant leucotrondhjemite dikeswwith concordant all1 units. leucotrondhjemi t e dikes i t h concordant c a cataclastic t a c l a s t i c f ofoliation l i a t i o n ccut u t a1 units. Sericitization S e r i c i t i z a t i o nofoplagioclase f plagioclasewas was followed followed by by small small scale scale faulting f a u l t i n gand and chlorite with adjacent ttoo the c h l o r i t evein veinemplacement emplacement w i t h conversion conversion of o f hornblende hornblende adjacent the veins veins to Garnets and l a s t s in i n the t h emetatuff metatuffwere were almost almost andmafic mafic cclasts t o chlorite c h l o r i t eand andepidote. epidote. Garnets completely basic questions questions aarise completely cchloritized h l o r i t i z e d at a t this t h i stime. time. Two Two basic r i s e here: here: (1) (1 ) which which o0ff the t h e units u n i t s is i sofo fvolcanic vo1 canicorigin, o r i g i n ,and and(2) (2)tot what o whatextent extentand and in metamorphism i nwhat what sequence sequence were were primary minerals minerals and and textures texturesmodified modifiedbyby metamorphism and and ccataclasis a t a c l a s i s in i neach each unit? unit? �-48- TABLE TABLE 88 MODAL AND CHEMICAL ANALYSES ANALYSES OF OF ROCKS ROCKS FROM FROM THE THE CONFLUENCE CONFLUENCE AREA AREA MODAL AND CHEMICAL I MÔdãl. Analyses Analyses Modal I MIN* MIN* Plag M ag 7829 7829 7829 B B A A 7929 7929 C C 78 65 65 Hb Hb Qtz Q tz Chi. Chl. 6? 6? 4? 4? 28 16 16 7830 7830 7830 7830 AA 58 58 BB 29 30 30 63 77 6 24 55 1 Trr T Tr Tr 1 Tr Tr 1 2 2 Ep. EP 1 <11 4 Op. OP I 7830 7830 17830 7830 17830 7830 7830 7830 7830 7830 7830 DD H .1I E F E F G ' H 61 78 68 53 61 ' 7711 78 69 69 68 53 8 11 11 66 9 9 6 6 14 14 32 32 16? 16? 13 13 4 4 33 5 17? 17? 66 33 11 33 5 2 2 * Minerals: Minerals :Plagioclase, PI agi o c l ase, Hornblende, Hornblende, Quartz, Quartz, Chlorite, Chl or1te, Epidote, Epi dote, Muscovite Muscovite Modal analysesusing using1000-point 1000-point counts.I dIdentification uncertain ffor Modal analyses counts. e n t i f i c a t i o n uncertain o r very very fif i nne-grai ned vvarieties e - g r a i ned arieties Chemi cal Analyses Analyses Chemical Si02 . 56.84 59.48 48.19 57.08 57.24 70.62 61.76 61.60 57.58 63.03 68.42 A1203 19.46 20.41 20.54 15.87 14.89 15.52 17.56 17.18 17.74 14.35 14.37 Fe2O 6.03 * 4.08 10.40 8.68 9.75 2.49 7.14 6.80 5.80 6.64 3.77 CaO 1.33 0.76 0.60 6.10 5.42 2.61 3.65 4.06 6.13 6.13 494 MgO bIg0 3.43 3.10 8.10 4.51 4.55 0.97 2.03 2.25 3.47 3.31 1.74 Na20 Na20 7.44 7.77 •4.68 3.66 3.16 4.45 3.29 3.38 3.96 2.69 3.02 K20 K2 0.71 1.26 1.51 0.72 1.36 1.43 2.02 2.11 1.89 1.18 0.99 Ti02 1102 0.51 0.49 0.65 0.46 0.61 0.28 0.56 0.51 0.34 0.27 0.22 MnO MnO 0.05 0.04 0.09 0.14 0.14 0.03 0.07 0.08 0.08 0.11 0.06 P25 2' 5' 0.21 0.10 0.27 0.02 0.13 0.05 0.21 0.25 0.23 0.03 0.00 LLOl OI 2.11 1.89 4.47 1.17 1.61 0.84 1.80 1.52 1.53 1.19 0.71 TOTAL TOTAL 98.11 99.39 99.50 98.41 98.85 99.30 100.1 99.74 98.73 98.94 98.22 * Includes IncludesFeO. FeO. �-49- banded, mafic banded, m a f i c hornblende— hornblende- plagioclase gnei1 fedspath1c hornblende tonaflte gnelsS edge of / C'. No. 7830). Figure 22-22-- Outcrop Outcropmap map showing showing geology geology and andsample sample llocations o c a t i o n s (Field (Fie1 d No. 7830). Chemicalanalyses analysesf ofor these rocks rocks are are tabulated tabulated in Chemical r these i n Tables Tables 2 and and 4. 4. Unit U n i t #1 # I consists consists of o faligned, aligned, dark darkgreen green("1), ( Y ),subhedral subhedralhornblende hornblende and and crush debris debris llenticular e n t i c u l a r plagioclase plagioclase laths l a t h s or o r its i t smylonitized myloni t i z e dequivalent equivalent - aa crush Although the the existence existence of o f anhedral, anhedral, bent, bent, and andbroken broken plagioclase plagioclasefragments. fragments. Although of and shadowy o f large, large,ovoid ovoidplagioclase plagioclasegrains grains and shadowy darker darker patches patches (best (bestseen seen on on weatheredsurfaces) surfaces) suggests rock, thin weathered suggests a va o lvolcaniclastic c a n i c l a s t i c p r oprotolith t o l i t h f ofor r t this h i s rock, thin section showst hthat laminationi is section study study shows a t aat t lleast e a s t some some o of f t hthe e lamination s ooff cataclastic cataclastic themalong alongsmall smallf afaults, all Thin seams seams o fofcchlorite, h l o r i t e , some some oof f them u l t s , ccut u t a11 origin. o r i g i n . Thin and chlorite c h l o r i t become e becomemuch much other sstructures other t r u c t u r e s i in n aall l l four f o u r rock rock units. u n i t s . Epidote and more abundanti ninhornblende hornblendenear nearthese thesec hchlorite veinlets. The more abundant l o r i t e veinlets. The cchloritization hloritization (Figure 23.) 23. ) and eepidotization was, therefore, therefore, post-kinematic. and p i d o t i z a t i o n ooff these these rocks rocks was, post-kinematic. (Figure - Unit about3030t oto60 60percent percente ellipsoidal U n i t #2 #2 is i s composed composed o of f about l 1 i p s o i d a l plagioclase plagioclase clasts c l a s t s in i n aa foliated, f o l i a t e d ,fine-grained fine-grainedmatrix m a t r i xofo plagioclase, f plagioclase, epidote, epidote, and and Chlorite-mantled garnets make upup about 0.5% cchlorite h l o r i t e(Figure (Figure24). 24). C h l o r i te-mantled garnets make about 0.5%ofo specimen f specimen 7830-E (Figure25). 25).Cataclastic Cataclasticfo1 foliation 7830-E (Figure i a t i o n is i s manifested manifested llocally o c a l l y by by interlensing interlensing plagioclase cclasts and tthinly chlorite c h l o r i t e folia. f o l fa. The The plagioclase l a s t s are a r e well-rounded we1 1-rounded and h i n l y coated coated with with chlorite c h l o r i t eor o rvery veryfine-grained fine-grainedquartz quartzand andcontains containszoned zoned inclusions i n c l usionsofo brown f brown L i t h i cfragments fragments and/or and/or glass glass shards shards were were apparently apparently biotite b i o t i t e and and pyrite. p y r i t e . Lithic (1980) at replaced by by cchlorite. replaced h l o r i t e . This unit u n i twas wasU-Pb U-Pb dated datedby byVan Van Schmus Schmus (1980) a t 1860 1860 m.y. m.y. Unit U n i t #3 #3 is i saahornblende—rich hornblende-rich ttonalite o n a l i t e with w i t hconspicuous conspicuous lamination but but I t s composition composition iiss similar s i m i l a r to, to,but b umore t more mafic mafic than, than, obvious llineation. less obvious i n e a t i o n . Its 7830-A. 7830-A. �-50- Unit U n i t #4 =4 iiss light l i g h tgreenish greenish gray gray feldspathic feldspathic tonalite tonalitegneiss gneisswhich which closely closely resembles thefeldspathic feldspathic amphibolites amphibolitesofof the the Big Big Falls area. resembles the area. However, Howevery iits ts cataclastic fabric color of the give tthis fabricand and the the deep deep green green color the hornblende hornblende give h i s rock rock quite aa different n thin t h i n section. section. Lensoidal differentappearance appearance iin Lensoi dal plagioclase plagiocl ase porphyroporphyroclasts post-kinematicálly c l a s t s are are surrounded surrounded by by fine finegrained grainedquartz quartzwhich whichmay may have have been been post-kinematically introduced. All cataclastic fabric A1 1units unitsdisplay displaya apronounced pronounced cataclastic fabric characterized characterized by by bent, benty broken, and1lenticulated and inter1 interlensing broken, and enticul ated plagioclase plagiocl ase and ensing foliation fo1 iationaccentuated accentuated by by accumulations chlorite and accumulations ofof chlorite and quartz-feldspar quartz-fe1 dspar crush crush debris. debris. Late kinematic kinematic leucotrondhjemite cut the the layering layering and and cataclastic cataclastic foliation leucotrondhjemi t e ddikes i kes cut fol iationbut b u themselves t themsel ves possess weak parallel to possess a aweak folfoliation iation parallel t o that t h a t Ini nthe theenclosina enclosina rocks. rocks. The The finefinegrained matrix of of the for concentration of cataclasis grained matrix the metatuff metatuff allowed allowed for concentration of cataclasis with with little l i t t l abrasion e abrasionand andfragmentation fragmentation of the the insulated insulated feldspar feldspar clasts. c l a s t s . This T h i s may may explain preservation of of primary textures in explain the the unusually unusually good good preservation primary textures i n these these rocks: rocks. A A profile profileofofminor minorelement element variation variation .across .across this t h i s outcrop outcrop isi sshown shown in in Figure 26. 7830D,aa rock rock composed composed coarse,lenticulated lenticulated plagioclase 26. Rock Rock 7830Dy of ofcoarse, clasts has c l a s t s ini naafine-grained fine-grainedquartz quartzmatri,ç matrih hasanananomalously anomalously low low V, V y Cr, Cryand andZn Zn content. The rock has has the the composition compositionb but not the the texture texture of aa trondhjemite. The rock u t not trondhjemite. The protolith of unknown. The protolith of this t h i srock rockis is unknown. Its I t s relatively relativelycoarse coarse grain grain size size suggest intrusive origin. suggest ananintrusive Stop 7: small outcropson onthe the south southside side of oftheEau Three smal 1 outcrops the Eau Claire River River 7: Three about 1/2 mile mile east 100-foot sequence sequence well-stratified, about 112 e a s t of Stop Stop 33 expose expose aa 100-foot ofofwell-stratified, but andsisiltstone b u t poorly poorly shorted shorted volcanic vo1 canic conglomerate conglomerate and 1tstone (Figure 8). 8). The The 1-7 1-7 m mplagioclase plagioclase and and blue quartz quartz clasts c l a s t s are are well wellrounded, rounded, and and quite quite evenly evenly distributed in i n aa well-stratified, we1 1- s t r a t i f i e dfine—grained y fine-grained plagioclase-chiorite plagioclase-chlori t e matrix. matrix. These rocksshow show onlylocalized localizedeeffects of cataclasis, These rocks only f f e c t s of cataclasis, and and most most closely closely resemble specimen 7830-F 7830-Faatt Stop 3. thebasis basisofof1lithologic similarity, resemble specimen 3. On On the ithologic similarityy the volcanic w i t h those those of of Unit U n i t #2 #2 at a tStop Stop 3.3. volcanic rocks rocks at a t Stop Stop 7 are correlated correlated with -- Figure 23 -—Chlori Chlorite-epidote veinlet (upper (upperl left te-epidote veinlet e f t to to Figure 23 lower lower right) r i g h t )cutting cuttingepidotized epidotizedplagioclase-hornblende plagioclase-hornblende gneiss. polars. Width gneiss. Location Location G. G. Crossed Crossed polars. Width of of photo photo == occurrenceofof epidote epidote iinn veinlet 4.2 4.2 m. mm. Note Note occurrence veinletwhere where iti tcrosses crosses hornblende hornblende crystals. crystals. �—51— - Figure 24 24 -— Rounded plagioclase n aa foliated foliated Figure Rounded plagioclaseclasts clastsi in and epiepimatrix of offine—grained fine-grained plagioclase, chlorite,and matrix plagioclase, chlorite, dote. chioritized dote. Location Location E. E. Small Small chlori tized garnet garnet right-center right-center and llithic i t h i cfragment fragment (dark) (dark) on on left. l e f t .Photo Photo width w i d t h is i s4.2 4.2 and mil 1imeters. Textural Textural lamination lamination (relict (re1i cbedding) t bedding) occurs occurs millimeters. in i nother otherspecimens specimens from from this thissame same location. location. -- Figure garnet in isheared and Figure 25 25 -- Chioritized Chloritized garnet n sheared andmetametamorphosed andesite tuff tuff or morphosed andesite o rtuffaceous tuffaceoussediment sedimentfrom from Location Location E.E. Note Noterounded rounded outline outlineofofpseudomorph. pseudomorph. Relict Relict garnet (g)remains remains inincore. core. Ordinary Ordinary illumination. i 11umination. garnet (g) Photo width is Photo width i s 4.2 4.2 millimeters. millimeters. �11 H G 0 5m. Distance F F 0 B N E— A SAIIPLE LOCATION C) L&i z C) z0 I- z 0 2 0 Figure 26 -- Major and minor element variations across outcrop at Stop #3. diagram are shown to scale. (Figure 22.) LOCATIONS SAMPLL.—I L) 0 C 0 0 U) 4-, 0 C 0) 4-, 00) I- U Sample numbers along base of each 5m. N.) U, �—53— - Figure 27 -- Relict Figure 27 R e l i c tbedding bedding in i n andesite andesite metatuff m e t a t u f f from from r t i n g . PlagPlagLocation 7829—C 7 8 2 9 4 (Stop (Stop#7) #7)showing showingpoor poors osorting. ioclase i o c l a s e clasts c l a s t sshow showconsiderable considerablebending bendingand and marginal margi nal fragmentation. s 4.2 fragmentation. Crossed Crossedpolars. polars. Photo Photowidth widthi is 4.2 mm. m. DISCUSSION: DISCUSSION: The pprotolith The r o t o l it hfor f o the r t h hornblende-bearing e hornblende-bearing gneisses gneisses which which enclose enclose the the The hornblende-bearing volcanic rocks rocks at a t Stop Stop 33has has not n o tbeen been established. established. The rocks rocks aatt this t h i slocation l o c a t i o nare areintermediate intermediatebetween between the t h e mafic mafic and and ffeldspathic eldspathic hornblendei sisaadeep deepgreen green( 7 ())) to The hornblende to amphibolites terrane. The amphibolites of o f the t h eCAC CAC terrane. moderate yellow-green 4C). Since Sie the thechemical chemicalanalyses analyses in i nFigure Figure 26 26 do do not not moderate yellow-green ddistinguish i s t i n g u i s hbetween between Fe Fe and Fe Fe ,, iittisi simpossible impossibletot ospeculate speculateOn on the the p). The anomalous partitioning anomalous p a r t i t i o n i n g of o firon i r o nini nthe thehornblende, hornblende, chlorite c h l o r i t eand andepidote. epidote. The eextinction x t i n c t i o n colors c o l o r s of o f chlorite c h l o r i t e minerals minerals comonly commonly rreflect e f l e c t differences differences in in yellow-gray is aluminian composition: yellow-gray i scommonly commonly a1 uminian pprochiorite; r o c h l o r i te; chocolate chocolatebrownbrownpurple purple iiss comonly commonly ferroane ferroane prochiorite; p r o c h l o r i te; deep deep (Prussian) (Prussian) blue b l u e is i spennine. pennine. In I n the the rocks rocks at a t Stop Stop 3, 3, pennine pennine is i s confined confined to t o hornblende hornblende aalteration, lteration, whereas whereas a1aluminian uminian p rprochiorite o c h l o r i t e i is s found found iinn the the mafic-poor mafic-poor volcanic volcanic rocks, rocks, although pennine pennineaalso occurs iinn these although l s o occurs these rocks rocks as as aa replacement replacement of o f garnets. garnets. Thus twochiorite Thus two c h l o r i t e minerals minerals coexist c o e x i s t in i n the t h evolcanic volcanic rocks, rocks, apparently apparently as as aa function of function o f the thechemical chemical composition composition ooff the t h e host host mineral. mineral. Structural age rrelationships amphibolitic S t r u c t u r a l and and age e l a t i o n s h i p s ooff volcanic volcanic and and amphibol i t i c rocks rocks at at The these llocations be cconfidently extrapolated rregionally. these o c a t i o n s cannot cannot be o n f i d e n t l y extrapolated e g i o n a l l y . The eastward increase iinn the increase the proportion proportion of o fvolcanogenic volcanogenic rocks, rocks, and and the t h e virtual v i r t u a disappearance l disappearance of amphibolitic rocks suggests a major transition, which might of amphi bol it i c rocks suggests a major t r a n s i t i o n , which mightbe beaasheared sheared and folded folded angular as suggested here, oorr possibly aa northwestand angular unconformity unconformity as suggested here, northwestIt should It should be be noted noted tthat h a t the the foliation f o l i a t i o nataStop t Stop#3#3bends bends trending trending ffault. ault. abruptly north-northwesterly, wwhile area, ffoliation abruptly north-northwesterly, h i l e eelsewhere l sewhere i nint hthis i s area, o l i a t i o n trends trends The relative freshness of cataclastic features might The r e l a t i v e freshness o f c a t a c l a s t i c features might west-northwesterly. west-northwesterly. work, pparticularly More ddetailed e t a i l e d f ifield e 1 d work, articularly support the cross-fault hypothesis. More support the cross-faul t hypothesis. wwith i t h small-scale smal 1-scale structures and and ppetrofabrics e t r o f a b r i c s will w i 11be benecessary necessary to t o resolve resol ve the problem. problem. �-55STOP STOP TITLE: #4 #4 KNIGHT POOL POOL META-BASALT META-BASALT KNIGHT LOCATION: Pool, Channey Channey Road, Road, North Fork Fork Qf o f Eau Eau Claire C l a i r eRiver, River, SE%,NE¼ NE% Knight Pool, SE¼, Sec. 10, 10, T26N, T26N, R5W, R5W, FFairchild a i r c h i l d 15' 15'Quadrangle. Quadrangle. Sec. AUTHOR: Paul E. Myers Paul E.Myers DATE:: DATE - March, 1980 March, 1980 SUMMARYO OF SUMMARY F FEATURES: Fine-grained, 1lineated amphibolite containingre1 relict Fine-grained, ineated amphi b o l it e containing ic t pillow p i 11ow structures(?) s t r u c t u r e s ( ? ) and and amygdules is cut discordantly by aplite veinlets which show different amygdules i s c u t discordantly by a p l i t e v e i n l e t s which show d i f f e r e n ttypes typesand and rocks, because evidenceooff several several ages off deformation, ages ooff deformation. ages deformation. These These rocks, because oof f evidence ages o deformation, including an eearly phaseo of are tentatively assigned i n c l u d i n g an a r l y phase f i sisoclinal o c l i n a l folding, f o l d i n , are t e n t a t i v e l y assigned to t o the the Chippewaamphibol amphibolites and younger(?) volcanicst to Chippewa i t e s and n onot t t otot hthe e younger ? ) volcanics o tthe h e east. east. ? DESCRIPTION: Fine-grained, mafic, mafic, epidote epidote amphibol amphibolites Fine-grained, i t e s wwith i t h r relict e l i c t pillow p i 1lowstructures structureswere were f i r s tisoclinally i s o c l i n a l lfolded y folded (Figure 28C),intruded intrudedby byaplite apl it eveinlets v e i n l e t s(Figure (Figure28A) 28A) first (Figure 28C), and then thenby byaabody bodyo of and f bbiotite i o t i t e granodiorite. granodiorite. Shearing Shearing iin n and and along along the t h e contact contact ooff the the granodiorite g r a n o d i o r i t econverted converted the t h e massive massive iintrusive n t r u s i v e rock rock to t o aamylonite mylonite gneiss. gneiss. This andcataclasis cataclasisfolded foldedt hthe This late l a t e episode episode ooff shearing shearing and e aaplite p l i t e vveinlets e i n l e t s in i n the the mafic amphibolite amphibolite (Figure (Figure28B). 28B).AAvveinlet of laminated mylónitegneiss gneissl ilies e i n l e t of laminated mylonite e s iin n the the mafic plareof planeof foliation f o l i a t i o nofo the f t h eamphibolite amphibolite(Figure.28B). (Figure28B). This This gneiss gneiss consists consists of o f eyeeyeshaped asts o of f pplagioclase l agiocl ase enveloped i o t i t e and and siliceous s i 1iceous shapedporphyrocl porphyroclasts envelopedi ninmantles mantleso fofbbiotite mylonite. Theplagioclase plagioclasei sis sstrongly myloni te. The t r o n g l y ssericitized. e r i c i t i z e d . Quartz-epidote-filled Quartz-epidote-fi 1l e dgash gash fractures perpendiculart otof ofoliation f r a c t u r e s developed developed perpendicular l i a t i o n during during stress stress release. release. The sheeting and andbbiotite The llineated i n e a t e d mafic mafic amphibolite amphibolite here here displays displays aapronounced pronounced sheeting iotite foliation form the the 1limbs f o l i a t i o naccentuated accentuated by by plagioclase plagioclase laminations laminations which which form imbs ooff highhighsmall fold Hornblende 1lineation i n e a t i on and and small f o l daxes axes plunge p l unge amplitude amp1 itude i sisoclinal o c l inal folds. f o l ds. Hornblende east at northeast aatt location east a t 50-75° 50-750 near the t h e bridge bridge and and 80° 80' northeast l o c a t i o n 7941 7941 (Figure (Figure 29.) 29. ) The offset sides The l lineations i n e a t i o n s are are o f f s e t by by east-west east-west vvertical e r t i c a l faults, f a u l t s ,north north sidesdown. down. �-56- - Figure Figure 28-28 Near-vertical Near-vertical face face of o fan an outcrop outcrop of of fine—grained amphibolite (dark)c cut byvei veinlets f i n e - g r a i ned amphi b o l it e (dark) u t by n l e t s ooff aplite a p l i t e veinlets, veinlets,one oneofo which f whichshows shows aa cataclastic cataclastic foliation f o l i a t i o n parallel p a r a l l e l to t o its i t swalls w a l l s(A). (A). The The aplite aplite vveinlets e i n l e t s cut c u t older 01der isoclinal i s o c l i n a lfolds f o l d sshown shown at a t C. C. AA catacataclastic c l o s e l yresentles resembles•the t h e granograno* c l a s t i c veinlet v e i n l e tata B t Bclosely diorite out jjust d i o r i t e which which crops crops out u s t north n o r t h of o f here. here. This This outcrop iiss at outcrop a t location l o c a t i o n 7941 7941 (Figure (Figure 29) 29 ) . �—57- Lc. 794Z 9P0'noo'/e rife k (Q'Pflphióo///e LOC 794/. / / -'I 'S / / 'I Oi Id 7938 • OC 7940 7939 P. Myers Figure 29 29 ----Geologic Geologicmap map of o f the theKnight Knight PoolArea. Area. Note s t e e p Figure eastward t o east-northeastward plunge oPool f small f o l d sNote and steep lineation. eastward to east—northeastward plunge of small folds and lineation. �________________ —59- STOP #5 TITLE: ROCK DAM DAM META-RHYOLITE ROCK LOCATION: LOCATION: Hay Creek 0.15 0.15 mile SE1/4, 1/4, NW 1/4 Sec. NW 1/4 Sec. 15, 15, Hay Creek m i l e downstream downstream from Rock Rock Dam, Dam, SE T26N, R4W; R4W;FFairchild T26N, a i r c h i l d 15' 15' Quadrangle Quadrangle . 9 -'c:i; ' I •.-— - ' -- AUTHOR: AUTHOR: Paul Paul E. E. Myers Myers DATE: DATE : - February, February, 1980 1980 SUMMARYOF OF FEATURES: SUMMARY Debate continuesonon significance Debate continues t h the e sig n i f i c a n c e o fofc criteria r i t e r i a used used tto o distinguish distinguish this "metamorphosed" rhyolitic volcanics ffrom "mylonitized" "metamorphosed" rhyol it i c volcanics r o m "myloni t i z e d " leucogranites. 1eucograni tes. IIff this stop doesnnot solve the the ""rhyolite-granite may at a tleast l e a sadd t addmore more stop does o t solve r h y o l i t e - g r a n i t e problem," problem," iti tmay fuel f u e l to t o the t h e ffire. ire. AA ffoliated, o l i a t e d , muscovite-bearing muscovi te-bearing ffelsic e l s i c mylonite myloni t e containing containing eyes eyes ooff strained strained quartz quartz in i n aa very very fine-grained fine-grained matrix rnatri xofofK-feldspar, K-fel dspar,quartz, quartz,and andmuscovite muscovite crops crops Dam,where wherei itt unconformably underlies conglomeratic oout u t below below Rock Rock Dam, unconformably underlies conglomeratic Mt. M t . Simon Simon is iN87°W, 31 ). Foliation F o l i a t i o n ini nthe thefelsic f e l s iniylonite c mylonite s N87OW, 85°N. 85ON. Sandstone (Figure (Figure31. Sandstone Complimentary and N77OE, N77°E,8's 8°Saccount accountf ofor Complimentary j ojoint i n t sets sets at a tN18°W, N18OW, 73°E 73OE and r tthe h e blocky The exposed exposedangular angularunconformity unconformity has has aa llocal appearanceoof appearance f tthe h e outcrop here. here. The ocal relief re1 i e fofo about f about55meters. meters. DESCRIPTION: DESCRIPTION: The mylonite mylonite iiss pale eyesoof The pale pink pink and and contains contains conspicuous conspicuous eyes f sstrained t r a i n e d quartz The rock clearly resembles a porphyritic rhyolite 1.0 2.5 mm long. 1.0 - 2.5 mm long. The rock c l e a r l y resembles a p o r p h y r i t i c r h y o l i t e with with quartz I n thin t h i n section, section, the thequartz quartz eyes eyes aresubare. subquartz phenocrysts phenocrysts oor r clasts. In rectangular commonly u r e NThey ) . They commonlypossess possess crush crush rectangular to t o lenticular l e n t i c u l ain r ioutline. n o u t l i n(Figure e . ( F i g30). trails: t h a t is, i s ,the t h ecoarse-grained coarse-grained cores cores display d i s p l a yan anoutward outward decrease decrease iin n grain grain t r a i l s : that contain coarse, size The quartz eyes eyes commonly commonly contain coarse, s i z e into i n t o the t h e fine-grained fine-grained matrix. matrix. The S t r a i n is i s indicated indicated pale high birefringence. birefringence. Strain pal e green green muscovite muscovite wwith i t h anomalously anomalously high matrix The m a t r i x is i scomposed composed ooff very very by the conspicuous lamellar, wavy by conspicuous lamellar, wavy eextinction. x t i n c t i o n . The ffine-grained i ne-grained K-feldspar K-fel dspar (microcline), (mi c r o c l i n e ) ,quartz, quartz, muscovite, muscovite, biotite, b i o t i t e ,and andmagnetite. magnetite. The magnetite magnetiteoccurs occursasasstreaks streaksalong alongf foliation The o l i a t i o n and and in i nmuscovite muscovite grains, grains, where where �-60appears to t o have have formed formed w i t h muscovite muscovite aat t the expense oof f primary iotite. iti tappears with the expense primarybbiotite. Estimated mineral composition Estimated mineral composition iis: s : K-feldspar, 57%';quartz, quartz, 35%; 35%;muscovite, muscovite, 3%; 3%; K-fel dspar, 57%; magnetite, and bbiotite, magnetite, 2%; 2%; and i o t i t e , 1%. 1%. In I n addition a d d i t i o n to t o the t h e quartz quartz eyes, eyes, this t h i s rock rock contains occasional e n t i c u l a r clusters c l usters of of relatively re1a t i vely coarse-grainedmuscovite, muscovi te, contains occasionall lenticular coarse-grained 30). qquartz, u a r t z , and and bbiotite i o t i t e(Figure (Figure30). A thet hbase of oRock A muscovite-rich muscovite-rich phyllite p h y l l i t ecrops cropsout o unear t near e base f RockDam. Dam. The The rock rock is i s composed composed oof f K-feldspar, K-fel dspar, quartz, quartz,and andmuscovite muscovi t e(approximately (approximately20%). 20%). The The quartz quartz eyes andb biotite are absent, absent,factors factorssuggesting suggesting eyes and i o t i t e are a a d i different f f e r e n t p protolith r o t o l i t h ffor o r this this rock. Since K-feldspar could not petrographically, Since the abundance abundance oof f K-fel dspar could n o t be be determined determined petrographically, comparison comparison wwith i t h the previous previous rock rock isi sbased basedmainly mainlyon onhand hand specimen specimen descriptions. Cataclastic of granite Catacl as ti c degradation degradation of g r a n i t e to t o mylonjte mylonj t e produces produces ssimilar, i m i l a r , but b u thopehope- fully f u l l ynot n o t identical, i d e n t i c a l ,features. features. The The cchief h i e f differences differences are: are: (1) (1 ) mylonitization myloni t i z a t i o n of rockst ytypically mylonitizes quartzf first; o f quartzofeldspathic quartzofel dspathic rocks p i c a l l y myloni t i z e s tthe h e quartz i r s t ; feldspars feldspars thus porphyroclasts; (2) sheared shearedgranites granitesare arecharacterized characterizedby by i interthus become become porphyrocl asts; (2) nterlensing with lensing slip s l i p planes planes coated coated w i t h phyllosilicates p h y l l o s i l i c a t e ssuch such as as mica mica oorr chlorite c h l o r i t eand and mylonite; and the the ffelsic (3) transitions t r a n s i t i o n sbetween between relatively r e l a t i v e l yunsheared unsheared ggranite r a n i t e and elsic mylonite; (3) mylonite can be be seen seeni ninthe the ffield. quartz eyes mylonite can i e l d . The The quartz eyes iinn the t h e absence absence ooff feldspar feldspar porphyroclasts suggestsa aprimary primaryo rorigin the quartz quartz - either e i t h e r as as porphyroclasts sstrongly t r o n g l y suggests i g i n f ofor r the phenocrysts other primary phenocrysts o or r asasc clasts l a s t s i in.a n a ttuff. u f f . No No other primary volcanic volcanic textures t e x t u r e swere were - observed observed here. here. The chemical composition compositionoof The chemical f tthis h i s rock rock (7931-B) (7931-B) as as presented presented in i nTable Table 11 on on page 13 shows showst this page 13 h i s rock rock to. t o contain containanomalously anomalously high high K,00and andanomalously anomalously low low A1203. themicrocline microcline and and mus musovite. A1203. The The K20 K20 iis s consumed consumed bybythe ovite. '2 0 -- Figure Micro9raph showing raph showing l e nlenticular t i c u l a r ccluster l u s t e r of of Figure .30 30 -—Micro strained magnetite s t r a i n e d quartz quartz (q), ( q ,muscovite muscovite Cm), (m) , bbiotite i o t i t e (b), (b) , magnetite 7 (black), epidote (black) ,and and epi dote ((e) e ) iin n texturally t e x t u r a l l ylaminated, 1ami nated, finefine- .grained m i c r o c l ine. grained quartz quartz and and microcline. . �N.) -0-0 0' U) • a. 'CD —a. a. -a CD -1)1 .. c-P 01 -s N .0 a.oC -' 01 mm c* —a- -• 0:3_ U)-1)-a. a. —' c-P 0 0-so U)OO U) CDX -s -sCD -a -a -I. o c-i- .JQi (a 0 (<mo -s 01-'. oi —JrI- 'a c-I-fl CD 01 a. 'a (a a. -I CD 01—J. c-P I <3 I 000' mm 3a. 'a -- Cl) 1 (I) ?I -fl <0' ..a. c-f u0t) 0.-,. c-I-CD 0(0 U) 0 0 :3 U) 0—' 0 1. 11 I a.n CD a. CD ci- 1 :3 c-I00 In ri-N :3- (D-a.c+ 0' InQa 10.0 :3•c-IC c- -'- —4 CD 0' CD PaCD U) 0 0'. 0 00 03cP3 CD -a U)--'. (a:3 J :3_:3 a. O I35CD 3 0 'a CD 0 S< (0 W (D0 0'< c-IG)< -J.:3 CD CD U) c+< :3-5 ci- 'aCD —-a 0 CD .a-5 a. Q,-a. .a. ç- (D c-P 01:3 CD a CD 00-0 3 —a U) Qk .4. c-P 0-< < c-POPi 03 U) CD a. c-I-CD ci-'. • CD —s a. --a.-'U)In0'. c-P o:3:3:3 c a .3 C -a.—' a. CD QICD a :3 V)c+1< U) 3 < CD i)(0 OOCDCDc - • Figure 32 Micrograph showing lensoid cored by i n a finegrained, laminated, f o l i a t e d m a t r i x o f s t r a i n e d quartz, K-fel dspar, muscovite, and nearly col or1ess c h l o r i t e . 0101(0 -s -'• C -- • -i-a• In (0 -Ii -a Figure 31 F o l i a t e d metarhyol i t e composed o f quartz, K-feldspar, muscovite, b i o t i t e , epidote, and magnetite. Steeply dipping s c h i s t o s i t y s t r i k e s N870W here. The metar h y o l i t e i s unconformably o v e r l a i n by conglomeratic M t . Simon Sandstone. Photo by Gene LaBerge, UW Oshkosh. �-63TITLE: METASEDIMENTARY ROCKSO OF THE SOUTH METASEDIMENTARY ROCKS F THE SOUTH FORK FORK AREA AREA LOCATION: Clark M; NE T26N,R4W: R4W: NE l1/4, / 4 , Sec. Sec. 1,1,T26N, C1 ark County County Highway Highway M; quadrangle, quadrangl e , Field F i e l d Location Location7832 7832 AUTHOR: Paul E. Myers DATE : - February, 1980 February, 1980 DATE: Stanley 15' 15' SUMMARY O OF SUMMARY F FEATURES: FEATURES: Mica-chlorite schist exemplify thet hmetasediments s c h i s tand and quartzite q u a r t z i t eata this t t h iquarry s quarry exemplify e metasediments Features ooff multiple m u l t i p l edeformation, deformation, and and high-grade high-grade metametaooff the t h e South South Fork Fork area. area. Features morphic minerals, which which ttypify amphiboliteterrane terrane tto morphic minerals, y p i f y the the Chippewa Chippewa amphibolite o the west west are absent iinn these age absent these rocks, rocks, aafactor f a c t o suggesting r suggestinga agreater greater ageand/or and/ormore morecomplex complex hhistory i s t o r y for f o r the theamphibolites. amphi bol ites . DESCRIPTION: DESCRIPTION: Metasediments exposed here(Figure (Figure33) 33)i ninclude: Metasediments exposed here c l ude: (1) (1 ) coarse coarse tot omedium-grained, medium-grained, with ffoliated, o l iated, müscovite-biotite muscovite-bioti t e qquartzite uartzite w i t h indistinct i n d i s t i n c trelict re1i ccross-bedding, t cross-bedding, (2) quartz-chlorite—biotite (2) q u a r t z - c h l o r i t e - b i o t i t eschist s c h i sshowing t showingspectacular spectacularkink—banding, kink-banding ,and and (3) lenticulated subordinatebbiotite (3) l e n t i c u l ated quartz-muscovite quartz-muscovi t e sschist c h i s t wwith i t h subordinate i o t i t e and and cchlorite. hlorite. On the basis basis ooff aa strong O n the stronggeophysical geophysical anomaly, anomaly, North North Central Central Mineral Mineral Ventures Ventures cores were werel later (1973)ddrilled (1973) r i l l e d two two cores cores aatt aa site s i t e 3.7 3.7 miles miles west west of o f here. here. These These cores ater studied petrographically by M.A. M.A. Piotruszewicz Piotruszewicz (1978) (1978) as as ppart. studied petrographically and and geochemically geochemical l y by art . of aa Masters of Masters tthesis h e s i s at a tthe t h eUniversity U n i v e r s i t yofoWisconsin-Milwaukee. f Wisconsin-Milwaukee. The The f first i r s t hole hole penetrated fine—grainedg rgraphitic schists; the hole from of the penetrated fine-grained a p h i t i c schists; the second second hole from the base base of the Mt. Sandstone 180 feet,t oto aa depth depth ooff 1075 M t . Simon Simon Sandstone a t at180 feet, 1075 ffeet e e t cut c u t through through quartzquartzmuscovite-chlorite-garnetsschist accessoryb ibiotite, muscovite-chlorite-garnet c h i s t wwith i t h accessory o t i t e , aactinolitic c t i n o l it i chornblende, hornblende, pyrite, p y r i t e , and and ccalcite. alcite. Small outcrops outcrops ooff fine—grained quartz-muscovite Small fine-grained quartz-muscovi t e sschist c h i s t along along South South Fork Fork 2 miles miles west ooff here Dam milest otothe the northeast northeast suggest suggestwidespread widespreadd idistriwest here and and at a t Mead Mead Dam 22 miles stribution of o f the the metasediments metasediments i in n tthis h i s area. area. �-64- The of quartz (84%), (12%), The qquartzite u a r t z i t e isi scomposed composed of (84%), muscovite muscovite (1 2%), bbiotite i o t i t e(2%) (2%) and accessoryplagioclase, plagioclase,ppyrite, and accessory y r i t e , and and cchlorite. h l o r i t e . The quartz is The quartz i s equigranular equigranular and and forms forms polygranular polygranular pods pods enclosed enclosed in i n muscovite. muscovite. The pods may maybeber relict The pods elict detriral d e t r i r a l grains. grains. The The rock lacks lacksbanding bandingand andisi squite q u i thomogeneous. e homogeneous. Sparse Sparse shreds shreds ooff fine-grained fine-grained brown brown bbiotite i o t i t eare areInterspersed interspersedwith w i t hthe t h emuscovite. muscovite. The kink-banded u a r t z - c h l o r i t e - b i o t i t e isi sa aspectacular spectacularrock rock whenseen seen The kink-bandedqquartz—chlorite-biotite when in Brown bbiotite i o t i t e flakes f l a k e shave have been been kink-folded, kink-folded, i n thin t h i nsection. section. (Figure (Figure 35) 35) Brown locally rep1aced l o c a l l yrotated r o t a t e dwith w i t hcleavage cleavage perpendicular perpendicular t to o ffoliation, o l i a t i o n , and and partially p a r t i a l l yreplaced by 1.0 m. Kink folds f o l d s have have an an amplitude amplitude ooff approximately approximately 1.0 mm. The by the the chlorite. c h l o r i t e . Kink The composition composition ofof tthis h i s rock rock is: i s : chlorite c h l o r i t e(57%), (57%),quartz quartz(38%), (38%),opaque opaque(3%), (3%),and and biotite The cchlorite h l o r i t e has has unusually unusually high i e f , isi spale palegreen, green, nonnonhigh re1 relief, b i o t i t e(1%). (1%). The pleochroic, yellow—gray p l eochroic, and andshows shows anomalous anomalous ye1 low-gray e xextinction t i n c t i o n colors. are with are interleaved interleaved w i t h the the folded folded cchlorite. hlorite. Quartz grains grains Quartz The The llenticulated, e n t i c u i a t e d , fine-grained fine-grainedquartz—muscovite quartz-muscovite sschist c h i s t has has essentially essentially the mineralogyasasthe thequartz, quartz,bbut higher rratio the same same mineralogy u t wwith i t h higher a t i o of o fmuscovite muscovite to t o quartz. quartz. AA chemical a specimen chemical analysis analysis ofo fthe t h emicaceous micaceous quartzite q u a r t z i t was e wasobtained obtainedfrom from a specimen taken (See Table 4; 4; 7832) 7832) A. (See taken at a t Location LocationA. Figure33-at aHighway Figure 33 --Geologic Geologicmap map of o fcounty countyquarry, quarry,Eau EauClaire C l a i r eRiver River t HighwayM.M. REFERENCE: REFERENCE: Piotruszewicz, analysis of of aa drill from western M.A., An An analysis d r i lcore l core from western Piotruszewicz, M.A., Clark Clark County, County, Wisconsin. Wisconsin. Unpub. thesis, University Unpub. M.M.S. S. thesis, U n i v e r s i t y of of Wisconsin, Wisconsin, Milwaukee, Milwaukee. 1978. 1978. �_______ ___ *:jfl C — — Pr — — ; — - r— — — - - j - a r — a" < -w- r— t — - - Figure Kink folds u a r t z - c h l o r i t e - b i o t i t e sschist chist Figure 34 34 —— Kink foldsi ninq quartz-chlorite—biotite PhotobybyGene GeneLaBerge. LaBerge. from f l o o r ,Location LocationC.C.Photo from quarry quarry floor, -- Figure 35 showingkink kinkfolds folds in 35 -- Photomicrograph Photomicrograph showing in Figure chlorite-quartz-biotite schist, Location B. c h l o r i te-quartz-bioti t e s c h i s t , Location B. BBiptite, iotite, now altered now ppartly a r t l y a1 t e r e d to t o chlorite, c h l o r i t e ,has hasbeen been folded folded also. also. �-67STOP STOP #8 #8 TITLE: - CATACLASTIC VEINLETS INHORNBLENDE-BIOTITE HORNBLENDE-BIOTITE METADIORITE METADIORITE CATACLASTIC VEINLETS IN LOCATION: LOCATION: Yellow River miles EE of of Cadott; Cadott;NW NW 1/4, 114, SE SE 1/4, 114. Sec. Sec. 33, 33, T29N, T29NY R6 R6W Yellow River 2 miles W Cadott 15' quadrangle Cadott 15 ' quadrangle I rç j - AUTHOR: AUTHOR: Paul Paul E. E. Myers Myers DATE: DATE : - March, 1980 March, 1980 '—_-__--——- I —r SUMMARY OF OF FEATURES: SUMMARY FEATURES : This contactbetween between foliated hornblende-bioti hornblende-biotite diorite This enigmatic enigmatic contact f a ifaintly n t l y foliated t e diori te and foliated metadacite(?) and strongly deformed, deformed, foliated metadaci t e ( ? ) (Figure 36)exemplifies 36) exempl i f i e s the themany many problems workingout out sequence sequencei ninrocks rocksaffected affected by by recurrent recurrent cataclasis, problems ofof working intrusion, folding, andand metamorphism. intrusion, folding, metamorphism. Field Fie1 d and and petrographic petrographic evidence evidence here, here, and places throughout throughoutthis this region, region, stron.gly the hypothesis and aatt most most places strongly support support the hypothesis tthat hat intrudedinto into more moreb brittle cataclastic veinlets veinlets and and dikes dikes are are synkinematically synkinematically intruded rittle rocks rocks at a t sub-anatectic sub-anatectic temperatures. temperatures. The The basic basic question question here here is, i s , "Under "Under what what conditions, and andaat whattime timewere werethethecataclastic cataclasticb ibiotite tonalite veinlets conditions, t what o t i t e tonalite veinlets (7904-B) emplaced?" empl aced?" DESCRIPTION: DESCRIPTION: chronologyf ifield on ffield AA chronology e l d sstation, t a t i o n , based based on i e l d relations relationsand and features features seen seen in in three, t h r e e tthin h i n sections sections(Myers (Myers7904-A-C) 7904-A-C) isi sproposed proposed below. be1 ow. Three Three pre-catacl pre-cataclastic astic protoliths protol i ths exist: exist:(1) Hornblende-biotite dacite dacite or o r tonalite, tonal i t e , (2) ( 2 )pegmatite, pegmatite, (1 )Hornblende-biotite and metadiorite. and (3) hornblende—biotite hornblende-bioti t e metadiori te. o r metatonalite(?) metatonal i t e ( ? ) iiss composed The foliated metadacite(?) of approxiThe foliated metadaci t e ( ? ) or composed of mately 50% plagioclase (An42), 50% plagioclase (An42),10% 10%fragmented fragmented and and altered a1 tered hornblende, hornblende,25% 25% fine-grained, fine-grained, polygonized, polygonized, strained quartz, quartz, and and 5% 5% bbiotite. i o t i t e . Plagioclase, hornblende, and arep apartially altered epidote, prochlorite, prochlorite, calcite, hornblende, and b i biotite o t i t e are r t i a l l y a1 tered tto o epidote, cal c i t e , The metadaci rnetadacite metatonalite(?) The t e oor r metatonal i t e ( ? ) has and magnetite(?) magnetite(?). has a conspicuous and conspicuouscata— catabent andand fragmented cclastic l a s t i cfoliation; foliation; bent fragmentedplagioclase plagioclaseporphyroclasts porphyroclastshave have ovoid ovoid outlines and outlines and fragmented fragmented hornblende hornblende crystal crystal remnants remnants have have been been dispersed dispersed along interlensing coarse, polygonal polygonal form form of of the quartz interlensing shear shear surfaces. surfaces. The The coarse, quartz and and the the replacement of hornblende by bbiotite cataclasis. replacement of hornblende by i o t i t esuggest suggest metamorphism metamorphism a after f t e r cataclasis. This isoclinal fold 36-E) . This rock rock contains contains several several detached detached isoclinal fold hinges hinges (Figure (Figure 36-E). . �_______________ -68- a granite g r a n i t e in in The pegmatite( n(not studiedi in The pegmatite o t studied n tthin h i n section) section) is i s probably probably a andand composed and quartz. quartz. composition: iti tisi leucocratic, s leucocratic, composed of o f pink pink feldspar feldspar and the quartz Feldspar el dspar cleavage cleavage planes planes are are conspicuously conspicuously bent, bent, and and the quartz locally l o c a l l yhas has been been llenticulated e n t i c u l a t e d by by cataclasis. cataclasis. The sheared hornbl hornblende-biotite The sheared ende-bioti t e meta—diorite meta-diori t e isi scomposed composed ooff reverse-zoned, reverse-zoned, strained, marginally (39%),fragmented, fragmented, subhedral subhedral marginal l ycrushed crushedplagioclase plagioclase(An54) (Ans4)(39%), green (54%),pale paleye1 yellow-brown green hornblende hornblende (54%), low-brown bbiotite i o t i t e in i nrandom random orientation o r i e n t a t i o nand and andpprochiorite, by a1 alteration Epidote and r o c h l o r i te, formed formed by t e r a t i o n ofo fhornblende hornblende distribution d i s t r i b u t i o n(3%). (3%). Epidote include coarse Accessories include coarse aapatite, patite, make up approximately approximately 3% 3%oof make up f the rock. rock. Accessories sphene, and magnetite magnetite (?). (?). sphene, and . Figure 36 36shows showsthe ther erelations The following f o l l o w i n gsequences sequences l a t i o n s ooff these these three rocks. rocks. The subsequent are possible: possible: (1) are I n t r u s i o n ofo ftonalite tonal it into e i n diorite t o d i o rand i t e and subsequentdeformation deformation ( 1 ) Intrusion with w i t h most most intense cataclasis c a t a c l a s i s and and development development o foff ofoliation l i a t i o n in i nthe t h emetadacites; metadacites; (2) subsequent (2) intrusion i n t r u s i o nof of diorite d i o r i t into e i n dacite t o daci tand e and subsequent deformation deformation wwith i t h localizalocal ization t i o n of o f isoclinal i s o c l i n a lfolding f o l d i n gand and cataclasis c a t a c l a s i s in i n the the dacite, dacite, possible possible Injection i n j e c t i o n of of Note felsic blocksoof moreb rbrittle f e l s i c "cataclastic " c a t a c l a s t i c dikes" dikes" into i n t othe thebroken broken blocks f more i t t l e ddiorite. i o r i t e . Note that the rrelative t h a t these these alternatives a1 t e r n a t i v e s reverse reverse the e l a t i v e ages ages ooff the the diorite d i o r i t e and and the the dacite. dacite. The curvatureofofthe thec cataclastic "veins" ccutting the ddiorite The curvature a t a c l a s t i c f ofoliation l i a t i o n near near tthe h e "veins" u t t i n g the iorite (B) the ddiorite andppulled apartt to (B) suggests suggests t that h a t the i o r i t e was was broken broken and u l l e d apart o aallow l l o w iintrusion n t r u s i o n of of Itisi sclear, clear,however, however, that t h a tcataclasis c a t a c l a s i saffected a f f e c t e dboth both the the the t h e more more ffelsic e l s i c rock. rock. It Note that t h a t the t h e folds f o l d s are diorite d i o r i t eand and the the dacite d a c i t e with w i t h its i t spegmatite pegmatite dikes. dikes. ftote detached, rootless, a factor suggesting considerably chaotic internal detached, rootless, f a c t o r suggesting considerably chaotic i n t e r n a l displacedisplace- are ment during or after folding ment during o r a f t e r folding. -.Metatonal i te with folded >'m//OLA/ q Ye//<? w ^?. . . . / Figure 3636---- BBiotite i o t i t e tonalite tonal i t e flaser f l a s e rgneiss gneiss veinlets v e i n l e t s (B) (B) cutting c u t t i n gmetadiorite metadiori t e (A) (A) Figure Antiformal hinges hinges in i n metadacite(?) metadacite(?) or o r metadiorite(?) metadiorite(?) plunge plunge steeply steeply northeast. northeast. Antiformal Fol i a t i o n in i nmetadacite(?) metadaci t e ( ? ) bends bends i into n t o ccataclastic a t a c l a s t i c veinlets v e i n l e t s(B). (B).Outcrop Outcrop slopes slopes Foliation gently toward toward tthe h e bottom f t the h e pprofile. rofile. gently bottomoof �-69 - -- Figure 37 A x i a l portion p o r t i o n of o fhinge hingeof o fdetached detached isoclinal isoclinal Figure 37 -- Axial fold Location E. E. Scale Scale iiss 66 inches inches long. long. f o l d segment, segment, Location Figure 38--- Nearly Nearly vvertical e r t i c a l cataclastic c a t a c l a s t i c veinlets v e i n l e t s cutting cutting . Figure 38 faintly f a i n t l yfoliated f o l i a t ehornblende d hornblendemetadiorite m e t a d i o r i t enear near location l o c a t i o nA. A. Note zoningoof with coarsel lentiNote zoning f vveinlet einlet w i t h concentration concentration ooff coarse enticular c u l a r feldspar feldspar porphyroclasts porphyroclasts near near the t h e center; center; quartzoquartzofeldspathic on photo photo f e l d s p a t h i c layers layersalong alongoutside outsideedges. edges. Line on is i s analogous analogous i in n location l o c a t i o n to t o veinlet v e i n l e tmargin margin described described in in Figure 39. 39. �-70- Biotite tonalite tonal i t eflaser f l aseraneiss aneiss Lenticular pl agiocl ase i n biot i t e f o l i a w i t h qiartz. P l agi ocl ase Quartz Biotite Hornblende -- 65% 20 15 0 Banded 1eucotrondhjemi eucotrondhiemi ttee Hornblende d i ori t e Banded Very coarse pl agi ocl ase w i t h shears and drag w i t h bent t w i n lamellae surrounded by f i n e r grained quartz - 40% 55 5 0 45% 5? 5 40 Figure 39 39 -- Cross section of of zoned cataclastic veinlet veinlet (Location Figure Cross section zoned cataclastic (Location B). B). Width Width of section section fromhornblende hornblende centerofofveinlet veinlet ((left) from d i odiorite r i t e ( r (right) i g h t ) t otocenter l e f t ) isi s7.0 7.0cm. cm. �-71— STOP STOP #9 #9 TITLE:: TITLE CADOIT INTRUSION CADOTT INTRUSION BRECCIA BRECCIA AND AND CATACLASTIC CATACLASTICROCKS ROCKS LOCATION: SW¼, T29N, R6W: Cadott quadrangle;F Field Locatiion 7905 LOCATION: SW s, NEs,NE¼, Sec.Sec. 31, 31, T29N, R6W: Cadott 15' 15' quadrangle; i e l d Locatiion 7905 AUTHOR: P. P. E. E. Myers Myers DATE: DATE : - February, 1980 February, 1980 SUMMARY OF SUMMARY O F FEATURES: FEATURES: Mafic amphi amphibolites andf ofoliated hornblendetonal tonalite containingi sIsoclinally l i a t e d hornblende it e containing o c l i n a l l y folded folded Mafic bol it e s and quartz, as angular angularxenoliths xenolithsi in quartz, aplite, apl ite, and and pegmatite pegmatite vveinlets e i n l e t s eexist x i s t as n aa 1lighter ighter biotite Folds iin n the the xenoliths xenoliths and and l lineations i n e a t i o n s iinn the t h e enclosing enclosing ttonalite onalite b i o t i t e tonalite. t o n a l i t e . Folds southeast (Figure 40) contains aa pervasive pervasive cataclastic cataclastic pplunge l unge southeast 40) The The bbiotite i o t i t e tonalite tonal it econtains ffoliation o l i a t i o n which which was was locally l o c a l l ybuckled buckled into i n t ochevron chevron folds, folds, which which plunge plunge steeply steeply northwest. The Thef first byby a second west. i r s t cataclastic c a t a c l a s t i cfoliation f o l i a t i o is n truncated i s truncated a secondone one (Location (Location A A in in discardat vveinlets The llater a t e r cataclastic c a t a c l a s t i c event event produced produced discordant e i n l e t s of o f leucoleucoFigure 40 40 ). The Figure trondhjemite gneissw iwith strong cataclastic parallel trondhjemi t e f lflaser aser gneiss t h a astrong catacl a s t i c f o lfoliation ' i a t i o n para1 l e l t to o ttheir heir walls (Figure of walls (Figure 42 42 ).). The The second second ccataclastic a t a c l a s t i c event event included included ssignificant i g n i f i c a n tamounts amounts of trendingf faults. sstrike-slip t r i ke-sl ipdisplacement displacement along a1ong west-northwest west-northwest trending aults. DESCRIPTION DESCRIPTION , The predominant predominantrock rocktype typehere herei sis ffoliated The o l iated tonalite tonal it ecomposed composed ooff plagioclase p l agi ocl ase 30-55%), quartz quartz (10-40%), hornblende (0-25%) (0-25%)and andbbiotite 30-55%), (10-40%), hornblende i o t i t e (0-15%). (0-1 5%). These ((An An minal' are partly min&?$'are p a r t lreplaced y replacedby by chlorite c h l o r i t e(of ( o several f several varieties), v a r i e t i e s ) ,epidote, epidote, and and Magnetite (1-5%) (1—5%) by-producti ninthe thecchioritization ssericite. e r i c i t e . Magnetite i s is i sisa aby-product h l o r i t i z a t i o nofo fhornblende. hornblende. The tonalites beenmyloni mylonitized and1ocal locally ites have have been t i zed and l y rrecrystallized e c r y s t a l I i z e d (Location (Location A). A). The tonal At A t locations locations A-D A-D (Figure (Figure 40) 40) bbiotite i o t i t e tonalite t o n a l i t e with w i t h an an older o l d e r ccataclastic a t a c l a s t i c ffoliaoliation containsl elenticular xenoliths of of chlorite.and t i o n (NlO-20°W) (N10-20OW) contains n t i c u l a r xenoliths c h l o r i t e a n d epidote-rich epidote-rich metameta- volcanic(?) rock.The The01older cataclastic vo1 cani c ( ? ) rock. der catacl a s t i c f o foliation l ia t i on i sis aaxial-planar x i a1 -planar t to o iisoclinally socl inal l y These rocks rocks are are ccut folded pegmatite, pegmatite, apl aplite, u t by by folded i t e , and and quartz quartz layers layers (Location (Location A). A). These a pervasive trendingf ofoliation pervasive N65-75°W N65-75 W trending l i a t i o n and and mylonitic m y l o n i t i cshear shear zones. zones. �-72- STRUCTURE SYMBOLS SYMBOLS STRUCTURE go0 80 c. compositional compositional layering 1ayeri ng 600 60" mica mica ffoliation oliation 70' 70. \ cataclastic c a t a c l a s t i c ffoliation, oliation, lenticulation 1enticul a t i o n "5oplunge of lineation G -- Figure Outcrop structure s t r u c t u r e map map of the the Yellow Yellow River River bridge bridge area, a r e a , Cadott Cadott Figure 40 40 -- Outcrop Figure -- Folded Folded iisoclinal s o c l i n a l folds folds Figure 41 41 -in mafic xenolithinin ffolmafic amphibolite amphibolite xenolith oliated i a t e d bbiotite t o t i t e tonalite. tonal i te. Lineation Lineation on on left l e f tside s i d eofofthe thexenolith xenolithplunges plunges550 55O southeast. southeast. Location EE -- Figure Figure 42 42 -- Folds Folds ini nbanded banded mafic mafic tonalite t o n a l i t e cut c u t by by aplite a p l i t e veins veins (left ( l e f tand and right) r i g h t )and and by by coarser coarser tonalite t o n a l i t e vein vein to with w i t h cataclastic c a t a c l a s t i c ffoliation o l i a t i o n parallel para1 1el to its i t swalls walls(center) ( c e n t e r )Location LocationG. G. �-73— West River bridge, bridge, ffoliated West oofthe f t h e Yellow Yellow River o l i a t e d biotite b i o t i t etonalite t o n a l i tencloses e enclosesangular angular xenoliths tonalite o fmore more mafic mafi c hornblende hornblende tonal it e or o r amphibolite amphi bol it e containing containing strongly strongly xenol iths of 43 ) Xenolith deformed aaplité p l i t e and and pegmatite pegmatite sstringers t r i n g e r s (Figure (Figure41 41 and and 43 Xenolith orientation orientation deformed Small Small ffolds o l d s within w i t h i n the the xenoliths xenoliths NIOOW. here (as (as at a t Little L i t t l eFalls) F a l l sis) about i s about here NlO°W. plunge southeast southeast at a t lO_600 10-60 (See (See Figure 40 40 ).). plunge CHRONOLOGY CHRONOLOGY The baseds osolely ont hthe cross-cutting rrelationships The ffollowing o l l o w i n g sequence sequence i sis based l e l y on e cross-cutting e l a t i o n s h i p s of of •features out features aatt this t h i s location, location,but b uthey t theycorrelate c o r r e l a t well e w e with l l w i tsquences h squencesworked worked o u t for for o t h e r areas. areas. other 1. maficp rprotolith coarse, tonal tonalitic it i camphibolite amphibol it e 1. (Oldest) (Oldest) Metamorphism Metamorphism o f of mafic o t o l i t h t to o coarse, accompanied segregation(?) stringers, quartz accompanied byby segregation(?) o f off efelsic l s i c stringers, quartz veins. veins. 2. with 2. Shear Shear ffolding olding w i t h formation formation oof f iisoclinal s o c l i n a l folds. folds. 3. 3. Intrusion I n t r u s i o n ooff light-colored 1ight-colored bbiotite i o t i t e tonalite tonal i t e ("foliated ( " f o l i a t e d tonalite") tonal i t e " ) with with formation formation of o f an an intrusion i n t r u s i o nbreccia breccia(Figure (Figure41 41 ). ). 4. 4. Cataclasis, Cataclasis, formation formation of o f more more isoclinal i s o c l i n a l folds f o l d s (Location (Location D). D). Cataclasis Cataclasismay may have accompanied t r u s i o n . (Figure 45). 45). have accompaniedi nintrusion. 5. 5. Local Local chevron chevron f ofolding l d i n g oof f ccataclastic a t a c l a s t i c ffoliation o l i a t i o n(Location (Location E, E, Figure Figure 44 44 ). 6. 6. Intrusion I n t r u s i o n of o fdarker darker tonalite t o n a l i t e(Location (Location 0) D) with w i t h formation formation of o f intrusion intrusion breccia containing xenoliths xenoliths ooff catacl cataclastically tonalite. breccia containing a s t i c a l l y deformed deformed 1ilighter g h t e r tonal ite. 7. 7. Intrusion I n t r u s i o n of o faplite a p l i t and e andpegmatite. pegmatite. 8. G Gand 8. Formation Formation oorr jntrusion(?) i n t r u s i o n ( ? ) of o fcataclastic c a t a c l a s t i cveinlets v e i n l e t(Locations s (Locations andH,H, Figures Figures 42 and and 45 45 ).). Strike-slip S t r i k e - s l i pdisplacement displacement along along west-northwest-trending west-northwest-trending ffaults. aults. 42 Figure -- Intrusion amphibolite iin Figure 43 43 -I n t r u s i o nbreccia breccia of o fbanded banded amphibolite n biobio- foliated f o l i a t e d biotite b i o t i t etonalite t o n a l i t eata Location t Location H. H. �-74- -- Figure 44 44 -- Chevron-fol Chevron-folded tonalite Figure ded f o lfoliation i a t i on i ninbbiotite i o t i t e tonal it e which contains contains tthe mafic amphi amphibolite xenoliths at which h e mafic bol it e xenoliths a t Location Location here plunge plungesteeply steeply nnorth(?) Horizontal outcrop. outcrop. E. Folds Folds here o r t h ( ? ) Horizontal -- Figure 45 -- Isoclinally I s o c l i n a l l yshear shear folded folded bbiotite i o t i t e tonalite tonalite Figure 45 tonalite. Cataclastic sstringers t r i n g e r s in in darker darker tonal it e . Location Location D. D. Catacl astic View north-northeast. foliation is N80°E, 750N. fo1 i a t i o nhere here i s N80OE, 75ON. View north-northeast. - �—75- STOP STOP #10 #10 TITLE: DIKES AT AT WISSOTA WISSOTA DAM DAM LOCATION: LOCATION: NNW W 1/4, T28N, R8W, R8W, Lake Quadrangle 1/4, Sec. Sec. 3, T28N, Lake Wissota Wissota 77 1/2' Quadrangle Field location, location,7835 7835++7906 7906 AUTHOR AUTHOR:: Paul E. Paul E. Myers Myers DATE: DATE : - December, 1977, and March, December, 1977, March, 1980 1980 SUMMARY OF FEATURES: FEATURES: SUMMARY OF A intrusion sequence exposedi in A complex complex intrusion sequence exposed n aa large outcrop outcrop (Figure (Figure47). 47) below below Wissota DDam (2.5m imi.) northeast of of Chippewa is: (1) protoclastic Wissota am 4.04.0kmkm(2.5 . ) northeast Chippewa F Falls a l l s is: protoclastic pegmatite bbiotite i o t i t e trondhjemite, trondhjemite, (2) (2) biotite b i o t i t etonalite, tonal i t e(3) , (3) pegmatiteand andquartz quartz veins, veins, and((5) trondhjemite ((4) 4 ) gabbro-diabase, gabbro-diabase, and 5 ) trondhjemi t e veinlets. A A ccataclastic a t a c l a s t i c zone zone cuts cuts and shows showsl eleft-lateral 40-50 meter through 33 and f t - l a t e r a l displacement. displacement. The The 40-50 meter gabbrogabbrounits 11 through diabasedike dike grades gradesinward inwardfrom fromaphanitic aphaniticbasalt basaltalong alongi its diabase t s walls to t o coarse coarse Inclusions of very very coarse coarse norite n o r i t e and and plagioclase plagioclase pyroxene gabbroi niniits pyroxene gabbro t s core. core. Inclusions occur along alongthe thenorth north wall wall of of the crystal fragments fragments occur the dike. dike. The The gabbro-diabase dike is i s intruded intruded by by coarse, coarse, pink p i n k trondhjemite trondhjemite (quartz (quartz + oligoclase) 01 igoclase) which which is is dike Thesemiddle middlet to rocks are smallffaults. ooffset f f s e t by by numerous numerous small a u l t s . These o llate a t e Precambrian Precambrian rocks are gravels and and ssilts t h i n outwash outwash gravels i l t s ofofPleistocene Pleistoceneage. age. overlain here here by by thin DESCRIPTION: DESCRIPTION.: Trondhjemite and Tonal Tonalite: Trondh jemi t e and ite: Theooldest rock aatt Wissota WissotaDDam gneissic bbiotite The l d e s t rock am i s isf afaintly i n t l y gneissic i o t i t e trondhjemite trondhjemite composed (50%),quartz quartz(35%), (35%),m microcline (5%),bbiotite composed of of01oligoclase i gocl ase (SO%), i crocl ine (5%), i o t i t e (5%), (5%), muscovite Weakf ofoliation muscovite (5%), (5%),and and abnormally abnormallyabundant abundant sphene. sphene. Weak l i a t i o n srikes s r i kesNl5°W N15OW and and (N2O-5O°W) G,D) The gneissic adamellite adamelliteisi cut s cut (N20-50°Wby by dikes dikes(Loc. (Loc.G,D) dips d i p s steeply steeply east. e a s t . The darkergray graybbiotite and and iirregular r r e g u l a rmasses masses (Loc. (Loc. I and and J) of of medium-grained, medium-grained, darker iotite tonalite t o n a l i t e (Loc. (Loc. D), D ) , which which locally l o c a l l y (Loc. (Loc. G) G ) contains contains llenticular e n t i c u l a r xenoliths xenoliths of of �___"ft. -76- bandedamphibol amphibolite Big The t tonalite o n a l i t e intrusions intrusions banded i t e s i similar m i l a r t oto tthat h a t seen seen aatt B i g Falls. F a l l s . The show nograin grainssize diminution along along contacts, contacts, and show no i z e diminution and tthe h e amphibolite amphi bol i t e xenoliths Someo foft hthe tonalite areoof such i irregular e tonal i t e masses masses are f such rregular are are relatively r e l a t i v e l yunaltered. unaltered. Some shape doubteexists as tto they are are iintrusions shape t hthat a t doubt x i s t s as o whether whether they n t r u s i o n s or o r segregations segregations in in sphene,sosoc hcharacteristic the trondhjemite trondhjemite. Euhedral Euhedral sphene, a r a c t e r i s t i c oof f the trondhjemite is is the trondhjemite. tonalite absent iin n tonalite tonal it esections sectionsexamined. examined. The The tonal it e isi scomposed composed ooff plagioclase p l agiocl ase absent (An-38), bbiaxial A l l minerals minerals ini nthese theserocks rocksshow show (An-38), i a x i a l quartz, quartz, biotite, b i o t i t e , and and epidote. epidote. All internal textures ccharacteristic f r a c t u r i n g and and dislocation, dislocation, although a1though the t h e mortar mortar textures haracteristic . i n t e r n a l fracturing of mylonitized of mylonitized plutonic p l u t o n i c rocks rocks are are absent. absent. The trondhjemite andtonal tonalite The trondhjemi t e and it e are cut c u t by by east-northeast-trending east-northeast-trending pegmatite, pegmatite, pegmatites showc rcrystal quartz and epidote vein1 veinlets. The pegmati t e s show y s t a l oorientation r i e n t a t i o n perpenperpenquartz and epidote ets. The ddicular i c u l a r to t o their t h e i rwalls--a w a l l s--afactor f a c t oindicating r i n d i c a t i nemplacement g emplacement underconditions undercondi t i o n s ooff no iisotopic tension oorr thermal tension thermal contraction. contraction. Although Although no s o t o p i cdates dateshave have been been obtained obtained from these rocks, it is probable that by correlation with similar from these rocks, i t i s probable t h a t by c o r r e l a t i o n w i t h s i m i l a r rocks rocks elseelsewhere, ttheir 1845mmillion where, h e i r age age is i sbetweer between 1820 1820 and and 1845 i l l i o n years. years. A discordant sheet sheetoof A tthin, h i n , branching branching discordant f ffoliated o l i a t e d biotite b i o t i t etrondhjemite trondhjemite (Loc. (Loc. D)-here cuts cuts and andooffsets the oolder by lleft-lateral here f f s e t s the l d e r rocks rocks by e f t - l a t e r a displacement l displacement (Figure (Figure 46) 46) The The ffoliated, o l i a t e d , mylonitized mylonitizedtrondhjemite trondhjemite layer l a y e risi 1-3 s 1-3meters meterswide wideand and trends trends Dragfolded foldedf ofoliation rocksi nindicates Drag l i a t i o n iin n the t h e enclosing enclosing rocks d i c a t e s 1eleft-lateral ft-lateral N55°W. N55OW. S l ickensi ded ffault a u l t surfaces surfaces elsewhere e l sewhere iinn this t h i soutcrop outcrophave have ddisplacement. i spl acement. Slickensided similar s i m i l a r strike s t r i k eand anddip d i pand and slickensides slickensides plunging plunging 5°NW, 5ONW, aaf afactor c t o r iindicating ndicating nearly horizontal, horizontal, lleft-lateral nearly e f t - l a t e r a l strike-slip s t r i k e - s l i displacement. p displacement. / -, / / —..g .- . .z- / '/ ,- I-—', —, d.. granite ,Pmati tei - I' ' drag folds rod\S%'SZ ? drag f o l d s roduce by sinistra s i n i s t r a displacement' displacemen — foliated f o l i a t e d biotite b i o t i t etrotIdhjen p / ,v/,ra ', , I 80' / -- i e l d sketch y l o n i t i c vveinlet e i n l e t in i n foliated f o l i a t e dtrondhjemi trondhjemite Figure Figure46 46 -- FField sketchooff mmylonitic te Location Location FF Diabase Diabase Dike: The rocks described described above abovewere werei nintruded shallow depth The rocks t r u d e d aatt shallow depth in i n Late Late Precambrian time (Â¥^I10 ("1100 m.y. dikes, one B.P. )by bynumerous numerous gabbro-diabase gabbro-diabase dikes, one ooff Precambrian time m.y. B.P.) Thevvertical e r t i c a l dike dike strikes strikes which iiss superbly which superbly exposed exposed i nin tthis h i s outcrop. outcrop. The Numerous apophyses apophyses N20—60°E margins aphanitic basalt. basalt. Numerous N20-60° andand hashas c h ichilled l l e d margins o fofaphanitic extendalong alongj ojoints extend i n t s iin n the the enclosing enclosing ggranitic r a n i t i c rocks rocks (Loc. (Loc. A, A, Figure Figure 47). 47). AA narrow zone ooff plagioclase xenoliths narrow zone p l agioclase and and hypersthene hypersthene gabbro gabbro xenol iths occurs occurs about about one one The llabradorite a b r a d o r i t e (An60) (An6,,) meter the nnorth wall of meter i inside n s i d e the o r t h wall o f the the dike dike at a tLocation Location B. B. The fragments are up up tto 20 centimeters centimeters long long and and are are ooriented with fragments are o 20 riented w i t h long long �-.77- -- Figure 47 47 -- Geologic Geologicmap mapofo Wissota f WissotaDam Dam area. area. Figure �-78- - were ffirst The fragments fragments were i r s trounded rounded by by directions parallel d i rections para1 1e l to t o the.dike the dike wall. wall . The corrosion during ddike ? ) and and llater a t e r broken broken iin n transit t r a n s i tupwards upwards during i k e intrusion. intrusion. corrosion ((?) Closely angular hypersthene hypersthene(C?) gabbroo rornnorite ? ) gabbro o r i t e xenoliths up up Closely associated associated angular to long cconsist t o 40 40 centimeters centimeters long o n s i s t of o f very very coarse, coarse, dark dark brown brown tto o dark dark olive olive gray hpersthene,now' now mostly gray hpersthene, mostly a1taltered e r e d t otot atalc, l c , iiddingsite, d d i n g s i t e , and and chlorite, c h l o r i t e , which which is i s intimately i n t i m a t e l yintergrown intergrown with w i t h very very coarse coarse plagioclase plagioclase llaths a t h s up up to t o 15 15 centicentiandhow how thesexenol xenoliths meters meters ini nmaximum maximum dimension. dimension. Where Where and d i did d these it h s ccrystallize? r y s t a l 1i z e ? (They gabbrosfound foundnear neart hthe baseo foflayered layeredi nintrusions (They cclosely l o s e l y resemble resemble gabbros e base t r u s i o n s llike ike those along the the nnorth those along o r t h shore shore of o f Lake Lake Superior.) Superior. ) Why Why aare r e tthe h e xenoliths xenol i t h sconcenconcentrated t r a t e d only only along along one one wwall a l l of o f the t h e intrusion? i n t r u s i o n ? How How ddid i d tthe h e dike d i k e form? form? The diabaseddike wassampled sampled contact with s contact w i t h gneissic gneissic The diabase i k e was a t at l o clocation a t i o n B Ba tati tits The trondhjemite, att distances trondhjemite, and and a distances of o f 6, 6, 25, 25,50, 50,and and120 120cm cm from from the t h e contact. contact. The rock almost plagioclase(An(An7_)) enstatite, rock iiss composed composed almost e n tentirely i r e l y o fofplagioclase e n s t a t i t e , and and (mostly magnetite,y pyrite, andi%@i hmtite) Opaques (mostly magnetite, r i t e , and t e )decrease decrease in in pegeonite. pegeoni te. Opaques 7 abundance inward(See (SeeTable Table9). 9). Plagioc Plagioclase abundance inward ase occurs occurs as anhedral anhedral to t osubhedral subhedral -- COMPOSITIONOF OFDIKE DIKE BORDERPHASES PHASES TABLE BORDER TABLE 99—- COMPOSITION MINERALS MINERALS Contact Contact 66 cm cm 25 cm cm 50 50 cm cm P l ag Plag 68% 68% 63% 63% 48% 48% 53% 53% 52% 52% 7+ 7+ 12+ 12+ 28 28 27 27 28 28 33 44 66 14 14 10 10 99 1 33 22 22 . --- Biotite Biotite --- Opaques Opaques 15 15 16 16 —— -— --- 99 8 8 44 1 1 1 1 -- Olivine 01 ivine Chlorite Chlorite Accessories 1 -- - 1 1 120 120 cm cm 1 22 1 i. -- TABLE 10-- SIZE SIZE VARIATION VARIATIONINWARD INWARD IN I N DIKE DIKE TABLE 10 o 40 80 20 40 80 (cm) Contact Distance from from (cm) 100 126 cm �-79- laths with m at w i t h size s i z eranging ranging from from 0.13 0.13 mm a t the the contact contact to t o 0.75 0.75 m mm at a t aa distance distance of of 120 m. An 120 mm. content in the An content the plagioclase plagioclaseincreases increases inward. inward. Enstatite Enstatite forms forms blocky blocky wedge-shaped, i ninterstitial t e r s t i t i a lgrains, grains,has hasa a2V2Vofof50-60°, 50-60° anda asize s i zfrom e from 0.10 mrn wedge-shaped, and 0.10 mm at of 120 m. (Table a t the the contact contact to t o0.50 0.50 mm mm aat t a a distance distance of 120 mm. (Table 10.) 10.) Finer Finer grained grained pigeoni t e forms forms pale i n k , weakly pigeonite pale greenish greenishbrown brownt otop pink, weaklypleochroic pleochroicfibers. fibers. Biotite Biotite increases in i n abundance abundance tto o about percent at a t aa distance distanceofof120 120mm mm from from the conconincreases about 66 percent tact. tact. -- Figure Figure 48 48 -- Intrusive Intrusivecontact contactbetween between chilled chilled basalt basalt (center) (center) and and anorthositic anorthosi t i c gabbro gabbro inclusion incl usion at a tLocation Location C. C. Note Note llate, a t e , fault-related faul t-related fracturing. fracturing. Photo Photo width width is i s 4.2 4.2 millimeters. millimeters. At A t location 1ocation B, B, the thediabase diabase dike d i ke is is cut cutby by aa 3-5 3-5 centimeter centimeter vein vein of of coarse-grained trondhjemite (oligoclase The rock rock isisunusual unusual coarse-grained trondhjemi t e (01 igoclase + quartz). quartz). The because of the the pervasive orange-red color color of the because of pervasive orange-red the plagioclase pl agiocl ase(dispersed (dispersed iron the degree t h i n section section by by the the iron oxides) oxides) and and the degree ofof sstrain t r a i n exhibited exhibited iinn thin quartz, an unusual unusualfeathery, feathery, lamellar lamellar undulatory extinction. undulatory extinction. quartz, which which shows shows an The plagioclase i n aa Since the vein vein occurs occurs in is locally locallybent bentand andcrushed. crushed. Since The pl agiocl ase is north—northwest zonewhich whichcuts cutsthe thediabase diabase dike,i tit is is not surprising surprising north-northwest f afault u l t zone dike, to strongly developed t o see see strain s t r a i n features, features, but b u t iti is t iunusual s unusualtot osee seeit iso t so strongly developed in in Late this rock Late Precambrian Precambrian rocks. rocks. Since Since the mineral mineral composition composition ofof this rock is isso so simple, an approximate The simple, iti twould wouldnot notbe be difficult d i f f i c uto l t calculate t o calculate an approximatenorm. norm. The quartz-plagioclase The trondhjemite trondhjemite dike offset by by dike is offset about 0.8. 0.8. The quartz-plagioclase ratio r a t i o isisabout small subsequently fibrous calcite, small faults f a u l t s which which were were subsequently f i lfilled l e d wwith i t h fibrous c a l c i t e , an an indication indication of considerable considerable post-diabase post-diabase aactivity c t i v i t y in i n this thisarea. area. . of �-80- - OOLOGY - WISSOTA ;-i?O:;OLOGY WISSOTADAM DAMAREA AREA 1 1 Metamorphism formation amphibolite tonalite) . Metamorphism andand formation of of amphibolite ( x e(xenoliths n o l i t h s i nintonal it e ) 2. emplacement 2 . Synkinematic Synkinematic emplacement of of f o lfoliated i a t e d b biotite i o t i t e trondhjemite trondhjemi t e with with development ooff foliation development f o l i a t i oNlO—15°W. n N10-1 OW. 3. (?) of of biotite 3. Intrusion I n t r u s i o n (?) b i o t i t e tonalite t o n a l i t e roughly roughly pparallel a r a l l e l tto o foliation foliation iinn the t h e trondhjemite trondhjemite (Location (Location G, G, D) D) 4. Left-lateral L e f t - l a t e r a l strike-slip s t r i ke-sl ifaulting p f a u l t i nand g and development of o f cataclastic cataclastic 4. development veinlets F, P, v e i n l e t s N45-55°W. ~ 4 5 - 5 5 O ~ (Locations .(Locations F, P, and and 0) 5. Intrusion 5. I n t r u s i o nofo fpegmetite pegmetite dikes dikes associated associated with w i t h thermal thermal contraction contraction and/or ccrustal r u s t a l tension. tension. (Location '(Location E.) E. ) and/or 6. E' 6. Jointing, J o i n t i n g , deposition deposition of o fepidote, epidote, and and small-scale small-scale faulting. fau 1t i n q . (Locatioii (Loca t 7. froma addifferentiatinç 7. Intrusion I n t r u s i o nofo fdiabase diabase with w i t hmagmaderived magma derived from ifferentiatino ) adepth. t depth.(Locations (Locations A, A, B, B, C, C, H) H) ssill(?) i l l ( ? at 8. Intrusion 8. I n t r u s i o nofo leucotrondhjemite f leucotrondhjenn'te dike dike (Location (Location B) B) 9. Faulting 9. F a u l t i n g and and development development o of f sstrain t r a i n features features in i n leucotrondhjenite leucotrondhjerii t e 10. 10. Precipitation P r e c i p i t a t i o n of o f calcite c a l c i t eveinlets veinletsini nthe thefault f a uzone.(LoCation l t zone.(Location B) B) 11. Erosion. 11. Erosion. , �- -81 -81- STOP STOP #11 #11 TITLE : TITLE: AMPHIBOLITES OF AMPHIBOLITES AND AND GRANITES GRANITES O F JIM JIM FALLS FALLS LOCATION: LOCATION: EE 1/2 Quadrangle 1/2 Sec. Sec. 30, 30, TT30 30N, N, RR77W, W , Jim JimFalls, F a l l sBloomer , Bloomer15" 15''Quadrangle AUTHORS: AUTHORS: DATE: DATE : Paul E. E. Myers Myers and and Douglas Doug1as R. R. Maercklein Maerckl e i n February, February, 1980 1980 SUMMARY O F FEATURES: FEATURES: SUMMARY OF Banded amphibolites, probably probably derived derived from from mafic mafic volcanicsand Banded amphibolites, volcanics and assocassociated intruded by by granites of i a t e d sediments, sediments, were were intruded o f diverse diverse composition composition and and ttheir heir cogenetic cogeneti c pegmatites pegmati t e s aatt several several times times ini nMiddle MiddlePrecambrian Precambrian time. time. Cataclasis, Catacl a s i s , folding produceda ahhighly deformedsystem systemo of f o l d i n gand andmetamorphism metamorphism produced i g h l y deformed f t tectonically ectonically interlensing only ppartial i n t e r l e n s i n g rock rock units u n i t s showing showing only a r t i a l preservation preservation ooff older o l d e r structures. structures. Prevailing Prevail i n g regional regional structural s t r u c t u r a lgrain g r a i nisi ENE. s ENE. Late Late Precambrian Precambrian diabase diabase dike dike i n t r u s i o n(1100 (1100 - 900 900m.y.?) my.?) followed followedprolonged prolonged erosion. erosion. intrusion - DESCRIPTION: DESCRIPTION: Garnetiferous gneissand andsschist with h i gh-amp1 itude Garneti ferous hornblende hornblende gneiss chist w i t h folded, f o l ded ,high-amplitude isoclines, i s o c l i n e s , (Figure (Figure49)persistent 49)persistentENE ENE strike s t r i k eand and steep steep dip d i pare arecut c u tsubconsubconcordantly from leuco-tonal leuco-tonalite cordantly by granitic g r a n i t i c rocks rocks ranging ranging in i ncomposition composition from it e to to occurred aatt several granite. Pegmatite Pegmatite ddike i k e i intrusion n t r u s i o n occurred several stages stages ooff "granite" "grani tell granite. i n t r u s i o n . The The oolder l d e r ggranitic r a n i t i c rocks rocks are are foliated f o l i a t e d and and locally l o c a l l ymylonitized. myloni t i z e d . intrusion. Shearing and boudinage boudinageofofpegmatite pegmatitesstringers themi into Shearing and t r i n g e r s transposed transposed them n t o oblique oblique concordance lamination iin concordance wwith i t h lamination n the t h e enclosing enclosing rocks rocks (Figure (Figure 51). 51 ). AArough rough correlation c o r r e l a t i o ncan canbe bemade made between between r relative e l a t i v e age age and and concordance concordance o of f vveinlets. einlets. At A t location l o c a t i o n A, A, thinly t h i n l laminated y laminatedamphibolite amphibolite was was intruded intruded by by granite g r a n i t e so so that lenticular slices of the amphibolite were dragged en echelon away t h a t l e n t i c u l a r s l i c e s of the amphibolite were dragged en echelon away from from coarse ggranite t h e wall w a l l (Figure54). (Figure54). The T h e coarse r a n i t e pegmatite pegmatite intruded intruded under under stress stress the �-82- contains en enechelon echelonfractures fracturesfi filled The amphi amphibolitecontains 11ed with w i t h very very coarse coarse quartz. q u a r t z . The bol itegranite (trondhjemite) contact is sheared, cataclastically blended, and regrani te (trondhjemi t e ) contact i s sheared, c a t a c l a s t i c a l l y blended, and Since the the ggranite r a n i t e intrusion i n t r u s i o nwas was apparently apparently crystallized crystal 1ized -- "granitized". "grani tized". Since guided bylamination laminationi ninthe the amphibolite, amphibolite,t the effects of guided by h e effects of cataclasis cataclasis In i nmodimodifying the the contact contact could could be be easily e a s i l yoverlooked. overlooked. Small (F-2) (F-2) folds at plunge gently gently east-northeast. east-northeast. These These are are a tLocation Location CC plunge Small folded F-i isoclinal folded F-1 i s o c l i n a lfolds, folds,and anda afew fewhinges hingescan can be be found found In i n the the outcrop. outcrop. The The geometryo fofthe thei sisolcinal folds, not by F-2 F-2 ffoldlng.ls geometry o l c i n a l folds, not modified modified by o l d i n g i s best best displayed displayed unusual nature nature of of the a t Location Location B. B. The The unusual t h e F—2 F-2 f ofolds l d s iIs s shown shown iin n Figure Figure 50. 50. at Since pegmatiteveins veinswere werec clearly involved iin Since aaplite p l i t e and and pegmatite l e a r l y involved n the t h e F-i F-1event,, event, and and since theseveins veinsalso alsocut cutt hthe appears tthat h a t the the since these e ggranitic r a n i t i c iintrusives n t r u s i v e s here, here, iittappears F-2 ffolding F-2 o l d i n g was was qqu.ite u i t e llate. ate. The The deformational sequence sequence is i ssuninarized summarizedon onpage page 83. of iisoclinally 83. Xenoliths Xenoliths of s o c l i n a l l yfolded folded amphibolite amphibolite occur occur iin n the the granite g r a n i t e (Figure (Figure 52). 52). The aeromagnetic aeromagnetic map map (Figure (Figure 55) The 55) shows shows aapronounced pronounced V-shaped V-shaped westward westward concon- vergence Jim Falls. Falls. The The low low magnetic magneticrrelief vergence aat t Jim e l i e f ofo fthe thebedrock bedrockbetween between these these two two magnetic (amphibolite) ridges iiss probably eastwardextension extensionoof the ggranitic magnetic (amphi bol i t e ) ridges probably an an eastward f the ranitic rocks exposed exposed iInn the and the thedam. dam. theChippewa Chippewa River Riverchannel channel between between Location LocationAA'and A well-defined, arcs southwestward map A we1 1-defined, discordant discordantridge ridge arcs southwestwardacross acrossthe the mapand andcrosses crosses the "amphibolite ridg&' about miles east east ooff the the "amphibol i t e ridge" about 22 miles the bridge bridge at a t Jim Jim Falls. Fa11s. The The feature dike ooff considerable size, possibly possibly the the dike that feature is i s probably probably a diabase diabase dike considerable size, that is i s exposed exposed at a tWissota WissotaDam. Dam. Petrography and and Geochemistry Geochemistry In I n contrast contrast to t o the the alumina-rich, a1 umina-rich, garnetiferous garnetiferous amphibolites amphibol ites of o f the t h e Cornell Cornel 1 area, the the amphibolites Falls area, amphibolites aatt Jim Jim F a l l s are are chemically chemically indistinguishable indistinguishable from from those those of o f the the Eau Eau Claire C l a i r eRiver Riverarea, area.and andare arecomposed composed of o f hornblende hornblende (45-65%), (45-65%), plagioclase p l agioclase (25-50%), epi epidote (5—15%) and ubiquitousaccessory accessory quartz,magnetite, magnetite,ppyrite, (25-50%), dote (5-1 5%) and ubiquitous quartz, yrite, Epidote iiss the sphene,and andcchlorite. sphene, h l o r i t e . Epidote t h e alteration a l t e r a t i o nproduct productofo hornblende. f hornblende. which which is tot omoderate (M) moderate bluish b l u i s h green green (v), ( V and ) , andshows shows aapronounced pronounced aalignligni s pale pale green green (o() The lamination lamination rresults lamination. The e s u l t s mainly mainly ments the plane ments i in n the plane of o f compositional compositional lamination. from changes o f hornblende hornblende and and plagioclase. p l agiocl ase. The The pplagioclase l agiocl ase occurs occurs from changesi nin proportion proportion of as betweenthe thewell-oriented well-oriented hornblende as "windows" "windows" between hornblende laths. IIts t s average average ssize i z e is is More than 95% of the less the hornblende, hornblende,and andi tit iiss typically t y p i c a l l yanhedral. anhedral More than 95% of the 1ess than than the Relict permits measurement e l i c t twinning twinningini na few a fewgrains grains permits measurement no twinning. twinning. R plagioclase shows shows no of By tthis h i s method method the the approximate approximate An An content was was found found to to of extinction e x t i n c t i o n angles. angles. By be betweenAnAn. and andAn An. With be between WithaaCaO:Na20:K20 CaO:Na20:K20 r aratio t i o ooff 86:10:4 86:10:4 (Table (Table 1) 1 ) such such aa compositions&ld st1u1dbebeanticipated. flticipated. composition . . As the oldest oldest recognizeable As iiss the the case case at a tCadott Cadott and and Wissota Wissota Dam, Dam, the recognizeable iintrusive ntrusive It Itisi sintruded intrudedby bydarker darker bbiotjte-hornblende i o t i te-hornblende tonal ijte t e and and aa later l a t e rtrondhjemite trondhjemite with w i t hpegmatite pegmatite segregations. segregations. Even the the pegmatites pegmatites are are K-feldspar K-feldspar iiss aa very very rare r a r econinodity commodity in i n these these rocks. rocks. Even adamellites, contain approximately equal parts parts K-fel K-feldspar sodic adamel 1ites , and and contain approximately equal dspar and and sodi c pplagioclase. l agiocl ase. The lack ooff K20 amphibolitessuggests suggestsf i rfirst-cycle The lack K20 iinn the the Chippewa Chippewa amphibolites s t - c y c l e reworking reworking of p r i m i t i v ebasaltic basal t i cbasement basement rocks. rocks. primitive rock herei sis aa ffoliated, rock here o l i a t e d , light l i g h tgray gray biotite b i o t i t etrondhjemite. trondhjemite. No rock rockseen seena at JimFFalls dikes) is No t Jim a l l s ((with w i t h the exception exception ooff the the diabase diabase dikes) i s devoid devoid the contacts contactsare aree ieither of of cataclastjc cataclastic fabrics. fabrics. Most Most oof f the t h e r t ototally t a l l y oor r ppartially artially modified by shearing shearing and andmechanical mechanicalintermixing intermixingoof contiguous rock rock units. units. modified by f contiguous �-83Chronology C h ronol ogy Based cross—cutting Based ononcross-cutting andand s t rstructural u c t u r a l r erelationships, l a t i o n s h i p s , tthe h e following chronchronology has been beenworked worked JimF Falls area: (1 (1) Archean( ?(?) basaltic ology has outout f ofor r t hthe e Jim a l l s area: ) Archean ) basal t i c vol- canism andassociated associated sedimentation, sedimentation, (2) converting the cani sm and (2) regiona.l regional metamorphism metamorphism converting the volcanics andi sisoclinal f o l d i n g , (3) ( 3 )cataclasis catacl a s i sforming formingultra— ultrao c l i n a l folding, vol canics tto o amphibolites amphi bol ites and mylonite zones,( (4) myloni t e zones, 4 ) ffaulting a u l t i n g and and bbrittle r i t t l edeformation, deformation, (5) ( 5 ) successive successive iintrusion ntrusion of with of at a t least l e a s tfour f o u rgranitic g r a n i t imagmas c magmas w i t h intervening i n t e r v e n i n g episodes episodes oof f ccataclasis'as a t a c l a s i s as evievidenced byt hthe occurrenceo of folded mylonite mylonite xenoliths in denced by e occurrence f folded i nsome some of the t h e younger younger prolonged Late Precambrian iintrusives n t r u s i ves (Figure (Figure52), 52).(6)(6) prolongederosion, erosion,and and(7)(7) Late Precambriandiabase diabase ddike i k e intrusion. i n t r u s i o n . This sequence sequence iiss modified modified from from Maercklein, Maercklein, 1974, 1974,p.p.16—20. 16-20. At least l e a s tthree t h r e edeformational defonnational episodes episodes can can be be distinguished here here as as they they can. can. eelsewhere l sewhere iinn the t h eChippewa Chippewa amphibolite amphi bol it e complex. complex. -- 15_200east-northeast. east-northeast. The The hinges hinges ooff Figure 49 -- F-2 F-2 folds f o l d shere hereplunge plunge about about 15-20' Figure 49 Throughgoing ccataclasis a t a c l a s i s and and iisoclinal s o c l i n a l F-i F-1folds f o l d scan canbe befound found in i n this, t h i s outcrop. outcrop. Throughgoing associated thesesstructural associated f faulting a u l t i n g have have llocally o c a l l y broken broken these t r u c t u r a l blocks blocks into i n t o lensoidal 1ensoi dal and bbrecciation seen i in blocks. Drag Drag ffolding o l d i n g and and and r e c c i a t i o n can can be be seen n the t h e limbs limbs of of some some ooff the F-2 F-2 folds. REFERENCES: Maercklein, 1974, Analysis Analysis ooff deformation Maercklein, Douglas Douglas R.,R., 1974, deformation aatt Jim Falls, F a l l s , Wisconsin, Wisconsin, unpublished M.S. thesis, thesis, University unpublished M.S. U n i v e r s i t yofo Wisconsin f Wisconsin-. Milwaukee. Milwaukee. - , Myers, Paul Paul E., E., and R., 1974, Myers, and Maercklein, Maercklein, Douglas Douglas R., 1974, 38th 38th Annual Annual TTn-State ri-State Geological Book, p. p. 35-42. F i e l dConference Conference Guide Guide Book, 35-42. Geol ogi c a l Field �-84- EXPI.MATION Diaba,. Oranit. p.g,iatit. EE Granit. Ultruylonit• I K 1.ldsp.r—nid ylonit. ,iul.s auphibolitic Wl.nLt* g,siai lopidholit. m u - 0'S'—. Xnfarr.d Dontact Vault _ ' 4- alic,of.ult.d a. utov*nq .txik. and .xt.nt Approxiont. fault Strik. anddip dipOf of f011mtionm foliation. 8trika and •trik. dip of of urti-1 ,sxtionl loliationa 8 t r h.and .ud dip foliation@ l.uinq and plunga of linantian lorisontal lin.ation phoning axial tra.. and bs.zinq and ping, of axis Mtifogn loon of unli antiloxos and .ynfos phowing atrik. of axial ira.. and .xtant CRH IIPPEWA C PPEWA A RRIVER I V E R link. and dip of ointa * Sink. •f vertical joint. — Sink, and dip of aultipla joint ayatan. 9 '9 aç Figure 50 of the Figure 50 --- Geologic Geologic map map of the Jim Falls area Jim area by by D.R. D.R. Maercklein, Maercklein, 1974 showinglocations locationsofof principal 1974 showing stops. �-85- -- Figure 51-51 Interlensing Inter1 ensingshear shear cutting c u t t i n ggranite g r a n i t epegmatite pegmatite at at Figure Location A. Lenticular white areas a r e q u a r t z , which tends Location A. Lenticular white areas are quartz, which tends t obe be locallized l o c a l l i z e dalong alongsurfaces surfacesofofmajor majorslippage. slippage.Sketch Sketchby by to Maercklein (1974, p. 61) Maercklein (1974, p. 61) 52-- P aPartially r t i a l l y assimilated and granitized g r a n i t i z e d amphibolite amphibolite Figure 52—— Figure assimilated and xenoliths i n b i o t i t e adaniellite(?) Contact is l o c a l l y disdisxenoliths in biotite adarnellite(?). Contact is locally cordant. Biotite-rich bands extend i n t o the adamell i t e ( ? cordant. Biotite—rich bands extend into the adamelltte(?)) from the the large l a r g e xenolith. xenolith. Location: Location: halfway halfway between between the t h edam dam from and bridge on west s i d e of t h e Chippewa River. and bridge on west side of the Chippewa River. �-86- Figure Boudinage structuresi ninpegmatite pegmatiteddikes Figure 53—— $3-- Boudinage structures i kes ccutting utting thinly t h i n l ylaminated laminated amphibolite amphibolite jjust u s t north north of o f the the bridge. bridge. Note Note accumulation accumulation ooff quartz quartz at a t points pointsofo fpegmatite pegmatiteseparation. separation. Sketch by Maercklein Maercklein (1974, (1974, p. p. 65) 65) Sketch �-87- i ibol.ite I I boflte amphibol ite .4 pegmat i te f granite-amphibolite ibolite 0 5m —4 granite amphibol ite ,/,* Figure 54—54-- Detailed geologic map map showing showing sheared n t r u s i v e contact contact Figure Detailed geologic shearedi intrusive o f "granite" i n t h i n l y banded amphibolite. Lenses o f amphibolite of granite" in thinly banded amphibolite. Lenses of amphibolite were carried c a r r i e d away away from by the the granite. granite. En En echelon echelon fractures fractures were fromthe the wall wall by were f i l l e d by quartz during contraction o f the pegmatite. Location were filled by quartz during contraction of the pegmatite. Location AA ��-89STOP #12 STOP TITLE:: TITLE CORNELL FLASER FLASER GNEISS GNEISS AND CORNELL AND AMPHIBOLITE AMPHIBOLITE LOCATION: A A BB SE%, West side Cornell SE¼,NE%, NE¼,Sec. Sec.18, 18,T31N, T31N,R6W: R6W: West sideo fofHwy. Hwy.64 64Bridge, Bridge, Cornell SWk, i4E¼,Sec. T31N, R6W: f Hwy. SW¼, Sec. 18, 18, T31N, R6W:East Eastside sideoof Hwy.64 64Bridge, Bridge, Cornell, Cornell, Cornell Cornel 1 15' 15' quadrangle. quadrangle. im, Photo taken 9/17/74 during duringdam dam Photo taken 9/17/74 repairs. repai r s . AUTHOR:: AUTHOR P.E. Myers P.E. Myers DATE:: DATE - September, 1974, September, 1974, March, March, 1980 1980 SUMMARY OF SUMMARY O F FEATURES: FEATURES : F'laser gneiss composed composed mica,quartz, quartz, feldspar feldspar and garnets is Flaser gneiss o fofmica, and sparse sparse garnets is tectonically fine—grained t e c t o n i c a l l yinterlensed i n t e r 1ensedwith w i t hthinly t h i nlaminated l y 1aminated fine-grainedbanded banded garnet garnet Although granite, granite, which which became became t hthe e f lflasergneiss, a s e r gneiss, was was probably probably amphibolite. Although Rocks aatt intruded iinto intruded n t o the t h e amphibolite, amphibolite, its i t scontact contacttoday today isi saashear shear zone. zone. Rocks stage iin tthis h i s locality l o c a l i t yshow show an an intermediate intermediate stage n the the tectonic t e c t o n i c interlensing i n t e r l e n s i n g shear shear and ccataclasis followed byby metamorphism and a t a c l a s i s of o f rocks rocks of o f disparate disparatelithology 1itho1ogy f o l 1owed metamorphism tto o garnet grade. grade. -- GARNETIFEROUSADAMELLITE ADAMELLITE FLASER FLASER GNEISS GNEISS LOCATION LOCATION AA -- GARNETIFEROUS 56) near water l level Garnetiferous, Garnetiferous, bbiotite i o t i t e flaser f l a s e rgneiss gneiss (Figure (Figure 56) near water e v e l aatt the the northwest corner corner of Cornel 1bridge bridgeis icomposed s composed ofo fcoarse coarselenses lensesand andzoned zoned northwest o f the t h eCornell Polygranular lensoids and and layers layers of of a r lensoids feldspar in mylonitic feldspar i n aamicaceous micaceous myloni t i c matrix. Polygranul untwinned untwi nned pplagioclase l agiocl ase (41%) (41 %) intergrown intergrown and and mantled mantled by anhedral anhedral microline m i c r o l ine(18%) ( 18%) Polygranular, strained strained are encased crush debris. Polygranular, are encased i in n a laminated, laminated, micaceous micaceous crush quartz (32%) forms long, long, thin quartz (32%) wwith i t h sutured sutured boundaries boundaries forms t h i nlaminae laminae and and lenses lenses which which impart the lamination seen seeni nin outcrop. outcrop. Very Very dark dark oolive impart t h e conspicuous conspicuous lamination l i v e green green to to pale yellowish with pale y e l l o w i s h green green biotite b i o t i t e(5%) (5%) w i t hcoarse coarsemuscovite muscovite(3%) (3%)and and occasional occasional �-90-- -- grains of o f epidote epidote and and garnet o the o l i a t e d crush crush debris. debris. This grains garnet are are confined confinedt to the ffoliated This rock morebbiotite less garnet garnet than than fflaser r o c k contains contains more i o t i t e and and less l a s e r gneiss gneiss aatt Locality L o c a l i t y B. B. Interlensing i n v o l v eseveral severalstages stages l&rlensing shear. shear ddislocation i s l o c a t i o n and and cataclasis normally normal l y involve of displacement, andand ablation of differential d i f f e r e n t i agrain l g r afracture, i n fracture, displacement, a b l a t i oaccompanied n accompaniedby by laminar flow of laminar flow o f crush crush debris debris with w i t h lateral l a t e r adisplacement, l displacement, ablation a b l a t i o nand andmixing mixing o f rocks. rocks. The The rock from from which which this t h i sgneiss gneissformed formed was was probably a coarse-textured' coarse-textured of componentmineral minerali nin aa ggranitic Each component r a n i t i crock rockbehaves behaves biotite b i o t i t equartz quartzmonzonite. monzonite. Each differently d i f f e r e n t l yunder undershearing shearing stress. stress. -- Stage 11 -- Protomylonite Protomylonite Stage Early Early strain s t r a i nisi expressed,as. s expressed as progressive progressive microscopic microscopic crushing of o f minerals, minerals , The lens is an first at corners, then on edges, and last on faces. f i r s t a t comers, then on edges, and l a s t on faces. The lens i s an equilibrium equilibrium accumulates form aatt all a l lscales. scales. Quartz Quartz is i s easily e a s i l yfractured f r a c t u r eand d and accumulates with w i t hfragmented fragmented form feldspar ani ninsulating rockoor mylonite encasing i l m ooff crushed crushed rock r llmylonitel' encasing rrelict elict feldspar as. as. an s u l a t i n g f film rock i is by aa ffaint lenses or o r °porphyroclasts". llporphyroclastsll. Such Such aa rock s characterized characterized by aint feldspar lenses textures are are sstill conspicuous. Primary textures t i 11 conspicuous. foliation f o l i a t i o nand andovoid ovoidshape shape of o f feldspars. feldspars. Primary -- Stage 22 -— Flaser FlaserGneiss Gneiss Stage With deformation, re1 relict With continued continued deformation, i c tfeldspar feldsparlenses lensesbecome become decidely lenlenmicai sis rreoiriented interlensing Primary mica e o i r iented along a1ong i n t e r l e n s i n g slip s l i pplanes, planes, soi dal (Figure (Figure 56). 56). Primary soidal micamay maybegin begint otoccrystallize and the becomes conspicuously l i a t e d . New New mica rystallize --and the rock becomes conspicuouslyf ofoliated. proportion ooff mylonite a t this t h i sstage. stage. The The proportion my1oni t e to t o surviving s u r v i v i n ggrains grainsincreases increases while while at re1i c feldspar t feldspar 1ensesbecome become thinned thinned by by ablation. ablation. Crenulatlon Crenulation or o r microfolding microfol d i ng relict lenses "tectonic xenoliths" xenoliths1' or o r lenlenor o r residual residual rock rock lenses lenses is i s comon common at a t this t h i sstage. stage. "tectonic ticular t i c u l a rfragments fragments of o f non-mylonitized non-mylonitized rock rock are are carried c a r r i e d along along in i n the the flowing flowing Drag ffolds o l d s and and ptygmatic ptygmatic folds f o l d sshow show differential d i f f e r e n t i amovement l movementand and granularmass. mass. Drag granular alongt hthin, Most ooff the the displacement displacement becomes becomes l olocalized, c a l ized along i n , interlensing i n t e r 1ensing turbulence. Most turbulence. zones ooff slippage s l ippage (Figure (Figure 59 59 ). ) zones . Figure -- Biotite from Figure 56 56 -B i o t i t etonalite tonal i tprotomylonite e protomyloni t e f r o mHamilton Hamil tonFalls, Fa1l s Eau , EauClaire C l a i r eCG. CO. Ends Ends ooff lenticulated l e n t i c u l a t e dplagioclase plagioclaseporphyroclast porphyroclastshow show no no twinning. twinning. Note Notecrushed crushed grain boundaries. boundaries. grain P=plagioclase, P=p1agiocl ase, B=biotite, B=bioti te,Q=quartz, Q=quartz,E=epidote, E=epi dote,Sp=sphene. Sp=sphene. - - �-91-. Stage 33 -Ul tramylonite Stage -- Ultramylonite Reductionofof relict relict rock ultimately Reduction rock and and mineral mineral lenses lenses by by ablation may may ultimately or in crystallization or i n crystal1 ization result in i n aa thinly t h i n l y laminated, laminated, fflinty l i n t y ultramylonite, u l tramylonite, result Relict feldspar lenses become mantled by new feldspar. Relict feldspar lenses become mantled by new feldspar. of new feldspar. new rock at Reversed zoning isi scommon. common. The The rock a t this thisstage stagebecomes becomes a blastomylonite blastomylonite. Reversed The The ppoint o i n t at a t which which feldspar feldspar regrowth regrowth begins begins varies even even from from one one part of of an an outcrop outcrop to to another. another. Reaction rates accelerate accelerate wwith: (1 )increased increased surface surfacearea area ini naccumulating accumulating i t h : (1) Reaction rates frictional heat and (3) pressure of mobilized water. frictional heat and (3) pressure of mobilized water. (2) (2) mylonite. myloni te. Anhedral form form of of the garnets of deformation them ininAnhedral garnets and and absence absence of deformation around around them Freshgarnet garneti is relatively rare s aa relatively raremineral mineral dicate their their late-kinematic late-kinematic age. age. Fresh Big Falls Fa1 1s are are Large, rrelict e l i c t garnets garnets at a t Big in rocks rocks of of the the Eau Eau Claire region. region. Large, altered altered totohornblende. hornblende. With W i t h rocks rocks that thathave havebeen beendeformed deformedand andmetamorphosed metamorphosed difficult totodiscriminate aatt least least three three times, times, iti tbecomes becomes difficult discriminatebetween between surviving surviving Urelictul 're1 ict" minerals minerals and and those those produced produced during during later 1atermetamorphism. metamorphism. FQliation and compositionallayering layering iinn rocks rocks at a t Cornell Cornell strike strikeN80°E ~80'~ Foliation and compositional samestructural structural elements elementsaat Fisher River 4 km northeast of N80 W. These These same t Fisher km northeast to to N80"W. here trend NN40°-50°E, factortaken takentoto indicate indicate aa major major flexure flexure in ~ o O - ~ O O E , a afactor i n the the rocks rocks here trend north of Cornell. north Cornel 1. -- LOCATION GARNETAMPHIBOLITE AMPHIBOLITEAND ANDSHEARED SHEAREDPEGMATITE PEGMATITE LOCATION B -- GARNET Laminatedgarnet garnetamphibolite amphibolitea tatLocation LocationB Bi sis representative representative of of the the Laminated "Cornell amphibolite" which crops out almost continuously for 4 km down the 'Cornell amphibolite" which crops out almost continuously for 4 km down the The amphibolite could also be classed as a gneissic, mafic Chippewa River. Chippewa River. The amphibol i t e could a1 so be classed as a gneissic, mafic hornblende tonalite composed of subhedral subhedral to to hornblende tonal i t e or orhornblende hornblende gneiss. gneiss. ItI tisi scomposed anhedral, lensoidal hornblende clusters (54%) with coarse, lensoidal anhedral , 1ensoi dal hornblende (54%) w i t h coarse, lensoidal porphyroporphyrofine-grained quartz. clasts of of twinned twinned plagioclase plagioclase (28%) (28%) and and fine-grained quartz. The The hornbleñde hornblende pale yellowish yellowish green; green; "7= 7= dark is i s strongly stronglypleochroic pleochroic(OC= (a=pale dark bluish green). green). Bandingi nin the the amphibolite amphibolite iIs s cut by by lenticular lenticularsegments segments of granite granite and and quartz quartz Banding Thepearly nearlyvertical vertical banding is thinly thinly interlensing veinlets. The banding is interlensingini n3 3dimensions, dimensions, Small, isoclinal and strikes strikes N80°E and N80 EtotoN800W. ~ 8 0 ~Small, ~ . isocl inal folds foldsplunge plunge at a t low low angles angles in in n the amphibolite amphibolite tend tend to to be be Garnets iin the plane plane of of compositional compositional banding. banding. Garnets evidence of of garnet porphyroNo evidence porphyrorandomly clustered and randomly clustered and have have ragged ragged borders. borders. No Thedistribution distribution of clusters shows showsl ilittle blasts rotation rotationwas was seen. seen. The of garnet garnet clusters ttle The garnets garnets appear relation totobanding relation banding or orfold foldmorphology. morphology. The appear to t o have have formed formed after most after most of the the particulate particulateflowage flowageofofthe therocks, rocks,asasevidenced evidenced by by the thegood good preservation of garnet the amphibolite. amphibol i te. preservation garnet crystal crystalapophyses apophyses iinn the Coarse,garnetiferous garnetiferous ffelsic are iinn Coarse, e l s i c flaser flasergneiss gneissand and sheared sheared pegmatite pegmatite are commonly intrudes amphi bol i t e intrudes amphibolite contact wwith contact i t h amphibolite amphibol i t e iin n this this outcrop. outcrop. Granite cormnonly relations ofofmost most granite granitebodies bodies aatt other other locations locations (Jim (Jim Falls). Intrusive relations i n the the area area are are obliterated obliterated by by shear shear displacement displacement and partial 1ization. in and partialrecrystal recrystallization. The occurrenceofofgarnet garneti in the flaser flaser gneiss n the gneiss indicates indicates that thatboth both rocks rocks were were The occurrence metamorphosed aftertectonic tectonic imbrication. metamorphosed after imbrication.An An excellent excel lentexample exampleog ogsheared sheared pegmatite pegmatite and rocks can the east east end end and other other coarse-grained coarse-grainedgranitic granitic rocks can be be seen seenjust just north north of the 64 bridge bridge aatt Location Location B B (Figure 58). Coarse, Coarse, bent, of the the Hwy. Hwy. 64 bent, lenticulated lenticulated and porphyroclasts are and fractured fractured feldspar porphyroclasts are enclosed enclosedinin aa fine-grained fine-grained matrix matrix of quartz-feldspar-muscovite quartz-fel dspar-muscovite crush crush debris. Some n the mylonite myloni t e Someflow flowfolds folds can can be be seen seeni in in some of these some of these rocks. rocks. �-92- -- Figure 57 57 -— Garnetiferous i o t i t eadaadaFigure Garnetiferous bbiotite A) m e l l i t e flaser gneiss (Location mellite flaser gneiss (Location A) Lensoidal feldspars feldspars1are are enclosed enclosed in i n aa Lensoidal recrystal 1 ized, f o l i a t e d matrix. recrystallized, foliated matrix. \ - Figure 58 58 -- Sheared Sheared pegmatte pegmatite (Location (Location BB Figure near eastern eastern bridge bridge abutment) abutment) Lensoids Lensoids of of near coarse K-fel dspar iin n matrix matrix of o f crush crush debris. debris. coarse K-feldspar �-93-93STOP #13 #13 STOP TITLE:: TITLE FISHER RIVER FISHER R I V E R BRECCIA BRECCIA LOCATION: LOCATION: NW¼.SW%, SW¼, Sec. T31N,R6W, R6W, Chippewa County, Cornell 15' 15' quadrangle NW*. Sec. 4, 4,T31N, Chippewa county, Cornell quadrangle AUTHOR:: AUTHOR P.E. P. E. Myers Myers DATE: DATE : - February, 1980 February, 1980 SUMMARY SUMMARY OF O F FEATURES: FEATURES: This unusual, This unusual, hheterolithic e t e r o l i t h i c breccia breccia contains contains clasts c l a s t s of o frock rocktypes types not n o tseen seen elsewhere elsewhere i in n tthe h e region, region, such such as as porphyritic p o r p h y r i t i cgabbro, gabbro, greenstone, greenstone, metapyroxenite(?), metapyroxeni t e ( ? ) , breccia iiss andesitic a n d e s i t i c ttuff, u f f , and and cataclastically c a t a c l a s t i c a l l ylaminated laminated granitic g r a n i t i c rocks. rocks. The The breccia enclosed onthe the nnorth and south south sides sides by by ffoliated enclosed on o r t h and o l i a t e d trondhjemite trondhjemi t e and and on on the t h e west west by gneissic obiotite-hornblende tonalite. by gneissic i o t i te-hornbl ende tonal ite. The The gneissic trondhjemite trondhjemi t eelsewhere e l sewhere metadiorite and tonal tonalite it e iinn the t h e area area (Fisher (Fisher River River Bridge) Bridge) contains contains abundant abundant metadiori t e and xenoliths which whichare areelongated elongated plane xenoliths i n in t h ethe plane of fof o l ifoliation. a t i o n . ItIt i is s ttentatively entatively proposedt hthat brecciau nunit, other xenoliths, xenoliths, iiss an proposed a t t hthe e breccia i t , l ilike k e tthe h e other an iinclusion n c l u s i o n in in trondhjemité, and andt hthat by ffaulting. was ooriginally r i g i n a l l y formed formed by aulting. tthe h e gneissic gneissic trondhjemite, a t iitt was DESCRIPTION: Reconnaissance scoured meitwater channeloof Fisher River Reconnaissance a1along ong t hthe e scoured g l glacial a c i a1 me1 twater channel f Fisher R i ver indicates tthat (Figure 59 h a t the t h e area area is i s underlain underlain by by gneissic gneissic tonalite t o n a l i t e and and (Figure 59 ) indi.cates trondhjernite and tonal tonalite. trondhjemi t e containing abundant abundant xxenolithic e n o l i t h i c masses masses oof f mmetadiorite e t a d i o r i t e and ite. The breccia breccia uunit, by ffoliated The n i t , which which is i s apparently apparently enclosed enclosed by o l i a t e d trondhjemite trondhjemite and and tonalite, non-sortedcclasts containsangular an u l a r to t osubrounded, subrounded, non-sorted l a s t s ooff ultramafic u ltramafic tonal ite, contains rock rock (metapyroxenite?), (metapyroxeni te?), massive massive and and porphyritic p o r p h y r i t i chornblende hornblendegabbros, gabbros ,hornblende hornblende , greenstone, andesite andesi t e tuff, tuff, and andmassive massi ve and and ccataclastically a t a c l a s t icall y bbiotite i o t i t etonalite, tonal it e greenstone, 1laminated aminated ggranitic r a n i t i c rocks rocks - probably probablytrondhjemite trondhjemi t e and and adamellite adamel 1it e (quartz (quartzmonzonite). monzoni t e ) - The dominantmineralogy mineralogy theserocks, rocks,i nincluding thosei in the breccia, The dominant of ofthese c l u d i n g those n the breccia, is (An2_),)quartz, , quartz,hornblende, hornblende, biotite, b i o t i t e ,and andK-feldspar. K-fel dspar. Accessory i s plagioclase plagioclase (An epidote, epi dote, cchlorite, h l o r i t e , * kaetite @ e t i tand/or e and/orpyrite p y r i t eare i r eubiquitous. ubiquitous. . �-.94- 90 0.5 mile mile 0.5 Figure 59 ---Geologic Geologic map map ooff the the Fisher Fisher River Riverarea. area. htg htg ==hornblende hornblende Figure 59 tonalite tonalite gneiss; bhtg bhtg == biotite-hornblende b i o t i te-hornbl ende tonal it e gneiss; gneiss; trg t r g==trondhtrondhtonal it egneiss; jemite d i o r i t e ;brb = r =breccia. breccia.Note Notefairly f a i r l gentle y gentlenorthwest northwest jemite gneiss; gneiss; di d i == diorite; plunge p l unge oof f 1lineation ineation in i n the the tonalite t o n a l i t egneiss. gneiss. �-95- Characteristics of Characteristics o f the t h e Breccia: Breccia: The breccia is of angular angular tto non-sortedcclasts of The breccia i s composed composed o-F o subrounded, subrounded, non-sorted l a s t s of chioritized massive tonalites, c h l o r i t i z e dultramafi u l t r a m a f irocks, c rocks, massiveand andlaminated laminated gabbros, gabbros, tonal i t e s , and and The ffine i n e tot omedium medium grained grained granitic andccrystal g r a n i t i c rocks, rocks, greenstones, greenstones, and r y s t a l ttuffs. u f f s . The Chlorite hlorite matrix plagioclase,quartz, quartz, and andbbiotite. m a t r i x is i s composed composed e sessentially s e n t i a l l y oof f plagioclase, iotite. C Epidote seams cutthrough throughthe the breccia breccia fragments andmmatrix seams cut fragments and a t r i x aatt high high angles. angles. Epidote occurs as as j joint occurs o i n t coatings coatings and and as as a a partial p a r t i a lreplacement replacement ooff mafic mafic minerals minerals in in the breccia. breccia. Clast size s i z e ranges ranges from f r o m 11 -- 20 20 cm cm with w i t h an an average avera e of about about 44cm. cm. The fragmentsshow show preferredo orientation (Figure 60 60),, which here iiss which here The fragments a a s usubtle b t l e preferred r i e n t a t i o n (Figure about N50°E,v vertical. no post-deposi post-depositional rounding oor fragabout N50°E e r t i c a l . The The clasts c l asts show show no t i o n a l rounding r fragmentation, as as would wouldbe beexpected expected breccia. Chalcopyrite mentation, i nina af afault u l t breccia. Chalcopyrite occurs occurs iinn the the matrix. ? Photographo of Fisher River River breccia breccia at Figure 60-60-0 Photograph f t hthe e Fisher at Figure widev variety tthis h i s location. location. Note Note wide a r i e t y oof f cclast l a s t llithology ithology tthe h e relatively r e l a t i v e l y high high clast/matrix c l a s t / m a t r i x ratio, r a t i o ,and andthe t h ecrude crude orientation off clasts. nnear-vertical e a r - v e r t i cal o rientation o c l asts . Chronology the Fisher Chronology oof f the Fisher River River Area: Area: chronologycan canbe besynthesized synthesizedfrom fromf i field observations iin AA chronology e l d observations n the t h e Fisher River River area. Table 7. area. Compare Compare wwith i t h Table *1. IIntrusion mafic hornbldnde gabbroand andddiorite *l. n t r u s i o n of o f mafic hornbldnde gabbro iorite *2. IIntrusion adamellite *2. n t r u s i o n of o f adamel 1it e and and trondhjemite trondhjemi t e probably 3. Shearing and 3. and cataclasis, cataclasis , probablyaccompanied accompaniedby byregional regionalmetamorphism metamorphism *4 Extrusion off basalt andesite(?)ttuff *4. Extrusion o b a s a l t and and andesite(?) uff 5. Intrusion mafic hornblende-bioti hornblende-biotite tonalite I n t r u s i o n of o f mafic t e tonal ite 6, Faulting 6. F a u l t i n g and and brecciation b r e c c i a t i o n - formation formation of o f the t h eFisher FisherRiver River breccia breccia 7. Intrusion I n t r u s i o n of of leucotrondhjemi leucotrondhjemi ttee 8. 8. Cataclasis, Cataclasis, metamorphism, metamorphism, l elenticulation n t i c u l a t i o n of o f pegmatites, pegmati tes, mylonite myloni t e '"veinlets" v e i n l e t s " with w i t h right-lateral r i g h t - l a t e r a displacement l displacement 9. 9. Intrusion I n t r u s i o nof o ftonalite tonal i t and e anddiabase diabase dikes dikes (Late (Late Precambrian) Precambrian) f e r r e d on h e basis breccia clast clast *posjtjon ini nsequence known.I nInferred ont the basis ofof breccia *Position sequence nnot o t known. 1lithology ithology and and structures. structures. - �-96Although u t the t h e trondhjemite trondhjemite Althoughno notrondhjemite trondhjemitedikes dikeswere wereseen seent otoc cut the breccia, breccia, the off iiss in i ncontact contact with w i t h the t h ebreccia breccia along along its i t snorth n o r t hand andsouth south sides. sides. The The ttrend rend o the breccia the breccia unit u n i t isi sN550E; ~ 5 5 its i~t sdip ~d i;pisi unknown. s unknown. At several locations l o c a t i o n s along along the the At several Fisher River River (south (south of here), here), the t h egneissic gneissicleucotrondhjemite leucotrondhjemi t econtains containsabundant abundant Fisher schistose mafic mafic i inclusions and1large xenoliths ooff metadiorite. xenoliths schistose n c l usions and arge xenoliths metadiori te. The it h s The xenol are elongated elongatedi nint hthe planeofoff ofoliation. are e plane l i a t i o n . It Itisi stherefore t h e r e f o r etentatively t e n t a t i v e l concluded y concluded t h a t the t h e breccia breccia uunit n i t iitself t s e l fisi sa alarge l a r g elensoidal lensoidalxenolith x e n o l i t hini nthe t h egneissic gneissicleucoleucothat trondhjemite. trondhjemi te. The leucotrondhjemite c l o s e l y resembles resembles that t h a tata Wissota t WissotaDam. Dam. The leucotrondhjemite here closely 1ocal ity, the t h etrondhjemite trondhjemi t e Is i s cut c u t by by gray gray tonalite tonal it e dikes. dikes. locality, As aatt that that As - Modeo fofFormation Formation FisherRiver RiverBreccia Breccia -PPossibilities, Mode of oft hthe e Fisher o s s i b i l i t i e s , Evaluations: Eva1uations: 1. Pyroclastic 1. P y r o c l a s t i c Breccia: Breccia: Fisher River breccia breccia (FRB) (FRB) contains contains mainly mainly. matrix, metamorphic and u t o n i c cclasts. l a s t s . The metamorphic andp lplutonic The matrix, now now rrecrystallized, e c r y s t a l 1ized, might might be be aa metatuff. metatuff. 2. Intrusion 2. I n t r u s i o n Breccia: Breccia: Matrix M a t r i x in i n not n o t discernably discernably aa plutonic p l u t o n i cigneous igneous rock; matrix m a t r i x lacks lacks flow flow fabric f a b r i c around around cclasts; lasts; 3. TTillite: 3. illite: Clasts in are too too angular; Clasts i n FRB FRB are angular; do do not not show show eevividence of transport. dence o f 4. Fault 4. Fault Breccia: Breccia: Recrystallized matrix doesnnot containre1 relict Recrystal 1i z e d m a t r i x does o t contain ic t The absence absenceooff post-depofault f a u l t gouge gouge texture. The post-depositional s i t i o n a lfragmentation fragmentation makes makes t the h e ffault a u l t breccia breccia hypothesis aa bbiti tshaky. hypothesis shaky. 5. 5. Talus Talus Breccia: Breccia: The1lithologic The it h o l o g i c heterogeneity, heterogeneity , aangularity n g u l a r i t y ooff The1likelyclasts, clasts, favor f a v o r this t h i s interpretation. i n t e r p r e t a t i o n . The ikelyhood hood f for o r preservation preservation of o f aa Precambrian Precambrian ssurficial urficial feature feature is i snot n o tgreat, great,however. however. Whatare aresome someother otherp possibilities? What o s s i b i l i t i e s ? How could the the mystery be How could be solved? solved? �—97— -97- STOP #14 STOP #14 TITLE: STRUCTURESI N IN QUARTZ QUARTZDIORITE, DIORITE, GRANITIC GRANITIC INTRUSIVES INTRUSIVESAND AND META-. METASTRUCTURES ANDESITE AT AT HOLCOMBE HOLCOMBE DAM. DAM. LOCATION: Holcombe Dam,SW Sw1/4 1/4 Sec. Sec. 28, T32N, T32N, R6W, R6W, Chippewa Chippewa County, Holcombe Dam, Cornell 15" 15" quadrangle. quadrangle. AUTHOR: AUTHOR: Stephanie Wurdinger,UUniversity Stephanie R.R. Wurdinger, n i v e r s i t y of o f Minnesota, Minnesota, Duluth Dul u t h DATE: DATE : - February, 1980 1980 SUMMARY OF SUMMARY O F FEATURES: FEATURES : Synkinematic quartz quartz ddiorite the lower lower amphibolite Synkinematic i o r i t ewas was metamorphosed metamorphosed t otothe amphibol it e facies during during F1 F folding. Granitic G r a n i t i c intrusives i n t r u s i v e sand anddikes, dikes,and anda ahypabyssal hypabyssal andesite wereintruded intrudedduring duringF F.,f ofolding thequartz quartzddiorite. andesite were l d i n g o of f the i o r i t e . These These rocks rocks were llater a shear zone exposed were a t e r converted converted to t oschist s c h i s1ong t along a shear zone exposedalong alongthe t h eChippewa Chippewa River. AA system systemofofN50W N5OW a dominantly f a u lfaults t s w i twith h a dominantly r i g hright t l a tlateral e r a l s tstrike r i k e ooffffset later major ffold l a t e rsegmented segmented aall l 1 rock rock units. The The major o l d deformations, deformations, and and thus thus the rock rock units u n i t sataHolcombe t HolcombeDam, Dam, are believed believed to t obe bePenokean Penokean in i n age. age. DESCRIPTION: DESCRIPTION: Holcombe IInn order order of o f decreasing decreasing age, age, the the rock rock units u n i t sofothe f the Holcombe area area are: are: banded gneissaat the Fisher River, Dam, banded gneiss t the River, quartz quartzdiorite d i o r i tat e Holcombe a t Holcombe Dam, and. and amphibolite River (Figure 61). amphi bol i t e schist s c h i s t along along the theChippewa Chippewa River 61 ). Gneissic quartz quartz diorite Gneissic d i o r i t eand andassociated associatedmeta-igneous rota-igneous rocks crop crop out out Ultramafic In age,the the l latter I n order order of o f decreasing decreasing age, a t t e r are: are: U1 tramafic and spotted i o r i t e , quartz quartz ddiorite i o r i t e gneiss, gneiss, and spottedmafic maficxenoliths xenolithsi ninthe thequartz quartzd diorite, g r a n i t e and and associated associated granite g r a n i t e dikes, dikes, and andmeta-andesite meta-andesi t e (Figure (Figure62). 62).These These granite u n i t s were were converted converted tto o schist s c h i s t along alongshear shear zones zones which which cross cross the t h e outcrop. outcrop. units below Holcombe HolcombeDam. Dam. below The quartz i o r i t e contains contains two two types types ooff inclusions: inclusions: hornblende The quartz ddiorite hornblende rrich ich u l t r a m a f i c inclusions, inclusions, and and spotted spotted mafic mafic inclusions. inclusions. Ultramafic ultramafic Ultramafic inclusions occur along along the the northwest northwestpportion quartzddiorite. occur o r t i o n ooff the t h e exposed exposed quartz i o r i t e . These These are are generally less l e s s than than 0.5 0.5 meters meters iin n length, length, although although one one iis s at a t least l e a s t22meters meters generally . ' l tramafi cinclusions in c l u s i ons composed f 75-85% hornblende 11-1 3% 1long. ong U Ultramafic areare composed of o75-85% hornblende andand 11—13% biotite b i o t i t ewith w i t ha asmall smallamount amount of o f plagioclase. plagioclase. C h l o r i t e occurs occurs as teration Chlorite as an an a1 alteration product of o f biotite b i o t i tand e and less commonlyofohornblende, f hornblende,and and can composemore more less commonly can compose than the rock. than 20% 20% oof f the Spotted mafic mafic inclusions inclusions occur occur along along the the southeast southeast section section ooff the Spotted the exposedquartz quartzddiorite. range from from aa few few centimeters centimeters to exposed i o r i t e . They They range t o more more than 66 meters iin meters n length. length. The i nthe. thebanded banded gneiss gneiss The same samerock rocktype type occurs occurs as as dikes in arecomposed composed of o f hornblend hornblend aatt the the Fisher Fisher River. River. Spotted Spotted mafic xenoliths xenol ithsare cclots l o t s to t o33mm mm iin n size s i z e in i naafine-grained fine-grained matrix m a t r i xofoplagioclase f plagioclaseand andhornblende. hornblende. A spotted iinA few few hornblende hornblende cclots l o t s are arepseudomorphs pseudomorphs aafter f t e r pryroxene. pryroxene. The The spotted nclusions are surrounded whiter i rinds plagioclase and quartz, are commonly commonly surrounded byby white n d s oof f plagioclase and quartz, probably due duet otothe the ppreferential probably r e f e r e n t i a l nucleation nucleation of plagioclase p'iagioclase on on the the inclusions inclusions during during iintrusion n t r u s i o n ooff the the quartz quartz ddiorite. iorite. . �-98- 2 27 A 34 3$ 0 - Figure 61-61 Geologic Geologicmap mapofo Holcombe f Hol combe area. area. Figure diorite, amphibol it e schist. d i o r i te.ams ams == amphibolite .5m1 bgn gneiss,, qd = quartz bgn = banded banded gneiss quartz The quartz diorite The quartz d i o r i t eisi as medium-grained, a medium-grained, dark darktot omedium medium grey grey rock rock Itisi sfaintly f a i n t l foliated y f o l i a t eand d andhas has white white disdiswith w i t h rusty r u s t yweathering weathering surfaces, surfaces. It continuous bandsand andl elenticles whichare aremore morequartz quartzr irich thant the continuous bands n t i c l e s which c h than h e rrest e s t of of Quartz diorite d i o r i t eisi composed s composed of o fplagioclase p l agiocl ase(32-51%), (32051%),quartz quartz(11-31%) ( 1l-31%) rock. Quartz the rock. range from from entirely e n t i r e l yhornblende hornblende and mafic minerals minerals (12-33%). (12-33%). Mafic minerals range and t o entirely e n t i r e l y biotite. biotite. to The quartz ddiorite medium-grained The quartz i o r i t eisi scutc uby t by medium-grained granite g r a n i t epods pods with w i t h migmigmatitic m a t i t i ccontacts contacts and and by by finer-grained finer-grained dikes dikes with w i t hsharp sharp contacts. contacts. The The granite rock g r a n i t e is i s aa pink, pink, faintly f a i n t l yfoliated foliated rockwhich which locally l o c a l l ycontains contains porphyritic porphyritic microcline grains grains reaching reaching 11 cm cm iin n size. size. Granitic G r a n i t i c rocks rocks consist consist of o f plagioplagioclase, of biotite, c l ase. microcline m i c r o c l ineand and quartz, quartz, with w i t hminor m i noramounts amounts of b i o t i t e .muscovite muscoviteand and epi dote. epidote. �LJ inclusions ITI Quartz diorlte Granite a Meta across the top of the outcrop in this figure. 0 Figure 62 -- Outcrop map of quart diorite gneiss at Holcoithe Granite dikes are unpatterned, and trend northeast Dam. Fault — Shear zones Strike of foliation N 100 ft '.O ',O �-100- The youngest n t r u s i v eunit u n iat t aHolcombe t HolcombeDam, Dam, aa hypabyssal hypabyssal andesite, andesite, The youngest iintrusive intrudes the t h e quartz quartz diorite d i o r i t eand and granite g r a n i t edikes dikes with w i t hsharp, sharp, steeply steeply dipping dipping intrudes contacts. It Itconsists consistsofo about f about10% 10% lineated l i n e a t e d hornblende hornblende grains n aa finefinegrainsi in grained Where the r a n i t e dikes, grained pale gray gray matrix. matrix. Where theandesite andesitecuts cutsthe theg granite dikes, iitt contains numerous numerous pale epidote. contains pale green green veins veins ooff epidote. Shear zones t the i o r i t e gneiss gneiss are long, long, narrow, narrow, Shear zoneswhich whichc ucut thequartz quartzddiorite sinuous zones f schist, containing pods pods ooff quartz y r i t e or o r of of quartz quartz sinuous zonesoof schist, containing quartz and and ppyrite and feldspar. and feldspar. The The shear i l l i m e t e r s to t o 1.5 1.5 meters meters wide wide shear zones zonesare areaa few fewmmillimeters and and aa few few centimeters centimeters to t o 60 60 meters meters long. long. They They ccut u t both iorite both the the quartz quartz ddiorite gneiss gneiss and and the t h e andesite. andesite. Schistose Schistose rocks rocks in i n the theshear shear zones zones are a r e thoroughly thoroughly recrystallized r e c r y s t a l l i z e d and and display d i s p l a y no no cataclastic c a t a c l a s t i c textures. textures. A A shear shear zone zone aatt the the northwest corner corner of o f the the outcrop outcrop isi scataclastic c a t a c l a s t iand c and mayhave have formed formed during during northwest may the t h e late l a t estages stagesofo fshear sheardeformation. deformation. Large, Large, unsheared unsheared lenses the lenses iinn the shear zone zone give give the t h eappearance appearance of o fhaving havingundergone undergone spheriodal spheriodal weathering. weathering. shear The three intrusive Dama lall containrrelict The three i n t r u s i v e rock rock units u n i t sata Holcombe t Holcombe Dam l contain elict igneous subhedral subhedral and and all a11have havemetamorphically metamorphically igneous and euhedral euhedral feldspars feldspars,,and induced induced ffabrics, a b r i c s , imparted imparted dominantly dominantly by by the the mafic mafic minerals. minerals. All A l l of o fthe the above mentioned i t s have r t i a l l y tto o thoroughly thoroughly recrystallized r e c r y s t a l 1ized above mentionedrock rocku nunits havep apartially in facies. i n the thelower loweramphibolite amphi bol it e facies. Late Late hydrothermal hydrothermal aalteration l t e r a t i o n occurred occurred along along fracture fracture systems systems to t o aa width width of o faafew few centimeters. centimeters. In I n altered a l t e r e d zones, zones, plagioclase plagioclase iiss altered a l t e r e d to to sericite s e r i c i t eor o rsaussurite, saussuri te, and and biotite b i o t i t eisi sconverted converted to t o chlorite. c h l o r i t e . Quartz Quartz is is partially and/or hornblende p a r t i a l l yreplaced replacedby byalbite a1b i t e and/orcalcite, c a l c i t eand , and hornblendehas has overovergrowths pale aactinolite. t e r a t i o ncould could alteration growths ofof pale c t i n o l i t e . This This type type of of hydrothermal hydrothermal a1 be metasomatismalong alongw with be produced produced by hydrogen hydrogen metasomatism i t h t hthe e iintroduction n t r o d u c t i o nofo Na20 f Na20 and andCO2. CO., STRUCTURAL STRUCTURALGEOLOGY: GEOLOGY : AA sumary affected rocks summary of o f deformations deformations which which affected rocks in i nthe t h eHolcoithearea Holcombe area is i s presented presented in i n Table Table 11. 11. The The only rock rock showing showing aall l l the the fold f o l ddeformations deformations isi sthe thebanded banded gneiss gneiss at a t the t h e Fisher FisherRiver. River. . F1 F folding f o l d i n gproduced produced aa dominantly dominantly east—west east-west f ofoliation, l i a t i o n , S,. S The quartz quartz The diorité showsananeast-west east-west d i o r i t at i aHolcombe t Holcombe Dam Dam shows f ofoliation, l i a t i o n , but b u t there t h e r eare areno noFF folds. F1F1even folds. This This suggests suggests iintrusion n t r u s i o n of o f the t h equartz quartz diorite d i o r i t eduring duringthe the event. S, F folding. S foliation f o l i a t i o nini nthe thequartz quartzdiorite d i o r i t gneiss e gneisswas was folded folded during d u r i n g Fà folding. F9 are ttight layering F ffolds o i l s are i g h t to t o isocljnal i s o c l i n a l folds f o l d sini nfoliation, f o l i a t i o ncompositional , compositional layering ahd fold a d iin n felsic f e l s i cveins. veins. F9 F fold F folding f o l d i n g occurred occurred aatt a a low, Ion, oblique oblique angle angle to t o F1 trends modrate ttoo steep westerly pplunging trends and and produced produced moderate steep (6O_800) (60-80° westerly l unging 1lineations. in e a h o m . Granite Granite intrusives i n t r u s i v e sand andthe thehypabyssal hypabyssal andesite andesi t e display d i s p l a y east-northeast east-northeast foliations f o l i a t i o n sand andsteep steeptot omoderate moderate lineations, 1ineations, suggesting suggesting that t h a t they they were were inintruded truded during during the theF2 F2event. event. During FF. folding, f o l i a t i o nand and fold f o l daxial a x i a lplanes planes in i nthe thegneissic gneissic During folding, foliation rocks at a tHolcmbe ~ o l c & n b were ewere broadly broadly warped warped along dippingnorth-south north-south rocks along aa steeply dipping axis. A t Holcombe Holcombe Dam, e aaxial x i a l planes planes of o fF2 F2folds, folds,and and metasomaticbands bands axis. At Dam,t hthe metasomatic of granite g r a n i t ewere were affected affected by bythe theF3 Fgevent. event. of �-101TABLE TABLE 11 11 Banded GneissBanded Fisher River River Quartz io r it e Quartz DDiorite Gneiss-Ho1 combe Gneiss-Holcombe Amphibolite Amphibol Ite Schist -Chippewa River -Chippewa Dam - - Isoclinal Isocl inal folds folds F1 Fl . Penetrative Penetrative S1 D1 £ foliation and Penetrative ffoliation ol iation lithologic layer- trending E-W ing trending E-W L1 L Penetrative ffold Penetrative old axis and and mineral mineral ineations 1ineations • Tight to Tight Isoclin- Tight Tight to to lsoclinal isoclinal folds a1 folds, folds, folding folding Isoclinal folds F2 F1, and L folding S1 F2 Fl,Sl,andLl foldingSl 1%' Penetrative Penetrative lineatlons in lineations in graniteand and andesandesgranite Ilife Ite £ I I F3 Broad warping Broad N-S trend trend along N-S . Broad warping Broad warping along N-S along N-S trend Folding ooff 54 Folding S4 and and shearing fonu form rootless folds folds Shear Shear zones zones crosscross- Schistosity Schistosit y and and cut aalll l rock Compositional cut rock units units Compositional at Late cataa cata- 1layering, &yering, N7OE WOE N70E. Late a t N7OE. clastic c l a s t i cshearing. shearing, Penetrative Penetrative lineation at llneation at about about 400 40ÂSw SW Faulting along Faul ting a1 ong discrete discrete planes and P120W aat tP150W N50W and N20W Faulting Faulting along a1ong discrete discrete planes p l anes at a tP150W N50W and andN2OW N2W Penetrative lineation at at about 400 about 40ÂSW SW Faulting along Faul t i n g a1 ong discrete discrete pplanes l anes at and P120W a tP150W N50W and N20W Late Late faulting S4 planes along 84 att N7OE a N70E I �-102- An extensiveperiod periodofof shearing shearingaffected affectedthe the quartz quartz ddiorite An extensive i o r i t e gneiss gneiss A series of of small small shear shear zones zones formed formed iinn the the gneiss, gneiss, and and intrusives. A coincident with the the formation formation of of the theamphibolite amphiboliteschist s c h i salong t alongthe theChippewa Chippewa amphiboliteschist schist displays displays aall The amphibolite l l the the same same structural characcharacRiver. The teristics the quartz quartz ddiorite t e r i s t i c sas asthe thesmaller smaller shear shear zones zones i in n the i o r i t e gneiss. gneiss. For this schist is this reason, reason, the the amphibolite amphibolite schist is interpreted interpreted tot orepresent represent aamajor major shear which crosscuts crosscuts the area. shear zone zone which area. Shear Shear zones zones iinn the thearea areatrend trendN7OE N70E and have lineations lineations which SW. A A linear linearnegative negativeaeromagnetic aeromagnetic and have whichaverage average400 40ÂSw. anomaly whichtrends trendsN70E N7OE across area probably resultofof this this anomaly which across thethe area i s is probably a aresult major shear shear zone. zone. The final phases of b rbrittle i t t l e faulting throughThe final phases of deformation deformationproduced produced faulting throughout the area. Faults trending trending N5OW N50W offsets l other features offsetsa lall other structural structural features the area. Faults i n the the area area (Figure (Figure 63). f t llateral ateral in 63). These Thesefaults faultsdisplay displayboth bothright rightand andl eleft s t r i k e separation, separation, although a1though right o f f s e tisi dominant. s dominant. strike right lateral offset Figure 63 NW-trending f afault u l t offFigure 63 --- NW-trending offsets i n forefores e t s of granitic granitic dikes. dikes. Dike Dike in ground is about 2 feet feet wide. wide. ground is about �-103- TITLE: PRELIMINARY ON THE THE GEOLOGY OFTHE THE JUMP JUMP RIVER VALLEY PRELIMINARY REPORT: REPORT ON GEOLOGY OF VALLEY LOCATION: LOCATION: Jump County Park Price County County to to JumpRiver Rivervalley valley from from Big Big Falls County Park iinn Price the east eastend end ofofHolcombe Hol combe Flowage Flowage in i n northeastern northeas ternChippewa Chippewa County. County. AUTHOR: AUTHOR: M.L. M. L Cummings Cummi ngs DATE: DATE: - March, March, 1980 1980 . SUMMARY OF FEATURES: FEATURES : SUMMARY OF Intermediate Intermediate tto o basic basic flows flows and and fragmental fragmental volcanic volcanic rocks rocks crop out along along the Riverand andi tits tributary valleys. volcanic blocks blocks and and aa plagiothe Jump Jump River s tributary valleys. Coarse Coarse volcanic clase porphyritic porphyritic felsite w i t h aa volcanic volcanic center center east east of clase f e l s i t eflow floware areassociated associated with the village granitic plutons an intrusive the villageofofJump Jump River. River. Several Several granitic plutons appear appear tto o form form an belt Oneofofthe theplutons plutonsisist otonalitic belt immediately immediately south south of of the theJump Jump River. One n a l i t i c in in composition and andwas wasemplaced emplaced before deformation thegranitic granitic plutons are composition before deformation b ubut t the are llate a t e or or post post kinematic. kinematic. INTRODUCTION: INTRODUCTION : Geologic mappingalong alongthe theJump JumpRiver Riverand andtributary tributary streams Geologic mapping streams in i n southwest southwest completed iin Price, southeast southeastRusk Rusk and and northeast northeastChippewa Chippewa Counties Counties was was completed n the the summerof of 1979. The mapped mapped areaextends extends from mileseast eastofof Big Big Fa1 Falls summer 1979. The area from 33 miles 1s County County Park in i n Price PriceCounty, County,west, west,tot Holcombe o HolcombeFlowage Flowage ini nnortheastern northeasternChippewa Chippewa County. County. Park Searchesfor for outcrops outcrops were werecarried carried out on Searches on the the North North and and South South Forks Forks of the the JumpRiver, River,Levi Levitt ShoulderCreek Creekand and Main Creek; tributaries of of Jump tt Creek, Creek, Shoulder Main Creek; a l l alltributaries the Jump Jump River. Localized Localized searches searchesf ofor outcropswere werecarried carriedout outononthe theLLittle r outcrops ittle Jump River and andthe the upper upper reaches reachesof of the North Jump River North Fork Fork ofofthe theJump Jump River Riverand andMain Main �-104- The search search ffor head—waters o r outcrops outcrops centered centeredon onstreams streamsthat t h ahave t have head-waters r ree•.. e o ; . The north n o r t h of o f Highway Highway 3 8 since these these streams streams served served as as major major channels channels for f o rmelt—water melt-water during deglaciation comunication, Adam Cahow, degl a c i a t i o n ofo fthe thearea area(personal (personal communication, Adam Cahow, 1979) 1979)and and thus were niore probably scoured to bedrock than other streams in the area. thus were more probably scoured t o bedrock than other streams i n area. This report This r e p o r t is i s based based primarily p r i m a r i l y on on field f i e l drelations r e l a t i o nand s andhand handsample sample descripdescripsamplesbbut section studies studieshave havebeen beencompleted completed on on some some samples u t are not not tions. Thin section available for all Further thin t h i n section sectionstudy, study,chemical chemicalanalyses analyses available a1 1samples. samples. Further and and sstructural t r u c t u r a l analysis analysisare arepresently presentlyunderway. underway. PREVIOUS WORK: WORK: The geology f t the h e Jump l l e y has o nonly l y b rbriefly i e f l y iinn The geologyoof JumpRiver Riverv avalley hasbeen beenreported reported area northwest northwest ooff the the i t e r a t u r e . The the lliterature. map The area t h e study studyarea areawas was included in i naamap ffor o r aa discussion discussionofo the f the FlambeauCopper Copper Deposit at a t Ladysmith Ladysmith (May, (May, 1977) 1977) but but Flambeau the discussion discussionooff tthe the h e rock rock uunits n i t s was was llimited i m i t e d to t o the t h eregional regional geology geology section section of description o f the the paper. paper. A A ffield i e l dtrip t r i stop p stop d e s c r i p t i owas n wasincluded includedini nthe theguidebook guidebook f o r the the1979 1979 meeting meeting of o f the t h eInstitute I n s t i t u on t e on Lake Superior GeologybybyLaBerge LaBerae for Lake Superior Geology (1979) ffor o r Big B i g Falls F a l l sCounty County Park Park aatt the t h e eastern eastern end end of the the present present study study area. area. (1979) Wurdinger 1980) and and Myers, Myers, (1974, (1974, 1980) 1980) have have mapped mapped southwest the Wurdinger (1979, (1979, 1980) southwest ooff the study River Valley. Valley. study area area along the the Chippewa Chippewa River ROCK ROCK UNITS: The rocks along along the t h e Jump Jump River n t a t i v e l y divided The volcanic volcanic rocks River have havebeen beent etentatively i n t o 1) 1) mafic mafic to t ointermediate intermediateflows flows and and 2) 2) basic basic tot ointermediate intermediatefragmental fragmental into volcanics (Figure 64). volcanics 64). Two areasoof mafic and and intermediate intermediate flows flows have havebeen beeni didentified. Two areas f mafic e n t i f i e d . The irst Thef first underlies area of o f the t h e Jump Jump River t h e confluence confluence ooff the the North North underlies the area River Valley Valley west west ooff the and f t the h e Jump f the i l l a g e ofo fJump Jump River. River. and South SouthForks Forkso of JumpRiver Rivert oto4% 4½miles mileseast eastoof the vvillage The second secondarea area1ilies southeast ooff the The e s southeast t h e village v i l l a g eofoSheldon f Sheldonalong alongShoulder ShoulderCreek Creek and west west along alongtthe JumpRiver Riverf for 2 miles. and h e Jump or 2 The fragmental volcanic volcanic rocks The fragmental rocks crop out o u t along along the t h e South South Fork Fork of o fthe t h eJump Jump River near 4½miles miles east east of of near Big B i g Falls F a l l s County County Park Park in i n Price P r i c eCounty County and and from from 4^ the River tto mileseast easto of thevvillage f the i l l a g e ooff the village v i l l a g e of o fJump Jump River o approximately approximately 3 3miles Sheldon. A coarsefragmental fragmentaluunit occursimmediately immediatelyeast easto fofthe thevvillage off A coarse n i t occurs illage o JumpRiver Riverand andappears appearst otorepresent representan anexplosive explosivevol volcanic center. Jump canic center. Since River flows approximately p a rparallel a l l e l t o to the r i k e ofof l lithologic ithologic Since the the Jump Jump River flows approximately thes tstrike units, the the stratigraphic s t r a t i g r a p h i cthickness thickness exposed exposed along e r iriver v e r iis s not n o t great. great. It units, alongt hthe It would a t f for o r the t h e area area east east of o f Sheldon Sheldon tthe h e fragmental fragmental volcanic units would appear appeart hthat volcanic units are underlain underlain by basic flows. The are u n i t smay may extend extend west west The fragmental fragmental volcanic volcanic units of Sheldon Sheldon as r y s t a l ttuffs u f f s that t h a t are are overlain o v e r l a i nby byintermediate intermediate flows flows of asfine-grained fine-grainedc crystal however a apossible u l t east Sheldon provides ambiguity t o to t hthis i s i ninterterhowever possiblef afault east ooff Sheldon providessome some ambiguity pretation. In i tappears appears tthat h a t basal t i c flows flows are are overlain o v e r l a i n by by iinternterI n general, general, It basaltic mediate o mafic fragmental volcanic rocks that t h a t were were deposited deposited from f r o m aa volcanic volcanic mediate tto mafic fragmental volcanic rocks center iinn the t h e area area east of o f the the village v i l l a g eofoJump f Jump River River and and this t h i s ini nturn t u r nwas was center buried by by intermediate buried intermediate flows, flows. Top i n d i c a t o r s in i n the the fragmental fragmental uunits n i t s indicate indicate lop indicators t h a t the the stratigraphic s t r a t i g r a p h i c section section isi soverturned overturned with w i t h tops tops facing facing south. south. Thus that Thus the proposed t r a t i g r a p h i csequence sequence is1ssouthward southwardyounging youngingsequence. sequence. proposedsstratigraphic The basic basic volcanics volcanics aatt the lowestsstratigraphic The the proposed proposed lowest t r a t i g r a p h i c level l e v e lofo the f t h eexposed exposed volcanic The fflows vol canic pile p i 1eare aremassive massive with w i t hlocally 1ocal ldeveloped y developedamygdaloidal amygdal o i d a l zones. zones. The 1ows �-n .1. (0 01 CD -.5 C Figure 64 rf -I 0 0 (0 -I. 0 -t 0 CD C, -- Geologic Map of CD -S -S CD -I. 3 CD the Jump River area. 'I •lt_. I / Ku:K — — _L±L_ —R —. I DIASASE SIRES FOlIATED TONALITE FLOWS COARSE TO FIRE FRAGMENTAl. VOLCANICS OVER TUNNED •EDDINS SIIEAR o FAULT ZONE STRIKE S DIP OF STRIKE $ DIP OF FOLIATION STRIKE S DIP OF WEDDING CONTACTS. INFERRED LOCATION OF OUTCROPS S TM SO L8 METASEDINENTART ROCKS Hf 1.1. IIJWINTERNEDIATE I SASIC METAVOLCASIC ROCKS ' RSQUARTZ MONZONITE, GSAP)PHYRIC 5 QUARTZ MONZONITE dl ROCKS LEGEND INTRUSIVC -t Ui CD �-106- are fine-grained and and weakly o c a l l y aa well we1 1developed developed sschistosity chistosit y are fine-grained weaklyschistose schistosebut butl locally i s found found to t o coincide coincide with w i t h late l a t eshear shearzones. zones. The e uunits n i t s iinnis Themineralogy mineralogyofoft hthe cludesactinolitic-hornblende, actinolitic-hornblende, plagioclase, plagioclase, epidote epidoteand andl olocally cludes c a l l y cchlorite. hlorite. . Overlying tthe basaltic Overlying h e basal t i c flows flows are are fragmental fragmental intermediate intermediate tto o basic basic volcanics. vol canics Theuunits includec rcrystal andc r crystal-lithic The n i t s include y s t a l and y s t a l -1 it h i c ttuffs u f f s and and 1lapilli-sized a p i l l i - s i z e d to t oblockblocksized The coarsest coarsest fragment fragment sizes sizes occur sized fragmental fragmental units. The occur from from immediately immediately east of the 16) tto miles up up rriver. east of the village v i l l a g eofofJump Jump River River (Stop (Stop 16) o 2 2 miles i v e r . Apparently this t h i s area area Is i s near near an an iirruptive r r u p t i v e center center since since llithic i t h i cblocks blocks to t o11foot f o o tIni ndiameter diameter are found found llocally. The ssize andt hthe are o c a l l y . The i z e ooff lithic l i t h i cfragments fragments decreases decreases and e r ratio a t i o of of ccrystal r y s t a l fragments fragments to t o lithic lit h ifragments c fragmentsincreases increasesaway away from from the volcanic center. center. Fine—grained beddedt utuffs and ash ash beds bedsoccur occur interbedded interbedded wwith Fine-grained bedded f f s and i t h coarse coarse fragmental fragmental beds i in Coarsec clasts beds n tthe h e area area ooff the t h e volcanic volcanic center. center. Coarse l a s t s ooff volcanic volcanic debris debris apparently ffell apparently e l l into i n t othe t h eaccumulating accumulating fine f i n e grained grained materials materials allowing a1lowing deterdeterminationoof top ffor Suchtop top iindicators mination f tthe h e sstratigraphic t r a t i g r a p h i c top o r the the volcanic volcanic ppile. i l e . Such ndicators havebeen beenfound foundi ninthe thearea areaoof the coarsest coarsest fragmental fragmental rocks rocksand andi in have f the n ccrystalrystalcase the the top top ooff the lithic I n each each case the l i t h i ctuffs t u f faway s awayfrom fromthe t h evolcanic volcanic center. center. In Sulfide mineralization m i n e r a l i z a t i o n up up to to volcanic pile volcanic p i l e isi ssouth southfacing f a c i n gand and isi soverturned. overturned. Sulfide 10 volumepercent percent (estimated (estimated iin sample)i is 10 volume n hand hand sample) s particularly p a r t i c u l a r l ycommon common iinn the the A pporphyritic o r p h y r i t i c ffelsic el s i c fragmental fragmental uunits, n i t s , 1locally ocal l y defining d e f i n i n g sulfide-rich sul f i d e - r i c hbeds. beds. A flow f l o w also a l s o occurs occurs In i n the t h e area area of o f the the volcanic volcanic center center along along with w i t h intermediate intermediate flows. The fine-grained The ffelsic e l s i c flow f l o wcontains containsplagioclase p l agiocl asephenocrysts phenocrysts ini na afine—grained m a t r i x and and may may be flow f l o w banded banded (Stop (Stop 17.). 17). The The f felsic e l s i c fflow l o w iis s the the only only ffelsic elsic matrix unit u n i t found found in i n the thestudy study area. area. The The volcanic center centermay may represent represent aacollapsed c o l l apsedsubmarine submarine caldera calderacomplex complex in fragmentaluunits representppart i n which which the coarse coarse fragmental n i t s represent a r t ooff tthe h e rims of o f the the caldera. caldera. The center center ooff the caldera wasf filled The caldera was i l l e dby byintermediate intermediate flows flows and and Intermediate intermediate to to Thef felsic representa ar hrhyolitic f e l s i cfragmental fragmental rocks. rocks. The e l s i c rocks rocks in i n the the area area may may represent yolitic felsic domedeveloped developedduring during caldera caldera resurgence supplying dome resurgence producing the t h e dome dome and and supplying felsic f e l s i cpyroclastic p y r o c l a s t i cmaterial m a t e r i a to l t othe t h caldera e calderacomplex. complex. The area south south ooff Sheldon on Shoulder ShoulderCreek Creeki sis underlain underlain by The area Sheldon on by an an intermediate prominently prominently pporphyritic o r p h y r i t i c fflow l o w uunit n i t that t h a t apparently apparently overlies over1 i e s the the fragmental fragmental uunit. nit. Westoof Sheldonand and apparently underlyingt hthe West f Sheldon apparently s t rstratigraphically a t i g r a p h i c a l l y underlying e f lflow o w uunit n i t are are fine f i n e grained grained intermediate intermediate crystal c r y s t a l tuffs t u f f sthat t h amay t maybe bethe thewestward westward extension extension ooff A fault occurs, A f a u l t occurs east east the crystal and crystal-lithic tuffs found to the east. t h e c r y s t a l and c r y s t a l - l i t h i c t u f f s found t o the east. of andmay mayhave have displaced area bbut o f Sheldon Sheldon and displaced u nunits i t s i nin tthe h e area u t the nature nature and and extent Locally along Shoulder Creek of thef afault ntero f movement movement ononthe u l t is i snot n o known. t known. L o c a l l y along Shoulder Creek i inter- mediatet oto ffelsic mediate e l s i c tuffs t u f f sappear appear to t o be be interlayered i n t e r l a y e r e d with w i t h the t h eintermediate intermediate flows flows (Stop 15) suggesting coeval eruption of flows and pyroclastics. (Stop 15) suggesting coeval eruption o f flows and pyrocl a s t i c s . Throughout thevolcanic volcanic sequence sequence Throughout the o fofs tstrike r i k e ooff bedding bedding i in n fragmental fragmental uunits nits Thesstrike units and and contacts between between units u n i t sranges rangesfrom fromN5OE N50E to t oN75E. N75E. The t r i k e ooff u n i t s in in the t h e area area ooff the t h e volcanic volcanic center center are are more more iirregular. rregular. INTRUSIVE UNITS: The iintrusives The n t r u s i v e s (Figure (Figure 64) 64) ini nthe t h eJump Jump River River Valley Valleyare arepoorly p o o r l yexposed exposed and and are represented by small small outcrops, outcrops, iinn cases outcrop iiss known are represented by cases only one one outcrop known ffor o r aa mostextensively extensivelyexposed exposed cropsoout pluton. The The most i n intrusive t r u s i v e crops u t aat, t , and and tto o the t h e east east occurs southeast southeast ooff the second occurs the of, Big B i gFalls F a l l sCounty County Park Park in i nPrice P r i c eCounty. County. AA second The River and and iiss best exposed vvillage i l l a g e of o fJump Jump River exposed onona at rtributary i b u t a r y ooff Levitt L e v i t tCreek. Creek. The �-107- same plutonintrudes intrudes volcanic volcanic units same pluton u n i t s at a tthe thewayside wayside park park ini nJump Jump River. River. AA t h i r dintrusive i n t r u s i v eis iknown s knownby byonly only2 2oro3r small 3 smalloutcrops outcropsin i an wooded a woodedarea area about about third ½m mile h i l e south south of o fShoulder ShoulderCreek Creek along alongCounty County highway highway H. H. A A ffourth o u r t h intrusive intrusive crops crops out o u t along along Main Main Creek Creek north of of the theJump Jump River. River. The The iintrusives n t r u s i v e s are are granitic A ffifth i f t hpluton p l u t o nisi exposed s exposed g r a n i t i cand and have have variable variable mineralogies mineralogies and and textures. A iinn low low outcrops outcrops south south of ofthe theJump Jump River Riveron onShoulder Shoulder Creek. Creek. The The i intrusive n t r u s i v e iiss tonalitic. Unmetamorphosed dikes crop outi ninthe the area area and and generally generally tonal i t i c . Unmetamorphosed b a sbasalt a l t dikes crop out strike N70E. s t r i keN7OE. The pluton pluton at The a t Big B i g Falls F a l l sCounty County Park Park isi sa amassive massive pink pink quartz quartzmonzonite monzonite cut c u t byminor by minor aplitic ap1i t i cand andpegmatitic pegmati t i c dikes. dikes. The The iintrusive n t r u s i v e has has also been desalso been described The ppluton contains subhedral subhedralgrains grainsooff pplagioclase, c r i bed by by LaBerge LaBerge (1979). (1979). The i uton contains l agiocl ase , anhedralorthoclase, orthoclase, quartz quartz and andbbiotite. anhedral i o t i t e . The plagioclase grains contain The plagioclase contain subsubhedral epidote; h l o r i t e is i s interlayered i n t e r l a y e r e d with w i t h biotite b i o t i t esuggesting suggesting that t h a t the the pluton p l uton hedral epidote; cchlorite has been weakf ofoliation been metamorphosed. metamorphosed. Locally L o c a l l y the t h e rock rock has has a weak l i a t i o n but b u t in i ngeneral general metamorphicf afabric metamorphic b r i c is i sweakly weakly developed. developed. AA w well zone cuts cuts the e l l developed developed shear shear zone iintrusive n t r u s i v e in i nthe thepark parkarea area (will ( w i lbe l bediscussed discussed below). below). One i l e west Onemmile west ooff the park the quartz quartz monzonite monzonitei sisi in park the n iintrusive n t r u s i v e contact contact with w i t h the the volcanic volcanic rocks rocks and contact contact metamorphic metamorphice feffects are observed observedi in the volcanics. and f e c t s are n the The pluton exposed exposedalong alongLevi Levitt Creek appears appearst otobe bemore moreg rgranitic The pluton tt Creek a n i t i c iinn composition. Thin sections ooff tthe unit Thin sections he u n i t indicate i n d i c a t e k-feldspar k-feldspar greater greater than than plagioclase. The occursasassmall smallgrains grainsi in the k-feldspar. The pplagioclase l agioclase occurs n the k-fel dspar. Muscovite occursi ninterstitially Muscovite occurs t e r s t i t i a l l ytot ofeldspars feldsparsand andquartz quartzand andappears appears to t o be be of of igneousoorigin. rep1aces k-feldspar k-fel dspar near near ssericitic e r i c i t i cmicroshears. igneous r i g i n . Fine Fine ssericite e r i c i t e replaces m i croshears Chloritized andt to extent iinn C h l o r i t i z e d biotite b i o t i t eisi sprominent prominent ini nthe themicroshears microshears and o aa llesser e s s e r extent the Handsamples samples of the areas the fresh rock. rock. Hand o f the i n t intrusive r u s i v e i n in areas t h athat t i n indicate d i c a t e l i little ttle deformation contain contain more morebbiotite. deformation iotite. . The pluton pluton south south ooff Shoulder Creekhas hasn not beenstudied studiedi nint thin The Shoulder Creek o t been h i n section at Theggranitic a t this t h i s time. time. The r a n i t i c intrusive i n t r u s i v e contains contains small small zzenoliths e n o l i t h s of o f volcanic volcanic rocks. A.fabric A. f a b r i cdue due to t ometamorphism metamorphism i is s nnot o t present present or o r isi sweakly weaklydeveloped. developed. Outcrops aresmall smalland and Outcrops are d i fdifficult f i c u l t tto o find. find. The along Main Creek Creeki is i uton exposed exposed a1 ong Main s a quartz monzonite monzoni t e characterized characterized The ppluton by granophyric on subhedral subhedral pplagioclase by granophyri c intergrowths developed developed on l agiocl ase grains. grains The feldspars are rred colored due duet to inclusions and andaalteration feldspars are e d colored o ffine i n e hematite hematite inclusions l t e r a t i o n of of the pluton pluton iiss locally Epidote iiss aa corrwon the l o c a l l y intense. intense. Epidote common aalteration l t e r a t i o n mineral. northare known known wwithin i t h i n aa mile m i l e both both southeast southeast and and northOutcrops ooff volcanic volcanic rocks rocks are west west ooff the t h e intrusive i n t r u s i v eoutcrops outcropsononMain MainCreek. Creek. . The The t tonalitic o n a l i t i c intrusive i n t r u s i v e isi snot notonly onlyunique unique in i nits i t scomposition composition but b u t also also Outcrops are are low, low, flat f l a tand andsmooth smooth and and have have in i n its i t sstrong strong foliated f o l i a t e d fabric. f a b r i c . Outcrops been found found iinn only Handsamples samples been o n l y one one area area along along Shoulder Shoulder Creek. Creek. Hand i n indicate d i c a t e bbiotite iotite and plagioclase are the main minerals while quartz is apparently minor.. and plagioclase are the main minerals w h i l e quartz i s apparently minor. Thin Thin The iintrusive section study has nnot beeni ninitiated. section study has o t been i t i a t e d . The n t r u s i v e is i sclearly c l e a r l pre—kinematic. y pre-kinematic. Contactswwith other iintrusive andso sothe the rrelation Contacts i t h other n t r u s i v e rocks rocks havenot have not been been found found and elation ooff the t h e tonalite tonal it eand andquartz quartz monzonite monzoni t e iintrusives n t r u s i v e s in i nthe thearea area isi snot n oknown t known but but textural the differences differencesi in the ttonalite t e x t u r a l relations r e l a t i o n s and and the n ffoliation o l i a t i o n suggests suggests tthat h a t the onalite intrusive i n t r u s i v e is i searlier e a r l i ethan r thanthe thequartz quartzmonzonite monzonite intrusives. intrusives. �-108- STRUCTURAL FEATURES: STRUCTURAL FEATURES: The sstructural The t r u c t u r a l elements elements of o f the the area area are areboth bothcontinuous continuous and and discontinuous. discontinuous. The main continuous structural element is schistosity. Commonly The main continuous s t r u c t u r a l element i s s c h i s t o s i t y . Commonly s cschistosity h i s t o s i ty iiss found found to t o be be parallel p a r a l l e to l t compositional o compositionalbanding, banding, contacts contacts and and bedding bedding iinn the the volcanics. i n t r u s i v discussed e discussedabove above is i s subsubvol canics. The t y iin n the the tonalitic tonal it i cintrusive Theschistosi schistosity Schistosity ty iiss locally l o c a l l yinfluenced influenced pparallel a r a l l e l to t o the the schistosity s c h i s t o s i t y ini nthe thevolcanics. volcanics. Schistosi by faults by f a u l t s and andyounger younger shear shear zones zones and and also appears appears to t o be be warped warped by large l a r g e open open ffolds. olds . The with The sschistosity c h i s t o s i t y associated associated w i t h discontinuous discontinuous sstructural t r u c t u r a l elements elements crosscrosscuts eearlier cuts a r l i e r schistosity s c h i s t o s i t y and and is i s often o f t e nrelateI r e l a t e dtot local o l o c ashear l shearzones zonesand/or and/or faults. Important faults. Important ffault havebeen beeni didentified areas, 1) Big a u l t zones zones have e n t i f i e d i in n 33 areas, B i g Falls Falls CountyPark, Park,2)2) east east ooff the County the village v i l l a g eofo fJump Jump River, River, and and 3) 3) east east of o fSheldon. Sheldon. casethe thef afault associatedwwith strongddisruption IInn each each case u l t zone zone i is s associated i t h strong i s r u p t i o n ofof eearlier arlier formedtextures textures and and fabrics. fabrics. formed AAtt Big Big Falls F a l l s the thefault f a u lhas t hasproduced produced aa significant s i g n i f i c a n zone t zoneofo myonite f myonitewhich which has subsequently subsequentlybeen beenrecrys recrystallized. The best exposed developmentooff the exposed development has t a l l ized. The mylonite side ooff the myloni t e iiss on on the south south side the river r i v e rini na anearly nearlycontinuous continuous group group of of outcrops. IInn the the outcrops outcrops the theprogressive progressivedevelopment development from from unsheared unsheared quartz monzonite mylonite quartz monzoni monzonite occursi nin aa distance distance ooff monzonit e t to o myloni t e ttoo unsheared unsheared quartz t e occurs about quartz monzonite monzoniteonone ieither sideoof the ffault about 500 500 feet. The The quartz t h e r side f the a d tappears appears to to be rock uunit. be the same same rock nit. Thef fault The a u l t east east of o f the the village v i l l a g eofoJump f Jump River River is i sspectacularly spectacularlyexposed exposed iin n the south bankoof the rriver. volcanics are are iintensely folded locally the south bank f the i v e r . The The volcanics n t e n s e l y folded l o c a l l yand and possible l large dragf ofold occursi ninthe thevolcanic volcanict utuffs the ssite. The ffault aa possible a r g e drag l d occurs f f s aat t the i t e . The ault area iiss also The geology geologyofofthe the ffault area also the the site s i t eofo an f anold o l dcopper coppermine. mine. The a u l t zone zone is is not andwwill n o t clearly c l e a r l y understood understood and i l l be be investigated investigated in i n thin t h i nsections sectionsand and by by analysis analysis of the ssite. o f structural s t r u c t u r a l data data from from the ite. The ffault The a u l t that t h a toccurs occurs south south of o fSheldon Sheldon is i s poorly poorlyexposed exposed iinn the the bed bed of of outcropsi nin the themiddle middleoof the rriver the Jump Jump River. Small Small outcrops f the i v e r are strongly s t r o n g l y dedeformedand andconsiderable considerablea lalteration occurs iin formed t e r a t i o n occurs n the the volcanic volcanic along along the the shore shore above bbut u t the fault f a u l titself i t s eis l f not i s nexposed o t exposed abovewater watereven even during during periods periods of o f low low stream flow. stream The sense senseoof displacementoor magnitudeo of displacementf ofor the three major The f displacement r magnitude f displacement r the major north to north t o northeast northeast trending trending fault f a u l tstructures structuresare arenot n o known. t known. However, However, i in n aall ll casesthe thef faults boundariesbetween between different cases a u l t s do do nnot o t form form boundaries different l i tlithologic h o l o g i c uunits n i t s oorr are characterized gradeacross acrossthe the ffault characterized by by aa change change in i n metamorphic metamorphic grade a u l t zone. zone. DISCUSSION: The onf field andl limited The ffollowing o l l o w i n g discussion discussion iiss based based on i e l d work work and i m i t e d thin t h i n section section and chemicalstudy studyand andi sistherefore thereforepreliminary preliminary iin and subject subject tto and chemical n nature nature and o reThe i intent so as as ttoo vision. The vision. n t e n t is i s to t ostimulate stimulatediscussion discussionon on the t h eproblems problems rraised a i s e d so improvei ninterpretation River Val Valley. improve t e r p r e t a t i o n of of the t h egeology geology of o f the theJump Jump River ley. The geologic geologic evolution evolution of The o f the theJump Jump River valley v a l l e y must must be be viewed viewed iinn terms terms of boundary between o f the the location l o c a t i o nand andnature natureofofthethe boundary betweenthe theChippewa Chippewa amphibolite amphi b o l it e �-109- complex volcani-sedimentaryprovince provincetto complex t to o the south south and and the Flambeau Flambeau volcani-sedimentary o the north north of the The boundary boundarywas waso roriginally theJump Jump River. The i g i n a l l y placed placed at a t the the Jump Jump River by by Myers (1974) based basedononthe thel olocation Myers (1974) c a t i o n of o f gravity g r a v i t yand andaeromagnetic aeromagnetic anamolies anamolies iinn the area, the nature area, however however the nature of o f the theboundary boundary was was not n o t defined. defined. Part P a r t of o f the the intent i n t e n t of o fthe thepresent present study study was was tto o investigate i n v e s t i g a t e the the field f i e l devidence evidence that t h a tmight might shed shed llight i g h t on on the thenature natureofo the f theJump Jump River Riverlineament lineament (Myers, (Myers, 1974) 1974) and and to to ' attempt to boundary t o define definethe thenature natureofothe f the boundarybetween between the the two two major major geologic geologic provinces provinces iin n the the west-central west-central part p a r tofo fWisconsin. Wisconsin. LaBerge (1979)pointed pointedout outtthat LaBerge (1979) h a t the lineament 1ineament is i s expressed expressed topographically, topographically , in patterns(Ervin and Haniuer, i n Bouguer Bouguer anomaly anomaly patterns (Ervin and Hammer,1974) 1974)and andononaeromagnetic aeromagneticmaps maps (Zietz, ( Z i e t z , Karl, Karl,and andOstrom, Ostrom, 1978). 1978). The The lineament has has comonly commonlybeen beenassumed assumed to to be by aa major major ffault be produced produced by a u l t zone zone (Cumings, (Cunnings, 1975) 1975) and and recently r e c e n t l ythe theJump Jump River Fault Faulthas hasappeared appeared in i nreports reports(Sims, (Sims,Cannon, Cannon, Mudrey, Mudrey, 1978). 1978). From From f field i e l d relations r e l a t i o n sthe theJump JumpRiver Riverlineament lineamentmay may be be shown shown t to o rresult e s u l t from from contrasting geophysicalc hcharacteristics andthe the gglacial contrasting geophysical a r a c t e r i s t i c s o of f 1lithologles itho1ogies and l a c i a l history h istory of topographicexpression expressionofof the the lineament lineament i is o f the the area. area. The The topographic s evident in.stream i n stream patterns patterns in i n the the area area and and by the valley v a l l e y of of the theJump Jump River. River. In I n the the field f i e l d the the course River can can be be shown shownt otobe beccontrolled course ooff the the Jump Jump River o n t r o l l e d by by bedding bedding iinn the the volcanic strong alignment volcanic rocks rocks along along the river r i v e rbanks. banks. The The strong a1 ignment of of stream stream valleys valleys in i n aa northeast-southwest northeast-southwest d idirection r e c t i o n i siscclosely l o s e l y rrelated e l a t e d t to o tthe h e gglacial l a c i a l history history of River and and 1local o f the thearea area(Cahow, (Cahow, personal personal coninunication, communication, 1979). 1979). The The Jump Jump River ocal streams servedasasmajor majorf l flood channelsf ofor waterduring during deglaciation deglaclation of of streams served o o d channels r mmelt e l t water the area area in i n the theprocess process carving carving large l a r g evalleys valleysand andscouring scouringtot obedrock bedrockini many n many places. The Riveri siscclearly than the the rriver The vvalley a l l e y ooff the t h e Jump Jump River l e a r l y llarger a r g e r than i v e r that that flows flows iinn the the valley. valley. Thus Thus iittwould would appear appear tthat h a t the the topographic topographic expression expression of of lineament may o t be o n t r o l l e d by major ttectonic e c t o n i c boundary boundary bbut u t by by the the the lineament maynnot beccontrolled by aa major in f l uences exerted l a c i a l run-off r u n - o f f and and bedding bedding sstructures t r u c t u r e s In i n the t h e volcanic vol cani c influences exerted by by gglacial rocks rocks ooff the the present present valley. The anamoly map mapfor for the area The Bouguer Bouguer anamoly areashows shows aa distinct area d i s t i n c tchange change in i n the the gravity g r a v i t yofothe f the areaacross acrossthe theJump Jump River River Valley. Valley. The The gravity maybebedue duet otothe thec contrasting g r a v i t y change change may o n t r a s t i n g ddensities e n s i t i e s ooff volcanic rocks rocks north north of belt of the of the the river r i v e r and and the the b e l t of of granitic g r a n i t i cplutons plutons south south of the river. r i v e r . It Itmust must be be emphasized t hthat a t the r a n i t i c rocks t otobebei nintrusive t r u s i v e i into n t o the t h e volvolemphasized theggranitic rocks can can be beshown shown canic andare arennot canic rocks rocks and o t i in n ffault a u l t contact contact with w i t h the the volcanics. volcanics. The aeromagnetic aeromagnetic anomaly the area sulfide-bearing anomaly f for o r the area can can also be be explained by contrasts between between sulfide-bearing tuffs northeastsstrike t u f f s and and sulfide—free sul f i d e - f r e e ggranitic r a n i t i c rocks. rocks. The The northeast t r i k e of of volcanic volcanic units units and the northeast and the northeast trends trends of of basalt b a s a l t dikes dikes ini nthe thevolcanic volcanicrocks rockswould wouldexpectedly expectedly produce some type magnetic contrast rockssouth southofof tthe produce some type o fofmagnetic con t r a s t t o to g rgranitic a n i t i c rocks h e rriver. iver. The JumpRiver River1lineament cant hthusly beexplained explainedbybythe thegeologic geologic features features iinn The Jump ineament can u s l y be rocks and and does does nnot o t necessarily r e q u i r e aa major major tectonic t e c t o n i cboundary boundary along along the the rocks necessarily require Jump River o explain the the observed observed geophysical Jump Rivert to geophysical and and topographic topographicfeatures features ooff the linearnent. lineament. The River Fault Mudrey, 1978) 1978) has The Jump Jump River Fault Zone Zone (Sims, (Sims, Cannon Cannon and and Mudrey, has also also been been placed placed iinn the the general general study study area, area, however however the presence presence ooff aa major major ffault a u l tzone zone of significant s i g n i f i c a ndisplacement t displacementdoes doesnot n o tappear appear tot obe besupporte.d supported by. b y ffield i e 1 devidence. evidence. It Itmay may be be argued argued tthat h a t the the plutonic p l u t o n i crocks rockssouth southofofthe theJump Jump River Riverwere were intruded intruded along such a fault zone, this would require the fault to be Middle Precambrian along such a f a u l t zone, t h i s would r e q u i r e the f a u l t t o be Middle Precambrian in River are are probably probably rrelated i n age age since since the the plutons plutons along along the the Jump Jump River e l a t e d tto o the the plutonic development The development o fofa af afault u l t aafter fter p l u t o n i cphase phaseofo the f t hPenokean e PenokeanOrogeny. Orogeny. The emplacement theplutons plutonsi is questionable since since the the plutons plutons can emplacement o fofthe s questionable can cclearly l e a r l y be be shown the vol volcanics suggesting1ilittle shown i nintrusive t r u s i v e i into n t o the canics suggesting t t l e post post intrusive i n t r u s i v e displacedisplacement ment along the the zone. zone. �-110- An aalternate l t e r n a t e hypothesis i s t o r y ofof the area iiss An hypothesist oto expain expainthe thegeologic geologich history the area t h a t the the Jump Jump River does nnot o t represent a major major tectonic t e c t o n i c boundary boundary but but that River Valley does represents u t o n i c a activity c t i v i t y during f t th h e volcanic volcanic rocks rocks representsnormal normalp lplutonic during deformation deformationoof in i n the thePenokean Penokean Orogeny. Orogeny. The The pplutonic l u t o n i c rocks rocks may may be n t e r p r e t e d as as forming forming be iinterpreted a roughly l linear i n e a r bbelt e l t of o f intrusives i n t r u s i v e s that t h a tisi ssub-parallel sub-paralleltot the o the beddingand and a roughly bedding possible ffold possible o l d structures s t r u c t u r e s in i n the the volcanic volcanic rocks. rocks. The chistosity The development developmento fofsschistosity pparallel a r a l l e l to t obedding bedding In i n the t h evolcanics volcanics can can be be interpreted i n t e r p r e t e d as as suggesting suggesting northnortheasterly trending major f o l d structures i n the area i f t h e c h i s t o s i t y is is easterly trending major fold structures in the area if the sschistosity axial planar to the folds. a x i a l planar t o t h e folds. Thus emplacement ooff plutons plutonsmay may have have been been Thus the emplacement guided by o l d crests c r e s t s and and troughs troughs that t h a thad had already a1 ready developed developed iin n the the guided by the the ffold volcanics. vol canics. Tonalitic Tonal it i cintrusives i n t r u s i v e swere wereemplaced emplaced pprior r i o r to t odeformation deformation and and the the sameoorientation same r i e n t a t i o n of of schistosity s c h i s t o s i t ywas wasimposed imposed on the t o n a l i t e as on the volcanics. on the tonalite as on the volcanics. IIn n an an attempt o further resolve the the disputes disputes over h e ssignificance i g n i f i c a n c e of the attempt tto further resolve over tthe of the geology the Jump Jump River Valley Valley aareconnaissance reconnaissance survey survey was was undertaken n tthe he geology ooff the undertakeni in Gilmanarea areaalong along tthe Yellow River River (Figure Gilman h e Yellow (Figure 64 metavolThe area area contains metavol64 ). The it e facies conditions but butsome some canic rocks rocks that t h a twere weremetamorphosed metamorphosed under underamphibol amphibolite facies conditions primary volcanic volcanic structures primary s t r u c t u r e s are arepreserved. preserved. The The local l o c a lmetamorphic metamorphic grade grade may may havebeen beeninfluenced influencedbybyi nintrusion and gabbroic gabbroici nintrusives have t r u s i o n ooff intermediate intermediate and t r u s i v e s that that have well1 developed have we1 developed sschistosity. c h i s t o s i ty. Basalt Basalt dikes dikesare areunmetamorphosed unmetamorphosed and and trend trend northeasterly. Since northeasterly. Since tthe volcanic rocks rocks sstill h e volcanic t i l lpreserve preserveprimary primary textures textures they they are i m i l a r to t o the t h e volcanic volcanicrocks rocksalong alongthe theJump Jump River River than than the the amphibolites amphiboli tes are more moressimilar exposed along tthe River aatt Jim Falls gneisses exposed along h e Chippewa Chippewa River F a l l soro rthe the gneissesat aHolcombe t HolcombeDam Dam exposed oorr Cornell. Cornell. The The ssimilarity i m i l a r i t yofo fthe t h evolcanic volcanicrocks rockstot those o those exposed ini nthe theJump Jump River Valley Valley would would argue argue against against a major major ffault a u l t zone zone or o r tectonic t e c t o n i cboundary boundary existing existing greater incidence incidence ooff plutonic betweenthe the Ye1 Yellow between low River and and the t h e Jump Jump River. The The greater plutonic rocks along the the Yellow River may mayr reflect rocks along Yellow River e f l e c t proximity proximity to t othe thecore coreofothe f t hPenokean e Penokean Orogenic Someo of Orogenic bbelt e l t rrather a t h e r than than a different d i f f e r e n tgeologic geologic province. province. Some f tthe h e questions questions about the the rrelation about e l a t i o n of o fthe thevolcanic volcanicrocks rocksini the n t hYellow e Yellowand andJump Jump River River Valleys Valleys will w i l lhopefully h o p e f u l l ybeberesolved resolvedbybymajor majorand andminor minorelement element chemistry chemistry presently p r e s e n t l y being being Theppossibility thetwo twor river prepared. The o s s i b i l i t y of o ffinding f i n d i n goutcrop outcropareas areas between between the i v e r valleys valleys i s dampened dampened bybythe o f swamps and and apparently t h i cthick k g l aglacial c i a l d rdrift i f t tthat hat is theexpanse expanseof swamps apparently lies iesbetween. between. 1 SUMMARY: SUMMARY: perplexing questions IInn sumary, summary, several several difficult d i f f i c u and l t and perplexing questionshave havebeen been raised raised about the nature of the boundary between the Chippewa Amphibolite complex about t h e nature o f the boundary between t h e Chippewa Amphibolite complex and and the Flabeau volcani—sedimentary province studies In Flabeau volcani-sedimentary province byby f i field e l d studies i n the t h eJump Jump River River andppetrologic Valley. AAtt present present the the available a v a i l a b l emapping, mapping, chemical chemical and e t r o l o g i c data data are not not As further study of materials collected able ttoo provide able provide definitive d e f i n i t i v eanswers. answers. As f u r t h e r study o f m a t e r i a l s c o l l e c t e d However, on on tthe he from on the the issues. from tthe h e area area continues, continues, new new 1light i g h tmay may be be shed shed on issues. However, basis of present information, a Jump River lineament may be reasonably accepted o f present information, a Jump River 1ineament may be reasonably accepted as markingthe thedifferences differences iinn geophysical as marking geophysical pproperties r o p e r t i e s ooff volcanic volcanic and and plutonic plutonic evidencei nin tthe rocks bbut not rocks ut n o t as as a major major tectonic t e c t o n i c break. break. The The evidence h e ffield i e l d does does not not appear to support a major Jump River Fault in the area. appear t o support a major Jump River Faul t i n area. ACKNOWLEDGEMENTS: ACKNOWLEDGEMENTS: study was was funded 102-155 f from r o m the niversity This study funded by by research research grant grant number nunter 102-155 the U University of Wisconsin Wisconsin - Eau Eau Claire. V. Lueth, R. R. Weegman, Weegman, and V. Lueth, andC.C.Lutzewitz Lutzewitz assisted assisted iinn field f i e l dmapping mapping and and L. Prueher, and i n sections r tthis his L. Prueher, andJ.J. Lauer Lauerprepared preparedt hthin sectionsf ofor study. All A l l were were students students in i nthe t h eDepartment Department of o f Geology, Geology, University U n i v e r s i t y of of WisconsinWisconsinEau Claire. Claire. Discussion Eau Discussion iin n the the field f i e l dwith w i t R. h R.Maass Maasswere were helpful helpful and andappreciated. appreciated. - �—111— REFERENCES CITED REFERENCES CITED Cumings, , M.M.L., L. , 1975, 1975, Petrology Petrology and and structure structure ofofPrecambrian Precambrian gneisses gneisses aatt Big Big Cummings M.S. Thesis, University of Falls, Eau Claire County, Wisconsin: Fa1 l s , Eau Claire County, Wisconsin: M.S. Thesis, ofMinnesota, Minnesota, Duluth uth Dul gravity map of Wisconin: EErvin, r v i n , C.P., C. P., Hammer, Hammer, S., 1974, 1974, Bouguer Bouguer anomaly anomaly gravity map of Mi sconin: Wisconsin Geological and Natural History Geological and Natural History Survey, Survey, Scale Scale 1:500,000 1 :500,000 LaBerge, G.L., G.L., 1979, River aatt Big Falls TripGuidebook Guidebook LaBerge, 1979, Jump Jump River FallsCounty County Park: Park: Field Trip No. 4, 4, University Natural History No. University of ofWisconsin Wisconsin - Extension, Extension, Geological Geological and and Natural Survey, p. Survey, p. 40-42 40-42 - - May, E.R., E.R., 1977, Supergeneenriched enrichedmassive massivesulfide sulfide 1977, Flambeau Flambeau - A A Precambrian Precambrian Supergene May, Wisconsin,V.V. 11,, p. 1-26 deposit: Geoscience Geoscience Wisconsin, 1-26 Myers, P.E., P.E., 1974, 1974, Precambrian Precambrian geology stop descriptions descriptions iinn the geology andand f i e field l d t r trip i p stop the Myers, Guidebook,38th 38thAnnual AnnualTri Tn-State Guidebook, -State Geological Geological Field Fiel dConference Conference Myers, P.P.E., Fieldtrip E., 1980, 1980, Fiel d t r i pstops stopsand and general general geology geology section section ini nthe theGuidebook, Guidebook, Myers, 26th 26th Annual Annual IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology Geology Sims, P.K., P.K., Cannon, W.F., Mudmy, Mudrey,M.G. M.G.J rJr., Sims, Cannon, W.F., . , 1978, 1978, Preliminary geologic geologic map map of Precambrian rocksi nin part part of northern northern Wisconsin: Wisconsin: UU.S. .S. Geological Geological Survey Survey Precambrian rocks Open-file Open-fi 1e Report Report 78-318, 78-31 8, Scale Scale 1:250,000 1 :250.000 Wurdinger, 1979, Structural Structural geology R. , 1979, geology of amphibolitic amphibol i t i c gneisses, gneisses ,Northeast Northeast Wurdi nger, S.S.R., Chippewa County,Wisconsin: Wisconsin:(abs) (abs)25th 25thAnnual AnnualI nInstitute Chippewa County, s t i t u t e on on Lake Lake Superior Superior Geology, Geol ogy , p.42 p .42 Wurdinger,S.R., S.R.,1980, 1980,Structures Structures quartzdiori diorite, granitic intrusives i n inquartz te, granitic intrusives and and Murdinger, 26thAnnual AnnualI Institute Guidebook, 26th n s t i t u t e on on Lake Lake meta andesites meta andesites ata Holcombe t HolcombeDam: Dam: GuIdebook, Superior Superior Geology Geol ogy Ztetz, I.,I . Karl, J.H., Ostrom, M.E., Preliminary aeromagnetic Zietz, , Karl, J .H., Ostrom, M.E.,1978, 1978, Preliminary aeromagneticmap map covering covering U.S. Geological Geological most of the Terrane in most theexposed exposed Precambrian Precambrian Terrane i n Wisconsin: Wisconsin: U.S. Survey Survey Miscellaneous Miscel 1aneous Field FieldStudy StudyMF—888, MF-888, Scale 1:250,000 1 :250,000 . �-113-1 13STOP STOP #15 #15 TITLE:: TITLE INTERMEDIATE PORPHYRITIC PORPHYRITIC FLOWS FLOWS AND AND TUFFS TUFFS LOCATION: LOCATION: Shoulder Creek SW¼, bridge. SWk,SW¼, SW%, Creek ata tRusk RuskCounty CountyHighway HighwayHHbridge. Sec. 33N.,R.R.4W, 4W,Sheldon Sheldon7½ 7%minute minutequadrangle quadrangle Sec. 29, 29, 1. T. 33N., / AUTHOR: AUTHOR : M.L. M.L. Cuninings Cumnings DATE: DATE : - March, March, 1980 1980 U SUMMARY OF SUMMARY O F FEATURES: FEATURES: Intermediate Intermediate pporphyritic o r p h y r i t i c flows flows are are interlayered i n t e r l a y e r e d with w i t hpossible possibleintermediate intermediate fine-grained developmento of fine-grained ttuff. u f f . Local stretched stretched phenocrysts phenocrysts and and development f sschistosity chistosity appears to rreflect rocks are are ccut appears t o e f l e c t late l a t eshearing. shearing. The The rocks u t by a northeast northeast trending trending basalt b a s a l t dike. dike. DESCRIPTION: DESCRIPTION : The Creeki is subparallel to The vvalley a l l e y of o f Shoulder Shoulder Creek s subparallel t o the t h e valley v a l l e yofo the f t h Jump e Jump River off topographic River which which iiss one one mile m i l e north. north. Study Study o topographic maps maps suggests suggests that t h a t Shoulder Shoulder Creek mayhave havebeen beena amelt-water melt-waterchannel channelduring duringdeglaciation deglaciation ooff the Creek may t h e area area and and may haveformed formeda apparallel may have a r a l l e l channel channel to t o the t h eJump Jump River. River. Shoulder Creek Creek provides provides several key exposures exposuresi nint hthe volcanics stratigraphy andi nintrusive several key e volcanic t r a t i g r a p h y and t r u s i v e hhistory i s t o r y ooff the t h e Jump Jump River Valley. Valley. Several Several 1lithologic it h o l o g i cunits u n i t scrop cropout outalong alonga a½4mile m i l elength l e n g t hofo Shoulder f ShoulderCreek. Creek. The mostprominent prominentrock rocktype typei sis an an intermediate intermediate pporphyri Phenocrysts The most o r p h y r i ttic i c flow. Phenocrysts �-114- of feldspar occur occuri in of plagioclase pl agioclase feldspar n aa sstrongly t r o n g l y rrecrystallized e c r y s t a l 1ized matrix. matrix. The The recrystallization due tto r e c r y s t a l l i z a t i o nmay may be be due o aa bbasalt a s a l t dike dike that t h a t intrudes intrudes the the outcrop. outcrop. The flow unit The flow u n i t isi sexposed exposed at a tthe thebridge bridgeononcounty countyhighway highwayH. H. Intermediate non-porphyri t i c uunits n i t s are nterlayered w i t h the flow flow Intermediate non-porphyritic are iinterlayered with unit be fine-grained fine-grained ttuffs. u n i t and and appear appear t to o be u f f s . Although Although a contact contact between between the the two two rock types i s not notexposed exposed iittappears appears tthat h a t the the contact contact has has aa sstrike t r i k e of o fNN 60 60 E. E. rock typesis A weakly o r p h y r i t i c , pinkish-gray pinkish-gray ffelsite e l s i t e crops crops out outini nthe thepasture pasturearea areawest west A weaklypporphyritic, o f the the highway highway and t o to bebe e i teither h e r a af l o w u nunit i t o or r aafine-grained uff. of andappears appears flow, fine-grainedt tuff. An uninetamorphosed unmetamorphosed b abasalt s a l t d idike k e crops o f highway highway H, H, however however the An cropsout out east east of contacts contacts of o f the t h edike dikeand andcountry countryrock rockare arenot n o exposed. t exposed. The The prominent inting prominentj ojointing i n the the dike dike that t h a tstrikes s t r i k e sapproximately approximately N75E N75E i sis believed o be t r i k e of of in believedt to be the the sstrike the dike. dike. A granitic g r a n i t i cintrusive i n t r u s i vcrops e crops i nwooded a woodedarea areaapproximately approximately½b mile mile A outout in a to NE¼,Sec. Sec.32, 32,T.1. 33 33 N., N., R. R. 44 W). W). The The ggranite r a n i t e contains contains t o the thesoutheast southeast(SW¼, ( S h , NEg, small xenoliths volcanic rock rock suggesting a t the r a n i t e i is s iintrusive n t r u s i v e into into small xenoliths ooff volcanic suggestingt hthat theggranite volcanics but b u t the contact contact of o f the the intrusive i n t r u s i v eand andvolcanics volcanics isi snot notexposed. exposed. the volcanics A shear zone zone iiss exposed approximately 3/8 3/8 mile A narrow narrow shear exposed approximately m i l e west west of of highway highway HH at zonehas hasaasstrike a t aa sharp sharp northward northward bend bend iin n the the creek. creek. The The zone t r i k e of o f NN 65 65 £E and and iis s vertical. v e r t i c a l . Alteration A l t e r a t i o n along along the thezone zone is i sprominent. prominent. The The sschistosity chistosity in volcanic rocks rocks has hasaasstrike and i is i n the the enclosing, enclosing volcanic t r i k e of ofN N 70 70 E E and s vertical v e r t i c a l and and may be rrelated the ffoliation may be e l a t e d to t o the theshear shear zone. zone. Often Often the o l i a t i o n ini nthe theintermediate intermediate flow units u n i t s isi sassociated associatedwith w i t hstretched stretchedfeldspar feldsparphenocrysts. phenocrysts. DISCUSSION: DISCUSSION: The interbedded ttuffs The interbedded u f f sand andintermediate intermediateflows flowsexposed exposedalong alongShoulder ShoulderCreek Creek and the Jump JumpRiver Riveri ninthe thevvicinity appeart otoeeither. and the i c i n i t y of o f Sheldon Sheldon appear i t h e r . sstratigraphically tratigraphical l y overlie the fragmental fragmentalc rcrystal andc rcrystal-lithic o v e r l i e or o r are are interbedded interbedded wwith i t h the y s t a l and y s t a l - 1 i t h i c tuffs tuffs that of intermediate t h a t crop crop out out to t o the the east. east. Eruption Eruption of intermediate flows flows in i nthis t h i sarea areamay may have beenroughly roughlyconcurrent concurrentwwith continuederuptions eruptionsaat the volcanic center have been i t h continued t the center which is exposed 7 miles to the east. eruptions may which i s exposed 7 miles t o east. These These eruptions may have have produced produced the the fine-grained fine-grained tuffs t u f f s that t h a tare areinterbedded interbedded with w i t h the the flows. flows. �-115- STOP #16 #16 STOP TITLE : TITLE: COARSE FRAGMENTAL FRAGMENTAL INTERMEDIATE INTERMEDIATE VOLCANIC VOLCANICROCKS ROCKS COARSE LOCATION: LOCATION: One mmile i l e east t h e village v i 1lageofoJump f Jump River River on on County CountyHighway HighwayMM. MM. One east ooff the S i t e of o l d highway 73 bridge. G. Smith Smith property. property. NE¼, NE$, NE¼, NE$, Site of old highway 73 bridge. G. R. 33W., W . , T.T.33N. 33N. Jump Jump River 7% minute minute quadrangle, quadrangle, 1971 1971 Sec. 7, 7, R. Sec. River 7½ i _ tii2 %/' ---, I •...;._,-___• .—. — ,—.--u-- -: _- __/ _/ / AUTHOR : AUTHOR: M.L. Cumings Cumings M.L. - March, 1980 1980 March, DATE: DATE: SUMMARY OF FEATURES : SUMMARY OF FEATURES: Coarse volcanic u nunits i t s t hthat a t are t e r l a y e r e d wwith i t h ffinely inely Coarse volcanicblocks blocksform formmassive massive arei ninterlayered The intermediate intermediate fragmental fragmental volcanics vol canics are a r e associated associated with w i t h porporThe p h y r i t i cintermediate intermediate flows flows inlilediately immediatelytot othe theeast eastofo the f t h emain mainoutcrop outcroparea. area. phyritic bedded tuffs. bedded tuffs. DESCRIPTION: DESCRIPTION: The most i s t i n c t rock rock unit u n i tini nthe thearea areais icomposed s composed of o f volcanic volcanic blocks blocks The mostddistinct Fragment s i z e i s v a r i a b l e b u t most fragments are f o o t i n diameter. up t o 1 up to 1 foot in diameter. Fragment size is variable but most fragments are inch in i ndiameter. diameter. The The volcanic rock fragments are t y p i c a l ly llarger a r g e r than than 11 inch volcanic rock fragments are typically touching and m a t r i x between c l a s t s i s sparse. The l i t h i c fragments range from touching and matrix between clasts is sparse. The lithic fragments range from b a s a l t i c t o fragments of exceptionally high plagioclase content. Clasts o basaltic to fragments of exceptionally high plagioclase content. Clasts off Vesi c l es d i f f e r i n gcomposition compositionappear appear to t o form form crude crude localized 1ocal i z e dconcentrations. concentrations. Vesicles differing are prominent i n many fragments and the vesicles are now f i l l e d by c h l orite are prominent in many fragments and the vesicles are now filled by chlorite �—116— and epidote. Porphyritic P o r p h y r i t i c clasts c l a s t scontain containplagioclase p l a g i o c l asephenocrysts. phenocrysts. Although A1 though and the clasts vary in textures and mineralogy they all are the clasts vary i n textures and mineralogy they a l l are intermediate in i ncomcomposition. The coarse coarsefragmental fragmentaluunits are interbedded interbeddedwwith fine-grained tuffaceous The n i t s are i t h fine-grained tuffaceous tuffaceous rocks rocks are are rich materials that t h a t are arecommonly commonly ddistinctly i s t i n c t l ybedded. bedded. The The tuffaceous rich tend ttoo be fine-grained. The The ffineineiinn epidote epidote and and feldspar and and tend be extremely extremely fine-grained. grained which is 10 W W which i s anomalous anomalous iin n the the Jump Jump River area. area. grained beds beds sstrike t r i k e NN 10 The The vvolcaniclastic o l c a n i c l a s t i c units u n i t s are are spatially s p a t i a l l yassociated associated with w i t h weakly weakly porphyritic porphyritic flows which which crop crop out out as as low low outcrops outcropsimmediately Immediatelyupupstream stream from flows from t h this i s l olocality. cality. Possible fragmental fragmentalu units arei ninterlayered the flows flows but Possible n i t s are t e r l a y e r e d wwith i t h the b u t textures textures are are poorly developed. poorly developed. Prominentveins veinscross-cut cross-cut the the coarse coarse fragmental fragmental uunits are to Prominent n i t s and and are t o varying varying degrees degrees deformed. deformed. The The tthickest h i c k e s t veins veins are areusually usuallyundeformed. undeformed. Thin sections sections of the wwalls r o m the a l l s ooff the the o f the the veins veins indicate i n d i c a t eeuhedral euhedral epidote epidote developed developed i in n ffrom vein quartz ffilling vein and and quartz i l l i n gthe t h eremaining remainingspace. space. DISCUSSION: DISCUSSION : The coarseness coarseness volcanicblocks blocksa at The of ofvolcanic t t hthis i s llocation o c a t i o n suggest suggest tthat h a t the the outoutcrops are are near nearaassignificant crops i g n i f i c a n t explosive explosive volcanic volcanic center. center. Similar S i m i l a r coarse coarse fragmental rocks rocks interbedded interbeddedwwith fine-grained ttuffs mental i t h fine-grained u f f s occur occur approximately approximately 2 miles mi 1es area between appearst to be underlain underlain by east oof f tthis h i s site. s i t e . The The area between appears o be by massive massive east intermediateflows flowsand andintermediate intermediate r i t i c , tuffs t u f f sand and possibly possibly intermediate t o to f e lfelsic, s i c , o often f t e n ypyritic, Less than ½ mile south (Stop 17) are outcrops of aa llapilli-sized a p i l l i - s i z e d tuffs. t u f f s . Less than h m i l e south (Stop 17 are outcrops of l o w or. o r possibly a felsite f e l s i t edome. dome. A A posposmassive,weakly weaklyp oporphyritic massive, r p h y r i t i c f felsite e l s i t e fflow sible interpretation of the volcanic rocks in the immediate area is a submarine s i b l e i n t e r p r e t a t i o n o f the volcanic rocks i n the immediate area i s a submarine collapsed caldera complex complexi nin which whichthe the coarse coarsefragmental fragmentalrocks rocksare areppart of the collapsed caldera a r t of the rim of the complex and the interior of the collapsed structure filled with rim of complex and the i n t e r i o r o f t h e collapsed s t r u c t u r e f i l l e d w i t h massivef efelsite flows and andintermediate intermediatet otof efelsic flows l s i c pyroclastic p y r o c l a s t i c materials. materials. The The massive lsite may representaaf felsite formedduring during aa caldera caldera resurgence stageaafter may represent e l s i t edome dome formed resurgence stage fter resurgent caldera complexes are possibly possibly Such resurgent complexes are the main main collapse had had occurred. occurred. Such Such an an environment has has mineralization. Such important in i n development development ooff economic economic mineralization. been suggestedf ofor Kuroko deposits deposits (Kouda, Korde, 1978) 1978) and andpossibly possibly the been suggested r Kuroko (Kouda, Korde, massive Noranda district deRosen—Spence, massive ssulfide u l f i d e mineralization mineral i z a t i o nin ithe n the Noranda d i s t r(Spence, i c t (Spence, deRosen-Spence, 1975). ? REFERENCES. CITED REFERENCES CITED Kouda, Korde,H.,H., 1978, 1978, Ring Ring structures, structures, resurgent resurgent cauldron, cauldron, and and ore Kouda, R.,R., Korde, Mining deposits iinn the the Hokuroku Hokuroku volcanic i e 1 d, northern northernAkita,, Aki ta, Japan: Japan: Mining deposits volcanic ffield, Geology, V. 28, Geology, V. 28, p. p. 233-244 233-244 Spence,D.D., D.D., deRosen-Spence, deRosen-Spence, A.F., 1975, The place mineralization A. F. , 1975, The place o f ofs usulfide lfide m ineralization Spence, EconomicGeology, Geology, V.V. 70, iinn the thevolcanic volcanicsequence sequenceata Noranda, t Noranda,Quebec: Quebec: Economic 70, p. 90-101 p. 90-101 �—117— STOP STOP #17 #I 7 TITLE: TITLE: PORPHYRITIC PORPHYRITIC FELSITE FELSITEFLOW FLON LOCATION: LOCATION : Along on the James James M i 1l e r A1 ong Levitt Levi ttCreek Creek south south of of County CountyHighway Highway DD on Miller Farm. SE¼,Sec. Sec. 7, NE& SEQs 7  R. R. 3 W., W e s T. T. 33 33N. N. Jump Jump River 7½ 7% minute minute Farm. NE¼, quadrangle, quadrangle 1971 1971 -, /'-- / :i ( _ -- / "I _I \/ -. 1Z14 - .. -*—___ i.J, •* — 220 - fr I, if jump-1 AUTHOR: AUTHOR : M.L. M.L. Cummings Cumnings DATE: DATE : - March, March 1980 1980 SUMMARY OF FEATURES: SUMMARY OF FEATURES : A fine-grained, fine-graineds weakly weakly porphyritic porphyritic felsite f e l s i tflow e flow formsmassive massiveoutcrops outcrops A forms along along Levitt LevittCreek. Creek. The The fel i t e contains contains aa possible possible metamorphic metamorphic fabric fel ssite fabric or relict by.bya alocal locally E-W shear shear zone zone which which 10 r e l i c tprimary primaryflow flowstructure structureand andisi cut s cut localE-W produces lineation iinn the produces aalineation the rock. rock. DESCRIPTION: DESCRIPTION : Two outcropsofof aa ffelsite Two outcrops e l s i t eoccur occurwest west ofofthe thefarm farmbuildings buildingsononthe theJames Jams Miller i nthe thebed bed of of Levitt LevittCreek. Creek. The The ffelsite e l s i t eisispink p i n kand andmassive. massive. Miller farm farm in Small to anhedral Small subheadral subheadral to anhedral plagioclase p1 agiocl ase phenocrysts phenocrysts occur in in aafine—grained f i ne-grained matrix dominated apparentlyby byquartz quartz and andfeldspar feldspar bbut sericite bands dominated apparently u t sericite bands with with minor chlorite define minor chlorite define aa fabric in i n the the rock. rock. . The irregular clots of The ffelsite e l s i t e isi scut cutbybya ashear shear zone zone containing containing irregular of white white quartz in i n an an outcrop outcrop immediately immediately west west of the the barn. barn. The The shear shear zone zone superimposes superimposes �-118aa secondary secondary sschistosity c h i s t o s ~ t yon on the the earlier e a r l i e r fabric f a b r i cand andlocally l o c a l l yproduces produces aa lineated lineated I fabric fabric iin n the the ffelsite. elsite. DISCUSSION: massivef efelsite AA massive l s i t e crops crops out out west west of of the thewayside wayside park parkalong alonghighway highway 73, 73, the ffelsites but but the the unit u n i t isi scoarser coarser grained grained than than the e l s i t e s at a t this t h i s location, location, possibly possibly becauseo fofcontact contactmetamorphic metamorphic effects from material. because effects from g r granitic a n i t i c i nintrusive t r u s i v e materi a1 . The bandingi in the massive The banding n the massive ffelsite e l s i t e may may be be aa metamorphically metamorphically induced induced ffabric abric or represent primary flow o r may may represent flow banding. banding. The e l s i t e s are are apparently apparently closely closely The ffelsites related to t o coarse coarse intermediate intermediate fragmental fragmental volcanic volcanic rocks rocks which which crop crop out o u t along along the Jump River approximately approximately %½mmile Possibly tthe Jump River i l e nnorth o r t h (Stop (Stop 16). 16). Possibly h e ffelsites elsites form a t e rhyolitic r h y o l i t i dome c dome formed formed during during caldera caldera resurgence resurgence iin n a large l a r g e collapsed collapsed form aa llate caldera complex. Stratigraphic suggestt hthat felsites t o p indicators i n d i c a t o r s would wou1 d suggest a t t the h e fe1 s i tes complex. S t r a t i graphi c top stratigraphically s t r a t i g r a p h i c a l 1yoverlie over1 i ethe t h ecoarse coarsefragmental fragmental rocks rocks exposed exposed tto o the the north. The intruded by by ggranitic The ffelsites e l s i t e s have have apparently apparently been been intruded r a n i t i c rocks rocks which which are. are. exposed t the terexposeda at the wayside waysidepark parkalong alonghighway highway7373t otothe thewest westand andalong alongan ani nintermitent m i l esouth south rnitent tributary t r i b u t a r ystream stream which which flows into i n t oLevitt L e v i tCreek t Creekless l e s sthan than¼%mile of development shearzone zone thef felsite o f the the present present ssite. i t e . The The development of oft hthe e shear c ucutting t t i n g the elsite appearst otobebel alater thant hthe appears t e r than e i nintrusion t r u s i o n ooff tthe h e granites granites since since ssimilarly i m i l a r l y oriented oriented shear zones zonesccut the ggranite park to shear u t the r a n i t e exposed exposed iin n the the wayside wayside park t o the the west. west. i I i 1 1 I �—119- STOP #18 STOP #18 TITLE:: TITLE CRYSTAL AND AND CRYSTAL-LITHIC CRYSTAL-LITHIC TUFFS CRYSTAL TUFFS LOCATION: LOCAT ION : Section line sections 15 22, T. Section line between between sections 15 and and 2Z9 T. 33N., 33N. R. R. 44W. W. along River behind behind the the farm Edwin and and*Gerald Gerald Ahlers. Jump the Jump Jump River farm of Edwin 7% minute quadrangle, quadrangle, 1971 1971 River 7½ AUTHOR: AUTHOR: M.L. M.L. Cuniings Cumings DATE:: DATE - March, 1980 1980 SUMMARY OF OF FEATURES: SUMMARY FEATURES: .W e11-bedded crystal -1 i t h i c tuffs tuffsare arebeautifully beautiful l exposed y exposed along along Well-bedded crystaland andcrystal crystal-lithic south bank the south Impact structures structures produced larger cclasts bank of the the Jump Jump River. Impact produced bybylarger lasts fall ing into materialsindicate indicate that that the the stratigraphic falling into finer finergrained grained bedded bedded materials unitsare areoverturned. overturned. tops of the the volcanic volcanic pile pileare aretot othe thesouth southand and that that the the units DESCRIPTION: DESCRIPTION: Well-exposed, streampolished polishedoutcrops outcropsofof tuffaceous tuffaceous of of various rocks Well-exposed9 stream rocks characteristics 0.75miles milesalong alongthe theJump Jump River River characteristics crop cropout outfor forapproximately approximately0.75 west of the Since the the river river flows west theEdwin Edwin and and Gerald Gerald Ahlers Ahlers property. Since flows approximately parallel to approximately parallel t o the thebedding bedding in i n the thevolcanics volcanicsthe theexposures exposures do do not provide aa thick stratigraphic nearly one one stratigraphic stratigraphic provide stratigraphicsection sectionand andmay may represent represent nearly level. level . �-120- Thelowest lowests stratigraphic The t r a t i g r a p h i c uunit n i t is i s farthest farthest north n o r t hand and isi sfine—grained, fine-grained, massive,l ilight green, intermediate intermediatec rcrystal tuff. Bedding Bedding iiss massive massive, g h t green, y s t a l tuff. massive and and can can be iidentified be d e n t i f i e d by by faint f a i n t bands bands that t h a t have have a a higher higher percentage percentage oof f sslightly l i g h t l y coarser coarser phenocryststhan than the the surrounding phenocrysts surrounding rock. The mainrock rocktype typei sisananintermediate intermediate rock iiss The main c r ycrystal-lithic s t a l - l i t h i c ttuff. u f f . The The rock prominently beddedw with the sstrike and dipping dipping 72' 72 N. prominently bedded i t h the t r i k e of of bedding bedding NN 60E 60E and N. AA coarse, approximately approximately44 inches incheslong, long, volcanic volcanic clasts coayse, c l a s t s has has been been found found that that apparently produced apparently ffell e l l into i n t othe theaccumulating accumulating finer-grained finer-grained tuffs t u f fand s and producedan an impact feature feature ffrom which aa sstratigraphic rom which t r a t i g r a p h i c top t o pdeterinatlon d e t e r i n a t i o can n canbebemade. made. The impact top of o f the the volcanic volcanic unit u n i tappears appears to t o be be to t o the the south south indicating i n d i c a t i n g that t h a tthe thebedding bedding top iiss overturned. overturned. Beds of. c r y s t a l tuff are interbedded interbedded w with i t h c rcrystal-lithic y s t a l - 1 it h i c tuff t u f falong along the the Beds of.crystal tuff are i n c h in i ndiameter diameter outcrop area. area. T y p i c a l l y lithic l i t h i fragments c fragmentsare areless l e s sthan than½ inch Typically and.are areofof intermediate composition. and composition. The The ttuffs u f f s contain contain plagioclase plagioclase crystals crystals and pyroxene ccrystals r y s t a l s that t h a tare arepseudomorphically pseudomorphica11y replaced rep1aced by byamphibole. amphi bo1e. and possible possible pyroxene The plagioclase plagioclase ccrystals Epidote also The r y s t a l s contain contain subhedral subhedral to t o anhedral anhedral epidote. epidote. Epidote a1so forms a r t of the matrix matrix between between ccrystal r y s t a l and and lithic l i t h i cclasts c l a s tin s isome n somesamples. samples. forms ppart of the Hornblende porphyrobl asts are f i de minerals mineral s are Hornblende porphyroblasts areprominent prominenti nin most mostbeds, beds,and andsu1 sulfide found ocal 1y in i nconcentrations concentrations of o f 22 percent. percent. found 1locally + DISCUSSION:: DISCUSSION , The The ttuffs u f f s exposed exposed aat t tthis h i s stop stop are are believed believed to t o be be related r e l a t e d to t oaacaldera caldera complexexposed exposed east thev ivillage JumpRiver River( 3(3miles milest otothe the east, east, Stop Stop 16). 16); complex east o f of the l l a g e oof f Jump Thet tuffs The u f f s in i n this t h i sarea areaare arepossibly possibly stratigraphic s t r a t i g r a p h i cequivalents equivalents of of the thecoarse coarse fragmental uunits fragmental n i t s at a t Stop Stop 16. 16. The The ggrain r a i n size size ofo ffragments fragments decreases decreases and and the proportion of lit h fragments i c fragmentsincreases increasesaway away from from the the proportion o f crystal c r y s t a lfragments fragments to t olithic volcanic center. To tthe westo of andl ilithic volcanic center. To h e west f t hthis i s ssite i t e the the ttuffs u f f s are are fine-grained fine-grained and thic fragments have not n o t been been observed. observed. The The rocks rocks have havebeen beenmetamorphosed metamorphosed under under fragments have epidote—amphibolite facies conditions buta aschistosi schistosity not strongly epidote-amphiboli t e facies conditions but t y i is s not strongly devel aped. developed. �-121— BIBLIOGRAPHY BIBLIOGRAPHY I u t o n i sm in* the Anderson, and Medari s, 1975 "Proterozoic r a n i t i c PPlutonism Anderson, Van VanSchmus, Schmus, and Medaris, 1975, "ProterozoicGGranitic in the Lake Superior Region and its Tectonic Implications," (abs). 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U n i v e r s i t yofo Minnesota f Minnesota Dul uth. uth. Cummings, Myers,P.P.E., Cumings , M.M.L., L., Myers, E. 1978, 1978 "Petrology and and Geochemistry Geochemistry ooff Amphibolites, Amphibol it e s Eau Claire Eau CClaire l a i r e River, River, Eau Eau C l a i r e County, County9 Wisconsin," Wisconsin9" (abs). (abs). 24th Annual Annual IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology. Geology. Cummings, Cummings, M.M.L., L., SScrivner, c r i vner9 J.V., J. V. 1980, 1980, "The ''Thesaprolite saprol itat e the a t tPrecambrian—Cambrian h e Precambrian-Cambrian Contact, Irvine Transactions, Wisconsin Wisconsin Contact I r v i n ePark, Park, Chippewa Chippewa Falls, Fa11s, Wisconsin." Wisconsin. I'Transactions, Academyo fofAArts, and LLetters. Acadew r t s 9 Sciences Sciences and e t t e r s . IInn press. press. Dutton, Dutton C.E., C. E. and and Bradley, Bradley, R.E., R. E., 1970, 1970, Lithologic, L i t h o l o g i c , Geophysical, Geophysical, and and Mineral Mineral CommodityMaps Mapso of PrecambrianRocks Rocksi in U.S. Commodity f Precambrian n Wisconsin. Wisconsin. U.S. Geol. Geol Survey. Survey. Misc. mv. Misc. Inv.Map Map1—631, 1-631, scale 1:500,000. 1:500,000. . Ervin, Gravity E r v i n 9C.P., C.P., Hammer, Hammer, S., S. 1974, 1974, Bouguer 90uguer Anomaly Anomaly G r a v i t y Map Map ooff Wisconsin, Wisconsin, Wisconsin Geological Geological and andNatural Natural H History Wisconsin i s t o r y Survey, Survey, Scale Scale 1:500,000. 1 :5OO,OOO. Glikson, Tonalite-Trondhjemite G I ikson, A.Y., A.Y. 1979, l979, "Early "Early Precambrian Precambrian Tonal ite-Trondhjemi t e SSialic i a l i c Nuclei," Nuclei, Earth Science Science Reviews, Reviews9 15, 15, 1-73. 1-73. Hess, H.H., Hess, H. H. 1960, 1960, "Stillwater " S t i l l w a t e Igneous r IgneousComplex," Complex9 Geological Geo1ogi c a l Society Society of o fAmerica, America, Memoir80, 80, p. p. 225. Memoir 225. 'I 1974-76ÂAeromagnetic Aeromagnetic map map sseries, e r i e s 9Wisconsin Wisconsin Geological Geological and and Karl and and Friedel, Friedel 1974-76, Natural History H i s t o r ySurvey, Survey9Scale Scale1:62500. 1 :62500. Kouda, Korde, H. 1978Â"Ring "Ring structures, structures,Resurgent Resurgent Cauldron, Cauldron9and and Ore Ore Kouda,R.,R., Korde, H., 1978, Deposits iin n the the Hokuroku Hokuroku Volcanic i e l d, Northern Northern Aki ta, Japan." Japan. Mining Deposits VolcanicFField, Akita, Mining. Geology, v. v. 28. Geology, 28. LaBerge, G.L., 1972, and Mylonite Mylonite Zones LaBerge9 G.L., 1972, "Lineaments "Lineaments and Zones iin n the the Precambrian Precambrian ooff Northern Northern Wisconsin," 18thAnnual AnnualI nInstitute W i s ~ o n s i n : ~18th s t i t u t e on on Lake Lake Superior Superior Geology, Geology, Abs., Abs., paper paper #27. #27. LaBerge, G.L.,. 1979, 1979, "Jump "JumpRiver Riveraat Falls LaBerge9 G.L., t BBig ig F a l l s County County Park." Park." Field F i e l dTrip T r i pGuidebook Guidebook No. 44, University U n i v e r s i t yofo fWisconsin-Extension, Wisconsin-Extension, Geological Geological and and Natural Natural History History No. Survey. LaBerge, G.L. G.L., and E., l980,"Middle 19809"MiddlePrecambrian Precambrian History H i s t o r yofo fMarathon Marathon LaBerge, and Palmer, Palmer, E., County, Wisconsin Wisconsin,"26th 26thAnnual AnnualI nInstitute Superior Geology, Fieldd County, s t i t u t e on on Lake Lake Superior Geology9 Fie1 Trip T r i p Guidebook Guidebook #2. #2. �-122- Maass, andVan VanSchmus, Schmus,W. W.R., 1980,"Precambrian TectonicHistory History. ooff the Maass, R.R.S., S., and R., 1980, "Precambrian Tectonic the Black River River Valley," Valley," 26th Black 26th Annual Annual Institute I n s t i t u t eononLake LakeSuperior SuperiorGeology, Geology, Field F i e l d Trip T r i p#2 #2Guidebook. Guidebook. Maass, R.S., Medaris, Medaris, Jr, L.G., L.G., and andVan VanSchmus, Schmus, W.R., W.R., 1980, 1980, "Archean "Archean and and Early Maass, R.S., Proterozoic Tectonic Proterozoic Tectonic History Hi s t o r y of o fNorth-Central North-Central Wisconsin," Wisconsin ,"26th 26thAnnual Annual MI., Abs. Abs. I n s t i t u t eon onLake Lake Superior Superior Geology, Geology, Eau Eau Claire, Institute Claire, WI., Maercklein, Douglas, Douglas,R.,R., 1974, 1974, "Analysis "Analysis ooff Deformation Deformation aatt Jim Jim Falls, Wisconsin," Wisconsin," Maercklein, Universityofo Wisconsin-Milwaukee. f Wisconsin-Mi lwaukee. unpublished unpublished M.S. M.S. Thesis, Thesis, University E. R., 1977, 1977,"Flambeau——A "Fl ambeau--A Precambrian fide May, May, E.R., PrecambrianSupergene SupergeneEnriched EnrichedMassive MassiveSul Sulfide Deposit," Geoscience Deposit," 1-26. GeoscienceWisconsin, Wisconsin,v.v.1,1, p. p. 1-26. Myers, P.E., P.E., 1974, geology descriptions iinn the Myers, 1974, Precambrian Precambrian geology andand f i efield l d t rtrip i p descriptions the guidebook, Geological Field guidebook, 38th Annual Annual Tn—State Tri-State Geological F i e l dConference. Conference. Myers, P.E., P.E., 1980, andf i efield Myers, 1980, General General i nintroduction t r o d u c t i o n and l d t trip r i p descriptions descriptions iin n Field Field Trip T r i p Guide Guide Book Book ffor o r 26th Annual Annual IInstitute n s t i t u t eon onLake LakeSuperior Superior Geology Geology Field Field Trip T r i p #1. #l. Myers, P.E., P.E., Cuniriings, M.L.,May, May,E.R.9 E.R.,Kopp, Kopp,R.A., R.A.,MWillis, i n i s , R.P., R.P., Bergstrom, Bergstrom, J. J. Myers, Cunnings, M.L.9 R., 1974, R., 1974, 38th 38th Annual Annual Tn-State Tri-State Geological GeologicalField F i e l dConference ConferenceGuidebook, Guidebook, 125 125 p. p. Piotruszewicz, M.A., M.A., 1978, "An Analysis Analysis ooff aa Drill 1978, "An D r i lCore l Corefrom fromWestern Western Clark Clark Piotruszewicz, County, Wisconsin," Wisconsin," unpub. unpub.M.S. M.S.thesis, thesis, University County, U n i v e r s i t yofo fWisconsin, Wisconsin, Milwaukee. Milwaukee. Sims, P. P.K., Tectonic and Mineral Deposits, K., 1976, 1976, "Precambrian "Precambrian Tectonic and Mineral Deposits, Lake Lake Superior Superior Sims, Region," Economic Geology, v. 71, Region," Economic Geology, 71, p.p.1092—1118. 1092-1118. Sims, P.K., P.K., Cannon, W.F., Mudrey,M.G., t4.G.,Jr., Jr., 1978, Sims, Cannon, W. F., Mudrey, 1978, "Preliminary "PreliminaryGeologic GeologicMap Map of Rocksi in Part of o f Precambrian Precambrian Rocks n Part o f Northern Northern Wisconsin," Wisconsin," U.S. U.S. Geological Geological Survey Open-file Open-file Report Survey Report 78-318, 78-318, Scale Scale 1:250,000. 1:250,000. Smith, E.I., 1978, E. I., 1978, "Precambrian "Precambrian Rhyolites Rhyol it e s and and Granites Granites in i n South-Central South-Central Smith, Wisconsin," Geol. Soc. Bull., v.v.89, Wisconsin," Geol. Soc. America America Bull., 89,p. p.875—890. 875-890. Spence,D.D., D.D., deRpsen-Spence, deRpsen-Spence, 1975, "The place mineralization Spence, A. F.A.F., , 1975, "The place o f ofs usulfide lfide m ineralization in EconomicGeology, Geology, v.v. 70. i n the thevolcanic volcanicsequence sequenceataNoranda, t Noranda,Quebec',' Quebec',' Economic 70. United States States Steel Steel Corporation, mapso of the Jim Jim FFalls 1973, unpi. unpl. aeromagnetic aeromagnetic maps f the alls United Corporation , 1973, area, W i sconsin. area, Wisconsin. . Van Schmus,W.R., W.R.,1974, 1974,"Chrono "Chronology PrecambrianEvents Eventsi in (abs). Van Schmus, W i sconsi dl (abs) 1ogy oof f Precambrian n Wisconsid' EOS.Trans. Trans.Amer. Amer.Geophys. Geophys.Union, Union,v.v. 55, 55, p. p. 465. EOS. 465; Van Schmus, 1976,"Early "Earlyand andMiddle MiddleProterozoic Proterozoic History History of Van Schmus , R.,R.,1976, o f the theGreat GreatLakes Lakes Area, North North America", America", PPhil. h i l . Trans. Area, Trans. R. R. Soc. Soc. Land. Lond. A. A. 280, 280,p.p.605—628. 605-628. f Igneous i t h the thePenokean Penokean Van Van Schmus, Schmus,R.,R., 1980, 1980,"Chronology "Chronologyoof Igneous Rocks Rocks Associated Associated w with Amer. Special Paper, #180, #180, Goldich Go1dichVolume. Vol me. Orogeny i in n Wisconsin", Orogeny Wisconsin",Geol Geol. Society Society Amer. Special Paper, . �-12 3— Willemse, J., J., 1969, 1969, "The "TheGeology Geology of o fthe theBushveld BushveldIgneous Igneous Complex, Complex, the the Largest Largest Willemse, Repository of o f Magmatic Magmatic Ore the World" World" ini nMagmatic Magmatic Ore Ore Repository Ore Deposits Deposits iinn the Deposits, Economic Economic Geology Pub1 i s h i n g Co.Co., , p.p.1l—22 -227 Deposfts, Geology Publishing Wurdinger, S.R., 1979, "Structural Geology Wurdinger, S.R., 197% "Structural Geology ooff Amphibolitic Amphibolitic Gneisses, Gneisses, Northeast Northeast Chippewa County,Wisconsin1', Wisconsin", (abs)25th 25thAnnual AnnualI nInstitute s t i t u t e on on Lake Lake Superior Chippewa County, (abs) Geology, Geology, p. p. 42. 42. Zietz, I.,I., Karl, J.H., Ostrom, M.E., "Preliminary Aeromagnetic Karl, J.H., Ostrom, M.E.,1978, 1978, "Preliminary AeromagneticMap Map Covering Most Ter.ranei in Most ooff the theExposed Exposed Precambrian Precambrian Ter.rane n Wisconsin," Wisconsin, I' U.S. U. S. Geological Survey, 1 :250,000. Survey, Miscellaneous Miscel laneous Field Fie1dStudy StudyMF-888, MF-888, 1:250,000. rkhthui � https://digitalcollections.lakeheadu.ca/files/original/8f32dbdeaf22a4f8e74619ec237c92d9.pdf 0aa27b9ebf391a523fcce1756843d276 PDF Text Text 26th Annual Institute on Lake Superior Geology FIELD TRIP 2 Precambrian Tectonic History of the Black River Valley GENERALIZED PRECAMBRIAN GEOLOGY OF THE EAU CLAIRE REGION Diabase + Gabbro Tonalite Trondhjemi te Volcanics and sediments Amphibolutes Shear zone May 7, 1980 University of Wisconsin-Eau Claire �_____ ___________ ___ : _______ _________ :. Chippe I A - A — Cjrtiss N cony a — NiII v — — — .— — aA+_4./ 2J ( r S 53 Ck Atr MeIose p0 r K SON A 2 NATPONA. 71 M c,u 0N R 0E N A / vv N E4R I 4 3 — 2 7 tevUe / ' - C — &H Wyele Ii - •1 yZLA 4rNaIkM La Crescerst ,_ el WIItI1 end1 nMaJto �PRECAMBRIANTECTONIC TECTONICHISTORY HISTORYOF OF THE THE BLACK BLACK RIVER PRECAMBRIAN RIVER VALLEY VALLEY Field Guide Guide Field R.S. Maass and and W.R. W.R. Van Van Schmus Schmus R.S. Maass Prepared for Prepared for Annual Meeting Meeting Twenty-Sixth Annual INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE University ofofWisconsin-Eau Wisconsin-Eau Claire Claire University Eau Wisconsin Eau Claire, Claire, Wisconsin May May 6-11,1980 6-11, 1980 �CONTENTS CONTENTS Page INTRODUCTION INTRODUCTION (W. (W. R. R. Van Van Schmus) Schmus) IITINERARY TINERARY 1 III • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 44 GEOLOGICAL STOP STOP DESCRIPTIONS DESCRIPTIONS GEOLOGICAL Stop Stop 1. 1. Stop Stop 2. 2. Stop Stop 3. 3. Stop 4. Stop 4. Stop Stop 5. 5. Stop 6. Stop 6. Stop 7. Stop 7. Stop 8. Stop Gnei ss near nearGreenwood Greenwood Gneiss 66 Neillsville Granite.................................. 99 Neillsville Granite Gneiss at atHumphrey Humphrey Farm Farm 12 . Gneiss NeillsvilleAugen AugenGneiss Gneiss 15 Neillsville Lake Arbutus 18 Lake Arbutus Granite 20 Gneiss along Black River River .. 20 Gneiss along East East Fork Fork of of Black 22 Hatfield Gneiss,Arbutus ArbutusDam Dam 22 Hatfield Gnelss, 27 Black River Granite 27 Black River Falls Granite • SUPPLEMENTAL LOCALITIES LOCALITIES SUppLn~ENTAL 29 29 DISCUSSION Maass) DISCUSSION(R. (R. S. S. Maass) 40 40 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS 42 REFERENCES REFERENCES 43 �INTRODUCTION INTRODUCTION W. R. Van Schmus Schmus R. Van W. The along The Precambrian Precambrianbedrock bedrockexposed exposed alongthe theBlack BlackRiver River iR iR west-central Wisconsin, River Falls to tonorth consists primarily primarily Wisconsin,from fromBlack Black River Falls northofofNeillsville, Neillsville, consists grieissic rocks plutônlc rocks. Archean gneissic rocks and and early Proterozoic Proterozolc (Penokean) (Penokean) plutonic rocks. of Archean TheseArchean Archeanrocks rocksare are the the westernmost westernmostexposures exposuresofof an an Archean Archeanterrane terrane that These extends River in inthe extendsfrom fromthe theBlack BlackRiver Rivereastward eastwardtotothe theWisconsin Wisconsin River thevicinity vicinity Gneissic rocks of Stevens Stevens Point and and Wisconsin Wisconsin Rapids rocks also occur occur Rapids (Figure (Figure 1). Gneissic to the the northwest, northwest, ininEau Counties(Myers (Myerseteta1., al., 1980), Eau Claire Claireand and Chippewa Chippewa Counties 1980), as theChippewa Chippewa Amphibolite Amphibolite Complex, Complex, but but they they may may not not be be Archean. Archean. as part ofofthe One ofof the One the major major problems problemsininunderstanding understandingthetheolder olderrocks rocksofof the the region region is how they similar rocks rocks ininthe thesouthern southern part partofofthe theCanadian Canadian Shield, Shield, how theyrelate relate to to similar or to to the either to to the thenorth northininnorthern northernWisconsin Wisconsin and and Michigan Michigan or the west west in the Minnesota River the Minnesota River Valley. N RAPIDS MILES I i 16 I KILOMETERS 26 Figure 1. 1. Geologic Geologic map thethedistribution mapofofcentral central Wisconsin Wisconsinshowing showing distribution of presumed Archean Penokean igneous presumed Archeangneiss gneiss(1), (1), Penokean igneous and and metamorphic metamorphicrocks rocks (2), (2), The Hatfield Hatfield 1500 rocks (3), and and Paleozoic Paleozoic cover cover (4). The 1500m.y. m.y.old old plutonic plutonic rocks Gneiss the block block of of gneiss gneiss (D) (D) Gneiss (Stop (Stop7)7) occurs occursalong alongthe thenorthern northernpart part of of the After Van between BlackRiver RiverFalls Fallsand andNeillsville. Neillsville. After between Black VanSchmus Schmus and and Anderson Anderson' (1977) (1977).. 1 �Most of of the Archeanrock rockin in central Wisconsin I~ost the known known Archean Wisconsin consists consists ofofbanded banded gneiss, migmatitic gneiss, gneiss, gneiss, or or niigmatite; migmatite; Archean Archean plutons plutons are are rare. rare. Regional studies (Van andAnderson, Anderson,1977) 1977) have haveshown shownbybyU-Pb U-Pbdating datingthat that the (Van Schmus Schmus and the gneiss and andmigmatite migmatiteinin the the eastern eastern part part of the m.y. old. gneiss the area area are are about about 2800 2800 m.y. Thereisis some someindication indicationfrom fromtheir theirRb-Sr Rb-Srresults resultsthat thatthe theprotolith protolith of the There the migmatitic gneiss gneiss in in the an earlier earlier crustal migmatitic the Dittsville Dittsyillearea areamay may have have had had an crustal history, but loss during during aa later later but the the results resultscould couldalso alsobe be explained explained by by Rb Rb loss metamorphism. Recent studies in Recent studies in the theBlack BlackRiver Riverarea area(Dubois (Duboisand andVan VanSchmus, Schmus, 1978; Van Schmus,unpub.) unpub.)have haveconfirmed confirmed an an Archean Archeanage agefor for those gneisses. 1978; Van Schmus, gneisses. The gneiss The gneissnear nearHatfield Hatfield(Stop (Stop7)7)yields yields zircons zirconsthat that are are analytically analytically indistinct ininage andandthethe Wisconsin indistinct age from from those those of of the the Pittsville Pittsville WisconsinRiver Riverareas areas (Figure the mean mean age samples is 2815 2815 +20 ~ 20 m.y. m.y. The (Figure 2); the age defined defined by by all all samples zircons are are tentatively tentatively interpreted zircon, rather zircons interpreted as as primary primary igneous igneous zircon, rather than than metamorphic orordetrital zircon, so so that thatthe theage ageofof2815 2815m.y. m.y.would would represent represent metamorphic detrital zircon, the time time of of the the protoliths protoliths (plutons, (plutons, volcanics) volcanics) of of the the the of crystallization of respective gneisses gneisses and and migmatites. of ofNeillsville (Stop 4) Zircon Zircon from fromsyenitic syenitic augen augengneiss gneisssouth south Neillsville (Stop 4) yields an age an age of 2535 2535 ÷+ 10 10 m.y. m.y. This This zircon isisalso alsoconsidered considered primary primary igneous igneous zircon, to the augen zircon, indicating indicatTng that thatthe theprotolith protolith to the augengneiss gneisswas was probably probably aa syenitic syenitic pluton pluton intruded intrudedinto intoolder oldergneiss gneissabout about2535 2535 m.y. m.y. ago. ago. a.6 0.6 r----,.-----,---,.------,-------;r------.----------,----,.------, •• Pittsville quarry (VS75-10) Pittsville quarry (VS75—10) Hatfield Gneiss Hatfield Gneiss(VS77—8) (VS77-8) o o Linwood quarry quarry (VS75-6) Linwood (VS75-6) o o Neillsville Auqen Neillsville AuqenGneiss Gneiss (VS76-25) (Vs76-25) - + 0.4 - co M N J ;:::l ........ a _, I 0.'/ /' ttaa ==2815 2815 ÷~ 20 20 m.y. m.y. \.0 o :/ o c'1 N I 1.5 .D 0... 0.2 '-------'-----_ _- L_ _-----l.. 0.2 I 0 a 2 2 I 4 4 6 6 •, o'~ o 0 p'/;' 2. 2.0 / • tb t == 2535 10 m.y. m.y . b 2535 +~ 10 . L -_ _---L-_ _--L I 8 10 12 L -_ _---L------! 14 16 16 Pb-207/U--235 Pb-207/U-235 Figure Figure 2. 2. U-Pb U-Pb plot data for zircon zircon fractions fractionsfrom fromArchean Archean rocks rocks in plot of of data central Wisconsin(Van (VanSchmus Schmus and and Anderson, Anderson, 1977; 1977;DuBois DuBoisand andVan VanSchmus, Schmus, central Wisconsin 1978; Van 1978; Van Schmus, Schmus, unpub.). The The Hatfield Gneiss is from near Stop 7, and and Hatfield Gneiss from near Stop 7, the NeillsvilleAugert Augen Gneiss Gneiss is is from from near near Stop Stop 4. 4. The ages given are the Neillsville The ages given are for for least squares fits to least squares fits to the the data. data. Decay constants as Decay constants asinin Steiger Steiger and and JMger Jger (1977). 22 �So far no other other Archean Archean ages So far no ages have havebeen beenobtained obtainedfor forgneissic gneissic rocks rocks in amphiboittegneiss gneissatatBig Big Falls Falls in Eau Layered amphibolite Eau Claire Wisconsin. Layered central Wisconsin. County yields Penokean age County yields a Penokean ageofofabout about1850 1850m.y. m.y.and andisis indistinguishable indistinguishable from results tonalite atatLittle Little Falls, a few milesaway away (Figure (Figure from results for for foliated tonalite Falls, a few miles 3; see also Myers et al., 1980). In the case of the Big Falls zircon the In the case of the Big Falls zircon the 3; see also Myers et al., 1980). possibilitystill still exists are metamorphic, formedduring during Penokean possibility exists that that they they are metamorphic, formed thethe Penokean Orogeny 1980) andand thatthat thethe protolith the Orogenyabout about1850 1850m.y. m.y.ago ago(Van (VanSchmus, Schmus, 1980) protolith to the Archean, but but for for the thepresent presentaaPenokean Penokean primary gneiss is Archean, gneiss primary age ageisis preferred. Granitic gneiss gneiss near near Greenwood Greenwood (Locality with an an (Locality10) 10)also alsoyields yields zircon zircon with apparent age beginning to appear appear that apparent ageof of 1850 1850m.y. m.y. (Figure (Figure 3). Thus, Thus, it it is beginning the 1850 1850 m.y. ofofNeillsville are indicative indicative the m.y.ages agestotothe thenorth northand andnorthwest northwest Neillsville are So far far younger gneisslc gneissicterrane, terrane,formed formedduring duringthethe PenokeanOrogeny. Orogeny. So of aa younger Penokean no linebetween between no Archean Archeanages agesare areknown knowninincentral central Wisconsin Wisconsinnorth north of aa line Neillsvilleand andStevens Stevens Point, Point, so so that thatthe theArchean Archean terrane terrane of ofcentral centralWisconsin Wisconsin Neillsville may not north (Sims, (Sims, 1976). 1976). This may not be be continuous continuouswith with Archean Archeanrocks rocksto to the the north clearly represents aa fundamental fundamental problem, is hoped hoped present present and and future clearly represents problem, and anditit is WisconsinArchean Archean terrane terrane in in proper proper studies helptotoplace placethe thecentral centralWisconsin studies will will help and geographic geographic perspective. perspective. geologic and 0.35 O. 35 t--------r-----..,.-------r-----...,.--------::-~ * 1.9 I *Gneissic Falls (VS73—25A) Gneissic tonalite, tonalite,Little Little Falls (VS73-25A) o Trondjhemite, Trondjhemite, Chippewa Chippewa Falls (VS77-1A,B) (VS77-1A,B) amphibolite, Big Falls o Layered Layered amphibolite, Falls(VS78-6) (VS78-6) 1.8 .— reference chord = = 1850 1850 m.y. - o— 1.7 0.30 co c 1 (v, M c.'j N * . I :::J --... 1.0 1.5 a c'J N I .0 0.. 0.25 -0.25 _.- * 0.20 0.20 '---------l..-- / 0/ 0. Granite, Neillsville •S Granite, Neillsville(VS76-18; (VS76-18; Stop Stop 2) 2) *Gneiss near *Gneiss nearGreenwood Greenwood (VS76-22; (VS76-22; Loc. Loc. 10) 10) •N Granite, Lake Lake Arbutus Arbutus (VS76-26; (VS76-26; Stop Stop 5) 5) •£ Granite, Granite, Black Black River River Falls (VS73-22; Stop 8) (VS73—22; Stop 8) -..L ..I....- I 3.0 3.5 I 4.0 Pb-207/U-235 4.5 -L- -.l I 5.0 5.5 Figure 3. U-Pb U-Pbplo! plot of data Figure~. data for for zircon zirconfractions fractionsfrom fromPenokean Penokean plutonic and gneissic rocks rocks ln in the and gnelssic the western western part of ofcentral centralWisconsin Wisconsin (Van (Van Schmus, Schmus, 1980, unpub.). Note 1980, N~te t~at Granite appears appears to that the the Neillsville Neillsville Granite to be be distinctly distinctly older than than the the main maln suite sUlte ofofsamples. samples. Decay Steiger and and Decayconstants constantsasas in in Steiger Thger (1977). JMger (1977). 33 �Analytical Analytical results results have have also also been been obtained obtainedfor for zircon zircon from from three three of Penokean granitic The Lake Lake the the Penokean granitic plutons plutons along along the the Black Black River River (Figure (Figure 3). The Arbutus are apparently apparently part of of the themain main Arbutus and andBlack BlackRiver RiverFalls Falls granites granites are 1820-1850m.y. m.y. old old series 1820-1850 series ofofPenokean Penokean plutons plutons throughout throughoutWisconsin Wisconsin (Van (Van Schmus, 1980), butbut thethe results forforthe Granite suggest Schmus, 1980), results theNeillsville Neillsville Granite suggest;tit ;s is slightly older,extending extendingthe thespread spread ofofPenokean Penokean plutonic back slightly older, plutonic activity activity back as far as as about about 1875 1875 m.y. m.y. ago. ago. as far During tripwe we will willstop stopatatseveral severallocalities localities examine Duringthis this field trip andand examine Several aspects representativelithologies lithologies and structures of of this terrane. representative and structures terrane. Several aspects geology will be highlighted, highlighted, including including a) a) the thenature nature and and of the the regional regional geology will be variability theArchean Archean units, units,b)b)comparison comparison of of deformational deformational features features variability ofofthe Archean and Penokean units, chronologies of Archean andof of Penokean units, and andc)c) comparison comparisonofofrelative relative chronologies based on relationships andthose those basedononabsolute absolute agemeasurements. measurements. based on field field relationships and based age In addition scheduled In addition totodescriptions descriptionsforfor scheduledstops, stops,we wehave have provided provided location andbrief briefdescriptions descriptionsofofadditional additionallocalities localities in location information information and Black River River valley ininorder ordertotoprovide provideasascomplete complete aa guide guide as as possible possible the Black the Precambrian rocks. to these these Precambrian ITINERARY ITINERARY ITINERARY Stop Page 1. 1. 2. 3. 3. 4. 4. 5. 5. Gneiss Gne iss near nea r Greenwood Greenwood..... . . . . . . . . . . . . •. . . . . . . . . . . . . . . . . . . . . . 66 Neillsville Granite Neillsville Granite......................................... 99 Gneiss at Gneiss atHumphrey Humphrey Farm Farm...................................... 12 12 Neillsville NeillsvilleAugen Augen Gneiss, Gneiss, Miller MillerFarm Farm 15 Lake Arbutus Arbutus Granite .....•................................... 18 Lake 5a. LUNCH LUNCH 6. 6. East East Fork Fork Gneiss, Gneiss, Black Black River River ..................•.......••.... Hatfield Gneiss, Hatfield Gneiss,Lake LakeArbutus ArbutusDam Dam.........•.................. Black River River Falls Granite. Black Granite.................................... 7. 7. 8. 8. 44 20 20 22 22 27 27 �_ _ : .5 H. - \ I ci /' -- - Ls4 \HY CR \MOS - r '— — R4 0 ilo,d S dl rfl 1 /Ss - \- P' 't ; c/ — FIELD TRIP TRIP STOPS STOPS 55 - —I-: -— T200 -I dl 1.c. Lf 'J y [//5o 1, r :- ci "( - - �STOP STOP 11 TITLE: IITLE: Banded tonaliteatat Greenwood Bandedgneiss gneissand andfoliated foliated tonalite Greenwood Former pit,E½, E~,NW¼, NW\, Sec. Sec. 3, 3, T.26N., T.26N.,R.2W. R.2W.(Owen (Owen Former gravel gravel pit, l5-minute 15-minute topographic topocraphic quadrangle, quadrangle, Clark Clark County). County). Proceed about 0.1 0.1 ml. dirt road, about mi. south south from from County County Highway Highway GGonona adirt road, keepingtotoleft left when roadsplits, splits, to keeping when road to aa small small outcrop outcrop of banded gneiss. gneiss. Continue banded Continueapproximately approximately0.2 0.2mi. mi. further further short trail trail down southonondirt dirt roads andtrails. trails. A short south roads and down to to the the Black River Riverfrom fromthe thecrest crestofofaasmall smallhill hill leads to foliated Black leads to tonalite, and when when water are low low aa peninsula peninsula of tonalite, and water levels levels are The outcrop foliated foliated tonalite tonaliteand andbanded banded gneiss gneiss isisexposed. exposed. The is located jog of the ;s located at at aashort shortwestward westward jog the Black Black River. River. LOCATION: AUTHOR: AUTHOR: SUMMARY: SUMMARY: R. R. S. Maass S. Maass (1980) (1980) The thatcan can be be seen seen are banded banded tonalitic The four four major major lithologies lithologies that tonalitic gneiss, amphiboliticxenoliths xenoljthsininfoliated foliated tonalite, tonalite, and aplitic to gneiss, amphibolitic and aplitic to pegmatitic pegmatitic veins. veins. The The older folded, but butapparently apparently older units units are are isoclinally isoclinally folded, Onthis this basis only one major phase phaseof of deformation deformation is is present. one major present. On basis the the rocks rocks are tentatively are tentativelyinterpreted interpretedasasearly earlyProterozoic Proterozoic(Penokean) (Penokean) rather rather than than Archean in age. age. Archean 66 �DESCRIPTION: The The first first outcrop outcrop isis aa small smallpatch patch(2(2'xx4') 4') of of tonalitic tonalitic Theaxial axial plane planeof of the the fold banded gneiss banded gneisswhich whichhas hasbeen beentightly tightly folded. The the fold axis E. and strikes N. N. 200 20° E. 70° W. W.~ the axis trends trends N. N. 15° 15° E. E. and and and dips 70° plunges 60°. . plunges 1 From oldest oldest Four can be be distinguished Four lithologies lithologies can distinguished along alongthe the river. river. From gneiss,large large amphibolite amphibolitexenoliths xenoliths in to youngest youngest these these are: banded banded gneiss, foliated tonalite, tonalite, foliated foliated tonalite, tonalite,and and aplitic aplitictotopegmatitic pegmatitic granitic granitic foliated veins. The composition, faintly faintly banded,and and conconThegneiss gneissisis tonalitic tonal itic inincomposition, banded, tains long, tains long, thin thin lenses lenses of ofamphibolite. amphibolite. Isoclinal Isoclinal folds foldscan canbebeseen seen on on close examination. examination. Foliation strikes strikesN.N. 20° 20°E.E.and and dips dips 85° 85° W., W., and and aa weakmineral minerallineation lineationinin the the plane plane of of foliation foliation plunges weak plunges steeply steeply to to the the north. The The rock rock consists consists primarily of ofquartz, quartz,andesine andesine (An (An 34-38), 34-38), and and biotite, withminor minoramounts amounts ofofhornblende, hornblende, sphene, sphene, and and epidote. The biotite, with foliation, which which is is parallel paralleltotothe thebanding, banding, isiswell welldefined defined by by the the foliation, orientation of biotite orientation biotitegrains grains and, and, to to aalesser lesser extent extent by by the the orientation orientation of hornblende. hornblende. The with minerals minerals averaging averaging bebeThe gneiss gne-issisis fine-grained, fine-grained, with tween 0.25 0.25 and and 0.75 0.75mm. mm. tween 1 by 30 30') ) Amphibolite Amphibolite of of undetermined undetermined origin origin occurs occursasaslarge large (up (up to to 8' 8 1 by xenoliths in in the the foliated foliated tonalite. This xenoliths amphibolite does does not appear appear to This amphibolite be generation as as the the amphibolite be of the the same same generation amphibolite lenses lenses in in the thebanded banded gneiss, gneiss, The xenoliths xenoliths are are strongly based onstructural structural and based on and mineralogic mineralogic grounds. grounds. The stron91y but only only weakly weakly foliated, foliated,and andininsome some cases cases unfoliated. They lineated, but andesine (An contain approximately approximately 60% 60% hornblende, hornblende, 40% 40% andesine (An 4—5O), 46-50), and and very minor amountsofofbiotite biotite and minor amounts and quartz. quartz. Figure 4. 4. Photomicrograph tonaliteshowing showing Figure Photomicrographofoffoliated foliated tonalite The upper upper and andlower lower halves halves of of the granoblastic the granoblastic texture. The section are are composed composed primarily quartz and and feldspar~ section primarily of of quartz feldspar; aa biotite biotiteand and hornblende hornblende rich rich segregation segregation runs runs through through Foliation trends fromleft left the center center of the the section. section. Foliation trends from the to to right. 77 �The tonaliteconsists consistsofof2 2toto1010mm mm segregations segregations of Thegray grayfoliated foliated tonalite felsic minerals and and similarly similarly sized sized segregations segregations of rnaflc mafic minerals, minerals, in felsic minerals which the grains are are only only 0.25 0.25 toto11mm mm (Figure (Figure 4). The The major which the individual grains minerals andesine (An and hornblende, hornblende, with minerals are are quartz, quartz, andesine (An33-36), 33-36), biotite, biotite, and minor amounts ofof microcline, epidote,and andsphene. sphene. The which minor amounts microcline, epidote, Thefoliation, foliation, which strikes N. N. 20° 20° E. E. and and dips defined by dips 78° 78° W., W., isis defined by the the orientation orientation of individual biotite grains grains and and by by the the orientation strung-out felsic individual biotite orientation of strung-out mineral and mafic mineral mineral and mafic mineral segregatlons. segregations. Small Smallinclusions inclusionsofofdioritic dioritic material are mineral lineation material are also also flattened flattened inin the the plane planeofof foliation. foliation. A mineral in the the plane plane of of foliation foliationtrends trendsN.N.15° 15°E.E.and andplunges plunges 600. 60°. In In addition addition to the the amphibolite amphibolite xenoliths, xenoliths, the the foliated foliated tonalite tonalite concontains small small inclusions inclusions ofofbanded banded gneiss. gneiss. Although contact between between the the Although the contact banded andand thethe foliated not exposed, exposed, the bandedgneiss gneiss foliatedtonalite tonalite is not the available available outcrop the contact contact be be parallel or or subparallel subparallel totothe thebanding banding crop requires requires that that the and foliation the gneiss gneiss and the tonalite. Measureand foliation of the andthe thefoliation foliation of of the ments indicate these two the ments indicatethat thatthe thefoliation foliation in in these twounits unitsisis parallel; the foliation can be be seen seen to change slightly orientationover over large large expoexpofoliation can to change slightly in orientation sures of sures of either either unit. Aplitictotopegmatitic pegmatiticgranitic granitic veins Aplitic veins which thethe banded whichintrude intrude bandedgneiss gneiss and tonalite have have been been openly folded. The planes andfoliated foliated tonalite openlytototightly tightly folded. The axial planes of these these folds the foliation foliation ininthe thesurrounding surrounding unit. folds are are parallel parallel to the The gneiss at atthis may be Proterozoic in age; age; The banded banded gneiss thislocality locality may be early early Proterozoic support thissuggestion suggestioncomes comes from from aa U-Pb U-Pb (zircon) age age of ofapproximately approximately support for this 1850 gneiss at atLocality the south. south. 1850m.y. m.y.from frombanded banded gneiss Locality10, 10,only only 22 miles miles to the In structures ininthe thebanded banded gneiss gneiss appear In addition, structures appeartoto be bethe theresult result of only one one deformation, deformation, whereas whereas gneisses gneisses of know know Archean Archeanage, age, when whensuffisufficently exposed, exposed, reveal indicativeofofpolyphase polyphase deformation. deformation. reveal structures structures indicative Because of of thethe gneiss is ispoor, stated Becauseexposure exposure gneiss poor,itit cannot cannotbebedefinitively definitively stated that itithas hasbeen been deformed deformed only once; and further investigation, perhaps only once; and further investigation, perhaps radiometric, is necessary necessary before age can can be radiometric, is before its its age be stated stated with with certainty. tonalitesoccurring occurringthroughout throughoutcentral centralWisconsin Wisconsinhave havebeen been Foliated tonalites radiometrically radiometrically dated datedatat between between1850 1850and and1830 1830m.y. m.y.(Van (VanSchmus, Schmus, 1980). 1980). The tonalite atatGreenwood Greenwood isis similar composition, texture, Thefoliated foliated tonalite similar in composition, and styletotothose thosedated datedunits unitsand andisisprobably probablythe thesame same and structural structural style general age. If thisis is case, deformationoccurred occurredduring duringthethe Penokean If this thethe case, deformation Penokean general age. Orogeny, east Orogeny, as as has has been beendemonstrated demonstratedalong alongthe theWisconsin WisconsinRiver Rivertoto the the east (Maass andothers, others, 1980). (Maa ss and 1980). B 8 �STOP STOP 22 Neillsville NeillsvilleGranite Graniteand and Granodiorite Granodiorite TITLE: LOCATION: ,LOCATION: Quarry, NW¼, NWl.;;, NWl.;;, Sec.Sec. 20,20, T.24N., R.2W. (Neillsville 15Quarry, NW¼, T.24N., R.2W. (Neillsville 15minute topographic topographic quadrangle, minute quadrangle, Clark County). County). Approximately 1 mile south south of ofU.S. U.S.Highway Highway 10 10 on on east east side sideofofTower TowerRoad. Road. 1 AUTHOR: AUTHOR: R. Van R. Maass and and W. W. R. Van Schmus Schmus (1980) R. S. Maass The Granite isisa atypical typicalPenokean Penokean pluton, pluton, TheNeillsville Neillsville Granite although geochronologic andand structural is probably probably although geochronologic structuraldata dataindicate indicatethat thatitit is slightly older Penokean slightly olderthan thanmost mostofofthethe Penokean Granites Granites ininWisconsin. Wisconsin. At At this lineatiori, but location the the granite graniteshows shows pronounced pronounced lineation, butdoes does not not have have aa SUMMARY: SUMMARY: cross—cutting dacite dacite dike pronounced dike and and overlying overlyingMt. Mt.Simon Simon pronouncedfoliation. foliation. A cross-cutting sandstone are exposed here. here. sandstone are also exposed DESCRIPTION: A recent recent quarrying operation operation has has provided provided excellent excellentexposure exposure of pink pink Neillsville NeillsvilleGranite Granite,cray 9raygranodiorite, granodiorite,aadacite dacite dike, dike, and and the the Precambrian-Cambrian Granite isisexposed exposed Precambrian—Cambrianunconformity. unconformity. The TheNeillsville Neillsville Granite of the at the the southern southern end end of the quarry, quarry, both both in in place place and and as as large large fresh fresh blocks blocks in rubble The blocks blocks provide provide an an opportunity opportunity to examine the strucexamine the in rubble piles. The ture in andclearly clearly show showthat thatthe thegranite granite is is lineated, ture in three three dimensions dimensions and lineated, Measurement thelineation lirieation on but (Figure 5). 5). Measurement ofofthe on three three nonnonbut not not foliated (Figure parallel surfaces, parallel surfaces,combined combined with stereographic stereographic techniques, techniques, reveals reveals aa trend trend of N. N. 25° 25° E. E. and and aa plunge plunge of 82°. 82°. 9 �Figure 5. Two Twofaces faces of aa block Figure.5. Granite, block of of Neillsville Neillsvjlle Granite, approximately nornial approxlmately normal to each each other, other demonstrate demonstrate the the presenceofof lineation lineatjon and ~rese~ce and the the abse~ce absenceofoffoliation foliation in this ln thls unit. unit. Figure PhotomicrographofofNeillsville Neillsville Granite Figure 6. 6. Photomicrograph Graniteshowing showing The section section contains granoblastic texture. The granoblastic contains porphyroporphyroblastic microcline, microcline, large large strained strained quartz quartz grains, grains, and and fine-grained fine-grained quartz, oligoclase, oligoclase, and and microcline. microcline. The fine-grained free. fine-grained quartz quartz in in nearly nearly strain strain free. 10 �The is composed composed of subequal amounts microcline, and and The granite granite is of subequal amountsofofquartz, quartz, microcline, 2%biotite. biotite. Trace oligoclase (An (An 26-28); 26-28); and and approximagely approximagely 2% Trace minerals minerals include muscovite,epidote, epidote,chlorite, chlorite, sphene, sphene,apatite, apatite,allanite, allanite, zircon, clude muscovite, zircon, and trimodal, consisting consisting and opaque opaque minerals. minerals. The Thegrain grainsize sizedistribution distribution is trimodal, highly strained strained quartz; of 22 to to 33nh mm porphyroclastic porphyroclastic microcline; microcline; 1 to 22 mm mm highly and 0.1 to 0.75 rrim quartz, microcline, and oligoclase. and 0.1 0.75 mm quartz, microcline, and The grained The finer finer grained minerals minerals exhibit gently gently curved curved grain grain boundaries boundaries (Figure (Figure 6). The lineaThe linea— tion is defined defined by by the individual biotite biotite grains, grains, aligned aligned tion is the orientation orientation of of individual clusters of of biotite, clusters biotite,and and trains trains of ofquartz quartz grains. grains. The an The absence absence of of an observable foliation foliation on observable on the themesoscopic mesoscopic scale scale is is supported supported by by its itsabsence absence on microscopic scale. scale. on the the microscopic 1 Thenorthern northernend endofofthe thequarry quarryisisaamixture mixtureofofNeillsville Neillsville Granite The Granite and is istexturally andaagray graygranodiorite granodioritewhich which texturallyand andstructurally structurally identical identical to the granite. Unclear contactrelationships relationshipsmake make difficult totodetermine the Unclear contact it itdifficult determine which unit younger. Petrographic the which unit isisyounger. Petrographicrelationships relationshipsare areso sosimilar similar that the trimodal grain grain size distribution two units two unitsmay may be be comagmatic. comagmatic. The The trimodal distributionobserved observed in the the granite granite is is also also present present in in the the granodiorite. granodiorite. The The only only difference biotite, the is that that the the granodiorite granodiorite contains contains twice twice as as much much biotite, the oligoclase oligoclase is An An 28-30, 28-30, and and microcline is less lessabundant. abundant. microcline is Small patches patches of of an Small an oligoclase porphyry porphyry dacite dacitedike dikeare areexposed exposed along along An An approximately trend and from these these scattered scattered exN. N. 35° E. E. trend and steep steep dip can can be be determined determined from 350 posures. The dike contains contains aa foliation foliation which The dike which also also trends trends N. N. 35° E., and E., arid dips steeply; steeply; a mineral lineation lirieation in the dips a strong strong mineral the plane plane of foliation foliationplunges plunges Poor exposure exposure prevents prevents more moreexact exact structural structural measurements, steeply. Poor measurements, but the mineral lineation lineation in the the mineral the dike dike isisprobably probably parallel parallel totothe themineral mineral lineation in in the the granite graniteand and graniodiorite. granodiorite. the wall of the the 350 floor and and wall the central central portion portion of ofthe thequarry. quarry. The composed ofofquartz, and The dike dike is composed quartz,oligoclase oligoclase (An (An 28-30), 28-30), biotite biotite and The texture is trimodal, consisting of 1 to 6 mm minor 6 mm minor microcline. The texture is trimodal, consisting of 1 oligoclase porphyroclasts, porphyroclasts,0.25 0.25toto0.75 0.75mm mm quartz quartz in in trains trainswhich whichmay may represent represent the the remains remains of predeformational predeformational quartz quartz phenocrysts, phenocrysts, and and aa groundground·Microscopic deformation mass are less less than than0.1 0.1mm. mm. Microscopic massinin which which the the grains are and recrystallization textures identical to and recrystallization textures are are nearly nearly identical to those those in the the granite granite The foliation in the dacite is presumed to have formed and granodiorite. The foliation in the dacite is presumed to have formed and granodiorite. during the deformationthat thatleft left the during the same same deformation the granite granite and and granodiorite granodiorite ununfoliated, suggesting foliated, suggesting that that the themechanical mechanical properties properties of the the rocks rocks played played a very very siqnificant role role inindetermining determining the the final structural structuralexpression expression a The Neillsville Neillsville Granite that the the structural Granite demonstrates demonstrates that of the the event. event. The expressionofofthe theevent eventisis also also spatially spatially variable. expression variable. Two the Twomiles miles to to the northeast (Locality 11) northeast 11) the the granite granite crops crops out out ininaanumber number of older older Herethe the granite granite exhibits aa moderately well developed foliaquarries. Here moderately well developed foliation in in addition addition to to aa mineral mineral lineation. tion Zircon has beenseparated separatedfrom from sample Neillsville granite granite colZircon has been a asample of of Neillsville The zircons are euhedral, light brown lected this quarry. quarry. The zircons are euhedral, light brown inin color, lected at at this and stubby (length:width transmitted light and somewhat somewhat stubby (length:widthisis about about 2:1). 2:1). In In transmitted light they show normal igneous igneousgrowth growth zoning; zoning; older cores they show normal cores or oryounger younger overgrowths overgrowths are absent. U-Pb U-Pb analyses onontwotwo fractions analyses have havebeen beenperformed performed fractions so so far, far, are absent. and the the results results (Introduction, (Introduction, Fig. that the the Neillsville Neillsville Granite and Fig. 3) 3) suggest suggest that Granite is slightly granitic plutons so far far dated slightlyolder olderthan thanmost mostPenokean Penokean granitic plutons so dated in moreprecise preciseestimate estimateof of the the age must await await further further analyses, Wisconsin. A more age must analyses, but but a preliminary preliminary estimate estimate isis1875 1875 ±~ 25 25 m.y. m.y. 11 11 �------ -------- - - ---- - - STOP STOP 33 TITLE: LOCATION: LOCATION: Gneiss at atHumphrey Humphrey Farm Farm Gneiss SE~, Sec. l5-minute topographic topographic SE¼, Sec.22, 22,T.24N.~ T.24N., R.2W. R.2W.(Neillsville (Neillsville 15-minute quadrangle, Clark County). County). Discontinuous Discontinuous outcrop outcropfor for 0.5 ml. mi. quadrangle, along the east bank bank of Black River, River, approximately approximately 0.3 mi. mi. along the east of the Black west of State StateHighways Highways 73-95, 73-95,behind behindthe theThomas Thomas E.E.Humphrey Humphrey west of farm (ask (ask permission permission before farm before crossing crossing land). See Stop formap. map. See Stop 2 for AUTHOR: AUTHOR: R. S. S. Maass Maass (1980) (1980) R. SUMMARY: Three types banded gneiss, gneiss, SUMMARY: Three types of of gneiss gneiss are are present: present: tonalitic tonalitic banded mafic to ultramafic orthogneiss, orthogneiss, and "injection gneiss." gneiss." The The mafic to ultramafic andtonalitic tonalitic uinjection have been been subjected polyphase deformation units have subjected to to polyphase deformationand andinterference interference folds folds complex folding are present. The are present. The rocks rocks have havenot not been beendated, dated, but but the the complex folding Archean ages indicates Archean indicates agesfor forthe the older older units. DESCRIPTION: This ofthe theBlack BlackRiver Riverdisplays displaysa adiverse diverseand andcomplex complex This stretch of group of gneisses gneisses plus some some mildly deformed dikes the gneisses. gneisses. group mildly deformed dikes crosscutting the Three sets gneiss are are present; present; the the oldest oldestisisa banded a banded gneiss gneiss thought thought Three sets of gneiss be a paragneiss; paragneiss; the to be the next next youngest youngestisisan anorthogneiss orthogneissofofmafic mafictotoultraultramafic composition; composition; the the youngest youngest is an "injection "injectiongneiss" gneiss"formed formedwhen when leucoleucomafic is an tonaliteintruded intrudedthe theparagneiss paragneiss and and orthogneiss. orthogneiss. The The percentage tonalite percentageof of leucotonalite varies varieswidely widelyininthe thescattered scatteredexposures, exposures,from fromless lessthan than5% 5% tonalite up up to to 100%. 100%. A (now amphibolite) in the thebanded banded A narrow narrow gabbroic gabbroic dike dike (now amphibolite) in gneiss may maybeberelated related to to the gneiss the orthogneiss. orthogneiss. Both Both sets of ofgneiss gneisshave have been been intruded by by diabase diabase and dikes. All All units unitshave havebeen been intruded andporphyritic porphyritic dacite dikes, metamorphosed amphibolitefacies. fades. metamorphosed atatamphibolite Furthest upstream Furthest upstream(to(tothe thenorth), north), the the outcrop outcropconsists consistsofof thin thin to thickly layered banded banded gneiss composition containing containing quartz, quartz, thickly layered gneissofof tonalitic tonalitic composition oligoclase-andesine, banding is is due andhornblende. hornblende. The The banding due to oligoclase-andesine, biotite, biotite, and alternating rich layers with biotite biotite (+(+hornblende) hornblende) rich layers with biotite poor poor layers. layers. alternating biotite The earlist deformation discernible discerniblein inthethe bandedgneiss gneisshas hasproduced produced The earlist deformati6n banded folds, forming forming an an axial planar foliation. Although FF, folds isoclinal folds, axial planar foliation. Although boudinage structures from this thls event event are rarely rarely seen, seen, highly highlyattenuated attenuated boudinage are structures from are abundant. three dimensional dimensional exposure, not abundant. Due Duetoto the the lack lack of three exposure,itit is is not possible measure either axes or the the elongation elongation of of the the boudins. boudins. possible to measure either the the fold axes The foliation, which isisparallel parallelto to banding,has hasbeen been openly openly to to The foliation, which thethe banding, tightly folded the axial planes folds tightly folded during during F!, F? deformation; deformation; the planes of these these folds are at high angle fold axes axes are are not consistently F are at a high angletoto the the foliation. foliation. F oriented, but but their their general general trend trend Is is totohe thesouthwest southwest with with plunges plunges of oriented, 50° to 85°. 50° 85°. The banded end of of the theexposure exposure has has been been intruded intruded by by The bandedgneiss gneissatat this this end to 88inch inchwide wide mafic mafic dike dike which which appears appears to have have been a 66 to beenoriginally originally aa medium totocoarse-grained now aa fine-grained amphibolite. medium coarse-gralnedgabbro, gabbro,but butisis now fine-grained amphibolite. gabbroicdike dike is truncated The dike has been been openly The gabbroic truncated by by aa The dike has openly folded. The 12 15 foot wide wide unfolded unfolded dike which which was 12 to to 15 wasformerly formerly aa diabase, diabase, but but is 12 12 �now also aa fine grained now also grained amphibolite. amphibolite. Despite amphibolite facies Despite the the amphibolite metamorphism, chilledmargins marginscan canstill still be metamorphism. chilled be recognized. recognized. The unThe dike dike is Unfoliated, but minerallineation lineation exists. exists, trendfoliated. butaamoderately moderately well developed developed mineral trending S. S. 500 50° W. 60°. W. and and plunging plunging 60°. The best best exposure exposureofofthe the injection injection gneiss The gneiss occurs occurs a short short distance distance The medium-grained medium-grainedleuco-tonalite leuco-tonalite phase which has has intruded downstream. The phase which the gneiss and andmafic mafic and and ultramafic ultramafic orthogneiss of the banded banded gneiss orthogneiss isiscomposed composed of nearly equal of quartz equal amounts amounts of quartz and and oligoclase (An (An 27-29), 27-29).and and minor minor (2-3%) biotite. The Theoligoclase oligoclase is 1 to 55 mm, andthe thequartz quartzisis 0.1 0.1 to (2-3%) biotite. mm. and but the the quartz appears may 2 rum, mm, but appears granulated; granulated; it it mayhave haveonce oncebeen been the thesame same size as size as the the oligoclase. The now amphibolite, The orthogneiss, orthogneiss, which which is is now amphibolite, is generally gabbroic in composition, but the generally gabbroic in composition, but the leuco-tonalite leuco-tonalite also also contains contains inclusions of ofultraniafic ultramaficgneiss gneisswhich whichconsists consistsof of muchasas99% 99% hornblende. hornblende. as as much Thefoliation foliation in The in the the injection injectiongneiss gneiss isischaotic; chaotic;blocks blocks ofofthe theortho orthoand and paragneisses (withtheir their earlier have paragneisses (with earlier foliation) foliation) havebeen beenrotated rotatedinto intorandom random orientations, and thefoliation foliation in the orientations, and the the leuco-tonalite leuco-tonalite swirls swirls in in almost almost all Thefoliation foliation inin the directions. The theleuco-tonalite leuco-tonaliteappears appears to to be be aa primary primary flow flow foliation. 1 displaying Figure 7. 7. Highly contorted contorted banded banded gneiss gneiss displaying Figure the fol ding of the interference due to the 'folding the axes axes of interference patterns due isoclinal F1 Fl folds. 13 �STOP STOP 44 TITLE: LOCATION: Neillsville AugenGneiss Gneiss Neillsville Augen Black River River at Miller Black MillerFarm. Farm. NW¼, NW~, NW~, Sec. NW¼, Sec.26, 26, T.24N., T.24N., R.2W. (Neillsville 15-minutetopographic topographic quadrangle, quadrangle, Clark Clark (Neillsville 15-minute County). Approximately StateHighway Highway 73-95, 73-95, Approximately 0.1 mi. west west' of ofState 0.1 mi. on the east of the on the east bank bank of the Black Black River. River. Follow Follow a a small small ravine ravine located 0.1 0.1 mi. south farmhouse to the located south of of the theMiller Miller farmhouse down down to the Black River, River, then Black then turn turn upstream; upstream; outcrop outcrop isissemi-continuous semi-continuous for 0.3 0.3 mi. mi. upstream. upstream. See Stop for map. map. See Stop 22 for AUTHORS: AUTHORS: R. Van R. Maass and and W. W. R. Van Schmus Schmus (1980) (1980). R. S. Maass SUMMARY: The Augen Gneiss SUMMARY: The Neillsville Neillsville Augen Gneissisis aa spectacular, spectacular, strongly strongly foliated rock with microcline to 55 cm rock is rock with microcline porphyroclasts porphyroclasts up up to cm in length. length. The The rock syenitic inincomposition composition and and is is interpreted interpretedtotobebederived derivedfrom fromananArchean Archean pluton that was intruded into the pluton was intruded the older older gneisses gneisses of the the region. region. It It is is 10 m.y. m.y. old old and, Archeanrocks rocksidentified identified so and, thus, thus, the the youngest youngest Archean so far 2535 + 10 in central central Wisconsin. Wisconsin. -I- Figure 8. 8. Neillsville NeillsvilleAugen Augen Gneiss. Gneiss. Both Both highly Figure deformed and undeformed microc1ine porphyrodeformed and nearly nearly undeformed microcline porphyroclasts occur in in aa fine—grained fine-grained matrix quartz, clasts occur matrix of of quartz, biotite, biotite,and and feldspar. feldspar. 15 15 �The spectacular NeillsvilleAugen Augen Gnelss, Gneiss, containcontainThe spectacularsyenitic syenltlc Nelllsvllle ing microcline porphyroc1asts crops out along along the the ing microcTine porphyroclastsupuptoto Scm 5 cminin length, length, crops Black River behind behindthe the Miller Miller farm. Black River farm. Many microcline Manyofofthe theoriginal orgtnal microcline have retained their phenocrysts are phenocrysts arehighly highly deformed, deformed,but butsome some have retained theirinitial initial euhedral shape shape (Figure (Figure 8). However, euhedra1 However,thethemajority majorityofofthose thosethat thatstill still appeareuhedral euhedralare areinternally Internally fractured. The appear The porphyroc1asts comprise porphyroclasts comprise as much as 50% 50%ofof the the gnelss. as much as gneiss. The The matrix, which the the minerals minerals are are matrix, in which than 0.2 m mm inindiameter, diameter, consists consistsofofapproximately approximately equal equal generally less than generally less amounts ofofmicroc1ine, biotite,and anduntwinned untwinned amounts niicrocljne, orthoclase, orthoclase, quartz, biotite, plagioclase. DESCRIPTION: DESCRIPTION: addition totothe thepreviously previouslymentioned mentioned minerals, minerals, the the gneiss gneiss conconIn addition tains minor minor quantities ofofepidote epidoteand and sphene sphene and andtrace trace quantities quantities of muscovite, apatite, allanite, allanite,zircon, zircon, opaque minerals. minerals. muscovite,chlorite, chlorite, apatite, andandopaque Quartz grains are coarser coarser than of the the matrix matrix minerals minerals are are Quartz grains that that are than the the rest of found inin "trains11 "trains" which which may may represent the remains of formerly frequently found represent the remains of muchlarger larger quartz quartz grains. Mortar much around the the rnicrocline microc1ine Mortar texture around porphyroc1asts evident, but butrecrystallization recrystallizationhas hashealed healed the the porphyroclastsisisstill still evident, fragments, and and most have gently curved curved grain grain boundaries. boundaries. fragments, most matrix matrix minerals minerals have producedmyrrnekite myrmekite around around the marmarRecrystallizationduring duringdeformation deformationproduced Recrystallization gins of the gins of of some some of the porphyroclasts. porphyroc1asts. The strike thegnelss gneissisisbetween between Thepredominant predominant strikeofofthe thefoliation foliation ininthe N. 75° 75° E. E. and and N. and the 87° to the the south. south. A A strong N. N. 85° 85° E., E., and the average averagedip dipis is 87° mineral lineatlori in the plane of the foliation trends S. 800 W. and mineral lineation in the plane of the foliation trends S. 80° W. and plunges 55° on on the the average, average, but but extremes plunges 55° extremes inin the the plunge plunge of 42° 42° and and 68° 68° have have been been recorded. Three shearing cut across across the Three small small zones zonesof of intense intense shearing inch in width. butthey theyare areonly only8 8Inches, inches,4 4inches, inches,and and 11 inch width. foliation, foliation, but They between N.N.55° three Theystrike strike between 55°E.E.and andN.N.65° 65°E.E.and anddip dipvertically. vertically. All three zones zones have havebeen beenrecrystallized. recrystallized. Zircons have have been Augen Zircons beenextracted extractedfrom fromananoutcrop outcropofofthe the Neillsville Neillsville Augen Gneiss ofHighway Highway 73, just justnorth northof of Cunningham Creek. Creek. Gneiss on on the the west west side of Cunningham The zircons zircons are are brown, euhedral and andshow showigneous igneouszoning; zoning;there thereisis no no evieviThe brown, euhedral analyses on on three dence coresorormetamorphic metamorphic overgrowths. overgrowths. U-Pb U-Pb analyses denceof of relict relict cores an age age of of 2535 2535 ++ 10 age is interpreted interpreted fractions of zircon zircon yield yieldan fractions of 10 m.y.; m.y.; this age as the age ageofofcrystallization crystallization of the as the the protölith proto1ithofofthe thegnelss gneiss and and Is is the the The highly highly deformed youngest Wisconsin. The deformed youngest Archean Archean age agemeasured measuredsosofar far in in Wisconsin. shows thethe Archean state of of this thisrock rockclearly clearly showsthat that Archeanterrane terranewas was subjected subjected major tectonism tectonism in late or orpost-Archean post-Archean time (e.g., <<2535 2535 m.y. m.y. ago). ago). to major in late time (e.g., It notknown known for forcertain certainwhere where ininthe theInterval interval2500-1850 2500-1850 m.y. m.y. ago ago It isisnot that this thisdeformation deformationoccurred occurred(Penokean (Penokean or orpre-Penokean?). pre-Penokean?). Upstream thethe Neillsville a series ofofthin Upstreamfrom from Neillsvllle Augen AugenGneiss, Gneiss, a series thintoto thickly thickly Some to niafic mafic composition composition isisexposed. exposed. Some layered gneisses of intermediate to layered gneisses of intermediate of the the units units are areporphyroclastic, porphyroclastic,but butthe theporphyroclasts porphyroc1asts are are smaller smaller than than those in the augen augen gneiss; they are are far farless lessabundant, abundant, and and they they are are generalgeneralthose in the gneiss they Someofofthe the units, units, both than microcline. microcline. Some both porphyroporphyroplagioclase rather rather than ly plagioclase clast abundant clast bearing bearing and and porphyroclast porphyroc1ast free, free,contain contain abundantmetamorphic metamorphic hornhornthe gneiss gneiss at this this end end of ofthe theoutcrop outcrop makes makes it blende. The The layering layering of of the it 16 �possible to study the style of detail than possible to study the of deformation deformation in more more detail than in the the unlayered augen gneiss. Numerous Numerous small scale andand large scale tight unlayered augen small scale large scale tightfold~, fold, and aa few few isoclinal isoclinal folds, observed Fere. and folds,can canbe be observed here. axes trend S. 80 Their axes trend S. 80 550, W. and and plunge between W. between 500 50° and and 55°, which is parallel totothe thetrend trendand andplunge plunge which is parallel theaugen augen gneiss. gneiss. The axial planes are parallel of the the mineral mineral lineation lineation ininthe The axial planes are dominant direction to the dominant to the directionofoflayering, layering,which whichisisparallel parallel to to the the foliation foliation in the structuresindicate indicatethat that all all units the augen augen gneiss. gneiss. These These structures units were were affected by folding event. fected by the the same same folding event. Downstream from Neillsville Augen AugenGneiss Gneiss biotite schist Downstream from thethe Neillsville is isa abiotite (see Locality Locality 14 (see 14 for for description), description),and andthen thenmore more interlayered interlayered porphyroclast porphyroclast bearing and andporphyroclast porphyroclastfree free units units (see (see Locality 15) 15) similar similarininappearance appearance bearing These upstream upstreamand anddownstream downstreamunits units probably probably represent to those those upstream. upstream. These sedimentaryand andvolcanic volcanic rocks rocks into into which gneiss protolith protolith was which the augen augen gneiss was sedimentary intruded. Near the middle middleof of the the exposure, the Neillsville Neillsville Augen Near the exposure, the Augen Gneiss Gneiss is by aa sizeable sizeable body body of of coarse-grained coarse-grained granitic graniticaugen augen gneiss. gneiss. The The intruded intruded by augen areonce onceagain againmicrocline, microcline,but but they they are are only only half as augen are as large large as as those those in the the older older augen augen gneiss, gneiss, and and the the younger youngerunit unit contains contains much muchless lessbiotite. biotite. Themineral minerallineations lineations in both The both units units are are equally equallywell welldeveloped developed and and parallel to each each other; however, however, the the younger youngerunit unit is only only weakly weakly foliated foliated ororeven even whether present ititisisnotnotclear clear whetherthetheyounger youngerunit unitwas wasememunfoliated. At present placedafter after the the foliation-forming foliation-forming state prior to the placed state of of deformation, deformation, and and prior the lineation-forming stage; it was priorto to the the entire was emplaced emplaced prior lineation-forming stage; or or whether whether it deformation and simply simply responded respondeddifferently differently due dissiniideformation and due to mechanical mechanical dissimiThe granitic granitic augen gneiss is unlike larities. The augen gneiss unlikeany any known known early Proterozoic Proterozoic rocks and and is is petrographically sorriewhat similartoto the the Neillsville Neillsville Augen somewhat similar Augen rocks Gneiss; an Archean Archean age age seems this isisthe thecase, case, Gneiss; therefore an seemsmost mostlikely. likely. If this the structural difference difference isis attributed attributedtotothe themechanical mechanical properties properties of the the rock, the rock, since since structures structuresobserved observed are are thought thought totohave have formed formed during during Penokean Orogeny final the the Penokean Orogeny(see (see final discussion). 17 �STOP STOP 55 TITLE: Lake Arbutus Arbutus Granite Lake NW~, NW~, Sec.Sec. 19,19, T.23N., 7~-minute topoNW¼, NW¼, T.23N.,R.2W. R.2W.(Hatfield (Hatfield 7½-minute Abandonedbridge bridge abutment graphic quadrangle, Clark Clark County). County). Abandoned abutment graphic quadrangle, LOCATION: LOCATION: 0.25 mi. mi. south south of ofState StateHighway Highway 95 95 bridge bridge over Black Black River, River, 0.25 west bank Black River. River. 2 mi. mi. north north ofofLake Lake Arbutus. Arbutus. west bank of of Black AUTHORS: AUTHORS: R. S. R. S. Maass Maass and and W. W. R. R. Van Van Schmus Schmus (1980) (1980) The undeformed, late-tectonic The Lake LakeArbutus ArbutusGranite Graniteisisaa typical typical undeformed, late-tectonic Penokean granitethat that is is intrusive Archean Penokean granite intrusiveinto intothethe Archeangneiss gneisscomplex. complex. StJM!'IARY: SU~1r'1ARY: The Lake LakeArbutus ArbutusGranite Granite is is aa medium-grained reddish granite granite The medium-grained reddish that contains feldspar, andand andesine contains quartz, quartz, perthitic perthiticalkali alkali feldspar, andesine(An (An 31-32) 31-32) in the ratios 1:1.5:1. the approximate approximate ratios DESCRIPTION: The which range range from from 0.5 0.5toto3 mm, 3 mm,have haveragged ragged boundaries boundaries The feldspars, feldspars, which and fractured internally (Figure (Figure 9). 9). A few few quartz quartz grains grains andare aresli9htly slightly fractured which havesurvived surviveddeformation deformation relativelyintact intact are are as as large large as as 22 mm, m, which have relatively but most most of the quartz quartz has has been been granulated less than than 0.5 0.5 imi. mm. Quartz but of the granulated to to less 18 �>~ L .' '~;';\~'ii/¥""i"*i; ......" Figure Figure 9. 9. Photomicrograph Photomicrograph of of Lake Lake Arbutus Arbutus Granite showing granulatedand andrecrystallized recrystallized quartz showing granulated quartz and and moderatelyfractured fractured feldspar. The moderately cloudy The feldspar feldspar is cloudy due sericftization. due toto sericitization. grain grain boundaries boundaries are are generally generally gently curved, curved, indicating indicatingmoderate moderate post post deforrnationalrecrystallization. recrystallization. The deformational free, hut but conconThegranite graniteisis biotite free, approximately 1% 1% chlorite which probably probably represents represents retrograded retrograded tains approximately chlorite which biotite. Alteration of of opaque opaque minerals, the minerals,and andsericitization sericitization of the feldspar feldsparmay may be be weathering weatheringphenomena. phenomena. Although microscopic microscopic textures textures indicate that was Although thatthe thegranite granite wasdeformed deformed andrecrystallized, recrystallized, no foliation ororlineation and no foliation lineationcan canbe be detected detected on on either the microscopic The granite granite appears the microscopic or or mesoscopic mesoscopic scale. The appears to to have have been been emplaced during latestages stagesof of Penokeandeformation deformationand andmetamorphism. metamorphism. emplaced during the late Penokean Zircons ofofthe Zircons were were separated separatedfrom froma asaMple sample thegranite granite collected collected at the of the on the the opposite opposite (east) (east) side side of the the base base of the old old bridge bridge abutment abutment on the river. The The zircons are are euhedral euhedral,, brown brown inin color, and and exhibit exhibitigneous igneous analysisofofone onefraction fraction (Introduction, (Introduction, Fig. zoning. U-Pb U-Pb analysis Fig. 3) 3) indicates indicates that the the Lake Lake Arbutus Arbutus Granite Granite belongs belongs to to the themain main population populationofofPenokean Penokean granite plutons and is about 1840 ± 20 m.y. old. A more percise plutons and is about 1840 + 20 m.y. old. more percise estimate estimate the age age will will have have to to await await additional additionalanalyses. analyses. of the 19 �STOP 6 STOP 6 TITLE: East Fork Gneiss Gneiss East Fork NW~, NW~, Sec.Sec. 4, 4, T.22N., (Hatfield topoNW¼, NW¼, T.22N.,R.2W. R.2W. (Hatfield 7.5-minute 7.5-minute topois along quadrangle, Jackson Jackson County). County). Outcrop Outcrop is along north north graphic quadrangle, shore East Fork the bridge bridge shoreof of the the East Forkof of the the Black Black River, River, east east of the on East Fork Fork Road. Road. on East LOCATION: LOCATI ON: AUTHOR: R. R. S. Maass (1980) (1980) S. Maass from most mostof of the the other SUMMARY: SUMMARY: The gneiss The gneiss exposed exposedhere hereisisdifferent different from gneisses inin the amphibole rich rich rather rather than than biotite gneisses the region regioninin that that ititisisamphibole the gneiss is cut rich. Both present, and and the gneiss is cut by by Both F F1 and F? F,,folding folding are present, 1 and post-deformat1onal dikes and of of diabase. diabase. post-deforrnatlonal d'tkes of of granite and In contrast contrast to to the theother otherbanded banded gneisses gneisses in region, the the In in the region, Someof of the East Fork East ForkGneiss Gneissisisamphibole amphibole rich richrather ratherthan thanbiotite biotite rich. Some layerscontain containasasmuch muchasas70% 70% hornblende. hornblende. In In addition addition to to melanocratic layers DESCRIPTION: hornblende, gneiss contains contains quartz quartz and and andesine andesine (An (An 33-35), 33-35), and and minor minor hornblende, the the gneiss amountsofofmicrocline, microcline, chlorite, amounts chlorite,epidote, epidote,sphene, sphene,and andopaque opaque minerals. minerals. 20 �The middle section of the outcrop is banded gneiss exhibiting large scale tight folds which are attributed to F deformation. The gneiss has been intruded by a diabase dike (which is nw amphibolite) and by a porphyritic dacite dike which is very weakly foliated, but strongly lineated. The foliation in the dacite strikes N, 25° E. and dips vertically, and the mineral lineation trends S. 25° W. and plunges 86°. The 0.5 to 3 mm phenocrysts in the dacite consist of euhedral microcline and andesine and slightly fractured quartz. Grain size in the recrystallized matrix is less than 0.1 mm. Near the downstream end of the exposure the banded gneiss becomes more felsic than usual. Biotite is less abundant, and hornblende rarely ac-irnpanies the biotite. There are small lenses and thin layers of quartzite, wh,ch are not present elsewhere in the gneiss. The banding becomes extremely contorted in this vicinity. F deformation is responsible for the random orientation of the axial plnes of folds, but the folding of axes of isoclinal F1 folds has resulted in interference patterns (Figure 7) and may be interpreted in a number of ways. The four most likely explanations are: 1) F1 folding was inhomogeneous, resulting in curvilinear xes; 2) F2 foldig was inhomogeneous; 3) some intermediate deformation folded the axes of the F folds, prior to F axes (remember that F, axes upstream are very inconsstent in orientatign). At this locality he second explanation is preferred since interference patterns are only ob- served where F? deformation has become unusually convoluted, and inhomogeneous F deformationis also the simplest explanation for the inconsistent oientation of F fold axes upstream. Why folding is so complex only at on small portioh of the outcrop is open to speculation, but one possiity is that we are in the core of a large unrecognized tight fold 1 the Hatfield Gneiss (Stop 7) exposure is complete enough to see an auiple of extreme contortion in the core of a large tight fold. 14 �Green subhedral euhedral hornblende hornblende ranges ranges from from 0.5 0.5 rum rnm to 22 miii; mm; Green subhedral to to euhedral the quartz feldspar are the quartz and and feldspar are 9enerally generally smaller, smaller,from from0.25 0.25toto1.5 1.5mm. rom. Chlorite is present some samples samples ininamounts amounts up up toto5%. 5%. It occurs as as layered layered present ininsome It occurs a~gregates, and and as as an product ofofhornblende, hornblende. The parallel aggregates, an alteration alteration product epidote gneiss varies epidote content content of of the the gneiss varies appreciably, appreciably, from from trace trace quantities, to as as much much as as 5%. 5%. In certain specimens specimens the so thoroughly thoroughly In certain the plagioclase plagioclase is so almostunrecognizable unrecognizable in thin saussuritized and saussuritized andsericitized sericitized that that ititisisalmost in thin section. The Theorientation orientation of of quartz quartz and andchlorite chlorite gra{ns grains defines definesthe thefoliation, foliation, while quartz, chlorite, chlorite,and and hornblende hornblende elongation while quartz, elongation defines defines the the lineation. lineation. Quartz crystallographically Quartzhas hasbeen been crystallographjcallyoriented orientedduring duringrecrystallization recrystallization to the extent extent that that nearly all quartz the nearly all quartz grains grains in some exsomethin thin sections sections go go to to extinction tinction atatapproximately approximately the the same same time. A narrow narrow granite dike dike composed composed of A of subequal subequalamounts amountsofofquartz, quartz, plagioclase, and alkali feldsparhas has intruded intrudedthe thebanded banded gneiss. gneiss. The clase, and alkali feldspar The dike dike also contains approximately approximately 1% 1% chlorite and trace trace amounts amounts of epidote. epidote. The contains chlorite and The granite differsfrom fromboth boththe theLake Lake Arbutus Arbutus Granite Granite (Stop (Stop 5) 5) and and the the Black Black granite differs River Granite (Stop that ititappears appears less less deformed, deformed, but but this River Falls Falls Granite (Stop 8) 8) in that in thin section. only apparent apparent in section. is only A medium-grained medium-graineddiabase diabasecontaining containingpyroxene, pyroxene,plagioclase plagioclaselaths, laths, A sphene, the banded banded gneiss. Based Based on on sphene, and and opaque opaqueminerals minerals has has intruded intruded the scattered exposure, the wide dike dike scattered exposure, the diabase diabase appears appearstotobe beaa 30 30to to 40 40 foot wide with dike is unfoliated, with chilled chilled margins. margins. The The dike unfoliated,unlineated, unlineatect,and andshows shows no no The original original minerals signs deformation inin thin section. section. The mineralshave have been been signs of of deformation The diabase may extensively extensively altered altered toto chlorite~ chlorite, epidote, epidote, and and sericite. sericite. The may be the gabbro gabbro at Stop Stop 7, 7, since since both both are are structurally structurallyand andmineral— mineralbe related related to the ogically similar. thegneiss gneissproduced produced an F folding folding ininthe Isoclinal F, anaxial axial planar planar foliafoliawhich is pafallel to to the the banding, banding, except except in hinges where where itit tion tion which is pai"allel in fold hinges transects banding. banding. The Thefoliation foliation has has been been subsequently subsequentlytightly tightly folded folded F deformation. deformation. FF2 fold axes axes are are nearly nearly horizontal, horizontal, trending trending both both during F2 axes is 25°; N. 70 E. E.2 and and S. S. 70° 70° W. W. The maximum plunge 25°;the themean mean he maximum plungeof of the axes N. 70 axial plane striking plunge is Synformed structures structures with an an average average axial plane striking plunge is 0°. Synformed N. 70° E. and dipping at atthis N. 70° E. and dipping 70° 70°N.N. predominate predominate thislocality. locality. �STOP STOP 77 TITLE: TITLE: LOCATION: LOCATION: AUTHORS: AUTHORS: Hatfield Gneiss,Lake LakeArbutus ArbutusDam Dam Hatfield Gneiss, SE¼, 3, T.22N., SE~, Sec. Sec. 3, T.22N., R.3W. R.3W. (Hatfield (Hatfield7½-minute 7~-minute topographic topographic quadrangle, Jackson Jackson County). County). Outcrop along the Black River quadrangle, Outcrop along the Black below the east half of Arbutus Dam. below the east half of Arbutus Dam. Approach mi. Approachisis on on 0.2 0.2 mi. long gravel gravel road long road that intersects intersects Clay Clay School Road'0.15 mi. School RoadO.15 west tracks. Additional outcrop west of of Green Green Bay Bay and and Western Western RR RR tracks. outcrop occurs mi.downstream downstream from fromdam. dam. occurs for for0.7 0.7mi. W. Van Schnus Schmus and S. l1aass Maass (1980) (1980) W. R. R. Van and R. R. S. SUMMARY: The the The main mainoutcrop outcrop area area immediately immediately below belowthe the dam damisis one one of of the SUMMARY: largest, ififnot notthe thelargest, largest, outcrops outcrops of of Archean Archeanrocks rocksininWisconsin. Wisconsin. The unitisisthe theHatfield Hatfield Gneiss,ananinterlayered interlayeredsequence sequence of of quartzoquartzoprincipal unit Gneiss, The rocks are as and minor amphibolite. The rocks are interpreted as feldspathic gneisses feldspathic qneisses and minor amphibolite. a metavolcanic metavolcanic sequence sequence that that was was formed formed 2815 2815m.y. m.y. ago ago and and deformed deformedatat least twice, with withthe thelatest latest deformation andmetamorphism metamorphism occuring deformation and occurirtg during during the Post-deformational cross-cutting cross-cutting mafic Penokean Orogeny, ago. Post-deformational mafic Penokean Orogeny, 1850 1850 m.y. m.y. ago. dikes dikes are are also also present presentatatthis this locality. locality. 22 22 �tI .....V .r: .., :>. f.il m ,.... :n 'M ::.:: 0 <:( p:) ....l ~ 0 >-:> (j) (j) ..... Q) ~ t:) "0 ...... Q) .... "-< +" oj ::r: r.r; oj CJ <:( 0-':.- !#:~ri (j) D. ..... (j) "0 Q) ::: ...... ..... I Q) +" t:) Q) (j) ...... .....U .., 0 (j) N·.... +" (j) 0 ,D ..... .r: c '"' ~ rot:) a oj ~ D. E h . Cambrian—Recent Cover 'M (j) 0:: I C oj h Q) > 'EU "' 0 ,D oj U I] {rf~~ (j) Q; .0<: 'r< "0 (j) UJ ro ,D ro 'r< 0 Met a—gabbro U 0.. 0 +-' VI E ro Cl +-' Diahase dikes Q) r--.. V1 :::l '-' c: Geologic map of Archean bedrock exposed south of Arbutus Dam. (Stop 7) < Hatfield Gneiss ,D c:: 1.::;?:] :>. t- (:0 Granitic Gueiss to Cue iss b ::> Quartzo-feldspa thic Geology by J. DuBois 1976-77 t- V) ;:J C h ,D ,D oj bJ) I ro +" (j) ::;; :::l .D s... c:( 40 ..c +-' :::l 0 V1 LIJ ~ "II ?~ ~ "'0 Q) V1 0 0.. X Q) ~ U 0 Fold Axes n UJ 0 ~ s... "'0 Q) .D s:: ro Q) ..c U s... c:( 0 c 4- C'J 0 0.. ro E ..., (j) (j) ~ U or- 01 0 r- 0 Q) G z 0 Q) .r: ..., \.. Figure 10. c.D s... ( :::l 01 or- L1.. �The principal unit exposed exposed (Figure the Hatfield HatfieldGneiss, Gneiss, an an The principal unit (Figure 10) 10) is the interlayered sequence ofofgranitic tona1iticgneiss gneisswith withconcordant concordant interlayered sequence granitic to to tonalitic muchofofthe theoutcrop outcropthe the layers layers are are 0.1 Over much 0.1 to to layers of amphibolite. amphibolite. Over layers of 3 cm pink to to gray, graY9 quartzo-feldspathic quartzo-feldspathic qneiss. gneiss. In some some parts cmthick, thick, pink the layers massive gneiss. gneiss. the layers are are thicker, thicker,approaching approaching several several meters meters of ofmassive Folding andfoliation foliation are Folding and are best best displayed displayed ininthe thethinner-banded thinner-banded portions. portions. The and consists consists Thequartzo-feldspathic quartzo-feldspathic gneiss gneiss has has aa granoblastic grarioblastic texture and of subequal subequal amonts and microcline. Mafic amontsofofquartz, quartz, plagioclase, plagioclase, and minerals represent represent less less than than 10% 10% in most most instances. instances. Normative abundances abundances minerals based on chemical analyses show that the quartz quartz abundance abundance is approxapproxbased on bulk bulk chemical analyses show that the plagioclase/orthoclase ratios vary vary from from about about imately constant constant and imately and that that plagioclase/orthoclase 1:1 (adamellite) to plagioclase (tonalite). 1:1 (adamellite) to primarily primarily plagioclase (tonalite). Theamphibolite amphiboliteisis interlayered interlayered with the The the quartzo-feldspathic quartzo-feldspathic gneiss gneiss and consists primarilyofofhornblende hornblendewith withabout about20% 20% epidote. epidote. The and consists primarily amphibolite has has been with the gneiss gneiss and and is is amphibolite beendeformed deformedalong along withthe therest rest of of the interpreted as originally originallyconcordant. concordant. The assemblage isisinterThe entire entire assemblage interinterpreted as preted as as having having formed formed from from an sequence ofof volcanic an interlayered iriterlayered sequence volcanic flows, sills (DuBois VanSchmus, Schmus, 1978). 1978). The The major metametapyroclastics, pyroclastics, ororsills (DuBois andandVan morphism currently amphibolite facies. Relict morphism currentlyrecorded recordedbybythe therocks rocksisis amphibolite pyroxene pyroxene has hasbeen beenfound foundinin some someofof the the quartzo-feldspathic quartzo-feldspathic gneiss gneiss samples, samples, suggesting either primary volcanic pyroxene or an earlier, higher grade suggesting either primary volcanic pyroxene or an earlier, higher grade period ofofmetamorphism. metamorphism. The Gneiss has event TheHatfield Hatfield Gneiss hasbeen beensubjected subjectedtotoananisoclinal isoclinal folding event an an axial planar foliation the layering, (F,) (F1) which whichproduced produced axial planar foliationparallel parallel to to the exept the foliation foliation transects in fold foldhinges hinges where where the transects the the layering. layering. The except in The foliation was then then tightly openly folded folded during during FF deformation; deformation; the the foliation was tightly totoopenly axial planes of these thesefolds foldsare areatathigh highangles angles foliation. F, to toth~th foliation. folds axial planes of F are rarely visible, areare conspicuous are visible,butbutF2F2folds folds conspicuouswherever wherever the the bandig banding is readily readilyapparent. apparent. Lineations (fold axes, crenulations, mineral mineral lineations) lineations) and andfoliafoliaLineations (fold axes, crenulations, tion were thegneiss gneissalong alonga a0.4 0.4mi. mi. long long stretch stretch of the were measured measured ininthe the river. Poles Poles toto foliation define define aa S axis which is identical axis which is essentially identical main grouping grouping of the the linear linear structural structuralelements elements to the the orientation orientation ofofthe themain (Figure 11). Fold (Figure Fold axes, the two two axes, when whenplotted plottedseparately, separately,fall fall into the groups in the quadrantofof the the stereonet, stereonet, with with the groups in the southeast southeast quadrant the vast vast majority majority plotting ininthe themain main group. group. groupof of F F1 fold axes in the A group fold axes in the core core of aa large were large tight FF fold were l clotted from the the rest rest of of th9 plotted separately separately from th~ linear linear structural structural eements. etrments. The The folding folding in in this this vicinity vicinityisishighly highlycomplex, complex, resulting resulting in in numerous numerous and and diverse interference interference patterns patterns from from the the folding folding of diverse of F, F axes. axes. Figure Figure 1? 12 illustrates illustratesone one of of the the simple simple interference interference patterns patterns.l The The axes of these axes these F1 quadrants F, folds folds plot plot ininallallfour four quadrantsofofthe thestereoniet stereonet with with plunges ran~­ olunges rang— irig from horizontal to vertical. ing from horizontal to which would would indicate aa later Girdles which simple folding pattern simple folding pattern of of the the F1 Fl axes axes do do not not exist, exist,and and the the interference theresult resultof of inhomogeneous deforpatterns are are therefore therefore believed believed totohebe the patterns inhomogeneous mation inin the the core core of of the mation the F2 F fold. 2 24 �N N ineation lineation poles to to foliafion poles foliation 485 485measurements measurements contours 0.2,1,3,5,10,15,20,25% 0.2,1,3,5,10,15,20,25%per per1% 1% area area 884 measurements 884 measurements contours % per contours 1,3,5,7,9 1,3,5,7, 9 % per 1% I% area area Lower hemisphere stereGgraphic projectionsofofstructures structures in Lower hemisphere stereographic projections the the Hatfield Hatfield Gneiss. Gneiss. (left) (left)Lineations Lineations defined defined by by fold fold axes, axes, crenulations, crenulations, and mineral elongations. The mean orientation of the lineaUons is S. and mineral The mean orientation of the lineations is S. 84° 84° E. E. with aa plunge plunge ofof51° 51°ESE. ESE. (right) Plot Plot of of poles poles to to foliation foliation yields yields aa mean for ~ trending S. 84° E. with with aa plunge of 52° ESE,virtually virtually identmean for trending S. 84° E. plunge of 52° ESE, identorientation for for the ical to to the the mean mean orientation the lineations. Figure 11. 11. Photo of the Photo of the Hatfield HatfieldGneiss Gneissshowing show~ng interference pattern pattern due duetoto folding folding of of the interference the axis aX1S of of an an The interference interference pattern pattern occurs isoclinal F1 Fl fold. The occurs in the core F2 fold. the core of of aa large, large, tight F2 12. Figure 12. �is inhomogerieous thisrelatively relatively small deformation is inhomogeneous in inthis small Although FF? deformation as a whole deforarea the outrop; outcrop; the the outcrop outcrop as whole exhibits exhibitshomogeneous homogeneous deforarea of the mation, as demonstrated demonstrated tightdistribution distribution of 94.5% the linear mation, as by by thethe tight 94.5% ofof the structural elements. structural elements. F fold axes axes are are never never exposed exposed in in 33dimensions dimensions F the anomalou anomalou~ area discussed), thus thus their their trend trendand and (except in (except in the area just just discussed), ageofofFF, folding is unclear, hut F2 folding plunge are are unknown. unknown. The The age folding unclear, but F folding 1 2 probably Penokean Penokean (see discussion). is probably (seefinal final discussion). Zircon has beenseparated separatedfrom from tonalitic layer of has been a atonalitic of the the gneiss gneiss on on Zircon the west bank bank of the the Black Black River, River,about about0.6 O.nmimidownstream downstrenm from from the the dam. dam. the west The zircons are The zircons are brown, brown, euhedral euhedral crystals crystals with withnormal normal igneous igneous zoning zoning and and no signs of of significant or relict relict cores. no signs significant overgrowths overgrowths or cores. U-Pb U-Pb analyses on on several show that unitisisessentially essentially sameage age(2815 (2815 several fractions fractions show that this unit thethe same + 20 m.y.) as gneissesinin central central Wisconsin (Introduction, 20 m.y.) as other other Archean Archean gneisses Wisconsin (Introduction, Ng. 2). This age ageisis interpreted interpretedasasthe thetime timeofofcrystallization crystallization (vol~ig. 2). This canism) the protolith protolith of canism) ofof the of the the Hatfield HatfieldGneiss. Gneiss. Rb-Sr Rb-Sr analyses analyses from several samples collected in the several samples collected the area area ofofStop Stop7 7and andfurther furtherdownstream downstream do not plot coherently isochrondiagram, diagram,indicatinq indicatinqpartial partial resetdo not coherently on on an an isochron resetting during ting duringsubsequent subsequentmetamorphism. metamorphism. However, However, these theseare are no no indications indications of crustal crustal history historyexceeding exceeding 2.8 2.8 b.y. b.y. 26 �STOP 8 STOP 8 TITLE: LOCATION: LOCATION: Black River River Falls Granite Black Granite NE¼, SE¼, Sec.15, 15,T.21N., T.21N.,R.4W. R.4W.(Black (Black River River Falls 15-minute NE~, SE~, Sec. 15-minute Outcrop occurs topographic quadrangle, Jackson Jackson County). County). Outcrop occurs along along topographic quadrangle, river andnorth north of State riverdownstream downstream from from dam dam and State Highway Highway 54. 54. .1 IA AUTHORS: AUTHORS: R. R. / S. Maass and and W. W. R. R. Van Van Schmus Schmus (1980) S. Maass SUMMARY: The typical,largely largely undeformed TheBlack BlackRiver RiverFalls Falls Granite Granite is is aa typical, undeformed SUMMARY: late-tectonic Penokean Penokean granite intrusive into intothe theArchean Archean gness gneiss late-tectonic granitethat that is is intrusive complex. DESCRIPTION: The The Black Black River River Falls Granite Granite crops crops out outbelow below aapower power gengenerating dam the heart heart of Black River Falls. The erating dam inin the Black River The pink, pink,medium—grained medium-grained biotite granite quartz,alkali alkali feldspar, biotite graniteconsists consists ofofsubequal subequal amounts amounts ofofquartz, feldspar, and normally and normally zoned zoned andesirte—oligoclase andesine-oligoclase (An (An25—33). 25-33). Biotite Biotitecomprises comprises approximately5%5% theunit, unit, 'and andretrograde retrogradechlorite chlorite deriverl derived from from biotite biotite approximately of ofthe constitutes another 1%. 1%. Trace and constitutes another Trace minerals minerals include include sphene, sphene,allanite, allanite, and epidote. 27 �PhotomicrographofofBlack BlackRiver River Falls Falls Granite. 13. Photomicrograph Granite. Figure 13. Nearly euhedral, andesine-oligoclase is Nearly euhedral, zoned zoned andesine-oligoclase is surrounded surrounded by fractured feldspars andrecrystallized recrystallized by fractured feldspars and and granulated granulated and grain is is visible visible ininthe thecenter center of of the the quartz. A biotite grain figure. Thefeldspars, feldspars, which whichoften often exhibit exhibit nearly The nearly euhedral euhedral outlines (Figure (Figure Thealkali alkali feldspars 13) range 13) range from from 11 to 44mm. mm. The feldspars consist consist of of both both microcline microcline and perthite, perthite, with Granulated and andrecrystallized recrystallized and with microcline microclinedominating. dominating. Granulated quartz from 0.1 0.1 to 1 mm, mm, have which quartz grains, grains, from havebeen beenderived derivedfrom from quartz quartz grains which were originally as Anhedraltoto subhedral subhedralbiotite biotite is often were originally as large largeasas2 2mm. mm. Anhedral often partially ororcompletely in chlorite. Selective partially completely replaced replaced in Selective sericitization sericitization of the the feldspars feldspars has has resulted resulted in in extensively extensively altered alteredplagioclase, plagioclase,modermoderately altered altered perthite, perthite,and and nearly nearly unaltered unaltered microcline. microcline. 1 On both microscopic and and mesoscopic Falls On both the the microscopic rnesoscopicscales, scales,the the Black Black River River Falls Granite unfoliated and Granite appears appears unfoliated and unlineated, despite despite microscopic microscopic textures textures which that itithas hasbeen been deformed deformed and the which indicate indicate that and recrystallized. recrystallized. As As with with the LakeArbutus ArbutusGranite Granite (Stop (Stop 5), 5), this Lake thisunit unitwas wasprobably probablyemplaced emplaced during during the late the latestages stages ofofPenokeari Penokean deformation. deformation. ti-Pb analyses on on two two zircon zircon fractions U-Pb analyses fractions('Ian (VanSchmus, Schmus, 19R0) 1980) indicate that the the Black Black River River Falls Granite Granite is is also also part partofofthe themain main population population of Penokean granitic plutons plutons and, and, like the Granite, is Penokean granitic the Lake Lake Arbutus Arbutus Granite, is about about 1840++ 20 20 m.y. m.y. old. 1840 28 �SUPPLEMENTAL LOCALITIES LOCALITIES SUPPLEMENTAL Page Page tonalite, Greenwood Park Park Foliated tonalite, Greenwood 31 31 10. Granitic gneisssouth southofofGreenwood Greenwood Granitic gneiss 31 11. Neillsville Granite, Granite, Neillsville 32 32 12. Gneiss, granite, sandstone sandstone at Sunburst Sunburst Village Village................ Gneiss, 32 32 13. Gneiss and and granite granite at Snyder Dam Gneiss 33 14. and gneiss, Schist and gneiss,Cunningham Creek 33 15, and gneiss, Schist and gneiss, Black River south of Cunningham Creek .. 34 16. Banded gneiss, Banded gneiss, Big Big Spring 34 17. Gneiss Gr,eiss at Morrison Morrison Creek 35 18. Gneiss, Gneiss, Black Black River RiveratatPowerhouse Powerhouse 35 19. Banded quarry near nearPowerhouse Powerhouse Bandedgneiss, gneiss, quarry 37 37 20. Gneiss Gneiss at Halls Halls Creek Creek 37 37 21. Gneiss Black River River Falls Gneissand andtonalite, tonalite, Black 38 38 22. Quartzite, Silver SilverMound Mound....................................... 38 23. Jackson County Iron Mine Jackson County Mi ne. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 39 9. 29 31 �___ _ __ ___ ,W \ Mill '¼3 15 14 JJ - ? )u '/ i1- k kI' -. ' -J-'L- (cLco rv H: R2\. - wgc-,j WI'c;>c-.4.{~ Joy bg • 887 __ r- - I":f~ '~l l \ ~ . ;::. SUPPLEMENTAL LOCALITIES LOCALITIES SUPPLEMENTAL 30 --—_- j1 1W o ÷ �SUPPLEMENTAL LOCALITIES SUPPLEMENTAL LOCALITIES tonalite, Greenwood Park Park Foliated tonalite, Greenwood LOCALITY 9: LOCALITY NW~, Sec. NW¼,NE~, NE¼, Sec.34, 34,T.27N., T.27N., LOCATION: R.2W. R.2W. (Owen (Owen15-minute 15-minute topographic topographic quadrangle, Clark County). See Stop 1 for locality quadrangle, County). See localitymap. map. Exposureisis on on the the west west bank bankof of the the Black Exposure Black River, which which requires requires aa ~/alk wading the the Black Black River River from from walk across across aa farmer's farmer's field field ororwading Greenwood Park. Greenwood 1 AUTHOR: R.S. Maass (1980) (1980) R.S. Maass EIYESCRIPTION: The foliated tonal ite atatGreenwood Parkisis nearly nearly identical OESCRIPTION: The foliated tonalite Greenwood Park to the the foliated foliated tonalite tonaliteatatStop Stop 1, 1,1.2 1.2miles miles to to the the south. south. The to The major difference is that better developed difference is that the the foliation, foliation,which which isisslightly slightly better developed here, here, has beenopen opentototightly tightly folded. has been folded. A fold axis axis trending trendingS.S.700 70 0W. W. and and plunging plunging 75° hasbeen beendetermined determined localitybybyplotting plotting poles polestoto foliation foliation on 75 0 has for for thisthis locality on Mineral lineation lineation in in the aa stereonet. Mineral the foliated foliated tonalite tonalitecould could not not be be accurately measured measured lackofofproper properexposure, exposure, accurately duedue to to lack butbut it it isis roughly roughly parallel to the statistically statisticallydetermined determined fold axis. axis. Granitic ap1ites similar similar totothose those to the Granitic aplites at Stop 1 Small faults with movement Stop 1 have have intruded intrudedthe thefoliated foliated tonalite. Small faults with movement on the the order of on of aafew few inches inches strike strikebetween betweenN.N.5Q0 60 0 E. E. and and N. N. 700 70 0 E. E. and and dip steeply. dip steeply. LOCALITY 10: LOCALITY LOCATION: Granitic Gneiss south southofofGreenwood Greenwood Granitic Gneiss SW~, NW~, Sec.Sec. 15,15, T.26N., R.2W. (Neillsville 15-minute topotopoSW¼, NW¼, T.26N., R.2W. (Neillsville 15-minute for locality See Stop 11 for graphic quadrangle, quadrangle, Clark Clark County). County). See locality graphic map. Rockisis exposed exposedinin bottom bottomof of old sand gravel quarry. map. Rock sand and and gravel Turn west junction ofofState StateHighway Highway 98 98 with Turn west on on gravel gravel road road at at junction ends after1.0 1.0mi.; mi.; turn turn north north for 0.1 State Highway Highway 73. 73. Road Road ends after 0.1 mile quarry. mile to quarry. AUTHOR: W.R. Van Van Schmus Schmus (1980) AUTHOR: W.R. DESCRIPTION: DESCRIPTION: The The exposed exposedbedrock bedrock consists consistsofofgranitic granitic grieiss gneiss with lenses lenses granitic gneiss of amphibolite; amphibolite; a tonal tonalite dike cuts cuts the the gneissic gneissic rocks. rocks. The The granitic gneiss ite dike consists consists of fresh fresh microcline, microcline, plagioclase, plagioclase, and and quartz; quartz; the amphibolite amphibolite is mostly fresh fresh hornblende hornblendewith withquartz quartzand andplagioclase; plagloclase;the thetonalite tonalite consists mostly consists U—Pbanalysis analysis of of of quartz, quartz, plagioclase, plagioclase, minor minor microc1ine, microcline, and andbiotite. biotite. U-Pb one zircon zircon fraction gneiss one fraction from from the thegranitic granitic gneisshas hasyielded yieldeda Penokean a Penokean age age (Introduction, Fig. 3), suggesting suggesting that locality are are (Introduction, FIg. that the the rocks rocksatat this this locality not not part part of ofthe theArchean Archean terrane terrane to to the the south. south. 11 �LOCALITY 11: LOCALITY S. Sec. 10, 10, T.24N., T.24N., R.2W. R.2W.(Neillsville (Neillsville 15-minute S. half, half,SW¼, SW~, Sec. 15-minute topoaraphic topographic quadrangle, quadrangle, Clark Clark County). County). Several quarries Several granite quarries exist in in this thisarea; area;see seeStop Stop 22for fordetailed detailedmap. map. LOCATION: LOCATION: AUTHOR: AUTHOR: Granite, Neillsville Neillsville Granite, R.S. R.S. Maass Maass (1980) (1980) TheNeillsville Neillsville Granite of old DESCRIPTION: The Graniteisisexposed exposed in inaanumber number of old quarries quarries to the Neillsville. The graniteininthis this vicinity differs to the northwest northwest ofofNeillsville. The granite differsfrom from that that at Stop Stop 22 in in that that ititisisfoliated, foliated, whereas whereas the the granite granite at at Stop Stop 22 is not. not. In In all all other otherrespects respects the the granites granites are are identical, identical,and and there there isisno no reason reason to believe that they believe they are are not not the the same same unit. Exposures Exposures here badly here are are too too badly weathered accuratelymeasure measure foliation, but are that weathered totoaccurately thethe foliation, but best best estimates estimates are (+ 100) dips 300 itit strikes strikesNN450 45 0 W 10 0 ) and and dips 30° (+100) (~lOO) to the the southwest. southwest. W (~ LOCALITY LOCALITY 12: LOCATION: LOCITION: AUTHOR: AUTHOR: SunburstVillage; '/illage; gneiss, Sunburst gneiss, granite, granite,sandstone sandstone N. edge edge SW¼ SW~ and S. S.edge Sec.Sec. 15, 15, T.24N., R.2W. (Neillsville N. and edgeNW~, NW¼, T.24N., R.2W. (Neillsville 15-minute topographic topographic quadrangle, quadrangle, Clark County). See Stop Stop 22 for for 15-minute County). See for detailed To get get to the detailed location locationmap. map. To the outcrop, outcrop, go go one one block block south of of U.S. Hwy.1010inin Neillsville Neillsville totoSunburst south U.S. Hwy. Sunburst Village VillageSchool. School. The outcrop outcrop is is both The both north north and and south south of of the theU.S. U.S. Hwy. Hwy. 10 10 bridge bridge over the Black Black River, River, on on the the east east bank. bank. over the R.S. Maass Maass (1980) (1980) R.S. The outcrop outcrop consists consists of massive quartzo-feldspathic gneiss, DESCRIPTION: The massive quartzo-fe1dspathic gneiss, DESCRIPTION: bandedgneiss gneiss tonalitic composition, maficgneiss, gneiss,and andananaplitic aplitic granitic banded ofoftonalitic composition, mafic dike. The gneiss and and banded banded gneiss gneiss appear appear very The massive massivequartzofeldspathic quartzofeldspathic gneiss similar to to the the Hatfield HatfieldGneiss Gneiss (Stop (Stop 7). 7). Isoclinal F1 Fl folds folds and and tight tight F2 F2 F1 folds occur occur throughout throughout the the gneiss. gneiss. F axes cannot cannot be be measured, measured, but but F2 F2 l fold axes axes the northwest northwest and and plunge axes can; can; they they trend trend to to the plungealmost almostvertically. vertically. Themafic mafic gneiss gneiss occurs occursasas large large blocks blocks and and thick thick concordant (?) layers The concordant (?) layers in the morefelsic, felsic, qneiss. Although the the mafic layers in the surrounding, surrounding, more gneiss. Although layers have have been been metamorphosed amphibolitefacies, facies, they they do metamorphosed to toamphibolite do not appear appear as as highly highly deformed deformed or as thoroughly thoroughlyrecrystallized recrystallized as as the the rest of as of the the gneiss. gneiss. One One possibility possibility is of sills, that they they are are remnants remnants of sills,but butthey theyhave havenot notbeen beenstudied studiedininenough enough detail to towarrant warrant any any firm firmconclusions. conclusions. A fine-grained fine-grained biotite-poor granite intruded into the granite dike dike has has been been intruded the banded mineral lineation lineation in banded gneiss. A mineral in the the dike dike trends trends S. S. 450 450 W. and plunges plunges W. and approximately 800,which whichisisclose close enough enoughtotothe theorientation orientation of of the approximately 80°, the F2 F2 fold fold axes to to imply the FF2 folding event and the formation axes imply aa connection connection between between the folding event and formation 2 lineation in of the the mineral mineral lineation in the the granite. granite. The Cambrian CambrianMt. Mt.Simon SimonFormation Formationisis exposed exposedononthe the south south side side of The of U.S. U.S. Hwy. the east east of of the the Black Black River. River. Hwy.10, 10,just just to to the 32 32 �LOCALITY LOCALITY 13: 13: T.24N.,R..3W. R.3W. (Neillsville 15-minute topotopoT.24N., (Neillsville 15-minute graphic graphic quadrangle, quadrangle, Clark Clark County). County). See map. SeeStop Stop22for for locality locality map. Outcrop on the the north northside sideofof U.S.Hwy. Hwy.10,10,along along Wedges Creek, Creek, Outcrop is is on U.S. Wedges just justbelow belowSnyder SnyderDam. Dam. NE~, NE¼, NE~, NE¼,Sec. Sec. 10, 10, LOCATION: LOCATION: AUTHOR: AUTHOR: Gneiss and SnyderDam Dam Gneiss and granite granite atatSnyder R.S. Maass R.S. Maass (1980) (1980) DESCRIPTION: The gneiss below Snyder any other gneiss gneiss The gneiss below Snyder Dam Damisisunlike unlike any observed this point point in observed upuptotothis in the the Black Black River River region. region. It It isiswispy wispy rather rather than banded, banded,and anditit is highly and quartz quartz rich. The than highlymicaceous micaceous and The average average quartz content is over over 50%, 50%, with biotiteand andmuscovite muscovite being being the the other other major major content with biotite constituents. Microcline content content isisgenerally generallybelow below10%. 10%. The The gneiss contains aa well contains well developed developed foliation foliation and and lineation, lineation, but but due due to to its itsunlayered unlayered nature it isis not nature it not possible possible to detect detect isoclinal FF folds, even even though though the the unit was probably subjected subjected to to this was probably this deformation. deformation. Ti~ht Tijht F2 F2 folding folding has has folded folded the the foliation, during F1 foliation,which whichisispresumed presumed to to have have formed formed during F folding. A pink biotite-poor granite pink biotite—poor granite which which has hasintruded intrudedthe the gneiss gneiss isis unfoliated, unlineated, and and as as best best can can be be determined determined in thin section, section,undeformed. undeformed. The The unlineated, in thin age granite is is unknown; unknown; it may be slightlyyounger younger than than the the ageof of the the granite it may be just just slightly 1850 may be be related related to to the the 1765 1765 m.y. m.y. old old granites granites 1850m.y. m.y.old oldgranites, granites, or or ititmay found throughout throughout the the state. found The CambrianMt. Mt.Simon SimonFormation Formation overliesthe the gneiss gneiss and and the the granite The Cambrian overlies along the the west westbank bank ofofWedges Wedges Creek. Creek. LOCALITY LOCALITY 14: 14: LOCATION: AUTHOR: AUTHOR: Schist and gneiss, gneiss,Cunningham Cunningham Creek Creek Schist and NW~, Sec.Sec. 26, 26, T.24N., R.2W. (Neillsville l5-minute topoNW¼,SW~, SW¼, T.24N., R.2W. (Neillsville 15-minute graphic quadrangle, Clark Clark County). County). See graphic quadrangle, SeeStop Stop22for for detailed location Outcrop is is east locationmap. map. Outcrop east of of State State Hwy. Hwy. 73-95, 73-95, on on the the north bank bank ofofCunningham Cunningham Creek. Creek. R.S. Maass R.S. Maass (1980) (1980) DESCRIPTION: Biotite schist,quartzofeldspathic quartzofeldspathicgneiss, gneiss,and andaugen augen gneiss gneiss are are Biotite schist, exposedaa short short distance exposed distance upstream upstream from from the theHwy. Hwy. 73-95 73-95 bridge bridgeover overCunningham Cunningham Creek. The Thebiotite biotite schist primarilyofof quartz quartzand andbiotite, biotite, with schist isis composed composed primarily with subordinate feldspar. Quartzofeldspathic subordinate bands and and augen augen bearing bands bands are are Quartzofeldspathic bands have been interlayered with schist. All ofofthese theseunits units have beenmeta— metainterlayered with the the biotite biotite schist. morphosed totoamphibolite morphosed amphibolitefacies faciesand anddisplay display granoblastic granoblastic textures. Augen Thebiotite biotite gneisses those described described at Stop Stop 44 also also occur occur here. here. The qneissessimilar similar to those beenisoclinally isoclinally folded schist and and interlayered gneisses gneisses have have been folded during during F1 F] F9 axes plunge deformation, folded during during F9 F? deformation. deformation. F fold axes plunge deformation, and andtightly tightly folded steeply inin all directions, trendisisS.S. 50 520W. steeply directions, but but the the dominant dominant trend W. with with aa plunge plunge of 80°. 80 0 . �LOCALITY 15: 15: LOCALITY Center Sec. Sec. 27, 27, T.24N., T.24N., R.2W. R.2W.(Neillsville (Neillsville 15-minute Center 15-minute topographic topographic quadrangle, Clark County). SeeStop Stop22for for detailed location quadrangle, County). See locationmap. map. LOCATION: AUTHOR: AUTHOR: Cunningham Schist and and gneiss, gneiss, Black BlackRiver Riversouth southof of CunninghamCreek Creek R.S. R.S. Maass Maass (1980) (1980) DESCRIPTION: A diverse diverse group group of schists, schists,gneisses, gneisses,and andmetavolcanic metavolcanic rocks rocks occurs along long stretch stretch ofofsemi-continuous semi-continuous outcrop outcrop along along the occurs along aa 0.6 0.6 mi. ml. long Black The same samebiotite biotite Black River, River,downstream downstream from from the themouth mouth ofofCunningham Cunningham Creek. Creek. The schist with interlayered interlayered quartzofeldspathic quartzofeldspathic units Locality 14 14 schist with units as as that that at at Locality appears at the themouth mouth ofofCunningham Cunningham Creek. Creek. Metamorphosed Metamorphosed basaltic basalticand anddacitic dacitic appears dikes crosscut crosscut the the schist; the dikes the basalt basaltisisnow nowan an amphibolite. amphibolite. Mafic banded banded gneisses gneisseswith with augen augenbearing bearinglayers layersand andaugen augen free freelayers layerssimilar similar to those those upstreamfrom fromthe theNeillsville Neillsville Augen upstream Augen Gneiss Gneiss (Stop (Stop 3) 3) crop crop out out mear mear the the major major bend in the Black an augen augengneiss gneiss containing bend in Black River. River. Further downstream, downstream, an feldspar porphyroclasts porphyroc1asts up up to to 44cm cm isisexposed. exposed. The encountered is The next next unit encountered a gneissconsisting consistingofof sharply sharply defined defined quartzite, quartzite, quartzofeldspathic, a banded banded gneiss quartzofeldspathic, and amphibolite layers. The The final final outcrop and amphibolite outcrop is is aalayered layered nietadacite metadacite to metarhyolite sequence, whichononthe thebasis basis of of structural metarhyo1ite sequence, which structural grounds grounds appears appears to be be younger than the gneisses. The dacites dacites and andrhyolites rhyolites are are porphyritic, younger than gneisses. The containing quartz quartz and and feldspar porphyroclasts porphyroclasts up up to 2mm 2mm inin aa matrix grains containing matrix of grains metavolcanicrocks rocks have havebeen beensignificantly significantly granulated less than than 0.1 0.1mm. mm. The The metavolcanic granulated and moderatelyrecrystallized. recrystallized. The and moderately which varies varies from from 11 mm mm to cm The layering, layering, which to 22 cm thick, strikesN.N.40° 40 0E.E.and anddips dips68° 68 0NW. NW. thick, strikes LOCALITY 16: LOCALITY NW¼,SE\, SE¼, Sec. T.23N.,R.3W. R.3W.(Hatfield (Hatfield 7½-minute NW\, Sec. 25,25,T.23N., 7~-minute topographic quadrangle, Clark County). quadrangle, County). The The gneiss along the the gneiss crops crops out out along western shore of Lake Arbutus at Big Spring; a small island western shore of Lake Arbutus at Big Spring; a small occurs offshoreatatthis this locality. locality. See occurs offshore See p. 30 general map map 30 for for general location. LOCATION: AUTHOR: Banded gneiss, Spring Banded gneiss, Big Spring R.S. Maass Maass (1980) (1980) R.S. DESCRIPTION: The bandedgneiss gneissatatBig BigSpring Spring is is mineralogically The banded mineralogicallyand and structurally structurally similar similartotothe theEast EastFork Forkgneiss gneiss at atStop Stop 6. 6. Exposure Exposure here here is poorer than at at Stop Stop 6,6, but but this is;sa amore poorer than more accessible accessible location. The melanoThe nielanocratic bearing, just as cratic layers layers ofofthe thegneiss gneissare arehornblende hornblende bearing, as in in the the East East Fork Fork 0 0 gneiss. F? F9 fold fold axes trend N. 85° E. and S. 85° W. with plunges ranging axes N. 85 E. and S. 85 W. with plunges ranging up up 0 to 35° 35 in in bach ~ach direction. 34 34 �LOCALITY LOCALITY 17: Gnelss at Morrison Gneiss Morrison Creek Creek LOCATION: NE corner, 22, T.22N., T.22N., R.3W. R.3W. (Hatfield (Hatfield7½-minute 7~-minute topographic topographic NE corner, Sec. Sec. 22, occurs in bed Outcrop occurs bed of of Morrison Morrison quadrangle, Jackson County). County). Outcrop quadrangle, Jackson Creek, downstream fromCounty CountyHwy. Hwy.KKbridge bridgeover over the the creek. See Creek, downstream from map, page page30, 30,for for general general location. map, AUTHORS: AUTHORS: W.R. Van and R.S. R.S. Maass W.R. Van Schmus Schmus and Maass (1980) DESCRIPTION: The pink, fine-grained fine-grained quartzofeldspathic quartzofeldspathic gneiss gneiss that Theunit unit is aa pink, is similar Black River downstream similartotomuch muchofofthe thegneiss gneissalong alongthethe Black River downstream from from Arbutus Arbutus Dam. Rb-Sr Creek do Dam. Rb-Sr analyses analyseson onsamples samplesofofgneiss gneissfrom fromMorrison 4orrison Creek do not not define isochron, but but they they appear to be less disturbed good isochron, appear to be less disturbed than than those those from from near near aa good Arbutus Damandand consistent withananage age 2.8b.y. b.y. for for the Arbutus Dam areare consistent with of of2.8 the gneiss. gneiss. It It appears that that the Penokean wereless less severe severe here here with appears the effects effectsof of Penokeanmetamorphism metamorphism were regard to to chemical alteration. The The gneiss gneiss does does have haveaa pronounced pronouncedfoliation, foliation, chemical alteration. regard 0 roughly transverse to the stream with a general strike of N. 160 W. and roughly transverse to stream with general strike of N. 16 W. and aa 0 dip of dip of 78° 78 E. E. LOCALITY LOCALITY 18: 18: LOCATION: Gneiss, on Black Black River Gneiss, Powerhouse Powerhouse on NW~, Sec. sec. NW¼, Sec.16, 16,and andSE~, SE¼, sec.9,9,T.22N., T.22N., R.3W. R.3W.(Black (Black River River Falls Semi— l5-minute topographic quadrangle, Jackson County). 15-minute quadrangle, Jackson County). Semicontinuous exposureoccurs occursononboth bothbanks banksofofthe theBlack BlackRiver River for for continuous exposure powerhouse. See See map map on on upstream of of the thepowerhouse. approximately 11 mile upstream following for detailed detailed location. following page page for AUTHOR AUTHOR R.S. Maass Maass (1980) (1980) PS. DESCRIPTION: DESCRIPTION: This isan anexcellent excellentexposure exposureofof Archeangneisses gneissesand andpresumed presumed This is Archean early Porterozoic Porterozoic andesitic andesitic and and dacitic daciticdikes, dikes,plus plus a gabbroof of unknown age. age. a gabbro unknown The The gneisses gneissesare arethinnly thinnly to massively massively layered, layered, ranging ranging inincomposition composition from from granitic to to dioritic, dioritic,with withtonailtic tonalitic to granodioritic compositionsdominating. dominating. to granodioritic compositions Many Manyofof the the layers layers are augen augen gneisses gneissescontaining containing feldspar feldspar porphyroclasts porphyroc1asts averaging 11 cm cm inin size, but also also containing containing quartz quartz porphyroclasts. porphyroclasts. The size, but gneisses daciticdikes dikeswhich whichhave havebeen been gneisses have havebeen beenintruded intrudedbybyandesitic andesitic to to dacitic A gabbro deformed gabbro deformedand andrecrystallized. recrystallized. Some Someofofthe thedikes dikesare are porphyritic. porphyritic. A near the the powerhouse powerhouse is Is weakly foliated, unit near weakly foliated,but butthe theorigin originofof the the foliation foliation is unclear. unclear. The to to amphibolite but The gneisses gneisses have have been beenmetamorphosed metamorphosed amphibolitefacies, facies, but it cannot be be ascertained ascertained at at what what grade grade the crosscutting crosscutting dIkes dikes were were it cannot recrystallized. Isoclinal F1 F folding folding produced produced ananaxial thegneisses gneisses axial planar planar foliation foliation ininthe which is re1ativ~lyconsistent consistentininorientation orientationin in downstream three-quarters three-quarters which is relatively thethe downstream of the the exposure, exposure, striking N. 450 45 0 W. W. and F2 folds striking N. anddipping dippingvertically. vertically. Tight F2 become more common toward At becomeprogressively progressively more common towardthe theupstream upstreamend endofof the the outcrop. At the upstream end folding is disharmonic (Figure the upstream endofofthe the exposure, exposure,FF2 folding disharmonic (Figure 14). 2 35 �1ap for localities 20 r'~ap for localities 18, 18, 19, 19,20 Disharmonic FF? folding Figure 14. Figure 14. Disharmonic in the the gneiss gneiss at folding in the upstreani end of of the Pwerhouse the upstream end Powerhouse outcrop. Interference patterns patterns here here may maybebedue duetotofolding foldingof of isoference folds, as clinal FF1 as at at Stops Stops 33 and and 7. 7. l folds, 36 36 �LOCALITY 19: LOCALITY NE¼, SE¼, Sec.17, 17,T.22N., T.22N.,R.3W. P.3W.(Black (BlackRiver River Falls Falls 15-minute NE~, SE~, Sec. 15-minute See map map on on preceeding quadrangle, Jackson Jackson County). County). See topographic quadrangle, from PowerhouseRoad Road page. Proceed 0.1 mile milesouth southfrom Proceed approximately approximately 0.1 Powerhouse The dirt dirt on aa gravel gravel and road to to an dirt road. on and sand sand road an overgrown overgrown dirt road. The road leads leads to aa small, small,abandoned abandoned quarry. quarry. road LOCATI ON: LOCATION: AUTHOR: AUTHOR: Banded Bandedgneiss gneiss at at quarry quarrynear nearPowerhouse Powerhouse R.S. R.S. Maass Maass (1980) (1980) DESCRIPTION: A banded consisting of ofalternating bandedgneiss gneiss consisting alternatingthin thin to to thick biotite free and biotite rich free and biotite richquartzofeldspathic quartzofeldspathic layers layers isisexposed exposed in in aasmall small quarry near the the Black near Black River, River. Many and melanocratic melanocratic layers layers contain Manyofof the the 1eucocratic leucocratic and alkali feldspar cminin length. Both alkali feldsparporphyroclasts porphyroclastswhich whichsometimes sometimes reach reach 33 em isoclinal tight F2 isocl inal F1 Fl and and tight F2 folds folds are are present present in in the the gneiss. gneiss. LOCALITY 20: 20: LOCALITY NE¼, NE~, NE~, NE, Sec. Sec. 30, 30, T.22N., T.22N., R.3W. R.3W. (Black (Black River River Falls Falls 15-minute 15-minute See preceeding page topographic quadrangle, quadrangle, Jackson Jackson County). County). See page topographic Outcrop is located for location locationmap. map. Outcrop located along along Halls HallsCreek Creekbetween between and the the Black Black River, River, and County Hwy. Hwy. E and and on on the west west bank bank of the the Black River from the the mouth of Halls Creek. Black River just justdownstream downstream from mouth of Creek. LOCATION: AUTHOR: Gneiss at Halls Halls Creek Creek Gneiss R.S. Maass Maass (1980) (1980) P.S. DESCRJPfION: DESCRIPrION: The basement rocks at at this crop out just justbelow below the the The basement rocks thislocality locality crop They are are micaceous micaceousfelsic felsic Cambrian Mt. Mt. Simon Simon Formation. Formation. They unconformity theCambrian unconformity with the The best best exposures are along units and clayey clayey intermediate "intermediate to mafic units. The exposures are along units and to rnafic Halls Creek where the Mt. Mt. Simon Simon Formation Halls Creek wherethe therelationship relationship with with the Formationisis clearly visible, visible. There Thereare aretwo twopossible possibleinterpretations interpretationsfor for the the rocks rocksat at this locality:a)a)they theyare arelow lowgrade gradeearly ear'lyProterozoic Proterozoicsedimentary sedimentary or volcanic volcanic locality: latter units; extremely weathered units; ororb)b)they theyareare extremely weatheredArchean Archean gneisses. gneisses. The The latter possibility stronglypreferred preferred since, since, 1)1)the therocks rocks appear appear very very similar possibility isisstrongly the deeply deeply weathered weathered portions the Hatfield HatfieldGneiss Gneiss exposed exposed at Stop 7, to the portions of of the at Stop which is also just below the unconformity; 2) some of the units here which is also just below the unconformity; 2) some of the units here consist consist entirely ofofclay entirely clayminerals mineralsplus plusquartz, quartz,which whichsuggests suggests weathering weathering rather rather than than low metamorphism;and andJ)3)there there are are no no known knownlow lowgrade gradeearly early Proterozoic low grade grade metamorphism; sedimentsoror alurnin(1Us aluruiriousvolcanic volcanicr'ocks rockselsewhere elsewhereinin the the Black Black r~iver River reqion. reqion, sediments "J) 3 •7 .J. �LOCALITY 21: LOCALITY 21 Gnelss andtonalite, tonalite, Black Gneiss and Black River River Falls NE~, NE~, Sec. l5-minute NE¼, NE¼, Sec.22, 22,T.21N., T.21N.,R.4W. R.4W.(Black (BlackRiver River Falls 15-minute quadrangle, Jackson Jackson County). County). See topographic quadrangle, SeeStop Stop88for for detailed LOCATION: LOCATION: East bank bankof of the the Black map. East Black River, 0.2 0.2 ml. mi. west west ofofU.S. U.S.Hwy. Hwy. map. 12. Dirt path path statring statringnear nearsharp sharp bend bend in road road leads leads to outcrop. outcrop. AUTHOR: AUTHOR: R.S. Maass (1980) (1980) R.S. Maass DESCRtPTION: The The gneiss banded and plagioclase, gnetss is Is banded andconsists consistsofof quartz, quartz, plagioclase, DESCRtPTION: alkali feldspar, feldspar, blotite, biotite,hornblende, hornblende, chlorite, chlorite,and andepidote. epidote. Thin Thin to to thick in the thegneiss gneissvaries variesprom from compositional compositional extremes extremes of quartzofeldspathic quartzofeldspathic layering in bands containing alkali bands containingas asmuch muchasas40% 40% alkalifeldspar feldspartoto bands bandsconsisting consistingentirely entirely and minor minor quartz. quartz. The The gneiss has been been intruded of hornblende, hornblende, plagioclase, and gneiss has by fine-grained diorite dioriteand anddiabase diabasedikes dikeswhich whichhave havebeen beenmetamorphosed metamorphosed to by fine—grained amphibolite and by by a fine fine grained grained lineated lineatedtonalite tonalitewhich whichwas was probably probably amphiholite facies fades and subjected to to the thesame same grade grade ofofmetamorphism. metamorphism. Age among the Age relationships relationships among units have have not not been been established intrusive units establisheddue duetotolack lackofof suitable suitable field field relationships. Isoclinal F1 F, folding folding produced produced ananaxial axial planar planarfoliation foliation which hasbeen beenopenly openlytototightly tiht1y folded which has folded during during F,F deformation, deformation. F2 F fold fold axes intn the defined /3 p froffl fro~ aa stereographic stereographic 2plot axes the gneiss, gneiss, statistically statistically defined plot of and mineral mineral lineations the Intrusive intrusive units units are are poles to poles to foliation, foliation, and lineations in the essentiallycolinear, co1inear,trending trending southeasterly andplunging plungingbetween between500 50 0 essentially southeasterly and and and 75°. 75°. LOCALITY LOCALITY 22: 22 LOCATION: LOCATION: AUTHOR: AUTHOR: Quartzite, Silver SilverMound Mound NE¼,NW~, NW¼, T.21N., R.3W. (Black River Falls15-minute l5-1nute NE~, Sec.Sec. 20,20, T.21N., R.3W. (Black River Falls See Stop Stop 88 for topographic quadrangle, quadrangle, Jackson Jackson County). County). See topographic map. Follow Follow a dirt dirtroad roadfrom fromBauer BauerRoad Road to to reach reach detailed detailed map. Silver Mound. Silver Mound. R.S. R.S. Maass Maass (1980) (1980) Thequartzite quartzite at Silver is white, nearly DESCRIPTION: The SilverMound Mound is nearly pure, pure~ and and DESCRIPTION: It isispoorly strongly lineated. It poorlyexposed, exposed, occurring occurring mostly mostly as as loose loose blocks blocks strongly lineated, It isisbelieved on of, and and along along the the sides sides of, of,the themound. mound. It believedtotohave haveformed formed on top top of, from chert beds associatedwith with the the Archean volcanic rocks rocks of of the from chert beds associated Archean volcanic the region. region. 38 �LOCALITY LOCALITY 23: LOCATION: LOCATION: AUTHOR: AUTHOR: Jackson County Mine Jackson County Iron Mine SW~, Sec. 15-minute topotopoSW¼, Sec.15, 15,T.21N., T.21N.,R.3W. R.3W.(Black (BlackRiver River Falls Falls 15-minute See p. p. 30 graphic quadrangle, quadrangle, Jackson Jackson County). County). See 30 for formap. map. R.S. R.S. Maass Maass (1980) (1980) DESCRIPTION: DESCRIPTION: The The Jackson in aa banded banded magnetite JacksonCounty CountyIron IronMine Mineisis In magnetite iron formation a alenticular center. The formationwhich whichcontains contains lenticulartalc talc schist schist zone zoneinin its center. iron formation formation isissurrounded surrounded on on both both sides sides by by aluminous aluminous quartzofe1dspathic quartzofeldspathic schists. Previously, magnetite was primary iron iron Previously, magnetite wasbelieved believedtoto be be the the only only primary oxide present hematite due duetoto weathering weatheringcaps capsthe thedeposit), deposit), but oxide present (secondary (secondary hematite but recently primary encounteredinin the the northwest northwest corner corner of of the primary hematite hematite was was encountered pit. The iron-richamphiboles,and amphibo1es,and The other other major major minerals minerals include include quartz, iron-rich garnet. The consists ofofthree threedominant dominantmineral mineralassemblages: assemblages: 1) 1) The schist schist consists quartz-chlorite-muscovite-anda1usite; quartz-chlorite-muscovite-andalusite;2)2) quartz-biotite-chlorite-staurolitequartz—biotite-chlorite-staurolitegarnet-andalusite-muscovite; garnet-andalusite-muscovite; and and3)3) quartz-biotite-plagioclase-muscovite quartz-biotite-placiioclase-muscovlte (Jones, 1978). 1978). (Jones, F folding folding produced produced aapenetrative F Isoclinal F1 penetrativeaxial axial planar planarfoliation. foliation. F1 axes plunge plunge lsteeply steeplyand andare areaccompanied accompanied by by parallel mineral mineral lineation l fold fold axes Axesofofopen opentototight tight FF2 folds defined by by the the orientation orientation ofofamphiboles. amphiboles. Axes folds defined are also parallel parallel to and F, F fold foldaxes axes are are are also to the the mineral mineral lineation; lineation; thus, thus,F,F,and believed be colinear. colinear. Structurally the the iron iron forthation formation 'ts ~s essentially believed to be identical totothe theArchean Archean gnelss gneiss terrane. terrane. Jones Jones (1978) the (1978) concluded concluded that that the does not theearly earlyProterozoic ProterozoicSuperior-type Superior-type model, model, but but iron formation formation does not fit fit the It may rather ititappears appears totobebeofofthetheArchean ArcheanAlgoma-type. Algoma-type. It may have have been been deposited in small basin basin on volcanic center. center. deposited in aa small on the the flanks flanks of aa volcanic Jones (1978) metamorphic events; was Jones (1978)defined definedtwo twodistinct distinct metamorphic events;the the first first was amphibolite fa~ies, thesecond second was was upper upper greenschist Based on on amphibolite fades, the greenschist facies. fades. Based textural features featuresheheconcluded concluded that thatthe thesecond secondevent eventwas was aamajor majorthermal thermal textural pulse, effect. The pulse, not not merely merely aa retrograde retrograde effect. Thepossibility possibility of of an an earlier, much suggested by presence of muchhigher higher grade gradeevent eventthan than these these two two is is suggested by the presence of kyanite, but the phase relationshipsofofthis this mineral mineralare arenot notatat all all clear. phase relationships clear. kyanite, but the 39 39 �DISCUSSION DISCUSSION OF OF THE THE TECTONIC TECTONIC HISTORY HISTORY In recent years years itithas hasbecome become increasingly increasinglyapparent apparent that thatthe thePenokean Penokean In recent Orogeny deformational Orogenywas wasa amajor majorigneous, igneous,metamorphic, rnetarriorphic,and and deformationalevent eventinin central central along the Wisconsin Wisconsin. This has has been been documented documented along Wisconsin River Riverbetween between Stevens Point Point and Wisconsin Rapids Rapids (Maass (Maassand andothers, others, 1980), 1980), and and as as this Stevens and Wisconsin guidebookillustrates, illustrates, along guidebook along the the Black Black River River as as well. Studies Studies in in progress progress indicate that of Wisconsin that the the entire entirecentral centralportion portion of Wisconsinhas hasbeen been subjected subjected folding during to regional regional amphibolite amphibolitefacies faciesmetamorphism metamorphism and and polyphase polyphase folding during the Penokean Penokean Orogeny. Orogeny. Periokeandeformation deformationbegan began withisoclinal isoclinal F, Penokean with F folding foldingwhich whichproduced produced aa penetrative axial axial planar planar foliation foliation parallel penetrative parallel totobanding blnding in in gneisses, gneisses, schists, schists, and iron iron formation, in fold the layering is and formation, except except in fold hinges hinges where where the is transected transected Susequentlythe thefoliation foliation was tightly totoopenly by foliation. was tightly openly folded folded during during by foliation. Susequently axial planes planesofof these thesefolds folds are are at at small F ; the F?; the nonpenetrative nonpenetrative axial small to large large the Wisconsin WisconsinRiver Riverthere thereisisaadistinct distinct angles Along the agles to FF foliation. Along break betwen tight tight and fold styles, break betwe~n and open open fold styles, thus thusfolding foldingcan canbebeseparated separated but along along the the Black Black River River there there is aa complete into F2 F~ and and FF3 phases, phases, but complete con coninto tinuumLfrom to open open folds and no possible. The The nontinuum fromtight tght to folds and no division division is possible. penetrative axial planes planes of penetrative of FF folds along along the the Wisconsin Wisconsin River River are are always always foliation. All fold at aa high high angle angle to the the fOliat1on. foldaxes axes are are colinear, colinear, and and parallel parallel to aa penetrative Archean penetrative mineral mineral lineation lineationwhich which isispresent presentininthethe Archeangneisses gneisses coliriearity of and most mostofofthe the early early Proterozoic Proterozoic intrusive rocks. and rocks. The The colinearity undersimilar similar stress structures suggests suggests that they they were were formed formed under stress conditions conditions deformational and during an an extended extended Penokean Penokean deformational and metamorphic metamorphic event. The complete completePenokean Penokean deformationalhistory history is is recorded The deformational recorded in gneisses gneisses of confirmed confirmed Archean not Archeanage, age,but butthe the presence presenceofofthese thesestructures structures is is rtot sufficient evidence to a rock, sufficient evidence by by itself itselfforforassigning assigningananArchean Archean age age to rock, since since there may also Proterozoic units which which were were subjected there may also be beearly early Proterozoic subjected to to the entire period gneissatatBig Big Falls Falls in entire period ofofPenokean Penokean deformation. deformation. A banded banded gneiss Eau indicative ofofpolyphase polyphase deformation deformation EauClaire Claire County Countycontains containsstructures structures indicative similar to to those those inin Archean Archean rocks rocks elsewhere elsewhereininthe theterrane, terrane,yet yet the the unit yields age (Introduction: (Introduction: Fig. Fig. 3). this yields an an early Proterozoic Proterozoic age 3). However, However, this gneiss is one of the thoroughlyrecrystallized recrystallized units units in the gneiss is one of the most most thoroughly the region, region, anditit isis not and not yet yetclear clearthat thatthe theage ageobtained obtained isisthe theprimary primary age age of the the gnei ss. gneiss. In the In the Black Black River River valley there there isisaastrong strongcorrelation correlationbetween between the the age of emplacement early Proterozoic Proterozoic intrusive intrusive rocks age of emplacement ofofearly rocks and and the the character character of the Theoldest oldest units units are the structure structurepresent present within withinthem. them. The are foliated foliated and and lineated; younger units but are are generally generally only only lineated; younger units may maycontain containa afoliation, foliation, but units tend lineated; and and the the youngest youngest units tend to to be be completely completely devoid devoid of any any prepreferred However,even evenininthe the unfoliated unfoliated and ferred orientation. However, and unlineated unlineated rocks, rocks, microscopic textures reveal microscopic reveal that thatsome someofofthem themhave havebeen been granulated granulated and and recrystallized (Lake Granite, Black recrystallized (Lake Arbutus Arbutus Granite, Black River River Falls Granite). Granite), Post kinematic granitic granitic rocks rocks inincentral centralWisconsin, Wisconsin. dated dated atat1760 1760 m.y., kinematic m.y. , may may or may may not be be assigned assigned totothe thePenokean PenokeanOroqeny Orogeny' structurally they are are structurally they distinctly thethe Penokean distinctlydifferent differentfrom fromthe therest rp.stof of Penokean intrusives intrusives 40 �Emplacement theearly earlyProterozoic Proterozoic intrusive intrusive rocks Emplacement of ofthe rocks occurred occurred throughthroughout the waning stages of F1 deformation and continued beyond the final out the waning stages Fl deformation and continued beyond the final stages stages activity. F1 deformationproduced producedthe thefoliation foliation present of kinematic kinematic activity. F] deformation present in in someofofthe theintrusive intrusive rocIs, some rocRs, and and the the older older intrusives, intrusives,having havingbeen been subsubjected to F1 Fl deformation deformation for greater period period of oftime timethan thanthe theyounger younger jected to for aa greater However, the generally contain contain aa better better developed developed foliation. intrusives, generally foliation. However, Neillsville Granitedemonstrates demonstrates that thatusing using the thedegree degree ofofdevelopment development of Neil]svi]le Granite Jue to foliation an indicator indicatorofof agecan canbebean an unreliable unreliablemethod. method. Due foliation asasan age inhomogeneous deformation graniteisis foliated foliated ininsome inhomogeneous deformation thethe granite some areas areas and and unfoijated in others. In addition, properties of aa given unfoliated others. In addition, the the mechanical mechanical properties given rock significantly significantly influence rock influence its itsstructural structuralresponse responsetotoa adeformational deformational event, event. The The Neillsville Granite, which which is unfoliated at at Stop Stop 2, is is intruded intruded Neillsville Granite, is unfoliated this locality localitybybyaadacite dacite dike dike which which is strongly strongly foliated. at this Although the the vast vast majority of Although of linear linearPenokean Penokean structures plunge plunge steeply, someare arenearly nearly horizontal. horizontal. There some There may mayalso alsobebeconsiderable considerablevariation variation in twomost mostlikely likely the trend of the the structures structures from from outcrop outcrop to to outcrop. outcrop. The The two the trend explanations for this variance are that the fold axes and mineral lineaexplanations for variance are that the fold axes and mineral lineations were foldedduring duringa alater later event, event, or or that that folding was orioinally tions were folded was originally noncylindrical. Stereographic Stereographicplots plots of of linear linear structural structuralelements elements have have not anypatterns patternsofof refolding, refoldino, therefore possibility not revealed revealed any therefore the the second second possibility is preferred. preferred. In In numerous numerous localities noncylindrical folding foldinghas hasbeen been localities noncylindrical observed mesoscopic scale,and andthere thereisis no no reason reasontoto believe believe that observed ononaamesoscopic scale, that it didnot notalso alsooccur occuronona amacroscopic macroscopic scale. scale. Unlike northern northern Wisconsin, Wisconsin, it did wherenortheasterly northeasterly structural structural trends where trendsseem seem to to dominate, dominate, there there isisnonodomdominant structural trend trend in in the the Black Black River River valley. inant structural Oneintriguing intriguing question remains to to be be resolved resolved is whether One question which which remains whether or not deformation occuredinincentral central Wisconsin during the deformation and and metamorphism metamorphism occured Wisconsin during the Archean. Three Three localities suggest that did. A A migmatite of ofArchean Archean localities suggest thatitit did. age (Van Schmusand andAnderson, Anderson, 1977)isisexposed exposedinin aa quarry quarry near age (Van Schmus 1977) near the the Wisconsin Wisconsin River, ininLinwood Linwood Township. Township. A A steeply plunging plunging mineral mineral linea— lineation which which formed formed during during the thePenokean Penokean Orogeny hinges of of tiori Orogenytransects transects the the hinges The relationship gently plunging isoclinal folds in the migmatite. The relationship gently plunging isoclinal folds in the migniatite. requires that the requires that the folds folds be be older older than than the the mineral mineral lineation, lineation, and and the the gentle plunge plunge of does not thepattern patternofofPenokean Penokean folding gentle of the the folds folds does not fit fit the Archean in the the area, area, suggesting suggesting that thatthe thefolds foldsareare Archeanininage age(Maass (Maass and and others, 1980). 1980). The The other are in the the Black Black River River valley: othertwo twolocalities localities are The Hatfield Hatfield in the the Hatfield HatfieldGneiss Gneiss and and ininthe theJackson Jackson County County Iron Iron Mine. Mine. The Gneiss contains contains relict Gneiss relicthypersthene hypersthene(Dubois (Duboisand andVan VanSchmus, Schmus, 1978), 1978), and and the formation contains contains significant quantitiesofofkyanite kyanite(Jones9 (Jones, 1978). 1978). the iron formation significant quantities These Theseminerals, minerals, and andtheir their textures, textures, suggest suggest that thatthere theremight mighthave havebeen been an metamorphic event facies. an earlier earlier metamorphic eventinin the the upper upperamphibolite amphibolitetoto granulite granulite facies. In addition there there is one one unexplained, unexplained, isoclinally In addition isoclinally refolded, refolded, isoclinal fold ininthe theHatfield HatfieldGneiss Gneisswhich which may may be be evidence evidencefor for an an older older folding event. 41 41 �Theselines lines of evidence are not not conclusive, These evidence are conclusive, and and the features features could could be be attributed to to an an early earlyProterozoic Proterozoic event. event. On On the hand, many many of the other hand, of the Archeangneisses gneissesinInthe the Black Black River River Valley Valley were were derived derived from from aa volcanicvolcanicArchean plutonic terrane, to expect and Ititwould would be be reasonable reasonable to expect that the the volcanic volcanic terrane, and rocks were were deformed deformed during during an an orogeny orogeny rocks during emplacement emplacementofofthe the plutons plutons or during associated Finally,most most other otherArchean Archean terranes terranes associatedwith with the the igneous igneousactivity. activity. Finally, Lake Superior Superior region region contain contain significant significant Archeandeformation deformation and and the Lake in the Archean metamorphism, sosothat thethesame is istrue Archean rocks metamorphism, that we weassume assume same truefor for the Archean rocks of the River valley. However, Penokean effectshave havelargely largely obliterated obliterated the Black Black River However, Penokean effects any Archean tectonic features. any Archean tectonic ACKNOWLEDGMENTS ACKNOWLEDGMENTS R. S. Maass hasreceived receivedsupport support for for the R. S. Maass has the work work covered covered here here from from the the Wisconsin Geological and Natural History Survey and the Wisconsin Geological and Natural Survey and the Department Department of Geology, UW-Madison. UW-Madison. W. W. R. R. Van Van Schmus Schmus has has been been supported by byNSF NSF grant EAR75-15007 andbybya agrant grant from from the EAR75-l5007 and the General General Research Research Fund, Fund, University University of Kansas. Much Muchofof the the field field work at Stop Kansas. work and and mapping mapping at Stop 77 was was done done by by 3. J. F. F. DuBois researchproject project at at the DuBois asasaaresearch the University UniversityofofKansas Kansas under under the grants the grants to readearly earlydrafts drafts of the W.R.V.S. L. L. G. G. Medaris Medaris read the text text and and provided provided many many to W.R.V.S. helpful comments. helpful comments. 42 �REFERENCES REFERENCES DuBois, and Van Van Schmus, Schmus, W.R., and geochronology geochronology of DuBois, J.F., J.F., and W.R., 1978, 1978, Petrology and of Archean Lake Arbutus Wisconsin (abs.). Archeangneiss gneissinin the the Lake Arbutus area, area, west-central west-central Wisconsin Program,Twenty-fourth Twenty-fourth Annual AnnualInstitute Institute on Program, on Lake Lake Superior SuperiorGeology, Geology, Milwaukee, 11. Milwaukee, p. p. 11. Jones, 1978, Geology formation and and associated associated rocks rocks of Jones, D.G., D.C., 1978, Geologyofof the the iron formation County Iron Mine, Mine, Jackson Jackson County, County, Wisconsin. Wisconsin. Unpub. M.S. Jackson County the Jackson Unpub. M.S. thesis, Univ. ll7p. Univ. Wisconsin, Wisconsin, Madison, Madison, 117p. Maass, Medaris, L.G., L.G.,Jr., Jr., VanSchmus, Schmus,W.R., W.R.,1980, 1980,Penokean Penokean Maass, R.S., R.S., Medaris, andand Van deformation in central deformation in central Wisconsin. Wisconsin. Geological Geological Society Society of ofAmerica America Special Paper 182, in press. Special Paper 182, press. Myers, Myers, P., Cummings, Cummings, M., M., and and Wurdinger, Wurdinger, S., S., 1980, 1980, Precambrian Precambrian geology geology of Valley, Wisconsin. the Chippewa Chippewa Valley, Wisconsin. Twenty-sixth on Lake Lake Twenty-sixth Annual Annual Institute Institute on Superior Trip No. No.1 Guidebook. Superior Geology, Geology, Field Field Trip 1 Sims, P. K., 1976, 1976, Precambrian Precambrian tectonics and mineral Lake Superior Superior Sims, P. K., tectonics and mineral deposits, Lake region. Economic p. 1092-1118. 1092-1118. EconomicGeology, Geology,v.v. 71, 71, p. Steiger, E., E., 1977, Subcommission Steiger, R.H., R.H.,and andJger, JMger, 1977, SubcommissionononGeochronology: Geochronology: Convention use of decay decay constants constants iningeogeo-and andcosmochronology. cosmochronology. Convention on on the the use Earth 36, p. p. 359-362. 359-362. Earth and and Planetary PlanetaryScience ScienceLetters, Letters, v. v. 36, Van Schmus,W.R!, W.R.,1980, 1980,Chronology Chronologyofofigneous igneousrocks rocksassociated associated with with the Van Schmus, the Penokean orogeny Geological Society of of America, America, Special Special Penokean orogeny in In Wisconsin. Geological Paper182, 182, in in press. Paper press. Van 1977, Gneiss Gneiss and and migmatite of Archean Archean Van Schmus, Schmus,W.R., W.R.,and andAnderson, Anderson,J.L., J.L., 1977, migmatite of age the Precambrian Precambrian basement basement of Wisconsin. Geology, aqe in the of central Wisconsin. v. 5, p.p.45—48. 45-48. v. 43 43 � https://digitalcollections.lakeheadu.ca/files/original/ffb99f6c9aadf623aa9dc3027e119852.pdf 759040e0a41da077762f726d0db4d2b3 PDF Text Text 26th Annual Institute on Lake Superior Geology FIELD TRIP 3 Petrology, Geochemistry, and Contact Relations of the Wausau and Stettin Syenite Plutons, Central Wisconsin GENERALllEO ""EC.....SRIAN GEOLOGY O~ THE [AU CLAIRE REGKlN • f'>:] Gobb'o bil T.oI'ldn,mt. ~~ Volconic. ooa _,,,,,,n,, ~ .o.",ph,Do''''' May 10,1980 University of Wisconsin-Eau Claire �26TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY FIELD TRIP #3 THE PETROLOGY) GEOCHEMISTRY AND CONTACT RELATIONS OF THE STETTIN AND WAUSAU SYENITE PLUTONS CENTRAL WISCONSIN by Mohan K. Sood Department of Earth Sciences Northeastern Illinois University Chicago, Illinois 60625 Paul E. Myers Department of Geology University of Wisconsin Eau Claire, Wisconsin 54701 Louis A. Berlin of Earth Sciences Northeastern Illinois University Chicago, Illinois 60625 Departmen~ May 10, 1980 �Additional copies of this guidebook may be purchased for $5.00 (U.S.) from: ILSG 180, Department of Geology University of Wisconsin-Eau Claire Eau Claire, Wisconsin 53706 or Sales, Wisconsin Geoloqic and Natural History Survey 1815 University AvenueMadison, Wisconsin 53706 �CONTENTS Petrology, geochemistry and contact relations of the Stetti n and Wausau Syenite Pl utons 1 Stop Descriptions 7 Stop 1, Rib Mountain 10 Stop 2, Wausau syenite pluton, core rim ...............•............... 12 Stop 3, Wausau syenite pluton, wall zone 15 Stop 4, Employers' Mutual Insurance Co 19 Stop 5, Stettin syenite pluton, wall zone .......•..................... 25 Stop 6, Amphibole syenite, intermediate zone 32 Stop 7, Amphibole syenite, intermediate zone 32 Stop 8, Stettin syen ite pluton, core zone 36 Mineralogy and miner.al chemistry 38 Petrochemi stry." 46 Di scussi on 51 Comparison of the References ~lausau and Stettin Plutons 54 57 �-1- PETROLOGY. GEOCHEMISTRY AND CONTACT RELATIONS OF THE STETTIN AND WAUSAU SYENITE PLUTONS CENTRAL WISCONSIN by Mohan K. Sood Paul E. Myers Louis A. Berlin INTRODUCTION Alkaline igneous rocks are characterized by the presence of a"'kali feldspars, sodic pyroxenes, amphiboles, and feldspathoids or quartz. Generally, a high content of volatiles (Cl, F, H~O, s, CO 2 ), rare elements (Nb, Ti, Zr, REE, Ta, Bi, and Be), and th~ presenc~ of unusual volatile bearing minerals (sodalite, eudialite, aenigmatite, astrophyllite, villaumite, etc.) impart alakline rocks a character of extreme chemical and mineralogical heterogeneity (Sorenson, 1974)--thus representing an interesting physiochemical system of magmatic crystallization. Alkaline rocks commonly occur in the following tectonic settings: a. Tectonically stable regions of the crust--continental platforms and Precambrian shield areas of North America b. Rift zones--East African Rift, Rhine-Oslo Graben, Montregion Province c. The intersection of fault zones--Greenland (Sorenson, 1970, 1974) GEOLOGY AND GEOCHRONOLOGY OF CENTRAL WISCONSIN The work of Weidman (1907) is the first effort to systematically describe the geology of north central Wisconsin. Recent re-examination of the area has been by LaBerge (1969, 1971), LaBerge and Myers (1972, 1973) and Myers (1973) in refinement of geological mapping and interpretation, Medaris et al. (1973) on the geology of the Wolf River Batholith, Van Schmus (1973), Van Schmus et al. (1980) in geochronological investigations of the region. Koellner (1974) on mineral chemistry, Berlin and Sood (1979) on geochemistry and petrogenetic models. �-2- ~ --~ ~ o / 150 :i? 8 ,, ~. ~ 0 60· r" • C) \ v 'P C''? :HIELD .. " ... •• \0 ; 1\ ~ .~BLACK U HILLS \ b.· \ • 130 0 • ... ~ •••• \ • SHIELD --'~-A ......"\ • • ,p rP " " '1'>-01- ." 140 0 0 •• ... • ..... D.·.· I. ~J:2~-~.: '- . ~ · /~ / W'i,~~"au / ~ • WICHITAS / - / ~ / /. ~ frV c~~ ,"- ·0~ 'i>~ ~ • • I ~ &y~-..; \ I :l~,0 Ch I /3) • • u/~ 'v «V 30 0'--. .... / / i. complexesv \ ~ • .. ~30° I 120 0 90 0 110 0 FIGURE 1 Occurrences of Alkaline Rocks of North America. The tectonic boundaries are generalized. ( From Barbee, 1976) �-3- The oldest rocks of the region are basement gneisses, schists, amph-iblites, and migmatites which are exposed in the Wisconsin RapidsStevens Point area (Figure 6b). However, the Central Wisconsin Cornplex (1800-1900 m.y.) composed of metamorphosed basalts, rhyolites and trachytes (Weidman, 1907, LaBerge and Myers, 1973) and associated granitic rocks (Dutton and Bradley, 1970) form the dominant exposures. (Not if you include rhyolite and granite in southeast Wisconsin, Smith, 1978). Intruding the Central Wisconsin Complex are the 1500 m.y. old anorogenic Wolf River Batholith and the two Wausau Syenite plutons (Van Schmus et al., L. Medaris, Jr., et al., 1975). The Wolf River Batholith is dominantly quartz(?) monzonitic with local phases of syenites, granite, and porphyries. Isolated masses of anorthosite occur within the batholith, but their relationship to the main body is not well understood. The Wausau Syenite Complex comprises a silica-rich phase of granitic quartz syenite-pyroxene amphibole syenite associated at Wausau and a nearly contiguous silica-poor (nepheline bearing) phase at Stettin. Both of the plutons have somewhat elliptical concentric zonal structures. (LaBerge and Myers, 1973). The geochronological stratigraphy is given in Table I. Regional geology is shown in Figure 2, Marathon County, Figure 3. Generalized geology of the two plutons is shown in Figure 4. TABLE I GEOCHRONOLOGICAL RELATIONS OF THE PRECAMBRIAN ROCKS OF CENTRAL WISCONSIN Unit Wausau Syenite Complex 1. Stettin body Major Rock Types Age (m.y.) pyroxene syenite, 1,520* amphibole syenite, tabular syenite, nepheline syenite 2. Wausau body granite, quartz 1,520* syenite, pyroxene+25 amphibole syenite Wolf River Batholith quartz monzonite, 1,500 syenite, granite +25 Central Wisconsin Complex basalt-rhyolite, 1,000-1,900** trachyte, quartz monzonite, granite Basement Complex gneiss, migmatite, uncertain, schist, granite 1,900* * Van Schmus, 1980, Chronology of igneous rocks associated with the Penokean orogeny of central Wisconsin, Geol. Society of America, Spec. Pap. 182 in press. �-4- A [XPLANATION PALEOZOIC tCXf~ Sedimentary rocks PRECAMBRIAN 11-. ":.1 II ~ Wall River 8atholith and Wausau Syenite Camp lex 1;+1 Granitic l;v~'tl Metavolcanic rocks B rocks Ar;~'rE:~:~, - 'I migmatite, schisl, granite, amphibolite FIGURE 2 2A--Generalized geochronologic map of Wisconsin showing the location of the Wolf River Batholith and related Wausau Syenite Complex (after Van Schmus et ~., 1975a) 2B--Inset of Figure 2A. Generalized geologic map of part of central Wisconsin (after Van Schmus et~. 1975b). �A. 7E R 5E R.8E R 9E ,.., l5 z ,.., iXl z I <..T1 ....~ .... I z '"N .... Mil . . o I I,! 2 I !5 ,I R.2E. A 3E R.4E R 5E R 6E - R 9E R 7E AlOE EXPLANATION GEOLOGY OF MARATHON COUNTY,WIS. (Interim Copy) D HI -[]illill WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY r==T"7I ~ LATE PRECA-MBRIAN I=--=:I Iiiiiiiil W .. ~ .•,_ ~ '~.:,;j. , ,. ""', -~ MIDDLE PRECAMBRIAN B o o o I , I Z:1 IS ! I I SCALE EITJ 4 r.:::::l ~ To..... nsn'pJR.nge .. 'ne o''''''''OU.'''O'I>'''''_ EARLY PRECAMBRIAN ~ Figure 3 -- Geologic map of Marathon County by LaBerge and History Survey, Interim Copy. Ge<.logy Mye~, b~ G l l.ee,ge ~nd P E fl,4ye,~ 1979 Wisconsin Geological and Natural �-6- m I Wall zone IT] Intermediate m zone core fmassive auartzitelxenolith-rich zone • Granite tI ol::===II mile PAUL E. MYERS 1976 Figure 4 -- Generalized geologic map of the Wausau and Stettin syenite bodies and the Ninemile granite pluton which intrudes the Wausau syenite. Section A-AI is shown in Figure �-7- STOP DESCRIPTIONS NO. TITLE AUTHOR(S) PAGE 1 Rib Mountain Summit Overlook Myers 10 2 Large quartzite and biotite schist xenoliths in the core rim, Wausau syenite pluton Myers 12 3 Flow structure of the wall zone, Wausau syenite pluton Myers 15 4 Lensoida1 quartz syenite, Employers' Mutual Insurance Company Myers &Sood 19 5 Contact relations and minerals in the wall zone, Stettin syenite pluton Myers &Soad 25 6 Amphibole syenite of the intermediate zone Sood &Myers 32 7 Amphibole syenite of the intermediate zone Scad Myers 32 8 The core zone of the Stettin syenite pluton Myers &Scad 36 & �-8- ,,- nv , , -'--";"/-"1"':',,+~...,..;.;.:;.~t+"''''IE~-.......''''~-''''-l .. \ ' r • •. ;-- ~" - p .. .. ,, , ,. ,~ .~-- ~~.: tTW .f ' / ,1 Figure 5 -- Field tr'ip #3 route map. Geological base map by LaBerge and I~yers (1979) . �-9- I fv fv -+---~~~--..L::'f;-~~ qol i : rJ ... ..J Isy \ ~ .- ,vVAUSAU I Iqsy \ "- , ... , ~ JI , Fi gure 6 -- Route map for stops ,1 J : - 4 in the Wausau syenite pluton. tv �-10- STOP #1 TITLE: RIB MOUNTAIN SUMMIT OVERLOOK LOCATION: Rib Mountain State Park observation platfonn, SE~ Section 8, T28N, R.7E., Wausau 15' quadrangle, Wausau west 7~' quadrangle AUTHOR: Paul E. Myers DATE: February, 1980 SUMMARY OF FEATURES: The Wausau syenite-quartz syenite pluton in two segments (Figure 3) and the more alkalic Stettin syenite pluton are exposed west of the Wisconsin River near Wausau in central Wisconsin. These Middle Precambrian (1520+15 m.y., Van Schmus, 1980) plutons are concentrically zoned and show a distinct northnortheasterly elongation. Each pluton has a contact metamorphic zone of syenitized wall rocks, an alkalic laminated, xenolith-rich wall zone, an intermediate zone and a core. Silica content increases inward in each pluton. DESCRIPTION: From this vantage point a good panorama of the region is available. Rib Mountain is the resistant remnant of a large, keel-shaped quartzite xenolith that forms a ring of xenolith five miles in diameter. To the southeast Mosinee Hill and to the southwest, Hardwood Hill are similar xenoliths of this ring structure. The flat, swampy area to the south is underlain by �-11the younger Ninemile pluton which intruded the southern part of the Wausau pluton. Parts of the quartz syenite rim and xenolithic masses are embedded in the Ninemile pluton. The southern segment" of the Wausau pluton is cilrt:ttlar in plan with a diameter of eight miles. Although the core and south half of this calderalike structure were intruded by quartz monzonite of the Ninemile pluton, its structure is preserved as a discontinuous ring of large xenoliths five miles in diameter. The largest of these xeno1iths--Rib Mountain quartzite is over two miles long. Bedding in the xeno1ith dips steeply southward toward the core. The top of the xenolith has been eroded leaving a keelshaped mass, slightly convex northward, and surrounded at depth by quartz syenite of the crescentic intermediate zone. Quartzite xenoliths near intrusive contacts are typically veined and impregnated by K-feldspar. Pyroxene and amphibole syenite, commonly containing volcanic xenoliths, form a discontinuous outer rim (wall zone) of the southern segment. The northern segment of the Wausau pluton is semicircular in plan with its truncated southern edge along the Rib River. The Stettin pluton is contiguous with it on the northwest. Although its size and internal structure are sim"'lar to that of the southern segment, its intermediate zone consists of coarse gray syenite, and volcanic xenoliths predominate. The older northern segment probably represents a caldera structure, which was partially destroyed by intrusion of the southern segment. The more alkalic Stettin pluton, northwest of here, is oval in plan with dimensions of 5.0 x 3.5 miles. Three major zones distinguished in mapping where; (l) a"wall zone comprising aplitic biotite syenite, nepheline syenite gneiss, and "tabular syenite", (2) an intermediate zone consisting of coarse grai~ed amphibole and pyroxene syenite with swirled flow lineation, and (3) a circular core zone one mile in diameter comprising a rim of magnetite-rich nepheline-hedenbergite-fayalite syenite, and an inner core of pyroxene syenite. Both the Wausau and Stettin plutons possess strongly metasomatized, but unassimilated xenolith-rich wall zones. Concentric cataclastic lamination was developed by high-angle displacements accompanying their forceful emplacement. Subsequent, more passive intrusion of the Ninemile granite caused a partial foundering of at least the southern part of the Wausau pluton. �-12STOP # 2 TITLE: Large Quartzite and Biotite Schist Xenoliths in the Core Rim, Wausau Syenite Pluton LOCATION: South end of Mosinee Hill, NE~, NE~ Sec.27, T28N, R7E Wausau 15' and Wausau West 7.5' quadrangles AUTHOR: Paul E. DATE: February, 1980 ~1yers, University of Wisconsin-Eau Claire SUMMARY OF FEATURES: This abandoned 3-M quarry exposes the south end of a large quartzite xenolith and a much smaller xenolith of biotite schist (Figure 1). The lensoidal shape of the large xenoliths is extrapolated from shapes of smaller ones throughout the intermediate zone. Near its contact with quartz syenite the quartzite is impregnated with very fine-grained, interstitial pink microcline which selectively replaced certain layers in the quartzite. The abundance of interstitial K-feldspar diminishes toward the center of the quartzite xenolith. Smaller quartzite xenoliths have been thoroughly granitized. The question of whether these xenoliths were carried up or down along the cylindrical wall of the Wausau syenite pluton is still not answered. The only significant bedrock occurrence of quartzite and biotite schist in this area is as xenoliths in the Wausau syenite pluton. The xenoliths have the following important characteristics: 1. They show concentric, zonal distribution and orientation around the quartz monzonitic corf'--·thf~ Ninemile pluton. �-13- FIGURE 7. Profile of the south end of Mosinee Hill 2. The largest xenoliths occur one mile outside the core. 3. The quartzite xenoliths are the largest because of their lower susceptibility to fragmentation and assimilation. 4. Flow structure in quartz syenite and feldspar lenticulation indicate intrusion of the quartz syenite as a viscous crystal mush. 5. Mafic xenoliths were biotitized, and quartzite xenoliths were granitized through the metasomatic addition of K 0 and Al 0 with selective replacement of quartzite by fine-~rained mfc~o­ cline along bedding planes. 6. Xenoliths north of the Rib River are dominantly metavolcanic rocks, whereas the xenoliths south of Rib River are dominantly quartzite, biotite schist and very subordinate non-foliated metadiabase. 7. Quartz grains in the quartz syenite and the outer part of the Ninemile pluton are granular, subangular, coarse grained and strained. THE NINEMILE PLUTON: The Ninemile pluton has a granite rim containing xenocrystic quartz. Samples taken at one-mile intervals across the pluton from north to south and from west to east show a decreasing percentage of xenocrystic quartz and an increasing amount of plagioclase toward the center of the pluton. The contact at the Ninemile pluton is locally discordant, as at Black Creek 1.7 miles northwest of here. Miarolitic cavities. some filled with large quartz crystals are common along the west side of the Ninem"i Ie pluton. They indicate shallow conditions of crystallization" �-14- Figure 8--Block diagram of the northeastern corner of the southern segment of the Wausau syenite pluton at Mosinee Hill showing abundant, well-oriented quartzite (q) and biotite schist (bs) xenoliths in a flowlaminated, lensoidal quartz syenite (lqsy). The Ninemile quartz monzonite pluton (qm) intruded the quartz syenite with only a local discordance. The lensoida1 s~enite is bounded on the east by a thin wall of amph"ibo1e syenite (asy) which is itself in fault contact eastward with felsic volcanics. These rocks are cut with sharp discordance by a prominent diabase (db) dike which is characterized by a strong reverse polarity. The Qal is Wisconsin River alluvium. The shaded rectangle shows the 1coation of the profile in Figure 1. �-15- STOP #3 TITLE: Flow Structure of the Wall Zone, Wausau Syenite Pluton LOCATION: " >4- " -.....-... 1',/;~';/~~, ..... ,.-~ ! Ha~~;'n~i..' 'j 'p3)t1' AUTHOR: i Paul E. Myers, Department of Geology, UW-Eau Claire DATE: February, 1980 SUMMARY OF FEATURES: 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 9). 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 rafted up or dropped down and brecciated in the viscous syenite magma (Figure 10). OESCR! PTION : According to Weidman (1907, p. 203-208) the IVIausau-type" quartz syenite is composed of alkali feldspars (orthoclase, microcline, albite, and microperthite), barkevite, hedenbergite, fayalite. biotite and quartz. Accessories include fluorite. apatite, magnetite. zircon and allanite(?). �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. 1. The oldest rocks here are xenoliths in the syenite. They include thoroughly recrystallized, schistose, amphibol1tic metavolcanics, quartzite, and virtually unaltered felsic tuff. Note that long dimensions of xenoliths tend to be parallel to lamination and/or foliation and that, despite lithologic disparity, their mutual alignment imparts a distinct structural "grain lt to the enclosing syenite--a factor believed to be of considerable significance in working out an emplacement mechanism for this pluton. 2. An early. fine-grained, flow-laminated lensoidal quartz syenite may represent a chilled phase. 3. Coarse-grained, flow-1ineated pyroxene-amphibole quartz syenite cuts the fine-grained phase with sharp discordance. This unit contains irregular, lensoida1 and tabular inclusions of amphibolite, 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 plasticized presumably because of lower melting point. A screen of schistose metadiabase(?) crosses the south end of the outcrop. Its thin western end shows plastic deformation and I pu11-outs", whereas its more brittle eastern end is segmented into many angUlar fragments (Figure ), 4. Late-staget 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. 5. Coarse, sadie amphibole crystallized along joint surfaces. It is suggested that many of the structures in the syenites and quartz syenites of the Wausau pluton indicate forceful, subvolcanic injection of dry, viscous syenite magma. Detailed structural analysis may in time reveal the mechanisms of magma flow and xenolith mixing within the magma. Do the xenoliths t for instance, represent fragments from a fault breccia formed initially during caldera collapse and later invaded by upwelling syenite magmas? �-17- Figure g--Amphibolite (a) xenolith with swirled lineation and thin Seams of syenite is cut by coarse pyroxene syenite (psy). Lenticular veins with walls of K-feldspar (Kf) and cores of quartz (q) show mutually crosscutting relations with an intervening offset along a small fault. Joint coatings are of coarse, sodic amphibole. �.;18- Fi gure lO--Segmented metadiabase screen in flow-banded lensoidal pyroxene syenite. �-19- STOP #4 TITLE: Lensoidal Quartz Syenite, Employers' Mutual Insurance Company LOCATION: NW~, SE~, AUTHOR: Paul E. Myers, and Manmohan Sood DATE: March, 1980 Sec. 27, T 29 N, R 7 E, Wausau West 7.5' Quadrangle SUMMARY OF FEATURES: Coarse-grained, pink and brownish gray quartz syenite containing up to 60 percent volcanic xenoliths (best seen on horizontal surfaces) is exposed in an old quarry behind the offices of Employers' Mutual Insurance Company. This rock exemplifies contaminated quartz syenite of the lIointermediate zone of the Wausau syenite pluton (Figure 3). Associated quartz syenite elsewhere in this zone contains large, metasomatized quartzite and/or mica schist xenoliths, the most spectacular of which is exposed on the summit of Rib Mountain. The Rib River 1I1ineament separates the two crescentic segments of the Wausau syen i te body. ll ll DESCRIPTION: The quartz syenite at this location is composed of coarse perthite (80%), quartz (10%), and sodic pyroxene partially replaced by mixtures of dark green amphibole, carbonate, and magnetite (10%). Quartz is interstitial. Large magnetite segregations can be observed along the road on the east side of this outcrop. Four facies of quartz syenite were recognized and analyzed chemically (See Table 2). The pink syenite contains up to 60% trachyte or rhyolite (?) xenoliths which are lensoidal with blunt, broken east ends and rounded (assimilated?) west ends. Their orientation is consistently N 7075 0 W, vertical in this area (Figure 10), and they are seen best on horizontal surfaces. Large quartzite xenoliths occur in the quartz syenite along the ridge crest north of here. The crescentic form of this part of the Wausau syenite body also shows as a conspicuous magnetic anomaly owing to the high concentration of magnetite as sheets and lenses in these rocks. The xenoliths �-20R 0 A 0 o o meter (in detailed area) I Figure 11-- Volcanic xenoliths (dotted) in flow-lineated amphibole quartz syenite (white). Outcrops in grassed area between three roads behind Employers' Mutual Insurance Company. show up on fresh surfaces mainly as slightly finer grained, darker colored masses. In addition to the angular volcanic xenoliths, the quartz syenite here contains mafic schlieren and clots showing irregular shape and orientation as well as gradational boundaries, a factor suggesting their more distant derivation and more thorough assimilation. Xenoliths of highly disparate lithology, and metamorphic grade occur side by side in these plutons. Their lenticular shape suggests mechanical segmentation before or during syenite intrusion. Convoluted flow lineation in amphibole syenite (as at the Old Technical Institute in Wausau) indicates viscous flow, probably due to water-deficiency of the magma. At many locations it is very difficult to distinguish the intrusive phase: indeed, one is hard-pressed to find an uncontaminated syenite exhibiting the features of a true intrusive rock. Sillimanite-bearing quartzite occurs as a tabular xenolith in fine-grained hornblende syenite 2.5 km west-northwest of here. The sillimanite suggest considerable upward transport of the xenolith from a high-grade metamorphic basement. The mica schist and metagabbro(?) xenoliths at Mosinee Hill and along the east side of the Wausau syenite body also suggest a deep-seated source. The close-spaced juxtaposition of xenoliths of disparate lithology indicates considerable vertical movement of wallrock fragments. To what degree did collapse modify these intrusive relationships? Does the quartz syenite represent a syenite magma which was contaminated by zenolithic quartzite? To what degree was the syenite able to assimilate xenoliths? Textural relations se~throughout the pluton suggest little assimilation but considerable dilation owing at least in part to explosive eruption. �-21- TABLE 2 Bulk chemical compositions of the four principal quartz syenite facies from Employers' Mutual Insurance Company Quarry. Description - EW-3 (WEST) Brownishgray EW-5 (EAST) Coarse~ dark gray NSI (SOUTH) Pink syenite~ with volcanic xenoliths SEI (NORTH) Medium-grained syenite Si0 2 63.05 63.55 63.90 64.10 Ti0 2 0.78 0.54 0.47 0.48 A1 0 12.60 15.16 14.14 15.17 1.91 1.25 5.42 4.58 FeO 7.72 3.48 1.32 1.44 MnO 0.34 0.16 0.14 0.12 MgO 0.41 0.16 0.45 0.09 CaO 2.66 1.72 1.35 1.50 Na 20 4.80 5.52 6.32 5.17 K20 H2O 4.22 5.67 6.34 5.57 0.76 0.42 0.56 0.26 P205 0.22 0.06 0.05 0.06 CO 2 0.28 1.92 0.62 0.09 BaO 0.094 0.066 0.024 0.036 Zr0 2 0.222 0.114 0.062 0.071 154 118 80 80 78 83 67 42 2 3 Fe 203 Rb Sr ppm In comparison with Nockolds' (1954) average syenite composition (see Table 2)~ these quartz syenites are richer in SiO, and total iron and poor in alkalies and lime. Their Rb and Sr contents are also low compared to other similar rocks. �-22- THE STETTIN SYENITE PLUTON Although Weidman (1907) mapped the geology of north-central Wisconsin and paid special attention to the mineralogy of the syenites near Wausau, Emmons and Snyder (1944) hypothesized formation of the Stettin syenite body by metasomatism of fe1dspathic rocks along shear zones with a1kalirich solutions derived from a subjacent granite batholith. Turner (1948) studied the heavy accessory minerals and radioactivity of the Stettin pluton, and Geisse (1951) described the petrography of this pluton. Petrographic and geochemical investigation of the mafic minerals and nepheline of the Stettin pluton initiated analytical studies which have been extended by the work of Sood and Berlin. The concentrically zoned Stettin pluton (Figure 12) is oval in plan, elongated northeasterly, with a length of 5.5 miles and a width of 4.0 miles. Older volcanic rocks enclosing the pluton have been extensively syenitized. The eastern and southern margin of the pluton is a complexly laminated series of altered volcanic screens and pendants and various, contaminated intrusive phases of the syenite including n~he1ine syenite. The wall zone comprises a discontinuous outer rim of gneissic nepheline syenite, and an inner layer of tabular syenite (Stop #5). The intermediate zone (Stops #6 and #7) is composed of amphibole and pyroxene syenite showing considerable variation in composition and texture. The amphibole syenite is commonly quartz-bearing. The core zone (Stop #8) is one mile in diameter and is located asymmetrically near the north end of the pluton. The core zone comprises a well-defined, cylindrical rim of indistinctly banded nepheline syenite surrounding a core of pyroxene syenite. Field relations indicate the following intrusion sequence: (l)PYr.qxene syenite, (2) nepheline syenite, (3) tabular syenite, (4) amphibole syenite. Numbers 3 and 4 could be reversed. This evidence is based wholly on field relations (Myers). It should also be emphasized that the intrusion sequence may not be the same as the crystallization seqence. Analytical work (Sood and Berlin, this guidebook) suggests a very late age for the nepheline syenite. (See discussion of petrochemistry beginning on page 46 ). A summary tabulation of paragenetic relations of minerals in each zone of the Stettin syenite pluton is presented with modification from Koellner (1974) in Table 3. �-23- -mv o • .... ..... ..... " ... ' ,.'. ," 45 0 00' , MILE I mv EXPLANATION Qal Qgt Alluvium Till Unconformity c gr .Jl psy Pyroxene Syenite aay syap Amphibole Syenite Syenite aplite .g E II v ~ Q. Granite c .g .Jl E II v e Q. tay Tabular Syenite nsy Isy Nepheline Syenite syv mvb fv Syenitized Volcanic S 8reccjated Malic Valtonics mv MalH Volcanics Lensoidal Syenite Felsic Volcanics Figure 12 -- Geologic map of the Stettin complex (after Myers. 1973) including localities of samples and field trip stops. �-24TABLE 3 PARAGENETIC RELATIONS OF MINERALS IN EACH ZONE OF THE STETTIN PLUTON rJONE PARAGENETIC RELATIONS ROCK TYPE Tabu1 ar Syenite (Myers, 1973) - - zircon-/ I pyroxene-! I-alkali feldspar-i ~ opaques-l green amphibole-1 I w z 0 N -l -l o::t: f-biotite~ Nepheline Syenite (Koell ner, 1974, p. 12) - - nephel i ne---j r-alkali feldspar-i ~ol ivine~ :3: I-- pyroxene-f w ropaques-! /- green amphi bo1 e.., f-biotite-i z 0 N w Pyroxene Syen ite 0:: ~alkali feldspar-, rapatite-I 0 u ~opaques-f r-ol i vinew r-pyroxene-t r-green amphibo1e-j z 0 N ~biotite~ karbonate-l ~b1ue amphibo1e- w I0< I-< Cl w :E: 0::: w l- z I-< Amphibole Syenite (Koellner, 1974, p.33) ~a1ka1i feldspar-l I-apa ti tei I-opaques-i I-- pyroxene-f r-- green amphi bo 1e-l I-biotite-l I-b1ue amphibole �-25STOP #5 TITLE: Contact relations and minerals in the Wall Zone, Stettin syenite pluton LOCATION: County Highway 0 at 10146 Stettin Road, Paul Knopp property, SE~, SE~, Sec. 22, T29N, R6E, Marathon 15' quadrangle, (Sample Location 92) AUTHORS: P.E. Myers and M.K.Sood DATE: February 1973, February 1980 SUMMARY OF FEATURES: The outermost rim of the Stettin pluton is gneissic nepheline syenite composed mainly of alkali feldspar, perthite, nepheline, aegirine, sodic amphibole and biotite. It is in sharp contact with, and veined by, tabular syenite composed of coarse, well-oriented laths of perthite, sodic amphibole, pyroxene, and lensoidal mafic inclusions composed essentially of the same minerals but in different porportions and of finer grain size. The mafic inclusions are well-oriented parallel to the tabular fabric of the enclosing syenite and to the wall of the pluton. They contain large perthite porphyroblasts of similar composition and size as those in the enclosing syenite. Zircons were mined at this site in the 1950's. Zircons from this site have given a UjPb age of 1520 + 20 m.y. by W.R. Van Schmus (oral communication). The chief questions to be answered at this site are: (1) how were the nepheline syenite and tabular syenite emplaced, and (2) to what extent is the present mineral assemblage a result of metasomatic replacement? �-26- The abundance of zircon and hastingsite amphibole, biotite and carbonate indicates a miaskitic trend for the nepheline and pyroxene syenites. The compositions of the nepheline and pyroxene syenites are very similar (Table ). According to Koellner (1974, p. 144) the amphibole syenite is agpiatic and could contain a carbonatite body. DESCRIPTION: The nepheline syenite (Figure 13, Tables 4 and 5) is a gray, banded rock composed here of perthitic feldspar nepheline, olivine, pyroxene, magnetite, amphibole, and biotite. Contorted aplitic and pegmatitic bands lie roughly parallel to the wall of the pluton about 1500 feet south of here. The nepheline occurs as blocky, pinkish grains which weather much more readily than the associated minerals, giving the rock a characteristic pitted appearance. Nepheline is partially altered to cancrinite and iron oxides. Banding, and mafic content of the nepheline syenite increase outward toward its contact with syenitized mafic volcanics which tren westnorthwesterly. In addition to the essential minerals listed above, common accessory minerals include zircon and sphene of unusually large size and abundance, apatite, fluorite, allanite, sodalite, pyrochlore and thorogummite(?). U/Pb dating of the zircons from this site by S. Goldich (oral comnunication) gave a minimum age of 1400 m.y. More recent analyses of these zircons by W.R. Van Schmus yielded a U/Pb age of 1520 + 10 m.y. Thus, the Stettin syenite is about 20 million years older than the Wolf River Batholith (oral communication). The gneissosity and isoclinal folding exhibited by the gneissic nephe'line syenite of the wall zone on the south side of the Stettin pluton suggest considerable differential movement of material a'long its outer wall. The extent to which metasomatism was involved during and after emplacement is not known. However, metasomatism was extensive, and that the nepheline syenite may consist in large part of metasomatized wall rocks. Zircon from this locality is deep red-brown, doubly terminated euhedral prisms up to 14 mm in length. Some crystals display geniculate twinning similar to that of rutile. Chemical analyses of three zircons from a nearby site (NW~ of Sec. 22) by F.B. Hall (in Weidman, 1907, p. 313) indicates an A1 03 content of between 4.28 and 7.80 percent and an Fe?03 content between 21.21 and 4.47 percent. Ca, Ti, Th and rare earths were sought but not detected. Brown pyrochlore octahedra up to 2 mm in diameter were found at this location by Weidman (1907, p. 308-309). Allanite is confined mainly to petmatitic portions in the nepheline syenite. Apatite and sphene of unusually large size show affinity for clusters of mafic minerals in the nepheline syenite. Large sphene c~ystals up to 7 mm in length can be collected from nepheline syenite lenses and masses near its contact with tabular syenite, �-27- The tabular syenite (Figure 14, Tables 4 & 5) is composed dominantly of coarse laths of m;croperthite. Vein and patch type perthites predom"inate. Po'ikilitic amphibole (hastingsite) rims pyroxene (intermediate between acmite and hedenbergite according to Koellner (1974, p. 65). The tabular fabric (Figure 15) is characterized by a random orientation of perthitic feldspar tablets in a plane parallel to the outer wall of the pluton and parallel to the long dimensions of mafic inclusions. Perthitic feldspar tablets within mafic inclusions and across their contacts are identical to those in the enclosing tabular syenite. The inescapable conclusions is that the perthitic feldspar is at least partly of metasomatic origin. Veins of tabular syenite locally cut the nepheline syenite gneiss in the old quarry face at this location. Mafic inclusions comprise from 5 to 80 percent of the tabular syenite. As the volume of mafic inclusions increases, the mafic minerals, mianly sodic amphibole, become coarsely poikilitic. Individual amphibole grains up to 12 centimeters long were observed in a small roadside excavation 1.5 miles east-southeast of here. Although the mafic inclusions contain a much higher percentabe of pyroxene and olivine than the enclosing tabular syenite, they are of about the same chemical composition. The tabular syenite forms the outermost layer on the north and west sides of the Stettin pluton where the nepheline syenite is absent. The abundance of mafic inclusions increases outward in the tabular syenite, suggesting considerable contamination by the basaltic wallrock. A unit mapped as lensoidal syenite and a closely associated syenite aplite (Myers, 1973) are found locally where the nepheline syenite is absent. The lensoidal syenite is an aplitic, gneissose rock consisting of mafic inclusions rich in biotite enclosed in an aplitic syenite. The syenite aplite is similar in texture and mineral composition but relatively free of mafic inclusions. �TABLE 4 MODAL COMPOSITIONS OF THE STETTIN ROCKS ROCK TYPE CORE ZONE Amphibole Syenite Pyroxene Syenite Tabular Syenite 6 and 504 65 46 2 92 87.4 80.2 26.4 63.6 17.6 75.7 6.6 61.4 SAMPLE NUMBERS* 10 77 503 108 Quartz Nepheline Perthite Albite Amphibole Pyroxene Biotite Bi 0 t i te (a1ter . ) Zi rcon Apati te Fl uorite Calcite Sphene Opaque minerals Al teration 7.1 6.6 2.9 1.4 80.7 0.5 11.2 83.5 83.0 8.6 90.3 0.2 5.1 0.6 0.2 0.3 0.2 0.5 0.1 0.2 Nepheline Syenite 13.6 0.6 5.5 4.1 0.5 19.1 8.4 4.6 29.5 0.2 0.6 0.4 0.4 0.1 0.4 1.0 0.7 0.1 0.5 0.1 0.4 *Sample numbers shown on Figure 12 0.3 0.2 I N en I 0.2 0.1 WALL ZONE INTERMEDIATE ZONE 0.3 0.1 0.2 0.3 1.3 0.3 1.1 0.5 0.5 �-29- TABLE 5 CHEMICAL COMPOSITIONS OF THE STETTIN ROCKS* CORE ZONE II Pyroxene Syenite INTERMEDIATE ZONE ROCK TYPE Amphibole Syenite WALL ZONE Tabular Syeni te Nepheline Syenite 46 2 92 61. 50** 57.45 56.95 54.10 16.23 16.62 16.93 21.02 16.32 3.13 2.55 5.20 2.58 2.93 3.41 2.10 2.70 5.66 1.68 5.98 2.12 7.08 0.01 0.02 0.08 0.14 0.24 0.21 0.07 1. 22 0.70 0.50 0.95 1. 10 2.15 1.43 2.64 0.51 4.03 Ha 20 5.92 6.92 7.07 6.51 5.97 6.49 6.71 7.81 5.81 ~O 4.31 5.11 5.19 5.51 5.67 5.15 5.02 5.99 4.84 H2O CO 2 0.73 0.83 0.70 logS 0.51 0.63 0.98 1.43 0.77 0.38 0.35 0.36 0.40 0.22 0.17 0.18 0.40 0.09 Ti0 2 0.72. 0.42 0.27 0.32 0.75 0.31 0.59 0.38 1. 32 P205 0: 11 0.04 0.06 0.07 0.13 0.07 0.13 0.50 0.49 MnO 0.23 0.12 0.15 0.18 0.26 0.22 0.30 0.07 0.29 S 0.010 0.004 0.003 0.008 0.034 O.OOg 0.023 0.000 0.044 0.102 0.165 0.260 0.171 0.11 0.100 0.140 0.001 0.079 10 70 503 108 6+504 5i02 66.10 65.20 64.70 61.95 59: 75 A1 203 Fe 203 13.24 15.59 15.86 16.04 2.61 2.36 2.45 FeD 4.12 2.22 MgO 0.43 CaD Samp1 e # zr0 2 Cl BaD { 0.013 0.024 0.071 0.105 0.241 0.143 0.215 0.03 65 0.010 0.010 0.345 0.02 0.150 0.160 0.103 0.086 0.025 0.02 0.208 Rb(ppm) 199. 152. 66. 133. 115. 102. Sr(ppm) 44 105. 17<t . 109. 57. 345. * Ana1yst-K. Ram1al, University of Manitoba **Tabu1ar Syenite �-30- Figure l3--Photomicrograph of nepheline syenite showing euhedral nepheline grains surrounded by a matrix of discrete albite crystals and amphibole. Crossed nichols. Figure l4--Photomicrograph of tabular syenite showing parallel alignment of feldspar crystals. Crossed nichols. �-31- Figure 15-- Typical fabric of tabular syenite showing coarse tablets of microperthite in random orientation parallel to the wall of the pluton. Microperthite laths in the 1ensoida1 mafic inclusions tend to have a preferred orientation parallel to those in the enclosing syenite. Some of the laths crystallized across the edges of inclusions, thus indicating a metasomatic origin of at least part of the microperthite. �-32STOPS #6 and #7 TITLE: Amphibole and Pyroxene Syenites of the Intermediate Zone LOCATION: Stop #6: Stop #7: J NW~, Sec. NW~, SW~, 14, T29N, R6E, Hamburg 151 quadrangle Sec. 14, T29N, R6E, Marathon 15' quadrangle .--' N 1 / 10 '- ". "- .- '0 .Ir/ "l Dr" 20.0."" R"' I"""~ rr AUTHORS: M.K. Sood and P.E. Myers DATE: Februa ry, 1980 SUMMARY OF FEATURES: Massive and flow-lineated, gray to pinkish-orange amphibole syenite (Stop #6) and pyroxene syenite (Stop #7) of the intermediate zone are composed dominantly of alkali feldspar and up to 35% poikilitic arfvedsonite amphibole which encloses nuclei of pyroxene. The amphibole syenite shows considerable variation in composition and texture from pegmatitic clots of quartz-bearing aplitic phases in single outcrops. Clots of coarse feldspar and poikilitic amphibole (up to 12 ern. long) are cornmon. Most outcrops display swirled flow ll'neation similar to that seen in amphibole quartz syenite at Stop #3 (Old Technical Institute, Wausau). The amphibole syenite contains a relatively large percentage of blue (riebeckitic) amphibole. Although the dominant mafic mineral in the pyroxene syenite ;s amphibole, pyroxene occurs in discreet grains not rimmed by amphibole. At a stone quarry 0.2 mile east of here, the pyroxene syenite shows spectacular schiller structure of the feldspar (moonstone). �-33- DESCRIPTION: Whereas the amphibole is characteristically pink in outcrop, the pyroxene syenite is a moderate-to-light olive gray with islands of coarse mafics enclosed in coarse tablets of randomly oriented feldspar. The amphibole syenite shows considerably greater textural variation, even at mesoscopic scale. Although vein-like and irregular masses of zoned pegmatite and aplite are common in all outcrops, the dominant rock type is medium-grained amphibole syenite with a faint to conspicuous lamination, with or without lineation created by alignment of feldspar tablets and lensoidal clots of mafic minerals--mainly amphibole and subordinate pyroxene. Pegmatitic phases of the amphibole syenite contain up to 12% quartz as coarse segregations commonly rimmed by blue (riebeckitic) amphibole. In thin section, mafics are clustered in acicular or radiating fibers. This zone to the southwest contains small sill-like masses of tabular syenite. The major mineral is micro-to mega-perthitic feldspar surrounding the mafic minerals which seemingly are later than the feldspars. The principal mafic mineral is bluish-green arfvedsonite-riebeckite amphibole (Table 8), sometimes mantling minor Fe-augite pyroxene. However, pyroxene is absent in some samples of this zone. Alteration of amphiboles to brown-red biotite is common in patches and along borders. The interesting feature of the amphibole grains is containment of a dark blue riebeckitic phase which is most common only in this unit. Some amphiboles poikilitically enclose euhedral feldspars (Figure 17). Accessories include zircon which is commonly zoned, quartz (up to 12%), fluorite, calcite, FeTi-oxides, apatite and allanite. �-34- Figure 16--Photomicrograph of aplitic syenite showing a fine-grained mass of anhedral perthitic feldspar. Crossed nichols. Figure 17--Photomicrograph of amphibole syenite showing poikilitic texture. Note the euhedral outlines of the feldspar crystals enclosed in the amphibole grain. �-35- Figure 18--Photomicrograph of pyroxene syenite showing zoned grain of aegirine-augite mantled byarfvedsonite. Crossed nichols. Figure 19--Photomicrograph of pyroxene syenite. Patch perthite showing albite twinning. Crossed nichols. �-36- STOP #8 TITLE: The Core Zone of the Stettin Syenite Pluton LOCATION: SW 1/4, SE 1/4 Sec. 2, T29N, R6E; H-amburg151 quadrangle ! I;': \ ,/ \ .t:". o. SIT / 10 08,/ o. ( -.. / / .0 '0 --' AUTHORS: Paul E. Myers and M. K. Sood DATE: February, 1980 ~_~. ~ _,,-,0 -) P 11 ~ I o 0 .... I '. '-----__ --_1\....' • c•. ". \ . SUMMARY OF FEATURES: The core of the Stettin syenite pluton comprises two distinct parts: (1) a cylindrical core margin of indistinctly banded or lineated, mediumgrained nepheline syenite and (2) an inner core of pyroxene syenite. Bent and crushed feldspar grains and a crude southeast-dipping layering were formed during or after emplacement of the core margin. The nepheline syenite core margin produced a pronounced donut-shaped magnetic anomaly about one mile in diameter. Drilling by Bear Creek Mining Company in the southeast corner of the inner core retreived about 250 feet of core classified by company geologists as larvikite. No carbonatite has been found, although the agpaitic trend of the rocks here suggests that such a carbonatite is possible (Koellner, 1974, p. 144). DESCRIPTION: The nepheline syenite of the core margin here is indistinctly banded or lineated. The weathered surface is pale yellowish gray with pitting due to differential weathering of the nepheline. The fresh nepheline is pale greenish brown and occurs as well-oriented, subhedral to euhedral grains enclosed by tablets of feldspar up to 2 em long. The feldspars, nepheline, and islands ofomafie minerals are elongated in a plane dipping southeast at between 60 and 70. This lamination is not parallel to the outer edge of the core margin at this location. Bent and broken feldspar and nepheline grains and lenticulation of mafic mineral clusters suggest shearing during or after intrusion. �-37- The dominant mineral is tabular microperthite (60% orthoclase with 40% rni]oclase ribbons). An additional 25% of the rock is subhedral to euhedral nepheline, which is partially altered to cancrinite. Mg-rich pyroxene and pleochroic, olive brown amphibole are of about equal abundance and make up about 20-30% of the rock. Accessory (2-5%) Mg-rich olivine and dark brown biotite accompany the other mafic minerals in lenticular clusters and islands occurring interstitially in the nepheline syenite. The biotite partially rims the amphibole and was probably formed at a late stage of crystallization. This unit produced a pronounced~ donut-shaped magnetic anomaly about one mile in diameter. Wiedman (1907~ p. 251) reports unusually large and abundant magnetite octahedra from streams northwest of here. The magnetite is apparently associated most closely with the olivine. �-38MINERALOGY AND MINERAL CHEMISTRY (STOP NO·s 5~ 6~ 7 and 8) by M. K. Sood and L. A. Berlin The principal mineral phases in Stettin Complex are perthitic feldspars, nepheline, sodic and calcic pyroxenes~ and sodic amphiboles whose representative chemistry is given in Table 4 and characteristics described below: Fel ds pa rs The major phase of feldspar is a microperthite in uniform veins showing parallel, subparallel~ or wavy lamellar intergrowths~ or as patches of one feldspar in the host (see plate 1). Both perthite and antiperthite are present, although perthite is more common than antiperthite. Frequently the tabular feldspar grains exhibit Carlsbad twinning and less cOll1l1only Mannebach twinn"ing. The perthitic feldspar constitutes 80 to 90 percent of the syenites and 60 to 75 percent of the nepheline syenites (Table 4). Distinct grains of albite have an average extinction angle of 15 0 , but are not common in any of the syenites. Microcline~ also present as distinct grains~ show its characteristic spindle-shaped polysynthetic twinning and wavy extinction, but is less abundant than albite as individual grains. The bulk compositions of the perthitic alkali feldspars were determined for nine samples of three major zones of the Stettin complex. The samples were homoge~ized to a sanidine phase at 1050° in a muffle furnace for 48 hours; then .620 = 201 feldspar - 101 KBr0 CuKa was measured and the molecular percent orthoclase was determined using the3 homogenized natural microcline-low albite x-ray determinative curve of Jones et al. (1969) The compositions are given below in Table 6. ---Table 6 THE MOLECULAR PERCENT ORTHOCLASE OF HOMOGENIZED PERTHITIC ALKALI FELDSPARS OF THE STETTIN ROCKS Sample .629 CuKa Mol %Or Core Zone pyroxene syenite 1.40 0 39 Intermediate Zone amphibole syenite 3 amphibole syenites 1.45 1.40 35 Rim Zone tabular syenite nepheline syenite nepheline syenite 1.43 1. 35 1.39 37 44 41 39 �Plate 1. A. Enlarged section patch perthite of Plate 3B. Crossed nicols B. Photomicrograph of vein perthite in amphibole syenite. Crossed nicols. I W 1.0 I TYPES OF PERTHITIC FELDSPARS IN ROCKS OF STETTIN COMPLEX: c. Enlarged section showing braided perthite. Crossed nicols. (a) PATCH PERTHITE (b) VEIN PERTHITE (c) BRAIDED PERTHITE �-40- The molecular percent orthoclase ranges from 35 to 44%; however, Or% is above 40% for the nepheline syenites and is less than 40% for the nephelinefree syenites. The intensity ratios of the 201 peaks of microcline and albite were determined for the perthitic feldspars by scanning in both directions between 20 0 and 23 0 -20 Cula' at 1/8 0 -28 per minute using 200 counts per full chart scale, a time constant of 5 seconds and a chart speed of 15 inches per hour. The angular positions were averaged from three scans. Then the goniometer was exactly centered on one peak at a time and the intensity was measured using a fixed time of ten seconds with a 2 second time constant. The background intensity was measured at the midpoint between the two peaks. Then: A = number of counts on microcline 201/10 s B = number of counts on low albite 201/10 s C = number of counts on the background/lO s The intensity ratio lalla = (A - C)/(B - C). The intensity ratio and the value of the bulk composition of Or%/Ab% for each of the perthitic feldspars studied were plotted on the granh of Kuellmer (1959)(Figure ~O). From this diagram, implications can be made as to the temperaturestructural state of the feldspars. From the plots a broadening ratio (8) is obtained. The broadening ratio is a measure of the distortion or structural mistakes in the two phases of perthite. The broadening ratio will decrease with slower crystallization and lower temperature since these conditions are favorable for the attainment of an ordered arrangement of Si and Al ions in the tetrahedral sites of the feldspar structure (Smith, 1974). The broadening ratios for the perthitic alkali feldspars of the Stettin rocks range from low (B = 0.30) to intermediate values (B = 0.9). This is an indication of the low temperature-structural state of these perthites, corresponding to the maximum to intermediate microcline-low a"lbite series determined from the positions of the 204 and 060 reflections. �-41- 10 ....T"T""1 r---___r"-~-_r__r_..,.....,.....,r_T'".,.._--......,.-_.,-...,.___r""""T'" 8 / 6 / / / / ~ // / <0"" ,,"" / ~" / o / / 1-4 / .......... o / / H .8 .6 .5 / / / / / / / / / / / / / / / .. / / / / / / / / / / , / f),~ ~. / / / / / / ~. //~ / / / "'~ / / "" <0"" / / / / ~ / // / / / / / / / / / / / .2 / / // / ~ .~. //// / ""~. e/ / / / / ,," '" ~ / ~" " /~" / / / / / / .4 .3 / / / / / /.. / / / ~ / / / / / // / / / / / ~. 2 / / // / / / 3 / / / // / 4 / / / 5 / / / / / / / / / / .2 .4 .6 .8 1 ORrHoe LASE ALBITE 2 6 8 10 % % figure 20 -- Plot of the bulk composition Or%/Ab% versus lolla for the 201 reflections of the two feldspar phases in the Stettin perthite samples for determination of their broadening ratio B (diagram after Kuellmer, 1959). �I TABLE 7 S;02 A1 203 Ti0 2 FeO MnO MgO CaO Na 20 K20 ELECTRON MICROPROBE CHEMICAL ANALYSES OF MAJOR MINERALS OF STETTIN COMPLEX Pyroxene * psy Feldspar tsy Nepheline * Amphiboles nsy 46.5 39.90 50.1 50.8 67.42 68.23 40.45 48.1 0.59 33.1 19.23 8.70 9.28 1.0 1.34 19.72 -0.26 3.17 -0.30 0.1 1. 31 -29.1 23.70 26.40 0.18 34.22 26.8 ---0.81 0.89 0.71 --1.00 1. 52 0.99 2.28 0.73 0.62 4.41 --0.13 11 .00 0.44 0.25 10.3 8.89 17.8 20.30 15.20 0.57 6.80 7.40 11 .23 2.14 3.30 2.40 N.D. 5.46 6.39 N.D. 0.27 1. 57 1. 75 -- ATOMIC PROPORTIONS Si Al Al Ti Fe Mg Ca Na K Fledspars Based on 8 oxygens 2.987 2.988 1.004 1.018 0 0 --- -0.021 0.635 0.361 Ae Di Hd * From Koellner (1974) ---0.012 0.954 0.015 Amphiboles Based on 23 oxygens 6.73 6.43 1. 52 1. 76 0.118 0 0.372 0.147 3.89 4.61 0.515 0.172 1.765 1.536 0.690 1.031 0.323 0.361 2.001 -0.42 0.004 0.930 0.38 0.797 0.194 Pyroxene * Based on 6 oxygens 1.990 0.010 0.017 0.008 0.786 0.261 0.862 0.044 -- -- 16.0 3.5 75.1 3.9 25.2 60.8 2.074 -0.064 0.010 0.902 0.060 0.480 0.538 -47.3 5.3 42.8 Nepheline * Based on 32 oxygens 8.76 7.352 --0.29 0.27 5.52 1 .315 Fe-Ti Oxides 0.44 0.25 7.57 90.40 1.19 Fe-Ti Oxides Based on 24 oxygens 0.119 0.079 1.530 20.310 0.272 I +::> N I �-43- Nepheline Nepheline is characterized by its euhedral rectangular form and parallel extinction in thin section. In hand specimen, crystals may reach 4 or 5 cm. in length and appear gray with a greasy luster. Nepheline grains show alteration along borders and cracks to a colorless mica, possibly paragonite (Deer et~., 1963). According to Koellner (1974) nephelines are enriched in Si by 15% and deficient in alk~ies by about 13% (also see Smith and Sahama, 1954). Figure 21 Photomicrograph of nepheline syenite showing nepheline grains (at left and right edges) in aplitic matrix of perthitic feldspar. Crossed nicols. �-44Pyroxenes Both sodic and calcic clinopyroxenes occur in the various rocks of the Stettin Complex. Representative chemical compositions are given in Table 8. Sodic pyroxenes, aegirine and aegirine~augite, occur as distinct grains as well as crystals rimmed with bluish-green amphibole. Some grains show color zoning with pale cores asd bright green rims. The average eatinction angle (X:C) of the cores is 28 , whereas that of the rims is 13-24 , implying outward increase of the aegirine content. Calcic pyroxenes (diopside-hedenbergite) are iron-rich with aegirine content of up to 10% (Koellner, 1974). In general, Na+Fe+ 3 content of the pyroxenes is highest 'in the rocks of the wall zone. Figure 22 Photomicrograph of pyroxene syenite. Zircon crystals (left of center) surrounded by arfvedsonite (dark) and aegirine-augite. Note biotite near the center of the photograph. Small colorless apatite crystals occur as inclusions in the mafic minerals. Stained alkali feldspar surrounds the cluster. Plane polarized light. �-45Amphiboles The dominant mafic mineral is a bluish green sodic amphibole. The absorption scheme of this mineral closely agrees with arfvedsonite: X = bluish green or greenish blue, Z = greenish brown or light brown. The amphibole grains have an average extinction angle (X:C) of 16 0 ; this corresponds to a composition of 26 Mg: (Mg + Fe+ 2 + Fe+ 3 + Mn) in the eckermannitearfvedsonite ~eries (Deer et a1., 1963). However, the extinction angles vary from 00 to 29. Some amphibole grains exhibit an optical character more closely resembling riebeckite and have an absorption scheme X = deep blue, Z = light blue. The extinction angle of these qrains is approximately 10 . Figure 23 Photomicrograph of bluish green arfvedsonite in amphibole syenite no. 108. Quartz at right edge. Plane Polarized light. X-ray diffraction powder patterns of the riebeckitic amphiboles show a d:spacing of 8.42 oA for the 110 reflection, compared to 8.50 0 A for arfvedson,te. The lower d-spacing is in close agreement with other riebeckite analyses. Both sodic and calcic amphiboles are Fe-rich. Their composition probably reflects differentiation. �-46Biotite It occurs "in small amounts in two distinct varieties. Both have strong pleochroism but exhibit different absorption schemes. One is reddish brown to dark brown, and the other is 1ight brown to dark green. This may suggest possibly reflecting different Ti, Fe+ 2 , Fe+ 3, and Mg contents (Hyama, 1959; Deer , et ~., 1963 ) . Accessory Minerals The only zirconium mineral so far found is zircon which occurs as zones prismatic crystals along clusters of mafic minerals especially in rocks of the Core Zone, e.g., pyroxene syenite. Other accessory minerals are sphene, fluorapatite, fluorite, calcite, Fe-Ti oxides. PETROCHEMISTRY Chemical compositions of the Stettin rocks are presented in Table 8. Table 9 compares average compositions of the Stettin rocks to those of Nockold's (1954). The average of the Stettin nepheline syenites show distinct differences from Nockold's average syenite. These Stettin samples, while only slightly higher in silica, are lower in A1 203 and NA 20 and higher in FeO, CaO and P205. The amphibole and pyroxene syenites, also sTightly higher in silica than Nockold's average syenite, are lower in A1 201 , MgO, CaO and K20, while higher in FeO, NA 20 and MnO. The differentiation i~dices (01 ~ normative quartz + orthoclase + albite + nepheline + leucite + kalsilite) (Thornton and Tuttle, 1960) for these Stettin rocks are given in Table 10. The average 01 for these rocks is 84.7, which represents a high degree of differentiation. However, nepheline syenites have the highest 01 of 88.9 and 93.9 respectively, indicating the greatest extent of differentiation among these rocks. The agpaitic indices of the Stettin samples are shown in Figure 24-A. Rocks of lower Si0 2 content, the nepheline bearing rocks, have lower agpaitic indices than the more silica rich rocks. This is a reflection of the higher alumina content, due to the presence of nepheline, in the nepheline syenites. The ratio Na 20/K?0 versus Si0 2 (Figure 24C) increases with increasing Si0 2 . This diagram shows two trends suggesting that the Stettin rocks belong to two series. Amphibole and pyroxene syenites appear to follow a continuous differentiation sequence. (Figures 24A-F). C.I.P.W. normative compositions are presented in Table 10. The normative compositions of the analyzed Stettin rocks were calculated in terms of NaA1Si0 4 , KA1Si0 4 and Si0;l and are plotted in the systems NaA1Si0 4 - KalSi0 4 - Si0 2 at 1000 bars PH 0 ~Figure 25). All of the rocks fall within the low temperature trough. 2 �-47- TABLE 8 CHEMICAL COMPOSITIONS OF THE STETTIN ROCKS* INTERMEDIATE ZONE 65.20 64.70 61.95 CORE ZONE 59.75 61.50** RIM ZONE 57.45 • 56.95 54.10 Si0 2 66.10 A1 203 Fe 203 13.24 15.59 15.86 16.04 16.23 16.62 16.93 21.02 16.32 2.61 2.36 2.45 3.13 2.55 5.20 2.58 2.93 3.41 FeO 4.12 2.22 2.10 2.70 5.66 1.68 5.98 2.12 7.08 MgO 0.43 0.01 0.02 0.08 0.14 0.24 0.21 0.07 1.22 CaO 0.70 0.50 0.95 1.10 2.15 1.43 2.64 0.51 4.03 Na 20 5.92 6.92 7.07 6.51 5.97 6.49 6.71 7.81 5.81 K20 H2O 4.31 5.11 5.19 5.51 5.67 5.15 5.02 5.99 4.84 0.73 0.83 0.70 1. 95 0.51 0.63 0.98 1.43 0.77 CO 2 0.38 0.35 0.36 0.40 0.22 0.17 0.18 0.40 0.09 Ti0 2 0.72 0.42 0.27 0.32 0.75 0.31 0.59 0.38 1. 32 P205 MnO 0.11 0.04 0.06 0.07 0.13 0.07 0.13 0.50 0.49 0.23 0.12 0.15 0.18 0.26 0.22 0.30 0.07 0.29 S 0.010 0.004 0.003 0.008 0.034 0.009 0.023 0.000 0.044 Zr0 2 0.102 0.165 0.260 0.171 0.11 0.100 0.140 0.001 0.079 0.215 C1 BaO 0.03 0.013 0.071 0.241 0.143 0.024 0.010 0.010 0.345 0.02 0.150 0.160 0.103 0.086 0.105 0.025 0.02 0.208 Rb(ppm) 199. 152. 66. 133. 115. 102. Sr(ppm) 44. 105. 174. 109. 57. 345. * Analyst-K. Ram1a1. University of Manitoba ** Tabular Syenite �TABLE 9 COMPARISON OF CHEMICAL COMPOSITIONS OF STETTIN WITH NOCKOLDS (1954) AVERAGES Average Stettin Nepheline Syenite Average Nepheline Syenite (Nockolds,1954) Average Stettin Syenite Average Syenite (Nockolds, 1954) 5i0 2 56.17 55.38 63.54 61.86 A1 203 Fe 203 18.09 21.30 15.39 16.91 2.97 2.42 2.62 2.32 FeO 5.06 2.00 3.36 2.63 ~~gO 0.50 0.57 0.14 0.96 I +::> co CaO 2.39 1.98 1.08 2.54 Na 20 6.78 8.84 6.49 5.46 K20 H2O 5.28 5.34 5.16 5.91 1.06 0.96 0.94 0.53* Ti0 2 0.76 0.66 0.50 0.58 P205 MnO 0.37 0.19 0.08 0.19 0.22 0.19 0.19 0.11 * includes only H20 I �TABLE 10 C.I.P.W. NORMATIVE COMPOSITIONS OF THE STETTIN ROCKS ROCK TYPE Sample Numbers* Q Or Ab An Ne 01 Hy lAc Di Mt I1 Pr i Ru Hm C Ap Z Hl Tn CC DI *Tabular Syenite 10 CORE ZONE Amphibole Syenite Pyroxene Syenite Tabular Syenite 6 and 504 65 77 503 100 12.44% 25.61 44.05 4.86% 30.06 51.92 2.80% 30.62 52.97 1.79% 32.28 51.92 7.22 5.31 2.36 5.91 1.89 0.51 0.76 0.01 1. 36 5.89 3.88 0.54 0.46 0.01 1. 65 2.70 2.70 3.28 0.61 0.01 1.04 1. 36 0.12 0.02 WALL ZONE INTERMEDIATE ZONE 33.40% 47.72 0.88 1.28 3.41 1.80% 30.62 52.44 2.22 Nepheline Syenite 46 2 92 29.50% 56.48 1.47 7.93 3.00 35.62% 38.39 2.11 14.86 0.96 28.39% 34.16 4.26 8.10 4.67 I +::> UJ 6.66 3.70 1. 36 0.06 5.06 0.61 0.02 9.82 3.70 1. 06 0.06 4. 17 0.76 10.65 4.86 2.43 0.06 0.34 O. 18 0.03 0.91 0.13 0.001 0.06 1.01 0.11 0.04 1. 62 0.34 0.18 0.06 1. 70 82. 1 0.10 0.18 0.02 86.8 0.13 0.37 0.04 86.4 0.17 0.18 0.02 0.34 0.02 0.02 0.90 86.0 0.50 82.4 0.17 0.15 0.58 84.9 93.9 88.9 0.20 70.6 I �-50- '#. I.t 0 2 0 8 Fig. A ~ Fig. B M 0 <'" 1.0 0 .......... 0 >< '" + 'if. 46 7 0 0 46 N O2 0 0.9 0 Z 92 6 0 92 0, '" 0 z 0.8 5 50 60 70 50 70 60 5 i0 2 0/0 5i0 2 % 15 3 Fig. C Fig. D 2 14 0 'if. to 13 0 0 ""'" '" >< 2 503 0 z'" o 0 2 92 46 0 z O~ 65 • lOB 12 '" 46 0 1 ~7 + .......... 0 10 6 65 11 77 0 6 ·10 92 10 50 70 60 50 0 60 5i0 2 5i0 2 % 70 ~ 2 0 2 6 20 Fig. E 0 Fig. F 6 0 46 #. 'if. 0 0 M 5 0 '" 10 4 50 10 50 70 60 77 503 < 92 ~ 6 92 15 5:' 0 >< 65 10 70 60 5i0 2 % 5i0 2 % 5 Fir.. G 92 4 0 3 #. 1.5 0 46 Fig. H 92 0 0 0 v 2 'if. Figure 24, A-H 1.0 0'" 108- 503 0.5 77 • 0 50 60 046 P _10 20 70 •" 10 " 6 I-- 0.0,0 • " " .77 65~OB 60. '.503 " 70 �-51DISCUSSION Due to chemical and mineralogical heterogeneity, the origin of alkaline igneous rocks is, in many cases, very complex and may be the result of several processes. Experimental studies of chemically equivalent synthetic silicate systems (Bailey and Schairer, 1966; Hamilton and MacKenzie, 1965; Schairer. 1967; Sood and Edgar, 1972; Sood, Platt and Edgar, 1970; Tuttle and Bowen, 1958) have provided a physicochemical framework to explain the crystalli'zation behavior of alkali magmas. Any petrogenetic model for the formation of alkaline rocks of the Wausau area must take into account: 1) the zoned nature of the complex 2) the presence of quartz-bearing aplitic and pegmatitic stages in the intermediate ring of amphibole syenite; 3) the fenitized zone surrounding the pluton; 4) the presence of volatile bearing minerals (flourite, calcite, apatite) in most syenites, and in the quartz monzonite II core ll (1) of the Wausau pluton; 5) major and trace element geochemistry of the syenites. Consideration with Respect to the System Nepheline-Kalsilite-Silica In Figure 25 normative composition of the Stettin rocks is plotted in the system Nepheline-kalsilite-silica at lKb PH 0 along with the composition of the rocks from Kangerdlugssuag intrusion, 2 East Greenland (Wager, 1965). These analyses may be interpreted to show a trend of silica depletion away from the Si0 2 apex. Rocks of the Intermediate Zone of amphibole syenite plot in the alkali feldspar-quartz region, near the alkali feldspar join, while pyroxene syenites of the Core Zone plot just below the alkali feldspar join. The positions of these syenites in the field show a silica depletion trend toward the center of the complex. From Figure 25, it appears that the trend of these amphibole anrl pyroxene syenites is up the alkali feldspar surface and "over " the thermal barrier, which is similar to the interpretation by Wager (1965) for the nordmarkites, pulaskites, and foyaites of the alkaline Kangerdlugssuaq intrusion. (In the nepheline-kalsilite-silica system at 5 Kb PH 0' these rock webs plot close to the feldspar cotectic or nephiline-feldspar 2 cotectic. This is in agreement with mineral paragenetic and textural relations.) Further interp~etations await the accumulation of additional data, especially on the Wausau pluton. �-52- 30~_-+. _ _-~---f\70 Feldspar II 30 - - + - - - - - 4 KAISi 2 0 6 Nepheline 1 IS 0 1 ~ ,~ 100 ..- L-_~L-_----':>L-_~ o NaAISi04 10 20 30 Kalsilite IS 1 \/ 40 " so Weight per <en!. \{ 60 1 70 80 90 KAISiO.cj Figure 25 __ Normative compositions of the Stettin rocks (closed circles) and the alkaline rocks of the Kangerd1ugssuaq intrusion, East Greenland (open circles) (Wager, 1965) plotted in the system NaA1Si04 - KA1Si04 Si0 2 at PH20 = 1000 bars (Fuda1i, 1963; Hamilton and MacKenzie, 1965). �-53- How could such inward silica depletion be caused? Two possible explanations are: (1) (2) Loss of the volatile phase in ~uilibrium with the melt. Such a volatile phase has alumina, alkali, and silica in the same proportion as feldspars (Tuttle & Bowen, 1958; Mackenzie, 1960). The presence of aplitic and pegmatitic phases and fenitization of the surrounding volcanics may be a reflection of separation of volatiles into a gaseous phase and eventual loss. The plot of the Stettin rocks close to cotectics in pertinent synthetic systems may be indicative of crystallization of major phases within narrow temperature limits. Short crystallization intervals are also related to silica and alkali content which control volatile distribution in liquid and gaseous phases (Sood & Edgar, 1970; Kogarko & Rhyaschi kov, 1961). The substitution of Fe+ 3 Al+ 3 in feldspars may contribute to silic~3depletion with crystallization of iron-rich albite (NaFe Si 0R). Only a small amount of Fe-Al substitution is necessary 2to fix silica and cause the liquid to shift from silica saturated to silica undersaturated trend (Bailey & Schairer, 1966). The general iron-rich and alumina-deficient nature of the syenites in comparison to Nockold1s (1954) averages and a limited Fe-content of feldspars favor such substitution. The Nepheline syenite in the Stettin pluton may, therefore, represent last residual liquids injected into the sheared wall zone. It may be concluded that alkaline rocks of Marathon County represent a "genetically related comagmatic series. The study of silicate systems and melting relations of rocks have amply demonstrated that magma composition lies close to the univariant lines or the invariant points, and very slight changes in initial liquid composition can give decidedly distinct liquid trends. Compositional differences in these alkaline rocks may be related to slight changes "in magma composition by fractional crystallization or by wallrock assimilation, or both. It is important to further refine their genetic and tectonic relations. Systematic geoche~ical data both on rocks and minerals are needed to assess if these rocks are formed from mantle derived magmas (tentatively note the low Rb and Sr contents for Wausau rocks) which reached crust through recurrent fracture systems. Such information will also be useful in the estimation of economic mineral potential of this area. Such rocks form in environments favorable to the concentration of a wide variety of elements. II �-54Comparison of the Wausau and Stettin Plutons P.E. Myers Despite obvious differences in size, shape, xenolith types, zoning sequences, and silica saturation, the Wausau and St~ttin plut?ns share several significant sinrilarities: (1) the pyroxene and amp~l~ole syen1t~s of the intermediate zone of the Stettin pluton are compos1tlonally equlvalent to the outer wall zone of the Wausau pluton, (2) the lensoidal quartz syenite and probably comagmatic Ninemile quartz monzonite of th~ Wausau,pluton, are probably the silica-rich end-members which would have dlfferen~lated from the Stettin pluton after crystallization of the amphibole syenlte. Koellner (1974, p. 31) reports contents of up to 15% in the pegmatitic p~ases of t~e amphibole syenite. The close spatial association of zoned granlte,pegmatlte veinlets (Stop #3) and quartzite xenoliths suggests at least locallzed . silification of quartzite and other sili-saturated wall rocks. The relatlve silica undersaturation of the Stettin pluton may be due in part to the low silica content of the volcanic rocks which it intrudes. The Wausau and Stettin plutons probably represent the near-surface "roots" of two collapse calderas (Figure 26). Miarolitic cavities in the margin of the Ninemile quartz monzonite indicate that the quartz monzonite intruded the caldera core and part of its rim to within a short distance of the surface. Although probably related in some way to the rapakivi granties of the Wolf River batholith, Van Schmus (1980, in press) has determined that the Wausau syenite plutons were intruded at 1520 m.y. as contrasted with a 1500 m.y. age for the Wolf River batholith. Thus, the syenites appear to represent an early, shallow, volcanic manifestation of Wolf River batholith intrusive activity. Evidence suggesting that the Stettin pluton is the older is: (1) fragments of porphyritic trachyte (?) similar to that now exposed on both sides of the Wisconsin River at Brokaw are found in the Wausau syenite (Stop #3); (2) the Stettin pluton produced a wider halo of syenitization and contains fewer unassimilated xenoliths. Shearing with chaotic vertical displacement and mixing of wallrock fragments greatest in the intermediate zone of the Wausau pluton and less important 1n the wall zone of the Stettin pluton. Semi-detached wallrock slices, partly sheared away from the cylindrical wall, are seen on the east and south sides of the Stettin pluton. By contrast, xenoliths in the contaminated intermediate zone of the Wausau pluton were completely detached and show no essent~al .r~lationship to contiguous wallrocks. Thus, there appears to have been slgnlflcantly greater vertical transport of xenoliths in the intermediate (caldera rim) zone of the Wausau pluton. The occurrence of sillimanite in q~artzite xenoliths at Rib Mountain (3-M quarry) and on a ridge about 1 1/2 mlle northwest of Stop #4 suggests a derivation from a deeper metamorphic basement. However, the possibility of the metasomatic origin of sillimanite should not be ruled out. There is certainly ample evidence of metasomatism - syenitization - of xenoliths throughout the pluton. ~as �-55- There is little doubt of the close genetic relationship of the Wausau, Ninemile, and Stettin plutons. Based on field relations, the cross section reconstruction is proposed (Figure 26). The concentric xenolith-rich zones, which typically show effects of shearing, suggest that the vertical movement, probably up and down, was localized in these caldera rim collapse structures. This suggests that the floor of the Wausau syenite caldera foundered in the upwelling Ninemile quartz monzonite. Our field and laboratory investigations are now focusing on the Wausau syenite and Ninemile plutons. After completion of this work, a much more detailed picture of magma emplacement conditions, sequence, and mechanism as well as its association with volcanism should be possible. �_ ----,/' ....... '/'-''-/''', JV'O... , , ~" ".'" ~~ ;' '" /" ", .... ,'... --_/ .......... ..... '" ~ ..... '" ...... - .......... SOUTHEAST ----.... '- A A' L . ST ETTIN PLUTON----...I '-1 PEI"\-'80 EXPLANATION ~ ~ Ninemile.quartz monzonite ~+ + +J Amphibole syenite +~ • ."'.~:."';"'. .', ~t.·'!:t~'* • .. .,;. ,.. .m ~ Gneissic nepheline and tabular syenite border facies Syenitized volcanic rocks ~ Lensoidal quartz syenite with xenoliths of biotite schist and quartzite ~ Alkalic extrusives, probably pyroclastics and subordinate flows ~L·.1·:~.'"J '.,,'. [±J Fi gure Pyroxene syenite - Quartz diorite Quartzite Older calc-alkaline volcanic rocks, mainly andesite and rhyolite Hypothetical northwest-southeast section across the Stettin and Wausau syenite plutons as they would have appeared about 1450 m.y. ago. Line A-A' represents the present land surface. See Fiqure 4 for location of section A-A'. I tTl 0) I �-57REFERENCES Bailey, O.K., and Schairer, J.F., 1966. The system Na 0 - A1 0 Fe203 - Si0 2 at 1 atms., and the petrogenesis of alkaline 2rocks. 2 3 Journal of Petrology. V.7, p. 114-170. Berlin, L.A., and Sood, M.K. (1979). Alkaline rocks of the Stettin area, Wisconsin Geol. Soc. Am., V. 11, No.5, p. 225-226. Barker, D.S., 1974. "Alkaline rocks of North America' in the Alkaline Rocks. Sorensen, editor. New York: John Wiley and Sons, p. 160-171. Bowen, N.L., 1928. The Evolution of the Igneous Rocks. Dover Publications, INc., p. 332. New York: Bowen, N.L., 1945. Phase equilibria bearing on the origins and differentiations of alkaline rocks. Am. J. Sci., V. 243, A., p. 75-89. Daly, R.A., 1910. V. 21, p. 87-118. Origin of a"lkaline rocks. Geol. Soc. Am. Bull., Deer, W.A., Howie, R.A., and Zussman, J., 1963. V. 2-4. New York: John Wiley and Sons. Rock Forming Minerals. Dutton, D.E., and Bradley, R.E., 1970. Lithologic geophysical and mineral commodity maps of Precambrian rocks in ~Jisconsin. U.S.G.S. Misc. Inv. Map 1-631, p. 15. area: Emmons, R.C., and Snyder, F.C., 1944. A structural sutdy of the Wausau Wisconsin Geological and Natural History survey, unpub. report. Emmons, R.C., 1953. Selected Petrogenic Relationships of Plagioclase. Geol. Soc. Am. Mem., V. 52, p. 142. Fudali, R.F., 1963. Experimental studies bearing on the origin of pseudoleucite and associated problems of alkali rock systems. Bull. Geol. Soc. Amer., V. 74, p. 110. Geisse, Elaine, 1951. The petrography of the syenites, nepheline syenites, and related rocks west of Wausau, Wisconsin. M.A. thesis, Smith college. Hamilton, D.L., and MacKenzie, W.S., 1960. Nepheline solid solutions in the system NaA1Si0 4 - KA1Si0 4 - Si0 2 . J. Petrology, V. 1, p. 56-72. Hamilton, D.L., and MacKenzie, W.S., 1965. Phase-equilibrium studies in the system NaA1Si0 4 (nepheline) - KA1Si0 4 (kalsilite) - Si0 2 -H 2). Min. Mag., V. 34, p. 215-231. Hayama, Y., 1959. Some considerations on the color of biotite and its relation to metamorphism. Jour. Geol. Soc. Japan, V. 65, p. 21. Henderson, J.R., Tyson, N.S., and Page, J.R., Aeromagnetic Map of the Wausau area, Wisconsin, U.S.G.S. Geophysical Investigations Map Gp-401, 1963. Hyndman, D.W., 1972. Petrology of Igneous and Metamorphic Rocks. New York: McGraw-Hill Book Co., p. 533. �-58Jones, J.B., Nesbitt, R.W., and Slade, P.G., 1969. The determination of the orthoclase content of homogenized alkali feldspar using 201 x-ray method. Min. Mag., V. 37, p. 489-496. Koellner, S.E. 1974. The Stettin Syenite Complex, Marathon County, Wisconsin: Petrography and Mineral Chemistry of olivine, pyroxene, amphibole, biotite, and nepheline, unpublished M.S. Thesis, University of Wisconsin - Madison. Kogarko, l.N. and Ryabchikov, 1.0., 1961. Dependence of the contents of halogen compounds in the gaseous phase on the chemistry of the magma. Geochemistry, V.12, p. 1195-1201. Kuellmer, F.J., 1959. X-ray intensity measurements on perthitic materials, I: theoretical considerations. J. Geol., V. 67, p. 648-660. laBerge, G.l., 1969. Preliminary report on the geology of the northern part of the Wausau East quadrange, Wisconsin. Wis. Geol. Nat. Hist. Survey Open File Report, p. 13. laBerge, G.l., 1971. Progress report on mapping of Precambrian geology in Marathon County, Wisconsin. Wis. Geol. Nat. Hist. Survey Open File Report, p. 27, maps. laBerge, G.l., and Myers, P.E., 1972. 1971 Progress report on mapping of Precarnbrian geology of I~arathon County, Hisconin. ~Jis. Geol. Nat. Hist. Survey Open File Report, p. 28, maps. laBerge, G.l., and Myers, P.E., 1973. 'Precambrian Geology of Marathon County', in Guidebook to Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, p.31-86. MacKenzie, W.S., 1960. Review of some contributions of experimental studies to petrology. Liverpool and r~anchester Geological Journal, V.2, p. 369-388. Medaris, Jr., l.G., Anderson, J.L., and Myles, J.R., 1973. The Wolf River Batholith - A late precambrian rapakivi massif in northeastern Wisconsin, in Guidebook to the Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, p. 9-30. Myers, P.E., 1973. ·Stettin syenite pluton-wall zone', in Guidebook to the Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, 75-76. Myers, P.E., The Wausau syenite of Central Wisconsin, Abs., Institute on lake Superior Geology, p. 42, 1976. Nockolds, S.R. 1954. Average chemical compositions of some igneous rocks. Geol. Soc. Amer. Bull., V.65, p. 1007-1032. Smith, J.V., 1974. p.627. Feldspar Minerals, V.l, New York: Springer-Verlag, Sood, M.K., and Edgar, A.D., 1970. Melting relations of undersaturated alkaline rocks. Meddelelsen Om Gronland. Bd. 181, Nr. 12, p. 41. �-59- Sood, M.K., and Edgar, A.D., 1972. The system diopside-forsteritenepheline-albite-leucite and its implication to the genesis of alkaline rocks. 24th Int. Geol. Congr. Montreal, V. 14, p. 68-74. Sood, M.K., Platt, R.G., and Edgar, A.D., 1970. Phase relations in portions of the system diopside-nepheline-kalsilite-silica and their importance in the genesis of alkaline rocks. Can. Miner., V. 11, p. 380-394. Sorensen, H., 1970. Internal structures and geological setting of the three agpaitic intrusions - Khibina and Lovozero of the Kola peninsula and Ilimaussaq, South Greenland. Can. Min., V. 10, p. 299-334. Sorensen, H., 1974. Sons, p. 622. The Alkaline rocks. New York: John Wiley and Thorton, C.P., and Tuttle, O.F., 1960. Chemistry of igneous rocks. I. Differentiation Index. Am. J. Sci., 258, p. 644-684. Tilley, E.E., 1957. Problems of alkali rock genesis. Lond., V. 113, p. 323-360. Q.J. Geol. Soc. Turner, D.S., 1948. Heavy accessory minerals and radioactive studies of the igneous rocks in the Wausau area: Ph.D. dissertation. Univ. of WisconsinMadison. Tuttle, O.F., and Bowen, N.L., 1958. Origin of granite in the light of experimental studies in the system NaA1Si 308 - KA1Si 308 - Si0 2 - H20. Geol. Soc. Am. Mem., V. 74, p. 153. Van Schmus, W. R., 1973. 'Chronology of Precambrian Rocks in Wisconsin', in Guidebook to the Precambrian Geology of Northeastern and Northcentral Wisconsin. Wis. Geol. Nat. Hist. Survey, p. 1-8. Van Schmus, W.R., Medaris, Jr., L.G., and Banks, P.O., 1975a. Geology and Age of the Wolf River Batholith, Wisconsin. Geol. Soc. Am. Bull., V. 86, p. 907-914. Van Schmus, W.R., Thurman, E.M., and Peterman, Z.E., 1975b. Geology and Rb-Sr Chronology of Middle Precambrian Rocks in Eastern and Central Wisconsin. Geol. Soc. Am. Bull., V. 86, p. 1255-1265. Wager, L.R., 1965. The form and internal structure of the alkaline Kangerdlugssuaq intrusion, East Greenland. Min. Mag., V. 34, p. 487-497. Weidman, S., 1907. The Geology of North Central Wisconsin. Nat. Hist. Survey Bull., V. 16, p. 697. Wis. Geol. Wright, T.L., 1968. X-ray and optical study of alkali feldspars: II an X-ray method for determining the composition and structural state from measurement of 20 values for the reflections. A. Min., V. 53, p. 88-104. Wright, T.L., and Stewart, D.B., 1968. X-ray and optical study of alkali feldspars: II determination of composition and structural state from refined unit-cell parameters and 2V. Am. l\1in., V. 53, p. 38-87. � https://digitalcollections.lakeheadu.ca/files/original/f93951c247fc58cf4b6675df14962fcb.pdf f7cbd59692bd8796e0f6943abbb81322 PDF Text Text 26Th Annual 26th Annual Institute on on Lake Superior Superior Geology Geology FIELD TRIP FIELD TRIP 4 ogy & The Precambrian Geol The Precambrian Geology & Tectonics Tectonics ounly Wisconsin of Marathon Marabon C Couniy Wisconsin P/n.h... P14q GENERALIZED PRECAMBRIAN PRECAMBRIAN GEOLOGY GEOLOGY OF THE THEEAU EAUCLAIRE CLAIREREGION REGICN Diabase Diabase Gabbro Gabbr0 Tonolite Tonolite Trondhjemite Trondhjemiie Volconics Volcanics and and sediments Amphibolites Amphibdiies + Shear zone I; Shear zone 1980 May 10, 10,1980 Claire University of Wisconsin-Eau Wisconsin-Eau Claire �FIELD FIELD TRIP TRIPGUIDEBOOK GUIDEBOOK FOR FOR THE MIDDLE COUNTY, WISCONSIN THE MIDDLEPRECAMBRIAN PRECAMBRIAN GEOLOGY GEOLOGY OF MARATHON MARATHON COUNTY, WISCONSIN Leaders Leaders Gene and EElizabeth Gene L.L. LaBerge LaBerge and l i z a b e t h Palmer Palmer Special Paper Paper THE PRECAMBRIAN AND TECTONICS TECTONICS OF THE PRECAMBRIAN GEOLOGY GEOLOGY AND MARATHON COUNTY, WISCONSIN MARATHON COUNTY, WISCONSIN by Gene Gene LL.* LaBerge LaBerge Prepared Prepared f for o r the t h e 26th 26th Annual Annual Meeting Meeting ooff the the INSTITUTE ON INSTITUTE ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Eau Eau CClaire, l a i r e , Wisconsin, Wisconsin, 1980 1980 �Co "VA—-.- -- E- 1Le ——-.0 9 C a -S ---A —--4 .0 -a '—i— CIVIL TAMIMS It- 'E' N). VA VA 111DM Il-I 'r • �CONTENTS CONTENTS Page ................................................... 1 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS ............................................... 1 GENERAL GENERAL GEOLOGY GEOLOGY ................................................ 1 EARLY(?) PRECAMBRIAN ........................................... 44 EARLY ( ? )PRECAMBRIAN Gneisses Gneisses and and Schists S c h i s t s ....................................... 44 MIDDLE MIDDLEPRECAMBRIAN PRECAMBRIAN ............................................. 66 METAVOLCANIC METAVOLCANICROCKS ROCKS ............................................. 6 Mafic M a f i c and and Intermediate I n t e r m e d i a t eMetavolcanic MetavolcanicRocks Rocks .................. 6 Felsic F e l s i cMetavolcanic MetavolcanicRocks Rocks .................................. 7 Metasedimentary MetasedimentaryRocks Rocks ...................................... 9 INTRUSIVE INTRUSIVEROCKS ROCKS ................................................ 10 10 Gabbroic Gabbroic Intrusions I n t r u s i o n s ........................................ 10 10 Ultramafic Ul t r a m a f i c Intrusions I n t r u s i o n s ...................................... 11 Granitic G r a n i t i c Intrusions I n t r u s i o n s ........................................ 11 INTRODUCTION INTRODUCTION 1 1 1 6 6 7 9 11 11 ............................................... 1313 The Wolf R River The Wolf i v e r Batholith B a t h o l i t h ...................................13 13 The The Syenite S y e n i t e Plutons Plutons ........................................ 14 14 Wausau Syenite Pluton Wausau Syenite Pluton ....................................... 14 14 Stettin S t e t t i nSyenite SyenitePluton P h t o n ..................................... 15 15 Diabase Diabase Dikes Dikes .............................................. 15 15 STRUCTURAL STRUCTURALGEOLOGY GEOLOGY ............................................. 15 15 Regional Regional Setting S e t t i n g ........................................... 15 15 Folding F o l d i n g .................................................... is 15 Faulting F a u l t i n g ................................................... 16 16 LATE LATEPRECAMBRIAN PRECAMBRIAN —1— �Page CONTENTS (continued) CONTENTS (continued) Deformed Volcanic Rocks .................................... Deformed Volcanic Rocks . Minor Structure Structure ............................................ Minor 21 21 ...........................................29 SUMMARY ........................................................ 30 REFERENCESCITED CITED ............................................... REFERENCES GEOLOGICALSTOP STOPDESCRIPTIONS DESCRIPTIONS ................................... 33 GEOLOGICAL TECTONICSPECULATION SPECULATION TECTONIC SUMMARY 31 ............................... Rib Falls Falls- -Deformed Deformed intrusion intrusionbreccia breccia ..................... Rib - Pillow Pillowbasalts basalts ArtusCreek Creek — Artus 34 37 - t ofof R i b River River ata tEmory Emory School School - Iiltramafics Ul tramafics at a tcontac contact Rib .........................................39 c gneiss Black Creek, Creek, Athens Athens -- Quartzofeldspathi Quartzofeldspathic gneiss ............ 41 Black eared rocks Athens County County Park Park—-Sh Sheared rocks ......................... 43 Athens - Lineated Lineated andesite andesite ........................... 45 Hamann Creek Creek — Hamann L i t t l e Eau EauP1Pleine River — - Gneiss Gneiss ........................... 47 elne River Little Wild Rozellville - -Ultramafic Wild Creek, Creek, Rozellville Ultramaficrocks rocks ................... 49 gneiss terrane terrane gneiss . . ILLUSTRATIONS ILLUSTRATIONS RouteMap Map Route .........................................Frontispiece Frontispiece Figure1 1 -. Geological map map of of northern northernWisconsin Wisconsin Geological Figure ............ 2 Figure 22- . Geologicalmap mapofofMarathon MarathonCounty County Figure Geological 3 Figure 33 -. Table of ofgeological geologicalevents events Table Figure ............... ...................... 5 ............................ Figure 55 -.Lahar Lahar ........................................... Figure Figure 56 -.Welded Welded ttuff u f f ..................................... Figure 8 Figure 44 -. Flow banded banded rrhyolite hyolite Figure Flow — 11 8 9 �CONTENTS (continued) CONTENTS (continued) ILLUSTRATIONS ILLUSTWTIONS Page continued) (continued) ........ Figure Simplified map of structural Figure 88 — .Simplified map of structural geology geology ............ Figure Aeromagnetic Aeromagneticmap map ................................ Figure 99- . Figure - Flaser Flaser gneiss gneiss .................................. Figure 10 10— Figure Foliated quartz quartz monzonite monzonite cut by by granite granite Figure 77 -.Foliated 12 12 17 17 19 19 20 20 ............... 2020 Figure Figure 12 12 — - Mylonite outcrop outcrop ............................... 22 22 Figure Texture of ofmylonite mylonite ............................ 22 22 Figure 13 13 -- Texture Figure Photomicrographs Figure 14 14 -. Photomicrographs of mylonite mylonite ................... 23 23 Figure Figure 15 15 -- Cataclastic Cataclastic degradation degradation of granite granite ............. 24 24 Figure Photomicrographofof fflaser - Photomicrograph l a s e r gneiss gneiss Figure1111 — Figure Boudinagedphenocrysts phenocrystsininf felsic Figure 16 16 — - Boudinaged e l s i c volcanics volcanics ..... 25 25 ........................... 2626 Figure Figure 18 18 --Diagram Diagram of of graben graben structure s t r u c t u r e .................... 30 30 Pillow Pillowlavas lavasononArtus ArtusCreek Creek ................................ 35 35 North—south cross—section of of northern North-south cross-section northern Wisconsin Wisconsin ............ 35 35 Sketch 43 Sketch map map of of Athens Athens Park Park .................................. 43 North—south North-south cross—section cross-section across acrossMarathon MarathonCounty County ........... 44 44 Photo 46 Photo of lineated lineatedandesite andesite ................................. 46 Figure Figure 17 17 - Deformed Deformed f efelsic l s i c tuff tuff Photo Photo of gneiss gneiss on on Little L i t t l eEau Eau Pleine PleineRiver River — 111 — ................. 48 48 �Special Special Paper Paper THE THE PRECAMBRIAN PRECAMBRIAN GEOLOGY GEOLOGY AND AND TECTONICS TECTONICS OF OF MARATHON MARATHON COUNTY, WISCONSIN WISCONSIN by Gene Gene L. L. LaBerge LaBerge �INTRODUCTION INTRODUCTION This more This paper paper iiss taken, taken, in i npart, p a r t from , froma a moreextensive extensive report r e p o r ton onthe t h egeology geology of by Paul Paul Myers andme mei nin ppreparation o f Marathon Marathon County County by Myers and r e p a r a t i o n for f o r the t h eWisconsin Wisconsin Geological are presented Geological Survey. Survey. More More ddetails e t a i l s on on the t h e geology geology are presented iin n that t h a t paper. paper. The iinterpretations n t e r p r e t a t i o n s expressed expressed here o t nnecessarily e c e s s a r i l y r reflect e f l e c t those those ooff the the The heredodon not Wisconsin Wisconsin Survey. Survey. They They are based based upon upon nnine i n e field f i e l dseasons seasonsofomapping f mappingbybyme me and reconnaissance mapping and six s i x by by Myers, Myers, ini naddition a d d i t i oto n textensive o extensive reconnaissance mappingbybyMyers Myers in i nEau Eau Claire C l a i r eand andChippewa Chippewa Counties. Counties. IIconsider a forum consider this t h i s field f i e l dtrip t r i (and p (andalla others) l l o t h e r sto ) tbe o be a forumfor f o discussion r discussion on on the the geology geology of o f the t h earea. area. This This paper paper and and stop s t o p descriptions d e s c r i p t i o n sare arepresented presented as background material as background m a t e r i a l ffor o r the the discussion. discussion. The The ttrip r i pisi sdesigned designedtot oshow show representative County,pparticularly r e p r e s e n t a t i v e examples examples oof f tthe h e geology geology ooff Marathon Marathon County, a r t i c u l a r l y those those exposures bearon ont hthe Some ooff the the exposures t hthat a t bear e sstructural t r u c t u r a l and and ttectonic e c t o n i c setting. s e t t i n g . Some exposures ande elicit exposures vvisited i s i t e d present present problems problems and l i c i t questions questions regarding r e g a r d i n g the t h e tectonic tectonic setting. problems and questions probably will not be fully answered; s e t t i n g . These These problems and questions probably w i l l n o t be f u l l y answered; however, however, II hope hope tthe h e ttrip r i pstimulates s t i m u l a t e sothers otherstot oponder ponderthese these questions, questions, and and to to propose alternate propose a1 t e r n a t e solutions. solutions. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This This paper paper isi sbased basedon on field f i e l mapping d mappingbybyPaul PaulMyers Myersand andme me that t h a thas hasbeen been funded funded by by the t h e Wisconsin Wisconsin Geological Geological Survey Survey since since1969. 1969. Their T h e i r continued continued support support is i s greatly g r e a t l yappreciated. appreciated. Some Some ofof tthe h e ideas expressed expressed hherein e r e i n are a r e the t h e outgrowth outgrowth of discussionswwith Paul Myers Myersdduring course ooff the o f numerous numerous discussions i t h Paul u r i n g tthe h e course t h e project p r o j e c tand and are a r e hereby herebyacknowledged. acknowledaed. Review comentsby byMike MikeMudrey Mudrey and3nane aearlier onon t h this i s and r l i e r vversion e r s i o n of o f the the Review coments manuscript most hhelpful. manuscript have have been been most e l p f u l . Paul Paul Myers Myers also a l s o reviewed reviewed the t h emanuscript manuscript and and offered o f f e r e d helpful h e l p f u lsuggestions. suggestions. Their T h e i r assistance assistanceisi acknowledged s acknowledged with with gratitude. gratitude GENERAL GENERALGEOLOGY GEOLOGY Marathon Countyi is Marathon County s situated s i t u a t e d near near the t h esouthern southernmargin marginofo the f theexposed exposed Precambrian shield^ Its Precambrian Shield. I t sregional r e g i o n a lsetting s e t t i n gin ithe n t hPrecambrian e Precambrianofo fWisconsin Wisconsin is is shown shown iin n Figure Figure 1. l aThe The bedrock bedrock is i spredominantly predominantlyPrecambrian Precambrianigneous igneousand and metamorphic rockswwith fewsscattered metamorphic rocks i t h aa few c a t t e r e d ooutliers u t l i e r s of o fPaleozoic Paleozoic sandstone sandstone that that unconformably rocks (Figure 2 ) . Early unconfomably ooverlie v e r l i e the t h e Precambrian Precambrian rocks ( F i g u r e 2). E a r l yPrecambrian(?) Precambrian(?) gneisses 1900may.) m.y.) vvolcanic gneisses and and Middle Middle Precambrian Precambrian ( (± t 1900 o l c a n i c rocks rocks are a r e intruded intruded by post—tectonic Middle Precambrian (VanSchmus, Schmus, by numerous numerous syn— syn- t to o post-tectonic-Middle Precambrian (+ ( t1850 1850m,y.) m.y . )(Van 1976) ranging iin fromquartz quartzd diorite 1976) pplutons l u t o n s ranging n composition composition from i o r i F e to t o granite. g r a n i t e . The The volcanic v o l c a n i c rocks rocks range range in i n composition composition from from bbasalt a s a l t to t o rhyolite r h y o l i t eand andoccur occuras as isolated andblocks blocksi nin tth i s o l a t e d pendants pendants and h e plutonic p l u t o n i crocks. rocks. Stratigraphic S t r a t i g r a p h i cand and structural s t r u c t u r a l relationships r e l a t i o n s h i p sofo the f t h evolcanic v o l c a n i crocks rockswithin w i t h i nindividual i n d i v i d u ablocks l blocksand and correlation c o r r e l a t i o nbetween between blocks blocks is i suncertain u n c e r t a i nbecause because of o flack l a c kofoexposures f exposuresand and deformation. deformation. Eastern Countyi sisuunderlain byt the Wolf RRiver Eastern Marathon Marathon County n d e r l a i n by h e Wolf i v e r bbatholith, a t h o l i t h , aa large Precambrian (1500 m.y.) ageage (Van Schmus l a r g eanorogenic anorogenic pluton p l u t o nofoLate f Late Precambrian (1500 m.y.1 (Van Schmusand and The circular Wausau and Stettin syenite bodies west others, 1975). others, 1975). The c i r c u l a r Wausau and S t e t t i n s y e n i t e bodies westof oWausau f Wausau —1— �PRECN4BRIAN of WISCONSIN Quartist. ODLE PRECAI4ThRIMI EAJLT PPNMPXMJ4 Gr.nitic P..ck. Qtanitic Packs zrcn—Fo=tion Metavoicanc Mock. Domiftsatly 'Metas.dLm.ntary .cks omAnat1y Metatotcanto Mocks L I oa.i,3.c Mocks Figure 11.. Generalized geological geological map of Precambrian rocks in in northern Generalized map of Precambrian rocks northern MarathonCounty County outlinedininthe thecentral central part part of the Wisconsin. Marathon i s is outlined the (Data in part state. (Data part from from Sims, Sims, 1976.) 1976.) —2— - 2 - �U) g C 0 C) 0 0) -S 0) -h 0 -o 0) 0 pJ -J I0 0 0 CD 0 N) CD 5 C -n —I. (0 wIsl•oNsFNefE,to(;IcALANpNAIUflALHIsIoR SURVEY Interim Copy) MARATHON COUNTY.WIS. OF GEOLOGY n -5-. (AT B PEE CAM BRIE N EXPLANATION EANLY PEECAMOHEAN - LI] — MIDDLE PEE CAMHBIAN SCALE �are related to Several are probably probably related t o the the Wolf Wolf River River batholith batholith (Myers, (Myers, 1976). 1976). Several small quartz monzonite porphyry plugs plugs and anddiabase diabasedikes dikes aare small monzonite porphyry r e aalso l s o of Late Late Precambrian age. Precambrian age. Several large northeast of cataclasis Several northeast and and northwest northwest zones zones of c a t a c l a s i s dominate dominate the the Major shear shear zones zonesand ands pspatially a t i a l l y related related structural geology geology (Figure (Figure 2). 2 ) . Major ultramafic gneissic rocks ul tramafic bodies bodies separate separate gneissic rocks from from the t h e greenschist greenschist facies f a c i e s Middle Middle Precambrian volcanic-plutonic volcanic—plutonic complex. within the Precambrian complex. Similar cataclastic c a t a c l a s t i c zones zones within the Middle Precambrian complexhave havethe the same sameo rorientation Middle Precambrian complex i e n t a t i o n as as the themajor majorboundary boundary fault f a u l tzones. zones. Field relationships suggest suggest aa long long history of of shearing shearing before, before, Field relationships during the plutonic plutonic rocks. rocks. during and and aafter f t e r emplacement emplacement ofofthe Three ages agesofof glacial glacial drift Three d r i fwere t wererecognized recognizedbybyLaBerge LaBerge (1971). (1971). Mickelson and others (1974) (1974) confirmed confirmedthe theexistence existenceofof the the three three drifts and others d r i f t sand andshowed showed tthat hat they range they range in age age from from pre-Wisconsin pre-Wisconsin to t o late l a t eWoodfordian. Woodfordian. Figure 33summarizes summarizes the geological the geological events events recognized recognized in inand and adjacent adjacenttot oMarathon Marathon County. County. EARLY(?) EARLY ( ? ) PRECAMBRIAN PRECAMBRIAN Gneisses and and Schists. Schists. Medium— coarse—grainedquartzofeldspathic quartzofeldspathic Gneisses Medium- t otocoarse-grained biotiteb i o t i t e -and andhornblende-bearing hornblende-bearing gneisses, gneisses, schists s c h i s t s and and migmatites migmatites underlie underlie northwestern MarathonCounty Countyand andoccur occurasasisolated isolated blocks blocks along northwestern Marathon along the the southern southern edge of the gneissic rocks edge of the county. county. The The gneissic rocks are are poorly poorly exposed exposed and and cconsist o n s i s t mainly mainly of large blocks and and widely widely scattered outcrops. The gneisses largefrost—heaved frost-heaved blocks outcrops. The gneisses range iin from ggranite range n composition composition from r a n i t e to t o quartz quartz diorite d i o r i t and e andhave havea aconspicuous conspicuous ffoliation o l i a t i o n and and lineation. l i n e a t i o n . Biotite B i o t i t eoro hornblende r hornblendeoroboth r bothcomprise comprise15—40 15-40 percent percent of the are garnetiferous. garnetiferous. The The common comon occurrence occurrence of of the rock rockand and some some phases phases are hornblende, have been metamorphosed hornblende, and and llocally o c a l l ygarnet, garnet,suggests suggeststhat t h athey t they have been metamorphosed facies. tto o amphibolite amphiboli te facies. Reconnaissance geologicmapping mappingt otothe the west west and and north north of Reconnaissance geologic of Marathon Marathon County County suggests suggests tthat h a t the the gneisses gneisses are a r e part p a r tofofa ahigh—grade high-grade metamorphic metamorphic t terrane e r r a n e tthat hat extends the west. west. Gneissic extends aat t lleast e a s t 60 60 miles miles to t o the Gneissic rocks rocks extend extend in in aa northeasterly direction along Countya tatl eleast along the the northern northern part p a r t of of Marathon Marathon County a s t t to o PPrairie r a i r i e Dells Dells in Lincoln (about 13 13 km kmnortheast northeastofofHMerrill). e r r i l l ) . The Lincoln County County (about The gneisses gneisses closely closely resemble those those of of the Miphibolite resemble the "Chippewa "Chippewa Anphi bol i t e Complex" Complex" described described by by Myers Myers (1974, ( 1 974, and Eau Claire Claire Rivers. theChippewa Chippewa and and Eau Rivers. and tthis h i s conference) conference) from fromexposures exposures along along the Knownexposures exposuresof of Precambrian Known Precambrian rocks between between Marathon Marathon'and and Chippewa Chippewa and and Eau Claire Claire Counties Counties are a r edominantly dominantlyhigh—grade high-grade metamorphic metamorphic rocks. The Eau The gneissic pattern of of gently gneissic rocks rocks have have aa ddistinctive i s t i n c t i v e aeromagnetic aeromagnetic pattern gently curving curving anomalies, compared w iwith t h a ablotchy magnetic highs the anomalies, compared blotchypattern pattern of of magnetic highs and and lows lows in in the remainder of of Marathon County (Figure (Figure 9). The Bouguer Bouguer Anomaly AnomalyGravity Gravity Map Map of remainder Marathon County 9 ) . The Ervin and Haniiier(1974) (1974)shows shows gneisses area of of zero to Ervin and Hammer t h ethe gneisses as as a daidistinct s t i n c t area to minus40 40mmilligals, with minus minus4040t otominus minus9090mmilligals minus i l l i g a l s , compared compared with i l l i g a l s in the the remainder remainder of of Marathon Marathon County. County. Therefore, the t h eknown known geology, geology, aeromagnetics aeromagnetics and gravity all part of aa and gravity a l lsuggest suggest that t h a tthe thegneisses gneisses ininMarathon Marathon County County aare r e part large "block" as shown on Figure 1 "block" as shown on Figure 1 . Gneissic rocks rocks in and and on on the the periphery periphery of ofMarathon Marathon County County aare r e strongly strongly Gneissic lineated, 1ineated, with with mineral mineral lineations lineations and and fold foldaxes axes plunging plunging 20°-60 200-600 west west in in the the plane of the the ffoliation plane of o l i a t i o n (Figure (Figure 8). 8 ) . For For example, example, llineations i n e a t i o n s and and fold foldaxes axes along the Rib west; fold Rib River near near Goodrich Goodrich ((in i n Taylor Taylor Co.) Co.) plunge plunge 30°—40 300-400 west; along the -4- �PERIOD OR OR ERA ERA GEOLOGICAL EVENTS EVENTS Pleistocene Pleistocene Woodfordian Drift (Late Woodfordian Drift (LateWisconsin) Wisconsin) MerrillI Drift Wisconsin) Drift(Early (Early Wisconsin) Merril Wausau Drift (Pre-Wisconsin?) Wausau Drift (Pre-Wisconsin?) - _-- - - — _,jJnconforthfty Un conformity Paleozoic Paleozoic Scattered Outliers Scattered Upper Upper Cambrian(?) Cambrian;?) Sandstone Sandstone Outliers jJnconformity Late Late Precambrian Precambrian Diabase Dikes Dikes (1200 m.y.?) Diabase m.y.?) Quartz Porphyry Porphyry Plugs Plugs Wolf Wolf River Batholith Batholith (1500 (1500 m.y.) m.y.) Unconformity Unconfonnity Emplacement Post-tectonic Plutons (1765 Emplacement ofofPost-tectonic (1765 m.y.) m.y .) Emplacement Syn—tectonicPlutons Plutons (1850 m.y.) Emplacement ofof Syn-tectonic m.y. ) Major Faulting Faulting in Major in Central Central Wisconsin Wisconsin Middle Middl e Precambrian Precambrian Volcanic-sedimentary (1900 m.y.) Vol canic-sedimentarySequence Sequence (1 900 m.y .) •— ? —? Unconfothity __, 7—.-—— 7 I) 7— 4 Metamorphism toto Amphibol i te Facies? Fades? Metamorphism Amphibolite Early Sedimentary-volcanic Early Sedimentary-volcanicSequence? Sequence? Unconformity Early Early Precambrian Precambrian Gneisses, Migmati Migmatites, Amphiboli tes Gneisses, tes, Amphibolites somegreater greater than than 2800 2800m.y. ni.y, old some anoutline outline of Figure 3. 3. Table Table showing showing an of geological geologicalevents eventsrecognized recognized in in central central Wisconsin. Wisconsin. —5— �axes Marshfield plunge about 20' 200west; west; strong strong mineral mineral llineation axes iinn gneisses gneisses near near Marshfield plunge about ineation in amphibolites amphibolites along along the t h e Little L i t t l eEau EauClaire ClaireRiver Riverin isoutheastern n southeasternMarathon Marathon County plunge60 600southwest; southwest;fold fold axes County plunge axes in migmatitic migmatiticgneisses gneissesata Greenwood t Greenwood (in (in Clark 36°west; west;and andfold foldaxes axesa tatNNeillsville e i l l s v i l l e (in ( i nClark ClarkCo.) Co.)plunge plunge Clark Co.) Co.) plunge plunge 35' 70° 70 west. west. . No published radiometric radiometric ages No published ages aare r e available available from fromthe thegneisses gneissesininMarathon Marathon County, andtherefore therefore ttheir County, and h e i r age age is is uncertain. uncertain. However, Van Van Schmus Schmus and and Anderson (1977)reported reported an an age ageof of more morethan than 2800 2800m.y. m.y.ffor Anderson (1977) o r migmatitie migmatitie gneisses gneisses at kmkmsouth Marathon s t u d i e s of of a t Pittsville P i t t s v i l l(25 e (25 southof of MarathonCounty). County). Structural studies gneisses several llocalities centralWisconsin, Wisconsin,and and radiometric radiometric dating dating o c a l i t i e sini ncentral gneisses aat t several led Maass andMedaris Medaris(1977) (1977)t otoconclude concludet hthat gneisses iinn central centralWisconsin Wisconsin Maass and a t tthe h e gneisses are (1978, and a r e mainly mainly of ofMiddle MiddlePrecambrian Precambrian age. age. Myers Myers (1978, and this t h i sconference) conference)showed showed that and Chippewa EauClaire Claire and ChippewaCounties Countieshad hadundergone undergone t h a t amphibolites amphibolitesand andgneisses gneissesini nEau two anddeformation deformationp rprior two periods periods of metamorphism metamorphism and i o r tto o being being included included inin1850 1850m.y. m.y. old than one age of of gneissic T h u s , there appears appears to t o be be more more than one age gneissic rocks rocks old piutons. plutons. Thus, in i n the the region. region. This This point point will willbebediscussed discussed further f u r t h e runder under the thesection sectionon on structure. structure. MIDDLE MIDDLE PRECAMBRIAN PRECAMBRIAN METAVOLCAN IC ROCKS METAVOLCANIC ROCKS Volcanic occur aas xenoliths, screens pendantsi nin iintrusive Volcanic rocks rocks occur s xenoliths, screens and and pendants n t r u s i v e rocks rocks and and and aas s rrelatively e l a t i v e l ycontinuous continuousareas areasini northern n northern andeastern easternMarathon MarathonCounty. County. They rangei nin composition compositionfrom frombasalt basaltt otor rhyolite They range h y o l i t e and and eexhibit x h i b i t aa wide wide variety variety of of textures textures and and primary primary sstructures, t r u c t u r e s , including including pillow pillowlavas, lavas,massive massive flows, flows, flow breccias, volcanogenic breccias, welded welded tuffs, t u f f s ,tuffs t u f fand s and volcanogenicsediments. sediments. The The rocks rocks have except near near llarger have undergone undergone l ilittle t t l emetamorphism metamorphism except a r g e r plutons, plutons, and and consequently, consequently, primary primary textures and and structures s t r u c t u r e s are a r e well well preserved preserved where where the t h e rocks rocks are a r e not not highly has been beenextensively extensively disrupted by by high1 ydeformed. deformed. The The volcanic sequence sequence has faulting f a u l t i n gand and intrusion, intrusion,forming formingisolated i s o l a t e dblocks blockssurrounded surrounded by by plutonic rocks. rocks. This, coupled with i t h the the generally generally poor poor exposure, exposure, precludes precludes establishing the the coupled w original volcanic volcanic stratigraphy. stratigraphy. U/Pb UIPb age n rrhyolite hyolite agedeterminations determinationsononzircons zirconsi in on the the east e a s t edge edge of Wausau indicate a t volcanic t h i sarea areaare a r e1900 1900 m.y. m.y. on of Wausau indicatet hthat volcanic rocks rocks iinn this old old (Van (VanSchmus, Schmus, 1975). 1975). Mafic Mafic and and Intermediate IntermediateMetavolcanic MetavolcanicRocks. Rocks. Basaltic Basaltic rocks, rocks, including including l a r q e areas areas in in t u f f sand and pillowed pillowed and and massive massive flows, a r e exposed exposed iin n several tuffs flows, are several large eastern, northern northern and and southern southern Marathon Marathon county, n aa number number of eastern, County, and and iin of smaller roof i t h i n plutons. plutons. Pillow Pillow lavas lavas are a r e relatively r e l a t i v e lwidespread y widespreadand and roof pendants pendants wwithin indicate subaqueous indicate that t h a tmany many of the the basalts basalts are a r ethe t h eresult r e s u lof t of subaqueous eruptions. eruptions. Although Although pillow pillow lavas lavasare a r ewidespread, widespread, most most outcrops outcrops are a r e frost-heaved frost-heaved and and therefore therefore cannot cannot be be used used ffor o r top top determinations. determinations. Porphyritic Porphyriticand andamygdaloidal amygdaloidal basalts basalts are a r ealso a l s ocoriinon comnon ininthe thesequence. sequence. The The basalts have have been been converted converted to to chlorite—rich chlorite-rich schists s c h i s t salong along zones zones of of intense intensedeformation. deformation. In In thin thinsection sectionthe theundeformed undeformed rocks rocks consist c o n s i s t ofofrandomly randomly oriented oriented epidote, epidote, a c t i n o l i t e ,chlorite, c h l o r i t esodic , sodic plagioclaseand andquartz, quartz,indicating indicatinggreenschist greenschist actinolite, plagioclase facies faciesmetamorphism. metamorphism. Primary Primary textures, including aa fine f i n efelty f e l tgroundmass y groundmass with with textures, including porphyritic porphyritic oro rglomeroporphyritic glomeroporphyritic ororamygdaloidal amygdaloidal textures, textures, are a r epreserved preserved in in places. the the basalts havehave beenbeen metamorphosed places. Adjacent Adjacent to t o larger l a r g e rgranitic g r a n i tplutons i c plutons basalts metamorphosed -6— �to I n some some roof roof t o aniphibolites amphibol i t e s or o rhornblende hornblende or o r pyroxene pyroxene hhornfelses o r n f e l s e s in i n others. o t h e r s . In pendants andesitesoccur occurbetween betweenb abasaltic andr hrhyolitic pendants t the h e andesites s a l t i c and y o l i t i c rocks. rocks. Because Because the t h e original o r i g i n a l extent e x t e n tand and the volcanic v o l c a n i c rocks rocks aare r e ppresent r e s e n t iin n scattered s c a t t e r e d blocks, blocks, the are llocally t h i c k n e s s of o f units u n i t sisi unknown. s unknown. Andesites Andesites are o c a l l y interbedded interbedded with with thickness "graywacke" suggesting subaqueous graywacke" and and conglomerate conglomerate suggesting subaqueous ddeposition. e p o s i t i o n . In I n eastern eastern Marathon Countyt hthe andesites aare with Marathon County e andesites r e interbedded interbedded w i t h dacites, d a c i t e s ,and andthe t h esequence sequence becomes more becomes p rprogressively o g r e s s i v e l y more r hrhyolitic y o l i t i c to t o the t h e northwest. northwest. Felsic F e l s i cMetavolcanic MetavolcanicRocks. Rocks. Felsic F e l s i c volcanic v o l c a n i c rocks rocks uunderlie n d e r l i e tthat h a t part p a r t of of Wausau WisconsinRRiver andoccur occure extensively Wausau e aeast s t o of f t the h e Wisconsin i v e r and x t e n s i v e l y tto o the t h e east e a s t and and north. north. They occur iinn several They aalso l s o occur several roof r o o fpendants pendants elsewhere elsewhere i in n tthe h e county county (Figure ( F i g u r e 2). 2). A wide vvariety A wide a r i e t y of o f volcanic v o l c a n i c rock r o c k types types are a r e represented, represented, including i n c l u d i n g water-laid water-laid (bedded) (bedded) t utuffs, f f s , welded welded t tuffs, u f f s , pyroclastic p y r o c l a s t i c breccias, breccias, flow f l o wbreccias, b r e c c i a s ,massive massive and sedimentsooff several several types. and flow—banded flow-banded r h rhyolites, y o l i t e s , llahars a h a r s and and volcanogenic volcanogenic sediments types. Lithic L i t h i ctuff t u fwith f w i some t h someinterbedded interbeddedvolcanogenic volcanogenic sediment sediment is i sthe t h emost mostcomon common with P y r o c l a s t i c breccias breccias w i t h clasts c l a s t s up up to t o at a tleast l e a s 20 t 20cm cm are a r e present present rock type. type. Pyroclastic rock in were i n several several localities, l o c a l i t i e sand , and wereprobably probablydeposited deposited near near vents. vents. Flow-banded Flow-banded r hrhyolite y o l i t e ((Figure F i g u r e 44), ) , lahars l a h a r s (Figure ( F i g u r e 5) 5) and and welded welded ttuffs uffs (Figure and along along tthe Rib 6 ) are a r e well w e l lpreserved preserved ini nWausau Wausau and he R i b River R i v e r east e a s t of o f Athens. Athens. ( F i g u r e 6) Relict Re1 i c t spherulites, s p h e r u l i t e s , perlitic per1 it i cracks c cracksand andintensely i n t e n s e l ywelded welded vitric v i t r i cfragments fragments (Figure probably were wereooriginally ( F i g u r e 6) 6 ) suggest suggest that t h a t some some ooff these these rrocks o c k s probably r i g i n a l l y obsidian. obsidian. Near Brokawv volcanic conglomerate,sandstone, sandstone,and ands siltstone Near Brokaw o l c a n i c conglomerate, i l t s t o n e are a r e interbedded interbedded The conglomerates conglomeratescconsist mainly onsist m a i n l y of o f boulders boulders with w i t h welded welded ttuffs u f f s and and lava l a v a flows. flows. The up cmi in diametero of rocksi ninaammatrix up tto o 20 20 cm n diameter f vvolcanic o l c a n i c rocks a t r i x oof f ffiner i n e r volcanic volcanic boulderso fofqquartzite andggranite However, boulders u a r t z i t e and r a n i t e aare r e aalso l s o present p r e s e n t in in fragments. However, The The vvolcanic o l c a n i c sandstones sandstones cconsist o n s i s t of o fround roundsand—size sand-size vvolcanic olcanic These uunits n i t s range range fragments, fragments, qquartz u a r t z ggrains, r a i n s , and and scattered s c a t t e r e d quartzite q u a r t z i t e pebbles. pebbles. These in i n thickness thickness from from aa few few meters meters to t o several several tens tens ofo meters f metersand and have have aa very very restricted r e s t r i c t e d distribution d i s t r i b u t i o nbetween between the t h e lava l a v a flows f l o w s or o r ash ash flows. flows. some some llayers. ayers. Except areas, tthe Except f for o r local l o c a l development development o of f ssericite e r i c i t e in i ndeformed deformed areas, h e ffelsic elsic extremely ffine volcanic evidence of ometamorphism. v o l c a n i c rocks rocks show show llittle i t t l or e ono r no evidence f metamorphism. The The extremely ine g r a i n size s i z e and and preservation p r e s e r v a t i o n of o f primary primary features f e a t u r e s such such as as shard shard structures s t r u c t u r e s also also grain indicates i n d i c a t e s aa general general l lack a c k oof f rrecrystallization. ecrystallization. Where Where tthe h e rocks rocks have havebeen been deformed, they t otos esericite r i c i t e sschists c h i s t s or o r the t h evolcanic v o l c a n i cfragments fragments deformed, theymay maybebeconverted converted may beeextensively deformed,asasdiscussed discussedl alater under tthe may be x t e n s i v e l y deformed, t e r under h e ssection e c t i o n on on structure. structure. The The ffelsic e l s i c volcanic v o l c a n i c rocks rocks are a r e interpreted i n t e r p r e t e dtot obebemainly m a i n l yaquagene aquagene ttuffs uffs w i t h interbedded interbeddedsediments. sediments. Thus Thus t hthey e y aare r e mmainly a i n l y s isimilar m i l a r i in n oorigin r i g i n to t o the the with weldedt utuffs, subaqueous andi nintermediate subaqueous mmafic a f i c and t e r m e d i a t e rocks. However, However, t hthe e welded f f s , flow flow banded andl alahars probablyoof banded r hrhyolites y o l i t e s and h a r s aare r e probably f ssubaerial u b a e r i a l oorigin. r i g i n . The The volcanic volcanic sandstones and conglomerates north of Wausau are believed to be alluvial sandstones and conglomerates n o r t h o f Wausau a r e b e l i e v e d t o be a l l u v i a l f a c i e s of o f the t h e volcanic v o l c a n i c rocks. rocks. Their T h e i r rrestricted e s t r i c t e d distribution d i s t r i b u t i o n and and iinternterfacies layered weldedt utuffs mayi nindicate l a y e r e d welded f f s may d i c a t e tthat h a t they they aare r e valley—fill v a l l e y - f i l l deposits d e p o s i t s on on Therefore, the subaerial felsic volcanic rocks t h e flanks f l a n k s of o f aavolcano. volcano. Therefore, t h e subaerial f e l s i c v o l c a n i c rocks the may may rrepresent e p r e s e n t vvolcanic o l c a n i c islands i s l a n d s ini na abasin basinofounknown f unknown dimensions. dimensions. The determinations on The oonly n l y age age determinations on volcanic v o l c a n i c rocks rocks ini nMarathon Marathon County County are are from a rhyolite along Wis. Hwy. 52 near the eastern city limits of f Wausau. from a r h y o l i t e along Wis. Hwy. 52 near t h e eastern c i t y l i m i t s oWausau. Van Schmus Schmus and (1975)r ereport U/Pbage ageononz izircons 1900m.y. m.y. ffor or Van and o t hothers e r s (1975) p o r t aaU/Pb r c o n s oof f 1900 I assume the other volcanic rocks are part of the same general these rocks. rocks. I assume t h e o t h e r v o l c a n i c rocks a r e p a r t o f t h e same general these p e r i o d of o f volcanism. volcanism. period —7— �Figure rhyolite Figure 4. 4. Flow Flow banded banded rhyol t e along along Rib Rib River River east e a s t ofofAthens. Athens. Figure Figure 5.5. Volcanic Volcanic mudflow mudflow (lahar) (lahar)deposits depositsataHighland t HighlandGrove Grove School of clasts n Wausau. Note Note the the mixture mixture of c l a s t s in in aafine f i n etuffaceous tuffaceous School ini Wausau. matrix. matrix. -8-8- �Welded t tuff u f f showing showing flattened f l a t t e n e dand andwelded welded shard shard fragments fragments Figure 6. 6. Welded along with w i t h rounded rounded phenocrysts. phenocrysts. Sample Sample is i s from fromWausau. Wausau. Metasedimentary Rocks. Rocks. Graywacke Graywacke and a t e associated i t h vvolcanic o l c a n i c rocks rocks ands lslate associatedwwith in i n north n o r t hcentral c e n t r aMarathon l MarathonCounty County(between (between Athens Athens and and Merrill) M e r r i l l were ) werenamed named the the 'HamburgSSlates' Weidman (1907). Mapping "Hamburg l a t e s " by byWeidman by LaBerge and Myers Myers i indicates LaBerge and n d i c a t e s aa Mapping by much more i t e d ddistribution i s t r i b u t i o n of o fmetasedimentary metasedimentary rocks, u r t h e r indicates indicates much morel i m limited rocks, and andf further that with t h a t they they are a r eextensively e x t e n s i v e l yand and complexly complexly interbedded interbedded w i t h volcanic v o l c a n i c rocks. rocks. Most Most of rocksaare o f the the sedimentary sedimentary rocks r e nnot o t ssufficiently u f f i c i e n t l y exposed exposed tto o aallow l l o w delineation d e l i n e a t i o n of of discrete quartz, d i s c r e t e units. u n i t s . The The coarser sediments sediments are a r e graywackes graywackes composed composed oof f quartz, plagic1ase p l a g i o c l a s e and and rock rock fragments. fragments. The The finer—grained f i n e r - g r a i n e d sediments sedimentswere weremetamorphosed metamorphosed to t o chlorite c h l o r i t e and/or and/or ssericite e r i c i t e slates s l a t e s oorr phyllites. p h y l l ites. Well Well bedded bedded aargillite r g i l l i t eand andgraywacke graywacke wwith i t h interbedded interbedded ttuff u f fisi sexposed exposed along CTH—W Wausau (Sec.12, 12,T.29N., T.29N., R.7E.). CTH-W n onorth r t h o of f Wausau (Sec. R.7E.). The The rock rock isi smedium medium to in thickness from about 1—30 t o fine f i n egrained, grained,with w i t layers h l a y e rranging s ranging i n thickness from about 1-30cm. cm. Excellent E x c e l l e n t examples examples of o f graded graded bedding bedding and and ssoft o f t sediment sediment deformation deformation ("slump ("slump structures") s t r u c t u r e s " ) are a r eexposed. exposed. Several units of rhyolitic lapilli tuff are interSeveral u n i t s o f r h y o l i t i c l a p i l l i t u f f a r e interbedded bedded wwith i t h the t h e graywacke—argillite. g r a y w a c k e - a r g i l l i t e . Some Some ofoft hthe e aargillite r g i l l i t eunits u n i tare s a rcomposed e composed mainly m a i n l y of o f volcanic v o l c a n i c fragments. fragments. Conglomeratic Conglomeratic u units n i t s wwithin i t h i n and h e top t o p of of andaatt tthe this (along tthe west end endooff tthe t h i s sequence sequence (along h e Wisconsin Wisconsin RRiver i v e r aat t tthe h e west h e bridge b r i d g e at at Brokaw) may be be volcanic conglomerates. Brokaw) may conglomerates. Welded Welded t utuffs, f f s , flow f l o wbreccias brecciasand and lahars lahars exposed alongt hthe westsside the Wisconsin (Sections 2,2, 3, 11, T.28N., T.28N., exposed along e west i d e oof f the Wisconsin RRiver i v e r (Sections 3, && 11, R.7E.) Quarry(NWk, (NW¼, Sec. T.28N.,R.7E.) R.7E.)aare R.7E.) and and in i nthe t h e3M 3MCompany Company Quarry Sec. 11,11, T.Z8N., r e iinternterbedded ands tstratigraphically bedded wwith i t h tthe h e conglomerates conglomerates and r a t i g r a p h i c a l l y overlie o v e r l i ethe t h egraywackegraywackeargillite a r g i l l i t sequence e sequence on on the t h e east e a s t side s i d e ofo fthe t h eWisconsin Wisconsin River. River. The The sedimentary sedimentary units, u n i t s , therefore, t h e r e f o r e , are a r eunderlain, underlain,interbedded interbedded with, w i t h , and and overlain o v e r l a i nby by volcanic volcanic rocks. They aare r e iinterpreted n t e r p r e t e d to t o be be facies f a c i e s of o fthe t h evolcanic v o l c a n i csequence sequence iinn the t h e area. area. rocks. They -9— �An isolated isolated area by, and An areaofofmetagraywacke metagraywacke and and conglomerate conglomerate surrounded surrounded by, and interbeddedwith withffelsic of interbedded e l s i c to t o intermediate intermediate volcanics volcanics is i s located located northwest northwest of Stratford (Sections (Sections 34, 34, 35, 35, 36, 36, T.28N., T.28N., R.3E., R.3E., and and Sec. Sec. 31, 31, T.28N., T.28N., R.4E.). R.4E.). A magnetichigh highi sis associated associatedwwith A prominent prominent magnetic i t h tthe h e sedimentary sedimentary uunits. n i t s . The The metagraywacke No o metagraywacke i sis ffine i n e tot omedium medium grained grained and a n d medium medium tto o massively massively bedded. bedded. N conglomeratecontains contains boulders boulders up graded bedding u p to t o 30 30cm cm The conglomerate graded bedding was was observed. The of quartzite, q u a r t z i t e ,iron—formation, iron-formation, felsic f e l s i cand andmafic maficvolcanic volcanicrocks rocksand andsome some plutonic The present present landowner reported that rocks. The landowner reported t h a t aamining miningcompany company from from Michigan Michigan ddrilled r i l l e d exploratory exploratory holes holes ffor o r iron iron ore ore in i nthe t h earea area during during the t h e late l a t e1950's. 1950's. Thus, sedimentaryrocks, rocks,mainly mainlygraywackes graywackes Thus, sedimentary andand s l aslates t e s o rora rargillites, gillites, are widely widely ddistributed county and andaare are i s t r i b u t e d throughout throughout tthe h e county r e ccharacteristically haracteristically nol alarge, area of associated with with volcanic rocks. associated rocks. However, However, no r g e , continuous continuous area The sedimentary rocks rocks was demonstrated iinn the sedimentary was demonstrated t h e present presentmapping mapping program. program. The widespreadassociation associationof of sediments volcanic rocks, rocks, however, widespread sediments wwith. i t h t hthe e volcanic however, iiss thethe environment helpful inininterpreting interpreting environmentini which n whichthe therocks rocksaccumulated. accumulated. INTRUSIVE ROCKS INTRUSIVE ROCKS The volcanic rocks The volcanic rocks have have been been intruded by by more more than than twenty twenty stock—like stock-like Most of of the plutons i nMarathon Marathon County. County. Most plutons range range in i n composition composition from from plutons in quartz ddiorite quartz i o r i t e to t ogranite; g r a n i t e ;however, however, several several gabbroic gabbroic intrusions are a r e also also Discordanceofof the the plutons, plutons, low gradeofof the the volcanic volcanic present. Discordance low metamorphic metamorphic grade rocks, and contactmetamorphic metamorphic suggestsc rcrystallization rocks, and generally meagre meagre contact e f feffects e c t s suggests ystallization of the of the intrusions intrusions at a t shallow shallow llevels e v e l s iin n the t h e earth's e a r t h ' s crust c r u s t with w i t h little l i t t lsubsequent e subsequent erosion. The The plutons would would probably probably be be classed classedasasupper uppermesozonal mesozonal. Gabbroic Intrusions. Several small gabbroic gabbroic intrusions intrusions of diverse diverse Gabbroic Intrusions. Several small texture, of diverse t e x t u r e , and and presumably presumably of diverse age, age, are a r e present presentininMarathon Marathon County. County. Most intrusions are intrusions a rmetamorphosed e metamorphosedand andsomewhat somewhat deformed. deformed. 2 A of metagabbro underlying approximately km2 iiss exposed A mass mass of metagabbro underlying approximately 20 20 km exposed along along the the EauClaire Claire River River in in the Wausau). Most of of the Eau the vicinity v i c i n i t yofofGallon Callon(east ( e a sof t of Wausau). Most the intrusion isi smassive massive gabbro gabbro with w i t h aa sub—ophitic sub-ophitic ttexture, e x t u r e , but b u tconspicuously conspicuously layered gabbro gabbroi is present llocally. the flanking flanking volcanic volcanic and layered s present o c a l l y . Although Although the and ggranitic ranitic rocks rocks are a r e extensively extensively deformed, deformed, the t h egabbro gabbro mass mass iiss largely largelyundeformed. undeformed. Inclusions of schistose occur in in the Inclusions schistose volcanic volcanic rocks rocks and and deformed deformed ggranite r a n i t e occur the gabbro suggesting suggestingt hthat the gabbro than the gabbro a t the gabbro iiss younger younger than the deformational deformational event event the surrounding surrounding rocks. rocks. aaffecting f f e c t i n g the Several are present in Several gabbroic gabbroic masses masses are insouthwestern southwesternMarathon Marathon County. County. mass northofofMarshfield Marshfield cconsists AA rrelatively e l a t i v e l yunmetaniorphosed unmetamorphosed mass s i tsituated u a t e d north o n s i s t s of coarse—grainedo pophitic gabbro and andaanorthositic coarse-grained h i t i c gabbro n o r t h o s i t i c gabbro. gabbro. This mass mass produces produces prominent oval oval aeromagnetic aeromagnetic anomaly. anomaly. aa prominent A gabbroic mass massalong alongthe theLLittle Pleine River A gabbroic i t t l e Eau Eau Pleine River (Secs. (Secs. 23, 23, 24, 24, T.26N., T.26N., R.3E., and Secs.17, 17, 18, 18, 19 19 && 20, 20, T.26N., T.26N., R.4E.) R.4E.) cconsists R.3E., and Secs. o n s i s t s of granular granular plaqioclase and hornblendewith with numerous numerousstrongly stronglyf ofoliated of plaqioclase and hornblende l i a t e d zones zones of amphibolite. This gabbroic gabbroicmass mass isi much s muchmore moredeformed deformedand andmetamorphosed metamorphosed than the one than the one nnorth o r t h of Marshfield, Marshfield, and and therefore therefore appears appears tto o be be older. older. - 10 - �Several small, small, widely Ultramafic U l t r a m a f i c Intrusions. I n t r u s i o n s . Several w i d e l y scattered s c a t t e r e d ultramafic u l t r a m a f i cbodies bodies composed serpentine are composed m amainly i n l y o foft atalc l c and and serpentine a r e located l o c a t e d ini nMarathon Marathon County. County. The ultramafic exposed,r erendering i f f i c u l ttot odetermine determine u l t r a m a f i c rocks rocks aare r e ppoorly o o r l y exposed, n d e r i n g i titddifficult their t h e i r size s i z eand andshape. shape. They They aare r e llocated o c a t e d along along major major zones zones ooff cataclasis, c a t a c l a s i s , and and thus thus iitt is i slikely l i k e l that y t h athe t t h bodies e bodiesare a r e elongated elongated pparallel a r a l l e l tto o the t h e sstrike t r i k e of o f the the zones. small ultramafic massalong alongt hthe AA small u l t r a m a f i c body body occurs occurs with w i t h the t h emetagabbro metagabbro mass e LLittle ittle Eau PPleine SE¼,Sec. Sec.20, 20, T.26N., T.26N., R.3E,). IIttisi scomposed composed mainly mainly Eau l e i n e River R i v e r (NE¼, (NEk, SEk, R.3E.). andt talc, olivine ooff serpentine serpentine and a l c , but b u t contains c o n t a i n s numerous numerous r e relict 1 i c t 01 i v i n e crystals. c r y s t a l s . The main exposure exposureo of main f t hthe e sserpentinite e r p e n t i n i t e is i s ini na apitp where i t wherequarrying q u a r r y i n gwas wasattempted. attempted. Themineralogy mineralogyand and hasnot n o tbeen been as as The t e texture x t u r e o foft hthe e r orock c k i nindicate d i c a t e tthat h a t iti thas intensely as the i n t e n s e l ymetamorphosed metamorphosed oorr deformed deformed as t h e associated associatedmetagabbro. metagabbro. Therefore, iti tprobably probably represents represents a a separate separate iintrusion n t r u s i o n rather r a t h e r than than an an ultramafic u l tramafic i m i l a r serpentine-talc s e r p e n t i n e - t a l cbody bodyexposed exposed ddifferentiate i f f e r e n t i a t e ofofthe t h egabbroic gabbroicmass. mass. AA ssimilar NW¼, Sec. 27, 27, T.26N., iinn aa roadcut roadcutsouth southofo Rozellville f R o z e l l v i(NW¼, l l e (NU%, NWk, SW¼, SWk, Sec. T.Z6N., R.4E.) R.4E.) Thus, also a l s o contains contains abundant abundant r relict e l i c t olivine o l i v i n eand andhas has only o n l y39.4 39.4 percent percent Si02. 3 0 2 . Thus, pyroxenites Feldspathic pyroxeni t e s cconsisting o n s i s t i n g of of it i tisi sprobably probablyaaserpentinized s e r p e n t i n i z e d dunite. duni t e . Feldspathic andp plagioclase andr eretaining sserpentinized e r p e n t i n i z e d pyroxene pyroxene and l a g i o c l a s e and t a i n i n g ttheir h e i r igneous igneous texture texture Sec. 2, NE¼, aare r e exposed exposed iinn the t h eSE¼, SEg, SE¼, SEij, Sec. 2, T29N., T.29N., R.3E. R.3E.and and NE%,NE¼, NEk, 5E¼, SEk, Sec. Sec. 27, 27, T.30N., T.30N., R.4E. R.4E. along aa major major fault f a u l tzone zoneini northwestern n northwesternMarathon MarathonCounty. County. Therefore, thant the Therefore, they they appear appear lless e s s deformed deformed than h e uultramafic l t r a m a f i c bodies bodies in i nsouthern southern and eastern Marathon and Marathon County. County. Granitic G r a n i t i c Intrusions. Intrusions. The volcanic-sedimentary sequence sequence and gneisses gneisses The volcanic—sedimentary Most ooff the have beeni nintruded by numerous numerouss tstock—like have been t r u d e d by o c k - l i k e p lplutons u t o n s o of f ggranite. r a n i t e . Most the composit'ional1.y zoned zoned and and contain c o n t a i n pendants, pendants, screens screens and and xxenoliths enoliths pplutons l utons are a r e compositionally ooff volcanic v o l c a n i c and and oolder l d e r plutonic p l u t o n i c rocks. rocks. Quartz heterogeneous Q u a r t z ddiorite i o r i t e intrusions i n t r u s i o n sare a r etypically t y p i c a l lsmall, y small, heterogeneousand and generally generally highly contaminated with inclusions of volcanic rocks, gabbro, pyroxenite, h i g h l y contaminated w i t h i n c l u s i o n s o f v o l c a n i c rocks, gabbro, p y r o x e n i t e , and metasedimentary rocks. AA conspicuous conspicuouse aeast s t t oto nnortheast o r t h e a s t ttrending r e n d i n g ccataclastic ataclastic and metasedimentary foliation is present in most of the plutons. Mineralogically, f o l i a t i o n i s present i n most o f the p l u t o n s . M i n e r a l o g i c a l l y , they they contain contain strongly s t r o n g l y zoned zoned plagioclase p l a g i o c l a s e (about (about An30), 20-30 20-30 percent percent quartz, q u a r t z , 10-30 10-30 percent percent hornblende hornblende o or r bbiotite i o t i t e or o r both, both, and and minor minor rnicrocline. microcline. Intrusions I n t r u s i o n s ranging ranging in i ncomposition composition from from quartz quartz monzonite monzonite tto o granite granite andddioritic Typically, iintrude n t r u d e the the volcanic v o l c a n i c rocks rocks and i o r i t i c bodies. bodies. T y p i c a l l y , the t h emargins margins are are highly quartz h i g h l y contaminated, contaminated, but b u t the t h e cores cores are a r erelatively r e l a t i v e homogeneous. l y homogeneous. Some Some quartz monzonitesappear appear quartzd idiorites, monzonites t o to bebe g r gradational a d a t i o n a l i n into t o quartz o r i t e s , but b u t dikes dikes of o f quartz quartz monzonitei nint hthe monzonite e ddioritic i o r i t i c rocks rocks suggest suggest ffracturing r a c t u r i n g and and iintrusion n t r u s i o n ooff the the The quartz pperipheral e r i p h e r a l ddioritic i o r i t i c rocks rocks by by later l a t e r phases phases oof f tthe h e intrusion. i n t r u s i o n . The monzonites havea apervasive pervasive monzoni t e s g egenerally n e r a l l y have c acataclastic t a c l a s t i c f ofoliation l i a t i o n which, which, in i n places, places, iiss truncated truncated by by non—foliated non-fol i a t e d ggranites r a n i t e s ((Figure F i g u r e 77), ) , suggesting suggesting tthat h a t the t h e granites granites are llater. are ater. The Many have have The ggranitic r a n i t i c plutons p l u t o n srange range ini nsize s i z efrom fromabout about5-130 5-130km2. km2 . Many concentric zoning wwith quartzddiorite c o n c e n t r i c zoning i t h aa ggranitic r a n i t i c core core and and quartz q u a r t z monzonite monzonite t oto quartz iorite Narrow bbut u t ddistinct i s t i n c contact t c o n t a cmetamorphic t metamorphichalos haloswere wereobserved observed around around border. Narrow several iintrusions werer recrystallized several n t r u s i o n s where where t hthe e f felsic e l s i c volcanic v o l c a n i c rocks rocks were e c r y s t a l l i z e d to t o aa massivesaccharoidal saccharoidalrock rockand andmmafic rockswere werer erecrystallized massive a f i c v volcanic o l c a n i c rocks c r y s t a l l i z e d to to Excellent x c e l l e n t examples examples oof f iintrusion n t r u s i o nbreccias brecciasare a r eexposed exposed hornblende hhornfelses. hornblende ornfelses. E on on tthe h e margins margins ooff some some i intrusions. ntrusions. — 11 �t a,- Figure Foliated quartz quartz monzonite g h t (with oliation monzoniteononr i right (with ffoliation Figure 7. 7. Foliated parallel on lleft. w i t h the the pencil) pencil)cut cutby by aamassive massive ggranite r a n i t e on e f t . The parallel with The pencil approximately on on the the contact. contact. pencil point point isi sapproximately The texturesand andmineralogy. mineralogy. The ggranitic r a n i t i c intrusions intrusions exhibit e x h i b i ta awide wide variety v a r i e t yofoftextures Quartz monzonitestend tendt otobe beporphyritic porphyritic with phenocrysts Quartz monzonites phenocrysts of plagioclase plagioclase (An20-30) o rormicrocline i n e r matrix of quartz, q u a r t z , feldspar feldsparand and (An20_30) microclineo rorboth bothi ninaa ffiner mafic minerals. minerals. Hornblende Hornblende iis s comon common in i n quartz quartzmonzonites, monzonites, comprising comprising as as much as20 20percent percentof of the rocks. much as rocks. Biotite B i o t i t eis ialso s a l sconvuion. o common. Granites Granites generally generally contain most conunon variety. most common v a r i e t y . Individual contain fewer fewer mafic mafic minerals, with with biotite b i o t i tthe e the Individual plutons berecognized recognizedbybytheir their mineralogy, mineralogy,oor plutons may may be r ttexture, e x t u r e , or o r both. both. The The intrusions intrusions aalso l s o ddiffer i f f e r in in color. color. Quartz Quartz monzonites r e ttypically y p i c a l l y gray gray and and monzonitesaare weather from ppink weather tto o a a buff buff color colorwhereas whereas granites range range from i n k to t o deep deep brick red. red. The variety of textures The variety textures exhibited exhibited by by the the granitic g r a n i t i crocks rockspresumably presumably reflects reflects differences ininthe t h eenvironment environment(temperature (temperatureand and pressure) pressure) and and chemistry chemistry differences (especially the time timeofof crystal1 crystallization. ization. (especially H20) H20) aat t the The Middle Precambrian volcanic-plutonic of Marathon Marathon County County is is The Middle Precambrian volcanic—plutonic portion portion of situated of the s i t u a t e d on on one one of the major major gravity gravity lows t h e state s t a t e(up (uptot ominus minus 90 90 ows in in the milligals) Rammer, mill i g a l s(Ervin ) ( E r vand i n and Hammer, 1974). 1974). The gravity low low iis The gravity s significantly s i g n i f i c a n t l ygreater greater than than that t h a t over over the thegneissic gneissicarea areadescribed describedabove. above. This This indicates indicates that t h a t the the area area is i s underlain underlain mainly mainly by by granitic g r a n i t i c rocks. rocks. The The general gravitylow lowsuggests suggests general gravity that t h a t the the volcanic volcanic pendants pendants ((at a t least l e a s t the the mafic mafic ones) ones) are a r e relatively r e l a t i v e l yshallow shallow features features in i n the the granitic g r a n i t i crocks. rocks. The mapofof the the area area (Zeitz ( Z e i t zand and The aeromagnetic aeromagnetic map others, others, 1977) 1977) iis s consistent consistent wwith i t h tthis h i s interpretation. i n t e r p r e t a t i o n . The The granites graniteshave have aa 1 low, low, flat f l amagnetic t magneticexpression expressionwhereas whereas the t h egabbros gabbros and and volcanics volcanicsproduce produce magnetic magnetic highs. highs. (This (This is i sthe t h ereverse reverseofofthe t h emagnetic magnetic pattern pattern described described elseelsewhere and Karl Karl (1977).) (1977).) The where in northern northern Wisconsin Wisconsin by by Mudrey Mudrey and The blotchy blotchymagnetic magnetic - 12 - �rocks in an area composed ppattern a t t e r n indicates i n d i c a t e s aa patchy patchy distribution d i s t r i b u t i o nofovolcanic f volcanic rocks i n an area composed largely l a r g e l y of o f granitic g r a n i t i c rocks. rocks. Only aa few few rradiometric agesaare from pplutonic Only a d i o m e t r i c ages r e aavailable v a i l a b l e from l u t o n i c rocks rocks in in Marathon Schmusand ando tothers (1976) obtained obtained a U/Pb Marathon County. County. Van m.y. Van Schmus h e r s (1976) U/Pb age age of o f 1850 1850 m.y. on on zircons z i r c o n s from from the t h e Kalinke K a l i n k equartz quartznionzonite monzonite ini nnortheastern northeasternMarathon Marathon County. County. The ggranitic off the The r a n i t i c rocks rocks in i nMarathon Marathon County County ((with w i t h the t h e exception exception o t h e Wolf Wolf River R i v e r Batholith Bath01 4 t hand andsyenite syeni t ebodies bodiesnear nearWausau, Wausau, described below) below) are a r e believed be1ieved tto o be be related r e l a t e d to t o aasingle s i n g l eigneous igneous event. event. All A l l are a r e intruded i n t r u d e dinto i n t owhat whatmay may reasonably be be iinterpreted reasonably n t e r p r e t e d as as aasingle s i n g l e(but ( b ucomplex) t complex)volcanic—sedimentary volcanic-sedimentary sequence. The various plutons plutons show shows isimilar, widespreadc acataclastic The various m i l a r , widespread t a c l a s t i c f ofoliation, liation, and many have gradational contacts from quartz diorites to is and many have g r a d a t i o n a l contacts from quartz d i o r i t e s t o granites. g r a n i t e s . IItt is conceivable conceivable tthat h a t the t h e various various granitic g r a n i t i crocks rocksare a r co—extensive e co-extensive at a tdepth depth and and form I f this t h i s interpretation i n t e r p r e t a t i o n is i s correct, c o r r e c t , the the form aa large l a r g e composite composite bbatholith. a t h o l i t h . If various plutons may maybebecupolas cupolasonont hthis various stock—like s t o c k - l i k e plutons i s l large a r g e bbatholith. a t h o l i t h . Numerous Numerous 1850m.y. m.y.oold l d pplutons l u t o n s aalso l s o intruded i n t r u d e d the t h e gneissic g n e i s s i c rocks rocks in i ncentral c e n t r a lWisconsin Wisconsin 1850 (Van Schmus, (Van Schmus, 1976). Chemical analyseso of 19ggranitic Chemical analyses f 19 r a n i t i c rocks rocks and and 88 vvolcanic o l c a n i c rocks rocks from from the the Becauset the county iindicate county n d i c a t e that t h a t they they are are calc—alkaline. calc-alkaline. Because h e vvolcanic o l c a n i c and and pplutonic l u t o n i c rocks rocks have have aa similar s i m i l a r age, age, have have undergone undergone a as similar i m i l a r sstructural tructural andaare suggest tthat hat hhistory, i s t o r y , and and are a r e chemically chemically ssimilar i m i l a r and r e sspatially p a t i a l l y related, r e l a t e d , II suggest they may be co-genetic. co-genetic. may be LATE PRECAMBRIAN PRECAMBRIAN The Late Precambrian The Late Precambrian i is s represented represented in i nMarathon Marathon County County by widely widely r a n i t e s ,syenites, syenites , ddistributed i s t r i b u t e d igneous igneous rocks, rocks, including i n c l u d i n g quartz q u a r t z monzonites, monzoni t e s , ggranites, and several several types types ooff diabase and ggranites The qquartz u a r t z monzonites monzonites and r a n i t e s are are and diabase dikes. The part small, circular p a r t of o f aa large l a r g e batholith b a t h o l i t hwhereas whereas the t h e syenites s y e n i t e s aare r e small, c i r c u l a r bodies. bodies. The diabase diabase ddikes mayrepresent represent tthe youngest Precambrian Precambrianrocks rocksi in The i k e s may h e youngest n tthe h e area. area. Wolf River RiverBBatholith The Wolf RRiver Batholith. The Wolf iver B a t h o l i t h . The The Wolf a t h o l i t h is i s aa major major Late Late Precambrianbbatholith Precambrian a t h o l i t h underlying u n d e r l y i n g at a tleast l e a s3500 t 3500km2 km2 ini neastern easternMarathon Marathon County County and aadjoining and others, others, 1975). and d j o i n i n g parts p a r t sofo northeastern f northeasternWisconsin Wisconsin(Van (VanSchmus Schmus and 1975). U/Pb ageononz zircons is i1500 m.y. Schmus U/Pb age i r c o n s i indicates n d i c a t e s that t h a t the t h ebatholith batholith s 1500 m.y.oldo (Van l d (Van Schmus western margin margin ooff the The western t h e batholith b a t h o l i t hwas wasmapped mapped during during and others, others, 1976). and 1976). The this t h i s survey. survey. The major major rock rock ttype The y p e of o f the t h eWolf Wolf River R i v e rBatholith B a t h o l i texposed h exposedini Marathon n MarathonCounty County iiss aa coarse—grained coarse-grained pporphyritic o r p h y r i t i c quartz quartz monzonite monzonite which which extends extends from from the the northeastern corner ooff the northeastern corner t h e county county approximately approximately ttwo-thirds w o - t h i r d s of o fthe t h eway way across across The southeastern southeasternppart off Marathon Countyi is underlain t h e county. county. The art o Marathon County s u n d e r l a i n by by aa the medium—grained quartz monzonite monzonite which which extends extends southwest southwest as as ffar medium-grained p oporphyritic r p h y r i t i c quartz ar Anderson (1975) (1975) and and Anderson Andersonand andCCullers as as Stevens Stevens Point. P o i n t . Anderson u l l e r s (1978) (1978) concluded concluded River chemicallyr related tthat h a t the t h e Wolf Wolf R i v e r BBatholith a t h o l i t h iis s chemically e l a t e d t to o aalkalic l k a l i c intrusions, intrusions, and thus is significantly different from the Middle Precambrian and thus i s s i g n i f i c a n t l y d i f f e r e n t from t h e Middle Precambrian plutons p l u t o n s to to the t h e west. west. The westernedge edgeo of Wolf RRiver Batholith The ccontact o n t a c t between between t hthe e western f t the h e Wolf iver B a t h o l i t h and and Precambrian rocks tthe h e Middle Middle Precambrian rocks i s is, , i in n ppart, a r t , aa major major fault f a u l tzone zone along along the the - 13 - �Claire Dells A t Eau Eau Claire Dells and and to t o the the northeast northeastnear near Hogarty Hogarty Eau Claire River. Eau Claire River. At hashas metamorphosed (Figure 1), I ) ,the theWolf WolfRiver RiverBatholith Batholith metamorphosed the sheared sheared volcanic and plutonic rocks and plutonic rocks (discussed (discussed later) l a t e r )tot ohornblende hornblendeand and pyroxene pyroxene hornfelses. hornfelses. However, southwestalong alongthe thecontact contacta azone zone However, f afarther r t h e r southwest of ofc acataclastic t a c l a s t i c f foliation oliation The sstrike morethan than1.5 1.5 km kmwide widecuts cutsthe theWolf WolfRiver RiverBatholith Batholith (Figure 2). 2 ) . The trike more and dipofof the the ffoliation w i t h that t h a tini nthe theolder olderrocks rocksand and and dip o l i a t i o n isi sconsistent consistent with suggests recurrence of of the deformation of the the Wolf suggests aa recurrence deformation after a f t e remplacement emplacement of Wolf River Batholith. Bath01 i t h . Twoe elliptical, l l i p t i c a l , concentrically concentricallyzoned zoned alkalic a1 kalic The Syenite Syenite Plutons. Two The plutons intruded the Middle Precambrian volcanic—plutonic complex just west west ~ l u t o n sintruded the Middle Precambrfan volcanic-plutonic comvlex just These plug—like plutons are i ke plutons-are These ~ l u ~ l of Wausau (Myers, 1976, this conference). Wausau (Myers, 1976, t h i s conference). about 1500m.y. m.y.old old and andaare chemicallyrelated related tto about 1500 r e chemically o the Wolf Wolf River Batholith Batholith (Van Schmus and others, 1976). (Van Schmus and others, 1976). Wausau syenitepluton pluton iiss approximately The Wausau syenite approximately WausauSyenite Syenite Pluton. Pluton. The Wausau 12 xx 27 kminin plan, plan, elongate concordantly northeast, northeast, and and consists consists of of aa wall 12 27 km elongate concordantly wall xenol i t h r i r zone of foliated amphibole syenite, an intermediate zone of xenolith—rich zone of f o l i a t e d amphibole an intermediate quartz syenite syenite and and aa core core of of quartz quartz monzonite monzonite( t(the "Ninemileg granite). quartz h e "Ninemile ranite"). southern half half of the syenite~pluton wasintruded intrudedand andp partially K wWausau a u s a u svenite l u t o nwas artially The The southern nearly complete completering ring of of very A nearly very large, larie, assimilated by by the the Ninemile Ninemile pluton. plut&. A lensoidal quartzite xenoliths the outer lensoidal xenoliths marks marks the outer part part of of the theintermediate intermediate zone. zone. The larger quartzite quartzite xenoliths xenoliths form ring of prominent The larger form aa ring prominent hhills, i l l s , including includingRib Rib Mountain, MosineeHill Hill and An intrusion breccia breccia marks marks the the Mountain, Mosinee and Hardwood Hardwood HHill. i l l . An contact ther eresistant on tthe tops of of the contact between between the s i s t a n t qquartzite u a r t z i t e on h e tops the hills h i l l sand andthe themore more readily on the lower readily eroded eroded syenite syenite exposed exposed on lower slopes. slopes. Quartzite Quartzite isi saccompanied accompanied schistosemetavolcanics metavolcanics and and metadiorite(?) The by l e r xenoliths of of schistose by smal smaller metadiorite(?).. The northern part of northern ofthe theWausau Wausau syenite pluton appears appears to t o be be repeated repeated (by (by low low Xenolith lithology, lithology, angle ffaulting?) sides of of the angle a u l t i n g ? ) on on opposite opposite sides the Rib Rib River. River. Xenolith size varyextensively extensivelywwithin i t h i n the pluton, pluton, although although s i z e and and rrelative e l a t i v e abundance abundance vary metavolcanicrocks, rocks, qquartzite, metavolcanic u a r t z i t e , schist s c h i s tand and metadiorite metadiorite are a r edominant. dominant. Xenoliths of contrasting contrasting lithology 1ithology are are chaotically chaotically mixed, mixed, especially especially in in the theintermediate intermediate Mixing probably probablyinvolved involvedconsiderable considerablevertical verticaltransport transport of of clasts zone. Mixing clasts during interpretation iiss significant during intrusion. (This (This interpretation s i g n i f i c a n t and and will will be be referred referred Longdimensions dimensionsofofxenoliths xenoliths aare concentric about the core. r e concentric about the tto o later.) l a t e r . ) Long Biotitized mafic mafic xenoliths xenoliths are a r e ubiquitous ubiquitous in the the quartz quartz syenite. syenite. The The amphibole andpyroxene pyroxene syenites thewall wall zone zonepossess possessa ad idistinct amphibole and syenites ofofthe s t i n c t flow lineation ininmost most places. places. The Ninemile Ninemile pluton pluton forms The forms the core core ofofthe theWausau Wausau Syenite Syenite and and appears appears ttoo have breached the southern part of the circular complex and spread have breached the southern part of t h e c i r c u l a r complex and spread iinto n t o aa Although the contact between the quartz large oval area to the southwest. between large oval area t o the southwest. Although the monzonitecore coreand andthe thesurrounding surrounding syenitei sisdiscordant, discordant, iitt appears monzonite syenite appears to be be Quartz monzonite in the space formerly occupied Quartz monzonite in space formerly occupied gradational in most places. gradational i n most places. by the the circular mafic xenoliths. by c i r c u l a rcore coremargin margin contains contains abnormally abnormally abundant abundant mafic It xenolith—contaminated I t isi sprobable probablethat t h athe t the xenol ith-contaminated "caldera—rim"(?) "caldera-rimt'(?) persisted within withoutappreciable appreciablel alateral w i t h i n the the upwelling upwelling magma magma without t e r a l dispersal or orcomplete complete assimilation. The Ninemile pluton pluton iiss aa coarse, The Ninemile coarse, equigranular equigranularhornblende—biotite hornblende-biotite quartz quartz The pluton pluton is monzonite similar in the Wolf monzonite similar in appearance appearance tto o the Wolf River Granite. Granite. The is A peripheral zone zone 2-3 2-3 km km wide wide isi smarked marked by by eelliptical l l i p t i c a and l andunderlies underlies218 218km2. km2. A - 14,- �numerous "rottengranite" granite"quarries quarriesindicating indicating tthat numerous "rotten h a t in i n this t h i szone zone the the rock rock has has almost completely llost almost completely o s t its i t scoherence. coherence. Stettin TheSStettin syenite pluton pluton iiss oval S t e t t i n Syenite Syenite Pluton. Pluton. The t e t t i n syenite oval in plan plan with with dimensions km; iitt isi sconcentrically dimensions ofof66xx 99 km; concentricallyzoned zoned and and elongate elongate northeasterly. northeasterly. The pluton intruded intruded mafic mafic volcanic volcanic rocks on the the west west and andffelsic The pluton rocks on e l s i c volcanic volcanic rocks rocks The pluton is divided into and associated sedimentary rocks on the east, and associated sedimentary rocks on the e a s t . The pluton is divided i n t o lensoidal syenite, syenite, (2) ( 2 )nepheline nepheline syenite, syeni t e , ffive i v e main, main, subconcentric subconcentric units: (1) lensoidal (3) tabular ( 4 amphibole ) amphibole syenite, syeni t e , and and (5) ( 5 )pyroxene pyroxene syenite. syenite. ( 3 ) tabular syenite, syenite, (4) Lensoidal syeni syenite, nepheline syenite andtabular tabular syeni syenite Lensoidal t e , banded banded nephel ine syeni t e and t e are a r e confined confined and pyroxene pyroxenesyenites syenites of of the Flow lineated amphibole amphibole and the tto o the the wall -wall zone. zone. Flow intermediate zone zoneenclose enclosea anearly nearlyc icircular coreof of pyroxene pyroxenesyenite syenitet hthat intermediate r c u l a r core a t iitt pluton was intruded two northeastrrimed i m e d by by nepheline n e p m n e syenite. syenite. The The pluton wasm r u d e d between between two trending shear extendingoutward outwardalong alongthe thef ofoliation. i t h apophyses apophyses extending liation. trending shear zones, zones, wwith The concentriccylindrical cylindrical structure subvolcanicintrusion intrusion of of the The concentric s t r u c t u r e suggests suggests subvolcanic the . Stettin plutons. S t e t t i nand andWausau Wausau pl utons pyroxeneand ando olivine diabase dikes dikes aare Diabase Diabase Dikes. Both Both pyroxene l i v i n e diabase r e present present in They are are characteristically andand unmetamorphosed Marathon c h a r a c t e r i s t i c a l undeformed l y undeformed unmetamorphosed Marathon County. County. They and may mayrepresent representthe theyoungest youngestigneous igneousrocks rocksbecause because they intrudea11 all older older and they intrude The dikes dikes range range uup wide, and rocks iinn the rocks the area. area. The p tto o 30 30 meters meters wide, and those those with with diabase dikes have have no no Most diabase exposedcontacts contactstrend trend eeast exposed a s t oorr northeast. Most magnetic "signature," but one prominentdike dikeexposed exposedi ninthe the"rotten "rotten granite" magnetic "signature," one prominent R i bMountain Mountain has has an an associated associated aeromagnetic aeromagnetic low that t h a t can can be be quarries south south of of Rib traced for kmfrom fromnorthern northernShawano Shawano County County westward westward across across most most f o rmore morethan than100 100km of Marathon Thus,aat Marathon County. County. Thus, t lleast e a s t this t h i s dike dike is i sreversely reversely polarized. polarized. Where Where exposed, iittisi a pyroxene diabase diabase about about 15 15 meters meters wide wide wwith exposed, s medium—grained a medium-grained pyroxene ith fine—grainedoolivine aa chilled c h i l l e d margin. margin. AA fine-grained l i v i n e diabase diabase is is exposed exposed in i n the thenorthwestern northwestern corner of the The rrelative e l a t i v e age age of of the theolivine o l i v i nand e andpyroxene pyroxenediabases diabases corner the county. county. The aare r e not not known. known. STRUCTURAL GEOLOGY GEOLOGY STRUCTURAL RegionalSettinq. Settin. Marathon MarathonCounty Countyi sison on the the southern southern margin marginof of a Regional a large large Middle Precambrian volcanic—sedimentarybasin basint hthat extends across across northern Middle Precambrian volcanic-sedimentary a t extends Wisconsin Although Middle Precambrian rocks are Wisconsin into i n t o Minnesota Minnesota and and Michigan. Michjgan. Although Precambrian rocks are widely widely distributed over over the t h e area, area, their t h e i rrelationship r e l a t i o n s h i pfrom fromone onearea area to t oanother another Sedimentaryrocks rocksaare dominantononthe theiron iron ranges iiss largely largelyunknown. unknown. Sedimentary r e dominant ranges tto o the the north, but b u trelatively r e l a t i v e lunmetamorphosed y unmetamorphosed volcanic and and plutonic plutonicrocks rockspredominate predominate rocks and iinn Marathon Marathon County. County. The The contacts between between these these low—grade low-grade rocks and gneisses, migmatites and amphibolites amphibolites extensively extensively developed migmatites and developed i in n central Wisconsin Wisconsin are are exposedin. in several several places places iin andMedaris Medaris(1977) (1977)i interpret exposed n the t h e county. county. Maass Maass and nterpret the gneisses in age, gneisses ttoo be be mainly mainly Middle Middle Precambrian Precambrian in age, also. a l s o . Contacts between between the Middle rocks,the the 1500 1500m.y. m.y.old old Wolf Wolf River River Batholith, Batholith, and the Middle Precambrian Precambrian rocks, and related syenite syenite plutons plutons are a r ealso a l s owell wellexposed exposedininMarathon MarathonCounty. County. Therefore, an understandingofofthe thes structural geologyofof tthis an understanding t r u c t u r a l geology h i s area area is i s important important to t o aa wide variety variety of rocks wide rocks over over a large large region. region. Folding. Although Although nearly nearly 4500 4500 km2 km 2 are a r e mapped mapped in Marathon Marathon County, County, no no Foldin%. clear—cut structural evidence clear-cut structural evidence for f o r large—scale large-scale folding folding was was established. established. In muchofofthe thecounty countythe thetrend trendofofd idistinctive i n the thevolcanic volcanic rocks rocks much s t i n c t i v e llithologies i t h o l o g i e s in topindicators indicators aare lacking in most of the However, top r e lacking most of the N . ~ O O E . to t oeast—west. east-west. However, iiss N.600E. - 15 - �volcanic rocks, rocks, and and the t h emassive massive nature nature and and broken broken surfaces surfaces of of most most outcrops outcrops and/or the dip dip and and sstrike and/or ffoliation o l i a t i o n prevents prevents determination determination ofof the t r i k e of the the layering. layering. Minor folds were observedinina afew fewwidely widelyscattered scatteredlocations, locations,and andininddifferent Minor folds were observed ifferent roof pendants, so ttheir folding is roof pendants, so h e i r significance significance regarding regarding pre—intrusive pre-intrusive folding is b u ttop topdeterminations determinations can can uncertain. Pillow lavas lavas are a r e widely distributed, distributed, but be madeonly onlya at twol olocalities. otherpillow pillow occurrences occurrencesa rare be made t two c a l i t i e s . The The other e a lall l ffrostrostheaved blocks, oor boulders picked picked from from ffields heaved blocks, r boulders i e l d s and and piled piled by by area area farmers. farmers. The general distribution distribution ofofvolcanic n MarathonCounty, County,however, however, The general volcanicrocks rocksin iMarathon In the the eastern eastern ppart a r t of the the county basalts are abundantt otothe the southeast southeast (near (near Ringle) Ringle) (Figure 2) county basalts a r e more more abundant 2) with toward Wausau. w i t h an an increase increase in i nintermediate intermediateand andfelsic f e l s irocks c rocks toward Wausau. Rhyolites Rhyolites predominate intermediate and predominate at a tWausau. Wausau. North North and and northwest northwest of of Wausau Wausau intermediate and mafic rocks of Wausau pillow lavas rocks again again predominate. predominate. West West of Wausau pillow lavas exposed exposed along along Artus Artus Creek (NE¼,NWk, NW¼, T.29N., R.6E.) indicatetops topst to the southeast, Creek (NEk, Sec.Sec. 29, 29, T.29N., R.6E.) indicate o the southeast, suggesting thethe Wausau suggesting tthat h a t the basalts basalts dip d i p beneath beneath the t h e rhyolites rhyolitesinin Wausau area. area. Assuming t hthat a t t hthe e basalts i s t r i b u t i o n of of volcanic volcanic Assuming basaltsunderlie underliethe therhyolites, rhyolites,the the ddistribution rocks suggestsaanortheast-trending northeast—trending synclinalstructure structurew with rocks suggests synclinal i t h i its t s axis axis approximately the mafic mafic tto approximately ata tWausau. Wausau. However, However, the o felsic f e l s i csequence sequence appears appears to to have beenduplicated duplicatedaat have been t lleast e a s t twice twice by by faulting f a u l t i n gsoutheast southeastofofWausau. Wausau. One One proposed .5 km km west west of the the Eau Eau Claire proposed f afault u l t is i s parallel paralleltot and o andapproximately approximately11.5 River, juxtaposing basalts on the west with rhyolites on the east. on the e a s t . The sequence sequence River, juxtaposing basalts on t h e west w i t h also appears along aa ffault appears tto o be be repeated repeated along a u l tzone zone extending extending from from Rothschild Rothschild northeasterly along complexpattern pattern of of volcanic along Little L i t t l Sandy e SandyCreek. Creek. The The complex volcanic rocks west of the Wisconsin River suggests that the succession rocks west t h e Wisconsin River suggests t h a t the successionhas hasbeen been repeated faulting ((or folding) in i n that t h a t area area as a s well. well. repeated bybyfaulting o r folding) may ther eresult of aa large large synclinal synclinal fold. may bebethe s u l t of fold. In addition folding and and ffaulting, addition to t o the thelarge—scale large-scale folding a u l t i n g , the the volcanic volcanic rocks rocks have beenextensively extensively segmented anddisrupted disruptedbybyintrusions. intrusions. However, have been segmented and However, the the general sequenceofofvolcanic volcanicrocks rocksinin roof roof pendants consistent with general sequence pendants i is s consistent w i t h the the broad pattern outlined broad pattern outlined above. above. This suggests suggests tthat h a t the t h e intrusions intrusionshave have engulfed engulfed the without extensively extensively aaltering the rocks rocks without l t e r i n g the t h e general general fold pattern. pattern. Faulting. The Marathon The Middle Precambrian vol canic-pl utonic complex complex ini nMarathon Middle Precambrian volcanic-plutonic County boundedonona lall sides by by major majorzones zonesofofccataclastic 8). County i is s bounded l sides a t a c l a s t i c rocks rocks (Figure 8). A of cataclastic from the the northeast A zone zone of c a t a c l a s t i c rocks rocks 1-5 1-5km km wide wide extends extends from northeast corner corner of the county downthe theEau Eau ClaireRiver Riverand andLLittle county southwest southwest down Claire i t t l e Eau Eau Claire River River Valleys about km tto o Lake Lake DuBay DuBay near county. There about 61 61 km nearthe the south south edge edgeof of the county. There curvesnorthwesterly northwesterlyand and continues continues northwest northwest up up the the Eau Eau Pleine Pleine River River Valley Valley iti tcurves about 32 km kmt oto Stratford Stratford where whereiitt curves againtoward towardNeil Neillsville. about 32 curves southwest southwest again 1svi 11e . Thus, large sygmoid sygmoidcurve curvet that been traced traced ffor Thus, the zone zone makes makes aalarge h a t has has been o r over over 120 km. Wolf River River Batholith lies and has metamorphosed km. The The Wolf l i e seast e a sof t of and haslocally locally metamorphosed area of of gneisses, the defoned deformed rocks. rocks. A A complex complex area gnei sses, migmatites migmati t e s and and amphibolites amphi bol i t e s (and local local low—grade low-grade metamorphic i e south south of of the thesegment segment along along the the (and metamorphicrocks) rocks)l lie Eau Pleine River. A t least l e a s t five f i v eultramafic ul tramafic bodies bodies occur occur along h i s be1 of alongt this beltt of Eau Pleine River. At cataclastic c a t a c l a s t i c rocks. rocks. A of cataclastic A similar similar broad broad zone zone of c a t a c l a s t i c rocks rocks extends extends in in aa southwesterly southwesterly direction direction along along the the northern northern edge edge of the the volcanic-plutonic volcanic-plutonicterrane terraneininMarathon Marathon County. County. It, I t ,too, too,separates separatesgneisses, gneisses,inigmatites, migmatites, and and amphibolites amphibolites on on the the north north from rocks to from the low-grade low-grade rocks t o the the south. south. The The ffault a u l tzone zone has has been been traced traced from from near Merrill southwest Athenst oto Milan Milanwhere wheref ofoliation near Merrill southwest through through Athens ~ l i a t i o ncurves curves in aa - 16 - �GREENSCYIST I RIVER F - —. I sr I GOODRICH MEDEORDS - I SNEISS —J r—-—-—-— r AND I . , I r si — zo• --- MARSAFIELD N 1 Cl . . •'21- ROZELLVILLE I I '# FAdES •GREENWODD • '— 30 ' (* _',- 2. .224; A> . S L .z t I-> ,,'P p. J7<v1 •poINT -s PITTSvILLE KM :: :4'"RhI/ER c414 > '' ICA4 . 4r. I NEILLsvILLg o N /pATwoLITH.n i<'< 1,41)b I — —.--— — — — -- -, WAU$AU:::LNj,tt44A< — # I so. 4v,',A I I I— ANTIGO I i/I, _....;.>GRtENSCNISt..:/Yv WOLF. 61.M. .' (::.;:::c:::::::. '4.4 /' AMPH/BOLITff 25 !J-!r MERRILL• _€.t — c ',aj7.N WISCONSINT C71j RAPIDS : Figure Figure 8. 8. Simplified S i m p l i f i e d map map oof f sstructural t r u c t u r a l relationships r e l a t i o n s h i p s in i n central central Wisconsin showingt h the Wisconsin showing e o rorientation i e n t a t i o n o of f 1linear i n e a r features f e a t u r e s in i n the the gneissic g n e i s s i c rocks rocksand andlow lowgrade grademetamorphic metamorphic rocks. rocks. Boundary Boundary ffaults aults are a r e shown shown iinn dashed dashed llines. i n e s . Outliers O u t l i e r s of o fgreenschist greenschist facies facies volcanic widely volcanic rocks rocks aare re w i d e l y ddistributed i s t r i b u t e d in i n the t h e areas areas labelled label led gneiss amphi bol it e . gneiss and and amphibolite. more more ssoutherly o u t h e r l y ddirection. i r e c t i o n . Several Several ultramafic u l t r a m a f i c bodies bodies also a l s o occur occur along along this this northern n o r t h e r n zone zone ooff cataclastic c a t a c l a s t i c rocks. rocks. Cataclastic C a t a c l a s t i c foliation f o l i a t i o nin i southwestern n southwestern Marathon Countysstrikes Marathon County t r i k e s nearly n e a r l y north—south, north-south, suggesting suggesting that t h a t the t h etwo twomajor major bounding corner of bounding ffault a u l t zones zones may may j join o i n near near the t h e southwest southwest corner o f the t h e county. county. However, combinationoof However, t the h e combination f gglacial l a c i a l and and Paleozoic Paleozoic cover cover effectively e f f e c t i v e l ymasks masks the the Precambrian themmmigmatitic, Precambrian i in n tthat h a t area. area. Gneisses, Gneisses, some some oof f them i g m a t i t i c , are a r e exposed exposed at at Greenwood, approximately22 22km kmwest westo of low-grade rocks rocks at f t the h e low-grade a t the thewestern western Greenwood, approximately edge T h i s suggests suggests that t h a t the t h elow lowgrade grade rocks rocks do do not not edge of o f Marathon Marathon County. County. This extend These two a t a c l a s t i czones zones coincide c o i n c i d ewith w i t haero— aerotwo major major ccataclastic extend to t o the t h e west. west. These magnetic lows and andl local magnetic and and ggravity r a v i t ylineaments. lineaments. Magnetic Magnetic lows o c a l highs highs parallel parallel - 17 - �the the structures (Figure (Figure 9). 9 ) . The The northern a t a c l a s t i czone zone separates separates aa northern ccataclastic prominent gravity low (over County)from fromsi.gnificant1y significantly higher prominent gravity (over Marathon Marathon County) higher gravity values values over over the the gneisses, gneisses, suggesting suggesting tthat h a t the structures structures involve involve gravity considerable thickness of of crust. considerable thickness crust. In addition additiontotothe themajor majorboundary boundary fault f a u lzone t zonenumerous numerous cataclastic c a t a c l a s t i czones zones are Their trend to trend iiss parallel to w i t h i n the t h evolcanic—plutonic volcanic-plutonic terrane, terrane. Their a r e present present within the major zones range range uup p tto o several km km wide wide and and consist consist major bounding bounding ffaults. a u l t s . The The zones of zonesofof intensely deformed rocks, including of branching branching and and recombining recombining zones deformed rocks, including mylonites, within w i t h i naabroader broader zone zone of of less l e s sdeformed deformed rocks. rocks. Cataclastic zones zones ccut u t the gneissic gneissic rocks rocks at a tGoodrich Goodrich Dells Dells on on the the Rib Rib River Thus, ccataclasis a t a c l a s i s in in River (Elizabeth (ElizabethPalmer, Palmer, verbal verbalcommunication, conimunication, 1979). 1979). Thus, the s not not restricted r e s t r i c t e d totothe t h eboundary boundary fault f a u l tzones. zones. ItI tappears appears to to the gneisses gneisses iis be zonesthroughout throughoutthe thearea, area,cutting cutting greenschist facies be present present in i n numerous numerous zones facies volcanics, plutons plutonsand and gneisses. gneisses. Therefore, Therefore, recognition recognitionand andan anunderstanding understanding of cataclastic the structural and c a t a c l a s t i crocks rocks are a r e important important to t ounderstanding understanding the and tectonic tectonic history history of ofcentral centralWisconsin. Wisconsin. Cataclastic resemblance metamorphosed Cataclastic rocks rocks have have aa superficial superficial resemblancetot oregionally regionally metamorphosed rocks, for which they are often mistaken. They differ in several important They d i f f e r i n several importantways: ways: rocks, f o r which they a r e often mistaken. (1) they have a linear distribution and cut non—deformed rocks; (2) they grade ( 1 ) they have a l i n e a r distribution and c u t non-deformed rocks; ( 2 ) they grade across numerous across sstrike t r i k e into i n t orocks rocksthat t h aare t a r not e notcataclastically c a t a c l a s t i c a ldeformed, l deformed, numerous examples of which which are are present i n Marathon Marathon County; County; (3) ( 3 they theypossess possess aaweak weak to to examples of present in prominent ( 4 )they theyare a r emarkedly markedly inequigranular inequigranular with with prominent ffoliation o l i a t i o n and and lineation; lineation; (4) shattered grains, and rocksshow show the ffine shattered grains, and some some rocks r e crecrystallization r y s t a l l i z a t i o n ofof the i n e matrix. matrix. 7 The typically consist The ccataclastic a t a c l a s t i c zones zones typically consist ofofa anetwork network ofofbraided braidedzones zones of of intense intense cataclasis c a t a c l a s i sseveral severalmm mtot omany many meters meters wide wide bordering borderinglens-shaped lens-shaped pods pods of of relatively r e l a t i v e lundeformed y undeformed rock. rock. Therefore, there iiss aa wide Therefore, there wide ddisparity i s p a r i t y in in the degree degree of cataclasis cataclasis over overshort shortdistances distancesalong alongand andacross across the t h ezones. zones. The lensoidal pattern pattern is The lensoidal t h i nsection sectiontot omap map i s present present on on all a l l scales scales from from thin units. The cross plutonic plutonic and and volcanic volcanic rocks rocks aalike, The ccataclastic a t a c l a s t i c zones zones cross l i k e , with with the the result r e s u l tthat t h a an t anextremely extremely wide wide variety varietyofofcataclastic c a t a c l a s t irocks c rockshave havebeen been produced. major rock types mapped produced. A A brief brief description descriptionofofthethe major rock types mapped isi spresented presented here. here. Flaser coarse grained grained rock rock wwith Flaser gneiss gneiss is i s aamedium medium tto o coarse i t h foliation f o l i a t i o nproduced produced by by the cataclastic c a t a c l a s t i c degradation degradation of plutonic plutonic rocks. rocks. It I tisi scharacterized characterized mesoscopically by aa pervasive pervasive lensoidal lensoidal structure mesoscopically by structure produced produced by by intersecting intersecting shear (Figure 10). Microscopically, the shear planes planes (Figure the rock rock isi smarkedly markedly inequigranular inequigranular fine with relatively r e l a t i v e l yundeformed undeformed porphyroclasts porphyroclasts of feldspar and and quartz with of feldspar quartz iinn aa fine grained grained matrix of of crushed crushed material material . Individual Individual fragments fragments tend tend tot obebecrushed crushed and with larger fragments and boudinaged, boudinaged, with fragments typically typicallyassuming assuming aalensoidal lensoidalshape shape (Figure andand magnetite Biotite,chlorite, c h l o r i t eepidote, , epidote, magnetiteformed formed during during (Figure 11). 11 ) Biotite, cataclasis along braided braided surfaces surfacest that cataclasis are a r e concentrated concentrated along h a t iintersect n t e r s e c t at a tangles angles of of10—30 10-30 degrees. degrees. This This imparts imparts aa streaky streakyappearance appearance tto o the the rocks. rocks. Lineation Lineation due of mineral theplane planeofofffoliation. due tto o elongation elongation of mineral grains grains is i s common common ininthe oliation. Flaser into undeformed plutonic rocks, Flaser gneiss gneiss grades grades on on one one hand hand into undeformed plutonic rocks, and and with with continued cataclasis into mylonite continued cataclasis mylonite or o r phyllonite. phyllonite. . - 18 - �Figure of the of central central Wisconsin. Figure 9. 9. Photograph Photograph of the aeromagnetic aeromagnetic map map of Wisconsin. Note Note the coincidence coincidence of the the major major boundary boundary faults f a u l t s (dashed (dashed white white lines) the ddistinctive w i t aeromagnetic h aeromagneticlineaments. 1 ineaments. Note Note aalso l s o the istinctive l i n e s )with magnetic pattern of Marathon magnetic pattern of that t h a tportion portionof of MarathonCounty Countyenclosed enclosed within within (Magnetic data data from from Karl, Karl,1973—75.) 1973-75.) the the dashed dashed llines. i n e s . (Magnetic — 19 - �— - . Quartz monzonite monzoni t e fflaser l a s e r gneiss gneiss showing showing typical typicallensoidal lensoidal Figure10. 10. Quartz Figure structure structureproduced produced by by intersecting intersectingshear shearplanes. planes. p 4, 2mm typical flaser Photomicrograph ofofaa typical f l a s e rgneiss gneissshowing showing the the Figure11. 11. Photomicrograph Figure fractured fractured porphyroclasts, porphyroclasts, matrix matrix and and lensoidal lensoidal structure. structure. -- 20 20 -- �Mylonite iiss typically typicallyaaflinty, f l i n t laminated y , laminated rock (Figures1212and and13) 13) Mylonite rock (Figures consisting mainly 14), and mainly of of finely finelycrushed crushedmaterial material(Figure (Figure 141, andmay maybe be compositionally compos~tionall ybanded. banded. Like flaser f l a s e r gneiss, gneiss, mylonite mylonite is i svery very inequigranular, inequigranular, but b u t has has a greater greater percentage percentage of crushed crushed matrix. Foliation Foliation surfaces surfaces are are closely spaced andtypically typically intersect spaced and i n t e r s e c t ata tless l e s sthan than1010degrees, degrees. Streaky Streaky lineation in by ""trains" i n the the direction direction of oftectonic tectonictransport transport isi sproduced produced by t r a i n s " of fine mineralsi in the plane planeofofccataclastic f i n e grained grained minerals n the a t a c l a s t i c ffoliation. o l i a t i o n . Detached Detached fold fold axes andi nintrafolial w i t h i n mylonites mylonites indicate indicate local folding. folding. axes and t r a f o l i a l folds folds within Polygonization andincrease increasei ningrain grains size of tthe i z e of h e ffine i n e matrix matrix indicates indicates Polygonization and recrystallization of ofmylonites mylonjtes locally. l o c a l l y . While While the parent parent rock rock for f o rmost most flaser determined, the the protolith protolith for f l a s e r gneisses gneisses can can be be determined, f o mylonites r mylonitesis imuch s muchmore more difficult MarathonCounty Countyhave have been been d i f f i c u l to t t oascertain ascertain(Figure (Figure 15). 1 5 ) . Mylonites Mylonites ini nMarathon derived wide variety variety of volcanic derived from from aa wide volcanic and and plutonic plutonic rocks. rocks. Whereas Whereas f felsic elsic mylonite hard,f flinty mylonite iis s comonly comonly aahard, l i n t y rock rock owing owing t to o iits t s high high silica s i l i c acontent, content, mylonite derived derived from from intermediate intermediate and o be hloritic mylonite and mafic mafic rocks rocks tends tends tto be more morec chloritic and Felsic and and intermediate intermediatetot omafic maficmylonites mylonitesarea rcommonly e comonly and schistose. schistose. Felsic intercalated. intercalated. Deformed Volcanic Rocks. rocksreact reactddifferently Deformed Volcanic Rocks. Volcanic Volcanic rocks i f f e r e n t l y to t o stress stress than do plutonic rocks. than do rocksa Indeed, Indeed, the l i t e r a t u r eonondeformed deformed volcanic volcanic rocks rocks is is the literature extremely presenceofofaawide widevariety variety of volcanic extremely vague vague and andmeagre. meagre. The The presence volcanic rocks rocks interspersed w i t h cataclastically c a t a c l a s t i c a l l ydeformed deformedplutonic plutonicrocks rocksin iMarathon n MarathonCounty County interspersed with provides an excellent opportunity to compare features in deformed volcanic provides an opportunity t o compare features i n deformed volcanic and volcanic rocks and plutonic rocks. rocks. Most Most of the t h e deformed deformed volcanic rocks are a r e strongly strongly foliated layer ssilicates. f o l i a t e ddue due to t o the theextensive extensive development development ofoflayer i l i c a t e s . Felsic Felsic volcanic volcanic rocks andmafic maficrocks rocksa are rocks tend tend tto o be be sericitic s e r i c i t i cwhereas whereas intermediate intermediate and r e c chloritic. hloritic. In some rhyolites the the phenocrysts phenocrystsa rare rotatedi ninto planeof of ffoliation some rhyolites e rotated t o tthe h e plane o l i a t i o nand and boudinaged (Figure 16). O e f o m t i o n of ofrhyol i t i c t tuffs u f f s rresults e s u l t s iinn flattening boudinaged (Figure 1 6 ) . Deformation flattening rhyolitic and/or and/or elongation elongation of the t h e volcanic volcanic fragments fragments (Figure (Figure 17). 17). In In some some rhyolites rhyolites the strain takenuup byrrecrystallization p by e c r y s t a l l i z a t i o n and and flowage flowage of s t r a i nappears appears to t o have have been been taken the matrix, leaving highly foliated n aa highly fol fated leaving relatively r e l a t i v e l yeuhedral euhedral phenocrysts phenocrysts i in sericitic s e r i c i t i cmatrix. matrix. Evidently Evidently the the nature nature of ofthe t h epre—existing pre-existing volcanic volcanic rock rock (e.g. a tuff (*a t u f f vs. vs. aa lava lava flow, flow, or or aa porphyritic porphyriticvs. vs.a anon-porphyritic non-porphyritic rock) rock) affects a f f e c t s the thebehavior behavior of ofthe t h erock rockduring duringdeformation. deformation. Deformation Oeformation of of fragmental fragmental andesites andesi t e s has has produced produced spectacular spectacular examples examples of elongated el ongated fragments. fragments. In areasthe the long long dimension dimensioni is 10 times times the the cross-sectional cross-sectional diameter In some some areas s 10 diameter of the hornblende and and plagioclase plagioclase phenocrysts the lineated lineatedfragments. fragments. Boudinaged Boudinaged hornblende phenocrysts accompany lineatedfragments fragments severall olocalities, accompany thethe1ineated in inseveral c a l i t i e s , suggesting suggesting dislocation dislocation rather than than simple simple fflattening. lattening. Minor structures are Precambrian Mesoscopic structures a r ewidespread widespread ini nPrecambrian Minor Structure. Structure. Mesoscopic rocks rocks in central central Wisconsin, Wisconsin, and and ttheir h e i r pattern pattern isi sinformative informativeregarding regarding the the structure mappingnorth, north, west west and and south south of Reconnaissance mapping structure of of the thearea. area. Reconnaissance Marathon County( (in Wood, Marathon County i n Lincoln, Lincoln, Taylor, Taylor,Clark, Clark, Wood,and andPortage PortageCounties) Counties)and and farther f a r t h e rwest westini nChippewa Chippewa and and Eau Eau Claire Counties Counties (Myers, (Myers, 1974, 1974, 1978, 1978, and and this this conference) discloseaa consistent consistentpattern pattern of of llinear i n gneissic gneissicrocks rocks conference) disclose i n e a r features features in in of minor minor ffolds, lineationsand and elongation elongation Axes of o l d s , mineral mineral lineations in central centralWisconsin. Wisconsin. Axes of of mafic mafic xenoliths(?) xenoliths(?) plunge plunge aatt a a relatively r e l a t i v e l y low low angle angle to t o the the west west ininmost most of In gneisses gneisses ini nand andnear nearMarathon Marathon County, County, 8 ) . In of the the gneissic gneissic rocks rocks (Figure (Figure 8). fold lineations plunge westa at 30-40°i ninthe theplane planeofofthe theffoliation. oliation. fold axes axes and and lineations plunge west t 30-40 Maass andMedaris Medaris(1977) (1977) iinterpret Precambrian Maass and n t e r p r e tthese thesetot obebeMiddle Middle Precambrian(Penokean) (Penokean) structures. Lineations in in the thegneisses gneisses steepen steepen tto o near near vertical near near the the s t r u c t u r e s . Lineations - 21 - �m y l o n i t e about about 1.6 1.6 km km southwest southwest of o f Athens Athens Figure Outcrop ooff rnylonite F i g u r e 12. 12. Outcrop along betweent hthe gneissesand andggreenschist along the boundary boundary between e gneisses r e e n s c h i s t ffacies a c i e s rocks. rocks. Figure F i g u r e 13. 13. Photograph ooff myloni Photograph m y l o n ite t e showing showing tthe h e ttypical y p i c a l streaky s t r e a k y and and lensoidal l e n s o i d a l character. character. - 22 — �-l.-i' fl - ;; r— flrSa 7we ac' afr*.e Figure 14a. typical mylonite 14a. Photomicrograph Photomicrograph ofof typical mylonitefrom fromMarathon Marathon Countyshowing showingt hthe abundance material and and tthe County e abundance of off ifine n e material h e close spacing of of shear spacing shear planes. planes. Photomicrographofoftypical typical mylonite Figure 14b. mylonite from from the the Brevard Brevard 14b. Photomicrograph Zone iin n the the southern southern Appalachians. Appalachians. Zone -—2323 -- �i'a:i T aAi• rT ., - L - -- 4j4 Figure the progressive Photographs showing showing the progressive cataclastic cataclastic gure15. 15. Photographs degradation granite (top) to undefomed granite t o mylonite mylonite(center) (cent( !gradation from from an an undefonited to Iultramylonite ultramylonite(bottom). (bottom). The The protolith protolithforf othe r the mylonitecan canbe mylonite established itablished where where the the transition t r a n s i t i o nis iexposed. s exposed. - -24 24- - �2 nun Figure Figure 16. 16. Deformed Deformed f efelsic l s i c volcanic rocks rocks showing showing aa ffoliated oliated s e r i c i t imatrix c matrix boudinagedphenocrysts phenocrysts that t h a thave havebeen been rotated rotated sericitic andand boudinaged into of ffoliation. i n t o the the plane plane of o l i a t i o n . Note crenulation folds folds in i n the the Note tthe h e crenulation matrix matrix of ofthe thelower lowerphotograph. photograph. - 25 - �: -- j,-- :tc '"r p. - t r 4, — tr -—-'I ; .WL'tfra 7tr *a L.4 a*2S' — Figure 17. 17. Photographs Photographs o foff efelsic l s i c tuff t u f f showing showing the t h e elongation e l o n g a t i o n of of deformed photo i is deformed fragments. fragments. Upper Upper photo s undefornied undeformed t utuff f f with w i t h angular, angular, equant photoshows shows equant cclasts. l a s t s . Lower Lower photo t y ptypical i c a l l elenticular n t i c u l a r longitudinal longitudinal section deformed ttuff. uff. s e c t i o n in i n aa deformed - 26 - �major boundary boundaryf fault wherethe thegneisses gneissesare arei in contact wwith major a u l t zones zones where n contact i t h greenschist greenschist facies volcanic-plutonic volcanic-plutonic rocks rocksininMarathon MarathonCounty. County. Lineations are Lineations are also present present in i n the thedeformed deformed volcanic volcanic and and plutonic rocks. rocks. Elongated cclasts phenocrystsplunge plungee aeast 5Q°or or steeper steeper in Elongated l a s t s and and boudinaged boudinaged phenocrysts s t aat t 50 in minor fold axes most of of the most the volcanic volcanicpendants. pendants. Several Several minor axes also plunge plunge steeply steeply Lineations including streaking east streaking and and elongation elongation of e a s t tto o nearly nearly vertical v e r t i c a l .. Lineations minerals and and xenoliths xenoliths are plutonic rocks. i n many many plutonic rocks. Boudinaged minerals are also present present in measuredlineations lineations Most measured quartz veins veins occur occur iinn both both volcanic volcanic and and plutonic rocks. rocks. Most quartz however, some somew with steep easterly easterly in plutonic i t h aa steep plutonic rock rock are are nearly nearly vertical v e r t i c a l;; however, Crenulationfolds foldsaare locally present, dip were were recorded. recorded. Crenulation r e locally present, indicating multiple dipping 1lineations absent iinn the the deformation. Westerly Westerly dipping ineations are are conspicuously conspicuously absent the orientation of low-grade low-grade rocks. Thus, Thus, the of minor minor structures structures suggests suggests tthat h a t the the two terraneshave haved idifferent structural histories. two terranes f f e r e n t structural Furthermore, Myers(1978) (1978)shows showsisolated isolated patches patchesof of volcanic rocks Furthermore, Myers rocks and and volcanogenic sedimentslying lying unconformably onthe the amphibolite amphibolite facies rocks volcanogenic sediments unconformably on rocks along the Eau Claire River i neastern easternEau Eau Claire Claireand and western western Clark Clark Counties. Counties. Eau Claire River in along (Note tthat River one Marathon n eastern Marathon (Note h a t this t h i s isi sa adifferent d i f f e r e nEau t EauClaire Claire Riverthan thanthethe onein i eastern The unconformi unconformity the amphibolite County.) t y between between the amphi bol i t e facies faciesgneisses gneissesand andgreen— greenCounty. ) The schist s c h i s t facies faciesvolcanogenic volcanogenic rocks rocks has has been been folded folded about about an an axis that t h a tplunges plunges 3Qoeeast This indicates indicates that t h a tthe thelow-grade low-grade rocks rockswere were deposited deposited 30 a s t (Myers, (Myers, 1978). 1978). This Furthermore, iitt argues on amphibolite facies facies rocks. argues against a ainst on aa basement basement ofofamphibolite rocks. Furthermore, kthe suggestion andMedaris Medaris(1977) (1977)t hthat the amphibolite amphibolite facies rocks suggestion by by Maass Maass and a t the roc s are simply equivalentsofofthe the greenschist greenschist facies are simply more more highly metamorphosed metamorphosed equivalents facies rocks rocks in inMarathon Marathon County. County. While the the minor minor structures in i n the thevolcanic—plutonic volcanic-plutonic terrane terrane have have aa While different surrounding rocks, the n the surroundinghigh—grade high-grade rocks, the d i f f e r e n torientation orientationthan thanthose thoseini the nature of the deformation within the low-grade rocks must be considered. nature the deformation w i t h i n the low-grade rocks must be considered. For example,the the deformation deformationi in the volcanic-plutonic terrane For example, n the terranemay may be be due due tto o (1) theplutonic plutonicrocks, rocks,oor 2 ) deformation deformation llater a t e r than, than, and and not not ( 1 ) emplacement emplacement of ofthe r ((2) necessarily relatedt to, the plutonic plutonic aactivity. necessarily related o , the c t i v i t y . If I f the the deformation deformation is i s related related to theplutonic plutonic rocks, rocks, cataclasis t o emplacement emplacement ofofthe c a t a c l a s i s around around each each intrusion should should be related related sspatially in orientation be p a t i a l l y and and in orientation to t o that t h a t pluton. pluton. Foliation Foliationtrends trendsmay may be expected expected tto around" the the plutons. IIff the the deformation deformation iiss not not related related be o "wrap "wrap around" to the deformation would be through—going the plutonic plutonicactivity, a c t i v i tthe y , the deformation would be through-going and and have have aa consistent pattern throughout consistent throughout the the terrane. Strike and and dip dip of ofnumerous numerous ccataclastic a t a c l a s t i c zones zones within the the volcanic—plutonic volcanic-plutonic terrane Cataclastic zones terrane are are similar to t othose those of ofthe themajor major boundary boundary ffaults. a u l t s . Cataclastic zones with a consistent plutonic rocks with consistent trend trend cut volcanic volcanic and and plutonic rocks aalike. like. A A pervasive pervasive ccataclastic a t a c l a s t i c foliation f o l i a t i o nwith w i t haaconsistent consistent regional regional trend trend (east ( e a s t or o r northeast) northeast) is is present i n most most of of the theMiddle MiddlePrecambrian Precambrian plutons plutons ini nMarathon MarathonCounty. County. The present in absenceofofpervasive pervasivec acataclastic plutons iiss aa absence t a c l a s t i c ffoliation o l i a t i o n ininLate LatePrecambrian Precambrian plutons major distinction major distinctionbetween betweenthem themand and Middle Middle Precambrian Precambrian rocks. rocks. Theage ageofofthe thedeformation deformation The i s isd idifficult f f i c u l t to t o establish. e s t a b l i s h . However, However, aa general general pattern of of deformation deformation and and intrusion intrusionwas was recognized recognized by by LaBerge LaBerge (1976), in in which the oldest oldest plutons plutons (quartz (quartz diori diorites) which the t e s ) typically typicallyare a r emore more intensely intensely deformed than quartz quartz monzonites monzonitestthat deformed than h a t intrude intrudethem. them. Granitic plutons plutons are are generally less l e s s cataclastically c a t a c l a s t i c a l l deformed y deformedthan thanquartz quartzmonzonites, monzonites, and and in i n places places — 27 — �(Figure 7) truncate ( F i g u r e 7) t r u n c a t e ccataclastic a t a c l a s t i c foliation f o l i a t i o nini quartz n quartzmonzonites. monzonites. IInn eastern eastern Marathon Countya ac acataclastic m.y.old o l(Van d (VanSchmus, Schmus, 1975) 1975) Marathon County t a c l a s t i c ffoliation o l i a t i o nini 1900 n 1900m.y. thethe 1850 rrhyolite h y o l i t eisi struncated truncatedbyby 1850m.y. m.y.old o l(Van d (VanSchmus, Schmus, 1976) 1976) Kalinke Kalinke quartz quartz westernmargin margin monzonite. The The western o f of t hthe e p lpluton u t o n i sisnnot o t ffoliated, o l i a t e d , but b u t the t h eeastern eastern margin iiss extensively margin e x t e n s i v e l y foliated f o l i a t e dalong alongthe t h eEau Eau Claire C l a i r eRiver R i v e rshear shear zone. zone. South- east plutons e a s t ooff Wausau Wausau g r agranitic n i t i c plutons c ucut t t h the e c acataclastic t a c l a s t i c f ofoliation l i a t i o n i in n aa similar similar foliated f o l i a t e dquartz q u a r t zmonzonite. monzonite. Similar S i m i l a r relationships r e l a t i o n s h i p sthroughout throughoutthe t h ecounty countysuggest suggest that over an an extended extendedpperiod time, and t h a t deformation deformation occurred occurred over e r i o d oof f time, and intrusions i n t r u s i o n s were were emplaced emplaced d during u r i n g t this h i s time. time. The The ccataclastic a t a c l a s t i c rocks rocks of o f the t h eEau Eau Claire C l a i r e River R i v e rzone zone were metamorphosed metamorphosedbybyt hthe 1500m.y. m.y.oold andothers, others, 1973) Wolf were e 1500 l d (Van (Van Schmus Schmus and Wolf 1.5 km widezone zoneo of River Batholith. km wide f ccataclasis a t a c l a s i s wwithin i t h i n the t h e Wolf Wolf River River R iver B a t h o l i t h . AA 1.5 Batholith B a t h o l i t h along along the t h e Little L i t t l Eau e EauClaire C l a i r River e R i v esuggests r suggestssubsequent subsequent deformation deformation of of the Since tthe EauCClaire zonei sispparallel h e Eau l a i r e RRiver i v e r zone a r a l l e l tto o other other the bbatholith a t h o l i t h as as well. w e l l . Since as much muchasas3636kmkm west Wolf River ccataclastic a t a c l a s t i c zones zones as west o f of t h ethe Wolf River B aBatholith, t h o l i t h , i tit iiss unlikely waswas produced by by emplacement u n l i k e l ythat t h a significant t s i g n i f i c a cataclastic n t c a t a c l a sdeformation t i c deformation produced emplacement ooff that t h a t batholith. batholith. Thus, I I believe b e l i e v e the t h e deformation deformation wwithin i t h i n tthe h e vvolcanic-plutonic o l c a n i c - p l u t o n i c tterrane e r r a n e is is Thus, a tectonic t e c t o n i c event eventcontemporaneous contemporaneous wwith i t h bbut u t not n o t necessarily n e c e s s a r i l y related r e l a t e dtot emplacement o emplacement Thecconsistent of o f the the plutons. p l u t o n s . The o n s i s t e n t oorientation r i e n t a t i o n of o f minor minor structures s t r u c t u r e s suggests suggests tthat hat iti tisi sa aregional r e g i o n aorogenic l orogenicdeformation deformationthat t h apre-dates t pre-datesemplacement emplacement ooff the t h e Wolf Wolf This deformation doesnnot appeart to be rrestricted River Batholith. deformation does o t appear o be e s t r i c t e d tot oMarathon Marathon River B a t h o l i t h . This County,f for County, o r lineations l i n e a t i o n s ini ngreenschist greenschistfacies f a c i e svolcanic v o l c a n i crocks rocksexposed exposed along along the the Jump NW Athens)aalso Jump RRiver i v e r iin n northwestern northwestern Taylor T a y l o r County County (40 (40 km km N W o of f Athens) l s o ddip i p steeply steeply Mudrey(1979, (1979,wwritten o m u n i c a t i o n ) also a l s o recorded recorded east-plunging east-plunging tto o the the east. east. Mudrey r i t t e n ccomunication) This llineations i n e a t i o n s ini nvolcanic v o l c a n i crocks rocksnear nearMonico Monicoini nOneida Oneida County. County. T h i s iis s similar similar Countyb but tto o the t h e lineations l i n e a t i o n s ini nMarathon Marathon County u t d distinctly i s t i n c t l y different d i f f e r e n tfrom from the t h e shallow shallow westerly Therefore, iitt w e s t e r l y ddip i p ooff lineations l i n e a t i o n s in i nthe t h eintervening i n t e r v e n i n ggneissic g n e i s s i c rocks. rocks. Therefore, appears haver eregional appears t to o have g i o n a l s significance i g n i f i c a n c e i in n tthis h i s part p a r tofo fthe t h eLake LakeSuperior Superior region. region. Xenoliths in Xenoliths i n some some iintrusions n t r u s i o n s also a l s o have have a bearing bearing on on the t h e possible p o s s i b l e age age of of the Biotite t h e gneissic g n e i s s i c rocks. rocks. B i o t i t e schist s c h i s tand and quartzite, q u a r t z i t e , mixed mixed in i nvarious various proportions proportions with mafic anduultramafic rocks, occur as xxenoliths n t r u s i v e rocks, occur as e n o l i t h s in in w i t h volcanic v o l c a n i c and and m a f i c and l t r a m a f i c i intrusive the Syeniteand andl eless abundantlyi nin oother t h e Wausau Wausau Syenite s s abundantly t h e r plutons. Quartzite Q u a r t z i t e inclusions inclusions are restricted m.y. oldo(Van Schmus, Wausau are r e s t r i c t e dto tthe o t h1500 e 1500 m.y. l d (Van Schmus,1976) 1976) Wausau Syenite Syenitecomplex. complex. A syenite km northwest of Wausau (5E¼, A quartzite q u a r t z i t exenolith x e n o l i t hin iquartz n quartz syeni3.2 t e 3.2 km northwest o f Wausau (SEk,SW¼, SWg, Sec. 21, 21, T.29N., T.29N., R.7E.) R.7E.) contains containsup upt to 12 percent percentssillimanite. Sec. o 12 i l l i m a n i t e . Xenoliths Xenoliths of of volcanic volcanic and and pplutonic l u t o n i c rocks rocks in i nthesame t h e same intrusion i n t r u s i o nare a r evirtually v i r t u a unmetamorphosed, l l y unmetamorphosed, suggesting suggesting tthat h a t the t h e sillimanite s i l l i m a n i tmay e mayhave havebeen beenproduced produced by by an an earlier e a r l i e rmetamorphic metamorphic event, and byt the event, and not n o t by by contact c o n t a c tmetamorphism metamorphism by h e ssyenite. y e n i t e . This suggests suggests an an upward upward transport t r a n s p o r t of o f the t h equartzite q u a r t z i t efrom froma ahigh-grade high-grademetamorphic metamorphic tterrane e r r a n e aatt depth, depth, perhaps onwhich whicht hthe The absence perhaps tthe h e basement basement on e vvolcanic o l c a n i c rocks rocks were were deposited. deposited. The absence m.y. old) o l d ) plutons p l u t o n s suggests suggests eeither i t h e r aa ooff quartzite q u a r t z i t e xenoliths x e n o l i t h s ini nolder o l d e r(1850 (1850 m.y. very very rrestricted e s t r i c t e d occurrence occurrence ooff the t h e quartzite q u a r t z i t e ini nthe t h ebasement basement oor r that t h a t the the qquartzite u a r t z i t e isi syounger younger than than the t h e 1850 1850 m.y. m.y. old o l d plutons plutons and and was was intruded i n t r u d e d only o n l y by by the t h e syenite. s y e n i t e . In I n the t h e latter l a t t e case, r case,quartzite q u a r t z i twould e wouldrepresent representfoundered foundered blocks blocks from aboveand andt hthe would nnecessarily bet the from above e s isillimanite l l i m a n i t e would e c e s s a r i l y be h e rresult e s u l t of o f contact contact However,i tit seems seemsu nunlikely metamorphism syenite. l i k e l y t hthat a t qquartzite u a r t z i t e (with (with metamorphism bybyt hthe e syeni t e . However, a a specific s p e c i f i c gravity g r a v i t yofo f2.7) 2.7)would wouldsink s i n kini na amagma magma tthat h a t ccarried a r r i e d ultramafic u l tramafic xenoliths x e n o l i t h s (with ( w i t h aa specific s p e c i f i c gravity g r a v i t yofo about f about3.4) 3.4) upward. upward. Therefore, Therefore, IIfavor favor the the interpretation i n t e r p r e t a t i o n that t h a tthe t h esillimanite-bearing s i l l i m a n i t e - b e a r i n gquartzite q u a r t z i twas e wascarried c a r r i e dupward upward from aa high—grade metamorphic basement basementalthough although II recognize recognizet that an aalternative h a t an lternative high-grade metamorphic -28- �Since tthick iinterpretation n t e r p r e t a t i o n is i s possible. p o s s i b l e . Since h i c k quartzites q u a r t z i t e sare a r euncommon uncommon iin n Early Early Precambrian sequences, theq uquartzite Precambrian sequences, the a r t z i t e iis s more more llikely i k e l yMiddle MfddlePrecambrian. Precambrian. The question then then aarises deeper level level The question r i s e s whether whether the t h e gneisses gneisses represent r e p r e s e n t aa deeper (higher ( h i g h e r pressure-temperature) pressure-temperature) ooff the t h e volcanic v o l c a n i c sequence, sequence, or o r whether whether they they represent an on which which tthe an older o l d e r basement basement on h e volcanics were were deposited. deposited. Mapping Mapping by andMyers Myersi in and around aroundMarathon MarathonCounty Countyshows shows LaBerge and n and t h that a t s structures t r u c t u r e s in in by LaBerge the haveaa ddifferent t h e gneisses gneisses have i f f e r e n t orientation o r i e n t a t i o nthan thanthose thoseini the n t hlow—grade e low-grade volcanic volcanic rocks. The The general general wwesterly plunge ooff lineations e s t e r l y plunge l i n e a t i o n sini the n t hgneisses e gneissescompared compared with rocks iindicates w i t h easterly e a s t e r l y plunging plunging lineations 1i n e a t i o n sini nthe t h elow—grade low-grade rocks n d i c a t e s tthat h a t the the gneisses and andlow-grade low-graderocks rockshave havebeen been subjected gneisses subjected t otod idifferent f f e r e n t stresses. stresses. While iittisi spossible p o s s i b l ethat t h aboth t bothstrain s t r a ipatterns n p a t t e r nmay s maybe beproduced produced by by a a single single While e l f e v e tthe h e differences d i f f e r e n c e s in i n regional r e g i o n a l patterns p a t t e r n s and and pperiod e r i o d of o f deformation, deformation, II bbelieve unconformabler erelationships (1978) aare unconformable l a t i o n s h i p s described described by by Myers Myers (1978) r e best explained explained by assuming assumingtwo twoperiods periods ooff deformation by deformation separated separated by by erosion. TECTONIC SPECULATION SPECULATION Precambrian IIffthe t h egneisses gneissesare a r eMiddle Middle Precambrian(as (assuggested suggestedbybyMaass Maass and and Medaris, 1979, oral Medaris, 1977, 1977, and and Van Van Schmus, Schmus, 1979, o r a l cormiunication) c o m u n i c a t i o n )and andthe t h elow—grade low-grade Precambrian Van a l s oMiddle Middle Precambrian(as (asdated datedbyby VanSchmus, Schmus, vvolcanic—plutonic o l c a n i c - p l u t o n i c terrane t e r r a n e isi salso 1975, 1976) 1976)and andi iff the weresubjected subjected 1975, t h e two two sequences sequences were t otod different i f f e r e n t periods periods of of deformation, deformation, then then there t h e r eare a r etwo twoperiods periodsofometamorphism f metamrphism and and deformation deformation represented I f this t h i s interpretation i n t e r p r e t a t i o n is is County. If represented iinn the t h e rocks rocksofo Marathon f E a t h o n County. hasconsiderable considerable regional r e g i o n a l significance. significance. ccorrect, o r r e c t , iti thas The ppostulated Middle Precambrian deformations in be The o s t u l a t e d two two Middle Precambrian deformations be represented represented throughout muchoof Superior region. region. It throughout much f tthe h e Lake Lake Superior I thas haslong l o n gbeen beenrecognized recognized that t h a t aa mild m i l d flexuring f l e x u r i n gand anderosion e r o s i o n occurred occurred during d u r i n g deposition d e p o s i t i o n of o f the t h eMiddle Middle - Precambriansedimentary sedimentaryrocks rocksexposed exposed variousi riron Van Precambrian onon t hthe e various o n ranges ranges ((cf. c f . Van Hise and and LLeith, For example, sequenceo of rocks ccontaining Hise e i t h , 1911). 1911 ). For example, tthe h e sequence f rocks o n t a i n i n g the the Kona, Randville River Kona, R a n d v i l l e and and Bad Bad R i v e r Dolomites Dolomites (the ( t h e Chocolay Chocolay Group Group ooff the t h eMarquette Marquette Range Supergroupo fofCannon Cannon and Gair,1970) 1970)underwent underwentg egentle Range Supergroup and Gair, n t l e f flexuring l e x u r i n g and and erosion rocks of othe e r o s i o n prior p r i o rtot odeposition d e p o s i t i o of n othe f t hless e l e deformed s s deformed rocks f t hMenominee e Menomineeand and Baraga The deformation deformationf following Baraga Groups. Groups. The o l l o w i n g deposition d e p o s i t i o n of o fthe t h eBaraga Baraga Group Group is is generally (Goldich, 1961). Deformation 1y referred r e f e r r e dtot oasasthe t hPenokean e Penokean Orogeny Orogeny (Goldich, 1961 ) . Deformation general increasesi nini intensity aattributed t t r i b u t e dtot othe t h ePenokean Penokean Orogeny Orogeny increases n t e n s i t y southward southward iin n the the Lake Superior Superior region. Precambrian If,indeed, indeed,two twoperiods periodsofoMiddle f Middle Precambriandeformation deformation Lake r e g i o n . If, are present, are present, the t h e gneisses gneisses and and amphibolites amphibolites in i ncentral c e n t r a Wisconsin l Wisconsinmay may be be aa manifestation post-Chocolay--pre-Menominee deformation deformation and and the the m a n i f e s t a t i o nofo fthe t h epost-Chocolay--pre-Menominee deformation in deformation i n the thelow—grade low-grade vvolcanic—plutonic o l c a n i c - p l u t o n i c rocks may may rrepresent e p r e s e n t the the "Penokean Orogeny." Orogeny." IIffonly deformation iiss present, o n l yone oneMiddle MiddlePrecambrian Precambrian deformation present, "Penokean the be E Early This t h e gneisses gneisses would would presumably presumably be a r l y Precambrian Precambrian iinn age. age. T h i s problem problem Regardlesso of ageo of gneisses,i itt is remains i s probable probable remains unresolved. Regardless f t hthe e age f t hthe e gneisses, which tthe tthat h a t they they represent represent the t h ebasement basement on on which h e volcanic v o l c a n i c rocks rocks were were deposited, deposited, for of of low-grade f o r relatively r e l a t i v e l small y smallisolated i s o l a t eareas d areas low-gradevolcanogenic volcanogenic sediments sediments (of (of Middle Precambrian age?)occur occurwwithin an area area of of dominantly Eau Middle Precambrian age?) i t h i n an dominantly gneisses gneisses in i nEau Claire I believe Therefore, I C l a i r e County. County. Therefore, b e l i e v e that t h a t the t h e volcanics volcanics are a r e a discrete, discrete, younger than the younger sequence sequence than t h e high—grade high-grade rocks. - 29 - �SUMMARY SUMMARY Gneissic rocks rocks ininnorthwestern northwesternand andextreme extremesouthern southernMarathon MarathonCounty County are n o tbeen been dated dated a r e probably probably tthe h e oldest o l d e s t rocks rocks in inthe t h earea, a r e a ,although althoughthey theyhave havenot Theymay maybe, be,a at t l least e a s t in part, p a r t ,Early EarlyPrecambrian Precambrian (more (more than than radiometrically. They 2500m.y. m.y.) 2500 ) or earlier e a r l i e rMiddle MiddlePrecambrian Precambrian rocks rocks that t h a tunderwent underwent amphibolite amphi bol i t e and deformation. deformation. IIff the thehigh-grade high-grade rocks rocks are a r e Middle Middle ffacies a c i e s metamorphism metamorphism and Precambrian,as assuggested suggestedbybyMaass Maass Medaris (1977), they z.ccorrelate Precambrian, andand Medaris (19771, they o r r e l a t e with with rocks of the Supergroupf afarther rocks theChocolay Chocolay Group Group of the the Marquette Marquette Range Range Supergroup r t h e r north Deformationof of these these rocks rocks would would then then be be postiinn the the Lake Lake Superior Superior region. region. Deformation The more more intense metamorphism and deformation metamorphism and Chocolay-.-pre-Menominee Group. Chocolay--pre-Menominee Group. The in central mayc ocorrelate regional flexuring flexuring of i t h t the h e ggentle e n t l e regional of central Wisconsin Wisconsin may r r e l a t e wwith Chocolay Group Grouprocks rocks(LaBerge (LaBergeand andMudrey, Mudrey,1979) 1979)t hthat occurred on on tthe Chocolay a t occurred h e iron iron ranges tto ranges o the the north. north. Erosion Erosion of these these gently gently deformed deformed rocks occurred occurred on on the the erosion must must have haveoccurred occurredi in b u t much much deeper deeper erosion n central Wisconsin Wisconsin iron ranges, ranges, but the amphibolite-facies amphibolite-facies gneissic rocks. tto o expose expose the rocks. The deposition of Groupsedimentary sedimentaryrocks rocks on on tthe h e iron iron ranges ranges The deposition ofMenominee Menominee Group may correlate with the onset of volcanism in central Wisconsin, where may c o r r e l a t e the onset of volcanism i n central Wisconsin, wheregreen— greensschist c h i s t facies f a c i e s volcanic volcanicrocks rocks rest r e s tunconformably unconformably on on amphibolite amphibolite ffacies a c i e s rocks. rocks. Most of of the volcanic indicating the Most volcanic rocks rocks are a r e subaqueous, subaqueous, indicating t h e presence presence of one one or or The volcanic rocks were then extensively intruded by granitic more basins. The volcanic rocks were then extensively intruded by g r a n i t i c more presenceofof high-grade high-grade rocks rocks juxtaposed plutons and and deformed. deformed. The The presence juxtaposed with with greenschist ffacies rock and and tthe preponderance greenschist a c i e s rock h e preponderance of of v evertical r t i c a l l ilineations, n e a t i o n s , including including boudinage boudinage s tstructures r u c t u r e s tthat h a t indicate indicate vertical v e r t i c amovement l movement on on the boundary boundary ffaults, aults, suggests gneisseswere wereu puplifted alongl large Then the general suggests t that h a t tthe h e gneisses l i f t e d along a r g e ffaults. a u l t s . Then general synclinal structure Marathon s t r u c t u r eofofthe t h evolcanic volcanicrocks rocksin in MarathonCounty County may may rresult e s u l t from from of tthe volcanic rocks rocks iinto graben—like' sstructure rrelative e l a t i v e subsidence subsidence of h e volcanic n t o aa "graben-like'' tructure ofnumerous numerous plutons plutons and and deformation deformation of those those plutons plutons (Figure 18). (Figure 1 8 ) . Intrusion of volcanics volcanics volcanios m lcanics / fit Oneisses .Migmatites Amphiholites Outliers of low— Graben Generally low—grade metamorphism Epizonal Plutons It Amphibolitee Migmatitee Some younger piutons grade rocks Some younger plutons north-south cross-section cross-section across acrosswestern western Figure 18. Figure 18. Idealized north-south Marathon Countyshowing showingthe thepostulated postulated graben graben sstructure. Marathon County tructure. - 30 - �suggests tthat h a t the t h e major major deformation deformation of the the area area continued continued throughout throughout most most of suggests of the plutonic activity. the plutonic a c t i v i t y . This This deformation deformation and c t i v i t ymay may correlate correlate andplutonic plutonic aactivity Penokean Orogeny 1961). with the thepost—Menominee post-Menominee event with event known knownas as the Penokean Orogeny(Goldich, (Goldich, 1961). Presumably the Presumably thearea areawas wasagain againelevated elevatedabove abovesea sealevel level and and subjected subjected ttoo i n the the area. a r e a . Emplacement erosion although f ofor r t hthis i s iis s largely lacking lacking in erosion althoughevidence evidence the anorogenic anorogenic Wolf and rrelated e l a t e d syenite syenite intrusions intrusions about about of the Wolf River River Batholith Batholith and 1500 m ~ y .ago n the area. a r e a . The The ffinal i n a lPrecambrian Precambrian 1500 m.y. agowas wasthe thenext nextmajor majorevent event iin event recorded t h e intrusion intrusionofofpyroxene pyroxene and and olivine o l i v i n ediabase diabase event recordedinin the the area area iiss the dikes, dikes, which which ccut u t aall l l older olderrocks rocks in inthe t h ecounty. county. REFERENCES REFERENCES CITED CITED a , 1975, 1975, Petrology Petrology and and geochemistry ith, Anderson, J3. . LL,, Anderson, geochemistryofofthe the Wolf Wolf River River Bathol Batholith, Unpublished Wisconsin—Madison, Unpublished Ph.D. Ph.D. Thesis, University Universityof of blisconsin-Madison, 297 297 p. p. Anderson, JJ. . LL.. and and Cullers, R. R . L., L . , 1978, 1978,Geochemistry Geochemistry and the Anderson, and evolution evolution of of the Wolf River Batholith, rapakivi massif massif in north Wolf River Bathol i t h , aa Late Late Precambrian Precambrian rapakivi north Wisconsin, Wisconsin, U.S.A., U.S . A * , Precambrian Precambrian Research, Research, vol. vol .7,7,pp. pp.287—324. 287-324. Cannon, andGair, Gair,J 3. Cannon, W W. . F.F.and . EE., . , 1970, 1970, AA revision of of stratigraphic s t r a t i g r a p h i nomenclature c nomenclature for rocks in in northern Geol. SOC. Soc. hAmer. Bull., f o r Middle Middle Precambrian Precambrian rocks northern Michigan, Michigan, Geol. e r . bull^, vol. V O .~81, Bl ,pp. pp.2843-2846. 2843-2846. Ervin, C. C. P. P. and and Hanwier, H a m r , S., 1974, Bouguer Bouguer anomaly map of Wisconsin, Wisconsin, S., 1974, anomaly gravity gravity map Wis. Wis. Geol. Geol. Nat. Nat. Hist. Hist.Survey. Survey. Goldich, S. S. S., S., Nier, Nier,A.A.0.,O .Baadsgaard, , Baadsgaard, H., H . , Hoffman, Hoffman, 3. J . H., H . , and andKrueger, Krueger, H. H . W., W., Goldich, 1961, The The Precambrian Precambrian geology Minnesota, Minn. Minn. Geol. Geol. 1961, geology and and geochronology geochronologyof of Minnesota, Survey, Bull. 41, Survey, Bull 41 ,193 193 p. p. . LaBerge, LaBerge, G. G. L. L . in i n LaBerge, LaBerge, G. G . L. L . and and Myers, Myers, P. P . E., E., 1971, 1971, 1971 1971 Progress Progress report report Marathon County, County, Wisconsin, Wisconsin, Wis. Wis. on mapping mappingTf Precambrian geology on of Precambrian geology iinn Marathon Geol. File Report, 28 28 p. p. Geol. Nat. Nat. Hist, Hist.Survey Survey Open Open F i l e Report, . LL., . , 1976, 1976, The The Central Central Wisconsin Wisconsin Batholith, 22nd Ann. Ann. Inst. I n s t . on on LaEerge, GC. LaBerge, Batholith, 22nd Lake Superior Geol., Geol., S St. MN, p. 36. 36. Lake Superior t . Paul, Paul, MN, LaBerge, Major sstructural LaBerge, G.C.LL., . , 1977, 1977, Major t r u c t u r a l features f e a t u r e s in i n Central Central Wisconsin Wisconsin and and ttheir heir implications on on the the Animikie Animikie Basin, Basin, 23rd 23rd Ann. Ann. Inst. I n s t .on onLake Lake Superior Superior Geol., Bay, OOnt., Geol., Thunder Thunder Bay, n t . , p. p. 23. 23. LaBerge, G. G . L. L . and and Myers, Myers, P. P a E. E. (in ( i n preparation), preparation),The Thegeology geologyofofMarathon Marathon County, Wisconsin, Wisconsin Wisconsin Geol. Geol. Nat. Nat, Hist. Hist. Survey. Survey. County, Wisconsin, LaBerge, C., 1979, LaBerge9C. G. L. L . and and Mudrey, Mudrey, MM. e G., 1979, Stratigraphic Stratigraphicframework framework of of Middle Middle Precambrian rocks iinn Wisconsin, Precambrian rocks Wisconsin, Wis. Wis. Geol Geol .. Nat. Nat. Hist. Hist. Survey. Survey. Maass, andMedaris, Medaris, LL. and plutonic plutonic rocks Maass, RR. . and . C., G . , 1976, 1976, Penokean Penokean s structures t r u c t u r e s and rocks in Counties, Wisconsin, Wisconsin, 22nd 22nd Ann. Ann. IInst. in Portage Portage and and Wood Wood Counties, n s t . on on Lake Lake Superior S t . Paul, Paul,MN, M N , p. p. 38. 38. Superior Geol., Geol ., St. . C., G . , Jr., J r . ,Anderson, Anderson, 3. J . L., L . , and andMyles, Myles, 3.J .R., R : , 1973, 1973,The The Wolf Wolf River River Medaris, LL. Medaris, Batholith Batholith -— -- AA late l a t ePrecambrian Precambrian rapakivi massif massif ini nnortheastern northeasternWisconsin Wisconsin - — 31 31 - - �in Guidebook of Northeastern Guidebook to the the Precambrian Precambrian Geology Geology of Northeastern and and North North Central Central Wisconsin, Wis. Wis. Geol. Geol. Nat. Nat. Hist. Hist. Survey, Wisconsin, Survey, pp. p p . 9-29. 9-29. Mickelson, 0. D. M. M. and and Knox, Knox, J3.. C., C . , 1974, 1974, Late LateQuaternary Quaternary environments environments of Mickelson, Wisconsin, Wisconsin, Amqua--Third Anqua--Third Biennial Meeting, Meeting, Madison. Madison. Mudrey,M.M. G., G., Jr. Mudrey, J r . (Ed.), (Ed.),1979, 1979,Middle MiddlePrecambrian Precambrian Geology Geology of of Northern Northern Number4,4,Wis. Wis,Geol. Geol.Nat. Nat. Hist. Hist. Survey, Wisconsin: Field Trip TripGuidebook Guidebook Number Survey, p. 44 P. Mudrey,M.M.G., G., JJr., Aeromagnetic 1977, Aeromagnetic map map of northern northern Mudrey, r . , and and Karl, Karl,3.J .H.,H.,1977, Wisconsin, Wisconsin, 24th 24th Ann. Ann. Inst. I n s t .ononLake LakeSuperior SuperiorGeology, Geology,Milwaukee, Milwaukee, WI, MI, p. 27. 27. p. Myers, PP. geologyjt~ in Guidebook 38th Ann. Ann. Tri-State Tn-State Myers, . E., E . , 1974, 1974, Precambrian Precambrian geology Guidebook f ofor r 38th Geological Geological Field Conf., Conf., Eau Eau Claire, Claire,WI, WI,pp. p p .1—3. 1-3. Myers, P. E., Syeniteofof Central Central Wisconsin, Wisconsin, 22nd Ann. IInst. Myers, P. E . , 1976, 1976, The The Wausau Wausau Syenite 22nd Ann. nst. on LakeSuperior SuperiorGeol., Geol., SSt. on Lake t . Paul, Paul, MN, MN, p. p . 42. 42. Myers, P.P. E., E., 1978, Structures iinn mica 1978, Structures mica schist s c h i s t and and quartzite q u a r t z i t e of ofthe theYounger Younger Myers, MetasedimentarySeries, Series, Geology GeologyofofWisconsin WisconsinField Field Trip Trip Stop, Metasedimentary Stop, Wis. Wis. Geol Geol . Nat. Hist. Survey. Nat. Survey. Myers, P. E., 5., 1980, E . , Cumings, Cumings, M. M. and and Wurdinger, Nurdinger, S., 1980, Early Earlyand and Middle Middle Myers, P. Precambrian amphibolites, Precambrian amphibol i tes, plutonic plutonicrocks, rocks,rnetavolcanics metavol canicsand andrnetasediments metasediments Valley, Wisconsin, 26th Annual Annual IInst. the Chippewa Chippewa Valley, Wisconsin, Guidebook Guidebook f ofor r 26th n s t . on on of the Lake Superior Geol., Geol., Eau Claire, WI. Lake Superior Eau Claire, WI. Van Hise, C.C. R. R. and and Leith, Leith, C. Van Hise, C. K., K . , 1911, 1911, Geology Geology of the the Lake Lake Superior Superior region, U.S.G.S. U.S.G.S. Mono. Mono. 52. 52. W . W. Van VanSchmus, Schmus, Medaris,L .L.GG., R.,R.,Medaris, . , JJr., r . , and and Banks, Banks, P. P. 0., O., 1975, 1975,Geology Geology and and age of the River Batholith, Wisconsin, Geol. Soc.hAmer. Bull., vol vol. age of the Wolf Wolf River Wisconsin, Geol . SOC. e r . Bull., 86, pp. pp.907—914. 907-914. Van Schmus, Schmus,W W. Thurman,E E. andPeterman, Peterman,ZZ. Van . R.,R.,Thurman, . M.M.and . EE., . , 1975, 1975, Geology Geology and and Rb/Sr Rb/Sr chronology of Middle Precambrian rocks in eastern and central Wisconsin, chronology of Middle Precambrian rocks in eastern and central Wisconsin, Geol. Bull., vol. e r . Bull., vol 86, 86,pp. pp.1255-1265. 1255-1265. Geol. Soc. SOC. hAmer. . VanSchmus, Schmus, 1976,Early Earlyand andMiddle MiddleProterozoic Proterozoichistory history of of the Van W. W. R.,R.,1976, t h e Great Great Lakesaarea, North America, America,PPhil. Lakes r e a , North h i l . Trans., Trans., Royal Royal Soc. SOC.London, London, vol. vol. 28Q, 280, pp. 605-628. pp. 605-628. Van Schmus, Schmus,W.W.R .R.and andAnderson, Anderson,J .3.L., L., 1977, Van 1977, Gneiss Gneiss and and migmatite of 6fArchean Archean age basementofofCentral Central Wisconsin, Wisconsin, Geology, Geology,vol. vol. 5, the Precambrian Precambrian basement 5, age in the pp. 45-48. pp. 45-48. Weidman, 1907, The Thegeology geologyofof North North Central Central Wisconsin, Wisconsin, Wis. Wis. Geol. Weidman, S .5., , 1907, Geol. Nat. Nat. Hist. Survey Survey Bull. 16, 16, 697 697 p. p. Zeitz, I.,I .1978, A new , 1978, A newdetailed detailedaeromagnetic aeromagneticmap map covering most most of the the PrecambrianShield Shieldinin Wisconsin, Wisconsin, 24th 24th Annual AnnualIInst. Precambrian n s t . on on Lake Lake Superior Geol., Milwaukee, WI, p. Geol., Milwaukee, WI, p . 41. 41. -- 32 32—- �C-EOLOG G E O L O G II CAL C A L STOP S T O P - 33 — DESCRIPTIONS D E S C R I P T ~ O ~ ~ S �Title: Title: - Artus Creek Artus Creek -- Pillow basalts. basalts. Location: In pasture pasture along along the the east e a s t side s i d e of of Artus Artus Creek. Creek. NE¼, NEk, NW¼, NW&, NW¼, Nl&i, (Marathon 15 minute quadrangle, (Marathon quadrangle, Marathon Marathon Sec. Sec. 29, T.29N., T.29N., R.6E. R.6E. (Get permission permission from from Harold Harold Theis Theis (pronounced (pronounced ""Tice"), Tice"), County.) (Get R. R. R. R. 2, 2,Marathon, Marathon, WI, MI,Phone: Phone: 715-845-2667.) 715-845-2667.) Author: Gene Gene LL.. LaBerge LaBerge (1980) (1980) This stop contains Description: This contains the the best pillow basalts best exposures exposures ofofpillow basalts in in Marathon County. Due Due t to o tthe h e iirregular rregular Marathon fracture f r a c t u r e pattern pattern on on the t h e surface surface of the the outcrop, •the pillows pillows are outcrop,.the a r e not not very very evident. they aare evident. However, However, they r e well exposed on several several small exposed on small south—facing south-facing ledges ffarther the road. road. ledges a r t h e r from from the The pillows pillows range in size The range in s i z e from from onef foot lless e s s than than one o o t tto o aatt least l e a s t three three Pillows are a r e widely widely i n diameter. diameter. Pillows ffeet e e t in used ffor used o r top top determination determination ini nmapping mapping volcanic rocks. volcanic rocks. The accompanying accompanying photo, taken taken aatt this photo, t h i s stop, s t o p ,shows shows the the cclassical l a s s i c a l domal domal top top and and pointed pointed bottom bottom of the 4fp of of the of the pillow. While While tthe he 9 the flows is is readily readilydetermined determined from from flows pillows, they they do do not not show show tthe h e sstrike. trike. This must by tracing aa must be be determined determined by ddistinctive i s t i n c t i v e lithology lithology (or ( o rpillowed pillowed unit). Where exposures aare Where exposures r e as as u nit) limited limited as as they they are a r eininMarathon Marathon County,i itt iiss extremely County, extremely d difficult ifficult thesstrike tto o determine determine the t r i k e of the t h e basalts. basalts. . The greenstones greenstoneshere here sodicplagioclase, plagioclase,a cactinolite, The c oconsist n s i s t of ofsodic t i n o l i t e , epidote, epidote, chlorite, anda actinolite c h l o r i t e ,and andminor minorcarbonate carbonate and and quartz. quartz. Epidote Epidote and c t i n o l i t e are a r e the the dominant minerals minerals ininsome t h e time time of of formation fornation the t h eselvages selvages dominant some samples. samples. AAtt the the pillows were hydratedbbasaltic glass (palagonite); ((rinds) r i n d s ) around around the were probably probably aa hydrated a s a l t i c glass (palagonite); however, they they aare dominantly quartz quartz and however, r e now now dominantly and epidote. The The mineralogy suggests suggests tthat h a t the therocks rockshave haveundergone undergone greenschist greenschistfacies f a c i e smetamorphism. metamorphism. ananeast—west Pillowed basalts basalts are a r e widely widely distributed d i s t r i b u t e dinin east-west trending trending Significance: Significance: Pillowed They are abundantly 'belt" across "belt" across northern northern Wisconsin. Wisconsin. They abundantly exposed exposed near near Pembine Pembine in in Marinette andsporadically sporadically exposed exposedt otot hthe westofoft there, Marinette County, County, and e west h e r e , including the the Monico area in Gravity Map The Bouguer Bouguer Anomaly Anomaly Gravity Map Monico area in Oneida Oneida County County (Mudrey, (Mudrey, 1979). 1979). The of Wisconsin 1974)suggests suggestst hthat theserather rather heavy rocks (a of Hamer, 1974) a t these heavy rocks h'isconsin (Ervin (Ervin && Hammer, resulting resulting gravity gravityhigh) high)extend extendalmost almostcontinuously continuouslyfrom fromthe theMichigan Michigan border border west Rhyolites are are also a l s o present present at a tmost most west beyond beyond Ladysmith Ladysmith in in Rusk Rusk County. County. Rhyolites localities l o c a l i t i e s along along tthis h i s belt, b e l t , indicating indicating aa long long belt b e l t of of volcanic volcanic aactivity. c t i v i t y . The The widespread occurrenceofofpillows pillowsindicates indicates aa submarine origin ffor widespread occurrence submarine origin o r most most of the the vol canics.. volcanics - 34 - �____ Middle Precambrian pillow lavas along Middle Precambrian pillow along Artus Artus Creek. Creek. aatt the the top top of of the the pillow. pillow. Pencil points Pencil points LLAKE AKE SUPERIOR WAUSAU WAUSAU MIDDLE PRECAMBRIAN PRECAMBRIAN GRANITIC Rocks GRANITIC ROCKS EARLY PRECAMBRIAN SEDIMENTARY ROCKS SEDIMENTARY ROCKS EARLY PRECAMBRIAN - -- VOLCANICROCKS ROCKS IYYI VOLCANIC GRANITIC ROCKS GRANITIC ROCKS DOLOMITE, D O L O M I T E , ETC. ETC. u"GREENSTOtjt' ~ ~ ~ & ~ s ~ o Generalized north-south north-south cross—section Generalized cross-section in in northern northernWisconsin Wisconsin showing showing the postulated volcanic rocks rocks iinn north the postulated relationship between between volcanic north central central Wisconsin and iron-formations iron—fonnationsand andother other sediments sedimentstoto the the north. Wisconsin and - 35 - ~ ~ m �Radioactive age dating dating on on these these rocks rocks indicates that Radioactive age t h a tthey theywere wereformed formed between 1900 1900 m.y. m.y. and between and about about 1825 1825m.y. m.y. ago ago(Van (VanSchmus, Schmus,Thurman Thurman and and Peterman, Peterman, ageas asthe the ironThus, they they are a r e approximately approximately the the same same age 1975; Sims, 1975; Sims, 1976). 1976). Thus, formation and on the the Gogebic Range,and andmust, must, therefore, therefore, have and graywacke graywacke on Gogebic Range, have formedas aspart part of of the basinof of deposition deposition --- the theAnimikie AnimikieBasin Basin (LaBerge, (LaBerge, formed the same same basin 1977) 1977) (see diagram). diagram) . The volcanic volcanic rocks have been beenextensively extensively intruded intruded by The rocks in i n Marathon Marathon County County have by volcanic belt ggranitic r a n i t i crocks rocks and and are a r e separated separated from from the main main volcanic b e l t by by aalarge largewedgewedgeshaped massofofgneisses gneissesand andamphibol amphibolites appear tto However, the ites t hthat a t appear o be be older. older. However, shaped mass volcanic rocks rocks here hereaare believedt otobe berelated relatedtto those ffarther r e believed o those a r t h e r north north in in volcanic Wisconsin because becausethey theyaare of the same age, and and were were formed formedmainly mainly iin Wisconsin r e of same age, n aa stops, we will examine subaqueous environment. At subaqueous environment. A t the the succeeding succeeding stops, we will examine the the relationships between these various variousrock rocksequences. sequences. relationships between these References: Gravity Map of Wisconsin; Ervin, C. C . PP.. and and Haniner, Hamer, SS., . , 1974, 1974, Bouguer Bouguer Anomaly Anomaly Gravity Map of Wisconsin; Wis. Geol. Geol. Nat. Nat. Hist. Wis. Hist. Survey. Survey. LaBerge,GG. Structural Features LaBerge, . LL., . , 1977, 1977, Major Major Structural Features ini nCentral CentralWisconsin Wisconsin and and Their Implications on the Animikie Basin; 23rd Annual n s t . on on Lake Lake Their Implications on the Animikie Basin; 23rd Annual IInst. Superior Geology, Geology, Thunder Thunder Bay. Bay. Mudrey, . , JJr. r . (Ed.), ( E d . ) ,1979, 1979,Middle MiddlePrecambrian Precambrian Geology Geology of of Northern Northern Mudrey, M.M. GG., Field Trip No.4,4, Wis. Wis. Geol. Geol. Nat. Nat. Hist. Wisconsin: Field Trip Guidebook Guidebook No. Hist. Survey, Survey, 44 p . 44 p. Sims, P. Sulfide K., 1976, 1976,Middle MiddlePrecambrian Precambrian Age Age of Volcanogenic Volcanogenic Massive Massive Sulfide Sims, P . K., Deposits Annual IInst. Deposits iinn Northern Northern Wisconsin; Wisconsin; 22nd 22nd Annual n s t . on on Lake Lake Superior Superior Geology, S St. Geology, t . Paul, Paul ,MN. MN. Van Schmus,WW. Thurman,MM. and Peterman, Peterman, Z.Z. E., E . , 1975, 1975,Geology Geologyand and Van Schmus, . R R., . , Thurman, . E.E. and Rb/Sr Chronology Chronology ooff Middle Precambrian Rocks iin Precambrian Rocks n Eastern Eastern and and Central Central Rb/Sr Geol. SOC. Soc. America AmericaBull., Bull., Vol. Wisconsin: Geol. Vol. 86, 86,pp. pp.1255-1265. 1255-1265. — 36 — �Title: Title: Rib intrusion breccia. Rib Falls --Deformed Deformed intrusion breccia. Location: West side of CTH-S w i t h0TH—U CTH-U ononnorth Rib West side CTH-S aatt ju junction nction with north side side of Rib River, corner, Sec. NE corner, Sec. 28, 28, T.29N., T.29N., R.5E., R.5E.,Marathon MarathonCounty County(Marathon (Marathon River. NE 15 minute quadrangle). quadrangle). Author: Author: Gene Gene LL.. LaBerge LaBerge (1980) (1980) Description: extensively Description : The The volcanic volcanic sequence sequence in i n Marathon Marathon County County has has been been extensively invaded by zoned zonedstocklike stocklikeggranitic invaded by r a n i t i c intrusions. intrusions. Many Many intrusions show extensive extensive intrusions show development intrusion breccias. development ofof intrusion breccias. The exposureconsists consists mainly mainly of quartz The exposure quartz diorite w i t habundant abundant quartz, quartz, plagioclase plagioclase and and chloritized chloritized mafics. mafics. Mafic diori t ewith Mafic to to intermediate volcanic(?) volcanic(?) xenoliths xenolithsranging rangingfrom fromabout about2 2cm cm tot oseveral severalmeters meters intermediate are a r e present present in i n several severalzones. zones. The The xenoliths show show aa wide n assimilation wide range. range i in in readily recognizable i n the the intrusive intrusivephase. phase* Some Some aare r e readily recognizable as asfine—grained fine-grained volcanic(?) i n the the quartz quartz volcanic(?) rocks; rocks; others othersare a r eexpressed expressed as a s mafic—rich mafic-rich cclots l o t s in Several late l a t egranitic g r a n i t i c(less ( l e s smafic) mafic)dikes dikes cut c u tthe the quartz quartz diorite d i o r i t eand and diorite. d i o r i t e . Several the the volcanic volcanic xenoliths. xenoliths. Plagioclase the quartz quartz diorite d i o r i t eranges ranges from from An2035 An20-35 and and shows shows prominent prominent Plagioclase iinn the zoning, resorption rims. rs as zoning, and and some some resorption rims. Quartz Quartz occu occurs a s ±+5—8 5-8 m grains grains (phenocrysts?) (phenocrysts?) and as similar sized and as sized clots c l o t s of offinely f i n e l ypolygonal polygonal quartz. quarty. Much the quartz quartzddiorite pervasivec cataclastic Much ofof the i o r i t e has has aa pervasive a t a c l a s t i c ffoliation o l i a t i o n that that strikes dips vvertically. N.45oE. and and dips e r t i c a l l y . Several s t r i k e s N.450E. Several prominent prominent vvertical, e r t i c a l ,N.45°E. 1 . 4 5 ' ~ .shear shear zones cross the outcrop zones cross outcrop area. area. They They appear appear to t o be bemost mostpronounced pronounced where where mafic mafic - 37 - �rocks Someofof the the zones maybe be sheared shearedmafic mafic dikes. rocks are are more more abundant. abundant. Some zones may However, in other zones the mafic material is extensively mixed with lensoidal However, in other zones the mafic material i s extensively mixed with lensoidal patchesofofplutonic plutonic rock, rock, suggesting suggestingt hthat theywere werei ninitially patches a t they i t i a l l y mafic-rich mafic-rich Lensoidal (boudinaged) blocks of of relatively intrusion breccias. breccias. Lensoidal (boudinaged) blocks r e l a t i v e l yunsheared unsheared plutonic rocks rocks are are separated separated from from one one another another by by aa network network of braided braided shear shear planes. planes . Features exposed exposedhere hereand andvariations variationson ont this h i s theme theme aare r e typical Significance: Features of many Middle Precambrian plutons in Marathon County. Intrusion breccias many Middle Precambrian plutons i n Marathon County. breccias country rocks aare r e comon comon and and widespread. widespread. Xenoliths and and country rocks are a r e generally generally Plutons aare typically zoned, metamorphosed onlyt otogreenschist greenschist facies. facies. Plutons with metamorphosed only r e typically zoned, with aa xenolith-rich quartz quartz diorite d i o r i t emargin margin and and aa more more ggranitic r a n i t i c core. core. Inner portions portions multiple of plutons plutons comonly commonly intrude intrude outer, outer,more more mafic mafic zones, zones, suggesting suggesting multiple common injections from from aa differentiating d i f f e r e n t i a t i nmagma. g magma. Quartz Quartz ddiorite i o r i t eisi the s the common intrusive phase in intrusion breccias phase in breccias into i n t o mafic/interinediate mafic/intermediate volcanics volcanics whereasgranite granite iiss more common volcanic xenoliths. xenoliths. This suggests w i twith h f efelsic l s i c volcanic suggests whereas more common of the the magma magma tthat h a t the the composition composition of i s is a tatl eleast a s t ppartially a r t i a l l y controlled controlled by by assimilation assimilation of intruded intruded material. material. Individual mineralogically ddistinct Individual plutons plutons aare r e rrelatively e l a t i v e l y small, small, and and aare r e mineralogically istinct from neighboring neighboring plutons, plutons, and from and roof pendants pendants of volcanic volcanic rocks rocks more more than than ten tenkms kms long are long a r e present. present. Most of Marathon MarathonCounty County includedi ninaamajor majorgravity gravity low low iinn central Most of i s isincluded Wisconsin This suggests the area suggests t that h a t the area iiss underlain underlain Wisconsin (Ervin (Ervinand andHammer, Hamer, 1974). 1974). This predominantlybybyg rgranitic rocks, probably probablyaalarge large batholith. batholith. The predominantly a n i t i c rocks, The ssurficial urficial geology suggests suggestsa acomposite compositebatholith batholithjjust geology u s t being being unroofed unroofed by by erosion. erosion. The The markedlycross-cutting cross—cuttingrelationships relationships of of the intrusion breccias, markedly the plutons, plutons, common comon intrusion breccias, low-grade metamorphism of ofthe n the low-grade regional regional metamorphism thevolcanics, volcanics, prominent prominentzoning zoning iin plagioclases aalll l indicate of the plagioclases indicateemplacement emplacement of the batholith batholithataupper t uppermesozonal mesozonal depths iin n the the crust. crust. tto o epizonal epizonal depths References: C. P.P .and andHammer, Hammer, S., 1974, 1974,Bouguer Bouguer Anomaly Anomaly Gravity Map Map of Wisconsin: Wisconsin: Ervin, C. Wis. Wis. Geol. Geol. Nat. Nat. Hist. Hist. Survey. Survey. - 38 - �Title: Title: Rib Ultramafics at a tcontact contact ofofgneiss gneiss Rib River Riverata Emory t EmorySchool School -- Ultramafics terrane. terrane. Location; SW¼, Sec.30, 30, T.30N., T.30N., R.5E., NW%, SW%, Sec. R.5E., Hamburg Hamburg 15' quadrangle. Location: NW¼, 15' quadrangle. Author: Author: Paul Claire (1978). Paul E.E.Myers, Myers,UW—Eau UW-Eau Claire (1978). (Revised (Revised by byLaBerge LaBerge &&Palmer, Palmer, 1980.) 1980.) Summary of Features: Summary of Features: AA small, small,ENE—trending, ENE-trending, llenticular e n t i c u l a rbody bodyofofmassive massive hornblende-biotite-tonalite-gneiss to t othe the north north metaperidotitet?)separates separates hornblende-biotite—tonalite-gneiss metaperidotite(?) from sedimentary from phyllites p h y l l i t e sofof sedimentaryparentage parentage to t othe thesouth. south. The The ultramafic ultramafic rock rock was alongaa major major ffault emplaced along a u l t which which raised raised more more highly highly was apparently apparently emplaced metamorphosed tonalite metamorphosed tonal i t e gneisses gneisses on on the the north. north. Discussion: Discussion: Muscovite Muscovite pphyllite h y l l i t e with w i t h foliation f o l i a t i o nand andsubparallel subparallel relict r e l i cbedding t bedding N74OE, 75°N 75ON and and subordinate cleavage cleavage N350E, N35CJE, 74°NW 74ONW i is s probably derived derived from from N74°E, aa felsic f e l s i cvolcanic volcanicrock. rock. Relict Relictquartz quartzand and feldspar feldsparclasts c l a s t s(staining ( s t a i n i nshow g show presence presence of both both potassium potassium feldspar feldspar and and plagioclase) plagioclase)and and bedding bedding are a r e best best seen horizontal surfaces towardtheir their fault seen on on horizontal surfaces toward f a u l t contact contact with w i t h the t h eultramafic ultramafic rock. The phyllites p h y l l i t econtain s contain streaked lensoids of K-feldspar diamondrock. The streaked lensoids of K—feldspar andand diamond— shaped shaped hematite hematitereplacements. replacements. AA conspicuous conspicuous lineation l i n e a t i o nformed formed by by the the intersection foliation plunges N360W at 68—74g. i n t e r s e c t i o of n of f o l i a tand i o n cleavage and cleavage plunges N36OW a t 68-74O. Bioti te-hornblende tonalite tonal i t epencil pencilgneisses gneissesalong alongRib RibRiver Rivernorth northofofhere here Biotite-hornblende have N50—650W ata~55—65°. have lineations l i n e a t i o nplunging s plunging ~50-65O t 55-650. Foliation, Foliation,where wherepresent, present, dips dips steeply NNW. steeply NNW. - 39 — �The coarse-grained coarse—grained ultramaficrock rocki is The ultramafic s composed composed ofofr relict e l i c t pyroxene(?) pyroxene(?) which appears tto beenaaltered andcchlorite. which appears o have have been l t e r e d to an an amphibole amphibole and h l o r i t e . The The presence plagioclase suggests suggestst that be aa feldspathic pyroxenite. presence ofof plagioclase h a t tthis h i s may may be pyroxenite. Another massive massivemafic mafic unit unit Some specimensa rare neargabbro gabbroi in Some specimens e near n composition. composition. Another composedofofamphibole, amphibole,epidote, epidote, and outcrops 6.6 6.6 km km southwest southwest of composed and sphene sphene outcrops here (NW¼, Sec.33, 33,T.30N., T.30N., R.4E.). At A t both both localities l o c a l i t i e sthe t h emafic mafic rocks rocks here (NWk, Sec. parallel between p a r a l l e l the thefault f a u lcontact t contact between gneissic gneissic rocks rocks on on the the north north and and lowlowgrade metavolcanic metavolcanic and metasedimentaryrocks rocks on on the the south. The The rrestricted estricted grade and metasedimentary occurrenceofof ultramafic rocks the two two terranes terranes suggests occurrence rocks between between the suggests tthat h a t they they lie along major high-angle faults and were emplaced during or after l i e along major high-angle f a u l t s and were emplaced during o r a f t e r ffaulting. aulting. Their lack lack of of foliation the llatter. the ultramafic ultramafic body a t t e r . Although Although the body iiss Their f o l i a t i o n suggests suggests the about 300 300meters meterswide widehere, here,iitt was about was not observed observed iinn outcrop outcrop along along the the Rib Rib River just just east Shapeand andextent extent of the River e a s t of of here. here. Shape thebody bodyare a r eunknown. unknown. A magneticlow lowp parallels A prominent prominent magnetic a r a l l e l s the fault f a u l tcontact contactbetween between the the gneisses gneisses and low—graderocks rocksf ofor nearly 60 along the km along t h e northern northernedge edge ofofMarathon Marathon and low-grade r nearly 60 km known County ((Zeitz, I tisi snot not knownwhether whether the themagnetic magnetic County Z e i t z , Karl, Karl,and andOstrom, Ostrom, 1977). 1977). It 'demagnetization'ofof rocks rocks along along the the ffault low iiss due low due to t o "demagnetization" a u l tzone, zone, or o rwhether whether aa numberofof reversely-polarized reversely—polarizedmafic maficand andultramafic ultramafic rocks rocks are number a r e present. present. References:: References J. H., andand Ostrom, M.M.E.,E 1977, Preliminary aeromagnetic I . ,Karl, Karl, J . H., Ostrom, . , 1977, Preliminary aeromagneticmap map Zeitz, I., covering terrane iinn Wisconsin: U.S. Geol. Geol. Wisconsin: U.S. covering most most of the t h e exposed exposed Precambrian Precambrian terrane Survey Misc. Field Survey Misc. Field Studies StudiesMap Map 888. 888. -40- �Title: Title: Black Q u a r t z o f e l d s p a t h i c gneisses. gneisses. Black Creek, Creek, Athens Athens - Quartzofeldspathic Location: Location: Along Along Black Black Creek a l l e y west west of o f Wis. His. Hwy. Hwy. 97 97 in i nAthens. Athens. NE¼, Creek vvalley NEi,, SW¼, Sec.31, 31, T.30N., T.30N., R.4E. SWi, Sec. R.4E. (Marathon (Marathon County) County) (Athens 15 15 minute minute quadrangle). Authors: Authors: Gene L. LaBerge and EElizabeth LaBerge and l i z a b e t h Palmer, Palmer, 1980. 1980. Gene L. Description: gneisses ooff variable D e s c r i p t i o n : Quartzofeldspathic Q u a r t z o f e l d s p a t h i c gneisses v a r i a b l e composition composition crop crop out o u t at at aa number number ooff places places ini nnorthwestern northwesternMarathon MarathonCounty. County. This T h i s exposure exposure i illustrates llustrates several several phases phases of o f the t h egneisses, gneisses, but b u numerous t numerous other o t h e r phases phases are a r e present. present. The southeasternend endo foft hthe exposure The southeastern e exposure c oconsists n s i s t s o fofa af efelsic l s i c rock with with lensoidal fragmentsi in medium-grained q uquartz-feldspar a r t z - f e l d s p a r fragments n aa ffiner—grainS iner-grained l e n s o i d a l , , medium—grained micaceous micaceous qquartzofeldspathic u a r t z o f e l d s p a t h i c matrix. m a t r i x . Muscovite and bbiotite Muscovite and i o t i t elaths l a t h swrap wraparound around the t h e lensoidal l e n s o i d a lfragments. fragments. The The rock rock appears appears tto o be be a metamorphosed metamorphosed f e felsic l s i c ttuff uff with planeofof ffoliation. c l a s t s elongated elongated i in n tthe h e plane oliation. A A more more mmafic a f i c ((amphibolitic) amphibolltic) w i t h the t h e clasts rock northwestoof rock occurs occurs northwest f tthe h e ffelsic e l s i c rock. rock. The composition,f fine The composition, i n e grain g r a i n size, s i z e , and and weakly t was derived d e r i v e d from from weakly ffoliated o l i a t e d character c h a r a c t e r of o f the t h emafic mafic rock rock suggest suggest that t h a t iti was aa mafic mafic rock is ont the The m a f i c rock i s bounded bounded on h e nnorth o r t h (near (near the t h e old old m a f i c flow f l o w or o r dike, d i k e . The dam) byaaf felsic dam) by e l s i c rock rock rich r i c hini npotassium potassium feldspar. f e l d s p a r . It I tcontains contains large l a r g e feldspar feldspar fragments and mmicrocline fragments and i c r o c l i n e in i n the t h erecrystallized r e c r y s t a l l i z egroundmass. d groundmass. It I tappears appears to t o be be aa sheared andr erecrystallized sheared and c r y s t a l l i z e d potassic potassic plutonic p l u t o n i c rock rock or o r gneiss. gneiss. Foliation N.~o'E. and and ddips i p s vvertically. e r t i c a l l y . Clasts C l a s t s in i n the the F o l i a t i o n here here strikes s t r i k e sabout about N.70°E. gneissic elongatedv evertically planeoof g n e i s s i c rocks rocks aare r e elongated r t i c a l l y i in n tthe h e plane f ffoliation. o l i a t i o n . Farther Farther - 41 - �from the the ccontact with from ontact w i t h the t h e greenschist greenschist facies f a c i e s rocks, rocks, fold f o l daxes axesand and mineral mineral For example, Dells example, aatt Goodrich Goodrich D e l l s on on lineations l i n e a t i o n s in i nthe t h egneisses gneisses plunge plunge westerly. w e s t e r l y . For the Rib River eight miles northeast of here, mineral lineations, fold axes t h e Rib River e i g h t m i l e s northeast o f here, mineral 1i n e a t i o n s , f o l d axes This is within is and m mafic and a f i c clot c l o tplunge plungewest west ata 350_700 t 35O-70 w i t h i n tthe h e N.85°E. N.8s0E. f foliation. o l i a t i o n . This in contrast to the east-plunging lineations in the greenschist facies i n c o n t r a s t t o t h e east-plunging l i n e a t i o n s i n t h e greenschist f a c i e s rocks rocks along Hamann Hamann Creek which along Creek which we wwe i l l will seesee l a t later e r onon t hthis i s t rtrip. ip. The northwestern northwesterncorner corner ooff Marathon Countyi is Marathon County s uunderlain n d e r l a i n by by Significance: S i g n i f i c a n c e : The aa variety v a r i e t y of o fquartzofeldspathic q u a r t z o f e l d s p a t h i c gneisses, gneisses, amphibolites amphibolites and and locally l o c a l l ymigmatites. migmatites. Reconnaissancemapping mapping westand andn onorth suggestst hthat Reconnaissance t o to t hthe e west r t h suggests a t tthe h e gneisses gneisses are are an extension extension ooff the an the complex complex high-grade high-grade metamorphic metamorphic t eterrane r r a n e tthat h a t extends extends at at l e a s t 60 60 miles m i l e s to t o the t h e west. west. The The llithologies i t h o l o g i e s closely c l o s e l yresemble resemble those those of o f the the least "ChippewaAmphibol Ajnphibolite Complex"described described by by Myers Myers (1974) (1974) from from exposures "Chippewa it e Complex" exposures iinn Knownexposures exposureso of Precambrianrocks rocks iinn Chippewa and l a i r e Counties. Counties. Known f Precambrian Chippewa andEau EauCClaire Clark County Marathonand andtthe Chippewa-EauC Claire area) are Clark County (between (between Marathon h e Chippewa-Eau l a i r e area) are dominantly high—grademetamorphic metamorphic rocks, although dominantly high-grade rocks, although s cscattered a t t e r e d o outliers u t l i e r s of of A ddistinctive istinctive low—grade metavolcanicand andmetasedimentary metasedimentaryrocks rocksaare low-grade metavolcanic r e present. present. A aeromagnetic andg rgravity aeromagnetic and a v i t y ppattern a t t e r n iis s also a l s o present present in i nthis t h i sfour—county four-county area. area. block' Thus, tthe gneisses iin Countyare aree vevidently Thus, h e gneisses n Marathon Marathon County i d e n t l y ppart a r t oof f a a large l a r g e "block" of o f gneisses gneisses as shown shown i in n Figure F i g u r e 1. 1. The age ooff these no rradiometric The age these gneisses gneisses is i s unknown unknown ssince i n c e no a d i o m e t r i c ages ages are are Myers(1980, (1980,t hthis conference) shows showst hthat However, Myers i s conference) a t ssimilar imilar aavailable. v a i l a b l e . However, gneisses iinn the River two periods periods of gneisses t h e Chippewa Chippewa R i v e r valley v a l l e y have have undergone undergone two o f deformation deformation Van Schmus Schmusand andAnderson Anderson (1977)r ereport and metamorphism metamorphismp rprior and i o r ttoo 1850 1850 rn.y. may. Van (1977) p o r t tthat hat similar s i m i l a rgneisses gneisses south south ofo fMarathon Marathon County County have have rradiometric a d i o m e t r i c ages ages ranging ranging from from andMedaris Medaris(1976) (1976)i ninterpret 1850 m.y. to Maass and t e r p r e t the t h e rocks rocks t o more more than than 2800 2800 m.y. may. Maass 1850 m.y. ReconnaissancebybyMyers Myers(1978) (1978)i nindicates d i c a t e s tthat hat to t o be be Middle Middle Precambrian Precambrian in i n age. age. Reconnaissance low rocks unconformably low grade grade vvolcanic o l c a n i c and and sedimentary sedimentary rocks unconformably ooverlie v e r l i e the t h e high h i g h grade grade terrane Claire Thus, the t h e high h i g h grade grade t e r r a n e along along the t h e Eau Eau C l a i r e River R i v e r in i nClark C l a r kCounty. County. Thus, rocks must be beoolder than greenschist greenschist ffacies rocks must l d e r than a c i e s volcanics. volcanics. If area rMiddle Precambrian I fthe t h egneissic g n e i s s i rocks c rocks e Middle Precambrianasassuggested suggestedbybyMaass Maass and and Medaris (1976), they must represent an earlier deformed and metamorphosed Medaris (1976), they must represent an e a r l i e r deformed and metamorphosed sequence thant that which we we ffind sequence than h a t which i n d in i nmost most ofo fMarathon Marathon County. County. References:: References 13., 1976, 1976, Penokean PenokeanS Structures andPPlutonic Maass, R. t r u c t u r e s and l u t o n i c Rocks Rocks iinn Maass, R. and' and Medaris, Medaris, L. G., Portage and Counties, Wisconsin: 22nd Annual AnnualI Inst. and Wood Wood Counties, Wisconsin: 22nd n s t . on on Lake Lake Superior Superior Geology, Geology, SSt. t . Paul, Paul, p. 38. 38. Myers, P. P. E., Myers, E., 1974, 1974, Precambrian Precambrian Geology Geology in i n Guidebook Guidebook ffor o r 38th 38thAnnual Annual Tn—State Tri-State Geological EauCClaire, Geological Field F i e l d Conference, Conference, Eau l s r e , pp. pp. 1-3. 1-3. E., 1978, Younger Myers, P. 1978, Structures S t r u c t u r e s in i nMica Mica Schist S c h i s tand and Quartzite Q u a r t z i t eofo the f the Younger MetaMetaMyers, P. E., Geol. sedimentary Series: Geol . ooff Wis. Idis. Field F i e l d Trip T r i p Stop, Stop, Wis. Wis. Geol. Geol . Nat. Nat. Hist. H i s t . Survey. Survey, sedimentary E. and 1980,EEarly and Middle Middle Precambrian PrecambrianAmphibol Miphibolites, Myers, P. E. and Cummings, Cumings, M.M.L.,L., 1980, a r l y and ites, Myers, P. Plutonic Valley, P l u t o n i c Rocks, Rocks, Metavolcanics, Metavolcanics, and and Metasediments Metasediments ooff the t h e Chippewa Chippewa V alley, 26th Annual Wisconsin: Eau C laire. WisConsin: Guidebook Guidebook f ofor r 26th Annual Inst. I n s t . on onLake LakeSuperior SuperiorGeol Geol ., ., Eau Claire. Van Schnius,W.W.R.,R.,and andAnderson, Anderson,J.J. L.~, L., 1977, 1977, Gneiss Gneiss and and Migmatite Migmatite of o fArchean Archean Age Age Van Schmus, in Geology,vvol. i n the thePrecambrian Precambrian Basement Basement ooff Central Wisconsin: Wisconsin: Geology, o l . 5, pp. pp. 45-48. 45-48. - 42 - �Title: Title: Athens Athens County County Park Park -- Sheared Sheared rocks. rocks. Location: Location: NE¼, NW¼, SW¼, T.29N.,R.4E. R.4E. (Athens (Athens 15 minute quadrangle) NE%, NW%, SM%, Sec.Sec. 6, 6,T.29N., quadrangle) Marathon County. County~ Authors: Authors: Gene LaBerge and and Elizabeth Elizabeth Palmer, Palmer,1980. 1980. Gene LL.. LaBerge Description: diverse lithologies Description: This This stop stop illustrates i l l u s t r a t e some s someofofthe thecomplex complex and and diverse lithologies developed along the major developed along major fault f a u l zones t zonesininMarathon MarathonCounty. County. Movement on the Movement on the f a u l t shave have evidently evidentlyjuxtaposed juxtaposed rocks rocks of ofvaried variedparentage parentage and and in i n various various faults stages c a t a c l a s t i cdegradation, degradation,producing producingextremely extremelyvariable, variable,complex complexzones. zones. stages of of cataclastic At the creek A t the the south south end end of the the exposure exposure aatt the the bend bend i in n the creek (refer ( r e f e r to t osketch sketch map), andand may bebe a metagraywacke. map), the the rock rockisi schistose, s schistose, may a metagraywacke. ItI tisi svariable in variable in composition, composition, with w i t h quartz, quartz, plagioclase, plagioclase, biotite, b i o t i t emuscovite , muscoviteand andhornblende hornblende the the dominant in the dominant minerals, minerals. Exposures Exposures in the small small creek creek entering enteringPotatoe PotatoeCreek Creekfrom from the the south south at a tthe thesouth southedge edge ofofthe themap map appear appear to t o be be deformed deformed ffelsic e l s i c volcanic volcanic rocks. rocks . North from the the schistose schistose rock are North (downstream) (downstream) from a r e several several exposures exposures of of well well foliated lens—shaped f o l i a t e dbiotite—rich biotite-rich flaser f l a s e rgneiss. gneiss. The The biotite b i o t i t encloses e encloses lens-shaped porphyroclasts and porphyroclasts ofofquartz quartzand andfeldspar feldspar andemphasizes emphasizes the thelens—structure. lens-structure. This rock appears to be a highly sheared pluton, or perhaps This rock appears t o be a highly sheared pluton, or perhapsaasheared sheared gneiss. gneiss. The larger grains show cataclastic degradation and alteration The grains show c a t a c l a s t i c degradation and a1 teration tto o sericite serici t e and and carbonate. carbonate. Deformed Deformed f efelsic l s i c volcanic volcanic rocks rocks are intimately intimatelymixed mixed with with the the biotite flaser gneiss. b i o t i t e f l a s e r gneiss. - 43 - �Exposures Exposures o of f f ifine-grained n e - g r a i n e d ppink, i n k , mylonitized m y l o n i t i z e d granitic g r a n i t i cgneiss gneissand and several several large l a r g e quartz q u a r t z veins veins are arepresent present about about 60 60 meters meters northeast northeast of o f the t h epark parkboundary. boundary. These appeart oto have havebeen beenp hphaneritic rocks tthat beenccataclastically These appear a n e r i t i c rocks h a t have have been ataclastically degraded. degraded. Significance: S i g n i f i c a n c e : A major major structural s t r u c t u r a lboundary boundary passes passes through through Athens Athens trending t r e n d i n g about about N600E. N60OE. South South ooff the t h e lineament lineament are a r e volcanic v o l c a n i c rocks rocks and and granites g r a n i t e s that t h a have t havebeen been only o n l y slightly s l i g h t lmetamorphosed. y metamorphosed. North North of o f the t h e lineament lineament the t h e rocks rocks are a r ehigh h i g hgrade grade gneisses, gneisses, amphibolites amphibolites and and migmatites migmatites (LaBerge, (LaBerge, 1977). 1977). Along Along the t h e lineament 1 ineament are a r e mylonites, mylonites, phyllonites p h y l l o n i t e sand and other o t h e r intensely i n t e n s e l ysheared sheared rocks rocks along along with w i t h aa number number oof f mmafic a f i c tto o ultramafic u l t r a m a f i c bodies. bodies. The width The w i d t h of o f the t h eshear shearzone zone ranges ranges up up to braided zones zonesoof km and and consists c o n s i s t s of o fnumerous numerous braided f iintense n t e n s e cataclasis cataclasis t o nearly n e a r l y 22km separated "pods"o fofr relatively separated by by lens—shaped lens-shaped "pods" e l a t i v e l yundeformed undeformed rock. In I n places, places, the deformation deformation affected a f f e c t e dmainly main1ythe t h elow—grade low-grade volcanic v o l c a n i c and and sedimentary sedimentary rocks. rocks. A A variety v a r i e t y of o frocks rocksappear appear to t ohave have been been involved i n v o l v e d in i nthe t h edeformation deformation here. here. AA similar side Marathon County s i m i l a rcataclastic c a t a c l a s t izone c zonealong alongthe t h south e south s i dof e o f Marathon County(see (seeCounty County map) gneisses iinto volcanics and map) bbrings r i n g s gneisses n t o contact c o n t a c t with w i t hlow—grade low-grade volcanics and iintrusions. ntrusions. The metamorphicrocks rocks bounded boundedon ontthe h e north n o r t h and and south south The presence presence of o f low—grade low-grade metamorphic by separated by by broad broadccataclastic by gneisses gneisses and and separated a t a c l a s t i c zones zones containing c o n t a i n i n g mafic m a f i cand and ultramafic scale block block ffaulting. volcanics u l t r a m a f i c bodies bodies iindicates n d i c a t e s llarge a r g e scale a u l t i n g . The The low—grade low-grade volcanics and granites with and g r a n i t e s appear appear tto o occupy occupy aa ggraben—like r a b e n - l i k e s structure tructure w i t h horsts h o r s t s of o fgneisses gneisses uplifted diagrami lillustrates u p l i f t e don on both both the t h e north n o r t hand and south. south. The The diagram l u s t r a t e s these these relationships r e l a t i o n s h i p s across across this t h i spart p a rof t oMarathon f MarathonCounty. County. These large scale faul ts appear to have been active over several hundred million years of time, and represent the major structural features in central Wisconsin. Gn e is see volcanics U Mignatites Amphibolites Outliers of low— grade rocks Some volcanics Graben Generally low—grade metamorphism Epizonal Plutona I Gneisses Ajnphlbolites Migmatites Some younger plutons younger plutons North—south cross-section across Marathon County. References: References : LaBerge, G.G.L., 1977, Major t r u c t u r a l features features in i nCentral Central Wisconsin Wisconsin and heir LaBerge, L., 1977, Major sstructural and ttheir implications imp1 i c a t i o n son on the t h eAnimikie Animikie Basin: Basin: 23rd 23rd Annual Annual IInstitute n s t i t u t e on on Lake Lake Superior Superior Geology, Geology, Thunder Thunder Bay. Bay. -- 44 -- �Title: Title: Hamann Creek-—Lineated Lineated andesite. andesite. Hamann Creek Location: Creeki in SE¼,Sec. Sec. 26, 26, T.28N., R.3E. Location: Along n SEk, R.3â‚ Marathon Along Hamann Hamann Creek Marathon County. County. (Stratford (Stratford15 15minute minutequadrangle) quadrangle) (Get (Get permission permissionfrom fromRoger RogerBohman, Bohman, Rt. 715—687—2343.) R t . 1,1 Stratford; , S t r a t f o rphone d ; phone 71 5-687-2343.) Author: Author: Gene L. LaBerge LaBerge Gene L. Description: is representative Description: This This exposure exposure is representative of the the intermediate intermediate volcanic volcanic rocks rocks ininMarathon MarathonCounty. County. The main rock rock type type iiss aa tuffaceous The main tuffaceous andesite andesite with with clasts c l a s t sabout about11 cm cm iinn diameter, diameter, but b u t .clasts c l a s t sup u p tot o10I 0cm cm long long are a r epresent present aa short short distance distanceupstream upstream from from the t h e bridge. bridge. Sandy Sandy textured "graywacke" isis interintertextured "graywacke" bedded withthe thet tuff bedded with u f f locally. locally. Exposures the pasture n the pasture to t o the the north north are are Exposures i in significantly s i g n i f i c a n t l ymore more siliceous siliceousthan thanthe t h eoutcrop outcropnear near the thebridge. bridge. Phenocrysts Phenocrysts of of plagioclase plagioclase and and hornblende hornblende aare r e vvisible i s i b l e in inplaces. places. The rock displays displays aa prominent prominentf ofoliation l i a t i o n and and llineation. i n e a t i o n . Foliation The rock Foliationand and layering appear to strike about N.85°E. Foliation layering appear t o s t r i k e about N.8s0â‚ Foliationdips dips600_8005. 60°-80° Lineation Lineation' consists consists of of elongation elongation ofofvolcanic volcanicclasts, c l a s t sextreme , extreme"smearing" "smearing" of of mafic mafic minerals plagioclase (Figure minerals and and boudinaged boudinaged plagioclase (Figure 1). 1 ) . Lineation Lineation dips dipsabout about50°E 50° in of foliation. in the the plane plane of f o l i a t i o n . South South of the theroad road exposures exposures along along the the creek creek are are dominantly mile south south along along the creek dominantlygraywacke. graywacke. Approximately Approximately one—half one-half mile creek are are, exposures deformed spectacularly deformedconglomerate. conglomerate. exposures of of aa spectacularly - 45 - �Theexposure exposurei sispart part of of a a large roof roof pendant pendant of volcanics, volcanics, and and Significance: The Siqnificance: exemplifies the type Rocks in in the exemplifies type of of deformation deformation within within the thependant. pendant. Rocks the immediate immediate area and elsewhere in in Marathon Countyhave haveaaconspicuous conspicuousmineral mineral lineation lineation and and area and elsewhere Marathon County boudinaged mineral grains. grains. Volcanic, boudinaged mineral Volcanic, plutonic plutonicand and sedimentary sedimentary rocks rocks are are lineated, suggesting of of thethe deformation post—dates suggesting that t h a t at a tleast l e a s part t part deformation post-dates emplacementofofthe the plutons. The The ffoliation o l i a t i o n and and lineations l i n e a t i o n shave have occurred occurred in in emplacement mappablezones zonest hthat have been beentraced traced ffor These features features mappable a t have o r more more than than 90 90 kms. kms. These are interpreted are interpreted to t o indicate indicatethat t h a the t thearea areahas hasbeen been subjected subjected to t o shearing shearing sstresses t r e s s e s and and tthat h a t the the stress s t r e s swas was taken taken up up along along shear shear zones zones in places, places, and and by pervasive pervasiveccataclasis by a t a c l a s i s iinn other other places. places. The llithologies hereand andt otothe the south southindicate indicate tthat The i t h o l o g i e s exposed exposed here h a t these these are are largely subaqueous volcanics. Welded Weldedr hrhyolitic largely subaqueous volcanics. y o l i t i c ttuffs, u f f s , flow flowbanded banded rrhyolites, hyolites, and lahars(not (notvvisited onthis this ttrip) and lahars i s i t e d on r i p ) indicate indicate that t h a t the the felsic f e l s i cvolcanics volcanics are are The other other supracrustal supracrustal rocks aatt least l e a s t partially p a r t i a l l y subaerial. subaerial. The rocks are a r e probably probably subaqueous,indicating indicating aa sizeable Middle basin in Central subaqueous, Middle Precambrian Precambrian basin Central Wisconsin. Lineated showing alignment and and boudinaging boudinaging of phenocrysts phenocrysts Lineated andesite showing ((the t h e black black lines on on the t h e 'shite white lensoidal lensoidal grains). grains). Note flote also the also the zones of f t and and right r i g h tmargins margins zones of more moreintense intensedeformation deformationnear nearl eleft bounding areas e s s deformation l e f t edge edge and and center photo). bounding areasofof lless deformation((left center of photo). - 46 - �Title: Title: - Little L i t t l eEau Eau Pleine Pleine River River Location: Location: N½, Sec. 31, T.26N. N'5, SW¼, SWi, SeC. T.26N., R.4E. R.4E. Marathon County, Marshfjeld Marathon County, Marshfield 15 15 minute quadrangle. minute quadrangle. (Get from Norbert Norbert Kolbeck, (Get permission permission from Kol beck, RRt. t . 2, 2, Auburndale, Auburndale, WI, MI, Box Box 148; 148; Phone Phone 715-384—8798.) 715-384-8798.) Author: Author: Gene L. LaBerge LaBerge Gene L. - — Gneiss. Gneiss. Description: in Description: Isolated Isolated blocks blocks ofofhigh highgrade grademetamorphic metamorphic rocks a r e present present in rocks are rocks rocks more more typically t y p i c a l l ymetamorphosed metamorphosed tto o greenschist facies. f a c i e s . This Thisexposure exposure represents aa small small block blockofofgneiss gneissand andmigmatite migmatitebounded bounded on on the t h e north northby by aa represents zone several hundred feet wide of ferruginous, sheared(?) quartz. zone several hundred f e e t wide ferruginous, sheared(?) quartz. Across Across the the valley rocks area rnon—foliated monzonites valleytot othe thesouth souththe the rocks e non-foliatedgranites g r a n i t eand s andquartz quartz monzonites that miles south intoi nWood l e a sseveral t several miles south t o WoodCounty. County. Other t h a textend extend ata tleast Other high highgrade grade junction metamorphic blocks an amphibolite amphibolite (metagabbro?) (metagabbro?) mass mass aatt the junction metamorphic blocks include an of contact with ofWis. Wis.Hwy. Hwy.97 97and andCTH—T CTH-T inin contact w i t h aarelatively r e l a t i v eunmetamorphosed l y unmetamorphosedultra— ultramafic major rock rock type type in in the area mafic rock. rock. The The major area is i s aa prominently prominently foliated f o l i a t e dquartz quartz diorite. diorite. This This exposure exposure is i s aa small small block block (lens?) ( l e n s ? )ofofhigh highgrade gradegneiss gneissofofapproximately approximately granodiorite migmatitei is present aatt the Some migmatite s present the western western end end of the the granodioritecomposition. composition. Some exposure. Small scale s c a l e folds folds are a r e relatively r e l a t i v e l coriinon y common in i nthe t h egneiss gneiss with w i t h near near exposure. Small horizontal horizontal fold foldaxes. axes. This This is i s ini ncontrast c o n t r a s t to t othe thenear near vertical v e r t i c a l fold foldaxes axes in in low rocks about about 33 miles miles northeast of low grade grade metasedimentary metasedimentary rocks of here. here. Thus, Thus, iitt isi s anomalous in metamorphic gradeand ands tstructurally with iits anomalous in metamorphic grade r u c t u r a l l y anomalous anomalous with t s surroundings. surroundings. - 47 - �An arcuate arcuate zone zone of of extremely extremelycomplex complex geology geology extends extends along along the the S i g n i f i c a n c e : An Significance: zonecconsists of aa wide wide vvariety The zone o n s i s t s of a r i e t y of of southern boundary boundary of o fMarathon MarathonCounty. County. The southern rock and metamorphic rock types, types, including i n c l u d i n gvolcanic, volcanic,plutonic, p l u t o n i sedimentary c , sedimentary and metamorphic rocks rocks Most ooff the t h e rocks rocks have have a a prominent prominent ffoliation o l i a t i o nand and w i t h no no apparent apparent pattern. p a t t e r n . Most with very different grade aare Rocks oof f very d i f f e r e n tmetamorphic metamorphic grade r e iinn contact c o n t a c t with with l i n e a t i o n . Rocks lineation. one as greenschist one another, another, such such as greenschist facies f a c i e s volcanics volcanics and and sediments sediments in i n contact contact Several ultramafic u l t r a m a f i c bodies bodies (probably (probably dunites) duni t e s ) w i t h gneisses gneisses and and amphibolites. amphiboli t e s . Several with shallow and andvvertical Both shallow e r t i c a l fold f o l daxes axes are a r e present, present, a r e present present in i nthe thezone. zone. Both are along with pervasiveccataclasis (andl olocal along w i t h aa pervasive a t a c l a s i s (and c a l r erecrystallization) c r y s t a l l i z a t i o n ) in i n plutonic plutonic rocks. rocks. The mixture The m i x t u r e of o f lithologies l i t h o l o g i eand s anddisparate d i s p a r a tmetamorphic e metamorphic grade grade in i na abroad broad zone suggestst etectonic zone ooff complex complex ' s•structure t r u c t u r e suggests c t o n i c mmixing i x i n g oof f tthe h e various various rock rock types. types. The area suggestive of o f aa megamelange, megamelange, w iwith t h a ar erelatively l a t i v e l y deep deep llevel e v e l in in The area iiss suggestive the the structure s t r u c t u r eexposed exposed along along the t h e southern southern part p a r tofo Marathon f MarathonCounty. County. Van Schmusand and Anderson (1977) dated gneisses west Van Schmus Anderson (1977) dated m i gmigmatitic m a t i t i c gneisses west o fofPPittsville ittsville The gneisses may The gneisses may be be the the (27 southoof (27 km km south f tthis h i s locality) l o c a l i t yat ) amore t morethan than2800 2800m.y. m.y. However, However, basement onwhich whicht the Middle Precambrian basement on h e Middle Precambrian vvolcanics o l canics were were deposited. the the structural s t r u c t u r a complexity l complexityalong alongthe t h southern e southernedge edgeofo Marathon f Marathon County County indicates indicates aa large-scale large-scale fault f a u l contact t c o n t a cbetween t between the t h e two two terranes. terranes. - - - j4 r I - M i g m a t i t i c gneiss gneiss characteristic c h a r a c t e r i s t i cofo the f t hhigh-grade e high-graderocks rocksexposed exposed Migmatitic along the the southern southernedge edge of o fMarathon Marathon County. County. along References : References: Van Schmus, 1977, Gneiss Gneiss and and Migmatite Migrnatite of o fArchean Archean Van Schmus,W.W.R.,R.,and andAnderson, Anderson,J .3. L., L., 1977, Age iinn the t h ePrecambrian Precambrian Basement Basement oof f Central Wisconsin: Wisconsin: Geology, Geology, vvol. o l . 5, 5, Age pp. 43-48. pp. 43-48. - 48 - �-- Ultramafic U l t r a m a f i c rocks. rocks. Title: T itle: Wild Creek, Creek,RRozeliville Wild ozellville Location: Ditch 1.5 miles D i t c h outcrop outcrop on on east e a s t side s i d e CTH—M CTH-M a t at t h ethe b r ibrink n k o foft hthe e hhill i l l 1.5 miles (Farmhouse d idirectly r e c t l y across across the the road road to t o the the south Rozellville. south oof f R o z e l l v i l l e . (Farmhouse W% corner, T.26N., R.4E., R.4E., Marathon Marathon County County. corner, Sec. Sec. 22, 22, T.26N., west.) west.) W¼ (Marshfield ( M a r s h f i e l d 15 15 minute minute quadrangle) quadrangle) Author: Author: Gene L. L. LaBerge Gene LaBerge The outcropcconsists The outcrop o n s i s t s pprimarily r i m a r i l y ooff a a talc-serpentine t a l c - s e r p e n t i n e rock. rock. Relict A chemical chemicalaanalysis n a l y s i s oof f tthis h i s rock rock R e l i c t olivine o l i v i n eisi svisible v i s i b lin e many i n manysamples. samples. A shows contains only o n l y 39.4 39.4 percent percent Si02, Si02, and and thus thus it i tprobably probably represents represents shows t hthat a t iitt contains intrusions I tisi sone oneofo fata least t l e a sfour t f o usuch r such i n t r u s i o nknown s knownalong along an an aaltered l t e r e d dunite. It Outcropsi in on tthe west sside and iin n tthe h e yyard a r d on h e west i d e ooff the t h e road road and n the the tthis h i s zone. zone. Outcrops creek creek tto o the t h e north n o r t h consist c o n s i s t of o fmafic m a f i cvolcanic v o l c a n i crocks rockswith w i t hpoorly p o o r l ypreserved preserved pillow Exposuresi nint the h e ffields ields p i l l o w structures s t r u c t u r e s indicating i n d i c a t i n g tops tops to t o the t h e south(?). south(?). Exposures quartzd diorite tto o the t h e southeast southeast a are r e a as tstrongly r o n g l y f ofoliated l i a t e d quartz i o r i t e ((tonalite) t o n a l i t e ) that that ( I tcontains c o n t a i n sbraided braided appears appears tto o be be aa relatively r e l a t i v e l yhighly h i g h lmetamorphosed y metamorphosed rock. (It Description: Description: zones zones ooff amphibolite a m p h i b o l i t e up up to t o several several feet f e ewide t widethat t h amay t mayhave havebeen beenproduced produced by by Similar metamorphism shear zones metamorphism of of shear zones i n in t h ethe q uquarz a r p . d idiorite.) orjte.) S i m i l a r quartz quartz ddiorite iorite t h ~area sarea and and is i sassociated associated with with and amphibolite uunderlie and amphibolite n d e r l i e at a t least l e a s t50 50km km iinn this the gneiss exposed at the previous stop. the gneiss exposed a t t h e previous The aaxis xis F o l i a t i o n in i nthis t h i sarea areatrends trendsN.6O°W. N . ~ o O W . and i p s vvertically. e r t i c a l l y . The Foliation andddips plungesv vertically ooff aa minor minor fold f o l dexposed exposed1.2 1.2km kmnorth n o r t halong alongCTH—M CTH-M plunges e r t i c a l l y and and would would suggest rright suggest i g h t lateral l a t e r amovement. l movement. - 49 - �This This and and oother t h e r ultramafic u l t r a m a f i c rocks rocks occur occur along along a a zone zone ooff strongly strongly foliated f o l i a t e d rocks rocks of o f highly h i g h l yvariable v a r i a b l ecomposition. composition. The rocks to The vvolcanic o l c a n i c rocks t o the the north n o r t h are are believed b e l i e v e d tto o be be ppart a r t of of the t h e greenschist g r e e n s c h i s t facies f a c i e s terrane t e r r a n e present present in in most ooff Marathon The f foliated o l i a t e d and and rrecrystallized e c r y s t a l l i z e d tonalites, t o n a l i t e s , quartz quartz most Marathon County. County. The monzonitesand andgneisses gneissest otot hthe southappear appeart otobe beppart e south a r t ooff aa higher h i g h e r grade grade monzonites Significance: Significance: metamorphict eterrahe metamorphic r r a n e t to o tthe h e south. south. However, However, llargely a r g e l yundeformed undefomed (and (and unmetamorphosed?) presentseveral several km unmetamorphosed?) p l uplutons t o n s a rare e present km tto o the t h e southwest southwest ini nWood Wood County, andr erelatively mafic vvolcanic County, and l a t i v e l y low l o w grade grade mafic o l c a n i c rrocks o c k s aare r e aalso l s o present p r e s e n t in in places. Therefore, Therefore, there t h e r e exists e x i s t s here hereaacomplex complex zone zone ooff mixed mixed rrock o c k types, types, which betweent hthe which bbasically a s i c a l l y mark mark tthe h e boundary boundary between e g rgreenschist e e n s c h i s t f afades c i e s tterrane e r r a n e in in MarathonCounty Countyand anda ah ihigher gradet eterrane do nnot Marathon g h e r grade r r a n e tto o the t h e south. south. We We do o t know know the the agesoof anyoof rocks, except ages f any f tthe h e rocks, except tthat h a t all a l lhave have been been interpreted i n t e r p r e t e d to t obe be Middle Middle Precambrian. - SQ - rkinko!J � 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, 1980 Description An account of the resource Institute on Lake Superior Geology. University of Wisconsin, Eau Claire, Wisconsin. May 6-10, 1980. 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 1980 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/120e905556b72cb3b85c97724adc63b1.pdf f816fd7a26d0eab0f8140bc1a62bda1b PDF Text Text A BSTRACTS a PROCEEDINGS Twenty Seventh Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY HELD AT THE KELLOGG CENTER MICHIGAN STATE UNIVERSITY EAST LANSING MICHIGAN MAY 14-15, 1981 �Award Guidelines SAM GOLDICH MEDAL Preamble The Institute on Lake Superior Geology was born on or around 1955, as documented by the fact that the 27th annual meeting will be held in 1981. The Institutes are exemplory in their continuing objectives of dealing with those aspects of geology that are related geographically to Lake Superioq of encouraging the discussion of subjects and sponsoring field trips which will bring together geologists from the academia, government surveys, and industry; and of maintaining an exceedingly informal but highly effective mode of operation. During the course of its existence the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the LL.S.G. by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the improvement of understanding of "Lake Superior" geology and its mineral deposits. The exemplory award was made by LL.S.G. to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Award Guidelines I) The medal shall be awarded annually by the Board of Directors, I.L.S.G., to a geologist whose name is associated with a substantial sustained interest in, or a major contribution to, the geology of the Lake Superior Region. 2) The Board of Directors, LL.S.G. shall appoint the Nominating Committee. Their annual nominee will be voted on at the annual business meeting. The initial appointment will be of three members, one to serve for three years, one for two, and one for one year, the member with the briefest incumbency to be chairman. After the first year the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In the third year this member shall be the chairman. The Committee membership should reflect the main fields of interest and geographic distribution of l.L.S.G. membership. 3) The Goldich Medal Nominating Committee shall select the medalist and will make its recommendation to the Board of Directors by November 1 of that year. 4) The Board of Directors normally will accept the nominee of the Comittee, will inform the medalist immediately, and will have one medal engraved appropriately for presentation at the May meeting. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. April 4, 1981 J. Kalliokoski, Chairman Bill Cannon Fred Kehlenbeck Glenn Morey Greg Mursky �ABSTRACTS and PROCEEDINGS Twenty Seventh Annual Meeting INSTITUTE ON LAKE SUPERIOR GEOLOGY I-bid at The Kellogg Center Michigan State Lhiversity East Lansing, Michigan May 14- 15, 1981 Sponsored by DEPARTMENT OF GEOLOGY, MICHIGAN STATE UNIVERSITY East Lansing, Michigan and MICHIGAN DEPARTMENT OF NATURAL RESOURCES, GEOLOGICAL SURVEY Lansing, Michigan F. W. Cambray, B. K. Parker, R. C. Reed, 3. W. Trow, T. A. Vogel 3. T. Wilband and S. E. Wilson Editors Gerraid Bennett Field Trip Coordinator and Director MINISTRY OF NATURAL RESOURCES, SAULTE STE. MARIE MINING DIVISION Saulte Ste. Marie, Ontario ��Thursday May 14, 1981 Session Chairpersons S. S. Goldrich and C. Laberge 1:30 to 1:50 1:50 to 2:10 2:10 to 2:30 A GEOCHEMICAL RECONNAISSANCE STUDY OF GROUNDWATER FROM AN EIGHTEEN COUNTY AREA OF NORTHWESTERN OHIO Mohr, Eileen T., Deering, Mark F., and Carlson, Ernest H. THE DISTRIBUTION OF LITHIUM, RUBIDIUM AND CESIUM IN LAKE MUDS NORTH OF LAKE SUPERIOR M. A. Vos and R. 3. Stevenato THE SIGNIFICANCE OF THE DISTRIBUTION OF CLASTIC LENSES WITHIN THE NEGAUNEE IRON FORMATION AT THE EASTERN END OF THE 2:30 to 3:00 3:00 to 3:20 3:20 to 3:40 PALMER BASIN, MARQUETTE SYNCLINORIUM, NORTHERN MICHIGAN *Mark S. Breithart and F. William Cambray Coffee Break PRELIMINARY ASSESSMENT OF RARE EARTH ELEMENT GEOCHEMISTRY OF VARIOUS IRON FORMATIONS OF THE LAKE SUPERIOR DISTRICT Elaine L. Slaughter, Susan E. Tituskiri, and John T. Wilband LITHOLOGIC AND SEDIMENTOLOCIC CHARACTERISTICS OF THE COPPER HARBOR CONGLOMERATE, NONESUCH SHALE AND FREDA SANOSTONE FORMATIONS OF NORTHERN MICHIGAN AND WISCONSIN Paul A. Daniels, Jr. 3:40 to 4:00 THE ROLE OF HYDROTHERMAL ALTERATION AND TECTONISM IN 4:00 to 4:20 WISCONSIN MOLYBDENITE OCCURRENCES 3. K. Greenberg RETROGRADE PREHNITE-PUMPELLYITE FACIES METAMORPHISM IN THE SOUTHERN VERMILION GRANITIC COMPLEX, NORTHERN MINNESOTA Robert L. Bauer 6:00 pm 7d30 pm Cash Bar Banquet Big TenRoorn Big Ten Room POST PRANDIAL Presentation of the Sam Goldich Medal by Dr. Samuel S. Goldich to Dr. Carl E. Ijutton ADDRESS by F. B. Van 1-buten entitled PHANEROZOIC OOLITIC IRONSTONE - A FACES MODEL (See abstract by F.B. Van Houten and D. Bhattacharyya) �Friday May 15, 198! Session Chairpersons 3. 1. Wilband and C. Anderson Coffee will be available from 8J0 a.m. 8:20 to 9:20 9:20 to 9:30 9:30 to 9:50 9:50 to 10:10 10:10 to 10:30 10:30 to 11:00 11:00 to 11:20 Decade of North American Geology - Open Discussion break WISCONSIN GRAVITY BASE STATION NET WORK--! 980 C. Patrick Ervin PALEOMAGNETISM OF THE MEMESAGEMASING AND CARIBOU LAKES NORITES, GRENVILLE PROVINCE, ONTARIO * S. Dey, D. T. A. Symons, and M. Stupavsky GEOPHYSICAL INVESTIGATIONS OF THE SLATE iSLANDS CRYPTOEXPLOSION STRUCTURE M. E. Bengtson, and R. P. Meyer, H. C. Halls, and 3. I-I. Karl, and D. Dushek Coffee Break JOINT ORIENTATION ANALYSIS IN THE NORTHERN MICI-{ICAN BASIN Timothy B. 1—blst 11:20 to 11:40 I 1:40 to 12:00 IMPACT AS A POSSIBLE ORIGIN FOR SUBSIDED BASINS Jack B. Hartung PRELIMINARY RESULTS OFA GRAVITY SURVEY IN THE EASTERN HALF OF THE IRON RIVER-CRYSTAL FALLS DISTRICT, IRON COUNTY, MICHIGAN * D. R. Paddock, K. Fujita, F. W. Cambray, and H. F. Bennett 12:00 Lunch 5ession Chairpersons Friday afternoon 3. W. Trow and 3. 3. Mancuso 1:30 to 1:50 SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS IN THE VICINITY OF THE HELEN MINE, WAWA, ONTARIO Mark Osterberg and R. L. Morton 1:50 to 2:10 PRE- AND POST-DORE SEQUENCES IN THE WAWA VOLCANIC BELT, ONTARIO 2:10 to 2:30 2:30 to 3:00 3:00 to 3:20 3:20 to 3:40 K. Attoh PETROGENETIC MODELS OF KEWEENAWAN BASALTIC ROCKS, UPPER MICHIGAN John T. Wilband and Pipob Wasuwanich Coffee Break PETROCHEMISTRY AND STRUCTURE OF THE MIDDLE PROTEROZOIC SUCCESSION, HURLEY-TO-MINONG, KEWEENAWAN VOLCANIC WISCONSIN * Hassan Au and Campbell Craddock EARLY PROTEROZOIC GABBROIC, DIORITIC, AND QUARTZ MONZONITIC INTRUSIONS IN THE MINNESOTA RIVER VALLEY: PETROLOGY AND SIGNIFICANCE 3:40 to 4:00 M. Dewitt Daggett THE PETROLOGY AND PETROGENESIS OF THE GAMITAGAMA IGNEOUS COMPLEX, WAWA, NORTHERN ONTARIO * Abdul Choudhry and T. E. Smith �27th Annual INSTITUTE ON LAKE SUPERIOR GEOLOGY Annual Banquet PHANEROZOIC OOLITIC IRONSTONE - A FACIES MODEL Address by delivered by F. B. Van 1—buten (Abstract by Van Houten & D. Bhattacharyya follows) �PHANEROZOIC OOLITIC IRONSTONE - A FADES MODEL F. B. Van Houten and D. Bhattacharyya Department of Geological and Geophysical Sciences, Princeton University Princeton, New Jersey 08544 Almost all of the Phanerozoic ferric oxide-chamosite oolitic ironstones are associated with detrital aeposits that accumulated in low energy, nearshore marine environments, commonly along a broadly embayed coastline. Processes and products were like those on the chenier coast of southwestern Louisiana and the front of the low-energy, wave-dominated Rhone Delta. There were no well-developed tidal features or large, well-winnowed shoreface sandbodies. A subdued, deeply weathered source supplied mature fine-grained sediment composed mostly of quartz, kaolinite, and iron and aluminum oxide. The detrital deposits are arranged in a of asymmetrical, upwardshoaling sequences produced by small- scale Ferruginous ooids formed on detritus-starved mudflats that supported abundant micro-organisms and burrowers. These sites were either mudflats along microtidal coasts protected by breaker bars remote from a prograding delta, or on delta-front and interd istributary coastal flats following delta abandonment. Most of the plastic ooids were carried from their place of origin by coastal currents, and in aecreting, cross-bedded Repeated interruptions in concentrated bars. accumulation of ooids permitted increased burrowing that commonly destroyed the bedding fabric, as well as precipitation of ferric oxide cement. Locally, lapses in bar building led marine mud. to deposition of laminated succession regressions. Each sequence commenced with muddy open shelf deposits locally associated with bioclastic debris, and culminated in either a prograding front of a small delta or a shoreline complex of bars anc lagoons. Waning of cietrital influx was accompanied by development of abundant Commonly ooid bars graded laterally or were succeeded by a thin ferruginous phosphatic intraclast lag deposit developed when waves ana currents of renewed transgression encroached on the detritus-starved mudflats and crests of ooid bars. Each mound of ooids and associated lag deposit was then buried by marine mud into, ooids. that accumulated during an early stage of rapid transgression and renewed supply of Specific control of the prograding sequences has not been established in many sediment. Some may reflect diversion of a major river to a more distant part of the cases. coastal plain while the abandoned muddy shelf continued to subside and was inundated by renewed transgression. Other sequences may reflect more regional control such as tectonic pulses of subsidence or repeated eustatic rise of sealevel. This facies model emphasizes the role of repeated upward-shaling sequences, of abrupt waning of sediment supply, and of renewed rapid rise of sea level as the local framework of accumulation of most oolitic ironstones. A similar sequence of fades dominated the less common development of oolitic ironstone along carbonate coasts. Within this framework both the iron-rich oolites and associated phosphatic intraclast lenses developed at or near the lithofacies discordance between successive sequences. �INSTITUTE ON LAKE SUPERIOR GEOLOGY Annual Goldich Medal Award for 1981 Will be presented to Carl E. Dutton at the Banquet Thursday evening Dr. Carl E. Dutton was born in Dunkirk, Ohio on January 24th 1904. He receivea his B.A. from DePauw University in 1926, his M.A. from the University of Illinois in 1928 and his Ph.D. from the University of Minnesota in 1931. He was a teaching assistant at the University of illinois, an Instructor at Minnesota and an Assistant Professor at Wayne State University and The University of Michigan. He jointed the U.S. Geological Survey in 1943, becoming regional geologist in 1948 and Research Geologist in 1962 and has been based in Madison, Wisconsin where he participated in the Mineral Resources Cooperative Program of the Wisconsin Geological and Natural History Survey and the USGS in addition to teaching some classes at the University. Carl Dutton has had a lifelong interest in the geology of the Precambrian, and particularly in the Great Lakes area. He is widely regarded as an authority on iron formations, he has served on the United Nations Committee on Iron Resources in Geneva in 1953-54 and studied iron ore deposits in Yugoslovia with the AID program in 1961. He is perhaps best known to us for his work in the Menominee District of Michigan and Wisconsin (USGS Prof. Paper 573 and Map 1-466, the Cuycera District, Minnesota (USGS Maps MF-99 & ME 181 the Iron River, Crystal Falls District, Michigan) (USGS Prof. Paper 570 & Map MF-225 and for his series of lithologic, geophysical and mineral commodity maps of the Precambrian Rocks of Wisconsin (USGS Map 1-631). He has written many other papers and particularly field guide books which have opened an understanding of the region for those of us who now try to follow in his footsteps. The members of the Institute are proud to recognize the achievements of one of their distinguished colleagues in the awarding of the 1981 Sam Goldich Medal to Dr. Carl E. Dutton. ��PRE- AND POST-DORE SEQUENCES IN THE WAWA VOLCANIC BELT, ONTARIO K. Attoh Hope College I-blland, Michigan 49423 An unconformity at the base of Dor Fm and equivalent sedimentary rocks marks a significant stratigraphic break on the basis of which the volcanic-sedimentary succession in the Wawa greenstone belt can be subdivided into pre- and post-Dor Sequences. The pre-Dor Sequence includes at least two cycles of mafic-felsic containing iron volcanism, each an formation unit, but only the lower mafic-felsic volcanic cycle which is terminated by an extersive siderite deposit completely preserved. Two post-Dore' Sequences have been identifiea; an older Sequence represented by a mafic flow unit, which directly overlies sedimen tary rocks equivalent to the Doré and a younger Sequence, which is structurally discordant with the underlying rnafic fLOW, is characterized by a distinct b reccia unit interpreted as a debris flaw. Post-Dora' Sequences do not contain iron formation is units. �RETROGRADE PRLHNITE-PUMPELLYITE FACIES METAMORPHISM IN THE SOUTHERN VERMILION GRANITIC COMPLEX, NORTHERN MINNESOTA Robert L. Bauer Department of Geology, Macalester College, and Minnesota Geological Survey St. Paub Minnesota 55105 Regional prehnite-pumpellyite metamorphism (M2) overprinted fades middle Most previous studies describing prehnite in biotite do not ascribe this lenses amphibolite facies (Ml) assemblages in the rocks of the southern Vermilion Granitic occurrence to reactions involving biotite, Complex, but pta-dated dynamic metamorphism associated with (M3) strike-slip displacement on the Vermilion prehnite components along biotite cleavage fault. The M2 event is defined on the basis of the occurrence of various combinations the prehnite, of Ca-Al silicates, pumpellyite, epidote, and grandite garnet along with chlorite, adularia, albite, sericite, sphene, i. calcite in the biotite schists, lamprophryes, and granitic rocks exposed in the area. The M2 phases may pervade a given sample, but are more commonly concentrated adjacent to thin quartz or adularia veins or fractures in the but rather to the introduction of all the traces. Observations made during the present study, including the albitization of plagioclase and the occurrence of prehnite, adularia, and sphene within a single chlorite pseudomorph after biotite, are consistent with following prehnite-forming the reaction: anorthite (component) + biotite + H20 = prehnite + chlorite + adularia + sphene sericite aligned parallel to the cleavage traces in The other Ca-At silicates occuring as lenses in biotite or chlorite may also have formed by similar reactions involving the breakdown of biotite. has a similar mode of occurrence, but also occurs in thin veins ± prehnite. M2 epidote and rare pumpellyite may occur as lenses in biotite or chlorite, but are more commonly associated with sericite or rare calcite as alteration products of plagioclase. M2 stability of the Ca-Al silicates indicate a rocks. The prehnite and grandite occur most commonly as lenses or barrel-shaped grains biotite or chlorite after biotite. Adularia No regional variations in the observed assemblages have been found which might indicate systematic spatial variations in the conditions of M2 metamorphism. Comparison of the coexisting mineral assemblages with experimental data on the occurs as fine-grained granular clusters in chlorite after biotite and is pseudomorphic after rutile needles in probable range of conditions for the metamorphism of 250 to 350 degrees chlorite in some of the lamprophyres. P(H20) = P(total). sphene centigrade and 2 to 4 kilobars at P(fluid) = �GEOPHYSICAL INVESTIGATIONS OF THE SLATE ISLANDS CRYPTOEXPLOSION STRUCTURE M. E. Bengtson, and R. P. Meyer Geophysical and Polar Research Center, Department of Geology and Geophysics University of Wisconsin, Madison, Wisconsin 53706 H. C Halls Department of Geology, Erindale College, University of Toronto Mississauga, Ontario, Canada L5L 1C6 3. H. Karl, and D. Dushek Department of Physics and Astronomy, University of Wisconsin Oshkosh, Wisconsin 54901 A survey of the underwater crater area (defined by an irregular arcuate bathymetric rise) surrounding the Slate Islands of northern Lake Superior is now nearly complete. A close order aeromagnetic survey (l000yd spacing, 425m above lake level) and a set of marine magnetic and high resolution 3.5kc bottom and subbottom profiles taken under flight lines has been acquired. These have revealed several short wavelength anomalies on the east side of the islands. The sources of these anomalies appear to be 1/2 km to 1 km below lake level and none seem to have any bathymetric expression. To the west a longer wavelength anomaly trending NW-SE This feature correlates predicted contact. The islands about a roughly defined arcuate magnetic high. Short wavelength has been delineated. with a igneous-sedimentary seem to be centered well previously anomalies have been found over the islands. A set of marine refraction and reflection records was also obtained. Data was recorded digtally. Large thicknessess (Up to I km) of a '-'3.5km/sec layer underlaid by a —5.5km/sec refractor have been detected exterior to the crater. Inside the crater rim, the 3.5km/sec layer is absent. Here, only a 4.8km/sec refractor, lying directly beneath recent sediments, has been detected. All layers appear to have a gentle southerly dip. �THE SIGNIFICANCE OF THE DISTRIBUTION OF CLASTIC LENSES WITHIN THE NEGAUNEE IRON FORMATION AT THE EASTERN END OF THE PALMER BASIN, MARQUETTE SYNCLINORIUM, NORTHERN MICHIGAN * Mark S. Breithart and F. William Cambray Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 The vertical and horizontal distribution of clastics found within the Negaunee Iron Formation in the eastern end of the Palmer Basin, T47N-R26W sections 26, 27, and 28, was studied to determine the geometry of the region at the time of deposition of the sediments. Previous work by Gair (1975), Davis (1965) and Mengel (1956) has suggested that a relict sedimentary Their conclusions were based upon and textural qualitative sedimentars' descriptions. This study has attempted to test this concept with a quantitative approach based upon the vertical and the Palmer Basin is basin. horizontal variation in amount, type, and grain size of clastics observed in the subsurface. The data indicates that the earlier models are correct and that the Palmer Basin is a relict sedimentary basin. The Palmer Basin is located on the south limit of the Marquette synclinorium in the Upper Peninsula of Michigan. It contains over 2,000 feet of middle Proterozoic age sediments and has been down-faulted along the E-W trending Palmer Fauilt relative to the main synclinorium. This study utilized 84,000 feet of core made available by the Cleveland-Cliffs Iron Company. two main The clastics were divided into matrix composition (chloritic vs. iron oxide). The size distribution was divided into coarse (1.05 ± .l5), medium (1.82 + .28) and fine (2.80 + types based upon .46 ':0. From petrographic analysis of over IOU thin sections of the clastics could best be * Presentation eligible Award for the Student classified as immature sediments of the lithic-quartz wacke clan. The quartz is subangular and is supported by a variable matrix of chlorite and iron oxides with minor cryptocrystalline quartz (chert) and carbonate. The majority of lithic fragments were either rounded chert or chloritic clasts. Feldspar was rarely noted. Most bedding contacts between clastics and iron formation are sharp. The vertical and horizontal variation indicates that: 1) the south margin of the Palmer Basin has a consistently higher percentage of coarse clastics with a chioritic type matrix dominating, 2) depositional centers of clastics varied with vertical position throughout the basin, and 3) the source areas for the clastics is indicated to be to the SW, S or SE. All of this supports the idea of the Palmer Basin being a relict sedimentary basin. The best model for the deposition of the sediments is one involving mass flows and/or submarine fans with migrating feeder channels and depositional centers. This would account for the high percentage of matrix, the immaturity of grains, the wide horizontal and vertical distribution and the sharp bedding contacts. A source area for the clastics low in feldspar is also inferred. The pattern is consistent with the concept of a basin which was progressively subsiding during deposition. The periodic supply of clastics by mass flow being controlled disturbances by perhaps associated with fault movements controlling the subsidence. �MIDDLE PROTEKOZOIC DEFORMATION IN NORTHERN AND CENTRAL WISCONSIN B. A. Brown and .1 K. Greenberg Wisconsin Geological and Natural History Survey, 1815 University Avenue Madison, Wisconsin 53706 Recent mapping and compilation by the Wisconsin Geological Survey has pointed out the compelling need for reinterpretation of the Proterozoic tectonic history of northern and central Wisconsin. Tectonic structures observed in this region were predominantly formed during the Penokean deformationM event, and have been modified locally and possibly on a regional scale by later events. In central Wisconsin, the Wolf River granitic complex of 1500 m.y. age represents a major plutonic event, covering over 3600 km2. A plutonic event of this magnitude would be expected to produce at least locally intense deformation as well as thermal metamorphism. Mapping in the Wisconsin Northeast sheet (Greenberg and Brown, revealed has 1980) metamorphic and deformational various features associated with the Wolf River complex, including: amphibolite-grade (I) metamorphism and intense folding near the northern margin of the Wolf River complex Langlade in and Lincoln Counties; (2) recrystallization and refoliation of the 1850 granitic complex Athelstane in southwestern Marinette County; (3) thermal metamorphism in the Mountain (Lahr, 1972) m.y. and Thunder Mountain areas; (4) crenulation and chevron folding of metavolcanic rocks in the Mountain area where earlier fabrics impinge at high angles to the granite's contact; tectonic reorientation in (5) Marathon and Portage Counties, as shown by (6) intense aeromagnetic trends; deformation observed in metavolcanic units caught between the Wolf River complex and major Penokean pluton in Marathon County (LaBerye, 1980). a eastern Deformation related to the emplacement of the Wolf River complex is restricted to the rocks south of the major structural boundary proposed by Brown and Greenberg (1980) and Greenberg and Brown (1980). Structures to the north of this boundary trend to the northeast in Lincoln County, gradually arching eastward until trends are east-west to slightly southeast in central Marinette County. In south-central Wisconsin, broad, open folding is preserved in widely scattered exposures of quartzite and underlying 1760 m.y. old rhyolites. If the interpretation of Dott and DaIziel (1972) is correct, and the quartzites are correlative over a wide area, considerable strain has been superimposed on the basement rocks of central Wisconsin the 1760 m.y. plutonic-volcanic episode, and the intrusion of the 1500 m.y. anorogenic Wolf River complex. Deformation appears to increase in intensity between from west to east. This is exhibited in contrasting modification minor the of the Sioux structural and Barron quartzites (west) with the obvious folding and metamorphism evident in McCaslin, Thunder Mountain, Baraboo, and Waterloo quartzites (east). The deformation is closely related in time to the resetting of Rb-Sr ages (1600 n.y.) observed widely in northcentral Wisconsin (Van Schmus, 1980; Sims and Peterman, 1980). The 1500 m.y. intrusive episode itself may be envisioned as a result of the 1600 m.y. event, just prior to (and during?) intrusion. Confirmed Archean rocks are known only in northernmost Wisconsin and as limitea exposures Proterozoic surrounded rocks in intruded by and Central Wisconsin. Current data indicate no Archean rocks exposed in the main part of the Proterozoic belt. volcanic The complexity of deformation observed in this belt is probably due to multiple deformation and intrusion during the Penokean event, with local, and possibly widespread overprinting by younger events at 1600 m.y. and associated with the 1500 m.y. Wolf River complex. The apparent absence of Archean ages in the volcanic belt of northeastern Wisconsin better supports this interpretation than alternatic'e interpretations which appeal to Penokean deformation overprinting Archean structures in this region. �THE PETROLOGY AND PETROGENESIS OF THE GAMITAGAMA IGNEOUS COMPLEX, WAWA, NORTHERN ONTARIO * Abdul Choudhry and T. E. Smith Department of Geology Windsor, Ontario, Canada, N9B 3P4 The Gamitagama Lake Complex is a plug-shaped, elliptical gabbroic complex of orthopyroxene Archean the respective parent magmas, at pressures less than 5 Kb, to give calc-alkalic differentiation trends within each series. age (Rb/Sr 2642 Ma), approximately 7 x 10 km in dimensions. It outcrops in the metasedimentarymetavolcanic rocks of the Shebandowan Greenstone Belt of the Superior Province, clinopyroxene + + titaniferous magnetite, crystallized out of Many of the rocks of the complex are cumulative in origin, and their major and approximately 40 km south of Wawa. trace Five intrusive phases are recognized in the complex, four of which are subalkaline. They include an olivine- bearing representative of the liquid line of descent. However, their incompatible element contents may be compared to those of other complexes considered to be cumulate rocks produced during calc-alkaline fractionation. The most basic rocks of each discrete, intrusive event are successively less basic in composition indicating that fractionation inner gabbroic series, partly surrounded by a middle zone of less basic, gabbroic rocks, and an outer group of dioritic rocks. The dioritic group includes hornblende- gabbro, diorite, quartzdiorite, quartzmonzodi orite, and tonalite. Arcuate outcrops of leucocratic granodiorite and granite occur within the diorite zone. The granites and diorites are cut by a large dyke- like body of quartz- monzonite which has alkaline affinities. In the olivine- bearing inner gabbroic series, olivine gabbronorite and gabbronorite dominate, and troctolite, norite, and andesine anorthosite are subordinate. In the middle zone of gabbroic rocks, gabbronorite and amphibole gabbronorite occur with lesser amounts of narita and pyroxene diorite. Late dykes of fine- grained gabbroic rocks with porphyritic amphibole and phlogopite intrude the inner and outer gabbroic series. the inner qabbroic series olivine + + titaniferous magnetite + clinopyroxene + orthopyroxene, and in the In plagioclase eligible for the chemistry Student is not occurring in the source magma chamber, at deeper levels. The late fine-grained gabbroic intrusions in the was complex contain amphibole and phlogopite phenocrysts. This suggests that the differentiation was controlled by the separation of amphibole and phiogopite at more than 10Kb pressure ("-'35 km depth). The complex is compared to several well described hornblende-beari ng gabbroic plutons occurring in the Cordilleran batholiths of North and South America. It is concluded that the Gamitagama Complex is most similar to the Guadalupe Complex in California. Within the Gamitagama Complex there is a complete range of rock types from troctolites, through amphibole gabbros and diorites, to quartz-diorites and granitoid rocks. It is considered to represent an excellent illustration of the fractionation of gabbroic ultimately yield granitoid rocks. middle gabbroic series plagioclase + * Presentation Award element melts to �EARLY PROTEROZOIC GAbI3ROIC, DIORITIC, AND QUARTZ MONZONITIC INTRUSIONS IN THE MINNESOTA RIVER VALLEY: PETROLOGY AND SIGNIFICANCE M. DeWitt Daggett Minnesota Geological Survey, University of Minnesota, St. Paul, MN 55108 present address, Noranda Exploration, Inc., Cobalt, ID 83229 Three, small, early Proterozoic plutons intrude the Archean gneiss terrane of the Minnesota River Valley south of Franklin, Redwood County, Minnesota. The largest is the Cedar Mountain Complex, a composite intrusion consisting of a chilled margin of diabase and microgabbro, a main body of flow-layered hornblende diorite, and a quartz monzonite core. This complex is 600 meters in diameter. Two smaller plugs consisting of 1) diabase and gabbro, and 2) granodiorite, crop out five kilometers east of Cedar Mountain. Cross cutting and orthoclase in diabase indicate that the parent melt was potassic. Assimilation of sialic crust during magma intrusion affected the final mineralogies chemistries of and the Franklin-area plugs. Xenoliths of Archean yneiss occur throughout the Cedar Mountain diorite and the gabbro plug to the east; emplacement of the plugs to a fairly shallow depth proceeded in part by stoping of the country rock. from these rocks suggest that the dioritic, These early Proterozoic intrusives may a part of a limited but widespread shallow level igneous event which occurred in the southern Lake Superior region about 1,760 m.y. ago. The Minnesota River Valley plugs are lithologically somewhat similar to the Fox River rhyolites and related granites of south-central Wisconsin, and to the granodioritic, and differentiated from monzonitic melts common gabbroic Amberg quartz monzonite and related intrusions of northeast Wisconsin. These parent magma by fractional crystallization rocks all occur as small, isolated, epizonal clinopyroxene, of olivine, and calcic plagioclase. Feldspar compositions range continuously from An80 in diabase and gabbro to An2 in quartz monzonite. Olivine in the diabase is Fo53 to Fo6. Clinopyroxene from diabase, gabbro, and intrusions or extrusive flows; they all possess a calc-alkaline chemical character. The presence of rare rhyolite clasts in conglomerate units of the middle-Proterozoic Sioux quartzite indicates the former existence of additional similar rocks in Minnesota. relationships between rock types identify three distinct stages of intrusion: l)gabbro, 2)diorite and granodiorite, and 3) quartz rnonzonite. Petrographic and mineral chemistry data a hornblende diorite is diopside or diopsidic The restricted range of augite. clinopyroxene compositions and the lack of iron enrichment trend for an overall clinopyroxene phenocrysts are evidence for melt with calc-alkaline original an affinities. High modal abundances of biotite be This 1,760 m.y. old igneous event followed the Penokean orogeny but preceded the more voluminous igneous activity which accompanied crustal extension in middleand late-Proterozoic time. �LITHOLOGIC AND SEDIMENTOLOGIC CHARACTERISTICS OF THE COPPER HARBOR CONGLOMERATE, NONESUCH SHALE AND FREDA SANDSTONE FORMATIONS OF NORTHERN MICHIGAN AND WISCONSIN Paul A. Daniels, 3r., Hunt Energy Corporation, Lansing, Michigan The Keweenawan Age Copper Harbor Interfingering with the Copper Harbor Conglomerate, Nonesuch (Shale) Formation, Conglomerate is the Nonesuch (Shale) Formation, an unoxidized sequence of gray-black siltstone, shale, and sandstone and Freda Sandstone formations comprise the Oronto Group and are found in outcrop over some 200 kilometers in northern western Upper Michigan. These formations are part of a volcanic-elastic sequence created in response to the formation of the Midcontinent Rift System. Although intercalated volcanics are found in the lower one-third of this group, the sedimentary depositional regime was dominant. Along the Keweenaw Peninsula three paleocurrent indicators for all formations show that the predominant paleoflow directions were generally in northerly directions. In contrast, sedimentary structures in the Copper Wisconsin and Harbor Conglomerate on the opposite side of the rift (i.e., Isle Royale) indicate stream flow was to the south and east. Harbor Depositionally, the Copper Conglomerate is a basinward-thickening of volcanogenic clastics wedge and subordinate volcanics that decreases in average grain-size upsection. Various facies comprise the Copper Harbor and these have interpreted collectively been as representing a prograding alluvial fan complex. Maximum thickness is on the with a maximum thickness of 215 meters. The Nonesuch contrasts with the redbed sequences, both above and below, by: 1) having been deposited in a reducing environment, 2) increased textural maturity, and 3) hydrocarbon, sulfide and chlorite content. The Nonesuch is interpreted as having been deposited in a rift-flanking lacustrine environment of varying depth. Initiation of lacustrine conditions probably occurred through disruption of existing drainages by alluvial, volcanic, and/or tectonic processes. As with the underlying Copper Harbor, a gradational contact exists with the overlying Freda Sandstone. The Freda Sandstone is a ferruginous, lithic sequence of cyclic sandstone and exceeding 3660 meters in maximum thickness. Although similar in appearance to some sandstones of the mudstone Copper Harbor Conglomerate, the Freda, overall, is of greater compositional maturity conglomerate facies are uncommon. The Freda is dominantly fluvial in origin and appears to have "overridden" the Nonesuch and environments. clast-supported and comprised of volcanic clasts with an overall compositional ratio of mafic to silicic plus intermediate clasts of about 2:1. The heavy-mineral suite for the Copper Harbor (as well as for the Nonesuch and Freda) mainly consists of ilmenite plus Although complex in detail, the overall depositional model for the three formations is one of siomple transgressive-regressive relationships between alluvial fan/ lacustrine/ fluvial environments (Elmore and Daniel; 1980b). Important aspects of such a model are that: I) all the formations are genetically related with no major unconformities between them, and 2) the intervening Nonesuch Formation is, at least in part, equivalent in age to the upper similar opaque minerals, and epidote. Copper Harbor and the lower Freda. order of 1830 meters. Principal lithologies are red-brown, oxidized, lithic graywacke volcanogenic conglomerates. The conglomeratic facies are predominantly and �I PALEOMAGNETISM OF THE MEMESAGEMASING AND CARIBOU LAKES NORITES, GRENVILLE PROVINCE, ONTARIO * S. Dey, D. 1. A. Symons, and M. Stupavsky Department of Geology, University of Windsor Windsor, Ontario, Canada N9B 3P4 The Memesagemasing and Caribou Lake 20 km2 stocks intruding the high rank granitic gneisses in the Crenville Province about 60 km S of the Grenville Front. Five cores yielding 10 specimens were drilled in the stocks at Sch of 24 and 26 sites respectively. Low-field magnetic susceptibility measurements show that both layered norites outcrop as oval, stocks have a central phase with magnetite content. a high their airborne magnetic anomaly pattern rather than invoking a funnel-shape. Anisotropy of magnetic susceptibility measurements show This explains that the norites are strongly layered even though most outcrops appear unbanded, and that the plutons have not been structurally compressed or tilted as previously suggested. AF, thermal, and chemical step demagnetization and general AF cleaning all isolate a stable remanence component with 95 percent confidence of r-.'3l0°, 5l in the Memesagemasing stock using conventional tiered statistical analysis. This component * Presentation eligible Award for the Student resides in titanomagnetite with numerous exsolution lamellae. The same component is isolated in the Caribou Lake stock by point density stereonet contouring only after AF cleaning. Its less stable remanence resides in coarser unexsolved t itanomagetite grains. Eight baked contact tests using more than 100 additional specimens and including 2 profiles show that: I) the norite remanence predates emplacement of the crossing cutting -.s 1250 Ma Sudbury olivine diabase dikes and — 1100 Ma granite pegmatite dikes, and 2) the norite was 2000 when the dikes were cooled to emplaced. The norite pole lies on the -'l760 Ma position of the North American APW path implying: 1) emplacement during the terminal stages of the Hudsonian Orogeny dated by Rb-Sr at r 1800 + 100 Ma ago; 2) possibly comagmatic emplacement with the Sudbury Irruptive which is —90 km NW in the Southern Province; ano 3) the juxtaposition of the Grenville and Southern Provinces as far back as 1760 Ma. �WISCONSIN GRAVITY BASE STATION NETWORK--1980 C. Patrick Ervin Department of Geology, Northern illinois Lkiiversity DeKaIb, Illinois 60115 The Wisconsin Geological and Natural History Survey has embarked regional gravity surveying upon a program. Mapping is being done on a one mile grid insofar as the road system and elevation control permit. The Northeast Wisconsin Sheet is "in press" and was presented at this meeting last year. The rest of the state will be covered in the coming years. A successful field program is dependent on the existence of a high precision, internally consistent base station network. To facilitate field operations, a base station should be readily accessible by auto, no more than 25-30 feet from a road or drive, to locate, permanent, relatively isolated from foot and vehicular traffic, and easy have a stable base on which to set the meter. Additionally, no point in the state should be more than about a 45 minute drive from a base station. A statewide base station network, consisting of 30 stations, was established in 1980 the summer of LaCoste-Romberg model C using two gravimeters. Use of two gravimeters doubles the number of ties between stations and facilitates error detection. The network was designed to include several extant oase stations and is in good agreement with the earlier measurements. �THE PENOKEAN OROGENY Samuel S. Goldich Department of Geology, Colorado School of Mines Golden, Colorado 804131 The Penokean orogeny, which occurred in the Lake Superior district approximately 1800 m.y. ago, was a complex event that involved more than mountain building by uplift followed by erosion. As in the development of the more recent mountain chains, igneous and metamorphic activity on a grand scale characterized the Penokean orogeny. Graywacke-argillite sequences with intercalated volcanic rocks were folded, metamorphosed, and intruded by a variety of igneous rocks ranging from gabbroic to granitic in composition. Published U-Pb zircon ages from Wisconsin and Michigan indicate two pulses of igneous activity. The older, 1835 ± 15 The data available at this time indicate more or less continuous igneous activity in the Lake Superior region between 1850 and 1750 m.y. ago. The 2600-m.y. old McGrath Gneiss of eastern Minnesota was strongly deformed during the Penokean orogeny. The U-Pb ages on zircons from the gneiss are strongly discordant and reflect the 1800-m.y. deformation. Similarly, old rocks in Wisconsin and in Michigan were severely affected by the Penokean orogeny, and the earlier geologic history, as a result, is difficult to decipher. The similarity in lithologic types and structural style of the rocks involved in the m.y. ago, involved a variety of rock types, 1800-m.y., whereas the younger pulse, 1760 ± ID m.y. ago, appears to have been restricted to granite and rhyolite. Unpublished U-Pb analyses of zircon concentrates from a large number of samples representing tonalitic to granitic rocks in east-central Minnesota are closely related in time, 1804÷ 24 m.y. Rb-Sr isochron ages for the rocks of east-central Minnesota range from 1700 m.y. to 1750 m.y. and are distinctly younger orogenic events in the Lake Superior region is striking. In each case metasedimentaryvolcanic accumulations, a variety of igneous intrusive rocks, and migmatitic development were involved. Regional folaing gave way to higher grades of metamorphism accompanying igneous activity, and late shearing with recrystallization are characteristic. Emplacement of pegmatite and aplite dikes followed each major than the corresponding U-Pb zircon ages. the orogenic event. 2600-m.y., and in older �THE ROLE OF HYDROTHERMAL ALTERATION AND TECTONISM IN WISCONSIN MOLYBDENITE OCCURRENCES .1. K. Greenberg Wisconsin Geological Survey Madison, Wisconsin 53706 Molybdenite is known to occur in three places in northeastern Wisconsin. These appear to be situated along a north-south region restricted near 88°W Molybdenum mineralization in longitude. Michigan's Upper Peninsula is also concentrated near the same longitude. In all Wisconsin cases, Penokean-age granite plutons are directly with the mineralization. The best known occurrence, near Middle Inlet in Marinette County, is in quartz veins within the Mount Tom granite body. The other two associated occurrences, near Amberg in Marinette County and in southeast Florence County, are pegmatite mineralizations. Chemically, the granite host rocks are calcalkaline to alkaline, with no "unusual" trace element characteristics. }—bwever, near the site of mineralization in veins or pegmatites, the host rocks show the effects of hydrothermal alteration, especially alkali Dramatic examples of metasomatism. potassium metasomatism are apparent at Middle Inlet and southeastern Florence County. The granite at Middle Inlet has also been albitized and silicified proximal to quartz veins. These alteration effects should be considered as essential guides in exploring for molybdenum in Wisconsin. Wisconsin occurrences of molybdenum are similar to those in older Precambrian terranes of the world, such as in Ontario and Western Australia. However, these cannot be equated with the extensive ore resources porphyry-type deposits represented by typical of younger plate tectonic environments. �IMPACT AS A POSSIBLE ORIGIN FOR SUBSIDED BASINS Jack B. l-brtung NationaL Research Council Senior Post-doctoral Research Associate Code SN6-NASA Johnson Space Center, F-kiuston, Texas 77058 Subsidence of basins, Michigan must basin, circular roughly intracontinental such have mechanism or energy source. as a the driving Mechanisms directly related to plate tectonics do not operate slowly enough to explain a record of almost continuous subsidence of the Michigan basin throughout the Paleozoic Era. Thermal contraction of the lithosphere underlying the basin is another mechanism, but even proponents of this idea recognize "little direct evidence that an initial heating actually occurred in the Michigan basin immediately before the start of subsidence." Another energy source which could lead to a subsiding basin is the impact event of an asteroid or comet roughly ID km in diameter. During such an impact material is excavated from depths of a few tens of km and deposited on the surrounding area. The is filled temporary cavity produced immediately by material that was originally below the cavity. The resulting structure, similar to those observed on the Moon and Mars, is a broad topographic low surrounded by higher rocks capped by ejecta deposits. Of particular importance is the likelihood that a state of isostatic equilibrium will be established or closely approached after motions directly related to the impact have The mass deficiency associated with the topographic low may be expected to be compensated for by excess mass related to more dense rocks centrally uplifted below the basin. Basin evolution ceased. with erosion of surrounding highlands and deposition within the basin. If proceeds it is required that isostatic equilibrium is maintained, the to the basin will subside in and the surrounding highlands will be uplifted. This response sediment load process will continue until the more dense material underlying the basin is returned approximately to its original level or until no topographic difference exists between the basin center and the surrounding area. A significant characteristic of this process is that the rate of subsidence is controlled entirely by the rate of sedimentation, which may be extremely slow or even nonexistent at times. On the Earth an evolved impact basin may take the appearance of a subsided sedimentary basin, something like the Michigan basin. �EVIDENCE FOR MULTIPLE DEFORMATION IN THE MIDDLE PRECAMBRiAN THOMSON FORMATION Timothy B. Hoist Department of Geology, University of Minnesota, Duluth Duluth, Minnesota 55812 The Thomson Formation of East-Central exhibits numerous structural features which have been interpreted to have formed during the Penokean Orogeny. In the Thomson-Cariton-Cloquet area there are open folds on a scale from centimeters to kilometers. The folds are upright, and Minnesota fold axes trend about east-west and are horizontal to gently plunging either east or west. An axial-planar cleavage, vertical or nearly vertical, is present. To the south there is a pervasive bedding-parallel foliation which has previously been interpreted as having formed in a metamorphic event which predated deformation. Evidence of the amount of compressional strain associated with foliation (Wood, 1974) as well as abundant extensional features (boudinage) within the foliation plane in this region suggest that the bedding-parallel foliation is associated with a deformation. Folds are with southern area, present in the geometries and attitudes similar to those in the north. A vertical crenulation cleavage, axial-planar to these folds where both are observable, is also present. The crenulation cleavage can be found even where folds are not found, in the area from Denham to Atkinson. The deformation which caused the bedding-parallel foliation must then pre-d ate that which caused the open, upright, sub-horizontal folds. Isoclinal, recumbant folds, to which the earlier foliation is axial-planar, have been found in several localities. These folds vary in scale from centimeters to meters. Fold hinges are fairly rare because of the isoclinal nature of the folds. The pervasive nature of this earlier foliation suggests that isoclinal, recumbent folds of a large scale also may be present. The deformation history involves an early stage of indicated isoclinal, recumbant folding, with the development of an axial planar foliation. A latter stage of deformation involved the development of open, upright folds, with an axial-planar foliation also, which is a crenulation cleavage where the earlier foliation is present, and a slaty cleavage where the earlier foliation is not present. Evidence for the earlier deformation has been found from Denham to just northeast of Atkinson, whereas evidence for the second deformation can be found in the entire region of Thomson Formation exposure. �JOINT ORIENTATION ANALYSIS IN THE NORTHERN MICHIGAN BASIN Timothy B. 1-blst Department of Geology, University of Minnesota, Duluth Duluth, Minnesota 55812 The orientations of 14,687 joints were measured at 142 locations in the Paleozoic rocks of the Michigan Basin. The data were for each of the four sets. The local variation could not be correlated with taken which ranged from Manitoulin Island on the east, the south Joint set orientation is independent of regional strike around the Michigan Basin Door Peninsula on the west and the northern which varies from about 020 degrees (N200E) to about 115 degrees (N65°W) in an area shore of Lake Superior on the north, the portion of the lower peninsula of Michigan on the south. The rocks at the sample localities range in age from Cambrian to Devonian. Most of the localities are in carbonate rocks, but data were taken from outcrops of sandstone and shale also. Almost all (over 98%) of the joints are vertical or nearly vertical. Four main joints sets are present in the northern Michigan Basin. The largest peak in the data is a joint set with a strike of about 054 degrees (N54°E). The second-largest peak in the data is a set with a strike of about 133 degrees (N47°W). Two peaks of about the same height are joint sets striking 002 degrees (N02°E) and 092 degrees (N88°W). Local mean orientation of any of the sets does vary from location to location, but is relatively consistent over the entire area lithogy, age of rock, or geographic location. across the study area. Possible structural trends in the Precambrian rocks below the Devonian rocks in the area, postulated from geophysical data, do not correlate with any of the joint sets. Trends of axes of folds present in the Paleozoic strata of the lower peninsula average about 135 degrees (N45°W). This suggests that the joint set of nearly the same strike direction may be related to these folds (the b-c joints of Price, 1966). In-situ stress measurements in the Paleozoic rocks of the mid-continent region (summarized in Haimson, 1978) show the maximum principal compressive stress in the horizontal plane to be quite consistent in orientation, averaging 053 degrees (N53°E). This suggests that the joint set with a nearly-idential strike may be extensional, and fairly recent in age. �A GEOCHEMICAL RECONNAISSANCE STUDY OF GROUNDWATER FROM AN EIGHTEEN COUNTY AREA OF NORTHWESTERN OHIO Mohr, Eileen T., Deering, Mark F., and Carison, Ernest H. Department of Geolgy, Kent State Lkiiversity Kent, Ohio 44242 A reconnaissance study of groundwater techniques showed sulfate and silica to be quality in Northwestern Ohio was undertaken in which 100 samples from actively pumping wells were collected. The major supply of groundwater for this area is from carbonate aquifers which locally evaporites contain and epigenetic present in concentrations of 4-1500 ppm and 7.2-29.0 respectively. ppm Fe, also determined spectrophotometri c by a mineralization that may be the source of natural trace element pollution. Major industrial centers and agricultural areas may also be a prime source of pollution. technique, ranged from 0.0 ppm to 11.2 ppm. The concentrations of K (1.0-34.4 ppm), Zn ( less than 40 ppb-l.7 ppm), Co less than 300 ppb), ana Na (5.5-150.6 ppm) were determined by atomic absorption techniques. Other trace elements including As, Cd, On site measurements of static water Cu, Be, Pb and Sr will be measured by level, temperature, (6.85-8.5 5), pH conductivity (100-2500 micromhos), alkalinity (83-580 ppm), F (0.2-2.8 ppm) and Cl (3-230 ppm) were made. Digital graphite furnace techniques, while Hg concentrations will be determined by a flameless AA method. It will be determined titration analyses performed on filtered, acidified samples indicated Ca to be present in concentrations from 27-560 ppm and Mg from 14-192 ppm, while spectrophotometric if any of the trace elements present a health hazard and should, therefore, limit water utilization or require special treatment of water supplies. �RB-SR DATING OF PRECAMBRIAN BASEMENT FROM ILLINOIS DEEP HOLE PROJECT CORE UPH-3 Carla W. Montgomery Department of Geology, Northern Illinois University DeKaib, Illinois 60115 Eble UPH-3 Deep core 840 m approximately of Precambrian granitic basement. Whole-rock samples taken over the full length of the Precambrian portion of the core fit a single Rb-Sr isochron with slope age of 1479 + 10 m.y. and initial 87Sr/86Sr of o.71i12 + .0025 (Iderrors). Mineral isochrons frorii measurements, indicating that these rocks have not been affected by any significant thermal event since that time. The initial strontium isotope ratio reflects some contribution of radiogenic Sr from older crust. The l479-m.y. age is similar to ages several core samples yield essentially the same age within the precision of the region, illinois penetrated reported for granitic rocks in Wisconsin, Missouri, and elsewhere in the mideontinent suggesting widespread activity at about that time. igneous ��PRELIMINARY RESULTS OFA GRAVITY SURVEY IN THE EASTERN HALF OF THE IRON RIVER-CRYSTAL FALLS DISTRICT, IRON COUNTY, MICHIGAN * D. R. Paddock, K. Fujita, F. W. Cambray, and H. F. Bennett Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 A gravity survey was conducted in the eastern portion of the Iron River-Crystal Falls district of Iron County, northern Michigan. Measurements were taken on five profiles, three east-west profiles to the south of Crystal Falls and two north-south profiles to the west of Crystal Falls. The stations along each profile were separated by an average of 750 meters. Altitude control was maintained by an altirrter and 1:24,000 topographic maps. Accuracy of the data after reduction to bouguer anomalies is about plus or minus 1.4 milligals. A maximum amplitude of 34 milligals is observed over the Iron-River Crystal Falls district. Our observed data are in agreement with those obtained by Bacon and Wyble (1952). The anomaly is centered to the south and west of the iron formation The shape of the anomaly indicates that the source is at depth. exposures. Several crustal models were developed to interpret the data. If the stratigraphic section reported in the literature is used, only a 9 milligal anomaly is obtained. * Student Presentation eligible Student Award Linear stretching of the stratigraphic succession requires a sedimentary thickness of greater than 40 km to fit the amplitude of the anomaly. With no stretching of the column, and an iron formation density of gm/cc, an increase of the iron formation thickness from 200 to 1200 meters is required. An increase in the 3.21 density of the Riverton Iron Formation to 3.56 gm/cc would reduce the total sedimentary thickness to the reported 12 km with an iron formation thickness of 600 These iron formation thicknesses greatly in excess of the reported average thickness of 200 meters. An alternative possibility is that the Paint River group and Badwater Greenstone are directly underlain by basalt. This model postulates a sedimentary thickness of 2800 meters (of which 200 is iron formation) and 1800 meters of greenstone. To fit the observed anomaly, an underlying basaltic meters. are layer of between 3200 ana 3900 meters is required. This could be caused by the sub-aqueous emplacement of basalts in a rift basin which has subsequently filled with sediments. for the ��PRELIMINARY ASSESSMENT OF RARE EARTH ELEMENT GEOCHEMISTRY OF VARIOUS IRON FORMATIONS OF THE LAKE SUPERIOR DISTRICT * Elaine L. Slaughter, Susan E. Tituskin, and John 1. Wilband Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 Several samples of banded ironformation (6W) from the Wawa district and the Gunflint, Vulcan, and Negaunee Iron Formations have been analyzed for their patterns to the carbonate samples. investigation to determine the use of REE as indicators of depositional environments and to investigate their mobility during intermediate to these groups. rare earth elements (REE) as part of an metramorphism, oxidation, and leaching. Our preliminary results cannot be interpreted too literally in terms of genetic modeling because the experimental base, such as exists for magmatic rock—forming minerals, is very weak for BIF sedimentary systems. The carbonate rich sediments of the Negaunee I.F. at the Empire Mine show relatively strong fractionation of the light REE (La/SM 3-5x chondrite) and have surprisingly uniform total abundances with respect to depth. The clastic lenses are in total considerably more enriched abundances yet show similar distribution * Student Presentation Student Award eligible for the The "jaspilite" and "hard ores" (Cliffs Shaft) of the Michigan formations are most REE enriched, Vulcan samples the least, and Tilden and Empire Mine oxide ores are We suggest the REE enrichment in the to be a response to solutions migrating through the formations (e.g. oxides Cannon, 1975 - hard ores) or depletions in response to increase in metamorphic grade (Vulcan). In the Empire and Tilden environments where carbonate to oxide reactions are obvious or implied, preliminary data indicate that the abundance of REE in the oxides are similar to that of the carbonates. Cherts, carbonates and oxides do not exhibit a Ce depletion. The Gunflint and Negaunee cherts have "terrestrial" REE patterns similar to other "land exposed" cherts. �THE DISTRIBUTION OF LITHIUM, RUBIDIUM AND CESIUM IN LAKE MUDS NORTH OF LAKE SUPERIOR M. A. yes and R. 3. Stevenato Ontario Geological Survey Oronto, Ontario A study of the distribution of Li, Rb and Cs in lake muds north of Lake Superior is funded by the Ministry of Northern Affairs under the Northern Industrial Mineral Study program, and is supervised by staff of Mineral Deposits Geological Survey. Ontario Section, Centre-lake samples covering an area of 27,700 sq. km. (NTS 42D, 1/2 of 42E, 52A, 1/2 of 52H), originally the Federal-Provincial collected for Uranium Reconnaissance Program of 1977, The primary were used in this study. purpose is to evaluate the geochemical response of lithium and related trace elemental concentrations in lake sediments and determine its potential as a tool for lithium exploration. The lake sediment samples were collected at an average ciensity of sample per 13 sq. km. A total of 1782 samples were 1 analyzed for Li, Rb and Cs by Barringer Ltd. not including randomly control reference and blind duplicate samples. Two hundred and four samples were analyzed for tin and tantalum. Lithium, rubidium and cesium were Magenta inserted analyzed by flame atomic absorption upon reverse HF/HCIO4/HNO3 The detection limits were 1 digestion. ppm, 10 ppm ppm respectively. Tantalum was analyzed by plasma emission upon reverse and a HF/HCIO4/HNO3 digestion The redissolution in 0.5 N HCI/HF. Tin was detection limit was 5 ppm. analyzed colourimetrically upon fusion with ammonium iodide; the detection limit being and 1 I ppm. Control reference, blind duplicate and field duplicate samples were utilized to determine the precision and accuracy of the data. Precision of the four different control samples ranged from 8% to 18% for lithium Blind and from 6% to 10% rubidium. duplicate accuracy was 16% and 20% for lithium and rubidium respectively, while field duplicate accuracy was 7% for Li and 12% for Rb. Cesium was not considered since most concentrations recorded were below the detection limit of the lab equipment. high lithium While generally coincide with concentrations high rubidium concentrations, no large anomalous regions were detected in a preliminary visual examination except in the area southwest of Progress of a detailed Thunder Bay. computer analysis amalgamating the data with major element and base metal values of the lake muds is discussed. �PETROGENETIC MODELS OF KEWEENAWAN BASALTIC ROCKS, UPPER MICHIGAN John T. Wilband and Pipob Wasuwanich Department of Geology, 206 Natural Science, Michigan State University East Lansing, Michigan 48824 Lower Keweenawan diabase dikes from Marquette-Baraga Counties, and middle Keweenawan Portage Lake Lavas from upper Michigan, can each be subdivided into two chemically distinct groups: a low Tb2- P205 group characterized by higher AI2O3 content, higher Mg ratio, and lower total Fe end REE abundances than a high Ti02-P2O5 group. Both groups, which are indistinguishable in the field, are enriched in the LREE relative to the HREE, and have similar normalized REE abundance patterns. respective type. The wide gap between the TiO2-P205 contents of each group cannot be resolved by a simple fractionation or mixing model, especially because the Ti02/P205 ratio remains remarkably constant within each group. We conclude that two sources perhaps from different depths or with separate REE signatures, are required to produce the two groups and suggest each linear trend is indicative of liquids derived by varying degrees of partial melting of these sources. Similar chemical the dikes have been trends within but nonparallel for each subgroup of the interpreted to mean that the magmatic processes must have This correlation can be interpreted to mean that the rocks, regardless of mode of formation, are coeval within their early opening stages of the Keweenawan rift in Michigan. Plots of La/Sm vs. La and Yb are linear basalt. same been operative during their emplacement in the �AUTHOR H. All and C. Craddock K. Attoh R. L. Bauer M. E. Bengtson, R. P. Meyer, I-I. C. Halls, 3. H. Karl, and D. Dushek M. S. Breithart and F. W. Cambray B. A. Brown and 3. K. Greenberg A. Choudhry and T. E. Smith M. D. Daggett P. A. Daniels, Jr. S. Day, D. T. A. Symons, and M. Stupavsky C. P. Ervin H. P. Gilbert S. S. Goldich 3. K. Greenberg 3. 8. Hartung 1. 6. F-blst 1. 8. HoIst E. T. Mohr, M. F. Deering, and F. H. Carlson C. W. Montgomery M. Osterberg and R. L. Morton D. S. Paddock, K. Fujit F. W. Cambray, and H. F. Bennett P. K. Sims and Z. E. Peterman F. L. Slaughter, S. E. Tituskin, and 3. T. Wilband F. B. Van 1-buten and D. Bhattacharyya M. A. Vos and 5. 3. Stevenato 3. T. Wilband and P. Wasuwanich TIME 3:00 to 3:20 Friday 1:50 to 2:10 Friday 4:00 to 4:20 Thursday LOflOto 10:30 Friday 2:10 to 2:30 Thursday 11:00 to 1 iao Thursday 3:40 to 4:00 Friday 3:20 to 340 Friday 3:20 to 3:40 Thursday 9:50 to 10:10 Friday 9ö0 to 9:50 Friday 9•30 to 9:50 Thursday lOdOto 10:30 Thursday 3:40 to 400 Thursday 11:20 to 11:40 Friday 1 h20 to 1 h40 Thursday 11:00 to 11:20 Friday h30 to 1:50 Thursday 11:40 to 12:00 Thursday 1:30 to 1:50 Friday 11:40 to 12:00 Friday 9:50 to 10:10 Thursday 300 to 3:20 Thursday Thursday evening 1:50 to 2:10 Thursday 2:10 to 2:30 Friday � https://digitalcollections.lakeheadu.ca/files/original/e0aa4ed07dd4add1745e0969cdcbfe3d.pdf edcf69eb414fe00bfd52b2bc8c45457a PDF Text Text Twenty Seventh Annual Meeting Institute a Lake Lansing, Michigan Stperior Geology May 11—12, 1981 The Huronian Between Sault Ste. Marie and Thessalon �I I THE HURONIAN ROCKS BETWEEN SAULT STE. MARIE AND THESSALON DISTRICT OF ALGOMA ONTARIO MAY 11-12, 1981 FIELD EXCURSION GUIDE Prepared By Gerald Bennett, Ontario Ministry of Natural Resources �I THE HURONIAN SUPERGROUP OF THE SAULT STE. MARIE AND THESSALON AREAS, ONTARIO I Introduction: Previous Work: The Huronian Supergroup is probably the most studied sequence of rocks in Canada with published observations going back to 1821. Knight (1915) investigated part of the areas and recognized volcanic rocks in the Thessalon area. Collins (1925) memoir included the first accurate geological map of the North Shore of Lake Huron and his stratigraphic subdivision of the Huronian has only recently been supplanted. McConnell (1927) described the rocks of the Sault Ste. Marie area and placed the Huronian rocks in their correct stratigraphic position. Chandler (1973, 1976) did detailed mapping for the Ontario Division of Mines in the area west of Wakomata Lake. Frarey (1977) culminated several seasons of mapping for the Geological Survey of Canada with the publication of a memoir on the geology between Sault Ste. Marie and Blind River. Frarey revised the stratigraphic scheme for the Sault Ste. Marie area and recognized additional Huronian volcanic rocks in the Aberdeen Lake area. The writer carried out ¾ mile to the inch mapping for the Ontario Geological Survey between Sault Ste. Marie and the Aberdeen Lake ares between 1974 and 1977. A study of the stratigraphic relationships of the Huronian volcanic rocks was begun in 1978 (Bennett in preparation). In addition to the above studies there are many studies of specific problems relating to the Huronian geology. Most of the significant theses and publications are given in the references accompanying this field guide. General Geology: The Lower Proterozoic (Aphebian) Huronian Supergroup forms part of the Southern Province of the Canadian Shield. These predominantly clastic sedimentary rocks form an eastwest trending belt about 35 miles (56 km) wide extending along the north shore of Lake Huron as far east as the Quebec border, a distance of approximately 200 miles (320 km). The total stratigraphic thickness of Huronian rocks is about 40,000 feet (12,000 m). �I -2An absolute age for the Huronian rocks has not yet been firmly established. The basal Huronian rocks lie unconformably upon Archean granitic rocks of the Superior Province which give K-Ar ages of 2,500 m.y. Nipissing diabase which intrudes the Huronian sequence has been dated by Sr-Rb methods at 2,150 m.y. (Van Schmus, 1965). The Huronian rocks along the north shore of Lake Huron are part of the Penokean Fold Belt and have undergone varying degrees of deformation and metamorphism. Radiometric dating of metamorphic rocks generally gives ages between 1,600 and 1,800 m.y. In the area between Sault Ste. Marie and the east end of Quirke Lake Syncline Huronian rocks are metamorphosed to lower greenschist facies and strata are deformed into open folds or a south to southwest dipping homocline. Normal fault sets strike northeast and northwest. Most movement occurred along northwest trending thrust faults (Frarey, 1977). East of the Quirke Lake Syncline the metamorphism and deformation is more intense. In the Sudbury-Espanola area dips are generally steep, folds are locally tight and the metamorphic grade is almandine-amphibolite facies (Card et al 1972). Elliot Lake Group: In the Sault Ste. Marie and Thessalon areas the Elliot Lake Group is represented by the Livingstone Creek, Thessalon, and Matinenda Formations. The McKim Formation, a very thick sequence of mudstones, siltstone and turbidites present in the eastern half of the Huronian belt has; not been recognized in the area between Sault Ste. Marie and Thessalon (Frarey, 1977) The Livingstone Creek Formation; The Livingstone Creek Formation is a clastic sedimentary sequence which overlies the Archean basement rocks and which is, in turn, overlain by the Thessalon Formation volcanics. In the Quirke Lake Syncline the Livingstone Creek Formation is missing and the Thessalon volcanics lie directly on the basement. In the Sault Ste. Marie area the Livingstone Creek Formation can be subdivided into a conglomerate member, a sandstone member, and a quartz-arenite member. The conglomerate member of variable thickness is locally present at the base of the formation, although in Morin Township, about 25 miles (40 km) north of the Thessalon area, the conglomerate member occurs at least one hundred feet (33 m) above the base. �I -3— TABLE OF FORMATIONS FOR THE SAULT STE. MARIE AND THESSALON AREAS I PHANEROZOIC (max. thickness in feet) CENOZOIC Pleistocene and Recent Gravel, sand, silt, clay and organic deposits Unconformity Paleozoic Ordovician Limestone, shale, sandstone Unconformity — PRECAMBRIAN LATE PRECAMBRIAN (PROTEROZOIC) Jacobsville Formation (+ 700) Sandstone, shale, conglomerate Unconformity KEWEENAWAN GROUP Mamainse Point Formation Basalt, rhyolite, conglomerate, diabase, felsite dikes Unconformity Olivine diabase dikes, lamprophyre dikes Intrusive Contact MIDDLE PRECAMBRIAN (PROTEROZOIC) Nipissing Diabase Gabbro, diabase, granophyre HURONIAN SUPERGROUP COBALT GROUP Bar River Formation (1000) Quartz arenite Gordon Lake Formation (1000) Siltstone, chert Lorrain Formation (8000) Arkose, quartz arenite, pebble conglomerate, siltstone, mudstone Gowganda Formation (3500) Matrix supported and clast supported conglomerates, siltstone, mudstone, wacke, arkose �-4Dis conformity QUIRKE LAKE GROUP Serpent Formation (800) Subarkose, conglomerate Espanola Formation (650) Grey limestone, siltstone, dolomite Bruce Formation (300) Matrix supported conglomerate Local Disconformity ROUGH LAKE GROUP Mississagi Formation (5000?) Subarkose, pebble conglomerate, arkose Aweres Formation Subarkose, arkose, clast and matrix supported conglomerate, siltstone Pecors Formation (Not recognized in Sault Ste. Marie area) Muds tone Ramsay Lake Formation Matrix supported conglomerate Local Disconformity ELLIOT. LAKE GROUP McKim Formation (Not recognized in Sault Ste. Marie area) Mudstone, siltstone, wacke Matinenda Formation Arkose, subarkose, quartz wacke, uraniferous quartz pebble conglomerate Disconformity Thessalon Formation (3500) Basalt, andesite, rhyolite, basaltic andesite, minor arkose, pebble conglomerate Dis conformity Livingstone Creek Formation (+ 1000) Subarkose, clast supported conglomerate, quartz arenite Unconformity EARLY PRECAMBRIAN (ARCHEAN) Late Intrusive Diabase, Rocks gabbro dikes Intrusive Contact U �-5-Plutonic Rocks Porphyritic quartz monzonite, granitic gneiss, migma t it e Intrusive Contact Metavolcanic-metasedimentary belts Mafic to felsic metavolcanics, metasedirnents, gabbro and porphyry intrusions Sources of Information: Frarey, 1977. Robertson et al, 1969. Bennett et al, 1975. U �1 1 — J LEGEND FOR FIGURE 1 Formation LAKE GROUP — ————— EARLY PRECAMBRIAN BASEMENT Livings tone Creek Formation Thessalon Formation ELLIOT LAKE GROUP Matinenda Formation HOUGH QUIRKE LAKE GROUP Gowganda Formation Lorrain Gordon Lake and Bar River Formations COBALT GROUP DIABASE LATE PRECAMBRIAN AND PALEOZOIC E'H NIPISSING I ____ I 4. Highway — — with number I II a__I h Thrust fault (Hanging wall) Fault Symbols �M. S S Superior Lake - ,' -s-- ...4. .It. Figure I j((tS of jrJortfl2tth &ibI'n pE,L&hy,J.,ord kobertsJA., 919. FrneyMJ-, I?fl s S Jonj. IkIwl.J G3I Field Iip 51095 Souls Ste. MorirthessolOfi Area Geotogy and Field Slops t (if �I —7— The conglomerate member consists of clast supported cobble to boulder conglomerate with coarse sandstone interbeds. The granitic megaclasts are typically pale grey in contrast to the pink to reddish granitic rocks which make up much of the basement. Clasts of diorite, gabbro, quartz and mafic volcanics are subordinate to the granitic component. granite The sandstone member forms the bulk of the Livingstone Creek Formation. This unit consists predominantly of fine to medium-grained, grey subarkose and arkose displaying planar and trough cross-beds. Interbeds of siltstone, mudstone or pebble conglomerate are rare within the sandstone member. The member is locally calcareous. An upper quartzarenite member of the Livingstone Creek Formation, up to 10 meters (30 feet) thick, has been recognized only in the Sault Ste. Marie area where it directly underlies the Thessalon flows. It is a pale grey to white, or yellowish grey, fine-grained, silicious subarkose and quartzarenite. The quartzarenite member is generally well sorted and finer grained than the subarkose member. The Livingstone Creek Formation is up to at least 1,200 feet (350 m) thick in the Sault Ste. Marie area. Frarey (1977) gives the thickness of the Livingstone Creek Formation in the Thessalon area as up to 300 feet (100 m). The Thessalon Formation: The Thessalon Formation (Frarey, 1967) is a predominantly volcanic sequence near or at the base of the Huronian Supergroup west of the nose of the Quirke Lake Syncline. The distribution of the Thessalon Formation is shown in Figure 2. The Thessalon Formation is underlain by the Livingstone Creek Formation as far east as the Crazy Lake area. In the Dollyberry Lake and Pecors Lake areas the Thessalon Formation lies directly on the Early Precambrian basement. Drill logs indicate that the Livingstone Creek Formation is missing throughout the Quirke Lake Syncline. In the Sault Ste. Marie and Aberdeen Townships areas the Thessalon Formation is up to at least 3,500 feet (1000 m) thick. In the Thessalon area the Huronian volcanics are about 1,500 feet (450 m) thick, but may be thicker under Lake Huron. In the Quirke Lake Syncline drill hole data indicates thickness from 0 to about 500 feet (150 m) of Thessalon Formation is present. b �cx 48' I I FEB Ii Paleozoic Rocks Grenville Province Rocks Sudbury Irrupttve Whitewater Group Rocks 10 kitom.tert LN Hutonian Superyroup -1 ftjj Archean Cc,. 0 0 8: Copper (]iIf Fo,r,iolion FEB Huronian Vokonic Rocks El Slobie Formation the Spiogge 111 Solinay I.ole Fotmotion (including and Runt Volcancs) El [Isle Mountain Formal,on Thesso$on Formation FIGURE 2 Presence confirmed by drilling Subsurface EnSenf [I Thenolon [ Dollyberry tale Area Presence assumed [.j Duncan iwp Area [ Aberdeen Twp Area [1 Crazy tale Arm NI Priors Fake Area H Cooper Lake Area Gabbro Anorthosile Rocks ni. 8 a 48 N.' —' lot �I -9Thin lenses of coarse, poorly-sorted arkose and quartz pebble conglomerate are locally present at the base, or intercalated with the lowermost few flows, of the Thessalon Formation. These clastic units are in places pyritic and radioactive. These radioactive quartz pebble conglomerates are not correlated with the uranium bearing Matinenda Formation of the Elliot Lake area because thin elastic units, lithologically identical to these at the base of the Thessalon Formation in the Sault Ste. Marie-Thessalon area, occur at the base of the Thessalon Formation in the Dollyberry Lake and Crazy Lake areas (Figure 2). At the latter location the Matinenda Formation overlies the volcanic rocks and there is evidence of disconformity between them. The available whole rocks chemical analyses suggest that the volcanic rocks of the Thessalon Formation can be subdivided into two groups or members, an (upper) tholeiitic basalt member, and a (lower) mixed member. There is some interfingering of these members, and in the Sault Ste. Marie area the mixed member is locally missing or very thin so that the basaltic member rests on the Livingstone Creek Formation. The mixed member varies in content from area to area. In the Sault Ste. Marie and Aberdeen Lake areas the mixed member is predominantly basaltic andesite with minor hawaiite. In the Thessalon area icelandite, rhyolite, tholeiitic andesite, high-magnesium tholeiitic basalt and mugearite are present. In the Dollyberry Lake area mugearite, hawaiite rhyolite, volcanic breccia and high-magnesium tholeiitic basalt, tholeiitic basalt and andesite have been identified. The (upper) tholeiitic basalt member is prominent in the Sault Ste. Marie and Aberdeen Lake areas where it is about 1,500 feet (500 meters) thick. The basalt member is thinner in much of the Thessalon area and apparently missing in the Dollyberry Lake and Pecors Lake areas of the Quirke Lake Syncline. The Thessalon Formation typically exhibits a greenschist mineralogy. The basalts are made up of albite, clinozoisite epidote, actinolite, chlorite and oxides. Primary clinopyroxene is locally preserved in basalts of the Sault Ste. Marie area. The icelandites and basaltic andesites generally contain biotite and stilpnomelane in addition to albite, chlorite actinolite epidote and quartz. Many, if not all of the volcanic rocks of the Thessalon Formation have undergone varying degrees of metasomatic alteration involving mainly addition of Na20, grain or loss of K)0, and loss of calcium. Spilitization is especially pron&inced in some parts of the Sault Ste. Marie area where metabasalts have soda contents of over 5 percent. �I - 10 Explanation - of Table 2: 1. Average analysis of tholeiitic basalt, Thessalon Formation, Thessalon area. 2. Average analysis of icelandite. Lower mixed member, Thessalon Formation, Thessalon area. 3. Average analysis of high magnesium basalt. Mixed member, Thessalon Formation, Thessalon area. 4. Average analysis of basaltic andesite. Mixed member, Thessalon Formation, Duncan Township area. 5. Average Hawaiite-mugearite. Mixed member, Thessalon Formation, Dollyberry Lake area. 6. Rhyolite. Mixed member, Thessalon Formation, Dollyberry Lake area. �j 1 59.03 50.65 14.26 2.43 S102 A1203 Fe203 1.304 0.174 1.31 0.28 0.02 0.14 0.78 0.89 0.28 7.78 3.31 0.58 1.02 0.13 0.023 0.21 0.20 2.12 0.28 99.32 12 103 81 Na20 K2O Ti02 S MnO CO2 1120+ H20- Total n Cr Ni 5 5 12 99.23 3.01 4.07 3.61 341 885 5 99.28 0.44 1.606 0.38 0.19 0.021 0.78 2.28 9.99 9.38 CaO 1.92 6.01 10.41 Mg0 7.41 10.32 1.94 9.89 50.46 3 FeO 2.47 14.04 2 1 Analysis No. Major Components in Weight Percent Trace Elements in Parts per Million CHEMICAL ANALYSES OF HURONIAN VOLCANIC ROCKS - 42 22 11 99.99 0.43 2.16 0.62 0.19 0.06 0.38 1.99 1.27 4.71 5.54 4.21 9.64 2.69 14.3 51.8 4 TABLE 2 6 5 51 — 8 1 99.8 0.38 0.51 0.09 0.04 0.03 0.23 0.75 4.07 3.66 0.94 0.62 2.23 1.08 14.5 70.5 43 9 100.21 0.41 1.80 0.19 0.17 0.07 0.42 2.27 0.95 5.90 4.65 2.73 9.51 4.15 15.3 51.69 5 �I - 12 - Rock names assigned using the Irvine and Baragar (1969) procedure were scrutinized by examination of immobile elements such as Ti, P, Al, Cr, Ni. A triangular diagram of TiO/P9Oç/ AlO proved useful in grouping the volcanic rocks. th Jener cation plot (Jensen, 1976) aided the classification of subalkaline rocks. The Matinenda Formation: The Matinenda Formation is the host of the major uranium deposits of the Elliot Lake area, and is by far the most commercially significant formation of the Huronian Supergroup. The Elliot Lake deposits and enclosing rocks are described by Robertson (1968, 1976), Roscoe (1969), Piennar (1963), Theis (1973), and others. In the Quirke Lake Syncline the Natinenda Formation overlies the volcanic rocks of the Thessalon Formation or, where the Thessalon Formation is absent, it lies on the Early Precambrian basement (Bennett, 1979a). The writer knows of no specific locality, either in outcrop, in mine workings, (personal communication with mine geologists) or from diamond drilling (Leahy, 1973) where rocks of the Matinenda Formation interfinger with the Thessalon volcanics. In at least two localities a regolith is preserved at the top of the Thessalon Formation in the Quirke Lake Syncline. It is the conclusion of the writer that a significant disconformity exists between the Thessalon and overlying Matinenda Formation. This is in contrast to the view held by Bottrill (1971) that the Matinenda Formation and the Huronian volcanics are essentially coeval. A unit of pale grey to yellowish subarkose overlying the Thessalon Formation in the Thessalon area and at one locality in the Sault Ste. Marie area is assigned to the Matinenda Formation by the writer (Bennett, l977a, l977b) In these areas the nature of the contact with the Thessalon Formation could not be determined. The Aweres Formation: A thick sequence of conglomerates and sandstones which overlie the Thessalon Formation in the Sault Ste. Marie area was termed the Aweres Formation by McConnell (1926) The lowermost member of the Aweres Formation is a discontinuous unit of clast-supported, metabasalt conglomerate up to 300 feet (100 meters) thick. Megaclasts �U - 13 - in the metabasalt conglomerate are more than 807 mafic metavolcanics of the Thessalon Formation with scattered megaclasts of grey sandstone from the underlying Livingstone Creek Formation. With increasing stratigraphic height the granitic clasts become more abundant in the conglomerates and the proportion of arkose matrix generally increases. This polymictic conglomerate member passes upward into a mixed conglomerate-sandstone member and finally into a member comprised mainly of arkose, subarkose with some wacke and siltstone as well as subordinate matrix-supported and clast-supported conglomerates. The total thickness of the Aweres Formation may be as much as 6,000 feet (2,000 meters), but this may be an exaggeration since there may have been a considerable primary dip. The correlation of the Aweres Formation has been a problem for some time. McConnell (1927) placed the Aweres Formation at the top of his "Soo Series" which included the Duncan (Thessalon Formation) and the Driving Creek (Livingstone Creek) Formation. The Soo Series was placed by McConnell directly below the Bruce Group (the present Bruce Formation). Hay (1964) considered the Aweres Formation equivalent to the Serpent Formation; and Roscoe (1967) correlated the Aweres Formation in the Mississagi Formation of the Hough Lake Group, and noted the presence of conglomerates resembling the Ramsay Lake Formation. Frarey (1977) tentatively correlated the lower, conglomeratic part of the Aweres Formation with the Ramsay Lake Formation and the sandstone-rich upper part with the Mississagi Formation. In 1977 the writer found, in the Sault Ste. Marie area, conglomerate resembling those of the Aweres Formation overlying yellowish, sericitic sandstone which he correlated with the Matinenda Formation (Bennett, 1976, l977b) The writer favours correlating the Aweres Formation with the Mississagi Formation and the Ramsay Lake Formation. The Aweres Formation appears to represent an alluvial fan complex formed as a clastic wedge at the base of a prominent fault scarp. The coarse, proximal deposits of the Aweres Formation may pass laterally and vertically into the Mississagi Formation. �U -14- I The Hough Lake, Quirke Lake, and Cobalt Groups: Each of these groups contains a repeated litho— logical assemblage which begins with matrix-supported conglomerate followed by mudstone, siltstone or limestone, and completed with the deposition of a thick sandstone sequence (Table 1) (Roscoe, 1967) The conglomeratic sequences (Ramsay Lake, Bruce, and parts of the Gowganda Formation) contain much matrix— supported conglomerate generally held to be glaciogenic. The only limestone in the Huronian is found in the Espanola Formation which is probably of shallow marine origin (Young, 1973) and represents the earliest record of platform sedimentation (Frarey and Roscoe, 1970). The thick cross-bedded arenite sequences (the Mississagi, Serpent and Lorrain Formations) had sources areas on the Archean craton to the north, northwest, and west (McDowell, 1957, Long, 1978, Hadley, 1968) For the most part these formations are fluvial (braided stream) deposits laid down on a great outwash plain (Frarey and Roscoe, 1970, Long, . 1978) A shallow marine or beach environment of deposition has been advocated for parts of the Lorrain Formation (Hadley, 1968, Pettijohn, 1970). It has been pointed out (Piennar, 1963; Roscoe, 1968; Frarey and Roscoe, 1970) that regoliths developed below the Matinenda Formation are depleted in iron, in contrast to more recent soils. Also, rocks of the lower three groups of the Huronian are drab coloured while those of the Cobalt Group, in particular the Lorrain and Gordon Lake Formations, contain reddish and maroon coloured hematite-bearing beds. Pyrite, apparently of detrital origin, is abundant in parts of the Matinenda Formation and is common in the Mississagi Formation but generally lacking in rocks of the Cobalt Group. These features have been interpreted as evidence for a change from essentially reducing atmosphere to an atmosphere containing free oxygen (Frarey and Roscoe, 1970). The large uranium deposits of the Elliot Lake area are considered by most recent workers to be of a placer or modified placer origin. The transportation of uraninite by surface streams is believed to be possible only under reducing atmospheric conditions (Roscoe, 1968). �U -15II A RIFT MODEL FOR HURONIAN SEDIMENTATION By G. Bennett and D. G. Innes The concept of a rift through Lake Huron is not entirely new. Kumarapeli and Saul (1966) postulated a westward extension of the St. Lawrence Valley rift passing along the north shore of Lake Huron to join the Lake Superior rift. Innes (1977) completed a detailed study of the Huronian volcanics in the Sudbury area and proposed that the volcanics were fissure eruptions associated with cratonic rifting. He noted the significance of the alkalic volcanics in the Dollyberry Lake area. The following is a scenario in an attempt to interpret the features of the Elliot Lake Group in an intracratonic rift environment. Early Rifting Stage: The Livingstone Creek Formation is interpreted as being deposited in a graben or graben complex with a conglomeratic sequence along fault scarps and a more distal sandstone facies. A period of relative crustal stability permitted the weathering and reworking of the Livings tone Creek sands to produce an upper quartzarenite member. a. Tectonic uplift, somewhere east of the present Elliot Lake area, bevelled the Livingstone Creek Formation. The upper quartz arenite member was removed east of the Sault Ste. Marie area and the entire sequence was eroded away in the Quirke Lake Syncline. b. Main Rifting Stage: Volcanism begins initially from central vents to provide the icelandite, rhyolite, tholeiitic and mildly alkalic rocks of the lower part of the Thessalon Formation. c. Rifting and volcanism continues with voluminous eruption of subaerial tholeiitic basalt which forms the upper member of the Thessalon Formation. d. A return of uplift east of the present Elliot Lake area causes a bevelling of the Thessalon Formation. The upper tholeiitic volcanic sequence is removed in the Quirke Lake Syncline and the entire formation is eroded further e. east. �U - 16 - f. Thermotectonic subsidence following the cessation of Thessalon volcanic activity results in an influx of sands and quartz and pyrite-rich gravels of the Matinenda Formation in the Elliot Lake area. In the Massey-Sudbury area volcanism is renewed with the extrusion of thick sequences of tholeiitic basalts of the Elsie Mountain and Stobie Formations, and finally the eruption of rhyolites of the Copper Cliff Formation. g. The gabbro-anorthosite complex (Agnew Lake Formation) between Massey and Sudbury were probably emplaced during one of the volcanic episodes. An earlier statement that the intrusive complex was equivalent to the Thessalon Formation and unconformably overlain by the volcanics of the Sudbury area (Bennett and Innes, 1979) did not stand up under further field investigations (our own) (Bennett, 1979) Late Rifting Stage: The end of Huronian volcanic activity is followed by a period of thermotectonic collapse. Some of the subsidence took place along one of the rift boundary faults which was later reactivated as the Murray Fault. The slowly subsiding basin is filled by fine clastic detritius of the McKim Formation. h. i. This elongate zone of subsidence and structurally weakened crust provides the initial trough for sedimentation from the craton. The basin expands laterally under the continuing load of Huronian sediments now represented by the Hough Lake, Quirke Lake, and Cobalt Groups. Perhaps other equally detailed scenarios may be constructed to account for the observed features of the Huronian Supergroup. However, the writers feel that any scheme to explain the origin of the Huronian basin must place emphasis on the rocks of the Elliot Lake Group, since these are the oldest preserved Huronian rocks. The Elliot Lake Group is atypical of Huronian sequences, since the former contains the only volcanic rocks of the Huronian succession. The volcanic suite contains tholeiitic and alkalic rocks typical of rift environments and large gabbro-anorthosite intrusions (or intrusion) with a stratigraphic position similar to that of the Duluth Complex of the Lake Superior Rift System. The Elliot Lake Group does not contain the conglomeratemudstone-arenite cycle of the overlying grQups. There is evidence of significant erosion intervals within the Elliot �I - 17 - Lake Group, and formations of the oldest Huronian group tend to be discontinuous or more variable in lithology and thickness along strike than formations of the overlying groups. Given a Huronian rifting event it is tempting to look upon the Penokean tectonism and magmatic events as the closing stage of a Wilson Cycle. Unfortunately the area south of the Huronian belt is covered by Phanerozoic rocks and it is not possible to choose between an intracratonic and continental marine environment for the bulk of the Huronian Supergroup. �____ U -17a—I LEGEND FOR FIGURE 3 I MIDDLE PRECAMBRIAN L+1 Nipissing Diabase Gabbro, diabase, granophyre HURONIAN SUPERGROUP Hough Lake Group Mississagi Formation E:::::] Subarkose, arkose, pebble conglomerate Elliot Lake Group Matinenda Formation Su1arkose, grit, conglomerate Thessalon Formation Mafic to intermediate metavolcanics Felsic Metavolcanics Livings tone Creek Formation Subarkose, granite-cobble conglomerate EARLY PRECAMBRIAN kU Felsic plutonic rocks S ymb — 01 S Fault (inferred) Strike and dip of bed or flow Anticlinal axis 0:7 Highway with number Secondary road �— (FJ Field Trip Slops Figure 3 + 4. + • + + + o I. - M11c3 J kdonifre Geology and Field Stops Thessalon Area LAKE HLIRON L----- -. • t I __________ C I. I. I. I. I. I_I. L LA- L LILLLL LL I. I. I. I. I. I. LI. LI. I. I. I. I. I. LI. I LI. I. I. I. I. I. I. LLLLLLLLLL I. I. L L I. L LLL I. I. I. I. L LLLL LLI. L L L L LI. LLLL I. LLLL I. I.I.I.LI.LLLLLLLLLL LLI.LLLLLLLLLI I. C - I. - I. I. I. - I. I. I. L I. I. I. I. I. I. I. I. I. I. I. I. I. I. I. ennefl in prepQrcxhorl Irorey1 1977. L, L, LLL lnformgtIL V'-. I. L L Source5 of 'L.) I. I. I. I. I. LC LI.L LLLLLI.LL LI. LI.LI. I. LI. I. I. LLLLLLI.LLLLLLLLLL LI. LI. I. LLLLI.LLI. I. LLLLLLLI.LI.L LI. LL LI. LI. LI LI. I.LLLI.I.I.LLLLI.LL ILL LI. LLL_r.,CI.LLLLLLI.I. I I. i-LI. .1 I. I LI. LI.I.LI.LLLLI.LLLLLI.LCLLL LLI.LI. LI.LLLCLI.LLLLLI.I.I.LLI L C L C L C C I.I. I.LI.LLI.LLLLLLLLI.LL L L L I. I. L = I. C L I. I. I. LI.LLI.I.I.I.I.L I.LLLI.I.LI.LLI.L LLLLLLI.LLLLLLLI- LI LLLLLLLLLL LI.LI. LLLLLLLL LLLLLLI LI.LL LLI.L LLLLLLLI.LI.LLLLLL LI. LI. i-LI. I. CCLI. LI. I. CLI. LLLI. I. I. LI. LI. CLI LI. I. LI.I.I.LL I. LI.LL I. LLL I. LI- I. I. LI. LI.I I.LLLI.LI.LLLLLLI.LI.LL I. L LI. I. LI. LI. LII. I. I. LI. I. LI. LI. I. I. I. I. LLLLLI. LI. LL L LI. I. LILLL-LLLLI.LLL LLI.LLLLI.I. I. LLLLL LI. LI. LI. LLLLI. LI. I. CLI. LLLL LI. CLLI. LLI.LI.I. - LLI.LI.LI.I. LLLLCLI.I.L LLLLL _LLLLL I.LLL - LI. LI. I. LI. LLLLLL LI. L LI. LI. I-I. LI. LI. I. LI. I. LI. LII. I. LL L LLLLLL L I. LLI. LLLL LLLLI.LI.ILL I. I. LI.:ILLCl LLI./LLLLLLLI.LL LLLLLLLI-LI. I. I- LI. I.LI. LLLLL LI. I. I. LI. LI. _I. LLLLLLLLLI.LI I. L C LL LLLL I. L LL I. LI. LLLLLLLLLL LI. LI. LI. LI. LLI. LI. LL I. LI. LI. LI.L LL I. ri-LI. LCI.LCI.LLLLLLL LI. LI. ILL LI. LI. L ti-I. LLI. I. ILL LI.I LI. L!LI. I. I. LI. LI.LLL LI. I.I. LI.LLLI. I. I. L I. I. I. LI. I. C LI. II.L LLL ILL LLLL I.LLLI.LLA L Kirkwood 1 �I - 18 - Description of Stops and Roadlog for the Huronian Supergroup in the Sault Ste. Marie •and Thessalon Areas Time constraints are uncertain. To allow for flexibility some optional stops have been included. Also included are some locations and very brief descriptions for those following the guide at their leisure. DAY 1: HURONIAN STRATIGRAPHY IN THE THESSALON AREA (Figure 3) The mileage count begins at the intersection of Highway 17 and Highway 129 at the town of Thessalon about 80 km (50 miles.) east of Sault Ste. Marie. KM MILES 00 00 Intersection of Highway 129 and Highway 17. at Thessalon. Continue east on Highway 17. Count begins at 0 km. 6.0 3.7 Pine Ridge Road and Highway17 east. right (south) on to Pine Ridge Road. 8.5 1.6 At Lake Huron.Cross causeway on foot to small, rocky island with boat house. This is private property. You should contact Guaranty Trust Realtor, Sault Ste. Marie, Ontario, for permission to enter. Stop 1 - Livingstone Creek Formation. STOP 1 Turn LIVINGSTONE CREEK FORMATION CONGL0RATE The clast-supported conglomerate is pale-grey to white weathering with megaclasts mainly of grey equigranular and porphyritic granitic rocks and subordinate mafic rocks. The maximum clast size is about 70 cm with most in the 5-25 cm range. The sparse matrix is poorly sorted grey a.rkose. A few arkose lenses are crudely cross-bedded. The gradational contact with the basement Early Precambrian granitic rocks is exposed on one of the small islands about .250 m (800 feet) east of here. At that location massive granite gives way to angular blocks of grey granite separated by sandstone. Over a few meters this regolith zone grades into clasts.upported conglomerate (See Robertson and Card, 1972, p.10). Return to vehicle at northwest end of causeway. �U - 19 KM MILES 00 00 STOP 2 - Outcrop west of road - Stop 2. LOWER (MIXED MEMBER) OF THESSALON FORMATION South end of Pine Ridge Road - Rocks here are dark grey-green, fine-grained tholeiitic andesite with areas of epidote alteration up to a meter across. A chemical analysis from near the shore of Lake Huron, about 100 m (300 feet) west of here, indicates the volcanics are tholeiitic andesite with a low TiO content (O.777). Similar volcanics have been ound near the base of the volcanic sequence in the Dollyberry Lake area. • Proceed north on Pine Ridge Road. .8 .5 Pink to redgranite along the road. Note contrast with colour of conglomerate clasts at Stop 1. 1.1 .7 Partly leichen covered outcrop east of road - Stop 3. REGOLITH BELOW LIVINGSTONE CREEK FORMATION STOP 3 The regolith here is a breccia comprised of blocks of grey granite and gneiss separated by fine-grained grey sandstone. The breccia probably formed as sand sifting down through a coarse rubble or talus. The blocks represent bleached equivalent of red and pink granite and gneiss found nearby. The bleaching is generally considered to be due to reduction of ferric iron under the influence of a reducing atmosphere. 1.7 STOP 4 1.1 Low outcrops along road - Stop 4. THESSALON ARKOSE Along east side of road are low outcrops of grey, coarse, poorly sorted arkose of the Thessalon Formation. Similar sandstones are found in the Sault Ste. Marie, Aberdeen Lake, and Dollyberry Lake areas. The Thessalon sandstones are found as thin discontinuous units between the Livingstone Creek Formation and the volcanics, or intercalated with the lowermost flows. �I - 20 KM - MILES The fine—grained volcanics in the area are icelandite in composition. They can usually be recognized by their very dark colour and faint bluish to purplish tint as a result of abundant, very fine biotite. 2.3 1.4 Highway 17 East. Continue north on Pine Ridge Road. 00 00 2.3 1.4 STOP 5 Weir's Farm. Private land. Inquire at farmhouse before continuing - Stop 5. Continue on foot through farm yard to long outcrop ridges in field to the east. Note: if access to farm is not possible the high magnesium tholeiite described below can be seen on the east side of the road about 300 m (1000 feet) south of farm gate. HIGH MAGNESIUM THOLEIITE OF THE THESSALON FM. An average analysis of this flow is given in Table 2. The high magnesium tholeiite is a relatively pale green colour in spite of its basic composition. The mineralogy is predominantly actinolite with subordinate albite. The normative composition suggests it was originally a clinopyroxene-rich basalt. The high magnesium tholeiite contains many irregular coarse-grained areas (pegmatoid patches). A chemical analysis of one of these patches indicates composition similar to a tholeiitic basalt. High magnesium tholeiite (with pegmatoid patches) have been identified in the Dollyberry Lake and Pecors Lake areas; providing evidence for stratigraphic equivalence with the Thessalon Formation (Bennett, in preparation). Continuing eastward to the furthest outcrop ridge. These are icelandites near the base of the Thessalon Formation. See Table 2 for composition. These flows are similar to those of Stop 4. Continuing southeast along farmers trail. �I - 21 MILES - Low outcrops of Livingstone Creek subarkose. The fine-grained, grey, cross-bedded subarkose is typical of the bulk of the Livingstone Creek Formation. South of the stockyard near Thessalon Station the upper part of the Livingstone Creek sandstone is very pale-grey and yellowish grey. Chemical analysis reveals a composition typical of a Huronian regolith (Bennett in preparation). Return to Pine Ridge Road. Outcrop of radioactive Thessalon Formation pyritic conglomerate in a field west of Pine Private land; obtain permission Ridge Road. at house. Here pale-pink and rusty, pyritiferous quartz-feldspar grit and conglomerate is This unit is at or exposed in a low outcrop. near the base of the Thessalon Formation. Note fresh appearance of pink feldspar ?Iphenocrysts?v as clasts in grit and conglomerate. -Assay indicates the radioactivity is due mainly to Very similar thorium (50 ppm, 0.1 lb./ton). radioactive conglomerate occurs at the base of the Thessalon Formation in the Crazy Lake area. Return to Highway 17 via Pine Ridge Road. Proceed west on Highway 17. 00 00 Highway 17 and Pine Ridge Road. 3.19 2.0 Turn off on to road to south. Field with old barn due south of turn-off. This is private Permission to enter may be obtained property. from owner who resides on north side of road just east of turn-off. Low outcrops in field Stop 6. near barn are rhyolite. STOP 6 RHYOLITE OF THESSALON FORMATION This is pink to grey, fine-grained rhyolite with large flattened amygdules filled with quartz and biotite or stilpnomelane. Dark staining is due to local concentration of The rhyolite consists mainly of a pyrite. fine-grained mosaic of albite, k-feldspar and quartz with very minor green pleochroic biotite. h �U - 22 KM - MILES Since this area is located near the crest of an anticlinal structure we are near the base of the Thessalon Formation. A felsic volcanic center was located in this area or perhaps under Lake Huron to the south. 00 00 Return, to Highway 17. 2.6 1.6 Intersection of Highway 129 and Highway 17. Outcrops of tholeiitic basalt are located just north of Highway 17 on Highway 129. Stop 7. STOP 7 Proceed west. THOLEIITIC BASALT OF THESSALON FORMATION The dark green amygdaloidal metabasalt consists mainly of fine albite, chlorite, epidoteclinozoisite, leucoxene, and minor quartz and oxides. The larger amygdules are generally concentrically zoned with quartz-calcite-epidote being a common sequence. Small amygdules are chlorite, quartz, calcite or epidote. This outcrop is located near the top of the Thessalon Formation. 00 .5 00 .3 Continue north on Highway 129. Low outcrop of very pale sandstone on east side of Highway 129 is Matinenda Formation. Stop 8. STOP 8 MATINENDA FORMATION SANDSTONE Fine-grained,pale pink to pale yellowish sandstone displays well developed trough crossbedding and yellow (sericitic) partings between beds. The trough cross-beds and sericite are typical of the Matinenda Formation but the fine-grain size is not. This rock type occurs as a unit up to a few hundred feet thick directly overlying the volcanics. The contact between the two was not observed in this area. Return to junction of Highway 129 and Highway 17. 00 00 Proceed west (turn right) on Highway 17. Outcrops found along the highway for the next five kilometers, with few exceptions, are Nipissing gabbro and part of a large sill which extends as far west as Bruce Mines-. �U -23MILE S 15.6 9.7 Waltonen Road. Continue on Highway 17. Oi.tcrops of Mississagi Formation on both sides of highway. Stop 9. MISSISSAGI FORNATION STOP 9 This is grey to pinkish-grey cross-bedded subarkose of the Mississagi Formation. Pebbly layers are mainly quartz, black chert and very sparse jasper. Very fine pyrite is concentrated in thin, continuous layers along fore-set beds and in the narrow pebble conglomerate layers. With a hand lens it can be seen that the pyrite is largely crystalline in outline while the distribution strongly suggests a detrital origin. Recently Innes and Colvine (1979) have suggested that the Huronian Supergroup is a potential host of base metal and gold deposits of sedimentary origin. Continue west on Highway 17. Town of Bruce Mines. 20 11.4 Junction of Route 561 and Highway 17. Town of Bruce Mines. Bruce Mines is the location of the first known copper deposits in the north shore region. Development work began on the veins in 1846 and production took place intermittently until 1921. Production statistics are incomplete but the grade appears to have been between 3 and 47 copper over five feet. Some orebodies were continuous for a length of over 1800 feet (550 m) The deposits are fissure veins of quartz, carbonate, chalcopyrite and bornite in Nipissing diabase and related granophyre (Frarey, 1977, Knight, 1915) Mineralized quartz vein in diabase outcrop on north side of Highway in Bruce Mines. Stop 10. STOP 10 MINERALIZED QUARTZ VEIN The vein is about 2 m (6 feet) wide but appears to pinch toward the northwest. It may be divided into three zones which are, from east to west, disseminated bornite and chalcopyrite in quartz, chalcopyrite, bornite, chalcocite and quartz: quartz-diabase breccia. The host �U - 24 - rock is Nipissing gabbro and granophyre. Some of the old workings can be seen just north of the highway. Thanks to the efficiency of the Cornish miners who first worked these veins, there is very little high-grade material left at the surface. YOU ARE THEREFORE ASKED NOT TO TAKE SAMPLES OF THIS VEIN. This is the last stop of Day 1 - Continue west on Highway 17 to Sault Ste. Marie. �____ U - 24a - LEGEND FOR FIGURE 4 —I LATE PRECAMBRIAN I I Jacobsville Formation Sandstone, siltstoné, conglomerate MIDDLE PRECAMBRIAN Nipissing Diabase Gabbro, diabase, granophyre r+ HURONIAN SUPERGROUP COBALT GROUP Lorrain Formation Quartzarenite, quartz-pebble conglomerate, arkose Gowganda Formation Paraconglomerate, siltstone, mudstone, arkose HOUGH LAKE GROUP E: Aweres Formation Arkose, subarkose, paraconglomerate, basalt cobble conglomerate, orthoconglomerate ELLIOT LAKE GROUP kI Thessalon Formation Tholeiitic basalt, basaltic andesite, spilite, arkos Li Livings tone Creek Formation Subarkose, granite cobble conglomerate, quartzarenit EARLY PRECAMBRIAN LLL1 Felsic Plutonic Rocks Quartz monzonite, gneissic granite, rnigrnatite ij1I1th Metavolcanic Rocks Mafic metavolcanics, amphibolite SYMBOLS 'w-' — jiuiu.. 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NJ �U - 24c - ISLAND LAKE AREA (FIGURE 4) DAY 2: The mileage log begins at the junction of Highway 556 and Highway 17 in the village of Heyden, about 15 km (10 miles) north of Sault Ste. Marie on Highway 17. KM MILES 00 00 Turn right (east) on Highway 556. 7.4 4.6 Abandoned section of Highway 556 branches off to the right. Turn off onto abandoned The abandoned section is highway and park. washed out about 100 m (100 yards) ahead. Vehicles with very low ground clearance may park a few hundred feet ahead on the right Walk north along old side of the road. highway to washout and from there walk about 500 feet (200 m) through the bush in an easterly to east-southeasterly direction as Ear as theAlgoma Central Railway track. Proceed northeast along the track to outcrops of dark green metabasalts of the Thessalon Stop llA. Formation. STOP hA SPILITES OF THE THESSALON FORMATION Dark green, massive and amygdaloidal spihite of the tholeiitic basalt member is exposed along both sides of the track. Amygdules up to 3 cm across contain quartz, epidote, pink Black chlorite amygdules albite, and calcite. a few millimeters across are characteristic of the mafic rocks of the Thessalon Formation. Amygdaloidal flow tops and flow breccia are found near the southwest end of the outcrop. Thin seams of chalcopyrite occur along fractures and veins of epidote, pink albite, and calcite are common. Primary clinopyroxene are generally presented in the basalts of this area. The soda content is from 3 to over 5 percent. Proceed southwest on the track across a gully which marks a fault between the volcanics and Stop llB. the overlying Aweres Formation. �U - 25 STOP 11B - AWERES FORMATION Clast-supported and matrix-supported conglomerates of the Aweres Formation are exposed in rock-cuts and outcrops along the tracks. The predominant megaclasts are mafic volcanics and granitic rocks with minor subarkose and dark chert in a matrix of coarse, poorly sorted subarkose and subwacke. Bedding planes are poorly defined. Continuing up-section the matrix becomes more abundant and contains many angular, shard-shaped fragments a few centimeters or less in size. A few pyrite nodules up to 12 cm across occur in the upper part of this section. The coarse arkose which makes up much of the upper part of the Aweres Formation is not exposed along the railway track section. A few kilometers south of here in Jarvis and Aweres Townships the conglomerates are found intercalated with coarse, poorly sorted arkose. The writer believes that the Aweres Formation represents a thick clastic wedge deposited along prominent fault scarps. KM MILES Return to Highway 556 either by continuing along the track or proceeding to the right through the bush for a few hundred feet (100 m). Continue east on Highway 556. 9.6 STOP 12 6.0 Rock-cut on the right. Stop 12. GOWGANDA MIXITE AND THESSALON SPILITE This is a good example of matrix-supported conglomerate (mixite) of the Gowganda Formation in fault contact with glomeroporphyritic spilite of the (upper) tholeiite basalt member of the Thessalon Formation. The conglomerate consists of clasts of pink granitic rocks, dark green volcanics and some quartz pebbles in an abundant dark green wacke This type of conglomerate is generally matrix. considered a tillite. �I - 26 - Using Irvine and BaragarTs (1971) procedure, the glomerophyritic volcanic would be classified as hawaiite, as would many of the upper tholeiitic basalts. The low Ti02 (0.7), low P205 content (0.077), and cromium content (110 ppm) shows that it is not. It is a spilite with over 4.87 total alkalis. The mineralogy is clinopyroxene, albite, chlorite, actinolite, epidote, and leucoxene. Turn round and proceed west for about 5 km (3 miles) on Highway 556 to the junction with Highway 552. Park near railway track on Highway 552 and locate a bush road on west side of Highway 552 near railway track. Continue on the bush road or trail which continues west and then turns north, up the A few hill for about 500 m (1500 feet) outcrops of brecciated granitic rocks and a small, low outcrop of fine-grained, red Keweenawan felsite dike is exposed on the One of the mineralized exploration trail. trenches of the Nystedt copper prospect is found near the trail near the crest of the . hill. Stop 13. NYSTEDT COPPER PROSPECT STOP 13 - Chalcopyrite occurs as seams, disseminated grains and massive patches in pink quartz syenite and breccia. Veinlets and disseminated grains of specular hematite are common in the surrounding rocks. This is one of four known major surface showings in the immediate area; a fifth occurs just east of Highway 552. Kennco Explorations (Canada) Ltd. optioned the property in 1965-66, and carried out a diamond drilling program. Assays from one diamond drill hole returned 0.78 copper over 95.3 feet. The copper deposits are set in pink syenite and chloritic granite-breccia consisting of fragments of gneissic and massive granite in a matrix of quartz, chlorite and feldspar. The granite breccia extends to the east of Highway 552 and there is well exposed in rock-cuts along the highway. Return to Sault Ste. Marie. �U - 27 - HURONIAN STRATIGRAPHY EAST OF SAULT STE. MARIE DAY 2 (Figure 1) Proceed east from Sault Ste. Marie on Highway 17 to the town of Echo Bay, a distance of about 25 km (15 miles). Turn left on Highway 638 in Echo Bay. 00 00 Town of Echo Bay. 1.1 1.3 Highway 638 East to Leeburn - 6.5 4.2 Outcrop on south side of highway. One to twofoot (.5 m) quartz-specular hematite vein in white, pale yellow medium-grained quartzarenite of the Lorrain Formation. 10.9 6.8 McCarroll Lake Road - Continue on Highway 638. 11.8 7.4 High rock-cut along both sides of road. turn left. Stop 14. GORDON LAKE FORNATION STOP 14 The rocks here are from the transition zone between the Gordon Lake Formation and the underlying Lorrain Formation. Rocks are pink to white fine-grained, well sorted silicious subarkose to quartzarenite with well developed cross-beds.. Ripple marks and slickensides are found on some partings. Sandstone sequence contains a narrow unit of laminated ferruginous siltstone with green (sericitic) partings. An east-west trending, 1 to 2-foot wide (30-60 cm) hematitic shear zone with wide flanking bleached zones is located near the east end of outcrop. 7.2 10.7 Gordon Lake Road - Continue on 638, left turn. 23.6 14.7 Bass Lake Road - Continue on 638. 24.4 15.1 Village of Leeburn.. 49.7 30.9 Center Line Road - Continue on 638, turn left. 31.8 19.8 Poplar Dale Road - 32.4 20.1 Route 638 - Continue on 638, turn left. MacKay Road - turn turn right on 638. left onto MacKay Road. �I - 28 ai MILES 34.3 21.3 STOP 15 - Proceed about 100 yards (100 m) north on MacKay Road to abandoned farm house on the Harnden farm. This is private property. Obtain permission to enter from resident of house east of Harnden farm. Proceed northwest on foot to pale grey outcrops on hill west of farm house. The outcrops on the north slope of the hill are outcrops of Mississagi Formation. Stop 15. MISSISSAGI, BRUCE, ESPANOLA, AND SERPENT FORMATIONS Pale grey subarkose of the Mississagi Formation display well developed cross-bedding with cosets about a meter thick. These exposures are typical of the upper half of the Mississagi Formation. The lower half of the formation is generally finer-grained, darker grey and approaches a subwacke in composition. A few hundred feet (less than 100 m) to the south is grey weathering, matrix-supported conglomerate of the Bruce Formation. The predominant clasts are granite, mafic metavolcanics, and quartz in an abundant, dark, quartz wacke matrix. This is the second of the extensive mixite units in the Huronian and like the Ramsay Lake and Gowganda mixites is generally considered to be a tillite. Further to the southwest the Espanola Formation is exposed. The Espanola Formation consists of three members: The Bruce limestone, the Espanola siltstone member, and the Espanola dolomite member. Only the Bruce limestone member is exposed here. The Bruce limestone member consists of alternating thin layers of pale grey, white or pink limestone and dark grey argillite and siltstone. The Bruce lime-. stone is generally highly deformed. Some discussion has arisen over whether or not the tight folding is tectonic or syndepositional (Young, 1973a, Frarey, 1977) The distinctive appearance and composition of the Espanola Formation along with its widespread distribution makes the Espanola Formation the most useful stratigraphic marker in the Huronian Supergroup. The Espanola Formation is overlain by the Serpent Formation, the lowermost part of which is exposed on a south-facing steep slope just �I - 29 KM - MILES south of the Espanola Formation outcrops. In this area the lowermost part of the Serpent Formation consists of a thin unit of tightly packed polymictic conglomerate with well rounded cobbles of granite, maic igneous rocks and small fragments of Bruce limestone (Frarey, 1977). Continuing to the south one, comes upon exposures of pale pink, mediurn-grained, well sorted, massive subarkose, which makes up most of the Frarey (1977) gives the Serpent Formation. composition of the subarkose at this location asquartz (807), plagioclase (20%) with traces of chlorite, zircon, tourmaline or hornblende and opaques. 000 000 Return to intersection of Highway 638 and 561. Turn left (south) on 561. 1.1 0.7 Polymictic matrix-supported conglomerate of the Gowganda Formation is exposed on both sides of road. 2.0 STOP 16 1.2 Large outcrop ridge west of road. Stop 16. GOWGANDA FORMATION Near the road thin beds of fine-grained, pink weathering sandstone are interbedded with dark green mudstone and siltstone. The sandstone beds have undergone considerable deformation and disruption which appears to have been the result of syndepositional slumping. A mixite0unit striking about 150° and dipping The about 45 south overlies the mudstone. mixite consists of rounded to angular clasts of granitic rocks up to over a meter (3 feet) long in an abundant dark green, wacke matrix. Just above the mixite unit, mudstone and siltstone contains large, well rounded balls of pink weathering sandstone producing an ttintraformational mixite". A 10-meter 30 feet) wide Nipissing type diabase strikes 140 near the crest of the outcrop. The features and relationships displayed in this exposure are typical of much of the middle part of the Gowganda Formation in the Sault Ste. Marie area. �U - 30 KM MILES Continue south on Highway 561. 7.4 4.6 The rocky, hill ½ to 1 mile to the west of the road reveal four of the six members of The most distant hill the Lorrain Formation. consists of the upper white quartzite member, the pinkish summit of the nearest hill is part of the upper red quartzite member; this is underlain by the jasper conglomerate member (white from a distance) which is in turn underlain by the, mostly tree covered, lower red quartzite member. The remaining purple siltstone and basal arkose members are further to the north but cannot be distinguished from this point. Mount Zion Road - Cotinue on Route 561. 8.1 5.0 Outcrops of jasper conglomerate. Stop 17. JASPER CONGLOMERATE OF THE LORRAIN FORMATION STOP 17 The jasper conglomerate (known locally as "puddingstone") is probably the most distinctive and attractive rock in the north shore area. It consists of rounded to angular pebbles up to 7 cm (3 inches) of quartz and abundant vancoloured Jasper. The jasper conglomerate and intercalated white quartzarenite units make up the jasper conglomerate member of the Lorrain This member is up to 200 m (600 feet) Formation. thick (Frarey, 1977). 8.5 5.3 Large, high outcrop area to the right (west) of Stop 18. Upper red quartzite. the road. UPPER RED QUARTZITE OF THE LORRAIN FORMATION STOP 18 The outcrop consists mainly of well cross-bedded, poorly sorted, reddish quartzarenite, with thin pebble conglomerate interbeds. The red colouring Thin seams of detnital is due to fine hematite. grey hematite can be seen along fore-set beds and within continuous layers of quartz and jasper The upper red quartzite pebble conglomerate. member varies from 260 m (850 feet) to as much as 20 m (1700 feet) (Frarey, 1977) Continue south on Highway 561. 9.5 5.9 Outcrop of white quartzite Ledyit Line Road. on west side of road. Stop 19. �I - 31 KM - I MILES STOP 19 UPPER WHITE QUARTZITE MEMBER OF LORRAIN FORMATION The outcrop consists mainly of white, to pink, medium-to-coarse-grained quartzarenite with scattered pebble layers. This is the uppermost and thickest member of the Lorrain Formation. It is the thickest member, about 740 m (2400 feet) (Frarey, 1977). — 12.8 7.8 Village of Rydal Bank. 00 00 Highway 561 turns left. Plurnmer road straight ahead. Proceed on Plunimer Road. 3.8 2.4 Plummer Road and West Road. Outcrops of Gordon Lake Formation on west side of West Road about 100 m (100 yards) north of junction. Stop 20. STOP 20 GORDON LAKE FORMATION Thinly bedded and laminated, fine-grained sandstone, siltstone, mudstone and chert are exposed here. Frarey (1977) suggests that some chert may be the result of the diagenetic replacement of siltstone. Curving, and branching mud cracks in mudstone beds are filled with fine sandstone. The Gordon Lake Formation contains sedimentary structures indicative of a stable, low energy environment, probably nearshore marine to littoral or in part lagoonal (Frarey, 1977). See Wood (1973) for a discussion of the depositional environment of the Gordon Lake Formation. Proceed northwest on Plummer Road. 7.2 4.5 Center Line Road. 8.3 5.2 Outcrops of white quartzite to the right (north). Continue to top of hill and park. Stop 21. Continue on Plununer Road. BAR RIVER FORMATION STOP 21 Almost all of the Bar River Formation consists of thick bedded, white quartzarenite similar in most aspects to the upper white quartzite of the Lorrain Formation. The rocks here are white to pale yellow quartzarenite with little visible structure. 00 00 Return to Center Line Road via Plunimer Road. Turn right (south on Center Line Road). �• U-s 3 t —— I * I 500 2000 Alteration feet (000 metres 3000 — a rknse • bjacke — GOUCAIIDA FOR1IAT!ON I is tone, conglomerate. EIIT1 titnia tutu' • ci Arkose, quartzite, conglomerate IIURONIA'4 SUPERGLOUP JORRA III FOROATION breccia LEGEND McGreQ 561 /'Highway 4 Radicactive occurrence NIFISSIN(; F ROTE ROZO IC JJj Gahbro, granophyre; diabase dikes 1000 4 't%%, >'—i N p Pyrite occurrence —Geological Sketch Map ol (lie McGregor Road Breccia Zone. FIGURE 5 //// I Fault (defined, inferred) SYMBOLS ::::::::::::::::.,j,,a!I ::::::::::::::::::::::::::::::::::::::: •.::c•:•:': aaaa r1 p fl �I - 32 KM - MILES Turn left (east) on Government 5.4 3.4 Government Road. 00 00 Road. 1.7 00 1.1 00 Caribou Road. 3.7 2.3 Outcrop on left (east side of road is sulfide stained outcrop of McGregor Road breccia. Fragments of Lorrain Formation arkose and quartzarenite are set in a quartz and pyrite Sulfide-rich samples gave values of matrix. 0.20 and 0.34 ounces of silver /ton). 3.8 2.4 This is private Tractor road to the right (west). Inquire at farmhouse directly east of here land. Outcrop area is located for permission to enter. about 100 m (100 yards) west of Caribou Road. (Stop 22, McGregor Road Breccia). STOP 22 Turn right (south) on Caribou Road. McGREGOR ROAD BRECCIA The McGregor Road breccia (Figure 5) is emplaced along the south side of a down-dropped fault block of basal arkose of the Lorrain Formation. The surrounding rocks are part of the Gowganda The breccia consists mainly of Formation. angular to rounded fragments of Gowgands siltstone and mudstone, and arkose, quartzarenite and jaspe.r conglomerate of overlying members of the Lorrain Formation. Fragments of jasper conglomerate are about 1000 m (3000 feet) below their stratiAlthough in places the breccia graphic position. is polymictic, there are localities where the predominant clast lithology varies (from south to north) in a manner corresponding to their original position in the Huronian stratigraphy. Near the west end of the breccia fractured Gowganda argillite is altered to a locally pyritic, hard, pink rock approaching pure albite Small radioactive occurrences in composition. (up to 10 times background) occur in the breccia. The breccia may be a fissure diatreme formed as a result of explosive degassing of magma along Alternatively, the breccia may be the a fault. result of fracturing and spalling along a dilatent zone formed along the down dropped fault block. �I - 33 KM MILES - Just north of the tractor road a Nipissing type diabase dike intrudes breccia consisting of arkose and quartzarenite of the Lorrain Formation along with brown weathering, dark green fragments of diabase. Continuing north the breccia is comprised mainly of fragments, blocks and fractured slabs of Lorrain quartzite. Continuing for about 200-300 m (yards) north and west are outcrops of pink, locally pyritic albitized, laminated mudstone of the Gowganda Formation. Continue south on Caribou Road to the Town of Bruce Mines. Turn right (west) on Highway 17. 00 00 Bruce Nines. 12.3 7.6 Village of Desbarats - Large pink outcrops of basal arkose of the Lorrain Formation just east Stop 23. of the village. BASAL ARKOSE MEMBER OF THE LORRAIN FOPNATION STOP 23 The basal arkose member is up to 500 m (1700) feet thick (Frarey, 1977). In Desbarats well sorted pink arkose of this member are exposed The dark spots in rock-cuts along Highway 17. commonly found in this member are due to fine hematite. Disseminated chalcopyrite and pyrite mineralization occurs in this member about 3 km (2 miles) northThe mineralization may be west of Desbarats. syngenetic but Pearson (1979) suggests a diagenetic origin. 13.3 STOP 24 8.6 Dark red to maroon outcrops of the purple siltstone member of the Lorrain Formation are exposed along the highway. Stop 24. PURPLE SILTSTONE MEMBER OF THE LORRAIN FORMATION This unit is a thick bedded, massive, fine-grained arkose and, silts tone with a hematitic matrix. It appears to be a relatively local, true red bed, and is evidence for an oxygen bearing (The unit is atmosphere during its deposition. about 30 m (100 feet) thick (Frarey, 1977). �U - 34 KM MILES 15.3 9.5 - I "Ripple Rock". Thinly bedded arkosic sandstone of the Lorrain Formation displays excellent examples of asymmetrical ripple marks. This outcrop is a designated historical site and should not be defaced. End of Field Trip - Return to Sault Ste. Marie. i �I - 35 - SELECTED BIBLIOGRAPHY OF THE HURONIAN ROCKS OF THE SAULT STE. MARIE AREA Bennett, G. 1977a: Huronian Volcanism, District of Algoma and Sudbury; pp. 102-103, in Summary of Fieldwork, 1977, by the Geological Branch, edited by V.G. Milne, 0. L. White, R. B. Barlow, and J. A. Robertson; Ontario Geological Survey Misc. Paper 75, 208p. *Bennett, G. 1978: Huronian Volcanism, Districts of Algoma and Sudbury, pp. 105-111, in Summary of Fieldwork, 1978, by the Ontario Geological Survey, edited by V. G. Milne, 0. L. White, R. B. Barlow, and J. A. Robertson; Ontario Geological Survey Misc. Paper 82, 235p. Bennett, G. l979a: Huronian Volcanism, Districts of Algoma and Sudbury; pp. 84-85, in Summary of Fieldwork, 1979, by the Ontario GeologicalSurvey, edited by V. G. Milne, 0. L. White, R. B. Barlow, and C. R. Kustra; Ontario Geological Survey Misc. Paper 90, 245p. Bennett, G. 1979b: The McGregor Road Breccia Zone, District of Algoma; pp.82-83, in Summary of Fieldwork, 1979, by the Ontario Geological Survey, edited by V. C. Mime, 0. L. White, R. B. Barlow, and C. R. Kustra; Ontario Geological Survey Misc. Paper 90, 245p. Bennett, G. 1979c: Geology of the Two horse Lake Area, District of Algoma; Ontario Geological Survey Open File Report 5277, 99p. with uncoloured geological map at 1 inch to ¼ mile. Bennett, G., Hillier, R.D., Nentwich, F., Dupuis, C,P.. and Pucovsky, M. 1975: Jarvis Lake—Garden River Area, District of Algoma; Ontario Div. Mines, Prelim. Map. Pp. 1064, Geol. Ser., scale 1 inch to ¼ mile or 1:15,840. *Bennett, G., Sawitsky, E., and Whittaker, P. 1976: Jarvis Lake-Duncan Township Area, District of Algoma; Ontario Div. Mines, Prelim. Map P1190, Geol. Ser., scale 1:15,840. Bennett, G., and Sawiuk, M. 1979: Jarvis Lake-Garden River Area, Southern Part, District of Algoma; Ontario Geological Survey, Prelim. Map P2241, Geol. Ser., scale 1:15,840. *See Addenda, page 42. �U - 36 - Bottrill, T.J. 1970: Geology and genesis of uranium deposits in the Huronian and associated geology, Blind River, Sudbury, and Gowganda areas, Ontario, (41 I, J, 0, F); in Report of Activities, Part A: April to October, 1969, pp. 57, 58; Geol. Surv. Can., Paper 70—i, pt. A, 25lp. Bottrill, T.J. 1971: Uraniferous conglomerates of the Canadian Shield; PP. 77-83,. in Report of Activities, Part A, Geol. Surv. Canada Paper 71-7; (R.G. Blackadar, editor), 259p. Card, K.D., Church, W.R., Franklin, J.M., Robertson, J.A., West, G.F., and Young, G.M. 1972: The Southern Province; PP. 336-379, in Variation in Tectonic Styles in Canada; edited by R. A. Price and J. W. Douglas, G.A.C. Special Paper No. 11, 688p. Card, K.D., and Pattison, E.F. 1973: Nipissing Diabase of the Southern Province, Ontario; in Huronian Stratigraphy and Sedimentation, pp. 7-37, edited by G. I. Young; Geol. Assoc. Canada Special Paper No. 12, 27 lp. Casshyap, S.M. 1969: Petrology of the Bruce and Cowganda Formations and its Bearing on the Evolution of Huronian Sedimentation in the Espanola-Willisville Area, Ontario (Canada); Palaeography, Palaeoclimatology, Palaeoecology, 6 (1969), PP. 5-36. Casshyap, S.M. 1971: Petrology and Sedimentation of Huronian Arenites, south of Espanola, Ontario; Can. J. Earth Sci., V. 8, pp. 20-49. Chandler, F.W. 1973: Geology of McMahon and Morin Townships, District of Algoma, Ontario Div. Mines CR112, 77p; accompanied by Map 2272, scale 1 inch to ½ mile. Chandler, F.W. 1976: Geology of the Saunders Lake Area, District of Algoma; Ontario Div. Mines CR155, 46p.; accompanied by Map 2331, scale 1 inch to ½ mile (1:31,680). Chandler, F.W., Young, G.M., and Wood, J. 1969: Diaspore in Early Proterozoic Quartzites (Lorrain Formation) of Ontario; Can. J. Earth Sci., v; 6, pp. 337-340. Church, W.R. 1971: The Nature and Evolution of Proterozoic and Phanerozoic Orogenic Belts; Abstract, Geol. Assoc. Canada, Mineral Assoc. Canada, Abstracts and Program, Sudbury, pp. 14-15. �I - 37 - Collins, W.H. 1925: North Shore of Lake Huron; Geol. Surv. Canada Mem. 143, l86p. Douglas, R.J.W. 1980: Proposals for Time Classification and Correlation of Precambrian Rocks and Events in Canada and Adjacent Areas of the Canadian Shield. Part 2: A Provisional Standard for Correlating Precambrian Rocks; Geol. Surv. Canada, Paper 80-24, l9p. Frarey, M.J. 1967: Three New Huronian Formational Names; Geol. Surv. Canada Paper 67-6, 3p. Frarey, M.J. 1977: Geology of the Huronian Belt Between Sault Ste. Marie and Blind River, Ontario; Geol. Surv. Canada Memoir 383, 87p., with four geological maps at a scale of 1:50,000. Frarey, M.J., and Roscoe, S.M. 1970: The Huronian Supergroup North of Lake Huron; in Synposium on Basin and Geosynclines of the Canadian Shield; A. J. Baer, ed., Geol. Surv. Can. Paper 70-40, pp. 143-158. Gay, A.L., and Grandstaff, D.F. 1980: Chemistry and Mineralogy of Precambrian Paleosols at Elliot Lake, Ontario, Canada; Precambrian Research, Vol. 12, No. 1-4, pp. 349-373. Giblin, P.E., Leahy, E.J., and Robertson, J.A. 1979: Sault Ste. Marie-Elliot Lake Sheet, Algoma, Manitoulin and Sudbury Districts; Ont. Dept. Mines Compilation Series, Map 2419, scale 1 inch to 4 miles (1:253,440). Original compilation by Compilation 1974-76. P. E. Giblin and E. J. Leahy, 1964, Map 2108, 1967. Grandstaff, D.E. 1980: Origin of Uraniferous Conglomerates at Elliot Lake, Canada, and Witwatersrand, South Implications for Oxygen in the Precambrian Africa: Atmosphere; Precambrian Research, Vol. 13, No. 1, pp. 1-26. Sedimentology of the Huronian Lorrain Hadley, D.G. 1968: Formation, Ontario and Quebec, Canada; Unpub. Ph.D. Thesis, Johns Hopkins University, Baltimore, Maryland, 3Olp. Sault Ste. Marie, Dist. of Algoma; Geol. Hay, R.E. 1961: Surv. Can., Map 26-l96l,scale 1 inch to 1 mile. The Geology of the Sault Ste. Marie Map Hay, R.E. 1963: Area; unpublished Ph.D. Thesis, McGill University, 325p. �I - 38 - Hughes, C.J. 1972: Spilites, Keratophyres and the Igneous Spectrum; Geol. Mag. Vol. 199, PP. 513-527. Innes, D.G. l972 Proterozoic Volcanism and Associated Suiphide Bearing Metasediments in the Sudbury Area, Ontario; unpublished B.Sc. Thesis, Laurentian University, 65p. Innes, D.G. 1977: Proterozoic Volcanism in the Southern Province of the Canadian Shield; unpublished M.Sc. Thesis, School of Graduate Studies, Laurentian University (Sudbury, Ontario), l5Op. Irvine, T.N., and Baragar, W.R.A. 1971: A Guide to the Chemical Classification of Common Volcanic Rocks; Canadian Jour. Earth Sci. Vol. 27, pp. 179-203. Jensen, L.S. 1976: A New Cation Plot for Classifying Subalkaline Volcanic Rocks; Ont. Div. Mines, Misc. Paper 66, 22p. Kimberly, M.M., Tanaka, R.T., and Farr, M.R. 1980: Composition of Middle Precambrian Uraniferous Conglomerates in the Elliot Lake-Agnew Lake Area of Canada; Precambrian Research, Vol. 12, No. 1-4, pp. 375-392. Knight, C.J. 1966: A Study of Rb-Sr Whole-Rock Ages of Volcanics on the North Shore of Lake Huron, Ontario, Canada; M.I.T.-138l-l4, Fourteenth Ann. Rep. (1966), U.S. At. Energy Comm. Contract AT (3O-l)-l38l, pp. 129-139. Knight, C.W. 1915: The North Shore of Lake Huron; Ont. Bur. of Mines Ann. Rept., Vol. 24, Pt. 1, 1915, pp. 216-241. Kumarapeli, P.S., and Saul, V.A. 1966: The St. Lawrence Rift Valley System: A North American Equivalent of the East African Rift Valley System; Can. Jour. Earth Sci., Vol. 3, pp. 639-658. Leahy, E.J. 1973: Diamond Drilling in the Huronian Supergroup, Sault Ste. Marie-Elliot Lake Area; Ont. Div. Mines, Geol. Br. Open File Report 5093. Lindsay, D.A. 1967: The Sedimentology of the Huronian Gowganda Formation, Ontario, Canada (With Special Reference to the Whitefish Falls Area); unpub. Ph.D. Thesis, The Johns Hopkins University, Baltimore, Maryland, 295p. �U - 39 - Lindsay, D.A. 1969: Glacial Sedimentology of the Precambrian Gowganda Formation, Ontario, Canada; Geol. Soc. America Bull., Vol. 80, PP. 1625-1702. Long, D.G.F. 1976: The Stratigraphy and Sedimentology of the Huronian (Lower Aphebian) Mississagi and Serpent Formations; unpublished Ph.D. Thesis, University of Western Ontario, 29lp. Long, D.G.F. 1978: Deposition Environments of a Thick Proterozoic Sandstone: The (Huronian) Mississagi Formation of Ontario, Canada; Canadian Jour. Earth Sci., Vol. 15, No. 2, pp. 190-206. McConnell, R.G. 1926: Sault Ste. Marie Area, District of Algoma; Ont. Dept. Mines, Vol. 35, Pt. 2, pp. 1-52 (Published 1927). Accompanied by Map 35a, scale 1 inch to 2 miles. McDowell, J.P. 1957: The Sedimentary Petrology of the Mississagi Quartzite in the Blind River Area. Ont. Dept. Nines, Geol. Circ. No. 6, 3lp. McLennan, S.M., Fryer, B.J., and Young, G.M. 1979: The Geochemistry of the Carbonate-Rich Espanola Formation (Huronian) with Emphasis of the Rare Earth Elements; Canadian Jour. Earth Sci., Vol. 16, No. 2, pp. 230-239. Moore, E.S. 1929: Ore Deposits near the North Shore of Lake Huron; Ont. Dept. of Mines, Vol. 38, Pt. 7, (published in 1930). Ovenshine, A.T. 1964: Glacial Interpretation of the Precambrian Gowganda Formation, North Shore of Lake Huron, Canada; Geol. Soc. Am., Abstr. (ann. mtg.), pp. 146. - Palonen, P.A. 1973: Paleogeography of the Mississagi Formation and Lower Huronian Cyclicity; in Huronian Stratigraphy and Sedimentation, ed. G. M. Young; Geol. Assoc. Canada, Spec. Paper 12, Pp. 157-168. Parviainen, E.A.U. 1973: The Sedimentology of the Huronian Ramsay Lake and Bruce Formations, North Shore of Lake Huron; unpublished Ph.D. Thesis, University of Western Ontario, London, Ontario. Pearson, W.N. 1978: Copper Netallogeny, Lake Huron, Ontario; Current Research, Part A, Geol. Surv. Canada, Paper 78-lA, pp. 263-268. �U - 40 - Pearson, W.N. 1979: Copper Metallogeny, North Shore Lake Huron, Ontario; Geol. Surv. Canada, Paper 79-lA, Current Research, pp. 289-304. of Pettijohn, F.J. 1957a: Paleocurrents of Lake Superior Precambrian Quartzites; Geol. Soc. Am., Bull., v. 68, pp. 469-480. Pettijohn, F.J. 1970: The Canadian Shield: A Status Report, 1970 (and discussion); in Symposium on Basins and Geosynclines of the Canadian Shield, ed. A. J. Baer, pp. 239-255, 262-265; Geol. Surv. Can., Paper 70-40, 265p. Pienaar, P.J. 1963: Stratigraphy, Petrography and Genesis of the Elliot Group, Blind River, Ontario, including the Uraniferous Conglomerate; Geol. Surv. Can., Bull. 83, l4Op. Robertson, J.A. 1963: Geology of the Iron Bridge Area; District of Algoma; Ont. Dept. Mines Geol. Rept. No. 17, 69p. Robertson, J.A. 1968: Geology of Township 149 and Township 150, District of Algoma; Ont. Dept. Mines Geol. Rept. 57, l62p. Accompanied by Maps 2113 and 2114, at a scale of 1 inch to mile. Robertson, J.A. 1976: The Blind River Uranium Deposits: The Ores and their Setting; Ontario Div. Mines, M.P. 65, 4Sp. Robertson, J.A., Frarey, M.J., and Card, K.D. 1969: The Federal-Provincial Committee on Huronian Stratigraphy: Progress Report; Ontario Dept. Mines and Northern Affairs, MP31, 26p. Robertson, J.A., and Card, lCD. 1972: Geology and Scenery, North Shore of Lake Huron; Ont. Mm. Nat. Resour., Geol. Guidebook No. 4, 224p. Roscoe, S.M. 1969: Huronian Rocks and Uraniferous Conglomerates; Geol. Surv. Can., Paper 68-40, 205p. Rupert, R.J., Leahy, E.J., and Mirza, 5. 1972: Subsurface Stratigraphy, Blind River-Elliot Lake Sheet, Dist. of Algoma; Ont. Div. Mines, Geol. Compil. Ser., Prelim. Map 753. Sims, P.1K., Card, K.D., Morey, G.B., and Peterman, Z.E. 1980: The Great Lakes Tectonic Zone: A Major Crustal Structure in Central North America; Geol. Soc. Am. Bull., Pt. 1, Vol. 91, pp. 690-698. h �U - 41 Syrnons, D.T.A., Wander and Volcanics; No. 7, pp. - and OtLeary, R.J. 1978: Huronian Paleomagnetism of the Thessalon Canadian Journal Earth Sci., Vol. 15, 1141-1150. Van Schmus, W.R. 1965: The Geochronology of the Blind River-Bruce Mines Area, Ontario; J. Geol., v. 73, pp. 755-780. Van Schmus, W.R. 1976: Early and Middle Proterozoic History of the Great Lakes Area, North America; Royal Soc. London, Phil. Trans., Ser. A., v. 280, pp. 605-628. Wood, J. 1970: Evidence for a Tropical Climate and Oxygenic Atmosphere in Upper Huronian Rocks of the Rawhide Lake-Flack Lake Area, Ontario (abstr.); in 16th ann. mtg. Inst. on Lake Superior Geol. program (Thunder Bay, Ont.), pp. 45, 46. Wood, J. 1973: Stratigraphy and Depositional Environments of Upper Huronian Rocks of the Rawhide Lake-Flack Lake Area, Ontario; Geol. Assoc. Canada Spec. Paper No. 12, pp. 73-95, edited by G.M. Young. Young, G.M. 1969: Geochemistry of Early Proterozoic Tillites and Argillites of the Gowganda Formation, Ontario, Canada; Geochim. Cosmochim. Acta, v. 33, pp. 483-492. Young, G.M. 1971: Stratigraphic and Sedimentological Framework of the Huronian Rocks of the Southern Province of the Canadian Shield; Abstract, Geol. Assoc. Canada, Mineral Assoc. Canada, Abstracts and Program, Sudbury, 1971, pp. 75-76. Young, G.M. l973a: Origin of Carbonate-Rich Early Proterozoic Espanola Formation, Ontario, Canada; Geol. Soc. Am., Bull., v. 84, pp. 135-160. Young, G.M., and Chandler, F.W. 1968: Possible Glacial Origin for Three Precambrian (Huronian) Conglomerates, North Shore of Lake Huron (abstr.); in 14th ann. mtg. Inst. on Lake Superior Geol. programSuperior, Wis.), pp. 42, 43. �U - 42 - ADDENDA: Bennett, C. 1977b: Garden River Indian Reserve Area, District of Algoma; pp. 104-106, in Summary of Fieldwork, 1977, by the Geological Branch, edited by V.G. Mime, O.L. White, R.B. Barlow, and J.A. Robertson, Ontario Geological Survey Misc. Paper 75, 208p. Bennett, C., and Innes, D.C. 1979: Huronian Volcanic Rocks, North Shore of Lake Huron, Ontario; 25th Annual Institute on Lake Superior Geology, Duluth, Minnesota, pp. 8. Bennett, C., and Innes, D.G. (in preparation): Huronian Volcanism, Ontario Geological Survey, Geological Report. � 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, 1981 Description An account of the resource Institute on Lake Superior Geology. Michigan State University, East Lansing, Michigan. May 14-15, 1981. 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 1981 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Contributor An entity responsible for making contributions to the resource H. All K. Attoh R. L. Bauer H. F. Bennett M. E. Bengtson D. Bhattacharyya M. S. Breithart B. A. Brown F. W. Cambray F. H. Carlson A. Choudhry C. Craddock M. D. Daggett P. A. Daniels, Jr. S. Day M. F. Deering D. Dushek C. P. Ervin K. Fujita H. P. Gilbert S. S. Goldich J. K. Greenberg H. C. Halls J. B. Hartung T.B. HoIst J. H. Karl R. P. Meyer E. T. Mohr C. W. Montgomery R. L. Morton M. Osterberg D. S. Paddock Z. E. Peterman P. K. Sims T. E. Smith F. L. Slaughter R.J. Stevenato M. Stupavsky D. T. A. Symons, S. E. Tituskin F. B. Van Houten M. A. Vos P. Wasuwanich J. T. Wilband https://digitalcollections.lakeheadu.ca/files/original/f1d5e221c5cffdc5a211c58e555219cd.pdf b5e94ac35469c5f8f9aa1d6ea0771619 PDF Text Text rn V I CD -I Twenty- Eighth I r C') C a) Annual C) CD -' C a) 0 CD IC —U , I Cl) Institute , on Lake Superior 1< 03 ts) (0 -S 03 (31 a I (a CD 0 0 Geology w 0 Cl) CD -< -' Survey C ano- a I''I CD S. Sponsored by Minnesota Geological CD 5 a I = CD 5- a) May 5 - 8 , 1982 International Falls, Minnesota �PROCEEDINGS PROCEEDINGS S ANNUAL TWENTY - E I G H T H ANNUAL TWENTY-EIGHTH INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR INSTITUTE GEOLOGY GEOLOGY S held held at at HOLIDAY INN INN NOLIDAY Highways Highways 11 1 1 and and 71 71 International Falls, Falls, Minnesota Minnesota 56649 56649 International I May May 5—8, 5-8, 1982 1982 under under the the sponsorship sponsorshipof of I Minnesota Minnesota Geological Geological Survey Survey University of of Minnesota Minnesota University 1633 1633 Eustis Eustis Street Street St. St. Paul, Paul, Minnesota Minnesota 55108 55108 G.B. G.B. Morey Morey and and John John Splettstoesser Splettstoesser I General General Editors Editors I �I TABLE TABLE OF OFCONTENTS CONTENTS p v V GENERAL GENERAL INFORMATION INFORMATION vv INSTITUTE INSTITUTEBOARD BOARD OF OFDIRECTORS DIRECTORS LOCAL LOCALCOMMITTEE COMMITTEE VI VI GOLDICH GOLDICHMEDAL MEDALCOMMITTEE COMMITTEE VI VI SESSION SESSIONCHAIRMEN CHAIRMEN VII VII ANNUAL BANQUET BANQUET SPEAKER SPEAKER ANNUAL VII VI I GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT VII VII ACKNOWLEDGMENTS ACKNOWLEDGMENTS VII VII IX CALENDAR CALENDAR OF OF EVENTS EVENTSM4D ANDPROGRAM PROGRAM p 1 ABSTRACTS ABSTRACTS 53 FIELD FIELD TRIPS TRIPS 1) 1.• 1 MINERAL MINERAL DEPOSITS DEPOSITS OF OFTHE THEFORT FORTFRANCES-MINE FRANCES-MINECENTRE CENTRE 55 ONTARIO AREA, ONTARIO 22.• ARCHEAN GEOLOGY GEOLOGY OF THE THEINTERNATIONAL INTERNATIONALFALLS-KABETOGAMA FALLS-KABETOGaMA ARCHEM4 AREA, MINNESOTA MINNESOTA AREA, I I I III 89 �GENERAL GENERAL INFORMATION INFORMATION 28th 28th Annual Annual INSTITUTE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTEON ONLAKE Holiday Holiday Inn Inn International International Falls, Falls, Minnesota Minnesota May May 5—8, 5-8, 1982 1982 Sponsored Sponsored by by Minnesota Minnesota Geological Geological Survey Survey University University of of Minnesota Minnesota 1633 1633 Eustis Eustis Street Street St. Paul, Paul, Minnesota Minnesota 55108 55108 INSTITUTE OF DIRECTORS DIRECTORS INSTITUTE HOARD BOARD OF State University, W.C. W.C. Cambray, Cambray, Department Department of of Geology, Geology, Michigan Michigan State University, East East Lansing, Lansing, Michigan Michigan (1981) (1981) M.F. M.F. Kehlenbeck, Kehlenbeck, Department Department of of Geology, Geology, Lakehead Lakehead University, University,Thunder ThunderBay, Bay, Ontario Ontario (1977) (1977) G. G. Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University university of of Wisconsin, Wisconsin, Milwaukee, Milwaukee, Wisconsin Wisconsin (1978) (1978) P.E. P.E. Myers, Department Department of of Geology, University University of of Wisconsin, Eau Eau Claire, Claire, Wisconsin Wisconsin (1980) (1980) R.W. R.W. Ojakangas, Ojakangas, Department Department of of Geology, Geology, University University of of Minnesota, Duluth, Duluth, Minnesota Minnesota (1979) (1979) R.C. R.C. Reed, Division, Department of Natural Reed, Geological Geological Survey Survey Division, Department of ~aturalSciences, Sciences, Lansing, Lansing, Michigan Michigan (secretary—treasurer) (secretary-treasurer) D.L. D.L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, Minnesota Minnesota (1982) (1982) V �I LOCAL LOCAL COMMITTEE COMMITTEE Conference Conference Chairman Chairman D.L. D.L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, 1633 1633Eustis EustisStreet, Street,St. St. Paul, Paul,Minnesota Minnesota55108. 55108. Conference Conference Treasurer Treasurer G.E. G.B. Morey, Morey, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University UniversityofofMinnesota, Minnesota, 1633 St. Paul, Paul, Minnesota Minnesota 55108. 55108. 1633 Eustis Eustis Street, Street, St. Field Field Trips Trips K. K. Howard Howard Poulsen, Poulsen, Queen's Queen's University, University, Kingston, Kingston, Ontario, Ontario, K7L X7L 3N6 3N6 Warren Warren C. C. Day, Day, Minnesota MinnesotaGeological GeologicalSurvey, Survey,University UniversityofofMinnesota, Minnesota, St. St. Paul, Paul, Minnesota Minnesota55108 55108 R.W. R.W. Ojakangas, Ojakangas, Department Departmentof of Geology, Geology, University UniversityofofMinnesota, Minnesota, Duluth, Duluth, Minnesota Minnesota 55812 55812 D.L. D.L. Southwick, Southwick, Minnesota MinnesotaGeological GeologicalSurvey, Survey,1633 1633Eustis EustisSt., St., St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Physical Physical Arrangements Arrangements Douglas Douglas Bergstrom, Bergstrom, Minnesota Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Mark Mark Jirsa, Jirsa, Minnesota Minnesota Geological Geological Survey, Survey,University Universityof ofMinnesota, Minnesota,St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Best Best Student Student Paper Paper Committee Committee W.F. W.F. Cannon, Cannon, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia Virginia 22092 22092 F.J. F.J. Sawkins, Sawkins, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 W.R. W.R. Zwickey, Zwickey, Kimberly—Clark Kimberly-Clark Corporation, Corporation, Neenah, Neenah, Wisconsin Wisconsin 54956 54956 MEDAL COMMITTEE COMMITTEE GOLDICH MEDAL GOLDICH C.L. c.L. Iverson, Iverson, U.S. U.S. Steel Steel Corporation, Corporation, Virginia, Virginia, Minnesota Minnesota 55792 55792 G.L. G.L. LaBerge, LaBerge, Geology Geology Department, Department, University University of WisconsinOshkOsh, Wisconsin-Oshkosh, Oshkosh, Wisconsin Wisconsin 54901 54901 Oshkosh, M.E. M.E. Ostrom, Ostrom, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, University of of Wisconsin Wisconsin — Extension, Extension, Madison, Madison, Wisconsin Wisconsin 53706 53706 University - VI �SESSION SESSIONCHAIRMEN CHAIRMEN I p R.L. R.L. Bauer, Bauer, Department Departmentof of Geology, Geology, Macalester Macalester College, College, St. St. Paul, Paul, Minnesota Minnesota55105 55105 V.W. V.W. Chandler, Chandler, Minnesota MinnesotaGeological GeologicalSurvey, Survey, St. St. Paul, Paul, Minnesota Minnesota55108 55108 J.C. J . C . Green, Green, Department Departmentof of Geology, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Duluth, 55812 Duluth, Minnesota Minnesota55812 P.L. P.L. McSwiggen, McSwiggen, Minnesota Minnesota Geological GeologicalSurvey, Survey, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 D.G. Meineke, Meriden Engineering, Hibbing, Minnesota 55746 D.G. Meineke, Meriden Engineering, Hibbing, Minnesota 55746 M.G. M.G. Mudrey MudreyJr., Jr., Wisconsin WisconsinGeological Geologicaland andNatural Natural History HistorySurvey, Survey, Madison, 53706 Madison, Wisconsin Wisconsin 53706 K.J. K.J. Schulz, Schulz, Department Department of of Earth Earth and and Planetary Planetary Sciences, Sciences, Washington Washington University, St. Louis, Louis, Missouri Missouri63130 63130 University, St. P.W. P.W. Weiblen, Weiblen, Department Department of of Geology Geologyand and Geophysics, Geophysics, University University of of Minnesota, Minneapolis, Minnesota 55455 Minnesota, Minneapolis, Minnesota 55455 I ANNUAL BANQUET BANQUET GUEST GUESTSPEAKER SPEAKER ANNUAL fice of of Marine Randolph RandolphA. A. Koski, Koski, Of Office Marine Geology, U.S. U.S. Geological Geological Survey, Survey, Menlo 94025 Men10 Park, Park, California California 94025 I GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Ralph W. Ralph W. of of Marsden, Marsden, Professor Professor&rieritus EmeritusDeparment Deparmentof ofGeology, Geology, University University Minnesota, 55812 Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 'I ACKNOWLEDGMENTS ACKNOWLEDGMENTS I The The organizing organizing committee committee of of 1982 1982 Institute I n s t i t u t e on on Lake Lake Superior Superior Geology Geology gratefully acknowledge the work of Mrs. Jeanne Perrin and Mrs. Linda Linda g r a t e f u l l y acknowledge t h e work of Mrs. Jeanne P e r r i n and Mrs. the Proceedings. Proceedings. McDonald in i n typing typing the the final f i n a l manuscript manuscript for f o r the McDonald VII VII �a a a a (I) —1 C) > -1 CI) 03 ABSTRACTS S — a �MAGNETIC INVESTIGATIONS INVESTIGATIONS OF OFTHE THEBARAGA BARAGACOUNTY COUNTY DIABASE DIABASE MAGNETIC BARAGA BARAGA COUNTY, COUNTY, MICHIGAN MICHIGAN T.D. p,nderson, Anderson, Union Oil Oil of of California, California, P.O. P.O. Box Box 76, 76, Brea, Brea, California California T.D. 92621; J.F. J.F. Diehi, Diehl, Michigan Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 92621; 4993 1 49931 ABSTRACT ABSTRACT Aeromagnetic data from parts of Aeromagnetic data from parts ofBaraga Baraga and andMarquette Marquette Counties, Counties,Michigan Michigan are are dominated dominated by by linear, linear,east—west east-west trending trendingmagnetic magnetic lows lows associated associated with with reversely • Close reverselymagnetized magnetized diabase diabasedikes dikes. Close examination examination of ofground groundmagnetommagnetom- eter profiles profiles shows shows that that prominent prominent dike dike intrusions intrusionssometimes sometimes occur occur as as eter groups of small, interrelated interrelated dikes. dikes. In In one one case case these thesedikes dikeswere were groups of 22 to to 44 small, found to thicken at 22 to km intervals intervals along along strike strikecausing causing found to thicken or or converge converge at to 33 km p in aeromagnetic • periodic maxima maxima in aeromagnetic anomalies anomalies. periodic The The ground ground magnetometer magnetometer propro- files normally exist filesalso alsoprovide provideevidence evidencethat that normallymagnetized magnetized diabase diabase dikes dikes may may exist sites in in more reversed dikes dikes at at 22 sites in in close closeassociation associationwith withthe the morecommon common reversed Baraqa County. Baraga County. The The magnetic magnetic anomalies anomalies of of Baraga Baraga County County Diabase Diabase intrusions intrusions diminish diminish in in magnitude under the the Baraga Baraga Plains Plains where where the the dikes dikes are are covered covered by by glacial glacial deposits deposits and and possibly possibly by by Jacobsville Jacobsville Sandstone. Sandstone. It was was found found that that estiestimates mates of of depth depth to to the the diabase diabase dikes dikes in In the the Baraga Baraga Plains Plains area area could could be be used used The to to interpret interpret basin basin structure structure on on the the surface surface of of the the Middle Middle Precambrian. Precambrian. The results showed evidence evidence of of aa possible possible valley or or ledge ledge in in the Middle Middle results ofof Keweenaw to the the Keweenaw Bay Bay to Precambrian representing representing aapossible possibleburied buriedextension extension Precambrian southwest from from L'Anse, LIAnse, Michigan. Michigan. southwest Several have reported Several investigators investigators have reported cells cells of of anomalous anomalous remanence remanence in in The Baraga Baraqa County County Diabase Diabase outcrops. outcrops. The variable variable intensity intensity and and small—scale small-scale in these these cells complexity of complexity of magnetization magnetization in cellsargue argue against against explaining explaining these these cells cellsasaslightning—induced lightning-induced magnetization. magnetization. Detailed Detailed paleomagnetic paleomagnetic sampling sampling of two of of these these cells cells suggests suggests that that the the observed observed patterns patterns result result from from of lightning—induced magnetization magnetization superimposed superimposed on dramatic lightning-induced dramatic susceptibility susceptibility It was variations in in the the diabase. diabase. was possible possible to to map map the the probable probable path path of of flow in in both both cases. cases. current flow It S 3 �FOLDING THE WESTERN Fl REcjjENT RECUMBENT FOLDINGININ THE WESTERN VEI4ILtON VERMILION F1 GREENSTONE-GRANITE NEMINNESOTA MINNESOTA GREENSTONE-GRANITE TERRANE, TERRANE, NE R.L. Bauer, Bauer, Department Department of of Geology, Geology, Macalester Macalester College, College, St. St. Paul, Paul, Minnesota Minnesota R.L. P.J. Hudleston, Hudleston, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of 55105; P.J. 55105; a Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT ABSTRACT granite-migmatite terrane terrane The Vermilion Vermilion Granitic Granitic Complex, Complex, aa granite—migmatite The recrystallized recrystallized in in the the amphibolite amphibolite facies, facies, is is in in fault fault contact contact along along its its southern southern boundary boundary with with the the Vermilion Vermilion district, district, aa greenstone—granite greenstone-granite Analysis terrane terrane in in the thegreenschist greenschist facies. facies. Analysis of of structural structural facing facing in in folded folded Archean Archean strata strata in in the the southern southern Vermilion Vermilion Granitic Granitic Complex Complex and and western western Vermilion Vermilion district district indicates indicates that that the the sedimentary sedimentary sequence sequence underunderwent Fl folding folding prior prior to to the the development development of of the the dominant dominant went recumbent recumbent F1 beF2 folds. folds. AA major major F2 F2 antiform antiform mappable mappable across across the the faulted faulted boundary boundary beF2 tween tween the the two two terranes, terranes, displays displays downward downward structural structural facing facing indicating indicating the the inversion of of this this portion portion of of the the sedimentary sedimentary sequence prior prior to to the the inversion To the southeast, in the Vermilion district, upward strucfolding. To the southeast, in the Vermilion district, upward strucF2 folding. F2 tural tural facing facing is is observed observed in in F2 F2folded foldedstrata. strata. The The regional regional change change in in structural structural facing facing to to the the southeast southeast is is attributed attributed to to crossing crossing of of the theaxial axial surface surface of of aa major major F1 Fl nappe. nappea Finite Finite strain strain data data determined determined from from clasts clasts in in the the greenschist greenschist facies facies sedimentary/volcaniclastic sedimentary/volcaniclastic units in the the Vermilion Vermilion greenstone greenstone terrane terrane can can be completely accounted for in terms of the deformation producing the be completely accounted for in terms of the deformation producing the to downslope downslope .F2 folds. Locally Locally intense intense F1 Fl folding folding is is therefore therefore attributed attributed to F2 folds. amphibolite facies soft sediment. However, slump slump movement movement of of soft sediment. However, amphibolite facies biotite biotite schists, making up part of the same F1 schists, making up part of the same Fl structure structure in in the the Vermilion Vermilion Granitic Granitic Complex, display display aa pronounced pronounced SSlfoliation foliationthat thatdeveloped developed parallel parallel to to Complex, We suggest that metabedding during the early stages of metamorphism. bedding during the early stages of metamorphism. We suggest that metamorphic occurring in in the lower to the the morphic dehydration dehydration reactions reactions occurring lower strata strata led led to development of high pore pressures in the upper portion of the sedimentary development of high pore pressures in the upper portion of the sedimentary ofhigh highpore porepressures pressuresand andgravitational gravitational instabilThe combination combination of instabilpile. pile. The ity during the F1 folding resulted in soft sediment slumping in the upper ity during the Fl folding resulted in soft sediment slumping in theupper strata while while the the lower lower strata strata underwent underwent strain strain and and metamorphic metamorphic strata Soft—sediment i folding recrystallization recrystallization during during F1 Fl folding. folding. Soft-sediment Fl folding in in the the Vermilion district could have led to a rather complex distribution Vermilion district led to a rather complex distribution of of Ely F l structures, Structures, because the the more competent volcanic flows, such as the Ely F1 greenstone, may may have have undergone undergone aa much much different different response response to to the the greenstone, folding. F l folding. F1 I I 4 4 �RB-SR RB-SRAND ANDSM-ND SM-ND ISOTOPIC ISOTOPIC STUDIES STUDIES OF OF PROTEROZOIC PROTEROZOICMAFIC MAFIC DIKES DIKES NORTHEASTERN MINNESOTA IN IN NORTHEASTERN MINNESOTA Warren V. Rama Kama Murthy, Murthy, Department Department of of Geology Geology and andGeophysics, Geophysics, Warren Beck Beck and and V. University of Minnesota, Minneapolis, MN 55455 University of Minnesota, Minneapolis, MN 55455 ABSTRACT ABSTRACT AA major major northwest—trending northwest-trending mafic mafic dike dike swarm swarm of of Proterozoic Proterozoic age age intrudes intrudes the 2.7 b.y.—old greenstone—granite terrane of northeastern Minnesota the 2.7 b.y.-old greenstone-granite terrane of northeastern Minnesotaand and adjacent adjacent southern southern Ontario. Ontario. Of Of these, these, two two large largevertical vertical composite composite dikes dikes a combined isotopic study. have have been been selected selectedfor for a combinedRb-Sr, Rb-Sr,Sm-Nd Sm-Nd isotopic study. These These dikes dikes intrude Complex Lake in in northeastnortheastKabetogama Lake intrudethe theVermilion VermilionGranitic Granitic Complexwest westof ofKabetogama This research was undertaken to complement petrologic ern ernMinnesota. Minnesota. This research was undertaken to complement petrologicand and paleomagnetic paleomagnetic studies studies which which are are being being done done by by David David Southwick Southwickof of the theMinneMinneHalls of sota sota Geological Geological Survey Survey and and by by Henry Henry Halls of the theUniversity Universityof ofToronto. Toronto. The dikes analyzed analyzedin in this this study colinear.Although Although The composite composite dikes study are arenearly nearlycolinear. they be followed followed continuously continuouslyon on the the aeromagnetic aeromagneticmaps, maps, we we infer inferfrom from they cannot cannot be structural, structural, petrologic petrologic and and geochemical geochemical characteristics characteristics that that they they are are probprobably ably parts parts of of aasingle singleintrusive intrusivebody. body. The The sites sites sampled sampled are are separated separated along along strike strike by by about about 2.5 2.5 km. km. An An earlier earlier reconnaissance reconnaissance of of this this dike dike swarm swarm yielded yielded K—Ar K-Ar ages ages ranging ranging from The eight eight samples samples analyzed analyzed for for the the present present study study plot plot b.y. The from 1.6 1.6 to to 2.2 2.2 b.y. The on on aa single single Rb—Sr Rb-Sr isochron isochron and and define define an an age age of of 2120 2120 t 67 67 m.y. m.y. The relarelatively ratio tively high high initial initial 87srfi6sr ^sr/^sr ratio of of 0.70449 0.70449 implies impliesthat thatthe thecrust crustwas was involved magmagenesis genesisororthat thatthe themagma magmawas wascontain— contaminvolved in in the theprocess processof ofdike dikemagma mated inatedduring duringemplacement emplacementinto intogranitic granitic rocks. rocks. The The fact fact that that samples samples from from plot on the same inner inner and and outer outer dikes dikes of of both both composite composite dikes dikes plot on the sane isochron isochron is is thethe dikes originated froom same suggestive suggestive that thatall all dikes originated froomthe the samesource. source. + The Assumin that that The Sm—Nd Sm-Nd data data from from these these dikes dikes do do not not form form an an isochron. isochron. Assuming the the emplacement emplacement age age is is 2120 2120 m.y., my., then then aa calculation calculationof of the theinitial initial '43Nd/ ^%id/ 144Nd ld4Nd isotopic isotopic ratios ratios for for these these samples samples reveals reveals that that the the source source region region for for the LREEdepleted. depleted. The The combined combined Sr Sr and and Nd Nd characteristics characteristics of of these these the magma magma is is LREE dikes (1) the the source source region region for for these these dikes dikes appears appears dikes suggest suggest 22 conclusions: conclusions: (1) to to be be in in the the mantle mantle and and not not in in the the crust, crust, and and (2) (2)the the dike dike magma magma was was subsesubsequently quently contaminated contaminated by by crustal crustal material material during during passage passage through through the the crust crust or or during during intrusion. intrusion. In In both both composite composite dikes dikes the the outer outer dike dike is is enriched enriched in in Rb Rb and and Rb/Sr Rb/Sr ratio to the the inner innerdike. dike. This This suggests suggests that that the the inner inner dikes dikes may may ratio relative relative to represent represent aa reinjection reinjection of of aa cumulate cumulate after after the themain mainpulse pulseof ofdike dikeinjecinjection. tion. 5 �STRATIFIED STRATIFIED OCEANS OCEANS AND AND THE ORIGIN ORIGIN OF OFIRON-FORMATION IRON-FORMATION William 22092 William F. F. Cannon, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia Virginia 22092 ABSTRACT ABSTRACT The great by those of great Proterozoic Proterozoic XX banded banded iron—formations, iron-formations, typified by the Lake Superior region, have long presented a geochemical enigma. Lake Superior region, have long presented a geochemical enigma. Vast quantities of iron iron must must have have been been dissolved dissolved in in and and precipitated precipitated from from seaseawater to deposits, form these yet iron is virtually insoluble water to these deposits, iron is virtually insoluble in in even even slightly oxygenated Thus, oxygenated water. water. Thus, many many investigators investigators have have concluded concluded that that anoxic water, in anoxic in which which iron iron is is more more soluble, soluble, must have have dominated dominated the the Proter— Proterozoic oceans and and that that iron—formations iron-formations were were deposited deposited as as that that water water was was ozoic XX oceans oxygenated. Most have assumed that this oxygenation of the oceans oxygenated. have assumed that this oxygenation the oceans was was aa unique event event in in the the evolution evolution of of the the atmosphere atmosphere and and hydrosphere hydrosphere caused caused by by the first appearance, roughly 2 billion years ago, of photosynthetic organthe first appearance, roughly 2 billion years ago, of photosynthetic organisms and and hence hence the the permanent permanent shift shift from from an an oxygen—free oxygen-free to to an an oxygen—rich oxygen-rich atmosphere. atmosphere. jn In contrast, contrast, research, research, largely largely in in the the petroleum petroleum industry, industry, in in the the past past few years years has has shown shown that that major major parts parts of of the the world's world's oceans oceans repeatedly repeatedly bebecame strongly strongly stratified stratified and and were were anoxic anoxic below below the the depth depth of of surface surface turbuturbulence lence for for substantial substantial periods periods of of Phanerozoic Phanerozoic time. time. These These so—called so-called ocean ocean anoxic anoxic events events took took place place during during periods periods of of major major marine marine transgression transgression and and warm Decreased oceanic warm climate. climate. oceanic circulation circulation resulted resulted from from warm warm climate, climate, and and increased increased oceanic oceanic productivity productivity resulted resulted from from equable equable climate climate and and exexpanded to create create an an panded highly highly productive productive shelf shelf seas. seas. These These conditions conditions combined combined to excess excess of of organic organic matter matter over over available available oxygen oxygen in in deep deep oceans oceans which led led to to anoxic anoxic conditions. conditions. The recurrence recurrence of ocean ocean anoxic anoxic events events throughout throughout Phan— Phanerozoic erozoic time time periodically periodically resulted resulted in in large large quantities quantities of of anoxic anoxic ocean ocean water water having relatively Mn, and PP and and probably probably relatively high high contents contents of of dissolved dissolved Fe, Fe, Mn, controlled controlled the the temporal temporal distribution distribution of of deposits deposits of of these these elements elements in in PhanPhanerozoic erozoic rocks. rocks. Such Such ocean ocean anoxic anoxic events events might might also also have have taken taken place place during during the the Precam— Precambrian, and brian, and they, they, in in addition addition to to one—time one-time only only oxidation oxidation related related to to permapermanent changes time, may changes in in the the atmosphere atmosphere and and oceans oceans during during Proterozoic Proterozoic XK time, have resulted resulted in in deposition deposition of of iron—formation. iron-formation. Thus, the the major major distinction distinction from from past past theories theories is is the the idea idea that that after after an an early early oxygen—free oxygen-free atmosphere atmosphere and ocean time, younger younger ocean may may have have been been oxidized oxidized initially initially in in Proterozoic Proterozoic KX time, oceans oceans were were probably probably capable capable of of returning returning to to anoxic anoxic conditions conditions and and depositdepositing ing iron—formations iron-formations even even in in the the presence presence of of an an oxygen—rich oxygen-rich atmosphere. atmosphere. - The Proterozoic Proterozoic KX banded banded iron—formations iron-formations of of the the Lake Lake Superior Superior region region seem by an an ocean—anoxic—event ocean-anoxic-event model model in in which which oceans oceans were were oxygenoxygenseem explainable explainable by ated both During periods iron-formation deposition. deposition. periods of of h t h before before and and after iron—formation ocean ocean anoxia, anoxia, the the deep deep oceans oceans acted acted as as geochemical geochemical sinks sinks for for iron, iron, and and the the anoxic anoxic waters waters were were enriched enriched in in dissolved dissolved iron. iron. Iron Iron was was then then precipitated precipitated in iron—formations iron-formations either either by by upwelling upwelling and and consequent consequent oxidation oxidation during during the the anoxic anoxic event event or or by by aa more more widespread widespread oxygenation oxygenation of of the the ocean ocean as as the the anoxic event event waned. waned. Iron—formations Iron-formations commonly occur occur at at several several stratigraphic stratigraphic horizons horizons in in iron—bearing iron-bearing regions (for (for instance, instance, at least least five five horizons horizons are are present present in in These repeated the of Michigan). Michigan). repeated cycles cycles of of deposition deposition seem seem the Proterozoic Proterozoic KX of more more consistent consistent with aa model model involving involving repeated repeated ocean ocean anoxia anoxia than than with with models models involving involving only only one one oxygenation oxygenation event. event. 6 �S STUDIES OF OF TUE MAGNETIC ANOMALY ANOMALY STUDIES THE NORTHERN NOBTHERN ANIMIKIE BASIN BASIN MAGNETIC • S Val W. W. Chandler, Chandler, Minnesota Minnesota Geological GeologicalSurvey, Survey,University UniversityofofMinnesota, Minnesota,St. St. Val Paul, Minnesota, Minnesota, 55108; 55108; Arthur Arthur B. B. Watts, Watts, Arco Arco Petroleum, Petroleum, Dallas, Dallas, Texas, Texas, Paul, 75221; L. Gulbranson, Gulbranson, Minnesota Minnesota Geological Geological Survey, Survey, University University of of 75221; and and Brian Brian L. Minnesota, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 Minnesota, ABSTRACT ABSTRACT Mesahi Iron Iron Range, Range, exposures exposures of of the the lower lower Except along along the the Mesabi Except Proterozoic Proterozoic Aniinikie Animikie Group Group are are widely widely scattered scattered and and wells wells penetrating penetrating to to As aa consequence, consequence, little little can can be be Archean basement basement are are nonexistent. nonexistent. As Archean • inferred inferred about about the the structure structure of of the the Animikie Animikie basin basin without without the the aid aid of of Detailed aeromagnetic data data recently recently acquired acquired by by the the geophysical data. data. Detailed aeromagnetic geophysical Minnesota Minnesota Geological Geological Survey Survey have have been been used used to to elucidate elucidate the the structure structure of of the the northern northern flank flank of of the the basin basin in in an an area area of of about about3500 3500 km2 km2 in in St. St. Louis Louis and Itasca Itasca Counties, Counties, Minnesota. Minnesota. and The The northern northern edge edge of of the the basin basin is ischaracterized characterized by by aa complex complex and and • • • (>SO0 gammas) ganmas) anomaly anomaly expression expression caused caused by by the the typically high—amplitude high-amplitude (>500 typically Biwabik Iron Iron Formation. Formation. AA broad broad zone zone with with smoother smoother anomaly anomaly expression expression and and Biwabik moderate moderate amplitudes amplitudes (100—SOD (100-500 gammas) gammas) extends extends about about 20 20 km km southward southward into into the the basin basin and and reflects reflects the the southward southward thickening thickening of of the the essentially essentially non— nonmagnetic magnetic slate slate and and graywacke graywacke of of the the Virginia Virginia Formation Formation that that overlie overlie the the iron-formation. The The anomalies anomalies within within this this zone zone are are thus thus assumed assumed to to arise arise iron—formation. , from from structures structures within within the the buried buried iron—formation iron-formation or or from from sources sources within within the the underlying underlying Archean Archean basement. basement. Beyond Beyond 20 20 km km into into the the basin basin the the magnetic magnetic anomaly character character becomes becomes extremely extremely subdued, subdued, reflecting reflecting deeply deeply buried buried anomaly anomaly anomaly sources sourcesbeneath beneath non—magnetic non-magnetic slate slateand andgraywacke. graywacke. Because the the overlying overlying slate slate and and graywacke graywacke are are essentially essentially Because non-magnetic, non-magnetic, magnetic magnetic depth depth estimates estimates will will indicate indicate source source tops tops either either in in the Archean basebase the Biwabik Biwabik Iron Iron Formation Formation or or in in the the immediately immediately underlying underlying Archean ment. Therefore Therefore these these depth depth estimates estimates should should delineate delineate the the general general shape shape ment. and and deep deep structure structure of of the the Animikie Animikie basin. basin. Depth Depth estimates estimates were were obtained obtained graphically from from maps maps and and by by computer—based computer-based estimates estimates along along flight flight graphically km profiles. The The results results reveal reveal aa gently gently dipping dipping shelf shelf out out to to about about 20 20 km profiles. south south of of the the edge edge of of the the basin, basin, where where depths depthsof of around around1 1 km kmare areindicated. indicated. AA structural structural relief relief of of aa few few hundred hundred meters meters is is inferred inferred to to be be superimposed superimposed upon this this shelf shelf along along the the southwest southwest extension extension of of the the Virginia Virginia horn. horn. upon Southward to steepen steepen abruptly abruptly to to depths depths Southward from from this this shelf shelf the the basin basin appears appears to in excess excess of of 22 1cm. km. South South of of 47N 47-Nthe thedepth depthestimates estimateson on aabroad broad east— eastin trending trending maximum maximum indicate indicate depths depths in in excess excessof of 33km. km. • The encouraging encouraging results results of of this this preliminary preliminary study study suggest suggest that that The further further geophysical geophysical work, work, including including similar similar studies studies over over the the remainder remainder of of the the basin basin and and also also seismic seismic investigations, investigations, would would be be fruitful. fruitful. The The implied implied thickening 20 km km into into the the basin basin may may reflect reflect aa transition transition thickening of of the the sequence sequence 20 from from aa stable stable shelf shelf to to the the more more mobile mobile environment environment characteristic characteristic of of the the Great Lakes Lakes tectonic tectonic zone. zone. Great S 7 �GRANITIC PHASES GRANITIC PHASES IN INTHE THENORTHERN NORTHERNBORDER BORDER ZONE ZONE THE VERMILION 0? THE VERMILION GRANITIC GRANITICCOMPLEX COMPLEX OF Warren C. Warren C . Day, Day, Minnesota Geological Geological Survey, 1633 1633 Eustis Street, St. Paul, Paul Weiblen, Weiblen, Department of Geology and Minnesota 55108; 55108; Paul and Geophysics, Geophysics, 108 108 Pillsbury Hall, 310 Pillsbury Pillsbury Pillsbury Drive SE, Minneapolis, Minnesota 55455 Vermilion Granitic an Archean granite—migmatite Granitic Complex Complex is is an Archean granite-miqmatite The Vermilion terrane which by the the extensive earlytonalite tonalite terrane which has has formed formed by extensive emplacement emplacement ofofearly to post—tectonic and syn— into supracrustal syn- to post-tectonic granite granite into supracrustal metamorphic metamorphic rocks rocks and (chiefly biotite biotite schist Two main main types of granite (chiefly schist in in the thestudy study area). area). Two granite occur along along the the northern biotite granite granite 1) aa grayish—pink occur northern border border zone: zone: 1) grayish-pink biotite and 2) Croix Granite), biotite—muscovite leucogranite. leucogranite. (Lac La Croix 2) a biotite-muscovite (Lac Granite), and Geochemical Geochemical and mineral studies studies have been been undertaken undertaken to to distinguish distinguish the the similarities and and differences two granite and to similarities differences between between these these two granite types, types, and to investigate the the origin Theresults results are are relevant investigate origin of of the theleucogranite. leucoqranite. The relevant to to the general of the the origin origin of batholithic granites granites in in the general problem problem of of late—stage late-stage batholithic greenstone—graniteterranes. terranes. greenstone-granite The Lac La Croix Granite, a major component of the Complex, occurs as batholithic phase phase and and as as the neosome portion portion of of the late—stage late-stage intrusive batholithic granite—rich migmatite. on the other hand hand occurs occurs only as as granite-rich migmatite. The leucogranite on small bodies bodies within within the neosome portions of the the schist—rich schist-rich migmatite and small the biotite biotite schist. granites are Qtz—Or—Ab abundances. However, The two two granites are similar in their Qtz-Or-Ab However, distinctive differences are seen seen in in accessory accessory phases and and in in major major element element Garnet is restricted to the and trace trace element element chemistry. chemistry. Garnet the leucogranite, leucogranite, magnetite is is common theLac LacLaLaCroix CroixGranite Granitebut butrare rare in in the whereas magnetite ,whereas common ininthe the leucogranite. The leucogranite lower in MgO, MgO, FeOt and and leucogranite. leucogranite is significantly significantly lower content in the leuco— Ti02 compared La Croix Croix Granite. Granite. The LaN Compared to to the the Lac La Lan content leucogranite ranges granite ranges from from 95 95 to to 140 140 xx chondrite. chondrite. garnet are locally developed Sillinanite, staurolite, muscovite, Sillimanite, staurolite, muscovite, and garnet within the the biotite biotite schist. schist. Thin veins of fine—grained fine-grained leucocratic leucocratic grano— granothick) and and pods podsof of pegmatite pegmatiteare are isoclinally isoclinally diorite and diorite and granite granite (few (few mm mu thick) folded and withinthe the host host biotite andandcommonly folded and boudinaged boudinaged within biotite schist, schist, commonly are are bordered by biotite selvage bordered selvage zones. zones. These veins coalesce into larger larger len— lenAs the As the ratio ratio of of leucogranite leucogranite to to biotite biotite ticular leucogranite leucogranite bodies. bodies. tends to crosscut schist increases, increases, the leucogranite leucogranite tends crosscut earlier earlier tectonic tectonic fabric. fabric. These relationships are compatible with an anatectic origin for the MgO, FeOt FeO and and TiO2 Ti02 content content of of the the leucogranite leucogranite may leucogranite. The low MgO, digestion of mafic minerals be attributed be attributed to low low degrees degrees of of (1) minerals (e.g. (e.g. (1) digestion The data biotite, amphibole, garnet, etc.) biotite, etc.) in the the source source during during melting. melting. The obtained thus far far suggest suggest therefore therefore that that the the leucogranite leucogranite is is an an anatectic anatectic supracrustal sedimentary sedimentary rocks, rocks, and and that that it it has melt produced produced from from (2) (2) supracrustal metasedimentary syntectonically into into higher portions of of moved syntectonically the metasedimentary Trace element analyses sequence. analyses are presently underway to to help help model the sequence. Trace origin of the the leucogranite. leucogranite. 8 �S HANSON GEOLOGY GEOLOGYOF OFTHE THECYPRESS, CYPRESS, HANSONANt) ANDSOUTH SOUTHARM ARM OF OF IQ4IFE KNIFELAKE LAKEAREA AREA NORTHEAST B.W.C.A., B.W.C.A., NORTHEASTMINNESOTA MINNESOTA TimothyFlood, Flood, Department Department ofofGeology, Geology, University University of ofMinnesota, Minnesota,Morris, Morris, Timothy Minnesota 56267 Minnesota 56267 ABSTRACT ABSTRACT Archean Archean volcanic volcanic and andvolcanogenic volcanogenic sedimentary sedimentary rocks rocks of of the theCypress, Cypress, Hanson and South Arm of Knife Lake area are located within the eastern Hanson and South Arm of Knife Lake area are located within the eastern vermilion vermiliondistrict districtand andlie lieininthree threeof ofGruner's Gruner's (1941) (1941)structural structuralsegments. segments. • The TheSpoon SpoonLake Lakesegment segmentisiscomposed composeddominantly dominantlyofofdacite daciteporphyry, porphyry,dac— dacThe graywacke is porphyry conglomerate and graywacke—argillite. ite porphyry conglomerate and graywacke-argillite. The graywacke isofof ite both both the thefeldspathic feldspathicand andlithic lithictype, type, and andis isinterbedded interbeddedwith with conglomerate. conglomerate. Two Twosmall smallfault faultslices slicesofofgreenstone greenstoneare arepresent presentwithin withinthe the segment segmentas asare are igneous and the sedimentary the Keweenawan diabasic dikes which intrude both Keweenawan diabasic dikes which intrude both the igneous and the sedimentary to500E 500Eand anddips dipssteeply steeplytotothe the Bedding strikes strikes predominantly predominantly 40° 400 to rocks. rocks. Bedding The Knife Lake synclinorium segment is composed southeast and northwest. southeast and northwest. The Knife Lake synclinorium segment is composed of tuff-maficconglomerate—mixed conglomerate-mixed conglomerate conglomerate unit, unit, and and aa of two twounits: units: aa tuff—mafic These two units are interbedded and gradational graywacke unit. younger younger graywacke unit. These two units are interbedded and gradational diabasicdike dikeisis present present ininthe into intoone oneanother. another. One One Keweenawan Keweenawan diabasic thesegment. segment. to near—vertical and dips Bedding strikes predominantly northeast Bedding strikes predominantly northeast and dips near-vertical tothe thenorthnorthwest. west. Significant Significant conclusions conclusions drawn drawn from from this this study study and and based based on on petrographic petrographic analysis and measurement, and interpretation of lineations, foliations analysis and measurement, and interpretation of lineations, foliationsand and primary primary sedimentary sedimentarystructures structuresinclude: include: 1) 1) The The granite granite pebble pebble conglomerate conglomerate of of the theKnife KnifeLake Lakegreenstone greenstoneunit unit (Gruner, 1941) is actually a greenstone pebble conglomerate. (Gruner, 1941) is actually a greenstone pebble conglomerate. 2) 2) source Source areas areas for for the the metasediments metasediments are are exclusively exclusively volcanic volcanic in in origin. origin. No No plutonic plutonicrock rockfragments fragmentswere wereobserved. observed. 3) 3) No No potassium potassium feldspar feldspar grains grains were were found foundeither either microscopically microscopically or or staining with sodium—cobaltinitrate, and no rock fragmentshave have by staining with sodium-cobaltinitrate, and no rockfragments by aa composition composition more more felsic felsicthan thandacite. dacite. 4) 4) No No Saganaga Saganaga detritus detritus was was deposited deposited within within the the sediments sediments and and hence hence and no no supporting supporting evidence evidence for for penecontemporaneous peneconteinporaneousvolcanism volcanism and unroof— unroofing of of the the Saganaga Saganaga batholith, batholith, as as suggested suggested by by previous previous investigainvestigaing tion, tion, was wasfound. found. 5) 5) Turbidite Turbidite sequences sequences in in all all segments segments are arecharacteristic characteristicturbidites turbidites corresponding to the theinner inneror or middle middlelobe lobeof ofa asubmarine submarinefan. fan. correspondingto 6) 6) The Knife Lake be acacThe structure structure of ofthe the Knife Lakesynclinorium synclinoriun segment segment can can be counted for in counted for in terms terms of of three three tectonic tectonic deformations. deformations. The The first first producedisoclinal isoclinal folds, deformation produced folds, the theaxes axesofofwhich which period of of deformation period to 50°E and plunge 30° to the northeast. The second second trend NN 40° 40 to 5 0  ° and plunge 300 to the northeast. The trend • • period to 60° 60- WW cleavage. cleavage. period of of deformation deformation produced produced aa pervasive pervasive NN 54° 54" to The regional scale scale and and The third third period period of of deformation deformation occurred occurred on on aa regional 9 S �produced major longitudinal faults, which have divided the present produced major longitudinal faults, which have divided the present area of study into petrographically distinct structural blocks. area of study into petrographical].y distinct structural blocks. 1 REFERENCE REFERENCE Gruner, J.W., 1941, Structural geology of the Knife Lake area of northeastStructural geology of the Knife Lake area of northeastGeological Society of America Bulletin, v. 52, p. 1577- Gruner, 1941, ern LW., Minnesota: ern Minnesota: 1642 1642. Geological Society of America Bulletin, v. 52, p. 1577— 10 �IRON-ENRICHED IRON-ENRICHED BASALTIC BASALTICFRAGMENTAL FRAGMENTAL ROCKS BOCKS ERUPTED ERUPTED IN INA ASHALLOW SHALLOWSUBAQUEOUS SUBAQUEOUS ENVIRONMENT, THE HEMLOCK FORMATION, FORMATION, AMASA AMASA QUADRANGLE, QUADRANGLE, MICHIGAN MICHIGAN ENVIRONMENT, THE HEMLOCK Charles Charles W. Geology and Graft, Department Department of of Geology and Geological Geological Engineering, Engineering, Graft, Michigan Michigan Technological Technological University, University, Houghton, Michigan Michigan 49931 49931 ABSTRACT ABSTRACT The Hemlock Formation Precambrian subaqueous The Hemlock Formation is is aa Precambrian subaqueous metavolcanic metavolcanic complex within the Oval in in Iron It isisoverlain complex within the Ainasa Amasa Oval IronCounty, County, Michigan. Michigan. It overlain by by whichoutlines outlinesthe the oval oval as the the Amasa Amasa Formation, Formation, a a banded banded iron—formation iron-formation which as The formation formation is is underlain well thethe Hemlock. well as as the theupper upper limits limitsofof Hemlock. The underlain by by the and the the Goodrich Quartzitewhich whichininturn turn rest rest on the Randville Randville Dolomite Dolomite and Goodrich Quartzite on the the Archean Archean basement of Bell Bell Creek Creek Granite Granite Gneiss. Gneiss. This study deals with formation in in thethe Amasa the the upper upper third thirdofofthe the formation Amasa7—1/2 7-1/2 minute minute quadrangle quadrangle just just east east of ofthe thetown townofofAmasa. Amasa. Approximately 5 square Approximately 5 square miles miles were mapped mapped for for correlation correlation with with the the previously mapped areas areas to the north and east in Kelso previously mapped in the the Ned Ned Lake Lake and and Kelso Thirty—five samples were analyzed Junction Junction Quadrangles Quadrangles respectively. respectively. Thirty-five analyzed for for Ten of geochemical correlation with pre—existing the Hemlock. from the Hemlock. Ten of pre-existing data data from Jesse D. these these were re—analyses re-analyses of samples taken by D . Jay Johnson (1975) (1975) and Jesse C. C . Dann Dann (1978). (1978). p lithologic variation variation occurs occurs within the the Significant chemical Significant chemical and and lithologic lithologies consist Main consist of massive Hemlock Formation. Formation. Main lithologies massive and and pillowed pillowed lavas, lavas, pillow pillow breccias, breccias, broken broken pillow pillow breccias breccias and and hyaloclastites. hyaloclastites. The first first basalts basalts of of the the Hemlock Hemlock chemically chemically resemble resemble oceanic tholeiites; later rocks rocks are are compositionally compositionally closer closer to to continental continental tholeiites. tholeiites. Minor amounts amounts The formation of rhyolite to have have been been erupted erupted in in 33 rhyolite also also occur. occur. formation appears to main cycles cycles of of volcanism volcanism with with increasing increasing iron iron enrichment enrichment (up (up to 24% FeO Iron—formations occur stratigraphically (total)). Iron-formations occur stratigraphically above above the iron—rich iron-rich (total)). these enriched enriched (icelandites). There may be a correlation between these basalts (icelandites). basalts and the basalts the deposition deposition of the the overlying overlying iron—formations. iron-formations. in shallow shallow water Hemlock was erupted in of the the Hemlock I infer that most most of I infer that because: because: a) a) there there is is aa high high percentage percentage of of interbedded interbedded volcaniclastic sedisedi- • b) the massive massive lava lava flows, flows, pillows pillows and and pillow pillow fragments fragments are ments and b) ments and vesicular. This implies implies subsidence of the the basement basement during during the the generally vesicular. emplacement of the the volcanics. volcanics. The Hemlock Formation reaches its maximum thickness of 7500 7500 m on on the the southwest southwest side side of of the the oval oval and and thins thins to to about about Johnson (1975) 750 mm to (1975) has shown shown that that this this increase increase is is to the the northeast. northeast. due to to actual actual stratigraphic stratigraphic thickening thickening and and is is not not structurally structurally related. related. Some time time after after volcanism volcanism the the rocks rocks underwent underwent low—grade low-grade regional regional metametamorphism (chlorite which was was followed by (chlorite grade in the Amasa Amasa Quadrangle), Quadrangle), which followed by the the Amasa structural structural uplift, uplift, producing producing the the oval. oval. REFERENCES igneous the Emperor igneous Major—element variation within the J .C., 1978, 1978, Major-element J.C., M.S. volcanic formations: M and Badwater Badwater volcanic complex the Hemlock and complex and the .S. Thesis, Michigan Michigan Technological Technological University. University. Dann, Dann, Johnson, D.J., D.J., 1975, 1975, Petrology of a portion of the Hemlock Formation, Formation, Iron County, Michigan: M.S. Thesis, Michigan Technological Michigan: M.S. Thesis, Michigan Technological University, University, 26 26 p.* P 11 11 �STRATIGRAPHY O' THE STRATIGRAPHY AND AND LITHOLOGY LITHOLOGY OF THEGLACIOGENIC GLACIOGENICSEDIMENTS SEDIMENT$ OF THE TWO HARBORS AREA, NORTHEASTERN THE TWO HARBORS NORTHEASTERN MINNESOTA MINNESOTA Laura Laura B. Gross, University University of of Minnesota, Minnesota, Duluth, mluth, Minnesota Minnesota 55812 55812 ABSTRACT ABSTRACT Several Several distinct distinct episodes episodes of of the the Late Late Wisconsin Wisconsin glaciation glaciation are are recorded recorded in the Quaternary deposits of the Two Harbors and. Whyte quadrangles the Quaternary deposits of the Two Harbors and Whyte quadrangles in in northeastern Ortho-tills northeastern Minnesota. Minnesota. Ortho-tills and a variety variety of of glacially glacially derived derived sediments, the Rainy Bainy and and sediments, including a clayey clayey diamicton, diamicton, are attributed attributed to the Superior lobe advances during the St. Croix and Automba phases advances during the St. Croix and Automba phases that that ococcurred The curred after after 16,000 16,000 years years B.P. B.P. The lithologic lithologic characteristics characteristics and and strati— stratigraphic distribution graphic distribution of of this this glacial glacial sedimentary sedimentary pile, along along with the origin of of the the red red clay clay are are elucidated elucidated in in this thisstudy. study. The The oldest oldest glaciation, glaciation, associated associated with the the St. St. Croix Croix phase, phase, is is reprerepresented in the northwestern part of the Whyte quadrangle by a distinctive in the northwestern part of the Whyte quadrangle by a distinctive topography topography of of the the southwest-oriented southwest-oriented drumlins drumlins (the (the Toimi Toimi drumlin drumlin field) field) and and abandoned subglacial subglacial streams. streams. These These features features are are attributed attributed to to the the Rainy Rainy lobe advance tunnel valley, valley, partially partially occupied occupied by by advance from from the the northeast. northeast. A tunnel Sullivan Lake, and small askers along Sullivan Creek were formed during ice ice Sullivan Lake, and small eskers along Sullivan Creek were formed during stagnation, when the the high high velocity velocity stream stream in in this this subglacial subglacial tunnel tunnel changed changed stagnation, when its habit from erosional to depositional. The drumlins consist its habit from erosional to depositional. The drumlins consist of of lodgelodgement till till with with aa strong strong northeast—trending northeast-trending fabric. fabric. Near Sullivan Sullivan Lake Lake glaglacial sediment thick. The drift drift is is grey grey to to brown brown (1OYR (10YR sediment is is more more than than 55 ina thick. 4/3), Large Large clasts clasts sandy to to stony, stony, with with aa sand:silt:clay sand:siltsclay ratio ratio of of 74:22:04. 74:22:04. 4/3), sandy are mainly lithic fragments of granite, granophyre, are mainly lithic fragments of granite, granophyre, greenstone, greenstone, and and gabbro. gabbro. The The glacial glacial sedimentation sedimentation associated associated with with the the Automba Automba phase phase of of the the SuSuperior lobe is recorded in a complex of deposits contained mainly lobe is recorded in a complex of deposits contained mainly in in the the Highland The sediments Highland Moraine. Moraine. sediments range range from from non—sorted, non-sorted, non—bedded non-bedded lodgelodgement ment till, till, to to supraglacially supraglacially derived derived debris, debris, including including gravity gravity flow flow deposdeposits and and well—sorted well-sorted fluvial fluvial and and lacustrine lacustrine sediments. sediments. The The lodgement lodgement till till of the brown (5YR (Sm 3/4), the Superior Superior lobe lobe is is reddish reddish brown 3/4), sandy sandy to to clayey, clayey, with a sand:silt:clay The clasts sandssi1t:clay ratio ratio of of 60:31:09. 60:31:09. clasts are are predominantly predominantly from from the the North Shore Shore Volcanics Volcanics (amygdaloidal (amygdaloidal basalt basalt and and rhyolite), rhyolite), granophyre granophyre and and red red sandstone sandstone of of Keweenawan Keweenawan age. age. The The Highland Highland Moraine Moraine is is aa hummocky hummocky kettle kettle and and kame kame topography topography in in the the northwestern northwestern part of of the the Two Two Harbors Harbors quadrangle quadrangle and and the the southeastern southeastern part part of by aa string string of of of the the whyte Whyte quadrangle. quadrangle. It It is is bordered on on its its western western edge edge by small Southeast of of small lakes, lakes, marking marking the the lateral lateral extent extent of of the the Superior Superior lobe. lobe. Southeast the abthe Highland Highland Moraine, Moraine, concentrated concentrated flows flows and and outwash outwash streams streams from from the the ablating lating Superior Superior lobe lobe deposited deposited aa variety variety of of slumped slumped glacial glacial sediments sediments and and gravel gravel lag lag debris. debris. Sediment Sediment supplied supplied from from stagnant stagnant ice ice sources sources and and melt— meltwater from from the the retreating retreating Superior Superior lobe lobe formed formed large large deltaic deltaic deposits deposits of of cross—bedded cross-bedded sands sands and and gravel, gravel, interfingered interfingered with with thin thin lenses lenses of of clay—rich clay-rich diamictons, by flow flow tills. tills. These These sediments sediments mark mark the the 348-366 348-366 mm and overlain overlain by diamictons, and strandline strandline of of Glacial Glacial Lake Lake Duluth, Duluth, aa proglacial proglacial lake lake which which formed formed along along the the margin of of the the retreating retreating Superior Superior lobe. lobe. Lacustrine Lacustrine clays, clays, deposited deposited concontemporaneously temporaneously with the the deltas, deltas, cover cover much much of of the the southern southern part part of of the the quadrangle (5YR 4/4), 4/4), with with aa quadrangle below below this this strandline. strandline. The The clay clay is is red/brown red/brown (5Th 12 �sand:silt:clay sand:silt:clay ratio r a t i oofof15:18:67, 15:18:67, and andranges rangesfrom frommassive, massive,highly highlyjointed, jointed, to finely laminated with pockets with with pebbly pebbly"lag "lagdeposits," deposits," t o f i n e l y laminated with pockets ofof "sand "sand nests," nests," to t overy veryplastic p l a s t i cand andstony. stony. It It is isexposed exposed extensively extensively along along the the lakeshore, streamvalleys, v a l l e y s , and andasa sthe t h esurficial s u r f i c i a ldeposit depositofof much much of of the the lakeshore, in i nstream North LakeSuperior. Superior. NorthShore ShoreofofLake Distinguishing till and and lake lake clay clayini nthe theLake LakeSuperior Superior Distinguishing between between clayey clayey till the south Though the red clay of region problematical. Though t h e red c l a y of t h e southshore, shore, the the region isisproblematical. "Douglas ''Douglas Till," T i l l , " isisattributed a t t r i b u t e dtot osubglacial subglacialprocesses processes(Johnson, (Johnson, 1980), l98O), my my investigation i n v e s t i g a t i o nconfirms confirmsthe t h einterpretation i n t e r p r e t a t i o nof of aalacustrine l a c u s t r i n eorigin o r i g i nof of the t h ered red clay c l a yalong alongthe t h enorth northshore shore(Moss, (Moss,1977), 1977). Restricted Restricted occurrence occurrencebelow belowhigh high association level strandlines, stacked lake terraces within the region, of l e v e l s t r a n d l i n e s , stacked lake t e r r a c e s within t h e region, association of "lag " l a g deposits," deposits," and andfine f i n elaminations laminationsindicate i n d i c a t e aa glacial g l a c i a l lacustrine l a c u s t r i n e rather rather than than subglacial subglacial origin o r i g i n for f o r the t h eclay—rich clay-rich diamicton diamicton of of the the North North Shore Shore of of Lake LakeSuperior. Superior. REFERENCES REFERENCES 1980, The The origin o r i g i n of of the the Lake Lake Superior Superior red red clay c l a y along alongWisconWisconM., 1980, Johnson, M., Johnson, sin's the Bayfield Bayfield peninsula: Peninsula: UnpubUnpubs i n ' s Lake Lake Superior Superior shoreline shoreline west west of of the lished M.S. thesis, University of Wisconsin, Madison, 90 p. l i s h e d M.S. t h e s i s , University of Wisconsin. Madison, 90 p. Moss, C.M., C.M., 1977, The The surf s u r f icial i c i a l and and environmental environmental geology geology of of the t h e French French 1977, Moss, Unpublished M.S. River quadrangle, St. Louis County, Minnesota: thesis, River quadrangle, St. Louis County, Minnesota: Unpublished M. S' thesis, University Universityof of Minnesota, Minnesota, Duluth. Duluth. I I p I I 13 �PRECAMBRIAN PRECAMBRIAN DIKE DIKESWARMS: SWARMS: PATTERNS PATTERNSAND AND PROBLEMS PROBLEMS H.C. H.C. Halls, Halls, Erindale Erindale Campus, campus, University University of of Toronto, Toronto, Mississauga, Mississauga, Ontario Ontario LSL L5L 1C6 1C6 ABSTRACT Precambrian Precambrian dikes dikes criss—cross criss-cross all all the the world's world's Precambrian Precambrianshields; shields; swarms swarms extend extend for for many many hundreds hundreds ofofkilometers, kilometers, and andobviously obviouslyrepresent represent Dikes Dikes are arecommonly commonly thought thought to to develop environment; develop in in aarift rift environment;preserved preservedswarms swarms along along the themargins margins of of the the Atlantic ~tlanticfor for example example represent represent the the earliest earliest rift rift stages stages in in the the formation formation of of this this ocean ocean during duringJurassic—Triassic Jurassic-Triassictimes. times. However However despite despite considerable considerable work work on on models models of ofrifting riftingand andsea—floor sea-floor spreading, spreading, little little work work has has been been done done on on dike dike swarms, swarms, particularly particularly the the enormous enormous Precambrian Precambrian ones ones that that are are not major question question about about not so so obviously obviouslyrelated relatedto tocontinental continentalseparation. separation. AA major these these and and younger younger swarms swarmsconcerns concernstheir theirmode modeofofemplacement. emplacement. What what is is the the form of of magma form and and location location magma chambers chambers that that fed fed these these swarms, swarms, how how has has the the magma of of dike swarm? magma flowed, flowed, and and what what controls controlsthe theorientation orientation dike swarm? major events in in Earth major magmatic magmatic events Earth history. history. Possible tothese these questions questions are are discussed discussed using using examples examples of of Possible solutions solutions to dike dike swarms swarms from from the the Canadian, Canadian, African, African, kustralian Australian and and Indian Indian 2+ 2+ Ga ca Shields. and geochemical Shields. tn In particular particular paleomagnetic, paleomagnetic, structural structural and geochemical results results will from thethe Matachewan—Hearst Kenora—Kabetogama will be begiven given from Matachewan-Hearstand and Kenora-Kabetogama swarms swarms that that have and direction of magma have bearing bearing on on regional regionalstructure structure andthe the direction of magmaflow. flow. By By analogy analogy with with more more recent recentdike dikeswarms, swarms, aaworking working hypothesis hypothesis that that shows magma dominantly sub—horizontal swarms shows promise promise is isthat that magmaflow flowisis dominantly sub-horizontalalong along swarms and changes petrology, and that thatlateral lateral changesinin petrology,geochemistry geochemistry and and fabric fabric may may help help to to locate ofof considerable importance locatemagma magma sources. sources. This This aspect aspectisis considerable importanceininmost most Precambrian Precambrian (and (andyounger) younger) dike dikeswarms swarms for forwhich which evolutionary evolutionarymodels modelshave have ' yet developed. yettotobebedeveloped. 14 �MICHIGAN'SS ENERGY ENERGY RESOURCES: RESOURCES: AAGEOLOGICAL GEOLOGICALPERSPECTIVE PERSPECTIVE MICHIGAN' Kalliokoski, Department Department of of Geology Geology and and Geological GeologicalEngineering, Engineering,Michigan Michigan JJ•. Kalliokoski, Technological Houghton, Michigan 49931 TechnologicalUniversity, University, Houghton, Michigan 49931 ABSTRACT ABSTRACT Michigan energy energy supply supply and and demand demand patterns patterns of of the the study study year year 1972 1972 Michigan (Fig. 1) 1) indicate indicate in in aa general general manner manner the thesituation situationas asititexists existsinin1982. 1982. (Fig. Line thicknesses thicknesses represent represent quantities quantities of of energy energy in in terms terms of of their their heat heat Line The wiggly wiggly line line at at top topisishydroelectric hydroelectricpower, power, the thesatellite satellite content. The content. symbol symbol is is nuclear nuclear power, power, and and blank blank box box above above "Transp." "Transp." represents represents the the use use of of oil oil by by the themanufacturing manufacturingindustry industryasasraw rawfeed feedfor forplastics. plastics. In In 1982 1982 coal coal consumption consumption is is down down by by about about one one third third and and oil oil is is up up by by aa like like amount, amount, some some of of the theshift shiftto toalleviate alleviateair airpollution. pollution. About About as as much much heat heat energy energy ultimately ultimately is is lost lost as as is isused, used, because becauseofofinefficiencies inefficiencies of of all all kinds kinds in in the the conversion conversionof of heat heat to touseful usefulenergy. energy. Michigan Michigan obtains obtains about about 1/5 1/5 of of its its gas gas and and oil oil from front in—state in-state sources. sources. Based on on aa review review of of the the occurrence occurrence and and possible possible quantities quantitiesof ofgeogeoBased logicaland and non—geological non-geological types types of of fuels fuels in in Michigan, Michigan, the the writer writer concludes concludes logical that that the the state state has has aafew fewenergy energyoptions optionsfor forthe thefuture future(Fig. (Fig.2). 2). On On the the right, right, for for purposes purposes of of comparison, comparison, are are shown shown the the fuel fuel requirements requirements for for On the the left left are are the the in—state in-state reserves reserves utilized utilized in in 1981, 1981, with with an an 1972. On 1972. estimate estimate of of the the years years that thatthey theywill willlast. last. In In the the center center are are listed listed the the resources resources to to which which Michigan Michigan might might turn turn as as the thepresent present reserves reserves become become continued energy self—sufficiency be level of exhausted, should some level of continued energy self-sufficiency be should some exhausted, deemed to to have have economic economic value. value. Coal Coal and and peat peat may may be be less less important important than than deemed In the the northern northern part part of of the the bitumen— bitumen- and and kerogen—containing kerogen-containing Antrim Antrim Shale. Shale. In the the lower lower peninsula peninsula several several hundred hundred square square miles miles are are underlain underlain by by this this shale that that contain contain between between 10 10 and and 15 15 gallons gallons per ton ton of of Fisher Fisher assay assay shale extractable oil oil across across30 30 feet. feet. extractable Production State Resources TODAY TODAY HYORO FUTURE FUTURE NNucl. 77 GAS 30 yr8 Antrim Sh. 50-100 yrs 10 yrs Figure Figure 22 Figure 11 Figure 15 LTt'J LtJ WOOD OIL - 1972 1972Rem. Reg. YARD YARD STICK STICK ILj hid....rnuj �THE VOLCANIC VOLCANIC ROCKS ROCKS OF OF THE THE UNNAMED UNNAMED FORMATION, FORMATION, THE PORCUPINE MOUNTAINS MOUNTAINS REGION, REGION, PORCUPINE MICHIGAN MICHIGAN - AA MIDDLE MIDDLE KEWEENAWAN ICEWEENAWAN ERUPTIVE CENTER ERUP2IVE CENTER - Paul J. J.Kopydlowski, Kopydlowski,Department Department of OfGeology Geology and and Geological Geological Engineering, Engineering,MichMichPaul igan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 igan ABSTRACT ABSTRACT The unnamed unnamed formation formation is isa aMiddle MiddleICeweenawan Kewenawan central central shield shield volcano volcano The (White, (White, 1972) 1972) which which crops crops out out in in the the vicinity vicinity of of the the Porcupine Porcupine Mountains Mountains in in the the Upper U p p r Peninsula Peninsulaof of Michigan. Michigan. Maximum Maximum surface surface thickness thickness of of this this lensoid— lensoidshaped formation formation is is about about 8,000 8,000 ft. in in the the Bergland Bergland and and Thomaston Thoroaston quadranquadranshaped gles. gles. The The volcanic volcanic pile pile gradually gradually narrows, narrows, eventually eventually wedging wedging out out in in the the Greenland quadrangle to to the the east east and and in in the the Little Little Girls Girls Point Point quadrangle quadrangle Greenland quadrangle to to the the west. west. The The formation formation is is conformable conformable on on and and is is aa continuation continuation of of the the underlying underlying Portage Portage take Lake Volcanics. Volcanics. Previously grouped with the Portage Previously grouped with the Portage ft. Lake Lake Volcanics, Volcanics, the the unnamed unnamed formation formation was was first first recognized recognized as as aa separate separate unit unit by by Johnson Johnsonand and White White (1969). (1969). The The distinction distinction between between the the two two units units is is that the the unnamed unnamed formation formation contains contains aa greater greater percentage percentage of of relatively relatively acidacidthat ic ic volcanic volcanic rocks. rocks. Overlying overlying and and locally locally interfingering interfingering with with the the unnamed unnamed formation is is the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. formation Spatial relationships relationships between between the the various various rock rock types types within within the the unnamed unnamed Spatial formation formation were were observed observed in in the the field. field. Samples Samples were were collected collected perpendicular perpendicular to to strike striketo to obtain obtain representative representativevertical verticalsections sectionsof ofthe theformation. formation. ForForty—seven ty-seven samples samples were were analyzed analyzed for for major major and and minor minor elements. elements. Compositions Compositions of baof the the lava lava flows flows within within the the unnamed unnamed formation formation range range from from rhyolite rhyolite to to basalt. salt. Mdesite Andesiteisisthe themost mostcommon commonrock rocktype. type. Twenty—five Twenty-five samples samples from from six six distinct topdistinct felsite felsite bodies bodies were were analyzed. analyzed. These These include: include: 1) 1) the the felsite felsite topping ping Copper Copper Peak Peak (Chippewa (ChippewaHill), Hill), 2) 2) the the felsite felsite that that makes makes up up the the highhighlands lands of of the the Porcupine Porcupine Mountains Mountains Wilderness Wilderness State State Park, Park, 3) 3) the the Chippewa Chippewa 2felsite elsite located between between White White Pine Pine and and Bergland, Bergland, 4) 4) two two quartz quartz latite latite flows flows within the the Porcupine Porcupine Mountains Mountains Wilderness Wilderness State State Park, Park, 5) 5)the the quartz quartz porphyporphywithin ry located located north north of of Bergland Bergland and and 6) 6 )an anash—flow ash-flowtuff tufflocated locatedaobut aobut77miles miles ry southeast southeast of of White White Pine. Pine. Emphasized Emphasized to to aa lesser lesser extent extent in in the the study study are are the the analyses analyses of of 15 15 basic basic and and intermediate intermediateflows. flows. Finally, Finally, 44 intrusions intrusions were were chemically chemically analyzed. analyzed. They They includes include: 1) 1) two two basaltic basaltic sills sills from from within within the 2 ) aa diorite diorite dike dike which which intrudes intrudesthe the felsite felsite of of the the the quartz quartz porphyry, porphyry, 2) Porcupine Porcupine Mountains Mountains and and 3) 3 ) aa diabase diabase granophyre yranophyre complex complex positioned positioned at at the the base base of of the the unnamed unnamed formation formationnear nearthe the western edge of the Matchwood quadwestern edge of the Matchwood quad— rangle. rangle. Evaluation Evaluation of of the thechemical chemical variance variance between between and indiand within within the the indi- vidual flows flows and and intrusions intrusions is is incomplete incomplete at the time time of of this thiswriting. writing. vidual at the Lavas of ofthe theunnamed unnamed formation formation may may have in an anenvironment environment simisimiLavas have erupted erupted in lar lar to to that that of of the the Tertiary Tertiary of of eastern eastern Iceland Iceland (Green, (Green,1977). 1977). Flood basalt basalt Flood flows interfingflows from from fissures fissures within within the the Midcontinent Midcontinent Rift Rift overlapped overlapped and and interfing— ered with with relatively relatively acidic acidic flows flows from from the the central central shield shield volcano. volcano. At At the the ered sane time, time, emplacement emplacement of of shallow shallow intrusions intrusions occurred occurred at at vent vent areas areas and and hyhysame drothermal drothermal activity activity took tookplace place locally. locally. The The central central shield shield volcano volcano of of the the unnamed formation formationdiffers differsfrom fromcentral central volcanoes volcanoesof of the theTertiary Tertiaryof of eastern eastern unnamed Iceland in in that that the theformer formeris ismuch muchlarger largerin insize sizeand andcontains containsa agreater greater Iceland percentage percentage of of andesite andesite than thanthe thelatter. latter. Dike Dike swarms swarms which which are are common common in in 16 4 � central centralvolcanoes volcanoesofofthe theTertiary Tertiaryof ofeastern easternIceland Icelandare arelacking lackingininthe theununAfter volcanism, the volcanic rocks of the unnamed named namedformation. formation. After volcanism, the volcanic rocks of the unnamedforformation mation were wereregionally regionallymetamorphosed metamorphosedtotothe thechlorite chloritefacies. facies. Subsidence Subsidence within the Lake Superior Syncline tilted the unnamed formation within the Lake Superior Syncline tilted the unnamed formationnorthward northward exposing exposinga across—sectional cross-sectionalview viewofofthe thecentral centralvolcano. volcano. Further Furtherfolding foldinginin the the vicinity vicinity of ofthe thePorcupine PorcupineMountains Mountainsresulted resultedininthe theformation formationofofthe the At its center, the unnamed formation Porcupine PorcupineMountain Mountainanticline. anticline. At its center, the unnamed formationisisexexposed posedforming formingthe thehighlands highlandswithin withinthe thePorcupine PorcupineMountains MountainsWilderness WildernessState State Park. Park. REFERENCES REFERENCES Green, J.c., J.C., Green, 1977, 1977, Keweenawan Keweenawanplateau plateauvolcanism volcanismininthe theLake LakeSuperior SuperiorRegion, Region, 16, p. 407—422. Geol. Geol. Association Associationof ofCanada, Canada,Special SpecialPaper Paperno. no. 16, p. 407-422.  Johnson, Johnson,R.F. R.F. and andWhite, White,W.S., W.S., 1969, 1969,Preliminary Preliminaryreport reporton onthe thebedrock bedrockgeolgeolMatchwood quadrangle, Ontonagon ogy ogy and andcopper copperdeposits depositsof of the the Matchwood quadrangle, OntonagonCounty, County, Michigan, Michigan, U.S. u.S. Geol. Geol. Survey, Survey,Open-file open-file Report. Report. White, White, W.S., W.S., 1972, 1972, Keweenawan Keweenawan flood floodbasalts basalts and and continental continentalrifting, rifting,Geol. Geol. Soc. no. 7,7,p.p. 732—734. 732-734. Soc. America, America, Abs. Abs. with withPrograms, Programs,v. v. 4,4,no. I I I S 17 S �HYDROTHERMAL PROCESSESAND M'IDMASSIVE MASSIVESULFIDE SULFIDE DEPOSITS HYDROTHERMAL PROCESSES DEPOSITS AT OCEANIC OCEANIC SPREADING SPREADING CENTERS CENTERS Randolph Randolph A. A. Icoski, Koski, U.S. U.S. Geological Geological Survey, Survey, 345 345 Middlefield MiddlefieldRoad, Road, Menlo-park, Menlo-Park, California 94025 California 94025 ABSTRACT ABSTRACT Active hydrothermal hydrothermal vents vents and and metal metal sulfide sulfide deposits deposits have have been been located located and and sampled sampled along along Pacific Pacific Ocean Ocean spreading spreading centers, centers, including including the the East East PacifPacific Rise, fica Ridge Ridge (Fig. (Fig. Rise, the the Galapagos Galapagos spreading spreading center, center, and and the the Juan Juan de de Fuca 1). These discoveries discoveries have have confirmed confirmed predictions, predictions, based based on on studies studiesof of heat— heat1 ) . These flow flow patterns, the the widely widely distributed distributed basal metalliferous metalliferous sedimentary sedimentary layer layer overlying overlying oceanic oceanic crust, crust, basalt/seawater—interaction basalt/seawater-interactionphenomena, phenomena, and and volcano— volcanogenic sulfide sulfide deposits deposits in in ophiolite ophiolite complexes, complexes, that fluids fluids circulating circulating through formedlithosphere lithosphereatat oceanic oceanic spreading spreadingcenters centers can can effective effectivethrough newly newly formed ly mineraldeposits deposits on onthe the sea sea floor. ly mobilize mobilize metals metals and and form form mineral floor. A for the A genetic genetic model model for the deposition deposition of of polymetallic sulfides sulfides at at medium— mediumto from aa magma magma to fast-rate spreading centers proposes that the heat flux from fast—rate spreading centers proposes that the heat flux chamber at aashallow level (1—3 1cm) the sea chamber emplaced emplaced at shallow level (1-3 km) below below the sea floor floorinduces induces convective recharge of of seawater lithoconvective flow flow and and continuous continuous recharge seawater through through permeable permeable litho- sphere along the flankstoward towardthe theheat heat source source (Fig. sphere from from along the oceanic—ridge oceanic-ridge flanks (Fig. 2). 2). 4 The The cycle cycle continues continues with with deep deep penetration penetration along along cracking cracking fronts fronts through through the the lava flows flows and and dike dike complex complex of of oceanic oceanic layer layer 22 to to levels levels near near the the magma magma chamber, chamber, and is is followed followed by by upwelling upwelling of of the the buoyant buoyant hydrothermal hydrothermal fluid fluid along fractures At high fractures and and faults faults to to the the sea sea floor. floor. high temperatures temperatures and and water/rock water/rock ratios, ratios, hydrolytic hydrolytic and and oxidative oxidative reactions reactions with with mafic mafic wallrock wallrock generate aa low—pH low-pH low—Eh low-Eh solution solution capable capable of of leaching leaching and and transporting transporting transition transition metals metals and and sulfur. sulfur. Cooling of of the the upwelling upwelling fluid fluid during during adiaadiabatic batic expansion expansion and and then then its its further further cooling cooling and and neutralization neutralization upon subsubsurface mixing mixing with with ambient ambient seawater seawater cause cause deposition deposition of of sulfide sulfide minerals minerals along rapid fluid fluid flow flow results results in in the the discharge discharge of of along subsurface subsurface channelways; channelways; rapid reduced fluid and seafloor/seaand the the deposition deposition of of massive massive sulfide sulfide at at the the seafloor/seawater water interface. interface. Oxidizing Oxidizing conditions on the the sea sea floor floor promote promote the the devel— development Un from from optnent of of distal distal silicate silicateand and oxide oxide facies facies and the the fractionation fractionation of Mn Fe. Fe. 0 Preliminary Preliminary investigations investigations of of sulfide sulfide deposits deposits along along the the Pacific Pacific Ocean Ocean ridge ridge system system reveal reveal considerable considerable diversity. diversity. For For example, example, on on the the East East PacifPacific ic Rise Rise at at lat. lat. 21°N, 21aN, composite composite mound—chimney mound-chimney edifices edifices composed composed of of Zn, Zn, Fe, Fe, and and Cu Cu sulfides, sulfides, Ca Ca and and Ba Ba sulfates, sulfates, and and silica silica overlie overlie basalt basalt in in aa horst— horstand—graben and-graben terrain terrain near near the the volcanically volcanically active active ridge ridge axis. axis. Active Active vents vents are in parparare vigorously vigorously discharging discharging high—temperature high-temperature (350°—400°C) (350°-40O0C fluid fluid rich rich in ticulate sulfide sulfide (black (black smokers) smokers) and silica silica (white (white smokers); smokers); the the latter latter host host exotic exotic communities communities of of worms, worms, crabs, crabs, and and clams. clams. In In the the southern southern trough trough of of the the Guaymas Guaymas Basin Basin in in the the Gulf Gulf of of California, California, hot hot springs springsare are depositing depositing mounds mounds of of Fe Fe and and Zn Zn sulfides sulfides (the (the unusual unusual assemblage assemblage pyrrhotite + + sphaler— sphaler- and talc on and ledges ledges of of Fe—rich Fe-rich talc on rapidly rapidlyaccumulating accumulating ponds ponds of of unconsolunconsolidated idated ooze ooze and and mud. mud. In addition, addition, hydrothermal hydrothermal activity generated generated by the its) ite) intrusion into water—saturated intrusion of of diabase diabase sills sills into water-saturated sediment sediment rich rich in inorganic organic material into gasoline—range material has hastransformed transformed the theorganic organicmaterial material into gasoline-rangehydrocarhydrocarbons. S 18 �170°W 90° 120° 150° 60° 70°N 600 30° mineral deposits Guaymas Basin DSDP 471\ East Pacific Riselat 21° East Pacific lat 13ON 0° East Pacific Rise lat 20's I I 25° S Figure Figure 19 1 1 ! �AXIS OF SPREADING . -IMASSIVE SULFIDE OXIDE & SILICATE HEAT SOURCE Figure Figure2 2 20 �On On the theGalapagos GalapagosRift Rift at atlong. long. 86°w, 86OW, hydrothermal hydrothermaldeposits depositsoccur occuralong along the the base base ofofnormal—fault normal-faultscarps scarpsbounding boundinga ahorstlike horstlikecentral centralridge. ridge. AA large(1,000 (1,000 mm long, long, 150 150 mm wide, wide, 35 35 mm thick) thick)prism prismofofCu—rich Cu-richand andZn—poor Zn-poor large massive massive sulfide sulfide with with numerous numerous large large inactive inactive chimneys chimneys has has formed formedalong along aa On the the southern southern Juan Juan de de Fuca Fuca Ridge, Ridge, encrustations encrustations south-facingescarpment. escarpment. On south—facing of of Zn—rich zn-rich and andCu—poor Cu-poormassive massivesulfide sulfideand andassociated associatedbenthic benthic organisms organisms mark nark aa series series of ofhydrothermal hydrothermal vents vents and andvent vent fields fieldsin ina aregion regionunderlain underlain sheetflows. The deposits deposits are arespatially spatiallyassoassolargelyby by glassy glassyferrobasalt ferrobasalt largely sheetf lows. The ciated ciated with with aa shallow shallowcleft cleftininthe theaxial—valley axial-valleyfloor. floor. Continued Continued research research on on hydrothermal hydrothermal systems systemsand andpolymetallic polymetallic sulfide sulfide deposits deposits on on the themidoceanic—ridge midoceanic-ridge system systemwill willstimulate stimulateand andimprove improvecurrent current concepts concepts in in such such diverse diverse fields fieldsas as ore ore genesis, genesis, mineral mineral exploration, exploration, evoluevolutionary tionarybiology, biology, and anddeep—seabed deep-seabedmining. mining. I I I 21 �A A GEOCHEMICAL GEOCHENICM. CORRELATION, CORRELATION, WITH WITH CORRELATIVE CORRELATIVE INFERENCES INFERENCESFROM FROM PETROGRAPHIC PETROGRAPHICAND AND PALEOMAGNETIC PALEOMAGNETIC DATA, DATA, OF OFTHE THEGREENSTONE G R E E N S W E FLOW, FLOW, KEWEENAW PENINSULA AND ROYALE, MICHIGAN KEWEENAW PENINSULA AND ISLE ISLE ROYALE, MICHIGAN I A.A. A.A. Longo, Longo, Department Department of ofGeology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan TechTechnological nological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 ABSTRACT ABSTRACT correlation correlation across across the the Lake Lake Superior Superior syncline syncline between between Isle IsleRoyale Royale and Peninsulaof of Michigan Michiganwas wasfirst first proposed and the theKeweenaw Keweenaw Peninsula proposed by by Lane Lane (1899). (1898). AA The The key key to to this this correlation correlation was was the thepresence presence of ofone oneimmense, immense,continuous continuous Middle Middle Ketqeenawan Keweenawan tholeiitic tholeiitic flow known known as as the the Greenstone Greenstone Flow Flow (GSF). (GSF). Thickness Thickness data data for for the the GSF GSF on on Isle Isle Royale Royale (Lane, (Lane, 1898 1898;1911) 191 1)and andthe theKewee— Keweenaw naw Peninsula Peninsula (Cornwall, (Cornwall, 1951) 1951) imply imply aa total total volume volume for for the the GSF GSF of of 1,000 1,000 km3, km3, which which has has been been viewed viewed as as "a "a conservative conservative estimate" estimate* (White, (White, 1960). 1960). Ru— Huher her (1973) (1973) confined confirmedthe thesimilarities similaritiesofofthe theGSF GSFononIsle IsleRoyale Royaleand andthe theICe— Keweenaw weenaw Peninsula, Peninsula, and and he he supported supported the the correlation. correlation. AA single single lava lava flow flow of of such such great great magnitude magnitude would would possibly possibly be be the the world's world's largest. largest. However, However, evievidence dence for for this this correlation correlation was was based based solely solely on on field fieldcriteria. criteria. This This paper paper is is the the first first quantitative quantitative study study to to test test the the validity validity of of the the proposed proposed corre— correlation. lation. AA total (34of ofwhich whichwere wereoriented) oriented)were were used used in in this this total of of 57 57 samples samples(34 The The samples samples were were collected collected in in stratigraphic stratigraphic sequence sequence across across the the GSF GSF at at Blake Blake Point, Point, Isle Isle Royale, Royale, Michigan, Michigan, and and at at Cliff Cliff Drive Drive and and Phoenix, Phoenix, Michigan Other Michigan on on the theKeweenaw KeweenawPeninsula. Peninsula. Other samples samples were were collected collected from from directly directly above above and and below below the the CS? GSF from from the the latter latterthree threesites, sites,from fromthe theGB? GSF in in the the MTh MTU experimental experimental mine, mine, and and from from aa drill drill core core through through the the GB? GSF in in SenSeneca, eca, Michigan. Michigan. The The latter latter two two sites sites were were places places where where oriented oriented sampling sampling was was not not possible, possible, and and the the GB? GSF was was the the thinnest thinnest (45—15 (45-75 m). m). study. study. I I II All All rocks rockswere wereanalyzed analyzedby byXR? XRFfor forboth bothmajor majorand andtrace traceelements. elements. Only Only specimens specimens least least affected affected by by migrating migrating hydrothermal hydrothermal fluids fluids were were chosen chosen for for chemical chemical evaluation. evaluation. These These sample sample sites sites were were ophitic ophitic zones zonesin inthe theflow, flow, which zones of of lowest lowest permeability permeability and and least least alteration. alteration. which are are the the zones Thin Thin sections sectionswere were studied studied to to observe observe changes changes in in mineralogy, mineralogy, mode, node, textexture and plagioclase composition. For samples with >35% plagioclase ture and plagioclase composition. For samples with >35% plagioclase an an XRD XRD method method for for plagioclase plagioclase determination determination was was utilized utilized (Smith (Smithand and Gay, Gay, 1958). 1958). Type Type and and degree degree of of alteration alterationwere were evaluated evaluatedto toassist assistininthe theselection selectionof of samples for geochemical analysis, and to aid in the interpretation of samples for geochemical analysis, and to aid in the interpretation of samples samples with with radically radicallydifferent differentgeochemistry. geochemistry. Core Core specimens specimens were were taken taken from from the the oriented oriented samples samples for for paleomagnetic palmagnetic evaluation. Statistical results of the remanent magnetism evaluation. Statistical results of the remanent magnetism on on Isle IsleRoyale Royale were compared to present (this paper) and previous work on Keweenaw were compared to present (this paper) and previous work on Keweenaw(Books, (Books, 1972). 1972). The The results results were were used used as as aa correlation correlationtool. tool. The The CS?, GSF, an an olivine olivinetholeiite, tholeiite, is is the the thickest thickest flow flow in in the the Portage Portage Lake Lake Volcanic Sequence of Michigan's Copper Country. Volcanic Sequence of Michigan's Copper Country. Thicknesses Thicknessesrange rangefrom from 30 30 to to 245 245 mm on on Isle Isle Royale Royale (Huber, (Huber, 1973) 1973)and and from from 45 45 to to 427 427 mm on on the the Keweenaw Keweenaw Peninsula (Cornwall, 1951). 22 �- The The flow flow is is stratified stratified due due to to differentiation differentiation into into chemically chemically distinct distinct fractions, fractions, which which are are the the pegmatitic pegmatitic lenses lenses with with associated associated granophyric granophyric dikes dikes Most differentiated differentiatedare are the the peg— pegand and sills sills (pegmatoids), (pegmatoids),and and ophitic ophitic zones. zones. Most matoids matoids whose whose frequency frequency varies varies proportionally proportionally with with total total flow flowthickness. thickness. These These coarse—grained coarse-grained fractions fractions vary vary in in thickness thickness and and shape, shape, usually usually occur occur as stratiform stratiform features, features, but but were were also also noted noted to to occur occur as as auto—intrusions auto-intrusions in in as the the columnar—jointed columnar-jointed melaphyre melaphyre on on Isle IsleRoyale. Royale. Pegmatoids Pegmatoids are are permeable permeable channelways channelways for for the the deuteric deuteric and andlater laterhydrothermal hydrothermal fluids. fluids. Therefore, Therefore, these for chemical chemical correlation correlation in in flood flood basalt basalt ter— terthese zones zones are are poor poor sites sites for ranes. ranes. ophitic Ophitic areas, areas, the the major major flow flow units, units, presumably presumably occurred occurred as as continuous continuous In thicker thicker portions portions of of layers layers in in the the upper upper and and lower lower sections sections of of the the GSF. GSF. In lenses with intermingling pegmatoids are subophitic to ophitic the GSF subophitic to ophitic lenses with intermingling pegmatoids are the GSF sandwiched sandwiched between between the the upper upper (UO) (UO) and and lower lower (LO) (LO) ophitic ophitic zones zones and and are are prepresumed stratigraphically discontinuous. sumed stratigraphically discontinuous. In In summary, summary, the the UO UO and and LO LO are are presumed presumed continuous continuous throughout throughout the the flow flow and and are are low low in in permeability; permeability; thus thus they they were were least least affected affected by by migrating migrating hydrothermal LO were were chosen chosen as as ideal ideal sites sites hydrothermal fluids. fluids. Therefore, Therefore, the the UO UO and and LU for chemical correlations within the Portage Lake Volcanics. for chemical correlations within the Portage Lake Volcanics. An An average average OS? GSF composition composition as as calculated calculated from from this this study study was: was: Trace Trace Elements Elements (ppm) (pp) Major Elements Elements (wt.%) (wt.%) Major CaC Si02 == 46.7 46.7 CaO Si02 == 15.1 Na20 Al^ 1 5 . 1 Na20 A1203 FeO ~ 112.8 2.8 K20 FeO* K20 = MgO MgO = 7.8 7.8 TiO, Ti02 p205 == 0.14 0.14 p205 == 9.9 9.9 = 2.1 = 2.1 = 0.4 0.4 =" Ba = 103.5 213.4 Cr Cu = 66.4 La = 10.9 Mn 1675.4 1.2 1.2 Ni = Pb = Rb S Sc Sn Sr = 258.7 V 194.7 186.2 Y <2 Zn Zr 7.8 <50 27.9 5.9 13.5 84.4 91.8 The The data data have have revealed revealed the the following followingfacts: facts: 1 • can be be demonstrated demonstrated within within ophitic remarkable chemical chemical homogeneity homogeneity can ophitic remarkable sections of of the the OS?. GSF. sections A A 2. Similar geochemistry geochemistry existed in all all sites sites analyzed analyzed with with the the exception exception the GB? from altered GSF from the MTU chlorite-prehnite-punpellyite altered MTU experiexperiof the the chlorite—prehnite—pumpellyite of mental mine. mine. mental 3. Most flows flows directly directly beneath beneath the the GSF GSF are are chemically chemically similar similar to to the the GB?, GSF, and believed believed to to be be part part of of aa magmatic magmatic cycle cycle which which terminated terminated with with the the extrusion extrusion of of the the GB?. GSF. 4. similar Similar petrology is found found in in all all OS? GSF sample sample sites sites except except the the altered altered OS? HTU mine. mine. GSF from from the the MTU 5. Flows Flows directly directly above above the the GB? GSF display display different different chemistry chemistry and and petrology petrology in most most sample sample sites. sites. in Petrology Petrology of of flows flows directly directlybeneath beneaththe theGB? GSF are are similar to tothe theGB?. GSF. similar 23 �- ' - . à 6. 6. statistically similar similar directions directions of of remanent magnetization Statistically magnetization are found found for the GSF on Isle Royale and the Iceweenaw Peninsula. the on Isle Boyale and the Keweenaw Peninsula. 7. 7 . statistically similar directions of remanent Statistically remanent magnetization magnetization direction direction are found for flows directly beneath the GSF on Kewee— found for flows directly the on Isle Isle Royale Royale and Keweenaw Peninsula (Books, 1972) which tend to diverge away from the diverge away from the mean mean Peninsula (Books, 1972) which remanent magnetization direction of the G5F. However, limited data direction of the GSF. However, exist. In light light of of all all the the data data collected collected for for this this study, study, no no inconsistencies inconsistencies were found to occur through the entire GSF. Since a possibility exists were found to occur through the entire GSF. that the GSF on Isle Royale and the GSF on the Keweenaw Peninsula are two on Isle Boyale and the GSF on the Keweenaw Peninsula separate flows from the same magmatic cycle, cycle, a positive correlation correlation cannot cannot be be proved. proved. ii I I I I 4I 1I 24 24 1 �URANIUM URANIUM IN IN LOWER LOWER PROTEROZOIC PROTEROZOICPHOSPHATE-RICH PHOSPHATE-RICHMETASEDIMENTARY METASEDIMENTARYROCKS BOCKS OF EAST-CENTRAL MINNESOTA EAST-CENTRAL MINNESOTA Peter Peter L. L. McSwiggen, McSwiggen, Minnesota Minnesota Geological Geological Survey, Survey, University University of of Minnesota, Minnesota, St. Paul, Paul, Minnesota Minnesota 55108 55108 ABSTRACT ABSTRACT Exploration for uranium uranium deposits deposits related related to to the the unconformity unconformity between between the lower Proterozoic Thomson Formation and the middle the lower Proterozoic Thomson Formation and the middle Proterozoic Proterozoic Fond Fond du du Lac Lac Formation Formation in in east—central east-central Minnesota Minnesota has has defined defined several several very very low low grade grade uranium uranium occurrences. occurrences. Most Most of of these these occurrences occurrences are are associated associated with with phosphosin the Thomson Formation, which consists dominantly phate—rich units phate-rich units the Thomson Formation, which consists dominantly of of interlayered interlayered feldspathic feldspathic graywacke, graywacke, siltstone, siltstone, and mudstone mudstone and and lesser lesser amounts of of carbonaceous carbonaceous mudstone, mudstone, dolomite, dolomite, quartzite quartzite and and volcanic volcanic rocks. rocks. The formation was deformed and metamorphosed under lower The formation was deformed and metamorphosed under lower greenschist greenschist to to middle middle amphibolite amphibolite facies facies conditions conditions during during the the Penokean Penokean orogeny orogeny approxiapproximately m.y. ago. ago. mately 1,870 1,870 m.y. Samples of the the phosphate phosphate units units from from two two localities localities were were studied studied to to characterize characterize the the uranium uranium occurrences. occurrences. The The Thomson Thomson Formation Formation at at these these lolocalities occurs at chlorite grade, and the uranium in the samples calities occurs at chlorite grade, and the uranium in the samples averages averages at ppm. The The phosphate phosphate units units are are relatively relatively thin, thin, having having aa maximaxiat least least 400 400 ppm. mum thickness of about 30 cm (Ulimer, 1981), and are intercalated mum thickness of about 30 cm (Ullmer, 19811, and are intercalated with with beds beds of black black to to gray gray recrystallized recrystallized chert, chert, and and lesser lesser amounts amounts of of carbonaceous carbonaceous slate slate and and siliceous siliceous carbonates. carbonates. The The units units consist consist of of both both conglomeratic conglomeratic The conglomerate is characterized and and thinly thinly laminated laminated rock. rock. The conglomerate is characterized by by angular angular to to subrounded pebbles of cryptocrystalline apatite and recrystallized of cryptocrystalline apatite and recrystallized chert chert set in in aa matrix matrix of of apatite, apatite, quartz, quartz, and and lesser lesser amounts amounts of of argillaceous argillaceous Both the pebbles and groundmass contain variable material. amounts of of carcarmaterial. Both the pebbles and groundmass contain variable amounts The thinly laminated rock consists of interlayered bonaceous bonaceous material. material. The thinly laminated rock consists of interlayered apatite, apatite, quartz, quartz, and and lesser lesser amounts amounts of of argillaceous argillaceous and carbonaceous carbonaceous material. material. textural textural arrangement arrangement of of the the uranium uranium in in these these phosphate—rich phosphate-rich samples indicates that samples indicates thatthe theuranium uranium has has had had aacomplex complex paragenetic paragenetic history. history. within the Much Much of of the the uranium uranium occurs occurs evenly evenly disseminated disseminated within the phosphatic phosphatic pebpebbles implying that that it it was was precipitated precipitated syngenetically syngenetically with with the the bles and layers, layers, implying The The phosphatic material, material, or or was was fixed fixed out out of of the the Thomson Thomson sea sea by by the the phosphatic phosphatic Concentrations sediments sediments on the the sea sea floor. floor. Concentrations of somewhat somewhat younger younger uranium uranium along planes recrysplanes that that parallel parallel the the tectonic tectonic foliation foliation imply imply secondary secondary recrysAdditional tallization, probably probably during during the the metamorphism. metamorphism. Additional concentrations concentrations of uranium uranium along along joint joint or or fracture fracture planes planes at at an an angle angle to to the the foliation foliation indicate indicate aa postmetamorphic postmetamorphic mobilization mobilization of of the the uranium. uranium. Uranium as overgrowths overgrowths around around pyrite pyrite grains grains and and as as individindividUranium also also occurs occurs as ual mineral mineral grains. grains. Nearly Nearly all all of of the the pyrite pyrite grains grains in in the the samples samples studied studied ual are are surrounded surrounded by by some some uranium uranium mineralization, mineralization, and and many many show show aa multi—stage multi-stage history of of replacement replacement of of the the pyrite pyrite by by aa uranium uranium phase. phase. The The individual individual uranium mineral grains grains commonly commonly contain contain other other phases, phases, such such as as pyrite pyrite and and possibly possibly barite. barite. These These mineral mineral grains grains are are typically typically subrounded subrounded to to rounded, rounded, Associated and contain contain 55—75 55-75 percent percent UO2. UO;. Associated with with the the uranium uranium in in these these grains grains are Pb, Pb, P, P, Ca, Ca, Fe, Fe, Ba, Ba, 5, S, Ti, Ti, Cu Cu and and Zn. Zn. are E., 1981, 1981, A mid—Proterozoic mid-Proterozoic phosphate phosphate occurrence occurrence in in east—central east-central Ullmer, E., Minnesota: Newsletter Newsletter IGCP IGCP Project Project 156, 156, no. no. 8, 8, p. p. 22—25. 22-25. 25 �MINERALOGIC AND OF ANORTHOSITES DULUTH MINERALCGIC AND TEXTURAL TEXTURAL VARIATIONS VARIATIONS OF ANORTHOSITES IN INTHE THE DULUTHCOMPLEX, COMPLEX, FOREST CENTER W QUADRANGLE, MINNESOTA FOREST CENTER NW I). James Miller, Jr. GeoJames D . Miller, Jr. and and Paul Paul W. W. Weiblen, Weiblen, Department Department of Geology Geology and and Geophysics, physics, University University of ofMinnesota, Minnesota, Minneapolis, Minnesota Minnesota 55455 55455 ABSTRACT ABSTRACT Although anorthositic rocks occur over over 60 60 percent of of the the exposure exposure area area of of the the Duluth Duluth Complex, Complex, they they are are inadequately inadequately studied studied and and poorly poorly understood. understood. The anorthosites anorthosites are to be gabbroic older gabbroicsequence sequence The are considered considered to be part partofofananolder was intruded by troctolite and gabbro, that that was intruded by troctolite and gabbro, but this this interpretation interpretation is is not not definitive. This report definitive. This report on on the the preliminary preliminary results results of of field field and and petrograph— petrographic ic studies studies is is part part of of aa broader broader study study to to acquire acquire new new data data that that bear bear on on the the origin of the anorthositic rocks. Detailed lakeshore mapping of the origin of the anorthositic rocks. Detailed the study study area I), which was previously mapped at reconnaissance scale in in 1968 1968 area (Fig. (Fig. 1), by Phinney, was was conducted conducted in in the the summer summer of of 1981. 1981. NW quadrangle quadrangle appear appear to to The anorthositic anorthositic rocks in in the the Forest Forest Center Center NW form aa cap over over troctolitic troctolitic rocks, rocks, which which are are exposed exposed in in three three separate separate Exposed contacts areas. areas. contacts between between troctolite troctolite and and anorthosite anorthosite are are commonly commonly broad, complex complex zones zones of of mixed rock rock types. types. The anorthositic anorthositic rocks rocks are are extremely extremely variable variable in inmineralogy, mineralogy, texture, texture, Igneous lamination laminationisis erratic erratic and structure structure over and over most most of of their theirexposure. exposure. Igneous over small contrasting rock over small distances distances and and contacts contacts between between contrasting rock types types can can genergenerThus stratigraphic ally be i~ ally be traced only on on an an outcrop outcrop scale. scale. stratigraphic control control is generally relationships generally nonexistent. nonexistent. Nevertheless, Nevertheless, three three consistent consistent contact contact relationshipâ have been been found: have found: outcrops, plagioclase plagioclase lamination in one rock type type is is par1) In 1) In some some outcrops, lamination in one rock parallel contact with a contrasting rock type having discordant alleltotothe the contact with a contrasting rock type having discordantpla— plagioclase lamination. lamination. This Thisis is taken taken to to imply implyintrusion intrusionofof the the first first rock qioclase rock type into type into the thesecond. second. 2) 2) similarly, a contrasting Similarly, where where plagioclase plagioclase lamination lamination wraps wraps around around a contrasting rock type, the the latter tobe bean aninclusion. inclusion. rock type, latterisisinterpeted interpetedto In other with concordant 3) other exposures, exposures, contrasting contrastingrock rocktypes types with concordantplagio— plagio3) In clase lamination each other across centimeter— to to meter—wide clase laminationgrade gradeinto into each other across centimetermeter-wide types displaying displaying gradational gradational contacts contacts are zones. Rock zones. Bock types are considered considered to to be be cogenetic. cogenetic. Based on these these relationships, Based on relationships,which which are are consistent consistentbetween between particular rock rock three stages emplacement been distinguished distinguished in types, types, three stagesof ofanorthosite anorthosite emplacement have have been in petrographic the as early, late. A the study study area area and and are are denoted denoted as early, main, main, and and late. A petrographic summary therock rocktypes typesofofeach eachstage stage is is given 1. summary ofofthe given in in Table Table 1. Five anorthosite have have been beenidentified identified (Table Five types types of ofmain—stage main-stage anorthosite (Table 1). 1). Over 80 percent Over 80 percent of the the total total anorthosite anorthosite exposure exposure consists of main—stage main-stage in large—spotted anorthosite and anorthosite (LSA) troctolitic (TAM) (LSA) in troctolitic anorthosite anorthosite (TAM) and large-spotted roughly difference between between these these two two types types is is roughly equal equal proportions. proportions. The major difference texture of olivine which in TAM and ophitic the the texture of olivine which is interstitial interstitial in ophitic in in LSA. LSA. 26 �à "in s s a I 6-10 I (Rio) 2) (E)uhedral, (S)ubhedral, - 8 % liii, plagioclase; Apt Medium = 16 - 22 Rio, 1—4 (I)nterstitiai, (S)ubophitic, (O)phitic, (R)ims on (O1)ivine, (V)ariable. - 22 liii, Apt I I - 40 mm 2 Rio, - % zoning with no. of cycles, V — variable. 8 mm. 6—8 Rio, lib <5—20mm 5-0 In t I S-0 <l-Smm S 10 mm S - 0 Trace-St S 0 5 2 mm S nsa ma, Coarse = 4-8 mm, I'egioatite 19 Rio, 10 Trace - R (01) — 3 5-0 5) Range represents uncertainty of rock type designation due to a lack of contact relatLonships. 4) 3) MS — normal sector t I C520ma % S <5—20mm 5 S ma R (01) — 1-5% 40 mm S-U - 5 ma S - 0• 6 cm 5-0 I 5 - <I - 3% R (01) S (A)nhedral, (V)nrinhlc. zoning, PS - patchy sector zoning, Osc(P) — oscillatory 1) Grain size measured normal to (010) in cumulus Modes are visual approximations TOTAL SECTIONS5 OIlIER MINERALS I mm <5mm S I I 1 Trace , '' (fib) cSmm % OikiocrystSize I i-S S Texture/Habit4 IRON OXIDE Oikiocryst Size a! % S* - -s " R (01) s Texture/habit4 5 — 40 mm <S mm - 20 - 2-10% 2 5-18% am, sIt 10 1, Anhedral 2 ma — 52 cm I I, Anhedral Oikiocryst Size I ORTHOPYROXENE S 0-2% 5-0 nsa V - S—0 2—lOt S E 80—95% Peux + Cpx Osc(I,5-2) A Peox + Cpx - S- Poor - Good 2-7% s2% S Excellent 90-97% - edium-Pegmati 0 Peox + Cpx NS ,oocl Medium Gabbroic Anorthosite 2—15% S_0 CT,IMOPYROXF.NE 01 MAIN STAGE Snail Spotted Anorthosite ________ ______ 5-15% : 0—5% I None • w Texture/Habit4 2 mm 1, Fqtuant 8-15% Peox Feox + Cpx flsc(2-3) 01 Cpx V - V MS V MS 80—95% Poor — Good V Good Medium — Coarse 80-90% - Poor Coarse Anorthosite __________ Large Spotted S - Medium Anorthosite Troctolitic 95-98% Excellent S PrfH1OGRAPHIC DESCRIPTIONS OP ANORTIIOSITES 0 S Excellent Mc,! I um Anorthosite ______ TABLE I V 85—95% Good - Medium Anorthosite STAGE S w —4 EARLY Troctolitic V N I'-, Texture/Habit4 Grain Size OI,IVINE Inclusions Zoning3 Habit2 PLAGI1LASE lamination Grain Size1 w " te Pair PS A S 1 3 (Rio) 55mm 1-5 5 % to mou None - S 1-3% None Fcox + Cpx MS - S 95-98% Poor - Medium - Coars1 Anorthosite a - V 0 - CI - 3 % ulmu 5—12 (Rio) 5-0 2—Smm 5 5 R (01) S 30 mm sum <I - 2% 10 - 0-5% 0.5 - 8 1, Equant 8-20% Feox + Cpx 75-85% S Tr. Coarse Poor - Pair Medium Anorthositic Troctolitic Au,.- I S �The other other three three main—stage main-stage rock rock types types occur occur in in gradational gradational contact contact only only with LSA. both TAM TAM and The early troctolitic troctolitic anorthosite occurs as inclusions in both occurrences of the early—stage LSA. Only two occurrences early-stage anorthosite were found as inclusions in clusions in LSA. LSA. Late—stage troctolitic anorthosite (TAL) Late-stage (TALI intrudes intrudes all all main-stage main-stage rock rock types. TAN and and TAL are petrographically types. TAM petrographically very similar similar (Table (Table 11)) and are distinguishable distinguishable in in the the field field only only where contact contact relationships relationships are are observed. observed. Major and minor element and microprobe microprobe analyses analyses of the the anorthosites anorthosites are are planned in in order order to to test test and and refine refine these these field field and and petrographic petrographic observa— observations tions. Figure 11 Figure - of the the Duluth Duluth Complex General geology aecLogy of Complex in in the th NE Minnesota. Forest Center NW quadrangle, HE EI!L*NA? InN £.r I, Pnt..*rl.. traltic •tflS1.at. In In...tsnt •1 in. P.. idIl P,.ca.n.. wiIC1Iø 28 �PROGRESS REPORT ON THE THE BEDROCK GEOLOGY GEOLOGY OF THE REPORT ON OF THE NORTHWEST MAP WISCONSIN MAP SHEET, SHEET, WISCONSIN M.G. M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological and Natural History History Survey, Survey, UniverUniversity Wisconsin—Extension, sityofof Wisconsin-Extension, 1815 University University Avenue, Avenue, Madison, Madison, Wisconsin Wisconsin 53706; G.L. G.L. LaBerge, LaBerge, Geology Geology Department, Department, University University of of Wisconsin, Wisconsin, Oshkosh, oshkosh, Wisconsin Wisconsin 54901; 54901; P.E. P.E. Myers, Myers, Department Department of of Geology, University University of of Wisconsin, Eau Eau Claire, Claire, Wisconsin Wisconsin 54701; 54701; and and W.S. W.S. Cordua, Cordua, Department Department of of Plant Plant and and Earth Earth Science, Science, University University of of Wisconsin, Wisconsin, River River Falls, Falls, Wisconsin Wisconsin 54022 54022 p ABSTRACT ABSTRACT Precambrian Precambrian rocks rocks have have been been the the focus focus of ofgeologic geologicmapping mapping in in the theNorthNorthThe area area is is bounded bounded on on the the north north and and The south 46O and and 45° 45O latitudes, latitudes, respectively; respectively; on on the the east east by by 900 90 longilongisouth by by the the 46° tude; tude; and and on on the the west west by by the the Wisconsin—Minnesota Wisconsin-Minnesota state state boundary. boundary. Bedrock Bedrock exposures to river river exposures in in the the east east half half of of the the map map sheet sheet are are generally generally limited limited to valleys; valleys; in in the the west west the the outcrops outcrops are are extremely extremely sparse, sparse, and and have have no no obvious obvious pattern. pattern. As As aa result, result, extensive extensive use use has has been been made made of of aeromagnetic aeromagnetic data data and and available available drill drill core core and and cuttings. cuttings. Gravity Gravity data data are are too too sparse sparse in in the the map map area area to to be be of of much much value. value. west west map map sheet, sheet, Wisconsin Wisconsin since since 1976. 1976. Archean Archean gneisses gneisses are are inferred inferred from from two two outcrops outcrops and and the the related related domal domal aeromagnetic aeromagnetic patterns near Fifield Fifield and and on on the the Chippewa Chippewa River River in in T.39N., T.39N., R.6W. Relations to other other units units are are not not known. known. R.6W. Relations of of these these rocks rocks to tower Lower Proterozoic Proterozoic units units include include aa dominantly dominantly metasedimentary metasedimentary sequence sequence trending centered near near Park Park Falls. Falls. Numerous electromagnetic trending east—northeast east-northeast centered Numerous electromagnetic anomalies this unit of Sternberg anomalies are areknown known from from this unit(Flambeau (FlambeauAnomaly Anomaly of Sternberg and and Clay, Clay, 1977), 1977), and and those those that that have have been been drilled drilled consist consist almost almost exclusively exclusively of of gargar- net—bearing net-bearing graphite graphite schists schists with with trace trace amounts amounts of of sulfide. sulfide. Typical Typical Pro— Proterozoic terozoic iron iron formations formations and and associated associated carbonate carbonate rocks rocks are are known known from from this this unit. to metavolcanic metavolcanic units units to to the the south south are are not not unit. Relations Relations of of this this unit unit to known known because because of of aa major major fault. fault. Although Although exposure exposure is is poor, poor, this this metavol— metavolcanic canic terrane terrane apparently apparently extends extends from from the the central central part part of of Price Price County County to to the Aeromagnetic expression expression and and available available the southern southern part part of of Taylor Taylor County. County. Aeromagnetic outcrops outcrops suggest suggest that that the the metavolcanic metavolcanic rocks rocks north north of of the the Jump Jump River River Fault Fault are are dominantly dominantly amphibolite amphibolite facies, facies, whereas whereas those south of the the fault fault are are greenschist greenschist facies facies and and more more felsic. felsic. Although Although not not seen seen in in this this map map area, area, relations by Myers Myers along along the the North North Fork Fork of of the the Eau Eau Claire Claire River River relations described described by suggest suggest that that the the greenschist—facies greenschist-facies rocks rocks unconformably unconformably overlie overlie the the amphib— amphibolite—facies olite-facies rocks. rocks. These These stratiform stratiform rocks rocks were were intruded intruded by by granitic granitic rocks rocks around 1,880 million years ago, and by granite near Radisson about 1,760 around 1,880 million years ago, and by granite near Badisson about 1,760 million million years years ago. ago. Two Two volcanogenic volcanogenic massive massive sulfide sulfide occurrences occurrences are are known known in in these these meta— metavolcanic rocks. In the late 1960's the Flambeau and Thornapple volcanic rocks. In the late 1960's the Flambeau and Thornapple deposits deposits were were discovered discovered by by aa subsidiary subsidiary of of Kennecott Kennecott Copper, Copper, and and 44 to to 66 million million tons of 4 percent copper ore were identified. tons of 4 percent copper ore were identified. Exploration Exploration has has continued continued in in the the area area but but no nodetails detailsare areavailable. available. Mineral Mineral potential potential is is considered considered good, good, particularly particularly in in the the greenschist greenschist felsic felsic rocks. rocks. After After deformation deformation of of the the Lower Lower Proterozoic Proterozoic rocks, rocks, aa Middle Middle Proterozoic Proterozoic conglomerate and quartzite sequence was deposited. conglomerate and quartzite sequence was deposited. The The principal principal unit unit is is 29 �I the Barron Quartzite of the Barron Quartzite of western western Rusk Rusk and and adjoining adjoining counties. counties. Present Present work restricts the the age m.y. restricts age of of the the quartzite quartzite sequence sequence between between 1,700 1,700 m .y. and 1,100 1,100 m.y. The Keweenawan diabase m.y. The younger younger is is controlled controlled by by presumed presumed Keweenawan diabase dikes dikes in in the the quartzite. Recently, U U.S. Department of of Energy .S. Department Energy National National Uranium Uranium Resource Resource quartzite. Recently, Evaluation work work suggested suggested some somepotential potential for Evaluation forunconformity unconformity related relateduranium uranium occurrences in occurrences in northern northernRusk RuskCounty, County, although althoughno nouranium uraniumanomalies anomalies were were Field work identified. Field suggested that identified. work by by DOE DOE contractors contractors suggested thata aweakly weaklymetamormetamorphosed regolith quartzite. phosed regolith is is unconformably unconformably overlain overlain by by the the quartzite. Iceweenawan volcanic rocks rocks on on the the western western edge edge of of the the map map sheet sheet adjacent adjacent Keweenawan volcanic to Minnesota, These Chenqwatana Volcanic Volcanic Group. Group. These to Minnesota, are are correlated correlated with with the the Chengwatana volcanic rocks are volcanic are poorly poorly exposed, exposed, but but where where studied, studied, tend tend to to consist consist of of thick basalt basalt flows thick flows that that have have been been metamorphosed metamorphosed to to grades grades ranging ranging from from zeo— zeolite Cordua and others (1979) lite to to lower lower greenschist. greenschist. Cordua and others (1979) have have previously previously reportreported the copper copper mineralization mineralization in in both the ed ott on the the Keweenawan Keweenawan volcanic volcanic rocks rocks and and the overlying overlying Upper Upper Cambrian Cambrian sandstones. sandstones. Mineral potential is is not not considconsidered significant. significant. I Faults are Faults are generally generally recognized recognized from from aeromagnetic aeromagnetic signatures. signatures. The The domdminant structure structure in in the the western part of the the map sheet is the St. St. Croix horst and its its bounding bounding faults faults including including the the Lake Lake Owen, Owen, Cottage Cottage Grove Grove and and Pine Pine Faults. Aeromagnetic lineament analysis and sparse sparse outcrop control control in in the the east half of the the map sheet, sheet, suggest suggest that that the northeast—trending northeast-trending faults were active during the active the Keweenawan inasmuch inasmuch as the the Barron Quartzite is cut by the faults. faults. We believe believe that that at at least least some some of of the the activity activity along along these these faults, faults, particularly Riverand andMonico Monico faults,isis early early Proterozoic particularly the the Jump Jump River faults, Proterozoic in in age, age, with reactivation • The The with reactivationduring during the theMiddle Middle and andpossibly possiblyLate LateProterozoic Proterozoic. principal fault,the the Hawkins Hawkinsfault, fault,is is defined defined entirely entirely principal northwest—trending northwest-trending fault, from aeromagnetic from aeromagnetic lineament lineament analysis. analysis. Mudrey's efforts have focused Mudrey's focused in the the northeastern northeastern part of the the map; La Berge in in the the southeast southeast corner; corners Myers Myers in in the the south—central, south-central, and and Cordua Cordua in in early version version of of the the east part of this the western parts. Pin An early this map was was pubwork in to lished by Sims, Cannon Cannon and and Mudrey Mudrey (1978). (1978). Work in future future years years relating relating to the Precambrian Precambrian rocks will be directed directed to to improved improved petrographic petrographic and and strucstrucdata. tural descriptions, and refined analysis of geophysical data. REFERENCES REFERENCES Cordua, W.S., W.S., Bauer, Bauer, D.P., D.P., Gilbertson, Gilbertson, J.P., J.P., Icoskelin, Koskelin, K.M., K.M., and and Oberli, Oberli, 1979, Geologic Geologic setting setting of copper J.W., 1979, copper mineralization mineralization in in Precambrian Precambrian J.W., (Iceweenawan) basaltic basaltic volcanics volcanics and and Upper Upper Cambrian Cambrian sediments sedinents in (Keweenawan) in the the St. St. Geological Labs.]: Geological Society Society Croix Falls Falls area, area, Wisconsin Wisconsin and and Minnesota Minnesota labs.]: of Mterica America Abstracts Abstracts with with Programs, Programs, v. 11, no. 5, 5, p. p. 227. 227. v. 11, P.K., W.F., M.G., Jr., Sims, P .K., Cannon, W .F., and Mudrey, M .G., Jr., 1978, 1978, Preliminary Preliminary geologic U.S. map of of Precambrian Precambrian rocks rocks in in part part of of northern northern Wisconsin: Wisconsin: U .S. Geological 78-318. al Survey Survey Open—File Open-File Report Report 78—318. Sternberg, B.IC. and Clay, C.S., anomaly; aa high-conductivity high—conductivity Sternberg, B.K. and C.S., 1977, 1977, Flaxttheau Flambeau anomaly; anomaly in &Heacocic, Heacock, in the the southern southern extension extension of of the theCanadian CanadianShield, Shield,in and physical its nature The Earth's crust; J.G., al., The Earth's crust; its nature physical J.G., et eds., al., properties: properties: American Geophysical Geophysical Union Union Monograph Monograph 20, 20, p. p. 501—530. 501-530. e., 30 �STRUCTURAL PIBALYSIS OF THE DULUTH COMPLEX FOREST CENTER NW QUADRANGLE, MINNESOTA Eugene E. Mullenmeister and James D. Miller, Jr., Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455 ABSTRACT We report here the results of a structural analysis of the joint, dike, and lineament orientations in a portion of the Duluth Complex. The study was initiated to document the brittle structures in the Complex and to integrate them into its structural history. Joint and dike orientations were measured in the field within a 26 km2 area. Lineament azimuths and lengths were measured from a high—altitude aerial photo (scale 1:39,000) that covers approximately 1,200 km2 and includes the smaller area studied on the ground. The dominant rock types of the Duluth Complex in this area are trocto— lite and anorthosite (see Miller and Weiblen, this volume, Fig. 1). These rocks intrude Archean metasedimentary rocks, greenstone, and granite of the eastern Vermilion district. Plagioclase lamination and modal layering in the troctolite generally are parallel to the basal contact which trends N70°E to N50°E. The dominant structural fabric of the metamorphic country rock trends NW to E-W. A total of 4,435 joint orientations were recorded and plotted on rose diagrams in 5° intervals. Only azimuths were recorded as most of the joints are near vertical. Three types of joints were recognized: unmin— eralized joints, joints filled with green chlorite (408 total), and joints filled with white sericite (169 total). The green chlorite—filled joints occur predominantly in the troctolite; 287 (94%) occur within 2 km of the contact. White sericite—filled joints are generally confined to the anorthosite. The major differences in fracture trend are related to rock type. Figures la and b summarize the azimuths of all joints measured in the trocto.-. lite and anorthosite, respectively. The troctolite contains predominant joint sets at N25°—45°W, N10°—20°E and N85°W—N85°E with lesser peaks at N65°-75°W and N50°—55°E. Total joints in the anorthosite define a prominent, broad peak at N50°—85°W. Considering only the mineralized joints (Figs. ic and d), the troctolite data retain only the N25°—45°W and N10°20°E sets. The mineralized joints in anorthosites show considerable scatter with 4 significant and 3 to 4 lesser peaks. Stereo plots were made of 33 diabase dikes (Fig. 2) and 34 granitic veins and dikes. Although considerable scatter is present, the mean dia— base dike strikes N51°E ± 26° and dips 51° ± 22° SE (1 std. dev.). The granitic dikes, which occur only in the anorthosite, show greater variation in orientation than do the diabase dikes but generally trend NNE to E-W. The azimuth and length of 437 aerial photo lineaments are plotted in Figure le. The total lineament data show a strong peak at N30°-45°E and lesser peaks at N10°—20°E and N5°—20°W. 31 �I The jointing jointing in in the the study study area area may may be be attributed attributed to to several several causes: The causes: ( 1 ) contraction during cooling of the contact-area rocks (we suggest that (1) contraction during cooling of the contact—area rocks (we suggest that most mineralized mineralized joints jointsmay may have haveformed formedininthis thismanner); manner); (2) upward propamost (2) upward propagation of of basement basement structure; structure; (3) ( 3 ) response response to to regional regional stresses; stresses; and and (4) (4) gation isostatic rebound due to erosion and glacial unloading. Diabase and granisostatic rebound due to erosion and glacial unloading. Diabase and granite dike dike orientations orientations indicate indicate tensional tensional stresses stresses oriented oriented NW-SE, normal ite NW—SE, normal to the Duluth Complex contact, during the later stages Keweenawan igneigneto the Duluth Complex contact, during the later stages ofofICeweenawan N to HE lineament orientaous activity in the area. The predominance of ous activity in the area. The predominance of N to NE lineatnent orientations probably probably is is biased biased by by glacial glacial scour, scour, but, but, nevertheless, most lineations nevertheless, most lineament trends may be related to joint and dike orientations. Definitive ment trends may be related to joint and dike orientations. Definitive evidence of faulting was found at only one location where a fault is oriorievidence of faulting was found at only one location where a fault is ented N20°E The extent of faulting in the area is difficult to assess ented N20°E. The extent of faulting in the area is difficult to assess and complex complex intrusive intrusiverelationships relationships. due to to poor poor exposure exposure and due Figure 1 Figure 1 I I Rose diagrams diagrams of of brittle brittle structures structures in in the the Duluth Complex. Rose Duluth Complex. I A) E) ram , TOTIL LIRNT CAm -t — VEIN .E FTIJI 'u_oil T0T TN POINTS S 2251 — 333 WA POINTS È - .E FTØI 5 W. m POINTS 432 CATA 107*. am 4fl = POINTS 9.S m POINTS 8.5 3 I CATA POINTS 4 B) Wa! Figure 2 /I1(N VEIN FACICA Figure 2 '0.033 Diabaae Dikes Dikes 2171 IOTA.. WA POINTS 37.5 oarn POINTS Diabase M I a- a. •4 .- '-.;z,,S .. C) I 1*XTt.L SOLE FACt : T0T ITA P011415 S 0 •1S. 410 —' 10.8 TR POINTS — w%as D) 'ElM %.E F7 i O.3 T0T TA POINTS * 160 3.3 CAIn POINTS 32 S �STRATIGRAPHY STRATIGRAPHYMID ANDDEPOSITIONAL DEPOSITIONALENVIRONMENT ENVIRONMENTOFOFARCHEAN ARCHEAN FELSIC VOLCANICS, WAWA, FELSIC VOLCANICS, WAWA,ONTARIO ONTARIO pp marK L.L. Nebel, Nebel, Department Department ofof Geology, Geology, University University ofofMinnesota—Duluth, Minnesota-Duluth, Mark Duluth, Minnesota 55812 Duluth, Minnesota 55812 ABSTRACT ABSTRACT Archean Archean volcanic volcanic rocks rocksof ofthe theWawa Wawaarea, area,ininthe theMichipicoten Michipicoten district district of northern Ontario, form part of the Wawa greenstone of northern Ontario, form part of the Wawa greenstone belt. belt. The Therocks rocks studied studiedare aresituated situatednortheast northeastofofthe thecity cityofofWawa, Wawa,and andcomprise comprisethe theupper upper portion portion of ofa amafic—to—felsic mafic-to-felsic volcanic volcaniccycle cyclewhich which includes includesthe theHelen HelenIron Iron deposit. Formation, a volcanogenic massive sulfide—type Formation, a volcanogenic massive sulfide-type deposit. On Onthe thebasis basisofofpreserved preservedprimary primarytextures texturesand andstructures, structures, the therocks rocks spherulitic, flow—laminated, can be be divided divided into: into: 1)1) massive, massive, flow-laminated, spherulitic, and and can lithophysae-bearing massive toto well-bedded well-bedded lithophysae-bearing lava lava domes domes and and flows, flows, 2)2 ) massive pyroclastic 3 )volcanogenic volcanogenicsedimentary sedimentaryrocks. rocks. pyroclasticrocks, rocks,and and3) One One series series of of pyroclastic pyroclastic rocks rocks exhibits exhibits aa marked marked lateral lateral facies facies of the change, change, with with coarse, coarse, massive massivebeds bedsininthe thecentral centralportion portion of thestudy studyarea area grading gradinglaterally laterallyeastward eastwardinto intothin thinand andgraded gradedbeds. beds. The Thechanges changesiningrain grain size and and bedding bedding characteristics characteristics indicate indicate a a westerly westerly source source for for the the size deposition. materials, materials,while whilethin thinand andgraded gradedbeds bedssuggest suggestsubaqueous subaqueous deposition. Volcanogenic Volcanogenic sedimentary sedimentary rocks rocks at at the the top topof ofthe thefelsic felsicvolcanic volcanic sucsuccontain Formation) cession cession (directly (directly underlying underlying the the Helen Helen Iron Iron Formation) contain numerous numerous sedimentary sedimentary structures structures indicative indicative of of shallow shallow water water deposition. deposition. paleocurrent analysis of cross—bed dip directions indicates Paleocurrent analysis of cross-bed dip directions indicatesaasource sourceto to the the west. west. vesiculated Vesiculated pillow—basalts pillow-basalts overlie overlie the the Helen Helen Iron Iron Formation Formation and and are are indicative indicativeof ofaashallow shallowsubaqueous subaqueousenvironment. environment, p The as having having been been deposited deposited in in The felsic felsic volcanic volcanic rocks rocks are are envisioned envisioned as Volcanic center(s) both both aa subaerial subaerialand and shallow shallowsubaqueous subaqueousenvironment. environment. Volcanic center(s)to to the the west west were were topographically topographically high high areas areas that that were were periodically periodically or or concontinuously tinuouslyexposed exposedabove abovethe thewater water surface, surface,whereas whereasthe theflanks flanks of of the thevolca— volcain a shallow basin. nos were were periodically periodically or or continuously continuouslysubmersed submersed in a shallow basin. nos S 33 �TIDAL BASIN OF OF THE TIDAL DEPOSITS DEPOSITS IN INTHE THEEARLY EARLY PROTEROZOIC PROTEROZOIC BASIN THE LaKE LAKE SUPERIOR SUPERIOR REGION-REGION-POKEGAJ4A FORMATION: FORMATION: EVIDENCE EVIDENCE FOR FOR SUBTIDAL-SHELF THE PALMS PALMS AND AND POKEGAMA SUBTIDAL-SHELF DEPOSITION DEPOSITION OF OF SUPERIOR—TYPE SUPERIOR-TYPE BANDED BANDEDIRON—FORMATION IRON-FORMATION Richard of Geology, University of DuRichard W. W. Ojakangas, Ojakangas, Department Department of Geology, University of Minnesota, Minnesota, Du- luth, luth, Minnesota Minnesota 55812. 55812. ABSTRACT ABSTRACT The Palms Palms Formation in Wisconsin Wisconsin and and Michigan Michigan and and the the correlative correlative PokegPokegThe Formation in ama Quartzite in Minnesota are interpreted interpreted as tidal deposits formed along the margins margins of of the the early early Proterozoic Proterozoic Animikie Animikie basin. basin. The well—exposed which extends extends for for 85 km along well-exposed Palms Formation, Formation, which along the the Gogebic Gogebic range, range, is 150 m thick and can be divided divided into into three units on the basis thin lower basis of of rock rock types types and and bedding bedding styles. styles. (1) AA thin lower unit consists consists of of unconformably overlies overli.es aa low-relief low—relief surthin—bedded argillaceous surthin-bedded argillaceous rocks rocks and unconformably Archeangranite granite and face of of Archean and greenstone greenstone and and older older Proterozoic Proterozoic sedimentary sedimentary thick middle unit consists consists of units. A thick middle unit of thin thinalternating alternatingbeds bedsof ofargil— argilunits. (2) (2) A lite, siltstone andand sandstone vary considerably texture and compolite, siltstone sandstonethat that vary considerablyinin texture and composition. sition. Bedding types types include include parallel, wavy, cross cross and and flaser flaser lamination, lamination, An upper unit and aa variety variety of of sedimentary sedimentary structures structures are are present. present. (3) An consists of thicker consists thicker beds of parallel and cross—bedded cross-bedded sandstone. other measurements and and 52 A total total of of 199 cjross—bedded cross-bedded measurements 52 measurements measurements of of other paleo—current indicators paleo-current indicators from the the Palms Palms Formation Formation yields yields aa crude crude bimodal— bimodalbipolar distribution, distribution, with a broad broad primary primary mode mode to to the the west west and and aa weaker weaker sandstones are are mineralogically mode to to the the east. east. The The sandstones mineralogically mature; most of the the grains are quartz grains. The sandstones sandstones of of the framework grains framework are rounded rounded quartz grains. The the middle middle whereas those are unit have sericitic matrix, those of the the upper upper unit unit are unit have an an abundant abundant, sericitic matrix, whereas texturally more texturally more mature. mature. The pokegama The Pokegama Quartzite Quartzite is is exposed exposed at at only only aa few few places places along along the the 130 130 km km long Mesabi range range on on what what was was about about the the northwest northwest margin margin of of the the Animikie Animikie However, basin. However, the the entire entire formation formation can can be be viewed viewed in in two two drill drill cores cores in in Sedimentary sequences sequences and the mineralogiwhich it thick. Sedimentary which it is is5050inm and and 26 26in m thick. paleocurrent plot plot (Nm38) (N38) is cal attributes are are similar similar to to the the Palms. Palms. The paleocurrent is north and bimodal—bipolar with primary modes to crudely bimodal-bipolar to the the north and south. south. By utilization utilization of of Waither's Walther's Law Law of of facies facies relationships relationships and and comparisons comparisons with modern environments, environments, it can can be be postulated postulated that that both both formations formations were were deposited under transgressive transgressive tidal tidal conditions. conditions. In this model, model, the the lower lower (shaly) facies (shaly) facies was was deposited deposited in in aa low—energy low-energy domain domain of of the the upper upper (shoreward) (shoreward) tidal tidal flat, flat, the the middle middle facies facies (shale—siltstone—sandstone) (shale-siltstone-sandstone) was was deposited deposited on on a middle middle tidal tidal flat flat under under alternating alternating low low and and high high energy energy conditions, conditions, and and the upper subtidal upper facies facies (sandstone) (sandstone) was was deposited deposited in in lower lower tidal tidal flat flat or or subtidal high—energy high-energy development. development. The Palms Palms and and Pokegama Pokegama formations formations pass upward upward into into the the Ironwood Ironwood and and Biwabik Iron Iron Formations, Formations, respectively. respectively. Again using Walther's Walther's Law, it it can can be postulated were deposited deposited on on a shelf located postulated that the the iron—formations iron-formations were seaward from subtidal sandstone sandstone facies. The The "cherty" "cherty" (coarser (coarser grained, grained, seaward from the the subtidal thicker bedded iron iron oxide—chert) oxide-chert) facies facies was was deposited deposited in in shallower shallower water water 34 �than than was was the the "slaty" "slaty" (finer (finer grained, grained, thinner thinner bedded, bedded, iron iron silicate—iron silicate-iron carbonate) carbonate) facies. facies. The The tidal—subtidal tidal-subtidal facies facies model model developed developed here here provides provides an an independent independent approach in evaluation of the environment of deposition of one approach in evaluation of the environment of deposition of one kind kind of of Lake Lake The model is primarily based upon Superior-type banded iron—formation. Superior-type banded iron-formation. The model is primarily based upon the the siliciclastic siliciclastic lithologies lithologies associated associated with with iron-formation iron-formation rather rather than than upon upon the the iron—formation iron-formationitself. itself. 35 �I SEDIMENTATION AND MID PETROLOGY OF ARCHEAN FELDSPATHIC FELDSPATHIC QUARTZITE SEDIMENTATION QUARTZITE AND CONGLOMERATE MINNESOTA CONGLOMERATE (SEINE (SEINE SERIES SERIES EQUIVALENT), EQUIVALENT), RAINY RAINY LAKE, MINNESOTA R.W. Ojakangas, Department Department of Geology, R.W. Ojakangas, Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, Minnesota 55812; and Jean New Jean M. M. Olson, Olson, Chevron, Chevron, Inc., Inc., 935 935 Gravier Street, New Orleans, Orleans, Louisiana Louisiana 70112 70112 I ABSTRACT ABSTRACT The greenstone belt which into the The greenstone belt which extends extends westward westward into the Rainy Rainy Lake Lake area area of of Minnesotafrom fromOntario Ontarioincludes includesaa clastic clastic succession succession of of feldspathic—lithic feldspathic-lithic Minnesota quartzite The quartzite quartzite forms an easterly easterly trending quartziteand andconglomerate. conglomerate. The forms an trending unit unit about 16 long and forms aa lens about 16 km km long and about about 0.8 0.8 km km wide, wide, and and the the conglomerate conglomerate forms lens of long and and 180 180m mthick thickatatthe thetop top of of the the unit. unit. The rocks are of 33 kin km long The rocks are about about vertical and and top The vertical top to to the the south south as as determined determined by by abundant abundant cross—bedding. cross-bedding. The quartzite—conglomerate unit unit of of the the Seine Series of Ontario quartzite-conglomerate Ontario occupies occupies the same stratigraphic position position 26 26 km to the the east, east, and and continues continues eastward eastward for another 40 km. another 40 km. contact of the contact The of the the feldspathic—lithic feldspathic-lithic quartzite quartzite with with the theunderlying underlying volcanic exposed Minnesota, quartzite—conglomerate volcanic rocks rocks isisnot not exposedinin Minnesota,and andthe the quartzite-conglomerate unit appears to be interbedded with greenschist. Thus it it has interunit appears to be interbedded with greenschist. Thus has been been interpreted as an essentially conformable contact (Ojakangas, 1972), but struc(Ojakangas, 1972), strucpreted tural complications complications and an unconformity unconformity may well be obscured obscured by the the lack lack of outcrop. To the east in Ontario near Mine Centre, an unconformable the east in Ontario near Mine Centre, an unconformable basal basal outcrop. contact has been been described described by by Lawson Lawson (1913) (1913) and Wood Hood (1980), (19801, and and Lawson Lawson also interpreted the contact in Minnesota as an unconformity. interpreted the contact in Minnesota as an unconformity. Paleocurrent Paleocurrent analysis analysis of of the the cross—bedding, cross-bedding, which which is is dominantly doninantly of of the the trough type, shows a strong mode to the southwest after a two—tilt correctrough type, shows to the southwest after a two-tilt correction, and and the the variance variance is is aa low low 4051. 4051. The cross—bedding cross-bedding style, the the lack lack of original shale, the abundance of original sandstone, the abundance of original shale, the abundance of original sandstone, the abundance of clay— clayey matrix in in the the sandstone, sandstone, and and the the variance variance are are all all suggestive suggestiveof of deposideposition in in aa braided braided stream stream environment. environment. The associated associated conglomerate, conglomerate, which is largely clasts as is largely clast clastsupported supported with with rounded rounded clasts as large largeasas25 25cm, cm,contains contains clasts of "granite," feldspar porphyry, quartz—feldspar porphyry, clasts of "granite," feldspar porphyry, quartz-feldspar porphyry, quartzite, quartzite, chert, and biotite schist. The conglomerate conglomeratecan can be be interpreted pro— chert, and biotite schist. The interpretedas asa a prograding alluvial fan deposit. Wood (1980) arrived at a similar interpretagrading alluvial fan deposit. Wood (1980) arrived similar interpretation for Lawson (1913) (1913) interpreted the the for the the equivalent equivalent Seine Seine Series, Series, and and Lawson sequence as fanglomerates and fluvial deposits. sequence fanglanerates fluvial The sources sources of the the detritus detritus in in the the quartzite quartzite and and conglomerate conglomerate are are ininterpreted to have been nearby volcanic rocks and coeval plutons intrusive been nearby volcanic rocks and coeval plutons intrusive The unconformity, into the the volcanic volcanic pile. pile. unconformity, if present all along the the belt, probably is a minor erosional surface within the volcanic—sedimentary probably is a minor erosional surface within the volcanic-sedimentary sesequence, similar to quence, similar tothat thatbetween between the theSaganaga Saganaga batholith batholith and and the theKnife KnifeLake Lake It in the Group Group in the eastern eastern Vermilion Vermilion district district of of northeastern northeastern Minnesota. Minnesota. It seems likely that that at at least least moderate moderate relief relief was was present present in in the the source source area, area, perhaps along the the southern southern edge edge of of aa long long fault fault block, block, with with alluvial alluvial fans fans adjacent to the the source source rapidly rapidly grading grading southward southward into into aa braided braided alluvial alluvial plain. Renewed upliftinin the the source source area area caused progradation of of the Renewed uplift caused aa progradation the fans fans over the alluvial Goldich and and over alluvial plain, at least least in in the the Minnesota Minnesota sequence. sequence. Goldich (1961), suggested suggested that that the tonalite on Grassy others km others (19611, Grassy Island, Island, just just 1.3 1.3 km north of the the conglomerate, conglomerate, was was aa possible possible source source of of some some clasts. clasts. 36 I �Wood Wood(1980) (1980)suggested suggestedthat thatthe theturbidites turbiditesofofthe theQuetico Queticometasedimenmetasedimentary taryunit unitwhich whichborders bordersthe thequartzite-conglomerate quartzite-conglomerateon onthe thesouth, south,may maybebethe the deep—water deep-water equivalent equivalent of ofthe theterrestrial terrestrialSeine SeineSeries. Series. The Themetamorphic metamorphic recrystallization theequivalent equivalentbiotite biotite metasedimentsand andof ofthe recrystallizationofofthe theQuetico Queticometasediments schistsjust justto tothe thesouth southofofthe theRainy RainyLake—Seine Lake-SeineRiver RiverFault FaultininMinnesota Minnesota schists mineralogic comparisons components makes detailed detailedoriginal original mineralogic comparisonsofoforiginal original componentsofof makes the biotite biotite schist schistwith withthose thoseofofthe thelower lowergrade gradequartzite quartziteimpossible. impossible. AA the limited limited study study of of zircon zircongrains grainsshows showsthat thatthere thereare aredifferences differencesin inthe the varieties varietiesof ofzircons zirconsininthe thetwo twounits, units,and andthis thiscan canbebeinterpreted interpretedasasevievidence dence of ofdifferent differentsource sourceareas. areas. However, However, horizontal horizontal movement movement along alongthe the Rainy Rainy Lake—Seine Lake-SeineRiver RiverFault Faultcould couldhave haveplaced placedwidely widelyspaced spacedsedimentary sedimentary georockunits unitswhich whichwere were derived derived from from different differentsources sourcesbecause because of oftheir their georock graphical graphicalpositions, positions, into intojuxtaposition. juxtaposition. Thus, Thus,original originallateral lateralfacies facies relationships relationships in in the theRainy Rainy Lake Lakevicinity vicinity cannot cannotbe beproven provenuntil untilmovement movement along alongthe thefault faultisisbetter betterunderstood. understood. REFERENCES REFERENCES Goldich,5.5., S.S., Nier, Nier,4.0., A.O., Baadsgaard, Baadsgaard,H., H., Hoffman, Hoffman,J.H. J.H. and andKrueger, Krueger,H.W., H.W., Goldich, 1961, 1961, The The Precambrian Precambriangeology geologyand andgeochronology geochronology of ofMinnesota: Minnesota: 193 p. sota Geol. Surv. Bull. 41, sota Geol. Surv. Bull. 41, 193 p. MinneMinne- Lawson,A.C., A.c., 1913, 1913, The The Archean Archeangeology geologyof ofRainy RainyLake Lakerestudied: restudied: Canada Canada Lawson, Geol. Survey Mem. 40, 115 p. Geol. Survey Mem. 40, 115 p. R.W., 1972, 1972, Rainy Rainy Lake Lakearea: area: in 2 Sims, Sims,P.K. P.K. and andMorey, Morey,G.B., G.B., Ojakangas,R.W., ojakangas, A centennial Volume, Minnesota Geol. A Centennial Volume, Minnesota Geol.Surv., Surv., Eds., Geology of Minnesota: Eds., Geology of Minnesota: 163-171. .p. 163—171. Wood, John, John, 1980, 1980, Epiclastic Epiclastic sedimentation sedimentation and and stratigraphy stratigraphy in inthe theNorth North Wood, Spirit Lake Spirit Lakeand andRainy RainyLake Lake areas: areas: aacomparison: comparison: Precambrian PrecambrianResearch, Research, V. v. 12, 12,p.p.227—255. 227-255. I p I 37 S �MINERALOGY OF GRANITIC GRANITIC ROCKS, MINERALOGY OF ROCKS, WISCONSIN WISCONSIN W.L. Geophysics, University W.L. Petro, Department Department of of Geology Geology & & Geophysics, University of of Madison, Madison, 53706 Madison, Wisconsin Wisconsin 53706 WisconsinWisconsin— ABSTRACT ABSTRACT Crystallization histories have have been Crystallization histories been determined determined for for several several Penokean Penokean plutons in in northern northern Wisconsin, Wisconsin, with with emphasis emphasis on on the the extent extent and and nature nature of of mineral equilibria equilibria developed developed during during magmatic magmatic as well asassubsequent subsequent subas well sub— solidus solidus conditions. conditions. Detailed Detailed electron electron microprobe microprobe analyses analyses of minerals minerals show show that most of the variation is equilibration to incomplete incomplete equilibration that most of the compositional compositional variation is due due to during during various various stages stages of of crystallization. crystallization. This is preserved preserved in in some some cases cases This is as zoned mineral grains, as zoned mineral grains, especially especially plagioclase. plagioclase. Systematic Systematic element element parpartitioning proximity titioning indicates indicates that that only only grains grains in incontact contactororclose close proximityhave have approached approached chemical chemical equilibrium. equilibrium. Comparison Comparison of of partitioning partitioning with with published published experimental experimental and and empirical empirical studies studies allows allows some some mineral mineral pairs pairs to to be be used used to to estimate estimate intensive intensive parameters parameters obtained obtained during during crystallization crystallization (e.g., (e.g., plagioclase alkali feldspar). feldspar). These These relations relations are are often often complicated complicated by by plagioclase — alkali more more than than one one superimposed superimposed event. event. flthough Although most most of of the the data data presented presented are are from from the the Penokean Penokean batholith batholith in in northern northern Wisconsin, Wisconsin, comparisons comparisons with with published published data data from from the the Wolf Wolf River River and and Wrntello Montello batholiths batholiths allow allow definition definition of of some some spatial spatial and and temporal temporal patterns patterns in in granitic granitic plutonism. plutonism. All All three three batholithic batholithic suites suites have have peraluminous peralminous and and metaluminous metalminous rocks, rocks, with with peralkaline Some mineralogical peralkaline rocks rocks absent. absent. mineralogical differences differences between between the the orogenic orogenic Penokean Penokean batholith batholith and and anorogenic anoroqenic Wolf Wolf River River and and Montello Montello batholiths batholiths are are similar similar to to differences differences between between Mesozoic—cenozoic Mesozoic-Cenozoic granitic granitic rocks rocks of of contrasted contrasted tectonic tectonicsetting. setting. - I I I '1 I 38 �MINERALOGY ANDMETAMORPHISM METANORPHISM PELITIC ROCKS, MINERALOGY AND OFOFPELITIC ROCKS, WISCONSIN WISCONSIN 0 Geophysics, University University of of W.L. Petro, Department Department of of Geology Geology && Geophysics, W.L. Petro, C.A. Geiger, Department of Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin 53706; 53706; C.A. Geiger, Department of Geophysical Geophysical Sciences, Sciences, University University of of Chicago, Chicago, Chicago, Chicago, Illinois Illinois 60637; 60637; C.V. C.V. Department of Geological Sciences, University of Maine—Orono, Guidotti, Department of Geological Sciences, University of Maine-Orono, Guidotti, Orono, Maine Maine 04469 04469 ABSTRACT ABSTRACT I Pelites Pelites from from several several locations locations in in Wisconsin Wisconsin have have been been sampled sampled for for Pelitic compositions are sensitive to grade of metamorphism so that Politic compositions are sensitive to grade of metamorphism so that petrographic petrographic analysis analysis to to determine determine metamorphic metamorphic assemblages assemblages can can define define relarelaIn addition, electron microprobe tive pressure and temperature conditions. tive pressure and temperature conditions. addition, electron microprobe study. study. 0 analyses analyses of selected selected mineral mineral pairs pairs allow allow estimates estimates of of pressure pressure and and tem— temperature based on comparisons with published experimental and empirical perature based on comparisons with published experimental and empirical studies studies (e.g., (e.g., garnet—biotite garnet-biotite Fe—Mg Fe-Mg exchange exchange equilibria). equilibria). Comparisons Comparisons with with published and unpublished literature allow spatial and temporal published and unpublished literature allow spatial and temporal patterns patterns of of Two major metamorphism to to be be determined. determined. major periods periods of of Proterozoic Proterozoic metametamorphism are politic rocks rocks of of Wisconsin, Wisconsin, and and each each period period are recorded recorded in in the the pelitic may may be be subdivided subdivided into into several several events. events. The The older older period period occurred occurred 1800—2000 1800-2000 Mya, and reached reached a peak peak of of amphibolite amphibolite grade grade in in parts parts of of northern northern and and Mya, This central Wisconsin. Wisconsin. This metamorphism metamorphism was was predominantly predominantly low low pressure pressure type type central (andalusite ± sillimanite) sillimanite) with one one important important exception exception being the the Powell Powell (andalusite kyanite kyanite locality locality where where medium medium pressure pressure was was obtained. obtained. High High pressure pressure metametaeclogite morphism morphism (i.e., (i.e., eclogite or or blueschist) blueschist) has has not not been recognized recognized in in Wisconsin, Wisconsin, which which is is an important important constraint constraint on on Penokean Penokean tectonic tectonic models. models. The The younger younger period period occurred occurred 1600—1700 1600-1700 Mya, and and was was low low grade grade over over much much of of northern reaching aa peak of amphibolite northern and central central Wisconsin, Wisconsin, reaching amphibolite grade grade at Waterloo. Waterloo. +  I I 39 �MINERAL UNERAI, DEPOSITS DEPOSITS OF OF THE THE FORT FORT FRANCES-MINE FRANCES-MINE CENTRE CENTRE AREA AREA K. K. Howard Howard poulsen, poulsen, Queen's Queen's University*, University*, Kingston, Kingston, Ontario, Ontario, X7L K7L 3N6 3N6 ABSTRACT ABSTRACT The Centrearea areaisis part part of The Fort Fort Frances—Mine Frances-Mine Centre of the theRainy Rainy Lake Lake region, region, an an area has played played aa significant area which which has significant role role in inthe theevolution evolutionof ofideas ideasabout about the the Archean Archean geology geology of of the the Canadian Canadian Shield. Shield. Since Since representatives representatives of of all all major rock types of Archean terranes (mafic to felsic metavolcanics, wackes major rock types of Archean terranes (mafic to felsic metavolcanics, wackes and and mudstones, mudstones, conglomerates conglomerates and and arenites, arenites, layered layered gabbroic gabbroic intrusions, intrusions, tonalitic intrusions and granodiorite—quartz monzonite tonalitic intrusions and granodiorite-quartz monzonite plutons) juxplutons) are are juxtaposed In taposed here, here, it it was was once once considered considered aa type type area. area. In addition addition to to the the lithological lithological diversity, diversity, aa wide wide variety variety of of mineral mineral deposit deposit types types is is present. present. Stratiform Stratiform volcanic—hosted volcanic-hosted mineralization mineralization consists consists of of ironstones, ironstones, base base metal suif ides and intercalations of the two. Four metal sulfides and intercalations of the two. Four sub—types sub-types are are recognized. ides (Gagne recognized. First, First, narrow narrow lenses lenses of of Zn—Pb Zn-Pb sulf sulfides (Gagne Lake Lake type) type) are are overlain overlain by by chert chert and andunderlain underlain by by sulfide—bearing, sulfide-bearing, altered altered lapilli lapilli tuff tuff which locally consists of a chlorite—cordierite—anthophyllite assemblage. which locally consists of a chlorite-cordierite-anthophyllite assemblage. mineralization (Port Second, Second, wide wide zones zonesofoflow—grade low-grade Zn—Cu Zn-Cu mineralization (PortArthur ArthurCopper Copper type) consist of 1— seams of to20—centimeter—wide 20-centimeter-wide seams of massive massive sphalerite— sphaleritetype) consist of 1- to chalcopyrite—pyrite chalcopyrite-pyrite which are are intercalated intercalated with with similar similar widths widths of of barren barren chlorite niafic conunonlya abrecciated brecciatedamygdaloidal amygdaloidal mafic chlorite schist. schist. The The host host rock rock is iscommonly metavolcanic, metavolcanic, but but felsic felsic volcanics volcanics occur occur both both above above and and below below the the mineramineralized lized zone. zone. Third, Third, Zn—Cu Zn-Cu mineralization mineralization (Pocket (PocketPond Pondtype) type) is is found found in in black black pyritic pyritic shale shale and and in inmassive massive pyrite—pyrrhotite pyrite-pyrrhotite lenses lenseswhich whichare areconconformable to 22 percent percent Zn Zn occur occur formable with with chert—magnetite chert-magnetite ironstones: ironstones: grades grades of of 1 1 to over over five—meter five-meter widths. widths. Fourth, Fourth, ironstones ironstones composed composed of ofchert—magnetite, chert-magnetite, massive ides and massive suif sulfides and minor minor skarn skarn commonly commonly contain contain only only traces traces of of chalcopyrite. chalcopyrite. Of Of the the above above four four types types of of mineralization, mineralization, the the first first two two represent represent low—grade low-grade volcanogenic volcanogenic sulfides sulfides localized localized at at particular particular strat— stratigraphic volcaniclastics. The The last last igraphic horizons horizons in in areas areas of ofabundant abundantfelsic felsicvolcaniclastics. two two types types are are analogous analogous to to Phanerozoic Phanerozoic Besshi—type Besshi-type mineralization mineralization and and are are found found in in volcanic volcanic sequences sequences dominated dominated by by mafic mafic metavolcanics, metavolcanics, gabbros gabbros and and metamorphosed metamorphosed wackes. wackes. Layered Layered gabbro—anorthosite gabbro-anorthosite sills sills contain contain both both sulfide sulfide and and oxide oxide mineralization. Chalcopyrite—pyrrhotite mineralization. Chalcopyrite-pyrrhotite lenses lenses containing containing minor minor pentpentlandite, landite, molybdenite, molybdenite, apatite apatite and and ilmenite ilmenite are are distributed distributed along along the the base base of of the the Grassy Grassy Portage Portageintrusion, intrusion, the thebest bestconcentrations concentrations comprising comprising the the Northrock 1.89 percent percent Cu. Cu. This This type type of of Northrock deposits deposits of of 300,000 300,000 tons tons grading grading 1.89 mineralization netand anddroplet droplettextures textures as as well mineralization displays displays magmatic magmatic net well as as local local zones ides and zones of of remobilized remobilized suit sulfides and hydrothermal hydrothermal alteration. alteration. At At aahigher higher stratigraphic stratigraphic level level in in the theintrusion, intrusion, lower lower grade grade Cu Cu mineralization mineralization is is found found within within aa siliceous siliceoushost host which which may may represent represent assimilated assimilated country country rock. rock. Fe-Ti Fe-Ti oxide oxide mineralization mineralization also also occurs occurs in in the the upper upper part part of ofthe theintrusion intrusion as as lenses lenses of ofdisseminated disseminatedtotomassive massivemagnetite—ilmenite magnetite-ilmenite and andasasirregular irregular masses rutile-apatite rock. rock. Oxide Oxide mineralization mineralization is is also also masses of of nelsonite, nelsonite, aa rutile—apatite well well developed developed in in the theSeine SeineBay Bay anorthositic anorthositicsill. sill. I Quartz Quartz vein vein mineralization mineralization is is of of two two types. types. Molybdenite, Molybdenite, with with pyrite pyrite and and local local chalcopyrite, chalcopyrite, occurs occurs in in quartz quartzstockworks stockworks and and extensional extensional veins veins 40 �with metasedimentary within within granodioritic granodioritic intrusions intrusionsnear nearcontacts contacts with metasedimentarycountry country gold, along with carbonates and ides, contrast In rocks. rocks. In contrast gold, along with carbonates and base base metal metal sulf sulfides, occurs occurs in in lenticular lenticular quartz quartz veins veins associated associated with with shear shear zones zones and and saddle saddle Gold—bearing reefs. reefs. Gold-bearing veins veins occur occur in in aa variety variety of of rock rock types types and and are are They greenschist—facies metamorphism. zones of to restricted be restricted to zones of greenschist-facies metamorphism. They can can be related related to to shear sheardisplacements displacementsononregional regionaltranscurrent transcurrentfaults faultsand andtheretherefore represent a late stage of mineralization. fore represent a late stage of mineralization. * AA distinctive distinctive clastic clastic ultramafic ultramafic unit unit is is exposed exposed within within the themafic mafic porporIt is likely of epiclastic origin tion tion of of the the volcanic volcanic succession. succession. It is likely of epiclastic originand andis is compositionally compositionally magnesian maqnesian (21 (21percent percent MgO). MgO). Local Local zones zonesof of foliated foliatedultra— ultramafic mafic rock rock contain contain disseminated disseminated Ni—Cu Ni-Cu sulfides sulfideswhich which may may result resultfrom frommetametamorphic morphic remobilization. remobilization. The The various various types types of of mineralization mineralization at at Rainy Rainy Lake Lake can can be be related related to to the the •8 •Â  geological geological evolution evolution of of the the rocks rocks of of the the region. region. Early Early volcanism volcanism and and iron and generated stratiforra systems related related hydrothermal hydrothermal systems generated stratiform iron and base base metal metal mineralization. mineralization. Coeval Coeval subvolcanic subvolcanic sills, sills, which which possibly possibly drove drove these these conconand yield magmatic sulfide to differentiated vective vective systems, systems, differentiated to yield magmatic sulfide and oxide oxide concentrations. concentrations. Granodiorite Granodiorite intruded intruded the the supracrustal supracrustal sequence sequence after after iniinitial tial folding folding and and local local stockworks stockworks developed developed near near pluton pluton contacts. contacts. Con— Continued tinned folding folding and and metamorphism metamorphism took took place place within within aatectonic tectonicwrench wrenchzone, zone, generating gold—bearing veins in dilational structures while remobilization generating gold-bearing veins in dilational structures while remobilization of of existing existing mineralization mineralization took tookplace. place. In In aa metallogenic metallogenic sense, sense, copper copper is is the only commodity which is common to all environments of mineralization: the only commodity which is common to all environments of mineralization: this this may may reflect reflect the the importance importance of of rifts rifts in in the the early early history history of of the the region. region. * Study Study supported supported by by Mineral Mineral Deposits Deposits Section, Section, Ontario Ontario Geological Geological Survey Survey * p I 41 p �GOLD GOLD MINERALIZATION MINERALIZATION MID AND OCCURRENCES OCCURRENCES IN IN THE THE ATIKOKAN AREA ATIXOXAN AREA B.R. B.R. $chnieders, Schnieders, Resource Resource Geologist, Ministry of Natural Resources, Thunder Natural Resources, Bay, Ontario Ontario ABSTRACT ABSTRACT Atikokan is is situated situated 200 200 3cm km west Bay and and earned earned its its mining mining west of Thunder Bay fame from the the discovery discovery of of the the Steep Steep Rock Bock Iron Iron Range Range in in the the late late 1930's. 1930's. Gold, however, however, was was discovered discovered in in the the Atikokan Atikokan and and Mine Mine Centre Centre areas areas in in the the late 1800's 1800's and and eventually eventually led led to to one one of of Ontario's Ontario's first first gold gold camps. camps. The general general geology geology of of the the area area consists consists of of early early Precambrian Precambrian rocks rocks of of the Wabigoon and and Quetico Quetico subprovinces, subprovinces, separated separated by by the the east—west east-west Quetico Quetico fault. The Wabigoon fault. Wabigoon subprovince, subprovince, to to the the north, north, consists consists of of metavolcanics, metavolcanics, minor metasediments metasediments and and granitic granitic batholiths. batholiths. The The Quetico Quetico subprovince subprovince consists of metasediments sists metasediments and and granitoids. granitoids. ultramafic plutons plutons occur occur Small ultramafic throughout throughout the the metasediments. metasediments. Within radius of of Atikokan, Atikokan, more than 50-km radius than 50 50 gold gold occurrences, occurrences, prosprosWithin aa 50—1cm pects and and past producers producers have have been been discovered discovered since since the the 1600's. 1800's. The ~tikoThe Atilco— kan kan gold study study performed performed by by the the Ontario Ontario Geological Geological Survey survey (Wilkinson, (Wilkinson, 1982) 1982) area; the MarmHarm— defined three three types types of of gold gold mineralization mineralization in in the the Atilcokan Atikokan area; ion Lake Batholith ion Lake Batholith type, type, the the contact contact zone zone type, type, and and the the metavolcanic—hosted, metavolcanic-hosted, Twenty—oneproperties properties in stratabound type. type. stratabound Twenty-one in the the area areawere were geologically geologically sampled, researched, mapped and mapped and sampled, researched, and petrographically petrographically and and geochemically geochemically studied. Geological observations studied. Geological observations and and data data from front the the Atikokan Atikokan Economic Economic GeolGeolwill also be presented in discussing discussing the the types types of of gold gold mineralmineralogy Program Program will also be ization, ization, genetic genetic models models and and exploration exploration targets targets and and techniques. REFERENCE deposits of Wilkinson, S.J., 1982, Gold deposits of the Atikokan Atikokan area: Wilkinson, $.J., 1982, Geological Geological Survey, Survey, Mineral Mineral Deposits Deposits Circular Circular 24, 24, 54 54 p. 42 Ontario Ontario �NATURE SEDIMENTARY ROCKS NATURE AND SIGNIFICANCE OF SHALLOW SHALLOW WATER WATER SEDIMENTARY ROCKS IN NORTHEASTERN IN NORTHEASTERN WISCONSIN WISCONSIN Klaus JJ.. Schulz, Schulz, Department of Earth Earth and and Planetary Planetary Sciences, Sciences, Washington Washington Klaus Ho. 63130 63130 and and U.S. U.S. Geological Geological Survey; Survey; Paul Paul K. K. Sims, University, St. St. Louis, Mo. U.S. Geological U.S. Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225 80225 Recent reconnaissance reconnaissance mapping in northern northern Wisconsin Wisconsin has resulted resulted in in the recognition of a shallow water, sedimentary sequence underlying the recognition of shallow water, sedimentary sequence underlying the Quinnesec Formation (HoskinLake Lake Granite) Granite) Formation and and overlying overlying the the Bush Bush Lake Lake lobe lobe (Hoskin of the These sediments the Dunbar Dunbar gneiss gneiss dome dome in in Florence Florence County. County. sediments were in in part recognized by Dutton (U.S.G.S. P.P. 1971) but were considered recognized by Dutton (U.S.G.S. P.P. 633, but considered 633, local deposits deposits within within the the metavolcanic metavolcanic Quinnesec Quinnesec Formation. Formation. The present present mapping, in conjunction mapping, conjunction with drill drill hole hole and and geophysical geophysical data, data, show show that that these sediments form an outward—facing, steeply—diping (70—80°) continuous these sediments form an outward-facing, steeply-diping (70-80"') continuous sequence along the western, western, northern and eastern eastern portions portions of of the the Dunbar Dunbar All dome. All the the rocks rocks in in this this area area lie lie within within the the garnet garnet zone zone of of the the Florence metamorphic node. Florence metamorphic node. poorly known but but The stratigraphy stratigraphy of the the sedimentary sedimentary succession succession is poorly consists of biotite schist, quartzite, marble, calc—silicate rock, meta— biotite schist, quartzite, marble, calc-silicate rock, metaGarnet and are present present in some arkose and some and graphite graphite schist. schist. and anda.lusite andalusite are the layers. The gross gross aspects aspects of some some of of these these rocks rocks resemble resemble those in the lower part of the the Marquette Marquette Range Range Supergroup Supergroup in in the the Menominee Menominee district district to to Marble and associated calc—silicate rocks exposed northwest the north. the north. and associated calc-silicate rocks exposed northwest of possible cryptalgal cryptalgal structures West Bass Lake contain contain siliceous, Bass Lake structures and siliceous, possible resemble parts of the Randville Dolomite, and a thick quartzite the Randville Dolomite, and a thick quartzite section section exposed along the Popple exposed along the Popple River, Diver, about about 33 km to to the the northwest, northwest, resembles resembles the the A h meta—arkose meta-arkose unit, unit, about about 100 100 mm thick, thick, is exposed exposed Sturgeon Quartzite. Quartzite. locally near the base of the sequence arkose and arkosic sequence and is not unlike arkose conglomerate conglomerate of of the the Fern Fern Creek Creek Formation. Formation. Although differences differences do schist—pelitic schist-politic compositions), exist exist (e.g. (e.9. greater abundance of greater of biotite biotite the metasedimentary rocks rocks exposed around the western margin margin of the western the Dunbar Dunbar dome dome have have affinities affinities with with those those characcharacteristic of the the basal basal Chocolay Chocolay Group Group of of the the Marquette Marquette Range Range Supergroup, Supergroup, is tentatively proposed. This correlation and a general correlation is and general correlation proposed. correlation suggests: suggests: 1) The rocks rocks of of the the Dunbar Dunbar dome dome represent represent pre—Chocolay pre-Chocolay basement basement in in 1) northeastern northeastern Wisconsin. Wisconsin. 2) 2) The Quinnesec Formation Formation is definitely Proterozoic in age and may be time time correlative correlative with the the Hemlock Hemlock Formation Formation of of Upper Michigan. Michigan. 3) 3) The Niagara Fault recently proposed recently proposed does not represent represent a crustal crustal suture suture zone zone as was by some authors. by some authors. 43 �I DUNBAR GNEISS GNEISS DOME DUNBAR DOME AND AND IMPLICATIONS IMPLICATIONS FOR FOR THE THE PROTEROZOIC STRATIGRAPHY STRATIGRAPHY OF OF NORTHERN NORTHERN WISCONSIN WISCONSIN P.K. Sims, UU.S. Geological Survey, P.K. .S. Geological Survey, Denver, Colorado Colorado 80225; 80225; Zell Zell E. E. Peterman, Peterman, U.S. Denver, Colorado 80225; Klaus J J. U.S. Geological Survey, Denver, . Schulz, WashingSt. Louis, Missouri 63130 ton University, St. ABSTRACT The The Dunbar Dunbar gneiss gneiss dome dome is is aa newly newly recognized recognized feature feature of of the the Proterozoic Proterozoic crystalline terrane crystalline terrane of of northeastern northeastern Wisconsin. Wisconsin. The dome is 20 km by 30 30 km across, trends northwest, km. across, northwest, and has aa structural structural relief relief greater greater than 11 km. The core core of of the the dome dome is is composed composed of of complexly complexly deformed deformed and and metamorphosed metamorphosed varied biotite gneisses, varied gneisses, foliated foliated megacrystic megacrystic granite, granite, and and foliated foliated gray gray tonalite. tonalite. It is unconformably mantled by less deformed metavolcanic rocks of the the Quinnesec Quinnesec Formation, Formation, and and locally locally by by quartzite, quartzite, marble, marble, meta—arkose, meta-arkose, These rocks dip steeply and biotite biotite schist. schist. These steeply and and face face stratigraphically stratigraphically as indicated by pillow pillow structures structures in in the The boundary beoutward, as indicated by the lavas. lavas. The outward, mantle is a zone about 500 500 mm wide wide characterized by by a a tween tween the the core and the mantle steeply plunging lineation, many cataclastic foliation, foliation, steeply plunging lineation, many small small bodies bodies of of compositionally diverse, diverse, syntectonic syntectonic granitoid granitoid rocks rocks that that are are confined confined to to compositionally Metathe mantle, mantle, and small small bodies bodies of of posttectonic posttectonic granite granite and and tonalite. tonalite. Metaamphibolite facies in most of the core and morphic zoning zoning is is concentric: concentric: amphibolite in the inner inner part part of of the the mantle mantle and and greenschist greenschist facies facies in in the the outer outer part. part. boundary was a zone The boundary zone of high high strain strain and and metamorphic metamorphic intensity intensity and and assoassoThe ciated anatexis that accompanied diapiric rise of the dome. The core is accompanied diapiric rise of the dome. The interpreted as a window exposing part of an extensive terrane terrane that suffered during diapirism dynamothermal prior to dynamothermal metamorphism metamorphism prior to diapirism; diapirism; during diapirism intense intense cataclasis in the boundary zone accompanied folding in the mantle. cataclasis zone mantle. Despite contrasting histories, rocks rocks of of the the core core and and the mantle mantle have have Despite contrasting histories, yielded nearly identical m.y. by the the U—Pb U-Pb zir1,860 m.y. yielded identical isotopic isotopic ages ages of about about 1,860 con method (Banks and Cain, 1969; Banks and Rebello, 1969), recalculated (Banks and Cain, 1969; Rebello, 1969), using new using new constants. constants. This apparent early Proterozoic age for both rock assemblages though simisimisemblages contrasts contrasts with the the domes domes in in northern northern Michigan Michigan which, though lar to the Dunbar dome in many ways, have cores of Archean basement to the Dunbar dome in many ways, have cores of Archean basement gneiss gneiss rocks and and granitoid granitoid rocks and mantles mantles of of early earlyProterozoic Proterozoicmetasedimentary metasedimentary and and Tentatively, from reconnaissance mapping metavolcanic rocks. metavolcanic rocks. Tentatively, from reconnaissance mapping the theDunbar Dunbar dome appearstoto be be just just one one of of the theseveral severaldomes domes in innorthern northernWisconsin Wisconsin havhavdome appears Where dated, these basement ing cores of Proterozoic rocks. cores of Proterozoic rocks. Where dated, basement rocks give ages of about about 1,850 1,850 n.y. m.y. (W.R. (W.R. Van Schmus, Schmus, oral oral comm., corn., 1981). 1981). We suggest that the norththe supracrustal supracrustal rocks that mantle the domes of northern Wisconsin are underlain by an extensive early Proterozoic amphibolite— underlain extensive amphiboliteThe supra— facies terrane facies terrane evidently evidently not not represented represented in in northern northern Michigan. Michigan. supracrustal rocks of northern Wisconsin, however, probably are coextensive crustal rocks northern are coextensive with the Marquette Range Range Supergroup Supergroup of of Michigan. REFERENCES Zircon ages ages of Precambrian Banks, .O., and Cain, Cain, J .A., 1969, Precambrian granitic granitic .Y.A., 1969, Zircon Banks, PP.O., Journal of Geology, v. 77, rocks, northeastern northeastern Wisconsin: Wisconsin: Journal 77, p. p. 208—220. 208-220. Banks, and Rebello, 1969, Banks, P.O., P.O., Rebello, D.P., D.P., 1969, Zircon Zircon age age of of Precambrian Precambrian rhyolite, rhyolite, Geological Society northeastern Wisconsin: northeastern Wisconsin: Geological Society of of America America Bulletin, Bulletin, v. v. 80, 80, p. 907—910. p. 907-910. 44 4 �PRELIMINARY PROGRAM PRELIMINARY RESULTS RESULTS OF OFAADRILLING DRILLING PROGRAMACROSS ACROSS THE THE GREAT GREAT LAKES LAKES TECTONIC TECTONICZONE, ZONE,CENTRAL CENTRALMINNESOTA MINNESOTA David David L. L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. Paul, Minnesota Minnesota55108 55108 Paul, ABSTRACT ABSTRACT The The Great Great Lakes Lakes tectonic tectonic zone zone (GLTZ), (GLTZ), aa complex complex intracratonic intracratonic deformed deformed belt Archean greenstone—granite greenstone-granite terrane terrane on on the the north north belt separating separating long—stable long-stable Jrchean from from multiply—reactivated multiply-reactivated Archean—Proterozoic Archean-Proterozoic gneiss gneiss terrane terrane on on the the south, south, has has been been defined defined in ineast—central east-central Minnesota, Minnesota, northern northern Wisconsin, Wisconsin, and and upper upper Michigan Michigan by by careful careful mapping mapping of of the the exposed exposed geology, geology, together together with with critical critical geochronologic geochronologic and and geophysical geophysical studies studies (Morey (Morey and and Sims, Sims, 1976; 1976; Sims Sims and and others, 1980). 1980). However, However, in in west—central west-central Minnesota, Minnesota, where where Precambrian Precambrian basebaseothers, ment ment is is concealed concealed by by thick thick glacial glacial drift, drift, the the trend trend and and extent extent of of the the GLTZ GLTZ have have been been inferred inferred largely largely from from regional regional gravity gravity and and aeromagnetic aeromagnetic patterns. patterns. During During the the past past two two years, years, aa traverse traverse across across the the GLTZ GLTZ approximately approximately at at longitude longitude 95°W 95OW in in central central Minnesota Minnesota has has been been investigated investigated by by COCORP COCORP seismic seismic reflection reflection profiling profiling and and also also by by detailed detailed gravity gravity and and aeromagnetic aeromagnetic surveys. surveys. Ten Ten holes holes over over aa distance distance of of 60 60km km have havebeen been drilled drilled into intobasement basement along along this this traverse traverse to to provide provide direct direct lithologic lithologic data data for for use use in ingeophysical geophysical modeling modeling (still (stillin in progress). progress). At At two two sites sites just just north north of of the theGLTZ, GLTZ,within withinthe thegreenstone—granite greenstone-granite block, the the drill drill encountered encountered massive, massive, coarse—grained coarse-grained amphibolite amphibolite derived derived block, from from gabbro gabbro and and aa closely closely allied allied quartz—poor quartz-poor hornblende hornblende quartz quartz diorite. diorite. At At aa site site just just south south of of the the GLTZ, GLTZ, within within the the gneiss gneiss block, block, the the drill drill encounencountered tered gneiss gneiss composed composed of of tonalitic tonalitic and and granitic granitic layers, layers, grossly grossly similar similar to the the Morton Morton Gneiss Gneiss of of the the Minnesota Minnesota River River Valley. Valley. Three drilled into into the the northern northern part part of of the the GLTZ GLTZ penetrated penetrated lowlow Three holes holes drilled grade grade metavolcanic metavolcanic and and volcaniclastic volcaniclastic rocks rocks of of intermediate intermediate composition. composition. Strong Strong cataclasis cataclasis is is evident evident in in two two cores cores drilled drilled close close to to the the inferred inferred north boundary. boundary. Two Two holes holes drilled drilled into into the the southern southern part part of of the the GLTZ GLTZ penepenenorth trated trated well—cleaved, well-cleaved, thin—bedded thin-bedded to to laminated, laminated, dark dark gray gray to to black black slate slate and and This metasiltstone. This slate slate is is lithologically lithologically akin akin to to various various Proterozoic Proterozoic metasiltstone. slates MilleLacs Lacsand andAnimikie AnimikieGroups Groups(although (althoughits itsage age is is not not known) known) slates in in the the Mule and and thus thus opens opens the the possibility possibility that that Proterozoic Proterozoic supracrustal supracrustal rocks may occur cur within within and and near near the the GLTZ GLTZ for for some some distance distance west west of of the the presently presently mapped mapped margin of of the the Animikie Animikie basin. basin. margin Biotite—hornblende high near near the the center center Biotite-hornblende diorite from from an an oval oval magnetic magnetic high the GLTZ has a panhedral or "lamprophyric" texture and is inferred to be of the GLTZ has a panhedral or "lamprophyric" texture and is inferred to be of Migmatized Miginatized biotite biotite paragneiss paragneiss from from the the flank km north north of of the the inferred inferred south south margin margin of of flank of of aa magnetic magnetic high high about about 22 km the the zone zone is is tentatively tentatively viewed viewed as as belonging belonging to to the the gneiss gneiss terrane. terrane. posttectonic, high—level high-level pluton. pluton. aa posttectonic, The GLTZ GLTZ in in central central Minnesota Minnesota is is occupied occupied largely largely by by low-grade low-grade meta— metavolcanic volcanic and and metasedimentary metasedimentary rocks rocks and and appears appears to to be be bounded bounded on on the the north north by aa major major steeply steeply dipping dipping fault fault zone. zone. No direct direct evidence evidence has has been been found found by 45 �ffor o r major faulting f a u l t i n g along along the t h e south south boundary, boundary, which instead may be an unconunconformable along part i t s length length with with Archean Archean and and possible possible formable contact contact along p a r t of of its Proterozoic Proterozoic supracrustal supracrustal rocks rocks resting r e s t i n g on on older older Archean Archean gneiss. gneiss. The ages ages of the GLTZ, GLTZ, and and their t h e i r structural s t r u c t u r a l relationship r e l a t i o n s h i p to to of the t h e supracrustal supracrustal rocks rocks in i n the granitoid g r a n i t o i d rocks, rocks, remain remain to t o be be demonstrated. demonstrated. REFERENCES REFERENCES Morey, G.E., G.B., Morey, and Sims, Sims, P.K., P.K., 1976, 1976, Boundary Boundary between between two two Precambrian Precambrian WW ter— tergeologic significance: Geological Society geologic significance: Geological Society of Nnerica America Bulletin, Bulletin, v. v. 87, 87, p. p. 141—152. 141-152. ranes and iits ranes in i n Minnesota Minnesota and ts S i m s , P.R., P.K., Card, Card, lcD., K . D . , Morey, Morey, G.E., G.B., and andPeterutan, Peterman, Z.E., Z.E., 1980, The The Great Great 1980, Sims, Lakes Lakes tectonic t e c t o n i c zone——a wneÑ major major crustal c r u s t a l structure s t r u c t u r e in i n central c e n t r a l North North Mteri— America: ca: Geological Geological Society Society of of America America Bulletin, Bulletin, Part P a r t I, I, v. v. 91, 91, p. p. 690—698. 690-698. 46 �WEATHERING AS RELATED WEATHERING OF ARCHEAN ARCHEAN ROCKS ROCKS AS BELATED TO TO IRON-FORMATIONS IRON-FORMATIONS G.M. Spencer, Jr., National Bank, Duluth, MNMN55812 G.H. Spencer, Jr., 619 619First First National Bank, Duluth, 55812 ABSTRACT ABSTRACT The The Archean Archean volcanic volcanic and and sedimentary sedimentary belts belts of of northern northern Minnesota Minnesota and and northwestern northwestern Ontario Ontario contain contain many many thin thin belts belts of of iron—formation. iron-formation. The The sedisedimentary mentary rocks rocks are are largely largely conglomerate, conglomerate, graywacke, graywacke, and and slate slate with with variable variable The amounts amounts of of volcanic volcanic material. material. The composition composition of of the the sedimentary sedimentary rocks rocks indicates indicates rapid rapid disintegration, disintegration, erosion, erosion, and and deposition deposition with with little little attenattendant dant oxidation oxidation and and leaching. leaching. In H20, C02, CO,, and and In the the earliest earliest period, period, the the atmosphere atmosphere was was accumulating accumulating H20, Basin waters were probably acidic as metals due to frequent vulcanism. Basin waters were probably acidic as metals N, due to frequent vulcanism. N2 were were dissolved dissolved out out of of the the volcanic volcanic rocks rocksat atthe thesame samerate rateasasthe thealkalis. alkalis. Within Within aa few few million million years years aa basin basin could could be be neutralized neutralized and and iron iron deposited deposited as as carbonate carbonate or or oxides, oxides, with with residual residual silica silica deposited deposited in in alternate alternate bands bands Clay was not flocculated as close because of seasonal flocculation. because of seasonal flocculation. Clay was not flocculated as close to to shore as was iron—formation which varied to deep deep water water fades facies shore as was iron-formation which varied from from shallow shallow to (Goodwin,1973). 1973). (Goodwin, Three Three types types of of iron—formation iron-formation are are present: present: a) a) the the Keewatin; Keewatin; the Lake Superior—Labrador Timiskaming or graywacke; and c) Timiskaming or graywacke; and c) the Lake Superior-Labrador Basin. Basin. the the In the In the b) b) Keewatin Keewatin type, type, iron iron occurs occurs with with chert chert as as siderite siderite or or iron iron oxides; oxides; these these components were derived from acid decomposition of pyroclastics components were derived from acid decomposition of pyroclastics with with some some The contribution contribution from from volcanic volcanic gases. gases. The volcanic volcanic gas gas quickly quickly decomposed decomposed under under acidic acidic conditions conditions and and alumina, alumina, alkalis, alkalis, and and silica silica formed formed clays clays in in It is believed the iron oxides and chert flocculated deeper deeper waters. waters. It is believed the iron oxides and chert flocculated and and precipitated precipitated closer closer to to the the sources sources of of the the decomposing decomposing volcanics, volcanics, while while some some soluble silica and alumina, being lighter and slower to flocculate, soluble silica and alumina, being lighter and slower to flocculate, were were removed. removed. The The Timiskaming Timiskaming or or graywacke graywacke type type of of iron—formation iron-formation is is associated associated with with These occur as thin beds and lenses chert chert and and slate slate beds. beds. These occur as thin beds and lenses of of iron iron oxides oxides deposited deposited during during quiet quiet periods periods of of turbidity turbidity flows, flows, and and are are related related to to rapid rapid There is sedimentation sedimentation in in troughs troughs adjacent adjacent to to steep steep mountain mountain chains. chains. There is little little indication decompsiindication of of active active vulcanism, vulcanism, but but bacterial bacterial action action in in mineral mineral decomposition tion may may have have occurred. occurred. Decomposition Decomposition of of the the pyroxenes pyroxenes and and amphibole amphibole minminerals erals in in graywacke graywacke resulted resulted in in aa pH pH of of more more than than9. 9. If If calcium, calcium, magnesium, magnesium, and and alumina alumina were were removed, removed, the the remaining remaining iron iron and and silica silica particles particles caused caused mutual mutual precipitation. precipitation. The Lake Lake Superior—Labrador Superior-Labrador Basin Basin type type of of iron—formation iron-formation occurs occurs on on the the flanks flanks or or shelves shelves of of the the Archean Archean masses. masses. These These deposits deposits may may be be 100 100 to to 300 300 meters meters thick thick and and 100 100 or or 200 200 kilometers kilometers in in strike strike length. length. Thin Thin beds beds of of carcarbonate, iron oxides, oxides, and and chert chert alternate, alternate, and and are are typified typified by by granular granular bonate, oolitic oolitic textures. textures. The The iron—formations iron-formations are are part part of of aa sedimentary sedimentary series series of of quartzite, quartzite, iron—formation, iron-formation, dolomite, dolomite, and and shale shale or or graywacke graywacke lying lying on on aa peneplained peneplained Archean Archean surface. surface. The sedimentary sedimentary sequence sequence is the result result of of transgressive seas seas spreading spreading over over aa peneplained peneplained and and glaciated glaciated surface surface and and sorting sorting the the pre—existing pre-existing sediments sediments into into sand, sand, silt, silt, and and clay clay fractions. fractions. 47 �Fine—grained Fine-grained materials such such as as volcanic volcanic ash ash or or clays clays were were susceptible susceptible to to rapid rapid chemical chemical decomposition decomposition in in both both acid acid and and alkaline alkaline conditions. conditions. The separation begun very early under under separation into oxides, oxides, clays clays and and solutes solutes may have have begun both both volcanic volcanic acid acid or or organic organic acid acid attack. attack. Silica Silica is is present present as as quartz, quartz, microcrystalline, microcrystalline, cristobalite, cristobalite, amorphous amorphous or opaline silica, and silica in solution. solution. The The two two intermediate intermediate forms forms may may alter alter to to quartz quartz grains, grains, chert, chert, clay, clay, or tests. be present present in in diatom diatom tests. or be Iron have formed formedhydroxides, hydroxides,oxides, oxides, carbonate carbonate sulfide sulfide or Iron materials materials may may have or migrated in solution. migrated in solution. Alumina mayhave havebeen beenremoved removed either acid acid or Alumina may in ineither or alkaline alkalineconditions conditionsororformed formedclays claysunder undernormal normal pH pH conditions. conditions. The The various various weathering possibilities depended on temperature, temperature, moisture, moisture, and and the the organic organic weathering possibilities depended on and mayhave havebeen beenaaparticular particular form and chemical chemical environment. environment. Iron—formations Iron-formations may form of of residual residual weathering weathering with with aa substantial substantial contribution contribution of of soluble soluble and and colloidal colloidaliron ironleached leachedfrom from nearby nearby soils soils or or sediments. sediments. REFERENCE REFERENCE Goodwin, 1973, Goodwin, A.M., A.M., 1973, Archean Archean iron—formations iron-formations and tectonic basins of the the Canadian Canadian Shield: Shield: Economic Economic Geology, Geology, v. v. 68, 68, p. p. 915—933. 915-933. 48 �SEASONAL SEASONAL THERMAL THERMAL ENERGY ENERGY STORAGE STORAGE (STES) (STES) SYSTEMS SYSTEMS IN IN MINNESOTA MINNESOTA Matt Matt Walton, Walton, Minnesota Minnesota Geological Geological Survey, Survey, 1633 Eustis Street, Street, St. St. Paul, Paul, Minnesota Minnesota 55108 55108 ABSTRACT ABSTRACT energy andand man—made "waste"heat heat provide provide alSeasonal Seasonal fluxes fluxes of ofsolar solar energy man-made "waste" al- ternatives ternatives to to fossil and and nuclear nuclear fuels fuels for for low—grade low-grade heat. heat. The key key is is Large be developed developed at at very very low—unit low-unit cost cost Large thermal thermal storage storage masses masses must must be because Geologic because of the the low low energy energy density density of of stored stored heat. heat. Geologic formations, formations, structures and and materials materials with with appropriate appropriate boundary boundary conditions conditions can can provide provide this this capacity. capacity. AA fluid fluid heat heat exchange exchange medium medium (air (air or or water) water) is is circulated circulated through through aa geologic geologic body body by by exploiting exploiting natural natural hydrogeologic hydrogeologic characteristics characteristics or or by by constructing constructing aa circulation circulation system. system. Diffusion and and dispersion dispersion of of heat are limited limited by by suitable suitable hydraulic hydraulic and and thermal thermal boundary boundary conditions. conditions. STES. STES. AA powerful powerful Aquifer Aquifer Thermal Thermal Energy Energy Storage Storage (ATES) (ATES)test test facility facility has has been been built on the St. Paul campus of the University of Minnesota to investigate on the St. Paul campus of the University of Minnesota to investigate storage storage of of superheated superheated water water in in aa deep, deep, confined confined lower lower Paleozoic Paleozoicaquifer. aquifer. Water from the Franconia—Ironton—Galesville aquifer is drawn from a supply from the Franconia-Ironton-Galesville well, well, heated heated in in aa heat heat exchanger exchanger and and injected injected in in aa heat heat storage storage well well in in the the Heat is extracted by reversing the cycle and injecting same aquifer. same aquifer. is extracted by reversing the cycle and injecting the the The spent spent water water back back in in the the supply supply well well with with no no net net loss loss of of water. water. The heat heat storage storage capacity capacity and and hydraulics hydraulics of of the the water—filled, water-filled, underground underground iron iron mines mines at Ely, Minnesota, are being investigated as the heat source for a at Ely, Minnesota, are being investigated as the heat source for acoinmun— community ity district district heating heating system. system. Heat extracted extracted by heat pumps pumps from from mine mine water water at ambient underground temperature during the winter can be replenished ambient underground temperature winter can be replenished during during the thesummer summer by exchanging exchanging chilled chilled mine mine water water for for sun—warmed sun-warmed surface surface In water from an open pit above the underground workings. front an open pit above the underground workings. In Blue Blue Earth, Earth, Minnesota, Minnesota, air is is drawn drawn through through aa grid grid of of drain drain tiles tiles buried buried in in glacial glacial the ground in the the winter, till, extracting extracting heat heat from from the ground in winter, returning returning heat heat to to the the till, ground in the and providing providing tempered temperedair air worth worth thousands thousands of of dollars ground in thesummer summer and dollars conditioning cost savings. air per per year year in inheating heating and and air conditioning cost savings- STES systemsinin deep deep and and shallow shallow aquifers, aquifers, soils, STES systems soils,massive massiveimpervious impervious rocks, rocks, processed processed rock rock materials, surface surface water water bodies bodies and and mined mined caverns caverns are are High temperature heat being investigated investigated in in aa number number of of countries. countries. High temperature heat sources sources include include cogenerated cogenerated or or rejected rejected heat heat from from energy energy conversion conversion and and industrial industrial standby heating capacity and processes, waste processes, waste incineration, incineration, heating capacity and intensified intensified solar solar radiation. radiation. Low temperature temperature sources sources include include seasonal seasonal temperature temperature regimes regimes in in air, air, soil soil and and rock, rock, surface surface water, water, ice ice and and ground ground water. water. Heat Heat pumps are are commonly commonly used used to to interface interface with with low low temperature temperature sources. sources. Heat Heat reservoirs reservoirs can can be be used used as as sinks sinks for for cooling cooling as as well well as as sources sources for for heating. heating. heating and summer cooling are major sinks for conventional Winter Winter heating and summer cooling are major sinks for conventional energy energy resources, resources, especially especially in ina amidcontinent midcontinent climate climate such as as Minnesota's, Minnesota's, but but the same same seasonal seasonal AAT be converted converted to toa amajor majorsource sourceofofnon—polluting non-polluting the T can can be thermal thermal energy energy where where suitable suitable geologic geologic formations formationsand and boundary boundary conditions conditions can can be be found found for forSTES. STES. 49 �- - - I - SIMILARITIES ININTHE REGIONAL THE KEWEENAWAN SIMITARITIES THE REGIONALGEOLOGY GEOLOGY OF OFINTRUSIVE INTRUSIVEROCKS ROCKSININ THE KEWEENAWAN MIDCONTINENTRIFT, RIFT, THE MIDCONTINENT THE PERMIAN PERMIAN OSLO OSLO RIFT, RIFT,AND ANDTHE THETERTIARY TERTIARYGEOLOGY GEOLOGY OF OF THE THE NORTH ATLANTIC NORTH ATLANTIC Paul W. Miller, Jr., Paul W. Weiblen Weiblen and and James James D. D. Miller, Jr.,Department DepartmentofofGeology Geologyand andGeoGeophysics, physics, University UniversityofofMinnesota, Minnesota,Minneapolis, Minneapolis,Minnesota Minnesota55455 55455 ABSTRACT the Oslo Oslo Rift and the TerIntrusive rocks in in the the Midcontinent Midcontinent Rift, Rift, the tiary tiary of of East East Greenland, Iceland, Iceland, and and the the Faeroe Faeroe Islands, Islands, exhibit exhibit similarisimilariof intrusive types types and and magma magma ties in the temporal temporal and spatial distribution of Burke and Dewey (1973) compositions. Burke (1973) related related all three three areas to triple triple rifting, and Green (1977) between the junction rifting, (1977) has noted the similarities similarities between extrusive rocks rocks of the the Lake Superior Superior region region and Iceland. Iceland. The intrusive intrusive rocks rocks in the the Midcontinent Rift can be divided into three Nephelinitic—carbonatitic and and alkaline plutonic rocks i) Nephelinitic-carbonatitic rocks reprerepregroups: i) km) complexes at the southern southern end of the ( < 10 km) the Kapuska— Kapuskasented by the small small (< 1). sing Structural Structural Zone and and the the Coldwell Coldwell Province, Province, respectively respectively (Fig. (Fig. 1). ii) Diabasic dikes and sills sills which which occur occur as as quartz quartz tholeiite tholeiite and and olivine olivine tholeiite The plutonic plutonic gabbrogabbro— tholeiite swarms swarms flanking flanking Lake Lake Superior Superior (Fig. (Fig. 1). 1). iii) The ic and associated differentiates differentiates represented represented by the the Crystal Crystal Lake Lake Gabbro Gabbro in in Ontario, the the Duluth Duluth Complex Complex in in Minnesota, and and the the Mellen Mellen Complex Complex in in Wisconsin 1). sin (Fig. (Fig. 1). The spatial of the intrusive units units referred referred to to above above is spatial distribution distribution of consistent with a triple junction tectonic setting in the take Superior consistent with triple junction setting Lake Superior region (Fig. 1). Analogoustectonic tectonic settings settings have for the 1). Analogous have been been proposed proposed for the region (Fig. Oslo Rift (Fig. Oslo (Fig. Similarities in Similarities in a) a) 2) 2 ) and the Tertiary geology geology of the geology of the three the geology the three areas areas the may nay North Atlantic (Fig. (Fig. 3). 3). be summarized as summarized as follows follows: The alkaline intrusion in in East East Greenland, Greenland, the Larvik Larvik alkaline lcangerdlugssuaq Kangerdlugssuaq intrusion Ring Complex in the Oslo Rift, and the Coldwell Complex in Ontario all all in the the occupy similar positions the rifting rifting directions directions in each each occupy positions relative relative to the juncto define define a failed failed arm arm of a triple junccase and all all may be construed construed to tion (Figs. 1—3). tion (Figs. 1-3). The extensive area of East Greenland b) extensive dike dike swarm swarm in in the the Icangerdlugssuaq Kangerdlugssuaq area Greenland b) shows six crosscutting intrusive relationships. However, the major six crosscutting intrusive relationships. However, sequences are an sequences an early early high—Ti high-Ti quartz quartz tholeiite tholeiite followed followed by by olivine olivine tholeiite of MORB affinity. The high—Ti quartz tholeiite is similar in tholeiite of MORE affinity. high-Ti composition to plateau basalts basalts of East Greenland and the Faeroe Island compositions are analogous to the the early early high-Ti high—Ti quartz quartz basalts. The two compositions tholeiite diabases and the second generation olivine tholeiite diabases tholeiite diabases and the second generation olivine tholeiite diabases in the In the the Oslo Oslo Rift, Rift, quartz quartz tholeiite compocompothe Lake Lake Superior Superior region. region. In sition is represented by fine—grained gabbroic intrusions and minor lava sition is represented fine-grained intrusions olivine tholeiite has been reported. flows. However, no no olivine tholeiite reported. In the the Oslo Oslo Rift, Rift, the the parent parent magma magma of of coarse-grained coarse—grained gabbroic gabbroic intrusions intrusions c) c) These intrusions may be less fracmay be related to quartz tholeiite. intrusions related to quartz tholeiite. tionated equivalents of the early magma (Anorthositic) series in (Anorthositic) series in the tionated equivalents of early The presumed parent magma for Duluth Complex. ~ u l u t hComplex. for the the Skaergaard Skaergaard intru— intru- 50 50 �sion, sion, formed formed during during the the Tertiary Tertiary rifting rifting in in the the North North Atlantic, Atlantic, is is comcomto the proposed parent magma composition for the troctolitic— parable parable to the proposed parent magma composition for the troctolitic- gabbroic intrusions gabbroic Keweenawan Keweenawan intrusions. These These rift rift systems systems exhibit exhibit an an expected expected progression progression of of magma magma types types of of Taken carbonatitic, alkaline, quartz tholeiite, and olivine tholeiite. carbonatitic, alkaline, quartz tholeiite, and olivine tholeiite. Taken totogether, The rel1) The relgether, the the intrusive intrusive rocks rocks in in these these rift rift systems systems suggest suggest that: that: 1) ative volume of magma produced during rifting increases through the ative volume of magma produced during rifting increases through the above above succession succession and and is is correlated correlated with with the the extent extent of of rifting: rifting: Oslo Oslo Rift Rift (minor), (minor), Keweenawan Keweenawan Rift Rift (intermediate), (intermediate), North North Atlantic Atlantic (extensive). (extensive). 2) 2) Quartz Quartz thotholeiite is is an an important important transitional transitional magma magma type type between between early early volatile—rich volatile-rich The Keeweenawan and and later later volatile—poor volatile-poor magmas. mamas. 3) 3) The Keeweenawan intrusive intrusive igneous igneous rocks rocks provide nq rifting riftinathan than herehereprovide aa more more complete complete record record of magma evolution during tofore tofore recognized recognized. - - REFERENCES REFERENCES C.K., 1973, 1973, Rifting and doming doming in in southern southern East East Greenland: Greenland: Brooks, C.K., Phys. Phys. Science, Science, v. v. 244, 244, p. p. 23—25 23-25. Nat. Nat. triple junctions: Burke, K., K., and and Dewey, Dewey, .3.F., J.F., 1973, 1973, Plume—generated Plume-generated triple junctions: key key indicators indicators in in applying applying plate plate tectonics tectonics to toold oldrocks: rocks: J. J. Geol., Geol., v. v. 81, 81, p. p.406—433 406-433. Green, J.C., J.C., 1977 1977 Keweenawan Keweenawan plateau plateau volcanism volcanism in in the the Lake Lake Superior Superiorarea, area, in Baragar, Coleman, Baragar, W.R.A., W.R.A., Coleman, L.C., L.C., and Hall, Hall, J.M., J.M., eds., eds., Volcanic Volcanic reregimes gimes of of Canada: Canada: Geol. Assoc. Canada Canada Spec. Spec. Paper Paper 16, 16, p. p. 407—422. 407-422. - FIGURES FIGURES I 1A c.YSUL I, 4r PvOSWA CO* PU X / ulOSON sflRI LLECOMftEP RRAA SIAA -t Fig. Fig. 1 1 Fig. Fig. 1 1 Fig. Fig. 2 2 Fig. 22 Fig. Pig. 33 Distribution of Keweenawan -- Distribution Keweenawan intrusive intrusive rocks rocks in in the the Lake Lake Superior Superior region region. -— Schematic Schematic map of of the the breakup breakup of of the the North North Atlantic, Atlantic, after after Brooks Brooks (1973). (1973) Fig. 33 — The The Jutland triple triple junction junction rift, rift, after after Burke Burke and and Dewey Dewey (1973). (1973). A, B, Rifting developed basins (double (double line) line) but but no no magmatism. magmatism. A, B, and C define define the the expected expected locus locus of of dominant dominant alkaline, alkaline, quartz quartz tholelite, tholeiite, and and olivine 1-3. olivine tholeiite tholeiite magnatism, magmatism, respectively, respectively, in in Figures Figures 1—3. - 51 �GEOLOGY GEOLOGY OF THE THEFRIDAY FRIDAYBAY BAYQUADRM4GLE, QUADRANGLE,MINNESOTA MINNESOTA K. K. Wirth, Wirth, G. G. Crouse Grouseand andU.N. H.H. Woodard, Woodard, R.D. R.D. Salisbury SalisburyDepartment Department of ofGeology, Geology, Be].oit Beloit College, College, Beloit, Beloit, Wisconsin Wisconsin 53511 53511 ABSTRACT ABSTRACT Detailed Detailed geologic geologic mapping mapping in in the the United United States States portion portion of of the the Friday Friday Bay quadrangle, Minnesota, was carried out during the 1981 field Bay quadrangle, Minnesota, was carried out during the 1981 fieldseason. season. The The quadrangle quadrangle is is situated situated in in the the southeast southeast contact contactzone zoneof ofthe theVermilion Vermilion Granitic Complex. The rocks of the Friday Bay quadrangle, and Granitic Complex. The rocks of the Friday Bay quadrangle, and adjacent adjacent areas, areas, comprise comprise aa typical typical granite—migmatite granite-migmatite terrane. terrane. The The oldest oldest rocks rocks in in the the Friday Friday Bay Bay quadrangle quadrangle are are high—grade high-grade metamormetamorphic biotite schists and amphibolites. phic biotite schists and amphibolites. These These rocks rocks were were probably probably originaloriginally ly deposited deposited as as intermediate intermediateto to mafic mafic composition compositionvolcaniclastic volcaniclasticsediments. sediments. AA general general north—south north-south compression compression system system folded folded the themetasedimentary metasedimentary sesequence into a large east—west trending synform. quence into a large east-west trending synform. The The axes axes of of small small folds folds closely closely parallel parallel the the orientation orientation of of the the axis axis of of the the large large synform synform suggestsuggesting that folding was due primarily to a single deformation event. A n early early ing that folding was due primarily to a single deformation event. An episode episode of of anatexis anatexis produced produced the thefirst firstneosome. neosome. Folding by the the emplacement emplacement of of aa large large leuco— leucoanatexis were were followed followed by Folding and and anatexis cratic cratic biotite biotite adamellite adarnellite mass to to the the north north and and west west of of the the Friday Friday Bay Bay quadrangle. quadrangle. Pressure—temperature Pressure-temperature data data from from feldspar feldspar composition composition pairs pairs in in pegmatites pegmatites indicate 600-680° ±+ indicate aa temperature temperature and and pressure pressure of of formation formation of of 600—680°C 50°C 5O0C at at 2—4 2-4 kilobars kilobarspressure. pressure. tate—stage late-stage cross—cutting cross-cutting dikes dikes of of pegma— tite and comprise thethe second neosome tite andaplite aplite comprise second neosomeand andinvaded invadedboth both the thecountry country rocks micro— rocks and and the the leucocratic leucocratic biotite biotiteadamellite. adamellite. Coarse Coarse phenoblasts phenoblastsofof micro- dine in aa late—stage late-stage cline were were formed formed in in the the contact contact zone zone of of the the batholith batholith in feldspathization feldspathizationevent. event. Retrograde Retrograde chlorite—facies chlorite-fades metamorphism, metamorphism, faulting faulting and and hydrothermal hydrothermal alalteration, teration, and and fracturing fracturing are are the the last last events events recorded recorded in in the the Precambrian Precambrian rocks rocks of of the the Friday Friday Bay Bay quadrangle. quadrangle. Joint Joint sets sets show show aa strong strong bimodal bimodal oriorientation. entation. The The strike strike and and dip dip of of the the country country rock rock layering layering and and foliation foliation and and late—stage late-stage faulting faulting appear appear to to be be the the major major factors factors controlling controlling the the distribution distribution and and orientation orientation of of the the two twojoint joint sets. sets. Future Future mapping mapping will will extend extend to to the the east, east, southeast southeast and and west west in in adjacent adjacent quadrangles. quadrangles. 52 �S V S -1 m ra -n FIELD C,) -D I, TRIPS W S �FIELDTRIP TRIPI I FIELD FRANCES - MINE CENTRE AREA, ONTARIO MINERAL DEPOSITS OF THE FORT by KingstOflt Ontario IC7L 3N6 K . H . Poulsen, Poulsen, Queen's Queen'sUniversitY, University, Kingston, mtar-lo K ~ T ,3 ~ 6 X.H. 55 �Paper Paper I1 - MINERAL DEPOSITS OF OF THE THE FORT FORT FRM4CES FRANCES - MINE MINE CENTRE CENTRE AREA, AREA, ONTARIO ONTARIO MINEM LL DEPOSITS by by K.H. K.H. Paulsen, Poulsen, Queens Queen's University, University, Kingston, Kingston, Ontario Ontario K7L K7L 3N6 3N6 TABLE TABLE OF OF CONTENTS CONTENTS INTRODUCTION INTRODUCTION REGIONAL REGIONAL SETTING SETTING Wabigoon Wabigoon Subprovince Subprovince Quetico Subprovince Quetico Subprovince Regional Regional Distribution Distribution of of Mineralization Mineralization GENERAL GENERAL GEOLOGY GEOLOGY Stratigraphy Stratigraphy Structure Structure Metamorphism MINERAL MINERAL DEPOSITS DEPOSITS Classification Classification Type Type Type Type Type Type Type Type 1: 1: 2: 2: 3: 3: 4: 4: Metavolcanic—hOsted Metavolcanic-hosted mineralization fflinera~~zai;i.on Gabbro—hosted Gabbro-hosted mineralization mineralization Vein mineralization mineralization Ultramaf ic—hosted mineralization mineralization Ultramafic-hosted REFERENCES REFERENCES CITED CITED FIELD FIELD TRIP TRIP II Introduction Introduction Stop Fe formation, formation, Nickel Nickel Lake Lake Stop 11 — Fe Stop Stop 22 — Zn, Zn, Cu, Fe Fe mineralization, mineralization, Pocket Pocket Pond Pond prospect prospect Stop Ni, Cu mineralization, mineralization, Belacoma Belacoma property property Stop 33 — Ni, Stop Stop 44 — Cu, Cu, Ni mineralization, mineralization, Northrock Northrock Mine Mine Stop Stop 55 — Ti, Ti, Fe Fe mineralization, mineralization, Traverse Traverse Bay Bay Stop Cu mineralization, mineralization, Mironski Mironski showing showing Stop 66 — Cu Stop Stop 77 — No Mo mineralization, mineralization, Bear Bear Pass Pass showing showing mineralization, Stellar Mine Stop 8 — Au mineralization, Stellar Mine , Stop 8 Cu mineralization, mineralization, Port Stop Stop 9 9 - Zn, Zn, Cu Port Arthur Arthur Copper copper Mine Mine Stop Stop 10 10 — Zn, Zn, Pb mineralization, mineralization, Pidgeon Pidgeon showing showing - -- 57 �INTRODUCTION INTRODUCTION The Archean The Archean rocks rocks of of the the Wabigoon Wabigoon subprovince subprovince of of northwestern northwestern Ontario Ontario host several several producing producing and and past—producing past-producing deposits deposits of of iron, iron, base base metals metals and and gold. gold. Most production production has has come come from from deposits deposits near near the the subprovince subprovince margins and and the the following following pages pages describe describe the the nature nature and and distribution distribution of of margins mineralization mineralization along along the the southwest southwest margin margin at at Rainy Rainy Lake. Lake. Studies of Rainy Lake mineralization have been supported supported by the the Mineral Mineral Deposits Deposits Section Section of of the the Ontario Ontario Geological Geological Survey. Survey. Discussions Discussions in in the field field with A.C. A.C. Colvine Colvine and and 3. Wood Wood of of the the OGS OGS have have been been valuable valuable in in clarifying clarifying the the data data presented. presented. Some Some of the the following following material has been adapted from from OGS summary summary of field field work reports reports prepared prepared by by the the auther. auther. S.T. Spivak S.T. Spivak drafted drafted the the figures. figures. Typing Typing and and drafting drafting services services for for this this manuscript manuscript were funded funded in in part part by by proceeds proceeds from from the the 1977 1977 LSI LSI meeting meeting at Thunder Thunder Bay. Bay. REGIONAL SETTING SETTING The Archean Archean rocks rocks of of the the Mine Centre—Fort Centre-Fort Frances Frances area area lie lie within within aa boundary zone zone between between the the Wabigoon Wabigoon and and Quetico Quetico subprovinces subprovinces of of the the Superior Superior structural structural province. province. In the Rainy River District of Ontario and adjacent parts by aa system system of of parts of of Minnesota, this this boundary boundary is is defined defined by steeply-dipping steeply-dipping dextral dextral wrench wrench faults, faults, the the largest largest of of which which are are the the ). These major wrench Quetico and Seine Seine River-Rainy River-Rainy Lake Lake faults faults (Fig. (Fig. 11). faults faults bound aa "wedge" "wedge" of of crust crust which which is is structurally structurally discordant discordant from from both both subprovinces subprovinces but, because because of of gross gross lithological lithological similarity, similarity, is is generally generally considered considered part of of the the Wabigoon Wabigoon subprovince. subprovince. Wabigoon Wabigwn Subprovince Subprovince The structure structure of of the the Wabigoon Wabigoon granite—greenstone granite-greenstone terrane terrane is is dominated dominated by domal domal features features of of variable variable size. size. The largest largest of these, such such as the the Rainy Lake Lake complex complex and and Irene—Eltrut Irene-Eltrut Lakes Lakes complex, complex, are are greater greater than than 50 50 km km in diameter diameter and and are are composed composed of of smaller smaller gneissic gneissic domes, domes, central central batholiths batholiths and marginal crescent—shaped crescent-shaped granitoid granitoid intrusions. intrusions. The larger larger complexes complexes and small small gneissic gneissic domes domes have have been been interpreted interpreted as as first first and and second second order order gneiss diapirs diapirs which are are the the product product of of gravitational, gravitational, solid solid state state remobiremobilization lization of tabular tabular batholiths batholiths beneath beneath aa supracrustal supracrustal sequence sequence (Schwerdtner al., 1979). 1979). Supracrustal Supracrustal metavolcanic metavolcanic and metasedimen— metasedimen(Schwerdtner et al., tary rocks rocks now now occupy the the margins margins of of the the gneissic gneissic domes domes with with the the largest largest stratigraphic stratigraphic thicknesses thicknesses preserved preserved between between first—order first-order structures, structures. Metavolcanic lithologies Metavolcanic lithologies dominate dominate and and comprise comprise metabasalt metabasalt flows flows with with local local accumulations of accumulations of flows, flows, and and pyroclastic pyroclastic and and epiclastic epiclastic rocks rocks of of interintermediate mediate to to felsic felsic composition. composition. as conglomerate, conglomerate, wacke, wacke, mudstone mudstone and and iron— ironMetasedimentary rocks rocks such such as formation commonly formation commonly form form units units within within the the volcanic volcanic sequences. sequences. A dolomite dolomite unit with with algal algal stromatolite stromatolite mounds mounds occurs occurs within within the the supracrustal supracrustal rocks rocks at Steeprock Steeprock Lake. Lake. Numerous stocks, stocks, commonly commonly of of quartz quartz monzonite, monzonite, intrude intrude Wabigoon subprovince the Wabigwn subprovince supracrustal supracrustal rocks rocks the supracrustal supracrustal rocks rocks (Fig. (Fig. 1). 1). 58 �0 01 . Figure 1: Figure 1: Regional Geology Geology (RED: (RBD: Rice Rice Bay Bay Dome, Dome, BP: BP: Bean Bean Pass Pass pluton, pluton, GP: GP: Grassy Grassy Portage Portage intrusion, i n t r u s i o n , RI: RI: Rest R e s t Island Island granite, g r a n i t e , OTL: OTL: ML: Mud Otter Tail T a i l Lake pluton, pluton, ML: Mud Lake pluton, pluton, SB: SB: Seine Bay By: Bad Vermilion Vermilion tonalite, iintrusion, n t r u s i o n , BV: t o n a l i t e , SG: SG: Seine Seine Group, Group, VG: VG: Vermilion Vermilion Granite). Granite). �are are metamorphosed metamorphosed to to assemblages assemblagescharacteristic characteristicof of the thegreenschist greenschistand and Patterns of metamorphism amphibolite amphibolitefacies facies(Ayres, (Ayres,1978). 1978). Patterns of metamorphism are are closely closely related relatedto tothose thoseof of the thegneissic gneissicdomes domessuch suchthat thathighest highestmetamorphic metamorphic grades grades are are indicated indicatedadjacent adjacentto tothe thefirst—order first-order structures. structures. With With the the exception exceptionof of aa few fewnorthwesterly—striking northwesterly-striking Proterozoic Proterozoicdiabase diabasedikes, dikes,most most of of the the Wabigoon Wabigoon subprovince subprovincerocks rocksin inthe theRainy Rainy River Kiver District Districtare areof of Archean Archeanage. age. Although Although there there is is discrepancy discrepancy among among ages ages derived derived by by difdifferent ferent geochronological geochronologicalmethods, methods, it it is isclear clearthat thatthe therocks rocksof of the thearea area were Ma. The The oldest oldest ages ages were thermally thermallyactive activein inthe theinterval interval2700 2700to to2400 2400Ma. reflect reflect widespread widespread igneous igneousactivity activitywhereas whereas successively successivelyyounger youngerages agesare are likely likely the the result result of of metamorphism, metamorphism, metasomatism, metasomatism, and and crustal crustal uplift. uplift. p e t i c o Subprovince Subprovince Quetico contrasts with with that that of The structure structureof ofthe theQuetico Quetico subprovince subprovince contrasts of the the The Wabigoon. Wabigoon. ItItisischaracterized bybya aconsistent strike of of metasedimentary characterized consistent strike metasedimentary units Seine River—Rainy fault. Near Near the the unitssub—parallel sub-parallelwith withthe the Seine River-Rainy Lake Lake fault. northern Quetico subprov— northernboundary, boundary,low—grade low-grade metasedimentary metasedimentary rocks rocksof ofthe the Quetico subprov- ince sets; an ince dip dip steeply steeply and and display display three three discrete discrete cleavage cleavage sets; an early early set set isis subparallel subparallel with with east—trending east-trending bedding bedding but but has has aa more more northerly northerly strike, strike, whereas whereas aa second secondset setwith with an aneven evenmore morenortheasterly northeasterlystrike strikemakes makesaa moderate moderate angle anglewith withbedding. bedding. AA late late set set includes includes crenulation crenulation cleavage cleavage and and kink kink bands bands which which strike strikenorthwesterly northwesterlyand anddeflect deflectthe theother othercleavages cleavagesas as well well as as bedding. bedding. The The metasedimentary metasedimentary strata stratacommonly commonly display displaygood goodgraded graded bedding youngingdirections directions that that despite bedding and and younging despite some some reversals, reversals,are aredomidominantly nantlynorthward northward (Hawley, (Hawley, 1930; 1930; Merritt, Merritt, 1934; 1934; Ojakangas, Ojakanqas, 1972; 1972; Harris, Harris, 1974; 1974; wood Wood et et al., al., 1980; 1980;this thisstudy). study). Southward, Southward, the the metasedimentary metasedimentary rocks rocks become become migmatitic migmatitic and and primary primary structures structuresand and cleavage cleavageare areobscured. obscured. Schist—rich miqmatitespossess possessbedding—parallel bedding-parallel Schist-rich and and granite—rich granite-rich jaigmatites foliations foliationswhich which are are folded folded into intolarge, large,open, open, shallow shallow plunging plunging structures structures which which trend trendeast—west east-west (Southwick, (Southwick,1972; 1972; Southwick Southwick and and Sims, Sims, 1980). 1980). Major Major antiforms coredbybymassive massivegranitoid granitoidbodies bodiesof of irreqular irregular antifoms are arecommonly commonly cored migmatitic terrane, terrane, the the These granites granites occur occur within within aa migmatitic shapes shapes (Fig. (Fig. 1). 1). These whichoccupies occupiesthe thecentral central part part of Vermilion Granitic GraniticComplex, Complex, which of the theQuetico Quetico Vermilion biotite schists areare metamorphosed The metasedimentary metasedimentary biotite schists metamorphosed to to subprovince. subprovince. The assemblages grade (Pine assemblages indicative indicative of ofaasouthward southward increase increasein inmetamorphic metamorphic grade (Pirie assemblages and Mackasey, Mackasey, 1978). 1978). pelitic Peliticrocks rockswith withgreenschist greenschistfacies facies assemblages and (chlorite-sericite; chlonite—biotite) chlorite-biotite) are are found found just just to to the the south south of of the the (chiorite—sericite; subprovince (biotitesubprovince boundary boundary whereas whereas amphibolite amphibolite facies facies assemblages assemblages (biotite— cordierite—staurolite—garnet-sillimanite; cordierite-staurolite-garnet-sillimanite; biotite—garnet—andalusite— biotite-garnet-andalusitestaurolite; staurolite; and and biotite—garnet-sillimanite) biotite-garnet-sillimanite) have have been been observed observed in in the the central central part part of of the the subprovince subprovince (Southwick, (Southwick, 1976; 1976; Pine Pirieand andMackasey, Mackasey, The observed observed sequence sequence of of assemblages assemblages is is consistent consistent with with moderate moderate 1978). The 1978). as metamorphic metamorphic pressures pressures of of 22to to44kb kband andtemperatures temperatures ranging ranging as as high high.as 600°C 600°C. Geochronological data from fromthis this part part of Geochronological data ofthe theQuetico Queticosubprovince subprovince show show that thatmost mostigneous igneousand andmetamorphic metamorphic events eventswere werebroadly broadlycontemporaneous contemporaneous subprovince. with those in the Wabigoon with those in the Wabiqoon subprovince. Regional Regional Distribution Distribution of of Mineralization Mineralization The The Rainy Rainy River River district district of of Ontario Ontario and and adjacent adjacent parts parts of of Minnesota Minnesota 1890's. Gold proprowere the site of intensive prospecting for gold in the were the site of intensive prospecting for gold in the 1890's. Gold duction duction from from small small mines mines in in the the interval interval 1893—1902 1893-1902 came came principally from 60 �Figure 2: Regional distribution of mineralization. Lo&. - Distribution of Mineralization • Rainy River 0 Zinc — Copper - Iron rormoton occurrence 20KM I I0-IOOoz. '0° - '000 oz '.000 - 10.000 oz- • 10,000-100,000 oz • S • • District, Ontario and adjacent Parts of S , — Minnesota. — H t0 �I two twoareas, areas, Mine MineCentre Centreand andAtikokan: Atikokan: these thesewere wereknown knownas as the theLower LowerSeine Seine and andUpper UpperSeine Seinegold goldregions, regions,respectively. respectively. Total Totalproduction productionat atthat thattime time and andduring duringsubsequent subsequentactivity activityreached reached25,000 25,000 oz. oz. Au Auand and3,000 3,000oz. oz. Ag. Ag. The Thedeposits depositsare areconcentrated concentratedalong alongthe thesubprovince subprovinceboundaries boundariesand andare are related In the the relatedspatially spatiallyto tothe themajor majorfaults faultsand andtheir theirsplays splays(Fig. (Fig.2). 2). In early earlypart part of ofthe the20th 20thcentury, century,some someexploration explorationfor foriron ironin inthis thisregion region resulted Sapawe, resultedin inlimited limitedproduction productionfrom fromthe theAtikokan AtikokanIron IronMine, Mine, near nearSapawe, between between1907 1907and and1911. 1911. The Themajor majoriron ironore oredeposits depositsat atSteeprock SteeprockLake Lakewere were developed developed during duringWorld World War War II I1and andproduction productionbegan beganin in1945, 1945,continuing continuing until until1979. 1979. Low Lowgrade gradeiron—formations iron-formations also alsoare arecommon commonin inthe theregion regionand and i— tend tendto tobe be concentrated concentratednear nearthe thesubprovince subprovinceboundaries. boundaries. Several Severalsignif signifiTwo cant cantprospects prospectscontaining containingbase basemetals metalsalso alsohave havebeen beendiscovered. discovered. Two broad broad types typesare arepresent: present: zinc—copper zinc-coppermineralization mineralizationoccurs occursat atspecific specific horizons horizonswithin within the themetavolcanic metavolcanicsuccession successionand andcopper—nickel copper-nickelmineralizamineralization tionis isassociated associatedwith withmafic maficand andultramafic ultramaficrocks, rocks,particularly particularlyintruintrusions sions(Fig. (Fig.2). 2). Although Although some someof of these these prospects prospects have have been been extensively extensively developed, developed,very very limited limitedbase—metal base-metal production productionhas hasbeen beenreported reportedfrom fromthis this Clearly there thereis is aa strong strongspatial spatialcorrelation correlationbetween betweenknown known region. Clearly region. In particular, particular, mineralizamineralizamineralization mineralizationand andthe thesubprovince subprovinceboundary. boundary. In tion tionrepresenting representingall allof ofthe theabove abovetypes typesisisconcentrated concentratedwithin withinthe thebounboundary theRainy RainyLake Lakearea. area. dary zone zonein inthe a a GENERAL GENERAL GEOLOGY GEOLOGY Stratigraphy Stratigraphy The The stratigraphy stratigraphyofofArchean Archeanrocks rocksatatRainy RainyLake Lakehas haslong long proved proved aa of A.C. (1913) established established aa source source of ofcontroversy. controversy. The The mapping mapping of A.C. Lawson Lawson (1913) stratigraphic stratigraphicnomenclature nomenclature which which included included the the dominantly dominantly metavolcanic metavolcanic a Keewatin Keewatin Group, Group, metasedimentary metasedimentary biotite biotiteschists schistsof of the theCoutchiching CoutchichingGroup, Group, and Using the the principles principles of of strucstrucand the the conglomerate—bearing conglomerate-bearingSeine SeineGroup. Group. Using tural Lawson interpreted interpretedthe theCoutchiching CoutchichingGroup Groupto tobe be the the tural superposition, superposition,Lawson oldest, With oldest, followed followed in inturn turnby by the theKeewatin KeewatinGroup Groupand andthe theSeine SeineGroup. Group. With the by Grout Grout and and his his coworkers coworkers(Grout (Groutet et al., al., the exception exception of of disagreement disagreement by 1951), 19511, this this stratigraphic stratigraphic interpretation interpretation has has prevailed prevailed until until recently recently (Poulsen, 1980a; 1980s; Wood Wood et et al., al., 1980). 1980). Unfortunately, Unfortunately, previous previous interpretainterpreta(Poulsen, tions be tions were were based based on on observations observations around around the the Rice Rice Bay Bay dome dome where where it it can can be As shown shown that that structural structural superposition superposition is is not not aa valid valid stratigraphic stratigraphic tool. tool. As revised stratigraphic stratigraphic column column(Table (Table1) 1)is is based based upon upon data data aa result, result, aa revised obtained obtained from from recent recent mapping mapping by by the the Ontario Ontario Geological GeologicalSurvey Survey (Wood (Woodet et al., al., The spatial distribu1980; Harris, 1974; Poulsen, 1980b; Poulsen, 1981). The spatial distribu1980; Harris, 1974; Poulsen, 198Db; Poulsen, 1981). tion 1. tion of of the the units units is is shown shownin in Figure Figure 1. structure Structure a In In the the fault zone which north, the Quetico Fault is represented by a 700 m—wide north, the Quetico Fault is represented by a 700 nt-wide fault zone which includes includes mylonite, mylonite, blastomylonite blastomylonite and, and, locally, locally, ultramylonite ultramylonite and and The mylonitic fabric strikes east and parallels parallels the the pseudotachylite. The nylonitic fabric strikes east and pseudotachylite. The mylonitic mylonitic rocks rocks are are commonly commonly offset offset by by small small dextral dextral fault zone. zone. The fault faults faults and, and, locally, locally, small small folds folds are are superimposed superimposed on on the the mylonite. mylonite. Rocks Bocks of the Wabigoon subprovince are exposed north of the fault. of the Wabiqoon subprovince are exposed north of the fault. TWO regional regional faults faults are are exposed exposed within within the the map map area area (Fig. (Fig. 3). 3). Two 62 �TABLE TABLE 11.• TABLE OF LITHOLOGIC TABLE OF LITHOLOGIC UNITS OMITSFOR FORTHE THEMINE MINECENTRE-FORT CENTRE-FORTFRANCES FRANCESAREA AREA LITHOLOGIC UNIT LITHOLOGIC Fault rocks rocks (12) Fault (12) DESCRIPTION DESCRIPTION Schists, Schists, mylonites, mylonites, cataclastites cataclastitesdeveloped developed on on heterogeneous lithologies heterogeneous lithologies Dyke Dyke rocks rocks (11) (11 ) Unmetamorphosed Unmetamorphosed granitoid granitoid rocks rocks (10) (10) Metamorphosed Metamorphosed conglomerate conglomerate and (9) and sandstone sandstone (9) Fault Fault Contact Contact Diabase, gabbrc', lamprophyre, quartz-feldspar quartz—feldspar Diabase, gabbro, lamprophyre, porphyry porphyry Intrusive intrusive Contact Contact Granite, Granite, granodiorite, granodiorite, monzonite, monwnite, monzo— monzodiorite, quartz quartz mon— quartz raonzonite, monwnite, quartz monzodiorite zodiorite Intrusive intrusive Contact Contact Conglomerate, Conglomerate, arkose, arkose, subarkose, subarkose, lithic lithic arenite, lithic lithic arkose arkose Angular Angular Unconformity Unconformity Metamorphosed ~etamorphosed granitoid (8) granitoid rocks rocks (8) Tonalite, Tonalite, trondhjemite, trondhjemite, granite granite gneiss, gneiss, Metamorphosed Metamorphosed gabbroic (7) gabbroic rocks rocks (7) Gabbro, melagabbro, leucogabbro, anortho— anorthosite, quartz quartz gabbro, gabbro, quartz quartz diorite, diorite, meta— meta- Metamorphosed Metamorphosed wackes wackes and (6) and mudstones mudstones (6) Metamorphosed Metamorphosed chemical chemical strata strata and and related related clastic (5) clastic rocks* rocks* (5) Ultramaf Ic metavolcanic metavolcanic Ultramafic rocks* rocks* (4) (4) Felsic Felsic metavolcanic metavolcanic rocks rocks (3) (3) Intermediate Intermediate metavolcanjc metavolcanic rocks (2) rocks (2) Mafic Mafic metavolcanic metavolcanic rocks (1 ) rocks (1) quartzofeldspathic quartzofeldspathicgneiss*** gneiss*** Intrusive Intrusive Contact Contact diabase**, , azuphibolite amphibolite diabase Intrusive Intrusive Contact Contact Biotite schist, schist, biotitic biotitic siltstone, siltstone, slate, slate, Biotite wacke, mudstone, mudstone, migmatite migmatite (biotitic (biotitic wacke, paleosome) paleosome) Chert, Chert, chert-magnetite, chert-magnetite, pyrite—pyrrhotite, pyrite-pyrrhotite, pyritic slates, slates, slate, slate, siltstone, siltstone, wacke wacke pyritic Metamorphosed Metamorphosed lapilli—tuff, lapilli-tuff, tuff, tuff, magnetic magnetic chlorite chlorite schist schist Metamorphosed Metamorphosed rhyolite rhyolite and and rhyodacite rhyodacite flows, flows, amygdaloidal flows, amygdaloidal flows, tuffs, tuffs, lapilli—tuffs, lapilli-tuffs, lapillistone, lapillistone, agglomerate agglomerate and and quartz quartz sericite sericite schist schist Metamorphosed andesite to to dacite dacite flows, flows, pilpu— lowed lowed and amygdaloidal amygdaloidal flows, flows, chioritic chloritic tuffs, tuffs, lapilli—tuff, lapilli-tuff, agglomerate, agglomerate, breccia breccia and and quartz—chlorite quartz-chlorite schist schist Metamorphosed Metamorphosed basaltic basaltic flows, flows, mafic mafic tuffs, tuffs, amphibolite, amphibolite, chlorite chlorite schist, schist, migmatite migmatite (axnphibolitic paleosome) ( amphibolitic paleosome) NOTES NOTES * Although Although the the table table represents represents the the broad stratigraphic stratigraphic order order among among these these rock rock types, types, local local intercalation intercalation of of lithologies lithologies is is common. common. this this type type are are common common throughout throughout the the volcanic volcanic succession succession and and consticonstitute tute aa substantial substantial fraction fraction of of the the total total thickness thickness of of metavolcanic metavolcanic rock. rock. Not Not necessarily necessarily orthogneiss. orthogneiss. ** Sills Sills of of ** *** 63 �a C' Figure 3: SEQUENCE VOLCANO-SEDIMENTARY : : B 3A Ao.S A Mo,S £ 2A • Ce.Ni B 0 Cu C • Ft,Ti : Port Arthur Copper Mine Pocket Pond Prospect Belacoma Property 5 6 4 Gagne Lake Occurrence Wind Bay Deposit Lochart Lake Farrington Boundary Occurrence Lithology and mineral deposits, Fort Frances—Mine Centre area. • Northrock Deposit Mironski Property Olive Mine Golden Star Mine Foley Mine Nickel Lake Iron Formation McTavish Prospect �In Inthe thesouth, south,the theSeine SeineRiver-Rainy Fliver-MinyLake LakeFault Faultisisexpressed expressedas asphyl— phyllitic liticshear shearzone w n ewhich whichstrikes strikeseasterly. easterly. The Therocks rocksto tothe thesouth southof of this this fault Quetico faultare arelargely largelymetasedimentary metasedimentarybiotite biotiteschists schistsof ofthe theQuetico subprovince. subprovince. At ~tleast leastthree threefold foldsets setsmay maybe berecognized recognizedininthe thearea areabetween betweenthe the The youngest youngestof of these theseconsists consistsof of small m a l l folds, folds,F3, ,F which which have have faults. faults. The northwesterly—striking northwesterly-strikingaxial axialsurfaces. surfaces. These Thesefolds foldsare arecommonly comonlymetre— metresized sizedand andpossess possessan anaxial axialplanar planarcrenulation crenulationcleavage. cleavage. Kink Kink bands bands also also are arecommon commonininthis thisfold foldset. set. Ductile Ductile shear shearzones, zones,particularly particularlywell well developed developed in incoarse—grained coarse-grainedrocks, rocks, also alsotend tendto tostrike strikenorthwesterly northwesterlyand and may theF3 F3fold foldset. set. may be begenetically geneticallyrelated relatedtotothe F3 colds foldsmay may be be observed observedsuperimposed superimposedon onthe thecleavage cleavageand andminor minorfolds folds F3 of F2folds foldsplunge plunge northeasterly northeasterlyand andsouthwesterly southwesterly ofananolder olderset. set. These TheseF2 and and vary vary in inwavelength wavelengthfrom fromaafew fewcentimeters centimetersto toaafew fewkilometers. kilometers. Axial Axial surfaces surfacesdip dipsteeply steeplyand andare arecommonly commonlycoplanar coplanarwith with aastrong strongpenetrative penetrative cleavage. F2 folds foldsand and cleavage cleavage are are dominant dominant in in defining defining the the strucstruccleavage. The The F2 tural astributionof of turalgrain grainof of the theregion regionand andstrongly stronglyinfluence influencethe thedistribution lithologic units. units. lithologic F2 folds folds in in the the Rice Rice Bay—Bear Bay-Bear Pass Pass Of importance importance is is the the fact fact that that F2 Of area areaface facedownward. downward. Observations Observations of of stratigraphic stratigraphictops, tops, based based on on graded graded beds antiformal bedsand andpillow pillowlavas, lavas,contradict contradictthe thestructural structuralorder ordersosothat thatantifortual features featuressuch suchas asthe theRice RiceBay Bay dome domeare arestratigraphic stratigraphicsynclines. synclines. degrees have been observed. beds with dips as low as 45 The Overturned beds with dips as low as 45 degrees have been observed. The Overturned entire significance significance of of the the downward downward facing facing is is undetermined, undetermined, but but it it is is entire clear must have have taken takenplace place in in order order to to invert invert clear that that an an earlier earlier deformation deformationmust the 1980). Large, Large, recumbent recumbent the stratigraphic stratigraphicsequence sequence(Poulsen (Poulsenet et al., al., 1980). F, folds folds are are inportant important to to an an understanding understanding of of the the distribution distribution of of litho— lithoF1 logic Eastward in in the the Mine Mine logic units units in in the theRice Rice Bay Bay Dome h m earea area(Fig. (Fig.4). 4). Eastward Centre Centre area, area, the thestructure structureappears appearsto tobe be aa simple simple northward—facing northward-facing limb limb of o The transition transition from from ductile ductile to to brittle brittle aa large largeupright uprightfold fold(Fig. (Fig.5). 5). The deformation deformation is is evidenced evidenced by by the the pervasive pervasive development development of of mesoscopic—scale mesoscopic-scale shear zones. zones. Two Two fundamental fundamental shear—zone shear-zone orientations orientations exist: exist: one one set set with with shear right—hand right-hand sense sense of of displacement displacement parallels parallels the the major major faults faults and and strikes strikes approximately approximately east east and and the the other other conjugate conjugate left—hand left-hand set set strikes strikes to to the the north-northwest. north—northwest. These These systematic systematic orientations orientations and and senses senses of of displacement displacement are are equally equally well well developed developed on on northward— northward- and and southward—facing southward-facing sequences, sequences, and and involve involve The shear shear zones zones are are interpreted interpreted to to broadly broadly postdate pestdate all rock rock types. types. The all folding. These These zones zones are are consistent consistent with with the the interpretation interpretation that that the the folding. thethe area is aisright—hand wrench 3ominant structure structureinin area a right-hand wrenchzone zoneof ofwhich which the the dominant boundary faults are merely the most obvious manifestation. two boundary faults are merely the most obvious manifestation. two Metamorphism Metamorphism The rocks rocks exposed exposed between between the the two two boundary boundary faults faults have have been been metametaThe morphosed to assemblages characteristic of the greenschist and morphosed to assemblages characteristic of the greenschist and amphibo— mphiboto amphibolite mphibolite facies facies The transition transition from from greenschist greenschist to lite facies. facies. The lite indicates a northwestward increase in grade and involves both indicates a northwestward increase in grade and involves both regional regional and an 65 �C' C.' —— . Figure 4: dome. 7a — overturned anticline (with plunge Antiform (with plunge) RICE BAY DOME AREA lOa —- Portog e 70 - over x Zn,Cu Geology of the Rice Bay Dome area. Rock types are keyed to Table 1. Note the recumbent antjcljne which IS refolded pillow lava, top shown overturned graded beds — Lithological contact Lithotype (see table I) Fault .7 Mineral occurrence Field Trip Stop �-J 0" F - --- / - Sb 8b ——— , Figure 5: Figure 5: Geology of of the the Mine Mine Centre centre area. area. Rock to Table Table m c k types types are are keyed keyed to 1. 1. Note that that younging information infornation obtained from from southwest southwest of area suggests that the the sequence sequence northwest northwest of of Bad m d the map area Vermilion Vermilion Lake Lake faces faces northwestward. northwestward. - p® x~ ....# anticline anticline (volcanics) (volcanics ) with with plunge plunge pi1lawlava7 lava top top 7' pillow syncline (canglornerates, (conglomerates, arenites arenites)) reclined syncline reclined ,/ 5< attitude attitudeand andfacing focingofofcross— crossfault bedding xAu x Au mineral occurrence occurrence bedding orenites arenites lithologic contact contact Field trip stop 0 @ Field stop 5 mi. I lithotype ((see see table I ) n n krn " I —- • Mine Centre Ic / 8c MINE CENTRE AREA 3b Turtle I �contact contact metamorphism metamorphism (Fig. (Fig. 3). 3). In In the the greenschist greenschist facies, facies, chlorite chlorite schists are common and chioritoid with chlorite and white mica schists are common and chloritoid with chlorite and white mica are are present present in the Shoal Lake area. Staurolite, andalusite, sillimanite, garnet, in the Shoal Lake area. Staurolite, andalusite, sillimanite, garnet,Mg— Mgchlorite chlorite and and biotite biotiteform forman anunaltered unalteredprograde progradeassemblage assemblage in inthe theBear Bear Passage Passage area, area,and and diopside—bearing diopside-bearing araphibolites amphibolites occur occur along along the the northeast northeast M,undant evidence of retrogressive metamargin of the Rice Bay Dome. Abundant evidence of retrogressive metamargin of the Rice m y Dome. The northwestward increase in throughout the area. morphism exists The northwestward increase in grade grade morphism exists throughout the area. a similar southward increase contrasts with within the boundary zone within the boundary zone contrasts with a similar southward increase in in the Quetico subprovince. subprovince. the Quetico MINERAL MINEPAL DEPOSITS DEPOSITS Classification Classification The Lakearea area has has aa long Rainy Lake long history history of ofmineral mineralexploration explorationand and The Rainy exploitation since the discovery of gold at Mine Centre in 1893. At At that that exploitation since the discovery of gold at Mine Centre in1893. time, three three deposits, deposits, the the Olive, Olive, Golden Golden Star, Star, and and Foley, Foley, were were worked, worked, and and tine, coupled coupled with with renewed renewed activity activity during during the the 1930's, 1930's, aa total total production production of of approximately 485 kg of Au and 20 kg of Ag was realized (Beard approximately 485 kg of Au and 20 kg of Ag was realized (Beardand and Garratt, 1976). 1976 ) Garratt, . The The noted noted similarity similarity of of iron—formations iron-formations at at Nickel Nickel Lake Lake with with those those at at Diamond— Michipicoten led to exploration around the turn of the century. Michipicoten led to exploration around the turn of the century. Diamonddrill minimum of of 22 million million tonnes tonne6 of of drill programs programs in in 1920 1920 and and 1955 1955 defined defined aa minimum magnetite—ilmenite mineralization hosted by anorthosite and gabbro magnetite-ilmenite mineralization hosted by anorthosite and gabbronorth north of 1969). of Seine Seine Bay Bay (Rose, (Rose,1969). since since the the mid mid 1950s, 1950s, exploration exploration in in the the region region has has been been focused focused The discovery of largely copper in in gabbro gabbro largely on on the the search search for for base base metals. metals. The discovery of copper at Grassy Portage Bay in 1958 led to the development of a 70 m two— at Grassy Portage Bay in 1958 led to the development of a 70 m twocompartment compartment shaft shaft and and aa 200 200 in m drift through through the the mineralization mineralization by by Recent exploration exploration programs programs have have Northrock Northrock Mines Mines Limited Limited in in1973. 1973. Recent investigated investigated zinc—copper zinc-copper mineralization mineralization hosted hosted by by metavolcanic metavolcanic rocks. rocks. Numerous occurrences have been evaluated by diamond—drilling and geophysigeophysiNumerous occurrences have h e n evaluated by diamond-drilling and cal to date, date, no no economically economically viable viable deposits deposits have have been been cal methods methods but, but, to outlined. outlined. rn In total, total, over over 75 75 individual individual mineral mineral properties properties have have been been developed developed Recent mapping by the Ontario Geological Survey to to various various degrees. degrees. Recent mapping by the Ontario Geological Survey (Poulsen, (Poulsen, 198Db; 1980b; Poulsen, mulsen, 1981) 1981) was was initiated initiated to to identify identify the the geological geological settings settings of of the the different different mineralization mineralization types types with with an an objective objective of of establishing All significant significant establishing exploration exploration criteria criteriafor forthis thisarea. area. All occurrences in terms terms of of strati— straticonsidered in of mineralization mineralization have have been been considered occurrences of These characteristics characteristics graphic graphic setting, setting, mineralogy mineralogy and and deposit depositmorphology. morphology. These scattered form form the the basis basis of of the the deposit depositclassification classificationshown shownininTable Table2.2. Scattered development, on which which there therehas hasbeen been no no development, have have been been noted noted minor occurrences, occurrences, on minor spatial distribution The spatial distribution of of selected selected but are are not not included included in in the the table. table. The but deposits deposits is is shown shown in in Figure Figure 3. 3. Descriptive Descriptive aspects aspects for for each each deposit deposit type type may may be be illustrated illustrated by by data data from particular^ emphasis emphasis on on the the largest largest from all all occurrences occurrences of of that that class class with with particular and and most most completely completely developed developed properties. properties. 68 �TABLE TABLE 2. 2. MINERAL DEPOSIT CLASSIFICATION MINERAL DEPOSIT CLaSSIFICATIONFOR FORFRANCES-MINE FRANCES-MINECENTRE CENTREAREA ARBA NUMBER NUMBER OP OF PROPERTIES EXAMPLES PROPERTIES EXAMPLES TYPE TYPE 1 1 FIELD FIELD TRIP TRIP STOP STOP NO. NO- - Stratabound Stratabound mineralization mineralization hosted hosted by by felsic to mafic metavolcanics — felsic to mafic metavolcanics A: A: Sphalerite—galena—chalcopyrite Sphalerite-galena-chalcopyrite associated associated with with siliceous siliceous volcanic volcanic rocks rocks 22 Gagne G a p e Lake Lake Pidgeon Pidgeon B: B: Sphalerite—chalcopyrite Sphalerite-chalcopyrite associated associated Sc amygdaloidal amygdaloidal with with intermediate intermediate to to maf mafic volcanic flows, tuffs and breccias volcanic flows, tuffs and breccias 99 Wind Wind Bay, Bay, Port Port Arthur Arthur Copper copper - 9 C: C: Sphalerite—chalcopyrite Sphalerite-chalcopyrite associated associated with with iron iron formation formation 4 4 McTavish, McTavish, Pocket Pocket Pond 2 - D: Lean Lean iron iron formation formation — mainly mainly chert— chertmagnetite and massive pyrite—pyrrhotite, magnetite and massive pyrite-pyrrhotite, minor chalcopyrite chalcopyrite common common 13 Reef Reef Point, mint, Nickel Lake, L Nickel ,& Shoal Shoal Lake Lake 10 1 - 22 — Mineralization Mineralization hosted hosted by by layered layered gabbroic gahbroic intrusions intrusions A: A: Chalcopyrite Chalcopyrite associated associated with with gabbro gabbro and and leucogabbro leucogabbro near near the the base of sills sills B: B: Disseminated Disseminated chalcopyrite chalcopyrite associated associated with with siliceous siliceous phases phases of of the the intrusions intrusions C: Ilmenite-magnetite-apatite-rutile lenses lenses C: Ilmenite—magnetite—apatite—rutile in in the the upper upper portions portions of of the the intrusions intrusions Northrock Northrock Island Island Bay Bay 4 1 Mironski Mironski 6 4 4 Traverse Traverse Bay Bay Seine Seine Bay Bay 5 26 26 Foley, Foley, Stell Golden Golden Star Star 77 1 - Vein Vein mineralization mineralization 33 — g A: Quartz—gold Quartz-gold sulfide sulfide veins veins in in shear shear zones wnes B: Quartz—molybdenite—pyrite wartz-molybdenite-pyrite veins veins in in unmetamorphosed unmetamorphosed granitoid granitoid rocks rocks 66 S Bear Bear Pass pass 7 Belacoma 3 - mineralization hosted by ultramafic 44 - Disseminated Disseminated chalcopyrite—pyrrhotite chalcopyrite-pyrrhotite mineralization hosted by ultramafic metavolcanics metavolcanics I 69 �Type Type 1: 1: Metavolcanic—hosted Metavolcanic-hosted mineralization mineralization Zinc—copper mineralization Zinc-copper mineralization at Painy Rainy Lake Lake occurs in in a number of specific volcanic volcanic environments. The mineralization at Gagne Lake (Type environments. The (Type 1A) 1A) consists of lenses of massive sphalerite and galena, as wide as 20 cm, lenses sphalerite as which parallel which parallel similar similar overlying overlying pyritic pyritic layers. layers. Rocks of the footwall footwall to to the south of the mineralized zone consist dominantly of rhyolitic south the zone consist dominantly rhyolitic lalapillistone which locally pillistone locally contains contains aa distinctive distinctive spotted spotted alteration alteration of of chlorite and centimeter—sized porphyroblasts of pinitized chlorite centimeter-sized porphyroblasts pinitized cordierite. The hanging—wall The hanging-wall rocks rocks consist consist of of fine—grained fine-grained siltstone siltstone and and chert chert which which locally form a coarse breccia having clasts as much as 50 cm in form coarse breccia clasts as as 50 in diameter. diameter. On strike strike with with the the mineralization, mineralization, the the breccia breccia contains contains clasts clasts of of massive massive pyrite. Although drilling to date by Armstrong—Hupchuk has shown the pyrite. Although drilling to date by Armstrong-Hupchuk has shown the mineralization mineralization to to be be very very thin, thin, the the geologic geologic setting setting and and alteration alteration show show aa resemblance to many volcanogenic massive sulfide deposits (Sangster, volcanogenic massive sulfide deposits (Sangster, resemblance 1972). Mineralization at the the Pidgeon Pidgeon property occupies occupies aa similar similar setting. setting. sphalerite-galena-chalcopyrite with with iron iron carcarHere en echelon echelon lenses lenses of sphalerite—galena—chalcopyrite bonates are are conformable conformable with with siliceous siliceous metavolcanic metavolcanic rocks. rocks. A diamond diamond yielded assays per tonne tonne have have felsic lapilli felsic lapilli more laterally more drill (7 ft) ft) true true width width drill intersection intersection of approximately approximately 22 m (7 of 0.53% 0.53% Zn, 1.76% 1.76% Pb. Low Ag values values as as high high as as 0.3 0.3 03. oz. Pyritic blebs in been been reported reported from from sulfide—rich sulfide-rich material. material. Pyritic tuff tuff typify typify the the zones zones of of footwall footwall alteration alteration which which are are extensive than individual individual sulfide sulfide lenses. lenses. Although the the Type Type lB 1B occurrences occurrences are are similar similar in in mineralogy mineralogy to to the the massive sulfide sulfide deposits deposits (sphalerite, (sphalerite, pyrite, pyrite, pyrthotite, pyrrhotite, chalcopyrite, chalcopyrite, minor galena), they they possess possess aa number number of of distinctive distinctive characteristics. characteristics. The host rock rock is is commonly commonly an an amygdaloidal, amygdaloidal, brecciated, brecciated, intermediate intermediate to to mafic mafic to 20 20 cm cm metavolcanic metavolcanic rock. rock. The mineralization occurs occurs as discrete discrete seams seams 11 to wide to 20 cm) of of barren barren wide which are are separated separated by substantial substantial widths (1 to chloritic host chloritic host rock. rock. At the the Wind Bay property, aa typical typical drill drill section section through through 50 50 mm of of tuffaceous chlorite and 8.6 8.6 mm in in schist yielded yielded two two mineralized mineralized zones, zones, 77 mm and tuffaceous chlorite schist 1.5% Zn Zn and and 0.2% 0.2% Cu Cu and and 1.1% 1.1% Zn Zn and and 0.09% 0.09% Cu, Cu, true width, which averaged averaged 1.5% Where the respectively (George 1980). Where respectively (George Armstrong, Armstrong, personal communication, communication, 1980). quartz—chlorite schist quartz-chlorite schist is is only only weakly weakly deformed, deformed, primary primary features features such such as as angular fragments and amygdules are recognizable, suggesting suggesting aa derivation derivation The distinctive distinctive chlorite schist unit is from volcanic flows flows and and tuffs. tuffs. The underlain to by rhyolite rhyolite lapillistone lapillistone and and tuff tuff which, which, near near the the underlain to the the south south by of abundant abundant pyrite pyrite and. and mutual contact, contains contains alteration consisting of chlorite schists schists are pyrrhotite blebs pyrrhotite blebs with minor minor chalcopyrite. chalcopyrite. The chlorite The stratistrati— rhyolite tuffs. The overlain by relatively unaltered quartz—eye quartz-eye rhyolite succession and locally graphic succession locally the the mineralized mineralized zones, are are dissected dissected by three laterally laterally extensive extensive mafic sills sills which are are slightly slightly discordant discordant to to the the strike of metavolcanic rocks. strike rocks. At the Port Arthur Copper Mine, the the stratigraphic stratigraphic setting setting of of the the mineralization is Here, the mineralization is virtually identical identical to to that that at at Wind Bay. Bay. Here, amygdaloidal and brecciated nature of of the the chloritic chloritic host host rock rock is is clearly clearly anygdaloidal 70 �evident. evident. Diamond Diamond drilling drilling by by Stratmat Stratmat Limited Limited revealed revealed aa zonal zonal arrangearrangement ment of of copper copper and and zinc zinc within within the the host host (Fig. (Fig. 6). 6). zinc—rich Zinc-rich zones zones are are underlain by copper—rich copper-rich mineralization. mineralization. The underlain to to the the south south by The latter latter was was mined in in 1916 1916 and and aa few few carloads carloads of of material material grading grading approximately approximately 3% 3% Cu Cu were were shipped shipped to to British British Columbia. Columbia. The by aa The mineralized mineralized horizon horizon is is succeeded succeeded abruptly abruptly to to the the north north by cherty cherty horizon horizon approximately approximately 11 mm wide wide which which in in turn turn is is overlain overlain by by felsic felsic quartz—eye quartz-eye tuffs tuffs which which forms forms aa thick thick hanging—wall hanging-wall sequence. sequence. Nine Nine occurrences occurrences of of the the Wind Wind Bay—Port Bay-Port Arthur Arthur Copper Copper type type occupy occupy aa single single stratigraphic stratigraphic horizon horizon which which is is exposed exposed over over aa strike strike length length exceeding These are are thought thought to to represent represent poorly poorly focused focused discharge discharge km. These exceeding 25 25 km. of Although these these deposits deposits collectively collectively reprerepreof metals metals over over aa large large area. area. Although sent no single single prospect prospect has has sent aa substantial substantial accumulation accumulation of of base base metals, metals, no been been shown shown to to have have sufficient sufficient metal metal content content or or tonnage tonnage to to be be economically economically viable viable at at this this time. time. Likewise, Likewise, mineralization mineralization of of Type Type IC 1C represents represents substantial substantial dispersion dispersion of of metal metal with with resulting resulting low low grade. grade. At At Pocket Pocket Pond Pond (Figure (Figure 1) 1) significant significant quantities quantities of of sphalerite sphalerite and and chalcopyrite chalcopyrite are are associated associated with with iron—formation iron-formation which which is is dominantly dominantly comcomposed The base base metals metals posed of of chert—magnetite chert-magnetite and and sulfide—bearing sulfide-bearing carbonates. carbonates. The are are hosted hosted by by aa unit unit of of pyritic, pyritic, black black shale shale and and siltstone siltstone which which is is immeimmediately single drill drill intersection intersection through through diately beneath beneath the the iron—formation. iron-formation. A single this this mineralization mineralization yielded yielded assays assays averaging averaging 1.73% 1.73% Zn Zn and and 0.09% 0.09% Cu over over aa true communication, 1980). 1980). Chip true width width of of 10 10 m (George (George Armstrong, Armstrong, personal personal communication, sampling McTavish Option, Option, sampling across across aa similar similar zone zone by by Noranda Noranda Mines Mines at at the the Mctavish Nickel Nickel Lake, Lake, yielded yielded average average assays assays of of 0.3% 0.3% Zn Zn and and 0.1% 0.1% Cu Cu (Resident (Resident Geologist's Geologist's Files, Files, Ontario Ontario Ministry Ministry of of Natural Natural Resources, Resources, Kenora). Kenora). AA second second type type of of mineralization, mineralization, more more massive massive than than this, this, occurs occurs at at the the main main showing showing at at Pocket Pocket Pond Pond where where aa small small lens lens of of massive massive pyrrhotite—sphalerite pyrrhotite-sphalerite less less than than 0.5 0.5 mm wide wide occurs occurs in in aa laterally laterally extensive extensive lenticular lenticular zone zone of of stratigraphiThe sulfides sulfides are are here here overlain overlain stratigraphi— massive massive pyrrhotite—pyrite. pyrrhotite-pyrite. The cally cally by by aa 0.3 0.3 mm layer layer of of chert—magnetite. chert-magnetite. The The host host rocks rocks for for all all of of the the type type 1C 1C mineralization mineralization are are quite quite mafic mafic and and consist consist of of basaltic basaltic flows flows and and coarse—grained coarse-grained amphibolites amphibolites which which likely likely clastic rocks rocks and and turbidite—type turbidite-type represent represent metadiabase metadiabase sills. sills. Ultramafic clastic Iron— metasedimentary metasedimentary rocks rocks occur occur at at higher higher stratigraphic stratigraphic levels. levels. Ironformation formation (Type (Type 1D) ID) is is aa common common constituent constituent of of the the predominantly predominantly mafic mafic volcanic volcanic terrane terrane in in the the western western part part of of the the study study area area at at localities localities such such as chertas Nickel Nickel Lake Lake and and Reef Reef Point. Point. There There is is aa common common association association of chert— magnetite magnetite beds beds immediately immediately adjacent adjacent to to aa massive massive pyrite—pyrrhotite pyrite-pyrrhotite zone, zone, which which at at some some localities localities contains contains minor minor chalcopyrite. chalcopyrite. Total Total thicknesses thicknesses of of aa few few metres metres are are rarely rarely exceeded exceeded and and whereas whereas the the immediate immediate host host is is comcommonly monly aa biotitic biotitic metasedimentary metasedimentary rock, rock, the the iron—formations iron-formations are are broadly broadly associated associated with with sections sections in in which which metabasalt metabasalt is is abundant. abundant. 7]. �PORT ARTHUR COPPER DEPOSIT ASSAY PLAN ;.,< quartz diorite - Shallow Drill Hole Projections > 2 % comb. Zn>Cu a >.2% comb. Zn>Cu >2% -- -" comb. Cu > Z n . 50 FT. 1 >.2% comb. Cu > Z n lithobgial contact fault Figure 6: Figure 6: 0 I Assay plan of the Port Arthur Copper deposit. DATA FROM: STRATMAT LTD Drill ~ l a n s Values shown are Assay plan of the Port Arthur the vertical projections of shallow diamond drill intersections Copper deposit. Values shown are the vertical projections approximateand nominally represent of theshallow distribution metals diamondofdrill intersections and represent the distribution of metals approximately nominally 75 feet below surface. ly 75 feet below surface. 72 I �Type Type 2: 2: Gabbro—hosted Gabbro-hosted mineralization mineralization Two Two large, large, steeply steeply dipping, dipping, layered layered gabbroic gabbroic sills, sills, the the Grassy Grassy Portage Portage and and Seine Seine Bay—Bad Bay-Bad Vermilion Vermilion intrusions, intrusions, are are exposed exposed in in the the study study area. area. Layering Layering is is expressed expressed by by modal modal variations variations in in mineralogy, mineralogy, chemical chemical variations variations across across strike, strike, and and rhythmic rhythmic mineral mineral layering, layering, which which is is well well exposed exposed in in the 1dgut Bedgut Bay Bay area. area. Rock Rock compositions compositions range range from from melagabbro melaqabbro to to anorthosite, anorthosite, and and internal internal layering layering suggests suggests that that Grassy Grassy Portage Portage intruintrusion sion faces faces southward, southward, whereas whereas the the Seine Seine Bay—Bad Bay-Bad Vermilion Vermilion intrusion intrusion faces faces northward. northward. The The basal basal part part of of the the latter latter intrusion intrusion is is truncated truncated by by the the Seine Seine River—Rainy River-Rainy Lake Lake Fault. Fault. Mineralization Mineralization occurs occurs at at three three specific specific horizons chalcopyritehorizons in in the the intrusions. intrusions. Basal Basal segregations segregations of of chalcopyrite— pyrrhotite—pentlandite pyrrhotite-pentlandite (Type (Type 2A) 2A) form form important important occurrences occurrences along along the the northern northern margin margin of of the the Grassy Grassy Portage Portage intrusion. intrusion. The The best best example example of of this this type type occurs occurs at at the the Northrock Northrock deposit, deposit, where where 300,000 300,000 tonnes tonnes of of material material The grading grading 1.89% 1.89% Cu Cu have have been been outlined. outlined. The mineralization mineralization is is hosted hosted by by gabbro, gabbro, metagabbro metagabbro and and leucogabbro leucogabbro near near the the base base of of the the Grassy Grassy Portage Portage intrusion intrusion at at the the contact contact with with pillow pillow lava lava and and pillow pillow breccia. breccia. MineralizaMineralization tion consists consists of of heavy heavy disseminations disseminations of of chalcopyrite chalcopyrite and and pyrrhotite pyrrhotite with with minor minor pentlandite pentlandite and and pyrite. pyrite. Ilmenite, Ilmenite, apatite apatite and and molybdenite molybdenite are are prespresent ent locally. locally. The The sulfide sulfide minerals minerals show show textures textures which which suggest suggest aa magmatic magmatic origin, origin, whereas whereas sulfide sulfide veins veins and and local local hydrothermal hydrothermal alteration alteration show show evievidence dence of of deuteric deuteric or or metamorphic metamorphic remobilization. remobilization. The The deposit deposit consists consists of of long and and 10 m wide. three three en en echelon echelon lenses, lenses, each each approximately approximately 50 50 in m long Several Several other other occurrences occurrences of of similar similar type type are are exposed exposed along along strike strike from from the the deposit deposit for for 88 km km to to the the northeast. northeast. Near pyrrhotiteNear the the top top of of the the Grassy Grassy Portage Portage Intrusion, Intrusion, disseminated disseminated pyrrhotite— chalcopyrite to siliceous siliceous zones zones within within the the chalcopyrite mineralization mineralization is is related related to intrusion intrusion (Type (Type 2B). 2B). Known Known as as the the Mironski MironSki showing, showing, this this occurrence occurrence was was drilled drilled by by Phelps Phelps Dodge Dodge Corporation Corporation of of Canada Canada Limited Limited in in 1966 1966 and and again again by by Belacoma Belacoma Mines Mines Limited Limited in in 1978. 1978. Approximately Approximately 300,000 300,000 tonnes tonnes of of material material Although these these zones zones grading (Harris,1974). 1974). Although Cu are are present present (Harris, grading 0.8 0.8 percent percent Cu may may represent represent granophyric granophyric differentiates, differentiates, their their sharp sharp contacts contacts and and generally generally blocky blocky nature nature suggest suggest that that they they are are assimilated assimilated blocks blocks of of country country rock rock near near the the roof roof of of the the intrusion. intrusion. In In the the central central to to upper upper levels levels of of both both intrusions, intrusions, substantial substantial accuaccumulations 2 0 occur occur as as lenticular lenticular mulations of of iron—titanium iron-titanium mineralization mineralization (Type (Type 2C) zones to massive massive magnetite magnetite ++ ilmenite ilmenite with with local local zones of of disseminated disseminated to apatite—rutile. apatite-rutile. Type 3: 3: Vein vein mineralization mineralization Type Although most most are are Quartz Quartz veins veins are are common common throughout throughout the the study study area. area. Although unmineralized, unmineralized, two two particular particular types types host host gold gold and and molybdenite molybdenite mineralizamineralization. Gold—bearing Gold-bearing veins veins (Type (Type 3A) 3A) in in the the area area have have been developed developed and tion. be the veins veins may may be exploited exploited intermittently intermittently since since the the 1890s. 1890s. In most cases, the related shear zones zones and and commonly commonly occupy occupy aa central central first—order first-order related to to discrete discrete shear 7c). Second—order Second-order veins are foliation—normal, foliation-normal, but third— thirdfissure (Figure (Figure 7c). fissure order sets sets are are foliation—parallel. foliation-parallel. order The The principal principal veins veins range range in in width width from from 10 10 cm cm to to 22 mm and and are are composed composed primarily primarily of of quartz quartz with with minor minor carbonate carbonate and and local local tourmaline. tourmaline. Visible 73 �5' C Aprox. aETI® FAULT Figure Figure7:7: Gold Golddeposits depositsofofthe theRainy BainyLake Lakearea. area. a) a)Metamorphic Metamorphiccontrols controlsonongold goldmineralization. mineralization. b) b)Rose Rosediagram diagramdepicting depictingthe theorientation orientationand anddisplacement displacement sensenses sesofofmesoscopic mesoscopicductile ductileshear shearzones. zones. c) c)Schematic Schematicdiagram diagramillustrating illustratingthe therelationship relationshipofofgold— goldbearing ductileshear shear bearingquartz quartzveins veins(principal (principalveins) veins)totoductile zones. zones. Such Suchzones zonesare arewell welldeveloped developedinincoarse—grained coarse-grainedplu— plutonic tonicrocks. rocks. I 74 a �gold and electrum were identified identified in a few few veins and sulfide sulfide minerals are Pyrite, sphalerite, present in substantial quantities. in substantial sphalerite, galena, galena, Scheelite has been chalcopyrite, arsenopyrite and argentite are common. common. Scheelite reported from gabbro—hosted gabbro-hosted quartz veins near Swell Swell Bay (Harris, (Harris, 1974). 1974). Gold content Gold content of of veins veins is is variable, variable, but but aa study study of of available available assay assay ppm Au may be realistically realistically sought data suggest that grade as high as 15 15 ppm m. over widths of approximately approximately 11 m . This represents represents the the approximate approximate average average grade of the two most successful successful past producers, the Olive and Golden Star Mines (Beard (Beard and and Garratt, Garratt, 1976). 1976). The shear zones The zones are systematically systematically oriented and show show senses senses of 7a,b). The displacement consistent with a right—hand right-hand wrench zone zone (Figures (Figures 7a,b). shear zones and their gold—bearing veins are found in most lithologies zones their gold-bearing in lithologies in the area (Table (Table 3), but there is a clear clear affinity affinity for for a coarse—grained coarse-grained trondhjemite suite. felsic plutonic host of the suite. felsic the earlier earlier tonalite tonalite — trondhjemite Although shear zones are present throughout the study area, only those ~lthough zones throughout the those which occur in rocks metamorphosed to to the the greenschist greenschist facies facies contain contain gold— gold, suggest late— bearing vein systems (Figure 7a). The above relationships a late systems (Figure 7a). tectonic emplacement of the veins in rocks which readily formed dilatant tectonic emplacement the in rocks readily formed zones zones at metamorphic grades grades suitable suitable for for precipitation precipitation of gold. gold. - TABLE 3. TABLE 3. LITHOLOGIC CONTROLS ON GOLD-BEARING GOLD-BEARING QUARTZ VEINS, MINE CENTRE-FORT FRANCES FRANCES AREA AREA Numberof of Veins Veins Number Host Rock Rock Type Host Type trondhjemite Tonalite, Tonalite, trondhjemite intermediate metavolcanic rocks Felsic, rocks Felsic, Metadiabase, amphibolite amphibolite Metabasalt, chlorite chlorite schist schist Gabbro, anorthosite anorthosite Conglomerate Conglomerate Quartz monzonite—granodiorite Quartz monzonite-granodiorite 46 16 9 5 4 1 0 TOTAL NUMBER TOTAL SOMBER OF VEINS 81 TOTAL NUMBER OF PROPERTIES TOTAL PROPERTIES 26 26 The molybdenite-bearing molybdenite—bearing veins (Type The (Type 3B) in the the Bear Pass—Rice Pass-Rice Bay These generally show area show no evidence of shear zone development. area show no evidence of shear zone development. These generally show sharp contacts with undeformed granodiorite or quartz monzonite and granodiorite quartz and are are The best with contacts with biotite schist. spatially associated associated . spatially contacts biotite schist. The is located at Bear locatedon onHighway Highway 11 1 1 at Bear Pass, Pass,where where molybdenite molybdenite and and occurrence is occurrence are abundant in tensional tensional quartz veins in the Bear Pass pluton pyrite are pyrite strike northerly and and westerly westerly and and the the best mineral(Figure 4). (Figure 4). The veins strike A number ization is is located located in in veins near near the the pluton margins. margins. A number of other quartz—pyrite—molybdenite occurrences to dikes dikes and and sills sills of of quartz-pyrite-molybdenite occurrences are are related related to The majority majority of molybmolyb— plutons. The granodiorite well removed from the main plutons. denite occurrences occurrences are are restricted restricted to to areas areas of of amphibolite amphibolite facies facies metamorphism. 75 �4I Type 4: mineralization Type 4: Ultramafic—hosted Ultramafic-hosted mineralization The magnetic, clastic unit in the RiceRice Bay—Redgut The magnetic, elasticultramafic ultramafic unit in the Bay-RedgutBay Bay area area hosts low—grade hostsa anumber numberofofshowings showingsofof low-gradecopper—nickel copper-nickel mineralization, mineralization, referred referred to to as as the the Belacoma Belacoma property. property. Disseminated Disseminated pyrrhotite pyrrhotite with some some chalcopyrite chalcopyrite occurs occurs as as blebs blebs and and stringers stringers in in narrow narrow zones zones of foliated foliated ultramafic ultramafic metavolcanic metavolcanic rocks. rocks. Reported grades are variable with best grab grab samples samples assaying assaying as as much much as as 0.29 0.29 percent percent Cu, Cu, 1.23 1.23 percent percent Ni, 0.17 0.17 percent Cu and and percent Co, Co, and and best best diamond—drill diamond-drill intersections intersections of of 0.45 0.45 percent percent Cu 0.12 0.12 percent Ni Ni over over 0.55 0.55 mm (Resident (Resident Geologist's Geologist's Files, Files, Ontario Ontario Ministry Ministry of of Natural Natural Resources, Resources, Kenora). Kenora). Away from from the the mineralized areas, the the ultramafic ultramafic metavolcanic metavolcanic rocks rocks contain contain approximately approximately 1150 1150 ppm ppm Ni Ni (average (average of 44 samples) samples) indicating indicating that that metamorphic metamorphic remobilization remobilization may have produced the the low—grade low-grade sulfide sulfide zones. zones. 4 REFERENCES REFERENCES CITED CITED Ayres, 1978, L.D., 1978, Metamorphism in in the the Superior Superior province province of of Northwestern Northwestern Ayres, L.D., Ontario to crustal crustal development, in Metamorphism Ontario and and its its relationship relationship to in in the the Canadian Canadian Shield, Shield, eds. eds. J.A. J.A. Fraser FraSer and and W.W. W.W. Heywood; ~eywood;Geol. Geol. Surv. Surv. Can., Can., Paper Paper 78—10, 78-10, p. p. 25—36. 25-36. Beard, R.C., and and Garratt, Garratt, G.L., G.L., 1976, 1976, Gold Gold deposits deposits of of the the Kenora—Fort Kenora-Fort Beard, R.C., I Frances Frances area, area, Districts Districts of of Kenora Kenora and and Rainy Rainy River; River; Ontario Ontario Div. Div. Mines, Mineral Mineral Deposits Deposits Circ. Circ. 16, 16, 46 46 p. p. Grout, F.F., F.F., Gruner, Gruner, LW., J.W., Schwartz, Schwartz, G.M., G.M., and and Thiel, Thiel, G.A., G.A., 1951, 1951. Grout, Precambrian Precambrian stratigraphy stratigraphy of of Minnesota; Minnesota; Geol. Geol. Soc. Soc. Am. Am. Bull., Bull., v. v. 62, 62, p. p. 1017—1078. 1017-1078. 4 Harris, Harris, F.R., F.R., 1974, 1974, Geology Geology of of the the Rainy Rainy Lake Lake area, area, District District of of Rainy Rainy River; Ontario Div. Mines, GR 115, 94 p. Accompanied by maps 2278 and and River; Ontario Div. Mines, GR 115, 94 p. Accompanied by maps 2278 1 inch to 1,' mile. 2279, scale 2279, scale 1 inch to 1h mile. Hawley, Hawley, J.E., J . E . , 1930, 1930, "Seine" "Seine" or or "Coutchiching"; "Coutchiching"; J. J. Geol., Geol., v. v. 38, 38, p. p. 52 1—547. 521-547. I Lawson, A.C., A.C., 1913, 1913, The The Archean Archean geology geology of of Rainy Rainy Lake Lake re—studied; re-studied; Can., Can., Lawson, Geol. 1 1 1 p. Geol. Sun., Sum., Mem. Mem. 40, 40, 111 I Merritt, Merritt, Am. Bull., ~ull., v. v. P.L., 1934, 1934, Seine—Coutchiching Seine-Coutchiching problem; problem; Geol. Geol. Soc. Soc. Am. P.L., 45, 45, p. p. 333—374. 333-374. Ojakangas, R.W., 1972, ojakangas, R.W., 1972, Rainy Rainy Lake Lake area, area, in & I Geology Geology of of Minnesota: Minnesota: aa centencentennial Sims and and G.B. G.B. Morey; Morey; Minn. Minn. Geol. Surv., nial volume, volume, eds. eds. P.IC. P.K. Sims Sum., p. p. 163—171. 163-171. Pirie,J., J., and andMackasey, Mackasey, W.O., W.O., 1978, 1978, Preliminary Preliminary examination examination of of regional regional Pine, metamorphism metamorphism in in parts parts of of Quetico Quetico metasedimentary belt, Superior province, &I Metamorphism Metamorphism in in the the Canadian Canadian Shield, Shield, eds. eds. J.A. J.A. province, Ontario; Ontario; in Fraser Fraser and and W.W. W.W. Heywood; Heywood; Geol. Geol. Surv., Surv., Can., Can., Paper Paper 78—10, 78-10, p. p. 37—48. 37-48. Poulsen, Poulsen, K.H. K.H. 1980a, 1980a, The The stratigraphy, stratigraphy, structure structure and and metamorphism metamorphism of of Archean unpubl. M.S. Archean rocks rocks at at Rainy Rainy Lake, Lake, Ontario; Ontario; unpubl. M.S. thesis, Lakehead University, University, 99 99 p. p. 76 76 I �Poulsen, K.H., K.H., 198Db, of mineralization in Poulsen, 1980b, The geological setting s e t t i n g of i n tthe h e Mine Centre—Fort Frances area, District of Rainy River; p. 162—168, District Rainy River; p. 162-168, in Centre-Fort Summary of Field Work, 1990, by the Ont. Geol. Sum., Surv., G. ed. V.G. V.G. Milne, Mime, Summary of F i e l d Work, 1980, by t h e Ont. Geol. O.L. White, R.B. Barlow, J.A. Robertston and A.C. A.C. Colvine; Ont. 0.L. R.B. Barlow, J.A. and Geol. Surv., p. Geol. Surv., Misc. Misc. Paper 96, 96, 201 201 p. Poulsen, K.H., 1981, K.H., 1981, The The geological geological setting s e t t i n g of mineralization in i n the Mine Mine Poulsen, Centre—Fort Frances area, p. 190—195 River; p. 190-195 in in Centre-Fort area, District of Rainy River; Summary of of F Field Work, 1981 1981 by by tthe Ont. Geol. Geol. Surv., Sun., ed. .7..wood, Wood, ed. J. Summary i e l d Work, h e Ont. O.L. White, R.B. O.L. R.B. Barlow and A.C. A.C. Colvine; Ont. O n t . Geol. Geol. Surv., Surv., Misc. Misc. Paper 100, 100, 255 255 p. p. Poulsen, K.H., Borradaile, and Kehlenbeck, Kehlenbeck, M.M., M.M., 1980, 1980, An An inverted K.H., Borradaile, G.J.. G.J. and Poulsen, .7. Earth Sci., Sci., v. . Earth v. 17, Archean succession succession at a t Rainy Rainy Lake, Lake, Ontario; Ontario; Can. Can. J 17, p. 1358—1369. p. 1358-1369. Rose, E.R., 1969, E.R., 1969, Geology Geology of titanium titanium and and titaniferous t i t a n i f e r o u s deposits deposits of of Canada; Rose, Geol. Surv. Geol. Surv. Can., Can., Econ. Econ. Geol. Geol. No. No. 25, 25, 171 171 p. p. Sangster, I).?., 1972, Precambrian Precambrian volcanogenic volcanogenic massive massive sulphide suiphide deposits deposits Sangster, D.F., 1972, Canada: a review; Geol. Sum. Surv. Can. Can. Paper 72-22, 72—22, 44 p. p. iin n Canada: review; Geol. Schwerdtner, Stone, D., Osadetz, K., K., Morgan, J., and Stott, S t o t t , G.M., G.M., Schwerdtner, W.M., W.M., Stone, D., Osadetz, Morgan, 3., 1979, Granitoid Granitoid complexes complexes and tthe Archean ttectonic 1979, h e Archean e c t o n i c record iin n the part Ontario; Can. Can. 3. v. 16, 16, p. p. southern p a r t of of northwestern Ontario; J. Earth Sci., Sci., v. 1965—197 7. 1965-1977. Southwick, D.L., D.L., 1972, p. 108—119 in 1972, Vermilion granite—migmatite granite-migmatite massif; massif; p. 108-119 & I Southwick, Geology of Minnesota: Minnesota: aa centennial centennial volume, volume, eds. eds. P.K. P.K. Sims Sins and and G.B. G.B. Morey; Minn. Morey; Minn. Geol. Geol. Surv., Surv., 623 623 p. p. Southwick, D.L., D.L., 1976, High—grade metamorphism metamorphism associated with the Southwick, 1976, High-grade Ontario; aabstracts Vermilion batholith, b a t h o l i t h , Minnesota — Ontario; b s t r a c t s Institute I n s t i t u t e on Lake Geology, 22nd Annual Meeting, Meeting, St. p. 61. St. Paul, Paul, Minn., Minn., p. 61. Superior Geology, - Southwick, D.L., D.L., and Sims, Granitic Southwick, Sins, P.K., P.K., 1980, 1980, The Vermilion G r a n i t i c Complex——a Complex--a new new name name for f o r old o l d rocks rocks in i n northern northern Minnesota: Minnesota: U.S. U.S. Geological Geological Survey Survey Professional Professional Paper Paper 1124, 1124, p. p. Al—All. At-All. Wood, J., Dekker, Dekker, J., J., Jensen, Jensen, J.G., J.G., Keay, J.P., J.P., and and Panagapko, Panagapko, D., D., 1980, 1980, Wood, 3., Keay, Geol. Surv. Surv. Prelim. Prelim. Ont. Geol. Mine Centre Centre area, area, District D i s t r i c t of of Rainy Rainy River; River; Grit. inch to maps P2201 P2201 and and P2202; Geological Geological Series, S e r i e s , scale s c a l e 1:15,840 1:15,840 or o r 11 inch 1/4 mile. Geology Geology 1976, 1976, 1977. 1 /4 mile. 1977. I: DESCRIPTIONS DESCRIPTIONS OF OF FIELD STOPS, K.H. K.H. Poulsen, Poulsen, leader leader FIELD TRIP I: The The field f i e l d trip t r i p is i s designed designed as a s aa one one day day excursion excursion illustrating i l l u s t r a t i n g the the It begins from Fort types and setting s e t t i n g of mineralization at a t Rainy Lake. Lake. It the size s i z e of of the the Frances and involves as a s many as a s 10 10 stops, s t o p s , depending depending upon upon the Many of of lookout at a t Bear Pass is is a suitable s u i t a b l e lunch lunch stop. stop. Many group. The scenic lookout properties and aare intermittthe he p r o p e r t i e s visited v i s i t e are d a rPRIVATE e PRIVATE and r e under under development development intermitProceed USE DISCRETION in gaining accessand andi nin sampling. sampling. Proceed PLEASE US E DISCRETION i n gaining access ttently. e n t l y . PLEASE o tthe h e Windy Point Bridge eastward 11 tto eastward from Fort Frances on Highway 11 77 �Lake NICKEL LAKE IRON IRON FORMATIONS FORMATIONS NICKEL iron formation, ironstone e iron formation, ironstone 30 minor folds with Su Su Ox Ox CB CB Figure Figure 8: 8: sulfide rich rich chert— chert- magnetite magnetite carbonates carbonates 30 d Field F i e l d trip t r i p stop stop no. no. 1. 1. 78 minor folds with plunge plunge 1/4 mi. 1/4 mi. �approximately approximately1313miles miles(21 (21kin) km) from from downtown downtown Fort Fort Frances. Frances. SET SETMILEAGE. MILEAGE. Proceed Proceed eastward eastward for for 4.4 4.4 miles miles (7 (7km) km) to to aa side side road road to to the the right right immeimmediately diately opposite opposite the the Ministry Ministry of of Transportation Transportation garage garage and and sand sand dome. dome. Park Park and and walk walk southward southward for for approximately approximately 1000 1000 feet feet (300 (300 m) m) along along the the priprivate 8 )to to an an outcrop outcrop 50 50 feet feet (1.5 (1.5 m) m) south south of of the the main main gate. gate. vate road road (Fig. (Fig. 8) - STOP STOP 11 — Nickel Nickel Lake Lake Iron Iron Formation Formation The The chert—magnetite chert-magnetite iron—formation iron-formation exposed exposed here here is is typical typicalof of many many At Nickel Lake, the iron—formation is hosted occurrences in the area. occurrences in the area. At Nickel Lake, the iron-formation is hosted by by amphibolites amphibolites and and defines defines aa major major synformal synformalfold fold which which mimics mimics the the shape shape of of the the lake lake (Fig. (Fig. 8). 8). The The minor minor folds folds which which are are prominent prominent in in this this outcrop outcrop are are coaxial coaxial with with the the major major structure structure and and are are of of tectonic tectonic origin origin as as evievidenced by axial planar cleavage exposed in a small glaciated outcrop denced by axial planar cleavage exposed in a small glaciated outcrop approximately approximately 100 100 feet feet (30 (30m) m) further further south. south. The The iron—formation iron-formation is is too too lean to be of economic significance but a shaft on the south side lean to be of economic significance but a shaft on the south side of of the the lake lake investigated investigated the the possibility possibility of of base base metals metals associated associated with with aa massive massive pyritic chert-magnetite-grunerite pyritic horizon horizon immediately immediately adjacent adjacent to to the the chert—magnetite—grunerite iron—formation. iron-formation. At At Reef Beef Point, Point, 6.2 6.2 miles miles (10 (10 km) km) west west of of here, here, metametamorphic morphic segregation segregation of of magnetite magnetite produced produced aa somewhat somewhat enriched enriched material material which which was was mined mined in in from from aa small smallopen open pit pit in in the the mid—1950's. mid-1950's. Return 11, proceed proceed approximately approximately 2.5 2.5 mi. mi. (4 ( 4km) km) eastward eastward Return to to Highway Highway 11, Turn left and proceed 1.6 miles (2.6 3cm) northward to to Highway Highway 502. 502. Turn left and proceed 1.6 miles (2.6 km) northward to to aa Turn right and drive approximately 400 dirt feet dirt road road just just past past aa creek. creek. Turn right and drive approximately 400 feet Walk to each each of of the the localities localitiesshown shownin inFigure Figure9. 9. m) and and park. park. Walk to (120 m) (120 - STOP STOP 22 — Pocket Pocket Pond Pond Zn—Cu—Fe Zn-Cu-Fe occurrences occurrences At At this this prospect, prospect, zinc zinc and and copper copper have have been been located located at at two two horizons horizons The selected localities shown on within within aa mafic mafic succession. succession. The selected localities shown on Figure Figure 99 illustrate illustrate the the nature nature of of the the mineralization mineralization as as well well as as the the host host rocks. rocks. Locality Locality 2a: 2a: metasedimentary metasedimentary rocks rocks Structurally, Structurally, these these outcrops outcrops of of biotite biotite schist schist are are located located on on the the northeast northeast margin margin of of the the Rice Rice Bay Bay Dome Dome as as confirmed confirmed by by the the bedding bedding orienorientation The rocks rocks are are part part of of the the historic historic tation observed observed at at this this locality. locality. The Coutchiching to Coutchiching Group Group of of Lawson Lawson (1913) (1913)and and were were once once thought thought to to be be basal basal to The "knotty" "knotty" beds beds here here the the volcanic volcanic sequence sequence exposed exposed to to the the northeast. northeast. The consist consist of of the the mineral mineral assemblage assemblage garnet—biotite—muscovite garnet-biotite-muscovite and and sillimanite. sillimanite. Locality Locality 2b: 2b: magnetic magnetic ultramafic ultramafic rock rock This This small small outcrop outcrop is is composed composed of of the the magnetic ultrabasic unit which It is is cut cut here here by by an an amphibolitic amphibolitic dike. dike. is is better better exposed exposed at at Stop Stop 3. 3. It Locality 2c: metabasalt metabasalt Locality 2c: This facing pillowed Pillowed metabasalts metabasalts here here face face southwestward. southwestward. This facing direction direction can can be be confirmed confirmed at at three three other other localities localities on on this this prospect prospect and and coupled coupled with with the the northeasterly northeasterly dip, dip, indicates indicates that that the the succession succession here here is is strucstrucThe amphibolite amphibolite facies facies metamorphic metamorphic assemblage assemblage in in these these turally turally inverted. inverted. The 79 �a a I a 4 wz 008 a I a a 2. a 0 Ñ- a -Z no. stop trip Field U3UaJ1 l ~ 'SI!DJ+ p dip PUD w k c f ' ONOd 13YOOd S ~ D O Jl Buippaq P S3ON3WnOOO ad - W - u Z 9: a M'JIlld Figure SMDI a (Sa x ^JiaaSt- d w piau SUOZ!JO~ e u o ~ s u o ~ ~ dOlS a 0 �rocks contains diopside; this is is consistent consistent with the the appearance appearance of silli— sillimanite at Locality 2a. at Locality 2a. Locality 2d: ides Locality 2d: lean lean massive massivesuif sulfides This This pit exposes exposes aa lens lens of of massive massive pyrite—pyrrhotite pyrite-pyrrhotite with with minor minor chalcopyrite. A narrow chert—magnetite unit stratigraphically chalcopyrite. chert-magnetite stratigraphically overlies overlies the the massive sulfides. The generally mafic nature of the host rocks massive sulfides. the rocks adjacent adjacent to to the the pit pit can can be be noted. noted. Locality 2e: 2e: main pit CAUTION: DEEP HOLE MOLE CAUTION: In this pit, the extension extension of the the zone zone exposed exposed at the the previous locallocality has been excavated. A A narrow zone of massive pyrrhotite-sphalerite pyrrhotite—sphalerite grading to as much as 14% 14% Zn was discovered discovered here and a few few loose loose pieces of similar material may be found on the dump. Diamond drilling showed that found the this zone had limited depth extent and that grades, averaged over zone that averaged over 10—foot 10-foot widths, were only of the order of 1 to 2% Zn. only of the order of 1 to 2% Locality 2f: Oxide Oxide facies facies iron—formation iron-formation This small outcrop thinly bedded This unit unit This small outcrop exposes exposes thinly bedded chert—magnetite. chert-magnetite. This immediatelyoverlain overlain to to has been traced across across the is immediately has been traced the entire entireproperty property and and is the skarn. the southwest southwestby bya anarrow narrowgarnet—pyroxene—epidote garnet-pyroxene-epidote skarn. Locality 2g: 2g: pyritic pyritic black Locality black shale shale stratigraphically underlies underlies the In addistratigraphically theiron—formation. iron-formation. In addito pyrite, the shale shale contains contains finely finely disseminated disseminated sphalerite: sphalerite: aa diamond drill intersection intersection yielded 1.73% 1.73% Zn over over 32.5 32.5 feet. feet. AA similar unit in in the the Nickel Nickel Lake Lake area area also also contains contains low low copper copper and and zinc zinc values. values. tion tion This This unit unit Return 1 1 and and turn turn left, left, Return to to Highway Highway 502, 502, return return southward southward to to Highway Highway 11 Walk eastward. Proceed east for and stop stop at right. Walk eastward. Proceed for 1.1 1.1 miles miles (1.8 (1.8 kin) km) and through the bush 600 feet feet (180 through (180 m) northward northward to to outcrops outcrops at south south side side of aa pond (Fig. (Fig. 10). 10). ic—hosted Cu-Ni Cu—Ni STOP 3: Ultramaf Ultramafic-hosted Locality 3a: These Locality These small small outcrops outcrops expose expose aa clastic clastic rock rock composed composed domidominantly of of fine—grained fine-grained ultramafic ultramafic material. material. The rock is magnesian rich (21% MgO) MgO) and both both clasts and matrix contain finely disseminated disseminated (21% small percentage of amphibolitic amphibolitic clasts clasts also also are are present. magnetite. A small The origin origin of of this this unit unit is is unknown unknown but but possibilities possibilities include include an an ultramafic ultramafic pyroclastic, an an epiclastic epiclastic rock rock derived derived from from ultramafic ultramafic flows, flows, or or aa prodprodIt is of of interest that that this unit is is idenidenuct of of magnesian magnesian metasomatism. metasomatism. It and texturally texturally totothe Steeprock is tical tical chemically and the Steeprock"ash—rock" "ash-rock" which which is conformable with the km) to to conformable the hematitic hematitic iron iron ore ore at Atikokan, 62 62 miles miles (100 (100 km) the the east. east. the south south side Proceed approximately 700 feet (210 (210 m) eastward around the the pond to small pits beside of the pond to small pits beside the thebush bush road. road. 81 �I v b Field Trip Stop gabbro; leucogabbro; garnetiferous N i c u } mineral occurrences quartz gabbro @ mt metosedimentary biotite schist facing of units ; pi1low lavas ; magnetic graded beds (overturned 1 I km ultromafic schist metobasalt ; pillowed I 1/2 mi. >^, ^S I I 6.. Figure 10: 10: Field F i e l d trip trip stops stops no. no. 3, 3, 4, 5, 5, and and 6 Figure 82 I �I Locality Locality 3b: 3b: These Thesepits pits have have been been developed developedon onfoliated foliatedmineralized mineralizedequivalents equivalentsof of the the ultramafic ultramaficunit. unit. Finely Finely disseminated disseminated chalcopyrite chalcopyriteand and pyrrhotite pyrrhotite are are present present and and assays assaysof of grab grabsamples samplesaverage averageapproximately approximately0.3% 0.3% Cu, Cu, 0.1% 0.1% Ni, Ni, 0.03% 0.03% Co. Co. Return 1 1 and and proceed proceed 1.6 1.6 miles miles (2.6 (2.6 km) km) southward; southward; turn turn Return to to Highway Highway 11 right THIS ROAD ROAD IS IS VERY VERY ROUGH ROUGH M4D AND NOT NOT SUITABLE SUITABLE right on on aa dirt dirt road. road. CAUTION CAUTION - THIS FOR FOR LOW—RIDING LOW-RIDING VEHICLES. VEHICLES. Proceed Proceedto tothe theend endof ofthe theroad road(it (itmay may be be necessary necessaryto towalk walk part part way). way). Note Note that that alternate alternate Stop Stop4A, 4A, north north of of the the railway 11, serves serves to to illustrate illustratesome someof of the thefeatures features railway overpass overpass on on Highway Highway 11, - mineralizationinin aa trench trench aa few feet from of Northrock—type Northrock-type mineralization few hundred hundred feet from the the of highway 10). highway (Fig. (Fig.10). STOP 4: The STOP 4: The Northrock Northrock Deposit Deposit This This deposit deposit was was discovered discovered in in 1959 1959 by by Noranda Noranda propsectors. propsectors. Subsequent Seemarand andNorthrock Northrock Mines, Mines, Subsequent development, development, followed followedby by options optionsto toSeemar led led to to the the sinking sinking of of aa 200-foot-deep 200-foot-deep two—compartment two-compartment shaft shaft in in 1973; 1973; aa 600—foot 600-foot drift drift was was driven driven eastward eastwardon on the the125—foot 125-foot level. level. The The drift drift cut cut through throughthe the three three lenticular lenticularore ore zones zonesand and sulfide—rich sulfide-rich material material was was stockpiled. Walk to to outcrops outcrops at at the the northwest northwest corner corner of of the the hoist hoist stockpiled. Walk building. building. Locality The footwallrocks rocks to to the the Grassy Grassy Portage PortageSill. Sill. The Locality 4a: 4a: These These are are the the footwall pillowed pillowed metabasalts metabasalts here here extend extend southwestward southwestwardfrom fromthe thevicinity vicinityof ofthe the previous previous stop stopand and throughout throughoutthis thisdistance distanceindicate indicatesouthward southwardyounging. younging. Walk Walk directly directly south south past past the the west west side side of of the the building building across acrossthe the Walk towards towards the the dump dump and and stop stop at at an an outcrop outcrop contact contact with with the the metagabbro. metagabbro. Walk to to the the right right of of the thecleared clearedarea. area. • Locality Locality4b: 4b: This This is is aa typical typical exposure exposure of of metagabbro metagabbro in in the the Grassy Grassy Portage The plagioclase: plagioclase: mafic mafic mineral mineral ratio ratio is is variable variable locally locally Portage Sill. Sill. The The and to leucogabbro. leucogabbro. The roelagabbroto and in in the the area area of of the the deposit deposit ranges ranges from from melagabbro sill sill consists consists of of uralitized uralitized pyroxene pyroxene and and altered altered plagioclase plagioclase (AnSO). (An50). Locality Locality 4c: 4c: • The The dump dump material material is is divided divided into into waste waste (east (eastside) side) and and ore ore (west (west In the dump, representative specimens of mineralized material can side). In the dump, representative specimens of mineralized material can side). Particular types types include: include: bleached bleached chalcopyrite—rich chalcopyrite-rich ore; ore; be be obtained. obtained. Particular net ides in dark gabbro; "spotted" net and and droplet—textured droplet-textured sulf sulfides "spotted" ilmenite—rich ilmenite-rich material with with biotite biotiterims rimson onilmenite ilmenitecores; cores;apatite—bearing apatite-bearing ores; ores;and and material molybdenite—bearing ore (rare). (rare). molybdenite-bearing ore Return 11; Stop Stop 0.9 0.9 mile mile (1.5 Return towards towards Highway Highway 11; (1.5 km) km) from from the the highway highway at to the at aa small small clearing clearing to the left left (Fig. (Fig.10). 10). STOP 5: ~Fe—Ti oxide mineralization STOP 5: e - ~oxide i mineralization in aa A A small small outcrop outcrop in in the theclearing clearingexposes exposesdisseminated disseminated magnetite magnetite in fine—grained fine-grained matrix matrix composed composed of of chlorite chlorite and and actinolite. actinolite. apatite apatite can can be be observed observed in in thin thin section. section. 83 Fine—grained Fine-grained �walk Walk northward northward along along an an abandoned abandoned drill drill road road for for approximately approximately 300 300 feet (100 (100 m) to to an an outcrop outcrop at at trail trail side. side. Here green apatite and reddish reddish brown rutile rutile crystals crystals comprise comprise an an irregular irregular mass of of "nelsonite". "nelsoniten. Such Such rocks are well known associates associates of anorthosites anorthosites and are are thought thought to to result result from Fe-Ti-P enriched enriched melt. melt. At this from liquid liquid immiscibility immiscibility in in an an Fe—Ti—p this locality locality quartz so so that that Ti02 nO2 grades the rutile poikilitically encloses abundant quartz grades do do not exceed exceed aa few few percent. percent. Return 11, turn turn left left and and proceed proceed back back northward northward approxiapproxiReturn to to Highway Highway 11, mately 0.3 0.3 mile (0.5 (0.5 km) km) to to aa road road leading leading to to the the right. right. Stop here and 1 1 to to the the north north side side of of the the walk northward northward along along the the east east side side of of Highway Highway 11 outcrop (Fig. outcrop (Fig. 10). 10). STOP occurrence STOP 6: 6: Disseminated Disseminated Cu, Cu, Mironsici Mironski occurrence The The light-coloured light-coloured siliceous siliceous rock rock exposed exposed here here contains contains fine fine dissemidissemimineralization was discovered discovered in in nated chalcopyrite chalcopyrite and and pyrrhotite. pyrrhotite. The mineralization 1966 as a result of highway construction, construction, and subsequent subsequent drilling drilling by Phelps—Dodge Ltd., Belacoma Mines, Mines, has has outlined outlined approximately approximately Phelps-Dodge Ltd., and and later later by by Belacoma 300,000 tonnes tonnes grading grading 0.8% 0.8% Cu. Cu. The siliceous siliceous host rock rock consists consists of of quartz—plagioclase—biotite and quartz-plagioclase-biotite and may may represent represent either either aa siliceous siliceous differendifferentiate of the tiate the gabbroic gabbroic intrusion intrusion or or an an assimilated assimilated country country rock. rock. The this outcrop outcrop is is near the the top top of the the latter appears to to be more likely as this intrusion where blocks of metavolcanic metavolcanic rock rock also also are are present. A trail, beginning on on the the opposite opposite side side of of the the highway, highway, leads leads westwesttrail, beginning ward to to aa number number of of small small exposures exposures and and pits pits which which illustrate illustrate the the nature nature Magnetite—ilmenite mineralization, which of the the mineralization. Magnetite-ilmenite which is is likely likely continuous with that exposed at Stop continuous Stop 5, was intersected intersected in in drill drill holes just to the north of these these exposures. exposures. 7: Mo Mineralization, Bear Pass STOP 7: Pass These These outcrops outcrops of of granodiorite granodiorite of of the the Bear Bear Pass Pass pluton pluton contain contain aa set set of northwesterly northwesterly striking striking quartz quartz veins veins which which contain contain pyrite pyrite or or pyrite pyrite ++ molybdenite. molybdenite. Veins range range in in width from from 0.5 0.5 cm cm to to 30 30 cm cm and and are are spaced spaced approximately Quartz-pyrite-molybdenite occur occur nearest nearest to to the the approximately 0.5 0.5 mm apart. apart. Quartz—pyrite—molybdenite bridge, whereas whereas to to the the west, quartz—pyrite quartz-pyrite veins veins give give way way to to sulfide—free sulfide-free veins. To To the the northeast, northeast, across across Bear Bear Pass, Pass, the the International International Nickel Nickel Company drilled Company drilled 55 holes holes in in 1966 1966 to to evaluate evaluate aa similar similar vein vein set. set. Assays up to to 0.65% 0.65% MoS2 MoS2 0ver Over 1.5 1.5 mm were were reported reported but but values values are are erratically erratically distributed. distributed. Traces molybdenite mineralimineraliTraces of of copper copper were were also also reported. reported. In total, molybdenite The zation is distributed over an area approximately 700 x 150 m. quartz distributed area approximately 700 x 150 m. The quartz veins in to be be extensional extensional in in nature, nature, have have in the the Bear Bear Pass Pass pluton pluton appear appear to sharp contacts with the the granodiorite, granodiorite, and and locally locally possess possess bleached bleached alteraalteraSome molybdenite occurs as dissem— tion selvages at the wallrock contact. selvages the contact. molybdenite occurs as disseniinations in inations in the the wallrock. wallrock. Reset Reset mileage mileage and and continue continue eastward eastward along along Highway Highway 11; 11; mileage mileage 12.2 12.2 (19.5 1cm) Turtle River Road; mileage 13.8 (22.2 km) turn right (19.5 km) Turtle River Road; mileage 13.8 (22.2 km) turn right on on aa priprivate dirt the road, road, turn turn around around and return back in'the dirt road, road, continue continue to to fork fork in' 84 �BAD VERMILION LAKE AREA xznscu OSSff Trondhjemite leucogabbro ;metadiabase felsic t u f f , lapilli tuff intermediate metavolcanic flows ;tuff mofic metavolcanics 0 0 Figure 11: 11: Field Field trip trip stops stops no. no. 88 and and 9. 9. 85 } mineral occurrence shaft I krn 1/2 mi. �I along along the the road road for for approximately approximately 1/8 1/8 mile mile (0.2 (0.2 km). km). AA trail trail leads leads westwestward ward through through the the bush, bush, across across aa marsh marsh to to aa series series of of outcrops. outcrops. AA shaft shaft and and dump dump may may be be found found approximately approximately 200 200 feet feet (60 (60 m) m) due due west west of of the the marsh marsh (Fig. (Fig. 11). 11). STOP STOP 8: 8: Au Au mineralization, mineralization, Stellar Stellar Mine Mine This This three—compartment three-compartment shaft, shaft, approximately approximately 50 50 feet feet deep, deep, was was sunk sunk in in 1934 1934 on on the the Rainbow Rainbow vein vein of of the the Stellar Stellar Mining Mining Property. Property. The The vein vein is is len— lenticular m) halfway halfway down down to as as much much as as 3.8 3.8 feet feet (1.2 (1.2 m) in shape shape and and widens widens to ticular in the the shaft. shaft. The The host host rock rock is is aa carbonate—rich carbonate-rich chlorite—sericite chlorite-sericite schist schist which which forms forms aa dextral dextral shear shear zone zone cutting cuttingequigranular equigranular trondhjemite. trondhjemite. Note Note the shear zone development the oblique oblique foliation foliationininthe the shear zoneand andthe thelocal local development of of third-order veins 7c). The The vein vein material material consists consists of of laminated laminated third—order veins (see (see Fig. Fig. 7c). quartz quartz and and ankerite ankerite with with local local siderite, siderite, pyrite, pyrite, pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite, sphalerite, Gold values values reported reported during during the the sphalerite, galena galena and and rare rare visible visible gold. gold. Gold shaft oz. per per tonne tonne shaft sinking sinking were were erratic erraticbut butaveraged averagedapproximately approximately 11 oz. along strike strike from across Surface sampling sampling along from across the the vein vein to to aa depth depth of of 24 24 feet. feet. Surface the the shaft shaft yielded yielded much much lower oz. per per tonne tonne approximately 0.2 0.2 oz. lower values, values, approximately across across 3—foot 3-foot widths. widths. At At the the time time of of development, development, the the vein vein was was traced traced on on surface surface for for 150 150 feet feet (45 (45 m) m) to to the the northeast northeast and and 60 60 feet feet (18 (18 m) m) to to the the southwest. southwest. In In addition addition to to the the shear shear zone—hosted zone-hosted quartz quartz veins, veins, the the outcrops outcrops near near the the shaft shaft provide provide aa good good opportunity opportunity to to examine examine the the equigranular equigranular trond— trondhjemite The trondhjemite, trondhjemite, along along with the the hjemite of of the the Mud Mud Lake Lake intrusion. intrusion. The gabbro—anorthosite gabbro-anorthosite to to the the south, south, forms forms aa concordant, concordant, possibly possibly subvolcanic, subvolcanic, intrusive intrusive complex complex which which has has been been mapped mapped for for aa length length of of 19 19 miles miles (30 (30 km). km). This This intrusive intrusive complex complex resembles resembles the the Bell Bell River River Complex Complex at at Mattagami, Mattagami, LakeComplex ComplexatatSturgeon Sturgeon Lake, Lake, Ontario Ontario Quebec and and the theBeidelman Beidelman Bay—Pike Bay-Pike Lake Quebec where the intrusions intrusions are where the are thought thought to to relate relatetotomassive massive sulfide sulfidemineralizamineralization in in tion overlying overlying volcanic volcanic strata. strata. A similar similar relationship relationship may exist exist bebestop. tween tween this this intrusion intrusion and and the the base base metal metal mineralization mineralization at at the the next next stop. Return Return to to Highway Highway 11; 11; turn turn right right and and proceed proceed eastward eastward for for 11 mile mile (1.5 (1.5 km), km), pull pull to to the the right right of of the the highway highway opposite opposite aa trail trail leading leading northward northward Walk along along the the trail trail to to the the cleared cleared area area into the the bush bush (Figure (Figure11). 11). walk into beside 6). beside aa water—filled water-filled pit pit (Figure (Figure 6). - CAUTION CAUTION - DEEP DEEP PIT PIT AND AND OPEN OPEN SHAFT. SHAFT. STOP STOP 9: 9: Zn, Zn, Cu Cu Mineralization, Mineralization, Port Port Arthur Arthur Copper Copper Mine Mine The The open open cut cut of of the the Port Port Arthur Arthur Copper Copper mine mine was was developed developed during during the the winter winter 1916—1917. 1916-1917. Later Later in in 1917 1917 aa 100—foot—deep 100-foot-deep shaft shaft with with aa first—level first-level "several" carloads carloads of of ore ore drift drift 200 200 feet feet long long were were developed. developed. In total, "several" The property was was grading 33 to to 3.5% 3.5% Cu Cu were were shipped shippedto toTrail, Trail,B.C. B.C.. • The grading further further developed developed by by aa 5,000—foot 5,000-foot drill drill program program in in 1956 1956 by by Stratmat Stratmat Limited. AA mineralized mineralized zone zone over over 600 600 feet feet (180 (180 m) m) long long and and 75 75 feet feet (23 (23 m) m) Limited. wide was was outlined. outlined. Mineralization Mineralization consists consists of seams seams and and stringers stringers of of wide pyrite, pyrite, sphalerite sphalerite and and chalcopyrite chalcopyrite in in aa host host composed composed of of amygdaloidal amygdaloidal chlorite schist. schist. The The mineralization mineralization is is crudely crudely zoned zoned (Fig. (Fig. 6) 6) with with aa chlorite zinc—rich toward the the stratigraphic stratigraphic top, top, and and aa copper—rich copper-rich zinc-rich north north zone, zone, toward 86 �-4 I 2 9 3 Figure 12: Field trip stop no. 10. 00 x Zn, Pb PIGEON Pb - e felsic motavolcanics intermediate metavolcanics mafic metavolcanics conglomerate , arenite — ——— 2.-' ——7 —— Pb 1/2 mi. pillow facing in bosalts mineral occurrences OCCURRENCE —— C--, . — — #0 �south zone. samples of mineralization may be found The south zone. Good samples found in the dump. dump. The distribution appearance of distribution of of mineralization mineralization can can be be noted noted by by the the "rusty11 "rusty" appearance unmineralized amygdaloidal metameta— the outcrop outcrop surface. surface. Good exposures of mineralized volcanic rock rock can can be noted just just east east of of the the open open cut. cut. AA siliceous, "cherty" unit unit which caps the mineralization is exposed in the northwestern "cherty" northwestern of the Smalloutcrops outcropsininthe the clearing clearing north part of the main main outcrop. outcrop. Small north of of here here expose unmineralized, dacitic tuff. These These give way way expose unmineralized,carbonate—bearing, carbonate-bearing, dacitic to quartz—eye tuff. The The footwall footwall rocks rocks to to the zone northward to quartz-eye tuff. the mineralized mineralized zone are not not exposed here and andaa gabbro-diorite gabbro—dioritesill sill separates separates the the mineralizaare exposed here mineralization from south which the south whichare arecomposed composed of of tion from the the nearest nearestvolcanic volcanicrocks rockstotothe chloritic felsic felsic tuff. chloritic tuff. Return 11, and proceed east for approximately 6.4 6.4 miles Return to Highway 11, (10.3 km). (10.3 Stop just before a point where the power line crosses crosses the road (Figure 12) and walk through through a "cut—over" (Figure "cut-over" area to a series of pits located located the ridge. Alternatively, roadside along the eastern margin of the ridge. Alternatively, roadsideexposures exposures and pits pits northeast of Highway 11 1 1 may be examined to illustrate illustrate the setting setting and of mineralization. STOP 10: Zn, Pb Pb mineralization, mineralization, Pidgeon Pidgeon Property Property The pits and outcrops outcrops here here expose expose stratabound stratabound sphalerite—galena sphalerite-galena This mineralmineral— mineralization associated associated with felsic felsic volcaniclastic volcaniclastic rocks. rocks. This ization was tested short diamond diamond drill drill holes holes in in 1969 1969 by by Kerr Kerr Addisson Addisson ization tested by short The mineralization mineralization Mines and and by by aa longer longer hole hole in in 1978 1978 by by Hanna Hanna Mines. Mines. The consists of lenticular consists lenticular masses of sphalerite—galena—ankerite sphalerite-galena-ankerite with with minor minor pyrite and Quartz veins are and chalcopyrite chalcopyrite in in aa siliceous, siliceous, sericitic sericitic host. host. Quartz during present and suggest suggest some some remobilization of mineralization during metamorphism. Spotted pyritic alteration is ubiquitous ubiquitous in the felsic felsic lapilli tuffs to the the northwest northwest (footwall?) (footwall?) of of the the mineralization: the the lapilli tuffs to Hanging wall Hanna program indicated Harma indicated low low zinc zinc values values within within this this zone. zone. Hanging core logs logs as as "andesite". "andesite". rocks are not exposed exposed here but are are described described in in core A roadside roadside outcrop outcrop to to the the northeast northeast contains contains minor minor magnetite magnetite iron— ironformation overlain southward-facing pillow pillow lavas lavas (Fig. (Fig. 12). 12). formation overlain by southward—facing TRIP. RETURN TO FORT FRANCES FRANCES MU) AND INTERNATIONAL INTERNATIONAL FALLS. FALLS. END OF TRIP. 88 �FIELD TRIP TRIP II: 11: FIELD ARCHEAN OF ARCHEAN GEOLOGY GEOLOGY O F THE THEINTERNATIONAL INTERNATIONAL FAILSflBETOGANA PALLS-KABETOGAMA AREA, MINNESOTA MINNESOTA AREA, by R.W. Ojakangas, Ojakangas, University University of of Minnesota, Minnesota, Duluth, Duluth, 55812 55812 R.W. W.C. W.C. Day, Minnesota Minnesota Geological Geological Survey, Survey, Day, St. S t . Paul, Paul, 55108 55108 and and D.L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, St. S t . Paul, Paul, 55108 55108 D.L. �Paper Paper 11 GENERALIZED GEOLOGY OF THE GEOLOGY OF THE RAINY RAINYLAKE LAKE AREA, MINNESOTA MINNESOTA by Richard W. Ojakangas Ojakangas Richard W. Minnesota, Minnesota, Duluth Duluth Duluth, Minnesota 55812 Ouluth, Minnesota 55812 University University of of INTRODUCTION INTRODUCTION The The Rainy Rainy Lake Lake area area is is in in the the western western part part of of an an east—northeast—trendeast-northeast-trending ing metavolcanic—metasedimentary metavolcanic-metasedimentary sequence sequence more more than than 300 300 km km long long and and 10 10 to to 30 km wide that lies adjacent to and astride the International Boundary. It that lies adjacent to and astride the International It is is bounded bounded on on the the south south by the the Vermilion Vermilion Granitic Granitic Complex Complex (Southwick, (Southwick, 1972; 1972; Southwick Southwick and and Sims, Sims, 1980) 1980) and and on on the the north north in in Ontario Ontario by by another another maszif massif of of Primary zircon ages and whole—rock granitic rocks of probable similar age. granitic rocks of probable similar age. Primary zircon ages and whole-rock Rb—Sr from the the Rainy Rainy Lake Lake area area suggest suggest that that all all of of the the rock—forming rock-forming Rb-Sr ages ages from events, except for the mafic dikes, occurred between 2700 m y . ago ago events, except for the mafic dikes, occurred between 2700 and and 2750 2750 m.y. (Peterman (Peterman and and others, others, 1972). 1972). Reconnaissance mapping Reconnaissance mapping was undertaken undertaken in in the the late late 1960's; 1960's; this this has has been published as the International Falls 1:250,000 sheet (Southwick and Ojakanpublished as the International Falls 1:250,000 sheet (Southwick and Ojakan— gas, 1979a). details on on the the geology geology can can be found found in in aa report report on on the the 1979a). More details then—proposed then-proposed Voyageurs National National Park Park (Minnesota (Minnesota Geological Geological Survey, Survey, 1969) 1969) and in in Ojakangas Ojakangas (1972). (1972). The The supracrustal supracrustal rocks rocks in in the the Rainy Rainy Lake Lake area area north north of of the the Rainy Rainy Lake— LakeSeine Seine River fault fault (Figure (Figure 1) 1) are are part part of of the the larger larger Wabigoon Wabigoon metavolcanic— metavolcanicmetasedimentary metasedimentary belt. belt. They They are are aa diverse diverse assemblage assemblage of of sedimentary, sedimentary, extruextrusive, and intrusive greenintrusive rock rock types, types, generally generally metamorphosed metamorphosed to to the the upper upper green— schist schist facies, facies, and (Ojakanand have have an an estimated estimated aggregate aggregate thickness thickness of of 2400 2400 mm (Ojakan— gas, 1972). 1972). In contrast, the biotite schist schist to to the the south south of the the Rainy Lake— LakeSeine Seine River River Fault Fault has has aa metamorphic metamorphic mineral mineral assemblage assemblage characteristic characteristic of of the facies. However, However, the the change change in in metamorphic metamorphic grade grade across across the amphibolite amphibolite facies. the The schist schist south south of of the fault fault is is somewhat somewhat transitional transitional rather rather than than sharp. sharp. The the the fault fault has has aa minimum thickness thickness of of 3600 3600 m. m. For to consider consider the the geology geology of of the the For descriptive descriptive purposes purposes it it is is useful useful to Rainy The central central belt Rainy Lake Lake area area as as consisting consisting of of three three lithologic lithologic belts. belts. The consists ic to to intermediate intermediate metavolcanic and consists of of aa complex complex assortment assortment of of mat mafic hypabyssal rocks hypabyssal rocks and and is is referred referred to to in in general general terms terms as as the the greenstone greenstone belt. belt. The on the the north north by by aa belt belt of of metagraywacke metagraywacke The greenstone greenstone belt belt is is flanked flanked on (passing I1 field field guide guide in (passing through Ranier; see stops 1 and 9 of the Trip II this this volume), volume), and and on on the the south south by by another another belt belt of of metagraywacke metagraywacke that that may may or or may not be correlative correlative with with the the metagraywacke metagraywacke to to the the north. north. The The south south belt belt of is broken by the the Rainy Riverfault fault (see (see stop of metagraywacke metagraywacke is broken by Rainy Lake—Seine Lake-Seine River stop 11 11 of of the field field guide). guide). A fourth fourth important important lithostratigraphic lithostratigraphic unit in in the the area This clas— clasarea consists consists of of feldspathic—lithic feldspathic-lithic quartzite quartzite and and conglomerate. conglomerate. This tic tic succession succession occurs occurs within within the the central central greenstone greenstone belt belt (see (see stops stops 22 and and 88 of the the field field guide). guide). 91 �0 0-J u-s a- u-s C 0 aD aC a- o Sc —Jo z'a Ilmm - Biotite schist schist a Metasedimentary unit unit Metasedimenmry (feldspathic quartzite (feldspathic quartzite and andconglomerate) conglomerate1 EEI tuffaceous biotite—chtorite tuffoceous biotite-chlorite schist, schist, chlorite schist, — actinohte schist, schist, chlorite chlorite-actinolite piltowed greenstone, fetsic tuff, pillowed greenstone, felsic tuff, metaplutonic rocks including felsite, and and metoplutonic including feisite, intermediate, mcfic mafic ond and ultramafic types intermediote, types Ililut' II I II Metavalcanic Metavolcon>c— metaplutonic rnetaplutonic unit unit: A .. Inclined bed, bed, overturned overturned I t EXPLANATION and bedding Vertical foliation Vertical foliation and bedding Y Inclined foliotion foliation and and bedding bedding Inclined + lncined lineation lineation Inclined Vertical foliation Vertical .2t *a Inclined Inclined foliation - -5' eo lop at Top of bedCin beds'in direction direction of arrow arrow -7 not determined Vertical bed, Vertical bed, top top direction direction not determined in direction direction of of dot Vertical bed, bed, top Vertical top in dot - 3t- Inclined bed. bed, top top direction direction not determined Inclined determined 2:c:;-5 e—7ç of the western part of the Figure 1. Figure 1. Geologic map of the Rainy Rainy Lake Lake area, area, Minnesota. From Ojakangas Ojakangas (1972). (1972). to 4) a 4, - a) 14 rn in in belt belt of ofg-reenstone greenstone feldspathic Metasedirnentary unit Metcsedimentory unit: feldspothic quartzite and and conglomerate conglomerate Racks Rocks racks, undivided Granitic rocks, undivided Hornblendegobbro gabbro and and diorite Hornblende diorite I'' m 4 M pie 40 -' Inclined bed, right right side side up up Inclined bed, 3" -- ... Contact Contact Short dash dash where whereinferred inferred or or gradational; gradational; Short dotted where dotted where concealed concealed by water water ....... Inferred fault fault Inferred Dotted where where concealed concealed by by water water Dotted --- islands Seven Sister �I p The The stratigraphic stratigraphic and and structural structural relationships relationships among among the the greenstone, greenstone, the the two two belts belts of of metagraywacke, metagrayuacke, and and the the feldspathic feldspathic quartzite—conglomerate quartzite-conglomerate sequence sequence have have been been debated debated for for decades. decades. The The problems problems are are discussed discussed briefly briefly in in later later sections. sections. Most ~ o s tvolcanic—sedimentary volcanic-sedimentary rock rock types types in in the the Rainy Kainy Lake Lake area area are are schis— schistose i— tose and and many many are are sheared, sheared, making makingrecognition recognitionof ofprimary primaryrock rocktypes typesdiff difficult. cult. Small Small bodies bodies and and dikes dikes of of granitic granitic rocks rocks intrude intrude the the metamorphic metamorphic rocks. rocks. Some Some of of these these previously previously have have been been called called Laurentian Laurentian granites granites (Law(Lawson, son, 1913; 1913; Hart Hart and and Davis, Davis, 1969; 1969;Peterman Petermanan.d aqd Goldich, Goldich, 1970). 1970). Late Late mafic mafic dikes dikes (2100—2200 (2100-2200 m.y.) my.) cut cut all all rocks rocks in in the the region region (Hanson (Hansonand and Malhotra, Malhotra, 1971). 1971). Exposures Exposures are are generally generally limited limited to to the the lake lake shores shores and and islands, islands, and and to to inland to the the For several several kilometers kilometers to inland knobs knobs of of the the Kabetogama Kabetogama Peninsula. Peninsula. For south, south, large large muskeg muskeg swamps swamps obscure obscure the the geology. geology. Metagraywacke Metagraywacke bothsides sidesofofthe thebelt belt of of greenstone is characterThe The metagraywacke metagraywacke onon both greenstone is character- ized dark—gray beds thatare aregenerally generally from from 55 to to 35 cm thick thick ized by by medium— medium- orordark-gray beds that 35 cm An excellent foliation, generally are as much as 1.2 m thick. but but are as much as 1.2 m thick. excellent foliation, generally parallel parallel to Original grain grain shapes shapes and and to bedding, bedding, is is given given by by well—aligned well-aligned biotite. biotite. Original Most samples are comsizes have been obliterated by recrystallization. samples are comsizes have been obliterated by recrystallization. posed 20-40 percent percent quartz, quartz, and and 10—15 10-15 percent percent posed of of 50—60 50-60 percent percent plagioclase, plagioclase, 20—40 Minor minerals include chlorite, muscovite, garnet, sillimanite, biotite. biotite. minerals include chlorite, garnet, sillimanite, staurolite, staurolite, hornblende, tourmaline, tourmaline, epidote, epidote, apatite, apatite, and and pyrite. South— Southwick (1972) described related biotite schists farther to wick (1972) described related biotite schists farther to the the south south in in greater greater detail. detail. • The The original original succession succession probably probably consisted consisted of of alternating alternating beds beds of of graded graywacke sandstones and generally thinner mudstones, the graded graywacke sandstones and generally thinner mudstones, the latter latter now now constituting Original bedding bedding survived survived the the constituting the the more more biotite—rich biotite-rich beds. beds. Original metamorphism. Graded beds beds have have been been obscured obscured by by metamorphism metamorphism at at most most locallocalmetamorphism. Graded ities, but can be detected even in some highly recrystallized schists. ities, can be detected even in some highly recrystallized schists. Other Other sedimentary sedimentary features, features, including including concretions, concretions, flame flame structures, structures, and and Turbidity load casts on the bottoms of a few beds, are rare. load casts on the bottoms of a few beds, are rare. Turbidity current current depodeposition sition on on submarine submarine fans fans provides provides aa likely likely model model for for sedimentation. sedimentation. Quartzite—Conglomerate Quartzite-Conglomerate Unit Unit in in the the Greenstone Greenstone Belt Belt Feldspathic—lithic Feldspathic-lithic quartzite quartzite and and conglomerate conglomerate constitute constitute aa clastic clastic sucsuccession within the predominant volcanogenic rocks of the greenstone cession within the predominant volcanogenic rocks of the greenstone belt. belt. This (19721, in in the the abstract abstract by by Oja— OjaThis succession succession is is described described in in Ojankangas Ojankangas (1972), 2 and 8 of the field guide kangas kangas and and Olson Olson in in this this volume, volume, and and in in stops stops 2 and 8 of the field guide in in fluvial-alluvial fan fan this volume. volume. It has been interpreted as a braided fluvial—alluvial association. association. this Metavolcanic Metavolcanic Rocks Bocks in in the the Greenstone Greenstone Belt Belt S A A complex complex volcanogenic volcanogenic association association that that includes includes tuffaceous tuffaceous schist, schist, felsic felsic tuff, felsite, felsite, greenschist, greenschist, pillowed pillowed greenstone, greenstone, iron—formation, iron-formation, 93 �felsic hypabyssal hypabyssal rocks, metadiorite, metagabbro, peridotite, and and anorthosite, makes up most of the the greenstone greenstone belt and is is intercalated intercalated with quartzite—conglomerate unit Shearing is pervasive in the quartzite-conglomerate unit described described above. above. Shearing in all the rocks, and positive identification identification of rock rock types types generally generally requires requires microscopic microscopic study. study. Chlorite, amphibole, amphibole, and and epidote epidote impart impart aa green green color to the the rocks. rocks. Tuffaceous schist, consisting Tuffaceous consisting of interstratified interstratified thin thin fine—grained fine-grained beds and of biotite-rich, biotite-rich, chlorite-rich, chlorite—rich, and and laiuinae laminae of and sericite—rich sericite-rich composition, composition, occurs occurs in in aa zone zone near near the the southern southern edge edge of of the the greenstone greenstone belt belt adjacent adjacent to to the ish Bay 8ay to the viviJackfish the southern southern metagraywacke metagraywacke belt, belt, and and extends extends from from Jack! Jackfish and Red Bed Sucker cinity of Cranberry Cranberry Island. Island. Another major body is is on Jackfish Is lands at at the the northern northern edge of the These rocks Islands the belt. These rocks are are interpreted interpreted to to be tuffaceous tuffaceous because because they they are are associated associated with with coarser coarser felsic felsic tuffs, tuffs, and and because because they they contain contain scattered scattered felsic felsic volcanic volcanic rock rock fragments fragments and and large large plagioclase grains in aa recrystallized recrystallized matrix matrix of of fine fine quartz quartz plagioclase grains (volcanic?) (volcanic?) in plagioclase, which up about about two thirds thirds of the and plagioclase, which malces makes up the rock. rock. Minor felsic felsic tuff tuff is is interbedded interbedded with with greenschist greenschist at at several several localilocalities. Exposures at the the eastern eastern end of Dryweed Island Island appear appear to to consist consist of lapilli tuff. lapilli tuff. Felsic flows Felsic flows occur occur in in aa few few small small exposures. exposures. Fine—grained, Fine-grained, dense dense meta— metaandesite commonly with with deformed deformed pillows, pillows, constitutes a andesite or or nietabasalt, metabasalt, commonly poorly poorly exposed exposed 360—meter-wide 360-meter-wide unit unit along along the the shoreline shoreline east east of of Birch Birch Point, Point, near the Rainy Lake. Lake. Other Other much much smaller smaller exposures exposures are are prespresthe western western end end of of Rainy ent ent on on islands. islands. fine-grained Rocks mapped as greenschist greenschist consist consist of thinly thinly bedded, fine—grained chlorite schist, chlorite—actinolite chlorite-actinolite schist, and actinolite actinolite schist. This This rock type is common throughout the belt of greenstone; it occurs both north occurs north common throughout the and south 1). south of the the quartzitrconglomerate quartzite-conglomerate unit unit (Fig. (Fig. 1). Sheared and altered altered metaplutonic rocks rocks of variable composition composition constiwnstitute the the bedrock of several several small small islands, especially especially in in the the eastern eastern part of of the the belt. belt. A small small island island just just off the the northeast northeast corner corner of Grindstone Grindstone island is Anorthosite comcomIsland is composed composed entirely entirely of of serpentinized serpentinized peridotite. peridotite. Anorthosite prises the the one one small small island island of of the the Seven Seven Sister Sister Islands Islands that that is is on on the the United States States side side of of the the International International Boundary. Boundary. Northern Zone Northern Zone of Granitic Granitic Rocks Rocks granitic rocks in the the western part of Medium-grained granitic rocksare arecommon common in western part ofRainy Rainy Lake, especially on the Ontario mainland and islands, and constitute the especially on the Ontario mainland and islands, and constitute the Lake, of aa large southern edge rocks that that lies lies to to the the north north of of southern edge of large area area of granitic rocks the Minnesota Minnesotaside side of of the Rainy Lake Lake volcanic—sedimentary the Bainy On the the volcanic-sedimentary sequence. sequence. On the International Boundary, gray,biotitic biotitic granitic International Boundary, gray, graniticrocks rocksoccur occur on on several several of of granitic rocks composition gran— the small granthe small islands. islands. The The granitic rockshave havethe thegeneral general compositionofof Grassy Island A large body of gray, sheared tonalite occurs on odiorite. odiorite. large sheared tonalite occurs on Grassy Island and is is intrusive green— and on the the adjacent and on adjacent islands islandsand and mainland, intrusiveinto into greenmainland, and schists. schists. 94 �I Late LateMafic MaficDikes Dikes Two Twowell—exposed well-exposedmafic maficdikes, dikes,from from4545toto7575meters meterswide, wide,which whichare arethe the youngest rocks in the area, are present on the islands in the western youngest rocks in the area, are present on the islands in the westernpart part of of Rainy RainyLake Lakeand andseveral severaladditional additionaldikes dikesare areexposed exposedsporadically sporadicallyininthe the These dikes strike N. 30—40° vicinity of International Falls. vicinity of International Falls. These dikes strike N. 30-400 W. W. and andare are vertical. Theyappear appearto tobe bealigned alignedwith withsimilar similardikes dikesininCanada Canadaand andsouthsouthvertical. They in Minnesota, and are part of a major dike swarm in the western part ward ward in Minnesota, and are part of a major dike swarm in the western part ofofthe theCanadian CanadianShield Shield(Southwick (Southwickand andDay, Day,1981). 1981). p STRUCTURAL STRUCTURALINTERPRETATION INTERPRETATION The Themajor major structural structuralgrain grainof ofthe theregion regionisiseast—northeast, east-northeast,and andisis given by major fold axes, faults, shear zones, bedding, and foliation. given by major fold axes, faults, shear zones, bedding, and foliation. Most Most ofof the the,bedded bedded rocks rocksare areinclined inclinedsteeply; steeply;the theonly onlyexception exceptionis isin inthe the Brule SaginawBay Bayarea areato tothe theeast, east,where wheregentle gentleopen openfolds foldsare are BruleNarrows NarrowstotoSaginaw elongated minerals, present. present. LineatiOn5mainly Lineations--mainly elongated minerals,schistosity—bedding schistosity-beddinginterintersections, plunge Both ENE. Both sections, and and minor minor fold foldaxes——generally axes~generally plunge30°—50° 30"-50a ENE. northwest— northwest- and and northeast—trending northeast-trendinglineaments, lineaments, some someof of which whichrepresent represent minor minor can be seen on aerial photographs. faults, can be seen on aerial photographs. faults, Lawson Lawson (1913) (1913)interpreted interpretedthe thebelt belt of ofgreenstone greenstoneand andassociated associated rocks rocks to be synclinal, with the quartzite unit (which he called to be synclinal, with the quartzite unit (which he calledHuronian) Huronian) in in the the core coreand and conglomerate conglomerate(also (alsocalled calledHuronian), Huronian), greenstone greenstone(called (calledCeewatin), Keewatin), and and biotite biotite schist schist(called (calledCoutchiching) Coutchiching)forming formingsuccessively successivelyolder older units units Grout (1925a), both north and south of the quartzite (Fig. 2A). noting both north and south of the quartzite (Fig. 2 A ) . Grout (1925a), noting that that all all the the cross crossbeds beds in inthe thequartzite quartzite face facesouthward, southward, interpreted interpreted the the major major structure to be anticlinal, and interpreted quartzite to lens out structure to be anticlinal, and interpreted quartzite to lens out near the be absent absent on on the thenorth northflank flank near the eroded eroded crest crest of of the theanticline anticlineand andto tobe • — (Fig. It is is noteworthy, noteworthy,however, however, that that the the northern northernconglomerate conglomerateunit unit 2B). It (Fig. 2B). mapped by both Lawson and Grout appears to consist of a few mapped by both Lawson and Grout appears to consist of a fewminor minorlenses lenses at at best, be assumed assumed to tobe be the thesame sameunit unit that that is is present present to to the the best, and and should shouldnot not be south southon onNeil NeilPoint. Point. Furthermore, Furthermore, greenschist greenschist occurs occurs both both stratigraphistratigraphibelow and above the feldspathic—lithic guartzite cally cally below and above the feldspathic-lithic quartzite and and conglomerate; conglomerate; these latter rock types are interbedded with greenschist. P Lawson thus, these latter rock types are interbedded with greenschist. Lawson thus, Such (1913)said said these these sediments sedimentswere weredeposited depositedupon upona amajor majorunconformity. unconformity. Such (1913) an an unconformity unconformity is isindeed indeed exposed exposedto tothe theeast east in in Ontario Ontario (Lawson, (Lawson,1913; 1913; Wood, If so, so, Wood, 1980) 1980)and and could couldbe be present, present, but but hidden, hidden, in in Minnesota Minnesota as as well. well. If (See the abstract by Ojakangas and Olson it it may may be be aa minor minor unconformity. unconformity. (See the abstract by Ojakangas and Olson in in this this volume.) volume.) Data Data obtained obtained during during my my study study permit permit aa different different structural structural interpretainterpretaNearly tion all strati— strati2 0 . Nearly all tion involving involvingboth both folding foldingand and faulting faulting(Fig. (Fig. 2C). graphic graphic tops tops in in the the belt belt of of greenstone greenstoneon on Rainy Rainy Lake Lake face facesouthward, southward, indicating The metagray— metagrayindicating aa lack lack of of major major folding folding within within the the belt belt itself. itself. the wacke wacke (biotite (biotiteschist) schist)that that lies liessouth southof of the the greenstone greenstoneunit unit faces faces northward, in an an area area several several p. 356) 356) in northward, as as previously previously noted noted by by Merritt Merritt (1934, (1934, p. kilometers Also, most most kilometers to to the the east, east, but but at at the the same same stratigraphic stratigraphicposition. psition. Also, metagraywacke Folding alone alone metagraywacke just just north north of of the the greenstone greenstone faces faces northward. northward. Folding for these cannot account account for these relationships; relationships: aa major major longitudinal longitudinal fault fault along along cannot to the the strike strike of of the the rock rock the southern southern boundary boundary of of the the belt, belt, parallel parallel to the units, units, seems seems necessary, necessary, and and aa fault fault along along the the northern northern boundary boundary of of the the greenstone greenstone belt belt apparently apparentlyalso alsois isrequired. required. 95 S �NNW NNW ssE SSE / / x A x (After Lawson, 1913 a) //__-__ — I (After Grout, 1925a) B i (Ojakan gas1 C NNW *4040* this report) 0 0 0 0 OSSE Generalized diagrammatic interpretation of this report D EXPLANATION I'' C m -Jo 02 Hornblende gabbro and and diorite Hornblende gabbro a- Granitic rocks, rocks, undivided undivided Rocks in in belt Rocks belt of of greentone greenstone a Melasedimentary unit: unit: te[dspathic Melasedimentary feldsoothic quartzite and quartzite and conglomerate conglome&e 'C 0 a, 'C U a, 0 a- U 3 0 -J "-I IIIIIIIIII{I - Metavolcanic metaplutonic unit: Metovolcanic —metaplutonic unit: tuttaceous tuffoceous biotite—chtorite biotite-chlorite schist, schist, chlorite schist, schist, chiorile-actinolite chlorite-actinolite schist, schist, chlorite pillowed greenstone, felsic tuft, tuff, greenstone, felsic telsite, fetsite, and and metaplutonic metaplutonic rocks rocks including including intermediate, matic and ultramafic types intermediate. mafic tvoes . . EEi Metosedimentary unit unit Metasedimentary (feldspathic (feldspathic quartzite quartzite and andconglomerate) conglomerate) 0 Biotite Biotite schist schist 4 Direction toward toward which Direction which stratigraphic stratigraphic top indicators indicators face face Figure Figure 2. 2. Diagrammatic Diagrammatic geologic geologic sections sections showing showing structural structural interpretainterpreta— of Lawson Lawson (1913), (19131, Grout Grout (1925a), (1925a), and and this t h i s report. report. Arrows tions of Arrows indimdi— cate directions directions of of stratigraphic stratigraphic tops. tops. Line of section X-X' shown shown on on section X—X' Figure Figure 1. 1 . From From Ojakangas Ojakangas (1972). (1972). 96 �Evidence of aa major of the the bbelt Evidence of major ffault a u l t along along the t h e southern southern boundary boundary of e l t inin- a   cludes cludes widespread widespread crinkling, crinkling, abundant abundant quartz quartz veins veins and and pods, pods, silicifica— silicificattion, i o n , slickensides, slickensides, and and cliffs c l i f f s (fault ( f a u l t scarpsfl. scarps?). Canadian Canadian geologic geologic maps maps show show aa major major fault f a u l t on on line l i n e with with this this fault f a u l t and and extending extending more more than than 200 200 km km Hawley (1930) and Merritt (1934), both of whom studied this t o the e a s t . Hawley (1930) and Herritt (19341, both of whom studied t h is to the east. fault it is is aa right r i g h t lateral l a t e r a l fault. f a u l t . The concluded it The f a u l t zone zone east e a s t of of Rainy Rainy Lake, Lake, concluded metamorphic the southern southern block block of of biotite b i o t i t e schist s c h i s t and and lower lower metamorphic grade grade (higher (higher in i n the in the northern greenstone block) indicates that the southern block i n t h e northern greenstone block) i n d i c a t e s t h a t t h e southern block also also to the t h e greenstone greenstone block. block. This This fault f a u l t is is now now called called moved upward upward relative r e l a t i v e to moved t h e Rainy Rainy Lake—Seine Lake-Seine River River fault f a u l t in i n Minnesota Minnesota (Southwick (Southwick and and Ojakangas, Ojakangas, the 197gb). Additional structural s t r u c t u r a l data data and and interpretations i n t e r p r e t a t i o n s can can be be found found in in 1979b). Additional Oj akangas. 0j akanqas . of of structural s t r u c t u r a l significance significance to to the t h e Rainy Rainy Lake Lake area area is is recent recent work work by by Poulsen has mapped Poulsen Poulsen (1980) (1980) and and Poulsen Poulsen and and others o t h e r s (1980). (1980). Poulsen has mapped nappe nappe structures s t r u c t u r e s in i n Ontario Ontario just j u s t 15 15 km km to to the t h e north north of of the t h e area a r e a under under discussion discussion The possibility of such structures being present in Minnesota must The p o s s i b i l i t y of such s t r u c t u r e s being present i n Minnesota must here. here. This is of relevance to the This is of relevance t o the be be considered considered in i n any any future f u t u r e detailed d e t a i l e d mapping. mapping. the metagraywacke 'Coutchiching problem,' the stratigraphic positioning of "Coutchiching problem," t h e s t r a t i g r a p h i c positioning of the metagraywacke u n i t s (biotite ( b i o t i t e schist) s c h i s t ) relative r e l a t i v e to to the t h e greenstones. greenstones. The The problem problem was was units discussed at a t some some length length by by Ojakangas Ojakangas (1972). (1972). discussed 97 �Paper 22 Paper GEOLOGY AND GEOCHEMISTRY GEOCHEMISTRY OF THE GEOLOGY AND THE VERMILION GRANIPIC GRANITICCOMPLEX COMPLEX Warren Warren C. C. Day, Minnesota Geological Geological Survey, 1633 1633 Eustis Eustis Street, St. St. Paul, Minnesota 55108 Minnesota 55108 INTRODUCTION INTRODUCTION Archean Archean granite granite and and migmatite migmatite of of the the Vermilion Vermilion Granitic Granitic Complex Complex form form the the southwestern southwestern portion portion of of the the Quetico Quetico subprovince, subprovince, aa major major petrotectonic petrotectonic division of the the Superior Superior Province Province of of the the Canadian Canadian Shield Shield that that extends extends eastward eastward from from northern northern Minnesota Minnesota into into Ontario. Ontario. The The northern northern margin margin of of the the Vermilion Vermilion Granitic Granitic Complex Complex grades grades into into aa broad broad belt belt of of biotite biotite schist schist which River fault fault by the the Rainy Rainy Lake—Seine Lake-Seine River which is is truncated truncated on on the the north north by (Southwick and Ojakangas, 1979a); (Southwick 1979a); the the fault fault marks the the north north boundary of the Quetico the Quetico subprovince subprovince in in Minnesota. Minnesota. Metavolcanic and metasedimentary metasedimentary rocks of the the Rainy Rainy Lake Lake area, area, part of of the the Wabigoon Wabigoon subprovince, subprovince, abut abut the the biotite The southern contact of the (Figure 1). 1). The southern contact the biotite schist schist across across the the fault fault (Figure Vermilion Vermilion Granitic Granitic Complex Complex is is defined defined by by the the Vermilion Vermilion fault, fault, south south of of which which are are the the metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks of of the the Vermilion Vermilion Vermilion Granitic district. The western western end end of of the the Vermilion Granitic Complex Complex is is defined defined by by the Vermilion Vermilion Biver fault fault and and the the convergence convergence of the the Rainy Rainy Lake—Seine Lake-Seine River fault. Bedrock exposureisisquite quiteextensive extensiveininthe the eastern eastern portion portion of of the Bedrock exposure the complex, quality and as the complex, but the the quality and quantity quantity of ofoutcrop outcropdiminish diminishwestward westward as the thickness of glacial cover thickness cover increases. increases. History of Investigations Investigations During During the the summer summer of of 1887 1887 H.V. H.V. Winchell, Winchell, H.W. H.W. Fairbanks, Fairbanks, W.F. W.F. Trussel Trussel and and two two "Indian "Indian canoe—men" canoe-men" set set out out in in two two birchbark birchbark canoes canoes from from Tower, Minnesota to conduct conduct aa geologic geologic expedition expedition in in northern northern Minnesota, Minnesota, Minnesota to journeying through Lake region. region. They They went went journeying through the theRainy RainyLake Lake and andKabetogama Kabetogama Lake from Vermilion Lake from Vermilion Lake north north up up the the Little Little Fork Fork River River to to the the international international boundary, and and then then eastward eastward along along Rainy Rainy Lake Lake River River (as (as the the Rainy Rainy River River was was then known)toto "Chadierre "Chadierre Falls" Falls" and Fromthere there they they prothen known) and Fort Fort Frances. Frances. From pro- ceeded along the the south take, south ceeded along south shore shore of of Rainy Rainy Lake, south into intoBlack BlackBay, Bay, portaged portaged into Lake, and peninsula by intoKabetogama Kabetogama Lake, and circumnavigated circumnavigated the theKabetogama Kabetogama peninsula by traveling Namakan travelingeastward eastwardthrough through Namakan and and Sand Sand Point PointLakes Lakes and and then thencoming coming back westward back westward through through Rainy Rainy Lake. Lake. During this this first first expedition expedition Winchell Winchell and his colleagues colleagues described described the the rocks rocks and and presented presented the the earliest earliest ideas ideas for for their their origin. origin. Grout (1923, Grout (1923, 1925b, 1925b, 1926) 1926) presented presented detailed detailed lithologic lithologic descriptions, descriptions, geochemical analyses, and geologic map of Vermilion Granite, the and aa geologic of the Vermilion the to the the terrane terrane now now called called the the Vermilion Vermilion Granitic Granitic name applied by Grout Grout to Geochronological work on rocks Complex. Geochronological rocks from from the the area area was initiated initiated by Goldich and others (1961) who determined a K—Ar age for the main (1961) who determined a K-Ar age for the main batho— bathoGoldich and others lithic phase of La Croix of the the Vermilion Vermilion Granite Granite (now (now termed termed the the Lac Lac La 98 �S 0 '0 S S I Generalized geologic map of the Vermilion Granitic Complex. The large—scale, east—west trending folds in the migatatite are clearly indicated by the map pattern between Pelican and Namakan Modified after Southwick and Sims (1980). Lakes. Figure 1. 0 0 �'reported Granite) Granite) of of about about 2,550 2,550 m.y. m. y. Peterman Petermanand andothers others(1972) (1972) 'reportedaa Pb—Sr Rb-Sr initial whole whole rock—isochron rock-isochron age age of of 2,680 2,680 12 95 m.y., my., with with an an 87sr/86sr ^sr/%r initial ratio ratio of of 0.7005 0.7005 ± 0.0012. 0.0012. Jahn Jahn and and Murthy Murthy (1975) (1975)determined determined aa more more refined refined Rb-Sr Rb-Sr whole whole rock—isochron rock-isochronage ageof of 2,700 2,700 ± 50 50 m.y., my., with with an an 7sr/86sr 87sr/86sr initial initial ratio ratioofof0.7004 0.7004 ±+ 0.0003. 0.0003. + + Recent Recent reconnaissance reconnaissancegeologic geologic mapping mapping of of the the Vermilion Vermilion Granitic Granitic Complex begun in in1968 1968 Complex and and the theMinnesota Minnesota portion portion of of the theRainy Rainy Lake Lakearea areawas wasbegun by by D.L. D.L. Southwick Southwickand and R.W. R.W. Ojakangas Ojakangasof of the theMinnesota Minnesota Geological GeologicalSurvey. Survey. Ojakangas Ojakangas published published aa description descriptionof of the thegeology geology in in the theRainy Rainy Lake Lake greenstone greenstone belt belt in in 1972, 1972, and and the the same same year year Southwick Southwick described describedthe thegranit— granitic Kabetogama, which which he he termed termed collectively collectively the the ic rocks rocks south south of of Lake Lake Icabetogama, Vermilion Vermilion granite—migmatite granite-migmatitemassif. massif. In In 1980 1980 Southwick Southwick and and Sims Sins replaced replaced the the informal informalterm termVermilion Vermiliongranite—migmatite granite-migmatite macsiC massif with with the theformal formalname name Vermilion the Vermilion Vermilion Granitic GraniticComplex, Complex, and and renamed renamed the Vermilion Granite Granite of ofGrout Grout (1925b) La Croix Croix Granite. Granite. The The most most recent recent geologic geologic map, map, at at (1925b) as as the the Lac Lac La scale scale 1:250,000, 1:250,000, was was published published by by Southwick Southwick and and Ojakangas Ojakangas(1979a). (1979a). 0 Lithologic Lithologic Units Units Lithologic be that that established establishedby by the the Lithologic nomenclature nomenclatureused used here here will will be IUGS Subcommission on the systematics of igneous rocks (Streckeisen, (Streckeisen, IUGS Suhcomission on the systematics of igneous rocks The three three most moat important important rock rock units units in in the the Vermilion Vermilion Granitic Granitic 1973). The 1973). Complex are migmatite, granite, and early plutonic rocks (Figure The 2). The Complex are migmatite, granite, and early plutonic rocks (Figure2). migmatite migmatite has has been been divided divided by by Southwick Southwick (1972) (1972)into into schist—rich schist-rich and and granite—rich The paleo— paleogranite-rich types typesdepending dependingon onthe theneosome/paleosome neosome/paleosomeratio. ratio. The somes of the migmatite are biotite schist, amphibolite, early migmatite, somes of the migmatite are biotite schist, amphibolite, early migmatite, and and early early plutonic plutonic rocks, rocks, and and the the neosomes neosomes are are two—mica two-mica leucogranite leucogranite and and The latter is similar to and grayish—pink biotite granite. presumably grayish-pink biotite granite. The latter is similar to and presumably cogenetic cogenetic with with the the Lac Lac La La Croix Croix Granite, Granite, the the dominant dominant batholithic batholithic phase phase of of The leucogranite neosome is present Vermilion Granitic Complex. the in the Vermilion Granitic Complex. The leucogranite neosome is present in small north thethecomplex small quantities quantities within within the the biotite biotiteschist schist northofof complex and and is isthe the Pink granite is the dominant dominant neosome in schist—rich migmatite. dominant neosome in schist-rich migmatite. Pink granite is the dominant neosome in rnigmatite classed as The early early plutonic plutonicrocks rocks neosome in migmatite classed as granite—rich. granite-rich. The within the complex range from granodiorite through tonalite/trondhjemite within the complex range from granodiorite through tonalite/trondhjenite These rocks rocks to and toquartz quartzdiorite diorite andform form small, small, generally generally irregular irregularmasses. masses. These the first igneous activity in the area, having been invaded represent on represent the first igneous activity in the area, having been invaded on all all scales scales by by the the 2,700 2,700 m.y.—old my.-old Lac Lac La La Croix Croix Granite. Granite. The The radiometric radiometric age age of of the the early early plutonic plutonic rocks rocks is is as as yet yet undetermined. undetermined. 4 VERMILION COMPLEX DESCRIPTIONS DESCRIPTIONS OF OF UNITS UNITSININTHE THE VERMILIONGRANITIC GRANITIC COMPLEX Biotite BiotiteSchist Schist I Biotite Biotite schist schist is is widely widely distributed distributed within within the the complex complex and and also also occurs occurs as as aa separate separate mappable mappable unit unit that that flanks flanks the the complex complex on on the the north north and west. west. Within Within the the complex complex the the biotite biotite schist schist occurs occurs as as more more or or less less and intact intact blocks blocks surrounded surrounded by by granite granite and and also also as as an an important important component component of of anan eguigranular, medium— equigranular, medium- to to Itisis the the paleosome paleosome of of migmatitic migmatitic rocks. rocks. It fine-grained schist schist composed composed dominantly dominantly of of quartz, quartz, plagioclase, plaqioclase, and and fine—grained 100 �I-. 0 F.' ~ o r l ymigmatite ,, I AMPHIBOLITE wvam wvom Amphiboiite migmotite CUTS 1 Burntside Gneiss WVb jrrelationships among lithologic ~ ~ i h & t o lower grade suprdcrustal rocks of the flanking greenstone belts BIOTITE SCHIST Wvbs I SCHIST -RICH MIGMATITE related to Lac La Cmix Granite Wvgm GRANITE-RICH MiGMATITE to Lac La Crolx Granite wvgm 1 CUT Late-stage, straight, sharpl i e d pegmatite dikes I complex. complex. Schematicdiagram diagramof ofthe the interrelationships among lithologic Figure2.2. schematic Figure Intrusiveunits unitsare are subdivisionsof of the thevermilion Vermilion GranitiC GraniticComplex. Complex. Intrusive subdivisions Names spelled arrangedwith withthe theyoungest youngestat at the thetop topof ofthe thediagram. diagram. Names spelled arranged outin inthe thecapital capitalletters letters are are the themore moreabundant abundantcomponents componentsof ofthe the out diorite and diorite ark gray hornblende quartz VERMILION GRANITIC COMPLEX I gobbm younger than and ... to IM vermilion Granitic Complex - 1 I �t biotite. biotite. Bedding Beddingand andgraded gradedbedding bedding are arewidely widelypreserved. preserved. Oriented Oriented biotite defines the strong schistosity, which is regionally biotite defines the strong schistosity, which is regionallyparallel parallelto to schist, Isoclinal folding is common in the with quartz quartz bedding. bedding. Isoclinal folding is common in the biotite schist, with stringers being and and feldspar feldspar"sweat—out" "sweat-out" pods pods and and stringers beingfolded foldedcongruently. congruently. biotite S of the thethe Vermilion The mineralogy mineralogy of the biotite biotiteschist schistnorth northofof VermilionGranitic Granitic The Complex is fairly constant, reflecting the chemical homogeneity Complex is fairly constant, reflecting the chemical homogeneity of of the the graywacke protolith. However, graywacke protolith. However, there there are are local local variations variations among among bedding bedding within the schist, as on the south shore of Kabetogama Lake horizons horizons within the schist, as on the south shore of Kabetogama Lakeby by Chippewa N., Chippewa Lodge Lodge CT. (T. 69 69N., R. R. 22 22W.), W.), where wheregarnet, garnet, staurolite, staurolite,and andsillisilli- land Sugarbush manite manite occur occur ininaluminous aluminous beds, beds, and andon on the thesouth southshore shoreofof SugarbushIsIsland ininKabetogama Lake,where wherefelsic felsic horizons horizons with with poikioblastic poikioblastic plagioclase Kabetogama Lake, plagioclase occur. occur. Migmatite migmatite The structure within within the the dominantly dominantly migmatitic migmatitic terrane terranein in The broad—scale broad-scale structure the thewest west part partof ofthe thecomplex complex is is delineated delineated by by foliation foliationwithin within the the Large folds foldswithin withinthe themigmatite migmatite trend trend roughly roughlyeast—west, east-west, paleosome. Large paleosome. flanking parallel to tothe themajor major structural structuralfabric fabricininthe the flankinggreenstone greenstone belts belts parallel (Southwick, 1979a). The The fold fold patterns patterns (Southwick,1972; 1972;Southwick Southwick and and Ojakangas, Ojakangas, 1979a). outlined outlinedby byschistose schistosepaleosomes paleosomes are arepreserved preserved even even into intothe thegranite—rich granite-rich 1978)states states "the consistency of migma— Southwick C (1978) "thestructural structural consistency of migmaportions. portions. Southwick tite paleosomes tite paleosomes in in the the western western portion portion of of the the Vermilion Vermilion Granitic GraniticComplex, Complex, even in in rocks rocks that that are are chiefly chiefly granite, granite, indicates indicates that thatthe thegranite granite even fraction, origin, was emplaced fraction,whatever whatever its its origin, was emplaced in ina amanner manner that that did did not not completely inin pre—existing The granite granite completely disrupt disrupt structural structuraltrends trends pre-existing rocks." rocks." The seems seems to to have have been been passively passively injected, injected,with withsome some flattening flatteningand andbroadening broadening of the thepre—existing pre-existing folds folds within within the thecountry country rocks. rocks. of The thethe complex predominantly The eastern easternportion portionofof complexisis predominantlymassive massiveLac LacLa La The perperCroix percent xenoliths. xenoliths. The Croix Granite, Granite, which which incorporates incorporates less lessthan than55 percent centage centage of of supracrustal supracrustal inclusions inclusions increases increases to to the thewest, west, with with the theli— lithology thology grading gradingregionally regionallyfrom frommassive massive granite granitethrough throughgranite—rich granite-rich In aa general general sense, sense, the the migmatite migmatite to toschist—rich schist-rich migmatite migmatite (Figure (Figure 1). 1). In Lac La La Croix Croix component component within within the the neosome neosome also also decreases decreases westward. westward. Lac Southwick Southwick (1972) (1972)argued argued that that the the schist—rich schist-rich migmatite migmatite of of the the western western porportion tion of of the thecomplex complexrepresents representsthe theinjected injectedand and remobilized remobilizedroof roofof ofaa batholith cored cored by by massive massive granite. granite. The The inferred inferred depth depth of of emplacement emplacement was was batholith on km (pressure (pressureof of 3-4 3-4 kb). kb). on the the order order of of 9—12 9-12 km The The structure structure and and fabric fabricof of the the migmatite migmatite vary vary on on the the outcrop outcrop scale, scale, depending depending on on the the amount amount of of neosome neosome present present and and the the manner manner of of its its In the the schist—rich schist-rich migmatite migmatite the the neosome neosome is is commonly commonly emplacement. In emplacement. interlayered interlayered with with the the paleosome, paleosome, producing producing aa stromatic stromatic structure structure (Mehnert, (Mehnert, commonly are small granitic stringers within the paleosome blocks Small granitic stringers within the paleosome blocks commonly are 1968). 1968). These leucocratic leucocratic boudinaged boudinaged and and thrown thrown into into small—scale small-scale isoclinal isoclinal folds. folds. These stringers stringers which which are are as as narrow narrow as as aa few few millimeters millimeters in in width, width, typically typically are are bordered by by aa biotite biotite selvage selvage zone. zone. bordered migmatitepresents presents several several fabric The granite—rich granite-rich migmatite fabric styles stylesdepending depending The emplacement. the degree of paleosome assimilation and manner of granite on the degree of paleosome assimilation and manner of granite emplacement. on 102 I �• Where Where the the granitic granitic neosome neosome is is dominant, dominant, paleosome paleosome blocks blocks (up (upto toten tenmeters meters Some paleosome blocks are sharp in size) are rafted in neosome. in size) are rafted in neosome. Some paleosome blocks are sharp and and distinct, distinct, typical typical of of an an agmatic agmatic migmatite, migmatite, many many have have the the pronounced pronounced flow flow fabric of a schlieren migmatite, and many are the ghostly, fabric of a schlieren migmatite, and many are the ghostly, digested digested remreuinants nants characteristic characteristicof of nebulitic nebulitic migmatite miqmatite (Mehnert, (Mehnert,1968). 1968). The The contacts contacts are contained are especially diffuse around tonalite blocks that are especially diffuse around tonalite blocks that are contained in in Lac lac The feldspar "halo" surrounding such inclusions is La Croix Granite. La Croix Granite. The feldspar "halo" surrounding such inclusions is interpreted interpreted as as representing representing alkali alkali metasomatism, metasomatism, with with the the introduction introduction of of potassium into the tonalite, and of calcium and sodium into potassium into the tonalite, and of calcium and sodium intothe thegranite. granite. The The neosome neosome of of the theschist—rich schist-richmigmatite miqmatite is iswhite white to tolight lightpink pink This is a coarse—grained to pegmatitic material leucogranite. leucogranite. This is a coarse-grained to pegmatitic material composed composed dominantly Muscovite, biotite biotite and and dominantly of of quartz, quartz, microcline microcline and and plagioclase. plagioclase. Muscovite, Garnet, epidote and zircon chlorite are common minor minerals. chlorite are common minor minerals. Garnet, epidote and zircon occur occur as as accessory accessory minerals. minerals. I • As As discussed discussed earlier, earlier, the the leucogranite leucogranite in in the the schist—rich schist-rich migmatite migmatite is intimately enfolded and boudinaged with the paleosome. is intimately enfolded and boudinaged with the paleosome. Poikioblastic Poikioblastic microcline microcline and and plagioclase plagioclase are are developed developed in in thin thin stringers stringers within within biotite biotite schist schist without without disruption disruption of of biotite biotite foliation foliation in in the the surrounding surrounding paleosome. paleosome. Southwick Southwick (1972) (1972)suggested suggested that that this this texture texture indicates indicates aa replacement origin or metasomatic growth of feldspar during metamorphism. replacement origin or metasomatic growth of feldspar during metamorphism. This be seen seen especially especially well well on on the the south south end end of of the the roadcut roadcut This texture texture can can be 6.6 6.6 miles miles north north of of Cusson, Cusson, Minnesota Minnesota along along U.S. U.S. Highway Highway 53. 53. The The neosome neosome of of the the granite—rich granite-rich migmatite migmatite is is predominantly predominantly grayishgrayishThe local mineralogy and chemical composition composition pink pink Lac Lac La La Croix CroixGranite. Granite. The local mineralogy and chemical of The neosome neosome of the the granite granite vary vary with with the the degree degree of of paleosome paleosome digestion. digestion. The also leucogranite and and Lac Lac La La also varies varies with with the the amount amount of of mixing mixing between between the the leucogranite Croix This is is seen seen along along the the Crane Crane Lake Lake Road, mad, north north of of Croix granitic granitic phases. phases. This the the junction junction with with the the Echo Echo Trail. Trail. Early Early Plutonic Plutonic Rocks Bocks Granodiorite, Granodiorite, trondhjemite, trondhjenite, tonalite, tonalite, and and quartz quartz diorite diorite represent represent the Although the earliest earliest igneous igneous activity activity in in the the Vermilion Vermilion Granitic Granitic Complex. Complex. Although these these rocks rocks occur occur as as relatively relatively minor minor intrusive intrusive bodies, bodies, they they hold hold aa key key to to understanding understanding the the early early geologic geologic and and geochemical geochemical evolution evolution of of the the region. region. In In most most cases cases crosscutting crosscutting relationships relationships easily easily establish establish relative relative ages, ages, but but radiometric radiometric dating dating has has not not been been conducted conducted on on these these earliest earliest phases phases to to determine determine their their absolute absolute ages. ages. P • Two to show show on on the the 1:250,000 1:250,000 Two early early plutonic plutonic units units are are large large enough enough to One is is an an east— eastscale scale geologic geologic map map by by Southwick Southwick and and Ojakangas Ojakangas (1979a). (1979a). One west trending trending body body of of biotite—hornblende biotite-hornblende quartz quartz diorite diorite which which crops crops out out west Sullivan BayBay of of Icabetogama tansouth southofof Sullivan KabetogamaLake Lake along the theAsh Ash River River Trail Trail3 3km along This rock rock has has aa massive, massive, mediwn—grained medium-grained hypidiomorphic hypidiomorphic (Figure 1). 1). This (Figure Modal proportions proportions of of the the leucocratic leucocratic minerals minerals are are plotted plotted in in texture. Modal texture. The melanocratic melanocratic minerals minerals hornblende hornblende and and biotite biotite comprise comprise up up Figure Figure 3a. 3a. The This biotite—hornblende biotite-hornblende quartz quartz diorite diorite is is to to 35 35 percent percent of of the the unit. unit. This crosscut crosscut by by numerous numerous dikes dikes and and irregular irregular masses masses of of biotite biotite granite granite and and The amphibole amphibole and and oxide oxide phases phases display display interesting interesting textural textural granodiorite. granodiorite. The 103 �a. QTZ rocks P LAG OR K QTZ QTZ /LOC Granite La Croix Granite 34.1 35.9 OR OR PLAG P LAG 33 N=45 v ~ = 4 5 \ FPLAG LAG OR QTZ C. "Ne N -9 .'— x Leucogranite /////////T Leucogranite OR Figure 3. Figure 3. vV ol 4) 29.6 4.4 44 QTZ 29.6 QTZ 5.6 OR 31.3 5.6 OR 34.3 7.3 PLAG 39.4 PLAG 39.4 73 N = 23 N=23 PL AG PLAG Modal abundances Data taken taken from Modal abundancesofofOr—Qtz—Pl. Or-Qtz-Pl. Data from Southwick Southwick (1972), Rye and Boy Roy (1978), (1978), and and unpublished unpublished data data on file at at Minnesota Minnesota (1972), Eye and on file Geological Survey. Geological Survey. a) Early Plutonic a) Plutonic Phases: o—granodiorite o-granodiorite along along Ash River; River; x— xgranodiorite on on west west side side of of Pelican Pelican La Lake; —small granodiorite ke;. -small bodies and neosomes of neosomes of early early migiuatites. migmatites. b) Lac La Croix Croix Granite Granite c)) Leucogranite Leucogranite c 104 �relationships relationships in in this this quartz quartz diorite, diorite, with with magnetite/hematite magnetite/hematite intergrowths intergrowths forming fine exsolution laaellae along cleavage forming fine exsolution lamellae along cleavage traces traces within within the the central central portion (ferrohastingsite). portion of of the the amphibole amphibole(ferrohastingsite). The The other other early early plutonic plutonic phase phase which whichhas hassignificant significantarea). areal exposure exposure is a weakly foliated, coarse—grained, biotite—hornblende granodiorite is a weakly foliated, coarse-grained, biotite-hornblende granodiorite that that occurs Modal proportions proportions are are 1 ) . Modal occurs at at the the west west end end of of Pelican Pelican Lake Lake (Figure (Figure1). plotted plotted in in Figure Figure3a. 3a. The The granodiorite granodiorite occupies occupies the the nose nose of of aa broad broad westwestplunging fold, with the east—west-trending limbs extending ward plunging fold, with the east-west-trending limbs extending into into ward to poor Due to poor exposure, exposure, the thestrat— stratgranite—rich granite-rich and and schist—rich schist-rich migmatite. migmatite. Due igraphic is uncertain, considered igraphic position position of of this this body body is uncertain, but but it itisis consideredto tobe be an early early plutonic plutonic phase. phase. an The The biotite biotite tonalite tonalite and and trondhjemite trondhjemitewithin within the theVermilion VermilionGranitic Granitic Complex Complex occur occur as as dikes dikes and and small small irregular irregular bodies bodies intruding intruding metamorphic metamorphic Locally these these create create an an early early migmatite migmatite which which is is crosscut crosscut country rock. rock. Locally country The tonalite and trondhjemby Lac Lac La La Croix Croix Granite Granite and and by by leucogranite. leucogranite. The tonalite and trondhjemby ite ite are are light light gray, gray, weakly weakly foliated, foliated, medium— medium- to to coarse—grained, coarse-grained, and and They intrude the country rockalong alongfoliation, foliation, hypidiomorphic hypidiomorphic in in texture. texture. They intrude the country rock and in in places places are are folded folded syntectonically syntectonically with with it. it. and Granite Granite Lac La La Croix Croix Granite Granite Lac This very very mass mass of of granite granite is is fairly fairly homogeneous homogeneous in in composition, composition, is is This r medium— medium- to to coarse—grained, coarse-grained, and and has has hypidiomorphic hypidiomorphic granular granular texture. texture. Floating Floating blocks blocks of of partly partly digested digested biotite biotite schist schist and and amphibolite amphibolite make make up up no no more more than than 55 percent percent of of the the rock rock within within the the area area mapped mapped (Southwick (Southwickand and to Ojakangas, 1979a). 1979a). Isolated Isolated megacrysts megacrysts of of microcline, microcline, ranging ranging from from 11 to Ojakangas, Pegmatitic and aplitic dikes cut the cm in in length, length, are are widespread. widespread. Pegmatitic and aplitic dikes cut the 15 cm 15 granite granite along along parallel parallel fractures, fractures, suggesting suggesting that that solidification solidification of of the the late—stage batholith batholith was was followed followed closely closely by by fracturing fracturing and and injection injectionof of late-stage Figure 3b 3b shows shows the the modal modal range range of ofthe thedominant dominant granitic material. material. Figure granitic medium-grained granite granite of of the the Lac Lac La La Croix. Croix. medium—grained Granite Graniteof ofthe theLac LacLa LaCroix Croixtype typeforms formsthe theneosome neosome of of migmatite migmatite that that. migmatite The color color of of the thegranite graniteininthe the migmatitediverges diverges flanks the the intrusion. intrusion. The flanks from grayish—pink from the the characteristic characteristic grayish-pink of ofthe themassive massive interior interior to to aa lighter lighter granite in is better better foliated The granite in the the migmatite migmatite is foliated pink or orpinkish—white. pinkish-white. The pink sub— suband it it also alsotends tendstoward towarda acoarser, coarser, than in inthe themassive massive interior; interior; and than accessory mineral mineral in in the Magnetite is isa acommon common accessory the pegmatitic texture. texture. Magnetite pegmatitic massive interior interiorofofthe the LacLa LaCroix, Croix,generally generallyforming forming medium-grained medium-grained massive Lac In the the border border neosome neosome and and late—stage late-stage pegmatites pegmatites the the subhedral crystals. crystals. In subhedral Grout (1923, (1923, en)euhedral euhedralcrystals. crystals. Grout magnetite occurs occurs as as large large (0.5 (0.5 to to 22 cm) magnetite 1926) 1926) first first noted noted this this occurrence occurrence and and surveyed surveyed these these magnetite magnetitepegznatites pegmatites for possible economic exploitation. for possible economic exploitation. Leucogranite U co g r a n it e Le • p The maincategory categoryof of granite granite in The second second main inthe theVermilion Vermilion Granitic GraniticComplex Complex The leucogranite is restricted The leucogranite is restricted is a gray to white two-mica leucogranite. is a gray to white two—mica leucogranite. 105 �13.2 16.9 16.8 54.5 69.0 70.4 64.7 65.2 7)) Amphibolite Amphibolite 7 8) 8 ) Trondhjemite Trondhjemite 9) 9 ) Granodiorite Granodiorite 10) Tonalite Tonalite 10) Tonalite 11) Tonalite * 14.1 47.5 6) 6 ) Amphibolite Amphibolite 1.78 1.90 0.74 0.75 0.73 6.73 9.03 6.58 9.10 ±0.06 0.13 ±0.08 3.16 33.00 1.79 1.84 11.68 13.05 8.21 11.40 ±0.22 0.57 +.29 1.42 ±0.27 t42 0.35 5.79 FeO(t) 2.40 MgO 0.50 0.30 0.23 1.00 0.74 1.11 1.50 ±0.07 0.10 ±0.05 0.19 0.53 +O.iO Ti02 5.29 5.29 4.21 4 .21 2.73 2 .73 3.50 3 .50 7.80 7 .80 11.48 7.63 7 .63 11.78 1 1.78 - 0.90 0.90 +O. 35 - 0.88 +0.19 ±0.19 - 2.72 2.72 +0.39 ±0.39 cao 4.06 3.564 5.62 6.30 3.28 2.88 3.74 1.56 ±0.87 2.60 ±0.87 2.64 ±0.71 3.66 Na20 1.61 2.19 1.26 0.93 0.94 0.92 1.82 1.05 ±1.05 5.65 ±0.49 5.81 ±0.27 2.93 1(20 H20 not determined determined H20 sample. Analyses done using atomic absorption with at least ten determinations on each element per sample. 17.5 19.90 15.9 53.4 5)) I'unphibolite 5 Amphibolite 14.1 ±1.01 49.1 15.3 +0.65 ±0.48 73.7 14.7 73.4 ±1.14 ±1.06 ±1.32 16.1 63.8 4) 4 ) Mtphibolite Amphibolite 3) 3 ) Leucogranite Leucogranite ave. ave . 2) 2) Lac Lac La La Croix Croix ave. ave. 1) Biotite Schist 1) Biotite Schist ave. ave. Al203 Major—element Major-element Composition of rocks in the Vermilion Granitic Complex 8i02 TABLE 1. TABLE 1. 0.06 0.05 0.02 0.03 0.19 0.22 0.12 0.19 0.02 +0.01 ±0.01 0.02 ±0.01 0.10 MnO No. NO. 10 5 7 99.52 99.87 99.67 99.46 99.27 99.92 98.96 99.78 98.97 99.41 98.13 Samples Total* Samples Total* �a NOTES FOR FOR TABLE TABLE NOTES 1) 1) • 1 1 Biotite schist schist (average (averageof of 77 rock rockanalyses), analyses),Kabetogaina Xabetogama Lake Lake area. area. Biotite 2 ) tac Lac La La Croix Croix Granite Granite (average (average of of 55 rock rock analyses), analyses), interior interior of of 2) batholith, 11 km km spacing spacing along alongEcho Echo Trail, Trail, east east of of Little LittleSioux SiouxIndian Indian batholith, River, Shell Shell Lake Lake quad. quad. River, Leucogranite Leucoqranite (average (average of of 10 10 rock rock analyses), analyses), small small bodies bodies in in biotite biotite schists and and schist—rich schist-rich miginatite, migmatite,Kabetogama Kabetogama Lake Lake area. area. schists 3) 3) 4 ) Medium—grained Medium-grained clinopyroxene—hornblende clinopyroxene-hornblende amphibolite amphibolite paleosome, paleosome, 0.8 0.8 km km 4) (0.5 (0.5 ml) mi) west of of Crane Crane Lake Lake Road Faad on on U.S. U.S. Forest Forest Service Service Vermilion Vermilion Falls Falls 17 W., Echo Lake quad. (8—1l—VGM—14). 35, T. 67 N., R. T . 67 N . , R . 17 W . , Echo Lake quad. (8-11-VGM-14). Road, SW~/.MW~/~, sec. 35, sec. Road, SWI/4NW1/4, Foliated Foliated coarse—grained coarse-grained biotite—hornblende biotite-hornblende amphibolite amphibolite paleosome, paleosome, 3.0 3.0 sec. km Road, NE1/4SE1/4, km (1.9 (1.9 mi) mi) south southof ofCrane CraneLake LakeononCrane CraneLake Lake Road, NE~/'sE~/~, sec. 35, 35, T. T. W., Echo Echo Lake Lake quad. quad. (8—10-VGM—1OA). (8-10-VGM-10A). 67 N., N., R. R. 17 17 q•, 67 5) 5) • 6) Foliated Foliated medium—grained medium-grained clinopyroxene—hornblende clinopyroxene-hornblende amphibolite amphibolite 6) paleosome, paleosome, 4.6 4.6 km km (2.9 (2.9 ml) mi) west west of of Elephant Elephant Lake Lake on on U.S. U.S. Forest Forest Service Service 18 W., Elephant Lake 19, T. 66 N., R. quad. Cusson Road, Road, NE1/4NW1/4, N E ~ / ~ N w sec. ~ , 66 N., R. 18 W., Elephant lake quad. Cusson sec. (8-12-VSM-4). (8—12—VSM—4). Coarsegrained paleosome, NW1/4SEI/4, Coarse-grainedamphibolite amphibolite paleosome, NW~/~SE~/', sec. sec. 22, 22, t. T. 65 65 N., N., R. R. W., Picket Picket Lake Lake quad. quad. (8—9—VAN—3). (8-9-VAM-3). W., 7) 7) 8) 8) Light—gray Light-gray biotite biotite trondhjemite, trondhjemite, same same location location as as 66 (8-12—VSM—1). (8-12-VSM-1). 9 ) Biotite Biotite granodiorite, granodiorite, same samelocation locationasas6 6(8—12-VSt4—3). (8-12-VSM-3). 9) 10) Light-gray hornblende biotite biotite tonalite, tonalite, same same locations locations as as 44 10) Light—gray hornblende (8-11-VGM-15). (8—11—VGt4—15). • 1 1 ) Foliated Foliated light—gray light-gray hornblende—biotite hornblende-biotite tonalite, tonalite, U.S. U.S. Highway Highway 53, 53, 2.9 2.9 11) km km (1.8 (1.8 mi) mi) west west of of St. St. Louis Louis Co. Co. Road Road 122 122 (8-14—VGM—A). (8-14-VGM-A). p I 107 16 16 �BIOTITE SCHIST BIOTITE SCHIST 10.00 oa: 6.00 cc 4.0 ci 2.00—— 0 10.00 6.00 U. —— — 1.00 2.00 1.00 .20—— — .20 .10 .10 .06 .06 : .01— — I I MG FE TI MN SI AL CA NA : .01 K METRGRRYMRCKE ME TA G 19 A I WA CKE 10.00 o 6.00 C 10.00 L U. 4.00 2 6.00 4.00 — 0 200 .40-— —— .40 LjJ ._j a- U, .20—— .20 .10 .10 .06 .06 .04— — .04 .02—— — .02 — .01 .01— I I I I I I MCFETI MNSI ALCANA K Figure 4. Major-element data normalized against average biotite schist Figure 4. Major—element data normalized against average biotite schist from Kabetogama Lake area. from Kabetogama Lake area. a) Biotite schist at Lake Kabetogama. Note narrow range in a) Biotite schist at Lake Kabetogama. Note narrow range in composition. composition. b) Metagraywacke from neighboring greenstone belts. b) Metagraywacke from neighboring greenstone belts. 108 I �to to small tothe theneosome neosome of of schist—rich schist-rich migmatite migmatite and and to small bodies bodies within within biotite biotite The leucogranite varies along the northern border of the complex. schist schist along the northern border of the complex. The leucogranite varies greatly greatly in in mineralogy, mineralogy, texture, texture, and and geochemistry. geochemistry. S * Figure Figure 3c 3c shows shows the the modal modal variability variability of of the theleucogranite. leucogranite. The The leucogrartite contains small but persistent amounts of primary muscovite leucogranite contains small but persistent muscovite and and garnet. garnet. Garnet Garnet typically typically makes makes up up aa few few percent percent of of the the leucogranite leucogranite whereas whereas it it is is totally totally absent absent from from the the Lac Lac La La Croix Croix Granite. Granite. Magnetite, Magnetite, on on the the other other hand, hand, is is aa common commonaccessory accessoryin inthe thet.ac Lac La Croix Croix but but is is rare rare in in the the leucogranite. leucogranite. The The texture texture of of the the leucogranite leucogranite varies varies locally locally from from medium—grained medium-grained hypidiomorphic Different textural textural hypidiomorphic granular granular to to coarse—grained coarse-grained pegmatitic. pegmatitic. Different subunits leucogranite commonly commonly cut cut across across one one another another (as (asat at Wooden Wooden subunits of of the the leucogranite Frog Frog Campground; Campground) Stop Stop 13, 13, field field trip trip II, 11, this this volume). volume). These These textural textural subunits subunits are are thought thought to to be be cogenetic wgenetic and and virtually virtually coeval. coeval. Possibly Possibly the the most most significant significant feature feature of of the the leucogranite leucogranite is is its its relation Along the the relation to to the the deformation deformation history history of of the the biotite biotite schist. schist. Along south south shore shore of of Kabetogama Kabetogama Lake Lake the the leucogranite leucogranite is is isoclinally isoclinally folded folded with with biotite biotite schist; schist; the the leucogranite leucogranite has has been been boudinaged boudinaged along along isoclinal isoclinal fold fold limbs, limbs, and and thickened thickened within within hinges. hinges. Physically Physically indistinguishable indistinguishable leucogranite The seemingly seemingly leucogranite also also cuts cuts discordantly discordantly across across these these folds. folds. The incongruent incongruent timing timing of of leucogranite leucogranite emplacement emplacement is is best best explained explained by by concontinual tinual mobilization mobilization of of granitic granitic material material during during deformation deformation of of the the biotite biotite schist. schist.  I GEOCHEMISTRY GEOCHEMISTRY Biotite Biotite Schist Schist 8 P 8 0 Major— Major- and and trace—element trace-element analyses analyses were were made made to to determine determine the the geochemgeochemical nature nature of of the the biotite biotite schist schist in in the the Kabetogama Kabetogama Lake Lake region. region. To To ical obtain obtain representative representative chemical chemical analyses, analyses, rock rock samples samples were were selected selected from from average of of seven the the least—weathered least-weathered massive massive beds beds of of schist. schist. Pat An average seven separate separate analyses Figure 4a 4a displays displays the the range range of of major major eleele1. Figure analyses is is listed listed in in Table Table 1. ments Although ments for for the the specimens, specimens, normalized normalized against against the the average average schist. schist. Although beds beds with with aluminous aluminous and and quartzofeldspathic quartzofeldspathic compositions compositions do do occur occur locally, locally, This conconthe typical typical biotite biotite schist schist has has fairly fairly constant constant modal modal mineralogy. mineralogy. This the sistency sistency is is reflected reflected in in limited limited variation variation in in major major element element abundances. abundances. Figure Figure 4b 4b shows shows the the major major element element composition composition of of volcanogenic volcanogenic graywacke graywacke from from neighboring neighboring terranes terranes normalized normalized against against the the average average comcomposition of of the the biotite biotite schist. schist. Two Two new new analyses analyses of of metagraywacke metagraywacke from from position the the Rainy Bainy Lake Lake greenstone greenstone belt belt are are displayed, displayed, along along with with published published values values for for the the Knife Knife Lake Lake Formation Formation (Arth (Arth and and Hanson, Hanson, 1975), 1975), aa metasedimentary metasedimentary rock rock from from Wabigoon Wabigoon subprovince subprovince (Williams, (Williams, 1978) 1978) and and aa sample sample of of Coutchiching Coutchiching metagraywacke metagraywacke (Goldich (Goldich and and Peterman, Peterman, 1978). 1978). The The only only signisignificant MgO content content of of the the neighboring neighboring ficant variation variation is is the the higher higher MgO The observed observed higher higher MgO MgO content content could could reflect reflect aa more more metagraywackes. The mafic mafic original original composition composition within within the the metagraywackes, metagraywackes, or or it it could could reflect reflect case, the the major element element chemical chemical adjustments adjustments during during metamorphism. metamorphism. In any case, 109 �compositionof of the the biotite from Icabetogaina Lakeregion region is is very composition biotiteschist schist fromthe the Kabetogama Lake very similar ofof neighboring volcanogenic similar to tothat that neighboring volcanogenicmetasedimentary metasedimentary rocks. rocks. In 5 the contentofofaabiotite biotite schist the rare rare earth earthelement element (REE) In Figure Figure 5 (REE) content schist from the the Icabetogama Lakearea area is is compared with that metagraywacke from Kabetogama Lake compared with thatof ofa a metagraywacke from the the Rainy Lake greenstone greenstonebelt belt at from Rainy Lake at Ranier, Ranter, Minnesota. Minnesota. Also Also depicted depicted are the KEE content content of ofmetasedimentary metasedimentary rocks rocksfrom from the theKnife KnifeLake LakeFormation Formation are theBEE (Arth and Hanson, 1975) 1975)and andfrom fromthe theCrystal Crystal Lake Lake area area of of Ontario (Arth and Hanson, Ontario The REE content of the biotite schist (Williams, BEE content schist from from the the (Williams, 1978). The Kabetogama Lake Kabetogama Lake area area is is clearly clearly within within the the range range of of volcanogenic volcanogenic metagraywacke metagraywacke from from neighboring neighboring terranes. terranes. From the From the earliest earliest observations observations there there has has been been general general agreement agreement that that the protolith for the biotite schist was bedded graywacke. the protolith for the biotite schist was bedded graywacke. Alexander in the of the Winchell, the 16th 16thAnnual Annual Report Report of the Geological Geological and and Natural Natural History History Winchell, in Survey of Minnesota Survey Minnesota (1888, "the crystalline crystalline schists schistsappear appear (1888,p.p. 367) 367)states, states, "the to to me to to have have been been original original sediments sediments which which have have been been partly partly decomposed decomposed and fixed fixed in in new new combinations combinations while while in in aa semi-plastic semi-plastic state state occasioned occasioned by by heat and alkaline waters." heat and alkaline waters." Even though though our methods of investigation investigation are are more sophisticated, sophisticated, nearly nearly one one century century later later the the same same view view is is held. held. I Amphibolite Amphibolite Four samples samples from from amphibolite amphibolite inclusions inclusions within within Lac Lac La La Croix Croix Granite Granite analyzed for for major abundance(Table (Table1); 1); trace trace element element content content were analyzed major element element abundance was determined determinedfor for one one of of these In Figure was these samples samples (Table (Table 22). ). In Figure 6a 6a the themajor major elements are normalized against a low—Ti elements low-Ti basalt from the the upper member of the (Schultz, 1980). 1980). This This stanstanthe Ely Greenstone Greenstone in in the the Vermilion Vermilion district district (Schultz, dard to dard was chosen chosen because because basalts basalts like like those those in in the the Vermilion Vermilion district district to the south Outlined the south are are likely likely protoliths protoliths for for the the amphibolite amphibolite xenoliths. xenoliths. Outlined in Figure 6b Schulz (1980) (1980) 6b are are the the ranges ranges for for Ely Ely basalt basalt reported reported by Schulz and Arth and Hanson Hanson (1975), (19751, and and for for Newton Newton Lake Lake basalt basalt (Schulz, (Schulz, 1980). 1980). This plot gives gives aa feel feel for for the the normal normal range range of of major elements elements in in neigh— neighboring basalts. basalts. Although there is distinct diversity in the the geochemistry do of the the individual individual amphibolite amphibolite xenoliths, xenoliths, their their major major element element data data do display basaltic content in significantly higher higher 1(20 K20 content is aa significantly display basaltic affinity. affinity. There is amphibolite xenoliths, which the amphibolite which could could be aa result result of of metasomatism metasomatism by the the enclosing granite. enclosing granite. content of xenolith is is chondrite-normalized PEE REE content of one one axnphibolite amphibolite xenolith The chondrite—normalized plotted ininFigure sample from thethe Newton plotted Figure7,7,along alongwith witha a sampleofofbasalt basalt from Newton Lake Lake REE contents contents (Arth and and Hanson, Hanson, 1975). 1975). Williams Williams (1978) (1978) reported reportedPEE Formation (Arth for two amphibolite inclusions for inclusions within early tonalite tonalite from the the Crystal crystal Lake area, Ontario, and BEE patterns patterns were were flat flat and noted noted that that the the normalized normalized REE (approximately 1 1 x chondrites), very similar similar to to the the Newton Newton Lake Lake basalt. basalt. (approximately 11 The REE content content of of the the analyzed analyzed amphibolite amphibolite inclusion inclusion is is less less than than The overall overall PEE that that of of these these other other metabasalts metabasalts (7—9 (7-9 xx chondrites). chondrites). In addition, the the inclusion has a depleted = similar to inclusion depleted light light PEE KEE profile (La/Smn (La/% = 0.75), 0.75), similar to Type II ocean basalts identified identified by by Bryan and others Type ocean floor floor tho].eiitic tholeiitic basalts (1976). (1976). There are There are two two viable viable hypotheses hypotheses for for the the origin origin of of the the amphibolite amphibolite xenoliths. One possibility is is that that they they are are cognate cognate inclusions, inclusions, repre— repre- 110 S S �U I- C z 0 3: 0 LU -J 0 4 (I) La Ce Nd Sm Eu Gd Tb Dy Er Yb Lu REE plot p l o tof:• o f :—biotite  ¥ - b i o t i schist t s c h i s(Kabetogama t (Kabetogama Lake); Lake); Figure 55. • REE Figure A —metagraywacke, Crystal Lake, Lake, Ontario 0 —metagraywacke -metagraywacke (Ranier, (Ranier,Mn) Mn);A-metagraywacke, Crystal Ontario Cl ; (Williams,1978); 1978); O-metagraywacke, Knife Knife Lake Lake Group Group (l¼rth (Arth and and (Williams, O—metagraywacke, (Haskin and and others, others, Normalized against against chondrites chondrites (Haskin Hanson, 1975). 1975). Normalized Hanson, 1968). 1968). Ui Ill �S TABLE TABLE 2.2. Trace in rocks Trace element element abundances abundance8 in rocks of of the theVermilion Vermilion Granitic Granitic Complex, Complex, in in ppm ppm Uu Th Th Ta Ta 1 2 — 2.5 0.20 0.092 7.8 0.56 3 2.8 10.4 0.45 4 5 1.7 1.8 6.2 24.9 0.33 0.48 4.23 3.40 3.5 U Sc sc 37.3 Cr cr Ni Ni 151 79 19.1 117 82 Co CO 51.0 25.5 Rb Rb Sr sr 12 141 142 113 Ba Ba Cs cs 87 559 La La Ce ce 2.39 6.7 Nd Nd Sm sm Fu FU Tb Tb .27 — 10.9 109 28 16.5 12.1 — 6.3 1.47 296 12.3 355 803 3.30 126 6.0 126 130 542 1.51 23.09 46.6 31.83 58.9 26.83 48.8 43.80 84.0 74 84 17 24 17 31 3.94 0.95 0.47 4.38 Yb Yb Lu LU 1.73 0.63 0.36 1.52 0.23 0.25 1.02 0.35 1.15 0.21 2.92 0.65 0.16 0.30 0.061 6.01 0.57 0.47 0.66 0.11 Hf Hf 1.24 3.53 3.99 3.49 5.33 Zr zr 1.52 134 145 133 148 NOTES: NOTES : 1) 1) Foliated Foliated paleosome paleosome composed composed of of medium—grained medium-grained clinopyroxene clinopyroxene hornblende hornblende amphibolite. km (2.9 (2.9 mi) mi) west west of of Elephant Elephant Lake Lake on on U.S. U.S. Forest Forest Service Service amphibolite. 4.6 4.6 km T. 66 66 N., N., R. R. 18 18 W., w., Elephant Elephant Lake Lakequad. quad. cussonRoad, Road,NE1/4, NE1/4, NW1/4, NW1/4, sec. sec. 19, 19, T. Cusson (8-12-VSM-4) (8-12-VSM—4). 2) 2) Biotite Biotiteschist, schist,Rocky RockyPoint PointResort, Resort,SW1/4SE1/4, SW~/'SE~/~, sec. sec. 6, 6, T. T. 69 69N., N., Kabetogama Kabetogama quad. quad. (8—15—MS—5). (8-15-MS-5). R. 21 21 W., w., ft. 3) Metagraywacke, Metagraywacke, Ranier, Banier, MN MN (8-19-7). (8-19-7). 3) 4) 4 ) Early Early tonalite, tonalite, 4.3 4.3 km km (2.7 (2.7 mi) mi) west west of of Crane Crane Lake Lake Road Road on on U.S. U.S. Forest Forest Service Vermilion Vermilion Falls Falls Road, Road, NWI/45E%, NWl/isEl/4, sec. sec. 33, 33, T. T. 6767N., N., R.R. 17 17 W., W., Service Kabustasa Lake quad. (8—11—VGM—19). (8-11-VGM-19). Icabustasa 5) La Croix Croix Granite Granite 2.4 2.4 km km (1.5 (1.5 mi) mi) east east of of Little little Sioux Sioux Indian Indian River River 5 ) Lac Lac La on sec. SE~/~NW~/', sec. 1,1, T. T. 65 65 N., N., R. R. 15 15 W., W., Shell Shell Lake Lakequad. quad. on Echo Echo Trail1 Trail, SE¼NW1/4, (VLG-4B 1. (VLG—4B). Neutron Neutron activation; activation; analyses analyses done done by by Klaus Klaus Schultz Schultz at at Washington Washington University, Mo. University, St. St. Louis, Louis, Mo. 112 �XENOLITHS RMPH IBOLI TEXENOLITHS AMPHIBOLITE 10.00 y 10.00 10.00 6.00 6.00 4.00 C a: cc C z 4.00 2.00 2.00 1 1.00 (I-) .40 .40 — -j a. .20 — — .10 — — .10 .06 .04 — — .06 — — .04 .20 ra: 0- U) I- 00 .60 .60 Lii • 02 .02 .01 .01 MG FE TI MN Si AL CA NA K VERMILION DISTRICT DISTRICTBASALTS BRSRLTS VERMILION 10.00 10.00 6.00 0 cc cc 4.00 — 6.00 4.00 cc 2.00— 2.00 1.00 1.00 0 I.- (F) I— -j 0- LU ra: U, I- .60 .40 .60 .40 — .20 — b. — .20 .10 .10 .06 .04 — .06 .04 .02 — .02 .01 .01 SI AL CA NA K Major-element data data normalized normalized against againstlow—Ti low-Ti basalt basaltfrom fromupper upper Figure6.6. Major—element Figure member of Ely Greenatone (Schulz, 1980). Greenstofle (Schulz, 1980). of Ely member ~mnhibolifce xenolithswithin withinvermilion VermilionGranitic GraniticComplex. COBplex. -.Amphibolite xenoliths a)a\ MG FE TI tIN ~~~ b)Ely ~ land and y Newton NewtonLake Lake basalts. basalts. b) 113 �uJ F- Ix zC I 0 0 uJ -J 0- C (I) 200 •1 4La Ce Nd Sm Eu Gd REE Tb Dy Ho Er REE plot of amphibolite xenolith and basalt from Newton Lake Normalized against chondrites (Haskin and others, 1968). Formation. Figure 7. Yb Lu �senting sentingunmelted m e l t e d residuum residuumfrom fromthe thesource sourceregion, region, that thatwere were brought brought up up The residual phase from partial within withinthe therising risinggranitic graniticdiapir. diapir. The residual phase from partial melting light BEE content content of of 15 15 to to 20 20 xx melting of of aa graywacke grakacke should shouldhave haveaalight . BEE and chondrites, chondrites, and and aaheavy heavy BEE REE content contentof of 3—5 3-5 xxchondrites chondrites(Arth (Arth and Hanson, Hanson, 1975). This This character character is is not not displayed displayed in in the the analyzed analyzed amphtholite amphibolite 1975). xenolith. xenolith. The The second second hypothesis hypothesisis is that thatthe theamphibolite amphibolitexenoliths xenolithswere were simply simply country rock which was intruded by and entrained within the rising country rock which was intruded by and entrained within the rising granit— granitic ic melt. melt. This This is is supported supportedby by the thebasaltic basalticatajor major element element affinities affinities and and trace traceelement element abundances abundancesin inthe theanalyzed analyzedsamples. samples. This This does does not not mean mean to to imply imply that that all all of of the the amphibolite amphibolite xenoliths xenoliths within within the the complex complex have have this this origin, origin, but but the the analyzed analyzed samples samples seem seem to to have have been been country country rock rockthat that was was incorporated by the encroaching granite. incorporated by the encroaching granite. Early Early Plutonic Plutonic Rocks Bocks Major Major element element abundances abundances were were determined determinedfor for four four samples samplesof of the the The trace element content trondhjemite—granodiorite trondhjemite-granodiorite suite suite (Table (Table1). 1). The trace element content for for one ~ 1 is is~ For each each of of these these rocks rocks the the A1203 one sample sample was was determined determined (Table (Table2). 2). For greater greater than than 15 15 wt%, wt%, placing placing them them in in the the high—Al203 high-A1203 trondhjemite trondhjemitegroup group of of Barker Barker and and others others (1976). (1976). Major Major element element analyses analyses for for three three trondhjemite trondhjemite samples (1980)are are plotted plotted in in samples previously previously obtained obtained by by Southwick Southwick and and Sims Sims(1980) Figure An average average of of these these seven seven was was Figure Ba 8a along along with with the the four four new new analyses. analyses. An used used for for normalization normalization in in Figures Figures 8a 8a and and Sb. 8b. AA wide wide composition composition spread spread within within this this class class of of rocks rocks is is seen seenin in Figure as separate separate small small 8a. This This is is not not surprising surprising since since the the rocks rocks occur occur as Figure Ba. bodies Factors such such as as difdifbodies throughout throughout an an area area of of more more than than 1000 1000 km2. km2. Factors ferences ferences in in source source rock rock composition, composition, mineral mineral fractionation fractionationduring during transport transport and and emplacement emplacement of of the the melt, melt, and and subsequent subsequent metamorphic metamorphic overoverprinting printing would would contribute contribute to to the the chemical chemical variations variations observed. observed. Figure Figure 8b 8b shows shows major major element element compositions compositions for for the theSaganaga Saganaga Tonalite Tonalite and FeO and and Systematic variations variationscan canbe beseen seenininFeO and Northern Northern Light Light Oneiss. Gneiss. Systematic Ti02, in constant TiO2, which which remain remain in constant ratio ratioeven even though though their theirabsolute absoluteabundances abundances mineralsuch suchasasilmenite ilmenitein in the the source A Fe—Ti Fe-Ti mineral source basalt basaltcould couldhave have vary. A vary. buffered and Ti02 Ti02during duringmelting, melting, resulting resulting in buffered the theFeO FeO and in the thesystematic systematic behavior behavior seen seen in in the the derived derived tonalites. tonalites. The trondhjemite-granodiorite The major major element element composition composition of of the the early early trondhjemite—granodiorite suite suite of of the the complex complex is is very very similar similar to to those those of of the the Saganaga Saganaga Tonalite Tonalite and and The only only discrepancy discrepancy is is in in the the Ti02 Ti02 content, content, the the Northern Northern Light Light Gneiss. Gneiss. The Ti02 More data data which could could reflect reflectrelative relative TiO,abundance abundance in in the thesource source rock. rock. More which are needed needed in in order order to to delineate delineate this thisdifference. difference. The The chondrite— chondriteare for one one sample sampleare are plotted plotted in Also SEE abundances abundances for in Figure Figure 9. 9. Also normalized PEE normalized depicted are are the the ranges ranges for for the the Saganaga Saganaga Tonalite Tonalite and and the the Northern Northern Light Light depicted Gneiss (Arth (Arth and and Hanson, Hanson, 1975). 1975). The The trondhjemite trondhjemite has has aa steep steep negative negative Gneiss The Light—REE Light-REE content content is is pattern (La/Lun 45), and and no no Eu Eu anomaly. anomaly. The (La/Lun == 45), pattern approximately approximately 33 times times greater greater than than that that of of the the Saganaga Saganaga tonalite, tonalite, while while The overall overall PEE BEE content content is is the heavy heavy PEE BEE abundances abundances are are quite quite comparable. comparable. The the very very similar similar to to the the Northern Northern Light Light Gneiss. Gneiss. 115 0 ~ �TRONDHJEMITE-GRRNODIORITE TRONDHJEM I TE—GARNOD IOn I IF SUITE SUITE 10.00 10.00 C cc cc C 6.00 4.00 — 4.00 cc 2.00 — 2.00 1.00 — 1.00 — .60 .40 I— 8.00 U, I- .60 .40 — — Lu -J a- .20 cc U, .10 — .10 Os — I- .04 — — .06 .04 .02— — — .02 .01 — — .01 : 10.00 a. — MG FE TI (IN SI AL CR NA — .20 K SRGRNRGR TONAL TONRLITE SAGANAGA ITE 10. 00 10.00 C 0 6.00 6.00 cc a 4.00 4.00 ci: ec C z cc ^p NORTHERN LIGHT GNEISS NORTHERN LIGHT GNEISS — — 2.00 — I— 6.00 4.00 2.00 (I) 1.00 eQ S uJ -J aci: (1) 1.00 .60 40 .20 — — — — .20 b. .10 .10 .06 I— .60 .40 .08 .04 — .04 .02 — .02 .0! .0! MG FE TI MN SI AL CR NA Figure Figure8.8. K Major—element Major-element data datanormalized normalizedagainst againstaverage averageof of seven sevenearly early plutonic emite—granodiorite samples. plutonictrondhj trondhjemite-granodiorite samples. a ) Trondhjemite—granodiorite Trondhjemite-granodioritesuite, suite,Vermilion VermilionGranitic Granitic Complex. Complex. a) b) b)Saganaga SaganagaTonalite Tonaliteand andNorthern NorthernLight LightGneiss. Gneiss. 116 �I I I I I I I I ARCHEAN I I I I I I I TONALITE -- U - F— C z 0 I0 U -j --- Vermilion Granitic Complex a- - C - - (I) en 4 --- I La La I Ce Ce 1 I Pr Pr Nd Nd I Pm Pm I Sm Sm I I I I Eu Eu Gd Gd Tb Dy Dy I Ho Ho I Er Er I Tm Tm I Yb Yb I Lu LU plot of early Archean tonalites tonalites from from northern northern Minnesota. Minnesota. PEE plot Figure Figure 9. 9. BEE •—early tonalite, Vermilion Granitic Complex; fl—Northern >-early tonalite, Vermilion Granitic Complex; S-Northern Light Gneiss; Saganaga Tonalite. Tonalite. Normalized Normalized against against Gneiss; shaded shaded area area is is Saganaga chondrites chondrites (Haskin 1968). (Haskin and and others, others, 1968) 117 �^ 10.00 l0.00 C a 6.00 — 4.00 — 4.00 cE 2.00 U-) cc 0 C 10.00 LRCLA LRCROIX CROIXGRANITE GRRNITE LAC — — a. a. — 6.00 4.00 — 2.00 1.00— — 1.00 .60 — — .40 — — .60 .40 -J 0 .20 — — — .20 cc .10 — — — .10 06 — .04 — — — — — .06 .04 — — — .02 .01 — — — .0! : — 10.00 I- F— = Li-i U) F-- OZ MG FE TI MN SI AL CA NA 10.00 lO00: Cec ccU C0 zcc LRCLA LR CROIX CROIXNEOSOME NEOSOME LAC &00 — 4.00— 400 2.00 F— K — - — 6.00 4.00 2 00 U) LOU— 1.00 .60 — I— .40 — - .60 .40 - .20 Li-i a- -J .20 — cc .10 — - .10 06— : .04 — - .06 .04 U) I— = b. .02— — - .02 .01 — — — 01 MG FE TI MN SI AL CA NA LEUCOGRRNITES LEUCOGRANITES 1000: 0 6.006.00 C a:!$ cca C a a: I— (I-) I— li-i 4.00 2.00 2.00— — 2.00 L00 • element chemistry. b) Lac La Croix Granite b) Lac La Croix Granite which comprises granitic which comprises granitic neosome in granite-rich neosome in granite—rich migmatite. migmatite. c ) Leucogranite from the c) Leucogranite northern border from zonethe of the northern border zone of the Vermilion Granitic Complex. Vermilion Granitic Complex. Note average of MgO, FeO(t) Note average of MgO, FeO(t) and TiOg are significantly and Ti02 are of significantly below those the massive below those of massive Croix. interior Lac Lathe interior t.ac La Croix. 00 .60 40 — .40 .10 u) I .60 — a: massive interior of Lac ~a massive interior of Lac La Croix Granite. Croix Granite. a) Massive interior of Lac a) interior of Lac LaMassive Croix Granite. Note La Croix Granite. Note limited range in major limited in major elementrange chemistry. 6MG — .20 normalized against average 20.00 4.00— 4.00 -J 0S K Figure 10. Major-element data Figure 10. Major—element data normalized against average — .20 C — .10 .06 — .06 .04 — .04 .02 — .02 .01 0I MG FE TI MN SI AL CA NA I K 118 I �Hanson Hanson and and Goldich Goldich (1972) (1972)and and Arth Arth and and Hanson Hanson (1972, (1972, 1975) 1975) advanced advanced aa partial melting model for the origin of the Saganaga Tonalite and partial melting model for the origin of the Saganaga Tonalite and Northern Northern Light Archean tholeiitic tholeiitic material material was was metametaLight Gneiss. Gneiss. They They argued argued that that Archean morphosed morphosed to to amphibolite amphibolite or or eclogite eclogite grade, grade, and and upon upon 20% 20% partial partial melting melting would would produce produce the the REE REE content content observed. observed. This This model model is is consistent consistent with with the the In order for this model to produce REE experimental work of Green (1973). experimental work of Green (1973). In order for this model to produce BEE abundances abundances found found in in the the trondhjemite trondhjemite of of the the Vermilion Vermilion Granitic Granitic Complex, Complex, the degree of partial melting would have been less (<5%) and/or the degree of partial melting would have been less (<5%) and/or the the source source basalt was slightly enriched in light REE. basalt was slightly enriched in light REE. Granite Granite Lac Lac La La Croix Croix Granite Granite Five Five rock rock samples samples spaced spaced approximately approximately 11 km km apart apart within within the the massive massive interior of the batholith were analyzed to establish a representative interior of the batholith were analyzed to establish a representative average average composition composition for for the the Lac Lac La La Croix Croix Granite. Granite. This This average average for for the the major elements is listed in Table 1, and is used for normalizing granite major elements is listed in Table 1, and is used for normalizing granite compositions Figure lOa 10a displays displays the the narrow narrow range range in in compositions in in Figures Figures ba—c. 10a-c. Figure The individual major element composition for the massive Mc La Croix. major element composition for the massive Lac La Croix. The individual compositions compositions of of five five Lac Lac La La Croix Croix neosome neosome portions portions from from granite—rich granite-rich As can be seen, migmatite are plotted in Figure tUb. there is is aa greater greater migmatite are plotted in Figure lob. As can be seen, there diversity in neosome compositions relative to the massive interior. diversity in neosome compositions relative to the massive interior. This This probably probably reflects reflects country country rock rock assimilation assimilation which which has has contaminated contaminated these these granite granite neosomes. neosomes. plotted is aa new new REE BEE analysis analysis from from the the massive massive interior interior 1 1 is plotted in in Figure Figure 11 of of the the Lac Lac La La Croix Croix Granite, Granite, compared compared with with the the field field for for Giants Giants Range Range granites granites (Arth (Arth and and Hanson, Hanson, 1975). 1975). Both Both the the Mc Lacl.a La Croix Croix and and Giants Giants Range Range granites Ce content content (between (between granites have have steep steep negative negative chondritic chondritic patterns, patterns, high high Ce 100—45 100-45 xx chondrites), aa negative negative Eu Eu anomaly, anomaly, and and low low Lu Lu content content (3.5—2.5 (3.5-2.5 xx chondrites). Arth Arth and and Hanson Hanson (1975) (1975) proposed proposed that that the the batholithic batholithic gran— granchondrites). ites ites were were derived derived from from 20-50% 20-50% partial partial melting melting of of aa short—lived short-lived (<50 (<50m.y.) my.) graywacke graywacke source source at at crustal crustal depths. depths. Sims Sins (1976) (1976) proposed proposed that that this this depth depth was kbars). was between between 99 and and 12 12 kilometers kilometers (2—3 (2-3 kbars). initial The 8sr/86sr initial ratio The low low ^sr/^sr ratio (0.7004) (0.7004) indicates indicates that that the the source source for for the This dicdicthe Lac Lac La La Croix Croix was was relatively relatively young young at at the the time time of of melting. melting. This tates tates that that the the batholithic batholithic granite granite did did not not melt melt from from early early or or middle middle Archean Archean sialic sialic crustal crustal material. material. However, tonalitic tonalitic to to granodioritic granodioritic plutonism plutonism did Therefore, it it is is did occur occur early early during during the the evolution evolution of of the thecomplex. complex. Therefore, feasible feasible that that the the batholithic batholithic granite granite may may have have melted melted from from slightly slightly older older tonalite tonalite and and granodiorite, granodiorite, or or from from short—lived short-lived graywacke, graywacke, as as Arth Arth and and Hanson (1975)originally originally suggested. suggested. Hanson (1975) Rye Rye and and Roy Roy (1978) (1978)investigated investigated the the Th—U—K Th-U-K systematics systematics of of the the Vermilion Vermilion Granitic Granitic Complex, Complex, trying trying to to delineate delineate the the origin origin of of granite granite within within the them.igmatite. migmatite. If If the the mtgmatite m b t i t e formed formed by by in in situ sit" partial partial melting melting in in a a closed closed system, system, the thesum sum of of the the thorium thorium and and uranium uranium in in the the paleosome paleosome should equal plus neosome neosome should equal the the original original starting starting protolith protolith composition. composition. plus foundthat that the Rye Rye and and Roy Roy found the radioelement radioelement content content within within the themigmatite migmatite exceeded by 22 to to 33 times starting exceeded by timesthe thepresumed presumed Knife Knife Lake—like Lake-like starting 119 �LU I- 0 z 0 0 I U -J 0 C (J) La Figure 1 1 . Ce Nd Sm Eu Gd Tb Dy Er Yb Lu REE plot of Lac La Croix Granite and range of Giants Range Figure Granite. 11. REE Normalized plot of Lac against La Croixchondrites Granite and (Haskin others, 1968). range and of Giants Range Granite. Normalized against chondrites (Haskin and others, 1968). 120 �0 composition. composition. They They concluded concluded that that the the additional additional thorium thorium and and uranium uranium were were introduced introduced into into the the migmatite migmatite system system by by the the granitic granitic leucosome leucosome component, component, possibly possibly having having been been transported transportedin in the the volatile volatile phase phase derived derived from from the the intruding intruding granitic granitic batholith. batholith. Leucogranite Leucogranite • were determined determined on on 10 10 leucogranite leucogranite samples Major Major element element abundances abundances were samples from from the the northern northern border borderzone zoneof ofthe theVermilion VermilionGranitic GraniticComplex. Complex. An An individual analyses average for these these is is listed average for listedin inTable Table 1. 1. The The individual analyses are are plotted plottedininFigure FigurelOc, lOc,normalized normalizedagainst againstthe theaverage averageLac LacLa La Croix Croix granite. Clearly there there is is aa wide wide range range in in major major element element composition composition granite. Clearly within within the the leucogranite, leucogranite, and and some some overlap overlap with with the the Lac Lac La La Croix Croix comcomposition The distinguishing distinguishing feature feature between between the the two two granite granite types types position field. field. The is is that that the the MgO, MgO, total total FeO, FeO, and and Ti02 Ti02 abundances abundances in in the the average average leucogranite leucogranite are are well well below below the the observed observed values values for for the the Lac Lac La La Croix. Croix. This This may may be be attributable attributable in in part part to to higher higher modal modal abundances abundances of of magnetite magnetite and and biotite biotite in La Croix Croix (Tables (Tables 111—22 111-22 and and 111—24; 111-24; Southwick, Southwick, 1972). 1972). in the the Lac Lac La The The origin origin of of the the leucogranite leucogranite is is ambiguous ambiguous and and complex, complex, with with field field The granite melt may have evidence allowing two end member hypotheses. The granite melt may have evidence allowing two end member hypotheses. been been generated generated from from biotite biotite schist schist during during ultrametamorphism ultrametamorphism as as an an in in situ situ melt phase, or it may have been produced within a separate source region melt phase, or it may have been produced within a separate source region and localThe best evidence evidence for for the the local— and injected injected into into the the biotite biotite schist. schist. The hypothesis is found in the biotite schist along the northern source source hypothesis is found in the biotite schist along the northernborder border There, one one can canobserve observenarrow narrowpegmatitic pegmatitic"sweat—out" "sweat-out" zone zone of of the thecomplex. complex. There, • • pods and thin thin granitic pods and granitic and and granodioritic granodioriticstringers stringerswhich which are arebordered bordered by by a a biotite These thin thin biotite selvage selvage zone zone depleted depleted in in leucocratic leucocratic minerals. minerals. These are syntectonically deformed with the biotite schist, stringers stringers are syntectonically deformed with the biotite schist, and and for the the Evidence for coalesce coalesce into into larger larger veins veins and and small, small, irregular irregular bodies. bodies. Evidence injection hyothesis is best seen within the schist—rich m.igmatite. injection hyothesis is best seen within the schist-rich migmatite. Paleosomes Paleosomes of of biotite biotite schist schist are are rafted rafted within within leucogranite, leucogranite, the theborders borders which are sharp and distinct, without obvious mineral depletion of of which are sharp and distinct, without obvious mineral depletion zones zones or or mafic mafic selvages. selvages. A plausible plausible explanation explanation for for the the origin origin of of the the leucogranite leucogranite is is aa comcomIn this scenario, anatectic bination of both end—member hypotheses. bination of both end-member hypotheses. anatectic melt was was generated generated within within aa volcanogenic volcanogenic metasedimentary metasedimentary pile pile at at crustal crustal levels levels This melt phase was during regional metamorphism and deformation. This melt phase was con— conduring regional metamorphism and deformation. tinually tinually being being formed formed and and remobilized remobilized syntectonically syntectonically within within the the metasedi— metasedimentary rocks, infiltrating into the structurally higher portion mentary rocks, infiltrating into the structurally higher portion of of the the The initiation of the early anatectic melt may have been triggered pile. pile. The initiation of the early anatectic melt may have been triggered by heat heat and and volatiles volatiles derived derived from from the the rising rising mass mass of of Lac Lac La La Croix Croix Granite Granite. I for the the Origin of the Summary Summary Model Model for Origin of the Vermilion Granitic GraniticComplex Complex A frameworkfor forthe the petrogenesis petrogenesis of of the A framework the Vermilion Vermilion Granitic Granitic Complex is Complex is is an iterated iterated version version of the the history history proposed proposed by outlined outlined below. below. This is This model model is is founded founded on on the the geologic geologic mapping mapping and and Southwick (1978). (1978). This Southwick structural structural studies studies of of Southwick Southwick (1972), (1972). Southwick Southwick and and Ojakangas Ojakangas (1979a) (1979al 121 �and Southwjck Southwick and and Sims Sins (1980). (1980). The geochemical geochemical guidelines for this this model are the the major and trace trace element element arguments arguments presented above, and and those those by by Goldich and others Goldich others (1972), (19721, Arth and and Hanson Hanson (1975), (19751, Barker Barker and and Arth (1976), (1976), and Rye Bye and and Roy Boy (1978). (1978). Trondhjemitic—granodiorite Trondhjemitic-granodiorite magmas were melted from from amphibolite/ amphibolite/ 11)) eclogite at mantle km) leaving leaving aa residue residue of of garnet, garnet, eclogite mantle depths depths (10 (10 kb; 30 30 km) pyroxene and/or hornblende. This early magma rose to the surface surface and vented, providing volcanogenic Small vented, volcanogenic detritus detritus for for the the graywacke graywacke sequence. sequence. Small of cosanguinous trondhjemite—granodioriteliquids liquids penetrated penetrated those cosanguinous trondhjemite-granodiorite those bodies of sedimentaryrocks, rocks, creating creating the Basaltic volcanism sedimentary the early earlymigmatite. migmatite. Basaltic volcanism added added a mafic to the the supracrustal supracrustal sedimentary a mafic component component to sedimentary sequence. supracrustal rocks metamorphosed, 2) 2) The The supracrustal rocks were were buried, buried,regionally regionally metamorphosed, and and tectonized. Incipient Incipient anatexis liquid of of the tectonized. anatexis occurred, occurred, producing producing liquid the leucogranite suite. suite. This leucogranite Thisleucogranite leucogranitewas wascontinuously continuouslyformed formed and and underunderwent went syntectonic syntectonic mobilization into higher portions of the supracrustal supracrustal pile. magma of of the the Lac Lac La Croix crustal levels (9—12 Croix Granite Granite krn) magma 33)) At At deeper deeper crustal (9-12 kin) plu— was generated from more complete partial melting of graywacke graywacke and/or and/or plutonic rock tonic rock of of the the tonalite—granodiorite tonalite-granodiorite suite. This episode of melting biotite. left a residue of plagioclase, amphibole, garnet, and pyroxene or biotite. ratio The low low intial intial $7Sr/86sr ^sr/^sr ratio suggests suggests that that the the source source for for the the Lac Lac La La Granite was younger Croix Granite younger than than 50 50 m.y. m.y. at at the the time time of of melting. melting. The Lac La Croix magma rose diapirically diapirically into the supracrustal supracrustal rocks rocks 4) 4) early migmatite. This rising heat source risingdiapir diapirmay may have have been been the heat source and early migrnatite. This that initiated and/or metasedimentary that initiated and/orperpetuated perpetuatedmelting meltingwithin withinthe the metasedimentary rocks. rocks. The granitic granitic diapir struc5) 5) The diapir passively passively intruded intrudedalong along the thepre—existing pre-existing structural grain, tural grain,assimilating assimilatingand and entraining entraining portions portions of of the thecountry country rock. rock. Granite—rich and and schist-rich schist—rich migmatites migmatites were were formed, formed, depending depending on on the the Granite-rich amountofofgranite granite intruded intruded into into the Volatile—rich fluids fluids amount the country country rock. rock. Volatile-rich accompaniedthe the granite accompanied graniteneosome, neosome, concentrating radioelements in the roof and border border zones zonesof of the the diapir. diapir. and structural effect granite emplacement tobroaden broaden and The structural effectofofthe the granite emplacementwas was to 6)) The 6 earlier regional flatten earlier flatten regional folds. The western portion of the Vermilion Granitic Complex was near the the roof roof of of the the granite granite diapir. diapir. 122 �. FIELD FIELD TRIP TRIP II: 11: THE INTERNATIONAL INTERNATIONALFALLS-ICABETOGANA FALLS-KABETOGAMA ARCHEAN GEOLOGY GEOLOGY OF THE ARCHEAN AREA, MINNESOTA MINNESOTA AREA, R.W. W.C. Day, Day, and and D.L. D.L. Southwick Southwick R.W. Ojakangas, Ojakangas, W.C. Objectives Objectives and and Regional Regional Relationships Relationships The objective objective of of this this field field excursion excursion is is to to illustrate illustratethe thegeology geology of of the two Archean Archean terranes in northern northern Minnesota. Minnesota. The The first first part part of of the the trip, trip, two terranes in 1—10, will focus on the metavolcanic and metasedimentary rocks stops 1-10, will focus on the metavolcanic and metasedimentary rocks of of stops the (Ojakangas, 1972), 1972), which which are are at at the the south south edge edge of of the the the Rainy Rainy Lake Lake area area (Ojakangas, wabigoon Wabigoon subprovince subprovince of of the the Superior Superior province province of of the the Canadian Canadian Shield Shield (see (see ~ i g s .I1 and and 2, 2, map map A). A). The The second second part, part, stops stops 11—18, 11-18, will will focus focus on on the the Figs. transition transition southward southward from from metagraywacke metagraywacke (biotite (biotiteschist) schist) into into the the Vermilion Granitic Granitic Complex Complex (see [see Figs. Figs. I1 and and 3, 3, map map B). B). The The rocks rocks at at stops stops Vermilion 11-18 are are all all in in the the Quetico Quetico subprovince. subprovince. 11—18 • The The trip trip starts starts in in the the metavolcanic—metasedimentary metavolcanic-metasedimentary terrane terrane of of the the Rainy Rainy Lake Lake area area east east of of International International Falls, Falls,Minnesota. Minnesota. Metagraywacke, Metagraywacke, greenstone, tuffaceous tuffaceous biotite—chiorite biotite-chlorite schist, schist, felsic felsic tuft, tuff, feldspathic feldspathic greenstone, quartzite, The Rainy Rainy Lake—Seine Lake-Seine River River be examined. examined. The quartzite, and and conglomerate conglomerate will will be fault fault (unexposed (unexposed in in Minnesota) Minnesota) marks marks the the boundary boundary between between greenschist greenschist facies facies metamorphic metamorphic lithologies lithologies to to the the north north and and somewhat somewhat higher—grade higher-grade metagraywacke bemetagraywacke (biotite (biotiteschist) schist) to to the the south, south, and and also also is is the the boundary boundary be— The broad broad belt belt of of biotite biotite tween the the Wabigoon Wabiqoon and and Quetico Quetico subprovinces. subprovinces. The tween schist schist south south of of the the fault fault originally originally was was included included in in the the Coutchiching Coutchiching Series of of Lawson Lawson (1913). (1913). The The equivocal equivocal relationship relationship of of these these metasedimen— metasedimenSeries tary on the the north north was was central central to to the the classic classic tary rocks rocks to to metavolcanic metavolcanic rocks rocks on debate debate about about the the stratigraphy stratigraphy and and structure structure of of the the Rainy Rainy Lake Lake area area (Adams (Adams and and others, others, 1905; 1905; Lawson, Lawson, 1913), 1913), and and still still has has not not been been firmly firmly resolved. resolved. In to the the proper proper stratigraphic stratigraphic posiposiIn view view of of the the continuing continuing uncertainty uncertainty as as to tion tion of of these these rocks, rocks, they they are are now now mapped mapped in in Minnesota Minnesota simply simply as as unnamed unnamed biotite schist. schist. Similar Similar rocks rocks directly directly along along strike strike in in Canada Canada have have biotite recently recently been been termed termed the the Quetico Quetico metasediments metasediments by by wood Wood (1980), (1980), who who proproposed posed that that the the name name be be used used informally. informally. Two—mica Two-mica leucogranite leucogranite of of proposed proposed anatectic anatectic origin origin has has been been emplaced emplaced The relative relative abundance abundance of of the the leucogranite leucogranite into into the the biotite biotite schist. schist. The increases southward toward toward the the Vermilion Vermilion Granitic Granitic Complex; Complex; the the north north conconincreases southward tact tact of of the the complex complex with with biotite biotite schist schist is is gradational gradational and and is is mapped mapped arbitrarily subequal to to biotite biotite arbitrarily at at the the horizon horizon where where leucogranite leucogranitebecomes becomessubequa]. Within the the contact contact zone zone the the biotite biotite schist schist is is also also intruded intruded by by schist. schist. within tonalite by grayish—pink grayish-pink tonalite and and granodiorite, granodiorite, which which in in turn turn are are cut cut across across by granite granite equivalent equivalent to to the the Lac Lac La La Croix Croix Granite, Granite, the the major major intrusive intrusive phase phase The nature nature of of of of Vermilion Vermilion Granitic Granitic Complex Complex (Southwick (Southwick and and Sims, Sims, 1980). 1980). The these these intrusive intrusive events events and and the the textures textures of of the the migmatites migmatites produced produced will will be be examined examined at at several several stops. stops. The road log log for for this this trip trip includes includes more more stops stops than than can can be be visited visited on on The The leaders leaders will will select select among among the the stops, stops, taking taking into into aa one—day one-day excursion. excursion. The account time of of day, day, and and group group desires. desires. account road road conditions, conditions, time 123 �to '-a 'a 9 3° 30' 0- I 0 48°30' , I I 5 10 Miles MAP ® Figure 1. General location map showing the areas covered by detailed maps A and B. -— in- 9245' �S ROAD LOG LOG ROAD • This road This road log l o g starts s t a r t s at a t the t h e intersection i n t e r s e c t i o n of of U.S. U.S. Highway Highway 53 53 and and Minnesota Highway 11 near the center of International Falls, Minnesota Highway 11 near the center of I n t e r n a t i o n a l F a l l s , Minnesota (3rd Ave. Ave. and 4 4th Part of the ttrip t h St.) St.) and terminates terminates at a t Ash Ash River. River. P a r t of rip duplicates stops in an earlier guidebook by Southwick and Ojakangas d u p l i c a t e s stops i n an e a r l i e r guidebook by Southwick and Ojakangas (1979b); tthe regional geology geology of of tthe area tto be covered is is shown aatt sscale cale (1979b); h e regional h e area o be 1:250,000 on the geologic map of Minnesota, International Falls sheet 1:250,000 on t h e geologic map of Minnesota, I n t e r n a t i o n a l F a l l s sheet Stops 1 1 tto plotted (Southwick and Ojakangas, Ojakangas, 1979a). 1979a). Stops o 11 aare re p l o t t e d on Fig. Fig. 2, 2, map A; stops 12-18 are on Fig. 3, map B. A; s t o p s 12-18 on Fig. 3, map B. Approximate Approximate Mileage [accumulated i n brackets] brackets1 Mileage [accumulated mileage mileage in S 0.0 0.0 [0.01 r0.01 Junction with with U.S. U.S. 53 and Minnesota Minnesota Highway Highway 11. Proceed east Junction 53 and 11. Proceed e a s t on on Highway 11. Highway 11. 1.4 1.4 [1.4] r1.41 Bridge. Bridge. 1.2 [2.6] [2-61 Junction with with Koochiching Koochiching County County Highway Highway 20; Junction 20; tturn u r n left l e f t (north) (north) tto o Ranier. Banter. 0.35 0.35 [2.951 [2.95] Metasedimentary rocks which Lawson STOP 1. STOP 1. Metasedimentary rocks which Lawson (1913) (1913) called c a l l e d the the Coutchiching in the Rainy Lake area are present near Coutchiching i n the Rainy Lake area a r e present near both both Fort Fort This exposure of Frances and IInternational n t e r n a t i o n a l Falls. Falls. This of metagraywacke (fine—grained biotite i s representative (fine-grained b i o t i t e schist) s c h i s t ) is The b best expoof tthe e s t expoof h e least l e a s t metamorphosed metamorphosed parts p a r t s of of this t h i s unit. unit. The ssure u r e has been a small knob just j u s t south of of the t h e municipal liquor growth, sodding and concrete have in in eestablishement, s t a b l i s h m e n t , but lichen growth, recent years p partially a r t i a l l y obscured the t h e original o r i g i n a l sedimentary N. 45° E./80° NW. NW. and sstructures. t r u c t u r e s . The beds have an attitude a t t i t u d e of of N. 45O E./80 display d i s p l a y excellent e x c e l l e n t grading with tops to t o the t h e northwest. northwest. Lineations plunge to the north—northeast SmallSmallnorth-northeast at a t 45—50°. 45-5O0. Lineations scale cross—bedding occurs locally in interbedded silty s c a l e cross-bedding locally i n s i l t y laminae visible places. and flame structures s t r u c t u r e s are v i s i b l e in i n a few places. o and Although aa few few llarge a r g e detrital d e t r i t a lgrains grainsofofquartz quartz andpla— plathese exposures consist dominantly of gioclase are present, present, these consist of g i o c l a s e are recrystallized plagioclase, with lesser amounts of ffinely i n e l y r e c r y s t a l l i z e d plagioclase, with lesser amounts of general the the rocks biotite; i s rare. rare. IIn n general qquartz u a r t z and b i o t i t e ; garnet garnet is resemble coarser grained garnet— garnet- and staurolite—bearing staurolite-bearing biotite biotite of the greenstone belt, b e l t , some some of sschists c h i s t s that t h a t crop out south of w i l l be be seen seen in i n the the last l a s t several several stops stops on on this this field field which will ttrip. rip. some route route to to Highway Highway 11. 11. Return over some 0.35 0.35 [3.31 (3.31 Junction with Highway 11; 11; tturn u r n left l e f t (east). (east). 2.5 2.5 [5.8] t5.81 Junction with with Koochiching Koochiching County Junction County Highways Highways 20 20 and and 109. 109. rright i g h t (south) (south) and and follow follow Highway Highway 109. 109. 125 Turn Turn �0\ t.J I-. 930 rns3, ms2, metasedimentary rocks, undivided; chiefly metagraywacke mniv, mixed volcanic and volcaniclastic rocks (chiefly mafic) fqc, feldspothic quartzite and conglomerate c Irnmv BEDDED ROCKS 1 Figure 2. Simplified geology map of the Rainy Lake area showing locations of stops through 11 dikes of Proterozoic age. Dl ABASE I\dl INTRUSIVE ROCKS �I 1.2 1 .2 [7.0] [7.01 P This exposure exposure of feldspathic—lithic feldspathic-lithic guartzite quartzite is is one one of a number that form a discontinuous easterly—trending belt 16 discontinuous easterly-trending 16 km long east—northeast, are long and and 0.8 0.8 km km wide. wide. The beds strike strike east-northeast, axe vertical to the the east east at at vertical to to slightly slightly overturned, overturned, and and plunge plunge to 3°55°. cross—beds indicate that the unit 3°-550 Abundant Abundant cross-beds indicate that the unit dips dips to to the the south. south. The The cross—bedding cross-bedding (trough—type) (trough-type) is is partially partially obscured obscured by shearing; shearing; it it is is best best seen seen on on the the south south side side of of the the exposure exposure about original clastic texture about 30 30 mm east east of of the the road. road. The is The original clastic texture is commonly commonly well well preserved preserved in in spite spite of of pervasive pervasive shearing. shearing. Quartz Quartz comprises comprises 50 50 percent of of the the rock; rock; other other grains grains in in the the abundant abundant sericitic sericitic matrix matrix include include felsic felsic to to intermediate intermediate volcanic volcanic rock rock fragments, plagioclase, plagioclase, K—feldspar, K-feldspar, felsic felsic plutonic plutonic rock rock fragments, fragments, carbonate carbonate and and pyrite. pyrite. This quartzite quartzite and and the the conglomerate are equivalent equivalent to to the the Seine Seine Series Series conglomerate of of stop stop 88 are (Seine (Seine Conglomerate) Conglomerate) to to the the east—northeast east-northeast in in Ontario Ontario in in the the same same greenstone greenstone belt. belt. Lawson Lawson (1913) (1913) called called these these units units Huronian, noted noted that that they they clearly clearly overlie overlie an an unconformity unconformity in in Huronian, Ontario, and and placed them them at at the the core core of of aa syncline. syncline. Grout Grout (1925a) (1925a) said said the the structure structure was was an an anticline. anticline. Ojakangas Ojakangas (1972), (19721, partly partly on on the the basis basis of of the the consistent consistent southerly southerly topping topping direcdirection of of the the cross—beds, cross-beds, interpreted tion interpreted them them to to be be part part of of aa southward-facing fault block. accompanying text southward-facing fault block. (See (See accompanying text in in this this volume.) The The quartzites quartzites are are interpreted interpreted as as braided braided stream stream volume.) deposits abstract by deposits with with the the source source to to the the north. north. (See (See abstract by Ojakangas and Olson, this volume.) Ojakangas and Olson, this volume.) STOP STOP 2. 2. Turn Turn around around and and return return to to Highway Highway 11. 11. [8.2] [8.21 Turn Turn right right (east) (east) and and proceed proceed to to low low rock rock outcrop outcrop on on left left (north) side of highway just west of Bohman Airways. (north) side highway just west of Bohman Airways. 0.9 STOP STOP 3. 3. 1.2 1.2 (9.1] [9.11 This This outcrop outcrop consists consists of two two lithologies: lithologies: (1) (1) aa mixed schist schist (thin (thin alternating alternating laminae laminae of of chloritic chloritic and and biotitic biotitic fine—grained fine-grained schist) schist) which which is is in in part part ankeritic ankeritic or or sideritic sideritic and ic hypabyssal (B) massive massive greenstone greenstone (metamorphosed (metamorphosedmat mafic hypabyssal and (B) intrusive intrusive rocks) rocks) on on the the northwest northwest part part of of the the outcrop. outcrop. Eastward Eastward along along strike strike are are greenschists. greenschists. The The mixed schist schist is is interpreted interpreted as as aa sheared sheared tuffaceous tuffaceousrock. rock. (This (This locality locality is is about north of Riverfault.) fault.) km north of the theRainy RainyLake—Seine Lake-Seine River about 2.5 2.5 km 0.1 0.1 [9.21 19-21 Continue across bridge bridge over Continue east east on on Highway Highway 111 1 across over Jackfish JackfishCreek. Creek. 0.2 0.2 Turn on on Koochiching County Turn left left(north (north Koochiching CountyHighway Highway 103. 103. (9.4] 19.41 0.4 0.4 STOP STOP 4. 4. (9.81 L9.81 Some Some traces traces of of sheared sheared pillows pillows may may be be present. present. About About 10 10 mm west west of of driveways driveways in in woods woods is is aa very very coarse—grained, coarse-grained, massive massive Greenschist .1—10, Greenschistoutcrops outcropsbybydriveways driveways J-10,.1—11 J-11and and.1—12. J-12. greenstone containing crystals with greenstone containing long long pyroxene pyroxene crystals with aa"branching" "branching" habit spihabit (quench (quench textures, rapid crystallization?) crystallization?) resembling resembling spi— nifex nifex texture. texture. 127 �S Proceed Proceed eastward. eastward. 0.8 0.8 (1.2 (1.2 mi mi in in from from Hwy Hwy 11) 11) 0.2 0.2 [10.81 [10.8] (1.4 (1.4 mi mi in in from from Hwy Hwy Greenschist Greenschist with with granitic granitic stringers stringers from from the the west west end end of of Grassy Grassy Island Island "tonalite", "tonalite", aa 44 km km long long by by 0.3 0.3 km km wide wide intrusion. intrusion. To To the the south south of of the the road road and and to to the the north north on on the the lakeshore NNW and and diabase dike dike which which trends trends NNW lakeshore is is aa 30 30 meter—wide meter-wide diabase has has been been dated dated at at about about 2200 2200 m.y. m.y. by by Hanson Hanson and and Maihotra Malhotra (1971). This This dike dike is is the the western western dike dike of of aa closely closely spaced spaced pair pair (1971). of of dikes dikes which which lines lines up up with with dike dikeexposures exposuresnear nearIcabetogama Kabetoqama Lake km to to the the south south and and with with other other dike dike exposures exposures as as far far as as Lake 22 22 km 40 40 km km to to the the southeast southeast and and as as far far as as 25 25 km km to to the the northwest northwest near near the the Quetico Quetico Fault. Fault. STOP STOP 5. 5. [10.61 (10.6] 11) 11) 0.4 greenschist and STOP STOP 6. 6. Large Large roadcut roadcut on on hilltop hilltop of of greenschist and "mixed "mixed schist" Disseminated boudinaged quartz quartz and and granite. granite. Disseminated schist" with with minor minor boudinaged pyrite pyrite and and minor minor chalcopyrite chalcopyrite are are present present in in this this cut. cut. I S Continue Continue south south past past other other outcrops outcrops of of biotite biotite schist schist and and seri— sericite cite schist schist (metamorphosed (metamorphosedfelsic felsic tuffs tuffs and and metasediments?). metasediments?). Junction 11. Junction with with Highway Highway 11. Turn Turn left left (east). (east). [11.2] Turn Turn 1.6 [12.8] Junction Junction Highway Highway 11 1 1 and and Koochiching Koochiching County County Highway Highway 138. 138. left left (north). (north). 0.3 [13.1] Crossing Crossing topographic topographic low low along along Rainy Rainy Lake—Seine Lake-Seine River River Fault. Fault. 0.45 [13.55] STOP 7. Gravel Gravel pit pit in in wood wood just just to to the the left left (west) (west) of of highway highway STOP 7. near near top top of of hill. hill. Sheared greenschist greenschist in the the Rainy Lake—Seine Lake-Seine Quartz and rusty River River Fault Fault zone zone is is visible visible here. here. Quartz rusty carbonate carbonate pods pods are are abundant abundant in in phyllitic phyllitic greenschist. greenschist. The The only only productive productive gold gold mine mine in in Minnesota Minnesota was was located located on on Little The km east east of of this this point. point. The Little America America Island Island just just 2.5 2.5 km Little Little America America mine, mine, in in aa 22 meter—wide meter-wide composite composite quartz quartz vein vein with with intermixed intermixed schist, schist, produced produced $4600 $4600 worth worth of of gold gold in in Several other other prospects prospects were were located located farther farther east. east. 1894—1895. 1894-1895. several On km to to the the east, east, aa prominent prominent gossan gossan is is On Bushyhead Bushyhead Island Island 66 km exposed exposed in in an an old old adit. adit. Continue Continue north. north. 0.1 - at next junction Fork and at junction as as well. well. Fork in in road road — bear right here and [13.65] 0.55 [14.2] S "Neil Point conglomerate" conglomerate" by garage and by house This unit, aa large large lens lens 180 180 m thick thick overlooking overlooking fault fault zone. zone. This and at least 4.5 km long, overlies the feldspathic—lithic and at least 4.5 km long, overlies the feldspathic-lithic quartzite clastquartzite of of stop stop 2. 2. The The massive massive conglomerate, conglomerate, largely largely clast— supported supported with aa biotitic biotitic and and feldspathic feldspathic sandy sandy matrix, matrix, concontains tains well—rounded well-rounded clasts clasts of of "granite," "granite," volcanic volcanic rocks, rocks, chert, chert, STOP STOP 8. 8. 128 �white quartzite white q u a r t z i t e and and biotite b i o t i t e schist. s c h i s t . Clasts 25 C l a s t s are a r e as a s large l a r g e as a s 25 cm. The conglomerate cm. The conglomerate is is interpreted i n t e r p r e t e d as a s an an alluvial a l l u v i a l fan fan deposit deposit which the sandstones sandstones (guartzite) ( q u a r t z i t e ) of of related related which prograded prograded over over the braided (See aabstract by Ojakanqas Ojakangas and braided streams. streams. (See b s t r a c t by and Olson, Olson, this this volume.)) volume. yollow ~ o l l o wroad road (which (which is is one—way) one-way) around around loop loop on on Neil Neil Point, Point, past past sstop t o p 77 to t o Highway Highway 11. 11. 0.0 Reset Mileage; Mileage; tturn Reset u r n right r i g h t (west) (west) on on Highway Highway 11 11 and and drive drive toward toward 3. IInternational n t e r n a t i o n a l Falls, F a l l s , past p a s t stop s t o p 3. 4.6 Junction Junction with with Koochiching Koochiching County County Highway Highway 332 332 (truck ( t r u c k by—pass by-pass Turn left around around International I n t e r n a t i o n a l Falls). F a l l s ) . Turn l e f t and and follow follow Highway Highway 332 332 (4.61 south. south. 0.6 [5.2] 0.3 [5.5] 0.4 Stop sign; junction with with 13th Street; S t r e e t ; tturn u r n left l e f t (east) ( e a s t ) con— conStop sign; junction ttinuing i n u i n g on on Highway Highway 332. 332. 9. Metaqraywacke Metagraywacke outcrops. STOP 9. STOP outcrops. These These are a r e located located on on aa 1.2 1.2 km wide metagraywacke metagraywacke belt, b e l t , within within the the broader broader greenstone greenstone belt, belt, that t h a t extends extends another another 40 4 0 km km to t o the the northeast northeast to t o Swell Swell Bay Bay of of Rainy Graded beds beds to to the t h e northeast northeast of of this this Rainy Lake Lake in i n Ontario. Ontario. Graded outcrop face face both both northwest northwest and and southeast, southeast, indicating indicating the the presence of of isoclinal i s o c l i n a l folds. folds. Additional outcrops 9. Additional outcrops of of metagraywacke metagraywacke as a s at a t stop s t o p 9. [5.9] 0.1 Right angle angle bend iin n road road to t o south. south. [6.0] 0.8 [6.8] 0.3 Large STOP Large STOP 10. 10. and amphibole. roadcut both chlorite roadcut of of ggreenschist r e e n s c h i s t containing containing both chlorite Minor magnetic iron—formation is also Minor magnetic iron-formation is a l s o present. present. This outcrop outcrop exhibits e x h i b i t s considerable considerable shearing, shearing, for f o r the t h e Rainy Rainy Lake—Seine River fault zone is just 0.3 mi to the south. Lake-Seine Elver f a u l t zone is j u s t 0.3 mi to the south. zone. Broad topographic Lake-Seine River Broad topographic low low is is the t h e Rainy Rainy Lake-Seine River ffault a u l t zone. [7.1] [7.8) Junction of Junction of Highway Highway 332 332 with with Koochiching Koochiching County County Highway Highway 24. 24. Turn right r i g h t (west). (west). 0.8 Junction 24 with with U.S. U.S. Highway Highway 53. 53. Junction of of Highway Highway 24 [8.6] (south). 1.1 STOP STOP 11. 11. 0.7 [9.7] Turn left left on both both sides Low outcrops outcrops on Low s i d e s of of U. U. S. S. Highway Highway 53. 53. TRAFFIC ISISHEAVY—-BE CAREFULI HEAVY--BE CAREFUL! Thebbiotite thisl locality is The i o t i t e schist s c h i s t (metagraywacke) (metagraywacke) a tatthis o c a l i t y is Rainy Lake—Seine River Lake-Seine River and therefore therefore is is within fault f a u l t and within the t h e Quetico superbelt. superbelt. approximately onemile mile south south of of the approximately one the 129 �Petrographically Petrographically the rock is quartwfeldspathic quartzofeldspathic biotite schist. It has equigranular texture texture with foliation has aa firie—grained, fine-grained, equigranular foliation biotite and and muscovite muscovite and and contains contains accessory accessory amounts amounts defined by biotite of fine—grained fine-grained poikiloblastic poikiloblastic garnet. garnet. Dikes Dikes of porphyritic porphyritic felsite lamprophyre cut across across schistosity felsite and and dark dark green, green lamprophyre schistosity and and bedding (strike (strike about about N90°E), N900E), and and are are parallel parallel to to aa second second cleavage (strike N70°E); N70-El; the the second second cleavage cleavage are axe the dikes and the cleavage (strike best seen seen on on top top of of the the east east outcrop. outcrop. These dikes may be related to the the volcanism volcanism within the the Rainy Lake greenstone greenstone belt related to to the to the north. north. I 0.0 RESET MILEAGE MILEAGEand and continue continue south U.S. 53. 53. BESET south on on U.S. 6.1 village of Village of Ericsburg; Ericsburg; continue continue south south on on U.S. U.S. 53. 53. [6.1] 5.9 Department of iatura1 Natural Resources Resources fire fire tower tower on on right right Minnesota Department [11.9] (west). (west). 0.7 Railroad overpass. Railroad overpass. [12.6] 1.6 [14.2) 7.1 121.3] village of Ray; sharp Village sharp corner corner at junction junction with Koochiching Koochiching U . S . 53. 53. County Highway Highway 217; 217; continue continue east east on on U.S. "Gateway Store" and junction junction with with St. St. Louis Louis County County Highway Highway 122. 122. Typical Typical northern northern Minnesota Minnesota walleye walleye on on left. left. Turn left (north) (north) Turn left and follow follow Highway Highway 122 122 toward toward Kabetogama Kabetogama Lake. Lake. [23.6] Junction with St. Louis Junction Louis County 123 123 (straight (straight ahead): turn turn left (west) and stay on Highway Highway 122. 122. (west) 3.3 [26.9) "Y" in in road at junction "Yn junction with St. Louis Louis County County Highway Highway 902; 902; con— continue tinue straight straight ahead ahead on on Highway Highway 902. 902. 0.3 [27.2] Paved road road ends; ends; continue continue on on gravel gravel road. road. 0.3 [27.5) St. Louis County Highways 673 Highway 902 ends at junction with St. to Rocky Point and 675; turn right and follow follow Highway 675 675 to Resort. 0.3 (27.8] Follow driveway on Obtain per— to Rocky Bocky Point Point Resort. Resort. Obtain perFollow on left left to mission mission from from resort resort owners owners before before examining examining outcrops. outcrops. 2.3 STOP STOP 12. 12. This outcrop on the the south south shore shore of Kabetogama Lake is transition zone between the relatively in the transition relatively granite—free granite-free to the the north, and and schist—rich schist-rich migmatite migmatite mapped mapped biotite schist schist to to the the south. with the the vermilion Vermilion Granitic Granitic Complex Complex to south. The amount amount of within the the biotite of leucogranite leucogranite within biotite schist schistincreases increasesfrom from north north Metamorphic recrystallizato in this zone. to south south in this transition transition zone. Metamorphic recrystallization tion has has obscured obscured original original textures textures here, but across across the the lake lake to north the the graded graded bedding bedding indicates indicates northward northward strati— stratito the the north graphic younging. graphic younging. 130 �H (A H Ia Int'l Falls vig vsm I — Ysm, schist—rich migmatite vhqd, hornblende quartz diorite PEN INSULA vlg, Lac LoCroix Granite vgm, granite—rich migmatite simplified geologic map of the Lake Kabetogama Kabetogama area showing Figure Figure 3. 3. Simplified locations locations of of stops stops 12 12 through through 18. 18. KABETOGAMA vgm vhqd VERMILION GRANITIC COMPLEX dikes of Proterozoic age. Chiefly metagraywacke; contains numerous small bodies of Ieucogranite near contact with vsm. METASEDIMENTARY ROCKS, UNDIVIDED ms2 DIABASE I\dI EXPLANATION �a The biotite biotite schist ofofthethe Icabetogama region has has aa The schist Kabetogama Lake Lake region fine—to to medium—grained, equigranularschistose schistosetexture. texture. Local finemedium-grained, equigranular Local a luminousbeds bedswithin withinthe theschist schist contain aluminous contain porphyroblasts porphyroblasts of of Schistosity, which is sillimanite, and staurolite. staurolite. Schistosity, is sillimanite, garnet, and parallel to,bedding, tobedding, is is isoclinally isoclinally folded. folded. generally parallel Pegmatite and coarse—grained coarse-grained leucogranite leucogranite are are enfolded enfolded and boudinaged concordantly concordantly within the the host biotite biotite schist. Dikes of granite granite that are physically indistinguishable indistinguishable from from the the folded leucogranite folded leucogranite cut cut across across the the schistosity schistosity and and isoclinal isoclinal folds. folds. I Return over Return over routes routes 675 675 and and 902 902 to to junction junction with with Highway Highway 122. 122. 0.0 0.0 RESET MILEAGE. MILEAGE. Turn Turn left left (east) (east) onto onto 122 122 and and proceed toward toward Chief Wooden Frog Frog Campground. Chief Wooden Campground. 0.4 0.4 "Y" in Highway 122, 'Y" 122, stay stay to to right. right. (0.4] [0.41 0.4 0.4 my,, "Y" in Highway in Highway 122; 122; stay stay to to left left on on 122. 122. [0.8) [0.81 0.5 [1.3]1 Chief Wooden Frog Frog Campground. Campground. Proceed Proceed to to camping camping area area B—3 B-3 (outcrop (outcrop description applies to any of the numerous low lying granitic outcrops granitic outcrops in in this this area). area). STOP STOP 13. 13. This This area area is is transitional transitional between between the the metasedimentary metasedimentary rocks to the south, with rocks to to the the north north and and schist—rich schist-rich migmatite to the leucogranite here greater than the amount amount of of leucogranite than at at Stop Stop 12. 12. Leucogranite thin veins that are syntectonically Leucogranite forms forms thin syntectonically enfolded enfolded and and boudinaged boudinaged with with the the schist, schist, and and also also forms forms lenticular lenticular bodies up to to aa few few hundred hundred feet feet long long which invade invade and and cut cut across across the the folds. folds. The leucogranite pegmaleucogranite has aa coarse—grained coarse-grained gneissic gneissic to to pegma— The mineralogy is is dominated dominated by quartz, microcline microcline and sodic sodic plagioclase, with accessory accessory garnet. garnet. The gneissic texture by biotite biotite and and primary primary muscovite. muscovite. texture is is defined defined by titic texture. titic texture. a Separate Separate textural textural subunits subunits of the the leucogranite leucogranite suite suite can can be be delineated delineated (pegmatitic, (pegmatitic, medium-grained medium-grained hypidiomorphic, hypidiomorphic, coarse—grained coarse-grained gneissic, gneissic, etc.), etc.), which which can can be be seen seen crosscutting crosscutting and and grading grading into into each each other. other. Although Although these these subunits subunits have have aa wide wide range range in in major major element element abundances, abundances, they they are thought thought to to be cogenetic. cogenetic. I Return Return over over same same route. route. 0.5 0.5 "Y" "Y" in in Highway Highway 122; 122; stay stay to to right right heading heading west. west. [1.8] [1.81 0.4 0.4 "Y" "Y" in in Highway Highway 122; 122; stay stay to to left left heading heading west. west. [2.2] E2.21 132 �0.4 [2.6] 3.3 [5.9] Stop sign, sign, junction Highway Highway 122 122 with with Highway Highway 902. 902. 122. (south) and continue on on Highway Highway 122. mm left Turn left Att Stop sign, sign, turn t u r n right r i g h t (south) (south) and and continue continue on on Highway Highway 122. 122. A top of hill south of junction is an excellent outcrop of a comt o p of h i l l of junction is of composite to aa swarm swarm of of p o s i t e diabase diabase dike. dike. Phis ^Phis dike dike belongs belongs to b.y.) that t h a t extends extends from from the the Proterozoic dikes (age (age about 2 b.y.) Mesabi Range, Minnesota to the vicinity of Kenora, Ontario; Range, Minnesota t o the v i c i n i t y of Kenora, Ontario; swan was another dike in i n tthe h e swarm was seen seen at a t stop s t o p 5. 5. (7.0] Junction Junction with with Highway Highway 123. 123. on 122. on 122. 0.4 Barney and Oscar's Oscar's Bar on left, l e f t , continue continue south, south, slow slow down. down. 1.1 Kay's Bar on left; Kay's l e f t ; continue south [7.4] 0.2 [7.6] Outcrops Outcrops on on both both sides s i d e s of of Highway Highway 122. 122. shoulder of of road. road. Pull P u l l vehicle onto outcrops on both sides STOP STOP 14. 14. Outcrops sides rich migmatite. Regionally this rich of of the t h e road are a r e of granite— graniterock type has 5 tto percent o 25 percent inclusions in a granitic neosome; the inclusions are biotite g r a n i t i c neosome; t h e are biotite inclusions i n Att this sschist, c h i s t , amphibolite, amphibolite, trondhjemite, trondhjemite, and and granodiorite. granodiorite. A locality most of the inclusions are trondhjemite. l o c a l i t y most of the inclusions a r e trondhjemite. On is aa glacially g l a c i a l l y polished polished On the the west west side s i d e of of the t h e road road is outcrop of migmatite with vague grayish grayish inclusions inclusions that t h a t are are partially p a r t i a l l y digested digested by by the t h e enclosing enclosing granite g r a n i t e neosome. neosome. Ductile and probably probably was the inclusions inclusions is is evident evident and was Ductile shearing shearing of of the associated with the emplacement emplacement of the granitic g r a n i t i c core of the complex complex to t o the the south. south. Plagioclase diffusion "halos" "halos" can be seen surrounding inclusions on the seen surrounding trondhjeiaitic trondhjemitic inclusions t h e ffresh r e s h roadcut on on the t h e east e a s t side s i d e of of the the road. road. Continue 122. Continue south south on on 122. 0.7 [8.31 1.5 [9.8] Stop sign, sign, junction junction with with U.S. U.S. 53. 53. proceed proceed west. west. mm Turnright r i g h tonto ontoU.S. U.S. 53 53 and and Pull Large roadcuts on on both both sides s i d e s of of U.S. U.S. 53. 53. P u l l off off highway onto onto shoulder. TRAFFIC IS IS HEAVY—PLEASE HEAVY-PLEASE BE BE CAREFUL. CAREFUL. STOP STOP 15. 15. These roadcuts encapsulate the structural s t r u c t u r a l and intruintruhistory ssive ive h i s t o r y of of the t h egranite—rich granite-rich migmatite migmatite in i n the t h eVermilion Vermilion Granitic The neosome neosomei sisl ilight gray tto g h t gray o pink pink granite granite G r a n i t i cComplex. Complex. The with aa coarse—grained, weaklygneissic gneissic texture. texture. Blocks with coarse-grained, weakly Blocks of of amphibolite, ttonalite, early migmatite a are biotite b i o t i t e sschist, c h i s t , amphibolite, o n a l i t e , and e a r l y migmatite re within the of asrafted r a f t e d within the granite g r a n i t e and and display display varying varying degrees degrees of asssimilation i m i l a t i o n and and deformation. deformation. Faint F a i n t outlines o u t l i n e s of of digested digested country country rock inclusions rock inclusions are a r e abundant. abundant. The included included blocks blocks of The of early e a r l ymigmatite migmatite have have paleosomes paleosomes of of amphibolite and and bbiotite amphibolite i o t i t e sschist, c h i s t , or amphibolite amphibolite alone, alone, and and 133 �neosomes of gray tonalite Much of tonalite or granodiorite. granodiorite. Much of the the ant— amphibolite phibolite is is coarse coarse grained grained and and foliated, foliated, with with aa "spotted" "spotted" appearance caused appearance caused by clusters clusters of biotite. Early migmatite paleosome and and blocks that that consist consist dominantly dominantly of of axnphibolite amphibolite paleosome tonalite neosome tonalite neosome typically typically show show agmatic agmatic structure, wherein wherein the amphibolite has been split amphibolite split into into distinct distinct pieces that that could could be fit £i back together together like like aa jigsaw jigsaw puzzle. puzzle. These east—trending east-trending cuts cuts are oriented oriented nearly parallel to to the planar fabric fabric of the the migmatite, and therefore therefore the the faces faces of the cuts appear to to contain contain a larger larger fraction fraction of inclusions inclusions than than is really really the the case case for for the the rock rock as as aa whole. whole. AA closer estimate of the the inclusion—to—granite inclusion-to-granite ratio ratio can can be made from from the the natural natural subhorizontal top of the the north north cut. cut. subhorizontal surface surface on the the top 0.0 MILEAGE. Turn RESET MILEAGE. Turn around around and and proceed proceed back back east east on on U.s. U.S. 53. 53. 1.5 Junction Junction with Highway Highway 122; 122; continue continue southeast southeast on on U.s. U.S. 53. 53. [1.5] 2.9 [4.4] 0.8 (5.2] Junction Junction with with St. St. Louis Louis County County Highway Highway 765 765 (Ash (AshRiver River Trail); Trail); turn turn left left (east). (east). Granite—rich migmatite, consisting of 5 to 10 percent percent STOP 16. STOP 16. Granite-rich inclusions in modally uniform, faintly gneissic granite, crops Numerous indefinitely River Trail. Numerous out just just north of the the Ash River lenses and layers of here, and bounded lenses and layers of pegmatite pegmatite occur occur here, and are are typical ofofgranite—rich in the typical granite-rich migmatite migmatite in theVermilion Vermilion Granitic Granitic Complex. Complex. Continue east Continue east on on Highway Highway 765. 765. 0.8 Cross over Daley Brook Brook in in marshy marshy area. area. [6.0) 3.7 right (south). (south). Outcrop on right (9.7) 17. This outcrop is dominantly a gray biotite-hornblende biotite—hornblende STOP 1 7. This quartz diorite, an early plutonic body within the quartz the Vermilion It is cut cut across by by numerous numerous veins veins of of Granitic Complex. It Granitic and pegmatite pegmatite believed believed to to be be related related to to the theLac Mc biotite granite and quartz diorite is massive with a uniform La Croix Croix Granite. The quartz mineralogic composition, mineralogic composition, and and has aa medium— medium- to to coarse—grained coarse-grained In thin thin section one one sees that hypidiomorphic granular hypidiomorphic granular texture. texture. In oxides are are exsolved fromthe the interior interior of iron oxides iron exsolved from ofthe theamphibole amphibole along cleavage traces. along cleavage traces. Continue eastward eastward toward towardthe the village village of Continue of Ash Ash River. River. 0.2 Sharp turn Sharp turn to to the the left left (north); (north); continue continue on on Highway Highway 765. 765. [9.9] 134 �0.6 Paved road road starts. starts. [10.5] 3.4 113.93 Ash Trail Trail Lodge. Park Park and and walk along along indistinct indistinct trail trail (starting by north side of green cabin) to top of hill bill at base (starting by of microwave—radio—relay. microwave-radio-relay. Obtain permission from cabin owners if cabin cabin is is occupied. occupied. STOP 18. STOP 18. This This large large knob knob of Lac Lac La Croix Croix Granite Granite (Vermilion (Vermilion Granite Granite of of Grout, Grout, 1923) 1923) is is part part of of aa crescent-shaped crescent-shaped body body that that occupies the occupies the hinge area of a large, east—plunging east-plunging fold. fold. It It contains no more than contains than 5 percent inclusions, several several of which microwave tower, are well displayed displayed near the the microwave tower, and and also also has has pegnatitic lenses. pegmatitic lenses. This This is is about as homogeneous homogeneous as the the Lac La Croix Croix Granite Granite gets gets in in the the northwest northwest part part of of the the Vermilion Vermilion Granitic Complex. Granitic Complex. Almost perfectly uniform granite granite crops crops out out some 50 km to some to the the southeast, southeast, well well beyond the the itinerary itinerary of this this field trip. field trip. The hilly vista to to the the southeast southeast is is typical typical of of terrain underlain terrain underlain by by the the Vermilion Vermilion Granitic Granitic Complex. Complex. Turn U.S. 53. 53. Turn around around and and return return over over Ash Ash River River Trail Trail to to U.S. 9.3 Junction with U.S. 53. 53. Junction with U.s. [23.2] END OF FIELD FIELD TRIP TRIP II. 11. FAILS. RETURN TO INTERNATIONAL INTERNATIONAL FALLS. 135 �I REFERENCES REFERENCES CITED, CITED, PAPERS PAPERS 11 and and 22 and and FIELD FIELD TRIP TRIP II I1 Adams, Adams, F.D., F.D., Bell, Bell, R., R., Lane, Lane, A.C., A.C., Leith, Leith,C.IC., C.K., Miller, W.G., W.G., and and Van Van Hise, Use, C.R., 1905, Report Report of of the the special special committee committee for for the the Lake Lake Superior Superior c.R., 1905, region: region: Journal Journalof of Geology, Geology, v. v. 13, 13, p. p. 89—104. 89-104. Arth, Arth, J.G., J.G., and and Hanson, Hanson, G.N., G.N., 1972, 1972, Quartz Quartz diorites diorites derived derived by by partial partial melting melting of of eclogite eclogite or or amphibolite amphibolite at at mantle mantle depths: depths: Contributions Contributions to to Mineralogy Mineralogy and and Petrology, Petrology, v. v. 37, 37, p. p. 161—174. 161-174. Arth, Arth, J.G., J.G., and and Hanson, Hanson, G.N., G.N., 1975, 1975, Geochemistry Geochemistry and and origin origin of of the the early early Precambrian Precambrian crust crust of of northeastern northeastern Minnesota: Minnesota: Geochimica Geochimica et et Cosmochimica v. 39, 39, p. p. 325—362. 325-362. Cosmochimica Acta, Acta, v. Barker, Barker, F., F., and and Arth, Arth, J.G., J.G., 1976, 1976, Generation Generation of of trondhjemite trondhjemite tonalitic tonalitic bimodal trondhjemite-basalt trondhjemite—basalt suites: suites: Geology, liquids Archean bimodal Geology, v. v. liquids and and Archean p. 596—600. 596-600. 4, p. 4, Barker, F., F., Arth, Arth, J.G., J.G., Peterman, Peterman, Z.E., Z.E., and and Friedman, Friedman, I., I., 1976, 1976, The The 1.71.7- to to Barker, 1.8— b.y. old old trondhjemites trondhjemites of of southwestern southwestern Colorado Colorado and and northern northern New New 1.8- b.y. Mexico: Mexico: Geochemistry Geochemistry and and depths depths of of genesis: genesis: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 87, 87, p. p. 189—198. 189-198. I Bryan W.B., W.B., Thompson, Thompson, G., G., Frey, Frey, T.A., T.A., and and Dickey, Dickey, J.S., J.S., 1976, 1976, Inferred Inferred setsetBryan tings tings and and differentiation differentiation in in basalts basalts from from the the Deep Deep Sea Sea Drilling Drilling Project: Project: Journal Journal of of Geophysical Geophysical Research, Research, v. v. 81, 81, p. p. 4285—4304. 4285-4304. S.S., Hanson, Hanson, G.N., G.N., Hallford, Hallford, C.R., C.R., and and Mudrey, Mudrey, M.G., M.G., Jr., Jr., 1972, 1972, Goldich, 3.5., Goldich, Saganaga Lake—Northern Early Early Precambrian Precambrian rocks rocks in inthe the Saganaqa Lake-Northern Light Light Lake Lake area,Minnesota—Ontario, Minnesota-Ontario, Part Part I, I, Petrology Petrology and and structure, structure, in &I Doe, Doe, area, B.R., B.R., and and Smith, Smith, D.K., D.K., eds., &.,Studies Studiesininmineralogy mineralogy and and Precambrian Precambrian America geology: geology: Geological GeologicalSociety Societyofof AmericaMemoir Memoir135, 135,p.p.151—177. 151-177. Goldich, 5.5., S.S., Nier, Nier, A.O., A.O., Baadsgaard, Baadsgaard, H., H., Hoffman, Hoffman, J.H., J.H., and and Krueger, Krueger, Goldich, H.W., H.W., 1961, 1961, The The Precambrian Precambrian geology geology and and geochronology qeochronology of of Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Bulletin Bulletin 41, 41, 193 193 p. p. 1978, Geology and geochemistry geochemistry of of the the Goldich, 5.5., S.S., and and Peterman, Peterman, Z.E., Z.E., 1978, Goldich, Rainy Rainy Lake Lake area, area, in &I Smith, Smith, I.E.M. I.E.M. and and Williams, Williams, J.G., J.G., eds., Proceedings Proceedings of of the the 1978 1978 Archean Archean Geochemistry Geochemistry Conference, Conference, p. p. 209—234. 209-234. &., Green, Green, D.H., D.H., 1973, 1973, Experimental Experimental melting melting studies studies on on aa model model upper upper mantle mantle composition at high pressure under water—saturated and water— composition at high pressure under water-saturated and waterundersaturated Earth and and Planetary Planetary Science Science Letters, Letters, v. v. undersaturated conditions: conditions: Earth 15, p. p. 37—53. 37-53. 15, Grout, rout, F.F., F.F., 1923, 1923, The The magnetite magnetite pegmatites pegmatite8 of of northern northern Minnesota: Minnesota: Economic Geology, v. 18, p. 253—269. Economic Geology, V. p. 253-269. 1925a, The The Coutchiching Coutchichinq problem: problem: Geological Geological Society Society of of Grout, F.F., F.F., 1925a, Grout, America America Bulletin, Bulletin, v. v. 36, 36, p. p. 351—364. 351-364. The Vermilion Vermilion batholith batholith of of Minnesota: Journal Journal of of 1925b, The Grout, Grout, F.F., F.F., 1925b, Geology, Geology, v. v. 33, 33, p. p. 467—487. 467-487. 136 I �Grout, F.F., F.F., 1926, 1926, The The geology and magnetite deposits deposits of northern northern St. Louis 770 Louis County, County, Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Bulletin Bulletin 21, 220 p. P- Hanson, Hanson, G .N., and Goldich, 8.5., S.S., 1972, 1972, Early Precambrian Precambrian rocks rocks in the G.N., Saganaga 11, Saganaga Lake—Northern Lake-Northern Light Light Lake Lake area, area, Minnesota—Ontario, Minnesota-Ontario, Part Part II, Petrogenesis, & inI Doe, B.R., B.R., and and Smith, Smith, DO.K., .K., eds., eds., Studies in minerminer— - a logy and and Precambrian Precambrian geology: America alogy geology: Geological GeologicalSociety Societyofof AmericaMemoir Memoir 135, 135, p. 179—192. 179-192. Hanson, G.N., G.N., and and Malhotra, Malhotra, R., R., 1971, 1971, K—Ar K-Ar ages ages of of mafic mafic dikes dikes and and evieviHanson, dence dence for for low—grade low-grade metamorphism metamorphism in in northeastern northeastern Minnesota: Geological v. 82, 82, p. p. 1107—1114. 1107-1114. Geological Society Society of of America America Bulletin, Bulletin, v. Hart, S.R., S.R., and and Davis, Davis, G.L., G.L., 1969, 1969, Zircon Hart, Zircon U—Pb U-Pb and and whole whole rock rock Rb-Sr Rb-Sr ages ages and early early crustal crustaldevelopment development near near Rainy Painy Lake, Lake, Ontario: Ontario: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 80, 80, p. p. 595-614. 595—614. LA., Haskin, Haskin, M.A., M.A., F.A., and andWildeman, Wildeman, TP.R., .R., 1968, 1968, Relative Relative Haskin, L.A., Frey, F.A., and absolute terrestrial terrestrial abundances of the the rare rare earths, earths, in inL.H. L.H. and absolute abundances of Anrens, ed., Origin distribution of Origin and and distribution theelements; elements;Pergamon Pergamon Press, Anrens, g., of the Press, New York, York, p. New p.889—912. 889-912. Hawley, J.E., Journal of Hawley, J. E., 1930, 1930, "Seine" "Seinen or or "Coutchiching": "Coutchiching": Journal of Geology, v. v. 38, 38, p. p . 521—547. 521-547. Jahn, Jahn, Bor-ming, and and Murthy, Murthy, V.R., V.R., 1975, 1975, Rb—Sr Rb-Sr isotopic isotopic studies studies of of the the Bor—ming, Vermilion Vermilion greenstone northeasternMinnesota: Minnesota: Geological Geological Society Society greenstone belt, belt, northeastern of p. 611. of America America Abstracts Abstracts with with Programs, Programs, v. v. 3, p . 611. 3, Lawson, A.C., A.C., 1913, 1913, The The Archean Archean geology geology of of Rainy Rainy Lake Lake restudied: restudied: Lawson, Geological Survey Geological Survey of of Canada Canada Memoir 40, 115 115 p. p. Mehnert, Mehnert, K.R., K.R., 1968, 1968, Migmatites Migmatites and and the the origin origin of of granitic granitic rocks; rocks; Elsevier Elsevier Publishing Company, Amsterdam, 393 p. Publishing 393 p . Merritt, P.L., P.L., Merritt, 1934,Seine—Coutchiching Seine-Coutchiching problem: 1934, problem: Geological Geological Society Society of America Bulletin, 45,p.p. 333-374. America Bulletin, v.v.45, 333—374. - Minnesota Minnesota Geological Geological Survey, Survey, 1969, 1969, The The proposed proposed Voyageurs Voyageurs National National Park Park — Its Its geology geology and and mineral mineral potential; potential: 16 16 p. p. ++ map. map. in Geology of Minnesota: centennial volume: &., Geology of Minnesota: A A centennial volume: Minnesota Minnesota Geological Geological Survey, Survey,p.p.162—171. 162-171. Ojakangas, R.W., R.W., 1972, Ojakangas, 1972, Rainy Rainy Lake Lake area, area, in Sims, Sims, P.K., P.K., and and Morey, Morey, G.E., G.B., eds., Peterman, Z.E., Z.E., and Goldich, 5.5., S.S., 1970, 1970, Early Precambrian Precambrian geology of the the Peterman, Rainy Eabs.1: Institute Institute on on Lake Lake Superior Superior Geology, Geology, 16th 16th Rainy Lake Lake district district [abs.]: Annual Annual Meeting, Meeting, Thunder Thunder Bay, Bay, Ontario Ontario [Proceedings], [Proceedings], p. p. 34. 34. Peterman, Z.E., Z.E., Goldich, Goldich, S.S., S.S., Hedge, Hedge, C.F., C.F., and and Yardley, D.H., D.H., 1972, 1972, Geochronology Geochronology of of the the Rainy Rainy Lake Lake region, region, Minnesota—Ontario, Minnesota-Ontario, in &I Doe, Doe, Studies in mineralogy and Precambrian B . R . , and Sims, P . K . , B.R., and Sims, P.R., eds., Studies in mineralogy and Precambrian geology: Geological Geological Society Society of of America America Memoir Memoir 135, 135, p. p. 193—215. 193-215. e., 137 �I I I Poulsen, K Poulsen, .H., K.H., 1980, The stratigraphy, structure and metamorphism of Archean rocks thesis, Lakehead Lakehead Archean rocks at at Rainy Rainy Lake, Lake, Ontario: Ontario: Unpub. Unpub. 14.5. M.S. thesis, p. University, Thunder Thunder Bay, Bay, Ontario, 99 99 p. K.H., Borradaile, J., and .M., 1980, Poulsen, Poulsen, K.!!., Borradaile, G. G.J., and Kehlenbeck, Kehlenbeck, MM.M., 1980, An An inverted inverted succession succession at Rainy Rainy Lake, Ontario: Canadian Canadian Journal Journal of Earth 17, p. p. 1358—1369. Sciences, v. Sciences, v. 17, 1358-1369. Rye, D.M., D.M., and Roy, Roy, R.F., R.F., 1978, 1978, The distribution distribution of thorium, uranium, and potassium Archean granites granites from from northeastern northeastern Minnesota: Minnesota: American American potassium in in Archean Journal of Journal of Science, Science, v. v. 278, 278, p. p. 354—378. 354-378. Schulz, K.J., K.J., 1980, 1980, The magmatic evolution evolution of the the Vermilion greenstone greenstone v. belt, NE Minnesota: Minnesota: Precambrian Precambrian Research, v . 11, 11, p. p. 215-245. 215—245. Sims, P .K., 1976, 1976, Early Precambrian Precambrian tectonic-igneous evolution evolution in the P.K., Vermilion district, Vermilion district, northeastern northeastern Minnesota: Geological Geological Society Society of of America Bulletin, America Bulletin, v. v. 87, 87, p. p. 379—389. 379-389. Southwick, D .L., 1972, Vermilion granite—migmatite granite-migmatite massif, in Sims, P .K., D.L., P.K., Morey, G G.E., eds., Geology of Minnesota: A centennial centennzl volume: and Wrey, .B., Minnesota Minnesota Geological Geological Survey, Survey, p. p. 108—119. 108-119. *., D.L., 1978, The Vermilion Granitic Complex, northern Minnesota, Southwick, D .L., and Williams, J J.G., eds., Proceedings Proceedings of the 1978 in Smith, I.E.M. I.E.M. .G., eds., Archean Geochemistry Archean Geochemistry Conference, p. p. 265—276. 265-276. - - Southwick, D.L., and D.L., and Day, W.C., W.C., 1981, 1981, Geology Geology and and petrology of Proterozoic Proterozoic mafic dikes, dikes, north—central north-central Minnesota Minnesota [abs.]: Labs.]: American Geophysical Union, Program Program for for 1981 1981 Midwest Meeting, Minneapolis. Minneapolis. of Minnesota, D.L., and Ojakangas, R.W., R.W., 1979a, 1979a, Geologic map of Southwick, D.L., International International Falls Falls Sheet: Sheet: Minnesota Geological Survey, scale 1:250,000. 1:250,000. Southwick, D.L., D.L., and Ojakangas, R.W., R.W., 1979b, Field trip trip guidebook guidebook for the the 1979b, western western Vermilion Vermilion district, district, northeastern northeastern Minnesota: Minnesota Minnesota 65 p. p. Geological Survey, Guidebook series series 10, 10, 65 - Southwick, D.L., D.L., P.K., 1980, 1980, The Vermilion Granitic Complex — AA and Sims, P.K., U.S. Geological Survey new name for old rocks in northern Minnesota: Minnesota: U .S. Geological Professional Professional Paper Paper 1124A, 1124A, p. p. Al—All. A1-All. Streckeisen, A .L., 1973, Plutonic rocks: rocks: Classification and A.L., chairman, 1973, nomenclature recommended nomenclature recommended by the IUGS IUGS Subcommission Subcommission on the Systematics Systematics of Igneous Igneous Rocks: cks: Geotimes, v. 18, p. 26—30. Geotimes, v. 18, p. 26-30. Williams, J.G., J.G., 1978, 1978, Geology of of the the Crystal Crystal Lake Lake area, area, Quetico Quetico in Smith, I.E.M. and Williams, J.G., Proceedings I.E.M. J.G., eds., Proceedings Subprovince, & p. 193—207. of the 1978 1978 Archean Geochemistry Conference, p. 193-207. *., Winchell, N.H., N.H., Geological Geological 1888, 1888, Sixteenth Sixteenth annual annual report report for for the the year 1887: 1887: Minnesota Minnesota and Natural History Survey, 504 p. and Natural History Survey, 504 p. 138 I �- a -- -_________ -4.- Wood, J., J., 1980, 1980, Epiclastic sedimentation Wood, sedimentation and and stratigraphy stratigraphy in in the the North Spirit Lake and and Rainy Rainy Lake comparison: Precambrian Precambrian Research, Research, Lake areas: areas: A comparison: V. 12, 12, p. p. 227—255. v. 227-255. 139 � 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, 1982 Description An account of the resource Institute on Lake Superior Geology. International Falls, Minnesota. May 5-8, 1982. 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 1982 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/a589506b71d64a5c9fb6d07486e47152.pdf b9d36aa3afb42bdaafbeb6c04ecddc0e PDF Text Text �PROCEED PROCEEDIINGS NGS TWENTY-NINTH ANNUAL TWENTY-NINTH ANNUAL INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIOR GEO LOGY GEOLOGY held h e l d at at Michigan Technological University University lioughton, Michigan Houghton, Michigan 49931 49931 11—14, 1983 1983 May 11-14, Organized by the the Department of of Geology and Geological G e o l o g i c a l Engineering Engineering with iin n ccooperation ooperation w ith Division of Education and Public The D i v i s i o n of P u b l i c Services Services Michigan Technological University University Houghton, Michigan Houghton, 49931 49931 J . Bornhorst and J. J . F. F. Diehl Diehl T. T. J. Editors Editors �TABLE OF OFCONTENTS CONTENTS Volume II Volume GENERAL INFORMATION INFORMATION j i PURCHASE INFORMATION INFORMATION FOR FOR PROCEEDINGS PROCEEDINGSVOLUME VOLUME PURCHASE ji INSTITUTE INSTITUTEBOARD BOARD OF DIRECTORS i LOCAL COMMITTEE COMMITTEE ii GOLDICH MEDAL COMMITTEE COMMITTEE GOLD ICR MEDAL ii SESSION SESSION CHAIRMEN CHAIRMEN ii ANNUAL BANQUET SPEAKER iii GOLDICH GOLDICH MEDAL RECIPIENT iii ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS iii iii REPORT 2 8 t h I.L.S.G. I.L.S.G. REPORT OF OF THE CHAIRMAN CHAIRMAN —- 28th iiv v vii vii CALENDAR OF EVENTS AND PROGRAM PROGRAM 1 1 ABSTRACTS ABSTRACTS TRIP 1 4 , 1983 1983 FIELD T R I P ON MAY 14, ROPES GOLD MINE AND THE MICHIGAN GOLD MINE 43 Volume II I1 FIELD TRIP ON MAY 11, 11, 1983 1983 FIELD GUIDE TO THE GEOLOGY OF THE KEWEENAW PENINSULA FIELD 1-116 �GENERAL INFOR11ATION GENERAL INFORMATION 29th Annual INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY University Michigan Technological University Houghton, Houghton, Michigan Michigan May 11—14, 11-14, 1983 1983 PROCEEDINGS VOLUME VOLUME PURCHASE INFORMATION FOR PROCEEDINGS Volume II && II I1 together t o g e t h e r for f o r sale s a l e at: at: The D i v i s i o n of Division of Education and Public P u b l i c Services Services University Michigan Technological University Volume II I1 only for f o r sale s a l e at: at: E. Bookstore E. R. R. Lauren Bookstore University Michigan Technological University OF DIRECTORS DIRECTORS INSTITUTE BOARD OF T.J. T . J . Bornhorst, Bornhorst, Department of of Geology and Geological Engineering, Engineering, Michigan Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan (Chairman, (Chairman, 1983) 1983) D.L. Southwick, Minnesota Geological Survey, Survey, St. S t . Paul, P a u l , Minnesota (1982) (1982) D.L. Southwick, W.C. Cambray, W.C. Cambray, Department of of Geology, Geology, Michigan State S t a t e University, U n i v e r s i t y , East East Lansing, Lansing, Michigan (1981) (1981) Michigan P.E. Myers, Myers, Department P.E. Department of of (1980) Geology, University U n i v e r s i t y of of Wisconsin, C l a i r e , Wisconsin Wisconsin Geology, Wisconsin, Eau Claire, R.C. i v i s i o n , Department of Natural N a t u r a l Resources, Resources, Lansing, Lansing, R.C. Reed, Reed, Geological Survey D Division, Department of Michigan Michigan (Secretary—Treasurer) (Secretary-Treasurer) 1 �LOCAL COMMITTEE COMMITTEE LOCAL Conference Chairman Chairman Conference T.J. T . J . Bornhorst, Bornhorst, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. Technological F i e l d Trips Trips Field T.J. T.J. Bornhorst Bornhorst J . Kalliokoski Kalliokoski J. J . B . Paces Paces J.B. W . I . Rose, Rose, Jr. Jr. W.I. D.M. Rossell Rossell D.M. All A l l at a t the t h e Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. P h v s i c a l Arrangements Arrangements Physical J a n e Berner, Berner, Coordinator Coordinator Jane Jean Joffee, J o f f e e , Secretary Secretary Jean D i v i s i o n of of Education Education and and Public P u b l i c Services Services Division Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. Best Student Student Paper Paper Committee Committee Best 53706. M.G. M.G. Mudrey, Mudrey, Jr., J r . , Wisconsin Wisconsin Geological Geological Survey, Survey, Madison, Madison, Wisconsin Wisconsin 53706. S.C. S.C. Nordeng, Nordeng, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. 49931. R. Rowe, Rowe, Exxon Exxon Minerals Minerals Company, Company, Rhinelander, Rhinelander, Wisconsin Wisconsin 54501. 54501. R. GOLDICH EDAL COMMITTEE COMMITTEE GOLD ICH M MEDAL G.L. G.L. LaBerge, LaBerge, Department Department of of Geology, Geology, University U n i v e r s i t y of of Wisconsin—Oshkosh, Wisconsin-Oshkosh, Oshkosh, Wisconsin Wisconsin 54901 54901 (Chairman). (Chairman) Oshkosh, R.L. R.L. Buchheit, Buchheit, Meridian Meridian Land Land and and Mineral Mineral Company, Company, Billings, B i l l i n g s , Montana Montana 59103. 59103. W.F. Cannon, Cannon, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, Virginia V i r g i n i a 22092. 22092. W.F. . CHAIRMAN SESSION CHAIRMAN SESSION W.S. Cordua, Cordua, Department Department of of Plant P l a n t and and Earth E a r t h Sciences, Sciences, University U n i v e r s i t y of of W.S. Wisconsin—River Wisconsin- River Falls, F a l l s , River River Falls, F a l l s , Wisconsin Wisconsin 54022. 54022. T.B. T.B. Holst, H o i s t , Department Department of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, Minnesota 55812. 55812. Minnesota A.M. Johnson, IInstitute A.M. Johnson, n s t i t u t eofofMineral MineralResearch, Research,Michigan MichiganTechnological Technological U n i v e r s i t y ,Houghton, Houghton, Michigan Michigan 49931. 49931. University, J . S . Klasner, Klasner, Department Department of of Geology, Geology, Western Western Illinois I l l i n o i s University, U n i v e r s i t y , Macomb, Macomb, J.S. I l l i n o i s 61455. 61455. Illinois Departmentofof Geology Geology and and Geological Geological Engineering, S.D. McDowell, McDowell, Department Engineering, Michigan Michigan S.D. Technological Technological University, U n i v e r s i t y ,Houghton, Houghton, Michigan Michigan 49931. 49931. :ii �N. Scofield, S c o f i e l d , Department of of Geology Geology and and Geological G e o l o g i c a l Engineering, Engineering, South South Dakota Dakota N. of Mines & Technology, Technology, Rapid City, School of C i t y , South Dakota 57701. 57701. D.L. Southwick, S t . Paul, P a u l , Minnesota 55108. D.L. Southwick, Minnesota Geological G e o l o g i c a l Survey, Survey, St. C.T. C T Young, Young, Department of of Geology and and Geological G e o l o g i c a l Engineering, Engineering, Michigan Michigan Technological U University, Houghton, Michigan 49931. Technological n i v e r s i t y , Houghton, 49931. .. ANNUAL ANNUAL BANQUET GUEST SPEAKER SPEAKER E. K Kesler, Department of of Geology, Geology, U University Michigan, Ann Arbor, Stephen E. e s l e r , Department n i v e r s i t y of of Michigan, Arbor, Michigan 48109. MEDAL GOLDICH M EDAL RECIPIENT Burton H. H. Boyum, Boyum, 1740 1740 Glendura Lane, Lane, Ishpeming, Ishpeming, Michigan 49849. ACKNOWLEDGEMENT S ACKNOWLEDGEMENTS The Organizing Organizing Committee of of the t h e 1983 1983 Institute I n s t i t u t e on Lake Superior S u p e r i o r Geology gratefully acknowledge the g r a t e f u l l y acknowledge t h e work of of JJulene u l e n e E. E. Erickson in i n typing t y p i n g drafts d r a f t s and final final manuscript for manuscript f o r the t h e Proceedings Proceedings Volumes. Volumes. 111 iii �REPORT REPORT OF THE THE CHAIRMAN 28th INSTITUTE ON LAKE SUPERIOR GEOLOGY 1982 The 28th Institute I n s t i t u t e on on Lake Superior Geology was hheld e l d May n May 5-8, 5—8, 1982 iin I n t e r n a t i o n a l Falls, F a l l s , Minnesota under the t h e sponsorship of International of the the Minnesota Minnesota Geological Survey. rofessional Survey. R e g i s t r a n t s numbered 147, 147, including i n c l u d i n g 121 p Registrants professional geologists g e o l o g i s t s and and 26 26 students. s t u d e n t s . The program included aa pre-meeting pre—meeting one-day one—day f i e l d trip t r i p to t o examine mineral occurrences iin n the o r t Frances-Mine entre field the F Fort Frances—Mine C Centre area, an overview overview of of a r e a , Ontario, Ontario, a post—meeting post-meeting one—day one-day field f i e l d ttrip r i p tto o pprovide r o v i d e an Falls Kabetogama, Minnesota, Minnesota, and tthe h e Archean geology near International International F a l l s and Kabetogama, four f o u r half—day half-day sessions s e s s i o n s of of technical t e c h n i c a l papers. papers. e r s o n s partic— particSeventy seven p persons pated p a t e d in i n the t h e pre—meeting pre-meeting trip, t r i p , 51 51 participated p a r t i c i p a t e d in i n the t h e post—meeting post-meeting trip, trip, oral presentation a p e r s were accepted for for o ral p r e s e n t a t i o n aatt tthe h e ttechnical echnical and 31 ppapers sessions. s e s s i o n s . Background papers for f o r the field f i e l d trips, t r i p s , ffield i e l d ttrip r i p road o g s , and road llogs, accepted w e r e published published in i n the the Proceedings Proceedinqs volume. volume. a c c e p t e d abstracts a b s t r a c t s were Att the A t h e Annual Dinner on on May 6, 6 , 1982 1982 Ralph Marsden was awarded the Institute's of his many ccontributions I n s t i t u t e ' s Goldich Medal in i n recognition r e c o g n i t i o n of o n t r i b u t i o n s tto o the the Institute I n s t i t u t e and and to t o the t h e geology geology of of the t h e Lake Lake Superior Superior region. region. The banquet address Koski of the U.S. U.S. Geological Survey, Survey, who a d d r e s s was given given by Dr. D r . Randolph Koskiaof described metal—precipitating d e s c r i b e d recent r e c e n t Oceanographic oceanographic research r e s e a r c h on m e t a l - p r e c i p i t a t i n g hhot o t ssprings prings along Pacific, a l o n g spreading s p r e a d i n g ridges r i d g e s in i n the t h e eastern eastern P a c i f i c , and sspeculated p e c u l a t e d on tthe h e rrole ole such hydrothermal systems production of of volcanicvolcanic— systems may have played in i n the production hosted h o s t e d sulfide s u l f i d e deposits d e p o s i t s in i n Archean Archean greenstone greenstone belts. belts. K. University, K. Howard Howard Poulsen, Poulsen, graduate graduate student s t u d e n t at a t Queen's Queen's U n i v e r s i t y , received received a cash award award for f o r presenting p r e s e n t i n g the the best b e s t paper paper by by aa student. s t u d e n t . His H i s paper was was entitled the Fort F o r t Frances—Mine Frances-Mine Centre Centre area." area." e n t i t l e d "Mineral "Mineral deposits d e p o s i t s of of the An open open discussion d i s c u s s i o n on on the the organization o r g a n i z a t i o n of of the t h e Institute I n s t i t u t e was held h e l d on the t h e evening evening of of May May 5, 5, 1982 1982 with w i t h J. J. Kalliokoski K a l l i o k o s k i acting a c t i n g as a s moderator. moderator. About and discussed a range of issues concerning the objec20 people attended a t t e n d e d and discussed of i s s u e s objectives pros the Institute, I n s t i t u t e the , the p r oand s andcons consof offormalization, f o r m a l i z a t i o n , and and tthe h e manner t i v e s of of the I n s t i t u t e now now manages manages or o r should should manage manage its its financial f i n a n c i a l affairs. affairs. iin n which the Institute Several w e r e passed passed arid and ttransmitted r a n s m i t t e d tto o the Board of of S e v e r a l informal informal motions motions were D i r e c t o r s for f o r consideration c o n s i d e r a t i o n at a t their t h e i r annual annual meeting. meeting. Many of of those those Directors attending a t t e n d i n g the t h e discussion d i s c u s s i o n were surprised s u r p r i s e d to t o learn l e a r n that t h a t the t h e IInstitute n s t i t u t e indeed of by-laws, by—laws, and aalso l s o hhas a s an does have a formal constitution c o n s t i t u t i o n and a set s e t of I.R.S. number as tax-exempt, non—profit non-profit organization. o r g a n i z a t i o n . The constitution constitution I.R.S. a s aa tax—exempt, and by—laws by-laws are a r e appended appended to t o this t h i s report. report. met 6, 1982 and took e t on May 6, The Board of of Directors D i r e c t o r s of of the t h e Institute Institute m the t h e following f o l l o w i n g action: action: 1. 1. Accepted with Geological the offer o f f e r of of the t h e Minnesota G e o l o g i c a l Survey to to with thanks thanks the maintain the mailing m a i l i n g list l i s t of of the t h e I.L.S.G. I.L.S.G. The list is i s now stored s t o r e d on a m a i n t a i n the floppy be amended amended easily e a s i l y on on the the Survey's Survey's word word processor. processor. f l o p p y disk d i s k and and can can be The Survey will update the list as instructed by each General Chairman Survey w i l l update t h e l i s t a s i n s t r u c t e d will mailing host i l l supply print—outs p r i n t - o u t s of of the t h e list l i s t and m a i l i n g llabels a b e l s tto o each h ost and w organizing o r g a n i z i n g committee. committee. iv �2. Agreed funds presently Agreed to t o leave l e a v e in i n Canada Canada those t h o s e I.L.S.G. I.L.S.G. funds that that p r e s e n t l y are a r e in in Canada, M.M. Kehienbeck, Kehlenbeck, Lakehead Lakehead University, U n i v e r s i t y , Thunder Thunder Canada, and and to t o appoint a p p o i n t M.M. Bay, Bay, Ontario, O n t a r i o , as a s custodian custodian of of the t h e Canadian Canadian account. account. The The Canadian Canadian monies obligations monies are a r e to t o be be used used against a g a i n s t I.L.S.G. I.L.S.G. o b l i g a t i o n s in i n Canada Canada to t o avoid avoid losses l o s s e s on on currency currency exchange. exchange. AA statement statement of of the the Canadian Canadian account account is is appended appended to t o this t h i s report. report. 3. Formally moved moved that t h a t henceforth henceforth one one dollar d o l l a r of of each each registration r e g i s t r a t i o n fee fee Formally w i l l be be set s e t aside a s i d e into i n t o aa special s p e c i a l fund fund to t o sustain s u s t a i n the the costs c o s t s of of striking striking will Goldich Goldich medals. medals. The w i l l be be kept kept separate s e p a r a t e from from The Goldich Goldich medal medal fund fund will I.L.S.G. operating o p e r a t i n g monies monies and and will w i l l be be maintained maintained in i n aa separate s e p a r a t e bank bank I.L.S.G. account. account. Under Under this t h i s plan p l a n enough enough money money will w i l l have have accumulated accumulated in i n 77 years y e a r s to t o strike s t r i k e aa batch batch of of 10 10 medals, medals, replacing r e p l a c i n g the the supply s u p p l y currently currently on hand. on hand. The The Board Board also a l s o noted noted for f o r the t h e record r e c o r d that t h a t the t h e first f i r s t Goldich Goldich S.S. Goldich, Goldich, the t h e second second to t o Carl C a r l Dutton, Dutton, and and the the medal was was awarded awarded to t o S.S. medal third t h i r d to t o Ralph Ralph Marsden, Marsden, leaving l e a v i n g 77 for f o r subsequent subsequent years y e a r s from from the the first first striking s t r i k i n g of of 10. 10. The The remaining remaining medals medals are a r e in i n the t h e custody custody of of G.B. G.B. Morey, Minnesota Minnesota Geological Geological Survey, Survey, and and are a r e stored s t o r e d in i n aa bank bank safety safety Morey, deposit d e p o s i t box box in i n Minneapolis. Minneapolis. 4. Instructed I n s t r u c t e d the t h e Secretary S e c r e t a r y — Treasurer T r e a s u r e r to t o move move I.L.S.G. I.L.S.G. funds from from the the funds present pays the the maximaxip r e s e n t non—interest—bearing non-interest-bearing account account to t o an an account account that t h a t pays mum mum rate r a t e obtainable o b t a i n a b l e while while maintaining maintaining liquidity. liquidity. 5. Noted Noted the t h e desire d e s i r e of of Robert Robert C. C. Reed, Reed, Secretary S e c r e t a r y — Treasurer, T r e a s u r e r , to t o retire retire from from his h i s position p o s i t i o n as a s of of the t h e next next Board Board meeting meeting in i n Houghton Houghton in i n May May 1983. 1983. AA new new Secretary S e c r e t a r y - Treasurer T r e a s u r e r will w i l 1 ,be b e elected e l e c t e d at a t the t h e Houghton Houghton Meeting. Meeting. - - - 6. Accepted ~ c c e p t e with dwith thanks thanks the t h e offer o f f e r of of the t h e Geology Geology Department Department of of the the University U n i v e r s i t y of of Wisconsin Wisconsin at a t Oshkosh Oshkosh to t o host h o s t the t h e 30th 30th I.L.S.G. I.L.S.G. at at Wausau, Wausau, Wisconsin Wisconsin in i n 1984. 1984. 7. Noted Noted with with anticipation a n t i c i p a t i o n the the informal informal offer o f f e r of of Charles Charles Blackburn, Blackburn, Ontario 1985 Institute Institute O n t a r i o Geological Geological Survey, Survey, Kenora Kenora Office, O f f i c e , to t o host h o s t the t h e 1985 in i n Kenora. Kenora. This T h i s offer o f f e r is i s understood understood to t o be be tentative, t e n t a t i v e , pending pending final final confirmation M r . Blackburn. Blackburn. c o n f i r m a t i o n from from Mr. 8. Moved be included i n c l u d e d each each year y e a r in in Moved that t h a t the t h e summary summary report r e p o r t of of the t h e Chairman Chairman be the c u r r e n t and and t h e next—following next-following Proceedings Proceedings volume volume so s o as a s to t o maintain maintain aa current public p u b l i c account account of of the theInstitute's I n s t i t u t e ' s affairs. affairs. 9. Appointed Appointed the t h e following following persons persons to t o serve s e r v e on on the t h e selection s e l e c t i o n committee committee for f o r recipients r e c i p i e n t s of of the t h e Goldich Goldich medal: medal: Gene y e a r term, term, Chairman Chairman (representing ( r e p r e s e n t i n g academia) academia) LaBerge, 11 year GeneLaBerge, Richard y e a r term, term, (representing ( r e p r e s e n t i n gindustry) industry) Richard Bucheit, Bucheit, 22 year William William Cannon, Cannon, 33 year y e a r term term (representing ( r e p r e s e n t i n g government) government) The The Board Board further f u r t h e r stipulated s t i p u l a t e dthat t h a t subsequent subsequent appointments appointments to t o fill fill vacancies on the committee should maintain the equal representation v a c a n c i e s on t h e committee should maintain t h e equal r e p r e s e n t a t i o n of of academia, academia, industry, i n d u s t r y , and andgovernment. government. V �11G. C. Moved that that the the committee committee to to select select the the best student student paper be appointed appointed the host host organizing organizing committee. committee. The The committee committee appointed appointed each year year by the should consist should consist of representatives representatives from academia, industry, and government. government . Financially the Financially the 28th 28th I.L.S.G. I.L.S.G. concluded concluded with with aa net net profit profit of of $2,210.64, and thus pumped some badly needed funds into the general general $2,210.64, and thus pumped some funds treasury recent deficit meetings meetings and treasury which which had had been been depleted depleted severely severely by recent In my opinion the the start—up start-up costs costs for for the the Goldich Goldich medal medal program. program. In opinion the the Institute is intellectually, and and it is Institute is in good shape both financially and intellectually, with a responsibility for with a sense sense of of satisfaction satisfaction and and relief relief that that I I turn over responsibility operations to Ted Bornhorst Bornhorst of 1983 operations of Michigan Michigan Tech. L. David L . Southwick Southwick David General General Chairman Chairman 28th 1.L-S.G. I.L.S.G. 28th July 30, 1982 1982 July 30, vi �CALENDER CALENDER OF EVENTS EVENTS AND AND PROGRAM PROGRAM TUESDAY, MAY 10, TUESDAY, 10, 1983 1983 7:00 p.m. —- 9:00 9:00 p.m. EARLY REGISTRATION REGISTRATION FOR FOR PARTICIPANTS PARTICIPANTS IN IN FIELD FIELD TRIP TRIP 1. 1. WEDNESDAY, WEDNESDAY, MAY MAY 11, 11, 1983 1983 8:00 8:00 a.m. a.m. —- 6:00 6:00 p.m. FIELD TRIP FIELD TRIP 1. 1. GEOLOGY THE KEWEENAW KEWEENAW PENINSULA, PENINSULA, GEOLOGY OF THE Rose and and J.B. J.B. Paces, Paces, MICHIGAN —- T.J. T.J. Bornhorst, Bornhorst, W.I. Rose leaders. leaders. 4:00 p.m. -- 10:00 p.m. 10:OO p.m. REGISTRATION —- MEMORIAL UNION BUILDING BUILDING 10:00 p.m. p.m. 7:00 p.m. —- 10:OO SMOKER AND CASH BAR 12, 1983 THURSDAY, 1983 THURSDAY, MAY MAY 12, 7:30 a.m. — - 4:30 4:30 p.m. p.m. REGISTRATION — MEMORIAL UNION BUILDING REGISTRATION - MEMORIAL BUILDING 8:20 a.m. — 8:20 - 8:25 a.m. 8:25 a.m. Dr. E.H.T. Whitten, Vice WELCOME TO MICHIGAN TECH, TECH, Dr. E.H.T. Whitten, Vice President Affairs, Michigan Technological President for for Academic Affairs, Technological University. University. 8:25 a.m. — 8:30 a.m. WELCOME TO WELCOME TO 29TH 29TH I.L.S.G., I.L.S.G., T.J. T.J. Bornhorst, Bornhorst, Chairman. Chairman. 8:30 a.m. — 12:00 p.m. TECHNICAL W.S. Cordua Cordua and and S.D. SD. McDowell, TECHNICAL SESSION I, W.S. McDowell, Co—Chairmen. Co-Chairmen. 8:30 a.m. John John C. C. Green Green —— -- COMPOSITION, COMPOSITION, ORIGIN ORIGIN AND AND EVOLUTION OF KEWEENAWAN MAGMAS REVIEW (invited (invited paper). paper). KEWEENAWAN MAGMAS - A REVIEW 9:00 a.m. Klaus J. -- GEOCHEMISTRY GEOCHEMISTRY OF THE THE VOLCANIC VOLCANIC ROCKS ROCKS Klaus J. Schulz Schulz —— OF OF NORTHEASTERN NORTHEASTERN WISCONSIN. WISCONSIN. 9:20 a.m. 9:40 a.m. 10:00 a.m. 10:20 a.m. *James D. Miller, Jr. Jr. -- MAJOR ELEMENT CHEMISTRY OF OF ELEMENT CHEMISTRY ANORTHOSITES ANORTHOSITES IN THE DULUTH COMPLEX, COMPLEX, SNOWBANK SNOWBANK LAKE LAKE THE DULUTH MINNESOTA. QUADRANGLE, MINNESOTA. A.P. Ruotsala, Paul Paul N. M. Stadnik Stadnik and T.J. Bornhorst Bornhorst —— -A.P. Ruotsala, COBALT, NICKEL AND COBALT, NICKEL AND VANADIUM CONTENTS OF PYRITE FROM VANADIUM CONTENTS PYRITE FROM MICHIGAMME SLATE, SLATE, MICHIGAN. MICHIGAN. MICHIGANME COFFEE COFFEE *Abelmonem A. Eldougdoug GEOLOGICAL AND GEOCHEMICAL -- GEOLOGICAL GEOCHEMICAL Eldougdoug —— CHARACTERISTICS GLEN CHARACTERISTICS OF THE VOLCANO-SEDIMENTARY GLEN TOWNSHIP FORMATION, TOWNSHIP FORMATION, EAST-CENTRAL EAST-CENTRAL MINNESOTA. MINNESOTA. vii vii �10:40 a.m. 11:00 a.m. M.L. M.L. Nebel Nebel and R.L. Morton Morton --- HYDROTHERMAL HYDROTHERMAL ALTERATION AT AT THE THE HELEN HELEN MINE, MINE, WAWA, WAWA, ONTARIO. ONTARIO. *Sarah *Sarah J. J. —— THE THE RELATIONSHIP Mills RELATIONSHIP BETWEEN THE BASAL Mills -- AND CLOUD ZONE CU-NI CU—NI SULFIDES, MINNAMAX MINNAMAX ZONE AND DEPOSIT, DEPOSIT, DULUTH DULUTH COMPLEX, COMPLEX, MINNESOTA. MINNESOTA. 11:20 a.m. *Warren ULTRAMETANORPHISM AND MIGMATITE MIGMATITE GENER— *Warren C. Day Day --- ULTRAMETAMORPHISM GENERIN THE ATION IN THEVERMILION VERMILIONGRANITE GRANITECOMPLEX, COMPLEX,NORTHERN NORTHERN MICHIGAN. MICHIGAN. 11:40 a.m. 11:40 a.m. *W.I. Petro —— IGNEOUS ROCKS ROCKS OF OF THE DISTRICT, -- IGNEOUS THE BARABOO BAMBOO DISTRICT, Petro WISCONSIN. WISCONSIN. 12:15 p.m. —- 1:45 p.m. 1:45 p.m. GROUP LUNCHEON, LUNCHEON, Dr. E.H.T. Whitten, Whitten, Vice President President for for Academic Academic Affairs, Affairs, Michigan Michigan Technological Technological University, University, Guest Guest Speaker. Speaker. ANNUAL ANNUAL MEETING, MEETING, I.L.S.G. I.L.S.G. BOARD 2:00 p.m. —- 5:00 p.m. 5:00 p.m. 2:00 p.m. p.m. TECHNICAL SESSION TECHNICAL SESSION II, 11, J.S. J.S. Kiasner Klasner and and C.T. C.T. Young, Young, Co—Chairmen. Co-Chairmen. *M.A. THREE-DIMENSIONAL STRUCTURE *M.A. Feighner Feighner --- THREE-DIMENSIONAL STRUCTURE OF OF THE THE CRUST AND UPPER MANTLE BENEATH LAKE SUPERIOR CRUST BENEATH THE THE LAKE SUPERIOR REGION. REGION. 2:20 2:20 p.m. p.m. C. Patrick LONG-WAVELENGTH GRAVITY Patrick Ervin Ervin --- LONG-WAVELENGTH GRAVITY ANOMALIES ANOMALIES GREAT LAKES IN THE GREAT LAKES REGION. REGION. 2:40 p.m. p.m. Robert J. Robert J. Ferderer, Ferderer, Val W. Chandler Chandler and Judson Judson Mead —— -GRAVITY MAGNETIC MODEL STUDIES GRAVITY AND MAGNETIC STUDIES OF OF THE THE SOUTHERN SOUTHERN DULUTH COMPLEX, NORTHEASTERN DULUTH NORTHEASTERN MINNESOTA. MINNESOTA. 3:00 p.m. Val —— Val W. W. Chandler Chandler -- PALEOMAGNETIC PALEOMAGNETIC AND AND MAGNETIC MAGNETIC ANOMALY ANOMALY STUDIES OF THE STUDIES THENORTHWESTERN NORTHWESTERN DULUTH DULUTH COMPLEX, LAKE LAKE COUNTY, MINNESOTA. MINNESOTA. 3:20 p.m. COFFEE COFFEE 3:40 p.m. STRUCTURE N.E. —— M.E. Bengtson, Bengtson,R.P. R.P.Meyer Meyerand andH.C. H.C.Halls Halls -- THE THE STRUCTURE OF THE SLATE SLATE ISLANDS ISLANDS AREA AREA OF OF LAKE LAKE SUPERIOR. SUPERIOR. 4:00 p.m. ORDOVICIAN CRYPTOEXPLOSION William William S. S. Cordua Cordua —— -- AN ORDOVICIAN CRYPTOEXPLOSION STRUCSTRUCTURE FROM TURE FROM NEAR ROCK ROCK ELM, ELM, PIERCE PIERCE COUNTY, COUNTY, WISCONSIN. WISCONSIN. 4:20 p.m. U.O. Atuanya, Atuanya, D.T.A. Symons —— PALEO— U.O. Symons and and N. M. Stupavsky PALEOStupavsky -MAGNETISM OF THE THE GUNFLINT GUNFLINT IRON IRON FORMATION FORMATION OF OF NORTH— NORTHWESTERN ONTARIO. WESTERN ONTARIO. 4:40 p.m. Kidjopa Attoh, Marc Vander Meulen and Daniel Daniel Brandsma Brandsma —— -MODELS FOR MODELS FOR THE THE COOLING COOLING OF OF THE THE PEAVY PEAVY POND POND COMPLEX: COMPLEX: IMPLICATIONS FOR THE METAMORPHIC METAMORPHIC EFFECT IN SURROUNDING IMPLICATIONS SURROUNDING ROCKS. ROCKS. viii viii �6:00 6:00 p.m. p.m. -- 77:30 : 3 0 p.m. p.m. COCKTAIL PARTY —- CASH CASH BAR 77:30 : 3 0 p.m. p.m. -- 9:30 p.m. 9:30 p.m. ANNUAL BANQUET Master of M a s t e r of Ceremonies C eremonies — - Dr. D r . Albert A l b e r t P. P . Ruotsala, R u o t s a l a , Michigan Michigan Technological T e c h n o l o g i c a l University. University. Guest - Dr. D r . Stephen S t e p h e n E. E . Kesler, K e s l e r , University U n i v e r s i t y of of G u e s t Speaker Speaker — Michigan, M i c h i g a n , "Precious " P r e c i o u s Metal M e t a l Deposits D e p o s i t s and and Metamorphic Metamorphic Processes". Processes". FRIDAY, MAY 13, FRIDAY, 13, 1983 1983 77:30 : 3 0 aa.m. .m. - 12:00 12:OO pp.m. .m. REGISTRATION -- MEMORIAL UNION BUILDING 8:30 12:00 pp.m. 8:30 a.m. a.m. —- 12:OO .m. TECI-INICALS ESESSION T.B. HHoist A.M. Johnson, TECHNICAL S S I O N 1III, 11, T.B. o i s t aand n d A.M. Co—Chairmen. Co-Chairmen. 8:30 a.m. J.K. J . K . Greenburg G r e e n b u r g —— -- RELATIVE AGE AGE AND AND TECTONIC TECTONIC SIGNIFICANCE SIGNIFICANCE OF PROTEROZOIC METASEDIMENTARY ROCKS IN I N THE THE UPPER MIDWEST. 8:50 a.m. REANY CREEK Mattson F.W. Cambray C a m b r a y —-- THE REANY CREEK FORMAFORMAa t t s o n and F.W. SS.R. .R. M MENOMINEE TION: T I O N : A MASS—FLOW MASS-FLOW DEPOSIT D E P O S I T OF OF POSSIBLE P O S S I B L EPOST POST MENOMINEE AGE. 9:10 a.m. AND STRUCTURAL *Fred S. S . Pulka —— -- DEPOSITIONAL DEPOSITIONAL AND STRUCTURAL FEATURE FEATURE OF OF THE UPPER FREDA FREDA SANDSTONE. SANDSTONE. - 9:30 -- EVIDENCE FOR FOR GLACIAL GLACIAL MARINE MARINE SEDIMENSEDIMEN**Lawrence L a w r e n c e C. C . Rosen R o s e n —— TATION IN I N THE EARLY PROTEROZOIC PROTEROZOIC GOWGANDA GOWGANDA FORMATION, FORMATION, ONTARIO, CANADA. NORTHEASTERN ONTARIO, CANADA. a.m. 9:50 a.m. COFFEE 10:20 a.m. Kehlenbach -- SUPERIMPOSED FOLDING AND AND ITS I T S IMPLICAIMPLICAM.M. e h l e n b a c h -— M.M. K TION T I O N ON ON THE THESHEBANDOWAN-QUETICO SHEBANDOWAN-QUETICO SUBPROVINCE SUBPROVINCE BOUNDARY, BOUNDARY, THUNDER BAY, ONTARIO. THUNDER BAY, ONTARIO. 10:40 a.m. FOR NAPPE T.B. H o i s—— t -- EVIDENCE EVIDENCE FOR NAPPE DEVELOPMENT DEVELOPMENT DURING DURING THE THE T . B . Hoist PENOKEAN OROGENYFROM FROM THE THE EARLY PENOKEAN OROGENY EARLY PROTEROZOIC PROTEROZOIC THOMSON THOMSON FORMATION, FORMATION, MINNESOTA. MINNESOTA. J.P. H.H. Woodard J . P . Kaszuba, K a s z u b a ,P.A. P.A.Schwarzweiier S c h w a r z w e l l and e r and H.H. W o o d a r—— d -- 11:00 a.m. FOLDED FOLDED ROCKS ROCKS IIN N THE THE EASTERN EASTERN CONTACT CONTACT ZONE ZONE OF OF THE THE . BATHOLITH. VERMILION BATHOLITH DOMES AND B.A. B.A. Brown B r o w n and J.G. J . G . Greenberg G r e e n b e r g —— -- GNEISS G N E I S S DOMES AND NOT— NOTSO-GNEISS DOMES IN I N THE PENOKEAN PENOKEAN TERRANES TERRANES OF O F NORTHERN NORTHERN S0-GNEISS WISCONSIN. 11:20 a.m. 12:15 p.m. — 1:15 p.m. GROUP LUNCHEON GROUP LUNCHEON - — REPORT ix FROM THE CHAIRMAN. CHAIRMAN. �1:30 p.m. — 4:30 p.m. 1:30 p.m. 1:50 p.m. TECHNICAL TECHNICAL SESSION S E S S I O N IV, I V Y D.L. D . L . Southwick S o u t h w i c k and and N. N. Scofield, Scofield, Co—Chairmen. Co-Chairmen. Gene -- LASALLE LASALLE FALLS F A L L S -- AN AN EXPOSED EXPOSED MASSIVE MASSIVE G e n e L. L . LaBerge L a B e r g e —— SULFIDE S U L F I D E DEPOSIT D E P O S I T IN I N FLORENCE FLORENCE COUNTY, COUNTY, WISCONSIN. WISCONSIN. *David * D a v i d A. A . Groves G r o v e s —— -- STRATIGRAPHY STRATIGRAPHY OF O F THE THE FOOTWALL FOOTWALL VOLCANIC VOLCANIC ROCKS ROCKS BENEATH BENEATH THE THE MATTABI MATTABI MASSIVE MASSIVE SULFIDE S U L F I D E DEPOSIT, DEPOSIT, STURGEON STURGEON LAKE, LAKE, ONTARIO. ONTARIO. 2:10 p.m. John John C. C . Green G r e e n --- PHYSICAL PHYSICAL VOLCANOLOGY VOLCANOLOGY OF O F THE THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANICS. VOLCANICS. 2:30 p.m. COFFEE COFFEE 3:00 p.m. Ted J . Smith, S m i t h , Paul P a u l L. L . Cloke C l o k e and and Stephen Stephen J. J. Kesler K e s l e r —— -T e d J. GEOCHEMISTRY GEOCHEMISTRY OF O F FLUID F L U I D INCLUSIONS I N C L U S I O N S FROM FROM ARCHEAN ARCHEAN AND AND PHANEROZOIC PHANEROZOIC GOLD GOLD DEPOSITS. DEPOSITS. 3:20 p.m. W.A. W.A. Bodwell, B o d w e l l , J.D. J . D . Strapko S t r a p k o and and G.J. G . J . Tonkin T o n k i n —— -- HISTORY, HISTORY, GEOLOGY, GEOLOGY, AND AND RECENT RECENT EXPLORATION EXPLORATION OF O F THE THE ROPES ROPES GOLD GOLD MINE, ( i n v i t e d paper). paper). MINE, MARQUETTE MARQUETTE COUNTY, COUNTY, MICHIGAN MICHIGAN (invited 4:10 p.m. *Dean * D e a n Rossell R o s s e l l —— -- ALTERATION ALTERATION OF O F THE THE DEER DEER LAKE LAKE PERIDOTITE PERIDOTITE IN I N THE VICINITY V I C I N I T Y OF O F THE THE ROPES GOLD GOLD MINE, MINE, MARQUETTE COUNTY, MICHIGAN. COUNTY , MICHIGAN. 4:30 4:30 p.m. p.m. ANNOUNCEMENT -- BEST B E S T STUDENT STUDENT PAPER PAPER AWARD AWARD ANNOUNCEMENT -- 1 4 , 1983 1983 SATURDAY, MAY MAY 14, SATURDAY, 8:00 a.m. a . m . —8:00 1. 1. 2. 2. 6:00 p.m. p.m. FIELD F I E L D TRIP T R I P II. 11. THE THE ROPES GOLD GOLD MINE MINE AND AND ITS I T S GEOLOGICAL GEOLOGICAT. SETTING S E T T I N G —- D. D. Rossell R o s s e l l and and J. J . Kalliokoski, K a l l i o k o s k i , leaders. leaders. U n d e r l i n e denotes d e n o t e s speaker speaker Underline *student * s t u d e n t paper paper x �ABSTRACTS 4BSTRACTS �2 of the t h e Gunflint G u n f l i n t Iron I r o n Formation of of Northwestern Ontario Ontario Paleomagnetism of U. U. 0. 0. ATUANYA, ATUANYA, D.T.A. D.T.A. SYMONS, SYMONS, and N. M. STUPAVSKY STUPAVSKY (Department (Department of of Geology, Geology, University U n i v e r s i t y of of Windsor, Windsor, Windsor, Windsor, Ontario, O n t a r i o , Canada Canada N9B 3P4) 3P4) Formation ooutcrops Bay, Ontario, The Gunf G u n f llint i n t I Iron r o n Formation u t c r o p s nnear e a r Thunder Bay, O n t a r i o , as as the unit t h e bbasal asal u n i t of of the t h e Animikie Series S e r i e s in i n the t h e Southern Province of of the the Canadian Precambrian Shield. S h i e l d . Paleomagnetic studies s t u d i e s on samples from 47 ssites i t e s employing alternating a l t e r n a t i n g field, f i e l d , thermal t h e r m a l and chemical demagnetdemagneti z a t i o n techniques t e c h n i q u e s lead l e a d to t o the t h e isolation i s o l a t i o n of of two major m agnetization ization magnetization components. The A component yields pole position component y ields a p ole p o s i t i o n of of l24°W, 124OW, 64°N 64ON (Sp = 100) to bbe primary oordiagenetic g o , 5m (Sm = 10') which is i s interpreted i n t e r p r e t e d 'to e aa primary r diagenetic (tjp == 90 component 23OO Ma. component aacquired c q u i r e d aat t -2300 Ma. A positive p o s i t i v e conglomerate conglomerate test t e s t supports supports this pole component gives gives a p o l e position p o s i t i o n of of 40°W, 40°W 7°S 7's t h i s conclusion. c o n c l u s i o n . The B component 130) (Sp which indicates the presence of a Hudsonian (tip == 8°, 8O, tjm = 13') i n d i c a t e s t h e presence of a Hudsonian 'm = orogenic metamorphic metamorphic ooverprint l72O Ma. Taken together orogenic v e r p r i n t aacquired c q u i r e d aat t -1720 Ma. Taken together "Penokean" orogeny orogeny of of tthe tthe h e rresults e s u l t s iindicate n d i c a t e tthat h a t tthe h e "Penokean" h e Southern Province iin United S States Province n tthe h e nnorthcentral o r t h c e n t r a l United t a t e s iis s eequivalent q u i v a l e n t to t o the the Hudsonian orogeny s l i g h t l y younger -l65O -1650 Ma Ma metamorphic orogeny in i n Canada. Canada. A slightly componetlt i is componetit s rrestricted e s t r i c t e d tto o aa few ssites i t e s in i n the t h e Gunflint. G u n f l i n t . Contact ttests ests w i t h a Keweenawan Logan Sill S i l l and and aa lava l a v a flow flow are a r e positive. positive. with �3 Models for forthe the Cooling Cooling of ofthe the Peavy PeavyPond Pond Complex: Complex:Implications Implications Models for the the Metamorphic Metamorphic Effect Effect in inSurrounding SurroundingRocks Rocks for ATTOH, KODJOPA KODJOPA (Department (Departmentof ofGeology, Geology,Hope HopeCollege, College,Holland, Holland,MIMI49423) 49423) ATTOH, VANDER MEULEN, MEULEN,MARC MARC (Department (Department of of Geology, Geology,Hope Hope College, College,Holland, Holland, VANDER MI 49423) 49423) MI BRANDSMA, BRANDSMA, DANIEL DANIEL (Department (Departmentof of Geological Geological Sciences, Sciences,University University of of Southern SouthernCalifornia, California,Los LosAngeles, Angeles,CACA90089) 90089) The Peavy Peavy Pond Pond Complex Complex(PVC), (PVC), located located'^ 12km 12km NW NW from from Iron Iron Mountain Mountain The in in northern northern Michigan, Michigan, is is comprised comprised predominantly predominantly of of gabbroic gabbroic and and dioritic dioritic intrusive intrusiverocks rocksexposed exposedin inan anarea area14km2. 14km2 It It is is interpreted interpreted as as aa sill-like sill-likebody body which which is is intrusive intrusive into into the the base base of of the the Michigamme Michigamme Fm Fm and and whose whose base base is is crudely crudely conformable conformable with with the the top top of of the the underunderlying Hemlock HemlockFm. Fm. lying . We We have have calculated calculated the the solidification solidificationpositions positions inside, inside,and and tempertemperature ature outside outside the the pluton pluton assuming assuming the the temperature temperatureof of emplacement emplacement of of the the magma magma is is % 1000°C 1000OC and and aa latent latent heat heat of of solidification solidification (AH) (AHs)asas % 100 100cal/gm. cal/gm. For For aa one-dimensional one-dimensional model, model, in in which which aa 3.2km 3.2km thick thick pluton pluton extending extending infinitely infinitelydownwards downwards cools cools by by conduction: conduction:the the 800°C 800° solidification 10 xx 10 103yrs yrs solidification position position is is .34km .34km from from the the contact contact after after % 10 during during which which time time the the maximum maximum temperature temperature reached reached at at the the contact contact is is In In this this model, model, the the PVC PVC is is completely completely solidified solidified 231 231 xx 103 103 yrs yrs 678'~. 678°C. after intrusion. intrusion. If If convection convection occurs occurs during during cooling, cooling, the the maximum maximum after temperature temperature at at the the contact contact is is 888°C 888% and and convection convection persists persists for for two-dimensional model model for for aa rectangular rectangular pluton pluton 157-x lo3 years. years. AA two-dimensional l57x (3.2 4.4km) produces produces maximum maximum contact contact temperatures temperaturesof ofonly only4970C. 497OC. (3.2 xx 4.4km) Temperatures Temperatures at at positions positions outside outside the the pluton, pluton, in in the the Michigamme Michigamme Fm, Fm, were calculated calculated from fromthe theone-dimensional one-dimensionalmodels. models. At At 2.6km 2.6km from from the the were contact, contact, aa position position corresponding corresponding to to the the mapped mapped staurolite staurolite isograd, isograd, the i3 yrs yrs is is 302°C, 302OC, during during the maximum maximum temperature temperature reached after 486 xx 103 cooling by by conduction. conduction. The The 5000C 5000C isotherm isotherm advances advances to to aa maximum maximum cooling distance of of % .78km .78km from from the the contact, contact, reaching reaching that that position position distance lo3years. years. During During cooling cooling involving involving convection, convection, the the after 76 76 xx iü after l.lkm from from the the contact, contact, maximum advance advance of of the the 500°C 500OC isotherm isotherm is is % 1.1km maximum lo3 yrs yrs after after intrusion, intrusion, and and the the maximum maximum temperature temperature arriving 100 100 xx i03 arriving reached at at the the staurolite stauroliteisograd isograd is is349°C. 349OC. reached The The calculated calculated temperatures temperatures (T) (T) outside outside the the pluton pluton are are much much lower lower than the the T-conditions T-conditions of of the the observed observed metamorphic metamorphiczones. zones. For For example, example, than the the temperature temperature for for the the staurolite staurolite isograd isograd is is estimated estimated from from the the garnet-biotite geothermometer geothermometer to to be be 540°C. 540°C Moreover, Moreover, the the T-gradient T-gradient garnet-biotite due to to thermal thermal effect effect of of PVC PVC is is % 80°C/km 80°C/k whereas whereas the the T-gradient T-gradient due 370C/km. inferred from from the the spacing spacing of of metamorphic metamorphic isograds isograds is is % 370C/km. inferred �4 The The Structure S t r u c t u r e of of the t h e Slate S l a t e Islands I s l a n d s Area Area of of Lake Lake Superior Superior M. E. E. Bengtson Bengtson and and R. R. P. P. Meyer Meyer (Geophysical (Geophysical and and Polar P o l a r Research Research M. Center, Department of of Geology Geology and and Geophysics, Geophysics, University U n i v e r s i t y of of C e n t e r , Department Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, WI W I 53706) 53706) H. H. C. C. Halls H a l l s (Erindale ( E r i n d a l e College, College, Mississauga, Mississauga, Ontario, O n t a r i o , Canada, Canada, and and Canada) Department Department of of Geology, Geology, University U n i v e r s i t y of of Toronto, Toronto, Canada) The The origin o r i g i n of of the t h e Slate S l a t e Islands I s l a n d s structure s t r u c t u r e of of northern n o r t h e r n Lake Lake Some propose the islands S u p e r i o r is i s the t h e subject s u b j e c t of of debate. d e b a t e . Some propose t h e i s l a n d s are are Superior the t h e result r e s u l t of of meteoritic m e t e o r i t i c impact impact while w h i l e others o t h e r s advocate a d v o c a t e an an endogenous endogenous marine magnetic magnetic and and seismic s e i s m i c survey survey was was undertaken undertaken to to o r i g i n . AA marine origin. examine this t h i s question. question. examine Over Over 1,500 1,500 km km of of magnetic magnetic and and 3.5—kHz 3.5-kHz sonic s o n i c profiles p r o f i l e s were were taken. taken. The The sonic s o n i c data d a t a have have been been used used to t o construct c o n s t r u c t aa bedrock bedrock bathymetry bathymetry map, i s similar s i m i l a r to t o aa bottom bottom bathymetry bathymetry map map constructed c o n s t r u c t e d from from map, which which is Both show show aa d a t a taken t a k e n by by the t h e Canadian Canadian research r e s e a r c h vessel v e s s e lBayfield. B a y f i e l d . Both data concentric c o n c e n t r i c pattern p a t t e r n centered c e n t e r e d on on the t h e islands. i s l a n d s . However, However, the t h e bedrock bedrock The sonic data topography topography exhibits e x h i b i t s almost almost 50% 50%greater g r e a t e r relief. r e l i e f . The s o n i c data also a l s o indicate i n d i c a t e that t h a t the t h e bedrock bedrock is i s more more chaotic c h a o t i c inside i n s i d e the t h e bathybathym e t r i c high h i g h that t h a t surrounds s u r r o u n d sthe t h eislands. islands. metric curvilinear AA magnetic magnetic contour c o n t o u r map map has h a s also a l s o been been constructed. c o n s t r u c t e d . AA curvilinear north—south n o r t h - s o u t h trending t r e n d i n g magnetic magnetic gradient g r a d i e n t east e a s t of of the t h e islands i s l a n d s marks marks the t h e boundary boundary between between the t h e Port P o r t Coldwell Coldwell complex complex and and Archean Archean basement basement It appears a p p e a r s that t h a t the t h e Port P o r t Coidwell Coldwell complex complex extends e x t e n d s at a t least least r o c k s . It rocks. km iinto n t o the t h e lake. l a k e . Short—wavelength Short-wavelength anomalies anomalies on on the t h e east e a s t side side 25 kin 25 of of the t h e islands i s l a n d s have have half—widths h a l f - w i d t h s that t h a t indicate i n d i c a t e source s o u r c e depths d e p t h s 1/2 112 to to These may may well w e l l be b e feeders f e e d e r s for f o r the the km below below the t h e lake l a k e surface. s u r f a c e . These 11 km P o r t Coidwell Coldwell complex. complex. Port West West of of the t h e islands, i s l a n d s , aa northwest—trending n o r t h w e s t - t r e n d i n g linear l i n e a r anomaly anomaly has h a s been been This T h i s is i s most most likely l i k e l y due due to t o aa basin—bounding basin-bounding fault, f a u l t , with with it. Keweenawan volcanics v o l c a n i c s lying l y i n g only o n l y south s o u t h of of it. Keweenawan identified. identified. This Finally, F i n a l l y , the t h e islands i s l a n d s seem seem to t o be b e surrounded surrounded by by aa magnetic magnetic low. low. This is i s consistent c o n s i s t e n t with w i t h an an arcuate a r c u a t e increase i n c r e a s e in i n depth d e p t h to t o aa coherent c o h e r e n t magmagn e t i c basement basement centered c e n t e r e d on on the t h e islands. islands. netic Over Over 250 250 km km of of explosion e x p l o s i o n seismic s e i s m i c reflection r e f l e c t i o n and and refraction r e f r a c t i o n lines lines of aa Twenty-five km km east e a s t of of the t h e islands, i s l a n d s , over over 700 700 mm of were taken. taken. Twenty—five were 3.5—km/s 3.5-km/s material m a t e r i a l overlies o v e r l i e s about about 500 500 mm of of aa 4.5—km/s 4.5-km/s material. material. These These velocities v e l o c i t i e s have have been been correlated c o r r e l a t e d with w i t h the t h e Bayfield—Jacobsville Bayfield-Jacobsville s a n d s t o n e s and and the t h e Oronto Oronto Group, Group, respectively. r e s p e c t i v e l y . These These sediments sediments sandstones overlie o v e r l i e aa 5.8—km/s 5.8-km/s refractor, r e f r a c t o r , which which is i s the t h e Port P o r t Coldwell Coldwell complex. complex. Twelve Twelve km km west west of of the t h e islands, i s l a n d s , the t h e sediments sediments thin t h i n to t o aa total total t h i c k n e s s of of less l e s s than t h a n 500 500 m. m. Here Here they t h e y overlie o v e r l i e aa 6.1—km/s 6.1-km/s refractor, refractor, thickness which is i s probably probably the t h e Archean Archean basement. basement. This T h i s thinning t h i n n i n g suggests s u g g e s t s that that which the Archean basement basement rocks. rocks. t h e islands i s l a n d s lie l i e onapre—Keweenawan onapre-Keweenawan ridge r i d g e of of Archean All A l l refractors r e f r a c t o r s outside o u t s i d e the t h e peripheral p e r i p h e r a l trough t r o u g h have have aa southerly s o u t h e r l y dip. dip. �5 The The Structure S t r u c t u r e of of the t h e Slate S l a t e Islands I s l a n d s Area Area of of Lake Lake Superior S u p e r i o r (continued) (continued) In Here I n the t h e trough, t r o u g h , there t h e r e is i s some some evidence e v i d e n c e of of minor minor faulting. f a u l t i n g . Here only o n l y small s m a l l amounts amounts of of Bayfield—Jacobsville B a y f i e l d - J a c o b s v i l l e sandstones s a n d s t o n e s remain. remain. However, However, up up to t o 11 km km of of aa material m a t e r i a l with w i t h apparent a p p a r e n t velocities v e l o c i t i e s of of 4.2 4.2 t o 4.5 4.5 km/s exists. e x i s t s . This T h i s represents r e p r e s e n t s either e i t h e r Oronto Oronto Group Group material material to Below this t h i s material m a t e r i a l is i s aa refractor refractor or o r some some type t y p e of of crater c r a t e r breccia. b r e c c i a . Below T h i s is i s probably probably with w i t h apparent a p p a r e n t velocities v e l o c i t i e s of of about about 5.5 5.5 km/s. km/s. This fractured f r a c t u r e d Archean Archean basement. basement. Minor Minor faulting f a u l t i n g southwest southwest of of the t h e islands i s l a n d s has h a s also a l s o been been observed. observed. The sense s e n s e of of motion is i s consistent c o n s i s t e n t with w i t h the t h e interpretation i n t e r p r e t a t i o n of of aa basin—bounding basin-bounding fault f a u l t with w i t h the t h e basin b a s i n to t o the t h e south. south. In I n summary, summary, the t h e magnetic and seismic s e i s m i c data d a t a indicate i n d i c a t e aa morphology that t h a t supports s u p p o r t s the t h e impact impact origin o r i g i n hypothesis, h y p o t h e s i s , although a l t h o u g h an a n endogenous endogenous origin o r i g i n cannot cannot be b e completely completely ruled r u l e d Out. out. �6 Gneiss Domes and Not—5o—Gneiss Not-So-Gneiss domes in i n the the Penokean Terranes T e r r a n e s of of Northern Wisconsin BROWN, BROWN, B.A. B.A. (Wisconsin (Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 W I 53705—4096) 53705-4096) 1815 University U n i v e r s i t y Ave., Ave., Madison, Madison, WI GREENBERG, J.G. J . G . (Wisconsin (Wisconsin Geological G e o l o g i c a l and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 1815 University U n i v e r s i t y Ave., Ave., Madison, Madison, WI W I 53705—4096) 53705-4096) The Northern Penokean terrane t e r r a n e (NPT) (NPT) and and the t h e Penokean Penokean volcanic volcanic belt b e l t (PVB) (PVB) of of northern n o r t h e r n Wisconsin Wisconsin are a r e each each characterized c h a r a c t e r i z e d by by aa distinct d i s t i n c t type type of major major gneissic g n e i s s i c pluton. p l u t o n . The The Northern Northern Penokean Penokean terrane t e r r a n e is i s intruded i n t r u d e d by by aa series s e r i e s of of mantled mantled gneiss g n e i s s domes. domes. These These bodies b o d i e s are a r e gneiss g n e i s s domes domes in i n the t h e true t r u e sense, s e n s e , consisting c o n s i s t i n g of of Archean Archean (up b.y. old) (up to t o 3.5 3.5 b.y. o l d ) granitic g r a n i t i c rocks r o c k s which were remobilized and ememplaced p l a c e d at a t their t h e i r present p r e s e n t crustal c r u s t a l level l e v e l during d u r i n g the t h e Penokean Penokean Orogeny Orogeny (1850 The domes domes are a r e mantled by metasedimentary rocks r o c k s of of (1850 m.y. m.y. ago). ago). The the t h e Marquette Range Range Supergroup, Supergroup, and and their t h e i r outlines o u t l i n e s are a r e clearly c l e a r l y dedelineated l i n e a t e d by by the t h e magnetic magnetic expression e x p r e s s i o n of of the t h e iron i r o n formations. formations. The The Penokean Penokean volcanic v o l c a n i c belt b e l t contains c o n t a i n s large l a r g e foliated f o l i a t e d granitic g r a n i t i c bodies bodies of of aa distinctly d i s t i n c t l y different d i f f e r e n t character. c h a r a c t e r . The The gneisses g n e i s s e s and and granites granites themselves themselves are a r e superficially s u p e r f i c i a l l y similar s i m i l a r to t o those t h o s e in i n the t h e NPT, NPT, but b u t isoisotopic m.y. Also, Also, t o p i c evidence evidence suggests s u g g e s t s ages ages ranging r a n g i n g from from 1760 1760 to t o 2000 2000 m.y. these t h e s e rocks rocks are a r e intrusive i n t r u s i v e into i n t o greenschist g r e e n s c h i s t facies f a c i e s metavolcanic rocks. r o c k s . The The domes domes in i n the t h e NPT were formed formed in i n aa region r e g i o n of of amphibolite amphibolite faèies f a c i e s metamorphism. metamorphism. The The gneissic g n e i s s i c rocks rocks of of the t h e PVB PVB are a r e complex, complex, multiphase m u l t i p h a s e plutonic p l u t o n i c bodies, b o d i e s , probably probably representing r e p r e s e n t i n g magma magma emplaced emplaced at at aa deep deep crustal c r u s t a l level, l e v e l , which which rose r o s e diapirically d i a p i r i c a l l y to t o form form large l a r g e concorconcordant I t has h a s been been suggested suggested by by other o t h e r authors a u t h o r s that t h a t gneisses gneisses d a n t plutons. p l u t o n s . It in i n the t h e PVB PVB represent r e p r e s e n t basement basement to t o the t h e volcanic v o l c a n i c sequence. sequence. If I f this t h i s is is the t h e case, c a s e , they they must be b e only only slightly s l i g h t l y older o l d e r or o r their t h e i r isotopic i s o t o p i c syssystems tems must have have been been thoroughly thoroughly homogenized during d u r i n g the t h e Penokean Penokean to to account account for f o r the t h e apparent a p p a r e n t lack l a c k of of Archean ages ages so s o common common in i n the t h e NPT NPT gneisses. gneisses . We We suggest s u g g e s t that t h a t the t h e gneissic g n e i s s i c plutons p l u t o n s of of the t h e PVB PVB are a r e comparable comparable in in overall o v e r a l l aspect a s p e c t to t o the t h e large l a r g e composite composite batholiths b a t h o l i t h s typical t y p i c a l of of Archean Archean Greenstone Greenstone belts b e l t s of of the t h e Superior S u p e r i o r Province. Province. The The nature n a t u r e of of the t h e plu— plutons, t o n s , when when considered c o n s i d e r e d with w i t h the t h e localized l o c a l i z e d nature n a t u r e of of the t h e metamorphism metamorphism and and the t h e chemical chemical character c h a r a c t e r of of the t h e metavolcanic rocks r o c k s argues a r g u e s for for comparison comparison of of the t h e PVB PVB with w i t h greenstone g r e e n s t o n e belts b e l t s of of known known Proterozoic Proterozoic age, a g e , such such as a s Flin F l i n Flon Flon and and Lynn Lynn Lake Lake in i n Canada. Canada. The The contrast c o n t r a s t in i n the t h e character c h a r a c t e r of of plutonism plutonism further f u r t h e r underscores underscores the imt h e differences d i f f e r e n c e s between between the t h e NPT NPT and and the t h e PVB, PVB, and and emphasizes emphasizes the t h e importance p o r t a n c e of of the t h e Niagara Niagara tectonic t e c t o n i c zone zone as a s aa fundamental fundamental boundary boundary separating s e p a r a t i n g these t h e s e terranes. terranes. �7 Paleomagnetic Paleomagnetic and and Magnetic Magnetic Anomaly Anomaly Studies Studies of of the the Northwestern Northwestern Duluth Duluth Complex, Lake Lake County, County, Minnesota Minnesota Complex, VAL W. CHANDLER CHANDLER (Minnesota (Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. VAL W. Paul, MN MN 55108) 55108) Paul, The The effect effect of of remanent remanent magnetization magnetization on on magTletic magnetic anomaly expression expression was was investigated investigated for for the the Bald Bald Eagle Eagle intrusion, intrusion, aa composite composite body body in in the the northwestern northwestern Duluth Duluth Complex. Complex. Unlike Unlike most most of of the the Duluth Duluth Complex, Complex, this this (30 1cm2) intrusion intrusion is is well well exposed exposed and and is is known known to consist (30 km2) consist of of an an outer outer (11 by 4 km) ring of of troctolitic troctolitic rocks rocks surrounding surrounding aa gabbroic gabbroic core. core. (11 km) ring The The magnetic magnetic anomaly anomaly expression expression in in the the area area does does not not correspond correspond to to either either the the Bald Bald Eagle Eagle intrusion intrusion or or surrounding surrounding features features in in that that indiindividual vidual anomalies anomalies appear appear to to be be shifted shifted eastward eastward from from their their probable probable sources. Broad, Broad, large—amplitude large-amplitude (>2000 02000 gammas) gammas) minima minima occur occur over over sources. parts impling that that reversely reversely polarized polarized parts of of the the Bald Bald Eagle Eagle intrusion intrusion impling rocks may may be be present. present. However, However, measured remanent remanent magnetizations magnetizations for for rocks oriented samples from five sites in the troctolitic oriented samples from five sites in the troctolitic rocks rocks and and two two sites sites in in the the gabbroic gabbroic rocks rocks indicate indicate that that the the Bald Bald Eagle Eagle intrusion intrusion actually has a remanent magnetization directed essentially actually has a remanent magnetization directed essentially along along the the average = 290°, 290° inclination inclination = 40°) 40° for for average normal normal direction direction (declination (declination = Keweenawan rocks rocks in in Minnesota. Minnesota. Thus, Thus, the the large large magnetic magnetic minima minima must must Keweenawan represent represent either either aa deep—seated deep-seated or or aa regional—scale regional-scale anomaly anomaly effect. effect. Remanent Remanent magnetization magnetization was was observed observed to to be be generally generally much much stronger stronger values in excess of 5 were than induced induced magnetization magnetization and and QQ values in excess of 5 were common. common. than To To correct correct for for the the anomaly anomaly effect effect of of the the strong strong remanent remanent magnetizamagnetization, reduction—to—pole filtering was done on a detailed tion, reduction-to-pole filtering was done on a detailed grid grid of of aeroaeromagnetic magnetic data data over over the the intrusion. intrusion. It It was was assumed assumed that that remanence remanence was was everywhere everywhere much stronger stronger than than induced induced magnetization magnetization and and total total polaripolarization 290 and and inclinainclinazation was was therefore therefore directed directed along along aa declination declination of of 290° tion of of 40°. 40° The The data data reduced reduced to to the the pole pole showed showed aa much much improved improved tion correspondence correspondence to to the the mapped mapped contacts contacts of of the the Bald Bald Eagle Eagle intrusion, intrusion, as as well as as to to contacts contacts of of several several surrounding surrounding features. features. Further Further proprowell cessing cessing of of the the reduced reduced data data by by high—pass high-pass filtering filtering revealed revealed intricate intricate structures structures within within individual individual rock rock units, units, and and appears appears to to have have isolated isolated a a previously previously unreported unreported fault fault intersecting intersecting the the Bald Bald Eagle Eagle intrusion intrusion and and extending extending northwestward northwestward at at least least as as far far as as the the basal basal contact contact zone zone of of the the Duluth Duluth Complex. Complex. The The results results of of this this study study demonstrate demonstrate the the power power of of reduction reduction to to the the pole pole in in accounting accounting for for complications complications arising arising i— from from strong strong remanent remanent magnetization. magnetization. The The procedure procedure should shouldsignif significantly cantly enhance enhance magnetic magnetic interpretations interpretations over over large, large, poorly poorly exposed exposed parts of of the the Duluth Duluth Complex. Complex. parts Alternating Alternating field field demagnetization demagnetization in in aa few few samples samples implies implies several several secondary secondary components, components, including including one one that that appears appears to to be be directed directed westwestward ward at at aa shallow shallow inclination. inclination. This This component component is is similar similar in in direction direction to to an an overprint overprint reported reported in in Michigan Michigan for for the the Copper Copper Harbor Harbor Conglomerate Conglomerate and and further further investigation investigationis is warranted. warranted. �8 An Ordovician O r d o v i c i a n Cryptoexplosion c r y p t o e x p l o s i o n Structure Structure An From Near Near Rock Rock Elm, Elm, Pierce P i e r c e County, County, Wisconsin Wisconsin From WILLIAM S. S . CORDUA, CORDUA, (Department (Department of o f Plant P l a n t and a n d Earth E a r t h Science, S c i e n c e , University university WILLIAM W I 54022) 54022) o f Wisconsin—River W i s c o n s i n - R i v e r Falls, F a l l s , River R i v e r Falls, F a l l s , WI of An An apparent a p p a r e n t cryptoexplosion c r y p t o e x p l o s i o n structure s t r u c t u r e centered c e n t e r e dnear n e a rRock RockElm, Elm, Pierce i s nearly n e a r l y circular c i r c u l a r with w i t h aa diameter d i a m e t e r of o f 6.5 6.5 P i e r c e County, County, Wisconsin W i s c o n s i n is k i l o m e t e r s and a n d an a n area a r e a of o f about a b o u t 33 33 km2. km 2 . The The structure s t r u c t u r e coincides coincides kilometers with pronounced reqional r e g i o n a l negative n e g a t i v e gravity g r a v i t y anomaly. anomaly. It I t is i s surrounded surrounded w i t h aa pronounced by by Prairie P r a i r i e du d u Chien Chien Group Group dolomites d o l o m i t e s which which are a r e folded, f o l d e d , faulted, f a u l t e d , and and brecciated b r e c c i a t e d within w i t h i n aa few few hundred h u n d r e d meters m e t e r s of o f the t h e edge e d g e of o f the t h e structure. structure. This i s particularly p a r t i c u l a r l y intense i n t e n s e within w i t h i n aa large, l a r g e , arcuate, arcuate, T h i s deformation d e f o r m a t i o n is fault-bounded f a u l t - b o u n d e d block b l o c k along a l o n g the t h e southern s o u t h e r n edge e d g e of o f the t h e structure. s t r u c t u r e . The The rocks r o c k s within w i t h i n the t h e structure s t r u c t u r e consist c o n s i s t of o f an a n unusual u n u s u a l sedimentary s e d i m e n t a r ysection. section. The exposed e x p o s e d base b a s e of o f the t h e section s e c t i o n is i s aa conglomeratic c o n g l o m e r a t i c quartz q u a r t z arenite arenite The containing c o n t a i n i n g chert, c h e r t , dolomite, d o l o m i t e rrhyolite, h y o l i t e , granite g r a n i t e and a n d quartzite q u a r t z i t e clasts. clasts. This T h i s unit u n i t forms forms aa domal domal uplift u p l i f t in i n the t h e middle m i d d l e of o f the t h e cryptoexplosion cryptoexplosion i s apparently a p p a r e n t l y overlain o v e r l a i n by by over over s t r u c t u r e . The The conglomeratic c o n g l o m e r a t i c sandstone s a n d s t o n e is structure. 30 meters m e t e r s of o f interbedded i n t e r b e d d e d grey g r e y pyritiferous p y r i t i f e r o u s shale s h a l e and and bioturbated bioturbated 30 T h i s in i n turn t u r n is i s overlain o v e r l a i n by by 77 meters m e t e r s of of f i n e - g r a i n e d quartz q u a r t z arenite. a r e n i t e . This fine—grained medium—bedded m e t e r s of o f massive, massive, medium-bedded fine—grained f i n e - g r a i n e d quartz q u a r t z arenite, a r e n i t e , 55meters friable a t least l e a s t 22 meters m e t e r s of o f ferruginous, f e r r u g i n o u s , medium— mediumf r i a b l e quartz q u a r t z arenite, a r e n i t e , and a n d at g r a i n e d quartz q u a r t z arenite. a r e n i t e . Lower Lower to t o middle m i d d l e Ordovician O r d o v i c i a n gastropods g a s t r o p o d s have have grained reportedly r e p o r t e d l y been b e e n found f o u n d in i n concretions c o n c r e t i o n s in i n the t h e shale, s h a l e , suggesting s u g g e s t i n g that that it i t is i s an a n anomalously a n o m a l o u s l y thick t h i c k section s e c t i o n of o f the t h e Readstown Readstown Member Member of o f the the S t . Peter P e t e r Formation. F o r m a t i o n . The The overlying o v e r l y i n g sands s a n d s could c o u l d thus t h u s correlate c o r r e l a t e with with St. T o n t i Member Member of o f the t h e St. S t . Peter P e t e r Formation, F o r m a t i o n , aa conclusion c o n c l u s i o n supported supported t h e Tonti the The shales s h a l e s and a n d other other by grain g r a i n size s i z e analysis a n a l y s i s and and heavy h e a v y mineral m i n e r a l studies. s t u d i e s . The by rocks r o c k s within w i t h i n the t h e cryptoexplosion c r y p t o e x p l o s i o n structure s t r u c t u r e have h a v e not n o t been been deformed deformed to to the Chien Formation F o r m a t i o n and and the t h e con— cont h e extent e x t e n t of o f the t h e surrounding s u r r o u n d i n g Prairie P r a i r i e du du Chien g l o m e r a t i c sandstones s a n d s t o n e s of o f the t h e central c e n t r a l dome. dome. glomeratic Diamonds Diamonds and and gold g o l d were reportedly r e p o r t e d l y found f o u n d in i n the t h e 1880's 1 8 8 0 ' s in i n the t h e gravels gravels from f r o m sixeams streams ddraining r a i n i n g tthe h e sstructure, t r u c t u r e , suggesting s u g g e s t i n g possible p o s s i b l e erosion e r o s i o n of of m i n e r a l i z e d bedrock. b e d r o c k . AA reconnaissance r e c o n n a i s s a n c e ground g r o u n d magnetic m a g n e t i c study s t u d y has has mineralized d e l i n e a t e d aa positive p o s i t i v e magnetic m a g n e t i c anomaly anomaly associated a s s o c i a t e d with w i t h the t h e northnorthdelineated w e s t e r n edge edge of o f the t h e structure, s t r u c t u r e , upstream u p s t r e a m from from the t h e former f o r m e r placer placer western I t is i s possible, p o s s i b l e , however, however, that t h a t the t h e minerals m i n e r a l s were w e r e eroding eroding o p e r a t i o n s . It operations. f r o m aa red r e d drift d r i f t cap c a p that t h a t partially p a r t i a l l y covers c o v e r s the t h e structure. s t r u c t u r e . So So far, far, from heavy heavy mineral m i n e r a l studies s t u d i e s of o f the t h e stream s t r e a m sediments s e d i m e n t s have h a v e yet y e t to t o turn t u r n up up any anomalies a n o m a l i e s that t h a t could c o u l d be b e related r e l a t e d to t o the t h e erosion e r o s i o n of o f mineralized mineralized any b e d r o c k or o r poorly p o o r l y exposed e x p o s e d plutons. plutons. bedrock i n c l u d e the the I m p o r t a n t constraints c o n s t r a i n t s on on the t h e structure's s t r u c t u r e ' s origin o r i g i n include Important circular c i r c u l a r shape, s h a p e , the t h e otherwise o t h e r w i s e undeformed nature n a t u r e of o f the t h e Paleozoic Paleozoic bedrock b e d r o c k in i n the t h e region, r e g i o n , and and the t h e post-Shakopee, p o s t - S h a k o p e e , pre-Readstown pre-Readstown timing timing o f the t h e intense i n t e n s e deformation. d e f o r m a t i o n . This T h i s Ordovician o r d o v i c i a n deformation d e f o r m a t i o n and a n d subsubof sequent s e q u e n t erosion e r o s i o n produced p r o d u c e d aa deep d e e p circular c i r c u l a r lowland l o w l a n d that t h a t progressively progressively filled f i l l e d with w i t h clay, c l a y , silt, s i l t , and and sand s a n d during d u r i n g St. S t . Peter P e t e r time. t i m e . The The strucstructure t u r e could c o u l d represent r e p r e s e n t an a n isolated i s o l a t e d explosive e x p l o s i v e volcanic v o l c a n i c feature, f e a t u r e , however, however, �9 of volcanic material does not tthe h e lack lack o f v olcanic m a t e r i a l anywhere in i n tthe h e region region d oes n o t ssupport upport tthis h i s interpretation. interpretation. A l t e r n a t i v e l y , the t h e structure s t r u c t u r e could c o u l d be b e an a n OrdoOrdoAlternatively, vician with Wells i t h sediment, s e d i m e n t , similar s i m i l a r to t o tthe he W ells v i c i a n astrobleme a s t r o b l e m e tthat h a t later l a t e r filled filled w Creek C r e e k and a n d Flynn F l y n n Creek structures s t r u c t u r e s in i n Tennessee. Tennessee. IIf f pplutonism l u t o n i s m and mineralization occurred have m ineralization o c c u r r e d in i n the t h e rregion, e g i o n , tthe h e pplutonism l u t o n i s m could could h a v e bbeen een triggered t r i g g e r e d by the t h e impact. i m p a c t . Alternatively, A l t e r n a t i v e l y , later l a t e r plutonism p l u t o n i s m and and mineralimineraliby ddeep—seated zzation a t i o n ccould o u l d hhave a v e bbeen e e n ccontrolled o n t r o l l e d by e e p - s e a t e d ffractures r a c t u r e s pproduced roduced So far, by the t h e impact. impact. f a r , however, however, no n o plutonic p l u t o n i c rocks r o c k s or o r features features characteristic of origin, orr characteristic o f iimpact mpact o r i g i n , such s u c h as a s shattercones, s h a t t e r c o n e s , ssuevites, uevites, o have been E l m structure. structure. A eejecta j e c t a bblankets lankets h ave b e e n found in i n or o r near n e a r the t h e Rock Rock Elm t h i r d alternative a l t e r n a t i v e is i s that t h a t the t h e structure s t r u c t u r e is i s related r e l a t e d to t o uplift u p l i f t and third differential d i f f e r e n t i a l weathering w e a t h e r i n g around a r o u n d aa large l a r g e unexposed unexposed pre—Readstown pre-Readstown pluton. pluton. Further F u r t h e r geologic g e o l o g i c studies, s t u d i e s , including i n c l u d i n g drilling, d r i l l i n g , heavy heavy mineral m i n e r a l analyses, analyses, seismic needed tto s e i s m i c arid and oother t h e r ggeophysical e o p h y s i c a l sstudies t u d i e s aare r e needed o further f u r t h e r elucidate elucidate the i n t e r e s t i n g structure. structure. t h e origin o r i g i n and and nature n a t u r e of o f this t h i s interesting �10 ULTRAMETAMORPHISM ULTRAMETAMORPHISM AND AND MIGMATITE THE MIGMATITE GENERATION GENERATION IN IN THE VERMILION GRANITE GRANITE COMPLEX, NORTHERN MINNESOTA VERMILION Warren C. (Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. C- Day Day (Minnesota Minnesota 55108) 55108) Paul, Minnesota Paul, ABSTRACT ABSTRACT The 2,700—m.y.—old The 2,700-m.y.-old Vermilion Vermilion Granitic Granitic Complex Complex (VGC) (VGC)is is aa granite—migma-qranite-migmatite terrane tite terrane consisting consisting of aa supracrustal supracrustal sequence sequence of biotite biotite schist, schist, tonalite, and The granite garnet—bearing tonalite, and granite. granite. The granite is is of of two two types: types: garnet-bearing two—mica leucogranite two-mica leucogranite (LEUG) (LEUG) and and the the biotite-bearing biotite-bearing Lac Lac La La Croix Croix Granite Granite (LLCG). The The syntectonic syntectonic LEUG LEUG occurs occurs as as stringers stringers and and small small bodies bodies within within (LLCG). the biotite the biotite schist, schist, forming forming the the neosome neosomeof ofschist-rich schist-richmiginatite. migmatite. The The LLCG LLCG supracrustal country rocks, forming neosome of granite— graniteintrudes the supracrustal forming the neosome rich rich migmatite migmatite and and the the batholithic batholithic part part of of the the VGC. VGC. Metamorphic Metamorphic and and geochemical studies elucidate the petrogenesis of these geochemical studies were undertaken to elucidate granite granite neosomes neosomes along along the the northern northern border of the the VGC in in the the Kabetogama Kabetogama Lake area. Lake area. Three MI was was the the main main Three phases phases of of metamorphism metamorphism affected affected the the area. area. Ml regional was a a post—tectonic post-tectonic event event produced produced by by prograde event, event, and and M2 was regional prograde was a late—stage deuteric late-stage deuteric alteration. alteration. M3 was a metamorphic metamorphic recrystallization recrystallization event event along along the the major major bounding bounding faults. faults. The The regional regional Ml M1 metamorphic metamorphic conconditions ditions were were estimated estimated from from the the mineral mineral assemblages assemblages in in the the biotite biotite schist. schist. Petrographic Petrographic evidence evidence indicates indicates that that Ml MI exceeded exceeded the the breakdown breakdown reaction reaction + H20 + QTZ = H2O and the STAR transformaSTAR ++ MUSCO MUSCO + = SIL BIO ++ GAR + the AND = = SIL SIL ++ BIO SIL transformaQTZ tion. tion. However, there is no evidence for the breakdown reaction reaction MUSCO + QTZ = H20. The The data data indicate indicate that that peak peak regional regional Ml MI conditions conditions = SIL SIL ++ K-SPAR ++ H2O. ranged from to 55 kbar. kbar. These These conditions conditions Overlap overlap miniminiranged from 650°C 650° to to 700°C 700° and and 44 to conditions (Ptotal (total = schist, implying an mum melting conditions - PHlo) of the biotite schist, implying H2o) anatectic anatectic origin origin for for the the LEUG. LEUG. The objective The objective of of the the geochemical geochemical studies studies was was to to determine determine if if any any comcompositional gradients attributed to to anatexis. anatexis. positional gradients in in the the migmatite migmatite can can be attributed Millimeter—scale samples Millimeter-scale samples were taken taken normal normal to to foliation foliation across across two two hypothesis that schist/restite/leucosome transitions transitions to test the hypothesis that the LEUG melted from from the the biotite biotite schist, schist, leaving leaving the the restite restite margin margin as as aa residual residual wisp of of LEUG LEUG neosome, neosome, and another phase. One One traverse traverse crossed crossed an an8—trim—wide 8-mm-wide wisp another transected transected the the interface interface between between aa larger larger vein vein of of LEUG LEUG neosome neosome and and biotite biotite Small cores were drilled schist. (6 mm, 2 g) were drilled and analyzed analyzed for for major and schist. Small cores (6 Corresponding modes (obtained trace trace elements. elements. Corresponding (obtained using plane polarized light light and indicate that that quartz quartz and and feldspar feldspar dominate the and cathodoluininescence) cathodoluminescence) indicate leucosome, leucosome, whereas biotite, apatite, apatite, and oxides oxides are concentrated concentrated in in the the restite margin. restite margin. Of these these minerals minerals only only apatite apatite would would concentrate concentrate the the rare— rareearth (REE) earth elements elements (PEE). . �11 The results results of of the the chemical chemical analyses analyses indicate: indicate: The 1 ) As expected, expected, the the major and and minor element element content content reflect reflect modal 1) variations across both both traverses. traverses. Therefore variations across MgO, FeOt, FeOt, 1(20, K20, Ti02, Zr, Co, Co, Therefore MgO, Ti02, Zr, Ni, Sc Na20 and Ni, Sc are are concentrated concentrated in in the the biotite-rich biotite-rich margin, whereas whereas NanO and Si02 SiOy are concentrated in in the the quartz quartz and and feldspar feldspar neosome. neosome. In both traverses, traverses, are concentrated the total REE abundances abundances are are greater greater in in the the schist schist and and restite restite margin than than the total in in the the neosome. neosome. The two 2) The two traverses traverses show show significant significant differences differences in in PEE REE profiles. profiles. These These 2) differences differences reflect reflect the the dynamic dynamic behavior behavior of of the the migmatite migmatite generation. generation. a) a) The narrow The narrow 8-mm 8-mm LEUG LEUG wisp wisp formed formed as as aa closed closed system. system. This is indiindiThis is cated cated by comparatively comparatively enriched enriched PEE REE abundances abundances in in the the apatite—rich apatite-rich restite restite margin. margin. b) b) The 5-cm LEUG LEUG vein vein formed formed as as an an open open system. system. The The expected expected The larger larger 5—cm REE enrichment REE enrichment in in the the apatite—rich apatite-rich restite restite margin was not not observed. Although both vein vein types types appear appear mineralogically similar, similar, they they formed formed under considerably considerably different different petrogenetic petrogenetic conditions. conditions. �12 Geological Characteristics of of the the Volcano—Sedimentary Volcano-Sedimentary Geological and Geochemical Geochemical Characteristics Glen Glen Township Township Formation, Formation, East—Central East-Central Minnesota Minnesota ABDELMONEM A. ELDOUGDOUG ELDOUGDOUG (Department (Department of of Geology Geology and and Geophysics, Geophysics, ABDELMONEM University University of of Minnesota, Minnesota, Minneapolis, Minneapolis,Minnesota Minnesota551155) 55455) Petrographic Petrographic study study of of twelve twelve drill drill cores cores reveals reveals that that the the Township Formation Glen Township Formation consists consists of of the the following: following: 1) slate, quartzites, 1) Pelitic slate, quartzites, and and metaconglomerates. metaconglomerates. 2) 2) Oolitic Oolitic jaspilite. jaspilite. magnetite—silicate—(minor carbonate carbonate and quartz) 3) Cherty and slaty magnetite-silicate-(minor facies Iron Iron Formation Formation (I.F.). facies (I.F.). 14)Pyrite, Pyrite, pyrite-pyrrohotite, pyrite—pyrrohotite, and and pyrrohotite pyrrohotite bearing graphitic 4) graphitic argillite—sulphide I.F. argillite-sulphide facies facies I.F. siderite—(minor silicate, silicate, magnetite, magnetite, and quartz) 5) Massive and banded siderite-(minor fades I.F. — carbonate carbonate facies I.F. 6) Ankerite bearing 6) Ankerite bearing feldspathic feldspathic metagreywacke. metagreywacke. 7) Metavolcanics (metaandesites, (metaandesites, metadiorites, crystal tuff). tuff). 7) metadiorites, and crystal - The The sequence sequence has has been assigned assigned to to the the lower lower part of of the the Mille Mille Lacs Lacs Group Group and was metamorphosed and deformed during during the the Penokean Penokean Orogeny Orogeny (,'1,900 to 1,850 (&1,900 1,850 m.y. m.y. ago). ago). Massive Massive quartz quartz veinlets veinlets containing containing pyrite, pyrite, siderite siderite and and minor minor chal— chalcopyrite are lower part of of the the copyrite are present present throughout throughout the the sequence. sequence. The lower pyrite or or pyrrhotite pyrrhotite mesobands graphitic argillite contains pyrite mesobands (up (up to to upper part of of this this argillite argillite 10 mm thick) and is 1 0 nun is highly highly folded. folded. The upper This horizon contains pyrite-pyrrhotite horizon. This horizon contains contains contains aa massive pyrite—pyrrhotite angular argillite and in angular fragments fragments of of graphitic argillite in some some places places appears appears to to indibe cemented by siderite, chlorite and quartz. Textural evidence indialteration cates that this horizon represents a site of hydrothermal alteration and and fracturing. fracturing. The in the the The occurrence occurrence of of sulphides sulphides as as highly folded folded mesobands mesobands in argillite indicates indicates that they are of syngenetic graphitic argillite syngenetic origin. (1968) and This is is in in accord with the conclusion reached by Han (1968) contrasts epigenetic origin originproposed proposed by by Theil Theil(19214) (1924) and and contrasts with with the the epigenetic Schwartz (1951). Schwartz (1951). Data on Au, Ag, Zn, Data Zn, Co, Co, Ni, Cu, Cu, and As in in the the different different iron iron forformation facies, facies, pyrite—siderite—quartz pyrite-siderite-quartz veinlets, veinlets, and associated associated rocks rocks The results results and preliminary preliminary models models of of are are presently presently being being collected. collected. The the distribution, distribution, and mobility of precious metals in this type of of geologic terrane will be discussed along with their implications implications for exploration. exploration. References References Han, Tsu-ming Tsu—ming (1968): ( 1968): Ore mineral relations in in the the Cuyuna Cuyuna sulphide sulphide Han, deposits, Minnesota. Mineraliuni Deposita (Berlin), v. 3, deposits, Minnesota. Mineralium Deposita (Berlin), v. 3,p. p. 109—1314. 109-134. Schwartz, Schwartz, G.M. G.M. (1951): (1951): Minnesota iron iron suiphide: sulphide: in in Mining Symposium, Symposium, Geology of of the the Cuyuna Cuyuna Range, Range, Univ. Minn. General General Ext. Div., Div., April April 1951, p. 1411—115. 1951, p. 44-45. Theil, Iron sulphides suiphides in magnetite magnetite belts Theil, G.A. G.A. (19211): (1924): Iron belts near near the the Cuyuna Cuyuna Range, Econ. Range, Econ. Geol., Geol., v.v.19, 19,p.p.1466—1472. 466-472. �13 Long-Wavelengt h G r a v i t y Anomalies in i n the t h e Great Great Lakes Region Long—Wavelength Gravity C. PATRICK PATRICK ERVIN (Dept. C. (Dept. of of Geology, Geology, Northern Northern Illinois I l l i n o i s University, University, DeKaib, DeKalb, IL 60115) 60115) To examine possible p o s s i b l e relationships r e l a t i o n s h i p s between the t h e sources s o u r c e s of of major gravitational g r a v i t a t i o n a l anomalies in i n central c e n t r a l North America, America, the t h e gravity g r a v i t y field field was digitized d i g i t i z e d at a t aa 40 40 km km interval i n t e r v a l to t o produce aa 60 60 x 40 40 grid. g r i d . Using tthe h e two-dimensional, a s a guide, g u i d e , these t h e s e data d a t a were then then two—dimensional, power spectrum as wavelength—filtered possible w a v e l e n g t h - f i l t e r e d to t o enhance p o s s i b l e continuities c o n t i n u i t i e s between the the regional r e g i o n a l anomalies. anomalies. The analysis a n a l y s i s reaffirms r e a f f i r m s the t h e lack l a c k of of any direct direct relationship r e l a t i o n s h i p between the t h e Kapuskasing Anomaly and the t h e anomalies to t o the the south. s o u t h . A deep—seated deep-seated continuity c o n t i n u i t y of of the t h e Midcontinent Gravity G r a v i t y High Basins tthrough h r o u g h tthe h e Michigan and Illinois Illinois B a s i n s and into i n t o the t h e Mississippi Mississippi i s implied i m p l i e d by by the t h e long—wavelength long-wavelength field. f i e l d . Inclusion I n c l u s i o n of of Embayment is wavelengths degrades degrades tthis but iintermediate n t e r m e d i a t e wavelengths h i s ccontinuity, ontinuity, b u t suggests s u g g e s t s tthe he presence of of a regional, r e g i o n a l , northwest—trending n o r t h w e s t - t r e n d i n g fracture f r a c t u r e system. system. �14 Three—dimensional Three-dimensional structure structure of of the the crust crust and and upper upper mantle mantle beneath beneath the the Lake Lake Superior Superior region region M.A. M.A. FEIGI4ER* FEIGHNER* (Dept. (Dept. of of Geology Geology and and Geological Geological Engrg., Engrg., Michigan Michigan Tech. University, University, Houghton, Houghton, MI MI 49931) 49931) Tech. The The structure structure of of the the crust crust and and upper upper mantle mantle was was investigated investigated by by the the use wave arrival arrival times times recorded by the Michigan— use of of tele.seismic teleseismic PP wave the Upper MichiganNorthern Northern Wisconsin Wisconsin (UNNW) (UMNW) Seismic Seismic Network. Network. Four Four methods methods were were used used to to decipher decipher the the structure structure of of the the crust crust beneath beneath the the region. region. They They were: were: travel travel time time residuals, residuals, apparent apparent velocity velocity (reciprocal (reciprocal of of slowness) slowness) and and azimuth azimuth values values calculated calculated for for events, events, ray ray tracing, tracing, and and three—dimensional three-dimensional inversion of of residuals. residuals. The The inversion inversion method method allowed allowed determination determination of of inversion velocity velocity variations variations in in the the mantle mantle to to depths depths of of 500 500 km. km. Results Results show show that that the the Mohorovcic Mohorovcic Discontinuity Discontinuity beneath beneath the the UMNW UMNW Network Network to to be be aa north—south north-south trending trending antiform, antiform, plunging plunging to to the the north north totowards the the axis axis of of the the Lake Lake Superior Superior syncline. syncline. Seismic Seismic station station MEW MEW (Mel— (Melwards len, len, Wisconsin), Wisconsin), located located on on the the eastern eastern flank flank of of the the Midcontinent Midcontinent GravGravity had events events that that arrived arrived 0.7 0.7 to 1.0 1.0 second earlier ity High High (MCII), (MGH), had earlier than than at at other other stations stations in in the the network. network. Inversion Inversion studies studies indicate indicate that that the the crust crust beneath beneath NEW MEW has has aa six six percent percent higher higher velocity velocity than than at at the the other other stations. From From ray ray tracing, tracing, the the crust crust was was also also found found to to be be thin thin near near stations. this station. station. Therefore, Therefore, aa high high velocity velocity material material underlying underlying the the MGH MGH Is is this suggested suggested with thinning thinning of the the crust crust of of about about 55 km. km. The The nature nature of of the the mantle mantle beneath beneath the the region region as as determined determined by by three— threedimensional dimensional seismic seismic inversion inversion indicate indicate that: that: (1) The upper upper mantle mantle beneath beneath portions portions of of the the MGH MGH may may be be denser denser (1) The than surrounding surrounding areas. areas. This This is is indicated indicated by by aa zone zone of of velocities velocities fastfastthan er than than the the layer layer average average in in the the40 40toto200 200kin km depth depth range. range. The The anomaly anomaly is is present in in the the gneiss gneiss terrane terrane in in northwestern northwestern Wisconsin Wisconsin but but disapdisapThis suggests suggests that that the the pears northward into into the the greenstone greenstone terrane. terrane. This velocity velocity structure structure in in the the upper upper mantle mantle beneath beneath the the MGH MGH is is dependent dependent upon upon basement basement terrane. terrane. (2) An An east—west east-west velocity velocity boundary boundary in in northern northern Wisconsin Wisconsin is is pres(2) ent ent in in the the 200 200 to to 350 350 km km depth depth range range of of the the mantle. mantle. The The boundary boundary has has aa lateral lateral extent extent of some some 300 300 km km and and could could represent represent an an ancient ancient suture suture rerelated lated to to the the collision collision of of plates plates during during the the Penokean Penokean orogeny. orogeny. This This also also suggests suggests that continental continental plates plates have have structures structures that that extend extend to to depths depths of of 350 350 km km and and are are stable stable for for periods periods of of time time of of 1.8 1.8 bIllIon billion years. years. (3) Shorter Shorter wavelength wavelength velocity velocity anomalies anomalies are are present present in in the the 350 350 (3) to 500 km depth 500 km depth range range and suggest suggest that that heterogeneities heterogeneities exist exist at at these these depths depths in in the the mantle. mantle. *Now at Chevron Chevron Geosciences, Geosciences, Houston, Houston, TX. TX. �15 Duluth Complex, Gravity and Magnetic Model Studies Studies of the Southern Southern Duluth Northeastern Minnesota Northeastern ROBERT J. FERDERER (Minnesota (Minnesota Geological 1633 Eustis Street, Street, Geological Survey, Survey, 1633 St. Paul, Paul, MN MN 55108) 55108) VAL VAL W. W. CHANDLER CHANDLER (Minnesota (Minnesota Geological Geological Survey, Survey, 1633 1633 Eustis Eustis Street, Street, St. St. Paul, MN 55108) 55108) Paul, MN JUDSON JUDSON MEAD MEAD (Dept. (Dept. of of Geology, Geology, Indiana Indiana University, University, Bloomington, Bloominqton, IN IN 47401) 47401) Large—amplitude gravity Large-amplitude gravity and magnetic anomalies anomalies are are associated associated with the dominantly mafic igneous middle Proterozoic Proterozoic the igneous rocks of the the middle Two—dimensional gravity (Keweenawan Supergroup) Supergroup) Duluth (Keweenawan Duluth Complex. Two-dimensional gravity and magnetic magnetic model model studies studies along along three three profiles profiles extending extending across across the the southern half of the Duluth Complex Complex were performed performed in southern the Duluth in order to investigate the Duluth Complex investigate the structure structure of the the Duluth Complex at at depth and and the the locations of The three tions of near—surface near-surface rock—magnetization rock-magnetization contrasts. contrasts. The three profiles intersect Duluth Complex files intersect the the basal contact contact of the the Duluth Complex near near 47°27' N., N., 92O07' 92°07' W.; W.; 47°12' N., 92O12' 92°l2' W.; W.; and 46°57' N., 92°16' W. 47O12' N., 46O57' N., 92O16' W. 47O27' The The northernmost northernmost profile profile trends trends N. 900 90 E., E., and and the the two two southern southern proprofiles trend Density, magnetic magnetic susceptibility files trend N. N. 105° 105O E. E. Density, susceptibility and and remanent remanent magnetization magnetization data data were were measured measured from from rocks rocks throughout throughout the the southern southern Duluth Duluth Complex. Complex. Gravity model studies studies were constrained constrained by densities densities determined determined from from seismic refraction seismic refraction data data and and field field samples. samples. Seismically Seismically determined determined densities and densities and gravity gravity models models are are mutually supportive supportive for for Duluth Duluth Complex/country rock density contrasts which extend to density contrasts extend to aa depth depth of 20 20 Gravity models further imply that the basal contact of km. km. further imply that the contact of the the Duluth Complex dips E. near near the the northernmost northernmost profile profile and and 60° 60 E. and and 550 5S0 Complex dips 25° 2S0 E. E. near near the the two two southern southern profiles. profiles. Model Model studies studies utilizing utilizing aeromagnetic aeromagnetic data data upward upward continued continued to to aa level imply that that most of the the magnetic anomaly anomaly expression expression of of level of 11 km imply the southern Duluth Complex the southern Duluth Complex can can be accounted accounted for for by eastward-dipping eastward-dipping sources located within the km of crust, 6 km crust, polarized polarized near near or or sources located within the upper 6 along the Keweenawan normal direction along the average average Keweenawan direction (inclination (inclination = 40°, 40° = 290°) direction of polarization polarization is is consistent consistent declination = declination 290°). This direction Magnetic with rock rock magnetization magnetization data data which which imply imply an an average average QQ of of 3. Magnetic 3. models datafurther furtherimply implythat that an an increase increase in models and and rock—magnetization rock-magnetization data in rock—magnetizationoccurs occurs eastward eastward across across the rock-magnetization thesouthern southernDuluth DuluthComplex. Complex. The The increase increase in in magnetization, together together with its its low-dipping low-dipping normal normal direction, direction, can can account account for for the the regional regional magnetic magnetic low low which which occurs occurs over over the western portion of the complex. the western portion of the complex. Several large-amplitude large—amplitude magnetic anomalies (<3500 (c3500 gammas) occur Several The westernmost along the along the northern northern profile. profile. The westernmost of of these, these, whose whose maximum maximum occurs at N., 91°42' W., is caused by oxide-rich oxide-rich occurs at 47°27' 47O27' N., 91°42 W., is thought thought to to be caused troctolitic rocks troctolitic rocks which have have been been observed observed in in drill drill core core from from this this area. area. It It is is probable probable that that highly magnetized magnetized sources, sources, used used to to model model aa N., 91°24' broader anomaly anomaly with aa maximum located located at at 47°27' 47O27' N., 91024' W., W., are are related related to to similar similar troctolitic troctolitic rocks, rocks, although although there there are are no no outcrop outcrop or or drill drill core core data data to to verify verify this this possibility. possibility. Both ~ o t hof of these these large large The pres— presmagnetic magnetic anomalies anomalies are are bounded bounded to to the the east east by by felsic felsic rocks. rocks. The �16 ence ence of of eastward-dipping eastward-dipping contacts contacts in in the the magnetic magnetic models models implies implies that that the the felsic felsic rocks rocks lie lie stratigraphically stratigraphically above above the the inferred inferred troctolitic troctolitic masses. It It follows follows that that the the troctolitic troctolitic and and felsic felsic rocks rocks may may be be genegenemasses. tically be several several troctolite-felsic troctolite-felsic intruintrutically related related and and that that there there may may be sions sions along along the the profile. profile. �17 Composition, Composition, Origin O r i g i n and and Evolution E v o l u t i o n of of Keweenawan Keweenawan Magmas Review Magmas —- aa Review JOHN JOHN C. C. GREEN GREEN (Dept. (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, Duluth, MN 55812) 55812) Duluth, MN masKeweenawan magma magma compositions compositions are a r e best b e s t approximated approximated by by the t h e masKeweenawan s i v e , least—altered l e a s t - a l t e r e d parts p a r t s of of the t h e abundant abundant aphyric a p h y r i c lavas l a v a s and and dikes. dikes. sive, Much more more study s t u d y is i s necessary n e c e s s a r y to t o be b e able a b l e to t o infer i n f e r with w i t h any any precision precision Much the t h e parent p a r e n t magmas magmas of of the t h e major major layered l a y e r e d intrusive i n t r u s i v e complexes. complexes. Lava analyses a n a l y s e s show show that t h a t the t h e most most primitive p r i m i t i v e liquids l i q u i d s were were high—Al high-Al Lava olivine ~ e + ~ =) 0.65—0.68, )0.65-0.68, rich rich o l i v i n e tholeiites t h o l e i i t e s with w i t h Mg Mg' (atomic (=atomicMg/(Mg Mg/ (Mg + Fe+2)) i n Ni N i and and Cr C r and and low low in i n the t h e incompatible i n c o m p a t i b l e elements elements such such as a s K, K, Ti, T i , P, P, in and and rare r a r e earths. e a r t h s . Olivine O l i v i n e tholeiites t h o l e i i t e s showing showing aa strong s t r o n g Fe Fe —- enrichment enrichment trend t r e n d to t o Mg MgO—0.45 -0.45 constitute c o n s t i t u t e the t h e most most abundant abundant lava l a v a type. t y p e . Also Also very very abundant are a r e "transitional" " t r a n s i t i o n a l " basalts b a s a l t s which which also a l s o tend tend to t o be b e Fe—rich Fe-rich but but abundant with w i t h increasing i n c r e a s i n g amounts amounts of of alkalies a l k a l i e s and and other o t h e r incompatibles. i n c o m p a t i b l e s . With With ininc r e a s i n g Si02 S i 0 2 and and alkalies a l k a l i e s these t h e s e merge merge into i n t o the t h e considerably c o n s i d e r a b l y less less creasing abundant abundant basaltic b a s a l t i c andesites a n d e s i t e s and and andesites a n d e s i t e s and and eventually e v e n t u a l l y icelandites. icelandites. R h y o l i t e s form form aa secondary secondary though though low low peak peak of of abundance. abundance. Minor Rhyolites Minor vavarieties r i e t i e s such s u c h as a s mugearite, mugearite, tholeiitic t h o l e i i t i c hawaiites, h a w a i i t e s , and and ferroandesite ferroandesite a r e locally l o c a l l y found found in i n the t h e North North Shore Shore Volcanic Volcanic Group Group (NSVG). (NSVG). are + -The most pprimitive The most r i m i t i v e oolivine l i v i n e ttholeiites h o l e i i t e s were probably derived d e r i v e d from from an undepleted u n d e p l e t e d spinel s p i n e l lherzolite l h e r z o l i t e mantle m a n t l e at a t moderate moderate 25—30% 25-30% melting m e l t i n g of of an d e p t h s (35—55 (35-55 1cm), km), w i t h perhaps n l y aa small s m a l l amount of olivine o l i v i n e fracfracdepths with perhaps oonly tionated t i o n a t e d out o u t in i n transit t r a n s i t to t o the t h e surface. s u r f a c e . The The origin o r i g i n of of the t h e Fe—enrichFe-enrichment trend t r e n d between between these t h e s e and and the t h e transitional t r a n s i t i o n a l basalts b a s a l t s is i s uncertain uncertain ment and and controversial. c o n t r o v e r s i a l . Were Were they t h e y derived d e r i v e d by by partial p a r t i a l melting m e l t i n g of of more more Fe— Fer i c h mantle m a n t l e than t h a n appears a p p e a r s in i n typical t y p i c a l peridotite p e r i d o t i t e xenoliths x e n o l i t h s in i n other other rich terranes? t e r r a n e s ? If I f so, s o , they t h e y must must have have resulted r e s u l t e d from from smaller s m a l l e r degrees d e g r e e s of of melting p r i m i t i v e tholeiites. t h o l e i i t e s . Are A r e they t h e y the t h e result r e s u l t of of fracfracm e l t i n g than t h a n the t h e primitive tional t i o n a l crystallization c r y s t a l l i z a t i o n of of the t h e primitive p r i m i t i v e composition? composition? Detailed D e t a i l e d modelmodeling i n g by by Brannon Brannon with w i t h major major and and trace t r a c e elements elements suggests s u g g e s t s not. n o t . Did Did primprimitive i t i v e basalt b a s a l t assimilate a s s i m i l a t e ancient a n c i e n t sialic s i a l i c crust? c r u s t ? Sr S r and and Nd Nd isotopes i s o t o p e s say say no. no. Did Did the t h e magmas magmas tend tend to t o equilibrate e q u i l i b r a t e with w i t h earlier e a r l i e r Keweenawan Keweenawan wall wall rocks r o c k s to t o produce produce this t h i s trend? t r e n d ? (Brannon (Brannon et e t al, a l , 1981.) 1981.) Could Could mixing mixing of of two end—members end-members (transitional ( t r a n s i t i o n a l basalt, b a s a l t , primitive p r i m i t i v e olivine o l i v i n e tholeiite) t h o l e i i t e ) be be two involved? involved ? The The origin o r i g i n of of the t h e compositional compositional trend t r e n d between between basaltic b a s a l t i c andesites andesites and and rhyolites r h y o l i t e s is i s almost almost as a s uncertain. u n c e r t a i n . Although Although mantle m a n t l e melting m e l t i n g can can be be ruled r u l e d out, o u t , various v a r i o u s combinations combinations of of fractional f r a c t i o n a l crystallization, c r y s t a l l i z a t i o n , crustal crustal m e l t i n g , wallrock w a l l r o c k reaction, r e a c t i o n , and and magma magma mixing mixing can c a n be b e entertained. entertained. melting, B a s i c chemical chemical data d a t a are a r e accumulating accumulating and and detailed d e t a i l e d modeling modeling necessary necessary Basic to narrow the possibilities is in progress. t o narrow t h e p o s s i b i l i t i e s i s i n p r o g r e s s . Reference Reference Brannon, J . C . , Haskin, Haskin, L.A. L.A. and and Green, Green, J.C., J . C . , 1981, 1981, Fractional F r a c t i o n a l crystal— crystalBrannon, J.C., lization l i z a t i o n in i n NSVG? NSVG? (abs.): ( a b s . ) : Geol. Geol. Soc. Soc. Amer. Amer. Abst. Abst. with w i t h Prog., Prog., v. v . 13, 13, p . 271. 271. p. �18 PHYSICAL VOLCANOLOGY VOLCANOLOGY OF OF THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANICS JOHN C. C. GREEN (Geology (Geology Department, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, tIinnesota Minnesota 55812) 55812) Although their t h e i r individual i n d i v i d u a l extents e x t e n t s are a r e not n o t so s o well w e l l controlled c o n t r o l l e d by drilldrillLake vvolcanics White, 1960), 1960), the of the iing n g aas s tthe h e PPortage o r t a g e Lake o l c a n i c s (e.g. (e.g. White, t h e llavas a v a s of the well North Shore Volcanic Group (NSVG) (NSVG) are are w e l l exposed and many of of their t h e i r original original volcanic v o l c a n i c features f e a t u r e s are a r e observable. o b s e r v a b l e . IIn n aa study s t u d y correlating c o r r e l a t i n g field f i e l d observations observations and physical with p h y s i c a l characteristics characteristics w i t h chemical type t y p e of of 198 198 flows, f l o w s , the t h e following following generalizations g e n e r a l i z a t i o n s have have emerged. emerged. very ((a) a ) Explosive activity a c t i v i t y was v e r y rare r a r e except except in i n some some icelandite i c e l a n d i t e and and rrhyolite h y o l i t e ash a s h flows. flows. Even in i n interflow i n t e r f l o w sediments, s e d i m e n t s , vesicular v e s i c u l a r ash, a s h , scoria, s c o r i a , and sshards h a r d s are a r e rare. rare. Many textures (b) (b) t e x t u r e s as a s well w e l l as a s structures s t r u c t u r e s point p o i n t to t o the t h e low low viscosity v i s c o s i t y of of these t h e s e lavas l a v a s on eruption. eruption. 60% of of the non—porphyritic and thus ( c ) 60% t h e fflows l o w s aare re n o n - p o r p h y r i t i c and t h u s were erupted e r u p t e d at at (c) temperatures l i q u i d u s temperatures, t e m p e r a t u r e s , thus t h u s contribcontribt e m p e r a t u r e s aatt lleast e a s t aass hhigh i g h aass their t h e i r liquidus uting u t i n g to t o their t h e i r high h i g h fluidity. fluidity. (d) (d) The tops t o p s of of some some transitional t r a n s i t i o n a l basalts, b a s a l t s , quartz q u a r t z tholeiites, t h o l e i i t e s , basaltic basaltic andesites but a n d e s i t e s and more ffelsic e l s i c flows are a r e rrubbly, ubbly, b u t the t h e surfaces s u r f a c e s of of all a l l of of the the olivine and many of of the o l i v i n e tholeiites t h o l e i i t e s and t h e more evolved flows are a r e smooth or o r ropy at at various v a r i o u s scales. scales. bases of p practically unlike (e) ( e ) The b a s e s of r a c t i c a l l y aall l l flows were liquid, liquid, u n l i k e the t h e basal basal rubble r u b b l e zone of of typical t y p i c a l Hawaiian Hawaiian aa a a flows. flows. Pipe vesicle (f) i p e amygdules and v e s i c l e cylinders c y l i n d e r s are a r e common in i n olivine o l i v i n e tholeiite tholeiite (f) P flows but b u t are a r e absent a b s e n t in i n more more evolved evolved compositions. compositions. parts (g) (g) Amygdules in i n the t h e upper p a r t s of of flows are a r e round or o r amoeboid in i n the the basalts b a s a l t s but b u t are a r e commonly elongate, e l o n g a t e , indicating i n d i c a t i n g greater g r e a t e r viscosity, v i s c o s i t y , in i n andesites, andesites, iicelandites c e l a n d i t e s and rhyolites. rhyolites. Columnar (h) (h) Columnar jjointing o i n t i n g may occur in i n all a l l compositions from olivine o l i v i n e tholeiite tholeiite to it. t o rhyolite, r h y o l i t e , but b u t many many exposures exposures are a r e not n o t good good for f o r recognizing r e c o g n i z i n g it. Eruptive I c e l a n d (fissure—fed ( f i s s u r e - f e d flood flood E r u p t i v e style s t y l e was much more like l i k e that t h a t of of Iceland basalts with b a s a l t s intercalated intercalated w i t h more evolved evolved central c e n t r a l volcanoes) volcanoes) than t h a n Hawaii ((all a l l shields). shields). Reference White, W.S., W.S., 1960, 1960, The The Keweenaw Keweenaw lavas l a v a s of of Lake Lake Superior, S u p e r i o r , An example of of flood flood White, An example b a s a l t s : Amer. J o u r . S c i . , v . 258-A, p. 367-374. basalts: Amer. Jour. Sd., v. 258—A, p. 367—374. �19 Relative Relative Age Age and Tectonic Tectonic Significance Significance of of Proterozoic Proterozoic Metasedimentary Metasedimentary Rocks Rocks in in the the Upper Upper Midwest Midwest Geological and Natural GREENBERG, J.K. GREENBERG, J.K. (Wisconsin (Wisconsin Geological Natural History History Survey, Survey, 1815 1815 University University Ave., Madison, Madison, WI WI 53705—4096) 53705-4096) rocks are Four groups of Proterozoic sedimentary sedimentary rocks are recognized recognized in in Precambrian of the These are the Precambrian the upper upper Midwest. These are rocks rocks of the the northern Penokean Penokean terrane Penokean volcanic volcanic belt (PVB), northern terrane (NPT), (NPT), the the Penokean (PVB), Each of interval (BI), the Baraboo interval (BI), and the the Keweenawan Keweenawan basins basins (K). (K). Each of the four groups is characteristic of different tectonic conditions prevailing during the Proterozoic evolution margin the Proterozoic evolution of the the southern southern margin of the the Superior Superior Craton. Craton. The oldest group occurs occurs as as sequences sequences within within the the northern northern Penokean Penokean The oldestgroup which developed immediately upon Archean basement about terrane, which include the Marquette Marquette Range Supergroup 1900 m.y. m.y. ago. ago. These These units units include Supergroup 1900 Wisconsin and and northern northern Michigan Michigan and and the theMille Mule Lacs Group in in Wisconsin were originally Minnesota. They Minnesota. They were originally deposited deposited on on aa stable stable continental continental which gave way with with time to deeper water environments environments indicative indicative shelf which of subsidence. subsidence. The The uppermost uppermost units units in in the the succession, succession, which which correcorrelate Paint River Groups, Groups, are predominantly the Baraga and Paint late with the These were deposited in turbidites turbidites and tholeiitic tholeiitic volcanic volcanic rocks. rocks. These in a series series of of rift rift basins. basins. At about about the the same same time time or or later later than than deposition deposition in in the the northern northern Penokean terrane, Penokean volcanic belt was Penokean terrane, sedimentation sedimentation in in the the Penokean was taking place to the the south south in in environments environments similar similar to to island island arc, arc, back arc, arc, and interarc interarc basin basin complexes. complexes. Metasedimentary Metasedimentary rocks rocks are are in this this predominantly predominantly volcanic now poorly preserved and/or exposed in which extends much of terrane which extends over over much of northern northern Wisconsin. Wisconsin. The The sedimensedimenunits which which were were preserved seem to be relatively thin and quite tary units variable. Outcrops Outcrops and drill—core variable. drill-core data data suggest suggest that that turbidites, turbidites, graphitic carbonate iron graphitic shales, shales, sulfidic sulfidic and carbonate iron formation, formation, silty silty dolomite, various types volcanogenic sediments were deposited dolomite, and various types of volcanogenic sediments were deposited around centers centers of of calc—alkaline calc-alkaline volcanism. volcanism. The The observed contrast contrast in in lithologies and depositional settings make make it unreasonable unreasonable to correlithologies correlate units units between the late the two two Penokean Penokean terranes. terranes. Both terranes terranes were were apparently apparently deformed deformed together together during during the the Penokean Penokean orogeny, orogeny, about about 1850 m.y. m.y. ago. ago. At this this time, time, the the simatic simatic arcs arcs and and basins basins (PVB) (PVB) were were 1850 ted sial sial (NPT) (NPT) along along the craton margin margin to accreted to to the the rif rifted to the the north. north. major depositional depositional period, the Baraboo Baraboo interval The third major interval is is interinterresult of subsidence on relatively immature preted as a result subsidence on immature continental continental post—orogenic felsic crust. felsic crust. This sedimentation sedimentation immediately immediately followed followed post-orogenic magmatism m.y. ago to rifting rifting and and atypiatypimagmatism 1760 1760 m.y. ago and and was was both both unrelated unrelated to cal modern passive margins. Analogues cal of modern passive margins. Analogues of of the the Baraboo Baraboo interval interval Arabian Shield, in the the Lower Lower probably occur in in the the Eocambrian of the the Arabian Shield, in Proterozoic adjacent Guiana Shield, Proterozoic adjacent to the the Guiana Shield, and possibly in in the the Lower Lower Proterozoic Proterozoic of of the the Athabasca Athabasca Basin. Basin. �20 Other than the well known known red Baraboo, Baraboo, Barron, the well Barren, and Sioux Sioux Quartz— Quartzites, rock units in ites, in the the Baraboo Baraboo interval interval include include five five other other facies: facies: micaceous micaceous quartzite, quartzite, conglomerate, conglomerate, argillite, argillite, chert, chert, and and iron—rich iron-rich chemical sediments chemical sediments (including (including rare rare dolomite). dolomite). These sediments sediments may have been deformed about 1630 m.y. ago, as some evidence about 1630 m.y. ago, as some evidence suggests; suggests; metamorphosed during however they were definitely deformed and metamorphosed during the the intrusion intrusion of of alkalic alkalic plutons plutons 1500 1500 m.y. m.y. ago. ago. Rift—related Keweenawan sedimentary Rift-related Keweenawan sedimentary units units were deposited deposited in in aa stable stable continental continental environment environment at least least 300 300 m.y. after after the the Baraboo Baraboo The mostly quartzitic interval. interval. quartzitic Keweenewan Keweenewan rocks rocks are are exposed exposed along along both shores shores of Lake Superior Superior and include include both pre— pre- and post—volcanic post-volcanic sequences. sequences. Keweenawan Keweenawan units units were only only mildly or or locally locally affected affected by by the heat of of rift rift magmatism. magmatism. They were not not significantly significantly deformed. deformed. The The association association of of depositional depositional and tectonic tectonic environments environments reprerepresented by each each of of the the four four sedimentary sedimentary groups groups is is as as follows: follows: DEPOSITIONAL ENVIRONMENT ENVIRONMENT DEPOSITIONAL TECTONIC TECTONIC ENVIRONMENT ENVIRONMENT GROUP GROUP TINE TIME NPT NPT Continental about Continental shelf, shelf, rift rift about basins 1900 1900 basins m.y. ago ago Development of Atlantic— Development Atlanticcontinental margin type continental PVB PVB about about Small ocean, arc arc basins basins 1900— 19001850 1850 m.y. ago ago Early stages stages of conti— continent—volcanic nent-volcanic arc arc orogeny orogeny BI BI Epicontinental basin basin about Epicontinental about 1760 1760 m.y. ago ago Metastable continental Metastable continental crust, crust, subsidence subsidence due due to to thin thin sial sial after after cratoni— cratoniz at ion zation K Intracontinental about about Intracontinental rift rift basins 1300— 1300basins 900 900 m.y. ago ago Tensional reactivation reactivation of tectonic tectonic weaknesses weaknesses in mature continental continental crust crust �21 S t r a t i g r a p h y of h e Footwall he Stratigraphy of tthe Footwall Volcanic Volcanic Rocks Rocks Beneath tthe M a t t a b i Massive Sulfide S u l f i d e Deposit, D e p o s i t , Sturgeon Lake, Lake, Ontario Ontario Mattabi (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, DAVID A. A. GROVES (Dept. Duluth, 55812) Duluth, MN 55812) The M Mattabi a t t a b i massive sulfide s u l f i d e deposit, d e p o s i t , situated s i t u a t e d in i n the t h e Wabigoon greenstone underlain is u n d e r l a i n by approximately a p p r o x i m a t e l y 22 km km of of predominantly g r e e n s t o n e belt, b e l t , is r o c k s in i n the t h e study s t u d y area a r e a are are m a f i c subaqueous subaqueous volcanic v o l c a n i c rocks. r o c k s . The rocks mafic trondhtterminated e r m i n a t e d by the t h e Beidelman Bay intrusion, i n t r u s i o n , a dioritic d i o r i t i c to t o trondh— jjemitic e m i t i c subvolcanic s u b v o l c a n i c sill. sill. D e t a i l e d geologic g e o l o g i c mapping and petrographic petrographic Detailed studies s t u d i e s have shown that t h a t this t h i s previously p r e v i o u s l y undifferentiated u n d i f f e r e n t i a t e d footwall footwall u n i t can be b e divided d i v i d e d into i n t o several s e v e r a l distinct d i s t i n c t volcanic v o l c a n i c deposit d e p o s i t types t y p e s on unit basis of p preserved primary ttextures, fragment type, mineralogy. tthe he b a s i s of r e s e r v e d primary e x t u r e s , fragment t y p e , and mineralogy. At A t the t h e base b a s e of of the t h e succession, s u c c e s s i o n , mafic m a f i c porphyritic p o r p h y r i t i c flows f l o w s and and flow flow breccias b r e c c i a s are a r e intruded i n t r u d e d by an a n altered a l t e r e d dioritic d i o r i t i c border b o r d e r phase of of the the mafic with Beidelman Bay intrusion. intrusion. The m a f i c fflows l o w s aare r e intercalated intercalated w i t h and overlain o v e r l a i n by thin t h i n felsic f e l s i c lavas l a v a s and hyaloclastites h y a l o c l a s t i t e s that t h a t grade g r a d e laterally laterally heterolithic iinto nto h e t e r o l i t h i c debris d e b r i s flows. flows. This T h i s felsic f e l s i c horizon h o r i z o n thickens t h i c k e n s on on both both western tthe he w e s t e r n and eastern e a s t e r n extremities e x t r e m i t i e s of of the t h e study s t u d y area a r e a and, and, locally, locally, Poorly bedded and graded m mafic iincludes n c l u d e s coarse c o a r s e block b l o c k and ash a s h layers. layers. P o o r l y bedded afic debris d e b r i s flows f l o w s overlying o v e r l y i n g this t h i s felsic f e l s i c horizon h o r i z o n are a r e composed largely l a r g e l y of of aphyric mafic w e s t of of Mattabi. Mattabi. aphyric m a f i c fragments and scoria s c o r i a and are a r e most common common west These deposits with d e p o s i t s interfinger i n t e r f i n g e r and mix w i t h felsic f e l s i c lavas l a v a s and flow f l o w breccias breccias east of of the t h e ore o r e deposit. d e p o s i t . The mine footwall f o o t w a l l horizon, h o r i z o n , approximately approximately m tthick, comprised of of ffelsic pyroclastic deposits h i c k , iis s comprised elsic p y r o c l a s t i c fflow low d e p o s i t s composed 200 m of poorly of coarse, coarse, p o o r l y graded tuff t u f f breccias b r e c c i a s and intercalated i n t e r c a l a t e d ash a s h beds. beds. The graded, immediate ffootwall o o t w a l l rrock o c k iis s aa ppoorly oorly g r a d e d , llapilli—rich a p i l l i - r i c h pyroclastic pyroclastic flow. of lower felsic w e s t and and east e a s t of of the the Thickening of f e l s i c flow f l o w horizons h o r i z o n s to t o the t h e west ore Comparisons of o r e deposit d e p o s i t suggest s u g g e s t at a t least l e a s t two felsic f e l s i c edifices. edifices. of felsic pyroclastic units felsic p yroclastic u n i t s immediately beneath b e n e a t h the t h e Mattabi M a t t a b i horizon h o r i z o n also also iindicate: ndicate: 1. 1. west An early e a r l y edifice e d i f i c e slightly slightly w e s t of of the t h e ore o r e deposit d e p o s i t produced beds and o overlying ccoarse o a r s e bbasal a s a l ppyroclastic y r o c l a s t i c beds v e r l y i n g aash s h beds that that ttruncate r u n c a t e mafic debris d e b r i s flow flow deposits. deposits. 2. 2. Later L a t e r volcanism east e a s t of of the t h e ore o r e deposit d e p o s i t produced subaqueous subaqueous pyroclastic grade westward into p y r o c l a s t i c fflows l o w s tthat hat g r a d e westward i n t o thinly t h i n l y bedded ash ash units. units. These flows f l o w s form form the t h e immediate immediate footwall f o o t w a l l at a t Mattabi. Mattabi. �22 Evidence Evidence for f o r nappe nappe development development during d u r i n g the t h e Penokean Penokean Orogeny Orogeny from from the the Early E a r l y Proterozoic P r o t e r o z o i c Thomson Thomson Formation, Formation, Minnesota Minnesota HOLST, HOLST, T.B., T.B., Department Department of of Geology, Geology, University U n i v e r s i t y of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 55812 The The Penokean Penokean orogeny orogeny (1,900—1,800 (1,900-1,800 m.y.) m.y.) was was aa major major tectonic tectonic event e v e n t in i n the t h e Great Great Lakes Lakes region r e g i o n of of North North America America involving i n v o l v i n g deformadeformation, t i o n , metamorphism metamorphism and and igneous igneous activity. a c t i v i t y . In I n Minnesota, the t h e effects effects of of Penokean Penokean deformation deformation are are most most clearly c l e a r l y seen s e e n in i n the t h e Thomson Thomson FormaFormaTwo major major phases phases of of Penokean Penokean defordefortion t i o n of of east—central e a s t - c e n t r a l Minnesota. Minnesota. Two F i folds f o l d s are are mation mation are a r e now now recognized recognized in i n the t h e Thomson Thomson Formation. Formation. F1 isoclinal well-developed S1 S l axial—planar a x i a l - p l a n a r foliafoliai s o c l i n a l and and recumbent recumbent with w i t h aa well—developed A s hinge h i n g e regions r e g i o n s of of F1 F l folds f o l d s are a r e rare, r a r e , the t h e S1 S l foliation f o l i a t i o n is is tion. t i o n . As usually u s u a l l y observed observed to t o be b e very v e r y nearly n e a r l y bedding bedding —- parallel p a r a l l e l in i n outcrop. outcrop. F2 F2 folds f o l d s are a r e open, open, upright u p r i g h t to t o steeply s t e e p l y inclined, i n c l i n e d , and and subhorizontal. subhorizontal. This There i s aa foliation f o l i a t i o n that t h a t is i s axial—planar a x i a l - p l a n a r to t o the t h e F2 F2 folds. f o l d s . This There is foliation i s aa crenulation c r e n u l a t i o n cleavage c l e a v a g e where where the t h e S1 S i foliation f o l i a t i o n is i s present present f o l i a t i o n is The and and aa slaty s l a t y cleavage c l e a v a g e where where the t h e S1 Sl foliation f o l i a t i o n does does not n o t exist. e x i s t . The second second deformation d e f o r m a t i o n affected a f f e c t e d the t h e entire e n t i r e region r e g i o n of of Thomson Thomson Formation Formation outcrop, o u t c r o p , while w h i l e the t h e effects e f f e c t s of of the t h e first f i r s t deformation deformation are a r e found found only only in i n the t h e southern s o u t h e r n two—thirds two-thirds of of Thomson Thomson Formation Formation outcrop. outcrop. Several S e v e r a l lines l i n e s of of evidence e v i d e n c e indicate i n d i c a t e that t h a t northward—directed northward-directed This nappes nappes developed developed during d u r i n g the t h e Penokean Penokean deformation d e f o r m a t i o n in i n Minnesota. Minnesota. This evidence e v i d e n c e includes i n c l u d e s petrologic p e t r o l o g i c differences d i f f e r e n c e s between between the t h e areas a r e a s of of one one and S1 foliation f o l i a t i o n in i n the the and two two deformations, d e f o r m a t i o n s , the t h e pervasive p e r v a s i v e nature n a t u r e of of the t h e S1 area f a c i n g direction d i r e c t i o n of of F2 F2 folds, f o l d s , and and the t h e rerea r e a in i n which which it i t is i s found, found, facing fraction f r a c t i o n pattern p a t t e r n of of the the l Sl foliation f o l i a t i o n in i ngraded graded greywacke—slate greywacke-slate sesequences, showing that an area of up to several hundred quences, showing t h a t a n area of up t o s e v e r a l hundred square s q u a r e km km is is on on the t h e upper upper limb limb or o r limbs limbs of of large l a r g e northward—directed n o r t h w a r d - d i r e c t e d recumbent recumbent folds f o l d s (nappes) (nappes) of of the t h e early e a r l y phase phase of of deformation. deformation. Recent Recent tectonic t e c t o n i c models models of of the t h e Penokean Penokean orogeny orogeny in i n Minnesota Minnesota have have suggested that i t was w a s an a n intracratonic i n t r a c r a t o n i c event e v e n t with w i t h local l o c a l compression compression t h a t it and metamorphism metamorphism caused caused by by vertical v e r t i c a l ttremobi1izationt " r e m o b i l i z a t i o n " of of basement basement r o c k s . The The existence e x i s t e n c e of of nappes nappes and and later l a t e r upright u p r i g h t folds f o l d s with w i t h axial— axialrocks. planar p l a n a r foliation f o l i a t i o n suggests s u g g e s t s a significant s i g n i f i c a n t amount amount of of horizontal h o r i z o n t a l shortenshortening. i n g . These These features f e a t u r e s are a r e quite q u i t e compatible compatible with w i t h the t h e suggestions s u g g e s t i o n s that that Penokean Penokean deformation deformation took t o o k place p l a c e in i n aa plate p l a t e boundary boundary collision c o l l i s i o n environenvironment. ment. �23 Folded Rocks Rocks in i n the t h e Eastern E a s t e r n Contact Contact Zone Zone of of the t h e Vermilion Vermilion Batholith Batholith Folded 53511) J . P . KASZUBA KASZUBA (Department (Department of of Geology, Geology, Beloit B e l o i tCollege, College, Beloit, B e l o i t , WIW I53511) J.P. P.A. SCHWARZWELLER SCHWARZWELLER(Department (Department of of Geology, Geology, Beloit B e l o i tCollege, College, Beloit, Beloit, P.A. W I 53511) 53511) WI H.H. WOODARD WOODARD (Department (Department of of Geology, Geology, Beloit B e l o i t College, College, Beloit, B e l o i t , WI W I 53511) 53511) H.H. Detailed D e t a i l e d geologic g e o l o g i c and and structural s t r u c t u r a l mapping mapping was was carried c a r r i e d out o u t in i n aa portion portion (7% minute) minute) quadrangle, quadrangle, Minnesota—Ontario Minnesota-Ontario during during of the t h e Jackfish J a c k f i s h Lake Lake (7½ of T h i s mapping mapping has h a s demonstrated demonstrated the t h e existence e x i s t e n c eof of t h e 1982 1982 field f i e l d season. season. This the This aa major major fold f o l d sequence, sequence, here h e r e named named the t h e Crooked CrookedLake LakeFold FoldSequence. Sequence. This sequence sequence lies l i e s within w i t h i n the t h e southeastern s o u t h e a s t e r n contact c o n t a c t zone zone of of the t h e Vermilion Vermilion B a t h o l i t h , north n o r t h of of the t h e Vermilion Vermilion fault f a u l t zone. zone. Batholith, The The oldest o l d e s t rocks r o c k s in i n the t h e quadrangle quadrangle are a r ebiotite b i o t i t eschists, s c h i s t s , amphibolites, amphibolites, and and metabreccias m e t a b r e c c i a s associated a s s o c i a t e d with w i t h younger younger leucocratic l e u c o c r a t i c biotite b i o t i t e adamellite adamellite and and migmatites. migmatites. The Theoldest o l d e s t rocks r o c k s were were graywackes graywackes and and shales, s h a l e s , basalts basalts and andesites, a n d e s i t e s , and and mafic mafic volcaniclastic v o l c a n i c l a s t i c sediments. sediments. Mafic Mafic breccias b r e c c i a s sugsugand g e s t nearby nearby sources s o u r c e s of of mafic mafic volcanics. volcanics. gest After A f t e r deposition d e p o s i t i o n of of the t h e sediments, sediments, aa major major period p e r i o d of of deformation deformation T h i s sequence sequence concono c c u r r e d to t o produce produce the t h e Crooked Crooked Lake Lake Fold Fold Sequence. Sequence. This occurred s e r i e s of of often o f t e n overturned o v e r t u r n e d synclines s y n c l i n e s and and anticlines a n t i c l i n e s that that sists s i s t s of of aa series wide range r a n g e of of orientations orientations plunge gently g e n t l y to t o the t h e east e a s t and and northeast. n o r t h e a s t . AA wide plunge of of major major fold f o l d axes a x e s and and axial a x i a l planes p l a n e s suggests s u g g e s t s that t h a t the t h e deformational deformational event was was characterized c h a r a c t e r i z e d by by complex complex disharmonic disharmonic folding. f o l d i n g . The The changing changing event The fold f o l d sequence sequence i s illustrated i l l u s t r a t e d in i n Fig. F i g . 1. 1. The shape of of one one of of the t h e folds f o l d s is shape (7%minute) minute) quadquadextends e x t e n d s westward westward across a c r o s s strike s t r i k e through through the t h e Friday F r i d a y Bay Bay (7½ rangle 10 kilometers k i l o m e t e r s and and may may extend extend even even farther, f a r t h e r , into into r a n g l e for f o r approximately approximately 10 t h e Iron I r o n Lake Lake (7½ (7%minute) minute) quadrangle quadrangle and and the t h e Vermilion Vermilion Batholith. B a t h o l i t h . SouthSouththe east e a s t of of the t h e Jackfish J a c k f i s h Lake Lake quadrangle quadrangle the t h e Crooked Crooked Lake Lake Folds F o l d s can can be be followed ( 7 % minute) minute) quadrangle quadrangle followed across a c r o s s strike s t r i k e into i n t o the t h e Basswood Basswood Lake Lake West West (7½ where where they they may may be be terminated t e r m i n a t e d against a g a i n s t aa splay s p l a y of of the t h e younger younger Vermilion Vermilion f a u l t zone. zone. The The minimum minimum total t o t a l across—strike a c r o s s - s t r i k e distance d i s t a n c e of of the t h e fold fold fault When followed followed along a l o n g strike s t r i k e to to i s approximately approximately 23 23 kilometers. k i l o m e t e r s . When sequence is sequence the t h e northeast n o r t h e a s t into i n t o Canada, Canada, individual i n d i v i d u a l folds f o l d s pass p a s s into i n t o leucocratic l e u c o c r a t i c biotite biotite a d a m e l l i t e of of the t h e Vermilion Vermilion Batholith. B a t h o l i t h . Their T h e i r position p o s i t i o n within w i t h i n the t h e batho— bathoadamellite l i t h can can be be recognized recognized by by systematic s y s t e m a t i c changes changes in i n foliation f o l i a t i o norientations. orientations. lith After A f t e r the t h e major major deformational d e f o r m a t i o n a l period, p e r i o d , the t h e sediments sediments were were metamorphosed metamorphosed Migmatization and and formation formation of of leucocratic t o amphibolite a m p h i b o l i t e grade. grade. Migmatization l e u c o c r a t i c bio— bioto tite t i t e adamellite a d a m e l l i t e occurred o c c u r r e d after a f t e r amphibolite a m p h i b o l i t e grade grade metamorphism. metamorphism. Regional Regional structural s t r u c t u r a l continuity c o n t i n u i t y between between the t h e older o l d e r biotite b i o t i t e schists s c h i s t s and and the t h e adamel— adamellite l i t e suggests s u g g e s t s that t h a t the t h e migmatization migmatization which which produced produced the t h e adamellite adamellite probably i n aa younger younger pile p i l e of of felsic f e l s i c volcanics v o l c a n i c s which which were were overoverprobably occurred o c c u r r e d in The formation formation of of the t h e migmatites migmatites may may be be l y i n g the t h e more more mafic mafic schists. s c h i s t s . The lying t h e result r e s u l t of of aa combination combination of of several s e v e r a l mechanisms: mechanisms: anatexis, a n a t e x i s , metasoma— metasomathe t i s m , and and subsequent subsequent intrusion. intrusion. tism, Several S e v e r a l episodes e p i s o d e s of of faulting f a u l t i n g and and fracturing f r a c t u r i n g have have taken t a k e n place. p l a c e . These These events e v e n t s produced produced narrow narrow zones zones of of cataclasis, c a t a c l a s i s , brecciation, b r e c c i a t i o n , and and hydrohydrothermal alteration. a l t e r a t i o n . As A s the t h e Vermilion Vermilion Batholith B a t h o l i t h is i s approached, approached, the the thermal �24 number of of faults f a u l t s increases i n c r e a s e s significantly. s i g n i f i c a n t l y . Apparent Apparent displacement displacement on on number t h e s e faults f a u l t s dies d i e s out o u t as a s the t h e faults f a u l t s pass p a s s northward northward into i n t o the t h e more more these massive rock rock of of the t h e Vermilion Vermilion Batholith. B a t h o l i t h . Most Most faults f a u l t s when when traced t r a c e d over over massive long long distances d i s t a n c e s are a r e deflected d e f l e c t e d to t o the t h e north n o r t h and and west west as a s if i f they they were were being being c o n t r o l l e d by by the t h e southeastern s o u t h e a s t e r n margin margin of of the t h e batholith. batholith. controlled The The formation formation of of strong s t r o n g joint j o i n t sets s e t s accompanied accompanied the t h e faulting f a u l t i n g events. events. Many of of these t h e s e joint j o i n t sets s e t s show show aa strong s t r o n g bimodal bimodal distribution d i s t r i b u t i o n which which corcorMany responds responds to t o the t h e primary primary layering l a y e r i n g directions d i r e c t i o n s in i n the t h e opposing opposing limbs limbs of of leucot h e Crooked Crooked Lake Lake Folds. F o l d s . These These joints j o i n t s seem seem to t o persist p e r s i s t into i n t o the t h e leuco— the cratic c r a t i c biotite b i o t i t e adamellite a d a m e l l i t e of of the t h e Vermillion V e r m i l l i o n Batholith B a t h o l i t h and and may may represent represent o r i g i n a l planes p l a n e s of of weakness weakness in i n the t h e pre—batholith p r e - b a t h o l i t h pile p i l e of of felsic f e l s i c extruextruoriginal s i v e rocks. rocks. sive 0 I TT 1/2. t(ILOMETER F i g u r e 1. 1. Changing Changing shape shape of of one one of of the t h e anticlines a n t i c l i n e s in i n the t h e Crooked Crooked Lake Lake Figure These sections s e c t i o n s are a r e drawn drawn perpendicular p e r p e n d i c u l a r to to Fold Sequence. Sequence. These Fold the t h e strike s t r i k e of of aa 1.5 1 . 5 kilometer k i l o m e t e r segment segment of of the t h e axial a x i a l plane p l a n e of of t h e fold. f o l d . Vertical V e r t i c a l scale s c a l e equals e q u a l s horizontal h o r i z o n t a l scale. scale. the �25 ANDITS ITS IMPLICATION SUPERIMPOSED SUPERIMPOSED FOLDING FOLDING AND IMPLICATION ON ON THE THE SHEBAN])JWAN-QUETICO SUBPROVINCE BOUNDARY, THUNDER BAY, ONTARIO. SHEBANDOWAN-QUETICO SUBPROVINCE BOUNDARY, THUNDER BAY, ONTARIO. of Geology, Geology, Lakehead Lakehead University, M.M. M.M. KEHLENBECK KEHLENBECK (Department (Department of University, Thunder Thunder P7B 5E1) Bay, 5E1) Bay, Ontario Ontario Detailed structural studies Detailed structural studies were were carried carried out out over over a a distance distance of of +O 40 km km along an an east-west east-west trending trending zone zone which which is is characterized characterized by aa lithological lithological transition transition from from aa dominantly dominantly metavolcanic metavolcanic terrain terrain south south of of the metasedimentary rocks rocks exposed exposed north north of of the the the zone zone to to well well stratified stratified metasedimentary zone. zone. This This lithologic lithologic change change from from basic basic flows flows and and intermediate intermediate to to felsic felsic volcanoclastic rocks to a a sequence of of greywackes, greyackes, slates, slates, and and turbidites turbidites has boundary has been been defined defined on on published published geological geological survey survey maps maps as as the the boundary between the Shebandowan andQuetico Queticosubprovinces subprovincesininthe the area area north between the Shebandowan and north and and northwest northwest of ofThunder ThunderBay. Bay. The The metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks have have been been subjected subjected to to regional regional greenschist greenschist facies facies metamorphism metamorphism and and possess possess aa single single well well defined bedding planes lanes (s0) are defined schistosity schistosity or or cleavage cleavage (51). Primary Primary bedding are well well preserved preserved in in the the metasedimentary metasedimentary rocks rocks as as are are primary primary structures structures such such as as graded graded bedding bedding and and cross cross bedding. bedding. Pillow Pillow structures, structures, although although not not uncommon, uncommon, are are often often too too deformed deformed to to permit permit determination determination of of local local tops tops or or of of primary primary bedding bedding surfaces surfacesin inthe theinetavolcanic metavolcanic succession. succession. (s~). (so) Based relationships, the the asymmetry asymmetry of of minor minor Based on on cleavage-bedding cleavage-bedding relationships, folds, local younging youngingderived derivedfrom fromprimary primary structures,aaset set of of folds folds, •and and local structures, folds has Field observations observations has been been delineated delineated in in the the metasedimentary metasedimentary sequence. sequence. Field in in aa number nuder of of fold fold hinge hinge zones zones have have clearly clearly shown shown that that the the subvertical, subvertical, northeast cleavageparallels parallelsthe the axial axial surfaces surfaces of of these these folds. folds. northeast striking striking SSlcleavage Observed intersection lineations lineations generally generally p1inge plunge steeply steeply to to the the Observed So/Si intersection northeast northeast and and are are coaxial coaxial with with the the axes axes of of these these folds. folds. Because Because of of their their steep steep plunge, plunge, the the structural structural facing facing of of the the folds folds is is primarily primarily sideways, sideways, and antiforms. These and hence hence they they cannot cannot be "beclassified classified as as synforms synformsor or antiforms. These folds folds therefore therefore form form aa set set of of vertically vertically plunging, plunging, sideways—closing sideways-closing folds. folds. so/sl When tracing tracing one one of of these these folds folds in in the the field field parallel parallel to to the the trace trace When of of the the axial axial surface, surface, aa number number of of reversals reversals in in the the structural structural facing facing direction direction of of the the fold fold occur. occur. In In some some portions portions the the structural structural facing facing direction direction is is to to the the northeast, northeast, elsewhere elsewhere to to the the southwest. southwest. ctending Extending such such observations observations over over the the entire entire area area reveals reveals the the existence existence of of distinctive distinctive regions regions in in which which the stratigraphy as a whole becomes younger toward the northeast, while the stratigraphy as a whole becomes younger toward the northeast, while other other parts parts indicate indicate an an overall overall stratigraphic stratigraphic younging younging to to the the southwest. southwest. The places where the reversals in the structural facing direction, The places where the reversals in the structural facing direction, and and mark the the position position of of the the therefore in in the the stratigraphic stratigraphic younging younging occur, occur, mark therefore trace trace of of the the axial axial surfaces surfaces of of an an earlier earlier set set of of folds. folds. Based on on the the structural structural data data from from this this area, area, it Based it is is suggested suggested that that the strata strata were folded folded about about gently gently plunging axes axes resulting in aa set set of of the resulting in IQfolds folds in in which which at at least least some some limbs limbs were were overturned. overturned. AA later isoclinal Fl isoclinal later refolding produced produced F2 Fz folds folds about about nearly nearly vertical vertical axes axes and and axial axial surfaces. surfaces. refolding The F2 F2 folding folding was was accompanied accompanied by by the the development development of of aa pervasive pervasive axial axial The planar schistosity schistosity or or cleavage. cleavage. planar Superimposed folding folding has has been been documented documented in in the the metasedimentary metasedimentary Superimposed rocks on on both both sides sides of of the the proposed proposed boundary boundary between between the the Shebandowan Shebandowan and and rocks Quetico Quetico subprovinces. subprovinces. No evidence evidence has has been been found found to to exclude exclude the the metavolcanic metavolcanic rocks from from the the folding folding demonstrated demonstratedin inthe themetasedinientary metasedimentary succession. succession. rocks �26 LaSalle Falls F a l l s -- An An Exposed Exposed Massive Massive Sulfide S u l f i d e Deposit Deposit LaSalle i n Florence Florence County, County, Wisconsin Wisconsin in GENE L. L. LA LA BERGE BERGE (Department (Department of o f Geology, Geology, University U n i v e r s i t y of of GENE Wisconsin-Oshkosh, Oshkosh, Oshkosh, WI W I 54901) 54901) Wisconsin-Oshkosh, La La Salle S a l l e Falls F a l l s (Pine (Pine Rapids) Rapids) on on the t h e Pine Pine River River in i n Florence Florence County, County, Wisconsin Wisconsin occurs o c c u r s at a t the t h e contact c o n t a c t between between felsic f e l s i c and and mafic mafic volcanic volcanic the rocks of o f the t h e early e a r l y Proterozoic P r o t e r o z o i c Quinnesec Quinnesec Formation. Formation. Along Along the rocks s o u t h side s i d eof o fthe t h ePine PineRiver Riverthe t hexposed e exposedrocks rocksare a r mainly e mainlymassive massive south and pillowed p i l l o w e d(?) ( ? ) greenstones greenstones with w i t hnumerous numerous massive massive and and layered layered and gabbroic dikes. d i k e s . Most Most exposures exposures have have aa prominent prominent foliation f o l i a t i o n and and gabbroic mineral mineral associations a s s o c i a t i o n s suggest s u g g e s t metamorphism metamorphism to t o lower lower amphibolite amphibolite f a c i e s . At A t LaSalle LaSalle Falls F a l l s and and on on the t h e north n o r t h side s i d e of of the t h e Pine Pine River River facies. the the dominant dominant lithology l i t h o l o g y of of the t h e Quinnesec Quinnesec Formation Formation is i s felsic f e l s i c volvolc a n i c rocks rocks that t h a t appear appear to t o be be coarsely c o a r s e l y fragmental. fragmental. Significant Significant canic pyrite, p y r i t e , pyrrhotite p y r r h o t i t e and and chalcopyrite c h a l c o p y r i t e are a r e disseminated disseminated in i n the t h e felsic felsic To the north the Quinnesec is in fault rocks a t LaSalle F a l l s . To t h e n o r t h t h e Quinnesec i s i n f a ult rocks at LaSalle Falls. contact c o n t a c t with w i t h the t h e Michigamme Michigamme Formation Formation along a l o n g the t h e Niagara Niagara Fault. Fault. To To the t h e south s o u t h the t h e volcanics v o l c a n i c s are a r e in i ncontact c o n t a c twith, w i t h ,and andintruded i n t r u d e d by, by, g r a n i t i c rocks rocks of o fthe t h eDunbar Dunbargneiss g n e i s sdome. dome. granitic sulfide deposit, a graphitic, fifty feet thick, occurs at the contact between the mafic The s u l f i d e d e p o s i t , a g r a p h i t i c , sulfide—rich s u l f i d e - r i c h sediment sediment zone zone The about f i f t y f e e t t h i c k , o c c u r s a t t h e c o n t a c t between t h e mafic about and felsic f e l s i c rocks. r o c k s . The The sedimentary sedimentary unit u n i t is i s mainly mainly aa finely f i n e l ylamlamand i n a t e d chloritic c h l o r i t i cand and sericitic s e r i c i t i cslate s l a twith e w i t discontinuous h discontinuous pyrite pyrite inated nun thick. t h i c k . Cherty Cherty layers l a y e r s are a r erelatively r e l a t i v e lcommon y common within within l e n s e s1 1 lenses —- 22 mm of the t h e zone. zone. Garnets Garnets are a r e abundant abundant in i n some some of t h e pelitic p o l i t i crocks. rocks. the Although only iiron Although only r o n sulfides s u l f i d e swere were observed observed in i n the t h esediments, sediments, drilling d r i l l i n gby bymining miningcompanies companies indicate i n d i c a t e the t h e presence presence of o fbase basemetal metal mainssulfide deposit underlies s u l f i d e s . The The main ulfide d e p o s i t apparently apparently u n d e r l i e s the the river river sulfides. channel removed channel below below tthe h e falls f a l l sand andhas h a sbeen beenlargely largely removed by by erosion. erosion. thisoccurrence occurrence along along the t h e Pine Pine River, River, aa base base metal metal I n addition a d d i t i o n to t o this In s u l f i d e d e p o s i t i n f e l s i c t u f f s h a s been d r i l l e d approximately approximately one one sulfide Massive sulfide deposits have also been reported m i l e t o t h e s o u t h . Massive s u l f i d e d e p o s i t s have a l s o been r e p orted mile to the south. the Quinnesec Formation in Marinette County. The i n t h e Quinnesec Formation i n M a r i n e t t e County. in The exposure exposure would would make make an an excellent e x c e l l e n t field f i e l d trip t r i p stop. stop. deposit in felsic tuffs has been drilled �27 The Reany Reany Creek Creek Formation: Formation: aaMass-Flow Mass-Flow Deposit Deposit of Possible of Possible Post Post Menominee Menominee Age Age S. R. of Geology, R. MATTSON MATTSON ((Department ~ e p a r t m e n t of Geology, Michigan Michigan SState t a t e University, University, East East Lansing, MI MI 48824-1115) 48824-1 115) F. W. (Departmentofof Geology, Geology, Michigan Michigan SState W. CAMBRAY CAMBRAY (Department t a t e University, University, East East Lansing, MI MI 48824-1115) 48824- 11 15) The Creek Formation crops out out in a narrow narrow east-west trending trending Reany Creek Formation (RCF) (RCF) crops The Reany belt to t o the t h e north north of of the t h eDead Dead River River storage storagebasin basin in in Marquette MarquetteCounty, County, Michigan. Michigan. Lithologiesofof tthe Lithologies h e formation are a r e meta-mudstones meta-mudstones with with both both round round and and angular, angular, matrix clasts (some matrix supported supported clasts (some up up to t o 33m m inindiameter); diameter);meta-arkosic-wackes; meta-arkosic-wackes; meta-feldspathic meta-feldspathic wackes; wackes; and and minor minor lithic greywackes greywackes which which also also have matrix matrix supported interpreted as being being of glacial glacial supported clasts. The The RCF R C F has has been been previously previously interpreted origin and stratigraphically origin and stratigraphically the t h e lowest lowest formation formation in in the t h eMarquette MarquetteSupergroup Supergroup This interpretation has (Puffet, 1969; 1969; Ojakangas, Ojakangas, 1982). 1982). This has largely largely been been supported supported by the by t h e presence presence of of matrix matrix supported supported clasts clasts which which were were interpreted interpreted as as glacial glacial drop stones. In this this report drop stones. In report the t h e RCF R C F isis interpreted interpreted asasa aproximal proximalmass-flow mass-flow The deposit. The RCF R C F has has similar lithologies and structural trends to t o the the Michigamme Michigamme slate. In sets of of mafic mafic dikes dikes occur occur in in the t h e Marquette Marquette area; area;Keweenawan Keweenawan In general, two t w o sets dikes and older older ssets of dikes dikes which whichaare Pre-Baraga inin age. age. The dikes and e t s of r e Pre-Baraga The base base of of the t h e RCF RCF lies unconformably tones. In In places unconformably on Archean Archean age a g egreens greenstones. places this this contact contact is is Keweenawan aage obscured by by the obscured t h e intrusion intrusion of of Keweenawan Keweenawan dikes. dikes. Keweenawan g e dikes also also No dikes of of an No dikes a n older older age age appear appear to t o cut c u t the t h e RCF. RCF. Regional mapping mapping(Puffet, (Puff et,1974) 1974)indicates indicatest hthat allolder older dikes dikes aare a t all r e truncated by by Regional the no aactual of t h e RCF. RCF. Detailed Detailedmapping mapping of of the t h e RCF R C F (this (this study) study) has has found found no c t u a l case of this truncation; truncation; however, however, many many dikes dikes have have been been observed observed to t o intrude intrude the the Menominee Group, Group, but but not not tthe Menominee h e RCF. RCF. occur occur within within the t h e RCF. RCF. Bedding-cleavage intersectionsand andminor minorfolds foldsaxes axes appear appear tto Bedding-cleavage intersections o indicate indicate aa shallow, doubly doublyplunging plungingsynform synformwith withananaxial axialplane plane dipping dippingslightly slightlytto shallow, o the the southwest. The The presence presence of of kink-bands kink-bands in cleavage indicates indicates aa F2 F2 deformation. deformation. southwest. Beddin& strikest otothe thenorthwest northwest and anddips dipstto Beddin t typically ically strikes o tthe h e southwest or northeast northeast Cleavage strikes strikes northwest (40-803.). ypCleavage northwest and and dips dips to t o the t h esouthwest southwest(55-80°). (55-80 1. (40-80 Measurementson on flow flow directional directional indicators indicators (e.g., (e.g., flute flute casts, Measurements casts, scour scour channels, channels, and tool marks) marks) suggest suggest north-south north-south transport directions directions (mean (mean NI7E N l 7 E or or SI7W, S17W, and N == 24) 24) and and aare r e similar to t o the t h e current current directions directions found found in in the t h e Michigamme Michigamme slate slate (Trow, personal communication). (Trow, All of of the structures of of the massAll t h e sedimentary sedimentary structures t h e RCF R C F can can be be explained explained by by aa massflow mechanism. Depositional models models which which involve involveaa glacial glacial environment flow mechanism. Depositional environment or or glacial marine marine environment environment are a r e unsupported unsupported by by any direct direct evidence evidence (e.g., (e.g., glacial glacial striations depositionala gage fortthe striations on on clasts). clasts). A A Post-Menominee Post-Menominee depositional e for h e RCF R C F is is supported by by tthe dikes and and tthe h e absence absence of of Menominee Menominee aage g e dikes h e apparent truncation truncation of of these dikes by by tthe RCF. Correlation h e RCF. Correlation of of the t h eHuronian Huronian tillites tillitesand and the t h eRCF R C Fwould would thus seem unjustified. �28 Major Element Anorthosites Duluth Complex Element Chemistry of of A n o r t h o s i t e s from the t h e Duluth Quadrangle, Minnesota Snowbank Lake Quadrangle, JANES D D. MILLER, JJR. . MILLER, R . (Dept. (Dept. of of Geology and and Geophysics, Geophysics, University U n i v e r s i t y of of JAMES Minnesota, 55455) MN 55455) Minnesota, Minneapolis, Minneapolis, MN Field petrographic F i e l d and p e t r o g r a p h i c studies s t u d i e s (1) (1) indicate i n d i c a t e that t h a t at a t least l e a s t three t h r e e stages stages main and and llate) of aanorthosite emplacement may may b be distinguished ((early, e a r l y , main a t e ) of n o r t h o s i t e emplacement e d istinguished in i n the t h e Duluth Complex in i n the t h e Snowbank Snowbank Lake quadrangle. quadrangle. P reliminary Preliminary e v a l u a t i o n of new microprobe d a t a on 18 a n o r t h o s i t i c gabbro and 22 evaluation of data on 18 anorthositic gabbro and samples from the ttroctolite r o c t o l i t e samples t h e study s t u d y aarea r e a defines d e f i n e s a number of of distinct distinct elationships w i t h i n and between the t h e anorthositic a n o r t h o s i t i c gabbro gabbro series series chemical rrelationships within and the t h e younger troctolitic t r o c t o l i t i c series. s e r i e s . Major and and minor element element abundances abundances olivine iin n pplagioclase l a g i o c l a s e (P1), (PI), o l i v i n e (01), ( 0 1 ) , clinopyroxene c l i n o p y r o x e n e (Cpx), (Cpx), orthopyroxene orthopyroxene (Opx), and and ooxide minerals Wee report (Opx), xide m i n e r a l s (Ox) (Ox) were analyzed. analyzed. W r e p o r t here h e r e the t h e gengeneral e r a l ccharacteristics h a r a c t e r i s t i c s of of the t h e major element element data. data. 1) Ass aa group, group, the t h e anorthositic a n o r t h o s i t i c suite s u i t e has h a s aa broad broad but b u t constant c o n s t a n t range r a n g e in in 1) A P1I composition (Fig. P (Fig. 1). 1 ) . When compared to t o the t h e troctolites t r o c t o l i t e s from the the study s t u d y aarea r e a and the t h e nearby South South Kawishiwi Kawishiwi Intrusion I n t r u s i o n (SKI—Fig. (SKI-Fig. 1, 1, 2), 2). higher tthe h e aanorthositic n o r t h o s i t i k rrocks o c k s aare re h i g h e r in i n An (Ca/Ca+Na+K) (Ca/ca+~a+K) over o v e r the t h e same same range mole%). This r a n g e of of Fo (Mg/Mg+Fe (Mg/Mg+Fe = = mg, mole%). T h i s relationship r e l a t i o n s h i p is i s also a l s o found found between gabbroic g a b b r o i c and anorthositic a n o r t h o s i t i c rocks r o c k s of of the t h e Stiliwater S t i l l w a t e r Complex Complex (3). (3). The m mg 2) 2) g ratio r a t i o of of the t h e mafic m a f i c phases p h a s e s in i n the t h e troctolitic t r o c t o l i t i c anorthosites a n o r t h o s i t e s of of all TAN, RAL) RAL) is main sstage olivine i s hhigher i g h e r tthan h a n in i n the t h e main tage o livine a l l stages s t a g e s (TAE, (TAE, TAM, ophitic (ANM) (Figs. (Figs. o p h i t i c aanorthosites n o r t h o s i t e s (LSA) (LSA) and the t h e main stage s t a g e anorthosite a n o r t h o s i t e (ANN) 1—4, Table mg 1-4, T a b l e 1). 1 ) . Gabbroic aanorthosite n o r t h o s i t e (CAM) (GAM) Cpx hhas a s intermediate intermediate m g rratios a t i o s (Table 1). 1). 3) The m mg mafic 3) g rratios a t i o s of of the the m a f i c phases p h a s e s indicate i n d i c a t e varying v a r y i n g degrees d e g r e e s of of equi— equimg llibrium i b r i u m over o v e r a cm scale. s c a l e . —— -- The m g relationship r e l a t i o n s h i p of of Opx rims r i m s on 01 0 1 in i n all all aanorthosites, n o r t h o s i t e s , indicates i n d i c a t e s that t h a t the t h e two two phases are a r e in i n disequilibrium d i s e q u i l i b r i u m (Fig. (Fig. 2); mineral 2 ) ; aadjacent djacent m i n e r a l pairs p a i r s plot p l o t below the t h e Fo—En Fo-En equilibrium e q u i l i b r i u m partitioning partitioning Ol—Opx p pairs ccurve u r v e (4). ( 4 ) . 01-Opx a i r s in i n troctolite t r o c t o l i t e are a r e near n e a r equilibrium. e q u i l i b r i u m . Over the mg the m g rrange a n g e cconsidered, o n s i d e r e d , the t h e equilibrium e q u i l i b r i u m curve c u r v e may may be be considered c o n s i d e r e d linear linear r i m s are a r e composition— compositionand simplified s i m p l i f i e d to: t o : Fo == -18.9 1.187 EnOpx. Enopx. Opx rims 18.9 + 1.187 aally l l y similar s i m i l a r to t o that t h a t in i n Opx—Ox Opx-Ox symplectites s y m p l e c t i t e s which which partially p a r t i a l l y replace r e p l a c e 01 01 in i s rare r a r e in i n the t h e troctolites. troctolites. i n aall l l anorthosites a n o r t h o s i t e s investigated, i n v e s t i g a t e d , but b u t is These symplectites s y m p l e c t i t e s are a r e thought thought to t o form form by low low temperature t e m p e r a t u r e (600—700°C), (600-700'~) , late l a t e magmatic to t o subsolidus s u b s o l i d u s oxidation o x i d a t i o n reactions, r e a c t i o n s , possibly p o s s i b l y involving involving mg some mass transfer t r a n s f e r (5). ( 5 ) . The result r e s u l t is i s an m g enrichment of of the t h e Opx r i m Opx Opx could c o u l d have have above that t h a t in i n equilibrium e q u i l i b r i u m with w i t h the t h e core c o r e 01. 01. The rim before formed b e f o r e or o r contemporaneously with w i t h the t h e symplectite. s y m p l e c t i t e . If I f before, b e f o r e , it it Textural rreequilibrated e e q u i l i b r a t e d during d u r i n g symplectite s y m p l e c t i t e formation. formation. T e x t u r a l evidence e v i d e n c e supports supports of Opx-Cpx Opx—Cpx intergrown mineral this -- The The En rratios a t i o s of intergrown m ineral t h i s interpretation. i n t e r p r e t a t i o n . —— pairs P), and of of Opx eexsolution 3, P ) , commonly aas s 001 1 rrims, i m s , and x s o l u t i o n lamellae lamellae p a i r s (Fig. ( F i g . 3, in a Cpx host (E) define a linear trend: + 1.2 EnCpx. l9.5 1 . 2 Encpx. in h o s t (El d e f i n e a l i n e a r t r e n d : Enop Enopx == -19.5 The m mg r i m Opx, Opx, g relationship r e l a t i o n s h i p of of intercumulus i n t e r c u m u l u s Cpx, Cpx, commonly commonly ophitic, o p h i t i c , and and rim which are mm scale, s c a l e , plot p l o t above the the a r e separated s e p a r a t e d by plagioclase p l a g i o c l a s e over a nun llinear i n e a r aarray r r a y (S) (S) indicating i n d i c a t i n g that t h a t most Cpx Cpx formed formed before b e f o r e the t h e Opx Opx or or before during —— The Fo—Encp i t reequilibrated reequilibrated d u r i n g symplectite s y m p l e c t i t e formation. f o r m a t i o n . -Fo-Enc b e f o r e it p compositions units broad p positive compositions of of the t h e vvarious arious u n i t s (Fig. ( F i g . 44) ) show aa single, s i n g l e , broad ositive trend. above, aan Fo—EnCpx t r e n d . From the t h e equilibrium e q u i l i b r i u m equations e q u a t i o n s dderived e r i v e d above, n Fo-Encpx + + x �29 hypothetical h y p o t h e t i c a l equilibrium e q u i l i b r i u m equation e q u a t i o n was was independently i n d e p e n d e n t l y calculated: calculated: Fo -42.1 ++1.425 1 . 4 2Encpx. 5 Encpx. Agreement Agreement of of this t h i s calculated c a l c u l a t e d curve c u r v e and and the the Fo == —42.1 data i s very v e r y good. good. d a t a is 4) 4) Cpx Cpx in i n inclusions i n c l u s i o n s in i n plagioclase p l a g i o c l a s e have h a v e lower lower En ratios r a t i o s than t h a n nearby nearby intercumulus 4, I). I ) . The The form form and and composition c o m p o s i t i o n of of these t h e s e inini n t e r c u m u l u s Cpx Cpx (Fig. ( F i g . 4, clusions, and o often c l u s i o n s , which which also a l s o contain c o n t a i n ilinenite i l m e n i t e and f t e n sodic s o d i c plagioclase, plagioclase, suggests m e l t inclusions. inclusions. s u g g e s t s that t h a t they t h e y represent r e p r e s e n t crystallized c r y s t a l l i z e d melt References: R e f e r e n c e s : 1) 1 ) Miller, Miller, J.D. J . D . and and Weiblen, Weiblen, P.W., P.W., 1982, 1982, Proceedings, P r o c e e d i n g s , 28th 28th ILSG, 26—28. P.W., 1982, 1982, Geol. Geol. Soc. Soc. Am. Am. Mem. Mem. 156, 1 5 6 , 57—82. 57-82. ILSG, 26-28. 2) Weiblen, Weiblen, P.W., 2) 3) I . S . , 1980, 1980, Geochini. Geochim. Cosinochim. Cosmochim. Acta, Acta, 3) Raedke, Raedke, L.D. L.D. and andMcCalluxn, McCallum, I.S., Suppi. Suppl. 12, 1 2 , 133—153. 133-153. 4) 4 ) Medaris, Medaris, L.G., L.G., 1969, 1969, Am. Am. J. J. Sd. S c i . 255, 255, 241—253. 241-253. a l . , 1982, 1982, Lithos L i t h o s 15, 1 5 , 173—182. 173-182. 55)) Zeck, Zeck, H.P., H.P., et e t al., Table T a b l e 1: 1: Compositional C o m p o s i t i o n a l range r a n g e of of mineral m i n e r a l phases phases Stage Rock An Fo An Fo Enoox Stage Rock Type(1) Type(1) Eflopx Early Early TAE TAE 59—70 54—60 54-60 67—70 LSA LSA 38—59 38-59 56—66 57—67 49—60 49-60 64—72 65—71 57—60 65—74 1 ANN ANM TAN TAM 55—72 60—66 54—64 52—66 57—66 TAL TAL 50—70 54—59 54-59 63—69 69—75 5 55—63 54—65 54-65 70—72 69—75 2 SSSA SA CAM GAM Ma Main in Late Late Troctolite Troctolite 65 1) 1) ' j FFo 0 EncDX_ ## samples samples Encpx , .- TAN TAM ± 60 TAE TAL x— x - Troct. Troct. 0- *- I 4 1 1 4 Olivine /Orthopyroxene lorthopyroxene Olivine 0 - LSA LSA o- Otivine Olivine /IPlagioclase Plagioclase 2 2) SKI 55. Troctolites 50 45. An 50 60 55 65 40 70 Enoøx Orthopyroxene Orthopyroxene/ ICilnopyroxene Clinopyroxene 80 55 Efloox 60 65 70 75 Olivine 1 Clinopyroxene 3) 4) 75 6 5 Fo ~ 60 - 70 *' 0$ 65 011* 01 60 : 55 55 60 65 70 75 55 60 65 70 75 �30 The Relationship R e l a t i o n s h i p Between the t h e Basal Zone and Cloud Zone Cu—Ni Cu-Ni Suif ides, Minnamax Deposit, Deposit, Duluth Duluth Complex, Complex, Minnesota Minnesota Sulfid e s , Minnamax (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, SARAH J. J. MILLS (Dept. Duluth, Duluth, Minnesota, 55812) 55812) The copper—nickel of tthe Minnamax d deposit, copper-nickel sulf s u l f iides d e s of h e Minnamax e p o s i t , Babbitt, Babbitt, Minnesota, are Minnesota, a r e located l o c a t e d within w i t h i n two zones of of the t h e Duluth Complex; Complex; these these basal Sulfide minerals aare r e the the b a s a l and cloud zones. zones. Sulfide m i n e r a l s in i n each each consist c o n s i s t of of cchalcopyrite, h a l c o p y r i t e , cubanite, c u b a n i t e , pentlandite, p e n t l a n d i t e , and and pyrrhotite. pyrrhotite. Rock units u n i t s identified i d e n t i f i e d in i n drill d r i l l core c o r e include i n c l u d e a thick t h i c k (—150 ( ~ 1 5 0meters) meters) both overlain underssulfide—poor u l f i d e - p o o r aanorthositic n o r t h o s i t i c troctolite t r o c t o l i t e which is is b oth o v e r l a i n and underu n i t s are are llain a i n by irregularly i r r e g u l a r l y mineralized m i n e r a l i z e d mixed mixed zones. zones. These mixed units composed of of v varying proportions of aanorthosite, composed arying p r o p o r t i o n s of n o r t h o s i t e , troctolite, t r o c t o l i t e , and picrite, with ranging from from ffine (l5mm). p icrite, w i t h ggrain r a i n ssize i z e ranging i n e tto o ppegmatitic e g m a t i t i c (~151n.m). A highly h i g h l y mixed unit u n i t lies l i e s at a t the t h e base b a s e (lower (lower 50 50 meters) m e t e r s ) of of the t h e Duluth Duluth greatest number of mafic pegmatites, Complex and exhibits e x h i b i t s the the g r e a t e s t number of m afic p e g m a t i t e s , rock rock iinclusions, n c l u s i o n s , and the t h e highest h i g h e s t abundance abundance of of Cu—Ni Cu-Ni sulf s u l f ides i d e s ("basal ("basal zone" zone" ssulf u l f iides). des) . Sulfide mineralization most abundant abundant in i n the t h e highly h i g h l y mixed basal basal Sulfide m i n e r a l i z a t i o n is i s most Smaller intervals mineralization unit u n i t of of each each core. core. i n t e r v a l s of of m i n e r a l i z a t i o n also a l s o occur o c c u r in in the unit hundred m meters t h e mixed u n i t several s e v e r a l hundred e t e r s above the t h e base b a s e in i n what have Characteristics been termed "cloud "cloud zones." zones." C h a r a c t e r i s t i c s common to t o both b o t h the t h e basal basal occur iin mixed or zone and and cloud cloud zone zone sulf s u l f ides i d e s are: a r e : 1) 1 ) sulf s u l f i ides d e s occur n tthe h e mixed or highly units, h i g h l y mixed u n i t s , but b u t are a r e absent a b s e n t from the t h e large, l a r g e , consistent c o n s i s t e n t anor— anorthositic ) ssulfide u l f i d e abundances change aabruptly bruptly t h o s i t i c troctolitic t r o c t o l i t i c units, u n i t s , 22) and aare r e generally g e n e r a l l y accompanied by a corresponding change in i n rock r o c k type, type, 3) the most abundant sulfides are associated with mafic pegmatites 3) t h e most abundant s u l f i d e s a r e a s s o c i a t e d w i t h m a f i c p e g m a t i t e s in in both ) tthe h e Cu/Cu+Ni rratios a t i o s aare re b o t h the t h e cloud and basal b a s a l zones, zones, and 44) approximately approximately 0.8 0.8 in i n each. each. This T h i s study s t u d y suggests s u g g e s t s that t h a t there t h e r e is i s a strong s t r o n g correlation c o r r e l a t i o n between mafic mafic pegmatites p e g m a t i t e s and sulfide s u l f i d e occurrence o c c u r r e n c e in i n both b o t h the t h e basal b a s a l and cloud cloud zones. zones. The sulf ides (and ppegmatites) which occur occur iin mixed uunits cone g m a t i t e s ) which n tthe h e mixed n i t s aare r e consulfid e s (and and tto discontinuous ssidered i d e r e d in i n this t h i s study s t u d y to t o be b e inagmatic magmatic and o form d i s c o n t i n u o u s pods pods of of relatively r e l a t i v e l y small s m a l l dimension. dimension. �31 Hydrothermal Alteration A l t e r a t i o n at a t the t h e Helen Helen Mine, Mine, Wawa, Ontario Wawa, Ontario M.L. NEBEL (Dept. M.L. (Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, MN 55812) Duluth, MN 55812) R.L. M MORTON R.L. ORTON (Dept. (Dept. of of Geology, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, MN 55812) Duluth, MN 55812) Felsic FormaF e l s i c vvolcanic o l c a n i c rrocks o c k s uunderlying n d e r l y i n g tthe h e Archean Helen Iron I r o n Formation include lava flows and domes, massive and bedded pyroclastic t i o n include l a v a flows domes, bedded p y r o c l a s t i c They have been v variably rocks, r o c k s , block b l o c k and ash a s h flows, flows, and and hyalotuffs. hyalotuffs. ariably altered hydrothermal solutions mineral— a l t e r e d by hydrothermal s o l u t i o n s to t o five f i v e chemically aand/or n d / o r mineralogically o g i c a l l y distinct d i s t i n c t alteration a l t e r a t i o n facies: f a c i e s : 1) 1 ) least l e a s t altered, a l t e r e d , 2) 2) sericite, sericite, 3) 4 ) chloritoid, c h l o r i t o i d , and and 5) 5 ) ankerite. ankerite. 3) chlorite, c h l o r i t e , 4) Least L e a s t aaltered l t e r e d rrocks o c k s have perhaps undergone spilitization, s p i l i t i z a t i o n , but but metamorhave been affected a f f e c t e d primarily p r i m a r i l y by regional r e g i o n a l greenschist g r e e n s c h i s t facies f a c i e s metamorphism, phism, and are are the t h e freshest f r e s h e s t rocks r o c k s to t o be b e found found in i n the t h e study s t u d y area. a r e a . The other named ffor dominant aalteration mineral o t h e r aalteration l t e r a t i o n ffacies a c i e s aare r e named o r tthe h e dominant lteration m ineral ppresent. resent. Sericite widespread (6x2 (6x2kin) km) semi—consemi-conS e r i c i t e facies f a c i e s alteration a l t e r a t i o n forms forms aa widespread formable zone beneath the t h e iron i r o n formation. formation. A less l e s s extensive e x t e n s i v e(2xl (2x1kin) km) pipe—like body, cconsisting of cchlorite, p i p e - l i k e body, o n s i s t i n g of h l o r i t e , cchioritoid, h l o r i t o i d , and aankerite nkerite facies alteration facie's a l t e r a t i o n zones, zones, cross—cuts c r o s s - c u t s the t h e sericite s e r i c i t e zone. zone. Based on mineralogy mineralogy and and cchemistry of the Based h e m i s t r y of t h e aalteration, l t e r a t i o n , and on the the of tthe zones, tthe geometry of h e aalteration l t e r a t i o n zones, h e ffollowing o l l o w i n g sequence of of events events Shallow for i s proposed. proposed. Shallow circulatcirculatf o r the t h e development of of the t h e alteration a l t e r a t i o n is ing heated by by aa ssubvolcanic w a t e r (1—3 (1-3 kin), km), heated u b v o l c a n i c intrusion i n t r u s i o n (possibly (possibly i n g sea water the of felsic within t h e JJubilee u b i l e e Stock), S t o c k ) , encountered rrocks o c k s of f e l s i c composition w ithin water—rock reactions the volcanic the v o l c a n i c succession. s u c c e s s i o n . Sea water-rock r e a c t i o n s evolved evolved an a n acidic, acidic, K—rich solution migrated upward, upward, rreacting with K-rich s o l u t i o n that t h a t migrated eacting w i t h overlying o v e r l y i n g felsic felsic plagioclase rrocks, o c k s , converting converting p l a g i o c l a s e to t o sericite s e r i c i t e and quartz q u a r t z by the t h e addition addition porosity of K and the t h e removal of of Na. N a . The p o r o s i t y in i n the t h e altered a l t e r e d rocks r o c k s was of decreased, widespread, relatively r e l a t i v e l y impermeable, impermeable, semi—conformsemi-conformd e c r e a s e d , forming a widespread, able hydrothermal system. a b l e sericitic s e r i c i t i c alteration a l t e r a t i o n zone over the t h e hydrothermal Deeper—circulating D e e p e r - c i r c u l a t i n g sea s e a water w a t e r reacted r e a c t e d with w i t h basaltic b a s a l t i c rock r o c k at a t depths depths greater Mg, Mn, Mn, and Ca relative e n r i c h e d in i n Fe, Fe, Mg, relative g r e a t e r than t h a n 3 km and became enriched This tto o tthe h e felsic f e l s i c rocks. rocks. T h i s second hydrothermal solution s o l u t i o n moved upward i t encountered the t h e previously p r e v i o u s l y altered, a l t e r e d , relatively r e l a t i v e l y impermeable impermeable where it Fracture cap rock. rock. F r a c t u r e and fault f a u l t systems were developed or o r reactivated reactivated l l o w i n g rreaction e a c t i o n of h i s ssolution olution w i t h sericite sericite rock, aallowing of tthis with iin n the the cap rock, This Mn and the the ffacies a c i e s rocks. rocks. T h i s involved the t h e addition a d d i t i o n of of Fe, Fe, Mg, and Mn att the t o form chlorite chlorite pyrophyllite a t h e expense of of K to removal of ± pyrophyllite ssericite. ericite. + �32 During During greenschist g r e e n s c h i s t facies f a c i e s metamorphism, metamorphism, the t h e assemblage assemblage chlorite chlorite + pyrophyllite p y r o p h y l l i t e was w a s converted c o n v e r t e d to t o chioritoid c h l o r i t o i d ++ quartz, q u a r t z , whereas whereas chlorite chlorite in i n the t h e absence absence of of an a n aluminum aluminum silicate s i l i c a t e phase phase remained remained stable. stable. + Near Near the t h e sea s e a floor, f l o o r , aa sudden sudden release r e l e a s e of of pressure p r e s s u r e on on the t h e solution, solution, coupled coupled with w i t h mixing of of cool c o o l sea s e a water, w a t e r , rapidly r a p i d l y decreased d e c r e a s e d carbon carbon dioxdioxide m a s s precipitation p r e c i p i t a t i o n of of iron i r o n carbonate c a r b o n a t eand andf f or— ori d e solubility, s o l u b i l i t y , causing c a u s i n g mass mation mation of of the t h e ankerite a n k e r i t e fades f a c i e s assemblage. assemblage. Precipitation P r e c i p i t a t i o n of of siderite siderite occurred sea floor. floor. o c c u r r e d on on the t h e sea The The absence absence of of base b a s e metals m e t a l s and and sulfur s u l f u r in i n the t h e Helen Helen deposit d e p o s i t sug— suggests h i g h water/rock w a t e r / r o c k ratio r a t i o for f o r the t h e hydro— hydrog e s t s aa low low temperature t e m p e r a t u r e and and aa high thermal thermal system. system. n Li H I Sericite SericiteAlteration Alteration I Chlorite Chlorite±iAl-Silicate AI-SilicateAlteration Alteration a ... :;::.. .... .p ::.+ :.:.::: Ankerite : AnkeriteAlteration Alteration .......... ......... Figure F i g u r e 1. 1. Alteration A l t e r a t i o n Model Model �33 IIgneous g n e o u s Rocks Rocks of of the t h e Baraboo Baraboo District, D i s t r i c t , Wisconsin Wisconsin W.L. W.L. PETRO PETRO (Dept. (Dept. of of Geology Geology and and Geophysics, Geophysics, University University of of Wisconsin, Wisconsin, Madison, Madison, WI W I 53706) 53706) Volcanic Volcanic rocks, r o c k s , granitic g r a n i t i c rocks r o c k s and and mafic mafic dikes d i k e s occur occur in i n the t h e Baraboo Baraboo district d i s t r i c t of of south—central s o u t h - c e n t r a l Wisconsin. Wisconsin. Recent Recent field f i e l d work work has h a s established e s t a b l i s h e d the t h e age age relations relations among these igneous rocks and the associated among t h e s e igneous r o c k s and t h e a s s o c i a t e d Baraboo Baraboo q u a r t z i t e , yielding y i e l d i n g important important information i n f o r m a t i o n on on the t h e geolgeolquartzite, ogic o g i c evolution e v o l u t i o n of of this t h i s part p a r t of of the t h e southern s o u t h e r n Lake Lake Superior Superior region. region. The The volcanic v o l c a n i c rocks r o c k s are a r e exposed exposed along a l o n g the t h e outer o u t e r margins margins of the quartzite ridges that outline the Baraboo synclinof t h e q u a r t z i t e r i d g e s t h a t o u t l i n e t h e Baraboo synclin— orium, orium, and and are a r e probably probably the t h e basement basement upon upon which which the t h e meta— metasedimentary sedimentary sequence sequence was was deposited. d e p o s i t e d . These These rocks r o c k s consist consist of of porphyritic p o r p h y r i t i c rhyolite r h y o l i t e flows, flows, tuffs t u f f s and and agglomerates. agglomerates. The The BaxterHollow B a x t e r H o l l o wgranite g r a n i t e contains c o n t a i n s sparse s p a r s e xenoliths x e n o l i t h s of of volcanic Where exposed exposed v o l c a n i c rocks r o c k sand andbanded b a n d e diron i r o n formation. formation. Where at a t the t h e base b a s e of of the t h e quartzite, q u a r t z i t e , the t h e chilled c h i l l e d margin margin has h a s been been dtsrupted disrupted by by granitic g r a n i t i c dikes. d i k e s . Mafic Mafic dikes d i k e s also a l s o intrude intrude the t h e Baxter Baxter Hollow Hollow granite. g r a n i t e . All A l l these t h e s e rocks r o c k s have have been been metamorphosed metamorphosed to t o low—grade low-grade assemblages. assemblages. The The relationship r e l a t i o n s h i p between between the t h e quartzite q u a r t z i t e and and granite g r a n i t e has has long From this t h i s new new informinformlong been been aa point p o i n t of of controversy. c o n t r o v e r s y . From ation, a t i o n , it i t is i s concluded concluded that t h a t the t h e quartzite q u a r t z i t e was was deposited deposited upon upon the t h e volcanic v o l c a n i c rocks, r o c k s , and and intruded i n t r u d e d by by the t h e Baxter Baxter Hollow Hollow granite. granite. �34 Depositional D e p o s i t i o n a l and and Structural S t r u c t u r a l Feature F e a t u r e of of the t h e Upper Freda Sandstone Sandstone Fred PULKA (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological Fred S. S. PULKA University, U n i v e r s i t y , Houghton, Houghton, MI M I 49931) 49931) The i s part p a r t of of the t h e Upper Upper Keweenawan Keweenawan Oronto Oronto Group. Group. The The The Freda Freda Sandstone Sandstone is upper upper beds beds of of the t h e Freda Freda exposed exposed at a t the t h e type t y p e locality l o c a l i t y at a t Freda, Freda, NI M I are are mostly mostly thin, t h i n , red, r e d , alternating a l t e r n a t i n g planar p l a n a r laminated laminated and and microtrough microtrough cross— crosslaminated laminated beds. beds. The The planar p l a n a r laminated laminated beds are a r e claystone c l a y s t o n e or o r very v e r y fine— fineto t o medium—grained medium-grained sandstone. sandstone. The The claystone c l a y s t o n e and and sandstone s a n d s t o n e are a r e distinct distinct The and non—gradational. non-gradational. The planar p l a n a r laminated laminated sandstones s a n d s t o n e s have have mica mica flakes flakes parallel p a r a l l e l to t o the t h e bedding and and often o f t e n have have parting p a r t i n g lineation l i n e a t i o n on on bedding bedding planes. p l a n e s . They They occasionally o c c a s i o n a l l y have have small s m a l l scale s c a l e straight s t r a i g h t to t o sinuous s i n u o u s current current ripple r i p p l e marks on the t h e bedding surface s u r f a c e causing c a u s i n g an undulating u n d u l a t i n g lamination lamination within w i t h i n the t h e horizontally h o r i z o n t a l l y laminated laminated beds beds due due to t o ripple r i p p l e migration. migration. The The microtrough microtrough cross—laminated cross-laminated beds beds usually u s u a l l y have have small s m a l l lunate l u n a t e ripple ripple Migration of of the t h e lunate l u n a t e ripples r i p p l e s probably probably marks marks on on the t h e bedding bedding planes. p l a n e s . Migration caused the t h e microtrough microtrough cross—lamination. c r o s s - l a m i n a t i o n . Raindrop Raindrop imprints i m p r i n t s can can be b e seen seen on some some lunate l u n a t e ripples r i p p l e s in i n close c l o s e association a s s o c i a t i o n with w i t h dessication d e s s i c a t i o n features. features. The claystone c l a y s t o n e planar p l a n a r laminated laminated beds are a r e alternating a l t e r n a t i n g greenish g r e e n i s h and and red r e d in in c o l o r . They commonly commonly have have distorted d i s t o r t e d or o r convolute c o n v o l u t e bedding. bedding. One One individual individual color. bed, bed, eight e i g h t inches i n c h e s thick t h i c k was was traced t r a c e d over over half h a l f aa mile. mile. The two two distinct d i s t i n c t grain g r a i n size s i z e facies f a c i e s and and the t h e bedding succession s u c c e s s i o n imply imply aa transitional f l u v i a l and and lacustrine l a c u s t r i n e condicondit r a n s i t i o n a l environment, environment, possibly p o s s i b l y between fluvial tions. t i o n s . The sandstone s a n d s t o n e mineralogy suggests s u g g e s t s aa mixed silicic s i l i c i c and and mafic volcanic volcanic source s o u r c e area. a r e a . The silicic s i l i c i c fraction f r a c t i o n has h a s aa high h i g h proportion p r o p o r t i o n of of strained s t r a i n e d quartz quartz suggesting s u g g e s t i n g aa subsidiary s u b s i d i a r y metamorphic metamorphic source. source. The Freda Sandstone Sandstone in i n this t h i s area a r e a has h a s aa well w e l l developed developed extensional e x t e n s i o n a l joint joint system striking N50E. The Freda is i s cut c u t by numerous normal s t r i k i n g approximately approximately N5OE. faults f a u l t s either e i t h e r perpendicular p e r p e n d i c u l a r to t o or o r parallel p a r a l l e l to t o the t h e joint j o i n t system. system. The The faults 30 feet. f e e t . Normal Normal faults faults f a u l t s have have vertical v e r t i c a l displacements d i s p l a c e m e n t s of of from from one one to t o 30 They parallel p a r a l l e l to t o the t h e master m a s t e r joint j o i n t system system occasionally o c c a s i o n a l l y have drag d r a g folds. f o l d s . They are i s lacking l a c k i n g along a l o n g the t h e faults. faults. a r e downthrown to t o the t h e west and mineralization m i n e r a l i z a t i o n is The faults t o the t h e master joint j o i n t system system are a r e the t h e most f a u l t s nearly n e a r l y at a t right r i g h t angles a n g l e s to The faulting f a u l t i n g and and abundant abundant and and are a r e frequently f r e q u e n t l y mineralized m i n e r a l i z e d with w i t h calcite. c a l c i t e . The folding developed late history f o l d i n g probably developed l a t e in i n the t h e subsidence h i s t o r y of of the t h e Lake S u p e r i o r Syncline. Syncline. Superior �35 Evidence for f o r Glacial G l a c i a l Marine Marine Sedimentation Sedimentation in i n the t h e Early E a r l y Proterozoic Proterozoic Evidence Gowganda Gowganda Formation, Formation, Northeastern N o r t h e a s t e r n Ontario, O n t a r i o , Canada Canada LAWRENCE C. C . ROSEN ROSEN (Dept. (Dept. of LAWRENCE of Geology, Geology, University U n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, Duluth, MN 55812) 55812) Uuluth, MN f o r glacial g l a c i a l marine sedimentation s e d i m e n t a t i o n in i n the t h e Gowganda Gowganda Formation Formation Evidence for (Huronian Gowganda—Elk Lake area (Huronian Supergroup) Supergroup) in i n the t h e Gowganda-Elk a r e a of of northeastern northeastern Ontario O n t a r i o changes changes the t h e previously p r e v i o u s l y known known regional r e g i o n a l distribution d i s t r i b u t i o n of of conticontinental n e n t a l glacial g l a c i a l and and glacial g l a c i a l marine marine sedimentary sedimentary facies. f a c i e s . Lindsey Lindsey (1969) (1969) interpreted i n t e r p r e t e d the t h e Gowganda Gowganda to t o be be aa marine marine deposit d e p o s i t in i n the t h e south s o u t h (Espanola— (EspanolaWhitefish Whitefish Falls) F a l l s ) and and aa continental c o n t i n e n t a l deposit d e p o s i t in i n the t h e north n o r t h (Cobalt (Cobalt area) area) which which includes i n c l u d e s the t h e area a r e a under under discussion d i s c u s s i o n here. here. In I n the t h e study s t u d y area, a r e a , the t h e Gowganda Gowganda rests r e s t s unconformably upon upon the t h e Archean Archean basement. i s from from 00 to t o >1700 >I700 mm thick thick basement. The The subhorizontal s u b h o r i z o n t a l formation formation is (based (based on drill d r i l l hole h o l e data) d a t a ) and and no no complete complete sections s e c t i o n s are a r e present. p r e s e n t . It It is i s a heterogeneous assemblage assemblage of of diamictites, d i a m i c t i t e s , orthoconglomerates, orthoconglomerates, gray— graywackes,arkoses, wackes,arkoses, siltstones, s i l t s t o n e s , argillites, a r g i l l i t e s , pebbly pebbly argillites, a r g i l l i t e s , and and breccias. b r e c c i a s . Lateral L a t e r a l and and vertical v e r t i c a l facies f a c i e s changes changes can can be b e rapid, r a p i d , however however the t h e graywacke—argillite g r a y w a c k e - a r g i l l i t e association a s s o c i a t i o n is i s abundant, abundant, widespread, widespread, and and conconstitutes dominant s t i t u t e s the thed o m i n a n tfacies. f a c i e s . Orthoconglomerates Orthoconglomerates and and massive massive to t o thick thick bedded bedded arkoses, a r k o s e s , occassionally o c c a s s i o n a l l y cross—bedded, cross-bedded, are a r e most most common common at a t the the base i s aa prominent prominent base of of the t h e section s e c t i o n and and again a g a i n near n e a r the t h e top. t o p . Diamictite D i a m i c t i t e is lithology l i t h o l o g y and and varies v a r i e s from from massive massive to t o weakly stratified s t r a t i f i e d with w i t h clasts c l a s t s up up to t o 1.2 1.2 m in i n apparent a p p a r e n t diameter; d i a m e t e r ; units u n i t s vary v a r y from from aa decimeter d e c i m e t e r to t o as a s much much as i n thickness. t h i c k n e s s . Wisps Wisps and and deformed deformed pieces p i e c e s of of sandy sandy material m a t e r i a l are are a s 20 20 mm in often o f t e n present p r e s e n t within w i t h i n the t h e diamictites. d i a m i c t i t e s . Contacts C o n t a c t s with w i t h other o t h e r units u n i t s can can be be sharp, s h a r p , irregular, i r r e g u l a r , or o r transitional. t r a n s i t i o n a l . The The diamictite d i a m i c t i t e is i s restricted r e s t r i c t e d to to the t h e lower lower two—thirds t w o - t h i r d s of of the t h e formation. formation. Interbedded Interbedded graywackes, graywackes, siltstones, s i l t s t o n e s , and and argillites a r g i l l i t e s commonly commonly conconstitute to 4 m thick s t i t u t e fining—upward fining-upward sequences sequences from from 22 cm cm t o 4 m t h i c k in i n the t h e lower lower portion p o r t i o n of of the t h e section s e c t i o n and and both both fining—upward fining-upward and and coarsening—upward coarsening-upward sequences in the upper part of the section. Internal sequences i n t h e upper p a r t of t h e s e c t i o n . I n t e r n a l stratification stratification includes i n c l u d e s graded beds, beds, ripple r i p p l e marks, marks, laminations, l a m i n a t i o n s , and and convolute c o n v o l u t e bedding. bedding. In I n addition, a d d i t i o n , features f e a t u r e s such such as a s ripped—up ripped-up clasts, c l a s t s , flame flame structures, s t r u c t u r e s , and and other o t h e r loading l o a d i n g phenomena phenomena are a r e present. p r e s e n t . Thinly Thinly laminated laminated siltstone s i l t s t o n e and and argillite 30 cm cm are a r e present present l a r g e as a s 30 a r g i l l i t e sequences sequences with w i t h lonestones l o n e s t o n e s as a s large thoughout thoughout the t h e lower lower two—thirds t w o - t h i r d s of of the t h e section. s e c t i o n . They They are a r e more more common common in the central and western portions i n t h e c e n t r a l and w e s t e r n p o r t i o n s of of the t h e study s t u d y area. a r e a . Lonestone Lonestone sequences t h i c k , while w h i l e individual i n d i v i d u a l units u n i t s vary v a r y from from 40 mm thick, sequences are a r e as a s much much as a s 40 11to 5 m thick. t o 5 m t h i c k . Breccias B r e c c i a s and and units u n i t s with w i t h soft s o f t sediment sediment deformation deformation structures s t r u c t u r e s are a r e fairly f a i r l y widespread widespread but b u t constitute c o n s t i t u t e aa minor minor part p a r t of of the the section; .5 to t o approximately approximately 44 mm thick. thick. s e c t i o n ; units u n i t s vary v a r y from from .5 The t h e Gowganda Gowganda in i n this t h i s area a r e a is is The following f o l l o w i n g depositional d e p o s i t i o n a l history h i s t o r y of of the Paleovalleys, P a l e o v a l l e y s , probably probably largely l a r g e l y tectonic t e c t o n i c in i n origin o r i g i n with with perhaps 1000 mm relief, r e l i e f , were were partially p a r t i a l l y filled f i l l e d by by fluvial fluvial perhaps as a s much much as a s 1000 processes p r o c e s s e s which which deposited d e p o s i t e d the t h e orthoconglomerates orthoconglomerates and and arkoses a r k o s e s prior p r i o r to to the t h e arrival a r r i v a l of of glacial g l a c i a l ice i c e in i n the t h e vicinity. v i c i n i t y . The The lonestones l o n e s t o n e s in i n the the laminated laminated units u n i t s are a r e interpreted i n t e r p r e t e d to t o be b e dropstones d r o p s t o n e s released r e l e a s e d from from meltmelting i n g icebergs i c e b e r g s or o r aa floating f l o a t i n g ice i c e shelf. s h e l f . The The paucity p a u c i t y of of unequivocable unequivocable indicated. indicated. �36 varved varved bedding bedding and and the t h e widespread widespread occurrence o c c u r r e n c e of of dropstone—bearing dropstone-bearing sequences sequences is i s suggestive s u g g e s t i v e of of aa glacial g l a c i a l marine marine rather r a t h e r than t h a n aa glacial glacial lacustrine l a c u s t r i n e environment. environment. The The weakly weakly stratified s t r a t i f i e d diamictites, d i a m i c t i t e s , in i n view view of of their t h e i r distribution d i s t r i b u t i o n and and transitional t r a n s i t i o n a l contacts c o n t a c t s with w i t h dropstone d r o p s t o n e units, units, are a r e interpreted i n t e r p r e t e d to t o be be the t h e products p r o d u c t s of of rapid r a p i d fallout f a l l o u t of of abundant abundant debris debris released r e l e a s e d beneath beneath an an ice i c e shelf. s h e l f . The The generally g e n e r a l l y thinner, t h i n n e r , massive massive diamic— diamictites t i t e s are a r e attributed a t t r i b u t e d to t o submarine submarine gravity g r a v i t y flow flow mechanisms mechanisms beneath beneath an an ice i c e shelf s h e l f or o r near n e a r the t h e margin margin of of aa melting m e l t i n g land—based land-based glacier. g l a c i e r . The The fining—upward fining-upward and and coarsening—upward coarsening-upward sequences sequences reflect r e f l e c t the t h e changing changing conditions c o n d i t i o n s within w i t h i n the t h e basin b a s i n as a s increases i n c r e a s e s and and decreases d e c r e a s e s in i n both b o t h energy energy and outwash. The The and sediment sediment supply supply occurred o c c u r r e d and and may may represent r e p r e s e n t submarine submarine outwash. graywackes graywackes resulted r e s u l t e d from from the t h e interaction i n t e r a c t i o n of of various v a r i o u s types t y p e s of of sediment sediment gravity dominantly turbidity t u r b i d i t y currents c u r r e n t s with w i t h subordinate subordinate g r a v i t y flows, f l o w s , dominantly fluidized/liquidized The more more well well f l u i d i z e d / l i q u i d i z e d flows flows and and possibly p o s s i b l y grain g r a i n flows. f l o w s . The sorted s i l t s t o n e s , and and argillites a r g i l l i t e s may may reres o r t e d and and laminated laminated sandstones, s a n d s t o n e s , siltstones, present p r e s e n t more more normal normal marine marine sedimentation. sedimentation. The The breccias b r e c c i a s and and deformed deformed units e i t h e r resedimentation r e s e d i m e n t a t i o n from from unstable u n s t a b l e depositional depositional u n i t s represent r e p r e s e n t either sites or minor tectonic instability. s i t e s o r minor t e c t o n i c i n s t a b i l i t y . The The distribution d i s t r i b u t i o n of of the t h e rock rock types t y p e s within w i t h i n the t h e thick t h i c k stratigraphic s t r a t i g r a p h i c column column suggests s u g g e s t s changing changing condiconditions t i o n s probably probably associated a s s o c i a t e d with w i t h advances advances and and retreats r e t r e a t s of of glaciers glaciers located Basin subsidence s u b s i d e n c e continued continued throughout throughout Gowganda Gowganda l o c a t e d to t o the t h e north. n o r t h . Basin time, allowing the great thickness of sediments to accumulate time, a l l o w i n g t h e g r e a t t h i c k n e s s of sediments t o accumulate and and be be preserved. preserved. In I n late l a t e Gowganda Gowganda time, time, amelioration a m e l i o r a t i o n of of the t h e climate c l i m a t e occuroccurred, r e d , indicated i n d i c a t e d by by the t h e lack l a c k of of glacial g l a c i a l features f e a t u r e s in i n the t h e deposits. deposits. Sedimentation Sedimentation appears a p p e a r s to t o have have been been largely l a r g e l y fluvial—deltaic, f l u v i a l - d e l t a i c , as a s also also evidenced in the overlying Lorrain Formation. e v i d e n c e d i n t h e o v e r l y i n g L o r r a i n Formation. �37 A l t e r a t i o n of of the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e in i n the t h e Vicinity Vicinity Alteration of the t h e Ropes Ropes Gold Gold Mine, Mine, Marquette Marquette County, County, Michigan Michigan of Geol. Engrg., Engrg., Michigan Michigan Technological Technological Dean Rossell R o s s e l l (Dept. (Dept. of of Geol. Geol. && Geol. Dean U n i v e r s i t y , Houghton, Houghton, MI M I 49931) 49931) University, Gold Gold mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Mine Mine is i s contained c o n t a i n e d entirely e n t i r e l y in i n an an east— eastwest west striking s t r i k i n g septum septum of of highly h i g h l y altered a l t e r e d felsic f e l s i c rock r o c k within w i t h i n the t h e serpentin— serpentini z e d Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Near Near the t h e Ropes Ropes Mine Mine the t h e serpentinite s e r p e n t i n i t e consist consist ized of two two principal p r i n c i p a l textural t e x t u r a l varieties: v a r i e t i e s : Type of A, with w i t h well w e l l preserved p r e s e r v e d relict relict Type A, B, showing showing recrystallized r e c r y s t a l l i z e d and and foliated f o l i a t e d textures, textures, igneous textures, t e x t u r e s , and and Type Type B, igneous probably produced produced by by shearing. s h e a r i n g . AA prominent prominent zone zone of of Type Type BB serpentinite serpentinite probably a l o n g the t h e north n o r t h shore s h o r e of of Deer Deer Lake Lake may may represent r e p r e s e n t an an extension e x t e n s i o n of of aa shear shear along zone along a l o n g the t h e felsic f e l s i c septum. septum. zone Compositionally, Compositionally, the t h e serpentinites s e r p e n t i n i t e s represent r e p r e s e n t altered a l t e r e d harzburgite h a r z b u r g i t e and and l h e r z o l i t e (Rossell ( R o s s e l l and and Kalliokoski, K a l l i o k o s k i , this t h i s volume). volume). An An original o r i g i n a l composicomposilherzolite t i o n a l zoning zoning or o r layering l a y e r i n g may may be b e reflected r e f l e c t e d by by wide wide variations v a r i a t i o n s in i n the t h e olivine olivine tional to t o pyroxene pyroxene ratios r a t i o s determined determined from from calculated c a l c u l a t e d mineral m i n e r a l modes, modes, but b u t the t h e scale scale of these t h e s e variations v a r i a t i o n s has h a s not n o t been been established. established. of + Serpentinite dolomite ±t magnesite magnesite S e r p e n t i n i t e has h a s been been extensively e x t e n s i v e l y altered a l t e r e d to t o aa talc t a l c + dolomite Major and and ±Â chlorite c h l o r i t e assemblage assemblage in i n aa zone zone adjacent a d j a c e n t to t o the t h e Ropes Ropes ore o r e body. body. Major trace t r a c e element element compositions, compositions, including i n c l u d i n g gold, gold, were were determined determined for f o r aa suite s u i t e of of talc—carbonate t a l c - c a r b o n a t e rocks r o c k s from from the t h e northern n o r t h e r n alteration a l t e r a t i o nzone. zone. From From this t h i s data d a t a relarelat i v e additions a d d i t i o n s and and losses l o s s e s of of chemical chemical components components were were computed computed by by two two methods: methods: tive f i r s t , a sassuming s u m i n g tthat h a t aalteration l t e r a t i o n ooccurred c c u r r e d at a t constant c o n s t a n t volume, volume, and and the the The first, The A 1 and and Sc Sc are a r e immobile immobile during d u r i n g alteration a l t e r a t i o n while w h i l e volume volume second assuming assuming that t h a t Al second i s allowed allowed to t o change. change. Changes Changes calculated c a l c u l a t e d using u s i n g the t h e first f i r s t method method appear appear to to is be b e more more consistent c o n s i s t e n t with w i t h observed observed mineralogical m i n e r a l o g i c a l changes changes than t h a n those t h o s e calculated calculated by the t h e latter l a t t e r method. method. by Talc—carbonate Talc-carbonate alteration a l t e r a t i o n at a t the t h e Ropes Ropes Mine Mine appears a p p e a r s to t o have have resulted r e s u l t e d in i n the the addition A l , and and the t h e removal removal of of H20 Hz0 and and Mg Mg from from the t h e serpentin— serpentinCO2, Ca Ca and and Al, a d d i t i o n of of CO2. i t e . Au Au abundance abundance in i n the t h e serpentinite s e r p e n t i n i t e samples samples analyzed analyzed were were found found to t o be b e near near ite. c r u s t a l averages. averages. Talc—carbonate Talc-carbonate samples samples showed showed greater g r e a t e r variation, v a r i a t i o n , but b u t gengencrustal erally e r a l l y had had Au Au concentrations c o n c e n t r a t i o n s equal e q u a l to t o or o r greater g r e a t e r than t h a n those t h o s e found found in i n serpen— serpent i n iites. tes. tin Gold may may have have been been transported t r a n s p o r t e d as a s aa carbonyl c a r b o n y l or o r carbonate c a r b o n a t e complex complex in i n aa Gold CO2 rich r i c h fluid f l u i d from from some some outside o u t s i d e source s o u r c e to t o the t h e ore o r e host h o s t rock. r o c k . Subsequent Subsequent CO2 c a r b o n a t e forming forming reactions r e a c t i o n s in i n the t h e ultramafic u l t r a m a f i c rock r o c k surrounding s u r r o u n d i n g the t h e ore o r e host host carbonate rock CO2 and/or r o c k sufficiently s u f f i c i e n t l y lowered lowered the t h e Pcoi a n d / o r decreased d e c r e a s e d the t h e acidity a c i d i t y to t o allow a l l o w for for structures d e p o s i t i o n of of gold gold in i n suitable suitable s t r u c t u r e s in i n the t h e ore o r e host h o s t rock. rock. deposition �38 C o b a l t , Nickel, Cobalt, Nickel, and Vanadium Contents of of P y r i t e from Michigamme Michigamme Slate, S l a t e , Michigan Michigan Pyrite A. P. P. Ruotsala, R u o t s a l a , Paul P a u l M. M. Stadnik, S t a d n i k , T. T. J. J . Bornhorst (Dept. (Dept. of of Geol. Geol. A. Geol. Engrg., Engrg., Michigan Michigan Tech. Tech. Univ., Univ., Houghton, Houghton, MI M I 49931) 49931) & Geol. i s an organic—rich o r g a n i c - r i c h metasedimentary rock r o c k in in S l a t e is The Michigamme Slate central Upper Peninsula of Michigan. central P e n i n s u l a of Michigan. The Michigan Geological G e o l o g i c a l Survey, Survey, with w i t h funding funding from from the t h e Department of Energy tested t e s t e d the t h e uranium uranium potenpotenof tthe Michigamme iin Marquette, Baraga Baraga and and IIron Counties w with ttial i a l of h e Michigamme n Marquette, r o n Counties ith drill ssix i x diamond d r i l l holes h o l e s (Trow, (Trow, 1979). 1979). IIn n tthis h i s study, s t u d y , pyrites p y r i t e s were separated material nickel, s e p a r a t e d from core core m a t e r i a l and analyzed for f o r cobalt, cobalt, n i c k e l , and vanadium with w i t h the t h e objective o b j e c t i v e of of determining d e t e r m i n i n g its i t s mode mode of of origin. origin. Most pyrites p y r i t e s fall f a l l into i n t o the t h e syngenetic s y n g e n e t i c field f i e l d of of Price P r i c e (1972), (1972), in in terms of of Co/Ni Co/Ni rratios; however, aa number number of of hhigh Co/Ni rratios were terms a t i o s ; however, i g h Co/Ni a t i o s were which fall found which f a l l into i n t o the t h e volcanic—exhalative v o l c a n i c - e x h a l a t i v e massive massive sulfide s u l f i d e field. field. References Trow, Trow, J., J . , 1979, 1979, Final F i n a l report r e p o r t diamond—drilling diamond-drilling for f o r geologic g e o l o g i c informainformaMiddle Precambrian Precambrian bbasins western portion of ttion i o n iin n tthe h e Middle a s i n s in i n tthe he w estern p o r t i o n of northern n o r t h e r n Michigan: Michigan: Geol. Geol. Surv. Surv. Div., Div., Michigan Dept. Dept. Nat. Nat. Re— ReOFR GJBX-162(79), CJBX—162(79), 44 UDOE OFR 44 p. p. ssources, o u r c e s , Lansing, Lansing, Open—File Open-File Report Report TJDOE Price, P r i c e , B.G., B.G., 1972, Minor elements elements in i n pyrites p y r i t e s from from the t h e Smithers Smithers map B.C. and eexploration of minor element studies x p l o r a t i o n aapplications p p l i c a t i o n s of studies aarea, r e a , B.C. (M.S. Thesis): T h e s i s ) : Univ. Univ. of of British B r i t i s h Columbia, Columbia, Vancouver, Vancouver, 270 270 p. p. (M.S. �39 Geochemistry of the the Volcanic Rocks of Northeastern Northeastern Wisconsin KLAUS Reston, Virginia Virginia J. SCHULZ SCHULZ (U.S. (U.S. Geological Geological Survey, Survey, Reston, KLAUS J. 22092) 22092) The The early early Proterozoic Proterozoic volcanic—plutonic volcanic-plutonic belt of north—central north-central Wisconsin Wisconsin is is well well exposed exposed in in the the northern northern half half of of Marinette Marinette County. County. In In this this area, area, the the volcanic volcanic sequence sequence has has been been informally informally divided divided into four formations Formation, the formations (Jenkins, (Jenkins, 1973): 1973): the Quinnesec Formation, McAllister McAllister Formation, Formation, the the Beecher Beecher Formation, Formation, and the the Pemene Pemene FormaFormaAlthough tion. Although stratigraphic stratigraphic relationships relationships between between these these are are still still tion. not fully fully resolved, resolved, it it appears appears that the overall section section represents represents a progression progression from from mafic mafic through through felsic felsic volcanics. volcanics. Although calc-alkaline affinity affinity has has been been recognized recognized Although aa general general caic—alkaline for the more felsic section, uncertainty uncertainty felsic portions of this volcanic section, still still remains as as to the the geochemical geochemical affinities of the basaltic rocks and their possible petrologic relationship relationship to the more felsic felsic volcanics. the present study, study, a suite suite of samples samples was collected volcanics. For the analysis (major for analysis (major elements, elements, rare rare earth, earth, and and other other trace trace elements) elements) with emphasis emphasis on on the the mafic mafic Quinnesec Quinnesec Formation. Formation. The diabases range The Quinnesec Quinnesec pillowed flows flows and associated diabases range from from basalt through through andesite andesite and show show little little evidence evidence of a trend in in iron iron high, A1203 and have variable, variable, though though generally high, enrichment. enrichment. They have elements (REE) (WE) show show aa wide wide range range Ti02 contents. contents. The rare earth elements low Ti02 in both total abundance abundance and and chondrite chondrite normalized normalized slopes. slopes. Most .14—.38 basalts show depletion with with [La/Smjn [LaISm] == .14-.38 show extreme light (L)REE (L)REE depletion (total range .14-.76). Two gabbro samples samples from from the the Sturgeon Sturgeon Falls Falls range .14—.76). sill, one of several large gabbroic sills within within the Quinnesec Forsill, mation, also show mation, show significant significant LREE LREE depletion depletion suggesting suggesting possible possible consanguinity with LREE The andesites andesites have enriched LREE consanguinity with the the basalts. basalts. The but relatively = ]1.23—1.47), 1.23-1.47), relatively low low total total REE REE abundances. abundances. ( [ ~ a / ~ =m ~ ([La/Sm]n whereas those Samples from the Beecher Formation are andesitic whereas Pemene Formation from the Pemene Formation are are rhyolitic. rhyolitic. The rhyolites rhyolites have higher REE REE abundances abundances and larger larger negative negative Eu anomalies anomalies than than the the andesites, andesites, show similar similar shaped, but show shaped, LREE—enriched LREE-enriched patterns. patterns. The The rhyolites rhyolites ppm) and higher Rb/Sr ratios than the also have lower Sr (55—133 (55-133 ppm) andesites S r ~ 3 6ppm). 0ppm). andesites ((Sr360 The The data data suggest suggest the the following following conclusions: conclusions: 11.. Quinnesec Formation basalts and related diabases are The Quinnesec compositionally Proterozoic compositionally distinct from the other early Proterozoic (i.e. Hemlock, Hemlock, Badwater, Badwater, etc.) etc.) basalts in in upper upper Michigan Michigan (i.e. which was was highly depleted and were derived from mantle which in large in large ion ion lithophile lithophile elements. elements. 2. 2. andesites of northeastern northeastern Wisconsin are not The basalts and andesites seperate related by crystal crystal fractionation fractionation but represent seperate melts melts from from compositionally compositionally distinct distinct sources. sources. 3. 3. The overall chemical characteristics characteristics of the Quinnesec Quinnesec basalts basalts �40 suggest affinities suggest affinities with with basalts basalts in in recent recent island—arcs island-arcs back—arc basins rather than those of the ocean and back-arc floor or floor or continental continental regions. regions. The The appearance appearance of of andesites and more andesites more felsic felsic units units with with these these basalts basalts supports such an island-arc island—arc to back-arc back—arc basin also supports environment. environment. Reference Reference Jenkins, A., 1973, 1973, Institute Institute on on Lake Lake Superior Superior Geology, Geology, Jenkins, R. R. A., 19th, 19th, p. p. 15—16. 15-16. �41 Geochemistry of of Fluid F l u i d Inclusions I n c l u s i o n s from from Archean Archean and and Phanerozoic Phanerozoic Gold Gold Deposits Deposits TED J. J. SMITH, SMITH, PAUL PAUL L. L. CLOKE, CLOKE, and and STEPHEN STEPHEN E. E. KESLER KESLER (Department (Department of of TED G e o l o g i c a l Sciences, S c i e n c e s , The The University U n i v e r s i t y of of Michigan, Michigan, Ann Ann Arbor, Arbor, MI MI Geological 48109) 48109) Fluid F l u i d inclusions i n c l u s i o n s from from various v a r i o u s Archean and and Phanerozoic Phanerozoic gold gold deposits deposits in i n metamorphic terrains t e r r a i n s were examined examined using u s i n g aa specially s p e c i a l l y designed designed gas gas chromatographic chromatographic analytical a n a l y t i c a l system system and and conventional c o n v e n t i o n a l heating/freezing heatinglfreezing techniques. techniques. The The inclusion i n c l u s i o n analyses a n a l y s e s indicate i n d i c a t e that, t h a t , in i n most most cases, c a s e s , the the fluids H20—C02 or H20—CH4—C02 m mixtures, with CO o r H20-CH4-C02 ixtures, w i t h trace t r a c e amounts amounts of of CO f l u i d s are a r e H20-C02 and and N2. No. Heating and and freezing f r e e z i n g measurements indicate i n d i c a t e the t h e presence p r e s e n c e of of low low salinity wt%NaCl), H20—C02 s a l i n i t y (<2 (<2 equiv. equiv. wtu%NaCl), H20-C02 and H20—CH4—C02 H20-CH4-CO2 fluid f l u i d inclusions, inclusions, confirming our o u r analyses. analyses. confirming Homogenization Homogenization of of the t h e inclusions i n c l u s i o n s occurred o c c u r r e d at at t e m p e r a t u r e s of of 220°C 220° to t o 380°C. 380°C Temperature and and f02 f o determinations determinations temperatures 2 diagrams were made made by plotting p l o t t i n g reaction r e a c t i o n lines l i n e s on on a02—temperature a 0 t e m p e r a t u r e diagrams 2utilizing u t i l i z i n g aa recently r e c e n t l y developed developed equation e q u a t i o n of of state s t a t e for f o r supercritical supercritical H20C02CH4 H20-Coy-CH4 fluids. fluids. Our Our results r e s u l t s indicate i n d i c a t e that t h a t the t h e fluids f l u i d s obtained obtained equilibrium n e a r the t h e QFM QFM e q u i l i b r i u m at a t temperatures t e m p e r a t u r e s of of 340°C 340° to t o 500°C 500° and and f02ts f ' s near 02. buffer. buffer. Isochores, I s o c h o r e s , also a l s o calculated c a l c u l a t e d from from the t h e equation e q u a t i o n of of state, s t a t e , indicate indicate high h i g h pressures p r e s s u r e s of of 2000 2000 to t o 4000 4000 bars. bars. �42 Jacobsville J a c o b s v i l l e Sandstone Sandstone Ridge Ridge in i n Keweenaw Keweenaw Bay Bay R. L. Wunderman Wunderman and and M. M. Rausch Rausch R. L. There There is i s aa north—northeast n o r t h - n o r t h e a s t trending t r e n d i n g lake l a k e bottom bottom ridge r i d g e of of Jacobs— Jacobsyule Sandstone in Keweenaw Bay (Fig. 1). A recent scuba dive v i l l e Sandstone i n Keweenaw Bay (Fig. 1 ) . A r e c e n t scuba d i v e conconfirms f i r m s the t h e presence p r e s e n c e of of subhorizontal s u b h o r i z o n t a l Jacobsville J a c o b s v i l l e Sandstone Sandstone 20 20 mm under under water w a t e r at a t aa point p o i n t 77 Km Km southeast s o u t h e a s t of of Portage P o r t a g e Entry Entry (88°22'W, (88¡22'W 46°56'N) 46'56'N) cropping cropping out o u t as a s aa detritus—free d e t r i t u s - f r e e north—west north-west facing f a c i n g scarp. s c a r p . At A t this this locality, l o c a l i t y , the t h e Jacobsville J a c o b s v i l l e Sandstone Sandstone is i s lithologically l i t h o l o g i c a l l y similar s i m i l a r to to s h o r e exposures. exposures. Warren Warren (1981, (1981, Figs. F i g s . 46 46 and and 47) 47) shows shows that that nearby shore this t h i s ridge r i d g e forms forms the t h e southeastern s o u t h e a s t e r n margin of of aa steep—sided s t e e p - s i d e d valley valley so s o that t h a t similar s i m i l a r excellent e x c e l l e n t exposures exposures of of bedrock are a r e likely l i k e l y to t o be b e found found Being sheltered s h e l t e r e d from from the t h e lake, lake, on the t h e northwest n o r t h w e s t ridge r i d g e face f a c e as a s well. w e l l . Being the t h e ridge r i d g e face f a c e more probably is i s related r e l a t e d to t o the t h e formation f o r m a t i o n of of the t h e steep— steepsided s i d e d valley v a l l e y than t h a n being b e i n g the t h e result r e s u l t of of wave erosion e r o s i o n on on aa lake l a k e cliff. cliff. Reference Reference Warren, Warren, E.J., E.J., 1981, 1981, The bedrock topography of the t h e Keweenaw Keweenaw Penninsula, Penninsula, dissertation), Michigan (Ph.D. (Ph.D. d i s s e r t a t i o n ) , Michigan Technological T e c h n o l o g i c a l University, University, Michigan Houghton, Houghton, 169 169 p. p. Figure F i g u r e 1: 1: Location L o c a t i o n Nap. Map. �43 ROPES ROPES GOLD GOLD MINE MINE AND AND ITS ITS GEOLOGICAL GEOLOGICAL SETTING SETTING Dean Dean Rossell Rossell and and 3. J. Kalliokoski Kalliokoski �44 THE ROPES GOLD GOLD MINE AND ITS ITS GEOLOGICAL GEOLOGICAL SETTING SETTING Dean Dean Rossell R o s s e l l and and J. J . Kalliokoski Kalliokoski INTRODUCTION INTRODUCTION Location Location The The Ropes Ropes Gold Gold Mine Mine is i s located l o c a t e d in i n Section S e c t i o n 29, 29, T48N—R27W, T48N-R27W, Marquette Marquette County, County, Michigan, Michigan, about three miles Ishpeming and and aa quarter q u a r t e r mile m i l e west of of Deer Deer Lake Lake (Figs. three m i l e s north n o r t h of of Ishpeming 1, ( F i g s . 1, 2). gold prosprosi s the t h e most most extensively e x t e n s i v e l y developed developed of of the t h e 20 20 or o r more more gold The Ropes Ropes Mine Mine is 2 ) . The pects p e c t s and and mines mines that t h a t comprise comprise the t h e Michigan Michigan gold gold belt. belt. His H i s tory tory Most of i s summarized summarized from from Broderick Broderick (1945). (1945). The Ropes ore ore of the t h e following f o l l o w i n g history h i s t o r y is body body was was discovered d i s c o v e r e d in i n 1880 1880 by by Julius J u l i u s Ropes Ropes while w h i l e he h e was was prospecting p r o s p e c t i n g for f o r asbestos asbestos among among the t h e outcrops o u t c r o p s of of the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Mining Mining operations o p e r a t i o n s at a t the t h e Ropes Ropes began began in i n 1882 1882 and and continued c o n t i n u e d until u n t i l 1897 1897 when when the t h e mine mine was was closed c l o s e d by by creditors. c r e d i t o r s . At At the t h e time time of of closing, c l o s i n g , 15 1 5 levels l e v e l s had been developed developed to t o the t h e east e a s t and and west west of of the t h e Curry Curry shaft, s h a f t , that t h a t reached reached aa depth d e p t h of of 244 244 meters. meters. During During the t h e 15 1 5 years y e a r s that t h a t the t h e mine mine was was in i t produced 1250 1250 kg kg of of gold gold and and 6200 6200 kg kg of of silver s i l v e r from from 145,000 145,000 tons t o n s of of i n operation o p e r a t i o n it ore, o r e , averaging a v e r a g i n g 5.96 5.96 g/ton g / t o n gold gold and and 28.05 28.05 g/ton g / t o n silver s i l v e r (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o , 1980). 1980). Around Around 1901 1901 some some 30,000 30,000 tons t o n s of of tailings t a i l i n g s were were cyanided. cyanided. In I n 1933 1933 the t h e Ropes property p r o p e r t y was acquired a c q u i r e d by the t h e Ishpeming Ishpeming Mining Mining Co., Co., which which continued continued surface s u r f a c e exploration e x p l o r a t i o n in i n the t h e area. a r e a . Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. bought bought aa majority majority interest i n t e r e s t in i n the t h e Ishpeming Ishpeming Mining Mining Co. Co. in i n 1934. 1934. From From 1934 1934 to t o 1942 1942 they t h e y conducted conducted an an extensive e x t e n s i v e exploration e x p l o r a t i o n program program of of diamond diamond drilling, d r i l l i n g , drifting d r i f t i n g on on the t h e 15th 1 5 t h level, l e v e l , and and resampling resampling of of the t h e old o l d workings workings in i n an a n attempt a t t e m p t to t o find f i n d an an extension e x t e n s i o n of of the t h e Ropes Ropes ore ore body it body (Fig. (Fig. 3). 3 ) . Although Although this t h i s work work found found no no major major extensions e x t e n s i o n s of of the t h e ore o r e body, body, it did d i d disclose d i s c l o s e over over aa million m i l l i o n tons t o n s of of lower lower grade grade ore o r e in i n the t h e ore o r e host h o s t rock r o c k surrounding surrounding the 1st and and 15th 1 5 t h levels, l e v e l s , average average t h e old o l d workings. workings. These These zones, zones, located l o c a t e d between between the t h e 1st 0.13 0.13 oz/ton o z / t o n gold gold and and 0.7 0.7 oz/ton o z / t o n silver. s i l v e r . In time restrictions r e s t r i c t i o n s on on precious precious I n 1942 1942 war war time metal m e t a l mining mining stopped stopped operations o p e r a t i o n s at a t the t h e mine, mine, preventing p r e v e n t i n g further f u r t h e r exploration e x p l o r a t i o n below below the t h e 15th 1 5 t h level. level. In t h e Ropes Ropes Mine, Mine, began began aa new new expor— export h e present p r e s e n t owner owner of of the I n 1974 1974 Callahan Callahan Mining Mining Corp., Corp., the ation a t i o n program program to t o confirm c o n f i r m and and try t r y to t o expand expand the t h e low low grade g r a d e ore o r e reserves r e s e r v e s established e s t a b l i s h e d by by the t h e Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. To To date d a t e this t h i s work work has h a s included i n c l u d e d rehabilitation r e h a b i l i t a t i o n of of the t h e old o l d mine mine workings, workings, an an extensive e x t e n s i v e surface s u r f a c e and and underground underground diamond diamond drilling d r i l l i n g camcampaign, worke x t r a c t i o n of of bulk b u l k samples samples for f o r metallurgical m e t a l l u r g i c a l tests, t e s t s , resampling resampling of of old o l d workp a i g n , extraction ings, remapping of of tthe i n g s , aand n d remapping h e surface s u r f a c e and underground underground geology geology (Skillings, ( S k i l l i n g s , 1981). 1981). Previous P r e v i o u s Geological G e o l o g i c a l Studies Studies The The only o n l y detailed d e t a i l e d geological g e o l o g i c a l work work on on the t h e Ropes Ropes Mine Mine is i s by by Broderick, Broderick, who who was was the the mine mine geologist g e o l o g i s t for f o r Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. In I n 1945 1945 Broderick B r o d e r i c k published p u b l i s h e d aa detailed d e t a i l e d description d e s c r i p t i o n of of the t h e Ropes Ropes ore o r e body body and and the t h e surrounding s u r r o u n d i n g peridotite. p e r i d o t i t e . SubSubsequent sequent published p u b l i s h e d work work on on the t h e geology geology of of the t h e surrounding surrounding area a r e a has h a s been been by by Boyum Boyum (1964, Puffett l974),Clark 1975), P u f f e t t (1966, (1966, 1 9 7 4 ) , - C l a r k and and others o t h e r s (1975), (1975), Cannon Cannon and and (1964, 1970, 1970, 1975), Klasner Klasner (1975), (1975), and and Morgan Morgan and and DeCristoforo D e C r i s t o f o r o (1980). (1980). The The latter l a t t e r provide p r o v i d e the t h e most most Information recent r e c e n t data d a t a on on the t h e overall o v e r a l l geology geology of of the t h e Ishpeming Ishpeming greenstone g r e e n s t o n e belt. b e l t . Information on on the t h e ore o r e host h o s t rock r o c k comes comes from from an an unpublished unpublished mine mine report r e p o r t by by Creasy Creasy (1981). (1981). �_______ 45 LEGEND PALEOZOIC 1 UPPER P R E C A M B R I A N 1 UPPER PRECAMBRIAN s.*imen*ory LOWER F i g u r e 1. Figure 1. Racks 1 PRECAMBRIAN L o c a t i o n o f t h e Ropes Gold Mine. Location of the Ropes Gold Mine. — ç.J , L. F' 7 LN'\ igan Mine — • \•_j 0 Feet 4000 (Cannon and Kiasner, 1975; Clark and others.1075) Proterozoic Proterozoje Marquette Range SuperOrOUP Marquette Range SupergrOUp Archean Archean Granite Granite 1-1 (Cannon and Klasner, 1975; Clark and others.1975) ]-k .... ,,\; \>,iDeer Deer Lake Peridotite K Lake Peridotite Age relations uncertain Age relations uncertain Kitchi Schist [ Kitchi Schist ]Agglomerate Agglomerate interned. to fels. volcs. r -5 5 F i l d trip stops Field trip stops GEOLOGY OF THE AREA AROUND GEOLOGY OF THE AREA AROUND THE ROPES AND MICHIGAN GOLD MINES Intermed. to fels. voics. d Amphibolite '.,.J Amphibolite F i g u r e 2.2. Figure Regional geology of t h e Ropes Mine and Michigan Mine a r e a . Regional geology of the Ropes Mine and Michigan Mine area. �46 PLAN, 15 LEVEL LEGEND . Figure 3a. 3a. Figure .. Geologic p l a n of t h e e a s t h a l f of t h e 1 5 t h l e v e l . Geologic plan of the east half of the 15th level. 4 + OOE c r o s s - s e c t i o n through t h e Ropes o r e body. Dar- 3b. F i g u r e3b. Figure 4 + OOE cross—section through the Ropes Dark e r l i n e s i n 3a and 3b r e p r e s e n t r e v e r s e f a u l t s d i p p iore n g body. 30' t o 40 ker lines in 3a and 3b represent reverse faults dipping 300 to 400 3b modified from unpublished maps and ( F i g u r e s 3a and t o the t h e south. south. to (Figures 3a and 3b modified from unpublished maps and c r o s s - s e c t i o n s p r e p a r e d f o r Callahan Mfning Corp. by Resource Excross—sections prepared for Callahan Mining Corp. by Resource Exp l o r a t i o n Inc., I n c . , 1982). 1982). ploration �47 part A large large p a r t of of the t h e report r e p o r t that t h a t follows f o l l o w s is i s taken t a k e n from from an M.S. M.S. thesis t h e s i s under under prepprepa r a t i o n by the t h e senior s e n i o r author, a u t h o r y on the t h e alteration a l t e r a t i o n of of the t h e Deer Lake Peridotite P e r i d o t i t e in in aration the vicinity the v i c i n i t y of the t h e Ropes Ropes Gold Gold Mine. Mine. Regional Geology within The Ropes Gold Mine is i s situated situated w i t h i n the t h e Ishpeming greenstone g r e e n s t o n e belt, b e l t y part p a r t of of which which is This Archean iin i s shown in i n Figure F i g u r e 2. 2. T h i s bbelt e l t iis s Archean n aage, g e y and geologically g e o l o g i c a l l y similar s i m i l a r to t o the the other belts o t h e r greenstone greenstone b e l t s that t h a t occur o c c u r in i n the t h e main part p a r t of of the t h e Superior S u p e r i o r Geological G e o l o g i c a l Pro— Province, part v i n c e > north n o r t h of of Lake Lake Superior. S u p e r i o r . It rrepresents e p r e s e n t s the t h e easternmost easternmost p a r t of of the t h e granite— granitegreenstone g r e e n s t o n e terrane t e r r a n e in i n Michigan Michigan (Sims, (Simsy 1976). 1976). On the west, the w e s t , the t h e greenstone g r e e n s t o n e belt b e l t is i s cut c u t by younger granites, g r a n i t e s y and and on on the t h e east e a s t it i t is is covered by Lake Superior S u p e r i o r and probably the t h e Jacobsville J a c o b s v i l l e Sandstone. Sandstone. On the t h e north n o r t h and south s o u t h the t h e Archean rocks r o c k s form the t h e basement for f o r the t h e mildly m i l d l y metamorphosed sedimentary sedimentary rocks r o c k s of of the t h e Marquette Range Supergroup that t h a t oucrop in i n the t h e Dead River R i v e r Basin Basin and and are are with Kitchi River i t c h i schists s c h i s t s aalong l o n g the t h e Carp R i v e r Falls F a l l s shear, s h e a r y possibly possibly iin n ffault a u l t ccontact ontact w i t h tthe he K a reactivated r e a c t i v a t e d Archean fault f a u l t (Sims (Sims and and others, o t h e r s , 1980). 1980). The greenstone g r e e n s t o n e belt b e l t consists c o n s i s t s of of several s e v e r a l thousand thousand feet f e e t of of felsic f e l s i c to t o mafic m a f i c volcanic volcanic rocks, with i t h an abundant pyroclastic p y r o c l a s t i c component, componenty that t h a t are a r e intruded i n t r u d e d by by Archean Archean perido— peridorocksy w of Deer Lake Lake aa gray gray granite g r a n i t e in in ttites i t e s and granitic g r a n i t i c plutons p l u t o n s (Table (Table 1). 1 ) . Northwest of Kitchi Schist Rb/Sr of 2490 m.y. m.y. (Van itchi S c h i s t gave a ~ b / S rage of (Van Schmus, Schmusy 1974, 1974> in in aamphibolite mphibolite K and Morgan and DeCristoforo, onr rand D e C r i s t o f o r o y 1980). 1980). The vvolcanic o l c a n i c rocks r o c k s are a r e assigned a s s i g n e d to t o the t h e Mona Kitchi K i t c h i Schist S c h i s t formation f o r m a t i o n (Van (Van Hise H i s e and Bayley, Bayley* 1895), 1 8 9 5 ) > and and Morgan Morgan and and DeCristoforo DeCristoforo (1980) with y c l e s y bbeginning eginning w i t h mafic o t e tthat h a t bboth o t h fformations o r m a t i o n s rrepresent e p r e s e n t vvolcanic o l c a n i c ccycles, (1980) nnote with and ending w i t h more felsic f e l s i c volcanic v o l c a n i c units. units. The K Kitchi i t c h i Schist S c h i s t is i s the t h e host h o s t for f o r the t h e Deer Lake Lake Peridotite P e r i d o t i t e (also ( a l s o referred r e f e r r e d to t o as a s DLP). DLP). of Deer Lakey Lake, the Kitchi the K i t c h i Schist S c h i s t consists c o n s i s t s of of a lower lower mafic member that that IIn n tthe h e vvicinity i c i n i t y of is of bbasaltic diabases, i s composed of a s a l t i c flows, flows, d i a b a s e s y and gabbros, gabbrosy all a l l of which generally g e n e r a l l y are a r e metametamorphosed to t o the t h e amphibolite a m p h i b o l i t e grade. grade. The upper part p a r t contains c o n t a i n s andesite a n d e s i t e flows, f l o w s y coarse coarse grained units, breccias, g r a i n e d ddacitic a c i t i c ppyroclastic yroclastic u n i t s * flow top top b r e c c i a s > and fine f i n e grained g r a i n e d pyroclastic pyroclastic or o r crystal c r y s t a l tuffs t u f f s (Morgan (Morgan and DeCristoforo, D e C r i s t o f o r o y 1980). 1980). Overlying the K i t c h i Schist S c h i s t is t h e Kitchi i s the t h e Mona Schist, S c h i s t y consisting c o n s i s t i n g of of pillow p i l l o w basalts b a s a l t s and and of of pyroclastic Puffett ffelsic elsic p y r o c l a s t i c rocks, r o c k s y some some now now schistose. schistose. P u f f e t t described d e s c r i b e d the t h e contact c o n t a c t between the Kitchi t h e Mona and K i t c h i Schists S c h i s t s as a s conformable (Puffett, ( P u f f e t t y 1974) 1974) whereas Morgan and and De— DeCristoforo on C r i s t o f o r o interpret i n t e r p r e t it i t to t o be b e an an unconformity, u n c ~ n f o r m i t ybased ~ on the t h e higher h i g h e r metamorphic metamorphic grade grade of of some units u n i t s in i n the t h e Kitchi K i t c h i Schist S c h i s t near n e a r the t h e contact c o n t a c t (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o y 1980). 1980). The Mona Schist S c h i s t has h a s been dated d a t e d as a s at a t least l e a s t 2750 2750 m.y. may. old o l d (Van (Van Schmus, Schmusy 1974, 1974y in in Morgan and DeCristoforo, D e C r i s t o f o r o y 1980). 1980). The Kitchi by aa nnortheast—trending body of of serpentinized K i t c h i Schist S c h i s t iis s t transected r a n s e c t e d by o r t h e a s t - t r e n d i n g body s e r p e n t i n i z e d ultra— ultramafic referred Km from from r e f e r r e d to t o as a s the t h e Deer Lake Peridotite. P e r i d o t i t e . The peridotite p e r i d o t i t e stretches s t r e t c h e s 6.5 6.5 Km River D e e r Lake. Lake. The DL? DLP is i s discordatit discordafit tto o most ontacts w ithin tthe h e Carp R i v e r Falls F a l l s Shear Shear to t o Deer most ccontacts within the Kitchi Schist, the K itchi S c h i s t , and for i s thought to t o be b e younger. younger. f o r this t h i s reason r e a s o n is Other ultramafic u l t r a m a f i c bodies b o d i e s in i n the t h e region r e g i o n are a r e the t h e Presque Presque Isle I s l e Peridotite, P e r i d o t i t e y northwest n o r t h w e s t of of of Marquette (Lewan, Puffett, (Lewany 1972; 1972; P u f f e t t > 1974) and the t h e Yellow Dog Dog Peridotite P e r i d o t i t e of of tthe h e ccity i t y of a g e y situated s i t u a t e d about about 20 20 miles m i l e s north—northwest north-northwest of of the t h e Ropes Ropes Gold Gold Mine Mine Lower Keweenawan age, (Klasner and o t h e r s y 1977; Morris and and Wilband, Wilbandy 1977). 1977). (Klasner others, �48 Table of of Formations Formations Ishpeming Greenstone Belt Belt PROTEROZOIC PROTEROZOIC Keweenawan Diabase dikes, d i k e s , Yellow Dog Peridotite Peridotite ?•arquette Marquette Range Range Supergroup Supergroup Q u a r t z i t e , dolomite, d o l o m i t e , slate, s l a t e ,conglomerant conglomerant Quartzite, banded banded iiron r o n formation, formation, and minor meta— metavolcanic v o l c a n i c rocks rocks -Unconformity ARCHEAN ARCHEAN River Dead R i v e r Pluton P l u t o n and Compeau Creek Gneiss Massive and foliated, f o l i a t e d , medium medium and coarse coarse g r a i n e d , intermediate i n t e r m e d i a t e to t o felsic f e l s i c plutonic plutonic grained, rocks rocks Intrusive Mona Mona SSchist chist Volcanic—plutonic baV o l c a n i c - p l u t o n i c ccycle y c l e of of pillowed p i l l o w e dba— ssalts, a l t s , ssericitic—chioritic e r i c i t i c - c h l o r i t i c sschist, c h i s t , rhy— rhyolite o l i t e tuff, t u f f , interlayered i n t e r l a y e r e d amphibolite a m p h i b o l i t e and eexhalites. xhalites. - ----------- Contact R e l a t i o n s h i p Uncertain Uncertain Contact Relationship Deer Lake Peridotite Peridotite Presque Isle I s l e Peridotite Peridotite ----------- --------------- S e r p e n t i n i z e d hharzburgite a r z b u r g i t e and lherzolite lherzolite Serpentinized Contact R elationship U ncertain Contact Relationship Uncertain Kitchi K i t c h i Schist Schist --------------- Volcanic-plutonic c y c l e of of gabbro, gabbro, dia— diaVolcanic—plutonic cycle bases b a s e s and basalts b a s a l t s (all ( a l l now now generally generally amphibolites), a m p h i b o l i t e s ) , intermediate i n t e r m e d i a t e and elsic and ffelsic agglomerates, ttuffs agglomerates, u f f s and flows flows ??? Basement Unknown Unknown Contact �49 ORE ORE HOST ROCK Occurrence Occurrence Ore grade grade mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Mine Mine is i s confined c o n f i n e d entirely e n t i r e l y within w i t h i n aa narrow narrow body of w i l l be b e referred r e f e r r e d to t o as a s the t h e ore o r e host h o s t rock r o c k or o r the t h e OHR. OHR. The OHR OHR of rock r o c k that t h a t will tabular body of silicic rock that strikes N70°E along its is of s i l i c i c r o c k t h a t s t r i k e s N70° a l o n g i t s i s a nearvertical, nearvertical* tabular s o u t h by talc—carbonate talc-carbonate surface i s bounded on the t h e north n o r t h and and south s u r f a c e exposure. exposure. The OHR is rock which grades laterally into the serpentinite of the Deer Lake Peridotite. t h e s e r p e n t i n i t e t h e Lake Peridotite. rock grades l a t e r a l l y i n t o The OHR is about 16 meters wide at the surface, near the Curry shaft, is 16 m e t e r s a t t h e s u r f a c e * n e a r t h e Curry s h a f t * and and gradgradually increases in width to over 30 meters along the 15th level (Fig. 3). Latu a l l y increases i n width t o 30 m e t e r s a l o n g t h e 1 5 t h l e v e l ( F i g . 3 ) . Laterally, e r a l l y * the t h e OHR OHR extends e x t e n d s over 1400 1400 feet f e e t to t o the t h e east e a s t of of the t h e Curry Curry shaft, s h a f t * pinching pinching Out o u t before b e f o r e it i t reaches r e a c h e s the t h e shore s h o r e of of Deer Lake Lake (Fig. (Fig. 4). 4). The origin OHR and and its i t s relationship r e l a t i o n s h i p to t o the t h e surrounding s u r r o u n d i n g serpentinite s e r p e n t i n i t e and and talc— talco r i g i n of of the t h e OHR The early miners e a r l y miners carbonate rocks of the Deer Lake Peridotite remains problematic. c a r b o n a t e r o c k s of t h e P e r i d o t i t e remains p r o b l e m a t i c . referred r e f e r r e d to t o the t h e OHR OHR as a s the t h e mineral m i n e r a l dike. d i k e . Broderick B r o d e r i c k described d e s c r i b e d the t h e OHR OHR as a s aa segment segment of Keewatin basic lavas and fragmentals, equivalent to the volcanic rocks of the the of b a s i c l a v a s and f r a g m e n t a l s * e q u i v a l e n t t o t h e v o l c a n i c r o c k s of Kitchi K i t c h i Schist S c h i s t to t o the t h e immediate immediate west, w e s t * and and proposed proposed that t h a t faulting f a u l t i n g probably probably played played aa 1945). major role OHR within w i t h i n the t h e peridotite p e r i d o t i t e (Broderick, (Broderick* 1945). r o l e in i n emplacing emplacing the t h e OHR Recent Recent workers workers generally g e n e r a l l y support s u p p o r t Broderick's B r o d e r i c k ' s contention c o n t e n t i o n that t h a t the t h e OHR OHR is i s principally principally Morgan and and volcanic, but disagree on its mode of emplacement within the peridotite. v o l c a n i c s b u t d i s a g r e e on i t s mode of emplacement w i t h i n t h e p e r i d o t i t e . Morgan DeCristoforo suggest that the Deer Lake Peridotite may represent at least in part D e C r i s t o f o r o s u g g e s t t h a t t h e Deer Lake P e r i d o t i t e may r e p r e s e n t a t l e a s t i n p a r t aa series DeCristoforo, s e r i e s of of koinatiitic k o m a t i i t i c l lava a v a fflows l o w s oor r ssubvolcanic u b v o l c a n i c iintrusions n t r u s i o n s (Morgan and D eCri~toforo~ If this were the case, the OHR could represent a conformable sequence of t h e c a s e * t h e OHR could r e p r e s e n t a conformable sequence of 1980). I f t h i s 1980). Neverthemore more felsic f e l s i c volcanics, v 0 1 c a n i c s ~extruded e x t r u d e d during d u r i n g aa hiatus h i a t u s in i n komatiitic k o m a t i i t i c volcanism. volcanism. Nevertheless, OHR* Morgan and and DeCristoforo D e C r i s t o f o r o (1980) (1980) conconl e s s * emphasizing emphasizing the t h e sheared s h e a r e d nature n a t u r e of the t h e OHR, sider s i d e r the t h e OHR OHR a faulted—in f a u l t e d - i n portion p o r t i o n of of the t h e older o l d e r Kitchi K i t c h i Schist. Schist. Creasy (1981) (1981) also a l s o supports s u p p o r t s aa volcanic v o l c a n i c origin o r i g i n for f o r the t h e OHR OHR and and suggests s u g g e s t s that t h a t the the Creasy OHR and and peridotite p e r i d o t i t e is i s the t h e result r e s u l t of of magmatic magmatic intrusion i n t r u s i o n of of the the j u x t a p o s i t i o n of of the t h e OUR juxtaposition Deer (Greasy* 1981). 1981). Evidence collected Deer Lake Lake Peridotite P e r i d o t i t e around around the t h e OHR OHR (Creasy, c o l l e c t e d by the the s e n i o r author a u t h o r from from the t h e serpentinite s e r p e n t i n i t e and talc—carbonate t a l c - c a r b o n a t e rocks r o c k s surrounding s u r r o u n d i n g the t h e OUR, OHR* senior l e a d s him to t o favor f a v o r the t h e view that t h a t the t h e juxtaposition j u x t a p o s i t i o n of of the t h e contrasting c o n t r a s t i n g rock r o c k types types leads i s largely l a r g e l y the t h e result r e s u l t of of tectonism. t e c t o n i s m . Figure is F i g u r e 55 shows shows aa possible p o s s i b l e analog a n a l o g where where aa s l i v e r of of metasedimentary rock, r o c k * similar s i m i l a r in i n dimensions to t o the t h e OUR, OHR* has h a s been been sheared sheared sliver Townshipy Vermont Vermont (Gregg, (Gregg* 1975). 1975). i n t o an Alpine-type u l t r a m a f i c body in i n Ludlow Township, into Alpine—type ultramafic These These points p o i n t s will w i l l be b e addressed a d d r e s s e d further f u r t h e r in i n later l a t e r sections. sections. of the t h e OUR OHR Petrography of Based on on examination examinationof o r e * tthin h i n ssection e c t i o n work* a n a l y s i s of of selected selected Based of ccore, work, and chemical analysis t h e OUR, OHR* Creasy interprets rock from the the OUR to be i n t e r p r e t s t h e OHR t o b e aa sequence sequence of of intermediate i n t e r m e d i a t e to to f e l s i c fragmental f r a g m e n t a l rock r o c k of of varying v a r y i n g particle p a r t i c l e size s i z e and and composition, composition3 minor minor intermediate intermediate felsic f l o w s and possibly p o s s i b l y volcanically v o l c a n i c a l l y derived d e r i v e d sediments sediments and and exhalites e x h a l i t e s (Creasy, (Greasy* 1981). 1981). He He flows a l s o has h a s found found aa preservation p r e s e r v a t i o n of of relict r e l i c t volcanic v o l c a n i c textures, t e x t u r e s * primarily p r i m a r i l y in i n thin t h i n section, section* also i n spite s p i t e of of the t h e intense, i n t e n s e * pervasive in OHR. Relict p e r v a s i v e alteration a l t e r a t i o n throughout throughout the t h e OUR. R e l i c t textures textures recognized by by Creasy Creasy include i n c l u d e pseudomorphs pseudomorphs of of pyroxenes, pyroxenes9 amphiboles amphiboles and and feldspars, feldspars, recognized h y d r a t i o n fractures f r a c t u r e s of of originally o r i g i n a l l y glassy g l a s s y rocks, r o c k s * and and aa general g e n e r a l fragmental f r a g m e n t a l aspect a s p e c t of of hydration many many of of the t h e rocks r o c k s (Creasy, (Creasy 1981). 1981) �Inc., 1982). Map of the surface geology in the vicinity of the Ropes Figure 4. Surface projection of the east end of the 15th level denoted Mine. (Map compiled using information from unpublished company by (o). maps prepared for Callahan Mining Corp. by Resource Exploration, 0 �H- 0 H- CDGQ P1 CD P1 U' CDCD(D rPP1 CD (DCD CD H- Cl) • C) H- CD rr c'—' 0 H- f:-4 CD Cl) H- I CI P1 0 Hi H- 0 '—' P1 H-CD Hi' ci- CD-DQ o 0 • CD Hi •HiI-' 0•. ri-CD CD ECD () ,—.. 0 rf CDP1 Or-PCDHi CD rP CD H- 0 Hi C ci- Hi Hi (DO 0 U' H- B '--'0 CD Hi(D C)QCD Hi C) P1 0 ci—I CD B H- Hi 0QCD-O 01) P1 P1 0 H- CDrfC) (DP1 P10 CD CDHiCDCD- CD CD P1o HiD) I-hB CD P1 '—' Hi -< DCDCD 0 P1 CD C) H- CD H-'--' CD P1 HiO o D)CD . CD 0 B C) CD-B CD CDD) C)Hi 'c'-HCD CD o HiCD rrHi II H- r C)rrH-H- P1 ii- H- CD C)CD CD• rtfi o Orr CD P1 o Figure 5. Surface map (upper) and cross-section (lower) of an alpine type serpentinite body from southeastern Ludlow Township, Vermont. The serpentinite is crossed by a sliver of Cram Hill Phyllite (thought to be tectonically emplaced) similar in dimensions to the Ropes Gold Mine ore host rock (Modified from Gregg, 1975). •0 -. CD -' 44Lt 3 0) __.. _ _ 0) --_ ,— V-' CD CI) i—c. C) -' 0 LiY —I/ :\J'ç-. / :__ I _ I :_. I —._! __I __, CD CD I— I I r -n ::::::::::::::::::::::::::::::::::::::::::::::::::L'j - _—--_—_-- rn 0 Z m U U' Hi �52 At A t the t h e discovery d i s c o v e r y pit p i t (Fig. (Fig. 1, 1, Stop Stop 1) 1 ) the t h e rock r o c k is i s aa quartz—chlorite—sericite quartz-chlorite-sericite schist schist with mm grains g r a i n s of of quartz. q u a r t z . To the t h e nnorth, o r t h , six s i x feet f e e t south s o u t h of of the the w i t h abundant abundant 0.1 0 . 1 to t o 0.3 0.3 nun contact with contact w i t h the t h e talc—carbonate—altered t a l c - c a r b o n a t e - a l t e r e d peridotite, p e r i d o t i t e , the t h e rock r o c k displays d i s p l a y s in i n thin t h i n secsecmicro—breccia ttexture ttion i o n aa micro-breccia e x t u r e consisting c o n s i s t i n g of of angular a n g u l a r fragments of of darker d a r k e r quartz— quartzmaterial 0.5 cchlorite hlorite m a t e r i a l (0.2 (0.2 to to 0 . 5 mm in i n maximum dimension) in i n a lighter l i g h t e r colored c o l o r e d quartz— quartzssericite e r i c i t e matrix. m a t r i x . There are a r e also a l s o a few few 11 mm mm quartz q u a r t z grains. grains. A t h e talc—carbonate talc-carbonate Att the highly i s aa fine—grained, fine-grained, h i g h l y fractured, f r a c t u r e d , quartz—sericite quartz-sericite ccontact o n t a c t tthe h e oore r e hhost o s t rrock o c k is by ccoarser sschist, c h i s t , sporadically s p o r a d i c a l l y rreplaced e p l a c e d by o a r s e r grained g r a i n e d sericite s e r i c i t e and by younger veinlets veinlets of c chlorite of h l o r i t e and and carbonate. carbonate. Broderick describes d e s c r i b e s four f o u r types t y p e s of alteration a l t e r a t i o n from from the t h e OHR OHR within w i t h i n the t h e mine: mine: seri— seripyritization, notes ccitization, i t i z a t i o n , cchloritization, h l o r i t i z a t i o n , silicification, s i l i c i f i c a t i o n , and p y r i t i z a t i o n , and n o t e s that that sericitization i s more prevalent p r e v a l e n t than t h a n chioritization c h l o r i t i z a t i o n (Broderick, (Broderick, 1945). 1945). s e r i c i t i z a t i o n is Carbonatization, C a r b o n a t i z a t i o n , generally g e n e r a l l y cconsidered o n s i d e r e d to t o bbe e confined c o n f i n e d to t o the t h e talc—carbonate t a l c - c a r b o n a t e rocks rocks OHR, h has noted by the OHR. ssurrounding u r r o u n d i n g tthe h e OHR, a s been noted t h e senior s e n i o r author a u t h o r to t o overlap o v e r l a p into i n t o the t h e OHR. Although carbonatization c a r b o n a t i z a t i o n is i s not n o t pervasive p e r v a s i v e throughout throughout the t h e OHR, OHR, it i t is i s intensely intensely matrix, veinlets, developed locally, l o c a l l y , rreplacing eplacing m a t r i x , forming small small v e i n l e t s , and rimming quartz quartz i s most prevalent p r e v a l e n t along along and sericitic s e r i c i t i c fragments. fragments. Carbonate aalteration l t e r a t i o n of of the t h e OHR is the t h e south s o u t h ccontact o n t a c t and hhas a s produced aa zone of of carbonate—quartz—chlorite c a r b o n a t e - q u a r t z - c h l o r i t e rock r o c k that that will w i l l be b e described d e s c r i b e d further f u r t h e r in i n the t h e section s e c t i o n on on talc—carbonate t a l c - c a r b o n a t e alteration. alteration. of the Chemistry of t h e Ore Host Rock of v various Chemical analyses a n a l y s e s of a r i o u s rock r o c k types t y p e s from the t h e OHR OHR are a r e listed l i s t e d in i n Table T a b l e 2. 2. Analyses 1, 1, 2, 2, 3 and 4 aare r e from Creasy (1981); (1981); analyses a n a l y s e s 5, 5, 6 and 77 are a r e new new analyses, a n a l y s e s , from from aa series of samples collected s e r i e s of c o l l e c t e d from the t h e chloritic c h l o r i t i c OHR OHR along a l o n g the t h e north n o r t h edge edge of of the t h e disdiscovery ppit i t (Fig. (Fig. 4), 4 ) , and analysed a n a l y s e d for f o r this t h i s paper by Drs. D r s . T. T. Bornhorst and and W.I. W . I . Rose, Rose, Jr. by X-ray X—ray 'fluorescence Jr f l u o r e s c e n c e analysis. analysis. . with Creasy (1981) (1981) nnotes o t e s that t h a t based on comparison w i t h less l e s s altered a l t e r e d rocks r o c k s of of similar s i m i l a r silica silica content, c o n t e n t , the t h e Ropes Mine rocks r o c k s are a r e characterized c h a r a c t e r i z e d at a t a given given silica s i l i c a content c o n t e n t by by greater greater than of MgO, MgO, v very t h a n aaverage v e r a g e vvalues a l u e s of e r y low CaO, CaO, low to t o very v e r y low low Na20, Na20, and and K20 K2O in i n two two ranges, ranges, vvery e r y low or o r moderately high. h i g h . Creasy attributes a t t r i b u t e s these t h e s e variations v a r i a t i o n sto t o the t h e pervasive p e r v a s i v e alteralteration has OHR, and concludes c o n c l u d e s that t h a t on both b o t h chemical chemical and and textural textural a t i o n that that h a s affected a f f e c t e d the t h e OHR, grounds, portions grounds, p o r t i o n s of of the t h e OHR resemble lithologies l i t h o l o g i e s found found in i n the t h e Kitchi K i t c h i and and Mona Mona Schists Schists (Creasy, (Creasy, 1981). 1981). major oxides, MgO 7, T Table The lighter l i g h t e r major oxides, M gO and Si02, SiO2, in i n the t h e new analyses a n a l y s e s (5, (5, 6, 6, 7, a b l e 2) 2) may be b e significantly s i g n i f i c a n t l y in i n error e r r o r due due to t o matrix m a t r i x effects e f f e c t s resulting r e s u l t i n g from from aa suspected s u s p e c t e d high h i g h volavolatile t i l e content. c o n t e n t . Nevertheless, N e v e r t h e l e s s , the t h e values v a l u e s of of the t h e heavier h e a v i e r minor minor and and trace t r a c e elements, elements, Ti02 and and Zr2O3, Zr203, which which aare llike i k e Ti02 r e uunlikely n l i k e l y to t o bbe e significantly s i g n i f i c a n t l y in i n error, e r r o r , suggest suggest a pparent a r e n t composition of of an intermediate i n t e r m e d i a t e igneous igneous rock, rock, possibly p o s s i b l y an a n andesite, a n d e s i t e , of of alkaline alkaline aaffinity. ffinity . Mineralization Mineralization mineralization The gold m i n e r a l i z a t i o n of of the t h e Ropes ore o r e body (Figs. ( F i g s . 3, 3, 4) 4) can can be b e subdivided subdivided into into two types mineralization t y p e s following f o l l o w i n g the t h e work work of of Broderick Broderick (1945): (1945): 1) 1 ) hhigher i g h e r grade grade m ineralization associated with associated w i t h quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins; v e i n s ; and 2) 2) lower lower grade, grade, disseminated d i s s e m i n a t e d minermineraalization l i z a t i o n that t h a t surrounds surrounds the t h e quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins. veins. �53 ANALYSES RNflLYSES OF OFORE OREHOST HOSTROCK ROCKSAMPLES SRMPLES 5102 S102 AL203 RL203 FE203 FE203 FED FED MGO MGO cflo CR0 NR2O NR20 K20 K2 0 1102 TI02 P205 P2 05 MNO MNO C02 C02 1 2 3 4 5 6 7 37.70 55.40 72.00 48.39 50.05 23 .80 12 .80 61.30 16.30 13 .20 15 .07 15.68 11.20 1 .'40 .64 3.10 10.28 .00 5.50 17.50 4.60 6.10 .24 .00 8 .27 .00 49.57 17.85 7.67 1.90 16.57 .60 .18 .64 .18 .11 .05 .26 .07 '4.20 .48 .02 .01 .20 96.30 95.68 10 .60 .40 .52 5.70 1.10 .29 .03 ----------. TOTAL TOTRL Table Table 2. 2. 91.34 .60 .02 .01 .59 .1? .03 .50 94.52 .38 4.70 1 .30 14.33 1.23 .00 11.67 .19 .35 .20 3.55 4.54 .08 .05 .98 .07 .05 .77 .1? .03 95.24 94.40 92.82 3.01 1.01 Selected S e l e c t e d analyses a n a l y s e s of of ore o r e host h o s t rocks. rocks. Samples Samples 1—4 1-4 taken taken from from Creasy, Creasy, 1981. 1981. Samples Samples 5—7 5-7 are a r e new new analyses a n a l y s e s for f o r this this paper. w t . percent. percent. No. 5, 5, contact c o n t a c t with w i t h talc— talcpaper. Analyses Analyses in i n wt. No. carbonate b, 66 feet f e e t south s o u t h of of contact; c o n t a c t ; 7, 7, discovery d i s c o v e r y pit. pit. c a r b o n a t e rock; rock; b, �54 The The quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins v e i n s still s t i l l remaining remaining in i n the t h e old o l d workings workings range r a n g e in i n thickthickness n e s s from from several s e v e r a l inches i n c h e s to t o several s e v e r a l feet, f e e t , and and Broderick Broderick reports r e p o r t s thicknesses t h i c k n e s s e s of of up up t o 38 38 feet f e e t for f o r veins v e i n s that t h a t had had already a l r e a d y been been mined. mined. Ore Ore veins v e i n s typically t y p i c a l l y strike s t r i k e northnorthto east, e a s t , oblique o b l i q u e to t o the t h e general g e n e r a l strike s t r i k e of of the t h e OUR, OHR, and and have have aa near—vertical n e a r - v e r t i c a l dip. d i p . Eight Eight major major veins v e i n s or o r vein v e i n systems systems were were exploited e x p l o i t e d during d u r i n g the t h e early e a r l y mining mining operations, o p e r a t i o n s , all all of which which pinched pinched out o u t along a l o n g strike s t r i k e and and with w i t hdepth. d e p t h . None None of of the t h e quartz—tetrahedrite quartz-tetrahedrite of v e i n s cross c r o s s the t h e OUR OHR contact c o n t a c t into i n t o the t h e surrounding s u r r o u n d i n g talc—carbonate t a l c - c a r b o n a t e rocks. r o c k s . These These veins veins veins are a r e composed composed mainly mainly of of white, w h i t e , splintery s p l i n t e r y quartz q u a r t z with w i t h minor minor tetrahedrite, t e t r a h e d r i t e , chalcopyrite, chalcopyrite, B r o d e r i c k (1945) (1945) also a l s o mentions mentions the t h e presence presence g a l e n a , pyrite p y r i t e and and rare r a r e native n a t i v e gold. gold. Broderick galena, One small s m a l l vein vein of sphalerite, s p h a l e r i t e , native n a t i v e silver, s i l v e r , aand n d rare r a r e molybdenite molybdenite and and tourmaline. t o u r m a l i n e . One of n e a r the t h e 1070 1070 cross—cut c r o s s - c u t on on the t h e 15th 1 5 t h level l e v e l consists c o n s i s t s primarily p r i m a r i l y of of massive massive chalcopyrite, chalcopyrite, near with w i t h galena, g a l e n a , tetrahedrite, t e t r a h e d r i t e , pyrite, p y r i t e , quartz q u a r t z and and possible p o s s i b l e ruby ruby silver s i l v e r widely widely scattered scattered S e v e r a l other o t h e r large l a r g e quartz q u a r t z veins veins along a l o n g thin t h i n carbonate—filled c a r b o n a t e - f i l l e d fractures f r a c t u r e s ini nthe t h evein. v e i n . Several within c o n t a i n large l a r g e pods pods of of pyrite p y r i t e but b u t no no signisigniw i t h i n the t h e OHR OHR with w i t h similar s i m i l a r orientation, o r i e n t a t i o n , contain f i c a n t gold. gold. ficant i s confined c o n f i n e d to t o the t h e hydrothermally hydrothermally altered altered The lower lower grade grade disseminated d i s s e m i n a t e d ore o r e generally g e n e r a l l y is The and pyritized p y r i t i z e d rock r o c k surrounding s u r r o u n d i n g the t h e quartz—tetrahedrite q u a r t z - t e t r a h e d r i t e veins. v e i n s . No No free f r e e gold gold has h a s been been and r e p o r t e d from from these t h e s e zones, zones, and and apparently a p p a r e n t l y most most of of the t h e gold gold and and silver s i l v e r is i s contained contained reported w i t h i n the t h e abundant abundant pyrite. p y r i t e . However, However, Broderick Broderick (1945) (1945) has h a s noted n o t e d that t h a t abundant abundant pyrite pyrite within i n the t h e OHR OHR does does not n o t necessarily n e c e s s a r i l y indicate i n d i c a t e ore o r e grade grade material, m a t e r i a l , in i n that t h a t some some pyritic pyritic in zones have have very v e r y low low gold gold values. values. zones i s not n o t evenly evenly distributed d i s t r i b u t e d throughout throughout the t h e OHR. OHR. The The Gold and and silver s i l v e r mineralization m i n e r a l i z a t i o n is Gold c l u s t e r i n g of of old o l d stopes s t o p e s shows shows that t h a t the t h e majority m a j o r i t y of of the t h e higher h i g h e r grade grade ore o r e was was found found clustering Smaller discontinuous d i s c o n t i n u o u s lenses l e n s e s of of ore ore along a l o n g the t h e south s o u t h contact c o n t a c t of of the t h e OUR OHR (Fig. ( F i g . 3). 3 ) . Smaller occur occur sporadically s p o r a d i c a l l y along a l o n g the t h e north n o r t h contact, c o n t a c t , but b u t generally g e n e r a l l y do do not n o t extend extend across a c r o s s to to OHR with w i t h very v e r y low low grades. grades. t h e south s o u t h contact, c o n t a c t , leaving l e a v i n g an an interior i n t e r i o r zone zone of of the t h e OHR the Skillings S k i l l i n g s (1981) (1981) reports r e p o r t s grades g r a d e s of of 0.15 0.15 oz/ton o z / t o n for f o r portions p o r t i o n s of of the t h e Ropes Ropes ore o r e body. body. Veins and and Evidence Evidence for f o r Faulting F a u l t i n g in i n the t h e OUR OHR Veins The OHR OHR has h a s undergone undergone obvious obvious deformation deformation shown shown locally l o c a l l y by by pronounced pronounced foliations, foliations, The i n t e n s e fracturing f r a c t u r i n g and vein v e i n development, development, boudinaged boudinaged quartz q u a r t z veins, v e i n s , and and faults. faults. intense H o w e v e r ,the t h e oore r e hhost o s t rrock o c k shows a r i e t y of However, shows aa wide wide vvariety of secondary alteration a l t e r a t i o n effects effects so s o pervasive p e r v a s i v e that, t h a t , in i n most cases, c a s e s , it i t has h a s not n o t been been possible p o s s i b l e to t o establish e s t a b l i s h suffisufficiently c i e n t l y distinctive d i s t i n c t i v e and and persistent p e r s i s t e n t map map units u n i t s to t o work work out o u t structural s t r u c t u r a l relationships. relationships. �55 Similarly, veins S i m i l a r l y , a number of of v e i n s are a r e exposed exposed within w i t h i n the t h e mine, mine, but b u t only o n l y aa few, few, none none of them m i n e r a l i z e d , show cross c r o s s cutting c u t t i n g relationships r e l a t i o n s h i p s to t o provide p r o v i d e data d a t a on on relative relative of mineralized, ages. a g e s . Thus, Thus, although a l t h o u g h the t h e available a v a i l a b l e data d a t a is i s insufficient i n s u f f i c i e n t for f o r determining d e t e r m i n i n g the t h e comcomplete vein p l e t e structural s t r u c t u r a l and v e i n emplacement emplacement history, h i s t o r y , several s e v e r a l features f e a t u r e s concerning concerning vein vein relationshipshavebeennoted. r e l a t i o n s h i p s h a v e b e e n n o t e d . For example, example, many small s m a l l quartz q u a r t z veins v e i n s scattered s c a t t e r e d throughthroughout o u t the t h e OHR show show cross—cutting c r o s s - c u t t i n g relationships, r e l a t i o n s h i p s , demonstrating d e m o n s t r a t i n g multiple m u l t i p l e periods p e r i o d s of of quartz q u a r t z vein v e i n formations. formations. Veins of banded carbonate c a r b o n a t e which which have have aa sporadic s p o r a d i c distribudistribut i o n throughout the t h e OHR, OHR, are a r e everywhere everywhere younger than t h a n quartz q u a r t z veins, v e i n s , where where crosscrosstion cutting c u t t i n g relationships r e l a t i o n s h i p s can c a n be b e observed. observed. The The entire e n t i r e sequence sequence of of ore o r e host h o s t rocks r o c k s and and the t h e surrounding s u r r o u n d i n g peridotite p e r i d o t i t e are a r e offset o f f s e t by by several s e v e r a l large l a r g e reverse r e v e r s e faults, f a u l t s , which strike s t r i k e to t o the t h e northeast n o r t h e a s t and and dip d i p between between 25° 25' and and 350 35' to t o the t h e south s o u t h (Fig. (Fig. 3; 3 ; 44 ++ 00 00 EE cross c r o s s cut). c u t ) . The The lower lower blocks b l o c k s are a r e rotated r o t a t e d clockclocka l o n g these t h e s e faults, f a u l t s , changing changing the t h e strike s t r i k e from from N70°E N70° at a t the t h e surface s u r f a c e to t o N80°E N80° at at wise along the t h e 15th 1 5 t h level. l e v e l . The larger l a r g e r reverse r e v e r s e faults f a u l t s are a r e commonly commonly marked by by one one to t o two two feet feet of breccia, but of b reccia, b u t the t h e smaller s m a l l e r ones ones commonly commonly contain c o n t a i n prismatic, p r i s m a t i c , terminated t e r m i n a t e d dolomite dolomite crystals, c r y s t a l s , with w i t h minor chalcopyrite c h a l c o p y r i t e and and pyrite. p y r i t e . Sprays of millerite of m i l l e r i t e are a r e also a l s o common common where reverse r e v e r s e faults f a u l t s cut c u t the t h e surrounding s u r r o u n d i n g talc—carbonate t a l c - c a r b o n a t e and and serpentinite. serpentinite. A A number of of older, o l d e r , high h i g h angle a n g l e faults f a u l t s are a r e also a l s o seen seen in i n the t h e mine mine workings, workings, but b u t most most appear to t o have have had had only o n l y limited l i m i t e d movement movement along a l o n g them. them. AA larger, l a r g e r , apparently a p p a r e n t l y high high angle, a n g l e , north—striking n o r t h - s t r i k i n g fault f a u l t offsets o f f s e t s the t h e OHR OHR to t o the t h e west of of the t h e Curry Curry shaft s h a f t (Fig. (Fig. 2). 2). DEER DEER LAKE LAKE PERIDOTITE PERIDOTITE Occurrence Occurrence The The Deer Lake Lake Peridotite P e r i d o t i t e is i s aa linear, l i n e a r , near—vertical n e a r - v e r t i c a l (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o , 1980), 1980); tabular t a b u l a r ultramafic u l t r a m a f i c body, body, now predominantly composed composed of of serpentinite. s e r p e n t i n i t e . The serpen— serpentinites t i n i t e s form form prominent ridges r i d g e s in i n the t h e area, a r e a , providing p r o v i d i n g good good exposures. exposures. Good outcrops outcrops are a r e also a l s o found found along a l o n g the t h e north n o r t h shore s h o r e of of Deer Deer Lake. Lake. In I n general, g e n e r a l , the t h e contacts c o n t a c t s between the t h e Deer Lake Lake Peridotite P e r i d o t i t e and and the t h e surrounding s u r r o u n d i n g Kitchi Kitchi Schist S c h i s t are a r e very v e r y poorly p o o r l y exposed, exposed, typically t y p i c a l l y denoted denoted by by narrow narrow depressions. d e p r e s s i o n s . This T h i s concontact t a c t does outcrop o u t c r o p at a t two two locations l o c a t i o n s west of the t h e spillway s p i l l w a y on on the t h e north n o r t h side s i d e of of Deer Deer Lake. There There the t h e contact c o n t a c t is i s marked marked by by aa 33 to t o 66 foot f o o t wide wide zone zone of of soft s o f t actinolite— actinolitechlorite c h l o r i t e schist, s c h i s t , possibly p o s s i b l y similar s i m i l a r to t o the t h e tremolite—chlorite t r e m o l i t e - c h l o r i t e zones zones described d e s c r i b e d by by Chidester C h i d e s t e r and and others o t h e r s (1978) (1978) at a t the t h e contacts c o n t a c t s of of the t h e Belvidere B e l v i d e r eultramaf u l t r a m a fIc i c body body in in Vermont. Vermont. Serpentinite S e r p e n t i n i t e near n e a r the t h e actinolite—chlorite a c t i n o l i t e - c h l o r i t e schist s c h i s t contains c o n t a i n s abundant abundant carcarbonate b o n a t e and and talc, t a l c , which which diminish d i m i n i s h abruptly a b r u p t l y away away from from the t h e contact. c o n t a c t . The Kitchi K i t c h i Schist Schist near n e a r this t h i s contact c o n t a c t is i s strongly s t r o n g l y chioritized c h l o r i t i z e d and and contains c o n t a i n s numerous numerous quartz q u a r t z veins. veins. The i s still s t i l l unclear. u n c l e a r . Broderick B r o d e r i c k (1945), (1945), Clark Clark The origin o r i g i n of of the t h e Deer Lake Lake Peridotite P e r i d o t i t e is and others o t h e r s (1975), (1975), and and most recently r e c e n t l y Creasy Creasy (1981) (1981) suggest, s u g g e s t , based based largely l a r g e l y on on the the and discordant Kitchi Schist, and locally well preserved d i s c o r d a n t nature n a t u r e with w i t h the t h e surrounding s u r r o u n d i n g K i t c h i S c h i s t , and l o c a l l y w e l l p r e s e r v e d cumulate cumulate olivine o l i v i n e textures, t e x t u r e s , that t h a t the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e is i s aa magmatic magmatic intrusion. intrusion. On On the t h e basis b a s i s of of chemical chemical similarities s i m i l a r i t i e s and and pillow—like p i l l o w - l i k e structures s t r u c t u r e s found found near n e a r Deer Deer Lake, Morgan and and DeCristoforo D e C r i s t o f o r o (1980) (1980) propose propose that t h a t all, a l l , or o r part, p a r t , of of the t h e Deer Deer Lake Lake Lake, Peridotite P e r i d o t i t e may may be b e komatiitIc k o m a t i i t i c flows. flows. As A s previously p r e v i o u s l y mentioned, mentioned, the t h e present p r e s e n t authors authors have noted noted structural s t r u c t u r a l and and textural t e x t u r a l similarities s i m i l a r i t i e s between between the t h e Deer Deer Lake Lake Peridotite Peridotite have and and Alpine type t y p e ultramafics, u l t r a m a f i c s , and and thus t h u s there t h e r e is i s the t h e added added possibility p o s s i b i l i t y that t h a t the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e may may have have crystallized c r y s t a l l i z e d elsewhere elsewhere and and subsequently s u b s e q u e n t l y was was emplaced emplaced as a s aa solid or semi—solid body, in a manner similar to that proposed for alpine—type s o l i d o r semi-solid body, i n a s i m i l a r t o t h a t proposed f o r a l p i n e - t y p e ultramafic u l t r a m a f i c bodies. bodies. �56 Petrography of of Serpentinites Serpentinites Petrography A, Two distinct d i s t i n c t types t y p e s of of serpentinites s e r p e n t i n i t e s are a r e seen seen in i n the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Type Type A, Two t h e most most common common variety v a r i e t y in i n surface s u r f a c e exposures, exposures, is i s dark d a r k gray gray on on fresh f r e s h surfaces, s u r f a c e s , with with the f i n e to t o medium medium grained g r a i n e d serpentine, s e r p e n t i n e , giving g i v i n g the t h e rock r o c k aa slightly s l i g h t l y greasy g r e a s y luster. l u s t e r . These These fine s e r p e n t i n i t e s generally g e n e r a l l y have have no no obvious obvious foliation, f o l i a t i o n , and and commonly commonly have have readily r e a d i l y idenidenserpentinites mm serpentine s e r p e n t i n e pseudomorphs pseudomorphs after a f t e r olivine o l i v i n e or o r pyroxene pyroxene outlined o u t l i n e d by by thin thin t i f i a b l e 1—5 1-5 mm tifiable s e l v a g e s of of white w h i t e carbonate c a r b o n a t e and and talc. t a l c . No No spinifex s p i n i f e x olivine o l i v i n e or o r pyroxene, pyroxene, considered considered selvages i n d i c a t i v e of of komatiitic k o m a t i i t i c flows, flows, were were recognized recognized anywhere. anywhere. indicative I n thin t h i n section, s e c t i o n , Type Type AA serpentinite s e r p e n t i n i t e frequently f r e q u e n t l y shows shows well w e l l developed developed serpentine serpentine In pseudomorphs after a f t e r olivine o l i v i n e and and pyroxene. pyroxene. The The pseudomorphed pseudomorphed olivine o l i v i n e commonly commonly shows shows pseudomorphs serpentine (1977), s e r p e n t i n e mesh mesh textures, t e x t u r e s , similar s i m i l a r to t o those t h o s e described d e s c r i b e d by by Wicks Wicks and and Whittaker Whittaker (1977), with w i t h subparallel, s u b p a r a l l e l , length—slow, length-slow, serpentine s e r p e n t i n e fibers f i b e r s growing growing toward toward the t h e grain g r a i n centers centers from original o r i g i n a l olivine o l i v i n e grain g r a i n boundaries b o u n d a r i e s and and fractures. f r a c t u r e s . In from I n some some sections s e c t i o n s accumulate accumulate textures r i m s of of dusty d u s t y magnetite, m a g n e t i t e , carbonate carbonate t e x t u r e s are a r e well w e l l preserved, p r e s e r v e d , outlined o u t l i n e d by by thin t h i n rims and talc t a l c (Fig. (Fig. 6). 6 ) . The The central c e n t r a l portions p o r t i o n s of of the t h e above above pseudomorphed pseudomorphed olivine o l i v i n e are are and replaced r e p l a c e d by by carbonate c a r b o n a t e and and talc, t a l c , which which are a r e generally g e n e r a l l y minor minor but b u t ubiquitous, u b i q u i t o u s , mineral mineral phases. phases. Serpentine S e r p e n t i n e pseudomorphs pseudomorphs after a f t e r pyroxene, pyroxene, called c a l l e d bastite b a s t i t e (Wicks (Wicks and and Whittaker Whittaker 1977) 1977) appear nun patches p a t c h e s of of parallel p a r a l l e l serpentine s e r p e n t i n e fibers f i b e r s which which mimic mimic one one of o f the the appear as a s 1—3 1-3 mm second relict r e l i c t cleavage c l e a v a g e is i s commonly commonly outlined o u t l i n e d by by sub— subpyroxene cleavage c l e a v a g e directions. d i r e c t i o n s . AA second pyroxene parallel p e r p e n d i c u l a r to t o the t h e serpentine s e r p e n t i n e orienta— orientap a r a l l e l lines l i n e s of of fine—grained f i n e - g r a i n e d magnetite, m a g n e t i t e , perpendicular t i o n . Bastite—rich mm wispy wispy flakes f l a k e s of of pleochroic pleochroic B a s t i t e - r i c h samples samples also a l s o contain c o n t a i n scattered s c a t t e r e d 1—3 1-3 mm .tion. c h l o r i t e with w i t h anomalous anomalous "Berlin " B e r l i n Blue" ~ l u e "birefringence, b i r e f r i n g e n c e , thought thought to t o be b e penninite. p e n n i n i t e . The The chlorite Type Type AA serpentinite s e r p e n t i n i t e textures t e x t u r e s correspond correspond to t o the t h e "Type "Type 3" 3" serpentine s e r p e n t i n e textures t e x t u r e s of of Wicks Wicks and Whittaker Whittaker (1977). (1977). and Type (1977) 'Type "Type 8" 8" Type BB serpentinite, s e r p e n t i n i t e , which which corresponds corresponds to t o Wicks Wicks and and Whittaker's W h i t t a k e r ' s (1977) serpentine s e r p e n t i n e texture, t e x t u r e , outcrops o u t c r o p s rarely r a r e l y but b u t is i s common common as a s 10—40 10-40 foot f o o t layers l a y e r s in i n drill drill The best b e s t surface s u r f a c e exposures exposures core c o r e from from the t h e serpentinites s e r p e n t i n i t e s south s o u t h of of the t h e Ropes Ropes ore o r e body. body. The Type BB serpeninite s e r p e n i n i t e ranges r a n g e s in i n color c o l o r from from 4 ) . Type a r e along a l o n g the t h e shore s h o r e of of Deer Deer Lake Lake (Fig. (Fig. 4). are pale i s extremely extremely fine f i n e grained, g r a i n e d , and and has has p a l e green green to t o yellowish y e l l o w i s h white w h i t e on on fresh f r e s h surface, s u r f a c e , is Commonly these t h e s e serpentinites s e r p e n t i n i t e s have have aa strong, strong, no recognizable r e c o g n i z a b l e relict r e l i c t igneous igneous textures. t e x t u r e s . Commonly no often o f t e n contorted c o n t o r t e d foliation, f o l i a t i o n , best b e s t seen seen on on weathered weathered surfaces. s u r f a c e s . Coarse Coarse grained g r a i n e d magnetite magnetite forms serv e i n l e t s and and streaks s t r e a k s along a l o n g foliations f o l i a t i o n s in i n most most Type Type BB ser— i r r e g u l a r veinlets forms prominent, prominent, irregular pentinites. pentiniteS. In I n thin t h i n section, s e c t i o n , Type BB serpentinite s e r p e n t i n i t e differs d i f f e r s from from Type Type AA in i n that t h a t no no pseudomorphic pseudomorphic t e x t u r e s are a r e preserved. p r e s e r v e d . Instead, I n s t e a d , serpentine s e r p e n t i n e occurs o c c u r s either e i t h e r as a s aa uniform, uniform, interintertextures locking 6c) or o r as a s strongly s t r o n g l y foliated f o l i a t e d (Fig. ( F i g . 6d). 6 d ) . Nearly Nearly white, white, l o c k i n g felted f e l t e d texture t e x t u r e (Fig. ( F i g . 6c) Type Type BB serpentinite s e r p e n t i n i t e from from drill d r i l l core, c o r e , contains c o n t a i n s abundant, abundant, very v e r y fined f i n e d grained, grained, secondary secondary dolomite. dolomite. Wicks Wicks and and Whittaker Whittaker (1977) (1977) have have correlated c o r r e l a t e d non—pseudomorphic non-pseudomorphic serpentine s e r p e n t i n e textures t e x t u r e s similar s i m i l a r to t o those t h o s e in i n Type Type BB serpentinites s e r p e n t i n i t e s with w i t h shearing s h e a r i n g proproc e s s e s and and prograde prograde metamorphic metamorphic environments. environments. cesses Whole—rock and Type Type BB Whole-rock X—ray X-ray diffraction d i f f r a c t i o n patterns p a t t e r n s of of aa number number of of samples samples of of Type Type AA and serpentinites s e r p e n t i n i t e s suggest s u g g e s t a difference d i f f e r e n c e in i n the t h e prevalent p r e v a l e n t serpentine s e r p e n t i n e structural s t r u c t u r a l variety variety i n the t h e two two types. t y p e s . Generally G e n e r a l l y Type Type AA serpentinite s e r p e n t i n i t e contains c o n t a i n s aa mixture m i x t u r e of of crystotile crystotile in and/or a n d / o r lizardite l i z a r d i t e with w i t h lesser l e s s e r amounts amounts of of antigorite. a n t i g o r i t e . Type Type BB serpentinite s e r p e n t i n i t e contains contains substantially s u b s t a n t i a l l y more more antigorite. a n t i g o r i t e . The presence p r e s e n c e of antigorite a n t i g o r i t e rather r a t h e r than t h a n crystotile crystotile or o r lizardite l i z a r d i t e is i s thought thought to t o be b e indicative i n d i c a t i v e of of prograde p r o g r a d e metamorphism, metamorphism, or o r serpentiniza— serpentinizat i o n in i n a higher h i g h e r pressure—temperature p r e s s u r e - t e m p e r a t u r e regime regime (Moody, (Moody, 1976). 1976). tion �57 6a 6b 6c 6d 6d t e x t u r e s from from the t h e Deer Deer Lake Lake Peridotite: Peridotite: Photomicrographs Photomicrographs of of serpentine s e r p e n t i n e textures a) a ) Type Type A A serpentinite, s e r p e n t i n i t e , serpentine s e r p e n t i n e pseudomorphs after a f t e r olivine; o l i v i n e ; b) b) Type A serpen— serpentinites, serpentinite, t i n i t e s , serpentine s e r p e n t i n e pseudomorph after a f t e r pyroxene pyroxene (bastite); ( b a s t i t e ) ; c) c ) Type Type BB serpentinite, recrystallized r e c r y s t a l l i z e d felted f e l t e d texture; t e x t u r e ; d) d ) Type Type BB serpentinite, s e r p e n t i n i t e , foliated f o l i a t e d texture. t e x t u r e . All All S c a l e on on all a l l photos, photos, 11 cm cm == 0.66 0.66 mm. mm. c r o s s e d polars. p o l a r s . Scale crossed F i g u r e 6; 6; Figure �37 A l t e r a t i o n of of the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e in i n the t h e Vicinity Vicinity Alteration of t h e Ropes Gold Mine, Marquette County, Michigan of the Ropes Gold Mine, Marquette County, Michigan Dean Dean Rossell R o s s e l l (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological M I 49931) 49931) University, Houghton, Houghton, MI University, i s contained contained entirely e n t i r e l y in i n an an east— eastGold mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Mine Mine is Gold west w e s t striking s t r i k i n g septum septum of of highly h i g h l y altered a l t e r e d felsic f e l s i c rock rock within w i t h i n the t h e serpentin— serpentini z e d Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Near Near the t h e Ropes Ropes Mine Mine the t h e serpentinite s e r p e n t i n i t e consist consist ized of two two principal p r i n c i p a l textural t e x t u r a l varieties: v a r i e t i e s : Type of Type A, A, with w i t h well w e l l preserved preserved relict relict igneous B, showing showing recrystallized r e c r y s t a l l i z e d and and foliated f o l i a t e d textures, textures, igneous textures, t e x t u r e s , and and Type Type B, probably produced produced by by shearing. shearing. AA prominent prominent zone zone of of Type Type BB serpentinite serpentinite probably along the t h e north n o r t h shore shore of of Deer Deer Lake Lake may may represent r e p r e s e n t an an extension extension of of aa shear shear along zone along along the t h e felsic f e l s i c septum. septum. zone Compositionally, Compositionally, the t h e serpentinites s e r p e n t i n i t e s represent r e p r e s e n t altered a l t e r e d harzburgite h a r z b u r g i t e and and l h e r z o l i t e (Rossell ( R o s s e l l and and Kalliokoski, Kalliokoski, this t h i s volume). volume). An An original o r i g i n a l composicomposilherzolite t i o n a l zoning zoning or o r layering l a y e r i n g may may be be reflected r e f l e c t e d by by wide wide variations v a r i a t i o n s in i n the t h e olivine olivine tional to t o pyroxene pyroxene ratios r a t i o s determined determined from from calculated c a l c u l a t e d mineral mineral modes, modes, but b u t the t h e scale scale of these t h e s e variations v a r i a t i o n s has h a s not n o t been been established. established. of + Serpentinite S e r p e n t i n i t e has has been been extensively e x t e n s i v e l y altered a l t e r e d to t o aa talc t a l c + dolomite dolomite ±Â magnesite magnesite ±2 chlorite c h l o r i t e assemblage assemblage in i n aa zone zone adjacent a d j a c e n t to t o the t h e Ropes Ropes ore o r e body. body. Major Major and and trace t r a c e element element compositions, compositions, including including gold, gold, were were determined determined for f o r aa suite s u i t e of of talc—carbonate talc-carbonate rocks rocks from from the t h e northern n o r t h e r n alteration a l t e r a t i o n zone. zone. From From this t h i s data d a t a relarelat i v e additions a d d i t i o n s and and losses l o s s e s of of chemical chemical components components were were computed computed by by two two methods: methods: tive The first f i r s t - aassuming s s u m i n g that t h a t alteration a l t e r a t i o n occurred occurred at a t constant c o n s t a n t volume, volume, and and the the The A 1 and and Sc Sc are a r e immobile immobile during during alteration a l t e r a t i o n while while volume volume second assuming assuming that t h a t Al second i s allowed allowed to t o change. change. Changes Changes calculated c a l c u l a t e d using using the t h e first f i r s t method method appear appear to to is be be more more consistent c o n s i s t e n t with w i t h observed observed mineralogical m i n e r a l o g i c a l changes changes than than those t h o s e calculated calculated by the t h e latter l a t t e r method. method. by Talc—carbonate Ropes Mine Mine appears appears to t o have have resulted r e s u l t e d in i n the the Talc-carbonate alteration a l t e r a t i o n at a t the t h e Ropes addition a d d i t i o n of of C02, CO2, Ca Ca and and Al, A l , and and the t h e removal removal of of H20 H2O and and Mg Mg from from the t h e serpentin— serpentini t e . Au Au abundance abundance in i n the t h e serpentinite s e r p e n t i n i t e samples samples analyzed analyzed were were found found to t o be be near near ite. c r u s t a l averages. averages. Talc—carbonate Talc-carbonate samples samples showed showed greater g r e a t e r variation, v a r i a t i o n , but b u t gengencrustal erally serpene r a l l y had had Au Au concentrations c o n c e n t r a t i o n s equal equal to t o or o r greater g r e a t e r than than those t h o s e found found in i n serpen— tinites. tinites. Gold may may have have been been transported t r a n s p o r t e d as a s aa carbonyl carbonyl or o r carbonate carbonate complex complex in i n aa Gold CO2 rich r i c h fluid f l u i d from from some some outside o u t s i d e source source to t o the t h e ore o r e host h o s t rock. rock. Subsequent Subsequent CO2 carbonate forming forming reactions r e a c t i o n s in i n the t h e ultraniafic u l t r a m a f i c rock t h e ore o r e host host carbonate rock surrounding the rock CO2 and/or rock sufficiently s u f f i c i e n t l y lowered lowered the t h e Pco2 and/or decreased decreased the t h e acidity a c i d i t y to t o allow allow for for structures d e p o s i t i o n of of gold gold in i n suitable suitable s t r u c t u r e s in i n the t h e ore o r e host h o s t rock. rock. deposition �38 Cobalt, Nickel, and Vanadium C o b a l t , Nickel, Vanadium Contents Contents of of Pyrite from Michiganime Slate, Michigan P y r i t e from Michigamme S l a t e , A . P. P. Ruotsala, R u o t s a l a , Paul P a u l M. M. Stadnik, S t a d n i k , T. T. J. Bornhorst (Dept. (Dept. of of Geol. Geol. A. & Geol. Engrg., Michigan Tech. Tech. Univ., Univ., Houghton, Houghton, MI M I 49931) 49931) Geol. Engrg., an oorganic—rich metasedimentary rock The Michigainme Michigamme SSlate l a t e iis s an r g a n i c - r i c h metasedimentary r o c k in in central Upper Peninsula of Michigan. central P e n i n s u l a of Michigan. The Michigan Geological G e o l o g i c a l Survey, Survey, with w i t h funding f u n d i n g from from the t h e Department of of Energy tested t e s t e d the t h e uranium potenpotential of the Marquette, Baraga and Iron with t i a l of t h e Michigamme in i n Marquette, I r o n Counties w ith ssix i x diamond drill d r i l l holes h o l e s (Trow, (Trow, 1979). 1979). In I n this t h i s study, s t u d y , pyrites p y r i t e s were were separated material nickel, s e p a r a t e d from ccore ore m a t e r i a l and analyzed for f o r cobalt, cobalt, n i c k e l , and with vanadium w i t h the t h e objective o b j e c t i v e of of determining d e t e r m i n i n g its i t s mode mode of of origin. origin. pyrites Price (1972), in in Most p y r i t e s fall f a l l into i n t o the t h e syngenetic s y n g e n e t i c field f i e l d of of P r i c e (1972), terms of of Co/Ni Co/Ni rratios; however, aa number number of of hhigh Co/Ni rratios were terms a t i o s ; however, i g h Co/Ni a t i o s were found which which ffall found a l l into i n t o the t h e volcanic—exhalative v o l c a n i c - e x h a l a t i v e massive massive sulfide s u l f i d e field. field. References Trow, J . , 1979, 1979, Final F i n a l report r e p o r t diamond—drilling diamond-drilling for f o r geologic g e o l o g i c informainformaTrow, J., Middle Precambrian Precambrian bbasins western of ttion i o n iin n tthe h e Middle a s i n s iin n tthe he w e s t e r n pportion o r t i o n of northern n o r t h e r n Michigan: Michigan: Geol. Geol. Surv. Surv. Div., Div., Michigan Dept. Dept. Nat. Nat. Re— ReLansing, Open—File ssources, o u r c e s , Lansing, Open-File Report UDOE UDOE OFR OFR GJBX—l62(79), GJBX-162(79), 44 44 p. p. Price, P r i c e , B.G., B.G., 1972, Minor elements in i n pyrites p y r i t e s from from the t h e Smithers Smithers map B.C. and e exploration of minor minor element studies x p l o r a t i o n aapplications p p l i c a t i o n s of studies aarea, r e a , B.C. (M.S. (M.S. Thesis): T h e s i s ) : Univ. Univ. of of British B r i t i s h Columbia, Columbia, Vancouver, Vancouver, 270 270 p. p. �39 Geochemistry Wisconsin Geochemistry of the the Volcanic Rocks of Northeastern Wisconsin J. SCHULZ Reston, Virginia 22092) KLAUS J. SCHULZ (U.S. (U.S. Geological Geological Survey, Survey, Reston, 22092) The early The early Proterozoic Proterozoic volcanic—plutonic volcanic-plutonic belt of north—central north-central northern half of Marinette Marinette County. Wisconsin is is well exposed in in the the northern area, the volcanic sequence has has been informally divided In this area, into Formation, the into four four formations formations (Jenkins, (Jenkins, 1973): 1973): the the Quinnesec Quinnesec Formation, the McAllister Peniene McAllister Formation, Formation,the theBeecher BeecherFormation, Formation,and andthe the PemeneForina— Formastratigraphic relationships relationships between these these are are still still tion. tion. Although stratigraphic not fully fully resolved, resolved, it it appears appears that that the the overall overall section section represents represents a a progression progression from from mafic mafic through through felsic felsic volcanics. volcanics. Although aa general general calc—alkaline calc-alkaline affinity affinity has been been recognized recognized felsic portions of this volcanic section, section, uncertainty for the more felsic still still remains remains as as to to the the geochemical geochemical affinities affinities of the the basaltic rocks rocks and their their possible possible petrologic petrologic relationship relationship to the the more felsic felsic volcanics. For For the the present present study, study, aa suite suite of samples samples was collected collected volcanics. elements, rare earth, earth, and other trace elements) for analysis (major (major elements, with emphasis with emphasis on on the the mafic mafic Quinnesec Quinnesec Formation. Formation. The The Quinnesec Quinnesec pillowed flows flows and associated associated diabases diabases range range from from basalt through through andesite andesite and show show little little evidence evidence of aa trend in in iron iron high, Al203 A1203 and and They have have variable, variable, though though generally generally high, enrichment. enrichment. They show a wide range range low Ti02 Ti02 contents. contents. The rare earth elements (REE) show low in both total total abundance abundance and and chondrite chondrite normalized normalized slopes. slopes. Most Most basalts basalts show show extreme extreme light light (L)REE (L)REE depletion depletion with [La/Sm]n [La/SmIn == .14.38 .14--38 Sturgeon Falls Falls (total range range .14—.76). .14-.76). Two gabbro samples from the Sturgeon (total sill, one of several large large gabbroic sills within the Quinnesec Quinnesec Forsill, mation, also mation, also show show significant significant LREE LREE depletion depletion suggesting suggesting possible possible LREE consanguinity with with the consanguinity the basalts. basalts. The andesites have enriched LREE relatively low ([La/SmJ ([La/SmIn == 1.23—1.47), 1.23-1.47), but relatively low total total REE REE abundances. abundances. Formation are andesitic whereas those Samples from the Beecher Formation those from the Pemene Pemene Formation from Formation are are rhyolitic. rhyolitic. The The rhyolites rhyolites have have higher higher REE REE abundances abundances and larger larger negative negative Eu anomalies anomalies than than the the andesites, andesites, but show show similar similar shaped, shaped, LREE—enriched LREE-enriched patterns. patterns. The The rhyolites rhyolites Rb/Sr ratios than than the the also have lower Sr (55—133 (55-133 ppm) and higher ~b/Sr andesites andesites ((Sr360 S r ~ 3 6ppm). 0ppm). The The data data suggest suggest the the following following conclusions: conclusions: 1. 1 . The The Quinnesec Quinnesec Formation Formation basalts and related related diabases diabases are are compositionally distinct from Proterozoic compositionally from the other early Proterozoic in upper Michigan (i.e. Badwater, etc.) etc.) basalts in (i.e. Hemlock, Badwater, which was highly depleted and were derived from from mantle which in large large ion ion lithophile lithophile elements. elements. 2. 2 . northeastern Wisconsin Wisconsin are The basalts and andesites of northeastern are not related by crystal crystal fractionation fractionation but represent seperate seperate melts melts from from compositionally compositionally distinct distinct sources. sources. 3. 3. The The overall overall chemical chemical characteristics characteristics of the the Quinnesec Quinnesec basalts basalts �40 suggest suggest affinities affinities with with basalts basalts in in recent recent island—arcs island-arcs back—arc basins rather than those of the ocean and back-arc the ocean floor floor or or continental continental regions. regions. The appearance appearance of of andesites andesites and more felsic felsic units with these these basalts also supports back—arc basin supports such such an an island—arc island-arc to back-arc environment. environment. Reference Reference Jenkins, R. A., 1973, Lake Superior . A., 1973, Institute Institute on on Lake Superior Geology, Geology, Jenkins, R 19th, p. 19th, p. 15—16. 15-16. �41 Geochemistry of of Fluid F l u i d Inclusions I n c l u s i o n s from from Archean Archean and and Phanerozoic Phanerozoic Gold Gold Geochemistry Deposits Deposits TED PAULL. J. SMITH, SMITH, PAUL L. CLOKE, CLOKE, and and STEPHEN STEPHEN E. E. KESLER KESLER (Department (Department of of TED J. Geological G e o l o g i c a l Sciences, S c i e n c e s , The The University U n i v e r s i t y of of Michigan, Michigan, Ann Ann Arbor, Arbor, MI MI 48109) 48109) F l u i d inclusions i n c l u s i o n s from from various v a r i o u s Archean Archean and and Phanerozoic Phanerozoic gold gold deposits deposits Fluid in i n metamorphic terrains t e r r a i n s were examined using u s i n g a specially s p e c i a l l y designed designed gas gas chromatographic chromatographic analytical a n a l y t i c a l system system and and conventional c o n v e n t i o n a l heating/freezing heatinglfreezing techniques. techniques. The The inclusion i n c l u s i o n analyses a n a l y s e s indicate i n d i c a t e that, t h a t , in i n most most cases, c a s e s , the the fluids CO f l u i d s are a r e H20—C02 H20-C02 or o r H20—CH4—C02 H20-CH4-C02 mixtures, m i x t u r e s , with w i t h trace t r a c e amounts amounts of of CO and N2. N2. and Heating and low and freezing f r e e z i n g measurements measurements indicate i n d i c a t e the t h e presence p r e s e n c e of of low salinity s a l i n i t y (<2 (<2 equiv. equiv. wt%NaCl), wt%NaCl), H20—C02 H20-C02 and and H20—CH4—C02 H20-CH4-CO2 fluid f l u i d inclusions, inclusions, confirming confirming our o u r analyses. analyses. Homogenization Homogenization of of the t h e inclusions i n c l u s i o n s occurred o c c u r r e d at at temperatures 220° to t o 380°C. 380°C Temperature and and f02 £ determinations determinations t e m p e r a t u r e s of of 220°C 2 were were made made by by plotting p l o t t i n g reaction r e a c t i o n lines l i n e s on on a02—teinperature a 0 t e m p e r a t u r e diagrams 2- utilizing u t i l i z i n g a recently r e c e n t l y developed developed equation e q u a t i o n of of state s t a t e for f o r supercritical supercritical H20-Coy-CH4 fluids. fluids. H20—C02—CH4 Our Our results r e s u l t s indicate i n d i c a t e that t h a t the t h e fluids f l u i d s obtained obtained equilibrium ' s near n e a r the t h e QFM QFM e q u i l i b r i u m at a t temperatures t e m p e r a t u r e s of of 340°C 340° to t o 500°C 500° and and f02ts f 02 buffer. buffer. Isochores, I s o c h o r e s , also a l s o calculated c a l c u l a t e d from from the t h e equation e q u a t i o n of of state, s t a t e , indicate indicate high h i g h pressures p r e s s u r e s of of 2000 2000 to t o 4000 4000 bars bars. �42 J a c o b s v i l l e Sandstone Sandstone Ridge Ridge in i n Keweenaw Keweenaw Bay Bay Jacobsville R. R. L. L. Wunderman Wunderman and and M. M. Rausch Rausch i s aa north—northeast n o r t h - n o r t h e a s t trending t r e n d i n g lake l a k e bottom bottom ridge r i d g e of of Jacobs— JacobsThere is yule v i l l eSandstone Sandstone in i n Keweenaw Keweenaw Bay Bay (Fig. (Fig. 1). 1 ) . AA recent r e c e n t scuba scuba dive d i v e conconfirms f i r m s the t h e presence p r e s e n c e of of subhorizontal s u b h o r i z o n t a l Jacobsville J a c o b s v i l l eSandstone Sandstone2020inm under under water w a t e r at a t aa point p o i n t 77 Km southeast s o u t h e a s t of of Portage P o r t a g e Entry Entry (88°22'W, (88O2ZvW, 46°56'N) 46'56'N) cropping A t this this cropping out o u t as a s aa detritus—free d e t r i t u s - f r e e north—west north-west facing f a c i n g scarp. s c a r p . At locality, l o c a l i t y , the t h e JJacobsville a c o b s v i l l e Sandstone is i s lithologically l i t h o l o g i c a l l y similar s i m i l a r to to nearby shore s h o r e exposures. exposures. Warren Warren (1981, (1981, Figs. F i g s . 46 46 and and 47) 47) shows shows that that this t h i s ridge r i d g e forms the t h e southeastern s o u t h e a s t e r n margin of of a steep—sided s t e e p - s i d e d valley valley so s o that t h a t similar s i m i l a r excellent e x c e l l e n t exposures of of bedrock are a r e likely l i k e l y to t o be b e found found on on the t h e northwest n o r t h w e s t ridge r i d g e face f a c e as a s well. w e l l . Being sheltered s h e l t e r e d from from the t h e lake, lake, t h e ridge r i d g e face f a c e more probably is i s related r e l a t e d to t o the t h e formation formation of the the t h e steep— steepsided being s i d e d vvalley a l l e y than than b e i n g the t h e result r e s u l t of of wave erosion e r o s i o n on aa lake l a k e cliff. cliff. Reference Reference Warren, E.J., E.J., Michigan Houghton, 1981, The bedrock topography topography of of the t h e Keweenaw Keweenaw Penninsula, Penninsula, (Ph.D. d i s s e r t a t i o n ) , Michigan Technological T e c h n o l o g i c a l University, University, (Ph.D. dissertation), 169 p. p. 169 Figure F i g u r e 1: 1: Location L o c a t i o n Map. Map. �43 ROPES GOLD MINE AND ITS I T S GEOLOGICAL SETTING SETTING Dean Rossell Kalliokoski D ean R o s s e l l and J. J. K alliokoski �44 THE THE ROPES ROPES GOLD GOLD MINE MINE AND AND ITS ITS GEOLOGICAL GEOLOGICAL SETTING SETTING Dean Rossell R o s s e l l and and J. J . Kalliokoski Kalliokoski INTRODUCTION INTRODUCTION Location Locat i o n The Ropes Gold Mine Mine is i s located l o c a t e d in i n Section S e c t i o n 29, 29, T48N—R27W, T48N-R27W, Marquette Marquette County, County, Michigan, Michigan, about t h r e e miles m i l e s north n o r t h of of Ishpeming Ishpeming and and aa quarter q u a r t e r mile m i l e west west of of Deer Deer Lake Lake (Figs. about three ( F i g s . 1, 1, 2). gold prosprosi s the t h e most most extensively e x t e n s i v e l y developed developed of of the t h e 20 20 or o r more more gold The Ropes Mine Mine is 2 ) . The pects p e c t s and and mines mines that t h a t comprise comprise the t h e Michigan Michigan gold gold belt. belt. History History Most i s summarized summarized from from Broderick Broderick (1945). (1945). The The Ropes Ropes ore ore Most of of the t h e following f o l l o w i n g history h i s t o r y is body body was was discovered d i s c o v e r e d in i n 1880 1880 by by Julius J u l i u s Ropes Ropes while w h i l e he h e was was prospecting p r o s p e c t i n g for f o r asbestos asbestos among among the t h e outcrops o u t c r o p s of of the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . Mining Mining operations o p e r a t i o n s at a t the t h e Ropes Ropes began in At i n 1882 1882 and and continued c o n t i n u e d until u n t i l 1897 1897 when when the t h e mine mine was was closed c l o s e d by by creditors. c r e d i t o r s . At the t h e time time of of closing, c l o s i n g , 15 1 5 levels l e v e l s had had been been developed developed to t o the t h e east e a s t and and west west of of the t h e Curry Curry shaft, s h a f t , that t h a t reached reached aa depth d e p t h of of 244 244 meters. meters. During During the t h e 15 1 5 years y e a r s that t h a t the t h e mine mine was was in i n operation o p e r a t i o n it i t produced produced 1250 1250 kg kg of of gold gold and and 6200 6200 kg kg of of silver s i l v e r from from 145,000 145,000 tons t o n s of of ore, o r e , averaging a v e r a g i n g 5.96 5.96 g/ton g / t o n gold gold and and 28.05 28.05 g/ton g / t o n silver s i l v e r (Morgan (Morgan and and DeCristoforo, D e C r i s t o f o r o , 1980). 1980). Around Around 1901 1901 some some 30,000 30,000 tons t o n s of of tailings t a i l i n g s were were cyanided. cyanided. In I n 1933 1933 the t h e Ropes property p r o p e r t y was was acquired a c q u i r e d by by the t h e Ishpeming Ishpeming Mining Mining Co., Co., which which continued continued surface s u r f a c e exploration e x p l o r a t i o n in i n the t h e area. a r e a . Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. bought bought aa majority majority interest i n t e r e s t in i n the t h e Ishpeming Ishpeming Mining Mining Co. Co. in i n 1934. 1934. From From 1934 1934 to t o 1942 1942 they t h e y conducted conducted an an extensive e x t e n s i v e exploration e x p l o r a t i o n program program of of diamond diamond drilling, d r i l l i n g , drifting d r i f t i n g on on the t h e 15th 1 5 t h level, l e v e l , and and resampling resampling of of the t h e old o l d workings workings in i n an a n attempt a t t e m p t to t o find f i n d an an extension e x t e n s i o n of of the t h e Ropes Ropes ore ore body it body (Fig. (Fig. 3). 3 ) . Although Although this t h i s work work found found no no major major extensions e x t e n s i o n s of of the t h e ore o r e body, body, it did d i d disclose d i s c l o s e over over aa million m i l l i o n tons t o n s of of lower lower grade grade ore o r e in i n the t h e ore o r e host h o s t rock r o c k surrounding surrounding the 1st and and 15th 1 5 t h levels, l e v e l s , average average t h e old o l d workings. workings. These These zones, zones, located l o c a t e d between between the t h e 1st 0.13 0.13 oz/ton o z l t o n gold gold and and 0.7 0.7 oz/ton o z l t o n silver. s i l v e r . In I n 1942 1942 war time t i m e restrictions r e s t r i c t i o n s on on precious precious metal m e t a l mining mining stopped stopped operations o p e r a t i o n s at a t the t h e mine, mine, preventing p r e v e n t i n g further f u r t h e r exploration e x p l o r a t i o n below below the t h e 15th 1 5 t h level. level. In t h e Ropes Ropes Mine, Mine, began began aa new new expor— export h e present p r e s e n t owner owner of of the I n 1974 1974 Callahan Callahan Mining Mining Corp., Corp., the ation a t i o n program program to t o confirm c o n f i r m and and try t r y to t o expand expand the t h e low low grade grade ore o r e reserves r e s e r v e s established e s t a b l i s h e d by by the t h e Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. To To date d a t e this t h i s work work has h a s included i n c l u d e d rehabilitation r e h a b i l i t a t i o n of of the t h e old o l d mine mine workings, an an extensive e x t e n s i v e surface s u r f a c e and and underground underground diamond diamond drilling d r i l l i n g camcampaign, worke x t r a c t i o n of of bulk b u l k samples samples for f o r metallurgical m e t a l l u r g i c a l tests, t e s t s , resampling resampling of of old o l d workpaign, extraction ings, remapping of of tthe i n g s , aand n d remapping h e ssurface u r f a c e and underground underground geology geology (Skillings, ( S k i l l i n g s , 1981). 1981). Previous P r e v i o u s Geological G e o l o g i c a l Studies Studies The i s by by Broderick, Broderick, who who was was the the The only o n l y detailed d e t a i l e d geological g e o l o g i c a l work work on on the t h e Ropes Ropes Mine Mine is mine mine geologist g e o l o g i s t for f o r Calumet Calumet and and Hecla Hecla Mining Mining Co. Co. In I n 1945 1945 Broderick B r o d e r i c k published p u b l i s h e d aa detailed d e t a i l e d description d e s c r i p t i o n of of the t h e Ropes Ropes ore o r e body body and and the t h e surrounding s u r r o u n d i n g peridotite. p e r i d o t i t e . SubSubsequent sequent published p u b l i s h e d work work on on the t h e geology geology of of the t h e surrounding surrounding area a r e a has h a s been been by by Boyum Boyum (1964, P u f f e t t (1966, (1966, 1974), 1974), Clark C l a r k and and others o t h e r s (1975), (1975), Cannon Cannon and and (1964, 1970, 1970, 1975), Puffett Klasner Klasner (1975), (1975), and and Morgan Morgan and and DeCristoforo D e C r i s t o f o r o (1980). (1980). The The latter l a t t e r provide p r o v i d e the t h e most most Information recent r e c e n t data d a t a on on the t h e overall o v e r a l l geology geology of of the t h e Ishpeming Ishpeming greenstone g r e e n s t o n e belt. b e l t . Information on the t h e ore o r e host h o s t rock r o c k comes comes from from an an unpublished unpublished mine mine report r e p o r t by by Creasy Creasy (1981). on (1981). �________ _______ 45 L o c a t i o n of t h e opes Gold Mine. Location of the Ropes Gold Mine. F i g u r1.e 1. Figure : :::::: —S'. I, / >j1 r ..— A • >< 7- A i ç.J c •••n'v Pv>,' t.JJ I < — r -, '. 47 A L NA Mine 1 0 Feet 4000 (cannon and Klasner, 1975: Clark and others.1975) Proterozoic Proterozoic . . ... . .., Marquette M a r ~ u e t Range t eRange Supergroup SupergrOUp (Cannon and Klasner, 1975; Clark and others,1975) 1-1 Archean Archean .... Granite Granite DeerLake LakePeridotite Peridotite I TAge3Deer relations uncertain ,;\,;:</ -5 '6 Field trip stops Field trip stops Age relations uncertain KitchiSchist Schist Kitchi ' r] Aggloherate Agglomerate 1-i Interned. to to fels. fels.voles. volcs. Intermed. GEOLOGYOF OFTHE THEAREA AREAAROUND AROUND GEOLOGY THE ROPES AND MICHIGAN GOLD MINES A c Amphibollte Amphiboilte F i g u r e 2. 2. Figure Regional geology of t h e Ropes Mine and Michigan Mine a r e a . Regional geology of the Ropes Mine and Michigan Mine area, �58 Composition of Serpentinites Because of difficulty in field recognition, no attempt was made during mapping In to distinguish pyroxene—rich and olivine—rich portions of the peridotite. general, olivine—rich ultramafics produce more magnetite when serpentinized than do the pyroxene—rich varieties. A large scale zonation of magnetic properties in the Deer Lake Peridotite, showing a highly magnetic core and less intensely magnetic margins (Morgan and DeCristoforo, 1980), suggests an olivine—rich core and pyroxene—rich margins. The chemical compositions of 10 representative serpentinites from the Deer Lake The MgO values reported in this study are signiPeridotite are given in Table 3. ficantly higher than those reported by Morgan and DeCristoforo (1980), but correlate well with those reported by Creasy (1981). After recalculating the chemical data to exclude volatiles, mineral modes were calculated for the serpentinite samples using a computer program. The dominant mineral phases in the calculated modes are olivine and orthopyroxene, with lesser amounts of diopside, magnetite, In the following paragraph chromite and, in pyroxene rich samples, of anorthite. The modal references to olivine and pyroxene also are to their calculated modes. The 10 samples in Table 3 are olivine to pyroxene ratios range from 0.28 to 1.93. plotted on an olivine—orthopyroxene—clinopyroxene ternary diagram in Figure 7. All of the analyzed samples from the Deer Lake Peridotite fall in or near the hartzburgite field. Ashely (1974), Coleman and Keith (1970), and Page (1967) report losses of Ca during serpentinization of primary ultramafic rocks. If substantial Ca has been lost from the Deer Lake Peridotite during serpentinization, the original ultramaf Ic rock may have had more diopside than shown in the calculated modes. Comparison of trace element abundances with calculated mineral modes reveals some In the samples analyzed in this study, A1203, Ti02 and Sc are engeneral trends. riched in pyroxene—rich serpentinites relative to the divine—rich ones. Increases in these abundances correlate with increasing chlorite in the serpentinite. Nb Cr303 and FeO show content appears to decrease with decreasing olivine content. The consistent pyroxene—rich samples. no consistent trends between olivine— and variation in the ratios of TiO2fAl2O3, Sc/Al203 for these samples imply that these serpentinites were originally derived from a single parent magma. Comparison of Serpentinite Compositions With Those of Other Ultramafics The determination of the origin of the Deer Lake Peridotite could have exploration significance. Morgan and Decristoforo (1980) noted that, based on their analyses, the composition of the Deer Lake Peridotite is close the komatiite field of Naldrett It follows that if the Deer Lake Peridotite represents komatiitic and Cabri (1976). volcanic rocks, the OHR might be an interflow tuff sequence, possibly with an associated, laterally extensive exhalite component. Many chemical criteria have been proposed to distinguish komatiitic rocks since the There now seems to be a con— recognition of ultramafic lavas in the late 1960's. census (Basaltic Volcanism Special Project, 1981) that komatiites are characterized 1) MgO values greater than 18 and less than 40 weight percent, but typically by: between 20 and 30 weight percent; 2) Tb2 less than 1%; 3) Ni greater than 100 ppm; In the serpentinite samples 4) Cr greater than 140 ppm; 5) CaO/Al203 0.8 to 1.1. analyzed for this study (with values recalculated to exclude volatiles; Table 2): �59 ANALYSES OF INITE SRMPLES SAMPLES RNRLYSES OF SERPENT SERPENTINITE 1 2 3 4 5 6 7 8 9 10 S102 RL203 FE203 FEO FEO MG0 M GO CR0 CRO NR2O 0 NR2 K20 K2 0 1-120+ H20+ T102 TI02 P205 P205 C02 C02 43.20 1.96 '42.55 .03 .00 42.18 39.88 41 .88 41.10 414 .146 1.71 .00 5.34 40.21 3.82 38.30 .98 .00 42.03 5.53 .00 .00 .00 2.07 .00 5.67 35.07 2.30 9.69 36.12 10.00 10.59 28 .60 .03 .00 .03 .00 .03 .01 .04 .02 27 .69 1.89 .06 12.21 31.85 3.14 5.43 37.73 1.48 5.58 34.29 4.36 9.70 6.70 6.20 8.20 6.80 .11 .01 .00 .02 .02 .05 .02 .07 .02 7.80 2.15 TOTAL TOTRL 102 .25 101 .06 100 .01 SC V CR Cu ZN .00 8.99 36.77 .27 .03 .00 11 85 .02 .03 .00 .05 .01 .00 .35 .04 .00 7.20 9.90 7.50 6.50 6.50 .27 .03 .214 .03 .01 .03 6.06 3.75 2.12 .01 .02 6 .8? .06 .01 5.08 .21 .02 .00 1.22 100 .00 100 .00 99.98 100.01 93.47 99.9? 97.87 19 126 19 123 8 15 82 7 s 17 43 70 2918 3343 3423 3940 2163 38 3* 22 13 60 62 66 50 60 98 7 12 52 25 59 49 37 49 1582 26 21 1 4 AU Table 33.. Peridotite. Peridotite. ppm. PPm. 17 .00 9.49 29.57 6 4667 .00 6.33 35.53 4.01 39 1989 27 5172 .00 .00 2.08 2274 20 64 1.60 .03 3 Selected S e l e c t e d analyses a n a l y s e s of of serpentinites s e r p e n t i n i t e s from the t h e Deer Lake Elements listed wt. l i s t e d as a s oxides o x i d e s in in w t . percent, p e r c e n t , others o t h e r s in in I' �60 OPX 0 PX a LherzOlite Wehrtde CPX CPX Clinopyroxenite Figure 7. Compositions of serpentinites from Table 3 plotted on Figure 7. of serpentinites from Coleman Table 3 and plotted on (Modified from Keith, nomenclatureCompositions ternary diagram. nomenclature ternary diagram. (Modified from Coleman and Keith, 1971). 1971). �61 1) 1 ) the t h e MgO MgO content, c o n t e n t , in i n every every sample, sample, is i s greater g r e a t e r than t h a n 30 30 weight weight percent, p e r c e n t , and and i s less l e s s than than s e v e r a l are a r e more more than than 40 40 weight weight percent; p e r c e n t ; 2) 2) Ti02 Ti02 in i n all a l l samples samples is several 1% and 1% and in i n most most samples samples is i s less l e s s than than 0.1%; 0.1%; 3) 3) for f o r all a l l samples samples both b o t h Cr C r and and Ni N i are are greater g r e a t e r than than 1000 1000 ppm; ppm; and and 4) 4) CaO/Al203 CaO/A1203 ratios r a t i o s range range from from 0.17 0.17 to t o 75.74. 75.74. The The wide wide variation v a r i a t i o n of of this t h i s ratio r a t i o probably probably reflects r e f l e c t s the t h e mobility m o b i l i t y of of Ca Ca during d u r i n g serpen— serpeni t can can be b e seen seen that t h a t Ti02, Ti02, t i n i z a t i o n and and carbonatization. c a r b o n a t i z a t i o n . From From this t h i s comparison comparison it tinization C r and and Ni N i fit f i t the t h e requirements requirements for f o r komatiite, k o m a t i i t e , but b u t all a l l would would be b e marginal marginal values. values. Cr Only some some of of the t h e MgO MgO values v a l u e s fit f i t the t h e criteria, c r i t e r i a , and and those t h o s e that t h a t do, do, also a l s o are a r e near near Only limit. t h e limit. the commonly used used plot p l o t for f o r distinguishing d i s t i n g u i s h i n g komatiitic k o m a t i i t i c rocks r o c k s from from tholeiitic t h o l e i i t i c rocks r o c k s is is AA commonly the t h e A1203 A1203 vs. v s . FeO/(FeO+MgO) FeO/(FeO+MgO) plot p l o t of of Naldrett N a l d r e t t and and Cabri C a b r i (1976) (1976) shown shown in i n Figure F i g u r e 8. 8. The The diagonal d i a g o n a l line l i n e in i n Figure F i g u r e 88 separates s e p a r a t e s plots p l o t s of of African A f r i c a n and and Canadian Canadian komatiites komatiites (x) from from those t h o s e of of tholeiitic t h o l e i i t i c Canadian Canadian synvolcanic s y n v o l c a n i c dikes d i k e s and and flows flows (o). ( 0 ) . All A l l ser— ser(x) pentinite t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e (listed ( l i s t e d in i n Table Table 33 and and plotted p l o t t e d as a s solid s o l i d dots dots p e n t i n i t e of of the on Figure F i g u r e 8) 8 ) fall f a l l in i n or o r near n e a r the t h e komatiitic k o m a t i i t i c side s i d e of of the t h e diagram. diagram. However, However, aa number number on of (*) also a l s o fall f a l l well w e l l within within of samples samples of of Alpine—type Alpine-type ultramafics u l t r a m a f i c s (plotted ( p l o t t e d as a s stars s t a r s (*) t h e komatiite k o m a t i i t e side s i d eof o f the t h e diagram. diagram. This T h i s lack l a c k of of discrimination d i s c r i m i n a t i o n is i s noted noted by by Naldrett Naldrett the who who points p o i n t s out o u t that t h a t many many other o t h e r ultramafic u l t r a m a f i c and and mafic m a f i c rocks r o c k s that t h a t are a r e not n o t related r e l a t e d to to w i l l plot p l o t on on the t h e komatiitic k o m a t i i t i c side s i d e of of the t h e diagram diagram (Naldrett, ( N a l d r e t t , 1980). 1980). k o m a t i i t e s will komatiites On On the t h e basis b a s i s of of the t h e plot p l o t in i n Figure F i g u r e 88 the t h e Deer Lake Peridotiteiskomatiitic. P e r i d o t i t e i s k o m a t i i t i c . HowHowever, e v e r , the t h e very v e r y high h i g h values v a l u e s of of MgO MgO for f o r many many of of the t h e serpentinite s e r p e n t i n i t e samples samples do do not not ( B a s a l t i c Volcanism, Vol.canism, correspond correspond with w i t h one one of of the t h e diagnostic d i a g n o s t i c features f e a t u r e s of of komatiites k o m a t i i t e s (Basaltic These high h i g h MgO MgO values v a l u e s are a r e considered c o n s i d e r e d by by the t h e senior s e n i o r author author S p e c i a l Project, P r o j e c t , 1981). 1981). These Special Moreover, most most recent recent t o be be typical t y p i c a l of of intrusive i n t r u s i v e and and alpine a l p i n e type t y p e ultramafics. u l t r a m a f i c s . Moreover, to classifications c l a s s i f i c a t i o n s of of ultramafic u l t r a m a f i c rock rock types t y p e s have have been been based based on on tectonic t e c t o n i c setting s e t t i n g rather rather than than chemistry c h e m i s t r y alone a l o n e (Naldrett, ( N a l d r e t t , 1980), 1980), implying implying that t h a t both b o t h compositional c o m p o s i t i o n a l and and field field evidence evidence should should be b e considered c o n s i d e r e d for f o r aa valid v a l i d designation. designation. Talc-Carbonate Alteration Alteration Talc—Carbonate Serpentine, S e r p e n t i n e , olivine, o l i v i n e , and and pyroxene, pyroxene, the t h e primary primary constituents c o n s t i t u e n t s of of serpentinites s e r p e n t i n i t e s and and peridotites, C02 and and break b r e a k down down p e r i d o t i t e s , are a r e unstable u n s t a b l e in i n the t h e presence p r e s e n c e of of fluids f l u i d s rich r i c h in i n CO2 a c c o r d i n g to t o the t h e following f o l l o w i n g reaction: reaction: according + + CO2 == 33 magnesite magnesite ++ 11talc t a l c + 33 H20 Hz0 s e r p e n t i n e + 33 CO2 22 serpentine (Deere, et e t al., a l . , 1965). 1965). (Deere, The The serpentinites s e r p e n t i n i t e s of of the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e have have been been altered a l t e r e d extensively e x t e n s i v e l y to t o talc talc and carbonate c a r b o n a t e in i n the t h e vicinity v i c i n i t y of of the t h e Ropes Ropes Mine. Mine. Here Here zones zones of of talc—carbonate t a l c - c a r b o n a t e rock rock and extend extend over over 400 400 feet f e e t to t o the t h e north n o r t h of of the t h e ore o r e host h o s t rock, rock, and and over over 200 200 feet f e e t to t o the the Both zones apparently pinch out eastward, but persist downward, s o u t h (Fig. ( F i g . 4). 4 ) . Both zones a p p a r e n t l y p i n c h o u t eastward, b u t p e r s i s t downward, south I n general g e n e r a l the t h e distribution d i s t r i b u t i o n of of talc— talca t least l e a s t to t o the t h e present p r e s e n t levels l e v e l s of of exploration. e x p l o r a t i o n . In at carbonate c a r b o n a t e alteration a l t e r a t i o n appears a p p e a r s to t o be b e largely l a r g e l y controlled c o n t r o l l e d by by the t h e distribution d i s t r i b u t i o n of of the the OHR. Due Due to t o the t h e difficulty d i f f i c u l t y of of recognizing r e c o g n i z i n g low low to t o moderate moderate abundances abundances of of talc t a l c and and OHR. carbonate 4 , refer r e f e r only o n l y to to c a r b o n a t e in i n hand hand sample, sample, talc—carbonate t a l c - c a r b o n a t e zones, zones, shown shown in i n Figure F i g u r e 4, zones zones in i n which which talc t a l c and and carbonate c a r b o n a t e constitute c o n s t i t u t e the t h e majority m a j o r i t y of of the t h e rock. r o c k . This This criterionhas c r i t e r i o n h a s undoubtedly undoubtedly led l e d to t o an an underestimation u n d e r e s t i m a t i o n of of the t h e extent e x t e n t of of talc—carbonate talc-carbonate alteration. alteration. �62 20 0 15 xx x Komatiite Komatiite r) 0 10 Tholeiite Tholeiite 0 0 0 CN -J x x * 5 x .. x x 0 .0 .2 .4 .8 .6 FEO/FEO+MGO AL203 VS FEO/FEO±MGO + Figure Variation V a r i a t i o n of of A1203 A1203 with w i t h FeO/(FeO FeO/(FeO + MgO) MgO) wt. wt. percent percent F i g u r e 8. 8. ratio: ( - ) = serpentinites s e r p e n t i n i t e s of of the t h e Deer Deer Lake Lake Peridotite, Peridotite, r a t i o : (-)= (x)= (x)= komatiites k o m a t i i t e s (data ( d a t a from from Naldrett N a l d r e t t and and Cabri, C a b r i , 1976), 1 9 7 6 ) , (°)= ( o ) =tho— tho- leiites l e i i t e s from from Dundonald Dundonald Sill S i l l and and Theo's Theo's Flow Flow (Data (Data from from Naldrett Naldrett and l 9 7 6 ) , (*)= (*)= Alpine A l p i n e type t y p e lherzolites l h e r z o l i t e s and and harzburgites harzburgites and Cabri, C a b r i , 1976), (data T o t a l Fe Fe is i s calculated c a l c u l a t e d as a s FeO FeO and and ( d a t a from from Menzies, Menzies, 1977). 1 9 7 7 ) . Total all ( F i g u r e modmoda l l analyses a n a l y s e s are a r e calculated c a l c u l a t e d to t o exclude e x c l u d evolatiles. v o l a t i l e s . (Figure ified i f i e d from fromNaldrett N a l d r e t t and andCabri, C a b r i , 1976). 1976). 1.0 �63 P e r i p h e r a l to t o the t h e talc—carbonate t a l c - c a r b o n a t e zones, zones, carbonate c a r b o n a t e alteration a l t e r a t i o n in i n the t h e serpentinite serpentinite Peripheral o c c u r s as a s pseudomorphic replacements of of serpentine s e r p e n t i n e veins v e i n s by carbonate. c a r b o n a t e . Veins occurs Veins g e n e r a l l y increase i n c r e a s e in i n abundance near n e a r the t h e margins of of the t h e talc—carbonate t a l c - c a r b o n a t e zones, zones, so so generally t h a t a single s i n g l e hand sample sample may may contain c o n t a i n several s e v e r a l generations g e n e r a t i o n s of of veins. v e i n s . In I n these these that a r e a s , younger s e t s of of veins, v e i n s , composed of of coarse—grain c o a r s e - g r a i n carbonate, c a r b o n a t e , typically t y p i c a l l y crosscrossareas, younger sets c u t older o l d e r veins v e i n s of of serpentine s e r p e n t i n e replaced r e p l a c e d by by carbonate. carbonate. cut i s typically t y p i c a l l y gradational, gradational, The contact c o n t a c t between serpentinite s e r p e n t i n i t e and talc—carbonate t a l c - c a r b o n a t e rock r o c k is o n l y by aa gradual g r a d u a l lightening l i g h t e n i n g in i n color c o l o r of of the t h e rock, rock, as a s talc t a l c and and carbonate carbonate marked only i n c r e a s e at a t the t h e expense expense of of the t h e serpentine s e r p e n t i n e matrix. matrix. S e r p e n t i n i t e features, f e a t u r e s , such such increase Serpentinite patterns aass vvein ein p a t t e r n s and serpentine s e r p e n t i n e pseudomorphs after a f t e r olivine, o l i v i n e , are a r e commonly preserved preserved f o r some distance d i s t a n c e into i n t o the t h e talc—carbonate t a l c - c a r b o n a t e zone. zone. However, However, serpentinite s e r p e n t i n i t e features features for mrn clots clots aare re o b l i t e r a t e d in i n more intensely i n t e n s e l y altered a l t e r e d rock, r o c k , which commonly commonly contain c o n t a i n 33 mm obliterated and thin t h i n contorted c o n t o r t e d seams seams of of chlorite. c h l o r i t e . The degree d e g r e e of of alteration a l t e r a t i o n varies v a r i e s widely throughout the the n o r t h and south s o u t h alteration a l t e r a t i o n zones, zones, with w i t h pods of of relatively r e l a t i v e l y fresh fresh throughout north serpentinite p reserved w i t h i n the t h e mapped b o u n d a r i e s of of the t h e alteration a l t e r a t i o n zones. zones. The serpentinite preserved within boundaries rratio a t i o of t a l c to t o carbonate c a r b o n a t e generally g e n e r a l l y varies v a r i e s from about 2.0 2.0 to t o 0.5, 0 . 5 , but b u t several several of talc s m a l l zones of t a l c (steatite) ( s t e a t i t e ) have been found in i n the t h e mine. mine. Both dolodolosmall of almost pure talc m i t e and magnesite have been formed formed during d u r i n g alteration a l t e r a t i o n of of the t h e serpentinite, s e r p e n t i n i t e , dolomite dolomite mite OHR. b e i n g the t h e most abundant, abundant, particularly p a r t i c u l a r l y near n e a r the t h e OHR. being t h e contact c o n t a c t with w i t h the t h e OHR, OHR, the t h e talc—carbonate t a l c - c a r b o n a t e rock r o c k changes changes composition, composition, so s o that that Near the quartz mineral q u a r t z and chlorite c h l o r i t e become significant significant m i n e r a l phases and talc t a l c becomes a minor phase. phase. Chidester C h i d e s t e r and others o t h e r s (1978) (1978) have proposed that t h a t similar s i m i l a r carbonate—quartz carbonate-quartz zones zones in i n the the Belvidere body rrepresent of ttalc—carbonate B e l v i d e r e Mountains ultramaf u l t r a m a f iIc c body e p r e s e n t tthe h e ffinal i n a l sstage t a g e of alc-carbonate occurring aalteration, lteration, o c c u r r i n g along a l o n g zones where C02—rich C02-rich fluids f l u i d s travelled t r a v e l l e d most freely. freely. nature The locally l o c a l l y gradational gradational n a t u r e of of the t h e south s o u t h wall w a l l contact c o n t a c t between carbonate—quartz— carbonate-quartzchlorite OHR, suggest s u g g e s t that t h a t talc—carbonate t a l c - c a r b o n a t e alteration a l t e r a t i o n has h a s also a l s o affected affected c h l o r i t e rock r o c k and the t h e OHR, the This OHR. T h i s is i s supported s u p p o r t e d by large l a r g e differences d i f f e r e n c e s between trace t r a c e element element abundances abundances t h e OHR. in near OHR, and and those t h o s e in in i n samples n e a r the t h e contact, c o n t a c t , which reflect r e f l e c t the t h e composition of of OHR, talc—carbonate t a l c - c a r b o n a t e rocks r o c k s further f u r t h e r from from the t h e contact. c o n t a c t . A similar s i m i l a r overlap o v e r l a p of of alteration alteration from talc—carbonate t a l c - c a r b o n a t e rocks r o c k s to t o more felsic f e l s i c rocks r o c k s has h a s been reported r e p o r t e d at a t the t h e Campbell Red Lake and and Dickenson gold gold mines in i n Canada Canada (MacGeehan (MacGeehan and and Hodgson, Hodgson, 1980). 1980). A A more discussion petrographic i s under complete d i s c u s s i o n of of p e t r o g r a p h i c changes in i n the t h e talc—carbonate t a l c - c a r b o n a t e zone zone is preparation p r e p a r a t i o n by Rossell R o s s e l l (M.S. (M.S. thesis, t h e s i s , in i n preparation). preparation). Relationship R e l a t i o n s h i p of of Talc—Carbonate Talc-Carbonate Alteration A l t e r a t i o n to t o Gold Gold Mineralization Mineralization It h has been proposed proposed by w writers It a s been r i t e r s such as a s Pyke (1976) (1976) that t h a t ultramafic u l t r a m a f i c rocks r o c k s may be the bed" from which the t h e "source "source bed" t h e gold in i n many deposits d e p o s i t s has h a s been derived. d e r i v e d . Pyke his based h i s arguments largely l a r g e l y on on the t h e close c l o s e spatial s p a t i a l association a s s o c i a t i o n between between ultramaf u l t r a m a fIc ic Ontario rrocks o c k s and the t h e gold deposits d e p o s i t s at a t Timmins, Timmins, O n t a r i o and in i n other o t h e r large l a r g e Precambrian gold camps. camps. Additional A d d i t i o n a l support s u p p o r t for f o r this t h i s point p o i n t of of view view came came from from Gottfrled G o t t f r i e d and and others presented o t h e r s (1972), (1972), who p r e s e n t e d evidence suggesting s u g g e s t i n g that t h a t primary gold gold abundances in in ultramafic u l t r a m a f i c rocks r o c k s are a r e higher h i g h e r than t h a n in i n most most other o t h e r rock r o c k types. t y p e s . Anhaeusser and others others (1975), and Sager Sager and and oothers (1975), and t h e r s (1982) (1982) ddispute i s p u t e tthis h i s cconclusion, o n c l u s i o n , and show that, t h a t , on a basis, i s no higher, h i g h e r , and and in in worldwide b a s i s , the t h e primary gold content c o n t e n t of of ultramafic u l t r a m a f i c rocks r o c k s is i s lower, lower, than t h a n crustal c r u s t a l averages. averages. many cases c a s e s is Pyke (1976) (1976) proposes that t h a t one reason r e a s o n for f o r the t h e relationship r e l a t i o n s h i p of of ultramafic u l t r a m a f i c bodies b o d i e s to to gold m mineralization i s that t h a t substantial s u b s t a n t i a l amounts of of gold were released r e l e a s e d from from the the i n e r a l i z a t i o n is ultramafic u l t r a m a f i c rocks r o c k s during d u r i n g carbonatization. c a r b o n a t i z a t i o n . The senior s e n i o r writer w r i t e r has h a s tested t e s t e d the t h e hypohypothesis t h e s i s by obtaining o b t a i n i n g neutron n e u t r o n activation a c t i v a t i o n gold analyses a n a l y s e s for f o r a suite s u i t e of of samples samples from from the north the n o r t h talc—carbonate t a l c - c a r b o n a t e zone at a t the t h e Ropes Mine, Mine, and for f o r serpentinites s e r p e n t i n i t e s from from the the �64 Peridotite. T h i s data d a t a should permit permit an evaluation e v a l u a t i o n of of the the surrounding Deer Lake Peridotite. This degree d e g r e e of of redistribution r e d i s t r i b u t i o n of of gold and other o t h e r elements during d u r i n g carbonate c a r b o n a t e alteration. alteration. i s not n o t satissatisThe d i r e c t comparison of of chemical data d a t a expressed as a s weight percent p e r c e n t is direct factory with f a c t o r y for f o r determining chemical changes associated associated w i t h metasomatic alterations alterations (Kerrich particularly is p a r t i c u l a r l y true t r u e when substantial s u b s t a n t i a l changes in in ( K e r r i c h and Fyfe, Fyfe, 1981). 1981). This T h i s is i s the t h e case c a s e when serpentinite s e r p e n t i n i t e (sp. ( s p . gr. gr. sspecific p e c i f i c gravity g r a v i t y accompany alteration, a l t e r a t i o n , as a s is 2.60) alters 2.60) a l t e r s to t o talc—carbonate t a l c - c a r b o n a t e (sp. ( s p . gr. g r . 2.70—2.90). 2.70-2.90). C h i d e s t e r (1962), (1962), N a l d r e t t (1966), (1966). and Barnes (1973) (1973) have concluded that t h a t talc— talcChidester Naldrett ccarbonate a r b o n a t e alteration a l t e r a t i o n is i s aa constant c o n s t a n t volume volume process. p r o c e s s . For this t h i s and and other o t h e r reasons reasons d i s c u s s e d by o s s e l l (Thesis ( T h e s i s in i n prep.) p r e p . ) constant c o n s t a n t volume was assumed when calcucalcudiscussed by R Rossell l a t i n g rrelative e l a t i v e changes n cchemistry, h e m i s t r y , uusing s i n g aa method u t l i n e d b y c h i d e s t e r (1972). (1972). lating changes iin method ooutlinedbyChidester Relative R e l a t i v e aadditions d d i t i o n s and subtractions s u b t r a c t i o n s have been calculated c a l c u l a t e d from the t h e data d a t a in i n Table 4 and listed 5. of the t h e initial i n i t i a l parent p a r e n t rock is i s assumed l i s t e d in i n Table Table 5. The composition of to t o bbe e that t h a t of of serpentinite s e r p e n t i n i t e sample sample No. No. 33 (Table (Table 3). 3 ) . Reasons for f o r choosing this t h i s parent parent rock composition are a r e given given by by Rossell R o s s e l l (Thesis ( T h e s i s in i n prep.). prep.). Samples in i n Table 55 are are contact. l i s t e d from left l e f t to t o rright i g h t according a c c o r d i n g to t o decreasing d e c r e a s i n g distance d i s t a n c e from from the t h e OHR contact. listed v i s u a l l y estimated e s t i m a t e d from from thin t h i n section s e c t i o n are a r e listed l i s t e d below below each each sample. sample. Mineral modes visually V a r i a t i o n s in i n abundance of of C, C , H, Ca, Mg, i t h distance d i s t a n c e from from OHR contact contact Variations H, Ca, Mg, A Al1 and Au w with are a r e shown graphically g r a p h i c a l l y in i n Figure F i g u r e 9. 9. The large l a r g e increases i n c r e a s e s in i n C and Ca shown in i n Figure F i g u r e 9a 9a and 9b 9b correspond to t o increasing increasing abundances of of dolomite. dolomite. Losses in i n hydrogen throughout throughout the t h e zone zone (Fig. (Fig. 9) 9) correscorrespond to with pond t o the t h e loss l o s s of of serpentine, s e r p e n t i n e , and are a r e consistent consistent w i t h the t h e partial p a r t i a l dehydration dehydration n a t u r e of of the t h e reaction r e a c t i o n given given on on an an earlier e a r l i e r page. page. Major gains g a i n s in i n Al A 1 (Figure ( F i g u r e 9c) 9c) nature correspond with contact. correspond w i t h the t h e increasing i n c r e a s i n g abundance of of chlorite c h l o r i t e near n e a r the t h e OHR contact. All A l l of of the t h e altered a l t e r e d serpentinite s e r p e n t i n i t e samples listed l i s t e d in i n Table 33 and shown shown graphically g r a p h i c a l l y in in Ass n noted F i g u r e 9d 9d show show significant s i g n i f i c a n t losses l o s s e s of of Mg. Mg. A o t e d before, b e f o r e , many of of the t h e analyses analyses Figure of host Mg, suggesting of ore ore h o s t rock show apparent a p p a r e n t increases i n c r e a s e s in i n Mg, s u g g e s t i n g that t h a t Mg, Mg, and and possibly possibly Fe, have migrated from the Fe, t h e talc—carbonate t a l c - c a r b o n a t e zones into i n t o the t h e ore o r e host h o s t rock. rock. In of rrelatively uncarbonatized sserpentinite from tthe Deer Lake Lake PPen— eriI n five f i v e samples of e l a t i v e l y uncarbonatized e r p e n t i n i t e from h e Deer dotite, i s certainly certainly d o t i t e , gold has h a s an average a v e r a g e abundance of of 2.8 2.8 ppb (range (range 1—4 1-4 ppb) which is However, these values not n o t greater g r e a t e r than t h a n abundances in i n other o t h e r types t y p e s of of igneous igneous rocks. r o c k s . However, these v alues not may n o t represent r e p r e s e n t the t h e initial i n i t i a l gold content c o n t e n t of of the t h e peridotite p e r i d o t i t e if i f substantial s u b s t a n t i a l gold gold were removed during d u r i n g serpentinization. s e r p e n t i n i z a t i o n . Gold values v a l u e s in i n carbonatized c a r b o n a t i z e d serpentinite serpentinite samples showed greater variation, with an average abundance of 3.4 3.4 ppb and a range samples showed g r e a t e r v a r i a t i o n , w i t h of 11 ppb. ppb. As A s shown shown in i n Figure F i g u r e 9e 9 e gold values v a l u e s increase i n c r e a s e significantly significantly from trace t r a c e to t o 11 most intensely iin n tthe h e most i n t e n s e l y altered a l t e r e d rocks r o c k s near n e a r the t h e ore o r e host h o s t rock r o c k contact. c o n t a c t . From the t h e data data available, a v a i l a b l e , it i t appears a p p e a r s that t h a t gold values v a l u e s increase i n c r e a s e with w i t h increasing i n c r e a s i n g alteration a l t e r a t i o n sugsuggesting being is b e i n g added, added, not n o t removed, removed, during d u r i n g talc—carbonate t a l c - c a r b o n a t e alteration alteration g e s t i n g that t h a t gold is of of the t h e Deer Lake Peridotite. Peridotite. Kerrich may pplay K e r r i c h and Fyfe Fyfe (1981) (1981) have have suggested suggested that t h a t ultramaf u l t r a m a f iic c rrocks o c k s may l a y an important role r o l e in i n localizing l o c a l i z i n g the t h e precipitation p r e c i p i t a t i o n of of gold gold from from hydrothermal hydrothermal solutions. s o l u t i o n s . They They propose that t h a t gold may be b e transported t r a n s p o r t e d as a s carbonyl c a r b o n y l or o r carbonate c a r b o n a t e complexes complexes in i n C02— C02rich r i c h hydrothermal hydrothermal fluids. f l u i d s . Subsequent ccarbonate a r b o n a t e forming reactions r e a c t i o n s involving i n v o l v i n g ultra— ultramafic rocks r o c k s may trigger t r i g g e r gold precipitation p r e c i p i t a t i o n by reducing r e d u c i n g the t h e partial p a r t i a l pressure p r e s s u r e of of C02 CO2 and/or a n d / o r decreasing d e c r e a s i n g acidity a c i d i t y (Kerrich ( K e r r i c h and and Fyfe, Fyfe, 1981). 1981). �65 RNRLYSES OF OFTALC TRLCCARBONATE CRRBONRTEROCKS ROCKS ANALYSES 1 1 S102 5102 RL203 AL203 FEO FEO MGO MGO CRO CO NR20 NA20 KZO K20 H20+ H20+ TI02 T102 P205 P205 C02 C02 46.21 46.21 1.65 1.65 7 .06 7.06 26.55 26.55 TOTRL TOTAL 98.45 98.45 CR MN NI Cu ZN 3 26.83 5.62 5.28 47.86 2.01 4.20 20 .55 4.59 4.78 22.78 7.25 14 5 6 7 8 9 10 42 .04 39.77 2.06 5.55 45.56 1.03 5.38 39.30 1.17 46 .12 52 .74 1.13 1.29 7.114 5.39 28 .39 4 .81 .05 .01 29 .01 5 .09 .04 .01 1.00 14.30 3.80 5.10 5.00 .05 .09 .0? .05 27 .63 8 .29 .05 .01 1.40 .04 .06 30 .63 .04 .01 25 .13 10 .67 .03 .01 .04 .06 .03 .05 .03 .05 .01 1.94 4.51 23.39 .05 .01 .06 .01 1.40 2.50 .14 .05 .13 .08 24 .01 11 .80 .03 .01 .80 .04 .07 3.96 18.11 8.68 11.35 13.147 9.79 13.47 8.25 4.11 99.33 99.19 99.51 99.27 101 .11 99.22 98.23 100 .22 100.41 8 14 14 1? 19 17 114 11 12 9 50 1558 56 1443 1829 1844 38 89 37 22 1029 1473 1899 20 36 30 37 66 1805 1799 21 1603 27 1255 1704 1736 59 1305 1358 2264 2303 1478 951 2466 2040 606 2816 19 30 25 42 28 146 1846 2494 28 56 35 54 29 80 6 2 2 1 11.98 .98 .04 .04 .o 1 .01 2.50 2.50 .07 .0? .02 .02 1 2.36 .36 12 ------------------- SC V 2 54 .32 1430 2901 2? 53 AU 19.02 9275 3723 1079 21 65 10 T a b l e 4. 4. Table 114 .85 < S e l e c t e d analyses a n a l y s e s of of talc—carbonate t a l c - c a r b o n a t e rocks r o c k s from from the t h e North North Selected a l t e r a t i o n zone. Samples a r e a r r a n g e d a c c o r d i n g t o i n c r e a s i n g disalteration zone. Samples are arranged according to increasing disO r e Host Host Rock Rock contact. c o n t a c t . Elements l i s t e d as o x i d e s i n t a n c e from from the t h e Ore tance Elements listed as oxides in wt. percent, p e r c e n t , other o t h e rin. i n ppm. ppm. wt. 1.1 .04 .01 �66 . Sample Sample1/9 10 10 9 9 88 7 7 66 55 4 4 33 2 2 1 1 +34.7, +34.7 +17.2 +17.2 Si Sl +23.9 +23.9 +10.5 +10.5 —1.9 -1.9 +16.8 +16.8 —3.4 -3.4 +11.3 +11.3 +21.6 +21.6 —30.0 -30.0 Al +28.8 +16.4 +25.0 +12.5 +111.5 +118.3 +118.3 +526.0 +386.5 +78.8 Fe* Fe* —37.0 -37.0 —43.8 -43.8 —22.4 -22.4 —39.9 -39.9 —41.4 -41.4 —48.1 -48.1 —53.4 -53.4 —40.1 -40.1 —48.4 -48.4 —22.0 -22.0 Mg —16.0 —18.9 —17.2 —17.3 —28.7 —27.7 —28.7 —37.4 —34.0 —21.4 Ca —4.9 +246.5 +241.6 +503.5 +636.6 +1017.6 +752.1 +311.3 +411.3 +43.0 H —20.1 —16.9 —35.5 —75.6 —29.0 —82.0 —86.2 —55..6 —76.4 —56.9 Ti +21.2 —9.1 +21.2 —9.1 +51.5 —27.3 0.0 +184.8 +203.0 +48.5 P —9.1 +81.8 +81.8 +172.7 +263.6 +609.1 +354.6 +545.4 +236.4 +45.4 C +89.3 +288.2 +585.5 +392.0 +542.0 +489.7 +332.8 +827.9 +92.8 +554.2 Mn —44.4 —16.7 +75.9 +75.9 +29.6 +71.3 +38.9 +275.0 +73.7 +38.0 Ni +27.4 +7.8 +17.6 +7.8 +2.9 —11.8 —6.9 —47.6 —.13.2 +39.2 Estimated mineral mineral modes modes Serp Serp 40% 40% 35% 35% 37% 37% —— -- 30% 30% -- --- -- -- -- Talc Talc 40% 40% 40% 40% 30% 30% 55% 55% 35% 35% 43% 43% 50% 50% 30% 30% 40% 40% 35% 35 % .Carb Carb 15% 15% 20% 20% 30% 30% 40% 40% 30% 50% 50% 40% 40% 60% 60Z 45% 45% 55% 55% Chl --- --- tr tr 1% 1% 3% 3% 6% 6% 9% 9% 7% 7% 8% 8% 2% 2% 5% 5% 5% 5% 4% 2% 2% 1% 3% 3% 3% 5% 5% Clii Opaques Opaque~ Qtz 3% 3% Table 5. 5. Calculated C a l c u l a t e d percent p e r c e n t losses l o s s e s and and gains g a i n s of of various v a r i o u s elements elements Table during 4. Cald u r i n g talc—carbonate t a l c - c a r b o n a t e alteration a l t e r a t i o n for f o r samples samples from frbm Table Table 4. culations c u l a t i o n s made assuming assuming volume remained remained constant c o n s t a n t during d u r i n g alteraalteration t i o n and the t h e initial i n i t i a l composition for f o r all a l l of of the t h e samples was that that sample 3, 3 , Table Table 3. 3 . Samples Samples arranged a r r a n g e d according a c c o r d i n g to t o decreasing decreasing of sample distance d i s t a n c e from from the t h e OHR OHR contact. contact. �67 25 25 20 20 a a z I. aa 15 In 9 I0 *0 U 0r 5 1 10 20 30 40 0 ¶0 0 So 40 DISTANCE IN DISTANCE IN FEET FEET 50 DISTANCE IN IN FEET DISTANCE FEET VARIASION IN IN C WITH WITH DISTANCE DISTANCE FROM THE ORE ORE HOST HOST ROCK ROCK CONIfrCT CONTACT VARIASION VARIATION IN IN CA VARIATION CA WITh WITH DISTANCE HOST ROCK ROCKCONTACT CONTACT DISTANCE FROM FROM ORE HOST 7 U UI U S UI 40 a 2 z In a a C 35 N 0 a 3 0 a z 2 , 10 20 30 40 20 So 1 DISTANCE FEET DISTANCE IN IN FEET VARIATIONOF OF Al. Al. WITH FROM ORE ORE HOST HOST ROCK VARIATION WITH DISTANCE DISTANCE FHOM ROCK CONIACI CONIACT , t 10 20 30 40 1 50 DISTANCE OISTANCE IN IN FEET FEET VARIATIONIN IN MG FROM THE VARIATION MG WIJH W11H DISTANCE DISTANCE FROM THE ORE ORE HOST HOST ROCK ROCK CONTACT CONTACT 12 40 9 a 2 U, 30 a 0 6 N I 2 l0 30 DISTANCE IN IN FEET FEET VARIATION VARIATIONIN IN AD AU WITH WITH DISTANCE DISTANCEFROM FROMTHE THEORE OREHOST HOSTROCK ROCKCONTACT CONTCr t 0 0 TO 10 20 30 40 50 50 DISTMCE FEET FROU FROMCONTACT CONTACT DISTANCE IN IN FEET VARIATION WITH DIS DISiANCE FROM ORE ORE HOST HOST ROCK ROCK CONTACT CONTACT VARIATIONOF OF H H WITH lANCE FROM Plots P l o t s showing changes in i n composition of of altered a l t e r e d ser— serFigure F i g u r e 9. 9. pentinites from Table 3 with distance from the ore host rock conconp e n t i n i t e s from Table 3 w i t h d i s t a n c e from t h e o r e h o s t rock tact t a c t (left ( l e f t axis). a x i s ) . Right Right axis a x i s represents r e p r e s e n t s composition composition of of the t h e asassumed parent p a r e n t rock rock (sample (sample 3, 3 , Table Table 3). 3)- I �68 d i s t r i b u t i o n of of talc—carbonate The wide distribution tal-c-carbonate rock rock in i n the t h e vicinity v i c i n i t y of of the t h e Ropes Ropes Mine Mine r e q u i r e d the t h e addition a d d i t i o n of of C02 C02 from from aa very very large l a r g e volume volume of of C02—rich C02-rich fluids f l u i d s to t o the the required a r e a . The The presence p r e s e n c e oof f sseveral e v e r a l ggenerations e n e r a t i o n s of r o s s - c u t t i n g ccarbonate arbonate v e i n s in in of ccross—cutting veins area. t h e talc—carbonate t a l c - c a r b o n a t e rock rock and and the t h e nearby nearby serpentine s e r p e n t i n e suggest s u g g e s t that t h a t this t h i s introduction introduction the of correlation of CO2 CO2 probably probably occurred o c c u r r e d over over aa protracted p r o t r a c t e d period p e r i o d of of time. time. The The c o r r e l a t i o n t h e distribution d i s t r i b u t i o n of of the t h e OHR OHR and and talc—carbonate t a l c - c a r b o n a t e rock rock suggest suggest that t h a t the t h e OHR OHR between the s e r v e d as a s aa channel—way channel-way to t o supply supply C02—rich C02-rich fluids f l u i d s to t o the t h e serpentinite. serpentinite. may have served i t may be be that t h a t the t h e disruption d i s r u p t i o n of of the t h e serpentinite, s e r p e n t i n i t e , by by the t h e emplaceemplaceConversely, it Conversely, of the t h e OHR, OHR, created c r e a t e d the t h e necessary n e c e s s a r y permeability p e r m e a b i l i t y to t o facilitate f a c i l i t a t e the t h e talc— talcment of c a r b o n a t e alteration. alteration. carbonate Evidence Evidence for f o r Shearing Shearing in i n the t h e Deer Deer Lake Lake Peridotite Peridotite If i s an alpine—type, a l p i n e - t y p e , tectonically t e c t o n i c a l l y intruded i n t r u d e d mass, mass, there there I f the t h e Deer Lake Peridotite P e r i d o t i t e is b e evidence evidence for f o r considerable c o n s i d e r a b l e deformation deformation within w i t h i n and and around around the t h e body. body. This This should be i s reviewed in i n the t h e paragraphs p a r a g r a p h s that t h a t follow. follow. is The The Deer Lake Lake Peridotite P e r i d o t i t e has h a s undergone undergone considerable c o n s i d e r a b l e shearing s h e a r i n g in i n the t h e vicinity v i c i n i t y of of c l e a r e s t evidence evidence is i s exposed exposed along along the t h e ore o r e host h o s t rock rock and and probably probably elsewhere. elsewhere. The clearest the OHR intercepts i n t e r c e p t s the t h e outcropping outcropping t h e shore s h o r e of of Deer Lake where the t h e surface s u r f a c e trend t r e n d of of the t h e OHR serpentinites. ORH trend, t r e n d , in i n aa zone zone some some 200 200 feet f e e t wide, wide, the t h e serpentinites serpentinites s e r p e n t i n i t e s . Along Along the t h e ORH B y locally l o c a l l y with w i t h aa strong s t r o n g foliation. f o l i a t i o n . As A s noted noted earlier, e a r l i e r , such such recrystalrecrystala r e Type Type B, exposed are lized s e r p e n t i n i t e textures t e x t u r e s can can be b e correlated c o r r e l a t e d with w i t h shearing s h e a r i n g (Wicks (Wicks and and Whittaker, Whittaker, l i z e d serpentinite A t Deer Deer Lake Lake the t h e Type Type BB serpentinite s e r p e n t i n i t e has h a s been been dolomitized, d o l o m i t i z e d , altering a l t e r i n g the t h e color color 1977). At 1977). from from medium medium green green to t o aa yellowish y e l l o w i s h white w h i t e . Such dolomitization d o l o m i t i z a t i o n also a l s o suggests s u g g e s t s that t h a t the the zone had had enhanced enhanced permeability. p e r m e a b i l i t y . The The serpentinite s e r p e n t i n i t e outcrops o u t c r o p s to t o the t h e north n o r t h and and south south zone of of the t h e shear s h e a r zone zone are a r e prodominantly prodominantly Type Type A A serpentinite, s e r p e n t i n i t e , with w i t h abundant, abundant, closely closely spaced fractures, f r a c t u r e s , as a s well w e l l as a s aa number number of of picrolite p i c r o l i t e and and cross c r o s s fiber f i b e r serpentine s e r p e n t i n e veins, veins, f e a t u r e s also a l s o suggest s u g g e s t deformation deformation for for p a r t i a l l y replaced r e p l a c e d by by carbonate. c a r b o n a t e . These features now partially t h e production p r o d u c t i o n of of the t h e openings openings (Jahns, (Jahns, 1967). 1967). the To the t h e immediate immediate south s o u t h of of the t h e shear s h e a r zone, zone, outcrops o u t c r o p s show show elongate e l o n g a t e pods, pods, resembling resembling pillows, s e r p e n t i n i t e , ranging r a n g i n g in i n size s i z e from from several several of relatively r e l a t i v e l y unveined Type A serpentinite, p i l l o w s , of inches i n c h e s nnear e a r the t h e shear s h e a r zone contact, c o n t a c t , to t o several s e v e r a l feet f e e t further f u r t h e r away from the t h e contact. contact. The pattern i s formed formed by prominent, prominent, anastomosing, anastomosing, 22 to t o 55 cm cm wide ribbons r i b b o n s of of closely closely p a t t e r n is spaced sets of 1 to 2 mm, subparallel veins of cross—fiber serpentine outlining mm, s u b p a r a l l e l v e i n s of c r o s s - f i b e r s e r p e n t i n e o u t l i n i n g the the s e t s of 1 t o Morgan and (1980) notea n o t e a resemblance resemblance in i n shape shape between these these and DeCristoforo (1980) pods. structures pillows s t r u c t u r e s and lava lava p i l l o w s and suggest s u g g e s t that t h a t they t h e y may be evidence for f o r an extrusive extrusive However, they differ from pillows origin o r i g i n for f o r the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . However, they d i f f e r from p i l l o w s in i n their their lack l a c k of of asymetrical a s y m e t r i c a l top t o p indicators: i n d i c a t o r s : rounded rounded tops t o p s and and cuspate c u s p a t e bases. b a s e s . By contrast, contrast, the noted t h e authors a u t h o r s have n o t e d similarities s i m i l a r i t i e s between these t h e s e structures s t r u c t u r e s and shear s h e a r polyhedra described d e s c r i b e d by Jahns Jahns (1967) (1967) in i n alpine a l p i n e type t y p e ultramafics u l t r a m a f i c s in i n Vermont Vermont (Figure ( F i g u r e 10). 10). Jahns J a h n s describes d e s c r i b e s shear s h e a r polyhedra as a s pillow—like p i l l o w - l i k e masses of of less l e s s broken broken or o r sheared sheared serpentinite s e r p e n t i n i t e in i n aa matrix m a t r i x of of highly h i g h l y sheared sheared serpeninite. s e r p e n i n i t e . Shear polyhedra form form along the margins of intensely sheared serpentinite along the of i n t e n s e l y sheared s e r p e n t i n i t e and and progressively p r o g r e s s i v e l y increase i n c r e a s e in in size s i z e away from from the t h e shear s h e a r zone zone (Jahns, (Jahns, 1967). 1967). However, However, the t h e shear s h e a r polyhedra polyhedra described described by Jahns J a h n s do do not n o t contain c o n t a i n the t h e cross c r o s s fiber f i b e r serpentine s e r p e n t i n e veins v e i n s that t h a t are a r e prominent prominent at a t Deer Deer Lake. Evidence for f o r shearing s h e a r i n g in i n the t h e talc—carbonate t a l c - c a r b o n a t e zones surrounding s u r r o u n d i n g the t h e OHR, OHR, from from underunder1) local development of contorted ground openings openings and and drill d r i l l cores, c o r e s , include: include: 1 ) l o c a l of c o n t o r t e d foliafoliations with t i o n s in i n intensely i n t e n s e l y altered a l t e r e d talc—carbonate t a l c - c a r b o n a t e zones along along w i t h obliteration o b l i t e r a t i o n of of relict relict serpentinite s e r p e n t i n i t e features; f e a t u r e s ; 2) 2) intense i n t e n s e boundinaging of of chlorite c h l o r i t e schist s c h i s t layers, l a y e r s , thought thought to t o represent r e p r e s e n t mafic dikes, d i k e s , in i n the t h e talc—carbonate t a l c - c a r b o n a t e zone; zone; 3) 3) abundance of of fracture fracture filling both f i l l i n g carbonate c a r b o n a t e in in b o t h the t h e talc—carbonate t a l c - c a r b o n a t e zones zones and the t h e serpentinites; s e r p e n t i n i t e s ; and 4) 4) boudinage of quartz veins. boudinage of q u a r t z v e i n s . �69 Country rocks Marginal zone of intensely sheared ser~entinite Intermediate zone of shear polyhedrons Core of irregularly broken and sheared serpentinite diagram Idealized d i a g r a m showing shear s h e a r zones z o n e s around a Figure F i g u r e 10. 10. Idealized serpentinite s e r p e n t i n i t e body, body, Roxbury Dist., D i s t . , Vermont Vermont (Jahns, ( J a h n s , 1967). 1967). �70 There is i s much evidence e v i d e n c e for f o r deformation within w i t h i n the t h e Deer Lake Peridotite, P e r i d o t i t e , as a s one i s an a p p a r e n t lack lack would expect expect for f o r an a n alpine—type a l p i n e - t y p e intrusion. intrusion. S i m i l a r l y , t h e r e Similarly, there is apparent of of contact c o n t a c t metamorphic effects e f f e c t s by the t h e Deer Lake Peridotite P e r i d o t i t e on the t h e ore o r e host h o s t rock rock and tthe Kitchi he K i t c h i Schist S c h i s t as a s one one would expect e x p e c t from from an a n intruded i n t r u d e d hot h o t body. body. F inally, Finally, tthe h e OHR in i n the t h e Deer Deer Lake Lake Peridotite P e r i d o t i t e shows, shows aa close c l o s e analogy a n a l o g yto t o tthe h e septum of of country country rock in rock i n the t h e alpine—type a l p i n e - t y p e ultramafic u l t r a m a f i c body body in i n Ludlow Ludlow Township, Township, Vermont Vermont (Gregg, (Gregg, 1975). 1975). Thus, writers Thus, for f o r these t h e s e reaons r e a o n s the the w r i t e r s favor f a v o r the t h e alpine—type a l p i n e - t y p e peridotite p e r i d o t i t e model. model. Conclusions Conclusions 1. 1. The ore o r e host host intermediate intermediate 2. 2. The available a v a i l a b l e information i n f o r m a t i o n suggests s u g g e s t s that t h a t the t h e Deer Lake Peridotite, P e r i d o t i t e , surrounding surrounding rock, was was o originally pluton, it tthe h e oore r e hhost o s t rock, r i g i n a l l y aa hharzburgite—lherzolite arzburgite-lherzolite p l u t o n , and that t h a t it was probably tectonically t e c t o n i c a l l y emplaced into i n t o the t h e Kitchi K i t c h i Schists S c h i s t s as a s aa solid. solid. 33.. The juxtaposition j u x t a p o s i t i o n of of the t h e Deer Lake Peridotite P e r i d o t i t e and the t h e ore o r e host h o s t rock rock is i s at at part lleast e a s t in in p a r t the t h e result r e s u l t of of tectonism. t e c t o n i s m . This T h i s tectonism t e c t o n i s m may or o r may not n o t have occurred o c c u r r e d concurrently c o n c u r r e n t l y with w i t h the t h e tectonic t e c t o n i c emplacement of of the t h e Deer Lake Peridotite. Peridotite. 4. The substantial s u b s t a n t i a l talc—carbonate t a l c - c a r b o n a t e alteration a l t e r a t i o n of of serpentinite s e r p e n t i n i t e and and portions p o r t i o n s of of the the OHR required r e q u i r e d the t h e introduction i n t r o d u c t i o n of of large l a r g e quantities q u a n t i t i e s of of CO2 CO2 into i n t o these t h e s e rocks. rocks. 5. The extent e x t e n t of of bution b u t i o n of of the the 6. The gold gold content c o n t e n t of of the t h e serpentinites s e r p e n t i n i t e s of of the t h e Deer Lake Peridotite P e r i d o t i t e (1—4 (1-4 ppb) ppb) is higher i s nnot ot h i g h e r than t h a n typical t y p i c a l crustal c r u s t a l material. material. 7 points l i t t l e or o r no loss l o s s of of gold from from The eexisting x i s t i n g eevidence vidence p o i n t s to t o there t h e r e bbeing e i n g little serpentinites s e r p e n t i n i t e s during d u r i n g talc—carbonate t a l c - c a r b o n a t e alteration alteration. 8. of gold mineralization body: aa h higher Two ttypes y p e s of gold m i n e r a l i z a t i o n aare r e found in i n the t h e Ropes ore o r e body: igher grade v vein mineralization mineralization. ein m i n e r a l i z a t i o n and aa lower lower grade g r a d e disseminated disseminated m ineralization. 9. possible of o origin mineralization: There aare r e several several p o s s i b l e modes of r i g i n for f o r the t h e gold m ineralization: 1. A) 1. 2. 2. B) 1. B) 1. 2. 2. rock r o c k at a t the t h e Ropes Gold Mine probably consists c o n s i s t s primarily p r i m a r i l y of of to felsic volcanic rock t o f e l s i c volcanic rock. talc—carbonate i s , in i n part, p a r t , controlled c o n t r o l l e d by the t h e distridistrit a l c - c a r b o n a t e alteration a l t e r a t i o n is, OHR. OHR. disseminated The d i s s e m i n a t e d gold g o l d ore o r e may represent r e p r e s e n t an a n early e a r l y syngenetic syngenetic deposition, with OHR, prior prior d e p o s i t i o n , aassociated ssociated w i t h the t h e formation f o r m a t i o n of of the t h e OHR, to t o its i t s emplacement within w i t h i n the t h e Deer Deer Lake Lake Peridotite. Peridotite. high—grade vein The high-grade v e i n ore o r e may represent r e p r e s e n t aa remobilized r e m o b i l i z e d facies, facies, derived disseminated ore, d e r i v e d from the t h e early early d isseminated o r e , and deposited d e p o s i t e d in in sites prepared s i t e s that t h a t were structurally structurally p r e p a r e d during d u r i n g emplacement of of the OHR. t h e OHR. high—grade v vein—type ore be with mineralizing The high-grade ein-type o r e may b e epigenetic, epigenetic, w ith m ineralizing fluids a n outside o u t s i d e source, s o u r c e , and the the f l u i d s introduced i n t r o d u c e d into i n t o the t h e OHR from an gold deposited d e p o s i t e d in i n structures s t r u c t u r e s formed during d u r i n g emplacement of of the t h e OHR i n t o the t h e Deer Lake Lake Peridotite. Peridotite. into The disseminated d i s s e m i n a t e d ore o r e represents r e p r e s e n t s aa halo h a l o around around the t h ehigh, h i g h grade grade v e i n s introduced i n t r o d u c e d from from the t h e same same outside o u t s i d e source. source. veins . �71 C) C) The The disseminated disseminated and and vein—type vein-type ores o r e s were were formed formed independently independently of of each each other. other. D) D) Gold complex inaCO2—rich Gold was was transported t r a n s p o r t e d as a s aa carbonyl c a r b o n y l or o r carbonate c a r b o n a t e complex inaC02-rich fluid OHR. Subsequent Subsequent f l u i d from from some some outside o u t s i d e source, s o u r c e , and and introduced i n t r o d u c e d into i n t o the t h e OHR. carbonate—forming carbonate-forming reactions r e a c t i o n s in i n the t h e ultramafic u l t r a m a f i c rock r o c k surrounding s u r r o u n d i n g the t h e OHR OHR caused caused the t h e deposition d e p o s i t i o n of of gold gold in i n structures s t r u c t u r e s formed formed in i n the t h e OHR OHR during d u r i n g its its emplacement emplacement into i n t o the t h e peridotite. peridotite. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS CallahanMining Mining Corporation Corporation for f o r making making available available The authors a u t h o r s would would like l i k e to t othank thankCallahan The some of of the t h e maps, maps, cross—sections, c r o s s - s e c t i o n s , and and rreports e p o r t s used used in i n the t h e preparation p r e p a r a t i o n of of this t h i s paper. paper. some They They would like l i k e to t o thank thank also a l s o Resource Resource Exploration, E x p l o r a t i o n , Inc., I n c . , in i n particular p a r t i c u l a r Grant Grant Tonkin Tonkin and Joe J o e Strapko, S t r a p k o , for f o r their t h e i r invaluable i n v a l u a b l e help. help. and This T h i s papers p a p e r s incorporates i n c o r p o r a t e s portions p o r t i o n s of of aa thesis t h e s i s in i n preparation by by Dean Dean Rossell, R o s s e l l , funded funded in by aa DMMMFC DMMMFC Fellowship Fellowship from fromHEW. HEW. i n part p a r t by the t h e Callahan Callahan Mining Mining Corporation Corporation and and by Thus D r s . T. T. Bornhorst Bornhorst and and William William Rose Rose for for Thus the t h e senior s e n i o r author a u t h o r would would like l i k e to t o thank thank Drs. help D r . W. W. Gregg Gregg for f o r assistance a s s i s t a n c e with w i t h photomicrographs. photomicrographs. Both Both h e l p along a l o n g the t h e way, way, and and Dr. of of us u s appreciate a p p r e c i a t e the t h e efforts e f f o r t s of of Karen Karen Rossell R o s s e l l and and Julene J u l e n e Erickson Erickson in i n getting g e t t i n g this this manuscript manuscript ready ready by by aa deadline. deadline. �72 REFERENCES REFERENCES Anhaeusser, C. W. S., Anhaeusser, C . R., R . , Fritze, F r i t z e , K., K . , Fyfe, F y f e , W. S., and Gill, Gill, Chemical mitive" Archean volcanics: mitive" volcanics: Chemical Geology, Geology, v. v. R. 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I., I., 1972, 1972, Distribution D i s t r i b u t i o n of of gold g o l d in in igneous i g n e o u s rocks: r o c k s : U.S. U.S. Geol. Geol. Survey Survey Prof. P r o f . Paper P a p e r 727, 727, 42 42 p. p. �73 Gregg, Gregg, W. W. J., J . , 1975, 1975, Structural S t r u c t u r a l studies s t u d i e s in i n the t h e Moretown and and Cram Hill H i l l units units near n e a r Ludlow, Ludlow, Vermont: Vermont: Unpublished Unpublished M.S. M.S. thesis, t h e s i s , State S t a t e Univ. Univ. New New York, York, Albany, p. Albany, 77 77 p. in Jahns, J a h n s , R. R. H., H . , 1967, 1967, Serpentinites S e r p e n t i n i t e s of of the t h e Roxbury Roxbury District, D i s t r i c t , Vermont, Vermont, in Wyllie, Wyllie, P. P . J., J . , ed., e d . , Ultramafic U l t r a m a f i c and and Related R e l a t e d Rocks: Rocks: Wiley Wiley and and Sons, Sons, Inc., I n c . , New New York, York, p. 137—160. 137-160. p. 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F., F., 1977, 1977, The The YelYellow Dog P Peridotite buried e r i d o t i t e and a possible possible b u r i e d igneous i g n e o u s complex of of Lower Kewee— Keweenawan nawan age a g e in i n the t h e Northern N o r t h e r n Peninsula P e n i n s u l a of o f Michigan: Michigan: U.S. U.S. Geol. Geol. Survey, Survey, O p e n - f i l e Report Report 77—93, 77-93, 65 65 p. p. Open—file Lewan, M. D., D . , 1972, 1972, Metasomatism Metasomatism and and weathering w e a t h e r i n g of o f the t h e Presque P r e s q u e Isle I s l e serpentin— serpentinLewan, M. Michigan Tech. Tech. Univ., Univ., Houghton, Houghton, ized i z e d peridotite, p e r i d o t i t e , Marquette, M a r q u e t t e , Michigan: Michigan: Michigan unpubl. unpubl. M.S. M.S. thesis, t h e s i s , 55 5 5 p. p. Moody, J. J. B., B . , 1976, 1976, Serpentinization: S e r p e n t i n i z a t i o n : aa review: review: Lithos, L i t h o s , v. v . 9, 9 , p. p. 125—138. 125-138. Morgan, Morgan, P.J., P . J . , and and DeCristoforo, D e C r i s t o f o r o , D. D. T., T., 1980, 1980, Geologic G e o l o g i c evolution e v o l u t i o n of of the t h e Ish— Ishpeming 11, p. p . 23—41. 23-41. peming Greenstone Greenstone Belt: B e l t : Precambrian Precambrian Research, R e s e a r c h , v. v. 11, Morris, M o r r i s , W. W. J., J . , and and Wilband, Wilband, J. J. T., T., 1977, 1977, Geochemistry Geochemistry of of the t h e Yellow Yellow Dog Dog plains plains 23 Inst. peridotite, p e r i d o t i t e , Marquette M a r q u e t t e County, County, Michigan Michigan (abst.): (abst.): I n s t . Lake Superior Superior Geology, Geology, Proceedings, P r o c e e d i n g s , Thunder Thunder Bay, Bay, Ontario, O n t a r i o , p. p. 35. 35. Naldrett, J . , 1966, 1956, Talc—carbonate T a l c - c a r b o n a t e alteration a l t e r a t i o n of o f some some serpentinized s e r p e n t i n i z e d ultra— ultraN a l d r e t t , A. A. 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M., M., 1983, 1983, Alteration A l t e r a t i o n of of the t h e Deer Lake Peridotite P e r i d o t i t e in i n the t h e vicinity vicinity of the t h e Ropes Ropes Gold Gold Mine, Mine, Marquette M a r q u e t t e County, County, Michigan: Michigan: M.S. M.S. thesis t h e s i s in in preparation, p r e p a r a t i o n , Michigan Michigan Tech. Tech. Univ. Univ. Sager, R., Meyer, Meyer, M., M., and Muff, Muff, R., R., 1982, 1982, Gold distribution d i s t r i b u t i o n in i n supracrustal supracrustal S a g e r , R., rocks Africa r o c k s from Archean greenstone g r e e n s t o n e bbelts e l t s of o f Southern Southern A f r i c a and from from Paleozoic Paleozoic ultramafic Alps: M Metallogenic u l t r a m a f i c complexes complexes of of the t h e European Alps: e t a l l o g e n i c and geochemical implications: i m p l i c a t i o n s : Econ. Econ. Geol., Geol., v. v. 77, 77, p. p. 1—24. 1-24. Sims, mineral Sims, P. P. K., K . , 1976, 1976, Precambrian tectonics t e c t o n i c s and m i n e r a l deposits, d e p o s i t s , Lake Superior Superior region: r e g i o n : Econ. Econ. Geol., Geol., v. v. 71, 71, p. p. 1092—1127. 1092-1127. Skillings S k i l l i n g s Mining Review, Review, 1981, 1981, Callahan C a l l a h a n nearing n e a r i n g decision d e c i s i o n on on major m a j o r project p r o j e c t for for Ropes 16. Ropes Mine: Mine: v. v. 70, 70, no. no. 39, 39, p. p. 16. Van Hise, H i s e , C. C. R., R., and Leith, L e i t h , C. C. K., K., 1911, The geology geology of o f the t h e Lake Superior S u p e r i o r region: region: U.S. U.S. Geol. Geol. Survey Survey Monograph Monograph 52, 5 2 , 641 6 4 1 p. p. - Wicks, F. F. J., J . , and Whittaker, W h i t t a k e r , E. E. J., J., 1977, 1977, Serpentine S e r p e n t i n e textures t e x t u r e s and and serpentinization: serpentinization: Canadian M Mineral., i n e r a l . , v. v. 15, 1 5 , p. p. 459—488. 459-488. �75 FIELD TRIP LOG ROPES GOLD MINE AND THE MICHIGAN GOLD MINE J. Kalliokoski Dean Rossell and J. �76 Log, Ropes Gold Gold Mine and and the t h e Michigan Gold Gold Mine Mine Road Log, Dean Rossell R o s s e l l and and J. J . Kalliokoski Kalliokoski Dean i s designed designed as a s aa one—day one-day excursion e x c u r s i o n to t o examine examine the t h e geological g e o l o g i c a l setting setting T h i s field f i e l d trip t r i p is This of the t h e Ropes Ropes and and Michigan Michigan gold gold mines. mines. The The trip t r i p involves i n v o l v e s five f i v e stops s t o p s (Fig. (Fig. 1), I ) , most most of on access.1 on private p r i v a t e property. p r o p e r t y . Please P l e a s e use u s e discretion d i s c r e t i o n in i n gaining g a i n i n g access.1 Proceed east e a s t from from Houghton to t o the t h e junction j u n c t i o n with w i t h County County Road Road 573 573 (traffic ( t r a f f i c light, light, Ishpeming). Turn left Ishpeming). l e f t and and continue c o n t i n u e around around Deer Deer Lake Lake for f o r 3.6 3.6 miles m i l e s (0.7 (0.7 miles m i l e s past past t h e Carp Carp Lake Lake intersection) i n t e r s e c t i o n ) to t o aa gravel g r a v e l side s i d e road road on on the t h e left. l e f t . Turn left, l e f t , continue continue the 650 650 feet. f e e t . Proceed on on foot f o o t 100 100 feet f e e t north n o r t h of of road road to t o aa pit p i t at a t base b a s e of of the t h e hill. hill. Stop 11—- Discovery Discovery Pit P i t (Fig. (Fig. ib) lb) Stop At A t this t h i s pit p i t Julius J u l i u s Ropes made made the t h e initial i n i t i a l discovery d i s c o v e r y of of the t h e Ropes Ropes Gold Gold Mine. Mine. Analyses of three t h r e e samples samples between the t h e pit p i t and and the t h e peridotite p e r i d o t i t e contact, c o n t a c t , uphill uphill the p i t suggest s u g g e s t the t h e ore o r e host h o s t rock to t o be b e an intermediate i n t e r m e d i a t e volcanic v o l c a n i c (Fig. (Fig. 2). 2). from the pit The contact i s exposed exposed c o n t a c t with w i t h the t h e strongly s t r o n g l y carbonatized c a r b o n a t i z e d Deer Deer Lake Lake Peridotite P e r i d o t i t e (DPL) (DPL) is a l o n g the t h e north n o r t h edge edge of of the t h e outcrop. o u t c r o p . This T h i s locality l o c a l i t y marks marks the t h e known known eastern e a s t e r n extent extent along of of the t h e ore o r e host h o s t rock rock septum, septum, the t h e host h o s t to t o gold gold mineralization. mineralization. In i n the t h e pit p i t is i s a quartz—chlorite—sericite q u a r t z - c h l o r i t e - s e r i c i t e schist s c h i s t with w i t h abunabunI n thin t h i n section s e c t i o n the t h e OHR in dant nun grains g r a i n s of of quartz. q u a r t z . To To the t h e north, n o r t h , six s i x feet f e e t south s o u t h of of the t h e contact contact d a n t 0.1 0 . 1 to t o 0.3 0 . 3 mm with w i t h the t h e talc—carbonate—altered t a l c - c a r b o n a t e - a l t e r e d peridotite, p e r i d o t i t e , the t h e rock r o c k displays d i s p l a y s in i n thin t h i n section s e c t i o n aa micro—breccia of darker quartzmicro-breccia texture t e x t u r e consisting c o n s i s t i n g oof f ssharply h a r p l y aangular n g u l a r fragments of d a r k e r quartz— nun quartz q u a r t z grains. g r a i n s . At A t the t h e talc—carbonate talc-carbonate s e r i c i t e matrix. m a t r i x . There There are a r e also a l s o aa few few 11mm sericite contact i s highly h i g h l y fractured, f r a c t u r e d , and sporadically s p o r a d i c a l l y replaced replaced c o n t a c t the t h e quartz—sericite q u a r t z - s e r i c i t e schist s c h i s t is by coarser c o a r s e r grained g r a i n e d sericite s e r i c i t e and and by younger younger veinlets v e i n l e t s of of chlorite c h l o r i t e and and carbonate. carbonate. OutReturn to t o the t h e gravel g r a v e l road road and and proceed proceed 450 450 feet f e e t west west to t o the t h e fork f o r k in i n the t h e road. r o a d . OutThis is also the T h i s i s a l s o t h e crops to the south are relatively uncarbonatized serpentinite. c r o p s t o t h e s o u t h a r e r e l a t i v e l y uncarbonatized s e r p e n t i n i t e . Continue 1200 feet along Continue 1200 f e e t a long approximate projection of the east end of the 15th level. approximate p r o j e c t i o n of t h e e a s t end of t h e 1 5 t h l e v e l . Reddish weathered outcrops along the road are the left fork to the shaft house. t h e l e f t f o r k t o t h e s h a f t house. Reddish weathered o u t c r o p s a l o n g t h e road a r e strongly s t r o n g l y carbonatized c a r b o n a t i z e d DLP DLP from from the t h e southern s o u t h e r n altered a l t e r e d zone. zone. S h a f t House House (Fig. (Fig. lb) lb) Stop 22 —- Shaft Stop The b buildings u i l d i n g s have been constructed c o n s t r u c t e d since s i n c e 1979 1979 as a s part p a r t of of the t h e Callahan Callahan Mining Mining Corp. Corp. frame is over the Curry The head i s t h e Curry shaft, shaft, The head on—going on-going exploration e x p l o r a t i o n at a t the t h e Ropes Ropes Mine. Mine. T h i s stop s t o p provides p r o v i d e s an an opporopporthe t h e principal p r i n c i p a l production p r o d u c t i o n shaft s h a f t from from the t h e late l a t e 1800's. 1800's. This s e c t i o n s. tunity to examine drill core, hand samples, and mine plans and cross sections. and p l a n s and c r o s s t u n i t y t o examine d r i l l c o r e , samples, g r a v e l road road follows follows Proceed on foot f o o t about 1200 1200 feet f e e t west past p a s t the t h e shaft s h a f t house. house. The gravel the contact of the ore host rock and the southern alteration zone of the Deer Lake t h e c o n t a c t of t h e o r e h o s t r o c k t h e s o u t h e r n a l t e r a t i o n zone of t h e Lake The road then turns south Peridotite K i t c h i Schist. S c h i s t . The road t h e n t u r n s s o u t h P e r i d o t i t e out o u t to t o the t h e contact c o n t a c t with w i t h the t h e Kitchi and follows Kitchi ( n o r t h ) and and the t h e DLP DLP (south). (south). i t c h i Schist S c h i s t (north) f o l l o w s the t h e contact c o n t a c t of of tthe he K he 1The Organizing Committee for f o r this t h i s 1983 1983 Field F i e l d Trip T r i p is i s appreciative a p p r e c i a t i v e of of the t h e permission permission given by D Dr. A.. Bouley, r . Bruce A Bouley, Chief Chief Geologist, G e o l o g i s t , Callahan Mining Corporation C o r p o r a t i o n to t o visit visit �______ ____ 77 R28W :} •_ I 27W -i••'--.._ .:::::)crv '"./A1 r. i'7 r< LN L lichigan Mine \I Proterozoic t 1- 0 Feet 4000 (Cannon and Klasner, 1975; Clark and others,1975) ' LA Marquette Range RangeSupergroup Supergroup Archean L T1 - Granite Granite IEIIIJ . pxa I-.> Deer Lake Peridotite Peridotite '5 '5 trip stops Field trip stops Age relations uncertain Age uncertain Kitchi Schist Schist Agglomerate GEOLOGY GEOLOGY OF THE AREAAROUND AREA.AROUND THE ROPES ROPES AND AND MICHIGAN MICHIGAN GOLD GOLD MINES MINES Intermed. to tels. volcs. Amphiboifte Deer Lake; ib, F i g u r e la, l a , Access to t o Deer l b , geology between Deer Lake Figure r,,1 e ?h-crn v i ~ h i oMfrip = nM i n ~ . tit h M �78 5 6 7 S102 s102 AL203 flL2 0 3 FE203 FE203 FEO FEO MG0 t4GO CR0 CRO NR2O NR20 (200 K2 1102 TI02 P205 P205 MNO MNO C02 c02 '48.39 15.07 10.28 .00 18.57 .60 50.05 15.68 8.27 '49.57 17.85 .18 .19 3.01 3.55 1.01 .08 .05 .00 TOTAL 95.24 SC 19 CR 131 171 NI 255 V Cu 10 ZN RB 119 68 SR 19 7.67 .00 .00 114.33 11.67 1.23 .98 .07 .05 .00 .35 .20 '4.54 .77 .17 .03 .00 94.40 92.82 20 124 175 191 < 10 95 79 26 13 94 48 178 < 10 138 114 20 Y 16 18 18 ZR NB 96 101 17 LA 17 15 129 21 12 12 CE 56 53 '42 Figure Figure 2. 2. Chemical analyses of the the ore host rock rock (by (by Bornhorst and and Rose, Rosey 1983). 1983)- Analyses Analyses in in wt. wt. percent. with talc—carbonate talc-carbonate rock; rock; percent. No. 5, 5 y contact contact with b), feet south south of of contact; contact; 7, 7 y discovery discovery pit. pit. b), 66 feet �Verde Antique Antique Quarry Quarry (Fig. ( F i g . ib) lb) Stop 33 —- Verde 79 The Deer Deer Lake Lake Peridotite P e r i d o t i t e is i s altered a l t e r e d extensively e x t e n s i v e l y to t o carbonate c a r b o n a t e and and talc t a l c along a l o n g the t h e Kitchi Kitchi The S c h i s t contact. c o n t a c t . In I n the t h e quarry q u a r r y the t h e serpentinite s e r p e n t i n i t e was was mined mined around around the t h e turn t u r n of of the t h e cencenSchist ttury u r y for f o r dimension dimension stone s t o n e ("verde ("verde antique" a n t i q u e " or o r "serpentine " s e r p e n t i n e marble"). marblet'). The contact c o n t a c t runs runs s l i g h t l y north n o r t h of of the t h e road. road. Thus, Thusy the t h e front f r o n t part p a r t of of the t h e pit p i t (now (now largely l a r g e l y removed) removed) slightly r o c k y but b u t some some remains remains on on the t h e west west side s i d e of of the t h e pit. pit. was primarily p r i m a r i l y talc—carbonate t a l c - c a r b o n a t e rock, was T h i s rock rock grades g r a d e s into i n t o moderately moderately carbonatized c a r b o n a t i z e d serpentinite, s e r p e n t i n i t e y now now exposed exposed along a l o n g the the This s o u t h and east e a s t sides s i d e s of of the south t h e quarry. q u a r r y . Carbonate Carbonate veins v e i n s are a r e abundant abundant in i n the t h e serpentinite, ~erpentinite~ w i t h as a s many many as a s four f o u r generations g e n e r a t i o n s seen seen in i n some some blocks. b l o c k s . Early with E a r l y veins v e i n s are a r e typically t y p i c a l l y carcarb o n a t e replacing r e p l a c i n g cross—fiber c r o s s - f i b e r serpentine s e r p e n t i n e and and picrolite. p i c r o l i t e . Younger veinlets bonate v e i n l e t s are a r e generally generally c o a r s e grained g r a i n e d carbonate c a r b o n a t e with w i t h no no pseudomorphic pseudomorphic textures. textures. coarse back to t o the t h e shaft s h a f t house, housey and and back back to t o intersection i n t e r s e c t i o n with w i t h CO C0573. Turn left l e f t and and Proceed back 573. Turn 1000 feet f e e t to t o where the t h e road road crosses c r o s s e s an an arm arm of of Deer Deer Lake. Lake. Be proceed 1000 Be careful; c a r e f u l ; the the road is i s narrow narrow and and traffic t r a f f i c can can be b e heavy. heavy. road S e r p e n t i n i t e along a l o n g Deer Deer Lake Lake (Fig. (Fig. 3) 3) Stop 44 —- Serpentinite Stop Outcrops along a l o n g the t h e shore s h o r e of of Deer Deer Lake Lake show show the t h e two two main main serpentine s e r p e n t i n e textural t e x t u r a l types types Outcrops d e s c r i b e d in i n the t h e text. t e x t . Samples Samples from from Outcrop Outcrop A A (Fig. (Fig. 3) 3) show show well—developed well-developed 1—5 1-5 mm mm described serpentine s e r p e n t i n e pseudomorphs after a f t e r olivine o l i v i n e and and aa probable p r o b a b l e cumulate cumulate texture. t e x t u r e . The serpen— serpent i n i t e is i s designated d e s i g n a t e d as a s "Type "Type A" A'' in i n the t h e text, t e x t y and and is i s the tinite t h e most most common common variety v a r i e t y on on o u t c r o p s of of DL?. DLP. outcrops At and lighter l i g h t e r in i n color c o l o r than than A t Outcrop Outcrop BB the t h e serpentinite s e r p e n t i n i t e is i s "Type—B", " T Y P ~ - B "finer—grained ~f i n e r - g r a i n e d and "Type—A", i s commonly commonly strongly s t r o n g l y foliated. f o l i a t e d . In In " T Y P ~ - A " shows ~shows no relect r e l e c t igneous igneous textures, t e x t u r e s y and and is the i s evidence e v i d e n c e of of shearing s h e a r i n g along a l o n g the t h e contacts c o n t a c t s between between the t h e ore o r e host h o s t rock rock t h e mine there t h e r e is and the t h e talc—carbonate t a l c - c a r b o n a t e zones. zones. Further, F u r t h e r y the t h e ore o r e host h o s t rock r o c k appears a p p e a r s to t o pinch pinch out o u t west west CO 573. 573. Thus, Thusy this t h i s zone zone of of non—pseudomorphic non-pseudomorphic serpentinite s e r p e n t i n i t e ("Type—B") ("Type-B1') may may reprerepreof CO sent s e n t the t h e extension e x t e n s i o n of of the t h e shear s h e a r zone zone beyond the t h e ore o r e host h o s t rock, r o c k y east e a s t into i n t o the t h e Deer Deer v e i n l e t s of of picrolite p i c r o l i t e and and cross—fiber cross-fiber Lake Peridotite. P e r i d o t i t e . These outcrops o u t c r o p s also a l s o display d i s p l a y veinlets Lake asbestos, a s b e s t o s , carbonate—replaced carbonate-replaced serpentine s e r p e n t i n e veinlets, v e i n l e t s y and and strongly s t r o n g l y jointed j o i n t e d peridotite. peridotite. At "Type-B" serpentinite s e r p e n t i n i t e occurs o c c u r s near n e a r the t h e waterline, w a t e r l i n e y in i n sharp s h a r p contact contact A t Outcrop Outcrop C, C y "Type—B" a r e formed formed with w i t h another a n o t h e r variety v a r i e t y that t h a t consists c o n s i s t s of of shear s h e a r polyhedra. polyhedra. These polyhedra are by by aa series s e r i e s of of anastomosing anastomosing sets s e t s of of subparallel s u b p a r a l l e l cross—fiber c r o s s - f i b e r serpentine s e r p e n t i n e veins, v e i n s y sursurrounding much less well rounding elongate e l o n g a t e bblocks l o c k s tthat h a t aare r e much less w e l l veined. v e i n e d . The The polyhedra polyhedra are a r e smaller smaller toward toward the t h e shear s h e a r zone, zoney and have been proposed as a s pillows p i l l o w s by Morgan and DeCristoforo Chemical These features f e a t u r e s are a r e discussed d i s c u s s e d in i n greater g r e a t e r detail d e t a i l in i n the t h e text. t e x t . Chemical (1981). analyses a n a l y s e s of of HR HR 197 197 and and HR 232 232 are a r e listed l i s t e d as a s Nos. Nos. 44 and and 10 10 in i n Table Table 33 in i n the t h e text. text. 41 Turn right r i g h t on on U.S. U.S.41 Proceed east and to t o U.S. U.S. 41. 41. Turn CO 573 573 to t o Cooper Cooper Lake Lake Road, Roady and e a s t along a l o n g CO right and 3.2 miles m i l e s to t o junction j u n c t i o n of of CO CO 478 478 (party ( p a r t y store s t o r e on on left). l e f t ) . Turn right and drive d r i v e about about 3.2 Turn left l e f t and and proproand t o junction j u n c t i o n with w i t h Diorite D i o r i t e Road Road (CO (CO 496). 496). Turn and continue c o n t i n u e 0.1 0 . 1 miles m i l e s to ceed 1.0 r i g h t fork f o r k and drive d r i v e 1.6 1 . 6 miles m i l e s to t o Gold Gold Mine Mine Lake Lake Road 1.0 miles mi1.e~to t o fork. f o r k . Take right r i g h t and and continue c o n t i n u e 0.4 0.4 miles miles (CO CU) marked by aa Gold Gold Mine Mine Lake Lake Realty R e a l t y sign. s i g n . Turn right (CO on foot f o o t along a l o n g dirt d i r t road road for for to t o dirt d i r t road road on on the t h e right, r i g h t y closed c l o s e d by by aa gate. g a t e . Proceed on extreme caution c a u t i o n around around fenced fenced areas a r e a s that t h a t mark mark 1300 1300 feet f e e t to t o old o l d mine mine workings. workings. Use extreme open shafts s h a f t s and and stopes. stopes. Stop 55 —- The The Michigan Mine The Michigan Mine operated o p e r a t e d from from 1890 1890 to t o 1898 1898 and and became the t h e second second largest l a r g e s t gold gold i n 1934, 1934, reopened in producer in i n the t h e Michigan gold gold belt b e l t —— 64 64 kg. kg. gold. gold. The mine was reopened mm— The minas processed. a mill hundrwl tens t m s of of ore was processed. The s e v e r a lhuftdred m i l l was constructed, c o n s t r u c t e d y and sevra1 -- �80 Figure F i g u r e 3. 3. S e r p e n t i n i t e outcrops, o u t c r o p s , shore s h o r e of of Deer Deer Lake. Lake. Serpentinite �81 eralogical e r a l o g i c a l zone zone was was exposed exposed about about 600 600 feet f e e t on on strike. s t r i k e . Six S i x shafts s h a f t s have have workings extend to a depth of 250 feet with levels at 60, 150, and extend t o a d e p t h of 250 f e e t w i t h l e v e l s a t 6OY 150, and 250 250 1972; Morgan and 1972; and DeCristoforo, D e C r i s t o f o r o , 1981). 1981). been been feet feet sunk and and sunk (Bodwell, (Bodwelly The The deposit d e p o s i t is i s situated s i t u a t e d in i n the t h e lower lower amphibolite a m p h i b o l i t e member member of of the t h e Kitchi K i t c h i Schist S c h i s t that t h a t is is intruded i n t r u d e d by by relatively r e l a t i v e l y fresh f r e s h appearing a p p e a r i n g quartz—feldspar q u a r t z - f e l d s p a r porphyry porphyry dikes. d i k e s . Quartz Quartz veins, veinsy erratic and w width found aalong e r r a t i c in i n strike, s t r i k e y dip. d i p and i d t h ggenerally e n e r a l l y aare r e found l o n g the t h e contact c o n t a c t between these these two two rock rock types. types. Pyrite—gold and the t h e property property P y r i t e - g o l d mineralization m i n e r a l i z a t i o n occurs o c c u r s along a l o n g the t h e margin margin of of quartz q u a r t z veins, v e i n s , and has t h e largest l a r g e s t weighing weighing over o v e r 15 1 5 oz., O Z . ~ h a s yielded y i e l d e d some some spectacular s p e c t a c u l a r high—grade high-grade specimens, specimensy the but b u t in i n general g e n e r a l the t h e values v a l u e s were w e r e sporadic. s p o r a d i c . Pyrite P y r i t e is i s the t h e principal p r i n c i p a l sulfide, s u l f i d e y with w i t h minor minor chalcopyrite, c h a l c o p y r i t e , galena, g a l e n a y sphalerite, s p h a l e r i t e y and and molybdenite molybdenite (Bodwell, (Bodwelly 1972). 1972). �____________________________________ CONSTITUTION CONSTITUTION OF OF INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY ' A r t i c l e II Article Name Name The name of of the t h e organization o r g a n i z a t i o n shall s h a l l be b e the t h e 'Institute " I n s t i t u t e on on Lake Lake Superior Superior Geology. " Geology." A r t i c l e II I1 Article Objectives Objectives o b j e c t i v e s of o f this t h i s organization o r g a n i z a t i o n are: are: The objectives A. A. B. B. C. C. A r t i c l e III 111 Article To To provide p r o v i d e aa means means whereby whereby geologists g e o l o g i s t s in i n the t h e Great G r e a t Lakes Lakes region region may exchsnge exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. may To To promote promote better b e t t e r understanding u n d e r s t a n d i n g of o f the t h e geology geology of of the t h e Lake Lake Superior Superior region. region. To plan p l a n and and conduct c o n d u c t geological g e o l o g i c a l field f i e l d trips. trips. To BY-LAWS I. I. Duties D u t i e s of of the t h e Officers O f f i c e r s and and Directors Directors A. A. Status Status 1. 1. No part p a r t of o f the t h e income income of of the t h e organization o r g a n i z a t i o n shall s h a l l inure i n u r e to t o the t h e benefit b e n e f i t of of I n the t h e event e v e n t of of dissolution d i s s o l u t i o n the t h e assets a s s e t s of of the the any member member or o r individual. i n d i v i d u a l . In any organization o r g a n i z a t i o n shall s h a l l be be distributed d i s t r i b u t e d to to (some tax t a x free f r e e urganization). organization). (some 2. 2. 3. 3. [To [To aavoid v o i d Federal F e d e r a l and State S t a t e income income taxes, t a x e s , the t h e organization o r g a n i z a t i o n should should be not n o t only o n l y "scientific" " s c i e n t i f i c " oro "educational" r " e d u c a t i o n a l "but b u talso a l s "non—profit."] o "non-profit."] be B. B. Ninn. Minn. Stat. S t a t . Anno. Anno. 290.01, 290.01. subd. subd. 44 ' 290.05(9) s. SOl(c)(3) 5Ol(c)(3) 1954 Internal I n t e r n a l Revenue Revenue Code Code s. 1954 A r t i c l e IV IV Article 2. 2. Membership Nembership 3. 3. s h a l l meet meet once once sa year, y e a r , preferably p r e f e r a b l y during d u r i n g the t h e month month of of The The organization o r g a n i z a t i o n shall p l a c e and and exact e x a c t date d a t e of of each e a c h meeting m e e t i n g will w i l l be b e designated d e s i g n a t e d by by A p r i l . The place April. t h e board b o a r d of o f directors. directors. the A r t i c l e VI VI Article C. C. Meetings Neetings 11. II. Directors Directors The The board board of of directors d i r e c t o r s shall s h a l l consist c o n s i s t of of the t h e Chairman, Chairman, Secretary—Treasurer Secretary-Treasurer and the t h e last l a s t three t h r e e past p a s t Chairmen; Chairmen; but b u t if i f the t h e board board should s h o u l d at a t any any time t i m e concons i s t of l e s s than t h a n five f i v e persons, p e r s o n s , by by reason r e a s o n of of unwillingness u n w i l l i n g n e s s or o r inability inability sist of less of any o f the t h e above persons p e r s o n s to t o serve s e r v e as a s directors, d i r e c t o r s , the t h e vacancies v a c a n c i e s on on the the of of board f i l l e d by by the t h e annual a n n u a l meeting m e e t i n g so s o as a s to t o bring b r i n g the t h e membership membership board may may be be filled of the t h e board b o a r d up up to t o five f i v e members. members. of A r t i c l e VII VII Article Officers Officers III. 111. B. B. A r t i c l e VIII VIII Article s h a l l be be elected e l e c t e d esch e a c h year y e a r by by the t h e board board of o f directors, directors, The Chairman shall s h a l l give q i v e due due consideration c o n s i d e r a t i o n to t o the t h e wishes w i s h e s of of any any group group that t h a t may may who shall promoting the t h e next n e x t annual a n n u a l meeting. m e e t i n g . Nis H i s term t e r m of o f office o f f i c e as a s Chairman Chairman be promoting w i l l terminate t e r m i n a t e at a t the t h e close c l o s e of of the t h e annual a n n u a l meeting meeting over o v e r which which he h e preprewill s i d e s or o r when his h i s successor s u c c e s s o r shall s h a l l have have been been appointed. a p p o i n t e d . He will w i l l then then sides s e r v e for f o r aa period p e r i o d of of three t h r e e years y e a r s as a s aa member member of of the t h e board board of of directors. directors. serve S e c r e t a r y - T r e a s u r e r shall s h a l l be be elected e l e c t e d at a t the t h e annual a n n u a l meeting. m e e t i n g . His His The Secretary—Treasurer t e r m of of office o f f i c e shall s h a l l be two two years y e a r s or o r until u n t i l his h i s successor s u c c e s s o r shall s h a l l have have term appointed. been appointed. Amendments Amendments T h i s constitution c o n s t i t u t i o n may be amended amended by by aa majority m a j o r i t y vote v o t e of of those t h o s e persons p e r s o n s who who This a r e personally p e r s o n a l l y present p r e s e n t at, a t , participating p a r t i c i p a t i n g in, i n , and and voting v o t i n g at a t any any annual annual are m e e t i n g of of the t h e organization. organization. meeting Keep Keep accurate a c c u r a t e attendance a t t e n d a n c e records r e c o r d s of of ell a l l annual a n n u a l meetings. meetings. Keep Keep accurate a c c u r a t e records r e c o r d s of of all a l l meetings m e e t i n g s of, o f , and and correspondence correspondence between, between, the t h e board b o a r d of o f directors. directors. Hold all a l l funds f u n d s that t h a t may may eccure a c c u r e as a s profits p r o f i t s from from annual a n n u a l meetings meetings or o r field f i e l d trips t r i p s and and to t o make make these t h e s e funds f u n d s svsilable a v a i l a b l e for f o r the the organization o r g a n i z a t i o n and operation o p e r a t i o n of of future f u t u r e meetings m e e t i n g s as a s required. required. It I t shall s h a l l be b e the t h e duty d u t y of of the t h e board board of of directors d i r e c t o r s to t o plan p l a n locations locations of o f annual a n n u a l meetings m e e t i n g s and and to t o advise a d v i s e on on the t h e organization o r g a n i z a t i o n end and financing financing of o f all a l l meetings. meetings. Dues and and Expenses Expenses 1. 1. There T h e r e shall s h a l l be b e no regular r e g u l a r membership membership dues. dues. 2. 2. Registration R e g i s t r a t i o n fees f e e s for f o r the t h e annual a n n u a l meetings m e e t i n g s shall s h a l l be b e determined determined by the t h e Chairmen Chairman in i n consultation c o n s u l t a t i o n with w i t h the t h e board board of of directors. directors. It It is i s strongly s t r o n g l y recommended recommended that t h a t these t h e s e be b e kept k e p t st a t aa minimum minimum to to encourage encourage attendance a t t e n d a n c e of of graduate g r a d u a t e students. students. Rules R u l e s or o r Order Order The The rules r u l e s contained c o n t a i n e d in i n Robert's R o b e r t ' s Rules R u l e s of o f Order Order shell s h a l l govern govern this this organization o r g a n i z a t i o n in i n all a l l cases c a s e s to t o which which they t h e y are a r e epplicsble. applicable. The officers o f f i c e r s of o f this t h i s organization o r g a n i z a t i o n shall s h a l l be b e aa Chairman Chairman and and aa Secretary—' SecretaryThe Treasurer. Treasurer. A. A. Preside P r e s i d e at a t the t h e annual a n n u a l meeting. meeting. Appoint all a l l committees committees needed needed for f o r the t h e organization o r g a n i z a t i o n of o f the the ennual a n n u a l meeting. meeting. Assume Assume complete c o m p l e t e responsibility r e s p o n s i b i l i t y for f o r the t h e orgsnizstion o r g a n i z a t i o n end and financing f i n a n c i n g of of the t h e annual a n n u a l meeting meeting over o v e r which which he h e presides. presides. It I t shall s h a l l be b e the t h e duty d u t y of o f the t h e Secretary—Treasurer S e c r e t a r y - T r e a s u r e r to: to: 1. 1. The The membership of the o r g a n i z a t i o n shall c o n s i s t of t h e board of directors. membership of t h e organization s h a l l consist o f the board of directors. g e o l o g i s t interested i n t e r e s t e d shall s h a l l be b e permitted p e r m i t t e d to t o attend a t t e n d and and participate p a r t i c i p a t e in in Any geologist v o t e at a t the t h e annual a n n u a l meetings. meetings. and vote A r t i c l e VV Article It It shall s h a l l be b e the t h e dutyof d u t y o f the t h e Chsirnsn Chairman to: to: IV. IV. Amendments Amendments These These by-lews by-laws may may be b e amended amended by sa majority m a j o r i t y vote v o t e of of those t h o s e persons p e r s o n s who who ere a r e personally p e r s o n a l l y present p r e s e n t at, a t , participating p a r t i c i p a t i n g in, i n , end and voting v o t i n g at a t any any ennuel annual meeting m e e t i n g of of the t h e organization; o r g a n i z a t i o n ; provided provided that t h a t such s u c h modifications m o d i f i c a t i o n s shell shall not n o t conflict c o n f l i c t with w i t h the t h e constitution c o n s t i t u t i o n as a s presently p r e s e n t l y adopted adopted or o r subsequently subsequently amended. �INSTITUTES INSTITUTES ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE INSTITUTE NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 DATE -- PLACE PLACE Minneapolis, MN Minneapolis, Houghton, MI Houghton, MI East E a s t Lansing, Lansing, MI MI Duluth, I'IN Duluth, MN Minneapolis, MN Minneapolis, Madison, Madison, WI WI Port Ont. (Thunder Bay) P o r t Arthu-r, A r t h u r , Ont. Bay) Houghton, MI MI Duluth, Duluth, MN Ishpeming, I shp emin g , MI MI St. Paul, St. P a u l , MN Sault S a u l t Ste. S t e . Marie, Marie, MI MI East Lansing, MI E a s t Lansing, MI Superior, S u p e r i o r , WI WI Oshkosh, WI Oshkosh, WI Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, Houghton, MI Houghton, MI Madison, WI Madison, WI Sault S a u l t Ste. S t e . Marie, Marie, MI MI Marquette, MI MI St. Paul, S t. P a u l , MN Thunder Bay, Bay, Ont. Ont. Milwaukee, WI WI Milwaukee, Duluth, MN Duluth, Eau Claire, C l a i r e , WI WI East E a s t Lansing, Lansing, MI MI IInternational n t e r n a t i o n a l Falls, F a l l s , MN Houghton, MI Houghton, MI Wausau, W WII Wausau, 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 In Michigan Technological Technological University University is is an an equal equal opportunity opportunity educational educational institutionlequal institution/equal opportunity Michigan opportunity employer. employer. � https://digitalcollections.lakeheadu.ca/files/original/47a23992a5300f3056d0a840ef01b365.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 .../ ... 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';- .-;::~ -~_/. ." ~_. =--" ~ "'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. U.S. Geolo- Butler, B.S. and Burbank, W.S., 1929, The copper deposits of Michigan: gical Survey Professional Paper 144, 238 p. the Mid—Continent Chase, C.G. and Gilmer, T.H., 1973, Precambrian plate tectonics: Gravity High: Earth and Planetary Science Letters, v. 21, p. 70—78. Chaudhuri, S. and Faure, G., 1968, Rubidium—strontium age of the Mount Bohemia intrusion in Michigan: Journal of Geology, v. 76, p. 488—490. Clarke, D.H., l974a, Lake Superior and Phoenix Mining Companies — Copper Mines of Keweenaw No. 4: Local Publication, Copper Mines of Keweenaw Series, 32 p. l974b, Copper Falls Mining Company — Copper Mines of Keweenaw No. 6: Local Publication, Copper Mines of Keweenaw Series, 36 p. No. 9: 1975, Northwest Copper Mining Association — Copper Mines of Keweenaw Local Publication, Copper Mines of Keweenaw Series, 28 p. 1976, The Cliff Mine — Copper Nines of Keweenaw No. 16: cation, Copper Mines of Keweenaw Series, 32 p. Local publi- Cornwall, H.R., l95la, Differentiation in lavas of the Keweenawan Series and the origin of the copper deposits of Michigan: Geological Society of America Bulletin, v. 62, p. 159—201. l95lb, Differentiation in magmas of the Keweenawan Series: Geology, v. 59, p. 151—172. Journal of l95lc, Ilmenite, magnetite, hematite, and copper in lavas of the Keweenawan Series: Economic Geology, v. 46, p. 51—67. �______________ ______________ Cornwall, H.R., 1954, Bedrock geology of the Delaware quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 51. l954a, Bedrock geology of the Phoenix quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 34. 1954c, Bedrock geology of the Lake Medora Quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 52. 1955, Bedrock geology of Fort Wilkins quadrangle: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 74. Cornwall, H.R. and Rose, H.J., Jr., 1957, Minor elements in Keweenawan lavas, Michigan: Geochemica et Cosmochimica Acta, v. 12, p. 209—224. 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, 1983 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 11-14, 1983. 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 1983 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/c2caa4000cd34c2d11aabbe70362e238.pdf 5aaa5cb9f07dbd04064727a8d6f121c6 PDF Text Text ___ ANNUAL THIRTIETH ANNUAL INSTITUTE INSTITUTE ON ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY SOUTH NORTH / U) //// ,ISLAND / / TRENCH /ANUE SM ARC 1OCEAN CRUST iL: I-. C) I- U) OLTZ — - _- i —--—- - -r + + + + + + + + + +++ + ++++++++ + + + + + + + + + + + + + +++ + + • + 4.4 + +++ ++ .4. — -7-- —/-ANIMIKIE -.— - — -- — — -— — —— — - -— —'-—S SEDIMENTS - 4 COLLISION + + + + + + + + + + + + + + + + + + + + + + ++ ++ + + + + + +++ + + + + + + + + + + 4- + + + + + + + + SNEISS DOMES W a u s a u , Wisconsin Wisconsin Wausau, A p r i l 24—28, 2 4 - 2 8 , 1984 1984 April �INSTITUTES INSTITUTES ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE NUMBER NUMBER INSTITUTE 11 22 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 II 11 12 12 13 13 14 14 15 15 16 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 - DATE DATE 1955 1955 1956 1956 1957 195 7 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 19 76 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 PLACE Minneapolis, MN Houghton, Houghton, MI MI East E a s t Lansing, Lansing, MI MI Duluth, MN Minneapolis, MN Minneapolis, WII Madison, W Ont. (Thunder Port P o r t Arthur, Arthur, Ont. (Thunder Bay) Bay) Houghton, MI MI Duluth, MN Duluth, Ishpeming, MI Ishpeming, MI St. S t . Paul, Paul, MN MN Sault S a u l t Ste. S t e . Marie, MI MI East Lansing, Lansing, MI MI Superior, S u p e r i o r , WI WI Oshkosh, WI WI Thunder Bay, Ont. Ont. Duluth, Duiuth, MN Houghton, MI MI WII Madison, W Sault MII S a u l t Ste. S t e . Marie, Marie, M Marquette, MI MI S t . Paul, Paul, MN St. Thunder Thunder Bay, Ont. Ont Milwaukee, WI WI Duluth, MN Duluth, Eau Claire, C l a i r e , WI WI East E a s t Lansing, MI MI Falls, IInternational nternational F a l l s , MN Houghton, MI Wausau, Waus au , WI WI Kenora, Kenora, Orit. Ont. . �Award Award Guidelines Guidelines SAM SAM GOLDICH GOLDICH MEDAL MEDAL Preamble Preamble The The Institute I n s t i t u t e on on Lake Lake Superior Superior Geology was born on or o r around 1955, as a s documented do'cumented by by the t h e fact f a c t that t h a t the t h e 27th 27th annual annual meeting meeting will w i l l be be held h e l d in i n 1981. 1981. The The Institutes Institutes are i n their t h e i r continuing continuing objectives o b j e c t i v e s of dealing d e a l i n g with w i t h those aspects a s p e c t s of a r e exemplary exemplary in geology geology that t h a t are a r e related r e l a t e d geographically geographically to t o Lake Lake Superior; Superior; of of encouraging encouraging the the discussion d i s c u s s i o n of of subjects s u b j e c t sand andsponsoring w i l l bring b r i n g together together sponsoring field f i e l d trips t r i p s which which will geologists surveys, and andiindustry; g e o l o g i s t s from from tthe h e academia, academia, government government surveys, n d u s t r y ; and and of of maintaining maintaining an but an exceedingly exceedingly informal informal b u t highly h i g h l y effective e f f e c t i v emode mode of of operation. operation. During i t s existence e x i s t e n c e the t h e membership membership of of the t h e Institute I n s t i t u t e (that ( t h a t is, i s , those those During the t h e course course of of its geologists g e o l o g i s t s who who indicate i n d i c a t e an an interest i n t e r e s t in i n the t h e objectives o b j e c t i v e s of of the t h e I.L.S.G. I.L.S.G. by by attending) attending) has has become become aware aware of of the t h e fact f a c t that t h a t certain c e r t a i n of of their t h e i r colleagues colleagues have made particularly particularly noteworthy noteworthy and and meritorious meritorious contributions c o n t r i b u t i o n s to t o the t h e improvement improvement of of understanding understanding of of "Lake Superior" geologyand andiits "Lake S u p e r i o r " geology t s mineral mineral deposits. deposits. The by I.L.S.G. I.L.S.G. tot oSam The exemplary exemplary award award was was made made by Sam Goldich Goldich in i n 1979 1979 for f o r his h i s many many contributions t h egeology geology of ofthe t h eregion 50 years. years. regionextending extendingover overabout about50 c o n t r i b u t i o n s to t othe Award Award Guidelines Guidelines 1) 1) The The medal medal shall s h a l l be be awarded awarded annually annually by by the t h e Board Board of of Directors, D i r e c t o r s , I.L.S.G., I.L.S.G., to t o aa geologist whose name is a s s o c i a t e d with w i t h aa substantial s u b s t a n t i a l sustained s u s t a i n e d interest i n t e r e s t in, i n , or or g e o l o g i s t whose name is associated aa major SuperiorRegion. Region. thegeology geologyofofthe t hLake e LakeSuperior major contribution c o n t r i b u t i o n to, t o ,the 2) 2 ) The The Board Board of of Directors, D i r e c t o r s , I.L.S.G. I.L.S.G. shall s h a l l appoint appoint the t h e Nominating Nominating Committee. Committee. Their w i l l be be voted voted on on at a t the t h e annual annual business b u s i n e s s meeting. meeting. The The Their annual annual nominee nominee will initial i n i t i a l appointment appointment will w i l l be be of of three t h r e e members, members, one one to t o serve s e r v e for f o r three t h r e e years, y e a r s , one one for the member member with w i t h the t h e briefest b r i e f e s t incumbency incumbency to t o be be f o r two, two, and and one one for f o r one one year, y e a r , the chairman. chairman. After A f t e r the t h e first f i r s t year year the t h e Board Board of of Directors D i r e c t o r s shall s h a l l appoint appoint at a t each each spring memberwho who w i will l l s eserve r v e f for o r tthree h r e e years. y e a r s . In In the t h e third t h i r dyear year s p r i n g meeting meeting one one new new member this thismember member sshall h a l l be be the t h e chairman. chairman. The The Committee Committee membership membership should should reflect r e f l e c t the the main main fields f i e l d s of of interest i n t e r e s t and and geographic geographic distribution d i s t r i b u t i o n of of I.L.S.G. I.L.S.G. membership. membership. 3) 3) The Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall s h a l l select s e l e c t the t h e medalist m e d a l i s t and and will will The make make its i t srecommendation recommendation tto o the t h e Board Board of of Directors D i r e c t o r s by byNovember November 1 t h a t year. year. 1 of of that 4)4) The The Board ~ o a r of dof Directors D i r e c t o r s normally normally will w i l l accept a c c e p t the t h e nominee nominee of of the the Committee, Committee, will w i l l inform inform the t h e medalist medalistimmediately, immediately, and andwill w i l have l haveone one medalengraved engraved medal appropriately a p p r o p r i a t e l y for f o r presentation p r e s e n t a t i o n at a tthe t h e May May meeting. meeting. I t is i s recpmmended recommended that t h a t the t h e Institute I n s t i t u t e set s e t aside a s i d e annually annually from fromwhatever whatever sources, sources, It such w i l l be be required r e q u i r e d to t o support support the t h e continuing continuing costs c o s t s of of this this award. award. such funds funds as a s will 5) 5) April ' 4 , 1981 1981 A p r i l 4, J. Kalliokoski, K a l l i o k o s k i , Chairman Chairman J. Bill B i l l Cannon Cannon Fred Fred Kehienbeck Kehlenbeck Glenn Glenn Morey Morey Greg Greg Mursky Mursky �region. To plan and conduct geological field trips. a c - m a a if 31 go a Â¥ a > 31 a a UJ a a w >à a 3 m - 0 c . 33 a 1) C u UE4-1 1) el U - + a s a c 3 - c- -- - aa m U .c IU 0 a. 33 el - n - 0 31 s U a >s 3 -m .c Id a 31 3 os 1) c a -1 a a -3 u à C -3 -- The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. Rules or Order Registration fees for the annual meetings shall be determined by the Chairman in consultation with the board of directors. It is strongly recommended that these be kept at a minimum to encourage attendance of graduate students. Ic 3 .c z0 I- - J= --- m 31 u a I- c U N M I- £- 0 U fat 0 u a c c 0 0 2 c amended. These by—laws may be amended by a majority vote of those persons who are personally present at, participating in, and voting at any annual meeting of the organIzation; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently Amendments 1. ) in, and voting at 4-1 31 0 M eat ion. -5 w 1) > fleet lug oh the orgaril u M m Amendments u U Ia There shall be no regular membership dues. - 1-1 - This const Itiit ion may be amended by a maor1ty Vote of those persons who are personally present at, participating any annual 1)- Dues and Expenses 0 5 B. u a m I- c a a IV. c The Chairman shall be elected each year by the board of directors. who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. his term of office as Chairman will terminate at the close of the annual meeting over which he presides or when his successor shall have been appointed. He will then serve for a period of three years as a member of the board of directors. The Secretary—Treasurer shall be elected at the annual meeting. His term of office shall be two years or until hits successor shall have been appointed. "0 A. s u a III. c a The officers of this organization shall be a Chairman and a Secretary— Treasurer. --:- 2. 2 1. -- Officers Keep accurate attendance records of all annual meetings. Keep accurate records of all meetings of, and correspondence between, the board of directors. Hold all funds that may accure as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. M It shall be the duty of the board of directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. 3. 2. 1. c -1 c a u a c The board of directors shall consist of the Chairman, Secretary—Treasurer and the last three past Chairmen; but if the board should at any time consist of less than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the annual meeting so as to bring the membership of the board up to five members. II. - Preside at the annual meeting. Appoint all committees needed for the organization of the annual meeting. Assume complete responsibility for the organization and financing of the annual meeting over which he presides. It shall be the duty of the Secretary—Treasurer to: 3. 2. 1. It shall be the duty of the Chairman to: l?m Directors C. B. A. Duties of the Officers and Directors Â¥r The organization shall meet once a year, preferably during the month of April. The place and exact date of each meeting will be designated by the board of directors. Meetings The membership of the organization shall consist of the board of directors. Any geologist interested shall be permitted to attend and participate In and vote at the annual meetings. Membership Minn. Stat. Anno. 290.01, subd. 4 290.05(9) 1954 Internal Revenue Code a. SOI(c)(3) (To avoid Federal and State income taxes, the organIzation should be not only "acientitic" or "educational" but also "non—profit.") No part of the income of the organization shall inure to the benefit of In the event of dissolution the assets of the any member or individual. organization shall be distributed to (some tax free organization). I. BY-LAWS c Article VIII this organization are: on Lake Superior To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. To promote better understanding of the geology of the Lake Superior objectives of Status C. B. A. The Objectives "Institute 0 Article VII Name The name of the organization shall be the Geology." a Article VI Article V Article IV Article III Article II Article I CONSTITUTION OF INSTITUTE ON LAKE SUPERIOR GEOLOGY ___________________________________ 33- �TABLEOF OFCONTENTS CONTENTS TABLE . . . . . . B O A R D OF O F DIRECTORS DIRECTORS . . . . . . BOARD L O C A L COMMITTEES COMMITTEES. . . . . . . LOCAL G O L D I C H MEDAL MEDAL COMMITTEE COMMITTEE . . . GOLDICH S E S S I O N CHAIRMEN CHAIRMEN . . . . . . . SESSION G O L D I C H MEDAL MEDAL RECIPIENT RECIPIENT . . . . GOLDICH A N N U A L BANQUET B A N Q U E T SPEAKER SPEAKER. . . . . ANNUAL ACKNOWLEDGEMENTS. . . . . . . . ACKNOWLEDGEMENTS G E N E R A L INFORMATION INFORMATION GENERAL . . R E P O R T OF O F THE T H E CHAIRMAN CHAIRMAN REPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F i e l d Trip T r i p II . . . . . . . . . . . Field P o s t e r Papers Papers. . . . . . . . . . . Poster T e c h n i c a l Sessions S e s s i o n s II and a n d II. 11. . . . Technical C A L E N D A R OF O F EVENTS E V E N T S AND AND PROGRAM. PROGRAM. CALENDAR . . . . 1i iii i iii iii ill iii iv iv iv iv iv iv iv iv v V vii . vii vii . Vii vii . Vii . viii A n n u a l Banquet Banquet Annual ix Technical Technical . . . . . . . . . . . . S e s s i o n s III I11 and and I V . . . . . Sessions ix ix . . . . . . . . . xi xi F i e l d Trips T r i p s 22 and a n d 3. 3. Field ABSTRACTS ABSTRACTS �GENERAL INFORMATION GENERAL INFORMATI ON 30th 30th ANNUAL ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE Held Held at at HOLIDAY HOLIDAY INN INN Wausau, Wisconsin, Wisconsin, 54901 Wausau, 54901 April A p r i l 26, 26, 27, 27, 1984 1984 sponsored by sponsored by The Geology The Geology Department Department The University The U n i v e r s i t yofo Wisconsin-Oshkosh f Wisconsin-Oshkosh Program Chairman Chairmanand andEEditor Program ditor Gene L. LaBerge LaBerge Gene L. 1 �INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS G. L. L. LaBerge, LaBerge, Department of G. of Geology, University of of Wisconsin—Oshkosh Wisconsin-Oshkosh, Oshkosh, Wisconsin, 54901 Oshkosh, 54901 (1984) (1984) Engineering, T. 3. Bornhorst, Department T. J. Bornhorst, Department of of Geology Geology and and Geological Geological Engineering, Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan, Michigan, 49931 49931 (1983) (1983) D. L. L. Southwick, Minnesota Geological Survey, Survey, 2642 2642 University University Avenue, Avenue, St. Paul, Minnesota, 55114 S t . Paul, 55114 (1982) (1982) tate U n i v e r s i t y , East F. W. F. W. Cambray, Department Department of of Geology, Geology, Michigan Michigan S State University, East Lansing, Michigan, 48824 Lansing, 48824 (1981) (1981) P. E. Myers, Department of P . E . Myers, of Geology, Geology, University of Wisconsin—Eau Wisconsin-Eau Claire, Claire, Eau Claire, C l a i r e , Wisconsin, 54701 54701 (1980) (1980) 3. K Kallioloski, Department of of Geology and Geological Engineering, Michigan J. a l l i o l o s k i , Department Michigan Technological University, U n i v e r s i t y , Houghton, Michigan, 49931 49931 (Secretary-Treasurer) (Secretary-Treasurer) SALES SALES t h e Abstracts A b s t r a c t sand andField Field T r iGuidebooks p Guidebooksmay maybe bepurchased purchased Copies of Copies of the Trip from . LaBerge , Geology , Uni v e r s i t y ooff from Gene GeneLL. LaBerge, GeologyDepartment Department, University Wisconsin-Oshkosh, Oshkosh, I , 54901. 54901. A Wisconsin—Oshkosh, Oshkosh, WWI, b s t r a c t s == $6.00; $6.00; Abstracts and III I 1 1= =$5.00 $5.00 each. each. Make Guidebooks I, Guidebooks I, III1and o: Makechecks checkspayable payable tto: I n s t i t u t eononLake LakeSuperior S u p e r i o rGeology. Geology. Institute 11 �LOCAL COMMITTEE L OCAL COMMITTEE Conference Chairman Chairman Gene L. L. LaBerge LaBerge Gene Trips Field F ield T rips P. K. P K. Sims, U.S. U.S. Geological Survey, Federal F e d e r a l Center, C e n t e r , Denver, Denver, Colorado, 80225 Colorado, 80225 Klaus J. J. Schuiz, Klaus Survey, National Center, Center, Schulz, U.S. U.S. Geological Survey, Reston, V Virginia, Reston, i r g i n i a , 22092 22092 Z e l l E. E. Peterman, U.S. Geological Survey, Survey, Federal F e d e r a l Center, Center, Zell Peterman, U.S. Denver, Colorado, Denver, Colorado, 80225 80225 Myers, Geology Department, Paul E. E. Myers, Department, University u n i v e r s i t y of of WisconsinWisconsinEau C l a i r e , Eau C l a i r e , Wisconsin, 54701 Claire, Claire, Wisconsin, 54701 W. L. L. Ueng, Ueng, D. W. D. K. K. Larue, Larue, R. R. L. L. Sedlock, D. D. A. A. Kasper, Kasper, S t a n f o r d University, University,, Stanford, Stanford, Department of Geology, Stanford California, C a l i f o r n i a , 94305 Registration R egistration LaBerge, Geology Department, Department, University U n i v e r s i t y of of WisconsinWisconsinS a l l y LaBerge, Sally Oshkosh, Oshkosh, Oshkosh, Wisconsin, Wisconsin, 54901 Oshkosh, 54901 Best Student Paper B e s t .Student Paper Committee Committee Paul E. Myers, Geology E . Myers, Geology Department, U n i v e r s i t y of of Wisconsin— WisconsinUniversity Claire, Eau C l a i r e , Eau Claire, C l a i r e , Wisconsin, Wisconsin, 54701 54701 W. Chandler, Minnesota Geological Survey, 2642 2642 U niversity Val W. Chandler, Minnesota Geological Survey, University Avenue, t . Paul, P a u l , Minnesota, Avenue, S St. Minnesota, 55114 Eugene C. C. Perry, P e r r y , Geology Department, Department, Northern Northern Illinois I l l i n o i s University, University, DeKaib,, Illinois, DeKalb I l l i n o i s , 61455 61455 GOLD ICH MEDAL MEDAL C COMMITTEE GOLD ICH OMMITTEE R. L. Buchheit, Meridian MeridianLand Landand andMineral MineralCompany, Company, Box Box 566, 566, L. Buchheit, Hibbing, Minnesota, 55746 55746 W. Cannon, U.S. U.S. Geological Survey, MS M S 954, National Center, Center, W. F. F. Cannon, Reston, Virginia, Reston, V i r g i n i a , 22092 22092 M. ~ a k e h e a dUniversity, University, M. F. Kehlenbeck, Department of Geology, Lakehead Bay, Ontario Thunder Bay, iii �SESSION SESSIONCHAIRMEN CHAIRMEN Robert of Geology, Robert L. L. Bauer, Bauer, Department Department of Geology, University University of of Missouri, Missouri, Columbia, Columbia, Missouri Missouri Theodore J. Bornhorst, Theodore J. Bornhorst,Department Department of ofGeology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan I. James Hoffman, Department Department of of Geology, Geology, University University of of WisconsinWisconsinJames I. Hoffman, Oshkosh, Oshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin Thomas R. Kalk, Kalk, Homestake Homestake Mining Mining Company, Company, P. P. 0. 0. Box Box 10628, 10628, Thomas R. Reno, Reno, Nevada Nevada John John S. S. Klasner, Klasner, Department Department of of Geology, Geology, Western Western Illinois Illinois University, U n i v e r s i t y , Macomb, Macomb, Illinois Illinois Gregory Gregory Mursky, Mursky, Department Department of of Geological Geological Sciences, Sciences, University University of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin P e t e r A. A. Nielsen, Nielsen, Department Department of of Geology, Geology, University University of of Wisconsin— WisconsinPeter Parkside, Parkside, Kenosha, Kenosha, Wisconsin Wisconsin Klaus J. Schulz, Schulz, U. U. S. S. Geological Geological Survey, Survey, National National Center, Center, MS M S 954, 954, Klaus J. Reston, Reston, Virginia Virginia GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Richard Richard W. W. Ojakangas, Ojakangas, Geology Geology Department, Department, University University of of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, Minnesota Minnesota ANNUAL ANNUAL BANQUET BANQUET SPEAKER SPEAKER Dr. D r . Charles Charles Meyer, Meyer, 380 380 Smith Smith Road, Road, Sedona, Sedona, Arizona Arizona ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS Any this type type requires r e q u i r e s the t h e cooperation cooperation of of many many individuals individuals Any conference conference of of this who t i m e . As who are a r e willing w i l l i n gto t o give giveof of their t h e i rtime. A s general g e n e r a l chairman chairman II sincerely sincerely have had had by by the t h e many many people people I I a p p r e c i a t e the t h e widespread widespread cooperation cooperation II have appreciate have have asked asked to t o help h e l p make make the t h e conference conference aa success. success. AA special s p e c i a l thanks thanks goes goes to m y colleagues colleagues at a t UW—Oshkosh, UW-Oshkosh, especially t o my e s p e c i a l l y our o u r secretary s e c r e t a r y Sara Sara Margis Margis for for the t h e typing t y p i n g and and many many other o t h e rfunctions functionsshe shehas hasperformed. performed. II couldn't c o u l d n ' t have have done it without without you youall. all. done it iv �REPORT OF OFTHE THECHAIRMAN CHAIRMAN REPORT 29th INSTITUTE INSTITUTE 29th ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY ON 1983 29th Institute I n s t i t u t eon onLake Lake Superior Superior Geology Geology was was held h e l d May May 11—14, 11-14, 1983 1983 at at The 29th The The meeting meeting was was Michigan Technological Technological University Universityini nHoughton, Houghton,Michigan. Michigan. The Michigan theMichigan Michigan Tech Tech Department Department of of Geology Geology and and Geological Geological EngineerEngineersponsored by by the sponsored Regising in i n cooperation cooperation with with the the Division Division of ofEducation Education and and Public P u b l i c Services. S e r v i c e s . Regising t r a n t s numbered numbered 173, 173, including i n c l u d i n g 119 119 pprofessional r o f e s s i o n a l geologists g e o l o g i s t s and and 54 54 students. students. trants The program program included included aa pre-meeting pre-meeting one one day day field f i e l d trip t r i p to t o provide provide an an overview overview The Michigan, aa post-meeting post-meeting one one day day the geology geology of of the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan, of the of f i e l d trip t r i p to t o the t h e Ropes Ropes and and Michigan Michigan gold gold mines mines near near Ishpeming, Ishpeming, Michigan Michigan and and field 70 persons persons participated p a r t i c i p a t e d in in four half—day half-day sessions s e s s i o n s of of technical t e c h n i c a l papers. papers. About About 70 four 60 participated p a r t i c i p a t e d in i n the t h e post-meeting post-meeting trip, t r i p , and and 31 31 about 60 tthe h e pre—meeting pre-meeting trip, t r i p , about The propropapers were were selected s e l e c t e d for f o r oral o r a l presentation p r e s e n t a t i o n at a t the t h e technical t e c h n i c a l sessions. s e s s i o n s . The papers I included 29th I n s t i t u t e were published i n two volumes. Volume ceedings of t h e ceedings of the 29th Institute were published in two volumes. Volume I included the accepted accepted abstracts a b s t r a c t s and and the t h e field f i e l d trip t r i p road road log l o g to t o the t h e Ropes Ropes gold gold mine. mine. the I1 was a geologic f i e l d guide f o r t h e Keweenaw Peninsula. Volume Volume II was a geologic field guide for the Keweenaw Peninsula. The Annual Annual Banquet Banquet was was held h e l d on on May May 12, 1 2 , 1983 1983 and and was was attended a t t e n d e dby by around around100 100 The people. Burt B u r t Boyum Boyum was was awarded awarded the t h e Institute's I n s t i t u t e 's Goldich ~ o l d i c Medal. hMedal. Unfortunately Unfortunately people. Burt was was o u t of of the the country countryand and Roy Roy Koski Koski accepted accepted the t h e medal medal in i n his h i sabsence. absence. Burt out Bob Reed was thanked by Ralph Marsden f o r h i s dedicated s e r v i c e f o r many years Bob Reed was thanked by Ralph Marsden for his dedicated service for many years a s the I n s t i t u t e ' s Secretary-Treasurer; this was Bob's l a s t meeting i n t h a t role. role. as the Institute 's Secretary—Treasurer; this was Bob 's last meeting in that The banquet address was given by D r . Stephen E. Kesler, University of Michigan, The banquet address was given by Dr. Stephen E. Kesler, University of Michigan, the CaribCaribwho compared n t r a s t e d precious e p o s i t s of e r t i a r y age age in i n the who comparedand andc ocontrasted preciousmetal metalddeposits of TTertiary bean to t o those thoseof ofArchean Archean age age in i nCanada. Canada. His H i s stimulating s t i m u l a t i n g talk t a l k provided provided a a fine fine bean touch tto o a meal meal of touch of prime primerib rib and andtrimmings. trinings. Dean Rossell, Rossell, graduate graduate student s t u d e n t at a tMichigan Michigan Technological Technological U n i v e r s i t y , received received Dean University, cashaward award of $200 ffor o r presenting p r e s e n t i n g the t h e best b e s t paper paper by by aa student. s t u d e n t . His of $200 H i s paper paper aa cash was eentitled n t i t l e d "Alteration " A l t e r a t i o n of of the the Deer Deer Lake e r i d o t i t e iin n tthe he v i c i n i t y of of the the was LakePPeridotite vicinity Ropes gold gold mine, mine, Marquette Marquette County, County, Michigan". Michigan". Dean Dean was co-leader of t h e ield Ropes was co—leader of the ffield ttrip r i ptot othe t h eRopes Ropesgold goldmine. mine. The The Best Student Paper Paper Coumtittee Committee recognized Best Student recognized aalll l s t u d e n t s for f o r their their good good p r e s e n t a t i o n s and i f f i c u l t to t o pick pick aa winner. winner. students presentations andfound founditit ddifficult the I n s t i t u t e and it is hoped t h a t t h Students p l a y an important r o l e i n Students play an important role in the Institute and it is hoped that thee q u a l i t y of of their theirpapers paperscontinues continuestot oimprove. improve. quality The Board Board of of Directors D i r e c t o r s of of the t h e Institute I n s t i t u t e met m e t on on May May 12, 12, 1983. 1983. Present Present at a t the the The T . J . Bornhorst (Chairman), D.L. Southwick, P.E. Myers, M.F. meeting were: meeting were: T.J. Bornhorst (Chairman), D.L. Southwick, P.E. Myers, M.F. Kehlenbeck, R.C. R.C. Reed Reed (Secretary-Treasurer) (Secretary-Treasurer) and and G.L. G.L. LaBerge LaBerge (incoming (incoming 1984 1984 Kehienbeck, Chairman). The Board took t h e following a c t i o n : Chairman). The Board took the following action: 1. 1. Accepted with w i t h thanks thanks the t h e continued continued offer o f f e r of of the t h e Minnesota Minnesota Geological Geological Survey Survey Accepted l i s t of of the t h e I.L.S.G. t o maintain maintain and and update update the t h e mailing mailing list I.L.S.G. to 2. 2. Accepted with w i t h enthusiasm enthusiasm the t h e offer o f f e r of of the t h e Ontario Ontario Geological Geological Survey Survey to t o host host Accepted t h e 31st 31st I.L.S.G. I.L.S.G. at a t Kenora, Kenora, Ontario Ontario in i n 1985. 1985. the 3. 3. Agreed that t h a t financing financing for f o r the t h e 1985 1985 meeting meeting in i n Kenora Kenora should should go go through through the the Agreed M.M. Kehlenbeck, Kehlenbeck, custodian. custodian. Canadian I.L.S.G. I.L.S.G. account, account, M.M. Canadian V �4. 5. Moved that t h a t the t h e summary summary report r e p o r t of of the t h e Chairman Chairman from from the t h e previous previous year, year, selection Award Constituion, the Goldich the t h e I n s t i t u t e ' s c o n s t i t u t i o n , t h e Goldich Award s e l e c t i o n rules, rules, a a list l i s t of of and location, and the address of the Secretary—Treasurer previous Institutes I n s t i t u t e s and l o c a t i o n , and t h e address of t h e Secretary-Treasurer (where previous Proceedings can be be obtained) obtained) be (where previous Proceedings Volumes Volumes can be included included iin n the the Proceedings Proceedings Volume. Volume. Institute's basis of Instructed I n s t r u c t e d that t h a t the t h e Chairman Chairman of of each each Institute I n s t i t u t e should should budget budget on on the t h e b a s i s of Excess money can be Excess money can be pre—registration w i t h the t h e goal g o a l of of breaking breaking even. even. p r e - r e g i s t r a t i o n with accumulated without I. I.R.S. R. S penalty. penalty. accumulated without . Moved Moved t hthat a t t transportation r a n s p o r t a t i o n to t o and and from from the t h e meeting meeting will w i l l be be paid p a i d for f o r the the This cost should be included in needed. This c o s t should be included in Goldich Award recipient, if Goldich Award r e c i p i e n t , i f needed. the t h e budget budget for f o r each each meeting. meeting. 7. Moved Moved that t h a t the t h eChairman Chairman of of each each Institute I n s t i t u t edecide decidewhat what expenses expenses are a r e reasonable reasonable 6. for f o r field f i e l d trip t r i ppresentation. presentation. 8. I t was was not n o t used used enough enough Decided to Decided t o discontinue discontinue the t h e I.L.S.G. I.L.S.G. Bibliography. Bibliography. It to of eeffort t o warrant warrant the t h e amount amount of f f o r t involved involved in i n updating. updating. 9. Discussed publication Discussed tthe he p u b l i c a t i o n of of aa special s p e c i a volume l volume of of papers papers as a s requested requested by by Tabled this issue until the 50th (via Dr. LaBerge). Dr. D r . Larue Larue ( v i a D r . LaBerge). Tabled this i s s u e u n t i l t h e 50th IInstitute. nstitute. 10. Noted papers extraneous extraneoust oto tthe Noted t that h a t papers h e ffield i e l d trip t r i pshould shouldnot n o tbe bepublished published in in BoardofofDDirectors' The Board i r e c t o r s ' ddesire e s i r e iis s to t o keep keep the the Proceedings Proceedings Volume. Volume. The the the Proceedings Proceedings Volume Volume uuncluttered. ncluttered. II. Appointed 1L.i.. i ~ . Kehlenbeck ~ . ( r e p r e s e n t i n g academia) academia) tto (representing o a a 3-year 3-year term term on on the the Medal Selection S e l e c t i o nCommittee. Committee. Dick Goldich Medal t h e1984 1984Chairman Chairman of Dick Buchheit Buchheit iiss the this thisCommittee. Committee. The The Board s t r u c t s the t h e Coxrnittee Committee tto o d e l i v e r the t h e name name of Boardi ninstructs deliver of t h e nominee nominee tto o the t h e Chairman Chairman by a t e r than than the by no no llater 12. of each each year. year. January 11 of January is Nominated G . Morey, Morey, JJ. . K a l l i o k o s k i , and r t hthe e I Institute's nstitute's Nominated G. Kalliokoski, and Paul PaulMyers Myersf ofor deadline necessary for f o r budget budget purposes. purposes. deadline i s necessary This This Secretary-Treasurer and i r e c t e d the t h e Chairman Chairman to t o accept accept other o t h e r nominations nominations Secretary—Treasurer andddirected from from the t h e membership. membership. The i l l be l e c t e d by by closed closed The new new Secretary-Treasurer Secretary—Treasurerw will be eelected b a l l o t vote vote of ofthe t h emembers members p resent. ballot present. 13. 14. I n s t r u c t e d the t h e new new Secretary-Treasurer o hold S . I.L.S.G. funds in i n an an Instructed Secretary-Treasurer tto hold UU.S. I.L.S.G. funds i n t e r e s t - b e a r i n g account account that t h a tpays pays the t h emaximum maximum i ninterest t e r e s t rrate a t e obtainable obtainable interest-bearing while high lliquidity. while maintaining maintaining high iquidity. i l l sell s e l land andhold holdProceedings Proceedings I n s t r u c t e d that t h a tthe t h eSecretary—Treasurer Secretary-Treasurer wwill Instructed Volumes from Volumes fromprevious previous meetings. The The eextra x t r a unsold unsold copies copies of of the t h eProceedings Proceedings Volumes w will i l l be o the t h e Secretary—Treasurer Volumes be given given tto Secretary-Treasurer aat t the t h e conclusion conclusion of of each each meeting. The eextra x t r a copies i l l be e p t until u n t i l the t h e next next year's y e a r ' smeeting meeting and and The copies wwill be kkept a f t e r that that after can be be discarded. discarded. Copies Copies of of previous previous volumes volumes can can be be obtained obtained can from t h e Secretary-Treasurer a t t h e c o s t of Xerox, s h i p p i n g and handling. from the Secretary—Treasurer at the cost of xerox, shipping and handling. The i l l be i s t e d on on the t h e back back of of the the The address address of of the t h e Secretary—Treasurer Secretary-Treasurer w will bellisted Proceedings Volume s o so t h athat t o rorders d e r s can r e c t e d t otot that hat o ffice. Proceedings Volume canbebed idirected office. 15. I n s t r u c t e d that t h a t the t h eSecretary-Treasurer Secretary-Treasurer print p r i n t I.L.S.G. I.L.S.G. s t a t i o n a r y and and make make Instructed stationary it available a v a i l a b l e to t o the t h e Chairman Chairman of of each each meeting. meeting. it Vi �16. 16. Moved that not be formalized beyond tthat t h a t the t h e Institute Institute n o t be formalized beyond h a t stated s t a t e d in i n the the Constitution. Constitution. 17. 17. Discussed and and suggested that t h a t group group travel t r a v e l arrangements arrangements for f o r the t h e 1985 1985 meeting in i n Kenora, Kenora, Ontario Ontario be investigated. i n v e s t i g a t e d . Ideas Ideas for f o r such transportation transportation included northward, perhaps perhaps arranged by by a UMD UND faculty included a bus from Duluth northward, faculty liaison, l i a i s o n , or o r possibly p o s s i b l y aa chartered c h a r t e r e d plane plane flight. flight. The The election e l e c t i o n for f o r aa new new Secretary—Treasurer Secretary-Treasurer was was held h e l d on on May May 13, 13, 1983. 1983. J. J. Kalliokoski, Kalliokoski, Department of of Geology and Geological Geological Engineering, Engineering, Michigan I ' m sure s u r e that t h a t the t h e Institute Institute U n i v e r s i t y , was elected e l e c t e d to t o the t h e post. p o s t . I'm Technological University, will w i l l benefit b e n e f i t from from Joe J o e 's ' s forthcoming effort e f f o r t as a s Secretary—Treasurer. Secretary-Treasurer. Financially Financially the 29th 29th I.L.S,G. I.L.S.G. concluded concluded with w i t h aa small small deficit. d e f i c i t . There is i s about about $2,900 $2,900 in in the U.S. account account and and about about $3,300 in i n the t h e Canadian Canadian account. account. t h e Institute's I n s t i t u t e ' s U.S. t a s k of t h e 29th 29th I.L.S.G. I.L.S.G. was an an enlightening e n l i g h t e n i n g experience experience in i n more more The task of organizing the ways than than one. I'm I ' m glad g l a d my responsibilities r e s p o n s i b i l i t i e s are a r e ending ending and and pass pass on on the t h e job job of of chairman Chairman to t o Gene Gene LaBerge, LaBerge, University University of o f Wisconsin, Wisconsin, Oshkosh. Oshkosh. 7Tdi Respectfully R e s p e c t f u l l y submitted, submitted, Theodore J. Bornhorst Bornhorst Theodore J. Chairman 29th 29th I.L.S.G. I.L.S.G. September September 21, 21, 1983 1983 , Houghton, Houghton, Michigan Michigan Vii vii �CALENDAR CALENDAR OF OF EVENTS EVENTS AND AND PROGRAM PROGRAII MONDAY, MONDAY, APRIL A P R I L 23, 2 3 , 1984 1984 - 6:00 6:00 p.m. p.m. - 9:00 9:00 p.m. p.m. DINNER DINNER AND AND ORIENTATION O R I E N T A T I O N FOR F O R PARTICIPANTS P A R T I C I P A N T S IN IN FIELD I. - Four Four Seasons Seasons Club, C l u b , Beecher, Beecher, F I E L D TRIP T R I P I. Wisconsin. Wisconsin. - TUESDAY, TUESDAY, APRIL A P R I L 24, 2 4 , 1984 1984 - 8:00 8:00 a.m. a.m. - 6:00 6:00 p.m. p.m. FIELD F I E L D TRIP T R I P I: I : GEOLOGY GEOLOGY OF O F THE THE EARLY EARLY PROTEROZOIC PROTEROZOIC ROCKS 1, Dunbar Dunbar ROCKS IN I N NORTHEASTERN NORTHEASTERN WISCONSIN-—Day WISCONSIN--Day 1, Gneiss-—Granitoid Sims, G n e i s s - - G r a n i t o i d Dome--P.K. Dome--P.K. S i m s , K.J. K . J . Schulz, Schulz, and E. Peterman. and ZZ.E. Peterman. . WEDNESDAY, WEDNESDAY, APRIL A P R I L 25, 2 5 , 1984 1984 - 8:00 8:00 a.m. a.m. - 4:00 4:00 p.m. p.m. - 7:00 p.m. - 10:00 1 0 : O O p.m. p.m. 7 : 0 0 p.m. -- 10:00 10:00 p.m. p.m. FIELD F I E L D TRIP T R I P I: I: GEOLOGY GEOLOGY OF O F THE THE EARLY EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS IN I N NORTHEASTERN NORTHEASTERN WISCONSIN--Day WISCONSIN--Day 2, 2, The T h e northeastern northeastern Wisconsin W i s c o n s i n volcanic volcanic rocks-— rocks-K.J. K.J. Schulz, Schulz, P.K. P . K . Sims, S i m s , and and Z.E. Z . E . Peterman. Peterman. REGISTRATION, R E G I S T R A T I O N , LOBBY, LOBBY, HOLIDAY HOLIDAY INN, I N N , WAUSAU WAUSAU 7:00 7:00 p.m. p.m. - 10:00 1 0 : O O p.m. p.m. SMOKER SMOKER AND AND CASH CASH BAR, BAR, HOLIDAY HOLIDAY INN, I N N , WAUSAU WAUSAU 7:00 p.m. 7 : 0 0 p.m. POSTER POSTER PRESENTATIONS PRESENTATIONS Bruce and J.K. J . K . Greenberg--EARLY G r e e n b e r g - - E A R L Y PROTEROZOIC PROTEROZOIC B r u c e A. A. Brown B r o w n and STRUCTURES OF O F NORTHEASTERN NORTHEASTERN WISCONSIN W I S C O N S I N AS AS CONSTRAINTS CONSTRAINTS STRUCTURES ON ON PENOKEAN PENOKEAN TECTONIC TECTONIC MODELS MODELS A 1 U. U. Faister--MINERALOGY F a l s t e r - - M I N E R A L O G Y OF OF PEGMATITES PEGMATITES IN I N THE THE WAUSAU WAUSAU Al PLUTON, PLUTON, MARATHON MARATHON COUNTY, COUNTY, WISCONSIN WISCONSIN King, John John H. H. Karl, K a r l , John John S. S . Kiasner, Klasner, and and E l i z a b e t h R. R. King, Elizabeth William W i l l i a m J. J. Jones-—COMPOSITE J o n e s - - C O M P O S I T E MAGNETIC MAGNETIC MAP MAP OF O F WISCONSIN WISCONSIN PRECAMBRIAN PRECAMBRIAN FROM FROM NEW NEW COMPILATION COMPILATION OF O F DIGITAL DIGITAL AEROMAGNETIC AEROMAGNETIC DATA DATA Dennis and Joseph Joseph ManCUSO--GEOLOGY Mancuso--GEOLOGY OF O F THE T H ELONE LONE D e n n i s Mackovjak M a c k o v j ak and MOUNTAIN MOUNTAIN GOLD GOLD PROSPECT, P R O S P E C T ,NORTHEAST NORTHEASTNEVADA NEVADA M.G. Mudrey, M u d r e y , Jr. Jr. a n d Kalliokoski--METALLOGENY _J. Kalliokoski--METALLOGENY THE M.G. andJ. OFO FTHE LAKE LAKESUPERIOR S U P E R I O RPRECAMBRIAN PRECAMBRIAN P.A. METAMORPHIC MINERAL MINERALASSEMBLAGE ASSEMBLAGE P . A . Nielsen--MDB N i e l s e n - - M D B -- AA METAMORPHIC DATABASE FOR FOR THE THE PRECAMBRIAN PKECAMBRIAN OF O F THE THE LAKE LAKESUPERIOR SUPERIOR DATABASE DISTRICT DISTRICT viii viii �- WEDNESDAY, WEDNESDAY^ A APRIL P R I L 225, 5 , 1984 - continued P.A. P.A. Nielsen--METAMORPHIC Nielsen--METAMOFSHIC CONDITIONS CONDITIONSAND ANDEVOLUTION EVOLUTION A SUPRACRUSTAL SEQUENCE INTRUDED OF SEQUENCE INTRUDED BY BY THE THE OF DUNBAR GNEISS, G N E I S S f FLORENCE AND AND MARINETTE L W I N E T T E COUNTIES, COUNTIESf NORTHEASTERN NORTHEASTERN WISCONS WISCONS IN IX Hemzacek--PRECAMBRIAN J. Hemzacek--PRECAMBRIAN E.C, Jr., J. Feng and J. E . C o PPerry, e r r y , Jr., EVAPORITES: EVAPORITES: PRESERVATION PRESERVATION OF OF SULFATE SULFATE IN I N QUARTZ QUARTZ PSEUDOMORPHS AFTER GYPSUM PsETJDoMoR2Hs *WL PPetro——CRYSTALLIZATION *WmLa e t r o - - C R Y S T A L L I Z A T I O N HHISTORIES I S T O R I E S OF OF'EARLY FARLY PROTEROZOIC PROTEROZOIC PLUTONS FROM FROM NORTHERN NORTHERN WISCONSIN *ristopher A. Scholz-—LATE POST-GLACIAL *Christopher A. S c h o l z - - L AAND T E AND POST-GLACIALLACUSTRINE LACUSTRINE SEDIMENT DISTRIBUTION LANl SUPERIOR SUPERIOR SEDIMENT D I S T R I B U T I O N IN I NWESTERN WESTERN LAKE FROM SSEISMIC FROM E I S M I C REFLECTION EW?LECTION PROFILES PROFILES Michael J.. Schwartz M ichael J S c h w a r t z and P.A. P.A. Nielsen--REGIONAL N i e l s e n - R E G I O N A L CONTROLS CONTROLS ON ON ARCHEANMETALLOGENY METALLOGENY THEUPPER UPPER PENINSULA PENINSULA OF ARCHEAN I NINTHE OF MICHIGAN MICHIGAN *Jjfl Sikkila-—PETROGRAPHIC GEOCHEMICAL *Kevin S i k k i l a - - P E T R O G R A P H I CAND AND GEOCHEMICAL STUDY STUDY OF OF THE THE MOUNTBOHENIA BOHIA STOCK, LAKEVOLCANICS, VOLWICS, MOUNT STOCK,PORTAGE PORTAGE LAKE KEWEENAW PENINSULA, MICHIGAN KENEENAW PENINSULA, MICHIGAN W.R. TOTO THE GEOCHRONOLOGY W.R. Van VanSchmus-—RECENT Schmus--=CENT CONTRIBUTIONS CONTRIBUTIONS THE GEOCHRONOLOGY OF OF O F THE PRECAMBRIAN O F WISCONSIN WISCONSIN NOTE; All Best e l i g i b l efor f o rthe the B e sStudent t S t u d e nPaper t P a p e Award r Award NOTE: A l l Papers P a p e r s eligible are marked wwith an aasterisk are i t h an s t e r i s k ((*) *I . APRIL THURSDAY, THURSDAYf A P R I L 226, 6 , 1984 1984 77:30 : 3 0 aa.m. .m. - 4:30 4 : 3 0 p.m. p.m. REGISTRATION, LOBBY, REGISTRATION, LOBBY, HOLIDAY HOLIDAY INN, I N N fWAUSAU WAUSAU 8:00 a.m. a.m. 8:OO -- 5:00 pp.m. 5:OO .m. PRESENTATIONS needn onot POSTER PRESENTATIONS t sstay tay ( A u(Authors t h o r s need with posters) w i t h posters) - .m. 8:OO a.m. - 11:50 aa.m. 8:00 a.m. TECHNICAL SSESSION E S S I O N I, I, Kalk, Kalk ,Co—chairmen Co-chairmen John S. John S . Kiasner, Klasner,Thomas T h o m a s R. R. 8:00 a.m. 8:OO a.m. WELCOME 3 0 t30th h I -I.L.S.G.-—Gene L.S . G - - - G e n e L.L. LaBerge LaBerge WELCOME TO TO 88:10 : l O a.m. a.m. Warren W a r r e nC.CDay-—GEOLOGY . Day--GEOLOGY OF OF THE THERAINY RAINY LAKE LAKE AREA, AREA, NORTHERN MINNESOTA-REVISITED NORTHERN MINNESOTA-=VISITED 8:30 a.m. 8:30 a-m- 8:50 a.m. *Steven * S t e v e n Osterberg——STRATIGRAPHY O s t e r b e r g - - S T R A T I G R A P H Y OF O F THE THE HEADWAY-COULEE MASSIVESULZHIDE SULPHIDE PPROSPECT, HEADWAY-COUUE MASSIVE ROSPECTf M a AREA, m ONTARIO ONTARIO NORTHERN NORTHERN ONAMAN ONAMANLLAKE AREA, NW PPeter e t e r J. u d l e s t o n and David D a v i d L. L . Southwick--THE Southwick--THE J. H Hudleston -ROLE SHEAR IN I N DEFORMATION DEFORMATION ROLE OF TRANSCURRENT SHEAR OF THE ARCHEAN ARCHEAN ROCKS F THE VERMILLION VERMILLION OF THE ROCKS OOF DISTRICT, D I S T R I C T , MINNESOTA MINNESOTA ix �- continued continued THURSDAY, APRIL A P R I L 26, 2 6 # 1984 1984 THURSDAY, 9:10 a.m. D a v i d P. P . Moecher M o e c h e r and and L.G. L.G. Medaris, Medaris, Jr.--LATE Jr.--LATE David ARCHEAN METAMOWHIC CONDITIONS AT GRANITE ARCHEAN METAMORPHIC CONDITIONS AT GRANITE F A L L S f MINNESOTA MINNESOTA FALLS, 9:30 a.m. Anth.ony Mariano M a r i a n o and andH.H. H.H. t/oodard__POTASSIUM Woodard--POTASSIUM Anthony LMETASOMATISM OF TRONDHJEMITE MIGMATITE METASOMATISM OF TRONDHJEMITE MIGMATITE WALLROCK, VERMILION COMPLEXt NORTHERN WALLROCK, VERMILION COMPLEX, NORTHERN MIrnSOTA MINNESOTA 9:50 a.m. COFFEE BREAK 10:10 a.m. and Gregory G r e g o r y Mursky-—MOBILIZATION Mursky--MOBILIZATION R.L. Hackenberg H a c k e n b e r g and R.L. O F URANIUM AND THORIUM WITHIN THE REPUBLIC EPUBLIC OF URANIUM AND THORIUM WITHIN THE METAMORJ?HIC NODE, NORTHERN MICHIGAN METAMORPHIC NODE, NORTHERN MICHIGAN 10:30 a.m. Anthony W. h e p e c k and . J . Bornhorst-BornhorsteAnthony W. SShepeck andTT.J. 10:50 a.m. Thomas J. K i r s l i n g C.W. , C.W. Montgomery, M o n t g o m e r y , arid and E.C. E.C. Thomas J. Kirsling, CHARACTERIZATION OF THE ORE HOST ROCK AT CHARACTERIZATION OF THE ORE HOST ROCK AT THE ROPES GOLD GOLD MINE, MINE, ISHPEMING, ISHPEMING,MICHIGAN MICHIGAN THE ROPES P e r r Jr.-—RB-SR y Jr.--RB-SRANDAND OXYGEN ISOTOPE SYSTEMATICS Perry OXYGEN ISOTOPE SYSTEMATICS OFARCHEAN ARCHEAN GREY G m GNEISSES G N E I S S E SOFOF THE SOUTHWESTERN OF THE SOUTHWESTERN BEARTOOTH MOUNTAINS MOUNTAINS BEARTOOTH 11:10 a.m. KarlE.ESeifert--TRACE . S e i f e r t - - T F l AELEMENT C E ELEMENT GEOCHEMISTRY O r Karl GEOCHEMISTRy or 1 1 ~ 3a.m. 0a . m 11:30 P a t r i c Ryan k R y a and n and P aW. u l Weiblen——pT W. W e i b l e n - - P T Patrick Paul SOME LAICE SUPERIOR JCTWEENAWAN B A S I C LAYERE.. SOME LAKE SUPERIOR KEWEENAWAN BASIC LAYERL INTRUSIONS INTRUS IONS AND N I AND NI ARSENIDE MINERALS I N THE DULUTH COMPLEX ARSENIDE MINERALS IN THE DULUTH COMPLEX U : s O a.m. a.m. 11:50 LUNCH BREAK BREAK LUNCH ANNUAL MEETING, I L .S .G . BOARD OF DIRECTORS ANNUAL MEETING, I.L.S.G. BOARD OF DIRECTORS p.m. -1 : 2 0 p.m. 1:20 4 : 2 0 p.m. p.m. 4:20 TECHNICAL S E SESSION S S I O N I I tII, T hTheodore e o d o r e J.J. B ornnorst, TECHNICAL Bornhorst, J a m e s I. H o f f m a n , C o c h a i r m e n James I. Hoffman, Co—chairmen 1:20 p.m. andTheodore TheodoreJ. J. Bornhorst-J a m e s B. B. Paces P a c e sand James Bornhorst—— 1:40 p.m. S.A. H a u c k and E.W. Kendall--COMPARISON OF MIDDLE S.A.Hauck and E.W. Kendall--COMPARISON OF MIDDLE ALTEFATIONt PARAGENESIS AND AGE ASSOCIATE ALTERATION, PARAGENESIS AND AGE ASSOCIATE WITH NATIVE NATIVE COPPER COPPER MINERALIZATION MINERALIZATION OF OF THE THE WITH KEZGGARGE FLOWf KEWEENAW PENINSULAf MICHIGAN KEARSARGE FLOW, KEWEENAW PENINSULA, MICHIGAN PROTEROZOIC IRON OXIDE RICH RICH ORE O m DEPOSITS. DEPOSITS. PROTEROZOIC IRON OXIDE MID-CONTINENT S .A. SOUTH AUSTRALIA, SWEDEN, U MID-CONTINENT, U.S.A., SOUTH AUSTRALIA, SWEDEN, AND T m PEOPLES =PUBLIC OF CHINA AND THE PEOPLES REPUBLIC OF CHINA . 2 :00 p .m. R.D. P o w e l l - - C L I M A T I C INFERENCES OF IRON-E'OFlMATION R.D. Powell-—CLIMATIC INFERENCES OF IRON-FORMATION FROM ASSOCIATED DIAMICTI!I'E F A C I E S SEQUENCES, FROM ASSOCIATED DIANICTITE FACIES SEQUENCES, GRIQUALAND WEST SUPERGROUP, SOUTH AFRICA GRIQUALAND WEST SUPERGROUP, SOUTH AFRICA x �- THURSDAY, THURSDAY APRIL A P R I L 26, 26 1984 1984 - continued continued 2:20 p.m. . E. E . Schuessler S c h u e s s l e r and and E.C. E .C. Perry, P e r r y Jr.-—METAMORPHISM Jr --LMETAMORPHISM AND GRIQUATOWN GRIQUATOWN IRON IRON FORMATIONS OF OF KtJRUMAN KURUMAN AND F O M T I O N S AND AND . ASSOCIATED ASSOCIATED MAKGANYENE L W G A N Y E N E DIAMICTITE, D I A M I C T I T E l CAPE CAPE PROVINCE, PROVINCEl SOUTH SOUTH AFRICA: AE'RICA: AASTABLE STABLE ISOTOPE I S O T O P EINVESTIGATION INVESTIGATION 2:40 2 : 4 0 p.m. p-m- COFFEE COFFEE BREAK BREAK 3:00 3:OO p.m. p-m. *Erik AS TECTONIC * E r i k G. G. Shaw——DIKES Shaw--DIKES AS TECTONIC INDICATORS INDICATORS IN I N THE THE EASTERN EAS'IERN LAKE LAKE SUPERIOR SUPEFSORREGION-STRUCTURAL EGION-STRUCTURAL AND AND PALEOMAGNETIC PALEOMAGNETIC CONSIDERATIONS CONSIDERATIONS 3:20 3:20 p.m. pem. *Ted * T e d R. Repesky--MAGNETOTELLURIC &pesky--mGNETWEUURIC P R O F I L E OF OF THE THE PROFILE JACOBSVILLE JACOBSVILLE SANDSTONE SANDSTOm 3:40 p.m. W.F. E. Ranjthun--PRELININARY Kean D. D.Mercer M e r c eand r and E . Ramthun--PRELIMINARY W.F. Kean, PALEOMAGNETIC PALEOMAGNETIC RESULTS FROM FROM THE THEBARABOO BARABOO QUARTZITE AND THE THE ASSOCIATED M S O C I A T E D RHYOLITE F S Y O L I T E AND AND QUARTZITE AND GRANITE WISCONSIN GRANITE INLIERS I N L I E R SOF OFSOUTH SOUTHCENTRAL CENT= WISCONSIN 4:00 p.m. L.G. MICROSTRUCTURE Soroka and and J. J. Josch--MORPHOLOGY, Josch--MORPHOLOGYl L.G. Soroka AND AND ACCRETION A C C E T I O N RATE RATE OF OF RECENT RECENT ALGAL ALGAL STROMATOLITES STROMATOLITES FROM LAKE,OTTERTAIL OTTERTAILCOUNTY, COUNTYl MINNESOTA MINNESOTA FROM EAGLE EAGLE LAKE, 4:20 p.m. Richard Richard 6:00 p.m. SOCIAL S O C I A L HOUR--CASH HOUR--CASH BAR BAR. 7:00 ANNUAL ANNUAL BANQUET BANQUET p.m. A. Pau.U-—LOCALIZED P a u l l - - L O C A L I Z E D ACCUMULATIONS ACCUMULATIONS OF O F UPSIDE UPSIDE A. DOWN !XWN TRILOBITE T R I L O B I T E PARTS PARTS IN I N CAVITIES C A V I T I E S WITHIN WITHIN A A SILUBIAN S I L U R I A N REEF REZE' AT AT RACINE, R A C I N E l WISCONSIN WISCONSIN Announcement of 1985 1985 Meeting M e e t i n g in i n Kenora, Kenoral Ontario Ontario A n n o u n c e m e n t of P r e s e n t a t i o n of of Goldich Goldich Award A w a r d to t o R. R. W. W. Ojakangas Ojakangas Presentation by by S.S. S.S. Goldich Goldich G u e s t Speaker-—Dr. Speaker--Dr. Charles Meyer Meyer Guest Charles "THE "THE ORE O m METALS METALS IN I N EARTH W T H HISTORY" HISTORYtt FRIDAY, 2 7 , 1984 1984 FRIDAYl APRIL A P R I L 27, 8:00 8 : O O aa.m. . m . -- 1 11:50 1 : 5 0 a . a.m. m. 8:00 a.m. 8:30 a.m. T E C H N I ~ SESSION S E S S I O III, N I I I lKlaus Klaus J. J. Schulz S c h u l z and and TECHNICAL Robert Robert L. L. Bauer, B a u e r Co—chairmen Co-chairmen P.K. Sims, S i m s lZ•.E. Z.E. Peterman, P e t e m a n # and and Klaus Klaus 3. J. Schulz—— Schulz-BK. AA PARTISAN THE EARLY EARLY PROTEROZOIC PROTEROZOIC PARTISAN REVIEW WZVIEW OF OF THE GEOLOGY OF OF WISCONSIN WISCONSIN AND AND ADJACENT ADJACENT MICHIGAN MICHIGAN GEOLOGY and D.L. D.L. Southwick--EARLY S o u t h w i c k - - E A R L Y PROTEROZOIC PROTEROZOIC G - B . Morey M o r e y and G.B. GEOLOGY GEOLOGY OF O F EAST-CENTRAL EAST-CENTRAL MINNESOTA-A MINNESOTA-A REVIEW W I E W AND AND REAPPRAISAL REAPPRAISAL xi �- FRIDAY, FRIDAYr APRIL A P R I L 27, 2 7 r 1984 1 9 8 4 - continued continued 8:50 8:50 a.rn. a.m. Grant G r a n t M. M. Young--THE Young--THE HURONIAN HURONIAN SUPERGROUP: SUPERGROUP: AN AN EXAMPLE EXAMPLE OF OF AN EARLY EARLY PROTEROZOIC PROTEROZOIC PASSIVE P A S S I V E MARGIN MARGIN SEQUENCE SEQUENCE 9:10 9:lO Gene J . Schulz S c h u l z and and Paul P a u l E. E. G e n e L. L . LaBerge, L a B e r g e , Klaus K l a u s J. Myers--THE Myers--THE PLATE TECTONIC HISTORY HISTORY OF OF NORTH NORTH CENTRAL CENTRAL WISCONSIN WISCONSIN a.m. a.m. 9:40 9 : 4 0 a.m. a.m. 10:10 1 O : l O a.m. a.m. COFFEE COFFEE BREAK BREAK Klaus 3. J. Schulz--EARLY S c h u l z - - E A R L Y PROTEROZOIC PENOKEAN PENOmN IGNEOUS IGNFOUS ROCKS OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION: REGION: GEOCHEMISTRY GEOCHEMISTRY AND AND TECTONIC TECTONIC IMPLICATIONS IMPLICATIONS 10:30 a.m. *Warren SM ISOTOPIC * W a r r e n Beck--ND Beck--ND AND ANDSM I S O T O P I C STUDIES S T U D I E S OF OF THE THE QUINNESEC I NNORTHEASTERN NORTHEASTERN QUINNFSEC AND AND HEMLOCK HEMLOCK FORMATIONS FORMATIONS IN WISCONSIN AND AND ADJACENT ADJACENT MICHIGAN MICHIGAN 10:50 a.m. Timothy CONSTRAINTS T i m o t h yB.B.Hoist--PENOKEAN Holst--PENOKEANTECTONICS: TECTONICS: CONSTRAINTS FROM GEOLOGY IIN FROM STRUCTURAL STRUCTURAL GEOLOGY N EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA 11:10 a.m. *Richard THE MULTIPLY * R i c h a r dC.CClark--MICROSTRUCTtJRES . Clark--MICROSTRUCTURES INI N THE MULTIPLY DEFORMED SLATE OF DEFORMED SLATE OF THE THETHOMSON THOMSON FORMATION, FORMATIONr EAST-CENTRAL MINNESOTA EAST-CENTMINNESOTA 11:30 a.m. G.A. Myers--BASEMENT F.W. Cambray, C a m b r a y t R.O. R . 0 . Meyer M e y eand r and F.W. G.A. Myers--BASEMENT COVER RELATIONS RELATIONS IN I NTHE TmMARQUETTE MARQUETTE AND AND REPUBLIC =PUBLIC COVER DISTRICTS, D I S T R I C T S MICHIGAN MICHIGAN 11:50 1 1 : S O a.m. a.m. -- 1:10 1 : l O p.m. p.m. LUNCH LUNCH BREAK BREAK 1:10 1 : l O p.m. p . m . -- 4:30 4 : 3 0 p.m. p.m. TECHNICAL S E SESSION S S I O N I V l IV, P e Peter t e r A.A.NNielsen i e l s e n and and TECHNICAL Gregory G r e q o r y Mursky, M u r s k y t Co—chairmen Co-chairmen 1:10 1 : l O p.m. p.m. and R.L. R.L. Sedlock--GEOLOGIC Sedlock--GEOLOGIC W.L. Ueng, U e n g l D.K. D.K. Larue L a r u e and W.L. HISTORY AND AND PALINSPASTIC P A L I N S P A S T I C RECONSTRUCTION RECONSTRUCTION OF OF THE THE HISTORY EARLY PROTEROZOIC PROTEROZOIC PENOKEAN PENOKBAN COLLISION C O L L I S I O N ZONE ZOm EARLY 1:30 1:30 p.m. p.m. John John S. S . K.lasner Klasner and and Dan D a n Osterfeld-—GRAVITY O s t e r f e l d - - G R A V I T Y MODELS MODELS OF OF GNEISS G N E I S S DOMES DOMES AND AND A A GRANITE GRANITE PLUTON PLUTON IN IN NORTHEASTERN IN NORTHEASTERN WISCONS WISCONSIN 1:50 p.m. FLichard O j a k a n g a s - - B A S ALOWER L LOWER PROTEROZOIC Richard W.W.Ojakangas--BASAL PROTEROZOIC GLACIOGENIC GLACIOGENIC FORMATIONS, FORMATIONStMARQUETTE MARQUETTE RANGE RANGE SUPERGROUP, SUPERGROTJF'r UPPER UPPER PENINSULA, PENINSULAr MICHIGAN MICHIGAN 2:10 p.m. S.S. S.S. 2:30 p.m. P.K. Sims--MIDDLE Z e l lE.E .Peterman P e t e n n a and n and Zell P.K. Sims--MIDDLE 2:50 p.m. COFFEE COFFEE BREAK BREAK Goldich--PRECAMBRIAN GEOCHRONOLOGY GEOCHRONOLOGY OF OF MINNESOTA MINNESOTA Goldich--PRECAMBRIAN PROTEROZOIC PROTEROZOIC EVENTS EVENTS IN I N NORTHEASTERN NORTHEASTERN WISCONSIN WISCONSIN AND AND ADJACENT ADJACENT RB-SR BIOTITE B I O T I T E AGES AGES MICHIGAN AS DEFINED BY MICHIGAN AS DEFINED BY RB-SR xii xii �FRIDAY, FRIDAY, APRIL A P R I L 27, 2 7 , 1984 1984 - continued continued - 3:10 p.m. Joseph Joseph J. J. Mancuso, M a n c u s o , Robert R o b e r t Brown, B r o w n , James J a m e s Harrison, Harrison, Alan Maharidge, M a h a r i d g e , Richard Richard Pennington P e n n i n g t o n and and Ronald R o n a l d Walden--GEOLOGY Walden--GEOLOGY OF O F THE THE GROVELAND GROVELAND MINE, MINE, FELCH DISTRICT, D I S T R I C T , MICHIGAN 3:30 p.m. Eugene E u g e n e C. C. Perry, P e r r y , Jr., J r a IS. S. Shen Shen and and C. C . Ueng—— Ueng-STABLE STABLE ISOTOPE I S O T O P E EVIDENCE EVIDENCEOF O FMETAMORPHISM METAMORPHISM AND AND HYDROTHERMAL ALTERATION, ALTERATION, NEGAUNEE NEGAUNEE IRON FORMATION, FORMATION, MICHIGAN MICHIGAN 3:50 p.m. Jeffrey K. G r e e n b e r g - - M A G H A T I S MAND AND THE BARABOO Jeffrey K. Greenberg--MAGMATISM THE BARABOO INTERVAL: INTERVAL: BRECCIAS, BRECCIAS, DIKES, D I E % , AND ANDMETASOMATISM METASOMATISM 4:10 p.m. Bruce AND THE THE B r u c eA.A.Brown-—LITHOLOGIC Brown--LITHOLOGIC DIVERSITY D I V E R S I T Y AND SEDIMENTARY-TECTONIC ENVIRONMENT DURING SEDIMENTARY-TECTONIC ENVIRO1ENT DURING DEPOSITION OF BARABOO B m O O INTERVAL INTERVAL (1760-1500 ( 1 7 6 0 - 1 5 0 0 MY) MY) D E P O S I T I O N OF ROCKS ROCKS 5:30 p.m. F I E L D TRIP TRIP II I1 DEPARTS DEPARTS FOR FOR IRON I R O N MOUNTAIN, MOUNTAIN, MICHIGAN MICHIGAN FIELD FROM FROM THE THE HOLIDAY HOLIDAY INN. INN. ( O v e r n i g h t in in (Overnight Dickinson D i d c i n s o n Inn.) IM.) SATURDAY, APRIL228, SATURDAY, APRIL 8 , 1984 1984 8:00 8:OO a.m. a.m. -- 5:00 5200 p.m. p.m. FIELD 11: EARLY EARLY PROTEROZOIC PROTEROZOIC TECTONOSTRATIGRApHIc TECTONOSTFUITIGRAPHIC F I E L D TRIP T R I P II: TERRANES TERRANES OF THE THE SOUTHERN SOUTHERN LAKE LAKE SUPERIOR S U P E R I O R REGION REGION by by W.L. W.L. Ueng, U e n g , D.K. D J C . Larue, L a r u e , R.L. R.L. Sedlock, S e d l o c k , and and D.A. D.A. Kasper, Kasper, Department D e p a r t m e n t of of Geology, Geology, Stanford S t a n f o r d University, Universityl Stanford, Stanford, California California 8:00 a.m. - 5:00 p.m. FIELD TRIP III: 111: GEOLOGY F I E L D TRIP GEOLOGY OF O F THE THE WAUSAU WAUSAU SYENITE S Y E N I T E COMPLEX, COMPLEX, by Paul P a u l E. E . Myers, Myers, Geology G e o l o g y Department, D e p a r t m e n t , University U n i v e r s i t y of of by W i s c o n s i n - E a u Claire, C l a i r e , Eau E a u Claire, C l a i r e , Wisconsin Wisconsin Wisconsin—Eau xiii xiii �(1) -I C) -I (1) w ABSTRACTS �Nd Studies Nd and and Sr S r Isotopic I s o t o p i c --S t u d i e s of of the t h e Quinnesec Quinnesec and --Northeastern and Adjacent Michigan N o r t h e a s t e r n Wisconsin Michigan Hemlock Hemlock Formations Formations in WARREN WAREEN BECK BECK (Dept. (Dept. of of Geology Geology and and Geophysics, Geophysics, University U n i v e r s i t y of of Minnesota, Minnesota, Minneapolis, 55455) Minneapolis, MN 55455) The Proterozoic P r o t e r o z o i c Penokean events e v e n t s of of the t h e southern s o u t h e r n Lake Lake Superior S u p e r i o r region region have recently terms of of Phanerozoic plate r e c e n t l y been been interpreted i n t e r p r e t e d iii i n terms p l a t e tectonic tectonic Two fundamentally fundamentally different d i f f e r e n t terrains t e r r a i n s may be found juxtaposed juxtaposed models. in i n the t h e northern n o r t h e r n Wisconsin—Upper Wisconsin-Upper Michigan Michigan region. r e g i o n . The northern n o r t h e r n terrain terrain has been interpreted i n t e r p r e t e d to t o represent r e p r e s e n t a continental c o n t i n e n t a l margin, margin, while w h i l e the the has terrain southern i s interpreted i n t e r p r e t e d to t o represent r e p r e s e n t an an s o u t h e r n volcano—plutonic volcano-plutonic t e r r a i n is The Penokean is interpreted i n t e r p r e t e d to t o represent r e p r e s e n t aa i s l a n d arc. arc. Penokean Orogeny Orogeny is island collision The following c o l l i s i o n event event between between these t h e s e two two terraines. terraines. f o l l o w i n g isotopic isotopic study study supports s u p p o r t s the t h e contention c o n t e n t i o n tthat h a t such models are a r e applicable a p p l i c a b l e to t o the the Penokean Penokean events. events. REE REE patterns p a t t e r n s from from tholeiitic t h o l e i i t i c basalts b a s a l t s and and gabbros gabbros from from the t h e southern southern terrain yield terrain y i e l d extremely LREE W E depleted d e p l e t e d signatures s i g n a t u r e s (Klaus (Klaus Schultz, S c h u l t z , 1983) 1983) similar to t o those t h o s e of of MOR MOR basalts. b a s a l t s . In I n contrast, c o n t r a s t , tholeiltes t h o l e i i t e s and and gabbros gabbros from the t h e northern n o r t h e r n terrain t e r r a i n yield y i e l d LREE LREE enriched e n r i c h e d patterns p a t t e r n s (Fox, (Fox, 1983), 19831, resembling continental c o n t i n e n t a l flood f l o o d basalt b a s a l t signatures. signatures. Tholeiitic and gabbros T h o l e i i t i c bbasalts a s a l t s and gabbros from the t h e southern s o u t h e r n terrain t e r r a i n define d e f i n e aa 143Nd/144Ndi sisochron with4.17 .95, . 9 5 ,and andananage a g eof of 1871 1871 ++- 57 57 my my o c h r o n withE& 4-17+ + (1~) . The The . age is i s interpreted i n t e r p r e t e d as a s aa ~crystallization r y s t a l l i z a t i o nage a g e and and is i s similar yimilar to U/Pb ages ages of of 1860 my o obtained t o U/Pb b t a i n e d for f o r several s e v e r a l granitic g r a n i t i c plutons p l u t o n s found found in in In the t h e southern s o u t h e r n terrain. terrain. I n contrast, c o n t r a s t , the t h e basalts b a s a l t s and and gabbros gabbros from from the the Other northern do not n o r t h e r n terrain t e r r a i n do n o t define d e f i n e aa Nd Nd isochron. isochron. Other isotopic i s o t o p i c data data suggest suggest however however that t h a t they they are a r e about about the t h e same same age age or o r slightly s l i g h t l y older. older. Calculating C a l c u l a t i n g initial i n i t i a l ratios r a t i o s for f o r 10 10 samples samples from from the t h e northern n o r t h e r n terrain terrain yields average 1143Nd/144Nd ofEdd=-2. Ed22.O4 This y i e l d s an average 4 3 ~ d / 1 4 4 ~ diinitial n i t i a l of 04 ++ 4.2. 4.2. This suggests suggests that t h a t the t h e source s o u r c e regions r e g i o n s for f o r the t h e two two terrains t e r r a i n s are ar; distinct, d i s t i n c t , with w i t h the the southern d e p l e t e d mantle source. source. s o u t h e r n tholeiites t h o l e i i t e s coming from a LREE depleted - The l a t e r therm_al thermal eevent v e n t of unknown orioriThe Rb/Sr Rb/Sr systematics s y s t e m a t i c s reveal r e v e a l aa later of unknown but but support support t h e above above thesis t h e s i s regarding r e g a r d i n g the t h e different d i f f e r e n t source source the regions r e g i o n s for f o r the t h e two two terrains. terrains. The northern n o r t h e r n terrain t e r r a i n ,yields i e l d s aa Rb/Sr Rb/Sr The errorchron ± 197 e r r o r c h r o n age of of 1550 + 197 my my (Lx), (LC),and andan an initial i n i t i a l °7SrI86Sr J7Sr/a6Sr ratio ratio w&eas the t h e southern s o u t h e r n terrain t e r r a i n suite s u i t e yields y i e l d s an a n age age of 0.70572 0.70572 + of + 14 (2s); (1); whereas of lY3 my my (1a), (LC), and and an an initial i n i t i a l 87Sr/86Sr 8 7 ~ r / 8 6of ~ r0.70258 ) of 1573 1573 ± 113 of 0.70258 + + 88 (2e (2-). age: overlap o v e r l a p the t h e age age of of emplacement emplacement of of the t h e very v e r y large l a r g e anorogenic ynorogenic Both ages Wolf Wolf River River Batholith, B a t h o l i t h , and and span span the t h e age age of of aa widespread widespread yet yet poorly poorly understood low—grade low-grade thermal thermal event event which affected a f f e c t e d much of of the t h e region region understood about 1700—1650 1700-1650 my my ago. ago. gin, gin, . + i n i t i a l 87Sr/86Sr 8 7 ~ r / 8 6ratio r~ a tri o (0.70572 (0.70572 + 1 4 ) from from the t h e northern n o r t h e r n terrain terrain The initial + 14) i s contained contained within w i t h i n the t h e field f i e l d for f o r continental contTnenta1 crustal c r u s t a l source s o u r c e regions regions is on i s not n o t clear c l e a r however however whether whether on an an 87Sr/86Sr a 7 ~ r / 8 6 evolution ~e rv o l u t i o n diagram. diagram. It is r e f l e c t s the t h e ccharacteristics h a r a c t e r i s t i c s of t h e source s o u r c e regions r e g i o n s of of the t h e Hemlock Hemlock this reflects of the i s aa reflection r e f l e c t i o n of of the t h e isotopic i s o t o p i c composition composition of of the the b a s a l t s , or o r rather r a t h e r is basalts, fluids f l u i d s which reset r e s e t the t h e Rb/Sr Rb/Sr systematics. systematics. I n contrast, c o n t r a s t , the t h e initial initial In 8 7 ~ r / 8 6 from ~ r the t h e southern s o u t h e r n terrain t e r r a i n (0.70258 (0-70258 + + 8) 8 ) is i s radically r a d i c a l l y difdif87Sr/86Sr from Ts contained c o n t a i n e d within w i t h i n the the f e r e n t from that t h a t of of the t h e northern n o r t h e r n terrain, t e r r a i n , and and is ferent 1 �field Hence the field for for source source regions regions for for basalts. basalts. Hence the Rb/Sr Rb/Sr systematics systematics are are consistent with the the Nd Nd isotopic isotopic systematics. systematics. In particular they they are are consistent with the thesis consistent with thesis that the the two two terrains terrains evolved evolved from from funfundamentally different source source regions, regions and damentally different and that that the northern northern terrain terrain tholeiites source region tholeiites and and gabbros gabbros were were generated generated from from aa source region with with a strong continental affinity, affinity* while the southern region tholeiites and gabbroic gabbroic sills were generated reservoir which sills were from aa reservoir which strongly generated from strongly resembles the modern day day MORE MORB source source regions. regions. For these these reasons reasons we we suggest that that this data is consistent suggest consistent with the existence existence of a suture suture zone between these two terrains, terrains* and that that this this data data supports supports the the above above mentioned plate plate tectonic tectonic model model of of the the Penokean Penokean events. events. 2 �Lithologic and tthe environment L i t h o l o g i c ddiversity i v e r s i t y and h e ssedimentary—tectonic e d i m e n t a r y - t e c t o n i c environment during deposition d uring d e p o s i t i o n of of Baraboo interval i n t e r v a l (176O—l500my) (1760-15OOmy) rrocks. ocks. Bruce A. A. Brown (Wisconsin (Wisconsin Geological and and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 1815 University Avenue, Nadison, Madison, W WII 53705) U n i v e r s i t y Avenue i s represented r e p r e s e n t e d by clastic c l a s t i c and and chemical chemical sediments sediments The Baraboo interval i n t e r v a l is deposited environment between between major major anorogenic anorogenic magmag— d e p o s i t e d iin n an eepicratonic p i c r a t o n i c environment matic m.y. ago (Greenberg (Greenberg and and Brown, Brown, 1984). 1984). This This m a t i c events e v e n t s 1760 and 1500 m.y. period of magmatism and ssedimentation followed tthe and cracra— p e r i o d of e d i m e n t a t i o n followed h e oorogenesis r o g e n e s i s and tonization t o n i z a t i o n of of the t h e Penokean Orogeny about about 1850 1850 m.y. m.y. ago. ago. Recent geologgeologic Wisconsin, and and ssubsurface i c mapping iin n ccentral e n t r a l Wisconsin, u b s u r f a c e sstudies t u d i e s iin n ssouthern outhern Wisconsin have produced significant new data on Baraboo interval significant d a t a on Baraboo i n t e r v a l rocks, rocks, of d deposition, history. ttheir h e i r environment of e p o s i t i o n , and their t h e i r tectonic tectonic h istory. The Baraboo interval b e s t known known for f o r red r e d quartzites, q u a r t z i t e s , such such as a s the the i n t e r v a l is best mapping and reexamination reexamination of of known Barron, Barrony Sioux, and and Baraboo. Baraboo. New mapping exposures, exposures, cores c o r e s and cuttings c u t t i n g s show show quartzite q u a r t z i t e in i n association a s s o c i a t i o n with w i t h argil— argililte, carbonaceous sslate, bedded chert, U t e y carbonaceous l a t e , bedded c h e r t , arkose, a r k o s e , siliceous s i l i c e o u s and and carbonate carbonate iron i r o n formation, formation, polymictic p o l y m i c t i c conglomerates, conglomerates, and and volcanogenic volcanogenic sediments. sediments. Att Baraboo, Baraboo, and and iin of ssoutheastern Wisconsin, aargillaA n the t h e ssubsurface u b s u r f a c e of o u t h e a s t e r n Wisconsin, rgillaceous rrocks, ceous o c k s , iiron r o n fformation, o r m a t i o n y and micaceous quartzite q u a r t z i t e occur occur in i n the t h e upper upper part parts p a r t of of the t h e section, s e c t i o n , above the t h e red r e d 4uartzites. q u a r t z i t e s . In In p a r t s of of central c e n t r a l and and northern Wisconsin, these n o r t h e r n Wisconsin, t h e s e lithologies l i t h o l o g i e s commonly commonly occur occur within w i t h i n aa few few distribution meters of the t h e base b a s e of of the t h e section. s e c t i o n . The areal a r e a l and vvertical ertical d istribution of depositional e p o s i t i o n a l environenvironof lithologies l i t h o l o g i e s aacross c r o s s Wisconsin Wisconsin suggests s u g g e s t s a complex d ment iin n which llocal o c a l hheterogeneities, e t e r o g e n e i t i e s y sstructural t r u c t u r a l oor r ttopographic, o p o g r a p h i c , ccontrolontrolled contemporaneous l e d the t h e distribution d i s t r i b u t i o n of of coarse c o a r s e sediments and allowed contemporaneous deposition d e p o s i t i o n of of mature quartz q u a r t z sandstones s a n d s t o n e s in i n one one area a r e a and and deposition d e p o s i t i o n of of shales presence of of volcanogenvolcanogen— s h a l e s and chemical sediments in i n another. a n o t h e r . The presence ic i c sediments suggests s u g g e s t s that t h a t local l o c a l rhyolitic r h y o l i t i c volcanism volcanism may may have have occurred occurred contemporaneously w i t h sedimentation, s e d i m e n t a t i o n , or o r that t h a t fresh f r e s h volcanic v o l c a n i c rocks rocks were were contemporaneously with exposed to within t o erosion erosion w i t h i n the t h e depositional d e p o s i t i o n a l basin. basin. The dominant deformational d e f o r m a t i o n a l structures s t r u c t u r e s in i n the t h e Baraboo Baraboo interval i n t e r v a l rocks rocks aare re o f t e n folds f o l d s overturned o v e r t u r n e d to t o the t h e south. s o u t h . Deformational i n t e n s i t y inoften Deformational intensity inccreases r e a s e s to t o the t h e east e a s t and and southeast. s o u t h e a s t . Greenschist G r e e n s c h i s t facies f a c i e s metamorphism metamorphism is is co=on comon throughout h e aarea r e a of exposure, exposure, with w i t h higher h i g h e r grade grade assemblages assemblages throughout tthe eevident v i d e n t only only iin n areas a r e a s where where tthese h e s e rocks r e iintruded, ntruded, p a r t i c u l a r l y by by rocks aare particularly granitic my age. age. g r a n i t i c rocks of 1500 1500 my i n t e r v a l was aa time t i m e of anorogenic anorogenic tectonic t e c t o n i c activity. activity. The Baraboo interval Early n the t h e interval, i n t e r v a l , rhyolitic r h y o l i t i c volcanism and sedimentation s e d i m e n t a t i o n were were probprobEarly iin m.y. ably contemporaneous. Anorogenic r e g i o n a l uplift u p l i f t at a t around 1630 1630 m.y. Anorogenic regional y e a r s ago may have been important important in i n the t h e initiation i n i t i a t i o n of of deformation deformation of of years t h e vvolcanic o l c a n i c and sedimentary rocks, r o c k s , as as w e l l as a s generation g e n e r a t i o n of of the t h e alkaalkathe well a g m a s which intruded i n t r u d e d the t h e already a l r e a d y deformed roëks rocks at a t around around 1500 1500 my. my. line m line magmas Greenberg, J * K . , and B.A. 3 . A . Brown, Brown, 1984, 1984, Cratonic C r a t o n i c sedimentation s e d i m e n t a t i o n during d u r i n g the the Greenberg, J.K., Proterozoic: P r o t e r o z o i c : aan n anorogenic connection in i n Wisconsin and and the t h e upper upper midmidw e s t , in i n press, p r e s s , Journal J o u r n a l of of Geology, March March 1984. 1984. west, 3 �Early Proterozoic E arly P r o t e r o z o i c structures s t r u c t u r e s of Northeastern N o r t h e a s t e r n Wisconsin Wisconsin as a s constraints c o n s t r a i n t s on Penokean tectonic t e c t o n i c models models ' B.A. BROWN BROWN (Wisconsin (Wisconsin Geological G e o l o g i c a l and N atural H i s t o r y Survey, Survey, 1815 UniUniB.A. Natural History versity W I 53705) 53705) v e r s i t y Avenue, Avenue, Madison, Madison, WI J.K. J . K . GREENBERG GREENBERG (Wisconsin (Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey, Survey, 1815 1815 University U n i v e r s i t y Avenue, Avenue, Madison, Madisony WI W I 53705) 53705) N i a g a r a tectonic t e c t o n i c zone hhas a s been d e s c r i b e d by e v e r a l aauthors u t h o r s as a The Niagara described by sseveral suture which s u t u r e along alongw h i c h aa PProterozoic r o t e r o z o i c vvolcanic o l c a n i c aarc r c terrane t e r r a n e (Penokean (Penokean volcanic volcanic belt) onto of an b e l t ) to t o the t h e south, s o u t h , was accreted accreted o n t o the t h e ssouthern o u t h e r n margin of a n Archean craton c r a t o n during d u r i n g the t h e Penokean Penokean Orogeny. Orogeny. In I n modern plate p l a t e tectonic t e c t o n i c concepts concepts this t h i s interpretation i n t e r p r e t a t i o n implies i m p l i e s compressional compressional deformation d e f o r m a t i o n which which should s h o u l d be be identifiable both i d e n t i f i a b l e on b o t h sides s i d e s of the t h e aids axLs of of suturing. s u t u r i n g . Recent geological geological maps of of of the t h e region r e g i o n show that t h a t indeed i n d e e d sstructural t r u c t u r a l trends t r e n d s on bboth o t h sides s i d e s of the t h e Niagara zone zone are a r e roughly roughly parallel. p a r a l l e l . However, Xowever, analysis a n a l y s i s of of structural structural data d a t a collected c o l l e c t e d in i n mapping of the t h e Penokean volcanic v o l c a n i c belt b e l t has h a s raised r a i s e d seserious r i o u s questions q u e s t i o n s regarding r e g a r d i n g the t h e nature n a t u r e of the t h e suturing s u t u r i n g process p r o c e s s and and the the strict s t r i c t applicability a p p l i c a b i l i t y of of modern modern plate p l a t e tectonic t e c t o n i c analogues. analogues. The structural i s characterized c h a r a c t e r i z e d by by s t r u c t u r a l pattern p a t t e r n within w i t h i n the t h e volcanic v o l c a n i c belt b e l t is tight t i g h t to t o isoclinal i s o c l i n a l folds f o l d s and a regional r e g i o n a l foliation f o l i a t i o n which which strike s t r i k e roughly roughly parallel p a r a l l e l to t o the t h e belt b e l t margins. margins. Lithologic L i t h o l o g i c contacts c o n t a c t s and and foliation f o l i a t i o n are are generally parallel, g e n e r a l l y p a r a l l e l y and and steep s t e e p dips d i p s (70° (70' to t o vertical) v e r t i c a l ) are a r e predominant. predominant. The The trends t r e n d s of these t h e s e regional r e g i o n a l structures s t r u c t u r e s aare r e locally l o c a l l y reoriented r e o r i e n t e d around large smaller granitic g r a n i t i c plutons. p l u t o n s . AlAll a r g e gneissic g n e i s s i c granitoid g r a n i t o i d complexes, complexesy and and smaller though these t h e s e complexes may include i n c l u d e many different d i f f e r e n t granitoid g r a n i t o i d phases, p h a s e s , ininternal t e r n a l foliation f o l i a t i o n patterns p a t t e r n s are a r e generally g e n e r a l l y concentric. c o n c e n t r i c . Regional foliation foliation generally g e n e r a l l y does not n o t pass p a s s through through the t h e granites. g r a n i t e s . Exceptions E x c e p t i o n s are a r e cases cases where plutons plutons p l u t o n s are a r e located l o c a t e d adjacent a d j a c e n t to t o major faults f a u l t s or o r smaller plutons are a r e between larger l a r g e r complexes. complexes. Steeply S t e e p l y plunging p l u n g i n g folds f o l d s which refold r e f o l d the the earlier e a r l i e r regional r e g i o n a l foliation, f o l i a t i o n , and strong s t r o n g subvertical s u b v e r t i c a l lineations l i n e a t i o n s are a r e comcow monly developed near n e a r the t h e granitic g r a n i t i c contacts c o n t a c t s and between closely c l o s e l y spaced spaced plutons. p l u t o n s . Greenschist G r e e n s c h i s t facies f a c i e s metamorphism metamorphism has h a s affected a f f e c t e d the t h e entire e n t i r e belt, belt, and h higher i g h e r grade g r a d e metamorphic assemblages are a r e developed developed around around intrusive intrusive rocks. r o c k s . Isotopic I s o t o p i c data d a t a suggest s u g g e s t that t h a t the t h e granitoid g r a n i t o i d rocks r o c k s are a r e roughly roughly the the same same age age as a s the t h e volcanic v o l c a n i c rocks, r o c k s y with w i t h no no indication i n d i c a t i o n of of older o l d e r basement basement remobilization as is is typical t y p i c a l in i n the t h e mantled mantled gneiss g n e i s s domes domes of of the t h e terrane terrane r e m o b i l i z a t i o n as to pattern t o the t h e north. n o r t h . The overall o v e r a l l picture p i c t u r e is of of a tectonic—metamorphic tectonic-metamorphic p attern very similar to only t o that t h a t of of Archean granite—greenstone g r a n i t e - g r e e n s t o n e tterranes, erranes, o n l y in in younger rocks r o c k s (Greenberg (Greenberg and and Brown, Brown, 1983; 1983; Brown Brown and and Greenberg, Greenberg, 1983). 1983). Available higher—grade metamorphic metamorphic assemblages assemblages and A v a i l a b l e data d a t a suggest s u g g e s t that t h a t higher-grade increased i n c r e a s e d strain s t r a i n intensity i n t e n s i t y are a r e functions f u n c t i o n s of o f location l o c a t i o n with w i t h respect r e s p e c t to to intrusive i n t r u s i v e bodies b o d i e s rather r a t h e r than t h a n proximity p r o x i m i t y to t o the t h e proposed proposed suture. s u t u r e . There There is i s no no evidence e v i d e n c e of of an a n increase i n c r e a s e in i n either e i t h e r deformnational d e f o r m a t i o n a l intensity i n t e n s i t y or o r metametamorphism morphism across a c r o s s the t h e belt b e l t towards towards the t h e Niagara Niagara zone. zone. Structures S t r u c t u r e s within within the t h e Niagara zone suggest s u g g e s t vertical v e r t i c a l movement, movement, rather r a t h e r than t h a n horizontal horizontal thrusting t h r u s t i n g typical t y p i c a l of of most most Phanerozoic Phanerozoic sutures. sutures. L. �arguments p r e s e n t e d above ssuggest u g g e s t tthat h a t tthe h e Niagara t e c t o n i c zone The arguments presented Niagara tectonic may b be more analogous boundaries w within Superior e more analogous to t o subprovince boundaries i t h i n the the S uperior Province than t h a n to t o a modern zone zone of of continental—scale c o n t i n e n t a l - s c a l e collision. c o l l i s i o n . All A l l of of the t h e known Penokean volcanic v o l c a n i c rocks rocks are a r e chemically chemically more more like l i k e modern moderntuag— magmas m a s than t h a n Archean Archean greenstonas g r e e n s t o n e s (Greenberg (Greenberg and and Brown, Brown, 1983). 1983) the Both the chemistry and the of tthis t h e sstructural t r u c t u r a l sstyle t y l e of h i s tterrane e r r a n e ssuggest u g g e s t aa tectonic tectonic environment transitional between modern modern plate-margin plate—margin convergence convergence and t r a n s i t i o n a l between Archean k c h e a n block—boundary block-boundary interactions. interactions. . Brown, B r o w n , B.A., B.A., and and J.K. J.K. Greenberg, Greenberg, 1983, Gneiss Domes and Not so s o Gneiss Domes Wisconsin, (abs.) Domes in i n the t h e Penokean terranes t e r r a n e s of of Northern Wisconsin, ( a b s .) Twenty— Twentyninth 6. n i n t h Institute I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology, Geology, Houghton, Houghton, p. p. 6. J.K., and r o t e r o z o i c Volcanic Rocks Rocks Greenberg, J.K.,, and B.A. B.A. Brown, Brown, 1983, 1983, Lower Lower PProterozoic and & I L.G. L.G. Medaris, H e d a r i s , Jr., Jr., and their t h e i r setting s e t t i n g in i n the t h e Lake Lake Superior S u p e r i o r District, D i s t r i c t , in ed. ed. Early E a r l y Proterozoic P r o t e r o z o i c Geology Geology of of the t h e Great Great Lakes Lakes Region, Region, Geological Geological Society S o c i e t y of of america, America, Memoir Memoir 160, 160, p. p. 67—84. 67-84. 5 �Basement Basement Cover Cover Relations Relations in in the t h eMarquette Marquetteand andRepublic RepublicDistricts, Districts,Michigan Michigan W. (Department (Department ofof Geological Geological Sciences, Sciences, Michigan Michigan State State CAMBRAY, F.F. W. CAMBRAY, University,East EastLansing, Lansing,Michigan Michigan48324-1115) 48824-1 115 ) University, MEYER, R. 0.(Lagoven (Lagoven S.A., S.A., Org. Org. Geologia, Geologia, Apartado Apartado 234, 234,Maturin, Maturin, Edo. Edo. MEYER, R. 0. Monagas, Venezuela, Venezuela, Zona ZonaPostal Postal6201) 6201) Monagas, G. A. A. (Superior (Superior Oil Oil Company, Company, Geoscience Geoscience Laboratory, Laboratory, 12401 12401 MYERS, G. MYERS, Westheimer, Houston, TX 77077) Westheimer, Houston, TX 77077) ItItisisproposed proposed that t h a tthe t h eArchean Archeanbasement basementbetween betweenthe t h eMarquette MarquetteTrough Troughand and the as an essentially t h eRepublic Republic Trough Trough behaved behaved as essentially rigid rigid material during during both both the the subsidence subsidence and and the t h e deformation deformationassociated associatedwith withthe t h ePenokean PenokeanOrogeny. Orogeny. In In the t h e subsidence subsidence phase phase the t h e basement basement fractured fractured into into several several rift riftbounded bounded troughs troughs in in which which sediment sediment accumulated accumulated to t ogreater greaterthickness thicknessthan thanthe t h esurrounding surrounding areas, areas,particularly particularlythe t h eBanded BandedIron IronFormation. Formation. During deformation was was effected in During subsequent subsequent compression compression deformation in the t h ebasement basementby by ductile ductileshear shearalong along mafic mafic dikes dikes which which were intruded during tthe h e rifting. Using Usingthe the sense of of shear shearon onthese thesedikes dikesiti tcan canbebeshown shownthat t h a tthe t h emaximum maximum principal principal stress stress sense during east of of north northand andwas wasfocussed focussed near nearthe t h etrough troughmargins, margins, dosing was was east during dosing becoming normal tto becoming normal o them, them, aa feature f e a t u r eobserved observed in in the t h eelastic elasticdeformation deformation of of plateswith with holes holes ininthem. them. In In addition addition the t h e data d a t ashows shows that t h a t the t h emaximum maximum shear shear plates strain occurs occurs on ondikes dikeswhich which are a r eapproximately approximately45° 4 5 O to t o the t h emaximum maximumprincipal principal strain stress f e a t u r econsistent consistentwith withnon-rotational non-rotational deformation deformation by bysimple simple stressdirection, direction, aa feature shear on on the t h edikes. dikes. shear This This type type of of deformation deformation resulted resulted in in translation translationofofrigid rigidblocks blocksofofbasement basement with no no internal internaldistortion. distortion. The Theoverlying overlyingsediments sedimentsresponded respondedaccordingly. accordingly. At At with t h e margins margins of of the t h e troughs troughs reactivated reactivated faults faultsresulted resulted ininthe t h ebasins basins dosing closinglike like the t h e jaws jaws of of aa vice vice producing producing high high strain in in the t h e troughs troughs and and relatively relatively low low strain strain the on the t h e platforms platforms ininbetween. between. One One locality locality on on the t h e south south side side of of the t h eRepublic Republic on Trough exemplifies exemplifies this. this. In In flat f l a tlying lyinguncleaved uncleaved Kona Kona Formation Formation shales shales the the Trough reduction spots spots are a r e flattened flattenedininthe t h ebedding. bedding. In In the t h e adjacent adjacent tilted tiltedhorizons horizons the the reduction spots are areoblique oblique to t othe t h ebedding bedding with withthe t h eX1A2 X i X 2 plane cleavage. spots plane lying lying parallel parallel ttoo deavage. b �Microstructures Multiply Deformed Deformed S Slate of tthe Formation, X i c r o s t r u c t u r e s iin n tthe h e Elultiply l a t e of h e Thomson Formation, East—Central East-Central Minnesota Xinneso t a of Geology, Geology, U University RIChARD RICIIARD C. C. CLARK CLAFC (Dept. (Dept. of n i v e r s i t y of of Minnesota ?finnesota Duluth, Duluth, Duluth, Minnesota 55812) Duluth, Xinnesota Early Proterozoic Thomson Formation Formation cconsists of iintercalated The E arly P r o t e r o z o i c Thomson o n s i s t s of ntercalated slate, s l a t e , slaty s l a t y greywacke and metagreywacke units. units. The formation f o r m a t i o n was was multiply deformed dduring Penokean orogeny orogeny (1900—1800 m.y.) rresultm u l t i p l y deformed u r i n g tthe h e Penokean (1900-1800 m.y.) esulting with me i n two major phases of of folding folding w i t h axial—planar a x i a l - p l a n a r foliation. f o l i a t i o n . The i n g in second deformation affected evidence a f f e c t e d the t h e entire e n t i r e study s t u d y area, a r e a , whereas whereas evidence of deformation is is found found only o n l y iin n the t h e extreme ssouthern o u t h e r n portion portion of the t h e first f i r s t deformation Later deformation, p possibly Kee— of the t h e study s t u d y area. area. L a t e r minor deformation, o s s i b l y related r e l a t e d to t o Keewenawan rifting, r i f t i n g , resulted r e s u l t e d in i n the t h e development of of kink—bands kink-bands in i n some some areas. areas. In southernmost aareas by bboth major Penokean Penokean defonndeformI n the t h e southernmost r e a s aaffected f f e c t e d by o t h major ations a t i o n s a crenulation c r e n u l a t i o n cleavage c l e a v a g e has h a s formed formed iin n the t h e fine—grained f i n e - g r a i n e d slates. slates. M.icrostructural evidence M.icrostructura1 evidence suggests s u g g e s t s that t h a t the t h e crenulation c r e n u l a t i o n cleavage c l e a v a g e developed similar to t o that t h a tproposed proposed by by Gray Gray and and by aa solution—deposition s o l u t i o n - d e p o s i t i o n pprocess r o c e s s similar Durney (1979). The pprinciple behind the process r i n c i p l e behind t h e ppressure r e s s u r e ssolution olution p r o c e s s is is of ssoluble minerals tthe h e ssolution o l u t i o n ttransfer r a n s f e r of oluble m i n e r a l s from sites s i t e s of of high h i g h chemical chemical The difference potential p o t e n t i a l to t o sites s i t e s of of low chemical potential. potential. d i f f e r e n c e in i n chein— chemica]. potential can be directly related to stress variations around i c a l p o t e n t i a l can b e d i r e c t l y r e l a t e d t o s t r e s s v a r i a t i o n s microfolds The grains g r a i n s along the t h e limbs are a r e subject subject m i c r o f o l d s (crenulation—folds). (crenulation-folds). stress (and ttoo a a higher h i g h e r normal normal stress (and tthus h u s a hhigher i g h e r chemical potential) p o t e n t i a l ) than than grains in the hinge zones. Soluble (such as as qquartz) u a r t z ) are are S o l u b l e sspecies p e c i e s (such the t h e g r a i n s i n t h e h i n g e zones. then limbs zones (or of tthe s tto o tthe h e hhinge i n g e zones ( o r oout u t of h e system t h e n transferred t r a n s f e r r e d from tthe he W into quartz causing tthe of rrelatively into q u a r t z vveins) e i n s ) causing h e ppassive a s s i v e cconcentration o n c e n t r a t i o n of elatively insoluble p h y l l o s i l i c a t e s into i n t o mica—rich mica-rich zones zones (zona3. ( z o n a l ccrenulation r e n u l a t i o n cleavcleavi n s o l u b l e phyllosilicates age) orr iinto mica—rich ccleavage seams ((discrete age) o n t o ddistinct i s t i n c t mica-rich l e a v a g e seams d i s c r e t e ccrenulation renulation cleavage) cleavage) in i n the t h e former former limb Limb zones. Kink-bands are a r e common common in i n the t h e slates slates at a t the t h e ttype y p e locality l o c a l i t yata Thomson t Thomson Kink—bands Dam. Kink-bands can f i n e d aas s small-scale o l d s having having Kink—bands canb ebed edefined small—scalemonoclinal monoclinal ffolds p l a n a r limbs limbs and planar normally found foundi in rocks wwith and angular a n g u l a r hinge hinge zones zones normally n rocks ith a definite p l a n a r anisotropy a n i s o t r o p y (such (such as a s cleavage). c l e a v a g e ) . Several S e v e r a l models have definite planar been t o explain e x p l a i n the t h e formation of of kink—bands. kink-bands. Two models that t h a t have have proposed to t h e Thomson Formation are a r e the t h e rotation r o t a t i o n model model ccharacteristics h a r a c t e r i s t i c s found in the and the t h e jjoint—drag o i n t - d r a g model. model. r o t a t i o n model model proposes h a t as a s deformdeformThe rotation proposes tthat aation t i o n proceeds, proceeds, the t h e foliation f o l i a t i o n within w i t h i n the t h e kink—band kink-band is is rotated r o t a t e d through through iincreasing n c r e a s i n g angles. angles. S i n c e tthe h e ffoliation o l i a t i o n remains h e kink-band Since remains hinged hinged aatt tthe kink—band boundary it i t is geometrically geometrLcally necessary n e c e s s a r y ffor o r tthe h e ffoliation o l i a t i o n to t o part p a r t oorr d i l a t e as asrotation r o t a t i o noccurs occursthus t h u screating c r e a t i n volume g volume expansion. expansion. As otation dilate As rrotation passes a c r i t i c a l point t h e f o l i a t i o n begins t o close. I t is possible, possible, however, for f o r the t h e sspaces paces w i t h i n the t h e dilated d i l a t e d foliation f o l i a t i o n to t o be b e filled f i l l e d by within precipitating p recipitating m i n e r a l s (such as q u a r t z o r c a l c i t e ) t h u s 'jamming1 the minerals quartz or calcite) thus 'jamming' the kink—band at kink-band a t an an intermediate i n t e r m e d i a t e stage. s t a g e . The joint—drag j o i n t - d r a g model proposes that that c t u a l l y broken f f s e t by h e a r along a l o n g the t h e kink—band kink-band tthe h e ffoliation o l i a t i o n is is aactually broken and and ooffset by sshear d u r i n g deformation. deformation. F u r t h e r deformation a u s e s rrotation o t a t i o n of the boundary during Further deformation ccauses of the kinked foliation f o l i a t i o n accompanied by slip s l i p along a l o n g individual i n d i v i d u a l folia f o l i a within w i t h i n the the kink—band. Triagular-shaped kink-band. Triagular-shaped vvoids o i d s (which (which llater a t e r may e ffilled illed w i t h qquartz uartz may bbe with o r calcite) c a l c i t e ) develop along the t h e kink—band kink-band boundary causing c a u s i n g volume volume expanexpanor sion s i o n of the t h e rock. rock. passes a critical point the foliation begins to close. It is 7 �Kink—bands Formation ccontain of b both Kink-bands of of the t h e Thomson Formation o n t a i n ccharacteristics h a r a c t e r i s t i c s of oth models indicating i n d i c a t i n g that t h a t aspects a s p e c t s of both b o t h models were were probably p r o b a b l y in i n operation. operation. The foliation f o l i a t i o n can be seen s e e n as a s discontinuous d i s c o n t i n u o u s (sheared) ( s h e a r e d ) or o r continuous c o n t i n u o u s across across kink—band boundary boundary even w within tthe h e kink-band i t h i n different d i f f e r e n t parts p a r t s of of the t h e same same kink—band. kink-band. Triangular—shaped voids Triangular-shaped v o i d s and dilation d i l a t i o n zones zones between between individual i n d i v i d u a l folia folia now ffilled with ((both b o t h now illed w i t h qquartz) u a r t z ) aare r e ppresent r e s e n t iindicating n d i c a t i n g volume expansion expansion of the of t h e rock. rock. S i n c e volume expansion h e rrock o c k iin n aa hhorizontal o r i z o n t a l ddirecirecSince expansion of of tthe tion t i o n is i s involved, i n v o l v e d y the t h e kink—bands kink-bands must have have formed formed at a t aa high h i g h structural structural level l e v e l where confining c o n f i n i n g pressures p r e s s u r e s were were low. low. They are a r e also a l s o thought thought to to of tthe have formed late l a t e iin n t the h e sstructural t r u c t u r a l hhistory i s t o r y of r e a y ppossibly o s s i b l y as a s aa h e aarea, result of Middle Middle PProterozoic Keewenawan aactivity (1100 m.y.). m.y). r e s u l t of r o t e r o z o i c Keewenawan c t i v i t y (1100 Reference Gray, D. G. G. and and ~ Durney, D., W. W., l1979, Crenulation u i n e ~D. 97gy C r e n u l a t i o n ccleavage l e a v a g e ddifferentiaifferentiaGray D. of ssolution—deposition ttion: i o n : iimplications m p l i c a t i o n s of o l u t i o n - d e p o s i t i o n processes: processes: JJournal o u r n a l of of Structural l yNo. No. 1, 1, pp. pp. 73—80. 73-80. S t r u c t u r a l Geology, Geology, Vol. Vol. 1, 8 �Geology northern Minnesota—revisited Minnesota-revisited Geology of of the the Rainy Rainy Lake Lake area, area, northern 25046,DFC, DFC, WARREN WARRJIN C. C. DAY, DAY, U.S. Box 25046, U.S. Geological Geological Survey, Survey,Box Mail Mail Stop Stop 905, 905, Denver, ~enGer,CO CO 80225 80225 Recent Recent geologic geologic mapping mapping of of the the 2,700—m.y.—old 2,700-m.y.-old Rainy Rainy Lake Lake area area of of northern northern Minnesota Minnesota provides provides new new insight insight into into the the tectonic tectonic development development of of the the area. area. The The Rainy Rainy Lake Lake area area trends trends northeast northeast across across the the Minnesota— MinnesotaOntario Ontario international international border, and lies lies within the the western western extension extension of of The area area is is the the Superior Superior province. province. The the Wabigoon Wabigoon greenstone greenstone belt belt of of the bounded bounded on on the the south south by by the the Rainy Rainy Lake—Seine Iake-Seine River River fault fault and and on on the the The Minnesota Minnesota segment segment of of the the area area is is north Queticofault. fault. The north by by the the Quetico composed composed of of volcanic and subvolcanic subvolcanic intrusive intrusive rocks rocks intercalated intercalated with with volcaniclastic, volcaniclastic~epiclastic, epiclastic, and and chemical chemical sedimentary sedimentaryrocks. rocks. These These rocks rocks The volcanic volcanic rocks rocks are are grade grade upward upward into into volcanogenic volcanogenic graywacke. graywacke. The the mafic rocks rocks have have tholeiitic tholeiitic affinity affinity and and bimodal bimodal in in composition: composition: the the the felsic felsic rocks rocks have have calc—alkaline calc-alkaline affinity. affinity. In In Minnesota Minnesota all all of of the the rock rock types types have have been been metamorphosed metamorphosed to to upper upper greenschist greenschistfacies. facies. The The Minnesota portion of the Rainy Lake area has been affected by The first first was was large—scale large-scale folding folding that that three deformationevents. events. The three major major deformation produced produced an an S1 Sl schistosity schistosity subparallel subparallel to bedding CS0), (So), and southwest— southwestplunging The second second event event plunging F1 Fl parasitic parasitic folds folds and and L1 Ll mineral mineral lineations. lineations. The produced produced tight, tight, upward—facing, upward-facing, asymmetric asymmetric folds, folds, 1—3 1-3 km km in in scale, scale,an anS2 S2 penetrative penetrative cleavage, cleavage, and and northeast—plunging northeast-plunging F2 F2 parasitic parasitic folds foldsand and L2 L2 mineral mineral lineations. lineations. The The last last deformation deformation event event produced produced the the Rainy Rainy Lake— LakeSeine Seine River River fault. fault. In upward—facing F2 folds and upright stratigraphy In Minnesota, the upward-facing stratigraphy contrast F2 folds folds observed observed in in Ontario. Ontario. Poulsen Poulsen contrast with with the the downward—facing downward-facing F2 and and others others (1980) (1980) concluded concluded that that the the stratigraphic stratigraphic succession succession to to the the northeast northeast in in Ontario Ontario is is inverted, inverted, probably as a result result of of large—scale large-scale recumbent folding. folding. Another Another contrasting contrasting feature feature is is the the metamorphic metamorphic grade grade recumbent of of graywacke graywacke units; units; those those in in Minnesota being greensthist greenschist facies, facies, whereas whereas those sillimanite-bearing amphibolite amphibolite facies. facies. those in in Ontario Ontario being being sillinianite—bearing AA structurally structurally consistent consistent model for for the the region region places the the rocks rocks in in Minnesota Minnesota on on the the upper upper (upward—facing) (upward-facing) limb, limb, and the the rocks rocks in in Ontario Ontario on on the lower lower (downward—facing) (downward-facing) limb limb of of aa major major F1 Fl recumbent recumbent fold. fold. This the This hypothesis hypothesis suggests suggests that that the the higher higher metamorphic metamorphic grade grade in in Ontario Ontario could could reflect reflect the the higher higher temperature temperature and and pressure pressure conditions conditions experienced experienced by by the the lower, lower, more more deeply deeply buried buried limb limb of of the the recumbent recumbent fold fold (fig. (fig. 1). 1). The The new structural structural model differs markedly from that of Ojakangas (1972), new (19721, who proposed that that the the inconsistencies inconsistencies in in stratigraphy stratigraphy and and structural structural style style proposed were caused caused by by the the juxtaposition juxtaposition of internally internally coherent, coherent, fault—bound fault-bound were structural structural blocks. blocks. 9 �Although Although the the structural structural model model proposed here satisfies satisfies the the geometrical geometrical relationships, relationships, several several problems problems remain. remain. For For example, example, the the location location of of the the F1 Fl recumbent recumbent fold axis is not known, nor is is there there any any documented documented evidence evidence of of thrust thrust faulting faulting associated with with nappe nappe structures structures that that might might have have been been developed developed during during the the F1 Fl recumbent recumbent folding folding event. event. Only through structural model by through testing testing and revision of the proposed structural further further detailed detailed geologic geologic mapping can can the structural structural development of the the Rainy Rainy Lake Lake area area be be fully fully resolved. resolved. NW NN SCHEMATIC SCHEMATIC CROSS CROSS SECTION SECTION OF THE THE OF RAINY F A I N Y LAKE LAKE AREA AREA SE SE MINNESOTA MINNESOTA ONTARIO ONTARIO Figure Figure 1. 1. Schematic Schematic cross cross section section of of the the Rainy Rainy Lake Lake area. area. The The Minnesota Minnesota rocks rocks are are on on the the upright upright limb, limb, whereas whereas the the Ontario Ontario rocks rocks are are on on the the overturned overturned limb limb of of aa regional regional F1 Fl recumbent recumbent fold(s). fold(s). tn In Minnesota Minnesota the Fl fold fold has has been been refolded refolded by by asymmetric asymmetric F2 F2 folds folds that that have have steep steep the F1 northwest—dipping northwest-dippingfold foldhinges. hinges. References References cited cited Ojakangas, R.W., 1972, 1972, Rainy Rainy Lake Lake area: area: in in Sims, Sims,P.K., P.K., and andNorey, Horey,G.B., G.B., Ojakangas, R.W., eds., eds., Geology Geology of of Minnesota: Minnesota: aa Centennial Centennial Volume, Volume, Minnesota Minnesota Geological GeologicalSurvey, Survey,p. p. 162—171. 162-171. Poulson, Poulson, K.H., K.H., Borradaile, Borradaile, G.J., G.J., and and Kehienbeck, Kehlenbeck, M.M., M.M., 1980, 1980, An An inverted inverted succession succession at at Rainy Rainy Lake, Lake, Ontario: Ontario: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v. v. 17, 17, p. p. 1358—1369. 1358-1369. 10 �Mineralogy of of Pegmatites Pegmatites in i n the t h e Wausau Wausau Pluton, Pluton, Marathon County, Countv. Wisconsin Wisconsin AL u U. u . FALSTER FXSTER (920 (920 McIntosh McIntosh Street, S t r e e t , Wausau, Wausau, WisconSin wisconsin 54401) 54401) The Wausau Pluton is a q quartz—rich phase of of g granitic quartz ssyenite— u a r t z - r i c h phase r a n i t i c .quartz yenitepyroxene is exposed exposed at a t Wausau, Wausau, Marathon Marathon County, County, pyroxene amphibole amphibole syenite s y e n i t e which which is Wisconsin. The The age age of the t h e body was determined to t o be 1,520 + + 25 25 m.y. may. (Van The (Van Schmus, S c h u s , 1980). 1980) The pluton p l u t o n is i s Cut c u t by by numerous numerouspegiriatitic pegmati& ddikes i k e s of generally g e n e r a l l y gentle g e n t l e dip. d i p . The Miarolitic M i a r o l i t i c cavities c a v i t i e s in i n these t h e s e dikes d i k e s yield y i e l d an astonishing a s t o n i s h i n g array a r r a y of o f accessory accessory minerals, m i n e r a l s , particularly p a r t i c u l a r l y Fe, Fe, Ti, T i , Be, B e , REE REE minerals minerals with w i t h lesser lesser amounts amounts Sb Sb and and Pb Pb bearing b e a r i n g species s p e c i e s and and rarely r a r e l y those those containing B, Nb, Nb, Ta. Ta. Variations V a r i a t i o n s in i n pocket constituents, c o n s t i t u e n t s , paragenesis, p a r a q e n e s i s , and and c o n t a i n i n g 3, morphology morpnology occur occur widely, not n o t only only from from pegmatite pegmatite to t o pegmatite pegmatite but b u t also also from from pocket pocket to t o pocket pocket within w i t h i n the t h esame samepeginatite. pegmatite. Pocket rupture, r u p t u r e , thermal thermal shock shock and and metasoinatic metasomatic eeffects f f e c t s are a r e very very often o f t e n seen. seen. - Several Several types types of of typical t y p i c a l assemblages assemblages can can be be distinguished: distinguished: a. Simple Simple pa.ragenesis paragenesis of pockets in i n small small dikes: dikes: Microcline, Microcline, albite a l b i t e and and quartz q u a r t z are a r e the t h e bulk minerals with few few accessories ~pseudomorphouslyreplaced replaced by by other other a c c e s s o r i e s like l i k e siderite s i d e r i t e (pseudomorphously Fe Fe minerals), m i n e r a l s ) , hematite, hematite, hisingerite, h i s i n g e r i t e , phenakite, phenakite, bertrandite, bertrandite, anatase. anatase . b. Complex Complex paragenesis paragenesis of of pockets pockets in i n larger l a r g e r dikes: dikes: Besides as above, c o n s i d e r a b l e variety v a r i e t y of of ~ e s i d e the st h e bulk bulk minerals minerals as above, aa considerable accessories a c c e s s o r i e s like l i k e sulfides s u l f i d e s and and sulfosalts s u l f o s a l t s (pyrite, ( p y r i t e , jamesonite, jamesonite, boulangerite, b o u l a n g e r i t e , and and others. o t h e r s . These are a r e unaltered u n a l t e r e d only if i f protected protected in i n other o t h e r mineral mineral phases.), p h a s e s . ) , siderite s i d e r i t e (replaced), ( r e p l a c e d ) , phenakite, phenakite, bertrandite, b e r t r a n d i t e , anatase, a n a t a s e , rutile, r u t i l e , brookite, b r o o k i t e , fluorite, f l u o r i t e , F—apatite, F-apatite, REE—minerals, FEZ-minerals, especially e s p e c i a l l y aa REE—rich FEZ-rich cheralite c h e r a l i t e and and others. others. c. Simple vuggy intermediate i n t e r m e d i a t e zones: zones: Simple paragenesis paragenesis of of vuggy Besides Besides the t h e bulk bulk minerals minerals large l a r g e amounts amounts of of hematite hematite and and less less cornonly ppyrite y r i t e ((replaced), r e p l a c e d ) , zzircon, i r c o n , ffluorite, luorite, F - a p a t i t e are are conmionly F—apatite found. found. d. Paragenesis of late l a t e stage s t a g e formation formation in i n solution s o l u t i o n etched e t c h e d zones zones near near Paragenesis pockets pockets with with quartz q u a r t z selectively s e l e c t i v e l y removed removed (and (and sometimes sometimes redeposited): redeposited): Besides Besides the t h e bulk bulk minerals minerals this t h i s environment environment is i s especially e s p e c i a l l y dominated dominated by by Ti T i oxides oxides (anatase, ( a n a t a s e , brookite, b r o o k i t e , rutile) r u t i l e ) and and often o f t e n accompanied accompanied by by i l m e n i t e , zircon, z i r c o n , bertrandite, b e r t r a n d i t e , cheralite c h e r a l i t e and and others. others. ilmenite, This is based based on on data d a t a collected c o l l e c t e d during d u r i n g excavation excavation of of over over This paper paper is it should should 760 pegmatite pegmatite pockets pockets in i n the t h e Wausau Wausau Pluton, Pluton, therefore, t h e r e f o r e , it 760 a fairly representative description. be be a f a i r l y r e p r e s e n t a t i v e d e s c r i p t i o n . 11 �PRECAMBRIAN GEOCHRONOLOGY IN MINNESOTA PRECAMBRIAN GEOCHRONOLOGY IN MINNESOTA S. GOLDICH GOLDICH (Department Engineering Colorado Colorado (Departmentofof Geological Geological Engineering, School of Mines, School Mines Golden, Go1 den CO CO 80401) 80401 ) S. - Orogeny has b u i 1dingl'.When When Orogeny hasbeen beendefined defined simply simply as as "mountain "mountain building". began studying geologists began studyingsimple simplemountains mountainsinindetail detail, they they found found that t h a t aa number number of geological geological processes processes were were involved. involved. These These can can be be defined simply as as mountain-building mountain-building or orogenic orogenic processes, processess but b u t the the defined simply only thing that agreeononi sis tthat there is only t h a t most most geologists geologists seem seem t otoagree h a t there is nothing simple about about mountain mountain building o rorogeny. orogeny. nothing simple building or The early early classification Precambrian The classificationofofthethe Precambrian rocks rocks ofofMinnesota, Minnesota summarized Grout (1951, GSA GSABull. Bull. 2Gs 26, 1017) 1017), divided the e teta lal. . (1951 the summarized byby Grout succession into into three uncon— succession three major majorgroups groups separated separated by by two two 'great" "great" unconformi t i e s . These These were of ofbath01 i t h i c intrusives in formities. werecut cut on on complexes complexes batholithic intrusives in andmetavol metavolcanic rocksre1 related to two folded metasedimentary metasedimentary and cani c rocks ated to two periods perf ods of orogeny. orogeny . K-Ar, early U-Pb agedeterminations determinationsf afailed K-Ars Rb-Sr, Rb-Srs and and early U-Pb age i l e d to resolve resolve the Laurentian Laurentian from fromthe theyounger youngerAlgoman A1 gomanorogeny. orogeny.The Theage agemeasurements measurments revealed aa complex complexgeological geologicalhistory history and andindicated indicated tthat revealed h a t the the time time interval was interval was small, smalls about about 50 50 m.y. m.y. Within W i t h i n recent recent years years notable notable imimprovementshave havebeen been made in analyticaltechniques techniquesand andininthe the ininprovements made i n analytical ages deterdeterparticularlyU-Pb U-Pb ages terpretation of of radiometric radiometric ages, ages s particularly mined onzircon zircon and andtititanite. tani t e . LateLate-tot opostkinematic postkinematicAlgoman A1 goman gramined on nites, the Minnesota geologists, are n i t e s , as asdefined definedbybyLawson Lawson and and the Minnesota geologistss are dated aatt 2,680 and the the Laurentian dated Zs680 Ma Ma and Laurentian orogeny orogeny at a t 2,735 Zs735 Ma. Ma. The The LaurLaupentian may may be be regarded regarded as as an an early earlyphase phase ofofthe theAlgornan Algoman orogeny orogeny as as has been beensuggested suggested a number of writers, local use, t e r s s b ubut t f ofor r local uses the the has by by a number of wri distinction is distinction i s useful. useful. New U-Pbdata datafrom fromeast-central east-central Minnesota Minnesota,1likewise, i kewise provide provide N ew U-Pb Ma).similar similar bbetter e t t e r resolution resolutionofofthe thePenokean Penokean orogeny orogeny (1,800-1870 (1 s800-1870 Ma), to the interval found in Wisconsin by Van Schmus and others. the interval found i n Wisconsin by Van Schmus and 12 �Maginatism and the Baraboo Baraboo Interval: Magmatism and Internal: Breccias, Dikes, Dikes, and Metasomatism Breccias, JEFFREY GREEIBERG (Wisconsin Geological and Natural History Survey, (Wisconsin Geological Survey, JEFFREY KK.O GREENBERG WI 53705) Madison, WI the known known expo=POIn breccias are arecoimnon common features features in in many of the In Wisconsin Wisconsin breccias The breccia The breccia sures of quartzites deposited during the Baraboo interval. sures quartzites during the Baraboo interval. white vein vein quartz matrix is is typically typically white quartz and partial voids containing containing clay clay quartz crystals. Dott (1970) and quartz crystals. Daiziel Dalziel and Dott (1970) previously attributed attributed the the an interpretation interpretation preprebreccias to to "explosive "explosive hydrothermal hydrothexmal activity't, activityft9an ferred ferred over over aa fault fault origin. origin. Fluid inclusions inclusions in in quartz quartz crystals crystals indiindicate cate temperatures temperatures of formation formation greater than expected from sedimentary fluids km fluids except except under ambient conditions at depths greater than 3 Ian below unlikely environment below the the Earth's Earth's surface. surface. This represents an unlikely brittle fracturing for the development of brittle fracturing and and undeformed uncieformed voids. voids. However, However, we have observed that all the breccias are associated with massive granite and and diorite, diorite, granitic granitic dikes and intrusions including massive pegmatites, and sometimes pegmatites, sometimes basaltic—andesitic basaltic-andesitic dikes. dikes. Most Most of of the the brecciated brecciated quartzites quartzites also also show showevidence evidenceof of metasotnatism metasomatism (late (late mag— magmatic?). metasomatic features matic?). Observed metasmatic features include: include: clay segregations segregations in which apparently contain contain feldspar pseudmorphs; pseudomorphs; unaltered in breccia which in altered quartzite; feldspar porphyroblasts in quartzite; tourmaline—quartz tourmaline-quartz veinlets in veinlets in quartzite; quartzite; and a d books books of of muscovite muscovite (to (to 11 cm cm diameter) diameter) . crystallized in vein quartz in vein quartz and and replacing replacing other other minerals minerals in in quartzite. quartzite. The above =antples examples of intrusion intrusion and metasomatism metasomatism occur in various various comThe above binations exposures of Baraboo, binations at at the the breccia breccia exposures Baraboo, Necedah, Necedah, Battle Battle Point, Point, Waterloo, Rib Mountain, and Hamilton Hamilton Mound. Waterloo, FUb Mountain, interpretation of the breccias is that they are analogous analogous Our present interpretation stockwork of quartz produced around around the the upper upper levels levels of of to the stockwork quartz veins veins produced porphyry-copper plutons. During During magma intrusion, intrusion* the the roof roof porphyry—copper mineralized mineralized plutons. rocks (quartzite) were were fractured fractured and and soaked soaked iii in hydrous fluids. rocks (quartzite) hydrous granitic granitic fluids. The fluids fluids and their particular effects vary vary with with distance distance from source plutons. Thus, plutons. Thus, as as in in some s m e Wisconsin examples, quartz Wisconsin examples, quartz veins and grade into into actual actual pegmatite pegmatite dikes dikes as as intrusions intrusions are are approached. approached. breccias grade The coincidence coincidence of quartzite breccias, intrusions, The intrusions, and metasomatism metasomatism have often often gone gone unrecognized. unrecognized. suggest controversial controversial relationships relationships which which have If isotopically isotopically dateable, dateable, the the intrusions intrusionscould couldspecify specifymininu.nn minimum ages If ages of within the units within the Baraboo Baraboo interval. interval. vailable =.vailable age agedata data are are confusing, confusing, quartzite exposures but the the quartzite exposures are are probably probably somewhere smewhere between between 1760 1760 and and 1500 1500 m.y. m.y. old. oldDalziel, I.WeD., and Dott, Dott, R.H., R.H., Jr., Jr., 1970, 1970, Geology Geology of of the the Baraboo Baraboo Dalziel, I.W.D., District, Wisconsin: District* Wisconsin: Wisconsin NaturaJ. History Historv Geological and and NaturaJ. Wisconsin Geological p. Survey, Information Circular Circular 17, 17, 164 164 p. Survey, Information 13 �Mobilization M o b i l i z a t i o n of of Uranium and Thorium Within the Metamorphic Node, Node, Northern Northern Michigan t h e Republic Metamorphic ROBERT L. L. HACKENBERG HACKENBERG (Conoco, (Conoco, Inc., I n c . , Lafayette, L a f a y e t t e , Louisiana) Louisiana) GREGORY (Dept. of of Geol. Geol. and and Geop. Geop. SSciences, University GREGORY MIJRSKY MURSKY (Dept. ciences, U n i v e r s i t y of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, Wisconsin Wisconsin 53201) 53201) The paper summarizes the t h e results r e s u l t s of of uranium uranium and and thorium thorium neutron neutron activation a c t i v a t i o n analysis a n a l y s i s of of 150 150 samples samples from from regionally r e g i o n a l l y metamorphosed metamorphosed Precambrian Precambrian rocks, r o c k s , which comprise comprise the t h e Republic Republic metamorphic metamorphic node, node, northern Six ccentered e n t e r e d around the t h e city c i t y of of Republic, Republic, n o r t h e r n Michigan. Michigan. Six bee delineated llithologic i t h o l o g i c rock r o c k uunits, n i t s , whose metamorphism can can b d e l i n e a t e d wholly wholly orr p partly biotite, sillimanite o a r t l y by chlorite, chlorite, b i o t i t e , garnet, g a r n e t , staurolite, s t a u r o l i t e , and and sillimanite considered. iisograds, s o g r a d s , were considered. The data, i s summarized in i n Figure F i g u r e 1, 1, indicates i n d i c a t e s that t h a t mobilmobild a t a , which is ization of uranium might h have units i z a t i o n of a v e taken t a k e n place p l a c e in i n rock rock u n i t s which higher metamorphism. This is have been subjected s u b j e c t e d to to h i g h e r grades g r a d e s of of metamorphism. T h i s is particularly p a r t i c u l a r l y evident e v i d e n t in i n metagranodiorite, m e t a g r a n o d i o r i t e , shale, s h a l e , and and nietadiabase. metadiabase. granitic metavolcanics The trends t r e n d s for for g r a n i t i c gneiss g n e i s s and m e t a v o l c a n i c s are a r e inconclusive inconclusive because these t h e s e two two rock r o c k units u n i t s do do not n o t appear a p p e a r in i n areas a r e a s represented represented orr intermediate metamorphism. by low o i n t e r m e d i a t e grades g r a d e s of of metamorphism. The concentrations c o n c e n t r a t i o n s of of thorium thorium (Figure ( F i g u r e 2) 2) iin n ggeneral e n e r a l follow f o l l o w the the of uranium uranium cconcentrations o n c e n t r a t i o n s and suggest s u g g e s t that t h a t at a t higher h i g h e r grades grades ttrends r e n d s of of of metamorphism there t h e r e has h a s been some mobilization m o b i l i z a t i o n of of thorium. thorium. The study metamorphism may may pplay s t u d y indicates i n d i c a t e s that t h a t hhigher i g h e r ggrade r a d e metamorphism l a y aan n mobilization of uranium, uranium, and perhaps iimportant m p o r t a n t rrole o l e iin n tthe he m o b i l i z a t i o n of p e r h a p s thorium, thorium, and that i t may contribute c o n t r i b u t e to t o the t h e formation f o r m a t i o n of of ore—forming ore-forming fluids. fluids. t h a t it Concentration C o n c e n t r a t i o n and precipitation p r e c i p i t a t i o n of of uranium from from such such fluids f l u i d s may may result r e s u l t in i n economic economic uranium uranium deposits. deposits- lL �N.P. signifies s i g n i f i e s lithology l i t h o l o g y not n o t present p r e s e n t in i n that t h a t metamorphic metamorphic F i g u r e 1. 1. N.P. Figure of s amples zone. Numbers i n p a r e n t h e s i s a r e number zone. Numbers in parenthesis are number of samples analyzed. analyzed. 15 15 �F i g u r e 2. 2. Figure N.P. N.F. signifies s i g n i f i e s lithology l i t h o l o g y not n o t present p r e s e n t in ir! that that metamorphic zone. zone. Numbers in i n parenthesis p a r e n t h e s i s are are number of of samples samples analyzed. analyzed. 16 �Comparison of Middle Proterozoic Iron Oxide Rich Ore Deposits, Mid—Continent, U.S.M., South AustraHa, Sweden, and the Peoples Republic of China S. A. (Union Carbide Carbide Corporation, Corporation, p. S. A. HAUCK, HAUCK, (Union P. Q• 0. Box Box 1029, 1029, Grand Grand Junction, Colorado Colorado 81502) 81 502) E. W. (UnionCarbide Carbide Corporation, Corporation, p. E. W . KENDALL, KENDALL, (Union P. a. 0. Box Box 1029, 1029,Grand Grand Junction, Colorado Colorado 81502) 81502) Middle Proterozoic Ga) iron oxide Proterozoic (1.8—1.1 (1.8-1.1 Ga) oxide rich richdeposits depositscomprise compri se aa diverse diverse family family ofofeconomically economically important, important,multicommodity multicommodity ore ore depodepogenetic grouping sits genetically related. The s i t s which which appear appear genetically The genetic grouping of these these appears to a deposits (previously not well described) gap (or deposits (previously not well described) appears t o f i l l a gap (or many time—tectonic transition zone) in many time-tectonic ore ore deposit deposit classifications Ga) banded iron formations between Lower (2.5—1.8 Ga) BIF) between Lower Proterozoic Proterozoic (2.5-1.8 formations ((BIF) Camonfeatures features of of these and and Phanerozoic iron iron oxide oxide deposits. deposits. Common these iron oxide deposits deposits include: oxide include: (1) iron 20%Fe Fe as as magnetite magnetite and/or and/or hematite; hematite; iron'contents contentsgreater greaterthan than20% (2) anomalous concentrations of of base Go, Mo), anomalous t to o economic economic concentrations base metals metals (Cu, ( C u , Co, Mo), precious metals precious metals (Au, (Au, Ag), Ag), and and U; U; (3) associated associated geochemical geochemical enrichment enrichment (occasionally (occasionallyeconomic) economic) in in LREE, LREE, Ba, P, Ba, P, F, F, and and Th; Th; (4) intimate i ntimate primary primary mixture mixture of o f iron iron sulfides sulfidesand andhematite hematite and/or and/or nagmagnetite; (5) host host rock rock and and mineralization mineralizationages agesbetween between 1.8 1.8 and and 1.1 1.1 Ga; Ga; (6) close relationship to close spatial spatial and and temporal temporal relationship t o anorogenic anorogenic ffelsic e l s i c domidomiand intrusi intrusives (rapakivi v i granites and and ves (rapaki nated, bimodal volcanics and ferrodiorites) ofoflower ferrodiorites) lower crustal crustal and and mantle mantle origin; (7) ore deposition deposition ininananupper upper crustal crustalsubvolcanic subvolcanicenvironment environment and/or and/or intracratonic or sedimentary basins; basins; intracratonic o rmarginal marginal (tensional) (tensional )sedimentary (8) very exceedingone onebil billion very large largetonnage, tonnage, commonly commonly exceeding lion tons. tons. Examples Examples include the the Kiruna include Kiruna District, Sweden Sweden (Kiirunavaara, (Ki irunavaara, Rektorn, and and Hauki deposits), deposits), Baiyan BaiyanOBo, OBo, Inner Mongolia, Mongolia, Peoples Peoples Republic Republic of P R C ) , Pilot Knob-Pea and Olympic Olympic Dam, Dam, China ((PRC), Knob—Pea Ridge, Missouri, and South Austral Australia. South i a. fill The Middle deposits are are found found in in marmarThe MiddleProterozoic Proterozoiciron iron oxide oxide rich rich deposits t o intracratonic, intracratonic, tensional tensional basins basins overlying Lower Lower Proterozoic Proterozoic ginal to Archean shields shields (Churchill, (Churchill, Gawler, Baltic, rocks on on the the margins margins of of Archean North China). China). The The basins arkoses, sandstones, and and minor(?) minor(?) basins contain arkoses, carbonates (sebkha?), s i c volcanics. volcanics. SedimenSedimencarbonates (sebkha?),volcaniclastics, volcaniclastics, and and fel felsic (SEDEX) hematitic iron formations formations ((++Cu, Cu, Ca, Co, Mo, exhalative (SEDEX) tary exhalative hematitic iron Mo, Au, Au, Ag, U, U, LREE, F ) are are interbedded interbedded with with these thesesediments sedimentsand andmay may LREE, P, Ba, F) form form ore ore deposits deposits (Pilot Knob Outcrop, Outcrop, Olympic Olympic Darn, Dam, Baiyan OBo, OBo, Hau(Pilot Knob Hauk1) subvolcanic rriagnetite magnetite and and magnetite-hematite magnetite-hematite ore depodepoki). Related Related subvolcanic -+ Cu, Cu, Co, P, FF)) may may be these basins basins (Pea (Pea s i t s ((+ sits Go, Mo, P, be associated associated with with these Ridge, Pilot Kiirunavaara). Ridge, Pi lot Knob Knob Subcrop, Subcrop, K i irunavaara) . . A review review of the geochemistry of these iron oxide oxide rich deposits deposits A the geochemistry of these suggests aa more more or less continuous differenti ation series. seri es. Overall, suggests less continuous differentiation Ti02 and and P205 P205 (fluorapatite) (f 1 uorapat i t e ) with with there are general decreases iinn TiO corresponding LREE, base base and and precious precious metals, metals, UU (Th), ( T h ) , F, corresponding increases increases in LREE, F, trendsare arecompatible compatiblewith witha acontinuing continuingdifferentiation differentiation aria ana Ba. These These trends w i t hdecreasing decreasing P P and and TI (and (and increaincreaof an iron iron rich rich immiscible immiscible liquid liquidwith of an 17 �The ffinal sing s i n g oxygen oxygen fugacity) f u g a c i t y ) cconditions. onditions. The i n a l ore ore deposit d e p o s i t composition composition an tectonic and t e c t o n i c position p o s i t i o n of of the t h e iron i r o n oxide o x i d e rich r i c hdeposits d e p o s i t s iiss rrelated e l a t e d to to when and andand when when and where where in i n the t h e crust c r u s t liquid l i q u i immiscibility d i m m i s c i b i l ioccurs t y occurs whenand and wheret hthe where e i riron o n ooxide x i d e r rich i c h ddifferentiate i f f e r e n t i a t e is i s released. released. ggl.obal l o b a l pperiod e r i o d of o f ccratonic ratonic greenstone belt b e l t sstyle t y l e ooff The oore ttectonics. ectonics. The r e deposits d e p o s i t s may may be be rrelated e l a t e d to t o other o t h e r lower lower crustal crustal rock i.e., r o c k types t y p e s known known tto o have have formed formed dduring u r i n g the t h e Middle M i d d l e Proterozoic, P r o t e r o z o i c , i.e., anorthosite a n o r t h o s i t e massifs—rapakivi m a s s i f s - r a p a k i v i ggranites r a n i t e s and and ttheir h e i r associated a s s o c i a t e dmagmatic magmatic Lake, Adirondacks, segregation (Allard s e g r e g a t i o n Fe—Ti-P Fe-Ti -P oore r e deposits d e p o s i t s (A1 l a r d Lake, Adirondacks, Nelson, Va). Production Va) P r o d u c t i o n and and ddifferentiation i f f e r e n t i a t i o n of o f immiscible i m m i s c i b l e iiron r o n oxide o x i d e rich rich 1liquids i q u i d sduring d u r i n ganorthosite a n o r t h o s i templacement e emplacementmay maybebethe t hcommon e common denominator denomi n a t o r ffor o r the t h e origin o r i g i nofo upper f upper and and lower lower crustal c r u s t a l iiron r o n oxide o x i d e deposits. deposits. Pasproducesu puplift emplacement o fofa anorthosites n o r t h o s i t e s produces l i f t and and extension e x t e n s i o n ttoo form form ssive i v e emplacement Accompanying lowerc rcrustal marginal and iintracratonic n a l and n t r a c r a t o n i c basins. basins. Accompanying lower u s t a l ppartial a r t ia1 marg melting me1 t ng generates generates rapakivi r a p a k i v i granite g r a n i t e suites s u i t e s and and rrelated e l a t e d areally a r e a l l y extenextenCoeval, aalkalic, f e l s i c volcanics. volcanics. Coeval, l k a l i c , intermediate i n t e r m e d i a t e and and mafic maf i c volcavolcassive ive felsic m i n o r ) and and iintrusions n t r u s i o n s are a r e also a l s o related r e l a t e d to t oanorthosite a n o r t h o s i t eemplaceemplacennics i c s ((minor) Related Related Upper Uooer Proterozoic P r o t e r o z o i c (1.1-0.5 (1.1 -0.5 Ga)-Lower Gal-Lower Paleozoic Paleozoic anoroanoroment. ment kegenic events are are* rrepresented e p r e s e n t e d bybyaabortive b o r t i v e r rifting i f t i n g ((Keeweenawan, Keeweenawan, Adeg e m events laidean and/or aalkalic 1 aidean Geosyncline, Geosyncl ine, Oslo Oslo Graben) Graben) and/or l k a l i cplutonism p l u t o n i s m(Delamerian (Delarneri an Paleozoic Orogeny, South AAustralia Orogeny, South u s t r a l i a and and Inner I n n e r Mongolia). Mongol ia). Paleozoic and and younger younger carbonatites and kkimberlites maybe beone oneo of c a r b o n a t i t e s and i m b e r l i t e s may f t the h e llast a s t events events to t o characcharacterize t e r i z e this t h i scratonization c r a t o n i z a t i o nprocess. process. These ore o r e deposits d e p o s i t s formed during during stabilization s t a b i 1i z a t i o n tthat h a t followed f o l l o w e d the the a a Archean Archean . The central U.S., from The c e n t r a l U.S., f r o m Missouri M i s s o u r i to t o the t h e Great Lakes region, has sseveral e v e r a l areas areas ooff favorable f a v o r a b l e rock r o c k types t y p e s and and tectonic t e c t o n i c settings s e t t i n g scompatible compatible Careful with w i t h these these ore o r e deposits. deposits. C a r e f u l geophysical geophysical modeling modeling combined combined with with geochemicalandand shouldl elead geochemical g egeologic o l o g i c i n tinterpretation e r p r e t a t i o n should a d t otoi identification dentification ant, ooff ddrillable r i 1 l a b l e ttargets a r g e t s ffor o r another of o f these economically economical l y import important, ggiant i a n t ore o r e deposits. deposits. 18 �Penokean tectonics: tectonics: central c e n t r a l Minnesota Ninnesota geology Constraints C o n s t r a i n t s from from sstructural tructural g e ~ l o g yin ir! east— east- HOLST, T.B., T.B., Department Department of of Geology, Geology, U University of !4innesota Minnesota Duluth, HOLST, n i v e r s i t y of Duluth* Duluth, Minnesota 55812 Duluth, 55812 In past have been been sseveral plate I n the the p a s t decade there t h e r e have everal p l a t e tectonic tectonic a l l ininmodels for f o r the t h e early e a r l y Proterozoic P r o t e r o z o i c Penokean Penokean orogeny. orogeny. These all volve plate boundaries and and some ssuggest v o l v e convergent convergent p l a t e boundaries u g g e s t ccollision, o l l i s i o n , or or models which suggest multiple t e c t o n i c models s u g g e s t that t h a t the the m u l t i p l e collision. c o l l i s i o n . Other tectonic Penokean was an intracratonic event emphasize the role of basement. Penokean w a s a n i n t r a c r a t o n i c e v e n t emphasize t h e r o l e of basement. They suggest basement was rremobilized, and h high s u g g e s t that t h a t basement e m o b i l i z e d , and i g h heat flow con— concentratad fundamental boundary boundary iin basement, tthe Great c e n t r a t e d aalong l o n g aa fundamental n tthe h e basement* he G reat Tectonic Lakes T e c t o n i c Zone. Zone. Recent sstructural of eearly i n east— eastRecent t r u c t u r a l sstudies t u d i e s of a r l y PProterozoic r o t e r o z o i c rrocks o c k s in central Minnesota have have rrevealed which cconstrain c e n t r a l Minnesota e v e a l e d sseveral e v e r a l ffacts a c t s which onstrain Minnesota, the tectonic 1. In I n Minnesota* the t e c t o n i c models of of the t h e Penokean Penokean orogeny: orogeny: 1. o l d i n g , each rresultesultPenokean orogeny orogeny iinvolved two main main phases phases of of ffolding, Penokean n v o l v e d two The first f i r s t phase p h a s e of o f defordefor2. p e n e t r a t i v e tectonic t e c t o n i c fabric. fabric. i n g in i n a penetrative ing mation involved of northward-directed northward—directed nappes in i n v o l v e d the t h e development of in some some (Z approxand w was accompanied by by aa llarge approxa s accompanied a r g e fflattening l a t t e n i n g sstrain t r a i n (Z aareas, r e a s , and imately vertical) well-developed foliation. f o l i a t i o n . 3. 3. The second second imately v e r t i c a l ) and and a well—developed of deformation deformation lled development of of uupright phase of e d tto o tthe h e development p r i g h t ffolds, o l d s , and was horizontal of over w a s accompanied by a h o r i z o n t a l sshortening h o r t e n i n g of o v e r 60% 60% (Z (Z north— northssouth o u t h and h orizontal). horizontal). could ppossibly decollement While tthese h e s e ffeatures e a t u r e s could o s s i b l y bbe e eexplained x p l a i n e d by decollement gravity—gliding g r a v i t y - g l i d i n g off o f f a rising r i s i n g ddiapir i a p i r (McGrath (McGrath Gneiss?) Gneiss?) they are are with convergent pplate ccertainly e r t a i n l y aalso l s o cconsistent onsistent w i t h aa convergent l a t e boundary environenvironment, with southward-dipping subduction s u b d u c t i o n zone. zone. Further, F u r t h e r , the t h e fabric fabric ment* w i t h a southward—dipping within w i t h i n the t h e McGrath Gneiss suggests s u g g e s t s that t h a t it i t was not n o t a diapir, d i a p i r , but l ~ was w at s involved phase of of Penokean Penokean ddeformation, involved iin n tthe h e eearly a r l y phase e f o r m a t i o n y pperhaps e r h a p s as nappe ccores Pennine Nappe Nappe Zone Zone of of tthe Alps) o orr as "embryonic nappe o r e s (as ( a s iin n Pennine h e Alps) as recently r e c e n t l y suggested s u g g e s t e d in i n the & e Helvetic Helvetic nappe" basement shear s h e a r zones, zones * as Nappe Thus it Nappe Zone. Zone. i t seems that t h a t the t h e sstructural t r u c t u r a l evidence e v i d e n c e in i n east— eastcentral Minnesota iis most eeasily accounted ffor by aa cconvergent c e n t r a l Minnesota s most a s i l y accounted o r by o n v e r g e n t plate plate boundary model, cconsistent with growing body body of of sstructural boundary model, onsistent w i t h tthe h e growing t r u c t u r a l and petrologic p e t r o l o g i c eevidence v i d e n c e from Wisconsin and Upper Michigan. Michigan. 19 �The of of Transcurrent Shear Shear in i n Deformation Deformation of of the the The Role -Archean ---Rocks of of the the Vermilion District, D i s t r i c t , Minnesota Minnesota .. P.J. P J Hudleston, Hudles t o n l Department Department of of Geology Geology and and Geophysics, Geophysics University U n i v e r s i t y of of Minnesota, Minnesota, 551455; Minneapolis, MN Minneapolisl MN 55455; DL. D.L. Southwick, SouthwicklMinnesota MinnesotaGeological GeologicalSurvey, Survey,26142 2642 University U n i v e r s i t y Ave., A V ~ St. .S ~t . Paul, Paul, MN MN 551114. 551 14. Deformed and and metamorphosed sedimentary sedimentary and volcanic volcanic rocks of the the Vermilion district an east-west east—westt rtrending e n d i n g bbelt e l t between between higher grade grade rocks rocks of the the d i s t r i c t occupy occupy an Vermilion Granitio Vermilion G r a n i t i c Complex Complex t to o tthe h e north n o r t h and and the t h e Giants G i a n t s Range Range bbatholith a t h o l i t h to t o the the south. A l l the t h e measured measured sstrain, t r a i n , aa cleavage, cleavage, and and aa mineral mineral llineation i n e a t i o n iin n this this south. AU belt b e l t are are attributed a t t r i b u t e d to t o the t h e 'main' !maintphase phaseofofdeformation deformation (D2) (D2) that t h a t followed followed an an earlier whichl eleft e a r l i e r nappe—forming nappe-forming event event (D1), (Dl), which f t l little i t t l e evidence evidence of of fabric. fabric. Previous assumed that t h a t the t h e D2 deformation resulted r e s u l t e d from north-south north-south Previous work work has has assumed compression compression across a c r o s s the t h e district, d i s t r i c t , presumably presumably related r e l a t e d to t o diapiric d i a p i r i c intrusion i n t r u s i o n of of the the batholithic number of of observations observations now now lead l e a d us us b a t h o l i t h i c bodies bodies to t o the t h e north n o r t h and and south. south. AA number to that aa significant s i g n i f i c a n t component component of t h i s deformation deformation resulted r e s u l t e d from from t o believe believe that dextral d e x t r a l shear shear across a c r o s s the thewhole whole region. region. Thus Thus tthe h e Vermilion Vermilion ffault, a u l t , aalate—stage late-stage strike—slip that bounds bounds the t h e Vermilion Vermilion ddistrict i s t r i c t to t o the t h enorth, n o r t h lmay may s t r i k e - s l i p sstructure t r u c t u r e that simply s h e a r regime regime that t h a t was w a s much much simply be be the t h e latest, l a t e s t l more brittle b r i t t l e expression expression of of aa shear more time. Features Features that t h a t are a r e indicative i n d i c a t i v e of of shear shear more widespread widespread in i n space space and and time. include zones with with sigmoidal sinoidal foliation include ductile d u c t i l e sshear h e a r zones f o l i a t i o n patterns, p a t t e r n s , highly h i g h l y schistose schistose zones of shear c l a s t s or o rpyrite p y r i t ecubes cubes with with zones with with the t h e development development of shear bands, bands, feldspar f e l d s p a r clasts of this asymmetric of the asymmetric ppressure r e s s u r e shadows, shadows, and and the t h e fact f a c t that t h a tthe t h easymmetry asymmetry of t h e F2 F2 ffolds o l d s is is predominantly of the predominantly ZZf ofor r aat t least l e a s t 15 15km km south south of t h e Vermilion Vermilion ffault. ault. The presence of of a large of simple The presence l a r g ecomponent component of simple shear s h e a r may may hhelp e l p explain e x p l a i n addiaddi- tional t i o n a l structural s t r u c t u r a lfeatures f e a t u r e sini a n simpler a simplerway waythan than otherwise otherwise possible. possible. Just J u s t south south of of the t h e Vermilion Vermilion fault f a u l tthe t h ecleavage cleavagelocally l o c a l l ybecomes becomes folded folded and and aa new new spaced spaced cleavage developsi in o r i e n t a t i o n tot othe t h eold o l dcleavage cleavageaway away from from the the cleavage develops n aa similar orientation folds. than iinterpreting this as as evidence evidence for f o r an an additional a d d i t i o n a l episode episode of of f o l d s . Rather Rather than n t e r p r e t i n g this deformation, we consideri tit ttoo be deformation, w e consider be due due to t o aa single s i n g l eprocess process of ofcontinuous continuous shear: shear: aa foliation f o l i a t i o ndevelops developsand and after a f t e r aa large l a r g e strain s t r a i n local l o c a l perturbations p e r t u r b a t i o n s result r e s u l t in in folding f o l d i n g of the the old o l d foliation f o l i a t i o nand and the t h e development development of new one x i a l planar p l a n a r to to of a new one aaxial the type of of perturbation t h e folds. f o l d s . The The same same type p e r t u r b a t i o n can can lead l e a d to t o the t h e juxtaposition j u x t a p o s i t i o n of ofzones zones of ~f of constrictional c o n s t r i c t i o n a l and and flattening f l a t t e n i n g strains, s t r a i n s , aa distinctive d i s t i n c t i v e feature f e a t u r eof of the therocks rocks of the the Vermilion Vermilion district d i s t r i c t otherwise otherwise hard hard to t o account account for. f o r . The The strain s t r a i n pattern pattern requires north-south component component of of shortening s h o r t e n i n g in i n addition a d d i t i o n to t o shear. shear. The r e q u i r e s aa north—south D2 The D2 deformation deformation in i n the t h e Vermilion Vermilion district d i s t r i c t can can therefore t h e y e f o r e be be characterized c h a r a c t e r i z e d as a s one one of of transpression: ( ? ) crustal c r u s t a l blocks blocks to to transpression: oblique oblique compression compression between between two two more more rigid r i g i d (?) the the north n o r t h and and south. south. 20 �Preliminary P r e l i m i n a r y Paleomagnetic Results R e s u l t s from the t h e Baraboo Quartzite Quartzite Rhyolite and G Granite and the t h e Associated Associated R h y o l i t e and r a n i t e IInliersof n l i e r s of South Central C e n t r a l Wisconsin W.F. (Dept. of of GGeological and Geophysical W.F. KEAN, KEAN, D. D. MERCER, MERCER, E. E. RAMI'HTJN wlTHU?? (Dept. e o l o g i c a l and Sciences, W I 53201) 53201) S c i e n c e s , University U n i v e r s i t y of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, WI The The Proterozoic P r o t e r o z o i c geology geology of of Wisconsin represents r e p r e s e n t s a fairly f a i r l y complex succession the s u c c e s s i o n of of tectonic t e c t o n i c events. e v e n t s . Of Of interest i n t e r e s t to t o this t h i s project p r o j e c t is the suite s u i t e of of rhyolitic r h y o l i t i c and and granitic g r a n i t i c inliers i n l i e r s of of the t h e Fox Fox River River Valley V a l l e y and and the t h e overlying o v e r l y i n g Baraboo Quartzite Q u a r t z i t e which span span the t h e time t i m e from from 1760 1760 m.y. may. ago to t o 1450 1450 m.y. m-y. ago. ago. A A total t o t a l of of 50 50 samples samples of of Baraboo Baraboo Quartzite Q u a r t z i t e were were collected c o l l e c t e d from from 15 1.5 sites samples were subs i t e s on both b o t h sides s i d e s of of the t h eBaraboo Baraboo Syncline. S y n c l i n e . The samples jected j e c t e d to t o both both alternating a l t e r n a t i n g field f i e l d (A.F.) (A.F.) demagnetization demagnetization and and thermal thermal demagnetization. remanence is demagnetization. The The rresults e s u l t s indicate i n d i c a t e that t h a t stable s t a b l eremanence is carried was set set before c a r r i e d by by hematite h e m a t i t e and and that t h a t the t h e magnetization m a g n e t i z a t i o n was b e f o r e the the major of the major ffolding o l d i n g of t h e syncline. s ~ c l i n e . The The within-site w i t h i n - s i t e directions d i r e c t i o n s are are tightly v a l u e s ranging from from 45 45 to t o 300, 300, and andct—95 a-95 t i g h t l y clustered c l u s t e r e dwith w i t hKK values values magneticddirections d e g r e e s . The The magnetic i r e c t i o n s aafter fter v a l u e s ranging ranging from from 118 8 tto o 55 degrees. unfolding u n f o l d i n g cluster c l u s t e r around around an an inclination i n c l i n a t i o n of 29° 29' and and aa declination d e c l i n a t i o n of of 1900. V.G.P. at a t about about 28°S, 2a0S, 90°W 90° which fits f i t s well w e l l with with 190° This T h i s gives g i v e s aa V.G.P. previously published North Torth American mericen Precambrian p r e v i o u s l y published Precambrian poles p o l e s for f o r the t h e time time range of of 220 220 m.y. may. ago ago to t o 1650 1650tn.y. may. ago. ago. We W e have have also a l s o obtained o b t a i n e d preliminary p r e l i m i n a r y results r e s u l t s from from several s e v e r a l rhyolites rhyolites from from the t h e Fox Fox River River Valley V a l l e y inliers. i n l i e r s . A.F. A.F. and and thermal thermal demagnetization demagnetization studies s t u d i e s show show these t h e s e samples samples to t o be b e magnetically m a g n e t i c a l l y softer, s o f t e r , but b u t reliable reliable directions d i r e c t i o n s can can be b e obtained. o b t a i n e d . Two dominant pole p o l e positions p o s i t i o n s are a r e found; found; is near n e a r 67°—87°N, 670-870N9 90°—150°W, 90°-150° and and the t h e other o t h e r is is near n e a r 2°—20°S, 2O-20°S one is 90°—120°W. 90'-120°W The The first f i r s t pole p o l e position p o s i t i o n is is reasonable r e a s o n a b l e for f o r 1630 1630 m.y. m.y. ago, ago, t h e second second is is similar similar to t o the t h e results r e s u l t s for f o r the t h e Baraboo Baraboo Quartzite. Quartzite. and the 21 �Composite Conposite Magnetic Yagnetic Ilap Flap of of Wisconsin Uisconsin Precambrian from fro^ New New Compilation Compilation of' Digital D i g i t a l Aerov!agnetic AeroL6amet i c Data Data of EIZABETH R. R. KING K I N G (U.S. (U.S. Geological Geological Survey, S u w e y YReston, Reston* VA VA 22092) 22092) ELIZABETH JOHN H. H. KARL EWU (Univ. (univ. of of Wisonsin, Wisonsiny Oshkosh, 0shkoshy WI W I 54901) 54901) JOHN JOHN SS. ELASNER KLASNER(Uestern (Ves t e r n Illinois I l l i n o i s Univ., Univ. Macomb, Macomb IL IL 61455) 61455) JOHN WILLIAM J. J. JONES JONCS (U.S. (U-S. Geological G e o l o g i c a l Survey, Surveyy Reston, R e s t o n y VA VA 22092) 22092) WILLIAM composite magnetic magnetic contour contour map map of of the t h e exposed exposed Precambrian Precambrian terrane terrane AA composite w i l l be be displayed d i s p l a y e d for f o r the t h e first f i r s t time. time. This This of northern n o r t h e r n Wisconsin Wisconsin will of mapy at a t aa scale s c a l e of of 1:250,000, 1:25OY00Oywas was prepared prepared from from 94 94 aeromagnetic aeromagnetic 15' 15' map, quadrangle Karl under under aa grant g r a n t from from the the quadrangle maps, mapsy which which were were compiled compiled by by Karl U.S. U.S. Geological G e o l o g i c a l Survey S u w e y from f r o u data d a t a he he obtained o b t a i n e d through through aa survey sur-~ey These conducted during d u r i n g 1973—77. 1973-77. These 94 94 recontoured r e c o n t o u r e d maps, mapsy at a t aa scale s c a l e of of conducted 1:62,500, 1:62y500y will w i l l replace r e p l a c e the t h e set s e t of of 86 8 6 maps maps currently c u r r e n t l y available a v a i l a b l e from fron t h e Wisconsin Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey. Sumey. The The 20— 20- and and the 100—gamma of the t h e previous p r e v i o u s set, s e t y are a r e continuous continuous 100-gamma contours, c o n t o u r s y unlike u n l i k e those t h o s e of m e myriad myriad of of detail d e t a i l on on the the and match match at a t quadrangle quadrangle boundaries. b o u n d a r i e s . The and composite c m p o s i t e magnetic magnetic map map from from this t h i s new new compilation c o m p i l a t i o n results r e s u l t s in i n much much more more coherent c o h e r e n t patterns p a t t e r n s that t h a t highlight h i g h l i g h t the t h e contrasts c o n t r a s t s in i n magnetic n a g n e t i c character character of the t h e underlying u n d e r l y i n g Precambrian Precambrian terranes. terranes of . This %is magnetic magnetic map, mapy in i n conjunction c o n j u n c t i o n with w i t h simple s i m p l e Bouguer Bouguer and and filtered filtered g r a v i t y maps maps of of the t h e same same area, a r e a y allows a l l o w s the gravity of the the t h e westward westward extension e x t e n s i o n of t h r e e major major tectonic t e c t o n i c belts b e l t s or o r terranes t e r r a n e s proposed proposed by by Klasner Klasner and and others others three (in ( i n press) p r e s s ) for f o r an a n area a r e a that t h a t includes i n c l u d e s the t h e eastern e a s t e r n part p a r t of of the t h e area area shown in i n the t h e composite composite magnetic magnetic map. mapshown P J a s n e r y J. J. S., S a yKing, Kingy E. E. R., R e Y and and Jones, J o n e s y W. V. J., J a yin i n press, p r e s s y Geologic Geologic Iaasner, i n t e r p r e t a t i o n of s r a v i t y and magnetic d a t a f o r n o r t h ern of gravity and magnetic data for northern interpretation M c h i g a n and and Wisconsin: 1Jisconsin: Society S o c i e t y of of Exploration E x p l o r a t i o n Geophysicists Geophysicists Michigan S p e c i a l Publication P u b l i c a t i o n on on the t h e Utility U t i l i t y of of Regional Regional Gravity G r a v i t y and and Special lfagnetic Anomaly Anomaly Naps. Maps Magnetic . 22 �Rb—Sr Rb-Sr and Oxygen Isotope I s o t o p e Systematics S y s t e m a t i c s of of Archean Archean Grey Gneisses of of the t h e southwestern southwestern Beartooth B e a r t o o t h Mountains Mountains T.J. T . J . KLRSLING, KIRSLINGy C.W. C.W. MONTGOMERY, MONTGOMF3Y, and and E.C. E.C. PERRY, PEXRY, JR. JR. Geology, Geology, Northern Northern Illinois I l l i n o i s University, U n i v e r s i t y , DeKaib, DeKalb* IL IL (Department of 60115) 60115) Rb—Sr Rb-Sr and oxygen oxygen isotopic i s o t o p i c analyses a n a l y s e s were were performed performed on on samples samples of of Archean gneiss from from the t h e Cooke Cooke City C i t y region r e g i o n of of the t h e Bear— Beark c h e a n grey g r e y granitic g r a n i t i c gneiss tooth t o o t h Mountains, Mountains9 Montana. Montana. A A whole—rock whole-rock Rb—Sr Rb-Sr isochron i s o c h r o n date d a t e for f o r this this unit 2700 m.y. m.y. is u n i t of of about about 2700 is accompanied accompanied by by an an elevated e l e v a t e d initial initial 87Sr/86Sr 8 7 s r / 8 6 s r ratio r a t i o of of 0.7054. 0.7054. A more systematically—collected s y s t e m a t i c a l l y - c o l l e c t e d regional regional suite s u i t e of of these t h e s e grey gneisses g n e i s s e s hints h i n t s at a t an a n age in i n excess e x c e s s of of 33 b.y., b.y.> suggesting incompletely homogenized older h a t aan n incompletely o l d e r component comprised comprised suggesting tthat a portion whole—rock 6180 l8 values p o r t i o n of of the t h e gneiss. g n e i s s . Although Although whole-rock v a l u e s for f o r the the gneiss +8.00 °/oo, g n e i s s (average (average +8.00 O/ooY range +6.98 +6.98 to t o +10.03 +10.03 0/00 O/oo relative r e l a t i v e to to SMOW) o r i g i n * the t h e values v a l u e s are are SMOW) tend to t o indicate i n d i c a t e a primary magmatic origin, largely of oolder metasedimentary l a r g e l y indistinguishable i n d i s t i n g u i s h a b l e from from t5180 6180 vvalues a l u e s of l d e r metasedimentary units t h e gneisses g n e i s s e s (+7.87 (+7.87 to t o +11.00 +ll.OO O/ooy u n i t s now found as a s rafts r a f t s in the values v a l u e s which are a r e lower lower than t h a n expected). e x p e c t e d ) . AA composite composite source s o u r c e would be be more more consistent c o n s i s t e n t with w i t h the t h e Rb—Sr Rb-Sr data d a t a and and initial i n i t i a l Sr S r ratio. r a t i o . The The 2700 m.y. date 2700 may. d a t e reflects r e f l e c t s the t h e age a g e of of a regional r e g i o n a l thermal thermal event, e v e n t , perpervasive m i x t u r e of of primary primary v a s i v e throughout the t h e Beartooth B e a r t o o t h Mountains. Mountains. AA mixture differentiated d i f f e r e n t i a t e d magma, m a g m a * perhaps perhaps contemporaneous contemporaneous with w i t h this t h i s thermal thermal e v e n t * with w i t h assimilated a s s i m i l a t e d older o l d e r crustal c r u s t a l material m a t e r i a l would would account account for for event, both the t h e sstrontit t r o n t i u m and and oxygen oxygen isotope i s o t o p e data. data. 23 �Gravity models Gravity m o d e l s of o f gneiss g n e i s s domes domes and a n d aa granite g r a n i t e pluton pluton in i n nnortheastern o r t h e a s t e r n Wisconsin Wisconsin John S. S. Kiasner K l a s n e r (Department (Department of of Geology, G e o l o g y , Western W e s t e r n Illinois I l l i n o i s University, University, Macomb, Illinois I l l i n o i s 61455 aand n d U.S. U.S. Geological G e o l o g i c a l Survey) Survey) Dan Osterfeld O s t e r f e l d (Department (Department of o f Geology, Geology, Western W e s t e r n Illinois I l l i n o i s University, University, Macomb, Macomb, Illinois I l l i n o i s 61455) 61455) Three density models T h r e e 22—dimensional -dimensional d ensity m o d e l s of o f granitoid g r a n i t o i d bodies b o d i e s have have been b e e n prepared p r e p a r e d from gravity g r a v i t y profiles p r o f i l e s in i n northeast n o r t h e a s t Wisconsin. Wisconsin. The profiles p r o f i l e s cross c r o s s the t h e Dunbar gneiss g n e i s s dome, another a n o t h e r probable p r o b a b l e gneiss g n e i s s dome dome west w e s t of o f the t h e Dunbar Dome, Dome, and a n d the t h e east e a s t lobe l o b e of o f the t h e Hoskin Hoskin Lake Lake which is part ggranite r a n i t e ppluton l u t o n which i s cconsidered o n s i d e r e d aa p a r t of o f the t h e Dunbar dome. dome. Pock Rock density 45 hand specimens Sims iindicate d e n s i t y aanalyses n a l y s e s oof f 45 s p e c i m e n s collected c o l l e c t e d by by P. P . KK. . Sims ndicate domes, which which aare predominantly rrocks o c k s oof f tthe h e domes, re p r e d o m i n a n t l y gneissic, g n e i s s i c , are a r e on on the the average a v e r a g e of of 0.21 0 . 2 1 gm/cm3 less l e s s dense d e n s e than t h a n the t h e surrounding s u r r o u n d i n g generally generally mafic i s an a n average a v e r a g e of o f 0.30 0.30 m a f i c volcanic v o l c a n i c rocks. r o c k s . The Hoskin Lake granite g r a n i t e is d e n s i t y models models gm/cm3 less l e s s dense d e n s e than t h a n the t h e volcanic v o l c a n i c country c o u n t r y rock. r o c k . The density domes eextend iindicate n d i c a t e tthat h a t tthe h e ggneiss n e i s s domes x t e n d to to a a depth d e p t h of o f 1.6 1 . 6 km km (1 ( 1 mile). mile). Gravity model sstudies of llarge G r a v i t y model t u d i e s of a r g e ppost o s t kkinematic i n e m a t i c pplutons l u t o n s ((ott E o t t and and Smithson, 1 9 6 7 ) , of o f similar s i m i l a r areal a r e a l dimension d i m e n s i o n as a s the t h e gneiss g n e i s s domes, domes, ininS m i t h s o n , 1967), d i c a t e that t h a t most o f them are on the t h e order o r d e r of o f 10 1 0 km km thick, t h i c k , much much thicker thicker dicate most of domes and tthan h a n tthe h e domes a n d pluton p l u t o n of o f this t h i s study. s t u d y . They nnote, o t e , however, however, the the P r e c a m b r i a n granitic g r a n i t i c bodies b o d i e s tend t e n d to t o be b e thinner t h i n n e r than t h a n this t h i s and a n d that t h a t they they Precambrian may be b e thinned t h i n n e d by by erosion. e r o s i o n . Although A l t h o u g h the t h e gneiss g n e i s s domes of o f this t h i s study study a r e likely l i k e l y synkinematic s y n k i n e m a t i c and and n o t exactly e x a c t l y the t h e same same as a s the t h e granite granite are not plutons m o d e l l e d by by Bott B o t t and a n d Smithson, S m i t h s o n , they plutons modelled t h e y appear a p p e a r to t o be b e unusually unusually thin. thin. I t is ppossible o s s i b l e that t h a t vvarying a r y i n g densities d e n s i t i e s with w i t h depth d e p t h do do not n o t permit permit It a n accurate a c c u r a t e estimate e s t i m a t e of o f their t h e i r true t r u e depth. d e p t h . On the t h e other o t h e r hand, h a n d , the the an e a s t lobe l o b e oof f the t h e Hoskin Lake granite g r a n i t e body is i s aa discrete d i s c r e t e pluton. p l u t o n . Its Its east s h a l l o w depth d e p t h aand n d the t h e fact f a c t that t h a t it i t lies l i e s within w i t h i n aa prominent p r o m i n e n t south s o u t h dipdipshallow i t may be be allochthonous a l l o c h t h o n o u s and and is is p ing m agnetic g r a d i e n t suggests s u g g e s t s that t h a t it ping magnetic gradient truncated t r u n c a t e d at a t depth. d e p t h . One possible p o s s i b l e scenario s c e n a r i o is i s that t h a t truncation truncation ooccured c c u r e d aalong l o n g south s o u t h dipping d i p p i n g thrust t h r u s t faults f a u l t s that t h a t are a r e tectonically tectonically aassociated s s o c i a t e d with w i t h the t h e proposed p r o p o s e d fliagara N i a g a r a ssuture u t u r e which i e s aabout b o u t four four which llies m i l e s north n o r t h of o f the t h e Hoskin Hoskin Lake Lake pluton. pluton. I f this t h i s is i s correct, c o r r e c t , then t h e n the the miles If g n e i s s domes also b e allochthonous a l l o c h t h o n o u s features f e a t u r e s that t h a t are a r e truncated t r u n c a t e d at at gneiss domes may may also be ddepth e p t h by thrust t h r u s t faults. f a u l t s . Alternately; A l t e r n a t e l y , the t h e shallow s h a l l o w depths d e p t h s of o f the the g n e i s s domes n d granite g r a n i t e pluton p l u t o n may be b e due d u e to t o uplift u p l i f t and and erosion. erosion. gneiss domes aand Reference Reference B o t t , Y.H.P., m i t h s o n , S.B., S . B . , 1967, 1 9 6 7 , Gravity G r a v i t y investigation i n v e s t i g a t i o n of of Bott, M.H.P., and and S Smithson, s u b s u r f a c e shape s h a p e aand n d mass distribution d i s t r i b u t i o n of o f granite g r a n i t e batholiths: batholiths: subsurface G e o l o g i c a l Society S o c i e t y of o f America America Bulletin, B u l l e t i n , v. v. 7 8 , p. p . 879—906. 879-906. Geological 78, 24 �The The Plate P l a t e Tectonic Tectonic History History of of North-central North-central Wisconsin Wisconsin GENE GENE L. L. LABERGE LABERGE (Geology (Geology Department, Department, University U n i v e r s i t y of of Wisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, WI W I 54901 54901 and and U.S. U.S. Geological Geological Survey) Survey) KALUS J. SCHULZ SCHULZ (U.S. ( U . S . Geological ~ e o l o g i c a Survey, lSurvey, Reston, Reston, VA VA 22092) 22092) KALUS 3. PAUL PAUL E. E. MYERS MYERS (Geology (Geology Department, Department, University University of of Wisconsin-Eau Wisconsin-Eau Claire, Claire, Eau Eau Claire, C l a i r e , WI W I 54701) 54701) Recent mapping in in north—central n o r t h - c e n t r a l Wisconsin indicates i n d i c a t e s the t h e presence of of three three Recent separate successions of Early Proterozoic volcanic rocks (Figure 1). Each s e p a r a t e successions of Early P r o t e r o z o i c v o l c a n i c rocks (Figure 1 ) . Each succession succession has has aa distinct d i s t i n c t lithology, l i t h o l o g y , structural s t r u c t u r a l pattern, p a t t e r n , and and metamorphic metamorphic grade. grade. These rocks tto the Archean Archean rocks o the t h e south south appear appear to t o be be best b e s texplained explainedby by These rocks rocks and and the aa plate p l a t e tectonic t e c t o n i c model. model. AA widespread widespread succession succession of of Early Early Proterozoic P r o t e r o z o i c quartzofeldspathic q u a r t z o f e l d s p a t h i c gneisses gneisses and amphibolite, derived mainly from subaqueous volcanic i s characterized characterized and amphibolite, derived mainly from subaqueous v o l c a n i c rocks rocks is by by amphibolite—facies amphibolite-facies metamorphism metamorphismarid and isoclinal i s o c l i n a l folding f o l d i n g about about westw e s t - to to northwest—trending northwest-trending axes. axes. These These metavolcanic metavolcanic rocks rocks were were intruded i n t r u d e d mainly mainly by by tonalites. t o n a l i t e s . Lithologies L i t h o l o g i e s are a r e characteristic c h a r a c t e r i s t i c of of island i s l a n d arcs, a r c s ,and andappear appear to t ohave have formed formed over aa north—dipping north-dipping subduction zOne zone (Figure (Figure2A). 2A). Dated the south south of of these t h e s e rocks rocks in i n central central Dated Archean Archean gneisses g n e i s s e s are a r e exposed exposed tto o the Wisconsin, Wisconsin, and and farther f a r t h e r south south typical t y p i c a l Archean Archean "greenstone "greenstone bbelt" e l t " llithologies i t h o l o g i e s of of iron—formations and foundi nind drill iron-formations and t u ftuffs f s a rare e found r i l l cores c o r e s and and aatt the the iron i r o nmine mine at at Black Black River River Falls. F a l l s . These These Archean Archean rocks rocks are a r e believed b e l i e v e d to t o be be part p a r t of of an an older older craton c r a t o n that t h a t collided c o l l i d e d with w i t h the the Early Early Proterozoic P r o t e r o z o i c island i s l a n d arc a r c(Figure (Figure2B). 2B). Metamorphism of the Early Metamorphism and and deformation deformation of E a r l y Proterozoic P r o t e r o z o i crocks rockswas was probably probably caused caused by by the t h e collision. collision. A A younger younger sequence sequence of of Early E a r l y Proterozoic P r o t e r o z o i c volcanic v o l c a n i crocks rocksunconforinably unconformably overlies overlies the the Archean Archean and and older o l d e r volcanic volcanic arc a r c in i n Marathon Marathon County County and and elsewhere. elsewhere. These These rocks rocks consist c o n s i s t of o fsubaqueous subaqueous bbasalt a s a l t to t o rhyolite r h y o l i t e that t h a t have have undergone undergone only only g r e e n s c h i s t - f a c i e s metamorphism, metamorphism, were were deformed deformed about about steeply s t e e p l y plunging plunging northeastnortheastgreenschist-facies trending w e r e extensively e x t e n s i v e l y intruded i n t r u d e d by by epizonal e p i z o n a l granites. g r a n i t e s . This This trending axes, axes, and and were succession isbelieved b e l i e v e dtot ohave haveformed formedata at continental—margin a continental-margin over overa asouthwardsouthwardsuccession is dipping zoneaas the ocean ocean bbasin dipping subduction subduction zone s the a s i n tto o the t h e north n o r t h closed closed (Figure (Figure2C). 2C). The The Niagara thethe boundary isinterpreted i n t e r p r e t e dtot be o be boundarybetween between these t h e s evolcanic volcanic Niagara fault f a u l t zone zone is assemblages andpplatform sedimentaryrocks rocksonont hthe Superiorccraton assemblages and l a t f o r m sedimentary e Superior r a t o n tto o the t h e north north (Figure (Figure2D). 2D). Deformation Deformation and andmetamorphism metamorphism associated a s s o c i a t e d with w i t h the the collision c o l l i s i o n of of these these volcanic Penokean Orogeny. volcanic belts b e l t swith w i t hthe t h eSuperior Superiorcraton c r a t o represent n r e p r e s e nthe t th e Penokean Orogeny. Dozens Dozens theArchean Archean and and Early Early u l t r a m a f i cbodies bodiesoccur occuralong alongthe t h boundary e boundarybetween between the of ultramafic of Proterozojc Proterozoic rocks rocks in i nCentral C e n t r a Wisconsin. l Wisconsin. In In addition a d d i t i o n to t onumerous numerous sulfide sulfide occurrences both Early Early PProterozoic n both r o t e r o z o i c ssuccessions, u c c e s s i o n s , aatt least l e a s tfour four occurrences (mostly (mostly ssmall) m a l l ) iin l o c a l i t i e swith w i t hsignificant s i g n i f i c a ngold t gold m i n e r a l i z a t i o nare a rknown e known in i nthe t h eproposed proposed localities mineralization collision c o l l i s i o nzone zoneini nCentral C e n t r aWisconsin. l Wisconsin. A of Early Early Proterozoic Proterozoic igneous igneousaactivity A third t h i r d and and youngest youngest ccycle y c l e of c t i v i t y is is represented represented by which unconformably unconformablyo overlie by rhyolites r h y o l i t e sat aWausau t Wausauand andCary CaryMound Mound which v e r l i e tthe h e older older sequences, are a r e gently g e n t l yfolded foldedabout aboutaxes axesplunging plunging100_200 10~-20Owest, west, arid and are a r e virtually virtually sequences, unmetamorphosed. r o c k s ~ w e l d e dt tuffs, u f f s , lahars, l a h a r sand , and flow-banded rhyolites-— rhyolites~ unmetamorphosed. These These rocks-—welded flow—banded a r e typical t y p i c a lcaldera c a l d e rtype a type rocks analogous o basin-and-range volcanic rocks in i n the the are rocks analogous to tbasin—and—range volcanic rocks Western Western United United States. S t a t e s . The rocks may The basin—and—range basin-and-range rocks may be be r e lrelated a t e d t otorrifting. ifting. Later of tthe River bbatholith Later faulting f a u l t i n gand andemplacement emplacement of h e Wolf Wolf River a t h o l i t h and and related related syenites s y e n i t e s during during the t h eMiddle Middle Proterozoic P r o t e r o z o i c has has further f u r t h e r complicated complicated the t h e geology. geology. 25 �________ 4 EXPLANATION EXPLANATION j — M I D D L E PROTEROZOIC PROTEROZOIC MIDDLE II.+l.+ + +f4. 90 E A R L Y PROTEROZOIC PROTEROZOIC EARLY Q R A N I T E AND A N D SYENITE SYENITE GRANITE [ A NO RTHO SITE QUA QUARTZITE RHYOLITE GRANITOID ROCKS [ii ARCHEAN ARCHEAN GREENSCHIST FAdES v0LCANIcS 777,,,,, QUARTZOFELDSPATHIC Q U A R T Z O F E L D S P A T H I C ONEISS QNEISS n I ii Q N E I S S , GREENSTONE QREENSTONE GNEISS, A N D GRANITE QRANITE AND 11111lllliIii1 Geological map map of of the t h e Precambrian Precambrian of of north n o r t h central c e n t r a l Wisconsin Wisconsin F i g u r e 1. 1. Geological Figure showing showing the t h e fault-bounded fault-bounded blocks blocks of of greenschist-facies g r e e n s c h i s t - f a c i e s volcanic volcanic rocks rocks alternating a l t e r n a t i n g with with amphibolite-facies a m p h i b o l i t e - f a c i e s volcanic v o l c a n i c rocks r o c k s and and the t h e Archean Archean rocks rocks to t o the t h e south. south. 26 26 �NORTH SOUTH // ——-1 SLANO ARC RNCH PLA1ORM SEIUENTS -— ANIMIKIE BASIN ,OCEAN CRUST — _. A B C ANIMIKIE SEDIMENTS - + + D Figure Figure 2. 2. . ++* ,—- -—- —.-----— — _s..—..— .-...-C - - —s.-.. — — —_. _ _.C + +4*4** + QMCS COLLISION GLL, I94 Block diacrransi lillustrating Elock diaqrams l u s t r a c i n q iie LISossth1e ~ 3 0 s s i bsequence l e sec;usnce of ofeven-as svencs in in the early tile e a r l y Proterocoic Proterozoic in i nWisconsin. \iisconsin. A. A. Developnt Development of of an anisland i s l a n darc a r cover overa anorth-dipping north-dipping subduction subduction offshore Platform sediments zone o f f s h o r e from the t h e Superior Superior Craton. Craton. Platform sediments formed ont the margin of of tthe formed on h e ppassive a s s i v e margin h e Superior Superior Craton. Craton. (Volcanic succession I.) I.) (Volcanic succession B. B. Archean craton c r a t o n from from the the' south south collides c o l l i d e s with the t h e island i s l a n d arc. arc. Continent-margin igneous activity C a c t i v i t y over a south-dipping south-dipping C.* Continent-margin basin subduction zone as a s the t h e ocean b a s i n on the t h e north n o r t h side s i d e of of the the island succession II, greenschist i s l a n d arc a r c closes. closes. (Volcanic succession 11, g reenschist facies f a c i e s rocks.) rocks. 1 D. D. C o l l i s i o n of t h e island i s l a n d arc a r c with the the p l a t f o r m sediments sediments and and Collision of the platform I11 - caldera—type caldera-type t h e Superior Craton. Craton. (Volcanic succession III the volcanics v o l c a n i c s in i n central c e n t r a l Wisconsin.) Wisconsin.) - 27 27 �Geology of of the t h e Lone Lone Mountain Mountain Gold Gold Prospect, P r o s p e c t , Northeast Northeast Nevada Nevada Geology MACKOVJAK and and JOSEPH JOSEPH MkNCIJSO WCUSO (Dept. Bowling Green Green DENNIS MACKOVJAK DENNIS (Dept. of of Geology, Geology, Bowling OH 43LO3) 43403) S t a t e University, U n i v e r s i t y , Bowling Bowling Green, Green, OH State The Lone Lone Mountain Mountain gold gold prospect prospect is i s located l o c a t e d in i n the t h e Independence Independence Range Range The of northeastern n o r t h e a s t e r n Nevada. Nevada. It It lies l i e s within w i t h i n the t h e Arseniéal A r s e n i c a l Gold Gold Belt Belt of of of C a r l i n y Getchell G e t c h e l l and and FMC—Freeport FMC-Freeport epithermal deposits d e p o s i t s along along with w i t h the t h e Carlin, epithermal mines (Fig. (Fig. 1). 1). mines Rock exposed exposed on on Lone Lone Mountain Mountain include: i n c l u d e : Ordovician Ordovician aflocthonous allocthonous Rock Silurianeugeosynclinal c h e r t s and s h a l e s (western f a c i e s rocks eueosynclinal cherts and shales (western facies rocks); ; Silu.rian— Devonian autocthonous miogeosynclinal Roberts Mountains Formation Devonian autocthonous miogeosynclinal Roberts Mountains Formation limestones ((eastern e a s t e r n ffacies a c i e s rrocks); o c k s ) ; and a r i o u s Tertiary T e r t i a r y intrusive i n t r u s i v e and and lixnestones and v various volcanic r o c k s y i n c l u d i n g t h e Nannies' Peak q u a r t z monzonite which forms volcanic rocks, including the Nannies' Peak quartz monzonite which forms t h e crest c r e s t of of Lone Lone Mountain. Mountain. the v a r i e t y of of siliceous s i l i c e o u s rocks rocks termed termed "jasperoids" " j a ~ p e r o i d s occur 'occur ~ w i t h i n the the AA variety within limestone beds beds of of the t h e Roberts Roberts Mountains Formation on on Lone Lone Mountain Mountain and and limestone Mountains Formation arsenic, g o l d y mercury, mercuryy arsenic, a r e associated a s s o c i a t e d with w i t h anomalous anomalous concentrations c o n c e n t r a t i o n s of of gold, are antimonyy and and thallium. t h a l l i u m . Field F i e l d and and laboratory l a b o r a t o r y investigation i n v e s t i g a t i o n by by the the antimony, authors identified i d e n t i f i e d four four types types of of jasperoids: j a s p e r o i d s : 1) 1)sandy sandy jasperoids, Jasperoids, authors which are a r e cavity c a v i t y filling f i l l i n g rocks rocks that t h a t consist c o n s i s t primarily p r i m a r i l y of of quartz q u a r t z sand sand which 2 ) fine-grained j a s p e r o i d s which a r e c a v i t y f i l l i n g rocks ; g r a i n s grains; 2) fine-.grained jasperoid.s, which are cavity filling rocks t h a t are a r e laminated laminated and and consist c o n s i s t primarily p r i m a r i l yofofsilt— s i l t -and. and clay—size c l a y - s i z e quartz quartz that g r a i n s ; 3 ) s i l i c i f i e d limestone j a s p e r o i d s , which a r e limestones in grains; 3) silicified limestone jasperoids, which are limestones in 4) J a s p e r o i d b r e c cias, which c a l c i t e has been replaced by q u a r t z ; a n d y which calcite has been replaced by quartz; and, ) jasperoid breccias, or which a r e c a v i t y f i l l i n g b r e c c i a s t h a t c o n s i s t o f fragments of any, which are cavity filling breccias that consist of fraents of any, or a l l of t h e p r e v i o u s l y l i s t e d rock t y p e s . Sandy j a s p e r o i d s , fine-grained all of the previously—listed rock types. Sandy jasperoids, fine-grained ( t h e "cavity " c a v i t y filling f i l l i n g jasperoids") j a s p e r o i d s " ) are are j a s p e r o i d s , and and jasperoid j a s p e r o i d breccias b r e c c i a s (the jasperoids, d e t r i t a l rocks t h a t occupy complex networks of s o l u t i o n c a v i t i e s and detrital rocks that occupy complex networks of solution cavities and f r a c t u r e s in i n the t h e coarse—grained coarse-grained limestone l i m e s t o n e of of the t h e Roberts Roberts Mountains Mountains fractures and/or interconnected i n t e r c o n n e c t e d bodies bodies as a s much much Formation. They They occur occur as a s isolated i s o l a t e d and/or Formation. a s one one thousand thousand feet f e e t in i n length. l e n g t h . Silicified S i l i c i f i e d limestone limestone jasperoids j a s p e r o i d s occur occur as i r r e g u l a r l y shaped shaped zones zones up up tto o thirty t h i r t y feet f e e t in i n length l e n g t h which which are are a s irregularly as adjacent to t o cavity c a v i t y filling f i l l i n g jasperoids. j asperoids adjacent . 'The solution s o l u t i o n cavities c a v i t i e s which which host h o s t the t h e cavity c a v i t y filling f i l l i n g jasperoids j a s p e r o i d s were were The formed and f i l l e d by k a r s t processes a f t e r t h e emplacement of t h e formed and filled by karst processes after the emplacement of the Nannies1 Peak Peak Intrusive. I n t r u s i v e . The The ddetritaJ. e t r i t a l qquartz u a r t z ggrains r a i n s iin n the t h e karst karst Nannies' c a v i t i e s were d e r i v e d from t h e coarse-grained l i m e s t o n e s of t h e Roberts Roberts cavities were derived from the coarse—grained limestones of the Mountains Formation. Mountains Formation. Multiple waves waves of of epithermal epithermal fluids, f l u i d s , related r e l a t e d to t o the t h e late l a t e Tertiary T e r t i a r y to to Multiple Recent igneous igneous system system on on Lone Lone Mountain, Mountainy moved moved preferentially p r e f e r e n t i a l l y through through Recent t h e filled f i l l e d solution s o l u t i o n cavities c a v i t i e s and and other o t h e r permeable permeable zones zones in i n the t h e Silurian— Silurianthe Devonian Roberts Roberts Mountains Mountains Formation. Formation. These These fluids f l u i d s deposited d e p o s i t e d early e a r l y and and Devonian l a t e calcite c a l c i t e in i n veins, v e i n s , silicified s i l i c i f i e d the t h e cavity c a v i t y filling f i l l i n g jasperoids j a s p e r o i d s and and late p o r t i o n s of of the t h e Roberts Roberts Mountains Mountains Formation Formation limestone, l i m e s t o n e , and and deposited deposited portions f i n e l y disseminated disseminated gold, g o l d y plus p l u s mercury, mercury, arsenic, antimony, and andthallium. thallium. a r s e n i c , antimony, finely We conclude conclude from from aa review review of of the t h e chronology chronology of of geologic geologic events events that that We have a f f e c t e d Lone Mountain t h a t t h e l o c a t i o n and d i s t r i b u t i o n of have affected Lone Mountain that the location and distribution of epithermal gold, g o l d y arsenic, a r s e n i c y antimony, antimonyy thallium t h a l l i u m and and accompanying accompanying epithermal 28 �silicification s i l i c i f i c a t i o n are a r e controlled c o n t r o l l e d more more by by the t h e "plumbing ''plumbing system" systemf1than t h a n by by the rocks in which they are found. t h e rocks i n which t h e y a r e found. The The epithermal e p i t h e r m a l fluids f l u i d s which which have have altered a l t e r e d and and mineralized mineralized the t h e rocks rocks of of Lone Lone Mountain Mountain are a r e related r e l a t e d to t o late late Tertiary T e r t i a r y to t o Recent Recent igneous igneous activity; a c t i v i t y ; however, the t h e mineralized m i n e r a l i z e d rocks rocks are are lower lower Paleozoic. Paleozoic. This This conclusion conclusion recognizing r e c o g n i z i n g the t h e importance importance of of the the "plumbing ffplumbingsystem" system1' rather r a t h e r than t h a n host h o s t rocks has serious s e r i o u s implications i m p l i c a t i o n s when vhen exploring for disseminated gold whether in Nevada or the exploring f o r disseminated in o r t h e Precambrian Precambrian volcanic—sedimentary volcanic-sedimentary terraines t e r r a i n e s of of the t h e Lake Lake Superior S u p e r i o r region. region. ' I '4 '4 '4 '4 '4 PANAMfl4T CITY, CSIILL,...' BALLARAT. CaflL-1— '——I Figure Figure 1. 1. Arsenical Arsenical gold gold belt belt of of Nevada Nevada (Modified from Joralemon, Joralernon,1978) 1978) (Modified from xx •e * * Lone Lone Mountain Mountain prospect prospect Gold Gold deposits deposits Conmiunities Communities 29 �Geology of of the t h e Groveland Groveland Mine, Minef Felch District, D i s t r i c t , Michigan Michigan JOSEPH ROBERT BROWNI BROWN, JAMES JAMES HAmSON, HARRISON, ALAN JOSEPH MANCtJSO, MANCUSOI ROBERT ALAX MAHARIDGE, WAR1DGEf RICHARD RICHARD PENNINGTON, PEN'NINGTONI RONALD RONALD WALDEN WALDEN (Dept. (Dept. of Geology, Bowling Bowling Green Green State OH 43403) 43403) S t a t e University, U n i v e r s i t y f Bowling Bowling Green, Green, OH The Groveland iron i r o n mine is is located l o c a t e d within w i t h i n the t h e Felch Felch Trough Trough in i n Central C e n t r a l Dickinson Dickinson County, County, Michigan. Michigan. The The Middle Middle Proterozoic Proterozoic rocks exposed expased in i n the t h e mine mine are a r e the t h e Randville Randville Dolomite, the t h e Feich Felch rocks Formation, Formation, the t h e Vulcan Iron I r o n Formation, FormationI and the t h e "northside "northside schist." gabbro sill s i l l intrudes i n t r u d e s the t h e northside n o r t h s i d e schist, s c h i s t I and and two two s c h i s t . " A gabbro nearly vertical nearly v e r t i c a l granite g r a n i t e dikes d i k e s trending trending north—south north-south cut c u t the t h e entire entire sequence. sequence. These rocks rocks were were folded, folded, faulted, f a u l t e d I and metamorphosed metamorphosed to amphibolite facies f a c i e s during during the t h e Penokean Penokean Orogeny. Orogeny. t o the t h e amphibolite The m metasedimentary exposed e t a ~ e d i m e n t a krocks ~ exposed in i n the t h e mine strike s t r i k e generally generally east-west east-west and dip d i p steeply s t e e p l y to t o the t h e north. north. James James et e t al. a l . (1961) (1961) and and Cumberlidge Stone (1964) (1964) concluded that t h a t the t h e Vulcan Iron Iron Cumberlidqe && Stone a s s y m e t r i c a l syncline syncline Formation Formation and surrounding surrounding rocks rocks form form aa tight, t i g h t , assymetrical More whose whose axial a x i a l plane plane dips d i p s to t o the t h e north n o r t h at a t approximately approximately 60°. 60° More recently r e c e n t l y (1978) (1978) the t h e Hanna Mining Company staff s t a f f proposed that t h a t the the rocks form aa faulted dipping ssteeply f a u l t e d inonocline monocline dipping t e e p l y to t o the t h e north n o r t h and and that c o r r e l a t i v e to t o the t h e Feich Felch t h a t the t h e "northside " n o r t h s i d e schist" s c h i s t " is not correlative Formation. Our (BGSUI 1982-84) 1982-84) suggests s u g g e s t s aa much much more more Our work in i n progress p r o g r e s s (BGSU, complex a array of rray o f faults f a u l t s and folds f o l d s to t o account for f o r the t h e repetition repetition of beds and the t h e apparent doubling in i n thickness t h i c k n e s s of of the t h e iron iron formation at a t the t h e mine mine site. site. formation Several Several faults f a u l t s are a r e clearly c l e a r l y visible v i s i b l e in i n the t h e mine. mine. The The east east i s bounded by a major fault f a u l t which strikes s t r i k e s NW—SE NW-SE he p i t is end of of tthe pit and dips d i p s steeply s t e e p l y to t o the t h e SW. SW. At A t this t h i s fault f a u l t the t h e iron i r o n formation formation terminates terminates abruptly a b r u p t l y against a g a i n s t Randville Randville Dolomite. Dolomite. Also, Also, aa set s e t of of faults E-W pparallel dip a r a l l e l tto o tthe h e iiron r o n formation and d ip f a u l t s sstrike t r i k e E-W f a u l t s offset o f f s e t the t h e granite g r a n i t e dikes dikes approximately vertically. v e r t i c a l l y . These faults and and appear to t o have right r i g h t lateral l a t e r a l and and normal normal components. components. A complex series s e r i e s of of nearly n e a r l y isoclinal i s o c l i n a l folds f o l d s is i s clearly c l e a r l y exposed exposed in of Randville Dolomite i n the t h e southwest southwest wall w a l l of of Dolomite in i n an outcrop of the t h e pit. p i t . This T h i s pattern p a t t e r n of of isoclinal i s o c l i n a l folding f o l d i n g may may be be characteristic characteristic of the t h e deformation of of all a l l the t h e metasedimentary units u n i t s in i n the t h e Feich Felch Trough. i s currently c u r r e n t l y in i n progress at a t the t h e mine mine and and Trough. More More work is elsewhere in Felch Trough in order tto better define i n tthe h e Felch i n order o b etter d e f i n e the t h e overall overall structure. structure. 30 - �References References James, H. L., L . , Clark, Clark, L. L. D., D . , Lamey, Lamey, C. C. A., A . , and and Pellijohn, P e l l i j o h n , E. E . J., J., James, H. 1961, in i n collaboration c o l l a b o r a t i o n with with Freedman, Freedman, J., J., Trow, Trow, J., J., and and 1961, K., Geology Geology of of central c e n t r a l Dickinson DickinsonCounty, County, Michigan: Michigan: Wier, K., Wier, U.S. Geol. Geol. Survey Survey Prof. Prof. Paper Paper 310, 310, 176 176p. p. U.S. Cumberlidge, J. J. T., T., and and Stone, Stone, J. J. G., G., 1964, 1964, The TheVulcan Vulcan IronIronCumberlidge, formation at a t the t h e Groveland GrovelandMine, Mine, Iron I r o n Mountain, Mountain, Michigan: Michigan: formation Econ. Geol., Geol., v. v. 59, 59, p. p. 1049—1106. 1049-1106. Econ. Birak, Birak, Donald Donald 3., J., 1978, 1978, Mineralogy Mineralogy and and petrology petrology of of the t h e Middle Middle Precambrian Precambrian rocks, rocks, Groveland g rove land Iron I r o n Mine, Mine, Dickinson Dickinson County, County, M.S. thesis, t h e s i s , Bowling Bowling Green GreenState State Msch.: Unpublished Unpublished M.S. Mich.: University, Bowling Bowling Green, Green, Ohio Ohio 43403, 43403, 149 149p. p. University, 3' �P o t a s s i u m Metasomatism Metasomatism of of Trondhjemite TrondhjemiteMigrnatite Miqmatite Walirock, Wallrock, Potassium V e r m i l i o n Complex, N o r t h e r n Minnesota Vermilion Complex, Northern Minnesota A . MARIANO MARIANO (Department (Department of of Geology, Geology, Beloit B e l o i t College, College, A. W I 53511) B e l o i t , Beloit, WI 53511) H . H . WOODARD WOODARD (Department (Department of of Geology, Geology, Beloit B e l o i t College, College, H.H. W I 53511) B e l o i t , Beloit, WI 53511) E x t e n s i v e collecting c o l l e c t i n g of of migmatite m i q m a t i t e walirock w a l l r o c k in i n the t h e southsouthExtensive e a s t e r n c o n t a c t zone of t h e Vermilion B a t h o l i t h h a s been eastern contact zone of the Vermilion Batholith has been c a r r i e d out o u t over o v e r the t h e past p a s t six s i x years y e a r s by by the t h e Beloit B e l o i t College College carried Department of of Geology. Geology. Potash P o t a s h feldspar f e l d s p a r distribution d i s t r i b u t i o n was was Department from the t h e Fourtown Fourtown Lake, Lake, Friday F r i d a y Bay, Bay, s t u d i e d in i n specimens specimens .from studied and Basswood Basswood Lake Lake West W e s t quadrangles q u a d r a n g l e s through through J a c k f i s h Lake, Lake, and Jackfigh f e l d s p a r staining, s t a i n i n g , cathodoluminescence, c a t h o d o l u m i n e s c e n c e , and and petrographic petrographic feldspar t e c h n i q u e s . The The specimens specimens investigated i n v e s t i g a t e d were were collected collected techniques. Granitefrom the t h e three t h r e e major major map map units u n i t s of of the t h e study s t u d y area. a r e a . Granitefrom (Mb) r i c h m i g m a t i t e (Mg) and b i o t i t e s c h i s t r i c h m i g m a t i t e(Mb) rich migmatite (Mg) and biotite schist-rich migmatite d i f f e r o n l y i n p e r c e n t a g e of g r a n i t i c m a t e r i a l (leucosome) differ only in percentage of granitic material (leucosome) r e l a t i v e to t o biotite b i o t i t e schist s c h i s t (paleosome). ( p a l e o s o m e ) . Leucocratic L e u c o c r a t i c biotite biotite relative i s t h e r o c k t y p e of t h e Vermilion b a t holith. a d a m e l l i t e (La) adamellite (La) is the rock type of the Vermilion batholith. The paleosome paleosome and and selvage s e l v a g e layers l a y e r s of of the t h e migmatites m i g m a t i t e s are are The ddevoid e v o i d of o f potash p o t a s h feldspar. f e l d s p a r . The The leucosomes leucosomes are a r e of of two two differdiffere n t r o c k t y p e s , t r o n d h j e m i t e and a d a m e l l i t e , depending on ent rock types, trondhjemite and adamellite, depending on amount of o f potash p o t a s h feldspar f e l d s p a r present. p r e s e n t . Leucosome Leucosome composition composition amount i s illustrated i l l u s t r a t e d in i n Fig. F i g . 1. 1. The The distribution d i s t r i b u t i o n of of the t h e potash potash is i s very v e r y selective s e l e c t i v e and andof' of a a non—gradational n o n - g r a d a t i o n a l nature. nature. ' ffeldspar e l d s p a r is T e x t u r a l relationships r e l a t i o n s h i p s indicate i n d i c a t e replacement r e p l a c e m e n t of of plagioclase plagioclase Textural i s late l a t e and and by potash p o t a s h feldspar. f e l d s p a r . Quartz Q u a r t z in i n the t h e leucosomes leucosomes is by r e p l a c e s the t h e feldspars. f e l d s p a r s . In I n the t h e field,the f i e l d , t h e pink p i n k adamellite adamellite replaces can be be seen s e e n cross c r o s s cutting c u t t i n g and and invading i n v a d i n g the t h e light l i g h t grey grey can t r o n d h j e m i t e l a y e r s and v e i n s . trondhjemite layers and veins. Specimens from from the t h e area a r e a mapped mapped as a s the t h e southeastern s o u t h e a s t e r n border border Specimens of t h e Vermilion b a t h o l i t h (La) show some c o m p o s i t i o n al of the Vermilion batholith (La) show some compositional l a y e r i n g w i t h r e s p e c t t o p o t a s h f e l d s p a r , a l t h o u g h t h e potash layering with respect to potash feldspar, although the potash i s much more uniform t h a n i n t h e f e l d s p a r d i s t r i b u t i o n feldspar distribution is much more uniform than in the leucosomes of of the t h e migmatites. m i g m a t i t e s . Textural T e x t u r a l relationships r e l a t i o n s h i p s indicate indicate leucosomes r e p l a c e m e n t of p l a g i o c l a s e by p o t a s h f e l d s p a r . replacement of plagioclase by potash feldspar. F i e l d and and laboratory l a b o r a t o r y evidence e v i d e n c e suggests s u g g e s t s that t h a t the t h e original original Field leucosome of of the t h e migmatite m i q m a t i t e walirock w a l l r o c k of of the t h e Vermilion Vermilion complex complex leucosome t r o n d h j e m i t i c . Later, L a t e r , through t h r o u g h potassium p o t a s s i u m metasomatism, metasomatism, was all a l l trondhjemitic. was much of of the t h e trondhjemitic t r o n d h j e m i t i c leucosome leucosome was was converted c o n v e r t e d to t o adamellite. adamellite. much The o r i g i n of some of t h e q u a r t z i n t h e s e m i g m a t i t e s may be The origin of some of the quartz in these migmatites may be the metasomatic p o t a s h f e l d s p a r . r e l a t e d t o t h e o r i g i n of related to the origin of the metasomatic potash feldspar. The rocks r o c k s mapped mapped as a s the t h e southeastern s o u t h e a s t e r n border b o r d e r of of the t h e Vermilion Vermilion The b a t h o l i t h show t h e same metasomatic r e l a t i o n s h i p s a the batholith show the same metasomatic relationships ass the m i g m a t i t e s , b u t on a more uniform b a s i s . I t i s p o s s i b l e that that migmatites, but on a more uniform basis. It is. possible t h e Vermilion b a t h o l i t h i t s e l f may have been a t o n a l i t i c o the Vermilion batholith itself may have been a tonalitic orr i n t r u s i o n which which was was later l a t e r transformed t r a n s f o r m e d to to t r o n d h j e m i t i c intrusion trondhjemitic a d a m e l l i t e through t h r o u g h extensive e x t e n s i v e potassium potassium metasomatism. metasomatism. If I f this this adamellite 32 �i s not n o t the t h e case, c a s e , than t h a n the t h e "batholith " b a t h o l i t h rocks" r o c k s " (La) ( L a ) examined examined is i n t h i s s t u d y a r e n o t t r u e b a t h o l i t h r o c k s b u t h i g hly in this study are not true batholith rocks but highly metasomatised ( g r a n i t i z e d ) w a l l rock. metasomatised (granitized) wall rock. A F i g u r e 1. 1. Plot P l o t of of the t h e relative r e l a t i v e percentages p e r c e n t a g e s of of modal modal quartz q u a r t z (Q), (Q), Figure a l k a l i f e l d s p a r ( A ) , and p l a g i o c l a s e (P) f o r t h e m i g m a t i t e alkali feldspar (A), and plagioclase (P) for the migmatite (La.). Percentages P e r c e n t a g e s are a r e plotted plotted leucosomes and and batholith b a t h o l i t hrocks r o c k s(La.). leucosomes on an I U G S c l a s s i f i c a t i o n t r i a n g l e . on an IUGS classification triangle. • - Trondhjemite leucosome leucosome Trondhjexnite - Adamellite leucosoe leucosome Adaxnelljte — £A — • Batholith rocks rocks -- Batholith 33 �LLate Archean Metamorphic Metamorohic Conditions - a t e Archean at at Granite G r a n i t e Falls, Fa11s ,Minnesota Minnesota - DAVIDP.P.MOECHER MOECHER (Dept. Geological Sciences, DAVID (Dept. Geological Sciences, U nUniversity i v e r s i t y ooff Michigan, Michigan, Ann Arbor, Arbor, Mi. Ann M i . 48109) 48109) L. GORDON MEDARIS, (Dept. Geology Geophysics, of L. GORDON MEDARIS, JR. JR. (Dept. Geology andand Geophysics, U nUniversity i v e r s i t y of Wisconsin-Madison, W i sconsi n-Madi son, Madison, Madison, Wi. W i 53706) 53706) . A detailed and bbarometric A d e t a i l e d geothermometric geothermometric and a r o m e t r i c iinvestigation n v e s t i g a t i o nhas hasbeen been completed Archeang granulite completed f ofor r Archean r a n u l i t e ffacies a c i e s gneisses gneisses aatt Granite G r a n i t e Falls, F a l l s , Mn. Mn. Garnetiferous and bbiotite-bearing G a r n e t i f e r o u s and i o t i t e - b e a r i n g variants v a r i a n t sofothe f t hhornblende-pyroxene e hornblende-pyroxene gneiss and ccordieritegneiss and o r d i e r i t e - and and orthopyroxene-bearing orthopyroxene-bearing vvariants a r i a n t s ooff the t h e gargarnet-biotite of oHimmelberg n e t - b i o t i t egneiss gneiss f Himmelberg(1968) (1968)contain contaia n number a numberofofassemblages assemblages ffor o r which which accurate accurate thermobarometric thermobarometric ccalibrations a l i b r a t i o n s have have recently r e c e n t l y been been calibrated. c a l ibrated. which occurs The composition composition ooff cordierite The c o r d i e r i t e(Mg/(Mg+Fe)=.80) (Mg/(Mg+Fe)=. 80) which r e q u i r e s metamorphic metamorphic cconditions o n d i t i o n s of of llocally o c a l l y in i n garnet-biotite g a r n e t - b i o t i t e gneiss gneiss requires approximately 710°C, 710°c 5.6kb, 5.6kb, and and X(H20)=.30 X(H20)=. SO (Lee (Lee and and Holdaway, Holdaway, 1977). 1977). Temperaturesoof 655°Cand and664 664°C havebeen been Temperatures f 65S° C have o bobtained t a i n e d f ofor r ccoexisting oexisting garnet g a r n e t and and clinopyroxene clinopyroxene (Ellis ( E l l i sand andGreen, Green, 1979) 1979) and and magnetite m a g n e t i t e and and ilmenite andLLindsley, i l m e n i t e (Spencer (Spencer and i n d s l e y , 1981), 1981) , in i n garnetiferous g a r n e t i f e r o u s hornblendehornblendeC o e x i s t i n g orthopyroxene orthopyroxene and n biobioandclinopycoxene clinopyroxenei in pyroxene gneiss. Coexisting pyroxene ttite-pyroxene i t e - p y r o x e n e ggneiss n e i s s yyield i e l d temperatures temperatures ffor o r clinopyroxene c l i n o p y r o x e n e consistentconsistently temperaturesf ofor l y around around 675°C 675 C ((Lindsley, L i n d s l e y , 1983), 1983), whereas whereas temperatures r oorthorthoGarnet, pyroxeneaare t o600°C. 600 C. Garnet, pyroxene r e l less e s s rreliable, e l i a b l e , ranging r a n g i n gfrom from500°C 500 C to ccordierite, o r d i e r i t e , and and biotite b i o t i t eini ngarnet-biotite g a r n e t - b i o t i t egneiss gneissexhibit e x h i b icomposit composittional i o n a l zoning zoning due due tto o partial p a r t i a l re—equilibration r e - e q u i l i b r a t i o n during d u r i n g cooling. c o o l i n g . The The rrims i m s of o f adjacent a d j a c e n t garnet g a r n e t and and cordierite c o r d i e r i t (Thompson, e (Thompson, 1976) 1976) and and garnet garnet and bbiotite and i o t i t e(Thompson, (Thompson, 1976, 1976, Ferry F e r r y and and Spear, Spear, 1978) 1978) yyield i e l dtempertemperwhereas cores oneg agarnet-cordierite aatures t u r e s of o f 620°C-630°C, 6 2 0 ~ ~ - 6 3C,0 whereas cores o fofone r n e t - c o r d i e r i t e ppair air yyield i e l d aatemperature temperature of o f660°C. 660 C. on the Pressure estimates based Pressure based on t h e assemblage assemblage orthopyroxenegarnet-plagioclase-quartz in garnet-plagioclase-quartz i ngarnetiferous g a r n e t i f e r o u shornblende-pyroxene hornblende-pyroxene gneiss (Bohlen gneiss (Bohlen and and oothers, t h e r s , 1983) 1983) and and garnet—biotite g a r n e t - b i o t i t e gneiss gneiss (Newton (Newton andPerkins, Perkins, 1982) 1982)l ilie and e iinn the t h e range range 4.7 4.7 to t o 5.3kb. 5.3kb. Application A p p l i c a t i o n of of barometer,based basedonont hthe Al-contentoof tthe h e orthopyroxene orthopyroxene barometer, e A1-content f oorthorthopyroxenei in pyroxene n eequilibrium q u i l i b r i u m with w i t h garnet g a r n e t (Harley ( H a r l e yand and Green, Green, 1982) 1982) is is pprohibited r o h i b i t e d for f o rthese thesegneisses gneisses because because ooff inappropriate i n a p p r o p r i a t e compositions. compositions. A A late l a t eArchean Archean metamorphic metamorphic geotherm geotherm of o f36°C/km 36Oc/km has has been been established e s t a b l i s h e d ffor o r the t h e gneisses gneisses aatt Granite G r a n i t e Falls, F a l l s , using u s i n gthe t h emost most reliable r e 1 i a b l eestimates estimatesofo temperature, f temperature,665°C, 665O~,based basedon on magnetite-ilrnenmagneti t e - i lmenite, i t e ,garnet-clinopyroxene, garnet-clinopyroxene,and andpyroxene pyroxenethermometry, thermometry, and and pressure, pressure, 5.0kb, on orthopyroxene-garnet-pl orthopyroxene-garnet-plagioclase—quartz 5. Okb, based based on a g i o c l ase-quartz e qequilibria. u i 1 ib r i a . Compared Compared t otoo tother h e r ggranulite r a n u l i t e terranes, t e r r a n e s , the t h emetamorphic metamorphic condicondittions i o n s at a t Granite G r a n i t e Falls F a l l s were were relatively r e l a t i v e l ylow lowini nterms termsofo temperature f temperature The ccalculated metamorphicgeotherm geotherm and pressure. The and a l c u l a t e d metamorphic i s is n onot t s isignifignifikyaniteccantly a n t l y different d i f f e r e n tfrom fromother o t h e rPhanerozoic Phanerozoic andalusitea n d a l u s i t e - and and kyanitesillimanite s i l l i m a n i t e facies f a c i e s series s e r i e s terranes. terranes. G r a n u l i t e facies f a c i e s conditions conditions Granulite mayhave havebeen beencaused caused same thermal regime may byby t hthe e same thermal regime t h that a t r eresulted s u l t e d iinn the Archean magmatism magmatism iin n the t h e southern southernCanadian Canadian t h e widespread widespread late l a t eArchean Shield. Shield. 3t �- Early Early Proterozoic P r o t e r o z o i c Geology Geology of of East-Central East-Central Minnesota Minnesota - AA Review Review and and Reappraisal Reappraisal G.E. G.B. MOREY MOREY and and DL. D.L. SOtJTHWICK, SOUTHWICK, Minnesota Minnesota Geological Survey, Survey, University University of of Minnesota, Minnesota, 2642 2642 University University Avenue, Avenue, St. St. Paul, Paul, Minnesota Minnesota 55114. 55114. Investigations I n v e s t i g a t i o n s by the t h e Minnesota Minnesota Geological Geological Survey Survey in i n east-central east-central Minnesota 15 years y e a r s have have shown shown that t h a t the t h e northwest northwest segment segment t h e past p a s t 15 Minnesota over over the of of the the Animikie Animikie basin b a s i n developed developed during d u r i n g early e a r l y Proterozoic P r o t e r o z o i c time t i m e over over and and approximately approximately parallel p a r a l l e l to to the the Great Great Lakes Lakes tectonic t e c t o n i c zone. zone. Although Although the the tectonic major Archean suture s u t u r e that t h a t clearly c l e a r l y remained remained an an imporimporis aa major t e c t o n i c zone zone is t a n t structural s t r u c t u r a l element element during during the t h e early e a r l y Proterozoic P r o t e r o z o i c evolution e v o l u t i o n of of the the tant Animikie is no no evidence evidence that t h a t the the zone zone ever e v e r defined defined aa Animikie basin, basin, there t h e r e is Proterozoic P r o t e r o z o i c continental c o n t i n e n t a l margin margin in i n Minnesota. Minnesota. Goldich 1961 were were the t h e first f i r s t to t o conclude conclude that that Goldich and and his h i s colleagues colleagues in i n 1961 the evolved through through an an eextensional t h e Aniinikie Animikie bbasin a s i n evolved x t e n s i o n a l sstage, t a g e , during which which stratified s t r a t i f i e d rocks rocks were were deposited, deposited, and and aa subsequent subsequent compressional compressional stage, stage, termed The Penokean Penokean deformation deformation was was viewed viewed by by termed the the Penokean Penokean orogeny. orogeny. The Goldich Goldich either e i t h e r to t o have have terminated terminated sedimentation, sedimentation, or o r to t o have have followed followed shortly s h o r t l y after a f t e r sedimentation sedimentation ceased. ceased. The The Penokean Penokean orogen oroqen can can be be divided divided into i n t o two two broad broad longitudinal l o n g i t u d i n a l zones zones on on the t h e basis b a s i s of of contrasting c o n t r a s t i n g styles s t y l e s of of deformation deformation and and grades grades of of metamorphism metamorphism -— aa northern northern stable stable zone zone and and aa southern zone termed termed tthe southern deformed deformed zone h e Penokean Penokean ffoldbelt. o l d b e l t . The The tectonic t e c t o n i c front front separating the two two zones zones coincides c o i n c i d e s with w i t h the the inferred i n f e r r e d northern n o r t h e r n edge edge of of s e p a r a t i n g the the the Great Great Lakes Lakes tectonic t e c t o n i czone zone in i nthe theArchean Archeanbasement, basement, and and isi smarked marked by by -- the t h e northern northern limit l i m i t of of aapenetrative p e n e t r a t i v ecleavage. cleavage. Little L i t t l edeformation deformation and and metamorphism occurred to the north n o r t h of of the the front, f r o n t ,whereas whereas south south of of metamorphism occurred t o the some some of of the the rocks rocks have have been been multiply m u l t i p l y folded folded and and metamorphosed. metamorphosed. it it Intrusive the orogen orogen include i n c l u d e small s m a l l to to moderate—size moderate-size plutons plutons I n t r u s i v e rocks rocks within within the of of late—tectonic l a t e - t e c t o n i c granodiorite g r a n o d i o r i t e and and sodic s o d i c granite, g r a n i t e , and and large l a r g e plutons p l u t o n s of of post—tectonic p o t a s s i c granite. g r a n i t e . Dikes, Dikes, sills, s i l l s , and and small s m a l l bodies bodies of of p o s t - t e c t o n i c potassic gabbroic, gabbroic, dioritic d i o r i t i cand and lamprophyric lamprophyric affinity a f f i n i t yalso a l s oare a r present e p r e s e nand t andwere were emplaced emplaced at a t different d i f f e r e n t times t i m e s throughout throughout the t h e evolution e v o l u t i o n of of the theorogen. orogen. Depositional ppatterns a t t e r n s rreflect e f l e c t contrasting c o n t r a s t i n g tectonic t e c t o n i c conditions c o n d i t i o n s in i n the the Depositional theAnimikie Animikie basin. basin. A northern and and southern southern segments segments of the northern A rrelatively e l a t i v e l y thin thin succession succession(2—3 (2-3 km) km) of of predominantly predominantly sedimentary sedimentary rocks rocks(Anirnikie (AnimikieGroup) Group) was w a s deposited deposited north n o r t h of of the the tectonic t e c t o n i c front, f r o n t , whereas whereas aa much much thicker t h i c k e r sucsucc e s s i o n (>6 ( > 6km) km) of of sedimentary sedimentary and ille cession and volcanic volcanic rocks rocks (Animikie (Animikie and and M Mule Lacs thefront. f r o n t . The Lacs Groups) Groups) was was deposited deposited south s o u t h of of the The depositional d e p o s i t i o n a l history history of these rocks rocks can can be be divided divided into i n t o five f i v ephases. phases. During During the the first f i r s t two two of these phases, phases, quartz—rich q u a r t z - r i c h rocks rocks derived derived from from source source areas a r e a s both both north n o r t h and and south south of of the t h e basin b a s i n were were deposited. deposited. In I n addition, a d d i t i o n , the the southern southern part p a r t of of the the basin b a s i n received received aa substantial s u b s t a n t i a l thickness thickness of of basic b a s i c volcanic volcanic rocks, rocks, carcarbonaceous bonaceous lutite, l u t i t e , and and iron—formation. iron-formation. During During the t h e third t h i r d phase, phase, aa variety variety of iron—formation iron-formation types types were were precipitated p r e c i p i t a t e d on on aa southward—facing southward-facing shelf, shelf, of the fourth f o u r t h phase phase represents r e p r e s e n t s aa transitional t r a n s i t i o n a l succession succession of of carcarwhereas the whereas bonaceous bonaceous lutite l u t i t e that t h a tformed formed as a s the the shelf s h e l ffoundered foundered into i n t odeep deepwater. water. During During the the last l a s t phase phase aa thick, t h i c k , southward—facing, southward-facing, flysch—like f l y s c h - l i k eclas c l a stic tic wedge wedge was was deposited deposited by by southward—flowing southward-flowing turbidity t u r b i d i t y currents. currents. 35 �The geologic history h i s t o r y outlined o u t l i n e d above above is i s broadly broadly comparable comparable with with that that of of the t h e Marquette Range Supergroup Supergroup in i n the t h e southeastern s o u t h e a s t e r n segment segment of of the the Animikie basin b a s i n in i n northern Wisconsin and and adjoining a d j o i n i n g Michigan. Michigan. Both sequences have sedimentological attributes a t t r i b u t e s similar s i m i l a r to t o those those of of Phanerozoic geosynclines and both can be best b e s t explained explained by by rifting r i f t i n g proproccesses e s s e s akin a k i n to t o those proposed to t o explain e x p l a i n the t h e opening opening of of aa Phanerozoic Phanerozoic protoceanic p r o t o c e a n i c basin. basin. However the t h e general g e n e r a l absence of structural s t r u c t u r a l and and litho— lithologic l o g i c evidence for f o r a cryptic c r y p t i c suture, s u t u r e , and and the t h e lack l a c k of of voluminous voluminous early early Proterozoic P r o t e r o z o i c volcanic v o l c a n i c rocks rocks like l i k e those those in i n the t h e Ladysmith—Rhinelander Ladysmith-Rhinelander volcanic v o l c a n i c belt b e l t of of northern Wisconsin raise r a i s e serious s e r i o u s problems for for paleogeographic reconstructions of ccentral Minnesota tthat con— r e c o n s t r u c t i o n s of e n t r a l Minnesota h a t iinvolve n v o l v e aa consuining suming ccontinental o n t i n e n t a l margin. However ssimilar imilar v o l c a n i c rocks may occur in in volcanic the subsurface subsurface of of Iowa Iowa and and southern Minnesota, Minnesota, and and their t h e i r absence absence from from ccentral e n t r a l Minnesota Minnesota may x p l a i n a b l e by e f t - l a t e r a l displacedisplacemaybebeeexplainable byaa major major lleft—lateral ment of of eearly Proterozoic age, perhaps concealed by the ment arly P r o t e r o z o i c age, t h e middle middle Proterozoic discontinuity P r o t e r o z o i c Midcontinent Midcontinent rift r i f t system. system. If I f such a d i s c o n t i n u i t y could could be i t would imply that t h a t the t h e volcanic rocks rocks of of north—central north-central demonstrated it Wisconsin and and the t h e rocks rocks of of the t h e Animikie Animikie basin b a s i n proper proper are a r e separate s e p a r a t e and and temporally discrete d i s c r e t e packages. packages. C o r r e l a t i o n s and paleogeographic rreconstructions e c o n s t r u c t i o n s aalso l s o aare r e hindered Correlations hindered by by an incomplete understanding of of the t h e deformational history h i s t o r y of of the t h e Penokean Penokean foldbelt. f o l d b e l t . For example T.B. T.B. Hoist Holst has shown shown that t h a t the t h e southern southern part p a r t of of i s characterized c h a r a c t e r i z e d by by an an t h e Penokean foldbelt f o l d b e l t in i n east—central e a s t - c e n t r a l Minnesota is the o l d e r "nappe—like" "nappe-like" structural s t r u c t u r a l geometry and aa superposed superposed younger younger older ""upright" u p r i g h t " sstructural t r u c t u r a l geometry, t h e "upright" " u p r i g h t " geometry geometry, whereas only the The iinferred n f e r r e d boundary boundary between between them them appears to occurs appears to o c c u r s tto o the t h e north. north. The s e p a r a t e rocks rocks of contrasting c o n t r a s t i n gmetamorphic metamorphic grade grade and and may may also a l s o correspond correspond separate tto o aa mappable break in i n aeromagnetic aeromagnetic data. data. Holst t e n t a t i v e l y concluded Hoist tentatively break was was the nose of of a major nappe—like nappe-like structure structure tthat h a t tthe h e sstructural t r u c t u r a l break during formed d u r i n g the t h e Penokean Penokean orogeny. orogeny. Alternatively, A l t e r n a t i v e l y , we u g g e s t t hthat a t the wessuggest th s t r u c t u r a l break break could could be be the t h e trace t r a c eofofa folded a f o l d e unconformity d unconformity beneath beneath the the structural Thomson Formation. The Thomson Formation. o s s i b l e presence presence in i n east—central e a s t - c e n t r a l Minnesota Minnesota of of The ppossible Proterozoic two eearly arly P r o t e r o z o i c successions separated s e p a r a t e d by aa major major pperiod e r i o d of folding of folding i s admittedly admittedly speculative. s p e c u l a t i v e . Nonetheless and metamorphism is Nonetheless it is now becoming obvious that t h a t the t h e evolution e v o l u t i o n of of the t h e Penokean Penokean foldbelt f o l d b e l t was was episodic w i t h alternating a l t e r n a t i n g periods of of compression and and periods p e r i o d s of of extenextene p i s o d i c with sion s i o n and sedimentation. sedimentation. Therefore we suggest s u g g e s t that t h a t the t h e Penokean Penokean orogeny orogeny should no longer longer be viewed viewed as a s a single s i n g l e event e v e n t sharply s h a r p l y marked marked in i n time. time. 36 �Metal].ogeny of the the Lake Lake Superior Superior Precambrian Metallo~env of Jr. M.G. M.G. MUDREY, MUDREY, Jr. (Wisconsin Geological and Natural History History Survey, Survey, 1815 University Avenue, Madison, Wisconsin 53706) 53706) J. J. KALLIOKOSKI KALLIOKOSKI (Department (Department of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 49931) 49931) For purposes purposes of of xnetallogenic metallogenic analysis, analysis, the the Lake Lake Superior Superior Precambrian Precambrian region region can can be be divided divided into into five five tectono—stratigraphic tectono-stratigraphic terranes: terranes: (1) (11 an an Archean an gneiss ~ n e i s s terrane terrane older older than than 3.0 3.0 Ga, Ga, and and (2) (2) an Archean Archean greenstone—granite sreenstone-granite terrane about about 2.7 2 * 7 Ca, Ga, the two two joined joined together together in in late late Archean time; an epicratonic cover on this Archean basement (3) time; (3) an epicratonic cover on this Archean basement of of an an Early Early Proterozoic Proterozoic iniogeoclina]. miogeoclinal assemblage assemblage and and associated associated epicratonic epicratonic rocks rocks (the (the Penokean Penokean orogen ororcen of of Minnesota—Michigan); Minnesota-Michigan); (4) (4) an Early Early Pro— Proterozoic assemblage terozoic eugeoclinal eugeoclinal assemblage of of intrusive and and extrusive extrusive rocks rocks with Archean with possible possible Archean basement basement (Wisconsin (Wisconsin inagmatic magmatic terrane) that that ! has aa cover cover of of intracratonic, intracratonic, an— anorogenic rhyolites, orogenic continental continental rhyolites, quartzites quartzites and and associated associated gran— granitic itic rocks rocks (Baraboo (Baraboo sepuence—4a) sequence-4a) and and is is intruded intruded at at 1.5 1.5 Ca Ga by by an— anorogenic orogenic alkalic alkalic granites granites (Wolf ( W a ..a River River seguence—4b); sequence-4b) ; and and (5) ( 5 ) aa Middle Middle Proterozoic Proterozoic (1.1 (1.1 Ga) Gal rift rift assemblage assemblage (Keweenawan (Keweenawan terrane— terraneMidcontinent Midcontinent rift rift system). system). - The The Early Proterozoic eugeoclinal Early Proterozoic eugeoclinal asassemblage attached the semblage was was attached to to the North North American American craton craton about about 1.85 1.85 Ca. Ga. The The Lake Lake Superior Superior craton craton has has L-.-..-..--. been stable been tectonically tectonically stable since since the Numbers the Keweenawan. Keweenawan. Numbers refer refer to to terranes. terranes. See See text. text. - 3' The The potential potential of of the the Archean Archean terrane terrane is is limited limited to to minor minor iron, iron, gold, gold, base base metals(?), metals(?), and and quality quality dimension dimension stone. stone. Greatest Greatest mineral mineral producproduction tion and and future future potential potential is is from from the the Proterozoic Proterozoic terrane. terrane. The Penokean Penokean orogen orogen contains contains the the major major iron—formations iron-formations in in aa basin basin in in The which the the sedimentary sedimentary fill fill thickens thickens southward southward from from about about 2,000 2,000 mm in in the the which Mesabi Mesabi and and Gogebic Gogebic iron iron ranges ranges on on the the northwest northwest to to about about 5,500 5,500 inm and and 8,000 8,000 inm in in the the Cuyuna Cuyuna and and Menominee Menominee ranges, ranges, respectively respectively The thinner thinner The sequences contain contain no no volcanic volcanic rocks, rocks, whereas whereas the the thicker thicker and and sedimento— sedimentosequences logically more complex miogeoclinal miogeoclinal sequences sequences south south of the the Mesabi Mesabi and and logically more complex east of of the the Gogebic Gogebic ranges ranges contain contain many many locally locally thick thick piles piles of of marine marine east tholejj.tic tholeiitic lavas. lavas. Other Other inetallogenic metallogenic settings on on the the Penolcean Penokean orogen orogen are related related to to Proterozoic Proterozoic unconformities unconformities and and subsequent subsequent epigenetic epigenetic enenare . . vironments. vironments. The The Wisconsin Wisconsin magmatic magmatic terrane, terrane, on on the the other other hand, hand, contains contains mineral mineral occurrences related related tà to both bothxuagntatism magmatism and temperature hydrothermal hydrothermal occurrences and high temperature deposition. deposition. Most Most important important are are the the massive massive sulfide sulfide deposits deposits along along aa belt belt of of fe].sic felsic to to intermediate intermediate calc—alkaline calc-alkaline volcanic volcanic rocks. rocks. These These 37 �bodies bodies exhibit exhibit many many similarities similarities to to the the Noranda— Noranda- and and Kuroko—type Kuroko-type ores ores including including general general form, form, mineral mineral zoning, zoning, disseminated disseminated footwall footwall mineralmineralization, and and mineralization mineralization succeeded succeeded by by aa period period of of sedimentation. sedimentation. ization, However, However, there there are are also also several several differences. differences. There There is is aa general general lack lack of of well well developed developed magnetic magnetic anomalies anomalies over over the the deposits deposits indicating indicating the the ababsence sence of of diagenetic diagenetic magnetite magnetite and and pyrrhotite; pyrrhotite; the the overlying overlying sediment sediment is is more a elastic than a chert; and although the major metal contents more a clastic than a chert; and although the major metal contents are are similar similar to to Archean Archean deposits, deposits, precious precious metal abundances abundances are are only only one—half one-half that that of of Canadian Canadian deposits, deposits, but but more similar similar to to those those in in Canadian Canadian Proter— Proter- ozoic deposits. deposits. ozoic Anorogenic Anorogenic sequences sequences include include the Baraboo, Baraboo, Wolf River River and and Keweenawan Keweenawan In In the the Baraboo Baraboo sequence sequence the the only only occurrences occurrences of of metallogenic metallogenic interest interest or or curiosity curiosity are are the the speculative speculative unconformity—related unconformity-related occuroccurrences rences of of uranium uranium and and the the minor, minor, thin thiniron—formations. iron-formations. The The Wolf Wolf River River sequence sequence contains contains minor minor occurrences occurrences of of U—Th, U-Th, REE, REE, and and possibly possibly Sn—W. Sn-W. By By contrast, the the Keweenawan Keweenawan is is aa copper—rich copper-rich province province and and contains contains major major contrast, stratiform stratiform. deposits deposits of native native copper copper in in basalts basalts and and interflow interflow congloconglomerates, merates, stratiform s t r a t i f o m deposits deposits of of copper copper sulfide sulfide in in black black shale, shale,. as as well well as Cu—Ni-(Co) Cu-Ni-(Co) concentrations concentrations in in the the basal basal part part of of the the Duluth Duluth Complex, Complex, as and Ti—V Ti-V concentrations concentrations in in melanogabbros melanogabbros of of the the Duluth Duluth Complex Complex and and and Mellen Intrusive. Intrusive. Mellen sequences. sequences. Some Some deposits deposits are are younger younger than than their their host host rocks rocks so so that, that, in in detail, detail, aa tectono-stratigraphic framework framework may may contain contain some some flaws. flaws. It It is is also also tectono—stratigraphic in some instances, younger epigenetic process have modified clear that that in some instances, younger epigenetic process have modified clear earlier earlier syngenetic syngenetic or or coeval coeval mineral mineral concentrations. concentrations. In In the the case case of of iron ores, ores, it it is is these these later later processes processes that that have have converted converted uneconomic uneconomic iron material material into into commercially comercially extractable extractable ores. ores. This study study was was undertaken undertaken to to set set the the mineral mineral deposits deposits in in this this region region This into into aa metallogenic metallogenic framework framework for for the the Lake Lake Superior Superior Precambrian Precambrian Volume Volume (DNAG). The DNAG DNAG text text will will ininof the the Decade Decade of of North North American American Geology Geology (DNAG). of clude abbreviated abbreviated descriptions descriptions of of the the more more important important mineral mineral deposit deposit clude types with with'data on past past or or current current production production (Keweenawan (Keweenawan copper; copper; Lake Lake types data on Superior iron iron ore) ore) or or on on reserves reserves or or resources resources Wisconsin Wisconsin zinc—copper; zinc-copper; Superior Minnesota Cu—Ni). Cu-Ni). Further, Further, the the tectono—stratigraphic tectono-stratigraphic framework framework allows allows Minnesota us to to propose propose metallogenic metallogenic settings settings for for still still other other kinds kinds of of mineral mineral us commodities, including including. Sn—W, Sn-W, diamonds, diamonds, petroleum, petroleum, and and Skellefta— Skellefta- and and commodities, Noril'sk-type nickel nickel occurrences. occurrences. Noril'sk—type 38 ��I Metamorphic Conditions and Evolution of a Supracrustal Sequence Intruded by the Dunbar Genesis, Florence and Morinette Counties, Northeastern Wisconsin PETER A. NIELSEN (Div. of Science, Univ. of Wis.-Parkside, Kenosha, Wi. 53141) A suite of lower Proterozoic graphitic-sulfidic metasediments and intercalated mafic to intermediate volcanics and volcaniclastics from Florence and Marinette Counties are described. The supracrustal sequence (Quinessic Fm of Dutton, 1971) is characterized by prograde metamorphic assemblages including: biotite-garnet-p I agioc lase-.quartz ± cordierite in metasediments, garnet amphibolites, and diopside-tremolite marbles. A late stage retrograde overprint is present in most samples studied to date. The most prevalent alteration includes: cordierite + pinite + sericite, garnet -. biotite + chlorite, and hornblende - actinolite + biotite ± chlorite. The local concentration of S in several horizons has led to the development of pyrite ± pyrhhotite with a loss of Fe from the silicate phases. The supracrustal sequence is intruded by pegmatites and quartz-.tourmaline veins analogous to those found within the Dunbar Gneiss Complex. The prograde assemblage suggests peak metamorphic conditions in the range 500-575°C at low to intermediate lithostatic pressure. The abundance of graphite, calcite, and pyrite ± pyrhhotite indicate that H2O <total and that CO2 and H2S were (at least on a local scale) major fluid components. Petrographic observations show an S1 foliation developed parallel to S0 bedding planes. A weakly developed S2 foliation developed during retrograde metamorphism and is defineciby second generation biotite. The S2 foliation is inclined to S1 by up to 900. Garnets in the graphitic-sulfidic pelites contain abundant oriented quartz inclusions producing a pseudo-tetragonal sector pattern. Occasional zoned plagioclase phenocrysts are preserved in the amphibiolites. The intruded Dunbar Gneiss ranges in composition from granite-granodiorite to biotite tonalite and locally contains abundant mafic inclusions. In many outcrops, the well foliated gneiss grades into migmatites. Multiple generations of pegmatite cut the Dunbar Gneiss and are highly deformed themselves. The gneiss displays a similar sequence of fabric develoment as that shown by the supracrustals (Sims, I 984, personal communication). Most of the samples discussed in this study were obtained from a series of diamond drill cores from the Bass Lake area, Florence County. These samples 'were made available by Kerr-McGee Corporation in Marquette, Michigan. Their cooperation is gratefully acknowledged. Dutton, C. E., 1971. Geology of the Florence Area, Wisconsin and Michigan, U.S.G.S. Professional Paper 633. '40 �- MOB Assemblage DataBase MOB -aa Metamorphic MetamorphicMineral Mineral Assemblage DataBasefor for the Precambrian the Lake LakeSuperior SuperiorDistrict District Precambrian ofofthe PETERA .A.NIELSEN NIELSEN (Divisionof of Science, PETER (Division Science, UW-Parkside, UW-Parkside, Kenosha, Kenosha, Wisconsin 53141) 53141) The MetamorphicDataBase DataBase(MDB) (MDB) databaseestablished established at i sisaa database a tUWUWThe Metamorphic Parksidedesigned designed facilitate the compilation, retrieval and Parkside t o tofacil i t a t e the compil ation, retrieval and subsequent plotting of data for for the subsequent plotting ofmetamorphic metamorphic mineral mineral assemblage assemblage data the consists of of two MOB consists two Precambrian Precambrianofofthe the Lake LakeSuperior SuperiorDistrict. District. MOB parallel LLOC data and other MLOC , one LLOCstoring storinglocation 1ocation data andthe the other MLOC para1 lel files, f i 1esone which contains containsaal list Relational Information which i s t of ofminerals minerals present. present. The The Relational Information ManagementSystem System(RIM) (RIM)supported supportedby by the the IBM used to Management IBM system system at a tUW—P UW-P i sis used to select user assemblages user specified specified 'critical' ' c r i t i c amineral l ' mineral assemblagesand andata tthe thesame same time retrieve corresponding LLOC LLOCcomponent. component. The retrievethethe corresponding The selected assemblages andcorresponding correspondinglocation locationdata data are are stored in an output i n an output assemblages and beprinted printed and andused usedasasinput inputt otoa aflatbed flatbedplotter plotter to ffile i l ewhich which may may be to producemaps mapsshowing. showing. arealdistribution distribution of produce thethe areal of specified speci fiedassemblages. assemblages. The relations between thevariables variables in in the The relations between the the LLOC LLOC f file i l e permit permit the the genergenerated ooutput u t p u t ffile i l e to to consist consist ofofdata data for fora asingle singlecounty, county,quadrangle, quadrangle, ated A complete sstate, t a t e , or or the theentire entireLake LakeSuperior SuperiorDistrict. District. A completeMOB MOB entry consists of line of of data consists of 22 componentscomponents- aa line of data datafor forLLOC LLOC and and aa column column of data inputconsists consistsofof an an identification identification number, for LLOC input number, county, county, forMLOC. MLOC. LLOC surfacesample,> sample,>0 depth core), latitude sstate, t a t e , depth depth ((0 0 == surface 0 = =depth i n in aa d rdrill i l l core), 1 a t i tude and longitude longitude (( degrees, degrees, minutes, minutes, and and seconds) seconds) age age of metamorphism metamorphism ( i(iff and known), termed ADINFO ADINFO which work known), and and aa string string termed whichindicates indicates the the type type of work which has has been beendone doneononthe thesample sample(thin (thinsection, section, microprobe data, bulk which microprobe data, bulk rock data, and contributor's name). rock chemical chemical data, and tth3 h i s contributor's name). The MLOC entry The MLOC entry consists of aa list thethe (equilibrium) mineral assemblage consists l i sof t of (equilibrium) mineral assemblageobserved observed in thin thin section sectionand and an an identification identificationnumber. number. Once the user mayselect select individual individual MDB, the user may Once aall l l data data are are entered entered into intoMOB, minerals or ccritical andobtain obtainaal list minerals or r i t i c a lmineral mineral pairs pairsororassemblages assemblages and ist of locations of locationswhere where the the specified specifiedassemblage assemblage occurs. occurs. I am am currently for the attempting to t o update update the theMetamorphic Metamorphic Mineral Mineral Assemblage Assembl age Map Map for the Lake Superior i s t r i c t(Morey, (Morey ,1978) 1978) incorporating incorporatingnew new data data and and Lake Superior DDistrict interpretations. IItt isi santicipated anticipated that that this this material material will will be be part part of aa contribution contributiontotothethe DNAG volume volume of the the Precambrian Precambrian of the Lake Lake DNAG of the SuperiorDistrict. District. AA sample s included i t h this Superior sampleinput inputform formi is included wwith abstract, and welcomeany any contributionsfor for inclusion abstract, and I would would welcome andand a l lallcontributions in MOB. MDB. in Morey, ., Metamorphism Metamorphism ininthe U .S .A. ,and and Morey, G.B G.B., theLake LakeSuperior Superiorregion, region, U.S.A., o crustal evolution; in Metamorphismofofthe theCanadian Canadian iits t s relation relationtot crustal evolution; in Metamorphism Shield,Geol. Geol .Surv. Surv.Can., Can.Paper , Paper 78-10,p.283—314, p .283-314, 1978 1978 Shield, 78—10, 4]. �L o c a t i o n ffile: ile: Location - LLOC County County ILOC 1 2 2 1 FLO FLO FLO FLO State State Depth Depth WI WI WI WI 140 .O 140.0 0. 0. Latitude Latitudeu 45 45 45 45 46 46 49 49 ' " 37.5 37.5 50.5 50.5 - Longitude " Longitude 88 88 22 5.2 22 5.2 88 17 88 5.2 17 5.2 ' SI I' Age Age PEN PEN PEN PEN ADINFO ADINFO IS TSPAN PAN IS TSPAN PAN M i n e r a l ffile: ile: Mineral MhOC MIiOC L i s t of o f minerals m i n e r a l s present p r e s e n t (( List no nomaximum) maximum) ifi fthe t h sample e sampleis i polymetamorphic, s polymetamorphic,It Is i trecommende1lhat i s recommendeflhat separate n codesand andages ages be b eassigned, assigned, along along separate identification i d e n t i f i c a t i ocodes with w i t h separate s e p a r a t e mineral mi n e r a l assemblage assemblage 1listings. is t i n g s . p t)* and LLOC LIOC are MLOC and r e iintegers n t e g e r sand and are a r e equal equal for f o r each each sample sample i In n tthe h e ffile i l e (MLOC=LLOC), (MLOC=LLOC), MLOC MLOC and are MLOC andLLOC hOCaare assigned a t t h e t i m e t h e d a t a a r e e n t e r e d i n t o MOB. are entered into MDB. assigned at the time the data MLOC MIOC M i n e r a l s present present Minerals QTZ EPI EPI IRE TRE CAL CAL 11 QTZ 22 BIO GAR GAR CTD CTD CIII CHLQTZ QTZPLA PLA BlO �Basal Lower Lower Proterozoic Proterozoic Glaciogenic Glaciogenic Formations, Formations, Basal Marquette Supergroup, Superqroup, Upper Upper Peninsula, Peninsula, Michigan Michigan Marquette RICHARD W. W. OJAKANGAS OJAWGAS (Department (Department of of Geology, Geology, University University of of Minnesota, Minnesota, RICHARD MN 55812) 55812) Duluth, MN Duluth, Three b a s a l Proterozoic formations i n t h e Upper Peninsula of Michigan Three basal Proterozoic formations in the Upper Peninsula of Michigan - the t h e Reany Reany Creek, Creek, Enchantment Enchantment Lake, Lake, and and Fern Fern Creek Creek -- are a r e interpreted i n t e r p r e t e d to to - The strongest s t r o n g e s t evidence evidence for f o r aa glaciogenic glaciogenic have had had glacial g l a c i a l origins. o r i g i n s . The have h i s t o r y is oversized lonestones (many of which a r e c l e a r l y dropstones) dropstones) history is oversized lonestones (many of which are clearly iinn laminated laminated shale-siltstone s h a l e - s i l t s t o n e beds beds that t h a t are a r e associated a s s o c i a t e d with with diamictites. diamictites. They are a r e interpreted i n t e r p r e t e d to t o have have been been dropped dropped into i n t o glaciomarine glaciomarine or o r glacia— q- l a c i o They llacustrine a c u s t r i n e environments environments from from either e i t h e r icebergs i c e bergs or o r ice i c e shelves. shelves. Other Other rock types types within within the t h e three t h r e e formations formations include include graded graded && ungraded ungraded clastclastrock " 4 ltetm-a MA-& AS 4.L..--Ap-: L.Aw= w L LLL= a a ~ ~- - 2supported conglomerate, conglomerate, sandstone, sandstone, and and siltstone. supported Most of the sand—sized g r a i n s in i n all a l l the t h e rock rock types types are a r e quartz. q u a r t z . The The Fern Fern Creek Creek and and Enchantment Enchantment grains Lake formations formations pass pass upward upward into i n t o formations Â'ormations of of quartz—sand; quartz-sand; the t h e Reany Reany Lake Creek has has aa faulted f a u l t e d upper upper contact. c o n t a c t . Microscopic Microscopic till till pellets p e l l e t s are a r e present present Creek i n t h e dropstone u n i t s of t h e Rean ,y Creek Formation. in the dropstone units of the Reany Creek Formation. LuALG. a ~ ~ e ~ uz as much i L t u ~ ~ a=. NU, unconformably UAGO~LOI-IMKJLY The three t h r e e formations, formations, separated separated by The as~ 80oukin, o v e r l i e Archean Archean basement. basement. They !rhey may may be be correlative c o r r e l a t i v e with with each each other, o t h e r , or or overlie s t i l l lower Proterozoic u n i t . t h e Reany Creek may be a younger b u t the Reany Creek may be a younger but still lower Proterozoic unit. ilnits Several workers workers have have proposed proposed correlations c o r r e l a t i o n s of of one one or o r more more of of the t h e units Several with the with the Gowganda Formation (interpreted to be of glacial origin) of t h e Huronian Hurc the Supergroup, 200 kin to the east in Ontario. The dropstone 6 u n i t - diamictite unit association in each unit strengthens this correlation. Radiomet ,oup Radiometric ages are not available in Michigan, but the Huronian Supergroup has been been bracketed between 2500 and 2100 rn.y. If any of the Michigan units ,its has prove to t o be uc younger Y U U A Y ~ Z than UILne Ontario uncarzo.gLacLogenxc rormaclons, then m e n another another prove the glaciogenic formations, i s i n d i c a t e d . e a r l y Proterozoic g l a c i a l episode early Proterozoic glacial episode is indicated. - 43 �Stratigraphy of the Headwav—Coulee Hassive Massive Sulfide S t r a t i g r a p h y of t h e Headway-Coulee Sulfide Prospect, P r o s p e c t , Northern Onaman Lake Area, Area, NW X? Ontario Ontario STEVE OSTERBERG (Dept. Geology, U University Minnesota—Duluth, (Dept. of of Geology, n i v e r s i t y of of Minnesota-Duluth, MM Duluth, ANN 55812) Headway—Coulee massive ssulfide within The Eeadway-Coulee u l f i d e pprospect, r o s p e c t , situated situated w i t h i n the the Archean Wabigoon g greenstone within located w i t h i n an intensely i n t e n s e l y altered altered r e e n s t o n e bbelt, e l t , is located succession m a f i c and and ffei.sic e l s i c metavolcanic, m e t a v ~ l c a n i cand and ~ intrusive i n t r u s i v e rocks. rocks. s u c c e s s i o n of of inafic Detailed mapping aand have shown tthat D e t a i l e d mapping d ppetrographic e t r o g r a p h i c sstudies t u d i e s have h a t the t h e vvolcanic olcanic l i t h o l o g i c a l units. units. ssuccession u c c e s s i o n can bbee divided d i v i d e d into i n t o several s e v e r a l distinct d i s t i n c t lithological Pillowed, Pillowed, massive, massive, and and breccjated b r e c c i a t d mafia m a f i c flows flows form form tthe h e bbase a s e of of the the volcanic vary v o l c a n i c succession s u c c e s s i o n and and are a r e about about 1.2 1.2 kzn k m 'thick. t h i c k . Flows v a r y from from aphan— aphanand have have an an amygdaloidal amygdaloidal ccontent iitic t i c to t o porp'nyritic, p o r p h y r i t i c , and o n t e n t ranging from from 00 to to mafia with a f i c flows are a r e interfingered interfingered w i t h and overlain o v e r l a i n by by lamlam8 percent. percent. The m inated bedded ffelsic hydrovolcanic rrocks, i n a t e d tto o tthickly h i c k l y bedded e l s i c hydrovolcanic o c k s , which range from crystal—rich and llapilli— and bblock—size c r y s t a l - r i c h aash s h and a p i l l i - and l o c k - s i z e ttuffs u f f s to t o aassociated s s o c i a t e d debris debris flow deposits. d e p o s i t s . These grade laterally l a t e r a l l y into i n t o thin t h i n ash—sized ash-sized deposits d e p o s i t s concontaining up tto fragments which which aare thought to t a i n i n g up o 15 ppercent e r c e n t fragments r e thought t o represent r e p r e s e n t reworked eequivalents q u i v a l e n t s of of the t h e hydrovolcanic hydrovolcanic rocks. rocks. Overlying Overlying the t h e hydrovolcanic hydrovolcanic units are tot obrecciated, units a r e spherulitic, ~ p h e r u l i t massive i cmassive ~ b r e c c i a t e d ,quartz—feldspar q u a r t z - f e l d s p a r porphyritic porphyritic is some some llava a v a flows flows which which may may or o rmay may not n o t be b e flow banded. banded. The The ffelsic e l s i c unit u n i t is 100 meters tthick 100 meters h i c k and extends extends along along sstrike t r i k e for f o rapproximately approximately 44 km; km; i t is is ooverlain v e r l a i n by pillowed to t o massive massive mafia m a f i c lavas. l a v a s . An An extensive e x t e n s i v e polymictic polpictic debris d e b r i s flow d e p o s i t which o n t a i n s cclasts l a s t s of a f i c and falsic f e l s i c volcanic, volcanic, deposit which c contains of m mafia g r a n i t e , and iiron granite, formation is iinterfingered with horizon r o n formation nterfingered w i t h the t h e felsic felsic h o r i z o n and have iits of the is bbelieved e l i e v e d tto o have t s oorigin r i g i n tto o tthe h e southwest of t h e study s t u d y area. area. it C r y s t a l - r i c h laminated tuffs t u f f s and tthickly h i c k l y bedded f r a g m e n t a l rocks Crystal—rich bedded fragmental and aassociated s s o c i a t e d ddebris e b r i s flow e p o s i t s aare r e bbelieved e l i e v e d tto o be t h e products p r o d u c t s of of flow ddeposits be the hydrovolcanic hydrovolcanic eruptions. e r u p t i o n s . Such eruptions form tuff cones with deposi— eruptions tuff w i t h deposittional i o n a l products dependent upon water to t o magma mapa ratios. ratios. Slumping and products dependent reworking would i n e l y laminated i s t a l eequivalents q u i v a l e n t s of reworking would produce produce ffinely laminated ddistal of such deposits deposits. . �Alteration, Alteration* Paragenesis Paragenesis and and Age Age Associated Associated with with Native Native'Copper Covper Mineralization Mineralization of of the the Kearsarge Kearsarge Flow, Flow* Keweenaw Keweenaw Peninsula, Peninsula* Michigan Xichigan James Paces and Theodore Theodore J. Bornhorst (Dept. (Dept. of of Geol. && Geol. Geol. Engrg., Engrg.* James B. Paces Michigan Michigan Technological Technological University, University* Houghton, Houghton* MI MI 49931) 49931) The The Portage Portage Lake Lake Volcanics Volcanics consists consists of of aa thick thick sequence sequence of of Keweenawan Keweenawan tholeiitic basalts which which hosts hosts a tholeiitic flood flood basalts a dormant dormant billion—dollar billion-dollar native native copper copper district. district. The The Kearsarge Kearsarge flow flow is is aa thick thick(60 (60kin) h)ophitic ophitic to to porphyritic porphyritic basalt basalt which which contains contains aa major major ore—producing ore-producing amygdaloidal amygdaloidal flow to10 10in m thick. thick. Seven Seven mines mines worked worked the the Kear— Kearflow top top ranging ranging from from00to sarge amygdaloid along a strike km and prosarge amygdaloid strike distance of more than than 12 12 km duced over 2.3 copper, the 2.3 billion lbs. of refined copper, the third third largest largest lode lode in the the district. district. Scoiber Stoiber and and Davidson Davidson (1959; (1959; Econ. Econ. Geol., Geol.* v. v. 54, 54*p. p. in 1250—1460) 1250-1460) documented an irregular irregular but generally symmetric symmetric banding banding of of secondary secondary minerals minerals within within the the flow flow top: top: chlorite chlorite and and microcline microcline were were deposited earliest earliest and farthest farthest away from from the zone zone of of highest highest permeapermeability, bility* later later epidote epidote and and quartz quartz were were confined confined to to the the most most permeable permeable horizons, horizons, and and calcite calcite filled filled the the remaining remaining pore pore space. space. Samples Samples of of Kearsarge Kearsarge flow flow top from from poor—rock poor-rock piles of the the Wolverine Wolverine Mine Mine confirm confirm this this broad paragenesis paragenesis on on aa single single amygdule amygdule scale. scale. Vesicle Vesicle walls walls are are lined with a thin layer of chlorite followed by a band of hematitehematite— dusted dusted microcline microcline crystals crystals which which terminate terminate in in euhedral euhedral pyramids. pyramids. Centers amygdules are filled with a complex combination combination of bladed Centers of amygdules epidote epidote with lesser lesser amounts amounts of fibrous fibrous prehnite, prehnite* euhedral euhedral to to anhedral anhedral quartz, quartz* native native copper, copper, and fine—grained fine-grained masses masses of of poorly—crystallized poorly-crystallized layer-silicates. Anhedral Anhedral calcite calcite fills fills remaining remaining open open pore pore space. space. layer—silicates. Rb—Sr Rb-Sr isotopic isotopic data data were obtained obtained from from aa suite suite of of secondary secondary minerals minerals from the the Wolverine Wolverine Nine. Mine. Early microcline microcline and chlorite chlorite define define an an iso— isofrom chron chron with an an age age of of 1,051 1,051 ±2 15 15 Na Ma and and an an initial initial Sr Sr ratio ratio of of 0.7145. 0.7145. The The age age of of the the Keweenawan Keweenawan lavas lavas within within the the Lake Lake Superior Superior basin basin has has been been constrained by a variety of workers and is best estimated estimated at about about 1,110 (Van Schmus Schmus and and others, others* 1982; 1982; Gaol. Geol. Soc. SOC. Amer. her. Memoir Memoir 156, 156, 1,110 Ma (Van Ma after after the the peak peak Thus* mineralization mineralization occurred occurred about about 50 50 Ma p. 165—171). 165-171). Thus, p. of ignous igneousactivity activity but but probably probably during during the the later later stages stages of of sedimentary sedimentary infilling of of the the rift rift basin. basin. Later calcites calcites and epidote epidote contain contain virvirinfilling tually tually no Rb and and have have Sr Sr ratios ratios which which cluster cluster about about aa value value of of 0.704. 0.704. They do do not not fit fit the the microcline—chiorite microcline-chlorite isochron. isochron. The The mineralizing mineralizing They fluids were apparently characterized by fluids by different early and late Sr isotopic compositions. compositions. We We interpret interpret this this data data as as evidence evidence for for variable variable isotopic sized fluid fluid convection convection during during the the evolution evolution of of the the mineralization mineralization event. event.' Whole-rock major and trace trace element chemical chemical compositions compositions have have been been Whole—rock determined across across aa 19.5 19.5in m section section of of the the Kearsarge Kearsarge flow. flow. It It is is determined apparent that some elements elements such P,y Sc, such as P Sc* YY,y and Zr have remained immobile while others have experienced a dramatic draktic redistriredistrilargely immobile bution during during the the metamorphic metamorphic event. event. Mass Mass balance balance calculations calculations have have bution been performed in an attempt attempt to determine whether trace trace elements elements (K, (Ky Rby.Ca and Sr in in particular) have behaved under open or closed closed rereRb, distribution distribution conditions. conditions. These These results results will will be be presented. presented. L.5 �Localized i n Cavities Cavities of tJpside—Down Upside-Down Trilobite T r i l o b i t e Parts P a r t s in Localized Accumulations Accumulations of w i t h i n aa Silurian. S i l u r i a n Reef t Racine, within Reef aat Racine, Wisconsin RICHARD RICHARD A. A. PAULL PAULL (Department (Department of of Geological Geological && Geophysical Geophysical Sciences, Sciences, The W I 53201) 53201) The University U n i v e r s i t y of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, WI Outcropping in Wisconsin Wisconsin and and adjacent a d j a c e n t states s t a t e s are are Outcropping Silurian S i l u r i a n reef r e e f cores c o r e s in generally of dolomite flanked f l a n k e d by outward outward dipping, dipping, g e n e r a l l y structureless s t r u c t u r e l e s s masses of medium medium to t o thick t h i c k beds beds that t h a t flatten f l a t t e n and and grade g r a d e laterally l a t e r a l l y into i n t o thinner thinner Large irregular cavities coon in bedded interreef dolomite. r e common in bedded i n t e r r e e f dolomite. b r g e i r r e g u l a r c a v i t i e s a are Some reef r e e f cavities cavities many many reef r e e f cores, c o r e s , and and may may be b e present p r e s e n t in i n flank f l a n k beds. beds. Some result but r e s u l t from solution, solution, b u t others o t h e r s containing c o n t a i n i n g concentrated c o n c e n t r a t e d accumulations accumulations of of fossils f o s s i l s were primary primary features f e a t u r e s formed formed during d u r i n g reef r e e f growth. growth. AA partially p a r t i a l l y quarried q u a r r i e d Middle Middle Silurian S i l u r i a n (Niagaran) (Niagaran) reef r e e f in i n Racine Racine DoloDolomite Wisconsin, exposes about 20 elongate elongate m i t e at a t Quarry Lake Park, P a r k * Racine, Racine* Wisconsin, about 20 bell—shaped wide) 3' bell-shaped or o r equant cavities c a v i t i e s ranging up to t o 8.5' 8.5' wide, 3 ' high, h i g h , and and extending 6' inward inward from from the t h e face f a c e of of the t h e rock r o c k exposure. exposure. Many Many of of the the extending 6' cavities c a v i t i e s couldn't c o u l d n ' t be b e ewmirted examined safely s a f e l y and several s e v e r a l were nonfossiliferous. nonfossiliferous. The The base b a s e of three t h r e e out o u t of five f i v e cavities c a v i t i e s selected s e l e c t e d for f o r detailed d e t a i l e d examinaexamination numbers of of nnested e s t e d masses of of fossils f o s s i l s dominated by t i o n contained llarge a r g e numbers inverted i n v e r t e d (concave—up) (concave-up) cephalons and ppygidia y g i d i a of of the t h e trilobite t r i l o b i t e Bumastus t h a t similar s i m i l a r accumulations accumulations might sp. sp. Previous workers have suggested that represent: protected with r e p r e s e n t : (1) (1) a p r o t e c t e d living l i v i n g environment w i t h reworking by scavscavengers, e n g e r s , (2) (2) a favored molting site, s i t e , (3) (3) wave and current c u r r e n t accumulations accumulations behind ( 4 ) settling s e t t l i n g of of disarticu— disarticubehind obstacles o b s t a c l e s or o r within w i t h i n depressions, d e p r e s s i o n s , or o r (4) lated is also a l s o possible p o s s i b l e that that l a t e d fossils f o s s i l s washed into i n t o natural n a t u r a l cavities. c a v i t i e s . It is unique and selective might account for s e l e c t i v e predation p r e d a t i o n might f o r the t h e fossil f o s s i l deposits. deposits. within The fact f a c t that t h a t most (all?) ( a l l ? ) of of the t h e cavities cavities w i t h i n the t h e reef r e e f core c o r e were were The filled with clay adds to the enigmatic nature of these features. once once f i l l e d w i t h c l a y adds t o t h e enigmatic n a t u r e of t h e s e f e a t u r e s . with Flume and and settling s e t t l i n g experiments experiments w i t h chitinous c h i t i n o u s carapaces c a r a p a c e s and and full full Flume dorsal of tthe (Limulussp.) sp.) ddisclose i s c l o s e that that d o r s a l exoskeletons exoskeletons of h e horseshoe horseshoe ccrab r a b (Limulus only only free—fall f r e e - f a l l into i n t o a nnonagitated o n a g i t a t e d ccavity a v i t y aallows l l o w s a high percentage p e r c e n t a g e of of concave-up forms forms to t o accumulate. accumulate. This documentation, plus p l u s the t h e disartic— disarticconcave—up u l a t e d and incomplete n a t u r e of ulated nature of Bumastus Bumastus in with i n association association w i t h lesser lesser numbers of of other o t h e r fossil f o s s i lforms, forms, suggests s u g g e s t s selective s e l e c t i v e sorting s o r t i n gof ofdead dead numbers organisms by size s i z e and and shape shape as a s they organisms they washed washed across a c r o s s the t h e submerged submerged rreef eef f l a t before b e f o r e failing f a l l i n g into i n t odepressions. depressions. flat - Although Although t this h i s project p r o j e c t solved solved the t h emystery mystery of of upside—down upside-down t rtrilobites, ilobites, it it failed f a i l e dtot oprovide p r o v i d enew new insight i n s i g h t into i n t o the t h e origin o r i g i n and and clays w i t h i n rreef e e f cavities. cavities. clays within L.6 accumulation of �Precambrian Precambrian Evaporites: Evaporites: Preservation Preservation of of Sulfate Sulfate in in Quartz Ouartz Pseudomorphs Pseuclomorphs After After Gypsum Gypsum E.C. FENG* AND AND J. HEMZACEK H W A C E K (Northern (Northern Illinois Illinois University) University) E.C. PERRY, PERRY* J. FENG, The The average average sulfur sulfur isotope isotope composition com osition of of trace trace amounts amounts of of anhydrite anhydrite preserved preserved in in the the 22 XX 10 10 year year old old Kona Kona Dolomite Eolomite from from 33 distinct distinct localities localities near near Marquette, Marquette, Michigan Michigan is is 13.23 13.23 /oo loo (CDT) (CDT) with with 0 aa total total range range of of 1.2 1.2 too. Much of of this this sulfate sulfate is is preserved preserved as as. loo. Much microscopic microscopic inclusions inclusions in in quartz quartz pseudomorphs pseudomorphs after after gypsum, gypsum* but but at at least least one one rock rock contains contains distinct distinct sulfate sulfate crystals crystals that that dissolve dissolve on on Conspicuous pseudomorphs pseudomorphs are are weathering weathering leaving leaving aa pitted pitted surface. surface. Conspicuous associated associated with with large, large* silicified silicified stromatolites stromatolites at at aa quarry quarry 99 km km southwest southwest of of the the center center of of Marquette Marquette on on highway highway 480. 480. Other Other pseudomorphs from from this this quarry quarry are are replaced replaced gypsum gypsum crystals crystals up up to to about about pseudomorphs 33 cm cm long, long* which which occur occur in in maroon maroon carbonate carbonate mudstone. mudstone. Y The The significance significance of of the the discovery discovery of of sulfate sulfate in in the the Kona Kona Dolomite Dolomitc is well documented is that that marine marine evaporites, evaporitesy which contain contain aa well documented record record of of the the highly highly variable variable sulfur sulfur isotope isotope composition composition of of the the Phanerozoic Phanerozoic ocean, ocean* are are almost almost nonexistent nonexistent in the PPecambrian ecambrianexcept except for foraa few few sporadic sporadic occurrences occurrences that that are are 1.2 1.2 XX 10 10 years years old old or or younger. younger. If If sulfate sulfate is is preserved preserved in in some some of of the the numerous numerous reported reported occurrences occurrences of of Proterozoic and and Archean Archean sulfate sulfate pseudomorphs pseudomorphs and and if if this this sulfate sulfate has has Proterozoic not not suffered suffered serious serious isotopic isotopic fractionation fractionation during during diagenesis diagenesis and and metamorphism, metamorphismyit it may may be be possible possible to to extend extend the the important important sulfur sulfur isotope isotope record record of of exogenic exogenic processes processes back back to to aa time time of of low low atmospheric atmospheric 5 oxygen. oxygen. Leaching with sulfate sulfate from from the the Kona KonaDolomite Dolomitei~ticate iicate Leaching experiments with that that the the last last few few per per cent cent of of sulfate sulfate extracted extracted is is depleted depleted in in SS by by about about 11 °too. O/oo. If If this this can can be be extrapolated extrapolated to to diagenetic diagenetic and and metamorphic metamorphic processes processes responsible responsible for for replacement replacement of of evaporita evaporite minerals, minerals* it it suggests suggests that3he that3gheoriginal originalisotope isotopecomposition compositionmay may have have been than the the value value we we have have measured. measured. been moderately moderately higher higher in in SS than However, However* in in the the absence absence of of aa large large and and uniform uniform external external reservoir reservoir of of sulfate, sulfate*the the extremely extremely uniform uniform sulfur sulfur isotope isotope value value that that we we have have obtained, obtained* independent independent of of sulfate sulfate concentration concentration variations variations of of 20X, 20Xyis is an an encouraging encouraging indication indication that that the the original original sulfur sulfur isotope isotope composition composition of of sulfate sulfate in in the the Kona Kona Dolomite Dolomite is is preserved. presemed. To To test test whether whether or or not not processes processes that that encapsulate encapsulate sulfate sulfate in in silica silica produce produce significant significantsulfur sulfur isotope isotopefractionation, fractionation*we weare are collecting silicified silicified material material in in Phanerozoic Phanerozoic evaporites evaporites in in order order to to collecting compare compare the the isotopic isotopic composition composition of of trace trace sulfate sulfate inclusions inclusions with with sulfate sulfate in in the the main main evaporite evaporiteminerals. minerals. After finding finding preserved preserved sulfate sulfate in in the the Kona Kona Dolomite, Dolomite, we we After solicited the the help help of of colleagues colleagues in in assembling assembling the the most most comprehensive comprehensive solicited possible collection collectionof of similar similarmaterial material from fromother otherlocalities. localities. To To be be possible valuable, valuable,the the sulfur sulfur isotope isotope record record of of sea sea water water sulfate sulfate must must be be reasonably pseudomorphs rezsonablycomplete. complete. So So far far we we have have received quar qua9zz pseudomorphs after dter gypsum gypsum (or (or celestite) celestite) fro frogMontana Montana(1.2 (1.2 XX10 10 years), years)* Nabberu Xabberu Basin, Autralia Au tralia(1.4 (1.4 to to22XX 10 10 years), years), and and Barberton, Barberton*South South Africa Africa Basin, (3.4 (3.4 XX 10 10 years). years). We We shall shall be be grateful grateful for for material material from from other other Precambrian or or Phanerozoic Phanerozoic localities localities of of silicified silicified evaporites evaporites or or for for Precambrian information information about about such suchlocalities. localities. It It is is our our hope hope that that such such material, material* although inconspicuous, inconspicuousymay may be be common commonand, andyultimately, ultimatelyyuseful. useful. although 47 Lf7 �Stable Isotope Metamorphism and Hydrothermal Stable Isotope Evidence of Metamorphism Hydrothermal Alteration, Alteration, Negaunee Iron Iron Formation, Formation, Michigan Michigan E.C. E.C. PERRY, PERRY? S. SHEN, SHENy AND C. C. UENG (Department (Department of of Geology, Geology, Northern Northern IL 60115) 60115) Illinois University, DeKalb, IL University, DeKaib, A3equilibriuin Af8equilibrium siderite, siderite, and and particularly particularly quartz, quartz, concenconcentrate trate 00 with with respect respect to to magnetite. magnetite. This fractionation fractionation becomes becomes less at high high temperature temperature so so that thatdufing dung metamorphism metamorphism aa redistriredistribution occurs, from quartz quartz and and siderite. siderite. bution occurs, and and magnetite magnetite gains gains 0 0 from Because oxygen of carbonate and and quartz quartz in in iron iron formation formation1s magnetite, 6 % 0 of quantitatively more abundant abundant than than oxygen oxygen of magnetite, of varies magnetite in in metamorphosed iron iron formation formation typically typically varies considerably considerably as a function function of bulk composition composition and metamorphic metamorphic temperature. This patten is is not characteristic characteristic of of low low grade grade temperature. This pattern mgamorphic zones m~~amorphic zonesof 02the the Negaunee Negaunee Iron Iron Formation. Formation. Instead, Instead, the the manetite is 0 of ygnetite is almost almost constant constant throughout throughout aa given given core 6 0 whereas Cs6 0 0 of of quartz quartz and and siderite siderite varies varies considerably. considerably. We whereas with a interpret this to indicate equilibration of the rocks vith metamorphic fluid. metamorphic fluid. Over a large temperature temperature range range the the oxygen oxygen isotope fractionation between between magnetite magnetite and water water is almost constant, while while that between between quartz or siderite siderite and water varies varies constanty by several several per per mil. mil. Thus, a fluid dominated system syst-emwould behave behave as as the the Negaunee Negaunee Iron Iron Formation Formation does. does. Further Further evidence evidence for for hydrothermal hydrothermal fluid movement in in this this region region is is the the disequilibrium disequilibrium reversal in quartz-siderite quartz—siderite oxygen isotope isotope fractionation fractionation that reversal that Formation cores. cores. occurs near the the base of several several Negaunee Negaunee Iron Iron Formation Cs metamorphism of zone Average temperature temperature of metamorphism zone II iron iron formation formation wide area, asodeterminec! as0determined by quartz-magnetite quartz—magnetite geothermgeotherm— over a wide ometry, is 320 2 . 1133 C. One of the cores characterized characterized by this this ometry, C. temperature contains a zone in which reaction is is temperature which the following reaction grunerite ++ CO CO, + H,O. observed: siderite siderite + minnesotaite ininnesotaite == grunerite H,O. If a a large part part of of zone zone I I was was balanced balanced during during metamorphism metamorphism at a temperatures and pressures near those that would release temperatures volatiles volatiles by such such a reaction, reaction, rock rock permeability permeability may have have increased greatly at this locality opening conduits for fluids fluids conduits for expelled expellea from zones of higher grade metamorphism nearer the Republic trough. Republic trough. If this explanation is valid, valid, the the conduits, conduits, explanation is once formed, formed, must have remained open to circulation circulation of fluids fluids after the peak temperature of metamorphism metamQrphism since both both high and low isotope isotope "temperatures" "temperatures1'are are recorded recorded in in the the permeable permeable zones. zones. low + Sills emplaced before before the main main regional metamorphic metamorphic event cores that that we we have have studied. studied. These These occur in the upper parts of of 22 cores sills have produced distinctive contact metamorphic metamorphic effects in in underlying iron formation that are clearly presemed preserved in the oxygen isotope composition composition of of quartz, quartz, carbonate, carbonate, and and magnetite. magnetite. oxygen isotope isotope "temperatures" "temperatures" are are recorded recorded near near the the sills, sills, High mineral isotope but in the outer margins of the contact zones "temperatures" "temperatures1' frozen in by the earlier metamorphism lower than than frozen metamorphism are distinctly lower the temperature of regional regional metamorphism. metamorphism. temperature of L8 �In excellent correlation 1ists In at at least least one core an excellent ~ists between between amount amount of of carbonate carbonate in in aa specimen specinen and and the the 56'3 3content content of of the the carbonate. carbonate. This This relatign relatign holds holds over over aa range range of of 8 3 CC of of approximately approximately _70/oo -7O/oo to to —ii -11 /oo /oo and and aa carbonate carbonate content content of of 19 19 to to 6%. 6%. 49 �Middle Proterozoic in Northeast Wisconsin and and Proterozoic Events in Northeast Wisconsin Rb-Sr Biotite Biotite Ages Ages Adjacent Michigan Michigan as as Defined Defined by by Rb—Sr Adjacent ZELL E. PETEBMAN and ZELL E . PETERMAN and P. K. SIMS SIMS.(U.S. Geological Survey, Suneys Denver Denver (U.S. Geological Federal Centery Center, M MS Federal S 963, 963 Denver, Denver* CO CO 80225) 80225) Systematic variations variations of Rb-Sr Rb—Sr biotite ages for Proterozoic and Systematic for Early Proterozoic and Late from the Marquette Marquette km from Late Archean Archean rocks rocks in in aa transect transect extending extending 130 130kin trough in northern Michigan to northeastern northeastern Wisconsin record trough in record uplift uplift events The biotite events in in the the Middle Middle Proterozoic Proterozoic (Figure).. (Figure).. The biotite ages ages have have aa trimodal distribution with peaks at 1.58 (19 samples), samples)* 1.32 1.32 ±2 trimodal distribution 1.58 2± 0.07 Ga (19 0.04 Ga Ga (26 (26 samples), samples)* and and 1.14 1.14 ±2 0.03 0.03 Ga Ga (9 (9 samples). samples). The 1.58—Ga 1.58-Ga peak is is a composite composite containing the tightly clustered 1.63 ±2 0.03 Ga ages ages for for the southern complex complex in in northern northernMichigan Michigan(Van (VanSchinus Schmusand and Woolsey, W001sey~1975) 1975) the southern and slightly The 1.32 to the the south. south. The 1.32 Ga Ga peak peak is is slightly younger younger ages ages from from areas areas to defined by biotite ages in the Felch trough area area (Aldrich (Aldrich and others, others, an area area extending extending southward across across the central part of the 1965) and in an the Dunbar gneiss Dunbar gneiss dome dome in in northeastern northeastern Wisconsin Wisconsin into into the the body body of of Atheistane Athelstane south of the The western western third Quartz Monzonite of Cain (1964) south the dome. The third of of the the dome is characterized by biotite ages that range range from from 1.11 1-11 to to 1.17 1.17 Ga. This Ga. This age age zone zone merges abruptly abruptly to to the the east east with with the the zone zone of of interinterages, and the eastern part of the yields still mediate ages* the dome yields still older older ages ages ranging ranging from from 1.46 1.46 to to 1.63 1.63 Ga. Ga. biotite—hosted Rb-Sr Rb—Sr system have resulted Resetting of the biotite-hosted system could could have resulted from from pulses related to igneous activity* activity, recrystalli~ation~ recrystallization, or thermal pulses or rapid rapid uplift uplift and and cooling. cooling. At least least two of the age peaks reflect complete resetting setting of of the the systems systems as as suggested suggested by by the the limited limited dispersion. dispersion. The The 0.03 Ga Ga biotite biotite ages ages for Archean Archean rocks of the southern southern complex complex 1.63 2± 0.03 have been correlated have correlated with with an an isotopically isotopically widely widely recognized recognizedbut but geologigeologically Precambrian rocks cally cryptic event that has affected Precambrian rocks over over much much of of Wisconsin (Van Woolseyy 1975). 1975). The The resetting resetting of of biotite biotite Wisconsin (Van Schmus Schmus and and Woolsey, ages western third of the Dunbar Dunbar dome at 1.14 Ga occurred occurred ages in in the the western 1.14 ±2 0.03 Ga contemporaneously contemporaneously with with Keweenawan Keweenawan rifting rifting and and igneous igneous activity. activity. The The coincidence of age discontinuities discontinuities with with northwestnorthwest— and northeastnortheast— coincidence zones with vertical vertical lineations suggests trending shear zones lineations (Figure) (Figure) strongly stronglysuggests vertical uplift uplift was was a causative factor in producing that differential vertical age pattern. the age pattern. Rapid Rapid erosion, erosion* an an inevitable inevitable corollary corollary to to rapid rapid upuplift, would would have have contributed Early Early Proterozoic Proterozoic detritus to Keweenawan Keweenawan lift* sands. sands. The significance biotite ages The significance of the 1.32—Ga 1.32-Ga peak of biotite ages is is less less certain. certain. (1965) suggested suggested aa thermal thermal event event at at this this time, time, but but others (1965) Aldrich and others did not not elaborate elaborate on on aa possible possible cause. cause. Possibly, Possiblyy the the surface surface now now characterized by the 1.32—Ga 1.32-Ga age group was during was uplifted and cooled during which the biotite systems systems were only the Keweenawan from a depth at which partially partially reset. reset. so �References References Aldrich, L. T., Davis, G. L.* L., and James, T.* Davis* James* H. L., 1965, 1965, Ages of of minerals minerals Aldrich* from metamorphic and from metamorphic and igneous igneous rocks rocks near near Iron Iron Mountains, Mountains*Michigan: Michigan: Journal of v. 6, 6 * P. p. 445—472. 445-472. Petrology9 v. Journal of Petrology, Cain, A., 1964, Pembine area, 1964, Precambrian Precambrian geology of the the Pembine area* northnorthCainy J. A.* eastern Wisconsin: Papers of eastern Wisconsin: Papers of Michigan Michigan Academy Academy of of Science, ScienceyArt, Art, and Letters* Letters, v. 49, 49* p. 81—103. 81-103. and Van Woolsey, L L. Rb—Sr geochronology Van Schmus, Schmus, W. R., R.* and W001sey~ . L., 1975, 197Sy Rb-Sr geochronology of of the Republic area, Canadian Journal Journal the Republic area* Marquette Marquette County, County9 Michigan: Michigan: Canadian Earth Sciences, v. 12, 12, p. p. 1723—1733. 1723-1733. of Earth Sciences* v. 51 �8 8' 88° S 1.66 1.60 *1.69 •1.69 , I.65 -65 *11 .60 .60 63 5% : 55 1.62 . 1.62 MICHIGAN MICHIGAN 1.68 •1.39 ,1 .261.34 , 36 ' 46° 1.09 1.28 / , / 7 .32 .33 1.25 1.32' WISCONSIN 1.6 SHEAR •1.39 I \ 1 0MILES MILES 10 00 e KILOMETERS o0 •13 8 I 10 KILOMETERS 10 . Y" I .'% 1 - *I- 3 9 •1.39 # I.1 Rb-Sr biotite b i o t i t e ages ages for f o r Early E a r l y Proterozoic P r o t e r o z o i c and and Late L a t e Archean Archean rocks r o c k s in in Rb—Sr n o r t h e a s t Wisconsin and a d j a c e n t Michigan. Data a r e from A l d r i c h and northeast Wisconsin and adjacent Michigan. Data are from Aldrich and o t h e r s (196.51, Van Schmus and Woolsey (19751, and Peterman and Sims others (1965), Van Schinus and Woolsey (1975), and Peterman and Sims (unpublished). Note Note the t h e close c l o s e correspondence correspondence between between age age discontinui— discontinui(unpublished). t i e s and known and p r o j e c t e d s h e a r zones i n n o r t h e a s t Wisconsin. ties and known and projected shear zones in northeast Wisconsin. 52 52 �Crystallization C r y s t a l l i z a t i o n Histories H i s t o r i e s of of Early E a r l y Proterozoic Proterozoic Plutons from Northern Wisconsin from W.L. W.L. PETRO PETRO (Dept. (Dept. of of Geology Geology && Geophysics, Geophysics, University University of Wisconsin, Wisconsin, Madison, Madison, WI W I 53706) 53706) JA variety v a r i e t y of of Early E a r l y Proterozoic Proterozoic plutons p l u t o n s isi sexposed exposed plutoris in The p l u t o n s vary vary from from gabbro gabbro i n northern northernWisconsin. Wisconsin. The to t o granite g r a n i t eini ncomposition, composition, are a r emesozonal mesozonal to t ohypabyssal hypabyssal in i n level l e v e l of of emplacement, emplacement, and aare r e syntectonic s y n t e c t o n i c to to posttectonic p o s t t e c t o n i c with with respect r e s p e c t to t o the t h e Penokean Penokean orogeny. orogeny. Recent and petrographic etrographic work h a s established established Recent field f i e l d and work has crystallization c r y s t a l l i z a t i o n histories h i s t o r i e s for f o r the t h e plutons p l u t o n s arid and their their aureoles, a u r e o l e s , yielding y i e l d i n g important important information information on on the the petrologic p e t r o l o g i c evolution evolution of of this t h i s part p a r t of of the t h e crust c r u s t in i n the the Lake Lake Superior Superior region. region. The The plutons plutons generally g e n e r a l l y contain contain multiple m u l t i p l e generations generations mineral assemblages, indicating i n d i c a t i n g complex complex crystallicrystallization z a t i o n histories. h i s t o r i e s . Posttectonic P o s t t e c t o n i c hypabyssal hypabyssal plutons plutons contain contain relict r e l i c t euhedral euhedral or o r embayment embayment textures textures representing s i l i c a t e melt. melt. r e p r e s e n t i n g crystallization c r y s t a l l i z a t i o n from from aa silicate Posttectonic P o s t t e c t o n i c epizonal epizonal plutons, plutons, pegmatites, pegmatites, and and aplites aplites exhibit e x h i b i t textures t e x t u r e s which probably represent r e p r e s e n t crystallicrystallization z a t i o n at a t or o r near near the t h e solidus. s o l i d u s . Syntectonic Syntectonic mesozonal mesozonal plutons exhibit e x h i b i t textures t e x t u r e s representing r e p r e s e n t i n g subsolidus subsolidus crystallization. c r y s t a l l i z a t i o n . All A l l of of the t h e plutons p l u t o n s are a r e overprinted overprinted by low—grade alteration products. of of Previously Previously unreported unreported electron e l e c t r o n microprobe microprobe deterdeterminations minations of of mineral mineral compositions compositions have have been been made made for for plagioclase p l a g i o c l a s e and and potassium potassium feldspars, f e l d s p a r s , biotites, b i o t i t e s , horn— hornblendes, garnets, b l e n d e ~ ,znuscovites, muscovites, g a r n e t s , and and ilmenites. ilmenites. The The mineral compositions compositions allow allow estimations e s t i m a t i o n s of of the t h e intensive intensive mineral parameters during ccrystallization parameters obtained obtained during r y s t a l l i z a t i o n .• Possible Possible equilibria e q u i l i b r i a involving two two feldspars f e l d s p a r sand andplagioclase— plagioclase- hornblende yield y i e l d temperatures temperaturesofof600—700°C 600-700° ffor o r epizonal epizonal hornblende rocks rocks and and 00—600°C 400-600° for f o r mesozonal mesozonal rocks. rocks. Intrusion I n t r u s i o n of of Penokean and post—Penokean post-Penokean plutons plutons occurred across a c r o s s batholithic b a t h o l i t h i c dimensions dimensions in i n northern northern occurred Wisconsin. Wisconsin. Most Most of of the t h e Early Early Proterozoic Proterozoic metamorphism metamorphism in i n the t h e plutons and and their t h e i r aureoles a u r e o l e s probably probably occurred occurred during intrusion i n t r u s i o n and and cooling coolingofofthe t h eplutoris. plutons. during According to t o this t h i s interpretation, i n t e r p r e t a t i o n , Early Early Proterozoic Proterozoic iccording metamorphism metamorphism in i n northern northern Wisconsin Wisconsin was w a s autometamorphism autometamorphism and and contact c o n t a c t metamorphism metamorphism on on aa regional r e g i o n a l scale. s c a l e . These These new new data d a t a and and interpretations i n t e r p r e t a t i o n s place p l a c e important important constraints constraints on on models models for f o r the t h e thermal thermal evolution evolution of of this t h i s part p a r t of of the t h e crust. crust. 53 �Climatic C l i m a t i c Inferences I n f e r e n c e s of of Iron—Formation Iron-Formation from from Associated Associated Diamictite D i a m i c t i t e fades f a c i e ssequences, sequences, Griqualand Griqualand West West Supergroup, S u ~ e r g r o u p South , South Africa Africa R..D. POWELL POWELL (Dept. (Dept. of of Geology, Geology,N o r t h e r n Illinois I l l i n o i s University, U n i v e r s i t y , DeKaib, DeKalb, R.D. Northern 60115) I l l i n o i s60.115) Illinois Makganyene Ongeluk Lava Lava (-2.2 (2.2 Ga Makganyene Diamictite D i a m i c t i t e underlies u n d e r l i e s Ongeluk G a B.P.) B.P.) at at t h e base base of of the t h e Postmasburg Postmasburg Group Group in i n Cape Cape Province, P r o v i n c e , South SouthAfrica. Africa. the The i s interpreted i n t e r p r e t e d as a s glacigenic, g l a c i g e n i c , which which puts p u t s environmental environmental The diamictite d i a m i c t i t e is constraints c o n s t r a i n t s (e.g. (e.g. temperature) temperature) on on the t h e formation formation of of associated a s s o c i a t e d iron— ironformation sedimentary sedimentary rocks. rocks. formation In I n outcrops, o u t c r o p s , diamictites d i a m i c t i t e s are a r e interstratified i n t e r s t r a t i f i e d with w i t h conglomerate, conglomerate, sandstone, shale s h a l e and and pebbly pebbly mudstone. mudstone. Direct D i r e c t evidence evidence for f o r the t h e dia— diasandstone, tnictites is two two features f e a t u r e s of of clasts: c l a s t s : striated s t r i a t e d sursurm i c t i t e s bbeing e i n g glacigenic g l a c i g e n i c is f a c e s and and facetted, f a c e t t e d , flat—iron f l a t - i r o n shapes. shapes. Most Most clasts c l a s t s are are chert c h e r t and and faces s t r i a t i o n s are a r e well w e l l retained r e t a i n e d on on their t h e i r surfaces. s u r f a c e s . In I n some some areas a r e a s up up striations to t o 10 10 percent p e r c e n t of of the t h e clasts c l a s t s are are striated s t r i a t e d (a ( a high high proportion p r o p o r t i o n in i n many many Pleistocene s t r i a e orientaorientaP l e i s t o c e n e glacigenic g l a c i g e n i c successions), s u c c e s s i o n s ) , and and multiple m u l t i p l e striae t i o n s also a l s o occur. occur. Some Some clasts c l a s t s (up (up to t o 22 percent p e r c e n t locally) l o c a l l y ) have have aa tions f l a t - i r o n form form produced produced during d u r i n g basal b a s a l transport t r a n s p o r t in i n aa glacier. g l a c i e r . The The flat—iron oligomictic o l i g o m i c t i c clast c l a s t composition, composition, often o f t e n cited c i t e d as as evidence evidence against against Underlying for— foras aa source s o u r c e control. c o n t r o l . Underlying can be be explained e x p l a i n e d as glaciation, g l a c i a t i o n , can n a t i o n s , which r e probably h e ssource, o u r c e , comprise iron—formation iron-formation and and tnations, which aare probably tthe carbonate rocks. rocks. Both Both carbonate c a r b o n a t e and and (iron—rich) ( i r o n - r i c h ) shale s h a l e clasts c l a s t s did did carbonate Therefore, n o t survive s u r v i v e long long transport t r a n s p o r t by by Pleistocene P l e i s t o c e n e glaciers. g l a c i e r s . Therefore, not c h e r t is is the t h e most most likely l i k e l y component component of of glacigenic g l a c i g e n i c sediment sediment in i n the the chert Makganyene Diamictite. D i a m i c t i t e . Glacial G l a c i a l pavements pavements have have been been noted noted by by prepreMakganyene viOus v i o u s workers, workers, however, however, none none were were found found during d u r i n g this t h i s study. s t u d y . If I f many many then absence absence of of aa of of the t h e sequences sequences are a r e glacimarine g l a c i m a r i n e (see ( s e e below), below), then widespread pavement pavement can can be be expected. expected. widespread Other arguments arguments are a r e made made for f o r aa glacigenic g l a c i g e n i c origin o r i g i n of of the t h e diamic— diamicOther C i t e succession s u c c e s s i o n using u s i n g lithofacies l i t h o f a c i e s sequence sequence analysis. a n a l y s i s . Some Some of of the the tite a s s o c i a t e d sorted s o r t e d units u n i t s are a r e sheet—like s h e e t - l i k e sandstone sandstone bodies bodies up up to t o 12m 12x11 associated t h i c k . They They are a r e fine— f i n e - to t o coarse—grained, coarse-grained, occasionally o c c a s i o n a l l y pebbly pebbly or or thick. g r i t t y , and and are a r e apparently a p p a r e n t l y structureless s t r u c t u r e l e s s or o r exhibit e x h i b i t horizontal h o r i z o n t a l Lami— lamigritty, Basal n a t i o n , medium—scale medium-scale trough trough cross—bedding cross-bedding and and channel channelforms. forms. Basal nation, conglomerates occur occur in i n the t h e channel channel forms. forms. AA flaggy f l a g g y sandstone s a n d s t o n e facies facies conglomerates is common common at a t the t h e base base of of the t h e succession. s u c c e s s i o n . Asymmetrical Asymmetrical and and symmetrisyietri— is c a t rrippled i p p l e d sandstone u r f a c e s are a r e draped draped with w i t h shale. s h a l e . The The sandstones sandstones cal. sandstone ssurfaces a r e interpreted i n t e r p r e t e d as a s braided b r a i d e d stream s t r e a m deposits d e p o s i t s probably probably in i n interaction interaction are w i t h aa shallow shallow marine marine environment. environment. with fineOther sorted s o r t e d facies f a c i e s are a r e lensoid l e n s o i d channels channels of of structureless s t r u c t u r e l e s s fine— Other t o inedium—grained medium-grained sandstone within w i t h i n diamictite. d i a m i c t i t e . The The channels channels are are to s t a c k e d or o r isolated i s o l a t e d and and include i n c l u d e blocks blocks of of diamictite. d i a m i c t i t e . The The interton— intertonstacked guing of sandstone w i t h diamictite d i a m i c t i t e indicates i n d i c a t e s the t h e genetic g e n e t i c rrocesses processes guing with of both b o t h facies f a c i e s were episodic, e p i s o d i c , or o r that t h a t the t h e sandstone s a n d s t o n e channels channels were were of l i m i t e d in i n spatial s p a t i a l position. p o s i t i o n . This T h i s type t y p e of of sequence sequence has has been been dedelimited s c r i b e d in i n Pleistocene P l e i s t o c e n e subglacial s u b g l a c i a l lithofacies. l i t h o f a c i e s . The The sequence sequence may may be be scribed 54 �subaqueous where where tthe compound ppara—till chansubaqueous h e ddiamictite i a m i c t i t e iis s aa compound a r a - t i l l and the t h e channels i n t e r p r e t a t i o n presents p r e s e n t s aa n e l s are a r e subaqueous subaqueous outwash. outwash. A submarine interpretation because ffluvial extremely hhigh ddifficulty i f f i c u l t y because l u v i a l ttraction r a c t i o n ccurrents u r r e n t s rrequire e q u i r e extremely ish be maintained maintained aatt tthe base of of aa more more dense sediment cconcentrations o n c e n t r a t i o n s tto o be h e base sea water column. column. of ice-proximal ice—proximal One section s e c t i o n eexhibits x h i b i t s ffacies a c i e s aassociations s s o c i a t i o n s ttypical y p i c a l of D i a m i c t i t e grades into i n t o and Out o u t of pebbly pebbly subaqueous environments. Diamictite xmidstone, breccia/conglomerate bedsy beds, and and tthin mudstone, breccia/conglomerate h i n sandstone beds. beds. Another stacked debris-flow debris—flow noses noses tthat have sstructureless ssection e c t i o n comprises stacked h a t have tructureless ddiamictite i a m i c t i t e cores c o r e s and outer o u t e r fissile f i s s i l e zones zones exhibiting e x h i b i t i n g flow flow structure. structure. occur iin and submarine, submarine, gglacial and non-glanon—glaDebris flows occur n tterrestrial e r r e s t r i a l and l a c i a l and cial Alluvial c i a 1 environments. A l l u v i a l ffan a n ddeposits e p o s i t s have aa geometry and facies facies Terrestrial associations a s s o c i a t i o n s that t h a t exclude them from from consideration. consideration. T e r r e s t r i a l ice— icecontact c o n t a c t environments environments include i n c l u d e resedirnented resedimented ddeposits e p o s i t s tthat h a t cannot be be excluded as a s a possible p o s s i b l e interpretation i n t e r p r e t a t i o n at a t some some localities. l o c a l i t i e s . Submarine debris flows aare very rrare water uunless by aa d e b r i s flows r e very a r e iin n shallow water n l e s s iinfluenced n f l u e n c e d by glacier. glacier. The succession s u c c e s s i o n is i s considered considered glacigenic. g l a c i g e n i c . The glacier g l a c i e r must have melting had a m e l t i n g base base because because glacifluvial g l a c i f l u v i a l deposits d e p o s i t s are a r e conunon. common. Frozen glaciers Antarctica today llack debase g l a c i e r s llike i k e tthose h o s e iin n A n t a r c t i c a today a c k common ffluvial l u v i a l deposits. was vala s probably an ice i c e cap and/or v alp o s i t s . The terrestrial t e r r e s t r i a l glacier glacier w ley l e y glaciers g l a c i e r s based on, on, and south s o u t h of of the t h e Ganyesa Ganyesa Dome. Dome. The glacier glacier probably nnot a s probably o t an iice c e sshelf h e l f because margin ffacing a c i n g the t h e eepeiric p e i r i c sea wwas tidal t i d a l ranges were sufficiently s u f f i c i e n t l y large l a r g e to t o make make an a n ice i c e shelf s h e l f unstable, unstable, even if Therefore, w a s made made of of cold cold ice. ice. T i f the t h e glacier g l a c i e r was h e r e f o r e y the t h e glacier glacier ended as a s aa tidewater t i d e w a t e r terminus. terminus. Furthermore, Furthermorey the t h e presence of of volcanic volcanic ash in of the water i n some of t h e compound ppara—till a r a - t i l l iindicates n d i c a t e s an open w a t e r iiceberg ceberg necessarily zone environment close c l o s e to t o shore. shore. That n e c e s s a r i l y excludes an ice ice shelf s h e l f environment. environment . d r i l l cores c o r e s show an iintimate n t i m a t e aassociation s s o c i a t i o n of of d i a m i c t i t e and Deep drill diamictite l a s t i c marine t h a t iinclude n c l u d e llean e a n iron— ironchemical and cclastic marine sedimentary rocks rocks that formations. The Makganyene glacier, g l a c i e r , on a narrow sshelf h e l f aatt the t h e margin of the t h e eepeiric p e i r i c ssea, e a , probably s aatt ppresent r e s e n t glacial glacial of probably enhanced enhanced upwelling upwelling aas margins. That upwelling m may margins. y have enhanced chemical sediment deposideposittion i o n (iron—formation, (iron-formation, chert, c h e r t , carbonate). carbonate). The climate c l i m a t e was n o t exexnot treme (cf. (cf. A n t a r c t i ~ a )bbut ~u t cool c f . Alaska) h a t inAntarctica), cool temperate temperate ((cf. Alaska) and and tthat inon iinterpretations of oxygen oxygen iisotope analyfference e r e n c e pputs u t s cconstraints o n s t r a i n t s on n t e r p r e t a t i o n s of s o t o p e analyof associated sses e s of a s s o c i a t e d chemical chemical sediments. sediments. 55 �Magnetotelluric MagnetotelluricProfile Profileof of the theJacobsville JacobsvilleSandstone Sandstone Ted Engrg., R. Repasky Repasky (Dept. (Dept.of ofGeol. Geol.&& Geol. ~eol. Engrg.,Michigan MichiganTechnological Technological Ted R. MI 49931) 49931) University,Houghton, Houghton,MI University, Seven Seven magnetotelluric magnetotelluric soundings soundingswere were conducted conducted along along aa NW—SE W-SE line line across across the the Jacobsville Jacobsville Sandstone, Sandstone,between between Keweenaw KeweenawBay Bay and and the the They have have provided provided Keweenawfault faultin inMichigan's Mchigan's Upper UpperPeninsula. Peninsula. They Keweenaw the sandstone an estimate of the thickness and resistivity of and an estimate of the thickness and resistivity of the sandstoneand the underlying underlyingbasement. basement. the The 1818seconds) seconds)toto Thesoundings soundingswere were of of aalong longenough enoughperiod period (up (upto to1818 Initial obtain obtain data datafrom fromlayers layersat atleast leastseveral severalkilometers kilometersinindepth. depth. Initial interpretation interpretationis is that that the thesandstone sandstonemay may be be one one to to two two kilometers kilometersthick, thick, Tapiola/OtterLake Lake area, area,the the sandstone sandstoneis is and that that northwest northwest of of the the Tapiola/Otter and underlain by by the the Portage Portage Lake Lake volcanics volcanics of of aa higher higher resistivity. resistivity. To To underlain the southeast southeast of of this this area area the the sandstone sandstone is is underlain underlain by by aa body body of of the lower lower resistivity resistivity rock, rock, perhaps perhaps Michigamme Michigame Slates Slates which which are are known known to to outcrop at at the the head head of of Keweenaw KeweenawBay. Bay. outcrop — Lake rn / 'I / 1,0 I- 0 20 Miles 10 2030 Km Figure 1.1. Figure Location of of soundings soundings(stations (stations1—7), 1-71, Location j, Jacobsville Sandstone; fn, Freda Sandstone and j, Jacobsville Sandstone; fn, Freda Sandstone and Nonesuch Shale; Shale; cli, ch, Copper Conglomer3te; Nonesuch Copper Earbor Harbor Conglomerate; pl, Portage Lake Lava Series; m, Michigamme Slats. p1, Portage Lake Lava Series; m, Michigamme Slate. 66 �Sounding Results Results Depth Depth KM K P4 00 19 419 Resistivities in in Ohm—meters Ohm-meters 62 —.4 38 3 83 7 =2 12 16 11 —10 — 39 —2 71 24 21 6 4 39 2 2 3 3, 140 217 937 986 48 4. 4 123 4 6 5 • PROFILE 2OOO—"\.._--—.__________-- I ioooi;7 . I(I, E. -2000 .. :. - Ui Ui N-N ,,, Figure 2. Figure 2. Sounding locations Sounding locationson onaa geologic geologic cross cross section. section. (Meabref and and Iiinze, Hinse, 1970) 1970) (Meshref 57 7 SE �P t and and Ni N i Arsenide Arsenide Minerals Minerals in i nthe theDuluth DuluthComplex Complex Pt (Mineral Resources Research of PATRICK J. J.RYAN PATRICK RYAN (Mineral Resources ResearchCenter, Center,University University of Minnesota, Minneapolis, MN 55455)s Minnesota, Minneapolis, MI 551455)* PAUL W.W.WEIBUN (Minnesota Geological 2642 University Ave., PAUL WEIBLEN (Minnesota GeologicalSurvey, Survey, 26142 University Ave., 55114) St.Paul, Paul, St. MNMN551114) S p e r r y l i t e (PtAs2), (PtAs21, maucherite maucherite (Ni3tts2), (Ni3As21, and and possibly possibly niccolite niccolite Sperrylite (NUS) have d e n t i f i e d in i n massive massive sulfide s u l f i d esamples samples from from the the Duluth Duluth (NiAs) have been beeni identified Complex. was made made iin n the course of aa survey survey of of The iidentification d e n t i f i c a t i o n was Complex. The the course 1) from from the the three representative representativemassive massive sulfide s u l f i d esamples samples (Table (Table 1) three MINNAMAX Shaft Shaft (located about 8 km Babbitt,MN). MN). MINNAMA.X (located about 8 isouth south of of Babbitt, One ssperrylite p e r r y l i t e grain grain was w a s found found as aa aa small, small, c5 a micrometer, 5 micrometer,euhedral euhedral One elongategrain grain maucheritewhich which in i nturn turnwas was crystal in i na alarger, largery crystal elongate ofofmaucherite Quantitative Quantitative electron microprobe analyses i n d i c a t e a deficiency of A for electron microprobe analyses indicate a deficiency of Ass for 2, 1 & 2). Minor elements o t a l less less stoichlometric s p e r r y l i t e (Table atcichiometric sperrylite (Table 2, 1 & 2). Minor elementst total The s p e r r y l i t e grain has a very complex i n t e r n a l wt. 5. than two than two wt. %. The sperrylite grain has a very complex internal s t r u c t u r e which which cconsists o n s i s t s of of an an inclusion inclusion of of aa blade blade of of graphite graphite (?) (?I structure T h i s proved proved to t o be be too toofine— fineand aa complex complex myrmeketic m m e k e t i c intergrowth. This and grained (2 ( 2 micrometer micrometer wide o r quantitative q u a n t i t a t i v eanalysis, analysis,however, however, grained wideblebs) blebs) ffor data indicate i n d i c a t ethe thepossible possiblepresence presence of of graphite, graphite, precious precious q u a l i t a t i v e data qualitative are metal alloys, tellurides, t e l l u r i d e s and , andbismuth bismuthminerals. minerals. These These phases phases are metal postulated on on the the basis b a s i s of of positive p o s i t i v e identification i d e n t i f i c a t i o n of of C, C , Cu, Cu, Au, Au, postulated B i , and and Pb Pb peaks peaks in i n x—ray x-ray dispersive dispersive (EDX) (EDXI and and scanning scanningAuger Auger Te, Bi, Te, microprobe spectra. spectra. Pd Pd was w a s identified i d e n t i f i e d in i n only only one one x—ray x-ray spectra s p e c t r a in i n aa microprobe B i i n t h e s p e r r y l i t e grain. myrmeketic bleb r i c h i n myrmeketic bleb rich in Bi in the sperrylite grain. embedded i in n an of obalcopyrite—cubanite. chalcopyrite-cubanite. embedded an intergrowth of Maucherite was w a s found found in i n all a l l three three samples samples studied. studied. Maucherite It is It is llight i g h t microscopy microscopy from from other other sulfide s u l f i d e and and its white, white, high high reflectivity r e f l e c t i d t y and and very very faint f a i n t pink pink arsenide minerals mineral8 by by its arsenide It was was found found in i n five f i v e polished polished sections sections as as small s m a l l blebs blebs t i n t . It tint. as long long needle—like n e e d l e l i k e stringers s t r i n g e r s (0.01 (0.01 to t o 1.5 1.5 mm rn (10 micrometer) (10 micrometer) and and as It was found i n all three major s u l f i d e phases--pyrrhotite, long). It was found in all three major sulfide phases——pyrrhotite, long). pentlanditey and and chalcopyrite—cubanite chalcopyrite-cubanite intergrowthz——but intergrowths-but makes makes up up less less pentlandite, of the the massive massive ore o r e samples. samples. Although w t . %% of than one one wt. Although the the inaucherite maucherite than grains appear appearhomogeneous homogeneous in i n reflected r e f l e c t e d light, l i g h t , electron electron microprobe microprobe grains analyses show show aa wide a r i a t i o n in i n Ni/As N i / A s and and Fe/Ni Fe/Ni ratios ratios analyzes widerange rangeofof vvariation N i - A s grain g r a i n is is clearly c l e a r l y outside outside the the (Table 2,2,3—5). 3-51. One One analysis of aa Ni—As (Table analysis of range of of maucherite maucherite compositions compositions (2) (2) and and approaches approaches the the composition composition of of range 6 ) . n i c c o l i t e (Table 2, One micrometer-sized mauchrite gave gave niccolite (Table 2, 6). One micrometer—sizedgrain grain iinn mauchrite an EDX EDX sspectra p e c t m for f o rosmium. osmium. an distinguished iin n reflected reflected distinguished Platinum mineralization and maucherite maucherite have have been been reported in Platinum mineralization and reported in Keweenawan rock8 & 3), 31, but (2 & data reported reported here irst but the the data Keweenawan rocks (2 hereisis the the ffirst we are a r eaware aware of of in i n the the Duluth Duluth Complex. Complex. The i d e n t i f i c a t i o nwe The new new data data identification emphasizes the the need need for f o r evaluation evaluation of of the the ore ore recovery recovery procedures procedures emphasizes have iguored ignored special s p e c i a l problems problems related r e l a t e d to t o arsenide araenide which up up to t onow now have which w h a tphases The data data leaves leaves the the question questionofofwhat minerals. The phases are a r e responsible responsible minerals. f o r platinum platinum metal metal group group elements i n assay assay values values unreunrefor elementsother other than than PPtt in solved (14). (4). solved 58 �Table 1. Samples Samples of the the Duluth Duluth Complex Complex examined r aarsenide r s e n i d e minerals. Table 1. examinedf ofor Sample Sample Type Location MIX-A AMX-A 11 kg sample of massive massive kg sample ssulfide, u l f i d e , rich r i c h in i nchalco-. chalcoppyri y r ite—cubarii te-cubanitete Suppliedbyby MINNAMAX from an Supplied MINNAMAX from an u n s p e c i f i e d llocality. ocality. unspecified AMX—B AM-B kg sized kg s i z e d sample sample of of massive massive ssulfide, u l f i d e , rich r i c hini pentlan— n pentlanddite i te Suppliedbyby MINNAMAX from Supplied MINNAMAX drift #417, 1055 1055 feet d r i f tround round #k17, below reference r e f e r e n cine MINNAMt&X i n MINNAMAX below shaft. 25 kg kg random massive sulsul25 random massive From the shaft dump. From t h eMINNAMAX MINNAMAX shaft dump. AMX—C M - C fide f i d e ore o r esample. sample. . Electron E l e c t r o n microprobe microprobe analyses rsenide m i n e r a l s iin n the the Table Table 22. analysesofof aarsenide minerals Duluth Duluth Complex. Complex. 1 Analysis Sample AMX—A3 Sample 1 22 MIX—A9 33 MIX—Al AMX-A 1 55 k 4 MIX—A2 66 MIX—Bk MIX-B 1 sS .10 .09 .0k -04 .52 .11 Ass A Fe Co co Ni Ni Cu cu Zn zn PPtt kO.82 kO.30 117.09 47 09 116.93 118.08 .15 55.19 .77 .07 .76 .13 1.01 .10 .20 .62 62 1.15 2.27 11.69 2.38 2-38 50.06 50.06 3.18 1.97 .80 118.59 118.90 110.57 0 0 0 0 0 0 0 57.82 58.96 .13 .09 .11 100.117 101.19 100.50 101.112 101.51 .010 1.670 .008 1.612 .0112 .0511 .00k .006 .005 .010 .025 0 0 .908 .906 Anions Anions . Cations 1.679 1.679 1.000 1.000 1.620 1.000 1,000 Total T otal 2.679 2.679 2.620 2.620 Total s S AAss Fe Co co NNii Cu cu Zn zn Pt Pt .0110 .53 0 0 0 0 .06 -06 100.25 10025 .0011 -004 2.085 2.085 .037 037 .13k -134 2.828 2.828 0 0 0 0 .001 .001 0 .0511 .011 .018 2.081 .068 .179 2.750 2.122 2.800 .1311 .111 .319 .052 2.75k 2.627 0 0 0 0 0 0 .002 .002 .002 2.089 2.089 3.000 3.000 2.135 2.135 3.000 3.000 20 133 2.133 3.000 3.000 2.81 8 2.818 5.089 5.089 5.135 5.135 5.133 5133 5.818 5.818 59 3.000 3.00 �Notes to t o Table Table 2: 2: Analyses Analyses were were made made ononthe theARL. ARL nine spectrometer electron e l e c t r o n microprobe in Dept. of of Geology, Geology, University of of Wisconsin, Wisconsin, Madison. Madison. Operating Operating i n the Dept. conditions: conditions: 15 15 K.V., r e e rrepliepliK.V., 0.05 0.05 microamperes microamperessample samplecurrent; current;t hthree cate countingtime timessufficient c a t e analyses analyses with with counting u f f i c i e n t to t o give give accuracies accuracies of of + of amount present for major elements and ÷ 50 wt. % wt. % + 5 w t . % amount present f o r major elements and + 50 wt. % f o r elefor 5 -m e r i t s present ments present aatt less lessthan thanone onewt. w t . %. %.X—ray X-ray intensity i n t e n s i t y data d a t awere were reduced from mineral mineral standards standards with standard corrections. reduced from standard ZAP ZAF corrections. References: References : 1) 1) Watowich, 1978, AApreliminary preliminary geological geological view Watowich, SS.N., .No, 1978, view of the the MINNAMAX copper—nickel deposit DuluthGabbro: Gabbro: 39th MINNAMAX copper-nickel deposit i n in t hthe e Duluth Annual Mining Symposium, Symposium,University University of of Minnesota, Annual Mining Minnesota, Minneapolis, Minneapolis, Minnesota, Paper 19, Minnesota, Paper 19, p. p. 1—11. 1-1 1. 2) 2) Geul, Geul, J.J.D., J.J.D., 1970, 1970,Geology Geology of ofthe theDevon Devon and and Pardee Pardee townships townships and and the Stuart S t u a r t location: location: Ontario Department Department of Mines Mines Geological Geological Report 87, 52 Report 87, 52 p. p. 3) 3) Kullerud, G., P., 1980. G., Private P r i v a t ecommunication communication in i n Ramdohr, Ramdohr, P., 1980. The The ore ore L) 4) Schiuter, Schluter , R.B. R .B. and and Landstroin, Landstrom, A.B., A .B., 1976, 1976, Continuous Continuous ppilot i l o t plant plant minerals Press, Vi, minerals and and ttheir h e i r intergrowths, intergrowths, Pergamon Pergamon Press, V I , p. p. L02. 402. testing of Duluth Duluth Complex Complex sulphides, t e s t i n gconfirms confirms f].oatability f l o a t a b i l i t y of sulphides, Mining Journal, v. v. 177, #L, #4, p. p. 80—83. 80-83. Mining Journal, Engineering Engineering * * Present address: Magaetic Magnetic Peripherals 7801 7801 Computer Computer Avenue Avenue Minneapolis, MN MN 5535 55435 60 �L a t e and and Late Western Western Post-Glacial Lacustrine L a c u s t r i n e Sediment Sediment Distribution D i s t r i b u t i o n in in Post—Glacial Lake Superior from Seismic R e f l e c t i o n P r o f i l e s Lake Superior from Seismic Reflection Profiles A. SCHOLZ SCHOLZ (Department (Department of of Geology, Geology, University U n i v e r s i t y of of Minnesota, Minnesotay CHRISTOPHER A. CHRISTOPHER Duluth, ~ z n e s o t a 55812) Duluth, Minnesota 55812) During the t h e summers summers of of 1982 1982 and and 1983, 1983y University U n i v e r s i t y of of Minnesota Minnesota During r e s e a r c h e r s acquired over 700 km of h i g h r e s o l u t i o n s e i s m i c profiles profiles researchers acquired over 700 km of high—resolution seismic in the t h e extreme extreme western western end end of of Lake Lake Superior Superior between between Duluth Duluth and and the the in Apostle Islands. I s l a n d s . The The normal—incidence, normal-incidence, 3.5 3.5 kHz kHz single—channel single-channel seismic seismic Apostle system employed employed had had limited l i m i t e d penetration p e n e t r a t i o n of of Proterozoic P r o t e r o z o i c bedrock bedrock and and system t i l l s , but b u t produced produced aa clear c l e a r and and detailed d e t a i l e d acoustic a c o u s t i c picture picture Superior Lobe Lobe tills, Superior of t h e fine-grained l a t e and p o s t g l a c i a l l a c u s t r i n e sediments. of the fine—grained late and post—glacial lacustrine sediments. i t h eeastastThe Duluth Duluth sub—basin sub-basin has subdued bathymetry bathymetry compared compared wwith The has aa subdued e r n Lake S u p e r i o r ' s v a l l e y s and r i d g e s . The b a s i n between Duluth and ern Lake Superior's valleys and ridges. The basin between Duluth and t h e Apostle Apostle Islands I s l a n d s deepens deepens gradually g r a d u a l l y from from the t h e west west and and south, s o u t h , but but the trough runs p a r a l l e l to to q u i t e r a p i d l y from t h e n o r t h , such t h a t a deep quite rapidly from the north, such that a deep trough runs parallel t h e axis a x i s of of the t h e basin b a s i n along along the t h e Minnesota Minnesota shoreline. s h o r e l i n e . This This depression depression the is first f i r s t distinguishable d i s t i n g u i s h a b l e in in the t h e west west near n e a r the t h e mouth mouth of of the t h e French FrenchRiver, River, is it achieves a c h i e v e s aa maximum maximum u n t i l it and deepens deepens and and broadens broadens northeastward, northeastward until and depth of of 290 290 meters meters off o f f Silver S i l v e r Bay Bay Minnesota. Minnesota. depth The major major stratigraphic s t r a t i g r a p h i c components components of of the t h e basin b a s i n are are Keweenawan Keweenawan The tills c l a s t i c and v o l c a n i c rocks, unconsolidated Superior Lobe g l a c i a l tills clastic and volcanic rocks, unconsolidated Superior Lobe glacial of Wisconsinan age, and t h e p o s t and l a t e g l a c i a l l a c u s t r i n e sediments of Wisconsinan age, and the post and late—glacial lacustrine sediments T i l l reflectors r e f l e c t o r s are a r e commonly commonly broad, broad, of Superior Superior and and earlier e a r l i e r lakes. l a k e s . Till of d i f f u s e and n o i s y y and a r e r a r e l y t r a c e a b l e over more t h a n a few diffuse and noisy, and are rarely traceable over more than a few kilometers. They appear o n l y s p o r a d i c a l l y a c r o s s t h e basin. The conconkilometers. They appear only sporadically across the basin. The t i l l and and lacustrine l a c u s t r i n e sediments sediments is i s generally g e n e r a l l y parallel parallel ttact a c t between between the t h e till t o the t h e present—day present-day lake l a k e bottom bottom but but in i n places p l a c e s may may show show relief r e l i e f several several to meters greater g r e a t e r than than the t h e modern modern depositional d e p o s i t i o n a l surface. s u r f a c e . This This contact c o n t a c t is is meters one of t h e most d i s t i n c t i v e f e a t u r e s on almost a l l t h e r e c o r d s and i one of the most distinctive features on almost all the records and iss d e f i n e d by by aa crisp c r i s p even—to—wavy even-to-wavy or o r diffracted d i f f r a c t e d reflector r e f l e c t o r which which separates separates defined t i l l signature s i g n a t u r e from from the t h e highly highly t h e noisy, n o i s y , commonly commonly reflection—free r e f l e c t i o n - f r e e till the t r a n s p a r e n t lacustrine l a c u s t r i n e unit. unit. transparent The lacustrine l a c u s t r i n e section s e c t i o n typically t y p i c a l l y contains c o n t a i n s numerous numerous high high continuity continuity The even-to-wavy r e f l e c t o r s which mimic t h e t i l l l a k e sediment c o ntact. even—to—wavy reflectors which mimic the till—lake sediment contact. o n t h e o r d e r of 25 Maximum accumulations of fine-grained sediments, Maximum accumulations of fine—grained sediments, onthe order of 25 meters, occur i n t h e a x i s of t h e North Shore Trough. R e f l e c t o r s within meters, occur in the axis of the North Shore Trough. Reflectors within onlap t h e s teep tthis h i s unit u n i t are a r ecommonly commonly pparallel arallel b u t w i t h i n t h e trough but within the trough onlap the steep trough s i d e s and o c c a s i o n a l l y d i v e r g e down basin. Contorted r e f l e ctors trough sides and occasionally diverge down basin. Contorted reflectors in certain c e r t a i n areas a r e a s suggest suggest slumping slumping and the t h e lack l a c k of of lacustrine l a c u s t r i n e sediments sediments in and has taken taken place p l a c e on on the t h e flanks f l a n k s of of the t h e trough. trough. Section Section thickness t h i c k n e s s and and has r e f l e c t o r concentration c o n c e n t r a t i o n increase i n c r e a s e from from the t h e basin b a s i n edges edges to t o the t h e basin basin reflector L a c u s t r i n e sediment sediment isopachs isopachs are a r e grossly g r o s s l y parallel p a r a l l e l to t o the t h e bathybathydeeps. Lacustrine deeps. m e t r i c contours except i n t h e extreme western p o r t i o n of t h e a r e a where metric contours except in the extreme western portion of the area where an anomalous sediment d i s t r i b u t i o n occurs. Offf tthe h e French and Lester Lester an anomalous sediment distribution occurs. Of French and Rivers are a r e concentrations c o n c e n t r a t i o n s of of sediment sediment of of up up to t o 20 20 meters meters which which are a r e not not Rivers r e l a t e d t o t h e modern bathymetry o r modern sediment focusing e f f e c t s. related to the modern bathymetry or modern sediment focusing effects. i s an a r e a of e l e v a t e d a c o u s t i c baseBetween t h e two "mud patches," Between the two "mud patches," is an area of elevated acoustic basement, approximately approximately 50 50 meters meters below below the t h e present p r e s e n t lake l a k e level l e v e l and and buried buried ment, 61 �3—5 3-5 meters m e t e r s beneath fine—grained f i n e - g r a i n e d sediments, sediments, which which externally e x t e r n a l l y resembles resembles a a broad, broad, curved, curved, spit—shaped spit-shaped sand sand body. body. AA linear l i n e a r submerged submerged ridge r i d g e close close and and parallel p a r a l l e l to t o the t h e Wisconsin shoreline s h o r e l i n e also a l s o at a t depth d e p t h of of 50 50 meters meters appears shallow appears to t o be be an an ancient a n c i e n t low low lake l a k e level l e v e l strand s t r a n d line. l i n e . These shallow water water features f e a t u r e s suggest s u g g e s t the t h e past p a s t existence e x i s t e n c e of of aa low low lake l a k e stage s t a g e 50 50 meters meters below below current c u r r e n t lake l a k e level. level. 62 �Metamorphism of of Kuruman Kuruman and and Griguatown Griquatown Iron Iron Formations Formations and and Metamorphism Associated Makganyene Diamictitey Cape Provincey South Associated Makganyene Diatnictite, Cape Province, South Africa: AA Stable Stable Isotope Isotope Investigation Investigation Africa: E. SCHUESSLER SCHUESSLERAND AND E.C. E.C. PERRY, PERRYyJR. JR. (Northern (Northern Illinois Illinois University) University) E. 6 Oxygen isotope isotopegeothermoinetry geothermometry of cores of of 2200X106 2200x10 m.y. may.old old Oxygen of cores Kuruman and Griquatown Iron Formations and overlying Makganyene Kuruman and Griquatown Iron Formations and overlying Makganyene Diamictite*Postmasburg Postmasburg Group, Groupy from from cores cores near near Postmasburg, PostnxasburgyCape Cape Diamictite, Province* South Africa indicate a maximum temperature of Province, South Africa indicate a maximum temperature of metamorphismofofabout about250°C. 250°C Large Large variations variations diagenes/burial metamorphism in the r5 0 of carbonates on the scale of cm indicates that the the in the tS 0 of carbonates on the scale of cm indicates that iron formation acted as a series of closed subsystems during iron formation acted as a series of closed subsystems during diagenesislmetamorphism and and has has remained remai ed closed closed to to post— postdiagenesis/metamorphism metamorphic isotope isotope exchange exchange for for 2X10 2x10 years. years. Thus, Thusy apart apart from from metamorphic metamorphic effects, effects* these these Proterozoic Proterozoic South South African African iron iron forformetamorphic mations retain retain aa record record of of primary primary isotope isotopecomposition. composition. mations diagenesi./burial 9 Proterozoic hemical sediments, sedimentsyincluding including iron ironformations, formationsy Proterozoic1ghemical lk0 compared to modern cherts and carbonates. are depleted in are depleted in 0 compared to modern cherts and carbonates. AA possible explanation of this effect is high ocean temperature and possible explanation of this effect is high ocean temperature and The intimate intimate consequent low low chert—water chert-water isotope isotope fractionation. fractionation. The consequent association of Makganyene Diamictite of glacial origin and iron association of Makganyene Diamictite of glacial origin and iron formation (Powelly this volume) effectively rules out such an formation (Powell, this volume) effectively rules out such an explanation and this iron iron ormation formationwas was precipitated precipitated explanation and implieslbhat implies1hat this by about about 10 10 0100 compared to the the from water water depleted depleted in in 00 by from /oo compared to modern ocean. ocean. modern Carbon isotope isotope composition composition of of carbonate carbonate in in core core from from the the Carbon Makganyene Diamictite varies sympathetically with magnetite Makganyene Diamictite varies sympathetically with niagnetite content in in aa way way that that suggests suggests the the reaction: reaction: content FeCO 3Fe304. 5Fe 0 + C or a ic FeCO ++ 3Fe 04. 5Fe203 2 3 + (or2anlc) 3 3oxide iron minerals in This relat=onsh$p 8e~weLn carbona?e and This relationship between carbonate and oxide iron minerals in the diamictite diamictite matrix matrix reinforces reinforces the the interpretation interpretation that that these these the minerals were were produced produced from from active, activeychemically chemically deposited deposited iron— ironminerals rich precursor precursor phases phases and, and, thus, thus*that that diamictite diamictitedeposition depositionwas, wasy rich contemporaneous with with the the chemical chemical precipitation precipitation of of iron iron in part, party contemporaneous in formationminerals. minerals. formation . Oxygen isotopic isotopic study study of of two two iron iron formation formation cores cores helps helps Oxygen interpret diageneticlmetamorphic processes occurring in interpret diagenetic/metamorphic processes occurring inththe rocks. In In core core CS119, CSl1gy carbonate carbonate is is coarse—grained. coarse-grained. Its Its 6 00 rocks. varies by by only only 11 O/oo suggesting low-temperature exchange with varies /oo suggesting low—temperature exchange with magnetite and and Si02 SiO followed by carbonate recrystallizaf~on and magnetite followed by carbonate recrystallizaon and 2 of isolation from from further further isoto ic exchange. exchange. In In CS12O, CS120y 6 00 of isolation isotoRic carbonate varies varies by by several several g/00 loo and and is is correlated correlated on on aa cm cm scale scale carbonate consequence of of this this pattern pattern is is that that with per percent centinagnetite. magnetite. AA consequence with several apparent apparent siderite—magnetite siderite-magnetite oxygen oxygen isotope isotopetemperatures temperatures several from this core are about 100° higher than quartz-magnetite from this core are about 100°C higher than quartz—magnetite temperaturesy while while quartz—siderite quartz-siderite "temperatures" "temperatures" are are often often temperatures, O°C To below 0°C. To explain explain oxygen oxygen isotopic isotopic values values for for quartz, quartzy mag— magbelow netite* and siderite in @is core* it is necessary to postulate netite, and siderite in is core, it is necessary to postulate that siderite siderite exchanged exchanged 00 with with magnetite magnetite at at relatively relatively low low that temperatureythen then ceased ceased to to react react while while magnetite magnetite continued continued temperature, Be 63 �to exchange isotopes with quartz to temperatures of about 250°C. 250°C Thus, it appears that before crystallization crystallization siderite siderite is is more reactive than quartz whereas after recrystallization recrystallization it it is is relatively isolated from from further further oxygen oxygen isotope isotope exchange. exchange. Other explanations are inconsistent with isotope geothermometry. �Early Proterozoic ProterozoicPenokean Penokean Igneous Igneous Rocks Rocks of the Lake Lake of the andTectonic Tectonic Imp1 Implications Geochemi stry and ications Superior Region: Region: Geochemistry Klaus J. J. Schulz Klaus Schuqz U.S. U-S- Geological Geoloqical Survey Survey National Center, National cenier*M.S. M S . 954 934 VA 22092 22092 Reston, VA The composition of of igneous rocks from The nature nature and and composition igneous rocks from ancient terranes terranes can can provide significant insights into active during theirr provide significant intothe thetectonic tectonicprocesses processes active during thei recently only only limited limiteddata data were were available for f o r the the Early Early formation. Until recently formation- igneousrocks rocksofof the the Lake Proterozoic Penokean 1900-184OMa) igneous Lake Superior Proterozoic Penokean ( 1900—l840Ma) region, region* particularly particularly those those that thatconstitute constitutethe thevolcanic—plutonic volcanic-plutonic terrane terrane of of withthe the recent recent review review of of available major major northern Wisconsin. Wisconsin- However, However* with element data for for volcanic by by Greenberg element data volcanic rocks rocksofofthe theregion region Greenbergand andBrown Brown (1983), (1983)* the acquisition the acquisitionofoftrace—element trace-el ement data data (including (incl udi ngrare—earth rare-earth element el ement data) data) for f o r the thevolcanic volcanicrocks rocksofofupper upperMichigan Michigan(Fox, (Fox*1983) 1983)and and northern northernWisconsin Wisconsin (Schulz,* 1983), and the the documentation documentationofofthe the compositional compositional characteristics characteristics 1983) * and (Schulz of the others, 1983), the granitoid granitoid rocks rocks ininnorthern northernWisconsin Wisconsin (Schulz (Schulz and and others* 1983)* the nature compositional aaffinities igneous can f f i n i t i e sofofthethe igneousrocks rocks cannow nowbebemore more nature and and compositiona1 fully evaluated usedto to understand understandthe thetectonic tectonicactivity activity during fully evaluated and and used during the the Early Proterozoic evolutionofof the the region. Early Proterozoic Penokean Penokean evolution region- In upper igneousrocks rockswithin within the the dmi dominantly nantly sediupper Michigan, Michigan, Penokean Penokean igneous mentary MarquetteRange Range Supergroup consist basaltf1flows andgabbroic gabbroicsf1 sills, mentary Marquette Supergroup consist of of basalt ows and 1s * andlesser lesser amounts amounts basalticand andrhyoli rhyolitic volcaniclastic and of ofbasaltic t i c volcanic1 astic rocks. rocks. These suites are distinctly lesser rhyolite distinctlybimodal bimodal with withbasalt basaltand and.lesser rhyolitepredominant, predominant* show strong tholeiitic iron enrichment trends, and relatively highconcenconcenshow strong tholei i t i c iron enrichment trends * and re1 ativelyhigh rocks are are compositionally The rocks compositional 1y lithophilee (LIL)elements. trations of of large—ion large-ion lithophi1 (LIL) elements- The similar those of of the simil a r to to continental—rift continental - r i f t and and plateau plateau volcanics volcanics such such as as those Keweenawan Supergroup LakeSuperior Superiorregion region and and those those of the Keweenawan Supergroup of of thetheLake theColumbia Columbia River Basalt Basalt Group Group of of Washington, Washington*Oregon, Oregon, and and Idaho. Idahovolcanic within the In northern northern Wisconsin, Wisconsi n 9 Penokean Penokean vo1 canic sequences sequences within the volcanic— volcanicplutonic p1 utonic terrane terrane consist consist 0f of basalt basalt through through andesite andesite and and rhyolite rhyolite flows f1 ows and and These volcanic volcanic rocks w i t h associated associated subvolcanic subvol canic iintrusives. ntrusives- These rocks pyroclasti cs with pyroclastics are caic—alkalineand andare areenriched enrichedi ninLIL LILelements elements( i(i.e., -e. * are dominantly dominantly calc-alkaline [La/YbJN=2.5—9.4) aredepleted depletedinin high-f high—field—strength [La/Yb]N=2.5-9.4) b ubut t are iel d-strength elelements ements ( i(i.e., .e. * Hf, Hf, Zr, Zr, Ta, Ta*etc.) e t c - )and andare aresimilar similartot volcanic o volcanicsequences sequences found found in recent recent In contrast, the (e.g., New arcs). In the New Hebrides Hebrides and and Japanese Japanese arcs) iisland—arcs sland-arcs (e-gbasalts Formationfrom fromnortheastern northeasternWisconsin Wisconsin basalts of of the theQuinnesec Quinnesec Formation areare t htholeiitic oleiitic [LalYb]~ 0.09-0.89]* = =0.09—0.89], in character, character* are a r e strongly strongly depleted depleted in inLIL LILelements elements [i.e., [i .e-[La/Yb]N and are compositional compositionally similar basinbasalts basalts (e.g. (e.g.,* Lau and are 1y simi l a r to to recent recent back—arc back-arc basin Lau Basin) and is1 island—arc tholeiites (e.g(e.g.,* Scotia Basin) and and-arc tholeiites Scotia arc). arc). The Penokeangranitoid granitoid rocks rocks of of northern northernWisconsin Wisconsin show show aa temporal temporal The Penokean progressionfrom fromgabbro gabbroand and dioritethrough throughtonal tonalite to granite. These progression diorite i t e to rocks are mostly mostlyca1 calc—alkaline, althoughslslightly alkaline rocks are c-a1 kaline* although ightly a1 kali ne varieties varieties ((i.e. i .e. Marinette MarinetteQuartz QuartzDiorite, Diorite*northeastern northeasternWisconsin) Wisconsin) are are also also present. present. The granitoids granitoids show increasefrom fromnorth northt oto south southacross acrossthe theterrane terrane in in The show ananincrease ratios and are compositionally K20lNa20 ratios and overall Si02 Si02 contents. contents- They They are cmposi tional ly ttheir h e i r K20/Na20 similar modern, (e.g. Japan) Japan) simil a r to togranitoids granitoidsfound foundinin modern*evolved evolved island—arcs i s1 and-arcs (e.g., and continental continental convergent-plate—margin settings (e.g. (e.g.,* Sierra and convergent-plate-margi n settings SierraNevada Nevada batholith). bath01 it h ) 65 65 �The The nature and and geochemistry geochemistry of the the Early EarlyProterozoic ProterozoicPenokean Penokeanigneous igneous •rocks rocks of the the Lake Lake Superior Superior region region strongly strongly suggest suggest the the operation operation ofofplate— platetectonic processes largely similar similar to processes largely t o those those active active today. today. The The data support support basalt-rhyolite aa tectonic modelo fof1)1)early earlycrustal crustalrrifting tectonic model i f t i n g (bimodal (bimodal basal t-rhyol i t e volcanism, volcanism, upper upper Michigan) and and spreading, spreading, 2) 2)subsequent subsequent subduction subduction and and formation of a volcanicarc arc(tholei (tholeiitic, formation of a complex compl ex volcanic i t i c ,and and caic-alkaline cal c-a1 kal i nevolcanism vol cani sm and plutonism,northern northernWisconsin), Wisconsin), thearc arcf ifirst and plutonism, andand collcollision ision of ofthe r s t with with Archean crust on continental—margin Archean crust on the the south southand and then thenwith withthe the continental-marginsequence sequence and Archeancrust crust of of upper Michigan on onthe the north north (i.e., and Archean upper Michigan (i.e., thet hPenokean e PenokeanOrogeny). Orogeny). References References Fox, p., 1983, Fox, Thomas Thomas P., 1983, Geochemistry Geochemistry of the theHemlock Hemlock metabasalt metabasalt and and Kiernan Kiernan thesis, Michigan sills, County, s i l l s Iron , Iron County,Michigan: Michigan: Unpubl. Unpubl. MS MS thesis, Michigan State State p. 81 p. University, 81 Greenberg, Jeffrey K., Greenberg, Jeffrey K., and and Brown, Brown, Bruce Bruce AA., . , 1983, 1983, Lower Lower Proterozoic volcanic volcanic Geol. rocks andt htheir Superiorddistrict: rocks and e i r setting in in the the southern southern Lake Lake Superior i s t r i c t : Geol. Soc. Memoir 160, 160, p. p. 67-84. Soc. America America Memoir 67-84. Schulz, Klaus J., J., 1983, the volcanic volcanic rocks Schulz, Klaus 1983, Geochemistry Geochemistry ofof the rocks of of northeastern northeastern 29th,Houghton, Houghton, I n s t i t u t eononLake LakeSuperior SuperiorGeology, Geology ,29th, Wisconsin [abs.]: Wisconsin Eabs.: Institute Michigan, Michigan. Schulz, J., Sims, Schulz, Klaus Klaus J., Sims, P. P. K., K., and andPeterman, Peterman, Zell ZellE., E., 1983, 1983,Geochemistry Geochemistry of Early [abs.]: Geol. Early Proterozoic Proterozoic granitic granitic rocks, rocks, northern northern Wisconsin Wisconsin Cabs.]: Geol Soc. Abstracts wwith Soc. America America Abstracts i t h Programs, Programs, v.v. 15, p. p. 681. 681. . 66 �Regional Reqional Controls Controls of Lower Precambrian Precambrian Metallogeny in in the the Upper Upper Peninsula of Michigan Michigan MICHAEL J. J. SCHWARTZ SCHWARTZ (Dept. (Dept. of ofGeology, Geology,Univ. Univ.1Nis.-Parkside, Wis.-Parkside, Kenosha, Wi. W i.53141) 53 1 4 1 ) PETER PETER AA. . NIELSEN NIELSEN (Dept. (Dept. of Geology, Geology, Univ. Wis.-Parkside, Wis.-Parkside, Kenosha, Wi. 53141) Kenosha, Wi. 53 141) This is an attempt attempt at atfinding findingany anylarge largescale scaleregional regional controls controls of metallogeny metallogeny in in the theUpper UpperPeninsula Peninsula of of Michigan. Michigan. To limit limit the the extent toArchean Archean extent of this this study study we we are are restricting restricting the the scope scope of ititto and and lower lower middle middle Precambrian Precambrian sections sections and and not not including including the Keweenaw which regional Keweenaw which has has obvious obviousstructural structural controls controls at aa regional level. an information information base level. We We have have gathered gathered an base of structural structural and and lithologic trends ( 1 :250000) and andsmall smallscale scale trends from fromboth bothlarge largescale scale(1:250000) (1:24000) maps and and an an unpublished M.S. thesis by Bodwell (1:24000) maps unpublished M. S. thesis Bodwell (1972, (1972, all reported MTU). Bodwell Bodwell covered covered all reported metal metal locations locations and and this this was was used as as the the primary primary data-base. data-base. By plotting plottingstructure structureand andlithology lithologyon ona abase basemap mapand andmaking making overlays of different (Au ++ Cu + Ag, overlays of different metal metal associations associations (Au Ag, Au Au ++ Ag, Ag, Au ++ base base metal metal sulfides, sulfides, Cu Cu + Mo, Mo, base base metal metal sulfides) sulfides) regional regional structural/lithologic structural/lithologic metallogenic metallogenic patterns patterns are are shown, shown, if i f present. present. For purposes purposes of simplification simplificationthe theUpper UpperPeninsula Peninsulahas hasbeen been divided divided into into three threeareas: areas: The Marquette Marquette Range, Range, The TheGogebic-Watersmeet Gogebic-Watersmeet area, area, and and the the Crystal CrystalFalIs-Menomonee-lron Falls-Menomonee-Iron River River areas. areas. This is is based on on some somephysical physical separation separation of of these areas. areas. These These areas areas have have a common although stratigraphic stratigraphic columns columns are are not common Paragenesis Paragenesis although not. exactly exactly the thesame. same. After After following following this thisprocedure procedure hopefully hopefully some some relations relations will become apparent. apparent. At A t this thispoint pointmy myresearch research isis not notcomplete complete but but some some apparent trends are are present. present. In the the Gogebic-Watersmeet Gogebic-Watersmeet area area gold deposits deposits seem seem to be confined greenstone belt and the very gold confined to aa greenstone near In near proximity. proximity. In the northern northern Marquette Marquette Range Range base base metal metal deposits follow the the limbs limbs of of an an apparent apparent fold. Bodwell, Bodwell, Willard Willard H., H., 1972. 1972. Geologic Compilation Compilation and and Nonferrous Nonferrous Metal Metal Potential, Potential, Precambrian Precambrian Section, Sect ion, Northern Northern Michigan, Michigan, unpublished MS thesis, thesis, MTU. 67 . �Trace Trace Element Element Geochemistry Geochemistry of of Some Some Lake Lake Superior Superior Keweenawan Keweenawan Basic Layered Intrusions Intrusions . KARL KART,, E. E. SEIFERT SEIFERT (Dept. (Dept. of of Earth Earth Sciences, Sciences, Iowa Iowa State S t a t e University, U n i v e r s i t y , Ames, Ames, IA 50011) 50011) IA Seven REE (La, Ce, Lu), C e , Sm, Sm, Eu, Eu, Tb, Tb, Yb, Yb, and andL u ) , Ca, Co, Cr, C r , Th, Th, Hf, Hf, Ta, Ta, Sr, Sr, SevenREE Rb, Rb, and and Ba B a have been determined by instrumental i n s t r u m e n t a l neutron activation activation analysis a n a l y s i s (IRAA) (INAA) for f o r rocks rocks from from the t h e Duluth complex, complex, Mineral Lake Lake intruintrusion, s i o n , and the t h e Rearing Rearing Pond Pond intrusion. i n t r u s i o n . The The trace t r a c e element element characteristics characteristics of of the t h e various v a r i o u s units u n i t s comprising these t h e s e intrusions i n t r u s i o n s can be combined combined in in their t h e i r appropriate a p p r o p r i a t e abundances to t o dderive e r i v e the t h e ccharacter h a r a c t e r of of their t h e i r parental parental magmas. For For the t h e Mineral Lake intrusion, i n t r u s i o n , this t h i s calculated c a l c u l a t e d composition is is compared to t o a chill c h i l l zone zone sample sample and and found found to t o be b e markedly markedly different. different. Insufficient data Insufficient d a t a aare r e aavailable v a i l a b l e on the t h e Rearing Pond iintrusion n t r u s i o n to to calculate c a l c u l a t e aa parental p a r e n t a l magma magma composition. composition. The parental p a r e n t a l magma compositions are a r e compared to t o the The t h e most primitive primitive It North Shore Shore volcanic v o l c a n i c composition composition to t o test t e s t for f o r aa genetic g e n e t i c relationship. r e l a t i o n s h i p . It North i s not n o t possible p o s s i b l e to t o derive d e r i v e the t h e intrusive i n t r u s i v e parental p a r e n t a l maginas magmas from is from the t h e most most p r i m i t i v e North Shore vvolcanic o l c a n i c composition by magmatic differentiation differentiation primitive v a r i o u s parental p a r e n t a l tnagmas magmas can e l a t e d by can only only be be rrelated by more more complex alone. The various alone. models. 68 �-- - - Dikes as as Tectonic Tectonic Indicators Indicators -Dikes in Lake Superior Superior Region Region — in the the Eastern Lake Structural Structural and and Paleomagnetic Paleomagnetic Considerations Considerations - Shaw E.G. Geology, University of Torontof Toronto, Erindale Erindale E .G. Shaw (Dept. (Dept. of of Geologyf College, Mississaugaf Mississauga, Ontario, Collegef Ontario, Canada Canada L5L L5L 1C6) lC6) The majority of rocks have undergone undergone complex Early The majori* of Archean rocks Precambrian deformation, and thus, are of limited use use in defining Precdrian deformation, nature and timing of pst-Archean post-Archean tectonic the nature tectonic events. events- It It is is clear, however, from the abundance abundance of faults and shear-zones shear—zones in clearf however, areas that shield axeas that later later Precambrian Precambrian tectonic tectonic events events of of some some kind kind have have indeed indeed occurred. occurrd- Where aa shield shield is is overlain overlain by Middle to to Late volcanic/sedimentary sequences, sequences, tilting, fault Late Precambrian Precambrian volcanic/sedimentary displacement, displacementf and and other other deformational deformational features features can can often often be be directly directly observed observed and and constraints constraints placed placed on on the the age age and and extent extent of of part, howeverf however, such Precambrian cover deformation- For the the most partf deformation. rocks are confined to localized rocks localized areas areas on on shield shield margins. Ernst Ernst and and Halls Halls (1984) (1984) have shown from a study of dikes in Kapuskasing Zone, dike attitudes the I?apuskasing Zonef that that dike attitudes and and paleomagnetic paleomagnetic signatures may may be used as tectonic tectonic indicators indicators in in the the Canadian Canadian signatures Shield. study, dikes of the same swarm which In their studyf the same which differed differed Shieldfrom the norm b both attitude and paleomagnetic direction from the t h in in attitude and paleomagnetic direction were were used to association with with to show show aa westward tilting of the crust in association upthrusting upthrusting along along the the eastern eastern margin margin of of the the Zone. Zone. Patches of lakeward—dipping lakeward-dipping Keweenawan Kewenawan volcanics volcanics and and Patches sediments show show that sediments that the the shield shield along along the the coast coast of of Lake Lake Superior Superior has has been heen involved involved in in basin basin subsidence. subsidence. These These Keweenawan Kewenawan rocks, rocks, however, shore and thus however, are are only only rarely rarely found along the eastern shore define the are insufficient insufficient to define the full full extent extent of of shield shield deformation deformation with basin basin developentdevelonent. On On the the other hand, associated with handf dikes are are pervasive both pervasive b t h on the Lake Superior coast and in the interior of ield (1951) (1951) observed observed that the the dikes dikes in the the shield. shield- Muff Nuffield in the the Montreal Montreal River River Harbour Harbour area area dip dip NE; NE; dikes dikes north north and and east east of of the the lake have been been observed lake have observed to to be be near—vertical. near-vertical. This This is is an an ideal ideal environment in apply and environment in which to apply and extend extend the the findings findings of of Ernst Ernst and and Halls. Halls addition, the Montreal Montreal River follows major fault In additionf follows a ma-jor fault that that may may be be the the southern southern extension extension of of the the eastern eastern boundary bundary thrust thrust of of the was thought that if the Kapuskasing Kapuskasing Zone. Zone- It was of if faulting faulting had been been of major major extent, extentf an an overprint overprint dating dating from from fault fault movement movement (and (and Kapuskasing activity in in general) general)would uld be Kapuskasing activity be evident evident in in the the paleomagnetic signature dikes cutting paleomagnetic signature of of dikes cutting the the fault. fault. The The purpose of this study, thenf then, was was to use use the palemagnetic palemagnetic signature attitude of dikes to signature and attitude of dikes to 1) 1) determine determine the the nature nature and and Keweenawan extent of eastern—shore eastern-shore shield shield deformation deformation related relatedto toKeweenawari extent of basin subsidence subsidence and and 2) 2) look look for for signs signs of of Kapuskasing Kapuskasing activity activity along the the Montreal Montreal River River fault. faultalong 69 �Thirty—nine Thirty-nine paleomagnetic paleomagnetic sites sites comprising comprising aa total total of of 300 300 samples were collected from northwest—trending diabase dikes samples were collected from northwest-trending diabase dikes along along two two traverses traverses roughly roughly normal normal to to the the eastern eastern shoreline shoreline of of Lake Lake Superior Superior and and oblique oblique to to the the trend trend of of the the dikes. dikes. The The northern northern traverse, traverse, about about 45 45 km km long, long, follows follows the the Montreal Montreal River River to to the the Since it it was was important imprtant to to know know the the structure structure and and coast. mast. Since paleomagnetism paleomagnetism of of dikes dikes in in aa relatively relatively stable stable area, area, aa southern southern traverse—remote traverse-remote from frompossible possibleinfluences influencesof of Kapuskasing Kapuskasing and and Lake Lake Superior This traverse traverse is is defomation-waschosen chosenas asaacontrol. control. This Superior deformation—was located located 55 to to 10 10 km km south south of of the the northern northern traverse, traverse, 35 35 km km from from the the and and extends eastward eastward for aa distance distanceof of7070km. km. Twenty—three Wenty-three dikes dikes in inthe thesouthern southern traverse traverseand and sixteen sixteendikes dikesin inthe thenothern nothern mast, coast, traversewere weresampled. sampled. traverse paleomagnetic direction, direction?there thereappear appear to to be ke at at least least Based on on paleomagnetic Based four four ages ages of dike intrusions intrusions in in the theinterior interiorcorresponding correspnding to to Keweenawan, Keweenawan, Sudbury, Sudbury, Matachewan Matachewan and and an an undated undated dike dike set set which which cuts cuts aa Huronian Huronian outlier outlier and and has has aa similar similar paleomagnetic paleomagnetic direction direction to to that that of of Abitibi Abitibi and and Preissac Preissacdikes. dikes. All All sampled sampled interior interior dikes dikes trend NW to N, and beyond about two km from the shoreline, trend W to N, and beyond about two km from the shoreline, dip dip In the the field, field, less less than than 55 to to 10 10 degrees degrees from from the the vertical. vertical. In samples samples generally generally appear appear fresh, fresh, though though apparent apprent deuteric deuteric Dikes within within about about two two km km alteration is present present in in some some margins. margins. Dikes alteration is of more westerly of the the shoreline shoreline tend tend to to have have aa more westerly trend trend and and all all dip dip NE NE at at angles angles ranging ranging from from 45 45 to to 70 70 degrees. degrees. These These dikes, dikes, in in comparison caparison with with those those of of the the interior, interior, are are more m r e altered altered and and sheared, sheared, especially especially at at the themargins. margins. An An easterly easterly rotation rotation of of approximately approximately 40 40 degrees degrees about about aa NW NW returns direction of returns both b t h the the attitude attitudeand andpaleomagnetic paleomagnetic direction of the the coastal dikes dikes to tothose thoseof ofthe thecontrol controlgroup. group. This is isininagreement agreement coastal with to return the with the rotation rotation needed needed to the Keenawan EQweenawan rocks in in the the combinationofofrotated rotated attitudes attitudes and south to the the horizontal. horizontal. The The combination @ axis axis paleotnagnetic poles—andalso also the the large paleomagnetic ples-and large degree degree of ofshearing— shearing- indicates dips and andstrikes strikes of the indicates that thatthe thepresent presentanomalous anomalous dips the coastal dikes are due to to tectonic rotation rotation and and not to to aa geographic geographic in orientation orientation of of the thetensional tensionalenvironment environmentduring during change in emplacement. enplacement. In In addition, addition, the the study study shows shows that, that, at at least least locally, locallyr aa rim been tilted in rim of of shield shield no no more than than 22 km wide has keen in response respnse to subsidence subsidence in in the the Lake Lake Superior SuperiorBasin. Basin. to Preliminary structural structural and and palenagnetic palemagnetic data data from from the the NW NW Preliminary trending dikes dikes cutting cutting the the Montreal Montreal River River Fault Fault suggest suggestthat that trending little little activity activiw has has occurred occurred in in the the area area since since emplacement emplacement of of these dikes. dikes. these 70 �Characterization C h a r a c t e r i z a t i o n of of the t h e Ore Ore Host Host Rock Rock at a t the the Ropes Gold Gold Mine, Mine, Ishpexning, Ishpeming, Michigan Michigan Ropes Anthony W. Shepeck Shepeck and and Theodore Theodore J. J. Bornhorst Bornhorst (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Anthony W. Engrg., 49931) M I 49931) Engrg., Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, MI Gold i s contained contained within w i t h i n an an Gold mineralization m i n e r a l i z a t i o n at a t the t h e Ropes Ropes Gold Gold Mine Mine is east—west east-west trending, t r e n d i n g , nearly n e a r l y vertical, v e r t i c a l , tabular, t a b u l a r , schistose s c h i s t o s e rock rock body body which The ore o r e host h o s t rock rock which .s i s surràunded surrounded by by the t h e Deer Deer Lake Lake Peridotite. P e r i d o t i t e . The (OHR) can be divided into four mappable units based on the relative (OIiR) d i v i d e d i n t o f o u r mappable u n i t s based on t h e r e l a t i v e abundance abundance of of layer l a y e r silicate s i l i c a t e minerals, m i n e r a l s , which which make make up up the t h e majority m a j o r i t y of of the OHR, and and whole whole rock rock chemical chemical composition: composition: 1) 1 ) mostly mostly sericite; sericite; t h e OHR, 2) 3 ) mostly mostly chlorite; chlorite; 2) about about equal e q u a l amounts amounts of of sericite s e r i c i t e and and chlorite; c h l o r i t e ; 3) and and 4) 4 ) chlorite c h l o r i t e and and carbonate. carbonate. Quartz Quartz is i s ubiquitous u b i q u i t o u s throughout throughout all all t h e units. u n i t s . Disseminated Disseminated pyrite p y r i t e and and lesser l e s s e r amounts amounts of of magnetite magnetite are are the also a l s o present. p r e s e n t . The The carbonate carbonate is i s dolomite dolomite with w i t h minor minor ankerite. a n k e r i t e . DisDisseminated seminated gold gold is i s most abundant abundant in i n the t h e more sericitized s e r i c i t i z e d and.silici— and.si1icified f i e d units. u n i t s . However, However, the t h e highest h i g h e s t gold gold values v a l u e s in i n the t h e mine mine are a r e assoassociated with quartz—sulfide veins which were the target for ciated with quartz-sulfide veins t h e t a r g e t f o r the t h e early early These veins v e i n s are a r e cross—cut cross-cut by by barren b a r r e n carbonate carbonate veins. veins. mining. These mining. The OHR units u n i t s can can be be The layer l a y e r silicate s i l i c a t e minerals minerals within w i t h i n the t h e various v a r i o u s OHR distinguished d i s t i n g u i s h e d by by composition, composition, structural s t r u c t u r a l type type and and textural t e x t u r a l criteria. criteria. In I n general, g e n e r a l , chiorites c h l o r i t e s are a r e clinochiore c l i n o c h l o r e but b u t in i n detail d e t a i l can can be be subdivided subdivided into: Ib chlorite, c h l o r i t e , relarelai n t o : Type Type 1) 1 ) an an early e a r l y fine—grained, fine-grained, lower lower ordered ordered lb tively with aa composition composition of of [(Mg11 2Fe08+2) t i v e l y enriched enriched in i n Mg Mg and Si [(Mgll.2Feo.8+2) S i with (Si71Al0g) is a (Si7.lAlc.g) 020 020(OH)16)] (OH)16)] which which commonly commonly defines d e f i n e s foliations f o l i a t i o n s and and is major and Type Type 2) 2) aa later l a t e r porphyroblastic, porphyroblastic, major component component of of the t h e matrix; m a t r i x ; and higher I I b chlorite, c h l o r i t e , which is i s relatively r e l a t i v e l y higher h i g h e r in i n Fe Fe and and Al A1 h i g h e r ordered ordered lib Seri— seriwith compositionofof[ ([(Mg.7Fe332) w i t h aa composition ~ ~71?e3. 8 . 3+2) ((Si58Al22) s i 5 8 ~ 1 2 . 2 )020 o~~ (OH)16]. (OH)16] cites Fe and and Mg Mg K, Al Al. muscovite muscovite with w i t h low low Na, N a , Fe c i t e s are a r e essentially e s s e n t i a l l y an an ideal i d e a l K, Type A) A) an an early e a r l y fine— fineand and can can also a l s o be b e subdivided subdivided into i n t o two two varieties: v a r i e t i e s : Type grained mica which which commonly commonly occurs o c c u r s in i n discrete d i s c r e t e blebs b l e b s or o r in i n torn torn grained 2. mica fragments; fragments; and Type B) B) a later l a t e r highly h i g h l y crystalline, c r y s t a l l i n e , coarser c o a r s e r 2m1 mica mica c h l o r i t e s are a r e rereThe Type Type 11 chiorites which which commonly commonly occurs occurs in i n the t h e matrix. matrix. The stricted s t r i c t e d to t o the t h e less l e s s intensely i n t e n s e l y altered a l t e r e d gold—poor gold-poor chlorite c h l o r i t e and and chlorite— chloritecarbonate carbonate units u n i t s of of the t h e OHR OHR whereas Type 22 chlorites c h l o r i t e s and and Type Type BB seri— sericites c i t e s are a r e predominantly found found in i n the t h e more gold—rich gold-rich sericite s e r i c i t e and and sericite—chlorite s e r i c i t e - c h l o r i t e units. u n i t s . The chlorite c h l o r i t e polytypes suggest suggest that t h a t the the later w a s formed formed at a t aa higher h i g h e r temperature temperature than than the the l a t e r Type 22 chlorite c h l o r i t e was earlier c h l o r i t e and e a r l i e r Type Type 11 chlorite and may be b e aa recrystallization r e c r y s t a l l i z a t i o n product product of of Type 1. 1. Their T h e i r compositions compositions reflect r e f l e c t the t h e composition composition of of the t h e fluid, fluid, Type rock and and water/rock w a t e r l r o c k ratios. r a t i o s . The overall o v e r a l l distribution d i s t r i b u t i o n of of the t h e various various types within reflection t y p e s of of layer l a y e r silicate s i l i c a t e minerals w i t h i n the t h e OHR may be a reflection of of hydrothermal hydrothermal gradients g r a d i e n t s established e s t a b l i s h e d during d u r i n g mineralization. mineralization. . zm1 The OHR is i s interpreted i n t e r p r e t e d as a s an an altered a l t e r e d and and sheared sheared rock rock and, and, as a s such, such, The OHR there i s only only speculative s p e c u l a t i v e evidence evidence as a s to t o the t h e original o r i g i n a l protolith. protolith. t h e r e is Whole—rock Whole-rock major and and trace t r a c e element element data d a t a on 63 63 samples samples indicate i n d i c a t e that that the t h e sericite, s e r i c i t e , sericite—chiorite s e r i c i t e - c h l o r i t e and the t h e cchlorite h l o r i t e units u n i t s are a r e composi— compositiortally than tthe t i o n a l l y ddifferent i f f e r e n t than h e Deer Lake Peridotite. P e r i d o t i t e . However, the the i s similar s i m i l a r iin n some e s p e c t s tto o tthe h e peridotite. peridotite. c h l o r i t e - c a r b o n a t e uunit n i t is chlorite—carbonate some rrespects Immobile element element ratios r a t i o s suggest suggest that t h a t the t h e sericite s e r i c i t e unit u n i t is i s similar s i m i l a r to to I=obile andesitic a n d e s i t i c members members of of the t h e Kitchi K i t c h i Schist. Schist. 71 �Petrographic Petrographic and and Geochemical Geochemical Study Study of of the the Mount Mount Bohemia Bohemia Stock, Stocky Portage Lake Lake Volcanics, VolcanicsyKeweenaw Keweenaw Peninsula, PeninsulayMichigan Michigan Portage Kevin Sikkila Sikkila (Dept. (Dept. of of Geol. Geol. && Geol. Geol. Engrg., Engrg.y Michigan Michigan Technological Technological Kevin , University, UniversityyHoughton, HoughtonyMI MI 49931) 49931) Mount 146 m) m) intruded intruded into into the the lower lower Mount Bohemii Bohemia is is aa small small stock stock (284 (284 xx 146 The majority majority of of Mount Mount Bohemia Bohemia section of of the the Portage Portage Lake Lake Volcanics. Volcanics. The section It has has aa stock is is an an altered, altered, medium— medium- to to coarse—grained coarse-grained diorite. diorite. It stock reconstructed reconstructed primary primary mineral mineral assemblage assemblage of of 45% 45% to to 50% 50% sodic sodic plagio— plagio(augite and and hornblende), hornblende), and and up up to to 30% to to 50% 50% mafic mafic minerals minerals (augite clase, 30% clase, considerable amounts amounts of of magnetite magnetite (exceeding (exceeding In addition, additionyconsiderable 3% quartz. quartz. In 3% 15% 15% in in some some areas) areas) are are more more or or less less ubiquitous ubiquitous throughout throughout the the rock rock the body body is is comcomsmall section section in in the the southeastern southeastern portion portion of of the body. AA small body. posed posed of of fine—grained fine-grained quartz quartz diorite diorite with with aa reconstructed reconstructed primary primary 30% quartz,. quartz,.. mineral mineral assemblage assemblage of of approximately approximately 60% 60% sodic sodic plagioclase, plagioclase, 30% A much smaller concentration of inagnetite, about 3%, 7% biotite. A much smaller concentration of magnetitey about 3%, and and 7% biotite. Presumably this quartz is found in this section of the intrusive. Presumably this quartz is found in this section of the intrusive. diorite diorite is is representative representative of of the the final final stages stages of of intrusive intrusive activity. activity. The alteration alteration The dioritehas dioritehasbeen been moderately moderately to to severely severelyaltered. altered. The The shows shows aa strong strong correlation correlation with with the the Lac Lac La La Belle Belle fissure, fissureyaa structural structural N20° through through the the intrusive, intrusivey indicating indicating aa preferential preferential feature striking striking N20°W feature channeling of of hydrothermal hydrothermal fluids. fluids. Potassium Potassium metasomatism metasomatism is is pervasive, pervasive, channeling although heaviest heaviest along along the the fissure, fissure, and and secondary secondary potassium potassium feldspar feldspar although is microscopically microscopically observable observable in in almost almost all all thin thin sections. sections. This, Thisycomcomis bined with with the the alteration alterationof ofprimary primarytnagnetite magnetite to to fine—grained fine-grained hematite, hematitey bined is responsible responsible for for the the pinkish pinkish coloration coloration that that gives gives hand hand specimens specimens the the is misleading appearance appearanceof syenite. Alteration Alteration products products which which are are misleading of aa syenite. epirelatable to to the the fissure fissure position position are: are: serpentine serpentine (from (from mafics); mafics); epi— relatable dote (from (from plagioclase, plagioclasey mafics); mafics); and and calcIte calcite (from (from plagioclase). plagioclase). AlterAlterdote ation products products whose whose abundance abundance is is inversely inversely related related to to the the position position of of ation the fissure fissure include: include: actinolite actinolite (from (from pyroxene) pyroxene) and and sericite sericite (from (from the plagioclase). Alteration Alteration of of mafic mafic minerals minerals to to chlorite chlorite occurs occurs everyeveryplagioclase). finewhere and and it it is is the the alteration alteration product product of of the the biotite biotite in in the the fine— where grained quartz quartz diorite. diorite. grained Geochemical variations variations within within the the intrusive intrusive follow follow aa few few general general Geochemical trends. Concentrations Concentrations of of mobile mobile elements elements such such as as Cu, Cu, Zn Zn and and Rb Rb are are treads. higher along along the the Lac Lac La La Belle Belle fissure. fissure. High High Rb Rb concentrations concentrations can can be be higher specifically correlated correlated with with the the presence presence of of secondary secondaryK—feldspar. K-feldspar. specifically and Ni Ni have have relatively relatively uniform uniform values values ZryVV and Immobileelements elementssuch suchas asZr, I=obile throughout the the diorite diorite rock rockbody. body. Cr Cr varies varies in in aa manner manner which which might might throughout be related related to to original originalmagmatic magmatic processes. processes. The The concentrations concentrations of of imimbe mobile elements elements are are distinctly distinctly different different between between the the main main diorite diorite mobile rock body body and and the the later—stage later-stage quartz quartz diorite. diorite. The Zr concentration concentration The Zr rock concentrations are are is higher higher in in the the more more silicic silicic rock, rocky and and Cr Cr and and VV concentrations is lower. lower. 72 �AA partisan partisan review review of of the the Early Early Proterozoic Proterozoic geology geology of of Wisconsin Wisconsin and and adjacent adjacent Michigan Michigan P. P. K. K. SIMS SIMS and and Z. Z. E. E. PETERMAN, PETERMAN, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225; 80225; KLAUS J. SCHULZ, SCHULZ, U.S. U.S. Geological Geological Survey, Survey, Reston, Reston, VA VA 22092 22092 KLAUS J. in the the Two Two contrasting contrasting sequences sequences of of Early Early Proterozoic Proterozoic rocks rocks are are present present in Wisconsin—Michigan interbedded northern epicratonic epicratonic sequence sequence of of interbedded Wisconsin-Michigan region: region: aa northern sedimentary sedimentary and and volcanic volcanic rocks rocks (Marquette (Marquette Range Range Supergroup Supergroup of of Michigan) Michigan) overlying overlying Archean Archean basement, basement, and and aa southern southern terrane terrane dominantly dominantly composed composed of of volcanic volcanic and and granitoid granitoid rocks rocks and and generally generally lacking lacking Archean Archean basement basement (Wisconsin (Wisconsin magmatic magmatic zone). zone). The The boundary boundary between between the the two two terranes, terranes, at at least least in in northeastern northeastern Wisconsin, Wisconsin, is is the the Niagara Niagara fault. fault. The Supergroup is is composed composed of of three three depositional depositional cycles cycles The Marquette Marquette Range Range Supergroup separated separated by by minor minor unconformities. unconformities. In In general, general, the the deposits deposits fine fine upward: upward: basal basal clastic clastic and and chemical chemical deposits, deposits, accumulated accumulated in in rift rift basins basins and and on on platforms platforms (Larue (Larue and and Sloss, Sloss, 1980), 1980), are are succeeded succeeded upward upward by by quartzose quartzose sandstone sandstone and and the the major major iron—formations iron-formations of of the the region. region. These These strata strata are are overlain overlain by by aa southward—thickening southward-thickening wedge wedge of of turbidites, turbidites, areally areally restricted restricted iron—formations iron-formations and, and, in in more more southerly southerly parts, parts, intercalated intercalated submarine submarine volcanic volcanic rocks, rocks, which which are are mainly The depositional depositional patterns patterns indicate indicate aa shelf shelf prograding prograding mainly pillow pillow basalts. basalts. The into being derived derived principally principally from from into aa deep deep water water environment, environment, the the detritus detritus being exposed Deposition took took place place on on aa passive passive exposed Archean Archean rocks rocks to to the the north. north* Deposition continental Sedimentation ceased ceased before before or or during during the the main main pulse pulse of of continental margin. margin. Sedimentation deformation Deformation involved involved sub— subdeformation accompanying accompanying the the Penokean Penokeanorogeny. orogeny. Deformation horizontal horizontal compression compression accompanied accompanied by by substantial substantial shortening shortening of of the the supracrustal supracrustal sequence sequence (Cannon, (Cannon, 1973) 1973) and, and, later, later, dominantly dominantly vertical vertical tectonism tectonism associated associated with with the the development development of of diapiric diapiric gneiss gneiss domes domes caused caused by by reactivation An annular annular pattern pattern of of metamorphism metamorphism reactivation of of Archean Archean basement basement gneiss. gneiss. An around around some some of of the the gneiss gneiss domes domes was was superposed superposed on on regional regional greenschist greenschist metamorphism. metamorphism. The age age of of the the Marquette Marquette Range Range is is poorly poorly defined, defined, but but it it is is bracketed bracketed The between Ic dikes dikes in in basement; basement; Beck and Murthy, 1982) between 2,120 2,120 m.y. m.y. (maf (mafic 1982) and and 1,820 1,820 m.y., Mary, Mich., Mich., that that cuts cuts the the m.y., the the age age of of aa granite granite body body at at Lake Lake Mary, supergroup. supergroup. The The volcanic volcanic rocks rocks in in the the supergroup supergroup as as indicated indicated by by rhyolite rhyolite in in the the Hemlock Hemlock Formation, Formation, are are about about 1,900 1,900m.y. m.y. old old (W. (W. R. R. Van Van Schmus, Schmus, written written comm., corn., 1983). 1983). They They are are largely largely bimodal bimodal with with abundant abundant tholeiitic tholeiitic basalt basalt and and minor minor high high1(20 K20 rhyolite. rhyolite. The The basalt basalt shows shows strong strong iron iron enrichment, enrichment,and and high high Ti02 Ti02 and and incompatible—element incompatible-element contents contents (Fox, (Fox, 1983); 1983); it it is is compositionally compositionally similar similar to to continental continentalbasalts. basalts. Except Except in in aa broad broad sense, sense, aa coherent, coherent, integrated integrated view view of of the the Wisconsin Wisconsin magmatic zone is lacking, partly because of meagre exposures and magmatic zone is lacking, partly because of meagre exposures and partly partly because because of of the the inherent inherent difficulties difficulties of of deciphering deciphering thick, thick, complexly complexly disturbed disturbed volcanic As aa generalization, generalization,the the magmatic magmatic zone zone is is composed composed of of volcanic accumulations. accumulations. As calc—alkaline calc-alkaline volcanic volcanic and and intrusive intrusive rocks rocks having having overall overall island—arc island-arc affinities, affinities, and and more more restricted restrictedgranitoid granitoid gneisses. gneisses* AA key key area area for for understanding understanding the the stratigraphy, stratigraphy,metamorphism, metamorphism, and and tectonic tectonic evolution evolution of of the the magtuatic magmatic terrane terrane is is the the Dunbar Dunbar dome dome and and vicinity vicinity in in northeastern northeasternWisconsin. Wisconsin. The The dome dome is is aa large—scale, large-scale,antiforma]. antiformal fold— fold- 73 �interference structure in diameter, diameter, modified modified by by diapirism and and by by interference structure about about 20 20 kin km in intrusion intrusion of of tonalite, tonalite, granodiorite, granodiorite, and and granite. granite. It provides a window exposing older older gneiss gneiss that evolved at at aa deeper deeper crustal crustal level level than than the the widespread supracrustal supracrustal rocks. rocks. The gneiss and the immediately immediately adjacent adjacent amphibolite facies, facies, whereas the supracrustal rocks are amphibolite the regional regional metamorphic metamorphic The grade of the supracrustals supracrustals in in the the area is is greenschist greenschist facies. facies. The stracigraphic succession succession in the dome area, area, from from oldest oldest to stratigraphic to youngest, youngest, is is (1) (1) (2) shallowgneiss, miginatite, and amphibolite (Dunbar Gneiss of Cain, 1964), (2) shallow— gneiss, migmatite, and amphibolite (Dunbar Gneiss of 1964), water sedimentary rocks, (3) (3) basalt-andesite-dacite basalt—andesite—dacite (Quinnesec Formation), Formation), and and be younger younger than the major major deformation (4) (4) rhyolite. The rhyolite appears to be stratigraphic succession and metamorphism. In a broad sense, this stratigraphic succession appears appears to to fit gneiss—granitoid domes across across northern fit the other gneiss-granitoid northern Wisconsin. of Early Early Proterozoic Proterozoic rocks rocks has has been been A similarly complex stratigraphy of determined Wisconsin (LaBerge Myers, 1984). determined in in central central Wisconsin (LaBerge and Myers, 1984). At least least three three in successions of volcanic rocks are distinguished on on the the basis of of differences differences in composition, metamorphism, metamorphism, and composition, and structural structural fabric. fabric. An older, older, widespread widespread subaqueous basaltic subvolcanic intrusion intrusion subaqueous basaltic succession succession with with abundant abundant tnafic mafic subvolcanic breccias, breccias, mainly of amphibolite amphibolite facies, facies, is is overlain overlain locally locally by by subaqueous subaqueous felsic—intermediate of upper upper felsic-intermediate volcanic rocks and intercalated sedimentary sedimentary rocks rocks of weakly metamorphosed, metamorphosed, partly greenschist greenschist facies. facies. At Wausau, a still younger, weakly subaerial volcanic-sedimentary volcanic—sedimentary succession subaerial succession is is present. present. Distinct Distinct episodes episodes of of granite the younger younger granite emplacement emplacement followed followed extrusion extrusion of the the older older basalt basalt and and the volcanics volcanics at at Wausau; the the younger younger granites granites are are leucocratic leucocratic and and have have high high K20/Na20 ratios. The K20/Na20 The age of the volcanic successions successions relative relative to to the the Early Early associated with gneiss in Proterozoic gneisses and foliated tonalite associated with Archean Archean gneiss in central (Maass, 1983) 1983) is is equivocal, equivocal, but but we we interpret interpret the the volcanic volcanic central Wisconsin (Maass, successions as being younger; younger; the gneisses are representative successions representative of of aa deeper deeper crustal level than the volcanic rocks. crustal level than the volcanic rocks. All the Wisconsin (regardless All the volcanic rocks in in Wisconsin (regardless of of stratigraphic stratigraphic age) age) and and associated granitoid the associated granitoid rocks rocks have have U—Pb U-Pb zircon zirconages agesofofabout about1,850 1,850tn.y. m.y. zircon dating in northeastern Wisconsin (Van Schmus, Schmus, 1980). 1980). Detailed zircon in northeastern Wisconsin (Peterman, unpublished data) indicates that the volcanic and granitoid granitoid rocks rocks (Peterman, m.y., crystallized in the short time span of 30 30 m .y., from from 1,865 1,865 to to 1,835 1,835 m.y. m.y. ago. ago. The structure structure of the Early Proterozoic Proterozoic rocks rocks in in Wisconsin Wisconsin is is complex. complex. On scale, the terrane consists of generally a regional regional scale, generally large large structural structural blocks blocks having diversely oriented internal internal structures structures that are bounded by by ductile ductile deformation deformation zones zones ("shear zones"). zones"). The recordpronounced pronounced The deformation zones record flattening in inthe thefoliation foliation planesand anda astrong strongcomponent component of flattening planes of vertical vertical movement movement (Palmer, (Palmer, 1980). 1980). Although is is intense is Althoughdeformation defQrmation intenseininthe theshear shear zones, zones, it it is generally is in scope, and generally isyounger younger than than the prevailing internal internal regional in scope, and structural fabric within structural fabric within the the blocks. blocks. The boundary boundary between Proterozoic The betweenthe the northern northern and and southern Early Early Proterozoic terranes, as fault, isismarked terranes, as indicated indicated by by the the Niagara Niagara fault, marked by by structures structures indicative of variable indicative variable but generally generally high strain strain (Larue, (Larue, 1983). 1983). On On both sides both sides of of the fault, foliation that that is is fault, the rocks generally have a steep south-dipping south—dipping foliation subparallel to the fault and a generally steep southwest-plunging stretching southwest—plunging stretching lineation. These These data, data, together together with high-angle reverse faults faults on on the the north north lineation. high—angle reverse suggest that the side of the shear zone (Bayley and others, 1966), 19661, suggest the Niagara Niagara fault itself is steeply steeply inclined inclined southward. southward. The westward continuation continuation of of the the 7L. �fault is is conjectural, conjectural, although although aa fault fault is is shown shown on on the the regional regional geologic geologic map map fault (Morey and and others, others, 1982). 1982). (Morey Differences in in lithology, lithology, chemical chemical composition composition of of volcanics, volcanics, and and Differences metamorphic and and structural structural style style suggest suggest that that the the two two Early Early Proterozoic Proterozoic metamorphic Several plate plate tectonic tectonic models models involving involving terranes largely largely evolved evolved separately. separately. Several terranes to and collision collision have have been been proposed proposed to subduction, and some combination combination of of rifting, rifting, subduction, some explain the the evolution evolution of of the the Early Early Proterozoic Proterozoic rocks rocks in in the the Michigan—Wisconsin Michigan-Wisconsin explain segment of of the the Lake Lake Superior Superior region region as as well well as as the the nature nature of of the the Penokean Penokean segment orogeny (Van Schmus, 1976; Cambray, 1978; Larue and Sloss, 1980; and Greenberg Greenberg orogeny (Van Schmus, 1976; Cambray, 1978; Larue and Sloss, 1980; and and Brown, 1983). On the basis of new chemical and structural data, Schulz and Brown, 1983). On the basis of new chemical and structural data, Schulz and others (1984) have proposed a tectonic model of early crustal rifting and and others (1984) have proposed a tectonic model of early crustal rifting and and spreading, subsequent subduction and formation of a complex volcanic arc, spreading, subsequent subduction and formation of a complex volcanic arc, and collision of of the the arc, arc, first first with with Archean Archean crust crust on on the the south south and and then then with with the the collision Archean crust crust of of upper upper Michigan Michigan continental margin margin (epicratonic) (epicratonic) sequence sequence and and Archean continental Culmination of of the the orogeny orogeny was was on the the north north (the (the Penokean ~enokeanorogeny). orogeny). Culmination on approximately 1,850 1,850m.y. m.y. ago. ago. approximately REFERENCES REFERENCES Bayley, R. R. W., W., Dutton, Dutton,C. C. E., E.,and and Lamey,C.C.A., A *1966, , 1966, Geology Menominee Bayley, Lamey, Geology ofof thethe Menominee iron-bearing district, district, Dickinson Dickinson County, County, Michigan Michigan and and Florence Florence and and iron—bearing U.S. Geological Geological Survey Survey Professional Professional Paper Paper Marinette Counties, Counties, Wisconsin: Wisconsin: U.S. Marinette 513, 96 96 p. p. 513, R., 1982, 1982, Rb—Sr Rb-Sr and and Sm—Nd Sm-Nd isotopic isotopic studies studies of of Beck, Warren, Warren, and and Murthy, Murthy, V. V. R., Beck, Proterozoic mafic mafic dikes dikes in in northeastern northeasternMinnesota Minnesota[abs.J: [abs.]: Proceedings, Proceedings, Proterozoic 28th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, International International Falls, Falls, 28th p. 5. 5. Minnesota, p. Minnesota, Cain, J. J. 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S., S., 1984, 1984, The The volcanic—plutonic volcanic-plutonic terrane t e r r a n e of of northern n o r t h e r n Wisconsin: Wisconsin: Implications I m p l i c a t i o n s for f o r Early E a r l y Proterozoic P r o t e r o z o i ctectonisin, tectonism, Lake Lake Superior S u p e r i o r region: region: Program Program with w i t h abstracts, a b s t r a c t s , Geological Geological Association A s s o c i a t i o n of of Canada—Mineralogical Canada-Mineralogical Association A s s o c i a t i o n of of Canada Canada (in ( i n press). press). Van Van Schmus, Schmus, W. W. R., R., 1976, 1976, Early E a r l y and and middle middle Proterozoic P r o t e r o z o i c history h i s t o r y of of the t h e Great Great Lakes Lakes area, a r e a , North North America: America: Royal Royal Society S o c i e t y of of London London Philosophical Philosophical Transactions, T r a n s a c t i o n s , set. ser. A280, A280, no. no. 1298, 1298, p. p. 605—628. 605-628. 1980, Chronology Chronology of of igneous igneous rocks rocks associated a s s o c i a t e d with w i t h the t h e Penokean Penokean orogeny orogeny in G.B. and and Hanson, Hanson, G. G. N., N., eds., eds., Selected S e l e c t e d studies s t u d i e s of of i n Wisconsin, Wisconsin, iinMorey, n Morey, G.B. Archean Archean gneisses gneiss= and and lower lower Proterozoic P r o t e r o z o i c rocks, rocks, southern s o u t h e r n Canadian Canadian shield: shield: Geological Geological Society S o c i e t y of of America America Special S p e c i a l Paper Paper 182, 182, p. p. 159—168. 159-168. 76 �Morphologr_Accretion and acrost-tmMicrostructur Mor~holom,Accretion Rate and of Recent Algal Stromatolites Stromatolites from from Ottertail Co., Eagle XI1 Ehgle Lake, Lake Ottertail Co. MN L.G. L.G. SOROKA SOROKA (Dept. (Dept. of of Earth W t h Sciences, Sciences St. Cloud Cloud State State University, University St. 56301) st. Cloud, cloud, MN 56301) Earth Sciences, J.A. J.A. Roach Hosch (Dept. of of Earth Sciencesy St. Cloud Cloud State State University, UniversityySt. St. Cloud, MN 56301) 56301) cloud, MN m ' hardened, structures Hardened, high high relief relief organo—sedimentary organo-sedimentary carbonate carbonate structures (stromatolites) have been been discovered growing as cauliflower—like (stromatolites) have cauliflower-like mounds boulders in in water water depths depths of of between between 1 11 1 and 15m l5m mounds on on cobbles cobbles and. and boulders along Co., lake is The lake is along the the south south shore shore of ofEagle Eagle Lake, Lake,Ottertail Ottertail C O MN. . ~MI?. The an an exceptionally exceptionally clear, clear, hard—water, hard-water, kettle kettle moraine moraine lake. lake. The The stromatolites ( oncobbles cobblesand and boulders), boulders ) which which stromatolites begin as encrustations encrustations(on gradually columns 0.5 to gradually evolve evolve into into hemispheroidaJ. hemispheroidal columns to O.8m 0.8m in in height. height. The stromatolite surface The stromatolite surface is is covered covered by by aa green green mat mat of of filamentous filamentous algae botryoidal surface Cladophora aegagropila rabenhorst. A A botryoidal surface algae - Cladophora - gagropila rabenhorst. growth formmerges mergesinto intoan an interior interior with interconnecting growth form withnumerous numerous interconnecting cavities cavitieswhich which are are populated populated by by gastropods, leeches, leeches,and and other other organisms. organisms. X—ray X-ray diffraction most of the diffractionanalysis analysisindicates indicates that that most of the - lithified. lithified interior interior consists consists of of low—magnesium low-magnesium calcite. calcite. The The dominant dominant interior interior microstructure, microstructurey as as revealed revealed by thin—sections thin-sections and and scanning scanning electron anhedral calcite electron microscopy, microscopy, consists consists of of non—laminated., non-laminated, anhedral calcite crystals crystalsand. and diatoms. diatoms. This This inicrostructure microstructure suggests suggests that that settling lake lake carbonates carbonates have been trapped trappedand andbound. bound by by the the filamentous filamentous algae. algae. Subsequent cementation cementation occurs by photosynthesis induced precipitation Subsequent of of calcite calcite from from the the saturated saturated lake lake water. water. Observable Observable in in scanning scanning electron as well well as as in in thin-sections thin—sections are are areas areas which micrographs as which show show electron xuicrographs laminations. laminations. These laminated areas areasmake make up up less less than than 5% 5% of of the the stromatolite appear to to form stromatolite and and appear form in in recesses recesses where the thebioinduced. bioinduced precipitation is not being being diluted by by the more more rapidly lake rapidly settling settling lake settling precipitation is not carbonates. carbonates. This This bioind.uced bioinduced precipitate of aamosaic mosaic of of precipitate consists consists of smaller -5~. smaller uniformly uniformlysized sizedarthedral anhedral calcite calcite crystals crystals measuring measuring1 l-5. Preliminary Preliminary uranium—thorium uranium-thorium series dating of series datingsuggests suggeststhat thatthe therate rate of accretion O.5m accretion is is extremely extremely slow. slow. AA sample sample obtained obtained from from inside inside aa 0.5m thick strosiatolite stromatolite indicated in excess excess of of 10,000 10,000 years. years. thick indicated an age age in This observed observed stromatolite stromatolite formation formation in a relatively This relatIvely deep freshwater environment environment may necessitate necessitate a re-evaluation water re—evaluation of their generally pdeoenvironmental interpretation. accepted pa.leoenvironmenta]. accepted interpretation. 77 �Geologic and PPalinspastic G e o l o g i c HHistory i s t o r y and a l i n s p a s t i c Reconstruction R e c o n s t r u c t i o n oof f the the Early Collision E a r l y Proterozoic P r o t e r o z o i c Penokean Penokean C o l l i s i o n Zone Zone By W.L. Ueng, Ueng, D.K. D.K. Larue, Larue, R.L. R.L. Sedlock Sedlock W.L. Dept. ooff Geology, S t a n f o r dCA CA Dept. Geology, Stanford S t a n f o r d University, Un i v e r s it y ,Stanford 9+3O5 94305 Thereaare twopprincipal There r e two r i n c i p a l early e a r l y Proterozoic P r o t e r o z o i c tectonic t e c t o n i c elements elements in i n the t h esouthern southern Lake SSuperior Lake u p e r i o r rregion: e g i o n : aa northern n o r t h e r npassive p a s s i v emargin marginassemblage, assemblage, and and aa southern southern The magmaticaarc assemblage,j ujuxtaposed magmatic r c assemblage, x t a p o s e d aalong l o n g tthe h e Florence—Niagara F l o r e n c e - N i a g a r a f afault. ult. The passive margin assemblage, assemblage,r erepresenting terminusoof p a s s i v e margin p r e s e n t i n g t hthe e ssouthern o u t h e r n terminus f tthe h e Superior Superior province p r o v i n c e ooff the t h e Canadian Canadian Shield, S h i e l d , is i s locally l o c a l l yfragmented fragmented into i n t o two two discrete discrete blocks assemblage; b l o c k s next n e x t to t othe t h econtact c o n t a cwith t w i tthe h t hmagmatic e magmatic assemblage; the t h eFlorence—Niagara Florence-Niagara These terranes and Crystal and C r y s t a l Falls F a l l s terranes. terranes. These t e r r a n e s aare r e sstratigraphically t r a t i g r a p h i c a l l ycomparable comparable but disjunct b ut d i s j u n c t from from the t h e rest r e s t of o fthe t h epassive p a s s i v emargin. margin. Paired shear zones zoness straddle the P a i r e d shear t r a d d l e th e FFlorence—Niagara l o r e n c e - N i a g a r a f a ufault: l t : t otot the h e nnorth o r t h ooff the the fault, f a u l t ,highly-deformed h i g h l y - d e f o r m e d strata s t r a t aofo the f t hFlorence—Niagara e F l o r e n c e - N i a g a r a terrane t e r r a n e define d e f i n e the the northern shear zone; zone;t to off the n o r t h e r n shear o tthe h e south s o u t h ooff the t h e fault, f a u l t highly—deformed , h i g h l y - d e f o r m e d rocks rocks o the northern magmat i c tterrarle e r r a n e define d e f i n e the t h e southern s o u t h e r n shear shear zone. zone. n o r t h e r n margin margin ooff the t h e magmatic There hasbeen been material There has l i tlittle t l e oor r no no m a t e r i a l ttransfer r a n s f e r across a c r o s s tthe h e ffault. ault. shear zones zoneswere werepprobably formedd during shear r o b a b l y formed u r i n g t terrane e r r a n e aaccretion. ccretion. These paired These p aired •The by pprobably .The eentire n t i r e region r e g i o n has has been been deformed deformed by r o b a b l y ffive i v e deformation d e f o r m a t i o n events. events. This only T h i s has has been been pprecisely r e c i s e l y documented documented o n l y nnorth o r t h ooff the t h e Florence—Niagara F l o r e n c e - N i a g a r a f afault, ult, The pparallel but b u t preliminary p r e l i m i n a r y data d a t a to t o the t h e south s o u t h support s u p p o r t this t h i s contention. contention. The arallel deformation sharedbybyd idifferent d e f o r m a t i o n h histories i s t o r i e s shared f f e r e n t tterranes e r r a n e s i in n tthis h i s region r e g i o n indicate indicate regimeo of tthat h a t aa NNE NNE ooriented r i e n t e d sshortening h o r t e n i n g regime f t the h e ffirst i r s tdeformation d e f o r m a t i o n was was responsible responsible Throughout Fl ddeformation e f o r m a t i o n l left eft ffor o r the t h e terrane t e r r a n e accretion. accretion. Throughout t hthe e r eregion, g i o n , t the h e F1 a 90and anda as eseries a set s e t of o f penetrative p e n e t r a t i v e foliations f o l i a t i o n soriented o r i e n t e dN7OW N70W 90 r i e s o foft itight g h t folds folds which sometimes sometimesi ninvolved Archaenccrystalline r y s t a l l i n ebasement, basement, such such as as at a tthe t h eAmasa Amasa which v o l v e d Archaen Oval. The secondphase phaseo fofddeformation The second e f o r m a t i o n i is s characterized c h a r a c t e r i z e d by by planar p l a n a relements elements o r i e n t e d N65E N65E 90; e l olocally c a l l y ccrossfolded r o s s f o l d e d by h i s deformation. deformation. oriented 90;F1Fl elements elementsa rare by tthis The bending bendingo of Nl54oorientation The f ooriginally r i g i n a l l y N7OW—trending N7OW-trending F1 Fl s t rstructures u c t u r e s i ninto t o aa N15W rientation is bandccutting i s concentrated c o n c e n t r a t e d in i na a50 SOkm kmwide w i d e NE—trending NE-trending band. u t t i n g through t h r o u g h approximately approximately Crystal C r y s t a l Falls, F a l l s , Michigan, Michigan, up up toward toward tthe h e ssouthern o u t h e r n t tip i p of o f the t h e Republic R e p u b l i c trough. trough. To tthe F2deformation d e f o r m a t i o nband bandbends. bends the t h e Florence—Niagara F l o r e n c e - N i a g a r a FFault. ault. To h e southwest, southwest, this t h i sF2 The o c a t i o n oof f this t h i s band band was r o b a b l y c ocontrolled n t r o l l e d i in n ppart a r t by by structures s t r u c t u r e s in in The l location waspprobably the t h e underlying under1 y i n gbasement. basement. The p r e s e n t s one r o d u c t ooff The Amasa AmasaOval Ovalr erepresents onesuch suchpproduct crossfolding c r o s s f o l d i n g and and does does not n o t represent r e p r e s e n taagneiss g n e i s sdome. dome. We proposet hthat the LakeSSuperior waso originally We propose a t th e ssouthcentral o u t h c e n t r a l Lake u p e r i o r rregion e g i o n was riginally W-NW t r e ntrending d i n g s t r structures u c t u r e s r eresulting s u l t i n g ffrom rom tterrane errane a ccretion. c h a r a c t e r i z e d by by W—NW characterized accretion. This thet hNE—trending T h i s regional r e g i o n a l structure s t r u c t u r was e wasmodified m o d i f i e dbyby e NE-trending deformation d e f o r m a t i o n band band which rotated trending which r o t a t e dprevious p r e v i o u sW—NW W-NW t r e n d i n g sstructures. tructures. 78 �Recent Contributions C o n t r i b u t i o n s to t o the t h e Geochronology of of the the Precambrian of of Wisconsin Wisconsin W. of Geologyy Geology, University W. R. R. VAN VA8 SCHMUS SCHMUS (Department of U n i v e r s i t y of of Kansas, Kansas, Lawrence, Lawrence KS KS 66045) 66045) Continued U-Pb U—Pb age studies s t u d i e s on zzircons i r c o n s from Precambrian units units throughout ccentral and NN Wisconsin Wisconsin have have helped helped tto document iin more o document n more throughout e n t r a l and detail d e t a i l the t h e occurrence of of rocks r o c k s formed formed during d u r i n g the t h e main main phase phase of of the the Penokean Orogeny in our i n Wisconsin and have improved o u r understanding of of the of central c e n t r a l Wisconsin. Wisconsin. In I n addition, a d d i t i o n  rresults e s u l t s from t h e Archean block of several llocalities presence of of pre-Penokean pre—Penokean E Early o c a l i t i e s sseem e e m tto o confirm tthe h e presence arly Proterozoic P r o t e r o z o i c igneous igneous units u n i t s in i n Wisconsin. Based on p previous results, it best i t still s t i l l seems b e s t to t o bracket bracket r e v i o u s and new results the M a . The 1860 Ma. t h e main phase of of Penokean Orogeny Orogeny between between 1830 1830 and and 1860 tendency for f o r plutonic p l u t o n i c units u n i t s with w i t h ages ages in i n the t h e older o l d e r part p a r t of of this this more sstrongly pronounced, b but range to t o be more t r o n g l y ffoliated o l i a t e d iis s sstill t i l l pronounced, u t nnot ot universal. units u n i v e r s a l . Several Several u n i t s have aalso l s o been found that t h a t yyield i e l d apparent ages from from 1870 1870 to t o 1920. 1920. IIn n some ccases a s e s iit t iis s ppossible o s s i b l e tthese h e s e aare re with component iin but Penokean uunits nits w i t h an iinherited n h e r i t e d oolder l d e r component n tthe h e zzircons, ircons b ut with iif f so s o this t h i s is i s not n o t obvious. obvious. Furthermore, Furthermores in i n some cases cases w i t h ages of of 1890 to Maa this possibility Thus, t o 1915 1915 M p o s s i b i l i t y has h a s virtually v i r t u a l l y been been ruled r u l e d out. o u t . Thusy these around 1900 M Maa probably probably rrepresent e p r e s e n t ttrue r u e aages, g e s y and tthe h e rrocks ocks t h e s e ages around from which tthey were obtained obtained aare remnants h e y were r e ttentatively e n t a t i v e l y iinterpreted n t e r p r e t e d as remnants of one o orr more more o older, pre—Penokean (or Penokean) igneous of l d e r * pre-Penokean ( o r eearlier a r l i e r Penokean) suites. and scattered s u i t e s . Most of of these t h e s e units u n i t s are a r e tonalitic, t o n a l i t i ~deformed, deformed, ~ scattered no ssingle, coherent o older Proterozoic over a llarge a r g e aarea, r e a * sso o tthat h a t no i n g l e  coherent lder P roterozoic terrane t e r r a n e or o r domain can can be identified i d e n t i f i e d at a t present. present.  Tonalitic gneiss near Marshfield, Marshfield, along tthe of tthe T onalitic g n e i s s near h e nnorthern o r t h e r n edge of he Central Archean block, block, yyields with U—Pb i e l d s zzircons ircons w i t h complex U-Pb C e n t r a l Wisconsin Archean discordance However, iit discordance patterns. p a t t e r n s . However, t is i s clear c l e a r that t h a t tthese h e s e zzircons i r c o n s are are about 3000 M Ma old, with a o l d , cconsistent onsistent w i t h eearlier a r l i e r rresults e s u l t s ssuggesting u g g e s t i n g that that Archean tterrane may be be aa remnant remnant of of tthe gneiss—migmatite h e oolder l d e r gneiss-migmatite tthis h i s Archean e r r a n e may province of of the t h e southern southern Lake Lake Superior Superior region. region. Zircons separated separated gneiss from ffelsic elsic g n e i s s near Fifield F i f i e l d also a l s o indicate i n d i c a t e an an age age of of 2950 2950 to t o 3000 3000 Ma, suggesting tthat Archean block iin Wisconsin is Ma9 h a t the t h e Archean n ccentral e n t r a l Wisconsin i s rrelated elated Wisconsin. tto o tthe h e oolder l d e r gneisses g n e i s s e s in i n northwestern Wisconsin. overall by tthe s sstill t i l l one The o v e r a l l tectonic t e c t o n i c ppicture i c t u r e ppreferred r e f e r r e d by h e aauthor u t h o r iis which most most of of tthe Penokean igneous igneous ssuite of nnorthern Wisconsin wwas as iin n which h e Penokean u i t e of o r t h e r n Wisconsin n continental c o n t i n e n t a l margin arc a r c complexes, complexes9 and and that t h a t more more than t h a n one one formed iin distinct period magmatism within distinct p e r i o d of of subduction-generated subduction-generated m a g m a t i s m occurred w ithin tthe h e interval i n t e r v a l 1920 1920 to t o 1820 1820 Ma. M a . However, However, outcrop and geochronologic control c o n t r o l is i s still s t i l l insufficient i n s u f f i c i e n t to t o constrain c o n s t r a i n the t h e model precisely. precisely. 79 �The The Huronian Huronian Supergroup: Supergroup: An An Example Example of of an an Early Early Proterozoic Proterozoic Passive Passive Margin Margin Sequence Sequence GRANT GRANT M. M. YOUNG, YOUNG, (Department (Department of of Geology, Geologyl University University of of Western Western Ontario, Ontarior London, London, Ontario, Ontario, Canada) Canada) Information such aas those of of tthe Information on passive margin successions such s those h e ppen-Atlantic eri-Atlantic The stratigraphic s t r a t i g r a p h i c succession succession region region has has come come from from geophysical geophysical work work and and drilling. d r i l l i n g . The differs d i f f e r s in i n different d i f f e r e n t areas areas but but the t h e classical c l a s s i c a l model model involves involves alkaline a l k a l i n e volcanics volcanics and and continental c o n t i n e n t a l sediments sediments deposited deposited in i n fault-bounded fault-bounded troughs, troughs, followed followed by by evaporites evaporites and, and, above above the t h e "break—up" "break-up" unconformity, unconformity, aa continental c o n t i n e n t a l margin margin succession succession comprising comprising the t h e terrace t e r r a c e wedge wedge and and continental c o n t i n e n t a l rise r i s e successions. successions. Huronian stratigraphy s t r a t i g r a p h y has has largely l a r g e l y been been interpreted i n t e r p r e t e d in i n terms terms of of aa tripartite tripartite Huronian d i a m i c t i t e s l argillites a r g i l l i t e s and and sandstones sandstones in i n ascending ascending sequence. sequence. cycle involving involving diamictites, cycle It is i s here here suggested suggested that t h a t the t h e Huronian Huronian succession succession (10—12 (10-12 km km in i n max. max. thickness) thickness) It may may be be the t h e result r e s u l t of of continental c o n t i n e n t a l fragmentation. fragmentation. The The lower lower Huronian, Huronian, below below the the Groupl includes includes syn-nift s y n - r i f t volcanics volcanics chemically chemically akin akin to t o those those of of the t h e Afar Afar Cobalt Group, Cobalt Triangle and and largely l a r g e l y continental c o n t i n e n t a l clastic c l a s t i c sediments sediments such such as a s those those of of the t h e Mississagi Mississagi Triangle and and Serpent Serpent Formations. Formations. These These formations formations are a r e of of limited l i m i t e d distribution d i s t r i b u t i o n and and display display major major thickness thickness and and facies f a c i e s changes changes consistent c o n s i s t e n t with with contemporaneous contemporaneous fault f a u l t activity. activity. Evaporitic Evaporitic facies f a c i e smay may be be represented representedby bycarbonates carbonates of of the t h e Espanola Espanola Formation Formation near near the t h e top top of of the t h elower lowerHuronian Huronian succession. succession. s tthe h e base base of of the the The betweent hthe lowerand andupper upperHuronian Huroriiani sistaken takenaas The boundary boundary between e lower Gowganda Formation. Gowganda Formation. In In the t h e southern southern part p a r t of of the t h e Huronian Huronian outcrop outcrop bbelt e l t there t h e r e is is aa profound from aa bbasin—full condition ttoo one profound change change from a s i n - f u l l condition one in i n which which resedimented resedimented glacio— glaciogenic me boundary boundary iis s interpreted i n t e r p r e t e d to t omean mean aa sudden sudden tectonic tectonic genic rocks rocks predominate. predominate. The foundering of the foundering of t h e basin. basin. In angular unconformity I n more more northerly areas a r e a s there t h e r eisi s ananangular unconformity between andunderlying underlyinglower lowerHuronian Huronianformations formationsand ands tstill i l l farther farther between the t h e Gowganda Gowganda and north Formationl lies norththe t h eGowganda Gowganda Formation i e s directly d i r e c t l yononArchean Archeanbasement basement rocks. rocks. These These r e l a t i o n s h i p s indicate i n d i c a t eboth both local l o c a land andregional regionalsubsidence subsidence and and the t h e transition t r a n s i t i o nfrom from relationships aa dominantly dominantly continental c o n t i n e n t a l to t o marine marine shelf-type shelf-type sedimentation. sedimentation. Relationships Relationships at at the thet h"break—up" t h ebase baseofofthet hGowganda e Gowganda Formation Formation are a r eequated equatedtot o e "break-up" unconformity unconformity that many I t differs, differs, t h a tcharacterizes characterizes manyyounger younger continental c o n t i n e n t a lmargin marginassemblages. assemblages. It however, however, in i n bearing bearing evidence evidence of of contemporaneous contemporaneousglaciation. g l a c i a t i o n . Similar Similar resedimented resedimented glaciogenic glaciogenic facies f a c i e s are a r e associated associated with with late l a t e Proterozoic Proterozoic continental c o n t i n e n t a l fragmentation fragmentation in i n the t h e Cordifleran Cordilleranregion. region. Rocks Rocks of of the t h e lower lower Huronian Huronian do be represented represented in i nthe t h eLake LakeSuperior Superior do not not appear appear ttoo be region, probably probably because e eearly a r l y rrifting i f t i n g did d i d not not extend extend that t h a t far f a rwest west but butthe the region, becauset hthe transgressionassociated transgression~associated with the t h e regional regional subsidence subsidence phase phase led l e d to t o deposition deposition of of with glaciogenic and succeeding marine platformal facies f a c i e s of of the t h e Chocolay Chocolay Group Group and and glaciogeriic MilleLacs LacsGroup Groupwhich whichare a r econsidered consideredtot obebeequivalent equivalenttot othe t h eupper upper possibly the t h e Mule possibly . Huronian. Huronian The The tectonic t e c t o n i csetting s e t t i n gofofthe t hHuronian e Huronian and and equivalent equivalent rocks rocks remains remains obscure obscure but but thickness thickness and and facies f a c i e s changes changes and and regional regional paleocurrent paleocurrent data d a t a suggest suggest that t h a t they they were were formed in i n an an intracratonic i n t r a c r a t o n i c rift r i f t setting s e t t i n g with with subsequent subsequent ocean ocean opening opening to t o the t h e east east formed to t o explain explain the t h e regional regional subsidence subsidencein i nGowganda Gowgandatimes. times. The The subsequent subsequent history h i s t o r y of of e a r l y Proterozoic Proterozoic rocks rocks of of the t h e south south shore shore of of Lake Lake Superior Superior has has been been interpreted interpreted early by by several s e v e r a l workers workers to t o involve involve aa period period of of ocean ocean opening opening and and closure. closure. Reference Reference Jr., 1983, 1983, Early Early Proterozoic Proterozoic Geology Geology of of the t h e Great Great Lakes Lakes Medaris, L.G. L.G. Jr., Medaris, Region: Region: Geological Geological Society Society of of ?merica America Memoir Memoir 160, 160, 141 141p. p. 80 � https://digitalcollections.lakeheadu.ca/files/original/6ec5aceba816c6c0c46889c5593283e9.pdf fdb8576dcdd5eb0c3d227a7562f52037 PDF Text Text Thirtieth Annual Institute on Lake Superior Geology FIELD TRIP GUIDE 1 TO THE GEOLOGY OF THE EARLY PROTEROZOIC ROCKS IN NORTHEASTERN WISCONSIN 46 APRIL 24—25, 1984 �Guide to the Geology of the Early Proterozoic Rocks in Northeastern Wisconsin Field trip leaders P. K. Sims K. J. Schulz Z. E. Peterman Prepared for 30th annual meeting of the Institute on Lake Superior Geology Wausau, Wisconsin, 1984 �CONTENTS DUNBAR GNEISS - GRANITOID DOME P.K. Sims, Z.E. Peterman, and K.J. Schulz 1 GEOCHEMISTRY OF THE DUNBAR GNEISS - GRANITOID DOME, N.E. WISCONSIN K.J. Schulz, P.K. Sims, and Z.E. Peterman 24 FIELD TRIP LOG AND DESCRIPTIONS, DUNBAR GNEISS GRANITOID DOME P.K. Sims, K.J. Schulz, and Z.E. Peterman 43 VOLCANIC ROCKS OF NORTHEASTERN WISCONSIN Klaus J. Schulz 51 FIELD TRIP LOG AND DESCRIPTIONS, VOLCANIC ROCKS OF NORTHEASTERN WISCONSIN Klaus J. Schulz a 81 �DUNBAR GNEISS—GRANITOID DOME By P. K. Sims..!!, Z. E. Peterman!J, and K. J. Schulz-.i ..!Ju.s. Geological Survey, Denver, CO 80225 — U.S. Geological Survey, Reston, VA 22092 .1 I UI I I I I I �Introduction [ As a part of regional investigations of the geology of the Precambrian rocks in the eastern part of the Lake Superior region (Michigan and Wisconsin), northeastern Wisconsin was chosen as one of the key areas for study because of its apparently unique geology and relatively abundant outcrop. In particular, the Dunbar dome and adjacent areas were chosen for emphasis. This terrane contains varied gneisses, amphibolite, and abundant granitoid rocks, all of Early Proterozoic age, and contrasts markedly with the adjacent terrane in northern Michigan. The study area also is a part of the Early Proterozoic east—trending volcanic belt in northern Wisconsin that contains economically promising strata—bound massive sulfide deposits. In addition, northeastern Wisconsin provides the opportunity to further study the age, extent, and cause of Middle Proterozoic events that reset Rb—Sr whole— rock and mineral ages throughout most of the eastern part of the Lake Superior region, as first noted by Aldrich and others (1965). This summary of the geology, geochronology, and geochemistry of the rocks within and adjacent to the Dunbar dome is derived from papers in preparation by us and previous publications on the regional geology of adjacent areas to the north (Bayley and others, 1966; Dutton, 1971). Earlier reports on the ages of rocks in the general area by Banks and Cain (1969), Banks and Rebello (1969), Van Schmus, Thurman, and Peterman (1975), and Van Schmus (1980) were extremely useful. R. A. F Jenkins, M. G. Mudrey, Jr., and W. C. Prinz introduced us to the geology of the area, and together with many others stimulated our interest in the geology and mineral potential. Summary of Geology [ F The Dunbar dome is one of several domes in northern Wisconsin that have cores of gneiss, migmatite, and granitoid rocks and are mantled by inetavolcanic and inetasedimentary rocks. Both the basement (core) and the mantle (cover) are of Early Proterozoic age. The domes occur within an east—trending curvilinear, convex northward belt at least 60 km wide that lies adjacent to the boundary of this terrane (Wisconsin magmatic zone) with the Michigan terrane to the north. The Michigan terrane, as defined here, consists of epicratonic metasedimentary and metavolcanic rocks (Marquette Range Supergroup) that unconformably overlie Archean basement rocks (Sims, Card, and Lumbers, 1981). The proposed boundary (Larue, 1983) between the two terranes is the Niagara (or Florence—Niagara) fault zone. domes in northern Wisconsin provide windows that expose parts of an The extensive deeper crustal succession that lies beneath the thick pile of metavolcanic rocks in northern Wisconsin. Apparently, an Archean basement is lacking. However, a Nd—Sm isotopic study of two samples of Dunbar Gneiss (Cain, 1964) yielded ages of 2,130 Ma and 2,280 Ma, which probably indicates a component of Archean material in the source or a small degree of contamination of the magma during its ascent through Archean crust. Lead—isotope data on massive sulfide deposits and associated rocks in the Early Proterozoic belt of metavolcanic rocks in northern Wisconsin support this conclusion (Afifi and others, in press). 1 �The Dunbar dome is a complex antifornial structure consisting of a central core and three lateral protuberances from the core, named the Niagara, Pembine, and Bush Lae lobes, respectively (fig. 1). The dome occupies an area of about 470 km • The stratigraphic—tectonic evolution of the dome spanned the relatively short time of about 30 Ma, from about 1,865 Ma to 1,835 Ma ago, during the Early Proterozoic. The dome coincides with a deep gravity depression of about 20 milligals (Ervin and Hammer, 1974), which is the southeasternmost low of a family of lows that extend about 35 km to the northwest. The central core of the Dunbar dome is composed of biotite gneisses, migmatite, granite gneiss, and amphibolite, assigned to the Dunbar Gneiss of Cain (1964), and three granitoid bodies, which he called the Marinette Quartz Diorite, a megacrystic phase of the Newingham Tonalite (included by Cain (1964) in the Dunbar Gneiss), and a large elliptical body of Hoskin Lake Granite. The Niagara and Bush Lake lobes are composed of two other bodies of granite, which differ somewhat from the Hoskin Lake Granite. The Pembine lobe consists mainly of the Newingham Tonalite (formerly called Newingham Granodiorite by Cain, 1964). The granitoid bodies intruded the Dunbar Gneiss and a narrow fringing zone of the mantling Quinnesec Formation (volcanic succession) and stratigraphically older tnetasedimentary rocks, and apparently were emplaced in the order, from oldest to youngest, Marinette Quartz Diorite, Newinghani Tonalite, and Hoskin Lake Granite. Granite peginatite and aplite are abundant throughout the dome, especially in the Dunbar Gneiss. K—metasomatlsm, which was approximately contemporaneous with emplacement of the Hoskin Lake Granite, appreciably modified rock compositions in the northern part of the central core subsequent to their crystallization. Potassium was introduced during or after a cataclastic (ductile) deformation that recrystallized plagioclase and other minerals, to yield core—mantle (or mortar) textures and shears. The granitoid bodies were emplaced at relatively shallow crustal depths. The supracrustal (cover) rocks compose a steeply dipping succession that dominantly faces stratigraphically outward from the core. They consist mainly of metavolcanic rocks and layered, maf Ic sills, assigned to the Quinnesec Formation, and coeval subvolcanic rocks (Twelve Foot Falls Quartz DIorite of Cain, 1964). The cover rocks also include a more local, thinner older succession of metasedimentary rocks, principally impure quartzIte, stromatolitic marble, caic—silicate rocks, and biotIte schist (metatuff?). The volcanic rocks are interpreted as having been deposited in deep water, whereas the sedimentary rocks have shallow—water attributes. Granltoid rocks in the dome have general geochemical cale—alkaline characteristics, but the Marinette Quartz Diorite is slightly alkaline. The Dunbar Gneiss has relatively low Rb/Sr ratios (0.10—0.99) and steep rare earth element (REE) patterns ([La/Yb} = 25—43). They probably represent metamorphosed volcanic and related subvolcanIc intrusive rocks. The Newingham Tonalite Is compositionally homogeneous having high Sr (690), low Rb—Sr (0.066), and steep REE patterns ([La/Ybin = 43). It is compositionally similar to many Archean tonalites, and probably was derived by partial melting of a basaltic parent. The Hoskin Lake Granite and the closely associated granites of Spikehorn Creek and Bush Lake range in composition from granodiorite to granite, have relatively low Sr (58—300), high Th (23—40), 2 �p Rb/Sr >1, variable REE ([Lain = 57—163), and negative Eu anomalies. The Marinette Quartz Diorite and Hoskin Lake Granite show overlapping major and trace element compositions, which apparently reflect partial K—tnetasomatistn of the quartz diorite. U—Pb zircon ages of rocks in the dome are clustered in therange 1,865 Ma to 1,835 Ma. The oldest rocks, the Dunbar Gneiss and the Quiñnesec volcanics, are about 1,865 Ma old, whereas the Marinette Quartz Diorite and the Newingham Tonalite are inferred to be about 1,860 Ma. The youngest rock unit, the granite body of Spikehorn Creek in the Niagara lobe, has an age of 1,835*6 Ma. Rb—Sr whole—rock and mineral ages are consistently reset and are 100 Ma or more younger than the zircon upper intercept ages, as discussed on following pages. The Duabar dome is interpreted as a large—scale fold—interference structure resulting from cross folding modified by diapirism and emplacement of the granitoid intrusive rocks. Many of the criteria indicative of diapirism, as listed by Brun and others (1981), are observed in the dome: (1) cleavage parallel to dome boundaries, (2) steeply plunging lineation in dome boundaries, and (3) higher strain intensities located on dome boundaries. The Dunbar dome is surrounded by an asymmetrical annular zone of metamorphism in the cover rocks. An amphibolite—facies zone ranging from less than 0.5 km wide to at least 8 km wide lies adjacent to the core, and gives The amphibolite zone is widest on way outward to greenschist—facies rocks. the northern margin where it transects the Niagara fault zone (Dutton, Within the core, the Dunbar Gneiss has amphibolite—facies mineral 1971). The assemblages, as oes the northern part of the Marinette Quartz Diorite. Dunbar Gneiss was metamorphosed during dynamothermal metamorph-ism accompanying whereas the annular metamorphic pattern, superposed on previously metamorphosed greenschist—facies supracrustal rocks during a late stage evolution of the dome, was dominantly the result of thermal metamorphism. Granite—tonalite dikes were emplaced into rocks in the amphibolite—facies zone during the younger thermal metamorphism. The rocks in the Dunbar dome and surrounding environs compose part of a magmatic terrane, termed the Wisconsin magmatic zone, that differs in stratigraphy, structure, mineral deposits, and igneous rock chemistry from the epicratonic Michigan terrane to the north. Accordingly, we conclude that the Wisconsin magmatic zone evolved separately from the Early Proterozoic terrane to the north, and is an exotic terrane that was attached to the North American continent during the Early Proterozoic. Apparently the boundary between the two Proterozoic terranes is the Niagara fault, as suggested by Larue (1983). The doming was probably in response to collision of the two crustal blocks, which triggered the Penokean orogeny. Rock Units The Dunbar dome is composed of compositionally varied gneisses, assigned to the Dunbar Gneiss, and 5 younger intrusive units, which were emplaced, from oldest to youngest, in the order Marinette Quartz Diorite, Newingham Tonalite, Hoskin Lake Granite, granite of Bush Lake, and granite of Spikehorn Creek The Marinette Quartz Diorite and the Hoskin Lake Granite were named (fig. 1). 3 �_____ EXPLANATION (Figure 1) MIDDLE PROTEROZOIC Diabase EARLY PROTEROZOIC I XsgI Granite of Spikehorn Creek {g] Granite of Bush Lake [XhJ Hoskin Lake Granite [] Newingham Marinette Quartz Diorite ix1 IX1 Metagabbro sills X. Quinnesec Formation 1 Twelve Foot Falls Quartz Diorite of Cain (1963) Metasedimentary rocks I X1 Dunbar Gneiss of Cain (1964); includes abundant pegmatite and aplite and, in northeast part of central core, foliated intrusive megacrystic granodiorite Approximate contact Fault, bar and ball on downthrown side Fault, relative movement not known Facing direction of pillow lava Metamorphic isofacies—gs, greenschist facies; am, amphibolite fades. After Bayley and others, 1966. — — Metamorphic isograd—bi, biotite; gar, garnet. After Dutton, 1971. Note: Rocks listed in inferred order, from youngest to oldest. �Figure 1.——Geologic map of Dunbar Gneiss—granitoid dome. from Dutton and Linebaugh, 1967. a S In part modified �by Prinz (1965); the Dunbar Gneiss and the Newingham Tonalite, formerly called the Newingham Granodiorite, were named by Cain (1964). The granites of Bush Lake and Spikehorn Creek are new, informal names for granite bodies previously called Hoskin Lake Granite (Bayley and others, 1966; Dutton, 1971). The Dunbar Gneiss, as used herein, differs from the earlier usage by Cain in excluding a moderately large body of Newingham Tonalite that intrudes the Dunbar in the northeast part of the central core (fig. 1). The Dunbar Gneiss consists of partly migmatized biotite gneisses, lesser amphibolite, and granite gneiss of dominantly tonalite composition. Some of the granite gneiss contains conspicuous feldspar megacrysts. Granite pegmatite and aplite form abundant subcortcordant sheets and steeply dipping dikes in the gneiss and amphibolite. The Dunbar Gneiss has been metamorphosed to amphibolite fades. The Marinette Quartz Diorite is composed of intermediate and mafic rocks that seem to form a layered intrusive succession. The northern part of the body, adjacent to the Hoskin Lake Granite, has ainphibolite—facies mineral assemblages. The Newingham Tonalite is a remarkably uniform gray, medium—grained, foliated rock that is cut by dikes of similarly foliated, slightly porphyritic tonalite. It composes the Pembine lobe of the Dunbar dome and part of the central core. It intrudes the Dunbar Gneiss and the volcanic rocks of the Quinnesec Formation. The foliation in the Newingham Tonalite is a cataclastic (ductile) foliation that is oriented northeastward. The Hoskin Lake Granite is a complex, crescent—shaped unit along the northern margin of the dome. The type Hoskin Lake Granite (Prinz, 1965; Bayley and others, 1966) is a distinctive rock characterized by oriented 1—5 cm tabular crystals of K—feldspar. Much of this fades also has K—feldspar porphyroblasts that lie athwart the foliation in the rock. As noted by Cain (1964), the southern margin of the granite is gradational into biotite gneisses of the Dunbar Gneiss and the Marinette Quartz Diorite, and evidence for an origin of the border phase of the granite by K—metasomatism is compelling. The granite of Spikehorn Creek, which composes the Niagara lobe, is a massive, medium— to fine—grained rock that contains sparse, small K—feldspar phenocrysts. A similar, although somewhat coarser grained rock in the Bush Lake lobe (granite of Bush Lake) is assumed to be approximately equivalent in age to the granite of Spikehorn Creek. Formerly, both were called Hoskin Lake Granite (Bayley and others, 1966; Dutton, 1971). Structure The Dunbar dome is an irregular asymmetrical structure that interrupts and distorts the regional northwest—trending structural pattern in northeastern Wisconsin. It is characterized by a consistent parallelism of structures in the cover (supracrustal) rocks and in the margins of the core and by strongly foliated and lineated rocks, indicative of high strain, along the core—cover boundary. It has an estimated structural relief greater than 2 km. The outline of the dome is interpreted as resulting from polydeformation accompanied by diapirism and emplacement of granitoid rocks. 6 �Small—Scale Structures From examination of small—scale structures in the field, a sequence of four successive deformational events has been delineated in rocks within the core and the immediately adjacent cover rocks. The principal structures developed during the successive deformations are listed in table 1. Trajectories of the planar structures and lineations are plotted in figure 2. Core Zone F D1 structures——The oldest recognized structure is a pervasive foliation (S1) that is subparallel to compositional layering in the Dunbar Gneiss. It is defined mainly by a preferred orientation of biotite and hornblende. A lineation related to S1 has not been recognized. Migmatization of the Dunbar occurred during or prior to S1. Possibly, S1 formed as an axial plane structure to early, rootless isoclinal folds. 5O F [ [ r P D2 structures——Folds (F2) are conspicuous in the Dunbar Gneiss. A major antiform orientedN. 600 W. and plunging 35°—45° SE. has been delineated in the southwestern part of the Dunbar dome, and second order folds are common on the limbs. The folds are upright, slightly asymmetrical, open to closed structures. Except locally, the folds do not transpose the older foliation (S1) and layering (S0). An axial plane foliation (S2) is best developed in the relatively massive tonalitic Dunbar Gneiss, where it is defined mainly by oriented tabular feldspars and biotite. A lineation (L2) that is parallel to fold axes (F2) is best developed in mica— and hornblende—rich gnelsses and schists and is expressed by elongate minerals and mineral aggregates. D2 preceded emplacement of the granitoid rocks in the Dunbar dome. D structures——Structures related to D3 are abundant in the northeastern part ot the central core of the dome and in the Penibine lobe. The deformation consisted of two apparently distinct phases, designated D3 and D3s, respectively (table 1), which probably resulted from the same stresses. During an early phase, the Marinette Quartz Diorite acquired a foliation and was folded into dominantly open folds that plunge gently southwest (fig. 2). Presumably at the same time, the Dunbar Gneiss in the north—central part of the core was refolded; the folds plunge gently northeastward and a mineral lineation given by aimed biotite aggregates and hornblende was developed parallel to fold axes. Subsequently, after emplacement of the Newiugham Tonalite, continued stresses produced a nearly pervasive cataclastic (ductile) foliation (S3..) defined mainly by oriented biotite and quartz leaves in the intrusive rock. The foliation is dominantly oriented northeastward and dips moderately to steeply southeastward. In the contact zone between the Newingham Tonalite and the Dunbar Gneiss, the S3.. foliation crosscuts that (S1) in the Dunbar Gneiss. An associated lineation generally is absent. Adjacent to the southeastern margin of the central core (bc. B, fig. 2), F3.. folds, which are mainly Z—type asymmetrical folds, are superposed on previously folded Marinette Quartz Diorite; hinge lines plunge moderately southwestward and axial surfaces dip southeastward, parallel to the associated S3.. foliation. These structures adjacent to the margin of the core are assigned to D3, but in part could be D4 structures. 7 �I I I I Figure 2.——Interpretive structure map, Dunbar dome Planar and linear structures —4— Si, inclined vertical —.,'.c L, showing plunge —. L2 , —H* — -. — Fault, relative movement not known —— Trend of magnetic anomaly Locality referred to in text L3 S3, - L3 ---f-f- f.. —4-- Fault, bar and ball on downthrown side 3 ....LLL t —i-— I I I S4 Foliation and lineation of uncertain designation Major F2 antiform 8 -- �Table 1.——Structural sequence, Dunbar dome D1 Foliation parallel to layering in Dunbar Gneiss (S1). D2 Northwest—oriented folds in Dunbar Gneiss and Quinnesec Formation (F2). Foliation parallel to axial planes of folds (S2). Local. Lineation parallel to fold axes (L2). Local. D2, Stretching lineation (L2,) parallel to local steeply plunging folds (F2)1) in cover—rocks, north side dome. D3 Foliation parallel to layering in Marinette Quartz Diorite (S3). Lineatlon (L3) parallel to fold axes (F3). D3, Cataclastic foliation parallel to axial planes of asymmetrical folds, northeast—trending (S1). Lineation (L3..) parallel to fold axes (F3,). D4 Mylonitic foliation (S4) in core—cover boundary. Stretching lineation (L4). 9 �D4 structures——D4 structures occur in the core—cover boundary. Inasmuch as they obliterate or strongly modify older structures in the core they are interpreted as being the youngest structures, although they could have overlapped D3. The dominant structures are a mylonitic foliation and a stretching lineation defined by elongate clasts, rare folds, mullions, and slickenside striae. They are most intensely developed on the north margin of the core (D, fig. 2) where the foliation dips 700_800 S., and the lineatlon uniformly plunges 600 Sw. The zone of mylonitic foliation is as much as 500 m wide; the foliation decreases in intensity inward from the boundary, indicating that this deformation is strongly controlled by the core—cover boundary. A comparable steep mylonitic foliation exists along the northwest boundary of the central core, but the lineation is flatter. A steep foliation and mineral lineation also exists at the extreme southwest margin of the core of the dome. It should be noted that the Pembine and Niagara lobes lack in their contact zones. structures Mantle zone The mantling metavolcanic and metasedimentary rocks were deformed together with the Dunbar Gneiss on northwest—trending fold axes during D2, and subsequently were deformed in the core—cover boundary by D3 and D4. On a regional basis, folds and related mineral lineations in the supracrustal rocks plunge moderately to steeply either to the southeast or the northwest. On the southern margin of the Dunbar dome, inclusions of the Quinnesec Formation in the Newingham Tonalite (see figs. 1 and 2) are folded; the folds plunge moderately gently southeastward, subparallel to the major D2 antiforin axis in the Dunbar Gneiss, clearly indicating that folding in both rock types was coaxial. The northwest—trending foliation and southwest—plunging mineral lineation in the Quinnesec Formation on the northeast side of the Rush Lake lobe are tentatively considered as late—stage D2 structures, and are designated as S2, and L2, respectively (fig. 2). In this area, F2 folds (as discussed above seem to be absent, presumably because they have been obliterated by S21 and both of which have fabrics indicative of high strain. As shown in figure 2 (bc. E), S2 Is redeformed adjacent to the northwest boundary of the central core by D3 structures. In this area, S—type, asymmetrical folds that plunge moderately southwestward and have a southeast—dipping axial plane foliation are developed adjacent to the boundary. They persist intermittently for a distance of 0.8 km away from the boundary. The Quinnesec Formation on the north, overturned margin of the dome is intensely deformed and has a close—spaced foliation and a steeply plunging stretching lineation resulting from D4. Pillows in the lavas are both flattened and stretched, and have length—width ratios of about 5:1. The stretching lineation is similar to that in the Quinnesec Formation on the northeast side of the Bush Lake lobe, but is more intense. As noted earlier, the Quinnesec also is intensely deformed on the northwest margin of the dome, In the same way, the Quinnesec is refoliated but the lineation is flatter. adjacent to the southwest margin and has a moderately plunging lineation oriented westward. In the reentrant along the southeast margin of the central 10 I �' core (fig. 2), the Quinnesec has a steep southeast—dipping foliation, and pillows are somewhat flattened; a mineral lineation plunges about 600 SW. As shown on figure 2, the structures are assigned to D3, but could in part have resulted from D4. Large—Scale Structure The Dunbar dome is interpreted as a large scale fold—interference structure resulting from superposition of F2 and F3 folds modified by diapirism and the emplacement of granitoid intrusive rocks. The outline of the central core of the dome is mainly the result of superposed F2 and F3 folding. Its southern margin is the southwest limb of the major northwest—trending F2 antiform cored by Dunbar Gneiss. Small—scale structures indicate that the antiform plunges moderately southeast (fig. 2), and in the crestal area both the Dunbar Gneiss and the overlying Quinnesec Formation are intruded by the large body of Newingham Tonalite (see fig. 1). Presumably, the antiform is doubly plunging, to account for the westward closure of the dome, but this cannot be confirmed because of the absence of exposures in the extreme western part of the dome. The steeply dipping cover rocks along the western margin and fabrics indicative of high strain indicate that diapirism was intense in this boundary zone. Diapirism also modified the southern margin of the central core, as indicated by an intense foliation and west plunging mineral lineation. — The northwest and southeast margins of the central core of the Dunbar dome are subparallel to small—scale D3 structures, and are interpreted as the limbs of a major northeast—oriented antiform. The reentrant of Quinnesec Formation between the central core and the Pembine lobe, shown by the map pattern (fig. 2), is a major synform. The F3 flattening folds in the Quinnesec Formation within the reentrant and on the northwest margin indicate that the core rocks behaved in a more viscous manner than the cover rocks, perhaps indicating inflation of the core during D3. The northern, overturned margin of the central core, between the Hoskin Lake Granite and the Quinnesec Formation, was the site of intense D4 deformation, which nearly completely obliterated older structures. We interpret these structures as resulting from inflation of the core, especially its northern part. Evidence exists for at least one second—order diapir in the first order one, of the type described by Schwerdtner and others (1979). This is provided by the Niagara lobe, which is composed of nearly undeformed granite of Spikehorn Creek that transects at nearly right angles the outer (eastern) margin of the central core, composed here of Marinette Quartz Diorite. The granite in the Niagara lobe has a steep foliation near its walls, and the contact is in •part at least tectonic. The volcanic rocks of the Quinnesec Formation are molded around the margin of the dome. We conclude that the lobe of granite flowed differentially upward and outward in a plastic state during a late stage of dome inflation, in a manner similar to that described by Brun and others (1981). As a consequence of the second—order diapir, a "cleavage triple point" was developed in the supracrustal volcanic rocks at the intersection of the Niagara lobe and the eastern margin of the main dome. 11 �_ U Major Events (see caption) , p Rb—Sr Ages Biotite I U 000 0 0 0 0 Aplite dikes WR isochron (22 samples) U—Pb I I ' 0 0 0 o Zircon Ages Amberg Granite 0 Atheistane Quartz Monzonite Spikehorn Creek Granite o 0 0 0 o Newingham Tonalite Dunbar Gneiss Quinnesec Formation Sm-Nd Ages Dunbar Gneiss I 1.0 I I I 1.2 I 1.4 I 1.6 Age, I 1.8 I. 0 0 2.0 Ga Figure 3.——Summary of selected isotopic ages for rocks of the Dunbar gneiss dome and environs. The events shown are: (1) the main interval of Penokean igneous activity, (2) the post—Penokean 1,760—Ma igneous event, (3) the 1,600*50 Ma event that disturbed isotopic systems throughout much of the Precambrian of Wisconsin, (4) emplacement of the Wolf River batholith, and (5) Keweenawan igneous activity. Isotopic ages shown are from Aldrich and others (1965), Banks and Cain (1969), Banks and Rebello (1969), Van Schmus (1980), and USGS (unpublished Rb—Sr, U—Pb, and Sm—Nd ages). 12 �Following this reasoning, the Bush Lake lobe is possibly also a second order diapir. I I P We interpret the D1 structure in the Dunbar Gneiss as having formed than, and at greater crustal depths, than the regional deformation (D2) of the Dunbar Gneiss and the supracrustal rocks, for the deformation was accompanied by amphibolite—facies metamorphism and migmatization of the layered rocks; whereas D2 took place under less intense metamorphic conditions, indicative of relatively shallow depths. earlier Analysis of the regional geology indicates that the Dunbar dome was developed during regional deformation related to the Penokean orogeny. The regional structural fabric and perhaps also the persistent southwest—plunging stretching lineation in the core—cover boundary of the dome, could have The resulted from subhorizontal compression oriented north—northeastward. northeast elongation of the central core and of the Pembine granitoid lobe appear to be related to more local forces, perhaps thermal perturbations within the core of the dome, for D3 structures are virtually confined to the dome. An origin of the dome through stacking of thrust sheets was considered, but rejected, because of the lack of stratigraphic evidence and other structures suggestive of thrusting. Geochronology 4 The effects of repeated tectonic and thermal overprinting of rocks within and adjacent to the Dunbar dome are recorded in a spectrum of highly discordant isotopic ages (fig. 3). The principal units within the dome formed between 1,862*5 Ma and 1,835*6 Ma as shown by U—Pb zircon ages for the Dunbar Gneiss and granite of Spikehorn Creek, the oldest and youngest units, The supracrustal Quinnesec Formation has a U—Pb zircon age of respectively. 1,866*39 Ma (Banks and Rebello, 1969), which is not resolvable from the ages of the core rocks. The Athelstane Quartz Monzonite of Van Schmus and others (1975), cropping out southeast of the Dunbar dome, was approximately coeval with some of the core rocks as shown by a U—Pb zircon age of 1,836*15 Ma The Amberg Quartz Monzonlte of Van Schmus and others (Banks and Cain, 1969). (1975) intrudes the Athelstane Quartz Monzonite and is equivalent in age to high—level granitoids and felsic volcanic rocks in central Wisconsin (Smith, Data for two fractions of zircon from a sample of the Arnberg Quartz 1983). Monzonite (Van Schmus, 1980) define a chord with an upper intercept age of 1,756*19 Ma. Sm—Nd model ages of 2,130 and 2,280 Ma for two samples of Dunbar Gneiss (fig. 3) are substantially older than the crystallization ages defined by the Other Early Proterozoic igneous rocks in northern Wisconsin have zircon data. yielded similar "old" Sm—Nd ages (Nelson and DePaolo, 1982). The Sm—Nd ages, together with Pb—isotope data (Afifi and others, in press), strongly indicate a major involvement of Archean crustal material in the genesis of Early Proterozoic volcanic and plutonic rocks and syngenetic mineralization. 13 �Post—doming events have severely perturbed Rb—Sr. whole—rock and mineral Twenty—two whole—rock samples (5 to 10 kg each), representing both massive and gneissic units wiin e Dunbar dome, define a Rb—Sr isochron of 1,688*28 Ma, with an initial Sr ratio of 0.7038*0.0013 (fig. 4). Sr/ We attribute the disturbance of the Rb—Sr system at the whole—rock scale to open— system behavior related to cataclasis that variably affected all of the units in the dome. Recrystallization of biotite (and microcline where present) and sericitization and epidotization of plagioclase facilitated the mobility of Rb and Sr. Fluids undoubtedly played a major role in the migration of Rb and Sr as well as other elements. A relation between rock composition and degree of resetting is suggested by an isochrg agg of 1,733*43 Ma obtained by regressing only those samples with Rb! 6Sr ratios less than 3. This separation roughly divig9s t data according to rock type with the granites (sensu stricto) having Rb! Sr ratios greater than 3 and the tonalites and granodiorites having ratios less than 3. This correlation between rock composition and degree of resetting of the Rb—Sr system Is probably related to differences in physical properties of the rocks. The granites, being less biotitic and more quartz rich than the tonalites and granodiorites, probably deformed in a more brittle fashion, which led to a higher permeability and thus a greater opportunity for interaction with a fluid phase. Some of the units, although open systems on the sample—size scale (tens of centimeters), 9pea to have ematged closed at larger scales. For example, average Rb! 6Sr and 8 Sr/ Sr values calculated for the Dunbar Gneiss (11 samples) by weighting each sample by its Sr content, are used to calculate a model age of 1,875*70 Ma, using an initial Sr ratio of 0.7017. Although the uncertainty is large, a model age is indistinguishable from the crystallization age given by the U—Pb zircon data. ages. Rb—Sr biotite ages of rocks within the Dunbar dome decrease from east to west (figs. 3 and 5). This variation is part of a regional pattern of Rb—Sr biotite ages that extends north to the Marquette trough (Peterman and Sims, 1984). Within this area, 54 biotite ages define a tripartite distribution with well defined modes at 1,580*70 Ma, 1,320*50 Ma, and 1,140*30 Ma. The older group is a composite that contains the tightly clustered 1,630*30 Ma ages for Archean rocks of the southern complex in northern Michigan (Van Schmus and Woolsey, 1975) and slightly younger ages from areas to the south (fig. 5). Van Schmus and Woolsey correlated the 1.63—Ga ages with a cryptic event that has affected Precambrian rocks over much of Wisconsin (fig. 3). A younger resetting event at 1,140*30 Ma, recognized mainly in the western third of the Dunbar dome, occurred contemporaneously with Keweenawan (Middle Proterozoic) rifting and igneous activity. The coincidence of age discontinuities with northwest— and northeast—trending, vertically lineated shear zones (fig. 5) strongly suggests that differential uplift was a causative factor in producing the age pattern. Apparently, stresses attendant with rifting were transmitted over considerable distances and resulted in reactivation of existing faults and vertical adjustments of large magnitude. The intermediate group of ages, 1,320*50 Ma, does not correlate with any known events in the region (fig. 3). Aldrich and others (1965) suggested a thermal event at this time, but they did not elaborate on a cause. Possibly, the surface now characterized by the 1,320—Ma age group was uplifted and cooled during the Keweenawan from a depth at which the biotite systems were only partially reset. 14 �1.2 DUNBAR DOME (ALL SAMPLES) 1.1 C/) T = 1688 ± 28 Ma IR = 0.7038 ± .0013 1.0 Co Co 0.78 L.. U) 1= 1733± 43 Ma IR = 0.7032 ± 0.9 0.76 Co 0.74 0.8 0.72 0.70 0.7o 4 0.0 12 8 87Rb 0.8 1.6 2.4 16 / 86 Sr Figure 4.——Whole—rock Rb—Sr isochron for samples of all units within the Dunbar dome. The isochron of 1,68828 Ma is8aseg on all of the samples (22). The inset shows samples with Rb! 6Sr ratios of less than 3 (mainly tonalites and granodiorites). 15 20 �R • 1.66 * ,1 .69 '1.80 • .63 MICHIGAN .65 1.55 I I 1.62 .68 I ,1.39 46° •..' I S — / ,/ I: I I I WISCONSIN SHEAR ,136 •1.39 I 0 I 10 MILES 0 I 10 KILOMETERS •1.39 I I Figure 5.——Rb—Sr biotite ages in billions of years (Ga) for Archean and Early Proterozoic rocks in northeastern Wisconsin and adjacent northern Michigan. Data are from Van Schmus and Woolsey (1975) for the southern Complex, Aldrich and others (1965) for the Felch trough area, and Peterman and Sims (unpublished) for the Dunbar dome and vicinity. 16 I I �_ Evolution of Dome r [ r p p The stratigraphic—tectonic evolution of the Dunbar dome spanned a relatively short time of about 30 Ma, from about 1,865 to 1,835 Ma (table 2), during the Early Proterozoic. The first recognized event was the formation of the volcanic and plutonic (tonalitic) protoliths of the Dunbar Gneiss, probably as part of a succession covering a large area in an oceanic regime. Following an early deformation (D1) at moderate crustal depths and the rise of the Dunbar Gneiss to shallower crustal levels, quartz sand, dolomite, and volcanic tuff(?) were deposited unconformably on the Dunbar Gneiss in a shallow—water environment. Later, vast quantities of tholeiitic volcanic rocks (Quinnesec Formation) were deposited in deep water, probably in a back—arc basin (Schulz, 1984). Comagmatic, subvolcanic sills of maf Ic composition were intruded into the Onset of regional compression produced a northwest—trending, volcanic pile. generally steeply dipping, structural fabric (D2) In the basement and supracrustal successions. After culmination of the regional deformation (D2), the Marinette Quartz Diorite was emplaced in the northeast part of the Dunbar dome, apparently as a layered, crescent—shaped sheet essentially along the contact between the underlying Dunbar Gneiss and the overlying Quinnesec volcanics. Subsequently, the Newinghain tonalite was intruded. The Newingham was emplaced at the base of the Quinnesec Formation, and it contains abundant xenoliths of both the Quinnesec Formation and the Dunbar Gneiss in the contact zone. The Marinette Quartz Diorite was emplaced before or during deformation D3, which produced dominantly northeast—trending structures in the rock and was accompanied by amphibolite—facies metamorphism in the hotter and deeper(?) northern part of the dome. During later stages of the deformation (D3i), the Newingham Tonalite was emplaced and then deformed. The major structure imposed on it was a cataclastic (ductile) foliation that dominantly trends northeastward and has a northwest vergence. A major northeast—trending antiforin resulting from deformation D3 produced the northeast—trending margins of the central core of the dome. Concomitantly with rise of the thermal isograds in the dome, the Hoskin Lake Granite was emplaced along the northern margin of the dome during late stages of D3, mainly as a magma but in part by K—metasomatic replacement of the Marinette Quartz Diorite and the Dunbar At this stage, K—bearing fluids permeated parts of the central core, Gneiss. selectively replacing parts of the Marinette Quartz Diorite and the Dunbar Gneiss, apparently by migration of the fluid along more permeable cataclastic K—metasomatism continued In the northern, hotter part of the dome; and zones. rise and inflation of the central core produced a northward vergence, and was accompanied by rotation of the country rocks in the margins of the dome into Contemporaneously, the cover conformity with the core—cover boundary (D4). rocks adjacent to the central core were metamorphosed to amphibolite facies. The thermal metamorphic aureole was exeedingly wide on the northern and northwestern margins of the central core, where the amphibolite fades zone is at least 8 km wide, far in excess of that to be expected by conduction of heat from a magma such as the Hoskin Lake Granite. The thermal activity in the core led to the emplacement of abundant granitoid dikes in the inner (amphibolite grade) part of the metamorphic aureole. Continued rise of the geotherms in the northern segment of the dome led to development of a granitic magma (granite of Spikehorn Creek), which was emplaced by outward, diapiric 17 �1,865 1,860 —— H 1,835 . Age in Ma D1 Deformation of Dunbar Gneiss and supracrustal rocks on northwest axes, to produce regional structural fabric D2 —_——— — I_J J U I Formation of volcanic and plutonic (tonalitic) protolith of Dunbar Gneiss Foliation parallel to layering in Dunbar Gneiss of Cain (1964); metamorphism of Dunbar to amphibolite facies, migmatization, and intrusion of granite pegmatite and aplite Unconformity Deposition of shallow—water sediments Uncoriformi ty Deposition of a thick succession of tholeiitic volcanic rocks (Quinnesec Formation) Deformation on northeast axes (restricted areally), after emplacement of Marinette Quartz Diorite and Newingham Tonalite Emplacement of Hoskin Lake Granite, in part by K—metasomatism of older rocks Continued rise in isotherms centered on northern part of core accompanied by diapiric rise of dome, rotation of older structures into conformity with core—cover boundary, and metamorphism of adjacent cover rocks and northern part of core rocks Emplacement of granite of Spikehorn Creek and, possibly, granite of Bush Lake into Niagara and Bush Lake lobes, respectively, as diapirs; and intrusion of aplite and pegmatite into Dunbar Gnelss Quartz—tourmaline veinlets and fluorite in brittle fractures Event D3 D4 Deformation Table 2.——Stratigraphic—tectonic evolution of Dunbar dome - �! flow into the Niagara lobe, a second—order dome. The granite of Bush Lake was intruded at about the same time. At a late stage of evolution of the Dunbar dome, quartz and tourmaline were mobilized into brittle fractures both within and outside the core, and fluorite was mobilized locally into fractures in the Hoskin Lake Granite. Tectonic Environment r r- [ Recognition that the Dunbar Gneiss and, by implication, other bodies of crystalline rocks in northern Wisconsin are cores of domal structures exposing deeper crustal rocks has an important bearing on the Proterozoic stratigraphy and paleogeography of the region during Early Proterozoic time. Crystalline rocks of Early Proterozoic age, such as those exposed in the Dunbar dome, have not been delineated in northern Michigan despite extensive, detailed mapping, and it seems certain that they are absent or at least of minor significance. Also, in northern Wisconsin, volcanic rocks dominate the su#racrustal sequence, whereas Interbedded sedimentary and volcanic rocks characterize the Marquette Range Supergroup in Michigan. Chemically, the volcanic rocks in the two parts of the region differ substantially. Those in northern Michigan, as indicated by volcanic rocks in the Hemlock Formation, are largely bimodal with abundant tholeiltic basalt and minor high—K20 rhyolite. The basalt shows strong iron enrichment and high T102 and incompatible—element contents (Fox, 1983); they are compositionally similar to continental rift basalts, such as those of the Keweenawan in Minnesota. In contrast, the volcanic rocks of the Quinnesec Formation range from basalt through andesite to rhyolite, lack strong iron enrichment, and have back—arc basin compositional affinities (Schulz, 1984). Other contrasts in the two areas are marked differences in the mineral deposits contained in the Early Proterozoic successions (Sims, 1976). Iron—formations and associated enriched iron deposits are the dominant ore deposits in the Marquette Range Supergroup of Michigan, whereas massive sulfide deposits are dominant in northern Wisconsin and iron—formations are thin and sparse. A critical stratigraphic problem is the relationship of the shallow—water sedimentary rocks in the Dunbar dome to the shallow—water deposits at the base (Chocolay Group) of the Marquette Range Supergroup. We suggested earlier (Schulz and Sims, 1982) that the strata in both areas are possibly correlative; but the chemical differences in the overlying volcanic rocks and other differences, such as the volume of Early Proterozoic plutonism in the two terranes, now lead us to interpret the sedimentary rocks as being homotaxial rather than stratigraphically correlative. Data presented here, together with regional geologic relationships (fig. 1; Morey and others, 1982), are consistent with an interpretation that the Wisconsin magmatic zone is an exotic terrane that evolved in an oceanic—arc setting and was attached to the North American continent during the Early Proterozoic. Apparently the boundary between the two Proterozoic terranes is the Niagara fault zone, as suggested by Larue (1983). Probably the doming, which exposes the gneiss and granitoid rocks in the cores, was in response to collision of the two crustal blocks, which triggered the Penokean orogeny. The westward extent of the Wisconsin magmatic zone remains equivocal, for if 19 �indeed it does extend across the midcontinent rift system into Minnesota, only remnants of the vast accumulation of Early Proterozoic volcanic rocks apparently remain there. * The conclusions reached here support the earlier interpretation of Van Schmus (1976), based on broad geologic considerations, that the Early Proterozoic epicratonic successions in the Great Lakes area accumulated at a continental margin. A variant of this interpretation later was presented by Cambray (1978) and Larue (1983). The earlier interpretation of one of us (Sims, 1976; Sims and others, 1981) that the Early Proterozoic sequences in the Great Lakes area accumulated in an intracratonic setting no longer is tenable for the whole region. On the basis of new chemical and structural data obtained in this and other parts of Wisconsin and northern Michigan, Schulz and others (1984) have proposed a tectonic model of early crustal rifting and spreading, subsequent subduction and formation of a complex volcanic arc, and collision of the arc, first with Archean crust on the south and then with the continental margin Proterozoic sequence and Archean crust of northern Michigan on the north (the Penokean orogeny). 20 �REFERENCES CITED Afifi kfifa, Doe, B. R., Sims, P. K., and Delevaux, M. N., 198.4, U—Th—Pb isotopic chronology of sulfide ores and rocks in the Early Proterozoic metavolcanic belt of northern Wisconsin: Economic Geology (in press). Aldrich, L. T., Davis, G. L., and James, H. L., 1965, Ages of minerals from metamorphic and igneous rocks near Iron Mountain, Michigan: Journal of Petrology, v. 6, p. 445—472. Banks, P. 0,, and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: Journal of Geology, v. 77, p. 208—220, r Banks, P. 0., and Rebello, D. P., 1969, Zircon age of a Precambrian rhyolite, northeastern Wisconsin: p. 907—910. Geological Society of America Bulletin, v. 80, Bayley, R. W., Dutton, C. E., and Lamey, C. A., 1966, Geology of the Menominee iron—bearing district, Dickinson County, Michigan, and Florence and Marinette Counties, Wisconsin: U.S. Geological Survey Professional Paper 513, 96 p. Brun, J. P., Gapais, D., and LeTheoff, B., 1981, The mantled gneiss domes of Kuopia (Finland): Interfering diapirs: Tectonophysics, v. 74, p. 283—304. r Cain, J. A., 1964, Precambrian geology of the Pembine area, northeastern Wisconsin: Papers of Michigan Academy of Science, Art, and Letters, v. 49, p. 81—103. Cambray, F. W., 1978, Plate tectonics as a model for the environment of deposition and deformation of the early Proterozoic (Proterozoic X) of northern Michigan: Geological Society of America Abstracts with Programs, v. 10, no. 7, p. 376. Dutton, C. E., 1971, Geology of the Florence area, Wisconsin and Michigan: U.S. Geological Survey Professional Paper 633, 54 p. Dutton, C. E., and Linebaugh, R. E., 1967, Map showing Precambrian geology of the Nenominee iron—bearing district and vicinity, Michigan and Wisconsin: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1—466 (scale 1:125,000). Ervin, C. P., and Hammer, S. H., 1974, Bouguer anomaly gravity map of Wisconsin: Wisconsin Geological and Natural History Survey (scale 1:500,000). Fox, T. P., 1983, Geochemistry of the Hemlock Metabasalt and Kiernan sills, Iron County, Michigan [Unpublished M.S. thesis]: East Lansing, Michigan, Michigan State University, 81 p. 21 �Larue, D. K., 1983, Early Proterozoic tectonics of the Lake Superior p region: Tectonostratigraphic terranes near the purported collision zone, in Medaris, L. G., Jr., Early Proterozoic geology of the Great Lakes region: Geological Society of America Memoir 160, p. 33—47. Morey, G. B., Sims, P. K., Cannon, W. F., Mudrey, M. G., Jr., and Southwick, D. L., 1982, Geologic map of the Lake Superior region, Minnesota, Wisconsin, and northern Michigan: Minnesota Geological Survey State Map Series 5—13 (scale 1:1,000,000). Nelson, B. K., and DePaolo, D. J., 1982, Crust formation age of the North American midcontinent: Geological Society of America Abstracts with Programs, v. 14, no. 7, p. 575. Peterman, Z. E., and Sims, P. K., 1984, Middle Proterozoic events in northeast Wisconsin and adjacent Michigan as defined by Rb—Sr biotite ages: Proceedings, 30th Annual Institute on Lake Superior Geology, Wausau, Wisconsin (in press). Prinz, W. C., 1965, Marinette Quartz Diorite and Hoskin Lake Granite of northeastern Wisconsin, in Cohee, G. E., and West, W. S., Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1964: U.S. Geological Survey Bulletin 1224—A, p. A1—A77. Ramberg, Hans, 1967, Gravity, deformation and the Earth's crust: Press, London, 214 p. Academic Schulz, K. J., 1984, Early Proterozoic Penokean igneous rocks of the Lake Superior region: Geochemistry and tectonic implications: Proceedings, 30th Annual Institute on Lake Superior Geology, Wausau, Wisconsin (In press). Schulz, K. J., LaBerge, G. L., Sims, P. K., Peterman, Z. E., and Kiasner, J. S., 1984, The volcanic—plutonic terrane of northern Wisconsin: Implications for Early Proterozoic tectonism, Lake Superior region: Program with Abstracts, Geological Association of Canada—Mineralogical Association of Canada, London, Ontario, Canada (in press). Schulz, K. J., and Sims, P. K., 1982, Nature and significance of shallow water sedimentary rocks in northeastern Wisconsin [abs.]: Proceedings, 28th Annual Institute on Lake Superior Geology, International Falls, Minnesota, p. 43. Schwerdtner, W. M., Stone, D., Osadetz, K., Morgan, J., and Stott, G. M., 1979, Granitoid complexes and the Archean tectonic record in the southern part of northwestern Ontario: Canadian Journal of Earth Sciences, v. 16, p. 1965—1977. Sims, P. K., 1976, Precambrian tectonics and mineral deposits, Lake Superior region: Economic Geology, v. 71, p. 1092—1118. 22 �1980, Boundary between Archean greenstone and gneiss terranes in northern Wisconsin and Michigan: Geological Society of America Special Paper 182, p. 113—124. Sims, P. K., Card, K. D., and Lumbers, S. B., 1981, Evolution of early Proterozoic basins of the Great Lakes region, in Campbell, F. H. A., ed., Proterozojc basins of Canada: Geological Survey of Canada Special Paper 81—10, P. 379—397. Sims, P. K., Peterman, Z. E., Zartman, R. E., and Benedict, F. C., 1984, Geology and geochronology of granitoid and metamorphic rocks of Late Archean age in northwestern Wisconsin: U.S. Geological Survey Professional Paper 1292—C (in press). Smith, E. I., 1983, Geochemistry and evolution of the early Proterozoic, post—Penokean rhyolites, granites, and related rocks of south—central Wisconsin, U.S.A.: Geological Society of America Memoir 160, p. 113—128. Van Schinus, W. R., 1976, Early and middle Proterozoic history of the Great Royal Society of London Philosophical Lakes area, North America: Transactions, ser. A280, no. 1298, p. 605—628. 1980, Chronology of igneous rocks associated with the Penokean orogeny Geological Society of America Special Paper 182, p. in Wisconsin: 159—168. Van Schmus, W. R., Thurman, E. M., and Peterinan, Z. E., 1975, Geology and Rb—Sr chronology of middle Precambrian rocks in eastern and central Geological Society of America Bulletin, v. 86, p. 1255—1265. Wisconsin: Van Schmus, W. R., and Woolsey, L. L., 1975, Rb—Sr geochronology of the Republic area, Marquette County, Michigan: Canadian Journal of Earth Science, v. 12, p. 1723—1733. 23 �I Geochemistry of the Dunbar gneiss—granitoid dome, Northeastern Wisconsin by K. J. Schulz!', P. K. Sims2/, and Z. E. Peterinan2l U.S. Geological Survey, Reston, VA 22092 2/ U.S. Geological Survey, Denver, CO 80225 2L �Introduction Samples from the major rock units that make up the Dunbar gneiss— granitoid dome have been analyzed for major and trace elements (including rare—earth elements — REE) to determine their compositional characteristics and aid in deciphering their petrogenesis. Representative analyses are presented in tables 1 and 2 and shown graphically in figures 1 through 9. Dunbar Gneiss Samples of Dunbar Gneiss range from tonalite to granite, are calc—alkaline (figs. 1 and 2), and define general trends of decreasing Al203, FeOT, MgO, CaO, Ti02, Na20, and Sr contents and increasing K20 and Rb contents with increasing Sb2 content. Except for mafic amphibolite units found interlayered with the Dunbar Gneiss, samples in which Sb2 is less than 60 weight percent appear to be absent. The rocks have Rb/Sr ratios ranging from about 0.15 to 1.0 (fig. 4) and K/Rb ratios ranging from about 260 to 160; increasing Rb/Sr ratios correlate positively with Si02 content. The chondrite—normalized REE data for Dunbar Gneiss samples are shown in figure 5. All samples show steep patterns with relatively enriched light—REE (chondrite—norinalized La=[La]1q=71—360) and depleted heavy—REE ([La/Yb]N=45—18; except one example at 217). The sample with the steepest slope and most depleted heavy—REE is from a leucocratic layer within more biotitic tonalite gneiss. The two samples having the lowest total REE abundances have the highest S102 content (i.e., 75 and 74 weight percent). Except for these two samples, the rocks show small negative Eu anomalies. 25 �Table 1.—— Representative analyses of samples from the Dunbar Gneiss and Newingham tonalite. Si02 A1203 Fe203 FeO MgO CaO Na20 1(20 Ti02 P205 MnO H20 H20 CO2 1 2 3 4 61.7 17.5 1.02 4.41 1.64 3.20 4.22 3.16 0.82 0.18 63.6 16.3 0.88 4.07 1.64 3.87 4.21 2.42 0.82 0.26 0.09 0.37 0.05 0.03 75.0 13.5 0.08 1.22 0.22 1.25 3.17 4.51 0.14 <0.05 <0.02 0.24 0.10 0.03 49.8 15.7 1.50 6.70 8.50 11.6 2.24 1.06 0.35 <0.05 0.19 1.68 <0.01 <0.01 0.09 0.85 0.02 0.03 *Rb — — — — Sr y Zr Nb Th Ta Hf Cr Co Sc Zn Rb Ba Cs La Ce Nd Sm Eu Gd Tb Yb Lu 118 443 5 66.6 18.0 1.1 2.4 1.6 4.5 4.1 1.7 0.37 0.18 0.03 0.82 0.10 0.05 229 232 — 282 6 68.0 15.7 0.51 2.64 1.38 3.53 3.88 2.15 0.37 0.13 0.04 — L0I=0.51 — 67 656 7.8 68 — 126 14.5 3.6 10.0 3.78 6.75 7.8 10.2 5.13 74 137 883 5.65 35.1 61.8 27 5.1 1.17 4.4 0.66 1.16 0.20 3.1 10.3 3.95 7.6 25 9.9 8.0 — 117 810 4.9 63.2 119 34 7.13 1.76 — 0.94 1.55 0.21 2.2 12.2 2.58 2.39 17 1.34 1.05 26 250 1620 10.9 26.1 42.1 15.9 2.47 0.67 1.4 — 0.52 0.06 — 0.46 0.14 0.74 323 39.5 45.8 117 42 80 4.22 3.8 6.0 — 1.14 0.45 — 0.38 2.07 0.33 0.96 2.6 0.44 2.0 14 8.77 6.74 — 40 570 0.81 12.5 22.8 7.2 1.27 0.44 — 0.11 0.18 0.03 Major and minor elements by rapid rock methods or XRF *By XRF analysis +By instrumental neutron activation analysis. L0I = Loss on ignition 1—3 — Dunbar Gneiss 4 — Amphibotite within Dunbar Gneiss 5—6 — Newingham tonalite 26 1.8 6.0 1.75 3.4 42 6.97 4.5 — 69 961 6.1 27.9 52.0 17 2.67 0.77 — 0.26 0.42 0.06 — �H eOT I _ Dashed Brown, 1982). lines show field for igneous rocks from convergent plate margins (from Figure 1.--Fe01-MgO-Na20+K20 diagram for rocks of the Dunbar diie. Na20 +1<20 — — gO — I1 I I' �co r') CD .4 C-,. 0 0 \ 0 \0 QD 0•-• 0 0 U 0 • . wt.%SiO I S 0 DG owO co0 Oc No Lake Granite (may include MQD) (data plotted includes that of Cudzilo, 1978). Circle with star = Atheistane tuartz Monzonite. Figure 2.--Moclified Peacok diagram for rocks of the Dunbar dome. New = Newingham tonalite, DG = Dunbar gneiss, MQD = Marinette Quartz Diorite, HLG = Hoskin 0 U I• UiL II iJ �— 2w1% Na10 — ———— Falls quartz diorite. Other labels as in figure 2. Figure 3.--K2O-Na20 diagram for rocks of Dunbar dome. ATH = Atheistane Quartz Monzonite; 1FF = Twelve Foot r') (0 — E I00 Sr ppm 0 H IC 0 -t--- 0 l—— — a— I I Figure 4.--.Rb-Sr variation in rocks of Dunbar dome and Athelstane Quartz Monzonite. Aplites ciii) -— ___ �(A) Lo Ce II Nd I \AMPH I I I I 5n uGdTh DUNBAR I I 'lb IlL GNEISS I J Formation. H - ——— Figure 5.--Chondrite normalized REE for samples of Dunbar Gneiss (solid lines) and amphibolite enclaves in gneiss (Amph). Doted field for basalts of the Quinnesec — foo- 100_ Figure 6.--Chondrite normalized REE for samples of Newingham tonalite. II Ii �The amphibolites within the Dunbar Gneiss are basaltic in composition (Table 1) and are generally similar to the basalts of the Quinnesec Formation (Schulz, this volume) except for having higher 1(20 and relatively enriched La and Ce contents. The rare—earth elements Sm through Lu show a steep positive slope in the amphibolites (fig. 5) whereas the slope of La to Ce is distinctly negative. The steep positive slope of the heavy REE is similar to that observed for Quinnesec basalts which are strongly depleted in light REE (fig. 5), suggesting that the amphibolites were originally also depleted in light REE. The present enrichment of light REE (i.e., La and Ce) in the amphibolites, as well as 1(20, may have resulted from inter- action with their surrounding light—REE—enriched felsic gneisses during amphibolite facies metamorphism. On the bases of the field and geochemical data, the protolith for the Dunbar Gneiss is interpreted, to have been a sequence of interlayered inter- mediate to felsic volcanic and related intrusive rocks. The overall compositional similarity with intermediate to felsic rocks of recent magmatic arcs formed at convergent—plate margins (Brown, 1982; fig. 1) suggests that the Dunbar Gneiss protolith may have formed in a similar tectonic setting. The steep REE patterns suggest that the parent maginas were probably derived from mafic to intermediate, garnet—bearing sources (Hanson, 1981), perhaps at lower crustal levels. The trace—element characteristics of the Dunbar Gneiss samples are distinct from those of the structurally younger intermediate to felsic volcanic rocks of northeastern Wisconsin (Schulz, this volume); this difference supports the structural interpretation that the Dunbar Gneiss represents the product of an older cycle of magtnatic activity. 31 �Newingham Tonalite The intrusive Newingham tonalite is remarkably hongeneous in composition and shows only a small range in Si02 content (fig. 2). The tonallte is higher in A1203, MgO, CaO, and Sr and is lower in FeOT, Ti02, K20, and Rb than the Dunbar Gneiss (Table 1 and figs. 3 and 4). It is also characterized by lower Rb/Sr ratios (<.10) (fig. 4) and higher K/Rb ratios (>260). The samples show steep REE patterns (fig. 6) ([La/Yb]N=48—40) somewhat similar to those of the Dunbar gneisses but with mostly lower total REE abundances and show either no or slightly positive Eu anomalies. A strong correlation exists between increasing Rb/Sr ratio, increasing total REE abundance, and decreasing magnitude of the Eu anomaly. This correlation reflects the role of plagioclase fractionation in the magmas parental to these rocks. The Newingham tonalite is calcic (fig. 2) and is compositionally similar to Archean tonalites such as those of the Vermilion district of Minnesota (Arth and Hanson, 1975) and elsewhere (O'Nions and Pankhurst, 1978). Their low Rb/Sr ratios, high Sr contents, and strong heavy—REE depletions have been considered indicative of melts derived by partial melting of eclogite or garnet amphibolite (Arth and Hanson, 1972). However, the relatively high light—REE contents of the Newingham tonalite samples would preclude a typical tholeiitic basalt (which has depleted or flat light REE) as a parent (Hanson, 1981). A lithologically heterogeneous lower crust, probably more mafic than the source for the protoliths of the Dunbar gneisses (i.e., lower feldspar content at high grades of metamorphism), may have been the source of the parent magma of the Newingham tonalite. 32 b �r Marinette Quartz Diorite The Marinette Quartz Diorite (MQD) is distinct from the other units of the Dunbar dome in having alkalic to alkali—calcic affinities (fig. 2). These affinites are reflected in the high total alkali, Ti02, P205, and REE contents of the nre mafic samples (Table 2). The Marinette Quartz Diorite has a complex northern border zone where it is intruded by and is in contact with the Hoskiri Lake Granite. Throughout a broad zone, the MQD is variably metasomatized and partially assimilated by the Hoskin Lake Granite, resulting in intermediate to felsic compositions that overlap with those of the granite. Away from this broad contact zone, the MQD appears to be relatively inafic and more uniform in composition although more data are needed to fully establish its original compositional range. The chondrite—normalized REE patterns for samples of MQD are shown in figure 7. Most of the samples have similar steep REE patterns in which [La]N ranges from 170 to 340 and [Th]N ranges from 6.5 to 12. Samples mostly show a small negative or no Eu anomaly; the one sample having a large positive Eu anomaly contains abundant megacrysts of plagioclase. Two samples from within the contact zone of the MQD with the Hoskin Lake Granite have lower REE abundances than the other samples (fig. 7) and patterns similar to those of the Hoskin Lake Granite (compare figs. 7 and 8). The alkaline affinity and trace—element characteristics of the MQD suggest that the parent magma was alkaline, perhaps an alkali basalt. The relatively early occurrence of alkaline magmatism in a dominantly caic—alkaline magmatic terrane appears to be somewhat anomalous but may have an analogue in the early alkalic plutons present within the caic—alkaline plutonic belt of California (Miller, 1977). 33 �Table 2.—— Representative analyses of samples from the Marinette Quartz Diorite, I Hoskin Lake Granite, granites of the Bush Lake and Niagara lobes, and associated late aplites. Si02 A1203 Fe203 FeO MgO CaO Na20 1(20 Ti02 P205 MnO H20 H20 CO2 1 2 3 51.8 16.8 1.97 7.77 3.50 6.18 3.88 2.62 2.42 65.0 15.9 0.64 3.01 1.56 3.20 4.30 3.69 0.79 0.18 0.07 0.44 0.02 0.04 69.1 15.0 0.56 2.67 0.91 1.91 3.45 4.69 0.51 0.11 0.05 0.63 0.13 0.08 0.64 0.15 1.23 0.07 <0.01 *Rb — — — — Sr Y Zr Th Ta Hf Cr Co Sc Zn Rb Ba Cs La Ce Nd Sm Eu Cd Tb Th Lu 3.1 19.4 3.85 5.87 6.4 28.5 13.1 94 84 701 4.36 57.2 118 60 10.2 2.50 8.6 1.01 2.20 0.325 28 23 3.50 4.63 17 9.67 6.35 58 128 1050 153 279 73.0 13.7 0.31 1.78 0.41 1.06 3.51 4.63 0.18 <0.05 0.05 — L0I—0.44 — 244 117 15 163 — 137 5 6 72.7 13.6 0.27 2.07 0.40 1.19 2.74 5.48 0.27 0.09 0.04 0.39 74.6 13.7 0.23 0.96 0.15 0.65 3.43 5.06 0.03 <0.05 0.03 — 0.12 L0I0.28 0.02 329 58 154 57 1: 33.7 4.61 5.91 22 5.75 3.31 44 25.4 5.50 4.9 46 23 2.41 18 159 705 4.21 56.3 85.6 28 28 4.43 0.89 3.3 0.39 1.38 0.19 1.70 — 244 466 7.1 32.0 59.0 18 3.22 0.54 — 0.52 1.14 0.19 7 74.2 14.5 0 0.65 0.12 0.43 5.21 3.90 <0.02 <0.05 <0.02 — L0I=0.17 — 270 143 31 :.5 3.42 54.3 83.1 4.21 1.12 3.3 0.34 1.08 0.15 4 454 9.75 98 35 60 I 3.90 5.0 2.54 4.85 47 283 787 5.73 69 121 48 8.45 0.88 9.0 0.85 2.6 0.43 24.0 5.78 2.80 23.2 2.90 22 28 0.74 3.20 — 321 184 12.8 19.6 42 16 4.05 0.29 — 0.99 3.51 0.54 6.6 0.60 18.1 — 459 65 1.5 5 11 — 3.9 0.03 — 1.44 11.1 1.56 Major and minor elements by rapid rock methods or XRF *By XRF analysis +By instrumental neutron activitation analysis. LOI = Loss on ignition 1—2 — Marinette Quartz Diorite 3—4 — Hoskin Lake Granite (4 from Niagara lobe) 5—6 — Granite of the Bush Lake lobe 7 — Aplite dike cutting Dunbar Gneiss I �4oo I MARINETTE QUARTZ DIORITE S. 100 40 to— —— 4 I I LaCe I Nd I I I I 5M EtLS Th Figure 7.--Chondrite normalized REE for samples of Marinette Quartz Diorite. 35 I I YbLLL �Hoskin Lake Granite and Granites of the Bush Lake and Niagara Lobes The granites of the Niagara and Bush Lake lobes and the Hoskin Lake Granite share overall chemical similarities although systematic differences are recognized (Table 2). Relative to the more felsic segments of the Dunbar Gneiss, these granites have slightly higher K20, Ti02 and Rb contents and lower A1203, MgO, CaO, and Na20 contents. The granite of the Niagara lobe and the Hoskin Lake body are compositionally similar except that the Hoskin Lake Granite has a slightly higher K20 content. Rb/Sr ratios range from about 0.55 to 2.0 (fig. 4) and show a positive correlation with increasing Sb2 content; K/Rb ratios range from about 250 to 155 and show a negative correlation with increasing Si02 content. The samples show light—REE enrichment, small to moderate negative Eu anomalies, and decreasing light—REE abundance with increasing Si02; they also show only slightly fractionated heavy—REE (fig. 8). The granite of the Bush Lake lobe is compositionally distinct from that of the other two bodies in being slightly higher in average Sb2 and 1(20 contents and in having higher K20/Na20, U/Th and Rb/Sr ratios. The REE patterns are also distinctive (fig. 8) and have large negative Eu anomalies, relatively flat heavy—REE slope, and significant depletion in the light—REE with increasing Si02 content. Intruding the western part of the Dunbar dome are numerous garnet— bearing aplite and pegmatite bodies. The aplites are strongly depleted, relative to the granites, in FeOT, MgO, CaO, Ti02, P205, MnO, Sr, Zr, Ba, Eu, and light—REE but are enriched in Y, Ta, Nb, Rb, and the heavy—REE (Table 2 and figs. 4 and 8). They also show very low Zr/Hf (<17) and Nb/Ta (<4.7) ratios. 36 �400- 100 - AP- 40—— Bi N 10 I I I LaC.e I I Tb Nd Figure 8.--Chondrite normalized REE for samples of Hoskin Lake Granite (HL), Bush Lake granite (BL) and aplites cutting Dunbar Gneiss (AP). 37 �I The compositional characteristics of these aplites are not compatible with their derivation by partial melting of the Dunbar Gneiss. Rather, they are interpreted as the late—stage differentiates of the granite of the Bush Lake lobe. Shown in figure 9 are the relative enrichments and depletions in the average composition of the aplites relative to the least fractionated granite of the Bush Lake lobe (i.e., lowest Si02 and highest Sr contents). The enrichment and depletion patterns are similar to those documented by Hildreth (1979) for the compositionally zoned silicic Bishop tuff except for Al, Mn, Sm, Hf and Th. Hildreth (1979; 1981) discussed in some detail the problems related to explaining such elemental fractionations by any model of crystal settling or rock assimilation, and he proposed a model of liquid—state convection—driven thermogravitational diffusion to account for the relative geochemical enrichments and depletions. However, Mittlefehldt and Miller (1983) have recently suggested that fractionation / of REE—rich accessory phases (in particular, monazite) in conjunction with feldspar and ferromagnesian phases can also produce similar geochemical patterns in felsic magmas. Present data for the granite of the Bush Lake lobe and aplite association do not allow critical testing of the alternative hypotheses. It may be significant, however, that Th and the light REE are depleted in the aplites relative to the granite of the Bush Lake lobe (fig. 9), perhaps reflecting the fractionation of monazite (Mittlefehldt and Miller, 1983). 38 * �(0 (A) TT1 fl -fl -n - Figure 9.--Enrichment factors in average aplite relative to Bush Lake granite compared to those of the Bishop tuff (Hildreth, 1979). See text for discussion. —— = �Conclusions The ineta—igneous rocks of the Dunbar gneiss—granitoid dome show a progression with progression of time to more silicic and higher 1(20 compositions. This reflects, at least in part, a progressive change in the nature the sources providing the more evolved magmas. The overall caic—alkaline nature of these rocks and their changes in chemistry with time are similar to those observed in recent maginatic arcs formed at convergent—plate margins (Brown, 1982). The compositions of these gneissic and granitoid rocks, particularly when taken in conjunction with the geological and geochemical evidence from the surrounding volcanic rocks (Schulz, this volume), strongly suggest that plate—tectonic and maginatic processes largely similar to those recognized to be active today were already operative in the Early Proterozoic. 4O b �r t References Arth, J. G., and Hanson, G. N., 1972, Quartz diorites derived by partial melting of eclogite or amphibolite at mantle depths: r Petrol., Contrib. Mineral. v. 37, p. 161—174. Arth, J. G., and Hanson, G. N., 1975, Geochemistry and origin of the early Precambrian crust of northeastern Minnesota: Geochim. Cosmochim. Acta, v. 39, p. 325—362. Brown, G. C., 1982, Calc—alkaline intrusive rocks: their diversity, evolution, and relation to volcanic arcs, in Thorpe, R. S., ed., Andesites: New York, John Wiley and Sons, p. 437—461. Cudzilo, T. F., 1978, Geochemistry of Early Proterozoic igneous rocks in northeastern Wisconsin and Upper Michigan [Ph. D. thesis]: Lawrence, University of Kansas, 194 p. Hanson, G. N., 1981, Geochemical constraints on the evolution of the early crust. Phil. Trans. Royal Soc. London, A 301, p. 423—442. Hildreth, E. W., 1979, The Bishop Tuff: zonation in silicic magma Evidence for the origin of compositional chambers. Geol. Soc. America Special Paper 180, p. 43—75. Hildreth, E. W., 1981, Gradients in silicic magma chambers: for lithospheric magmatism: implications Jour. Geophys. Res., v. 86, p. 10153—10192. Mittlefehldt, D. W., and Miller, C. F., 1983, Geochemistry of the Sweetwater Wash Pluton, California: implications for "anomalous" trace element behavior during differentiation of felsic magmas: Geochim. Cosmochim. Acta, v. 47, p. 109—124. Miller, Calvin F., 1977, Early alkalic plutonism in the calc—alkalic batholith belt of California: Geology, v. 5, p. 685—688. 41 �O'Nlons, R. K., and Pankhurst, R. J., 1978, Early Archean rocks and geochemical evolution of the Earth's crust: p. 211—236. Earth Planet. Sci. Letters, v. 38, �I FIELD TRIP LOG AND DESCRIPTIONS DUNBAR GtIEISS — GRANITOID DOME :I By P. K. Sims, K. J. Schulz, and Z. E. Peterman —. .•a 2141 LISt D FLNCE _ ;:--_ *— I % 1 FERN'2 2 to!. — — I —i — .- !-••--• I —a.— J FLORENCE CO - -- ..-—.-- —-.——.——-—. ——--— - . .' OAGARA .. . —- a--—-— -. -2 ii ——-- -- IS4 -: MARINETTE CO - H OF UICHIGAU -: —J---___-1--_j_ --. . . S — — .-= - S 1-- —i -. -- - -—-- -- -—- DUNmAR4_L — --= GOODVAF2 - - . . .-.. —- —- - - —- -- I —=— —— —- . — — - OEECHER ii .. - ---ReId -.-.trip Dunbar . S - -I - —;: :i; L3 - ¼ L . -. �e. FIELD EXCURSION Road Log $ Log begins and ends at Dunbar, Wisconsin — at junction of First Street and U.S. highway 8. Descriptions of field stops are given separately on following pages. Mileage 0.0 Dunbar. 1.6 Junction of Marinette County highway U and U.S. highway 8. Continue westward. 4.5 Turn right (north) on secondary road to Coleman Lake Club. Permission should be obtained from Manager of the Coleman Lake Club of Goodman, Wisconsin. 6.2 Clearing at house and barn. Walk eastward about 800 feet to outcrops of Dunbar Gneiss (Stop 1). Return to vehicles and proceed south back to U.S. highway 8. 7.9 Junction with U.S. highway 8. 10.8 Drive west on U.S. highway 8. Turn left (east). I Junction of U.S. highway 8 with Marinette County highway U. left (north) on Co. U. Turn I 12.0 Turn left (west) on Spur Lake road (secondary road). 13.9 Outcrops on east side road (Stop 2) of Dunbar Gnelss. County highway U. 15.8 Junction, Spur Lake road and Co. U. 16.2 Outcrops on east side road (Stop 3). road cut (Dunbar Gneiss). Return to I I Walk eastward from blasted I 20.5 Junction Co. U and Co. B. Turn right (east) on Co. B and proceed due E (including dirt road) for 0.5 ml. 21.0 Turn right (south) on secondary road and proceed for 0.5 mi. will park here. Walk south on unimproved road to Stop 4. 21.7 (Stop 4). Gneiss. 22.4 Return to vehicles, and proceed north to Co. hy B. Junction of east—west secondary road. Turn left and proceed onto Co. B. 22.8 Farmhouse just east of junction of Co. B and Co. U. Obtain permission from owner. Walk south to outcrop (Quinnesec volcanics) behind barn. (Stop 5). Return to vehicles. Proceed east on Co. B. Cars Outcrop on knob is a highly deformed fades of Dunbar I I �Mileage 28.2 Junction of Co. B with north—south asphalt road. 31.6 Curve in road to left (east). 31.9 Outcrop south side of asphalt road on small knob. (Stop 6A). A companion outcrop (Stop 6B) to be observed is on north side of road, about 0.1 mile west of Stop 6. Return to east—west asphalt road and proceed east. 36.2 Junction asphalt road with County highway N. Turn right (south). Continue eastward. Turn right (east) on Co. N. 37.9 Railway crossing. Park and walk north along railway. (Stop 7) includes 3 separate outcrops, A, B, and C. Return to cars, and proceed east on Co. N into the town of Niagara. 39.9 Junction Co. N and U.S. highway 141. proceed through Niagara. 43.1 Junction of U.S. highway 8 with U.S. 141. 46.3 (Stop 8). Outcrop east side of highway exposing the contact zone between granite of Spikehorn Creek and Quinnesec volcanics. Return to cars and proceed south on U.S. 141—8 through Pembine. 52.4 Junction U.S. hy. 8 and U.S. 141—8. 58.0 (Stop 9). Outcrops on north side highway 8. proceed west to Dunbar. 61.2 Dunbar, Wisconsin. End of log. L5 Turn right on U.S. 141 and Proceed south on hy 141—8. Turn right (west) on hy. 8. Return to cars and �Description of Field Stops Stop 1. SW1/4 SW1/4 sec. 21, T.37N., R.18E., Goodman 7—1/2 minute quadrangle. Outcrops in partly grassy and wooded area, 1,000 feet east of Coleman Lake Club road. Large outcrops of Dunbar Gneiss——interlayered biotite gneisses with a few thin, intercalated layers of amphibolite, cut by abundant white pegmatite and pink aplite. Layers generally 1—24 inches thick. All rocks deformed by northwest—trending folds having steeply dipping limbs and axial planes striking N.45—50°W.; folds plunge 4O°SE. The foliation (S1) is subparallel to layering Some pegmatite shows incipient boudinage. (S0). On the northwest part of outcrop, foliation planes oriented N.80W., 45°S. have a crenulation and mineral lineation plunging 45° S.25°W. that is younger than F1. Probably it is related to strain near core—cover boundary. The northwest—trending folds and accompanying southeast— plunging lineation is virtually identical to the structure elsewhere in the Dunbar Gneiss in the central core of the dome. This gneiss has a U—Pb discordia age of 1,862*5 Ma. The Rb—Sr system in this rock has been reset, and a Rb—Sr biotite age on one sample is 1,125 Ma. Suggested additional stop; it will not be visited on this field excursion. SE1/4 SE1/4 sec. 19, T.37N., R.18E., Goodman quadrangle. Rock knob adjacent to cleared area, southeast of dirt Moderately homogeneous hornblende—biotite gneiss. Rock has road. a strong foliation and lineation, indicative of high strain. Foliation, N.5O°W., 900; lineatlon (mineral alinement), 800 S.50°E. Gneiss is cut by 2—3—inch blotite granite dikes and by pink pegmatite and aplite. The steeply plunging lineation is characteristic of structures of rocks in and near the core—cover boundary, where ductility contrasts during diapirism were large. One sample gave a Rb—Sr biotite age of 1.13 Ga. Stop 2. Center sec. 15, T.37N., R.18E., Dunbar 7—1/2 minute quadrangle. Excellent, partly lichen—free outcrops of migmatitic Dunbar Gneiss. -Consists mainly of compositionally layered rocks, biotite gneiss and lesser amphibolite, intruded by megacrystic biotite granite gneiss, granite pegmatite, and aplite. All rocks are Foliation: N.5O—55°W., 90°. Foliation, expressed by deformed. biotite and hornblende alinement, is generally parallel to compositional layering but locally transects intrusive contacts of niegacrystic granite gneiss at 100_150 angles. The protolith of the layered gneiss here and at Stop 1 is considered to be caic—alkaline volcanic rocks. 46 �Stop 3. SW1/4 SWl/4 sec. 13, T.37N., R.18E., Dunbar 7—1/2 minute quadrangle. Blasted outcrop of Dunbar Gneiss on east side Co. U and outcrops on ridge extending to east. The outcrop in road cut is site of USGS sample W143 and, apparently, of dated sample 5 of Banks and Cain (1969). Sample W143 gave a U—Pb zircon concordia upper intercept age of 1,862*5 Ma and a lower intercept age of 471*23 Ma. Aplite from this outcrop has a Rb—Sr model age of 1.4 Ga. The outcrops east of the road cuts are composed mainly of a megacrystic granite gneiss that contains rafts of layered amphibolite. Lineation in the amphibolite plunges 200_250 N.85°—90°E. Locally, the amphibolite is refolded by folds having N.50°W. steep axial surfaces. The granite gneiss has a pervasive N.70°W. foliation. The granite gneiss (Dunbar Gneiss) tonalite, and is interpreted Stop 4. has the composition of as a plutonic protolith. SE1/4 NW1/4 sec. 36, T.38N., R.18E., Dunbar 7—1/2 minute Rock knob near south end of north—south dirt road that quadrangle. connects with Florence County highway B. Biotite augen gneiss which is interpreted as an intensely deformed variety of Dunbar Gneiss. Foliation, N.75°E., 85°S.; lineatlon, 300 S.45°W. The high strain apparent in the rock is the result of strong ductile deformation in the vicinity of the core— cover boundary; the outcrop is less than 1,000 ft from the boundary. Stop 5. NW1/4 SW1/4 sec. 25, T.38N., R.18E., Dunbar 7—1/2 minute Outcrop south of farmhouse at junction of Florence quadrangle. Outcrop of County highways U and B. Ask permission of owner. metavolcanics and coarser grained metagabbro (amphibolite grade) of Quinnesec Formation. Two periods of folds are visible in the An older, dominant foliation (S2..), N.20°—4O°W., 45°SW. and rocks. accompanying lineation (L ..), 450 S.65°W., is deformed by small— scale asymmetrical folds F4) (S—type) that plunge 500 S.8O°W. The The folds have an axial plane foliation (S4), N.55°E. .900. younger deformation (D4) exhibits transitional brittle—ductile The outcrop is about 0.6 ml northwest of the core—cover behavior, boundary. The younger folds and foliation are interpreted as the result of flattening strain caused mainly by outward inflation (to the northwest) of the central core of the dome against the Similar asymmetrical folds (S—type) can be seen in metavolcanics. outcrops of the same rocks on the west side of highway U in SE1/4 SE1/4 sec. 26, T.38N., R.18E. L.7 �p Stop 6. Stop 7. SE1/4 sec. 28, T.38N., R.19E. Outcrops in rock knobs on both sides of asphalt road along bottom of section 28. Outcrops on south side of road (A) shows partial replacement of Dunbar Gneiss by K—feldspar, to yield Hoskin Lake—type granite; outcrop on north side of road is typical of much of the Hoskin Lake Granite (B). SE1/4 Outcrops along Chicago, Milwaukee, St. Paul and Pacific Railway north of Florence County hy. N, Iron Mountain 7—1/2 minute Secs. 7 and 18, T.38N., R.20E. quadrangle. Involves about a 2 mi walk along railway. A. Outcrop of Hoskin Lake Granite, 0.2 ml north of County highway N. The granite is coarse grained and has abundant large tabular K—feldspar grains that give a foliation, It contains inclusions of volcanic rocks N.85°W. 65°S. from the Quinnesec. Numerous fractures transect the granite. B. SW1/4 Outcrop in blasted cut, 0.2 ml north of station A. sec. 7, T.38N., R.20E. A 45—ft—wide wedge of intensely foliated amphibolite (Quinnesec Formation) occurs in the It strikes N.70°W. and dips 75°S. Hoskin Lake Granite. The adjacent granite is intensely fractured (brittle— ductile deformation). The wedge is interpreted as a tectonic block, faulted into the granite. Tourmaline veins are present in the southern part of the cut. C. Outcrop of Quinnesec volcanics, east side of railway SW1/4 sec. 7, T.38N., R.20E. The metavolcanics tracks. (amphibolite grade) have a strong, close—spaced foliation (S4) (N.80°W., 65°S.) and a steep stretching lineation (4) (62° S.15°W.) expressed by mineral alinement, rodding, boudins, crinkles, and flattened and stretched pillows. Deformed pillows can be seen on crest of knob, near south end of outcrop. Tight folds (F4) that plunge parallel to the linear fabric and have N.80°W., 65°S. axial surfaces can be observed at places. The high strain exhibited here is indicative of the intense deformation on the overturned, north margin of the central core of the Dunbar dome, and is controlled by the core—cover boundary. Qualitative estimates of stretched pillows indicate a maximum Deformation is indicative of length to width ratio of about 5:1. transitional brittle—ductile behavior. Suggested additional stop; it will not be visited on this Outcrop of metamorphosed Marinette Quartz Diorite, 0.2 mi south of County highway N on railway. The quartz diorite is a layered gneiss (amphibolite fades) that locally is cut by small dikes of 1-loskin Lake Granite and leucogranite. The layering dips moderately to gently and is folded into round—crested open upright folds that plunge 300 S.15W. A conspicuous mineral lineation is subparallel to fold hinges. trip. �Stop 8. SW1I4 sec. 1, T.37N., R.20E., Pembine NW 7—1/2 minute quadrangle, east side U.S. highway 8—141; blasted cut. Outcrop is the southern margin of the granite of Spikehorn Creek in the Niagara lobe against Quinnesec Formation. Contact of main body of granite is a steep fault whose surface is coated by chlorite. The granite is reddened by alteration of feldspar, and itself is faulted. It contains small inclusions of aiuphibolite. Dikes of granite of Spikehorn Creek and leucogranite intrude the Quinnesec on the south side of the faulted contact. Suggested additional stop: Outcrop 0.5 miles north of Stop 8; it will not be visited on this trip. This outcrop shows the contact of the granite of Spikehorn Creek with an inclusion of vólcanics from the Quinnesec. The granite, on north side of contact, is reddened, and in the contact zone contains veins of gray and smoky quartz, tourmaline, and pyrite. In the contact zone, the rocks have a cataclastic (mainly ductile) foliation and a steep lineation (plunges 75°SE.). A gray porphyry cuts the metavolcanic rocks in the southern part of the outcrop; both rock types are cut by dikes of red leucogranite. This lobe (Niagara lobe) of granite is interpreted as a diapir that bulged outward from the central core during a late stage in the evolution of the Dunbar dome, as evidenced by the uniformity of the granite, its lack of a penetrative foliation, and a foliation in the surrounding metavolcanics that conforms closely to the core—cover boundary. The granite is the youngest dated rock in the dome; it has a U—Pb zircon discordia age of 1,8366 Ma. Stop 9. (Time permitting) SW1/4 SE1/4 sec. 34, T.37N., R.19E., Dunbar NE 7—1/2 minute quadrangle. Smooth outcrops in cleared area, 150 ft north of U.S. highway 8, adjacent to trail. Contact zone of This outcrop of Newingham Tonalite contains Newingham Tonalite. inclusions of aniphibolite and biotite gneiss (Dunbar Gneiss). On east side of draw, the tonalite is reddened by surface alteration. In draw, contact can be seen between Dunbar Gneiss and the tonalite; it strikes N.55°E. and dips steeply. Foliation in the gneiss—is N.50°—55°E., 70°SE; foliation (S31) in tonalite is N.80°E., 65°SE. The foliation in the tonalite is younger than that in the gneiss; it crosseuts the contact but is only weakly developed in the gneiss. This structural relationship can be seen at many places in the contact zone between the Dunbar Gneiss and the Newingham Tonalite. Suggested additional stop; it will not be visited on this SE1/4 NW1/4 sec. 21, T.36N., RI9E., Twelvefoot Falls 7—1/2 minute quadrangle. Twelvefoot Falls on North Branch Pike River, in this stop is about 3.5 mu Twelvefoot Falls County Park. Note: south of U.S. highway 8, and can be reached via the Lily Lake Road. trip. L9 �Spectacular outcrops along the river expose the Twelvefoot Falls Quartz Diorite of Cain (1964). The outcrops are on the southern margin of a wide shear zone that strikes N.70°W. and dips 75°—85°N., and is more than a mile wide; lineations are nearly vertical. The same strongly foliated rocks at Eighteenfoot Falls on the northern line of section 21 also are sheared in the same fashion. At Twelvefoot Falls, relatively unsheared but highly altered quartz diorite occurs on the south side of the falls. Elsewhere, however, the quartz diorite has a strong, close—spaced foliation expressed by shears and alined muscovite and chlorite, which was formed by transitional brittle ductile deformation. At the falls, an 18—inch—wide dacite dike is parallel to a fault that strikes N.70°W. and dips ca. 80°N. Thin sections of rocks in the broad, northwest—trending shear zone (Twelvefoot Falls shear zone) show abundant shears, generally filled with chlorite or muscovite, and extreme alteration of hornblende and plagioclase. Garnet is a local metamorphic mineral. Microcline is present at places in fractures in the rocks. 50 �p 1* r1 Volcanic Rocks of Northeastern Wisconsin by Klaus J. Schulz U.S. Geological Survey, Reston, Va 51 22092 �INTRODUCTION Volcanic rocks of northeastern Wisconsin were examined as a part of the regional investigations of the geology of the Precambrian rocks in Wisconsin and Upper Michigan. The Pembine 15" quadrangle was chosen for particular emphasis because it contains relatively abundant outcrops of volcanic rocks and adjoins areas previously mapped or currently under investigation. The rocks in this area are the easternmost exposures of the east—trending volcanic—plutonic belt in northern Wisconsin that contains at least four stratabound, base—metal, massive sulfide deposits. The volcanic rocks of northeastern Wisconsin occur south of the Menominee and Iron River—Crystal Falls iron—bearing districts and are separated from rocks of the Marquette Range Supergroup by the Niagara fault zone (see Bayley and others, 1966; Dutton, 1971). The volcanic rocks were originally designated the "Quinnesec schist" by Van Hise and Bayley (1900) after outcrops of greenstone schists and associated tnafic intrusive rocks found at Quinnesec Falls on the Menominee River in southern Dickinson County, Michigan. The name was subsequently changed to Quinnesec Greenstone by Leith and others (1935) and to Quinnesec Formation by James (1958). James applied the term Quinnesec Formation to the belt of green— stone, amphibolite, and schist in the southern part of Dickinson County, Michigan, and the adjacent parts of Wisconsin. 52 �Although the name Quinnesec Formation is presently accepted and widely used to designate the volcanic and associated rocks in northeastern Wisconsin, Jenkins (1973) noted that at least four lithologically distinct volcanic units could be defined in the central part of the Pembine quadrangle. Jenkins considered three of these units sufficiently different from the lithologies of the type area of the Quinnesec Formation (Prinz, 1959; He pro- Bayley and others, 1966) to warrant their separate designation. posed the informal names McAllister formation, Beecher formation, and Pemene formation for these units. Recently, DePangher (1982) proposed that the Quinnesec Formation be designated the Quinnesec Group consisting of five lithostratigraphic units having formational status. For the purposes of this report, the informal nomenclature proposed by Jenkins (1973) for the volcanic rocks of the area is used (see fig. 1). I recognize that formal revision of the present stratigraphic nomenclature of the volcanic rocks of the area is warranted. However, such revision should not be undertaken until after present mapping and regional compilation efforts are completed. This summary of the geology and geochemistry of the volcanic rocks of northeastern Wisconsin is based largely on my work on the rocks in the Pembine 15" quadrangle (relatively detailed mapping in the north and reconnaissance mapping in the south) and the thesis studies of Hall (1971), Jenkins (1973), Cudzilo (1978), and DePangher (1982). Inasmuch as the mapping and regional compilation of the geology of the area are still incomplete, this summary represents only an interim report. volcanic rocks north and northwest of the Pembine quadrangle were 53 The �____ _____________________ EXPLANATION (Figure 1) Early Proterozoic Athelstane Quartz Monzonite Xsg Spikehorn Creek granite Xnt Newingham tonalite Marinette Quartz Diorite Granodiorite (includes diorite to granite) Xtq4,d X pT'2 v A1C AbC Twelve Foot Falls Quartz Diorite Pemene formation of Jenkins (1973): spherulitic rhyolite. dominantly micro— McAllister formation of Jenkins (1973): andesitic breccias. Beecher formation of Jenkins (1973): and felsic volcaniclastic rocks. Quinnesec Formation: basaltic and andesites, dacites, dominantly basalt and diabase with some andesite, metagabbro sills (Xmg), peridotite (Xp), tuff (Xqt), and breccia (Xqtb). --— ——— '-I * Approximate contact Fault Facing direction of pillow lava Strike and dip of bedding Field trip stop locations 51 �r ri I I I U 55 �described by Bayley and others (1966) and Dutton (1971), respectively, who also summarized earlier work in the region. Greenberg and Brown (1983) recently reviewed the major—element geochemistry of the volcanic rocks of northeastern Wisconsin. GENERAL GEOLOGY Volcanic and associated rocks are relatively well exposed in an arcuate belt east and north of the Dunbar gneiss—granitoid dome in Narinette and Florence Counties of northeastern Wisconsin. Volcanic rocks and associated sedimentary rocks are also exposed in scattered outcrops in a belt south of the dome (Cummings, 1978), but their stratigraphic relation— ships to the volcanic rocks to the east cannot be directly established because of intervening glacial cover. To the north and northeast, the volcanic sequence is truncated by the Niagara fault (Bayley and others, 1966 and Dutton, 1971), which marks a major discontinuity in the rocks of the region. North of this fault, rocks of the Michigamme Formation and other units of the Marquette Range Supergroup occur along with basement uplifts of Archean gneissic rocks. To the south, the supracrustal rocks of northeastern Wisconsin are bounded by the Atheistane Quartz Monzonite (Medaris and others, 1973); to the west of the Dunbar dome, outcrop is lost under glacial drift. 56 �The supracrustal sequence includes units of basalt, andesite, dacite and rhyolite flows and volcaniclastic material, and locally, sedimentary rocks including graywacke, black graphitic slates, and iron—formation. Pyritic to pyrrhotitic massive sulfide bodies are also present locally (Hollister and Cummings, 1982; LaBerge, 1983). Gabbro sills are common, particularly in the northern part of the sequence (Bayley and others, 1966). Serpentinite bodies, commonly with some associated gabbros are also present locally (see fig. 1). The units of the Dunbar gneiss—granitoid dome intrude the volcanic rocks west of the Pembine quadrangle, and the Atheistane Quartz Monzonite intrudes them to the south. Small intrusive bodies ranging from hornblendite and gabbro to granite and including lamprophyre dikes and plugs are widespread, particularly in the southeastern part of the volcanic sequence in the Pembine quadrangle. The Twelve Foot Falls Quartz Diorite (Wadsworth, 1962) intrudes volcanic rocks in the area south of the Dunbar dome (see fig. 1 of Sims and others, in this field guide). The supracrustal rocks and associated subvolcanic intrusive rocks are variably replaced by greenschist facies mineral assemblages throughout the eastern outcrop area but contain assemblages as high grade as amphibo— lite fades adjacent to the Dunbar gneiss—granitoid dome and further to the west. The rocks were regionally folded on northwest—trending axes and are now at or near vertical in attitude throughout much of the area, but they commonly lack a penetrative cleavage in the east. As a result, primary textures and structures are generally well preserved. Units generally face outwards from the margins of the Dunbar dome and Atheistane intrusion. 57 �P The volcanic and associated rocks are broken into several blocks or segments by high—angle faults. High—angle faults also appear to bound the major lithologic units in the Pembine quadrangle (Jenkins, 1973; see fig. 1). Because of uncertainties in the amount of displacement on these faults and the complexity of folding, detailed correlations between blocks have not been possible. As mentioned in the "Introduction", four major volcanic units have been recognized in the Pembine quadrangle (Jenkins, 1973); the Quinnesec Formation, the McAllister formation, the Beecher formation, and the Pemene formation. These formations, in the order listed, represent progressively more silicic rock units. Jenkins suggested that the order of naming above represented the order of decreasing age. This conclusion was based largely on an analogy with other volcanic terranes, which commonly show a progression to more silicic rock compositions with time. Insofar as this analogy is valid and applicable to the volcanic sequence in the Pembine quadrangle, the stratigraphic sequence proposed by Jenkins (1973) may be valid. However, significant lateral variations in the nature of volcanic rocks can also occur and could be difficult to decipher after deformation. Present geologic data support the interpretation that the Quinnesec Formation (as used by Jenkins) is the oldest volcanic unit. The relative ages of the other units, however, remain uncertain. The regional structure indicates that the McAllister formation may be younger than the Beecher formation but older than the Pemene formation. work is required to resolve the stratigraphy of these units. 58 Further I �Until recently, the age of the volcanic rocks in northeastern Wisconsin was a point of controversy. Van Hise and Bayley (1900) and Bayley (1904) originally interpreted the "Quinnesec schists" as early Precambrian principally because of the striking similarity of these rocks to Archean greenstones elsewhere in the Lake Superior region. Van Hise and Leith (1911) subsequently assigned the Quinnesec Formation to a pOst— Michigamme age (i.e. middle Precambrian) on the base of the interpretation of Hotchkiss that the Michigamme Formation graded upwards into volcanic rocks in Florence County, Wisconsin. Dutton later reinterpreted the relationship in this area and placed a fault between the volcanic rocks to the south and Michigamme Formation to the north. Bayley and others (1966) and Dutton (1971), while acknowledging that decisive field evidence to establish the age of the Quinnesec Formation was lacking, favored an early Precambrian age. Banks and Rebello (1969) reported a U—Pb zircon age of 1,866±39 Ma for a rhyolite sample from an area west of the Pembine quadrangle and south of the Dunbar dome. This age, which is not resolvable from the ages of the rocks of the Dunbar dome (see Sims and others, this field guide), is now generally taken as that of the volcanic sequence throughout northeastern Wisconsin although this rhyolite locality is isolated from the main areas of outcrop. Recently, Warren Beck of the University of Minnesota has obtained a similar age for the basaltic rocks of the Quinnesec Formation by the Sm—Nd technique (Beck, personal communication, 1984). Thus, the age of the volcanic rocks of northeastern Wisconsin now seems to be established as Early Proterozoic and not Archean as once thought. Their age is similar to that obtained for the massive sulfide 59 �deposits near Crandon, Monico, and Ladysinith to the west (Sims, 1976) and to ages of other volcanic and plutonic rocks of the northern Wisconsin magmatic terrane (Van Schmus, 1980). It is still uncertain, however, whether the Early Proterozoic inagmatic rocks of northern Wisconsin are significantly younger than the rocks of the Marquette Range Supergroup in Upper Michigan. STRATIGRAPHY The four lithostratigraphic units that compose the volcanic rock sequence in the Pembine quadrangle are described below. Although the rocks are metamorphosed at least to the greenschist facies, the prefix 'meta" is generally omitted throughout this report for simplicity. Quinnesec Formation The Quinnesec Formation, as used in this report, is the dominant volcanic unit in the Pembine quadrangle extending from the northern border to at least the middle of the quadrangle (fig. 1). thickness is not known because of the complexities Its stratigraphic of folding and faulting but is probably on the order of several thousand meters. The Quinnesec Formation consists predominantly of pillowed to massive tholeiltic basalt, diabase, and lesser pillowed and fragmental andesite. Andesite increases in abundance southward in the unit and is generally plagioclase and clinopyroxene phyric and aniygdaloidal. Basalt is generally pillowed, and pillow shape and size vary between areas. Locally, basaltic pillow breccia and highly variolitic pillow lava is encountered, particularly near the center of the quadrangle. 60 In the north—central �part of the map area, several distinctive tuff and breccia units are present (fig. 1). Fragments are very fine grained, light green, and commonly amygdaloidal and appear to be more siliceous than their matrix. Felsic tuffs and breccias are also present particularly in the southern part of the unit. (Felsic fragmental units were also reported by Bayley and others (1966) and Dutton (1971) to exist north and northwest of the Pembine area. Fine to medium—grained diabase is common throughout the unit and is particularly abundant in the northern part. A distinctive quartz bearing diabase extends over a wide area in the north—central part south of the tuff and breccia units (fig. 1). Dikes of diabase are locally identified and may represent feeders to overlying flows. Sedimentary rocks are rare within the Quirtnesec Formation. Where present, they consist mostly of chert, graywacke, slate, and iron—formation. Iron—formation, occurring as thin units interlayered with clastic sedimentary rocks or tuffs, consists of interlayered chert and siderite (Cummings, 1978). The Quinnesec Formation is intruded in the western part of the map area by the Marinette Quartz Diorite, the Newingham tonalite, and the Spikehorn Creek granite (fig. 1). To the south, it is in fault contact with the Pemene formation. 61 �McAllister Formation The McAllister formation extends in an east—west belt in the south— central h part of the map area (fig. 1) and ranges in thickness from about I 300 meters in the west to 3,000 meters in the east (Jenkins, 1973). The unit is steeply dipping; limited evidence indicates that it is probably northward facing. It consists of basaltic to andesitic breccia and locally massive flows. Fragments in the breccia are distinctive in containing large pyroxene crystals generally replaced by amphibole. Amygdules are also common in some fragments. An increase in fragment size to the east indicates that the source area for this dominantly volcaniclastic unit may be east of the present Menominee River. Beecher Formation The Beecher formation extends in a north—facing, east to southeast— striking belt in the southern part of the map area and is in contact to the south with the intrusive Athelstane Quartz Monzonite (fig. 1). unit is at least 3,000 meters thick (Jenkins, 1973). The The lower part consists dominantly of plagioclase and clinopyroxene phyric andesite and dacite lavas and pyroclastics. acidic fragmentals predominate. Upwards in the unit, bedded tuffs and Black slates are also locally present in the upper part of the unit. The lower part of the Beecher formation, where intruded by the Athelstane Quartz Monzonite, has a well—developed foliation and steeply plunging lineation. Dikes of Atheistane Quartz Monzonite are present only for a short distance from the intrusive contact. 62 �I Pemene Formation The Pemene formation occurs over a broad oval area in the south—central part of the map area (fig. 1) and is well outlined by the local topography. It is at least 2,000 meters thick and consists predominantly of micro— spherulitic, plagioclase—phyric rhyolite and rhyodacite lavas and breccias. The flows are interlayered with a few thin, graded sedimentary units, suggesting that the rhyolite flows were possibly extruded subaqueously. Individual flows were estimated by Jenkins (1973) to range from about 150 to 400 meters in thickness. The Pemene formation shows little evidence of a penetrative structural fabric. The flows show a southward dip in the north and are near vertical in the south. Jenkins (1973) interpreted the structure of the formation as an east—trending, asymmetric, doubly plunging syncline. INTRUSIVE ROCKS A variety of intrusive of the Pembine quadrangle. rocks is found within the supracrustal These range from sequence clearly synvolcanic bodies like the diabases to post—tectonic lamprophyric dikes and plugs. The intrusive rocks associated with the Dunbar gneiss—granitoid dome are discussed by Sims and others (this field guide) and are not further considered herein. 63 �Gabbro Bodies Numerous large gabbro bodies are present within the Quinnesec Formation, particularly north and northwest of the Pembine quadrangle (Bayley and others, 1966). These bodies are more or less conformable to the mafic lavas and probably represent synvolcanic sills. Two such bodies are present in the Pembine quadrangle (fig. 1). The smaller body in the northwest part of the area consists of medium to coarse— grained gabbro and diorite and locally contains abundant hornblendite to gabbro xenoliths. Intrusive breccia is locally developed where diorite dikes intruded the gabbro (e.g. road cut, Highway 8, NE1/4SE1/4, sec. 24, T.38N., R.20E.). A larger gabbroic body, named the Sturgeon Falls sill by Prinz (1959), occurs along the east side of the Menominee River in Michigan and trends southeast for a distance of at least 12 km. Both the upper and lower portions of this sill are fault bounded, the northern fault being an extension of the Niagara fault. The Sturgeon Falls sill is unique in having serpentinite and pyroxenite along the north side. The pyroxenite generally occurs between the gabbro and serpentinite but also forms narrow bands within the gabbro. and anorthositic gabbro compose the bulk of the sill. Gabbro Anorthosite is locally well developed within the gabbroic part of the sill whereas magnetite—rich gabbro composes the southwestern part. The overall strati— graphy of the sill, with ultramafic rocks along the northern side and magnetite gabbro along the southern side suggests that the sill faces southwest. The consistency of the stratigraphy further suggests that the body may represent a differentiated sill similar in many respects to the 6L S �Kiernan sills within the Hemlock Formation in Michigan (Bayley, 1959). However, the Sturgeon Falls sill is compositionally distinct from the Kiernan sills (see discussion below). On the basis of overall similarity in metamorphism, structure, and composition between the Sturgeon Falls sill and the Quinnesec Formation basalts, the sill is interpreted as synvolcanic in age, although Bayley and others (1966) considered the gabbroic sills as "post—Animikie" in age. Peridotite Bodies Several small peridotite bodies, now altered to serpentinite, occur in the south—central part of the map area, but the largest and best exposed body occurs in the north—central portion within the Quinnesec Formation basalt (fig. 1). This peridotite body trends east and outcrops discontinuously for a distance of about 4.5 km. The peridotite shows few primary textures, contains serpentinte and large magnetite crystals, and Is locally cut by veins of carbonate and cross—fiber asbestos. Mineralog— ically banded and massive gabbro, locally cut by mafic to ultramafic(?) dikes, occurs south of the periodotite and locally appears to also crosscut it. At the western end, the peridotite is cut by pyroxenite dikes composed of coarse (1—5 cm) amphibole pseudomorphs after pyroxene. Foliation and banding in the associated gabbro are more or less at right angles to the lithologic contacts. Also, dikes found cutting the gabbro and serpentinite do not appear outside the body. These features suggest that this serpentinite—gabbro body may be fault bounded and tectonically emplaced. 65 �Biotite—Pyroxene Diorites Several bodies of biotite—clinopyroxene—bearing diorite to quartz diorite intrude the Pemene and McAllister formations (fig. 1). Rocks range from fine to medium grained and contain variable amounts of amphibole, clinopyroxene, plagioclase, biotite and quartz. apatite are also present as minor phases. Opaque minerals and Most of the amphibole appears to be pseudomorphous after pyroxene. Miscellaneous Bodies Several small bodies of dacite porphyry and blue quartz—eye porphyry occur within the volcanic units in the southern half of the Pembine quadrangle. These probably represent subvolcanic intrusions related to the felsic volcanic rocks of the Beecher and Pemene formations. Several lamprophyre dikes and plugs have been identified within the map area. These are generally small bodies and are difficult to distinguish from mafic volcanic rocks in the lichen—covered outcrops of the area. The lamprophyres consist of prismatic hornblende and biotite crystals in a feldspar matrix. Atheistane Quartz Monzonite The Atheistane Quartz Monzonite intrudes the Beecher formation in the southern part of the Pembine quadrangle (fig. 1) and extends for an unknown distance to the south and west. It consists dominantly of medium to coarse grained quartz monzonite and locally contains numerous metavolcanic inclusions. The Atheistane Quartz Monzonite is dated at 1,836±15 Ma (Banks and Cain, 1969). The Amberg Granite, which intrudes the Athelstane Quartz Monzonite in the southern part of the map area, is 1,756+19 Ma (Van Schmus, 1980). 66 �GE OCHEMI STRY Representative analyses of volcanic rocks from units within the Pembine quadrangle are presented in Table 1. are shown in figures 2—8. Their compositional variations Greenberg and Brown (1983) recently reviewed the majorelement chemistry of volcanic rocks from northeastern Wisconsin and concluded that they are dominantly calc—alkaline and exhibit characteristics of rocks found in modern volcanic arcs. The data of this study confirm these conclusions and provide further information on the nature and evolution of the volcanic sequence. The overall caic—alkaline character of the northeastern Wisconsin volcanic rocks is shown by the AFM diagrams. (fig. 2) and Jensen cation (fig. 3) However, many of the basalts, diabases, and gabbros of the Quinnesec Formation are tholeiitic. Figures 2 and 3 also illustrate the marked compositional differences between the volcanic rocks of northeastern Wisconsin and those of the Marquette Range Supergroup in Upper Michigan, which are bimodal, show strong iron enrichment trends, and are enriched in Ti02 relative to those in northern Wisconsin. Chondrite—normalized rare—earth—element (REE) patterns for Quinnesec basalts and diabases are shown in figures .4 and 5. Most of the samples are characterized by marked light—REE depletions ([La/Yb]N=.lO—.54) even more extreme than is typical of ocean—floor basalts (fig. 4). REE abundances show a wide range ([YbIN7—25) that only poorly correlates with MgO content. The relative depletion of light—REE generally increases as REE abundance decreases, suggesting that these basalts may represent melts derived by progressive partial melting of the same mantle source. 67 �I Table 1.—- Representative analyses of volcanic rocks from the Pembine 0 Quadrangle, northeastern Wisconsin. I 2 1 Sb2 Al203 Fe203 FeO MgO CaO Na20 1(20 Ti02 '2S MnO H20 H20 49.7 16.3 1.9 6.7 8.1 12.8 2.0 0.27 0.53 0.09 0.18 1.4 0.17 47.8 15.9 3.2 8.0 8.8 11.5 0.81 0.10 0.43 0.07 0.17 3.2 0.08 CO2 4 3 53.4 15.5 48.4 15.5 2.1 7.7 4.1 2.5 9.5 7.7 9.8 2.1 5.8 4.7 0.27 0.18 1.1 1.2 0.19 0.14 3.4 0.09 0.15 0.18 Ba Zr Y Nb Cr 400 Co Sc 41 56 87 16 31 22 <5 105 53 59 1.1 0.17 7 8 70.2 13.4 0.97 4.2 0.78 74.6 13.5 0.84 1.3 4.7 2.2 0.19 5.9 0.43 0.12 0.13 0.96 0.10 0.29 0.09 0.03 0.65 0.11 2.1 1.3 1.7 .06 :.24 151 47 80 35 <5 14 37 43 0.093 2.20 0.22 135 104 80 25 307 104 392 1130 61 17 99 21 1005 166 43 8 <5 6 14 11 469 2 36 40 26 29 223 46 46 0.30 1.99 0.25 —— 0.27 — —— La Ce Sm Eu Tb Yb Cu 1.37 3.90 1.36 0.49 1.88 1.02 0.53 0.50 2.34 0.38 2.12 6.79 2.81 1.00 1.04 3.80 0.58 3.27 9.6 2.58 0.91 0.65 2.65 0.36 0.62 0.54 2.58 0.37 0.37 0.20 0.20 1.7 0.065 1.02 0.14 0.28 0.60 12.8 1.4 6.0 7.0 5.5 2.8 2.2 0.07 Ta Hf Th U —— 60.9 0.21 3.0 89 54 43 23 <5 56.2 16.5 2.4 7.6 3.8 8.0 3.4 0.34 0.92 0.16 0.18 3.1 <:.96 Sr 6 5 0.13 1.40 0.53 0.21 0.27 2.37 3.72 1.43 4.82 16.4 33.3 3.43 0.83 0.54 1.90 0.28 12.1 2.15 0.73 0.49 1.80 0.27 184 1.7 69 631 173 40 14 2 4.48 6.51 2.20 0.7 12.0 0.79 5.12 7.65 2.29 27.5 58.6 7.28 1.63 1.20 4.97 0.78 29.4 67.9 7.80 1.47 1.16 5.53 0.81 12.9 0.74 - 1 ii 1—2 3—4 5 6 7—8 Quinnesec diabases Quinnesec basalts Quinnesec andesite Beecher andesite Pemene rhyolites U 68 �0a, I I- 0w Li- 0 Cb4 + 0c1 z Figure 2.-—Fe01-—MgO—Na20+K20 diagram for volcanic rocks of Wisconsin (stipled field) compared to volcanic rocks ofnortheastern upper Michigan (dot—dash fields) and Monico area of Wisconsin (dashed fields). 69 �A1203 Cation % + Ti02 NE WISCONSIN MICHIGAN SI.c Aufl INI,I, (Ok,.a MgO •— •— — — • • rocks are all tholeiitic. i, u i — a 1•1 Figure 3.--Jensen cation diagram (Jensen, 1976) for volcanic rocks of northeastern Wisconsin (stars) and upper Michigan Rocks of northeastern Wisconsin plot mainly in the calc-alkaline field while the upper Michigan (dash uields) D FeO+ �The strong light—REE depletion indicates that this source had undergone prior partial melting. This conclusion has recently been confirmed by the Nd isotopic work of Warren Beck (Beck, personnal communication, 1984). These strongly light—REE depleted basalts are similar to those of the lower units of the Troodos Complex (Kay and Senechal, 1976). A smaller group of basalts from the Quinnesec Formation are only moderately depleted in light—REE (fig. 5). These are very similar in many respects to modern ocean floor basalts (figs. 5—8). The two gabbro samples from the Sturgeon Falls sill have light—REE depletion patterns similar to those of the basalts (fig. 4). The chondrite—normalized REE patterns for one Quinnesec Formation r andesite, two Beecher formation andesites, and three Pemene formation rhyolites are shown in figure 6. r in The samples show progressive enrichment light—REE, and, with increasing total REE abundances, show larger negative Eu anomalies. These REE patterns are typical of calc—alkaline volcanic rocks of modern arc systems (e.g., North Island, New Zealand, r Reid, 1983). The general island—arc compositional affinities of the northeastern Wisconsin volcanic rocks are further illustrated in figures 7 and 8 in terms of Y—Cr variations and Hf/Th—Ta/Th ratio variations, respectively. Like the volcanic rocks in modern arcs, the rocks of northeastern Wisconsin show marked depletions in high—valance cations like Zr, Hf, Ta, Y, and Ti. The basalt samples from the Quinnesec Formation that plot in the fields of mid—ocean ridge basalts in figures 7 and 8 represent the group of basalts in which light—REE are only moderately depleted (fig. 5). 71 �I I I Figure 4.-—Chondrite normalized REE for some Quinnesec Formation basalts and gabbros of the Sturgeon Falls sill. 40- MORB = field for mid-ocean ridge basalts. QzINNEsEc BsALrs N190 - 10 I 7Z - - 4 L Ce. SwEu. Tb Lu. Figure 5.--Chondrite normalized REE for some Quinnesec Formation basalts. Average MORB shown by dashed field. 72 �I 6.--Chondrite normalized REE for one Quinnesec Formation andesite (56.5, Si02), Figuretwo Beecher formation andesites (61-62, Si02) and three Pemene formation rhyolites (71-73.5, Si02). 73 �— I I I / I 10 iii I I / , '\ I, Yppm II • I I IAT — ,_ — \ I,/ / 50 I I MORB 'I 100 III —— —i I Ta/Th H — : is! • ±. similarity between Hemlock and Keweenawan volcanic rocks. Hemlock data from Fox (1983). Figure 8.--I-If/Th vs Ta/Th variation in volcanic rocks of northeastern Wisconsin (stars) (after Noiret and others, 1981). Note I.- I- — — —.: — — I_ Wisconsin volcanic rocks. IAT=Island arc tholeiite field; MORB=Iiid-ocean ridge basalt field. (After Pearce, 1982). Figure 7.--Cr-Y variation for northeastern 105 50 100 0 aa- E 500 1000 I I 4JJ �TECTONIC IMPLICATIONS Both the nature and geochemistry of the volcanic rocks of northeastern Wisconsin suggest that the rocks formed in a magtnatic arc similar in many respects to modern oceanic island—arcs (e.g., like those of the western Pacific, Hamilton, 1979). The presence of tectonically emplaced ultramafic rocks (ophiolite fragments(?)) with basalts of mid—ocean—ridge chemical affinities further indicates such an environment of formation. The general absence in Upper Michigan of magmatic rocks having similar affinities suggests that the associated subduction was to the south. The eventual collision of the maginatic arc formed as a result of the southward subduction probably resulted in the deformation event recognized as the Penokean Orogeny (Schulz and others, 1984). Thus, the Niagara fault zone, as proposed by Larue (1983), probably represents the zone of suturing between the magmatic arc terrane (northern Wisconsin volcanic—plutonic belt) and the Archean crust and miogeosynclinal cover sediments (passive margin sequence; Marquette Range Supergroup) to the north. One feature typical of many subduction—zone assemblages but notably missing from northern Wisconsin is a melange sequence representing rocks of a possible fore—arc basin and accretionary wedge. Drilling Project Recent Deep Sea drilling in the western Pacific, however, has shown that arc systems situated over steeply dipping Benioff zones commonly lack both fore—arc basins and abundant trench sediments (Uyeda, 1983). This finding suggests that the northern Wisconsin magmatic system may have formed over a steeply dipping subduction zone, thus precluding accumulation of a thick sedimentary wedge. 75 �The overall nature and geochemistry of the rocks of the northern Wisconsin volcanic—plutonic belt strongly suggest that tectonic processes during the Early Proterozoic generally were similar to plate—tectonic processes operating today. Although many aspects of the geology, tectonics, and paleogeography remain to be established for the Early Proterozoic rocks of the Lake Superior region, they now seem to represent another example of the Wilson cycle (i.e. opening and closing of an ocean basin) in the geologic record. 76 I �References Banks, P. 0., and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: Jour. Geology, v. 77, P. 208—220. Banks, P. 0., and Rebello, D. P., 1969, Zircon age of a Precambrian rhyolite, northeastern Wisconsin: Geol. Soc. America Bull., v. 80, p. 907—910. Bayley, R. W., 1959, Geology of the Lake Mary quadrangle, Iron County, Michigan: U.S. Geol. Survey Bull. 1077, 112 p. Bayley, W. S., 1904, The Menominee iron—bearing district of Michigan: U.S. Geol. Survey Mon. 46, 513 p. Bayley, R. W., Dutton, C. E., and Lamey, C. A., 1966, Geology of the Menominee iron—bearing district, Dickinson County, Michigan, and Florence and Marinette Counties, Wisconsin: U.S. Geol. Survey Prof. Paper 513, 96 p. Cudzilo, T. F., 1978, Geochemistry of Early Proterozoic igneous rocks in northeastern Wisconsin and Upper Michigan [Ph. D. thesis]: Lawrence, University of Kansas, 194 p. Cummings, M. L., 1978, Metamorphism and mineralization of the Quinnesec Formation, northeastern Wisconsin [Ph. D. thesis]: Madison, University of Wisconsin, 190 p. DePangher, Michael, 1982, The geology, geochemistry, and petrology of the Quinnesec Group east of Pembine, Marinette County, Wisconsin [M. S. thesis]: Salt Lake City, University of Utah, 210 p. Dutton, C. E., 1971, Geology of the Florence area, Wisconsin and Michigan: U.S. Geol. Survey Prof. Paper 633, 54 p. Fox, T. P., 1983, Geochemistry of the Hemlock metabasalt and Kiernan sills, Iron County, Michigan [M. S. thesis]: University, 81 p. 77 East Lansing, Michigan State �I Greenberg, J. K. and Brown, B. A., 1983, Lower Proterozoic volcanic rocks and their setting in the southern Lake Superior district, in Medaris, L. G., Jr., ed., Early Proterozoic geology of the Great Lakes region: Geol. Soc. America Mem. 160, p. 67—84. Hall, G. I., 1971, A study of the Precambrian greenstones in northeastern Wisconsin, Marinette County [M.S. thesis]: Milwaukee, University of Wisconsin, 80 p. Hamilton, Warren, 1979, Tectonics of the Indonesian region: U.S. Geol. Survey Prof. Paper 1078, 345 p. Hollister, V. F., and Cummings, M. L., 1982, A summary of the Duval massive sulfide deposit, Marinette County, Wisconsin: Geoscience Wisconsin, v. 6, p. 11—20. 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. Jenkins, R. A., 1973, The geology of Beecher and Pemene townships, Marinette County, Wisconsin [abs.]: 19th Institute on Lake Superior Geology, p. 15—16. Jensen, L. S., 1976, A new cation plot for classifying subalkalic volcanic rocks: Ontario Dept. Mines Misc. Paper 66, 22 p. Kay, R. W., and Senechal, R. G., 1976, The rare earth geochemistry of the Troodos ophiolite complex: Jour. Geophys. Res., v. 81, p. 964—970. LaBerge, G. L., 1983, LaSalle Falls — an exposed massive sulfide deposit in Florence County, Wisconsin [abs.]: Geology, p. 26. 78 29th Institute on Lake Superior 4 �Larue, D. K., 1983, Early Proterozoic tectonics of the Lake Superior region: Tectonostratigraphic terranes near the purported collision zone, in Medaris, L. G., Jr., ed., Early Proterozoic geology of the Great Lakes region: Geol. Soc. America Mem. 160, p. 33—47. Leith, C. K., Lund, R. J., and Leith, Andrew, 1935, Pre—Cambrian rocks of the Lake Superior region, a review of newly discovered geologic features, with a revised geologic map: U.S. Geol. Survey Prof. Paper 184, 34 p. Medaris, L. G., Jr., Van Schmus, W. R., Lahr, M. M., Myles, J. R., and Anderson, J. L., i973, Field trip locality 2 in Guidebook to the Precambrian geology of northeastern and northcentral Wisconsin, 19th Institute on Lake Superior Geology, p. 43—45. Noiret, Gerard, Montigny, Raymond, and Allegre, C. J., 1981, Is the Vourinós Complex an island arc ophiolite: Earth Planet. Sci. Letters, v. 56, p. 375—386. Pearce, J. A., 1982, Trace element characteristics of lavas from destructive plate boundaries in Thorpe, R. S., ed., Andesites: New York, John Wiley and Sons, p. 525—548. Prinz, W. C., 1959, Geology of the southern part of the Menominee district, Michigan and Wisconsin: U.S. Geol. Survey Open—File Report, 221 p. Reid, Frank, 1983, Origin of the rhyolitic rocks of the Taupo volcanic zone, New Zealand: Jour. Volcanology and Ceotherm. Res., v. 15, p. 315—338. Schulz, K. J., LaBerge, G. L., Sims, P. K., Peterman, Z. E., and Kiasner, John, 1984, The volcanic—plutonic terrane of northern Wisconsin——Implications for Early Proterozoic tectonism, Lake Superior region [abs]: Association of Canada, in press. 79 Geological �Sims, P. K., 1976, Middle Precambrian age of volcanogenic massive sulfide deposits in northern Wisconsin [abs.]: 22nd Institute on Lake Superior Geology, p. 57. Uyeda, Seiya, 1983, Comparative subductology: Episodes, v. 1983, p. 19—24. Van Hise, C. R., and Bayley, W. S., 1900, Description of the Menominee special quadrangle, Michigan: U.S. Geol. Survey Geol. Atlas, Folio 62, 13 p., 3 maps. Van Hise, C. R., and Leith, C. K., 1911, The geology of the Lake Superior region: U.S. Geol. Survey Mon. 52, 641 p. Van Schmus, W. R., 1980, Chronology of igneous rocks associated with the Penokean orogeny in Wisconsin: Geol. Soc. America Special Paper 182, p. 159—168. Wadsworth, W. B., 1962, Petrogenesis of a quartz diorite pluton near Pembine, Wisconsin [M.S. thesisi: Evanston, Ill., Northwestern University, 89 p. 80 �h I Field Trip Log and Descriptions of Stops to accompany Volcanic Rocks of Northeastern Wisconsin by Klaus J. Schulz 81 �r'.) ! — — '—I — / I COMM )NWEALT4 I 7*1 T IV p OJMAI\ i7 1I ii T.I7.I1 ,, /- : 5'H k.- H Ii.] Red trIp S tops, Dunber dome. .- 4 ,T IETTE MFffEA - . L!c •1 ± - ,f - - p a - STATCOFIICHIGAPI JH + To1z + — '"" Rock\ J!$i$I=t rip — L- : uit __ ____ I I., �Field Excursion Road Log Log begins at the Pembine Post Office, Wisconsin, on U.S. Highway 141—8 and ends with Stop H at Pemene Falls. Descriptions of stops are given separately on the following pages. Mileage 0.0 Pembine Post Office, Wisconsin, on U.S. Highway 141—8. 8.7 Junction with U.S. Highway 8. Proceed north. Turn right (east) and proceed to Norway, Michigan. 13.15 Turn right and proceed to Vulcan, Junction with U.S. Highway 2. Michigan. 14.8 Turn right on Main Street in Vulcan. Pass Vulcan Middle School on right. 15.5 Follow right fork in road onto River Road. 17.5 Bridge across Menotninee River. 17.95 Turn right onto secondary road going to Sturgeon Falls Dam. 18.1 Outcrop on west (right) side of road. of the Sturgeon Falls sill. STOP Al. Serpentinite Return to vehicles and proceed south. 18.5 Take left fork in road down to Sturgeon Falls Dam. 18.6 Outcrop to north (right). sill. STOP A2. Gabbro of the Sturgeon Falls Return to vehicles and proceed back through Vulcan and Norway to U.S. Highway 141—8 toward Pembine. Go south (left) on U.S. Highway 141—8 to intersection with Kremlin Road (just north of Pembine). 36.3 Junction with Kremlin Road. Turn left (east). 83 �Mileage 38.0 Railroad tracks (Soo line) and bridge across the South Branch Pemebonwon River. Park vehicles on right shoulder of road and walk along trail going east along the south side of the river. STOP B. Tuff unit of the Quinnesec Formation. Return to vehicles and proceed east on Kremlin Road. 40.35 Junction with dirt road going south. 40.75 Junction with east—west 43.35 Outcrop south side of road. Quinnesec Formation. back to Kremlin Road. Turn right. dirt road. Turn left. STOP C. Pillow basalt of the Return to vehicles, turn around and proceed (Note — We backtrack because beavers have flooded the dirt road further to the east). 46.35 Junction with Kremlin Road. Turn right and proceed east for about 2.3 miles. 48.65 Turn left (north) onto dirt road and proceed 0.35 miles. 49.0 Outcrops on both sides of road. STOP D. Foliated gabbros and massive diabases associated with large serpentinite body of the Quinnesec Formation. and Return to vehicles, turn around, return to Kremlin Road. 49.35 Turn left (east) onto Kremlin Road. 50.9 Junction with road to Pemebonwon Dam and Quiver Falls. right 51.05 Turn (south) and proceed 0.15 miles to railroad tracks. Cross railroad tracks (Soo line) and take sharp left onto dirt road. 51.8 Quiver Falls. Quinnesec STOP E. Formation. Pillowed and variolitic basalts of the Return to vehicles, turn around, and return to U.S. Highway 141—8 via Kremlin Road. 84 I �Mileage 60.25 Junction of Kremlin Road with U.S. Highway 141—8. Turn left (south) and proceed 3.75 miles to County Z. Turn left (east). 64.0 Junction with County Z. 70.85 Junction with Marek Road. Turn right (south), proceed 0.15 miles, and park. 71.00 Outcrop on east (left) side of road. of the McAllister formation. STOP F. Volcanic breccia Return to vehicles and continue south 1 mile. 72.0 Outcrop on east (left) side of road. rocks of the Beecher formation. STOP G. Felsic volcaniclastic Return to vehicles, turn around, and go back to County Z. 73.3 Turn right (east) onto County Z and continue east across the Menominee River. [ 77.45 Turn left (north) onto dirt road and proceed north about 1.05 miles to dirt road going down (west) to river. 78.5 Turn left onto dirt road toward river. 78.65 Pemene Falls. STOP H. Rhyolites of the Pemene formation. to vehicles and return via Return County Z to U.S. Highway 141. TRIP NOTE: time If END permits, we will make an additional stop. At intersection of County Z and Highway 141, turn left (south) and proceed about 4 miles to intersection of Highway 141 and Black Sam Road. southeast of intersection. 85 Outcrop is in field, �Description of Field Stops STOP Al. NW1/4SWI/4 sec. 26, T.39N., R.29W., quadrangle. Faithorn 7 1/2—minute Outcrop extends along low hill to the northwest. The knob next to the road and several outcrops to the northwest consist of serpentinite. The serpentinite is fine grained, is green to black, and is cut by thin seams of carbonate and asbestos. have a silky luster and are reddish brown. Many fracture surfaces The rock consists mostly of colorless antigorite, carbonate minerals, and magnetite. Rare chromite grains are also present. To the northwest along this outcrop, the serpentinite is interlayered with, and/or is cut by, fine grained diabase and porphyritic (plagioclase) diabase. Serpentinite is found at several localities along the north side of the Sturgeon Falls sill and appears to lie near the base of body. Locally, pyroxenite is found between the serpentinite and gabbro. STOP A2. Sturgeon Falls Dam, El/2 sec. 27, T.39N., R.29W. Faithorn 7 1/2—minute quadrangle. Outcrops of gabbro extend to the northwest and southeast and represent the major part of the Sturgeon Falls sill as presently exposed. Locally, the gabbro is cut by thin shear zones and contains basalt inclusions (near steps to dam). A major fault, which appears to truncate the top of the sill, passes southeastward along the river just west of these outcrops. The gabbros consist of varying proportions of plagioclase and pyroxene, which are mostly replaced by saussurite and amphibole, respectively. clinopyroxene is locally preserved and shows abundant, fine exsolution lamellae. To the southeast, the top of the sill consists of magnetic, magnetite—rich ( 3%) gabbro. 86 Fresh �Two gabbro analyses from this sill are given below; one an anorthositic gabbro and the other a magnetite—rich gabbro. The relative depletion in light REE and other trace—element characteristics shown by these samples are similar to those of the Quinnesec basalts, suggesting that they may be cogenetic. Also, the low trace—element abundances in both gabbro samples suggest that they are cumulate rocks. Composition of Sturgeon Falls sill r gabbro samples 2 1 Si02 A1203 Fe203 FeO MgO CaO Na20 1(20 Ti02 P205 MnO r 3.8 7.2 13.0 1.7 11.4 7.2 10.9 1.9 0.16 0.13 0.06 2.2 0.18 0.01 Rb 4 Sr 85 y Nb Ta Cr Co Sc Hf La Ce Sm Eu Tb Yb Lu 0.09 1.6 0.06 0.20 2.4 0.16 0.10 0.11 H20 Ba Zr Anorthositic 1.4 44.1 13.2 7.0 H20 Co2 1 — 2 — 49.3 21.6 <5 86 45 34 8 28 12 <5 12 <5 —— —— 124 39 3 74 29.6 0.21 62 0.46 0.39 1.07 0.44 0.31 0.19 0.78 0.12 0.79 2.3 0.80 0.33 0.25 0.88 0.17 gabbro Magnetite—rich gabbro 87 �Nl/2 sec. 36, T.37N., R.20E., Pembine 7 1/2—minute quadrangle. STOP B. Outcrops of intermediate to felsic tuffs are exposed along both sides of the South Branch Pemebonwon River. I Rocks consist of very fine grained, grayish—green to light—green tuffs and interlayered quartz eye tuffs. The rocks have a strong foliation striking N.60°E. and dipping 75°SE. and have a lineaton plunging 75°S.1O°W. Locally, plagioclase crystal tuffs (or porphyritic flows?) are also present. This unit strikes northeast, is intruded by the Newingham tonalite on the north, and is in apparent fault contact with the Quinnesec Formation basalts to the south. phyre. The unit is It is also intruded by quartz porphyries and grano— representative of felsic tuffs found within the Quinnesec Formation to the north and northwest. STOP C. SW1/4NE1/4 sec. 27, T.37N., R.21E., Faithorn 7 1/2—minute quad— rangle. Low open outcrop just south of road. This outcrop is relatively lichen free and shows pillows of basalt (or andesite?) of the Quinnesec Formation. Outcrops to the northwest consist of similar pillowed flows and pillow breccia. variolites are locally observed. N.8O°W. and generally face south. Amygdules and Pillows in this area strike about A sample from an outcrop to the northwest was analyzed and shows high Si02 (62.4 wt.%) and low MgO (4.3 wt.%) contents. However, the strong alteration of the sample (reflected in a very low CaO content — 3.3 wt.% — and high Na2O and 1(20 contents) makes this analysis suspect. 88 I �STOP D. NW1/4NE1/4 sec. 22, T.37N., R.21E. quadrangle. Faithorn 7 1/2—minute Outcrops extend both west and east of road. This stop is to examine some of the gabbroic and diabasic rocks associated with the large peridotite body in the north—central part of the map area. The peridotite is not exposed in these outcrops but occurs about 1/4 mile to the northwest. One of the most distinctive rock types exposed here is a strongly foliated gabbro (outcrop to left (west) of road). The gabbro is altered, and plagioclase is replaced by saussurite and pyroxene is replaced by amphiboles. The foliation strikes N.1O°—20°E. and dips 7O°NW.; it is almost at right angles to the strike of the ultramafic—inafic body and the strike of foliations in surrounding rocks. Locally in other outcrops, banded gabbros having mineral layering are present; this banding also strikes at a high angle to the trend of the body. Another distinctive rock type present in this outcrop is a fine—grained, gray, mottled diabase. The mottled appearance results from small (2—3 mm) oikocrysts of quartz (this is the myrmikitic basalt of G. I. Hall (1971, M. S. thesis, Univ. Wis., Milwaukee). More normal textured diabases of somewhat varying grain size are also present. These rocks lack the strong foliation of the gabbro but are similarly altered. In the outcrop area to the right of the road (east), the generally massive diabases are cut by thin (15 cm wide) dikes of diabase and pyroxenite(?). These dikes weather to a reddish brown and strike northwest. Similar dikes have been observed to the west but have not been recognized outside this ultramafic—inafic body. 89 �The relationship between the various gabbroic and diabasic rocks of these outcrops and elsewhere within this body remains uncertain. diabases represent dikes cutting the foliated gabbro? Could the Diabase is found crosscutting the ultramafic rocks of this body in outcrops to the northwest. Could they represent a system of sheeted dikes? Ultramafic rocks (not exposed at this stop) occur predominately along the north side of the body and at its western end. The ultrainafic rocks are all highly altered but locally show some preserved primary textures. Peridotite and pyroxenite appear to have been the main lithologies. At the western end of the body, large dikes(?) of coarse—grained, altered pyroxenite appear to cut and include serpentinite. Both the structural features of the rocks of this ultramafic—mafic body and the apparent restriction of dikes within it suggest that this body was tectonically emplaced. Could this ultramafic—mafic body represent a slice of Early Proterozoic ocean floor or is it just a disrupted differentiated sill? Samples have been submitted for chemical analysis, however, the altered nature of many of these rocks may preclude meaningful results. STOP E. Quiver Falls on the Menominee River. Sl/2, sec. 24, T.37N., R.21E., Outcrops exposed mainly Faithorn 7 1/2—minute quadrangle. along river bank. Follow road north to the river bank. Outcrops of largely undeformed pillow basalt of the Quinnesec Formation are exposed along the bank. This is one of the few places in the area where pillows can be viewed in three dimensions. They face south and appear to. be slightly overturned. The basalt is very fine grained, is light gray—green, and contains small, skeletal pseudomorphs of olivine. go �Return to parking area and take trail going south to river bank. Outcrop on the left (north) side of the trail presents one of the petrologic wonders of this area. At the top of the slope is a variolitic basalt in which the varioles are generally small. Down slope, these varioles are much larger (cm size) and compose the bulk of the flow. These structures are nre resistant to weathering than their surrounding matrix. The variolitic structures are round to ovoid, are pink, and are concentrically zoned. The zoning consists of a thin reddish—brown rim followed inward by a white zone and a pink core. The varioles consist of albite, an altered skeletal mafic phase (pyroxene?), microcrystalline material, quartz, and secondary carbonate minerals with hematite staining. Varioles found in basaltic rocks generally consist of radial growths of plagioclase formed as a result of rapid growth in cooling pillows or later devitrification of glass. host basalt. In composition, these are similar to their The varioles observed here, however, are more siliceous than their matrix and have textural features distinct from normal basaltic varioles. They most resemble the siliceous varioles described from Archean basalts of the Abitibi Belt of Ontario (Gelinas and others, 1976, Canadian Jour. Earth Sci., v. 13, p. 210—230), which have been interpreted as quenched immiscible liquids. Samples of the matrix and varioles from this outcrop are being analyzed to test this possibility. STOP F. NE1/4NE1/4 sec. 22, T.36N., R.2lE., Miscauno Island 7 1/2—minute quadrangle. Small hill on east side of road. This stop is to examine a typical exposure of the McAllister formation. The rock is a breccia consisting of porphyritic vesicular andesite fragments in a tuffaceous matrix. The fragments are characterized by 1—5—mm—long, 91 �dark—green hornblende pseudomorphs after clinopyroxene. be massive and lack flow structures. Units tend to Fragments appear to increase in size (>15 cm) in outcrops to the east, suggesting that a vent area is across the river in Michigan. STOP G. NW1/4NW1/4 sec. 26, T.36N., R.21E., Miscauno Island 7 1/2—minute quadrangle. Outcrop on hill on east side of road. This outcrop shows typical lithologies of the upper part of the Beecher formation. Lithologies range from fine—grained tuffs and crystal tuffs to coarser fragmental units. The coarser units contain rounded to sub— angular pink to white felsite and gray porphyritic dacite fragments in a Crystal tuffs mostly contain albitized feldspar pale to dark—green matrix. and a few quartz fragments. are to the north. In some tuff beds that show grading, tops The lower part of this formation consists mostly of dark—green porphyritic andesites and gray porphyritic dacites. STOP H. Pemene Falls, SW1/4SW1/4 sec. 16, T.37N., R.28W., Miscauno Island 7 Exposed 1/2—minute quadrangle. Outcrop along river bank. along the bank of the Menominee River at Pemene Falls are rhyolites of the Pemene formation. The rocks are dark gray to reddish gray, contain few phenocrysts, and are generally microspherulitic. Phenocrysts, many of which are glomeroporphyritic, consist of euhedral to subhedral albite. quartz and albite. The microspherules consist of radial intergrowths of Flow banding and breccias (flow breccia?) are observed in some outcrops west of this stop and probably represent upper and lower parts of rhyolite flows. Locally, thin felsite dikes can be seen cutting the rhyolites. 92 �Suggested additional stop (will not be visited on this trip unless time permits). STOP I. Low, open outcrop east side of U.S. Highway 141, NW1/4SW1/4 sec. 10, T.35N., R.2OE., Amberg 7 1/2—minute quadrangle. Outcrop consists of Athelstane Quartz Monzonite cut by dikes of Amberg Granite (after Medaris and others, 1973, 19th Annual Inst. Lake Superior Geology field guide). The Athelstane Quartz Monzonite intrudes the Beecher formation north of this stop and extends for several kilometers to the south and west. It is pink, medium to coarse grained, and allotriomorphic granular, and it contains both biotite and hornblende. Its distinctive appearance is due to the presence of pink perthitic microcline and white plagioclase. a cataclastic foliation. present in the outcrop. In the road cut, the Athelstane shows Small metavolcanic inclusions are also locally The Atheistane was dated by P. 0. Banks and J. A. Cain (1969, Jour. Geol., v. 77, p. 208—220) as 1,836+15 Ma, which is similar to the age of the Hoskin Lake Granite to the north. The Athelstane Quartz Monzonite is compositionally distinct from other granitoid rocks of the area in being significantly lower in Rb and having lower Rb/Sr and higher K/Rb ratios. The Amberg Granite is gray, medium to fine grained, and hypidio— morphic granular; it contains mainly biotite as the major ferromagnesian phase. Van Schmus (1980, Geol. Soc. America Special Paper 182, p. 159—168) determined the age of the Amberg as 1,756+19 Ma. Thus, it is equivalent in age to the high—level granitoids and felsic volcanic rocks in central Wisconsin. 93 � https://digitalcollections.lakeheadu.ca/files/original/a125dd7f19263dc54ad1df3ea5a18df2.pdf f9e418a6dd261cb50829c70f96e79ea8 PDF Text Text I Thirtieth Annual Institute on Lake Superior Geology FIELD TRIP 2 EARLY PROTEROZOIC TECTONOSTRATIGRAPHIC TERRANES OF THE SOUTHERN LAKE SUPERIOR REGION: FIELD TRIP GUIDE WITH SUMMARY Iron for.itlon PAINT RIVER GROUP YOltinics qqnrtzlt. BARAGA GROUP —I 71 FAULT CONTACT APRIL 28, 1984 �Early Proterozoic Tectonostratigraphic Terranes of the Southern Southern Lake Lake Superior Superior Region: Region: Field with F i e l d Trip Guide w i t h Summary Field F i e l d Trip Trip Leaders Leaders W. L. L. Ueng W. D. K. D. K. Larue R L. Sedlock R. L. D. A. A. Kasper D. Prepared for meeting of of tthe Prepared f o r 30th annual meeting he IInstitute n s t i t u t e on Lake Superior Geology Geology Wisconsin, 1984 Wausau, Wisconsin, 1984 �______ EARLYPROTEROZOIC PROTEROZOIC TECTONOSTRATIGRAPRIC T!lCTONOSTRATIGRAPHIC EARLY TERBAmSOP OFTHE TRESOUTHERN SOWl'EfERNLAZE LARZ SUPERIOR SUPERIOR REGION: REGION: TERRAZ!S TRIP GUIDE GUIDE WITH WITHSUMMARY SUMMARY FIELD TRIP FIELD W.L. Ueng ueng W.L. D.K. Lame Lame D.K. R.L. Sedlock Sedlock l.L. D.A. lasper Kasper D.A. Geology, Stanford Stanford University University Dept. Geology, Dept. Stauford CL CA 94305 94305 Stanford INTRODUCTION Geologic studies s t u d i e s in in the the Lake Lake Superior Superior region region Geologic ur~derventa a minor minor revolution revolution in i n 1976 1976 with with the the underwent The Ttm present present paper paper relies r e l i e s on on aa previous previous study study recently r e c e n t l y published published (Larue, (Lame, 1983) 1983) concerning concerning the the geology of the g e o l o w of the acuthcentral southcentral tot osoutheast southeastLake Lake P r w i o u s l y one cue of of us ussuggested suggested Superior Superior region. r e g i m . Previously (Lame, (Larue, 1983) 1983) that t h a t early e a r l yProterozoic Proterozoic rocks rocks of of the the publication of of Van V a n Schmue' Schma' paper the publication papers-king suiarizing the geolow and aud speculating about about early e a r l y Proterozoic Proterozoic geology Schen~ tectonicsofofthe theGreat GreatLakes Lakesregion. region. Van VanSchimia tectonics rock that aabelt b e lof t of calc-alkalinemagmatic ma-tic rock propoaed that proposed cab—alkaline extending across across northern aorthenaWisconsin Wisconsin represented represented the the extending Lake Lake Superior Superior region r e g i m can can be be described described in i n terms tenus of of aa 2) including: including: number of of discrete d i s c r e t e tarranea terranes (Pig. (Fig. 1,1, 2) number aa miogeocline udogeocline (terranes ( t e r r a n e s A,B), A,B), aa probably probably composite composite erge and magmatic terrane t e r r a (en) (mt) (Lab (Laberge andMeyers, Meyers, in in magnetic press) and and two tvo smaller, smaller, complicated complicated terranes terranes press) ccmposed of of miogeoclinal miogeoclinal lithologies, l i t h o l o g i e s , the the composed Florence—Niagara Florence-Niagara and and Crystal Crystal Falls F a l l s terraces terranes (FNt, (FNt, was suggested it was suggested that t h a t the the m t ) . In I n Larue Lame (1983), (19831, it Clt). had exhumed resmants remnants of ofanauAndean—type Andean-type arc a r cwhich whichhad exhumed formed on on an an older olderpassive passivemargin, margin, exposed exposed to t o the the formed north (Pig. (Fig. I). 1). Cambray Cambray (1978), (19781, Larue Larueand andSboss Sloss north (1980) and aud more more recently recencly Greenberg Greenberg and and Brown Brown (1983) (1983) (1980) proposed instead instead that t h a t an an arc arc terrane terrane collided collidedwith with proposed passive continental continental margin margin about about1.8—1.9 1.8-1.9 b.y. bay. ago. ago. aa passive — 4 GUNF I Vy 0 ONTARIO 404 * • 100% • I n Rocks Rocksyounger younger than than eaily eariy Proterozoic Proterozoic W°"° I.I plutonics and andvolcanics voicanks Marquette Range SuDergroup and equivalent rocks Archesn green8tomArcheangroenstone--1granlt. terran. granite terrano • 1Arch.an gneles ol Fig. Fig. 1 1 A. A. Location of of the t h e Lake Lake Superior Superior Region. Region. (After (After Morey, Morey, et Location e t al,1982) a1.1982) tarTan. �—2— this this deformation by examining examiningthe the sstructural deformation by tructural mt represents represents an m arc a r c terrane terrane that t h a t collided collided with u i t h and and mt probably overthrust the themiogeocline, miogeocline, and and that t h a t the the probably FNt kwere r e aalso l s o probably probably emplaced -laced during his CFt and and FNt during tthis CYt The fault f a u l t that t h a t separates separates major accretion event. event. The major the mt m t and and the the terranes t e r r a n e composed s composed of of miogeoclinal miogeoclind the l i t h o l o g i e sisi knoem s k n m as an the the Florence—Niagara Florence-Niagara ffault, ault, lithologies and may suture. and, mayrepresent represent aa suture. Proterozoic Proterosoic The present present paper paper is is aimed aimed at a t discussing discussing the the The f o l l w i n g points: 1) aa brief b r i e freview reviewofofthe thegeology geolw following points: 1) of the the southern southern Lake Lake Superior Superior region; 2) recent recent of region; 2) tlutwe vehave havemade made in i n the thesouthern southernLake Lake studies that studies Superior region region astride a s t r i d ethe t h eFlorence-Niagara Florence-Niagara Superior Specifically, we we present presentdata dataconcerning concerning f a u l t . Specifically, fault. s t r u c t u r a l evolution evolution of of the thearea areasurrounding surrounding the the structural We wwill i l l stress s t r e s s the thecomplicated complicated nature Y t u r e of of suture. We suture. The The rresponsibilities e s p o n s i b i l i t i e s for f o rwork work are a r e as a sfollows: follows: W.L. D.K. Larue, Larue, W.L. Ueng, Ueng, regional regional deformation deformatica model; model; O.K. regional regional studies; studies; R.L. R.L. Sedlock, S d l o c k , deformation deformation in in These magmatic D. Kasper, Kasper, geochemistry. geochemistrv. These m a p a t i c tterrane; e r r a e ; D. studies studies were were supported supported by by the t h e National National Science Science Foundation EAR 80—08202, 8048202, 81—08564) 81-08564) to t o O.K. D.K. Foundation(NSF (NSFLAP. Larue Larue and and by by the t h e U.S. U.S. Geological GeologicalSurvey. Survey. history I n addition, addition, we we present present h i s t o r y of of each each terrane. terrane. In some new new exciting e x c i t i n g data c?ataon on the t h egeochemistry geochemistry of of early early some shales shales in i n the the Lake Lake Superior Superior region. region. We We begin begin with with aa discussion discussion of of lithologies l i t h o l o g i e s in i n the the southern southern Lake Lake Superior Superior region, region, followed followed by by aa do not not attempt We do attempt structural s t r u c t u r a l analysis analysisand andsummary. sumnary. We to t o modify modify eexisting x i s t i n g tectonic t e c t o n i c models models in i n this t h i spaper. paper. IL' IM 2 t& "• 2 I I : FI 03 I z 0 I I C., II'a •' • AMASA OVAl. MARQUETTE TROUGH 3. Idealized NW—SE cross located i.n section of Florence Niagara and Crystal Falls terranes Fig. 2. CRYSTAL FAU.$ FI.osvsce-NsaeasA wAGUATIC TERRANS II- Q PAINT RIVER Fig. 1 -j o I' 'I. r 31,v&i) p - zUi 2Ui — I TEANU I WIST FLANK OF AMASA OVAL CAST FLANK OF AMA$A OVAL FCLCN TROUeH MANOUCYTE TROUGH I I I 4 A U I a I I I 44 . I I I I I ,. ZZ <a a Fig. Fig. 1 1 C. C. Stratigraphy of of units u n i t s discussed discussed in i n text. text. Stratigraphy �—3— OLOGY OF THE MIOOCLT.NE General - Older Precambrian Older Precambrian Precambrian Basement Basement.• Older Precambrian exposed only 2 is showniin basement shown n Figure 2 is exposed only Lfl i n the the miogeocline, and miogeocline, and can be be divided divided into i n t o two two types: types: Huronian (2.2—2.3 b.y.) Huroniau sstrata t r a t a (2.2-2.3 b.y.1 and andArchean Archean (>2.4 02.4 by.) b-y.) ccrystalline r y s t a l l i n e rocks (Van (Van Schmus, S c h s , 1976). 1976). ifuronian Eurmiau strata s t r a t a are a r e rrelatively e l a t i v e l y rare r a r e in i nthe t h eLake Lake Superior region (Van (Van Schmus, Schmus, 1976) 1976) and and aare r e not not Sims (1976) (1976) divided divided tthe he here. Morey and Sima discussed here. Lake Superior region rocks into Archean rocks i n t o aayounger younger Lake Superior region Archean (2.7—2.5b.y.), b.y.), northern, granits—greenstone (2.7-2.5 granite-greenstone southern, terrane an older older (>3.0 b.y.), southern, terrane and and au 03.0 b.y.1, Archeanrocks rocks iin n Figure gamiasic gneissic terrane t e r r a n e (Fig. (Fig. 1). 1). Archean 2 are 2 a r e iin n their t h e i r gneissic m e i s s i c terrana. terrane. Supergroup. a! Supergroup. Marquette Marquette The Chocolay Chocolay Group Group uncomfornably uuconfomably overlies o v e r l i e s older olderPrecambrian Precambrian basement, basement, consists of consists of basal basalconglomerate conglomerate overlain overlain successively by qquartaits, successively by u a r t z i t e , dolomite, dolanite, and and slate s l a t e and and of the is the t h elowermost lowermost unit u u i t of t h eMarquette Marquette Range Rauge Supergroup (Fig. (Fig. 23). 2B). Menominee Groups tstrata M m d n e e Group r a t a rrest e s t unconformably uuconformably on on consist of of quartaite Chocolay Group Group strata, s t r a t a , and a d consist q u a r t z i t e or or muddy overlain by muddy qquartzite u a r t z i t e overlain by banded bauded iron iron formation formation overlies Baraga Group Group o v e r l i e sthe t h Menominee e Mendnee (Pig. (Fig. 23). 2B). The Baraga Group Group aat t lleast e a s t locally l o c a l l yuncouformably, uuconform~bly, and aud consists consists of dominantly sandyand andmuddy muddyt uturbidites rbidites of dominantly deep—water deep-water sandy and volcanic volcanic uuits. units. and Sub terrane AA Subterrane The osiogeocliae miogeoclineMis divided divided iinto The n t o subterranes subterraues A A and (Fig. 2), have ddifferent and BB (Fig. 21, which which ham i f f e r e n t geologic geologic features but features but are a r e not not separated separatedby by any any apparent apparent maj majororsstructural t r u c t u r a l discontinuity. Boundaries and Distinguishins Distinguishing Features. Boundaries & Subterrane ItA is ia inferred i n f e r r e d to to be fault—bound f a u l t - b d on m the the west on the the south with west with with the the Cit CFtand and fault—bound fault-bound on tthe h e FNt, F N t , is ia overlain overlain to t othe t h eeast e a sby t byPhanerozoic Phanerozoic cover, cover, and and is is apparently apparently continuous continuous to t o the the nortwest nortwest is (sub terrane B) A is (subterrane B) and to t o the the north. north. Subtarrane Subterrane A unique with regard regard to to the the other terranes unique with terranes discussed because it it lacks here because lacks the thethick thicksequence sequence of ofBaraga Baraga Group volcanicsofof the the Cit Group volcanics CFt and and subterrane subterrane B, B, and and significant s i g n i f i c a n t mappable units u u i t s in i nthe t h eBaraga BaragaGroup Group composedofofmature mature (quartzose (quartzose and carbonate) composed carbonate) lithologies FNt. l i t h o l o g i e s as in i n the t h e FNt. of Stratigrephy. The oldest Stratigraphx. oldest Proterozoic Proterozoic rocks of those of of the Chocolay Group, subterrane A are those Group, which include l o c a l l y thick accumulations accumulatims of of quartzite quartzite include locally quartzitea and iron formation f0m.athII and dolomite. dolomite. Muddy quartzitea of of the the M e n k n e e Group uncmfomably overlie w e r l i e strata strata Menominee Group unconformably of the the Chocolay Group Group and and aare r e relatively r e l a t i v e l y thin. thin. of Baraga Group slates sandstones, locally i m sandstones, locally s l a t e s and ddirty with volcaniclastic (James and and others, others, volcaniclastic interbeds interbeds (James 19681, 1968), cap the sequence. sequence. Larue Larue and and Sloss Sloss (1980) and Larue (1981a) have have (1980) and Lame (l981a) suggested that t h a t the the Felch Felch and and Menominee Menominee s tstructural ructural suggested troughs were sedimentary basins during troughs during Chocolay Chocolay Group sedimentation. sedimentatim. This interpretation is based i n t e r p r e t a t i o n is on on the presence presence of of trough—parallel trough-parallel paleocurrent paleocurrent vectors from in the the areas areas frao cross—beds cross-beds iin n q u a r t z i t e in quartaite within s t r u c t u r a l troughs. troughs. The within the the structural The Felch basin basin was was n w expressed expressed by by bound on eeither i t h e r side sideby byplatforms, p l a t f o m a ,now exposed Archaen Archaen basement. basement. Archean basement is is exposed Archean basement a~the the northeast side side of the present only cmly on the Menominee Menominee trough. The southwest southwest margin margin of of the the Menominee The Menominee trough is is sstructurally complicated and and not not well well trough t r u c t u r a l l y complicated the basin basin may may understood. IIn uuderstood. n fact, f a c t , this t h i s side, s i d e , oof f the Menominee basin may may have been been open, have open, such such that t h a t tthe he M e n d n e e basin have had only have only one onewell—defined well-defined margin. margin. Group sedimentation, Felch During Menominee M e n d n e e Group sedimentation, the t h e Felch Menominee basins Menominee basins received received little l i t t l e sediment. sediment. basins became Apparently, tthe Apparently, h e basinn became iinactive n a c t i v e during during this this period, period, and and it it isisnot notknown known whether whether these these basins basins were reactivated during were reactivated duringBaraga BaragaGroup Group The complex complexsstructural sedimentation. The sedimentation. t r u c t u r a l and and overprinting of of these metamorphic overprinting these strata s t r a t a precludes precludes Baraga Group s e d i ~ t o l o g i canalysis. analysis. Baraga Group ddetailed e t a i l e d sedimentologic sediments represent represent products products of of regional regional deep-water deep-water sediments sedimentation. and and Sub terrane B is d different terrane BB is Miogeoclinal sub Hiogeoc1iaal subterrane i f f e r e n t from from it contains contains much greater greater subterrane A because it inafic igneous Proterozoic mafic volumes of early e a r l y Proterozoic igneous rocks. rocks. The basement basementofofsubterrane subterrane BB is Stratigraphy. S t r a t i g r a p b . The Archeangneiss gneisswhich whichf forms thecore coreofof aa large Archean o r m the large Figure dome, dme, the southern southern tip t i p of of which which is isshown shown in in F icre lfarquette Range r a t a mantle maatle the the RangeSupergroup Supergroups tstrata La. Marquette U. Chocolay Group Groupddolomites comprise tthe o l m i t e s comprise he dome. Chocolay lowermostpart part of of the sedimentary drape, and lowermost sedimentary drape, and are are overlain by volcanics and overlain by Baraga Baraga Group Group volcanics and sediment. sediment. particular a r t i c u l a r interest i n t e r e s t is is the the ICiernan Kiernan sills sills Of p iintrusive n t r u s i v e complex ccmplex which is is of of greatest g r e a t e s t thickness thickness to to the southwest of of the the domes domea (Fig. (Fig. 23) 2B) but but is is probably equivalent equivalent to probably t o sscattered, c a t t e r e d , smaller mafic intrusions i n t r u s i o n s that t h a t occupy occupy a a similar s i m i l a r sstratigraphic tratigraphic the perimeter pposition o s i t i m around a r d the perimeter of of the t h e dome d a m (Cannon, 1978). Where Where it it is is thickest, t h i c k e s t , the t h e iCiemnan Kiernan complex complex ultramafic rock c o n s i s t s of: 1)1)a acumulate—layered cumulate-layerad ultramafie consists base (lO0—300m); (100-3001~); 2) aa cumulate cumulate and aud isotropic i s o t r o p i c gabbro gabbro medial section and 3) k d ; and 3) aa pillow pillow basalt b a s a l t cap cap secticm(1—3 (1-3 1cm); medial byr ribbon charts and andt turbiditic d woverlain e r l a i n by i b b a ~cherta urbiditic ((>1 > l kion) ash beds m), and and iiron r o n formation formation (the (the beds ("lOO (-100 d, Mansfield member; —200m)in)(descriptions (descriptions from Gair member; a200 and and Weir, Weir, 1956; 1956; Bayley, Bayley, 1959; Weir, 1967). The Kiernan complex probablyoriginated originatedasastthe Xiernan c m p l e x probably h e ffloor l o o r of of aa volcanic within ccontinental volcanic basin basin within o n t i n e n t a l crust, c r u s t , during during deposition d e p o s i t i m of of Baraga Baraga Group Group sstrata t r a t a (Fox (Fox 1982; 1982; Wilband and and others, i n prep.). prep.). others, in Crystal Falls F a l l s Terrane Terrane Boundaries Boundaries and Distinguishing Features. Features. The CFt is roughly equidimensional in i n shape and is Cit is iinferred n f e r r e d to t o be fault—bound. fault-bound. The CFt i n fault fault Cit is in contact on m the t h e south with with the t h e FNt F N t (Fig. (Fig. lIt). 2A). Art An inferred ffault inferred a u l t to t o the the east separates separates the the Cit CFtfrom frcm tterrane e r r a e A, A, and and an au inferred i n f e r r e d ffault a u l t tto o tthe h e north separates the the CFt ( t h e latter l a t t e r two two Cit from terrane B B (the boundaries are ffault a u l t boundaries a r e inferred i n f e r r e d based on m truncation truncation of aeromagnetic trends sshown of h m on on the the map by Zietz Zietz and Kirby, Kirby, 1971). and 1971). There is insufficient outcrop to to define the exact boundaries boundaries of and of the southwest southwest arid 1; however, hawever, faults f a u l t s are are sides of of terrane terrane 1; west sides iinferred n f e r r e d based on m preliminary preliminary study study of of aeroinagnetic aerumagnetic anomalies. anamalies. Stratigraphy. S tratigraph~. N No unequivocal Chocolay o mequivocal Chocolay or Menominee M e n d n e e Group Group rocks are a r e present n the t h e Cit. CFt. present iin Baraga Group extrusive extrusive volcanics volcanics (Badwater(Badwater— Greenstone) r e iin n ffault a u l t contact Greens tone) aare contact with Chocolay i n the W of of the the Cit. CFt. Group strata s t r a t a of of the the E'Nt Flit in the S SW Presumably deep-water deep-water turbiditic t u r b i d i t i c sandstones sandstones and and p e l i t e s of of the the Paint Paint River—Group River-Group unconfommably(?) mconformably(?) pelites o v e r l i e Saraga Baraga Group Group strata s t r a t a (James (James and and others, others, overlie 1968). A deep-water storm-wave base) origin deep—water (below storm—wave base) origin �-4-. MAGMATIC TERRANE TERRAME 1: CRYSTAL FALLS TERRANE TERRANE 3: FLORENCE-NIAGARA TERRANE ARCHEAN BASEMENT FAULT - inferred FAULT 4s04s* Florence—NIagara Fault 1 2 PIne River Block Fig. 2 A. 3 Unnamed Block 4 Keyes Lake Block TerTanem in the south central Lake Superior region. (1983). I4AGNATIC TERRANE KIERNAN SILLS Iron formation volcanics PAINT RIVER GROUP m quartzlta I— BARAGA GROUP NENONINEE GROUP CHOCOLAY GROUP I FAULT . Inferred '2 FAULT >1 FAULT ,4 CONTACT CONTACT Fig. Fig. 22 B. B. Terrane aap of Terrae map of Fig. 2A 2A with with geology geology superimposed. super-osed- After Larue �—5— £5 is proposed because of of the t h e fine—grained, fine-grained, thin—beddednature nature of these thin-bedded these rocks; rocks; their their extent without ssignificant i g n i f i c a n t lateral l a t e r a l extent without evidence evidence of of deposits; intefingering with v i t h shallow—water shall-ter deposits; and and formation thicknessthicknesses within ttheir h e i r significant s i g n i f i c a n t formation no evidence sequences tthat sequences h a t show w evidence of of shall.owing. shallatring. The Terrane The Florence—Niagara Florence-Niagara Terrane PNtisis at Architecture. Architecture. The The FNt a t least l e a s t40 40ion km long long and cconsists and o n s i s t s of of aanumber number of major steeply—dipping steeply-dipping separate ddisparate faults f a u l t s that t h a t separate i s p a r a t e tithologies l i t h o l o g i e s and (3ayley and others, offset of f s e t metamorphic isograds isograds (Bayley others, major ffaults 1966; 1966; Dutton, 1970). Four of these these major a u l t s in in define tthree tthe h e Ft4t FNt define h r e e composite composite f fault a u l t sslices l i c e a with with width of about Ion;the the Pine Pine River? River, ccumulative u m l a t i v e width about 5—8 5-8 h; tthe h e Keyes Keyes Lake Lake and and an intermediate i n t k m e d i a t eunnamed uammed block ccalled a l l e d the t h e 8essie BessieRabbit Babbitblock blockby byLame U r u eand andIjeng Ueng will in the A# w i l l be be shown shown in the (submitted) (Pig. (Fig. ZA). (submitted) 2k). As composed structure s t r u c t u r e section, section, these these three threeblocks blocks are a r e ccmposed of additional addititma1 ffault a u l t slices s l i c e sand and thus thus aare r e composite. The contains Chocolay, Chocolay, The Pine Pine River block contains Mmtominee Baraga 3araga Group Menominee and and Baraga Group sstrata. t r a t a . The Beraga Groupcomprises comprisestb th. M Michigasme in tthe i c h i w e S Slate l a t e in h e Pine Pine Group block, and consists River block, c o n s i s t s mainly mainly of ppelites, e l i t e s , of of deep—waterorigin, origin, and probable deep-water and a fault—bound f a u l t - b o d uunit nit q u a r t z i t e representing representing 0.5 km thick of 0.5 thick of pebbly quartzite shallow—water deposition. ororf lfluvial u v i a l deposition. shallmmrater The intermediateffault The intermediate a u l t slice s l i c e isispoorly poorlyexposed, exposed, and pillow pillow and contains Paint River Group strata and s t r a t a and basalts b a s a l t s of ofthe theBadwater Badwater Greenstone Greenstone which vhich aare r e folded folded in syncline (Dutton, The Paint Paint i n aa SE—closing SE-closing syncline (Dutton, 1970). 1970). Th. River Group Group iin n this t h i s intermediate block contains contains two two principle p r i n c i p l e lithologies, l i t h o l o g i e s , iron i r o nformation formation and and slate slate vwith i t h thin t h i n graded graded sandstone sandstone interbeds. interbeds. Dutton plate (1970, p l a t e 5) 5 ) show. shmm tthat h a t th. thesouthwestern southwestern ffault ault that unnamed block truncates truncates t h a t defines the the unnamed ntetanorphic isograds, demonstrating the metamorphic themovement movement on on the the ffault a u l t occurred occurred after a f t e rregional regionalmetamorphism. mtawrphiam. i The Keyes Lake block is The is similar s i m i l a r to t o the t h e Pine Pine River block, River block, containing containing Chocolay, Cheeolay, Mencminee Manominee and and Baraga Group Groups strata. Baraga t r a t a . Michigasne X i c h i w e SSlate l a t e of tthe he Saraga Group Group includes includes another fault—bound Baraga fault-bound uunit n i t 0.3 0.3 Ion thick qquartzite km thick u a r t z i t e representing representing shallow shallow marine oorr fluvial f l u v i a l deposition, deposition, aalso l s o studied by Nilsen (1965). studied by (1965). Pillow 3adwater Greenstone Greenstone (Fig. (Fig. 23) Pillow baaalts basalta of of the the Badwater 2B) p a r t of of the the aare r e present iin n tthis h i s block blocki ninthe thevest st part florence Florence County County Quadrangle. Quadrangle. Magnetic terrane Magmatic terrane In the terrane, granitoid the magnetic magmatic terrane, g r a n i t o i d and and gneissic gneissic rocks of Penokean Penokean age r e mantled mantled by highly highly rocks age aare deformed deformedunits unitsofof three three major majorlithotypes: lithotypes: 1) 1) a schistose ssuite, u i t e , consisting of of felsic f e l s i c to to predominantly mafic metavolcanic metavolcanic rocks the rocks of of the ; 2) Quinnesec Formation (Bayley (Bayley and and others, 1966) 1966); 2) a inetasedimentary u i t e , consisting scattered metasedinentary rock rock ssuite, consisting of of scattered outcrops of u a r t z i t e and slate; s l a t e ; and and 3) 3) aa gabbroic gabbroic of q quartzite s u i t e , which which includes includes pillowed pillowed and and massive manaive basalt, basalt, suite, gabbroeofof varying varying cmposition, composition, and and llocal massive gabbrca ocal diabase dikes. The granitoid diabase dikes. granitoid and and gneissic rocks that form the the core core of t h a t form of the t h e magnetic magmatic terrace terrane have have been sshownb by by Schulz Schulz (1983) (1983) to t o have have calc—alkaline calc-alkaline a f f i n i t i e s , suggesting aa nagmatic magmatic arc origin. origin. The affinities, volcanic rocks rocks of c h i s t o s e suite s u i t e bear volcanic of the sschiatose geochemical of arc envirmments environments geochemical signatures signatures ttypical y p i c a l of (Cudzillo, 1978). (Cudzillo, 1978). The gabbroic gabbroic suite s u i t emay may be be interpreted as the the roots roots of of this t h i sarc arccomplex. complex. Archaen i n southcentral southcentralWisconsin Wisconsin Archaengneiss gneiss present present in (Fig. IA) ia not considered considered here. here. LA) is STRUCTURE Miogeocline and Crystal Crystal Falls F a l l s Terrane Terrane Structural S t r u c t u r a l features f e a t u r e s of of Early Early Proteroroic Proterozoic rocks rocks andCFt Cit north north of of the iin n the the iniogeocline FNt are are miogeocline and the FNt generally oriented E—W E-W except at a t the t h eAmasa Amasa Oval, Oval, generally oriented Smith Smith Creek Creek Uplift, U p l i f t ? Kiernan Kiernan SSills, i l l s , and and eastern eastern (Fig. 3). margin of of the Cit (Fig. 3). Most Moat structural structural 'margin t h e CFt troughs in E-W, such such troughs i n the miogeocline are a r e oriented E—W, as the Marquette trough, t h e Marquette trough, Felch trough, trough, and Calumet trough. The Sagola trough. Sagola structural s t r u c t u r a l basin, basin, however, hovever, WNW NW and becomes parallel p a r a l l e l to t o the the bends toward toward the the W Oval. The penetrative penetrative Uplift Smith Creek U p l i f t and Amasa Amasa Oval. formed during during tthe deformation ((see ffoliation o l i a t i o n fomed h e ffirst i r s t deformation see which i*this t h i sregion region whichcomeonly coumonlystrikes s t r i k e1*1W, s WNW, below) i'. also andbecomes becomesp parallel a l s o bends bends toward toward the t h eNNW NNW and a r a l l e l with with Transverse tto Amasa Oval. Oval. Transverse the of the the Amasa o these these the axis of structural s t r u c t u r a l bends, bends, tectonolithologic t e c t o n o l i t h o l o g i cassemblages assemblages change iin change n the the miogeoclinal miogeoclinal assemblage: assemblage: most most material ssignificantly, i g n i f i c a n t l y , the the amount amount of of volcanic volcanic m a t e r i a l in in the the Baraga Group Group increases increases dramatically dramatically tot othe the14—SW W-SW across the Amaaa Oval (from t o 3). B). across t h e Amasa (from subterrane subterr~A eA to deformation have have been been recognized Five phases of deformation miogeocline, CFt, and FNt TNt ofof tthe iin n the t h e miogeocline, CFt, and b e southern southern Lake Superior region based on cross—folds cross-folds and and is cross—cutting kleavages leavages (deformation t h e TNt FNt is cross-cutting ( d e f m t i o n in the considered in considered i n detail d e t a i l below)(iig. below)(Fig. 3). 3). Four of these phases aare r e characterized by ssteeply t e e p l y dipping dipping cleavages and axial cleavages a x i a l planes planes of minor folds. folds. These deformation fabrics regionally in f a b r i c s are a r e recognized recognized regionally in the t h e . area a r e a north of of magmatic magmatic terrane. terrane. The other P3, is deformation, F3, phase of deformation, M defined defined by subhorizontal cleavages which generally subhorizontal ccrenulation r m u l a t i o n cleavages dip d i p less l e s s than thau 35 35 degrees. degrees. This This set s e t of subhorizontal crenulatiom cleavage cleavage is recognized recognized subhorizontal crenulation everywhere Crystal Fells everywhere but iin n tthe he C rystal F a l l s terrane. terrane. TI, most pervasive pervasive F l , the t h e earliest e a r l i e s t and and -st characterized by tthe deformation, ia characterized h e following following defomation, is planar structures: structures: slaty s l a t y cleavage, c h i s t o s i t y , and cleavage, sschistosity, aaxial x i a l planfolds. In planes of minor folds. I n spite s p i t e of of later later deformations, aaxial x i a l planes of minor folds folds and deformations, planes of of tthis deformation, S SI, regionally ffoliations o l i a t i o m of h i s defomation, l , regionally sstrike t r i k e N7OW N70W and dip d i p vertically v e r t i c a l l y (for ( f o r example, example, Fig. Fig. 6k, Lame, 1983). Only in 6A, from Larue, i n the t h e neighborhood of of the Amasa Amasa Oval, Kiernan Sills, the S i l l s , and SE ppart a r t of of the the CFt have have Sl rotated by F2 Cit Si surfaces bean been passively rotated P2 orientation NNW. tto o an o r i e n t a t i o n of of NNW. Apical angles of of Fl Fl folds m ccharacteristically h a r a c t e r i s t i c a l l y ttight, i g h t , lless e s s than folds aare than 60 60 degrees, profiles degrees, and and fold p r o f i l e s can comuonly coaw~onlybe categorized iinto l C , and type 3 folds of categorized n t o type lB, LC, type 13, Ramsey's Ramaay's cclassification l a s s i f i c a t i o nscheme schema (1967). (1967). Apical of these NNW-trending NNW—trendimg F Fll folds folds a are angles of r e uusually sually extremely small amall such h a t isoclinal i s o c l i n a l folds folds and and such tthat transposed layerslayers are present. The tranapoaed a r enot notuncomeonly unconw~mlypresent. The ffoliation, o l i a t i o n , which vhich ranges ranges from f r m a closely c l o s e l y spaced spaced penetrative alignment of ppiety penetrative alignment of l a t y minerals minerals to to a spaced cleavage, comuonly ffoliation o l i a t i m or cleavage, conmuonly parallels p a r a l l e l s bedding, bedding, eespecially s p e c i a l l y in i n the Limbs limbs of of isoclines. isoclines. The P2 F2 deformation S l surfaces and and deformation refolded refolded the the $1 formed formed a a set s e t of of crenulation crenulation cleavages cleavages and and open open folds. Ax.al c r e n u l a t i m cleavages, cleavages, $2 S2 M a 1 planes and crenulation of t r i k e consistently c o n s i s t e n t l y N65E N6SE throughout throughout the the of F2, P2, sstrike ) , indicating i n d i c a t i n g that t h a t later l a t e r deformations deformations region (Pig. (Fig. 3 3), ffailed a i l e d tto o regionally r e f o l d Ti F l and and P2 F2 structures. structures. regionally refold Fold axes axes of of F2 f o l d s form f o m aa great g r e a t circle circle Fold P2 minor minor folds d i s t r i b u t i m on on stereogram stereogram because because the the P2 F2 distribution a t already already folded folded deformation represents represents folding folding of of an surface. Apical surface. 70 degrees degrees to to angles are a r ecomuonly coummly 70 Apical angles 120 degrees, and fold f o l d profiles p r o f i l e s indicate i n d i c a t e type type 13 1B and and 120 degrees, and 1IC C folds. folds. Depending on m host host rock rock lithology, lithology, �—6— ranges from ional crenulation cleavage crenulation cleavage of P2 F2 ranges from aa zonal cleavage cleavage in i n pelitic p e i i t i c rocks rocks to t o discrete, discrete, disccntinuäus cleavage iinn netavolcanics diacontinu6us cleavage metavolcanics or sandstones. IIn folds Si sandstones. n places, P2 F2 deformation deformation folds Sl folds or ffoliations o l i a t i o n s into i n t ominor minor chevron chevron folds or kinks. kinks. The deployment deployment of P2 F2 deformation deformation ffabrics a b r i c s is not not F2 minor homogeneousthroughout throughoutthe thearea area studied. studied. P2 homogeneous folds were were observed obserred only in inthe theCFt CFtand andthe theHemlock Hemlock Pormation sslates Formation l a t e s above the Fiernar& Kiernan SSills. i l l s . The The development P2 crenulation cleavages is is also also development of of F2 intense when most intense when Si S l surfaces surfaces are a r e oriented oriented NNW. BMW. The P3 deformation d•formmtioni sis characterized characterized by The F3 by subhorizontal crenulation crenulation cleavages cleavages (dips <(35 35 degrees) which iintersect degrees) which n t e r s e c t with Sl 31 foliations f o l i a t i o n s to t oform fom lineatione. abundant ation lineations. abundant subhorizontal crenul crenulation These subhorizontal cleavages dip These d i p away, away, on all all sides, sides, from tthe h e Amasa Amasa Oval Oval and and the the Peavy Pond Pond intrusive. These subhorizontal foliations intrusive. These f o l i a t i o n a indicate indicate subvertical shortening, subvertical shortening, probably probably associated associated with with Fig. 3. 3. Fig. uplift. basement u p l i f t . between this The rrelation e l a t i o n between t h i s phase deformation andbasement basementisisb ebest s t i illustrated l l u s t r a t e d by by deformation and tthe h e case case of of the the Peavy Peavy Pond t r u s i v e (Fig. 3 ) . The Pondi nintrusive (Pig. 3). of subhorizontal subhorizontal crenulation cleavages cleavages dipping away away from the Peavy Peavy Pond related Pond stock can reasonably be related of tthe Pondiintrusive. tto o the emplacement emplacement of h e Peavy Peavy Pond n t r u s i v e . So So iitt isisreasonable reasonable enough enough tto o bbelieve e l i e v e tthat h a t the the presence of subhorizontal crenulation c r e n u l a t i a i cleavages cleavages presence of subhorizontal dipping away from l s o the t h e result r e s u l t of of from hAmasa s a Oval is aalso Archean basement p l i f t even even though this t h i s uplift u p l i f t was was basementuuplift by any detectable any d e t e c t a b l e thermal thermal not accompanied by aactivity. c t i v i t y . In the t h e Peich Felch trough, trough,Calumet Calumet trough trough and and Taylor mine, subhorizontal cleavages Taylor mine, the the subhorizontal cleavages may nay aalso lso be related r e l a t e d to t o mobilization mobilization of crystalline be of crystalline basement. But d i f f i c u l t to to basement. n these But iin theseareas, areas,itit is difficult doiint the exact piece of pin down h e exact of basement basement involved. involved. This phase of deformation can subdivided iinto nto This phase of deformation can be be subdivided different d i f f e r e n t sets s e t sof ofsubhori.zontal subhorizontal crenulation crenulation cleavages based on which which part p a r t of basement uuplift plift baaed an of basement Deformation in Florence—Niagara and Deformation i n the the iniogeocline, miogeocline, Florence-Niagara and Crystal Crystal Falls Falls terranes. terranes. �—7— that t h a t each set s e t is is related r e l a t e d to. to. Rowever, However, cross—cutting cross-cutting relations r e l a t i o n s among among cleavages cleavages indicate indicate that t h a t the the time time slot s l o t for f o r formation formation of of these these subhorizontal subhorizontal cleavages cleavazes was was confined between between deformations, 14. Therefore Therefore it it seems seems that that F2 and andF4. deformations, 12 Archean Archean crystalline c r y s t a l l i n e basement basement of of the the study study area area was was regionally in the t h e Cit CFt (where no no regionally remobilized, renobilized, except in crystalline c r y s t a l l i n e basement if i f exposed), exnosed). during during this t h i s phase phase of s u b h o r i z o k a l ccleavage l e a v a g e in i n tthe h e INt FNt . o f deformation. deformation. Subborizontal problematic, but may maya also ber related problematic, but l s o be e l a t e d tto o this this period of regional period of regional uuplift. plift. is is The 14 deformation is marked marked by by sporadic sporadic The F4 deformation is occurrences steeply dipping occurrences of of NW—striking, NW-striking, steeply dipping minor minor fold erenulation planes, planes, fold axial a x i a l surfaces, surfaces,kink, kink. and andcrenulatiom which cross—cutppreexisting which cross-cut r e e x i s t i n g ffabric. a b r i c . The The solid solid evidence is shown shown by by refolding evidence of of this t h i s deformation is or or crenulating crenulating 13 F3 subhorizontal subhorizontal crenulation crenulation cleavages. minor folds folds observed observedinin the the ffield F4 minor ield cleavages. 14 70 degrees degrees to have apical angles angles ranging ranging from from 70 t o 120 120 have degrees. is represented represented by by aa set s e t of of F5 deformation deformation is 15 crenulations and steeply-dipping NS—striking US-striking crenulationa andsome some steeply—dipping open folds with open folds with apicat a p i c a l angles angles greater g r e a t e rthan than100 100 Fold pprofiles r o f i l e s indicate i n d i c a t e that t h a tmost most of of 15 F5 degrees. Fold Crenulation folds 1B and and lC 1C folds. Crenulation folds are a r e type type 13 cleavages of this cleavages of t h i sdeformation deformation range range from from a a zonal zonal cleavage tto o discontinuous, discontinuous, discrete discrete crenulation cleavage cleavage and is i scoenonly connonly present present whenever whenever the t h e 31 31 cleavage and surfaces EW. EW. surfaces are a r eoriented oriented In phasea of of I n spite s p i t e of of the the fact f a c t that t h a tfive f i v ephases deformation wererecognized recognizedi nintthis deformation were h i s region, only only the twoepisodes episodes of ofdeformation defoimation 11, Fl, and and 12, F2, t h e first f i r s ttwo were were eeffective f f e c t i v e in i n constructing constructing the the regional regional structural s t r u c t u r a l features. features. The extremely intense extremely i n t e nNNE—SSW s e NMB-SSW oriented of FFll constructed oriented shortening shortening regime regime of constructed aa series trending tright s e r i e sofofWNW WMU trending i g h t folds folds and and shear shear zones zones which which sometimes sometimes involved Archaen Archaen basement baaemant such as as the Oval, and Creek Uplift. Uplift. The the Amasa Amasa Oval, and Smith Smith Creek The 12 72 deformation folded the the eexisting 11 structural deformation cross croasfolded x i s t i n g F1 structural •f1O •XO$ trending features f e a t u r e s and locally l o c a l l y rotated r o t a t e d them them into i n t oNNW NNW trending structures. The crossfolding crossfolding origin o r i g i n of of Amasa Amasa Oval Oval s t r u c t u r e s . The instead is supported supported by by the the i n s t e a d of of gneiss gneiss doming doming is following following observations: observations: 1. The The ffact a c t that t h a t structures s t r u c t u r e s in i n strata s t r a t a of of the the Supergroup mantling mantling the Marquette Range Marquette Range Supergroup t h e Archean Archean basement of the Oval iindicate basement of the Amasa Amasa Oval ndicate crossfolding. crossfolding. 2. A NNW A sset e t of ofpenetrative penetrative NNW trending trending s u b v e r t i c a l foliations, f o l i a t i o n s , which is is pervasively pervasively subvertical developed developed in i n the the sediments sediments mantling mantling the the basement, is is found to t o be cross—cut cross-cut by later later deformation deformation fabrics f a b r i c s 52, S2, S3. S3. Both the the cross—cutting cross-cutting relations r e l a t i o n s and and the the correlation correlation with NNW trending trending Fl F l folds folds in i n Crystal C r y s t a l Falls Falls t e r r a n e indicate i n d i c a t e that t h a t this t h i s is a set s e t of of rotated rotated terrane Si S l foliations. foliations. 3. The The same same set s e t of of NNW NNW treading l i a t i o n s is is 3. trendingf ofoliations t h e most most prevalent prevalent foliation f o l i a t i o ndeveloped developedini nAmasa Amasa the Oval Oval Archean Archean basement. basement. 4. 4. Lack Lack of metamorphic metamorphic aureol aureol related r e l a t e d to t o Amasa Amasa Oval Oval discredits d i s c r e d i t s the t h e possible origin o r i g i n by by gneiss gneiss doming. doming. 5. The The subhorizontal subhorizontal crenulation crenulation cleavage cleavage 5. r e l a t e d to t o basement uplift u p l i f t cross—cuts cross-cuts which was related the NNW trending trending 31. Sl. t h e NNW The The presence presence of of 53 S3 subhorizontal subhorizontal cleavages cleavages in in t h i s region region indicates i n d i c a t e s that t h a t basement uplift u p l i f t presided presided this over over the the miogeocline miogeocline once. once. Rowever, However, the the major major structural s t r u c t u r a l features f e a t u r e s in i n this t h i s region region were constructed constructed mainly by o r i z o n t a l shortening shortening p r i o r to to mainly by periods periods of of hhorizontal prior basement basement uuplift. plift. Florence—Niagara Terrane Florence-Niagara Terrane The Florence—Niagara Florence-Siagara terrane t e r r a n e consists c o n s i s t s of of at at The e i g h t fault—bound fault-bound slices s l i c e s striking s t r i k i n g NU (Bayley eight NW (Bayley least least and and others, others, 1966; 1966; Dutton, Dutton, 1970; 1970; Larue Larue and and Gang, Ueng, in in prep.) is based based on on prep.) (Fig. (Fig. 4). 4). Recognition of faults f a u l t s is truncation truncation of of regional regional stratigraphy s t r a t i g r a p h y(Fig. ( f i g . 2A) 2A) (Bayley (Bayley and and others, 1966; 1966; Dutton, Dutton, 1970), 1970), changes changes in in structural or fabric f a b r i c across lithic lithic s t r u c t u r a l style s t y l e or boundaries, boundaries, and and stratigraphic s t r a t i g r a p h i c relations r e l a t i o n s (Larue (Lame and and Gang, Ueng, in i n prep.), prep.), as as discussed discussed below. below. Fault slices slices 3, 3, 7 and and 7A 7A are a r e defined defined on on the the basis b a s i s of of stratigraphy s t r a t i g r a p h y each represents shallow-marine to to fluvial f l u v i a l quartzices q u a r t z i t e scontiguous contiguous on on both both sides s i d e s with with apparently volcanogenic sslates apparently deep—water, d e e p w a t e r , volcanogenic l a t e s (Larue, (Larue, 1983). Contacts Contacts are a r e sharp, sharp, though no no obvious obvious 1983). P*it Rlv.r 3rou (Iron ormatton In bleci ,. 3ew.s, Gessnajon. MIhism,,. 31MlchlgçmmSlat. (quartzjt. ( q ~ r t ~ $tIDDI.d) Â¥tIpohd i f M•nomi• GrOUD Menominee aroup \.sdIm.ntary conteCt MOUNTAIN CllocoI.y Groi,p Pandall,. Dol.m*t. Contact Fig. 4. Geology of the Florence—Niagara terrane. �—8— truncations truncations aare r e present. present. All A l l fault f a u l tpackets packets except except packet 88 contain contain homoclinal homoclinal south—facing south-facing sstrata. trata. block, contains 3abbitt block, Packet 8, 8 , tthe h e Bessie Bessie Babbitt contains aa major fold. fold. Your Four different d i f f e r e n t types types of of structural s t r u c t u r a l fabric f a b r i c are are A l l are a m characterized characterized by by recognized in i n the t h eYNt. FNt. ALL aa dominant cleavage,oor byaaxial surfaces tthat dominant cleavage, r by x i a l surfaces hat Elongation lineationa lineations and steeply. Elongation sstrike t r i k eW—NW W-NW and d idip p steeply. associated associated with with such such foliations f o l i a t i o n splunge plunge down down ddip i p in in all where bulk bulk extension extension a l l cases cases except except in i npacket packet1,1,where fold axes, axes, aa llocally o c a l l y parallels p a r a l l e l sshallowly—plunging shallouly-plunging fold probable product of probable product of superimposed superimposed sstrains trains axes in packets packets 1) VoId f o l d axes (compaction andtectonic). tectonic). 1) (compaction and 1 and and 55 are a r e aubhorizontal subhorizontal or or shallowly shallowly plunging, plunging, 2) -Fold Fold axes axes in i n packets packets 22 NW—SE. 2) and trend E—W and E-W tto o HW-SE. and 77k plane (Fig. (Fig. 6B). 6B). and A are a r e girdled girdledini a n NW—SE a SW-SE plane Si, Sl, IN Mn I TT1S It Geologic map arly P r o t e r o i o i c rocks rocks Fig. mapofofeearly Proterozoic Fig. 5. 5. Geologic IM), MI, (?I, Iron Mountain Mountain ((IN), near Iron MI, Florence Florence (F), WI, and Niagara (N), WI. UI. WI, and Niagara (N), Florence-Uiagara Florence—Niagara (FH) Fault separates separates passive passivemargin margin (FE Fault assemblage assemblage to t o the thenorth north(Miogeo/Cracon (Miogeo/Craton— - autochthonous sedimentary sedimentary cover cover of Superior FNt = Superior Province basement; basement: YNt Florence-Niagara t eterrace; r r a e ; CFt Florence—Niagara Cit • Crystal Falls F a l l s terrace) t e r r a e )from frommagmatic magmatic aarc r c terrace terrane (mt) ranitoids (me) to t o the the south south (stipples ( s t i p p l e s— g granitoids and gneiss; ma netasedimentary rocks; rocks; gg and gneiss: os - metasedimentary = gabbroic gabbroic ssuite; u i t e ; v — metavolcanic schiacs). boundshigh high sstrain s c h i s t s ) . Jagged line l i n e bounds train belt e i t h e r side of of the the b e l t developed on either fault; f a u l t ; queried line l i n e denotes tentative tentative location location of boundary. Solid Solid llines ines bounding passive margin terranes and passive margin terraces and within FTNt U t are a r e faults; faults: ssolid o l i d Lines l i n e s in i ntat mt within aare r e lithologic l i t h o l o g i c contacts (after ( a f t e r K. Schulz K. Schulz and and P. S k , unpub. unpub. map) h a t way may aalso l s o be P. Sims, map) tthat ffaults. a u l t s . as * locations locations of slickenside slickenside sstriations t r i a t i o n s used used in i n stress s t r e s s axes axes calculations ext). V e r t i c a l l y lined lined calculations (see (see ttext). Vertically pattern denotes a u l t sslices l i c e s in in denoteslow-strain low-strainf fault TNt. FNt. - - - - • Fig. 66 Fig. 6*—c. Lower hemisphere stereographic 6a-e. stereographic Dl p r o j e c t i o n s of structural s t r u c t u r a l data d a t a for f o r Dl projections (accretion-related) deformation. C ircles (accretion—related) Circles - = ffold o l d axes; axes; squares squares— poles tto o aaxial xial 1, 2, 3 axes of the stress ellipsoid; Z are axes of strain eellipaoid. l l i p s o i d . a. a. miogeosyncline/craton miogeoayncline/craton folds; b. TNt folds; b. FHt folds with inferred i n f e r r e d X, Y, ZZ I, Y, sstrain t r a i n axes: s t r e s s axes axes from axes; c. c. FNt TNt stress fton slickenside sstriations t r i a t i o n s with with inferred i n f e r r e d951 95% slickeneide confidence i r c l e s ; d. d. tat m t folds; e. mt confidence ccircles; e. tnt stress s t r e s s axes. axes. surfaces; r e axes of the s t r e s s surfaces: 1, 2, 3 aare X, Y, e l l i p s o i d ; X, Y, Z a r e axes of s t r a i n intermediate aaxis of sstrain) have ((parallel p a r a l l e l tto o tthe h e intermediate x i s of t r a i n ) have been strained s t r a i n e d toward the direction d i r e c t i o n of of finite finite axes pparallel extension. Fold Fold axes a r a l l e l to t o the t h e intermediate intermediate extension. aaxis x i s of strain s t r a i n rotate r o t a t e less l e s s than t h a nthose t h o s e askew, askew, thus thus aa of fabric girdled The oorigin r i g i n of fabric girdled ddistribution i s t r i b u t i o n results. r e s u l t s . The understood, but but measured is poorly poorly understood, measured sstrains trains type 33 is indicate i n d i c a t e X/Z X/Z rratios a t i o s of of up up to t o 10, 10, and and therefore t h e r e f o r e the the fabric f a b r i c is is aalso l s o related r e l a t e d to t o large l a r g e strains. strains. Fabric representedi in seems represented n ffabric abric 3 3 with with aa Fabric 4 seems are 4, 6, 6, and 77 a 3) Fold axes in packets 3, 3, 4, r e steeply steeply 3) downthe theregional regional ffoliation. oliation. inclined and plunge plunge down in packet 8 also 4) Fold Fold axes in packet 8 a l s o plunge steeply but have been by cross—folds cross-folds with *4 N-S axial axial been complicated by The ffirst planes. i r s t three t h r e e fabrics f a b r i c s (1—3) (1-3) are are planes. The of ddifferent interpreted as a s products products of i f f e r e n t strain strain f a b r i c 2) 2) histories. h i s t o r i e s . The girdled fold axes ((fabric represents the the highly highly sstrained equivalent of of the represents t r a i n e d equivalent the f i r s t ffabric a b r i c type type (for ( f o rexample, example, Sanderson, Sanderson, 1973). 1973). first That iis, That s , initially i n i t i a l l ysubhorizontal subhorizontal fold foldaxes axes superposed superposed deformation deformation about about aaN—S N-S aaxial x i a l plane plane folds with planes aare (S2). Minor Minor folds with N—S N-S a xaxial i a l planes r e not (52). present elsewhere present elsewhere in i n the the FNt. Crenulations with TNt. Crenulacions aaxial x i a l surfaces surfaces parallel p a r a l l e l to t o those those described described in i n the the iniogeocline (12—V5) present sporadically, miogeocline (F2-F5) era a r e present sporadically, but but age age rrelations e l a t i o n s can not be specified s p e c i f i e d other other than than post—Si. pos t-Sl. FTNt. Nt. Metamorphism was relative Metamorphism r e l a t i v e complicated complicated in i n the the Early folding was not associated with �—9— Cross-folds iin n packet packet 88 significant s i g n i f i c a nmetamorphism. t metamorphism. Cross—folds pre—dated p r e d a t e d garnet grade grade metamorphism. metamorphism. S S ttrtke—s r i k e s llLp ip faulting f a u l t i n g(NW—striking) ( W s t r i k i n g ) with withassociated associated garnet garnet grade grade metamorphism metamorphism is is observed observed in i n packet packet 4. 6. Slickensid. Slickenside striations s t r i a t i m son on faults f a u l t swere -re studied studied (ma Fig. 4), calculated from (m i ninFig. 4 I yand and mean mean sstress t r e s s axes axas calculated from such data (technique of A. A. Michaels, Michaels, submitted). submitted). such data (technique of Results are a r e shown shown iinn Figure Figure 6C, 6C, and and stress s t r e s s axes axes Results parallel p a r a l l e l strain s t r a i naxes. axes. Magmatic Terrane Mamatic To To aa first f i r a approximation, t approximation, the thenorthern northern edge edge of of the terrane cam be bbest the magiaatic magmatic terrane can be e s t thought thought of of as a s aa wide highly highly strained 2-4 2-6 km km wide s t r a i n e d zone z m e that thatstrikes s t r i k eN7OW, s U7W, parallel (Fig. 53). p a r a l l e ltot othe t hFlorence—Niagara e Florence-Niagara FFault a u l t (Fig. 5B)In In detail, d e t a i l , the t h e penetrative penetrative vvertical e r t i c a l foliation f o l i a t i m that that defines ha8 been been refolded refolded defines the t h e shear shear zone zone fabric f a b r i c has about duringa asubsequent subsequent about subvertical subverticalaxes axes during deformation deformation event. went. In I n this t h i sregion region aa dominant dominant sstructural t r u c t u r a l feature f e a t u r e is is Gneiss dm*, done, which which SSims (pers. come., the t h e Dumbar Dtmbar Gneiss i w (pers. c~nm.~ 1982) 1982) invokes invokes to t o accoimt account for f o r variable v a r i a b l e foliat3.on foliation attitudes a t t i t u d e s at a t the the edges edges of of the the gneiss gneiss body. b*. Relative andl alater Relative timing timing of of gneise gneiss doming doming and t e r folding folding of the is the penetrative penetrative ffoliation o l i a t i a t near near the the fault f a u l t is unresolved. unresolved. Structural S t r u c t u r a lSynthesis Synthesis of of the the Magmatic Mamutic Terrane. Terrane. The D l , produced produced The eearliest a r l i e s t recognizable recornizable deformation, d e f o r m t i a x , Dl, aa penetrative, WNW—striking penetrative, subvertical, s G v e r t i c a 1regionally , regionally WlW-striking foliation f o l i a t i o n Si Sl with with aa steep steepdown—dip dom-dip mineral mineral B d i n a g e and and dismembered dismembered i sisoclinal oclinal lineation l i n e a t i o n 1.1. Ll. Boudinage folds indicate Early indicategreat g r e astrain t s t r a iaccompanied n accompmiedDI.. D l . Early metamorphism wassynkinamatic synkineaatic with with Dl D l and aad metamorphism MlMlwas probably attained amaphibolit. probably attained amphibolite ffacies a c i e s PT P-T conditions. Subsequent open opea to t o tight t i g h t folding folding conditima. Subsequent comprised 32; these these folds folds range cm to t o km km in in cmprised D2; range from f r m cm wavelength, have subvertical subvertical axes, wavelength, have axes, and and do do not not signify signifyaapenetrative penetrativedeformation defonnatim event. went. Retrograde M2, generated generated Retrograde thermal t h e w 1metamorphism, metamorphism, M2, randomly oriented amphibole amphiboleand andc hchlorite randmly oriented l o r i t e that that overprint It is is not not M l metamorphic metamorphic fabric. fabric. It overprint the Ml known orsyn—32. SF-D2. known whether 112 M2 iiss post— post- or Several Dl Several sstructural t r u c t u r a l features features indicate i n d i c a t e that t h a t Dl accompanied accompanied bybyggreat r e a t sstrain. t r a i n . Isoclinally Isoclinally folded folded compositional compositional layering and, and, in i n some some mnetaseditnencary metasedhentary rocks, rocks, bedding, bedding, is is almost almost always almys was was The The rresultant e s u l t a n t boudins bdins have or major major planes planea oriented oriented have ttheir h e i r long long axes axes or tectonically t e c t o n i c a l l y dismembered. dismembered. parallel p a r a l l e l to t o the the penetrative penetrative SSl l ffoliation. o l i a t i o n . Pressure Pressure shadows aroundsaue some mineralgrains grainslend lend support support ttoo shadows around mineral an of Ll an iinterpretation n t e r p r e t a t i o n of Ll as as a a stretching s t r e t c h i n g lineation. lineation. Finally, Finally,when when 32 D2 folding folding is is removed, removed, Dl D l fold axes axes define a great great circle c i r c l e distribution d i s t r i b u t i o n within aa constant N7OW N70W constant mean mean aaxial x i a l surface surfaceofofapproximately approximately (Fig. (Fig. 63). 6D). Renoval 3eanoval of of 32 D2 folds folds also a l s o yields y i e l d s aa point point maximum lineations plunging plunging maximum of of mineral mineral (stretching) ( s t r e t c h i n g ) lineations steeply steeply southwest. southwest. From From this t h i s geometry geometry we we infer infer axes D l to t o be XX axes of of the the strain s t r a i n ellipsoid e l l i p s o i d during during Dl subvertical, WNW—ESE, subvertical, Y subhorizontal subhorizontal WUW-ESE, and and ZZ corresponds with subhorizontal subhorizmcal NNE—SSW. NNE-SSW. Hence Renee XX corresponds with with S Sl, Ll, XY plane plane corresponds corresponds with l , and and the the Ll, the the XY shortening shortening direction d i r e c t i o n ZZ lies l i e n roughly roughly normal nonnal to t o 1170W N70W and Fault. and the Florence—Niagara Florence-Niagara Fault. Further Dl Further support support for f o r this t h i a orientation o r i e n t a t i m of of the t h e Dl strain s t r a i n axes axes was was recently recently obtained obtained from from slickenside slickenside striations m t . Using Using aa s t r i a t i o n s on on minor minor faults f a u l t s in i n the the at. computer computer program program developed developed by by Andrew Andrew Michael Michael of of Stanford Stanford University, we we calculated calculated axes axes of the the stress 1, 2, 2, 3) 3) that t h a t coincide coincide s t r e s s ellipsoid e l l i p s o i d (sigma (sigma 1, almost exactly with the strain Y, and X 2, Y, X s t r a i n axes, axes, Z, (Pig. (Fig. 6E). 6E). The close c l o s e agreement agreement of of axes axes markedlyddifferent orientations o r i e n t a t i o n s derived derived from f r a u two two markedly ifferent techniques, coupled with the the tiny t i n y 95% 95% confidence confidence circles c i r c l e s for f o r the t h e sigma sigaa values, values, strongly strongly indicate indicate NNE—SSW NNE-SSW shortening shortening and and subvertical s u b v e r t i c a l extension extension during during Dl. Dl. The earliest e a r l i e s tmetamorphism, metamorphism, Mi, M l , was was synkinematic synkinematic The Dl D l as a s evidenced evidenced by by alignment alignment of of relict relict amphibole mphibole grains g r a i n s within within the t h e Si S l foliation f o l i a t i mplane planeand and p a r a l l e l to t o Li. Ll. In I n thin t h i n section, s e c t i m , however, however, lLttle little parallel or or none of of the t h e original o r i g i n a l MMl 1 mineral assemblage can be be identified i d e n t i f i e d due due to t o retrograde retrograde metamorphism metamorphism during during with with M2. 112. During D2, D2, Dl D l layering layering was was folded folded about about subvertical s u b v e r t i c a l axes both at a t outcrop a t c r o p scale, s c a l e , where close close t o open open cm an to t o meter wavelength wavelmgth folds folds are a r e observed, observed, to and at a t map map sscale, c a l e , where wherehomogeneous hmogeneous domains domaim having and variable, but always always steep, steep, orientations o r i e n t a t i o n s of of Dl Dl foliation/layering f o l i a t i o n / l a y e r i n g are a r e best b e s t explained explained as a s limbs limbs of of open folds f o l d s with with wavelengths wavelengths measured measured in i n kin. km. Axial Axial open surfaces of of these these folds f o l d s are a r e variable v a r i a b l e but usually imply No penetrative penetrative imply E—W E-W to t o NW—SE W S E shortening. shortening. No S—surface acccmpanies 32. D2. S-surface or lineation l i n e a t i o naccompanies The preponderance prepcaderaace of randomly—oriented randomly-oriented green green amphibole andc hchlorite rocks ofof aall amphibole and l o r i t e i in n rocks l l lithocypes lithotypes suggests s q g e s t s tthat h a t the the magnetic magmatic terrane t e r r a n e experience experience late late N l amphibolite amphibolite thennal metamorphic metamorphic r retrogression e t r o g r e s s i m of Ml thermal facies f a c i e sassemblages assemblages tot o112 M2 greenschist facies facies assemblages. We havewnoddirect We have i r e c t evidence evidence ppertaining ertaining to M2 iiss post— post- or syn—D2. SF-D2. t o whether whether 112 AL& present present in i n the t h e magmatic magmatic terrane t e r r a n e are a r e local local Also areas in inwhich which crenulations c r e n u l a t i m s are a r edeveloped developed that that areas appear tto o be a r a l l e l to t ocrenulation c r e n u l a t i mcleavages cleavages in in appear be pparallel the FNt. However, miogeocline and and TNt. t h e miogeoclin. Hwever, we we do do not not have have enough data data at a t present present to t o conclude conclude whether whether aall ll enough def-tim phases obsemed n the the miogeocline miogeocline are are deformation phases observed iin present m t , and and whether whether the t h e ordering ordering of of present iin n th. t h e at, these these events events is similar. similar. RICH STRAIN BELT: NATURE OF THE 1ff—TNT BOUNDARY. The TNt mt and and northern northern tnt m t define aa high high as ttrain rain The b e l t , where fold fold axes axes have have been been locally l o c a l l y strained strained belt, i n t o parallelism p a r a l l e l i s u with with the the direction d i r e c t i o n of of finite finite into extension (Fig. (Fig. 5)(Larue 5)(Larue and and Ueng, Ueng, submitted; submitted; extension Sedlock and and tarmac, Larue, 1983). 1983). Other Other features features Sedlock associated with t h i s g r e a t s t r a i n a r e isoclinal isoclinal assocated with this great strain are folds, dismembered dimembered folds, f o l d s , type type 22 and and 33 folds folds (of (of folds, Ramsay, 1967) 1967) and and transposed layering. layering. Large Rainsay, Large thome inferred i n f e r r e d here here occur occur only only s t r a i n s such such as as those strains r a r e l y in i nrocks rocks north north of of the the FNt. FNt. The rarely The southern southern bomdary ofof the s t r a i n belt b e l thas hasnot notbeen been boundary the high high strain adequately defined. defined. We adequately conclude that F N ~and and We conclude t h a t the the FNt northern northern part part of of the t h e met m t represents represents a a high high strain strain belt b e l t straddling straddling the the Florence—Niagara Florence-Niagara Fault. Fault. is developed developed within within the the northern zone zone (FNt) (F'!?t)is northern me The miogeoclinal mna.ogeoclinal assemblage rocks, whereas the southern assemblage rocks, whereas the southern zone aaffects f f e c t s only onlyarc a r cassemblage assemblage rocks rocks (northern (northern zone part p a r t of of tnt). mt). Structural S t r u c t u r a l fabrics f a b r i c s are a r e nearly nearly @ig. 63—f). 6B-E). This i d e n t i c a l(Ftg. Ldentcal This high high strain s t r a i n belt belt probably formed formed during during terrane terrane accretion. accretion. probably Other zones zones of of high high strain s t r a i n including including shear shear Other zones occur occur locally l o c a l l y throughout throughout the t h e miogeocline and zones miogeocline and represent zones zones of of increased increased sstrain train probably represent resulting frcm localized localized weaknesses weaknesses in i n the the basement. basement. r e s u l t i n g from CEOCHE1fISTRY GEOCXEMISTRY Provenance of of Marquette Marquette Range Range Supergroup Supergroup Provenance �-10— sandstones sandstones is not not well wallconstrained constrainedbecause because Provenance Provenance studies s t u d i e s using using slate s l a t e geochemistry geochemistry have have been been made made by by Carrels Garrels and and MacKenzie MacKenzie (1971), (19711, Cameron Cameron and and Carrels Garrels (1981) (1981) and and others,, others,. who who used used geochemistry geochemistry to t o separate separate slates s l a t e s of of volcanic volcanic and and I n our our study, study, we we made made 106 106 continental continental provenance. provenance. In ternary 7) a r e showu shown (Pig. (Fig. 7) ternary diagrams diagrams of of which which 4 are diagenesis diagenesis and and metamorphism metamorphism has has altered a l t e r e dand and destroyed fragments such such tthat destroyed 1.LthLc l i t h i c fragments h a t modified modified assemblages exist. Petrographic assemblages exist. Petrographic studies s t u d i e s of of only mly s l i g h t l ymetamorphosed metamorphosed sandstones n d i c a t e s an an slightly sandstones iindicates older Precambrian Precambrian source for f o r the theChocolay, Chocolay, older Menoininee (Lame, 1981) Menominee (Larue, 1981) and and Baraga Baraga Groups Groups (Alvin, (Alwin, 1979). 1979). Rovever, Emever, aa ssignificant i g n i f i c a n t portion poztion of of the the late, Marquette Range Range Supergroup Marquette Supergroupisis represented represented by by sslate, whose provenance i f f i c u l t to to whose provenanceisis extremely extremelyddifficult establish e s t a b l i s hpetmographically. petrographically. To To try t r y to t ocharacterise c h a r a c t e r i z ethe theprovenance provenance of of the the slates, samples wesent seatabout about6060 samplesfrom f r a nthroughout throughout s l a t e s ,we average average argillite, a r g i l l i t e , average average granite g r a n i t e and and average average green. the Canadian Canadiau shield s h i e l d (Roaov (Ronov and and g r e e n stone t m e from from the Migdisw, 1971). 1971). In In addition, addition, analyses analyses of of the the Migdieov, 3adwater Badwater Greenstone Greenstone are a r e plotted p l o t t e d ini nFigure Figure7.7. Sample. our study study are a r e mostly mostly from f r a n the the Samples used used in i n our areas areas discussed discussed herein, herein, but but we we also a l s o included included samples samples from f r a u the t h e Marquette trough trough (especially ( e s p e c i a l l y the the S i a o Slate S l a t e of of the the Menominee M e n d n e e Group Group which which underlies underlies Siamo the t h e Negatntee Negauuee Iron Iron Formation). Formatirm). sectiai to t o the the the early e a r l yProterozoic Proterozoic section th. Barrangem—Maj antsCorporation, Corporation, who Barrmger-Majenta who made made major and and t r a c e element element studies s t u d i e susing usinginduced inducedcoupled coupledplasma platrace techniques (ICP). Several Several duplicate duplicatesamples sampleswere were techniques (IcP). sent 45%. Ton Tau Vogel Vogel sent and and errors e r r o r s were = r e in i n all a l cases l cases<5Z. Two Two basic basic populati.ons populations are a r e recognized recognized in i n the the (Michigan has (Xichigau State S t a t e University, . , 1980) 1980) has university, per¶ pers.e m c., ternary ternary diagrams diagrams presented presented herein herein ini nwhich which formational f o r n a t i o n a l groupings groupings occurred. occurred. Slates S l a t e s interbedded interbedded had had similar s i m i l a r success success with with them. than. CaO representing representing different d i f f e r e n tcombinations c m b i n a t i o n s of of major major and and minor elementsofof the the sslates, minor elements l a t e s ; and and also a l s o plotted plotted •2O K20 !m CU U B 5sdw s...i_ • Hdi U cI. C £ A Mu,amli. • Waws S o amco.y S avenge Thom, .. K,0 Fig. Fig. 7 7 Ternary Ternary plots p l o t s of of slate s l a t e geochemistry. geochemistry. 1(20 �—11— with ultramature ultramature quartzites q u a r t z i t e s and m d dolomites d o l d t e s ofof the the with ChocolayGroup Groupgenerally generallyplot p l o tini na atight t i g h tcluster cluster Chocolay Such near composition composition of of the theaverage averagegranite. granite. Such near potassic and andalulaLnous aluminous slates s l a t e swere wereprobably probably pOtasSC i l l i t i and c , and derived from a continental o r i g i n a l l yillitic, originally derived from a continental source. Slates S l a t efrom s frm e M e n d n e eand andBarags Baraga thet hMencminee source. (includingHemlock Hemlock Slates) S l a t e s )seem seemtot orepresent represent mixed (including mixed Some slates s l a t e sfrom fram source-continental plus plus volcanic. volcanic. Some source—continental theSismo SiamaSlate S l a t ehave havebulk bulkgeochemistry geochemistry similar s i m i l a rtot o the greenstones, probably probably indicating i n d i c a t i n gaavolcanogenic vo1caogenic greenscones, source. Although Although volcanic volcanicrocks rockshave havebeen been source. e Group recognized in i nthe theupper upperpart p a rof t the of ttlenominee h e M e n d n eGroup recognized is the the first f i r s t indication i n d i c a t i m that that (Prinz, 1976), 19761, this t h i s is (Prinz, pre-irm formatim t r a t a , specifically s p e c i f i c a l l the y t hSiamo e Siaw pre—iron formation sstrata, Gairand and S l a t econtain containvolcanogenic volcanogenic material. material. Gait Slate Thadm (1968) (1968) proposed, proposed, also a l s o cm m the t h e basis b a s i sofof Thaden geochemistry, that t h a tcertain c e r t a iof n of WeweSlates Slates geochemistry, thethe Wewe (uppennostomit m i t of of the t h e ChocolayCroup Chocolay'Group ini nthe the (uppermost s i n g l edata data !hrquette trough) trough)were werevolcanogenic. volcanogenic. AA single Marquette p l o t t e dini nFigure Figure7.7. pointfrom fromGait Gair and and Thaden Thadm ia point is plotted SUMMARY This This study study establishes e s t a b l i s h e s that t h a tthe theProterozoic Proterozoic ininthe t h esouth southcentral c e n t r aLake l LakeSuperior Superiorregion region have have suffered suffereda acomplicated, complicated,polyphase polyphasedeformation deformation The exact exact tectonic t e c t o n i c interpretation i n t e r p r e t a t i o nofofeach each history. history. The deformation deformatim event w e n t is is not not yet y e tfully f u l l understood. y understood. However, it isi sclear c l e a rthat t h athe t t hCFt, e CFt,E'Nt, E N t ,tat, m t ,and a d However, it rocks rocks miogeocline miogeocline have have undergone mdergone parallel p a r a l l e deformation l deformation El, r d n g aall l l deformations deformations except except Fl, By removing h i s t o r i e s . By histories. some assemblages some interesting i n t e r e s t i n gtectonotithological tectonolitho1ogical assemblages are a r eobserved: observed:thet hnon—volcanic e non-volcanic miogeocline miogeocline (subterrane A), submarine (aubterrane A), submarine tholeiitic t h o l e i i t i cvolcanics volcanicsofof subterrane subterrane B; B; basin basin floor f l o o r deposits deposits (Crystal ( C r y s t a lFalls Falls terrane), t e r r a e ) ,highly highlystrained s t r a i n e dfault f a u lpackets t packets(TNt), (FNt),and and the NE NEtot oSW SW in i nsequence. sequence. t h emagmatic magmatic terrane, terrane,from from These These assemblages assemblages were were juxtaposed juxtaposed together together by by the the end end of ofdeformation deformation Fl. Fl. Lacer Laterdeformations deformationswere were responsible r e s p m s i b l e for f o r rotation r o t a t i m of of the theregional regionalstructural structural features f e a t u r e s (Fig. (Fig. 8). 8). appearsthat t h avolcanism t volcanism conclusim, ititappears InI nconclusion, occurred Marquette Range occu=ed sporadically sporadi&llythroughout th~oughm tMarquette Range appearsthat t h aChocolay t Chocolay S u ~ e r x r o sedimentation. us~e d b t a t i m . ItItappears Supergroup Group ~ r & - s sediments e d - h e n t s were were derived exclusively exclusivelyfrom f r a naa with aa continental(older (olderPrecambrian) Precambrian) source, source, with continental minor influx i n f l u xofofvotcanogenic volcanogenicsedimentation sedimentatim minor its depositional depositional history. history. occurring late l a t e ini nits occurring Uncmformably overlying overlyingMenominee M e n d n e e Group uartzites Uncouformably Group qquartzites a l s orepresent representpurely purelycontinental continentalprovenance, provenance, but but also Siama Slate S l a t e turbidites t u r b i d i t - contain containsignificant s i g n i f i c a namounts t amounts Siano yetriot notascertained) ascertained)ofofvolcanogenic volcanogenic slates. slates. (asyet (as Volcanics are a r e also a l s ointerstratified i n t e r s t r a t i f i with e d with Mendnee Votcanics Mencminee Group iron formation formatim in i nthe theGagebic GogebicRange h g e (Prina, (Prim, Group Baraga Group Group sslates l a t e s also a l s ocontain containboth both 1976). Baraga 1976). continentally-derived, mixed, mixed, and and continentally—derived, volcanogenically-derived slates s l a t e s•. Thus, Thus, volcanism volcanism volcanogenically-derived seema to t o have have been been significant s i g n i f i c a n t and and long—lived lmg-lived from frm seems M e n d n e e Group through Baraga BaragaGroup Group Menaminee Group through sedimentatim. Volcanic Volcanic rocks rocks of of this t h i sage ageare are sedimentation. knto represent continental tholeiites t h o l e i i t e abased basedon on knotin to represent otherstudies studies(Fox, (Fox,1982; 1982;Cudzillo, Cudzillo,1978). 1978). other Pejemim Fig. 88 Fig. AP 1i Pt P a l i n s p a s t i c restoration r e s t o r a t i o n of of the the southern southern Lake Lake Superior Superior region. region. Palinepastic I. Cuupare with with Figure Figure 1. Compare �—12— 15.5 Field F i e l d Trip T r i pRoad Road Log Log Mileage 0.0 Leave Dickinson Dickinson Inn, Inn, Iron Leave Iron Mountain, Mountain, Michigan Xichigan (Fig. (Fig. at—i) EL-1) 0.1 Eight turn onto (U.S. 2). 2). Right m t o Stephenson Stephenson (U.S. south). (Go (Go south). 4.2 4.2 Town of Quitmesec 4.6 4.6 Excellent continuous Fumee Creek. Creek. Excellent Fume8 continuous of Randvilie exposure. of Good exposures Randville Dolomite. Dolomite. Good (This will w i l l be be Stop Stop aalgal l g a l structures. structures. (This 4). 8 -4 Norway. Town Tom of Norway. 13.1 Turn S t r e e t 1. ,Turn Flashingl light Flashing i g h t ((State S t a t e Street). of Loretto. Loretto. Town of left. (North). Tom left. (North). 13.7 Right on Right m paved paved' road. mad. 14.8 Left on m gravel gravel road. road. at—I RL-1 Stop 11 Sturgeon Falls F a l l s dam. dam. Park at at to end of road. road.. Obtain permission to look at a t rocks from from dam dam keeper. keeper. Excellent exposures expoeures of of Archean granitoid basement. Fern Creek g r a n i t o i d basement. Formation, Formation, and, and, down down the t h e road road aa piece, piece, Sturgeon Quartzite. Quartzite. Fern Creek and basal Quartzite Sturgeon Q u a r t z i t e represent represent b asal umits u n i t s of the the Chocolay Chocolay Group. Group. Pettijohn This outcrop outcrop is is famous famous because P e t t i j o h n (1943) (1943) and Tray (1948) claimed claimed tthat and T r w (1948) h ~ the the t Fern Fern Creek Creek More recently, recently, represents glacial represents g l a c i a l sedimentation. sedimentation. More tarot L a r w (1981a) (1981a) suggested suggested an an alluvial a l l u v i a lorigin o r i g i nwas wasmore more appropriate. Because Because the t h e rocks rocks aatt the t h e damsite damsite aare re extremely deformed, deformed, compelling compellingddata i l l probably probably extremely a t a wwill us (U. Last suamer, one never never be presented. ~ r e s e n t e d . Last s-er, one of of us (D. Leaper) Kaaper) sspent i e n t one m e week week studying studying the t h e Fern Fern Creek Creek was as as aa section, and and concluded concluded tthat h a t the t h e sequence sequence was whole fining—upward(see (seeFigure FigureRL-21, at—i),but but tthat whole fining-upuard hat several fining—upward severalsmaller smaller fining-upward and andcoarsening—upward coarsaing-upward conclude the basal cycles are cycles a r e apparent. apparent. We We conclude t hthat a t the basal sections represents channelized channelized deposits deposits sec tiom representS sequences), whereas the (fining—upward (fining-upuard sequences), the upper upper sandier sections represent progradation p r o g r a d a t i m of of sandier sheet—like sheet-like sand sand bodies (coarsening upward package of of channelized o v e r a l l package channelized en overall sequences). Such an sequences). bodies, capped by sheet—sand sheet-sand bodies, capped by by bodies overlain by .- Location map LocatLon map of Stops Stops 1—5. 1-5. (Map (Map courtesy of tourist t o u r i s tbureau) bureau) courtesy of �—13— perhaps is also a l s o allowable. allowable. perhaps aa glacial g l a c i a l fan fan delta d e l t a is nearshore nearshore sands sands of of the the Sturgeon Sturgeon Quartaite Quartzite seems seems best best interpreted i n t e r p r e t e d as a s the the flooding flooding of of aa fan fan delta. delta. That is, aa fat fandelta d e l t awith withmore moreproximal proximal channelized channelized That is, gravels gravels and and d i s t a l sheet sheet sands, sands, feeding feeding aa nearshore nearshore environment, envircument, was was drowned drowned by by aa rise r i s e in i n sea sea level. level. The The Sturgeon Sturgeon Quartzite Quartzite is is also a l s o an an interesting interesting i t s great g r e a t thickness thickness (( 700 m) m) and and unit, because because of of its unit, 700 extremely unidirectional u n i d i r e c t i o n a l paleocurrents paleocurrents (directed (directed extremely SE). SE). The The sedimentology s e d h e n t o l o g y of of the t h e Sturgeon Sturgeon Quartzite Quartzite distal Although we prefer p r e f e r the the fan fan delta d e l t a argument, argument, Although we is is discussed in i nLarue Larue (1980). (1980). discussed lOmi til 4o - plane P1 PI — plane laminated laminated - rippled rippled rr— RL—2 RL-2 15.5 Stratigraphic Fern Creek Creek Foretatin Formation dam (Stop (Stop 1). 1). Fern S t r a t i g r a p h i c section section at a t Fern Fern Creek Creek dam topping Numbers here here are a r e facies f a c i e s described described in i nappendix. appendix. topping in i n Sturgeon SturgeonQiiartzite. Quartzite. Numbers Leave dam. Leave Sturgeon SturgeonFalls F a l l s dam. toward toward Loretto. Loretto. Go Go back back 16.5 Right Xight on on main main road. road. 17.3 Left Left on cm road road (back (back to t o toretto). Loretto). Right Right on m U.S. U.S. 22 at a t Loretto. Loretto. 22 • 4 234. Left Left on on Section Section Street S t r e e t (town (townofof Norway). Norway). Section Forest Street. Section becomes becomes Forest Street. Left cm Pine Pine Drive. Drive. Left on 23.7 - black mdstone black— mudstone i nnudstones mudstones t h i n l y bedded bedded sandstones sandstones in thinly black black with with bars bars — Stop Hanbury 2~? Slates S l a t e snear near HaaburyLake. Lake. As As Stop2A shown shown in In Figure Figure 4& of of the thetext, t e x tLariie , Lameand and Ueng (submitted) (submitted) separate the the Ceng fault-bomd Florence—Niagara Florence-Niagara terrane fault—bound terrane (FNt) from f r m the t h e other other rocks rocks of of the the (FNt) Marquette Marquette Range Range Supergroup Supergroup and and on waderlying Archean Archean basement, basement, based based on underlying differences in i n structure s t r u c t u r eand and lithology lithology differences FNt. The The separation separation of of obsemed in i n the t h e FNt. observed FNt from from the the rest r e s tofofthe theLake Lake the PNt the Superiormiogeoc miogeocline was based based in i n large large Superior line was h b u r y Lake. Lake. part on on studies s t u d i e s made made at a t Ranbury part S t r a t a exposed exposed at a t Hanbury Ranbury Lake Lakeare are Strata thought Michigame thought to t orepresent representthethe Michigamne Formation of of the t h e Baraga BaragaGroup. Group. However, Formation Hwever, unlikeother other MichigamaeFormation Formation unlike Michigataite strata, s t r a t a , rocks rocks ata tflanbury Ranbury Lake Lake include include q u a r t z i t e s (probably (probably turbidites) t u r b i d i t e s ) and and quartzites dolomites (deep—water?). (deep-water?). dolomites Deep-water Deep—water �—14— a r e not present present qquartzites u a r t z i t e s and and dolomites dolomites are elsewhere in i n the t h e Lake Superior Superior region region iin n the Michigarene Formation tto Michigame Formation o our our the lithology lithology of of knowledge. knwledge. Therefore, the not Lake is strata s t r a t a exposed exposed aatt Ranbury Ranbury Lake is not ddirectly i r e c t l y comparable ccmparable to t o Nichigarane Xichigamma Formation F o m a t i m sstrata t r a t a iin n the miogeoclinal miogeocliual Superior region region (north Lake Superior realm realm of the Lake (north E'Nt). of the FMt). Lake rocks aat Ranbury Lake Secondly, Secondly, the the rocks t Eanhry great have experienced g r e a t strain. s t r a i n . Fold Fold axes axes have been been stretched stretched into i n t o local local direction parallelism p a r a l l e l i m with with the the d i r e c t i a of of bulk bulk This extension. is not not observed observed This is elsewhere in the t h e Lake Lake Superior Superior region regia elsewhere in except except perhaps perhaps near near the theRepublic Republic Mine. Mine- a stretching s t r e t c h i n g direction d i r e c t i o n observed elsewhere. elsewhere. Bedding is is locally locally transposed into transposed i n t o the the foliation foliation (Fig. RL-3A). RL—3A). Quartz veins are (Fig. are boudinaged and bowlinaged and folded llocally. ocally. 24.0 24.0 Folds (Fig. (Fig. RL—33) XL-3B) have have axes axes sub—parallel of extension, sub-parallel to t o direction d i r e c t i o n of extension, have attenuated attenuatedlimbs, limbs,aare have r e ttight i g h t to to isoclinal, i s o c l i ~ land ,aud have have probably undergone great g r e a t ffinite i n i t e strain. s t r a i n . Larue and Ueng (in (in preparation) suggest X/Z X/Z rratios preparation) a t i o s of of around arouad 10 10 aare r e required required to t o account account for for the observed fabric f a b r i c and and structures. structures. Att Stop A Stop 2k, ZA, 1ev l w outcrops outcrops by by the the show examples examples of near Hanbuq Ranbury of slate s l a t e near rroad o d show WNW, and Foliation Lake. F Lake. o l i a t i m strikes s t r i k e s WIW* and dips dips wrinkle llimeation ineatian steeply south. south. A wrinkle downthe thef ofoliation, plunges ~ l u n g e adown l i a t i o n , pparallel a r a l l e l to to -- .- RL—3 I&-3 Stop 2B. bend in road. 2B. Park near near bend road. Ask Stop permission p e r m i s s i a tto o trespass trespass from from nice nice people people hill in i n house hcuse before curve. curve. Hike up hill behind house house tto o crest, c r e s t , down down to t o small small pasture, up to bill pasture, t o next low h i l l where spectacular folds folds are a r e exposed. exposed. Fold of Formation, Stop Stop 2. Fold of Nichigasmie Hichigame Formation, 2. 25.7 25.7~ Turn around and backtrack to t o U.S. U.S. 2. 2. Left on m U.S. U.S. 22 (go (go west). west). 27.6 27.6 Right turn turn m d i r t road a f t e r "Begin Only" Only1' sign. outcrop. orientation o r i e n t a t i m from frrm the the previous outcrop. Att Stop 2, f o l d axes are a r e girdled g i r d l e d in in a A 2, fold A t Stop Stop 3, 3, constant mean axial a x i a l plane. plane. At axes aare ffold o l d axes r e aall l l aubhorizontal subhorizontal in i n the the Larue and same mean mean aaxial x i a l plane. plane. Larue and Ueng Ueng (submitted) suggestt hthat (submitted) suggest a t tthere h e r e iis s aa sstructural t r u c t u r a l discontinuity d i s c o n t i n u i t y tthat h a t separates separates the highly the highly strained s t r a i n e d rocks rocks of of outcrop 22 with the t h e less l e s s strained s t r a i n e drocks rocks observed observed in in the Mianro Munro mine. on dirt road after + Stop St0 3. 3. Munro Munro mine. Bayley and others Baytey and 1966) consider that t h a t the t h e Monroe mine (1966) Monroe mine exposes only m l y Trader's Trader's Iron—bearing Iron-bearing exposes member Vulcan IIron r m Formation. Formation. memberofof the the Vulcan These rocks rocksaare These r e tthin h i n bedded, bedded* ssiliceous, iliceous, and are are ttightly and i g h t l y folded folded locally. locally. The The regional t r u c t u r e ofofthe i t is regionalsstructure theppit is a south—dippinghomocline homocline cauplicated complicated by south-dipping minor folds. folds. Fold axes axes plunge plunge subhorizontally, and a subhorizontally, x i a l planes planes dip dip axial steeply. Some box steeply. box folds present and folds aare r e present have x i a l plane. plane. have one onesubhorizontal subhorizontal aaxial Slickenside striations s t r i a t i o n s on bedding Slickenaida surfaces are a r e distributed d i s t r i b u t e d iin n aa plane plane perpendicular the fold axis. perpendicular tto o the R ~ KRofmaun, S O ~ ~ Utthe h,e Canadian Canadiau Rams stromatotite stromatolite expert, expert, told t o l d us us (lP8l) (1?81) that that ttrace r a c e fossils f o s s i l s had had been described described aatt tthis his locality, l o c a l i t y , but but together together we found found none. none. The principal p r i n c i p a l point of of this t h i s outcrop outcrop is is changeinin fold fold axis the marked marked change Go back back to t o U.S. U.S. 22 and and proceed proceed NW NW (turn (turn 29.7 29.7 rright). ight). Exposed at Stop 4. Creek. Stop Fumee Fume Creek. 4. Exposed a t Fiance Fumee an excellent excellenthomoclinal hmoclinal Creek is an south—dipping south-dipping s esectionof c t i o n . of Randvilla Randville dolomite, dolomite, iin n fault f a u l t contact contact with with Michigasme Michigame Formation (Bayley and others, others, This T h i s upper upper ppart a r t of of the t h e Randville Randville contains almost no no clastic c l a s t i c detritus. detritus. Minor folds with axes f o l d s ,with axes subparallel s u b p a r a l l e l to to a r e present present a t Stop Stop 33 are those observed at locally l o c a l l y in i n cherty cherty beds. beds. Algal Algal RL4) on on sstructures t r u c t u r e s aare r e exposed (Fig. (Fig. BL—4) the t h e railroad r a i l r o a d grade perpendicular to t o the the 1966). creek. creek.. �—1.5— 1L—4 Cr'tptalgal structures, Stop 4 Go back to car. Proceed NW on U.S. 2. 30.2 Turn right at tovn of Quinnesec. 33.1 Turn left at Lake Antoine Rd. 34.3 Stop at Randvifle Quarry. Stop 5. You could spend months studying this outcrop. Strained and folded algal structures, strained msdcracks, minor folds, intraclastic dolomite, mud—draped ripples (Fig. RL—5) • Mote the abundance of coars.—grainsd sand in this lover part of the Randville. The sand is feldspathic and derived from a gremitic source. Excellent exposures of Exudville Dolomite are also found on the island lO m to the WNW. Structurally, the most interesting problem here is that the algal structures have beet stretched parallel to local fold axes (trending U, plunging 15—40°)(Fig. RL—5A). Most stretching i.ineations in the Florence—Niagara terrane plunge about 70—90°W. Fold axis parallel stretching lineationi can occur when a coiitpac ted rock is then strained. Another interesting structure is one we call "tornado" structures (Pig. (Fig. RL—5E,F). RL-SE,F). These These are a r e deformed d e f d algal a l g a l stromatolites strmnatolitesthat t h a have t havebeen been folded in folded such such that t h a t they they look, look, in cross—section, cross-section, like l i k e aatornado tornado couching touchhg dove. features of down. Other Other deformation deformaticm features of the the stromatolites s t r m a t o l i t e s include include folding folding of of individual individuallaminae. laminae. These These stroisatolites strmnatolitesobviously obviously represent represent intertidal i n t e r t i d a lstructures s t r u c t u r e sbecause because they they are are interstratified i n t e r s t r a t i f i e dwith with and—cracked mud-cracked strata. strata. Another Another interesting i n t e r e s t i n g point point to to reflect m is is the the nonstrous mmstroua thickness thickness r e f l e c t on (700 Dolomite in (700 m) m) of of the the P.andville Randville Dolumite i n the the FNt. FNt. Was Was this t h i s really r e a l l y deposited deposited on on Sturgeon Sturgeon Quartzite? Quartzite? �-16— RL—5 RL-5 of strained Plan P l a vi.ew dsu of s t r a i n e d cryptalgal cryptalgal stronatolite s t r a u a t o l i t edomes. domes. Lineation Lineation plunges plunges A. A. about W. &andville Randville Dolomite, Doldte, about 300 300 V. Stop Stop 5. 5. 3,C. B,C. Cross—sections Cross-sections of of strained strained Folded cryptalgal c r y p t a l g a l structures, s t r u c t u r e s , Stop Stop 5. 5. 1). D. Folded cryptalgal c r y p t a l g a l lamination. laminatim. E,F. E,F. Tornado Tornado structures s t r u c t u r e s (folded (folded algal a l g a l co1mins). columns). . G. Molar Molar teeth t e e t h ini nRandville Randville1)oloiaite, Dolomite, Stop Stop 5. 5. Origin Origin unknown. mhown. Proceed on at Lake Lake Antoine Antoine Rd. Rd. which which Proceed beccmes Margaret becomes Margaret Street. Street. 35.7 35 •7 Turn rright i g h t at a t U.S. U.S. 2. 2. From From here at the the Turn here on f i e l d guide guide gets gem sketchy sketchy iin n that the the field individual males miles aren't a r e n ' t counted. counted. individual H o v e v e r , there ia only only on. onemore more stop stop Rovever, there is left left i n this t h i s field f i e l d trip. t r i p . (Fig. (Fig. RL—6 RL-6 is is aa in map). map). RL—6 RL-6 Drive onU.S. U.S. 22 for Drive NW NW at for approximately 15 miles miles uuntil approximately 15 n t i l you you reach reach In the the the t h e town tm of of Florence, Florence, Wisconsin. Wisconsin. In c e n t e r of of town, tm, take take County County Road Road N U south south center (turn ( t u r n left l e f tfrom fromU.S. U.S. 2). 2). Drive Drive for for about on NNuuntil n t i l iitt intersects intersects about 33 miles miles on County Comity Road Road D. D. Turn Turn tight r i g h t at a t UD and and proceed proceed for f o r about about 11 mile mile until u n t i l you you see see the D a m public public the road road to t o the thePine PineRiver RiverDam Map Map showing showing Florence Florence and and vicinity, v i c i n i t y , Wisconsin Wisconsin and and Stop Stop 6. 6. of local l o c a l tourist t o u r i s t bureau) bureau) (Map courtesy of �—17— * ;_-_—ø ..*NATICN r1 —. ,uT — ,I * —. I em— . •1 I I .—— — —- RL-8 RL—8 Pebbly sandstones sandstonesini n "Michigamue Pebbly "Michigamue Layering sketched sketched Fornmtim" at a tStop Stop6A. 6A. Layering Formation" —F— i n at a t left. left. in — — - .—— RL-7 RL—7 '4— a Nfl1 Blowup of of Fig. Fig. RL—6 m - 6 with with geology, geology, from from Slow-up Duttm, Duttoti, 0 1971. 1971. access (see (sea Fig. Fig. RL—6). m-6). Take Take this t h i s road road access ( i t only m l y goes goes south) south) to t o the theend end and and park park (it near the the water water (see ( s e a Fig. Fig. RL—7). RL-7). near Walk back back up up the the road road¼k mile atile until until Walk reach the hill crest, outcrops are m. off to t othe thewest west150 150u. off you reach the h i l l c r e s t , outcrops a r e you 0 x/Y 4. Stop 6a 6a Stop isan auexposure exposure of of Stop 6a 6a is Stop pebbly quartaitic q u a r t z i t i csandstones sandstones (Fig. (Fig. RL—8) RL-8) pebbly i n the t h eflichiganme Michigamne Formation Fonuatim of of the the in 0 00 0 0 Florence-Niagara terraue. The rocks rocks are are Florence—Niagara tarrane. The exposed in i na asouth—facing south-facing homocline, humocline, exposed kiltmeter i n maximum about half halfa akilometer about in maximum thickness. Strata S t r a t aare a r ecomposed composed of of thickness. pebble beds, beds, sandstone sandstone beds beds and a d pebbly pebbly pebble sandstone beds beds are arecoemomly cam~mly sandstone plane-laminated or or cross—laminated. cross-laminated. plane—laminated 2• Sediments aare r e extremely rare Sediments extremely quartzose, quartzoee, tare a r g i l l i t epebbles pebbles are a r epresent. present. argillite Depositim occurred occurred in i n shalloti shallcw water water Deposition (Nilsen, 1965), 19651, possibly possibly by by fluvial fluvial (Nilsen, processes. processes. Pebbles in i n the the quartzite q u a r t z i t ehave havebeen been Pebbles stretchedinto i n t cigar—shaped o cigar-shaped stretched ( c m s t r i c t i a a lstrain)(Fig. s t r a i n ) ( F i gRL—9). . RL-9). (constrictioital Such extreme extreme sstrains t r a i n smake make paleocurrent paleocurrent Such s t d i e a (Nilsen, (Nilsen, 1965) 1965) doubtful. doubtful. studies Go back t o the thedam damand andwalk walkdown down to to Go back to the rocks rocksexposed exposed below b e l w the thedam. dam. the Y/z RL-9 RL—9 S t r a i ndata data(Rf/Ø ( ~ f /technique) $t e c h i q u e )from fromStop Stop6A 6A Strain ( h o l l w c i r c l e s , squares, t r i a n g l e s ) and (hollow circles, squares, triangles) and northern quartzite q u a r t z i t e (packet (packet 77 of of squares, squares, northern t r i a n g l e s ) and and northern northern quartzite q u a r t z i t e (packet (packet triangles) 7 of Fig. + f i l l e d c i r c l e s ) and Lake 7 of Fig. 4; filled circles) and Antoine area area (Stop (Stop 5)(hexagon). S)(hexagon). Antoine Lake �—18— Stop 6b. the spillway spillvay of 6b. Exposed Exposed aalong l m g the of the dam dam is is a spectacular spectacular homodtinal homoclinal (? top indicators i n d i c a t o r s are a r e rare) r a r e ) section s e c t i m of of sslate l a t e with llocal o c a l sandstone sandstone interbeda. interbeds. In I n the t h e hills h i l l s just j u s t north north of the t h e spilluay spillway are a r e highly deformed deformed volcanic rocks rocks (agglomerates (agglauerates of of Dutton, Dutton, 1970). 1970). Interesting I n t e r e s t i n g features features at a t the the damsite damsite are a r e foliations f o l i a t i m with v i t h . sstrongly t r a a g l y developed developed down down dip dip lineation. lineatiaa. This This lineation l i n e a t i m can can be shown shom to t o be be of of two two origins: aa stretching s t r e t c h i n g lineation lineatim and an intersection i n t e r s e c t i a a (foliation (foliatim x foliation) f o l i a t i m ) intersection. intersection. Zoned garnets garneta are a r e locally l o c a l l y present and and define define aashallowly—plunging sballwly-plunging l i n e a t i o n i n the dominant d d n u n t NW—trending Wtrending f o l i a t i m (Fig. BL—l0). BL-10). lineation in foliation (Fig. slates s l a t e s and and volcanics. volcanics. This This great g r e a t change change in accmpanied by i n stratigraphy s t r a t i g r a p h y is i s not accompanied any gradational g r a d a t i m a l changes, changes, and therefore therefore we conclude that t h a t Stop 6a and and 6b are are separated by aa major major fault. fault. separated by In I n susmarizing s m a r i z i n g the t h e FNt, F N t , the the occurrence of of shallow s h a l l w water wager quartzites quartzites in Stop 6a 6a and nd also i n two llocations o c a t i o n s ((at a t Stop a l s o to to the NW; see see Fig. Fig. 4) 6) in in contact contact with with deep—water volcanogenic shales d e e p w a t e r l olocally c a l l y volcanogenic shales suggests th8t both both quartzite q u a r t z i t e units u n i t s are are suggests that fault f a u l tbound. bound. Further, Further, the t h e changes changes in in structural s t r u c t u r a l style s t y l e between between slaty s l a t y rocks rocks and and those those of of the t h eChocolay Chocolay and and Menominee Mendnee Groups Groups suggests suggests aa fault f a u l t separation as as w e l l . Finally, F i n a l l y , if i f one one adds adds these these faults faults well. to t o those those previously previously described described by by Bayley and a d others others (1966) (1966) and aud Dutton D u t t m (1970), one one reaches FNt is a reaches the the conclusion conclusion that t h a t the the FNt collage collage of of fault f a u l t bound bound slices. slices. is a - Optional O p t i m a l Field F i e l d Stop Stop — Paint P a i n t River Dam Dam Location: Location: Return Return to t o Florence, Florence, Wisconsin, and proceed proceed NW on m U.S. U.S. 22 to to WisconsinT and Crystal Falls, When you you reach reach F a l l s , Michigan. Michigan. When the blinking blinking red l i g h t i n Crystal C r y s t a l Falls Falls (intersection on ( i n t e r s e c t i m with with M—69), M-69)* proceed proceed on U.S. U.S. I2 past pastthe theRed RedOwl Owl (one (one block, block, on on red light in and and iinto n t o the t h e left l e f t curve c u m of U.S. U.S. 2 (about (about 22 blocks blocks from from blinking red red light). l i g h t ) . Turn Turn rright i g h t on on the t h e Street s t r e e t next next to t o the theabandoned abandoned gas gas station s t a t i mand andproceed proceed down d m h hill, i l l , cross cross the t h e Paint P a i n t River River (about (about 11 mile) mile) and and park park in i n dirt d i r t lot l o t on a lleft. eft. right), right), Walk dam spillway. spillway. Walk over to t odam Geology: Geology: The Riverton The R i v e r t m iron iron formation formati- exposed exposed aatt this t h i sdamsite damsitewas was deformed by three t h r e e phases pbases of of deformation, deformation, deformed by the the 71, F l , 72, F2, and and 75 F5 events eveats discussed discussed in in m-10 RL—l0 Oriented SE), Oriented garnecs garnets (plunging (plunging SE), cross—cutting tineatian. Quarter cross-cutting down—dip d m - d i p lineation. Quarter Formation, Stop for f o r scale. scale. Michigmmse Michiganme Formation, St- 6B. 6B. Folds Folds with with steeply steeply plunging plunging axes axes disrupt d i s r u p t the theregional r e g i a a homocline l homocline and and can cun be be shown shmm to t o be be associated associated with with strike—slip s t r i k e s l i p fault f a u l t zones. zones. The The structural s t r u c t u r a l history h i s t o r y of of the the tlm text, t e x t ,tot form o forma acomplicated cauplicatedmosaic mosaic the of of folds. folds. Axial planes planes of ofFL F l folds folds comeonly and c o m ~ m l ysstrike t r i k e WNW WtW and d idip p v evertically, rtically, except except those those Fl F l folds foldscropping cropping out outon on the bankofof tthe t h e NE NE bank h e rriver i v e r (Figure (Figure Axial a-11). Axial planes planes ofofFL F l folds folds RL—Il). exposed NE bank bank were were rrotated o t a t e d by by aa exposed on m the t h eNE later l a t e r folding folding event event of of F5 F5 to t o aa NS NS orientation. o r i e n t a t i a a . Apical Apical angles augles of of FL F l folds folds generally type lb, ib, lcl cand generally show s h w type and type type 33 folds folds of Ramsay's Ramsay's cclassification l a s s i f i c a t i o nscheme scheme outcrop is discussed discussed in i nLarue Lame and and Ueng Ueng outcrop is (in ( i n preparation). preparation). The The dominant dauinunt NW NW The beds beds were were folded folded by by 71 F l to to (1967). Th. form two ssets e t s of of homoclinal homoclinal limbs limbs with with fom m strikes N5OW EV. Because Because the the s t r i k e of s of NSOW and and2W. foliation of the is aa product product of the earliest earliest f o l i a t i m is with with respect respect to t o the the flattening f l a t t e n i n g planes planes of of later not the l a t e r deformations. deformations. aare r e not the same, same, the the fold f o l d styles s t y l e s of of later l a t e deformations r deformations imprinted two limbs limbs are a r e also also imprinted on m these these two distinctively d i s t i n c t i v e l y different. d i f f e r e n t . In the the southwest part of of the southwest part the outcrop, outcrop, the t h e 72 F2 trending trending homocline homocline with bedding—parallel bedding-parallel during tthis deformation. deformatim. Metamorphism Metamorphism during his deformation l w grade. grade. The The def o m a t i m was was probably probably low second second ffoliation, o l i a t i o n Twhich which cross—cuts cross-cuts the the first f i r s t at a t high high angles, anglesToccurred occurred next, nextTand and was was associated associated with withbiotite—grade biotite-grade metamorphism. metamorphism. Strike—slip St r i k e s l i p faulting f a u l t i n g was was concurrent of folds concurrent with with development developwnt of folds with with steep steep axes axes occurred occurTed last l a s tand andwas Was also a l s o associated associated with with garnet garnet grade grade metamorphism. Garnets Garnets grew greu with with long long axes axes parallel p a r a l l e l to t o the theextension extension direction directim (subhorizontal). (subhorizontal). Suninary Swmary of of Stop Stop 6. 6. orientations o r i e n t a t i o a a of of these thesehomoclinal humoclinal limbs limbs deformation folded the the2W EW striking s t r i k i n g Fl Fl limb limb into i n t o aa series s e r i e s of of open open folds folds with with fold f o l d axes axes plunging 50 50 degrees NE, NET in i n aa NE—striking NE-striking axial a x i a l plane. plane. Apical Apical angles angles of of these these folds folds range range from from 100 100 to t o 120 120 degrees fold profiles degrees and and fold p r o f i l e s indicate i n d i c a t e type type lb l b and and Ic l c folds. folds. What What should should strike s t r i k eeven e v m the themost most casual casual observer observer about is the the contiguity contiguity of of about Stop Stop 66 is shallow s h a l l w water water quarazites q u a r t z i t e s with with deep—water deep-water These open open folds are Theae folds are the t h e result r e s u l t of of the the small small angle angle between between the EW trending trending 71 F l limb limb and and N65E N65E the 2W flattening planes of striking s t r i k i n g f l a t t e n i n g planes of 72 F2 deformation. A t the the northern northernend end of of deformatim. At this t h i s outcrop outcrop the t h e F2 F2 deformation deformation formed formed aa �—19— 1 1A Fl folding cr.stsd two homoclin.. (So) ThSSS honiOcSln•s w., r.foldsd by F2 aL—IIA,B Structure of the Paint River daetsite. SO wsr rsfold.d again by F3 See toad1og. �—20— sseries e r i e s of of much m c h ttighter i g h t e r folds, folds, with with fold fold SW, by by deforming deformingthe t hN5OW e N5OW plunging SW, Apical angles oriented angles of of Fll fold orimted F f o l d limb. Apical 80 comonly smaller than than 80 these folds are a r ecoamonly degrees degrees aand d ffold o l d pprofiles r o f i l e s indicate i n d i c a t e type type folds. These These ttight ight llb, b , ic l c and and type 33 folds. ffolds o l d s ppartially a r t i a l l y reflect r e f l e c t the the parallelism parallelism of the of t h e original. o r i g i n a l N5OW N5OW s tstriking r i k i n g FFl l fold fold limb with with the the shortmi-g sherteni..g ddirection limb i r e c t i o n of deformation regime. regime. F2 defamation the P2 axes axes Secause the P2 Because F2 deformation defonuation of aa previously previously represents folding of represents axes plunge folded surface, 12 F2 fold f o l d axes plunge aatt great angles and and define define aa g r e a t ccircle ircle various anglea distribution d i s t r i b u t i o n on on the the stereogran stereoRram RL—llB).. ( F ~ z . RL-llB).. (Pig. The F3, 13, 14 The F4 deformations, defonoatims, which which are are other outcrops ((see present iin n other s e e ttext) e x t ) aare re FS not not recorded in i n this t h i s outcrop. outcrop. The 15 deformation bends bands the eastern p part deformation a r t of of parallelism tthis h i s outcrop iinto nto p a r a l l e l i m with the river. Apical angles of P5 F5 folds folds are are coamonly 120 degreea degrees and fold p profiles comonly rofiles show type type ib, show lb, lic c folds. folds. - bank of tths On the t h e NE NE bank h e rriver,most iver;mst trendingfolds folds with with aapical of the the N—S N-S trending pical angles smaller than thau 80 80 degrees are a r e 11 Fl However, folds rotated by P5 F5 (Pig. (Pig. 11). 11). Uwever, there 15 folds exposed at NE there are a r e aa few feu FS a t NE bank judging from the ccharacteristic h a r a c t e r i s t i c 120 120 degree apical a p i c a l angle. angle. Groveland Kine Mine Grweland sec 31 T42N set 31 P.29W R29W T4m Location: mine Location: The Groveland G n e is a recently abandoned iron the i r o n mine in the Felch trough (see (see Pig. Fig.aL—i RL-1 or o rJames Jams and and Take M95 others, 1966 1966ffor location). Take others, o r location). M95 north about a b a t 12 miles from from Iron Mountain, turn east e a s t (right) ( r i g h t ) on County County Road R o d 569, and ffollow signs to and o l l w signs t o the theGroveland Groveland mine. mine. must have have permission permissiont otogget e t iinto n t o the the You mast pit! p it! Geology: G eolm: Mostspectacular spectacular in Moat i n tthis his pit is the Chocolay Group Randville p i t is Dolomite over Manominee Menknee D o l d t e i n f a u l t ccontact mtact 5 in fault Group Group Iron Iron Pormation; Formation; t hthis i s ffault a u l t is is iisoclinal s o c l i n a l folded. folded. Therefore, h i s fault fault Therefore, tthis represent a folded tthrust may represent h r u s t fault. fault. Unfolding the fault f a u l t reveals a m i n h minimum heave of several. hundred meters several hundred (Fig. RL—12). RL-12). (Pig. The mine also a l s o contains c m t a i n a numerous examples of of folds, folds, gorgeous gorgeous foliations, foliatiune, Idnks, k i n k , metamorphic minerals and on on and and on. on. East of of town town of Alpha T42N S E k SE ¼ sec 7 T42N P.32W R32w Location: Location: Start S t a r t from town town of of Crystal FFalls, the intersection Crystal a l l s , the i n t e r s e c t i o n of of Highway 69 and and Highway Uighway 2. Drive south Highway 2. 1)rive south on a Highway 2 for f o r 2.8 2.8 miles. miles. Take right right on the the iintersection n t e r s e c t i o n to t o town of Alpha. Alpha. Drive for f o r 0.7 0.7 miles. miles. Stop at a t a roadcut roadcut outcrop over over aa small small hill. hill. original N7OW Geology: The o riginal N 70W trending Fl folds iin trendmg n the Dunn Creek I&-12 R.endvitle Randville DDolomite o l d t e i ninftault a u l t contact contact over Croveland Mine, Vulcan IIron Vulcan r o n Formation, Formation, Groveland Xine, Contactisis iisoclinally west west face. face. Contact soclinally Pacing directions folded. Pacing folded. d i r e c t i munknown. unknown. slate NlSW s l a t e were folded by by 12 F2 ttoo aaH1SW Axial planes planes of trending oorientation. trending r i m t a t i o n . Axial of these fold6 foldsaare these r e sstill t i l l vertical. v e r t i c a l . Fold Fold styles s t y l e s of of these folds f o l d s are a r e still s t i l l similar similar to P1l folds exposed at t o tthose hme F a t Paint P a i n t River River dam dam except except with v i t h tighter t i g h t e r apical a p i c a l angles. angles. Fold Fold profiles p r o f i l e s coamonly commonly show s h m type type ib, l b , Ic, lc, folds. At A t the the eastern e a s t e r n and end of of and type type 33 fold.. outcrop, en SW oriented F2 P2 fold tthis h i s outcrop, an EW f o l d was refolded by N N—S 15 refolded -S oriented o r i m t e d F5 deformation. Fold axes here are deformation. are generally plunging north. north. sec 31 NW NU of of Stager Stager Lake Lake NW NW ¼ k see 31 242N TUN P.32W R32W Location: Start Location: S t a r t from from town town of of Highway 22 south. south. Crystal Falls. Falls. Take Righway Take rright ight 9.5 miles. miles. Take Drive for f o r roughly roughly 9.5 turn t u r n on the t h e intersection i n t e r s e c t i o n to t o Stager Lake. Drive for 2.4 miles miles northwest, northwest, Lake. f o r 2.4 passing Stager d i r t road road Stager Lake. Lake. Take a dirt cross the the rrailroad before the tto o cross a i l r o a d rright i g h t before the paved road road bends bends from from NW NW to t o NNE. NNE. You is will u i l l come come tto o an open f i e l d . There is field. another rrailroad another a i l r o a d track track about about 200 200 yards yards away from you in away i n the the southwest. southwest. Pick up up your and hhit i t this t h i s railroad railroad your backpack backpack and track. Hike track. Uike for f o r 3/4 314 mile toward NW on on This outcrop is tthis h track. track. ~ is present on on both both sides s i d e s of of the the track. track. Description: Descriptim: Deformed Deformed Dunn Creek Creek slate s l a t e here shows shows beautiful b e a u t i f u l isoclinal isoclinal and very very tight t i g h t folds. folds. They They are a r e 71 '?I folds and 72 folds which had been folds been rotated r o t a t e d by F2 deformation to t o a N—S N-S trending trending orientation. orientation. Fold profiles p r o f i l e s coumonly coammly show folds. Apical show ib, lb, lc, l c , and and type type 33 folds. angles are a r e cormonly coamonly smaller than than 30 30 degrees. degrees. Pold Fold axes axes are a r e generally generally gently gently dipping. dipping. Some dismembered isoclinal isoclinal folds are folds a r e present. present. The extreme extreme of these folds is probably probably fflattening l a t t e n i n g of folds is accumulated from f r a t strain s t r a i n regimes regimes of of Vt, Fl, 72, F2, and and 15. F5. �21 NW NW ofof PPeavy e a 7 Pond Pond NEI/4 m1/4 sec sec 24 24 232W R32W T42N T42N Ranlock dam dam NE1/4 NE1/4 sec see 18 18 231W R 3 l W T43N T43N Hemlock Prom From town town of of Crystal Crystal drive drive 4.2 4.2 miles milea east e a s t on on Highway Righ-y 69. 69. Turn Turn to t o south south at a t the the intersection intersection Drive 3.4 miles south to M a r y . Drive 3.4 miles south t o Lake Lake Mary. passing passing Lake Lake Mary. Mary. Turn Turn right r i g h t at a t the the Drive on on this t h i sgrl.t g r i t road road 3—way 3-way junction. junction. Drive toward for miles till till you t w a r d the t h e SW SW f o r 11miles you come cme to t o aa fork. fork. Take Take the the road road on on right r i g h t and and slowly slowly drive d r i v e for f o r another another 0.35 0.35 miles. miles. Stop Stop exactly exactly where where the the road road begins begins to to descend. outcrop in deacend. Search Search for f o r the the.outcrop i n the the woods woods to t o your your right r i g h t which which is is about &cut 20 20 yards yards away away from f r m you. you. Location: Go Go back back and and pass pass the the Location: me-lane bridge. bridge. Take Take right r i g h t turn turn one—lane heading heading north a t t h e t h r e e way way jtmctim. Drive Drive all a l l the the way way to t o the the end end junction. of the t h e road. road. Ask Ask for f o r permission p e m i s s i o n from from aa of very very nice n i c e person, person, Bob Bob Graph, o enter enter Graph, tto Location: Location: Falls, Falls, Geology: G e o l m : Examine Examine the the pelitic pelitic portion There are a r e three three p o r t i a of of the the outcrop. outcrop. There sets s e t s of of cleavages cleavages present present in i n the the rock, rock, i.e. i.e. one one set s e t of of slary s l a t y cleavage, cleavage, two two Sets sets of of crenulatiam c r e n u l a t i m cleavages. cleavages. The The Si S l slaty slaty cleavage NE and and is is crenulated crenulated by by cleavage strikes s t r i k e s NE S2 S2 which which strikes s t r i k e s N65E. N65E. Both Both Si S l and and 32 S2 cleavages cleavages dip d i p vertically. v e r t i c a l l y . However, Rowever, 33 S3 is is aa set s e t of of subhorizomtal subhorizontal crenulation crenulation cleavage and ccrosscutting cleavage dipping dipping NW NW aad rosscutting both both Si Sl and and S2. S2. The The 33 S3 crenulation crenulation cleavage cleavage here here belongs b e l m g s to t o aa group group of of subhorizomtal subhorizontal crenuiatiom c r e n u l a t i m cleavage cleavage dipping f r m the the Peavy Pea- Pond Pond dipping away away from intrusive, is located located SE SE of of where where Intrusive, which which is you you stand. stand. Neighborhood see 20 20 Neighborhood of of Mansfield Mansfield mine. mine. sec T43N T63N 2.31W R3lW - t h e darn. dam. the Geology: Geologp AA series s e r i e s of of fault f a u l tbound bound packets of of cherry cherty sediments sediments and and pillows pillows packets a the the cliff c l i f f at a t the the northern northern a r eexposed exposed on are end of of dam. d m . The end The rhythmic rhythmic banding banding of of sedimeuts here here are a r e mixtures mixtures of of sediments tuffaceous sediments sediments and and chert. chert. Graded Graded tuffaceous bedding isnot notcoamon. conmon. These These sediments sediments bedding is resemble ribbon r i b b m cherts c h e r t s which which represent represent resemble deep deep sea sea sediments sediments in i n orogenic orogenic beits. belts. Sane fallen f a l l e u blocks blocks on on the t h e northern northern bank bank Some of the the river, r i v e r , if i fyou you can can cross cross the the of river, r i v e r , show show depositional depositional contacts contacts among among t h r e e major major lithotypes, l i t h o t y p e s , the the massive massive lava lava three aad pillows, pillows, agglomerates, agglomerates, and and flown and flows ribbon ribbon charts. cherts. The The deployment deployment of of the t h one—mile e one-mile thick t h i c k differentiated d i f f e r e n t i a t e d sills s i l l s (Hiernan (Kiernan s i l l s . ) , pillow pillow lavas, lavas, ferrugenous ferrugenous sills), sediments (iron ( i r o n formation), formation), and and ribbon ribbon sediments t hneighborhood e neighborhoodof of Redockdam dam c h e r tininthe chert Hemlock and and Mansfield M u a f i e l d mine mine draws draws close close resemblance resemblance to t o the t h e upper upper part p a r t of of that the the ophiolite. It is t r u e that ophioiite. chemistry of of Hemlock Redock volcanics volcanics and and chemistry Kiernan s i l l s i s not depleted depleted enough enough to to It is true Kiernan silla is not Location: Locatim: Go Go back back to t o Highway Righway 69. 69. Drive Drive east east for f o r 300 300 yards yardson oaHighway Righway 69. 69. Take the sign sign of of Take left l e f t after a f t e r spotting spotting the HD.0CX EEMLOCK DAM. DAM. Drive Drive north north for f o r 2.8 2.8 miles miles till, Take the the right right ti11 you you come came to t o aa fork. fork. Take road Drive road passing passing the the one—lane oae-lane bridge. bridge. Drive for f o r another another 0.2 0.2 miles miles till t i l lyou you hit h i t the the first f i r s tseries seriea of of toed road cut cut outcrops. outcrops. Geology: Geoloa: north at the three Some Some Hemlock Redock pillows p i l l m and and are The slates slates a r e present present here. here. The exposed exposed aatt the the south south side side of of the theroad road are areaamixture mixtureofoftuffaceous tuffaceoussediments sediments and The slates s l a t e swere were baked baked by by the the and chert. chert. The neighboring Sills foam neighboring Hiernan Kiernan S i l l s tot oform abundant a F n d a n t porphyoblasts. porphyoblasts. Under Under m.croscope, tucroscopeT these these porphyroblasts porphyroblasts are are nothing uith nothing but but pockets pockets of of chert chertdoped dopedwith some tiny tourmaline same tiny toumaline crystals. c r y s t a l s . However, Rowever* slates slates porphyroblasts porphyroblasts in i n outcrops outcrops half half aa mile mile south show south of of here here cocnly comonly show chiastolite chiastolite pseudomorphs. pseudomorphs. Climb Climb up up the the northern northern hill h i l l of of this t h i soutcrop. outcrop. AA cliff c l i f f made made of of pillows ispresent presentata the t the westernend a d of of pillows is western this t h i s bill. h i l l . The The depositionai depositional surface surface outlined by the thepillows p i l l - faces faceswest west and and outlined by dips dips vertically. v e r t i c a l l y . This N-S striking s t r i k i n g and and This N—S vertically v e r t i c a l l y dipping dipping depositional depositional surface surface by the thebedding bedding of of slates slates i s paralleled paralleled by and and rhythmic rhythmic layering layering in i n ier'nan Kiernan Sills. Sills. .s Among Ammg the the over over2—mile 2-mile thick thickHemlock Redock volcanics volcaaics SW SW of the t h eAmasa Amasa oval, oval, pillows pillows a r e ubiquitously ubiquitously present prenent regardless regardless of of are stratigraphic s t r a t i g r a p h i c position. position. MORE. However, HouwerTthe the be characterized characterized be by by MORB. in front f r o n t of of geological setting s e t t i n g presented presented in geological you is is as very very rare r a r e case case in i n the t h eworld world you where a layered layered intrusion i n t r u s i o nwas was emplaced emplaced where i n t oaavery very thick thick pillow pillow basalt b a s a l tsequence. sequence. into SW of h s a N NWk 10 R32W TUN SW of Arnasa secsec 10 232W T44N A map map of Kelso Junction Junction Location: A Location: of Kelso quadr-.s.G.s. B u l l e t i n1226, 1226* quadrangle (U.S.G.S. Bulletin p l a t e 1) 1)will w i l lbe beneeded needed to t o get get to t o this this plate outcrop. outcrop. Start S t a r tfrom f r m Paint P a i n t River Riverdam dam (optional 1) and and drive d r i v e north. north. (optional outcrop outcrop 1) It It about 11 11miles miles of of driving. driving. isisabout Geolom: Some Some Hemlock Hemlock sslates l a t e sand and Geology: volcanicsare are exposedamong among several several volcanics exposed s m a l l mounds w m d s scattered s c a t t e r e d within within 100 100 yards yards small here. here. Three phases phases of of deformation deformation are are Three i n these these rocks, rocks* i.e. i.e. Fl, F l ,F2, E2* r e g i s t e r e d in registered s h m by by very very tight t i g h t folds folds and and F l isisshown Fl penetrative slaty s l a t y cleavage. cleavage. The aa penetrative The Fl Fl slaty s l a t y cleavage cleavage strikes s t r i k e s N15W N15Wand andisis coemonly conmonly present present all a l lthrough through the therocks rocks here. here. P2 F2 crenulation crenulation cleavage cleavage is is very very conmanly characterized characterized by by s u b t l e , but but isis coianonly subtle, s e t of of vertical v e r t i c a lcrenulation crenulation lineations lineations aa set P3. F3. showing on on netavolcanics metavolcanicsand and showing carbonaceous slates. s l a t e s . Stretched Stretched carbonaceous agglomerate pebbles pebbles plunge plunge vvertically e r t i c a l l y in in agglomerate p a r a l l e with l withF1xF2 E l f l 2 crenulation crenulation parallel l i n e a t i o n s . P3 E3 isis aa set s e t of of lineatione. subhorizontal crenulation crenulation cleavage cleavage that that subhorizontal Fl. dips25 25degrees degreeswest westand and croescuts crosscuts Fl. dips Some ssimilar i m i l a r sets s e t s of of subhorjzontal subhorizontal Some cleavagesdipping dippingaway awayfrom from the the Amasa Amasa cleavages oval have have been be- observed. observed. oval �—2 2— The subhorizocital flattening flattening plane The subhorizontal plane shoen by F3 13 cleavage cleavagehere here requires requires the the s h o m by basement to Oval basememt uplift ofofthe uplift theAmasa Amasa.Ova1 to account for the the vertical account for vertical shortening. shortening. basement However, the However, the uplift uplift of Archean basement later than ovalitas to in Amasa oval'has to occur occur later than in !,masa the 11 and 12 the Fl F2 deformation deformation because because 13 F3 Si and 52. cleavage crosscuts croascuts both Sl cleavage S2. Apparently, th. Apparently, themagnitude magnitude of this this uplift uplift wasminor minorsuch suchthat thatthe thedipa dip. of of the van the vertical Si vertical Slcleavage cleavage has has not been been rotated rotatedmuch. much. Peterson's Farm Peterson's T4IN SE1/4 R3OU T41N Sill4 sec sac 19 530W Location: Location: Start Start from fraa town town of of miles on Randvilie, Randville* drive drive south south for for 7.5 7.5 miles county road road 607. 607. Turn right and aud drive drive 2.2 miles to 2 .2 miles to the the end end of of the the road. road. Or when v h a you leave leave Randvills, Randville, drive drive south south for 6 6.5 State 95. Turn m State Turn left .5 miles on and drive for 1 1.2 and .2 miles till you hit 607 Make right right turntheading CComty -ty 607.• Malee u m heading for k mile. mile. Turn north for Turn left left and and drive another 2.2.2 miles till till you another 2 miles you hit the end end and ask of road. Get out out of of the the car and of the road. permission from from the the owner. m e r . The The outcrops outcrops permissica from are are scattered scattered about about 150 150 yards yards M15E N15E f rm you. You- Description: The The HMichiga i c h i g m slate slate these rocks rocks registered registered at at exposed in these i.e. least least 46deformations, defonuatiaw* i .e. 11, Fl, 13, F3* 14, F4, Almosta11 all the the pelitic politic portions purtims of of F15. 5. Almost these these rocks rock record 3 sets seCa of ofcleavages cleavages the best outcrop Rwever, the autcrop is is at at least. least. However, 15 feet feet wids an 8—foot tall, m 8-foot tall, 15 wide block block hill. Here Here sitting sitting atop a very gentle gentle hill. the 51 Sl slaty cleavage is ia crenulated by the S3 crenulatiom crenulatim cleavage. The crenulatiom S3fabric fabrici.e is so so intense intense crenulatim of of 33 that that it itresembles resembles bedding, bedding* but it it is is not. The cleavages were vere The 53 S3 crenulation crenulatim cleavages trending fold fold by by 14. F.5. folded into into a a NW trending 15 F5 crenulation crenulation cleavage is imprinted on everything exposed exposed here. here. To the the middle toward vest west end end of of this this outcrop, outcrop, another toward eubhorizomtal cleavage cleavage is clearly set of subhorizontal present. preseut. This set of subhorizontsl subhorizontal cleavage cleavage dips dipa SE SE and and may very very well well be be Peavy Pond related to to the the uplift of Peavy Pond intrusive. APPENDIX Facies descriptions Facies descriptions of stratigraphic stratigraphic section section at Fern Fern Creek dam (Stop (Stop 1). 1). Facies 1: Facies 1: Disorganized matrix—supported matrix-supported conglomconglomerate. erate. Mean grain grain size: size: 10 10 cm. cm. Sedimentary strucstructures: tures: massive (amalgamated?) (amalgamated?) beds, tectonically tectonically Facies , alligned alligned clasts clasts subparallel subparallel to to cleavage. cleavage. Facies thickness: thickness: 2-5 m. m. Lower Lower contact: contact: irregular. Upper Upper 2—5 debris contact: tabular, tabular, abrupt. abrupt. Interpretation: Interpretation: debris flow deposits. Facies 2: Pebbly Pebbly muddy muddy sandstone. sandstone. Mean grain Facies 2: size: Sedimentary structures: size: mu. Sedimentary structures: massive 0.5 mu. (amalgamated?) (amalgamated?) beds. beds. Facies thickness: thickness: 33 m. m. Lower Lower contact: tabular. tabular. Upper Upper contact: contact: not exposed. Interpretation: debris Interpretation: debris flow flow deposits. deposits. Facies 3: Facies 3: Ripple and plane—laminated plane-laminated fine fine grained grained sandstone. Mean grain 0.3 sandstone. grain size: size: 0 .3 cm. m. Bed thickness: thickness: 1—20 cm, mean — 33 cm. a,mean cm. SS:Sh SS:Sh •= 1—3. 1-3. Sedimentary 1-20 structures: ripple plane—laminations, convoluted structures: ripple and plane-laminations, bedding. Facies 1—2 n. bedding. Facies thickness: thickness: 1-2 m. Lower Lower contact: contact: tabular. Upper contact: contact: tabular or scoured. scoured. Interpretation: Lower Interpretation: Lower to to transitional transitional flow flow regime regime bedf oms. bedforms. Facies 4: 4: Interbedded Facies Interbedded sandstone sandstone and and shale. shale. ted Bed SH =<I-10. ' 1—10. thickness 1-30 1—30 cm. cm, mean — 10 10 cm. SS: SS: SH thickness structures: mud-draped mud—draped ripples, Sedimentary structures: Sedimentary ripples, diffuse diffuse plane plane laminations, laminations, massive massive beds. beds. Facies Facies thickness: thickness: Upper contact: 2—9 m. 2-9 m. Lower Lower contact: contact: tabular. Upper contact: tabular or scoured. Interpretation: Interpretation: Lower flow deposits interbedded with with suspended load deposregime deposits its. Facies 5:: Massive medium mediumto,coarse to coarse grained sandFacles 5 sand0.7 am. mu. SS:Sh SS:Sh = 10. 10. stone. Mean grain grain size: size: 0.7 Sedimentary structures: mud—draped ripples, Sedimentary structures: rare mud-draped ripples, diffuse plane laminations, laminations, massive massive (amalgamated?) (amalgamated?) beds. 11—12 m. beds. Facies Facies thickness: thickness: 11-12 m. Lower contact: contact: tabular, abrupt. Upper tabular, Upper contact: contact: tabular, tabular, abrupt. abrupt. Interpretation: Interpretation: Lower to transitional transitional flow flow regime regime sheet—flow deposits. deposits. sheet-flow Facies Fine—grained sandstone. Mean grain Facies 6: 6: Fine-grained grain size: size: ted thickness: thickness: 1—15 4 cm. 0.3 ma. mu. Bed 1-15 cm, mean mean — 4 cm. 0.3 SS:Sh = > > 10. SS:Sh Sedimentary structures: structures: ripples. ripples. 4—6 m m. . Lower contact: contact: tabular, tabular, Facies thickness: thickness: 4-6 abrupt. Upper contact: contact: gradational gradational into into the the Sturgeon Interpretation: Lower Sturgeon Quartzite. Interpretation: Lower to tc transitional transitional flow flow regime regime deposits. deposits. - - - �References Alwin, Alvin, Seven, Bevan, 1979, 1979, Sedimmitology Sedimmtology of of the the Tyler Tyler Pormation: Geological Formation: Geological Society Society of of America America no. 5, Abstracts with Programs, Programs, v. 11, 11, no. 5, p. p. 225. 225. 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Cudzilo, T.F., LI., 1978, 1978, Geochemistry Geochemistry of of Early Proterosoic Proterozoic Igneous Rocks, Northeastern Ph.D Wisconsin and h.D thesis thesis and Upper Upper Michigan. Michigan. P Univ. h i v . Pauses, Kansas, Lawrence, Lawrace, 194 1% pp. (-pub.). pp. (unpub.). Dutton, of the Florence area, Dutton, C.E., C.E., 1971, 1971,Geology G e o l m of area, Wisconsin Wisconsin and and Michigan: Michigan: U.S. U.S. Geological Survey Survey Professional Paper Paper 633, 633, p. p. 54. 54. Fox, Fox, T.P., T.P., 1983, 1983, Geochemistry of the t h eHemlock Hemlock metabasalt and andKiernan Riernanssills, metabasalt i l l s , Iron IronCounty, County, Michigan (M.S. Michigan SState (M.S. thesis): thesis): Xichigan Xichigan tate University, East East Lansing, Lansing, 81 81 p. p. 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James, H.L., L.D., Lamey, Lamey, C.L., C.L., and James, H.L., Clark, Clark, L.D., Pettijohn, P e t t i j o b , P.3., F.J., 1961, 1961, Geology Geology of central central Dickinson County, County, Michigan: Michigan: U.S. U.S. Geological Survey Professional P r o f e s s i o n d Paper Paper 310, 310, 176 176 p.James, p.James, H.L., Dutton, Dutton, C.E., C.E., Pettijohn, Pettijohn, 1.3., F.J., and Weir, W.L., and ore ore deposits deposits of of the Geology and t h e IIron ron River—Crystal River-Crystal Pails F a l l s district, d i s t r i c t , Iron Iron County, County, IC., 1968, K., 1968, Michigan: U.S. Michigan: U.S. Geological Geological Survey Survey Professional Professional Paper 570, 570, 134 134 p. p. Laberge, G., Meyers, P., Laberge, G., and Meyers, P., 1984, 1984, Two Two early early Proterozoic Proterozoic successions successions in i n central c e n t r a l Wisconsin Wisconsin Geological and ttheir h e i r tectonic t e c t o n i c significance: significance: Geological Bulletin, Society of Society of America America B u l l e t i n , in i n press. press. . Larue, D.K., 1981, 1981,The TheChocolay ChocolayGroup: Group: an an early early Larue, DL, Proterozoic cratonic Proterozoic c r a t o n i c sequence, sequence, Geological Geological Society of of America Bulletin, B u l l e t i n , v. p. 435. 435. v. 92, 92, p. D.K., 198lb, The early Menominee Larue, D.K., 1981b, The e a r l y Proterozoic Proterozoic Menominee Group Group siliciclastic s i l i c i c l a s t i c sediments sediments of of the the southern southern Evidence ffor Lake Superior Superior region: region: Evidence or sedimentation iin n platformal platformal and and basinal basinal setting: Journal of setting: of Sedimentary Sedimentaq Petrology, Petrolom, v. V. 51, p. p. 397—414. 397414. Larue, D.R., 1983, Procerozoic tectonics L a n e , D.K., 1983, Early Proterozoic t e c t o n i c s of of region: tectonostratigraphic tthe h e Lake Lake Superior region: teetonostratigraphic tcerranes e r r a n e s near the the purported purported collision c o l l i s i o n zone: zone: America, Memoir Geological Society of of America, Memoir 160, 160, , p. 33-47. p. 33—47. L.L., 1980, D.L, and Sloe., Larue, D.K., Sloss, L.L., 1980, Early basins of of the Lake Proterozoic sedimentary sedimentary basins t h e Lake Superior region: Superior region: Geological Society Society of of America Bulletin, B u l l e t i n , Pt. I, v. 91, 450-452; P a r t 11, v. 91, v. 91, 1836—1874. 1836-1874. Pt. I, v. 91, 450—452; Part II, W.L., 1984, and D.K., and Ueng, Ueng, W. L., 1984, Structural Structural Larue, D.K., history, h i s t o r y , ffinite i n i t e strain s t r a i nand and oblique oblique orientation orientation of folds in i n ffault a u l t packets of the early early Proterozoic terrane, Lake P r o t e r m o i c11 F lorence—Niagara o r a c e - N i a g a r a terrane, Lake Journal Superior region, Superior region, U.S.A.: U.S.A.: Journal of of Structural. Structural Geology, submitted. submitted. Geology, 1976, Boundary Sims, Morey, G.B., G.B., and and S b s , P.R., P.K., 1976, B o m d a q between between Moray, and iits two Precambrian W 0 Precambrian W tterranes e r r a n e s in Minnesota and ts geological significance: significance: Geological Society Society of of America Bulletin, B u l l e t i n , v. v. 87, 87, p. p. 141—152. 141-152. Moray, G.G., G.G., Simm, Sims, P.K., P.R., Canurn, Cannon, W.F., W.P., Mudrey, Mudrey, JJr., r., Morey, D.R., 1982, M.G., and M.G., and Southwick, Scuthwick, D.K., 1982, Geologic map of the of t h e Lake Lake Superior Superior Region, Region, Minnesota, Minnesota, Wisconsin, Wisconsin, and and Northern Northern Michigan. Michigan. Minnesota Minnesota Survey Geological S w e y State S t a t eMap Map Series S e r i e sS—13. S-13. Nilsen, Nilsen, LI., T.E., 1965, 1965,Sedimentology Sedimmtology of of middle middle Precambrian hAniaiikesn orence Precambrian i m i k e a n qquartz u a r t z iites, t e s , Fl. Florence County, Wisconsin: County, Wisconsin: Journal of of Sedimentary Sedimentary v. 35, p. 805—817. 805-817. Petrology, v. 35, p. Pettijohn, F.J., 1.3., 1943, Basal Ruronian Huronian c conglomerates Pettijohn, 1943, Basal onglmerates of Menominee M e n d n e e and Calumet districts, d i s t r i c t s , Michigan: Michigan: 'r. Journal of no. 6, of Geology, v. 51, no. 5 , p. p. 387—397. 387-397. Prinz, W.C., W.C., 1976, Correlative iron-foamations iron—formations and 1976, Correlative Prinz, volcanic rocks of Precambrian age, of Precambrian age, Northern Michigan: 22nd h Annual n u a l Institute I n s t i t u t e on Lake Michigan: Superior Geology, Geology, p. p. 47. 47. Ramsay, J.G., J.G., 1967, 1967, Folding Folding and and fracturing f r a c t u r i n g of of rocks: York, McGraw-Hill, McGraw—Hill, 568 rocks: New York, 568 p. p. Ronav, A.B., A.A., 1971, 1971, Geochemical Geochemical' Ronov, A.B., and and Migdisov, A.A., history of the crystalline h i s t o r y of c r y s t a l l i n e basement and and the sedimentary sedimentary cover of of the the Russian and and North American platforms: p l a t f m : Sedimentology, v. v. 16, 16, p. 137-185. p. 137—185. �Sanderson, D.J., D.J., 1973, of fold axes Sanderson, 1973, The The development development of axes oblique oblique tto o the the regional regional trend: trend: Tectonophysics, V. 16,p.p.55—70. 55-70. v. 16, Schulz, K.J., of the volcanic Schulz, K.J., 1983, 1983,Geochemistry Geochemistry of rocks of northeastern northeastern Wisconsin: Wisconsin: IInstitute n s t i t u t e of 39—40. meeting, p. p. 39-40. Lake Superior Geology, Geology, 29th meeting, Sedlock, R.L., Lt., and 1983, and Larue, Larue, D.c., D.K., 1983, Deformation and and metamorphism metamorphism of of a Penokean aarc r c and possible rout, north Wisconsin: ccollision o l l i s i o n zone, Wisconsin: Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, v. 15, v. 15, p. p. 683. 683. Sims, P.K., 1976, S h , P.K., 1976, Precambrian Precambrian tectonics tectonics and mineral deposits, Lake Lake Superior Superior region: Economic Economic Geology, v. v. 71, 71, p. p. 10924127. 1092-1127. J.W., 1968, 1948, The The Sturgeon Sturgeon Quartzite Quartzite of the Trow, J.W., Menominee (Ph.D. thesis), Menominee District, D i s t r i c t , Michigan (Ph.D. thesis), University University of of Chicago, Chicago, 60 60 p. p. W.R., 1976, Van Schrus, Schmus, W.R., 1976, Early and middle Proterozoic Proterozoic history h i s t o r y of of the the Great Great Lakes Lakes area, area, Royal Society Society of London London North America: America: aoyal Philosophical Philosophical Transactions, Transactions, ser. ser. A, A, V. v. 280, p. 605—628. 605-628. p. and Anderson, Anderson, .T.L., J.L., 1977, 1977, Gaeisa Gneiss Van Schmua, Van Schmus, W.R., W.R., and of Archean age in the and migmatite of Archean age t h ePrecambrian Precambrian Geology, v.v. 5, of central basement of c e n t r a lWisconsin: Wisconsin: Geology, 5, p. 45-48. p. 45—48. igneous racks W.P.., 1980, Chronology Van Schmus, Schmus, W.R.,1980, Chronology of igneous rocks Penokean Orogeny Orogeny iinn associated with the the Penokean Wisconsin: Geological Society of America Wisconsin: America Special Special Paper Paper 182, 182,p.p.159—168. 159-168. Junctiot Weir, K.L., .L., Geology Weir, Geology of the Kelso Kelso Junction U.S. Michigan: U Quadrangle, Iron County, County, Michigan: .S. Geological SurveyBSulletin Geological Survey u l l e t i n 1226, 1226, 47 47 p. p. Zeitz, 1981, Aeromagnetic I., and Kirby, Kirby, J.R., J.L, 1981, I., and Aeromagnetic map map the western western part part of of the the northern northern peninsula peninsula of the of Michigan Michigan and part of of northern Wisconsin: Wisconsin: of U.S. U.S. Geological Survey Survey Map Map GP—750. GP-750. � https://digitalcollections.lakeheadu.ca/files/original/91870340a2a6b77947c39380cb574654.pdf 7e0f5344cc06f22c3e3a1ac3a078af35 PDF Text Text 30th 30th Annual Annual Institute on Lake Superior Superior Geology Geology FIELD TRIP 3 TH WAUSAU SYE NTTE CO M PLEX THEE WAUSAU SYENI E COMPLEX WA U S AU PLUTON W AU S A U N I NEM 1 L E P LU T 0 N miles April 28, 28, 1984, Wausau, Wausau, Wisconsin Wisconsin �30TH 3 0ANNUAL ANNUAL ~ ~ INSTITUTE INSTITUTEONONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY #3 FIELD TRIP TRIP #3 FIELD THE WAUSAU WAUSAU SYENITE SYEN I T E COMPLEX COMPLEX THE CENTRAL CENTRAL WISCONSIN* WISCONSIN* by P a u l E. E. Myers Myers Paul D e p a r t m e n t of o fGeology Geology Department U n i v e r s i t yofo Wisconsin f Wisconsin University Eau C l a i r e , W i s c o n s i n54701 54701 Eau Claire, Wisconsin K . Sood Sood Mohan K. Mohan Department D e p a r t m e n t of o f Earth E a r t hSciences Sciences Northeastern N o r t h e a s t e r n I Illinois l l i n o i s University University Chicago, C h i c a g o , Illinois I 1 1 i n o i 60625 s 60625 L o u i s A. A . Berlin Berlin Louis Department D e p a r t m e n t of o f Earth E a r t hSciences Sciences Northeastern N o r t h e a s t e r n I Illinois l l i n o i s University University Chicago, C h i c a g o , Illinois I 1 l i n o i 60625 s 60625 Falster A1 U. U. Faister Al 9 2 0 McIntosh M c I n t o s h Street Street 920 Wausau, Wisconsin Wisconsin Wausau, 54401 .54401 ** For F o r sale s a l e by b yPaul P a u l E. E. Myers, M y e r s , Department D e p a r t m e n t ooff Geology, G e o l o g y , University University o f Wisconsin, Wisconsin, of Eau Eau Claire, C l a i r e , Wisconsin Wisconsin 54701 5 4 7 0 1 [$6.00] [$6.00] �INTRODUCTION This Guidebook i sis aa major one used used in 1980 1980 for for the the 26th 26th Annual Annual This Guidebook major revision revision of one IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology. Geology. That waswritten written by That volume volume was by Sood, Sood, Myers, Myers, and Berlin. Berlin. Subsequent Subsequentmore moredetailed detailed mapping mappingand andanalyses analysesof of rocks and and and minerals minerals from the the southern southern portion portion of the havenecessitated necessitatedt hthis revision. AA from the Complex Complex have i s revision. comprehensive paper geology and and petrology petrology ofofthe the Wausau Syenite SyeniteComplex Complex comprehensive paperon on the the geology Wausau iiss forthcoming. forthcoming. Syenitic Weidman Syenitic rocks rocks ofofthe theWausau Wausau area area were were first Weidman (1907) (1907) as as f i r sdescribed t describedbyby part of aa general general report reporton on the thegeology geology of ofnorthern northern Wisconsin. Wisconsin. AA greater than than part of normal amount inint hthat a t report o the the mineralogy mineralogy of the normal amountofofattention attentionwas wasdevoted devoted report tto of the syenites. andSnyder Snyder(1(1944), Turner ((1948), syeni t e s . Emmons Emmons and 944), Turner 1 948), and and Giesse Giesse (1951) (1 951 ) subsequently subsequently studied studied mainly mainly the the mineral mineral associations associationsofofthe theWausau Wausau Syenite. Syenite. The The plutons plutons of of the the WausauSyenite Syenite Complex Complexwere weremapped mapped 1971—1976 part mappingproject project by Wausau in in1971-1 976 as as part ofofaamapping by Wisconsin Geological Geological and and Natural History HistorySurvey Survey(LaBerge (LaBerge and and Myers, Myers, 1984). 1984). the Wisconsin Koellner (1974) studied the units in the Koellner (1 974) studied the mineral mineral chemistry chemistry of the the various various mapped mapped units the Stettin S t e t t i n syenite syenite pluton. pluton. Her data have have been h i s guideguideHer excellent excellent data beenincorporated incorporatedinin tthis book with geochemical and and mineral mineral chemical-petrographic chemical-petrographic book with gratitude. Additional geochemical studies on by by Falster Falster (1984), (1984), Myers, Myers, Medaris,(University Medaris,(University of studies are being being carried on Wisconsin-—Madison), Madison),and and Sood (Northeastern University). Sood (Northeastern I1 1Illinois inois University). Wisconsin GENERAL GEOLOGY GENERAL GEOLOGY Central Wisconsin Central Wisconsin is i s on on the thesouthernedge southernedge of ofthe theexposed exposed Precambrian Precambrian Shield Precambrianrocks rocksare aresparsely sparsely exposed exposedthrough throughglacial glacial cover, 1 ) . The The Precambrian cover, ((Figure ~ i g u r e1). along streams, and andasasscattered scatteredi ninliers. The aeromagnetic aeromagneticmap mapbybyZietz Zietz and and others along streams, l i e r s . The (1978) anomaly gravity gravity map (1974) permit (1 978) and and the Bouguer Bouguer anomaly map by by Ervin Ervin and and Hammer Hammer (1 974) permit extrapolation ofofcontacts contactsbetween between isolate i s o l a t eexposures. exposures. Archeanmigmatites, migmatites, gneisses, gneisses, and andsschists are confined Archean c h i s t s of Archean Archean age age are confined to to lenticular region between l e n t i c u l a r fault f a u lslices t s l i c ein s the in the region betweenStevens Stevens Point Point and and Black Black River River Falls. Falls. They havebeen beenreferred referred tto 1984, p. p. 247) o informally informally (LaBerge (LaBerge and and Myers, Flyers, 1984, 2 4 7 ) as as the the They have "Stevens U-Pbzircon zircon age age dated dated aat than 2,800 2,800 m.y. m.y. old. t more more than "Stevens Point Point Complex," Complex," and and U-Pb by Van Schmus( 1 (1977, 1980).Syenitic Syeniticaugen augengneiss gneissa at a U—Pb by Van Schmus 9 7 7 , 1980). t NNeillsville e i l l s v i l l eyields yields a U-Pb gneisses and and amphibol amphibolites zircon age age of of 2,535 2,535 ++10 10m.y. m.y. (Van (VanSchmus, Schmus, 1980). 1980). Archean Archean gneisses ites occur north north of the been occur the Niagara ~Tagarafault f a u l tininnorthern northernWisconsin, Wisconsin,and andit ihas t has beensuggested suggested (LaBerge, oral communication, 1984)t hthat noArchean Archeancrust underlies the (LaBerge, oral communication, 1984) a t no crust underlies the region region betweenthese theseroughly roughlypara1 parallel east-northeast-trending fault between 1 el east-northeast-trending f a u l tsystems. systems. Older Proterozoic Proterozoic rocks regionare are quartz-sillimanite quartz—sillimanite sschist, Older rocks of the the Wausau Wausau region chist, biotite b i o t i t eschist, s c h i s tand , andamphibolite-grade amphibolite-grademetavolcanic metavolcanic rocks rocks northwest northwest of of the theAthens Athens Amphibolitic gneisses of volcanic n d t otonalitic nalitic gneisses of volcanic and and gabbroic gabbroic parentage parentage aand fault. f a u l t . Amphibolitic make ttoo trondhjemitic trondhjemiticorthogneisses orthogneisses makeupu pananeast—northeast—trending east-northeast-trending belt beltofofamphibo— amphibolite—grade amphibolite (Myers,.1974)in l974)in the 1 i te-grade rocks rocks comprising comprising the the Chippewa Chippewa amphi bol i t e complex compl ex (Myers, rocksofof similar similar lithology region region west west and and north north of ofMarathon Marathon County. County. Amphibolitic Amphibolitic rocks are interleaved with south of of are with Archean Archean migmatites migmatites in the the "Stevens "Stevens Point Point complex" complex" south MarathonCounty. County.The Theolder older succession successioni is Marathon s characterized characterized by by amphibolite-grade amphibolite-grade metametamorphic mineralogy mineralogyaand west-t to northwest—plungingisocl isoclinal n d westo northwest-plunging inal folds folds deformed deformed by by morphic moreopen, open,coaxial coaxial folds. folds. Basal Basal quartzite quartzite and rocks in more and pelitic p e l i t i cmetasedimentary metasedimentary rocks byby numerous tthis h i s older oldersuccession succession are are overlain overlainbybyvolcanic volcanicrocks, rocks,and andintruded intruded numerous syntectonic tonalites, granodiori t e(LaBerge s (LaBergeand andMyers, Myers, 1984, 1984, , andgranodiorites tonal i t e s ,trondhjemites, trondh jemi tes and p. 246). p. 246). Theyounger youngerEarly EarlyProterozoic Proterozoicsuccession successionconsists consistsprimarily primarily of of greenschist-facies greenschist-facies The calc-alkaline overlies basal t-rhyol i t esequence sequence that t h a t unconformably unconformably over1 i e s the older 01 der cal c-a1 kal ine basalt-rhyolite succession (Myers (Myers and 1980). Structures in in the thegreenschist greenschistsequence sequence succession and others, others, 1980). �—2— FIGURE 11 FIGURE GENERALIZED PRECAMBRIAN PRECAMBRIANGEOLOGY GEOLOGY GENERALIZED of of NEST-CENTRAL WISCONSIN* WISCONSIN* WEST-CENTRAL E X P L A N A T I O N EXPLANATION R a p a k i v i - t y p e g rgranites a n i t e s and s o c i a t e d i nintrusive t r u s i v e rrocks o c k s oof f tthe h e Wolf Wolf River R i v e r batholith batholith Rapakivi—type anda sassociated - S y e n i t e , quartz q u a r t zsyenite, s y e n i t equartz , q u a r tmonzonite z monzoniteof othe f t hWausau e Wausausyenite s y e n i t ecomplex complex Syenite, Quartzite E: Quartzite = - - - ' - - - U N ON C OFNORM F O RITY M —--.-——-'....—— I T Y '—'---—-'-UNC Metagabbro Metagabbro Anorthosite Anorthosite C a l c - a l k a l i n e i nintrusive t r u s i v e rrocks o c k s cconsisting o n s i s t i n g mmainly a i n l y o of f ggranite, r a n i t e , ggranodiorite, r a n o d i o r i t e , ttonalite, onalite, Calc—alkaline and quartz q u a r t z diorite; d i o r i t e ;commonly commonly ffoliated o l i a t e d and/or a n d / o r lineated lineated and Metasedimentary r orocks c k s i n including c l u d i n g p hphyllite, y l l i t e , cchlorite h l o r i t e schist, s c h i s t ,micaceous rnicaceous quartzite, quartzite, Metasedimentary t u f f a c e o u s sandstone, sandstone, ssiltstone; i l t s t o n e ; greenschist g r e e n s c h i s t facies. facies. tuffaceous Calc-a1 k a l i n e metavolcanic m e t a v o l c a n i c rrocks, ocks, m a i n l y bbasaltic a s a l t i c flows f l o w s and and aandesite n d e s i t e tto o rhyolite rhyolite Calc-alkaline mainly p y r o c l a s t i c rocks; r o c k s ; greenschist g r e e n s c h i s t facies facies - U N C ON N FCONFORM ORMITY —---U I LmMiphibolites illllhJ!IJ (?)T Y (?)—___—-—--- hphibol ites STRUCTURESYMBOLS SYMBOLS STRUCTURE 7 Approximate exposed edge o f Precambrian basement '7 Approximate exposed edge of Precambrian basement ---2 Contact, Contact, dashedwhere where inferred inferred —7 dashed C L> Contact based on aeromagnetic anomalies L7 Contact based on aeromagnetic anomalies R## F a u l toro rshear shearzone, zone, dashed dashed where where inferred; i n f e r r e d ; commonly c m o n l y wwider i d e r tthan h a n line line Fault ** From LaBerge LaBerge and 1984. From and Myers, 1984. �-3— trend and plunge plunge easterly. LaBerge trend northeasterly and and Myers Myers (1984) (1984) proposed LaBerge and proposed tthat hat the amphibolite—grade amphibolite-grade succession s pre—Penokean pre-Penokean in inage and t hthat a t i itt represents represents successioni is age and history. The majory yet-unrecognized yet-unrecognized part of aa major, of Wisconsin Wisconsin Precambrian Precambrian history. The amphibolitegrade succession with the theChocolay Chocolay Group Group in inwestern western Michigan Michigan and and grade succession may maycorrelate correlate with northern Wisconsiny while the the greenschist greenschist rocks rocksmay may correlate correlatewith withthethe Menomonie northern Wisconsin, Menomonie and/or Baraga Baraga Groups. Groups. The inal folds, fo1 ds higher highergrade grademetamorphism metamorphism and itic The isocl isoclinal andtonal tonalitic intrusives ininthe succession o l d e rpre-Penokean y pre-Penokean intrusives theolder older successionmay may thus thusrepresent representan an older, orogeny. The Proterozoic amphibolite-grade amphi bol i te-grade and and greenschist—grade greenschist-grade rocks ain The Early Early Proterozoic rocksare are over1 overlain nconformably and intruded intruded by by anorogenic anorogenic granites nconformablybybyrhyolite rhyolite pyroclastics pyroclastics and granites of of approximately 1760 1760may. n.y. age age (Smithy (Smith, 1978). 1978). Similar approximately Similar rocks rocks ininthe theBrokaw Brokaw area area ofWausau Wausau may o this t h i syounger youngersequence. sequence. Possibly north of may belong belong tto Possibly also also associated associated with these these volcanic volcanic and and intrusive intrusiverocks rocksare areyounger younger quartzites quartzitessuch such as as those those exposed Baraboo, F1 Flambeaü Ridge,and andBarron BarronHi1 Hills, ambeau Ridgey 1 s Wisconsin. Wisconsin. The Mountain exposed aat t Barabooy The Rib Mountain and MosineeHill Hill quartzites quartzites may also be beof of tthis and Mosinee may also h i s age. age. These These metasedimentary metasedimentary rocks are associated associated locally withdolomite, dolomiteyferruginous ferruginousslate, s l a t enietaconglomerate y metaconglomerate and and chert. chert. are locally with Widespreadfolding folding and and wrench wrenchfaulting faulting at n.y. ago of Widespread a tbetween between 1630-1600 1630-1600 m.y. ago was was of o producea asignificant significant resetting of Rb-Srisotope isotopesystems. systems. s u f f i c i e n tintensity i n t e n s i t to y tproduce sufficient resetting of Rb—Sr These wrenchf afault trend about the Stevens Stevens Point-Neillsville Point—Neillsville These wrench u l t systems systems trend about east—west east-west inin the area and and east—northeast east-northeast in region northwest northwestofofWausau. Wausau. The area in the region The Jump JumpRiver* River, Gilman, Gilmany Monico, andAthens Athensf afaults were probably probably developed developedororreactivated reactivated during during tthis Monicoy and u l t s were h i s major major kinematic event. kinematic event. Although the the Wausau SyeniteComplex Complex (WSC) intruded most thefaulting faulting Although Wausau Syenite (WSC) was was intruded a f tafter e r most of ofthe in this t h i sregion, regionysome some reactivation of of old oldfaults f a u l t scaused caused minor minor offsets o f f s e t s and and local local cataclasi s.. catacl asis,. THE WAUSAU THE WAUSAU SYENITE SYENITE COMPLEX COMPLEX The Wausausyenite syenitecomplex complex(WSC) (WSC) coeval Wolf Riverbath01 batholith are part part The Wausau andand coeval Wolf River i t h (WRB) (WRB) are 1,770 1,030 n.y.anorogenicy anorogenic,granite granite plutons plutons tthat of aa NE—SW—trending NE-SW-trending b e l tbelt of of 1 ¶77 t o to 1 ¶O3 may. hat extends from fromthe the Ba1 Baltic States (Figure t i c Shield Shield to t o the thesouthwestern southwestern United United States (Figure 2). extends 2). Theseplutons plutonsrepresent representthe the llast of Precambrian These a s t major major episode episode of Precambrian g granitic r a n i t i c intrusion in the (1983)has hascompared compared Anderson (1983) thethec hcharacteristics a r a c t e r i s t i c s of the Lake Lake Superior Superior region. regiono Anderson these anorogenic anorogenicplutonsy plutons,and andshows shows dominant rapakivia faffinity. these t h athat t thethe dominant typetype i s is of of rapakivi finity. crystallization According ttoo Anderson (1983, According Anderson (1 983 p. p. 133) 133) crystal 1 ization of ofthese these potassic, potassicyiron-enriched iron-enriched magmas placeaat temperatures between between640 640and and790° 790°Cand andlow lowt ototal t o took o k place t temperatures magmas t a l pressures, pressuresy generally lless than22 kb. kb. The Thepresent presentl i nlinear continuityofoftthis generally e s s than e a r continuity h i s belt b e l t of of roughly roughly coeval plutons and andt htheir apparentshallow shallowdepth depth intrusionsignify signify aa lack lack of coeval plutons e i r apparent of ofintrusion concludes major subsequent subsequentcontinental continental rearrangement rearrangemento rormajor majorup1 uplift. major i f t . He He concl udes tthat hat magmas crustal derivation derivationofofthe the magmas was was aa rresult e s u l t of ofthermal thermal doming doming in in the themantle mantle and and andand mangeritic magma emplacement tthat h a t cogenetic cogeneticanorthositic anorthositic mangeritic magma emplacementmay may have have played played an an active role heatofoffusion fusionaat lower crustal crustal levels. Anderson active role in ingenerating generating necessary necessary heat t lower Anderson of a p1 utonsdo do not notshow show aa consistent consistent age age progression progression of a track, t r a c k yand and feels that t h a t the theplutons that the wasrelated relatedtoto development development the thermal thermal event event was of of a faa ifailed l e d r irift. ft. Four concentrically-zonedy concentrically—zoned,cylindrical cylindrical alkaline plutons make Four alkaline plutons makeupu pthe theWSC. WSC. According to and others(1(l975a, 1981), TheSStettin ing to Van Van Schmus Schmus and others 975ay 1 l975b, 975by 1981 ) The t e t t i n syenite pluton p1 uton crystallized andNinemile Ninemilegranite granitepluton pluton crystallized crystallized WRB and crystallized 1,520 1 y520m.y. m.y. ago, agoywhile whilethe theWRB 1,500 m.y. n.y. ago. He feels that systemsare are clean clean enough enought oto assure assure tthat 1,500 ago. H e feels t h a tthe theU—Pb U-Pb systems hat the in ages This difference difference in radiometric the difference difference in ages iis s real. This radiometric age age is i s in inaccord accord with cross-cutting the ffield. The ooldest, alkaline with cross-cutting relationships relationships shown shown ininthe i e l d . The l d e s t y most most alkaline Stettin zone and S t e t t i n pluton pluton(Figure (Figure3,3,#1) # Ihas ) hasa wall a wall zone andcore corerimmed rimmed by by nepheline nepheline syenite. syenite. Following the emplacement theSStetting Fo1 lowing the emplacement ofofthe t e t t i n g pluton, p1 uton three threepipe—like pipe-1 i ke plutons p1 utonswere were intruded in series s e r i e ssouth-southwest south-southwest from fromWausau: Wausau: the Wausau pluton intruded in the Wausau pluton(Figure (Figure 3, #2), #2) the Rib pluton consisting consisting mostly the Rib Mountain Mountain pluton mostly of quartz quartz syenite syenitewith withnumerous numerous large xenoliths (Figure 3 # 3 ) , and and ffinally i n a l l y the the Ninemile Ninemile granite granite pluton pluton (Figure (Figure s3,y #4). #4). xenoliths (Figure 3, #3),  �-4- / / Figure F i g u r e 22 —-- Proterozoic P r o t e r o z o i c anorogenic a n o r o g e n i c granite g r a n i t ecomcomplexes p l e x e s of o f North N o r t h America America (Anderson, (Anderson, 1983, 1983, p. p. 135) 135) 042 miles Figure -- Components Components ooff the t h eWausau Wausau F i g u r e 33—— syenite s y e n i t e complex. compl ex. �—5-. The ssouthern o u t h e r n hhalf a l f of o fthe t h eWausau Wausau pluton p l u t o n was was stoped s t o p e d by b y the t h e Rib R i bMountain Mountain pluton, p l u t o n ,whose whose The were ooccupied ccore o r e and and ssouthern o u t h e r n rrim i m were c c u p i e d bby y t the h e NNinemile i n e m i l e ggranite r a n i t e pluton. pluton. G Granite r a n i t e and and monzonitea paplites qquartz u a r t z monzonite l i t e s fform o r m aappartial a r t i a l core c o r e rim r i m in i nthe t h esouthern s o u t h e r n lobe l o b e of o fthe t h eNine.Ninem i l e pluton, p l u t o n 9and and occupy occupy sseveral e v e r a l llarge, a r g e 9 irregular i r r e g u l a rareas areas west, west, southeast, s o u t h e a s t , and and north north mile of o f the t h eWasuau Wasuau complex. complex. S u b h o r i z o n t a l pegmatite p e g m a t i t e ddikes i k e s and and pods pods iin n the t h e Ninemile Ninemile Subhorizontal granite mineral g r a n i t e contain c o n t a i n miarolitic m i a r o l i t i cavities c c a v i t i whose e s whose m i n e r aassemblages l assemblages indicate i n d i c a t ethermal thermal shockand ands hshallow shock a l l o w c rcrystallization y s t a l 1 i z a t i o n (Faister, ( F a 1 s t e r 91984). 1984). Several Several younger, younger, possibly possibly related werei nintruded r e l a t e d quartz q u a r t z monzonite monzonite pporphyry o r p h y r y pplugs l u g s were t r u d e d a cacross r o s s f afaults u l t s t that h a t ccut u t the the The Wausau Wausau hasa as m small ssyenites. y e n i t e s . The p l pluton u t o n has a l l c core o r e oof f ggranite r a n i t e which w h i c h closely c l o s e l yresembles resembles N i n e m i l e ggranite. r a n i t e . IIn n general genera1 the t h e intrusive i n t r u s i v esequence sequence represents represents a a continual continual tthe h e Ninemile eenrichment n r i c h m e n t o of f t the h e ddifferentiating i f f e r e n t i a t i n gmagmas magmas i ninssilica. ilica. Figure which shows showst hthe F i g u r e 44 is i s aageologic g e o l o g i cmap map of o f Marathon Marathon County, County, which e ccontext o n t e x t ooff the the Wausaus ysyenite complex Wausau e n i t e complex andand i t sitsd discordance i s c o r d a n c e w iwith t h r erespect s p e c t t oto eeast-northeasterly ast-northeasterly trends A pportion o r t i o n of o f the t h e Wolf W o l f River R i v e r batholith b a t h o l i t hcan canbe beseen seen t r e n d s iin n the t h e older o l d e r rocks. rocks. A in i n the t h e eastern e a s t e r nquarter q u a r t e rofoMarathon f MarathonCounty. County. The Wolf The W o l f RRiver i v e r bbatholith a t h o l i t h is i sseparated separated from h e Wausau Wausau s ysyenite e n i t e ppluton l u t o n bby y aa major m a j o r fault f a u l tsystem systemwhich w h i c h bends bends abruptly a b r u p t l ywestward westward from tthe along a l o n g the t h e southern s o u t h e r n border b o r d e r of o fMarathon Marathon County. County. The The Wausau Wausau ssyenite y e n i t e complex complex occupies occupies the t h e concave concave pportion o r t i o n ooff this t h i s bend. bend. It I tisi spossible p o s s i b l ethat t h athe t t hsyenite e s y e n i tcomplex e complexhad had an an iimportant m p o r t a n t kkinematic i n e m a t i c iinfluence nfluence — - asast that h a t ooff aa knot k n o t --on onthe t h edevelopment development ooff the the ffaults, a u l t s , although a1 though the t h e syenite s y e n i t e iiss clearly c l e a r l yoffset o f f s e tby b ymany many ooff them them ((later l a t e r reactivation). reactivation). Figure showingt the F i g u r e 5 is i saageologic g e o l o g i cmap map of o fthe t h eWausau Wausau syenite s y e n i t e complex complex showing h e sstops t o p s ffor or tthis h i s ffield i e l d ttrip. r i p . Several x t r a stop s t o p descriptions d e s c r i p t i o n s are a r e included i n c l u d e dso sothat t h a one t onemay may Several eextra use The base base map mapf for use t the h e ffield i e l d guide g u i d e for f o r self—guided s e l f - g u i d e d f ifield e l d ttrips. r i p s . The o r the t h e geology geology is i s from f r o mLaBerge LaBerge and and Myers Myers 1984 1984 rreport e p o r t on on the t h eGeology Geology of o fMarathon Marathon County County being being published pub1 i s h e d by b y the t h e Wisconsin Wisconsin Geological G e o l o g i c a l and and Natural N a t u r a l Survey. Survey. Additional A d d i t i o n a l mapping mapping ssince i n c e submission submission oof f tthe h e map r tthe h e Survey e p o r t has e s u l t e d in mapf ofor Survey rreport has rresulted i n some some rrevisions e v i s i o n s -particularly p a r t i c u l a r l yofothe f t hWausau, e Wausau, Rib R i bMountain, Mountain, and and Ninemile N i n e m i l e plutons. p1 utons. Figure showingl olocations Some ooff i s aa topographic t o p o g r a p h i c map map showing c a t i o n s ooff stops s t o p s and and routes. r o u t e s . Some F i g u r e 66 is tthese h e s e wwill i l l not n o t be be vvisited i s i t e d dduring u r i n g t the h e f field i e l d trip t r i p owing o w i n g tto o time t i m e llimitations. i m i t a t i o n s . These maps werep lplotted ont the maps were o t t e d on h e ffollowing o l l o w i n g 15' 1 5 ' topographic t o p o g r a p h i c quadrangles quadrangles (clockwise ( c l o c k w i s e from f r o m the the Hamburg,MMerrill, nnorthwest: o r t h w e s t : Hamburg, e r r i l l ,Wausau, Wausau, and and Marathon. Marathon. �LATE PRECAMBRIAN EABLY PRECAMBRIAN MIDDLE PRECAMBRIAN SCALE Figure 4 -- Geologic map of Marathon County by LaBerge and Myers, 1979 Wisconsin Geological and Natural History 3urvey, Interim Copy. WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY Imt.ro Copy) MARATHON COUNTY,WIS. OF GEOLOGY EXPLANATION 0) �EXPLANATION EXPLANATION f - e-i STRUCTURE SYMBOLS SYMBOLS STRUCTURE a Alluvium go Glacial G l a c i a l outwash outwash gt Glacial G l a c i a l t till ill /-l.-#..-l N UJ t_> LATE LATE PROTERO- Contact: dashed dashed where where dashed f e r r e d ; dotdashedwhere wherei ninferred; tted e d where where covered covered UNCONFORMITY—.._---—... UNCONFORMITY- db Diabase Diabase Dike QD qp Quartz monzonite monzonite porphyry Quartz .~ o r.o h- v-r v . Granite aplite it e Granite apl Ninemile Ninemile granite g r a n i t e and and quartz monzonite monzoni t e Quartz syenite syenite Amphibole Amphibole ssyenite yenite Pyroxene-bearing te Pyroxene—bearingsyeni syenite zol C ZOIC AI '' ga ng qs as PS sv sa Syenitized Syeni t i z e d volcanic v o l c a n i c rocks rocks Syenite aplite it e Syeni t e apl Fault: dashed dashed where where iinferred; n f e r r e d ; dotted d o t t e dwhere where covered 70 70 \ S t r i k e and and ddip i p of o f layering layering Strike so 80 < S t i k e and and ddip i p oof f ffoliation oliation Stike (Border phase) phase) r.-I /'""-I is Hybrid Hybrid llensoidal e n s o i d a l syenite syenite Nepheline Nephel i n e ssyenite yenite ts Tabular Tabular syenite syenite ns LI MAP AREA I"- ig Leucocratic Leucocratic granite granite qm Quartz Quartz monzonite monzonite qd Quartz Quartz ddiorite i o r i t e and and ddiorite iorite vs Volcanogenic Vol canogenic sedimentary sedimentary rocks rocks -J LI Felsic F e l s i c volcanic v o l c a n i c rocks rocks iv Intermediate Intermediate volcanic rocks rocks my Mafic volcanic volcanic rocks rocks Mafic fv q Metaquartzite Metaquartzi t e bs Biotite B i o t i t e schist schist am Amphibolite Amphi bol it e Scale, miles Scale, miles .3 2 1984 1984 -- Figure5 5—— Figure GEOLOGIC MAP OF OF THE GEOLOGIC MAP WAUSAU COMPLEX, WAUSAU SYENITE COMPLEX, CENTRAL WISCONSIN WISCONSIN CENTRAL y Paul by PaulE. E. Myers Myers �—7- - // Wausau Pluton Rib Mountain Pluton a qm N r qd qm �0 -.5 r1 0 c-I- U, -.5 0 -I, 0) 3 (D c-I- 0 -S (D• m F i g u r e 6-- F i e l d t r i p r o u t e map f o r s t o p s 1 t h r o u g h 1 1 . — , GM *_ .— 0 0 3 —— — 0 - CONS I SW 1-625w 2 3 OW - ROAL 20 FEET SW - 16 — ' / 21 . J 4 - '1. •1 — 15W — 2$ - - - : lOW , .ci WAUSAU QUADRANGLE WISCONSIN—MARATHON CO. IS MINUTE SERIES (TOPOGRAPHIC) — 8945 WISCONSIN—MARATHON CO. IS MINUTE SERIES (TOPOGRAPHIC) MARATHON QUADRANGLE a 5 NILOMETSOS 21GM SifT - Mitts — —— —— STATE OF WISCONSIN �-9— STOP #1 STOP #1 - TITLE: TITLE- RIB MOUNTAIN SUMMIT SUMMIT - -GENERAL GENERALGEOLOGY GEOLOGY RIB MOUNTAIN LOCATION: R i b Mountain Mountain SState t a t e Park Park oobservation b s e r v a t i o n platform: p l a t f o r m : SE/4 SE/4 Sec. Sec. 8,8, T28N, T28N, Rib R7E; Wausau Wausau115' Quadrangle, Wausau West7.5' 7.5' Quadrangle R7E; 5 ' Quadrangle, Wausau West Quadrangle DATE:: DATE - March, March, 1984 1984 DESCRIPTION: Fromt hthis vantageppoint, can gget From i s vantage o i n t , one one can e t aa general general perspective p e r s p e c t i v e of o f the t h e major major elements ooff the elements t h e geology geology and and geography geography of o f the t h eWausau Wausau region. r e g i o n . This T h i s observation observation andaall edgeooff nnearly ttower o w e r and l l of o fRib R i bMountain Mountain are a r e on on the t h e upturned u p t u r n e d edge e a r l y vertical v e r t i c a lbeds beds ooff very v e r y coarse—grained c o a r s e - g r a i n e d mmetaquartzite e t a q u a r t z i t e wwith i t h ttops o p s facing f a c i n g southward. southward. Facing F a c i n g ddirection irection andooccasional iiss indicated i n d i c a t e dbyb ysparsely s p a r s e l yexposed exposed cross—bedding c r o s s - b e d d i n g and c c a s i o n a l rripple i p p l e forms. forms. The RRib Mountainqquartzite The i b Mountain u a r t z i t e is i s an an arcuate, a r c u a t e , keel-shaped keel-shaped xenolith x e n o l i t hembedded embedded in in quartz thet hnorthern q u a r t z ssyenite: y e n i t e : iti tisi situated s s i t u a t eon d on e n o r t h e r edge n edgeofo the f t h eRib R i bMountain Mountain syenite-quartz b' s y e n i t e - q u a r t z ssyenite y e n i t e ppluton, l u t o n , whose whose c ocore r e ( j(just u s t ssouth o u t h oof f hhere) e r e ) iiss occupied o c c u p i e d by ggranite r a n i t e and and qquartz monzoniteo of u a r t z monzonite f t the h e nnorthern o r t h e r n llobe o b e ooff the t h e Ninemile N i n e m i l e ppluton. luton. MosineeHHill oni it) Mosinee i 1 1 ssoutheast o u t h e a s t oof f hhere e r e ((the t h e knob knob wwith i t h tthe h e radio r a d i o antenna antenna on t ) and and Hardwood h i hill l l southwest Hardwood southwesto fofhere herea rare e s i similar, m i l a r , bbut u t ssmaller m a l l e r qquartzite u a r t z i t e xenolith xenolith remanents t hthat a t aare r e l olocated c a t e d i in n analogous s i t i o n s i nint hthe e ccylindrical y l i n d r i c a l Rib Rib remanents analogousp opositions Mountain ppluton. The qquartzite Mountain l u t o n . The u a r t z i t e xenoliths x e n o l i t h s form f o r m about about three—quarters t h r e e - q u a r t e r s o of f aa ccircle ircle with miles. w ith a a diameter d i a m e t e r ooff about about 55 m i l e s . Relict R e l i c t bedding b e d d i n g in i n the t h e quartzites q u a r t z i t e sata Mosinee t Mosinee H i l l (STOP (STOP ##2) 2 ) and H i l Hill l i s isp aparallel r a l l e l t to o eelongation l o n g a t i o n ddirection i r e c t i o n of o f the the Hill andHardwood Hardwood lenticular l e n t i c u l a r xenoliths. xenol it h s . A by 3M 3MCCorporation asaa ssource A large, l a r g e , abandoned abandoned qquarry, u a r r y , ooperated p e r a t e d by o r p o r a t i o n as o u r c e oof f roofing roofing ggranules, r a n u l e s , aaffords f f o r d s an an excellent e x c e l l e n t exposure exposure oof f tthe h e quartzites. quartzites. A A pporphyritic o r p h y r i t i c diabase diabase dike d i k e cuts c u t s through t h r o u g h qquartzites u a r t z i t e s on on tthe h e south s o u t h wwall a l l of o f the t h e quarry, q u a r r y , and and is i s traceable traceable 2 miles iinn float f l o a tforf oabout r about 2 m i l eto s tthe o t hwest—southwest. e west-southwest. The qquarry The u a r r y iis s located l o c a t e d on on the the west R i b Mountain M o u n t a i n aabout b o u t oone-half ne-half m i l e west here. west end end ooff Rib mile west ooff here. The endoof Rib Mountainq quartzite bodyi sis ooffset The eeast a s t end f tthe he R i b Mountain u a r t z i t e body f f s e t by by a a small northeasts m a l l northeast- trending t r e n d i n g ffault. a u l t . This T h i s ffault a u l t is i s parallel p a r a l l e l with w i t h larger l a r g e r faults f a u l t s of o f similar s i m i l a r trend t r e n d that that cut c u t the t h e edges edges of o f the t h e Rib R i b Mountain Mountain pluton. pluton. The Wausaup lpluton andt hthe Rib Mountain ppluton resemblance: ttheir The Wausau u t o n and e R i b Mountain l u t o n show show an an uncanny uncanny resemblance: heir Rib River ccontact o n t a c t is i s covered covered bby y R ib R i v e r aalluvium l l u v i u m jjust u s t north n o r t h of o fRib R i bMountain. Mountain. Each Each ooff tthe h e plutons p l u t o n s is i s cored c o r e d by b y granite, g r a n i t e ,and andeach each contains c o n t a i n s aa large l a r g emass mass of o f metaquartzite metaquartzite iinn its i t snorthern n o r t h e r nedge. edge. One One is i s tempted tempted to t o suggest suggest tthat h a t the t h e apparent a p p a r e n t "duplication" "duplication" was producedb by low-angle was produced y 1ow-angl e f afaulting. u l t i n g . However, e two u t o n s a are r e s significantly i g n i f i c a n t 1y However,t hthe twop ipl'itons different d i f f e r e n t ini nmineral m i n e r a lcomposition c o m p o s i t i o n and and in i n the t h e types t y p e s of o f xenoliths x e n o l i t h s making making up up ttheir heir has aa broad broad intermediate iintermediate n t e r m e d i a t e zones. zones. The The Wausau Wausau s syenite y e n i t e has i n t e r m e d i a t e zone zone of o famphibole amphibole ssyenite y e n i t e containing c o n t a i n i n g mainly m a i n l y metavolcanic m e t a v o l c a n i c xxenoliths, e n o l i t h s , while w h i l e the t h e Rib R i b Mountain M o u n t a i n pluton pluton intermediate zone iiss composed i n t e r m e d i a t e zone composed d odominantly m i n a n t l y o f of q uquartz a r t z s ysyenite e n i t e ( w(with i t h aat texture e x t u r e strongly strongly resembling andxenol xenoliths resembl i n g aarkose) r k o s e ) and it h s mmainly a i n l y o of f mmetaquartzite, e t a q u a r t z i t e , bbiotite i o t i t e schist, s c h i s t , and and amphibol amphi b o l iite. te . Interesting mode I n t e r e s t i n g questions q u e s t i o n s arise a r i s eas astot othe t h origin e o r i g and i n and modeofoemplacement f emplacement of o f these these Thesschists, xxenoliths. e n o l i t h s . The c h i s t s , amphibolite, a m p h i b o l i t e , and and possibly p o s s i b l y at a t least l e a s tsome some of o f the t h e metametaqquartzite u a r t z i t e xenoliths x e n o l i t h sshow show higher h i g h e r grades grades of o fregional r e g i o n a lmetamorphism metamorphism t than h a n iis s displayed displayed in complex i n the t h e rocks r o c k s surrounding s u r r o u n d i n g the t h e Wausau Wausau complex a t ati tits s ppresent r e s e n t llevel e v e l of o fexposure. exposure. It brought I tisi stherefore t h e r e f o r einferred i n f e r r ethat d t h athese t t h e sxenoliths e x e n o l i t hwere s were b r o u g h up t upfrom f r o maamore more highly highly metamorphosed basement. metamorphosed basement. Volcanic V o l c a n i c xxenoliths, e n o l i t h s , like l i k ethose t h o s eseen seenini nthe t h Wausau e Wausau syenite syenite aatt Stop S t o p 33 may may rrepresent e p r e s e n t mmaterial a t e r i a l ccollapsed o l l a p s e d iinto n t o the t h e pluton p l u t o n during d u r i n gcaldera c a l d e r asubsidence. subsidence. �-10STOP STOP ## 22 TITLE: Large Quartzite i o t i t e Schist Schist Xenoliths Xenoliths in inthe t h eCore Core Large Quartzite and andBBiotite Rim, Syenite Pluton R i m , Wausau Wausau Syeni t e Pl uton LOCATION:: South South end LOCATION end of Mosinee Mosinee Hill, HillNE¼, , NEkyNE¼ NEk Sec.27, Sec.27, T28N, TZ8N,R7E R7E Wausau15' 15' and and Wausau WausauWest West7.5' 7.5' quadrangles Wausau AUTHOR: Paul Claire Paul E. E. Myers, Myers, University University of ofWisconsin-Eau Wisconsin-Eau C laire DATE: DATE : February, February ,1980 1980 SUMMARY SUMMARY OF OF FEATURES: FEATURES: This abandoned 3-Mquarry quarryexposes exposesthe thesouth southend endofofaa large large quartzabandoned 3-M quartz- ite smallerxenolith xenolithofofbbiotite i t e xenolith xenolith and and aa much much smaller i o t i t e schist s c h i s t (Figure (Figure 1). 1). The lensoidal shape of the the large extrapolatedfrom fromshapes shapes The lensoidal shape of l a r g e xenoliths xenoliths isi sextrapolated with of smaller smaller ones ones throughout throughout the the intermediate intermediate zone. zone. Near Near iits t s contact contact with quartz syenite syenite the the qquartzite very fine-grained, fine-grained, iinquartz u a r t z i t e is i s impregnated impregnated wwith i t h very nterstitial t e r s t i t i a pink l pinkmicrocline microcl inewhich which selectively s e l e c t i v e l yreplaced replaced certain c e r t a i n layers layers The abundance abundance i n the the quartzite. q u a r t z i t e . The of of i ninterstitial t e r s t i t i a l K-feldspar K-feldspar diminishes diminishes in toward centerofof the the qquartzite toward t the h e center u a r t z i t e xenolith. Smaller Smaller qquartzite u a r t z i t e xenoxenoliths question of whether l i t h shave have been been thoroughly thoroughly granitized. granitized. The The question whether these these xenoliths were carried up up oor downalong alongthe thecylindrical cylindrical wall wall of the xenoliths were carried r down the Wausau syenitepluton plutoni sis sstill Wausau syenite t i l lnot notanswered. answered. Theonly only ssignificant occurrenceofofqquartzite andbbiotite The i g n i f i c a n t bedrock bedrock occurrence u a r t z i t e and iotite schist in ithe Wausau s c h i s t in in this t h i sarea areaisi as s asxenoliths xenoliths n the Wausau syenite syenite pluton. pluton. The The xenoliths following important xenoliths have have tthe h e following important ccharacteristics: haracteristics: showconcentric, concentric,zonal zonalddistribution 11.. They They show i s t r i b u t i o n and and orientation orientationaround around Ninemile pluton. tthe h e quartz quartz monzonitic monzonitic core—-the c o r e ~ t h eNinemile �—11— FIGURE 7--7--Profile south end end of Mosinee Mosinee Hill FIGURE Profile of of the south Hill 2. The occur one one mile outside the the core. core. The largest largest xenoliths occur mile outside 3. Thequartzite quartzite xenoliths xenoliths are The are the the largest largest because because ofof ttheir h e i r lower lower susceptibility totofragmentation susceptibility fragmentation and and assimilation. 4. Flow structure in in quartz quartz syeni syenite andfeldspar feldsparlenticulation lenticulation inFlow structure t e and dicate intrusion dicate intrusion of of the thequartz quartzsyenite syeniteas asaaviscous viscous crystal crystalmush. mush. 5. Mafic xenol xenoliths werebioti biotitized, i ths were t i zed, and and quartzite quartzite xenoliths xenol i thswere were Mafic addition of of KK 0 and Al granitized through through the the metasomatic metasomatic addition and A 1 00 with selective quartzitebybyf ine-grained fine-rained m?c?omcowith selective replacement rep1 acement ofofquartzite dine cl i nealong a1ongbedding bedding planes. planes . 6. Xenoliths north Xenoliths north of of the theRib RibRiver Riverare aredominantly dominantly metavolcanic metavolcanic rocks, rocks, whereasthe thexenoliths xenoliths south southof of Rib Rib River River are quartzite, whereas are dominantly dominantly quartzite, bbiotite i o t i t eschist s c h i sand t andvery verysubordinate subordinatenon-foliated non-foliatedmetadiabase. metadiabase. 7. Quartzgrains grainsi in the quartz quartz syenite syenite and andthe the outer outer part part of of the Quartz n the the Ninemile pluton Ninemi l e pl uton are a r e granular, granular, subangular, subangular, coarse coarse grained grained and and strained. THE THE NINEMILE NINEMILE PLUTON: PLUTON: The Ninemilepluton pluton has hasaa granite granite rim containing The Ninemile containing xenocrystic xenocrystic quartz. quartz. Samples taken at one-mile intervals across the pluton from north to Samples taken a t one-mile intervals across the pluton from north to south and and from from west west tto percentageof of xenocrystic south o east e a s t show show aa decreasing decreasing percentage quartz and an increasing increasing amount amountofof plagioclase plagioclase toward toward the the center center of the quartz and an the pluton. The Thecontact contactaat the Ninemile pluton is locally discordant, t the Ninemile pluton i s locally discordant, as as at at Black Creek1.7 1.7miles milesnorthwest northwest here. Miarolitic cavities, some Black Creek of ofhere. Miarol i t i c cavities, some f ifilled lled with along the the west w i t h large large quartz quartzcrystals crystalsare arecommon common along west side of of the theNinemile Ninemile 1 i z a t i on. They indicate shallow conditions of crystal They indicate shallow conditions of crystallization. pluton. pl uton. �—12- Figure 8--Block diagram o f t h e n o r t h e a s t e r n corner of t h e southern Figure corner southern segment8-Block of t h e diagram Wausau s of y e nthe i t e northeastern p l u t o n a t Mosinee H iof l l the showing abundant, segment Hill showing u ? r t z i t esyenite (q) andpluton b i o t iat t eMosinee s c h i s t (bs) x e n o l i t h sabundant, i n a floww e l l - o r i eof n t ethe d qWausau well—oriented quartzite (q) and biotite schist Cbs) xenoliths flowlaminated, l e n s o i d a l q u a r t z syeni t e (lqsy). The Ninemile q u ain r t zamonzlaminated, lensoidal quartz syenite (lqsy). o n i t e p l u t o n (am) I n t r u d e d the q u a r t z s y e n i t eThe w i tNinemile h o n l y aquartz l o c a l monzdiscordonite pluton (qm) intruded the quartz syenite with ance. The l e n s o i d a l s e n i t e i s bounded on t h e e a sonly t by aa local t h i n wdiscordall o f ance. The slensoidal syenite is bounded wall wofi t h which i s i t s e l f on i nthe f a ueast l t c oby n t aa c t thin eastward amphibole y e n i t e (asy) amphibole syenite (asy) which is itself in fault contact eastward f e l s i c volcanics. These rocks are c u t w i t h sharp discordance by with a felsic volcanics. are icut byreverse a diabase These (db) d i rocks k e which s cwith h a r a sharp c t e r i z ediscordance d b y a strong prominent prominent diabase (db) dike which is characterized by a strong reverse p o l a r i t y . The Qal i s Wisconsin R i v e r alluvium. The shaded r e c t a n g l e polarity. alluvium. The shaded rectangle shows t h e lThe c o a tQal i o n is of Wisconsin the p r o f i lRiver e in F i g u r e 7. shows the icoation of the profile in Figure 7. Fiqure 9-- Camera l u c i d a drawing o f slabbed specimen o f quartz s y e n i t e breccia Figure Cameraangular lucida drawing ( q )quartz , b i o tsyenite i t e s c hbreccia i s t (bs), c o n t a i9—-— n i n g aligned, c l a s t s of o f slabbed banded qspecimen u a r t z i t e of containing aligned, banded are quartzite biotite schist (bs), and feldspar feldspar ( f ) . Qangular u a r t z i t eclasts c l a s t of boundaries t y p i c a(q), l l y sutured and embayed and (f). QuartziteThis clastrock boundaries are typically sutured and embayed by K-feldspar metacrysts. i s i n t e r p r e t e d as a caldera r i m collapse by K—feldspar metacrysts. This rock is interpreted as a caldera rim collapse breccia. Specimen from the r i d g e west o f Rib Mountain. breccia. Specimen from the ridge west of Rib Flountain. �—13— Figure quartzite from the eeast side of of Figure 10-lo-- Granitized Granitized quartzite from the a s t side Mosinee Hill. Banding iiss relict Mosinee Hill. r e l i c tbedding. bedding. Figure 11-.— Coarsemicrocline microcline and and quartz quartz xenocrysts 11-- Coarse xenocrysts from quartz from the west side Mosinee Hill. quartz syenite syenite from the west side of Mosinee Hill. The ar Thematrix matrix iiss angul angular quartz grains quartz grains have have sstrain t r a i n laniellae. lamellae. The Width of of picture isi s3.4 3 . 4mm. mm. quartz and and K—feldspar. K-feldspar. Width �-14STOP STOP #3 #3 AUTHORS: AUTHORS: Mineralogy Bodies M i n e r a l o g y ooff Pegmatite Pegmatite B o d i e s iin n the t h e Ninemile N i n e m i l e Pluton Pluton North N o r t h Central C e n t r a l Sec0 Seco 19, 19, 1T28 28N, N, RR7 7E,E,Wausau Wausau 15t 1 5 ' Quadrangle. Quadrangle. South South side side of miles page 8 ]1 o f County County Highway Highway NN aabout b o u t 44 m i l e s west w e s t of o f US-51,[See US-51 .[See map, map, page and Paul PaulMyers, Myers,UUniversity Al A1 Faister, F a l s t e r , 920 920 McIntosh M c I n t o s h St., St., Wausau, Wausau, and n i v e r s i t y ooff DATE DATE:: - Wisconsin Eau CClaire W i s c o n s i n — Eau laire March, March, 1984 1984 TITLE: TITLE : LOCATION: - SUMMARY OF FEATURES: SUMMARY OF FEATURES: The Ninemile emplaceda at The N i n e m i l e ppluton l u t o n was was emplaced t sshallow h a l l o w ddepth e p t h ((probably p r o b a b l y less l e s s than t h a n 44 km) km) in i n the t h e core c o r e and and southern s o u t h e r n rrim i m of o f the t h e Rib R i b Mountain M o u n t a i n ppluton l u t o n and and iin n the t h e older o l d e r metametaandp lplutonic vvolcanic, o l c a n i c , metasedimentary, metasedimentary, and u t o n i c rrocks o c k s ssurrounding u r r o u n d i n g i tit.. The The Ninemile Ninemile pluton p l u t o n is i s composed composed oof f bbiotite-hornblende i o t i t e - h o r n b l e n d e granite g r a n i t e and and quartz q u a r t z monzonite, monzonite, and and iiss P e g m a t i t e pods pods locally l o c a l l y crowded crowded wwith i t h i inclusions n c l u s i o n s oof f qquartzite, u a r t z i t e , schist, s c h i s t , and and syenite. s y e n i t e . Pegmatite in N i n e m i l e pluton p l u t o n occur o c c u r as: a s : (1) ( 1 ) small s m a l l schlierenlike s c h l i e r e n l i k emasses, masses, (2) ( 2 )zoned zoned dikes dikes i n the t h e Ninemile with vugsi in ( 3simple, ) s i m p l e ,poorly p o o r l yzoned zoned bodies b o d i e s wwith i t h vugs n tthe h e iinternterw i t h miarolitic m i a r o l i t i ccavities, c a v i t i e s ,(3) mediate zone,and and( 4(4) showings eselective andc crystallization m e d i a t e zone, ) l late a t e stage s t a g e bbodies o d i e s showing l e c t i v e eetching t c h i n g and rystallization ooff accessory a c c e s s o r y minerals. m i n e r a l s. DESCRIPTION: The NNinemile Na—feldspar The i n e m i l e ppluton l u t o n is i scomposed composed ooff K—feldspar, K-feldspar, N a - f e l d s p a r ( t(together o g e t h e r uusually, sually, Quartz Q u a r t z grains g r a i n s have have rounded—polygonal shape, resemble like andand c l oclosely s e l y resemble g r agrains i n s f r ofrom m q u quartzite a r t z i t e 1i ke tthat hat r o u n d e d - p o l y g o n a l shape, Hematite andTTi—rich e m a t i t e and i - r i c h b biotite i o t i t e are are exposed exposed aatt Rib R i b Mountain M o u n t a i n and and Mosinee Mosinee HHill i l l. H Ninemile The N i n e m i l e ppluton l u t o n contains c o n t a i n s numerous numerous ppegmatitic e g m a t i t i c pods pods and and ddikes, ikes, llocally o c a l l yabundant. abundant. The which w h i c h aare r e sshallow h a l l o w ddipping i p p i n g eexcept x c e p t nnear e a r t hthe e mmargin a r g i n o of f t the h e ppluton, l u t o n , a factor f a c t o r suggesting suggesting pegmatite emplacementi nincconcentric zonesooff thermal p e g m a t i t e emplacement o n c e n t r i c zones t h e r m a l contraction. c o n t r a c t i o n .Deep Deepweathering weathering of o f the t h e Ninemile N i n e m i l e ggranites, r a n i t e s , especially e s p e c i a l l y in i n aa circular c i r c u l a zone r zonenear n e a r its i t srim, r i mhas , hasproduced produced which has been beenq quarried use as as ppaving aa ferruginous f e r r u g i n o u s gruss gruss w h i c h has u a r r i e d f ofor r use a v i n g mmaterials a t e r i a l s ffor o r over over abundance andt the 90 years. 90 years. The The abundance o f of f l ufluorite o r i t e and h e cconcentric o n c e n t r i c sstructure t r u c t u r e of o f the t h e Ninemile Ninemile pluton mosti nintense t e n s e wweathering e a t h e r i n g r ereflect f l e c t t the h e llocal o c a l effects effects p l u i o n suggest s u g g e s t t that h a t tthe h e zones zones oof most of e t c h i n g and and solution s o l u t i o n of o f quartz q u a r t zgrains g r a i n swith w i t hconsequent consequent o f the t h e formation f o r m a t i o n of o fHF HF to t o cause cause etching ddisaggregation i s a g g r e g a t i o n oof f tthe h e rock. rock. but as pperthite), b u t not n o t always always as e r t h i t e ) , quartz, q u a r t z , biotite b i o t i t and e andamphibole. amphibole. Pegmatite P e g m a t i t e Types Types and and Mineralogy Mineralogy Study N i n e m i l epluton p l u t o nis i hampered s hampered by b ypoor p o o rexposure. exposure. S t u d y ooff pegmatites p e g m a t i t e s in i n the t h eNinemile However,more moret hthan 800 c a v i t i e s ini nover o v e800 r 800pegmatite p e g m a t i t ebodies b o d i e shave have been been However, a n 800 m imiarolitic a r o l i t i c cavities examinedand and examined d edescribed s c r i b e d i n ind edetail t a i l bby y A.A. FFalster. a l s t e r . The The ssearch e a r c h ffor o r pegmatite p e g m a t i t e bodies bodies i s aided a i d e d considerably c o n s i d e r a b l y bby y s tstudying u d y i n g d idistribution s t r i b u t i o n oof f ccertain e r t a i n pplants, l a n t s , infrared i n f r a r e d aerial aerial is average ssize The average i z e •of o f pockets p o c k e t s is is photography, andssubtle photography, and u b t l e vvariations a r i a t i o n s in i ntopography. t o p o g r a p h y . The meters 15 ccentimeters dimension,a lalthough 4.5 xx 1.2 1.2 x 1 meters i n maximum maximum dimension, t h o u g h p opockets c k e t s upupt oto4.5 aabout b o u t 15 e n t i m e t e r s in IIn n addition a d d i t i o n to t oregular r e g u l a pockets, r p o c k e t s ,some some pegmatite p e g m a t i t e dikes d i k e s contain contain have have been been found. found. Some v every r y f ifine n e mmicrocrystalline i c r o c r y s t a l l i n e material m a t e r i a lhas hasbeen been taken t a k e n from f r o m these these vuggy vuggy zones. zones. Some vugs. vugs. masses 1. s c h l i e r e n - l i k emasses masses of o f small s m a l l size s i z eand andsimple s i m p l emineralogy. m i n e r a l o g y . These masses 1. Simple, Simple, schlieren-like are a r e common common i n in t h the e v i vicinity c i n i t y ooff larger l a r q e r dikes. d i k e s . Zoning Z o n i n g iis s generally g e n e r a l l y not n o t well w e l l developed. developed. Grain with G r a i n ssize i z e iincreases n c r e a s e s rregularly e g u l a r l y inward, inward, w i t h the t h e coarsest c o a r s e s t crystals c r y s t a l s ini nthe t h ehanging hanging wall Mineralogy: albite, w a l l near n e a r the t h e center c e n t e r (indicating ( i n d i c a t i n gvapor v a p o r nourishment). nourishment). M i n e r a l o g y : mmicrocline, i c r o c l i n e , a1 b ite, qquartz, u a r t z , and and a few few accessories a c c e s s o r i e s including i n c l u d i n g siderite s i d e r i t e(pseudomorphed (pseudomorphed bby y ggoethite, o e t h i t e , hematite, hematite, f e l d s p a r and and quartz, q u a r t z , and and and oother minerals), and ther m i n e r a l s ) , hematite, h e m a t i t e , hisingerite, h i s i n g e r i t e ,second second generation g e n e r a t i o n feldspar anatase,ssulfides, u l f i d e s , and and ssulfosalts. ul fosal ts. rrare a r e phenakite, p h e n a k i t e , anatase, 1 �—15— 2. zoned,t ytypically Complexly zoned, p i c a l l y l large a r g e ddikes i k e s wwith i t h wwell-formed e l l - f o r m e d mmiarolitic i a r o l i t i c cavities. cavities. 2. Complexly Dikes oof f tthis h i s kind k i n d are a r e typically t y p i c a l l ylarger l a r g e rthan t h a n10 1 0xx10 1 0xx0.2 0.2 meters meters and and eexhibit x h i b i t wellwellDikes defined with d e f i n e d zoning zoning w i t h wall w a l l zones, zones, intermediate i n t e r m e d i a t ezones, zones, and andcore c o r ezones. zones. While W h i l e the the wall w a l l zones zones aare r e usually u s u a l l y poorly p o o r l y defined, d e f i n e d , the t h eintermediate i n t e r m e d i a t ezones zones generally g e n e r a l l y consist consist of zonesoof o f graphic g r a p h i c zones, zones, blocky b l o c k y zones zones (usually ( u s u a l l y near n e a r cores) c o r e s ) and and pocket pocket zones f aaplite. pl i t e . Mineralogy microcline, i c r o c l i n e , albite, a l b i t e , and and quartz q u a r t z are a r e the t h e essential e s s e n t i a l minerals, minerals, M i n e r a l o g y i is s ddiverse: iverse: m often o f t e n occurring o c c u r r i n g ini ntwo twooro more r moresuccessive s u c c e s s i v e generations. g e n e r a t i o n s . Accessory Accessory m i n e r a l s include include minerals several s e v e r a l or o r numerous numerous s pspecies e c i e s o foft hthe e f following: o l l o w i n g : sulfides sul fides — - ppyrite, y r i t e , sphalerite, s p h a l e r i t e , galena; galena; - jamesonite, jamesonite, boulange i t e and and other o t h e r identified i d e n t i f i e dspecies; s p e c i e s ;carbonates carbonates sulfosalts— sulfosalts boulangeite s i d e r i t e (commonly (commonly r ereplaced p l a c e d b ybyF Fe' e m i n e r a l s 1like ike goethite, g o e t h i t e , hematite, h e m a t i t e , and and lepido1e p i d o siderite minerals c r o c i t e )calcite, c a l c i t emangano—calcite , mangano-cal c i t e and and ankerite(?); a n k e r i t e ( ? ) Be—minerals ; Be-mineral s such such as as phenakite, phenaki t e , crocite) b e r t r a n d i t e , bavenite, baveni t e , euclase, e u c l ase, and and beryl; b e r y l and ; andREE—rich REE-ri ch (Th-poor) bertrandite, (Th-poor)ccheralite, h e r a l it e , xenotime, monazite, and xenotime, monazite, and ssynchisite—parisite. ynchisite-parisite. Dikes showt hthe shock: i i.e. Dikes ooff this t h i s type t y p ecommonly commonly show e e feffects f e c t s oof f tthermal h e r m a l shock: . e . brecciated brecciated pockets pockets showing showing secondary secondary overgrowths overgrowths and and cementation. cementation. In a few cases the I n a few cases t h e pockets pockets were all1 fluids, were rrapidly a p i d l y evacuated evacuated oof f a1 f l u i d s and , andmetastable m e t a s t a b l e feldspar f e l d s p a r assemblages assemblages ccrystallr y s t a l 1ized while i z e d from f r o m eescaping s c a p i n g f lfluids uids w h i l e coating c o a t i n g aall l l earlier e a r l i e pocket r p o c k e tphases. phases. 3. with 3. Simple Simple bodies bodies w i t h extensive e x t e n s i v e vuggy vuggy rregions e g i o n s iinn the t h e intermediate i n t e r m e d i a t e zone. zone. These zoning. Wall Wall and andi interThese ddikes i k e s aare r e llarge, a r q e , thick, t h i c k ,and anddodonot n oshow t showwell—developed w e l l - d e v e l o ~ e d zoninq. ntermediate zones ccontain m e d i a t e zones o n t a i n patchy p a t c h y quartz q u a r t z cores. cores. Large c a v i t i e s are a r e rare, rare, Large mmiarolitic i a r o l it i c cavities but b u t myriads m y r i a d s ooff tiny t i n y vesicles v e s i c l e sabound abound in i n the t h e intermediate i n t e r m e d i a t ezone. zone. Maximum Maximum s size i z e ooff these t h e s e ccavities a v i t i e s is i sabout a b o u t 0.5 0.5 - -1.5 1.5centimeters. c e n t i m e t e r s .Dominant Dominant minerals m i n e r a l s are a r e microcline, microcline, albite, a1 b i t e , quartz, q u a r t z , and and tiny t i n y(<1.0 (<1.0 millimeter) m i l 1 i m e t e rhematite ) h e m a t i t ecrystals. c r y s t a l sAccessory . Accessory minerals minerals include i n c l u d e zircon, z i r c o n , fluorite, f l u o r i t e ,F—apatite. F-apatite. L a t e sstage tage m i l k y quartz q u a r t z veins v e i n s cut c u t these these Late milky dikes d i k e s in i n about about 50 50 percent p e r c e n t of o f the t h e cases. cases. 4. andc crystallization 4. Pegmatite Pegmatite bbodies o d i e s wwith i t h l alate t e sstage t a g e sselective e l e c t i v e eetching t c h i n g and r y s t a l l i z a t i o n of of accessory minerals. Although similar in many respects to the complexly A l t h o u g h s i m i l a r i n many r e s p e c t s t o t h e c o m p l e x l y zoned zoned large large accessory minerals. dikes described above, they differ in several significant respects. They typically d i k e s d e s c r i b e d above, t h e y d i f f e r i n s e v e r a l s i g n i f i c a n t r e s p e c t s . They t y p i c a l l y show ani ninward owingt to removalbby show an w a r d d diminution i m i n u t i o n i in n qquartz u a r t z ccontent o n t e n t owing o removal y ccorrosive o r r o s i v e ffluids. luids. Spaces originally filled with quartz were filled by graphic intergrowths Spaces o r i g i n a l l y f i l l e d w i t h q u a r t z were f i l l e d b y g r a p h i c i n t e r g r o w t h s of o fquartz quartz and growtho of wasaccompanied accompanied and feldspar. f e l d s p a r . Secondary Secondary growth f ffeldspars e l dspars was b y by c r ycrystallization s t a l 1 i z a t i o n of of Ti T i oxides o x i d e s (anatase ( a n a t a s e brookite b r o o k i t e rutile) r u t i l e )and and ilmenite. i l m e n i t e . Other Other m i n e r a l s include i n c l u d e Ti Ti minerals bearing b e a r i n g hematite h e m a t i t e (Ti (Ti = = 2-3 2-3 percent), p e r c e n t ) , zircon, z i r c o n , muscovite, muscovite, bertrandite, b e r t r a n d i t e , phenakite, phenakite, cheralite, xenotime, and others. c h e r a l i t e , xenotime, and o t h e r s . — Internal and44above) above) I n t e r n a l Evolution E v o l u t i o nofoMegmatite f MegmatiteDikes Dikes(Types (Types22and Development Development o f ofa av every r y t hthin, i n , fine-grained f i n e - g r a i n e d contact c o n t a c t zone zone (0.5 (0.5 -- 2 centimeters) centimeters) was zone containing c o n t a i n i n g elongate e l o n g a t e bbiotite. iotite. was ffollowed o l l o w e d bby y ccrystallization r y s t a l l i z a t i o n of o fan an extensive e x t e n s i v e wall w a l l zone Vapor nourishment ffed Vapor nourishment e d ccrystals r y s t a l s growing g r o w i n g down down from f r o m hangingwall. h a n g i n g w a l l . Finer F i n e r grained g r a i n e d parts parts of o f the t h e wall w a l lzone zone grew grew upwards upwards ffrom r o m t the h e ffootwall, o o t w a l l , with w i t hoccasional o c c a s i o n a ldevelopment development ooff a coarse-grained c o a r s e - g r a i n e d aggregate aggregate iinn pockets pockets of o f vapor vapor nourishment. nourishment. Rising R i s i n g vapors itially vaporsi ninitially formed coarse - f e l d s p a r i ning rgraphic a p h i c i nintergrowth t e r g r o w t h wwith i t h qquartz, u a r t z , and and llater a t e r blockky blockky formed coarseKK—feldspar K—feldspar. K-feldspar. Quartz Q u a r t z formed formed large l a r g emonomineralic m o n o m i n e r a l i c masses masses in i n the t h eupper—median upper-median ppart a r t of of the t h e dike. d i ken A A few few vvery e r y llarge a r g e crystals c r y s t a l s of o f siderophyllite s i d e r o p h y l l i t eformed formed at a tthe t h ecore c o r emargin. margin. As quenchmay mayhave havea faffected As the t h e pocket pocket stage s t a g e was was approched approched aa ppressure r e s s u r e quench f e c t e d t hthe e ffluid luid yielding y i e l d i n g an an aplite, a p l i t e , while w h i l e in i nother o t h e r sections s e c t i o n s of o f the t h e dike, d i k e , miarolitic m i a r o l i t i ccavities c a v i t i e sformed. formed. These bessingular, These ccavities a v i t i e s may may be i n g u l a r , relatively r e l a t i v e l ylarge l a r g eopenings, openings, oro they r t h e ymay maybe be extensive extensive areas areas iin n the t h e intermediate i n t e r m e d i a t e zone zone ooff tiny t i n yvesicles v e s i c l e swith w i t hmaterial m a t e r i aresembling l r e s e m b l i n ga asponge. sponge. At A t later l a t e stages, r stages,metasomatism metasomatism or o r hydrothermal hydrothermal replacement replacement of o f some some pocket p o c k e t consituents consituents sets other s e t s inwith i n - w i t halteration a l t e r a t i o nofo siderite, f s i d e r i t epyrite, , p y r i t eand , and o t h eminerals r m i n e r a l stot ogoethite, g o e t h i t e , hematite, hematite, hydration h y d r a t i o n of o f phenakite phenaki t e to t o bertrandite, b e r t r a n d i t e , corrosion c o r r o s i o nofo quartz f q u a r t and z andfeldspars f e l dspars(adularia— (adula r i a habit), h a b i t ) , pocket p o c k e t rupture r u p t u r e and and thermal t h e r m a l shock shock oof f pocket p o c k e t cconstituents, o n s t i t u e n t s , resealing r e s e a l i n g of o f the the pocket, pocket, and and continued c o n t i n u e d ccrystal r y s t a l growth growth or o rcomplete complete degassing, degassing, deposition d e p o s i t i o n of o fmetastable metastable feldspar microcline; f e l d s p a r assemblages assemblages ( h(high-sanidine, i g h - s a n i d i n e , oorthoclase, r t h o c l ase, and and iintermediate ntermediate m i c r o c l i n e ; R. R. Martin Martin pers. pers. com., corn., 1983), 1983), and and hhermetical e r m e t i c a l ssealing e a l i n g ooff the t h e pocket(any ~ o c k e(ta n y ffluid l u i d entering e n t e r i n gthe t h epocket pocket �_____ _____ -16— at a t this t h i stime t i m ewould w o u l d quickly q u i c k l yreact r e a c with t w i t hthe t h metastable e m e t a s t a b l ephases.) phases.) C o r r o s i v e ffluids luids Corrosive then t h e n remove remove qquartz u a r t z ffrom r o m ggraphic r a p h i c intergrowths. i n t e r g r o w t h s . uAlpine_typeu "Alpine-type'' m i n e r a l s are a r e then then minerals deposited The llatest a t e s t phase phase of o f pegmatite p e g m a t i t e eevolution v o l u t i o n involves i n v o l v e s the the d e p o s i t e d in i n voids. v o i d s . The formation f o r m a t i o n of o f clay c l a y minerals, m i n e r a l s , etching e t c h i n gofo fpocket p o c k e tconstituents, c o n s t i t u e n t s ,and anddestruction d e s t r u c t i o ndue due to and MMartin, t o weathering w e a t h e r i n g (Jahns, (Jahns, 1955 1955 and and 1982, 1982, Foord Foord and a r t i n , 1979, 1979, Martin, M a r t i n , 1982, 1982, Cern9. tern;. 1982, 1982, Falster, F a l s t e r , 1983.) 1983.) (1) (2) ?T,.z:;7\I /\ ,'K )( • )< )( • • X,('X,( X. / ,t )< x )( >. i ,'—/\ / t, — (3) . x (4) / \I' /"\I\— —— \ / —. • :._r— '. ..';'z( . • • . . • ,< X ''x x (X x . t71/\/\/\J— I/',/\ //,/_\/_I I/\ /N'' i,N\/—, //\ P e g m a t i t e schlieren: s c h l i e r e n : (2) ( I ) Pegmatite (1) ( 2 )Simple S i m p l e"vuggy" "vuggy" pegmatite p e g m a t i t e dike: d i k e :(3)( 3Zoned ) Zoned pegmatite p e g m a t i t e dike; d i k e ; (4) ( 4 )Zoned Zoned dike d i k e with w i t h solution-etched so1 u t i o n - e t c h e d regions. regions. E x p l a n a t i o nofo Symbols f Symbols Explanation ]L"S'i -L m p I= Aplite A p l i t econtact c o n t a c zone t zone I1- 1 Coarse feldspar feldspar Coarse Wall w a l lZone zone lzi Pocket ((or o r aplite a p l i t e unit) unit) Pocket Quartz Q u a r t zCore Core So1 u t i o n - e t c h e d region region Solution—etched Coarse Coarse quartz-feldspar q u a r t z - f e l dspar l o - - Types o fofppegmatite e g m a t i t e bbodies o d i e s i in n tthe h e Ninemile N i n e m i l e pluton. pluton. F i g u r e10—— Figure Types The and ttextural The Ninemile N i n e m i l e granite g r a n i t e itself i t s e lshows f showsmuch much compositional c o m p o s i t i o n a l and e x t u r a l variation: variation: miarolitic xenolithIc common, eespecially s p e c i a l l y that t h a t portion p o r t i o n of of m i a r o l i t i cavities c c a v i t i eand s and x e n o l i t h imaterial c m a t e r i are a l arecommon, the t h e Ninemile N i n e m i l e pluton p l u t o noccupying o c c u p y i n g the t h e southern s o u t h e r n rim r i mofo fthe t h eRib R i bMountain M o u n t a i npluton, p l u t o n ,where where much much sstoped t o p e d rrim i m materials m a t e r i a l s were were never n e v e r completely c o m p l e t e l y assimilated. a s s i m i l a t e d . Table T a b l e1 1 on on page page16 16 gives modal compositions taken andand E—W g i v e s brief b r i edescriptions f d e s c r i p t i o and n s and modal c o m p o s i t i o nfor s f17 o r samples 17 samples t a k einn N-S i n N-S E-W traverses t r a v e r s e s across a c r o s s the t h e pluton. p l uton. �-1 7- —17— TABLE TABLE 1 1 —- MODAL MODAL COMPOSITION COMPOSITION OF O F NINEMILE NINEMILE GRANITE GRANITEPLUTON PLUTON ** -- 1 K- SAMPLE SAMPLE NUMBER* NUMBER* KFel d Feld Plag e r t h Plag -Perth 24 12 28 12 24 72395 28 72395 12 51 72392A 51 12 72392A 723928 62 72392B . 62 62 72391A 66 62 72391A 55 10 72391B 55 72391B 46? 16 72393 46? 72393 10 57 10 10 72394A 10 72394A 23 99 47 72394B 23 72394B 33 30 32 72390A 30 72390A 55 60 72390B 60 72390B 21 12 28 21 72390C 12 72390C 8? 14 8? 72390D 30 14 723900 55 50? 30? 72389 30? 72389 42? 16? 55 72388A 16? 72388A 55 54 723888 723885 41 23 72387A 23 72387A 42 55 25 723878 42 72387B 55 70 72386 72386 37 i7 29 72385 72385 Q Q Bi Bi Am Am 35 35 Tr Tr - 31 31 2 35 35 2 — 29 29 3 — — 21 21 — — 35 35 2 21 21 — - 19 19 - — — 27 27 28 28 32 32 35 35 15 15 26 26 35 35 26 26 25 25 22 22 0.6 0.6 44 77 33 — 37 — — 65 65 76 76 40 40 -- - — 26 — — 10 I - 35 35 — -- 64 64 60? 60? 110 0 34 34 - — 1 16 16 99 40 40 28 28 31 31 22 33 99 Tr Tr - - 55 Tr Tr 22 22 15 15 22 22 25 25 26 26 88 60 60 55 15 15 — - - - 23 23 - — 77 55 34 34 - — 1 1 1 1 1 1 - 22 1 1 — <1 44 46 46 15 15 25 25 22 1 - — 1 88 10 10 — - — — 21 21 28 28 1166 -— 1 1 Rock C lassification North North Rock Classification Leucogranite Leucograni t e Biotite B i o t i t egranite granite Quartz Quartz syenite s y e n i t e W/ w/ xenocrystic xenocrystic quartz quartz Biotite B i o t i t egranite granite Leucogranite Leucogranite Gneissic Gneissic qsy qsy oorr granite g r a n i t e aplite aplite Hematiticquartz quartzmonzonite monzonite Hematitic veins Quartz Quartz syenite s y e n i t e or o r nnzonite m n z o n i t ew/ w/ qq veins B i o t i t equartz quartzmonzonite mnzonite Biotite Biotite B i o t i t egranite granite B i o t i t equartz quartzmonzonite mnzonite Biotite Altered biotite A l t e r e d b i o t i t egranite granite Leucogranite Leucograni t e Hornblende—biotite Hornblende-biotite granite granite Biotite B i o t i t egranite granite Biotite B i o t i t egranite granite Granite Graniteprotomylonite pmtomylonite Leucogranite Leucograni t e Biotite-hornblende Biotite-hornblendequartz quartzmonzonite monzonite sohh Sotth west 'West Hornblende-biotlte quartz moite Hornblende-biotite quartz moii% ite Leuco—quartz Leuco-quartz monzonite mnzonite Granite pmtomylonite Graniteprotomylonite Biotite B i o t i t egranite granite Nnphibole—biotite syenite Ampbi b o l e - b i o t i t e syeni t e (xennllth) (xennl it h ) Mafic syenogabbro Mafic syenogabbro (xenolith) (xenolith) Biotite syenite (xenolith) B i o t i t e syenite (xenolith) Schistose Schistose quartz—plagioclase quartz-plagioclase aplite aplite Quartz Quartzmonzonite monzonite flaser f l a s e rgneissl gneiss Quartz Quartzmonzonite mnzoni t e I — - -- - 1 — 72399 72399 72251 72251 72400 72400 72401A 72401A 72401B 72401B 72401C 72401C 72402A 72402A 72402B 72402B 7294 7294 72403 72403 2 -2 3 - 2 1 <1 - -- -- 1 Sample Sample Location LocationMap Map 1 1 I -"- FA<+ East - I �-18STOP #4 #4 STOP TITLE : TITLE: Metaconglomerate inclusion(?) in the thewest west edge edge of of the the Metaconglomerate inclusion(?)inin quartz quartz syenite in Rib Mountain Mountain Pluton Pl uton Rib NE/4, Sec. Sec. 22, 2 Z Y TT 28 28 N, N y RR 66E,E yMarathon Marathon 15' 15'Quadrangle Quadrangle [See [Seemap, mapypp 88 ]] NW14 NE/4 LOCATION: NW/4 LOCATION: AUTHOR: Paul E. E. Myers, Myersy University UniversityofofWisconsin Wisconsin—- Eau Eau Claire Claire Paul AUTHOR: March, DATE : Marchy1984 1984 DATE: DESCRIPTION: DESCRIPTION: Large Large boulder boulder piles piles south south of ofthe theroad roadcontain containnumerous numerous boulders boulders of highly highly deformed metaconglomerate which cutbybysmall small dikes dikes and and veins veins of quartz quartz syenite syenite deformed metaconglomerate which i s iscut Despite lack of outcrop here, the size, abundance, and uniqueness s i z e y abundancey and uniqueness Despite lack of outcrop herey the and granite. granite. and of that broken loose from a bedrock of this t h i srock rockindicate indicate t h aitt was i t was broken loose from a bedrockledge ledgeby byaafarmer farmer Ninemile granite isi sexposed exposed just east e a s tand and south south of of and hauled h i s pile. pile. Ninemile and hauledinto into tthis here, abundant hereyand and quartz quartzsyenite syenitewith with abundantmetasedimentary metasedimentary and and metavolcanic metavolcanic xenoliths xenoliths similar (Mosinee HHill) i l l ) isi sexposed exposed just east e a s t and and north north of of S t o p #2 #2 (Mosinee similartotothose thoseseen seen at a t Stop There is good enough exposure in this area to that there are There i s good enough exposure in t h i s area t o indicate t h a t there are here. here. several trendingf afaults which have have broken broken the the western N-S and and NE—SW NE-SW trending u l t s which western edge edge of the the several N-S Rib plutoninto into sslices. Rib Mountain Mountain pluton l i c e s . Thus, Thusy the the contact contact relations relations of ofthe therocks rocksseen seen inin these with distribution distribution of these rock rock piles, p i l e s ycombined combined with ofrock rocktypes types ininthe thesurrounding surrounding area, areay can usedtoto develop developa aconception conception relationshipsinin sspite can be be used of of t htheir e i r relationships p i t e of of the the lack lack of of exposure. exposure. The metaconglomerate containsf1flattened andfo1 folded clasts quartzite, The metacongl omerate contains attened and ded c1 a s t s of of banded banded quartzite metafine-grained or metasediment?), fine-grained biotite b i o t i t eschist s c h i sand t andgneiss gneiss(felsic ( f e l s volcanic i c volcanic or metasediment?) metamorphosed fine—grained rocks with porphyritic, morphosed fine-grained a n dandesitic(?) e s i t i c ( ? ) vo1volcanic canic rocks with re1relict i c t porphyriticy vesicular metadioritey and and metagabbro. metagabbro. One One cclast l a s t looks looks vesicular and and tuffaceous tuffaceous textures, texturesymetadiorite, beend idifferentially The cclasts l a s t s have have been f f e r e n t i a l l y flattened flattened with with simulsimul1 i keamphibole amphibole syenite! syeni te! The like Quartzite clasts, c l a s t sbecause y because taneous development of ofa ab ibiotite—chlorite o t i t e - c h l o r i t e ffoliation. o l i a t i o n . Quartzite taneous development of of resistance resistance to t oflattening, f l a t t e n i n gremained y remainedquite quiteround: round:the theschistose schistosemetavolcanic metavolcanic clasts clasts were greatly fflattened, were greatly l d t t e n e d y so so that t h a t their t h e i rlength/thickness lengthlthickness ratios r a t i o s are are up u p to t o 12. 12. of close kink-like folds A later l a t e r episode episode of close folding folding produced produced kink-like folds with with (Figure 11). 11 ). A (Figure consequent second-stagedeformation deformationofof the the cclasts. consequent second-stage lasts. Granitic thethe metaconglomerate Graniticdikes dikesand and veinlets veinletscutting cutting metaconglomerate discordantly discordantlyshow showaa pronounced reductioniningrain grain ssize thethe metacongomerate xenoliths -pronounced reduction i z e in the the vicinity v i c i n i t of y of metacongomerate xenoliths probably in the the water asaa rresult probably due due tto o a change change in water content content in in the the granite granitemagma magma as e s u l t of of Some of the contains granules of quartz Some of the granite contains granules quartz stoping fo much wallrock. stoping fo much wallrock. in tthis K-feldspar in h i s granite granite is is (xenocrysts?) up u p tto o 10 10 millimeters inindiameter. diameter. K-feldspar (xenocrysts?) relationships are are compatible compatiblewith with the the interpretation interpretation that These relationships that highly perthitic. p e r t h i t i c . These highly the rocks rocks here here are are near near the the contact contact between between aa xenolith-rich quartzsyenite syeniteand and the xenolith-rich quartz the (1 500 m.y.). m.y.). the younger younger Ninemile Ninemil e granite (1500 a Andesite Andesite cs cs Chlorite schist schist fv fv Felsic Felsic volcanics volcanics a Porphyritic Porphyritic andesite andesi t e Quartzite qq Quartzite md md Metadiorite Metadiorite pa pa g 11- - Texture Textureofofdeformed deformedand andmetamorphosed metamorphosed polymicti conglomerate. polymicticcconglomerate. Figure 11-Figure �—19— The The mmatrix a t r i x iis s foliated f o l i a t e dand and micaceous micaceous wwith i t h llenticular e n t i c u l a r fragments fragments of o f quartzoquartzoThe cclast l a s t 1lithologies it h o l o g i e s feldspathic andbbiotite. f e l d s p a t h i c rock r o c k (metavolcanic?), (metavo1 c a n i c ? ) , qquartzite, u a r t z i t e , and i o t i t e . The indicate i n d i c a t e deposition d e p o s i t i o n near n e a r the t h e contact c o n t a c t between between aa ccratonic r a t o n i c terrane t e r r a n e mantled m a n t l e d bby y qquartzite uartzite The volcanic portion of the conglomerate resembles those and and aa vvolcanic o l c a n i c terrane. t e r r a n e . The v o l c a n i c p o r t i o n o f t h e conglomerate resembles those possible exposednearby: nearby:t the exposed h e qquartzite, u a r t z i t e , however however has has no no present p r e s e n t nearby n e a r b y source. source. IItt isi spossible that the volcanics were overlain by platform quartzites, eroded, and then deformed t h a t t h e v o l c a n i c s were o v e r l a i n b y p l a t f o r m q u a r t z i t e s , eroded, and t h e n deformed first f i r s tby byflattening f l a t t e n i n gwith w i t development h development oof f foliation f o l i a t i o nand and then t h e n by b y close c l o s e folding folding These types of deformation are not seen in the greenschist facies ( F i g u r e 12). 12). These t y p e s o f d e f o r m a t i o n a r e n o t seen i n t h e g r e e n s c h i s t facies (Figure metavolcanic and pplutonic m e t a v o l c a n i c and l u t o n i c rocks r o c k s of o fcentral c e n t r aMarathon l MarathonCounty County — tthe h e region r e g i o n surrounding surrounding the t h e Wausau Wausau ssyenite y e n i t e complex. complex. - F i gure 1212- Sequence Sequence oof f deformation d e f o r m a t i o n in i n the t h emetaconglomerate. metaconglomerate. Figure F o l i a t i o n was was pprobably r o b a b l y developed d u during r i n g i n iinitial t i a l fflattening lattening Foliation developed ooff the t h e quartzite q u a r t z i t e clasts c l a s t s and and later l a t e rbuckled b u c k l e d by b y close-folding. close-folding. P a r t of o f the t h e chlorite c h l o r i t ewas was replaced r e p l a c e d by by biotite b i o t i t eduring d u r i n gemplaceemplacePart ment ooff the t h e Rib R i b Mountain Mountain pluton. pluton. ment The r o c k s showing showing t hthese e s e t ytypes p e s oof f ddeformation e f o r m a t i o n and t h o l o g y favor favor The absence absence ooff rocks andl ilithology t h e conclusion c o n c l u s i o n that t h a t tthey h e y represent r e p r e s e n t materials m a t e r i a l s carried c a r r i e dupwards upwards during d u r i n g syenite syenite the . empl acement emplacement. Figure Zoned F i g u r e 13—— 13-- Zoned d i k edikes s o f aofp aplitic l i t i c Nr'iineniile i n e m i l e ggranite r a n i t e ccutting uttjng foliated, f o l i a t e d , schistose s c h i s t o s ehiotite b i o t imetaconalomerate t e wetaconalomeratefrom f r o mLoc. LOC.72065 72065 �-20— STOP STOP #5 #5 TITLE: TITLE: Border B o r d e r Phases Phases ooff the t h eWausau Wausau Pluton Pluton LOCATION: LOCATION: WisconsinRRiver Wisconsin i v e r aatt Old O l d Technical T e c h n i c a l Institute, I n s t i t u t eWausau. y Wausau. NEkY 3sy NE¼, NEkY NE¼,Sec. Sec. 35, Wausau115' West7%' 7½' quadrangles. quadrangles. T29N, R7E. T29Ny R7E. Wausau 5 ' and and Wausau Wausau West Lfi'i, Ik1 i flI I R p• rir - 8 •'> . '°r 4. AUTHOR: AUTHOR: Paul E. E. Myers, University Paul Myersy U n i v e r s i t y of o f Wisconsin Wisconsin DATE DATE:: March, Marchy 1984 1984 -- Eau Eau Claire Claire SUMMARY OF FEATURES: SUMMARY OF FEATURES: Flow-lineated F l o w - l i n e a t e d amphibole amphibole ssyenite y e n i t e ccontaining o n t a i n i n g sheet-like s h e e t - l i k e masses masses ooff syenitized syenitized andmmafic aswwell as bblocky ssiliceous i l i c e o u s metavolcanic m e t a v o l c a n i c rrocks o c k s and a f i c s cschist h i s t as e l l as l o c k y xxenoliths e n o l i t h s ooff well bbiotite i o t i t eamphibolite a m p h i b o l i t eand andmetavolcanic m e t a v o l c a n i c rocks r o c k s resembling r e s e m b l i n g tthose h o s e aatt Brokaw Brokaw i is s we11 Xenolith e n o l i t h oorientrientexposed exposed aalong l o n g tthe h e overflow o v e r f l o w channel channel of o fthe t h epower powerdam dam ini nWausau. Wausau. X Thessyenite zonedy rrootless, o o t l e s s y steeply steeply aation t i o n is i s northwesterly n o r t h w e s t e r l y here. here. The y e n i t e i is s cut c u t by by zoned, with ddipping i p p i n g pegmatite p e g m a t i t e vveins eins w i t h quartz q u a r t z cores. cores. LLate a t e f fracture-filling r a c t u r e - f i l l i n g veinlets v e i n l e t s of of rreibeckite e i b e c k i t e are a r e locally l o c a l l yabundant. abundant. DESCRIPTION: Weidman's 203-208) "Wausau-typet' tWausau-type qquartz 907y p.p. 203-208) u a r t z ssyenite y e n i t e isi scomposed composed ooff Weidman's (1(1907, aalkali l k a l i feldspars: f e l d s p a r s : orthoclase, o r t h o c l a s e , microcline, m i c r o c l i n e yalbite, a l b i t e and y andmicroperthite m i c r o p e r t h i t eand and less less abundantb abarkevikite, r k e v i k i t e y hhedenbergite, e d e n b e r g i t e y f afayalite, y a l i t e , bbiotite, i o t i t e yand and quartz. q u a r t z . Accessory abundant minerals allanite(?). a p a t i t e ymagnetite, magneti t e y zzircon, i r c o n and and a1 l a n ite(?). m i n e r a l s i include n c l u d e f lfluorite, u o r i t e apatite, Cross-cutting throughout C r o s s - c u t t i n g relationships r e l a t i o n s h i p shere h e r etypify t y p i fthose y t h o sseen e seen t h r o u g h o uthe t t h Wausau e Wausau a j o r components components a rare e ddescribed e s c r i b e d below n oorder r d e r of o f decreasing d e c r e a s i n g age. age. pluton. Major belowi in pluton. M 1. The The ooldest l d e s t rrocks o c k s aare r e xxenoliths e n o l i t h s ooff schistose s c h i s t o s e biotite b i o t i t eamphibolite a m p h i b o l i t e and and slightly resembl i n gthose t h o s e ata tBrokaw. Brokaw. s1 i g h t l yaltered a1 t e r e dfelsic f e l s metavolcanics i c m e t a v o l c a n i c sresembling Sheet—like masses andf ofoliated S h e e t - l i k e masses o f of s i siliceous l i c e o u s and l i a t e d mafic m a f i c rocks r o c k s occur o c c u r on on the the These iinclusions end ooff the ~ i g u r e114, 4 y Loc. LOC. C). C). These n c l u s i o n s have have ssouth o u t h end t h e exposure exposure ((Figure a andn nearly a pronounced pronounced n onorthwesterly r t h w e s t e r l y s tstrike r i k e and e a r l y v vertical e r t i c a l dip. d i p . This T h i s fabric fabric iiss consistent c o n s i s t e n t with w i t h the t h e concentric c o n c e n t r i c structure s t r u c t u r eofo the f t h Wausau e Wausau pluton p l u t o n northnorthwest here. AA hhighly i g h l y altered a l t e r e d mafic m a f i c xenolith x e n o l i t h at a t Location L o c a t i o n AA (Figure ( F i g u r e 15) 15) west ooff here. has sswirled has w i r l e d ffoliation o l i a t i o nand and isi scut c u by t b yrootless r o o t l e s pegmatite s p e g m a t i t eveins v e i n swith w i t hK—feldK-feldSome o of f t hthe e mmafic a f i c vvolcanic o l c a n i c xenoliths x e n o l i t h s have have walls sspar par w a l l s and and quartz q u a r t z cores. cores. Some rrelict e 1 i c tporphyritic p o r p h y r i t i ctextures: t e x t u r e s mafic : m a f i xenoliths c x e n o l i t h sare a r enow nowbiotite-rimmed biotite-rimmed subhedralccrystals subhedral r y s t a l s ooff hastingsite h a s t i n g s i t e and and ferrohastingsite f e r r o h a s t i n g s i t e (Figure ( ~gure i 15,Loc. 15 LOC. B). 0). �—21- 4 N 0 1•> Figure 15-- Amphibol Amphibolite xenolith F i g u r e 15-i t e ((a) a ) xenol i t h with w i t h swirled swirled lineation l i n e a t i o n and and thin t h i n seams seams oof f ssyenite y e n i t e (Loc. (Loc. A, A, Fig. Fig. 14). Pegmatitic Pegmati t i c vveins e i n s have have KK-feldspar - f e l d s p a r (Kf) ( K f ) cores cores and and qquartz u a r t z (q) ( q ) cores. c o r e s . Late L a t e ffracture-filling r a c t u r e - f i l 1 i n gveins veins are a r e filled f i l l e dwith w i t hcoarse c o a r s elaths l a t h sofo sodic f s o d i camphibole. amphibole. Biotite B i o t i t eand and amphibole amphibole in i n amphibolite a m p h i b o l i t e are a r e about about the t h e same same ccomposition o m p o s i t i o n asast hthose o s e i in n tthe h e enclosing, enclosing, fflow—lineated l o w - 1 i n e a t e d ssyenite y e n i t e (determined ( d e t e r m i n e d by b y microprobe). microprobe). Figure F i g u r e14—— 14-- SSketch k e t c h map map showing showing llocations o c a t i o n s oof f points p o i n t s ooff interest interest Bar B a r sscale c a l e iin n sketch s k e t c h is i s 66 inches i n c h e s long. l o n g . View View is is oblique o b l i q u e toward t o w a r d northwest. northwest. 2. An An eearly, a r l y , flow-laminated, f l o w - 1 aminated, ffoliated o l i a t e d quartz q u a r t z syenite s y e n i t e containing c o n t a i n i n g llenticular enticular xenoliths x e n o l i t h s ooff porphyritic p o r p h y r i t i c felsic f e l s i cvolcanic v o l c a n i crocks r o c k s and and biotite b i o t i t eamphibolite amphibolite with w i t h relict r e l i cmafic t m a f i phenocrysts c p h e n o c r y s t s isi sexposed exposed at a t Location L o c a t i o n B. B. 3. Coarse—grained, amphiboleq uquartz Coarse-grained, f l flow-lineated o w - l i n e a t e d amphibole a r t z s syenite y e n i t e ccuts u t s tthe h e fine-grained fine-grained phase (Loc. B) phase (Loc. B ) with w i t h sharp s h a r p discordance. d i s c o r d a n c e . Although A l t h o u g h tthe h e llensoidal e n s o i d a l and and tabular tabular iinclusions n c l u s i o n s in i n this t h i srock r o c kshow show a a northwesterly n o r t h w e s t e r l y oorientation, r i e n t a t i o n , the t h eenclosing enclosing syenite s y e n i t eshows shows hhighly i g h l y discordant d i s c o r d a n t flow f l o w lineation l i n e a t i o n with w i t hswirls s w i r l sand andeddies eddies Considering C o n s i d e r i n g t the h e llack a c k of of suggesting andvviscosity. s u g g e s t i n g cconsiderable o n s i d e r a b l e tturbulence u r b u l e n c e and iscosity. deformation in the sheets of biotite amphibolite and siliceous metavolcanic d e f o r m a t i o n i n t h e s h e e t s o f b i o t i t e a m p h i b o l i t e and s i l i c e o u s m e t a v o l c a n i c rock r o c k iinn this t h i s syenite, s y e n i t e , aamodel model requiring r e q u i r i n g turbulent t u r b u l e n t flow f l o w in i nthe t h eenclosing enclosing syenite be prot o trouble. t r o u b l e . The The appearance appearance of o f discordance d i s c o r d a n c e may may be pros y e n i t e magma magma r uruns n s i ninto duced duced bby y o obliquity b l i q u i t y ooff lineation l i n e a t i o nwith w i t hrespect r e s p e c ttot othe t h eeroded e r o d e d rock r o c k surface. surface. 4. Late—stage, L a t e - s t a g e , r rootless" o o t l e s s " granite g r a n i t e pegmatite p e g m a t i t e veins v e i n s with w i t h quartz q u a r t z cores c o r e s probably probably rrepresent e p r e s e n t rresidual e s i d u a l lliquid i q u i d segregations s e g r e g a t i o n s along a l o n g incipient i n c i p i e n t thermal t h e r m a l contraction contraction The ppegniatites fractures f r a c t u r e s iin n the t h e crystallized c r y s t a l l i z e d syenite. s y e n i t e . The e g m a t i t e s may may dderive e r i v e from from uunassimilated n a s s i m i l a t e d ssiliceous i 1 i c e o u s rrocks, o c k s , possibly p o s s i b l y feldspathized f e l d s p a t h i z e d qquartzites. uartzites. 5. Coarse, amphibole( a(arfvedsonite andr i riebeckite) Coarse, ssodic o d i c amphibole r f v e d s o n i t e and e b e c k i t e ) ccrystallized r y s t a l 1 i z d d along along fracture appeart otoc ucut f r a c t u r e surfaces1and s u r f a c e s a n d appear t aall l l other o t h e r structures. structures. At Location B, m mafic and ffelsic L o c a t i o n B, a f i c and e l s i c xenoliths x e n o l i t h s are a r e aligned a l i g n e d N1OW, NlOW, v evertical r t i c a l iinn aa medium-grained medium-grained t a btabular u l a r s ysyenite e n i t e w iwith t h a af afabric b r i c ssimilar i m i l a r to t o that t h a tseen seen in i nthe t h emargin margin This h i s rock r o c k is i s cut c u tdiscordantly d i s c o r d a n t l ybyb coarse y c o a r s egray g r a yamphibole amphibole ooff the t h e Stettin S t e t t i n pluton. pluton. T �-22.-22. syenite. Thin, lenticular l e n t i c u l a a.plite r a p l i t veinlets e v e i n l e thave s have o r i e n t a t i oof n N75°W, o f N75OW,40°S 40° ananorientation s y e n i t e . Thin, These common podsand andv eveinlets These sshallow h a l l o w ddips i p s aare r e common i n in g rgranitic a n i t i c pods i n l e t s iin n the t h e syenite. syenite. The ssheet-like, h e e t - l i k e , foliated f o l i a t e dbiotite b i o t i amphibolite t e a m p h i b o l i tat e Location a t L o c a t i oCn has C has e appearance The thet happearance of o f aa dike d i k e (Figure ( F i g u r e 16), 1 6 ) , but b u t its i t scontacts c o n t a c t sare a r e highly h i g h l yconvoluted, c o n v o l u t e d , and and ffoliation oliation is i s deformed, deformed, aalthough l t h o u g h i tit iis s also a l s o locally l o c a l l ycut c u tby b ythe t h e syenite. s y e n i t e . The The cuspate cuspate edge haswhisps whispswwhich edge ooff the t h e amphibolite a m p h i b o l i t e sheet s h e e t has h i c h t atail i l oout u t into i n t o the t h e syenite syenite (Figure ( F i g u r e 17). 17). The The ttrace r a c e of o f lineation l i n e a t i o non onthe t h erock r o c ksurface s u r f a c egives g i v e sthe t h eimpression impression o f sharp s h a r p discordance d i s c o r d a n c e between between t hthe e aamphibolite m p h i b o l i t e ssheet h e e t and e l lineated i n e a t e d syenite. syenite. of andt hthe Irregularities I r r e g u l a r i t i e in s ithe n t hshape e shapeofothe f t hsyenite—amphibolite e s y e n i t e - a m p h i b o l i t e contact c o n t a c t can can give g i v e the the impression i m p r e s s i o n tthat h a t the t h e amphibolite amphibol i t e contains c o n t a i n s ssyenite y e n i t e inclusions i n c l u s i o n s (Figure ( F i g u r e 18). 18). The samea amphibolite is The same m p h i b o l i t e s sheet h e e t onont hthe e eeast a s t sside i d e ooff the t h e channel channel at a t Location L o c a t i o n DD is broken which can canbe bef fitted broken iinto n t o angular a n g u l a r fragments fragments which i t t e d back back together t o g e t h e r again. again. It It is i s therefore t h e r e f o r eapparent a p p a r e n t that t h a t the t h emechanical mechanical behavior b e h a v i o r ooff the t h e amphibolite a m p h i b o l i t e in i n the the syenite s y e n i t e varied v a r i e d significantly s i g n i f i c a n t l yover o v e rshort s h o r tdistances. distances. North North t — * Figure F i gure 16-16-- Deformed, Deformed, f foliated o l i a t e d biotite b i o t i t eamphibolite amphi b o l i t esheet s h e e tini namphiamphibole syenite at Location C. b o l e s y e n i t e a t L o c a t i o n C. Is I s iti a t dike a d i k which e whichwas was intruded i n t r u d e d at a tan an e a r l y stage s t a g e ooff syenite s y e n i t e ccrystallization, r y s t a l l i z a t i o n , then t h e n carried c a r r i e d to t o its its early p r e s e n t location l o c a t i o n during d u r i n g intrusion i n t r u s i o n of o fa asyenitic s y e n i t i crystal c c r y s t amush? l mush? present y can seen Slight, bebeseen S l i g h t ,but b u probably t p r o b a b l ysignificant s i g n i f i c a ndifferences t d i f f e r e n c ein s mineral i n m i n e rchemistry a l c h e m i s t rcan when amphiboleand andb ibiotite when amphibole o t i t e ccompositions o m p o s i t i o n s i in n vvarious a r i o u s inclusions i n c l u s i o n s are a r e compared compared t to o ttheir heir composition c o m p o s i t i o n iin n the t h e coarse coarse and and ffine i n e grained g r a i n e d varieties v a r i e t i e s ofo fthe t h eamphibole amphibole syenite. syenite. Table T a b l e 2 is i s aacompilation c o m p i l a t i o n of o fmicroprobe m i c r o p r o b e date d a t e for f o r these t h e s e minerals m i n e r a l s as as well w e l l as as i n the t h e syenite s y e n i t eand and in i nthe the plagioclase, p l a g i o c l a s e , which which is i s aa persistent p e r s i s t e n taccessory a c c e s s o r y mineral m i n e r a l in inclusions. i n c l usions. �—23- Figure edgeof of foliated, Figure 17-- Cuspate Cuspate edge f o l i a t e d ,sheet—like sheet-1 ikemass mass of biotite b i o t i t eamphibolite amphibolite ininlineated lineatedamphibole amphibole syenite. syenite. Bar scale scale iiss 66 inches Location C. Bar inches long. long. Location C. Figure 18-18—-Pseudoxenol Pseudoxenolith syeniteinin bbiotite Figure i t h of ofsyenite i o t i t eamphibamphibolite 01 i t e ata tLocation Location C. C. �-24- Figure Segmented amphibolite F i g u r e 19—— 19-- Segmented b i obiotite t i t e am p h i b o l i t e ssheet h e e t iinn lineated, l i n e a t e d , coarse-grained c o a r s e - g r a i n e d amphibole amphibole ssyenite. y e n i t e . Location L o c a t i o n D. D. Rule R u l e iis s six s i x inches i n c h e s long. long. TABLE 22 TABLE ANALYSESOF OFMAJOR MAJORMINERALS MINERALS SYENITESAND ANDINCLUSIONS INCLUSIONSAT ATFIELD FIELD TRIP STOP ELECTRON MICROPROBE MICROPROBE ANALYSES I NINSYENITES SFOP #5 #5 AMPHIBOLES WPHIBOLES Si02 Ti02 A12O3 FeO + FeO + MgO MgO CaO CaO MoO MnO Na20 K20 TOTAL rOTAL Fe2 03 I DESCRIPTION DESCRIPTION A/4* 43.30 1.44 6.64 Fe203 28.84 3.60 28.84 3.60 9.93 9.93 0.99 0.99 2.24 1.03 98.01 38.01 Green amphibole Green amphibole i n inf ofoliated l i a t e d bbiotite iotite amphibolite a m p h i b o l i t e xxenolith e n o l i t h in i n syenite syenite B/3 42.07 1.40 6.32 32.55 32.55 1.56 1.56 9.28 9.28 0.69 0.69 2.24 1.16 97.27 37.27 Medium—grained. Medium-grained. eearly a r l y phase phase amphiamphi- D/6 43.20 1.54 6.35 29.63 29.63 2.75 2.75 9.72 9.72 0.79 0.79 2.32 1.14 97.44 97.44 G/5 42.20 1.77 8.14 25.92 25.92 5.03 5.03 10.79 10.79 0.62 0.62 2.12 1.23 H/2 41.32 1.36 8.10 29.04 29.04 2.76 2.76 10.63 10.63 0.81 0.81 1.89 1.32 97.23 97.23 35.54 35.54 3.77 11.67 31.07 4.34 0.02 0.45 0.04 9.10 96.00 96.00 35.29 3.34 11.43 35.77 1.93 0.04 0.35 0.00 8.93 98.08 98.08 D/4 36.39 2.36 10.96 32.87 3.65 0.14 0.27 0.01 8.98 95.84 95.84 G/5 35.96 3.62 12.36 27.14 6.70 0.02 0.34 0.06 9.21 95.41 Yellow—orange Y e l l ow-orange t to o orange—brown orange-brown f ofolia 1i a in i n biotie—amphibole b i o t i e - a m p h i b o l e sschist chist HI? 35.64 3.49 12.82 30.74 3.91 0.02 0.52 0.02 9.19 96.35 96.35 Raggedyyellow—brown Ragged e l l o w - b r o w n wwith i t h green, green, anhedral amphibole amphiboleand andf lfluorite anhedral uorite bbole o l e syenite: s y e n i t e : green green amphibole amphibole olive o l i v e green green to t oolive o l i v ebrown brownamphiamphibbole o l e in i n lineated l i n e a t e damphibole amphibole syenite syenite green amphibole amphibolei in brownbbiotite n brown iotite 97.82 97.82 green cclots l o t s or o r plagioclase plagioclase BIOTI TES BIOTITES A/2 A12 8/1 I Green amphibolei in Green amphibole n lineated, l i n e a t e d ,coarse— coarsegrained g r a i n e d amphibole amphibole ssyenite, y e n i t e , late l a t ephase phase I Yellow—brownw with Yellow-brown i t h mmetamict e t a m i c t zzircon ircon iinn green green amphibole: amphibole: amphibolite a m p h i b o l i t e xeno. xeno. Olive O l i v e brown brown wwith i t h aapatite p a t i t e in i ngreen green amphibole amphibole cclusters lusters Yellow—brown Yellow-brown a nanhedral h e d r a l b ibiotite o t i t e with with ffluorite l u o r i t eini green n greenamphibole amphi b o l e PLAGIOCLASE FELDSPAR FELDSPAR D/2: 1.73%An 0/2: 1.73%An SampleLLocations: Sample ocations: G/3: G/3: 10.24-18.41%An 10.24-18.4l%An Avg. Avg. 13.12%An 13.12%An H/3: 8.83-l2.44%An 8.83-12.44%An H/3: Zoned Zoned Plag. Plag. = =1O.68—8.67%An. 10.68-8.67%An. SamplesA Aand andB Ba rare fromL oLocation 14: Sample SampleG Gi sisf from andHHi is i g u r e 14: r o m LLocation o c a t i o n CC, , and s from from Samples e from c a t i o n B Bi ninFFigure Location Location D 0 iin n Figure F i g u r e 14. 14. ** Field F i e l dnumber/number number/number of o f analyses a n a l y s e s averaged averaged �—25— -25STOP #6 STOP TITLE:: TITLE LOCATION: AUTHOR: Contaminated Amphibole Quartz Quartz Syenite Contaminated Amphibole Syenite—- Wausau Wausau Pluton Old quarry behind Old behind Employers' Employers1 Mutual Mutual Insurance Insurance Company Company ooffices, ffices, NW/4, SE/4, SE/4, Sec. Sec. 27, NW/4, 27, TT 29 29 N, N , RR 77E;E ;Wausau Wausau West West 7.5' Quadrangle Quadrangle Paul Paul E. E. Myers, Myers, University U n i v e r s i t yofo fWisconsin W i s c o n s i n— - Eau Eau Claire Claire April,1 , 1984 Apri 1984 DESCRIPTION: DESCRIPTION: Coarse pink and and brownish brownishgray grayamphibole amphibolequartz quartzsyenite syenite iiss well exposed in in Coarse pink we 11exposed relatively leadinginto into the the offices offices of of r e l a t i v e l y fresh fresh faces faces of of an an old old quarry quarry along along aa road road leading Four facies were Employers' Mutual Employers' Mutual Insurance InsuranceCompany. Company. Four were recognized: recoanized : (1) . ( 1 )brownish brownish gray quartz-bearing quartz—bearingsyeni syenite, (2) coarse, coarse, dark dark gray gray amphi amphibole syenite, ((3) 3 ) pink pink gray t e , (2) bole syenite, quartz syenite , and(4)( 4medium—grained ) medium-grained pinkish syeni t e with withabundant abundant volcanic vol canicxenoliths, xenol i thsand brown brownishgray grayamphibole amphibole quartzsyenite syenitewith withmagnetite magnetitesegr segrations. ations. brown t to o brownish quartz The pinksyeni syenites havea ad idistinctly higher Fe3+/Fe" Fe3/Fe ratio The pink t e s have s t i n c t l y higher r a t i o than than ) (See Table (See Table 33 ). Magnetite sheets and irregular masses occur in the medium— the gray gray syenites syenites Magnetite sheets and irregular masses occur in the mediumThe magnetitegrained syenite syenite along along the the road road on onthe the east east side side of of the grained the outcrop. outcrop. The bearing aeromagnetic on the themap map bearing quartz syenite syeniteforms forms aalarge, large,crescentic crescentic aeromagneticanomaly anomalyon by Tyson, and and Page, Page, (1963). (1963). The by Henderson, Henderson, Tyson, The anomaly anomaly iis s concentric concentricand andconcordant concordant with the the structure structureofofthe theWausau Wausau pluton. pluton. The concentric structure structure of this plutonisi accentuated s accentuatedby bythe theoccurrence occurrence The concentric t h i spluton large quartzite just north north of ofhere hereon on the thetree—covered tree-covered hhillside i l l s i d e of of numerous, numerous, large Unlike the Rib quartzite xenolith, xenoliths. Unlike Rib Mountain Mountain quartzite xenolith,this t h imass s masscomprises comprisesmany many Orientation of smaller quartzite blocks. of xenoliths xenoliths here here and and elsewhere elsewhere in the the smaller blocks. Orientation Wausau plutoni sisconcentric concentricand andnearly nearlyvertical vertical — aa factor strongly stronglysuggesting suggesting Wausau pluton subvolcanic emplacement withsuccessive successivecollapse collapse and and intrusion intrusion ofofmagma subvolcanic emplacement with magma into xenolithsaat concentric of the The xenoliths t tthis h i s location location concentric fracture systems systems of the caldera caldera rim. The are quite unlike pluton: they are unlikethose thoseanywhere anywhere eelse l s e in in the theWausau Wausau pluton: they consist almost almost showing pre-intrusion metamorphism. pre-intrusion metamorphism. eentirely n t i r e l y ofoffelsic f e l s ivolcanics c volcanics showingvirtually v i r t u a l lno y no (See Figure (See Figure 20 20 ). DATE: DATE : - - 0 meter (n detafled area) Figure 20-s i c volcanic i t h s (dotted) flow-1 ineated Figure 20-- Fel Felsic volcanic xenol xenoliths (dotted) in flow-lineated amphibole quartz syenite. amphibole quartz �-26— TABLE 33 TABLE Bulk compositionso foft hthe Bulk chemical chemical compositions e f ofour u r pprincipal r i n c i p a l quartz q u a r t z syenite syeni t e facies f a c i e s from from Employers' Mutual Mutual Insurance InsuranceCompany Company Quarry. Quarry. - Description Description — EW-5 EN-5 EW-3 EN-3 (WEST) (WEST) ( EAST) (EAST) NSI NSI (SOUTH) (SOUTH) BrownishBrowni shgray gray Coarse, Coarse, dark dark gray gray Pink Pink syenite, syeni te, with with volcanic v o l cani c xenoliths xenol it h s 1 SEI SE I (NORTH) (NORTH) Medium-grained Medi urn-grai nec syenite syeni t e 63.05 63.55 63.90 64.10 Ti02 0, 0.78 0.54 0.47 0.48 A1203 12.60 15.16 14.14 15.17 Fe203 1.91 1.25 5.42 4.58 FeO FeO 7.72 3.48 1.32 1.44 MnO ^In0 0.34 0.16 0.14 0.12 MgO w 0.41 0.16 0.45 0.09 CaO CaO 2.66 1.72 1.35 1.50 Na2O 1a20 4.80 5.52 6.32 5.17 4.22 5.67 6.34 5.57 H20 +zO 0.76 0.42 0.56 0.26 P205 0.22 0.06 0.05 0.06 CO2 ;02 0.28 1.92 0.62 0.09 BaO BaO 0.094 0.066 0.024 0.036 Zr02 Zr02 0.222 0.114 0.062 0.071 154 118 80 80 78 83 67 42 Si02 S i 0, n È,O 1(20 K2 Rb sr Rb Sr ppm P P ~ In with I n comparison comparison w i t h Nockolds' Nockol ds ' (1954) (1954) average average syenite syeni t e composition composi t i o n (see (see ), these these quartz q u a r t z syenites syenites aare r e rricher i c h e r in i nSi09 S i O and and total t o t a l iron i r o nand andpoor poor Table ), Table contents a'e a e also a l s olow lowcompared compared to to T h e i r Rb Rb and and SSrr contents in i n alkalies a l k a l i e s and and lime. lime. Their other o t h e r similar s i m i l a r rocks. rocks. * From Sood, Myers, Myers, and andBBerlin, From Sood, e r l i n , 1980, 1980, p. 21 21 6 �—27- STOP STOP #7 #7 TITLE: TITLE : Quartz-sillimanite-muscovite andqquartzite Quartz-sillimanite-muscovite sschist c h i s t and u a r t z i t e xxenoliths e n o l i t h s in in LOCATION: LOCATION: SE¼ SEk , AUTHOR: AUTHOR : Paul Paul E. E. Myers, Myers, University U n i v e r s i t y of o fWisconsin Wisconsin -- Eau Eau Claire Claire quartz q u a r t z syenite s y e n i t e of o fthe t h eWausau Wausau pluton. pluton. T29N,R7E; R7E;Wausau Wausau quadrangle[ F[Figure , NE¼, NEk, T29N, 1 515' ' quadrangle i g u r e 6] 61 - March, March, 1984 1984 DESCRIPTION: DESCRIPTION : DATE: DATE : Xenoliths mainly X e n o l i t h s in i n the t h eWausau Wausau ssyenite y e n i t e ppluton l u t o n aare re m a i n l y ssyenitized y e n i t i z e d mafic m a f i c and and interinterFelsic abundant, as as F e l s i c metavolcanic metavol c a n i c rocks r o c k s are a r e locally l o c a l l yabundant, at a t the t h e old o l dTechnical T e c h n i c a l School School (Stop ( S t o p 5), 5), and and may may rrepresent e p r e s e n t pportions o r t i o n s ooff the t h e volcanic volcanic mediate metavolcanic mediate metavol c a n i c rocks. rocks. cover which ccollapsed and were were sstoped c o v e r sequence sequence which o l l a p s e d and t o p e d bby y tthe h e rising r i s i n gsyenite s y e n i t magmas. e magmas. Mica Mica sschist c h i s t and and quartzite q u a r t z i t eare a r ecommonly commonly aassociated s s o c i a t e d i in n the t h e intermediate i n t e r m e d i a t e zones zones of of both and R Rib b o t h the t h eWausau Wausau and i b Mountain Mountain plutons p l u t o n s and andmay may represent r e p r e s e n tsamples samples ofo basement f basement rocks underlie C o n s i d e r a b l e v avariation r i a t i o n i in n 1lithology, it h o l o g y , r o c k s which w h i c h under1 i e the t h e volcanic v o l c a n i c rocks. r o c k s . Considerable size, s i z e , shape, shape, and and relative r e 1 a t i v eabundance abundance of o f xenoliths xenol i t h ssuggests suggestsmixing m i x i n gofo basement f basement and and cover c o v e r rocks r o c k s by b y complex complex subsidence subsidence and and resurgence resurgence ooff the t h e syenite s y e n i t emagmas magmas aatt shallow Not oonly n l y is i s the t h econcentric c o n c e n t r i c structure s t r u c t u r eofo these f t h e s eplutons p l u t o n sexpressed expressed s h a l l o w depth. depth. Not by a y e r i n g and and oorientation r i e n t a t i o n of o f xenoliths, x e n o l i t h s ,but b uxenolithology t x e n o l i t h o l o gshows y shows b y compositional c o m p o s i t i o n a l llayering a crude eachbluton. crude cconcentric o n c e n t r i c zzoning o n i n g wwithin i t h i n each luton. The dominantl i tlithology The dominant h o l o g y o of f xxenoliths e n o l i t h s aat t tthis h i s locality l o c a l i t yisi sillimanite—bearing s sillimanite-bearing lineated, 1 i n e a t e d , quartz-muscovite q u a r t z - m u s c o v i t e sschist c h i s t with w i t h aa pronounced pronounced t etectonite c t o n i t e ffabric a b r i c (Figure ( F i g u r e 21). 21 ). Figure Photomicrograph( w(with half—crossed F i gure 21—— 21 -- Photomicrograph i t h ha1 f - c r o s s e d ppolars) ol a r s ) of quartz-sillimanite-muscovite schist. s c h i s t . Elongated, Elongated, o f quartz—sillimanite-muscovite polygonal p o l y g o n a l qquartz u a r t z ggrains r a i n s show show ssimilar i m i l a r eextinction x t i n c t i o n positions positions and and eelongation l o n g a t i o n p aparallel r a l l e l t to o ssillimanite i l l i m a n i t e tufts. t u f t s . Width Width of of photomicrograph photomicrograph is i s4.0 4.0mm. mm. AA nearby metaquartzite n e a r b y xenolith x e n o l i t h isi scoarse—grained c o a r s e - g r a i n e d which which m e t a q u a r t z i t e with w i t h sutured s u t u r e d grains g r a i n sand and no no strain s t r a i n lamellae. l a m e l l a e . Sillimanite S i l l i m a n i t e isi sabsent. absent. This T h i s rock r o c kclosely c l o s e lresembles y resemblesthe t hmeta— e metaquartzites mineral q u a r t z i t e s ofo fRib R i bMountain. Mountain. The The strong s t r o n g contrast c o n t r a s t ini nthe t h etextures t e x t u r eand s and m i n e r acompol compositions s i t i o n s of o fthese t h e s e two two rocks r o c k s suggests suggests wwidely i d e l y ddifferent i f f e r e n t origins. o r i g i n s . Although A l t h o u g h sillimanite sillimanite can metasomatically metasomatic can form form m e t a s o m a t i c a l l y i nin metasomatic a uaureoles r e o l e s o f of g rgranitic a n i t i c pplutons, l u t o n s , iits ts o c c u r r e n c e hhere e r e i ninaasschistose c h i s t o s e r orocks c k s w with i t h a ad distinct i s t i n c t ttectonite e c t o n i t e fabric f a b r i ctends tends to to occurrence rule r u l e out o u t that t h a t possibility. p o s s i b i l i t y . (See (See Figure F i g u r e 22.) 22.) �-28- Figure 22-F i g u r e 22 -- Photomicrograph P h o t o m i c r o g r a p h o of f qquartz—sillimanite u a r t z - s i l l i m a n i t e sschist c h i s t (A) (A) and metaquartzite N o t e sutured s u t u r e d grain g r a i n boundaries b o u n d a r i e s and and and m e t a q u a r t z i t e (B). ( B ) . Note lack W i d t h of o f image image is i s1.5 1.5mm. mm. l a c k ooff sillimanite s i l l i m a n i t e in i n B. B. Width �—29— THE THE STETTIN STETTIN SYENITE SYENITEPLUTON PLUTON ?ç Wausau Pluton Figure Generalizedgeologic geologicmap map Figure 23-— 23-- Generalized o foft hthe e SStettin t e t t i n syenite s y e n i t e pluton. pluton. Excerpted Excerpted from 6 in i n this t h i sguidebook. guidebook. from Figure Figure 6 Although (1907)mapped mapped geologyofof nnorth-central Although Weidman Weidman (1907) t hthe e geology o r t h - c e n t r a l Wisconsin Wisconsin and near Wausau, and paid p a i d special attention a t t e n t i o ntot othe t hmineralogy e mineralogyofofthet hsyenites e syenites near Wausau, Emmons and Snyder (1944) hypothesized formation o f oft hthe e SStettin t e t t i n syenite syeni t e Emmons and Snyder (1944) hypothesized formation body by metasomatism metasomatism rocksalong alongshear shearzones zoneswwith body by of off efeldspathic l d s p a t h i c rocks i t h aalkalilkalirich r i c hsolutions s o l u t i o n sderived d e r i v e d from from aa subjacent subjacent granite g r a n i t e batholith. bath01 it h . Turner Turner (1948) (1948) studied accessoryminerals mineralsand and s t u d i e d the t h e heavy heavy accessory r a radioactivity d i o a c t i v i t y ofof tthe h e SStettin tettin pluton, described tthe petrographyofof tthis pluton, and and Geisse Geisse (1951) (1951) described h e petrography h i s pluton. pluton. PetPetrographic and and geochemical geochemi c a l i ninvestigation rographic v e s t i g a t i o n of of the t h emafic mafic minerals mineral sand andnepheline nephel i n e o f the t h e Stettin S t e t t i npluton p l u t o ninitiated i n i t i a t eanalytical d a n a l y t i cstudies a l s t u dwhich i e s which have been extended of have been extended by by the t h e work work of of Sood S00d and and Berlin B e r l i n (in ( i nSood sood and and others, others, 1980) 1980) The zonedSStettin (Figure2323) oval in The cconcentrically o n c e n t r i c a l l y zoned t e t t i n ppluton l u t o n (Figure ) i is s oval i n plan, plan, elongated with elongated nnortheasterly, ortheasterly, w i t h a length l e n g t h of of 5.5 5.5 miles m i l e s and and aa width w i d t h of of 4.0 4.0 miles. miles. Older 01 der volcanic v o l c a n i c rocks rocks enclosing enclosing the t h e pluton p i uton have have been been eextensively x t e n s i v e l y syenitized. syeni ti zed. The eastern and and southern southernmargin marginoof The eastern f tthe h e ppluton l u t o n is i saacomplexly complexly laminated laminated series series of of altered a l t e r e dvolcanic v o l c a n i cscreens screensand andpendants pendants and and various, various, contaminated contaminated iintruntrusive of the s i v e phases phases of t h e syenite s y e n i t e including i n c l u d i n gnepheline n m h e l i n e syenite. syenite. The The wall w a l l zone zone comprises discontinuous oouter comprises aa discontinuous u t e r rrim i m of gneissic g n e i s s i cnepheline nepheline syenite, syenite, and and an The intermediate i n t e r m e d i a t e zone zone (Stops (Stops an inner i n n e r layer l a y e r of o f tabular t a b u l a r syenite s y e n i t e (Stop (Stop # ).). The #6 #6 and and #7) #7) isi scomposed composed of o f amphibole amphibole and and pyroxene pyroxene ssyenite y e n i t e showing showing considerconsider- . �-30- able variation ini ncomposition able composition and and texture. The The amphibole amphibolesyeni syenite t e is i s comcommonly quartz-bearing. quartz-bearing. The monly core zone zone (Stop (Stop#8) #8) iiss one one mile in in diameter diameter The core and iiss located near the the north north end endof of the and located asymmetrically asymmetrically near the pluton. pluton. The The core zone comprises well-defined, cylindrical rim rim of indistinctly banded zone comprises a a we1 1-defined, cylindrical indistinctly banded nephnepheeline l i n e syenite syenite surrounding surrounding aa core core of of pyroxene pyroxene syenite. syenite. Field Field relations relations indicate the the following fol lowing intrusion intrusionsequence: sequence: (1) (1 ) pyroxene pyroxene syenite, (2) ( 2 ) nepheline neohel ine syenite, (4)(4) amphibole Numbers syeni t e , (3) (3)tabular tabularsyenite, syenite, amphibolesyenite. syenite. Numbers 33and and 44could could be be This evidence basedwholly whollyononf ifield reversed. This evidence i is s based e l d relations (Myers). (Myers). It It should that the as should also be be emphasized emphasized that the intrusion intrusionsequence sequencemay may not not be be the thesame same as work (Sood (Sood and t h i sguidebook) guidebook) and Berlin, Berlin, this the crystallization crystal 1izationseqence. seqence. Analytical work the suggests a t e age age ffor o r the the nepheline nephel ine syenite. (See (See discussion discussion of suggestsaavery veryllate of petrochemistry beginning beginningon onpage page31 31 ). A tabulationofofparagenetic parageneticrelations relations of of minerals A summary summary tabulation minerals in i n each each zone zone of from Koeliner Koel l n e r the Stettin w i t h modification modification from the S t e t t i n syenite syeni t e pluton pi uton isi spresented presented with 27, p. (1974) in Figure (1974) Figure 27, p. 36. 36. The section section on onMineral Mineralchemistry chemistryand andpetrology, petrology,originally originally contained The contained in #3 by by Sood Sood and and Berlin has has been been excerpted excerpted the 1980 1980 Wausau Wausau f ifield e l d trip t r i pGuidebook Guidebook #3 unchanged andincorporated incorporatedinin tthis unchanged and h i s guidebook. guidebook. �—31— MINERALOGY AND MINERAL MINERALOGY AND MINERAL CHEMISTRY CHEMISTRY (STOP NO'S (STOP NO's 88 through through 12) 12) M.K. Sood,P,E..Myers, PE. .Myers,and and LA. Beii M.K. Sood, L.A..Berlirt 1 The The pprincipal r i n c i p a l mineral mineral phases phases i in n SStettin t e t t i n Complex Complex a are r e pperthitic e r t h i t i c feldspars, f e l dspars, nepheline, nepheline, sodic sodic and and calcic c a l c i cpyroxenes, pyroxenes,and andsodic sodicamphiboles amphiboles whose whose representarepresentative t i v e chemistry chemistry is i s given given in i nTable Tab1 e and and ccharacteristics h a r a c t e r i s t i c sdescribed described below: below: Eel dspars Fel dsoars The major phase phaseo of The major f f feldspar e l d s p a r iiss aa microperthite m i c r o p e r t h i t eini nuniform u n i f o r mveins veinsshowing showing p a r a l l e l , subparallel, s u b p a r a l l e l ,orowavy r wavylamellar l a m e l l a rintergrowths, intergrowths, oro as r aspatches patches of o fone one parallel, feldspar f e l d s p a r in i n the t h e host. host. Both e r t h i t e and and aantiperthite n t i p e r t h i t e are a r e present, present, Both pperthite although thanaantiperthite. although perthite p e r t h i t eisi smore morecommon common than n t i p e r t h i t e . Frequently Frequently the t h e tabular tabular f e l d s p a r grains g r a i n sexhibit e x h i b iCarlsbad t Carlsbad t w i n n i nand g and l e sconinonly s commonlyMannebach Mannebach twinning. feldspar twinning less twinning. The pperthitic e r t h i t i c feldspar f e l d s p a r constitutes c o n s t i t u t e s 80 80 to t o90 90percent percent of o f the t h esyenites s y e n i t e s and and 60 60 to to The 75 percent ooff the 75 percent t h e nepheline nepheline syenites syenites (Table (Table 4). 4). ]50, b u t Distinct D i s t i n c tgrains g r a i n s of o falbite a l b i t have e havean anaverage average extinction e x t i n c t i o n angle angle of o f 15O, but are any of of the a r e not n o t common common i nin any t h e syenites. syenites. Microcline, as ddistinct M i c r o c l ine, also a l s o present present as i s t i n c t grains, grains, show show i its t s characteristic characteristic spindle-shaped and wavy wavye extinction, spindle-shaped ppolysynthetic o l y s y n t h e t i c ttwinning w i n n i n g and x t i n c t i o n , but b u t is i sless l e s sabundant abundant than than aalbite l b i t e as as individual i n d i v i d u a l grains. grains. The compositionsoof The bbulk u l k compositions f tthe h e pperthitic i f e l d s p a rwere s weredetermined determined e r t h i t i c alkali a1 k a lfeldspars for f o r nine n i n esamples samples of o f three t h r e emajor major zones zones of of the0Stettin t h e s t e t t i ncomplex. complex. The The samples samples were i n aa muffle m u f f l e furnace furnace for f o r48 48hours; hours; were homogenized homogenized t oto aa ssariidine a n i d i n e phase phase at a t 1050 1050 in then KBrO3 CuKcx and tthe 201feldspar f e l d s p a- r101 - 101 KBr03 CuKa was was measured measured and h e molecular percent percent ~ 2= 0=201 then 20 orthoclase using tthe o r t h o c l a s e was was determined determined using h e homogenized homogenized n anatural t u r a l mmicrocline-low i c r o c l i n e - l o w aalbite lbite x-ray The compositions compositions are a r e given given x-ray determinative d e t e r m i n a t i v e curve curve ooff Jones Jones eetal. t a1. (1969) (1969) The below below in i n Table Table 44 Table Table 44 THE THE MOLECULAR MOLECULAR PERCENT PERCENTORTHOCLASE ORTHOCLASEOF OFHOMOGENIZED HOMOGENIZED PERTHITIC PERTHITIC ALKALI ALKALIFELDSPARS FELDSPARSOF OFTHE THESTETTIN STETTINROCKS ROCKS Sample Sample 29 CuKa Mol Mol % % Or Or 1.40° 39 1.45 1.40 35 39 1.43 1.35 1.39 37 44 Core Core Zone Zone pyroxene pyroxene syenite syenite Intermediate I n t e r m e d i a t eZone Zone amphibole amphi b o l e syenite syeni t e 33 amphibole amphibole syenites syenites Rim Rim Zone Zone tabular tabu1 a r syenite syeni t e nepheline nepheline syenite syenite nepheline nephel i n e syenite syeni t e 41 The molecular percent percent orthoclase o r t h o c l a s eranges rangesfrom from3535to t44%; o 44%; however,Or% Or% The however, i s above above 40% 40% f for o r tthe h e nepheline nepheline ssyenites y e n i t e s and l e s s than than 40% 40% ffor o r the t h e nephelinenephelineis and iiss less free f r e e syenites. syeni t e s . �-32— The iintensity The n t e n s i t y ratios r a t i o s ofofthe the201 701peaks peaks of of rnicrocline microcline and and albite a l b i t ewere were determinedf ofor determined r tthe h e pperthitic e r t h i t i cfeldspars feldsparsbybyscanning scanning in i nboth both directions directionsbetween between 200 and230-20 23°-20CCukc l/8°-20 per per minute minuteusing using200 200counts countsper perf ufull 20 and u k a a tat1/8°-2 l l chart chart scale, seconds and and a chart c h a r t speed speed of 15 15 inches inches per per hour. hour. s c a l e , aa time time constant constant ofof5 5seconds The angular positions The angular positions were were averaged averaged from from three three scans. scans. Then Then the goniometer goniometer was exactly centered on on one one peak time and and the the intensity i n t e n s i t was y wasmeasured measured was exactly centered peak aatt a time using aa fixed time time ofoften tenseconds seconds with w i t h aa22second second time time constant. constant. The using The background intensity was measured at the midpoint between the two peaks. ground i n t e n s i t y was measured a t the midpoint between the two peaks. counts on onmicrocl microcline 2b1/l0 ss AA == number number ofof counts ine 201/10 B counts on on low low aalbite B == number number ofof counts l b i t e 201/10 201/10 Ss C of counts C == number number of counts on on the thebackground/b background/IO ss Then: The The i nintensity t e n s i t y r ratio a t i o I'o"a 0/I = (A (A - C)/(B C)/(B - C). C). The thethe bulk composition of of Or%/Ab% Or%/Ab% The iintensity n t e n s i t y ratio r a t i oand andthe thevalue valueof of bulk composition of the of ffor o r each each of the perthitic p e r t h i t i cfeldspars feldsparsstudied studied were were plotted plotted on on the the graph araph of Kuellrner (1959)(Figure24). Kuel lmer (1959) (Figure 2 4 ) . Fromt this as tto From h i s diagram, diagram, implications implications can can be be made made as o the t h e temperaturetemperature(B) From t hthe e pplots l o t s aa broadening broadening rratio a t i o (B) sstructural t r u c t u r a l state s t a t e of of the the feldspars. feldspars. From is obtained. i s obtained. the ddistortion The broadening rratio The a t i o isi saameasure measure ofof the i s t o r t i o n or o r structural structural The broadening ratio will decrease The broadening r a t i o will decrease mistakes mistakes iin n the two two phases phases ofof pperthite. erthite. with slower crystallization and lower temperature since these conditions slower c r y s t a l l i z a t i o n and lower temperature since these conditions are are ions favorable for of Si and favorable f o r the the attainment attainment ofofananordered ordered arrangement arrangement of and Al A1 ions in the the tetrahedral tetrahedral sites s i t e s ofofthe thefeldspar feldsparstructure s t r u c t u r e(Smith, (Smith,1974). 1974). The broadening thep eperthitic alkali of the kali feldspars feldspars of the Stettin Stettin The broadening r a tratios i o s f o for r the r t h i t i c a1 This is 0.9). This is rocks range from low (B = 0.30) to intermediate values (B rocks range from low (B = 0.30) t o intermediate values ( B = an indication indication of the of these an the low low temperature-structural temperature-structural sstate t a t e of these pperthites, erthites, correspondingt to the maximum intermediatemicrocline-low microcline-lowaalbite corresponding o the maximum t o tointermediate l b i t e series series determined from the positions of the 204 and 060 reflections. determined from the positions of the 204 and 060 r e f l e c t i o n s . // 8— 6 5 // 4 3 2 o / i .8 / // ,/ 5 4 // b',•'• • // / .1 .2 // / ///, /, /,/ / // / ,/ — — / — // / / / — — / / / // /// // / / // 24-- Plot compositions Figure 24—— Plotof of bulk compositions Or%/ versus I Olo/lafor / I f o r tthe h e 201 201 reOr%/Ab% Ab% versus 7 ••," / // 7 / ,/ / / /i / ii 11111! I .1 ., // // // / / /' q' / / . / / /71 // / .2 / // // // // / / / // / , / "/ // /7 //// 6 // / /. .4 .6 .8 1 O RTHOCLASE % ORTHOCLASE % ALBITE ALBITE % % f l e c t i o n s of of the thetwo twofeldspar feldsparphases phases fboctions S t e t t i n perthite p e r t h i t efor f odetermin-. r determinthe Stettin in the ation broadening r ratios a t i o s ((B) B ) aafter fter ation of broadening Kucilmen, 1959. Kucllmen, 1959. I I 2 I I 4 6 I 8 10 �-33TABLE 55 TABLE ELECTRON ELECTRONMICROPROBE MICROPROBECHEMICAL CHEMICALANALYSES ANALYSESOF OFMAJOR MAJORMINERALS MINERALS OF OF STETTIN STETTIN COPPLEX DUPLEX I Feidsoar Fpldi nar Si02 SiO, A1203 A1203 67.42 19.23 Ti02 T i O2 ---- FeO FeO -- MnO MnO -- 40.45 19.72 8.70 9.28 1.0 3.17 1.31 0.1 34.22 26.8 -—— ------ ---- CaO CaO 0.44 0.25 7.40 7.40 6.39 6.39 11.23 0.27 K20 K2 à 68.23 MgO MOO Na20 Na20 I bo1es 39.90 --- NnDI' nsy 48.1 Pyroxene Pyroxene DSV DSV 50.1 0.59 0.26 0.26 0.81 1.00 1.52 23.70 23.70 0.89 2.28 0.73 0.62 4.41 29.1 10.3 8.89 17.8 2.14 3.30 2.40 1.57 1.75 —— 20.30 20.30 0.57 0.57 N.D. N.O. tsv Fe-TI Fe-TI 50.8 ~ e o h eine* l Nehe1ine 46.5 OxIds Oxides 1.34 1.34 0.30 0.30 26.40 26.40 33.1 0.25 50.8 0.71 0.99 11.00 .oo 11 6.80 N.D. N.D. -- 0.18 0.18 ------- Fledspars Fledspars Based Based on 8 oxygens oxygens on Ainphiboles Based Amphiboles Based on 23 23 oxygens oxygens Si Si 2.987 2.988 2.988 6.73 6.43 6.43 Al 1.004 1.018 1.76 Al 0 0 1.52 1.52 0.118 0.118 Ti --- -- 3.89 3.89 0.515 0.515 4.61 Mg ---- Ca 0.021 0.012 1.765 1.765 Na 0.635 0.954 K 0.361 0.015 0.690 0.323 0.323 Fe 0.372 0.372 0 0 0.147 0.147 Pyroxene Based Based on 66 oxygens oxygens 2.001 1.990 2.074 2.074 0.010 --0.010 -0.42 0.017 0.064 0.42 0.017 0.064 -- ------ 0.13 15.20 5.46 5.46 —- -— Nepheline {epheline Based on on 32 32 oxygens oxygens 8.76 7.352 7.352 ------- Fe..Ti Fe-Ti Oxides Oxides Based on 24 24 oxygens oxygens 0.119 0.079 1.530 0.004 0.004 0.930 0.930 0.008 0.008 0.786 0.786 0.010 0.902 0.902 0.261 0.862 0.862 0.060 0.060 ---- 1.536 1.536 0.38 0.38 0.797 0.797 0.480 0.480 0.27 ------ 1.031 1.031 0.194 0.194 0.044 0.044 0.538 0.538 5.52 5.52 -- 0.172 0.172 —— -- 16.0 3.9 3.9 Di 3.5 3.5 Hd 75.1 25.2 25.2 60.8 60.8 Ae 11.19 .I9 --- * * 0.44 7.57 7.57 90.40 -— ATOMIC PROPORTIONS PROPORTIONS 0.361 -- —— -—— 0.29 1.315 - 20.310 20.310 0.272 --- 47.3 47.3 5.3 5.3 42.8 42.8 - * From From Koeliner Koellner (1974) (1974) Nephel i me ne Nepheline by iits r e c t a n g u l a r , blocky b l ocky Nephel i n e i is s ccharacterized h a r a c t e r i z e d by t s subhedral subhedral tto o euhedral, euhedral , rectangular, Nephaline ssyenite form a r a l l e l eextinction x t i n c t i o n iin n thin t h i n section. s e c t i o n . Nephaline y e n i t e pegmatites pegmatites con-. conform and andp parallel n hand hand specimen specimen t the h e nnepheline e p h e l i n e iiss cm llont. e n t . IIn ttam a i n nepheline n e p h e l i n e ccrystals r y s t a l s up up to t o 55 cm Alteration ppinkish i n k i s h and and greasy greasy in i nappearance. appearance. A l t e r a t i o n leaves leaves gray, gray, etched etched surfaces s u r f a c e s of of negative 8, and a n c r i n i t e isi common s common at a tSTOP STOP 8, and n e g a t i v e rrelief e 1 i e fagainst a g a i n s t feldspar f e l d s p a r and and quartz. quartz. Cancrinite r e p o r t s that t h a t the t h enephelines nephelines from from K o e l l n e r (1974) (1 974) reports paragonite paragoni t e has has been been rreported. e p o r t e d . Koeliner the andd deficient alkalies 15% and e f i c i e n t iin n a1 k a l i e s by by S i by byabout about 15% t h e Stettin S t e t t i n pluton p l u t o n are a r e enriched e n r i c h e d in i n Si about 13%. 13%. Pyroxenes Pyroxenes Both ssodic andccalcic occurinint hthe Both o d i c and a l c i c cclinopyroxenes l i n o p y r o x e n e s occur e SStettin t e t t i n pluton. p l u t o n . Representative chemical compositions compositions aare chemical r e ggiven i v e n in i n Table Tab1 e 55above. above. Aegiring A e g i r i n g and and aaegirine-augite egirine-augi t e may zonedwwith may oor r may may nnot o t be rimmed rimmed bby y ssodic o d i c amphiboles. amphiboles. Some Some a rare e c color o l o r zoned i t h bbright right green green rrims i m s and and ppale a l e yyellowish e l l o w i s h green green cores. cores. Average Average eextinction x t i n c t i o n angles angles of o fpyroxene pyroxene cores iiss 28°, This cores 28O, whereas whereas t hthat a t oof f tthe h e rrims i m s iis s 13 13 to t o 24°. 24'. T h i s suggests suggests an an outward outward increase inn aegiring increase i aegi r i n g content. content. Calcic Cal c i c pyroxenes pyroxenes (diopside—hedenbergite) ( d i o p s ide-hedenbergi t e ) aare r e iironronrich r i c h with w i t h aegirine a e g i r i n econtent c o n t e n tup uptot o10% 10% (Koeliner, ( K o e l l n e r , 1974). 1974). In I n general, general, Na Na ++ ~Fe3 e ^ +is is photomicrograph, FFigure highest h i g h e s t iinn the t h e wall w a l l zone. zone. See See photomicrograph, i g u r e 24. 24. �—34- Figure pyroxene ssyenite. F i g u r e 25—25-- Photomircograph Photomircograph oof f pyroxene y e n i t e . Zircon Zircon crystals by bdark c r y s t a l s (left ( 1 e of f t center) o f c e n t esurrounded r ) surrounded y d a arfvedson— rk arfvedsonite i t eand and aegirine-augite. a e g i r i n e - a u g i t e . Mafic M a f i c cluster c l u s t e r enclosed e n c l o s e d in in stained f e l d s p a r . Plane Plane ppolarized o l a r i z e d 1light. ight. s t a i n e d alkali a1 k a l ifeldspar. Amphibol Amphi b o les es b l u i s hgreen greensodic s o d i camphibole amphibole with w i t han anabsorption absorption The The dominant dominant mmafic a f i c mmineral i n e r a l iiss aa bluish scheme c closely l o s e l y rresembling e s e m b l i n g aarfvedsonite: r f v e d s o n i t e : XX == bbluish l u i s h green green or o r greenish g r e e n i s h blue; b l u e ; ZZ== scheme greenish g r e e n i s h brown brown oor r light l i g h tbrown. brown. Average Average eextinction x t i n c t i o n angle a n g l e is i s 16°. 16O. Late L a t e blue blue amphibole deepbblue; l u e ; ZZ == 1light i g h t blue. blue. amphibole i is s riebeckite r i e b e c k i t e with w i t h absorption a b s o r p t i o n sheme: sheme: XX == deep Extinction E x t i n c t i o n angle a n g l e of o f these t h e s e grains g r a i n s is i s very v e r y low. low. X-ray X-ray diffraction d i f f r a c t i o npowder powder patterns patterns of reflection o f the t h e riebeckite r i e b e c k i t e give g i v e 8.42A 8.42A ffor o r the t h e ll0] [110] r e f l e c t i compared o n comparedto t o8.50A 8.50A for for arfvedsonite a r f v e d s o n i t e [110] [I1 0 1 reflections. r e f 1 e c t i o n s . All A1 1ofo the f t h amphiboles e amphi b o l es are a r eiron—rich. iron-rich. Biotite Biotite Two Two vvarieties a r i e t i e s of o f biotite b i o t i t eoccur o c c u rsparsely s p a r s e l yini nthe t h eStettin S t e t t pluton: i n p l u t o dark n : d aorange— r k orange- brown, and llight brown, and i g h t olive o l i v egreen greentot obrown. brown. This T h i s indicates i n d i c a t e stwo two genetic g e n e t i cassociations associations of Mn2. Electron o f biotite b i o t i t ewith w i t hbimodal bimodal partitioning p a r t i t i o n i n gofo Ti, f T iFe2, , ~ e *Fe3, + , ~ eand 3 + , and ~n2'. E l e c t r omicro— n microprobe aanalysis n a l y s i s of o f biotite b i o t i t efrom s f r othe m t hStettin e S t e tpluton t i n p l uby t o nMyers by Myers shows e orange-brown probe shows thet horange-brown varieties v a r i e t i e s to t obe be Ti T iand and Fei+ rich. rich. Accessory Accessorv Minerals Mineral s Numerous havebeen beeni didentified. Numerous aaccessory c c e s s o r y mminerals i n e r a l s have entified. They They iinclude n c l u d e zzircon, i r c o n , fluorfl uor- apatite, a p a t i t e , fayalite, f a y a l i t e ,magnetite, m a g n e t i t e , sphene, sphene, f lfluorite, u o r i t e , ccalcite, a l c i t e , cancrinite, c a n c r i n i t e , allanite, a1 l a n i t e , pyrochlore, p y r o c h l ore, and andmany many others. others. Modal ccompositions o m p o s i t i o n s o fofSStettin t e t t i n rocks r o c k s are a r e included i n c l u d e d in i n Table T a b l e 6. 6 . (from ( f r o m Koeliner, K o e l l n e r , 1974). 1974). Modal �—35- TABLE TABLE 66 ?43DAL OF MODAL COMPOSITIONS COMPOSITIONS O F THE THE STETTIN STETTINROCKS ROCKS INTERMEDIATE INTERMEDIATEZONE ZONE Amphibole Amphibole Syenite Syenite ROCK TYPE - CORE CORE ZONE ZONE Tabular Tabular Syenite Syeni t e Pyroxene Pyroxene Syenite Syeni t e 66 and and 504 504 WALL MALLZONE ZONE Nepheline iepheline Syenite Syeni t e AMPLE NUMBERS* 10 77 503 100 uartz ephellne 7.1 6.6 2.9 1.4 26.4 17.6 6.6 80.7 83.5 90.3 83.0 87.4 80.2 63.6 75.7 61.4 8.6 0.2 5.1 13.6 5.5 4.1 0.5 19.1 8.4 4.6 29.5 0.2 0.6 0.4 0.4 1.0 Perthite lblte mphibole 0.5 11.2 0.6 Pyroxene Blotite' 0.2 Biotite (alter.) 0.6 Zircon 0.2 patite Fluorite 0.3 0.2 65 46 92 2 0.5 0.1 0.7 0.1 0.2 0.5 Calcite Calcite 0.3 0.1 Sphene Sphene Opaque minerals Opaque minerals AlteratIon 1.1 0.1 0.1 0.3 0.2 1.3 0.1 0.4 0.2 0.3 0.3 0.4 0.5 0.5 from from Sood, Sood, Myers, Myers, and and Berlin, Berlin, 1980, 1980, p. p . 28. 28. GXPLANAIION 0 Qel *JI,vh,m Qet Tin gr I including including localities l o c a l i t i e sofo fsamples samples and and ffield i e l d trip t r i pstops. stops. Granit, pay Pyranin, say *mpliib.i. Sy.ait. apap Stettin complex (after Myers. 1973) Figure of the Figure 26-.. 26%Geologic Geologic map map of the S t e t t i n complex ( a f t e r Myers, 1973) 4 I I Unt,ni.rmii Sp,nIe S,niI. aplit.  tay lty 1.b.,i., Itbultr Sp.iji. Sltiiite nay nç NiphnIia• Mtphtiint Syenit* Sytnitt lay Iiy ayv Syv nvb mvb L.n..Idi Lçmulday.niI. Sytniit ivfv i.lik FeliitV.k..,na hlimniti lulit Mrnlliislienka vçitrnk U.n mv Spanitiand Sltnifi~ç V,lc.niu Volconiti Irntjafed I n t t i a t t dMaftc MalitVeltanks Vsltanio �—36- FIGURE FIGURE 27 27 PARAGENETIC RELATIONS RELATIONS OF MINERALS IN EACH EACH ZONE ZONE OF OF THE THE STETTIN STETTINPLUTON PLUTON PARAGENETIC OF MINERALS - - - C R Y S T A L L I Z A T I O N CRYSTALLIZATION RROCK O C K TYPE T Y P E LU TABULAR SYENITE TABULAR (Myers, 1973) 1973) - -- - - SSEQUENCE E Q U E N C E - - —z zircon —I i rcon 4 —pyroxene4-!-pyroxene I —1 j_.alka1i ~ a kal l i feldspar— feldspar4 f—opaques_._ IÑopaques green amphiboles— - 1I green amphi bol es--4 I k1_biotite__I b i o t i te+ -J NEPHELINE NEPHELINE SYENITE SYENITE (Koellner, ( K o e l l n e r , 1974, 1974, P. 1 2 ) —nepheline -nephel i ne1-' -I I—alkali k a l kal i feldspar—I feldspar4 lI—olivine—I -olivine4 +pyroxene j I—pyroxene--I- opaques—l 1opaquesÑ —green g r e e n amphiboles.—4 amphi bol esÑ- Jbiotite—4 à ˆ - b i o tte-à PYROXENE SYENITE PYROXENE SYENITE (Koellner, (Koel 1n e r , 1974, 1974, p. P. 12) 12) I1.-alkali - a1 kal i feldspar—I f e l d s p a r -I I- a p a t i te-i Eapatite-i - opaques-l — opaques—I ivine----4 I— 01 olivine————.-$ + pyroxeneI— pyroxene— LU + — green g r e e n amphibole—S amphi boleÑ i—biotite—.. t- b i o t i t e 4 N1 pfrcarbonate.-4 carbonate-t i—blue I- bl ue amphibole— amphi bol e- LU H- LU AMPHIBOLE AMPHIBOLE SYENITE SYENITE (Koeliner, ( K o e l l n e r , 1974, 1974, p. 33) P. 33) I—alkali l- a1 kal i feldspar—I feldspar-l Iapatite4 k a p a t i te-1 LU I—opaques—4 kopaquesl +I—pyroxene p y r o x e n e 4—I )—green amphibole—I +green amphi bol e à ‘ tI—biotite—4 Ñbi0tite- H- I—blue IÑb ue amphibole— amphi bol e - FromSood, Sood,Myers, Myers,and andBerl Berlin, From in 1980, p. 24 24 1980, p. �—37— STOP STOP #8 #8 Nepheline syenite and syenitized volcanic rocks, Stettin pluton wall zone LOCATION: County Highway U on hill crest 0.5 mile east of Little Rib River; a- TITLE: Nepheline syenite and syenitized volcanic rocksy S t e t t in p1 uton wall zone LOCATION: County Highway U on h i l l c r e s t 0.5 mile e a s t of L i t t l e Rib River; , Sec. Sec. 18, 15' quadrangle. SSW W ,, SSW W , 18, T29N, T29N, R7E; R 7 E ; Wausau Wausau 15' quadrangle. (See Fig. 6). (See Fig. 6). Paul AUTHOR: Paul E. E . Myers, Myers, University University ofofWisconsin Wisconsin — - Eau Eau Claire AUTHOR: April, 1984 DATE DATE: April, 1984 SUMMARY OF OF FEATURES: SUMMARY FFATURFL: was Intrusion of of the theStettin S t e t t ipluton n pluton wasaccomplished accomplished by by peeling peeling slices s l i c e saway away from from the cylindrical andand carrying them upward causing much cylindricalwalls walls carrying them upwardwhile while causing muchmetasomatic metasomatic alteration a l t e r a t i o n through through the the addition addition of ofalkalies a1 kaliesand andalumina. alumina. The The border phases phases and aalterations l t e r a t i o n s typical and typical of of the the Stettin of the the eastern eastern border border of S t e t t i n pluton pluton are are well well exposed alongthe thehighway highwaya tatt hthis exposed along i s location. DESCRIPTION: The dominantrock rocktypes typesa at ( 1pyroxene, ) pyroxene,amphibole, amphiboleyand and The dominant t tthis h i s location location are: are:(1) olivine—bearing nephelinesyenite syenite pegmatite, pegmatite, and and variously variously syenitized olivine-bearing nepheline syenitized mafic mafic volcanic rocks. hybrid types types are are present volcanic rocks. Many Many hybrid present also. Through Throughaddition addition of K, K y Na, Na, and Al the volcanic rocks convertedlocally locally to of and A 1 the rocks were were converted t o aplitic a p l i t i rocks c rockscomposed composed of sodic amphibole(s), amphibole(s),b ibiotite, feldspar ((perthite). altered n d a1alkali ka1 i feldspar ~ e r t h i t e ) The ~ a1 sodic o t i t e $ aand The tered volcanic rocks canic rocks have have aa ccharacteristic h a r a c t e r i s t i csplotchy splotchyororstreaked streakedappearance appearance owing owing tto o local local pinkish color variation in in mineral mineral proportions: proportions: fine-grained fine-grained K-feldspar K-feldspar imparts imparts aa pinkish and tto o the the altered altered portions portions ofofthe thevolcanic volcanicrocks, rocksy andprimary primarypyroxenes pyroxenes are a r e altered ttoo Na-Fe Na-Fe pyroxenes. pyroxenes. 490' A B C 390' sv ==syenitized syenitizedvolconics volcanics syenite ns = nepheline nepheline syenite 2p0' 100' —EAST--'my 9' = syenite ss = syenite mv= mof Ic volcanic mv= mafic volcanic rocks rocks Geologics strip Figure 28—— 28-- Geologic t r i p map map along County C o u n t y Hiqhway Hiqhway U. U. The nephel nepheline syenite pegmatite pegmatiteaatt Location of very The ine syenite Location AA (Figure ( ~ i g u r 28) e28) isi scomposed composed of a n d 1 to 22 centimeter centimeter subhedral subhedral ccrystals rystals coarse subhedral ribbon perthite perthite and coarse subhedralgrains grainsof of ribbon of pinkish, nepheline (10—20%). (10-20%). Dark Dark mineral mainly dark dark green green to to pinkish$altered altered nepheline mineral iiss mainly Accessory minerals r e zircon, a p a t i t e $and and monazite, monaziteyellow green green amphibole. amphibole. Accessory mineralsaare zircon, apatite, B are composed composed ofofplagiocalse, The mafic Location B The mafic volcanic volcanic rocks rocks aatt Location plagiocalse, pperthitic erthitic a1 ka1 i feldspar, feldsparygreen green amphibole, amphiboley brown o t i t e y and and anhedral t iiss alkali brownb ibiotite, anhedralepidote. epidote.I It 1 locally cut cut by by syenite syenite veinlets. veinlets. have dark dark areas areas of residual residua1 mafic mafic rock rocknow now Syenitized volcanic rocks rocks at a t CC have Syenitized composed ofofanhedral 01 ivegreen green composed anhedralgreen greenamphibole amphibole( X(X= =dark darkyellow yellow green; green; ZZ == dark dark olive to brown) brown) clustered c1 ustered with with subhedral subhedral blue—gray amphibole (riebeckite) andcclots ti1 ue-gray amphi bo1 e (riebecki t e ) and l o t s of pale yellow—green yellow-green epidote. Brown o t i t e occurs coarser vvarieties. arieties. Brownb ibiotite occurs in in coarser �-38STOP #9 STOP TITLE: Contact relations and minerals in in the Contact relations and minerals the Wall Wall Zone, Zone, SStettin t e t t i n syenite syenite pluton pl uton LOCATION: County Highway t e t t i n Road, Road, Paul Highway O 0 aatt 10146 10146 SStettin Paul Knopp Knopp property, SEkYSE¼, SE%, Sec. 22, 22, T29N, T29N, R6E, R6E, Marathon Marathon 15' quadrangle, quadrangley(Sample SE¼, (Sample Location 92) 92) AUTHORS: P.E. P . E . Myers Myers and and M.KSbod M.KeSi50d DATE: DATE : February 1973, February 1973, February February 1980 1980 SUMMARY OF FEATURES: SUMMARY OF FEATURES: Theoutermost outermostrim rimofofthe theSStettin The t e t t i n pluton pluton is i s gneissic gneissic nepheline nepheline syenite syenite composed mainly alkali feldspar, perthi perthite, composed mainly of of a1 ka1 i feldspar, t e , nepheline, nephel iney aegirine, sodic sodic amphiboleand andbbiotite. amphibole i o t i t e . It I t isi sininsharp sharpcontact contactwith, with,and andveined veined by, by, tabular tabular syenite coarse,we1 well-oriented lathsof of perthite, perthi t e ysodic sodicamphiamphi syeni t e composed composed of ofcoarse, 1-oriented laths bole, pyroxene, lensoidal mafic essentially of of the bole, pyroxene, and and lensoidal mafic inclusions inclusions composed composed essentially the same minerals different porportions porportionsand andofoff finer grain size. The b ubut t inindifferent i n e r grain same minerals mafic inclusions inclusionsare arewe11 well-oriented parallel to to the the tabular tabular fabric of the mafic -oriented parallel the enclosing syenite syenite and andt oto the the wall wall of of the They contain contain large large perthenclosing the pluton. pluton. They perthite i n the the enclosing enclosing i t e porphyroblasts porphyroblasts of similar similarcomposition composition and and size s i z e as a s those those in weremined mineda tatt hthis Zircons from from tthis Zircons were i s ssite i t e in in the the 1950's. 1950's. Zircons his syenite. Zircons site 20m.y. m.y.bybyW.R. W .R. Van Van Schmus Schmus (oral comcoms i t ehave have given givenaaU/Pb U/Pb age age ofof1520 1520+ 20 munication). The chief chief questions questions to to be answereda tatt hthis The be answered i s ssite i t e are: are: (1) (1)how how were were the the nepheline syenite syenite and and tabular tabular syenite syenite emplaced, and(2) (2)to to what whatextent extent iiss nepheline emplaced, and the present metasomaticreplacement? replacement? present mineral mineral assemblage assemblage aa result resul tofofmetasomatic + �—39- The abundance abundance zirconand andhastingsite hastingsiteamphibole, amphibole,bbiotite The of ofzircon i o t i t e and and carbonate indicates miaskitic trend trend for forthe thenepheline n e ~ h e l i nand eandpyroxene pyroxene syenites. syenites. bonate indicates aa miaskitic The compositionsofof the the nepheline and pyroxene pyroxenesyeni syenites very similar similar The compositions nepheline and t e s aare r e very (Table (Table 6). 6). According According tto o Koeliner Koellner (1974, (1974 p. p. 144) 144) the syenite the amphibole amphibole syeni t e iiss agpiatic and and could could contain contain aa carbonatite carbonatitebody. body. agpiatic DESCRIPTION: DESCRIPTION: The nepheline syenite (Figure (Figure 30, The nephel ine syenite 303 Tables Tables 6 and and 7) 7) is i saagray, grayybanded banded rock here feldspar nephel nepheline, olivine, pyroxene, rock composed composed here of ofp eperthitic r t h i t i c feldspar i ne9 olivine pyroxeney magnetite, amphibole, amphibole,and andbbiotite. magnetite i o t i t e . Contorted Contorted aaplitic p l i t i cand andpegmatitic pegmatiticbands bands 1lie i e roughly roughly parallel parallel tot othe thewall wallofofthe thepluton plutonabout about1500 1500 feet f e e t south south of of here. here. The nepheline occurs occurs as as blocky, which weather b10cky~pinkish pinkishgrains grains which weathermuch muchmore more The nepheline readily than minerals, giving giving the the rock rock aa characteristic characteristic than the the associated associated minerals9 pitted pittedappearance. appearance. Nepheline Nepheline i sisppartially a r t i a l l y altered altered to to cancrinite cancrinite and and iron iron oxides. Banding9 Banding, and andmafic maficcontent contentof of the the nepheline nepheline syenite increase increase outoutward toward towardi its ward t s contact contact with w i t h syenitized syenitized mafic mafic volcanics volcanics which which tren tren westwestcommon addition tot othe theessential essentialminerals mineralslisted l i s t eabove, d abovey common northwesterly. In addition accessory minerals include include zircon and of unusually unusually large size accessory minerals and sphene sphene of size and and abundance, abundancey a papatite, a t i t e , f lfluorite, uori t e , allanite, a1 lani t e 9sodalite, soda1 i t e ,pyrochlore pyrochloreand and thorothorodatingofof the the zircons zircons from fromt this gummite(?). U/Pb U/Pb dating h i s site s i t e by by S. S. Goldich Goldich (oral (oral gummite(?). communication) gave gave aa minimum ageof of 1400 More recent recent analyses analyses of of comunication) minimum age 1400 m.y. m.y. More these zircons yielded aa U/Pb age of of 1520 W.R. Van Van Schmus Schmus yielded U/Pb age 1520 ++ 10 m.y. m.y. these zircons by by W.R. Thus, the SStettin t h z n the the Wolf Wolf Thus9 the t e t t i n syenite syenite is i s about about 20 20 million million years years older older than (oralcommunication). communication). River Bath01 i t h (oral River Batholith The gneissosity and andisoclinal isoclinal folding The gneissosity folding exhibited exhibited by by the the gneissic gneissic nephnepheline side of of the Stettin e l i n e syenite syenite of of the the wall wall zone zone on on the the south south side S t e t t i n pluton pluton suggestconsiderable considerabledifferential differential movement materialalong alongi its suggest movement ofofmaterial t s outer The extent extent to wasinvolved involved during during and wall. The to which which metasomatism metasomatism was and aafter f t e r ememplacement iiss not placement not known. known. However,metasomatism metasomatism was extensive,and andt hthat However9 was extensivey a t the nepheline syenite may consist in in large wall rocks. nepheline syenite may consist large part partofofmetasomatized metasomatized wall rocks. Zircon from red-brown, Zircon from tthis h i s locality l o c a l i t yis ideep s deep red-brownydoubly doublyterminated terminatedeuhedeuhedcrystalsdisplay display geniculate geniculate twinSome crystals in length. Some ral prisms prisms up up to to 14 14mm rnm in Chemicalanalyses analysesofof three three zircons from ning similar to to tthat of rrutile. from ning similar h a t of u t i l e . Chemical a nearby Sec. 22) 22) by by F.B. (NWg ofof Sec. F.B. Hall Hall (in ( i Weidman, n Weidmany1907, 1907Âp. p. 313) 313) nearby site s i t e(NW¼ indicates indicates an an A1203 A1203 content content of of between between 4.28 4.28 and and 7.80 7.80 percent percentand and an anFe903 Fe O3 Ca, Ti, Th and rare earths we'e Th and rare earths wege content between 1.21 and 4.47 percent. Cay Ti between 1.21 and 4.47 percent. sought but but not detected. sought detected. Brown pyrochiore octahedra octahedrauup to 22 mm mminin diameter diameterwere werefound foundaat Brown pyrochlore p to t tthis his location (1907, p. p. 308-309). location by byWeidman Weidman (1907, 308-309). Allanite isi sconfined confined mainly mainly to to petmatitic petmatitic portions portions ini nthe thenepheline nepheline syenite. syen i t e . Apatite and spheneofofunusually unusuallylarge larges isize show Apatite and sphene z e show a f faffinity i n i t y ffor o r clusters Large sphene crystals up to of mafic maf i c minerals mineral s in the the nepheline nephel ine syenite. syeni te. Large sphene crystal s up mminin length length can 77 mm can be be collected collected from fromnepheline nephelinesyenite syenitelenses lensesand andmasses masses near near iits t s contact contact with tabular tabular syenite. syenite. �-40- The tabular syenite The tabular syenite (Figure (Figure29, 2 9 ,Tables Tables66&i7)7 )is icomposed s composed dominantly dominantly of coarse coarse laths of of microperthite. microperthite. Vein patch type perthites Vein and and patch perthitespredompredominate. Poikilitic c amphi bole (hastingsite) (hastingsi t e )rims rimspyroxene pyroxene (intermediate (intermediate bebePoi ki1 i t i amphibole tween acmite andhedenbergi hedenbergite accordingt otoKoe1 Koeliner (1974, p. p. 65). 65). The tween acmi t e and t e according lner (1974, The tabular fabric orientation of fabric (Figure (Figure29) 29) isi scharacterized characterizedby by aarandom random orientation perthitic p e r t h i t i c feldspar feldspar tablets tablets in in aa plane plane parallel to t o the the outer outer wall wall of of the the pluton parallel to of mafic pluton and and parallel t o the thelong longdimensions dimensions of mafic inclusions. Perthitic PerthTtic feldspar tablets within within mafic mafic inclusions inclusions and and across across their t h e i r contacts contacts are are identical to t othose those ini nthe theenclosing enclosing tabular tabular syenite. syenite. The The inescapable conconclusions is that of of metasomatic t h a t the the perthitic p e r t h i t i cfeldspar feldspar isi sata least t l e a spartly t partly metasomatic clusions is origin. Veins of tabular syenite Veins of syenite locally locallycut cutthe thenepheline nepheline syenite syenite gneiss gneiss in the location. Mafic inclusions inclusionscomprise comprise from from the old old quarry quarry face face aatt this t h i s location. 5 to of the of mafic mafic inclusions t o 80 80 percent percent of the tabular tabular syenite. syenite. As As the volume volume of increases, amphibole, become increases, the the mafic maficminerals, minerals,mianly mianlysodic sodic amphiboley become coarsely coarsely poikilitic. Individual amphibole amphibole grains up u p to to 12 12centimeters centimeters long longwere were poi ki1 i t i c . Individual observed in aa small 1.5 miles observed in small roadside roadside excavation excavation 1.5 miles east-southeast east-southeast of here. here. Although Although the mafic mafic inclusions inclusionscontain containa amuch much higher higherpercentabe percentabe ofofpyroxene pyroxene and olivine than and olivine than the the enclosing enclosing tabular tabular syenite, syenite,they theyare areofofabout aboutthe thesame same chemical chemi ca1 composition. composi tion. The tabular syenite The tabular syenite forms forms the the outermost outermost layer layer on on the the north northand andwest west sides sides of the the Stettin S t e t t i npluton plutonwhere where the the nepheline nepheline syenite syenite is i sabsent. absent. The The abundance maficinclusions inclusionsincreases increasesoutward outwardi ninthe the tabular tabular syenite, abundance ofofmafic suggesting considerablecontamination contaminationbybythe thebasaltic basaltic wallrock. A A uunit nit suggesting considerable mapped lensoidalsyenite syenite and andaaclosely closely associated associated syenite syenite aplite mpped asaslensoidal a p l i t e(Myers, (Myers, 1973) are found found locally locally where 1973) are where the the nepheline nepheline syenite is i s absent. absent. The The lensoidal a1 syenite syenite is i san an aplitic, a p l i t i cgneissose y gneissose rock rock consisting consisting of of mafic mafic inclusions inclusions rich in syeniteaaplite The syenite p l i t e is is in biotite b i o t i t eenclosed enclosed in i n an an aaplitic p l i t i csyenite. syenite. The similar relatively free u t relatively f r e e of of mafic mafic composition bbut similar in i ntexture textureand and mineral mineral composition inclusions. Figure 29 29 Typical Typicalfabric fabricofof tabular syenite showingcoarse coarse Figure tabular syenite showing tablets of o fmicroperthite microperthite in inrandom random orientation to the the tablets orientation parallel parallel to wall of o f the the pluton. pluton. Microperthite Microperthite laths laths in inthe thelensoidal lensoidal mafic mafic inclusions tend tend to have have aa preferred to inclusions preferredorientation orientation parallel parallel to those those in in the theenclosing enclosing syenite. syenite. Some Some o fofthe thelaths laths crystallized crystallized across the edges edges ooff inclusions, inclusions,thus thusindicating indicating a metasomatic across a metasorriatic origin origin of o f at atleast leastpart partofo fthe themicroperthite. microperthite. �-41- Figure 30—— 30-- Photomicrograph syeniteshowing showing Figure Photomicrographofof nepheline nepheline syenite , rectangular nephel ine surrounded by a1 b i t eand and euhedral euhedral, rectangular nepheline surrounded by albite green amphibole. amphi bol e Crossed Crossed po1ars pol a r s green . Figure 31—— 31-- Photomicrograph syeniteshowing showing paraparaFigure Photomicrographofoftabular tabular syenite l l e l a1 ignment of p e r t h i t i c feldspar l a t h s o r t a b l e t s . llel alignment of perthitic feldspar laths or tablets. Crossed polars. pol ars. Crossed �-42STOP STOP #10 #10 TITLE: TITLE: LOCATION: LOCATION: "Moonstone" dikes in syenite of Intermediate "Moonstone" dikes in pyroxene—amphibole pyroxene-amphibole syenite IntermediateZone Zone the Stettin Stettim syenite syenite pluton. pluton. of the North side s i d e of ofCounty County Highway Highway UU, , 0.7 miles east e a s t ofofCounty CountyHighway Highway 0; North 0.7 miles SW:, SE4, SE?, Sec. Sec. 28, 28, T29N, T29N, R6E; R6E; Marathon Marathon 15' quadrangle [See [See Figure Figure 6] 61 SW, 15' quadrangle — &II 1) S F fl - AUTHOR: AUTHOR: Paul E. Myers, University of Wisconsin - April, 1984 April ,1984 DATE: DATE : - Eau Claire DESCRIPTION : DESCRIPTION: Coarsely crystallized syenite dikes containing containingpperthitic Coarsely crystallized syenite pegmatite pegmatite dikes e r t h i t i c feldspar feldspar crystals dark brownish amphibole-pyroxene u p tot o3535centimeters centimeterslong longcut cut dark brownishgray gray amphi bol e-pyroxene crystal s up moonstone" iiss characterized syenite in in this t h i sweathered weathered roadside roadside outcrop. outcrop. The The "moonstone" characterized by and brownish by aa soft s o f tirridescence irridescence and brownishsheen sheenimparted impartedbybyclose—spaced close-spaced ribbon ribbon green to bluish green amphibole I n t e r s t i t i a lpoikilitic poikil i dark t i c dark green t o bluish green amphibole perthite perthite lamellae. lamellae. Interstitial and dark greenish pyroxeneoccur occur bboth in the o t h in the pegmatite pegmatite dikes dikes and dark greenish brown brown tto o green green pyroxene and enclosing syenite. and enclosing syenite. A just north A large stone stone quarry quarry in the the woods woods just north of ofhere herewas was operated operated sporadically until by Mr. Mr. Gilbert Gilbert Schultz whoi sis, incidentally, disturbed until about about 20 20 years years ago ago by Schul t z who , incidentally, disturbed when rockhoundsinvade invade quarrywithout withoutpermission. permission.he hequarry quarryhas hasvertical vertical rock when rockhounds hishisquarry rock walls and deep water - DANGEROUS! syeniteinint hthis - DANGEROUS! TheThesyenite i s quarry quarry is is and is i s filled f i l l ewith d with deep water predominantly massive, brownish gray gray syenite massive, coarse—grained, coarse-grained, medium medium brownish syenitecomposed composed of perthite laths l a t h s with poikilitic p o i k i l i t amphibole i c amphiboleand andvery verysubordinate subordinategreen greenpyroxene. pyroxene. Pegmatite dikes exposed exposedininthe theSchul Schultz Quarryare arenearly nearly vertical vertical, ,reach t z Quarry reach 0.7 0.7 mm Pegmatite dikes width, and structure" (Figure and show show aaddistinctive i s t i n c t i v e "comb "comb structure" (Figure 32). 32). Interstitial I n t e r s t i t i a amphi-. l amphiboles boles are coarser coarser in in the the dikes, dikes,and andtend tendtot obebeconcentrated concentratedalong along dike dikemargins. margins. The dikes appear appeart otohave havecrystallized crystallized into opening conditions of The dikes opening fissures under under conditions arge, fresh fresh boulders boulders of of aa very very mafic mafic dike dikerock rock - lamprophyre lamprophyre Several 1large, extension. Several (?) the quarry, quarry, bbut ( ? ) wer wer observed observed ininthe u t ttheir h e i r relationship relationshiptot othe thesyenite syeniteisiunknown. s unknown. - / / / 'I — 1 / I" 6 inches ' , ,' '' /- \i' 0 ' — '... Figure 32—— "Comb"s tstructure 32-- "Comb" r u c t u r e in in syenite pegmatite dike pegmatite dike cutting cutting amphibole-pyroxene syenite in amphibole-pyroxene syenite the Schultz Schul t z Quarry Quarry 0.2 0.2 miles miles north of .north of here. here. Amphibole Amphibole is is poikilitic, occurs p o i k i l i t iand c , and occurswith withgreen green pyroxene. —I . '\ / I] \ — �-43STOP #11 #11 STOP - TITLE: TITLE : LOCATION: LOCATION: AUTHOR: AUTHOR: - DATE: DATE : Amphibole and Pyroxene PyroxeneSyenites Syenitesin in the Intermediate Amphibole and IntermediateZone Zone Marathon15' 15' quadrangle: quadrangle: See See Fig. Fig. 6. NW N W ,, SW SW ,, Sec. Sec. 14, T29N, T29N, R6E; R6E; Marathon 6. Paul Paul E. E. Myers, Myers, University University ofofWisconsin Wisconsin— - Eau Eau Claire April, April ,1984 1984 SUMMARY OF FEATURES: SUMMARY OF FEATURES : Massive and flow-lineated, flow—lineated,gray orange amphibole—pyroxene Massive and graytot opinkish pinkish orange amphibole-pyroxene syenite of onboth bothsides sidesofof the the road roadaat exposed on t tthis his of the the Intermediate Intermediate Zone Zone iis s well well exposed rock closely closelyresembles resemblesthe thepyroxene—bearing pyroxene-bearing syenite described described locality. 1 ocal i ty. This rock on page42. 42.The Thesyenites syenitesjust justnorth northand andwest westofofhere herecontain containl ilittle on page t t l e or orno no pyroxene, anddisplay display complex complexflow flow structures structures resembling those aatt the pyroxene, and resembl ing those the Old Old amphibolesyenite syenite north north of here The amphibole here contains contains Technical #5). The Technical IInstitute n s t i t u t e (Stop (Stop #5). the dominant mafice mineral mineral in abundant riebeckite. Although abundant riebeckite. Although the dominant mafice in the the pyroxenepyroxenebearing bearing syenite here here isi samphibole, amphibole, the thepyroxene pyroxene occurs occurs as as grains grainsrimmed rimmed by by Quartz-bearing aplites a p l i t e sare arecommon common in amphibole amphibole syenites they they were were amphibole. Quartz-bearing not in the n o t observed observed in the pyroxene-bearirg pyroxene-bearirtg syenites. syenites. DESCRIPTION: DESCRIPTION : Whereas the i s is c hcharacteristically a r a c t e r i s t i c a l l y pink outcrop, the the Whereas theamphibole amphibole pink in outcrop, pyroxene syeni t e i sis aa moderate-to-1 i ght oolive l i v e gray gray wwith i t h islands islands of pyroxene syenite moderate-to-light coarse mafics enclosed enclosedi nin coarse coarsetab1 tablets of randomly oriented fel felde t s of randomly oriented dcoarse mafics spar. spar. The amphibole syenite showsconsiderably considerablygreater greatertextural textural varThe amphi bole syeni t e shows variation, i a t i o n ,even evenata mesoscopic t mesoscopic scale. scale. Although A1 though vein-1 i ke and and iirregular rregular vein-like masses ofof zoned l i t e aare r e common common inina all l l outcrops, the the masses zonedpegmatite pegmatiteand anda paplite dominant rock medium-grained amphibole syenite aint dominant rock type type iiss medium-grained amphibole syenitewith withaaffaint t o conspicuous conspicuous lamination, r without created by by alignalignto lamination,with with oor without lineation created ment of feldspar feldspar tablets ment of t a b l e t s and and lensoidal lensoidal clots c l o t s ofofmafic maficminerals--mainminerals--mainly 1yamphibole amphibole and and subordinate subordinate pyroxene. pyroxene. Pegmatitic Pegmatitic phases phases of the theamam- syenitecontain containupuptot 12% o 12% quartzasascoarse coarsesegregations segregations cornmonphibole syenite quartz common1y rimmed rimmed by r i e b e c k i t i c )amphibole. amphibole. ly by blue blue ((riebeckitic) fibers. thin section, section, mafics mafics aare r e clustered In thin clusteredinin acicular acicular or or radiating radiating fibers. This the southwest containssmall smalls isill-like of tabular This zone zone tto o the southwest contains l l - l i k emasses masses of syenite. syeni t e . The major mineral mineral iiss micro-to micro-to mega-perthitic mega-perthi t i c feldspar feldsparsurrounding surrounding The major mafic minerals minerals which which seemingly a t e r than than the the feldspars. feldspars. The The the mafic seeminglyare arellater principal mafic mafic mineral mineral isi sbluish-green bluish-green arfvedsonite-riebeckite arfvedsonite-riebeckiteamphiamphibole (Table sometimes mantling mantl inq minor minor Fe-augite Fe-augite pyroxene. pyroxene. However, However, (Table ), sometimes pyroxene of tthis pyroxene iis s absent absent in in some some samples samples of h i s zone. zone. Alteration A1 t e r a t i o n of ofaniphiamphiboles to t o brown-red brown-red biotite b i o t i t eis icommon s common in in patches patches and and along along borders. borders. boles of aa dark dark The iinteresting n t e r e s t i n g feature feature of ofthe theamphibole amphibole grains grains isi scontainment containment of The blue riebeckitic r i e b e c k i t i cphase phase which which is i s most most common common only i s uunit. n i t . Some blue onlyi nint hthis Some amphiboles poikilitically amphi boles poi kil i t i c a l l yenclose encloseeuhedral euhedral feldspars feldspars (Figure (Figure ). ). Accessories include zircon which which isi scommonly commonly zoned, to Accessories include zircon zoned, quartz quartz (up to 12%), allanite. 12%), f fluorite, l u o r i t e , calcite, c a l c i t e ,FeTi-oxides, FeTi-oxides, apatite a p a t i t e and and a1 lanite. �-44- Figure Photomicrographofof amphibole amphibole syenite Figure 33—— 33-- Photomicrograph s y e n i t e showing showing poikilitic poi kil i t iamphibole c amphiboleenclosing enclosingeuhedral euhedral feldspar feldspar grains. grains. (From Sood, Myers, Myers, and andBerl Berling, ~ r o mSood, ing, 1980, 1980, p. p. 34). 34). with Figure 34-— 34-- Photomicrograph Photomicrograph of pyroxene syeni t e with Figure of pyroxene syenite zoned zoned aegirine-augite aeqi rine-auqi t emantled mantled by byarfvedsonite. arfvedsoni t eCrossed e Crossed polars. p. 35). 351, polars. (from (fromSood, Sood. Myers, Myers, and and Berline, Berl i n e ,1980, 1980, p. �-45STOP STOP #12 #12 TITLE: The Core CoreZone Zoneofofthe theSStettin The t e t t i n Syenite Syenite Plutori Pluton LOCATION: LOCATION: SW 1/4, SE SE 1/4 1/4 Sec. S W 1/4, Sec. 2, 129N, T29N, R6E; R6E; Hanthurg151 Hmburg 15' quadra,nle quadrangle William Powell requiredfor for entry. Powell property. property. Permission Permission required AUTHOR:: AUTHOR,: Paul E. Paul E. Myers Myers,, DATE: DATE : February, 1980, February, 1980, University University ofo Wisconsin f Wisconsin — - Eau Eau Claire April, Apri 1 ,1984 1984 SUMMARY OF FEATURES: SUMMARY OF FEATURES: The coreofof the the SStettin twoddistinct The core t e t t i n syenite syenite pluton pluton comprises comprises two i s t i n c t parts: parts: (1) banded (1 ) aa cylindrical cylindricalcore coremargin margin of of indistinctly indistinctly bandedororlineated, lineated,mediummediumgrained nepheline syenite syenite and and (2) (2) an grained nepheline an inner core core of of pyroxene pyroxene syenite. Bent Bent and crushed crushedfeldspar feldspar grains grains and and and a crude crude southeast-dipping southeast-dipping layering layering were were formed during during oorr after of the nepheline syenite formed a f t e remplacement emplacement of the core core margin. margin. The The nepheline magnetic anomaly about one one mile core margin margin produced produced aa pronounced pronounced donut-shaped donut-shaped magnetic anomaly about the southeast southeast corner corner of of iinn diameter. diameter. Drilling DrillingbybyBear BearCreek Creek Mining Mining Company Company inin the the inner core the core retreived retreived about about 250 250 feet f e e t of of core coreclassified classifiedbybycompany company geologists geologists carbonatite has been beenfound, found,a1although theaagpaitic as No carbonati t e has though the pal t i c trend trend of of as 1larvikite. arvi kite. No the rocks suggestst hthat suchaacarbonatite carbonatite iiss possible the rocks here here suggests a t such possible (Koellner, Koellner, 1974, 1974, p. 144). 144). p. ? DESCRIPTION: The nephelinesyenite syeniteofof the the core core margin marginhere herei sis indistinctly indistinctly banded The nepheline banded or or weatheredsurface surface paleyellowish yellowishgray graywith withppitting The weathered i s ispale i t t i n g due due to lineated. The fresh nepheline The fresh nepheline iiss pale pale greenish greenish differential differentialweathering weathering of of the thenepheline. nepheline. The brown andoccurs occursasaswe1 well-oriented, 1-oriented, subhedral subhedral to euhedral euhedral grains grains enclosed enclosed by by brown and The feldspars, feldspars, nepheline, up to to22cm cm long. long. The nepheline, and and islands islands tablets of of feldspar feldspar up of mafic ofm a f i c minerals minerals are are elongated elongated inina aplane planedipping dippingsoutheast southeastatabetween t between60 60and and This lamination is not parallel to the outer edge of the core margin at i s parall el to the outer edge of the core margin a t This 1 amination 70g. 70 . and broken brokenfeldspar feldspar and andnepheline nephelinegrains grainsand andlenticulation lenticulation Bent and tthis h i s location. location. Bent of mafic shearingduring duringororaafter mafic mineral mineral clusters suggest suggest shearing f t e r intrusion. �-46- The dominant w i t h40% 40% tabular microperthite microperthite(60% (60%orthoclase orthoclasewith The dominantmineral mineral iiss tabular An additional 25% of the rock i s subhedral t o euhedral oligoclase ribbons). ribbons). An oligalase additional 25% of the rock is subhedral to euhedral nepheline, which a r t i a l l y altered a l t e r e d to t o cancrinite. cancrinite. Mg-rich Mg-rich pyroxene pyroxene and and nepheline, whichi sisppartially pleochroic, olive o l i vbrown e brownamphibole amphiboleare a r of e of about equal abundanceand andmake makeup up pleochroic, about equal abundance about 20-30% 20-30% of rock. Accessory Accessory (2-5%) (2-5%) Mg-rich o l i v i n e and dark. brown about of the rock. Mg-rich olivine and dark.brown b i o t i t eaccompany accompany the n llenticular e n t i c u l a r clusters c l u s t e r sand and islands islands biotite theother other mafic maficminerals mineralsi in i n the nephel ine syeni t e . The b i o t i t e p a r t i a l l yrims rims occurring i n t e r s t i t i a l l y occurring interstitially in the nepheline syenite. The biotite partially the amphibole amphibole and formed a t at a a l alate t e stage rystallization. the andwas wasprobably probably formed stageofofccrystallization. donut-shaped magnetic magneticanomaly anomaly about about one one u n i produced t produceda apronounced, pronounced,donut-shaped This unit This Wiedman (1907, p. 251 ) reports unusually large and abundant i ndiameter. diameter. Wiedman mile in mile (1907, p. 251) unusually large and abundant The magnetite apparently magnetite octahedra octahedra from from streams streams northwest here. The magnetite northwest of here. magnetite iiss apparently i t h the livine. associated most associated mostclosely closelywwith the oolivine. �-47-. PETR0CHEMISTRY PETROCHEMISTRY** Chemicalcompositions compositionso foft hthe Chemical e SStettin t e t t i n rocks rocks are a r e presented presented in i n Table Table 77 Table 8compares averagecompositions compositions rocks ttoo those Table 8 compares average o f oft hthe e S Stettin t e t t i n rocks those of o f Nockold's Nockold's The average averageo of f t hthe e SStettin t e t t i n nepheline nephel i n e syenites syeni t e s show show ddistinct i s t i n c t differences differences (1954). The from samples,wwhile from Nockold's Nockold's average average syenite. s y e n i t e . These t e t t i n samplesy h i l e oonly n l y sslightly lightly These SStettin higher in Al903 NA2O higher CaO O3 and NA and 0 and h i g h einr FeO, i n FeO* CaOand andP205. P205. h i g h e r in i nsilica, s i l i c aare * alower r e lower i n A1 and Theamphibole amphiboleand and pyroxene in ssilica The pyroxene s y esyeniths, n i t $ s y a l salso o s ? islightly g h t l Y h higher igher i n i l i c a than than Nockold's Nockold's average average ssyenite, y e n i t e y are a r e lower lower ini nAl20., A1 0 MgO, MgOyCaO CaO and and 1(90, K2OY wwhile h i l e higher higher in q u a r t z ++ i nFeO, FeO*NA2O NA20 and andMnO. MnO. The The ddifferentiation i f f e r e n t i a t i o n 2 i?dices i d d i c e s (DI ( D I = normative normtive quartz albite oorthoclase r t h o c l a s e ++a1 b i t e + nepheline nepheline ++l eleucite u c i t e ++ kkalsilite) a l s i l i t e )(Thornton (Thornton and and Tuttle, Tuttle* 1960) rocks are are given g i v e n in i n Table Table 99 .. The The average averageDDI 1960) f for o r these these SStettin t e t t i n rocks I ffor o r these these rocks degreeo of rocks iiss 84.7, 84. 7*which which represents represents aa hhigh i g h degree f ddifferentiation. ifferentiation. However, However* nepheline ssyenites havet hthe 88.9 and and93.9 93.9r respectively, nepheline y e n i t e s have e hhighest i g h e s t DDI I ofof 88.9 e s p e c t i v e l y y indicating indicating the t h e greatest g r e a t e s t extent e x t e n t of o f differentiation d i f f e r e n t i a t i o among n among these these rocks. rocks. The aagpaitic The g p a i t i c indices i n d i c e s of o fthe t h eStettin S t e t t samples i n samplesare a rshown e shownini nFigure F i g u r 35—A. e 35-A. Rocks lower Si02 Si09 ccontent, Rocks oof f lower o n t e n t * the t h e nepheline nepheline bearing b e a r i n g rocks, r o c k s * have have lower lower agpaitic agpaitic thant the mre ssilica This iiss a reflection iindices n d i c e s than h e more i l i c a rich r i c h rocks. rocks. This r e f l e c t i o n of o f the t h e higher higher aluminaccontent, due t to o n t e n t * due o tthe h e presence presence oof f nnepheline, e p h e l i n e * iin n the t h e nepheline nepheline syenites. syenites. alumina The versusSi02 Si02 ((Figure increaseswwith The rratio a t i o Na20/K20 Na20/K20 versus F i g u r e 35C) 35C) increases i t h increasing i n c r e a s i n g Si02. Si02. This showstwo twotrends trendssuggesting suggestingt hthat This diagram diagram shows a t t hthe e SStettin t e t t i n rocks rocks belong belong to to two Amphiboleand andpyroxene pyroxenes ysyenites appeart to o l l o w aa continuous continuous two sseries. e r i e s . Amphibole e n i t e s appear o ffollow differentiation . I.Paw. normative normative compositions compositions d i f f e r e n t i a t i o nsequence. sequence. (Figures (Figures35E-G). 35E-G). CC.I.P.W. are presented The normative normativecompositions compositionso of analyzed SStettin The f tthe h e analyzed tettin presented in i n Table Table 99 of oNaA1SiO4, KA1SiO4 S i O and and aare r e plotted plotted rocks were were calculated c a l c u l a t e dini nterms terms f NaA1SiO4 KAlSi04 and and SiO All of Si02 K a l S i 0 4- S i 0 2 aatt 11000 0 0 0 bbars a r s PH 0 Figure f ~ i c j u r e 36). 36). A11 of iin n tthe h e ssystems y s t e m s NNaA1Si0 a A l S i 0 -- KalSiO4 2 tthe h e rocks rocks ffall a l l within w i t h i nthe ?helow lowtemperature temperature trough. trough. TABLE 77 TABLE nE — -— — —— {EMICAL COMPOSITIO OF STETTIN PLUTON ROCKS CHEMICAL COMPOSITION -— ROCK ROCK TYPE TYP — Sarrale Q w l e 9# 10 — CORE C ORE ZONE ZONE INTERMEDIATE ZONE ZONE froxene Syenite yeni te Anphibole Syenite Syeni t e 70 WALL ZONE jabular 503 503 108 64.70 64.70 61.95 59.75 61.S0** 65 — — Nepheline l i n e Syenite Syenite 6+504 6+504 — 46 22 5745 5695 56.95 92 92 sSb2 i o2 66.10 A1203 13.24 15.59 15.86 15.86 16.04 16.23 16.62 16.93 21.02 21.02 16.32 Fe203 2.61 2.36 2.45 2.45 3.13 2.55 2.55 5.20 2.58 2.93 2.93 3.41 FeO FeO 4.12 2.22 2.10 2.10 2.70 5.66 5.66 1.68 5.98 2.12 7.08 7.08 MgO M90 0.43 0.01 0.02 0.08 0.14 0.14 0.24 0.21 0.07 1.22 1.22 cao 0.70 0.50 0.95 0.95 1.10 2.15 1.43 2.64 0.51 4.03 %O3 Fe2° CaO • 5.92 6.92 7.07 7.07 6.51 5.97 6.49 6.71 7.81 5.01 K0 '5O 4.31 5.11 5.19 5.19 5.51 5.67 5.15 5.02 5.99 4.84 4.84 620 "zO 0.73 0.83 0.10 0.70 1.95 0.51 0.63 0.98 1.43 0.77 0.77 0.38 0.35 0.36 0.36 0.40 0.22 0.17 0.18 0.40 0.09 0.09 h2 CO2 c02 T1102 i o2 0.72 0.42 0.27 0.27 0.32 0.75 0.31 0.59 0.38 0.38 1.32 '05 2 '5 ' 0.11 0.04 0.06 0.07 0.13 0.13 0.07 0.13 0.50 0.50 0.49 0.49 nO Nlo 0.23 0.12 0.15 0.15 0.18 0.26 0.26 0.22 0.30 0.07 0.07 0.29 s 0.010 0.004 0.003 0.008 0.034 0.034 0.009 0.023 0.000 0.000 0.044 0.102 0.165 0.260 0.171 0.11 0.100 0.140 0.001 0.079 0.079 S ( l2r02 m2 0.03 Cl BaO Bao 0.013 0.010 0.024 0.024 0.150 0.071 -— Rb(pprn) P.~(PP~ Sr(ppm) 199. 44 0.010 0.01c 0.160 0.16( 0.345 0.02 0.103 0.086 152. 66. 133. 115. 105. 174. 174. 109. — — -—— Mar * Analyst-K. ~na1ys.t-K. Racial. Ramla1 , University U n i v e r s i t yofo fManitoba **Tabular **la u l a r yeni t e 0.105 0.105 0.241 0.143 0.215 *Modjfjed yenite *Modified fror.i f m r - i Sooci, S O O C ! ~ F!"ersy and Berlin, Uerl i r ~1980. 1989. * vers, and 57. I 54.10 65.20 0.025 0.025 0.02 0.02 0.208 0.208 102. 345. —. �-48-48TABLE TABLE 88 COMPARISON OF CHEMICAL CHEMICAL COMPOSITIONS COMPOSITIONS OF OF STETTIN COMPARISON OF STETTIN WITH WITHNOCKOLDS NOCKOLDS (1954) (1954)AVERAGES AVERAGES . Average Average SStettin tettin Nepheline Syeni t e Nephel ine Syenlte Syenite (Nockolds,1954) (~ockolds.1954) S102 sio2 56.17 Al203 A1203 Average Average Nepheline Nephel b e Average Average SStettin tettin Syenite Syenl t e Average Average Syenite Syeni t e (Nockolds, 1954) 1954) (Nockolds, 55.38 63.54 61.86 18.09 21.30 15.39 16.91 Fe203 2.97 2.42 2.62 2.32 FeO FeO 5.06 2.00 3.36 2.63 MgO w 0.50 0.57 0.14 0.96 CaO CaO 2.39 1.98 1.08 2.54 Na20 Na20 6.78 8.84 6.49 5.46 5.28 5.34 5.16 5.91 1.06 0.96 0.94 0.53* Ti02 1102 0.76 0.66 0.50 0.58 P205 p2° 0.37 0.19 0.08 0.19 0.22 0.19 0.19 0.11 Fe203 1(20 %O A 1120 "2O InÔ M~O' * Includes $ncludesonly o n l yH20 H20 from from Socd, Soc,d, Myers, Myers, and and Berlin, Berlin, 1980, 1980, p. p. 48. 48. TABLE TABLE 99 C.I.P.W. C.I.P.W. NORMATIVE NORMATIVECOMPOSITIONS COMPOSITIONSOF OFTHE THESTETTIN STETTINROCKS ROCKS 1 ROCK ROCK TYPE TYPE 10 Or 12.44% 25.61 Ab 44.05 Q CORE CORE ZONE ZONE Amphibole Amphi bole Syenlte Syeni t e Pyroxene Pyroxene Syenite Sveni t e L Sample Sample Numbers* Numbers* INTERMEDIATE INTERMEDIATEZONE ZONE 77 4.86% 30.06 51.92 503 2.80% 30.62 52.97 100 Ac Dl Mt Ii Pr Ru and and 504 504 1.79% 32.28 51.92 Tabular Tabular Syenite Syeni t e 65 65 47.72 30.62 52.44 2.22 1.28 3.41 7.22 5.31 1.04 1.36 0.12 0.02 2.36 5.91 1.89 0.51 0.76 0.01 1.36 5.89 3.88 0.54 0.46 0.01 1.65 2.70 2.70 3.28 0.61 0.01 Nepheline Nephel i n e Syenite Syeni t e 46 6.66 3.70 1.36 0.06 5.06 0.61 0.02 29.50% 35.62% 28.39% 56.48 1.47 7.93 3.00 38.39 34.16 4.26 8.10 4.67 9.82 3.70 1.06 0.06 Hl Tn 0.34 0.18 0.06 1.70 0.10 0.18 0.02 0.13 0.37 0.04 CC DI *Tabular *Tabular Syenite Syeni t e 2.11 14.86 0.96 4.17 0.76 10.65 4.86 2.43 0.06 0.91 C Z 92 1.62 Nm Ap 2 1.80% 33.40% 0.88 An Ne 01 My 66 WALL WALL ZONE ZONE 82.1 86.8 86.4 0.17 0.18 0.02 0.34 0.02 0.02 0.90 0.50 82.4 86.0 0.17 0.15 0.58 0.34 0.18 0.03 0.13 1.01 0.001 0.11 0.04 0.06 0.20 84.9 93.9 88.9 70.6 �__ _________________ __________________________ ________________ -49- Q2o I' 7)0 - 108 44 6 a 09 1 0 .. 0 108 65' 46 02 K 0 92 --08 30 60 70 50 60 S.O 94 70 SiO 94 IS® 20 4 I * 0 3 503 2 108 2l2 O 46 460 0 0 92 0 '10 97 0 I 50 70 60 60 50 70 0.05% 0 o ®20 ° 108 '8 65 0 92 . 6 77 IS C 92 l0 I IC 60 60 50 70 SiO % 70 507% 92 i 0 .5 3 046 0 2 20 l0 I 2 0.5 ,l0 60 5102 94 046 20 C 50 1.0 70 0.C 50 S \ " •" 65 "503 60 70 502 96 Figure F i g u r e 35-35-- Chemical Chemical trends t r e n d s of o f major major elements e l e m e n t s versus v e r s u s Si02 Si02 for p o 50) 50) f o r Stettin S t e t t i n pluton p l u t o n rocks r o c k s (from (from Sood Sood and and others, o t h e r s , 1980, 1980, p0 �-50DISCUSSION M. Sood and M. K. K. Sood andL.L. A.A. Berlin Due chemicaland andmineralogical mineralogicalheterogeneityy heterogeneity,the theorigin origin of of alkaline Due t to o chemical alkaline igneous rocks rocks iis, and may maybebethe ther result igneous s ininmany many cases, casesy very very complex complex and e s u l t of several several processes. Experimental icate Experimentalstudies studiesofofchemically chemicallyequivalent equivalentsynthetic syntheticsi1 silicate systems (Bai (Bailey systems 1ey and and Schairer, Schai r e r y1966; 1966; Hamilton Hami 1ton and and MacKenzie, MacKenziey 1965; 1965; Schairer, Schairer l a t t and and Edgar, Edgary 1970; 1970; Tuttle T u t t l eand andBowen, Boweny 1967; 1967; Sood Soodand andEdgary Edgar, 1972; 1972; Sood, Sood,PPlatt 1958) haveprovided providedaaphysicochemical physicochemicalframework framework to explain the crystallization 1958) have t o explain t h e crystal 1 ization behavior behavior of of alkali a1 ka1magmas. i magmas. Any petrogenetic model modelf for the formation thethe Wausau Any petrogenetic o r the formation of of alkaline a l k a l i n erocks rocksofof Wausau area must take take iinto area must n t o account: account: nature of the zoned nature thecomplex complex 11)) the zoned 2) 2) the presence quartz-bearingaaplitic the presence ofof quartz-bearing p l i t i c and and pegmatitic pegmatitic stages stages in in tthe h e intermediate intermediate ring of ofamphibole amphibole syenite; syenite; 3) 3) the the fenitized fenitizedzone zone surrounding surrounding the pluton; pluton; 4) 4) the presence volatile bearingmineral minerals (flourite, calcite, the presence ofofvo1 a t i l e bearing s (f1 ouri t e ca1 ci t e 'core" (?) i nmost most syenites, s y e n i t e s yand and in in the the quartz quartz monzonite monzonite "core" (?) aapatite) p a t i t e ) in of the Wausau pluton; t h e Wausau pluton; major and and ttrace geochemistryofof the the syenites. 5) major r a c e element element geochemistry 5) Consideration wwith the System SystemNephel Nepheline-Kalsilite-Silica Consideration i t h Respect Respect t oto the ine-Ka1 s i 1i te-Si 1 ica In normativecomposition composition rocksi sisplotted plotted iinn the 36 normative of of thethe S tStettin e t t i n rocks the In Figure Figure 36 along wwith i t h the t h e composition composition of system Nepheline-kalsilite-silica at H along a t 1Kb 1Kb PH system Nepheline-kalsilite-silica East Greenland Greenland (Wager, (Wagery 1965). 1965). the rocks intrusion, 22 East rocks from from Kangerdlugssuag Kangerdl ugssuag intrusion Theseanalyses analysesmay may interpretedt otoshow showa atrend trendofofssilica These be be interpreted i l i c a depletion depletionaway away from from the Si02 Si02 apex. apex. Rocksofoftthe IntermediateZone Zoneofofamphibole amphibole syenite plotinin tthe Rocks h e Intermediate syenite plot h e aalkali lkali feldspar-quartz region, near the alkali feldspar join, while pyroxene syenites near t h e a1 ka1 i fe1 dspar j o i n y w h i 1 e pyroxene syeni t e s fe1 dspar-quartz region, The positions positions of of the Zoneplot plotj ujust belowthe thea lalkali feldspar join. join. The the Core Core Zone s t below k a l i feldspar these syenites in the field show a silica depletion trend toward the center center these syenites i n the f i e l d show a s i 1 ica depletion trend toward the of the thecomplex. complex. From Figure36, 36, iitt appears amphibole appears that t h a t the t h etrend trendofofthese these amphiboleand andpyroxene pyroxene From Figure syenites iiss up the thermal thermal bbarrier, "over" the arriery feldsparsurface surface and and 1overt' syenites up the t h e alkali a1 kali feldspar which is similar to the interpretation by Wager (1965) for the nordmarkites, which i s s i m i l a r t o the i n t e r p r e t a t i o n by Wager (1965) f o r the nordmarkitesy pulaskites, pulaski t e s y and and foyaites foyai t e s of of the thealkaline a1 kal ineKangerdlugssuaq Kangerdl ugssuaq intrusion. (In the the nepheline-kalsilite-silica nephel ine-kalsil i t e - s i l i c asystem system at a t 55Kb Kb H PH o y these rock rock webs webs plot close close to t o the the feldspar feldsparcotectic c o t e c t i coro nephiline-feldspar r nephiline-feldspar 22 ccotectic. o t e c t i c . This is mineral paragenetic parageneticand andtextural texturalrrelations.) i s ininagreement agreement wwith i t h mineral e l a t i o n s . ) Further interpretations await the accumulation of additional data, i n t e r p r e t a t i o n s await the accumulation of additional d a t a y especially especially on on the the Wausaup1 pluton. Wausau uton. �—51— S i0 100 5 K A IS 1308 Nlephehne N e p h e l i n e ssss 100 / ,, 0 10 N aA ISs104 io4 ,, 20 20 . *- 30 30 / /'$6 01 / 8 2 0 / K a l s i l i t e ss 10 / / '/ 40 40 J 50 50 Weight cent. W e ~ g hper tper cent. V 60 60 70 70 -d 80 80 90 90 o 0 100 100 KAISIO4 KAlSiO4 Figure Figure 36-3 6 . - -Normative Normative compositions compositions ofof tthe h e SStettin t e t t i n rocks rocks (closed ( c l o s e d circles) circles) and and the t h e alkaline a l k a l i n erocks rocksofothe f t hKangerdlugssuaq e Kangerdlugssuaq intrusion, i n t r u s i o nEast y EastGreenland Greenland (open NaA1SiO4 (open circles) c i r c l e s (Wager, ) (Wager,1965) 1965)plotted p l o t t ein d the i n tsystem h e system NaA1Si04 --KA1SiO4 KAlSiO4 -Si02 Hamilton and 1963; Hamil ton andMacKenzie, MacKenzie 1965). 1965). Si02 at a tH2O P H==1000 ~ 1000 ~ bars b a r s(Fudali, (Fudali1963; �-52— How could such such inward inward ssilica How could i l i c adepletion depletionbebecaused? caused? Two Two possible explanations explanations are: are: (1) (1 ) Loss of the the volatile Loss of v o l a t i l e phase phase iineuilibrium n equilibriumwith with the themelt. melt. Such Such aa volatile alumina, a1 alkali, v o l a t i l ephase phase has has alumina, kali and and silica s i l i c aininthe thesame same propro- portion 1958; portion as a sfeldspars feldspars(Tuttle ( T u t t& l e Bowen, & Bowen? 1958;Mackenzie, Mackenzie?1960). 1960). The presenceofofap1 aplitic and feni fenitization i t i c and and pegmatitic pegmati t i c phases phases and tization The presence of beaa rreflection of the t h esurrounding surrounding volcanics volcanics may may be e f l e c t i o n of of separation separation of of volatiles v o l a t i l e into s i n tao gaseous a gaseousphase phase and and eventual eventual loss. l o s s . The The plot plot of pertinentsynthetic synthetic of the the Stettin S t e t t i nrocks rocks close c l o s e to t o cotectics c o t e c t i c s ini npertinent systems maybebeindicative indicativeofof ccrystallization systems may r y s t a l l i z a t i o nofofmajor majorphases phases crystallization within within narrow narrow temperature temperature 1limits. imi ts. Short Short crystal 1 ization intervals intervals are a r e also a l s o related r e l a t e d to t o silica s i l i c aand andalkali a l k a l content i contentwhich which control control volatile phases i n l i qand u i d gaseous and gaseous phases(Sood (Sood&&Edgar, Edgar? v o l a t i l edistribution d i s t r i b u t i oin n liquid 1970; Rhyaschi kov 1961). 1961 ) . 1970; Kogarko Kogarko && Rhyaschikov, (2) contribute to The The ssubstitution u b s t i t u t i o n of Fe3 ~ e A13 A' I ~' ~ in i n feldspars feldspars may may contribute to silic depletion w i t h crystallization crystal1 ization of of iron-rich iron-rich albite a1 b i t e s i 1 icq depletion with Fe-Alssubstitution (NaFe ~ 0i ) . Only Only aa small small amount amount ofof Fe-A1 u b s t i t u t i o n is is (NaFe 33Si20). thel liquid necessary2t8 f i x silica s i l i c aand and cause cause the i q u i d to t o shift s h i f tfrom from necessary th fix silica s i l i c asaturated saturatedtot osilica s i l i cundersaturated a undersaturatedtrend trend(Bailey (Bailey&&Schairer, Schairer? general iron-rich iron-rich and 1966). 1966). The The general and alumina-deficient alumina-deficient nature nature of of the syenites syenites inincomparison comparison tot oNockold's Nockold's(1954) (1954)averages averages and and aa limited 1imited Fe-content Fe-content of feldspars fe1 dspars favor favor such such substitution. substitution. The Nephelinesyenite syeniteinin the the SStettin The Nepheline t e t t i n pluton pluton may, may, therefore, t h e r e f o r e ?represent represent last l a s t residual residual liquids l i q u i d sinjected injectedinto i n t the o thesheared sheared wall wall zone. zone. ItI tmay may be be concluded concluded tthat h a t alkaline a1 kal inerocks rocksofofMarathon Marathon County County represent represent study of of silicate The study s i l i c a t esystems systems aa "genetically "geneticallyrelated r e l a t e dcomagmatic comagmatic series." s e r i e s . ' ' The and melting rocks have amply demonstrated t i n g relations re1 a t i o n of s of rocks have amply demonstratedthat t h magma a t magmacomposicomposi and me1 tion lies l i e sclose close to t othe theunivariant univariant lines l i n e soro rthe theinvariant i n v a r i a n tpoints, points?and and very very slight in iinitial s l i g h t changes changes in n i t i a lliquid l i q u icomposition d composition can can give give decidedly decidedly ddistinct istinct differences fferences in these these alkaline a1 ka1 inerocks rocksmay may be be Composi t i ona1 di trends. Compositional 1 i q u i d trends. liquid related compositionbybyfractional fractionalccrystallization r e l a t e d to t o slight s l i g hchanges t changes ininmagma magma composition rystallization I t isi simportant important to t o further f u r t h e r refine refine assimilationy or o r both. both. It o r by by wallrock wallrock assimilation, or geochemical data both both on on their t h e i r genetic genetic and and tectonic relations. r e l a t i o n s . Systematic geochemical rocks minerals are assess iiff these rocks and and minerals a r e needed needed t to o assess these rocks rocks are a r eformed formed from from mantle note the the low and Sr Sr contents contents ffor Rb and or mantle derived derived magmas magmas ( t e(tentatively n t a t i v e l y note low Rb Wausau rocks)which whichreached reachedc rcrust through recurrent recurrent fracture Wausau rocks) u s t through f r a c t u r esystems. systems. Such Such information will also information will a l s obe beUseful useful ininthe t h eestimation estimationofofeconomic economic mineral mineral potential potential thisarea. area.Such Suchrocks rocks form form ini nenvironments environments favorable favorable to t o the t h econcentration concentration of this of aa wide wide variety v a r i e t yofofelements. elements. . �—53— DISCUSSION DISCUSSION P.E. Myers Myers P.E. The of The ffour o u r plutons p l u t o n s ofo fthe t h eWausau Wausau syenite s y e n i t e complex complex share share many many ccharacteristics h a r a c t e r i s t i c s of lithology Moreovery they t h e yshow show l i t h o l o g yand and chemistry c h e m i s t r y which which llink i n k them them in i n age age and and oorigin. r i g i n . Moreover, a general genera1 ddifferentiation i f f e r e n t i a t i o n trend t r e n d from f r o m tthe h e peralkaline p e r a l k a l i n e SStetting t e t t i n g ssyenite y e n i t e wwith i t h iits ts nepheline n e p h e l i n e syenite s y e n i t e rim r i mand andcor c o rmargin m a r g i nthrough t h r o u g hthe t h eWausau Wausau and and Rib R i b Mountain Mountain plutons plutons which southeastward andf ifinally which aare r e ccharacterized h a r a c t e r i z e d bby y aasoutheastward i n cincrease r e a s e i n in s i lsilica, i c a * and n a l l y to to the A l t h o u g h tthere h e r e is i s no no t h e Ninemile N i n e m i l e ppluton l u t o n w with i t h i tits s ccore o r e r rim i m oof f aaplitic p l i t i c granite. g r a n i t e . Although obvious o b v i o u s sstructural t r u c t u r a l control c o n t r o l ofo fthe t h ecomplex, complexyiti does t doesoccupy occupy aa major m a j o r flexure f l e x u r e near near the andi nintermediate t h e boundary boundary between between mmafic a f i c and t e r m e d i a t e EEarly a r l ' y Proterozoic P r o t e r o z o i c metavolcanic m e t a v o l c a n i c rocks rocks on on the t h e west west and and ffelsic e l s i c to t ointermediate i n t e r m e d i a t emetavolcanic m e t a v o l c a n i c rocks r o c k s on on the t h e east. e a s t . The The complex complex l lies i e s only o n l y about about 25 25 miles m i l e swest west of o fthe t h eexposed exposed western w e s t e r n edge edge of o f the t h ecoeval coeval Wolf g r a n i tshares e sharesmany manymineralogical m i n e r a l o g i c a land and t h eNinemile N i n e m i l egranite Wolf River R i v e r batholith, b a t h o l i t h and * andthe chemical h a r a c t e r i s t i c s with w i t h the t h e Wolf W o l f River R i v e r batholith: b a t h o l i t h :they t h e yboth b o t hhave have rapakivi rapakivi chemical ccharacteristics affinities. p1 u t o npermit p e r m isome t someconclusions conclusions Aspects ooff concentric c o n c e n t r i c zoning z o n i n g ofo feach eachpluton a f f i n i t i e s . Aspects remain as as to t othe t h eactual a c t u amechanism(s) l mechanism(s) as i n t r u s i o sequence, n sequence*although a l t h o u g hproblems problems remain as to t o intrusion of o f emplacement. emplacement. Xenoliths absenti in Stettin X e n o l i t h s are a r e nnearly e a r l y absent n tthe he S t e t t i n pluton, p l u t o n ythe t h e oldest oldest p o s s i b l ybecause because the t h e conduit c o n d u i twas was developed developed more a p i d l y and/or and/or in more rrapidly sequence* possibly i n the t h esequence, The occurrence o c c u r r e n c e of o f metametabecause because tthe h e Stettin S t e t t i npluton p l u t o nhas hasbeen beenmore moredeeply d e e p l yeroded. eroded. The volcanic with v o l c a n i c xenoliths xenol i t h sclosely c l o s e l yresembling resembl i n grocks r o c k sexposed exposed nearby n e a r b y aalong long w i t h xenoliths xenol i t h s of micas schists andqquartzites o f high—grade h i g h - g r a d e mica c h i s t s and u a r t z i t e s suggests suggests cconsiderable o n s i d e r a b l e vvertical e r t i c a l mixing mixing of a l o n gthe t h ewalls w a l l sofothe f t hWausau e Nausauand and Rib R i b Mountain Mountain plutons. plutons. o f wallrock w a l l r o c kfragments fragments along These were ppenetrating These pplutons l u t o n s were e n e t r a t i n g a high-grade h i g h - g r a d e metamorphic metamorphic t eterrane r r a n e aatt depth, depth, aa factor f a c t o r suggesting s u g g e s t i n g the t h e presence presence of o f an an earlier e a r l i e Proterozoic r P r o t e r o z o i succession c s u c c e s s i o nbeneath beneath the the volcanic v o l c a n i c rocks. rocks. The The problem problem ooff the t h e "two "two Proterozoic P r o t e r o z o i csuccessions" s u ~ c e s s i o n shas ' has ~ been been recently and Myers Myers(1984.) (1984.)The Thex xenoliths r e c e n t l ydiscussed d i s c u s s e d by b y LaBerge LaBerge and e n o l i t h s iinn the t h e intermediate intermediate zones andRRib Mountainp lplutons zones ooff the t h e Wausau Wausau and i b Mountain u t o n s i nindicates d i c a t e s tthe h e initial i n i t i aemplacement l emplacement of o f syenite s y e n i t emagma magma dduring u r i n g aa ffirst i r s thigh—volume high-volume ssurge, u r g e * pprobably r o b a b l y wwith i t h venting v e n t i n g at a t the the surface. s u r f a c e . The The first-surge f i r s t - s u r g e magma magma t hthen e n c crystallized r y s t a l 1 i z e d inward i n w a r d from f r o m tthe h e dylindrical cylindrical walls, w a l l s , forming f o r m i n g the t h ewall w a l lzones. zones. Then Then (for ( f o rthe t h eWausau Wausau and and Rib R i b Mountain Mountain plutons), p1 u t o n s ) with and ccollapse w i t h repeated r e p e a t e d resurgence resurgence and o l l a p s e aalong l o n g ccylindrical y l i n d r i c a lshear shearzones, zonesythe t h edeeper deeper wallrock c o l l apse w a l l r o c kfragments fragments were were mixed mixed wwith i t h those t h o s e carried c a r r i e d downward downward bby y an a r l i e r collapse aneearlier phase. phase. This wou1 d eexplain x p l a i n the t h e tendency tendency ffor o r concentric c o n c e n t r i c elongation e l o n g a t i o n of o f xenoliths xenol i t h s T h i s would and and ttheir h e i r zonal zonal distribution. d i s t r i b u t i o n . IfI fthe t h esouthwesterly s o u t h w e s t e r l y track t r a c kofo the f t h plutonic e p l u t o n isequence c sequence i s possible p o s s i b l e that t h a t other o t h e rsyenitic s y e n i t i cplutons p l u t o n sexist e x i s in t i Wisconsin, n Wisconsiny can be be ggeneralized, e n e r a l i z e d * i itt is can but younger rrocks and gglacial The aeromagnetic aeromagneticmap map b u t are a r e obscured obscured beneath beneath younger o c k s and l a c i a l deposits. d e p o s i t s . The of many anomaliess isimilar o f Wisconsin Wisconsin shows shows many c i circular r c u l a r anomalies m i l a r tto o those t h o s e characterizing c h a r a c t e r i z i n g the the Wausau and Myers Myers, 1983, Wausau ssyenite y e n i t e (See (See LaBerge LaBerge and 1 983* Plates P l a t e s11 and and 2). 2). Features iindicating Features n d i c a t i n g shallow s h a l l o w intrusion i n t r u s i o ndepth d e p t h are: a r e :(1) ( 1abundance ) abundance of o f nearly nearly h o r i z o n t a l pegmatite p e g m a t i t e pods i a r o l i t i c ccavities a v i t i e s in i nthe t h eNinemile N i n e m i l e granite; granite; horizontal podsand andmmiarolitic ( 2 ) concentric, c o n c e n t r i c * cylindrical, c y l i n d r i c a l discordant d i s c o r d a n t structure s t r u c t u r e of o fthe t h eplutons, p l u t o n s yand and (3) ( 3 ) low low (2) metamorphic grade metamorphic grade andand r e lrelative a t i v e s i simplicity m p l i c i t y oof f sstructure t r u c t u r e in i n wallrocks. wallrocks. Some problems i s t cconcerning o n c e r n i n g t hthe e age e n e t i c r relationships e l a t i o n s h i p s of o f the the Some problemse xexist ageand andg genetic g r a n i t e aplite, a p l i t e which * whichoccupies o c c u p i e s aa large l a r g e area a r e a outside o u t s i d e the t h e plutons, p l u t o n s y but b u t isi sconfined confined granite mainly m a i n l y to t o the t h e region r e g i o nadjacent a d j a c e n t to t othe t h eNinemile N i n e m i l e pluton. p l u t o n . In I n essence, essence* the t h e aplite aplite is i s aa finer f i n e rgrained g r a i n e dvariety v a r i e t yofo the f t h eNinemile N i n e m i l e granite. g r a n i t e . However, Howevery mmiarolitic i a r o l i t i c cavities cavities and podsand andd idikes and pegmatite p e g m a t i t e pods k e s a rare e v every r y r arare r e i in n tthe h e aplite. a p l i t e . However, However* tthe h e aplite aplite may rrepresent e p r e s e n t an an early e a r l y phase phase of o f granite g r a n i t eintrusion i n t r u s i owhich n which precededemplacement emplacement of of may preceded the t h e Nineniile N i n e m i l e granite. g r a n i t e . The The aplite ap1 it econtains c o n t a i n splagioclase p l a g i o c l asephenocrysts p h e n o c r y s t sofo euhedral f euhedral plagioclase p l a g i o c l a s e and and tends tends tto o be be leucocratic: l e u c o c r a t i c : biotite b i o t i t eisi usually s u s u a l l ythe t h eonly o n l ymafic m a f i cmineral, mineral, and and its i t sabundance abundance i is s usually u s u a l l y less l e s s than t h a n 55 percent. p e r c e n t . Mantling M a n t l i n g of o fK-feldspar K - f e l d s p a r by b ysodic sodic p l a g i o c l a s e is i s common. common. I tIt i is s tentatively t e n t a t i v e l y concluded concluded t that h a t tthe h e ggranite r a n i t e aaplite p l i t e isi san an plagioclase early e a r l y intrusive i n t r u s i v ephase phase of o fthe t h eNinemile N i n e m i l e granite. granite. �-54Another problem problem concerns u a r t z monzonite monzoni t e pporphyry o r p h y r y p1 ugs (See (See F i g u r e 5). 5). Another concerns two two qquartz plugs Figure These ssmall m a l l pplug—like l u g - l i k e bbodies o d i e s c consist o n s i s t oof f aa light—colored, l i g h t - c o l o r e d , aphanitic a p h a n i t i c matrix m a t r i x and and These l a r g e K—feldspar K - f e l d s p a r pphenocrysts h e n o c r y s t s showing a r t i a l fragmentation f r a g m e n t a t i o n and and resorption. resorption. large showingp partial Quartz Q u a r t z phenocrysts p h e n o c r y s t s aare r e granular g r a n u l a r and and anhedral. anhedral. These l u t o n s aare r e strung s t r u n g out out These pplutons along County and a l o n g aa NW-SE NW-SE aaxis x i s across across Marathon Marathon County, and were were intruded i n t r u d e dthrough t h r o u g hpost—syenite post-syenite faults. They aare r e iinterpreted n t e r p r e t e d as as being b e i n g tthe h e "last " l a s t gasp" gasp1' of o f the t h eNinemile N i n e m i l e granite granite f a u l t s . They emplacement empl acement episode. Whole Whole rrock o c k and and trace t r a c e element element geochemistry geochemistry are a r eunder underway wayby b yMyers Myers and and Sood, Sood, while o s t u d mineralogy y m i n e r a l o g yand and mineral m i n e r a l chemistry c h e m i s t r y of o f the the w h i l e Falster F a l s t e r will w i l continue l c o n t i n u etot study pegmatites A comprehensive comprehensive ggenetic—petrological e n e t i c - p e t r o l o g i c a l model model p e g m a t i t e s iin n the t h e Ninemile N i n e m i l e pluton. pluton. A is be ppublished I tisi shoped hoped i s being b e i n gdeveloped, developed, and and should s h o u l d be u b l i s h e d wwithin i t h i n the t h e next n e x t year. y e a r . It that t h a t the t h e reader/participant r e a d e r / p a r t i c i p a n t may may f find i n d aa rresearch e s e a r c h pproject r o j e c t oof f iinterest n t e r e s t in i n this this relatively p a r tofo the f t h Precambrian e Precambrian shield s h i e l dofo Wisconsin. f Wisconsin. r e l a t i v e l ywell w e lexposed l exposed part P. wishes tto P. Myers Myers wishes o express express hhis i s gratitude g r a t i t u d etot othe t h eWisconsin WisconsinGeological G e o l o g i c a l and and Natural H i s t o r ySurvey Survey for f o rsponsoring s p o n s o r i n g field f i e l work d workduring d u r i nthe g t hsummers e summers of o f19711971N a t u r a l History 1976 1976 with w i t h Gene Gene LaBerge LaBerge in i n Marathon Marathon County. County. The The Survey Survey has has also a l s o provided p r o v i d e dmany many consultants. thin t h i n sections s e c t i o n s and and the t h e assistance a s s i s t a n c e of o f the t h e Survey Survey Staff S t a f f as as consultants. �A Figure — 37—- —S. EXPLANATION WAUSAU PLUTON —S. —S. S. Older caic-alkaline volcanic rocks, mainly andesite and rhyolite Quartzite Quartz diorite Alkalic extrusives, probably pyroclastics and subordinate flows Lensoidal quartz syenite with xenoliths of biotite schist and quartzite Syenitized volcanic rocks Gneissic nepheline and tabular syenite border facies Pyroxene syenite Amphibole syenite Ninemile quartz monzonite -S.' —•—. SOUTHEAST — Hypothetical northwest-southeast section across the Stettin and Wausau syenite plutons as they would have appeared about 1450 m.y. ago. Line A-A' represents the present land surface. rT1 1/i [; ...'I , / / '.—___, 01 01 �-56REFERENCES REFERENCES Anderson, J.L., 1980, 1980,Mineral Minerale qequilibria andc crystallization Anderson, J.L., u i l i b r i a and r y s t a l 1 i z a t i o n conditions conditions iin n the the Late Late Precambrian Precambrian rrapakivi a p a k i v i massif, massif, Wisconsin, Wisconsin, American American Journal Journal of o f Science Science v. v. 280, 280,P.p.289—332. 289-332. Anderson, J.L., 1983, Anderson, J.L., 1983, Proterozolc Proterozoic anorogenic anorogenic ggranite r a n i t e plutonism p l utonism of o f North North America, America, Geological Geological Society Societyofo America f AmericaMemoir Memoir 161, 161, p.p.133—154. 133-154. 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LaBerge, G.L., and LaBerge, G.L., and Myers, Myers, P.E., P.E., 1972. 1972. 1971 1971 Progress Progress report r e p o r ton onmapping mapping of o f Precambrian Precambrian geology geology of of Marathon Marathon County, County, Wisconin. Idisconin. His. His. Geol. Geol. Nat. Nat. Hist. Hist. Survey Survey Open Open FFile i l e Report, Report, p. p. 28, maps. maps. LaBerge, G.L., and 'Precambrian Geology Geology of o fMarathon Marathon LaBerge, G.L., and Myers, Myers, P.E., P.E., 1973. 1973. 'Precambrian County', County', ini nGuidebook Guidebook to t oPrecambrian Precambrian Geology Geology ooff Northeastern Northeastern and and Northcentral Wisconsin. Wis. Wis. Geol. Geol. Nat. Nat. Hist. H i s t Survey, . Survey,p.31—86. p.31-86. 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M e l t i n g relations r e l a t i o n sofo undersaturated f undersaturated Sood, M.K., and Sood, M.K., and Edgar, Edgar, A.D., A.D., 1970. 1970. Melting alkaline a l k a l i n erocks. rocks. Meddelelsen Meddelelsen Om Om Gronland. Gronland. Bd. Bd. 181, 181. Nr. Nr. 12, 12, p. p. 41. 41. Sood, Sood, M.K. M.K., • and and Edgar, Edgar, A.D. A.D., • 1972. 1972. The system system ddiopside—forsteriteiopside-forsteriteThe nephel i n e - a l b i t e - l e u c i t e and s iimplication m p l i c a t i o n to t o the the genesis genesis of o f alkaline alkaline nepheline-albite—leucite andi tits rocks. rocks. 24th 24th mt. I n t .Geol. Geol. Congr. Congr. Montreal, Montreal, V. V. 14, 14, p.p.68—74. 68-74. Sood, M.K., P Platt, Sood, M.K., l a t t , R.G., R.G., and andEdgar, Edgar, A.D., A.D., 1970. 1970. Phase Phase r relations e l a t i o n s in in portions p o r t i o n s of o f the thesystem system diopside-nepheline--kalsilite-silica diopside-nepheline-kalsilite-silica and and their t h e i importance r importance in i n the the genesis genesis of o f alkaline a l k a l i n e rocks. rocks. Can. Can. Miner., Miner., V. V. 11, 11, p. p. 380-394. 380-394. Sood, M.K., Myers, P.E., and Sood, M.K., Myers, P.E., and Berlin, B e r l i n , L.A., L.A., 1980, 1980,The Thepetrology, petrology,geochemistry. geochemistry. and contact relations Wausau S t e t t iand n and Wausau syenite s y e n i t e plutons. plutons. Central Central Wisconsin. 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P.O. 1975, 1975, 1975a, 1975a, Chronology Chronology of of Precambrian rocksi ninWisconsin, Wisconsin,I: I: The The Wolf WolfRiver Riverbbatholith, a t h o l i t h , aa rapakivi r a p a k i v imassif massif Precambrian rocks approximately 1500m.y. m.y.old, old, Geological GeologicatSociety AmericaB uBulletin, v. 86, approximately 1500 Society o of f America l l e t i n , v. 86, p. p. 907-914 907-914 Van W.R., Thurman,E.M., E.M., and and Peterman, Peterman, Z.E., Z.E., l975b, Van Schmus, Schmus, W. R., Thurman, 1975b, Geology Geologyand andchronchronology of of Precambrian Precambrian rocks Rb-Sr data o r tthe h e oolder l d e r rocks rocks in in ology rocksi ninWisconsin, Wisconsin,11: II: Rb-Sr dataf for eastern and and ccentral e n t r a l Wisconsin, Wisconsin, Geological Geological Society eastern Society ooff America America BBulletin u l l e t i n v. v. 86, 86, p. p. 1255—1265. 1255-1265. Wager, formand andi ninternal Wager, L.R., L.R., 1965. 1965. 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Wright, ando poptical studyooff aalkali Wright, T.L., T.L., and andStewart, Stewart, D.B., D.B., 1968. 1968. X—ray X-ray and t i c a l study lkali feldspars: feldspars : III 1determination determination of o fcomposition composition and and sstructural t r u c t u r a l state s t a t efrom fromrefined refined unit-cell Mm., V. u n i t - c e lparameters l parametersand and2V. 2V. Am. Am. Min., V. 53, 53, p. p. 38-87. 38-87. � 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, 1984 Description An account of the resource Institute on Lake Superior Geology. Wausau, Wisconsin. April 24-28, 1984. 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 1984 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English